STUDENT ABSTRACTS
Spiral Structure in the Galaxy M74
Why are spiral galaxies spiral? This thesis is a response to that question.
Rather than offering an explanation of the origin of spiral galaxies, I am
presenting a description of the phenomenon observed. My case study is the
galaxy M74, a beautiful face-on spiral in the constellation Pisces. I begin by
considering the case of an M74 where no force is acting on the galactic disk to
create spiral arms. I use this idealized, smoothed-out version of M74 as a
base case to which to compare the actual M74. This comparison results in a
description of the perturbation of the disk of M74 in terms of its luminosity
relative to the base case.
Chapter 1 is an introduction to galaxies and the history of their observation.
Spiral density wave theory is summarized in Chapter 2. Background information
and past research are addressed in Chapter 3, while the observations necessary
for the project are described in Chapter 4. Chapter 5 is an account of the
processing and analysis of the data and contains the actual data in the form of
azimuthal graphs of the galactic disk. Results and conclusions are found in
Chapter 6.
An Investigation of Salt Dependent Inactivation of Antibiotic Peptides Found in
Xenopus laevis Lung Tissue
Current research into the molecular mechanisms of the disease cystic fibrosis
has suggested several new paths of study which may lead to the development of
novel treatments. Studies on the concentration of NaCl in patients' airways
show that the salt-dependent inactivation of natural antibiotic peptides may be
a major cause of infection. This study performed antibiotic activity assays on
Xenopus laevis lung tissue, and found no inactivation by NaCl. Peptides which
are not susceptible to salt inactivation may be purified and used as a drug to
treat cystic fibrosis.
Calcium Control of NPY mRNA Levels in PC12 Cells
Neuropeptides, like neurotransmitters, are messenger molecules that are
released in response to depolarization of a cell membrane and subsequent
calcium influx. Different channel types have different activation kinetics,
duration of activation, and/or cellular localization, and these differences may
play an important role in the functioning of the cell. Neurotransmitter
release in different developmental stages appears to be controlled by calcium
influx through different channels, and neuropeptides may be similarly
responsive. In this thesis, I begin to study how calcium influx affects
genetic regulation of neuropeptide Y mRNA, to see whether this process is
calcium regulated, and if the regulation is similar to regulation of
neurotransmitter and neuropeptide release. Preliminary results were gathered
and analyzed, and no significant response was found, however future
normalization of the results may provide better resolution.
A Study of the Past and Present Ecology of the American Chestnut (Castanea
dentata [Marsh.] Borkh.) in a Northern Hardwood Forest
This is a study of the past and present ecology of the American chestnut in the
2500 acre northern hardwood dominated Hopkins Memorial Forest (HMF) in
Williamstown, MA, which lies on the extreme northern edge of the natural range
of chestnut in this mountainous region. The study is based on a variety of
different kinds of data including tree core increments, broad and fine scale
mapping, historical observations, use of historical property and land used
boundaries, and data from a permanent plot study in the HMF. The permanent
plot data cover a wide range of physiographic variation and document almost 60
years of succession, the first complete survey being finished in 1937, and the
last in 1996. The permanent plot study includes data on the herb/shrub layer,
preblight chestnut logs, extensive tree core data, and live and dead stems of
all standing trees 0.5 in, DBH.
In the presettlement forest, chestnut probably occupied as much as 60% of the
canopy on well drained, south facing slopes below ridges which were prone to
natural disturbances. In the postsettlement forests of Williamstown, in early
to mid-successional stands (abandoned from agriculture in the 1870s and 1880s)
on south facing slopes, especially bordering agricultural fields, chestnut
occupied as much as 75% of the canopy. The persistence of chestnut sprouts in
the understudy today, makes chestnut a good indicator of land which, at the
peak of blight introduction, was adjacent to chestnut forests and abandoned
from agriculture, particularly pasture, between 1890 and 1910.
Canopy openings caused by overstory defoliations in the late 1960s allowed for
dramatic increases in chestnut sprout density in the 1970s. These defoliations
may also have caused an increase in huckleberry cover. While in the 1970s
chestnut basal area was concentrated in dense sprout colonies on land that was
recently reclaimed pasture at the peak of blight damage, in the 1990s chestnut
basal area was concentrated in large surviving trees on land that was mature
chestnut forest at the peak of blight damage: On xeric, south facing slopes
with open canopies, chestnut grows more rapidly than all other species, and it
is not uncommon to find chestnuts which reach the canopy and bear fruit. The
largest chestnuts are found on slightly more mesic sites, but are out competed
by other species, and, as a result, do not bear fruit. The patchy distribution
of sites suitable to chestnut growth in the northern hardwood forest may allow
for the occurrence of relatively blight free "islands" of breeding trees.
Three breeding populations have been identified in the HMF, including one
population which may be a unique dwarf ecotype above 2000 ft. elevation.
The peak of blight damage in Williamstown was probably around 1920. Chestnut
was replaced by beech which spread clonally into gaps left by chestnut. Today
beech is generally the most important species on plots formerly occupied by
chestnut although red oak is the most important species on plots prone to
disturbance. Red oak most closely initiates the former role of chestnut,
although chestnut probably responded (and still does) more quickly to increased
light availability. On a few plots dominated by beech, oak actually occupies a
slightly larger canopy percentage than beech due to the persistence of large
canopy oaks. Neither species, however, has assumed the dominant canopy role
which chestnut once played. Increment cores taken from preblight chestnut logs
which were established on land that was once pastured show rapid and steady
growth, whereas large trees in today's forest often exhibit up to two decades
of relatively suppressed growth before showing strong release.
The role of insects as pollinators and blight dispersers is also studied and
discussed.
Preliminary Purification of a Transcription Factor that Deactivates
Interleukin-4 Expression in Murine Mast Cells
In mast cells, normal transcriptional regulation of the cytokine Interleukin-4
(IL-4) gene requires the activity of several upstream DNA sequences. One of
these, the Neg-1 element, behaves like a negative regulator both in vivo and in
vitro. Reporter gene experiments show that loss of Neg-1 from the IL-4
regulatory region causes more rapid transcription, and electrophoretic mobility
shift analysis (EMSA) shows that the Neg-1 sequence forms a specific complex
with nuclear proteins from mast cell nuclear extracts. To further investigate
the regulatory functioning of this DNA sequence, we undertook to isolate the
transcription factor with which it interacts. Accordingly, crude murine mast
cell nuclear extracts were fractionated over a heparin-sepharose affinity
resin. This method effectively separated the specific Neg-1 binding factor
from the majority of nuclear proteins. In addition, partially purified binding
factor retained the electrophoretic mobility and specific binding activity
present in the crude extracts. To purify the Neg-1 binding factor further,
partially purified samples were fractionated over a Neg-1-sepharose resin.
Neg-1 binding proteins were eluted from the resin as a peak, but EMSA showed
that relatively few of these proteins retained the electrophoretic mobility and
specificity of the crude complex. Most binding proteins formed a
Neg-1-unspecific complex of unexpectedly high electrophoretic mobility. This
may mean that the Neg-1 complex contains several protein factors, and that the
purification steps separate them somehow. Alternatively, the higher mobility
complex observed with purified samples may be the result of a non-specific
binding activity. These possibilities will be distinguished before work in
this area continues.
Sphingoid Long-Chain Bases in Wounding Signal Transduction
Sphingolipids and their derivatives have been implicated in animal signal
transduction. The possibility of an analogous function for sphingolipids in
plant signal transduction led to this research into the plant wounding
response. Viral, bacterial, and herbivore damage initiate plant systemic
acquired resistance which coordinates intracellular and extracellular processes
to defend the plant from further damage. Phaseolus vulgaris leaves were
pinched to mimic herbivore damage and the leaf long-chain bases were extracted
after a time interval. Long-chain bases were identified and quantified using
HPLC. Modified sphingoid bases, 4-hydroxysphinganine (phytosphingosine) and
8-sphingenine, consistently exhibited a transient increase 0.5 - 2.0 hours
following wounding. Other long-chain bases, 4-hydroxy-8-sphingenine in
response to wounding may indicate long-chain bases contribute to wounding
signal transduction.
Site-Specific Mutagenesis of the Putative Magnesium Ion Binding Domain of
Vaccinia Deoxyuridine Triphosphatase
The enzyme deoxyuridine triphosphatase (dUTPase) is involved in nucleotide
metabolism and is important in maintaining DNA fidelity during replication.
dUTPase activity is present in a variety of organisms, including prokaryotes,
eukaryotes, and viruses. There are five highly conserved motifs in the amino
acid sequences of organisms that encode this enzyme, and they may be essential
for the activity of the enzyme.
Vaccinia virus encodes a 16.2 kD dUTPase that requires magnesium ions for
activity. Motif 3 contains a Walter B sequence, a series of four hydrophobic
amino acids followed by an aspartic acid residue. Walker B sequences have been
implicated as the magnesium ion binding sites in enzymes that require this ion
for activity. Using site-specific mutagenesis, the aspartic acid residue in
the Walter B sequence of vaccinia virus dUTPase was altered in order to
characterize the amino acid's contribution to the structure and function of the
enzyme. Initially, this mutagenesis was attempted using a phagemid that
unexpectedly expressed the vaccinia virus dUTPase gene. This vaccinia dUTPase
activity interfered with the success of the Kunkel method of generating
site-specific mutants. Therefore, another phagemid that did not express the
vaccinia dUTPase gene was employed in order to generate mutants in the putative
magnesium ion binding domain.
After the mutant enzymes have been purified, activity rests will be performed
to determine the way in which the mutations affect the ability of dUTPase to
bind and hydrolyze dUTP. Further studies will ascertain whether each mutant
enzyme can associate as a homotrimer, the native configuration of the wild-type
enzyme.
Bilateral Selective Axotomy of the Mauthner Neuron and its Effect on the Fast
Startle Response of the Goldfish (Carassius auratus)
The Mauthner cells (M-cells) are thought to be involved in the C-start startle
response in the goldfish, Carassius auratus. However, the exact role of these
cells in this response has been the topic of debate for the past several
decades. Studies have attempted to remove M-cell output through a variety of
methods in order to see its contribution to the C-start response.
In this study, C-start response probability in goldfish undergoing bilateral
selective axotomy of the Mauthner axon is not diminished when compared to
controls. These results do not agree with previous selective axotomy results
which have instead shown a significant decrease in C-start responsivity after
double axotomy. Our results support the existence of a parallel neuronal
circuit which can mediate the C-start response in the absence of M-cell
output.
However, we believe that our results are not complete. Not all fish who went
through this study could have their status as a double axotomy fish verified.
The probability, though, is high that a number of surgically attempted double
axotomy fish will turn out to be double axotomies after completion of
morphological analysis. Inclusion of these putative double axotomy fish in
data analysis does show a significant decline in C-start responsivity which
leads us to speculate that the M-cell has an excitatory role over other neurons
involved in the C-start. Further study will be needed to ascertain which
conclusion is more accurate.
Differences in Morphology Imply Differences in Physiology for the Inputs to the
Mauthner Cell Axon Cap
The Mauthner Cells (M-cells) are two large, identifiable, bilateral neurons in
the goldfish, Carassius auratus, involved in the fast startle response.
Surrounding the M-cell axon hillock and initial segment is the axon cap which
consists of a central core and peripheral region surrounded by a glial cap wall
(Bodian, 1937). The two inputs that terminate within the axon cap, namely the
excitatory spiral fibers and the inhibitory interneurons, govern M-cell
excitability. The PHP cells ensure that only one M-cell fires in response to
an above threshold stimulus and that a given M-cell does so only once (Furukara
& Furshpan, 1963; Faber and Korn, 1978; Kjorn & Fabver, 1983); Hackett
& Faber, 1983; Faber et al., 1989). The inhibitory interneurons, known as
PHP cells, can be divided into two groups, collateral and commissural, based on
their physiology and morphology.
This study was designed to determine whether more inputs terminate within the
axon cap than have been identified previously. The morphology of the cell
bodies of the comissural and collateral cells projecting to the cap was also
studied to examine whether these cells can be divided into different subclasses
based on the number of processes originating from their cell bodies. In
addition, immunohistochemistry using the rabbit KC polyclonal antibody was used
to determine the presence and distribution of potassium channels within the
axon cap.
We conclude that multipolar and bipolar collateral PHP cells exist that may
participate in "feedforward" inhibition of the Mauthner Cell in response to
visual stimuli. A separate group of unipolar cells was identified in this
study that are located in the vicinity of the bipolar and multipolar collateral
cells and that also project to the axon cap. In addition, unipolar and
multipolar commissurant cells were identified that participate in "feedforward"
inhibition of the Mauthner Cell. Therefore, differences in cell body
morphology (unipolar, bipolar and multipolar) imply that each type of PHP cell
plays a slightly different physiological role based on the types of inputs it
receives. Finally, the Kv2.1 voltage gated potassium channel appears to be
accumulated densely on the spiral fibers within the axon cap region.
The Influence of Testosterone on Song Plasticity in the Adult Male Zebra Finch
Zebra finches (Taeniopygia guttata), like other species of close-ended song
learners, acquire their song during a restricted period in early development.
Recent studies with zebra finches have shown that normal song development
requires a period of low levels of circulating testosterone (T). A natural
increase in T levels may contribute to the crystallization of song in young
males by curtailing neural plasticity. Following the close of the critical
period at 90 days of age, loss of plasticity allows the male zebra finch to
retain one characteristic song for a lifetime. Under abnormal circumstances,
however, such as deafness or damage to the tracheosyringeal (ts) nerve, changes
to syllable syntax will occur in adulthood. This study investigates whether
raising T levels in adult male zebra finches inhibits the type of vocal
plasticity seen following ts nerve injury. Six pairs of adult male zebra
finches were matched for song similarity and genetic relatedness. One bird
from each pair received a testosterone silastic implant, the other received an
implant filled with flutamide, a competitive inhibitor of testosterone. One
month later, both groups underwent ts nerve surgery. The songs of all birds
were recorded every two weeks thereafter for three and a half months and then
analyzed. The flutamide treated group showed a significantly larger number of
song alterations than did the testosterone treated group. The inhibitory
influence of testosterone on song learning in the zebra finch thus extends
beyond the close of the critical period. In addition, a novel type of song
change occurred consisting of a reorganization of syllable order without an
accompanying deletion or addition. Finally, flutamide was found to hasten
addition of song syllables. While previous studies found that additions
appeared at two weeks following surgery or later, 42.9% of additions in the
songs of the flutamide group occurred one to three days after ts nerve injury.
The ability of anti-androgens to promote syllable changes suggests that
following ts nerve injury, T once again performs the plasticity-inhibiting role
it does in juvenile finches. Since syntactical changes such as additions and
deletions require the involvement of the recursive loop, a song pathway
normally inactive during adulthood, the song nuclei of the recursive loop may
once again become responsive to testosterone and its plasticity-inhibiting
effects following tracheosyringeal nerve injury.
Pharmacologic Delay of Puberty: Effects on Song Learning in the Zebra Finch
Zebra finch males learn their songs from a tutor in a process that culminates
with song crystallization around 90 days of age, when syllables are fixed in a
permanent order which the bird will sing for the rest of his life (Immelman,
1969). Many lines of evidence suggest that testosterone may play a role in
song crystallization. The first major testosterone surge in zebra finch males
occurs around day 75, and this, the hormonal event that marks puberty, is
coincident with the onset of song stereotypy (Prove, 1983). Furthermore,
castrated zebra finches add syllables to their songs at ages when learning is
normally complete (Arnold, 1975), castration combined with antisteroid
treatment blocks the production of mature, stereotyped song (Bottjer &
Hewer, 1992), and males treated with testosterone early in life produce
crystallized songs prematurely (Korsia & Bottjer, 1991). Thus, it appears
that high plasma testosterone levels may close sensitive periods by curtailing
the capacity for sensory learning.
The present study used steroid antagonists in an effort to prolong the period
of neural plasticity and hold open the window during which sensorimotor
learning can occur. Flutamide, a testosterone antagonist, and fadrozole, an
aromatase inhibitor, were used to block the two pathways, direct and indirect
(estradiol-mediated), by which testosterone affects the zebra finch brain at
puberty. The songs of treated birds differed from those of controls in several
respects. Most notably, 61.5% of treated birds added syllabes after 75 days of
age, when songs are normally stable, whereas no control birds added syllables
during this time. Additions were limited to the same few basic types of
call-like notes in all treated birds that added syllables. Both the position
of added syllables within the song and the age at which new syllables were
added differed significantly with respect to the treatment group of the
subject. Changes in syllable morphology and syllable deletions were also
observed in treated birds. Thus, this study gave several indications that
neural plasticity was prolonged in birds in which testosterone's actions had
been blocked with antisteroid treatment.
Coordinated Regulation of Lipid Metabolism in Plants: Regulation of Microsomal
Phosphatidate Phosphatase Activity in Zea Mays by Sphingoid Long-chain Bases
Previous studies in animal model systems have established several mechanisms
through which sphingolipids can act to regulate lipid biosynthesis, but there
have been no investigations to date of similar effects in plants. This study
showed that the presence of high intracellular concentrations of sphingoid
long-chain bases induced by treatment of tissues with fumonisin can be
correlated with down-regulation in the biosynthesis of both sterols, and
phospholipids, specifically phosphatidylcholine and phosphatidylethanolamine.
In addition, it was shown that the presence of D-sphingosine and
DL-erythro-dihydrosphingosine, but not DL-threo-dihydrosphingosine or
phytosphingosine, appears to significantly inhibit the enzymatic activity of
microsomal phosphatidate phosphatase. These findings suggest that sphingoid
long-chain bases may play a significant role in the regulation of lipid
metabolism in sweet corn (Zea Mays).
The Distribution of Herbaceous Species in Primary and Secondary Woodlots in
Williamstown
Following settlement of Williamstown, Massachusetts in 1753, the landscape was
carved out for agricultural and industrial purposes, activities which had a
profound effect on the native flora of the region's temperate forests,
especially the herbaceous layer. Precolonial forests that have not been
affected by agricultural practices are termed primary forests, while forests
which have regrown on land that was previously cultivated, grazed or heavily
logged are termed secondary. Many secondary woodlots have been recolonized
with trees representing late-stage succession, showing that regeneration of a
canopy resembling pre-colonial forest can happen in a relatively short amount
of time. By contrast, the herbaceous layers differ greatly in primary and
secondary woodlots, the latter having less diversity and species richness than
the former. Myrmecochorous (ant-dispersed) species are virtually absent from
secondary woodlots, suggesting that the limiting factor to colonization's
dispersal mechanism. Past land use, however, is not the only factor that
affects herbaceous communities. Herbaceous flora are also affected by
tree-layer composition, with communities in hemlock-dominated woodlots
extremely sparse even though the forest is primary. Limestone soils and rocky
outcrops give way to richer herbaceous communities, and most species seem to
flourish in very moist conditions. In a comparison between north and
south-facing sites, the dry, acid soils of south-facing sites give rise to less
rich herb layers.
Physical Mapping of the Tetrahymena thermophila Macronuclear Genome via
Chromosomal Fragmentation
The ciliated protozoan Tetrahymena thermophila contains two nuclei that have
distinct morphologies. The somatic macronucleus is developed from the
germ-line micronucleus shortly after conjugation by processes involving
extensive DNA amplification, splicing, and sequence rearrangement. Although
the mechanisms involved in the formation of the macronucleus from the
micronucleus have recently been characterized, little is known of the
arrangement of the genes themselves on the macronuclear chromosomes.
The goal of this project was two-fold. The first objective was to develop a
system that will enable Tetrahymena DNA sequences to be mapped within
individual macronuclear chromosomes in a relatively quick and easy manner,
using a procedure that has been developed for use in Saccharomyces cerevisiae.
The proposed procedure employs two vectors that will hold macronuclear
sequences and will undergo homologous recombination with an endogenous
macronuclear chromosome to produce two fragmented chromosomes upon
linearization and transformation into Tetrahymena. The second objective was to
develop two vectors that will enable a fragmented Tetrahymena macronuclear
chromosome to be shuttled between Tetrahymena and Saccharomyces cerevisiae to
allow for the study of macronuclear fragments in isolation from the rest of the
genome. Progress has been made in the construction of both sets of vectors.
While the Tetrahymena/yeast vectors have not been made, the plan for their
construction has been developed. Also, the first set of vectors has been
constructed and characterized. With these new fragmentation vectors, the main
goal of transforming Tetrahymena with a macronuclear sequence can now be
attempted.
A Quantitative and Molecular Population Genetics Study of Larval Chorus Frogs
This project studied the meta-population genetics of the Chorus Frog Pasudacris
triseriata on North Government and South Government Islands off the NE tip of
Isle Royale, MI. Clutches of eggs were collected from each island, hatched,
and raised in controlled environments. Month-old tadpoles were photographed
and frozen.
Quantitative morphometric analysis was conducted via the photographs. From
this analysis, strong evidence for gene-pool variation between subships,
between regions within islands, and between islands was found. Physical traits
found to vary included the tail muscle height, and tailfin height--both of
which may play a role in predator avoidance. The heritability for these two
genetically controlled factors was calculated. This is the first rigorous
examination of the population genetics of P. triseriata on Isle Royale, and the
first quantification of heritability in wild chorus frogs.
Further analysis was done on survivorship, demonstrating that South Government
tadpoles had higher mortality rates than tadpoles from North Government. This
indicates that the south government population has a decreased fitness--perhaps
due to inbreeding.
Qualitative genetic analysis was conducted on the frozen tissue using PCR
technology. Polymorphisms were discovered and counted using RAPD markers.
These data support the morphometric work in showing a significant amount of
genetic variation within the metapopulation. Not enough markers were
accumulated to perform statistical analyses of significant value.
Protein-DNA Interactions at the recA Operator in Bacillus subtilis: A
Thermodynamic Approach to Understanding the Roles of DinR and ComK in
Competence Development
The RecA protein is required for induction of the SOS DNA repair system and
general genetic recombination in Bacillus subtilis. In an uninduced cell,
expression of the recA gene is repressed by the LexA protein. During SOS
induction following DNA damage, a basal level of Rec A is activated to trigger
the autocatalytic cleavage of LexA, which is then incapable of repressing recA.
Evidence suggests that competence induction of recA proceeds in the absence of
LexA cleavage (Lovett et all, 1989) through interaction of the competence
transcription factor ComK with the recA promotor region (Hahn, 1994). This
study investigates the binding of LexA and ComK to the recA promoter region in
hopes of further elucidating the mechanism by which expression of recA is
induced during competence development. Mobility shift assays were used to
determine the dissociation constants (KD) for the interaction of
both proteins with the recA promoter region. The KD was determined
to be 4nM for LexA and 150nM for ComK. Based on these results and the expected
intracellular concentration of ComK, it seems unlikely that induction of recA
during competence is a result of the displacement of LexA by ComK alone. In
conjunction with other experiments, this suggests that SOS induction and the
cleavage of LexA may be necessary for efficient competence expression of recA.
Studies on Neuropeptide Y Release from PC12 Cells
I have performed experiments to determine an effective method for harvesting
and measuring Neuropeptide Y (NPY) from PC12 cell cultures. Several attempts
were made to measure baseline levels of PC12 cellular neuropeptide Y. NPY from
cell harvests were extracted with assay matrix and milliQ water to determine
the effect of different extraction solvents on NPY detection. Enzyme
immunoassay (EIA) of both assay matrix and milliQ water-extracted samples
produced a detectable amount of NPY only once. Complete masking of NPY spikes
added prior to extraction suggests possible degradation during the procedure.
EIA using HEPES-buffered saline (HBS) were also performed to determine the
reliability of our experimental incubation medium as an assay solution. NPY
standards prepared in HBS produced consistently larger absorbance values
compared to those of assay matrix standards. Rehydration of HBS standards in
assay matrix was demonstrated to transfer NPY effectively from HBS to assay
matrix, although concentrating the standards interferes with NPY detection.
The Effects of Hindlimb Suspension on Phosphoglycerate Mutase Activity and
Steady State mRNA Levels in Muscles of the Rat Hindlimb
Mammalian skeletal muscle fibers can be classified into several fiber types
based on their physiological properties, biochemical composition and metabolic
characteristics. Many muscle fibers have the capacity for long-term adaptation
to changing work demands and exhibit plasticity under conditions which alter
the weight-bearing stress imposed on the muscle. One such condition is
hindlimb suspension, in which all weight-bearing stress is removed from the
muscle. As a result of hindlimb suspension, muscle fiber type expression
switches from fibers which utilize oxidative metabolism to fibers which rely on
glycolytic metabolism. Phosphoglycerate mutase (PGAM-M) is an enzyme vital to
the final stages of glycolysis. To study the effects of hindlimb suspension on
this glycolytic enzyme, we analyzed the steady state mRNA levels and the
enzymatic activity of PGAM-M in four hindlimb muscles of control rats and in
rats which had undergone a month of hindlimb suspension. In the oxidative
soleus muscle, PGAM-M mRNA was increased following suspension while three other
glycolytic muscles showed no significant change in PGAM-M mRNA levels and
PGAM-M specific activity following suspension. Activity levels decreased
significantly in both the soleus and extensor digitorum longus (EDL). These
results suggest the involvement of other mechanisms regulating PGAM-M gene
expression. We also observed lower PGAM-M specific activity as well as lower
PGAM-M mRNA levels in the oxidative control muscle (soleus) as compared with
the glycolytic control muscles. This finding indicates that the increase in
PGAM-M specific activity in the soleus is pretranslationally regulated.
Construction of EXM1 and EXM2 Gene Deletions in S. Cerevisiae
EXM1 and EXM2 (Exit from Mitosis) are two novel Saccharomyces
cerevisiae genes putatively identified to be involved in a checkpoint
regulatory mechanism that monitors cellular exit from mitosis. In order to
characterize more completely the roles of these genes in this checkpoint
system, two different gene deletion techniques were employed in an attempt to
disrupt the function these genes in vivo. Because an EXM2 plasmid construct
with amenable restriction sites was available, simple cloning steps were used
to generate successfully an 84% deletion of the open reading frame of EXM2. To
create this gene disruption, 684 base pairs (BPS) of the 786 bp EXM2 open
reading frame was replaced with a hisG-URA3-hisG construct that can undergo
mitotic recombination to eliminate the URA3 marker. Unlike EXM2, none of the
existing plasmid constructs containing EXM1 had convenient restriction sites
suitable for the conventional cloning procedure used to generate the EXM2
deletion. Thus, the creation of an EXM1 null allele was attempted through the
use of double fusion PCR, a technique that completely and precisely eliminates
the open reading frame of the gene. Double fusion PCR was successful in
generating a genetic construct suitable for transformation into yeast that
contained the LEU2 selectable marker flanked by the 3' and 5' adjacent regions
of the EXM1 gene. Because this complete fusion product could not be amplified
by PCR, however, this EXM1 null construct could not be integrated into yeast
due to the low concentration of DNA used in the transformation. These results
suggest that the conventional cloning procedure employed to make the EXM2 gene
deletion is more efficient and reliable than the double PCR fusion technique
used for the EXM1 null allele. Once the EXM1 and EXM2 gene disruptions have
been completely constructed and integrated into diploid yeast, the phenotypes
of these deletion mutants can further clarify the in vivo functions of these
genes.
The Vaccinia Virus dUTPase Gene: Disruption in Tissue Culture and
Site-Specific Mutagenesis of a Conserved Motif
Vaccinia virus is a large double-stranded DNA virus that replicates in a host
cell's cytoplasm. The virus relies little on host functions and encodes many
of the enzymes involved in DNA metabolism and synthesis. One such enzyme is
dUTPase. Found in a variety of organisms, dUTPase is thought to play a role in
nucleotide precursor metabolism and in the prevention of uracil incorporation
in DNA. Studies of the vaccinia dUTPase protein has shown that it requires a
Mg2+ cofactor for catalysis. It is thought that Mg2+may
associate with the third of five highly conserved motifs in the enzyme. This
motif resembles a Walker B sequence, implicated as a Mg2+ binding
site in a variety of NTPases.
The present study had two objectives. The first goal was to alter the
conserved aspartic acid residue located at position 82 in the third motif, the
putative Walter B sequence. Using site-specific mutagenesis, this aspartic
acid residue was successfully changed to an asparagine and to a glutamate.
Mutant proteins possessing these changes lacked dUTPase activity.
Pre-incubation with excess Mg2+ failed to restore activity to the
mutants. Thus, the aspartic acid residue at position 82 was shown to be
essential for the enzyme's activity.
The second objective was to disrupt the dUTPase gene within the vaccinia genome
using a dominant selectable marker. The failure of a previous attempt to
disrupt the dUTPase gene suggested that the gene was essential, although it had
been eliminated in large scale genomic deletions. One such deletion mutant
possessed a small plaque phenotype that was not screened for in the previous
attempt to disrupt the dUTPase gene. In this study, recombinant virus was
produced and formed plaques with an unusually small size. However, technical
difficulties delayed the isolation of recombinant virus from live monolayers,
which was eventually accomplished by switching cell lines. Once this
recombinant virus is purified, it will be analyzed by southern blot to
determine if the dUTPase gene has been disrupted.
Detour Ahead: Retinal Ganglion Cells Directed to a Foreign Muscle Target
Retinal ganglion cells (RCGs) are the group of central interneurons that form
the sole output of the retina to the brain. They are capable of highly
specific regeneration into the optic tectum in lower vertebrates, which can
lead to functional recovery of vision. Though RGCs show a particularly strong
affinity for the optic tectum, they can be surgically directed to non-optic
regions of the brain where they are capable of forming functional synapses. In
the present study, RGCs of goldfish were axotomized by transection of the optic
nerve, and their regeneration was redirected to the superior oblique muscle
with a nerve bridge made from the posterior lateral line nerve of the fish.
After allowing 60-90 days for regeneration, numerous RGC axons could be traced
into the lateral line implant and the superior oblique muscle, where they
appeared to form synapses. This is the first report of vertebrate central
interneurons forming synapses on a peripheral muscle target. following
stimulation of the implant, long-latency EMG responses were recorded in the
superior oblique muscle, indicating that the synapses formed are functional.
These EMG responses have a light-sensitivity, for after a period of 30-60
minutes of almost complete darkness, some EMG responses increased in amplitude
by up to 167%. However, RGCs are glutamatergic, whereas acetylcholine is the
neurotransmitter at the vertebrate neuromuscular junction. Hence, these
results imply a phenotypic change of neurotransmitter for either the
pre-synaptic or post-synaptic cells in this novel neuromuscular junction.
Addition by Subtraction: Early Catecholaminergic Lesion of the Zebra Finch
Area X Leads to Increased Number of Notes in Song
The male zebra finch (Taeniopygia guttata) learns its song from adult tutors
during a sensitive period spanning days 25 to 90 post-hatch. Around day 90,
song "crystallizes," or stops changing.
The zebra finch forebrain nucleus Area X is necessary for normal song
development but not for normal maintenance of adult song (Scharff &
Nottebohm, 1991). A developmental trend in which the catecholaminergic
innervation of Area X increases throughout the sensitive period has recently
been characterized (Soha et al., 1996). This experiment determined the effects
of depleting catecholamines in Area X during the sensitive period on song
acquisition.
Juvenile zebra finches aged 30 to 45 days were given stereotaxic
microinjections of either the catecholaminergic neurotoxin 6-OHDA or a saline
(vehicle) solution. compared to birds receiving saline injections, birds
treated with 6-OHDA had greater numbers of notes in their songs and had more
variable songs according to the sequence linearity measure. The greater
variability reflected by 6-OHDA-treated birds' lower sequence linearity scores
arose from their singing more atypical internal transition types than sham
birds.
There were no significant differences in catecholamine histofluorescence in
brain sections from sham-operated and 6-OHDA-treated birds sacrificed at six
months post-surgery. This finding verified Soha's result that significant
ingrowth of catecholaminergic terminals into Area X can continue until late in
the sensitive period.
Because the trend of increasing catecholaminergic innervation in Area X
continues at least up to and perhaps past the time of crystallization, it is
unclear whether catecholamines in Area X facilitate song plasticity or
contribute to closing down the sensitive period. This study's results could be
interpreted as consistent with a model in which catecholamines help end the
sensitive period.
On the Way to Cellular Localization of EXM2
Fidelity of the eukaryotic cell cycle, a highly regulated sequence of temporal
events, is critical for survival of the eukaryotic organism; an error occurring
at any stage of the cell cycle could result in cell death and severe genetic
damage to the organism (Allen et al., 1994). Because of the importance of the
cell cycle, it is logical that the cell exercises tight control over the
ordering of the cell cycle events.
One manner in which control over the cell cycle is exercised is through the
check point mechanism. A number of regulatory checkpoints exist throughout the
cell cycle at points such as entry-into and exit-from mitosis (Agarwal et al.,
1995, Weinert et al., 1994). At these checkpoints, the cell cycle pauses to
verify that all prior events were successfully completed. If the events were
not successfully completed, the cell cycle engine would pause until necessary
repairs of damage or completion of upstream events were ensured (Enoch and
Norbury, 1995, Hartwell and Kastan, 1994).
Therefore, a careful study of checkpoint control mechanisms of the genes
involved in checkpoints is critical. Two genes called EXM1 and EXM2 isolated
from the organism S. cerevisiae have been implicated in the exit-from-mitosis
checkpoint (Raymond, 1996). This work begins the examination of the cellular
localization of EXM2. A pET21-a(+)-EXM2 plasmid was prepared through the
subcloning of EXM 2 from the pWR1054 plasmid into the pET21-a(+) vector.
Subcloning was accomplished through the creation of restriction sites flanking
the EXM2 gene. These sites were used in the excision of the EXM2 and
subsequent ligation into the pET21 vector between corresponding restriction
sites. The EXM2 ORF is located downstream of the pET vector's T7 promotor and
upstream of the pET vector's His-6 tag. Future work will involve
overexpression and purification of the Exm2 protein, followed by preparation of
antibodies to the protein. These antibodies can then be used in a variety of
manners, including indirect immunofluorescence experimentation. This can lead
to the cellular localization of the Exm2 protein and thus, will further the
characterization of a potentially important checkpoint gene.
SPF1, A Cold-Sensitive Suppressor of cdc14-7, Regulates Exit from Mitosis
Proper cell cycle progression is necessary for maintenance of an organism. One
essential component of the yeast (Saccharomyces cerevisiae) cell cycle is
CDC14. CDC14 encodes a protein tyrosine phosphatase which contains other
functional domains (Wan et al., 1991, Shirayama et al., 1996). The goal of
this work was to study two extragenic suppressors of temperature-sensitivity of
cdc14-7, sup1-15 and sup9-13. In this study, it was determined that sup1-15
and sup9-13 are two alleles of the same gene, SFP1 (Split Finger
Protein 1). SFP1 has a nuclear localization sequence and two
Cys2 His2 zinc-finger domains split by approximately 40
amino acids (Blumberg and Silver 1991). It was determined that sup1-15 cannot
suppress lethality of a cdc14-disruption mutant, indicating that suppression is
not through a complete bypass of CDC14 function. An sfp1-null mutant was
created, found to be cold-sensitive, and found to suppress
temperature-sensitivity of cdc14-7. Results found from creation of the
sfp1-null indicate that suppression of temperature-sensitivity of cdc14-7 does
not involve restoration of a protein-protein interaction between sfp1 and
cdc14. Microscopic observations show random bud polarity in sup1-15 cells.
cdc14-7, sup1-15 double mutants had abnormal mitotic spindles. Compared to
wild type, sfp1-null mutants display an altered reaction to treatment with
nocodazole, showing a delay in cell cycle arrest. These data suggest that sfp1
may interact, not only with CDC14, but with many other members of the
exit-from-mitosis machinery in controlling an exit-from-mitosis checkpoint
through one of a number of possible models.
Using Random Amplified Polymorphic DNA Markers to Study the Genetics of
Tetrahymena thermophila
Tetrahymena thermophila, a ciliated protozoan, has two nuclei: the
macronucleus and the micronucleus. During conjugation, the macronuclear genome
is created by extensive DNA rearrangement and deletion of a copy of the
micronuclear genome. To investigate macronuclear development, polymorphic
markers (occurring between two inbred strains B and C3) on chromosome 5 were
obtained through RAPD PCR methods (outlined in Brickner et al., 1996) and used
as probes. Probes were hybridized to target DNA on Southern blots made from
pulsed field gel electrophoreses of Tetrahymena's macronuclear genome. With
some exceptions, obtaining micronuclear probes through RAPD PCR proved to be an
expedient and reliable method. The results give some clues into macronuclear
genome processing and development.
Analysis of Plant Sphingolipids: Relevance to the Cancer-Preventative Effects
of Dietary Fruits and Vegetables
Sphingolipids are involved in a number of signaling pathways including ion
transport and cell growth. Recently, sphingolipid involvement in cell growth
has been examined with respect to possible cancer-preventative properties. It
was discovered that milk sphingolipids and glycosphingolipids inhibit the
formation of colonic cysts. The interest in dietary sphingolipids has led to
our research on the composition of glucosylceramide long-chain bases in plants,
given that plant-rich diets are associated with decrease incidence of cancer,
and studies aimed at testing plant sphingolipids as cancer-preventative agents
are planned. Glucosylceramides are the prevalent glycosphingolipid in plant
cells. Our results show similar long-chain base profiles for apple, tomato and
summer squash which contained a large amount of cis- and trans-double bonds.
Potato was predominantly di-hydroxy long chain bases with equal amounts of both
cis- and trans-double bonds. Broccoli proved to be an anomaly with 30% of the
long-chain bases as 4-hydroxysphinganine (t18:0) which does not appear in any
other type of plant published to date. These results are a first step in more
comprehensive studies examining the effects of plant sphingolipids as
cancer-preventative agents.
The Genetic Structure of Arctic Disjunct Populations of Sagina nodosa
(Caryophyllaceae), Isle Royale, Michigan
On the islands at the northeastern end of Isle Royale National Park, Michigan
there exist populations of arctic plant species that are completely disjunct
from their main home ranges in the arctic. In this project I mapped the
disjunct ranges of six of these arctic species on 27 different islands at the
NE end of Isle Royale. Tissue samples were taken from two species, Sagina
nodosa (Caryophyllaceae) and Saxifraga tricuspidata (Saxifragaceae), and a
variety of different protocols were used to attempt to extract genomic DNA from
these samples. Using random amplified polymorphic DNA (RAPD) analysis, I
examined the population structure of Sagina nodosa. This analysis revealed 40
different polymorphic loci (based on four 10 oligonucleotide primers). These
variable loci showed that 90.2% of the genetic diversity was partitioned within
populations, while 9.8% occurred among populations. Further, the island
populations were highly differentiated, with an FST value of 0.546
(indicating extensive population subdivision). Internal structure of the
island populations was not based on relatedness of geographically close
individuals, as there was no correlation between increasing genetic distance
with increasing geographic separation between individuals. Cluster analysis
revealed that there may be some within population genetic structuring based on
distance above the average water-line. Data from the North Government Island
population suggest that individuals that grow close to the water are more
closely related to each other than to individuals from higher on the shore.
The pattern shown by the Isle Royale arctic disjuncts, where island populations
are highly differentiated, but still retain extensive genetic diversity within
populations, is probably maintained by a balance of genetic drift, genetic
structuring within populations mediated by differential selection, and rare
gene flow events between populations.
Photoaffinity Labeling and Proteolytic Cleavage of Vaccinia Virus dUTPase
Deoxyuridine triphosphatase (dUTPase) plays a critical role in the growth cycle
of cells and thus serves as a possible target for gene therapy.
Characterization of dUTPase's active site may facilitate the development of
chemotherapeutic agents and is therefore an important step in this process.
The experiments performed in the present study were directed towards the
specific goal of characterizing the dUTP binding site in vaccinia dUTPase via a
procedure that is generally used to identify nucleotide binding sites on
proteins. This technique is based on a combination of photoaffinity labeling,
which covalently links the protein and a radiolabeled target nucleotide at the
protein's active site, and proteolytic cleavage, which subsequently digests the
labeled protein at specific and characteristic sites. Separation and
identification of labeled products by SDS-PAGE and autoradiography reveal
peptide domains that are likely involved in nucleotide binding. Before
proceeding with this technique, it was first necessary I) to demonstrate
successful cleavage of dUTPase by our selected proteolytic reagents and ii) to
show that our chosen nucleotide substrate, ATP, covalently crosslinks to
dUTPase in a manner that is specific, competitive, and dependent on UV
exposure, thereby demonstrating its utility for photoaffinity labeling. Here,
we report the derivation of protocols for digestion of dUTPase by
hydroxylamine, cyanogen bromide, and endoproteinase Lys-C; and we report
unsuccessful initial attempts at demonstrating the utility of ATP as a
cross-linking substrate analog for future photoaffinity labeling experiments.
Kinetic Studies of the LexA Repressor Autodigestion: Determination of
Temperature Dependence and Thermodynamic Parameters
The Bacillus subtilis SOS DNA-repair system is comprised of approximately 20
din (damage inducible) genes which are constitutively
repressed by the 22.7-Kd protein, B. subtilis LexA. When DNA damage occurs in
a B. subtilis bacterial cell, the LexA repressor undergoes cleavage to allow
for the expression of the din genes and thereby activate the full SOS
response.
Repressor cleavage is mediated by a second protein, RecA, activated by a
single-stranded DNA signal generated by the damaging agent. The cleavage has
been characterized as an intramolecular general base-catalyzed hydrolysis of
the peptide bond between the alanine-91 and glycine-92 residues of the protein.
In the proposed cleavage model, an ionized lysine residue abstracts a proton
from the oxygen of a serine residue and thereby activates the serine oxygen
towards nucleophilic attack of the carbonyl carbon of the peptide bond.
This work investigates the autodigestion of the repressor in vitro in order to
further elucidate the mechanism of B. subtilis LexA cleavage. The
thermodynamic parameters of the reaction were determined by examining the pH
dependence of the reaction rate at two different temperatures, 37[ring]C and
47[ring]C. The rate assays were done in high pH boric acid buffers to effect
ionization of the catalytic lysine residue and thereby cleavage in vitro.
A pKa of 9.52 and a kmax of .91/hour were determined for the
37[ring]C autodigestion of B. subtilis LexA; at 47[ring]C, a pKa of 9.12 and
kmax of 1.41 were determined. Using these results, the
thermodynamic parameters of the reaction with wild-type repressor were
calculated. For the ionization step, the following were found: [Delta]G=13.5
kcal/mol, [Delta]S=14.9 cal/K
*mol, and [Delta]H=18.1 kcal/mol. For the
activation step, [Delta]G=23.3 kcal/mol, [Delta]S=49.4 cal/K
*mol and
[Delta]H=8.0 kcal/mol.
Synthesis and Partial Characterization of Ruthenium Lewis Acid-Urea
and
Ruthenium Lewis Acid-Amide Complexes
Transition metal Lewis acid complexes with carbonyls are applicable for a
number of fields, including organic synthesis, and can sometimes provide a
simpler model for biological systems. The carbonyl groups of ureas and amides
were examined. The urea ligands used in this analysis were urea,
1,1-dimethylurea and1,3-dimethylurea. Mass spectral analyses, conducted in
lieu of combustion analyses, provide evidence for coordination between the urea
ligands to the ruthenium. The amide ligands used in this analysis included
acetamide, 2-pyrrolidinone, and dimethylformamide. Dynamic behavior may be
occurring within the dimethylformamide complex because of steric
considerations, such as E vs. Z isomerization. Spectroscopic
characterization of the ruthenium-urea and ruthenium-amide complexes provides
evidence for [sigma] coordination between the lone pair of electrons on the
oxygen of the ligand to the ruthenium.
Complex Dynamics in a Modeled System of Two Coupled Oscillators
Most hormone concentrations in the body are regulated by negative feedback
mechanisms in which the production and release of hormones are regulated
according to the concentration of related species. Many hormones are released
in a pulsatile manner. A wide range of pulsatile release patterns have been
observed in different hormonal systems. The mechanism driving these complex
release patterns is not known in most cases. The mechanistic complexity needed
to sustain complex hormonal release patterns is a matter of much recent
conjecture.
A simple six-species, ten-parameter model of two chemical oscillators coupled
through their external products is analyzed to investigate the possibility of a
simple system's ability to sustain complex dynamical behaviors like the release
patterns observed for hormones in vivo. Although analytical methods for
measuring hormone concentrations in vivo have improved greatly in recent
years, it remains very expedient to observe the behavior of models similar to
the physiological systems in question to answer questions about mechanisms and
reasons behind hormone release.
The simple model of two coupled oscillators coupled through negative feedback
to their external products sustains a wide range of different periodic, chaotic
and other dynamical behaviors. The coupling between the two oscillators is the
element responsible for the appearance of these behaviors. The range of
dynamical behaviors observed in the model demonstrates that something as simple
as a physiological feedback loop with similar coupling between circulatory
concentrations of hormones and production centers could be the source of
complex hormone release patterns observed in vivo.
Synthesis of Organic Electrochromic Materials based on Benzoquinone Centers and
Attempted Synthesis of an Anthraquinone Ligand for a Ruthenium-Polypyridine
Complex
The synthesis of the potentially useful electrochromic compound
2,5-bis--(4,4-dipyridyl)-3,6-dioxy-1,4-benzoquinone (1) was attempted in
a variety of solvents and conditions. Using
2,3,5,6-tetrachloro-1,4-benzoquinone and six equivalents of 4,4-dipyridyl in
refluxing acetonitrile for 12 hours resulted in a 58% yield of
2-(4,4-dipyridyl)-3-oxy-5,6-dichloro-1,4-benzoquinone (2) as determined by
1H-NMR, 13C-NMR, and FT-IR. The yield was increased to
78% in refluxing o-dichlorobenzene. Using
2,3,5,6-tetrafluoro-1,4-benzoquinone and six equivalents of 4,4-dipyridyl in
chloroform at room temperature resulted in a 66% yield of 2. Using
2,3,5,6-tetrafluoro-1,4-benzoquinone and one equivalent of 4,4-dipyridyl in
chloroform at room temperature resulted in a mixture of products that contained
2 as well as an unidentified compound which could not be isolated that could be
1.
Synthesis of a Chiral Benzene-Ruthenium (II) Catalyst for Use
in
Hydrogenation Reactions
The goal of this project was to synthesize a chiral catalyst with a ruthenium
center for use in hydrogenation reactions. Attempts at synthesizing the
catalyst involved coordinating various chiral phosphine ligands to a
benzene-ruthenium molecule by cleaving the dimer,
[(u6-C6H6)RuCl2]2. Preliminary
procedures entailed synthesizing the catalyst by allowing the dimer to react
with the ligand directly. However, low yields necessitated producing a
precursor molecule,
[(u6-C6H6)RuCl(CH3CN)2]+PF6-,
to the catalyst. Reactions between the dimer and NH4PF6
in CH3CN resulted in the production of this precursor which,
when reacted with the phosphine ligand bis(diphenylphosphino)butane
(CHIRAPHOS), resulted in the production of the catalyst in high yield. A
determination of the effectiveness of the catalyst in the chiral hydrogenation
of 3-methyl-2-cyclohexen-1-one resulted in 100% conversion to
3-methylcyclohexanone. The optical activity of this product was not determined
at this time.
Preparation and Electrochemical Investigation of Mono- and
Bis-Pyridinium
Anthraquinones
The goal of this research has been the preparation and electrochemical
investigation of a series of mono- and bis- pyridinium anthraquinones in order
to determine the effects of pyridinium substituent position and number on
reduction potentials. The 2-(4-dimethylaminopyridinium) anthraquinone and
1,8-(4-dimethylaminopyridinium)anthraquinone were readily prepared in
respective yields of 48.2% and 39.8%. The
1,5-(4-dimethylamino-pyridinium)anthraquinone was prepared in 68.6% yield by
isolation and purification of the mono-pyridinium product of the
1,5-dichloro-anthraquinone and subsequent reaction with
4-dimethylaminopyridine. Electrochemical characterization of the prepared
pyridinium anthraquinones shows that pyridinium substituent position and number
can be used to modestly modify the reduction potentials of anthraquinones. In
order to expand upon this work, the preparation of mixed pyridinium
anthraquinones was also attempted. Although no successful preparations were
carried out, mixed pyridinium anthraquinones may be synthesized by the
isolation of the mono-pyridinium product of the 1,5-dichloroanthraquinone and
subsequent reaction with a different pyridine. The preparation of pyridinium
hydroanthraquinones was also attempted in order to more fully characterize the
pyridinium anthraquinones. Unfortunately, this reaction was unsuccessful under
a variety of conditions
An FT-IR Study of the Interactions of Sulfur Dioxide and Soot
from
-100deg.C to -150deg.C Abstract
The realization in the last 10 to 20 years that heterogeneous reactions in the
atmosphere play an important role in atmospheric chemistry has led to increased
interest in studying atmospherically relevant gas-solid and gas-liquid
reactions in a laboratory setting. One current puzzle in atmospheric chemistry
is that in some situations, such as in contrails of high altitude jets or
industrial plumes, there is an observed overabundance of sulfuric acid and
underabundance of sulfur dioxide compared to what is expected from models based
on known chemical reactions. Some researchers have suggested that
SO2 conversion to H2SO4 on the surface of soot
particles may explain these observations.
Using a vacuum system designed for the infrared spectroscopic study of
atmospherically relevant surface reactions, I investigated the interactions of
SO2 and soot over the temperature range of -100deg.C to -150deg.C
and the pressure range of 10-7 to 10-4 Torr. I observed
and quantified sub-bulk rapid adsorption of SO2 to soot and a slower
adsorption on, or diffusion into, soot by SO2. Developing a kinetic
model to explain the rapid adsorption, I estimated the initial sticking
coefficient of SO2 on soot to be 0.01 (0.004 to 0.05) at -135deg.C.
When soot is exposed to SO2 under sub-bulk growth conditions, one or
more reaction products that absorb in the 1050 to 1200 cm-1 region
form on the soot. This reaction product or products desorb with heating to
-80deg.C. Other reaction products absorbing at below 1000 cm-1 form
on soot when exposed to SO2 and higher trace concentrations of
H2O. These reaction products absorbing below 1000 cm-1
form a non-volatile residue believed to be H2SO4.
Future work will continue this investigation of SO2 and soot
attempting to quantify what I observed and also moving to warmer, more
atmospherically relevant, temperatures.
Preliminary Characterization of Two Interacting Sequences Within the
Interleukin-4 NEG-1 Negative Regulatory Element in Murine Mast Cells
A Negative Regulatory Element termed NEG-1 which functions in mast cells has
been previously identified in the murine Interleukin-4 promoter. (Weiss,
unpublished results) Reporter gene assays identified two subregions, termed
Neg 1A and Neg 1B, which are critical to NEG-1 function. Mutation of either
region in reporter gene constructs led to significant increases in reporter
gene activity, which demonstrates that Neg 1A and Neg 1B do not function
independently. An oligonucleotide which spans NEG-1 was used as probe in
Electrophoretic Mobility Shift Assays (EMSAs) with nuclear extracts from murine
mast cells to determine which bases are critical for protein binding to this
region. Cold competition experiments, using molar excesses of Neg 1A and Neg
1B, indicated that Neg 1A, but not Neg 1B is critical for protein binding to
NEG-1. The NEG-1 oligonucleotide, however, extends only two base pairs past
the Neg 1B site, and for protein to be able to bind this site, more of the 3'
flanking region is likely needed. In this study, oligonucleotides spanning Neg
1B only, termed Neg 1B, and the entire NEG-1 region (with more of the Neg 1B 3'
flanking region), termed Neg 1A+B as well as a mutant version of the Neg 1A+B
oligonucleotide were used as probe in EMSAs. Neg 1B was unable to form a
specific DNA-nuclear protein complex under a variety of binding conditions.
Neg 1A+B forms a complex of higher mobility than the complex formed with Neg
1A. These results support a cooperative model of protein binding to Neg 1A and
Neg 1B.
The Menschutkin Reaction of Strained Heterocyclic Systems
The pseudo first order rate constants for the Menschutkin reaction of
2,3-dimethylquinoline 7, 2,3-dihydro-1H-cyclopenta[b]quinoline 8,
1,2-dihydrocyclobuta[b]quinoline 9, 2-benzylpyridine 10,
2-benzhydrylpyridine 11, and 1-azatriptycene 12 with iodomethane in
acetonitrile-d3 at 50 [ring]C were measured by proton NMR
spectrometry. Duplicate kinetic runs gave precise (<= +/- 2.8%) linear (R
coefficient >= 0.993) rate constants. Ring strain effects on basicity were
not correlated with the observed rate constants. Ring strain effects on
molecular geometry and steric interference were applied to explain the trends
in relative reaction rates across compounds 7-9 and 10-12.
A Concise Route to Isocanthine Alkaloids
A concise synthesis of
5,6-dihydro-4H-indolo[3,2,1-ij][1,6]naphthyridine (6), an isomer
of canthine (3), was attempted in three steps from indole-3-carboxaldehyde (9).
The key step, an intramolecular hetero Diels-Alder reaction, gave the desired
isocanthine only as a minor product. An analogous synthesis of
1-methyl-isocanthine (14) was likewise unsuccessful. A concise four-step
synthesis of isocanthin-6-one (8) was attempted. 4,5-Dihydro-isocanthin-6-one
(11), the direct precursor of 8, was synthesized in three steps in 45% overall
yield. Preliminary attempts to oxidize 11 to 8 with DDQ were unsuccessful.
Low Temperature Collisional Electronic Quenching of Nitric Oxide
Laser-Induced Fluorescence (A2[Sigma]+, v'= 0)
Following single photon excitation (A2[Sigma]+, v'= 0
<- X2[Pi], v" = 0) of nitric oxide (NO), we study the behavior of
the fluorescence transition (A2[Sigma]+, v'= 0 ->
X2[Pi], v" = 3) in the presence of NO, argon, methanol, benzene,
thiophene, toluene, and cyclohexane between 215 K and 300 K. By examining the
fluorescence decay lifetime of a gas mixture containing NO and a collision
partner as a function of the partial pressure of the collision partner, we
determine the quenching cross section ([sigma]) of the collider, a term
reflecting the electronic collisional quenching effect of the collider on the
fluorescence quantum yield of the gas mixture. The temperature dependence of s
reveals information about the transfer of energy between the excited NO
molecule and the quenching species.
The argon and cyclohexane room temperature and low temperature quenching cross
sections are negligible, reflecting their non-existent dipole moments and
non-aromatic structures. Impurities in the gas sample, in particular water,
account for an insignificant increase in the quenching cross sections of these
colliders with increasing temperatures.
NO, methanol, benzene, thiophene, and toluene are efficient quenchers with
quenching cross sections significantly larger than gas kinetic cross sections.
As the temperature decreases the quenching efficiency of these five molecules
increases. Using the Parmenter attractive force model, the cross-sectional
temperature dependence of the five molecules is analyzed . The potential well
depths of NO, methanol, benzene, thiophene, and toluene are 49 cm-1,
112 cm-1, 118 cm-1, 105 cm-1, and 126
cm-1, respectively. Based on the dipole moments, polarizabilities,
and electron affinities of each molecule, the calculated potential well-depths
support the hypothesized dominance of collision complex formation and
near-resonant electronic energy transfer at low temperatures. There is no
conclusive evidence, however, that the near-resonant energy transfer accounts
for the observed increase in quenching cross sections at low temperatures.
Phil-Tor: Natural Language Preprocessing in Filtering Techniques
As the size of on-line information resources increases exponentially, new tools
are becoming necessary to navigate the informational glut. Recently,
information retrieval has turned to artificial intelligence as one method for
counteracting the low signal-to-noise ratios that plague most search queries.
This thesis applies machine learning to the task of content-based filtering,
with a specific examination of how natural language preprocessing affects
filtering performance. It is hypothesized that a vocabulary consisting of
adjacency bigrams will facilitate improved learning, as opposed to a vocabulary
consisting of word tokens. We collect a data set suitable for document rating
research. We will show that natural language analysis in the form of adjacency
bigrams does not improve performance. We will also describe a learning
algorithm that outperforms similar filters on small training sets.
Adding Concurrency to LOOM
Over the past decade, both object-oriented and concurrent programming languages
have become popular tools for solving complex problems, and language designers
have recognized that combining these two paradigms can be useful. Concurrency
allows object-oriented languages to address more types of problems and
potentially speed up execution. Object-oriented features can improve the
organization of concurrent programs and potentially remove some of the
low-level process control by encapsulating it in object structure. In this
thesis, we explore the addition of concurrency to the object-oriented language
LOOM, focusing on providing a safe, easy to use language for programmers
familiar with object-oriented programming but not necessarily with concurrency.
We introduce a large grain of concurrency by identifying processes with
objects, and allow these objects to communicate both synchronously and
asynchronously using the existing message structure. Special semantics for
self-inflicted messages prevent deadlock when processes send messages to
themselves, but mutually referential objects can cause deadlock. Conditional
synchronization of message reception is handled with separately inheritable
pre- and post-condition sections in classes, avoiding extensive redefinitions
of synchronization constraints in subclasses and most forms of inheritance
anomaly.
Sackung on Dead Indian Hill, Park County, Wyoming
Sackung, or gravitational spreading of the ridge-top of Dead Indian Hill
(elevation, 2644 m) has resulted in a summit trench approximately 70 m wide and
400 m long as well as uphill-facing scarps and small linear trenches. Dead
Indian Hill, a cuesta located just south of the mouth of the canyon of Clarks
Fork of the Yellowstone River, is part of a monocline of Paleozoic and Mesozoic
sedimentary rocks with an east dip ranging from 6 to 15 degrees. The summit
trench trends 015o, the primary joint set is oriented at
020-030o, and a secondary set trends 120-130o. Talus
mantles both the east and west slopes, and a block slope and block stream
extend beyond the talus on the east side. The blocks of the taluses, block
slope, block stream, and bedrock at the summit trench are competent sandstone
of the Pennsylvanian Tensleep Formation. Beneath are the shales and limestones
of the incompetent Upper Mississippian/Lower Pennsylvanian Amsden Formation.
Field observations are used to determine how this summit trench fits existing
theories of sackung initiation. Potential weaknesses include the dipping
bedding planes which could accommodate slippage of sandstone over shale, and
the joints which are subparallel to the main trench. Furthermore, solution
cavities in the limestones of the Madison and Amsden Formations include a sink
in nearby Sunlight Basin as well as several caverns in the US 296 roadcuts near
the top of Dead Indian Pass. The shales have locally failed numerous times,
including landslides in Cambrian to Cretaceous shales throughout the area and a
large landslide in the Cambrian Gros Ventre formation on the west side of Dead
Indian Hill. These shales could contain one or more failure surfaces. Removal
of lateral support has resulted from downcutting by the Clarks Fork and the
creek along Dead Indian Gulch; this has destabilized the slopes, especially on
the east side where Dead Indian Gulch has removed the toe of the dip slope of
the Tensleep and Amsden Formations. Other potential factors include seismic
shaking, which could trigger slope failure, and the structure at the site,
which includes several steep faults. Furthermore, a former wetter and/or
colder climate could facilitate rock falls and movement of joint blocks by
increasing fluid pressure and periglacial activity.
It is most likely that the sackung at Dead Indian Hill was caused by the
removal of the toe of the dip slope by fluvial erosion to the east of the
summit, with probable seismic triggering. Failure is hypothesized along the
contact of the Tensleep and Amsden Formations, or slightly below it, with
elevated pore pressure reducing the friction along the plane to permit sliding.
Stress analysis suggests failure along planes dipping at 60o; these
planes are most likely joints.
The Shores of Wyoming: Depositional Environments of the Middle Cambrian
Flathead Sandstone, Park County, Wyoming
The Flathead Sandstone of northwestern Wyoming and Montana is a quartz-rich
sheet sandstone overlying the Archean igneous and metamorphic basement rocks of
the area. It represents the first cycle of deposition as the Cambrian sea
transgressed over the craton, and is Middle Cambrian in age. Little detailed
work has been done on the Flathead Sandstone, and its provenance and
environment of deposition are poorly understood.
This project uses petrographic analysis and stratigraphic evidence to
distinguish the various marine and continental environments present during the
deposition of the formation in the Clarks Fork area. The purpose of this study
is not only to learn more of the Flathead Sandstone in its manifold variations,
but also to contribute to the understanding of ancient transgressive deposits
in general.
Internal structures, textures, and mineralogic composition point to both marine
and fluvial facies in the Flathead Sandstone. Fluvial facies are distinguished
by pebble lag deposits, submature textures, and feldspathic composition.
Structures evident within the fluvial facies are trough cross-stratification,
cut-and-fill structures, and thin horizontal bedding. Marine facies are on
average medium-grained, texturally mature quartz arenites, some of which
display horizontal feeding traces or vertical burrows. Sedimentary structures
include thick horizontal bedding, low-angle planar and trough cross-bedding,
and hummocky cross-stratification.
Point-count data indicate a craton interior provenance with some evidence for
basement uplift. The composition of the sandstone is consistent with
derivation from the underlying granitic rocks. However, a portion of the
samples contains detrital chert and metamorphic quartz, suggesting contribution
from a metamorphic source.
The Quaternary Evolution of Waldron Island, Northern Puget Lowland, Washington
Thick deposits of unconsolidated sediments on Waldron Island and in the
adjacent channels of the northern Puget Lowland record the advance and retreat
of the Cordilleran ice sheets most recently between 18,000 and 13,500
14C years before present. I mapped beach cliff exposures on Walron
Island along Cowlitz Bay, North Bay, and at Point Hammond. I collected
striation data and made measurements of preserved channel orientation in order
to establish paleoflow directions. In addition, I conducted marine seismic
surveys along a trackline west from Cowlitz Bay around Waldron Island to Mail
Bay. The data from these surveys was used to correlate submarine sediments
with onshore exposures.
Reconnaissance mapping and seismic surveys and well log data demonstrate that
much of Waldron Island is blanketed with unconsolidated sediment that in places
reaches >160 m in thickness. Basal crossbedded sands and gravels are
probably the Esperance Sand member of the Vashon drift and provide an excellent
basis for correlation with the regional stratigraphy of Armstrong and
Easterbrook. The absence of major preserved thickness of Vashon till on Waldron
suggests that erosional processes at the glacier bed were active throughout the
glaciation. As ice retreat accelarated after 14.0 ka, the development of
extensive subglacial drainage contributed to continued erosion. The bulk of
the deposits filling channels in the Esperance Sand appear to be related to
meltwater erosion beneath the glacier and deposition at the glacial terminus.
In addition, the high pressure subglacial meltwater streams probably
contributed to the deep scour observed in the channels around Waldron Island.
Seismic reflection profiles offshore of beach cliff exposures provide data
critical to a three dimensional reconstruction of the sedimentation processes
in operation at Waldron at the close of the last glaciation. Major bedrock
channels exposed in seismic surveys cross-cut the regional structural grain
indicating minimal structural control on sedimentation.
Dates obtained by 14C dating of preserved marine invertebrates at
Point Hammond combined with previously reported data demonstrate a trend of
declining age as one moves northward through the San Juan Islands, consistent
with backwasting of the Vashon ice sheet and subsequent isostatic rebound as
proposed by Dethier et al. (1995). Rapid shallowing of local sea level at
Waldron Island is demonstrated by the juxtaposition of deep marine species
(Clinocardium ciliatum. ) with shallow intertidal species (Saxidomus
gigantea ). Dating of the faunal succession at Point Hammond indicates an
isostatic rebound rate of at least 16 cm yr -1 during the first 500
years after glacial retreat.
Geochemistry and Tectonic Setting of Proterozoic Amphibolites From the
Southern Front Range and Northern Wet Mountains, Central Colorado
Most of the Early Proterozoic supracrustal rocks of south-central Colorado are
complexly interlayered pelitic schists, felsic gneisses, and amphibolites which
have experienced a regional amphibolite-grade metamorphic event at about 1700
Ma and multiple intrusive and deformational events. Amphibolites from the
southern Front Range, Arkansas River Canyon, and northern Wet Mountains are
found concordantly interlayered with, or as pods or xenoliths within
biotite-quartz-plagioclase gneiss and gneissic granites. Amphibolites are
closely associated with pelitic schists and calc-silicates in the southern
Front Range and are interlayered with felsic volcanics in the Arkansas River
Canyon. An age of ~1720 Ma for a granitoid that intrudes the layered gneiss
sequence provides a minimum age for the wall-rock package in this area.
Amphibolite samples collected from twenty-nine localities throughout the field
area were petrographically and geochemically analyzed in order to determine
their origins and tectonic settings. Modal analysis identifies most of the
samples as ortho-amphibolites containing relatively equal amounts of amphibole
and plagioclase, and minor quartz and biotite. The high grade of metamorphism
and deformation has erased any primary structures or textures which might
positively identify their protoliths. Most samples display a crystalloblastic
fabric, although a few have retained what could be relict sedimentary layering
or relict igneous textures. Geochemical analyses of major elements by XRF and
trace elements by XRF and INAA makes it possible to identify the origin and
tectonic setting for amphibolites from the southern Front Range and northern
Wet Mountains. When plotted on N-MORB-normalized spider diagrams and REE plots
all display trends similar to volcanic arc basalts, with an enrichment of LILEs
and LREEs and a depletion of HFSEs and HREEs. When plotted on various tectonic
discriminant diagrams for basalts, all cluster in the volcanic arc field. On
the diagrams, a distinction can be made between amphibolites from the southern
Front Range and northern Wet Mountains. Rocks from the northern Wet Mountains
have a relatively higher enrichment in LILEs and LREEs than those from the
southern Front Range. Samples from the northern Wet Mountains also
consistently plot as calc-alkaline basalts, while those from the southern Front
Range plot as volcanic arc tholeiites. Because samples from the northern Wet
Mountains have a relatively high alkali enrichment and plot as calc-alkaline
basalts, they are part of a more evolved "continental"-like arc system.
Samples from the southern Front Range, with their lower alkali enrichment and
identification as volcanic arc tholeiites, are part of a more primitive, less
evolved arc system.
Because the geochemical trends shown by rocks from each of the two regions are
so distinct, they may represent two separate arc systems. These two arc
systems presumably developed independently and collided with one another and
with the North American Craton sometime late in the Early Proterozoic, though
the nature of their collision can not be determined from this study. The
results of this investigation were compared with those from studies done in
Arizona where the boundary between the Yavapai and Mazatzal provinces was
defined. The geochronologic, lithologic, and structural characteristics of the
units found in the southern Front Range and northern Wet Mountains, as well as
the geochemical data obtained for the amphibolites of this study, would
characterize this region as a component of the Yavapai province. However, the
position of the province boundary in this part of Colorado is still unresolved.
Quaternary History and Evolution of Submarine Banks, Northern Puget Lowland,
Washington
The Cordilleran ice sheet, which last retreated through the northern Puget
Lowland about 14.0 14C yr BP (13.5 ka), left a thick mantle of
glacial deposits in its wake. Submarine banks up to 12 km in length with
volumes of at least 1.5 km3 line the seafloor in this region; marine
seismic surveys show that these banks are composed of Quaternary sediments
as thick as 300 m. This report examines the glacial history of five of
these marine banks: Alden, Middle, Hein, Smith, and Eastern Bank.
We collected seismic reflection data throughout the Puget Lowland during the
summers of 1995 and 1996; seismic tracklines included profiles of seven marine
banks. Based on previous studies of submarine glacial deposits, I used seven
seismic facies associations for analysis of our data, including bedrock, till,
glaciomarine sediments, glaciomarine diamict, sand and gravel, silt and sand,
and marine fill. My interpretation of glacial history for each bank depended
upon two primary considerations: (1) the relative distribution, thicknesses,
and stratigraphic relationships of these facies as indicated in the seismic
record, and (2) bank morphology and orientation relative to paleoflow.
The morphology and internal sedimentary composition of the marine banks reflect
local conditions at the ice margin during deposition. As the Cordilleran ice
front approached the San Juan Islands during retreat, the calving rate at the
terminus decreased. Ice grounded on the substrate, reaching a temporary
stillstand in several locations. Where terminus stability lasted for decades,
sediment flowing through meltwater channels beneath the ice accumulated at the
margin in the form of ice-contact submarine fans, deltas, and moraines, with
paleoflow typically to the south-southwest. Alden Bank formed as a terminal
moraine at the margin of an ice lobe grounded east of Alden. Middle, Hein, and
Eastern Banks formed as ice-contact submarine fans along an ice margin that
gradually retreated to the northeast, moving from one bedrock high to the next.
Ice lay along the northern and eastern margins of Smith Bank during its
deposition, forming a curved terminus around the bank; the combination of
deposition from both sides created a composite bank feature with
characteristics of both a moraine and an ice-contact submarine fan. Each of
these banks accumulated over a period of tens of years and no more than 200
years.
The interaction between rising sea level and isostatic rebound through the
Holocene has modified the bank forms we see today. Surficial sediment has been
eroded up to 20 m from the bank tops and accumulated in thicknesses of less
than 50 m along the bank margins. Waves have been eroding those bank surfaces
exposed above sea level, such as Smith Island, at rates of 0.2-1.0 m/yr since
about 5 ka. Glacial processes have been a dominant force as the landscape of
the Puget Lowland has evolved through the late Quaternary.
Evidence of Seasonality and Climatic Cycles From the Upper Cretaceous El
Gallo Formation of Baja California
Like the climate of almost all other west coasts around the latitude of
30o north and south of the equator, Baja California has a dry heat,
deserts, and sparse vegetation. Almost no research has focused on the climate
of Baja California during the Late Cretaceous, when the terrestrial El Gallo
Formation was deposited along the Pacific Coast of this area. The
paleolatitude of the El Rosario area was only about 4o farther south
than it is today, based on paleomagnetic data (Filmer and Kirshvink, 1989;
Renne et al., 1996; Bohnel, 1997). The El Gallo Formation was deposited in a
fore-arc basin during a period of rapid tectonic uplift of the Alisitos
Formation and the Peninsular Ranges Batholith. The overall architectural
sedimentary structure of the El Gallo Formation represents a major transverse
river system that is associated with orogenic highlands. The field site for
this study is El Jabon Canyon, on the northwest side of El Rosario. A thick
sedimentary package of 15 alternating sandstone and siltstone cycles of the
upper El Disecado Member of the El Gallo Formation, capped by a basal
conglomerate belonging to the overlying Rosario Formation, is well exposed.
Levels of cyclicity and seasonality are indicated through a) sedimentary cycles
within the stratigraphy; b) small scale cyclicity apparent in color
variegations in paleosols; c) synthesis of all previous research regarding the
biota and climate of Late Cretaceous Baja California. During Late Cretaceous
time, the El Rosario area supported a diverse biota, including abundant
gymnosperm, angiosperm and palm trees, and a fauna including dinosaurs,
amphibians, and therian mammals (Cevallos-Ferriz, 1997; Lillegrave, 1976;
Morris, 1974; and Kilmer, 1963). These data are used to test the hypothesis of
Weaver (1990) that a poleward flowing current, not unlike the anomalous Leeuwin
Current off Western Australia today, modified the climate of Cretaceous Baja
California.
Dynamic Coastal Facies of the Alisitos Formation At Punta San Isidro, Baja
California, Mexico
Exposures of the Lower Cretaceous (Aptian-Albian) Alisitos Formation at Punta
San Isidro, Baja California, Mexico, include a series of pyroclastic,
conglomerate, and sandstone units interbedded with limestone (biohermal beds
composed of the rudist Caprinuloidea perfecta). These lithologies are
exhibited within a stratigraphic thickness of less than 125 m. A sandstone
unit contains abundant fossil wood with tree limbs up to 55 cm long and 5 cm in
diameter, testifying to the close proximity of the shoreline. Two
conglomeratic units bear andesite cobbles encrusted by oysters (Arcostrea
sp.?). This relationship implies a rocky shoreline of late Early
Cretaceous age, which predates the well-preserved rocky shorelines of Late
Cretaceous and Pleistocene ages also exposed on the present coast. The
interlayering of pyroclastic and reworked clastic units with nearly pristine
limestones presents a scenario of marine life attempting to establish itself
along a coastline subject to nearly continuous explosive volcanic activity. In
one case, bivalves were incorporated into a pyroclastic deposit, as debris
swept into a lahar of terrestrial origin or in a mass flow resulting from a
hydromagmatic explosion. Proximal volcanic activity to Punta San Isidro is
demonstrated by a series of andesitic dikes, feeding the 10 m-thick andesite
flow locally forming the uppermost stratigraphic unit of the Alisitos
Formation.
The fossils preserved at Punta San Isidro conform to the back reef facies of
the model provided by Coogan et al. (1972) of Cretaceous rudist reefs. The
interlayering of limestone and volcaniclastic units demonstrates that during
periods of rapid volcanogenic sedimentation, the marine fauna was temporarily
eliminated from the local sea bottom. This is consistent with the model of
Heikoop et al. (1996), who relate substrate and water depth to the effects of
proximal volcanism.
The Alisitos succession is often structurally complex, i.e. tightly folded,
faulted, and intruded by Late Cretaceous igneous rocks. Inland exposures of
bedrock are deeply weathered, further complicating the interpretation of faults
and folds. The constant wave action on the Pacific coastal cliffs around Punta
San Isidro provides the advantage of fresh Alisitos exposures. The fault
structures on these exposures are quite apparent and are not significant
impediments to stratigraphic interpretation. The advantages of coastal
exposure apply also to bedding structures and fossils, especially trace
fossils.
Pliocene to Recent Carbonate Dunes at Punta Chivato, Baja California Sur, Mexico
Studies of modern and lithified dunes on the gulf coast of Baja California are
scarce. Anderson (1950) observed a calcareous eolianite on Isla Carmen, and
Walker and Thompson (1968) mention dunes in the interfingering of ancient
coastal facies at San Filipe. Ives (1959) identifies sediment source and
mechanism of formation of a carbonate dune field in Sonora. None approaches
the depth or extent of this study in drawing inferences about regional
atmospheric circulation conditions and their continuity over time, or the
effects of the wind field on carbonate sedimentation with implications for
sustained upwelling-induced biological productivity in the Gulf of
California.
The carbonate sedimentary environment in the Gulf of California is closely
controlled by prevailing seasonal winds. Distribution and growth orientations
of krummholz, especially leatherplant (Jatropha cuneata) and copal
(Bursera hindsinia) trees, illustrate the predominance of strong winter
winds from the north at Punta Chivato. Modern sediments developed in this
windward setting are described in terms of distribution and composition.
Extensive dune deposits stretch up to 1.2 km inland and attain elevations of 60
m along the north coast of the promontory. Sediment composition of beaches and
dunes determined by point-counting is 40% - 80% calcium carbonate, indicative
of high marine productivity in surrounding waters. Lithics derived from the
surrounding volcanic bedrock are a secondary constituent. Shelly fauna
indicative of a high wave-energy environment, such as molluscs, dominate the
bioclast fraction. The low amount of red algae debris reflects the absence of
rhodolith fields along the north shore. Rhodoliths are currently forming
offshore to the east and are subsequently transported south to a protected bay.
This rough biological zonation is a direct result of the windward/leeward
dichotomy that exists across the promontory of Punta Chivato.
Post-Mid-Pliocene karst deposits scattered on the north shore of Punta Chivato
are investigated for evidence of continuity in the windward environment.
Weakly to well-consolidated outcrops occur between 11 m above sea level (close
to the coast) and 50 m above sea level, set inland on slopes of arroyos. The
similar distribution of paleobeaches and paleodunes along the north shore, and
their overwhelming, mollusc-dominated bioclast content, establishes the
windward setting of the north shore through the Pleistocene and possibly back
to the Middle Pliocene. Previous study has shown current conditions to have
existed at Punta Chivato during the Lower and Middle Pliocene (Simian and
Johnson, 1997). In addition, Libbey and Johnson (1997) show that Pleistocene
5e sediment composition on the southern shores of the promontory are 80% - 90%
rhodolith-derived red algae hash. This study, then, completes the model of
persistent windward/leeward shores at Punta Chivato from Pliocene times through
today. The continuity in wind field and sustained high levels of marine
productivity recorded in the geological record argue for consistent upwelling
circulation in the Gulf of California over the last 3-4 Ma.
A Hybrid Systems Approach to the Problem of Balancing an Inverted Pendulum
This thesis is a brief introduction to modern control theory and an
introduction to the hybrid systems approach to problems in control theory. We
consider the classic nonlinear control problem of balancing an inverted
pendulum as a function minimization problem from the point of view of optimal
control theory and as a dynamical system from the point of view of the hybrid
systems approach developed by Guckenheimer and Johnson. We demonstrate the
usefulness of the hybrid systems approach for considering questions of both
stability and optimality in balancing the inverted pendulum, and we delineate
some of the questions that need to be considered if the hybrid systems approach
is to be applied to control problems of stability and optimality in general.
Comparison of Ordinary Differential Equation Models of HIV Infection
Many ordinary differential equation models have been bused in research
on HIV to test treatment effectiveness and to define and describe the dynamics
between HIV and the immune system. In this thesis three such models (presented
by McLean et al., Perelson et al. and Hraba et al.) are compared with and
without treatment incorporated. The conclusions of this comparison are as
follows. The McLean model, which is very similar to the Perelson model, but
designed to model dynamics during treatment, is robust only for initial
conditions which reflect an infected steady-state and not for infection
dynamics from initial inflection or after the completion of a treatment course.
Treatment dynamics are compared between the Perelson and McLean models.
Particular treatments were implemented on both the Hraba and Perelson models
yielding the conclusion that, though the models are quite different, they give
similar predictions of relative treatment effectiveness.
Cost Minimizing Networks Separating Immiscible Fluids in R2
Cost minimizing networks model certain behavior of immiscible fluids in the
plane. This paper proves the existences of minimizers of straight lines with
an upper bound on the number of nodes, closely following the work of Alfaro.
It provides some basic examples of minimizers. The paper also gives sufficient
conditions for an upper bound on the number of regions meeting around a point.
Characterization of Completions of Integral Domains
Christer Lech characterized the complete local (Noetherian) rings that are
completions of domains. We reprove Lech's result showing that a complete local
ring T is the completion of a local domain if and only if no integer of T is a
zero divisor, and, unless equal to (0), the maximal ideal of T does not belong
to (0) as an associate prime ideal. Moreover, suppose p != M is a prime ideal
of T such that Q is an associated prime of T implies Q [Atilde] p, and suppose
that |{q Œ Spec T | q À p}| [sterling] | T/M2| and p
intersected with the prime subring of T is the zero ideal. In this case, we
construct a local domain A such that
=
T and the generic formal fiber ring of A is local with p*AK the
maximal ideal where K is the quotient field of A.
Weak Mixing, III0 Staircase Zd Actions
This thesis presents two new examples of staircase Zd actions,
functions mapping points from Zd x R to R. Expanding on the work of
Silva/Adams and Touloumtzis, the first construction is shown to be an infinite
measure preserving action with weakly mixing basis transformations. The second
and more interesting example is a type III0 action with weakly
mixing basis transformations. In addition, the several concepts and criteria
applying to Z2 actions are generalized to their Zd
counterpart.
Bayesian Prediction Intervals for Symmetric Shrinking Linear Smoothers
In many statistical problems, it is important to estimate the relationship
between a dependent variable y and some independent variables, so that given
values for the independent variables, a 95 percent prediction interval for y
can be computed. Here we describe how Bayesian methods can be used to
calculate prediction intervals for a class of modeling methods called symmetric
shrinking linear smoothers. We show that how well these "Bayesian prediction
intervals" perform can be related to simple properties of the smoother. When
one "smoothing parameter" is chosen optimally, we show that Bayesian prediction
intervals perform well asymptotically for generalized ridge regression. For
other smoothers, the asymptotic performance of Bayesian prediction intervals is
conjectured to depend on the eigenvalues of a linear operator called the
covariance operator.
Outer-crossing Numbers: A New Parameter for Graphs
Outer-crossing numbers of graphs are defined and basic properties are given.
The outer-crossing numbers of complete bipartite graphs are found. Some
conjectures and a generalization to surfaces other than the plane are discussed.
Efficient Transmission of Quantum Mixed States
The amount of information contained in a quantum pure state is well defined and
there exists a known method of transmitting pure state information in the most
efficient manner possible. In this thesis we attempt to attain a similar
understanding of quantum mixed states. We propose a likely value for the
information content of mixed states and show that under certain conditions this
value characterizes the efficiency with which a sequence of mixed states can be
transmitted. Also, we find a simple way of characterizing certain coding
strategies ("cluster codes") and obtain a formula for their efficiency.
Finally, we outline an algorithm which we believe will bring about maximally
efficient mixed state information transmission in the limit of large messages.
Nonlinear Dynamics in a Mode-Locked Ti:Sapphire Laser
This thesis presents research done on the non-linear dynamics of a Ti:sapphire
laser. The appearance of higher periodicities in the pulse train was examined
in depth, period two, period three and quasi-periodicity were seen. The
spatial properties of these higher periodicities were also studied and the
relative pulse heights were found to vary across the laser beam. Double
pulsing was also observed. A computer model of the laser was begun; at this
point only the first order cw beam is modeled.
Entanglement
Entanglement is a type of correlation between particles that is much stronger
than any correlation that could exist in classical physics. Originally studied
in the context of the quantum theory and its interpretation, entanglement has
come into its own recently in the study of quantum information. In this thesis
we explore some of the history of this notion of entanglement and then present
a formula that quantifies the amount of entanglement present for a certain
subclass of states in the simplest correlatable system: a pair of two-level
particles. We conclude by discussing how this expression might be made correct
for all states of this system.
Stability of Pulsar Radiation Mechanisms
Despite repeated attempts to describe the pulsar magnetosphere in general
physical terms, none of the current models of the pulsar radiation mechanism
has yet achieved either internal self-consistency or complete general
acceptance. However, since the models differ primarily in their placement of
the radio emitting region, it is possible to use observations of the long-term
stability of the pulse profile to place constraints on the likelihood of
certain mechanisms. Since the pulsar magnetic field can be treated as
approximately dipolar and since a dipole field drops off as 1/r3,
those regions of the magnetosphere that are farther from the pulsar are less
tightly bound to the magnetic field, and are likewise less tightly bound to the
pulsar. Emission mechanisms located in these regions farther from the pulsar
are therefore more sensitive to local field perturbations that could affect the
long-term stability of the pulse profile.
We conducted observations of the pulsars PSR 0329+54 and PSR 1933+16 in two
groups, one in August and September of 1996 and the other in January of 1997,
for the purpose of analyzing the stability of each of the pulse profiles over
the course of a few months. We reduced each of the observations and extracted
the Full Width at Half-Maximum (FWHM) for the main peak of each profile. A
comparison of the median FWHM for each pulsar for the earlier sample against
that from the later sample yielded no statistically significant traces of
instability of aberration. Since the sample size was smaller than we would
have liked and time constraints required that the comparison was drawn across
only a few months, a more thorough study would be necessary in order to make a
conclusive statement about the nature of the pulsar emission mechanism.
However, even though it is not currently possible to rule out one of the models
completely, our results support the polar cap model of radio emission over the
outer magnetosphere gap (relativistic beaming) model.
The Design, Construction, and Application of an Atomic Beam Apparatus
This thesis will describe the design, construction, and application of an
atomic beam apparatus. Experiments to measure the Stark shift and Stark mixing
effect on the 6P1/2 -> 6P3/2 transition in thallium
will be described. The final portion of the thesis will consider future
experiments.
Highly precise parity non-conserving effects in thallium have been measured.
However, theoretical thallium wavefunctions are not so precise as the
experimental measurements. Thus, if the predictions and measurements do not
agree, it is not evident whether the disagreement is due to imprecision in the
wavefunctions, or possible inaccuracies in the Standard Model. In order to
ameliorate this problem, we have devised several experiments (such as measuring
the Stark effect) that will check the accuracy of the thallium wavefunctions
independent of the parity non-conserving effects.
Effects of Directed Forgetting on Implicit Memory Tasks
The directed forgetting effect refers to the enhanced performance on a
free-recall test and on a yes/no recognition test of items followed by
"remember" cues relative to items followed by "forget" cues. Two explanations
have been proposed to account for the directed forgetting effect observed on
explicity memory tests. Three experiments were conducted to test the selective
encoding account and the selective retrieval account of the directed forgetting
effect by investigating whether a directed forgetting effect can be observed on
implicit memory tests. A significant directed forgetting effect was observed
for the implicity memory tests, word-fragment completion (Experiment 1),
category production (Experiment 2), and general knowledge questions (Experiment
3). Overall, the pattern of findings reported here indicate that the directed
forgetting effect reported on explicity memory tests using a mixed-list
presentation design is due to differential encoding of items followed by
remember relative to forget cues rather than due to retrieval inhibition.
The Effect of Anxiety on the Central Executive Function.
One of the major theories proposed to account for the pattern of findings
related the effect of anxiety on cognitive performance is the working memory
capacity theory, articulated by Eysenck (1979). According to this theory,
high levels of state anxiety lead to deficits in cognitive performance by
creating task-irrelevant processing, resulting in a restriction in functional
capacity of the working memory system. The purpose of this study was to
directly investigate the effect of anxiety on the central executive function,
the system responsible for the allocation of working memory resources. Five
experiments were conducted to investigate this question. Results indicate that
in four of the five experiments conducted, the anxiety manipulation failed to
significantly increase self-reported state anxiety in the experimental group
relative to the control group. In the five experiments reported, there was no
observable difference in performance between the experimental and control
groups on either the central executive tasks or the digit span and Stroop
tasks, two tasks previously shown to be influenced by state anxiety. This
current set of findings is inconclusive regarding whether the central executive
function is influenced by anxiety. Implications for future research in this
area are discussed.
The Development of Preschool Children's Understanding of False Belief in Fairy
Tales
Two studies explored preschool children's understanding of the false beliefs in
fairy tales. In the first study, groups of 3-, 4-, and 5-year-olds listened to
tape-recorded versions of a familiar and unfamiliar fairy tale read in either a
dramatic or an ordinary tone of voice. Children were also tested on standard
measures of false belief. Three-year-olds performed below chance on both their
understanding of the protagonist's mental state and on false belief, whereas
the two older groups performed above chance on both measures. Neither story
familiarity nor voice influenced children's understanding of the protagonist's
beliefs. In the second study, 3- and 4-year-olds listened to a familiar fairy
tale presented in either traditional form or in a form that made the
protagonist's beliefs more salient. Four-year-olds performed better when
mental states were more explicit, but 3-year-olds remained below chance.
Results were discussed in terms of changes in representational thought
occurring around 4 years.
Genetic Influences on Anxiety: Differential Neurosteroid Responsivity in
Selectively-bred Rats
Roman High Avoidance (RHA) and Roman Low Avoidance (RLA) rats were selectively
bred from Wistar rats using an active-avoidance paradigm; this breeding has
resulted in an increased "emotionality" in RLA rats, as evidenced by, for
example, increased grooming and defecation rates. RLA rats also have decreased
3H-diazepam binding as well as decreased GABA-stimulated
Cl- uptake in cortex. This experiment investigated whether response
to the neuroactive steroid allopregnanolone (AP), a positive modulator of the
GABAA receptor, would also differ in these two lines. Rats were
tested as neonates (one week) and as adults using measures of both emotional
behavior and activity. In neonates, AP, as previously reported by this
laboratory, decreased the number of ultrasonic vocalizations after maternal
separation. RHA pups vocalized more and were more active than RLA pups and, on
both measures, they had a greater responsivity to AP. As adults, RHA rats had
a greater anxiolytic response to AP on the plus maze test compared to RLA rats.
Furthermore, adult RHA rats were more active than RLA rats, with RHA activity
significantly decreased in response to the highest AP dose. RLA rats also had
increased plasma levels of AP after swim stress compared to RHA rats. These
results suggest that behavioral differences in these two psychogenetically bred
lines may be due to divergent functioning of the neuromodulatory neurosteroid
system.
Gender Issues and Identity Development
The Extended Measure of Ego Identity Status-2 (EOM-EIS-2), Narcissistic
Personality Inventory (NPI), Rosenberg Self Esteem scale (RSE), and Social
definition measure using the Thematic Apperception Test (TAT) were administered
to 33 male and 60 female senior Williams College students who had also
participated in a similar study when they were entering college (Cramer, 1995).
The present study was partially a follow up o these subjects to determine their
developmental pathways and to study sex differences in Identity Development.
The study also sought to investigate links between Social definition and Ego
Identity Status, Narcissism and Self Esteem. No sex differences emerged in the
Ego Identity Statuses, Social definition scores, or Self Esteem, but males
scored higher than females on measures of Narcissism, with higher scores on
Maladaptive Narcissism and subscales of Vanity, Exhibitionism and Entitlement.
Subscales of Social definition revealed that females were more socially focused
and perceived more causality in the world. Self Esteem was significantly
correlated with the Achieved status for both sexes, and Self Esteem was
significantly correlated with Narcissism and all three subscales which comprise
Adaptive Narcissism. Vanity was significantly positively correlated with the
Social definition measure of individual focus. Overall the study implies that
sex differences do not exist in the Ego Identity Statuses, but that females
have a tendency to be more socially focused and to perceive more causality.
The Relationships Between the Dimensions of Impulsivity and Delay and
Probability Discounting
The multi-dimensional structure of impulsivity was investigated by factor
analysis of 95 self-report items from various psychometric inventories.
Measures of delay and probability discounting were also obtained to determine
their association with the dimensions of impulsivity. A questionnaire
containing the I-7 Questionnaire, other impulsiveness-related items, and a
series of monetary choice items allowing estimation of delay and probability
discounting rates, was administered to 407 participants at three colleges.
Exploratory principal components analysis identified six factors: Cognitive
Impulsiveness/Carelessness, Planning/Seriousness, Venturesomeness,
Attention/Distraction, Carefree/Happy-Go-Lucky, and Impatience. The delay
discounting measure loaded on the impatience factor and correlated with both
scales from the I-7. The probability discounting measure failed to load on any
of the factors, although it did correlate with the I-7 Venturesomeness scale.
Motivating Self-control by Linking Future Rewards
Two experiments were conducted to test the effect of linking future rewards on
motivating self-control (Ainslie, 1975, 1992). Participants were offered
choices between smaller immediate rewards and larger rewards at different
delays until delays at which the participants made impulsive choices of the
smaller rewards were found. These same rewards were then embedded in a linked
series of identical future choice pairs and participants would reverse their
previous impulsive choice and instead choose the larger rewards in the series.
In Exp. 1 (n=60) participants made choices between monetary rewards and the
reward linking effect was significant in all conditions, all ps < .05. In
Exp. 2 (n=34) participants made choices between different quantities of pizza.
Linking occurred only in a condition in which the participants had to make a
one time choice between al of the larger rewards and all of the smaller
rewards, p < .05.
Attributions in Saudi Arabia and Israel: The Presence of the Correspondence
Bias and the Effects of Suspicion
Previous research has shown that individuals tend to think more in trait terms
than do collectivists which means they might be more inclined to make the
correspondence bias. Past research on attributions found that suspicion is an
antidote to the correspondence bias among Americans. The present research
employed two different paradigms to examine attributions among Saudi Arabian
office workers and Israeli high school students, and measured their levels of
individualism/collectivism. The results of this study (1) showed that both the
Saudi Arabians, who tended to be collectivist, and the Israelis, who straddled
individualism and collectivism, made correspondent inferences when making
attributions about a person's behavior, (2) revealed that both Saudi Arabians
and Israelis who had not been asked to make previous attributions made fewer
correspondence inferences when describing their friends' behaviors, and (3)
suggested that ulterior-motive information effects Saudis' and Israelis'
inference processes, making them less vulnerable to the correspondence bias.
Self Regulating Processes for Enhanced Performance in Athletic and Academic
Domains Under Pressure
This research examined the effects of self-regulating processes on performance
under pressure, both in athletic and in academic domains. Three experiments
manipulated the pressure under which participants were asked to perform a task.
Study 1 examined the effects of visualization, distraction, and
self-affirmation on participant's performance under pressure in an athletic
setting, and the results indicated that only self-affirmation was effective in
reducing the debilitating effects of the pressure. Study 2 found that
self-affirmation was effective in reducing the negative effects of pressure on
participants' performance on math problems. Study 3 found that under
conditions of pressure, women did significantly worse than men on a series of
math problems, but that self-affirmation eliminated this difference. Study 4
involved a survey of basketball players from the Italian National ... and from
a small college in the U.S. to assess players' intuitions and behaviors
relevant to performance under pressure and self-regulation processes. The
implications of this research for performance under pressure, and of the
viability of several self-regulating processes, are discussed.
The Levels-of-Processing Effect in Implicit Memory Tasks: It's Not an Artifact
In recent years, a distinction has been made between explicit and implicit
memory. Two explanations (the separate system account and the transfer
appropriate processing account) have been proposed to account for the pattern
of dissociations observed between explicit and implicit memory measures. The
transfer appropriate processing account (TAP) predicts that a
levels-of-processing effect will be observed in conceptually-driven implicit
memory measures but not in data-driven implicit memory measures. Researchers
have recently reported a levels-of-processing effect in data-driven implicit
memory measures when processing is manipulated using a between-subjects design
or in a within-subjects blocked list design (Challis & Brodbeck, 1992;
Thapar & Greene, 1994.) The current study tests the hypothesis that the
levels-of-processing effect previously reported in data-driven implicit memory
measures is the result of non-lexical processing of the study items in the
shallow encoding condition. Lexical processing of the words were manipulated
by instructing subjects to read each word aloud prior to making the encoding
judgment. Results reveal a significant levels-of-processing effect in anagram
solution, a data-driven implicit memory task. These findings suggest that the
levels-of-processing effect previously reported in data-driven implicit memory
measures is not an artifact of truncated processing of the blocked list items.
Implications for the transfer appropriate processing account and the separate
systems account of the explicit/implicit memory distinction are discussed.
Political Debate Strategies
Political campaigns often set a low percentage-of-the-vote expectation for
their candidates (a "low pitch") in primary campaigns and caucuses, so that
they may claim that their candidates have done "better than expected." It is
often the case that the surprising candidate receives more media attention and
exposure than the actual winner. When campaigns apply the same strategy to
political debates, however, complications arise, since there is no clear
measure of performance in debates (as total votes provides in primaries). Some
research has shown that the sue of a low pitch in political debates simply
lowers viewer's expectations and their subsequent performance ratings;
they assimilate the low pitch. The present study attempts to discover if a
positive post-debate "spin" of performance could lead to contrast effects,
boosting ratings of a candidate's performance even higher, while also examining
all other combinations of high, low and no pitches and high and no spins. In
an effort to simulate actual network debate coverage, the present study also
includes a source manipulation; the pitches and spins come from either the
media or the campaigns themselves. Results show that a low pitch followed by a
high spin is deadly when used by a campaign for its own candidate, while it
works quite effectively when presented by the media. It is likely that
communicator credibility accounts for this difference. Discussion of other
secondary findings is also included.
Cross Cultural and Developmental Differences in Suspicion and the Fundamental
Attribution Error
This research tries to determine if the fundamental attribution error is truly
fundamental by testing for the appearance of the correspondence bias in Indian
subjects using the essay paradigm. It also examines the effects of suspicion
to determine if it can reduce the occurrence of the correspondence bias in
Indian subjects as it has been shown to occur in the American subjects tested
in most other studies. A second aspect considered by this study was a
developmental approach that used the essay paradigm to examine the emergence of
the correspondence bias and the effects of suspicion on second and fifth
graders. Results indicate a very strong tendency for the Indian subjects in
the first study to make correspondence inferences regardless of the presence of
ulterior motives. Results from the developmental study indicate a tendency for
the fifth graders to discount more than the second graders. The second graders
were not significantly affected by the suspicion condition whereas the fifth
graders were affected by the ulterior motives and showed more thinking.
Implications and possible reasons for these reasons for these results are
discussed.
Delay Discounting and the Time Course of Regret
Two experiments were conducted to test the predictions of a discounting theory
of the time course of regret. In Experiment 1 (n=16), participants were
induced to make an impulsive decision of a smaller, earlier reward over a
larger, later reward. They were then contacted by telephone on 5 subsequent
days and asked to rate their satisfaction with their decision. As predicted,
satisfaction with the choice of the smaller reward decreased up until the day
that the larger reward would have been available, then increased slightly,
p<.0001. In Experiment 2 (n=61), a discounting explanation
of the difference in the time course of regret over actions and inactions was
examined. As is usually found with hypothetical scenarios, regret for a single
action was greater than for a single inaction when both led to the same
outcome, shown here for the first time with real rewards. However, due to a
failure of one of the manipulations, it was impossible to test the prediction
that multiple inactions would be regretted more than single actions over time.
Transaction Costs, Risk and Practice in Myopic Decision-making
Normative economic models assume that individuals discount delayed rewards at
constant rates over time (exponentially), but recent studies using real rewards
indicate that discounting rates decrease with delay, consistent with hyperbolic
model (Kirby, 1997). However, the effects of transaction costs, risk and
practice have remained unexplored in studies using real rewards to assess the
fits of different discounting models. Participants (N=102) bid in a series of
second-bid auctions for real delayed monetary rewards. Their bids represented
their present discounted value of the delayed rewards. The predicted effects
of transaction costs and risk were disconfirmed, and there were no effects of
practice. In all conditions the hyperbolic model outperformed the exponential
model. In addition, a significant correlation (r = -0.37) between
participants' discounting rates and college GPAs supported the external
validity of discounting rate as a measure of impulsivity.
Diagnosing Dementia in Parkinson's Disease: A Cognitive Screening Battery
Primary neurodegenerative dementia is under diagnosed in the United States.
Because of this, considerable effort has been put forth to develop brief
diagnostic techniques suitable for use in primary care practices. One such
technique is the `7-Minute Screen.' This neurocognitive instrument has been
shown to be both highly sensitive and specific to Alzheimer's Disease (AD).
There are, however, other diseases which produce dementia. The purpose of the
present study was to determine if the `7-Minute Screen' would also be useful in
diagnosing dementia due to Parkinson's Disease (PD). To accomplish this, 21
patients with PD recruited from the Movement Disorders Clinic (n = 16) at the
Brigham and Women's Hospital in Boston and a local neurology practice (n = 15)
and 19 age and education matched controls recruited from the community
underwent the `7-Minute Screen.' Patients and controls subsequently underwent
a comprehensive neuropsychological battery. The clinical standard of diagnosis
for Parkinson's Disease dementia (PDD) indicated that 3 of the PD patients were
demented. The `7-Minute Screen' detected all 3 patients for a sensitivity of
100%. Of control patients, none were demented. The `7-Minute Screen' detected
1 of 19 controls as demented, for a specificity of 95%. Additionally,
non-demented PD patients performed worse than controls on all
neuropsychological tests in the comprehensive battery. We conclude that the
`7-Minute Screen' may be useful in primary care settings for discriminating
between demented and non-demented PD patients. The data from this study also
suggest that PD patients who do not meet clinical criteria for PDD, have subtle
cognitive deficits.
Inadmissible Evidence and Juror Noncompliance: A Further Investigation of the
Just Verdict Motivation
The present experiments investigated the role of the need for cognition (NC) in
two aspects of the juror decision-making process: (1) selective compliance with
a judicial admonishment to disregard, and (2) the tendency to overcorrect
against the perceived biasing influence of unreliable evidence. In Experiment
1, 105 mock jurors read a criminal trial summary in which an incriminating
wiretap was ruled admissible, inadmissible because it was illegally obtained,
or inadmissible because it was unreliable (participants in a control group
never heard the wiretap evidence). As expected, mock jurors were more likely
to disregard unreliable evidence than reliable evidence regardless of its
admissibility, and this selective compliance was found to be the result of
their overt motivation to render a "just" verdict. This selective compliance
was found only in high NC mock jurors, who, compared to low NC mock jurors were
more likely to arrive at such a "just" verdict. High NC mock jurors also
exhibited some overcorrection in the inadmissible-unreliable condition,
estimating the probability of the defendant's guilt to be significantly lower
than control participants did. Experiment 2 further investigated the just
verdict motivation by presenting participants with trial scenarios involving
different types of evidence and different grounds for inadmissibility. As
expected, mock jurors recognized that legal guidelines of admissibility are
based on a due process model, even though their own perceptions of the strength
of the evidence were influenced by reliability concerns.