A fast method for fuzzy neural modeling and refinement

In the identification of complex dynamic systems using fuzzy neural networks, one of the main issues is the curse of dimensionality, which makes it difficult to retain a large number of system inputs or to consider a large number of fuzzy sets. Moreover, due to the correlations, not all possible network inputs or regression vectors in the network are necessary and adding them simply increases the model complexity and deteriorates the network generalisation performance. In this paper, the problem is solved by first proposing a fast algorithm for selection of network terms, and then introducing a refinement procedure to tackle the correlation issue. Simulation results show the efficacy of the method.

Low power field programmable gate array implementation of fast digital signal processing algorithms: characterisation and manipulation of data locality

Dynamic power consumption is very dependent on interconnect, so clever mapping of digital signal processing algorithms to parallelised realisations with data locality is vital. This is a particular problem for fast algorithm implementations where typically, designers will have sacrificed circuit structure for efficiency in software implementation. This study outlines an approach for reducing the dynamic power consumption of a class of fast algorithms by minimising the index space separation; this allows the generation of field programmable gate array (FPGA) implementations with reduced power consumption. It is shown how a 50% reduction in relative index space separation results in a measured power gain of 36 and 37% over a Cooley-Tukey Fast Fourier Transform (FFT)-based solution for both actual power measurements for a Xilinx Virtex-II FPGA implementation and circuit measurements for a Xilinx Virtex-5 implementation. The authors show the generality of the approach by applying it to a number of other fast algorithms namely the discrete cosine, the discrete Hartley and the Walsh-Hadamard transforms.

Generation and optimization of electron currents along the walls of a conical target for fast ignition

The interaction of an ultraintense laser pulse with a conical target is studied by means of numerical particle-in-cell simulations in the context of fast ignition. The divergence of the fast electron beam generated at the tip of the cone has been shown to be a crucial parameter for the efficient coupling of the ignition laser pulse to the precompressed fusion pellet. In this paper, we demonstrate that a focused hot electron beam is produced at the cone tip, provided that electron currents flowing along the surfaces of the cone sidewalls are efficiently generated. The influence of various interaction parameters over the formation of these wall currents is investigated. It is found that the strength of the electron flows is enhanced for high laser intensities, low density targets, and steep density gradients inside the cone. The hot electron energy distribution obeys a power law for energies of up to a few MeV, with the addition of a high-energy Maxwellian tail.

Whose play is it anyway?: Theatre Studies, Translation Studies and translation for the stage

This article explores the historical neglect of translation as a consideration in the study and practice of theatre in the United States and Europe. While the study of literature is fairly strictly divided between English-language and Comparative Literature departments, theatre and drama have shown little concern about language as a barrier to reception of the dramatic text. Arguably, this discrepancy may be traced to a fundamental gap between the perceived status of the novel as a completed work of art and the playtext as work of art in progress, waiting to find its completion in performance.

Fast automatic two-stage nonlinear model identification based on the extreme learning machine

It is convenient and effective to solve nonlinear problems with a model that has a linear-in-the-parameters (LITP) structure. However, the nonlinear parameters (e.g. the width of Gaussian function) of each model term needs to be pre-determined either from expert experience or through exhaustive search. An alternative approach is to optimize them by a gradient-based technique (e.g. Newton’s method). Unfortunately, all of these methods still need a lot of computations. Recently, the extreme learning machine (ELM) has shown its advantages in terms of fast learning from data, but the sparsity of the constructed model cannot be guaranteed. This paper proposes a novel algorithm for automatic construction of a nonlinear system model based on the extreme learning machine. This is achieved by effectively integrating the ELM and leave-one-out (LOO) cross validation with our two-stage stepwise construction procedure [1]. The main objective is to improve the compactness and generalization capability of the model constructed by the ELM method. Numerical analysis shows that the proposed algorithm only involves about half of the computation of orthogonal least squares (OLS) based method. Simulation examples are included to confirm the efficacy and superiority of the proposed technique.

Investigating the mechanism of the H 2-assisted selective catalytic reduction (SCR) of NOx with octane using fast cycling transient in situ DRIFTS-MS analysis

A mechanistic study of the H-2-assisted Selective Catalytic Reduction (SCR) of NOx with octane as reductant over a Ag/Al2O3 catalyst was carried out using a modified DRIFTS cell coupled to a mass spectrometer Using fast transient cycling switching of H-2 with a time resolution of a few seconds It was possible to differentiate potential reaction intermediates from other moieties that are clearly spectator species Using such a periodic operation mode effects were uncovered that are normally hidden in conventional transient studies which typically consist of a single transient In experiments based on a single transient addition of H-2 to or removal of H-2 from the SCR feed it was found that the changes in the concentrations of gaseous species (products and reactants) were not matched by changes at comparable timescales of the concentration of surface species observed by IR This observation indicates that the majority of sur face species observed by DRIFTS under steady-state reaction conditions are spectators In contrast under fast cycling experimental conditions It was found that a surface isocyanate species had a temporal response that matched that of N-15(2) This suggests that some of the isocyanate species observed by infrared spectroscopy could be important intermediates in the hydrogen-assisted SCR reaction although it is emphasised that this may be dependent on the way in which the infrared spectra are obtained It is concluded that the use of fast transient cycling switching techniques may provide useful mechanistic information under certain circumstances.

Optical and infrared observations of SN 2002dj: some possible common properties of fast-expanding Type Ia supernovae

As part of the European Supernova Collaboration, we obtained extensive photometry and spectroscopy of the Type Ia supernova (SN Ia) SN 2002dj covering epochs from 11 d before to nearly two years after maximum. Detailed optical and near-infrared observations show that this object belongs to the class of the high-velocity gradient events as indicated by Si, S and Ca lines. The light curve shape and velocity evolution of SN 2002dj appear to be nearly identical to SN 2002bo. The only significant difference is observed in the optical to near-infrared colours and a reduced spectral ernission beyond 6500 A. For high-velocity gradient SNe Ia, we tentatively identify a faster rise to maximum, a more pronounced inflection in the V and R light curves after maximum and a brighter, slower declining late-time B light curve as common photometric properties of this class of object. They also seem to be characterized by a different colour and colour evolution with respect to 'normal' SNe Ia. The usual light Curve shape parameters do not distinguish these events. Stronger, more blueshifted absorption features of intermediate-mass elements and lower temperatures are the most prominent spectroscopic features of SNe Ia displaying high-velocity gradients. It appears that these events burn more intermediate-mass elements in the outer layers. Possible connections to the metallicity of the progenitor star are explored.

Effects of external axial magnetic field on fast electron propagation

A scheme employing an external axial magnetic field is proposed to diagnose the intrinsic divergence of laser-generated fast electron beams, and this is studied numerically with hybrid simulations. The maximum beam radius of fast electrons increases with the initial divergence and decreases with the amplitude of the axial magnetic field. It is indicated that the intrinsic divergence of fast electrons can be inferred from measurements of the beam radius at different depth under the axial field. The proposed scheme here may be useful for future fast ignition experiments and in other applications of laser-generated fast electron beams. (C) 2011 American Institute of Physics. [doi:10.1063/1.3630925]

Fast Retinal Vessel Detection and Measurement Using Wavelets and Edge Location Refinement

The relationship between changes in retinal vessel morphology and the onset and progression of diseases such as diabetes, hypertension and retinopathy of prematurity (ROP) has been the subject of several large scale clinical studies. However, the difficulty of quantifying changes in retinal vessels in a sufficiently fast, accurate and repeatable manner has restricted the application of the insights gleaned from these studies to clinical practice. This paper presents a novel algorithm for the efficient detection and measurement of retinal vessels, which is general enough that it can be applied to both low and high resolution fundus photographs and fluorescein angiograms upon the adjustment of only a few intuitive parameters. Firstly, we describe the simple vessel segmentation strategy, formulated in the language of wavelets, that is used for fast vessel detection. When validated using a publicly available database of retinal images, this segmentation achieves a true positive rate of 70.27%, false positive rate of 2.83%, and accuracy score of 0.9371. Vessel edges are then more precisely localised using image profiles computed perpendicularly across a spline fit of each detected vessel centreline, so that both local and global changes in vessel diameter can be readily quantified. Using a second image database, we show that the diameters output by our algorithm display good agreement with the manual measurements made by three independent observers. We conclude that the improved speed and generality offered by our algorithm are achieved without sacrificing accuracy. The algorithm is implemented in MATLAB along with a graphical user interface, and we have made the source code freely available. 

Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions

The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of mu m-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given.

Recent fast electron energy transport experiments relevant to fast ignition inertial fusion

A number of experiments have been undertaken at the Rutherford Appleton Laboratory that were designed to investigate the physics of fast electron transport relevant to fast ignition inertial fusion. The laser, operating at a wavelength of 1054 nm, provided pulses of up to 350 J of energy on target in a duration that varied in the range 0.5-5 ps and a focused intensity of up to 10(21) W cm(-2). A dependence of the divergence of the fast electron beam with intensity on target has been identified for the first time. This dependence is reproduced in two-dimensional particle-in-cell simulations and has been found to be an intrinsic property of the laser-plasma interaction. A number of ideas to control the divergence of the fast electron beam are described. The fractional energy transfer to the fast electron beam has been obtained from calibrated, time-resolved, target rear-surface radiation temperature measurements. It is in the range 15-30%, increasing with incident laser energy on target. The fast electron temperature has been measured to be lower than the ponderomotive potential energy and is well described by Haines' relativistic absorption model.

Effect of laser intensity on fast-electron-beam divergence in solid-density plasmas

Metal foil targets were irradiated with 1 mu m wavelength (lambda) laser pulses of 5 ps duration and focused intensities (I) of up to 4x10(19) W cm(-2), giving values of both I lambda(2) and pulse duration comparable to those required for fast ignition inertial fusion. The divergence of the electrons accelerated into the target was determined from spatially resolved measurements of x-ray K-alpha emission and from transverse probing of the plasma formed on the back of the foils. Comparison of the divergence with other published data shows that it increases with I lambda(2) and is independent of pulse duration. Two-dimensional particle-in-cell simulations reproduce these results, indicating that it is a fundamental property of the laser-plasma interaction.

Fast plasma heating in a cone-attached geometry - towards fusion ignition

We have developed a PW (0.5 ps/500J) laser system to demonstrate fast heating of imploded core plasmas using a hollow cone shell target. Significant enhancement of thermal neutron yield has been realized with PW-laser heating, confirming that the high heating efficiency is maintained as the short-pulse laser power is substantially increased to a value nearly equivalent to the ignition condition. It appears that the efficient heating is realized by the guiding of the PW laser pulse energy within the hollow cone and by self-organized relativistic electron transport. Based on the experimental results, we are developing a 10kJ-PW laser system to study the fast heating physics of high-density plasmas at an ignition-equivalent temperature.

Characterization of Li-7(p,n)Be-7 neutron yields from laser produced ion beams for fast neutron radiography

Investigations of Li-7(p,n)Be-7 reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson , J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3x10(19) W cm(-2). The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3x10(8) sr(-1) for CH primary targets and up to 2x10(8) sr(-1) for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180degrees that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography. (C) 2004 American Institute of Physics.

A theoretical color-velocity correlation for supernovae associated with gamma-ray bursts

We carry out the first multi-dimensional radiative transfer calculations to simultaneously compute synthetic spectra and light curves for models of supernovae driven by fast bipolar outflows. These allow us to make self-consistent predictions for the orientation dependence of both color evolution and spectral features. We compare models with different degrees of asphericity and metallicity and find significant observable consequences of both. In aspherical models, we find spectral and light curve features that vary systematically with observer orientation. In particular, we find that the early-phase light curves are brighter and bluer when viewed close to the polar axis but that the peak flux is highest for equatorial (off-axis) inclinations. Spectral line features also depend systematically on observer orientation, including the velocity of the Si II 6355 Å line. Consequently, our models predict a correlation between line velocity and color that could assist the identification of supernovae associated with off-axis jet-driven explosions. The amplitude and range of this correlation depends on the degree of asphericity, the metallicity, and the epoch of observation but we find that it is always present and acts in the same direction. © 2012. The American Astronomical Society. All rights reserved..