103,532 research outputs found
Detecting relic gravitational waves in the CMB: A statistical bias
Analyzing the imprint of relic gravitational waves (RGWs) on the cosmic
microwave background (CMB) power spectra provides a way to determine the signal
of RGWs. In this Letter, we discuss a statistical bias, which could exist in
the data analysis and has the tendency to overlook the RGWs. We also explain
why this bias exists, and how to avoid it.Comment: 4 pages, 1 figur
A Nonthermal Radio Filament Connected to the Galactic Black Hole?
Using the Very Large Array, we have investigated a non-thermal radio filament
(NTF) recently found very near the Galactic black hole and its radio
counterpart, SgrA*. While this NTF -- the Sgr A West Filament (SgrAWF) --
shares many characteristics with the population of NTFs occupying the central
few hundred parsecs of the Galaxy, the SgrAWF has the distinction of having an
orientation and sky location that suggest an intimate physical connection to
SgrA*. We present 3.3 and 5.5 cm images constructed using an innovative
methodology that yields a very high dynamic range, providing an unprecedentedly
clear picture of the SgrAWF. While the physical association of the SgrAWF with
SgrA* is not unambiguous, the images decidedly evoke this interesting
possibility. Assuming that the SgrAWF bears a physical relationship to SgrA*,
we examine the potential implications. One is that SgrA* is a source of
relativistic particles constrained to diffuse along ordered local field lines.
The relativistic particles could also be fed into the local field by a
collimated outflow from SgrA*, perhaps driven by the Poynting flux accompanying
the black hole spin in the presence of a magnetic field threading the event
horizon. Second, we consider the possibility that the SgrAWF is the
manifestation of a low-mass-density cosmic string that has become anchored to
the black hole. The simplest form of these hypotheses would predict that the
filament be bi-directional, whereas the SgrAWF is only seen on one side of
SgrA*, perhaps because of the dynamics of the local medium.Comment: 9 pages, 4 figures, accepted for ApJ Letter
Electrical transport in the ferromagnetic state of manganites: Small-polaron metallic conduction at low temperatures
We report measurements of the resistivity in the ferromagnetic state of
epitaxial thin films of La_{1-x}Ca_{x}MnO_{3} and the low temperature specific
heat of a polycrystalline La_{0.8}Ca_{0.2}MnO_{3}. The resistivity below 100 K
can be well fitted by \rho - \rho_{o} = E \omega_{s}/sinh^{2}(\hbar
\omega_{s}/2k_{B}T) with \hbar \omega_{s}/k_{B} \simeq 100 K and E being a
constant. Such behavior is consistent with small-polaron coherent motion which
involves a relaxation due to a soft optical phonon mode. The specific heat data
also suggest the existence of such a phonon mode. The present results thus
provide evidence for small-polaron metallic conduction in the ferromagnetic
state of manganites.Comment: 4 pages, 4 figures, submitted to PR
CARS spectroscopy of the () band in
Molecular hydrogen is a benchmark system for bound state quantum calculation
and tests of quantum electrodynamical effects. While spectroscopic measurements
on the stable species have progressively improved over the years, high
resolution studies on the radioactive isotopologues , and
have been limited. Here we present an accurate determination of
transition energies in the fundamental vibrational
band of the ground electronic state, by means of high resolution Coherent
Anti-Stokes Raman Spectroscopy. With the present experimental uncertainty of
, which is a fivefold improvement over previous
measurements, agreement with the latest theoretical calculations is
demonstrated.Comment: 9 pages, 3 figure
A New Perspective of the Radio Bright Zone at The Galactic Center: Feedback from Nuclear Activities
New observations of Sgr A have been carried out with the VLA using the
broadband (2 GHz) continuum mode at 5.5 GHz, covering the central 30 pc region
of the RBZ at the Galactic center. Using the MS-MFS algorithms in CASA, we have
imaged Sgr A with a resolution of 1", achieving an rms 8 Jy/beam, and a
dynamic range 100,000:1.The radio image is compared with X-ray, CN
emission-line and Paschen- images obtained using Chandra, SMA and
HST/NICMOS, respectively. We discuss several prominent radio features. The "Sgr
A West Wings" extend 5 pc from the NW and SE tips of the ionized "Mini-spiral"
in Sgr A West to positions located 2.9 and 2.4 arc min to the NW and SE of Sgr
A*, respectively. The NW wing, along with several other prominent features,
including the "NW Streamers", form an elongated radio lobe (NW lobe), oriented
nearly perpendicular to the Galactic plane. This radio lobe, with a size of
14.4 pc x 7.3 pc, has a known X-ray counterpart. A row of three thermally
emitting rings is observed in the NW lobe. A field containing numerous
amorphous radio blobs extends for a distance of ~2 arc min beyond the tip of
the SE wing; these features coincide with the SE X-ray lobe. Most of the
amorphous radio blobs in the NW and SE lobes have Paschen-
counterparts, suggesting that a shock interaction of ambient gas concentrations
with a collimated nuclear wind (outflow) that may be driven by radiation force
from the central star cluster within the CND. Finally, we remark on a prominent
radio feature located within the shell of the Sgr A East SNR. Because this
feature -- the "Sigma Front" -- correlates well in shape and orientation with
the nearby edge of the CND, we propose that it is a reflected shock wave
resulting from the impact of the Sgr A East blast wave on the CND.Comment: 18 pages, 9 figures, ApJ accepte
Recent Trends in Hospitalization for Acute Myocardial Infarction in Beijing: Increasing Overall Burden and a Transition From ST-Segment Elevation to Non-ST-Segment Elevation Myocardial Infarction in a Population-Based Study
Comparable data on trends of hospitalization rates for ST-segment elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI) remain unavailable in representative Asian populations.To examine the temporal trends of hospitalization for acute myocardial infarction (AMI) and its subtypes in Beijing.Patients hospitalized for AMI in Beijing from January 1, 2007 to December 31, 2012 were identified from the validated Hospital Discharge Information System. Trends in hospitalization rates, in-hospital mortality, length of stay (LOS), and hospitalization costs were analyzed by regression models for total AMI and for STEMI and NSTEMI separately. In total, 77,943 patients were admitted for AMI in Beijing during the 6 years, among whom 67.5% were males and 62.4% had STEMI. During the period, the rate of AMI hospitalization per 100,000 population increased by 31.2% (from 55.8 to 73.3 per 100,000 population) after age standardization, with a slight decrease in STEMI but a 3-fold increase in NSTEMI. The ratio of STEMI to NSTEMI decreased dramatically from 6.5:1.0 to 1.3:1.0. The age-standardized in-hospital mortality decreased from 11.2% to 8.6%, with a significant decreasing trend evident for STEMI in males and females (P < 0.001) and for NSTEMI in males (P = 0.02). The rate of percutaneous coronary intervention increased from 28.7% to 55.6% among STEMI patients. The total cost for AMI hospitalization increased by 56.8% after adjusting for inflation, although the LOS decreased by 1 day.The hospitalization burden for AMI has been increasing in Beijing with a transition from STEMI to NSTEMI. Diverse temporal trends in AMI subtypes from the unselected "real-world" data in Beijing may help to guide the management of AMI in China and other developing countries
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