Voltage Span Research Articles

Effects of magnetic field on two-dimensional superconducting quantum interference filters

We present an experimental study of two-dimensional (2D) superconducting quantum interference filters (SQIFs) in the presence of a magnetic field B. Although the nonlinear dynamics of the 2D SQIF are much more complex than those of previously studied one-dimensional SQIFs, we found for the 2D SQIF a similar dependence of the voltage V on the magnetic field applied, which is characterized by a unique delta-like dip at B=0. The voltage span of the dip depends on the distribution of areas of the individual loops, and on the bias current, and it scales proportionally to the number of rows simultaneously operating at the same working point. In addition, the voltage response of individual rows of the 2D SQIF is sensitive to the field gradient generated by a control line superimposed on the homogeneous field of a coil. This feature suggests the use of these devices as highly sensitive absolute detectors of spatial gradients of the magnetic field.

Flooded utilization and electrochemical voltage spectroscopy studies on nickel electrodes

A group of standard nickel electrodes were evaluated at different test temperatures and in different electrolyte concentrations. These production quality electrodes came from different backgrounds in terms of number of charge/discharge cycles, cycling temperature, electrolyte concentration, and cobalt level in the active material. The results of the matrix of tests using the flooded utilization (FU) technique demonstrated that capacity gains are available when cycling at lower temperatures and when higher concentrations of KOH are used as the electrolyte. Electrochemical voltage spectroscopy (EVS) scans were also taken for the complete matrix of tests. Since the cycling conditions used in the FU technique are much closer to those in actual cell cycling tests, they will be emphasized in this study in regard to the capacity trends. Comparative EVS scans were helpful in displaying the shifting potentials of the charging peaks of the active material relative to the oxygen evolution characteristics of these electrodes. The voltage span between the potential at which the active material is charged and the potential at which the co-evolution of oxygen becomes a significant parallel reaction determines the charging efficiency for the recharge step and is the root cause of the differences in useable electrode capacity.

Electrochromic Devices Incorporating Cr Oxide And Ni Oxide Films:: A Comparison

Transparent films of Cr oxide and Ni oxide were made by reactive DC magnetron sputtering in Ar+O 2+H 2. They displayed anodic electrochromism with charge capacities similar to that of W oxide. Cr oxide was stable in acidic environments, while Ni oxide was stable in basic environments. Electrochromic devices were made with pristine Cr oxide or Ni oxide films operating in conjunction with W oxide and a proton conducting electrolyte. Of the two oxides, Cr oxide film allowed device operation at a lower voltage span, while the device with Ni oxide film yielded a higher transmittance in the bleached state, a larger absorptance modulation, and a more neutral color.

Calibration and temperature compensation of silicon pressure sensors using ion-implanted trimming resistors

A piezoresistive silicon pressure sensor with bipolar on-chip signal conditioning circuits permits offset voltage, full scale span and temperature coefficient of offset voltage and full scale span to be calibrated from a trimming ion-implanted resistors. The ion-implanted resistors with temperature coefficient of 1700 ppm/°C or 4700 ppm/°C were fabricated by the same process as that used for the base and piezoresistors. The fabricated sensor exhibits a sensitivity of 40.5 mV/kPa and temperature coefficient of 46 ppm/°C at the temperature range of −10 to 70°C.

Corrections to the Capacitance between Two ElectrodesDue to the Presence of Quantum Confined System

We have studied the capacitance between two parallel plates enclosing a quantum confined system and its dependence on the applied voltage. The concepts of capacitance and differential capacitance are discussed together with their applicability to systems characterized by single.electron tunneling. We determine the tunneling thresholds by means of a formalism based on the minimization of the system free energy and we retrieve, as a special case, Luryi′s quantum capacitance formula. We apply our method to the study of an idealized system made up of a number of quantum dots with random size distributed according to a gaussian. Results are shown for different choices of the position of the dots between the plates and of the voltage span applied to perform the measurement of the differential capacitance.

Properties of an A-current in slowly and rapidly adapting stretch receptor neurones of lobster

A previously unnoticed outward membrane current has been identified, characterized and specified as a so-called A-current in the slowly and rapidly adapting lobster stretch receptor neurone. In both cells the current was, after blockage of a tetrodotoxin-sensitive Na + current and a tetraethylammonium- and 4-aminopyridine-sensitive delayed rectifier current, seen to activate fully within about 25 ms of square-shaped depolarizations beyond voltage levels of -40 to -30 mV and, then, to inactivate completely with a (voltage independent, within the voltage span under observation) time constant of 110 ms. The A-currents of rapidly and slowly adapting receptors were noticed to differ significantly from each other in that the A-current of the rapidly adapting cell is activated, and inactivated, at 10-15 mV more negative voltage levels than the A-current of the slowly adapting cell. Also, the maximum permeability of the A-channel system appeared to be distinctly larger in the rapidly than in the slowly adapting cell. Both of these circumstances were able to explain why, at a given level of membrane depolarization, a markedly stronger A-current is activated in the rapidly than in the slowly adapting cell. On the basis of experimental data it was possible to formulate a mathematical A-current description which was incorporated into a previously published model of the lobster stretch receptor neurone. Using this model, evidence was obtained that the A-current may play a functionally significant role (in the rapidly adapting cell) by increasing the speed of action potential repolarization and thereby enhancing the cell's dynamic stimulus sensitivity.

Accurate low voltage analogue CMOS timer for mixed-signal integrated circuits

An analogue timer which generates a constant time delay that relies only on device geometry ratios and the frequency of a reference clock signal is described. The timer uses the discharge of a capacitor by a constant current over an appropriate voltage span both determined by a special bias circuit driven by the clock in such a way as to eliminate the influence of supply voltage, process parameters and temperature. This circuit is suitable for low-voltage operation.

Nearly chirp-free electroabsorption modulation using InGaAs-InGaAlAs-InAlAs coupled quantum wells

We present an electroabsorption modulator based on slightly asymmetric InGaAs-InGaAlAs-InAlAs coupled quantum wells operated in the normally-off mode. The device exhibits a large change of the absorption coefficient in the vicinity of the zero-bias exciton peak wavelength with a very small change of the refractive index. The maximum excursion of the chirp parameter over the entire span of the bias voltage is less than /spl plusmn/0.1 for a specific wavelength or /spl plusmn/0.4 over a 12/spl sim/14 -nm range. This structure is promising for low-chirp, high bit-rate electroabsorption modulators. >

Comparison of anodization spectroscopy with SIMS and RBS measurements for the characterization of Nb/AlAlO x/NB Josephson junction structures

The thin tunneling barrier in a Nb/AlAlO x /Nb was characterized by anodization spectroscopy, SIMS and RBS. From the anodization spectroscopy we can get the film thickness from the voltage span and, most importantly, also the sharpness of the Nb/AlO x and Al/Nb interfaces around the tunneling barrier. Comparison of the anodization profiles with SIMS depth profiles and RBS spectra shows that the anodization spectroscopy can be used to characterize the junction quality.

A new scheme of symbiosis: ligand- and voltage-gated anion channels in plants and animals.

Anion channels in the plasma membrane of both plant and animal cells participate in a number of important cellular functions such as volume regulation, trans-epithelial transport, stabilization of the membrane potential and excitability. Only very recently attention has turned to the presence of anion channels in higher plant cells. A dominant theme among recent discoveries is the role of Ca2+ in activating or modulating channel current involved in signal transduction. The major anion channel of stomatal guard cell protoplasts is a 32-40 pS channel which is highly selective for anions, in particular NO3-, Cl- and malate. These channels are characterized by a steep voltage dependence. Anion release is elicited upon depolarization and restricted to a narrow voltage span of -100 mV to the reversal potential of anions. During prolonged activation the current slowly inactivates. A rise in cytoplasmic calcium in the presence of nucleotides evokes activation of the anion channels. Following activation they catalyse anion currents 10-20 times higher than in the inactivated state thereby shifting the resting potential of the guard cell from a K(+)-conducting to an anion-conducting state. Patch-clamp studies have also revealed that growth hormones directly affect voltage-dependent activity of the anion channel in a dose-dependent manner. Auxin binding resulted in a shift of the activation potential towards the resting potential. Auxin-dependent gating of the anion channel is side- and hormone-specific. Its action is also channel-specific as K+ channels coexisting in the same membrane patch were insensitive to this ligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of high-frequency components of signal-averaged QRS complex in chinese patients with acute myocardial infarction. A prospective study for prediction of ventricular tachycardia.

A prospective study was undertaken of the high-frequency components of the terminal portion of the QRS complex in 38 Chinese patients with acute myocardial infarction (AMI) (mean age 62 +/- 5.6 years) within the first week after the acute event (5.5 +/- 1.2 days). Another 44 normals served as controls (mean age 57 +/- 9.6 years). The electrocardiogram was averaged at a filter band pass of 80-300 Hz. The low voltage span (LVS) of the signals less than 40 microV in the terminal portion of QRS, the root-mean-square (RMS) voltage (V) of terminal 40 msec of the QRS complex, and the total duration of signal-averaged QRS vector complex were measured in both the normal subjects and patients. The LVS was abnormally prolonged in 16 of 38 patients (42%), and in only 16% of normals (p less than 0.05). The RMS-V was abnormal (less than 25 microV) in 29 of 38 patients (76%), and in only 20% of normals (p less than 0.0005), and the signal-averaged QRS vector complex was abnormal (greater than 120 msec) in 26 of 38 patients (68%), and only 9% of normals (p less than 0.005). There was no significant correlation between any of the signal-averaged parameters, the site of AMI and total creatine kinase (CK) or CK-MB values. The signal-averaged parameters also showed no relationship to either the cardiothoracic (C/T) ratio or the left ventricular ejection fraction, determined by the Tc-99 m pertechnetate first pass blood pool technique. Holter ECG monitoring was performed twice in all AMI patients, at 7 to 18 days after the acute event (12 days average) and 3 weeks after the first recording. There were only four episodes of non-sustained ventricular tachycardia (VT), all during the second monitoring period. Three episodes (10%) occurred in patients with positive late potentials (LPs), defined by an RMS-V less than 25 microV in the terminal portion of QRS vector; one episode (11%) occurred in patients with negative LPs (9 patients). Although the incidence of LPs is significantly higher in patients with an AMI than in normal controls, the LPs detected by body surface signal-averaged ECG did not predict the occurrence of in- and out-of-hospital VTs. Thus, after AMI, Chinese patients may not be as prone to develop VTs as are Caucasians. Furthermore, the appearance of LPs is independent of cardiac size and left ventricular ejection fraction.

Frequency tuning in the electroreceptive periphery

Our studies are concerned with the frequency tuning that is provided by the electrical resonance of tuberous electroreceptors. Frequency selectivity had previously been measured in the electroreceptor's afferent fibers, and resonant conductances in the electroreceptor cell membrane had been implicated in producing the selectivity. With transdermal application of sinusoidal current, we measured the frequency dependence of the impedance of small areas of the electroreceptor/skin structure of the weakly electric fish Sternopygus and Eigenmannia, and used our data to make a quantitative linear model of the structure. The qualitative form of the model was proposed by Bennett (1). The quantitative model allows us to estimate the frequency selectivity of the voltage across the innervated membrane of the electroreceptor cells. The frequency selectivity of electroreceptor cell voltage derived from our data are as sharp as the neural selectivity at frequencies close to the most sensitive frequency. Many of our measurements supported the linear system model. However, spontaneous electroreceptor voltage oscillations were detected in some of our specimens, suggesting that the electroreceptors can operate in a regime of active nonlinearity. A simple explanation for the observed oscillations is that they arise when damping in the electroreceptor cell's resonant membrane is negative for a limited span of membrane voltage surrounding the resting voltage. The response of oscillating units to sinusoidal current was compatible with this explanation. We report experimental observations bearing on the consequences of active nonlinearity for the frequency tuning of a resonant system.

The lightning performance of unshielded steel-structure transmission lines

A method is presented for calculating the lightning performance of unshielded steel-structure transmission lines. The method is an adaptation of the Anderson/IEEE method for shielded lines, and it incorporates an algorithm for calculating separate magnitudes and frequency distributions of the strokes to the towers and the strokes to the conductors. The results of applying the method to 230 kV, 500 kV and 765 kV lines are presented, and the effects of voltage class, span and form of striking distance equation are discussed. >

Depolarization elicits two distinct calcium currents in vertebrate sensory neurones

The calcium currents of rat sensory neurones (of the IX and X cranial nerves) grown in culture were studied using whole cell recordings. In cells loaded with CsCl, and bathed in a solution where Na was replaced by choline or Tris, a step depolarization from -80 mV to 0 mV elicited the well-documented sustained Ca current (iCa,s). In contrast, depolarization from -80 mV to -60 mV and up to -20 mV evoked a distinct transient inward current (iCa,t) which could be isolated by imposing an internal pCa 7. It relaxed in about 100 ms and could possibly occur independently of the former current. The transient current was only affected by manipulation of the Ca concentration in the external medium and therefore was considered to be also a transfer of Ca. Ba was shown to act as a substitute with a lower affinity than Ca. The maximal amplitude of this current was in the order of a few hundred pA in Ca 5 mM and Mg 2 mM. Both activation and inactivation occurred in the same voltage span. The underlying event was studied using noise analysis and compared to the Ca transfer occurring during the sustained current as measured in chromaffin cells by Fenwick et al. (1982). We found them to be of similar amplitude.

Polarizability and Electrocapillary Measurements of the Nitrobenzene–Water Interface

Abstract Electrocapillary curves have been measured of the interface between nitrobenzene solution of tetrabutylammonium tetraphenylborate and aqueous solution of lithium chloride using a dropping electrolyte solution electrode under the precise control of the electrical potential difference and of the ion transfer current across the interface. The nitrobenzene–water interface could be electrically polarized over the voltage span of 300 mV. The residual current was explained as due to both the transfer of tetrabutylammonium ion and tetraphenylborate ion through the interface and the charging current at the interface. The electrocapillary curve was parabolic in shape. The surface charge vs. potential curve derived from the electrocapillary curve agreed with that obtained from the differential capacity vs. potential curve of the interface. The results indicate that the interface can virtually be treated as an ideal polarized interface over a certain potential range.

Integrated piezoresistive pressure sensor with both voltage and frequency output

An on-chip integrated piezoresistive pressure sensor with both voltage and frequency outputs has been developed. The sensor chip, having a size of 3 × 3.8 mm 2, was realized by the use of a standard bipolar IC process. The output voltage span is 1 to 4 V for a pressure range of 0 to 750 mmHg. The pressure sensitivity of the voltage output is 4 mV/mmHg. The non-linearity is less than 0.4 % of the full scale. The sensitivity of the frequency output is about 30 kHz for a 750 mmHg change in pressure. The output is in the T 2L level. The temperature coefficient of the sensitivity is less than 0.06%/°C in the temperature range −20 to 110 °C.

Three-micro-electrode voltage clamp experiments in calf cardiac Purkinje fibres: is slow inward current adequately measured?

1. The three-micro-electrode voltage clamp method (Adrian, Chandler & Hodgkin, 1970) was adapted for the study of regenerative inward currents in cardiac muscle. The adequacy of measurements of slow inward current in cardiac Purkinje fibres was assessed. 2. Membrane current density is reported simultaneously by total applied current (IT), along with a longitudinal voltage difference signal (delta V), recorded between two intracellular micro-electrodes. 3. Non-linear cable calculations show that delta V is a more faithful measure of membrane current density than IT as peak inward current increases. Quantitative agreement between delta V and IT only occurs when both signals report the membrane characteristics that would be obtained with an ideal longitudinal space clamp. 4. Agreement between delta V and IT is thus a useful criterion for satisfactory experimental measurements which we applied to the slow inward current. This component was elicited by depolarizing steps from a holding potential near =45 mV in the presence of tetrodotoxin. The IT signal was compared directly with delta V/R, where R is an effective longitudinal resistance that was experimentally determined. 5. delta V/R and IT showed very good agreement in both peak amplitude and time course at all potentials studied. 6. Radial non-uniformity during the measured peak slow inward current was estimated by calculations assuming clefts 200 A wide with a uniform distribution of ionic channels. The calculated voltage span from surface to centre was always less than 5 mV, and the measured I-V characteristics showed little distortion. 7. In another check, I-V characteristics and slow response membrane action potentials were compared. The measured peak current showed good agreement with the product (total preparation capacitance) x (rate of rise). 8. The experimental and theoretical analysis suggest that the measurements of slow inward current are a good approximation to genuine membrane properties.

Titanium disulphide: A solid solution electrode for sodium and lithium

Single crystals of Ti xS 2 (x = 0.002, 0.01, 0.02) have been incorporated into an electrochemical cell with propylene carbonate as an aprotic solvent. Sodium or lithium was electro-intercalated into the Van der Waals layers associated with these crystals using coulometric titrations to produce a solid solution electrode of the type MyTi xS 2, and open circuit voltages were measured as a function of the alkali metal content (0 < y < 1.0) at ambient temperatures. Discontinuities were observed in the emf-composition curves for sodium, but a smooth curve with a voltage span of only 0.5V (2.4 − 1.9V) was recorded for the intercalation of lithium. Electrochemical pulse experiments also enabled values to be derived for the chemical diffusion coefficients of sodium and lithium in MyTi xS 2. These values, which ranged from 10 −6 to 10 −10 cm 2/s, were strongly influenced by the presence of extra titanium in the Van der Waals layer associated with increasing deviation from stoichiometry in the original Ti xS 2 crystals.