279 research outputs found
Embeddings into outer models
We explore the possibilities for elementary embeddings , where
and are models of ZFC with the same ordinals, , and
has access to large pieces of . We construct commuting systems of such maps
between countable transitive models that are isomorphic to various canonical
linear and partial orders, including the real line
The Role of Learning in Olfactory Sensitivity
INTRODUCTION: In recent years the psychological literature has reflected an increasing interest in the role of learning in perception. On the theoretical level, this interest is expressed principally by the considerable attention given to two current attempts to account for perceptual learning (Gibson & Gibson, 1955a: Postman, 1955). On the empirical level, the problems of industry and the military have generated a multitude of investigations in this area. These problems range in diversity from the training of military personnel in the identification of aircraft to the training of tasters in the food industry.
The remainder of this chapter will be devoted to a critical analysis of the theoretical formulation of perceptual learning and to a review of the empirical findings relevant to the present experiment
Pair Events in Superluminal Optics
When an object moves faster than emissions it creates, it may appear at two
positions simultaneously. The appearance or disappearance of this bifurcation
is referred to as a pair event. Inherently convolved with superluminal motion,
pair events have no subluminal counterparts. Common examples of superluminal
motions that exhibit pair events include Cherenkov radiation, sonic booms,
illumination fronts from variable light sources, and rotating beams. The
minimally simple case of pair events from a single massive object is explored
here: uniform linear motion. A pair event is perceived when the radial
component of the object's speed toward the observer drops from superluminal to
subluminal. Emission from the pair creation event will reach the observer
before emission from either of the two images created. Potentially observable
image pair events are described for sonic booms and Cherenkov light. To date,
no detection of discrete images following a projectile pair event have ever
been reported, and so the pair event nature of sonic booms and Cherenkov
radiation, for example, remains unconfirmed. Recent advances in modern
technology have made such pair event tracking feasible. If measured, pair
events could provide important information about object distance and history.Comment: 13 pages, 3 figures. in press: Annalen der Physi
Fostering Distance Education:Lessons From a United States-England Partnered Collaborative Online International Learning Approach
Quantum effects after decoherence in a quenched phase transition
We study a quantum mechanical toy model that mimics some features of a
quenched phase transition. Both by virtue of a time-dependent Hamiltonian or by
changing the temperature of the bath we are able to show that even after
classicalization has been reached, the system may display quantum behaviour
again. We explain this behaviour in terms of simple non-linear analysis and
estimate relevant time scales that match the results of numerical simulations
of the master-equation. This opens new possibilities both in the study of
quantum effects in non-equilibrium phase transitions and in general
time-dependent problems where quantum effects may be relevant even after
decoherence has been completed.Comment: 7 pages, 7 figures, revtex, important revisions made. To be published
in Phys. Rev.
Topologically protected quantum bits from Josephson junction arrays
All physical implementations of quantum bits (qubits), carrying the
information and computation in a putative quantum computer, have to meet the
conflicting requirements of environmental decoupling while remaining
manipulable through designed external signals. Proposals based on quantum
optics naturally emphasize the aspect of optimal isolation, while those
following the solid state route exploit the variability and scalability of
modern nanoscale fabrication techniques. Recently, various designs using
superconducting structures have been successfully tested for quantum coherent
operation, however, the ultimate goal of reaching coherent evolution over
thousands of elementary operations remains a formidable task. Protecting qubits
from decoherence by exploiting topological stability, a qualitatively new
proposal due to Kitaev, holds the promise for long decoherence times, but its
practical physical implementation has remained unclear so far. Here, we show
how strongly correlated systems developing an isolated two-fold degenerate
quantum dimer liquid groundstate can be used in the construction of
topologically stable qubits and discuss their implementation using Josephson
junction arrays.Comment: 6 pages, 4 figure
Molecular defect (Gla+ 14----Lys) and its functional consequences in a hereditary factor X deficiency (factor X" Vorarlberg").
Factor X (FX) "Vorarlberg" is a congenital FX deficiency characterized clinically by a mild bleeding tendency. Homozygous individuals have a FX activity of less than 10% in the extrinsic system and 25% in the intrinsic system. FX antigen is 20%. Using molecular techniques, two point mutations were detected in the coding sequence of the FX Vorarlberg gene: a G----A at base pair 160 in exon II resulting in a change of Gla14 (GAA) to Lys (AAA); a G----A at base pair 424 in exon V resulting in a change from Glu102 (GAG) to Lys (AAG). The mutations abolished a TaqI restriction site in exon II and an MnlI site in exon V. To determine whether these mutations are present on one or on both alleles, restriction analyses of amplified exon II and exon V fragments were performed. Analysis of the pedigree showed that the genotype for the mutation on exon II (homozygous versus heterozygous) correlates with the severity of the phenotypic coagulation defect. We therefore conclude that the mutation in exon II is responsible for the functional defect in FX Vorarlberg. We have also purified the mutant FX protein from patient plasma. Purified FX Vorarlberg is indistinguishable from normal FX on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its activity is 15% of normal FX upon activation with factor VIIa/tissue factor, 75% upon activation with factor IXa/factor VIIIa, and 100% upon activation with RVV. Activation at varying Ca2+ concentrations shows that the affinity of FX Vorarlberg for Ca2+ is decreased. Factor Xa Vorarlberg is able to convert prothrombin at a normal rate but also shows decreased affinity for Ca2+ in this interaction. Upon addition of Ca2+, FX Vorarlberg does not undergo the same conformational change as normal FX. Our data show that FX Vorarlberg has a decreased affinity for Ca2+ which impedes a normal conformational change. This leads to a decreased rate of activation by factor VIIa/tissue factor and by factor IXa. The decrease is much more marked for the extrinsic than for the intrinsic pathway
Adiabatic evolution of a coupled-qubit Hamiltonian
We present a general method for studying coupled qubits driven by
adiabatically changing external parameters. Extended calculations are provided
for a two-bit Hamiltonian whose eigenstates can be used as logical states for a
quantum CNOT gate. From a numerical analysis of the stationary Schroedinger
equation we find a set of parameters suitable for representing CNOT, while from
a time-dependent study the conditions for adiabatic evolution are determined.
Specializing to a concrete physical system involving SQUIDs, we determine
reasonable parameters for experimental purposes. The dissipation for SQUIDs is
discussed by fitting experimental data. The low dissipation obtained supports
the idea that adiabatic operations could be performed on a time scale shorter
than the decoherence time.Comment: 10 pages, 4 figures, to be pub.in Phys Rev
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