149 research outputs found
Structure and properties of the stable two-dimensional conducting polymer Mg5C60
We present a study on the structural, spectroscopic, conducting,
and
magnetic properties of Mg5C60, which is a two-dimensional (2D)
fulleride polymer. The polymer phase is stable up to the
exceptionally
high temperature of 823 K. The infrared and Raman studies
suggest the
formation of single bonds between the fulleride ions and
possibly
Mg-C-60 covalent bonds. Mg5C60 is a metal at ambient
temperature, as
shown by electron spin resonance and microwave conductivity
measurements. The smooth transition from a metallic to a
paramagnetic
insulator state below 200 K is attributed to Anderson
localization
driven by structural disorder
Enhancing superconductivity: Magnetic impurities and their quenching by magnetic fields
Magnetic fields and magnetic impurities are each known to suppress
superconductivity. However, as the field quenches (i.e. polarizes) the
impurities, rich consequences, including field-enhanced superconductivity, can
emerge when both effects are present. For the case of superconducting wires and
thin films, this field-spin interplay is investigated via the
Eilenberger-Usadel scheme. Non-monotonic dependence of the critical current on
the field (and therefore field-enhanced superconductivity) is found to be
possible, even in parameter regimes in which the critical temperature decreases
monotonically with increasing field. The present work complements that of
Kharitonov and Feigel'man, which predicts non-monotonic behavior of the
critical temperature.Comment: 8 pages, 2 figures, EPL forma
Operation of a superconducting nanowire quantum interference device with mesoscopic leads
A theory describing the operation of a superconducting nanowire quantum
interference device (NQUID) is presented. The device consists of a pair of
thin-film superconducting leads connected by a pair of topologically parallel
ultra-narrow superconducting wires. It exhibits intrinsic electrical
resistance, due to thermally-activated dissipative fluctuations of the
superconducting order parameter. Attention is given to the dependence of this
resistance on the strength of an externally applied magnetic field aligned
perpendicular to the leads, for lead dimensions such that there is essentially
complete and uniform penetration of the leads by the magnetic field. This
regime, in which at least one of the lead dimensions lies between the
superconducting coherence and penetration lengths, is referred to as the
mesoscopic regime. The magnetic field causes a pronounced oscillation of the
device resistance, with a period not dominated by the Aharonov-Bohm effect
through the area enclosed by the wires and the film edges but, rather, in terms
of the geometry of the leads, in contrast to the well-known Little-Parks
resistance of thin-walled superconducting cylinders. A theory, encompassing
this phenomenology, is developed through extensions, to the setting of parallel
superconducting wires, of the Ivanchenko-Zil'berman-Ambegaokar-Halperin theory
for the case of short wires and the Langer-Ambegaokar-McCumber-Halperin theory
for the case of longer wires. It is demonstrated that the NQUID acts as a probe
of spatial variations in the superconducting order parameter.Comment: 20 pages, 18 figure
Mapping of functionalized regions on carbon nanotubes by scanning tunneling microscopy
Scanning tunneling microscopy (STM) gives us the opportunity to map the
surface of functionalized carbon nanotubes in an energy resolved manner and
with atomic precision. But this potential is largely untapped, mainly due to
sample stability issues which inhibit reliable measurements. Here we present a
simple and straightforward solution that makes away with this difficulty, by
incorporating the functionalized multiwalled carbon nanotubes (MWCNT) into a
few layer graphene - nanotube composite. This enabled us to measure energy
resolved tunneling conductance maps on the nanotubes, which shed light on the
level of doping, charge transfer between tube and functional groups and the
dependence of defect creation or functionalization on crystallographic
orientation.Comment: Keywords: functionalization, carbon nanotubes, few layer graphene,
STM, CITS, ST
Phase diagrams of in Double Exchange Model with added antiferromagnetic and Jahn-Teller interaction
The phase diagram of the multivalent manganites , in
space of temperature and doping , is a challenge for the theoretical
physics. It is an important test for the model used to study these compounds
and the method of calculation. To obtain theoretically this diagram for
, we consider the two-band Double Exchange Model for manganites with
added Jahn-Teller coupling and antiferromagnetic Heisenberg term. In order to
calculate Curie and N\'{e}el temperatures we derive an effective Heisenberg
model for a vector which describes the local orientation of the total
magnetization of the system. The exchange constants of this model are different
for different space directions and depend on the density of electrons,
antiferromagnetic constants and the Jahn-Teller energy. To reproduce the well
known phase transitions from A-type antiferromagnetism to ferromagnetism at low
and C-type antiferromagnetism to G-type antiferromagnetism at large , we
argue that the antiferromagnetic exchange constants should depend on the
lattice direction. We show that ferromagnetic to A-type antiferromagnetic
transition results from the Jahn-Teller distortion. Accounting adequately for
the magnon-magnon interaction, Curie and N\'{e}el temperatures are calculated.
The results are in very good agreement with the experiment and provide values
for the model parameters, which best describe the behavior of the critical
temperature for .Comment: 13 pages, 5 figure
ПРИМЕНЕНИЕ ТЕХНОЛОГИИ БИОУПРАВЛЕНИЯ ДЛЯ ТРЕНИНГА БЕРЕМЕННЫХ ПРИ МОНИТОРИРОВАНИИ СОСТОЯНИЯ СИСТЕМЫ МАТЬ – ПЛОД
Raining influence with biofeedback on system mother fetus was investigated. The technique of biofeedback training for the pregnant women was developed, which had main objective to control of parameters of vegetative nervous system by means of breath. The technique was tested on a group of pregnant wo men on term of a gestation of 32–35 weeks. It is established: change of a functional condition of mother influences level of sympathetic regulation of a heart rhythm of a fetus.Исследовано влияние тренинга на основе технологии биоуправления на систему мать – плод. Разработана методика БОС-тренинга для беременных женщин, основная цель которой – управление параметрами вегетативной нервной системы с помощью дыхания. Методика опробована на группе беременных на сроке гестации 32–35 нед. Установлено, что изменение функционального состояния матери влияет на уровень симпатической регуляции сердечного ритма плода
Thermometry with spin-dependent lattices
We propose a method for measuring the temperature of strongly correlated
phases of ultracold atom gases confined in spin-dependent optical lattices. In
this technique, a small number of "impurity" atoms--trapped in a state that
does not experience the lattice potential--are in thermal contact with atoms
bound to the lattice. The impurity serves as a thermometer for the system
because its temperature can be straightforwardly measured using time-of-flight
expansion velocity. This technique may be useful for resolving many open
questions regarding thermalization in these isolated systems. We discuss the
theory behind this method and demonstrate proof-of-principle experiments,
including the first realization of a 3D spin-dependent lattice in the strongly
correlated regime.Comment: 22 pages, 8 figures v2: Several references added; Section on heating
rates updated to include dipole fluctuation terms; Section added on the
limitations of the proposed method. To appear in New Journal of Physic
Angular momenta creation in relativistic electron-positron plasma
Creation of angular momentum in a relativistic electron-positron plasma is
explored. It is shown that a chain of angular momentum carrying vortices is a
robust asymptotic state sustained by the generalized nonlinear Schrodinger
equation characteristic to the system. The results may suggest a possible
electromagnetic origin of angular momenta when it is applied to the MeV epoch
of the early Universe.Comment: 20 pages, 6 figure
Far-infrared vibrational properties of linear C60 polymers: A comparison between neutral and charged materials
We report the far-infrared transmittance spectrum of a pure phase of the orthorhombic high-temperature and high-pressure C-60 polymer and compare the results with a previously published spectrum of the charged RbC60 orthorhombic polymer. Assignments for both spectra are made with the aid of first-principles quantum molecular dynamics simulations of the two materials. We find that the striking spectral differences between the neutral and charged linear fullerene polymers can be fully accounted for by charge effects on the C-60 ball
Co-ordinated regulation of flowering time, plant architecture and growth by FASCICULATE: the pepper orthologue of SELF PRUNING
Wild peppers (Capsicum spp.) are either annual or perennial in their native habitat and their shoot architecture is dictated by their sympodial growth habit. To study shoot architecture in pepper, sympodial development is described in wild type and in the classical recessive fasciculate (fa) mutation. The basic sympodial unit in wild-type pepper comprises two leaves and a single terminal flower. fasciculate plants are characterized by the formation of floral clusters separated by short internodes and miniature leaves and by early flowering. Developmental analysis of these clusters revealed shorter sympodial units and, often, precocious termination prior to sympodial leaf formation. fa was mapped to pepper chromosome 6, in a region corresponding to the tomato SELF-PRUNING (SP) locus, the homologue of TFL1 of Arabidopsis. Sequence comparison between wild-type and fa plants revealed a duplication of the second exon in the mutants' orthologue of SP, leading to the formation of a premature stop codon. Ectopic expression of FASCICULATE complemented the Arabidopsis tfl1 mutant plants and as expected, stimulated late flowering. In agreement with the major effect of FASCICULATE imposed on sympodial development, the gene transcripts were localized to the centre of sympodial shoots but could not be detected in the primary shoot. The wide range of pleiotropic effects on plant architecture mediated by a single ‘flowering’ gene, suggests that it is used to co-ordinate many developmental events, and thus may underlie some of the widespread variation in the Solanaceae shoot architecture
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