Investigation of the temperature field in a turbulent air flow in the channels with structured packing

Temperature distribution and intensity of temperature pulsations in the airflow in a complex heat exchanger of “Frenkel packing” type were studied experimentally. Measurements were carried out at the airflow between two corrugated plates with triangular embossing, directed at 90° relative to each other. The temperature in the flow was measured by a special thermocouple probe. The hot junction of the thermocouple did not exceed 10 μm. The effect of contact points and Reynolds number on static characteristics of temperature in a turbulent airflow is analysed. The main attention is paid to temperature distribution in an elementary cell. According to the studies, there is a considerable difference between temperature distributions in the flow at the back and front sides of the channel.     

Synthesis and characterization of chromium and molybdenum(0) complexes bearing the (pentafluoroethyl)diphenylphosphine (pfepp) ligand

The synthesis and characterization of two Group VI pentacarbonyl complexes (pfepp)M(CO)₅ (M = Cr 1, Mo 2; pfepp = PPh₂C₂F₅) are reported. Thermolysis of M(CO)₆ and pfepp in refluxing octane afforded 1 and 2 in moderate yields. These complexes were completely characterized by multinuclear NMR, IR and elemental analysis. X-ray structures for these complexes indicated they were isostructural, crystalizing in triclinic unit cells with four molecules per asymmetric unit. A comparison of the bond lengths in 1 and 2 to other (L)M(CO)₅ complexes showed a relationship between the M-C_ax bond length and the electronic influence of the phosphine ligand, and establishes the pfepp ligand as neither electron-rich nor electron-poor. A comparison of IR data with other (L)M(CO)₅ complexes also indicates the pfepp ligand is electronically neutral, with an electronic influence that approximates phosphites.     

A tensor-based dictionary learning approach to tomographic image reconstruction

We consider tomographic reconstruction using priors in the form of a dictionary learned from training images. The reconstruction has two stages: first we construct a tensor dictionary prior from our training data, and then we pose the reconstruction problem in terms of recovering the expansion coefficients in that dictionary. Our approach differs from past approaches in that (a) we use a third-order tensor representation for our images and (b) we recast the reconstruction problem using the tensor formulation. The dictionary learning problem is presented as a non-negative tensor factorization problem with sparsity constraints. The reconstruction problem is formulated in a convex optimization framework by looking for a solution with a sparse representation in the tensor dictionary. Numerical results show that our tensor formulation leads to very sparse representations of both the training images and the reconstructions due to the ability of representing repeated features compactly in the dictionary.     

A parameter-choice method that exploits residual information

Most algorithms for choosing the regularization parameter in a discrete ill-posed problem are based on the norm of the residual vector. In this work we propose a different approach that seeks to use all the information available in the residual vector, and we show how to use statistical tools and fast Fourier transforms to extract this information efficiently. This approach leads to a computationally inexpensive parameter-choice rule based on the normalized cumulative periodogram, which is particularly suited for large-scale problems. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Discrete optimization problems with interval parameters

Optimization problems on graphs with interval parameters are considered, and exponential and polynomial bounds for their computational complexity are obtained. For a certain subclass of polynomially solvable problems, two algorithms are proposed—one of them for finding an optimal solution and the other one for finding a suboptimal solution. Sufficient conditions for the statistical efficiency of the algorithm for finding a suboptimal solution are obtained.     

Switched wave packets: a route to nonperturbative quantum control

The dynamic Stark effect due to a strong nonresonant but nonionizing laser field provides a route to quantum control via the creation of novel superposition states. We consider the creation of a field-free "switched" wave packet through adiabatic turn-on and sudden turn-off of a strong dynamic Stark interaction. There are two limiting cases for such wave packets. The first is a Raman-type coupling, illustrated by the creation of field-free molecular axis alignment. An experimental demonstration is given. The second case is that of dipole-type coupling, illustrated by the creation of charge localization in an array of quantum wells.     

Spatial structure of the flow at round jet outflow into a narrow channel

Results on visual studies of the flow structure in case of the round submerged jet in a narrow channel are presented. These studies were carried out for the laminar and turbulent flows. The typical large-scale structures and zones of intensive turbulent mixing were identified in the flow. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00417-a).     

Photoinduced Degradation of the Optical Properties of Colloidal Ag<Subscript>2</Subscript>S and CdS Quantum Dots Passivated by Thioglycolic Acid

The results of studying degradation of the optical properties of colloidal Ag₂S and CdS quantum dots (QDs) 2.6–3.2 nm in size passivated by thioglycolic acid (TGA) are presented. The photoluminescence intensity of colloidal Ag₂S QDs has been found to decrease under laser irradiation at a wavelength of 445 nm, beginning with the effective power of 10 mW. The observed effect is interpreted as a photochemical reaction of formation of new nonradiative-recombination channels in Ag₂S QDs upon excitation. It is established for colloidal CdS QDs passivated by TGA that a decrease in the optical density in the entire absorption spectrum and the luminescence intensity is accompanied by precipitation of the colloidal particles in a cell and related to photodegradation of the passivating shell.     

A Class of Baker–Akhiezer Arrangements

We study a class of arrangements of lines with multiplicities on the plane which admit the Chalykh–Veselov Baker–Akhiezer function. These arrangements are obtained by adding multiplicity one lines in an invariant way to any dihedral arrangement with invariant multiplicities. We describe all the Baker–Akhiezer arrangements when at most one line has multiplicity higher than 1. We study associated algebras of quasi-invariants which are isomorphic to the commutative algebras of quantum integrals for the generalized Calogero–Moser operators. We compute the Hilbert series of these algebras and we conclude that the algebras are Gorenstein. We also show that there are no other arrangements with Gorenstein algebras of quasi-invariants when at most one line has multiplicity bigger than 1.