1,273 research outputs found
Parametric Evolution for a Deformed Cavity
We consider a classically chaotic system that is described by a Hamiltonian
H(Q,P;x), where (Q,P) describes a particle moving inside a cavity, and x
controls a deformation of the boundary. The quantum-eigenstates of the system
are |n(x)>. We describe how the parametric kernel P(n|m) = , also
known as the local density of states, evolves as a function of x-x0. We
illuminate the non-unitary nature of this parametric evolution, the emergence
of non-perturbative features, the final non-universal saturation, and the
limitations of random-wave considerations. The parametric evolution is
demonstrated numerically for two distinct representative deformation processes.Comment: 13 pages, 8 figures, improved introduction, to be published in Phys.
Rev.
Wigner Random Banded Matrices with Sparse Structure: Local Spectral Density of States
Random banded matrices with linearly increasing diagonal elements are
recently considered as an attractive model for complex nuclei and atoms. Apart
from early papers by Wigner \cite{Wig} there were no analytical studies on the
subject. In this letter we present analytical and numerical results for local
spectral density of states (LDOS) for more general case of matrices with a
sparsity inside the band. The crossover from the semicircle form of LDOS to
that given by the Breit-Wigner formula is studied in detail.Comment: Misprints are corrected and stylistic changes are made. To be
published in PR
Reduction of circulating cholesterol and apolipoprotein levels during sepsis
Sepsis with multiple organ failure is frequently associated with a substantial decrease of cholesterol levels. This decrease of cholesterol is strongly associated with mortality suggesting a direct relation between inflammatory conditions and altered cholesterol homeostasis. The host response during sepsis is mediated by cytokines and growth factors, which are capable of influencing lipid metabolism. Conversely lipoproteins are also capable of modulating cytokine production during the inflammatory response. Therefore the decrease in circulating cholesterol levels seems to play a crucial role in the pathophysiology of sepsis. In this review the interaction between cytokines and lipid metabolism and its clinical consequences will be discussed
E10 and SO(9,9) invariant supergravity
We show that (massive) D=10 type IIA supergravity possesses a hidden rigid
SO(9,9) symmetry and a hidden local SO(9) x SO(9) symmetry upon dimensional
reduction to one (time-like) dimension. We explicitly construct the associated
locally supersymmetric Lagrangian in one dimension, and show that its bosonic
sector, including the mass term, can be equivalently described by a truncation
of an E10/K(E10) non-linear sigma-model to the level \ell<=2 sector in a
decomposition of E10 under its so(9,9) subalgebra. This decomposition is
presented up to level 10, and the even and odd level sectors are identified
tentatively with the Neveu--Schwarz and Ramond sectors, respectively. Further
truncation to the level \ell=0 sector yields a model related to the reduction
of D=10 type I supergravity. The hyperbolic Kac--Moody algebra DE10, associated
to the latter, is shown to be a proper subalgebra of E10, in accord with the
embedding of type I into type IIA supergravity. The corresponding decomposition
of DE10 under so(9,9) is presented up to level 5.Comment: 1+39 pages LaTeX2e, 2 figures, 2 tables, extended tables obtainable
by downloading sourc
Propagation of travelling waves in sub-excitable systems driven by noise and periodic forcing
It has been reported that traveling waves propagate periodically and stably
in sub-excitable systems driven by noise [Phys. Rev. Lett. \textbf{88}, 138301
(2002)]. As a further investigation, here we observe different types of
traveling waves under different noises and periodic forces, using a simplified
Oregonator model. Depending on different noises and periodic forces, we have
observed different types of wave propagation (or their disappearance).
Moreover, the reversal phenomena are observed in this system based on the
numerical experiments in the one-dimensional space. As an explanation, we
regard it as the effect of periodic forces. Thus, we give qualitative
explanations to how reversal phenomena stably appear, which seem to arise from
the mixing function of the periodic force and the noise. And the output period
and three velocities (the normal, the positive and the negative) of the
travelling waves are defined and their relationship with the periodic forces,
along with the types of waves, are also studied in sub-excitable system under a
fixed noise intensity.Comment: Some references and information are added in the modified version.
Accepted, The European Physical Journal
Technology Directions for the 21st Century
New technologies will unleash the huge capacity of fiber-optic cable to meet growing demands for bandwidth. Companies will continue to replace private networks with public network bandwidth-on-demand. Although asynchronous transfer mode (ATM) is the transmission technology favored by many, its penetration will be slower than anticipated. Hybrid networks - e.g., a mix of ATM, frame relay, and fast Ethernet - may predominate, both as interim and long-term solutions, based on factors such as availability, interoperability, and cost. Telecommunications equipment and services prices will decrease further due to increased supply and more competition. Explosive Internet growth will continue, requiring additional backbone transmission capacity and enhanced protocols, but it is not clear who will fund the upgrade. Within ten years, space-based constellations of satellites in Low Earth orbit (LEO) will serve mobile users employing small, low-power terminals. 'Little LEO's' will provide packet transmission services and geo-position determination. 'Big LEO's' will function as global cellular telephone networks, with some planning to offer video and interactive multimedia services. Geosynchronous satellites also are proposed for mobile voice grade links and high-bandwidth services. NASA may benefit from resulting cost reductions in components, space hardware, launch services, and telecommunications services
Characteristics of Quantum-Classical Correspondence for Two Interacting Spins
The conditions of quantum-classical correspondence for a system of two
interacting spins are investigated. Differences between quantum expectation
values and classical Liouville averages are examined for both regular and
chaotic dynamics well beyond the short-time regime of narrow states. We find
that quantum-classical differences initially grow exponentially with a
characteristic exponent consistently larger than the largest Lyapunov exponent.
We provide numerical evidence that the time of the break between the quantum
and classical predictions scales as log(), where is
a characteristic system action. However, this log break-time rule applies only
while the quantum-classical deviations are smaller than order hbar. We find
that the quantum observables remain well approximated by classical Liouville
averages over long times even for the chaotic motions of a few
degree-of-freedom system. To obtain this correspondence it is not necessary to
introduce the decoherence effects of a many degree-of-freedom environment.Comment: New introduction, accepted in Phys Rev A (May 2001 issue), 12 latex
figures, 3 ps figure
Sintomatologia ansiosa e depressiva em famílias com filhos adolescentes: Qual o papel da diferenciação do self dos pais?
A literatura tem realçado o impacto da história familiar de psicopatologia no
desenvolvimento de perturbações emocionais nas gerações mais novas e a associação
entre o nível de diferenciação do self e diversos quadros clínicos (e.g., ansiosos e
depressivos). Com recurso a um desenho quantitativo transversal e a uma amostra de
104 tríades familiares (mãe, pai e filho/a adolescente), o presente estudo pretende
analisar: a associação entre a sintomatologia depressiva e ansiosa de mães e pais e
filhos/as adolescentes; e o papel mediador da diferenciação do self das mães e dos pais
na relação entre a sintomatologia depressiva e ansiosa de mães e de pais e a
sintomatologia depressiva e ansiosa dos/as filhos/as adolescentes. Os resultados
mostram que: a sintomatologia depressiva e ansiosa do pai e da mãe são preditoras do
nível de diferenciação do self do pai e da mãe; a relação entre a sintomatologia
depressiva da mãe e dos/as filhos/as é mediada pela diferenciação do self da mãe; e a
sintomatologia ansiosa da mãe é preditora da sintomatologia ansiosa dos/as filhos/as.
Apesar de os resultados sugerirem que a mãe tenha também um papel central na
transmissão de adversidade aos filhos, apontam para que a sintomatologia ansiosa e
depressiva de pais e filhos se associem de formas diferentes. Este estudo tem
implicações para a prática clínica e para a literatura na área da psicologia clínica e
psicologia da família, ao relevar o impacto da sintomatologia da mãe e do seu nível de
diferenciação do self no desenvolvimento de psicopatologia na adolescência.The literature has highlighted the impact of the family psychopathology history on the
development of psychopathology in the younger generations and the association
between the level of self differentiation and various clinical conditions (e.g., anxiety and
depression). Using a quantitative cross-sectional design and a sample of 104 family
triads (mother, father and adolescent child), the present study aims to analyze: the
association between depressive and anxious symptomatology of mothers and fathers
and adolescent children; and the mediating role of the self-differentiation of mothers
and fathers in the relationship between the depressive and anxious symptomatology of
mothers and fathers and the depressive and anxious symptomatology of the adolescent
children. The results show that: the depressive and anxious symptomatology of the
father and the mother are predictors of the level of differentiation of the self of the
father and the mother; the relationship between the depressive symptomatology of the
mother and the child is mediated by the differentiation of the mother's self; and the
anxious symptomatology of the mother is a predictor of the anxious symptomatology of
the child. Although the results suggest that the mother also has a central role in the
transmission of adversity to the children, they point out that the anxious and depressive
symptomatology of parents and children associate in different ways. This study has
implications for clinical practice and for literature in clinical psychology and family
psychology, by highlighting the impact of the mother's symptomatology and mothers’
level of self differentiation in the development of psychopathology in adolescence.Orientação: Ana Priost
An examination of the relationship between hotspots and recombination associated with chromosome 21 nondisjunction
Trisomy 21, resulting in Down Syndrome (DS), is the most common autosomal trisomy among live-born infants and is caused mainly by nondisjunction of chromosome 21 within oocytes. Risk factors for nondisjunction depend on the parental origin and type of meiotic error. For errors in the oocyte, increased maternal age and altered patterns of recombination are highly associated with nondisjunction. Studies of normal meiotic events in humans have shown that recombination clusters in regions referred to as hotspots. In addition, GC content, CpG fraction, Poly(A)/Poly(T) fraction and gene density have been found to be significant predictors of the placement of sex-averaged recombination in the human genome. These observations led us to ask whether the altered patterns of recombination associated with maternal nondisjunction of chromosome 21 could be explained by differences in the relationship between recombination placement and recombination-related genomic features (i.e., GC content, CpG fraction, Poly(A)/Poly(T) fraction or gene density) on 21q or differential hot-spot usage along the nondisjoined chromosome 21. We found several significant associations between our genomic features of interest and recombination, interestingly, these results were not consistent among recombination types (single and double proximal or distal events). We also found statistically significant relationships between the frequency of hotspots and the distribution of recombination along nondisjoined chromosomes. Collectively, these findings suggest that factors that affect the accessibility of a specific chromosome region to recombination may be altered in at least a proportion of oocytes with MI and MII errors
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