166 research outputs found

    Stenodrepanum bergii Harms

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    Am Rande der Salinas von Catamarca En las orillas de las salinas, cerca del F.C.C.A., 1/2 legua de TotoralejospublishedVersio

    A systematic study of spin-dependent recombination in GaAs1x_{1-x}Nx_x as a function of nitrogen content

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    A systematic study of spin-dependent recombination (SDR) under steady-state optical pumping conditions in dilute nitride semiconductors as a function of nitrogen content is reported. The alloy content is determined by a fit of the photoluminescence (PL) intensity using a Roosbroeck-Shockley relation and verified by a study of the GaN-like LO2_2 phonon peak in a Raman spectroscopy map. PL spectra taken from alloys of the form GaAs1x_{1-x}Nx_x where 0.022<x<0.0360.022 < x < 0.036 exhibit PL intensity increases when switching from a linearly- to a circularly-polarized pump up to a factor of 5 for x=0.022x = 0.022. This work used a 1.39 eV laser with a radius of 0.6 μ\mum. The observed SDR ratio monotonically decreases with increasing xx, reaching 1.5 for x=0.036x = 0.036. Moreover, the excitation power required to obtain maximum SDR systematically increases with increasing xx, varying from 0.6 mW for x=0.022x = 0.022 to 15 mW for x=0.036x = 0.036. These observations are consistent with an increase in the density of electronically active defects with increasing nitrogen content, both those responsible for the SDR as well as other, standard Shockley-Read-Hall (SRH) centers.Comment: 11 pages, 5 figures; work presented at the International Conference on the Physics of Semiconductors, Sydney, 202

    Deep-level structure of the spin-active recombination center in dilute nitrides

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    A Gallium interstitial defect (Gai_{\textrm{i}}) is thought to be responsible for the spectacular spin-dependent recombination (SDR) in GaAs1x_{1-x}Nx_x dilute nitride semiconductors. Current understanding associates this defect with two in-gap levels corresponding to the (+/0) and (++/+) charge-state transitions. Using a spin-sensitive photo-induced current transient spectroscopy, the in-gap electronic structure of a xx = 0.021 alloy is revealed. The (+/0) state lies \approx 0.27 eV below the conduction band edge, and an anomalous, negative activation energy reveals the presence of not one but \textit{two} other states in the gap. The observations are consistent with a (++/+) state \approx 0.19 eV above the valence band edge, and a hitherto ignored, (+++/++) state \approx 25 meV above the valence band edge. These observations can inform efforts to better model the SDR and the Gai_{\textrm{i}} defect's local chemical environment.Comment: 6 pages, 5 figures plus Supplementary Materia

    Injection Drug Use as a Mediator Between Client-perpetrated Abuse and HIV Status Among Female Sex Workers in Two Mexico-US Border Cities

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    We examined relationships between client-perpetrated emotional, physical, and sexual abuse, injection drug use, and HIV-serostatus among 924 female sex workers (FSWs) in Tijuana and Ciudad Juarez, two large Mexico-US border cities. We hypothesized that FSWs’ injection drug use would mediate the relationship between client-perpetrated abuse and HIV-seropositivity. The prevalence of client-perpetrated emotional, physical, and sexual abuse in the past 6 months was 26, 18, and 10% respectively; prevalence of current injection drug use and HIV was 12 and 6%, respectively. Logistic regression analyses revealed that client-perpetrated sexual abuse was significantly associated with HIV-seropositivity and injection drug use, and that injection drug use was positively associated with HIV-seropositivity. Injection drug use partially mediated the relationship between client-perpetrated sexual abuse and HIV-seropositivity. Results suggest the need to address client-perpetrated violence and injection drug use when assessing HIV risk among FSWs

    Sex Differences in the Brain: A Whole Body Perspective

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    Most writing on sexual differentiation of the mammalian brain (including our own) considers just two organs: the gonads and the brain. This perspective, which leaves out all other body parts, misleads us in several ways. First, there is accumulating evidence that all organs are sexually differentiated, and that sex differences in peripheral organs affect the brain. We demonstrate this by reviewing examples involving sex differences in muscles, adipose tissue, the liver, immune system, gut, kidneys, bladder, and placenta that affect the nervous system and behavior. The second consequence of ignoring other organs when considering neural sex differences is that we are likely to miss the fact that some brain sex differences develop to compensate for differences in the internal environment (i.e., because male and female brains operate in different bodies, sex differences are required to make output/function more similar in the two sexes). We also consider evidence that sex differences in sensory systems cause male and female brains to perceive different information about the world; the two sexes are also perceived by the world differently and therefore exposed to differences in experience via treatment by others. Although the topic of sex differences in the brain is often seen as much more emotionally charged than studies of sex differences in other organs, the dichotomy is largely false. By putting the brain firmly back in the body, sex differences in the brain are predictable and can be more completely understood
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