30,627 research outputs found
Energy-momentum and angular momentum densities in gauge theories of gravity
In the \bar{\mbox{\rm Poincar\'{e}}} gauge theory of gravity, which has
been formulated on the basis of a principal fiber bundle over the space-time
manifold having the covering group of the proper orthochronous Poincar\'{e}
group as the structure group, we examine the tensorial properties of the
dynamical energy-momentum density and the ` `
spin" angular momentum density of the
gravitational field. They are both space-time vector densities, and transform
as tensors under {\em global} - transformations. Under {\em local}
internal translation, is invariant, while
transforms inhomogeneously. The dynamical
energy-momentum density and the ` ` spin"
angular momentum density of the matter field
are also examined, and they are known to be space-time vector densities and to
obey tensorial transformation rules under internal \bar{\mbox{\rm
Poincar\'{e}}} gauge transformations. The corresponding discussions in
extended new general relativity which is obtained as a teleparallel limit of
\bar{\mbox{\rm Poincar\'{e}}} gauge theory are also given, and
energy-momentum and ` ` spin" angular momentum densities are known to be well
behaved. Namely, they are all space-time vector densities, etc. In both
theories, integrations of these densities on a space-like surface give the
total energy-momentum and {\em total} (={\em spin}+{\em orbital}) angular
momentum for asymptotically flat space-time. The tensorial properties of
canonical energy-momentum and ` ` extended orbital angular momentum" densities
are also examined.Comment: 18 page
Unitary-process discrimination with error margin
We investigate a discrimination scheme between unitary processes. By
introducing a margin for the probability of erroneous guess, this scheme
interpolates the two standard discrimination schemes: minimum-error and
unambiguous discrimination. We present solutions for two cases. One is the case
of two unitary processes with general prior probabilities. The other is the
case with a group symmetry: the processes comprise a projective representation
of a finite group. In the latter case, we found that unambiguous discrimination
is a kind of "all or nothing": the maximum success probability is either 0 or
1. We also closely analyze how entanglement with an auxiliary system improves
discrimination performance.Comment: 9 pages, 3 figures, presentation improved, typos corrected, final
versio
Fluidized reduction of oxides on fine metal powders without sintering
In the process of reducing extremely fine metal particles (av. particle size or = 1000 angstroms) covered with an oxide layer, the metal particles are fluidized by a gas flow contg. H, heated, and reduced. The method uniformly and easily reduces surface oxide layers of the extremely fine metal particles without causing sintering. The metal particles are useful for magnetic recording materials, conductive paste, powder metallurgy materials, chem. reagents, and catalysts
Electrical pump-and-probe study of spin singlet-triplet relaxation in a quantum dot
Spin relaxation from a triplet excited state to a singlet ground state in a
semiconductor quantum dot is studied by employing an electrical pump-and-probe
method. Spin relaxation occurs via cotunneling when the tunneling rate is
relatively large, confirmed by a characteristic square dependence of the
relaxation rate on the tunneling rate. When cotunneling is suppressed by
reducing the tunneling rate, the intrinsic spin relaxation is dominated by
spin-orbit interaction. We discuss a selection rule of the spin-orbit
interaction based on the observed double-exponential decay of the triplet
state.Comment: 4 pages, 4 figure
Flow-field in a vortex with breakdown above sharp edged delta wings
The behavior of vortex-flow, accompanied with breakdown, formed above sharp-edged delta wings, was studied experimentally as well as theoretically. Emphasis is placed particularly on the criterion for the breakdown at sufficiently large Reynolds number
Investigation of environmental change pattern in Japan. Observation of present state of agricultural land-use by analysing LANDSAT data
The author has identified the following significant results. Species and ages of grasses in pastures were identified, and soils were classified into several types using LANDSAT data. This data could be used in a wide area of cultivation, reclamation, or management planning on agricultural land
Risk- & Regret-Averse Bidders in Sealed-Bid Auctions
Overbidding, bidding more than risk-neutral Bayesian Nash Equilibrium, is a widely observed phenomenon in
virtually all experimental auctions. The scholars within the auction literature propose the risk-averse preference
model to explain overbidding structurally. However, the risk-averse preference model predicts underbidding in
such important classes of auctions as all-pay auctions. To solve this discrepancy, we construct a structural model
of bidding behavior in sealed-bid auctions, one in which bidders may regret their decisions. Our model nests both
risk-averse and regret-averse attitudes and aims to explain overbidding in a wider class of auctions. We first derive
equilibrium first-order conditions, which are used for estimation and calibration analyses, and show monotonic
increasing properties of equilibrium bidding functions. Second, we carry out structural estimation and calibration
analyses based on experimental data from Kagel and Levin (1993) and Noussair and Silver (2006). With these
structurally estimated parameters, we test the significance of bidders’ risk-averse and regret-averse attitudes.
The estimation results show that bidders exhibit weak risk-averse (close to risk-neutral) and strong regret-averse
attitudes. Furthermore, regret-averse attitudes are significant when bidders anticipate losing. Calibration results
demonstrate that our risk- & regret-averse model can explain overbidding across all of the above IPV auctions.
Third, we simulate our model with the estimated parameters and obtain revenue rankings numerically. This
allows us to confirm the revenue supremacy in all-pay auctions reported in experimental auction literature. We
discuss extensions to asymmetric and Common-Value (CV) auctions in our online appendix
- …