Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Leaky”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Techniques for correcting transmission errors in video adaptive delta modulation channels

We investigated the effects of channel errors on an adaptive delta modulator used to encode video signals. The investigation revealed that channel errors caused a permanent shift in the dc level of the delta modulator's estimate. Errors in the step size, on the other hand, were transitory and had no noticeable effect on the received pictures. We then presented three error correction schemes to minimize the visibility of the channel errors in the received picture. The first scheme required the transmitter to periodically send the correct dc level of the estimate to the receiver. The second method employed a leaky integrator, and the third method used line-to-line interpolation

Scheinberg, N.↗
NASA NTRS1977

An investigation of techniques for the measurement and interpretation of cosmic ray isotopic abundances

An instrument, the Caltech High Energy Isotope Spectrometer Telescope was developed to measure isotopic abundances of cosmic ray nuclei by employing an energy loss - residual energy technique. A detailed analysis was made of the mass resolution capabilities of this instrument. A formalism, based on the leaky box model of cosmic ray propagation, was developed for obtaining isotopic abundance ratios at the cosmic ray sources from abundances measured in local interstellar space for elements having three or more stable isotopes, one of which is believed to be absent at the cosmic ray sources. It was shown that the dominant sources of uncertainty in the derived source ratios are uncorrelated errors in the fragmentation cross sections and statistical uncertainties in measuring local interstellar abundances. These results were applied to estimate the extent to which uncertainties must be reduced in order to distinguish between cosmic ray production in a solar-like environment and in various environments with greater neutron enrichments.

Wiedenbeck, M. E.↗
NASA NTRS1977

Secondary antiprotons - A valuable cosmic-ray probe

Even in the absence of antiprotons in the primary cosmic rays, a flux of secondary antiprotons will be produced in collisions between cosmic rays and interstellar gas. The predicted antiproton fraction increases with increasing cosmic-ray confinement, so that observations of antiprotons will provide a probe of models of cosmic-ray confinement. It is shown that the expected antiproton fraction (for energies of at least about 10 GeV) ranges between 0.00023 for the 'leaky box' model and 0.0018 for the 'closed box' model. In addition, attention is called to the fact that a detection of cosmic-ray antiprotons at or above a level of 0.0002 will provide a valuable lower limit to the antiproton lifetime.

Steigman, G.↗
NASA NTRS1977

Charge composition and energy spectra of cosmic-ray nuclei at energies above 5 GeV per nucleon

A scintillation-Cerenkov counter telescope, with three gas Cerenkov counters for energy determination between 5 and 90 GeV per nucleon, has been exposed for a net total of 4.5 sq m sr hr in two balloon flights in 1974. The measurement yields the chemical composition and energy spectra of cosmic-ray nuclei in the charge range 5-28. The differential spectral indices of oxygen and of the iron group are measured to be 2.67 plus or minus 0.04 and 2.5 plus or minus 0.08 above 5.4 GeV per nucleon, respectively. The results are interpreted in the context of the 'leaky-box' model of cosmic-ray confinement and propagation.

Caldwell, J. H.↗
NASA NTRS1978

On the propagation of cosmic rays in the Galaxy

Cosmic ray propagation in the Galaxy is examined within the framework of the leaky-box model, whereby phenomenological aspects of diffusion and propagation are related to the physical properties of the interstellar medium. The model is parameterized by data on composition, spectra, spectral change as a function of energy, and cosmic ray particle lifetime. It is assumed that electrons and nucleons have a common source within the Galaxy (probably associated with supernova remnants). Lifetime data and leakage length are compared with radio synchrotron and gamma-ray data to establish a place of origin for cosmic rays observed at earth, i.e., at a radius of 0.5-1.0 kpc from earth. It is noted that if the escape length becomes energy independent, all nuclear spectra will flatten, while the electron spectrum remains unchanged.

Ormes, J.↗
NASA NTRS1978

Relative abundance of antiprotons and antihelium in the primary cosmic radiation

The paper reports measurement of the antiproton-to-proton and antihelium-to-helium ratios in the 4-100 GeV/c range. A superconducting magnet spectrophotometer obtained the data during a balloon flight in May 1976. The upper limit value for the antiproton ratio is 0.0005 in the 4.2-12.5 GeV/c range. This value is only slightly higher than the expected value for a leaky box-model and nearly equal to the value expected in the Peter-Westergard model. It is suggested that this upper limit value rules out the closed galaxy model. Upper limit values for the antihelium ratio are 0.000058 in the 4-10 GeV/c range; less than 0.0001 in the 4-33 GeV/c range; and less than 0.01 in the 33-100 GeV/c range. The interpretation of the raw data is explained.

Badhwar, G. D.↗
NASA NTRS1978

The mean mass of the abundant cosmic-ray nuclei from boron to silicon at 1.2 GeV per atomic mass unit

Results are presented for an investigation of cosmic-ray isotopic composition in which a balloon-borne instrument was used to perform an isotopic analysis of the abundant elements from B through Si in the energy range from 1.0 to 1.6 GeV/amu. The technique employed, which depends on the effect of earth's magnetic field on incoming cosmic rays, and reduction of the observational data are described in detail. Mean masses of the elements B, C, N, O, Ne, Mg, and Si are extracted from normalized Cerenkov spectra and evaluated in terms of the 'leaky box' model of galactic propagation and confinement. The implications of the results for cosmic-ray sources are shown to be consistent with the nucleosynthesis of certain isotopes in the cosmic rays in explosive carbon burning under the conditions of peak temperature, density, and neutronization expected in an explosion of a massive highly evolved star. The possibility of alternate interpretations is noted.

Dwyer, R.↗
NASA NTRS1978

Abundances and spectra for cosmic-ray nuclei from lithium to iron for 2 to 150 GeV per nucleon

Measurements of primary cosmic-ray composition and energy spectra made with a balloon-borne superconducting magnetic spectrometer are described. Results for both 6.7 g/sq cm equivalent vertical atmospheric depth and the top of the atmosphere are presented for the absolute and relative integral abundances, the differential energy spectra, and the spectral indices for cosmic-ray nuclei from Li to Fe and energies of 2 to 50 GeV/n. It is found that propagation effects can explain essentially all the elemental abundances, that the abundances of Li, Be, and B for rigidities below 10 GV/c are consistent with an energy-independent mean interstellar path length of 4.5 + or - 0.5 g/sq cm for the 'leaky box' propagation model, that the abundances of all elements above 10 GV/c are consistent with a path length that decreases as the inverse n-th power of rigidity, and that n equals 0.6 (+0.4, -0.3) for the simplest assumptions made in fitting the source spectra.

Orth, C. D.↗
NASA NTRS1978

The isotopic composition of galactic cosmic ray lithium, beryllium and boron

The isotopic composition of galactic-cosmic-ray Li, Be, and B has been measured near 100 MeV/nucleon by using the University of Chicago IMP 7 and IMP 8 cosmic-ray telescopes during 1973-1975. The measured abundances allow detailed checks of models of interstellar propagation and solar modulation to be made and conclusions to be drawn concerning the spectral forms at the source and the minimum solar modulation level. For example, comparing these results with local interstellar spectra calculated by using a 'leaky box' model, it is found that if solar modulation is ignored, there is no unique leakage mean free path consistent with all the observations. However, by taking account of a sizable level of residual solar modulation, excellent agreement is obtained between the calculated and measured abundances. Thus, these isotopic abundances confirm the old hypothesis that cosmic-ray Li, Be, and B are produced as secondaries in interstellar space.

Garcia-Munoz, M.↗
NASA NTRS1979

A secondary tracer approach to the derivation of galactic cosmic-ray source isotopic abundances

A formalism has been developed for deriving cosmic-ray source isotopic abundances from observed local abundances using a purely secondary nuclide as a tracer of spallation production during propagation. Although the formalism is based on the leaky-box model of cosmic-ray propagation, it is shown that source abundances derived by the tracer technique are reasonably independent of detailed propagation models. The tracer formalism also permits a quantitative evaluation of the effects of observational uncertainties on deduced source abundances. It is shown that statistical errors in the observed abundances and uncertainties in the spallation cross sections are at present the dominant sources of uncertainty. The latter error can be reduced with increased detector size or exposure time, while the former can be minimized by measurements of the relative production cross sections. As a specific example, the tracer technique is applied to the isotopes of sulfur and calcium, and the level of uncertainties which must be achieved to distinguish evolutionary differences between solar-system material and cosmic ray-source material are established.

Stone, E. C.↗
NASA NTRS1979

Evidence for the deficiency of short cosmic ray pathlengths and a physically realistic explanation - The no-near-sources model

Recent observations of the charge and energy spectra of cosmic-ray nuclei are used to construct secondary-to-primary charge ratios at the two ends of the charge spectrum. These ratios are found to be inconsistent with the ad hoc leaky-box model of cosmic-ray propagation which leads to an exponential pathlength distribution. Models for which the pathlength distribution function is deficient in short pathlengths provide a more consistent picture. Several of these models, both ad hoc and physical, are investigated. The physical model considered is one for which detailed galactic propagation parameters and boundary conditions are used and for which there exist no near sources of cosmic rays over a time interval corresponding to a few times the cosmic-ray age.

Lezniak, J. A.↗
NASA NTRS1979

The extension of the concept of the cosmic-ray path-length distribution to nonrelativistic energies

The concept of the cosmic-ray path-length distribution is examined. The corresponding cosmic-ray propagation calculational procedure has been justified theoretically at relativistic energies (Ginzburg and Syrovatskii, 1964) where the effects of ionization energy loss are negligible. The present paper extends the use of the path-length distribution concept in cosmic-ray propagation calculations to nonrelativistic energies. Sufficient constraints to effect this extension are presented. The solution of the cosmic-ray propagation equations in terms of a Green's function approach is also investigated and is used to provide a formulation of the path-length distribution at nonrelativistic as well as relativistic energies in terms of the cosmic-ray source distribution and the propagation characteristics of the interstellar medium. The leaky-box model of cosmic-ray propagation is also examined.

Lezniak, J. A.↗
NASA NTRS1980

Emulsion chamber observations of primary cosmic-ray electrons in the energy range 30-1000 GeV

The results of a series of emulsion exposures, beginning in Japan in 1968 and continued in the U.S. since 1975, which have yielded a total balloon-altitude exposure of 98,700 sq m sr s, are presented. The data are discussed in terms of several models of cosmic-ray propagation. Interpreted in terms of the energy-dependent leaky-box model, the spectrum results suggest a galactic electron residence time of 1.0(+2.0, -0.5) x 10 to the 7th yr, which is consistent with results from Be-10 observations. Finally, the possibility that departures from smooth power law behavior in the spectrum due to individual nearby sources will be observable in the energy range above 1 TeV is discussed.

Nishimura, J.↗
NASA NTRS1980

Energy spectra of cosmic-ray nuclei to above 100 GeV per nucleon

Energy spectra of cosmic-ray nuclei boron to iron have been measured from 2 GeV per nucleon to beyond 100 GeV per nucleon. The data were obtained using an ionization calorimeter flown on a balloon from Palestine, Texas. The 3450 kg payload floated at 7 g/sq cm for almost 24 hours. The results are in excellent agreement with those of other workers where overlaps exist. The spectra are not consistent with single power laws, and demonstrate the power of using a single technique sensitive over a large dynamic range. The data are consistent with the leaky box model of cosmic-ray propagation. The boron data indicate that the cosmic-ray escape length decreases with increasing energy as E to the -(0.4 + or - 0.1) up to 100 GeV per nucleon. Secondary nuclei from iron are also consistent with this dependence. Predicted changes in the energy dependence of the ratios of primary nuclei O/C and (Fe + Ni)/(C + O) are also observed.

Simon, M.↗
NASA NTRS1980

Comparative energy spectra of z equals 3-8 nuclei in the energy range 200 MeV/nuc to 3 GeV/nuc

The energy spectra and charge ratios of Li, Be, B, C, N, and O nuclei in the energy range 200 MeV/nuc to 3 GeV/nuc are examined with measurements obtained during a 50 hour balloon flight in 1977 from a telescope containing several scintillation and Cerenkov counters. The ratios Li/C, Be/C, and B/C are compared with predictions based on the leaky box interstellar propagation model showing that the ratios steadily increase in the apparent interstellar matter path length down to energies of about 400 to 600 MeV/nuc, where it is between 6.5 and 7.5 g/square cm. The effects of solar modulation upon the ratios are considered for energies less than about 1 GeV/nuc as well as for a modulation parameters of phi not less than 400 MV. By examining the ratios Li/Be, Li/B, and Be/B as a function of energy, it is shown that the Li/Be ratio is most sensitive to the solar modulation effects, and that the observed changes in this ratio with energy can be explained by a relatively large modulation consistent with a phi equal to 400 MV in 1977.

Webber, W. R.↗
NASA NTRS1981

On the nature of the cosmic ray positron spectrum

A calculation was made of the flux of secondary positrons above 100 MeV expected for various propagation models. The models investigated were the leaky box or homogeneous model, a disk halo diffusion model, a dynamical halo model, and the closed galaxy model. In each case the parameters of these models were adjusted for agreement with the observed secondary or primary ratios and Be 10 abundance. The positron flux predicted for these models was compared with the available data. The possibility of a primary positron component was considered.

Protheroe, R. J.↗
NASA NTRS1982

Studies of single-mode injection lasers and of quaternary materials. Volume 1: Single-mode constricted double-heterojunction AlGaAs diode lasers

Constricted double-heterojunction (CDH) lasers are presented as the class of single-mode nonplanar-substrate devices for which the lasing cavity is on the least resistive electrical path between the contact and the substrate. Various types of CDH structures are considered under three general topics: liquid-phase epitaxy over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. Ridge-guide CDH lasers have positive-index lateral-mode confinement and provide: single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150 C; light-current characteristics with second-harmonic distortion as low as -57 dB below the fundamental level; threshold-current temperature coefficients, as high as 375 C (pulsed) and 310 C (CW); constant external differential quantum efficiency to 100 C; and lasing operation to 170 C CW and 280 C pulsed. Semileakyguide CDH lasers have an asymmetric leaky cavity for lateral-mode confinement and provide single-mode operation to 15 to 20 mW/facet CW and to 50 mW/facet at 50% duty cycle. Modulation characteristics and preliminary reliability data are discussed.

Botez, D.↗
NASA NTRS1981

A measurement of the cosmic-ray antiproton flux and a search for antihelium

Balloon-borne instrument measurements are presented of the cosmic-ray antiproton flux between 130 and 320 MeV, as well as the results of a search for antihelium between 130 and 370 MeV per nuclear. The antiprotons are found to have a spectral shape similar to the protons, down to about 100 MeV. Calculations of the expected flux of these particles under the assumption that they were created by collisions of high-energy cosmic rays with the interstellar gas, using the standard leaky box model for propagation in the Galaxy, predict a flux two orders of magnitude smaller than that observed. The discrepancy between calculation and experiment may be evidence that cosmic-ray protons have passed through more than 5.0 g/sq cm of material during their lifetime. The search for cosmic-ray antihelium sets a 95% confidence level upper limit on the antihelium/helium ratio of 0.000022.

Buffington, A.↗