136 research outputs found
Prototype Analog Front-end for Negative-ion Gas and Dual-phase Liquid-Ar TPCs
We report on the recent development of a versatile analog front-end
compatible with a negative-ion -TPC for a directional dark matter search
as well as a dual-phase, next-generation (10~kt) liquid argon TPC
to study neutrino oscillations, nucleon decay, and astrophysical neutrinos.
Although the operating conditions for negative-ion and liquid argon TPCs are
quite different (room temperature \textit{vs.} 88~K operation,
respectively), the readout electronics requirements are similar. Both require a
wide-dynamic range up to 1600 fC, and less than 2000--5000 e noise for a
typical signal of 80 fC with a detector capacitance of ~pF. In order to fulfill such challenging requirements, a prototype ASIC
was newly designed using 180-nm CMOS technology. Here, we report on the
performance of this ASIC, including measurements of shaping time, dynamic
range, and equivalent noise charge (ENC). We also demonstrate the first
operation of this ASIC on a low-pressure negative-ion -TPC.Comment: accepted by JINS
Deep Chandra observations of TeV binaries I: LSI +61 303
We report on a 95ks Chandra observation of the TeV emitting High Mass X-ray
Binary LSI +61 303, using the ACIS-S camera in Continuos Clocking mode to
search for a possible X-ray pulsar in this system. The observation was
performed while the compact object was passing from phase 0.94 to 0.98 in its
orbit around the Be companion star (hence close to the apastron passage). We
did not find any periodic or quasi-periodic signal (at this orbital phase) in a
frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3 sigma
upper limit for the presence of a periodic signal of ~10% (although this limit
is strongly dependent on the frequency and the energy band), the deepest limit
ever reached for this object. Furthermore, the source appears highly variable
in flux and spectrum even in this very small orbital phase range, in particular
we detect two flares, lasting thousands of seconds, with a very hard X-ray
spectrum with respect to the average source spectral distribution. The X-ray
pulsed fraction limits we derived are lower than the pulsed fraction of any
isolated rotational-powered pulsar, in particular having a TeV counterpart. In
this scenario most of the X-ray emission of LSI +61 303 should necessarily come
from the interwind or inner-pulsar wind zone shock rather than from the
magnetosphere of the putative pulsar. Furthermore, we did not find evidence for
the previously suggested extended X-ray emission (abridged).Comment: 9 pages, 6 figures, MNRAS in pres
Deep Chandra observations of TeV binaries II: LS 5039
We report on Chandra observations of the TeV emitting High Mass X-ray Binary
LS 5039, for a total exposure of ~70ks, using the ACIS-S camera in Continuos
Clocking mode to search for a possible X-ray pulsar in this system. We did not
find any periodic or quasi-periodic signal in the 0.3-0.4 and 0.75-0.9 orbital
phases, and in a frequency range of 0.005-175 Hz. We derived an average pulsed
fraction 3sigma upper limit for the presence of a periodic signal of ~15%
(depending on the frequency and the energy band), the deepest limit ever
reached for this object. If the X-ray emission of LS 5039 is due (at least in
part) to a rotational powered pulsar, the latter is either spinning faster than
~5.6 ms, or having a beam pointing away from our line of sight, or contributing
to ~15% of the total X-ray emission of the system in the orbital phases we
observed.Comment: 9 pages, 5 figures, MNRAS in pres
Thermal X-ray Emission from the Shocked Stellar Wind of Pulsar Gamma-ray Binaries
Gamma-ray loud X-ray binaries are binary systems that show non-thermal
broadband emission from radio to gamma rays. If the system comprises a massive
star and a young non-accreting pulsar, their winds will collide producing
broadband non-thermal emission, most likely originated in the shocked pulsar
wind. Thermal X-ray emission is expected from the shocked stellar wind, but
until now it has neither been detected nor studied in the context of gamma-ray
binaries. We present a semi-analytic model of the thermal X-ray emission from
the shocked stellar wind in pulsar gamma-ray binaries, and find that the
thermal X-ray emission increases monotonically with the pulsar spin-down
luminosity, reaching luminosities of the order of 10^33 erg/s. The lack of
thermal features in the X-ray spectrum of gamma-ray binaries can then be used
to constrain the properties of the pulsar and stellar winds. By fitting the
observed X-ray spectra of gamma-ray binaries with a source model composed of an
absorbed non-thermal power law and the computed thermal X-ray emission, we are
able to derive upper limits on the spin-down luminosity of the putative pulsar.
We applied this method to LS 5039, the only gamma-ray binary with a radial,
powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of
~6x10^36 erg/s. Given the energetic constraints from its high-energy gamma-ray
emission, a non-thermal to spin-down luminosity ratio very close to unity may
be required.Comment: Published in ApJ. 9 pages, 6 figure
Stage-Specific Inhibition of MHC Class I Presentation by the Epstein-Barr Virus BNLF2a Protein during Virus Lytic Cycle
gamma-herpesvirus Epstein-Barr virus (EBV) persists for life in infected individuals despite the presence of a strong immune response. During the lytic cycle of EBV many viral proteins are expressed, potentially allowing virally infected cells to be recognized and eliminated by CD8+ T cells. We have recently identified an immune evasion protein encoded by EBV, BNLF2a, which is expressed in early phase lytic replication and inhibits peptide- and ATP-binding functions of the transporter associated with antigen processing. Ectopic expression of BNLF2a causes decreased surface MHC class I expression and inhibits the presentation of indicator antigens to CD8+ T cells. Here we sought to examine the influence of BNLF2a when expressed naturally during EBV lytic replication. We generated a BNLF2a-deleted recombinant EBV (ΔBNLF2a) and compared the ability of ΔBNLF2a and wild-type EBV-transformed B cell lines to be recognized by CD8+ T cell clones specific for EBV-encoded immediate early, early and late lytic antigens. Epitopes derived from immediate early and early expressed proteins were better recognized when presented by ΔBNLF2a transformed cells compared to wild-type virus transformants. However, recognition of late antigens by CD8+ T cells remained equally poor when presented by both wild-type and ΔBNLF2a cell targets. Analysis of BNLF2a and target protein expression kinetics showed that although BNLF2a is expressed during early phase replication, it is expressed at a time when there is an upregulation of immediate early proteins and initiation of early protein synthesis. Interestingly, BNLF2a protein expression was found to be lost by late lytic cycle yet ΔBNLF2a-transformed cells in late stage replication downregulated surface MHC class I to a similar extent as wild-type EBV-transformed cells. These data show that BNLF2a-mediated expression is stage-specific, affecting presentation of immediate early and early proteins, and that other evasion mechanisms operate later in the lytic cycle
Fermi Large Area Telescope View of the Core of the Radio Galaxy Centaurus A
We present gamma-ray observations with the LAT on board the Fermi Gamma-Ray
Telescope of the nearby radio galaxy Centaurus~A. The previous EGRET detection
is confirmed, and the localization is improved using data from the first 10
months of Fermi science operation. In previous work, we presented the detection
of the lobes by the LAT; in this work, we concentrate on the gamma-ray core of
Cen~A. Flux levels as seen by the LAT are not significantly different from that
found by EGRET, nor is the extremely soft LAT spectrum
(\G=2.67\pm0.10_{stat}\pm0.08_{sys} where the photon flux is \Phi\propto
E^{-\G}). The LAT core spectrum, extrapolated to higher energies, is
marginally consistent with the non-simultaneous HESS spectrum of the source.
The LAT observations are complemented by simultaneous observations from Suzaku,
the Swift Burst Alert Telescope and X-ray Telescope, and radio observations
with the Tracking Active Galactic Nuclei with Austral Milliarcsecond
Interferometry (TANAMI) program, along with a variety of non-simultaneous
archival data from a variety of instruments and wavelengths to produce a
spectral energy distribution (SED). We fit this broadband data set with a
single-zone synchrotron/synchrotron self-Compton model, which describes the
radio through GeV emission well, but fails to account for the non-simultaneous
higher energy TeV emission observed by HESS from 2004-2008. The fit requires a
low Doppler factor, in contrast to BL Lacs which generally require larger
values to fit their broadband SEDs. This indicates the \g-ray emission
originates from a slower region than that from BL Lacs, consistent with
previous modeling results from Cen~A. This slower region could be a slower
moving layer around a fast spine, or a slower region farther out from the black
hole in a decelerating flow.Comment: Accepted by ApJ. 32 pages, 5 figures, 2 tables. J. Finke and Y.
Fukazawa corresponding author
Population Genetic Analysis of Propionibacterium acnes Identifies a Subpopulation and Epidemic Clones Associated with Acne
The involvement of Propionibacterium acnes in the pathogenesis of acne is controversial, mainly owing to its dominance as an inhabitant of healthy skin. This study tested the hypothesis that specific evolutionary lineages of the species are associated with acne while others are compatible with health. Phylogenetic reconstruction based on nine housekeeping genes was performed on 210 isolates of P. acnes from well-characterized patients with acne, various opportunistic infections, and from healthy carriers. Although evidence of recombination was observed, the results showed a basically clonal population structure correlated with allelic variation in the virulence genes tly and camp5, with pulsed field gel electrophoresis (PFGE)- and biotype, and with expressed putative virulence factors. An unexpected geographically and temporal widespread dissemination of some clones was demonstrated. The population comprised three major divisions, one of which, including an epidemic clone, was strongly associated with moderate to severe acne while others were associated with health and opportunistic infections. This dichotomy correlated with previously observed differences in in vitro inflammation-inducing properties. Comparison of five genomes representing acne- and health-associated clones revealed multiple both cluster- and strain-specific genes that suggest major differences in ecological preferences and redefines the spectrum of disease-associated virulence factors. The results of the study indicate that particular clones of P. acnes play an etiologic role in acne while others are associated with health
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