9,899 research outputs found
The LiAl/FeS2 battery power source for the future
Advanced high power density rechargeable batteries are currently under development. These batteries have the potential of greatly increasing the power and energy densities available for space applications. Depending on whether the system is optimized for high power or high energy, values up to 150 Wh/kg and 2100 W/kg (including hardware) are projected. This is due to the fact that the system uses a high conductivity molten salt electrolyte. The electrolyte also serves as a separator layer with unlimited freeze thaw capabilities. Life of 1000 cycles and ten calendar years is projected. The electrochemistry consists of a lithium aluminum alloy negative electrode, iron disulfide positive electrode, and magnesium oxide powder immobilized molten salt electrolyte. Processed powders are cold compacted into circular discs which are assembled into bipolar cell hardware with peripheral ceramic salts. The culmination of the work will be a high energy battery of 40 kWh and a high power battery of 28 kWh
Low temperature properties of the infinite-dimensional attractive Hubbard model
We investigate the attractive Hubbard model in infinite spatial dimensions by
combining dynamical mean-field theory with a strong-coupling continuous-time
quantum Monte Carlo method. By calculating the superfluid order parameter and
the density of states, we discuss the stability of the superfluid state. In the
intermediate coupling region above the critical temperature, the density of
states exhibits a heavy fermion behavior with a quasi-particle peak in the
dense system, while a dip structure appears in the dilute system. The formation
of the superfluid gap is also addressed.Comment: 8 pages, 9 figure
Fluctuations Do Matter: Large Noise-Enhanced Halos in Charged-Particle Beams
The formation of beam halos has customarily been described in terms of a
particle-core model in which the space-charge field of the oscillating core
drives particles to large amplitudes. This model involves parametric resonance
and predicts a hard upper bound to the orbital amplitude of the halo particles.
We show that the presence of colored noise due to space-charge fluctuations
and/or machine imperfections can eject particles to much larger amplitudes than
would be inferred from parametric resonance alone.Comment: 13 pages total, including 5 figure
A simple formula for pooling knowledge about a quantum system
When various observers obtain information in an independent fashion about a
classical system, there is a simple rule which allows them to pool their
knowledge, and this requires only the states-of-knowledge of the respective
observers. Here we derive an equivalent quantum formula. While its realm of
applicability is necessarily more limited, it does apply to a large class of
measurements, and we show explicitly for a single qubit that it satisfies the
intuitive notions of what it means to pool knowledge about a quantum system.
This analysis also provides a physical interpretation for the trace of the
product of two density matrices.Comment: 5 pages, Revtex
Anti-aliasing with stratified B-spline filters of arbitrary degree
A simple and elegant method is presented to perform anti-aliasing in raytraced images. The method uses stratified
sampling to reduce the occurrence of artefacts in an image and features a B-spline filter to compute the final
luminous intensity at each pixel. The method is scalable through the specification of the filter degree. A B-spline
filter of degree one amounts to a simple anti-aliasing scheme with box filtering. Increasing the degree of the B-spline generates progressively smoother filters. Computation of the filter values is done in a recursive way, as part of a sequence of Newton-Raphson iterations, to obtain the optimal sample positions in screen space. The proposed method can perform both anti-aliasing in space and in time, the latter being more commonly known as motion blur. We show an application of the method to the ray casting of implicit procedural surfaces
Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow
We perform molecular dynamics simulations of model granular systems
undergoing boundary-driven planar shear flow in two spatial dimensions with the
goal of developing a more complete understanding of how dense particulate
systems respond to applied shear. In particular, we are interested in
determining when these systems will possess linear velocity profiles and when
they will develop highly localized velocity profiles in response to shear. In
previous work on similar systems we showed that nonlinear velocity profiles
form when the speed of the shearing boundary exceeds the speed of shear waves
in the material. However, we find that nonlinear velocity profiles in these
systems are unstable at very long times. The degree of nonlinearity slowly
decreases in time; the velocity profiles become linear when the granular
temperature and density profiles are uniform across the system at long times.
We measure the time required for the velocity profiles to become linear
and find that increases as a power-law with the speed of the shearing
boundary and increases rapidly as the packing fraction approaches random close
packing. We also performed simulations in which differences in the granular
temperature across the system were maintained by vertically vibrating one of
the boundaries during shear flow. We find that nonlinear velocity profiles form
and are stable at long times if the difference in the granular temperature
across the system exceeds a threshold value that is comparable to the glass
transition temperature in an equilibrium system at the same average density.
Finally, the sheared and vibrated systems form stable shear bands, or highly
localized velocity profiles, when the applied shear stress is lowered below the
yield stress of the static part of the system.Comment: 11 pages, 14 figure
Groundstate and Collective Modes of a Spin-Polarized Dipolar Bose-Einstein Condensate in a Harmonic Trap
We report new results for the Thomas-Fermi groundstate and the quadrupolar
modes of density oscillations of a spin- polarized dipolar interacting
Bose-Einstein condensate for the case when the external magnetic field is not
orientated parallel to a principal axis of a harmonic anisotropic trap.Comment: Final version, published in Physical Review
Linear and Non Linear Effects on the Newtonian Gravitational Constant as deduced from the Torsion Balance
The Newtonian gravitational constant has still 150 parts per million of
uncertainty. This paper examines the linear and nonlinear equations governing
the rotational dynamics of the torsion gravitational balance. A nonlinear
effect modifying the oscillation period of the torsion gravitational balance is
carefully explored.Comment: 11 pages, 2 figure
Driven Heisenberg Magnets: Nonequilibrium Criticality, Spatiotemporal Chaos and Control
We drive a -dimensional Heisenberg magnet using an anisotropic current.
The continuum Langevin equation is analysed using a dynamical renormalization
group and numerical simulations. We discover a rich steady-state phase diagram,
including a critical point in a new nonequilibrium universality class, and a
spatiotemporally chaotic phase. The latter may be `controlled' in a robust
manner to target spatially periodic steady states with helical order.Comment: 7 pages, 2 figures. Published in Euro. Phys. Let
One-loop fermionic corrections to the instanton transition in two dimensional chiral Higgs model
The one-loop fermionic contribution to the probability of an instanton
transition with fermion number violation is calculated in the chiral Abelian
Higgs model in 1+1 dimensions, where the fermions have a Yukawa coupling to the
scalar field. The dependence of the determinant on fermionic, scalar and vector
mass is determined. We show in detail how to renormalize the fermionic
determinant in partial wave analysis, which is convenient for computations.Comment: 36 pages, 5 figure
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