10,489 research outputs found
Chaos and a Resonance Mechanism for Structure Formation in Inflationary Models
We exhibit a resonance mechanism of amplification of density perturbations in
inflationary mo-dels, using a minimal set of ingredients (an effective
cosmological constant, a scalar field minimally coupled to the gravitational
field and matter), common to most models in the literature of inflation. This
mechanism is based on the structure of homoclinic cylinders, emanating from an
unstable periodic orbit in the neighborhood of a saddle-center critical point,
present in the phase space of the model. The cylindrical structure induces
oscillatory motions of the scales of the universe whenever the orbit visits the
neighborhood of the saddle-center, before the universe enters a period of
exponential expansion. The oscillations of the scale functions produce, by a
resonance mechanism, the amplification of a selected wave number spectrum of
density perturbations, and can explain the hierarchy of scales observed in the
actual universe. The transversal crossings of the homoclinic cylinders induce
chaos in the dynamics of the model, a fact intimately connected to the
resonance mechanism occuring immediately before the exit to inflation.Comment: 4 pages. This essay received an Honorable Mention from the Gravity
Research Foundation, 1998-Ed. To appear in Mod. Phys. Lett.
Initial pseudo-steady state & asymptotic KPZ universality in semiconductor on polymer deposition
The Kardar-Parisi-Zhang (KPZ) class is a paradigmatic example of universality
in nonequilibrium phenomena, but clear experimental evidences of asymptotic
2D-KPZ statistics are still very rare, and far less understanding stems from
its short-time behavior. We tackle such issues by analyzing surface
fluctuations of CdTe films deposited on polymeric substrates, based on a huge
spatio-temporal surface sampling acquired through atomic force microscopy. A
\textit{pseudo}-steady state (where average surface roughness and spatial
correlations stay constant in time) is observed at initial times, persisting up
to deposition of monolayers. This state results from a fine
balance between roughening and smoothening, as supported by a phenomenological
growth model. KPZ statistics arises at long times, thoroughly verified by
universal exponents, spatial covariance and several distributions. Recent
theoretical generalizations of the Family-Vicsek scaling and the emergence of
log-normal distributions during interface growth are experimentally confirmed.
These results confirm that high vacuum vapor deposition of CdTe constitutes a
genuine 2D-KPZ system, and expand our knowledge about possible
substrate-induced short-time behaviors.Comment: 13 pages, 8 figures, 2 table
Physical properties of the Schur complement of local covariance matrices
General properties of global covariance matrices representing bipartite
Gaussian states can be decomposed into properties of local covariance matrices
and their Schur complements. We demonstrate that given a bipartite Gaussian
state described by a covariance matrix \textbf{V}, the
Schur complement of a local covariance submatrix of it can be
interpreted as a new covariance matrix representing a Gaussian operator of
party 1 conditioned to local parity measurements on party 2. The connection
with a partial parity measurement over a bipartite quantum state and the
determination of the reduced Wigner function is given and an operational
process of parity measurement is developed. Generalization of this procedure to
a -partite Gaussian state is given and it is demonstrated that the
system state conditioned to a partial parity projection is given by a
covariance matrix such as its block elements are Schur complements
of special local matrices.Comment: 10 pages. Replaced with final published versio
Simulação de dados meteorológicos para avaliação de impactos de mudanças climáticas na agricultura.
Neste trabalho foi utilizado o simulador climático LARS-WG. Esse simulador é baseado em um modelo semiempírico, ou seja, para o processo há a utilização de parâmetros estatísticos em sua formulação e também a necessidade de calibrações para as devidas aplicações
Nursing Home-Acquired Pneumonia Presenting at the Emergency Department
Nursing home-acquired pneumonia (NHAP) is one of the most common infections arising amongst nursing home residents, and its incidence is expected to increase as population ages. The NHAP recommendation for empiric broad-spectrum antibiotic therapy, arising from the concept of healthcare-associated pneumonia, has been challenged by recent studies reporting low rates of multidrug-resistant (MDR) bacteria. This single center study analyzes the results of NHAP patients admitted through the Emergency Department (ED) at a tertiary center during the year 2010. There were 116 cases, male gender corresponded to 34.5 % of patients and median age was 84 years old (IQR 77-90). Comorbidities were present in 69.8 % of cases and 48.3 % of patients had used healthcare services during the previous 90 days. In-hospital mortality rate was 46.6 % and median length-of-stay was 9 days. Severity assessment at the Emergency Department provided CURB65 index score and respective mortality (%) results: zero: n = 0; one: n = 7 (0 %); two: n = 18 (38.9 %); three: n = 26 (38.5 %); four: n = 30 (53.3 %); and five; n = 22 (68.2 %); and sepsis n = 50 (34.0 %), severe sepsis n = 43 (48.8 %) and septic shock n = 22 (72.7 %). Significant risk factors for in-hospital mortality in multivariate analysis were polypnea (p = 0.001), age ≥ 75 years (p = 0.02), and severe sepsis or shock (p = 0.03) at the ED. Microbiological testing in 78.4 % of cases was positive in 15.4 % (n = 15): methicillin-resistant Staphylococcus aureus (26.7 %), Pseudomonas aeruginosa (20.0 %), S. pneumoniae (13.3 %), Escherichia coli (13.3 %), others (26.7 %); the rate of MDR bacteria was 53.3 %. This study reveals high rates of mortality and MDR bacteria among NHAP hospital admissions supporting the use of empirical broad-spectrum antibiotic therapy in these patients
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