16,584 research outputs found
In vitro method to study antifungal perfusion in Candida Biofilms
Antimycotic perfusion through Candida biofilms was demonstrated by a modification of a simple in vitro diffusion cell bioassay system. Using this model, the perfusion of three commonly used antifungal agents, amphotericin B, fluconazole, and flucytosine, was investigated in biofilms of three different Candida species (i.e., Candida albicans, Candida parapsilosis, and Candida krusei) that were developed on microporous filters. Scanning electron microscopy revealed that C. albicans formed a contiguous biofilm with tightly packed blastospores and occasional hyphae compared with C. parapsilosis and C. krusei, which developed confluent biofilms displaying structural heterogeneity and a lesser cell density, after 48 h of incubation on nutrient agar. Minor structural changes were also perceptible on the superficial layers of the biofilm after antifungal perfusion. The transport of antifungals to the distal biofilm-substratum interface was most impeded by C. albicans biofilms in comparison to C. parapsilosis and C. krusei. Fluconazole and flucytosine demonstrated similar levels of perfusion, while amphotericin B was the least penetrant through all three biofilms, although the latter appeared to cause the most structural damage to the superficial cells of the biofilm compared with the other antifungals. These results suggest that the antifungal perfusion through biofilm mode of growth in Candida is dependent both on the antimycotic and the Candida species in question, and in clinical terms, these phenomena could contribute to the failure of Candida biofilm-associated infections. Finally, the in vitro model we have described should serve as a useful system to investigate the complex interactions that appear to operate in vivo within the biofilm-antifungal interphase.published_or_final_versio
Serendipitous discovery of an extended X-ray jet without a radio counterpart in a high-redshift quasar
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led
to the discovery of an extended X-ray jet associated with the high-redshift
background quasar B3 0727+409, a luminous radio source at redshift z=2.5. This
is one of only few examples of high-redshift X-ray jets known to date. It has a
clear extension of about 12", corresponding to a projected length of ~100 kpc,
with a possible hot spot located 35" from the quasar. The archival high
resolution VLA maps surprisingly reveal no extended jet emission, except for
one knot about 1.4" from the quasar. The high X-ray to radio luminosity ratio
for this source appears consistent with the amplification
expected from the inverse Compton radiative model. This serendipitous discovery
may signal the existence of an entire population of similar systems with bright
X-ray and faint radio jets at high redshift, a selection bias which must be
accounted for when drawing any conclusions about the redshift evolution of jet
properties and indeed about the cosmological evolution of supermassive black
holes and active galactic nuclei in general
Global Constraints on Effective Dark Matter Interactions: Relic Density, Direct Detection, Indirect Detection, and Collider
An effective interaction approach is used to describe the interactions
between the spin 0 or spin 1/2 dark matter particle and the degrees of freedom
of the standard model. This approach is applicable to those models in which the
dark matter particles do not experience the standard-model interactions, e.g.,
hidden-sector models. We explore the effects of these effective interaction
operators on (i) dark matter relic density, (ii) spin-independent and
spin-dependent dark matter-nucleon scattering cross sections, (iii) cosmic
antiproton and gamma ray fluxes from the galactic halo due to dark matter
annihilation, and (iv) monojet and monophoton production plus missing energy at
the Tevatron and the Large Hadron Collider (LHC). We combine the experimental
data of relic density from WMAP7, spin-independent cross section from XENON100,
spin-dependent cross section from XENON10, ZEPLIN-III, and SIMPLE, cosmic
antiproton flux from PAMELA, cosmic gamma-ray flux from -LAT, and
the monojet and monophoton data from the Tevatron and the LHC, to put the most
comprehensive limits on each effective operator.Comment: 39 pages, 10 figures; a number of references added; a new section
about applicable models is added in the appendix; treatment of data sets are
modified; comments on LEP monophoton, FERMI-LAT dSphs data, and other
discussion. arXiv admin note: substantial text overlap with arXiv:1104.532
Re-parameterization Invariance in Fractional Flux Periodicity
We analyze a common feature of a nontrivial fractional flux periodicity in
two-dimensional systems. We demonstrate that an addition of fractional flux can
be absorbed into re-parameterization of quantum numbers. For an exact
fractional periodicity, all the electronic states undergo the
re-parameterization, whereas for an approximate periodicity valid in a large
system, only the states near the Fermi level are involved in the
re-parameterization.Comment: 4 pages, 1 figure, minor changes, final version to appear in J. Phys.
Soc. Jp
Discovery of an unidentified Fermi object as a black widow-like millisecond pulsar
The Fermi Gamma-ray Space Telescope has revolutionized our knowledge of the
gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray
pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the
outer-gap model predicts different sites of emission for the radio and
gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible
in the radio. Here we report the discovery of a "radio-quiet" gamma-ray
emitting MSP candidate by using Fermi, Chandra, Swift, and optical
observations. The X-ray and gamma-ray properties of the source are consistent
with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical
and X-ray data. We suggest that the source is a black widow-like MSP with a
~0.1 solar-mass late-type companion star. Based on the profile of the optical
and X-ray light-curves, the companion star is believed to be heated by the
pulsar while the X-ray emissions originate from pulsar magnetosphere and/or
from intra-binary shock. No radio detection of the source has been reported yet
and although no gamma-ray/radio pulsation has been found, we estimated that the
spin period of the MSP is ~3-5 ms based on the inferred gamma-ray luminosity.Comment: 6 pages, 2 figures; accepted for publication in ApJ
Slip energy barriers in aluminum and implications for ductile versus brittle behavior
We conisder the brittle versus ductile behavior of aluminum in the framework
of the Peierls-model analysis of dislocation emission from a crack tip. To this
end, we perform first-principles quantum mechanical calculations for the
unstable stacking energy of aluminum along the Shockley partial
slip route. Our calculations are based on density functional theory and the
local density approximation and include full atomic and volume relaxation. We
find that in aluminum J/m. Within the Peierls-model
analysis, this value would predict a brittle solid which poses an interesting
problem since aluminum is typically considered ductile. The resolution may be
given by one of three possibilites: (a) Aluminum is indeed brittle at zero
temperature, and becomes ductile at a finite temperature due to motion of
pre-existing dislocations which relax the stress concentration at the crack
tip. (b) Dislocation emission at the crack tip is itself a thermally activated
process. (c) Aluminum is actually ductile at all temperatures and the
theoretical model employed needs to be significantly improved in order to
resolve the apparent contradiction.Comment: 4 figures (not included; send requests to [email protected]
Depressive symptoms are common among rural Malawian adolescents
BackgroundDepressive conditions cause about 25 million disability adjusted life years in low-income countries annually. The incidence of depression rises after puberty, and the young age distribution in these countries may cause a high burden of adolescent depression. We aimed to assess the prevalence of reported depressive symptoms among rural adolescents in Malawi. Additionally, we assessed the association between birth weight, childhood growth, gender, and pubertal maturity and depressive symptoms. MethodsWe followed 767 children from the foetal period until 15-years-of-age. We used the Short Mood and Feelings Questionnaire (SMFQ) to examine reported depressive symptoms at 15years. The questionnaire was translated to local language and then back-translated until inaccuracies were not detected. Anthropometry was conducted at 1, 24, 120, and 180months of age. We performed regression models with imputed data to assess associations between the independent variables and depressive symptoms. As a sensitivity analysis, we ran the same regression models with participants with no missing data. ResultsA total of 523 participants were seen at 15years. The mean SMFQ score was 15 with 90% (95%CI 87-92%) of the participants scoring 11 points, the traditional cut-off for screening for depression. Birth weight, growth, gender, and pubertal maturity were not associated with the SMFQ score in the primary imputed analyses. In the sensitivity analysis, birth weight was associated with the SMFQ score in all models. ConclusionsThe prevalence of reported depressive symptoms was high among the studied population. It is uncertain how well the traditional cut-off of 11 points identifies children with clinically significant depressive symptoms in our sample. Our data do not support a hypothesis of an association between growth, gender, or pubertal maturity and depressive symptoms. Nevertheless, our results highlight the importance of the awareness of mental health problems in low-income countries.Peer reviewe
Explicit Zeta Functions for Bosonic and Fermionic Fields on a Noncommutative Toroidal Spacetime
Explicit formulas for the zeta functions corresponding to
bosonic () and to fermionic () quantum fields living on a
noncommutative, partially toroidal spacetime are derived. Formulas for the most
general case of the zeta function associated to a quadratic+linear+constant
form (in {\bf Z}) are obtained. They provide the analytical continuation of the
zeta functions in question to the whole complex plane, in terms of series
of Bessel functions (of fast, exponential convergence), thus being extended
Chowla-Selberg formulas. As well known, this is the most convenient expression
that can be found for the analytical continuation of a zeta function, in
particular, the residua of the poles and their finite parts are explicitly
given there. An important novelty is the fact that simple poles show up at
, as well as in other places (simple or double, depending on the number of
compactified, noncompactified, and noncommutative dimensions of the spacetime),
where they had never appeared before. This poses a challenge to the
zeta-function regularization procedure.Comment: 15 pages, no figures, LaTeX fil
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