4,984 research outputs found
Adapting to variable prismatic displacement
In each of two studies, subjects were exposed to a continuously changing prismatic displacement with a mean value of 19 prism diopters (variable displacement) and to a fixed 19-diopter displacement (fixed displacement). In Experiment 1, significant adaptation (post-pre shifts in hand-eye coordination) was found for fixed, but not for variable, displacement. Experiment 2 demonstrated that adaptation was obtained for variable displacement, but it was very fragile and is lost if the measures of adaptation are preceded by even a very brief exposure of the hand to normal or near-normal vision. Contrary to the results of some previous studies, an increase in within-S dispersion was not found of target pointing responses as a result of exposure to variable displacement
Comment on ``Consistent Sets Yield Contrary Inferences in Quantum Theory''
In a recent paper Kent has pointed out that in consistent histories quantum
theory it is possible, given initial and final states, to construct two
different consistent families of histories, in each of which there is a
proposition that can be inferred with probability one, and such that the
projectors representing these two propositions are mutually orthogonal. In this
note we stress that, according to the rules of consistent history reasoning two
such propositions are not contrary in the usual logical sense namely, that one
can infer that if one is true then the other is false, and both could be false.
No single consistent family contains both propositions, together with the
initial and final states, and hence the propositions cannot be logically
compared. Consistent histories quantum theory is logically consistent,
consistent with experiment as far as is known, consistent with the usual
quantum predictions for measurements, and applicable to the most general
physical systems. It may not be the only theory with these properties, but in
our opinion, it is the most promising among present possibilities.Comment: 2pages, uses REVTEX 3.
Atemporal diagrams for quantum circuits
A system of diagrams is introduced that allows the representation of various
elements of a quantum circuit, including measurements, in a form which makes no
reference to time (hence ``atemporal''). It can be used to relate quantum
dynamical properties to those of entangled states (map-state duality), and
suggests useful analogies, such as the inverse of an entangled ket. Diagrams
clarify the role of channel kets, transition operators, dynamical operators
(matrices), and Kraus rank for noisy quantum channels. Positive (semidefinite)
operators are represented by diagrams with a symmetry that aids in
understanding their connection with completely positive maps. The diagrams are
used to analyze standard teleportation and dense coding, and for a careful
study of unambiguous (conclusive) teleportation. A simple diagrammatic argument
shows that a Kraus rank of 3 is impossible for a one-qubit channel modeled
using a one-qubit environment in a mixed state.Comment: Minor changes in references. Latex 32 pages, 13 figures in text using
PSTrick
A Nonlinear Theory for Predicting the Effects of Unsteady Laminar, Turbulent, or Transitional Boundary Layers on the Attenuation of Shock Waves in a Shock Tube with Experimental Comparison
The linearized attenuation theory of NACA Technical Note 3375 is modified in the following manner: (a) an unsteady compressible local skin-friction coefficient is employed rather than the equivalent steady-flow incompressible coefficient; (b) a nonlinear approach is used to permit application of the theory to large attenuations; and (c) transition effects are considered. Curves are presented for predicting attenuation for a shock pressure ratio up to 20 and a range of shock-tube Reynolds numbers. Comparison of theory and experimental data for shock-wave strengths between 1.5 and 10 over a wide range of Reynolds numbers shows good agreement with the nonlinear theory evaluated for a transition Reynolds number of 2.5 X 10(exp 5)
Virtual Worlds and the Transformationof Business: Impacts on the U.S. Economy, Jobs, and Industrial Competitiveness
Virtual Worlds, immersive and collaborative environments on the Internet, also referred to as Web 3D, are likely to transform the global business environment. Developed out of online games, social networking, and Web services, Virtual Worlds benefit from several technologies that enhance their usefulness, including massively scaled games, avatars, cloud/on-demand/grid computing, on-demand storage, and next-generation networks. What this paper describes is how corporations in this century will begin to use new technologies to transform the methods of production, the generation of services, and the management of people and processes. To make our case, this paper:Explains Virtual Worlds and how on-demand/utility/grid computing, on-demand storage, and next-generation networks support their commercialization.Explores how Virtual Worlds and the technologies that support them can change the nature of the firm and influence collaboration in business.Describes the changes that give rise to collaborative enterprise, including the two likely main forms of organization: the multi-industry conglomerate and the modern guild system. We also explore how enhanced collaboration has the power to extend and alter the ways in which today's firms create products and services and redefine relationships with suppliers and customers.Discusses how Virtual Worlds and supporting technologies will affect U.S. industrial competitiveness and provides policy recommendations in a number of areas, including deployment and adoption of Virtual Worlds, collaboration, skills development, and the ideal business environment needed for full and rapid adoption of these new technologies
Deterministic and Unambiguous Dense Coding
Optimal dense coding using a partially-entangled pure state of Schmidt rank
and a noiseless quantum channel of dimension is studied both in
the deterministic case where at most messages can be transmitted with
perfect fidelity, and in the unambiguous case where when the protocol succeeds
(probability ) Bob knows for sure that Alice sent message , and when
it fails (probability ) he knows it has failed. Alice is allowed any
single-shot (one use) encoding procedure, and Bob any single-shot measurement.
For a bound is obtained for in terms of the largest
Schmidt coefficient of the entangled state, and is compared with published
results by Mozes et al. For it is shown that is strictly
less than unless is an integer multiple of , in which case
uniform (maximal) entanglement is not needed to achieve the optimal protocol.
The unambiguous case is studied for , assuming for a
set of messages, and a bound is obtained for the average
\lgl1/\tau\rgl. A bound on the average \lgl\tau\rgl requires an additional
assumption of encoding by isometries (unitaries when ) that are
orthogonal for different messages. Both bounds are saturated when is a
constant independent of , by a protocol based on one-shot entanglement
concentration. For it is shown that (at least) messages can
be sent unambiguously. Whether unitary (isometric) encoding suffices for
optimal protocols remains a major unanswered question, both for our work and
for previous studies of dense coding using partially-entangled states,
including noisy (mixed) states.Comment: Short new section VII added. Latex 23 pages, 1 PSTricks figure in
tex
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