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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.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Boom potential of a rotating satellite in sunlight

An interpretation is provided for the behavior of long boom potential measurements taken on the spinning P78-2 (SCATHA) satellite at near geosynchronous altitudes. This study uses data taken during a quiet day, with the satellite in sunlight. The data show periodic variations with a maximum amplitude of 6 V. The theory explains why the variations correlate well with sun direction but not with the geomagnetic field. A current balance model, assuming a Maxwellian distribution of photoelectrons, is studied. The photoelectron temperature, the degrees of positive charging of the boom and of the satellite, and the ambient electron flux are calculated. Deviations from the model are discussed.

Lai, S. T.↗
NASA NTRS1988

Complete positive ion, electron, and ram negative ion measurements near Comet Halley (COPERNIC) plasma experiment for the European Giotto Mission

Participation of U.S. scientists on the COPERNIC (COmplete Positive ions, Electrons and Ram Negative Ion measurements near Comet Halley) plasma experiment on the Giotto mission is described. The experiment consisted of two detectors: the EESA (electron electrostatic analyzer) which provided three-dimensional measurements of the distribution of electrons from 10 eV to 30 keV, and the PICCA (positive ion cluster composition analyzer) which provided mass analysis of positively charged cold cometary ions from mass 10 to 210 amu. In addition, a small 3 deg wide sector of the EESA looking in the ram direction was devoted to the detection of negatively charged cold cometary ions. Both detectors operated perfectly up to near closest approach (approx. 600 km) to Halley, but impacts of dust particles and neutral gas on the spacecraft contaminated parts of the data during the last few minutes. Although no flight hardware was fabricated in the U.S., The U.S. made very significant contributions to the hardware design, ground support equipment (GSE) design and fabrication, and flight and data reduction software required for the experiment, and also participated fully in the data reduction and analysis, and theoretical modeling and interpretation. Cometary data analysis is presented.

Lin, Robert P.↗
NASA NTRS1990

Energetics and crystal chemistry of Ruddlesden-Popper type structures in high T(sub c) ceramic superconductors

The formation of Ruddlesden-Popper type layers (alternating slabs of rocksalt and perovskite structures) is seen in these oxides which is similar in many respects to what is seen in the system Sr-Ti-O. However, it was observed that there are some significant differences, for example the rocksalt and perovskite blocks in new superconducting compounds are not necessarily electrically, unlike in Sr-Ti-O systems. This will certainly render an additional coulombic bonding energy between two different types of blocks and may well lead to significant differences in their structural chemistry. In the higher order members of the various homologous series, additional Cu-O planes are inserted in the perovskite blocks. In order for the unit cell to electrically neutral the net positive charge on rocksalt block (which remains constant throughout the homologous series) should be balanced by an equal negative charge on perovskite block. It, thus becomes necessary to create oxygen vacancies in the basic perovskite structure, when width of the perovskite slab changes on addition of extra Cu-O planes. Results of atomistic simulations suggest that these missing oxygen ions allow the Cu-O planes to buckle in these compounds. This is also supported by the absence of buckling in the first member of Bi-containing compounds in which there are no missing oxygen ions and the Sr-Ti-O series of compounds. Additional results are presented on the phase stability of polytypoid structures in these crystal chemically complex systems. The studies will focus on the determination of the location of Cu(3+) in the structures of higher order members of the La-Cu-O system and whether Cu(3+) ions or oxygen vacancies are energetically more favorable charge compensating mechanism.

Dwivedi, Anurag↗
NASA NTRS1989

Positive cloud-to-ground lightning detection by a direction-finder network

Consideration is given to the ability of an automatic direction-finder network to identify cloud-to-ground flashes that effectively lower positive charge to the ground (+CG flashes). Records from an extremely low frequency system are examined to determine whether or not 340 +CG flashes detected by the network have coincident waveforms characteristic of +CG flashes. It is found that false detection in the system is negligible for +CG flashes with range-normalized amplitudes of at least 50 direction-finder units. Also, it is shown that no more than about 15 percent of the +CG flashes detected by the system at smaller amplitudes are false detections.

Macgorman, Donald R.↗
NASA NTRS1989

On the binding energy of He(n)+, for n = 2-7

The atomization energy of small positively charged He clusters has been studied using ab initio methods that include correlation. The atomization energy increases monotonically with cluster size. The inclusion of correlation changes the nature of the bonding and hence changes the structure of the most stable cluster.

Rosi, Marzio↗
NASA NTRS1990

Bounds on halo-particle interactions from interstellar calorimetry

It is shown that the existence of neutral interstellar clouds constrains the interaction of any particulate dark-matter candidate with atomic hydrogen to be quite small. Even for a halo particle of mass 1 PeV (10 to the 6 GeV), it is shown that the cross section with hydrogen must be smaller than the typical atomic cross section that is expected for a positively charged particle bound to an electron. The argument presented is that if the clouds are in equilibrium, then the rate at which energy is deposited by collisions with dark-matter particles must be smaller than the rate at which the cloud can cool. This argument is used to constrain the interaction cross section of dark matter with hydrogen. Remarks are made on the general viability of charged dark matter. Comments are also made on a bound which derives from the dynamical stability of the halo.

Chivukula, Sekhar R.↗
NASA NTRS1989

The effect of ionization on the infrared absorption spectra of PAHs: A preliminary report

The emission lines observed in many interstellar IR sources at 3.28, 6.2, 7.7, 8.7, and 11.3 microns are theorized to originate from polycyclic aromatic hydrocarbons (PAHs). These assignments are based on analyses of lab IR spectra of neutral PAHs. However, it is likely that in the interstellar medium that PAHs are ionized, i.e., are positively charged. Besides, as pointed out by Allamandola et al., although the IR emission band spectrum resembles what one might expect from a mixture of PAHs, it does not match in details such as frequency, band profile, or relative intensities predicted from the absorption spectra of any known PAH molecule. One source of more information to test the PAH theory is ab initio molecular orbital theory. It can be used to compute, from first principles, the geometries, vibrational frequencies, and vibrational intensities for model PAH compounds which are difficult to study in the lab. The Gaussian 86 computer program was used to determine the effect of ionization on the infrared absorption spectra of several small PAHs: naphthalene and anthracene. A preliminary report is presented of the results of these calculations.

Defrees, Doug J.↗
NASA NTRS1990

Middle atmosphere electrical structure during MAC/EPSILON

Extensive use of rocket-launched probes during the the MAC/EPSILON campaign at the Andoya Rocket Range, Norway, has enabled the characterization of the region's electrical environment for all four flight series. The first rocket salvo was conducted during daylight (October 15, 1987) and the subsequent three occurred at night (October 21 and 28 and November 12, 1987), all of them during geomagnetically disturbed conditions. Measurements of polar electrical conductivity, ion mobility, and number density are presented, and their associated structure is investigated for local auroral ionization effects. This is believed to be the first time that Gerdien condenser mobility measurements have indicated a heavy-ion presence (positively charged aerosols) in the auroral mesopause region.

Mitchell, J. D.↗
NASA NTRS1991

Current collection and current closure in the Tethered Satellite System

Current collection and closure-path modeling are examined analytically with respect to the Tethered Satellite System (TSS). A particle-in cell code is compared with a one-dimensional unmagnetized fluid code to model the behavior of a positively charged satellite in the ionosphere. The morphology of the sheath and the sheath-region processes are thus examined, and the influence of ions leaving the sheath region is found to cause the attraction of an electron current that is 40 times greater than the steady state value. The enhancement is transient and enhances the acceleration of the electrons in the sheath. A set of modified MHD equations, including those for ion inertia, quasineutrality, and electron drift, is employed to model TSS current closure. Whistler modes are found to exist and can be excited as the TSS passes through the ionosphere. Important conclusions include a significant fluctuation level in the steady state sheath, an ion void which affects the electron population, and some long-lived electrons trapped in the settled sheath with respect to two directions.

Drobot, Adam↗
NASA NTRS1993

Ionospheric plasma flow about a system of electrically biased flat plates

The steady state interaction of two electrically biased parallel plates immersed in a flowing plasma characteristic of low earth orbit is studied numerically. Fluid equations are developed to describe the motion of the cold positively charged plasma ions, and are solved using finite-differences in two dimensions on a Cartesian grid. The behavior of the plasma electrons is assumed to be described by the Maxwell-Boltzmann distribution. Results are compared to an analytical and a particle simulation technique for a simplified flow geometry consisting of a single semi-infinite negatively biased plate. Comparison of the extent of the electrical disturbance into the flowing plasma and the magnitude of the current collected by the plate is very good. The interaction of two equally biased parallel plates is studied as a function of applied potential. The separation distance at which the current collected by either plate decreases by five and twenty percent is determined as a function of applied potential. The percent decreases were based on a non-interacting case. The decrease in overall current is caused by a decrease in ionic density in the region between the plates. As the separation between the plates decreases, the plates collect the ions at a faster rate than they are supplied to the middle region by the oncoming plasma flow. The docking of spacecraft in orbit is simulated by moving two plates of unequal potential toward one another in a quasi-static manner. One plate is held at a large negative potential while the other floats electrically in the resulting potential field. It is found that the floating plate does not charge continuously negative as it approaches the other more negatively biased plate. Instead, it charges more and then less negative as ionic current decreases and then increases respectively upon approach. When the two plates come into contact, it is expected that the electrically floating plate will charge rapidly negative to a potential near that of the other plate.

Herr, Joel L.↗
NASA NTRS1994

Double layer hydroxide minerals as host structures for bioorganic molecules

A central problem in molecular evolution concerns the selective concentration from dilute, multicomponent solution of source molecules into a reactive environment, where formation of larger molecular assemblages can take place. Minerals consisting of positively charged, separable metal hydroxide sheets have proven capable of these functions. This common structural type is represented by minerals such as pyroaurite (Mg-Fe(3+) hydroxide), hydrotalcite (Mg-Al), green rust Fe(2+)-Fe(3+) and others. Effective interlayer sorption is demonstrated for orthophosphate and condensed phosphates, anionic alkyl compounds, polypeptides, nucleic acids, cyanide complexes and glycolaldehyde phosphate, the latter shown to readily oligomerize to form and selectively retain racemic hexose -2, 4, 6-phosphates, preferentially of altrose (Pitsch, et al, 1993). The selective aldomerization and retention effects correlate with the charge distribution in the host mineral structure and the stereochemistry of the substrate molecules. Interaction between nucleic acid bases, and between the cyanide groups of glycolaldehyde phosphate nitrile at the low water activity in the mineral interlayer is indicated by doubling of the monomeric separation of the hydroxide mineral sheets.

Lee, Ton↗
NASA NTRS1994

Microphysical growth state of ice particles and large-scale electrical structure of clouds

Cloud temperature, liquid water content, and vertical air velocity are all considered in evaluating the microphysical growth state of ice phase precipitation particles in the atmosphere. The large-scale observations taken together with in situ measurements indicated that the most prevalent growth condition for large ice particles in active convection is sublimation during riming, whereas the most prevalent growth condition in stratiform precipitation is vapor deposition. The large-scale electrical observations lend further support to the idea that particles warmed by riming into sublimation charge negatively and particles in vapor deposition charge positively in collisions with small ice particles.

Williams, Earle↗
NASA NTRS1994

Photon-dominated regions around cool stars: The effects of the color temperature of the radiation field

We have investigated the influence of the color temperature of the illuminating radiation field on the chemical and thermal structure of photon-dominated regions (PDRs). We present the results of a study of the photoelectric efficiency of heating by large molecules such as polycyclic aromatic hydrocarbons (PAHs) and very small grains for radiation fields characterized by different effective temperatures. We show that the efficiency for cooler (T(sub eff) approximately = 6000-10,000 K) stars is at most an order of magnitude smaller than that for hotter (T(sub eff) approximately = 20,000-30,000 K) stars. While cooler radiation fields result in less ultraviolet photons capable of heating, the efficiency per absorbed photon is higher, because the grains become less positively charged. We also present detailed calculations of the chemistry and thermal balance for generic PDRs (n(sub 0) approximately = 10(exp 3), G(sub 0) approximately = 10(exp 3)). For cooler radiation fields, the H/H2 and C(+)/C/CO transition layers shift toward the surface of the PDR, because fewer photons are available to photodissociate H2 and CO and to ionize C. The dominant cooling lines are the (C II) 158 micron and the (O I) 63 micron lines for the hotter radiation fields, but cooling by CO becomes dominant for a color temperature of 6000 K or lower. The (C II)/CO and (O I)/CO ratios are found to be very good diagnostics for the color temperature of the radiation field.

Spaans, Marco↗
NASA NTRS1995

The simulation of complete 11 and 12 year modulation cycles for cosmic rays in the heliosphere using a drift model with global merged interaction regions

Two-dimensional, time-dependent drift models have done exceptionally well in explaining major modulation features, especially during the A less than 0 magnetic polarity cycle of the heliospheric magnetic field when positively charge particles are drifting in along the heliospheric neutral sheet (HNS). These models were found to do well when the heliospheric 'tilt angles' alpha less than approximately 30 deg (le Roux & Potgeiter). However, they seem to do less well when alpha greater than approximately 30 deg during A less than 0 cycles seem to fail when this happens in A greater than 0 cycles. Progress was made in understanding these phases of the modulation cycle when merged interaction regions (MIRs) were incorporated in time-dependent drift models (Potgieter et al.). It was also explicitly shown that in obtaining large step decreases in cosmic rays, the MIRs had to be global, i.e., having a latitudinal extent of more than approximately 60 deg. Other classes of MIRs, such as local MIRs and co-rotating MIRs were found to be of secondary importance for establishing long-term modulation. In a previous paper we studied the effects of two consecutive, identical global MIRs, together with a changing wavy HNS, on long-term modulation (Potegieter & le Roux). This approach gave a very natural and convincing explanation for the observed step decreases in cosmic-ray modulation. Emphasis was placed in the declining and recovery phases of the 11 yr modulation cycle. In this paper, four consecutive, nonidentical global MIRs, in combination with a varying wavy HNS, were included in our time-dependent drift model in order to do simulations closer to what was observed between 1977 and 1987. By doing this we could model, for the first time, complete 11 and 22 yr cycles in the heliospheric modulation of galactic cosmic-rays, including the solar magnetic polarity reversals.

Le Roux, J. A.↗
NASA NTRS1996

Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

Treatment of relatively concentrated aqueous solutions of 0-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Bohler, Christof↗
NASA NTRS1996

Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

Treatment of relatively concentrated aqueous solutions of O-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Boehler, Christof↗
NASA NTRS1998

Isotopic Enrichment of Boron in the Sputtering of Boron Nitride with Xenon Ions

An experimental study is described to measure the isotopic enrichment of boron. Xenon ions from 100 eV to 1.5 keV were used to sputter a boron nitride target. An ion gun was used to generate the ion beam. The ion current density at the target surface was approximately 30 microA/sq cm. Xenon ions impinged on the target surface at 50 deg angle to the surface normal. Since boron nitride is an insulator, a flood electron gun was used in our experiments to neutralize the positive charge buildup on the target surface. The sputtered secondary ions of boron were detected by a quadrupole mass spectrometer. The spectrometer entrance aperture was located perpendicular to the ion beam direction and 10 mm away from the target surface. The secondary ion flux was observed to be enriched in the heavy isotopes at lower ion energies. The proportion of heavy isotopes in the sputtered secondary ion flux was found to decrease with increasing primary ion energy from 100 to 350 eV. Beyond 350 eV, light isotopes were sputtered preferentially. The light isotope enrichment factor was observed to reach an asymptotic value of 1.27 at 1.5 keV. This trend is similar to that of the isotopic enrichment observed earlier when copper was sputtered with xenon ions in the same energy range.

Ray, P. K.↗
NASA NTRS1998

Reconstructing Ancient Forms of Life

Progress in the past three months has occurred in two areas, reconstruction of ancestral proteins and improved understanding of chemical features that are likely to be universal in generic matter regardless of its genesis. Ancestral ribonucleases have been reconstructed, and an example has been developed that shows how physiological function can be assigned to in vitro behaviors observed in biological systems. Sequence data have been collected to permit the reconstruction of src homology 2 domains that underwent radiative divergence at the time of the radiative divergence of chordates. New studies have been completed that show how genetic matter (or its remnants) might be detected on Mars (or other non-terrean locations.) Last, the first in vitro selection experiments have been completed using a nucleoside library carrying positively charged functionality, illustrating the importance of non-standard nucleotides to those attempting to obtain evidence for an "RNA world" as an early episode of life on earth.

Benner, Steven A.↗