174 research outputs found

    Two-Rowed Hecke Algebra Representations at Roots of Unity

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    In this paper, we initiate a study into the explicit construction of irreducible representations of the Hecke algebra Hn(q)H_n(q) of type An1A_{n-1} in the non-generic case where qq is a root of unity. The approach is via the Specht modules of Hn(q)H_n(q) which are irreducible in the generic case, and possess a natural basis indexed by Young tableaux. The general framework in which the irreducible non-generic Hn(q)H_n(q)-modules are to be constructed is set up and, in particular, the full set of modules corresponding to two-part partitions is described. Plentiful examples are given.Comment: LaTeX, 9 pages. Submitted for the Proceedings of the 4th International Colloquium ``Quantum Groups and Integrable Systems,'' Prague, 22-24 June 199

    Near-threshold electron injection in the laser-plasma wakefield accelerator leading to femtosecond bunches

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    We gratefully acknowledge the support of the UK EPSRC (grant no. EP/J018171/1), the EU FP7 programmes: the Extreme Light Infrastructure (ELI) project, the Laserlab-Europe (no. 284464), and the EUCARD-2 project (no. 312453).The laser-plasma wakefield accelerator is a compact source of high brightness, ultra-short duration electron bunches. Self-injection occurs when electrons from the background plasma gain sufficient momentum at the back of the bubble-shaped accelerating structure to experience sustained acceleration. The shortest duration and highest brightness electron bunches result from self-injection close to the threshold for injection. Here we show that in this case injection is due to the localized charge density build-up in the sheath crossing region at the rear of the bubble, which has the effect of increasing the accelerating potential to above a critical value. Bunch duration is determined by the dwell time above this critical value, which explains why single or multiple ultra-short electron bunches with little dark current are formed in the first bubble. We confirm experimentally, using coherent optical transition radiation measurements, that single or multiple bunches with femtosecond duration and peak currents of several kiloAmpere, and femtosecond intervals between bunches, emerge from the accelerator.Publisher PDFPeer reviewe

    On the accretion disc properties in eclipsing dwarf nova EM Cyg

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    In this paper we analyzed the behavior of the unusual dwarf nova EM Cyg using the data obtained in April-October, 2007 in Vyhorlat observatory (Slovak Republic) and in September, 2006 in Crimean Astrophysical Observatory (Ukraine). During our observations EM Cyg has shown outbursts in every 15-40 days. Because on the light curves of EM Cyg the partial eclipse of an accretion disc is observed we applied the eclipse mapping technique to reconstruct the temperature distribution in eclipsed parts of the disc. Calculations of the accretion rate in the system were made for the quiescent and the outburst states of activity for different distances.Comment: 6 pages, 3 figures, accepted in Astrophysics and Space Scienc

    Организация деятельности педагога по совершенствованию умений диалогической речи у детей старшего дошкольного возраста.

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    В работе рассмотрены основы психического и речевого развития детей старшего дошкольного возраста, охарактеризованы лингво-методические основы развития диалогической речи у старшего дошкольного возраста, раскрыто содержание деятельности педагога по совершенствованию умений диалогической речи у детей старшего дошкольного возраста, разработан комплекс педагогических мероприятий по теме исследования

    Algorithms for Enumerating Circuits in Matroids

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    We present an incremental polynomial-time algorithm for enumerating all circuits of a matroid or, more generally, all minimal spanning sets for a flat. This result implies, in particular, that for a given infeasible system of linear equations, all its maximal feasible subsystems, as well as all minimal infeasible subsystems, can be enumerated in incremental polynomial time. We also show the NP-hardness of several related enumeration problems

    Structure of the Partition Function and Transfer Matrices for the Potts Model in a Magnetic Field on Lattice Strips

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    We determine the general structure of the partition function of the qq-state Potts model in an external magnetic field, Z(G,q,v,w)Z(G,q,v,w) for arbitrary qq, temperature variable vv, and magnetic field variable ww, on cyclic, M\"obius, and free strip graphs GG of the square (sq), triangular (tri), and honeycomb (hc) lattices with width LyL_y and arbitrarily great length LxL_x. For the cyclic case we prove that the partition function has the form Z(Λ,Ly×Lx,q,v,w)=d=0Lyc~(d)Tr[(TZ,Λ,Ly,d)m]Z(\Lambda,L_y \times L_x,q,v,w)=\sum_{d=0}^{L_y} \tilde c^{(d)} Tr[(T_{Z,\Lambda,L_y,d})^m], where Λ\Lambda denotes the lattice type, c~(d)\tilde c^{(d)} are specified polynomials of degree dd in qq, TZ,Λ,Ly,dT_{Z,\Lambda,L_y,d} is the corresponding transfer matrix, and m=Lxm=L_x (Lx/2L_x/2) for Λ=sq,tri(hc)\Lambda=sq, tri (hc), respectively. An analogous formula is given for M\"obius strips, while only TZ,Λ,Ly,d=0T_{Z,\Lambda,L_y,d=0} appears for free strips. We exhibit a method for calculating TZ,Λ,Ly,dT_{Z,\Lambda,L_y,d} for arbitrary LyL_y and give illustrative examples. Explicit results for arbitrary LyL_y are presented for TZ,Λ,Ly,dT_{Z,\Lambda,L_y,d} with d=Lyd=L_y and d=Ly1d=L_y-1. We find very simple formulas for the determinant det(TZ,Λ,Ly,d)det(T_{Z,\Lambda,L_y,d}). We also give results for self-dual cyclic strips of the square lattice.Comment: Reference added to a relevant paper by F. Y. W

    Active Galaxies in the UV

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    In this article we present different aspects of AGN studies demonstrating the importance of the UV spectral range. Most important diagnostic lines for studying the general physical conditions as well as the metalicities in the central broad line region in AGN are emitted in the UV. The UV/FUV continuum in AGN excites not only the emission lines in the immediate surrounding but it is responsible for the ionization of the intergalactic medium in the early stages of the universe. Variability studies of the emission line profiles of AGN in the UV give us information on the structure and kinematics of the immediate surrounding of the central supermassive black hole as well as on its mass itself.Comment: 29 pages, 13 figures, Ap&SS in pres

    Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2

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    We have measured the spin structure functions g2p and g2d and the virtual photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0 < Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is significantly smaller than the sqrt{R} positivity limit over the measured range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range 0.02 < x < 0.8.Comment: 12 pages, 4 figures, 1 tabl

    Measurements of the Q2Q^2-Dependence of the Proton and Neutron Spin Structure Functions g1p and g1n

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    The structure functions g1p and g1n have been measured over the range 0.014 < x < 0.9 and 1 < Q2 < 40 GeV2 using deep-inelastic scattering of 48 GeV longitudinally polarized electrons from polarized protons and deuterons. We find that the Q2 dependence of g1p (g1n) at fixed x is very similar to that of the spin-averaged structure function F1p (F1n). From a NLO QCD fit to all available data we find Γ1pΓ1n=0.176±0.003±0.007\Gamma_1^p - \Gamma_1^n =0.176 \pm 0.003 \pm 0.007 at Q2=5 GeV2, in agreement with the Bjorken sum rule prediction of 0.182 \pm 0.005.Comment: 17 pages, 3 figures. Submitted to Physics Letters
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