2,398,315 research outputs found
Faceted anomalous scaling in the epitaxial growth of semiconductor films
We apply the generic dynamical scaling theory (GDST) to the surfaces of CdTe
polycrystalline films grown in glass substrates. The analysed data were
obtained with a stylus profiler with an estimated resolution lateral resolution
of m. Both real two-point correlation function and power spectrum
analyses were done. We found that the GDST applied to the surface power spectra
foresees faceted morphology in contrast with the self-affine surface indicated
by the local roughness exponent found via the height-height correlation
function. This inconsistency is explained in terms of convolution effects
resulting from the finite size of the probe tip used to scan the surfaces. High
resolution AFM images corroborates the predictions of GDST.Comment: to appear in Europhysics Letter
Pressure anisotropy generation in a magnetized plasma configuration with a shear flow velocity
The nonlinear evolution of the Kelvin Helmholtz instability in a magnetized
plasma with a perpendicular flow close to, or in, the supermagnetosonic regime
can produce a significant parallel-to-perpendicular pressure anisotropy. This
anisotropy, localized inside the flow shear region, can make the configuration
unstable either to the mirror or to the firehose instability and, in general,
can affect the development of the KHI. The interface between the solar wind and
the Earth's magnetospheric plasma at the magnetospheric equatorial flanks
provides a relevant setting for the development of this complex nonlinear
dynamics.Comment: 11 pages, 7 figures, submitted to Plasma Phys. Control. Fusio
Non-standard matrix formats of Lie superalgebras
The standard format of matrices belonging to Lie superalgebras consists of
partitioning the matrices into even and odd blocks. In this paper, we study
other possible matrix formats and in particular the so-called diagonal format
which naturally occurs in various applications, e.g. in superconformal field
theory, superintegrable models, for super W-algebras and quantum supergroups
Coordinate representation for non Hermitian position and momentum operators
In this paper we undertake an analysis of the eigenstates of two non
self-adjoint operators and similar, in a suitable sense, to
the self-adjoint position and momentum operators and
usually adopted in ordinary quantum mechanics. In particular we discuss
conditions for these eigenstates to be {\em biorthogonal distributions}, and we
discuss few of their properties. We illustrate our results with two examples,
one in which the similarity map between the self-adjoint and the non
self-adjoint is bounded, with bounded inverse, and the other in which this is
not true. We also briefly propose an alternative strategy to deal with
and , based on the so-called {\em quasi *-algebras}.Comment: Accepted in Proceedings of the Royal Society
Subproton-scale cascades in solar wind turbulence: driven hybrid-kinetic simulations
A long-lasting debate in space plasma physics concerns the nature of
subproton-scale fluctuations in solar wind (SW) turbulence. Over the past
decade, a series of theoretical and observational studies were presented in
favor of either kinetic Alfv\'en wave (KAW) or whistler turbulence. Here, we
investigate numerically the nature of the subproton-scale turbulent cascade for
typical SW parameters by means of unprecedented high-resolution simulations of
forced hybrid-kinetic turbulence in two real-space and three velocity-space
dimensions. Our analysis suggests that small-scale turbulence in this model is
dominated by KAWs at and by magnetosonic/whistler fluctuations
at lower . The spectral properties of the turbulence appear to be in
good agreement with theoretical predictions. A tentative interpretation of this
result in terms of relative changes in the damping rates of the different waves
is also presented. Overall, the results raise interesting new questions about
the properties and variability of subproton-scale turbulence in the SW,
including its possible dependence on the plasma , and call for detailed
and extensive parametric explorations of driven kinetic turbulence in three
dimensions.Comment: 6 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
Phase-dependent heat transport through magnetic Josephson tunnel junctions
We present an exhaustive study of the coherent heat transport through
superconductor-ferromagnet(S-F) Josephson junctions including a spin-filter
(I) tunneling barrier. By using the quasiclassical Keldysh Green's
function technique we derive a general expression for the heat current flowing
through a S/F/I/F/S junction and analyze the dependence of the thermal
conductance on the spin-filter efficiency, the phase difference between the
superconductors and the magnetization direction of the ferromagnetic layers. In
the case of non-collinear magnetizations we show explicitly the contributions
to the heat current stemming from the singlet and triplet components of the
superconducting condensate. We also demonstrate that the magnetothermal
resistance ratio of a S/F/I/F/S heat valve can be increased by the
spin-filter effect under suitable conditions.Comment: 8 pages; 6 figure
Inter-dependence of the volume and stress ensembles and equipartition in statistical mechanics of granular systems
We discuss the statistical mechanics of granular matter and derive several
significant results. First, we show that, contrary to common belief, the volume
and stress ensembles are inter-dependent, necessitating the use of both. We use
the combined ensemble to calculate explicitly expectation values of structural
and stress-related quantities for two-dimensional systems. We thence
demonstrate that structural properties may depend on the angoricity tensor and
that stress-based quantities may depend on the compactivity. This calls into
question previous statistical mechanical analyses of static granular systems
and related derivations of expectation values. Second, we establish the
existence of an intriguing equipartition principle - the total volume is shared
equally amongst both structural and stress-related degrees of freedom. Third,
we derive an expression for the compactivity that makes it possible to quantify
it from macroscopic measurements.Comment: 5 pages, including 2 figures, To appear in Phys. Rev. Let
Charm and longitudinal structure functions with the Kharzeev-Levin-Nardi model
We use the Kharzeev-Levin-Nardi model of the low gluon distributions to
fit recent HERA data on charm and longitudinal structure functions. Having
checked that this model gives a good description of the data, we use it to
predict and to be measured in a future electron-ion collider. The
results interpolate between those obtained with the de Florian-Sassot and
Eskola-Paukkunen-Salgado nuclear gluon distributions. The conclusion of this
exercise is that the KLN model, simple as it is, may still be used as an
auxiliary tool to make estimates both for heavy ion and electron-ion
collisions.Comment: 6 pages, 7 figure
Estimative for the size of the compactification radius of a one extra dimension Universe
In this work, we use the Casimir effect to probe the existence of one extra
dimension. We begin by evaluating the Casimir pressure between two plates in a
manifold, and then use an appropriate statistical analysis in
order to compare the theoretical expression with a recent experimental data and
set bounds for the compactification radius
Manifestation of a spin-splitting field in a thermally-biased Josephson junction
We investigate the behavior of a Josephson junction consisting of a
ferromagnetic insulator-superconductor (FI-S) bilayer tunnel-coupled to a
superconducting electrode. We show that the Josephson coupling in the structure
is strenghtened by the presence of the spin-splitting field induced in the FI-S
bilayer. Such strenghtening manifests itself as an increase of the critical
current with the amplitude of the exchange field. Furthermore, the effect
can be strongly enhanced if the junction is taken out of equilibrium by a
temperature bias. We propose a realistic setup to assess experimentally the
magnitude of the induced exchange field, and predict a drastic deviation of the
curve ( is the temperature) with respect to equilibrium.Comment: 4.5 pages, 3 color figure
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