6,298 research outputs found
Radiation Transfer in the Cavity and Shell of Planetary Nebulae
We develop an approximate analytical solution for the transfer of
line-averaged radiation in the hydrogen recombination lines for the ionized
cavity and molecular shell of a spherically symmetric planetary nebula. The
scattering problem is treated as a perturbation, using a mean intensity derived
from a scattering-free solution. The analytical function was fitted to Halpha
and Hbeta data from the planetary nebula NGC6537. The position of the maximum
in the intensity profile produced consistent values for the radius of the
cavity as a fraction of the radius of the dusty nebula: 0.21 for Halpha and
0.20 for Hbeta. Recovered optical depths were broadly consistent with observed
optical extinction in the nebula, but the range of fit parameters in this case
is evidence for a clumpy distribution of dust.Comment: MNRAS accepted; 10 Fig
A Microscopic Mechanism for Muscle's Motion
The SIRM (Stochastic Inclined Rods Model) proposed by H. Matsuura and M.
Nakano can explain the muscle's motion perfectly, but the intermolecular
potential between myosin head and G-actin is too simple and only repulsive
potential is considered. In this paper we study the SIRM with different complex
potential and discuss the effect of the spring on the system. The calculation
results show that the spring, the effective radius of the G-actin and the
intermolecular potential play key roles in the motion. The sliding speed is
about calculated from the model which well agrees with
the experimental data.Comment: 9 pages, 6 figure
Momentum space metric, non-local operator, and topological insulators
Momentum space of a gapped quantum system is a metric space: it admits a
notion of distance reflecting properties of its quantum ground state. By using
this quantum metric, we investigate geometric properties of momentum space. In
particular, we introduce a non-local operator which represents distance square
in real space and show that this corresponds to the Laplacian in curved
momentum space, and also derive its path integral representation in momentum
space. The quantum metric itself measures the second cumulant of the position
operator in real space, much like the Berry gauge potential measures the first
cumulant or the electric polarization in real space. By using the non-local
operator and the metric, we study some aspects of topological phases such as
topological invariants, the cumulants and topological phase transitions. The
effect of interactions to the momentum space geometry is also discussed.Comment: 13 pages, 4 figure
Effect of random disorder and spin frustration on the reentrant spin glass phase and ferromagnetic phase in stage-2 Cu_{0.93}Co_{0.07}Cl_{2} graphite intercalation compound near the multicritical point
Stage-2 CuCoCl graphite intercalation compound
magnetically behaves like a reentrant ferromagnet near the multicritical point
(). It undergoes two magnetic phase transitions at
( K) and ( K). The static
and dynamic nature of the ferromagnetic and reentrant spin glass phase has been
studied using DC and AC magnetic susceptibility. Characteristic memory
phenomena of the DC susceptibility are observed at and . The
nonlinear AC susceptibility has a positive local maximum at
, and a negative local minimum at . The relaxation time
between and shows a critical slowing down: with and sec. The
influence of the random disorder on the critical behavior above is
clearly observed: , , and . The
exponent of is far from that of 3D Heisenberg model.Comment: 15 pages, 16 figures, submitted to Phys. Rev.
Self-assembled ErAs islands in GaAs for optical-heterodyne THz generation
We report photomixer devices fabricated on a material consisting of self-assembled ErAs islands in GaAs, which is grown by molecular beam epitaxy. The devices perform comparably and provide an alternative to those made from low-temperature-grown GaAs. The photomixer's frequency response demonstrates that the material is a photoconductor with subpicosecond response time, in agreement with time-resolved differential reflectance measurements. The material also provides the other needed properties such as high photocarrier mobility and high breakdown field, which exceeds 2×10^5 V/cm. The maximum output power before device failure at frequencies of 1 THz was of order 0.1 µW. This material has the potential to allow engineering of key photomixer properties such as the response time and dark resistance
Dislocation model for aseismic fault slip in the transverse ranges of Southern California
Geodetic data at a plate boundary can reveal the pattern of subsurface displacements that accompany plate motion. These displacements are modelled as the sum of rigid block motion and the elastic effects of frictional interaction between blocks. The frictional interactions are represented by uniform dislocation on each of several rectangular fault patches. The block velocities and fault parameters are then estimated from geodetic data. Bayesian inversion procedure employs prior estimates based on geological and seismological data. The method is applied to the Transverse Ranges, using prior geological and seismological data and geodetic data from the USGS trilateration networks. Geodetic data imply a displacement rate of about 20 mm/yr across the San Andreas Fault, while the geologic estimates exceed 30 mm/yr. The prior model and the final estimates both imply about 10 mm/yr crustal shortening normal to the trend of the San Andreas Fault. Aseismic fault motion is a major contributor to plate motion. The geodetic data can help to identify faults that are suffering rapid stress accumulation; in the Transverse Ranges those faults are the San Andreas and the Santa Susana
Next-to-next-to-leading logarithmic threshold resummation for deep-inelastic scattering and the Drell-Yan process
The soft-gluon resummation exponents G^N in moment space are investigated for
the quark coefficient functions in deep-inelastic structure functions and the
quark-antiquark contribution to the Drell-Yan cross section dsigma/dM.
Employing results from two- and three-loop calculations we obtain the
next-to-next-to-leading logarithmic terms alpha_s (alpha_s ln N)^n of G^N to
all orders in the strong coupling constant alpha_s. These new contributions
facilitate a reliable assessment of the numerical effect and the stability of
the large-N expansion.Comment: 9 pages, LaTeX, 2 eps-figure
Anticardiolipin Antibodies Recognize β(2)-Glycoprotein I Structure Altered by Interacting with an Oxygen Modified Solid Phase Surface
Anticardiolipin antibodies (aCL) derived from the sera of individuals exhibiting the antiphospholipid syndrome (APS) directly bind to beta(2)-glycoprotein I (beta(2)-GPI), which is adsorbed to an oxidized polystyrene surface. Oxygen atoms were introduced on a polystyrene surface by irradiation with electron or gamma-ray radiation. X-ray photoelectron spectroscopy revealed the irradiated surfaces were oxidized to generate C-O and C=O moieties. aCL derived from either APS patients or (NZW x BXSB)F-1 mice bound to beta(2)-GPI coated on the irradiated plates, depending on the radiation dose. Antibody binding to beta(2)-GPI on the irradiated plates was competitively inhibited by simultaneous addition of cardiolipin (CL)-coated latex beads mixed together with beta(2)-GPI but were unaffected by addition of excess beta(2)-GPI, CL micelles, or CL-coated latex beads alone. There was a high correlation between binding values of aCL in sera from 40 APS patients obtained by the anti-beta(2)-GPI enzyme-linked immunosorbent assay (ELISA) using the irradiated plates and those by the beta(2)-GPI-dependent aCL ELISA. Therefore, aCL have specificity for an epitope on beta(2)-GPI. This epitope is expressed by a conformational change occurring when beta(2)-GPI interacts with an oxygen-substituted solid phase surface
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