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At least 361 records · Page 20

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NASA NTRS1971

Sub-nanosecond ranging possibilities of optical radar at various signal levels and transmitted pulse widths

The behavior of the photomultiplier is considered, as well as the method of derivation of the photomultiplier output pulse and its relation to the reflected light pulse width and amplitude, and the calibration of range precision and accuracy. Pulsed laser radars with light pulse widths of 30, 3, and 0.1 nanosec a considered, with the 0.1 nanosec system capable of highest precision in several modes of operation, including a high repetition rate, single photoelectron reception mode. An alternate calibration scheme using a fast, triggerable light pulser is described in detail.

Poultney, S. K.↗

NASA NTRS1972

Experimental investigation of self-induced transparency and pulse delay in ruby.

We have investigated the self-induced transparency effect in ruby over a range of input energies which range from linear absorption to full transparency. The transmission, pulse delay, and pulse broadening were studied as a function of input energy. The transition region is narrower than that found in similar studies of the CO2/SF6 system; this is consistent with predictions based on ensembles of two-level systems. Included are the first pulse-delay and pulse-broadening curves to be obtained for the ruby system.

Asher, I. M.↗

NASA NTRS1972

A comparison of quasi-steady with short-pulse discharge thruster operation.

The performance and erosion behavior of a solid teflon pulsed plasma thruster were determined when the accelerator nozzle was operated either as a short pulse discharge thruster or as a quasi-steady thruster. Comparisons were made for two different initial discharge energy levels and also for breech propellant feed and side propellant feed configurations. The limited number of test results showed thrust efficiency, based upon directly measured thrust, of short pulse discharge operation to be better than quasi-steady operation when the comparison is made at the same specific impulse. Short pulse operation also experienced less erosion.

Guman, W. J.↗

NASA NTRS1973

Peak-holding circuit for extremely narrow pulses

Circuit was developed which can stretch pulses in 50- to 3200-ns range to make them acceptable for pulse-height analyzers. Circuit uses high-speed wide-band amplifier, does not need excessive frequency compensation, and can handle pulses one-tenth of width normally required by pulse analyzers.

Oneill, R. W.↗

NASA NTRS1974

Analysis and synthesis of a fluid sonic pulse system

A nonlinear sonic system is described that includes a delay line. Short-lived pulses with a high repetition frequency circulate through the system. The analysis was carried out by defining the reflection factor at the load and then dividing the input pulse according to duration into sections of appropriate width. The response was determined for each section, the response to the whole pulse being given by the sum of the responses at the sections. This makes it possible to broach the synthesis of a sonic system that will give an output pulse of the desired form.

Boita, M.↗

NASA NTRS1974

Arterial pulse wave pressure transducer

An arterial pulse wave pressure transducer is introduced. The transducer is comprised of a fluid filled cavity having a flexible membrane disposed over the cavity and adapted to be placed on the skin over an artery. An arterial pulse wave creates pressure pulses in the fluid which are transduced, by a pressure sensitive transistor in direct contact with the fluid, into an electric signal. The electrical signal is representative of the pulse waves and can be recorded so as to monitor changes in the elasticity of the arterial walls.

Kim, C.↗

NASA NTRS1974

Analytical studies of ultrashort optical pulse propagation in a resonant absorbing medium

Resonant absorption in a laser pulse can be reduced to zero if the trailing part induces stimulated emission and returns the absorbed energy back to the pulse. This kind of effect is called Self-Induced Transparency (SIT). Analytic descriptions of short pulse propagation in a resonant medium, based on Slowly Varying Envelope Approximation (SVEA) and in linear media, have been extended in studies of SIT along two principal directions: First, to improve the SVEA by introducing Short Pulse Approximation (SPA); and second, to consider the effect of nonlinear refractive index.

Lee, C. T.↗

NASA NTRS1974

Individual pulse polarization properties of three pulsars

Both average and individual pulse polarization measurements at 430 MHz are presented for three pulsars: PSR 0823 + 26, PSR 0834 + 06, and PSR 2303 + 30. In each case, the average Stokes parameter waveformes are found to depend on the individual pulse polarization properties in a complicated manner. The average waveforms are in general depolarized by pulse-to-pulse fluctuations in polarization state at a given longitude. Two of the three objects exhibit variations of both linear and circular polarization which are associated with quasi-periodic subpulse modulation phenomena in a manner similar to that reported for linear polarization in PSR 0809 + 74 by Taylor et al. (1971.).

Rankin, J. M.↗

NASA NTRS1974

Laser pulse analysis

The paper describes attempts to improve the satellite range measurements obtained with a laser ranging system. The transmitted and received ranging pulses were displayed on an oscilloscope and photographed. The pulse images were measured and the measurement data analyzed by computer. The range errors are reduced by utilizing information contained in the shapes of the return pulses. The problem of determining the center of the irregular return pulse is discussed. The results of the investigation show that the corrections made from the oscilloscope photographs improve the accuracy of the range measurements.

Lehr, C. G.↗

NASA NTRS1975

Electromagnetic pulse from supernovae

Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

Colgate, S. A.↗

NASA NTRS1976

Optical pulsations in HZ Herculis. 5. Pulse-resolved spectrophotometry

Digital spectra of HZ Herculis were obtained with 10 A resolution in the 3,600 - 6,000 A region, synchronously dividing the 1.24-s optical pulsation period into eight 155-ms phase bins. The optical pulses are detected in the data, but their fractional amplitude is only 0.08 percent, a factor of 4 less than typically observed. The separate spectra of each one-eighth of the pulse are identical to within the statistics of the observation. If the X-ray to optical pulse reprocessing mechanism concentrates the optical pulsations into discrete spectral line features, data require the pulses to be distributed among more than four such lines.

Margon, B.↗

NASA NTRS1976

Acoustic pulse propagation in a duct with flow

The effect of a mean flow on acoustic pulse propagation in a wind tunnel of rectangular cross-section is considered both experimentally and theoretically. Pulse shapes in the wind tunnel are recorded by microphones located upstream and downstream of a source. A theoretical model of pulse propagation from a point source located in an infinitely-long rectangular duct carrying a uniform flow is considered. The convective wave equation with boundary conditions appropriate to hard walls is solved by using the Laplace transform. For the input pulse shape used in the experiments, the solution is obtained by numerically evaluating the inverse Laplace transform. The results of experiment and theory are seen to be in good agreement.

Cole, J. E., III↗

NASA NTRS1976

The period-pulse-width distribution of pulsars and their division into three classes

The period-pulse-width (P-W) distribution of sample of 41 pulsars has been reanalyzed under two versions of a model where radiation is beamed from magnetic polar caps which are isotropically oriented with respect to the rotation axis of the neutron stars (IOPC models). It is found that neither IOPC model can explain the P-W distribution of the entire sample. Pulsars with simple unimodal (U) or complicated multimodal (M) pulse shapes show significantly different P-W distributions. Class M pulsars have a narrower P-W distribution than do class U pulsars and, taken separately, are compatible with either IOPC model. Class U pulsars divide into two subgroups, those with relatively narrower pulses (UN) and those with relatively wider pulses (UW), each of which is compatible with either IOPC model. One interpretation of these results is that the pulsars in classes UN, M, and UW have different intrinsic beam sizes, roughly in the ratios 1:2:4, respectively. The possible origins of the three classes are discussed in terms of the force-balance magnetosphere model (Roberts et al., 1972, 1973), where the differences may be attributed to different-mass neutron stars and the structure of the polar caps. An alternative interpretation is that the angle between the rotation and emission axes is not isotropically distributed, but can take only certain preferred values.

Roberts, D. H.↗

NASA NTRS1976

Laser range measurements using non-Gaussian pulse shapes

Many optical ranging systems currently use laser pulses of approximately Gaussian shape with widths of a few nanoseconds or less. The present paper shows that a substantial improvement in accuracy can be obtained for a given pulse length by means of laser ranging systems using conventional length (long) pulses with a sharp leading edge pulse distribution. The accuracy in such a case will improve roughly linearly with the signal strength. Order statistics is used to estimate the round-trip level travel time from the arrival time of the earliest photoelectron.

Ghigo, F. D.↗

NASA NTRS1978

On the nature of the sources of hard pulse X-ray radiation

Besides the identified sources of cosmic pulse X-ray radiation with globular clusters NGC 6624, NGC 1851 and MXB 1730-335 several new identifications were made. The source in Norma was probably identified with globular cluster NGC 5927, the source in Aquila with globular cluster NGC 6838 (M71), and the source in Puppis with globular cluster NGC 2298. Gamma pulses discovered by the Vela satellites and X-ray pulses thoroughly measured by the SAS-3, Ariel-5, and ANS satellites are thought to be the same phenomenon. The sources of such a radiation must be some kind of peculiarity at the central part of globular clusters; it is most probably a massive black hole. The sources of hard pulse radiation which cannot be identified with globular clusters are considered to be a new kind of galactic object, invisible globular clusters, which are naked nuclei of globular clusters.

Shklovskiy, I. S.↗

NASA NTRS1978

The high-energy pulsed X-ray spectrum of HER X-1 as observed with OSO-8

Her X-1 was observed from 1977 August 30 to September 10 using the High-Energy X-Ray Scintillation Spectrometer on board the OSO-8 satellite. The observation, during which the source was monitored continually for nearly an entire ON-state, covered the energy range from 16 to 280 keV. Pulsed flux measurements as a function of binary orbit and binary phase are presented for energies between 16 and 98 keV. The pulsed flux between 16 and 33 keV exhibited a sharp decrease following the fourth binary orbit and was consistent with zero pulsed flux thereafter. The pulsed spectrum was fitted with a power law, a thermal spectrum without features, and a thermal spectrum with a superposed gaussian centered at 55 keV. The latter fit has the smallest value of chi - squared per degree of freedom, and the resulting integrated line intensity is 1.5 superscript + 4.1 subscript - 1.4 x .001 photons s superscript-1 cm superscript-2 for a width of 3.1 superscript + 9.1 subscript -2.6 keV. This result, while of low statistical significance, agrees with the value observed by Trumper (1978) during the same On-state.

Maurer, G. S.↗

NASA NTRS1979

A0535+26 - Refined position measurement and new pulse period data

The hard, pulsing, transient X-ray source A0535+26 has been observed with SAS 3 on three occasions during 1977-1978. These observations have yielded a precise position measurement (20 arcsec error radius), which renders the identification of A0535+26 with the Be star HDE 245770 virtually certain. The pulse phase was tracked for about 9 days in April 1978 and clearly showed both first and second derivatives in the pulse period. An analysis of these timing data, combined with data from previous observations, leads to the following conclusions: (1) a significant fraction of the observed changes in pulse period is probably intrinsic to the compact X-ray star (e.g., accretion torques on a neutron star), and (2) conservative limits on binary orbital parameters tend to further confirm a long orbital period (at least about 20 days).

Li, F.↗

NASA NTRS1978

Pulse compression inside an actively AM mode-locked Nd:YAG laser using a liquid Kerr cell

A mode-locked Nd:YAG laser capable of generating pulses substantially shorter than the present limit of 30-50 ps, while retaining the stability of active mode locking, would be a useful development. This study presents a simplified theoretical analysis and a preliminary experimental verification of the use of an optical Kerr cell as a passive lossless pulse compressor inside a Q-switched and actively mode-locked YAG laser. The theoretical model indicates possible compression to as short as about 5 ps in a typical low-power Nd:YAG laser. The preliminary experimental results show substantial pulse compression via the predicted mechanism, though still not below about 30 ps. The technique appears capable, however, of pulse compression to substantially shorter values without the instabilities, statistical fluctuations, or energy losses associated with saturable-absorber mode locking.

Duerinckx, A. J.↗