79 research outputs found
Russia: A Eurasian Anomaly
From the Washington University Office of Undergraduate Research Digest (WUURD), Vol. 13, 05-01-2018. Published by the Office of Undergraduate Research. Joy Zalis Kiefer, Director of Undergraduate Research and Associate Dean in the College of Arts & Sciences; Lindsey Paunovich, Editor; Helen Human, Programs Manager and Assistant Dean in the College of Arts and Sciences Mentor(s): James Wertsc
On the geometry of Hamiltonian chaos
We show that Gutzwiller's characterization of chaotic Hamiltonian systems in
terms of the curvature associated with a Riemannian metric tensor in the
structure of the Hamiltonian can be extended to a wide class of potential
models of standard form through definition of a conformal metric. The geodesic
equations reproduce the Hamilton equations of the original potential model when
a transition is made to the dual manifold, and the geodesics in the dual space
coincide with the orbits of the Hamiltonian potential model. We therefore find
a direct geometrical description of the time development of a Hamiltonian
potential model. The second covariant derivative of the geodesic deviation in
this dual manifold generates a dynamical curvature, resulting in (energy
dependent) criteria for unstable behavior different from the usual Lyapunov
criteria. We discuss some examples of unstable Hamiltonian systems in two
dimensions giving, in particular, detailed results for a potential obtained
from a fifth order expansion of a Toda lattice Hamiltonian.Comment: 7 pages TeX, Figure captions, 4 figures (eps). Some clarifications,
added reference
Self-Wiring of Neural Networks
In order to form the intricate network of synaptic connections in the brain,
the growth cones migrate through the embryonic environment to their targets
using chemical communication. As a first step to study self-wiring, 2D model
systems of neurons have been used. We present a simple model to reproduce the
salient features of the 2D systems. The model incorporates random walkers
representing the growth cones, which migrate in response to chemotaxis
substances extracted by the soma and communicate with each other and with the
soma by means of attractive chemotactic "feedback".Comment: 10 pages, 10 PostScript figures. Originally submitted to the
neuro-dev archive which was never publicly announced (was 9710001
Entropy measures as geometrical tools in the study of cosmology
Classical chaos is often characterized as exponential divergence of nearby
trajectories. In many interesting cases these trajectories can be identified
with geodesic curves. We define here the entropy by with
being the distance between two nearby geodesics. We derive an
equation for the entropy which by transformation to a Ricatti-type equation
becomes similar to the Jacobi equation. We further show that the geodesic
equation for a null geodesic in a double warped space time leads to the same
entropy equation. By applying a Robertson-Walker metric for a flat
three-dimensional Euclidian space expanding as a function of time, we again
reach the entropy equation stressing the connection between the chosen entropy
measure and time. We finally turn to the Raychaudhuri equation for expansion,
which also is a Ricatti equation similar to the transformed entropy equation.
Those Ricatti-type equations have solutions of the same form as the Jacobi
equation. The Raychaudhuri equation can be transformed to a harmonic oscillator
equation, and it has been shown that the geodesic deviation equation of Jacobi
is essentially equivalent to that of a harmonic oscillator. The Raychaudhuri
equations are strong geometrical tools in the study of General Relativity and
Cosmology. We suggest a refined entropy measure applicable in Cosmology and
defined by the average deviation of the geodesics in a congruence.Comment: Final Versio
Gene Essentiality Analyzed by In Vivo Transposon Mutagenesis and Machine Learning in a Stable Haploid Isolate of Candida albicans
This work was supported by European Research Council Advanced Award 340087 (RAPLODAPT) to J.B., the Dahlem Centre of Plant Sciences (DCPS) of the Freie UniversitÀt Berlin (R.K.), Israel Science Foundation grant no. 715/18 (R.S.), the Wellcome Trust (grants 086827, 075470, 101873, and 200208) and the MRC Centre for Medical Mycology (N006364/1) (N.A.R.G.). Data availability.All of the code and required dependencies for analysis of the TnSeq data are available at https://github.com/berman-lab/transposon-pipeline. Library insertion sequences are available at NCBI under project PRJNA490565 (https://www.ncbi.nlm.nih.gov/bioproject/PRJNA490565). Datasets S1 through S9 are available at https://doi.org/10.6084/m9.figshare.c.4251182.Peer reviewedPublisher PD
Immunocytochemical localization of the GABAA/benzodiazepine receptor in the guinea pig cochlear nucleus: evidence for receptor localization heterogeneity
Immunocytochemistry with a monoclonal antibody against the GABAA/benzodiazepine receptor showed labeled axo-dendritic synapses in the anteroventral cochlear nucleus. In the dorsal cochlear nucleus, label was seen apposing both axo-somatic and axo-dendritic terminals. The results suggest a heterogeneous distribution of GABA receptors, together with a possible segregation of receptor subtypes between somata and dendrites in certain neurons. The presence of cytoplasmic labeling in some neurons might reflect a higher receptor turnover rate in these neurons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27639/1/0000015.pd
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