1,197 research outputs found
Quasivariational solutions for first order quasilinear equations with gradient constraint
We prove the existence of solutions for an evolution quasi-variational
inequality with a first order quasilinear operator and a variable convex set,
which is characterized by a constraint on the absolute value of the gradient
that depends on the solution itself. The only required assumption on the
nonlinearity of this constraint is its continuity and positivity. The method
relies on an appropriate parabolic regularization and suitable {\em a priori}
estimates. We obtain also the existence of stationary solutions, by studying
the asymptotic behaviour in time. In the variational case, corresponding to a
constraint independent of the solution, we also give uniqueness results
Regulation of nuclear mechanics and the impact on DNA damage
In eukaryotic cells, the nucleus houses the genomic material of the cell. The physical properties of the nucleus and its ability to sense external mechanical cues are tightly linked to the regulation of cellular events, such as gene expression. Nuclear mechanics and morphology are altered in many diseases such as cancer and premature ageing syndromes. Therefore, it is important to understand how different components contribute to nuclear processes, organisation and mechanics, and how they are misregulated in disease. Although, over the years, studies have focused on the nuclear lamina—a mesh of intermediate filament proteins residing between the chromatin and the nuclear membrane—there is growing evidence that chromatin structure and factors that regulate chromatin organisation are essential contributors to the physical properties of the nucleus. Here, we review the main structural components that contribute to the mechanical properties of the nucleus, with particular emphasis on chromatin structure. We also provide an example of how nuclear stiffness can both impact and be affected by cellular processes such as DNA damage and repair
Role Of Disorder In The Conduction Mechanism In Polyanilines
We present the first theoretical calculations of the electronic structure of long (200 rings) linear chains of polyaniline, ranging in composition from leucoemeraldine to emeraldine, allowing for compositional disorder in that the sequence of quinoid-benzenoid groups is random. We show that random protonation of the disordered polymers may induce p-type conductivity: This process pulls the Fermi energy down into the valence band, past localized band tails, to extended states. The effect is only seen if disorder is taken into account. © 1989 The American Physical Society.63778678
Parameter estimation of a pulp digester model with derivative-free optimization strategies
The work concerns the parameter estimation in the context of the mechanistic modelling of a pulp digester. The problem is cast as a box bounded nonlinear global optimization problem in order to minimize the mismatch between the model outputs with the experimental data observed at a real pulp and paper plant. MCSFilter and Simulated Annealing global optimization methods were used to solve the optimization problem. While the former took longer to converge to the global minimum, the latter terminated faster at a significantly higher value of the objective function and, thus, failed to find the global solution.info:eu-repo/semantics/publishedVersio
Combining landscape fire simulations with stand-level growth simulations to assist landowners in building wildfire-resilient landscapes
The wildfire regime in Portugal has been responsible for millions of hectares of burnt
area, and Alvares parish is no exception. In 2017, a severe wildfire burnt 60% of its area. Land
abandonment has been increasing since the mid 20th century, and a large fraction of the forest area
belongs to quasi-absent landowners. This has given rise to large, almost unbroken expanses of
undermanaged forests that, in combination with rugged topography, originates a landscape prone to
large, intense wildfires. Thus, a change in landscape composition and structure capable of reducing
flammability and promoting fuel discontinuity is urgently needed. A fire spread simulator and a
forest growth simulator were combined to show the impact of improving management at landscape
level. It was assumed that the probability of large wildfires may be reduced by setting aside forest
area for the implementation of a fuel break network (FBN) and increasing the area under sustainable
forest management. Three levels of management intensity were simulated by restricting the area of
Quasi-absent non-industrial owners to 34.5%, 20.1%, and 8.5% of the Alvares forest area, in favor
of increasing the area of active and semi-active non-industrial owners (current, moderate, and high
management scenarios). Different FBN extents, representing four levels of network implementation
priority were combined with the management levels, resulting in 12 scenarios. To evaluate the impact
of fire, simulations assuming no-fire, no-FBN, and current management intensity were performed,
whereas the impact of operation costs was assessed assuming reduced costs for silvicultural operations.
Per hectare simulations were then scaled up to the parish level and volume harvested and net
present values were used to compare the management improvement scenarios. Results showed that
fire has major repercussions on forest income, but these impacts can be minimized. Intensifying forest
management and implementing the first priority FBN segments originated substantial improvements
in financial outcome from timber production, close to those obtained for the full FBN implementation.
Results also evidenced contrasting contributions from industrial and non-industrial owners with the
later evidencing unbalanced cash-flows derailing the possibility for interesting forest incomes. The
coupling of fire and forest growth simulations can be an interesting approach to assess the impact of
different management and policy scenarios and inform policiesinfo:eu-repo/semantics/publishedVersio
A fragilidade da população idosa
O desenvolvimento populacional de idosos contribuindo para o aumento de sua vulnerabilidade, decorrente do avanço da idade. Esta revisão relacionou idosos em Instituições de Longa Permanência para Idosos (ILPIs) e com alto índice de depressão, em razão de que essas doenças prejudicam sua qualidade de vida, tornando-os mais vulneráveis a essas situações, por se sentirem totalmente incapazes de enfrentá-las. Sendo assim, esse trabalho tem como objetivo reforçar a importância de profissionais da saúde capacitados para lidar com esses idosos, para que não haja uma piora no quadro clínico ou que leve a óbito por conta dessas doenças
Inflation and the Scale Dependent Spectral Index: Prospects and Strategies
We consider the running of the spectral index as a probe of both inflation
itself, and of the overall evolution of the very early universe. Surveying a
collection of simple single field inflationary models, we confirm that the
magnitude of the running is relatively consistent, unlike the tensor amplitude,
which varies by orders of magnitude. Given this target, we confirm that the
running is potentially detectable by future large scale structure or 21 cm
observations, but that only the most futuristic measurements can distinguish
between these models on the basis of their running. For any specified
inflationary scenario, the combination of the running index and unknown
post-inflationary expansion history induces a theoretical uncertainty in the
predicted value of the spectral index. This effect can easily dominate the
statistical uncertainty with which Planck and its successors are expected to
measure the spectral index. More positively, upcoming cosmological experiments
thus provide an intriguing probe of physics between TeV and GUT scales by
constraining the reheating history associated with any specified inflationary
model, opening a window into the "primordial dark age" that follows the end of
inflation.Comment: 32 pages. v2 and v3 Minor reference updates /clarification
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