Reconstruction of Sparse Vectors in White Gaussian Noise

We consider the problem of reconstruction of a sparse vector observed against a background of white Gaussian noise. The sparsity is assumed to be unknown. Two approaches to statistical estimation in this case are discussed, namely, the model selection method and threshold estimators. We propose a method of selecting a threshold estimator based on the principle of empirical complexity minimization with minimal conservative penalization.     

Compressible-liquid motion in porous medium with flowing and stagnant regions

Filtration equations taking into account both flowing and stagnant regions of a porous medium [1] are solved for a semiinfinite region by the fractional-differentiation method [2, 3], For a given arbitrary pressure change at the boundary of the region the filtration rate at this boundary may be determined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 1, pp. 140–144, January, 1980.     

Low Temperature Decoherence by Electron–Electron Interactions: Role of Quantum Fluctuations

We derive a general expression for the conductivity of a disordered conductor with electron–electron interactions (treated within the standard model) and evaluate the weak localization correction _wl employing no approximations beyond the accuracy of the definition of _wl . Our analysis applies to all orders in the interaction and extends our previous calculation by explicitly taking into account quantum fluctuations around the classical paths for interacting electrons (pre-exponent). We specifically address the most interesting low temperature limit and demonstrate that such fluctuations can only be important in the perturbative regime of short times while they are practically irrelevant for the Cooperon dynamics at longer times. We fully confirm our conclusion about the existence of interaction-induced decoherence of electrons at zero temperature for the problem in question. We also demonstrate irrelevance of a perturbative calculation by Aleiner et al. (AAV) [J. Low Temp. Phys. 126, 1377 (2002)] and refute AAV's critique of our earlier analysis.     

Experimental study of the residual activity induced by 950 MeV/u uranium ions in stainless steel and copper

As a preparatory work for constructing the FAIR facility at GSI, samples of stainless steel and copper were irradiated by 950 MeV/u ²³⁸U ions and depth-profiles of residual activity were measured by gamma-ray spectroscopy. The isotopes with dominating contribution to the residual activity were identified and their contributions were quantified. In contrast to the previous study performed at lower energies, the activities could no longer be determined from the full-assembly target measurements. Depth-profiling of residual activity of all identified isotopes had to be completed by measurements of individual target foils. The activity contributions were then obtained by integration of the depth-profiles.     

Construction of a network of optical frequencies for a CO2 laser interferometer

Translated from Izmeritel'naya Tekhnika, No. 11, pp. 41–43, November, 1990.     

Isotope-modified silicon layers obtained by plasma enhanced chemical vapor deposition from gaseous silicon tetrafluoride

Layers of silicon with an isotope composition that differs from the native composition have been obtained by the method of plasma enhanced chemical vapor deposition from gaseous silicon tetrafluoride. The deposited layers possess an amorphous structure and high oxygen content. The Raman spectra and the spectra of optical transmission in the IR range are presented. The in-depth distribution of Si isotopes has been determined using the second ion mass spectrometry techniques.     

Experimental and computational study of the pyrocarbon and silicon carbide barriers of HTGR fuel particle

HTGR safety is secured by a system of barriers limiting the emission of fission products from the core into the surrounding environment during normal operation and postulated anticipated accidents. An experimental-computational analysis of two fundamentally important barriers — fuel kernels and their coating, whose function is to contain radionuclides and to protect workers and the environment, is examined. The function of the barriers and the requirements which they must satisfy are examined for HTGR fuel particles. The results of post-reactor studies are analyzed. Mathematical models and computational codes simulating the behavior of fuel particles are analyzed. Probabilistic-statistical models and the GOLT code are being developed to evaluate the behavior of fuel particles under irradiation. Together with other models, this code is used for comparative test calculations of the behavior of particle fuel under normal irradiation conditions (<1300°C). The first results of such calculations are discussed. __________ Translated from Atomnaya énergiya, Vol. 105, No. 1, pp. 14–25, July, 2008.