Pulse Shape Changes Research Articles

The 35 day dependence of the pulse shape of Hercules X-1

An interesting finding regarding the pulse shape change of Hercules X-1 is reported. By inspecting Her X-1 observations made by various detectors over various epochs, it is found that during the decay phase of the 35-day cycle high state the first-peak flux (of the double-peaked main pulse) is attenuated more than the second-peak flux. Accepting that the 35-day cycle is a consequence of the wobbling of the accretion disk, a model is proposed in which the first-peak emission and the second-peak emission emanate from two different emitting regions (two magnetic poles). According to this model, during the decay phase of the 35-day cycle the column density of the coronal gas along the line of sight to the first-peak emission region is greater than that to the second-peak emission region. Thus the Compton scattering attenuation of the first peak is larger at a given moment during the decay phase. Implications of the model are discussed.

On: “A technique for the continuous representation of dispersion in seismic data” by J. C. Robinson (GEOPHYSICS, August 1979, p. 1345–1351).

Robinson’s paper concerns a topic of discussion in which geophysicists often find interest in attempting to describe the effect of the propagating medium on pulse wave shape and subsequently removing anelastic distortion. The present theory of linear anelastic wave propagation associates a dispersive mechanism and an absorptive mechanism with the change in pulse shape during propagation (Futterman, 1962; Ginzburg, 1955). In deference to causal considerations, these two mechanisms have been related to one another through the approximation of the Kramers‐Kronig relation.

Does PSR0329 + 54 have companions?

An extensive pulse timing programme has been carried out over the past 10 years for several pulsars1–5. The timing observations revealed a wide range of different effects such as glitches, noise in the pulsar rotation and unexpectedly large second time derivatives of the rotation frequency. We suggest here that these unexpectedly large values of v may be caused by a binary motion with an orbital period, Pb, longer than the span of timing observations. Even a distant planet of a relatively low mass (100 M⊕ for Pb = 50 yr) would influence v. In the case of PSR0329+54, besides a large v term, a quasi-sinusoidal modulation shows up in timing residuals. This 3-yr periodicity may be caused by: (1) a change in pulse shape, (2) precession of a magnetic dipole axis, or (3) a small planet (m = 0.06 − 0.57 M⊕) orbiting the pulsar.

Periodic timing residuals in pulsating binary X-ray sources and orbital precession in Hercules X-1

Intrinsic variations of pulse frequency and reflection of pulses produce systematic residuals in pulse arrival times from pulsating binary X-ray sources. We use an iterative technique to calculate higher-order terms in the arrival time curve of a variable-frequency binary source. We also formulate a general framework for studying time delays caused by reflection of pulses. By applying these methods to Her X-1, we find that reflection effects and variations in pulse frequency due to accretion torques, stellar wobble, and changes in pulse shape can mimic the effects of orbital precession with the 35 d period. We suggest observational tests to resolve this ambiguity in the interpretation of the timing data.

Theory of non-linear wave propagation with application to the interaction and inverse problems

The propagation of non-linear deformation waves in a dissipativc medium is described by a unified asymptotic theory, making use of wave front kinematics and the concepts of progressive waves. The mathematical models are derived from the theories of thermoclasticity or viscoclasticity taking into account the geometric and physical non-linearities and dispersion. On the basis of eikonal equations for the associated linear problem the transport equations of the nth order are obtained. In the multidimensional case the method of matched separation of initial equations is proposed. The interaction problems which occur in head-on collisions and in reflection from boundaries or interfaces are analyzed. Conditions are also studied when the interaction of non-linear waves does not take place. The inverse problem of determining materials properties according to pulse shape changes is discussed.

Polarization Phenomena in CdTe Nuclear Radiation Detectors

Nuclear radiation detectors made from high resistivity chlorine doped cadmium telluride grown by the travelling heater method were evaluated. Short term performance for α, ß, and γ radiations was good but the long term performance (>1 min) was degraded by a decrease in the full energy pulse height and γ-ray efficiency with time after the bias voltage was applied. A model which considers the effects of deep acceptors which slowly ionize (~103 s) to an equilibrium concentration ~5 × 1011/cm3 can explain the experimental findings on the changes of pulse shape, pulse amplitude, capacitance, energy resolution, and γ-ray efficiency with time. The operating conditions required for satisfactory stability in these detectors may be inconvenient to the user.

Optical Polarization of the Crab Nebula Pulsar. IL Observational Results and FITS by the Relativistic Vector Model

We present three years of observations of the optical polarization of the Crab Nebula pulsar and show that they are fitted quite well by the relativistic rotating vector model. The main pulse is fiited by a rotational velocity of BETA =0.56 and the interpulse by BETA =0.42-0.44. There appear to be secular changes in the angular parameters defining this model and in the overall levels of polarization. However, no changes in the unpolarized pulse shapes have been detected. A free nutation of the central neutron star is proposed to explain these changes. (auth)

Some invariance properties of the wide-band ambiguity function

Certain changes in pulse shape do not affect the resolution capability of a sonar system. These changes can be expressed as mathematical transformations that leave invariant important properties of the wide-band ambiguity function. Such transformations provide a large number of signal and filter functions, all of which satisfy a given range-Doppler resolution requirement. The sonar designer can then choose the signal and filter that best satisfy other system constraints (e.g., ease of signal generation and filter synthesis, clutter suppression capability, and peak power).

Dynamic properties of rocks and composite structural materials

The response of natural rocks and concrete-like composites to dynamic loading was studied by measuring the passage of stress waves in ballistically-suspended Hopkinson bars. The substances considered include various plutonic rocks exhibiting a wide spectrum of grain sizes, as well as sedimentary, volcanic and structural materials, the latter consisting of combinations of Portland cement and special types of igneous aggregates. Transient loading was accomplished by the central longitudinal impact of a 1/2-in. diameter steel sphere at projectile velocities ranging up to 10,000 in/sec. The shape and velocity of propagation of the symmetric components of the resultant pulses were recorded at various stations along the bars by means of surface strain gages or sandwiched quartz crystal pressure transducers. The metamorphosis of the transient served as the basis for the delineation of the macroscopic behavior mechanisms of these materials. Results both from a single wave passage and from records involving multiple reflections indicate that some rocks exhibited virtually no change in pulse shape, while attenuation in increasing degree was observed in the volcanic materials with no noticeable alteration in wave profile. On the other hand, pulse propagation in a sandstone revealed a significant change in pulse shape. The artificial composites behave similarly to conventional concrete, with only minor amounts of attenuation and no dispersion of the transient. Static properties of the various specimens were examined both in the unshocked and shocked state, revealing little difference in all but one case, namely diorite; mechanical tests and petrographic examination of such samples showed significant deterioration in the physical characteristics as a consequence of wave passage.

Pulse Shapes of Creeping Waves around Soft Cylinders

The process of diffraction of sound waves by finite obstacles is now commonly analyzed in terms of creeping waves that encircle the scattering object azimuthally. For the example of a soft infinite circular cylinder, we have studied the scattering of pulsed sound waves, both of delta-function and of finite-step-function shape (with or without harmonic modulation). We investigated the changes in pulse shape that occur as the pulse propagates over the cylinder surface. This constitutes an extension of previous work by Friedlander and by the present authors in which only the initial rise of the creeping pulses was obtained numerically, and it has been accomplished by an asymptotic expansion in the Laplace-transform variable s.

MULTIPLE STIMULATED BRILLOUIN SCATTERING FROM A LIQUID WITHIN A LASER CAVITY

By inserting a liquid cell between the ruby and the output reflector of a high power, passively Q-switched ruby laser, marked changes in pulse shape, output power and spectral characteristics were observed. These effects are explained in terms of stimulated Brillouin scattering, from the liquid, effectively replacing reflection from the output mirror above a well-defined power level. Time-resolved Fabry-Perot interferograms confirm this explanation and reveal that the output actually consists of a number of pulses, overlapping in time and corresponding to successive Brillouin orders.

Phase Change Associated with Total Internal Reflection at a Strong Negative Gradient

During an investigation of convergence-zone propagation in the Mediterranean, it was remarked that the explosion-pulse arrivals, which had suffered refraction at the extremely strong negative gradient near the surface, had been subjected to a drastic change of pulse shape. The first arrival that had suffered one deep refraction but no shallow refraction showed no evidence of change of pulse shape, except the normal broadening owing to absorption. The pulses were sampled and Fourier transforms were made, revealing that a phase-change independent of frequency of the order of π/2 had occurred in the case of arrivals with one shallow turning point, and one of the order of π for those with two shallow turning points. Theory predicts a phase change of π/2 on total internal reflection at an inhomogeneous layer and this could well be the cause of the effect observed; however, no evidence of phase change at the deep turning point has been found.

ATTENUATION AND DISPERSION OF SHEAR WAVES IN PLEXIGLAS

Wuenschel (1965) measured the attenuation of plate waves in a Plexiglas sheet, finding a value of [Formula: see text] for the attenuation coefficient at frequency f(cps). Using only the first term in the attenuation, he then employed the results of Futterman (1962) to predict the intrinsic dispersion which should accompany this attenuation. Good agreement was obtained between the predicted and observed dispersion. Changes in pulse shape with distance traveled proved to be a sensitive indicator of the presence and nature of the dispersion; when pulses at a location remote from the source were predicted on the basis of a pulse observed near the source plus the transmission characteristics of the material, inclusion of the Futterman dispersion substantially improved the match between predicted and observed waveforms.

PP and crustal structure

Haskell's formulation for reflection of P waves at the base of a solid crust is extended to include overlying liquid layers. Normalized displacement and the phase shift at the base of the crust as a function of angle of incidence and frequency are calculated for two continental models and an oceanic model. Complex reflection coefficients are inverse Fourier transformed to the time domain to show the change of pulse shape upon reflection. These time traces show that the water layer of the oceanic model causes the main difference between continental and oceanic reflections. Sample seismograms from a deep shock were compared to the theoretical records; they were found to be consistent. It is concluded that the amplitude ratio PP/P as a function of frequency obtained from seismograms can be used to decipher the detailed structure at the point of reflection only after the radiation pattern of the source, attenuation of waves during propagation, and crustal transmission response at the receiver are properly taken into account.

Diffusion Measurements in a Fully Ionized Cesium Plasma

Diffusion coefficients both parallel (D∥) and perpendicular (D⊥) to a magnetic field have been measured in a fully ionized plasma. Pulses of potassium plasma were launched at one end of a steady state, fully ionized cesium plasma column, and D∥ and D⊥, along with the macroscopic drift velocity of the column, were found from the change of pulse shape. Experimental values for D∥ agree very well with theory. However, values for D⊥ do not agree with present theoretical predictions. It is observed that D⊥ is inversely proportional to the number density, while theory predicts direct proportionality.

Propagation of Stress Waves in Linear Viscoelastic Solids

A number of problems associated with the propagation and reflection of stress pulses in linear viscoelastic solids are discussed. The correlation between experimental observations and theoretical predictions for specimens of various plastics are considered and computational methods for predicting the changes in pulse shape that result from the dispersion and attenuation produced by viscoelastic solids are described. The changes in pulse shape that take place when a mechanical pulse is reflected at the boundary between two viscoelastic solids is also considered. It is shown that under some conditions a pulse of compression may produce an s-shaped reflected pulse, part of which is tensile and part of which is compressive. Some recent work on the propagation of dilatational pulses in blocks of plastics is also described, and it is shown that this work throws considerable light on the viscoelastic losses associated with volume changes in these materials. Finally, a brief discussion of wave propagation under conditions where linearity no longer obtains is included.

Time-Intensity Characteristics of a Single-Discharge Emission Source

Spectral line intensity vs time measurements were obtained from single, high-energy discharges by means of a photo-multiplier and cathode ray oscillograph. Effects of small changes in current pulse shape upon line intensities are observed for lines representing the first, second, and third spectra of aluminum. Line intensity peaks are observed in the spectra of ionized atoms, especially during the initial steep current rise of short duration pulses It is concluded that an improvement in the spectrographic sensitivity of spectra of ionized atoms can be achieved by employing an electrical pulse of extremely short duration in combination with detectors, which will resolve and record intensity maxima.

Notes on microwave ferromagnetics research

The paper is a report on several of the research projects undertaken in the Radio Research Department of the Bell Laboratories.Ceramic Ferroxdure has been studied at 9, 24 and 48kMc/s, and it has been established that the strong absorption at 48kMc/s is due to resonance caused by a crystalline-anisotropy field of 18000 oersteds. This material has been used as a filter, as the active element in millimeter-wave field-displacement isolators, and as a broad-banding element in a 24kMc/s Faraday rotator.Broad-banding of Faraday rotators has also been carried out by using a dielectric cylinder surrounding the ferrite rod. Such an element has been used to build a circulator giving good performance from 10.7 to 11kMc/s.Rectangular-waveguide resonance isolators have previously either yielded poor reverse-to-forward attenuation ratios, or provided very little reverse attenuation. By using dielectric loading adjacent to the ferrite element, it has been possible to obtain ratios of about 100 : 1 and reverse losses of more than 20dB per inch at 11kMc/s.Studies have been made of the changes in pulse shape and attenuation which occur when ferrite devices are driven by power at kilowatt levels. Some of the results confirm the new spin-wave theory of non-linear ferrite behaviour proposed by Suhl and Anderson.A circulator employing ferrite-loaded coupled waveguides has been constructed for the first time and the idea has been proved feasible. This type of circulator may possess an advantage in high-power applications, since the full power is not applied to the ferrite.A Faraday-rotation switch has been built for 58kMc/s which is capable of turning transmission on or off in 1 microsec. This shows promise for radar and modulator applications.

SCALE MODEL SEISMIC EXPERIMENTS

AbstractAn experimental arrangement is described using an electric spark as source and barium titanate as a detector. Model experiments were made in water with the source mounted above the surface. The effect on the pulse shape on transmission through the air‐water interface and the change of pulse shape with depth were investigated. A number of profiles are presented of reflections from a slate slab immersed in the water with different arrangements of the model and detector.