arXiv subjects

Sergei Skorik

Publications and source records attributed to Sergei Skorik.

7 recordsLinked to original sources

arXiv2000

On a cepstrum-based speech detector robust to white noise

We study effects of additive white noise on the cepstral representation of speech signals. Distribution of each individual cepstrum coefficient of speech is shown to depend strongly on noise and to overlap significantly with the cepstrum distribution of noise. Based on these studies, we suggest a scalar quantity, V, equal to the sum of weighted cepstral coefficients, which is able to classify frames containing speech against noise-like frames. The distributions of V for speech and noise frames are reasonably well separated above SNR = 5 dB, demonstrating the feasibility of robust speech detector based on V.

cs.CL↗

arXiv1997

Exactly unsolved problems of interacting 1D fermions

Applications of the integrable system techniques to the non-equilibrium transport problems are discussed. We describe one-dimensional electrons tunneling through a point-like defect either by the s-d exchange (Kondo) mechanism, or via the resonanse level (Anderson) mechanism. These models are potential candidates to be solved exactly in the presence of arbitrary external bias. We draw attention also to several mesoscopical systems which can be tackled by the massless form-factor approach, as perturbations of integrable models. The basic unperturbed model is the massless sine-Gordon model with the interaction (cosine) term restricted to one point, which is integrable. It is being perturbed by the second interaction term, which destroys integrability. Quasi-exact results can be obtained by making use of the basis of massless quasiparticles of the sine-Gordon model.

cond-mat.mes-hall↗

arXiv1997

Exact non-equilibrium current from the partition function for impurity transport problems

We study the partition functions of quantum impurity problems in the domain of complex applied bias for its relation to the non-equilibrium current suggested by Fendley, Lesage and Saleur (cond-mat/9510055). The problem is reformulated as a certain generalization of the linear response theory that accomodates an additional complex variable. It is shown that the mentioned relation holds in a rather generic case in the linear response limit, or under certain condition out of equilibrium. This condition is trivially satisfied by the quadratic Hamiltonians and is rather restrictive for the interacting models. An example is given when the condition is violated.

cond-mat.mes-hall↗

arXiv1997

Comment on ``Exact non-equilibrium transport through point contacts in quantum wires and fractional quantum Hall devices''

Fendley, Ludwig and Saleur [Phys. Rev. B52 (1995) 8934] have obtained an expression for the non-equilibrium current through a constriction in the quantum Hall bar based on the Bethe ansatz technique and the Bolzmann equation. In this Comment we draw attention to a serious flaw in their derivation. We argue that their result is correct in the linear response limit but should be taken with a care out of equilibrium for finite bias. The reason is in the use of the equilibrium scattering matrix in the place of the transition probability amplitude out of equilibrium, the substitution which was not shown to be legimate.

cond-mat.mes-hall↗

arXiv1997

Exact current-current Green functions in strongly correlated 1D systems with impurity

We derive an exact expression for the Kubo conductunce in the Quantum Hall device with the point-like intra-edge backscattering. This involves the calculation of current-current correlator exactly, which we perform using form-factor method. In brief, the full set of intermediate states is inserted in the correlator, and for each term the closed mathematical expression is obtained. It is shown that by making a special choice of intermediate states in accordance with the hidden symmetries of the model, one achieves fast convergence of the series, thus proving the form-factor approach to be especially powerfull. This review is based on the joint work with H.Saleur and F.Lesage.

cond-mat.mes-hall↗

arXiv1996

Topics in 2D integrable field theories with boundary interactions

We study different aspects of integrable boundary quantum field theories, focusing mostly on the ``boundary sine-Gordon model'' and its applications to condensed matter physics. The first part of the review deals with formal problems. We analyze the classical limit and perform semi-classical quantization. We show that the non-relativistic limit corresponds to the Calogero-Moser model with a boundary potential. We construct a lattice regularization of the problem via the XXZ chain. We classify boundary bound states. We generalize the Destri de Vega method to compute the ground state energy of the theory on a finite interval. The second part deals with some applications to condensed matter physics. We show how to compute analytically time and space dependent correlations in one-dimensional quantum integrable systems with an impurity. Our approach is based on a description of these systems in terms of massless scattering of quasiparticles. Correlators follow then from matrix elements of local operators between multiparticle states -- the massless form-factors. Although, in general an infinite sum of these form-factors has to be considered, we find that for the current, spin and energy operators only a few (two or three) are necessary to obtain an accuracy of more than 1\%. Our results hold for arbitrary impurity strength, in contrary to the perturbative expansions in the coupling constants. As an example, we compute the frequency dependent condunctance, at zero temperature, in a Luttinger liquid with an impurity, and also discuss the susceptibility in the Kondo model and the time-dependent properties of the two-state problem with dissipation.

hep-th↗

arXiv1994

Solution of the Thirring Model with Imaginary Mass and Massless Scattering

The Thirring model with imaginary mass (or the sine-Gordon model with imaginary coupling) is deeply related to all the flows between minimal conformal theories. We solve this model explicitely using the Bethe ansatz. We find that there are Left and Right moving massless excitations with non trivial LR scattering. We compute the S matrix and recover the result conjectured by Fendley et al.

hep-th↗