1,369 research outputs found
Properties of the Ultrathin Multilayer Ground State of Fe/Pd
The technological evolution in the recent years allowed us to improve computers. Consequently, the numeric calculus with computational methods had a big progress. In theoretical physics that had a benefit with this technology, we can highlight the calculation of the solids\u27 electronic structure. Using the first principles method, LMTO (Linear Muffin-Tin Orbital) with the ASA (Atomic Sphere Approximation) approximation, we will study the band structure in the magnetic multilayers. The choice of these methods was based on two aspects: (a) The computer available to perform the job; a CRAY super computer that belongs to the Supercomputer National Center. Because the LTMO method presents good vectorization, it allows us to perform calculations with many atoms in the unitary cell, which would be too difficult with a smaller computer. (b) The fact that the LMTO method already presented good results in studies like intermetallic alloys and of iron nitride substituted
Collisional rates for the inelastic Maxwell model: application to the divergence of anisotropic high-order velocity moments in the homogeneous cooling state
The collisional rates associated with the isotropic velocity moments
and
are exactly derived in the case of the
inelastic Maxwell model as functions of the exponent , the coefficient of
restitution , and the dimensionality . The results are applied to
the evolution of the moments in the homogeneous free cooling state. It is found
that, at a given value of , not only the isotropic moments of a degree
higher than a certain value diverge but also the anisotropic moments do. This
implies that, while the scaled distribution function has been proven in the
literature to converge to the isotropic self-similar solution in well-defined
mathematical terms, nonzero initial anisotropic moments do not decay with time.
On the other hand, our results show that the ratio between an anisotropic
moment and the isotropic moment of the same degree tends to zero.Comment: 7 pages, 2 figures; v2: clarification of some mathematical statements
and addition of 7 new references; v3: Published in "Special Issue: Isaac
Goldhirsch - A Pioneer of Granular Matter Theory
Analysis of thylakoid membrane protein complexes from maize by Blue-Native Gel Electrophoresis and Tandem Mass Spectrometry
Stable Equilibrium Based on L\'evy Statistics: Stochastic Collision Models Approach
We investigate equilibrium properties of two very different stochastic
collision models: (i) the Rayleigh particle and (ii) the driven Maxwell gas.
For both models the equilibrium velocity distribution is a L\'evy distribution,
the Maxwell distribution being a special case. We show how these models are
related to fractional kinetic equations. Our work demonstrates that a stable
power-law equilibrium, which is independent of details of the underlying
models, is a natural generalization of Maxwell's velocity distribution.Comment: PRE Rapid Communication (in press
Development of high-gain gaseous photomultipliers for the visible spectral range
We summarize the development of visible-sensitive gaseous photomultipliers,
combining a semitransparent bi-alkali photocathode with a state-of-the-art
cascaded electron multiplier. The latter has high photoelectron collection
efficiency and a record ion blocking capability. We describe in details the
system and methods of photocathode production and characterization, their
coupling with the electron multiplier and the gaseous-photomultiplier operation
and characterization in a continuous mode. We present results on the properties
of laboratory-produced KCsSb, CsSb and NaKSb photocathodes and
report on their stability and QE in gas; KCsSb photocathodes yielded QE
values in Ar/CH(95/5) above 30% at wavelengths of 360-400 nm. The novel
gaseous photomultiplier yielded stable operation at gains of 10, in
continuous operation mode, in 700 Torr of this gas; its sensitivity to single
photons was demonstrated. Other properties are described. The successful
detection of visible light with this gas-photomultiplier pave ways towards
further development of large-area sealed imaging detectors, of flat geometry,
insensitive to magnetic fields, which might have significant impact on light
detection in numerous fields.Comment: 22 pages, 12 figures, for submission to JINS
Governance: Concepts And Emergence In Brazilian Education
The text discusses the polysemy of the term governance in different fields of knowledge, with a particular emphasis on the field of Education. Then, it discusses the state-of-the-art of governance in the education area, from an analytical-descriptive literature review based on content analysis. This paper analyzes governance in specialized literature by conducting a survey of the papers found in the databases of the Scientific Electronic Library Online and the Brazilian Digital Library of Theses and Dissertations during the period 2004-2015. The results indicate that the term governance has been increasingly used in discussions about changes in the state's role and the phases of educational public policies, by force of the public-private partnerships. However, there is also a need to broaden the debate on educational governance in Brazilian academic circles, in view of the limited number of studies identified.249393996
An exact solution of the inelastic Boltzmann equation for the Couette flow with uniform heat flux
In the steady Couette flow of a granular gas the sign of the heat flux
gradient is governed by the competition between viscous heating and inelastic
cooling. We show from the Boltzmann equation for inelastic Maxwell particles
that a special class of states exists where the viscous heating and the
inelastic cooling exactly compensate each other at every point, resulting in a
uniform heat flux. In this state the (reduced) shear rate is enslaved to the
coefficient of restitution , so that the only free parameter is the
(reduced) thermal gradient . It turns out that the reduced moments of
order are polynomials of degree in , with coefficients that
are nonlinear functions of . In particular, the rheological properties
() are independent of and coincide exactly with those of the
simple shear flow. The heat flux () is linear in the thermal gradient
(generalized Fourier's law), but with an effective thermal conductivity
differing from the Navier--Stokes one. In addition, a heat flux component
parallel to the flow velocity and normal to the thermal gradient exists. The
theoretical predictions are validated by comparison with direct Monte Carlo
simulations for the same model.Comment: 16 pages, 4 figures,1 table; v2: minor change
Cystic fibrosis – Comparison between patients in paediatric and adult age
AbstractCystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians. Although most cases are diagnosed in childhood, diagnosis in adults is apparently increasing.ObjectiveEvaluate the adult population with CF, comparing patients who were diagnosed before and after 18 years of age.MethodsRetrospective analysis of patients followed in three main medical centres in Portugal in 2012. Comparison of two groups: G1 – patients diagnosed at <18 years and G2 – patients diagnosed at ≥18 years.Results89 adults were identified: 61.8% in G1, 38.2% in G2. Gender distribution was similar in both groups. Average age in G2 was higher (38.3±8.4 vs. 26.8±6.1 years, p<0.001). Respiratory symptoms most frequently led to CF diagnosis in all patients, mainly in adulthood. There was a greater percentage of patients homozygous for the mutation delF508 in G1 (43.6 vs. 8.8%, p=0.02). Respiratory and pancreatic function, and body mass index (BMI) showed a higher severity in G1 (G1 vs. G2: FEV1: 54.6±27.3 vs. 29.9±64.6%, p=0.177; pancreatic insufficiency 72.7 vs. 26.5%, p<0.001; BMI 20.2±3.4 vs. 22.2±4.8, p=0.018). Pseudomonas aeruginosa and methicillin-sensitive Staphylococcus aureus were the most frequently isolated microorganisms. Lung transplantation rate was higher in G2 (20.6 vs. 10.9%, p=0.231) while mortality rate was higher in G1 (0 vs. 3.6%, p=0.261). Hospital admission rate was higher in G1 as well as mortality rate.ConclusionThe results suggest that patients with CF diagnosed in childhood have characteristics that distinguish them from those diagnosed in adulthood, and these differences may have implications for diagnosis, prognosis and life expectancy
Exact steady state solution of the Boltzmann equation: A driven 1-D inelastic Maxwell gas
The exact nonequilibrium steady state solution of the nonlinear Boltzmann
equation for a driven inelastic Maxwell model was obtained by Ben-Naim and
Krapivsky [Phys. Rev. E 61, R5 (2000)] in the form of an infinite product for
the Fourier transform of the distribution function . In this paper we
have inverted the Fourier transform to express in the form of an
infinite series of exponentially decaying terms. The dominant high energy tail
is exponential, , where and the amplitude is given in terms of a converging
sum. This is explicitly shown in the totally inelastic limit ()
and in the quasi-elastic limit (). In the latter case, the
distribution is dominated by a Maxwellian for a very wide range of velocities,
but a crossover from a Maxwellian to an exponential high energy tail exists for
velocities around a crossover velocity , where .
In this crossover region the distribution function is extremely small, .Comment: 11 pages, 4 figures; a table and a few references added; to be
published in PR
- …