115,788 research outputs found
What can we learn from Dijet suppression at RHIC?
We present a systematic study of the dijet suppression at RHIC using the
VNI/BMS parton cascade. We examine the modification of the dijet asymmetry A_j
and the within-cone transverse energy distribution (jet-shape) along with
partonic fragmentation distributions z and j_t in terms of: qhat; the path
length of leading and sub-leading jets; cuts on the jet energy distributions;
jet cone angle and the jet-medium interaction mechanism. We find that A_j is
most sensitive to qhat and relatively insensitive to the nature of the
jet-medium interaction mechanism. The jet profile is dominated by qhat and the
nature of the interaction mechanism. The partonic fragmentation distributions
clearly show the jet modification and differentiate between elastic and
radiative+elastic modes
A Study of H2 Emission in Three Bipolar Proto-Planetary Nebulae: IRAS 16594-4656, Hen 3-401, and Rob 22
We have carried out a spatial-kinematical study of three proto-planetary
nebulae, IRAS 16594-4656, Hen 3-401, and Rob 22. High-resolution H2 images were
obtained with NICMOS on the HST and high-resolution spectra were obtained with
the Phoenix spectrograph on Gemini-South. IRAS 16594-4656 shows a
"peanut-shaped" bipolar structure with H2 emission from the walls and from two
pairs of more distant, point-symmetric faint blobs. The velocity structure
shows the polar axis to be in the plane of the sky, contrary to the impression
given by the more complex visual image and the visibility of the central star,
with an ellipsoidal velocity structure. Hen 3-401 shows the H2 emission coming
from the walls of the very elongated, open-ended lobes seen in visible light,
along with a possible small disk around the star. The bipolar lobes appear to
be tilted 10-15 deg with respect to the plane of the sky and their kinematics
display a Hubble-like flow. In Rob 22, the H2 appears in the form of an "S"
shape, approximately tracing out the similar pattern seen in the visible. H2 is
especially seen at the ends of the lobes and at two opposite regions close to
the unseen central star. The axis of the lobes is nearly in the plane of the
sky. Expansion ages of the lobes are calculated to be approximately 1600 yr
(IRAS 16594-4656), 1100 yr (Hen 3-401), and 640 yr (Rob 22), based upon
approximate distances
Effect of vacuum exhaust pressure on the performance of MHD ducts at high B-field
The effect of area ratio variation on the performance of a supersonic Hall MHD duct is investigated. Results indicate that for a given combustion pressure there exists an area ratio below which the power generating region of the duct is shock free and the power output increases linearly with the square of the magnetic field. For area ratios greater than this, a shock forms in the power generating region which moves upstream with increasing magnetic field strength resulting in a less rapid raise in the power output. The shock can be moved downstream by either increasing the combustion pressure of decreasing the exhaust pressure. The influence of these effects upon duct performance is presented
High B-field, large area ratio MHD duct experiments
Studies of the effect of area ratio variation on the performance of a supersonic Hall MHD duct were extended up to area ratios of 6.25/1. It is shown that for a given area ratio there is a combustion pressure above which the power generating region of the duct is shock free and the power output increases linearly with the square of the magnetic field. Below this pressure a shock forms in the duct which moves upstream with increasing magnetic field strength and results in a less rapid rise in power output
Increase in soil organic carbon by agricultural intensification in northern China
Acknowledgements. This research was supported by National Natural Science Foundation of China (no. 31370527 and 31261140367) and the National Science and Technology Support Program of China (no. 2012BAD14B01-2). The authors gratefully thank the Huantai Agricultural Station for providing of the Soil Fertility Survey data. We also thank Zheng Liang from China Agricultural University for the soil sampling and analysis in 2011. Thanks are extended to Jessica Bellarby for helpful discussion and suggestions.Peer reviewedPublisher PD
The Supergiant Shell LMC2: II. Physical Properties of the 10^6 K Gas
LMC2 has the highest X-ray surface brightness of all know supergiant shells
in the Large Magellanic Cloud (LMC). The X-ray emission peaks within the
ionized filaments that define the shell boundary, but also extends beyond the
southern border of LMC2 as an X-ray bright spur. ROSAT HRI images reveal the
X-ray emission from LMC2 and the spur to be truly diffuse, indicating a hot
plasma origin. We have obtained ROSAT PSPC and ASCA SIS spectra to study the
physical conditions of the hot gas interior to LMC2 and the spur. Raymond-Smith
thermal plasma model fits to the X-ray spectra, constrained by HI 21-cm
emission-line measurements of the column density, show the plasma temperature
of the hot gas interior of LMC2 to be kT = 0.1 - 0.7 keV and of the spur to be
kT = 0.1 - 0.5 keV. We have compared the physical conditions of the hot gas
interior to LMC2 with those of other supergiant shells, superbubbles, and
supernova remnants (SNRs) in the LMC. We find that our derived electron
densities for the hot gas inside LMC2 is higher than the value determined for
the supergiant shell LMC4, comparable to the value determined for the
superbubble N11, and lower than the values determined for the superbubble N44
and a number of SNRs.Comment: 29 pages, 5 figures, to be published in Ap
A multi-wavelength view of galaxy evolution with AKARI
AKARI's all-sky survey resolves the far-infrared emission in many thousands
of nearby galaxies, providing essential local benchmarks against which the
evolution of high-redshift populations can be measured. This review presents
some recent results in the resolved galaxy populations, covering some
well-known nearby targets, as well as samples from major legacy surveys such as
the Herschel Reference Survey and the JCMT Nearby Galaxies Survey. This review
also discusses the prospects for higher redshifts surveys, including strong
gravitational lens clusters and the AKARI NEP field.Comment: Accepted for Publications of the Korean Astronomical Society
(September 30, 2012 issue, volume 27, No. 3), Proceedings of the Second AKARI
conference, Legacy of AKARI: A Panoramic View of the Dusty Universe. 6 page
Many-Body Electronic Structure of Americium metal
We report computer based simulations of energetics, spectroscopy and
electron-phonon interaction of americium using a novel spectral density
functional method. This approach gives rise to a new concept of a many-body
electronic structure and reveals the unexpected mixed valence regime of Am 5f6
electrons which under pressure acquire the 5f7 valence state. This explains
unique properties of Am and addresses the fundamental issue of how the
localization delocalization edge is approached from the localized side in a
closed shell system.Comment: 4 pages, 3 figure
MCViNE -- An object oriented Monte Carlo neutron ray tracing simulation package
MCViNE (Monte-Carlo VIrtual Neutron Experiment) is a versatile Monte Carlo
(MC) neutron ray-tracing program that provides researchers with tools for
performing computer modeling and simulations that mirror real neutron
scattering experiments. By adopting modern software engineering practices such
as using composite and visitor design patterns for representing and accessing
neutron scatterers, and using recursive algorithms for multiple scattering,
MCViNE is flexible enough to handle sophisticated neutron scattering problems
including, for example, neutron detection by complex detector systems, and
single and multiple scattering events in a variety of samples and sample
environments. In addition, MCViNE can take advantage of simulation components
in linear-chain-based MC ray tracing packages widely used in instrument design
and optimization, as well as NumPy-based components that make prototypes useful
and easy to develop. These developments have enabled us to carry out detailed
simulations of neutron scattering experiments with non-trivial samples in
time-of-flight inelastic instruments at the Spallation Neutron Source. Examples
of such simulations for powder and single-crystal samples with various
scattering kernels, including kernels for phonon and magnon scattering, are
presented. With simulations that closely reproduce experimental results,
scattering mechanisms can be turned on and off to determine how they contribute
to the measured scattering intensities, improving our understanding of the
underlying physics.Comment: 34 pages, 14 figure
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