2,952 research outputs found
Phase retrieval with polarization
In many areas of imaging science, it is difficult to measure the phase of
linear measurements. As such, one often wishes to reconstruct a signal from
intensity measurements, that is, perform phase retrieval. In this paper, we
provide a novel measurement design which is inspired by interferometry and
exploits certain properties of expander graphs. We also give an efficient phase
retrieval procedure, and use recent results in spectral graph theory to produce
a stable performance guarantee which rivals the guarantee for PhaseLift in
[Candes et al. 2011]. We use numerical simulations to illustrate the
performance of our phase retrieval procedure, and we compare reconstruction
error and runtime with a common alternating-projections-type procedure
Prediction of physical-chemical and fire hazard characteristics by carbon chain rules. 2. Carboxylic acids
Investigation of the dependence of physico-chemical and fire hazard properties from the chemical structure of carboxylic acids is carried out. Forecasting of the boiling temperature, the flash point, the temperature and the concentration flammability limits, the heats of combustion and vaporization is performed by the carbon chain rules (CCR). The following empirical equations for the calculation of physico-chemical and fire hazard indices from the conventional carbon chain and from the number of carbon atoms are proposed for the convenience of practical application of the CCR. A comparative analysis of the proposed methods for the flash point calculating and the already known methods of GOST 12.1.044-89, Mendeleev and ACD/Lab 2014 is carried out. It is shown, basically, that the new methods give more accurate calculation results than the comparison design procedures. © Siberian Federal University. All rights reserve
A generating functional approach to the Hubbard model
The method of generating functional is generalized to the case of strongly
correlated systems, and applied to the Hubbard model. For the electronic
Green's function constructed for Hubbard operators, an equation using
variational derivatives with respect to the fluctuating fields has been derived
and its multiplicative form has been determined. Corrections for the electronic
self-energy are calculated up to the second order with respect to the parameter
W/U (W width of the band), and a mean field type approximation was formulated,
including both charge and spin static fluctuations. The equations for the
Bose-like Green's functions have been derived, describing the collective modes:
the magnons and doublons. The properties of the poles of the doublon Green's
functions depend on electronic filling. The investigation of the special case
n=1 demonstrates that the doublon Green's function has a soft mode at the wave
vector Q=(pi,pi,...), indicating possible instability of the uniform
paramagnetic phase relatively to the two sublattices charge ordering. However
this instability should compete with an instability to antiferromagnetic
ordering.Comment: 31 pages, 7 figures, to be published in Eur. Phys. J.
Field‐aligned current distribution in the transition current system
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95630/1/jgra17447.pd
An efficient MPI/OpenMP parallelization of the Hartree-Fock method for the second generation of Intel Xeon Phi processor
Modern OpenMP threading techniques are used to convert the MPI-only
Hartree-Fock code in the GAMESS program to a hybrid MPI/OpenMP algorithm. Two
separate implementations that differ by the sharing or replication of key data
structures among threads are considered, density and Fock matrices. All
implementations are benchmarked on a super-computer of 3,000 Intel Xeon Phi
processors. With 64 cores per processor, scaling numbers are reported on up to
192,000 cores. The hybrid MPI/OpenMP implementation reduces the memory
footprint by approximately 200 times compared to the legacy code. The
MPI/OpenMP code was shown to run up to six times faster than the original for a
range of molecular system sizes.Comment: SC17 conference paper, 12 pages, 7 figure
Rate of steady-state reconnection in an incompressible plasma
The reconnection rate is obtained for the simplest case of 2D symmetric
reconnection in an incompressible plasma. In the short note (Erkaev et al.,
Phys. Rev. Lett.,84, 1455 (2000)), the reconnection rate is found by matching
the outer Petschek solution and the inner diffusion region solution. Here the
details of the numerical simulation of the diffusion region are presented and
the asymptotic procedure which is used for deriving the reconnection rate is
described. The reconnection rate is obtained as a decreasing function of the
diffusion region length. For a sufficiently large diffusion region scale, the
reconnection rate becomes close to that obtained in the Sweet-Parker solution
with the inverse square root dependence on the magnetic Reynolds number,
determined for the global size of the current sheet. On the other hand, for a
small diffusion region length scale, the reconnection rate turns out to be very
similar to that obtained in the Petschek model with a logarithmic dependence on
the magnetic Reynolds number. This means that the Petschek regime seems to be
possible only in the case of a strongly localized conductivity corresponding to
a small scale of the diffusion region.Comment: 11 pages, 3 figure
- …