231 research outputs found
Fermi edge singularity in neutral electron-hole system
In neutral dense electron-hole (e-h) systems at low temperatures, theory
predicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton
condensation. Optical excitation allows creating e-h systems with the densities
controlled by the excitation power. However, the intense optical excitations
required to achieve high densities cause substantial heating of the e-h system
that prevents the realization of dense and cold e-h systems in conventional
semiconductors. In this work, we study e-h systems created by optical
excitation in separated electron and hole layers. The layer separation
increases the e-h recombination time and, in turn, the density for a given
optical excitation by orders of magnitude and, as a result, enables the
realization of the dense and cold e-h system. We found a strong enhancement of
photoluminescence intensity at the Fermi energy of the neutral dense ultracold
e-h system that evidences the emergence of excitonic Fermi edge singularity due
to the Cooper-pair-like excitons at the Fermi energy
Enhanced light intensity increases flavonol and anthocyanin concentrations but reduces flavone levels in the cotyledons of common buckwheat seedlings
The effects of two light intensities on the concentration of several flavonoids were investigated in the cotyledons of common buckwheat seedlings. The study was performed on four days old seedlings of cvs. Hruszowska, Panda, Kora and Red Corolla. One group of seedlings was grown under exposure to 180 ± 20 μmol · m−2 · s−1 photosynthetically active radiation, whereas the other group was exposed to 360 ± 20 μmol · m−2 · s−1. The experiment lasted 5 days. The results revealed that light intensity induces changes in the levels of flavonols and flavones. Increased light intensity contributed to a decrease in the concentrations of all flavone C-glucosides: orientin (luteolin-8-C-glucoside) and iso-orientin (luteolin-6-C-glucoside), and apigenin: vitexin (apigenin-8-C-glucoside) and iso-vitexin (apigenin-6-C-glucoside). Simultaneously, a substantial increase in the content of flavonols, i.e. quercetin O-glycosides, was found. To the best of our knowledge, this is the first evidence to demonstrate the contrary responses of plant flavonols and flavones to light intensity. The content of anthocyanin also increased under exposure to higher light intensity. Our results indicate that quercetin O-glycosides can play a similar role to anthocyanins in the cotyledons of common buckwheat seedlings. Results of correlation analysis indicate that the increase in flavonol and anthocyanin concentrations in response to higher light intensity is maintained through reduced accumulation of flavones and proanthocyanidins
Hyperon Polarization in the Constituent Quark Model
We consider mechanism for hyperon polarization in inclusive production. The
main role belongs to the orbital angular momentum and polarization of the
strange quark-antiquark pairs in the internal structure of the constituent
quarks. We consider a nucleon as a core consisting of the constituent quarks
embedded into quark condensate. The nonperturbative hadron structure is based
on the results of chiral quark models.Comment: 14 pages, LaTeX, 2 Figures, References adde
Effect of the 5-HTTLPR polymorphism on affective temperament, depression and body mass index in obesity
Background and aim: Many studies show high prevalence of affective disorders in obese patients.
Affective temperament is a subclinical manifestation of such conditions. The 5-HTT gene encoding the
serotonin transporter may be involved in both mood and eating dysregulation. The aim of this study was
to investigate the influence of a polymorphism in the 5-HTT gene on affective temperament types,
depressive symptoms and Body Mass Index (BMI) in obese patients.
Methods: This study involved 390 patients (237 females, and 153 males) with obesity. The TEMPS-A
questionnaire, Beck Depression Inventory (BDI) and Hamilton Depression Rating Scale (HDRS) were used
to evaluate affective temperaments and prevalence of depression. DNA was obtained for serotonin
transporter gene-linked polymorphism (5-HTTLPR) genotyping.
Results: In obese patients S/S genotype was associated with depressive and L/L with cyclothymic temperament.
Subjects with L/L genotype presented significantly higher BMI and greater intensity of
depressive symptoms in BDI and HDRS. Females scored higher in anxious and depressive, while males in
hyperthymic, cyclothymic and irritable temperaments. Females scored higher in BDI (subjective
depression) while males in HDRS (objective depression).
Limitations: TEMPS-A, BDI and HDRS are frequently used in studies on affective disorders. However,
these methods do not examine all dimensions of mood and personality.
Conclusions: In obese patients S allele of 5-HTTLPR was associated with development of depressive
temperament while L allele corresponded with greater obesity and prevalence of depression. Different
mechanisms may be involved in manifestation of depression in males and females with obesity
Information transmission in oscillatory neural activity
Periodic neural activity not locked to the stimulus or to motor responses is
usually ignored. Here, we present new tools for modeling and quantifying the
information transmission based on periodic neural activity that occurs with
quasi-random phase relative to the stimulus. We propose a model to reproduce
characteristic features of oscillatory spike trains, such as histograms of
inter-spike intervals and phase locking of spikes to an oscillatory influence.
The proposed model is based on an inhomogeneous Gamma process governed by a
density function that is a product of the usual stimulus-dependent rate and a
quasi-periodic function. Further, we present an analysis method generalizing
the direct method (Rieke et al, 1999; Brenner et al, 2000) to assess the
information content in such data. We demonstrate these tools on recordings from
relay cells in the lateral geniculate nucleus of the cat.Comment: 18 pages, 8 figures, to appear in Biological Cybernetic
Electrophysiological characterization of texture information slip-resistance dependent in the rat vibrissal nerve
<p>Abstract</p> <p>Background</p> <p>Studies in tactile discrimination agree that rats are able to learn a rough-smooth discrimination task by actively touching (whisking) objects with their vibrissae. In particular, we focus on recent evidence of how neurons at different levels of the sensory pathway carry information about tactile stimuli. Here, we analyzed the multifiber afferent discharge of one vibrissal nerve during active whisking. Vibrissae movements were induced by electrical stimulation of motor branches of the facial nerve. We used sandpapers of different grain size as roughness discrimination surfaces and we also consider the change of vibrissal slip-resistance as a way to improve tactile information acquisition. The amplitude of afferent activity was analyzed according to its Root Mean Square value (RMS). The comparisons among experimental situation were quantified by using the information theory.</p> <p>Results</p> <p>We found that the change of the vibrissal slip-resistance is a way to improve the roughness discrimination of surfaces. As roughness increased, the RMS values also increased in almost all cases. In addition, we observed a better discrimination performance in the retraction phase (maximum amount of information).</p> <p>Conclusions</p> <p>The evidence of amplitude changes due to roughness surfaces and slip-resistance levels allows to speculate that texture information is slip-resistance dependent at peripheral level.</p
Spin alignment measurements of the and vector mesons at RHIC
We present the first spin alignment measurements for the and
vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
= 0.32 0.04 (stat) 0.09 (syst) for the
( GeV/c) and = 0.34 0.02 (stat) 0.03
(syst) for the ( GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for and in Au+Au collisions were also measured
with respect to the particle's production plane. The result,
= 0.41 0.02 (stat) 0.04 (syst), is consistent with that in p+p
collisions, = 0.39 0.03 (stat) 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo
corrected, published in PRC.77.06190
Exploring a Controls-Based Assessment of Infrastructure Vulnerability
Assessing the vulnerability of an enterprise's infrastructure is an important step in judging the security of its network and the trustworthiness and quality of the information that flows through it. Currently, low-level infrastructure vulnerability is often judged in an ad hoc manner, based on the criteria and experience of the assessors. While methodological approaches to assessing an organisation's vulnerability exist, they are often targeted at higher-level threats, and can fail to accurately represent risk. Our aim in this paper therefore, is to explore a novel, structured approach to assessing low-level infrastructure vulnerability. We do this by placing the emphasis on a controls-based evaluation over a vulnerability-based evaluation. This work aims to investigate a framework for the pragmatic approach that organisations currently use for assessing low-level vulnerability. Instead of attempting to find vulnerabilities in infrastructure, we instead assume the network is insecure, and measure its vulnerability based on the controls that have (and have not) been put in place. We consider different control schemes for addressing vulnerability, and show how one of them, namely the Council on Cyber Security's Top 20 Critical Security Controls, can be applied
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