19,021 research outputs found
Narrow Band Chandra X-ray Analysis of Supernova Remnant 3C391
We present the narrow-band and the equivalent width (EW) images of the
thermal composite supernova remnant (SNR) 3C391 for the X-ray emission lines of
elements Mg, Si, & S using the Chandra ACIS Observational data. These EW images
reveal the spatial distribution of the emission of the metal species Mg, Si, &
S in the remnant. They have clumpy structure similar to that seen from the
broadband diffuse emission, suggesting that they are largely of interstellar
origin. We find an interesting finger-like feature protruding outside the
southwestern radio border of the remnant, which is somewhat similar to the
jet-like Si structure found in the famous SNR Cas A. This feature may possibly
be the debris of the jet of ejecta which implies an asymmetrical supernova
explosion of a massive progenitor star.Comment: 9 pages, 4 embedded figures, Chinese Journal of Astronomy and
Astrophysics (ChJAA), in pres
Multiple conducting carriers generated in LaAlO3/SrTiO3 heterostructures
We have found that there is more than one type of conducting carriers
generated in LaAlO3/SrTiO3 heterostructures by comparing the sheet carrier
density and mobility from optical transmission spectroscopy with those from
dc-transport measurements. When multiple types of carriers exist, optical
characterization dominantly reflects the contribution from the high-density
carriers whereas dc-transport measurements may exaggerate the contribution of
the high-mobility carriers even though they are present at low-density. Since
the low-temperature mobilities determined by dc-transport in the LaAlO3/SrTiO3
heterostructures are much higher than those extracted by optical method, we
attribute the origin of high-mobility transport to the low-density conducting
carriers.Comment: 3 figures, supplemental materia
Relativistic Hydrodynamic Cosmological Perturbations
Relativistic cosmological perturbation analyses can be made based on several
different fundamental gauge conditions. In the pressureless limit the variables
in certain gauge conditions show the correct Newtonian behaviors. Considering
the general curvature () and the cosmological constant () in the
background medium, the perturbed density in the comoving gauge, and the
perturbed velocity and the perturbed potential in the zero-shear gauge show the
same behavior as the Newtonian ones in general scales. In the first part, we
elaborate these Newtonian correspondences. In the second part, using the
identified gauge-invariant variables with correct Newtonian correspondences, we
present the relativistic results with general pressures in the background and
perturbation. We present the general super-sound-horizon scale solutions of the
above mentioned variables valid for general , , and generally
evolving equation of state. We show that, for vanishing , the
super-sound-horizon scale evolution is characterised by a conserved variable
which is the perturbed three-space curvature in the comoving gauge. We also
present equations for the multi-component hydrodynamic situation and for the
rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
Solution of Ordinary Differential Equations in Gradient-Based Multidisciplinary Design Optimization
A gradient-based approach to multidisciplinary design optimization enables efficient scalability to large numbers of design variables. However, the need for derivatives causes difficulties when integrating ordinary differential equations (ODEs) in models. To simplify this, we propose the use of the general linear methods framework, which unifies all Runge-Kutta and linear multistep methods. This approach enables rapid implementation of integration methods without the need to differentiate each one, even in a gradient-based optimization context. We also develop a new parallel time integration algorithm that enables vectorization across time steps. We present a set of benchmarking results using a stiff ODE, a non-stiff nonlinear ODE, and an orbital dynamics ODE, and compare integration methods. In a modular gradient-based multidisciplinary design optimization context, we find that the new parallel time integration algorithm with high-order implicit methods, especially Gauss-Legendre collocation, is the best choice for a broad range of problems
Non-abelian dynamics in first-order cosmological phase transitions
Bubble collisions in cosmological phase transitions are explored, taking the
non-abelian character of the gauge fields into account. Both the QCD and
electroweak phase transitions are considered. Numerical solutions of the field
equations in several limits are presented.Comment: 8 pages, 2 figures. Contribution to the CosPA 2003 Cosmology and
Particle Astrophysics Symposium. Typos correcte
Third order perturbations of a zero-pressure cosmological medium: Pure general relativistic nonlinear effects
We consider a general relativistic zero-pressure irrotational cosmological
medium perturbed to the third order. We assume a flat Friedmann background but
include the cosmological constant. We ignore the rotational perturbation which
decays in expanding phase. In our previous studies we discovered that, to the
second-order perturbation, except for the gravitational wave contributions, the
relativistic equations coincide exactly with the previously known Newtonian
ones. Since the Newtonian second-order equations are fully nonlinear, any
nonvanishing third and higher order terms in the relativistic analyses are
supposed to be pure relativistic corrections. In this work we derive such
correction terms appearing in the third order. Continuing our success in the
second-order perturbations we take the comoving gauge. We discover that the
third-order correction terms are of -order higher than the second-order
terms where is a gauge-invariant combination related to the
three-space curvature perturbation in the comoving gauge; compared with the
Newtonian potential we have to the linear
order. Therefore, the pure general relativistic effects are of -order
higher than the Newtonian ones. The corrections terms are independent of the
horizon scale and depend only on the linear order gravitational potential
perturbation strength. From the temperature anisotropy of cosmic microwave
background we have . Therefore, our present result reinforces our
previous important practical implication that near current era one can use the
large-scale Newtonian numerical simulation more reliably even as the simulation
scale approaches near the horizon.Comment: 9 pages, no figur
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