1,419 research outputs found
Topographically Distinct Epidermal Nociceptive Circuits Revealed by Axonal Tracers Targeted to Mrgprd
The brain receives sensory input from diverse peripheral tissues, including the skin, the body's largest sensory organ. Using genetically encoded axonal tracers expressed from the Mrgprd locus, we identify a subpopulation of nonpeptidergic, nociceptive neurons that project exclusively to the skin, and to no other peripheral tissue examined. Surprisingly, Mrgprd+ innervation is restricted to the epidermis and absent from specialized sensory structures. Furthermore, Mrgprd+ fibers terminate in a specific layer of the epidermis, the stratum granulosum. This termination zone is distinct from that innervated by most CGRP+ neurons, revealing that peptidergic and nonpeptidergic epidermal innervation is spatially segregated. The central projections deriving from these distinct epidermal innervation zones terminate in adjacent laminae in the dorsal spinal cord. Thus, afferent input from different layers of the epidermis is conveyed by topographically segregated sensory circuits, suggesting that at least some aspects of sensory information processing may be organized along labeled lines
On the Role of Global Warming on the Statistics of Record-Breaking Temperatures
We theoretically study long-term trends in the statistics of record-breaking
daily temperatures and validate these predictions using Monte Carlo simulations
and data from the city of Philadelphia, for which 126 years of daily
temperature data is available. Using extreme statistics, we derive the number
and the magnitude of record temperature events, based on the observed Gaussian
daily temperatures distribution in Philadelphia, as a function of the number of
elapsed years from the start of the data. We further consider the case of
global warming, where the mean temperature systematically increases with time.
We argue that the current warming rate is insufficient to measurably influence
the frequency of record temperature events over the time range of the
observations, a conclusion that is supported by numerical simulations and the
Philadelphia temperature data.Comment: 11 pages, 6 figures, 2-column revtex4 format. For submission to
Journal of Climate. Revised version has some new results and some errors
corrected. Reformatted for Journal of Climate. Second revision has an added
reference. In the third revision one sentence that explains the simulations
is reworded for clarity. New revision 10/3/06 has considerable additions and
new results. Revision on 11/8/06 contains a number of minor corrections and
is the version that will appear in Phys. Rev.
Brief Note: Ohio Lamprey, Ichthyomyzon bdellium (Petromyzonidae), in Ohio: A Review and Recent Records
Author Institution: Ohio Department of Natural Resources, Division of Natural Areas and Preserves, and Department of Life Science, Otterbein CollegePrior to 1983 only isolated specimens of Ohio lamprey {Ichthyomyzon bdellium) were collected at a few sites in the Ohio River drainage of Ohio, where it is listed as an endangered species. Seining surveys of the Little Muskingum River in 1983 and 1992 discovered a concentration of unattached adults in a riffle in May, as well as a recently metamorphosed subadult and an ammocoete, indicating that the species probably spawns there. Other Ohio River tributaries may support spawning populations as well
Crystallization of random trigonometric polynomials
We give a precise measure of the rate at which repeated differentiation of a
random trigonometric polynomial causes the roots of the function to approach
equal spacing. This can be viewed as a toy model of crystallization in one
dimension. In particular we determine the asymptotics of the distribution of
the roots around the crystalline configuration and find that the distribution
is not Gaussian.Comment: 10 pages, 3 figure
Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
We combine 131 new medium-resolution (R~2000) J-band spectra of M, L, and T
dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97
previously published BDSS spectra to study surface-gravity-sensitive indices
for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9.
Specifically, we use an established set of spectral indices to determine
surface gravity classifications for all M6-L7 objects in our sample by
measuring equivalent widths (EW) of the K I lines at 1.1692, 1.1778, 1.2529 um,
and the 1.2 um FeHJ absorption index. Our results are consistent with previous
surface gravity measurements, showing a distinct double peak - at ~L5 and T5 -
in K I EW as a function of spectral type. We analyze K I EWs of 73 objects of
known ages and find a linear trend between log(Age) and EW. From this
relationship, we assign age ranges to the very low gravity, intermediate
gravity, and field gravity designations for spectral types M6-L0.
Interestingly, the ages probed by these designations remain broad, change with
spectral type, and depend on the gravity sensitive index used. Gravity
designations are useful indicators of the possibility of youth, but current
datasets cannot be used to provide a precise age estimate.Comment: 33 pages, 13 figures, ApJ in pres
The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
We present a sequence of high resolution (R~20,000 or 15 km/s) infrared
spectra of stars and brown dwarfs spanning spectral types M2.5 to T6.
Observations of 16 objects were obtained using eight echelle orders to cover
part of the J-band from 1.165-1.323 micron with NIRSPEC on the Keck II
telescope. By comparing opacity plots and line lists, over 200 weak features in
the J-band are identified with either FeH or H2O transitions. Absorption by FeH
attains maximum strength in the mid-L dwarfs, while H2O absorption becomes
systematically stronger towards later spectral types. Narrow resolved features
broaden markedly after the M to L transition. Our high resolution spectra also
reveal that the disappearance of neutral Al lines at the boundary between M and
L dwarfs is remarkably abrupt, presumably because of the formation of grains.
Neutral Fe lines can be traced to mid-L dwarfs before Fe is removed by
condensation. The neutral potassium (K I) doublets that dominate the J-band
have pressure broadened wings that continue to broaden from ~50 km/s (FWHM) at
mid-M to ~500 km/s at mid-T. In contrast however, the measured
pseudo-equivalent widths of these same lines reach a maximum in the mid-L
dwarfs. The young L2 dwarf, G196-3B, exhibits narrow potassium lines without
extensive pressure-broadened wings, indicative of a lower gravity atmosphere.
Kelu-1AB, another L2, has exceptionally broad infrared lines, including FeH and
H2O features, confirming its status as a rapid rotator. In contrast to other
late T objects, the peculiar T6 dwarf 2MASS 0937+29 displays a complete absence
of potassium even at high resolution, which may be a metallicity effect or a
result of a cooler, higher-gravity atmosphere.Comment: 53 pages, 21 figures, data will be available at
http://www.astro.ucla.edu/~mclean/BDSSarchive
Outcomes of Sphincter of Oddi Manometry When Performed in Low Volumes
Background. Sphincter of Oddi manometry is a highly specialized procedure associated with an increased risk of procedural complications. Published studies have typically been performed in large volume manometry centers. Objective. To examine the outcomes and complication rate of SOM when performed in small volumes. Design. Retrospective analysis at a tertiary care referral hospital that infrequently performs Sphincter of Oddi manometry. Patient records were reviewed for procedural details, patient outcomes, and complications after sphincter of Oddi manometry. Results. 36 patients, 23 (23 type II sphincter of Oddi dysfunction (SOD), 13 type III SOD) underwent sphincter of Oddi manometry and were followed up for mean of 16 months. Nine Type II patients (90%) with elevated basal sphincter pressures noted symptom improvement after sphincterotomy compared with only 3 patients (43%) of the patients with normal basal pressures. In type III SOD, 7 patients had elevated basal SO pressure and underwent sphincterotomy. Three patients (43%) improved. There were six
(16%) procedure-related complications. There were four cases
of post ERCP pancreatitis (11%), all of which were mild.
Conclusion. In low numbers, sphincter of Oddi
manometry can be performed successfully and safely by experienced
biliary endoscopists with results that are comparable to large
volume centers
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Pervasive Genetic Hitchhiking and Clonal Interference in 40 Evolving Yeast Populations
The dynamics of adaptation determines which mutations fix in a population, and hence how reproducible evolution will be. This is central to understanding the spectra of mutations recovered in evolution of antibiotic resistance1, the response of pathogens to immune selection2,3, and the dynamics of cancer progression4,5. In laboratory evolution experiments, demonstrably beneficial mutations are found repeatedly6–8, but are often accompanied by other mutations with no obvious benefit. Here we use whole-genome whole-population sequencing to examine the dynamics of genome sequence evolution at high temporal resolution in 40 replicate Saccharomyces cerevisiae populations growing in rich medium for 1,000 generations. We find pervasive genetic hitchhiking: multiple mutations arise and move synchronously through the population as mutational “cohorts.” Multiple clonal cohorts are often present simultaneously, competing with each other in the same population. Our results show that patterns of sequence evolution are driven by a balance between these chance effects of hitchhiking and interference, which increase stochastic variation in evolutionary outcomes, and the deterministic action of selection on individual mutations, which favors parallel evolutionary solutions in replicate populations
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