551 research outputs found
The more often you see an object, the easier it becomes to track it
Is it easier to track objects that you have seen repeatedly? We compared repeated blocks, where identities were the same from trial to trial, to unrepeated blocks, where identities varied. People were better in tracking objects that they saw repeatedly. We tested four hypotheses to explain this repetition benefit. First, perhaps the repeated condition benefits from consistent mapping of identities to target and distractor roles. However, the repetition benefit persisted even when both the repeated and the unrepeated conditions used consistent mapping. Second, repetition might improve the ability to recover targets that have been lost, or swapped with distractors. However, we observed a larger repetition benefit for color-color conjunctions, which do not benefit from such error recovery processes, than for unique features, which do. Furthermore, a repetition benefit was observed even in the absence of distractors. Third, perhaps repetition frees up resources by reducing memory load. However, increasing memory load by masking identities during the motion phase reduced the repetition benefit. The fourth hypothesis is that repetition facilitates identity tracking, which in turn improves location tracking. This hypothesis is consistent with all our results. Thus, our data suggest that identity and location tracking share a common resource
Sample convection in liquid-state NMR: Why it is always with us, and what we can do about it
AbstractMany NMR experiments on liquids suffer if the sample convects. This is particularly true for applications, such as the measurement of diffusion, that rely on spatial labelling of spins. It is widely assumed that, in most well-conducted experiments with stable temperature regulation, samples do not convect. Unfortunately this is not the case. It is shown here that typical NMR samples show measurable convective flow for all but a very narrow range of temperatures; convection is seen both above and below this range, which can be as small as a degree or so for a mobile solvent such as chloroform. This convection is driven by both vertical and horizontal temperature gradients.Measurements of convection velocity are presented for a range of samples, sample tubes, probes, and temperatures. Both decreasing sample tube inner diameter and changing sample tube material from glass to sapphire can slow convection markedly, with sapphire tubes being particularly effective. Such tubes are likely to be particularly helpful for accurate measurement of diffusion by NMR
Superfield Theories in Tensorial Superspaces and the Dynamics of Higher Spin Fields
We present the superfield generalization of free higher spin equations in
tensorial superspaces and analyze tensorial supergravities with GL(n) and SL(n)
holonomy as a possible framework for the construction of a non-linear higher
spin field theory. Surprisingly enough, we find that the most general solution
of the supergravity constraints is given by a class of superconformally flat
and OSp(1|n)-related geometries. Because of the conformal symmetry of the
supergravity constraints and of the higher spin field equations such geometries
turn out to be trivial in the sense that they cannot generate a `minimal'
coupling of higher spin fields to their potentials even in curved backgrounds
with a non-zero cosmological constant. This suggests that the construction of
interacting higher spin theories in this framework might require an extension
of the tensorial superspace with additional coordinates such as twistor-like
spinor variables which are used to construct the OSp(1|2n) invariant
(`preonic') superparticle action in tensorial superspace.Comment: LaTeX, 30 pages, no figures. V2. Discussion on conventional
constraints extended, typos corrected, JHEP style, to appear in JHE
Three-algebra for supermembrane and two-algebra for superstring
While string or Yang-Mills theories are based on Lie algebra or two-algebra
structure, recent studies indicate that M-theory may require a one higher,
three-algebra structure. Here we construct a covariant action for a
supermembrane in eleven dimensions, which is invariant under global
supersymmetry, local fermionic symmetry and worldvolume diffeomorphism. Our
action is classically on-shell equivalent to the celebrated
Bergshoeff-Sezgin-Townsend action. However, the novelty is that we spell the
action genuinely in terms of Nambu three-brackets: All the derivatives appear
through Nambu brackets and hence it manifests the three-algebra structure.
Further the double dimensional reduction of our action gives straightforwardly
to a type IIA string action featuring two-algebra. Applying the same method, we
also construct a covariant action for type IIB superstring, leading directly to
the IKKT matrix model.Comment: 1+15 pages, no figure; Refs added, Accepted for publication in JHE
Quantum theta functions and Gabor frames for modulation spaces
Representations of the celebrated Heisenberg commutation relations in quantum
mechanics and their exponentiated versions form the starting point for a number
of basic constructions, both in mathematics and mathematical physics (geometric
quantization, quantum tori, classical and quantum theta functions) and signal
analysis (Gabor analysis).
In this paper we try to bridge the two communities, represented by the two
co--authors: that of noncommutative geometry and that of signal analysis. After
providing a brief comparative dictionary of the two languages, we will show
e.g. that the Janssen representation of Gabor frames with generalized Gaussians
as Gabor atoms yields in a natural way quantum theta functions, and that the
Rieffel scalar product and associativity relations underlie both the functional
equations for quantum thetas and the Fundamental Identity of Gabor analysis.Comment: 38 pages, typos corrected, MSC class change
Polyhedral Analysis using Parametric Objectives
The abstract domain of polyhedra lies at the heart of many program analysis techniques. However, its operations can be expensive, precluding their application to polyhedra that involve many variables. This paper describes a new approach to computing polyhedral domain operations. The core of this approach is an algorithm to calculate variable elimination (projection) based on parametric linear programming. The algorithm enumerates only non-redundant inequalities of the projection space, hence permits anytime approximation of the output
Evaluación de los efectos de la incorporación de las herramientas web 2.0 en el diseño de nuestra práctica docente
A lo largo del curso 2011/2012, un grupo de profesores venimos
desarrollando un Proyecto De Innovación y Mejora de la Calidad Docente,
subvencionado por la Universidad Complutense (PIMCD nº 169) cuya
finalidad es diseñar y desarrollar, para la asignatura “Orientación educativa y
Acción tutorial” del grado de Maestro, propuestas metodológicas que
incorporen diferentes herramientas colaborativas en línea (herramientas web
2.0) para potenciar el trabajo colaborativo y para facilitar el aprendizaje
significativo.
Tres son los ejes que están centrando nuestro trabajo:
1. Formación del profesorado para el uso de herramientas web 2.0.
2. Diseño: integración de lo aprendido para el diseño de propuestas
metodológicas apoyadas en el uso de dichas herramientas.
3. Evaluación del proceso: análisis crítico de las efectos que la
incorporación de las herramientas web 2.0 pueda tener en la mejora
de nuestra competencia y los beneficios para el aprendizaje de
nuestros estudiantes. Esta evaluación, a su vez, se focalizará en dos
cuestiones: mejora de la competencia digital de los profesores
(conocimiento y maneo de las herramientas web 2.0) y valoración de
los materiales diseñados para su utilización en el aula, analizando los
beneficios que la utilización de herramientas 2.0 puede tener en el
logro de un aprendizaje significativo por parte del alumnado.
El trabajo que presentamos a continuación hacer referencia a la
valoración de las actividades diseñadas para uno de los grupos de
docencia con los que hemos venido trabajando durante el curso 2011-
2012.Peer Reviewe
ABJM models in N=3 harmonic superspace
We construct the classical action of the Aharony-Bergman-Jafferis-Maldacena
(ABJM) model in the N=3, d=3 harmonic superspace. In such a formulation three
out of six supersymmetries are realized off shell while the other three mix the
superfields and close on shell. The superfield action involves two
hypermultiplet superfields in the bifundamental representation of the gauge
group and two Chern-Simons gauge superfields corresponding to the left and
right gauge groups. The N=3 superconformal invariance allows only for a minimal
gauge interaction of the hypermultiplets. Amazingly, the correct sextic scalar
potential of ABJM emerges after the elimination of auxiliary fields. Besides
the original U(N)xU(N) ABJM model, we also construct N=3 superfield
formulations of some generalizations. For the SU(2)xSU(2) case we give a simple
superfield proof of its enhanced N=8 supersymmetry and SO(8) R-symmetry.Comment: 1+35 pages, minor changes, a reference added, published versio
Photomodulation of transmembrane transport and potential by stiff-stilbene based bis(thio)ureas
NWOSupramolecular & Biomaterials Chemistr
Infrared Features of the Landau Gauge QCD
The infrared features of Landau gauge QCD are studied by the lattice
simulation of and . We
adopt two definitions of the gauge field; 1) linear 2) and
measured the gluon propagator and ghost propagator. Infrared singularity of the
gluon propagator is less than that of tree level result but the gluon
propagator at 0 momentum remains finite. The infrared singularity of ghost
propagator is stronger than the tree level. The QCD running coupling measured
by using the gluon propagator and the ghost propagator has a maximum
at around and decreases as approaches 0.
The data are analyzed in use of formula of the principle of minimal
sensitivity(PMS), the effective charge method and the contour-improved
perturbation method, which suggest necessity of the resummation of perturbation
series in the infrared region together with existence of the infrared fixed
point. Kugo-Ojima parameter saturates at about -0.8 in contrast to the
theoretically expected value -1.Comment: RevTex4, 9 pages, 10 eps figures, Typos corrected. To be published in
Phys. Rev. D(2004
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