2,656 research outputs found
Generalized nonuniform dichotomies and local stable manifolds
We establish the existence of local stable manifolds for semiflows generated
by nonlinear perturbations of nonautonomous ordinary linear differential
equations in Banach spaces, assuming the existence of a general type of
nonuniform dichotomy for the evolution operator that contains the nonuniform
exponential and polynomial dichotomies as a very particular case. The family of
dichotomies considered allow situations for which the classical Lyapunov
exponents are zero. Additionally, we give new examples of application of our
stable manifold theorem and study the behavior of the dynamics under
perturbations.Comment: 18 pages. New version with minor corrections and an additional
theorem and an additional exampl
A Curvature Principle for the interaction between universes
We propose a Curvature Principle to describe the dynamics of interacting
universes in a multi-universe scenario and show, in the context of a simplified
model, how interaction drives the cosmological constant of one of the universes
toward a vanishingly small value. We also conjecture on how the proposed
Curvature Principle suggests a solution for the entropy paradox of a universe
where the cosmological constant vanishes.Comment: Essay selected for an honorable mention by the Gravity Research
Foundation, 2007. Plain latex, 8 page
Establishment of economic thresholds for olive moth, Prays oleae (Bern.) in Tras-os-Montes region
A mathematical model is presented which aims to establish the economic
thresholds for the flower generation of olive moth, Prays oleae (Bern.) in TrĂ s-os-
Montes (north-eastern Portugal). The model is based on observations taken between
1993 and 1998, on olives of the oil variety Cobrançosa, grown under rain-fed
conditions and without pesticide treatments for several years. It takes into account
factors such as cost and efficacy of spraying, environmental impact, expected yield,
price and crop losses. According to this model the control of the pest is justified
when the percent of flower infestation is between 4.0 % and 6.0 % during the years
of intermediate and high expected yields, (i.e., about 2400 kg/ha) and between 8.0 %
and 11.0 % in the years of lower expected yields (i.e. approximately 1000 kg/ha) for
prices usually practised in the region
Counting solutions from finite samplings
We formulate the solution counting problem within the framework of inverse
Ising problem and use fast belief propagation equations to estimate the entropy
whose value provides an estimate on the true one. We test this idea on both
diluted models (random 2-SAT and 3-SAT problems) and fully-connected model
(binary perceptron), and show that when the constraint density is small, this
estimate can be very close to the true value. The information stored by the
salamander retina under the natural movie stimuli can also be estimated and our
result is consistent with that obtained by Monte Carlo method. Of particular
significance is sizes of other metastable states for this real neuronal network
are predicted.Comment: 9 pages, 4 figures and 1 table, further discussions adde
Culpability and Willingness to Pay to Reduce Negative Externalities: A Contingent Valuation and Experimental Economics Study
Financial Economics,
The impact of urban spatial structure on travel demand in the United States
The authors combine measures of urban form and public transit supply for 114 urbanized areas with the 1990 Nationwide Personal Transportation Survey to address two questions: (1) How do measures of urban form, including city shape, road density, the spatial distribution of population, and jobs-housing balance affect the annual miles driven and commute mode choices of U.S. households? (2) How does the supply of public transportation (annual route miles supplied and availability of transit stops) affect miles driven and commute mode choice? The authors find that jobs-housing balance, population centrality, and rail miles supplied significantly reduce the probability of driving to work in cities with some rail transit. Population centrality and jobs-housing balance have a significant impact on annual household vehicle miles traveled (VMT), as do city shape, road density, and (in rail cities) annual rail route miles supplied. The elasticity of VMT with respect to each variable is small, on the order of 0.10-0.20 in absolute value. However, changing several measures of form simultaneously can reduce annual VMT significantly. Moving the sample households from a city with the characteristics of Atlanta to a city with the characteristics of Boston reduces annual VMT by 25 percent.Housing&Human Habitats,Roads&Highways,Environmental Economics&Policies,Economic Theory&Research,Transport Economics Policy&Planning,Economic Theory&Research,Roads&Highways,Transport Economics Policy&Planning,Geographical Information Systems,Housing&Human Habitats
On Higgs and sphaleron effects during the leptogenesis era
We discuss the effects of various processes that can be active during the
leptogenesis era, and present the Boltzmann equations that take them into
account appropriately. A non-vanishing Higgs number asymmetry is always
present, enhancing the washout of the lepton asymmetry. This is the main new
effect when leptogenesis takes place at GeV, reducing the final
baryon asymmetry and tightening the leptogenesis bound on the neutrino masses.
If leptogenesis occurs at lower temperatures, electroweak sphalerons partially
transfer the lepton asymmetry to a baryonic one, while Yukawa interactions and
QCD sphalerons partially transfer the asymmetries of the left-handed fields to
the right-handed ones, suppressing the washout processes. Depending on the
specific temperature range in which leptogenesis occurs, the final baryon
asymmetry can be enhanced or suppressed by factors of order 20%--40% with
respect to the case when these effects are altogether ignored.Comment: one reference adde
Repair of Ruptured Abdominal Aortic Aneurysm after Cardiac Arrest: a Case Report
The management of abdominal aortic aneurysms, especially ruptured abdominal aortic aneurysms, continues to challenge vascular surgeons. A ruptured abdominal aortic aneurysm is associated with a high mortality rate. If cardiopulmonary resuscitation is required before surgical repair, mortality rates are said to be even higher. However, cardiac arrest in patients with ruptured abdominal aortic aneurysm does not accurately predict a nonsalvageable state or preclude functional survival. In these cases, agressive management may be the only hope for survival, and cardiac arrest should not as such contraindicate repair. The objective of this study is to present a successful case of repair of ruptured abdominal aortic aneurysm after cardiac arrest.info:eu-repo/semantics/publishedVersio
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