Showing papers on "Impulse (physics) published in 1988"

Impulse coupling to targets in vacuum by KrF, HF, and CO2 single‐pulse lasers

Abstract: We present a laser‐target scaling model which permits approximate prediction of the dependence of ablation pressure, mechanical coupling coefficient, and related parameters in vacuum upon single‐pulse laser intensity (I), wavelength (λ), and pulse width (τ) over extremely broad ranges. We show that existing data for vacuum mechanical coupling coefficient for metallic and endothermic nonmetallic, surface‐absorbing planar targets follows this empirical trend to within a factor of 2 over 7 orders of magnitude in the product (Iλ(τ)1/2). The comparison we present is valid for intensity equal to or greater than the peak‐coupling intensity Imax, where denseplasma formation mediates laser‐target coupling. Mechanical coupling coefficients studied ranged over two orders of magnitude. The data supporting this trend represent intensities from 3 MW/cm2 to 70 TW/cm2, pulse widths from 1.5 ms to 500 ps, wavelengths from 10.6 μm to 248 nm, and pulse energies from 100 mJ to 10 kJ. With few exceptions, data approximating one‐dimensional or planar expansions were selected. Previously, meaningful scaling of ablation pressure parameters with I, λ, τ was not possible because existing data concentrated in a small range of these parameters. Our own data, obtained in the low‐ and midrange of (Iλ(τ)1/2), completes the experimental picture. Since this new data was derived from five separate experiments with specialized character and purpose, detailed accounts of this work will appear separately. In this paper, we summarize the experimental conditions and selectonly those data which are relevant to the scaling issue. We find that laboratory‐scale laser experiments can often give impulse coupling data which agree with results from much higher‐energy experiments without much error, and at much lower cost. We review a theory of vacuum laser ablation, specialize it to a quantitative description of mechanical coupling, and show that the resulting model provides a simple physical description which comes quite close to the observed empirical trend. This is accomplished with minor elaborations of the theory as originally presented to account for the temperature dependence of plasma ionization states, while adhering to the premise that a simple and generally applicable treatment of laser impulse production should be available. The theoretical model can quantitatively predict vacuum ablation pressure foropaque targets without adjustable parameters to the factor‐of‐2 accuracy in which we are interested. Other published scaling models omit one or more of the important variables, lack broad applicability, or deviate more noticeably from the observed trend.

A new general estimation curve for predicting the impulse impedance of concentrated earth electrodes

Abstract: This is a further development of the experimental curve published by A.V. Korsuntsev (see Elektrichestvo, no.5, p.31-5 (1958)). The use of this curve does not require any knowledge of the critical soil ionization constant. The characteristic dimension of an electrode has been redefined to give a good resolution between two-dimensional and three-dimensional electrode geometries. The curve predicts the impedance approximately 6 mu s after the onset of the impulse, which is representative of the impedance of electrodes at the time of the peak lightning current of first strokes. >

Control of Contractile Properties Within Adaptive Ranges by Patterns of Impulse Activity in the Rat

Abstract: These experiments explore the relationship between patterned impulse activity and contractile properties of skeletal muscles. Soleus (SOL) and extensor digitorum longus (EDL) muscles of adult rats were denervated and stimulated directly from 4 to 15 weeks with the same number of pulse trains at different intratrain pulse frequencies (1-500 Hz), with different numbers of pulse trains (864-4,320,000 pulses/d) at the same intratrain pulse frequencies, or with different combinations of pulse trains at 10 and 100 Hz. Chronic stimulation of the denervated SOL resulted in twitch times-to-peak and half-relaxation times that varied in a graded manner between values longer than those in the normal SOL to values as fast as those in the normal EDL, depending upon the pattern used. Increasing pulse frequencies (constant number) resulted in faster twitches, lower twitch/tetanus ratios, increasing post-tetanic potentiations, and larger tetanic tensions. Increasing pulse numbers (constant frequencies) resulted in slower twitches, lower twitch/tetanus ratios, post-tetanic depressions, and higher fatigue indices. The effect of varying the pulse number on twitch parameters was greater at low frequencies (10-20 Hz) than at high frequencies (100 Hz). SOL muscles receiving pulse trains at both 10 and 100 Hz became much faster than muscles receiving pulse trains at 10 Hz only, even in the experiments where the stimulation pattern contained 9 times as many pulses at 10 as at 100 Hz. Chronic stimulation of both the denervated and the innervated EDL with large numbers of pulses at 10 or 15 Hz resulted in twitches that were only half as slow as those induced in the SOL by the same "slow" patterns. In addition, these patterns led to a marked decrease in maximum tetanic tension and a marked increase in twitch/tetanus ratio. During stimulation with a small number of pulses at 150 Hz, on the other hand, twitch speed, twitch/tetanus ratio, and maximum tetanic tension remained normal or almost normal. We conclude that the isometric twitch and related properties of the rat SOL muscle can be graded within wide "adaptive ranges" by varying either the number or the frequency of pulses. In the EDL, the corresponding adaptive ranges appear much narrower, suggesting that the EDL and the SOL contain intrinsically different muscle fibers.

Force variability in isometric responses.

Abstract: In the present study we examined the contribution of different impulse parameters to peak force variability in an isometric task. Five experiments are reported that each held constant a different impulse parameter while allowing the other impulse parameters to vary. The results indicate that change in force level is the parameter that has the greatest effect on peak force variability, although time to peak force and preload also systematically influence response variability. A formula that accommodates the relation between impulse parameters and force variability is proposed. The data suggest that even in isometric tasks, it is the force-time properties of the impulse, rather than discrete parameters such as peak force, that determine the outcome variability.

The generalized integration method for predicting impulse volt-time characteristics for non-standard wave shapes-a theoretical basis

Abstract: A theoretical basis for the integration method of predicting the strength of insulation subjected to impulses of nonstandard wave shapes is presented. Two theoretical approaches are developed for a general physical model of impulse breakdown applicable to gaseous, liquid, and solid insulation, and from an energy-balance model applied to an incipient breakdown channel in a general dielectric. It is therefore not surprising to find that the integration method is reasonably successful as a tool for predicting nonstandard wave-shape insulation strengths, using as input the data derived from tests with standard-wave-shape impulses. Numerical results are presented that provide an understanding of the shape of volt-time curves. An energy balance model has also been used to derive the resistance of the channel after breakdown has occurred. >

Impulse corona simulation for flue gas treatment

Abstract: The lack of experimental results on transport coefficients in flue gases makes the macroscopic discharge models not applicable to the simulation of impulse corona for flue gas treatment. In the present paper the microscopic formulation, based on Boltzmann and Poisson's equations, is analyzed and a simplified model is derived. This has been numerically implemented in two sections: in the first one a quasi-uniform, steady-state Boltzmann equation is solved to calculate the electron and ion transport characteristics in any mixture of atmospheric gases IN,, 0,, CO,, H,OI; in the second section the conservation equations for electron, positive and negative ions are solved, together with Poisson's equation . The model has been applied to the simulation of impulse corona discharges in air and flue gases with different compositions. The results indicate that H,O and 0, are the mixture components that play a major role in the attachment processes Iat high and low field respectively); as a consequence the corona characteristics are very much affected by the flue gas composition. The optimization of any treatment process must therefore account for the possible variations of the gas composition: the admixture of gaseous products that lead to an improvement of pulse corona characteristics may also be considered.

The Kelvin impulse: application to cavitation bubble dynamics

Abstract: The Kelvin impulse is a particularly valuable dynamical concept in unsteady fluid mechanics, with Benjamin and Ellis [2] appearing to be the first to have realised its value in cavitation bubble dynamics. The Kelvin impulse corresponds to the apparent inertia of the cavitation bubble and, like the linear momentum of a projectile, may be used to determine aspect It is defined aswhere ρ is the fluid density, o is the velocity potential, S is the surface of the cavitation bubble and n is the outward normal to the fluid. Contributions to the Kelvin impulse may come from the presence of nearby boundaries and the ambient velocity and pressure field. With this number of mechanisms contributing to its development, the Kelvin impulse may change sign during the lifetime of the bubble. After collapse of the bubble, it needs to be conserved, usually in the form of a ring vortex. The Kelvin impulse is likely to provide valuable indicators as to the physical properties required of boundaries in order to reduce or eliminate cavitation damage. Comparisons are made against available experimental evidence.

Transportation theory of multiple scattering and its application to seismic coda waves of impulse source

Abstract: The energy distribution of elastic waves in an infinite elastic medium with uniformly and randomly distributed scatterers has been researched. The scattering process is assumed to be isotropic and without conversions between wave types. We get the equation on the distribution of energe density in time and space covering single as well as multiple scattering. Taking physical symmetry of the field into account, it can be simplified. In the case of small earthquakes, the energy source of elastic waves can be assumed as a short pulse emitted isotropically at t=0. The first-order approximate solution in the 3-dimensional space can be obtained, and it is equivalent to Sato's solution for single scattering. In the 2-dimensional space the complete analytical solution has been derived by the mathematical inductance which leads to a conclusion that the codas of surface waves can give the Q-factor related to intrinsic absorption. The equation obtained in this paper is more general.

Adhesion of spheres by thin liquid films

Abstract: Thin liquid films may produce significant adhesion between solid bodies, such as powder agglomerates and ultra-flat surfaces. The adhesive force can be split into two components; the meniscus force and a viscous component which, at sufficiently high deformation rates, will become dominant. This paper presents an analysis for the viscous component of adhesion acting between spheres coated by thin liquid layers, which is expressed as the impulse required to separate the spheres. This impulse depends on the radii and surface roughness of the spheres, and the fluid viscosity and thickness. The dependence on the roughness and quantity of fluid is unexpectedly weak (i.e. logarithmic). The predictions of the analysis are confirmed by direct experiment using a simple force pendulum.

Kinetics of VO2 with impulse and step exercise in humans

Abstract: The constancy of the time course (i.e., dynamic linearity) of the O2 uptake (VO2) response to exercise was examined by testing the law of superposition on data from impulse and step work rate forcings. Two impulses (10 s at a 235-W increase above a 25-W base line, I-235; and 5 s at a 475-W increase above a 25-W base line, I-475), four steps (ST) (25-65 W, ST1; 65-105 W, ST2; 25-105 W, ST3; and 25-145 W, ST4), and the corresponding off-transient responses were performed six to eight times by each of five subjects. The integrated area (G) of the VO2 response for I-235 was similar to that of ST1 and ST2 (P greater than 0.05); the I-475 G was significantly greater (P less than 0.05). The time constant of VO2 during the step function on-transient response for the second exponential component was significantly faster for ST1 and significantly slower for I-235 and I-475 than for ST2, ST3, and ST4 (P less than 0.05). However, I-235 and I-475 time constants for VO2 were not different from the ST off-transient values. Attempts to superimpose the integral of the impulse on the ST data showed that the early rapid increase in VO2 in the ST was underpredicted by the impulse and that the impulse response lagged behind the ST at all points before steady state. It can be concluded that VO2 kinetics failed the test of superposition and are therefore described by a nonlinear dynamic system.

Interaction of fiber orientation and direction of impulse propagation with anatomic barriers in anisotropic canine myocardium.

Abstract: We developed a computer model of the interaction of impulse propagation with anatomic barriers in uniformly anisotropic tissue. Its predictions were confirmed experimentally by using an in vitro cut to create a 6 X 1-mm anatomic barrier in 12 canine epicardial strips. The model predicted that long, thin barriers located parallel to the direction of impulse propagation would have little effect in delaying conduction regardless of the arrangement of cardiac fibers. In this situation, the mean experimental ratio of postcut to control conduction times across the barrier was 1.05:1.00 in 10 tissues. When impulses were proceeding perpendicular to an anatomic barrier, significant distal conduction delay was predicted and found to occur only when the conduction from pacing to recording sites was initially longitudinal to fiber orientation (mean experimental ratio, 2.34:1.00 in five tissues) but not transverse to fiber orientation (ratio, 1.08:1.00 in five tissues). We conclude that the direction of initial impulse propagation and the orientation of myocardial fibers have large effects on the degree to which anatomic barriers delay activation in cardiac tissue. These findings may have implications for the participation of anatomic barriers in reentrant circuits.

Method for noninvasive blood-pressure measurement by evaluation of waveform-specific area data

Abstract: A microprocessor-controlled, oscillometric method for determining a patient's systolic, diastolic, and mean arterial pressure, practiced in a system comprising an inflatable, occluding cuff, a pump and a valve coupled to the cuff, and monitoring apparatus coupled to the cuff adapted to measure cuff pressure and recurring blood-pressure pulsations occurring in the cuff that are caused by each heart contraction occurring in a measurement cycle. Cuff pressure is raised to a level above the patinet's systolic pressure, and progressively reduced in a stepwise fashion to an ending cuff pressure. A fixed number of pulsations are measured and processed at a first and second cuff-pressure step, and a generally lesser number of oscillations are measured and processed at a third and subsequent cuff-pressure steps. The method includes a first artifact rejection technique used to check for false data relative to the formation of each blood-pressure pulsation. Further, the method includes calculating, for each blood-pressure pulsation, the impulse of a force that is exerted upon the patinet's blood from, and during, each heart contraction that occurs in the measurement cycle. An impulse value is stored relative to each pulsation. A second artifact rejection technique is used, beginning at the second cuff-pressure step, to generate a prediction curve for predicting a next, expected-to-be-stored pulsation impulse value for a next, lower cuff-pressure step. The second artifact rejection technique is also used to repeatedly smooth the prediction curve based on the difference between a pulsation's calculated impulse value and its respective predicted impulse value. A final, smoothed curve is generated reflecting a final impulse value for each cuff-pressure step. From the final curve, the desired blood pressure parameters are derived and displayed in the form of arabic numerals by means of an LCD readout.

Simulation of the magnetostrictive performance of Terfenol‐D in mechanical devices

Abstract: A dynamic simulation model has been developed. Registered data from static measurements of the magnetostrictive strain for different magnetizations and mechanical stresses are used as numerical input. Easy examination of differences in dynamic performance between samples of different compositions and manufacturing methods is also possible due to a computer‐aided input data handling system. The shape of the imposed magnetization can be a step, impulse, sinusoidal, or an arbitrary function. The mechanical load can be a prescribed force against the magnetostrictive element or an arbitrarily chosen mechanical impedance. The model has been verified against dynamic measurements in an experimental setup for sinusoidal and impulse magnetizations. Comparison between the model and the experimental data reveals that the model is a powerful tool for designing magnetomechanical devices based on giant magnetostrictive materials.

Median filters: a tutorial

Abstract: The author defines median filters and describes their properties. The concepts of impulse removal and root signals are discussed. The state-space approach for studying median filters is covered, as well as the threshold-decomposition technique. >

Distortion-free measurement of high impulse voltages

Abstract: It is shown that every high voltage divider has a limited bandwidth of some MHz, resulting in a limitation for the measurement of front oscillations or front-chopped lightning impulse voltages. It is pointed out that a voltage divider can be easily calibrated and can be constructed to prevent EMC-problems during impulse voltage measurement. Using a spherical electric field sensor with optoelectronic data transmission, a voltage measurement system with an upper bandwidth of 25 MHz has been constructed. The advantage of this system is the distortion-free measurement of all impulse test voltages in any circuit. After a short review of the principle and characteristics of the sensor, some practical applications are highlighted, showing that it can improve high-voltage measurement. >

Multiple impulse solutions to McKean's caricature of the nerve equation. II. Stability

Abstract: We study McKean's caricature of a nerve conduction equation where H is the Heaviside function. It is proved that an n-ple impulse solution resembling the superposition of n unstable solitary impulses has at most 2n - 1, and at least n, unstable modes: exactly n unstable modes corresponding to the amplitudes and the rest of them corresponding to the spacings. The n amplitude modes always exist. We prove also that for an n-ple impulse solution resembling the superposition of n stable solitary impulses, there are at most n - 1 unstable modes and all of them are of spacing type.

Multiple impulse solutions to McKean's caricature of the nerve equation. I—existence

Abstract: McKean's caricature of the nerve equation: is considered. The H in (1) is the Heaviside function. We prove the existence of multiple impulse solutions consisting of any finite number of pulses. These solutions are referred to as n-ple impulse solutions, where n is an arbitrary positive integer.

Frequency-modulated impulse response photothermal detection through optical reflectance. 1: Theory.

Abstract: The 3-D theory of impulse response photothermal detection in opaque (i.e., photothermally saturated) solids through the dependence of the surface temperature optical reflectance on the mathematical equivalent of an optical impulse (the Green’s function) is presented. The theory is extended to include the effects of the finite spatial extent of the photothermal laser source. Explicit expressions for the time-dependent temperature field have been obtained in the experimentally important cases of semi-infinite solids and solids of finite thickness in contact with thermally insulating or conducting backings.

Linear maps and impulse responses

Abstract: Several results are given concerning the representation of causal (mainly) linear operators defined on a set of locally integrable inputs. These results establish the existence of impulse responses and associated integral representations, as well as the convergence of a classical sum to an integral, in a general setting in which a certain continuity condition plays a central role. They also provide necessary and sufficient conditions for a causal linear operator to have a convolution representation with a continuous impulse-response function. >

Piezo electric impulse sensor

Abstract: An impulse sensor comprises a container vessel with a first cavity with an end wall, from which a force receiving member having an axially disposed elongated cavity extends; a transducer retainer member disposed in the first cavity in an affixed arrangement and having a second cavity with a deflective wall containing at least one Piezo electric element in a squeezed arrangement; and a force transmitting member anchored to and extending from the deflective wall of the second cavity, which force transmitting member extends through the end wall of the first cavity and into the elongated cavity included in the force receiving member and is secured to the closed end of the elongated cavity at the extremity thereof; wherein an impulse or force laterally exerted to the force receiving member changes the level of squeezing on the Piezo electric element and generates an electromotive force from the Piezo electric element.

Scaled impulse energy approximation for model reduction

Abstract: It is shown that the impulse energy approximation technique for model reduction can be improved by scaling in the frequency domain. The method remains simple to use and retains the stability property of impulse energy approximation. Criteria are given for choosing an appropriate scaling parameter. An example illustrates the technique. >

Enhanced precipitation efficiency of electrostatic precipitators by means of impulse energization

Abstract: To assess the benefits of impulse energization with different coals, experimental industrial research was performed at a 70 MWe thermal power plant. Two technologies for impulse power supplies were tested over 10000 h of operation. The results of the tests, performed according to ASME standards, demonstrated that impulse energization has great advantages over conventional energization and ensures a collection efficiency from 99.6 to 99.9%, corresponding to emission levels below 50 mg/Nm/sup 3/, with a reduction in absorbed power from about 0.5 to about 0.1 Wh/Nm/sup 3/. Tests showed that with impulse energization there was a considerable decrease both in solid particulate emissions (about 90%) and in energy consumption (about 80%), as compared with conventional (AC rectified voltage) energization. Almost the same improvement was obtained when the flow rate in the experimental channel was increased to 1.8 times the nominal value, thus indicating low sensitivity to gas velocity variations. Thus, the suitability of the technology for complying with the targets set by environmental regulations, even in the presence of difficult solid particulate, was proved. >

Alternatives to the impulse response h(t) to describe the acoustical behavior of conical ducts

Abstract: In unidimensional acoustical systems, the impulse response h(t) at the input section, which describes the pressure evolution originated at this section by the introduction of a flow unit impulse through it, relates pressure p(t) and flow u(t) at the input section by means of the convolution product p=h*u. If damping and radiation are small, it is interesting to find other functions of faster decay than h(t) in order to improve the convolution convergence. As alternatives to h(t), this article studies the impulse responses h’(t) and h‘(t), which correspond to the modified systems that result when coupling the original acoustical system input section to a cylindrical anechoic termination and a conical anechoic termination, respectively. These functions h’(t) and h‘(t) are related to the plane‐wave reflection function Rp−(t) and spherical‐wave reflection function Rs−(t), respectively. The comparison of these three impulse responses shows that the use of h’(t) and h‘(t), though of faster decay than h(t) in pr...

A complete model of a single layer air-cored reactor for impulse voltage distribution

Abstract: A numerical method developed for the computation of impulse voltage distribution in a single-layer air-cored reactor is discussed. The method uses lumped parameters with mutual coupling as suggested by H.W. Dommel (IEEE Trans. Power App. Sys., vol.88, p.388-99, 1969) for transmission lines. The capacitance coefficients have been computed by the charge simulation method. The method includes the mutual inductances, the mutual capacitances, the winding resistance, the capacitance to ground and the insulation resistance. Three implicit methods, trapezoidal integration with damping, trapezoidal integration, and backward Euler, have been used to obtain the companion network. Three test cases are examined: published one to test the numerical method and two measured cases to show the agreement between the computed and the measured results for the actual reactors. The effect of the parameters on the solution has been studied. The method is simple since it involves only the solution of a system of linear equations. >

Elastic scattering of protons by 16O, 40Ca, and 208Pb at 200, 500, and 800 MeV: Relativistic and nonrelativistic analyses based on the impulse approximation.

Abstract: Systematics of Dirac impulse approximation predictions for cross sections and spin observables in elastic proton scattering by /sup 16/O, /sup 40/Ca and /sup 208/Pb at energies of 200, 500 and 800 MeV are presented. The analysis is based on an optical potential constructed from complete sets of Lorentz invariant NN amplitudes. The NN amplitudes are determined from a relativistic meson exchange model of the nuclear force. Comparisons are made with the original form of the Dirac impulse approximation, which is based on five Fermi terms to represent the NN interaction, and with the Schroedinger form of the impulse approximation. For the Dirac analyses, there is implicit coupling to virtual nucleon-antinucleon states. In order to illustrate these contributions, the Dirac equation is recast in the form of the Schroedinger equation and the resulting Schroedinger potentials are separated into ''no-pair'' and virtual-pair parts. The resulting virtual-pair part of the central potential is typically 25 MeV at the center of the nucleus for 200 MeV to 800 MeV protons. A reasonable description of the experimental data is obtained over a broad energy range and over a wide variation of nuclear size when the analysis is based on complete sets of Lorentz-invariant amplitudes. 34more » refs., 23 figs.« less

Fluid pressure impulse nut runner

Abstract: An impulse unit (10) is disclosed which provides for a symmetric transfer of torque between a case (16) and spindle (18) selectively for one or two impulses for each relative rotation between the case and spindle. A pair of cylindrical rollers (84, 86) is provided to isolate two symmetric chambers between the case and spindle to transfer torque therebetween. The use of cylindrical rollers reduces the overall wear in the tool, improves oil sealing capability during long time use, and reduces the cost of manufacture.