75,820 research outputs found
Integrated design optimization research and development in an industrial environment
An overview is given of a design optimization project that is in progress at the GE Research and Development Center for the past few years. The objective of this project is to develop a methodology and a software system for design automation and optimization of structural/mechanical components and systems. The effort focuses on research and development issues and also on optimization applications that can be related to real-life industrial design problems. The overall technical approach is based on integration of numerical optimization techniques, finite element methods, CAE and software engineering, and artificial intelligence/expert systems (AI/ES) concepts. The role of each of these engineering technologies in the development of a unified design methodology is illustrated. A software system DESIGN-OPT has been developed for both size and shape optimization of structural components subjected to static as well as dynamic loadings. By integrating this software with an automatic mesh generator, a geometric modeler and an attribute specification computer code, a software module SHAPE-OPT has been developed for shape optimization. Details of these software packages together with their applications to some 2- and 3-dimensional design problems are described
Two and three-dimensional shock-shock interactions on the blunt leading edges of the hypersonic inlets
The effect of shock impingement on the blunt leading edges of the top and sidewall compression type inlet of a scramjet engine is studied numerically. The impinging shock is caused by the vehicle forebody. The interaction of this forebody shock with the inlet leading edge shock results in a very complex flowfield containing local regions of high pressure and intense heating. This complex flowfield in calculated by solving the Navier-Stokes equations using a finite volume flux splitting technique due to van Leer. To resolve the finer details of the flow structure as well as to predict the surface heat transfer accurately, adaptive grid technique is used in the analysis. Results of the present numerical study are compared with available experimental results
Non-Equilibrium Production of Photons via \pi^0\to 2\gamma in DCC's
We study production of photons via the non-equilibrium relaxation of a
Disoriented Chiral Condensate with the chiral order parameter having a large
initial amplitude along the \pi^0 direction. Assuming the validity of the low
energy coupling of the neutral pion to photons via the U_A(1) anomalous vertex,
we find that for large initial amplitudes along the \pi^0 direction, photon
production is enhanced by parametric amplification. These processes are
non-perturbative with a large contribution during the non-equilibrium stages of
the evolution and result in a distinct distribution of the produced photons and
a polarization asymmetry. For initial amplitudes of the \pi^0 component of the
order parameter between 200-400 MeV, corresponding to energy densities between
1-12 GeV/fm^3 we find a peak in the photon distribution at energies between
\approx 300 -600 MeV. We also find polarization asymmetries typically between
5-10%. We discuss the potential experimental impact of these results as well as
the problems associated with its detection.Comment: 36 pages, 14 figures, uses revte
The propensity of molecules to spatially align in intense light fields
The propensity of molecules to spatially align along the polarization vector
of intense, pulsed light fields is related to readily-accessible parameters
(molecular polarizabilities, moment of inertia, peak intensity of the light and
its pulse duration). Predictions can now be made of which molecules can be
spatially aligned, and under what circumstances, upon irradiation by intense
light. Accounting for both enhanced ionization and hyperpolarizability, it is
shown that {\it all} molecules can be aligned, even those with the smallest
static polarizability, when subjected to the shortest available laser pulses
(of sufficient intensity).Comment: 8 pages, 4 figures, to be submitted to PR
CP violating anomalous top-quark couplings at the LHC
We study the T odd correlations induced by CP violating anomalous top-quark
couplings at both production and decay level in the process gg --> t t_bar -->
(b mu+ nu_mu) (b_bar mu- nu_mu_bar). We consider several counting asymmetries
at the parton level and find the ones with the most sensitivity to each of
these anomalous couplings at the LHC.Comment: 14 LaTeX Pages, 1 EPS Figure, minor typos correcte
Evolution of Supermassive Black Hole Binary and Acceleration of Jet Precession in Galactic Nuclei
Supermassive black hole binary (SMBHB) is expected with the hierarchical
galaxy formation model. Currently, physics processes dominating the evolution
of a SMBHB are unclear. An interesting question is whether we could
observationally determine the evolution of SMBHB and give constraints on the
physical processes. Jet precession have been observed in many AGNs and
generally attributed to disk precession. In this paper we calculate the time
variation of jet precession and conclude that jet precession is accelerated in
SMBHB systems but decelerated in others. The acceleration of jet precession
is related to jet precession timescale and
SMBHB evolution timescale , . Our calculations based on the models
for jet precession and SMBHB evolution show that can be as
high as about with a typical value -0.2 and can be easily detected. We
discussed the differential jet precession for NGC1275 observed in the
literature. If the observed rapid acceleration of jet precession is true, the
jet precession is due to the orbital motion of an unbound SMBHB with mass ratio
. When jets precessed from the ancient bubbles to the currently
active jets, the separation of SMBHB decrease from about to
with an averaged decreasing velocity and evolution timescale . However, if we assume a steady jet precession for many cycles,
the observations implies a hard SMBHB with mass ratio and
separation .Comment: 29 pages, no figure, Accepted for publication in Ap
Temperature independent band structure of WTe2 as observed from ARPES
Extremely large magnetoresistance (XMR), observed in transition metal
dichalcogendies, WTe, has attracted recently a great deal of research
interests as it shows no sign of saturation up to the magnetic field as high as
60 T, in addition to the presence of type-II Weyl fermions. Currently, there
has been a lot of discussion on the role of band structure changes on the
temperature dependent XMR in this compound. In this contribution, we study the
band structure of WTe using angle-resolved photoemission spectroscopy
(ARPES) and first-principle calculations to demonstrate that the temperature
dependent band structure has no substantial effect on the temperature dependent
XMR as our measurements do not show band structure changes on increasing the
sample temperature between 20 and 130 K. We further observe an electronlike
surface state, dispersing in such a way that it connects the top of bulk
holelike band to the bottom of bulk electronlike band. Interestingly, similar
to bulk states, the surface state is also mostly intact with the sample
temperature. Our results provide invaluable information in shaping the
mechanism of temperature dependent XMR in WTe.Comment: 7 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1705.0721
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