1,916 research outputs found
Universally diverging Grueneisen parameter and the magnetocaloric effect close to quantum critical points
At a generic quantum critical point, the thermal expansion is more
singular than the specific heat . Consequently, the "Gr\"uneisen ratio'',
\GE=\alpha/c_p, diverges. When scaling applies, \GE \sim T^{-1/(\nu z)} at
the critical pressure , providing a means to measure the scaling
dimension of the most relevant operator that pressure couples to; in the
alternative limit and , \GE \sim \frac{1}{p-p_c} with a
prefactor that is, up to the molar volume, a simple {\it universal} combination
of critical exponents. For a magnetic-field driven transition, similar
relations hold for the magnetocaloric effect .
Finally, we determine the corrections to scaling in a class of metallic quantum
critical points.Comment: 4 pages, 1 figure; general discussion on how the Grueneisen exponent
measures the scaling dimension of the most relevant operator at any QCP is
expande
Avaliação dos níveis de ácidos gordos essenciais (DHA, AA e EPA) em doentes submetidos a dietas restritivas em proteínas
Bose-Einstein Condensation of S = 1 Ni spin degrees of freedom in NiCl2-4SC(NH2)2
It has recently been suggested that the organic compound
NiCl-4SC(NH) (DTN) exhibits Bose-Einstein Condensation (BEC) of the
Ni spin degrees of freedom for fields applied along the tetragonal c-axis. The
Ni spins exhibit 3D XY-type antiferromagnetic order above a field-induced
quantum critical point at T. The Ni spin fluid can be
characterized as a system of effective bosons with a hard-core repulsive
interaction in which the antiferromagnetic state corresponds to a Bose-Einstein
condensate (BEC) of the phase coherent Ni spin system. We have
investigated the the high-field phase diagram and the occurrence of BEC in DTN
by means of specific heat and magnetocaloric effect measurements to dilution
refrigerator temperatures. Our results indicate that a key prediction of BEC is
satisfied; the magnetic field-temperature quantum phase transition line
approaches a power-law at low temperatures,
with an exponent at the quantum critical point,
consistent with the BEC theory prediction of .Comment: 4 pages, 4 figure
The spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation
This paper presents the spatially resolved star formation history (SFH) of
nearby galaxies with the aim of furthering our understanding of the different
processes involved in the formation and evolution of galaxies. To this end, we
apply the fossil record method of stellar population synthesis to a rich and
diverse data set of 436 galaxies observed with integral field spectroscopy in
the CALIFA survey. The sample covers a wide range of Hubble types, with stellar
masses ranging from to . Spectral
synthesis techniques are applied to the datacubes to retrieve the spatially
resolved time evolution of the star formation rate (SFR), its intensity
(), and other descriptors of the 2D-SFH in seven bins of
galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and five bins of stellar
mass. Our main results are: a) Galaxies form very fast independently of their
current stellar mass, with the peak of star formation at high redshift (). Subsequent star formation is driven by and morphology, with less
massive and later type spirals showing more prolonged periods of star
formation. b) At any epoch in the past the SFR is proportional to ,
with most massive galaxies having the highest absolute (but lowest specific)
SFRs. c) While nowadays is similar for all spirals, and
significantly lower in early type galaxies (ETG), in the past scales well with morphology. The central regions of today's ETGs are
where reached the highest values (Gyrpc), similar to those measured in high redshift
star forming galaxies. d) The evolution of in Sbc systems
matches that of models for Milky-Way-like galaxies, suggesting that the
formation of a thick disk may be a common phase in spirals at early epochs.Comment: 21 pages, 11 figures, 1 table, accepted for publication in Astronomy
& Astrophysics, abstract abridged for arXiv submissio
The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales
This paper presents the mass assembly time scales of nearby galaxies observed
by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record
method of the stellar populations to the complete sample of the 3rd CALIFA data
release, with a total of 661 galaxies, covering stellar masses from 10
to 10 M and a wide range of Hubble types. We apply spectral
synthesis techniques to the datacubes and process the results to produce the
mass growth time scales and mass weighted ages, from which we obtain temporal
and spatially resolved information in seven bins of galaxy morphology and six
bins of stellar mass (M) and stellar mass surface density
(). We use three different tracers of the spatially resolved
star formation history (mass assembly curves, ratio of half mass to half light
radii, and mass-weighted age gradients) to test if galaxies grow inside-out,
and its dependence with galaxy stellar mass, , and morphology.
Our main results are as follows: (a) The innermost regions of galaxies assemble
their mass at an earlier time than regions located in the outer parts; this
happens at any given M, , or Hubble type, including
the lowest mass systems. (b) Galaxies present a significant diversity in their
characteristic formation epochs for lower-mass systems. This diversity shows a
strong dependence of the mass assembly time scales on and
Hubble type in the lower-mass range (10 to 10), but a very
mild dependence in higher-mass bins. (c) All galaxies show negative
log age gradients in the inner 1 HLR. The profile
flattens with increasing values of . There is no significant
dependence on M within a particular bin, except for
the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
Agricultura familiar no Estado da Paraíba: uma análise a partir de tabulações especiais do Censo Agropecuário 2006.
Este artigo objetiva analisar a importância socioeconômica e as desigualdades que caracterizam a agricultura familiar no estado da Paraíba. Para tanto, utiliza dados de ?tabulações especiais? do Censo Agropecuário 2006, elaboradas segundo o recorte da Lei da Agricultura Familiar e das normas do Plano Safra da Agricultura Familiar 2006/2007. O trabalho mostra que a agricultura familiar é o segmento social mais relevante no rural paraibano. Todavia, há uma grande heterogeneidade e desigualdade social no interior dessa categoria de produtores, onde a maioria são extremamente pobres e apenas uma pequena parcela consegue sobreviver a partir das atividades agropecuárias. Essa constatação revela o risco de considerar a agricultura familiar como um setor homogêneo e, ao mesmo tempo, abre novas possibilidades de pesquisa que podem ampliar o campo de ação das políticas públicas de desenvolvimento rural
Amphibia, Anura, Hylidae, <i>Sphaenorhynchus botocudo</i> Caramaschi, Almeida and Gasparini, 2009: First state record and first record out of the type locality
This study presents the first record of the recently-described Lime Treefrog Sphaenorhynchus botocudoCaramaschi, Almeida, and Gasparini, 2009 in the state of Bahia, and the first record out of its type locality
Agricultura familiar no Estado da Paraíba: uma análise a partir de tabulações especiais do censo agropecuário 2006.
O objetivo deste artigo é demonstrar o peso socioeconômico da agricultura familiar paraibana com base em ?tabulações especiais? do Censo Agropecuário 2006, apresentando os principais segmentos que se destacam no interior dessa categoria de produtores e a composição da renda. As ?tabulações especiais? foram elaboradas segundo o recorte da Lei da Agricultura Familiar e a partir das normas do PRONAF vigentes no Plano Safra 2006/2007. O trabalho mostra que a agricultura familiar é o segmento social predominante no rural paraibano. Todavia, há uma grande heterogeneidade e desigualdade social no interior dessa categoria de produtores, onde a maioria são extremamente pobres e apenas uma pequena parcela consegue sobreviver a partir das atividades agropecuárias. Essa constatação revela o risco de considerar a agricultura familiar como um setor homogêneo e, ao mesmo tempo, abre novas possibilidades de pesquisa que podem ampliar o campo de ação das políticas públicas de desenvolvimento rural
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