958 research outputs found
The 2010 MW 6.8 Yushu (Qinghai, China) earthquake: constraints provided by InSAR and body wave seismology
By combining observations from satellite radar, body wave seismology and optical imagery, we have determined the fault segmentation and sequence of ruptures for the 2010 Mw 6.8 Yushu (China) earthquake. We have mapped the fault trace using displacements from SAR image matching, interferometric phase and coherence, and 2.5 m SPOT-5 satellite images. Modeling the event as an elastic dislocation with three segments fitted to the fault trace suggests that the southeast and northwest segments are near vertical, with the central segment dipping 70° to the southwest; slip occurs mainly in the upper 10 km, with a maximum slip of 1.5 m at a depth of 4 km on the southeastern segment. The maximum slip in the top 1 km (i.e., near surface) is up to 1.2 m, and inferred locations of significant surface rupture are consistent with displacements from SAR image matching and field observations. The radar interferograms show rupture over a distance of almost 80 km, much larger than initial seismological and field estimates of the length of the fault. Part of this difference can be attributed to slip on the northwestern segment of the fault being due to an Mw 6.1 aftershock two hours after the main event. The remaining difference can be explained by a non-uniform slip distribution with much of the moment release occurring at depths of less than 10 km. The rupture on the central and southeastern segments of the fault in the main shock propagated at a speed of 2.5 km/s southeastward toward the town of Yushu located at the end of this segment, accounting for the considerable building damage. Strain accumulation since the last earthquake on the fault segment beyond Yushu is equivalent to an Mw 6.5 earthquake
Sufficient stochastic maximum principle in a regime-switching diffusion model
We prove a sufficient stochastic maximum principle for the optimal control of
a regime-switching diffusion model. We show the connection to dynamic
programming and we apply the result to a quadratic loss minimization problem,
which can be used to solve a mean-variance portfolio selection problem
Surface spin-transfer torque and spin-injection effective field in ferromagnetic junctions: Unified theory
We consider theoretically a current flowing perpendicular to interfaces of a
spin-valve type ferromagnetic metallic junction. For the first time an
effective approach is investigated to calculate a simultaneous action of the
two current effects, namely, the nonequilibrium longitudinal spin injection and
the transversal spin-transfer surface torque. Dispersion relation for
fluctuations is derived and solved. Nonlinear problem is solved about steady
state arising due to instability for a thick enough free layer.Comment: 9 page
Approximation of excitonic absorption in disordered systems using a compositional component weighted CPA
Employing a recently developed technique of component weighted two particle
Green's functions in the CPA of a binary substitutional alloy we
extend the existing theory of excitons in such media using a contact potential
model for the interaction between electrons and holes to an approximation which
interpolates correctly between the limits of weak and strong disorder. With our
approach we are also able to treat the case where the contact interaction
between carriers varies between sites of different types, thus introducing
further disorder into the system. Based on this approach we study numerically
how the formation of exciton bound states changes as the strengths of the
contact potentials associated with either of the two site types are varied
through a large range of parameter values.Comment: 27 pages RevTeX (preprint format), 13 Postscript figure file
Rotational and Vibrational Dynamics of Interstitial Molecular Hydrogen
The calculation of the hindered roton-phonon energy levels of a hydrogen
molecule in a confining potential with different symmetries is systematized for
the case when the rotational angular momentum is a good quantum number. One
goal of this program is to interpret the energy-resolved neutron time of flight
spectrum previously obtained for HC. This spectrum gives direct
information on the energy level spectrum of H molecules confined to the
octahedral interstitial sites of solid C. We treat this problem of
coupled translational and orientational degrees of freedom a) by construction
of an effective Hamiltonian to describe the splitting of the manifold of states
characterized by a given value of and having a fixed total number of phonon
excitations, b) by numerical solutions of the coupled translation-rotation
problem on a discrete mesh of points in position space, and c) by a group
theoretical symmetry analysis. Results obtained from these three different
approaches are mutually consistent. The results of our calculations explain
several hitherto uninterpreted aspects of the experimental observations, but
show that a truly satisfactory orientational potential for the interaction of
an H molecule with a surrounding array of C atoms has not yet been
developed.Comment: 53 pages, 9 figures, to appear in Phys. Rev B (in press). Phys. Rev.
B (in press
Magnetic-field dependence of electron spin relaxation in n-type semiconductors
We present a theoretical investigation of the magnetic field dependence of
the longitudinal () and transverse () spin relaxation times of
conduction band electrons in n-type III-V semiconductors. In particular, we
find that the interplay between the Dyakonov-Perel process and an additional
spin relaxation channel, which originates from the electron wave vector
dependence of the electron -factor, yields a maximal at a finite
magnetic field. We compare our results with existing experimental data on
n-type GaAs and make specific additional predictions for the magnetic field
dependence of electron spin lifetimes.Comment: accepted for publication in PRB, minor changes to previous manuscrip
Mode-hop-free tuning over 135 GHz of external cavity diode lasers without anti-reflection coating
We report an external cavity diode laser (ECDL), using a diode whose front
facet is not antireflection (AR) coated, that has a mode-hop-free (MHF) tuning
range greater than 135 GHz. We achieved this using a short external cavity and
by simultaneously tuning the internal and external modes of the laser. We find
that the precise location of the pivot point of the grating in our laser is
less critical than commonly believed. The general applicability of the method,
combined with the compact portable mechanical and electronic design, makes it
well suited for both research and industrial applications.Comment: 5 pages, 5 figure
Zeeman effects on the impurity-induced resonances in d-wave superconductors
It is shown how the resonant states induced by a single spinless impurity in
a d-wave superconductor evolve under the effect of an applied Zeeman magnetic
field. Moreover, it is demonstrated that the spin-orbit coupling to the
impurity potential can have important and characteristic effects on the
resonant states and their response to the Zeeman field, especially when the
impurity is close to the unitary limit. For zero or very small spin-orbit
interaction, the resonant states becomes Zeeman splitted by the magnetic field
while when the spin-orbit coupling is important, new low-lying resonances arise
which do not show any Zeeman splitting.Comment: 5 pages with 5 eps figures embedded. To appear on Phys. Rev.
Computational approaches for understanding the diagnosis and treatment of Parkinson's disease
This study describes how the application of evolutionary algorithms (EAs) can be used to study motor function in humans with Parkinson's disease (PD) and in animal models of PD. Human data is obtained using commercially available sensors via a range of non-invasive procedures that follow conventional clinical practice. EAs can then be used to classify human data for a range of uses, including diagnosis and disease monitoring. New results are presented that demonstrate how EAs can also be used to classify fruit flies with and without genetic mutations that cause Parkinson's by using measurements of the proboscis extension reflex. The case is made for a computational approach that can be applied across human and animal studies of PD and lays the way for evaluation of existing and new drug therapies in a truly objective way
Electron Spin Relaxation in a Semiconductor Quantum Well
A fully microscopic theory of electron spin relaxation by the
D'yakonov-Perel' type spin-orbit coupling is developed for a semiconductor
quantum well with a magnetic field applied in the growth direction of the well.
We derive the Bloch equations for an electron spin in the well and define
microscopic expressions for the spin relaxation times. The dependencies of the
electron spin relaxation rate on the lowest quantum well subband energy,
magnetic field and temperature are analyzed.Comment: Revised version as will appear in Physical Review
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