400 research outputs found

    Efferent controls in crustacean mechanoreceptors

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    International audienceSince the 1960s it has been known that central neural networks can elaborate motor patterns in the absence of any sensory feedback. However, sensory and neuromodulatory inputs allow the animal to adapt the motor command to the actual mechanical configuration or changing needs. Many studies in invertebrates, particularly in crustacea, have described several mechanisms of sensory-motor integration and have shown that part of this integration was supported by the efferent control of the mechanosensory neurons themselves. In this article, we review the findings that support such an efferent control of mechanosensory neurons in crustacea. Various types of crustacean proprioceptors feeding information about joint movements and strains to central neural networks are considered, together with evidence of efferent controls exerted on their sensory neurons. These efferent controls comprise (1) the neurohormonal modulation of the coding properties of sensory neurons by bioamines and peptides; (2) the presynaptic inhibition of sensory neurons by GABA, glutamate and histamine; and (3) the long-term potentiation of sensory-motor synapses by glutamate. Several of these mechanisms can coexist on the same sensory neuron, and the functional significance of such multiple modulations is discussed

    Modulation of Phenol Oxidation in Cofacial Dyads

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    The presentation of two phenols on a xanthene backbone is akin to the tyrosine dyad (Y[subscript 730] and Y[subscript 731]) of ribonucleotide reductase. X-ray crystallography reveals that the two phenol moieties are cofacially disposed at 4.35 Å. Cyclic voltammetry reveals that phenol oxidation is modulated within the dyad, which exhibits a splitting of one-electron waves with the second oxidation of the phenol dyad occurring at larger positive potential than that of a typical phenol. In contrast, a single phenol appended to a xanthene exhibits a two-electron process, consistent with reported oxidation pathways of phenols in acetonitrile. The perturbation of the phenol potential by stacking is reminiscent of a similar effect for guanines stacked within DNA base pairs.National Institutes of Health (U.S.) (GM5R01

    Condições e Obstáculos ao Empreendedorismo no Brasil: Conditions and Barriers to Entrepreneurship in Brazil

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    O presente artigo versa sobre os fatores estruturais, sócio- políticos, culturais, organizacionais e institucionais que suportam as atividades empreendedoras no campo empresarial. Em nosso estudo apresentamos de forma resumida os resultados do estudo Global Entrepreneurship Monitor (GEM), no qual focaremos os resultados obtidos em relação ao Brasil. Deste modo, visamos verificar as condições que afetam o empreendedorismo nacional deste país. Iniciamos nossa reflexão pela apresentação da origem e do significado do ato de empreender, tal qual concebido originalmente pela ciência econômica. Em um segundo momento, expomos alguns dados atuais acerca das características do empreendedorismo brasileiro, para finalmente apresentar o resultado comentado do estudo do GEM-Brasil. Concluímos que embora o Brasil seja um país que tem evoluído em termos de um maior empreendedorismo de oportunidade, como uma conseqüência da expansão econômica que viveu o país nos anos recentes, onde o empreendedorismo de necessidade começa a dar lugar a uma classe empresarial mais bem preparada e escolarizada; este setor ainda carece de maiores aportes em termos de educação e capacitação, bem como maiores investimentos em P&D, o que significaria a alavancagem necessária a empreendimentos inovadores com grande potencial de internacionalização, haja vista as novas redes de relações internacionais estabelecidas nas últimas décadas, na qual se inclui a CPLP

    High-resolution near-IR Spectral mapping with H2_{2} and [Fe II] lines of Multiple Outflows around LkHα\alpha 234

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    We present a high-resolution, near-IR spectroscopic study of multiple outflows in the LkHα\alpha 234 star formation region using the Immersion GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted emission of HH 167 allowed us to distinguish at least three separate, spatially overlapped, outflows in H2{_2} and [Fe II] emission. We show that the H2{_2} emission represents not a single jet, but complex multiple outflows driven by three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted H2{_2} outflow at a low velocity, \VLSR << ++50 {\kms}, with respect to the systemic velocity of \VLSR == -11.5 {\kms}, that coincides with the H2{_2}O masers seen in earlier radio observations two arcseconds southwest of VLA 2. We found that the previously detected [Fe II] jet with |\VLSR| >> 100 {\kms} driven by VLA 3B is also detected in H2{_2} emission, and confirm that this jet has a position angle about 240°\degree. Spectra of the redshifted knots at 14\arcsec-65\arcsec northeast of LkHα\alpha 234 are presented for the first time. These spectra also provide clues to the existence of multiple outflows. We detected high-velocity (50-120 {\kms}) H2{_2} gas in the multiple outflows around LkHα\alpha 234. Since these gases move at speeds well over the dissociation velocity (>> 40 {\kms}), the emission must originate from the jet itself rather than H2{_2} gas in the ambient medium. Also, position-velocity diagrams and excitation diagram indicate that emission from knot C in HH 167 come from two different phenomena, shocks and photodissociation.Comment: 32 pages, 12 figures, 2 tables, Accepted for publication in the Astrophysical Journa
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