Efficient determination of thermodynamic properties from a single simulation

A method for calculating the density of states of a system directly from its trajectory in phase space is described. As a specific example, the method is applied to the Monte Carlo simulation of a two‐dimensional Ising model. The energy distribution function is calculated from the density of states and the associated Helmholtz free energy per spin is calculated for various system sizes and temperatures and shown to be in excellent agreement with the exact results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69798/2/JCPSA6-99-10-7993-1.pd

Effects of spatial dimensionality and steric interactions on microtubule-motor self-organization

Active networks composed of filaments and motor proteins can self-organize into a variety of architectures. Computer simulations in two or three spatial dimensions and including or omitting steric interactions between filaments can be used to model active networks. Here we examine how these modelling choices affect the state space of network self-organization. We compare the networks generated by different models of a system of dynamic microtubules and microtubule-crosslinking motors. We find that a thin 3D model that includes steric interactions between filaments is the most versatile, capturing a variety of network states observed in recent experiments. In contrast, 2D models either with or without steric interactions which prohibit microtubule crossings can produce some, but not all, observed network states. Our results provide guidelines for the most appropriate choice of model for the study of different network types and elucidate mechanisms of active network organization

Finding the right partners? Examining inequalities in the global investment landscape of hydropower

Clean and affordable energy is crucial to achieve a sustainable future. Despite being controversial, hydropower remains the predominant low-cost and reliable source of energy at global level, as it stabilizes the provision of electricity and it bears the power peaks without losing efficiency. However, hydropower requires huge upfront investments and patient functional capital. Under the Paris Agreement, countries committed to direct financial capital flows towards a low-emission pathway in order to enable the transition. Furthermore, private capital strongly engaged with a transition towards a climate-smart economy. The aim of this work is to study the investment system behind hydropower, investors’ behaviour and the optimal allocation of finance to favour the deployment of capital flows. We use Bloomberg Energy Finance database to track public–private investments over the past century (1903–2020). We use network models to represent the hydropower project financing landscape as a network of co-investments. We find that investors are highly localized, with continental players mostly interacting with counterparts in the same area of the world. Powerful exceptions are international organisations and multilateral banks which coinvest across the globe. They also tend to support low-income and fragile countries, meeting their mandate of sustainable development champions. Multilateral banks and international organisations are the most critical actors in enabling public–private co-investments; they activate partnerships with a wider diversity of investors within the network creating more opportunities for blended finance tools. Our results offer a novel perspective on finance for the energy transition: it challenges the idea that more capital invested is better and calls for a more efficient allocation of the available resources

Multilayer film stability

We apply a linear stability analysis to examine the effect of misfit stress on the interface diffusion controlled morphological stability of multilayer microstructures. The stresses could be the result of misfit strains between the individual film layers and/or between film and substrate. We find that misfit between the layers in the film can destabilize the multilayer structure in cases where the thinner layer is elastically stiffer than the thicker layer. The rate at which these instabilities develop increase with increasing misfit and decreasing interfacial energy. Even when there is no misfit between layers, the misfit between the multilayer film and substrate can destabilize the interfaces. This type of instability occurs whether the thinner layers are stiffer or more compliant than the thicker ones. By appropriate choice of the elastic moduli mismatch between layers and relative layer thicknesses, the presence of an interlayer misfit can suppress the instability caused by the substrate misfit. We present stability diagrams that can be used to design stable, multilayer films using all of the degrees of freedom commonly available in multilayer film deposition. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71112/2/JAPIAU-82-10-4852-1.pd

Manufacturing High-Fidelity Lunar Agglutinate Simulants

The lunar regolith is very different from many naturally occurring material on Earth because it forms in the unique, impact-dominated environment of the lunar surface. Lunar regolith is composed of five basic particle types: mineral fragments, pristine crystalline rock fragments, breccia fragments, glasses of various kinds, and agglutinates (glass-bonded aggregates). Agglutinates are abundant in the lunar regolith, especially in mature regoliths where they can be the dominant component.This presentation will discuss the technical feasibility of manufacturing-simulated agglutinate particles that match many of the unique properties of lunar agglutinates

Secretory vesicles are preferentially targeted to areas of low molecular SNARE density

Intercellular communication is commonly mediated by the regulated fusion, or exocytosis, of vesicles with the cell surface. SNARE (soluble N-ethymaleimide sensitive factor attachment protein receptor) proteins are the catalytic core of the secretory machinery, driving vesicle and plasma membrane merger. Plasma membrane SNAREs (tSNAREs) are proposed to reside in dense clusters containing many molecules, thus providing a concentrated reservoir to promote membrane fusion. However, biophysical experiments suggest that a small number of SNAREs are sufficient to drive a single fusion event. Here we show, using molecular imaging, that the majority of tSNARE molecules are spatially separated from secretory vesicles. Furthermore, the motilities of the individual tSNAREs are constrained in membrane micro-domains, maintaining a non-random molecular distribution and limiting the maximum number of molecules encountered by secretory vesicles. Together our results provide a new model for the molecular mechanism of regulated exocytosis and demonstrate the exquisite organization of the plasma membrane at the level of individual molecular machines

An evaluation of the implementation of Georgia's Pre-k program: Report of the findings from the Georgia Early Childhood Study (2002-03)

After ten years, Georgia continues to lead the nation in providing full day, publicly subsidized Pre-K to four-year-olds whose parents choose to enroll them. In this report, we assess the extent to which differences in the way Pre-K is implemented affect children's development. Do teachers with higher levels of education have more positive impacts on children's development? Do teaching styles make a difference in terms of children's outcomes by the end of kindergarten? Do children taught using certain curricula fare better than those taught using others? Answers to questions such as these can assist Pre-K administrators in refining Georgia's program and inform those in other states who are developing or expanding their prekindergarten programs