3,736 research outputs found
Temperature-stable Gunn-diode oscillator
Oscillator consisting of Gunn diode embedded in coaxial circuit has excellent temperature stability and low fabrication costs as compared with automatic-frequency-control crystal oscillators
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
Negative Magnetoresistance of Granular Metals in a Strong Magnetic Field
The magnetoresistance of a granular superconductor in a strong magnetic field
destroying the gap in each grain is considered. It is assumed that the
tunneling between grains is sufficiently large such that all conventional
effects of localization can be neglected. A non-trivial sensitivity to the
magnetic field comes from superconducting fluctuations leading to the formation
of virtual Cooper pairs and reducing the density of states. At low temperature,
the pairs do not contribute to the macroscopic transport but their existence
can drastically reduce the conductivity. Growing the magnetic field one
destroys the fluctuations, which improves the metallic properties and leads to
the negative magnetoresistance.Comment: 4 pages, 1 figure, RevTe
Towards Uniform Gene Bank Documentation In Europe – The Experience From The EFABISnet Project
In the EFABISnet project, a collaborative effort of EAAP, FAO and partners from 14 European countries, in cooperation with the European Regional Focal Point for Animal Genetic Resources (ERFP), national information systems for monitoring the animal genetic resources on breed level were established in Austria, Cyprus, Estonia, Georgia, Iceland, Ireland, Italy, Netherlands, Slovakia, Slovenia, Switzerland, and United Kingdom. The network was soon extended beyond the project plans, with the establishment of EFABIS databases in Finland, Greece, and Hungary. The network was then complemented by a set of inventories of national gene bank collections to strengthen the documentation of ex situ conservation programmes. These documentation systems were established by the National Focal Points for management of farm animal genetic resources. Here we present the experience gained in establishment of these national inventories of gene banks and their relevance to the Strategic Priority Areas of the Global Plan of Action which could be useful for other areas in the world
Impurity effects in unconventional density waves in the unitary limit
We investigate the effect of strong, nonmagnetic impurities on
quasi-one-dimensional conventional and unconventional density waves (DW and
UDW). The conventional case remains unaffected similarly to s-wave
superconductors in the presence of weak, nonmagnetic impurities. The
thermodynamic properties of UDW were found to be identical to those of a d-wave
superconductor in the unitary limit. The real and imaginary part of the optical
conductivity is determined for electric fields applied in the perpendicular
directions. A new structure can be present corresponding to excitations from
the bound state at the Fermi energy to the gap maximum in addition to the usual
peak at 2\Delta. In the dc limit, universal electric conductivity is found.Comment: 9 pages, 5 figure
Magnetoresistance of Granular Superconducting Metals in a Strong Magnetic Field
The magnetoresistance of a granular superconductor in a strong magnetic field
is considered. It is assumed that this field destroys the superconducting gap
in each grain, such that all interesting effects considered in the paper are
due to superconducting fluctuations. The conductance of the system is assumed
to be large, which allows us to neglect all localization effects as well as the
Coulomb interaction. It is shown that at low temperatures the superconducting
fluctuations reduce the one-particle density of states but do not contribute to
transport. As a result, the resistivity of the normal state exceeds the
classical resistivity approaching the latter only in the limit of extremely
strong magnetic fields, and this leads to a negative magnetoresistance. We
present detailed calculations of physical quatities relevant for describing the
effect and make a comparison with existing experiments.Comment: 24 pages, 10 figure
Thermal conductivity in B- and C- phase of UPt_3
Although the superconductivity in UPt_3 is one of the most well studied,
there are still lingering questions about the nodal directions in the B and C
phase in the presence of a magnetic field. Limiting ourselves to the low
temperature regime (T<<Delta(0)), we study the magnetothermal conductivity with
in semiclassical approximation using Volovik's approach. The angular dependence
of the magnetothermal conductivity for an arbitrary field direction should
clarify the nodal structure in UPt_3.Comment: 4 pages, 5 figure
Neutrino spin rotation in dense matter and electromagnetic field
Exact solutions of the Dirac--Pauli equation for massive neutrino with
anomalous magnetic moment interacting with dense matter and strong
electromagnetic field are found. The complete system of neutrino wavefunctions,
which show spin rotation properties are obtained and their possible
applications are discussed.Comment: 11 pages, latex, misprints are correcte
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. We find that the shift
of the upper critical field is connected with the pinning properties of a
superconductor.Comment: 4 page
Optical conductivity of superconducting Sr_2RuO_4
We compute the optical conductivity of 2D f-wave superconductors and also of
the multigap model proposed recently by Zhitomirsky and Rice at T=0K in the
Born limit. The presence of interband impurity scattering was found to play an
important role: the contributions from the two bands mix up, and new structures
are seen in the tunneling density of states and in the optical spectrum as
well, corresponding to interband transitions.
This will provide a sensitive test in selecting the competing models for the
triplet superconductivity in Sr_2RuO_4.Comment: 7 pages, 9 figure
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