S-matrix poles and the second virial coefficient

For cutoff potentials, a condition which is not a limitation for the calculation of physical systems, the S-matrix is meromorphic. We can express it in terms of its poles, and then calculate the quantum mechanical second virial coefficient of a neutral gas. Here, we take another look at this approach, and discuss the feasibility, attraction and problems of the method. Among concerns are the rate of convergence of the 'pole' expansion and the physical significance of the 'higher' poles.Comment: 20 pages, 8 tables, submitted to J. Mol. Phy

Receiving Aphasia Intervention in a Virtual Environment: The Participants’ Perspective

Background: Digital technology is making an increasing contribution to aphasia therapy. However applications of virtual reality are rare. EVA Park is a virtual island developed with and for people with aphasia. It is a multi-user environment, which enables people with aphasia to interact with support workers, therapists and each other. The first study to use EVA Park in aphasia rehabilitation demonstrated significant gains in functional communication. This paper augments the findings of that study, by reporting results from qualitative interviews conducted with the 20 study participants. Aims: This study aimed to determine the views of participants about the intervention that they received in EVA Park, and the impacts of that intervention. Long-term retrospective views were also explored. Methods & Procedures: Participants took part in 1:1, semi-structured interviews two weeks before (Entry) and to weeks after (Exit) the intervention. Questions focussed on activities undertaken by participants, communication, changes since the stroke and uses of technology. Exit interviews additionally explored participants’ views and experiences of EVA Park and any perceived impacts of the intervention. A sub-set of 5 participants was interviewed at least one year later, to explore long term recollections of the EVA Park intervention and any perceived long term impacts. Interview data were transcribed and subject to framework analysis. Outcomes & Results: The thematic framework comprised 10 parent themes and 33 sub-themes. Following ‘affect’, the largest single theme related to EVA Park, with 636 coded references. Comments were overwhelmingly positive. EVA Park intervention was strongly associated with fun and enjoyment. Participants particularly valued their relationship with the support workers who delivered the intervention. The virtual locations and activities in EVA Park were also appreciated, together with the contact with other participants. Perceived impacts related to communication, activity, computer use and confidence. Most participants in the long term interviews described maintained impacts. Conclusions: These interview results indicate that the first intervention delivered in EVA Park was highly acceptable to participants and perceived as beneficial. They augment the findings of our experimental study and suggest that EVA Park could be a valuable addition to the resources available to practising clinician

The influence of defined ante-mortem stressors on the early post-mortem biochemical processes in the abdominal muscle of the Norway lobster, Nephrops norvegicus (Linnaeus, 1758)

The effects of four different ante-mortem stressors (exercise, emersion, starvation and a patent infection with the parasite Hematodinium sp.) on post-mortem processes have been investigated in the abdominal muscle of Norway lobster Nephrops norvegicus by measuring changes in the pH, the levels of glycogen, l-lactate, arginine phosphate, ATP, ADP, AMP, IMP, HxR, Hx and the adenylate energy charge (AEC) over a time course of 24 h with samples being taken at 0, 3, 6, 12 and 24 h. The acute stresses of intense exercise and 2 h emersion resulted in a premature onset of anaerobic glycolysis, leading both to an enhanced glycogen depletion rate and an early accumulation of l-lactate. The chronic stressors, starvation and parasite infection, resulted in a complete ante-mortem depletion of muscle glycogen and consequently the failure of post-mortem glycolytic fermentation. Post-mortem pH and ATP inter-conversion were significantly altered in chronically stressed animals. Ante-mortem, a rapid, almost complete depletion of arginine phosphate was observed in all stress groups. The AEC was altered significantly by all stresses, indicating a strong energy demand. The findings suggest that ante-mortem stressors strongly influence the post-mortem biochemical processes. The laboratory-based results are compared to 'field' data and effects on post-harvest product quality are discussed

Time-Dependent Density Functional Theory of Open Quantum Systems in the Linear-Response Regime

Time-Dependent Density Functional Theory (TDDFT) has recently been extended to describe many-body open quantum systems (OQS) evolving under non-unitary dynamics according to a quantum master equation. In the master equation approach, electronic excitation spectra are broadened and shifted due to relaxation and dephasing of the electronic degrees of freedom by the surrounding environment. In this paper, we develop a formulation of TDDFT linear-response theory (LR-TDDFT) for many-body electronic systems evolving under a master equation, yielding broadened excitation spectra. This is done by mapping an interacting open quantum system onto a non-interacting open Kohn-Sham system yielding the correct non-equilibrium density evolution. A pseudo-eigenvalue equation analogous to the Casida equations of usual LR-TDDFT is derived for the Redfield master equation, yielding complex energies and Lamb shifts. As a simple demonstration, we calculate the spectrum of a C$^{2+}$ atom in an optical resonator interacting with a bath of photons. The performance of an adiabatic exchange-correlation kernel is analyzed and a first-order frequency-dependent correction to the bare Kohn-Sham linewidth based on Gorling-Levy perturbation theory is calculated.Comment: 18 pages, 4 figure

Integral representation of one dimensional three particle scattering for delta function interactions

The Schr\"{o}dinger equation, in hyperspherical coordinates, is solved in closed form for a system of three particles on a line, interacting via pair delta functions. This is for the case of equal masses and potential strengths. The interactions are replaced by appropriate boundary conditions. This leads then to requiring the solution of a free-particle Schr\"{o}dinger equation subject to these boundary conditions. A generalized Kontorovich - Lebedev transformation is used to write this solution as an integral involving a product of Bessel functions and pseudo-Sturmian functions. The coefficient of the product is obtained from a three-term recurrence relation, derived from the boundary condition. The contours of the Kontorovich-Lebedev representation are fixed by the asymptotic conditions. The scattering matrix is then derived from the exact solution of the recurrence relation. The wavefunctions that are obtained are shown to be equivalent to those derived by McGuire. The method can clearly be applied to a larger number of particles and hopefully might be useful for unequal masses and potentials.Comment: 18 pages, 2 figures, to be published in J. Math. Phy

Medidas experimentales de desplazamientos micrométricos basadas en vórtices ópticos

In this work, a system for measuring micrometer-displacements based on the characteristics of optical vortices is presented. In the proposal, a binary vortex-producing lens (BVPL) programmed to generate optimized optical vortices is transversally displaced from the optical axis, inducing perturbations on the optical characteristics of the vortices that are used as transduction parameters. Specifically, the method proposed theoretically by Anzolin et al. [18], which is based on the asymmetry of the intensity patterns of the off-axis optical vortices, is studied experimentally by using BVPLs. Experimental implementation is completely described and compared with theoretical results, likewise, metrological characteristics of the experimental metrological system are analyzed. Based on the results, we experimentally confirm the possibility of creating high sensitivity metrological systems by using optical vortices, opening the door for new vortex metrology techniques.En este trabajo, un sistema para medir desplazamientos micrométricos basados en las características de vórtices ópticos es presentado. En la propuesta, una lente productora de vórtices binaria (BVPL) programada para generar vórtices ópticos optimizados es desplazada transversalmente del eje óptico, induciendo perturbaciones en las características ópticas de los vórtices que son usadas como parámetros de transducción. Específicamente, el método propuesto por Anzolín et al [18], el cuál es basado en la asimetría de los patrones de intensidad de los vórtices ópticos fuera del eje, es estudiado experimentalmente usando BVPLs. Se describe completamente la implementación experimental y se compara con los resultados teóricos, así mismo, se analizan características metrológicas del sistema metrológico experimental. En base a los resultados, confirmamos experimentalmente la posibilidad de crear sistemas metrológicos de alta sensibilidad utilizando vórtices ópticos, abriendo la puerta para nuevas técnicas de metrología de vórtices.Centro de Investigaciones Óptica

Seasonal nutritional status in Norway lobsters, Nephrops norvegicus (L.): Are females nutritionally compromised over the winter? (Forthcoming)

Norway lobsters, Nephrops norvegicus, are sediment-dwelling decapod crustaceans that excavate burrows from which they make short excursions to feed by predation and scavenging. The females of this species are known to reside within their burrows for an extended period of time over the winter while brooding their eggs. The aim of this study was to assess the likelihood of these females being able to feed during this brooding period. Biophysical and biochemical measurements that had previously been shown to change with starvation under laboratory conditions in male N. norvegicus were taken for female N. norvegicus under similar conditions. These measurements were also compared in both sexes obtained from monthly trawl samples from the Clyde Sea Area, Scotland, UK, together with trawl composition data. The laboratory study showed that the hepatosomatic index, and the copper, lipid and water content of the hepatopancreas can be used as indicators of the state of starvation in females, as in males. In the wild, both sexes have reduced nutritional status during the winter, but not to the degree seen in animals starved for 20 weeks in aquarium trials. This study does not support the hypothesis that females cease feeding over winter, during their brooding period. Firstly, some females were unable to sustain ovary development during starvation under controlled conditions, contrary to field observations. Secondly, field data suggests that there is no sex-specific reduction in nutritional status

Algoritmo memético con operadores de inteligencia artificial para el CARP con inicio y fin no determinado y bio-bjetivo

The arc routing problem with a variable starting/ending position (Open Capacitated Arc Routing Problem - OCARP), in its classic version, pursues the best strategy to serve a set of customers located in the network arcs using vehicles. Compared to the Capacitated Arc Routing Problem (CARP), the OCARP lacks of constrains that guarantee that each vehicle ought to start and end the tour at a given vertex (also known as a depot). The aim of this paper is to propose a heuristic to find an efficient frontier for the main objective functions: minimize the number of vehicles and the total cost. Additionally, a hybrid algorithm that complements the genetic algorithm with artificial intelligence operator is proposed.El Problema de ruteo de vehículos sobre arcos con punto de inicio/fin variable (Open Capacitated Arc Routing Problem - OCARP), en su versión clásica, busca determinar la mejor estrategia para servir un conjunto de clientes localizados en los arcos de una red usando vehículos. A diferencia del Capacitated Arc Routing Problem (CARP), el OCARP no tiene las restricciones que aseguran que cada vehículo debe iniciar y terminar su ruta en un vértice dado (también conocido como depósito). El objetivo de este trabajo es proponer una heurística para encontrar la frontera eficiente dados dos objetivos: minimizar el número de vehículos y minimizar el costo total. Adicionalmente se propone complementar la heurística, la cual es basada en algoritmos genéticos, con operadores de inteligencia artificial