Dynamics of the polar aurora

Scientific conference (2012)

Magnetic Properties of Fe2GeMo3N; an Experimental and Computational Study

in Journal of Materials Chemistry (2012), 22

A polycrystalline sample of Fe2GeMo3N has been synthesized by the reductive nitridation of a mixture of binary oxides in a flow of 10% dihydrogen in dinitrogen. The reaction product has been studied by ... [more ▼]

A polycrystalline sample of Fe2GeMo3N has been synthesized by the reductive nitridation of a mixture of binary oxides in a flow of 10% dihydrogen in dinitrogen. The reaction product has been studied by magnetometry, neutron diffraction and M€ossbauer spectroscopy over the temperature range 1.8 # T/K # 700. The electronic properties have been modelled by DFT and Monte Carlo methods. Fe2GeMo3N adopts the cubic h-carbide structure with a ¼ 11.1630(1) at 300 K. The electrical conductivity was found to be 0.9 mU cm over the temperature range 80 # T/K # 300. On cooling below 455 K the compound undergoes a transition to an antiferromagnetic state. The magnetic unit cell contains an antiferromagnetic arrangement of eight ferromagnetic Fe4 tetrahedra; the ordered atomic magnetic moments, 1.90(4) mB per Fe atom at 1.8 K, align along a <111> direction. DFT predicts an ordered moment of 1.831 mB per Fe, albeit with a N eel temperature of >549 K. Monte Carlo calculations confirm that the experimentally determined magnetic structure is the lowest-energy antiferromagnetic structure. These results emphasise the potential of these computational methods in the search for new magnetic materials. [less ▲]

Social Entrepreneurship: Definitions, Drivers and Challenges

in Volkmann, Christine K.; Tokarski, Kim Oliver; Ernst, Kati (Eds.) Social Entrepreneurship and Social Business: An Introduction and Discussion With Case Studies (2012)

Despite widespread acknowledgement that social entrepreneurship and social enterprise remain highly contextual –and, therefore, contestable– notions which can be interpreted in various ways depending on ... [more ▼]

Despite widespread acknowledgement that social entrepreneurship and social enterprise remain highly contextual –and, therefore, contestable– notions which can be interpreted in various ways depending on the ideology and the goals of the institutions championing them (Dart 2004; Dey & Steyaert 2010; Nicholls 2010c), there are common features upon which most scholars and commentators can agree. This chapter aims to capture the essence of what social entrepreneurship is and also of what it is not. The chapter is structured as follows. The following section examines the concept of social entrepreneurship and reviews a number of definitions in order to highlight common features. Then, social entrepreneurship is compared with, and differentiated from, related –but distinctive– concepts. After this, the fourth section looks at the origins and drivers of social entrepreneurship in an historical perspective. Finally, this chapter concludes by suggesting a number of challenges for practice, policy and research in this field. [less ▲]

A mathematical model of adult subventricular neurogenesis.

in Journal of the Royal Society, Interface (2012)

Neurogenesis has been the subject of active research in recent years and many authors have explored the phenomenology of the process, its regulation and its purported purpose. Recent developments in ... [more ▼]

Neurogenesis has been the subject of active research in recent years and many authors have explored the phenomenology of the process, its regulation and its purported purpose. Recent developments in bioluminescent imaging (BLI) allow direct in vivo imaging of neurogenesis, and in order to interpret the experimental results, mathematical models are necessary. This study proposes such a mathematical model that describes adult mammalian neurogenesis occurring in the subventricular zone and the subsequent migration of cells through the rostral migratory stream to the olfactory bulb (OB). This model assumes that a single chemoattractant is responsible for cell migration, secreted both by the OB and in an endocrine fashion by the cells involved in neurogenesis. The solutions to the system of partial differential equations are compared with the physiological rodent process, as previously documented in the literature and quantified through the use of BLI, and a parameter space is described, the corresponding solution to which matches that of the rodent model. A sensitivity analysis shows that this parameter space is stable to perturbation and furthermore that the system as a whole is sloppy. A large number of parameter sets are stochastically generated, and it is found that parameter spaces corresponding to physiologically plausible solutions generally obey constraints similar to the conditions reported in vivo. This further corroborates the model and its underlying assumptions based on the current understanding of the investigated phenomenon. Concomitantly, this leaves room for further quantitative predictions pertinent to the design of future proposed experiments. [less ▲]

Caractérisation des plantations privées de teck (Tectona grandis L.f.) du département de l'Atlantique au Sud-Bénin

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2012), 16(4), 441-451

Teak plantations are an undeniable asset, representing socio-economic and environmental importance in South Benin. Plantation owners see teak as an asset, enabling them to supplement their income through ... [more ▼]

Teak plantations are an undeniable asset, representing socio-economic and environmental importance in South Benin. Plantation owners see teak as an asset, enabling them to supplement their income through timber production and sales. Sustainable management of teak plantations requires a high level of knowledge and understanding of the resource by plantation owners. The snowball sampling method was used in order to reach private teak plantations owners. This is a chain sampling method, which uses information from the first informant (plantation owner) to trace the others in the sample. Data were collected on the socio-economic status of plantation owners, and on both the geographical location and the size of the plantations. Dendrometrical parameters were measured through strip sampling. Factor analysis followed by hierarchical classification and stepwise discriminant analysis were performed in order to build a profile of the owners. We have identified 2,431 owners and 2,624 plantations. Young plantations (up to 5 years old) represent 16.4% of the total plantation area, high forests 12.7% and coppices 70.9%. Overall, these plantations were small in size (average = 0.44 ha). The number of trees per ha was found to be high, regardless of the forest system (respectively 3,371 trees/ha for young plantations, 3006 trees/ha for high forests and 6305 trees/ha for coppice). These high numbers reflect the fact that the trees represent farm-grown timber. Four groups of owners were distinguished: smallholder farmers seeking income (group 1), small city dweller planters and those motivated by securing their properties (group 2), city dweller planters with medium size plantations (group 3); and owners with large-scale plantations (group 4). All groups were willing to secure their land or be involved in the timber trade. The specific characteristics of each group need to be taken into account in considering the sustainable management of private teak plantations in South Benin. [less ▲]

A Bayesian approach for modeling origin–destination matrices

in Transportation Research. Part A : Policy & Practice (2012), 46(1), 200212

The majority of origin destination (OD) matrix estimation methods focus on situations where weak or partial information, derived from sample travel surveys, is available. Information derived from travel ... [more ▼]

The majority of origin destination (OD) matrix estimation methods focus on situations where weak or partial information, derived from sample travel surveys, is available. Information derived from travel census studies, in contrast, covers the entire population of a specific study area of interest. In such cases where reliable historical data exist, statistical methodology may serve as a flexible alternative to traditional travel demand models by incorporating estimation of trip-generation, trip-attraction and trip-distribution in one model. In this research, a statistical Bayesian approach on OD matrix estimation is presented, where modeling of OD flows derived from census data, is related only to a set of general explanatory variables. A Poisson and a negative binomial model are formulated in detail, while emphasis is placed on the hierarchical Poisson-gamma structure of the latter. Problems related to the absence of closed-form expressions are bypassed with the use of a Markov Chain Monte Carlo method known as the Metropolis–Hastings algorithm. The methodology is tested on a realistic application area concerning the Belgian region of Flanders on the level of municipalities. Model comparison indicates that negative binomial likelihood is a more suitable distributional assumption than Poisson likelihood, due to the great degree of overdispersion present in OD flows. Finally, several predictive goodness-of-fit tests on the negative binomial model suggest a good overall fit to the data. In general, Bayesian methodology reduces the overall uncertainty of the estimates by delivering posterior distributions for the parameters of scientific interest as well as predictive distributions for future OD flows. [less ▲]

Quel(s) futur(s) pour la Forêt de Soignes ? Adéquation des essences à leurs stations face aux changements climatiques

in Soignes - Bulletin trimestriel des Amis de la Forêt de Soignes (2012), (n° spécial), 80-85

Het Zoniënwoud straalt ongereptheid uit, heeft een respectabele ouderdom en staat op een moeilijke ondergrond : deze factoren geven de statige beukenkathedraal iets kwetsbaars. Het bos lijdt onder de wind ... [more ▼]

Het Zoniënwoud straalt ongereptheid uit, heeft een respectabele ouderdom en staat op een moeilijke ondergrond : deze factoren geven de statige beukenkathedraal iets kwetsbaars. Het bos lijdt onder de wind en is gevoelig voor hitte en droogte. Het evenwicht met zijn omgeving wordt hierdoor steeds wankeler en de bedreiging door de klimaatverandering gaat zwaarder wegen. Deze objectieve vaststelling kan verschillende reacties uitlokken : keuze voor een veel dynamischere bosbouw naargelang van de verjongingen, geleidelijke verrijking van het bos met soorten die beter gedijen in de toekomstige omstandigheden, zoals de wintereik, of evolutie naar een gemengd en ongelijkvormig hooghout dat beter bestand is tegen verstoring en dat het aanzicht van het Zoniënwoud drastisch zou wijzigen. De liefde voor de beukenkathedraal mag dan wel sterker zijn dan de rede, het is in elk geval nodig de aanplanting van beuken voor een tiental jaar op te schorten, minstens tot er meer zekerheid is over de wetenschappelijke voorspellingen. [less ▲]

Toujours pas facile de faire des vieux os

in Tempo Médical (2012), 348

Cost-effectiveness of Bazedoxifene compared with Raloxifene in the treatment of postmenopausal osteoporotic women

in Arthritis and Rheumatism (2012), 64(S10), 834

Discovery of a Mississippian Reef in Turkey: The Upper Viséan Microbial-Sponge-Bryozoan-Coral Bioherm from Kongul Yayla (Taurides, S Turkey)

in Turkish Journal of Earth Sciences (2012), 21(3), 375-389