Biomedical subjects
Publications and source records attributed to A S Mel'nikov.
We propose a mechanism of quantum pumping mediated by the spectral flow in a voltage-biased superconductor/insulator/normal-metal/insulator/superconductor quantum junction and realized via the sequential closing of the minigaps in the energy spectrum in resonance with the Josephson frequency. We show that the pumped dc current exhibits giant peaks at rational voltages.
The interplay of geometrical and Andreev quantization in mesoscopic superconductors leads to giant mesoscopic oscillations of energy levels as functions of the Fermi momentum and/or sample size. Quantization rules are formulated for closed quasiparticle trajectories in the presence of normal scattering at the sample boundaries. Two generic examples of mesoscopic systems are studied: (i) one-dimensional Andreev states in a quantum box and (ii) a single vortex in a mesoscopic cylinder.
The influence of vilon (Lys-Glu) on 1.2-dimethylhydrazine-induced neoplasia in mice has been studied. After treatment with 10 microg/kg, tumors developed in 14.3% which survived until first tumor detection (46 weeks) while, in control group, tumors occurred in 60%. Vilon-related inhibition of preneoplastic alterations in the kidneys was reported.
Several key experiments have revealed a rich variety of vortex structures in mesoscopic superconductors in which only a few quanta of magnetic flux are trapped: these structures are polygon-like vortex 'molecules' and multi-quanta giant vortices. Ginzburg-Landau calculations confirmed second-order phase transitions between the giant vortex states and stable molecule-like configurations. Here we study theoretically the electronic structure and the related phase-coherent transport properties of such mesoscopic superconductor systems. The quasiparticle excitations in the vortices form coherent quantum-mechanical states that offer the possibility of controlling the phase-coherent transport through the sample by changing the number of trapped flux quanta and their configuration. The sample conductance measured in the direction of the applied magnetic field is determined by the transparency of multi-vortex configurations, which form a set of quantum channels. The transmission coefficient for each channel is controlled by multiple Andreev reflections within the vortex cores and at the sample edge. These interference phenomena result in a stepwise behaviour of the conductance as a function of the applied magnetic field, and we propose to exploit this effect to realize a vortex-based quantum switch where the magnetic field plays the role of the gate voltage.
Correlation of development of tumor pathology and macro- and microhematuria was investigated in the experiments using 50 male rats with N-butyl-N-(4-hydroxybutyl)-nitrosoamine-induced tumors of the urinary bladder. Our highly-sensitive agent Azopiram was employed to monitor hematuria. Microhematuria, which subsequently developed into macrohematuria as tumor matured and turned malignant, was identified as early as at such incipient neoplastic changes as focal hyperplasia of the urothelium and micropapillomatosis. The test can be used outside clinic as a measure of self-control in recurrent cancer of the urinary bladder.
On the basis of the Bogoliubov-de Gennes theory we develop an analytical description of low-energy extended quasiparticle states around an isolated flux line in a superconductor with gap nodes. The wave functions of these excitations and the corresponding density of states are shown to be strongly influenced by the interaction with a pure gauge potential due to the Aharonov-Bohm scenario.
The effect of peptide vilon (Lys-Glu) on urinary bladder carcinogenesis in rats was studied. Urinary bladder tumors were induced with a selective carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine. The tumors developed in 56% vilon-treated animals and in 75.5% controls. Vilon 2-fold decreased the incidence of preneoplastic and early neoplastic changes in urinary bladder mucosa and significantly inhibited carcinogenesis.
Experimental data on the effect of peptides--Vilon (Lys-Glu) and Epitalon (Ala-Glu-Asp-Gly)--on induction of urinary bladder tumors in rats are presented. Treatment with Vilon was followed by a significant fall in tumor incidence in 56% of experimental animals, as compared with 75.5% in control, as well as inhibition of early-onset neoplastic changes in the bladder mucosa. No inhibitory effect of Epitalon was recorded.