9,769 research outputs found
Analysis of the velocity field of granular hopper flow
We report the analysis of radial characteristics of the flow of granular
material through a conical hopper. The discharge is simulated for various
orifice sizes and hopper opening angles. Velocity profiles are measured along
two radial lines from the hopper cone vertex: along the main axis of the cone
and along its wall. An approximate power law dependence on the distance from
the orifice is observed for both profiles, although differences between them
can be noted. In order to quantify these differences, we propose a Local Mass
Flow index that is a promising tool in the direction of a more reliable
classification of the flow regimes in hoppers
Counterion density profiles at charged flexible membranes
Counterion distributions at charged soft membranes are studied using
perturbative analytical and simulation methods in both weak coupling
(mean-field or Poisson-Boltzmann) and strong coupling limits. The softer the
membrane, the more smeared out the counterion density profile becomes and
counterions pentrate through the mean-membrane surface location, in agreement
with anomalous scattering results. Membrane-charge repulsion leads to a
short-scale roughening of the membrane.Comment: 4 pages, 4 figure
Timed Consistent Network Updates
Network updates such as policy and routing changes occur frequently in
Software Defined Networks (SDN). Updates should be performed consistently,
preventing temporary disruptions, and should require as little overhead as
possible. Scalability is increasingly becoming an essential requirement in SDN.
In this paper we propose to use time-triggered network updates to achieve
consistent updates. Our proposed solution requires lower overhead than existing
update approaches, without compromising the consistency during the update. We
demonstrate that accurate time enables far more scalable consistent updates in
SDN than previously available. In addition, it provides the SDN programmer with
fine-grained control over the tradeoff between consistency and scalability.Comment: This technical report is an extended version of the paper "Timed
Consistent Network Updates", which was accepted to the ACM SIGCOMM Symposium
on SDN Research (SOSR) '15, Santa Clara, CA, US, June 201
Liquid Crystals in Electric Field
We present a general theory of electric field effects in liquid crystals
where the dielectric tensor depends on the orientation order. As applications,
we examine (i) the director fluctuations in nematic states in electric field
for arbitrary strength of the dielectric anisotropy and (ii) deformation of the
nematic order around a charged particle. Some predictions are made for these
effects.Comment: 9pages, 2figure
Spin-phonon coupling in multiferroic RCrO (R-Y, Lu, Gd, Eu, Sm): A Raman study
Raman study on a select few orthochromites, RCrO (R = Y, Lu, Gd, Eu and
Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd
and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu).
While anomalies in most of the observed phonon frequencies in all these
compounds may result from the distortion of CrO octahedra due to size
effect and magnetostriction arising from Cr-ordering, the anomalous behavior of
their linewidths observed at TN for the compounds with only magnetic R-ion
suggests spin-phonon coupling. The presence of spin-phonon coupling and the
anomalies in the low frequency modes related to R-ion motion in orthochromites
(R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments
play important role in inducing switchable electric polarization.Comment: 6 pages (two column format), 7 figures; The updated version of the
manuscript can be found at Euro. Phys. Lett. 101, 17008 (2013
Torqued fireballs in relativistic heavy-ion collisions
We show that the fluctuations in the wounded-nucleon model of the initial
stage of relativistic heavy-ion collisions, together with the natural
assumption that the forward (backward) moving wounded nucleons emit particles
preferably in the forward (backward) direction, lead to an event-by-event
torqued fireball. The principal axes associated with the transverse shape are
rotated in the forward region in the opposite direction than in the backward
region. On the average, the standard deviation of the relative torque angle
between the forward and backward rapidity regions is about 20deg for the
central and 10deg for the mid-peripheral collisions. The hydrodynamic expansion
of a torqued fireball leads to a torqued collective flow, yielding, in turn,
torqued principal axes of the transverse-momentum distributions at different
rapidities. We propose experimental measures, based on cumulants involving
particles in different rapidity regions, which should allow for a quantitative
determination of the effect from the data. To estimate the non-flow
contributions from resonance decays we run Monte Carlo simulations with
THERMINATOR. If the event-by-event torque effect is found in the data, it will
support the assumptions concerning the fluctuations in the early stage of the
fireball formation, as well as the hypothesis of the asymmetric rapidity shape
of the emission functions of the moving sources in the nucleus-nucleus
collisions.Comment: Grant reference adde
Universal reduction of pressure between charged surfaces by long-wavelength surface charge modulation
We predict theoretically that long-wavelength surface charge modulations
universally reduce the pressure between the charged surfaces with counterions
compared with the case of uniformly charged surfaces with the same average
surface charge density. The physical origin of this effect is the fact that
surface charge modulations always lead to enhanced counterion localization near
the surfaces, and hence, fewer charges at the midplane. We confirm the last
prediction with Monte Carlo simulations.Comment: 8 pages 1 figure, Europhys. Lett., in pres
Elastic and magnetic effects on the infrared phonon spectra of MnF2
We measured the temperature dependent infrared reflectivity spectra of MnF2
between 4 K and room temperature. We show that the phonon spectrum undergoes a
strong renormalization at TN. The ab-initio calculation we performed on this
compound accurately predict the magnitude and the direction of the phonon
parameters changes across the antiferromagnetic transition, showing that they
are mainly induced by the magnetic order. In this material, we found that the
dielectric constant is mostly from phonon origin. The large change in the
lattice parameters with temperature seen by X-ray diffraction as well as the
A2u phonon softening below TN indicate that magnetic order induced distortions
in MnF2 are compatible with the ferroelectric instabilities observed in TiO2,
FeF2 and other rutile-type fluorides. This study also shows the anomalous
temperature evolution of the lower energy Eu mode in the paramagnetic phase,
which can be compared to that of the B1g one seen by Raman spectroscopy in many
isostructural materials. This was interpreted as being a precursor of a phase
transition from rutile to CaCl2 structure which was observed under pressure in
ZnF2.Comment: 8 pages, 8 figures, updated version accepted in PR
Fertilizantes e corretivo da acidez do solo em pimenta-de-cheiro (Capsicum chinense) cultivada no Estado do Amazonas (1ª aproximação).
Clima e solo. Semeadura e plantio. Amostragem de solo. Calagem e adubação. Adubação de plantio. Adubação de manutenção. Análise foliar
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