A model independent determination of ∣Vub∣|V_{ub}| using the global q2q^2 dependence of the dispersive bounds on the B→πlνB\to\pi l\nu form factors

We propose a method to determine the CKM matrix element $|V_{ub}|$ using the global $q^2$ dependence of the dispersive bound on the form factors for $B\to \pi l\nu$ decay. Since the lattice calculation of the $B\to \pi l\nu$ form factor is limited to the large $q^2$ regime, only the experimental data in a limited kinematic range can be used in a conventional method. In our new method which exploits the statistical distributions of the dispersive bound proposed by Lellouch, we can utilize the information of the global $q^2$ dependence for all kinematic range. As a feasibility study we determine $|V_{ub}|$ by combining the form factors from quenched lattice QCD, the dispersive bounds, and the experimental data by CLEO. We show that the accuracy of $|V_{ub}|$ can be improved by our method.Comment: 12 pages, 13 figure

Simplified numerical form of universal finite type invariant of Gauss words

In the present paper, we study the finite type invariants of Gauss words. In the Polyak algebra techniques, we reduce the determination of the group structure to transformation of a matrix into its Smith normal form and we give the simplified form of a universal finite type invariant by means of the isomorphism of this transformation. The advantage of this process is that we can implement it as a computer program. We obtain the universal finite type invariant of degree 4, 5, and 6 explicitly. Moreover, as an application, we give the complete classification of Gauss words of rank 4 and the partial classification of Gauss words of rank 5 where the distinction of only one pair remains.Comment: 12 pages, 3 table

Extreme self-organization in networks constructed from gene expression data

We study networks constructed from gene expression data obtained from many types of cancers. The networks are constructed by connecting vertices that belong to each others' list of K-nearest-neighbors, with K being an a priori selected non-negative integer. We introduce an order parameter for characterizing the homogeneity of the networks. On minimizing the order parameter with respect to K, degree distribution of the networks shows power-law behavior in the tails with an exponent of unity. Analysis of the eigenvalue spectrum of the networks confirms the presence of the power-law and small-world behavior. We discuss the significance of these findings in the context of evolutionary biological processes.Comment: 4 pages including 3 eps figures, revtex. Revisions as in published versio

Charge injection, electroluminescence, and ageing of an epoxy resin in high divergent fields

[INTRODUCTION]Most experimental studies of electrical ageing have concentrated on semi-crystalline polymers such as those used in cable insulation and capacitors (see for example [1]). Theoretical models [2-4] for electrical ageing have been developed on the basis of these studies. The consensus is that ageing involves the formation of low-density regions, though the mechanisms responsible are disputed. For example, bond scission by high-energy electrons [2,5], and mechanical deformation have both been suggested. Both of these mechanisms are related to charge injection and the subsequent formation of high local fields. The semi-crystalline polymers studied so far have similar chemistries and almost identical morphologies. They tend, therefore, to show many similarities in, for example, the size of the energy barriers for the ageing reaction, critical ageing levels, and field dependence of ageing [4]. These similarities make it difficult to discriminate between mechanisms. Epoxy resins, however, are network polymers with a different molecular chemistry to that of the semi-crystalline polymers and are thus ideal to evaluate the proposed ageing mechanisms. We have therefore studied an epoxy resin (CY1301) under both uniform field and high divergent field conditions. Uniform field conditions were used to gain baseline characteristics for the properties of the unaged epoxy resin, and also for the effects of electrical ageing in low fields. Studies in high divergent fields were made using an electrode arrangement adapted from that of [6]. A number of wires set approximately 0.5mm apart were embedded, parallel to the flat faces, in thin (290 m ) flat samples. The radius of the wires ranged from 5 m (gold plated tungsten) to 25 m (tungsten). Relatively small voltages applied to the wires (5 kV DC) therefore produced local fields up to 170 kV/mm depending upon the wire radius chosen. These field levels are high enough to inject space-charge [6] without leading to instantaneous failure. This geometry, therefore, may both inject charge and simulate local stress enhancements arising from charge accumulation. The number of wires is large (30) so that the volume affected is big enough to allow changes on ageing to be detectable

The decay of space charge in a glassy epoxy resin following voltage removal

The PEA technique is used to measure the distribution of space charge in an epoxy resin after polarisation for one week at an applied field of 7.14kV/mm over a range of temperatures. The decay of the space charge is followed for times up to 114 hours after removal of the voltage and analysed in terms of a number of alternative decay mechanisms. It is shown that the rate-determining stage of the decay mechanism is that of a thermally activated process that has been associated with charge de-trapping. At times greater than 102s the de-trapping process behaves as though the space charge field does not exist and the retention time of the space charge depends only upon the depth of the deepest occupied traps and the temperature

PCA Tomography and its application to nearby galactic nuclei

With the development of modern technologies such as IFUs, it is possible to obtain data cubes in which one produces images with spectral resolution. To extract information from them can be quite complex, and hence the development of new methods of data analysis is desirable. We briefly describe a method of analysis of data cubes (data from single field observations, containing two spatial and one spectral dimension) that uses Principal Component Analysis (PCA) to express the data in the form of reduced dimensionality, facilitating efficient information extraction from very large data sets. We applied the method, for illustration purpose, to the central region of the low ionization nuclear emission region (LINER) galaxy NGC 4736, and demonstrate that it has a type 1 active nucleus, not known before. Furthermore, we show that it is displaced from the centre of its stellar bulge.Comment: 4 pages, 1 figure, 1 table, to be published in the Proceedings of the IAU Symposium no. 26

Effects of Joint-Fixing on the Velocity of the Racket Head in the Tennis Serve

The velocity of the racket head in a tennis serve is one of the significant factors in a match. The fastest velocity of the racket head before impact may be performed by the appropriate sequence of segmental rotations. Anderson (1979) and Miyashita et al. (1980) reported that there was a close relationship between the muscular activities patterning in the overarm throw and the tennis serve. Elliott (1983) observed the movement pattern for the power serve in tennis using kinematic data. However, there were no reports concerning effects of joint fixing on the velocity of the racket head in a tennis serve. The purpose of this study was first to investigate the serving motion in tennis by means of a kinematic method. Second, it was to more clearly define the appropriate sequence of segmental rotations employed

Robust multi-fidelity design of a micro re-entry unmanned space vehicle

This article addresses the preliminary robust design of a small-scale re-entry unmanned space vehicle by means of a hybrid optimization technique. The approach, developed in this article, closely couples an evolutionary multi-objective algorithm with a direct transcription method for optimal control problems. The evolutionary part handles the shape parameters of the vehicle and the uncertain objective functions, while the direct transcription method generates an optimal control profile for the re-entry trajectory. Uncertainties on the aerodynamic forces and characteristics of the thermal protection material are incorporated into the vehicle model, and a Monte-Carlo sampling procedure is used to compute relevant statistical characteristics of the maximum heat flux and internal temperature. Then, the hybrid algorithm searches for geometries that minimize the mean value of the maximum heat flux, the mean value of the maximum internal temperature, and the weighted sum of their variance: the evolutionary part handles the shape parameters of the vehicle and the uncertain functions, while the direct transcription method generates the optimal control profile for the re-entry trajectory of each individual of the population. During the optimization process, artificial neural networks are utilized to approximate the aerodynamic forces required by the optimal control solver. The artificial neural networks are trained and updated by means of a multi-fidelity approach: initially a low-fidelity analytical model, fitted on a waverider type of vehicle, is used to train the neural networks, and through the evolution a mix of analytical and computational fluid dynamic, high-fidelity computations are used to update it. The data obtained by the high-fidelity model progressively become the main source of updates for the neural networks till, near the end of the optimization process, the influence of the data obtained by the analytical model is practically nullified. On the basis of preliminary results, the adopted technique is able to predict achievable performance of the small spacecraft and the requirements in terms of thermal protection materials