9,609 research outputs found
Filmes finos de WN e ALN e suas aplicações na fabricação de transitores mesfet
No full textOrientador: Peter Jurgen TatschDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: Neste trabalho são caracterizados filmes finos de WN e AlN obtidos por sputtering DC em ambiente de Nitrogênio. Diodos Schottky sobre GaAs são utilizados para caracterizar os filmes de WN. Os diodos são submetidos a tratamentos térmicos visando o estudo da estabilidade térmica dos contatos, ensaiando a fabricação dos transistores MESFET. A caracterização dos diodos é baseada em medidas I-V para a obtenção do fator de idealidade e da altura de barreira Schottky. Os dispositivos estáveis termicamente apresentaram valores de 1,3 e 0,55 eV respectivamente. Os diodos ainda foram submetidos a passivação por plasma. Os filmes de AlN foram caracterizados a partir de capacitores MIS, obtendo-se a constante dielétrica e a densidade de cargas do filme, de 8,7 e 0,9xl011cm-2 respectivamente. Os Fihnes de AlN também foram usados satisfatoriamente como capa para implantação iônica e recozimento, que também é uma etapa de processamento de transistores MESFETAbstract: Tungsten Nitride (WN) and Aluminum Nitride (AlN) thin films were deposited by DC sputtering in Nitrogen ambi~nt and characterized in this work. Gallium Arsenide Schottky diodes were used in the characterization of WN films. The diodes were subject to thermal treatments to study the thermal stability of the contacts, as in the fabrication process of MESFET transistors. The diodes characterizations were based in I-V measurements to obtain the ideality factor(n) and the Schottky barrier height(?b). The thermally stable devices show n=1.3 and { ?b =O.55eV respectively. The diodes were also submitted to a plasma passivation processo The AlN thin films were characterized using MIS capacitors and the dielectric constant and effective charge density obtained were 8.7 and O.9x1011 cm-2 respectively. The AlN films were used satisfactory as a cap layer to íon implantation and annealing, which is a process step of MESFET transístorsMestradoMestre em Engenharia Elétric
Theory of phase separation kinetics in polymer–liquid crystal systems
No full textWe introduce a kinetic model describing the phase separation in the mixture of long rod-like molecules and long chain-like molecules. The model uses the angular distribution function for the orientations of the rods as a dynamical variable. The energetics is based on the nonlocal Onsager theory for the rods combined with a nonlocal extension of the Flory-Huggins theory. The kinetics explicitly takes into account the preferential diffusion along the rods. We computed the phase diagrams in this model and found a number of transitions leading to phase separation. We also performed numerical simulations of the phase separation kinetics and studied the resulting morphologies. (C) 2002 American Institute of Physics
Experimental setup included wn-rearing and social isolation.
No full text<p>Experimental setup included normal acoustic and social rearing for control birds, and a continuous white-noise exposure and social isolation for wn-reared birds. The song output of one control male and one wn-reared male are shown in spectrogram form on the right: the control males sang a normal song, typical of normal/tutored zebra finches; and the wn-reared males sang a scratchy, perseverative song, typical of untutored/isolate song. Although we did not systematically study the differences in vocal output, we used song production as a means to verify the effectiveness of the white noise exposure and isolation since song development in males depends on both natural auditory spectro-temporal cues and social interactions.</p
Single neuron information values greater for ML-Noise than song in wn-reared condition.
No full text<p>A. Pairwise difference in Gamma Information rates (bits/s) for Song vs. ML-Noise estimated for single neurons for control birds (left) and wn-reared birds (right). Neurons in the auditory forebrain of wn-reared birds encode for ML-Noise more optimally than Song, while auditory neurons in control birds encode both ML-Noise and Song equally well. Even upon adjusting for firing rate differences using a general linear model, wn-reared neurons have higher Gamma Information values than the control neurons for both Song and ML-Noise, with a larger effect for ML-Noise (see Results). B. To control for potentially small differences in the types of receptive fields found in wn-reared birds compared to control birds, we also estimated the Gamma Information (bits/s) for single neurons in control birds that had similar (‘matched’) SIs to the receptive fields found in wn-reared birds. The pairwise difference in Gamma Information for Song vs. ML-Noise is still negligible in the matched control case, while the neurons in wn-reared birds encode for ML-Noise more optimally than Song. Even upon adjusting for firing rate differences using a general linear model, neurons from the wn-reared condition still have higher Gamma Information values than the matched control neurons for both Song and ML-Noise, and once again the effect size is larger for the ML-Noise stimuli than for the Song stimuli (see Results).</p
Hyperinvariant subspaces of bilateral shift operators with converging weighted sequences: {wn}, {w-n}, n = 1, ..., 8.
No full textEstudiamos la existencia de subespacios hiperinvariantes de operadores desplazamiento bilateral ponderados e invertibles definidos sobre un espacio de Hilbert con base ortogonal {en}, n perteneciendo a Z, por la expresión T en = wn en+1, donde las sucesiones {wn} y {w-n}, con n = 1, ..., 8, son convergentes.In this paper we study the existence of hyperinvariant subspaces of invertible weighted bilateral shift operators defined on a Hilbert space with orthogonal base {en}, n belonging to Z, by the expression T en = wn en+1, where the sequences {wn} y {w-n}, with n = 1, ..., 8, are convergent
Ionization Stratification in WN Winds
No full text: We performed measurements of the emission line widths on ultraviolet, optical, and infrared spectra of 10 Wolf-Rayet stars belonging to the WN subtype. Our goal is to investigate whether or not ionization stratification exists in all Wolf-Rayet stars which have a "momentum problem". Ionization stratification can be observed via the dependence of line width on ionization potential. Our multi-wavelength approach allows us to obtain line widths of blend-free lines while at the same time covering a wide range of ionization potentials. Assuming a linear relation, we model the data with least-squares fits, and we give the slopes and errors. We find a high probability for the existence of a correlation between the strength of the ionization stratification as measured by these slopes and the wind performance numbers. This is the expected behavior if a stratified ionization structure plays a role in extracting a sufficiently large momentum from the radiation field to accelerate Wolf-Rayet win..
Example neural responses from a control bird and a wn-reared bird to a subset of the selectivity stimuli.
No full text<p>Spectrographic representation of exemplars of a subset of stimulus types (Con, Pips, Tones, WN) and corresponding neural responses for 2 recording sites, one from a control adult (top) recorded in L1 and the other from a wn-reared bird recorded in L3 (bottom). Note that sound begins at 0.5 s. For the neural response, both the spike raster for 10 trials (middle) and the PSTH (denoted by spikes/s on the bottom) are shown. These examples were chosen to reflect the characteristics in the average neural responses in control adults versus wn-reared adults: the recording site from the control adult shows robust responses to Con and WN, whereas the recording site from the wn-reared adult shows decreased responses to Con and enhanced responses to Tones. In this example, as in the average data, the wn-reared recording site was more variable (Con FF = 1.16 and Pip FF = 1.40) than the control recording site (Con FF = 0.91 and Pip FF = 0.91). While these responses were chosen as illustrative of the average neural responses, we also found a wide range of response properties, including neurons in wn-reared animals that showed strong and reliable responses to song (as shown below). The spontaneous background activity was variable across units in both control and wn-reared birds but similar in rate across the two rearing conditions. To conserve space, we omitted showing the response to Ripples.</p
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Microstructure, Mechanical and Tribological Properties of Advanced Layered WN/MeN (Me = Zr, Cr, Mo, Nb) Nanocomposite Coatings
No full textDue to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10−6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions
WN-Salience: A Corpus of News Articles with Entity Salience Annotations
No full textEntities can be found in various text genres, ranging from tweets and web pages to user queries submitted to web search engines. Existing research either considers all entities in the text equally important, or heuristics are used to measure their salience. We believe that a key reason for the relatively limited work on entity salience is the lack of appropriate datasets. To support research on entity salience, we present a new dataset, the WikiNews Salience dataset (WN-Salience), which can be used to benchmark tasks such as entity salience detection and salient entity linking. WN-Salience is built on top of Wikinews, a Wikimedia project whose mission is to present reliable news articles. Entities in Wikinews articles are identified by the authors of the articles and are linked to Wikinews categories when they are salient or to Wikipedia pages otherwise. The dataset is built automatically, and consists of approximately 7,000 news articles, and 90,000 in-text entity annotations. We compare the WN-Salience dataset against existing datasets on the task and analyze their differences. Furthermore, we conduct experiments on entity salience detection; the results demonstrate that WN-Salience is a challenging testbed that is complementary to existing ones.</p
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