Mechanisms of Interference in Vibrotactile Working Memory

In previous studies of interference in vibrotactile working memory, subjects were presented with an interfering distractor stimulus during the delay period between the target and probe stimuli in a delayed match-to-sample task. The accuracy of same/different decisions indicated feature overwriting was the mechanism of interference. However, the distractor was presented late in the delay period, and the distractor may have interfered with the decision-making process, rather than the maintenance of stored information. The present study varies the timing of distractor onset, (either early, in the middle, or late in the delay period), and demonstrates both overwriting and non-overwriting forms of interference

Hestenes' Tetrad and Spin Connections

Defining a spin connection is necessary for formulating Dirac's bispinor equation in a curved space-time. Hestenes has shown that a bispinor field is equivalent to an orthonormal tetrad of vector fields together with a complex scalar field. In this paper, we show that using Hestenes' tetrad for the spin connection in a Riemannian space-time leads to a Yang-Mills formulation of the Dirac Lagrangian in which the bispinor field is mapped to a set of Yang-Mills gauge potentials and a complex scalar field. This result was previously proved for a Minkowski space-time using Fierz identities. As an application we derive several different non-Riemannian spin connections found in the literature directly from an arbitrary linear connection acting on Hestenes' tetrad and scalar fields. We also derive spin connections for which Dirac's bispinor equation is form invariant. Previous work has not considered form invariance of the Dirac equation as a criterion for defining a general spin connection

New Discrete Basis for Nuclear Structure Studies

A complete discrete set of spherical single-particle wave functions for studies of weakly-bound many-body systems is proposed. The new basis is obtained by means of a local-scale point transformation of the spherical harmonic oscillator wave functions. Unlike the harmonic oscillator states, the new wave functions decay exponentially at large distances. Using the new basis, characteristics of weakly-bound orbitals are analyzed and the ground state properties of some spherical doubly-magic nuclei are studied. The basis of the transformed harmonic oscillator is a significant improvement over the harmonic oscillator basis, especially in studies of exotic nuclei where the coupling to the particle continuum is important.Comment: 13 pages, RevTex, 6 p.s. figures, submitted to Phys. Rev.

Dynamical description of the buildup process in resonant tunneling: Evidence of exponential and non-exponential contributions

The buildup process of the probability density inside the quantum well of a double-barrier resonant structure is studied by considering the analytic solution of the time dependent Schr\"{o}dinger equation with the initial condition of a cutoff plane wave. For one level systems at resonance condition we show that the buildup of the probability density obeys a simple charging up law, $| \Psi (\tau) / \phi | =1-e^{-\tau /\tau_0},$ where $\phi$ is the stationary wave function and the transient time constant $\tau_0$ is exactly two lifetimes. We illustrate that the above formula holds both for symmetrical and asymmetrical potential profiles with typical parameters, and even for incidence at different resonance energies. Theoretical evidence of a crossover to non-exponential buildup is also discussed.Comment: 4 pages, 2 figure

Switching the stereochemical outcome of 6-endo-trig cyclizations; Synthesis of 2,6-Cis-6-substituted 4-oxopipecolic acids

A base-mediated 6-endo-trig cyclization of readily accessible enone-derived α-amino acids has been developed for the direct synthesis of novel 2,6-cis-6- substituted-4-oxo-L-pipecolic acids. A range of aliphatic and aryl side chains were tolerated by this mild procedure to give the target compounds in good overall yields. Molecular modeling of the 6-endo-trig cyclization allowed some insight as to how these compounds were formed, with the enolate intermediate generated via an equilibrium process, followed by irreversible tautomerization/neutralization providing the driving force for product formation. Stereoselective reduction and deprotection of the resulting 2,6-cis-6-substituted 4-oxo-L-pipecolic acids to the corresponding 4-hydroxy-L-pipecolic acids was also performed

String Theory on Warped AdS_3 and Virasoro Resonances

We investigate aspects of holographic duals to time-like warped AdS_3 space-times--which include G\"odel's universe--in string theory. Using worldsheet techniques similar to those that have been applied to AdS_3 backgrounds, we are able to identify space-time symmetry algebras that act on the dual boundary theory. In particular, we always find at least one Virasoro algebra with computable central charge. Interestingly, there exists a dense set of points in the moduli space of these models in which there is actually a second commuting Virasoro algebra, typically with different central charge than the first. We analyze the supersymmetry of the backgrounds, finding related enhancements, and comment on possible interpretations of these results. We also perform an asymptotic symmetry analysis at the level of supergravity, providing additional support for the worldsheet analysis.Comment: 24 pages + appendice

Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States

We present the study of weakly bound, neutron-rich nuclei using the nuclear shell model employing the complex Berggren ensemble representing the bound single-particle states, unbound Gamow states, and the non-resonant continuum. In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body finite depth (Woods-Saxon) potential and a residual two-body interaction. We discuss the basic ingredients of the Gamow Shell Model. The formalism is illustrated by calculations involving {\it several} valence neutrons outside the double-magic core: $^{6-10}$He and $^{18-22}$O.Comment: 19 pages, 20 encapsulated PostScript figure

Response of macroinvertebrates to experimental nutrient and fish additions in European localities at different latitudes

The sedimentary and plant-associated macroinvertebrate communities have been examined in a series of mesocosm experiments carried out in five locations, in Finland, Sweden, UK, Northwest Spain and Mediterranean Spain (the International Mesocosm Experiment). The experiments were designed to investigate how shallow lake ecosystems respond to the addition of nutrients and planktivorous fish along a climate gradient. Nutrient additions increased sedimentary benthos densities and total biomass to a plateau at intermediate levels of nutrients. The effect was greater in the warmest localities. Beyond the saturation point a further increase in nutrient loading had different effects depending on locality. Only in the southernmost site (in Mediterranean Spain), did it induce a shift to a turbid phase and macrophyte disappearance. Thus there are breakpoints in the relationship with nutrients, leading to alternative sediment communities subsequent to the water alternative states. Presence of fish increased the densities and biomass of sediment macroinvertebrates, more clearly in the more southern locality, where the fish Gambusia did not prey in the bottom animals. A stabilising role of macrophytes was observed by cutting them, samples taken three weeks after cutting indicated a higher effect of fish on the sediment community when macrophytes were not present. Nutrients tended also to increase densities of plant associated macroinvertebrates at low levels with a flattening of response at intermediate levels and a decline at high levels. At high fish level the numbers and biomass of plant-associated macroinvertebrates were lowered in all cases, because of increased predation. However fish addition at low level in most cases had the opposite effect, because their predation pressure was not high and regeneration of nutrients through their activities might increase food availability and control invertebrate predators. Fish influenced especially community composition, because they prey selectively. Addition of fish at low densities increased macroinvertebrate diversity. A diel migratory cycle was observed in plant-associated macroinvertebrates, but only in the southerly locations. Latitudinal influences on the structure of the macroinvertebrate communities occur but that they operate indirectly. There was a prominent effect of nutrients on these communities so that starting trophy is very important. Fish effects are layered on these and depend to a large extent on the particular range of diet of the species involved.Se ha estudiado la comunidad de macroinvertebrados bentónicos del sedimento así como la de los asociados a los macrófitos en una serie de mesocosmos concebidos para un experimento múltiple simultáneo llevado a cabo en cinco localidades europeas: Finlandia, Suecia, Reino Unido (UK), Noroeste de España y Levante Español. El experimento fue diseñado para investigar como responden los ecosistemas de lagos someros a los aportes de nutrientes y a la abundancia de peces planctívoros a lo largo de un gradiente climático. La adición de nutrientes incrementó la densidad del bentos del sedimento y su biomasa hasta estabilizarse a niveles intermedios de nutrientes, siendo este efecto mayor en las latitudes más bajas y cálidas. Más allá del punto de saturación, un aumento adicional de la carga de nutrientes tuvo efectos diferentes dependiendo de la localidad y solo en el lugar de menor latitud, (en el Levante Español) indujo el cambio hacia una fase turbia, con desaparición de los macrófitos, esto es, hay puntos de ruptura relacionados con la carga de nutrientes que conducen a comunidades alternativas en el sedimento, subsiguientes a los mencionados estados alternativos en las aguas someras. La presencia de peces aumentó la densidad y biomasa de los macroinvertebrados del sedimento, ello también más claramente en la localidad situada más al Sur, ya que el pez planctívoro ensayado (Gambusia) por lo general no depreda en los animales del sedimento. Se observó también el papel estabilizador de los macrófitos comparando las muestras tomadas antes y después de que estos fueran cortados, por ejemplo se observó un efecto mayor de los peces en las comunidades del sedimento cuando los macrófitos no estaban presentes. Los nutrientes tendieron también a incrementar las densidades de los macroinvertebrados asociados a los macrófitos cuando se aportan a bajos niveles, con una estabilización de la respuesta para los valores intermedios y un declive para los valores más altos. Cuando se adicionaron densidades altas de peces, el número y biomasa de los macroinvertebrados asociados a los macrófitos descendieron en todos los casos, como resultado del aumento de la depredación. Sin embargo, las adiciones a baja densidad de peces, en la mayoría de los casos, tuvo el efecto contrario, ya que su presión de depredación no es alta y pueden contribuir a la regeneración de los nutrientes a través de la vía detrítica que incrementa la disponibilidad de alimento, así como al control de otros invertebrados depredadores. La presencia de peces influenció especialmente la composición de la comunidad, ya que su depredación es selectiva. La adición de peces en bajas densidades aumentó la diversidad de los macroinvertebrados. También fue observado que el ciclo diario de migración en los macroinvertebrados asociados a los macrófitos, es más importante en las localidades ubicadas en las latitudes de más al Sur. Las influencias latitudinales en la estructura de las comunidades de macroinvertebrados, si bien sucede, opera indirectamente. Hay un efecto dominante de los nutrientes en estas comunidades, y el nivel trófico de las condiciones iniciales es muy importante. Los efectos de los peces se subordinan al de los nutrientes y dependen en gran medida de la dieta de las especies involucradas

GeantV: Results from the prototype of concurrent vector particle transport simulation in HEP

Full detector simulation was among the largest CPU consumer in all CERN experiment software stacks for the first two runs of the Large Hadron Collider (LHC). In the early 2010's, the projections were that simulation demands would scale linearly with luminosity increase, compensated only partially by an increase of computing resources. The extension of fast simulation approaches to more use cases, covering a larger fraction of the simulation budget, is only part of the solution due to intrinsic precision limitations. The remainder corresponds to speeding-up the simulation software by several factors, which is out of reach using simple optimizations on the current code base. In this context, the GeantV R&D project was launched, aiming to redesign the legacy particle transport codes in order to make them benefit from fine-grained parallelism features such as vectorization, but also from increased code and data locality. This paper presents extensively the results and achievements of this R&D, as well as the conclusions and lessons learnt from the beta prototype.Comment: 34 pages, 26 figures, 24 table

An investigation of uniform expansions of large order Bessel functions in Gravitational Wave Signals from Pulsars

In this work, we extend the analytic treatment of Bessel functions of large order and/or argument. We examine uniform asymptotic Bessel function expansions and show their accuracy and range of validity. Such situations arise in a variety of applications, in particular the Fourier transform of the gravitational wave signal from a pulsar. The uniform expansion we consider here is found to be valid in the entire range of the argument