26,334 research outputs found
Recommended from our members
Sand Penetration By High-Speed Projectiles
Tungsten projectiles were shot into sand at velocities between 600 and 2200 m/s. Penetration was maximum at about 775 m/s. Below that velocity, projectiles were apparently stabilized by a fin set. Above that velocity, projectiles were broken by transverse loads. High-speed penetration resulted in comminution of sand particles, reducing their size by about 1000 times.Mechanical Engineerin
Assessing the performance of protective winter covers for outdoor marble statuary: pilot investigation
Outdoor statuary in gardens and parks in temperate climates has a tradition of being covered during the winter, to protect against external conditions. There has been little scientific study of the environmental protection that different types of covers provide. This paper examines environmental conditions provided by a range of covers used to protect marble statuary at three sites in the UK. The protection required depends upon the condition of the marble. Although statues closely wrapped and with a layer of insulation provide good protection, this needs to be considered against the potential physical damage of close wrapping a fragile deteriorated surface
Lower bounds for communication capacities of two-qudit unitary operations
We show that entangling capacities based on the Jamiolkowski isomorphism may
be used to place lower bounds on the communication capacities of arbitrary
bipartite unitaries. Therefore, for these definitions, the relations which have
been previously shown for two-qubit unitaries also hold for arbitrary
dimensions. These results are closely related to the theory of the
entanglement-assisted capacity of channels. We also present more general
methods for producing ensembles for communication from initial states for
entanglement creation.Comment: 9 pages, 2 figures, comments welcom
Geometric phases and anholonomy for a class of chaotic classical systems
Berry's phase may be viewed as arising from the parallel transport of a
quantal state around a loop in parameter space. In this Letter, the classical
limit of this transport is obtained for a particular class of chaotic systems.
It is shown that this ``classical parallel transport'' is anholonomic ---
transport around a closed curve in parameter space does not bring a point in
phase space back to itself --- and is intimately related to the Robbins-Berry
classical two-form.Comment: Revtex, 11 pages, no figures
Validation of mid-infrared spectrometry in milk for predicting body energy status in Holstein-Friesian cows
Collisions with ice-volatile objects: Geological implications
The collision of the Earth with extra-terrestrial ice-volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. These bodies would be analogs of the ice satellites found for the Jovian planets and suspected for comets and certain low density bodies in the Asteroid belt. Five generic end-members are postulated: (1) water ice; (2) dry ice: carbon-carbon dioxide rich, (3) oceanic (chloride) ice; (4) sulfur-rich ice; (5) ammonia hydrate-rich ice; and (6) clathrate: methane-rich ice. Due to the volatile nature of these bodies, evidence for their impact with the Earth would be subtle and probably best reflected geochemically or in the fossil record. Actual boloids impacting the Earth may have a variable composition, generally some admixture with water ice. However for discussion purposes, only the effects of a dominant component will be treated. The general geological effects of such collisions, as a function of the dominant component would be: (1) rapid sea level rise unrelated to deglaciation, (2) decreased oceanic pH and rapid climatic warming or deglaciation; (3) increased paleosalinities; (4) increased acid rain; (5) increased oceanic pH and rapid carbonate deposition; and (6) rapid climatic warming or deglaciation
Spectral Statistics and Dynamical Localization: sharp transition in a generalized Sinai billiard
We consider a Sinai billiard where the usual hard disk scatterer is replaced
by a repulsive potential with close to the
origin. Using periodic orbit theory and numerical evidence we show that its
spectral statistics tends to Poisson statistics for large energies when
, while for
it is independent of energy, but depends on . We apply the approach of
Altshuler and Levitov [Phys. Rep. {\bf 288}, 487 (1997)] to show that the
transition in the spectral statistics is accompanied by a dynamical
localization-delocalization transition. This behaviour is reminiscent of a
metal-insulator transition in disordered electronic systems.Comment: 8 pages, 2 figures, accepted for publication in Phys. Rev. Let
Correlations of chaotic eigenfunctions: a semiclassical analysis
We derive a semiclassical expression for an energy smoothed autocorrelation
function defined on a group of eigenstates of the Schr\"odinger equation. The
system we considered is an energy-conserved Hamiltonian system possessing
time-invariant symmetry. The energy smoothed autocorrelation function is
expressed as a sum of three terms. The first one is analogous to Berry's
conjecture, which is a Bessel function of the zeroth order. The second and the
third terms are trace formulae made from special trajectories. The second term
is found to be direction dependent in the case of spacing averaging, which
agrees qualitatively with previous numerical observations in high-lying
eigenstates of a chaotic billiard.Comment: Revtex, 13 pages, 1 postscript figur
Penegelolaan Berbasis Community Based Tourism pada Objek Wisata Air Panas Pawan Kabupaten Rokan Hulu Provisi Riau
Emphasizes aspects of community-based tourism activities that focus on the community, from the community, by the community for the community.Rokan Hulu has a wide range number of attractions, but which became the excellent potential that is only four; Hot Pawan attractions, Attractions Hot Hapanasan, attractions Lake Sipogas and attractions Waterfall Aek Matua.Attractions hot Pawan a tourist attraction run by the three parties of Regional Government, Rural and Community Government. People who work most management remedy given freedom Attraction manage Hot Pawan by the government through the Department of Culture and Tourism of Rokan Hulu. But does the government involve the community who worked as the manager of the community-based tourism activities as activities Planning, Investor, Implementation, Management and Evaluatio
Dynamical diffraction in sinusoidal potentials: uniform approximations for Mathieu functions
Eigenvalues and eigenfunctions of Mathieu's equation are found in the short
wavelength limit using a uniform approximation (method of comparison with a
`known' equation having the same classical turning point structure) applied in
Fourier space. The uniform approximation used here relies upon the fact that by
passing into Fourier space the Mathieu equation can be mapped onto the simpler
problem of a double well potential. The resulting eigenfunctions (Bloch waves),
which are uniformly valid for all angles, are then used to describe the
semiclassical scattering of waves by potentials varying sinusoidally in one
direction. In such situations, for instance in the diffraction of atoms by
gratings made of light, it is common to make the Raman-Nath approximation which
ignores the motion of the atoms inside the grating. When using the
eigenfunctions no such approximation is made so that the dynamical diffraction
regime (long interaction time) can be explored.Comment: 36 pages, 16 figures. This updated version includes important
references to existing work on uniform approximations, such as Olver's method
applied to the modified Mathieu equation. It is emphasised that the paper
presented here pertains to Fourier space uniform approximation
- …