Radiative association and the synthesis of long carbon chain molecules in interstellar clouds
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Bates, D. R.↗
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Status of the Esa-earthnet LANDSAT-4 TM Ground Processing Chain
The European program of the European Space Agency received a mandate to upgrade the two existing LANDSAT stations operating in Europe, Kiruna in Sweden and Fucino in Italy, to acquire and process TM data. The salient features of the TM systems are summarized, and the preliminary results of the acceptance tests being carried out using the TM passes acquired in Fucino are reviewed before the X band downlink anomaly of LANDSAT-4.
Fusco, L.↗
Shock tube measurements of growth constants in the branched-chain ethane-carbon monoxide-oxygen system
Exponential free radical growth constants have been measured for ethane carbon monoxide oxygen mixtures by monitoring the growth of oxygen atom concentration as manifested by CO flame band emission. Data were obtained over the temperature range of 1200 to 1700 K. The data were analyzed using an ethane oxidation mechanism involving seven elementary reaction steps. Calculated growth constants were close to experimental values at lower temperatures, up to about 1400 K, but at higher temperatures computed growth constants were considerably smaller than experiment. In attempts to explain these results additional branching reactions were added to the mechanism. However, these additional reactions did not appreciably change calculated growth constants.
Brokaw, R. S.↗
Development of kinematic equations and determination of workspace of a 6 DOF end-effector with closed-kinematic chain mechanism
This report presents results from the research grant entitled Active Control of Robot Manipulators, funded by the Goddard Space Flight Center, under Grant NAG5-780, for the period July 1, 1988 to January 1, 1989. An analysis is presented of a 6 degree-of-freedom robot end-effector built to study telerobotic assembly of NASA hardware in space. Since the end-effector is required to perform high precision motion in a limited workspace, closed-kinematic mechanisms are chosen for its design. A closed-form solution is obtained for the inverse kinematic problem and an iterative procedure employing Newton-Raphson method is proposed to solve the forward kinematic problem. A study of the end-effector workspace results in a general procedure for the workspace determination based on link constraints. Computer simulation results are presented.
Nguyen, Charles C.↗
Joint-space adaptive control of a 6 DOF end-effector with closed-kinematic chain mechanism
The development is presented for a joint-space adaptive scheme that controls the joint position of a six-degree-of-freedom (DOF) robot end-effector performing fine and precise motion within a very limited workspace. The end-effector was built to study autonomous assembly of NASA hardware in space. The design of the adaptive controller is based on the concept of model reference adaptive control (MRAC) and Lyapunov direct method. In the development, it is assumed that the end-effector performs slowly varying motion. Computer simulation is performed to investigate the performance of the developed control scheme on position control of the end-effector. Simulation results manifest that the adaptive control scheme provides excellent tracking of several test paths.
Nguyen, Charles C.↗
A value-chain analysis of software productivity components
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Boehm, Barry W.↗
Markov Chains For Testing Redundant Software
Preliminary design developed for validation experiment that addresses problems unique to assuring extremely high quality of multiple-version programs in process-control software. Approach takes into account inertia of controlled system in sense it takes more than one failure of control program to cause controlled system to fail. Verification procedure consists of two steps: experimentation (numerical simulation) and computation, with Markov model for each step.
White, Allan L.↗
Learning-based position control of a closed-kinematic chain robot end-effector
A trajectory control scheme whose design is based on learning theory, for a six-degree-of-freedom (DOF) robot end-effector built to study robotic assembly of NASA hardwares in space is presented. The control scheme consists of two control systems: the feedback control system and the learning control system. The feedback control system is designed using the concept of linearization about a selected operating point, and the method of pole placement so that the closed-loop linearized system is stabilized. The learning control scheme consisting of PD-type learning controllers, provides additional inputs to improve the end-effector performance after each trial. Experimental studies performed on a 2 DOF end-effector built at CUA, for three tracking cases show that actual trajectories approach desired trajectories as the number of trials increases. The tracking errors are substantially reduced after only five trials.
Nguyen, Charles C.↗
Dust around AFGL 2688, molecular shielding, and the production of carbon chain molecules
The molecular, IR, and optical maps of the evolved carbon star AFGL 2688 (the 'Egg' Nebula) are all consistent with a model of a bipolar outflow of approximately 0.0001 solar masses/yr that stopped as this object evolved beyond the asymptotic giant branch about 200 years ago. In order to explain the extended HC7N emission around this star, it is proposed that carbon grains are collisionally fragmented as they supersonically steam through the circumstellar envelope.
Jura, M.↗
Interaction of various mechanical activity models in regulation of myosin heavy chain isoform expression
The purpose of this study was to determine the effects of a novel combination of mechanical activity paradigms on the isomyosin distribution in rat hindlimb muscles. Thirty female Sprague-Dawley rats were divided into five experimental groups as follows: normal control, functional overload (OV) of the plantaris, OV in conjunction with hindlimb suspension (OV-S), and a combination of OV-S and either static standing weight-bearing activity (OV-SS) or high-incline treadmill exercise (OV-SE). OV of the plantaris resulted in significant hypertrophy and significant fast-to-slow isomyosin shifts. These changes were completely inhibited by the addition of hindlimb suspension (OV-S). Also, neither of the two weight-bearing regimes (OV-SS and OV-SE) was able to attenuate the suspension-induced atrophy. In the vastus intermedius and vastus lateralis, however, OV-SS was able to partially retard the atrophy associated with suspension. In both the plantaris and vastus intermedius, only OV-SS was able to partially reverse the slow-to-fast isomyosin transitions associated with suspension. These results suggest that the type of mechanical activity is important in determining adaptation to altered loading conditions, with OV-SS appearing more effective than OV-SE in reversing the effects of unweighting.
Diffee, Gary M.↗
Effect of hydrocarbon type and chain length on uniform flame movement in quiescent fuel-air mixtures
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GASES - COMBUSTION↗
Chain Breaking and Branching in the Active-particle Diffusion Concept of Quenching
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Belles, Frank E↗
The EURECA telecommanding chain: Experience with packet telecommand and telemetry systems
The European Retrieval Carrier (EURECA) was launched on its first flight on the 31st July 1992 by the Space Shuttle Atlantis. EURECA is characterized by several new on-board features, most notable Packet Telemetry and a partial implementation of Packet Telecommanding using an early version of the Command Operation Procedure (COP-1) protocol. EURECA has also very low contact time with its Ground Station, with a consequent high number of out-of-visibility onboard operations. This paper concentrates on the implementation and operational experience with the COP-1 Protocol and the effect the short ground contact time has on the design of the Commanding System. Another interesting feature is that the COP-1 is implemented at the control center rather than at the ground station. The COP-1 protocol also successfully supported the mission during the launch where commands were sent via NASCOM and the Shuttle.
Mueller, C.↗
Watson: A new link in the IIE iron chain
Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the IIE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new IIE iron. Whole rock Watson silicate shows an enrichment in K and P (each approximately 2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa20), opx (Fs17Wo3), capx (Fs9Wo14)(with very fine exsolution lamellae), antiperthite feldspar (An1-3Or5) with less than 1 micron exsolution lamellae (An1-3Or greater than 40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of approximately 300X and 100-150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or13, and in the presence of antiperthite.
Olsen, Edward↗
Atmospheric Condensational Properties of Ultrafine Chain and Fractal Aerosol Particles
The purpose for the research sponsored by this grant was to lay the foundations for qualitative understanding and quantitative description of the equilibrium vapor pressure of water vapor over the irregularly shaped, carbonaceous particles that are present in the atmosphere. This work apparently was the first systematic treatment of the subject. Research was conducted in two complementary components: 1. Calculations were performed of the equilibrium vapor pressure of water over particles comprised of aggregates of spheres in the 50-200 nm radius range. The purposes of this work were two-fold. First, since no systematic treatment of this subject had previously been conducted, its availability would be directly useful for quantitative treatment for a limited range of atmospheric aerosols. Second, it would provide qualitative indications of the effects of highly irregular particle shape on equilibrium vapor pressure of aggregates comprised of smaller spheres.
Marlow, William H.↗
Abundances of Linear Carbon-Chain Molecules in Supernovae
This paper evaluates the condensation of carbon solids in a gas of pure C and O atoms when these exist within the interior of an expanding young supernova. We calculate the abundances of large carbon molecules, which serve as nucleations for condensation of graphites. Additional information is contained in the original extended abstract.
Clayton, D. D.↗
The Specificity of Peptide Chain Extension by N-Carboxyanhydrides
We have used amino acids activated by carbonyldiimidazole to study the enantiospecificity of peptide elongation in aqueous solution. Peptide primers Glu(sub 10) and Ala3Glulo were elongated with the enantiomers of arginine, glutamic acid, asparagine, phenylalanine, serine and valine. The homochiral addition was always the more efficient reaction; the enantiospecificity was large in some cases but very small in others. In every case Ala(sub 3)Glu(sub l0) was elongated more efficiently than Glu(sub 10).
Wen, Ke↗
Haughton-Mars Project Expedition 2005: Interplanetary Supply Chain Management & Logistics Architectures
The 2005 expedition to the Haughton-Mars Project (HMP) research station on Devon Island was part of a NASA-funded project on Space Logistics. A team of nine researchers from MIT went to the Canadian Arctic to participate in the annual HMP field campaign from July 8 to August 12, 2005. We investigated the applicability of the HMP research station as an analogue for planetary macro- and micro-logistics to the Moon and Mars, and began collecting data for modeling purposes. We also tested new technologies and procedures to enhance the ability of humans and robots to jointly explore remote environments. The expedition had four main objectives. We briefly summarize our key findings in each of these areas.
deWeck, Olivier↗