Measurement of the Bending Strength of Vapor-Liquid-Solid Grown Silicon Nanowires

The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor-liquid-solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 μm, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young's modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation. © 2006 American Chemical Society

Distribution of Ophioglossum reticulatum L. in South America. A case of long-distance jump dispersal?

The objective of this exploratory work is to test the hypothesis that South American populations of Ophioglossum reticulatum L. derive from Africa. Spores cross the Atlantic transported by wind and arrive in South America in recurrent migration. Three-dimensional (backward and forward) trajectories of spores between Africa and South America were calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT4). The model showed possible backward trajectories in the low troposphere arriving in South America with probable origin in Northwestern Africa. The results support the hypothesis of long-distance dispersal of the studied species. Including vertical motion in the model runs allowed obtaining valuable and novel information about the migration routes. The trade winds combined with the South American monsoon could be a dispersal vehicle for the disseminules from Northwestern Africa to the eastern slopes of the Andes. As the monsoon is a periodic regional atmospheric circulation pattern, transcontinental migration can be assumed to be a recurring phenomenon that provides genetic exchange and prevents speciation by reproductive isolation. Modelled forward trajectories connect the neotropics with Africa-Madagascar, but they seem to be less effective due to their travelling altitudes. This hypothesis might explain the absence of infraspecific taxa restricted to different geographic locations.Facultad de Ciencias Naturales y Muse

Distribution of Ophioglossum reticulatum L. in South America : A case of long-distance jump dispersal?

Fil: Meza Torres, Esteban I.. Instituto de Botánica del Nordeste. CONICET-UNNE. Corrientes; ArgentinaFil: Cerne, Bibiana. Departamento de Ciencias de la Atmósfera y los Océanos. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Ulke, Ana G.. Departamento de Ciencias de la Atmósfera y los Océanos. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Morbelli, Marta Alicia. Cátedra de Palinología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

The diffusion of calculative and collaborative HRM practices in European firms

The aim of this paper is to trace and explain variations in calculative and collaborative human resource management (HRM) practices between companies and across national borders. Variations and similarities are explained in terms of the convergence and divergence of HRM practices determined by national institutions, and the increasing influence of multinational companies (MNCs). We explore the diffusion of HRM practices in Europe over time, using data sets from two surveys conducted in several European countries in 1995 and 2000. We use institutional explanations for the development of three selected bundles of HRM practices: individual, calculative performance-oriented practices; collective incentive schemes for the alignment of interests; and collaborative practices that seek to enhance the commitment of employees. We found substantial effects of country-specific institutions and of the country of origin of MNCs, which clearly support the institutional duality thesis. Foreign-owned MNCs, especially those that are US-based, appear to moderate country-specific institutional effects on the diffusion of the three HRM bundles