Impulsive Character Research Articles

El Niño impact on atmospheric polar motion excitation

We study the influences of El Niño phenomena on correlations between short‐period variations of atmospheric and geodetic excitation functions of polar motion during 1980–1998. The correlation between these two excitation functions varies with time, with correlation coefficients computed for 1 year spans reaching maxima of 0.7–0.8. Series of these correlation coefficients themselves correlate with El Niño and Southern Oscillation Index (SOI) data, indicating the influence of El Niño and SOI on atmospheric and geodetic excitation functions of polar motion and on polar motion itself. The maximum correlation coefficients for Niño 4 sea surface temperature data is equal to 0.8 in the case of El Niño events in 1983 and 1987. Impacts of El Niño on polar motion have an impulsive character causing irregular variations of polar motion during the El Niño epochs.

Electromagnetic Radiation and the Computer Systems Data Security Problem

This problem stems from two basic facts. The first is connected with the physics of the processes taking place in digital electronic equipment. The second is due to the way of representing, processing, and transferring the information. The presence of current pulses in power buses due to the impulse character of the functioning of the digital integrated circuits, the existence of inductive and capacity parasite connections, which cause the emergence of high frequency current, and the impulse character of the currents in connecting cables and interface chains all cause the emergence of parasite electromagnetic emissions, which are transmitted as electromagnetic waves. At the same time, in the cables of the power supply alternating currents are induced in such a way that the power supply circuitry becomes a source of secondary wide band emission.

Prolonged plastic deformation related to the microindentation of MgO single crystals

The plastic deformation regions near the indentations on the (0 0 1) plane of MgO single crystals were investigated for an indentor under load and after unloading. It was established that the completion of slip-line structures arising during indentor penetration occurred during indentor removal. The presence of prolonged plastic deformation has been explained by considering the impulse character of the microindentation process of MgO at room temperature.

Impulse Character of Radionuclide Concentration Changes in the Near Ground Layer of Air

Impulse Character of Radionuclide Concentration Changes in the Near Ground Layer of Air

Spatial correlations and solvation interaction in a two-component mixture of adhesive fluids

First, the phase behavior and the spatial correlations in the two-component mixture of adhesive fluids denoted by (1) and (2) are studied on the basis of the solution to the Percus–Yevick/Ornstein–Zernike equation. The isotherm slopes for the correlation function between unlike particles exhibit singularities at the interparticle distances which are the multiple of the molecular size of both species (1) and (2) as a consequence of the impulse character of 1-1, 2-2, and 1-2 adhesive potential of interaction. Then, the above system is treated as an adhesive solvent mixture in which the solvent mediated force between the hard solutes (3) mimicking liophobic colloids is studied. The solution of the Percus–Yevick/Ornstein–Zernike equation for a three-component mixture comprising the two-component adhesive solvent system and the hard sphere colloid is applied in the limit of vanishing solute concentration. Due to the layering of the solvent molecules, the solvation force oscillates with the periods equal to the molecular diameters of both solvent components. The force between the macroparticles in the one-component adhesive solvent [A. Jamnik, D. Bratko, and D. Henderson, J. Chem. Phys. 94, 8210 (1991)] tends to vanish at the critical condition of the model fluid. On the contrary, the solvation force in the two-component adhesive system remains finite even at the critical conditions of the solvent mixture at the specified composition.

Coherent THz Phonons Driven by Light Pulses and the Sb Problem: What is the Mechanism?

Femtosecond laser pulses generate in Sb coherent ${E}_{g}$ phonons at $\ensuremath{\approx}3.4\mathrm{THz}$, in addition to oscillations of ${A}_{1g}$ symmetry accounted for by the phenomenological displacive-excitation model. Experiments agree with theoretical calculations showing that the coherent driving force in absorbing materials like Sb is determined by Raman processes, as in transparent media. The Raman formalism provides a unifying approach for describing light-induced motion of atoms of both impulsive and displacive character.

Role of photospheric footpoint shear in the impulsive dynamics of the solar corona

A frequently observed feature of a solar flare is its impulsive growth from a relatively quiescent background. This imposes a significant constraint on magnetic reconnection models which propose to account for flares: not only should the time scale be fast, but it must also exhibit an impulsive character. It is shown that the spatial width of the shearing motion of the photospheric footpoints has a significant qualitative effect on the time‐evolution of the current sheet and the reconnection electric field in a two‐dimensional coronal loop with a neutral line. The reconnection dynamics for localized footpoint shear profiles does not show an impulsive phase and occurs on a Sweet‐Parker time scale (∼ η−1/2), whereas the reconnection dynamics with broad shear profiles occurs on a faster time scale with a weaker dependence on the resistivity (∼η−1/5), and furthermore, exhibits an impulsive phase due to flux pile‐up near the reconnection layer.

The dynamics of chromospheric spicules

We present the observational results on chromospheric spicules obtained at the Sayan observatory 50 cm coronograph. To investigate the evolution of chromospheric spicules, we analysed spicule spectra of strong chromospheric lines measured simultane­ ously at three altitudes above the solar limb during 5-60 min with a time resolution of 10 to 20 s. The spatial resolution was better than 1", and the spectral resolution was 0.03A in A 6563A. The appearance of a spicule at a given altitude is preceded by an sharp increase in line-of-sight velocity and/or in line half-width at a lower level. Generally, the evolution has a non-monotonous impulsive character. Changes of line-of-sight velocities and other parameters of the line profile can be represented as the superposition of slow, evolutionary changes and fluctuations with periods of about 80 to 120 s. The amplitude of line-of-sight velocity fluctuations is 2-3 km/sec and tends to increase with height. By studying the phase delays of the fluctuations at different heights, we found that the propa­ gation velocity exceeds 300 km S-l , and that the disturbances do not necessarily propagate upwards.

On Differential Systems with Quadratic Impulses and Their Applications to Lagrangian Mechanics

This paper is concerned with the basic dynamics and a class of variational problems for control systems of the form \[({\text{E}})\qquad \dot x = f(t,x,u) + g(t,x,u)\dot u + h(t,x,u)\dot u^2 \] These systems have impulsive character, due to the presence of the time derivative $\dot u$ of the control. It is shown that trajectories can be well defined when the controls u are limits (in a suitable weak sense) of sequences $(u_n )$ contained in the Sobolev space $W^{1,2} $. Roughly speaking, one can say that, in this case, the $\dot u_n $ tend to the square root of a measure. Actually, this paper shows that the system (E) is essentially equivalent to an (affine) impulsive system of the form \[\dot x = f(x) + g(x)v + h(x)\dot w,\] where $v \in L^2 $ and $\dot w$ is a nonnegative Radon measure not smaller than $v^2 $. This provides a characterization of the closure of the set of trajectories of (E), as the controls u range inside a fixed ball of $W^{1,2} $. The existence of (generalized) optimal controls for variational problems of Mayer type is also investigated. Since the main motivation for studying systems of form (E) comes from Rational Mechanics, this paper concludes by presenting an example of an impulsive Lagrangian system.

Penalties for small arms noise assessment.

Proper assessment of the noise created by Army testing and training remains a question that is not fully answered. The most difficult noises to assess are the impulsive noises generated by large weapons, small arms, and helicopters. Currently, general community noise is assessed using the A-frequency weighting and some form of ‘‘energy equivalent’’ level. In the United States, the day–night average sound level is used. For clearly impulsive sound, adjustments or ‘‘penalties’’ are sometimes added to the formulation to account for the increase in annoyance generated by the impulsive character of the sound. One purpose of the present test was to further define and develop adjustments or ‘‘penalties’’ that can be used to assess military noise vis-á-vis normal, urban noises. The study was designed as a paired comparison test where the subjects were presented pairs of sounds and asked, for each pair, which was more annoying, the first or the second sound. The test sounds came from one of three categories of military sources that were: (1) tracked vehicles, (2) small arms fire, or (3) large blasts. The other sound in a pair was one of two control sounds that were: (1) the sound of a wheeled vehicle passing by, or (2) a computer-generated noise. This paper concentrates on small arms noise. The results are for measurements made outdoors−even when the subjects are situated indoors. This is considered to be the proper location since common noise such as traffic is normally assessed on the basis of outdoor levels. The small-arms penalty averages about 8–10 dB across conditions of windows closed or open or subjects outdoors.

Dynamics of the two-step photodissociation of azomethane

Time-resolved coherent anti-Stokes Raman spectroscopy (CARS) measurements have revealed aspects of energy disposal in the 355 nm photodissociation of gas phase azomethane. Interpretation of these results is aided by earlier experiments that kinetically resolved the two steps of dissociation leading to two methyl radicals and a nitrogen molecule. Methyl radicals were observed with zero to four quanta of vibrational excitation in the ν2 out-of-plane deformation mode. Kinetic analysis showed the first-step methyl radicals to carry far more ν2 excitation than the second-step methyl radicals. Through simulation of band contours, a rotational temperature was estimated for the vibrationally unexcited second-step methyls. In addition, nascent vibrational and rotational populations were determined for the nitrogen photoproduct, which is formed in the second dissociative step. These experimental findings are compared to the results of impulsive and statistical models of energy partitioning in this system. It appears that the first step may have significant impulsive character. In the second step, some experimental findings are predicted accurately by the separate statistical ensemble (SSE) model, while other findings fall outside the range spanned by the impulsive and SSE predictions. It is suggested that the second-step energy distributions may reflect the effects of specific exit channel interactions superimposed on statistical partitioning of available energy. Quantum chemical computations on the second step’s reaction path (leading from the methyldiazenyl radical intermediate to the methyl radical and nitrogen photoproducts) should permit deeper understanding of the dissociation dynamics.

Neuropsychodynamics of alcoholism and addiction: Personality, psychopathology, and cognitive style

The literature on the neuropsychology, personality, and psychopathology of alcoholism and addiction is reviewed. Neuropsychological studies of substance abusers have found deficits in abstract concept formation, set-maintenance, set-shifting, behavioral control, and cognitive flexibility. However, the evidence that these deficits are the result of direct substance effects on the brain is slim. Both alcoholics and as-yet nondrinking offspring of alcoholics have been found to be deficient in verbal skills and language functioning. Personality studies of alcoholics and addicts have emphasized such characteristics as field dependency, external locus of control, attenuated time extension, poor ego strength, and disturbed object relations. The psychopathology of alcoholics and opiate abusers seems to be dominated by impulsive character disorder, although there may also be a subgroup of anxious, depressed substance abusers. The present review integrates brain-behavioral perspectives with the data on personality and psychopathology, focusing on the relevance of a multidimensional neuropsychological model to psychodynamic concepts of ego functioning and the substance abusers' problems in the regulation of affect and behavior. It is argued that the concept of cognitive style is useful for understanding the relationship of neuropsychological functioning to personality dynamics, and that this approach can be especially productive in understanding the addictions.

A switched-source model for simulating Arctic undersea noise

A switched-source model is developed for simulating the impulsive character of Arctic undersea noise. The model is based on one proposed by S. V. Czarnecki [“Nearly optimal detection of signals in non-Gaussian noise,” Ph.D. thesis, Dept. of EECS, Princeton Univ. (October 1983)] where impulsive and normal background noise regions are treated as coming from two independent Gaussian sources with differing variance. P. K. Willet and J. B. Thomas [IEEE J. Ocean. Eng. OE-12, 29–37 (1987)] have suggested that the dual mode noise sequence can be treated as stationary and dependent if the state of the source selection switch is governed by a two-state Markov process. In this paper a statistical analysis is conducted on a 10-min time series of Fram 2 noise data in order to provide a complete stochastic description of real noise data within the framework of such a model. An earlier point process analysis is extended by examining the duration and amplitude of burst events. Results of the analysis are used to specify the dual source characteristics, and the terms of the transition matrix for the Markov process.

The Uses and Abuses of the Acoustic Analogy in Helicopter Rotor Noise Prediction

This paper is theoretical in nature and addresses applications of the acoustic analogy in helicopter rotor noise prediction. It is argued that in many instances the acoustic analogy has not been used with care in rotor noise studies. By this it is meant that approximate or inappropriate formulations have been used. By considering various mechanisms of noise generation, such abuses are identified and the remedy is suggested. The mechanisms discussed are thickness, loading, quadrupole, and blade-vortex interaction noise. The quadrupole term of the Ffowcs Williams-Hawkings equation is written in a new form which separates the contributions of regions of high gradients such as shock surfaces. It is shown by order of magnitude studies that such regions are capable of producing noise with the same directivity as the thickness noise. The inclusion of this part of quadrupole sources in current acoustic codes is quite practical. Some of the difficulties with the use of loading noise formulations of the first author in predictions of blade-vortex interaction noise are discussed. It appears that there is a need for development of new theoretical results based on the acoustic analogy in this area. Because of the impulsive character of the blade surface pressure, a time scale of integration different from that used in loading and thickness computations must be used in a computer code for prediction of blade-vortex interaction noise.

On the dispersion of cylindrical impulsive gravitational waves

An exact solution, describing the dispersion of a wave packet of gravita­tional radiation, having initially (at time t = 0) an impulsive character, is analysed. The impulsive character of the wave-packet derives from the space-time being flat, except at a radial distance ϖ = ϖ 1 (say) at t = 0, and the time-derivative of the Weyl scalars exhibiting δ-function singu­larities at ϖ = ϖ 1 , when t → 0. The principal feature of the dispersion is the development of a singularity of the metric function, v , and of the Weyl scalar, ψ 2 , when the wave, after reflection at the centre, collides with the still incoming waves. The evolution of the metric functions and of the Weyl scalars, as the dispersion progresses, is illustrated graphically.

Bandwidth expansion effects on the voltage deviation parameter (Vd) of MF and HF atmospheric radio noise

Medium frequency atmospheric radio noise measured during periods in 1980 and 1981, and recorded on digital tape in 100‐kHz bandwidth has been analyzed to model effects of bandwidth on the noise envelope voltage deviation parameter (Vd). It has been found that the magnitude of this impulsiveness parameter Vd for a given noise sample increases with increasing bandwidth at a slower rate than predicted by CCIR report 322 (International Radio Consultative Committee, Geneva, 1964). Moreover, the rate (slope) is not constant, but rather becomes steeper as the initial (narrower bandwidth) Vd increases due to the impulsive character of the noise at the time of measurement. A simple model based on multiple regression analysis of the MF data allows estimation of Vd in a new bandwidth from a measured Vde using the equation Vd = Vde + (0.4679 + 0.2111 Vde) log BWR, where BWR is the ratio of the new bandwidth to the measured bandwidth. The reason for the unexpectedly small slope lies in the fact that the average envelope voltage, formerly assumed to be independent of bandwidth, increases with increasing bandwidth, but at a slower rate than the rms envelope voltage. Preliminary analysis of a few HF (4–8 MHz) noise recordings indicates a similar behavior in bandwidth effects on Vd.

Impulsiveness of vibration as an additional factor in the hazards associated with hand-arm vibration.

Impulsiveness is defined as the difference between peak and root-mean-square signals. As the difference varies in time, the cumulative distribution function has been used to describe the probability of achieving a certain value of impulsiveness. To make numerical comparison of different vibration signals possible, an impulse index has been selected from the cumulative distribution function. Symptoms of vibration-induced white finger were observed and compared to those expected on the basis of measurements taken according to guidelines of the International Organization for Standardization (ISO). Agreement was found for chain-saw vibration. In the case of pedestal grinding, the ISO draft underestimated the hazardous effects of vibration. Stone workers using pneumatic hammers were exposed to highly impulsive but asymmetrical vibration. The corresponding asymmetry was not, however, observed between the symptoms of the left and right hands, a finding which indicates that coupling between the tool and the hand is important for impulse vibration. The results suggest that the impulse character of vibration increases the risk of vibration-induced pathology. The analysis of high-impulse acceleration peaks obtained by the method presented in this study could provide additional data necessary to improve risk assessment.

Radio observations of the solar neutron flare of 3 June, 1982

In this paper the solar neutron and white-light flare is studied on the basis of radioastronomical observations. It is shown that the 3 June, 1982 flare had an impulsive character. A strong shock wave (M A ≥ 2.9) was observed unusually soon after the impulsive phase of the flare. The radio spectrum of this event shows that the primary acceleration process probably occurred in the region with an electron density of n e = 4.4 × 1015 m−3. The pulsations of the type IV radio burst, observed 15 min after the mass ejection process, manifest the reconnection process in the post-flare stage.

Coulomb interaction in the final state of electron impact ionization: Effects on the triple differential cross section.

An approach to the calculation of the impulsive (e,2e) cross section, which extends the plane-wave-impulse approximation to include the long-range tails of the Coulomb interaction in the final state, is presented. The model divides the collision space into two regions: an inner sphere where short-range forces are active and responsible for the impulsive character of the collision, and an outer region where the tails of the Coulomb interactions act on the charged free particles, which can be treated in a semiclassical way. An extensive comparison between the predictions of this model and experimental data relative to atomic hydrogen and helium, as derived from the literature, is presented. The model constitutes an improvement over previous impulsive models, mainly for the angular distributions of (e,2e) events.

High impulse acceleration levels in hand-held vibratory tools. An additional factor in the hazards associated with the hand-arm vibration syndrome.

The measurement of the root-mean-square (rms) acceleration of vibration does does not take into consideration the short high peak values of the vibratory signal, which may be a hazard contributing to the development of vibration-induced disease. A method for evaluating the impulse character of vibratory signals is given, and impulsiveness is defined as the difference between the peak and rms signals. Measurements were taken during pedestal grinding, during chain sawing with three different generations of saws, and during chiseling with a pneumatic hammer. The measurements comprised (i) analyses done according to the International Organization for Standardization (ISO) draft, (ii) an evaluation of impulsiveness, and (iii) an analysis of the short-time history transient. The risk of vibration-induced white fingers was estimated by the ISO method, and the results were compared with those observed. It was found that the analysis of impulsiveness provided additional data and partly explained the observed symptoms of vibration-induced white fingers. The parameters for the impulsiveness of the vibration signal agreed with the short-time history analysis.