391 research outputs found
Unbiased All-Optical Random-Number Generator
The generation of random bits is of enormous importance in modern information
science. Cryptographic security is based on random numbers which require a
physical process for their generation. This is commonly performed by hardware
random number generators. These exhibit often a number of problems, namely
experimental bias, memory in the system, and other technical subtleties, which
reduce the reliability in the entropy estimation. Further, the generated
outcome has to be post-processed to "iron out" such spurious effects. Here, we
present a purely optical randomness generator, based on the bi-stable output of
an optical parametric oscillator. Detector noise plays no role and no further
post-processing is required. Upon entering the bi-stable regime, initially the
resulting output phase depends on vacuum fluctuations. Later, the phase is
rigidly locked and can be well determined versus a pulse train, which is
derived from the pump laser. This delivers an ambiguity-free output, which is
reliably detected and associated with a binary outcome. The resulting random
bit stream resembles a perfect coin toss and passes all relevant randomness
measures. The random nature of the generated binary outcome is furthermore
confirmed by an analysis of resulting conditional entropies.Comment: 10 pages, 4 figure
On the nature of the ultraluminous X-ray transient in Cen~A (NGC 5128)
We combine 9 ROSAT, 9 Chandra, and 2 XMM-Newton observations of the Cen~A
galaxy to obtain the X-ray light curve of 1RXH J132519.8-430312 (=CXOU
J132519.9430317) spanning 1990 to 2003. The source reached a peak 0.1-2.4
keV flux F_X>10^{-12} ergs cm^{-2} s^{-1} during a 10~day span in 1995 July.
The inferred peak isotropic luminosity of the source therefore exceeded 3
10^{39} ergs s^{-1}, which places the source in the class of ultra-luminous
X-ray sources. Coherent pulsations at 13.264 Hz are detected during a second
bright episode (F_X >3 times 10^{-13} ergs cm^{-2} s^{-1}) in 1999 December.
The source is detected and varies significantly within three additional
observations but is below the detection threshold in 7 observations. The X-ray
spectrum in 1999 December is best described as a cut-off power law or a
disk-blackbody (multi-colored disk). We also detect an optical source, m_F555W
~ 24.1 mag, within the Chandra error circle of 1RXH J132519.8-430312 in HST
images taken 195~days before the nearest X-ray observation. The optical
brightness of this source is consistent with a late O or early B star at the
distance of Cen A. If the optical source is the counterpart, then the X-ray and
optical behavior of 1RXH J132519.8-430312 are similar to the transient Be/X-ray
pulsar A 0538-66.Comment: 7 pages, 8 figures. ApJ (accepted
Deep Observation of the Giant Radio Lobes of Centaurus A with the Fermi Large Area Telescope
The detection of high energy (HE) {\gamma}-ray emission up to about 3 GeV
from the giant lobes of the radio galaxy Centaurus A has been recently reported
by the Fermi-LAT Collaboration based on ten months of all-sky survey
observations. A data set more than three times larger is used here to study the
morphology and photon spectrum of the lobes with higher statistics. The larger
data set results in the detection of HE {\gamma}-ray emission (up to about 6
GeV) from the lobes with a significance of more than 10 and 20 {\sigma} for the
North and the South lobe, respectively. Based on a detailed spatial analysis
and comparison with the associated radio lobes, we report evidence for a
substantial extension of the HE {\gamma}-ray emission beyond the WMAP radio
image in the case of the Northern lobe of Cen A. We reconstruct the spectral
energy distribution (SED) of the lobes using radio (WMAP) and Fermi-LAT data
from the same integration region. The implications are discussed in the context
of hadronic and leptonic scenarios
Probing Lorentz Invariance at EeV Energy
Pierre Auger experiment has detected at least a couple of ray events above
energy 60 EeV from the direction of the radio-galaxy Centaurus A. Assuming
those events are from Centaurus A, we have calculated the number of neutral
cosmic ray events from this source for small values of the degree of violation
in Lorentz invariance. Our results show that a comparison of our calculated
numbers of events with the observed number of events at EeV energy from the
direction of the source can probe extremely low value of the degree of this
violation.Comment: 8 pages,4 figure
Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure
High pressure structural distortions of the hexagonal close packed (hcp)
element zinc have been a subject of controversy. Earlier experimental results
and theory showed a large anomaly in lattice strain with compression in zinc at
about 10 GPa which was explained theoretically by a change in Fermi surface
topology. Later hydrostatic experiments showed no such anomaly, resulting in a
discrepancy between theory and experiment. We have computed the compression and
lattice strain of hcp zinc over a wide range of compressions using the
linearized augmented plane wave (LAPW) method paying special attention to
k-point convergence. We find that the behavior of the lattice strain is
strongly dependent on k-point sampling, and with large k-point sets the
previously computed anomaly in lattice parameters under compression disappears,
in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press
RXTE Observations of the Anomalous Pulsar 4U 0142+61
We observed the anomalous X-ray pulsar 4U 0142+61 using the Proportional
Counter Array (PCA) aboard the Rossi X-ray Timing Explorer (RXTE) in March
1996. The pulse frequency was measured as f = 0.11510039(3) Hz with an upper
limit of df/dt < 4 * 10^(-13) Hz/s upon the short term change in frequency over
the 4.6 day span of the observations. A compilation of all historical
measurements showed an overall spin-down trend with slope df/dt = (-3.0 +/-
0.1) * 10^(-14) Hz/s. Searches for orbital modulations in pulse arrival times
yielded an upper limit of a_x sin i < 0.26 lt-s (99% confidence) for the period
range 70 s to 2.5 days. These limits combined with previous optical limits and
evolutionary arguments suggest that 4U 0142+61 is probably not a member of a
binary system.Comment: 20 pages (LaTeX) including 7 figures. Accepted for publication in the
Astrophysical Journa
Ambient particulate matter and biomass burning:an ecological time series study of respiratory and cardiovascular hospital visits in northern Thailand
Background
Exposure to particulate matter (PM) emitted from biomass burning is an increasing concern, particularly in Southeast Asia. It is not yet clear how the source of PM influences the risk of an adverse health outcome. The objective of this study was to quantify and compare health risks of PM from biomass burning and non-biomass burning sources in northern Thailand.
Methods
We collected ambient air pollutant data (PM with a diameter of < 10 μm [PM10], PM2.5, Carbon Monoxide [CO], Ozone [O3], and Nitrogen Dioxide [NO2]) from ground-based monitors and daily outpatient hospital visits in Thailand during 2014–2017. Outpatient data included chronic lower respiratory disease (CLRD), ischaemic heart disease (IHD), and cerebrovascular disease (CBVD). We performed an ecological time series analysis to evaluate the association between daily air pollutants and outpatient visits. We used the 90th and 95th percentiles of PM10 concentrations to determine days of exposure to PM predominantly from biomass burning.
Results
There was significant intra annual variation in PM10 levels, with the highest concentrations occurring during March, coinciding with peak biomass burning. Incidence Rate Ratios (IRRs) between daily PM10 and outpatient visits were elevated most on the same day as exposure for CLRD = 1.020 (95% CI: 1.012 to 1.028) and CBVD = 1.020 (95% CI: 1.004 to 1.035), with no association with IHD = 0.994 (95% CI: 0.974 to 1.014). Adjusting for CO tended to increase effect estimates. We did not find evidence of an exposure response relationship with levels of PM10 on days of biomass burning.
Conclusions
We found same-day exposures of PM10 to be associated with certain respiratory and cardiovascular outpatient visits. We advise implementing measures to reduce population exposures to PM wherever possible, and to improve understanding of health effects associated with burning specific types of biomass in areas where such large-scale activities occur.This study was funded by the Medical Research Council (MRC) (MR/R006210/1)
and the Thailand Research Fund (TRF) (RDG603009)
A Catalog of Candidate Intermediate-luminosity X-ray Objects
ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-ray
point sources in galaxies other than our own. X-ray observations of normal
galaxies with ROSAT and Chandra have revealed that off-nuclear, compact,
Intermediate-luminosity (Lx[2-10 keV] >= 1e39 erg/s) X-ray Objects (IXOs,
a.k.a. ULXs [Ultraluminous X-ray sources]) are quite common. Here we present a
catalog and finding charts for 87 IXOs in 54 galaxies, derived from all of the
ROSAT HRI imaging data for galaxies with cz <= 5000 km/s from the Third
Reference Catalog of Bright Galaxies (RC3). We have defined the cutoff Lx for
IXOs so that it is well above the Eddington luminosity of a 1.4 Msun black hole
(10^38.3 erg/s), so as not to confuse IXOs with ``normal'' black hole X-ray
binaries. This catalog is intended to provide a baseline for follow-up work
with Chandra and XMM, and with space- and ground-based survey work at
wavelengths other than X-ray. We demonstrate that elliptical galaxies with IXOs
have a larger number of IXOs per galaxy than non-elliptical galaxies with IXOs,
and note that they are not likely to be merely high-mass X-ray binaries with
beamed X-ray emission, as may be the case for IXOs in starburst galaxies.
Approximately half of the IXOs with multiple observations show X-ray
variability, and many (19) of the IXOs have faint optical counterparts in DSS
optical B-band images. Follow-up observations of these objects should be
helpful in identifying their nature.Comment: 29 pages, ApJS, accepted (catalog v2.0) (full resolution version of
paper and future releases of catalog at http://www.xassist.org/ixocat_hri
High Energy gamma-rays From FR I Jets
Thanks to Hubble and Chandra telescopes, some of the large scale jets in
extragalactic radio sources are now being observed at optical and X-ray
frequencies. For the FR I objects the synchrotron nature of this emission is
surely established, although a lot of uncertainties - connected for example
with the particle acceleration processes involved - remain. In this paper we
study production of high energy gamma-rays in FR I kiloparsec-scale jets by
inverse-Compton emission of the synchrotron-emitting electrons. We consider
different origin of seed photons contributing to the inverse-Compton
scattering, including nuclear jet radiation as well as ambient, stellar and
circumstellar emission of the host galaxies. We discuss how future detections
or non-detections of the evaluated gamma-ray fluxes can provide constraints on
the unknown large scale jet parameters, i.e. the magnetic field intensity and
the jet Doppler factor. For the nearby sources Centaurus A and M 87, we find
measurable fluxes of TeV photons resulting from synchrotron self-Compton
process and from comptonisation of the galactic photon fields, respectively. In
the case of Centaurus A, we also find a relatively strong emission component
due to comptonisation of the nuclear blazar photons, which could be easily
observed by GLAST at energy ~10 GeV, providing important test for the
unification of FR I sources with BL Lac objects.Comment: 39 pages, 6 figures included. Modified version, accepted for
publication in Astrophysical Journa
The role of rs2237781 within GRM8 in eating behavior
Introduction: The glutamate receptor, metabotropic 8 gene (GRM8) encodes a G-protein-coupled glutamate receptor and has been associated with smoking behavior and liability to alcoholism implying a role in addiction vulnerability. Data from animal studies suggest that GRM8 may be involved in the regulation of the neuropeptide Y and melanocortin pathways and might influence food intake and metabolism. This study aimed to investigate the effects of the genetic variant rs2237781 within GRM8 on human eating behavior. Methods: The initial analysis included 548 Sorbs from Germany who have been extensively phenotyped for metabolic traits and who completed the German version of the three-factor eating questionnaire. In addition, we analyzed two independent sample sets comprising 293 subjects from another German cohort and 430 Old Order Amish individuals. Genetic associations with restraint, disinhibition, and hunger were assessed in an additive linear regression model. Results: Among the Sorbs the major G allele of rs2237781 was significantly associated with increased restraint scores in eating behavior (P = 1.9 9 10?4; b =+1.936). The German cohort and the Old Order Amish population revealed a trend in the same direction for restraint (P = 0.242; b =+0.874; P = 0.908; b =+0.096; respectively). A meta-analysis resulted in a combined P = 3.1 9 10?3 (Z-score 2.948). Conclusion: Our data suggest that rs2237781 within GRM8 may influence human eating behavior factors probably via pathways involved in addictive behavior
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