9,957 research outputs found
Nonlinear ER effects in an ac applied field
The electric field used in most electrorheological (ER) experiments is
usually quite high, and nonlinear ER effects have been theoretically predicted
and experimentally measured recently. A direct method of measuring the
nonlinear ER effects is to examine the frequency dependence of the same
effects. For a sinusoidal applied field, we calculate the ac response which
generally includes higher harmonics. In is work, we develop a multiple image
formula, and calculate the total dipole moments of a pair of dielectric
spheres, embedded in a nonlinear host. The higher harmonics due to the
nonlinearity are calculated systematically.Comment: Presented at Conference on Computational Physics (CCP2000), held at
Gold Coast, Australia from 3-8, December 200
Searching for Dark Matter Signals in the Left-Right Symmetric Gauge Model with CP Symmetry
We investigate singlet scalar dark matter (DM) candidate in a left-right
symmetric gauge model with two Higgs bidoublets (2HBDM) in which the
stabilization of the DM particle is induced by the discrete symmetries P and
CP. According to the observed DM abundance, we predict the DM direct and
indirect detection cross sections for the DM mass range from 10 GeV to 500 GeV.
We show that the DM indirect detection cross section is not sensitive to the
light Higgs mixing and Yukawa couplings except the resonance regions. The
predicted spin-independent DM-nucleon elastic scattering cross section is found
to be significantly dependent on the above two factors. Our results show that
the future DM direct search experiments can cover the most parts of the allowed
parameter space. The PAMELA antiproton data can only exclude two very narrow
regions in the 2HBDM. It is very difficult to detect the DM direct or indirect
signals in the resonance regions due to the Breit-Wigner resonance effect.Comment: 24 pages, 8 figures. minor changes and a reference added, published
in Phys. Rev.
BOOST: A fast approach to detecting gene-gene interactions in genome-wide case-control studies
Gene-gene interactions have long been recognized to be fundamentally
important to understand genetic causes of complex disease traits. At present,
identifying gene-gene interactions from genome-wide case-control studies is
computationally and methodologically challenging. In this paper, we introduce a
simple but powerful method, named `BOolean Operation based Screening and
Testing'(BOOST). To discover unknown gene-gene interactions that underlie
complex diseases, BOOST allows examining all pairwise interactions in
genome-wide case-control studies in a remarkably fast manner. We have carried
out interaction analyses on seven data sets from the Wellcome Trust Case
Control Consortium (WTCCC). Each analysis took less than 60 hours on a standard
3.0 GHz desktop with 4G memory running Windows XP system. The interaction
patterns identified from the type 1 diabetes data set display significant
difference from those identified from the rheumatoid arthritis data set, while
both data sets share a very similar hit region in the WTCCC report. BOOST has
also identified many undiscovered interactions between genes in the major
histocompatibility complex (MHC) region in the type 1 diabetes data set. In the
coming era of large-scale interaction mapping in genome-wide case-control
studies, our method can serve as a computationally and statistically useful
tool.Comment: Submitte
Impurity resonance states in electron-doped high T_c superconductors
Two scenarios, i.e., the anisotropic s-wave pairing (the s-wave scenario) and
the d-wave pairing coexisting with antiferromagnetism (the coexisting scenario)
have been introduced to understand some of seemingly s-wave like behaviors in
electron doped cuprates. We considered the electronic structure in the presence
of a nonmagnetic impurity in the coexistence scenario. We found that even if
the AF order opens a full gap in quasi-particle excitation spectra, the mid-gap
resonant peaks in local density of states (LDoS) around an impurity can still
be observed in the presence of a d-wave pairing gap. The features of the
impurity states in the coexisting phase are markedly different from the pure AF
or pure d-wave pairing phases, showing the unique role of the coexisting AF and
d-wave pairing orders. On the other hand, it is known that in the pure s-wave
case no mid-gap states can be induced by a nonmagnetic impurity. Therefore we
proposed that the response to a nonmagnetic impurity can be used to
differentiate the two scenarios.Comment: 5 pages, two-column revtex4, 5 figures, author list correcte
Nonlinear ac response of anisotropic composites
When a suspension consisting of dielectric particles having nonlinear
characteristics is subjected to a sinusoidal (ac) field, the electrical
response will in general consist of ac fields at frequencies of the
higher-order harmonics. These ac responses will also be anisotropic. In this
work, a self-consistent formalism has been employed to compute the induced
dipole moment for suspensions in which the suspended particles have nonlinear
characteristics, in an attempt to investigate the anisotropy in the ac
response. The results showed that the harmonics of the induced dipole moment
and the local electric field are both increased as the anisotropy increases for
the longitudinal field case, while the harmonics are decreased as the
anisotropy increases for the transverse field case. These results are
qualitatively understood with the spectral representation. Thus, by measuring
the ac responses both parallel and perpendicular to the uniaxial anisotropic
axis of the field-induced structures, it is possible to perform a real-time
monitoring of the field-induced aggregation process.Comment: 14 pages and 4 eps figure
A climatology of the F-layer equivalent winds derived from ionosonde measurements over two decades along the 120°-150°E sector
International audienceThe vertical equivalent winds (VEWs) at the F-layer are analyzed along the 120°-150°E longitude sector with an emphasis on their latitudinal dependence. The VEWs are derived from the monthly median data of fourteen ionosonde stations over two decades. The results show that the VEWs have considerable dependences on the magnetic latitude with an approximate symmetry about the magnetic equator. They are mostly controlled by the electric field drifts in the magnetic equatorial region, and shift to be mostly contributed by neutral winds at mid-latitudes. The relative contribution of the two dynamic factors is regulated by the magnetic dip in addition to their own magnitudes. The VEWs generally have opposite directions and different magnitudes between lower and higher latitudes. At solar minimum, the magnitudes of VEWs are only between -20 and 20m/s at lower latitudes, while at higher latitudes they tend to increase with latitudes, typically having magnitudes between 20-40m/s. At solar maximum, the VEWs are reduced by about 10-20m/s in magnitudes during some local times at higher latitudes. A tidal analysis reveals that the relative importance of major tidal components is also different between lower and higher latitudes. The VEWs also depend on local time, season and solar activity. At higher latitudes, the nighttime VEWs have larger magnitude during post-midnight hours and so do the daytime ones before midday. The VEWs tend to have an inverse relationship with solar activity not only at night, but also by day, which is different from the meridional winds predicted by the HWM93 model. The latitudinal dependence of VEWs has two prevailing trends: one is a maximum at the highest latitudes (as far as the latitudes concerned in the present work); the other is a mid-latitude maximum. These two latitudinal trends are mostly dependent on season, while they depend relatively weakly on local time and solar activity. The latitudinal gradients of VEWs also show a tendency of a mid-latitude maximum, except that there are much stronger latitudinal gradients at southern higher mid-latitudes in some seasons. The gradients during daytime are much smaller at solar maximum than minimum, whereas they are generally comparable at night under both solar activity levels
DC-conductivity of a suspension of insulating particles with internal rotation
We analyse the consequences of Quincke rotation on the conductivity of a
suspension. Quincke rotation refers to the spontaneous rotation of insulating
particles dispersed in a slightly conducting liquid and subject to a high DC
electric field: above a critical field, each particle rotates continuously
around itself with an axis pointing in any direction perpendicular to the DC
field. When the suspension is subject to an electric field lower than the
threshold one, the presence of insulating particles in the host liquid
decreases the bulk conductivity since the particles form obstacles to ion
migration. But for electric fields higher than the critical one, the particles
rotate and facilitate ion migration: the effective conductivity of the
suspension is increased. We provide a theoretical analysis of the impact of
Quincke rotation on the apparent conductivity of a suspension and we present
experimental results obtained with a suspension of PMMA particles dispersed in
weakly conducting liquids
Comparison of Two Ventilation Systems in a Chinese Commercial Kitchen
A numerical simulation of an indoor thermal environment in a Chinese commercial kitchen has been carried out using indoor zero-equation turbulence model. Two different ventilation systems in a Chinese commercial kitchen have been simulated. The results calculated for two different models show the airflow, temperature distribution and human thermal comfort index-PMV and PPD value. The simulation results indicate that both methods are capable of enhancing the capture and containment performance of cooking effluent effectively. Under the first condition, not only is unnecessary cooling load reduced and energy consumption of the air conditioning system economized, but a perceived thermal comfort environment can be provided. However, the supply air velocity and air temperature of the spot diffuser are restricted. In contrast, the perceived level of thermal comfort is not improved under the second circumstance. Further, the energy consumption of this case is higher than the former. Finally, the indoor thermal environmental properties have been analyzed
- …