Cathode Follower Research Articles

How acetylcholine gives rise to current at the motor end‐plate

How acetylcholine gives rise to current at the motor end‐plate

A Cathode Follower Power Amplifier

In circular accelerators and particularly in storage rings it is essential that the total impedance, as seen by the beam, be kept below some critical value. A model of the accelerating system was built using a single ended cathode follower amplifier driving a ferrite loaded cavity. The system operated at 234.5 KHz with a peak output voltage of ± 10 kV on the gap. The dynamic output impedance, as measured on the gap, was < 15 ohms.

Beam Position Measurement System at the Argonne Rapid Cycling Synchrotron

The position measurement system for the Rapid-Cycling Synchrotron (RCS) was originally designed with a four-plate, combined function, capacitive pickup pi electrode situated in each of the six short straight sections. During subsequent operation, it was discovered that these electrodes were limiting the aperture and, therefore, were being activated by the circulating proton beam. In addition, the activation made it difficult to maintain the active electronic components in the RCS tunnel. The new position measurement system has been designed to eliminate these problems. The electrode's horizontal and vertical dimensions have been increased and the plates reorientated for simpler, separate function signal processing. A passive impedance matching network has replaced the active cathode follower, eliminating maintenance requirements in the accelerator tunnel. The Radio Frequency (RF) beam signals are transmitted directly to the Main Control Room (MCR) for processing.

Intracellular action potential changes induced in both ventricles of the rat by an acute right ventricular pressure overload.

Eleven open chest, artificially ventilated rats were used to observe and compare the intracellular potential changes induced in the right and left ventricles by an acute right ventricular overload. Graded right ventricular hypertension was produced by external constriction of the main pulmonary artery. Transmembrane potentials were obtained using floating glass microelectrodes filled with 3 mol X litre-1 KCl and connected to a cathode follower through a silverchloride-silver junction. Following right ventricular overload, the level of resting potential was depolarised by 20% on the right ventricle and by 4% on the left (P less than 0.001). The repolarisation was not significantly affected. A significant correlation (P less than 0.01) was observed between the increase of right ventricular pressure and the depolarisation of resting right ventricular potential. The right ventricular distension which occurs in our experimental model thus induces a diastolic depolarisation of right ventricular muscle cells which cannot be neglected in the interpretation of the peripheral ECG changes.

Common Anode Amplifier Development

As accelerator beam intensity increases, loading of the RF system becomes a serious problem. Typical solutions include careful accelerating cavity design and active feedback schemes. Since the goal is to provide a low accelerating gap impedance, it is possible to simply drive the gap with a low output impedance amplifier. The "common anode" (also called cathode follower) configuration seems to be ideally suited for such an amplifier but has not received much attention in high power amplifier applications. This paper describes the construction and testing program of high power common anode configured RF amplifiers carried out at the Zero Gradient Synchrotron (ZGS). While amplifiers of this type seem limited to lower frequency accelerator applications, they may prove to be a viable alternative to the more conventional approaches currently in use.

8] Flash photolysis techniques

This chapter describes the classes of subunits used for flash photolysis as it is applied to enzymology and discusses the principles governing their choice for specific ends. The essential feature of flash photolysis is that light is used to displace an equilibrium or to perturb a steady state in a time that is short when compared with the dark relaxation time. It is convenient to express the brightness of a source in terms of the first-order rate constant for photodissociation of a complex exposed to it, although this is a quantity which depends very much both on the photosensitive system and on the physical layout of the apparatus. For data recording, a photomultiplier with a cathode follower, or an operational amplifier in the current-to-voltage mode, is used to drive a suitable cathode-ray oscillograph. It is suggested that flash photolysis cannot be regarded as a standard biochemical procedure, and an experimenter must set up his own apparatus. It is for this reason that this chapter deals in generalities, rather than offering specific descriptions of apparatus. The relatively restricted range of application of flash methods has discouraged manufacturers from offering commercial instruments, and it remains true that the method has not been fully exploited, especially in conjunction with modern flash equipment and in flow–flash systems.

Automated resonance-bar damping measurement system

This paper describes an automated internal friction measurement system which allows continuous resonant-frequency tracking and continuous recording of damping and resonant frequency during resonance-bar internal friction experiments. A phase-locked loop based on a phase detector maintains the system at resonant frequency although the frequency may change during the course of an experiment. A modified White cathode follower is used to overcome capacitive loading effects in coaxial cables between the damping system and electronic controlling–recording components. In this manner, monitoring and recording components may be located at distances of tens of meters from the drive-detector-specimen damping system, which may in turn be located in some hostile environment of interest. The automated system may be used with damping measurement systems which employ piezoelectric, electromagnetic, or electrostatic drive-detection transducers.

Observed temporal summation effects for lingual vibrotactile threshold measurements

Investigations using mechanical stimulation to measure lingual threshold sensitivity have resulted in conflicting assumptions concerning the nature of underlying neural transducers. A basic question concerns whether or not exteroceptive touch receptors in the lingual surface summate energy in response to displacement of tissues. This study tested the hypothesis that these receptors would demonstrate temporal summation as a function of pulse duration time. The stimulus unit included an audio oscillator, frequency counter, electronic switch, interval timer, amplifier, and electromagnetic vibrator. The measurement unit consisted of an accelerometer, cathode follower, microphone amplifier, and vacuum‐tube volt‐meter. Vibrotactile lingual thresholds for 250 Hz were obtained for four groups of normal speaking adult subjects using respective pulse duration times of 50, 100, 200, and 400 msec. Peak values were recorded in millivolts and converted to dB re one micron rms. Temporal summation was observed up to 200 msec reaching an asymptote around 400 msec. Findings supported the position that tactile transducers in mucous tissues respond to vibratory displacements in the same ways as pressure receptors in other cutaneous tissues.

Spectral response of n-type InSb in the submillimeter range

The spectral response of an n-type InSb bolometer and a Golay detector were compared between about 10 and 100 cm −1. The optical systems were held nearly constant and major wave number dependent deviations were removed from the data. The relative responsivities are given with the detector, cathode followers, and preamplifiers treated as a single component with the detector.

A Solid State Integrator for a Digital Dosemeter

Methods of integrating dose during radiotherapy treatment range from electromechanical to electronic, each method being satisfactory for all or part of the range of current produced by the ionization chamber associated with the therapy machine. Farr (1957) describes how a d.c. low-inertia integrating motor whose speed of rotation is proportional to applied voltage can be used. Ionization chamber current is converted to a voltage which is amplified and applied to the motor; the number of revolutions made by the motor over a period of time indicates the integrated current or dose delivered by the machine. An alternative method is to integrate the ionization current in a capacitor and measure the resulting voltage with an electrometer valve or similar device. Watson (1963) describes a circuit of this type which employs a moving coil relay to determine a level of voltage to which the capacitor has became charged. When the relay operates it causes a second relay to discharge the capacitor and the cycle of events is repeated; hence for each operation of the relay a signal is available to operate a counter. A similar arrangement is described by Naylor (1964), but in place of the moving coil relay a cold cathode trigger tube is used. When the voltage excursion on the capacitor has reached the same value as that required to ignite the tube, the resulting change in anode potential is used via a cathode follower to discharge the capacitor. The application of semiconductors to the integration of ionization current has been investigated by Kemp, Bottrill and Klevenhagen (1968).

Patterned activity of the buccal ganglion of the nudibranch mollusc Archidoris pseudoargus.

Patterned activity of the buccal ganglion of the nudibranch mollusc Archidoris pseudoargus.

Spontaneous activity of neurons in the visceral ganglion of Aplysia depilans

The membrane potential, impulse activity (mostly spontaneous) and, in some cases postsynaptic potentials, have been recorded in vitro under optical control (glass micropipets, cathode follower, oscilloscope with movie camera and/or ink writing recorder) in neurons of the visceral ganglia of Aplysia depilans. The value of the membrane potential is usually 40 mV. The majority of cells entered by the microelectrode show no spontaneous nerve impulse-spike activity. Statistical analysis of the spontaneous impulse activity made with records taken mostly from autoactive pacemaker neurons (using a computer), shows that these neurons generate relatively regular nerve impulses (the inter-spike interval histograms are often approximated by a Gaussian shape), irrespective of marked differences in mean values of the inter-spike intervals. Construction of special types of interval histograms and statistical comparison of corresponding distributions demonstrated, in several neurons, that the occurrence of inhibitory postsynaptic potentials tends to postpone the onset of the subsequent spike. Statistical description of in vitro recorded activity of neurons may be used for establishing correlations between metabolic and functional aspects.

Radiocontamination of the environment and its effects on the mother and fetus—III: Part II—Retention of cesium 137 by pregnant women, placentae and infants

The total body counter employed in this study has bccn presented elsewhere cz~) and consists of four large plastic scintillator units, each block measuring 50/50/15 cm, placed at 30 cm over a Lucite plate counting bed at equal distances. A similar arrangement with four other scintillation blocks was placed 10 cm below the counting plastic bed. Each plastic scintillator block was optically linked with a photomultiplicr of 5 in. dia; the ratio between the photocathodc area of the photomultiplicr and the scintillation block is about 5 per cent, which diminishes the efficiency of the system. The combined output from the units reached a cathode follower and wcrc mixed and passed to a linear amplifier. The output of the amplifier was further fed into three single-channel analyzers with associated sealers. For the potassium 40 peak (1455kcV) two singlechannel analyzers selected the pulse, each of the analyzers being set at half of the peak; the sum of the two pulses was attributed to 40 K, while the third analyzer was adjusted to the photopeak of a~Cs. The counting system was calibrated by body phantoms of a wide variety of lengths and weights, filled with distilled water containing a known amount of KC1 or 137Cs. The calibration constants were found to show a linear relationship with the body weight between 36 and 70 kg; the correction was made for the weights of the subjects measured. The sensitivity of the instruments was controlled by counting 18~Cs point sources. Fifteen minutes counts wcrc made on each subject; the background level was periodically measured throughout the day for I hr. The data wcrc processed by a digital computer (Burroughs-5500): with a counting time of 15m in, the statistical accuracy (q-a) was respectively -4-1.5 and 4-65 per cent for 40 K and 137Cs, assuming a body burden of 150 g stable potassium and 10 nc aXVCs. However, the absolute uncertainties arising from calculation errors may amount to 4-5 per cent.

Study of base pressure fluctuations behind a cone in supersonic flow

Study of base pressure fluctuations behind a cone in supersonic flow

Activity of neurons of somatosensory cortex during local strychnine poisoning

The types of re sponse of neurons in the somatosensory cortex to peripheral stimulation and the character of their reaction to direct electrical stimulation has already been examined (2, 3). A common component of all the individual responses of these neurons to these forms of stimulation was a temporary quiescence, probably due to inhibition. Since observations (4, 8, 9) have shown that strychnine abolishes the phenomena of inhibition, it was interesting to study the changes in the character of the responses to peripheral stimulation during local strychnine poisoning. It might also be expected that the application of strychnine, by abolishing inhibitory influences, would in turn facilitate excitation of the neurons of the surface layers of the cortex. The activity evoked in this manner would readily be distinguished by its selectivity and its greater potency from the activity evoked by direct electrical stimulation of the cortex. It was assumed that by performing experiments along these lines a more meaningful analysis could be made of interneuronal relationships in the primary somatosensory cortex. METHOD Cats were anesthetized with Nembutal (50 mg/kg, intraperitoneall y). Preparatory operations included tracheotemy, the application of stimulating electrodes to forelimb nerves, drainage of the 4th ventricle, and exposure of the sigmoid gyri of both hemispheres. Neurons in circumscribed areas of the posterior sigmoid gyri corresponding to the site of primary projection of forelimb nerves were investigated. Strychnine poisoning was produced by application of filter paper soaked in a 1% solution of strychnine nitrate to the area of the cortex to be investigated. The potentials of the neurons were detected by glass microelectrodes filled with 3 M KC1 with a resistance of 5-15 M~. The surface corticogram was recorded with a silver ball electrode. Potentials from the microelectrode were passed through a cathode follower (while those from the macroelectrode were passed directly)to a UBP 1-02 amplifier and, with a "Meopta" tape winder, were photographed from the screen of a D-581 twin-beam oscilloscope. The grid current of the cathode follower was less than 10-11 A. The nerves were stimulated with 0.5-msec rectangular pulses, applied through radio-frequency output from EST-7 generators.

A microwave temperature-jump apparatus for the study of fast reactions in solution

An apparatus for the determination of the rates of fast chemical reactions in solution is described. The temperature of a solution is raised, by means of a pulse of microwaves, by about 0.4 degK; the resulting shift of chemical equilibrium is followed spectrophotometrically with the help of a short-response photoelectric system and oscilloscope. The light beam passing through the solution must be of high intensity, in order to achieve a satisfactory signal-to-noise ratio, and a photocell is therefore used in preference to a photomultiplier. The photocell is connected directly to an amplifier without an intermediate cathode follower, in order to reduce electrical pick-up. Reactions with half-times down to about 1 μsec can be studied, and rate constants accurate to within about ±10% can be derived. In favourable cases, rate constants up to 1010 1. mole-1 sec-1 could be determined.

Impulses from single nerve fibres recorded in man using microelectrodes.

OUR knowledge of impulse patterns in the different types of afferent nerve fibres is based chiefly on animal experiments. It is true that Hensel and Boman1 recorded action potentials from single cutaneous nerve fibres in man using the microdissection method, but this method cannot be used in routine clinical examinations. Moreover, it only allowed investigation of the cutaneous nerves and not of other types of nerve fibres. We therefore considered it of interest to develop a method for recording from single nerve fibres in man using microelectrodes. For this purpose glass-coated platinum-iridium wire electrodes were used, made according to the method described by Wolbarsht and Wagner2. The wire had a diameter of 400µ. It was electrolytically polished to a tip of 0.5–1µ As shown by Wolbarsht and Wagner, it is possible to free the metal tip from the glass insulation over a surface of optional size and thereby obtain electrodes of different impedance. In our electrodes the impedance ranged between 40 and 100 kΩ at 1,000 c/s. The electrodes were sterilized by immersion in boiling water for 20 min and then connected to a preamplifier with a cathode follower, the action potentials being displayed on an oscilloscope. A loud-speaker and a tape recorder with a frequency response of 400–19,000 c/s were also used.

Cascaded R–C Networks and Phase-shift Oscillators

This article briefly describes the salient features of the simple three section C–R phase-shift oscillator which is met quite early in electronics laboratory courses. The frequency of operation and the gain required for oscillation are shown to depend on the output impedance of the amplifier which feeds the C–R network. By using a directly coupled cathode follower, the C–R network can be driven under almost ideal conditions where the C–R network determines the frequency and gain requirement. A simple and rapid method for calculating the frequency and gain for a cascade of ‘n’ identical sections is given, in general form, along with a graph of gain and frequency/no. of sections. A three section C–R network with tapered sections is analysed from the point of view of the gain required for the limiting case of extremely steep taper. The R–C transmission line with distributed parameters is considered and the gain required for the open-circuit line type of oscillator is shown to be – coshπ. The limiting gain required for a large number of identical sections appears to approach — coshπ, but this is not proved.

Two high power potentiostats for fuel-cell and fused salt electrolysis studies

The application of potentiostatic techniques to large scale laboratory and pilot plant studies in such fields as fuel-cell investigation and metal production by fused salt electrolysis, has led to the development of high power potentiostats, which can supply currents as high as fifty amperes. Two instruments intended for these purposes are described.The first is a carrier-frequency potentiostat, with a twelve-tube (parallel connected) class B output stage, which can supply 10 V, 50 A. Overload protection is secured by a relay circuit.The other instrument illustrates the recent possibilities afforded by the combination of semi-conductors and electron tubes. To have a high input impedance and a low drift, the first stage is fitted with high gain pentodes, in a symmetrical configuration. Dc stability can be further improved by a Goldberg type drift-correcting chopper amplifier (Zerostat), which compares the potential difference between the reference and working electrode with a controlling voltage, and supplies to the main amplifier a corrective signal. The second stage, a cathode follower, drives the transistor output stage. As transistors are easily damaged by overloads, a current-limited dc supply is included. Polarity of output voltage (±20 V) and current (±10 A) can reverse without switching.

A miniature cathode follower for single cell recording in awake, unrestrained animals

A small, light weight cathode follower has been described which is particularly suited for studies of single cell activity in awake, unrestrained animals. It can be mounted directly on the micro-manipulator.