8,871 research outputs found
Revivals, collapses and magnetic-pulse generation in quantum rings
Using a microscopic theory based on the density matrix formalism we
investigate quantum revivals and collapses of the charge polarization and
charge current dynamics in mesoscopic rings driven by short asymmetric
electromagnetic pulses. The collapsed state is utilized for sub-picosecond
switching of the current and associated magnetization, enabling thus the
generation of pulsed magnetic fields with a tunable time structure and shape
asymmetry which provides a new tool to study ultrafast spin-dynamics and
ratchet-based effects.Comment: 4 pages, 2 figure
Solutions in Self-Dual Gravity Constructed Via Chiral Equations
The chiral model for self-dual gravity given by Husain in the context of the
chiral equations approach is discussed. A Lie algebra corresponding to a finite
dimensional subgroup of the group of symplectic diffeomorphisms is found, and
then use for expanding the Lie algebra valued connections associated with the
chiral model. The self-dual metric can be explicitly given in terms of harmonic
maps and in terms of a basis of this subalgebra.Comment: Plain Latex, 13 Pages, major revisions of style in the above proof,
several Comments added. Version to appear in Physical Review
Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux
We study theoretically the charge polarization and the charge current
dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses
and threaded by an external static magnetic flux. It is shown that the
pulse-induced charge polarization and the associated light-emission is
controllable by tuning the external magnetic flux. Applying two mutually
perpendicular pulses triggers a charge current in the ring. The interplay
between this nonequilibrium and the persistent currents is investigated and the
conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP
Class of Einstein--Maxwell Dilatons
Three different classes of static solutions of the Einstein--Maxwell
equations non--minimally coupled to a dilaton field are presented. The
solutions are given in general in terms of two arbitrary harmonic functions and
involve among others an arbitrary parameter which determines their
applicability as charged black holes, dilaton black holes or strings. Most of
the known solutions are contained as special cases and can be non--trivially
generalized in different ways.Comment: Published in Physical Review D, R310 (1995
Deformation of quantum mechanics in fractional-dimensional space
A new kind of deformed calculus (the D-deformed calculus) that takes place in
fractional-dimensional spaces is presented. The D-deformed calculus is shown to
be an appropriate tool for treating fractional-dimensional systems in a simple
way and quite analogous to their corresponding one-dimensional partners. Two
simple systems, the free particle and the harmonic oscillator in fractional-
dimensional spaces are reconsidered into the framework of the D-deformed
quantum mechanics. Confined states in a D-deformed quantum well are studied.
D-deformed coherent states are also found.Comment: 12 pages, some misprints have been corrected, two figures are adde
The role of bacteria in pine wilt disease: insights from microbiome analysis.
Pine Wilt Disease (PWD) has a significant impact on Eurasia pine forests. The microbiome of the nematode (the primary cause of the disease), its insect vector, and the host tree may be relevant for the disease mechanism. The aim of this study was to characterize these microbiomes, from three PWD-affected areas in Portugal, using Denaturing Gradient Gel Electrophoresis, 16S rRNA gene pyrosequencing, and a functional inference-based approach (PICRUSt). The bacterial community structure of the nematode was significantly different from the infected trees but closely related to the insect vector, supporting the hypothesis that the nematode microbiome might be in part inherited from the insect. Sampling location influenced mostly the tree microbiome (P < 0.05). Genes related both with plant growth promotion and phytopathogenicity were predicted for the tree microbiome. Xenobiotic degradation functions were predicted in the nematode and insect microbiomes. Phytotoxin biosynthesis was also predicted for the nematode microbiome, supporting the theory of a direct contribution of the microbiome to tree-wilting. This is the first study that simultaneously characterized the nematode, tree and insect-vector microbiomes from the same affected areas, and overall the results support the hypothesis that the PWD microbiome plays an important role in the disease's development
Teores de minerais do capim canarana-erecta-lisa (Echinochloa pyramidalis) em três idades.
bitstream/item/34012/1/CPATU-CirTec54.pd
Edge phonons in black phosphorus
Exfoliated black phosphorus has recently emerged as a new two-dimensional
crystal that, due to its peculiar and anisotropic crystalline and electronic
band structures, may have potentially important applications in electronics,
optoelectronics and photonics. Despite the fact that the edges of layered
crystals host a range of singular properties whose characterization and
exploitation are of utmost importance for device development, the edges of
black phosphorus remain poorly characterized. In this work, the atomic
structure and the behavior of phonons near different black phosphorus edges are
experimentally and theoretically studied using Raman spectroscopy and density
functional theory calculations. Polarized Raman results show the appearance of
new modes at the edges of the sample, and their spectra depend on the atomic
structure of the edges (zigzag or armchair). Theoretical simulations confirm
that the new modes are due to edge phonon states that are forbidden in the
bulk, and originated from the lattice termination rearrangements.Comment: 15 pages, 4 figure
Theory of thermal spin-charge coupling in electronic systems
The interplay between spin transport and thermoelectricity offers several
novel ways of generating, manipulating, and detecting nonequilibrium spin in a
wide range of materials. Here we formulate a phenomenological model in the
spirit of the standard model of electrical spin injection to describe the
electronic mechanism coupling charge, spin, and heat transport and employ the
model to analyze several different geometries containing ferromagnetic (F) and
nonmagnetic (N) regions: F, F/N, and F/N/F junctions which are subject to
thermal gradients. We present analytical formulas for the spin accumulation and
spin current profiles in those junctions that are valid for both tunnel and
transparent (as well as intermediate) contacts. For F/N junctions we calculate
the thermal spin injection efficiency and the spin accumulation induced
nonequilibrium thermopower. We find conditions for countering thermal spin
effects in the N region with electrical spin injection. This compensating
effect should be particularly useful for distinguishing electronic from other
mechanisms of spin injection by thermal gradients. For F/N/F junctions we
analyze the differences in the nonequilibrium thermopower (and chemical
potentials) for parallel and antiparallel orientations of the F magnetizations,
as evidence and a quantitative measure of the spin accumulation in N.
Furthermore, we study the Peltier and spin Peltier effects in F/N and F/N/F
junctions and present analytical formulas for the heat evolution at the
interfaces of isothermal junctions.Comment: to be published in PRB (in press), 19 pages, 19 figure
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