FACULTY PUBLICATIONS
ASTRONOMY
A New Look at Carbon Abundances in Planetary
Nebulae. IVImplications for Stellar
Nucleosynthesis
R.B.C. Henry, K.B. Kwitter, and J.A. Bates
’98
Astrophysical Journal, 531, 928 (2000)
This paper is the fourth and final report on a project
designed to study carbon abundances in a sample of planetary nebulae (Pne)
representing a broad range in progenitor mass and metallicity. We present newly
acquired optical spectrophotometric data for three Galactic Pne, IC 418, NGC
2392, and NGC 3242, and combine them with UV data from the IUE Final Archive for
identical positions in each nebula to determine accurate abundances of He, C, N,
O, and Ne at one or more locations in each object. We then collect abundances
of these elements for the entire sample and compare them with theoretical
predictions of Pne abundances from a grid of intermediate-mass star models. We
find some consistency between observations and theory, lending modest support to
our current understanding of nucleosynthesis in stars below 8 solar masses in
birth mass. Overall, we believe that observed abundances agree with theoretical
predictions to well within an order of magnitude, but probably not better than
to within a factor of two or three. However, even this level of consistency
between observations and theory enhances the validity of published
intermediate-mass stellar yields of carbon and nitrogen in the study of the
abundance evolution of these elements.
Deuterium in the Galactic Centre as a Result of Recent
Infall of Low-metallicity Gas
D.A. Lubowich, Jay M. Pasachoff, Thomas J. Balonek, Thomas
J. Millar, Christy Tremonti,
Helen Roberts, and Robert P. Galloway ’96
Nature, 405, 1025-1027, 29 June (2000)
The Galactic Centre is the most active and heavily processed
region of the Milky Way, so it can be used as a stringent test for the abundance
of deuterium (a sensitive indicator of conditions in the first 1,000 seconds in
the life of the Universe). As deuterium is destroyed in stellar interiors,
chemical evolution models predict that its Galactic Centre abundance relative to
hydrogen is D/H = 5 x 10-12, unless there is a continuous source of
deuterium from relatively primordial (low-metallicity) gas. Here we report the
detection of deuterium (in the molecule DCN) in a molecular cloud only 10
parsecs from the Galactic Centre. Our data, when combined with a model of
molecular abundances, indicate that D/H = (1.7 ± 0.3) x 10-6,
five orders of magnitude larger than the predictions of evolutionary models with
no continuous source of deuterium. The most probable explanation is recent
infall of relatively unprocessed metal-poor gas into the Galactic Centre (at the
rate inferred by Wakker). Our measured D/H is nine times less than the local
interstellar value, and the lowest D/H observed in the Galaxy. We conclude that
the observed Galactic Centre deuterium is cosmological, with an abundance
reduced by stellar processing and mixing, and that there is no significant
Galactic source of deuterium.
Fire in the Sky: Comets and Meteors, the Decisive
Centuries, in British Art and Science
R.J.M. Olson and J.M. Pasachoff
Cambridge University Press, paperback version
(1999)
Science Explorer: Astronomy
J.M. Pasachoff
Prentice-Hall, Junior-high school science
(2000)
Science Explorer: Sound and Light
J.M. Pasachoff
Prentice-Hall, Junior-high school science
(2000)
A Field Guide to the Stars and Planets
J.M. Pasachoff
Houghton Mifflin Co., 4th edition, The
Peterson Field Guide Series (2000)
Comets, Meteors, and Eclipses: Art and Science in Early
Renaissance Italy
R.J.M. Olson and J.M. Pasachoff
Bull. Am. Astron. Soc. 31, #4, p. 1080
(1999)
We discuss several topics relating artists and their works
with actual astronomical events in early Renaissance Italy to reveal the
revolutionary advances made in both astronomy and naturalistic painting. Padua,
where Galileo would eventually hold a chair at the University, was already by
the fourteenth century (trecento) a renowned center for mathematics and nascent
astronomy (which was separating from astrology). It is no wonder that when
Enrico Scrovegni commissioned the famous Florentine artist Giotto di Bondone to
decorate his lavish family chapel (c. 1303) that in the scene of the Adoration
of the Magi Giotto painted a flaming comet in lieu of the traditional Star of
Bethlehem. Moreover, he painted an historical apparition he recently had
observed with a great understanding of its scientific structure: Halley’s
Comet of 1301 (since Olson’s first publication of this idea in
Scientific American we have expanded the argument in several articles and
talks). While we do not know the identity of the artist’s theological
advisor, we discuss the possibility that Pietro d’Abono, the Paduan
medical doctor and “astronomer” who wrote on comets, might have been
influential. We also compare Giotto’s blazing comet with two others
painted by the artist’s shop in San Francesco at Assissi (before 1316) and
account for the differences. In addition, we tackle the question how
Giotto’s pupil, Taddeo Gaddi, who is documented as having been blinded by
a solar eclipse, reflects his observations in his frescoes in Santa Croce,
Florence (1328-30). Giotto also influenced the Sienese painter Pietro
Lorenzetti, two of whose Passion cycle frescoes at Assisi (1316-20), contain
dazzling meteor showers that hold important symbolic meanings in the
cycle’s argument but more importantly reveal that the artist observed
astronomical phenomena, such as the “radiant” effect, which was
first recorded by Alexander von Humboldt in 1799 and only accepted in the
nineteenth century. Lorenzetti also painted sporadic, independent meteors,
which do not emanate from the radiant, demonstrating that he observed this
phenomenon as well. (It is significant that these artists knew the differences
between comets and meteors, facts which were not absolutely established until
the eighteenth century.) We demonstrate that artistic and scientific visual
acuity were part of the burgeoning empiricism of the fourteenth century that
eventually yielded modern observational astronomy. Our work on comets has been
funded in large part by the National Endowment for the Humanities and by the
Getty Grant Program.
Durer’s Bolide
R.J.M. Olson and J.M. Pasachoff
Apollo, November, p. 58 (1999)
We examine a Durer painting in the National Gallery, London,
whose reverse shows an astronomical object. We identify the object as a bolide,
an exploding meteoroid, and not as a comet, as previously supposed.
The Williams College Expedition to Rimnicu
Vilcea
J.M. Pasachoff
Proceedings of the NATO Advanced Study Institute on
Advances in Solar Research at Eclipses, from Ground and from Space, J.P.
Zahn and Magda Stavinschi, eds., Springer-Verlag, in press (2000)
Fabulous Planetariums in Valencia and New
York
J.M. Pasachoff
Newsletter of Commission 46 on the Teaching of Astronomy of
the International Astronomical Union, #52, March pp. 3-4 (2000)
physics.open.ac.uk/IAU46/newslet.html
Astronomical Tables
J.M. Pasachoff
Included in Physicists’ Desk Reference
(Springer-Verlag). (2000)
Eclipse Observations of Coronal Structure, Polarization,
and Oscillations
from 11 August 1999
J.M. Pasachoff, B.A. Babcock, K.D. Russell ’00, S.K.
May ’00
Abstract in the Bull. Am. Astron. Soc. 32, #2,
2000, pp. 750-751
We report on CCD observations of the corona from Rimnicu
Vilcea, Romania, during the total solar eclipse of 11 August 1999. One
experiment searched for oscillations in the 530.3-nm coronal green line at about
1 Hz by digitizing at 10 Hz, as a determination of the coronal oscillation
spectrum to test models of magnetohydrodynamic heating. The optical system was
improved in several ways since the 1998 expedition, as was monitoring of the
filter. The series of images was aligned and Fourier transforms were examined
for individual pixels and groups of pixels. No oscillations were clearly
detected above the 1% level, though statistical analysis continues at this
writing. A second experiment took a series of 36 images through one filter
wheel that contained three filters near 400 nm and a second filter wheel
containing polarizers at three angles plus a parfocal clear filter. The results
include a polarization map of a quadrant of the sun and an attempt to map the
coronal temperature. The temperature map uses techniques suggested by Cram
(1976) through a determination of the extent to which scattering off
high-temperature electrons wash out the photospheric Fraunhofer lines. Low-pass
filtering of our resultant images show detail in the form of coronal loops but
do not show much non-radial structure in the temperature variations. We also
compare composite photographic observations with EIT images from eclipse
day.
The expedition was supported by NSF grant ATM-9812408,
National Geographic Society grant 6449-99, the Keck Northeast Astronomy
Consortium, and NASA SOHO/EIT guest-investigator grant
NRA-98-03-SEC-051.
BIOLOGY
Luc7p, a Novel Yeast U1 snRNP Protein with a Role in 5'
Splice Recognition
P. Fortes, D. Bilbao, M. Fornerod, G. Rigaut, W. Raymond,
Assistant Professor of Biology, and I.W. Mattaj
Genes & Develop., 13, 2425-2438
(1999)
The characterization of a novel yeast-splicing factor, Luc7p,
is presented. The LUC7 gene was identified by a mutation that causes
lethality in a yeast strain lacking the nuclear cap-binding complex (CBC).
Luc7p is similar in sequence to metazoan proteins that have arginine-serine and
arginine-glutamic acid repeat sequences characteristic of a family of splicing
factors. We show that Luc7p is a component of yeast U1 snRNP and is essential
for vegetative growth. The composition of yeast U1 snRNP is altered in
luc7 mutant strains. Extracts of these strains are unable to support any
of the defined steps of splicing unless recombinant Luc7 is added.
Although the in vivo defect in splicing wild-type reporter introns in a
luc7 mutant strain is comparatively mild, splicing of introns with
nonconsensus 5' splice site or branchpoint sequences is more defective in the
mutant strain than in wild-type strains. By use of reporters that have two
competing 5' splice sites, a loss of efficient splicing to the capproximal
splice site is observed in luc7 cells, analogous to the defect seen in
strains lacking CBC. CBC can be coprecipitated with U1 snRNP from wild-type,
but not from luc7, yeast strains. These data suggest that the loss of
Luc7p disrupts U1 snRNP-CBC interaction, and that this interaction contributes
to normal 5' splice site recognition.
Cellular Morphologies of cdc14, sfp1 and cdc14
sfp1 Mutants
L. Paliulis ’97, M. Byrne ’98, W. Raymond,
Assistant Professor of Biology
Molec. Biol. of the Cell., 10, 130a
(1999)
Cdc14 and Sfp1 comprise part of the network of proteins
important for exit from mitosis. Cdc14, an essential dual-specificity protein
phosphatase, indirectly regulates CLB-kinase activity. Sfp1, a split
zinc-finger protein, plays multiple roles in cell cycle regulation.
Cdc14 mutants arrest in late anaphase/early telophase when incubated at
the restrictive temperature (360C). Loss of function of sfp1
suppresses temperature-sensitivity of a cdc14-7 mutant. We sought a
cellular explanation for the genetic interaction between cdc14 and
sfp1. Although cdc14-7 sfp1 double mutants can grow at the
restrictive temperature for cdc14, cells do not display wild-type
morphology. Like cdc14-7 single mutants, cdc14-7 sfp1 double
mutants at 360C form a long projection, at the tip of which actin is
polarized. In contrast to cdc14 mutants at 360C, cdc14-7
sfp1 double mutants exhibit a diffuse spread of chromatin throughout the bud
projection, with apparent spindle breakdown. Thus, loss of sfp1 function
suppresses the temperature-sensitivity of cdc14 mutants without
completely suppressing cdc14’s morphological defects. Sfp1
single mutants do not display long bud projections. Sfp1 cells have
apparently normal actin and microtubule distributions. However, haploid sfp1
mutants have unusual bud scar patterns when compared to the spinal bud scar
pattern of wild-type controls. We propose that the bud polarity defect of
sfp1 mutants might contribute to the viability of cdc14-7 sfp1
double mutants.
Expression of Myogenic Regulatory Factors in Reloaded
Muscle
S.J. Swoap, Assistant Professor of Biology, L. Olmsted and
M. Genovesi
FASEB Journal, 14(4), A317 (2000)
MyoD is Necessary and Sufficient for Myosin Heavy Chain
IIB Expression
S.J. Swoap, Assistant Professor of Biology, D.L. Adams, D.J.
Seward, J. Haney, and M. Rudnicki
Med. Sci. Sports Exer., 32(5), 542
(2000)
Physiological Characterization of Supramedullary/Dorsal
Neurons of the Cunner, Tautogolabrus adspersus
S.J. Zottoli, Professor of Biology, F.R. Akanki ‘01,
N.S. Hiza ‘02, D.A. Ho-Sang, Jr. ‘02, M. Motta ‘00, X. Tan
‘02, K.M. Watts ‘02, and E.A. Seyfarth
Biol. Bull., 197, 239-240 (1999)
The somata of large neurons can be found on the dorsal surface
of the medulla oblongata (supramedullary neurons) and spinal cord (dorsal cells)
in many teleost fish. Thirty-five to forty of these neurons are arranged in a
single, median, longitudinal row, from the posterior end of the fissura
rhomboidalis through the anterior portion of the spinal cord of the cunner,
Tautogolabrus adspersus. Comparative physiological studies have
indicated that these cells in the cunner and other teleost fish make electronic
connections with one another, and that they respond to tactile inputs from the
skin. We report on some physiological properties of these cells with the
ultimate goal of determining their function.
The Mauthner Cell: What Has It Taught us?
Steven J. Zottoli, Professor of Biology, Donald S.
Faber
The Neuroscientist, 6(1), 25-38 (2000)
The Mauthner cell (M-cell) is one of the few identifiable
neurons in the vertebrate central nervous system. The ability to locate the
M-cell, along with its inputs and outputs, has resulted in important findings in
diverse areas of neurobiology including the molecular biology of neurons,
synaptic and systems physiology, behavior, development, and neuroethology. The
review provides a brief overview of the M-cell and then focuses on recent
studies applying state-of-the-art techniques to address new issues and revisit
old ones. One advantage of this preparation is the ability to conduct
multidisciplinary studies from the subcellular to behavioral levels. For
example, studies of activity-dependent changes in the strength of mixed
electronic and chemical synapses on the M-cell’s lateral dendrite in vivo
have been correlated with changes in the probability of eliciting a fast startle
response initiated by the M-cell and its associated circuits. Similarly, it is
now possible to image the activity of the M-cell and its homologs while
observing motor behavior in zebrafish larvae. These approaches will provide
direct tests of the functional properties of complex neural networks. Moreover,
molecular mechanisms that underlie neuronal development can be tested directly
with this neuron and its segmental homologs, because these cells occur in
singular pairs at defined locations. Finally, after spinal cord injury, the
M-cell’s axon regenerates, but does not follow its original course, and
the startle response gradually recovers. The accessibility of the M-cell system
offers the promise that strategies employed in restoring the function of a
neural network will be revealed. Thus, we anticipate that the M-cell system
will become a favored preparation for multidisciplinary studies on the neuronal
basis of behavior and the recovery of behavior after
injury.
CHEMISTRY
Assembly of a Catalytic Unit for RNA Microhelix
Aminoacylation Using Nonspecific RNA Binding Domains
Joseph W. Chihade, Assistant Professor of
Chemistry,
& Paul Schimmel, The Scripps Research Institute
Proc. Nat. Acad. Sci. USA, 96(22), 12316
(1999)
A novel assembly of a catalytic unit for aminoacylation of an
RNA microhelix is demonstrated here. This assembly may recapitulate a step in
the historical development of tRNA synthetases. The class-defining domain of a
tRNA synthetase is closely related to the primordial enzyme that catalyzed
synthesis of aminoacyl adenylate. RNA binding elements are imagined to have
been added so that early RNA substrates could be docked proximal to the
activated amino acid. RNA microhelices that recapitulate the acceptor stem of
modern tRNAs are potential examples of early substrates. In this work, we
examined a fragment of E. coli alanyl-tRNA synthetase which catalyzes
aminoacyl adenylate formation, but is virtually inactive for catalysis of RNA
microhelix aminoacylation. Fusion to the fragment of either of two unrelated
nonspecific RNA binding domains activated microhelix aminoacylation. While the
fusion proteins lacked the RNA sequence specificity of the natural enzyme, their
activity was within 1-2 kcal mol-1 of a truncated alanyl-tRNA
synthetase that has aminoacylation activity sufficient to sustain cell growth.
These results show that, starting with an activity for adenylate synthesis,
barriers are relatively low for building catalytic units for aminoacylation of
RNA helices.
Science for Kids Outreach Programs: College Students
Teaching Science to Elementary School Students and Their Parents
Birgit G. Koehler, Assistant Professor of Chemistry, Lee Y.
Park, Associate Professor of Chemistry, & Lawrence J. Kaplan, Professor of
Chemistry
J. Chem. Ed., 76, 1505-1509 (1999)
For a number of years we have been organizing and teaching a
special outreach course during our Winter Study Program (the month of January).
College students plan, develop, and present hands-on workshops to fourth grade
students and their parents, with faculty providing logistical support as well as
pedagogical advice. Recent topics have included “Forensic Science,”
“Electricity and Magnetism,” “Chemistry and Cooking,”
“Waves,” “Natural Disasters,” “Liquids,”
“Pressure,” “Color and Light,” “Momentum and
Inertia,” “Illusions,” and “The Senses.” The
two-hour-long workshops, held one weekend on campus, emphasize hands-on
experiments involving both the kids and the parents. Handouts for each workshop
give instructions for doing several experiments at home. This program has been
a great success for all involved: the college students gain insight into an
aspect of science and what it takes to develop and teach that topic, the
elementary school students participate in an exciting and challenging scientific
exploration, and the parents have a chance to learn some science while spending
time working on projects with their children. We provide an overview of the
pedagogical aims of our current approach and a sense of the time-line involved
in putting together such a program in a month.
A New Synthesis of N-Phenyl Lactams
J. Hodge Markgraf, Professor of Chemistry emeritus,
& Carolyn A. Stickney ’00
J. Heterocycl. Chem., 37, 109-110
(2000)
The synthesis of N-phenyl lactams by phase transfer
oxidation of N, N-(polymethylene)anilines with potassium
permanganate is reported. Thus, N-phenylazetidine is oxidized to
N-phenyl β-lactam, which constitutes the first preparation of a
β-lactam in which the carbonyl function is introduced after formation of
the four-membered ring.
The Age of the Port Morant Formation, Southeastern
Jamaica
Simon F. Mitchell, University of New Brunswick, Ron K.
Pickerill, University of the West Indies, Bonnie A.B. Blackwell, Research
Scientist, & Anne R. Skinner, Senior Lecturer
Caribbean Journal of Earth Science, 34, 1-4
(2000)
Two samples from the Port Morant Formation in southeastern
Jamaica have been dated using electron spin resonance (ESR). Petrographic
analysis showed some dissolution of the primary coralline aragonite as well as
secondary mineral precipitation within the coral pore space in one sample, which
also showed large associated uncertainties for accumulated doses calculated from
the ESR growth curves. Therefore the age, 125 ± 7 kyr, for the sample
probably represents a minimum age, being a weighted average of the date of the
original skeletal aragonite and that for the secondary mineral phase. The
second specimen yielded a single age of 132 ± 7 kyr. Although we feel that
this is an accurate age, no single date can be considered to be totally reliable
by itself. The ages suggest that at least part of the Port Morant Formation was
deposited during the late Isotope Stage 6 and probably early Stage 5e. More
dates from the unit, however, are necessary to confirm this
conclusion.
Turing Patterns in a Self-Replicating Mechanism with
a
Self-Complementary Template
Enrique Peacock-López, Associate Professor of
Chemistry, Geoffrey Hutchison ’99,
& Leo L. Tsai
’98
Journal of Chemical Physics, 113, 6512-6515
(2000)
A variety of nonlinear chemical models, such as the
Selkov-Schnakenberg, exhibit Turing patterns. The Templator, which is based on
a minimal autocatalytic monomer-dimer system, is a newer two-variable model also
able to show Turing patterns. Here we find that the dynamic behavior of the
Templator is quite similar to other models with cubic nonlinearities. This is
demonstrated through a series of computer simulations in two dimensions
utilizing the cellular automata approach. The selection of parameter values is
based on linear stability analysis, which provides a relatively simple method of
predicting Turing pattern formation. The simulations reveal spot, labyrinth,
and striped patterns, in agreement with the predictions of the analysis. Other
behaviors, such as honeycomb patterns, are also observed. For some parameter
values, we study transient spot replication. Our findings strongly suggest that
the Templator may belong to the same class of models previously studied by
Pearson.
ESR Dating: Is It Still an Experimental
Technique?
Anne R. Skinner, Senior Lecturer
Applied Radiation and Isotopes, 52, 1311-1316
(2000)
Nearly twenty-five years ago, Motoji Ikeya demonstrated the
potential of ESR dating. From a single substance (stalagmitic carbonate) and a
single site (Akiyoshi Cavern), the field has grown to include materials from all
over the world and time periods from a few thousand years ago to several million
years ago. A vigorous program of instrumentation development has increased the
precision of measurements as well as opening up new ways of collecting and
interpreting spectra. Yet there are still references to ESR dating as an
‘experimental’ technique, one which cannot be trusted to produce
dates that are accurate or precise. This paper discusses areas for which this
is true and suggests what should be done to convince skeptics. Other areas for
which the evidence suggests that ESR is at least as reliable as
‘standard’ methods are also be covered.
Improvements in Dating Tooth Enamel by ESR
Anne R. Skinner, Senior Lecturer of Chemistry, Bonnie A.B.
Blackwell, Research Scientist,
N. Dennis Chasteen, University of New
Hampshire, Junlong M. Shao, University of New Hampshire, & Stephanie S. Min
’98
Applied Radiation and Isotopes, 52, 1337-1344
(2000)
Determining growth curves for ESR dating requires artificial
irradiation of sample aliquots. This process can introduce short-lived effects
not relevant to the geological or archaeological signal. Annealing to remove
these effects is required to obtain accurate calculated ages. When the
short-lived peaks are different from the dating signal, their disappearance is
easy to monitor during annealing, and one can also be certain that the annealing
process does not affect the dating signal. For tooth enamel, however, the
short-lived signal is simply an unstable enhancement of the dating signal. The
apparent De from growth curves created immediately after irradiation
is considerably greater than post-annealing results although the shape of the
curve is unchanged. A variety of annealing techniques have been used on an
ad hoc basis. A detailed study of annealing both natural and
artificially irradiated samples allows a rational choice of method, as well as
confirming the lifetime of the dating signal. Corrections for other types of
interference are also discussed.
Absolute CH Radical Concentration in Rich Low-Pressure
Methane-Oxygen-Argon Flames via Cavity Ringdown Spectroscopy of the
A2Δ-X2Π
John W. Thoman, Jr., Associate Professor of
Chemistry,
& Andrew McIlroy, Sandia National Laboratories
Journal of Physical Chemistry A, 104, 4953-4961
(2000)
We measure absolute methylidyne (CH) radical concentrations in
a series of rich 31.0-Torr (4.13 kPa) methane-oxygen-argon flames using cavity
ringdown spectroscopy. Probing via the CH A2Δ-X2Π transition near 430
nm gives a sensitivity of 3x109 cm–3 for our experimental conditions,
yielding a signal-to-noise ratio greater than 1000 for the strongest transitions
observed. We measure profiles of CH mole fraction as a function of height above
a flat-flame burner for rich flames with equivalence ratios of 1.0, 1.2, 1.4,
and 1.6. These flames are modeled using the following mechanisms: 1) the GRI
Mech 2.11, 2) a mechanism by Prada and Miller, 3) a modified GRI 2.11 mechanism,
which employs a more realistic increased CH + O2 rate coefficient, and 4) the
new GRI Mech 3.0. Generally good agreement between the models and the data is
found, with the GRI 3.0 and modified 2.11 mechanisms best reproducing the data.
The greatest discrepancies are observed at the richest stoichiometry, where all
of the models predict a wider CH profile shifted further from the burner than
experimentally observed.
COMPUTER SCIENCE
Comparing Object Encodings
Kim B. Bruce, Luca Cardelli, and Benjamin C.
Pierce
Information and Computation 155, pp. 108-133
(1999).
Abstract: Recent years have seen the development of several
foundational models for statically typed object-oriented programming. But
despite their intuitive similarity, differences in the technical machinery used
to formulate the various proposals have made them difficult to compare.
Using the typed lambda-calculus,
F≤ω as a common
basis, we now offer a detailed comparison of four models: (1) a recursive-record
encoding similar to the ones used independently by Cardelli, Reddy, and Cook and
others; (2) Hofmann, Pierce, and Turner's existential encoding; (3) Bruce's
model based on existential and recursive types; and (4) Abadi, Cardelli, and
Viswanathan's type-theoretic encoding of a calculus of primitive
objects.
Feature Selection vs. Theory Reformulation: A Study of
Genetic Refinement of Knowledge-based Neural Networks
Brendan Davis Burns and Andrea Danyluk, Assistant Professor
of Computer Science
Machine Learning, 38(1/2), 89-107
(2000)
Expert classification systems have proven themselves effective
decision makers for many types of problems. However, the accuracy of such
systems is often highly dependent upon the accuracy of a human expert’s
domain theory. When human experts learn or create a set of rules, they are
subject to a number of hindrances. Most significantly experts are, to a greater
or lesser extent, restricted by the tradition of scholarship which has preceded
them and by an inability to examine large amounts of data in a rigorous fashion
without the effects of boredom or frustration. As a result, human theories are
often erroneous or incomplete. To escape this dependency, machine learning
systems have been developed to automatically refine and correct an
expert’s domain theory. When theory revision systems are applied to
expert theories, they often concentrate on the reformulation of the knowledge
provided rather than on the reformulation or selection of input features. The
general assumption seems to be that the expert has already selected the set of
features that will be most useful for the given task. That set may, however, be
suboptimal. This paper studies theory refinement and the relative benefits of
applying feature selection versus more extensive theory reformulation.
Problem Definition, Data Cleaning, and Evaluation: A
Classifier Learning Case Study
Foster Provost, Bell Atlantic Science and Technology and
Andrea Danyluk, Assistant Professor of Computer Science
Informatica, 23, 123-136 (1999)
The Workshop on AI Approaches to Time-Series Problems, jointly
sponsored by the Fifteenth National Conference on Artificial Intelligence
(AAAI-98) and the International Conference on Machine Learning (ICML-98), was
held in Madison, Wisconsin, on 27 July 1998. The organizing committee consisted
of Andrea Danyluk of Williams College, and Tom Fawcett and Foster Provost, both
of Bell Atlantic Science and Technology. There were approximately 30
attendees.
The goal of the workshop was to bring together AI researchers
who study time-series problems along with practitioners and researchers from
related fields. These problems are of particular interest because of the large
number of high-profile applications today that include historical time series
(for example, prediction of market trends, crisis monitoring). The focus was
primarily on machine-learning and data-mining approaches, but perspectives on
statistical time-series analysis and state-space analysis (for example, work on
hidden Markov models) were also included.
Software Mode Changes for Continuous Motion
Tracking
Karuppiah, Patrick Deegan, Elizath Araujo, Yinlei Yang, Gary
Holness, Zhigang Zhu,
Barbara Staudt Lerner, Assistant Professor of Computer
Science, Deepak Roderic Grupen and Edward Riseman
Proceedings of Int. Workshop on Self Adaptive Software,
Oxford (2000)
Robot control in nonlinear and nonstationary run-time
environments presents challenges to traditional software methodologies. In
particular, robot systems in “open” domains can only be modeled
probabilistically and must rely on run-time feedback to detect whether
hardware/software configurations are adequate. Modifications must be effected
while guaranteeing critical performance properties. Moreover, in multi-robot
systems, there are typically many ways in which to compensate for inadequate
performance. The computational complexity of high dimensional sensorimotor
systems prohibits the use of many traditional centralized
methodologies.
We present an application in which a redundant sensor array,
distributed spatially over an office-like environment can be used to track and
localize a human being while reacting at run-time to various kinds of faults,
including: hardware failure, inadequate sensor geometries, occlusion, and
bandwidth limitations. Responding at run-time requires a combination of
knowledge regarding the physical sensorimotor device, its use in coordinated
sensing operations, and high-level process descriptions. We present a
distributed control architecture in which run-time behavior is both preanalyzed
and recovered empirically to inform local scheduling agents that commit
resources autonomously subject to process control specifications. Examples will
be available from our search and rescue platform.
A Model for Compound Type Changes Encountered in Schema
Evolution
Barbara Staudt Lerner, Assistant Professor of Computer
Science
ACM Transactions on Database Systems, (2000)
Schema evolution is a problem that is faced by long-lived
data. When a schema changes, existing persistent data can become inaccessible
unless the database system provides mechanisms to access data created with
previous versions of the schema. Most existing systems that support schema
evolution focus on changes local to individual types within the schema, thereby
limiting the changes that the database maintainer can perform. We have
developed a model of type changes incorporating changes local to individual
types as well as compound changes involving multiple types. The model describes
both type changes and their impact on data by defining derivation rules to
initialize new data based on the existing data. The derivation rules can
describe local and non-local changes to types to capture the intent of a large
class of type change operations. We have built a system called Tess (Type
Evolution Software System) that uses this model to recognize type changes by
comparing schemas and then produces a transformer that can update data in a
database to correspond to a newer version of the
schema.
GEOSCIENCES
Changes in a Fringing Reef Complex over a Thirty-Year
Period: Coral Loss and Lagoon Infilling at Mary Creek, St. John, U.S. Virgin
Islands
Rónadh Cox, Assistant Professor of Geosciences, et
al.
Bulletin of Marine Sciences, 66, 269-277
(2000)
Recent decline in the diversity and percent cover of hard
corals in reef environments worldwide has been extensively documented (Done,
1992; Gladfelter, 1982; Kuta and Richardson, 1996; Precht and Aronson, 1997;
Rogers, 1990). To understand this decline, long-term records of reef
environments (e.g. Aronson and Precht, 1997; Hughes, 1994; Precht and Aronson,
1997) are essential, but relatively few such records exist.
The subject of this study is a fringing reef in the U.S.
Virgin Islands, the Mary Creek reef complex (MCRC), located within the St. John
national park. In addition to the 1998 Winter Study field project reported
here, the MCRC has been the site of several undergraduate research projects over
the last thirty years (MacLeod, 1986; Mayall, 1993; Stoeckle, et al., 1968). In
aggregate, these studies furnish a picture of large-scale change in the MCRC
between 1968 and 1998. During this time, the reefs of St. John have been
subject to increasing tourist visitation and impact from human settlements (e.g.
Hubbard, et al., 1987; MacDonald, et al., 1997) and the island has been battered
by several hurricanes (e.g. Rogers, et al., 1991), but the long-term effects of
these phenomena are unknown because continuous reef-monitoring programs in the
National Park have been undertaken only recently. No multi-decade studies have
been published to date, and to the best of our knowledge, the MCRC is the only
reef in the area for which such a continuous record exists.
Substantial changes have occurred in the MCRC over the last
thirty years. In 1968 the reef crest zone was dominated by dense stands of
Acropora palmata, and the reef was actively prograding; in 1986 few A. palmata
colonies remained alive; and in 1998 only two living colonies, both small (about
30 cm high, with fronds less than 30 cm across), were recorded. During the same
period the average water depth in the back-reef zone decreased, from about 1.5 m
in 1968 to about 0.4 m in 1998, which corresponds to an average sediment
aggradation rate of approximately 3.6 cm/year.
The present situation in the MCRC may result from a
combination of factors, and it is possible that the affected coral communities
will reestablish in the future. The interplay of environmental stimuli and
their effects on reef ecology, and in particular the role of time, are only
beginning to be understood (Done, 1992). Therefore, the existing 30-year record
makes this site an excellent candidate for a long-term reef monitoring study.
Quaternary Evolution of the Rio Grande Near Cochiti Lake,
Northern Santo Domingo Basin, New Mexico
David P. Dethier, Professor of Geosciences
New Mexico Geological Society Guidebook, 50,
371-378 (1999)
Quaternary base-level change in the northernmost Santo Domingo
basin records the effects of damming and knickpoint migration upstream in White
Rock Canyon and the influence of middle Pleistocene climate change. Quaternary
changes were superimposed on complex base-level responses to changes in upstream
sediment delivery, volcanism in the western Cerros del Rio and movement along
the La Bajada fault zone in the late Pliocene and early Pleistocene. During
Quaternary time, the Rio Grande cut the modern White Rock Canyon, initially
transporting large quantities of sediment into the northernmost Santo Domingo
basin, then incising this fill and underlying bedrock, stranding a series of
inset, mainly fill terraces. Two principal pulses of aggradation, separated by
>40 m of incision, can be distinguished in the surficial geologic record near
the southern end of White Rock Canyon: an early Pleistocene episode
(Q1) that began with eruption of the upper Bandelier Tuff and another
episode (Q2) in middle Pleistocene time. Base-level lowering of ~60
m, punctuated by relatively brief periods of aggradation (Q3 and
Q4), dominated geomorphic changes in the northernmost Santo Domingo
basin from about 300 ka to present. Middle and late Pleistocene incision
records decreased sediment load or increased stream power that resulted from
upstream drainage evolution and pluvial/interpluvial cycles of increased
amplitude.
Preliminary Map of Landslide Deposits in the Los Alamos
30’ by 60’ Quadrangle, New Mexico
P.E. Carrara
David P. Dethier, Professor of Geosciences
U.S. Geological Survey Miscellaneous Field Studies Map
MF-2328 (1999)
About 150 landslides, including many previously unrecognized
and unmapped deposits have been identified in the Los Alamos 30’ x
60’ quadrangle by reconnaissance surficial geologic mapping. These
landslides range in size from small earthflows and rock slumps (less than 0.10
km2) to large earthflows, rock slumps, translational slides, debris
avalanches, and complex landslides greater than 10 km2 (Varnes,
1978). Landslide deposits underlie about 4 percent of the map area, and about
230 km of roadways are either underlain by landslides or are within 100 m of a
landslide. This estimate was calculated on the basis of all roadways indicated
on the Los Alamos 30’ x 60’ quadrangle base map (primary and
secondary hard-surfaced highways, light-duty roads, unimproved roads, and
trails).
Pleistocene Incision Rates in the Western USA Calibrated
Using Lava Creek B Tephra
David P. Dethier, Professor of Geosciences
Geological Society of America Abstracts with Programs,
31 (7), A-422 (1999)
The Lava Creek B ash bed (LCB), erupted from the Yellowstone
caldera at about 0.64 Ma, provides a datum for measuring long-term incision
rates along rivers from the Mississippi to west of the Rocky Mountains.
Incision rates provide information about local rates of exhumation and can be
used, in some cases, to estimate the rate of rock uplift or to assess the effect
of climate change. The LCB is widely preserved in the western United States
because of its substantial volume, broad initial dispersal and the aggrading
environment into which it fell. Widespread drainage incision after LCB
deposition isolated it from rapid fluvial erosion. Calculated rates of incision
since early middle Pleistocene time range from less than 2 to 30 cm per thousand
years. Rates are high in most areas near the Rocky Mountains and downstream
along rivers draining extensive mountainous catchments and are lowest east of
the High Plains and along the Snake River in Idaho. Incision rates along many,
but not all, rivers decrease downstream. Increasing rates of downcutting along
several major rivers in the late Pleistocene suggest that the balance of stream
power, sediment transport and bed resistance was altered by some aspect of
climate, including local drainage integration. Regional and temporal patterns
of incision suggest that increased runoff from the Rocky Mountains governed
middle and late Pleistocene downcutting. However, these data cannot be used to
exclude regional rock uplift as a significant control of Pleistocene
incision.
Chronology and Divergent Flow Directions during Latest
Pleistocene Ice Retreat, Northeastern Puget Lowland
David P. Dethier, Professor of Geosciences
Geological Society of America Abstracts with Programs,
32(6), A-10 (2000)
Cordilleran ice retreated rapidly from the northern Puget
lowland in latest Pleistocene time, fragmenting across deep channels and complex
topography near the San Juan Islands and stabilizing only where the ice front
grounded. Radiocarbon ages from shell in proximal glaciomarine sediment and
local flow indicators suggest that ice-flow direction reoriented from S to SW,
locally W during collapse of the tidewater margin of the Puget Lobe between
about 13.6 and 12.8 ka (uncorrected shell ages). Ice retreated from Smith
Island and central Whidbey Island by about 13.6 ka and collapsed to fluctuating
tidewater margins N and E of Bellingham sometime after 13.0 ka. Striae and
other indicators at elevations above 500 m suggest that the maximum Puget Lobe
flowed toward 170o. As ice thinned and retreated, striae cut at
lower elevations and sparse drumlins mapped between the western San Juan Islands
and the lower Skagit Valley record ice lobes: (1) confined by local topography,
(2) flowing from different source areas, and (3) responding to calving drawdown.
From N. Whidbey to Lummi Island, particularly near Deception Pass, a population
of striae trends from 225 to 260o. On N. San Juan Island, Waldron
Island, and locally near Mt. Vernon ice flowed toward 220 to 250o
during retreat. North of Victoria and locally in the western San Juan Islands,
however, low-elevation striae and drumlins trend near 160o. Despite
the diversity of directions, crosscutting striae are rare. At several sites
field evidence and multiple populations of striae demonstrate that local flow
directions reoriented >60o, presumably as ice flow responded to
the approach of calving margins. West and southwest-trending striae cut on N.
Whidbey and Fidalgo Island after 13.5 ka suggest reorientation of local flow
from a deeply embayed Puget Lobe. By about 13 ka, ice had disappeared from the
Strait of Georgia leaving a complex, SW-flowing ice mass in the Noosack
Valley.
Voluminous Laharic Inundation of the Lower Skagit River
Valley, Washington-A Product of a Single Large Mid-Holocene Glacier Peak
Eruptive Episode?
Joe D. Dragovich and D.T. McKay, Jr., Dept. of Natural
Resources, Division of Geology
David P. Dethier, Professor of
Geosciences
James E. Beget, Univ. of Alaska
Geological Society of America Abstracts with Programs,
32(6), A-11 (2000)
Deposits of Glacier Peak eruptive events(s) are preserved in
the lower Skagit River valley as 3-15 m high terraces adjacent to the Skagit
River flood plain. The cities of Lyman, Sedro Woolley, and Burlington rest on
terraces composed of dacite-rich sand and sandy gravel that is interpreted to be
a non-cohesive laharic run-out. New outcrops, 14C ages,
stratigraphic relations, dacite clast petrographic and geochemical data, and
laharic sand composition suggest that the voluminous Kennedy Creek volcanic
assemblage (KCA) of Beget (1981) reached the Puget Sound. The KCA is mostly a
laharic-pyroclastic surge volcanic complex that originated from Glacier Peak
volcano (GP). Near La Conner and the Puget Sound, 135 km downvalley from GP,
the distal lahar can be traced as a 3-18 m-thick semi-continuous stratum using
well and boring logs and isolated outcrops. This distal lahar is overlain by
estuarine or deltaic sediments. The Skagit Valley segment of the lahar appears
to originate from a single eruptive episode on the basis of the upward fining
from crystal-dacite lithic sandy gravel (gravel 50-80% dacite) to sand (41-56%
dacite). Hypersthene-hornblende-phyriac vesicular dacite clast samples from 18
lahar sites (near GP to La Conner) have similar REE, trace and major element
geochemistry suggesting a single eruptive event. Charcoal in laharic sand near
Lyman yielded an age of 4,780±80 yr BP, similar to the 5,100-5,500 yr BP
age of the KCA. Along the flanks of GP, Beget (1982) estimated a total original
volume of 23 km3 for the KCA. The >3,400 and <6,700 yr BP
Dusty and Baekos Creek assemblages of Beget (1982) have an estimated total
original volume of >10 km3, and could correlate with the KCA.
Maximum-minimum lahar estimates in the lower Skagit River basin suggest an
additional 2-3 km3 for the KCA. Thus, if our correlations are
correct, the preserved KCA may have a volume >15 km3.
Biological Zonation on a Rocky-Shore Boulder Deposit:
Upper Pleistocene Bahía San Antonio (Baja California Sur,
Mexico)
Markes E. Johnson, Professor of Geosciences
Jorge
Ledesma-Vázquez, Facultad de Ciencias Marina, Univ. Autonoma de Baja
California
Palaios, 14, 569-584 (1999)
During Late Pleistocene time, a shallow embayment covering
more than six hectares near Punta San Antonio (Baja California Sur, Mexico) was
flooded from the Gulf of California to a depth of about 14 m. More than 400 m
of shoreline along the inner perimeter of this bay consists of fitted boulders
derived from adjacent tectonic blocks of Cretaceous granodiorite and Miocene
andesite. In most places, the 1-m-thick boulder bed unconformably blankets
Miocene tuff related to the Upper Comondú Group. Elsewhere it sits on
Lower Pliocene limestone belonging to the San Marcos Formation. Stabilized
through extensive cementation by coralline red algae, the rim of the boulder bed
forms a steep rocky shoreline reposed between 50o and 70o.
Biological zonation is expressed both laterally and vertically by the remains of
more than 30 species of marine intertidal organisms that colonized the uneven
face of the boulder bed under varying conditions of wave activity and shore
orientation. An exposed outer shore preserves vertical zonation among in situ
mollusks differentiated between an upper zone, characterized by Modiolus
capax, and a lower zone of Codakia distinguenda. A more sheltered
inner shore shows vertical differentiation between an upper zone, including
Ostrea palmula and Crucibulum scutellatum, and a lower zone still
featuring Codakia distinguenda (but with different associates). At the
rear of the embayment, a small protected cove was well sheltered from wave
activity. Here an upper zone is dominated by large coral colonies of Porites
californica, together with diverse mollusks, in contrast to a lower zone
depleted in corals but retaining much the same mollusk assemblage.
Upper Pleistocene marine terraces correlated with oxygen
isotope substage 5e follow elevations close to 12 m above present sea level
throughout the surrounding gulf-coast region. The top of the extensive boulder
bed at Punta San Antonio is 27.5 m above present sea level, but its seaward
margin is connected by a continuous ramp to a 13-m level on the present
shoreline. The boulder bed represents a local anomaly in average coastal uplift
since the last interglacial epoch (corrected for eustasy) that is three and a
half times the normal regional rate (17 cm/1,000 yr as opposed to 5 cm/1,000
yr). Ongoing uplift associated with the adjacent tectonic block that
contributed granodiorite to the Punta San Antonio boulder bed is
implicated.
Transtensional Tectonics Linked to Pliocene Geology of
“El Coloradito Fault Zone” at Punta El Mangle, Baja California Sur,
Mexico
Markes E. Johnson, Professor of Geosciences
David Backus,
Research Associate
Jorge Ledesma-Vázquez, Facultad de Ciencias Marina,
Univ. Autonoma de Baja California
Fifth International Meeting on Geology of the Baja
California Peninsula, 13-14 (1999)
Basin-and-Range style extension opened the Gulf of California
during the Late Miocene and left behind horst-and-graben structures with a
prevailing north-south signature along the east margin of the Baja California
Central Domain. Changeover to the present tectonic regime of transform-rift
faults in the Gulf of California occurred in the Late Pliocene about 3.5 Ma.
Surprisingly little evidence of transtensional tectonics related to the oblique
plate boundary between the Baja California peninsula and Gulf of California is
expressed in the Pliocene geology of the Central Domain. Previous studies in
the Loreto Basin (by Umhoefer, et al., 1994 and by Bigioggero, et al, 1995)
describe a thick accumulation of Upper Pliocene fan deltas overprinted by
dextral-normal faults to the south and a volcanic center at Cerro Mencenares
overprinted by normal faults to the north. A prominent fault on the east margin
of Cerro Mencenares runs parallel to Arroyo El Mangle for more than 6 km.
Transtensional tectonics are invoked as causal factors in the development of
both areas, although local fault traces show little or no strike-slip motion and
their orientation is typically north-south in agreement with the regional
pattern of east-west crustal extension.
Our reconnaissance study of Pliocene geology on Ensenada el
Mangle (25 km north of Loreto) shows that the southern Loreto Basin is isolated
from Cerro Mencenares by a zone of tectonic quiescence in which limestone strata
(<30 m thick) rest unconformably on Miocene andesite from the Comondú
Group. These carbonates form low ramps on a dip of 6o that abut the southeast
flank of Cerro Mencenares. The El Mangle ramps are comparable to those
surrounding Pliocene islands at Punta Chivato and San Nicolas in the
Bahía Concepción region. Age of the El Mangle ramps is Pliocene
based on the abundant pectenid fossils Aequipecten abietis and
Nodipecten subnodosus. Occurrence of the less common echinoid
Clypeaster marquerensis indicates a mid- to Late Pliocene age. Very
different strata border Ensenada el Mangle across the north side of a newly
discovered fault zone, named “El Coloradito” for the red coloration
along part of the exposed fault plane. The trend of this fault is unusual:
N55W with a dip of 58oS. Conformable in sequence, the first
stratigraphic package is >125 m in thickness, and includes a basal andesite
breccia, interbedded sandstones and mudstones, a columnar basalt, and a
fossiliferous volcanic breccia, all diping 25-35o E on a strike of N
34-40oE. The top of this sequence is truncated by a single limestone
bed with abundant oysters. It is <3 m in thickness and also thermally
altered red in color. This marker has the appearance of a carbonate ramp, but
its dip is oversteepened at 12o (twice the normal value for the
development of a synsedimentary ramp). A second series comprising the
contiguous outer cliffs of Punta El Mangle is formed by volcaniclastic strata
(>125 m thick) dipping 28o NE on a strike of N10oW. As
yet undated, the distinctiveness of these two stratigraphic packages in contrast
to the simplicity of adjacent Pliocene carbonate ramps on the Ensenada el Mangle
points to major tectonic tilting of an allochthonous block. Notably, El
Coloradito Fault Zone strikes offshore parallel to the transform faults
associated with the Carmen and Farallon rifts in the Gulf of California.
Landward in the opposite direction, it also fails to cross the prominent
north-south fault that runs parallel to Arroyo El Mangle.
Evidence for Low-Angle Normal Faulting in the Acadian
Orogen: Is the Chester Dome a Core Complex in Vermont?
Paul Karabinos, Professor of Geosciences
Geological Society of America Abstracts with Programs,
31, A-370 (1999)
The Chester and Athens domes in southeastern Vermont are
classic examples of mantled gneiss domes. The elongate pair, here referred to
simply as the Chester dome, were interpreted as being cored by Middle
Proterozoic basement rocks and unconformably mantled by an inner sequence of
Late Proterozoic to Ordovician cover rocks and an outer sequence of Silurian and
Devonian cover rocks (Doll, et al., 1961). The core and inner mantling sequence
were deformed during the Ordovician Taconian orogeny and again, together with
the outer mantling sequence, during the Devonian Acadian orogeny. More
recently, many of the lithologic contacts in the Chester dome have been
reinterpreted as thrust faults of presumed Taconian age (e.g. Ratcliffe, et al.,
1997).
The most dramatic characteristic of the Chester dome, however,
is not structural repetition of the highly distinctive lithologies but rather a
zone of extreme attenuation of some of the inner mantling units. Around the
southern half of the Chester dome, the zone of attenuation includes the Pinney
Hollow, Ottauquechee, and Stowe Formations and is bounded by the Hoosac
Formation (below) and Missisquoi Formation (above). The Missisquoi Formation is
also dramatically thinned around the northern half of the Chester dome
indicating that there the upper boundary of the attenuated zone is near the
contact with the Silurian and Devonian rocks of the outer mantling sequence.
The zone of attenuation includes rocks with spectacular spiral inclusion trails
in garnet and equally spectacular oxygen-isotope zoning in garnet which
indicates infiltration of externally derived fluids during garnet growth
(Chamberlain and Conrad, 1993). In excellent exposures around the southern
margin of the Chester dome, boudinaged layers are common in and near the
attenuated zone and kinematic indicators suggest a tops-to-the-east sense of
displacement. Garnets structurally below the zone of attenuation commonly
contain textural unconformities indicating two stages of garnet growth. The
second stage of garnet grew during Acadian decompression from 9.7 to 7.2 kbar
(Vance and Holland, 1993). The available data are most consistent with the
attenuated zone being a ductile low-angle normal fault which accommodated
gravitational collapse during and after the emplacement of nappes in western New
Hampshire and eastern Vermont.
Distinguishing Grenvillian Basement from Pre-Taconian
Cover Rocks in the Northern Appalachians
Paul Karabinos, Professor of Geosciences
John N.
Aleinikoff, U.S. Geological Survey
C. Mark Fanning, Australian National
University
American Journal of Science, 299, 502-515
(1999)
Distinguishing Grenvillian basement rocks from pre-Taconian
cover sequences in the Appalachians is a first-order problem essential for
accurate structural interpretations. The Cavendish Formation in southeastern
Vermont presents a classic example of this problem. Doll and others (1961)
showed the Cavendish Formation as younger than the Middle Proterozoic Mount
Holly Complex but older than the lithologically similar Cambrian Tyson and
Hoosac Formations. More recently, the name Cavendish Formation has been
informally abandoned and its metasedimentary units have been mapped as the Tyson
and Hoosac Formations of Late Proterozoic to Cambrian age. In a radical
departure from these interpretations, Ratcliffe and others (1997) reassigned
metasedimentary rocks of the Cavendish Formation to the Mount Holly Complex
based on an inferred intrusive relationship between them and a 1.42 Ga tonalite.
This new age assignment, if correct, requires a completely new structural
interpretation of the region.
SHRIMP and Pb evaporation ages of detrital zircons extracted
from a quartzite layer from Cavendish Gorge near the proposed intrusive contact
with the tonalite constrain the time of deposition of the Cavendish Formation.
Grain shapes of the zircons vary from euhedral to nearly spherical. Virtually
all the grains have pitted surfaces and show at least some rounding of edges and
terminations; grains exhibit oscillatory zoning typical of zircons that
crystallized from a magma. Single-grain Pb evaporation analyses of ten zircons
and SHRIMP analyses of 15 zircons all yield ages less than 1.42 Ga. Seven of
the grains are consistent with derivation from the Bull Hill Gneiss that
postdates the Grenville orogenic cycle and predates deposition of the Cavendish
Formation. Thus, the metasedimentary units of the Cavendish Formation should
not be assigned to the Mount Holly Complex.
A Review of the Pikes Peak Batholith, Front Range,
Central Colorado: A “Type Example” of A-Type Granitic
Magmatism”
R. A. Wobus, Professor of Geosciences, and others
Rocky Mountain Geology, 34 (2), 289-312
(1999)
The ~1.08-Ga Pikes Peak composite batholith of central
Colorado is a type example of an a-type granitic system. From the 1970s through
the 1990s, details of the field relations, mineralogy, major and trace element
compositions, and isotopic geochemistry of Pikes Peak rocks were documented, and
they reveal the existence of two chemical groups, a potassic and a sodic series.
The potassic series (~64-78 wt % SiO2) includes the Pikes Peak
Granite, which is mostly coarse-grained biotite ± hornblende syenogranite
and minor monzogranite that dominates the batholith. The potassic series also
includes fine- to medium-grained biotite granite found in numerous, small,
late-stage plutons throughout the batholith. The sodic series is found in seven
plutons comprised of a wide range of rock types (~44-78 wt % SiO2),
including gabbro, diabase, syenite/quartz syenite, and fayalite and sodic
amphibole granite.
Differences in petrologic and geochemical characteristics
between the sodic and potassic series indicate different petrogenetic histories.
Major and trace element and strontium and oxygen isotopic data were used by some
workers to hypothesize that mantle-derived alkali basalt underwent crystal
fractionation and reaction with lower crustal rocks to generate syenitic magmas
of the sodic series, which subsequently underwent further fractionation to
produce sodic granites. Recent studies involving estimates of oxygen
fugacities, along with additional trace element and neodymium isotopic data,
also support a basalt fractionation model for the sodic series, but suggest only
minor crustal involvement. Gabbros and diabase dikes associated with the sodic
series appear to have been derived from mantle sources that previously had been
affected by a subduction event, based on neodymium isotopic and trace element
data.
Some workers propose that the potassic series also formed by
fractionation of syenitic and/or basaltic magmas coupled with reaction with
intermediate rather than lower crust. Other workers propose a model in which
genesis of the potassic series was dominated by partial melting involving
tonalitic sources, with fractionation and perhaps magma mixing playing
subordinate roles in generating compositional diversity among the potassic
granitoids. The Pikes Peak batholith thus formed by emplacement of at least two
petrogenetically different granite types, which were emplaced close together in
space and time and which exhibit geochemical characteristics typical of A-type
granites.
Petrogenesis of the Sugarloaf Syenite, Pikes Peak
Batholith, Colorado
Rachel Beane ’93
R. A. Wobus, Professor of
Geosciences
Rocky Mountain Geology, 34 (2), 313-324
(1999)
Sugarloaf Peak is one of seven sodic plutons that lie within
or adjacent to the ca. 1.08-Ga Pikes Peak batholith in central Colorado. This
report represents the first study of the Sugarloaf plutons. Major element and
modal analyses from the other six plutons (Lake George, Tarryall, Rampart Range,
West Creek, Mt. Rosa, and Spring Creek), together with data presented here,
indicate that sodic and potassic rocks from all of them were produced by
fractional crystallization of mantle-derived basaltic magmas.
The Sugarloaf pluton is composed of fine-grained,
medium-grained, coarse-grained, and pegmatitic syenite. The syenites lack
quartz and are dominated by perthitic feldspar and ferrorichterite amphibole.
The fined-grained syenite intrudes the medium- and coarse-grained syenites. The
Sugarloaf pluton is surrounded by coarse-grained Pikes Peak Granite, which is
the predominant rock type in the batholith. The linear arrangement of six of
the seven sodic plutons parallel to major Precambrian fault trends suggests that
the emplacement of Sugarloaf pluton may be rift-related.
The Sugarloaf syenites have high total alkalis, high FeO
(total), low CaO, and low MgO concentrations. They are also enriched in rare
earth elements (REE) and high field strength elements (HFSE). Pronounced trace
element variation among the Sugarloaf syenites can be explained partially by
models of fractional crystallization. A plot of Ba versus Sr shows that
compositions of the syenites closely follow modeled fractionation vectors for
potassium feldspar. The fractional crystallization trends show that
fine-grained syenite is the most chemically evolved, consistent with field
relations that show the fine-grained syenite intruded the medium- and
coarse-grained syenites. Accessory mineral fractionation, release of volatiles,
or removal of pegmatitic fluids also may have influenced geochemical variations
among the Sugarloaf syenites.
Undergraduate Research – The Consortium
Approach
R. A. Wobus, Professor of Geosciences
Geological Society of America Abstracts with Programs,
31 (7), A-386 (1999)
While no one questions the value of undergraduate research as
a vital component of geoscience curricula, departmental limitations may preclude
the implementation of such a program at some institutions. Limitations of
faculty size, time, and resources may be especially acute in the small
departments of liberal arts colleges, which may experience the additional burden
of geographic isolation.
Several of these impediments can be surmounted if small
departments create regional or even national consortia to collaborate especially
in the area of undergraduate research, though other forms of sharing and
cooperation (lab facilities, journal subscriptions, visiting speakers, etc.) may
naturally and profitably result. And while collaboration is most effective in
the summers during intercollegiate research projects in the field and lab, there
are clear advantages to such programs operating year-round.
I will describe two undergraduate research consortia which I
helped to establish – one regional with four colleges, one national with
twelve. For 15 years these consortia have supported hundreds of undergraduates
and tens of faculty who have worked as colleagues on dozens of research projects
in the U.S. and abroad. Non-collegiate funding for these two alliances came
largely from NSF and from the W. M. Keck Foundation. It is hoped that funding
agencies will continue to recognize not only the educational value of consortial
research for undergraduates, but also its economy and efficiency over supporting
many smaller programs individually. Strategically, geoscience faculty should
plan to work closely with their school’s administrators in charge of
fund-raising and development; word of the new funding initiatives that
eventually resulted in the formation of both the consortia to be described first
came from such administrative personnel.
Petrogenesis of the Pikes Peak Batholith,
Colorado
R. A. Wobus, Professor of Geosciences, and others
Geological Society of America Abstracts with Programs,
31 (7), A-261 (1999)
The ~1.08-Ga Pikes Peak batholith (PPB) of central Colorado is
a “type” example of A-type granitic magmatism. Rocks of the PPB can
be divided into two groups, based on chemical and mineralogical characteristics:
(1) a potassic series (~64-78 wt % SiO2; K/Na = 0.95-2.05), which is
dominated by biotite granite and comprises >97% of PPB exposures, and (2) a
sodic series (~44-78 wt % SiO2; K/Na = 0.32-1.36), which includes
gabbro/diabase, syenite/quartz syenite, and fayalite-sodic amphibole-bearing
granites.
Gabbros and mafic dikes associated with the sodic granitoids
have εNd(T) (+3.5 to –3.0) that
are lower than depleted mantle. Primitive mantle-normalized trace element
patterns for PPB mafic rocks exhibit overall enrichments but Nb-Ta depletions,
suggesting derivation from mantle sources that were previously affected by
subduction-related processes. However, assimilation of 1.7-Ga arc-derived crust
during ascent/emplacement cannot be ruled out.
The voluminous potassic granites are interpreted as partial
melts derived from crustal sources of tonalitic composition, based on
εNd(T) values (-0.3 to –2.7,
which overlap with values for exposed ~1.7-Ga tonalites/granodiorites in the
region) and good matches between major element compositions of the potassic
granites and experimental melts (e.g., Patiño Douce, 1997). In contrast,
syenites and granites of the sodic series cannot be explained as crustal melts,
but are interpreted as fractionation products of mantle-derived mafic magmas.
High temperature and low oxygen fugacity estimates (e.g., Frost, et. al., 1988)
support a fractionation origin for the sodic granitoid magmas, as do their
εNd(T) (-0.7 to +2.2) and trace
element characteristics. Release of fluorine-rich volatiles and/or removal of
pegmatitic fluids could have modified abundances of Ce, Nb, Zr, and Y in some
sodic granitoid magmas.
Working Together for Our Own Best Interest –
Sustainable Collaboration in the Keck Geology Consortium
Cathryn Manduca ’80
Eric Grosfils, Pomona
College
R. A. Wobus, Professor of Geosciences
EOS, 80 (46), F111 (1999)
The Keck Geology Consortium was formed in 1987 by a grant from
the W.M. Keck Foundation to increase opportunities for student and faculty
research and to reduce faculty isolation. The consortium consists of the
geology departments of 12 geographically distributed liberal arts colleges.
Together they form a vibrant community that can sustain a large cooperative
research program and attract funding. The consortium program has two goals:
enhancing undergraduate education through collaborative research with faculty
and providing substantive opportunities for faculty professional growth.
Success is measured by the impact of the program on students, faculty, and
alumni. Students and alumni give the program high marks for scientific
training, developing interpersonal and communication skills, testing their
interest in scientific careers, and assisting them in finding future
opportunities. Faculty particularly value the opportunity to work with
colleagues and the enhanced research opportunities that collaboration provides.
They report that the research experiences feed back directly into their
classroom teaching, to the benefit of all their students. The consortium
program is sustainable because the benefits to individual students and faculty
motivate their enthusiastic participation.
While the consortium was developed to address departmental
needs, it also reflects and impacts national educational agendas. The
consortium program has helped to promote the integration of research and
undergraduate education nationally by documenting the impact of the program on
students and faculty, through workshops and presentations, as a leader in
community-wide discussion (e.g. Shaping the Future of Earth Science Education)
and by providing an example of a successful program. There is no doubt that
collectively we have had experiences, opportunities and impacts that we could
not have had individually.
Petrology and Geochemistry of Late-Stage Intrusions of
the A-Type, Mid-Proterozoic Pikes Peak Batholith (Central Colorado, USA):
Implications for Petrogenetic Models
R. A. Wobus, Professor of Geosciences, and others
Precambrian Research, 98, 271-305
(1999)
The ~1.08 Ga anorogenic, A-type Pikes Peak batholith (Front
Range, central Colorado) is dominated by coarse-grained, biotite ±
amphibole syenogranites and minor monzogranites, collectively referred to as
Pikes Peak granite (PPG). The batholith is also host to numerous small,
late-stage plutons that have been subdivided into two groups (e.g. Wobus, 1976.
Studies in Colorado Field Geology, Colorado School of Mines Professional
Contributions, Colorado): (1) a sodic series (SiO2 = ~44-78 wt %;
K/Na = 0.32-1.36) composed of gabbro, diabase, syenite/quartz syenite and
fayalite and sodic amphibole granite; and (2) a potassic series (SiO2
= ~70-77 wt %; K/Na = 0.95-2.05), composed of biotite granite and minor quartz
monzonite. Differences in major and trace element and Nd isotopic
characteristics for the two series indicate different petrogenetic
histories.
Potassic granites of the late-stage intrusions appear to
represent crustal anatectic melts derived from tonalite sources, based on
comparison of their major element compositions with experimental melt products.
In addition, Nd isotopic characteristics of the potassic granites
[εNd (1.08 Ga) = -0.2 to –2.7]
overlap with those for tonalites/granodiorites [ca. 1.7 Ga Boulder Creek
intrusions; εNd (1.08 Ga) = -2.4 to
–3.6] exposed in the regions. Some of the partial melts evolved by
fractionation dominated by feldspar. The late-stage potassic granites share
geochemical characteristics with most of the PPG, which is also interpreted to
have an anatectic origin involving tonalitic crust. The origin of monzogranites
associated with the PPG remains unclear, but mixing between granitic and mafic
or intermediate magmas is a possibility.
The Vinalhaven “Diabase” – a Volcanic
Hybrid in the Coastal Maine Magmatic Province
Erik W. Klemetti ’99
R. A. Wobus, Professor of
Geosciences
Geological Society of America Abstracts with Programs,
32 (1), A-28 (2000)
The Silurian (?) Vinalhaven diabase (VHD) described by G. O.
Smith (1907) rims the northwest edge of Vinalhaven Island in Penobscot Bay, ME.
It occurs in a sill-like body about 150 m thick within the Seal Cove formation
(Gates, in review) but locally contains a vesicular flow unit and a breccia of
uncertain origin above the sill. Within the sill the VHD is a very homogenous
dark gray massive rock characterized by 1-5 mm quartz “eyes”
(xenocrysts) distributed throughout. Petrographically it is aphanitic with an
intergranular (not diabasic) groundmass of andesine and clinopyroxene with
slightly larger grains of spongy cellular plagioclase and quartz xenocrysts with
ocellar rims.
XRF and INAA analyses show that this “diabase” in
all its forms is geochemically an intermediate rock, with silica values ranging
from 52 to nearly 62%. LILE’s are enriched from 10 to 40X MORB, and
REE’s are slightly fractionated (LaN/LuN about 4) with a moderate negative
Eu anomaly. According to the Zr/TiO2 vs. Nb/Y classification of Winchester and
Floyd (1977), all samples plot as andesite or basaltic andesite. On tectonic
discriminant diagrams for basaltic rocks, the VHD shows continental margin arc
or mature island arc affinities, though these signatures may have been induced
by hybridization. The petrographic and geochemical features of the VHD strongly
suggest that it is a product of mixing of basaltic and granitic melts, evidence
of which is vividly displayed by the plutonic rocks at the base of the
Vinalhaven granite pluton in the southern part of the island (Wiebe and others,
1999) and in other volcano-plutonic centers of the Coastal Maine Magmatic
Province such as Isle au Haut and Mt. Desert Island.
Felsic Volcanic and Volcaniclastic Rocks of Vinalhaven
Island, Maine
Jennifer L. Newton ’99
R. A. Wobus, Professor of
Geosciences
Geological Society of America Abstracts with Programs,
32 (1), A-62 (1999)
The northwest part of Vinalhaven Island in Penobscot Bay,
Maine, is underlain by a volcanic complex of probable Silurian age. In
stratigraphic order the units, as defined by G. O. Smith (1907), are the
Thorofare Andesite, the Vinalhaven Diabase (see Klemetti and Wobus, this
volume), and the Vinalhaven Rhyolite (VHR). Gates (in review) has proposed the
name “Perry Creek formation” for the bedded volcaniclastic deposits
beneath the flow-landed rhyolites of the VHR. This report describes the Perry
Creek lithologies in some detail and provides extensive new geochemical data for
the VHR.
The Perry Creek formation grades from basal layers of
well-sorted maroon siltstones and sandstones (some containing the trace fossil
Chondrites into tuffs and breccias with fragments of mafic to
intermediate volcanics. The upper layers are breccias dominated by pebble-sized
clasts of flow-banded rhyolite. Most horizons are matrix supported (lahars?)
and some contain low-angle cross-beds. The base of the VHR as defined by Gates
is a thick breccia layer with cobble to boulder-sized fragments of flow-banded
rhyolite. The remainder of the VHR contains a wide variety of extraordinarily
well preserved volcanic textures and structures: air-fall tuffs (some with
accretionary lapilli), welded tuffs, tuff breccias, and flows and autobreccias
with well-defined flow-banding (locally containing spherulites up to 15 cm in
diameter). Some of the thickest flows could be remnants of exogenous domes.
Geochemically most of these rocks are true rhyolites, though early air-fall
tuffs plot as rhyodacites which are chemically similar to the Vinalhaven Granite
in the southern half of the island. MORB-normalized spider diagrams for the
rhyolites and granites show parallel patterns, and both units plot on the
boundary between “within-plate” and “volcanic-arc”
fields in tectonic discriminant diagrams (consistent with other volcano-plutonic
assemblages of similar age to the northeast in coastal
Maine).
MATHEMATICS
Systoles for Hyperbolic Knot and Link
Complements
Colin C. Adams, Mark Hopkins Professor of Mathematics
Alan Reid
Proceedings of the Cambridge Philosophical Society,
128, 103-110 (2000)
The systole length of a 3-manifold is the length of the
shortest geodesic in the manifold. We prove that if L is a knot in the 3-sphere
S3 with hyperbolic complement then the systole length of the
complement is at most 7.35534... . Improved bounds are obtained for particular
types of knots and for manifolds containing particular surfaces.
Alternating Graphs
Colin C. Adams, Mark Hopkins Professor of Mathematics
K. Foley, J. Kravis ‘98, R. Dorman, S. Payne
Journal of Combinatorial Theory, Series B, 77,
1, 96-120 (September 1999)
In this paper we generalize the concept of alternating knots
to alternating graphs and show that every abstract graph has a spatial embedding
that is alternating. We also prove that every spatial graph is a subgraph of an
alternating graph. We define n-composition for spatial graphs and generalize
the results of Menasco on alternating knots to show that an alternating graph is
n-composite for n=0,1,2,3 if and only if it is “obviously
n-composite'” in any alternating projection. Moreover, no closed
incompressible pairwise incompressible surface exists in the complement of an
alternating graph. We then generalize results of Kauffman, Murasugi, and
Thistlethwaite to prove that the crossing number of an even-valent rigid-vertex
alternating spatial graph is realized in every reduced alternating projection
with no uncrossed cycles and, if the graph is not 2-composite, the crossing
number is not realized in any non-alternating projection. We give examples
showing that this result does not hold for graphs with vertices of odd valence
or graphs with uncrossed cycles.
Isoperimetric Cusps on Hyperbolic
3-Manifolds
Colin C. Adams, Mark Hopkins Professor of Mathematics
Michigan Mathematics Journal, 46, 3,
515-531 (1999)
Given a choice C of one of a set of specified isometry types
of maximal cusps, it is shown that three disjoint simple closed curves can be
removed from any closed 3-manifold or two disjoint simple closed curves can be
removed from a cusped hyperbolic 3-manifold so that the resulting manifold M' is
hyperbolic and one of the cusps in M’ is isometric as a maximal cusp to C.
The isometry types of the possible maximal cusps include ones of volume 4, 6,
2√3, 2(1+√3) and 8√3/5. If one more curve is removed, maximal
cusps of volumes 8, 10, 2√7, √11 and √15 can also be realized.
A similar result is proved for totally geodesic boundaries as well..
Into Thin Air
Colin C. Adams, Mark Hopkins Professor of Mathematics
Mathematically Bent Column, Mathematical Intelligencer,
22, 1, 21-22 (2000)
Mathematics as mountain climbing.
Research Announcement
Colin C. Adams, Mark Hopkins Professor of Mathematics
Mathematically Bent Column, Mathematical Intelligencer,
22, 2, 26-27 (2000)
Mathematics through the personals.
The Heart of Mathematics: An Invitation to Effective
Thinking
Edward B. Burger, Associate Professor of Mathematics
Michael Starbird
Key College Press in cooperation with Springer-Verlag,
(2000)
In this new innovative textbook, the authors put special
emphasis on the deep ideas of mathematics and present the subject in a lively
and entertaining fashion. Throughout the text, the authors present the subject
as a way of thinking that can be used to solve problems, analyze situations, and
model the world around us. The book is accompanied by a kit including 3D
glasses, CD-ROM, and other hands-on manipulatives.
On Real Quadratic Number Fields and Simultaneous
Diophantine Approximation
Edward B. Burger, Associate Professor of Mathematics
Monatshefte fur Mathematik, 128, 201-209
(2000)
Here we provide a necessary and sufficient condition on the
partial quotients of two real quadratic irrational numbers to insure that they
are elements of the same quadratic number field over Q. Such a condition
has implications to simultaneous diophantine approximation. In particular, we
deduce an improvement to Dirichlet’s Theorem in this context which, as an
immediate consequence, shows the Littlewood Conjecture to hold for all numbers
from the same quadratic number field.
On Simultaneous Diophantine Approximation in the Vector
Space Q + Qa
Edward B. Burger, Associate Professor of Mathematics
The Journal of Number Theory, 82, 12-24
(2000)
Beginning with an improvement to Dirichlet’s Theorem on
simultaneous approximation, in this paper we introduce an algorithm, in sympathy
with the classical continued fraction algorithm, to generate the sequence of
best approximates to certain simultaneous systems. We then produce best
possible upper bounds for the associated diophantine inequalities. In addition,
we consider implications within the geometry of numbers and investigate the
converse of the sharpened version of Dirichlet’s result. Finally, we
close with some remarks on the Littlewood Conjecture in this context.
On Diophantine Approximation below the Lagrange
Constant
Edward B. Burger, Associate Professor of Mathematics
Jonathan Todd ’96
Fibonnaci Quarterly, 38, 136-144
(2000)
Let a be a real quadratic irrational and
m(a) the Lagrange constant for a. For any c, 0 <
c < m(a), we explicitly compute the finite list of
positive integers q satisfying q||aq|| < c, and
determine the optimal lower bound for c to ensure solvability of the
inequality. This extends and generalizes results of Tognetti, Van Ravenstein
and Winley.
Pleasures vs. Problems
Edward B. Burger, Associate Professor of Mathematics
Michael Starbird
The Notices of the American Mathematical Society,
47, (2000)
In this opinion piece, the authors examine how the mathematics
community could inspire and entice others to explore mathematics.
Groups and Characters
Victor E. Hill IV, Thomas T. Read Professor of
Mathematics
Chapman & Hall Publishers, (November
1999)
Group representation and character theory is both
elegant and practical, with important applications to quantum mechanics,
spectroscopy, crystallography, and other fields in the physical
sciences. This text offers an easy-to-follow introduction to the
theory of groups and of group characters. Group theory is covered through
the Sylow Theorems and the full subgroup structure of A5.
Numerous character tables are worked out in full, along with a
presentation of real and induced characters that lead to the table for
S5.
Formal Fibers at Height One Prime Ideals
Susan Loepp, Assistant Professor of Mathematics
Journal of Pure and Applied Algebra, 148,
191-207 (2000)
In this paper, we construct examples of local unique
factorization domains so that not only can the dimension of the generic formal
fibers of these domains be controlled, but also the dimension of the formal
fibers for infinitely many height one prime ideals.
The Math Chat Book
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
Math Assn. Amer., (2000)
A popular book based on the TV show and column. Illustrated
by James Bredt.
Geometric Measure Theory: A Beginner’s
Guide
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
Academic Press, Third Edition, (2000)
An easy-going, illustrated introduction for the newcomer to
this fast-growing and somewhat technical field. The third edition presents, for
the first time in print, the recently announced proofs of the Double Bubble
Conjecture (equal and unequal volumes) and the Hexagonal Honeycomb
Conjecture, as well as treatments of the Weaire-Phelan counterexample to
Kelvin’s Conjecture and Almgren’s optimal isoperimetric inequality.
There is also a new chapter on immiscible fluids and crystals. In these areas,
undergraduates have made important contributions.
Instability of the Wet X Soap Film
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
Kenneth Brakke
J. of Geom. Anal., 8, 749-767 (1998)
We show that adding slight thickness to a soap film shaped
like an X leaves it unstable, although adding much thickness makes it stable.
Analogous questions about other singularities remain controversial.
100-Year-Old Kelvin Conjecture Disproved by Weaire and
Phelan
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
Math Horizons, (September 1999)
Popular account of a surprising new way to partition space
into unit volumes, upsetting the 100-year-old Kelvin conjecture.
Recollections of Fred Almgren
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
J. Geom. Anal., 8, (1998)
Recollections of student and colleagues.
Does the Millennium begin on January 1,
2000?
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
Congressional Quarterly Researcher, 9,
899 (October 15, 1999)
Congress needs to know that the millennium begins with 2001.
Math Chat
Frank Morgan, Dennis Meenan (’54) Centennial Professor
of Mathematics
MAA Web Page, (1998-present)
Biweekly column with questions, answers, and prizes.
Available at the MAA web page at www.maa.org.
Borrowing Strength without Explicit Data
Pooling
Jerome Reiter, Assistant Professor of Mathematics
Amer. Math. Monthly, 107, 24-32 (2000)
Increasingly, causal questions are being answered with
statistics. For both scientists and consumers, it has become important to
understand how valid causal studies can be designed and how suspicious studies
can be identified. This paper aims to further these understandings by
explaining the statistical principles and techniques that underlie valid studies
of causal relationships. It explains how randomized experiments yield reliable
estimates of causal effects and describes techniques used to estimate causal
effects in non-randomized studies.
Zd Staircase Action
Cesar E. Silva, Professor of Mathematics
Terry Adams
Ergodic Theory and Dynamical Systems, 19,
837-850 (1999)
We define staircase Zd actions. We first prove
that staircase Zd actions satisfying a general condition are mixing.
Then we describe how to extend the results to the staircase Zd
actions. Thus, we have constructed explicitly rank one mixing Zd
actions which include natural analogues to the well-known staircase
transformation.
Infinite Ergodic Index Zd Actions in Infinite
Measure
Cesar E. Silva, Professor of Mathematics
With E. Muehlegger ’97, A. Raich ’98, M.
Touloumtzis ’96, B. Narasimhan ’97 and W. Zhao
Colloquium Mathematicum, 82, (2), 167-190
(1999)
We construct infinite measure-preserving and nonsingular rank
one Z
d-actions. The first example is ergodic infinite measure
preserving but with non-ergodic, infinite conservative index, basis
transformations; in this case we exhibit sets of increasing finite and infinite
measure which are properly exhaustive and weakly wandering. The next examples
are staircase rank one infinite measure preserving Z
d-actions; for
these examples we show that the individual basis transformations have
conservative ergodic Cartesian products of all orders, hence infinite ergodic
index. We generalize this example to obtain a stronger condition called power
weakly mixing. The last examples are nonsingular Z
d-actions for each
Krieger ratio set type with individual basis transformations with similar
properties.
PHYSICS
Quantum Coherent Dynamics of Molecules: A Simple Scenario
for Ultrafast Photoisomerization
Daniel P. Aalberts, M.S.L. du Croo de Jongh, Leiden
University, Brian F. Gerke ’99, and
Wim van Saarloos, Leiden
University
Physical Review A, 61, 040701 (2000)
We analyze the coherent dynamics of optically excited alkenes
in a fully correlated 3D tight-binding model with extended Hubbard interactions.
The scenario that emerges is that the steric repulsive interactions are the
driving force behind ultrafast cis-trans photoisomerizations. This resolves the
apparent discrepancy between values for the torsional stiffness obtained from
band structure potentials and from vibrational spectra. The mechanism is
illustrated in quantitative detail for ethylene and is also shown to yield a
promising scenario for the coherent dynamics of molecules like
retinal.
Nonlinear dynamics in Ultrafast Lasers
S.R. Bolton, R.A. Jenks ’98, C.N. Elkinton ’98,
and G. Sucha
IEEE LEOS newsletter, 14(2), 7, (2000)
In the last decade ultrafast laser science and technology has
undergone revolutionary growth. Femtosecond sources are now used routinely as
probes of ultrafast processes in biological, chemical, and physical systems, as
well as for applications in communications and medicine. All femtosecond lasers
rely on intensity dependent optical response-that is
on optical nonlinearity, to produce and shape the pulses. The formalism of
nonlinear dynamics and chaos explains the behavior of complex systems with such
nonlinear interactions, and can predict their instabilities. Far from being a
mere mathematical curiosity, the nonlinear dynamics approach to lasers has
yielded a wealth of basic knowledge pertinent to laser development, as for
example in controlling semiconductor laser instabilities. Despite their general
utility, these approaches have only recently been applied to the study of
femtosecond laser systems. Here we briefly describe our work on two such
systems: the additive pulse modelocked laser (APM) operating at 1.55 microns,
and the Kerr lens modelocked Titanium Sapphire laser (KLM) operating at
800nm.
Electronic Four-particle Correlations in Semiconductors:
Renormalization of Pump-probe Oscillations
U. Neukirch, S.R. Bolton, L.J. Sham, and D.S.
Chemla
Physical Review B, 61(12), R7835
(2000)
The nonlinear optical response of excitons in a single ZnSe
quantum well is investigated by pump-probe measurements. In counter-circular
polarization configuration at negative delay, Δt, spectral oscillations are
observed the period of which is energy dependent. Whereas at energies above the
1S exciton the usual Epp=h/Δt dependence is found, the period
strongly deviates from that value at energies below the exciton. Model
calculations reveal that this behavior is caused by the bound biexciton state in
the four-particle correlations.
Polariton-Biexciton Transitions in a Semiconductor
Microcavity
U. Neukirch, S.R. Bolton, N.A. Fromer, L.J. Sham, and D.S.
Chemla
Physical Review Letters, 84(10), 2215,
(2000)
The influence of four-particle correlations on the nonlinear
response of a semiconductor microcavity is determined by a pump-and-probe
investigation. Experiments are performed on a specially designed non-monolithic
microcavity which contains a single ZnSe quantum well. In this system, the
biexciton binding energy exceeds both the normal-mode splitting between exciton
and cavity mode and all relevant damping constants. Strong spectral features
below the excitonic resonance are observed in the nonlinear response. These
features are unique to the counter-polarized configuration which allows for
excitation of the bound biexciton state. Comparison with model calculations
shows that in this case the coherent nonlinearity is completely dominated by
biexciton-exciton interactions beyond the Hartree-Fock approximation.
Molecular Constants and Rydberg-Klein-Rees Potential
Curve for the Na2 13Sg- State
Y.M. Liu, J.A. Li, D.Y. Chen, L. Li, K.M. Jones, B. Ji, R.J.
Le Roy
J. Chem. Phys., 111 (8), 3494 (1999)
Transitions into the doubly excited Na2 13Sg- state
have been analyzed using near-dissociation expansions (NDE) to represent the
vibrational energies and inertial rotational constants, while the centrifugal
distortion constants were held fixed at “mechanically consistent”
values calculated from the Rydberg–Klein–Rees (RKR) potential
implied by those G(upsilon) and B-upsilon functions. The input data cover the
range upsilon = 0 to 57 and N up to 47, and the fit yields upsilon(D) =
61.41(±0.10) and D-0 = 3385.70(±0.2) cm-1.
Fitting Line Shapes in Photoassociation Spectroscopy of
Ultracold Atoms: A Useful Approximation
K.M. Jones, P.D. Lett, E. Tiesinga, et al.
Physical Review A, 61, 012501 (2000)
Line shapes observed in photoassociation spectroscopy of
ultracold (T<1 mK) atoms are asymmetric and the peak of the line is shifted
by a temperature-dependent amount from the zero-temperature threshold. In
principle, calculating the line shape requires a full knowledge of both the
ground- and excited-state potentials. We demonstrate here that an approximation
based on the Wigner threshold law for scattering yields a relatively simple
expression which allows one to extract line positions and linewidths directly
from the data. The formula contains a few parameters (threshold frequency,
linewidth, temperature, height) and does not require a detailed knowledge of the
molecular potentials involved. We illustrate the utility of this approach with
examples for Na photoassociation at 500 mK and also discuss the limitations of
the approach.
Spectroscopy of Autoionizing Doubly-Excited States in
Ultracold Na2 Molecules
Produced by
Photoassociation
A. Amelink, K.M. Jones, P.D. Lett, et al.
Physical Review A, 61, 042707 (2000)
We have performed photoassociation spectroscopy to study the
doubly excited states of Na2 involved in the associative ionization
of colliding Na(3P) atoms. Rovibrational levels of two doubly excited
potentials connected to the P3/2 + P3/2 asymptote, one of 0u+ and one of 1u
symmetry, have been identified. These two doubly excited potentials dominate
the route to ionization used in photoassociation experiments of cold Na. Binding
energies and rotational constants for all the vibrational levels with binding
energies <50 GHz have been measured. The asymptotic potentials and
short-range ionization probabilities are extracted from the data.
Single- Color Photoassociative Ionization of Ultracold
Sodium:
The Region from 0 to –5 GHz
Kevin Jones, et al.
Physical Review A, 62, 013408 (2000)
We have measured the rate of production of Na2+
ions in collisions of ultracold Na atoms held in a magneto-optical trap (MOT) as
a function of probe laser detuning using a single-color probe beam. The ion
rate is measured with the atoms mainly in the 3S(f = 2) level (“bright
MOT”) or the 3S(f = 1) level (“dark MOT”). Using recent
experimental information about the doubly excited autoionizing states of
Na2, we find that the large structures in the first 5 GHz red of the
atomic transition frequency are due to a doubly resonant excitation process with
levels in the 0g- potential (asymptotically connected to 3S1/2 + 3P3/2) as the
intermediate states, and levels in the 0u- and 1u potentials (asymptotically
connected to 3P3/2 + 3P3/2) as the final autoionizing states. We can account
for nearly all of the observed structure in this region of the spectra for both
the bright and dark MOT.
Hyperfine splitting and Isotope Shift Measurements Within
the 378 nm 6P1/2 -
7S1/2 Transition in 203T1 and
205T1
D.S. Richardson, R.N. Lyman ’99, and P.K.
Majumder
Physical Review A, 62, 012510 (2000)
Using a frequency-doubled diode laser system, we have measured
the hyperfine splitting in the (6s27s)7S1/2 excited state
of the two naturally occurring thallium isotopes. For thallium 205T1
and 203T1 we find frequency intervals of 12294.5(1.5)MHz and
12180.5(1.8)MHz respectively. This measurement addresses an earlier discrepancy
in measured values for these intervals. At the same time, we have measured,
with a factor of fifty improved precision, the 205T1-203T1
isotope shift within the 378 nm 6P1/2-7S1/2
transition.
Entanglement of Formation
William K. Wootters, Professor of Physics
Quantum Communication, Computing, and Measurement 2,
ed. by P. Kumar, et al., Kluwer Academic/Plenum, New York, 2000.
At least three distinct information-theoretic measures of
quantum entanglement have been proposed in recent years. This paper highlights
one of them, the entanglement of formation, as well as a related quantity called
the tangle. The tangle can be used to express a simple law of entanglement,
limiting the extent to which a single qubit may be simultaneously entangled with
each of two other qubits.
Distributed Entanglement
Valerie Coffman, Joydip Kundu, and William K. Wootters,
Professor of Physics
Physical Review A, 61, 052306, (2000)
Consider three qubits
A, B, and
C which may be
entangled with each other. We show that there is a trade-off between
A’s entanglement with
B and its entanglement with
C.
This relation is expressed in terms of a measure of entanglement called the
concurrence, which is related to the entanglement of formation. Specifically,
we show that the squared concurrence between
A and
B, plus the
squared concurrence between
A and
C, cannot be greater than the
squared concurrence between
A and the pair
BC. This inequality is
as strong as it could be, in the sense that for any values of the concurrences
satisfying the corresponding equality, one can find a quantum state consistent
with those values. Further exploration of this result leads to a definition of
an essential three-way entanglement of the system, which is invariant under
permutations of the qubits.
PSYCHOLOGY
Perspective Effects in Nondeontic Versions of the Wason
Selection Task
Alexander Staller, Steven A. Sloman, and Talia Ben-Zeev,
Assistant Professor of Psychology
Memory & Cognition, 28, 396-405
Perspective effects in the Wason four-card selection task
occur when people choose mutually exclusive sets of cards depending on the
perspective they adopt when making their choice. Previous demonstrations of
perspective effects have been limited to deontic contexts—that is, problem
contexts that involve social duty, like permissions and obligations. In three
experiments, we demonstrate perspective effects in nondeontic contexts,
including a context much like the original one employed by Wason (1966, 1968).
We suggest that perspective effects arise whenever the task uses a rule that can
be interpreted biconditionally and different perspectives elicit different
counterexamples that match the predicted choice sets. This view is consistent
with domain-general theories but not with domain-specific theories of deontic
reasoning—for example, pragmatic reasoning schemas and social contract
theory—that cannot explain perspective effects in nondeontic
contexts.
Personality, Personality Disorders, and Defense
Mechanisms
Phebe Cramer, Professor of Psychology
Journal of Personality, 67, 535-554
(1999)
The prototype approach was used to assess the presence of
personality features associated with borderline, narcissistic, histrionic, and
psychopathic personality syndromes in a sample of 91 young adults from the Block
and Block (1980) longitudinal study. These personality prototypes were found to
be related to the use of denial and projection, and especially to the immature
manifestations of those defenses, in ways consistent with theory.
Gender Identity: Affected by Social Change?
Phebe Cramer, Professor of Psychology and Heather Westergren
’96
Journal of Personality Assessment, 73, 19-30
(1999)
To determine whether social changes in attitudes toward the
role of men and women have influenced gender identity measures, 60 male and
female college students were assessed using both a Thematic Apperception Test
measure (May’s, 1966, Deprivation/Enhancement measure) and a self-report
measure (Bem’s, 1974, Sex Role Identity [BSRI]), both of which were
developed more than 20 years ago. Although some recent research has found the
BSRI to no longer differentiate between men and women (Twenge, 1997; Wilcox
& Francis, 1997), this study found significant gender differences for both
gender identity measures.
Change in Defense Mechanisms during Psychoanalysis and
Psychotherapy:
A Case Study
Phebe Cramer, Professor of Psychology
The Psychoanalytic Study of Lives Over Time: Clinical and
Research Perspective on Children Who Return to Treatment
in
Adulthood, 309-330 (1999)
The chapter discusses the use of defense mechanisms in the
analysis of a 10 year old boy, as these are revealed in successive psychotherapy
sessions. Developmental changes are noted as the therapy progresses. The
chapter points out how empirical investigation supports both theory and clinical
observation.
Ego Functions and Ego Development:
Defense
Mechanisms and Intelligence as Predictors of Ego Level
Phebe Cramer, Professor of Psychology
Journal of Personality, 67, 735-760
(1999)
This study considers the contribution of two ego
functions—intelligence and defense mechanisms—to ego developmental
level. Two independent assessments of ego level were related to IQ and defense
mechanism use in a sample of 89 young adults. Whereas IQ and defense were
themselves found to be unrelated, both variables predicted ego level: The
relation with IQ was linear, whereas the relation with defense was curvilinear.
In addition, the relation between defense and ego level varied as a function of
IQ level. At low levels of IQ, stronger use of Denial and Projection was
associated with higher ego levels. At high IQ levels, strong use of Denial was
associated with lower ego levels, whereas moderate use of Projection was
associated with higher ego levels.
The Thematic Apperception Test
Phebe Cramer, Professor of Psychology
Encyclopedia of Psychology, American Psychological
Association and Oxford University Press. (2000)
A review of the history, rationale and use of the TAT.
Clinical and research approaches are discussed. Problems for assessing
reliability and validity are considered.
The Development of Identity: Gender Makes a
Difference
Phebe Cramer, Professor of Psychology
Journal of Research in Personality, 34, 42-72
(2000)
Gender-based differences in the relation between Identity
status and personality configurations of 200 male and female college students
were studied. For statuses based on commitment (the Achieved and Foreclosed
identities), the personality configuration of males and females was more similar
than that of males and females in statuses lacking commitment (Moratorium and
Diffused). Further, the importance of four personality dimensions that had been
hypothesized (Grotevant, 1987) to promote identity development (ego-resilience,
openness to experience, self-esteem, and self-monitoring) was found to vary as a
function of gender, as did the self-descriptions of males and females in each
identity status.
Subsidy Shock: Reframing Judgments of College Sticker
Prices
George R. Goethals, Professor of Psychology and
Cynthia
McPherson Frantz, University of Massachusetts
Basic and Applied Social Psychology, 21, 167-175
(1999)
Three studies tested the hypotheses that (a) people think
college tuition is too high, (b) people know very little about the subsidies
colleges provide, and (c) providing people with subsidy information leads them
to judge college prices as more reasonable. The results offered qualified
support. First people generally thought that public school charges were
reasonable, but that private school charges were unreasonable. Second, people
were aware of the subsidies provided by public schools, but were often unaware
of those provided by private schools. Third, after receiving subsidy
information, people increased their reasonableness ratings of private school
prices but not public school prices. This was true even when they correctly
estimated the private schools’ subsidies. Making subsidy information
salient seems to reframe reasonableness judgments.
Responding to Blame in Family Therapy: A
Constructionist/Narrative Perspective
Myna L. Friedlander, SUNY at Albany, Laurie Heatherington,
Professor of Psychology
and Abbe L. Mars ’93
The American Journal of Family
Therapy, 28, 133-146 (2000)
Blaming events (N = 25) were identified in seven interviews
conducted by prominent theorists who espouse a constructionist or narrative
approach to family treatment. Congruent with this perspective, we used
conversation analysis (Gale, 1996) and the grounded theory method of constant
comparison (Corbin & Strauss, 1990) to identify the therapists’
behaviors and strategies following blame expressed by family members. Results
indicated three core categories or themes of therapists’ responses to
blame—Ignoring/Diverting, Acknowledging/Challenging, and
Reframing—subsuming 17 individual codes (e.g., challenging all-or-none
thinking, highlighting neutral information, interrupting, focusing on
competence). The most frequent code was focusing on the positive.
A Developmental Perspective on Peer
Rejection:
Mechanisms of Stability and Change
Marlene J. Sandstrom, Assistant Professor of Psychology and
John D. Coie
Child Development, 70, 955-966 (1999)
This study examines factors associated with the relative
stability of peer rejection among elementary school-aged children. Forty-four
initially rejected children (some of whom improved their social status while
others remained rejected over a 2-year period) were recruited from a larger
sociometric sample. Prospective analyses were conducted to determine whether
peer nominated aggression and children’s perceptions of their own status
in fourth grade were predictive of status improvement by the end of fifth grade.
In addition to prospective analyses, initially rejected children and their
mothers were invited to participate in a retrospective interview about their
social experiences over the past 2 school years. Results of prospective and
retrospective analyses suggested that perceived social status, participation in
extracurricular activities, locus of control, and parental monitoring were all
positively related to status improvement among initially rejected children.
Surprisingly, aggressive behavior also was positively related to status
improvement among initially rejected boys.
The Relationship of Daily Mood and Stressful Events to
Symptoms in
Juvenile Rheumatic Disease
Laura E. Schanberg, Marlene J. Sandstrom, Assistant
Professor of Psychology, Kathleen Starr, Karen M. Gill, John C. Lefebvre,
Francis J. Keefe, Glenn Affleck, and Howard Tennen
Arthritis Care and Research, 13, 33-41
(2000)
The purpose of this study was 3-fold: 1) to assess the
feasibility of a daily diary for use with children with juvenile rheumatic
disease (JRD), 2) to describe daily variation in mood, stressful events, and
symptoms in children with JRD, and 3) to examine the extent to which daily mood
and daily stressful events predict daily symptoms in children with JRD. Twelve
children with JRD completed a daily booklet for 7 days. The daily booklet
included measures of daily mood, daily stressful events, daily symptoms, and
daily function. The children also completed a visual analog scale for pain and
the Children’s Depression Inventory. Subjects showed good compliance with
scheduled completion and return of the daily diaries. Results indicated that
children with JRD showed variability in daily mood, frequency of daily stressful
events, and daily symptoms across days. Multilevel fixed effects models showed
that more negative daily mood and more daily stressful events significantly
predicted increased reports of fatigue, stiffness, and cutting back on daily
activities. Negative daily mood also correlated with increases in daily
reported pain. These results indicate that daily diary research is both
feasible and potentially informative in children with JRD. Our data emphasize
the need for further investigation into the role of daily mood and daily
stressful events on disease course in JRD.
The Spotlight Effect in Social Judgment: An Egocentric
Bias in Estimates of the Salience of One’s Own Actions and
Appearance
T. Gilovich, V.H. Medvec, and K. Savitsky, Assistant
Professor of Psychology
Journal of Personality and Social Psychology,
78, 211-222 (2000)
This research provides evidence that people overestimate the
extent to which their actions and appearance are noted by others, a phenomenon
we dub the "spotlight effect." In Studies 1 and 2, participants who were asked
to don a t-shirt depicting either a flattering or embarrassing image
overestimated the number of observers who would be able to recall what was
pictured on the shirt. In Study 3, participants in a group discussion
overestimated how prominent their positive and negative utterances were to their
fellow discussants. Studies 4 and 5 provide evidence supporting an
anchoring-and-adjustment interpretation of the spotlight effect. In particular,
people appear to anchor on their own rich phenomenological experience and then
adjust—insufficiently—to take into account the perspective of
others. The discussion focuses on the manifestations and implications of the
spotlight effect across a host of everyday social phenomena.
When Social Worlds Collide: Overconfidence in the
Multiple Audience Problem
L.D. Van Boven, J. Kruger, K. Savitsky, Assistant Professor
of Psychology, and T. Gilovich
Personality and Social Psychology Bulletin, 26,
619-628 (2000)
Individuals sometimes try to convey different identities to
different people simultaneously or to convey certain information to one
individual while simultaneously concealing it from another. How successfully
can people solve these "multiple audience" problems, and how successfully do
they think they can? On the one hand, the research presented here corroborates
previous findings that people are rather adept at such tasks. In Study 1,
participants who adopted different identities in preliminary interactions with
two other participants (acting the part of a studious "nerd" with one and a
fun-loving "party animal" with the other) were able to preserve these identities
when they interacted subsequently with both individuals at the same time. In
Study 2, participants were able to communicate a "secret word" to one audience
while simultaneously concealing it from another. Despite their skill at these
tasks, however, participants in both studies were overconfident in their
abilities, believing that they were better able to solve these multiple audience
problems than they actually were.
What Every Skeptic Should Know About Subliminal
Persuasion
N. Epley, K. Savitsky, Assistant Professor of Psychology,
and R.A. Kachelski
Skeptical Inquirer, 23, 40-45; 58 (1999,
Sept./Oct.)
Classic research by cognitive and social psychologists
suggests that subliminally presented stimuli can be perceived and can influence
individuals’ low-level cognitions. More recent investigations suggest
that such stimuli can also affect individuals’ high-level cognitive
processes, including attitudes, preferences, judgments, and even their
behavior.
The Spotlight Effect and the Illusion of Transparency:
Egocentric Assessments of How We’re Seen by Others
T. Gilovich and K. Savitsky, Assistant Professor of
Psychology
Current Directions in Psychological Science, 8,
165-168 (1999)
We review a program of research that examines people’s
judgments about how they are seen by others. The research indicates that people
tend to anchor on their own experience when making such judgments, with the
result that their assessments are often egocentrically biased. Our review
focuses on two biases in particular, the "spotlight effect," or people’s
tendency to overestimate the extent to which their behavior and appearance are
noticed and evaluated by others, and the "illusion of transparency," or
people’s tendency to overestimate the extent to which their internal
emotional states "leak out" and are detectable by others.
Sex-Dependent Behavioral Effects of the Neurosteroid
Allopregnanolone
(3α, 5α-THP) in Neonatal and Adult Rats
after Postnatal Stress
Betty Zimmerberg, Sharon H. Rackow ’98 and Karen P.
George-Friedman
Pharmacology Biochemistry and Behavior, 64,
717-724 (1999)
The neuroactive steroid allopregnanolone
(3a-hydroxy-5a-pregnan-20-one, 3α,5α-THP) has been shown to be
involved in the central nervous system's response to stress. This experiment
investigated whether response to the neuroactive steroid allopregnanolone, a
positive modulator of the GABAA receptor, would be altered in
neonatal or adult rats previously exposed to a chronic stressor - daily maternal
separation during the first week of life. Subjects were then tested either as
neonates or adults. In neonates, allopregnanolone decreased the number of
ultrasonic vocalizations after brief maternal separation. Previously separated
subjects vocalized less and were less active than controls, but were not more
sensitive to allopregnanolone on either measure. In adulthood, subjects with a
prior history of maternal separation had a greater grooming response to a novel
environment after a ten minute cold water swim test than non-separated subjects.
Allopregnanolone reduced grooming, but, again, there was no difference due to
stress history. A significant effect of gender was noted in the adult subjects
- females were largely responsible for the effects reported. These results
suggest that early maternal separation stress can produce an habituation
response in neonates and a long-term sensitization response to later novel
stress in adults. However, since the behavioral effects of allopregnanolone
were not differentially influenced by this early stress history, the neuroactive
steroid/GABAA receptor complex may not be the major mediator of these
early stress sequela. Results indicating that females were more responsive to
allopregnanolone than males are discussed in light of previous
findings.