553 research outputs found
Hysteresis in the Mott Transition between Plasma and Insulating Gas
We show that hysteresis can occur in the transition between a neutral plasma
and the insulating gas consisting of neutral pairs bound by Coulomb attraction.
Since the transition depends sensitively on the screening length in the plasma,
regions of bistability occur in density--temperature phase space. We present
numerical results which indicate where these regions occur for systems such as
spin-polarized hydrogen, positronium gas, and excitons in a semiconductor.Comment: 9 pages (Latex/RevTex), 6 postscript figures which are in compressed
and uuencoded file, prepared using the utility "uufiles" and separately
submitted. They should be automatically included with the text when it is
downloaded. Figures also available in hard copy from the authors
([email protected]; [email protected]); paper submitted to
Phys. Rev.
O impacto da terapêutica de ressincronização cardíaca nas células produtoras de IL-17 circulantes em doentes com insuficiência cardíaca avançada: efeito anti-inflamatório da terapêutica de ressincronização cardíaca
Provas públicas apresentadas à Escola Superior de Saúde Dr. Lopes Dias do Instituto Politécnico de Castelo Branco para o cumprimento dos requisitos necessários à obtenção do título de Especialista.OBJETIVO: As células produtoras de IL-17 circulantes têm sido implicadas no
ambiente inflamatório da insuficiência cardíaca crónica (ICC) e associadas a um mau
prognóstico da doença. O objetivo deste trabalho foi avaliar o impacto da terapêutica
de ressincronização cardíaca (TRC) na frequência e atividade funcional das células
Th17 e Tc17, assim como a expressão de mRNA de IL-17 em doentes com ICC.
MÉTODOS: Foram incluídos neste estudo 28 doentes com ICC, avaliados antes da TRC
(T0) e 6 meses após (T6), e 15 controlos saudáveis. As células Th17 e Tc17 do sangue
periférico foram analisadas por citometria de fluxo e a quantificação do mRNA de IL17 por PCR em tempo-real.
RESULTADOS: As células Tc17 tendem a estar mais elevadas nos doentes com ICC
submetidos à TRC que nos controlos (0.92% (0.24-3.32) versus 0.60% (0.09-3.68),
sem atingir significado estatístico. Depois da TRC, a frequência de células Tc17
diminui significativamente, chegando a níveis semelhantes aos encontrados no grupo
controlo (HG) (0.92% (0.24-3.32) ao T0 versus 0.56% (0.21-4.20) ao T6, p<0.05),
devido, maioritariamente, aos doentes que responderam à TRC. Além disto, a
expressão do mRNA de IL-17 foi apenas detetada num pequeno número de doentes
respondedores ao T0 (27%) e apenas detetado num doente respondedor ao T6 (7%).
Inversamente, nos doentes não-respondedores, a expressão de mRNA de IL-17
aumenta da avaliação inicial (17%) para T6 (42%).
Relativamente às células Th17 não foram encontradas diferenças significativas
entre o HG e os doentes com ICC ao T0 e ao T6.
CONCLUSÃO: A resposta inflamatória mediada pelas células produtoras de IL-17 do
SP parece ser suprimida pela TRC, particularmente nos doentes respondedores.ABSTRACT: PURPOSE: IL-17-producing T cells have been implicated in the inflammatory milieu
of chronic heart failure (CHF), which implies a dismal prognosis in affected patients.
The aim of this study was to evaluate the impact of cardiac resynchronization therapy
(CRT) on the frequency and functional activity of Th17 and Tc17 cells, as well as, on
IL-17 mRNA expression in patients with CHF.
METHODS: 28 patients with CHF, analysed before CRT (T0) and 6 months later (T6),
and 15 healthy controls (HG) were enrolled in this study. Circulating Th17 and Tc17
cells were evaluated by flow cytometry. The quantification of IL-17A mRNA
expression was performed by real-time PCR.
RESULTS: Circulating Tc17 cells tended to be higher in CHF patients submitted to
CRT than in HG (0.92% (0.24-3.32) versus 0.60% (0.09-3.68), although not reaching
statistical significance. The frequency of Tc17 cells in CHF patients significantly
decreases after CRT reaching levels similar to those of HG (0.92% (0.24-3.32) at T0
versus 0.56% (0.21-4.20) at T6, p<0.05), mainly due to responders to CRT.
Additionally, the expression of IL-17 mRNA was detected in a few number of
responder patients at T0 (27%) and only detected in one responder at T6 (7%).
Conversely, in non-responders, the proportion of patients exhibiting IL-17 mRNA
expression increases from baseline (17%) to T6 (42%).
No significant differences were observed in Th17 cells between HG, CHF patients
in T0 and patients in T6.
CONCLUSION: The inflammatory response mediated by circulating IL-17 producing
cells seems to be suppressed by CRT, particularly in responders.N/
Theory for Metal Hydrides with Switchable Optical Properties
Recently it has been discovered that lanthanum, yttrium, and other metal
hydride films show dramatic changes in the optical properties at the
metal-insulator transition. Such changes on a high energy scale suggest the
electronic structure is best described by a local model based on negatively
charged hydrogen (H) ions. We develop a many-body theory for the strong
correlation in a H ion lattice. The metal hydride is described by a large
-limit of an Anderson lattice model. We use lanthanum hydride as a prototype
of these compounds, and find LaH is an insulator with a substantial gap
consistent with experiments. It may be viewed either as a Kondo insulator or a
band insulator due to strong electron correlation. A H vacancy state in LaH
is found to be highly localized due to the strong bonding between the electron
orbitals of hydrogen and metal atoms. Unlike the impurity states in the usual
semiconductors, there is only weak internal optical transitions within the
vacancy. The metal-insulator transition takes place in a band of these vacancy
states.Comment: 18 pages, 16 figures and 6 tables. Submitted to PR
Transformation of in-plane in at fixed oxygen content
This paper reveals the origin of variation in the magnitude and temperature
dependence of the normal state resistivity frequently observed in different
YBCO single crystal or thin film samples with the same . We investigated
temperature dependence of resistivity in thin films
with 7- and 6.90, which were subjected to annealing in argon at
400-420 K (). Before annealing these films exhibited a non-linear
, with a flattening below 230 K, similar to and
observed in untwinned and twinned YBCO crystals, respectively.
For all films the annealing causes an increase of resistivity and a
transformation of from a non-linear dependence towards a more
linear one (less flattening). In films with 7- the increase of
resistivity is also associated with an increase in . We proposed the
model that provides an explanation of these phenomena in terms of thermally
activated redistribution of residual O(5) oxygens in the chain-layer of YBCO.
Good agreement between the experimental data for , where t is
the annealing time, and numerical calculations was obtained.Comment: 8 pages, 9 figures, submitted to PR
Equation of state and magnetic susceptibility of spin polarized isospin asymmetric nuclear matter
Properties of spin polarized isospin asymmetric nuclear matter are studied
within the framework of the Brueckner--Hartree--Fock formalism. The
single-particle potentials of neutrons and protons with spin up and down are
determined for several values of the neutron and proton spin polarizations and
the asymmetry parameter. It is found an almost linear and symmetric variation
of the single-particle potentials as increasing these parameters. An analytic
parametrization of the total energy per particle as a function of the asymmetry
and spin polarizations is constructed. This parametrization is employed to
compute the magnetic susceptibility of nuclear matter for several values of the
asymmetry from neutron to symmetric matter. The results show no indication of a
ferromagnetic transition at any density for any asymmetry of nuclear matter.Comment: 23 pages, 8 figures, 2 tables (submitted to Phys. Rev. C
Decoupling of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy
The spin-1/2 antiferromagnetic zig-zag ladder is studied by exact
diagonalization of small systems in the regime of weak inter-chain coupling. A
gapless phase with quasi long-range spiral correlations has been predicted to
occur in this regime if easy-plane (XY) anisotropy is present. We find in
general that the finite zig-zag ladder shows three phases: a gapless collinear
phase, a dimer phase and a spiral phase. We study the level crossings of the
spectrum,the dimer correlation function, the structure factor and the spin
stiffness within these phases, as well as at the transition points. As the
inter-chain coupling decreases we observe a transition in the anisotropic XY
case from a phase with a gap to a gapless phase that is best described by two
decoupled antiferromagnetic chains. The isotropic and the anisotropic XY cases
are found to be qualitatively the same, however, in the regime of weak
inter-chain coupling for the small systems studied here. We attribute this to a
finite-size effect in the isotropic zig-zag case that results from
exponentially diverging antiferromagnetic correlations in the weak-coupling
limit.Comment: to appear in Physical Review
Formation of two-dimensional weak localization in conducting Langmuir-Blodgett films
We report the magnetotransport properties up to 7 T in the organic highly
conducting Langmuir-Blodgett(LB) films formed by a molecular association of the
electroactive donor molecule bis(ethylendioxy)tetrathiafulvalene (BEDO-TTF) and
stearic acid CH(CH)COOH. We show the logarithmic decrease of dc
conductivity and the negative transverse magnetoresistance at low temperature.
They are interpreted in the weak localization of two-dimensional (2D)
electronic system based on the homogeneous conducting layer with the molecular
size thickness of BEDO-TTF. The electronic length with phase memory is given at
the mesoscopic scale, which provides for the first time evidence of the 2D
coherent charge transport in the conducting LB films.Comment: 5 pages, 1 Table and 5 figure
The unusual electronic structure of the "pseudo-ladder" compound CaCu2O3
Experimental and theoretical studies of the unoccupied electronic structure
of CaCu2O3 single crystals have been performed using polarization-dependent
x-ray absorption spectroscopy and band structure calculations. The measured
hole distribution shows an unusual large number of holes in orbitals parallel
to the interlayer direction which is in agreement with the theoretical
analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate
picture. The corresponding strong interlayer exchange is responsible for the
missing spin gap generic for other two-leg ladder cuprates.Comment: 4 pages, 3 figures include
Atomic layering at the liquid silicon surface: a first- principles simulation
We simulate the liquid silicon surface with first-principles molecular
dynamics in a slab geometry. We find that the atom-density profile presents a
pronounced layering, similar to those observed in low-temperature liquid metals
like Ga and Hg. The depth-dependent pair correlation function shows that the
effect originates from directional bonding of Si atoms at the surface, and
propagates into the bulk. The layering has no major effects in the electronic
and dynamical properties of the system, that are very similar to those of bulk
liquid Si. To our knowledge, this is the first study of a liquid surface by
first-principles molecular dynamics.Comment: 4 pages, 4 figures, submitted to PR
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal
nonlinear response function, we derive a nonliear equation in which the mixed
state Hall resistivity can be expressed as an analytical function of magnetic
field, temperature and applied current. This equation enables one to compare
quantitatively the experimental data with theoretical model. We also find some
new scaling relations of the temperature and field dependency of Hall
resistivity. The comparison between our theoretical curves and experimental
data shows a fair agreement.Comment: 4 pages, 3 figure
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