Diagnosis of weaknesses in modern error correction codes: a physics approach

One of the main obstacles to the wider use of the modern error-correction codes is that, due to the complex behavior of their decoding algorithms, no systematic method which would allow characterization of the Bit-Error-Rate (BER) is known. This is especially true at the weak noise where many systems operate and where coding performance is difficult to estimate because of the diminishingly small number of errors. We show how the instanton method of physics allows one to solve the problem of BER analysis in the weak noise range by recasting it as a computationally tractable minimization problem.Comment: 9 pages, 8 figure

Possible d+id scenario in La_{2-x}Sr_{x}CuO_4 by point-contact measurements

We analyze the results of point-contact measurements in La_{2-x}Sr_{x}CuO_{4} (LSCO) previously reported as a clear evidence of the separation between gap and pseudogap in this copper oxide. Here we show that, in addition to this, the conductance curves of our point-contact junctions -- showing clear Andreev reflection features -- can be interpreted as supporting a nodeless d_{x^2-y^2}+id_{xy}-wave symmetry of the gap in LSCO. The results of our analysis, in particular the doping dependence of the subdominant d_{xy} gap component, are discussed and compared to the predictions of different theoretical models.Comment: 6 pages, 4 eps figures, presented at SATT11 Conference (Vietri sul Mare, March 2002). To appear in Int. J. Mod. Phy

Creating a Database of Helicopter Main Rotor Acoustics for Validation of CFD Methods

The work presents recent experiments at the Kazan National Technical University (KNRTU-KAI), related to helicopter acoustics. The objective is to provide a database of near-field experimental data suitable for CFD validation. The obtained set of data corresponds to a Mach-scaled rotor of known planform. An advantage of the current dataset is that direct near-field acoustic data is made available and this allows easy and direct comparisons with CFD predictions, without the need to use far-field aeroacoustic methods

Evidence for pseudogap and phase-coherence gap separation by Andreev reflection experiments in Au/La_{2-x}Sr_{x}CuO_4 point-contact junctions

We present new Au/La_{2-x}Sr_{x}CuO_{4} (LSCO) point-contact conductance measures as a function of voltage and temperature in samples with 0.08 <= x <= 0.2. Andreev reflection features disappear at about the bulk Tc, giving no evidence of gap for T > Tc. The fit of the normalized conductance at any T < Tc supports a (s + d)-wave symmetry of the gap, whose dominant low-T s component follows the Tc(x) curve in contrast with recent angle-resolved photoemission spectroscopy and quasiparticle tunneling data. These results prove the separation between pseudogap and phase-coherence superconducting gap in LSCO at x <= 0.2.Comment: 4 pages, 4 eps figures, 1 table (RevTeX). Labels added to Fig. 1; Fig. 3 resized; references added; short discussion about ballistic contact regime adde

Semiclassical treatment of logarithmic perturbation theory

The explicit semiclassical treatment of logarithmic perturbation theory for the nonrelativistic bound states problem is developed. Based upon $\hbar$-expansions and suitable quantization conditions a new procedure for deriving perturbation expansions for the one-dimensional anharmonic oscillator is offered. Avoiding disadvantages of the standard approach, new handy recursion formulae with the same simple form both for ground and exited states have been obtained. As an example, the perturbation expansions for the energy eigenvalues of the harmonic oscillator perturbed by $\lambda x^{6}$ are considered.Comment: 6 pages, LATEX 2.09 using IOP style

Loop series for discrete statistical models on graphs

In this paper we present derivation details, logic, and motivation for the loop calculus introduced in \cite{06CCa}. Generating functions for three inter-related discrete statistical models are each expressed in terms of a finite series. The first term in the series corresponds to the Bethe-Peierls (Belief Propagation)-BP contribution, the other terms are labeled by loops on the factor graph. All loop contributions are simple rational functions of spin correlation functions calculated within the BP approach. We discuss two alternative derivations of the loop series. One approach implements a set of local auxiliary integrations over continuous fields with the BP contribution corresponding to an integrand saddle-point value. The integrals are replaced by sums in the complimentary approach, briefly explained in \cite{06CCa}. A local gauge symmetry transformation that clarifies an important invariant feature of the BP solution, is revealed in both approaches. The partition function remains invariant while individual terms change under the gauge transformation. The requirement for all individual terms to be non-zero only for closed loops in the factor graph (as opposed to paths with loose ends) is equivalent to fixing the first term in the series to be exactly equal to the BP contribution. Further applications of the loop calculus to problems in statistical physics, computer and information sciences are discussed.Comment: 20 pages, 3 figure

Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

Equations describing the linear evolution of a non-dissipative Langmuir wave in inhomogeneous nonstationary anisotropic plasma without magnetic field are derived in the geometrical optics approximation. A continuity equation is obtained for the wave action density, and the conditions for the action conservation are formulated. In homogeneous plasma, the wave field E universally scales with the electron density N as E ~ N^{3/4}, whereas the wavevector evolution varies depending on the wave geometry