990 research outputs found
Symmetry and Temperature dependence of the Order parameter in MgB2 from point contact measurements
We have performed differential conductance versus voltage measurements of
Au/MgB2 point contacts. We find that the dominant component in the conductance
is due to Andreev reflection. The results are fitted to the theoretical model
of BTK for an s-wave symmetry from which we extract the value of the order
parameter (Delta) and its temperature dependence. From our results we also
obtain a lower experimental bound on the Fermi velocity in MgB2.Comment: 7 pages (Including figure captions) and 4 figure
Quantum Transition State Theory for proton transfer reactions in enzymes
We consider the role of quantum effects in the transfer of hyrogen-like
species in enzyme-catalysed reactions. This study is stimulated by claims that
the observed magnitude and temperature dependence of kinetic isotope effects
imply that quantum tunneling below the energy barrier associated with the
transition state significantly enhances the reaction rate in many enzymes. We
use a path integral approach which provides a general framework to understand
tunneling in a quantum system which interacts with an environment at non-zero
temperature. Here the quantum system is the active site of the enzyme and the
environment is the surrounding protein and water. Tunneling well below the
barrier only occurs for temperatures less than a temperature which is
determined by the curvature of potential energy surface near the top of the
barrier. We argue that for most enzymes this temperature is less than room
temperature. For physically reasonable parameters quantum transition state
theory gives a quantitative description of the temperature dependence and
magnitude of kinetic isotope effects for two classes of enzymes which have been
claimed to exhibit signatures of quantum tunneling. The only quantum effects
are those associated with the transition state, both reflection at the barrier
top and tunneling just below the barrier. We establish that the friction due to
the environment is weak and only slightly modifies the reaction rate.
Furthermore, at room temperature and for typical energy barriers environmental
degrees of freedom with frequencies much less than 1000 cm do not have a
significant effect on quantum corrections to the reaction rate.Comment: Aspects of the article are discussed at
condensedconcepts.blogspot.co
Local and macroscopic tunneling spectroscopy of Y(1-x)CaxBa2Cu3O(7-d) films: evidence for a doping dependent is or idxy component in the order parameter
Tunneling spectroscopy of epitaxial (110) Y1-xCaxBa2Cu3O7-d films reveals a
doping dependent transition from pure d(x2-y2) to d(x2-y2)+is or d(x2-y2)+idxy
order parameter. The subdominant (is or idxy) component manifests itself in a
splitting of the zero bias conductance peak and the appearance of subgap
structures. The splitting is seen in the overdoped samples, increases
systematically with doping, and is found to be an inherent property of the
overdoped films. It was observed in both local tunnel junctions, using scanning
tunneling microscopy (STM), and in macroscopic planar junctions, for films
prepared by either RF sputtering or laser ablation. The STM measurements
exhibit fairly uniform splitting size in [110] oriented areas on the order of
10 nm2 but vary from area to area, indicating some doping inhomogeneity. U and
V-shaped gaps were also observed, with good correspondence to the local
faceting, a manifestation of the dominant d-wave order parameter
Perception about the importance of feeding in a group of hematologic cancer patients
Introducción: Los pacientes oncohematológicos presentan
habitualmente déficits nutricionales derivados de su
enfermedad, sus tratamientos y efectos secundarios, etc.
Sin embargo, apenas existen datos descriptivos del empleo
de recomendaciones dietéticas, y de la auto-percepción del
paciente de su utilidad en su enfermedad.
Objetivos: Evaluar la percepción de la importancia de
la alimentación en un grupo de pacientes con cáncer
hematológico.
Materiales y métodos: 111 pacientes oncohematológicos
auto-registraron un cuestionario con preguntas sociosanitarias
y de percepción personal de la importancia de la
alimentación en su enfermedad.
Resultados: La edad media fue 40,0 ± 12,8 años (64,86%
mujeres). El diagnóstico y el tratamiento más frecuente fue
linfoma (83,78%) y quimioterapia (92,80%). Un 75% consideró
“muy importante” la relación entre enfermedad
oncohematológica y estado nutricional. Sólo un 54,1%
recibió consejo dietético. Y un 53,2% y 50,5% consideró
que el consumo de suplementos nutricionales mejoraría
su calidad de vida y/o enfermedad respectivamente.
Conclusiones: Un porcentaje importante de pacientes
presentaron estados avanzados de su enfermedad. Sin
embargo, la mitad del colectivo no había recibido pautas
dietéticas a pesar del elevado interés por recibir atención
nutricional. Por tanto, la valoración nutricional del
paciente oncohematológico así como la implementación
de un soporte nutricional personalizado deberían formar
parte de la práctica clínica habitualIntroduction: Oncohematologic patients usually present
nutritional deficits associated with the disease, the treatments
and side effects, etc. However, there are hardly any
descriptive data about the dietary recommendations used
and the patient’s self-perception of its usefulness in their
disease.
Aim: To assess the self-perception of the nutritional
importance in a group of oncohematologic patients.
Materials and methods: 111 oncohematologic patients
self-reported a questionnaire containing items about
socio-sanitary data and self-perception of the nutritional
importance in their disease.
Results: The mean age was 40.0 ± 12.8 years (64.86%
women). The most frequent diagnosis and treatment was
lymphoma (83.78%) and chemoteraphy (92.80%). 75%
considered “very important” relationship between oncohematologic
disease and nutritional status. Only 54.1%
received dietary advice. And 53.2% and 50.5% considered
that the use of nutritional supplements improve quality
of life and/or disease respectively.
Conclusions: A significant percentage of patients had
advanced stages of their disease. However, half the group
had not received dietary advice despite high interest in
receiving nutritional care. Therefore, the nutritional
assessment and the personalized nutritional support
implementation of the patient should be included in routine
clinical practic
A self-consistent quantum master equation approach to molecular transport
We propose a self-consistent generalized quantum master equation (GQME) to
describe electron transport through molecular junctions. In a previous study
[M.Esposito and M.Galperin. Phys. Rev. B 79, 205303 (2009)], we derived a
time-nonlocal GQME to cure the lack of broadening effects in Redfield theory.
To do so, the free evolution used in the Born-Markov approximation to close the
Redfield equation was replaced by a standard Redfield evolution. In the present
paper, we propose a backward Redfield evolution leading to a time-local GQME
which allows for a self-consistent procedure of the GQME generator. This
approach is approximate but properly reproduces the nonequilibrium steady state
density matrix and the currents of an exactly solvable model. The approach is
less accurate for higher moments such as the noise.Comment: 9 pages, 4 figure
Estrogen-Receptor Expression and Function in Thymocytes in Relation to Gender and Age
The expression of estrogen receptor (ER) in thymocytes was studied in young, middle-aged, and
old (2, 12, and 24 months, respectively) female and male C57BL/6J mice. Western immunoblots
prepared from the thymocytes of females of all age groups showed the presence of a 67-kD
protein band, which has been associated with the apparent MW of denatured ER. Flow cytometry
analysis o,f cells stained with a monoclonal anti-ER antibody (clone 13H2) disclosed ER
expression in both females and males of all age groups. In vivo treatment with estradiol (E2) led
to an increase in the specific activity of thymic creatine kinase (CK) in the female mice, whereas
the male thymocytes responded with an increase in CK activity only on treatment with
dihydrotestosterone (DHT). The data show no differences in ER expression between male and
females, but the receptor appears not to be functional in males. Interestingly, when estradiol was
applied to co-cultures of lymphoid-depleted fetal thymus (FT) explants and bone-marrow cells,
or thymocytes, from young and old females, it resulted in increased cellularity of cultures
containing cells of the young, and not those of the old. The proportion of CD4/CD8 phenotypes
of the developing cells in these cultures was not affected by E2 treatment. These observations
provide a new insight into ER expression and function in T-cell development in relation to
gender and age
Superconductivity of the spin ladder system: Are the superconducting pairing and the spin-gap formation of the same origin?
Pressure-induced superconductivity in a spin-ladder cuprate
SrCaCuO has not been studied on a microscopic level so
far although the superconductivity was already discovered in 1996. We have
improved high-pressure technique with using a large high-quality crystal, and
succeeded in studying the superconductivity using Cu nuclear magnetic
resonance (NMR). We found that anomalous metallic state reflecting the
spin-ladder structure is realized and the superconductivity possesses a
s-wavelike character in the meaning that a finite gap exists in the
quasi-particle excitation: At pressure of 3.5GPa we observed two excitation
modes in the normal state from the relaxation rate . One gives rise
to an activation-type component in , and the other -linear
component linking directly with the superconductivity. This gapless mode likely
arises from free motion of holon-spinon bound states appearing by hole doping,
and the pairing of them likely causes the superconductivity.Comment: to be published in Phys. Rev. Let
Master-equations for the study of decoherence
Different structures of master-equation used for the description of
decoherence of a microsystem interacting through collisions with a surrounding
environment are considered and compared. These results are connected to the
general expression of the generator of a quantum dynamical semigroup in
presence of translation invariance recently found by Holevo.Comment: 10 pages, latex, no figures, to appear in Int. J. Theor. Phy
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