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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A 3D visualization system for molecular structures

The properties of molecules derive in part from their structures. Because of the importance of understanding molecular structures various methodologies, ranging from first principles to empirical technique, were developed for computing the structure of molecules. For large molecules such as polymer model compounds, the structural information is difficult to comprehend by examining tabulated data. Therefore, a molecular graphics display system, called MOLDS, was developed to help interpret the data. MOLDS is a menu-driven program developed to run on the LADC SNS computer systems. This program can read a data file generated by the modeling programs or data can be entered using the keyboard. MOLDS has the following capabilities: draws the 3-D representation of a molecule using stick, ball and ball, or space filled model from Cartesian coordinates, draws different perspective views of the molecule; rotates the molecule on the X, Y, Z axis or about some arbitrary line in space, zooms in on a small area of the molecule in order to obtain a better view of a specific region; and makes hard copy representation of molecules on a graphic printer. In addition, MOLDS can be easily updated and readily adapted to run on most computer systems.

Green, Terry J.↗
NASA NTRS1998

A Synthesis of Fluid Dynamics and Quantum Chemistry for the Design of Nanoelectronics

In 1959, during a famous lecture entitled "There's Plenty of Room at the Bottom", Richard Feynman focused on the startling technical possibilities that would exist at the limit of miniaturization, that being atomically precise devices with dimensions in the nanometer range. A nanometer is both a convenient unit of length for medium to large sized molecules, and the root of the name of the new interdisciplinary field of "nanotechnology". Essentially, "nanoelectronics" denotes the goal of shrinking electronic devices, such as diodes and transistors, as well as integrated circuits of such devices that can perform logical operations, down to dimensions in the range of 100 nanometers. The thirty-year hiatus in the development of nanotechnology can figuratively be seen as a period of waiting for the bottom-up and atomically precise construction skills of synthetic chemistry to meet the top-down reductionist aspirations of device physics. The sub-nanometer domain of nineteenth-century classical chemistry has steadily grown, and state-of-the-art supramolecular chemistry can achieve atomic precision in non-repeating molecular assemblies of the size desired for nanotechnology. For nanoelectronics in particular, a basic understanding of the electron transport properties of molecules must also be developed. Quantum chemistry provides powerful computational methods that can accurately predict the properties of small to medium sized molecules on a desktop workstation, and those of large molecules if one has access to a supercomputer. Of the many properties of a molecule that quantum chemistry routinely predicts, the ability to carry a current is one that had not even been considered until recently. "Currently", there is a controversy over just how to define this key property. Reminiscent of the situation in high-Tc superconductivity, much of the difficulty arises from the different models that are used to simplify the complex electronic structure of real materials. A model-independent approach has been proposed, that sacrifices the plentiful molecular orbitals and Bloch functions of conventional approaches, for a single three-dimensional observable quantity, the electron momentum density Pi(sub rho). This quantity is simply the probability of any electron having momentum rho, multiplied by the total number of electrons in the system (the position of the electron is uncertain). We have explored the utility of this new approach in providing a fundamental understanding of the electron transport properties of molecules that have provi been nominated as candidates for components in the design of nanoelectronics; phenylene-ethynylene oligomers. Some of the molecular systems that have been studied are sketched below.

MacDougall, Preston J.↗
NASA NTRS1984

Engineering correlations of variable-property effects on laminar forced convection mass transfer for dilute vapor species and small particles in air

A simple engineering correlation scheme is developed to predict the variable property effects on dilute species laminar forced convection mass transfer applicable to all vapor molecules or Brownian diffusing small particle, covering the surface to mainstream temperature ratio of 0.25 T sub W/T sub e 4. The accuracy of the correlation is checked against rigorous numerical forced convection laminar boundary layer calculations of flat plate and stagnation point flows of air containing trace species of Na, NaCl, NaOH, Na2SO4, K, KCl, KOH, or K2SO4 vapor species or their clusters. For the cases reported here the correlation had an average absolute error of only 1 percent (maximum 13 percent) as compared to an average absolute error of 18 percent (maximum 54 percent) one would have made by using the constant-property results.

Gokoglu, S. A.↗
NASA NTRS1991

Visualization of DNA molecules in time during electrophoresis

For several years individual DNA molecules have been observed and photographed during agarose gel electrophoresis. The DNA molecule is clearly the largest molecule known. Nevertheless, the largest molecule is still too small to be seen using a microscope. A technique developed by Morikawa and Yanagida has made it possible to visualize individual DNA molecules. When these long molecules are labeled with appropriate fluorescence dyes and observed under a fluorescence microscope, although it is not possible to directly visualize the local ultrastructure of the molecules, yet because they are long light emitting chains, their microscopic dynamical behavior can be observed. This visualization works in the same principle that enables one to observe a star through a telescope because it emits light against a dark background. The dynamics of individual DNA molecules migrating through agarose matrix during electrophoresis have been described by Smith et al. (1989), Schwartz and Koval (1989), and Bustamante et al. (1990). DNA molecules during agarose gel electrophoresis advance lengthwise thorough the gel in an extended configuration. They display an extension-contraction motion and tend to bunch up in their leading ends as the 'heads' find new pores through the gel. From time to time they get hooked on obstacles in the gel to form U-shaped configurations before they resume their linear configuration.

Lubega, Seth↗
NASA NTRS1976

Hydrogen chloride test set

Detector uses tertiary amine, which makes reaction fairly specific for relatively small highly polarized hydrogen chloride molecule. Reaction is monitored by any microbalance capable of measuring extremely small mass differences in real time.

Workman, G. L.↗
NASA NTRSDate not supplied

Development of Flexible Energy Storage Device for Wearable Electronics using All-organic Composites

As the demands and applications of wearable electronics increase, the need of power supply for wearable electronics becomes the critical issue. Both batteries and capacitors can be used as power supplier. In terms of energy storage device, capacitors have many advantages over the batteries, but have a lower energy storage density. To improve the energy density, composites, in which inorganic particles are embedded in a polymer matrix, have been identified as a promising approach to create the dielectrics with a higher energy storage density. The physics behind the composite approach is that the inorganics have a higher dielectric constant and polymers can stand with a higher electric field so that the composites can exhibit a relative dielectric constant and stand with a relative electric field. Therefore, the composites can exhibit a higher energy storage density. However, the embedment of inorganic particles into polymer severely reduces the flexibility of the polymer. To develop flexible energy storage ultracapacitors as an energy storage device for wearable electronics, an all-organic composite approach, in which a dielectric polymer is mixed with polar organic molecules, is introduced. It is experimentally found that by adding a small amount of polar organic molecules into dielectric polymers, the polymers exhibits a high dielectric constant and can stand with a higher electric field. More importantly, the flexibility of the all-organic composites is better than the polymer matrix. Therefore, the all-organic composites can be a strong and promising candidate for the development of flexible energy storage devices for the wearable electronics. In this study, three different dielectric polymers and three different polar molecules were studied. All the all-organic composite systems exhibit a significant improvement on the energy storage density. These new flexible energy storage devices are being developed to be fabricated with on-demandadditive electronics manufacturing processes, so that they can be fabricated when needed in space on the International Space Station and planned lunar habitat and other future missions. These flexible energy storage devices will provide the storage in concert with other printed power generation devices to allow crew health and structural health monitoring sensor devices and systems to be self-powered, not requiring any external power or batteries.

energy storage↗
NASA NTRS1973

Determination of meteor parameters using laboratory simulation techniques

Atmospheric entry of meteoritic bodies is conveniently and accurately simulated in the laboratory by techniques which employ the charging and electrostatic acceleration of macroscopic solid particles. Velocities from below 10 to above 50 km/s are achieved for particle materials which are elemental meteoroid constituents or mineral compounds with characteristics similar to those of meteoritic stone. The velocity, mass, and kinetic energy of each particle are measured nondestructively, after which the particle enters a target gas region. Because of the small particle size, free molecule flow is obtained. At typical operating pressures (0.1 to 0.5 torr), complete particle ablation occurs over distances of 25 to 50 cm; the spatial extent of the atmospheric interaction phenomena is correspondingly small. Procedures have been developed for measuring the spectrum of light from luminous trails and the values of fundamental quantities defined in meteor theory. It is shown that laboratory values for iron are in excellent agreement with those for 9 to 11 km/s artificial meteors produced by rocket injection of iron bodies into the atmosphere.

Friichtenicht, J. F.↗
NASA NTRS2001

Models of Protocellular Structure, Function and Evolution

In the absence of any record of protocells, the most direct way to test our understanding, of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard Medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids in which a small number of functional molecules are selected from a large, random population of candidates. The selected molecules are next vastly multiplied using the polymerase chain reaction.

New, Michael H.↗
NASA NTRS2001

Models of Protocellular Structure, Function and Evolution

In the absence of any record of protocells, the most direct way to test our understanding of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard Medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids in which a small number of functional molecules are selected from a large, random population of candidates. The selected molecules are next vastly multiplied using the polymerase chain reaction. A mutagenic approach, in which the sequences of selected molecules are randomly altered, can yield further improvements in performance or alterations of specificities. Unfortunately, the catalytic potential of nucleic acids is rather limited. Proteins are more catalytically capable but cannot be directly amplified. In the new technique, this problem is circumvented by covalently linking each protein of the initial, diverse, pool to the RNA sequence that codes for it. Then, selection is performed on the proteins, but the nucleic acids are replicated. Additional information is contained in the original extended abstract.

New, Michael H.↗
NASA NTRS1980

The aeronomy of vibrationally excited ozone

Theoretical calculations show that above 80 km in the earth's atmosphere the production of vibrationally excited ozone by chemical processes leads to number densities which are usually larger than those expected for local thermodynamic equilibrium. Quenching of highly excited molecules produced in O+O2+M, O3+M provided a significant source of the lower lying states above the mesopause while the 9.6 microns emission of O3 (0,0,1) was a major sink. Analysis of available laboratory results implied that reactions involving excited ozone play a significant role in the global ozone balance despite the relatively small abundance of the molecule. However, this effect is implicit in many of the rate coefficients currently used in stratospheric calculations. In the upper mesosphere and lower thermosphere, where the excited state populations differ from those for thermal equilibrium, published reaction rate data are not necessarily applicable to aeronomic calculations.

Frederick, J. E.↗
NASA NTRS2000

Evolutionary Cell Computing: From Protocells to Self-Organized Computing

On the path from inanimate to animate matter, a key step was the self-organization of molecules into protocells - the earliest ancestors of contemporary cells. Studies of the properties of protocells and the mechanisms by which they maintained themselves and reproduced are an important part of astrobiology. These studies also have the potential to greatly impact research in nanotechnology and computer science. Previous studies of protocells have focussed on self-replication. In these systems, Darwinian evolution occurs through a series of small alterations to functional molecules whose identities are stored. Protocells, however, may have been incapable of such storage. We hypothesize that under such conditions, the replication of functions and their interrelationships, rather than the precise identities of the functional molecules, is sufficient for survival and evolution. This process is called non-genomic evolution. Recent breakthroughs in experimental protein chemistry have opened the gates for experimental tests of non-genomic evolution. On the basis of these achievements, we have developed a stochastic model for examining the evolutionary potential of non-genomic systems. In this model, the formation and destruction (hydrolysis) of bonds joining amino acids in proteins occur through catalyzed, albeit possibly inefficient, pathways. Each protein can act as a substrate for polymerization or hydrolysis, or as a catalyst of these chemical reactions. When a protein is hydrolyzed to form two new proteins, or two proteins are joined into a single protein, the catalytic abilities of the product proteins are related to the catalytic abilities of the reactants. We will demonstrate that the catalytic capabilities of such a system can increase. Its evolutionary potential is dependent upon the competition between the formation of bond-forming and bond-cutting catalysts. The degree to which hydrolysis preferentially affects bonds in less efficient, and therefore less well-ordered, peptides is also critical to evolution of a non-genomic system. Based on these results, a new computational object called a "molnet" is defined. Like a neural network, it is formed of interconnected units that send "signals" to each other. Like molecules, neural networks have a specific function once their structure is defined. The difference between a molnet and traditional neural networks, is that input to molnets is not simply passed along and processed from input to output units, but rather it is utilized to form and break connections(bonds), and thus to form new structures. Molnets represent a powerful tool that can be used to understand the conditions under which chemical systems can form large molecules, such as proteins, and display ever more complex functions. This has direct applications, for example to the design of smart,synthetic fabrics. Additional information is contained in the original.

Colombano, Silvano↗
NASA NTRS1990

Carbon chemistry in dense molecular clouds: Theory and observational constraints

For the most part, gas phase models of the chemistry of dense molecular clouds predict the abundances of simple species rather well. However, for larger molecules and even for small systems rich in carbon these models often fail spectacularly. Researchers present a brief review of the basic assumptions and results of large scale modeling of the carbon chemistry in dense molecular clouds. Particular attention is to the influence of the gas phase C/O ratio in molecular clouds, and the likely role grains play in maintaining this ratio as clouds evolve from initially diffuse objects to denser cores with associated stellar and planetary formation. Recent spectral line surveys at centimeter and millimeter wavelengths along with selected observations in the submillimeter have now produced an accurate inventory of the gas phase carbon budget in several different types of molecular clouds, though gaps in our knowledge clearly remain. The constraints these observations place on theoretical models of interstellar chemistry can be used to gain insights into why the models fail, and show also which neglected processes must be included in more complete analyses. Looking toward the future, larger molecules are especially difficult to study both experimentally and theoretically in such dense, cold regions, and some new methods are therefore outlined which may ultimately push the detectability of small carbon chains and rings to much heavier species.

Blake, Geoffrey A.↗
NASA NTRS1987

Potential energy surfaces for atomic oxygen reactions: Formation of singlet and triplet biradicals as primary reaction products with unsaturated organic molecules

The experimental study of the interaction of atomic oxygen with organic polymer films under LEO conditions has been hampered by the inability to conduct detailed experiments in situ. As a result, studies of the mechanism of oxygen atom reactions have relied on laboratory O-atom sources that do not fully reproduce the orbital environment. For example, it is well established that only ground electronic state O atoms are present at LEO, yet most ground-based sources are known to produce singlet O atoms and molecules and ions in addition to O(3P). Engineers should not rely on such facilities unless it can be demonstrated either that these different O species are inert or that they react in the same fashion as ground state atoms. Ab initio quantum chemical calculations have been aimed at elucidating the biradical intermediates formed during the electrophilic addition of ground and excited-state O atoms to carbon-carbon double bonds in small olefins and aromatic molecules. These biradicals are critical intermediates in any possible insertion, addition and elimination reaction mechanisms. Through these calculations, we will be able to comment on the relative importance of these pathways for O(3P) and O(1D) reactions. The reactions of O atoms with ethylene and benzene are used to illustrate the important features of the mechanisms of atomic oxygen reaction with unsaturated organic compounds and polymeric materials.

Jaffe, Richard L.↗
NASA NTRS1990

Laboratory simulation of interstellar grain chemistry and the production of complex organic molecules

During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared (5000 to 500 cm(-1), 2 to 20 microns m), the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these astronomical spectra with the spectra of laboratory ices one can determine the composition and abundance of the icy materials frozen on the cold (10K) dust grains present in the interior of molecular clouds. These grains and their ice mantles may well be the building blocks from which comets are made. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, researchers present the infrared spectra of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds. The last component was incorporated into this particular experiment as a tracer of the behavior of a non-aromatic hydrocarbon. The change in the composition that results from ultraviolet photolysis of this ice mixture using a UV lamp to simulate the interstellar radiation field is shown. Photolysis produces CO, CO2, CH4, HCO, H2CO, as well as a family of moderately volatile hydrocarbons. Less volatile carbonaceous materials are also produced. The evolution of the infrared spectrum of the ice as the sample is warmed up to room temperature is illustrated. Researchers believe that the changes are similar to those which occur as ice is ejected from a comet and warmed up by solar radiation. The warm-up sequence shows that the nitrile or iso-nitrile bearing compound produced during photolysis evaporates between 200 and 250K, suggesting that it is carried by a small molecular species. These molecules could be similar to the source material in Comet Halley that is ejected in grains into the coma, freed by sublimation, and photolyzed by solar radiation to produce the observed jets.

Allamandola, L. J.↗
NASA NTRS1984

The significance of far-infrared spectra of the interstellar medium

This paper deals with the analysis of interstellar clouds through infrared and submillimeter observations. The determination of temperature, density, state of ionization and abundance of different chemical constituents is discussed for clouds exhibiting a range of optical depths. There is a preferred choice of spectral features useful for examining different types of gaseous complexes. The prospects for improving the understanding of chemical reaction schemes in interstellar clouds are outlined. Prime advances may be expected in improved data on the abundance of atoms; diatomic hydrides; other small, hydrogen-containing molecules; and their ions.

Harwit, M.↗
NASA NTRS1987

IRAS surface brightness maps of reflection nebulae in the Pleiades

Surface brightness maps at 12, 25, 60, and 100 microns were made of a 2.5 deg x 2.5 deg area of the reflection nebulae in the Pleiades by coadding IRAS scans of this region. Emission is seen surrounding 17 Tau, 20 Tau, 23 Tau, and 25 Tau in all four bands, coextensive with the visible reflection nebulosity, and extending as far as 30 arcminutes from the illuminating stars. The infrared energy distributions of the nebulae peak in the 100 micron band, but up to 40 percent of the total infrared power lies in the 12 and 25 micron bands. The brightness of the 12 and 25 micron emission and the absence of temperature gradients at these wavelengths are inconsistent with the predictions of equilibrium thermal emission models. The emission at these wavelengths appears to be the result of micron nonequilibrium emission from very small grains, or from molecules consisting of 10-100 carbon atoms, which have been excited by ultraviolet radiation from the illuminating stars.

Castelaz, Michael W.↗
NASA NTRS1989

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.

Greene, Thomas P.↗
NASA NTRS1990

Detection of the 3.3-micron feature in two starburst galaxies

This paper reports the detection of the 3.3-micron emission feature in the center of two external galaxies: IC 694 (interacting with NGC 3690) and NGC 4194 (a merger). This feature has been previously detected in various galactic and extragalactic objects and is thought to be due to very small grains or large molecules that probably belong to the Polycyclic Aromatic Hydrocarbon (PAH) family. Its presence, as well as the IRAS colors, strongly suggest that these galaxies are dominated by starbursts rather than active nuclei. From publishing data and the present observations, the brightness of the feature in different galaxies is studied. A simple model of radiative transfer shows that the 3.3-micron feature brightness of a given galaxy allows the determination of the unreddened surface brightness of the galaxy stellar content. In galaxies with relatively large extinction, the 3.3-micron feature (and the other PAH related features) is therefore a useful spatial indicator of star-formation activity in their centers.

Dennefeld, M.↗