Efficient cardiac diffusion tensor MRI by three-dimensional reconstruction of solenoidal tensor fields

Tensor tomography is being investigated as a technique for reconstruction of in vivo diffusion tensor fields that can potentially be used to reduce the number of magnetic resonance imaging (MRI) measurements. Specifically, assessments are being made of the reconstruction of cardiac diffusion tensor fields from 3D Radon planar projections using a filtered backprojection algorithm in order to specify the helical fiber structure of myocardial tissue. Helmholtz type decomposition is proposed for 3D second order tensor fields. Using this decomposition a Fourier projection theorem is formulated in terms of the solenoidal and irrotational components of the tensor field. From the Fourier projection theorem, two sets of Radon directional measurements, one that reconstructs the solenoidal component and one that reconstructs the irrotational component of the tensor field, are prescribed. Based on these observations filtered backprojection reconstruction formulae are given for the reconstruction of a 3D second order tensor field and its solenoidal and irrotational components from Radon projection measurements. Computer simulations demonstrate the validity of the mathematical formulations and demonstrate that a realistic model of the helical fiber structure of the myocardial tissue specifies a diffusion tensor field for which the first principal vector (the vector associated with the maximum eigenvalue) of the solenoidal component accurately approximates the first principal vector of the diffusion tensor. A priori knowledge of this allows the orientation of the myocardial fiber structure to be specified utilizing one half of the number of MRI measurements of a normal diffusion tensor field study.     

The Role of Elastic Recovery in Formation of Tribological Properties of Ultra-High-Molecular Weight Polyethylene with Various Sizes of Initial Powder

Russian Physics Journal - The mechanical and tribological characteristics of ultra-high molecular weight polyethylene (UHMWPE) with identical molecular weight, but different sizes of the initial...     

The Effect of Physical-Chemical Nature of UHMWPE and PPS Thermoplastic Matrices on the Formation of Mechanical and Tribological Properties of their Carbon Fiber Filled Composites

Russian Physics Journal - The effect of carbon fiber dimensions on mechanical and tribological properties of the composites based on two thermoplastic matrices of different physical-chemical nature...     

Measurement of the absorption coefficient for UCN at a copper surface

The probability of ultra-cold neutron capture at a copper surface was measured by the activation method. The experimental absorption coefficient is well accounted for by a calculation which takes into account the presence of a CuO-layer at the surface of a Cu-film.     

Spectra of H-like Cu,Zn and Ga

The spectra of Cu XXIX, Zn XXX and Ga XXXI excited in a low-inductance vacuum spark plasma have been obtained for the first time. A mathematical noise-suppression method was used for the spectrum of Ga XXXI.     

Mesoscale plastic deformation of aluminum polycrystals

A study is made of the mechanism of plastic deformation at the mesoscale level in flat specimens of aluminum polycrystals. The mechanism is examined with the use of high-resolution optical-television system TOMSC-1. It is shown that a multilevel mesoscale structure is formed in the specimen as it is deformed. The formation of this structure leads to the appearance of two types of stationary waves 120 μm and 4.8 mm long. The results are interpreted within the framework of a hierarchy of mesoscale levels of deformation and are linked with the decisive role of surface oxide films in the formation of the mesoband structure and stationary waves associated plastic flow. Institute of the Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 31–39, January, 1997.     

Pseudopotential study of the thermodynamic characteristics of supercooled Mg and Zn melts

We use a pseudopotential and thermodynamic perturbation theory to study the thermodynamic characteristics of metallic Mg and Zn melts. A system of solid spheres is selected, to be the ground state. Our calculations of the melting temperature, entropy, and volume are in good agreement with experiment, and the calculated results are insensitive to the choice of pseudopotential. As the temperature is lowered the diameter of the solid spheres and the packing density increase. In addition, there is a marked decrease in the melt's self diffusion coefficient, reflecting the possibility of forming an amorphous structure.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 4, pp. 20–24, April, 1984.     

Luminescence from ZnO/MgO nanoparticle structures prepared by solution techniques

The optical and structural properties of mixed ZnO/MgO particles prepared by solution techniques are investigated by the cathodoluminescence and electron microscopy techniques. The samples annealed at 400–1000 °C show well crystalline wurtzite structure of the ZnO (MgZnO) particles with the size in range of 10–100 nm. Annealing at high temperatures (>700 °C) leads to Mg diffusion in ZnO and Mg_xZn_1−xO alloy formation. The blue shifts of the near-band-edge emission as a result of the alloy band gap widening and quantum confinement effect for the small size particles are demonstrated.