1,804 research outputs found
A Derivation of the Luminosity Function of the Kuiper Belt from a Broken Power-Law Size Distribution
We have derived a model of the Kuiper belt luminosity function exhibited by a
broken power-law size distribution. This model allows direct comparison of the
observed luminosity function to the underlying size distribution. We discuss
the importance of the radial distribution model in determining the break
diameter. We determine a best-fit break-diameter of the Kuiper belt
size-distribution of 30<Db<90 km via a maximum-likelihood fit of our model to
the observed luminosity function. We also confirm that the observed luminosity
function for m(R) ~ 21-28 is consistent with a broken power-law size
distribution, and exhibits a break at m(R)=26.0+0.7-1.8.Comment: Accepted by Icarus 25 pages, 2 tables, 2 figure
Momentum--dependent nuclear mean fields and collective flow in heavy ion collisions
We use the Boltzmann-Uehling-Uhlenbeck model to simulate the dynamical
evolution of heavy ion collisions and to compare the effects of two
parametrizations of the momentum--dependent nuclear mean field that have
identical properties in cold nuclear matter. We compare with recent data on
nuclear flow, as characterized by transverse momentum distributions and flow
() variables for symmetric and asymmetric systems. We find that the precise
functional dependence of the nuclear mean field on the particle momentum is
important. With our approach, we also confirm that the difference between
symmetric and asymmetric systems can be used to pin down the density and
momentum dependence of the nuclear self consistent one--body potential,
independently. All the data can be reproduced very well with a
momentum--dependent interaction with compressibility K = 210 MeV.Comment: 15 pages in ReVTeX 3.0; 12 postscript figures uuencoded; McGill/94-1
Fractional Quantum Hall States of Clustered Composite Fermions
The energy spectra and wavefunctions of up to 14 interacting quasielectrons
(QE's) in the Laughlin nu=1/3 fractional quantum Hall (FQH) state are
investigated using exact numerical diagonalization. It is shown that at
sufficiently high density the QE's form pairs or larger clusters. This
behavior, opposite to Laughlin correlations, invalidates the (sometimes
invoked) reapplication of the composite fermion picture to the individual QE's.
The series of finite-size incompressible ground states are identified at the QE
filling factors nu_QE=1/2, 1/3, 2/3, corresponding to the electron fillings
nu=3/8, 4/11, 5/13. The equivalent quasihole (QH) states occur at nu_QH=1/4,
1/5, 2/7, corresponding to nu=3/10, 4/13, 5/17. All these six novel FQH states
were recently discovered experimentally. Detailed analysis indicates that QE or
QH correlations in these states are different from those of well-known FQH
electron states (e.g., Laughlin or Moore-Read states), leaving the origin of
their incompressibility uncertain. Halperin's idea of Laughlin states of QP
pairs is also explored, but is does not seem adequate.Comment: 14 pages, 9 figures; revision: 1 new figure, some new references,
some new data, title chang
Improved lower bounds for the ground-state energy of many-body systems
New lower bounds for the binding energy of a quantum-mechanical system of
interacting particles are presented. The new bounds are expressed in terms of
two-particle quantities and improve the conventional bounds of the Hall-Post
type. They are constructed by considering not only the energy in the
two-particle system, but also the structure of the pair wave function. We apply
the formal results to various numerical examples, and show that in some cases
dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
Structures for Interacting Composite Fermions: Stripes, Bubbles, and Fractional Quantum Hall Effect
Much of the present day qualitative phenomenology of the fractional quantum
Hall effect can be understood by neglecting the interactions between composite
fermions altogether. For example the fractional quantum Hall effect at
corresponds to filled composite-fermion Landau levels,and
the compressible state at to the Fermi sea of composite fermions.
Away from these filling factors, the residual interactions between composite
fermions will determine the nature of the ground state. In this article, a
model is constructed for the residual interaction between composite fermions,
and various possible states are considered in a variational approach. Our study
suggests formation of composite-fermion stripes, bubble crystals, as well as
fractional quantum Hall states for appropriate situations.Comment: 16 pages, 7 figure
Periodic corrugation on dynamic fracture surface in brittle bulk metallic glass
Dynamic crack propagation in a model brittle bulk metallic glass (BMG) is studied. Contrary to other brittle glassy materials, the authors find nanometer scale out-of-plane periodic corrugations along the crack surface of the BMG. The nanoscale periodicity remains nearly constant at different loading rates. An interpretation is presented to explain the evolution and the periodic coalescence of the nanometer scale cavities along the crack surface. The observation sheds light on the origin of dynamic fracture surface roughening in brittle materials and could be generally applicable to brittle materials
Fermion Chern Simons Theory of Hierarchical Fractional Quantum Hall States
We present an effective Chern-Simons theory for the bulk fully polarized
fractional quantum Hall (FQH) hierarchical states constructed as daughters of
general states of the Jain series, {\it i. e.} as FQH states of the
quasi-particles or quasi-holes of Jain states. We discuss the stability of
these new states and present two reasonable stability criteria. We discuss the
theory of their edge states which follows naturally from this bulk theory. We
construct the operators that create elementary excitations, and discuss the
scaling behavior of the tunneling conductance in different situations. Under
the assumption that the edge states of these fully polarized hierarchical
states are unreconstructed and unresolved, we find that the differential
conductance for tunneling of electrons from a Fermi liquid into {\em any}
hierarchical Jain FQH states has the scaling behavior with the
universal exponent , where is the filling fraction of the
hierarchical state. Finally, we explore alternative ways of constructing FQH
states with the same filling fractions as partially polarized states, and
conclude that this is not possible within our approach.Comment: 10 pages, 50 references, no figures; formerly known as "Composite
Fermions: The Next Generation(s)" (title changed by the PRB thought police).
This version has more references and a discussion of the stability of the new
states. Published version. One erroneous reference is correcte
Qualidade de Vida e Atitudes dos Idosos Face à Velhice
A problemática do envelhecimento tem assumido, nos últimos anos, uma
crescente importância na consciência coletiva da população, tornando-se cada vez mais importante compreender a população idosa e a sua realidade.
Posto isto, foi realizado um estudo quantitativo e correlacional, que teve como
objectivo avaliar a qualidade de vida e atitudes face à velhice de idosos, bem como a
relação entre estas e as variáveis sociodemográficas e familiares.
Foram inquiridos 100 idosos, com mais de 65 anos e sem deficit cognitivo . Para
a recolha de dados utilizou-se uma entrevista estruturada, constituída dados
sóciodemográficos do idoso, WHOQOL-AGE (Caballero, Miret, Power, Chatterji,
Tobiasz-Adamczyk, Koskinen, Leonardi, Olaya, Haro &Ayuso-Mateos, 2013) e o AAQ
( Laidlaw, Power, Schmidt and the WHOQOL-OLD Group, 2007).
Dos resultados destacamos os seguintes: A amostra é constituída por 52% de
idosos do sexo masculino tendo uma média de idades de 74,7 (DP=6,8). È no fator
Perdas Psicossociais e no Desenvolvimento Psicológico que os idosos têm uma melhor
atitude face ao envelhecimento. É no item “Tem dinheiro suficiente para satisfazer as
suas necessidades?” que os idosos apresentam uma menor qualidade de vida.
Não ter doença diagnosticada e ser do sexo masculino permitem ter melhores
atitudes face ao envelhecimento.
A Qualidade de Vida está relacionada com a idade, com o estado de saúde e com
a intensidade de preocupação da família. Constatou-se que os idosos que não estão
institucionalizados apresentam uma melhor qualidade de vida e uma melhor atitude face à velhice. Quem não precisa de ajudas técnicas para se movimentar apresenta uma melhor qualidade de vida.
Diferenças nas atitudes face ao envelhecimento consoante a residência onde
habita são significativas nas mudanças físicas e no desenvolvimento psicológico sendo
que os idosos que não vivem em lares têm uma atitude mais positiva em ambos os
fatores. / Over the past few years the issue of aging has played a growing importance in the population`s collective consciousness becoming increasingly important to
understand the elderly population and this reality.
Therefore a quantitative correlational study was performed to assess the quality
of life of seniors and their attitudes towards old age, and the relationship between these
and the socio-demographic and family factors.
100 seniors with more than 65 years and without cognitive deficit were
surveyed. For data collection we used a structured interview consisting of sociodemographic data of the elderly, WHOQOL-AGE (Caballero Miret Power Chatterji
Tobiasz-Adamczyk Koskinen Leonardi Olaya Ayuso-Mateos & Haro 2013) and AAQ
(Laidlaw Power Schmidt and the WHOQOL-OLD Group 2007).
We highlight: The sample is composed of 52% of males with a mean age of 74.7
(SD = 6.8). It is in the factor Psychosocial Losses and Psychological Development that
elderly people have a better attitude towards aging. It is in the item "Do you have
enough money to meet your needs?" that seniors show less quality of life.
Not having illness and being male allows having better attitudes towards aging.
Quality of Life is related to age, health condition and the intensity of family
concerns. It was observed that the elderly who are not institutionalized have a better
quality of life and a better attitude towards old age. Who does not need assistive devices to move around has a better quality of life.
Differences in attitudes towards aging, according to residency, are significant in
physical changes and psychological development, thus verifying that elderly who do not
live in nursing homes have a more positive attitude in both factors
Asymptotics and zeros of Sobolev orthogonal polynomials on unbounded supports
In this paper we present a survey about analytic properties of polynomials
orthogonal with respect to a weighted Sobolev inner product such that the
vector of measures has an unbounded support. In particular, we are focused in
the study of the asymptotic behaviour of such polynomials as well as in the
distribution of their zeros. Some open problems as well as some new directions
for a future research are formulated.Comment: Changed content; 34 pages, 41 reference
Metal Phenolic Networks as Tunable Buffering Systems
The buffering effects displayed by pH responsive polymers have recently gained attention in diverse fields such as nanomedicine and water treatment. However, creating libraries of modular and versatile polymers that can be readily integrated within existing materials remains challenging, hence restricting applications inspired by their buffering capacity. Herein, we propose the use of metal phenolic networks MPNs as tunable buffering systems and through mechanistic studies show that their buffering effects are driven by pH responsive, multivalent metal phenolic coordination. Owing to such supramolecular interactions, MPNs exhibit amp; 8764;twofold and fourfold higher buffering capacity than polyelectrolyte complexes and commercial buffer solutions, respectively. We demonstrate that the MPN buffering effects are retained after deposition onto solid supports, thereby allowing stabilization of aqueous environmental pH for 1 week. Moreover, by using different metals and ligands for the films, the endosomal escape capabilities of coated nanoparticles can be tuned, where higher buffering capacity leads to greater endosomal escape. This study forms a fundamental basis for developing future metal organic buffering material
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