1,889,748 research outputs found
Symmetries and time operators
All covariant time operators with normalized probability distribution are
derived. Symmetry criteria are invoked to arrive at a unique expression for a
given Hamiltonian. As an application, a well known result for the arrival time
distribution of a free particle is generalized and extended. Interestingly, the
resulting arrival time distribution operator is connected to a particular,
positive, quantization of the classical current. For particles in a potential
we also introduce and study the notion of conditional arrival-time
distribution
Three-dimensional tracking solar energy concentrator and method for making same
A three dimensional tracking solar energy concentrator, consisting of a stretched aluminized polymeric membrane supported by a hoop, was presented. The system is sturdy enough to withstand expected windage forces and precipitation. It can provide the high temperature output needed by central station power plants for power production in the multi-megawatt range
Portable linear-focused solar thermal energy collecting system
A solar heat collection system is provided by utilizing a line-focusing device that is effectively a cylindrically curved concentrator within a protected environment formed by a transparent inflatable casing. A target, such as a fluid or gas carrying conduit is positioned within or near the casing containing the concentrator, at the line focus of the concentrator. The casing can be inflated at the site of use by a low pressure air supply to form a unitary light weight structure. The collector, including casing, concentrator and target, is readily transportable and can be used either at ground level or on rooftops. The inflatable concentrator can be replaced with a rigid metal or other concentrator while maintaining the novel advantages of the whole solar heat collection system
Method and device for the detection of phenol and related compounds
A method is described which permits the selective oxidation and potentiometric detection of phenol and related compounds in an electrochemical cell. An anode coated with a gel immobilized oxidative enzyme and a cathode are each placed in an electrolyte solution. The potential of the cell is measured by a potentiometer connected to the electrodes
Sensitivity of neutron radii in the sigma_-$ rho_ coupling corrections in relativistic mean field theory
We study the sensitivity of the neutron skin thickness, , in a Pb
nucleus to the addition of nucleon-sigma-rho coupling corrections to a
selection (PK1, NL3, S271, Z271) of interactions in relativistic mean field
model. The PK1 and NL3 effective interactions lead to a minimum value of =
0.16 fm in comparison with the original value of = 0.28 fm. The S271 and
Z271 effective interactions yield even smaller values of = 0.11 fm, which
are similar to those for nonrelativistic mean field models. A precise
measurement of the neutron radius, and therefore , in Pb will place
an important constraint on both relativistic and nonrelativistic mean field
models. We also study the correlation between the radius of a 1.4 solar-mass
neutron star and .Comment: 40 pages 13 figures. to be published in Physical Review
Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at
In this paper we analyze different contributions to the magnetoresistance of
magnetic tunneling junctions at low voltages. A substantial fraction of the
resistance drop with voltage can be ascribed to variations of the density of
states and the barrier transmission with the bias. However, we found that the
anomaly observed at zero bias and the magnetoresistance behavior at very small
voltages, point to the contribution of inelastic magnon-assisted tunneling. The
latter is described by a transfer parameter , which is one or two orders
of magnitude smaller than , the direct transmission for elastic
currents. Our theory is in excellent agreement with experimental data, yielding
estimated values of which are of the order of / ~ 40.Comment: 13 pages, 4 figures (in postscript format). PACS numbers: 72.25.-b,
73.23.-b, 72.10.D
The upper atmosphere
Energy transfer, and heat sinks and sources in upper atmosphere for composition and temperature behavio
QCD Factorization for Semi-Inclusive Deep-Inelastic Scattering at Low Transverse Momentum
We demonstrate a factorization formula for semi-inclusive deep-inelastic
scattering with hadrons in the current fragmentation region detected at low
transverse momentum. To facilitate the factorization, we introduce the
transverse-momentum dependent parton distributions and fragmentation functions
with gauge links slightly off the light-cone, and with soft-gluon radiations
subtracted. We verify the factorization to one-loop order in perturbative
quantum chromodynamics and argue that it is valid to all orders in perturbation
theory.Comment: 28 pages, figures include
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