198,990 research outputs found
Effects of horizontal vibration on hopper flows of granular materials
The current experiments investigate the discharge of glass spheres in a planar wedge-shaped hopper (45 degree sidewalls) that is vibrated hoizontally. When the hopper is discharged without vibration, the discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With horizontal vibration, the discharge rate increases with the velocity of vibration as compared with the discharge rate without vibration. For a certain range of acceleration parameters (20-30 Hz and accelerations greater than about 1 g), the discharge of the material occurs in an inverted-funnel pattern, with the material along the sides exiting first, followed by the material in the core; the free surface shows a peak at the center of the hopper with the free surface particles avalanching from the center toward the sides. During the deceleration phase of a vibration cycle, particles all along the trailing or low-pressure wall separate from the surface and fall under gravity for a short period before reconnecting the hopper. For lower frequencies (5 and 10 Hz), the free surface remains horizontal and the material appears to discharge uniformly from the hopper
First-principles study of the Young's modulus of Si <001> nanowires
We report the results of first-principles density functional theory
calculations of the Young's modulus and other mechanical properties of
hydrogen-passivated Si nanowires. The nanowires are taken to have
predominantly {100} surfaces, with small {110} facets. The Young's modulus, the
equilibrium length and the residual stress of a series of prismatic wires are
found to have a size dependence that scales like the surface area to volume
ratio for all but the smallest wires. We analyze the physical origin of the
size dependence, and compare the results to two existing models.Comment: 5 pages, 3 figure
Effects of Horizontal Vibration on Hopper Flows of Granular Material
This study experimentally examines the flow of glass spheres in a wedge-shaped hopper that is vibrated hoizontally. When the hopper is discharged without vibration, discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With vibration, the discharge of the material occurs in reverse, with the material along the sides exiting first, followed by the material in the central region. These patterns are observed with flow visualization and high-speed photography. The study also includes measurements of the discharge rate, which increases with the amplitude of the velocity of vibration
Analysis of photon-atom entanglement generated by Faraday rotation in a cavity
Faraday rotation based on AC Stark shifts is a mechanism that can entangle
the polarization variables of photons and atoms. We analyze the structure of
such entanglement by using the Schmidt decomposition method. The
time-dependence of entanglement entropy and the effective Schmidt number are
derived for Gaussian amplitudes. In particular we show how the entanglement is
controlled by the initial fluctuations of atoms and photons.Comment: 6 pages, 3 figure
Self-dual Maxwell Chern-Simons Solitons In 1+1 Dimensions
We study the domain wall soliton solutions in the relativistic self-dual
Maxwell Chern-Simons model in 1+1 dimensions obtained by the dimensional
reduction of the 2+1 model. Both topological and nontopological self-dual
solutions are found in this case. A la BPS dyons here the Bogomol'ny bound on
the energy is expressed in terms of two conserved quantities. We discuss the
underlying supersymmetry. Nonrelativistic limit of this model is also
considered and static, nonrelativistic self-dual soliton solutions are
obtained.Comment: 18 pages RevTex, 2 figures included, to appear in Phys. Rev.
Government Policy in Support of Domestic Agriculture: Costs and Benefits, The United States
Agricultural and Food Policy,
Parallel transport on non-Abelian flux tubes
I propose a way of unambiguously parallel transporting fields on non-Abelian
flux tubes, or strings, by means of two gauge fields. One gauge field
transports along the tube, while the other transports normal to the tube.
Ambiguity is removed by imposing an integrability condition on the pair of
fields. The construction leads to a gauge theory of mathematical objects known
as Lie 2-groups, which are known to result also from the parallel transport of
the flux tubes themselves. The integrability condition is also shown to be
equivalent to the assumption that parallel transport along nearby string
configurations are equal up to arbitrary gauge transformations. Attempts to
implement this condition in a field theory leads to effective actions for
two-form fields.Comment: significant portions of text rewritten, references adde
First-principles calculation of mechanical properties of Si <001> nanowires and comparison to nanomechanical theory
We report the results of first-principles density functional theory
calculations of the Young's modulus and other mechanical properties of
hydrogen-passivated Si nanowires. The nanowires are taken to have
predominantly {100} surfaces, with small {110} facets according to the Wulff
shape. The Young's modulus, the equilibrium length and the constrained residual
stress of a series of prismatic beams of differing sizes are found to have size
dependences that scale like the surface area to volume ratio for all but the
smallest beam. The results are compared with a continuum model and the results
of classical atomistic calculations based on an empirical potential. We
attribute the size dependence to specific physical structures and interactions.
In particular, the hydrogen interactions on the surface and the charge density
variations within the beam are quantified and used both to parameterize the
continuum model and to account for the discrepancies between the two models and
the first-principles results.Comment: 14 pages, 10 figure
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