Energy dependence of non-local potentials

Recently a variety of studies have shown the importance of including non-locality in the description of reactions. The goal of this work is to revisit the phenomenological approach to determining non-local optical potentials from elastic scattering. We perform a $\chi^2$ analysis of neutron elastic scattering data off $^{40}$Ca, $^{90}$Zr and $^{208}$Pb at energies $E \approx 5-40$ MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local form for the optical potential. We introduce energy and asymmetry dependencies in the imaginary part of the potential and refit the data to obtain a global parameterization. Independently of the starting point in the minimization procedure, an energy dependence in the imaginary depth is required for a good description of the data across the included energy range. We present two parameterizations, both of which represent an improvement over the original potentials for the fitted nuclei as well as for other nuclei not included in our fit. Our results show that, even when including the standard Gaussian non-locality in optical potentials, a significant energy dependence is required to describe elastic-scattering data.Comment: 6 pages, 3 figures, accepted by Phys. Rev. C Rapid Communicatio

Oxygen vacancies at the origin of pinned moments in oxide interfaces: the example of tetragonal CuO/SrTiO3_3

Obtaining an accurate theoretical description of the emergent phenomena in oxide heterostructures is a major challenge. Recently, intriguing paramagnetic spin and pinned orbital moments have been discovered by x-ray magnetic circular dichro\"ism measurements at the Cu $L_{2,3}$-edge of a tetragonal CuO/SrTiO$_3$ heterostructure. Using first principles calculations, we propose a scenario that explains both types of moments, based on the formation of oxygen vacancies in the TiO$_2$ interface layer. We show the emergence of a paramagnetic 2D electron gas hosted in the interface CuO layer. It is invisible at the Ti $L_{2,3}$-edge since the valence of the Ti atoms remains unchanged. Strong structural distortions breaking both the local and global fourfold rotation $C_4$ symmetries at the interface lead to the in-plane pinning of the Cu orbital moment close to the vacancy. Our results, and in particular the pinning of the orbital moment, may have implications for other systems, especially monoxide/dioxide interfaces with similar metal-oxygen bond length and weak spin-orbit coupling.Comment: 11 pages, 9 figure

Informal Entrepreneurship: An Integrative Review and Future Research Agenda

Informal entrepreneurship (IE) has received increased recognition because of its theoreticaldistinctiveness and practical relevance. However, the burgeoning literature on IE is difficult tonavigate, due to its rapid growth across different disciplines. Through an integrative review, weintroduce a novel typology of informal entrepreneurs that captures their heterogeneity acrossvarious contexts. We point out a dynamic perspective of IE, consisting of three pathways—thereactive formalizing, theproactive formalizing, and theinformalizing pathways—along which informalentrepreneurs move, acquiring or foregoing regulative legitimacy. Our review extends the theoryon IE, outlines promising research avenues, and suggests relevant practical implications

Hybrid Organizations: Origins, Strategies, Impacts, and Implications

This introduction to the special issue on hybrid organizations defines hybrids, places them in their historical context, and introduces the articles that examine the strategies hybrids undertake to scale and grow, the impacts for which they strive, and the reception to them by mainstream firms. It aggregates insights from the articles in this special issue in order to examine what hybrid organizations mean for firms and practicing managers as they continue to grow in number and assume a variety of missions in developing and developed countries

Hybrid Organizations: Origins, Strategies, Impacts, and Implications

This introduction to the special issue on hybrid organizations defines hybrids, places them in their historical context, and introduces the articles that examine the strategies hybrids undertake to scale and grow, the impacts for which they strive, and the reception to them by mainstream firms. It aggregates insights from the articles in this special issue in order to examine what hybrid organizations mean for firms and practicing managers as they continue to grow in number and assume a variety of missions in developing and developed countries

Phacelia (Phacelia tanacetifolia Benth.) affects soil structure differently depending on soil texture

Aims: We studied the effects of Phacelia tanacetifolia, increasingly used as a cover-crop species in arable agricultural systems, upon soil structural properties in the context of two contrasting soil textures. We hypothesised there would be differential effects of the plants upon soil structure contingent on the texture. Methods: A sandy-loam and a clay soil were destructured by passing through 2 mm sieves, and planted with Phacelia in a replicated pot experiment, with associated unplanted controls. X-ray Computed Tomography was used to visualise and quantify the soil pore networks in 3D. Results: For the sandy-loam soil, there was no impact of plants upon aggregate size distribution porosity, pore connectivity, and pore surface density decreased in the presence of plants, whereas for the clay, there was a significant increase of aggregates <1000 μm, the porosity was constant, the pore-connectivity decreased, and surface density increased in the presence of plants. Conclusions: Plants can impact the structural genesis of soil depending on its inherent textural characteristics, leading to a differential development of pore architecture in different contexts. These results have implications both from an ecological perspective and in terms of the prescription of plants to remediate or condition soil structure in managed systems

Structuring the Field of Social Entrepreneurship: A Transatlantic Comparative Approach

During recent years, social entrepreneurship has been receiving greater recognition from the public sector, as well as from scholars (Stryjan, 2006; Weerawardena and Sullivan Mort, 2006). Encouraging social initiatives has been on our governments' agenda for a while. European policy makers claim the importance of social enterprises as 'they not only are significant economic actors, but also play a key role in involving citizens more fully in Society and in the creation and reproduction of social capital, by organizing, for example, opportunities for volunteering' (European Commission, 2003). Consequently, several European states have created specific legal forms for this kind of initiatives. On the other hand, famous business schools all around the world have created centres for research and education programmes in social entrepreneurship. So far, academic research in social entrepreneurship 'has largely been focused on defining what it is and what it does, and does not, have in common with commercial entrepreneurship' (Nicholls, 2008: 7)

Impact of plants upon soil structural genesis and dynamics

Soils are a fundamental component of terrestrial ecosystems, and support a myriad of functions via interactions between their physical and biological properties, mediated by soil structure. Soil structure is dynamic, and modified by biotic factors including plant roots. The mechanisms involved include enmeshment, exudation and rhizodeposition of C-rich materials, which adhere soil particles and serve as substrate for microbes - which in turn can further structure the soil. The overall aim of this study was to determine the effects of vascular plants upon soil structural genesis. These interactions were determined in different contexts, using aggregate size-distribution profiling and X-ray Computed Tomography to visualise and quantify soil structure in situ. Using long-term field studies (50 y) on a sandy and a clay soil, it was shown that the degree of plant presence in a soil had substantial effects upon its structure. Perennial plants (grassland) significantly increased porosity, pore size diversity and pore connectivity, compared to bare fallow soil which decreased these characteristics. The addition of organic manure to an arable soil had essentially the same effect upon structure as grassland management, revealing the profound effect of addition of manure upon soil structure. Moreover, an initially bare-fallow soil apparently required at least 10 years since conversion to show a partial recovery of soil structure due to the presence of plants. Further investigation in controlled pot experiments revealed that contrasting soil textures (sandy vs. clayey) induced differential effects of plants upon soil structural genesis, both in terms of aggregate size distribution and in situ soil structural properties. Furthermore, it was found that different plant species growing in the same sandy-loam soil had differing effects on soil structural genesis and microbial community phenotype, relatable to their contrasting root architectures. The key overall conclusion is that plant effects upon soil structure are context dependent, contingent upon the inherent cohesiveness of the soil texture, the plant species involved, and time. The concept of ‘optimal pore-architecture’ was developed from these observations of the differential impact of plants depending on soil texture: plant responses appear to be modulated by the initial state of soil structure and inherent soil properties

Etude des plaques de Peyer de l'intestin du souriceau nouveau-né comme voie possible de pénétration du virus du cancer mammaire de la souris (MMTV)

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