1,409 research outputs found
Positive Measure Spectrum for Schroedinger Operators with Periodic Magnetic Fields
We study Schroedinger operators with periodic magnetic field in Euclidean
2-space, in the case of irrational magnetic flux. Positive measure Cantor
spectrum is generically expected in the presence of an electric potential. We
show that, even without electric potential, the spectrum has positive measure
if the magnetic field is a perturbation of a constant one.Comment: 17 page
Phase Separation and Charge-Ordered Phases of the d = 3 Falicov-Kimball Model at T>0: Temperature-Density-Chemical Potential Global Phase Diagram from Renormalization-Group Theory
The global phase diagram of the spinless Falicov-Kimball model in d = 3
spatial dimensions is obtained by renormalization-group theory. This global
phase diagram exhibits five distinct phases. Four of these phases are
charge-ordered (CO) phases, in which the system forms two sublattices with
different electron densities. The CO phases occur at and near half filling of
the conduction electrons for the entire range of localized electron densities.
The phase boundaries are second order, except for the intermediate and large
interaction regimes, where a first-order phase boundary occurs in the central
region of the phase diagram, resulting in phase coexistence at and near half
filling of both localized and conduction electrons. These two-phase or
three-phase coexistence regions are between different charge-ordered phases,
between charge-ordered and disordered phases, and between dense and dilute
disordered phases. The second-order phase boundaries terminate on the
first-order phase transitions via critical endpoints and double critical
endpoints. The first-order phase boundary is delimited by critical points. The
cross-sections of the global phase diagram with respect to the chemical
potentials and densities of the localized and conduction electrons, at all
representative interactions strengths, hopping strengths, and temperatures, are
calculated and exhibit ten distinct topologies.Comment: Calculated density phase diagrams. Added discussions and references.
14 pages, 9 figures, 4 table
Neutrophils—From Bone Marrow to First-Line Defense of the Innate Immune System
Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue
Recovery from PTSD following Hurricane Katrina
Background: We examined patterns and correlates of speed of recovery of estimated posttraumatic stress disorder (PTSD) among people who developed PTSD in the wake of Hurricane Katrina. Method: A probability sample of prehurricane residents of areas affected by Hurricane Katrina was administered a telephone survey 7–19 months following the hurricane and again 24–27 months posthurricane. The baseline survey assessed PTSD using a validated screening scale and assessed a number of hypothesized predictors of PTSD recovery that included sociodemographics, prehurricane history of psychopathology, hurricane‐related stressors, social support, and social competence. Exposure to posthurricane stressors and course of estimated PTSD were assessed in a follow‐up interview. Results: An estimated 17.1% of respondents had a history of estimated hurricane‐related PTSD at baseline and 29.2% by the follow‐up survey. Of the respondents who developed estimated hurricane‐related PTSD, 39.0% recovered by the time of the follow‐up survey with a mean duration of 16.5 months. Predictors of slow recovery included exposure to a life‐threatening situation, hurricane‐related housing adversity, and high income. Other sociodemographics, history of psychopathology, social support, social competence, and posthurricane stressors were unrelated to recovery from estimated PTSD. Conclusions: The majority of adults who developed estimated PTSD after Hurricane Katrina did not recover within 18–27 months. Delayed onset was common. Findings document the importance of initial trauma exposure severity in predicting course of illness and suggest that pre‐ and posttrauma factors typically associated with course of estimated PTSD did not influence recovery following Hurricane Katrina. Depression and Anxiety, 2011. © 2011 Wiley‐Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87167/1/20790_ftp.pd
Paralytic Impact of Centrifugation on Human Neutrophils
Centrifugation is a common step in most of the popular protocols for the isolation of neutrophils
from whole blood. Inconsistent results from previous studies on neutrophils may originate
from an underestimation of the centrifugation effect, as in consequence impaired, not native cells,
being investigated. We hypothesize, that centrifugation significantly impairs major neutrophil functions.
However, there is no data yet whether the application of g-force itself or the product of g-force
and duration of centrifugation (=“g-time”) defines the impact on neutrophils. Neutrophils were
isolated from whole blood via centrifugation with different g-times and subsequently analyzed via
live cell imaging for migration, as well as via flow cytometry for oxidative burst and surface antigen
expression. Chemotactic migration was significantly reduced with increasing g-time. Oxidative burst
decreased likewise the higher the g-time applied. Expression of CD11b was no longer upregulated
in response to an n-formylmethionine-leucyl-phenylalanine (fMLP) stimulus in neutrophils having
experienced high g-time during the isolation process. We conclude that centrifugation “paralyzes”
neutrophils in the form of a significant decrease in functionality. Future investigations on neutrophil
granulocytes should reduce the g-time load as far as possible
Synchrotron Cooling in Energetic Gamma-Ray Bursts Observed by the Fermi Gamma-Ray Burst Monitor
We study the time-resolved spectra of eight GRBs observed by Fermi GBM in its
first five years of mission, with 1 keV - 1 MeV fluence
erg cm and signal-to-noise level above 900 keV. We
aim to constrain in detail the spectral properties of GRB prompt emission on a
time-resolved basis and to discuss the theoretical implications of the fitting
results in the context of various prompt emission models. We perform
time-resolved spectral analysis using a variable temporal binning technique
according to optimal S/N criteria, resulting in a total of 299 time-resolved
spectra. We fit the Band function to all spectra and obtain the distributions
for the low-energy power-law index , the high-energy power-law index
, the peak energy in the observed spectrum , and
the difference between the low- and high-energy power-law indices . Using the distributions of and , the
electron population index is found to be consistent with the "moderately
fast" scenario which fast- and slow-cooling scenarios cannot be distinguished.
We also apply a physically motivated synchrotron model, which is a triple
power-law with constrained power-law indices and a blackbody component, to test
for consistency with a synchrotron origin for the prompt emission and obtain
the distributions for the two break energies and ,
the middle segment power-law index , and the Planck function temperature
. A synchrotron model is found consistent with the majority of
time-resolved spectra for these eight energetic Fermi GBM bursts with good
high-energy photon statistics, as long as both the cooling and injection break
are included and the leftmost spectral slope is lifted either by inclusion of a
thermal component or when an evolving magnetic field is accounted for.Comment: 20 pages, 7 figures, 8 tables, accepted for publication in A&
Social learning across symbolic cultural barriers in non-human cultures
Social learning is key in the development of both human and non-human animal
societies. Here, we provide quantitative evidence that supports the existence
of social learning in sperm whales across socio-cultural barriers, based on
acoustic data from locations in the Pacific and Atlantic Oceans. Sperm whale
populations have traditionally been partitioned into clans based on their vocal
repertoire (what they say) of rhythmically patterned clicks (codas), and in
particular their identity codas, which serve as symbolic markers for each clan.
However, identity codas account for between 35% and 60% of all codas vocalized
depending on the different clans. We introduce a computational modeling
approach that recovers clan structure and shows new evidence of social learning
across clans from the internal temporal structure of non-identity codas, the
remaining fraction of codas. The proposed method is based on vocal style, which
encodes how sperm whales assemble individual clicks into codas. Specifically,
we modeled clicking pattern data using generative models based on variable
length Markov chains, producing what we term "subcoda trees". Based on our
results, we propose here a new concept of vocal identity, which consists of
both vocal repertoire and style. We show that (i) style-delimited clans are
similar to repertoire-delimited clans, and that (ii) sympatry increases vocal
style similarity between clans for non-identity codas, but has no significant
effect on identity codas. This implies that different clans who geographically
overlap have similar styles for most codas, which in turn implies social
learning across cultural boundaries. More broadly, the proposed method provides
a new framework for comparing communication systems of other animal species,
with potential implications for our understanding of cultural transmission in
animal societies
Luciferin production and luciferase transcription in the bioluminescent copepod Metridia lucens
Bioluminescent copepods are often the most abundant marine zooplankton and play critical roles in oceanic food webs. Metridia copepods exhibit particularly bright bioluminescence, and the molecular basis of their light production has just recently begun to be explored. Here we add to this body of work by transcriptomically profiling Metridia lucens, a common species found in temperate, northern, and southern latitudes. In this previously molecularly-uncharacterized species, we find the typical luciferase paralog gene set found in Metridia. More surprisingly, we recover noteworthy putative luciferase sequences that had not been described from Metridia species, indicating that bioluminescence produced by these copepods may be more complex than previously known. This includes another copepod luciferase, as well as one from a shrimp. Furthermore, feeding experiments using mass spectrometry and 13C labelled L-tyrosine and L-phenylalanine firmly establish that M. lucens produces its own coelenterazine luciferin rather than acquiring it through diet. This coelenterazine synthesis has only been directly confirmed in one other copepod species
Continuum description of profile scaling in nanostructure decay
The relaxation of axisymmetric crystal surfaces with a single facet below the
roughening transition is studied via a continuum approach that accounts for
step energy g_1 and step-step interaction energy g_3>0. For diffusion-limited
kinetics, free-boundary and boundary-layer theories are used for self-similar
shapes close to the growing facet. For long times and g_3/g_1 < 1, (a) a
universal equation is derived for the shape profile, (b) the layer thickness
varies as (g_3/g_1)^{1/3}, (c) distinct solutions are found for different
g_3/_1, and (d) for conical shapes, the profile peak scales as
(g_3/g_1)^{-1/6}. These results compare favorably with kinetic simulations.Comment: 4 pages including 3 figure
- …