PubMed Health⌕ Search

Biomedical subjects

A I Larkin

Publications and source records attributed to A I Larkin.

8 recordsLinked to original sources
PubMed2004

Dephasing in disordered metals with superconductive grains.

The temperature dependence of electron dephasing time tau(phi)(T) is calculated for a disordered metal with a small concentration of superconductive grains. Above the macroscopic superconducting transition line, when electrons in the metal are normal, Andreev reflection from the grains leads to a nearly temperature-independent contribution to the dephasing rate. In a broad temperature range tau(-1)(phi)(T) strongly exceeds the prediction of the classical theory of dephasing in normal disordered conductors, whereas magnetoresistance is dominated (in two dimensions) by the Maki-Tompson correction and is positive.

Journal Article↗
PubMed2002

Coulomb blockade with dispersive interfaces.

What quantity controls the Coulomb blockade oscillations if the dot-lead conductance is essentially frequency dependent? We argue that it is the conductance at the imaginary frequency given by the effective charging energy. The latter may be very different from the bare charging energy due to the interface-induced capacitance (or inductance). These observations are supported by a number of examples, considered from the weak and strong coupling (perturbation theory versus instanton calculus) perspectives.

Journal Article↗
PubMed2002

Persistent current in superconducting nanorings.

The superconductivity in very thin rings is suppressed by quantum phase slips. As a result, the amplitude of the persistent current oscillations with flux becomes exponentially small, and their shape changes from sawtooth to a sinusoidal one. We reduce the problem of low-energy properties of a superconducting nanoring to that of a quantum particle in a sinusoidal potential and show that the dependence of the current on the flux belongs to a one-parameter family of functions obtained by solving the respective Schrödinger equation with twisted boundary conditions.

Journal Article↗
PubMed2001

Disorder and quantum fluctuations in superconducting films in strong magnetic fields.

We find that the upper critical field in a two-dimensional disordered superconductor can increase essentially at low temperatures. This happens due to the formation of local superconducting islands weakly coupled via the Josephson effect. The distribution of the superconducting islands is derived. It is shown that the value of the critical field is determined by the interplay of the proximity effect and quantum phase fluctuations. The shift of the upper critical field is connected with the pinning properties of a superconductor.

Journal Article↗
PubMed2001

Quantum superconductor-metal transition in a proximity array.

A theory of the zero-temperature superconductor-metal transition is developed for an array of superconductive islands (of size d) coupled via a disordered two-dimensional conductor with the dimensionless conductance g = Planck's over 2 pi/e(2)R(square)>>1. At T = 0 the macroscopically superconductive state of the array with lattice spacing b>>d is destroyed at g<g(c) approximately 0.1ln(2)(b/d). At high temperatures the normal-state resistance between neighboring islands at b = b(c) is much smaller than R(Q) = h/4e(2).

Journal Article↗
PubMed1978

[Method of partitioning polyene macrolide antibiotics].

Levorin and mycoheptin, polyenic antibiotics were separated into 3 and 7 heptaenic components respectively by the method of disc electrophoresis in 7.5 per cent polyacryl amide gel prepared with tris-HCl buffer, pH 8.9. It was shown that nystatin had different composition as dependent on the organism producing it. The results of electrophoresis confirmed the data of the counter-current distribution.

Antifungal Agents↗
PubMed1977

[Effect of mineral phosphorus on mycoheptin biosynthesis].

The effect of mineral phosphorus in doses of 22.8 to 684 gamma/ml in a synthetic medium on biosynthesis of mycoheptin, an antifungal antibiotic was studied. It was found that the maximum productivity of the mycelium was at the phosphorus concentration in the medium equal to 22.8--45.6 gamma/ml and the concentration of 91.2 gamma/ml was optimal for the growth of the antibiotic-prodicing organism. The phosphorus optimal concentrations for the growth and antibiotic synthesis phases did not coincide that provided consideration of phosphorus as a limiting factor useful in control of the antibiotic biosynthesis. The content of pphosphorus in the medium 6 times higher than the optimal concentration did not inhibit the biomass accumulation and had no significant effect on the colony morphology.

Antifungal Agents↗