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  • 1
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    Structure of a cofactor-deficient nitrogenase MoFe protein (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-04-16
    Description: One of the most complex biosynthetic processes in metallobiochemistry is the assembly of nitrogenase, the key enzyme in biological nitrogen fixation. We describe here the crystal structure of an iron-molybdenum cofactor-deficient form of the nitrogenase MoFe protein, into which the cofactor is inserted in the final step of MoFe protein assembly. The MoFe protein folds as a heterotetramer containing two copies each of the homologous alpha and beta subunits. In this structure, one of the three alpha subunit domains exhibits a substantially changed conformation, whereas the rest of the protein remains essentially unchanged. A predominantly positively charged funnel is revealed; this funnel is of sufficient size to accommodate insertion of the negatively charged cofactor.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schmid, Benedikt -- Ribbe, Markus W -- Einsle, Oliver -- Yoshida, Mika -- Thomas, Leonard M -- Dean, Dennis R -- Rees, Douglas C -- Burgess, Barbara K -- New York, N.Y. -- Science. 2002 Apr 12;296(5566):352-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Chemistry and Chemical Engineering, Mail Code 147-75CH, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11951047" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Azotobacter vinelandii/*enzymology ; Binding Sites ; Crystallization ; Crystallography, X-Ray ; Dimerization ; Hydrogen Bonding ; Models, Molecular ; Molecular Sequence Data ; Molybdoferredoxin/*chemistry/genetics/*metabolism ; Protein Conformation ; Protein Folding ; Protein Structure, Quaternary ; Protein Structure, Secondary ; Protein Structure, Tertiary ; Static Electricity ; Surface Properties
    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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  • 2
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    Nucleotide-iron-sulfur cluster signal transduction in the nitrogenase iron-protein: the role of Asp125 (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-11-06
    Description: Electron transfer in nitrogenase involves a gating process initiated by MgATP (magnesium adenosine triphosphate) binding to Fe-protein. The redox site, an 4Fe:4S cluster, is structurally separated from the MgATP binding site. For MgATP hydrolysis to be coupled to electron transfer, a signal transduction mechanism is proposed that is similar to that in guanosine triphosphatase proteins. Based on the three-dimensional structure of Fe-protein, Asp125 is likely to be part of a putative transduction path. Altered Fe-protein with Glu replacing Asp has been prepared and retains the ability for the initial nucleotide-dependent conformational change. However, either MgADP or MgATP can induce the shift and Mg binding to the nucleotide is no longer essential.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wolle, D -- Dean, D R -- Howard, J B -- New York, N.Y. -- Science. 1992 Nov 6;258(5084):992-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry, University of Minnesota, Minneapolis 55455.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1359643" target="_blank"〉PubMed〈/a〉
    Keywords: Adenosine Diphosphate/metabolism ; Adenosine Triphosphate/*metabolism ; Aspartic Acid/*metabolism ; Azotobacter vinelandii/enzymology ; Binding Sites ; Crystallization ; Electron Transport ; Glutamates ; Glutamic Acid ; Iron-Sulfur Proteins/*metabolism ; Molecular Structure ; Mutagenesis, Site-Directed ; Nitrogenase/chemistry/genetics/*metabolism ; Protein Conformation ; Signal Transduction/*physiology
    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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  • 3
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    Supercooled Large Droplet Icing Flight Research Program (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: During the past three winters, the NASA Glenn Research Center at Lewis Field conducted icing research flights throughout the Great Lakes region to measure the characteristics of a severe icing condition having Supercooled Large Droplets (SLD). SLD was implicated in the 1994 crash of the ATR-72 commuter aircraft. This accident focused attention on the safety hazard associated with SLD, and it led the Federal Aviation Administration (FAA) to identify the need for a better understanding of the atmospheric characteristics of this icing condition. In response to this need, Glenn developed a cooperative icing flight research program with the FAA, the National Center for Atmospheric Research, and the Atmospheric Environment Service of Canada. The primary objectives were to (1) characterize the SLD icing condition in terms of important icing-related parameters (such as cloud droplet size, cloud water content, and temperature), (2) develop and refine SLD icing weather forecast products, and (3) document and measure the effects of SLD ice accretions on aircraft performance.
    Keywords: Air Transportation and Safety
    Type: Research and Technology 1999; NASA/TM-2000-209639
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  • 4
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    Update on SLD Engineering Tools Development (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The airworthiness authorities (FAA, JAA, Transport Canada) will be releasing a draft rule in the 2006 timeframe concerning the operation of aircraft in a Supercooled Large Droplet (SLD) environment aloft. The draft rule will require aircraft manufacturers to demonstrate that their aircraft can operate safely in an SLD environment for a period of time to facilitate a safe exit from the condition. It is anticipated that aircraft manufacturers will require a capability to demonstrate compliance with this rule via experimental means (icing tunnels or tankers) and by analytical means (ice prediction codes). Since existing icing research facilities and analytical codes were not developed to account for SLD conditions, current engineering tools are not adequate to support compliance activities in SLD conditions. Therefore, existing capabilities need to be augmented to include SLD conditions. In response to this need, NASA and its partners conceived a strategy or Roadmap for developing experimental and analytical SLD simulation tools. Following review and refinement by the airworthiness authorities and other international research partners, this technical strategy has been crystallized into a project plan to guide the SLD Engineering Tool Development effort. This paper will provide a brief overview of the latest version of the project plan and technical rationale, and provide a status of selected SLD Engineering Tool Development research tasks which are currently underway.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2004-213072 , E-14548 , Rept-2003-01-2127 , FAA In-Flight Icing/Ground De-Icing International Conference; Jun 16, 2003 - Jun 20, 2003; Chicago, IL; United States
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  • 5
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    Validation of NASA Thermal Ice Protection Computer Codes (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An experimental program was generated by the Icing Technology Branch at NASA Glenn Research Center to validate two ice protection simulation codes: (1) LEWICE/Thermal for transient electrothermal de-icing and anti-icing simulations, and (2) ANTICE for steady state hot gas and electrothermal anti-icing simulations. An electrothermal ice protection system was designed and constructed integral to a 36 inch chord NACA0012 airfoil. The model was fully instrumented with thermo-couples, RTD'S, and heat flux gages. Tests were conducted at several icing environmental conditions during a two week period at the NASA Glenn Icing Research Tunnel. Experimental results of running-wet and evaporative cases were compared to the ANTICE computer code predictions and are presented in this paper.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2001-210907/PT3 , E-12786/PT3 , NAS 1.15:210907/PT3 , AIAA Paper 97-0051 , 35th Aerospace Sciences Meeting and Exhibit; Jan 06, 1997 - Jan 07, 1997; Reno, NV; United States
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  • 6
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    A Study of Large Droplet Ice Accretions in the NASA-Lewis IRT at Near-Freezing Conditions (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This report documents the results of an experimental study on large droplet ice accretions which was conducted in the NASA-Lewis Icing Research Tunnel (IRT) with a full-scale 77.25 inch chord Twin-Otter wing section. This study was intended to: (1) document the existing capability of the IRT to produce a large droplet icing cloud, and (2) study the effect of various parameters on large droplet ice accretions. Results are presented from a study of the IRT's capability to produce large droplets with MVD of 99 and 160 microns. The effect of the initial water droplet temperature on the resultant ice accretion was studied for different initial spray bar air and water temperatures. The initial spray bar water temperature was found to have no discernible effect upon the large droplet ice accretions. Also, analytical and experimental results suggest that the water droplet temperature is very nearly the same as the tunnel ambient temperature, thus providing a realistic simulation of the large droplet natural icing condition. The effect of temperature, droplet size, airspeed, angle-of attack, flap setting and de-icer boot cycling time on ice accretion was studied, and will be discussed in this report. It was found that, in almost all of the cases studied, an ice ridge formed immediately aft of the active portion of the de-icer boot. This ridge was irregular in shape, varied in location, and was in some cases discontinuous due to aerodynamic shedding.
    Keywords: Air Transportation and Safety
    Type: NASA-TM-107142/REV1 , E-10072-1 , NAS 1.15:107142 , ARL-MR-294 , AIAA Paper 96-0934 , 34th Aerospace Sciences Meeting and Exhibit; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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  • 7
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    Freezing Rain as an In-Flight Icing Hazard (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Exposure to supercooled large drops (SLD-subfreezing water droplets with diameters greater than approx. 50 microns) can pose a significant threat to the safety of some aircraft. Although SLD includes both freezing drizzle (FZDZ) and freezing rain (FZRA), much of the SLD research and development of operational SLD forecast tools has focused on FZDZ and ignored FZRA, regarding is as less of a hazard to aviation. This paper provides a counterpoint case study that demonstrates FZRA as a significant in-flight icing hazard. The case study is based on flight and meteorological data from a joint NASA/FAA/NCAR SLD icing research project collected on February 4, 1998. The NASA Twin Otter Icing Research Aircraft experienced a prolonged exposure to "classical" FZRA that formed extensive ice formations including ridges and nodules on the wing and tail, and resulted in a substantial performance penalty. Although the case study provides only a singular FZRA event with one aircraft type, it is clear that classical FZRA can pose a significant in-flight icing hazard, and should not be ignored when considering SLD issues.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2000-210058 , E-12260 , NAS 1.15:210058 , Aviation, Range and Aerospace Meteorology; Jan 10, 1999 - Jan 15, 1999; Dallas, TX; United States
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  • 8
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    Overview of High Speed Close-Up Imaging in an Icing Environment (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The Icing Branch and Imaging Technology Center at NASA Glenn Research Center have recently been involved in several projects where high speed close-up imaging was used to investigate water droplet impact/splash, and also ice particle impact/bounce in an icing wind tunnel. The combination of close-up and high speed imaging capabilities were required because the particles being studied were relatively small (d 〈 1 mm in diameter), and the impact process occurred in a very short time period (t(sub impact) 〈〈 1 sec). High speed close-up imaging was utilized to study the dynamics of droplet impact and splash in simulated Supercooled Large Droplet (SLD) icing conditions. The objective of this test was to evaluate the capability of a ultra high speed camera system to acquire quantitative information about the impact process (e.g., droplet size, velocity). Imaging data were obtained in an icing wind tunnel for spray cloud MVD 〉 50 m. High speed close-up imaging was also utilized to characterize the impact of ice particles on an airfoil with a thermally protected leading edge. The objective of this investigation was to determine whether ice particles tend to "stick" or "bounce" after impact. Imaging data were obtained for cases where the airfoil surface was heated and unheated. Based on the results from this test, follow on tests were conducted to investigate ice particle impact on the sensing elements of water content measurement devices. This paper will describe the use of the imaging systems to support these experimental investigations, present some representative results, and summarize what was learned about the use of these systems in an icing environment.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2004-212925 , AIAA Paper 2004-0407 , E-14357
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  • 9
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    Additional Investigations of Ice Shape Sensitivity to Parameter Variations (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A second parameter sensitivity study was conducted at the NASA Glenn Research Center's Icing Research Tunnel (IRT) using a 36 in. chord (0.91 m) NACA-0012 airfoil. The objective of this work was to further investigate the feasibility of using ice shape feature changes to define requirements for the simulation and measurement of SLD and appendix C icing conditions. A previous study concluded that it was feasible to use changes in ice shape features (e.g., ice horn angle, ice horn thickness, and ice shape mass) to detect relatively small variations in icing spray condition parameters (LWC, MVD, and temperature). The subject of this current investigation extends the scope of this previous work, by also examining the effect of icing tunnel spray-bar parameter variations (water pressure, air pressure) on ice shape feature changes. The approach was to vary spray-bar water pressure and air pressure, and then evaluate the effects of these parameter changes on the resulting ice shapes. This paper will provide a description of the experimental method, present selected experimental results, and conclude with an evaluation of these results.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2006-214227 , E-15474 , AIAA Paper 2006-0469 , 44th Aerospace Sciences Meeting and Exhibit; Jan 09, 2006 - Jan 12, 2006; Reno, NV; United States
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  • 10
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    Preliminary Investigation of Ice Shape Sensitivity to Parameter Variations (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A parameter sensitivity study was conducted at the NASA Glenn Research Center's Icing Research Tunnel (IRT) using a 36 in. chord (0.91 m) NACA-0012 airfoil. The objective of this preliminary work was to investigate the feasibility of using ice shape feature changes to define requirements for the simulation and measurement of SLD icing conditions. It was desired to identify the minimum change (threshold) in a parameter value, which yielded an observable change in the ice shape. Liquid Water Content (LWC), drop size distribution (MVD), and tunnel static temperature were varied about a nominal value, and the effects of these parameter changes on the resulting ice shapes were documented. The resulting differences in ice shapes were compared on the basis of qualitative and quantitative criteria (e.g., mass, ice horn thickness, ice horn angle, icing limits, and iced area). This paper will provide a description of the experimental method, present selected experimental results, and conclude with an evaluation of these results, followed by a discussion of recommendations for future research.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2005-213562 , E-15008 , AIAA Paper 2005-0073 , 43rd Aerospace Sciences Meeting and Exhibit; Jan 10, 2005 - Jan 13, 2005; Reno, NV; United States
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