8,766 research outputs found
Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality
The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode.Comment: 23 pages, 10 figures, accepted for publication on Journal of Plasma
Physic
Phenomenological viability of orbifold models with three Higgs families
We discuss the phenomenological viability of string multi-Higgs doublet
models, namely a scenario of heterotic orbifolds with two Wilson lines,
which naturally predicts three supersymmetric families of matter and Higgs
fields. We study the orbifold parameter space, and discuss the compatibility of
the predicted Yukawa couplings with current experimental data. We address the
implications of tree-level flavour changing neutral processes in constraining
the Higgs sector of the model, finding that viable scenarios can be obtained
for a reasonably light Higgs spectrum. We also take into account the tree-level
contributions to indirect CP violation, showing that the experimental value of
can be accommodated in the present framework.Comment: 31 pages, 12 figures. Comments and references added. Final version to
be published in JHE
Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals
A new analytical expression for the size-dependent bandgap of colloidal
semiconductor nanocrystals is proposed within the framework of the finite-depth
square-well effective mass approximation in order to provide a quantitative
description of the quantum confinement effect. This allows one to convert
optical spectroscopic data (photoluminescence spectrum and absorbance edge)
into accurate estimates for the particle size distributions of colloidal
systems even if the traditional effective mass model is expected to fail, which
occurs typically for very small particles belonging to the so-called strong
confinement limit. By applying the reported theoretical methodologies to CdTe
nanocrystals synthesized through wet chemical routes, size distributions are
inferred and compared directly to those obtained from atomic force microscopy
and transmission electron microscopy. This analysis can be used as a
complementary tool for the characterization of nanocrystal samples of many
other systems such as the II-VI and III-V semiconductor materials.Comment: 9 pages, 5 figure
Crescimento e produção de matéria seca de mudas de dendezeiro em função do tempo de pré-viveiro e da percentagem de ocupação da bandeja pelos tubetes.
Este trabalho teve como objetivo verificar a influência do tempo de permanência das mudas no pré-viveiro e da percentagem de ocupação da bandeja pelos tubetes no crescimento e na partição de matéria seca de mudas de dendezeiro
Viveiro internacional de observação de arroz de sequeiro para América Latina - VIOAL-S/79.
bitstream/item/26073/1/pesqandamento20.pd
Evaluation of Microencapsulation of The UFV-AREG1 Bacteriophage in Alginate-Ca Microcapsules using Microfluidic Devices
The indiscriminate use of antibiotics and the emergence of resistant
microorganisms have become a major challenge for the food industry. The purpose
of this work was to microencapsulate the bacteriophage UFV-AREG1 in a calcium
alginate matrix using microfluidic devices and to study the viability and
efficiency of retention. The microcapsules were added to gel of propylene
glycol for use as an antimicrobial in the food industry. The technique showed
the number of the phage encapsulation, yielding drops with an average 100-250
m of diameter, 82.1 2% retention efficiency and stability in the gel
matrix for 21 days. The gel added to the microencapsulated phage showed
efficiency (not detectable on the surface) in reducing bacterial contamination
on the surface at a similar level to antimicrobial chemicals (alcohol 70%).
Therefore, it was possible to microencapsulate bacteriophages in alginate-Ca
and apply the microcapsules in gels for use as sanitizers in the food industry.Comment: 8 pages, 5 figure
Geometric approach to nonvariational singular elliptic equations
In this work we develop a systematic geometric approach to study fully
nonlinear elliptic equations with singular absorption terms as well as their
related free boundary problems. The magnitude of the singularity is measured by
a negative parameter , for , which reflects on
lack of smoothness for an existing solution along the singular interface
between its positive and zero phases. We establish existence as well sharp
regularity properties of solutions. We further prove that minimal solutions are
non-degenerate and obtain fine geometric-measure properties of the free
boundary . In particular we show sharp
Hausdorff estimates which imply local finiteness of the perimeter of the region
and a.e. weak differentiability property of
.Comment: Paper from D. Araujo's Ph.D. thesis, distinguished at the 2013 Carlos
Gutierrez prize for best thesis, Archive for Rational Mechanics and Analysis
201
Eficiência de Metarhizium anisopliae (Metsch) sorokin no controle de cigarrinhas-das-pastagens (Hemiptera: Cercopidae) em Brachiaria bryzantha em Rondônia-Brasil.
O objetivo desta pesquisa foi avaliar a eficiência de Metarhizium anisopliae (isolado ESALQ 1037) em diferentes formulações, dosagens de conídeos e número de aplicações no controle da cigarrinha-das-pastagens, conduzida em ensaio de campo em pastagem de capim-Marandu (Brachiaria bryzantha), no Município de Corumbiara, RO, no período de dezembro de 2007 a fevereiro de 2008. O isolado foi aplicado a partir das 17h, sob temperatura média de 18° C e umidade relativa de 69%. O volume de calda utilizado foi de 300 L/ ha-1, utilizando-se pulverizador a CO². As doses aplicadas foram de 0,5 x109, 1 x109, 2 x109 conídios viáveis/ha-1, com vazão de 300 litros/ha-1. As avaliações procederam-se aos 0, 15, 32, 45, 61 e 75 dias, sendo uma antes das aplicações, e cinco após as aplicações do entomopatógeno, contando-se as cigarrinhas (ninfas) por ponto de 0,0625 m² (quadrado de 0,25 m x 0,25 m). Aos 0 dias a infestação era de 153,6 ninfas/ m². Foi observado que os níveis de ninfas diminuíram com a aplicação de M. anisopliae em todos os tratamentos. Pelos resultados obtidos, o tratamento mais eficiente foi o Metarril SC 2 x109 conídios viáveis/ha-1, na formulação de óleo emulsionável, com duas aplicações (94,19%). Conclui-se que, o M. anisopliae (ESALQ 1037) constitui-se em uma alternativa promissora para o manejo integrado das cigarrinhaspastagens em capim-Marandu (B. brizantha) para a Agricultura Familiar em Rondônia
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