Voltage Noise Analysis Research Articles

Noise and Electrical Characteristics of Composites Filled with Onion-like Carbon Nanoparticles.

Polymer matrix composites filled with carbon nanoparticles are promising materials for many applications, but their properties strongly depend on the particle features, concentration and distribution within the matrix. Here we present a study of the electrical resistivity and the low-frequency voltage fluctuation of composites based on epoxy resin filled with onion-like carbon (OLC) of different sizes (40–250 nm) above the percolation threshold, which should clarify the electrical transport characteristics in these materials. Electrical measurements were performed in the temperature range of 78 to 380 K, and voltage noise analysis was carried out from 10 Hz to 20 kHz. At low temperatures (below 250 K), thermally activated tunneling, variable-range hopping and generation–recombination of charge carriers take place. Above 250 K, the rapid expansion of the matrix with the temperature increases the resistivity, but above ~330 K, the conductivity of the matrix becomes significant. Quasi one-dimensional electrical transport is observed in composites with the smallest particles (40 nm), while in composites with the largest particles (220–250 nm), the dimensionality of the electrical transport is higher. The temperature dependence of the electrical conductivity of composites with smaller particles is more sensitive to matrix expansion.

A Railgun Test Bench and Standardized Methodology for Muzzle Voltage Noise Analysis

This paper presents the design, development, and initial testing results of a small-bore railgun and test bench for the study of muzzle voltage traces. An analysis of the noise observed on voltage traces taken from the muzzle during motional and locked-armature operations is presented and discussed. The average velocities for a 3.38-g projectile were 50 m/s over a series of 21 tests. The railgun is powered by a sequentially fired pulse-forming network consisting of six electrolytic capacitor banks. Typical current and voltage characteristics are approximately 20-kA peak current at 275 V for a 6-ms pulse train length. Noise root-mean-square voltage and noise margins are extracted from the muzzle voltage waveforms and discussed. This investigation also develops a quantitative method to analyze muzzle voltage noise, which can be applied to any electromagnetic launcher. The technique reveals a new and interesting result that shows noise levels were greatest during early pulses of the firing sequence and generally decreased with subsequent pulses. This demonstrates that the technique has the potential to provide insight into the nature of the armature-rail sliding contact.

Unusual dependence of resistance and voltage noise on current inLa1−xSrxMnO3ultrathin films

We report on measurements of current-resistance effects in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ ultrathin films deposited by molecular beam epitaxy. dc transport and voltage noise spectral density analyses have been performed in the temperature range of $10--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the results are compared with existing theoretical models. A possible connection between the explanation of the electrical transport properties and the two-level tunneling systems model, used for the voltage noise analysis, is proposed.

Dc transport properties and resistance fluctuation processes inSr2FeMoO6polycrystalline thin films

We performed transport measurements and voltage noise analysis on ${\mathrm{Sr}}_{2}\mathrm{Fe}\mathrm{Mo}{\mathrm{O}}_{6}$ thin films, in zero applied magnetic field as a function of temperature $T$, down to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The samples, grown by pulsed laser deposition on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrates, showed a negative resistivity thermal coefficient and, at $T<50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the observed temperature dependence of resistivity and the $I\text{\ensuremath{-}}V$ curves were correctly described by the fluctuation-induced tunneling model which assumes the presence of intergranular tunneling of charge carriers. Moreover, the analysis of the low temperature resistance fluctuation processes, pointed out the presence of a voltage noise component independent of the frequency within the whole investigated bandwidth with a spectral density directly proportional to the square of the bias current. We interpreted this unusual behavior as a possible consequence of tunneling intergranular processes.

Spectrum analysis of voltage noise of moving vortex lattice and dynamic phase transition

Using Langevin molecular dynamics method, we have studied the voltage noise spectrum generated by current-driven vortices as a function of the magnetic field an d current. It is found that the broad band noise (BBN) at low frequencies decrea ses with increasing magnetic field, it decreases at the magnetic field near th e vortex dynamic transition field FP， and the Lorentze narrow ba nd noise (NBN) at high frequencies appears. As the magnetic field increases near the melt ing field Fm, the NBN peak goes up and shifts towards higher freq uencies. In the elastic motion region of vortices with strong driving currents, NBN exhib its the washboard-like shape. This behavior arises from the periodic modulation of the translational velocity of vortices, suggesting that there is a Bragg gla ss phase with the translation order in the vortex lattices of the layered superc onductors.

Monte Carlo analysis of voltage noise in sub-micrometre semiconductor structures under large-signal regime

Using an ensemble Monte Carlo technique, we investigate voltage noise (related to diffusion noise sources) in GaAs n+nn+ structures operating under large-amplitude periodic signals. A pronounced noise contribution around the frequency of the excitation signal f0 is evidenced. This contribution is mainly associated with the time-varying field sustained by the n region. Its presence and importance depends on the length of the n region and the value of f0. This additional contribution in the voltage noise spectrum tends to disappear for values of f0 beyond the cut-off of the noise related to the n region. On the other hand, the level of low-frequency noise under large-signal conditions is higher than under small-signal operation due to the increase of the effective resistance of the structures.

Analysis of voltage noise in forward-biased silicon bipolar homojunctions: Low- and high-injection regimes

An ensemble Monte Carlo (EMC) simulator has been used to study bipolar transport in silicon p+n and pn+ homojunctions under forward-bias conditions, both in low- and high-injection regimes. The study focuses on a microscopic analysis of voltage fluctuations in such devices. The method of voltage-noise operation mode provides spatial analysis of the spectral density of voltage fluctuations under constant-current conditions. In the low-frequency range, the presence of shot, thermal, and excess noise due to hot carriers was found when the bias conditions were modified. Also, the EMC method permits ready evaluation of the noise equivalent temperature in both structures from the observed voltage fluctuations.

Application of Electrochemical Noise Analysis to Study the Corrosion Behavior of Aluminum Composites

This paper investigates the possibility of using electrochemical voltage noise analysis to study the corrosion behavior of a few composite materials obtained by reinforcing an aluminum matrix with either particles or particles or fibers (Saffil, ). The ranking of the corrosion resistances exhibited by the various materials, according to the noise analysis technique, appears to agree with the results obtained by linear polarization resistance and weight loss measurements and with the observation of the specimen surfaces by scanning electron microscopy. The recording of both polarization curves and galvanic current densities flowing between reinforced and nonreinforced aluminum electrodes shows that the driving force for the corrosion process is the cathodic process of oxygen reduction, which can be affected by the nature and the shape of the reinforcement.

Analysis of voltage noise in a high Tc superconductor

Based on recent mesurements we present a theoretical analysis of voltage noise as function of both temperature and magnetic field. Nonlinearity of noise power in applied magnetic field can be caused by the many-body dynamics effect of vortex. Thus vortex motions may be highly correlated, suggesting that in the flux creep region such many-body dynamics effect can cause the observed (1/f) β noise power spectrum, by showing a maximum with the highest applied magnetic field at a critical temperature and a possibility of self-organized criticality.

Action of antibodies directed against the acetylcholine receptor on channel function at mouse and rat motor end‐plates.

1. The acute effects of antibodies (both polyclonal and monoclonal) raised against the acetylcholine receptor were studied at mouse and rat end-plates. Isolated muscles were incubated in solutions containing antibody for 2 1/4 to 3 1/2 h. Intracellular microelectrode techniques were then used to record miniature end-plate potentials (MEPPs) and voltage noise. 2. Most antibody preparations investigated did not reduce MEPP amplitudes as compared with controls. One monoclonal (C7) and one polyclonal (J) preparation irreversibly reduced MEPP amplitudes. Both preparations caused reductions in acetylcholine-induced depolarization and associated channel opening frequency (from voltage noise analysis). Single-channel depolarization was not altered by these antibodies. 3. On the basis of these and previous results, four antibody binding regions on the receptor surface were distinguished according to whether channel function and/or alpha-bungarotoxin binding were affected. Although most antibody preparations did not affect channel function, monoclonal antibody C7 appeared to alter function by acting on the channel itself so as to prevent channel opening.

The effect of chronic neostigmine treatment on channel properties at the rat skeletal neuromuscular junction

We have studied the effects of chronic neostigmine treatment on single channel properties at the rat skeletal neuromuscular junction. Rats received 0.86 mg kg-1 neostigmine (s.c.) daily for 9-11 days. Microelectrode recordings were then made from the extensor digitorum longus muscle. The amplitude of miniature endplate potentials was significantly reduced in muscles from neostigmine-treated rats as compared with controls. Acetylcholine (2-5 microM) applied in the bath produced a depolarization and associated channel opening frequency (from voltage noise analysis) which were significantly reduced in neostigmine-treated muscles with respect to controls. The depolarization resulting from the opening of a single channel (from voltage noise analysis) and single channel open time and conductance (from current noise analysis) were not significantly changed by chronic neostigmine treatment. It is concluded that chronic neostigmine treatment causes an adaptive reduction in the number of functional acetylcholine receptors at the endplate without otherwise affecting single channel properties themselves.

Voltage noise in honeybee drone photoreceptors

Voltage noise analysis was performed on membrane potentials recorded from the photoreceptor cells of the honeybee drone. Voltage power spectra showed an increase in noise amplitude on passing from the dark to moderate light; with strong light noise fell to near the dark level. At intermediate light intensities the noise was reduced by application of tetrodotoxin. The probable effects on the power spectra of electrical coupling between cells are discussed. It is tentatively estimated that the unitary event in weak light is a conductance increase of 20 pS. The results are compared with previous results from photoreceptors of other species that appear to be specially adapted to weaker illuminations.

Voltage noise accompanying chemically-induced depolarization of insect photoreceptors

Intracellular potentials are recorded from photoreceptors in a superfused preparation of the retina of a locust compound eye. Chloral hydrate and alkyl alcohols induce a rapid, superfusing reversible depolarization of these photoreceptors when dissolved in the saline. Analysis of voltage noise accompanying depolarization by chloral hydrate suggests that depolarizing ionic pathways are opened briefly and randomly in time in the photoreceptor membranes. This conclusion is supported by measurements of the cell resistance and of voltage noise amplitude as a function of membrane potential. Replacement of superfusate sodium by choline reversibly reduces the effects of chloral hydrate, suggesting that the ionic pathways opened are permeable by sodium. The voltage noise induced by chloral hydrate is compared to that during depolarization by steady illumination of the same cell. As the illumination intensity is increased, the amplitude and the shape of the power spectrum of light-induced voltage noise approach those of drug-induced noise at the same depolarization level. The possibility that these phenomena represent alterations in the mechanism of phototransduction is discussed.

Plasmalemma Voltage Noise in Chara corallina

Voltage noise analysis is applied to plasmalemma ion transport in Chara corallina. There is a component in the noise power spectrum that is probably associated with current fluctuations within passive transport channels, and another component that may be associated either with fluctuations in the number of open channels, or with active transport. The data allow the calculation of time constants that may be attributable to molecular level events in these transport processes.