Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “sequencer”

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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Surface deformation associated with the November 23, 1977, Caucete, Argentina, earthquake sequence

The 1977 Caucete (San Juan) earthquake considered in the present paper occurred near the Sierra Pie de Palo in the Sierras Pampeanas tectonic province of western Argentina. In the study reported, coseismic surface deformation is combined with seismic observations (main shock and aftershocks, both teleseismic and local data) to place constraints on the geometry and slip of the main fault responsible for the 1977 earthquake. The implications of the 1977 event for long-term crustal shortening and earthquake recurrence rates in this region are also discussed. It is concluded that the 1977 Caucete earthquake was accompanied by more than 1 m of vertical uplift.

Kadinsky-Cade, K.↗
NASA NTRS1987

Rotation and kinematics of the premain-sequence stars in Taurus-Auriga with Ca II emission

Radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren 'HVR', (1986) are reported. Most of the velocities are determined to better than 2 km/s precision. The kinematic properties of the Ca II emission stars with strong Li are found to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. It is suggested following Jones and Herbig (1979), that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.

Hartmann, Lee W.↗
NASA NTRS1987

The chromospheres and coronae of five G-K main-sequence stars

Previous data and high and low dispersion IUE observations of Chi 1 Ori, Alpha Cen A, Xi Boo A, Alpha Cen B, and Epsilon Eri are used to model the atmospheres of these stars from the high chromosphere to the corona. The energy lost by radiation and transferred by thermal conduction is investigated to establish the heating requirements, and results similar to those found for the solar atmosphere are found. The observed emission measurement distribution below 100,000 K can be described by a model in which Alfven wave energy input, observed through nonthermal line broadening, is balanced by radiation losses. Comparison of the coronal, transition region, and chromospheric pressures shows scaling relations which are compatible with previous flux correlations.

Jordan, C.↗
NASA NTRS1987

N-15/N-14 variations in Cretaceous Atlantic sedimentary sequences - Implication for past changes in marine nitrogen biogeochemistry

Unusually low delta N-15 found in early to middle Cretaceous beds rich in marine organic matter from two separate eastern Atlantic Ocean basins is reported. These findings constitute unambiguous evidence that the N contained in these strata is the end result of biogeochemical processes that differed substantially from those that operated on the N contained in intervening organic carbon-poor strata and younger marine sediments. The data indicate that the low N-15 relative abundance is the consequence of pelagic rather than postdepositional processes. Reduced ocean circulation, increased denitrification, and hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of the sedimentary N-15 depletion.

Rau, Greg H.↗
NASA NTRS1988

Linear prediction of stationary vector sequences

The class of all linear predictors of minimal order for a stationary vector-valued process is specified in terms of linear transformations on the associated Hankel covariance matrix. Two particular transformations, yielding computationally efficient construction schemes, are proposed.

Baram, Yoram↗
NASA NTRS1987

Three-dimensional hydrodynamical simulations of stellar collisions. I - Equal-mass main-sequence stars

Two distinct mass-loss mechanisms are noted in the present, fully three-dimensional calculations of collisions between identical stars. While strong shocks in nearly head-on collisions lead to high-velocity jets perpendicular to the collision axis, with increasing mass loss as impact velocity at infinity increases from zero to 2.3 times the escape velocity from the stellar surface, low velocity encounters lead to a sharp increase in mass loss at impact parameters that correspond to nearly-grazing collisions in a two-stage process. In the first stage, the two stars become gravitationally bound due to the encounter's energy dissipation; these binary components then violently coalesce during subsequent periastron passage.

Benz, Willy↗
NASA NTRS1988

A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

Ake, Thomas B.↗
NASA NTRS1988

Theoretical energies for the n = 1 and 2 states of the helium isoelectronic sequence up to Z = 100

The unified method described previously for combining high-precision nonrelativistic variational calculations with relativistic and quantum electrodynamic corrections is applied to the 1s2 1S0, 1s2s 1S0, 1s2s 1S0, 1s2s 3S1, 1s2p 1P1, and 1s2p 3P(0.1,2) states of helium-like ions. Detailed tabulations are presented for all ions in the range Z = 2-100 and are compared with a wide range of experimental data up to (Kr-34)+. The results for (U-90)+ significantly alter the recent Lamb shift measurement of Munger and Gould (1986) from 70.4 + or - 8.3 to 71.0 + or - 8.3 eV, in comparison with a revised theoretical value of 74.3 + or - 0.4 eV. The improved agreement is due to the inclusion of higher order two-electron corrections in the present work.

Drake, G. W.↗
NASA NTRS1988

Superheavy magnetic monopoles and main-sequence stars

The interactions of superheavy monopoles with stars of mass 0.6-25 solar masses are studied. It is shown that captured monopoles cluster near the stellar center, and that their contribution to the total stellar luminosity and their effects on the structure of stars will be unobservable as long as the flux is significantly below the Parker (1970, 1971) bound. It is suggested that all but the strongly magnetic stars will retain a substantial fraction of the monopoles they capture.

Frieman, Joshua A.↗
NASA NTRS1988

Dust discs around low-mass main-sequence stars

The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit.

Wolstencroft, R. D.↗
NASA NTRS1989

Atomic data for opacity calculations. XI - The carbon isoelectronic sequence

Close-coupling calculations are carried out for radiative processes in neutral carbon and a number of carbon-like ions; energy levels, oscillator strengths, and photoionization cross sections have been computed for all bound states of the type 2 s(j)2p(k)nl with n not above 10 and 1 not above 3. The R-matrix method is employed to solve the coupled equations with a ten-state eigenfunction expansion for the parent ion C II and an eight-state expansion for the other boron-like target ions. A number of selected results for oscillator strengths are presented and compared with earlier data, as well as for photoionization cross sections with autoionizing resonance structures. Isoelectronic trends are discussed. The present results for the oscillator strengths of C I and N II are found to differ significantly from some earlier theoretical works for a number of transitions. However, the present C I f values are in excellent agreement with recent calculations and experimental results.

Luo, D.↗
NASA NTRS1990

Limit on overshooting from the convective core in upper main-sequence stars

Overshooting of convective elements far beyond the classical Schwarzschild convective core boundary in theoretical models of massive ZAMS stars is found to lead to significant reductions of stellar luminosity and radius, provided that the temperature gradient in the overshoot region can be approximated by the adiabatic gradient. Comparison of these theoretical models with binary star data for the range of 5-15 solar masses indicates that the ratio of overshoot distance to pressure scale height is probably less than 1.5. This result apparently excludes any overshooting theories that predict very extended adiabatic convective cores.

Stothers, Richard B.↗
NASA NTRS1990

The evolutionary sequence of planetary nebulae

A first-order solution to the problem of nebular evolution is presented and used to construct photoionization models with the correct ionized gas geometry with respect to the central star. The models are used to investigate the evolution of the central star in terms of a 'transformed' H-R diagram in which H-beta luminosity replaces stellar luminosity and the nebular excitation class takes the place of stellar effective temperature. It is shown that the optically thick PN in the Magellanic Clouds behave as ram-pressure confined H II regions trapped between the shocked remnants of AGB wind and the high-velocity stellar wind of the PN nuclei.

Dopita, M. A.↗
NASA NTRS1990

An evolutionary sequence of low frequency radio astronomy missions

Many concepts for space-based low frequency radio astronomy missions are being developed, ranging from simple single-satellite experiments to large arrays on the far side of the moon. Each concept involves a different tradeoff between the range of scientific questions it can answer and the technical complexity of the experiment. Since complexity largely determines the development time, risk, launch vehicle requirements, cost, and probability of approval, it is important to see where the ability to expand the scientific return justifies a major increase in complexity. An evolutionary series of increasingly capable missions, similar to the series of missions for infrared or X-ray astronomy, is advocated. These would range from inexpensive 'piggy-back' experiments on near-future missions to a dedicated low frequency array in earth orbit (or possibly on the lunar nearside) and eventually to an array on the lunar farside.

Jones, Dayton L.↗