510 research outputs found
New Diffraction Results from the Tevatron
We present new results from studies on diffractive dijet production and
exclusive production of dijet and diphoton obtained by the CDF Collaboration in
proton-antiproton collisions at the Fermilab Tevatron.Comment: 4 pages, To be submitted to the proceedings of the 41st Rencontres de
Moriond - QCD and High Energy Hadronic Interactions, La Thuile, Italy, 18-25
March 200
How to Measure the Quantum State of Collective Atomic Spin Excitation
The spin state of an atomic ensemble can be viewed as two bosonic modes,
i.e., a quantum signal mode and a -numbered ``local oscillator'' mode when
large numbers of spin-1/2 atoms are spin-polarized along a certain axis and
collectively manipulated within the vicinity of the axis. We present a concrete
procedure which determines the spin-excitation-number distribution, i.e., the
diagonal elements of the density matrix in the Dicke basis for the collective
spin state. By seeing the collective spin state as a statistical mixture of the
inherently-entangled Dicke states, the physical picture of its multi-particle
entanglement is made clear.Comment: 6 pages, to appear in Phys. Rev.
Rapid Thermalization by Baryon Injection in Gauge/Gravity Duality
Using the AdS/CFT correspondence for strongly coupled gauge theories, we
calculate thermalization of mesons caused by a time-dependent change of a
baryon number chemical potential. On the gravity side, the thermalization
corresponds to a horizon formation on the probe flavor brane in the AdS throat.
Since heavy ion collisions are locally approximated by a sudden change of the
baryon number chemical potential, we discuss implication of our results to RHIC
and LHC experiments, to find a rough estimate of rather rapid thermalization
time-scale t_{th} < 1 [fm/c]. We also discuss universality of our analysis
against varying gauge theories.Comment: 9 pages, 7 figures. v2: minor clarifications, version to appear in
PR
Chandra X-Ray Study of Galactic Supernova Remnant G299.2-2.9
We report on observations of the Galactic supernova remnant (SNR)
G299.22.9 with the {\it Chandra X-Ray Observatory}. The high resolution
images with {\it Chandra} resolve the X-ray-bright knots, shell, and diffuse
emission extending beyond the bright shell. Interior to the X-ray shell is
faint diffuse emission occupying the central regions of the SNR.
Spatially-resolved spectroscopy indicates a large foreground absorption
( 3.5 10 cm), which supports a
relatively distant location ( 5 kpc) for the SNR. The blast wave is
encountering a highly inhomogeneous ambient medium with the densities ranging
over more than an order of magnitude ( 0.1 4 cm).
Assuming the distance of 5 kpc, we derive a Sedov age of
4500 yr and an explosion energy of 1.6 10
ergs. The ambient density structure and the overall morphology suggest that
G299.22.9 may be a limb-brightened partial shell extending to 7 pc
radius surrounded by fainter emission extending beyond that to a radius of
9 pc. This suggests the SNR exploded in a region of space where there is
a density gradient whose direction lies roughly along the line of sight. The
faint central region shows strong line emission from heavy elements of Si and
Fe, which is caused by the presence of the overabundant stellar ejecta there.
We find no evidence for stellar ejecta enriched in light elements of O and Ne.
The observed abundance structure of the metal-rich ejecta supports a Type Ia
origin for G299.22.9.Comment: 16 pages (AASTex emulator style), 3 Tables, 10 Figures (including 1
color: Figure 1), Accepted by Ap
Intermittency and local Reynolds number in Navier-Stokes turbulence: A cross-over scale in the Caffarelli-Kohn-Nirenberg integral
We study space-time integrals, which appear in the Caffarelli-Kohn-Nirenberg (CKN) theory for the Navier-Stokes equations analytically and numerically. The key quantity is written in standard notations δ(r)=1/(νr)∫Qr(∇,u)2dxdtδ(r)=1/(νr)∫Qr∇u2dxdt, which can be regarded as a local Reynolds number over a parabolic cylinder Q r . First, by re-examining the CKN integral, we identify a cross-over scale r∗∝L(∥∇u∥2L2¯¯¯¯¯¯¯¯¯¯¯¯∥∇u∥2L∞)1/3,r*∝L‖∇u‖L22¯‖∇u‖L∞21/3, at which the CKN Reynolds number δ(r) changes its scaling behavior. This reproduces a result on the minimum scale r min in turbulence:r2min∥∇u∥∞∝ν,rmin2‖∇u‖∞∝ν, consistent with a result of Henshaw et al. [“On the smallest scale for the incompressible Navier-Stokes equations,” Theor. Comput. Fluid Dyn.1, 65 (1989)10.1007/BF00272138]. For the energy spectrum E(k) ∝ k −q (1 < q < 3), we show that r * ∝ ν a with a=43(3−q)−1a=43(3−q)−1. Parametric representations are then obtained as ∥∇u∥∞∝ν−(1+3a)/2‖∇u‖∞∝ν−(1+3a)/2 and r min ∝ ν3(a+1)/4. By the assumptions of the regularity and finite energy dissipation rate in the inviscid limit, we derive limp→∞ζpp=1−ζ2limp→∞ζpp=1−ζ2 for any phenomenological models on intermittency, where ζ p is the exponent of pth order (longitudinal) velocity structure function. It follows that ζ p ⩽ (1 − ζ2)(p − 3) + 1 for any p ⩾ 3 without invoking fractal energy cascade. Second, we determine the scaling behavior of δ(r) in direct numerical simulations of the Navier-Stokes equations. In isotropic turbulence around R λ ≈ 100 starting from random initial conditions, we have found that δ(r) ∝ r 4 throughout the inertial range. This can be explained by the smallness of a ≈ 0.26,with a result that r * is in the energy-containing range. If the β-model is perfectly correct, the intermittency parameter a must be related to the dissipation correlation exponent μ as μ=4a1+a≈0.8,μ=4a1+a≈0.8, which is larger than the observed μ ≈ 0.20. Furthermore, corresponding integrals are studied using the Burgers vortex and the Burgers equation. In those single-scale phenomena, the cross-over scale lies in the dissipative range.The scale r * offers a practical method of quantifying intermittency. This paper also sorts out a number of existing mathematical bounds and phenomenological models on the basis of the CKN Reynolds number
Merger of black hole-neutron star binaries in full general relativity
We present our latest results for simulation for merger of black hole
(BH)-neutron star (NS) binaries in full general relativity which is performed
preparing a quasicircular state as initial condition. The BH is modeled by a
moving puncture with no spin and the NS by the -law equation of state
with and corotating velocity field as a first step. The mass of the
BH is chosen to be or , and the rest-mass
of the NS with relatively large radius of the NS
--14 km. The NS is tidally disrupted near the innermost stable
orbit but --90% of the material is swallowed into the BH and resulting
disk mass is not very large as even for small BH mass . The result indicates that the system of a BH and a massive disk
of is not formed from nonspinning BH-NS binaries irrespective
of BH mass, although a disk of mass is a possible outcome
for this relatively small BH mass range as --4. Our results
indicate that the merger of low-mass BH and NS may form a central engine of
short-gamma-ray bursts.Comment: 14 pages. To appear in a special issue of Classical and Quantum
Gravity: New Frontiers in Numerical Relativit
Cross-clamping of the descending thoracic aorta leads to the asymmetrical distribution of propofol during cardiopulmonary bypass surgery
Low- and Medium-Dispersion Spectropolarimetry of Nova V475 Sct (Nova Scuti 2003): Discovery of an Asymmetric High-Velocity Wind in a Moderately Fast Nova
We present low-resolution () and medium-resolution ()
spectropolarimetry of Nova V475 Sct with the HBS instrument, mounted on the
0.91-m telescope at the Okayama Astrophysical Observatory, and with FOCAS,
mounted on the 8.2-m Subaru telescope. We estimated the interstellar
polarization toward the nova from the steady continuum polarization components
and H line emission components. After subtracting the interstellar
polarization component from the observations, we found that the H
emission seen on 2003 October 7 was clearly polarized. In the polarized flux
spectrum, the H emission had a distinct red wing extending to km s and a shoulder around km s, showing a
constant position angle of linear polarization \theta_{\rm *}\simeq
155\arcdeg\pm 15\arcdeg. This suggests that the nova had an asymmetric outflow
with a velocity of km s or more, which is six
times higher than the expansion velocity of the ionized shell at the same
epoch. Such a high-velocity component has not previously been reported for a
nova in the `moderately fast' speed class. Our observations suggest the
occurrence of violent mass-loss activity in the nova binary system even during
the common-envelope phase. The position angle of the polarization in the
H wing is in good agreement with that of the continuum polarization
found on 2003 September 26 (--0.6 %), which disappeared
within the following 2 d. The uniformity of the PA between the continuum
polarization and the wing polarization on October 7 suggests that the axis of
the circumstellar asymmetry remained nearly constant during the period of our
observations.Comment: 27 pages, 7 figures, accepted for publication in A
Binary orbits as the driver of γ-ray emission and mass ejection in classical novae
Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel �10,000 solar masses of material at velocities exceeding 1,000 km/s. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of the thermonuclear runaway, prolonged optically thick winds, or binary interaction with the nova envelope. Classical novae are now routinely detected in GeV gamma-rays, suggesting that relativistic particles are accelerated by strong shocks in nova ejecta. Here we present high-resolution imaging of the gamma-ray-emitting nova V959 Mon at radio wavelengths, showing that its ejecta were shaped by binary motion: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of gamma-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are gamma-ray emitters
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