294,144 research outputs found
Numerical procedure for three-dimensional hypersonic viscous flow over aerobrake configuration
A numerical method, which is simpler and more efficient than others currently in use, is proposed for the computation of the full viscous flow over an aerobrake body in hypersonic stream at high altitude. It treats the shock layer surrounding the blunt forebody and the near wake behind the base simultaneously by formulating the Navier-Stokes equations in conformal and azimuthal-angle coordinates. The computational domain is confined by the body wall, outflow surface and the shock, which is adjusted along the coordinate normal to the wall in the course of iterations. Because of the optimal grid and a well developed alternating direction implicit factorization technique for the governing equations, reasonably accurate results can be obtained with a 28 x 36 x 7 grid and 400 time-marching iterations. Excellent agreement of shock location is found between the present result and the schlieren photograph. Details of the base flow and shear layer impingement on the cylindrical aft body are presented for an adiabatic wall case
A 3-dimensional Navier-Stokes-Euler code for blunt-body flow computations
The shock-layer flowfield is obtained with or without viscous and heat-conducting dissipations from the conservative laws of fluid dynamics equations using a shock-fitting implicity finite-difference technique. The governing equations are cast in curvilinear-orthogonal coordinates and transformed to the domain between the shock and the body. Another set of equations is used for the singular coordinate axis, which, together with a cone generator away from the stagnation point, encloses the computation domain. A time-dependent alternating direction implicit factorization technique is applied to integrate the equations with local-time increment until a steady solution is reached. The shock location is updated after the flowfield computation, but the wall conditions are implemented into the implicit procedure. Innovative procedures are introduced to define the initial flowfield, to treat both perfect and equilibrium gases, to advance the solution on a coarse-to-fine grid sequence, and to start viscous flow computations from their corresponding inviscid solutions. The results are obtained from a grid no greater than 28 by 18 by 7 and converged within 300 integration steps. They are of sufficient accuracy to start parabolized Navier-Stokes or Euler calculations beyond the nose region, to compare with flight and wind-tunnel data, and to evaluate conceptual designs of reentry spacecraft
Monolayer protection for eletrochemical migration control in silver nanocomposite
©2006 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/89/112112/1DOI:10.1063/1.2353813The authors introduced an effective approach of using monolayer-protected silver nanoparticles to reduce silver migration for electronic device interconnect applications. Formation of surface complex between the carboxylate anion and surface silver ion reduces the solubility and diffusivity significantly of migration components and therefore contributes to effective migration control. A fundamental understanding of the mechanism of silver migration control was conducted by studying the current-voltage relationships of the nanocomposites with a migration model. The control of silver migration enables the application of the silver composites in fine pitch and high performance electronic device interconnects
QCD resummation for light-particle jets
We construct an evolution equation for the invariant-mass distribution of
light-quark and gluon jets in the framework of QCD resummation. The solution of
the evolution equation exhibits a behavior consistent with Tevatron CDF data:
the jet distribution vanishes in the small invariant-mass limit, and its peak
moves toward the high invariant-mass region with the jet energy. We also
construct an evolution equation for the energy profile of the light-quark and
gluon jets in the similar framework. The solution shows that the energy
accumulates faster within a light-quark jet cone than within a gluon jet cone.
The jet energy profile convoluted with hard scattering and parton distribution
functions matches well with the Tevatron CDF and the large-hadron-collider
(LHC) CMS data. Moreover, comparison with the CDF and CMS data implies that
jets with large (small) transverse momentum are mainly composed of the
light-quark (gluon) jets. At last, we discuss the application of the above
solutions for the light-particle jets to the identification of highly-boosted
heavy particles produced at LHC.Comment: 22 pages, 13 figure
X-Ray Spectral Variability in Cygnus X-1
Spectral variability in different energy bands of X-rays from Cyg X-1 in
different states is studied with RXTE observations and time domain approaches.
In the hard tail of energy spectrum above keV, average peak aligned
shots are softer than the average steady emission and the hardness ratio
decreases when the flux increases during a shot for all states. In regard to a
soft band lower keV, the hardness in the soft state varies in an
opposite way: it peaks when the flux of the shot peaks. For the hard and
transition states, the hardness ratio in respect to a soft band during a shot
is in general lower than that of the steady component and a sharp rise is
observed at about the shot peak. For the soft state, the correlation
coefficient between the intensity and hardness ratio in the hard tail is
negative and decreases monotonically as the timescale increases from 0.01 s to
50 s, which is opposite to that in regard to a soft band. For the hard and
transition states, the correlation coefficients are in general negative and
have a trend of decrease with increasing timescale.Comment: 14 pages, 3 figures, accepted by Ap
Evaluation of ASTER GDEM ver2 using GPS measurements and SRTM ver4.1 in China
The freely available ASTER GDEM ver2 was released by NASA and METI on October 17, 2011. As one of the most complete high resolution digital topographic data sets of the world to date, the ASTER GDEM covers land surfaces between 83°N and 83°S at a spatial resolution of 1 arc-second and will be a useful product for many applications, such as relief analysis, hydrological studies and radar interferometry. The stated improvements in the second version of ASTER GDEM benefit from finer horizontal resolution, offset adjustment and water body detection in addition to new observed ASTER scenes. This study investigates the absolute vertical accuracy of the ASTER GDEM ver2 at five study sites in China using ground control points (GCPs) from high accuracy GPS benchmarks, and also using a DEM-to-DEM comparison with the Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) SRTM DEM (Version 4.1). And then, the results are separated into GlobCover land cover classes to derive the spatial pattern of error. It is demonstrated that the RMSE (19m) and mean (-13m) values of ASTER GDEM ver2 against GPS-GCPs in the five study areas is lower than its first version ASTER GDEM ver1 (26m and -21m) as a result of the adjustment of the elevation offsets in the new version. It should be noted that the five study areas in this study are representative in terms of terrain types and land covers in China, and even for most of mid-latitude zones. It is believed that the ASTER GDEM offers a major alternative in accessibility to high quality elevation data
Ratcheting Heat Flux against a Thermal Bias
Merely rocking the temperature in one heat bath can direct a steady heat flux
from cold to hot against a non-zero thermal bias in stylized nonlinear lattice
junctions that are sandwiched between two heat baths. Likewise, for an average
zero-temperature difference between the two contacts a net, ratchet-like heat
flux emerges. Computer simulations show that this very heat flux can be
controlled and reversed by suitably tailoring the frequency ( 100
MHz) of the alternating temperature field.Comment: 5 pages, 6 figure
- …