Spectral transport model for turbulence

The spectrum of inhomogeneous turbulence is modeled by an approach that is not limited to regimes of large Reynolds numbers or small mean-flow strain rates. In its simplest form and applied to incompressible flow, the model depends on five phenomenological constants defining the strength of turbulence coupling to mean flow, turbulence transport in physical and wave-number space, and mixing of stress-tensor components. The implications for homogeneous isotropic turbulence are investigated in detail and found to correspond well to the conclusions from more fundamental theories. Under appropriate limiting conditions, a turbulent system described by the model will relax over time into a state of approximate spectral equilibrium permitting a reduction to a one-point model for the system that is substantially like the familiar K- model. This yields preliminary estimates of the present model's parameters and points to the way to improved modeling of flows beyond the applicability of the K- method.     

D.C. Representability of closed sets in reflexive Banach spaces and applications to optimization problems

A closed subsetM of a Hausdorff locally convex space is called d.c. representable if there are an extended-real valued lsc convex functionf and a continuous convex functionh such that $$M = \{ x \in X:f(x) - h(x) \leqslant 0\} .$$ Using the existence of a locally uniformly convex norm, we prove that any closed subset in a reflexive Banach space is d.c. representable. For d.c. representable subsets, we define an index of nonconvexity, which can be regarded as an indicator for the degree of nonconvexity. In fact, we show that a convex closed subset is weakly closed when it has a finite index of nonconvexity, and optimization problems on closed subsets with a low index of nonconvexity are less difficult from the viewpoint of computation.     

Pulsed NMRON oscillatory free induction decay signals in the angular distribution of gamma radiation from plated60CoFe

Results for an inhomogeneously broadened⁶⁰CoFe NMRON sample have been obtained for gamma detected single pulse (nutation) and two pulse (free induction decay) experiments in the region of intermediate-to-lowR(=₁/). Here ₁ is the angular frequency measure of the strength of the ferromagnetically enhanced RF field at the nucleus and is the HWHM of the inhomogeneously broadened line. Comparisons of the oscillatory FID signals obtained are made with the theoretical predictions of the following paper [6].     

Hail embryons detection in clouds using passive and active radars in millimeter and submillimeter wave bands

Two detection methods of hail embryons in a cloud are discussed in the paper: combined passive/active and purely active sensing of a convective cloud from board of air or space carrier. The first method makes it possible to determine the spectral dependence of absorption coefficient by oversized drops in convective cloud in the millimeter (MM) and submillimeter (SbMM) wavebands. With this purpose a highly sensitive 16-channel Dicke radiometer is used. In the second method a multiwave (12 wavelength) active radar is used to determine the spectral dependence of backscatter coefficient in the same wavebands. Variation of these spectral characteristics in time makes possible the detection of physical processes taking place in a cloud, such as drops drowth and evaporation, as well as transition of oversized drops into the overcooled state. The instant of water/ice phase transition in oversized drops is determined in both methods by means of active radar in SbMM waveband (in the transparency window of ice and atmosphere, 0.64 mm). Corresponding hardware, antennas, and wavelengths are considered for active/passive and purely active sensind of clouds. The effect of antenna beamwidth in SbMM on anomalous backscatter is discussed.Finally the authors would like to acknowledge the helpful discussions and assistance of Dr. K.E.Karapetyan in calculation of the antenna E characteristics.     

Exact solution of a vertex model ind dimensions

We consider a class of vertex models describing directed lines on a lattice in arbitraryd dimensions, and solve the model exactly for the Cartesian lattice and in the case that each loop of lines carries a fugacity - 1. Our analysis, which can be carried out for arbitrary lattices, is based on an equivalence of the vertex model with a dimer problem. The dimer problem is, in turn, solved using the method of Pfaffians. It is found that the system is frozen below a critical temperatureT _cwith the critical exponent = (3 –d)/2.     

Surface studies on polycrystalline YBa2Cu3O7−δ with Auger electron and low-energy electron energy-loss spectroscopy

Chemical and electronic properties of scrapecleaned YBa₂Cu₃O_7–(YBCO) ceramics, which were also annealed in vacuum or exposed to H atoms or O₂ molecules, were studied at room temperature by applying Auger electron (AES) and low-energy electron energy-loss spectroscopy (LEELS). Scanning electron micrographs showed such scraped surfaces to consist mainly of small, fractured YBCO crystallites, i.e. of clean YBCO surfaces. With only one exception, all low-energy AES lines were found to be shifted in energy compared to data recorded with surfaces of metallic Cu and Y. The analysis of the high-energy AES lines indicated the existence of non-stoichiometric material in grain boundaries. At least 25 different LEELS features were recorded. The 24.9-eV energy loss, which is due to the excitation of bulk valence-electron plasmons, indicates an enhanced oxygen deficit _s 0.8 at scrape-cleaned YBCO surfaces. Annealing of scraped YBCO samples at approximately 700 K in vacuum and also their exposure to hydrogen atoms resulted in an additional oxygen depletion within a few atomic layers near to the surfaces. These oxygen deficiencies were found to increase the intensity ratios of low-and high-energy AES lines of Cu, Ba, and Y and to intensify the energy-loss peak at 4.4 eV which has been attributed to O–Cu–O dumbbells.