A molecular perspective on the limits of life: Enzymes under pressure

From a purely operational standpoint, the existence of microbes that can grow under extreme conditions, or "extremophiles", leads to the question of how the molecules making up these microbes can maintain both their structure and function. While microbes that live under extremes of temperature have been heavily studied, those that live under extremes of pressure have been neglected, in part due to the difficulty of collecting samples and performing experiments under the ambient conditions of the microbe. However, thermodynamic arguments imply that the effects of pressure might lead to different organismal solutions than from the effects of temperature. Observationally, some of these solutions might be in the condensed matter properties of the intracellular milieu in addition to genetic modifications of the macromolecules or repair mechanisms for the macromolecules. Here, the effects of pressure on enzymes, which are proteins essential for the growth and reproduction of an organism, and some adaptations against these effects are reviewed and amplified by the results from molecular dynamics simulations. The aim is to provide biological background for soft matter studies of these systems under pressure.Comment: 16 pages, 8 figure

Quasi-Monte Carlo sparse grid Galerkin finite element methods for linear elasticity equations with uncertainties

We explore a linear inhomogeneous elasticity equation with random Lam\'e parameters. The latter are parameterized by a countably infinite number of terms in separated expansions. The main aim of this work is to estimate expected values (considered as an infinite dimensional integral on the parametric space corresponding to the random coefficients) of linear functionals acting on the solution of the elasticity equation. To achieve this, the expansions of the random parameters are truncated, a high-order quasi-Monte Carlo (QMC) is combined with a sparse grid approach to approximate the high dimensional integral, and a Galerkin finite element method (FEM) is introduced to approximate the solution of the elasticity equation over the physical domain. The error estimates from (1) truncating the infinite expansion, (2) the Galerkin FEM, and (3) the QMC sparse grid quadrature rule are all studied. For this purpose, we show certain required regularity properties of the continuous solution with respect to both the parametric and physical variables. To achieve our theoretical regularity and convergence results, some reasonable assumptions on the expansions of the random coefficients are imposed. Finally, some numerical results are delivered

The Effects of Random and Seasonal Environmental Fluctuations on Optimal Harvesting and Stocking

Abstract. We analyze the harvesting and stocking of a population that is affected by random and seasonal environmental fluctuations. The main novlty comes from having three layers of environmental fluctuations. The first layer is due to the environment switching at random times between different environmental states. This is similar to having sudden environmental changes or catastrophes. The second layer is due to seasonal variation, where there is a significant change in the dynamics between seasons. Finally, the third layer is due to the constant presence of environmental stochasticity|between the seasonal or random regime switches, the species is affected by fluctuations which can be modelled by white noise. This framework is more realistic because it can capture both significant random and deterministic environmental shifts as well as small and frequent uctuations in abiotic factors. Our framework also allows for the price or cost of harvesting to change deterministically and stochastically, something that is more realistic from an economic point of view. The combined effects of seasonal and random fluctuations make it impossible to find the optimal harvesting-stocking strategy analytically. We get around this roadblock by developing rigorous numerical approximations and proving that they converge to the optimal harvesting-stocking strategy. We apply our methods to multiple population models and explore how prices, or costs, and environmental fluctuations in uence the optimal harvesting-stocking strategy. We show that in many situations the optimal way of harvesting and stocking is not of threshold type

Cooling concepts for the CVD diamond Brewster-angle window

The chemical vapor deposition (CVD) diamond Brewster-angle window is a very promising broadband radio-frequency (RF) output window solution for frequency step-tunable high power gyrotrons foreseen in nuclear fusion devices like DEMO. Since gyrotrons operate in the megawatt-class power range, active cooling of the output window during operation is mandatory for long pulse operation. In this paper, different indirect cooling layouts were investigated and compared by finite element method (FEM) thermal and structural analyses. Scenarios with different power and frequency beam were taken into account in the analyses

Cooling concepts for the CVD diamond Brewster-angle window

The chemical vapor deposition (CVD) diamond Brewster-angle window is a very promising broadband radio-frequency (RF) output window solution for frequency step-tunable high power gyrotrons foreseen in nuclear fusion devices like DEMO. Since gyrotrons operate in the megawatt-class power range, active cooling of the output window during operation is mandatory for long pulse operation. In this paper, different indirect cooling layouts were investigated and compared by finite element method (FEM) thermal and structural analyses. Scenarios with different power and frequency beam were taken into account in the analyses

Surface Functionalization by Monolayers of Immobilized Thiophene-based Linear pi-Conjugated Systems

Date du colloque&nbsp;: 10/2008</p