15,446 research outputs found
Cosmic Microwave Background Statistics for a Direction-Dependent Primordial Power Spectrum
Statistical isotropy of primordial perturbations is a common assumption in
cosmology, but it is an assumption that should be tested. To this end, we
develop cosmic microwave background statistics for a primordial power spectrum
that depends on the direction, as well as the magnitude, of the Fourier
wavevector. We first consider a simple estimator that searches in a
model-independent way for anisotropy in the square of the temperature (and/or
polarization) fluctuation. We then construct the minimum-variance estimators
for the coefficients of a spherical-harmonic expansion of the
direction-dependence of the primordial power spectrum. To illustrate, we apply
these statistics to an inflation model with a quadrupole dependence of the
primordial power spectrum on direction and find that a power quadrupole as
small as 2.0% can be detected with the Planck satellite.Comment: Published in Phys. Rev. D; 8 pages; 1 table; Table 1 corrected;
references adde
Multi-photon effects in energy losses spectra
Effect of radiation of many photons by a single electron traversing a target
is discussed. When the summary energy of emitted photons (the energy losses
spectrum) is measured only, the photon spectrum is distorted comparing with the
photon spectrum in one interaction. Influence of this effect is discussed for
the cases (1) bremsstrahlung (described by Bethe-Heitler formula), (2) the
strong Landau-Pomeranchuk-Migdal effect and (3) transition radiation.
Qualitative picture of the phenomenon is discussed in detail. Comparison with
the recent SLAC experiment in relatively thick target (2.7% of the radiation
length), where the effect of emission of many photons by a projectile is very
essential, shows perfect agreement of the theory and data.Comment: LaTeX2.09, 19 pages, 5 PostScript figure
Knowledge-Driven Contrast Gain Control is Characterized by Two Distinct Electrocortical Markers
Sensitivity to variations in luminance (contrast) is fundamental to perception because contrasts define the edges and textures of visual objects. Recent research has shown that contrast sensitivity, in addition to being controlled by purely stimulus-driven mechanisms, is also affected by expectations and prior knowledge about the contrast of upcoming stimuli. The ability to adjust contrast sensitivity based on expectations and prior knowledge could help to maximize the information extracted when scanning familiar visual scenes. In the present study we used the event-related potentials (ERP) technique to resolve the stages that mediate knowledge-driven aspects of contrast gain control. Using groupwise independent components analysis and multivariate partial least squares, we isolated two robust spatiotemporal patterns of electrical brain activity associated with preparation for upcoming targets whose contrast was predicted by a cue. The patterns were sensitive to the informative value of the cue. When the cues were informative, these patterns were also able to differentiate among cues that predicted low-contrast targets and cues that predicted high-contrast targets. Both patterns were localized to parts of occipitotemporal cortex, and their morphology, latency, and topography resembled P2/N2 and P3 potentials. These two patterns provide electrophysiological markers of knowledge-driven preparation for impending changes in contrast and shed new light on the manner in which top-down factors modulate sensory processing
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Changes in the intestinal microbiota after a short period of dietary over-indulgence, representative of a holiday or festival season
The effects on the intestinal microbiota of a short period of marginal over-eating, characteristic of holiday or
festival periods, were investigated in a pilot study. Fourteen healthy male subjects consumed a diet rich in
animal protein and fat for seven days. During this period, the subjects significantly increased their dietary
energy, protein, carbohydrate and fat intakes by 56, 59, 53 and 58%, respectively (all P < 0.05). The mean
weight gain of 0.27 kg was less than the expected 1 kg, but this was consistent with a degree of under-reporting
on the baseline diet. Fluorescence in situ hybridisation analysis confirmed the relative stability of each
individual’s faecal microbiota but showed considerable variations between them. The diet was associated with
a significant increase in numbers of total faecal bacteria and the bacteroides group, as detected by the universal
bacterial probe (DAPI) and Bacteroides probe (Bac 303), respectively. Overall, there was a decrease in
numbers of the Lactobacillus/Enterococcus group (Lab 158 probe; 2.8 ± 3.0% to 1.8 ± 1.8%) and the Bifidobacterium
group (Bif 164 probe; 3.0 ± 3.7% to 1.7 ± 1.2%), although there was considerable inter-individual
variation. Analysis of the relative proportions of each bacterial group as a percentage of the subject’s total
bacteria showed a trend for a change in the intestinal microbiota that might be considered potentially
unhealthy
The origin and evolution of lactation
The presence of mammary glands is the defining morphological feature of mammals. The recent assembly of the bovine genome and a report in Genome Biology that links the milk and lactation data of bovine and other mammalian genomes will help biologists investigate this economically and medically important feature
Dissipative dynamics of superfluid vortices at non-zero temperatures
We consider the evolution and dissipation of vortex rings in a condensate at
non-zero temperature, in the context of the classical field approximation,
based on the defocusing nonlinear Schr\"odinger equation. The temperature in
such a system is fully determined by the total number density and the number
density of the condensate. A vortex ring is introduced into a condensate in a
state of thermal equilibrium, and interacts with non-condensed particles. These
interactions lead to a gradual decrease in the vortex line density, until the
vortex ring completely disappears. We show that the square of the vortex line
length changes linearly with time, and obtain the corresponding universal decay
law. We relate this to mutual friction coefficients in the fundamental equation
of vortex motion in superfluids.Comment: 4 pages, 3 figure
Collapse of the charge ordering gap of Nd_{0.5}Sr_{0.5}MnO_{3} in an applied magnetic field
We report results of tunneling studies on the charge ordering compound
Nd_{0.5}Sr_{0.5}MnO_{3} in a magnetic field up to 6T and for temperature down
to 25K.We show that a gap (2\Delta_{CO} \approx 0.5eV opens up in the density
of state (DOS) at the Fermilevel (E_F) on charge ordering (T_{CO}=150K) which
collapses in an applied magnetic field when the charge ordered state melts.
There is a clear correspondence between the behavior of the resistivity and the
gap formation and its collapse in an applied magnetic field. We conclude that a
gap in the DOS at E_F is necessary for the stability of the charge ordered
state.Comment: 4 pages REVTeX, 5 postscript figures included, submitted to Phys.
Rev. Let
Exercise Beliefs and Behaviours of Individuals with Joint Hypermobility Syndrome/ Ehlers Danlos Syndrome-Hypermobility Type
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Disability & Rehabilitation on 10 November 2017, available online at: https://doi.org/10.1080/09638288.2017.1398278. © 2017 Informa UK Limited, trading as Taylor & Francis GroupPurpose: To explore exercise beliefs and behaviours of individuals with Joint Hypermobility syndrome/Ehlers–Danlos syndrome – hypermobility type and to explore patient experiences of physiotherapy.Methods: A cross sectional questionnaire survey design was used to collect quantitative and qualitative data from adult members of the Hypermobility Syndromes Association and Ehlers–Danlos Syndrome Support UK. Descriptive and inferential statistics were used to analyse the data. Qualitative data was analysed thematically.Results: 946 questionnaires were returned and analysed. Participants who received exercise advice from a physiotherapist were 1.75 more likely to report high volumes of weekly exercise (odds ratio [OR] = 1.75, 95% confidence interval [CI] = 1.30–2.36, p < 0.001) than those with no advice. Participants who believed that exercise is important for long-term management were 2.76 times more likely to report a high volume of weekly exercise compared to the participants who did not hold this belief (OR = 2.76, 95% CI = 1.38–5.50, p = 0.004). Three themes emerged regarding experience of physiotherapy; physiotherapist as a partner, communication – knowledge, experience and safety.Conclusion: Pain, fatigue and fear are common barriers to exercise. Advice from a physiotherapist and beliefs about the benefits of exercise influenced the reported exercise behaviours of individuals with Ehlers–Danlos syndrome – hypermobility type in this survey.Peer reviewe
Corneoscleral laceration and ocular burns caused by electronic cigarette explosions
PURPOSE: To report cases of acute globe rupture and bilateral corneal burns from electronic cigarette (EC) explosions. METHODS: Case series. RESULTS: We describe a series of patients with corneal injury caused by EC explosions. Both patients suffered bilateral corneal burns and decreased visual acuity, and one patient sustained a unilateral corneoscleral laceration with prolapsed iris tissue and hyphema. A review of the scientific literature revealed no prior reported cases of ocular injury secondary to EC explosions; however, multiple media and government agency articles describe fires and explosions involving ECs, including at least 4 with ocular injuries. CONCLUSIONS: Given these cases and the number of recent media reports, ECs pose a significant public health risk. Users should be warned regarding the possibility of severe injury, including sight-threatening ocular injuries ranging from corneal burns to full-thickness corneoscleral laceration
The Landau-Pomeranchuk-Migdal effect and transition radiation in structured targets
The radiation from high-energy electrons is investigated for the case when a
target consists of several separated plates. The spectrum of radiation is
considered in the region in which the bremsstrahlung is under influence of the
multiple scattering of a projectile (the LPM effect), the polarization of a
medium and the hard part of the boundary radiation contribute. In this region
the general expression for the radiation spectrum is obtained for the -plate
target. A qualitative description of the arising interference pattern is given.Comment: LaTeX2.09, 22 pages, 3 PostScript figure
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