26,509 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
Effects of Solution, Soil and Sand Cultures on Nodulation and Growth of Phasey Bean
Plants of phasey bean (Macroptilium lathyroides cv. Murray) were grown in nitrogen-free
nutrient solution, sod, or sand culture in a naturally-Nt glasshouse. Nodulation, dry matter accumulation in plant parts, and seed yields were assessed. Partitioning of symbiotic nitrogen into various
plant parts during vegetative and reproductive growth stages was also determined. In all culture
media, nodule number and size increased with plant age but the rate of increase was generally greater
in solution than in the other cultures. In sand culture, the dry weight per nodule and per plant, and
plant growth were significantly suppressed. Although tap root elongation was consistently better in
solution than soil or sand culture, leaf development and dry matter accumulation in roots and stems
were enhanced by solution culture only during flowering and fruiting stage. Seed yields were significantly
increased by solution culture, an effect apparently associated with increased symbiotic nitrogen
fixation. During vegetative growth, nitrogen accumulated largely in the leaves and stems but pods
were major sinks of nitrogen during the reproductive growth stage. The benefits and applications of
solution culture in the study of nodule development and collection of root samples for acetylene reduction
assays are discussed
Numerical study of spin quantum Hall transitions in superconductors with broken time-reversal symmetry
We present results of numerical studies of spin quantum Hall transitions in
disordered superconductors, in which the pairing order parameter breaks
time-reversal symmetry. We focus mainly on p-wave superconductors in which one
of the spin components is conserved. The transport properties of the system are
studied by numerically diagonalizing pairing Hamiltonians on a lattice, and by
calculating the Chern and Thouless numbers of the quasiparticle states. We find
that in the presence of disorder, (spin-)current carrying states exist only at
discrete critical energies in the thermodynamic limit, and the spin-quantum
Hall transition driven by an external Zeeman field has the same critical
behavior as the usual integer quantum Hall transition of non-interacting
electrons. These critical energies merge and disappear as disorder strength
increases, in a manner similar to those in lattice models for integer quantum
Hall transition.Comment: 9 pages, 9 figure
Global Cosmological Parameters Determined Using Classical Double Radio Galaxies
A sample of 20 powerful extended radio galaxies with redshifts between zero
and two were used to determine constraints on global cosmological parameters.
Data for six radio sources were obtained from the VLA archive, analyzed, and
combined with the sample of 14 radio galaxies used previously by Guerra & Daly
to determine cosmological parameters. The results are consistent with our
previous results, and indicate that the current value of the mean mass density
of the universe is significantly less than the critical value. A universe with
of unity is ruled out at 99.0% confidence, and the best fitting
values of in matter are and
assuming zero space curvature and zero cosmological
constant, respectively. Note that identical results obtain when the low
redshift bin, which includes Cygnus A, is excluded; these results are
independent of whether the radio source Cygnus A is included. The method does
not rely on a zero-redshift normalization.
The radio properties of each source are also used to determine the density of
the gas in the vicinity of the source, and the beam power of the source. The
six new radio sources have physical characteristics similar to those found for
the original 14 sources. The density of the gas around these radio sources is
typical of gas in present day clusters of galaxies. The beam powers are
typically about .Comment: 39 pages includes 21 figures, accepted to Ap
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
Classification of Overlapped Audio Events Based on AT, PLSA, and the Combination of Them
Audio event classification, as an important part of Computational Auditory Scene Analysis, has attracted much attention. Currently, the classification technology is mature enough to classify isolated audio events accurately, but for overlapped audio events, it performs much worse. While in real life, most audio documents would have certain percentage of overlaps, and so the overlap classification problem is an important part of audio classification. Nowadays, the work on overlapped audio event classification is still scarce, and most existing overlap classification systems can only recognize one audio event for an overlap. In this paper, in order to deal with overlaps, we innovatively introduce the author-topic (AT) model which was first proposed for text analysis into audio classification, and innovatively combine it with PLSA (Probabilistic Latent Semantic Analysis). We propose 4 systems, i.e. AT, PLSA, AT-PLSA and PLSA-AT, to classify overlaps. The 4 proposed systems have the ability to recognize two or more audio events for an overlap. The experimental results show that the 4 systems perform well in classifying overlapped audio events, whether it is the overlap in training set or the overlap out of training set. Also they perform well in classifying isolated audio events
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