333 research outputs found
On the uneven distribution of the Copelata of the Fernando de Noronha area
Durante uma viagem à ilha Fernando de Noronha em Janeiro de 1954, a Dra. M. Vannucci e o Dr. E. F. Nonato coletaram amostras de plancton em várias estações ao norte e ao sul da ilha. A tabela 1 mostra o número das estações, sua posição geográfica, outros dados tais como salinidade, hora de coleta, profundidade local e da coleta, tipos de redes usados, etc, assim como o número e a porcentagem de cada espécie de Gopelata encontrada em cada amostra. Comparando a população de Copelatá capturada ao norte e ao sul da ilha verificou-se que havia uma diferença bem marcada nas porcentagens das diferentes espécies por amostra, e que as águas do sul e do norte da ilha mostraram um quadro diferente de freqüências (Fig. 1) assim como foi diferente de cada lado da ilha a porcentagem das Famílias Oikopleuridae e Fritillaridae. Estas predominaram ao sul enquanto aquelas predominaram ao norte da ilha. Para estes fatos existem duas explicações possíveis: - ou a ilha funcionou como obstáculo às águas da Corrente Sul Equatorial provocando no seu lado noroeste uma subida de água das camadas inferiores e modificando assim as condições hidrológicas características da região, ou as diferenças observadas de amostra para amostra (Fig. 2) foram devidas não a diferenças hidrológicas, mas, sim a diferentes "nuvens" de Gopelata que ocorreram ao norte e ao sul da ilha, durante a época em que foi feita a coleta. H. longicauda mostrou ligeiro acréscimo na porcentagem relativa às outras espécies, quando coletada com rede pelágica (A) na superfície, quando comparada com as porcentagens em que ocorre em amostras coletadas por outras redes em profundidades maiores. A ocorrência de espécies neríticas (O. dioica e F. abjörnseni) nas estações mais próximas da costa (2 e 7) ambas situadas sobre a plataforma insular, não vem confirmar a idéia de Lohmann (1896, p. 109) de que haja influência da costa brasileira sobre a ilha, pois a intensidade da corrente Sul Equatorial nessa região em direção NW torná-la-ia muito improvável, e sim confirma a teoria de Ekman (1953, p. 313) de que as pequenas ilhas oceânicas agem como costas. As estações ao norte da ilha mostraram como população de Gopelata característica nestas amostras, em porcentagem decrescente as espécies O. fusiformis, F. borealis; e S. longicauda ou vice-versa, F. pellucida, e F. formica e S. magnum ou vice-versa; as do sul da ilha, freqüências elevadas de F. borealis, H. longicauda e porcentagens menores de O. fusiformis, F. pellucida e F. formica
On the uneven distribution of the Copelata of the alcatrazes area
Neste trabalho são estudados os Copelata coletados durante a viagem do "Igaraty" à Ilha de Alcatrazes. A lista das estações, sua localização, as datas e outros dados sobre as águas da área pesquisada, assim como o número e a porcentagem de ocorrência de cada espécie em cada amostra estão na Tabela 1. Todas as coletas foram feitas com uma rede "standard" (Sverdrup et al - 1954, p. 379, fig. 91-d). Comparando os dados hidrográficos, fornecidos por informação pessoal do Dr. I. Emílsson, com os nossos, podemos concluir que, nestas amostras, as águas vindas do norte (vide estações 6, 7 e 9) são caracterizadas pela presença de O. rufescens em grande abundância; as águas costeiras, pela presença de F. pellucida (vide estações 1, 10 e 11) e as águas misturadas (vide estações 5 e 8, Tabela 1 e Figura 1) são caracterizadas pela ocorrência de II. longicauda, O. fusiformis e F. pellucida em freqüências elevadas. Houve ocorrência ainda de "nuvens" de F. haplostoma na estação 10, fato comum em águas costeiras e superficiais do Japão (Tokioka, 1951 e 1955). A influência da termoclina observada nas estações 5 e 9 não foi considerada significativa pois foi pequena a quantidade de água atravessada pela rede abaixo dela, em comparação com a grande quantidade ocorrida acima da mesma. O aparecimento de Tectillaria fertilis aumenta o limite sul de distribuição desta espécie no Atlântico, pois era conhecida apenas nas correntes quentes do hemisfério norte deste oceano (Lohmann, 1896, p. 30)
Native NIR-emitting single colour centres in CVD diamond
Single-photon sources are a fundamental element for developing quantum
technologies, and sources based on colour centres in diamonds are among the
most promising candidates. The well-known NV centres are characterized by
several limitations, thus few other defects have recently been considered. In
the present work, we characterize in detail native efficient single colour
centres emitting in the near infra-red in both standard IIa single-crystal and
electronic-grade polycrystalline commercial CVD diamond samples. In the former
case, a high-temperature annealing process in vacuum is necessary to induce the
formation/activation of luminescent centres with good emission properties,
while in the latter case the annealing process has marginal beneficial effects
on the number and performances of native centres in commercially available
samples. Although displaying significant variability in several photo physical
properties (emission wavelength, emission rate instabilities, saturation
behaviours), these centres generally display appealing photophysical properties
for applications as single photon sources: short lifetimes, high emission rates
and strongly polarized light. The native centres are tentatively attributed to
impurities incorporated in the diamond crystal during the CVD growth of
high-quality type IIa samples, and offer promising perspectives in
diamond-based photonics.Comment: 27 pages, 10 figures. Submitted to "New Journal of Phsyics",
NJP-100003.R
Nanodiamonds-induced effects on neuronal firing of mouse hippocampal microcircuits
Fluorescent nanodiamonds (FND) are carbon-based nanomaterials that can
efficiently incorporate optically active photoluminescent centers such as the
nitrogen-vacancy complex, thus making them promising candidates as optical
biolabels and drug-delivery agents. FNDs exhibit bright fluorescence without
photobleaching combined with high uptake rate and low cytotoxicity. Focusing on
FNDs interference with neuronal function, here we examined their effect on
cultured hippocampal neurons, monitoring the whole network development as well
as the electrophysiological properties of single neurons. We observed that FNDs
drastically decreased the frequency of inhibitory (from 1.81 Hz to 0.86 Hz) and
excitatory (from 1.61 Hz to 0.68 Hz) miniature postsynaptic currents, and
consistently reduced action potential (AP) firing frequency (by 36%), as
measured by microelectrode arrays. On the contrary, bursts synchronization was
preserved, as well as the amplitude of spontaneous inhibitory and excitatory
events. Current-clamp recordings revealed that the ratio of neurons responding
with AP trains of high-frequency (fast-spiking) versus neurons responding with
trains of low-frequency (slow-spiking) was unaltered, suggesting that FNDs
exerted a comparable action on neuronal subpopulations. At the single cell
level, rapid onset of the somatic AP ("kink") was drastically reduced in
FND-treated neurons, suggesting a reduced contribution of axonal and dendritic
components while preserving neuronal excitability.Comment: 34 pages, 9 figure
High chromosomal variation in wild horn fly Haematobiairritans (Linnaeus) (Diptera, Muscidae) populations
The horn fly, Haematobiairritans is an obligate haematophagous cosmopolitan insect pest. The first reports of attacks on livestock by Haematobiairritans in Argentina and Uruguay occurred in 1991, and since 1993 it is considered an economically important pest. Knowledge on the genetic characteristics of the horn fly increases our understanding of the phenotypes resistant to insecticides that repeatedly develop in these insects. The karyotype of Haematobiairritans, as previously described using flies from an inbred colony, shows a chromosome complement of 2n=10 without heterochromosomes (sex chromosomes). In this study, we analyze for the first time the chromosome structure and variation of four wild populations of Haematobiairritans recently established in the Southern Cone of South America, collected in Argentina and Uruguay. In these wild type populations, we confirmed and characterized the previously published "standard" karyotype of 2n=10 without sex chromosomes; however, surprisingly a supernumerary element, called B-chromosome, was found in about half of mitotic preparations. The existence of statistically significant karyotypic diversity was demonstrated through the application of orcein staining, C-banding and H-banding. This study represents the first discovery and characterization of horn fly karyotypes with 2n=11 (2n=10+B). All spermatocytes analyzed showed 5 chromosome bivalents, and therefore, 2n=10 without an extra chromosome. Study of mitotic divisions showed that some chromosomal rearrangements affecting karyotype structure are maintained as polymorphisms, and multiple correspondence analyses demonstrated that genetic variation was not associated with geographic distribution. Because it was never observed during male meiosis, we hypothesize that B-chromosome is preferentially transmitted by females and that it might be related to sex determination.Fil: Forneris, Natalia Soledad. Universidad de Buenos Aires. Facultad de Agronomia; ArgentinaFil: Otero, Gabriel. Universidad de Buenos Aires. Facultad de Agronomia; ArgentinaFil: Pereyra, Ana. Universidad de Buenos Aires. Facultad de Agronomia; ArgentinaFil: Repetto, Gustavo. Universidad de Buenos Aires. Facultad de Agronomia; ArgentinaFil: Rabossi, Alejandro. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Quesada Allue, Luis Alberto. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Basso, Alicia L.. Universidad de Buenos Aires. Facultad de Agronomia; Argentin
Development and characterization of a diamond-insulated graphitic multi electrode array realized with ion beam lithography
The detection of quantal exocytic events from neurons and neuroendocrine cells is a challenging task in neuroscience. One of the most promising platforms for the development of a new generation of biosensors is diamond, due to its biocompatibility, transparency and chemical inertness. Moreover, the electrical properties of diamond can be turned from a perfect insulator into a conductive material (resistivity ~mΩ·cm) by exploiting the metastable nature of this allotropic form of carbon. A 16‑channels MEA (Multi Electrode Array) suitable for cell culture growing has been fabricated by means of ion implantation. A focused 1.2 MeV He+ beam was scanned on a IIa single-crystal diamond sample (4.5 × 4.5 × 0.5 mm3) to cause highly damaged sub-superficial structures that were defined with micrometric spatial resolution. After implantation, the sample was annealed. This process provides the conversion of the sub-superficial highly damaged regions to a graphitic phase embedded in a highly insulating diamond matrix. Thanks to a three-dimensional masking technique, the endpoints of the sub-superficial channels emerge in contact with the sample surface, therefore being available as sensing electrodes. Cyclic voltammetry and amperometry measurements of solutions with increasing concentrations of adrenaline were performed to characterize the biosensor sensitivity. The reported results demonstrate that this new type of biosensor is suitable for in vitro detection of catecholamine release
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