1,081 research outputs found
Phase Transitions of Charged Scalars at Finite Temperature and Chemical Potential
We calculate the grand canonical partition function at the one-loop level for
scalar quantum electrodynamics at finite temperature and chemical potential. A
classical background charge density with a charge opposite that of the scalars
ensures the neutrality of the system. For low density systems we find evidence
of a first order phase transition. We find upper and lower bounds on the
transition temperature below which the charged scalars form a condensate. A
first order phase transition may have consequences for helium-core white dwarf
stars in which it has been argued that such a condensate of charged helium-4
nuclei could exist.Comment: 20 pages, 3 figures. Version accepted for publication in JHE
On an Analytical Framework for Voids: Their abundances, density profiles and local mass functions
We present a general analytical procedure for computing the number density of
voids with radius above a given value within the context of gravitational
formation of the large scale structure of the universe out of Gaussian initial
conditions. To this end we develop an accurate (under generally satisfied
conditions) extension of unconditional mass function to constrained
environments, which allowes us both to obtain the number density of collapsed
objects of certain mass at any distance from the center of the void, and to
derive the number density of voids defined by those collapsed objects. We have
made detailed calculations for the spherically averaged mass density and halo
number density profiles for individual voids. We also present a formal
expression for the number density of voids defined by galaxies of a given type
and luminosity. This expression contains the probability for a collapsed object
of certain mass to host a galaxy of that type and luminosity as a function of
the environmental density. We propose a procedure to infer this function, which
may provide useful clues as to the galaxy formation process, from the observed
void densities.Comment: 14 pages, 7 figures, MNRAS in pres
A hierarchy of voids: Much ado about nothing
We present a model for the distribution of void sizes and its evolution in
the context of hierarchical scenarios of gravitational structure formation. We
find that at any cosmic epoch the voids have a size distribution which is
well-peaked about a characteristic void size which evolves self-similarly in
time. This is in distinct contrast to the distribution of virialized halo
masses which does not have a small-scale cut-off.
In our model, the fate of voids is ruled by two processes. The first process
affects those voids which are embedded in larger underdense regions: the
evolution is effectively one in which a larger void is made up by the mergers
of smaller voids, and is analogous to how massive clusters form from the
mergers of less massive progenitors. The second process is unique to voids, and
occurs to voids which happen to be embedded within a larger scale overdensity:
these voids get squeezed out of existence as the overdensity collapses around
them. It is this second process which produces the cut-off at small scales.
In the excursion set formulation of cluster abundance and evolution, solution
of the cloud-in-cloud problem, i.e., counting as clusters only those objects
which are not embedded in larger clusters, requires study of random walks
crossing one barrier. We show that a similar formulation of void evolution
requires study of a two-barrier problem: one barrier is required to account for
voids-in-voids, and the other for voids-in-clouds. Thus, in our model, the void
size distribution is a function of two parameters, one of which reflects the
dynamics of void formation, and the other the formation of collapsed objects.Comment: 23 pages, 9 figures, submitted to MNRA
Formation of voids in the Universe within the Lemaitre-Tolman model
We develop models of void formation starting from a small initial fluctuation
at recombination and growing to a realistic present day density profile in
agreement with observations of voids. The model construction is an extension of
previously developed algorithms for finding a Lemaitre-Tolman metric that
evolves between two profiles of either density or velocity specified at two
times. Of the 4 profiles of concern -- those of density and velocity at
recombination and at the present day -- two can be specified and the other two
follow from the derived model. We find that, in order to reproduce the
present-day void density profiles, the initial velocity profile is more
important than the initial density profile. Extrapolation of current CMB
observations to the scales relevant to proto-voids is very uncertain. Even so,
we find that it is very difficult to make both the initial density and velocity
fluctuation amplitudes small enough, and still obtain a realistic void by
today.Comment: MN2e LaTeX style file, 17 pages, 16 figures, 22 figure files;
replecement has minor changes in reference
Photometric Properties of Void Galaxies in the Sloan Digital Sky Survey DR7 Data Release
Using the sample presented in Pan:2011, we analyse the photometric properties
of 88,794 void galaxies and compare them to galaxies in higher density
environments with the same absolute magnitude distribution. In Pan et al.
(2011), we found a total of 1054 dynamically distinct voids in the SDSS with
radius larger than 10h^-1 Mpc. The voids are underdense, with delta rho/rho <
-0.9 in their centers. Here we study the photometric properties of these void
galaxies. We look at the u - r colours as an indication of star formation
activity and the inverse concentration index as an indication of galaxy type.
We find that void galaxies are statistically bluer than galaxies found in
higher density environments with the same magnitude distribution. We examine
the colours of the galaxies as a function of magnitude, and we fit each colour
distribution with a double-Gaussian model for the red and blue subpopulations.
As we move from bright to dwarf galaxies, the population of red galaxies
steadily decreases and the fraction of blue galaxies increases in both voids
and walls, however the fraction of blue galaxies in the voids is always higher
and bluer than in the walls. We also split the void and wall galaxies into
samples depending on galaxy type. We find that late type void galaxies are
bluer than late type wall galaxies and the same holds for early galaxies. We
also find that early type, dwarf void galaxies are blue in colour. We also
study the properties of void galaxies as a function of their distance from the
center of the void. We find very little variation in the properties, such as
magnitude, colour and type, of void galaxies as a function of their location in
the void. The only exception is that the dwarf void galaxies may live closer to
the center. The centers of voids have very similar density contrast and hence
all void galaxies live in very similar density environments (ABRIDGED)Comment: 10 pages, 25 figure
Skyrmion Multi-Walls
Skyrmion walls are topologically-nontrivial solutions of the Skyrme system
which are periodic in two spatial directions. We report numerical
investigations which show that solutions representing parallel multi-walls
exist. The most stable configuration is that of the square -wall, which in
the limit becomes the cubically-symmetric Skyrme crystal. There is
also a solution resembling parallel hexagonal walls, but this is less stable.Comment: 7 pages, 1 figur
The Luminosity, Colour and Morphology dependence of galaxy filaments in the Sloan Digital Sky Survey Data Release Four
We have tested for luminosity, colour and morphology dependence of the degree
of filamentarity in seven nearly two dimensional strips from the Sloan Digital
Sky Survey Data Release Four (SDSS DR4). The analysis is carried out at various
levels of coarse graining allowing us to address different length-scales. We
find that the brighter galaxies have a less filamentary distribution than the
fainter ones at all levels of coarse graining. The distribution of red galaxies
and ellipticals shows a higher degree of filamentarity compared to blue
galaxies and spirals respectively at low levels of coarse graining. The
behaviour is reversed at higher levels of coarse graining. We propose a picture
where the ellipticals are densely distributed in the vicinity of the nodes
where the filaments intersect while the spirals are sparsely distributed along
the entire extent of the filaments. Our findings indicate that the regions with
an excess of ellipticals are larger than galaxy clusters, protruding into the
filaments. We have also compared the predictions of a semi-analytic model of
galaxy formation (the Millennium Run galaxy catalogue) against our results for
the SDSS. We find the two to be in agreement for the galaxies and for
the red galaxies, while the model fails to correctly predict the filamentarity
of the brighter galaxies and the blue galaxies.Comment: 14 Pages, 2 tables, 11 figures, Accepted for publication in MNRAS,
new section added for a comparison with semi analytical models of galaxy
formation, substantial revisio
Early and efficient detection of Mycobacterium tuberculosis in sputum by microscopic observation of broth cultures.
Early, efficient and inexpensive methods for the detection of pulmonary tuberculosis are urgently needed for effective patient management as well as to interrupt transmission. These methods to detect M. tuberculosis in a timely and affordable way are not yet widely available in resource-limited settings. In a developing-country setting, we prospectively evaluated two methods for culturing and detecting M. tuberculosis in sputum. Sputum samples were cultured in liquid assay (micro broth culture) in microplate wells and growth was detected by microscopic observation, or in Löwenstein-Jensen (LJ) solid media where growth was detected by visual inspection for colonies. Sputum samples were collected from 321 tuberculosis (TB) suspects attending Bugando Medical Centre, in Mwanza, Tanzania, and were cultured in parallel. Pulmonary tuberculosis cases were diagnosed using the American Thoracic Society diagnostic standards. There were a total of 200 (62.3%) pulmonary tuberculosis cases. Liquid assay with microscopic detection detected a significantly higher proportion of cases than LJ solid culture: 89.0% (95% confidence interval [CI], 84.7% to 93.3%) versus 77.0% (95% CI, 71.2% to 82.8%) (p = 0.0007). The median turn around time to diagnose tuberculosis was significantly shorter for micro broth culture than for the LJ solid culture, 9 days (interquartile range [IQR] 7-13), versus 21 days (IQR 14-28) (p<0.0001). The cost for micro broth culture (labor inclusive) in our study was US 11.35 per sample for the LJ solid culture. The liquid assay (micro broth culture) is an early, feasible, and inexpensive method for detection of pulmonary tuberculosis in resource limited settings
The Feasibility and Impact of Delivering a Mind-Body Intervention in a Virtual World
Introduction: Mind-body medical approaches may ameliorate chronic disease. Stress reduction is particularly helpful, but face-to-face delivery systems cannot reach all those who might benefit. An online, 3-dimensional virtual world may be able to support the rich interpersonal interactions required of this approach. In this pilot study, we explore the feasibility of translating a face-to-face stress reduction program into an online virtual setting and estimate the effect size of the intervention. Methods and Findings: Domain experts in virtual world technology joined with mind body practitioners to translate an existing 8 week relaxation response-based resiliency program into an 8-week virtual world-based program in Second Lifeâ„¢ (SL). Twenty-four healthy volunteers with at least one month's experience in SL completed the program. Each subject filled out the Perceived Stress Scale (PSS) and the Symptom Checklist 90- Revised (SCL-90-R) before and after taking part. Participants took part in one of 3 groups of about 10 subjects. The participants found the program to be helpful and enjoyable. Many reported that the virtual environment was an excellent substitute for the preferred face-to-face approach. On quantitative measures, there was a general trend toward decreased perceived stress, (15.7 to 15.0), symptoms of depression, (57.6 to 57.0) and anxiety (56.8 to 54.8). There was a significant decrease of 2.8 points on the SCL-90-R Global Severity Index (p<0.05). Conclusions: This pilot project showed that it is feasible to deliver a typical mind-body medical intervention through a virtual environment and that it is well received. Moreover, the small reduction in psychological distress suggests further research is warranted. Based on the data collected for this project, a randomized trial with less than 50 subjects would be appropriately powered if perceived stress is the primary outcome
Evolutionary Ecology of Prokaryotic Immune Mechanisms.
Published onlineJournal ArticleReviewBacteria have a range of distinct immune strategies that provide protection against bacteriophage (phage) infections. While much has been learned about the mechanism of action of these defense strategies, it is less clear why such diversity in defense strategies has evolved. In this review, we discuss the short- and long-term costs and benefits of the different resistance strategies and, hence, the ecological conditions that are likely to favor the different strategies alone and in combination. Finally, we discuss some of the broader consequences, beyond resistance to phage and other genetic elements, resulting from the operation of different immune strategies.S.V.H. received funding from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement no. 660039. We also acknowledge the NERC, the BBSRC, the Royal Society, the Leverhulme Trust, the Wellcome Trust, and the AXA research fund for funding
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