Página 2 dos resultados de 253 itens digitais encontrados em 0.005 segundos

## Avaliação de duas tecnologias de controle para acionamento de sistema de aquecimento resistivo em creche suína; Evaluation of two control technologies for activation of resistive heating system in swine nursery

Juliana de Souza Granja Barros
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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O uso de sistemas de aquecimento em creches suínas é necessário para proporcionar conforto térmico e bem-estar aos animais dentro das instalações. A maioria dos equipamentos de fornecimento de calor utilizados na suinocultura demanda energia elétrica; cujo custo é sempre crescente. Portanto, há a necessidade de ajustes nos sistemas de aquecimento hoje empregados, com o intuito de viabilizar o uso racional de energia elétrica pelo setor. Deste modo, por meio da aplicação de um sistema eletrônico de controle da temperatura dentro das creches é possível manter o bem-estar e o desempenho produtivo do animal, com maior eficiência do uso de energia elétrica, em relação a dispositivos de controle tradicionais, como por exemplo, o termostato. O objetivo deste trabalho foi comparar duas tecnologias de controle de temperatura quanto ao uso racional de energia elétrica, manutenção das condições de conforto térmico e de desempenho produtivo dos animais em fase de creche. Os tratamentos estudados foram: resistências elétricas suspensas controladas por termostato digital simples, que representou a testemunha, e resistências elétricas suspensas controladas por controlador PID (Proporcional, integral e derivativo). Os tratamentos foram analisados quanto ao consumo de energia elétrica (kWh)...

## Desenvolvimento de novas soluções em materiais para resistência de chuveiros elétricos

Silva, Gabriel Beltrame Derner
Tipo: Dissertação de Mestrado Formato: 102 p.| il., grafs., tabs.
POR
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## Continuous Registration of Membrane Input Resistances of Small Plant Cells Using a Double-Pulse Current Clamp Technique for Single-Electrode Impalements 12: Comparison with the Conventional Two-Electrode Method

Schefczik, Kurt; Simonis, Wilhelm; Schiebe, Michael
Tipo: Artigo de Revista Científica
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To measure the cell input resistance in Elodea leaf cells, a new single-microelectrode method was explored by comparing the results with conventional two-microelectrode experiments. The new method takes advantage of the difference in the frequency response curves between electrode and cell impedances. By application of electrical stimuli, which contain specific frequency bands, the different impedances can be analyzed separately. To get a distinct separation in the frequency response of cell and electrode, respectively, the electrode capacitance has to be compensated during the impalement. Different time constants of the cell membrane can be accounted for by adjustment of the stimulus length. It is shown that both the single- and the double-electrode method yield the same results, even if the cell input resistances change considerably during the course of the experiment. This demonstrates the usefulness of the new single-electrode method for continuous measurements of cell membrane resistances, especially in cells so small that the double-electrode method is no longer applicable.

## Localization and electrical characteristics of a giant synapse in the spinal cord of the lamprey.

Ringham, G L
Tipo: Artigo de Revista Científica
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1. Physiological and morphological experiments were carried out to determine the characteristics of a giant synapse in the lamprey spinal cord. The presynaptic element is a Müller fibre, running the length of the spinal cord, and the post-synaptic element is a lateral interneurone. 2. Injection of the interneurone with fluorescent dye revealed several dendritic processes extending into the region of the Müller fibres and spreading over a longitudinal distance of about 150 mum. Electron microscopic examination of the Müller fibres confirmed that they do not send out processes to form synapses. Thus, the synapse is between the cylindrical fibre and one or more dendritic branches of the interneurone. 3. Measurements with intracellular electrodes showed the Müller fibres to have input resistances of about 1 Momega and space constants of 1-0-1-7 mm. The space constant was larger for hyperpolarizing pulses than for depolarizing pulses because of delayed recitification. The interneurones had input resistances of about 6 Momega. 4. The neurones were electrically as well as chemically coupled. When a current-passing electrode was placed in the fibre and hyperpolarizing pulses applied, the amplitude of the electrical coupling potential recorded from the interneurone was maximal at one position of the current-passing electrode and decreased as the electrode was moved away from the optimal position. The decrease in amplitude with electrode displacement indicated that the region of synaptic contact was very restricted. 5. The electrical synapse was highly rectifying...

## Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions

Zheng, Ruiting; Gao, Jinwei; Wang, Jianjian; Chen, Gang
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
EN
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Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions.

## An analysis of the relationships between subthreshold electrical properties and excitability in skeletal muscle

Pedersen, Thomas H.; L.-H. Huang, Christopher; Fraser, James A.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
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Skeletal muscle activation requires action potential (AP) initiation followed by its sarcolemmal propagation and tubular excitation to trigger Ca2+ release and contraction. Recent studies demonstrate that ion channels underlying the resting membrane conductance (GM) of fast-twitch mammalian muscle fibers are highly regulated during muscle activity. Thus, onset of activity reduces GM, whereas prolonged activity can markedly elevate GM. Although these observations implicate GM regulation in control of muscle excitability, classical theoretical studies in un-myelinated axons predict little influence of GM on membrane excitability. However, surface membrane morphologies differ markedly between un-myelinated axons and muscle fibers, predominantly because of the tubular (t)-system of muscle fibers. This study develops a linear circuit model of mammalian muscle fiber and uses this to assess the role of subthreshold electrical properties, including GM changes during muscle activity, for AP initiation, AP propagation, and t-system excitation. Experimental observations of frequency-dependent length constant and membrane-phase properties in fast-twitch rat fibers could only be replicated by models that included t-system luminal resistances. Having quantified these resistances...

## Stability of electrical coupling despite massive developmental changes of intrinsic neuronal physiology

Parker, Philip R.L.; Cruikshank, Scott J.; Connors, Barry W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Gap junctions mediate metabolic and electrical interactions between some cells of the central nervous system. For many types of neurons, gap junction-mediated electrical coupling is most prevalent during early development, then decreases sharply with maturation. However, neurons in the thalamic reticular nucleus (TRN), which exert powerful inhibitory control over thalamic relay cells, are electrically coupled in relatively mature animals. It is not known whether TRN cells or any neurons that are electrically coupled when mature are also coupled during early development. We used dual whole-cell recordings in mouse brain slices to study the postnatal development of electrical and chemical synapses that interconnect TRN neurons. Inhibitory chemical synapses were seen as early as postnatal day four but were infrequent at all ages, whereas TRN cells were extensively connected by electrical synapses from birth onward. Surprisingly, the functional strength of electrical coupling, assayed under steady state conditions or during spiking, remained relatively constant as the brain matured despite dramatic concurrent changes of intrinsic membrane properties. Most notably, neuronal input resistances declined almost eight-fold during the first two postnatal weeks...

## Possible room temperature superconductivity in conductors obtained by bringing alkanes into contact with a graphite surface

Kawashima, Yasushi
Tipo: Artigo de Revista Científica
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Electrical resistances of conductors obtained by bringing alkanes into contact with a graphite surface have been investigated at room temperatures. Ring current in a ring-shaped container into which n-octane-soaked thin graphite flakes were compressed did not decay for 50 days at room temperature. After two HOPG plates were immersed into n-heptane and n-octane at room temperature, changes in resistances of the two samples were measured by four terminal technique. The measurement showed that the resistances of these samples decrease to less than the smallest resistance that can be measured with a high resolution digital voltmeter (0.1μV). The observation of persistent currents in the ring-shaped container suggests that the HOPG plates immersed in n-heptane and n-octane really entered zero-resistance state at room temperature. These results suggest that room temperature superconductor may be obtained by bringing alkanes into contact with a graphite surface.

## Carbon Fiber Epoxy Composites for Both Strengthening and Health Monitoring of Structures

Salvado, Rita; Lopes, Catarina; Szojda, Leszek; Araújo, Pedro; Gorski, Marcin; Velez, Fernando José; Castro-Gomes, João; Krzywon, Rafal
Tipo: Artigo de Revista Científica
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This paper presents a study of the electrical and mechanical behavior of several continuous carbon fibers epoxy composites for both strengthening and monitoring of structures. In these composites, the arrangement of fibers was deliberately diversified to test and understand the ability of the composites for self-sensing low strains. Composites with different arrangements of fibers and textile weaves, mainly unidirectional continuous carbon reinforced composites, were tested at the dynamometer. A two-probe method was considered to measure the relative electrical resistance of these composites during loading. The measured relative electrical resistance includes volume and contact electrical resistances. For all tested specimens, it increases with an increase in tensile strain, at low strain values. This is explained by the improved alignment of fibers and resulting reduction of the number of possible contacts between fibers during loading, increasing as a consequence the contact electrical resistance of the composite. Laboratory tests on strengthening of structural elements were also performed, making hand-made composites by the “wet process”, which is commonly used in civil engineering for the strengthening of all types of structures in-situ. Results show that the woven epoxy composite...

## Análise intervalar de circuitos elétricos

Grigoletti, Pablo Souza; Dimuro, Graçaliz Pereira; Barboza, Luciano Vitória; Reiser, Renata Hax Sander
Tipo: Artigo de Revista Científica
POR
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## X-ray spectrometry investigation of electrical isolation in GaN

Kucheyev, S. O.; Toth, M.; Phillips, M. R.; Williams, J. S.; Jagadish, C.; Li, G.
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
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Electrical isolation of n-type GaN epilayers bombarded with MeV light ions is studied by energy dispersive x-ray spectrometry(EDS). We show that the maximum bremsstrahlung x-ray energy (the Duane–Hunt limit) can be used to monitor the isolation process in GaN. This method allows the dose region above the threshold dose for isolation to be conveniently studied, whereas the application of conventional (low-voltage) electrical techniques in this dose range with large sheet resistances of the material (≳10¹¹ Ω/sq) is often impossible due to comparable parasitic resistances of the experimental setup. A correlation of EDS and resistance measurements of GaN strongly suggests that the magnitude of sample charging scales with the number of ion-beam-produced deep electron traps which are empty at equilibrium. The results presented demonstrate the utility of EDS as a powerful and simple technique to study electrical isolation in wide band-gap semiconductors.

## Avaliação energetica e exergetica de um sistema gerador de processos psicometricos

Paulo Martins Leal
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
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## Substrate resistance extraction using a multi-domain surface integral formulation

Vithayathil, Anne M. (Anne Marie), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 66 p.; 2538710 bytes; 2545057 bytes; application/pdf; application/pdf
EN_US
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In recent years, mixed-signal designs have become more pervasive, due to their efficient use of area and power. Unfortunately, with sensitive analog and fast digital circuits sharing a common, non-ideal substrate, such designs carry the additional design burden of electromagnetic coupling between contacts. This thesis presents a method that quickly extracts the electroquasistatic coupling resistances between contacts on a planar, rectangular, two-layer lossy substrate, using an FFT-accelerated multi-domain surface integral formulation. The multi-domain surface integral formulation allows for multi-layered substrates, without meshing the volume. This method has the advantages of easy meshing, simple implementation, and FFT-accelerated iterative methods. Also, a three-dimensional variant of this method allows for more complex substrate geometries than some other surface integral techniques, such as multilayered Green's functions; this three-dimensional problem and its solution are presented in parallel with the planar substrate problem and solution. Results from a C++ implementation are presented for the planar problem.; by Anne M. Vithayathil.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science...

## Electrical coupling between cones in turtle retina.

Detwiler, P B; Hodgkin, A L
Tipo: Artigo de Revista Científica
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1. The electrical coupling between cones of known spectral sensitivity in the peripheral part of the turtle's retina was studied by passing current through a micro-electrode inserted into one cone and recording with a second micro-electrode inserted into a neighbouring cone. 2. Spatial sensitivity profiles were determined by recording flash responses to a long narrow strip of light which was moved across the impaled cones in orthogonal directions. These measurements gave both the length constant lambda of electrical spread in the cone network and the separation of the two cones. 3. The cone separation determined from the spatial profiles agreed closely with that measured directly by injecting a fluorescent dye into two cones. 4. The length constant lambda varied from 18 to 39 micron with a mean of 25 micron for red-sensitive cones and 26 micron for green-sensitive cones. 5. The majority of cone pairs studied were electrically coupled provided they had the same spectral sensitivity and were separated by less than 60 micron: thirty-two out of thirty-six red-red pairs, two out of two green-green pairs, none out of eight red-green pairs: no blue cones were observed. 6. The strength of electrical coupling was expressed as a mutual resistance defined as the voltage in one cell divided by the current flowing into the other. Mutual resistances decreased from a maximum value of about 30 M omega at separations close to zero to 0.2 M omega...

## Ouabain on active transepithelial sodium transport in frog skin: studies with microelectrodes

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
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Studies were done with isolated frog skin to determine the effects of 10(-4) M ouabain on the electrophysiological parameters of outer and inner barriers of the Na-transporting cells. Microelectrodes were used to impale the skins from the outer surface to determine the intracellular voltages (Vsco) under conditions of short-circuiting and under conditions where a voltage clamp was used to vary the transepithelial voltage, VT. From this, the electrical resistances of outer (Rfo) and inner (RI) barriers were estimated. In addition, the driving force for active transepithelial Na transport (ENa = E'1) was estimated from the values of VT when the Vo = 0 mV (Helman and Fisher. 1977. J. Gen. Physiol. 69: 571-604). Studies were done with skins bathed with the usual 2.4 meq/liter [K]i in the inner solution as well as with reduced [K]i of 0.5 and 0 meq/liter. Characteristically, the responses to ouabain could be described by an initial rapid phase (5-10 min) during which time the Ri was increased markedly and the E'1 was decreased from control values. Thereafter, during the slow phases of the response, the resistances of both outer and inner barriers increased continuously and markedly with time leading ultimately to essentially complete inhibition of the short-circuit current. Similar studies were done with skins exposed to 10(-4) M amiloride in the outer solution. Although estimates of Ri could not be obtained under these conditions...

## Application of electrical analogues for control analysis of simple metabolic pathways.

Sen, A K
Tipo: Artigo de Revista Científica
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I have used electrical analogues for calculating the Flux Control Coefficients of metabolic pathways. An analogue circuit consists of resistances that are connected in series (or parallel) with a voltage (or current) source. In constructing the analogues, each of the enzymes in the pathway is associated with a resistance whose magnitude depends on the Elasticity Coefficients of the enzymes. These circuits can be designed in a heuristic fashion directly from the configuration of the pathway, without the necessity of writing down the governing equations with the use of Summation and Connectivity Theorems. The Flux Control Coefficients of the enzymes are represented by voltages across (or currents through) the resistances and are determined by an application of Ohm's Law. Results are given for (a) a simple linear pathway without feedback or feedforward regulation, and (b) a linear pathway with feedback inhibition. The analogue circuits are also convenient for assessing the relative importance of the various enzymes in flux control, and for simplifying the structure of a given pathway.

## Electrical behaviour of myenteric neurones in the gastric antrum of the guinea-pig.

Tack, J F; Wood, J D
Tipo: Artigo de Revista Científica
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1. Intracellular microelectrodes were used to study the electrical behaviour of ganglion cells in the myenteric plexus of the antrum of the guinea-pig stomach. In the absence of any information on antral myenteric neurones, the aim was to characterize the electrical behaviour and identify biophysical properties of the neurones that could be related to specialized organization of the neural microcircuits in this physiologically important division of the stomach. 2. Myenteric neurones in the gastric antrum were classified into four subtypes based on electrophysiological properties. These were gastric I, II, III and AH/type 2 neurones. Gastric I neurones were characterized by repetitive spike discharge during intraneuronal injection of depolarizing current, by higher input resistances and by lower resting membrane potentials than the other cell types. Gastric II neurones did not discharge repetitively. They discharged one or two spikes only at the beginning of depolarizing current pulses. Gastric III neurones did not discharge action potentials in response to depolarizing pulses. These neurones had higher membrane potentials and lower input resistances than the other types. A fourth type of neurone discharged one or more spikes during depolarizing current pulses and had long-lasting hyperpolarizing after-potentials associated with the spikes. The behaviour of these neurones was like AH/type 2 neurones found elsewhere in the enteric nervous system. 3. Action potentials in gastric I and II neurones were abolished by tetrodotoxin. Spikes of the AH/type 2 cells were not abolished by tetrodotoxin due to a calcium component of the inward current. Application of tetraethylammonium broadened the spikes. This was reversed by removal of Ca2+ from the bathing medium. 4. The hyperpolarizing after-potentials of AH/type 2 neurones were suppressed by removal of Ca2+ from the bathing medium. Treatment with 4-aminopyridine decreased the amplitude and duration of the after-hyperpolarization...

## Electrical Spin Injection in Multi-Wall carbon NanoTubes with transparent ferromagnetic contacts

Sahoo, S.; Kontos, T.; Schönenberger, C.; Sürgers, C.
Tipo: Artigo de Revista Científica
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We report on electrical spin injection measurements on MWNTs . We use a ferromagnetic alloy Pd$_{1-x}$Ni$_{x}$ with x $\approx$ 0.7 which allows to obtain devices with resistances as low as 5.6 $k\Omega$ at 300 $K$. The yield of device resistances below 100 $k\Omega$, at 300 $K$, is around 50%. We measure at 2 $K$ a hysteretic magneto-resistance due to the magnetization reversal of the ferromagnetic leads. The relative difference between the resistance in the antiparallel (AP) orientation and the parallel (P) orientation is about 2%.; Comment: submitted to APL version without figures version with figures available on http://www.unibas.ch/phys-meso/

## Quantum Algorithms for Approximating the Effective Resistances in Electrical Networks

Wang, Guoming
Tipo: Artigo de Revista Científica
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The theory of electrical network has many applications in algorithm design and analysis. It is an important task to compute the basic quantities about electrical networks, such as electrical flows and effective resistances, as quickly as possible. Classically, to compute these quantities, one basically need to solve a Laplacian linear system, and the best known algorithms take $\tilde{O}(m)$ time, where $m$ is the number of edges. In this paper, we present two quantum algorithms for approximating the effective resistance between any two vertices in an electrical network. Both of them have time complexity polynomial in $\log{n}$, $d$, $c$, $1/\phi$ and $1/\epsilon$, where $n$ is the number of vertices, $d$ is the maximum degree of the vertices, $c$ is the ratio of the largest to the smallest edge resistance, $\phi$ is the expansion of the network, and $\epsilon$ is the relative error. In particular, when $d$ and $c$ are small and $\phi$ is large, our algorithms run very fast. In contrast, it is unknown whether classical algorithms can solve this case very fast. Furthermore, we prove that the polynomial dependence on the inverse expansion (i.e. $1/\phi$) is necessary. As a consequence, our algorithms cannot be significantly improved. Finally...

## Effects of high-field electrical stress on the conduction properties of ultra-thin La2O3 films

Miranda, Enrique Alberto; Molina, J.; Kim, Y.; Iwai, H.