Rate Of Voltage Change Research Articles

Transient analysis of p-n-p-n optoelectronic devices

p-n-p-n optoelectronic devices were analyzed using a coupled junction model, an equivalent circuit model, and a physical model. The accuracy of these models was confirmed by comparison with experimental data. The result of the authors' analysis was a new understanding of the dynamic properties of p-n-p-n devices. The authors found that the onset of switching depends only on the voltage across the forward-biased outer junctions, not on the total applied bias. Turn-on delay is dependent on the rate of voltage change across the outer junctions and the efficiency of the laser emitter. Fast turn-off of two-terminal devices is theoretically possible by applying a reverse bias during the turn-off transient. dV/dt induced switching can be avoided by proper design. Based on the authors' models, the maximum large-signal operating frequency of two-terminal p-n-p-n devices was estimated to be approximately 240 MHz. >

Digitized Cardiac Potentials Recorded with CR Leads: Development of a Portable Electrocardiograph

Digitized Cardiac Potentials Recorded with CR Leads: Development of a Portable Electrocardiograph

Direct electrophysiological actions of pentobarbital at concentrations achieved during general anesthesia

Pentobarbital and alpha-chloralose are widely used for experimental anesthesia, but their direct electrophysiological actions at anesthetic concentrations are unknown. Trough and peak concentrations measured by high-performance liquid chromatography averaged 27 +/- 3 and 45 +/- 13 mg/l (means +/- SD) for pentobarbital and 41 +/- 15 and 103 +/- 13 mg/l for alpha-chloralose in dogs receiving them for general anesthesia. The direct effects of each agent on papillary muscle action potentials obtained from guinea pigs killed by decapitation were studied in vitro. Pentobarbital increased action potential duration to 95% by 24 +/- 6 and 33 +/- 4% at 25 and 50 mg/l (P less than 0.001 for each), respectively, and caused corresponding increases in effective refractory period. Furthermore, pentobarbital reduced maximum rate of voltage change (Vmax) of phase 0 in a voltage-, rate-, and concentration-dependent fashion, suggesting use-dependent sodium channel blocking actions. The voltage dependence of Vmax was shifted by 3.7 +/- 1.7 (P less than 0.01) and 6.5 +/- 1.8 mV (P less than 0.001) by 25 and 50 mg/l pentobarbital, respectively. In canine ventricular muscle, pentobarbital caused rate- and concentration-dependent decreases in Vmax and increases in action potential duration and refractory period over a concentration range of 5-100 mg/l. alpha-Chloralose was devoid of direct electrophysiological effects in both species. We conclude that pentobarbital has potentially important electrophysiological actions on ventricular tissues at concentrations required for general anesthesia and may confound the results of in vivo studies.

Applications and stability of a thermoelectric enzyme sensor

Remarkable room-temperature sensitivity and stability have been achieved with thermoelectric enzyme sensors that detect the heat generated by various substrates reacting selectively on their enzyme-immobilized surfaces. Thin-film thermopiles together with cross-linked membranes of glucose oxidase and catalase have been employed to measure a linear voltage response to glucose [30 nV/ (mg/dl)] for concentrations ranging from 16 to 280 mg/dl in oxygen-saturated solutions. 90% response time values are typically less than six seconds. One sensor stored at room temperature and operated intermittently did not significantly change its response to glucose over the course of five days, and ultimately failed after nine days. Another sensor stored at 37°C exhibited a daily decrease in sensitivity and failed after five days. Four sensors operated continuously at room temperature showed an average normalized decline in response to glucose of 0.0087 ± 0.0005 h −1 and operating times ranging between 30 and 78 h. Through the use of alternative enzymes, other sensors have been made that respond to either hydrogen peroxide or urea. The use of an alternative sensing mode in which the rate of voltage change is measured following a step change in concentration appears to extend the upper range of linear response to glucose.

Immuno-FET sensor

An immuno-FET sensor was constructed using immobilized anti-human serum albumin, polyvinylbutyral membrane and an Ion Sensitive Field Effect Transistor (ISFET). The characteristics of this sensor system were investigated using human serum albumin (HSA) as a standard substrate. A linear relationship was obtained between the initial rate of the differential gate output voltage change and the logarithmic value of the HSA concentration. HSA was determined in the range 0.01 – 1 mg ml −1. The effect of pH was investigated. In the alkaline range, the response increased in proportion to pH value (pH 7.0, 9.0). In contrast, in the acid range, the response was not observed (pH 3.0, 4.0). The reusability was also investigated. After five cycles, the relative activity had decreased by approximately 80%.

Glucose Sensor Based On an Amorphous Silicon Isfet

Abstract An amorphous silicon ion sensitive field effect transistor (a-ISFET) was first applied to glucose sensors. When glucose oxidase was immobilized on the membrane, the sensor gave a linear relationship between the initial rate of the gate output voltage change and the logarithmic value of glucose concentration between 0.1 and 1 mg/ml at pH 7.0, 37°C. Determination of glucose was possible within 1 min. the system can be used for three weeks with only slight loss of enzymatic activity.

Inosine Sensor Based on an Amorphous Silicon Isfet

Abstract A sensor for the determination of inosine was prepared by a combination of the enzyme system (shown below) and an amorphous silicon ISFET (a-ISFET). Nucleoside phosphorylase and xanthine oxidase were covalently immobilized on polyvinylbutyral membrane containing 1, 8-diamino-4-aminomethyloctane. The optimum conditions for determination of inosine were pH 7.5, 32[ddot] C. The sensor gave a linear relationship between the initial rate of the output gate voltage change and the logarithm of inosine concentration between 0.02 and 0.1 mM. Determination of inosine was possible within 7 min. The system could be used for two weeks with about 35% loss of enzymatic activity.

Development of microbiosensors

AbstractSemiconductor fabrication technology was used for development of ion sensitive field effect transistor (ISFET) and micro‐electrodes which have been utilized as transducers of enzyme‐based microbiosensors. A urea sensor consisted of two ISFETs; one ISFET is urease‐coated ISFET and the other ISFET is reference ISFET. A linear relationship was obtained between the initial rate of voltage change and the logarithm of urea concentration over the range 1.3 to 16.7 mM. ATP and hypoxanthine sensors were also developed utilizing ISFET as a transducer. Furthermore, microelectrodes such as hydrogen peroxide and oxygen sensors were prepared by the silicone fabrication technology. A glucose sensor consisted of a hydrogen peroxide electrode and immobilized glucose oxidase membrane. A linear relationship was observed between the current increase and the concentration of glucose (1–100 mg dl−1). A microoxygen electrode was constructed from Au electrodes, polymer matrix containing alkaline electrolyte and a photocross‐linkable polymer membrane. This electrode was used as a transducer in microglucose sensor. A microglutamic acid sensor is also described.

Acetylcholine Sensor Based on Ion Sensitive Field Effect Transistor and Acetylcholine Receptor

Abstract A new type of acetylcholine sensor was made with an Ion Sensitive Field Effect Transistor (ISFET) and acetylcholine receptor. The acetylcholine receptor was fixed on a polyvinylbutyral membrane which covered the ISFET gate. When acetylcholine was injected into this system, the differential gate output voltage gradually Shifted to the positive side and reached a constant value. This response was due to the positive charge of acetylcholine. A linear relationship was obtained between the initial rate of the differential gate output voltage change and the logarithmic value of the acetylcholine concentration. Acetylcholine was fixed in the range 0.1-10μM. When the acetylcholine receptor was immobilized with the lipid membrane, the response was amplified with both the positive charge of acetylcholine and sodium ion flux through the acetylcholine receptor's channel. Therefore, the difference in the differential voltage between the acetylcholine receptor-ISFET systems with and without the lipid membrane ...

A microsensor for urea based on an ion-selective field effect transistor

The pH response of a pH-sensitive field-effect transistor (FET) is not affected by a ca. 1-μm thick membrane formed from λ-aminopropyltriethoxysilane and glutaraldehyde over the gate insular by a vapor deposition method. The response between pH 5.5 and 8.5 is ca. 61 mV pH −1 at 37°C in 5 mM Tris-HCl buffer. When urease is immobilized on the membrane, the sensor gives a linear relationship between the initial rate of the output gate voltage change and the logarithmic value of urea concentration between 16.7 and 167 mM. Determination of urea is possible within 30 s. The optimum pH is 6.0–6.5, at 37°C. The system can be used for 20 days with only slight loss of enzymatic activity.

Valsalva‐Induced Variations in the Intracardiac Signal

Variations in the intracardiac signal may substantially affect the sensing function of cardiac pacemakers. As the Valsalva maneuver causes a change in heart volume, its effect on the intracardiac signal was studied in seven patients with an adequate escape rhythm who had permanent ventricular pacemakers. During generator replacement, they were asked to perform a standardized Valsalva maneuver. An increase from the baseline amplitude ranging from 5% to 70% was noted during forced expiration against the closed glottis. There was a decrease from the baseline ranging from 15% to 50% after termination of this maneuver. Similar changes were noted for the rate of voltage change (slew rate). The magnitude of these alterations was most pronounced in patients with comparatively low intracardiac amplitudes. Because marked changes in the intracardiac signal can result from the Valsalva maneuver, it might be an important source of undersensing among patients with permanent pacemakers.

Threshold switching characteristics

The paper describes experiments on thresholds switches, based on a multicomponent chalcogenide glass (Te40As35Ge7Si18) of about 1 μm thickness, and pyrolytic graphite electrodes. The results demonstrate that “forming processes” (of presumably electrolytic character) in the off-state affect only the contact area which is not engaged in filamentary conduction when the switch is in the on-state. The detailed on-state characteristics are shown to depend on (a) the maximum on-current reached during the switching event, and (b) the rate of voltage change, and this is why depend on the external series resistance. Forming processes in the on-state must arise from a very different mechanism, and the operational reality of the minimum holding current has been established. The resultsfavor non-thermal interpretations of threshold switching as such, albeit inevitably with certain “thermal overtones”.

Earlier onset of QRS in anterior precordial ECG leads: precision of time interval measurements.

Onset of QRS was compared between simultaneously recorded conventional ECG leads in 84 subjects with clinically normal hearts from a defined population sample. Mean onset of QRS was 6.4 msec earlier in lead V1 and 7.4 msec earlier in V2 than in lead II. These differences were statistically significant. The measuring system was adapted from drafting techniques and took into account variations in paper speed which occurred during recording. Interobserver differences equivalent to greater than 1 msec occurred in 3.9% of timeline measurements, but in in 38% of QRS onset measurements. The lower precision in measuring QRS onset may be attributed to baseline oscillations and to the relatively slow rate of voltage change at the onset of ventricular depolarization.

A transient excited state model for sodium permeability changes in excitable membranes

In this paper we explore the properties of a mathematical model for the passive sodium permeability system of excitable membranes. This model is distinguished by the explicit inclusion of a rate constant which depends not on instantaneous voltage, but on rate of voltage change. Actually, the model is a rather modest modification of the Hodgkin-Huxley model, but displays some behaviors which the H-H model does not. Among these behaviors are a pronounced inactivation shift (for certain parameter values), a difference between inactivation time constant as measured by turning off a sodium current under sustained depolarization and as measured by double pulse experiments, skip runs under sustained current stimulation, and accommodation to slowing rising currents.

Glass Microelectrode Studies on Intramural Papillary Muscle Cells

Although the electrophysiological properties of intramural ventricular myocardial cells are important to an understanding of cardiac excitation and conduction, they have not been well defined. The paucity of information stems from limitations on the depth of penetration by glass microelectrodes and from difficulties in perfusing the deep layers. Therefore, a tissue slicing technique that satisfactorily exposes all the layers of a papillary muscle specimen from the endocardium to the epicardium was developed for electrophysiological examination. Glass microelectrodes were then used to explore these slice preparations to define the electrophysiological characteristics of intramural cells in the normal dog. Transmem-brane potentials recorded from subendocardial and deep myocardial cells in the papillary muscle slices were comparable to those recorded from standard preparations. Similarities included action potential duration and configuration, relationships among resting potential, action potential configuration, and extracellular potassium concentration, and dependency of action potential duration on cycle length. However, the average magnitudes of measured electrophysiological characteristics were consistently greater in the subsurface cells tested in papillary muscle slices than they were in the surface cells tested in the standard preparations, i.e., resting potential was 2-4 my more negative, action potential amplitude was 7-9 my larger, and maximum rate of voltage change (maximum dV/dt) was 40-140 v/sec larger. Deep myocardial tissues also exhibited enhanced responsiveness (the curve relating activation potential to maximum dV/dt of the response shifted up and to the left), cell populations with large maximum dV/dt, and estimated conduction velocities in excess of three times those in the surface cell layers. These findings provide a reasonable explanation for (1) discrepancies between previously reported values for ventricular conduction velocity, (2) rapid impulse spread to the papillary muscle tip, and (3) bidirectional activation of the papillary muscle and large trabeculae. They also suggest the possibility of functional pathways that facilitate rapid activation of the deep myocardial lavers.

The Physical Interpretation of Mathematical Models for Sodium Permeability Changes in Excitable Membranes

This paper deals with the physical interpretation of existing mathematical models which describe the transient sodium conductance changes in excitable membranes. It is shown that there are clear limitations to the specificity of inferences which may be drawn about physical mechanism from the behavior of abstract models. Within these limitations, it is shown that a pronounced inactivation shift is not necessarily evidence for coupling between the events responsible for the rise and inactivation of the sodium conductance, but that the inactivation shift may be associated with an event whose rate explicitly depends on the rate of continuous voltage change or magnitude of instantaneous voltage change.

Frequency stability of gunn oscillators with variation of ambient temperature

The factors controlling the frequency dependence of Gunn oscillators with ambient temperature variations are determined from an analysis of the equivalent circuit. By considering a simple I/V characteristic and the domain growth time, a model of the electron current waveform is obtained, which includes the temperature dependent properties of the Gunn diode. This leads to an equivalent negative conductance and a parallel susceptance. The domain capacitance contributes an additional susceptance. In the delayed domain mode, the transit time variation with temperature is the dominant factor and df/dT is about — 1 MHz/°C, except for high device temperature where the magnitude increases rapidly. In the quenched domain mode, elimination of the transit frequency variation causes lower df/dT magnitudes which become positive at low device temperatures. The rapid increase in df/dT at high temperatures for both the delayed and quenched domain modes is caused by the reduction in negative mobility, which increases the domain growth time. The rate of voltage change across the device is shown to delay the current drop from threshold for about 0·1 of the oscillator period. Good agreement for the experimental curve of df/dT at maximum power output is obtained with the theoretical delayed domain mode, for delays of less than 0·06 of the oscillator period. With the operating frequency to transit frequency ration of 0·9, the analysis shows that quenched domain operation is not normally possible. However, the rate of change of device voltage is shown to cause domain quenching. Experimental curves of df/dT against temperature for undercoupled oscillators agree qualitatively with the theoretical quenched domain mode curves. These show very low average drift rates of less than 100 kHz/°C. An increasing delay period for current drop is indicated at higher temperatures in agreement with the increasing domain growth time. Experimental results for n+ contacted C.W. devices operating in 50 Ω, λ/2 coaxial cavities and decoupled by 2 dB from maximum power were better than 100 kHz/°C over a temperature range of 100°C.

The electro-oxidation of polycyclic aromatic hydrocarbons in acetonitrile studied by cyclic voltammetry

The electro-oxidation of 9,10-diphenylanthracene results in a relatively stable radical-cation with a rate of charge-transfer of the order 1 cm sec − at a platinum electrode in acetonitrile. 1,2-Benzanthracene exhibits behaviour approaching that of diphenylanthracene at high rates of voltage change (500 V sec −. At lower sweep-rates, irreversible chemical reactions intervene leading to further oxidation, the standard potentials of subsequent steps being close to that for the first charge-transfer. Anthracene, pyrene, phenanthrene and triphenylene exhibit similar limiting behaviour of anodic currents and peak potentials at high scan-rates, which is identified with the formation of radical cations: the cations of these hydrocarbons have a life-time of a few milliseconds. The common supposition that the primary electrode process involves the formation of the dipositive ion is thus incorrect. Moreover, conventional polarographic oxidation potentials of the unsubstituted compounds are controlled by chemical reaction. The reversible oxidation potentials for the charge-transfer step have been evaluated from the data at high rates of voltage sweep.

A New Polarograph

By use of a current recording system of negligible damping, polarograms which yield correct values of the half-wave potential may be obtained even at a high rate of voltage change. In addition, greater sensitivity is obtained due to the use of peak currents instead of average currents. The construction and performance of an instrument based on this system is described.