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  • Spacecraft Propulsion and Power  (11)
  • Lunar and Planetary Science and Exploration  (3)
  • Guanylate Cyclase/antagonists & inhibitors/metabolism  (1)
  • ENVIRONMENT POLLUTION
  • 2005-2009  (15)
  • 1
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    Two chemoreceptors mediate developmental effects of dauer pheromone in C. elegans (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-10-03
    Description: Intraspecific chemical communication is mediated by signals called pheromones. Caenorhabditis elegans secretes a mixture of small molecules (collectively termed dauer pheromone) that regulates entry into the alternate dauer larval stage and also modulates adult behavior via as yet unknown receptors. Here, we identify two heterotrimeric GTP-binding protein (G protein)-coupled receptors (GPCRs) that mediate dauer formation in response to a subset of dauer pheromone components. The SRBC-64 and SRBC-66 GPCRs are members of the large Caenorhabditis-specific SRBC subfamily and are expressed in the ASK chemosensory neurons, which are required for pheromone-induced dauer formation. Expression of both, but not each receptor alone, confers pheromone-mediated effects on heterologous cells. Identification of dauer pheromone receptors will allow a better understanding of the signaling cascades that transduce the context-dependent effects of ecologically important chemical signals.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4448937/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4448937/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kim, Kyuhyung -- Sato, Koji -- Shibuya, Mayumi -- Zeiger, Danna M -- Butcher, Rebecca A -- Ragains, Justin R -- Clardy, Jon -- Touhara, Kazushige -- Sengupta, Piali -- F32 GM077943/GM/NIGMS NIH HHS/ -- P30 NS045713/NS/NINDS NIH HHS/ -- P30 NS45713/NS/NINDS NIH HHS/ -- R01 CA024487/CA/NCI NIH HHS/ -- R01 CA24487/CA/NCI NIH HHS/ -- R01 GM056223/GM/NIGMS NIH HHS/ -- R01 GM56223/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2009 Nov 13;326(5955):994-8. doi: 10.1126/science.1176331. Epub 2009 Oct 1.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology and National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19797623" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Caenorhabditis elegans/genetics/*growth & development/*physiology ; Caenorhabditis elegans Proteins/genetics/physiology ; Calcium/metabolism ; Cell Line ; Chemoreceptor Cells/metabolism ; Cyclic AMP/metabolism ; Cyclic GMP/metabolism ; GTP-Binding Protein alpha Subunits, Gi-Go/physiology ; Gene Expression Regulation, Developmental ; Genes, Helminth ; Guanylate Cyclase/antagonists & inhibitors/metabolism ; Hexoses/chemistry/physiology ; Humans ; Mutation ; Pheromones/*physiology ; Receptors, G-Protein-Coupled ; Reproduction ; Signal Transduction ; Transfection
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 2
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    Recent Advances in Nuclear Powered Electric Propulsion for Space Exploration (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: Nuclear and radioisotope powered electric thrusters are being developed as primary in-space propulsion systems for potential future robotic and piloted space missions. Possible applications for high power nuclear electric propulsion include orbit raising and maneuvering of large space platforms, lunar and Mars cargo transport, asteroid rendezvous and sample return, and robotic and piloted planetary missions, while lower power radioisotope electric propulsion could significantly enhance or enable some future robotic deep space science missions. This paper provides an overview of recent U.S. high power electric thruster research programs, describing the operating principles, challenges, and status of each technology. Mission analysis is presented that compares the benefits and performance of each thruster type for high priority NASA missions. The status of space nuclear power systems for high power electric propulsion is presented. The paper concludes with a discussion of power and thruster development strategies for future radioisotope electric propulsion systems,
    Keywords: Spacecraft Propulsion and Power
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Overview of the Mars Science Laboratory Parachute Decelerator Subsystem (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In 2010 the Mars Science Laboratory (MSL) mission will deliver NASA's largest and most capable rover to the surface of Mars. MSL will explore previously unattainable landing sites due to the implementation of a high precision Entry, Descent, and Landing (EDL) system. The parachute decelerator subsystem (PDS) is an integral prat of the EDL system, providing a mass and volume efficient some of aerodynamic drag to decelerate the entry vehicle from Mach 2 to subsonic speeds prior to final propulsive descent to the sutface. The PDS for MSL is a mortar deployed 19.7m Viking type Disk-Gap-Band (DGB) parachute; chosen to meet the EDL timeline requirements and to utilize the heritage parachute systems from Viking, Mars Pathfinder, Mars Exploration Rover, and Phoenix NASA Mars Lander Programs. The preliminary design of the parachute soft goods including materials selection, stress analysis, fabrication approach, and development testing will be discussed. The preliminary design of mortar deployment system including mortar system sizing and performance predictions, gas generator design, and development mortar testing will also be presented.
    Keywords: Lunar and Planetary Science and Exploration
    Type: IEEE Aerospace Conference; Mar 03, 2007 - Mar 10, 2007; Big Sky, MT; United States
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    NASA TECHNICAL REPORTS
  • 4
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    Application of Stereo PIV on a Supersonic Parachute Model (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Mars Science Laboratory (MSL) is the next step in NASA's Mars Exploration Program, currently scheduled for 2011. The spacecraft's descent into the Martian atmosphere will be slowed from Mach 2 to subsonic speeds via a large parachute system with final landing under propulsive control. A Disk-Band-Gap (DBG) parachute will be used on MSL similar to the designs that have been used on previous missions, however; the DBG parachute used by MSL will be larger (21.5 m) than in any of the previous missions due to the weight of the payload and landing site requirements. The MSL parachute will also deploy at higher Mach number (M 2) than previous parachutes, which can lead to instabilities in canopy performance. Both the increased size of the DBG above previous demonstrated configurations and deployment at higher Mach numbers add uncertainty to the deployment, structural integrity and performance of the parachute. In order to verify the performance of the DBG on MSL, experimental testing, including acquisition of Stereo Particle Imaging Velocimetry (PIV) measurements were required for validating CFD predictions of the parachute performance. A rigid model of the DBG parachute was tested in the 10x10 foot wind tunnel at GRC. Prior to the MSL tests, a PIV system had never been used in the 10x10 wind tunnel. In this paper we discuss some of the technical challenges overcome in implementing a Stereo PIV system with a 750x400 mm field-of-view in the 10x10 wind tunnel facility and results from the MSL hardshell canopy tests.
    Keywords: Lunar and Planetary Science and Exploration
    Type: AIAA Paper 2007- 0070 , E-17866 , AIAA 47th Aerospace Sciences Meeting; Jan 05, 2009 - Jan 08, 2009; Orlando, FL; United States
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    NASA TECHNICAL REPORTS
  • 5
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    Sensitivity Testing of the NSTAR Ion Thruster (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: During the Extended Life Test of the DS1 flight spare ion thruster, the engine was subjected to sensitvity testing in order to characterize the macroscopic dependence of discharge chamber sensitivity to a +\-3% vatiation in main flow, cathode flow and beam current, and to +\5% variation in beam and accelerator voltage, was determined for the minimum- (THO), half- (TH8) and full power (TH15) throttle levels. For each power level investigared, 16 high/low operating conditions were chosen to vary the flows, beam current, and grid voltages in in a matrix that mapped out the entire parameter space. The matrix of data generated was used to determine the partial derivative or senitivity of the dependent parameters--discharge voltage, discharge current, discharge loss, double-to-single-ion current ratio, and neutralizer-keeper voltage--to the variation in the independent parameters--main flow, cathode flow, beam current, and beam voltage. The sensititivities of each dependent parameter with respect to each independent parameter were determined using a least-square fit routine. Variation in these sensitivities with thruster runtime was recorded over the duration of the ELT, to detemine if discharge performance changed with thruster wear. Several key findings have been ascertained from the sensitivity testing. Discharge operation is most sensitve to changes in cathode flow and to a lesser degree main flow. The data also confirms that for the NSTAR configuration plasma production is limited by primary electron input due to the fixed neutral population. Key sensitivities along with their change with thruster wear (operating time) will be presented. In addition double ion content measurements with an ExB probe will also be presented to illustrate beam ion production and content sensitivity to the discharge chamber operating parameteres.
    Keywords: Spacecraft Propulsion and Power
    Type: IEPC-2007-010 , International Electric Propulsion Conference; Sep 17, 2007 - Sep 20, 2007; Florence; Italy
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    NASA TECHNICAL REPORTS
  • 6
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    Vibration test and analysis of the NEXIS ion engine (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Interest in science objectives at the outer planets, specifically at the moons of Jupiter, has spurred the development of high-power electric propulsion systems under the Prometheus program.
    Keywords: Spacecraft Propulsion and Power
    Type: AIAA Paper 2005-4412 , 41st AIAA Joint Propulsion Conference; Jul 10, 2005 - Jul 13, 2005; Tuscon, AZ; United States
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    NASA TECHNICAL REPORTS
  • 7
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    Destructive physical analysis of hollow cathodes from the Deep Space 1 Flight spare ion engine 30,000 hr life test (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Destructive physical analysis of the discharge and neutralizer hollow cathode assemblies from the Deep Space 1 Flight Spare 30,000 Hr life test was performed to characterize physical and chemical evidence of operationally induced effects after 30,372 hours of operation with beam extraction. Post-test inspection of the discharge-cathode assembly was subdivided into detailed analyses at the subcomponent level. Detailed materials analysis and optical inspection of the insert, orifice plate, cathode tube, heater, keeper assembly, insulator, and low-voltage propellant isolator were performed. Energy dispersive X-ray (EDX) and scanning electron microscopy (SEW analyses were used to determine the extent and composition of regions of net deposition and erosion of both the discharge and neutralizer inserts. A comparative approach with an un-operated 4:1:1 insert was used to determine the extent of impregnate material depletion as a function of depth from the ID surface and axial position from the orifice plate. Analysis results are compared and contrasted with those obtained from similar analyses on components from shorter term tests, and provide insight regarding the prospect for successful longer-term operation consistent with SOA ion engine program life objectives at NASA.
    Keywords: Spacecraft Propulsion and Power
    Type: 29th International Electric Propulsion Conference, Princeton University; Oct 31, 2005 - Nov 04, 2005; NJ; United States
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    NASA TECHNICAL REPORTS
  • 8
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    Experimental and analytical investigation of a modified ring cusp NSTAR engine (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A series of experimental measurements on a modified laboratory NSTAR engine were used to validate a zero dimensional analytical discharge performance model of a ring cusp ion thruster. The model predicts the discharge performance of a ring cusp NSTAR thruster as a function the magnetic field configuration, thruster geometry, and throttle level. Analytical formalisms for electron and ion confinement are used to predict the ionization efficiency for a given thruster design. Explicit determination of discharge loss and volume averaged plasma parameters are also obtained. The model was used to predict the performance of the nominal and modified three and four ring cusp 30-cm ion thruster configurations operating at the full power (2.3 kW) NSTAR throttle level. Experimental measurements of the modified engine configuration discharge loss compare well with the predicted value for propellant utilizations from 80 to 95%. The theory, as validated by experiment, indicates that increasing the magnetic strength of the minimum closed reduces maxwellian electron diffusion and electrostatically confines the ion population and subsequent loss to the anode wall. The theory also indicates that increasing the cusp strength and minimizing the cusp area improves primary electron confinement increasing the probability of an ionization collision prior to loss at the cusp.
    Keywords: Spacecraft Propulsion and Power
    Type: 29th International Electric Propulsion Conference, Princeton University; Oct 31, 2005 - Nov 04, 2005; Princeton, NJ; United States
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    NASA TECHNICAL REPORTS
  • 9
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    Results of a 2000 hour wear test of the NEXIS ion engine (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Nuclear Electric Xenon Ion System (NEXIS) ion thruster was developed for potential outer planet robotic missions under NASA's Prometheus program. This engine was designed to operate at power levels ranging from 16 to over 20 kWe at specific impulses of 6000 to 7500 s for burn times of up to 10 years, satisfying the requirements of nuclear electric propulsion systems such as that on the proposed Prometheus 1 mission to explore the icy moons of Jupiter. State-of-the-art performance and life assessment tools were used to design the thruster. Following the successful performance validation of a Laboratory Model thruster, Development Model hardware was fabricated and subjected to vibration and wear testing. The results of a 2000-hour wear test are reported herein. Thruster performance achieved the target requirements and was steady for the duration of the test. Ion optics performance was similarly stable. Discharge loss increases of 6 eV/ion were observed in the first 500 hours of the test and were attributed to primary electron energy decreases due to cathode insert conditioning. Relatively high recycle rates were observed and were identified to be high-voltage-to-ground arcs in the back of the thruster caused by wire insulation outgassing and electron penetration through the plasma screen. Field emission of electrons between the accelerator and screen grids was observed and attributed to evolution of field emitter sites at accelerator grid aperture edges caused by ion bombardment. Preliminary modeling and analysis indicates that the NEXIS engine can meet mission performance requirements over the required lifetime. Finally, successful validation of the NEXIS design methodology, design tools, and technologies with the results of the wear test and companion performance and vibration tests presents significant applicability of the NEXIS development effort to missions of near-term as well as long-term interest for NASA.
    Keywords: Spacecraft Propulsion and Power
    Type: 29th International Electric Propulsion Conference, Princeton University; Oct 31, 2005 - Nov 04, 2005; Princeton, NJ; United States
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    NASA TECHNICAL REPORTS
  • 10
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    The VHITAL program to demonstrate the performance and lifetime of a bismuth-fueled very high isp hall thruster (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In the Very High Isp Thruster with Anode Layer (VHITAL) Program the performance, plume and lifetime capability of the radiatively-cooled two stage, bismuth-fueled VHITAL-160 will be characterized in the US and Russia.
    Keywords: Spacecraft Propulsion and Power
    Type: AIAA Joint Propulsion Conference 2005; Jul 11, 2005 - Jul 14, 2005; Tucson, AZ; United States
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