Reconstruction of the blood flow velocity vector as an additional mode of ultrasonic tomograph

The possibility of simultaneous reconstruction of the blood flow velocity vector and spatial distributions of the speed of sound and absorption coefficient in a medical ultrasonic tomograph is discussed. The operating capacity of the proposed spatial-correlation method for determining the blood flow velocity vector is confirmed by experiments on a tomograph prototype.     

Phase equilibria and structures of phases in the chitosan—polyvinyl alcohol systems

Russian Chemical Bulletin - Phase equilibria in the mixtures of polyvinyl alcohol (PVA) and chitosan were revealed. Structures of the phases were identified. The temperature and concentration...     

Effects of Dry-Jet Wet Spinning Parameters on Properties of Polysulfone Hollow Fiber Membranes

Russian Journal of Applied Chemistry - The influence of parameters of the dry-jet wet spinning process was studied on properties of porous polysulfone hollow fiber membranes. The air gap distance,...     

Heterogeneities of grain boundary arrangement in polycrystals

Data on mutual arrangements of different types of grain boundaries in polycrystals are presented. The heterogeneity in grain boundary distribution, namely, the effect of gathering low-angle or special tilt grain boundaries is found in pure aluminum thin films, in sheets of Fe-3% Si alloy and in Al₂O₃ doped with MgO or MgO and Y ₂O₃. The local texture, i.e., formation of colonies or clusters of close-oriented grains is considered as a reason of this heterogeneity. The influences of grain boundary gathering on the transport properties of polycrystals and on the crack propagation are discussed. A new concept of effective grain size is suggested to analyze the relationship between material microstructures and material properties.     

Impurity transport in a dual-porosity medium with sorption

A nonstationary model of impurity transport in a dual-porosity (fractured porous) medium with sorption is proposed. It is shown that the equilibrium between dissolved and adsorbed phases is absent for a prolonged time, which leads to the development of nonclassical impurity transport regimes. Parameter values are found for which the behavior of the system cannot be described using the conventional model of equilibrium sorption even at large times for which the equilibrium between dissolved and adsorbed components should be established.     

Locally 2-fold symmetric manifolds are locally symmetric

A manifold is locally k-fold symmetric if for any point and any k-dimensional vector subspace tangent to this point, there exists a local isometry such that this point is a fixed point and the differential of the isometry restricted to that k-dimensional vector subspace is minus the identity. We show that for \(k \ge 2\), Riemannian, pseudoriemannian, and Finslerian locally k-fold symmetric manifolds are locally symmetric.     

Nonconservation of the fermion number and the limiting density of fermionic matter (two-dimensional gauge model)

Conclusions Thus, at the present time there are two possible ways for instability to develop in gauge theories at high fermion density. In the four-dimensional Abelian model considered in [1] there is ultimately formed an anomalous state characterized by zero density of the real fermions, zero scalar condensate, and large gauge field condensate. In the two-dimensional model considered in the present paper, the effects of the complicated vacuum structure have the consequence that the system undergoes a transition to a normal state with low fermion density above a topologically nontrivial vacuum, this transition being accompanied by nonconservation of the fermion number. It is of undoubted interest to clarify which of these possibilities is realized in realistic non-Abelian four-dimensional theories (for example, in the standard model of electroweak interactions), i. e., to consider the existence of stable anomalous states in such theories. This question will be considered in later papers.Institute of Nuclear Research, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 68, No. 1, pp. 3–17, July, 1986.     

Quantum integrability of Beltrami-Laplace operator as geodesic equivalence

Given two Riemannian metrics on a closed connected manifold , we construct self-adjoint differential operators such that if the metrics have the same geodesics then the operators commute with the Beltrami-Laplace operator of the first metric and pairwise commute. If the operators commute and if they are linearly independent, then the metrics have the same geodesics. Received: 11 February 2000; in final form: 20 August 2000/ Published online: 17 May 2001     

Emergence of differences in potential in wood as a result of natural changes in temperature

The emergence of differences in potential in a natural macromolecular heterogeneous structure (wood) upon natural changes in temperature with allowance for humidity is considered. It is shown that the magnitude of the emerging difference in potential in the wood is proportional to the change in temperature and grows along with the humidity of the wood.     

Mixed Formulations of Bending Problems for Homogeneous Elastic Plates and Beams

Mixed formulations of bending problems for homogeneous plates (beams) are proposed, whose essence is that the deformation of a plate (beam) near its fixed boundary is described by the threedimensional elasticity equations, and the remaining part by the conventional equations of plate (beam) bending. At the interface between these regions, the solutions of these equations are joined. The mixed formulation allows one to describe the threedimensional stress state in the neighborhood of the fixed boundaries of plates (beams) and take into account the complex nature of the fixing conditions. Finiteelement implementation is more efficient for the mixed formulations of plate (beam) bending problems than for the wellknown threedimensional formulations.