28,701 research outputs found
Lande g-tensor in semiconductor nanostructures
Understanding the electronic structure of semiconductor nanostructures is not
complete without a detailed description of their corresponding spin-related
properties. Here we explore the response of the shell structure of InAs
self-assembled quantum dots to magnetic fields oriented in several directions,
allowing the mapping of the g-tensor modulus for the s and p shells. We found
that the g-tensors for the s and p shells show a very different behavior. The
s-state in being more localized allows the probing of the confining potential
details by sweeping the magnetic field orientation from the growth direction
towards the in-plane direction. As for the p-state, we found that the g-tensor
modulus is closer to that of the surrounding GaAs, consistent with a larger
delocalization. These results reveal further details of the confining
potentials of self-assembled quantum dots that have not yet been probed, in
addition to the assessment of the g-tensor, which is of fundamental importance
for the implementation of spin related applications.Comment: 4 pages, 4 figure
The multi-thermal and multi-stranded nature of coronal rain
In this work, we analyse coordinated observations spanning chromospheric, TR
and coronal temperatures at very high resolution which reveal essential
characteristics of thermally unstable plasmas. Coronal rain is found to be a
highly multi-thermal phenomenon with a high degree of co-spatiality in the
multi-wavelength emission. EUV darkening and quasi-periodic intensity
variations are found to be strongly correlated to coronal rain showers.
Progressive cooling of coronal rain is observed, leading to a height dependence
of the emission. A fast-slow two-step catastrophic cooling progression is
found, which may reflect the transition to optically thick plasma states. The
intermittent and clumpy appearance of coronal rain at coronal heights becomes
more continuous and persistent at chromospheric heights just before impact,
mainly due to a funnel effect from the observed expansion of the magnetic
field. Strong density inhomogeneities on spatial scales of 0.2"-0.5" are found,
in which TR to chromospheric temperature transition occurs at the lowest
detectable scales. The shape of the distribution of coronal rain widths is
found to be independent of temperature with peaks close to the resolution limit
of each telescope, ranging from 0.2" to 0.8". However we find a sharp increase
of clump numbers at the coolest wavelengths and especially at higher
resolution, suggesting that the bulk of the rain distribution remains
undetected. Rain clumps appear organised in strands in both chromospheric and
TR temperatures, suggesting an important role of thermal instability in the
shaping of fundamental loop substructure. We further find structure reminiscent
of the MHD thermal mode. Rain core densities are estimated to vary between
2x10^{10} cm^{-3} and 2.5x10^{11} cm^{-3} leading to significant downward mass
fluxes per loop of 1-5x10^{9} g s^{-1}, suggesting a major role in the
chromosphere-corona mass cycle.Comment: Abstract is only short version. See paper for full. Countless pages,
figures (and movies, but not included here). Accepted for publication in the
Astrophysical Journa
Topological confinement in graphene bilayer quantum rings
We demonstrate the existence of localized electron and hole states in a
ring-shaped potential kink in biased bilayer graphene. Within the continuum
description, we show that for sharp potential steps the Dirac equation
describing carrier states close to the K (or K') point of the first Brillouin
zone can be solved analytically for a circular kink/anti-kink dot. The
solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations
as functions of the height of the potential step and/or the radius of the ring
Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets
Using a model of nonmagnetic impurity potential, we have examined the
behavior of planar vortex solutions in the classical two-dimensional XY
ferromagnets in the presence of a spin vacancy localized out of the vortex
core. Our results show that a spinless atom impurity gives rise to an effective
potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex
All-sky Relative Opacity Mapping Using Night Time Panoramic Images
An all-sky cloud monitoring system that generates relative opacity maps over
many of the world's premier astronomical observatories is described.
Photometric measurements of numerous background stars are combined with
simultaneous sky brightness measurements to differentiate thin clouds from sky
glow sources such as air glow and zodiacal light. The system takes a continuous
pipeline of all-sky images, and compares them to canonical images taken on
other nights at the same sidereal time. Data interpolation then yields
transmission maps covering almost the entire sky. An implementation of this
system is currently operating through the Night Sky Live network of CONCAM3s
located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT
(South Africa) and the Canary Islands (Northwestern Africa).Comment: Accepted for publication in PAS
Caracterização in silico de genes de expansina presentes em cafeeiro (Coffea arabica L.).
As expansinas (EXPs) são proteínas que promovem o relaxamento e extensão da parede celular em plantas, sendo codificadas por uma multifamília gênica e classificadas em: ?-expansinas, ?-expansinas, expansin-like A (EXLA) e expansin-like B (EXLB). Estas proteínas atuam no alongamento celular, maciez dos frutos, abscisão, germinação e polinização. As ?-expansinas representam a maior família e relacionam-se diretamente com o controle da extensão da parede celular em processos de desenvolvimento. Visto que a maturação uniforme dos frutos de café contribui para a qualidade da bebida, este trabalho teve por objetivo identificar e caracterizar in silico genes de expansinas envolvidas neste processo. Através da mineração dos dados do Genoma Café foram encontrados 28 contigs referentes às EXPs, sendo dois contigs de EXLB, um de EXLA e os demais pertencentes à família das ?-expansinas. Dentro desta ultima família foram identificados quatro contigs relacionados com o desenvolvimento dos frutos do cafeeiro. Comparação dos contigs obtidos nos bancos do Projeto Genoma Café e de contigs no banco de dados HarvEST Coffea permitiu a caracterização in silico da expressão dos contigs nos diferentes estádios de maturação dos frutos
NUTRITIVE VALUE, TOTAL PHENOLIC CONTENT AND RADICAL SCAVENGING ACTIVITY BEFORE AND AFTER DIGESTION OF THE LEAVES OF SIX GRAPEVINE (VITIS VINIFERA L.) CULTIVARS.
Identificação e caracterização molecular de genes envolvidos no metabolismo de diterpenos específicos do cafeeiro.
Apesar de pouco estudado, os lipídeos do café desempenham papel importante na qualidade da bebida e do aroma. Cerca de dez a vinte por cento da fração lipídica do café corresponde a diterpenos que além da provável relação com a qualidade também estão relacionados com a questão do café e a saúde. As espécies de Coffea são as únicas capazes de sintetizar os diterpenos cafestol, caveol e seus compostos derivados (16-O-metilcafestol, 16-O-metilcaveol). Visando um entendimento maior dos genes envolvidos na formação dos diterpenos de café, foi realizado um estudo in silico da expressão de três genes que codificam para as primeiras etapas da sua via de biossíntese ? copalil difosfato sintase (CPS), caureno sintase (KS) e caureno oxidase (KO). Posteriormente foi feita uma análise da expressão destes genes durante o desenvolvimento de frutos de Coffea arabica cv. IAPAR 59 e Coffea canephora cv. Apoatã. Este estudo permitiu a identificação de um gene para a CPS e KS e dois para a KO. A análise in silico revelou níveis e perfis de expressão específicos para cada gene. Os resultados obtidos in vivo apresentaram algumas diferenças dos dados obtidos in silico, e a comparação de C. arabica e C. canephora também revelou perfis de expressão diferentes para os genes estudados. Esses dados serão confirmados por RT-PCR e um estudo geral do transcriptoma, usando macroarranjos desenvolvidos a partir do Projeto Genoma Café, será iniciado para identificar os outros genes envolvidos nessa via metabólica.Biotecnologia aplicada à cadeia agroindustrial do café
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