Accommodation of the misfit strain energy in the BaO(100)/MgO(100) heteroepitaxial ceramic interface using computer simulation techniques

Static atomistic simulation techniques have been employed to investigate the accommodation of the misfit strain energy in the BaO(100)/MgO(100) interface. The materials return to their natural (bulk) lattice parameters a few planes from the interface, while maintaining expanded or contracted lattice parameters at the interface to ensure charge matching of counter ions. BaO also forms three-dimensional islands when grown on MgO(100), in accordance with molecular beam epitaxy results. This behaviour is attributed to the instability of a monatomic BaO layer on MgO compared with a BaO bilayer

Explaining international variations in self-employment : Evidence from a panel of OECD countries

Organisation for Economic Cooperation and Development (OECD) data from 1972 to 1996 reveals substantial differences in the levels and trends of self-employment rates across countries. This article uses recently developed panel integration and cointegration techniques to explore the determinants of aggregate self-employment rates. We find that within the panel, self-employment rates are positively and significantly related to personal income tax rates and negatively and significantly related to the unemployment benefit replacement rate. This accords a central role to government tax and transfer policies, in contrast to nonrobust influences from macroeconomic variables, which have been widely used in previous studies

Nanostructuring of β-MnO₂:The important role of surface to bulk ion migration

Manganese oxide materials are attracting considerable interest for clean energy storage applications such as rechargeable Li ion and Li-air batteries and electrochemical capacitors. The electrochemical behavior of nanostructured mesoporous beta-MnO, is in sharp constrast to the bulk crystalline system, which can intercalate little or no lithium; this is not fully understood on the atomic scale. Here, the electrochemical properties of beta-MnO2 are investigated using density functional theory with Hubbard U corrections (DFT+U). We find good agreement between the measured experimental voltage, 3.0 V, and our calculated value of 32 V. We consider the pathways for lithium migration and find a small barrier of 0.17 eV for bulk beta-MnO2, which is likely to contribute to its good performance as a lithium intercalation cathode in the mesoporous form. However, by explicit calculation of surface to bulk ion migration, we find a higher barrier of &gt;0.6 eV for lithium insertion at the (101) surface that dominates the equilibrium morphology. This is likely to limit the practical use of bulk samples, and demonstrates the quantitative importance of surface to bulk ion migration in Li ion cathodes and supercapacitors. On the basis of the calculation of the electrostatic potential near the surface, we propose an efficient method to screen systems for the importance of surface migration effects. Such insight is valuable for the future optimization of manganese oxide nanomaterials for energy storage devices.</p

Timescales of IP(3)-evoked Ca(2+) spikes emerge from Ca(2+) puffs only at the cellular level

The behavior of biological systems is determined by the properties of their component molecules, but the interactions are usually too complex to understand fully how molecular behavior generates cellular behavior. Ca(2+) signaling by inositol trisphosphate receptors (IP(3)R) offers an opportunity to understand this relationship because the cellular behavior is defined largely by Ca(2+)-mediated interactions between IP(3)R. Ca(2+) released by a cluster of IP(3)R (giving a local Ca(2+) puff) diffuses and ignites the behavior of neighboring clusters (to give repetitive global Ca(2+) spikes). We use total internal reflection fluorescence microscopy of two mammalian cell lines to define the temporal relationships between Ca(2+) puffs (interpuff intervals, IPI) and Ca(2+) spikes (interspike intervals) evoked by flash photolysis of caged IP(3). We find that IPI are much shorter than interspike intervals, that puff activity is stochastic with a recovery time that is much shorter than the refractory period of the cell, and that IPI are not periodic. We conclude that Ca(2+) spikes do not arise from oscillatory dynamics of IP(3)R clusters, but that repetitive Ca(2+) spiking with its longer timescales is an emergent property of the dynamics of the whole cluster array

Understanding Collaboration: Introducing the Collaborative Governance Case Databank

Studying collaborative governance has become a booming business. However, the empirical literature still struggles to produce robust generalizations and cumulative knowledge that link contextual, situational and institutional design factors to processes and outcomes. We still have not mustered the broad and deep evidence base that will really help us sort fact from fiction and identify more and less productive approaches to collaboration. The current empirical evidence in the study of collaborative governance consists chiefly of small-N case studies or large-N surveys. The challenge is to move from case-based, mid-range theory building to more large N-driven systematic theory-testing, while also retaining the rich contextual and process insights that only small-N studies tend to yield. This article, and the articles in the accompanying special issue, introduces an attempt to provide this middle ground – the Collaborative Governance Case Database. The database has been developed to serve as a free common pool resource for researchers to systematically collect and compare high-quality collaborative governance case studies. This article is an introduction to the database, exploring its design, opportunities and limitations. This article is also an invitation; inviting all researchers to freely use the cases in the database for their own research interest and to help strengthening the database by adding new cases there are eager to share with colleagues