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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Definition of Mutually Optimum NDI and Proof Test Criteria for 2219 Aluminum Pressure Vessels. Volume 2: Optimization and Fracture Studies

Certain behavioral aspects associated with fracture and crack extension that cannot be studied using other techniques were evaluated with the ultrasonic method. Characterization of collimated beam techniques showed that significant beam width reduction could be accomplished. Techniques for collimation are given. The crack-opening displacement-gage correction-factor study showed that displacement resulting from crack opening and that from plasticity could be readily differentiated. Crack closure studies using both ultrasonic and crack-opening displacement measurements showed an opening and closing behavior associated with load-unload curves. The results of this work were in general agreement with the closure concepts of Elber. Ultrasonic measurements used to study the nature of flaw extension characteristics associated with failure of the ligament between the flaw front and back surface showed that penetration could occur by an abrupt fracturing after subcritical growth or by continuous growth.

Schwartzberg, F. R.↗
NASA NTRS1978

Magnetosheath bursts of predominantly medium nuclei observed with Imp 8 on February 16, 1974

This paper presents observations made with detectors aboard Imp 8 of a unique series of charged particle bursts that occurred on February 16, 1974, while the spacecraft was traversing the dawn magnetosheath region. This event was unlike any other observation of Imp 7 and 8 in 5.5 years of operation in orbit. The measurements are most directly interpreted as an intense (6000/(sq cm s sr MeV/nucleon)), highly collimated beam flowing in the antisolar direction composed of medium (carbon, nitrogen, or oxygen) nuclei. Both the degree of collimation in arrival direction and the composition are unique to this event. The event is possibly an important signature of terrestrial O(+) ions escaping from the magnetosphere.

Armstrong, T. P.↗
NASA NTRS1979

Plume Characterization of a One-Millipound Solid Teflon Pulsed Plasma Thruster, Phase 2

Measurements of the pulsed plasma thruster (PPT) plume upstream mass flux were made in the Molecular Sink (MOLSINK) vacuum facility in order to minimize the plume-tank wall reflected mass flux. Using specially designed collimators on 4 rows of Quartz Crystal Microbalanced (QCMs) mounted on a support extending radially away from the plume axis, measurements were made of the mass flux originating in a thin slice of the PPT primary plume at an arbitrary dip angle with respect to the thruster axis. The measured and analytically corrected mass flux from particles reflected from the MOLSINK walls was substracted from the collimated QCM measurements to improve their accuracy. These data were then analytically summed over dip angle to estimate the total plume backflow upstream of the thruster nozzle. The results indicate that the PPT backflow is of order 10 to the minus 10th power g/square cm/pulse in the region from 38 to 86 cm from the PPT axis in the nozzle exit plane. This flux drops with the square of the radial distance from the PPT axis and is comparable to the backflow of an 8 cm ion thruster, which has performance characteristics similar to those of the PPT.

Rudolph, L. K.↗
NASA NTRS1980

Multispectral scanner optical system

An optical system for use in a multispectral scanner of the type used in video imaging devices is disclosed. Electromagnetic radiation reflected by a rotating scan mirror is focused by a concave primary telescope mirror and collimated by a second concave mirror. The collimated beam is split by a dichroic filter which transmits radiant energy in the infrared spectrum and reflects visible and near infrared energy. The long wavelength beam is filtered and focused on an infrared detector positioned in a cryogenic environment. The short wavelength beam is dispersed by a pair of prisms, then projected on an array of detectors also mounted in a cryogenic environment and oriented at an angle relative to the optical path of the dispersed short wavelength beam.

Stokes, R. C.↗
NASA NTRS1981

Radio jet refraction in galactic atmospheres with static pressure gradients

A theory of double radio sources which have a 'Z' or 'S' morphology is proposed, based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy. The model describes a collimated jet of supersonic material bending self-consistently under the influence of external static pressure gradients. Gravity and magnetic fields are neglected in the simplest case except insofar as they determine the static pressure distribution. The calculation is a straightforward extension of a method used to calculate a ram-pressure model for twin radio trails ('C' morphology). It may also be described as a continuous-jet version of a buoyancy model proposed in 1973. The model has the added virtue of invoking a galactic atmosphere similar to those already indicated by X-ray measurements of some other radio galaxies and by models for the collimation of other radio jets.

Henriksen, R. N.↗
NASA NTRS1981

Control of the Soft X-ray Polychromator on the Solar Maximum Mission Satellite

The Soft X-ray Polychromator on the Solar Maximum Mission Satellite consists of two largely independent instruments: the Flat Crystal Spectrometer, a highly collimated scanning spectrometer mounted on a raster platform, and the Bent Crystal Spectrometer, a broadly collimated spectrometer providing high time-resolution (128 ms) spectra for the study of rapidly evolving phenomena. Each instrument is controlled by a microcomputer system built around an RCA 1802 microprocessor. This paper presents a discussion of the motivation for using a microprocessor in this application, and the design concepts that were implemented. The effectiveness of the approach as seen after several months of operation will also be discussed.

Springer, L. A.↗
NASA NTRS1981

Analysis of solar X-ray emission line profiles

The high spatial and spectral resolution solar X-ray observations of an active region in which an X-ray and radio gradual rise and fall was in progress are reported. The correlations of highly collimated X-ray scans with the magnetic data indicate the presence of a hot localized region of X-ray emission near the end of the magnetic neutral line. A thermal interpretation of the continuum observed from this region is consistent with an emission temperature of 3 x 10 to the 48th/cu cm and an electron temperature of 10 to the 7th K. A model of the temperature distribution of the X-ray emitting material within the collimator field of view is derived using the resonance lines of Ne X, Ne IX, and Fe XVII. Most of the emission measure is at temperatures less than 2,000,000 K, but some high-temperature material with an electron temperature between 5,000,000 K and 7,000,000 K is required.

Burek, A. J.↗
NASA NTRS1983

A balloon-borne instrument for high-resolution astrophysical spectroscopy in the 20-8000 keV energy range

The Low Energy Gamma ray Spectrometer (LEGS) is designed to perform fine energy resolution measurements of astrophysical sources. The instrument is configured for a particular balloon flight with either of two sets of high purity germanium detectors. In one configuration, the instrument uses an array of three coaxial detectors (effective volume equal to or approximately 230 cubic cm) inside an NaI (T1) shield and collimator (field of view equal to or approximately 16 deg FWHM) and operates in the 80 to 8000 keV energy range. In the other configuration, three planar detectors (effective area equal to or approximately square cm) surrounded by a combination of passive Fe and active NaI for shielding and collimation (field of view equal to or approximately 5 deg x 10 deg FWHM) are optimized for the 20 to 200 keV energy range. In a typical one day balloon flight, LEGS sensitivity limit (3 sigma) for narrow line features is less than or approximately .0008 ph/cm/s square (coaxial array: 80 to 2000 keV) and less than or approximately .0003 ph/square cm/s (planar array: 50 to 150 keV).

Paciesas, W. S.↗
NASA NTRS1982

Theory of electron-positron showers in double radio sources

A black hole of mass of about 300 million solar masses is assumed to be present in the nucleus of an active galaxy or quasar. With an axial magnetic field near 1000 gauss, a potential drop 10 to the 19th volts is generated by the unipolar induction of a rotating accretion disk surrounding the black hole. The possibility that the acceleration of electrons or positrons in the unipolar fields initiates an electromagnetic cascade shower at distances at least 10 to the 16th cm from the black hole is investigated. The scattering medium for the shower is considered to be the spectrum of low energy photons originating from the inner region of the disk. It is found that at completion of the cascade, power-law energy spectra of relativistic electrons and positrons and of gamma-rays emerge under appropriate conditions. If the cascade-initiating particles are collimated, the electrons and positrons emerge in a collimated beam. Such beams may power extragalactic double radio sources.

Burns, M. L.↗
NASA NTRS1982

Modulated Multiple Slit Camera for improved localization of gamma ray bursts

An instrument is described in which a cylindrical modulation collimator is added to one half of a Multiple Slit Camera (MSC) coded-aperture imaging system. The instrument provides gamma-ray burst positions from a single spacecraft that are as precise as the best positions from the long-baseline network of interplanetary spacecraft. The determination of fine positions is described, and the fine-position capability is shown to operate over about two-thirds of the MSC's nearly all-sky field of view. It is noted that the addition of the modulation collimator only slightly reduces the system's sensitivity and can improve the location precision for gamma-ray bursts and slower hard-X-ray transients to about 0.1 sq arcmin.

Gorenstein, P.↗
NASA NTRS1984

Sonic levitation apparatus

A sonic levitation apparatus is disclosed which includes a sonic transducer which generates acoustical energy responsive to the level of an electrical amplifier. A duct communicates with an acoustical chamber to deliver an oscillatory motion of air to a plenum section which contains a collimated hole structure having a plurality of parallel orifices. The collimated hole structure converts the motion of the air to a pulsed. Unidirectional stream providing enough force to levitate a material specimen. Particular application to the production of microballoons in low gravity environment is discussed.

Dunn, S. A.↗
NASA NTRS1984

Muon spin rotation studies

The bulk of the muon spin rotation research work centered around the development of the muon spin rotation facility at the Alternating Gradient Synchrotron (AGS) of Brookhaven National Laboratory (BNL). The collimation system was both designed and fabricated at Virginia State University. This improved collimation system, plus improvements in detectors and electronics enabled the acquisition of spectra free of background out to 15 microseconds. There were two runs at Brookhaven in 1984, one run was devoted primarily to beam development and the other run allowed several successful experiments to be performed. The effect of uniaxial strain on an Fe(Si) crystal at elevated temperature (360K) was measured and the results are incorporated herein. A complete analysis of Fe pulling data taken earlier is included.

Source record↗
NASA NTRS1985

Radio and optical observations of the jets from L1555 IRS 5

New high-sensitivity radio continuum and optical observations of jets associated with the recently formed star IRS 5 are presented. The observations suggest that IRS 5 is the source of a collimated high-velocity outflow of partially ionized gas that produces the observed bipolar molecular outflow in L1551. The emission from the jets can be traced for over 10 arcsec from IRS 5; the jets are aligned with the axis of the molecular bipolar outflow observed by Snell, Loren, and Plambeck (1981). The integrated radio spectrum of the jets is flat, indicating emission by an optically thin plasma. The total mass of ionized gas is estimated to be 0.4-8 x 10 to the -6th solar mass. The absence of optical emission from the northeast jet is best explained by the presence of a dense disk of gas that lies perpendicular to the outflow axis which obscures the northeast jet and may also be responsible for collimating the outflow into two initially opposed jets.

Snell, R. L.↗
NASA NTRS1985

Quantitative analysis of hard X-ray 'footpoint' flares observed by the solar maximum mission

Amplifier gain and collimator hole size variations across the field of view, amplifier/filter efficiency, variations in effective collimator hole size and angular response with photon energy, dead-time, and hard X-ray plate transmission, are among the factors for which instrumental corrections have to be incorporated to effect reliable correction and deconvolution of images from the SMM satellite's Hard X-ray Imaging Spectrometer (HXIS). Attention is given to the substantial Poisson noise in these energy bands. The maximum entropy deconvolution/correction routine developed for establishing the spatial structure reliably inferrable from HXIS data is presented, together with the results of the application of this routine to the three impulsive flares reported by Duijemian et al. (1982) from April 10, May 21, and November 5, 1980.

Mackinnon, A. L.↗
NASA NTRS1986

A spectrometer to measure the diffuse, astronomical extreme ultraviolet background

The present grazing incidence spectrometer for measuring the diffuse astronomical background between 80 and 650 A uses a wire grid collimator to define a 40-arcmin by 15-deg field of view. After passing through the collimator, radiation impinges on an array of plane reflection gratings. An array of mirrors then focuses the diffracted light through a thin filter onto a microchannel plate detector. The resulting system focuses to a few arcmin and produces spectra with 10 to 20 A resolution. Performance characteristics of the spectrometer are discussed.

Labov, Simon↗
NASA NTRS1987

Bipolar flows, molecular gas disks, and the collapse and accretion of rotating interstellar clouds

Rigorous numerical models of the collapse and accretion of rotating, axisymmetric, isothermal interstellar clouds are studied. The results show that molecular gas disks and evacuated bipolar cavities both appear to be natural consequences of the collapse of rotating interstellar clouds. Dynamically significant magnetic fields may not be necessary for explaining either phenomenon. The models strongly support theoretical models of the type where an isotropic wind from a pre-main sequence star is extrinsically collimated by a rotationally derived molecular gas cloud. The models imply that collimation should be strongest on small scales where rotational effects are most important, i.e., in the dense region of the molecular gas disk.

Boss, Alan P.↗
NASA NTRS1988

Passive tilt compensation in an FTS using a double-sided flat retroflector

An optical configuration for a tilt-compensated Fourier transform spectrometer is presented. An expanded and collimated He-Ne laser beam was passed through the interferometer and the collimated output was observed visually. The double-sided mirror was tilted through angles approaching 1 deg with no apparent degradation in the interference quality.

Jennings, Donald E.↗