954 research outputs found
Quantum tunneling between paramagnetic and superconducting states of a nanometer-scale superconducting grain placed in a magnetic field
We consider the process of quantum tunneling between the superconducting and
paramagnetic states of a nanometer-scale superconducting grain placed in a
magnetic field. The grain is supposed to be coupled via tunneling junction to a
normal metallic contact that plays a role of the spin reservoir. Using the
instanton method we find the probability of the quantum tunneling process and
express it in terms of the applied magnetic field, order parameter of the
superconducting grain and conductance of the tunneling junction between the
grain and metallic contact
Josephson transport through a Hubbard impurity center
We investigate the Josephson transport through a thin semiconductor barrier
containing impurity centers with the on-site Hubbard interaction of an
arbitrary sign and strength. We find that in the case of the repulsive
interaction the Josephson current changes sign with the temperature increase if
the energy of the impurity level (measured from the Fermi energy of
superconductors) falls in the interval . We predict strong temporal
fluctuations of the current if only a few centers present within the junction.
In the case of the attractive impurity potential () and at low
temperatures, the model is reduced to the effective two level Hamiltonian
allowing thus a simple description of the nonstationary Josephson effect in
terms of pair tunneling processes
Microscopic theory of thermal phase slips in clean narrow superconducting wires
We consider structure of a thermal phase-slip center for a simple microscopic
model of a clean one-dimensional superconductors in which superconductivity
occurs only within one conducting channel or several identical channels.
Surprisingly, the Eilenberger equations describing the saddle-point
configuration allow for exact analytical solution in the whole temperature and
current range. This solution allows us to derive a closed expression for the
free-energy barrier, which we use to compute its temperature and current
dependences
Research on modes of plasma generation in low-pressure discharge for themal radiation processes
In this work a theoretical research on modes of low-pressure glow discharge generation and its parameters in a large area hollow cathode are carried out. The relations describing the dependence of the burning voltage on the gas pressure and the geometry of the system were obtained. It is shown that it is possible to adjust the ion current density and burning voltage by external current injection independently of the surface area and material of the processed parts. This work also carries out a numerical study of the influence of plasma parameters on the heating of processed parts. Theoretical results are compared with experimental data
The Expression of the Epithelial Blood-group Substances: Normal and Malignant Tissues
The blood-group isoantigens are macromolecules localized to the plasma membranes of certain epithelial tissues.2,11-15 These substances are not detectable on the epithelium once it has undergone malignant transformation.2,9,13 Results of this investigation have demonstrated that the loss of detectability of the blood-group isoantigens does not appear to be related to a "masking" effect by an increase in surface sialic acid. Using fluorescein-labeled lectins specific for sugar subunits which are components of the blood-group oligosaccharide chain, it was found that the malignant cells and cells of the para basal layer of normal oral epithelium had high levels of N-acetyl-D-glucosamine (GlcNAC), the subterminal sugar residue of the blood-group chain. The basal cells of normal epithelium and a minority of the malignant cells demonstrated levels of D-galactose-N-acetyl-D-galactosamine, which are the most proximal blood-group sugar subunits, as well as subunits of other membrane antigens. Our results indicate that malignant cells seem to be capable of synthesizing the blood-group oligosaccharide chains to the same level as the normal cells of the para basal layer of stratified squamous epithelium. This level is just subjacent to the terminal D-galactose residue of the blood-group precursor chain. Increased or decreased differentiation characteristics of squamous cell carcinomas did not alter the level of blood-group synthesis. However, there may be a correlation between the level of synthesis of these antigens and the ability of the cells to demonstrate motility and to proliferate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66719/2/10.1177_00220345800590112001.pd
Generation of low-temperature plasma by low-pressure arcs for synthesis of nitride coatings
Experiments were performed to study gas, metal, and mixed metal-gas plasmas. The plasmas were generated with the use of an arc evaporator and a gas-plasma source with a hot filament and hollow cathode that were operated independently or simultaneously. It has been revealed that the arc current of gas-plasma source affects the parameters of the metal-gas plasma and the element concentrations in the coatings. It has been demonstrated that the characteristics of the nitride coatings produced by plasma-assisted vacuum-arc deposition can be controlled by varying the parameters of the arc in the gas-plasma source
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