17,533 research outputs found
Quasi-perpendicular fast magnetosonic shock with wave precursor in collisionless plasma
A one-dimensional particle-in-cell (PIC) simulation tracks a fast
magnetosonic shock over time scales comparable to an inverse ion gyrofrequency.
The magnetic pressure is comparable to the thermal pressure upstream. The shock
propagates across a uniform background magnetic field with a pressure that
equals the thermal pressure upstream at the angle 85 at a speed that is
1.5 times the fast magnetosonic speed in the electromagnetic limit.
Electrostatic contributions to the wave dispersion increase its phase speed at
large wave numbers, which leads to a convex dispersion curve. A fast
magnetosonic precursor forms ahead of the shock with a phase speed that exceeds
the fast magnetosonic speed by about . The wave is slower than the
shock and hence it is damped.Comment: 4 pages, 3 figure
Dual-fermion approach to the Anderson-Hubbard model
We apply the recently developed dual fermion algorithm for disordered
interacting systems to the Anderson-Hubbard model. This algorithm is compared
with dynamical cluster approximation calculations for a one-dimensional system
to establish the quality of the approximation in comparison with an established
cluster method. We continue with a three-dimensional (3d) system and look at
the antiferromagnetic, Mott and Anderson localization transitions. The dual
fermion approach leads to quantitative as well as qualitative improvement of
the dynamical mean-field results and it allows one to calculate the hysteresis
in the double occupancy in 3d taking into account nonlocal correlations
Mean-field embedding of the dual fermion approach for correlated electron systems
To reduce the rapidly growing computational cost of the dual fermion lattice
calculation with increasing system size, we introduce two embedding schemes.
One is the real fermion embedding, and the other is the dual fermion embedding.
Our numerical tests show that the real fermion and dual fermion embedding
approaches converge to essentially the same result. The application on the
Anderson disorder and Hubbard models shows that these embedding algorithms
converge more quickly with system size as compared to the conventional dual
fermion method, for the calculation of both single-particle and two-particle
quantities.Comment: 10 pages, 10 figure
Dual Fermion Method for Disordered Electronic Systems
While the coherent potential approximation (CPA) is the prevalent method for
the study of disordered electronic systems, it fails to capture non-local
correlations and Anderson localization. To incorporate such effects, we extend
the dual fermion approach to disordered non-interacting systems using the
replica method. Results for single- and two- particle quantities show good
agreement with cluster extensions of the CPA; moreover, weak localization is
captured. As a natural extension of the CPA, our method presents an alternative
to the existing cluster theories. It can be used in various applications,
including the study of disordered interacting systems, or for the description
of non-local effects in electronic structure calculations.Comment: 5 pages, 4 figure
Metal-Insulator-Transition in a Weakly interacting Disordered Electron System
The interplay of interactions and disorder is studied using the
Anderson-Hubbard model within the typical medium dynamical cluster
approximation. Treating the interacting, non-local cluster self-energy
() up to second order in the
perturbation expansion of interactions, , with a systematic incorporation
of non-local spatial correlations and diagonal disorder, we explore the initial
effects of electron interactions () in three dimensions. We find that the
critical disorder strength (), required to localize all states,
increases with increasing ; implying that the metallic phase is stabilized
by interactions. Using our results, we predict a soft pseudogap at the
intermediate close to and demonstrate that the mobility edge
() is preserved as long as the chemical potential, , is
at or beyond the mobility edge energy.Comment: 10 Pages, 8 Figures with Supplementary materials include
Trigonometric Parallaxes of Massive Star Forming Regions: II. Cep A & NGC 7538
We report trigonometric parallaxes for the sources NGC 7538 and Cep A,
corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04]
kpc, respectively. The distance to NGC 7538 is considerably smaller than its
kinematic distance and places it in the Perseus spiral arm. The distance to Cep
A is also smaller than its kinematic distance and places it in the Local arm or
spur. Combining the distance and proper motions with observed radial velocities
gives the location and full space motion of the star forming regions. We find
significant deviations from circular Galactic orbits for these sources: both
sources show large peculiar motions (> 10 km/s) counter to Galactic rotation
and NGC 7538 has a comparable peculiar motion toward the Galactic center.Comment: 21 pages, 8 figures; to appear in the Astrophysical Journa
Ice morphology modification and solute recovery improvement by heating and annealing during block freeze-concentration of coffee extracts
Several treatments on ice blocks can be applied during block freeze-concentration to increase the solute recovery from the ice. In the present study, the changes in the ice block’s temperature and the application of annealing during the block freeze-concentration of aqueous coffee extracts were studied. The ice block was subjected to heating and annealing prior to the thawing stage. The effect of coolant temperature during ice block heating (T = -10 and -5 °C) and the application of annealing (+, -) on solute recovery and ice structure morphology was evaluated. The use of annealing during block freeze-concentration modified the ice crystal morphology and increased the solute recovery only when it is applied at the highest temperature. In general, the annealing process increased the size and circularity of the ice crystals, consequently improving the solute recovery. Thus, annealing can be used to increase the solute recovery during block freeze-concentration.Postprint (published version
Phase Stability in the Two dimensional Anisotropic Boson Hubbard Hamiltonian
The two dimensional square lattice hard-core boson Hubbard model with near
neighbor interactions has a `checkerboard' charge density wave insulating phase
at half-filling and sufficiently large intersite repulsion. When doped, rather
than forming a supersolid phase in which long range charge density wave
correlations coexist with a condensation of superfluid defects, the system
instead phase separates. However, it is known that there are other lattice
geometries and interaction patterns for which such coexistence takes place. In
this paper we explore the possibility that anisotropic hopping or anisotropic
near neighbor repulsion might similarly stabilize the square lattice
supersolid. By considering the charge density wave structure factor and
superfluid density for different ratios of interaction strength and
hybridization in the and directions, we conclude that phase
separation still occurs.Comment: 8 pages, 11 figure
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