20,009 research outputs found
Vestibular inputs to premotor interneurons in the feline C1-C2 spinal cord
The resting length of respiratory muscles must be altered during changes in posture in order to maintain stable ventilation. Prior studies showed that although the vestibular system contributes to these adjustments in respiratory muscle activity, the medullary respiratory groups receive little vestibular input. Additionally, previous transneuronal tracing studies and physiological experiments demonstrated that propriospinal interneurons in the C1-C2 spinal cord send projections to the diaphragm motor pool. The present study tested the hypothesis that C1-C2 interneurons mediate vestibular influences on diaphragm activity. Recordings were made from 145 C1-C2 neurons that could be antidromically activated from the C5-C6 ventral horn, 60 of which had spontaneous activity, during stimulation of vestibular receptors using electric current pulses or whole-body rotations in vertical planes. The firing of 19 of 31 spontaneously active neurons was modulated by vertical vestibular stimulation; the response vector orientations of most of these cells were closer to the pitch plane than the roll plane, and their response gains remained relatively constant across stimulus frequencies. Virtually all spontaneously active neurons responded robustly to electrical vestibular stimulation, and their response latencies were typically shorter than those for diaphragm motoneurons. Nonetheless, respiratory muscle responses to vestibular stimulation were still present after inactivation of the C1-C2 cord using large injections of either muscimol or ibotenic acid. These data suggest that C1-C2 propriospinal interneurons contribute to producing posturally-related responses of respiratory muscles, although additional pathways are also involved in generating these responses
Lepton Flavor Non-Universality in B-meson Decays from a U(2) Flavor Model
We address the recent anomalies in semi-leptonic -meson decays using a
model of fermion masses based on the flavor symmetry. The new
contributions to transitions arise due to a tree-level
exchange of a vector boson gauging a subgroup of the flavor
symmetry. They are controlled by a single parameter and are approximately
aligned to the Standard Model prediction, with constructive interference in the
-channel and destructive interference in the -channel. The current
experimental data on semi-leptonic -meson decays can be very well reproduced
without violating existing constraints from flavor violation in the quark and
lepton sectors. Our model will be tested by new measurements of transitions and also by future electroweak precision tests, direct
searches, and - conversion in nuclei.Comment: 23 pages, 2 figures, references added, matches published versio
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Temporal Changes in the Fishes of Waller Creek and Invasion of the Variable Platyfish
This poster was presented at the second Waller Creek Symposium held on the University of Texas campus at the Recreational Sports Center on May 7, 2018.Waller Creek is an entirely urban creek flowing 11km through Austin, Travis County, Texas into Ladybird Lake. We gather the historic fish data, all held in our own Fishes of Texas Project database (Hendrickson and Cohen, 2018), for the creek and attempt to describe temporal change in the fauna of the creek. Minimal samples exist from the 1940’s and ’50s, but its fish fauna is rigorously sampled in the 1970’s when Edwards (1976) first formally surveyed the creek. It was uncollected in the 1980s. The Hendrickson lab, working with the public, local schools and universities, began sampling the creek in the 1990’s and continues to do so. These two sources (Edwards and Hendrickson Lab) are the main generators of data and we compared pre- and post-1980s data largely generated by these two sources. The fish fauna remains dominated by the same seven species Edwards collected in the 1970s (Gambusia affinis, Campostoma anomalum, Astyanax mexicanus, Lepomis megalotis, Lepomis cyanellus, Cyprinella lutrensis, and Herichthys cyanoguttatus), with the exception of an invasive species (Xiphophorus variatus), first detected in 2004, that is now the dominant species in the creek. Two of these seven species are firmly established non-natives (Astyanax mexicanus and Herichthys cyanoguttatus). Most of the less common native species collected in the 1970’s are no longer present (Ameiurus melas, Dionda flavipinnis, Fundulus zebrinus, Lepomis humilis, Lepomis macrochirus) or rare (Cyprinella venusta, Micropterus salmoides, Pimephales promelas) based on the data.Integrative BiologyWaller Creek Working Grou
Improving Receiver Performance of Diffusive Molecular Communication with Enzymes
This paper studies the mitigation of intersymbol interference in a diffusive
molecular communication system using enzymes that freely diffuse in the
propagation environment. The enzymes form reaction intermediates with
information molecules and then degrade them so that they cannot interfere with
future transmissions. A lower bound expression on the expected number of
molecules measured at the receiver is derived. A simple binary receiver
detection scheme is proposed where the number of observed molecules is sampled
at the time when the maximum number of molecules is expected. Insight is also
provided into the selection of an appropriate bit interval. The expected bit
error probability is derived as a function of the current and all previously
transmitted bits. Simulation results show the accuracy of the bit error
probability expression and the improvement in communication performance by
having active enzymes present.Comment: 13 pages, 8 figures, 1 table. To appear in IEEE Transactions on
Nanobioscience (submitted January 22, 2013; minor revision October 16, 2013;
accepted December 4, 2013
Using Dimensional Analysis to Assess Scalability and Accuracy in Molecular Communication
In this paper, we apply dimensional analysis to study a diffusive molecular
communication system that uses diffusing enzymes in the propagation environment
to mitigate intersymbol interference. The enzymes bind to information molecules
and then degrade them so that they cannot interfere with the detection of
future transmissions at the receiver. We determine when it is accurate to
assume that the concentration of information molecules throughout the receiver
is constant and equal to that expected at the center of the receiver. We show
that a lower bound on the expected number of molecules observed at the receiver
can be arbitrarily scaled over the environmental parameters, and generalize how
the accuracy of the lower bound is qualitatively impacted by those parameters.Comment: 6 pages, 2 figures, will be presented at the 3rd IEEE International
Workshop on Molecular and Nanoscale Communications (MoNaCom 2013) in
Budapest, Hungar
Optimal Receiver Design for Diffusive Molecular Communication With Flow and Additive Noise
In this paper, we perform receiver design for a diffusive molecular
communication environment. Our model includes flow in any direction, sources of
information molecules in addition to the transmitter, and enzymes in the
propagation environment to mitigate intersymbol interference. We characterize
the mutual information between receiver observations to show how often
independent observations can be made. We derive the maximum likelihood sequence
detector to provide a lower bound on the bit error probability. We propose the
family of weighted sum detectors for more practical implementation and derive
their expected bit error probability. Under certain conditions, the performance
of the optimal weighted sum detector is shown to be equivalent to a matched
filter. Receiver simulation results show the tradeoff in detector complexity
versus achievable bit error probability, and that a slow flow in any direction
can improve the performance of a weighted sum detector.Comment: 14 pages, 7 figures, 1 appendix. To appear in IEEE Transactions on
NanoBioscience (submitted July 31, 2013, revised June 18, 2014, accepted July
7, 2014
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