Nonequilibrium Evolution of Correlation Functions: A Canonical Approach

We study nonequilibrium evolution in a self-interacting quantum field theory invariant under space translation only by using a canonical approach based on the recently developed Liouville-von Neumann formalism. The method is first used to obtain the correlation functions both in and beyond the Hartree approximation, for the quantum mechanical analog of the $\phi^{4}$ model. The technique involves representing the Hamiltonian in a Fock basis of annihilation and creation operators. By separating it into a solvable Gaussian part involving quadratic terms and a perturbation of quartic terms, it is possible to find the improved vacuum state to any desired order. The correlation functions for the field theory are then investigated in the Hartree approximation and those beyond the Hartree approximation are obtained by finding the improved vacuum state corrected up to ${\cal O}(\lambda^2)$. These correlation functions take into account next-to-leading and next-to-next-to-leading order effects in the coupling constant. We also use the Heisenberg formalism to obtain the time evolution equations for the equal-time, connected correlation functions beyond the leading order. These equations are derived by including the connected 4-point functions in the hierarchy. The resulting coupled set of equations form a part of infinite hierarchy of coupled equations relating the various connected n-point functions. The connection with other approaches based on the path integral formalism is established and the physical implications of the set of equations are discussed with particular emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with non-equilibrium evolution beyond Hartree approx. based on the LvN formalism, has been adde

Modelling range dynamics under global change: which framework and why?

1. To conserve future biodiversity, a better understanding of the likely effects of climate and land-use change on the geographical distributions of species and the persistence of ecological communities is needed. Recent advances have integrated population dynamic processes into species distribution models (SDMs), to reduce potential biases in predictions and to better reflect the demographic nuances of incremental range shifts. However, there is no clear framework for selecting the most appropriate demographic-based model for a given data set or scientific question. 2. We review the computer-based modelling platforms currently used for the development of either population- or individual-based species range dynamics models. We describe the features and requirements of 20 software platforms commonly used to generate simulations of species ranges and abundances. We classify the platforms according to particular capabilities or features that account for user requirements and constraints, such as (i) ability to simulate simple to complex population dynamics, (ii) organism specificity or (iii) their computational capacities. 3. Using this classification, we develop a protocol for choosing the most appropriate framework for modelling species range dynamics based in data availability and research requirements. We find that the main differences between modelling platforms are related to the way in which they simulate population dynamics, the type of organisms they are able to model and the ecological processes they incorporate. We show that some platforms can be used as generic modelling software to investigate a broad range of ecological questions related to the range dynamics of most species, and how these are likely to change in the future in response to forecast climate and land-use change. We argue that model predictions will be improved by reducing usage to a smaller number of highly flexible freeware platforms. 4. Our approach provides ecologists and conservation biologists with a clear method for selecting the most appropriate software platform that meets their needs when developing SDMs coupled with population-dynamic processes. We argue that informed tool choice will translate to better predictions of species responses to climate and land-use change and improved conservation management.Miguel Lurgi, Barry W. Brook, Frédérik Saltré and Damien A. Fordha

Possibilities and Limitations of Photoactivatable Cytochalasin D for the Spatiotemporal Regulation of Actin Dynamics

The study of the actin cytoskeleton and related cellular processes requires tools to specifically interfere with actin dynamics in living cell cultures, ideally with spatiotemporal control and compatible with real time imaging. A phototriggerable derivative of the actin disruptor Cytochalasin D (CytoD) is described and tested here. It includes a nitroveratryloxycarbonyl (Nvoc) photoremovable protecting group (PPG) at the hydroxyl group at C7 of CytoD. The attachment of the PPG renders Nvoc-CytoD temporarily inactive, and enables light-dosed delivery of the active drug CytoD to living cells. This article presents the full structural and physicochemical characterization, the toxicity analysis. It is complemented with biological tests to show the time scales (seconds) and spatial resolution (cellular level) achievable with a UV source in a regular microscopy setu

Possibilities and Limitations of Photoactivatable Cytochalasin D for the Spatiotemporal Regulation of Actin Dynamics

The study of the actin cytoskeleton and related cellular processes requires tools to specifically interfere with actin dynamics in living cell cultures, ideally with spatiotemporal control and compatible with real time imaging. A phototriggerable derivative of the actin disruptor Cytochalasin D (CytoD) is described and tested here. It includes a nitroveratryloxycarbonyl (Nvoc) photoremovable protecting group (PPG) at the hydroxyl group at C7 of CytoD. The attachment of the PPG renders Nvoc-CytoD temporarily inactive, and enables light-dosed delivery of the active drug CytoD to living cells. This article presents the full structural and physicochemical characterization, the toxicity analysis. It is complemented with biological tests to show the time scales (seconds) and spatial resolution (cellular level) achievable with a UV source in a regular microscopy setup</div