800 research outputs found
Large deviations of a modified Jackson network: stability and rough asymptotics
Consider a modified, stable, two node Jackson network where server 2 helps
server 1 when server 2 is idle. The probability of a large deviation of the
number of customers at node one can be calculated using the flat boundary
theory of Schwartz and Weiss [Large Deviations Performance Analysis (1994),
Chapman and Hall, New York]. Surprisingly, however, these calculations show
that the proportion of time spent on the boundary, where server 2 is idle, may
be zero. This is in sharp contrast to the unmodified Jackson network which
spends a nonzero proportion of time on this boundary.Comment: Published at http://dx.doi.org/10.1214/105051604000000666 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Kinetic studies of HIV-1 and HIV-2 envelope glycoprotein-mediated fusion
BACKGROUND: HIV envelope glycoprotein (Env)-mediated fusion is driven by the concerted coalescence of the HIV gp41 N-helical and C-helical regions, which results in the formation of 6 helix bundles. Kinetics of HIV Env-mediated fusion is an important determinant of sensitivity to entry inhibitors and antibodies. However, the parameters that govern the HIV Env fusion cascade have yet to be fully elucidated. We address this issue by comparing the kinetics HIV-1(IIIB )Env with those mediated by HIV-2 from two strains with different affinities for CD4 and CXCR4. RESULTS: HIV-1 and HIV-2 Env-mediated cell fusion occurred with half times of about 60 and 30 min, respectively. Binding experiments of soluble HIV gp120 proteins to CD4 and co-receptor did not correlate with the differences in kinetics of fusion mediated by the three different HIV Envs. However, escape from inhibition by reagents that block gp120-CD4 binding, CD4-induced CXCR4 binding and 6-helix bundle formation, respectively, indicated large difference between HIV-1 and HIV-2 envelope glycoproteins in their CD4-induced rates of engagement with CXCR4. CONCLUSION: The HIV-2 Env proteins studied here exhibited a significantly reduced window of time between the engagement of gp120 with CD4 and exposure of the CXCR4 binding site on gp120 as compared with HIV-1(IIIB )Env. The efficiency with which HIV-2 Env undergoes this CD4-induced conformational change is the major cause of the relatively rapid rate of HIV-2 Env mediated-fusion
Fulminant immune-mediated necrotising myopathy (IMNM) mimicking myocardial infarction with non-obstructive coronary arteries (MINOCA)
A 74-year-old man, with inflammatory arthritis, recently commenced on adalimumab, presented with a 4-week history of left-sided chest pain, malaise and shortness of breath. Admission ECG showed age-indeterminate left bundle branch block. Troponin T was 4444 ng/L (normal range <15 ng/L) and acute coronary syndrome treatment was commenced. Catheter angiogram revealed mild-burden non-obstructive coronary disease. Cardiac magnetic resonance (CMR) was performed to refine the differential diagnosis and demonstrated no myocardial oedema or late gadolinium enhancement. Extracardiac review highlighted oedema and enhancement of the left shoulder girdle muscles consistent with acute myositis. Creatine kinase was subsequently measured and significantly elevated at 7386 IU/L (normal range 30–200 IU/L in men). Electrophoresis clarified that this was of predominantly skeletal muscle origin. Myositis protocol MRI revealed florid skeletal muscle oedema. The MR findings, together with positive anti-Scl-70 antibodies, suggested fulminant immune-mediated necrotising myopathy presenting as a rare mimic of myocardial infarction with non-obstructive coronary arteries, diagnosed by careful extracardiac CMR review
Spectroscopic Discovery of the Broad-Lined Type Ic Supernova 2010bh Associated with the Low-Redshift GRB 100316D
We present the spectroscopic discovery of a broad-lined Type Ic supernova (SN
2010bh) associated with the nearby long-duration gamma-ray burst (GRB) 100316D.
At z = 0.0593, this is the third-nearest GRB-SN. Nightly optical spectra
obtained with the Magellan telescopes during the first week after explosion
reveal the gradual emergence of very broad spectral features superposed on a
blue continuum. The supernova features are typical of broad-lined SNe Ic and
are generally consistent with previous supernovae associated with low-redshift
GRBs. However, the inferred velocities of SN 2010bh at 21 days after explosion
are a factor of ~2 times larger than those of the prototypical SN 1998bw at
similar epochs, with v ~ 26,000 km/s, indicating a larger explosion energy or a
different ejecta structure. A near-infrared spectrum taken 13.8 days after
explosion shows no strong evidence for He I at 1.083 microns, implying that the
progenitor was largely stripped of its helium envelope. The host galaxy is of
low luminosity (M_R ~ -18.5 mag) and low metallicity (Z < 0.4 Z_solar), similar
to the hosts of other low-redshift GRB-SNe.Comment: 6 pages, 4 figures, 1 table, submitted to ApJ Letter
Anomalies in low-energy Gamma-Ray Burst spectra with the Fermi Gamma-Ray Burst Monitor
A Band function has become the standard spectral function used to describe
the prompt emission spectra of gamma-ray bursts (GRBs). However, deviations
from this function have previously been observed in GRBs detected by BATSE and
in individual GRBs from the \textit{Fermi} era. We present a systematic and
rigorous search for spectral deviations from a Band function at low energies in
a sample of the first two years of high fluence, long bursts detected by the
\textit{Fermi} Gamma-Ray Burst Monitor (GBM). The sample contains 45 bursts
with a fluence greater than 2 erg / cm (10 - 1000 keV). An
extrapolated fit method is used to search for low-energy spectral anomalies,
whereby a Band function is fit above a variable low-energy threshold and then
the best fit function is extrapolated to lower energy data. Deviations are
quantified by examining residuals derived from the extrapolated function and
the data and their significance is determined via comprehensive simulations
which account for the instrument response. This method was employed for both
time-integrated burst spectra and time-resolved bins defined by a signal to
noise ratio of 25 and 50 . Significant deviations are evident
in 3 bursts (GRB\,081215A, GRB\,090424 and GRB\,090902B) in the time-integrated
sample ( 7%) and 5 bursts (GRB\,090323, GRB\,090424, GRB\,090820,
GRB\,090902B and GRB\,090926A) in the time-resolved sample ( 11%).} The
advantage of the systematic, blind search analysis is that it can demonstrate
the requirement for an additional spectral component without any prior
knowledge of the nature of that extra component. Deviations are found in a
large fraction of high fluence GRBs; fainter GRBs may not have sufficient
statistics for deviations to be found using this method
Disappearance of the Progenitor of Supernova iPTF13bvn
Supernova (SN) iPTF13bvn in NGC 5806 was the first Type Ib SN to have been
tentatively associated with a progenitor candidate in pre-explosion images. We
performed deep ultraviolet (UV) and optical Hubble Space Telescope (HST)
observations of the SN site 740 days after explosion. We detect an object in
the optical bands that is fainter than the pre-explosion object. This dimming
is likely not produced by dust absorption in the ejecta; thus, our finding
confirms the connection of the progenitor candidate with the SN. The object in
our data is likely dominated by the fading SN, which implies that the pre-SN
flux is mostly due to the progenitor. We compare our revised pre-SN photometry
with previously proposed progenitor models. Although binary progenitors are
favored, models need to be refined. In particular, to comply with our deep UV
detection limit, any companion star must be less luminous than a late-O star or
substantially obscured by newly formed dust. A definitive progenitor
characterization will require further observations to disentangle the
contribution of a much fainter SN and its environment.Comment: 8 pages, 3 tables, 3 figures. Accepted for publication in ApJ
First results from 2+1 dynamical quark flavors on an anisotropic lattice: light-hadron spectroscopy and setting the strange-quark mass
We present the first light-hadron spectroscopy on a set of
dynamical, anisotropic lattices. A convenient set of coordinates that
parameterize the two-dimensional plane of light and strange-quark masses is
introduced. These coordinates are used to extrapolate data obtained at the
simulated values of the quark masses to the physical light and strange-quark
point. A measurement of the Sommer scale on these ensembles is made, and the
performance of the hybrid Monte Carlo algorithm used for generating the
ensembles is estimated.Comment: 24 pages. Hadron Spectrum Collaboratio
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