34,998 research outputs found
Odd Triplet Pairing in clean Superconductor/Ferromagnet heterostructures
We study triplet pairing correlations in clean Ferromagnet (F)/Superconductor
(S) nanojunctions, via fully self consistent solution of the Bogoliubov-de
Gennes equations. We consider FSF trilayers, with S being an s-wave
superconductor, and an arbitrary angle between the magnetizations of
the two F layers. We find that contrary to some previous expectations, triplet
correlations, odd in time, are induced in both the S and F layers in the clean
limit. We investigate their behavior as a function of time, position, and
. The triplet amplitudes are largest at times on the order of the
inverse ``Debye'' frequency, and at that time scale they are long ranged in
both S and F. The zero temperature condensation energy is found to be lowest
when the magnetizations are antiparallel.Comment: Four pages, including four figure
Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication
Probability for Primordial Black Holes in Multidimensional Universe with Nonlinear Scalar Curvature Terms
We investigate multi-dimensional universe with nonlinear scalar curvature
terms to evaluate the probability of creation of primordial black holes. For
this we obtain Euclidean instanton solution in two different topologies: (a)
- topology which does not accommodate primordial black holes and (b)
-topology which accommodates a pair of black holes. The
probability for quantum creation of an inflationary universe with a pair of
black holes has been evaluated assuming a gravitational action which is
described by a polynomial function of scalar curvature with or without a
cosmological constant () using the framework of semiclassical
approximation of Hartle-Hawking boundary conditions. We discuss here a class of
new gravitational instantons solution in the -theory which are relevant
for cosmological model building.Comment: 18 pages, no figure. accepted in Phys. Rev.
Cotton Price Policy and New Cereal Technology in the Malian Cotton Zone
During the last decade, cotton production and area have been declining as a result of depleting soil nutrients and low cotton prices in the cotton zone of Mali. This paper shows that the Malian government’s 2011 policy to increase the farm gate cotton price as a response to world cotton price increase enhances farm income but has less impact on cotton than on maize production. A complementary policy of introducing new sorghum technologies would have an equal impact on farmers’ incomes in the cotton zone of Mali.Cotton prices, improved sorghum technology, discrete stochastic programming, Mali, Agricultural and Food Policy, Farm Management, International Development, Production Economics, Risk and Uncertainty,
Inhibitory synchrony as a mechanism for attentional gain modulation
Recordings from area V4 of monkeys have revealed that when the focus of
attention is on a visual stimulus within the receptive field of a cortical
neuron, two distinct changes can occur: The firing rate of the neuron can
change and there can be an increase in the coherence between spikes and the
local field potential in the gamma-frequency range (30-50 Hz). The hypothesis
explored here is that these observed effects of attention could be a
consequence of changes in the synchrony of local interneuron networks. We
performed computer simulations of a Hodgkin-Huxley type neuron driven by a
constant depolarizing current, I, representing visual stimulation and a
modulatory inhibitory input representing the effects of attention via local
interneuron networks. We observed that the neuron's firing rate and the
coherence of its output spike train with the synaptic inputs was modulated by
the degree of synchrony of the inhibitory inputs. The model suggest that the
observed changes in firing rate and coherence of neurons in the visual cortex
could be controlled by top-down inputs that regulated the coherence in the
activity of a local inhibitory network discharging at gamma frequencies.Comment: J.Physiology (Paris) in press, 11 figure
Mechanisms of two-color laser-induced field-free molecular orientation
Two mechanisms of two-color (\omega + 2\omega) laser-induced field-free
molecular orientation, based on the hyperpolarizability and ionization
depletion, are explored and compared. The CO molecule is used as a
computational example. While the hyperpolarizability mechanism generates small
amounts of orientation at intensities below the ionization threshold,
ionization depletion quickly becomes the dominant mechanism as soon as ionizing
intensities are reached. Only the ionization mechanism leads to substantial
orientation (e.g. on the order of || > 0.1). For intensities typical
of laser-induced molecular alignment and orientation experiments, the two
mechanism lead to robust, characteristic timings of the field-free orientation
wave-packet revivals relative to the the alignment revivals and the revival
time. The revival timings can be used to detect the active orientation
mechanism experimentally
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