223 research outputs found
Magnetic Instabilities and Phase Diagram of the Double-Exchange Model in Infinite Dimensions
Dynamical mean-field theory is used to study the magnetic instabilities and
phase diagram of the double-exchange (DE) model with Hund's coupling J_H >0 in
infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic
(AF) phases, the DE model supports a broad class of short-range ordered (SRO)
states with extensive entropy and short-range magnetic order. For any site on
the Bethe lattice, the correlation parameter q of a SRO state is given by the
average q=, where theta_i is the angle between any spin and
its neighbors. Unlike the FM (q=0) and AF (q=1) transitions, the transition
temperature of a SRO state (T_{SRO}) with 0<q<1 cannot be obtained from the
magnetic susceptibility. But a solution of the coupled Green's functions in the
weak-coupling limit indicates that a SRO state always has a higher transition
temperature than the AF for all fillings p<1 and even than the FM for 0.26\le p
\le 0.39. For 0.39<p<0.73, where both the FM and AF phases are unstable for
small J_H, a SRO phase has a non-zero T_{SRO} except close to p=0.5. As J_H
increases, T_{SRO} eventually vanishes and the FM dominates. For small J_H, the
T=0 phase diagram is greatly simplified by the presence of the SRO phase. A SRO
phase is found to have lower energy than either the FM or AF phases for 0.26\le
p0 but appears for J_H\neq 0. For
p near 1, PS occurs between an AF with p=1 and either a SRO or a FM phase. The
stability of a SRO state at T=0 can be understood by examining the interacting
DOS,which is gapped for any nonzero J_H in an AF but only when J_H exceeds a
critical value in a SRO state.Comment: 38 pages, 11 figures, submitted to New Journal of Physic
Método de aclimatização de mudas de orquídeas em garrafas PET.
bitstream/item/55348/1/CIT11003.pd
The dust properties and physical conditions of the interstellar medium in the LMC massive star forming complex N11
We combine Spitzer and Herschel data of the star-forming region N11 in the
Large Magellanic Cloud to produce detailed maps of the dust properties in the
complex and study their variations with the ISM conditions. We also compare
APEX/LABOCA 870um observations with our model predictions in order to decompose
the 870um emission into dust and non-dust (free-free emission and CO(3-2) line)
contributions. We find that in N11, the 870um can be fully accounted for by
these 3 components. The dust surface density map of N11 is combined with HI and
CO observations to study local variations in the gas-to-dust mass ratios. Our
analysis leads to values lower than those expected from the LMC low-metallicity
as well as to a decrease of the gas-to-dust mass ratio with the dust surface
density. We explore potential hypotheses that could explain the low observed
gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas
or of optically thick HI or variations in the dust abundance in the dense
regions). We finally decompose the local SEDs using a Principal Component
Analysis (i.e. with no a priori assumption on the dust composition in the
complex). Our results lead to a promising decomposition of the local SEDs in
various dust components (hot, warm, cold) coherent with that expected for the
region. Further analysis on a larger sample of galaxies will follow in order to
understand how unique this decomposition is or how it evolves from one
environment to another.Comment: 24 pages, 16 figures, accepted for publication in MNRA
Composição bromatológica da silagem de dez cultivares de mandioca.
A mandiocultura apresenta grande importância na região Nordeste, sobretudo por estar presente em todas as regiões a fazer parte tanto da cultura quanto da economia da região. Esta cultura apresenta uma gama de resíduos que podem ser utilizados na alimentação de animais. Um dos mais importantes é a maniva ou parte aérea que muitas vezes é desperdiçada no campo. Uma das maneiras de se aproveitar este material pode ser a ensilagem, que conservará o material para ser utilizado na época seca, onde há déficit de alimentos para os animais. O objetivo deste trabalho foi verificar a qualidade bromatológica de silagens de mandioca oriundas de duas estações experimentais e de dez cultivares diferentes (Lagoão, BRS Verdinha, Irará, Caravela, 9783/13, BRS Poti Branca, BRS Tapioqueira, Amansa Burro e BRS Caipira) com idade de 10 meses. Foram utilizados para a confecção das silagens mini silos laboratoriais de PVC com 10 cm de diâmetro e 30 cm de comprimento, lacrados com tampas de PVC e presilhas de metal. O material vegetal da mandioca in natura foi colhido no mesmo dia da confecção das silagens. Para cada tratamento foram confeccionados seis mini silos, sendo 3 de cada local de colheita, totalizando 60 repetições, em um delineamento experimental inteiramente casualizado (DIC). Após 180 dias os silos foram abertos e analisados quanto a sua composição bromatológica. O genótipo influenciou os teores de proteína bruta, fibra em detergente neutro e fibra em detergente ácido das silagens (P0,05). As cultivares Caravela e BRS Caipira apresentaram os melhores parâmetros bromatológicos entre as cultivares estudadas
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