Showing papers on "Impulse (physics) published in 1973"

Multimode theory of graded-core fibers

Abstract: New technologies of fiber manufacture and a demand for unusual fiber qualities in communication systems have intensified the interest in a comprehensive theory of multimode fibers with nonuniform index distributions This paper deals with a general class of circular symmetric profiles which comprise the parabolic distribution and the abrupt core-cladding index step as special cases We obtain general results of useful simplicity for the impulse response, the mode volume, and the near- and far-field power distributions We suggest a modified parabolic distribution for best equalization of mode delay differences The effective width of the resulting impulse is more than four times smaller than that produced by the parabolic profile Of course, practical manufacturing tolerances are likely to influence this distribution A relation is derived between the maximum index error and the impulse response

Adaptive channel memory truncation for maximum likelihood sequence estimation

Abstract: Maximum likelihood data sequence estimation, implemented by a dynamic programming algorithm known as the Viterbi algorithm (VA), is of considerable interest for data transmission in the presence of severe intersymbol interference and additive Gaussian noise. Unfortunately, the required number of receiver operations per data symbol is an exponential function of the duration of the channel impulse response, resulting in unacceptably large receiver complexity for high-speed PAM data transmission on many channels. We propose a linear prefilter to force the overall impulse response of the channel/prefilter combination to approximate a desired truncated impulse response (DIR) of acceptably short duration. Given the duration of the DIR, the prefilter parameters and the DIR itself can be optimized adaptively to minimize the mean-square error between the output of the prefilter and the desired prefilter output, while constraining the energy in the DIR to be fixed. In this work we show that the minimum mean-square error can be expressed as the minimum eigenvalue of a certain channel-dependent matrix, and that the corresponding eigenvector represents the optimum DIR. An adaptive algorithm is developed and successfully tested. The simulations also show that the prefiltering scheme, used together with the VA for two different channel models, compares favorably in performance with another recently proposed prefiltering scheme. Limiting results for the case where the prefilter is considered to be of infinite length are obtained; it is shown that the optimum DIR of length two must be one of two possible impulse responses related to the duobinary impulse response. Finally we obtain limiting results for the case where the transmitting filter is optimized.

Changes in the statistics of transmitter release during facilitation

Abstract: 1. The statistical nature of transmitter release during facilitation was studied at single synaptic sites by recording extracellular excitatory junctional potentials from the claw opener muscle in crayfish. 2. At low temperatures, single quanta could be counted in the responses to nerve impulses. The distribution of the number of quanta observed (x) was most accurately described by assuming that x is a binomial random variable. 3. A quantitative estimate was made of the effects of errors in counting quanta due to the simultaneous release of quanta and the release of quanta which were not individually detectable above the noise of the recording system. Such errors of observation cannot account for the deviation of quantal release from a Poisson distribution. 4. Facilitated release occurred in the responses to the second of two closely following nerve impulses and in the responses to successive impulses in a tetanus. In both cases, the increase in the average number of quanta released (m) could be attributed entirely to an increase in the probability (p) that available quanta were released. 5. The results can be interpreted most easily in terms of a model in which the maximum number of releasable quanta is limited by a finite number of discrete release sites within recording distance of the microelectrode. In this model, the binomial parameter n is an estimate of the number of these sites, and the statistical parameter p is a compound probability depending on the rate of re-occupying sites after a nerve discharge and the probability that an impulse activates an occupied site.

Theory for momentum transfer to a surface with a high‐power laser

Abstract: A model is developed for the momentum transferred to a solid from a laser‐supported gaseous detonation wave initiated in air above the surface. One‐dimensional gasdynamic analysis is used for the detonation wave moving away from the surface and cylindrical blast‐wave theory is employed to partially account for two dimensional effects. Momentum transfer coupling coefficients (impulse/laser energy) are calculated which are functions of the laser energy flux, pulse duration, and the beam and target surface areas. Results are compared with recent experimental data obtained using a high‐power CO2 laser.

Experimental and Analytical Studies of the Effect of Non-Standard Waveshapes on the Impulse Strength of External Insulation

Abstract: Various analytical methods are available for predicting the performance of insulation stressed by lightning voltages of non-standard waveshape. This paper describes experimental and analytical studies for evaluating the effectiveness of the prediction methods. Flashover characteristics of typical line insulation were determined using standard and non-standard impulse waves viz., long front, partially chopped and oscillatory impulses. The standard impulse data were used to calibrate the analytical models, which were then used to predict the performance of the insulation stressed by non-standard impulses for comparison with the experimental data.

Spallation and the generation of surface waves by an underground explosion

Abstract: Underground nuclear explosions, even though they are thoroughly contained, invariably produce spallation. This mass of earth and rock, kicked up by the initial shock wave, falls back within a second or two. It is possible that the surface waves observed from explosions originate from the impact of this material. This hypothesis has been investigated, first, by estimating the spall impulse from accelerometer data, computing the surface wave amplitudes consistent with this impulse, and comparing the results with observed amplitudes and, second, by performing computer explosion simulation experiments with and without spallation and comparing the amplitudes of the resulting surface waves. The comparison of the amplitudes consistent with the spall momentum with the observed Rayleigh amplitudes at ranges of 50–500 km indicates that the spall has sufficient impulse to account for these waves. The computer simulation experiments show that the Rayleigh amplitudes corresponding to realistic inelastic spallation have several times the amplitude of Rayleigh waves computed from purely elastic behavior. The surface wave for the spallation case is also delayed relative to the wave from the elastic source.

A new approach to optimum pulse shaping in sampled systems using time-domain filtering

Abstract: A new approach to time-domain pulse shaping in digital sampled systems is described. The proposed method allows time-limited impulse responses with optimum specified energy distribution in the frequency domain to be generated. Additional constraints to guarantee zero intersymbol interference are easily taken into account. Nyquist-type pulses which have the maximum possible amount of their total energy concentrated below some given frequency are one particularly important application. An example of such an impulse response with only 6 percent excess bandwidth is presented which shows that 99.96 percent of the energy can be concentrated in the desired bandwidth with a pulse 16 baud intervals long that can be generated using a read-only memory (ROM) with only 256 bits of storage. This new class of signals can be used advantageously for waveform generation and processing in digital data systems.

In situ shear wave velocity by cross-hole method

Abstract: ALTHOUGH THE CROSS-HOLE METHOD (DESCRIBED IN THE PAPER) USING ONLY TWO BOREHOLES APPEARS TO BE SIMPLE AND CONVENIENT FOR SOME APPLICATIONS, PRACTICAL EXPERIENCE PROMPTS SEVERAL QUESTIONS. THE WAVES GENERATED IN THIS METHOD ARE PREDOMINANTLY COMPRESSIONAL. ALSO, LARGE AMPLITUDE CHARACTERISTICS VIBRATIONS AND CHATTERING ARE BROUGHT INTO PLAY, ALL FACTORS WHICH MAKE IDENTIFICATION OF SHEAR WAVE ARRIVALS DIFFICULT. THE TRIGGERING TRANSDUCER, ATTACHED TO A METAL PLATE AT THE TOP OF THE EXCITER ROD, PROBABLY HAS BUILD-UP CHARACTERISTICS DIFFERENT FROM THOSE OF THE TRANSDUCER ON THE SOIL. SINCE THIS IS AN IMPORTANT FACTOR IN OBTAINING THE INTERVAL TIME, INFORMATION ON THE TRIGGERING PULSE STATE WOULD BE USEFUL. CORRECTIVE MEASURES ARE SUGGESTED. EXPERIMENTS HAVE BEEN PERFORMED WITH THE SKEW CROSS- HOLE METHOD AND TEST RESULTS ARE GRAPHICALLY ILLUSTRATED. THE IDENTIFICATION OF SH-WAVES OR THE DETERMINATION OF THE TIME OF ARRIVAL IS EASY. IDENTIFICATION OF SV-WAVES IS NOT AS EASY AS REVERSAL OF THE DIRECTION OF THE EXCITING IMPULSE IS DIFFICULT. THE ABILITY TO EXCITE AND IDENTIFY BOTH SH AND SV ARRIVALS PERMITS THE DEGREE OF ANISOTROPY OF THE SOIL TO BE DETERMINED.

Performance Study of a Solid Fuel-Pulsed Electric Microthruster

Abstract: A study of the over-all operating characteristics of a parallel rail solid fuel-pulsed microthruster is presented. Specifically, the effect of several electrical circuit parameters (capacitance, inductance, resistance) on performance (impulse bit, specific impulse, efficiency) has been investigated. The experimental results, combined with a simple model for the mass ablation and the acceleration mechanisms, provide useful correlations between thruster geometrical and electrical circuit parameters and its performance. These results should be useful in improving the performance and optimizing the design of a thruster for a given mission.

Method and apparatus for compensating fluid flow for a variable physical condition

Abstract: A method and system for compensating a manifestation of fluid flow for a variable physical condition of the fluid in which pulses from a condition response transducer and from a fixed frequency oscillator are algebraically combined to control the duration of a gating impulse initiated responsively to fluid flow. The gating impulse is utilized to pass pulses from the oscillator as packets of pulses in which the number of packets is related to fluid flow and in which the number of pulses in each packet is related to the variable physical condition of the fluid.

Ion-acoustic wave response to an impulse disturbance

Abstract: The ion acoustic wave response to an impulse disturbance is experimentally examined for two different exciting mechanisms. The differences and similarities are noted for the double-plasma (D-P) and plate excitation methods. The observed response agrees well with that predicted from a self-similar study of a fluid equation model which includes the effects of Poisson's equation.

Multiple air gun array of varied sizes with individual secondary oscillation suppression

Abstract: An underwater seismic source for generating an improved seismic signal employing a spaced array of air guns of different sizes to generate an initial bubble impulse and to suppress the cumulative effect of secondary bubble impulses. The combination includes means for providing further secondary bubble suppression integral with one or more of the guns in the array. The sizes, minimum spacings, and secondary bubble suppression techniques are intimately combined to provide an underwater seismic source having an acoustic pressure signature wherein the amplitude of the initial impulse, including the signal reflected from the water surface, is from eight to twelve times the amplitude of any subsequent bubble impulses, including their surface reflections.

Impulse reaction resulting from the in‐air irradiation of aluminum by a pulsed CO2 laser

Abstract: The impulse reaction resulting from the in‐air irradiation of aluminum by a high‐intensity pulsed CO2 laser is experimentally examined in this study. Power densities of the order of 107−108 W/cm2 are obtained for focused beam energies between 100 and 700 J and pulse durations of between 15 and 50 μ sec. The targets are mounted in a sensitive pendulum in order to measure the total recoil impulse. The time history of the impulse during irradiation is determined by an interferometric technique. In addition, thermocouples are used to monitor the rear surface temperature of the thin (0.05 cm) targets. The thermal and mechanical response of the target is dominated by the effects of a high‐intensity leading edge of the laser pulse. The precursor spike generates an opaque plasma at the target surface which effectively shields the target from the incident energy. Impulse and pressure transmitted to the target are related, therefore, to reaction of the expanding plasma against the target surface. Impulse coupling coefficients (I/E) between 5 and 7.8 dyn sec/J are measured for this mechanism of impulse production. The major contribution to the total impulse is associated with the plasma pressure during the initial stages of the plasma‐surface interaction. The peak pressures generated during this time are found to depend on the second power of the initial beam intensity. It follows that the corresponding impulse coupling coefficients should increase linearly with beam intensity. However, a net increase in I/E is not realized at higher beam energies because of absorption losses (air breakdown) along the beam path.

Impulse loading of targets by subnanosecond laser pulses

Abstract: Measurements of the impulse received by graphite and aluminum targets exposed to a 250‐psec laser pulse are reported. Experiments were conducted in air and vacuum at incident energies between 0 and 20 J. In both environments, there is a definite energy threshold, which is lower in air than in vacuum, below which no momentum is transferred. For a given energy above threshold, the impulse generated in air is greater than in vacuum.

New factorized off-shell prescription for the distorted-wave impulse approximation in knockout reactions

Abstract: The distorted-wave impulse approximation for knockout reactions, when written following a Faddeev prescription, contains a fully off-shell T matrix whose arguments are coupled to those of the distorted waves. We show how the on- shell T matrix may be expanded around its half-shell point and an approximate factorized distorted-wave impulse approximation obtained with the major off-shell effect included. The off-shell ambignity present in the standard treatments is thereby eliminated. (auth)

On the positive-pion photoproduction from 3 He nuclei

Abstract: The pion photoproduction from three-body nuclei in the energy region of the first pion-nucleon resonance is calculated in the impulse approximation, including an estimation of the rescattering terms, and compared to recent experimental results. It is shown that the proper kinematics and the inclusion of theS′ andD states into the three-body nuclear wave function explains fairly well the position of the pion-nucleus resonance and the behaviour of the cross-section at fixed momentum transfer for the whole investigated region. The calculations are performed for several types of nuclear wave functions. The results are sensitive to the value of theD-state radius. The stability of the calculated curves with respect to the choice of the amplitude for the pion photo-production on nucleon is tested. At fixed angle, the measured cross-section disagrees with the bare impulse approximation calculations for higher values of the momentum transfer. In this case, the influence of the rescattering terms is discussed.

Transient Response of a Point-Excited Submerged Spherical Shell

Abstract: The transient responses of a submerged spherical shell to a concentrated impulse and Heaviside load are obtained by using the classical mode method and the Laplace transform. For long time solutions, only a relatively small number of modes are sufficient, while for the short time response, a large number of modes must be used in order to achieve acceptable accuracy. For the lower modes, the inversion integral involves only simple poles and can be evaluated by Cauchy’s residue theorem. For the higher modes it is necessary to use asymptotic approximations and the inversion involves branch points and poles. A spherical wave approximation, similar to Haywood’s cylindrical wave approximation, is also used to solve the transient problem. It is found that the approximation accurately predicts the maximum peak response for the impulse load, while it underestimates the response for the Heaviside load.

Circuit for generating a single high voltage subnanosecond pulse from a step recovery diode

Abstract: A series connected electronic circuit including in combination a trigger generator, an impulse generator, a filter circuit having an inductance L, a step recovery diode having a forward resistance RF and a reverse capacitance CR and an optimal bias circuit coupled to the step recovery diode. The trigger generator produces a train of pulses having a relatively long time interval, T, between each pulse; these pulses are then coupled to the impulse generator which produces an impulse having a Fourier component predominant at a frequency omega in response to each trigger pulse. The filter circuit converts each impulse into a damped sine wave having an angular frequency omega and a damping constant delta RF/2L. The sine wave is coupled to the step recovery diode which generates a single high voltage subnanosecond pulse having a half period, tp/ pi square root LCR in response to each damped sine wave.

Pulsed plasma microthruster for synchronous meteorological satellite /SMS/

Abstract: Two completely self contained variable thrust flight prototype plasma propulsion systems using solid teflon as propellant were designed, built and laboratory tested. The impulse bit amplitude of each thruster is 25 micro lb-sec. Impulse bits can be provided at rates varying from 50 ppm to 110 ppm. The total impulse capability is 400 lb-sec. Only 23 watts of bus power are required at maximum pulse rate. The system was subjected and passed the required vibration schedule and thermal vacuum test after a minor change in capacitor end face material. A 13 million discharge life test of the system was subsequently performed.

Geophone impulse tester

Abstract: Method and apparatus for testing all the channels of a seismic system simultaneously, each channel comprising a string of geophones and recording means to record the signals received by the geophones. The geophones are exercised to stimulate their normal response, in two modes, automatically and sequentially; the unbalanced impulse mode detects a bad string by a deviation from a null line, and the current impulse mode provides a record of the system response to a pre-determined impulse on the seismic record itself.

Network time domain measurement system

Abstract: The forward and backward scattered energy of a high frequency network exposed to an incident base band impulse of electromagnetic energy in a transmission line is sampled by a compensation sampling system and the incident wave and reflected and transmitted response waves are employed in performing discrete Fourier transformations in a computation process yielding the complex characteristics of the network.

Experimental study of solitary waves in a nonlinear transmission line

Abstract: Several properties of solitary waves were measured on a nonlinear transmission line. These include the transition from a linear dispersive response into a solitary wave response as the amplitude of a narrow voltage impulse is increased, and an observation of the recurrence phenomena of solitary waves.

Interpretation of some properties of AV conduction with the help of analog stimulation

Abstract: For a better understanding of the phenomenological characteristics of A-V nodal conduction the impulse propagation through a transmission line consisting of units obeying the Bonhoeffer-Van der Poll equations was studied. It appears that impulse propagation through such a transmission line shows similarity with A-V nodal conduction.

Minimum impulse three-body trajectories.

Abstract: A rapid and accurate method of calculating optimal impulsive transfers in the restricted problem of three bodies has been developed. The technique combines a multi-conic method of trajectory integration with primer vector theory and an accelerated gradient method of trajectory optimization. A unique feature is that the state transition matrix and the primer vector are found analytical without additional integrations or differentiations. The method has been applied to the determination of optimal two and three impulse transfers between the L2 libration point and circular orbits about both the earth and the moon.

On the attenuation of transient spherical waves in a four-element viscoelastic model and its implications

Abstract: In a four-element model, which consists of two Voigt elements in series, the impulse responses of spherical waves for particle displacement, velocity, acceleration and strain are computed numerically. These impulse responses are shown to be useful in synthesis for the desired wave response through convolution, between the input of the source function and the impulse responses. The rate of decay of peak amplitude versus distance, as waves radiate out, is examined in the region close to the source which may be nuclear or dynamite explosives and found to be linear in log-log scale. The amplitude spectra of the unit impulse response are obtained through Fourier analysis, and the model is found to behave as a low pass filter. With the properly chosen elastic constants for springs in the model and damping coefficients for dashpot, it is seen that, like the earth materials, the attenuation exponent (in neper/1000 ft) versus frequency in the model is approximately linear. One of the results observed byCollins andLee [1] is fitted by the model. The model thus simulates more nearly the wave in earth materials close to the source than the Voigt solid.