162,123 research outputs found
GPS source solution of the 2004 Parkfield earthquake
We compute a series of finite-source parameter inversions of the fault
rupture of the 2004 Parkfield earthquake based on 1 Hz GPS records only. We
confirm that some of the co-seismic slip at shallow depth (<5 km) constrained
by InSAR data processing results from early post-seismic deformation. We also
show 1) that if located very close to the rupture, a GPS receiver can saturate
while it remains possible to estimate the ground velocity (~1.2 m/s) near the
fault, 2) that GPS waveforms inversions constrain that the slip distribution at
depth even when GPS monuments are not located directly above the ruptured areas
and 3) the slip distribution at depth from our best models agree with that
recovered from strong motion data. The 95th percentile of the slip amplitudes
for rupture velocities ranging from 2 to 5 km/s is, 55 +/- 6 cm.Comment: 24 pages including supp. material
Phonon-mediated electron spin phase diffusion in a quantum dot
An effective spin relaxation mechanism that leads to electron spin
decoherence in a quantum dot is proposed. In contrast to the common
calculations of spin-flip transitions between the Kramers doublets, we take
into account a process of phonon-mediated fluctuation in the electron spin
precession and subsequent spin phase diffusion. Specifically, we consider
modulations in the longitudinal g-factor and hyperfine interaction induced by
the phonon-assisted transitions between the lowest electronic states. Prominent
differences in the temperature and magnetic field dependence between the
proposed mechanisms and the spin-flip transitions are expected to facilitate
its experimental verification. Numerical estimation demonstrates highly
efficient spin relaxation in typical semiconductor quantum dots.Comment: 5 pages, 1 figur
Inclusive angular distribution of alpha and Li fragments produced in the Fe-C and Fe-Pb collisions at 1.88 GeV/u
The LS (laboratory system) emission angles theta for 2188 and 298 Li fragments, produced inclusively in relativistic Fe-C and Fe-Pb collisions, have been measured in reference to incident Fe-ion beam tracks nearby in nuclear emulsion. An empirical differential frequency formula, dN(cot theta) = exp (a + b cot theta)d(cot theta) is obtained with the constant b approx. = -0.026 at 1.88 GeV/u, which seems to be independent on the kinds of target nucleus as well as on the kinds of projectile fragments
Recent developments in multilevel optimization
Recent developments in multilevel optimization are briefly reviewed. The general nature of the multilevel design task, the use of approximations to develop and solve the analysis design task, the structure of the formal multidiscipline optimization problem, a simple cantilevered beam which demonstrates the concepts of multilevel design and the basic mathematical details of the optimization task and the system level are among the topics discussed
Quantum Dynamics for de Sitter Radiation
We revisit the Hamiltonian formalism for a massive scalar field and study the
particle production in a de Sitter space. In the invariant-operator picture the
time-dependent annihilation and creation operators are constructed in terms of
a complex solution to the classical equation of motion for the field and the
Gaussian wave function for each Fourier mode is found which is an exact
solution to the Schr\"odinger equation. The in-out formalism is reformulated by
the annihilation and creation operators and the Gaussian wave functions. The de
Sitter radiation from the in-out formalism differs from the Gibbons-Hawking
radiation in the planar coordinates, and we discuss the discrepancy of the
particle production by the two methodComment: LaTex 12 pages, no figure; CosPA2011, Peking Univ., Oct. 28-31, 2011;
references added; to be published in International Journal of Modern Physics:
Conference Serie
Geographical Coarsegraining of Complex Networks
We perform the renormalization-group-like numerical analysis of
geographically embedded complex networks on the two-dimensional square lattice.
At each step of coarsegraining procedure, the four vertices on each square box are merged to a single vertex, resulting in the coarsegrained
system of the smaller sizes. Repetition of the process leads to the observation
that the coarsegraining procedure does not alter the qualitative
characteristics of the original scale-free network, which opens the possibility
of subtracting a smaller network from the original network without destroying
the important structural properties. The implication of the result is also
suggested in the context of the recent study of the human brain functional
network.Comment: To appear in Phys. Rev. Let
Quantum paramagnetic ground states on the honeycomb lattice and field-induced transition to N\'eel order
Motivated by recent experiments on BiMnO(NO), and a
broader interest arising from numerical work on the honeycomb lattice Hubbard
model, we have studied the effect of a magnetic field on honeycomb lattice spin
models with quantum paramagnetic ground states. For a model with frustrating
second-neighbor exchange, , we use a Lindemann-like criterion within spin
wave theory to show that N\'eel order melts beyond a critical . The
critical increases with a magnetic field, implying the existence of a
field-induced paramagnet-N\'eel transition over a range of . We also study
bilayer model using a spin- generalization of bond operator mean field
theory. We show that there is a N\'eel-dimer transition for various spin values
with increasing bilayer coupling, and that the resulting interlayer dimer state
undergoes a field induced transition into a state with transverse N\'eel order.
Finally, we study a spin-3/2 model which interpolates between the Heisenberg
model and the Affleck-Kennedy-Lieb-Tasaki (AKLT) parent Hamiltonian. Using
exact diagonalization, we compute the fidelity susceptibility to locate the
Neel-AKLT quantum critical point, obtain the spin gap of the AKLT parent
Hamiltonian, and argue that AKLT state also undergoes field-induced Neel
ordering.Comment: 8 pages, revised longer version of arXiv:1012.0316. Corrected factor
of 2 error in Eq.[16], replotted Fig.[4] and revised the critical
needed to stabilize interlayer dimer state. We thank S. V. Isakov for
discussions which uncovered this erro
Gravitational Effects in Quantum Mechanics
To date, both quantum theory, and Einstein's theory of general relativity
have passed every experimental test in their respective regimes. Nevertheless,
almost since their inception, there has been debate surrounding whether they
should be unified and by now there exists strong theoretical arguments pointing
to the necessity of quantising the gravitational field. In recent years, a
number of experiments have been proposed which, if successful, should give
insight into features at the Planck scale. Here we review some of the
motivations, from the perspective of semi-classical arguments, to expect new
physical effects at the overlap of quantum theory and general relativity. We
conclude with a short introduction to some of the proposals being made to
facilitate empirical verification.Comment: 24 pages, 3 figures, review article. Submitted to Contemporary
Physic
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