Lasing in Single Cadmium Sulfide Nanowire Optical Cavities

The mechanism of lasing in single cadmium sulfide (CdS) nanowire cavities was elucidated by temperature-dependent and time-resolved photoluminescence (PL) measurements. Temperature-dependent PL studies reveal rich spectral features and show that an exciton-exciton interaction is critical to lasing up to 75 K, while an exciton-phonon process dominates at higher temperatures. These measurements together with temperature and intensity dependent life-time and threshold studies suggest that lasing is due to formation of excitons, and moreover, have implications for the design of efficient, low-threshold nanowire lasers.Comment: 4 figure

Pion production in high energy cosmic ray collisions

Calculations on pion energy and angle distribution in center of hydrodynamic inelastic model for nucleon-nucleon collisio

630-mV open circuit voltage, 12% efficient n-Si liquid junction

We report the first experimental observation of a semiconductor/liquid junction whose open circuit voltage Voc is controlled by bulk diffusion/recombination processes. Variation in temperature, minority-carrier diffusion length, and/or in majority-carrier concentration produces changes in the Voc of the n-Si/CH3OH interface in accord with bulk recombination/diffusion theory. Under AM2 irradiation conditions, the extrapolated intercept at 0 K of Voc vs T plots yields activation energies for the dominant recombination process of 1.1–1.2 eV, in accord with the 1.12-eV band gap of Si. A crucial factor in achieving optimum performance of the n-Si/CH3OH interface is assigned to photoelectrochemical oxide formation, which passivates surface recombination sites at the n-Si/CH3OH interface and minimizes deleterious effects of pinning of the Fermi level at the Si/CH3OH junction. Controlled Si oxide growth, combined with optimization of bulk crystal parameters in accord with diffusion theory, is found to yield improved photoelectrode output parameters, with 12.0±1.5% AM2 efficiencies and AM1 Voc values of 632–640 mV for 0.2-Ω cm Si materials

Toward a New Paradigm for the Evolution of Developmental and Growth-Pattern Systems in Plants and Animals

Genetically controlled and environmentally responsive mutation as a significant feature of evolution has very likely occurred on different genomic levels. The evolution of developmental and growth-pattern systems in plants and animals could have occurred through a karyotypic mutator system creating controlled, frequent genomic changes on the karyotypic level in response to environmental stresses, such as temperature changes. Such a mutator system generating controlled karyotypic changes at very high frequency in response to stress was discovered. in the fungus, Aspergillus nidulans, once classified within the plant kingdom. This mutator system is itself representative of a basic, responsive developmental system producing changes in growth-pattern, morphology, and changes ensuing in a new pattern of differentiation, which are adaptive. Such a developmental, karyotypic mutator system may itself have evolved, through its own self-controlled evolution, into types of complex developmental systems that, through controlled, specific, and minute karyotypic changes during ontogeny, could control patterns of development in plants and animals, integrating different levels of organization. The deeper implications for development and evolution are illustrated, suggesting a new paradigm

Plastic deformations in mechanically strained single-walled carbon nanotubes

Antiferromagnetic manipulation was used to controllably stretch individual metallic single-walled carbon nanotubes (SWNT's). We have found that SWNT's can sustain elongations as great as 30% without breaking. Scanned gate microscopy and transport measurements were used to probe the effects of the mechanical strain on the SWNT electronic properties, which revealed a strain-induced increase in intra-tube electronic scattering above a threshold strain of ~5–10 %. These findings are consistent with theoretical calculations predicting the onset of plastic deformation and defect formation in carbon nanotubes

First-principles study of the Young's modulus of Si <001> nanowires

We report the results of first-principles density functional theory calculations of the Young's modulus and other mechanical properties of hydrogen-passivated Si nanowires. The nanowires are taken to have predominantly {100} surfaces, with small {110} facets. The Young's modulus, the equilibrium length and the residual stress of a series of prismatic wires are found to have a size dependence that scales like the surface area to volume ratio for all but the smallest wires. We analyze the physical origin of the size dependence, and compare the results to two existing models.Comment: 5 pages, 3 figure

Statistical inference of the generation probability of T-cell receptors from sequence repertoires

Stochastic rearrangement of germline DNA by VDJ recombination is at the origin of immune system diversity. This process is implemented via a series of stochastic molecular events involving gene choices and random nucleotide insertions between, and deletions from, genes. We use large sequence repertoires of the variable CDR3 region of human CD4+ T-cell receptor beta chains to infer the statistical properties of these basic biochemical events. Since any given CDR3 sequence can be produced in multiple ways, the probability distribution of hidden recombination events cannot be inferred directly from the observed sequences; we therefore develop a maximum likelihood inference method to achieve this end. To separate the properties of the molecular rearrangement mechanism from the effects of selection, we focus on non-productive CDR3 sequences in T-cell DNA. We infer the joint distribution of the various generative events that occur when a new T-cell receptor gene is created. We find a rich picture of correlation (and absence thereof), providing insight into the molecular mechanisms involved. The generative event statistics are consistent between individuals, suggesting a universal biochemical process. Our distribution predicts the generation probability of any specific CDR3 sequence by the primitive recombination process, allowing us to quantify the potential diversity of the T-cell repertoire and to understand why some sequences are shared between individuals. We argue that the use of formal statistical inference methods, of the kind presented in this paper, will be essential for quantitative understanding of the generation and evolution of diversity in the adaptive immune system.Comment: 20 pages, including Appendi

Violences en famille : quelles réponses institutionnelles ?

Si la famille est en général synonyme d'intimité et de relations de confiance, elle peut également être un lieu d'abus, de contrôle ou de violences. Les diverses formes de violences qui se déroulent dans la sphère privée ont été dénoncées dès les années 1970 par les mouvements féministes. Elles ont alors fait l'objet d'une variété de politiques et d'actions publiques ayant pour vocation de défendre et d'accompagner les victimes, de punir et soigner les agresseurs ou de rétablir des liens familiaux distendus. En s'attachant à la façon dont ces violences ont été définies dans des contextes différents, en Europe, en Amérique du Nord et en Amérique latine, cet article a pour ambition de donner à voir les perspectives variées que recouvrent des catégories d'action publique aussi diverses que violences conjugales, violences domestiques, violences intrafamiliales ou encore féminicides ou fémicides, et les conséquences que ces différentes visions du problème ont sur sa prise en charge. Largement influencé par les études genre et la sociologie des problèmes publics, cet article, notamment à travers la présentation des contributions qui composent ce numéro de la revue Enfances Familles Générations, entend questionner les notions de violences de genre dans le cadre familial, dont les frontières sont fluctuantes et investies de façon variée, ainsi que les formes d'institutionnalisation du problème et les solutions qui sont envisagées