1,665 research outputs found
Revealing A Head-on Major Merger in the Nearby NGC 6338 Group with Chandra and VLA observations
By analyzing the Chandra archival data of the nearby NGC 6338 galaxy group,
we identify two X-ray bright clumps (N-clump and S-clump) within the central
100 kpc, and detect an arc-like X-ray brightness discontinuity at the south
boundary of the N-clump, which is defined as a cold front with a gas flow Mach
number of M<0.8. Furthermore, at the north-east boundary of the S-clump
(dominated by galaxy NGC 6338) another X-ray edge is detected that corresponds
to a weaker cold front. Therefore, the two clumps are approaching each other
approximately from opposite directions, and the group is undergoing a head-on
collision that is in a stage of pre-core passage. This merger scenario is also
supported by the study of the line-of-sight velocity distribution of the group
member galaxies. The merger mass ratio is about 1:1.8 as estimated from the
central gas temperature of the two clumps, which suggests the merger is most
likely to be a major merger. We also analyze the VLA 1.4 and 4.9 GHz radio
data, but we do not detect any extended radio emission that is associated with
the merger.Comment: Accepted by Ap
Exploring the total Galactic extinction with SDSS BHB stars
Aims: We used 12,530 photometrically-selected blue horizontal branch (BHB)
stars from the Sloan Digital Sky Survey (SDSS) to estimate the total extinction
of the Milky Way at the high Galactic latitudes, and in each line
of sight. Methods: A Bayesian method was developed to estimate the reddening
values in the given lines of sight. Based on the most likely values of
reddening in multiple colors, we were able to derive the values of and
.
Results: We selected 94 zero-reddened BHB stars from seven globular clusters
as the template. The reddening in the four SDSS colors for the northern
Galactic cap were estimated by comparing the field BHB stars with the template
stars. The accuracy of this estimation is around 0.01\,mag for most lines of
sight. We also obtained to be around 2.40 and map within
an uncertainty of 0.1\,mag. The results, including reddening values in the four
SDSS colors, , and in each line of sight, are released on line. In
this work, we employ an up-to-date parallel technique on GPU card to overcome
time-consuming computations. We plan to release online the C++ CUDA code used
for this analysis.
Conclusions: The extinction map derived from BHB stars is highly consistent
with that from Schlegel, Finkbeiner & Davis(1998). The derived is around
2.40. The contamination probably makes the be larger.Comment: 16 pages, 13 figures, 4 tables, accepted for publication in A&
Three-Dimensional Modeling of the Plasma Arc in Arc Welding
Most previous three-dimensional modeling on gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool dynamics and assumes the two-dimensional axisymmetric Gaussian distributions for plasma arc pressure and heat flux. In this article, a three-dimensional plasma arc model is developed, and the distributions of velocity, pressure, temperature, current density, and magnetic field of the plasma arc are calculated by solving the conservation equations of mass, momentum, and energy, as well as part of the Maxwell\u27s equations. This three-dimensional model can be used to study the nonaxisymmetric plasma arc caused by external perturbations such as an external magnetic field. It also provides more accurate boundary conditions when modeling the weld pool dynamics. The present work lays a foundation for true three-dimensional comprehensive modeling of GTAW and GMAW including the plasma arc, weld pool, and/or electrode
Three-dimensional numerical study of flow characteristic and membrane fouling evolution in an enzymatic membrane reactor
In order to enhance the understanding of membrane fouling mechanism, the
hydrodynamics of granular flow in a stirred enzymatic membrane reactor was
numerically investigated in the present study. A three-dimensional Euler-Euler
model, coupled with k-e mixture turbulence model and drag function for
interphase momentum exchange, was applied to simulate the two-phase
(fluid-solid) turbulent flow. Numerical simulations of single- or two-phase
turbulent flow under various stirring speed were implemented. The numerical
results coincide very well with some published experimental data. Results for
the distributions of velocity, shear stress and turbulent kinetic energy were
provided. Our results show that the increase of stirring speed could not only
enlarge the circulation loops in the reactor, but it can also increase the
shear stress on the membrane surface and accelerate the mixing process of
granular materials. The time evolution of volumetric function of granular
materials on the membrane surface has qualitatively explained the evolution of
membrane fouling.Comment: 10 panges, 8 figure
4-{4-Methyl-2-[(methÂyl)(2-methylÂphenÂyl)amino]-1,3-thiaÂzol-5-yl}-N-(3-methylÂphenÂyl)pyrimidin-2-amine
In the title compound, C23H23N5S, the thiaÂzole ring and pyrimidine ring are almost coplanar, making a dihedral angle of 4.02 (9)°. in the crystal, weak interÂmolecular N—H⋯N interÂactions link pairs of molecules into centrosymmetric dimers
A Comprehensive 3-D Model on Gas Metal Arc Welding
A unified comprehensive model was developed to simulate the transport phenomena occurring during the gas metal arc welding process. An interactive coupling between arc plasma; melting of a continuously fed electrode; droplet formation, detachment, transfer, and impingement onto the workpiece under the influences of several competing forces including gravity, electromagnetic force, arc pressure, plasma shear stress, and surface tension; and weld pool dynamics all were considered. The transient distributions of current density, arc temperature, arc pressure, melt flow velocity and melt temperature in the droplet and in the weld pool were all calculated. Based on the unified model, the following investigations were conducted: 1) the effect of welding current on droplet generation, especially the use of pulsed current to achieve the one-droplet-per-pulse (ODPP) metal transfer; 2) the determination of dynamically stabled wire feed speeds for given welding conditions; 3) the effects of surface active elements (Marangoni effect) on the weld pool flow and solidified weld profile; 4) the fundamental mechanisms leading to the formation of ripples; 5) the issues associated with the beginning and the end of the welding (limited penetration and the formations of crater); 6) the deflection of arc plasma by an external magnetic field
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