5,314 research outputs found
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
Submillimeter-Wave Measurements and Analysis of the Ground and ν2 = 1 States of Water
In order to facilitate further studies of water in the interstellar medium, the envelopes of late-type stars, jets, and shocked regions, the frequencies of 17 newly measured H_2 ^(16)O transitions between 0.841 and 1.575 THz are reported. A complete update of the available water line frequencies and a detailed calculation of unmeasured rotational transitions and transition intensities as a function of temperature are presented for the ground and ν_2 = 1 state levels below 3000 cm^(-1) of excitation energy. The new terahertz transitions were measured with a recently developed laser difference frequency spectrometer. Six of these transitions arise from the ν_2 = 1 state, and the other 11 are in the ground state; all have lower state energies from 700 to 1750 cm^(-1) and should be accessible to Stratospheric Observatory For Infrared Astronomy (SOFIA) through the atmosphere. The transitions near 0.850 THz are accessible from the ground with existing receivers. Observations of the newly measured ν_2 = 1 state transitions, which include the 1_(1, 1)-0_(0, 0) fundamental at 1.2057 THz and five other very low J transitions, should provide valuable insights into role played by the ν2 = 1 state in the cooling dynamics of jets, shocks, masers, and strongly infrared-pumped regions. The line list is presented to assist in the planning of observational campaigns with the Far-Infrared Space Telescope (FIRST) and other proposed space missions with which a full suite of water observations can be carried out
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