Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Positive charge”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Radioprotective Thiolamines WR-1065 and WR-33278 Selectively Denature Nonhistone Nuclear Proteins

Differential scanning calorimetry was used to study the interactions of nuclei isolated from Chinese hamster V79 cells with the radioprotector WR-1065, other thiol compounds, and polyamines. Differential scanning calorimetry monitors denaturation of macromolecules and resolves the major nuclear components (e.g. constrained and relaxed DNA, nucleosome core, and nuclear matrix) of intact nuclei on the basis of thermal stability. WR-1065 treatment (0.5-10 mM) of isolated nuclei led to the irreversible denaturation of nuclear proteins, a fraction of which are nuclear matrix proteins. Denaturation of 50% of the total nonhistone nuclear protein content of isolated nuclei occurred after exposure to 4.7 mM WR-1065 for 20 min at 23 C. In addition, a 22% increase in the insoluble protein content of nuclei isolated from V79 cells that had been treated with 4 mM WR-1065 for 30 min at 37 C was observed, indicating that WR-1065-induced protein denaturation occurs not only in isolated nuclei but also in the nuclei of intact cells. From the extent of the increase in insoluble protein in the nucleus, protein denaturation by WR-1065 is expected to contribute to drug toxicity at concentrations greater than approximately 4 mM. WR-33278, the disulfide form of WR1065, was approximately twice as effective as the free thiol at denaturing nuclear proteins. The proposed mechanism for nucleoprotein denaturation is through direct interactions with protein cysteine groups with the formation of destabilizing protein-WR-1065 disulfides. In comparison to its effect on nuclear proteins in isolated nuclei, WR-1065 had only a very small effect on non-nuclear proteins of whole cells, isolated nuclear matrix, or the thiol-rich Ca (2+) ATPase of sarcoplasmic reticulum, indicating that WR-1065 can effectively denature protein only inside an intact nucleus, probably due to the increased concentration of the positively charged drug in the vicinity of DNA.

Booth, Valerie K.↗
NASA NTRS2001

Meteoric Material: An Important Component of Planetary Atmospheres

Interplanetary dust particles (IDPs) interact with all planetary atmospheres and leave their imprint as perturbations of the background atmospheric chemistry and structure. They lead to layers of metal ions that can become the dominant positively charged species in lower ionospheric regions. Theoretical models and radio occultation measurements provide compelling evidence that such layers exist in all planetary atmospheres. In addition IDP ablation products can affect neutral atmospheric chemistry, particularly at the outer planets where the IDPs supply oxygen compounds like water and carbon dioxide to the upper atmospheres. Aerosol or smoke particles from incomplete ablation or recondensation of ablated IDP vapors may also have a significant impact on atmospheric properties.

Grebowsky, Joseph M.↗
NASA NTRS2001

Viscosity Coefficient Curve Fits for Ionized Gas Species Grant Palmer

Viscosity coefficient curve fits for neutral gas species are available from many sources. Many do a good job of reproducing experimental and computational chemistry data. The curve fits are usually expressed as a function of temperature only. This is consistent with the governing equations used to derive an expression for the neutral species viscosity coefficient. Ionized species pose a more complicated problem. They are subject to electrostatic as well as intermolecular forces. The electrostatic forces are affected by a shielding phenomenon where electrons shield the electrostatic forces of positively charged ions beyond a certain distance. The viscosity coefficient for an ionized gas species is a function of both temperature and local electron number density. Currently available curve fits for ionized gas species, such as those presented by Gupta/Yos, are a function of temperature only. What they did was to assume an electron number density. The problem is that the electron number density they assumed was unrealistically high. The purpose of this paper is two-fold. First, the proper expression for determining the viscosity coefficient of an ionized species as a function of both temperature and electron number density will be presented. Then curve fit coefficients will be developed using the more realistic assumption of an equilibrium electron number density. The results will be compared against previous curve fits and against highly accurate computational chemistry data.

Palmer, Grant↗
NASA NTRS2001

Wave Activity in Europa's Wake: Implications for Ion Pickup

Intense wave power at frequencies near and below the cyclotron frequencies of heavy ions was detected in Europa's wake during the E11 and E15 flybys. The fluctuations are mainly transverse to the background magnetic field. Wave characteristics indicate that they are ion cyclotron waves driven by positively charged pickup ions. In both flybys there is evidence, derived from the wave polarization, for pickup of negatively charged chlorine ions. When the moon is near the center of the Jovian current sheet, the pickup rate inferred for the E15 flyby is larger than that for the E11 flyby, when the moon is outside the Jovian current sheet. The wave power does not provide exact pickup density values because the waves are observed in regions where their growth has not yet fully developed. At the edges of the wake region, low-frequency (< K+ gyrofrequency) magnetohydrodynamic waves are also present. We identify magnetic field signatures that are reminiscent of interchange/ballooning of mass-loaded flux tubes from the wake/pickup region expanding into ambient medium that is less dense.

Volwerk, M.↗
NASA NTRS2001

Analysis of Carbon Nanotube Metal-Semiconductor Diode Device

We study recently reported drain current I(sub d)-drain voltage V(sub d) characteristics of a carbon nanotube metal-semiconductor diode device with the gate voltage V(sub g) applied to modulate the carrier density in the nanotube. The diode was kink-shaped at the metal-semiconductor interface. It was shown that (1) larger negative V(sub g) blocked I(sub d) more effectively in the negative V(sub d) region, resulting in the rectifying I(sub d)-V(sub d) characteristics, and that (2) positive V(sub g) allowed I(sub d) in the both V(sub d) polarities, resulting in the non-rectifying characteristics. The negative V(sub d) was the Schottky reverse direction, judging from the negligible I(sub d) behavior for a wide region of -4 V (is less than) V(sub d) (is less than) 0 V, with V(sub g) = -4 V. Such negative V(sub g) would attract positive charges from the metallic electrodes (charge reservoir) to the nanotube and lower the nanotube Fermi energy (E(sub F)). With larger negative V(sub g), the experiment showed that the Schottky forward direction (V(sub d) (is greater than) 0) had a smaller turn-on voltage and the Schottky reverse direction (V(sub d) (is less than) 0) was more resistant to the tunneling breakdown. Therefore, the majority carriers in the transport would be electrons since they can see a lower tunneling barrier (shallower built-in potential) in the forward direction when E(sub F) is lowered, and a thicker tunneling barrier (Schottky barrier) in the reverse direction due to the reduction in the electron density when E(sub F) is lowered.

Yamada, Toshishige↗
NASA NTRS1998

Fifteen Years of Laboratory Astrophysics at Ames

Tremendous strides have been made in our understanding of interstellar material over the past fifteen years thanks to significant, parallel developments in two closely related areas: observational astronomy and laboratory astrophysics. Fifteen years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon-rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In the dense ISM, these cold dust particles are coated with mixed-molecular ices whose compositions are very well known. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the ISM. This great progress has only been made possible by the close collaboration of laboratory experimentalists with observers and theoreticians, all with the goal of applying their skills to astrophysical problems of direct interest to NASA programs. Such highly interdisciplinary collaborations ensure fundamental, in depth coverage of the wide-ranging challenges posed by astrophysics. These challenges include designing astrophysically focused experiments and data analysis, tightly coupled with astrophysical searches spanning 2 orders of magnitude in wavelength, and detailed theoretical modeling. The impact of our laboratory has been particularly effective as there is constant cross-talk and feedback between quantum theorists; theoretical astrophysicists and chemists; experimental physicists; organic, physical and petroleum chemists; and infrared and UV/Vis astronomers. In this paper, two examples of the Ames Program will be given. We have been involved in identifying 9 out of the 14 interstellar pre-cometary ice species known, determined their abundances and the physical nature of the ice structure. Details on our ice work are given in the paper by Sandford et al. Our group is among the pioneers of the PAH model. We built the theoretical framework, participated in the observations and developed the experimental techniques needed to test the model. We demonstrated that the ubiquitous infrared emission spectrum associated with many interstellar objects can be matched by laboratory spectra of neutral and positively charged PAHs and that PAHs were excellent candidates for the diffuse interstellar band (DIB) carriers. See Salama et al. and Hudgins et al.

Allamandola, L. J.↗
NASA NTRS2002

Analysis of Carbon Nanotube Metal-Semiconductor Diode Device

We study recently reported drain current Id-drain voltage Vd characteristics of a carbon nanotube metal semiconductor diode device with the gate voltage Vg applied to modulate the carrier density in the nanotube. The diode was kink-shaped at the metal-semiconductor interface. It was shown that (1) larger negative Vg blocked Id more effectively in the negative Vd region, resulting in the rectifying Id-Vd characteristics, and that (2) positive Vg allowed Id in the both Vd polarities, resulting in the non-rectifying characteristics. The negative Vd was the Schottky reverse direction, judging from the negligible Id behavior for a wide region of -4 V less than Vd less than 0 V, with Vg = -4 V. Such negative Vg would attract positive charges from the metallic electrodes (charge reservoir) to the nanotube and lower the nanotube Fermi energy (EF). With larger negative Vg, the experiment showed that the Schottky forward direction (Vd greater than 0) had a smaller turn-on voltage and the Schottky reverse direction (Vd less than 0) was more resistant to the tunneling breakdown. Therefore, the majority carriers in the transport would be electrons since they can see a lower tunneling barrier (shallower built-in potential) in the forward direction when EF is lowered, and a thicker tunneling barrier (Schottky barrier) in the reverse direction due to the reduction in the electron density when EF is lowered.

Yamada, Toshishige↗
NASA NTRS1998

The Unidentified Infrared Emission Bands: Identified

The so-called Unidentified Infrared or simply UIR bands, the infrared emission band spectrum associated with a wide variety of interstellar objects, can be modeled in detail by laboratory spectra of neutral and positively charged polycyclic aromatic hydrocarbon (PAH) mixtures. Fits are presented for the UIR emission from the protoplanetary nebula IRAS 22272+5435, the diffuse galactic medium, and the Orion HII/photodissociation front - a selection of objects which span the evolutionary range of interstellar material. These data directly address the spectroscopic criticisms previously leveled at the PAH hypothesis and demonstrate that PAH-related molecular species are indeed responsible for this widespread emission. Furthermore, these fits reflect the structure, abundance, and ionization state of the interstellar PAHs and, in turn, provide direct insight into the processes of carbon nucleation, growth and evolution in circumstellar shells and the interstellar medium. To date, no other candidate material which has been proposed to account for the UIR emission can as readily and specifically reproduce these spectral variations. Given the ubiquity of these species, this work demonstrates the tremendous potential of these species as probes of a new and heretofore largely unexplored facet of astrochemistry - potential which should make PAHs the probe of the next millennium much as CO has been for the last quarter century.

Hudgins, Douglas M.↗
NASA NTRS2000

Concentration of simple aldehydes by sulfite-containing double-layer hydroxide minerals: implications for biopoesis

Environmental conditions play an important role in conceptual studies of prebiotically relevant chemical reactions that could have led to functional biomolecules. The necessary source compounds are likely to have been present in dilute solution, raising the question of how to achieve selective concentration and to reach activation. With the assumption of an initial 'RNA World', the questions of production, concentration, and interaction of aldehydes and aldehyde phosphates, potential precursors of sugar phosphates, come into the foreground. As a possible concentration process for simple, uncharged aldehydes, we investigated their adduct formation with sulfite ion bound in the interlayer of positively charged expanding-sheet-structure double-layer hydroxide minerals. Minerals of this type, initially with chloride as interlayer counter anion, have previously been shown to induce concentration and subsequent aldolization of aldehyde phosphates to form tetrose, pentose, and hexose phosphates. The reversible uptake of the simple aldehydes formaldehyde, glycolaldehyde, and glyceraldehyde by adduct formation with the immobilized sulfite ions is characterized by equilibrium constants of K=1.5, 9, and 11, respectively. This translates into an observable uptake at concentrations exceeding 50 mM.

NASA Discipline Exobiology↗
NASA NTRS1999

Modeling the unidentified infrared emission with combinations of polycyclic aromatic hydrocarbons

The infrared emission band spectrum associated with many different interstellar objects can be modeled successfully by using combined laboratory spectra of neutral and positively charged polycyclic aromatic hydrocarbons (PAHs). These model spectra, shown here for the first time, alleviate the principal spectroscopic criticisms previously leveled at the PAH hypothesis and demonstrate that mixtures of free molecular PAHs can indeed account for the overall appearance of the widespread interstellar infrared emission spectrum. Furthermore, these models give us insight into the structures, stabilities, abundances, and ionization balance of the interstellar PAH population. These, in turn, reflect conditions in the emission zones and shed light on the microscopic processes involved in the carbon nucleation, growth, and evolution in circumstellar shells and the interstellar medium.

Spectrophotometry, Infrared↗
NASA NTRS1991

Two-dimensional life?

A model [Wachtershauser, G. (1988) Microbiol. Rev. 52, 452-484], according to which life started in the form of a monomolecular layer of interacting anionic metabolites electrostatically bound to a positively charged surface, is examined critically. The model raises a number of thermodynamic and kinetic difficulties.

NASA Discipline Number 52-20↗
NASA NTRS1997

Mineral induced phosphorylation of glycolate ion--a metaphor in chemical evolution

Bilateral surface-active minerals with excess positive charge concentrate glycolate and trimetaphosphate ion from l0(-3) m aqueous solution to half-saturation of the internal surface sites, and induce phosphorylation of glycolate ion in the mineral with trimetaphosphate, sorbed from l0(-2) m solution. By utilizing reactants from dilute solution at near-neutral pH, and eliminating the need for participating organic nitrogen compounds, the reaction comprises several elements considered necessary for geochemical realism in models for molecular evolution.

NASA Discipline Exobiology↗
NASA NTRS2005

Electrical and Optical Property of Ferroelectric BaTiO3:Eu

We studied various electrical and optical properties of Europium (1 atomic %) incorporated BaTiO3 film on n-Si(100) substrate. The thin film structure was analyzed by X-ray diffraction. Film thickness and optical refractive index were measured with an ellipsometer. P-E hysteresis measurement shows the remnant polarization of 37 micro C/sq cm in BaTiO3:Eu film. C-V measurements on the pure BaTiO3 film show recovery of capacitance across sweeping voltage ranges with a narrow transition zone due to the polarization change. On the other hand, C-V and I-V measurements on the BaTiO3:Eu film show that Europium incorporation increases positively charged states in the BaTiO3 layer such that BaTiO3:Eu/n-Si interface behaves like a leaky p-n junction.

Park, Yeonjoon↗
NASA NTRS2004

Thermodynamic Conditions Favorable to Superlative Thunderstorm Updraft, Mixed Phase Microphysics and Lightning Flash Rate

Satellite observations of lightning flash rate have been merged with proximal surface station thermodynamic observations toward improving the understanding of the response of the updraft and lightning activity in the tropical atmosphere to temperature. The tropical results have led in turn to an examination of thermodynamic climatology over the continental United States in summertime and its comparison with exceptional electrical conditions documented in earlier studies. The tropical and mid-latitude results taken together support an important role for cloud base height in regulating the transfer of Convective Available Potential Energy (CAPE) to updraft kinetic energy in thunderstorms. In the tropics, cloud base height is dominated by the dry bulb temperature over the wet bulb temperature as the lightning-regulating temperature in regions characterized by moist convection. In the extratropics, an elevated cloud base height may enable larger cloud water concentrations in the mixed phase region, a favorable condition for the positive charging of large ice particles that may result in thunderclouds with a reversed polarity of the main cloud dipole. The combined requirements of instability and cloud base height serve to confine the region of superlative electrification to the vicinity of the ridge in moist entropy in the western Great Plains.

Williams, E.↗
NASA NTRS2004

The Investigation Of Carbon Contamination And Sputtering Effects Of Xenon Ion Thrusters

The Electro-Physics Branch of the NASA Glenn Research Center investigates the effect of atomic oxygen, environmental durability of high performance power materials and surfaces, and low earth orbit. One of its current projects involves the analysis of ion thrusters. Ion thrusters are devices that initiate a beam of ions to a target area. The type of ion thruster that I have been working with this Summer of 2004 emits positively charged Xenon (Xe(+)) atoms through two grids, the screen grid and the accelerator grid, after it enters an ionization chamber. Insulators are used to mechanically hold and separate these two grids. A propellant isolator, an instrument that closely resembles insulators, is placed in front of the ionization chamber. Both the insulator and isolator are made with a ceramic compound and filled with insulating beads. The main difference between the two devices is that the propellant isolator allows gas to flow through, in this case, the gas is Xe(+) and the insulators do not. In order to avoid carbon deposits and other contaminating chemicals to settle on the insulators and propellant isolator, a metal shadow shield is placed around them. These shadow shields function as a protectant and can be shaped in numerous configurations. Part of my job responsibility this summer is to investigate the effectiveness of different shadow shields that are utilized on three different ion engines: the NSTAR (NASA Solar Electric Propulsion Technology Application Readiness), JIMO (Jupiter Icy Moons Orbiter), and NEXIS (Nuclear Electric Xenon Ion System). Using calculus and other mathematical tactics, I was asked to find the total flux of carbon contamination that was able to pass the protectant shadow shield. I familiarized myself with the software program, MathCad2004, to help perform some mathematical computations such as complex integration. Another method of studying the probability of contamination is by experimental simulation. After attaining the precise parameters of the actual shadow shields, I created replicas of three types of shadow shielding to be used to undergo testing. It will be placed in a machine that produces carbon atoms at a high temperature of 200 C. or beam is aimed at a targeted material. As a result of this collision, atoms and other particles are ejected out of the target surface. Another part of my internship consisted of research on sputter ejection, or the angle distribution of sputtered material. This research entailed finding the past results of sputter ejection investigation as well as creating another type of mock simulation. Other minor projects include calculating the path of Xe(+) gas through the insulating beads of the isolators and assisting my mentor in collecting data for his paper for the Joint Propulsion Conference & Exhibit to be held July 11-14,2004 in Fort Lauderdale, Florida.

Prak, Moline K.↗
NASA NTRS2005

Exploring the Feasibility of Electrostatic Shielding for Spacecrafts

NASA is moving forward towards the agency's new vision for space exploration in the 21st Century encompassing a broad range of human and robotic missions including missions to Moon, Mars and beyond. Exposure from the hazards of severe space radiation in deep space long duration missions is the show stopper. Langley has developed state-of-the-art radiation protection and shielding technology for space missions. The payload penalty demands a very stringent requirement on the design of the spacecrafts for human deep space missions. The exploration beyond low Earth orbit (LEO) to enable routine access to more interesting regions of space will require protection from the hazards of the accumulated exposures of space radiation, Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE), and minimizing the production of secondary radiation is a great advantage. There is a need to look to new horizons for newer technologies. The present investigation explores the feasibility of using electrostatic shielding in concert with innovative materials shielding and protection technologies. The asymmetries of the radiation shielding problem would be exploited in the electrostatics shielding process. The goal is to repel enough positive charge ions so that they miss the spacecraft without attracting thermal electrons. Conclusions are drawn about the advantages the electrostatic shielding, should it be successful, would bring to the radiation protection design process.

Tripathi, R. K.↗
NASA NTRS2005

METHOD OF PRODUCING AND ACCELERATING AN ION BEAM

A method of producing and accelerating an ion beam comprising the steps of providing a magnetic field with a cusp that opens in an outward direction along a centerline that passes through a vertex of the cusp: providing an ionizing gas that sprays outward through at least one capillary-like orifice in a plenum that is positioned such that the orifice is on the centerline in the cusp, outward of the vortex of the cusp; providing a cathode electron source, and positioning it outward of the orifice and off of the centerline; and positively charging the plenum relative to the cathode electron source such that the plenum functions as m anode. A hot filament may be used as the cathode electron source, and permanent magnets may be used to provide the magnetic field.

Foster, John E.↗
NASA NTRS1996

Proton Fluence Prediction Models

Many spacecraft anomalies are caused by positively charged high energy particles impinging on the vehicle and its component parts. Here we review the current knowledge of the interplanetary particle environment in the energy ranges that are most important for these effects, 10 to 100 MeV/amu. The emphasis is on the particle environment at 1 AU. State-of-the-art engineering models are briefly described along with comments on the future work required in this field.

Proton Fluence Prediction Models spacecraft anomal↗