Showing papers on "Pulse duration published in 1979"

Surface Discharges on Teflon, Mylar and Kapton

Abstract: FEP Teflon, Mylar and Kapton H are compared from the point of view of charged-area scaling of discharge current pulse properties. The properties measured are peak current, pulse duration, released charge and energy dissipated in a load resistor, all for 20 keV incident electrons at a current density of 80 nA/cm2. In general it is found that the three materials are more similar than dissimilar, and furthermore that this similarity extends to discharge damage as well, the damage being identified as a combination of subsurface filamentary tunnels and surface grooves. The experimental observations are used to motivate a theory of discharge arc propagation in which the propagation velocity is controlled by the rate of removal of excess charge via wave propagation along a filamentary tunnel filled with an overdense plasma.

Time‐domain photoacoustic spectroscopy of solids

Abstract: Most conventional photoacoustic spectroscopy of solids has employed a periodically modulated light source. The availability of high‐intensity pulsed light sources of short pulse duration makes possible the study of the time response of a photoacoustic system in which the solid is excited by a single optical pulse. A one‐dimensional theoretical model is presented in which the time dependence of the photoacoustic response is evaluated for systems of variable optical absorption coefficient and sample thickness. The analysis is restricted to the case for which nonradiative relaxation processes occur instantaneously on the time scale of the measurement. Typical response curves for optically excited systems are presented and interpreted in terms of physical processes occurring in the cell.

Analysis of compression of frequency chirped optical pulses by a strongly dispersive grating pair.

Abstract: An optical pulse compression medium formed by two parallel gratings can be strongly dispersive if the diffracted beam emerges at grazing angle from the surface of the first grating. Strong dispersion makes possible temporal compression of broad incident pulses. However, sufficiently strong dispersion is accompanied by a nonlinear variation of group delay with carrier frequency, which will cause the envelope of the compressed pulse to be distorted and limit the minimum attainable pulse width. Strong dispersion as a limiting influence upon compression of linearly chirped pulses is examined for the grating pair at several laser wavelengths. Specific examples are discussed for the compression of CO2 laser pulses at 10.6-μm wavelength.

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Abstract: Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 A for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.

A computer simulation of laser annealing silicon at 1.06 μm

Abstract: A computer simulation of laser annealing ion‐implanted silicon with 1.06‐μm radiation at energy densities of 38–76 MW/cm2 shows that the amorphous surface layer of the silicon melts. Quantitative predictions for the depth of the molten zone and the impurity distribution as a function of peak laser intensity and pulse duration agree well with published experimental observations. Additional analysis indicated that pulse duration, peak power density, and the impurity implantation depth are of primary importance in controlling the laser annealing process. Also, step junctions may be produced for optimal values of these parameters.

A nanosecond surface discharge study in low pressures

Abstract: The developing velocities of the positive and negative corona streamers on insulating plates have been measured by using the dust figure technique at low pressure in air. By applying nanosecond time pulses from 10‐ to 50‐nsec duration to a needle point where the insulating plate is sandwiched in between the needle and plate electrodes, the diameters of the recorded dincharge pattern against the pulse duration in a pressure range of 150 to 760 Torr were obtained. The maximum velocities of the developing corona streamers which were measured at a voltage of 13.0 kV were 3.0×108 cm/sec in the positive case and 2.5×108 cm/sec in the negative case for a pressure of 150 Torr. Moreover, when a time pulse of 10 nsec was applied to the needle point at a pressure of less than 250 Torr, the velocity of the positive streamer seemed to reach a limiting value for a given voltage, while the negative increased proportionately to the inverse of the pressure. The resulting polarity effect suggests that when the nanosecond p...

Pulse spreading and wandering in random media

Abstract: Two possible mechanisms are responsible for the temporal broadening of pulses propagating in a turbulent medium. The ensemble averaged pulse may be broadened owing to the fact that each realization of the ensemble is spread in time as a consequence of scattering. It may also come about because of the wandering of the pulse. In this paper these two mechanisms are studied. First, the two-frequency and the four-frequency mutual coherence functions for the field are obtained for both the Rytov approximation and the asymptotic saturated condition. They are then used to compute the spreading and wandering of the pulse. It is found that under the condition of weak scattering, pulse wandering dominates the contribution to the broadening of the pulse. In the saturated region, however, pulse spreading becomes the dominant factor. Explicit expressions for the spreading and wandering are derived for some examples.

Electronic tissue stimulator with output signal controls

Abstract: In a transcutaneous nerve stimulating apparatus, the stimulating pulse wave form is shaped and manipulated to accommodate specific physiological parameters, and to allow multiple non-interfering electrode administrations. The stimulating pulse wave form, of desired pulse rate, pulse duration, and pulse amplitude, optionally includes successive pulses of alternating plurality, which may all be coupled to a single electrode, alternately coupled to plural electrodes, or the like. Pulse decay is controlled, as is pulse rise time. Voltage regulation is provided to the pulse generation apparatus.

Microwave-induced auditory responses in guinea pigs: Relationship of threshold and microwave-pulse duration

Abstract: Auditory brainstem-evoked electrical responses of guinea pigs were used to determine microwave energy thresholds for perception of pulsed radiations. A klystron was used to generate 918-MHz microwaves at pulse widths between 10 and 500 μs; the microwaves were fed into a circular waveguide that partly enclosed a guinea pig's head. At pulse widths less than 30 μs, thresholds were related to the density of absorbed energy (and to the density of incident energy). The minimal absorbed energy density per pulse is 5 mJ kg−1. As the width of the pulse increased, the threshold energy increased. For pulses longer than 70 μs, thresholds were related to the peak of the incident power density. The maximal power density of incident radiation is 90 mW cm−2 in the circular waveguide. The dependence of the evoked response on the width of the microwave pulse is in excellent agreement with predictions of thermal-expansion theory. These results provide more evidence that the microwave auditory effect is caused by a thermal expansion in the exposed head.

Thermal control system

Abstract: In a space shuttle, payloads are individually temperature controlled by means of a liquid control loop in heat exchange relationship with both the payload and a radiator or shuttle cold plate. The liquid pump is driven at a variable speed to control the heat transferred between the load and the radiator or cold plate, and the motor may be reversed to by-pass the radiator through check valves. The radiator includes heat pipes seated in elongated, high thermal conductivity extrusions and retained therein by elongated springs. The motor is a brushless DC motor isolated from the pump by a magnetic clutch and thermal isolator. The motor is driven by a digital circuit which provides a single pulse to each set of windings during each energizing time frame. The width of that pulse is modulated to provide for speed control. Pulse width modulation is by means of a one-shot, the pulse duration of which is controlled by a speed control signal.

Isotopic selectivity of IR laser photodissociation of CF 3 I molecules

Abstract: The selectivity dependence of multiphoton dissociation of CF3I on the conditions of excitation (pulse duration, concentration of the isotope under excitation and gas pressure) has been studied. It has been shown that the main mechanism of selectivity loss isV-V exchange during a laser pulse. The elaborated model is in good agreement with the experiment.

Tuned switched-mode power supply

Abstract: A tuned switched-mode power supply for producing a stabilized d.c. output voltage by controlling the duration of the conducting period of a bidirectional switch as a function of the output voltage. The drive switching pulses for the switch are subjected to a pulse duration modulation control followed by a frequency control in such a way that the switch-off pulses have a substantially pre-determined time duration which is longer than half a cycle of the tuning frequency of the power supply.

Structure and observable characteristics of laser driven ablation

Abstract: Numerical hydrodynamic‐heat flow simulations of spherical ablation have been done with sufficient spatial resolution to show the details of the ablation front structure. These simulations show a continuous qualitative change in the velocity spectrum of expanding ions with increasing laser pulse length, ranging from approximately isothermal behavior from short pulse to ablative behavior from longer pulses. The ablative behavior is characterized by an energetic peak in the ion spectrum, a characteristic of ablation that is experimentally observable. The longer pulse cases are found to be in good agreement with the stationary flow model of ablation.

Apparatus for supplying high power electric loads operated in a pulse-like manner, especially for X-ray equipment

Abstract: The invention relates to an apparatus for supplying high-power electric loads operated in a pulse-like manner, particularly to X-ray equipment. The apparatus makes use of the mechanical energy of rotation of a flywheel rotated through a time period which is substantially longer than the pulse duration of the load by a driving power being substantially smaller than the pulse power of the load to generate a supply voltage for the load in expense of this mechanical energy. The driving period of the flywheel and the associated moderate driving power provide an energy balance with the short pulses with high power consumption. The apparatus comprises a generator unit with at least one electric rotary machine which has a rotor that rotates together with the flywheel. The excitation of the rotary machine is provided by a field power supply being controlled by a control unit. The control unit controls the excitation of the generator unit to provide predetermined output voltage and current levels for the load. The apparatus according to the invention can provide a specified operation control for the load. According to an aspect of the invention a method has been provided for carrying out fluorography which can see to an increased sensed light intensity. According to this method fluoroscopy is carried out by pulsed X-ray irradiation with small average intensity and high pulse intensity, in which the repetition frequency of the pulse is high enough to provide for a continuous light sensation. Such pulsed irradiation provides for an image on the fluoroscopic screen in which the sensed light intensity is increased by the ratio of the peak and average radiation intensities compared to the light intensity of a conventional continuous irradiation with the average intensity.

A New Optical Communication System Using the Pulse Interval and Width Modulated Code

Abstract: This paper proposes a new optical communication system using the Pulse Interval and Width Modulated Code. It is constructed as combinations of pulse width and interval. Then it is easy to understand that the transmission capacity of this Code is bigger than those of Pulse Width Modulation and/or Differencial Pulse Position Modulation.

Fuel feed device

Abstract: PURPOSE: To improve the acceleration performance by providing a quantity-increasing means performing the quantity-increasing correction for fuel corresponding to the quantity of an accelerator pedalling in acceleration, as well as a continuation means continuing the quantity-increasing correction for fuel corresponding to the quantity of pedalling after completion of pedalling. CONSTITUTION: The fuel feed device of an SPI-type engine which conducts fuel jetting at one point in the upperstream of a manifold is constituted by an acceleration sensor 1, a control unit 3 controlling a fuel-jetting valve 2 according to the output signal from the sensor 1, and an operational state detecting circuit 4 outputting various signals indicating the state of operation of the engine, such as number of rotation and temperature of cooling water. On the occasion, the control unit 3 is constituted by providing a quantity-increasing correction circuit 12 in addition to the existing basic pulse computing circuit 8, driving circuit 9 and additional pulse generating circuit 10. This correction circuit 12 is constituted so that the pulse duration of the basic pulse signal from the circuit 8 can be changed throughout a fixed times in accordance with the number of pulse signals from the sensor 1. COPYRIGHT: (C)1981,JPO&Japio

Non-simultaneous auditory masking in the goldfish, Carassius auratus

Abstract: Auditory thresholds were determined for 500 HZ pure tone pulses of 15, 25 and 50 ms duration presented leading, following or simultaneously with noise pulses of 50 or 250 ms duration. Masking by the noise decreased: (i) with an increase in tone pulse duration; (ii) with a shortening of the noise pulse duration; and (iii) as the interval between tone and noise pulses was increased from 0 to 350 ms. The effect of the noise was independent of whether the noise led or followed the pure tone. It is suggested that the most significant factor affecting masking was the duration of the interval between tone and noise, and that the site for the interactions between signals is central to the inner ear.

Electronic controlled fuel injection device

Abstract: PURPOSE: To prevent excessive fuel from being fed and control air-fuel ratio in the cylinders by varying the number of times if injection in accordance with the driving conditions of a engine and changing the injection pulse length corresponding to the number of times of injection. CONSTITUTION: The injection control circuit 12 changes the number of pulses per pulse length of the fuel injection pulse signal and a unit engine rotation corresponding to the output voltage from the pressure sensor 11. The multiplication circuit 13 generates the pulse signal by multiplying the pulse length of the fuel injection pulse signal sent out from the injection control circuit 12 by the compensation signal from the compensation circuit 14 to correct fuel feeding rate in accordance with the driving conditions of the engine 1. The injection pulse signals can be obtained by passing both output signals from the injection control circuit 12 and the multiplying circuit 13 through the OR circuit 15, and said signal is amplified and applied to the electromagnetic coil of the electromagetic type fuel injection valve 9. COPYRIGHT: (C)1980,JPO&Japio

Gear mesh testing instruments

Abstract: The present invention relates to a gear mesh testing instrument in which the transmission error occurring between the two gears to be tested (the driving gear and the driven gear) is measured while both gears are rotating while intermeshed with each other. A pulse generator is connected to the rotating shaft of the driving gear, and of the driven gear, respectively, so as to produce two pulse signals having frequencies proportional to the number of the rotation of the gears. Then, the two pulse signals are introduced into the gear number compensating circuit so as to be converted into two pulse signals having a same frequency. The transmission error is proportional to the phase difference between the two pulse signals having the same frequency, which phase difference is proportional to the ratio of the phase difference time between the two pulse signals to the period of pulse signal. As a consequence, the phase difference time is converted into a clock pulse number by means of the time difference calculation circuit, while at the same time the reciprocal of the period is calculated by means of a reciprocal calculation circuit. The clock pulse number and reciprocal of the period are multiplied in a multiplier so as to obtain the phase difference.

Vorrichtung zum ueberwachen des betriebsverhaltens der ventile eines kolbenkompressors

Abstract: The device exhibits a vibration pick-up for each cylinder head and a phase transmitter (10) in the area of the crank drive which detects the respective position of the crank angle. In addition, a multiplexer (33), a detector (38) for the pulse duration and a logic element (40) are provided. The detector (38) picks up the signal output by the vibration pick-up instantaneously switched on via the multiplexer (33). The logic element (40) receives the signal coming from the phase transmitter (10) and the signal processed in the detector (38). The pulse duration of the vibration signal and its phase angle result in output signals in the logic element (40) which are displayed in a recording device (42). The curves shown in the recording device show whether the valves of the compressor are "blowing" or "chattering" so that the compressor can be switched off, if necessary.

Spectral change mechanism in the pulsed high‐pressure sodium arc

Abstract: The enhancement of radiative output of the pulsed high‐pressure sodium discharge in the blue region of the visible spectrum is due principally to radiation from the nd2D→3p2P transitions of the sodium atom where n=4–15. Excitation of these upper energy levels results from a transient non‐steady‐state increase in plasma temperature to about 5500 °K in the center of the arc. This temperature decays to a value near that encountered in steady‐state excitation conditions in a time comparable to the empirically optimized pulse duration and to the previously determined time for plasma temperature relaxation.

An estimate of the nucleation time in the martensitic transformation

Abstract: A method for the determination of nucleation times for martensitic transformation is described. The method utilizes a shock wave that, upon being reflected at a free surface, generates a tensile wave with a pulse duration that increases as it moves away from the surface. Once the duration of the reflected pulse is large enough for nucleation to occur, transformation can take place. The width of the martensite free layer adjoining the surface is measured and compared with wave predictions. A nucleation time can be obtained. The method requires that the temperature, pulse amplitude, and alloy composition be such that only the reflected tensile wave induce martensite transformation. For the experimental conditions used by Snell, Shyne, and Goldberg10 the nucleation time is found to be less than 55 nanoseconds.

Dial pulse restorer

Abstract: A dial pulse restorer for receiving and restoring telephone dial pulses which may be distorted, and also for discriminating telephone-hang-up pulses which may be applied to a telephone line when a remote telephone coupled to the telephone line hangs up. A particular use for such a dial pulse restorer is to control the functions of dictation apparatus operatively coupled to one end of the telephone line in response to the operation of the dial mechanism at the remote telephone. The dial pulse restorer comprises a transition pulse generator for generating transition pulses in response to telephone pulse transitions that are received over the telephone line, such telephone pulse transitions being received either in response to telephone dial pulses or to a telephone hang-up pulse. A window generator is responsive to a transition pulse to generate a window pulse of predetermined duration and substantially centered on the expected time of occurrence of the next following transition pulse. A control pulse generator produces a control pulse in the event that the next-following transition pulse occurs during the window pulse duration; and a hang-up pulse detector indicates the receipt of a telephone hang-up pulse if a transition pulse does not occur during the window pulse duration.

Hole drilling studies with a variable pulse length CO2 laser

Abstract: A transversely excited CO 2 laser has been used to investigate the interaction between laser pulses of duration ≈ 40 μs, and metallic targets. The dependence of machining efficiency on power density has been studied, and high speed photography has been used to compare interactions with different pulse durations. Metallurgical analysis has revealed important structural effects in both mild steel and aluminum samples.

Coherent optical image amplification by an injection‐locked dye amplifier at 632.8 nm

Abstract: Coherent amplification of images illuminated by the 632.8‐nm radiation of He‐Ne has been successfully demonstrated using a two‐stage injection‐locked pulsed dye amplifier technique. A gain of three times has been measured using Cresyl Violet 620 and Rhodamine B in ethanol, while maintaining signal bandwidth, relative phase, and direction, over a one‐quarter μs pulse duration. A space bandwidth product of 500 000 was obtained by incorporation of the image amplifier into an optical image processing system.