Two-band fast Hartley transform

This article has been made available through the Brunel Open Access Publishing Fund.Efficient algorithms have been developed over the past 30 years for computing the forward and inverse discrete Hartley transforms (DHTs). These are similar to the fast Fourier transform (FFT) algorithms for computing the discrete Fourier transform (DFT). Most of these methods seek to minimise the complexity of computations and or the number of operations. A new approach for the computation of the radix-2 fast Hartley transform (FHT) is presented. The proposed algorithm, based on a two-band decomposition of the input data, possesses a very regular structure, avoids the input or out data shuffling, requires slightly less multiplications than the existing approaches, but increases the number of additions

Favorable and unfavorable lactation modulates the effects of electrical stimulation on brain excitability: A spreading depression study in adult rats

AbstractAimsWe investigated how different nutritional states resulting from distinct lactation conditions modulate the effects of cortical electrical stimulation (CES) on the excitability-related phenomenon known as cortical spreading depression (CSD).Main methodsWistar rats were reared in different litter sizes with 12, 6 or 3 pups, designated as malnourished (M), well-nourished (W) and overnourished (Ov), respectively. CSD was recorded for 4h on 2 cortical points of each cerebral hemisphere at baseline and after CES. CES was applied for 20min on the left cortex using a bipolar electrode placed between the CSD recording electrodes. Paired Student t test and ANOVA followed by Tukey test were used for statistical analysis (p<0.05).Key findingsThe lactation conditions significantly influenced body weight (the M and Ov groups presented the lowest and largest average weight, respectively) and modified the CSD velocities of propagation in adulthood (Ov<W<M CSD velocity). CES increased CSD velocity of propagation in the stimulated hemisphere in all groups, and in the non-stimulated hemisphere (8.66%±1.38) in the Ov group only. We observed nutritional-dependent CES effects on cortical excitability as evaluated by the different CSD velocities across the three groups (mean±sem, M (10.13%±1.70), Ov (14.65%±1.10) and W (25.70%±5.05)).SignificanceThese findings suggest valuable mechanisms of action for the brain stimulation techniques, which have gained importance because of their increasing use for the treatment of neuropsychiatric diseases. Data also suggest modulation of CES-effects by baseline excitability (as determined by the early nutritional state)

Análisis de solvencia en empresas no financieras: modelo estático versus modelo dinámico

El objetivo de este trabajo es establecer empíricamente una priorización razonada de los modelos estático y dinámico de evaluación de solvencia a la hora de realizar el diagnóstico financiero empresarial, en base a la bondad y grado de aciertos experimentados. Se utilizaron empresas concursadas como empresas objetivamente insolventes, en donde pudimos constatar el modelo más preciso en detección de insolvencias, resultando ser, además, el más completo, puesto que nos permitía reconocer claramente los tres momentos clave en el proceso de generación de solvencia, que se identifican con las posibles causas de dificultad financiera

Magnetoresistance of Three-Constituent Composites: Percolation Near a Critical Line

Scaling theory, duality symmetry, and numerical simulations of a random network model are used to study the magnetoresistance of a metal/insulator/perfect conductor composite with a disordered columnar microstructure. The phase diagram is found to have a critical line which separates regions of saturating and non-saturating magnetoresistance. The percolation problem which describes this line is a generalization of anisotropic percolation. We locate the percolation threshold and determine the t = s = 1.30 +- 0.02, nu = 4/3 +- 0.02, which are the same as in two-constituent 2D isotropic percolation. We also determine the exponents which characterize the critical dependence on magnetic field, and confirm numerically that nu is independent of anisotropy. We propose and test a complete scaling description of the magnetoresistance in the vicinity of the critical line.Comment: Substantially revised version; description of behavior in finite magnetic fields added. 7 pages, 7 figures, submitted to PR

Bianchi type II models in the presence of perfect fluid and anisotropic dark energy

Spatially homogeneous but totally anisotropic and non-flat Bianchi type II cosmological model has been studied in general relativity in the presence of two minimally interacting fluids; a perfect fluid as the matter fluid and a hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field equations have been solved by applying two kinematical ans\"{a}tze: we have assumed the variation law for the mean Hubble parameter that yields a constant value of deceleration parameter, and one of the components of the shear tensor has been considered proportional to the mean Hubble parameter. We have particularly dwelled on the accelerating models with non-divergent expansion anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we consider in the context of dark energy, can produce results that can be produced in the presence of isotropic fluid in accordance with the \Lambda CDM cosmology. However, the derived model gives additional opportunities by being able to allow kinematics that cannot be produced in the presence of fluids that yield only isotropic pressure. We have obtained well behaving cases where the anisotropy of the expansion and the anisotropy of the fluid converge to finite values (include zero) in the late Universe. We have also showed that although the metric we consider is totally anisotropic, the anisotropy of the dark energy is constrained to be axially symmetric, as long as the overall energy momentum tensor possesses zero shear stress.Comment: 15 pages; 5 figures; matches the version published in The European Physical Journal Plu

Some anisotropic universes in the presence of imperfect fluid coupling with spatial curvature

We consider Bianchi VI spacetime, which also can be reduced to Bianchi types VI0-V-III-I. We initially consider the most general form of the energy-momentum tensor which yields anisotropic stress and heat flow. We then derive an energy-momentum tensor that couples with the spatial curvature in a way so as to cancel out the terms that arise due to the spatial curvature in the evolution equations of the Einstein field equations. We obtain exact solutions for the universes indefinetly expanding with constant mean deceleration parameter. The solutions are beriefly discussed for each Bianchi type. The dynamics of the models and fluid are examined briefly, and the models that can approach to isotropy are determined. We conclude that even if the observed universe is almost isotropic, this does not necessarily imply the isotropy of the fluid (e.g., dark energy) affecting the evolution of the universe within the context of general relativity.Comment: 17 pages, no figures; to appear in International Journal of Theoretical Physics; in this version (which is more concise) an equation added, some references updated and adde

Density-functional calculation of ionization energies of current-carrying atomic states

Current-density-functional theory is used to calculate ionization energies of current-carrying atomic states. A perturbative approximation to full current-density-functional theory is implemented for the first time, and found to be numerically feasible. Different parametrizations for the current-dependence of the density functional are critically compared. Orbital currents in open-shell atoms turn out to produce a small shift in the ionization energies. We find that modern density functionals have reached an accuracy at which small current-related terms appearing in open-shell configurations are not negligible anymore compared to the remaining difference to experiment.Comment: 7 pages, 2 tables, accepted by Phys. Rev.

Response function analysis of excited-state kinetic energy functional constructed by splitting k-space

Over the past decade, fundamentals of time independent density functional theory for excited state have been established. However, construction of the corresponding energy functionals for excited states remains a challenging problem. We have developed a method for constructing functionals for excited states by splitting k-space according to the occupation of orbitals. In this paper we first show the accuracy of kinetic energy functional thus obtained. We then perform a response function analysis of the kinetic energy functional proposed by us and show why method of splitting the k-space could be the method of choice for construction of energy functionals for excited states.Comment: 11 page

Using smart meters to estimate low voltage losses

Losses on low voltage networks are often substantial. For example, in the UK they have been estimated as being 4% of the energy supplied by low voltage networks. However, the breakdown of the losses to individual conductors and their split over time are poorly understood as generally only the peak demands and average loads over several months have been recorded. The introduction of domestic smart meters has the potential to change this. How domestic smart meter readings can be used to estimate the actual losses is analysed. In particular, the accuracy of using 30 minute readings compared with 1 minute readings, and how this accuracy could be improved, were investigated. This was achieved by assigning the data recorded by 100 smart meters with a time resolution of 1 minute to three test networks. Smart meter data from three sources were used in the investigation. It was found that 30 minute resolution data underestimated the losses by between 9% and 24%. By fitting an appropriate model to the data, it was possible to reduce the inaccuracy by approximately 50%. Having a smart meter time resolution of 10 minutes rather than 30 gave little improvement to the accuracy