Showing papers on "Pulse duration published in 1972"

Dual oscillator, variable pulse duration electrotherapeutic device

Abstract: A first multi-vibrator produces square wave pulses of constant voltage for a 15 second period with a three second "off" interval in between each pulse. The 15 second pulses are converted into ramp pulses of the same period and interval. The ramp pulses are used to control a second multivibrator which produces a series of constant voltage square wave pulses during the 15 second period. Each succeeding square wave pulse during the 15 second period is of a slightly longer duration so that there is a constant increase in the time duration of the square wave pulses during each 15 second period. The cycle is repeated after the 3 second "off" interval between the 15 second pulse periods. The varying square wave pulses are used to trigger separate 4KHZ and 6KHZ voltage oscillators. Each oscillator produces output pulses at their respective frequencies of the same duration and interval as the square wave inputs. The frequency pulses are amplified by separate amplifiers and the amplified pulses are applied by a body probe to the patient. Zener diodes are provided at the output of each amplifiers to limit the maximum possible voltage that may be applied to the patient.

Some Characteristics of a 600 kV Flash X-ray Tube

Abstract: The performance of a continuously pumped flash X-ray tube has been studied in the voltage range 250-600 kV Dose, pulse length, beam quality, source size and spatial distribution of the radiation were measured It is shown that the output intensity is maximized if the tube impedance is 23 times the internal impedance of the pulser

Generation of Single Picosecond and Subpicosecond Light Pulses

Abstract: Picosecond light pulses passing through a saturable absorber show considerable pulse shortening. For instance, under special favorable conditions the pulse duration was found to be reduced from 8 to 2. 6 psec in a single transit. Using a multiple‐absorber‐amplifier system, light pulses were shortened from 8 to 0.7 psec in five transits. The shortest pulse seen in our experiments had a duration of less than 0.5 psec. Calculations based on a two‐level approximation of the absorbing medium agreed well with the experimental results.

Effect of H2 Pressure on Pulsed H2+F2 Laser. Experiment and Theory

Abstract: Stimulated emission predictions and measurements for an H2+F2 laser are compared for H2 pressures from threshold to stoichiometric, a range of several orders of magnitude. Slowly flowing, helium‐diluted, 50 torr mixtures are initiated photolytically. Two dilution ratios and two output couplers are considered, and good agreement is found for time‐to‐threshold and pulse duration vs H2 pressure. Spiking, relaxation oscillations, and possibly mode beating, features not modeled, are observable in some pulses; however, predicted intensity vs time generally agrees in pulse shape with laser output. Observed and predicted peak intensities nearly match for low H2 pressure, and the predicted increase of peak intensity with low H2 is followed fairly well. For H2 in the vicinity of one‐tenth stoichiometric, the peak intensity data show an abrupt leveling off, while the calculations predict a continuing increase. This disagreement most probably cannot be attributed to uncertainties in the kinetic model. All rate modifications considered have proven incapable of producing a change sufficiently large or abrupt to explain this feature of the data. Experimental results are presented supporting the notion that parasitic oscillations cause this change in laser output.

Electromigration in conductor stripes under pulsed dc powering

Abstract: Thin Ti–Au films on sapphire were powered using pulsed dc. The incidence of electromigration damage is a complex function of pulse duration and repetition rate. For a given total ``exposure'' (fixed current density for a fixed total on‐time) the damage may be reduced or eliminated by using duty cycles less than 100%.

Signal Resolution via Digital Inverse Filtering

Abstract: Research in numerous areas is directed toward the resolution of multiple overlapping signals in a noisy environment. These areas include radar, sonar, speech, seismology, and electrophysiology. Sometimes matched filters are used; other times inverse filters are employed. This paper discusses one approach to the analysis of the resolution of inverse filters. Our method is to compromise the trade-off between signal resolution and the output signal-to-noise ratio (SNR). A performance measure for the inverse or deconvolution filter is defined as a quantity proportional to the harmonic mean of the resolution and the SNR. An optimum output pulse duration is obtained using this criterion, where the pulse shape has been previously selected and the input signal waveform is known. In addition, upper and lower bounds for the output pulse duration are presented. Graphs are given which allow the designer to select the optimum inverse filter output pulse duration for a desired signal resolution and an estimated SNR.

Temporal Resolution of Tonal Pulses

Abstract: Temporal resolution, as defined by the minimum detectable gap between successive tonal pulses, was observed to decrease as a direct function of both the frequency disparity between successive pulses and the duration of the pulses. An interaction between frequency disparity and pulse duration was also observed.

Experimental investigation of transient stimulated Raman scattering in a linearly dispersionless medium.

Abstract: The results of numerical calculations of the transient stimulated Raman scattering reported previously have been verified experimentally under conditions where both linear dispersion and self-focusing effects were negligible The existence of a delay between maxima of the laser and Stokes pulses is experimentally demonstrated for the first time, while the pulse shortening in time via Raman scattering is established more firmly than in previous work The incident-laser-pulse duration, generated-Stokes-pulse duration, and delay between intensity maxima for the laser and Stokes pulses were measured with the two-photon absorption-fluorescence technique The effective phonon-dephasing time is determined via spontaneous Raman scattering By using these measured quantities, inferences are made as to the magnitude of the transient gain and the shape of the exciting picosecond laser pulse

Supersonic electrical‐discharge copper vapor laser

Abstract: A copper vapor laser, utilizing a pulsed discharge transverse to a supersonic flow of copper vapor, argon, and helium and oscillating at 5106 and 5782 A, has been built and tested. Laser energy densities per pulse of 2.5 μJ cm−3 have been achieved to date. Laser pulse widths of up to 185 nsec have been obtained with delay times after initiation of the current pulse of 220–250 nsec. Both the delay time and pulse width are in good agreement with theoretical predictions. Quenching of the laser pulse is shown to be due to a rapid increase in the rate of equilibration of the lasing levels by electron collisions, and to a decrease in the differential pumping of the lasing levels from the ground state because of a decay in the electron temperature.

Piezoeletric Current from x‐Cut Quartz Subjected to Short‐Duration Shock‐Wave Loading

Abstract: When an x‐cut quartz disk is subjected to an impulsive load, the piezoelectric current in an external short circuit is ordinarily an accurate time‐resolved replica of the stress history at the input electrode. Recently, it has been observed that stress pulses whose durations are less than the shock‐wave transit time through the disk sometimes produce anomalous current‐vs‐time responses. In the present work, x‐cut quartz disks are subjected to stress pulses of six different durations and with amplitudes from 9 to 29 kbar. Carefully controlled accurately known pulses are applied to the samples by the impact of projectile‐mounted quartz disks of various thicknesses. The piezoelectric current accompanying each stress pulse is continuously monitored as the pulse propagates through the sample disk. It is found that the anomalous current is a consequence of shock‐induced conductivity in the region of the quartz disk that has been shock loaded and subsequently unloaded to a lower stress value. The threshold for conductivity is found to depend upon both stress amplitude and pulse duration. The threshold is further determined to be controlled both by a critical unloading stress value and by a critical electric field value. The critical unloading stress value is found to be 11.2±0.7 kbar, and the critical electric field is found to be (2.8±0.3) ×105V/cm.

Diagnostic apparatus for automatically generating an intensity-time diagram showing points of minimum involuntary muscle movement

Abstract: Both amplitude and pulse width of pulses applied to the muscle are varied automatically, a given number of pulses being applied at a given amplitude and pulse width prior to increasing the amplitude. The given number varies with the pulse width. The amplitude is increased until involuntary muscle movement results. The same procedure is repeated at the subsequent pulse width.

A simplified model for predicting gain, saturation, and pulse length for gas dynamic lasers

Abstract: A single time-scale model is developed to describe the 10.6-μ laser energy extraction from an initially inverted N 2 -CO 2 catalyst mixture where the energy is stored primarily in the N 2 vibration. This condition is typical of high-pressure gas dynamic lasers, but the methods are general and applicable to other systems. In the absence of external pumping, the nitrogen can be regarded as an energy source that is depleted on a time scale \tau = \tauNAT(1 + I_{0}/I), \tauNAT being the minimum possible time scale governed by collisional processes, τ determines the pulse time for Q -switched laser mixtures or the required streamwise cavity length for CW gas dynamic lasers. The derived saturation intensity I 0 also appears in the expression for saturated gain (for collision broadened cases) g = g_{0}/(1 + I/I_{0}) , where g 0 is approximately the small signal gain at a given nitrogen vibrational temperature, g 0 decays on the same intensity-dependent time scale τ as the nitrogen vibrational energy.

Variable Ultrafast Photographic Shutter

Abstract: We propose an ultrafast shutter, based on the saturable properties of polymethine cyanide dyes, with a variable shutter speed of 10–40 psec and more. With this, one can measure the pulse duration of the mode‐locked ruby laser pulse. We can also deduce the fluorescence decay time of these solutions employed.

Pulse propagation in a two-mode waveguide

Abstract: The results of an earlier paper, describing pulse propagation in multimode dielectric waveguides with random coupling, are specialized to the two-mode case. Because of their greater simplicity, the results for this special case provide more insight into the mechanism of pulse shortening due to mode coupling. The two-mode theory yields a formula for the width of a pulse carried by coupled guided modes that is found to hold also for four modes, so that it may be true for an arbitrary number of modes. This formula [eq. (23)] contains only the measurable distance required to establish the steady-state power distribution and the length of uncoupled pulses. The pulse length formula is identical with Personick's important result. Our treatment suggests that the characteristic length appearing in this formula may be accessible to measurement.

Theory of the D. C. Motor Controlled by Power Pulses Part I - Motor Operation

Abstract: This paper describes the theoretical relations between currents, fluxes and pulse duration in a DC motor energized by power pulses. From these values, the average torque and speed as well as their instantaneous variations are calculated. The non-linearity of the magnetic circuit is considered by a suitable approximation of the magnetization curve and the resulting error is evaluated. Numerical examples illustrate the characteristics of a shunt and series motor for several types of pulse control. A companion paper1 discusses in detail different braking methods, proprietory commutation phenomenons and additional iron and copper losses. Also, a Fourier analysis of the current pulses is presented.

Method and apparatus for detecting absolute value amplitude of am suppressed carrier signals

Abstract: Apparatus for detecting the absolute value amplitude of amplitude modulated suppressed carriers includes first and second product detectors which use quadrature phases of a locally generated reference carrier to product detect the modulated carrier producing first and second vector components of the amplitude of the information signal, and an output circuit for obtaining the vector sum of the two components of the information signal amplitude to thereby provide a signal which is proportional to the absolute value amplitude of the information signal. In one embodiment, the vector sum of the two components of the information signal amplitude is obtained by amplitude modulating quadrature phases of a high frequency carrier in separate amplitude modulators, summing the amplitude modulated signals thus produced, and demodulating the resultant signal to translate the high frequency carrier back to the base-band and thereby recover the amplitude information.

Method and apparatus for checking metallic objects by monitoring its effect on one cycle of an alternating field

Abstract: A method and apparatus of checking metallic objects to determine whether they conform to a desired standard by passing the object between the primary and secondary coils of a transformer so that the amplitude of the A.C. voltage output from the secondary is varied. Then the half-wave amplitude of this output is compared with the amplitude of a reference A.C. voltage, which is also used to energize the primary coil, to determine whether the halfwave amplitude of the output lies within a predetermined range correlated to the desired standard. To make allowance for the fact that the output is above the lower limit for longer than it will be above the upper limit if this latter is exceeded, the comparison is by first and second comparators relating to the lower and upper limit respectively, the first comparator giving an output pulse when the upper limit is exceeded. The output pulse for the first comparator is divided into two paths one to a negator giving an output pulse assigned the binary value 1 to an input of a NAND-gate, the other path leading to a first flip-flop which when triggered by the output pulse from the first comparator gives an output pulse also assigned binary value 1 to another input of the NAND-gate. The output from the second comparator is fed to a second flip-flop which if triggered by a pulse for the second comparator gives an output pulse of binary value 0 to a third input of the NAND-gate, otherwise the absence of a pulse from the second flip-flop has a binary value 1. Only when all the three inputs to the NAND-gate are each of value 1 will output for the gate change for binary value 1 to 0 to indicate that the object satisfies the desired standard. The flip-flops are reset automatically, to permit evaluation of each output pulse from the comparator.

Heating of Laser Plasmas for Thermonuclear Fusion

Abstract: In this survey the experimental results of the investigation of the laser produced plasmas in a wide interval of energy and light pulse duration are reported. The processes taking place at a dense plasma heated by laser radiation for the obtaining of a thermonuclear yield have been analyzed. The directional motion for heating in the various schemes using cumulative effects is discussed.

Ultrasonic thermometry using pulse techniques.

Abstract: Ultrasonic pulse techniques have been developed which, when applied to inert gases, provide temperature measurements up to 8000 K. The response time can be less than 1 msec. This is a significant feature in studying shock-heated or combusting gases. Using a momentary contact coupling technique, temperature has been measured inside steel from 300 to 1500 K. Thin-wire sensors have been used above 2000 K in nuclear and industrial applications where conditions preclude the use of thermocouples, resistance devices, or optical pyrometers. At 2500 K, temperature sensitivity of 0.1% is obtained in Re wire sensors 5 cm long by timing five round trips with an electronic instrument that resolves the time interval between selected echoes to 0.1 microsec. Sensors have been operated at rotational speeds over 2000 rpm and in noisy environments. Temperature profiling of up to ten regions using only a single guided path or beam has also been accomplished.

Hot water heating system

Abstract: In the hot water heating system disclosed herein, a sensing means such as a thermistor provides a first electrical control signal which represents deviation of outlet water temperature from preselected value and a flowmeter provides a pulsating electrical signal having a frequency which varies as a function of rate of flow through the heating system. An output signal is generated having a frequency equal to that of the pulsating signal and a squarewave pulse duration which varies as a function of the first control signal. Heater means are then energized by the output signal so as to provide a thermal input to the heating system which is substantially proportional to the product of water output temperature deviation and flow rate. This control minimizes output temperature fluctuations due to thermal inertia and heater lag.

Pulse nitrogen laser at high repetition rate

Abstract: An output of 1.5 W of average power at 3371 A is obtained from a pulsed nitrogen laser operating at a repetition rate of 1200 Hz. Pulse powers up to 300 kW are observed, with 10-ns pulse duration. The high repetition rate is made possible through the use of a closed-cycle transverse gas flow system to supply fresh ion-free gas to the laser for each pulse.

Aircraft starter control system

Abstract: A control system for automatically closing a solenoid-operated air valve that supplies pressurized air to rotate an air turbine starter motor of an aircraft engine when the starter rotor reaches a predetermined rotational speed. The control system senses rotation of the starter rotor and produces a pulse train wherein each of the pulses generated has a duration which is a function of the rotational speed of the starter rotor and compares each pulse duration to a reference pulse which corresponds to a predetermined rotational speed of the starter rotor. When the duration of the rotor pulses decreases to a point where they are shorter in duration than a reference pulse, the supply of pressurized air is removed from the starter, thereby removing power from the starter at the predetermined speed.

Electronic watt-hour meter with digital output representing time-integrated input

Abstract: An electronic meter, such as a watt-hour meter, arranged to process an input signal which has an amplitude varying instantaneously with time, such as a wattage signal, and to provide a digital output signal representing the time-integrated value of the input signal, for example, a digital output representing accumulated watt-hours of electrical power. The meter applies the time-varying input signal to a pulse width modulating means to convert the input signal into a pulse signal in which the pulse width varies in correspondence to the amplitude of the input signal. The modulated pulse signal drives a gating circuit which controls the application of a steady clock pulse signal from a generator to a pulse counting means providing a digital signal output representing the cumulative total of clock pulses applied thereto through the gating circuit. The gating circuit, in response to the modulated pulse signal, applies a proportion of the total clock pulses which corresponds in number to the time-integrated value of the input signal, thereby providing the desired digital watt-hour output.

Passage of an ultrashort coherent light pulse through a semiconductor

Abstract: A theory is given of the resonant interaction between an ultrashort coherent light pulse and a semiconductor, which occurs when the pulse duration is less than the polarization or phase memory relaxation time. It is shown that, under certain conditions, a stationary 2? pulse can form. Numerical estimates of the velocity of propagation of a stable pulse are obtained for a typical semiconductor.

A Precision Current Pulse Generator for NMR Self‐Diffusion Measurements by the Pulsed Gradient Technique

Abstract: An apparatus is described for delivering controlled pulses of current into an inductive load. Digital logic is utilized for control of the pulse duration, and current feedback is used to control the magnitude of the pulse. The apparatus was designed to enable NMR self‐diffusion measurements to be obtained by the pulsed gradient technique, and diffusion results are shown for number 15 white mineral oil using pulse durations of 10 msec and magnitudes of over 25 A.

Frequency burst communication system

Abstract: A digital or analog signal containing information is discriminated into identifiable bit bundles of information which are modulated into pulses of an oscillating current whose pulse length corresponds to a particular bundle of information which is of shorter duration than the unmodulated bundle of information and which is multiplexed by time zones.

Magnetooptic disk utilizing MnBi thin films

Abstract: A study has been made of a magnetooptic disk memory using MnBi thin films. The present experimental device is equipped with a MnBi medium vacuum deposited on a glass disk 139 mm in diameter and 20 mm thick, and with a rotation mechanism in which gas bearings were employed. A writing clock frequency of 1 MHz, a bit diameter of 2 μm, a bit density of 220 bits/mm, a track density of 170 tracks/mm, and reading at 5 MHz have all been achieved. In this case, the writing conditions were a writing power of 70 mW, a medium speed of 5.2 × 103mm/s, and a pulse duration of 400 ns. The empirical relationships among the medium speed, laser power for writing, and the light pulse duration are in good agreement with the theoretical ones.

Pulse Propagation in Straight Circular Elastic Tubes

Abstract: : An experimental investigation of elastic waves produced by the longitudinal impact of strikers with straight 2024 aluminum tubes of 1-in. dia and wall thickness of 0.035 in. (thin walled), 0.095 in. (medium thick-walled), and 0.5 in. (solid bar) was performed by means of the Hopkinson bar technique. For most of the tests the strikers consisted of 1/2-in-dia steel balls; however, 1/4-in-dia, 3/16-in-dia and 1/8-dia steel balls were also used to permit variation in pulse duration. Both central and eccentric impact were achieved by firing the striker from an air gun at a predetermined pressure against the carefully positioned target; the initial velocity of the striker was measured whenever necessary. Longitudinal strain records of the resulting pulse from positions both on the inside and outside surfaces of the hollow specimens and on the outside of the solid bar were obtained by using strain gages of either foil or semiconductor type; some transverse strain histories were also measured concurrently. The transient longitudinal strains were predicted theoretically by solving the one-dimensional Rayleigh-Love equation of wave propagation in a semi-infinite tube with the aid of a computer program. The input to the program consisted of the measured strain record at the first gage station. Reasonable agreement between the data and the results of these calculations was obtained. An experimental investigation of the effect of shortening the pulse duration, the relation between the transverse and longitudinal strain at the same position, and the nature of the antisymmetrical component in the eccentric shots was also undertaken. (Author)