Showing papers on "Impulse (physics) published in 1972"

The motion of a vortex filament with axial flow

Abstract: Infinitesimal waves on a uniform vortex with axial flow are studied The equation for the frequency of helical waves is obtained, and solved for the case of long waves which leave the internal structure almost unaltered A method is developed to obtain results for vortices of non-uniform structure and for displacements which are not necessarily small compared with the core radius The approach consists of balancing the Kutta—Joukowski lift force, the momentum flux due to the axial motion, and the ‘tension’ of the vortex lines A general equation for the motion of a vortex filament is obtained, valid for arbitrary shape and internal structure, and in the presence of an external irrotational velocity field When the axial flow vanishes, the method is equivalent to using the Biot—Savart law for the self-induced velocity, with a suitable cutoff The impulse of a vortex filament is discussed and its rate of change is given

Total Binding Energies of Nuclei, and Particle-Removal Experiments

Abstract: Under the assumptions of the impulse approximation, there is a relation between the cross section for removing a particle from a system and the total binding energy of the system, if it is bound by two-body forces. This relation is established and applied to the ($p,2p$) reaction on nuclear targets. Data from recent experiments are used to obtain values for the total binding energy of the protons in various nuclei, which are then compared with the measured values.

Momentum transfer and plasma formation above a surface with a high‐power CO2 laser

Abstract: An experiment was performed to measure the total impulse transferred to a surface by a high‐power pulsed 10.6‐μ laser under atmospheric conditions, and also to determine the degree to which the observed plasma decouples the laser energy from the surface. Specific interest was directed toward conditions under which a ``radiation‐driven detonation wave'' may form due to the presence of a surface. The momentum transferred in dyn sec/J decreases with an increase in the ratio of incident energy to spot area since a larger fraction of the energy is decoupled from the surface.

Laser‐induced stress‐wave and impulse augmentation

Abstract: A series of experiments were performed on aluminum targets in order to find simple methods of increasing the stress and impulse using a laser. It was found by coating the aluminum targets with thin layers of transparent relatively volatile materials that order‐of‐magnitude increases were obtained over irradiating bare targets. Stress‐wave amplitudes of 7.9 kbar were measured.

Identification in the presence of initial conditions

Abstract: An on-line method is developed for the determination of the parameters of a linear continuous finite-dimensional system in the presence of initial conditions. This is achieved through the use of successive integration of not only the system excitation and response signals but also an impulse of unit strength. The conditions under which the proposed method gives a unique solution is presented in the form of a theorem.

The electric strength of Perspex as a function of voltage rise time

Abstract: The electric strength of Perspex was measured using impulse voltages reaching their maximum values in times ranging from 05 μs to 10 000 μs. For sphere-sphere electrodes the electric strength is 60 MV cm−1 at the shortest rise time, 131 MV cm−1 at 177 μs, and 84 MV cm−1 for slowly rising direct voltage. Similar trends were found for point-plane electrodes. The results are consistent with a rapid accumulation of negative space charge close to the cathode, and a positive space charge close to the anode.

Level crossings of nondifferentiable shot processes

Abstract: An expression for the expectation of level crossings of a class of nondifferentiable shot processes that involve impulse responses having discontinuities is derived. Its first term is essentially the Rician formula [l, pp. 51-53] except that the random variables (y_o, \dot{y}_o) in the integrand are conditioned on nonoccurrence of discontinuities and can be interpreted as yielding the contribution of "smooth" crossings; the second term then describes the direct contribution of the jumps. The moments of (y_o, \dot{y}_o) reflect the influence, at the points of continuity of the process y(t) , of the jumps at its points of discontinuity. Whereas in differentiable processes (y, \dot{y}) are orthogonal, here (y_o, \dot{y}_o) are correlated; furthermore, although y_o converges in distribution to y and E[\dot{y}_o] is finite and nonzero in general, evidently \dot{y} has no finite moments. In the Gaussian limit of large densities of counts of the underlying Poisson process, an explicit formula is obtained in terms of known parameters. The Rician term is slightly altered by the correlation between y_o and \dot{y}_o . On the other hand, the additional term has a component that increases as the square root of the average number of counts. In various practical cases either the bounded Rician or the diverging term can be dominant. An example of particular interest is examined in detail.

Discontinuities and shock waves in the interplanetary medium and their interaction with the magnetosphere.

Abstract: The discontinuous structure of the solar wind is described with emphasis on properties related to geomagnetic impulses. Some of the discontinuities are clearly hydromagnetic shocks and tangential discontinuities, and can produce a significant change in the momentum flux at the magnetosphere boundary. Such a change generates an impulse which propagates through the magnetosphere to the Earth where it is observed world-wide as an impulse in magnetograms. The propagation process is not reviewed here, but the relation between the initial cause (discontinuity) and the final effect (geomagnetic impulse) is reviewed in detail. The various types of impulses are examined, and are related qualitatively to the various types of discontinuities. The magnitude of an impulse is related to the change in the momentum flux. The propagation time and the rise time depend on the propagation process rather than on the initial state. Double shocks have not been observed, but a reverse shock has been identified. Giant pairs can be caused by a shock followed by a tangential discontinuity, and regular pairs may be due to complementary tangential discontinuities.

Nuclear magnetic resonance spectroscopy employing difference frequency measurements

Abstract: A modified impulse type Fourier transform type of nuclear magnetic resonance spectrometer wherein the direct measurement of difference frequencies between a single reference resonance line and the multiple resonance lines of the sample under analysis is provided, which provides weighting of the sample decay response by its local signal-to-noise ratio resulting in simplified system components and avoidance of stringent conditions with respect to the stability of the static unidirectional magnet field. A nonlinear detector forms the desired difference frequencies and weighting function. A first embodiment employs analog-to-digital conversion and a signal averaging computer with the resultant difference frequencies of the sample response Fourier-transformed to obtain the desired spectrum. A second embodiment avoids the analog-to-digital converter and the computer, utilizing instead a form of analog Fourier analyzer to obtain the output spectrum.

A High Quality Voltage Divider Using Optoelectronics for Impulse Voltage Measurements

Abstract: By applying an optical measuring system, which consist of light emitting diode, optical fiber light guide and photomultiplier, a high quality shielded resistance divider for impulse voltage measurements, whose response time is less than 5 ns, has been obtained The characteristics have been verified experimentally

Large Deformations of Rigid-Viscoplastic Structures under Impulsive and Pressure Loading

Abstract: It has recently been shown that by imposing a time-independent kine-matically admissible displacement field on a rigid-plastic structure the approximate determination of its response to pressure or impulsive loading can be reduced to the investigation of an equivalent one-degree-of-freedom system. In the present paper this approximation is generalized to structures of rigid-viscoplastic material undergoing moderately large deformations. The analysis leads to a nonlinear second-order differential equation the solution of which is obtained by using numerical methods. The investigation of a circular plate shows that this approximate method leads to simple calculations and its accuracy is satisfactory. As expected, the numerical results confirm that strain-rate sensitivity and geometry changes have an important influence on the maximum permanent deflections. In addition, a comparative study shows that the usual approximation according to which the pressure pulse is replaced by an equivalent impulse g...

USSR electric impulse de‐icing system design

Abstract: THREE MAIN DE‐ICING METHODS have for long been in use: thermal, mechanical and chemical. Systems incorporating any of these methods are in use on most aircraft throughout the world.

Performance testing of a solid propellant pulsed plasma microthruster.

Abstract: Extensive performance testing has been carried out on a solid propellant, pulsed plasma microthruster essentially identical to the four units aboard the DOD, Lincoln Experimental Satellite (LES)-6. Tests include measurements of thrust, specific impulse, thrust vector, impulse bit repeatability, intermittency and endurance. The results show good impulse bit repeatability and a well defined thrust vector. The impulse bit, with a 1.85-joule input, was found to be approximately 26 micronewton-seconds at 190 seconds specific impulse. Based upon the results of the intermittency tests, a better understanding of the intermittency mechanism has been achieved.

Adjustable pattern water sprinkler system

Abstract: In order to accommodate odd shaped areas to be sprinkled, an impulse sprinkler is supported by apparatus which permits tilting the impulse sprinkler from the vertical in any radial direction. As a result, the sprinkler pattern is altered from a circle (or portion of a circle) to an ellipse-like (or portion thereof) shape.

Use of a sampling oscilloscope for velocity measurements and frequency comparisons of impulse acoustic surface waves

Abstract: A simple method of phase-shift and velocity measurements of impulse surface waves in an active delay line is related. Using Lissajous's displays on a sampling oscilloscope, accurate measurements are performed, even though the transmitted signal is disturbed by r.f. leakage, echoes or spurious modes. The same technique is applied to the frequency determination of a convoluted signal in a nonlinear device.

Propellant sidefeed-short pulse discharge thruster studies

Abstract: The technique of feeding a solid propellant into the discharge from the sides of the discharge was evaluated. The thrust/power ratio could be significantly effected by the included angle of V-shaped propellants and by the electrode length. This result implies that when results are compared at the same specific impulse it is possible to obtain higher thrust efficiencies. In particular, it was found that for a given discharge energy the thrust/power ratio correlated with propellant mass. Increasing the integral simultaneously increases both the gas dynamic and electromagnetic thrust. An analytic expression was formulated for ablated mass which comprehensively describes experimental data in terms of geometry and electrical parameters. The correlation of the product impulse x specific impulse with discharge energy was also described. It is suggested that the reliability of dry energy storage capacitors does not equal the reliability of liquid impregnated units when the comparison is made at the same joules/Kg rating.

On the response of the ocean to impulse

Abstract: A preliminary investigation on transitory motions of “inertial” period is made with the help of simple models. The amplitudes of the displacements are evaluated when an initial impulse and a sudden cooling are imposed on a non-homogeneous sea. Then the effects of spatial variations or of lateral boundaries are considered. Allowing for a density stratification, the frequencies and phase dispersions corresponding to the diverse inertial modes are given. DOI: 10.1111/j.2153-3490.1972.tb01562.x

Electrothermal hydrazine thruster development.

Abstract: Results of testing of several electrically-heated, thermal-decomposition hydrazine thrustors in the 5- to 70-mlb thrust range. Propellant supply pressures are compatible with those typical of larger catalytic thrustors. With a 5-W power input, pulsed specific impulse varies from about 165 to 215 sec, depending on duty cycle. The thrustors yield highly reproducible 1-mlb-sec impulse bits with 50-msec command pulse widths. The steady-state specific impulse exceeds 230 sec for thrust levels above 10 mlb.

Electronic ignition system

Abstract: A solid state control unit for a high potential generating system which is connected in series with an impulse signal and coil to maximize coil charging time between discharges thereof by means which eliminates eratic impulses from affecting the system and includes means to adjust the timing of the impulses for maximum efficiency and performance.

Neutronics analysis of an open-cycle high-impulse gas core reactor concept

Abstract: A procedure was developed to calculate the critical fuel mass, including the effects of propellant pressure, for coaxial-flow gas-core reactors operating at 196,600 newtons thrust and 4400 seconds specific impulse. Data were generated for a range of cavity diameter, reflector-moderator thickness, and quantity of structural material. Also presented are such core characteristics as upper limits on cavity pressure, spectral hardening in very-high-temperature hydrogen, and reactivity coefficients.

Method for determining the speed of a vehicle

Abstract: A method of determining the speed of vehicle, particularly a ship by the transmission of coherent waves, with echo signals being received at a plurality of points along a receiving line extending parallel to the azimuth direction, with both phase and amplitude information of the received echo signals being recorded as a function of the receiving time, while applying a reference signal, thereby forming one-dimensional holograms, employing an impulse repetition having a time interval T between successive impulses such that the distance d, traveled by the vehicle within the time interval T is less than one-half of the overall distance between the first and last of said receiving points, (defining the length L of the receiving line), i.e. d< L/2 in which a cross correlation function of the one-dimensional holograms of an impulse and the following impulse is formed, whereby the vehicle speed may be calculated from the positions of the correlation maximums.

Impulse propagation from photically discharged neurones in the visual system.

Abstract: Direct pathways were shown microphysiologically in the cat from SC, a fast one to DLGN and a slow one to VLGN. Evidence for these was provided by showing antidromic unit responses in SC following stimulation of DLGN or VLGN deep layers. The pathway from SC to DLGN was studied from the point of view of the probabilities that an impulse would propagate through it when its parent neurone is discharged by light stimuli or in spontaneous discharges. These probabilities were assessed in term of the rates at which such propagation took place. The latter was determined by use of the collision technique, which provided the information when an impulse propagated and when it did not in a fiber following a neuronal discharge. Total field flashes were shown to discharge the neurones in such a way that it resulted in firm propagation through the fibers of SC neurones which projected to DLGN. In contrast, spontaneous discharges have shown failures of such propagation as well which indicated a lower probability for impulse propagation to DLGN in the latter type of neuronal discharges.

The Impulse Generators at Les Renardieres

Abstract: This paper discusses some of the problems associated with the generation of lightning and switching impulses for research on U.H.V. systems. The solutions adopted for the impulse generators installed in the new U.H.V. laboratory of Electricite de France are described, and some performance details are given.

Remote control with selective evaluation of impulse patterns

Abstract: A receiver programmed to respond to either an individual command impulse pattern or to an individual command and a collective command impulse pattern. This is accomplished by opening two links in the command key so that the receiver is responsive both to the individual command and a collective command. In this state, both received commands would match the impulse pattern associated with the receiver. When these two links are closed, the receiver is only responsive to the individual commands.