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  • 1
    Publikationsdatum: 2019-07-13
    Beschreibung: The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 +/- 0.2) 10(exp 6) cu km of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC-E-DAA-TN40014 , Science (ISSN 0036-8075) (e-ISSN 1095-9203); 354; 6311; 438-441
    Format: text
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  • 2
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Die Rolle von Metalloenzymen in wichtigen biologischen Prozessen hat in den letzten Jahrzehnten zunehmend Beachtung gefunden. Von den vielen chemischen Reaktionen, die durch Enzyme gesteuert werden, sind nur wenige eine so große Herausforderung wie die Mehrelektronen-Redoxreaktionen. In neueren Untersuchungen ist es gelungen, einige strukturelle und mechanistische Merkmale derartig redoxaktiver Metalloenzyme aufzuklären, doch im Hinblick auf den Mechanismus der Substratumwandlung tappt man weiterhin im Dunkeln. Wegen der Komplexität von Metalloenzymsystemen verwendet man einfachere Modellsysteme, um strukturelle oder funktionelle Merkmale des Enzyms nachzuahmen. In Mehrelektronen-Redoxenzymen sind vermutlich mehrere Metallatome an der Substratbindung und den anschließenden Redoxreaktionen beteiligt. Brauchbare Imitatoren der Funktionen von Mehrelektronen-Redoxenzymen benötigen deshalb vermutlich ebenfalls zwei oder mehr Metallzentren für eine ausreichende Wirksamkeit. Diese Metallzentren übernehmen folgende Funktionen: 1) sie verbessern die Affinität des Substrats zum Katalysator, 2) sie erhöhen die Geschwindigkeit des Elektronentransfers auf das gebundene Substrat, 3) sie steigern die Reaktivität des gebundenen Substrats und 4) sie verhindern störende Nebenreaktionen. Eine Bewertung dieser Faktoren hinsichtlich ihrer Wichtigkeit könnte für die Entwicklung solcher Katalysatoren hilfreich sein. Cofaciale Metallodiporphyrine sind ideale Dimetallmodellkomplexe, weil bei ihnen die geometrischen und elektronischen Eigenschaften des synthetischen Reaktionszentrums gezielt beeinflußt werden können. Die anhand von Modellstudien gewonnenen Erkenntnisse können dazu beitragen, die Wirkmechanismen von Metalloenzymen aufzuklären und neue homogene Katalysatoren für Mehrelektronen-Redoxreaktionen zu entwickeln.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 3
    ISSN: 0570-0833
    Schlagwort(e): Metalloproteins ; Homogeneous catalysis ; Redox chemistry ; Porphyrin complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The role of metalloenzymes in important biological transformations has attracted increasing attention over the past several decades. Of the many chemical transformations mediated by enzymes, few are as challenging as multielectron redox reactions. Recent studies have revealed a partial structural and mechanistic description of these redox-active metalloenzymes, but there is much still to be learned regarding the mechanisms of substrate transformation. Due to the complexity of the metalloenzyme systems, simplified model systems are employed to mimic structural or functional features of the enzyme. In multielectron redox enzymes, several metals are probably in-volved in both substrate binding and the subsequent redox reactions. Thus, functional mimics of multielectron redox enzymes might also need two or more metal centers to be efficacious. The roles of multiple metal centers are to (1) increase the substrate's affinity for the catalyst, (2) increase the rate of electron transfer to the bound substrate, (3) increase the reactivity of the bound substrate, and (4) inhibit deleterious side reactions. Deter-mining the importance of each factor may help in the development of these catalysts. Cofacial metallodiporphyrins, because of the control they provide over the geometric and electronic properties of the synthetic reaction center, are ideal bimetallic model complexes. The knowledge gained from model studies will help in understanding the mechanisms of metalloenzymes and can be used to design new homogeneous catalysts to effect multielectron transformations.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 4
    Publikationsdatum: 2017-10-02
    Beschreibung: Topography observations of Mars being acquired by MOLA are providing data on surface features, polar caps, and clouds, and on possible future landing sites.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: Lunar and Planetary Science XXXI; LPI-Contrib-1000
    Format: text
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  • 5
    Publikationsdatum: 2019-07-13
    Beschreibung: The Gravity Recovery and Interior Laboratory (GRAIL) mission has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k2. Lunar structure includes a thin crust, a deep mantle, a fluid core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future GRAIL will search for evidence of tidal dissipation and a solid inner core.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC-E-DAA-TN7319 , 44th Lunar and Planetary Science Conference; Mar 18, 2013 - Mar 22, 2013; The Woodlands, TX; United States
    Format: application/pdf
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  • 6
    Publikationsdatum: 2019-07-13
    Beschreibung: MESSENGER observations from orbit around Mercury have revealed that a large contiguous area of smooth plains occupies much of the high northern latitudes and covers an area in excess of approx.6% of the surface of the planet [1] (Fig. 1). Smooth surface morphology, embayment relationships, color data, candidate flow fronts, and a population of partly to wholly buried craters provide evidence for the volcanic origin of these plains and their emplacement in a flood lava mode to depths at least locally in excess of 1 km. The age of these plains is similar to that of plains associated with and postdating the Caloris impact basin, confirming that volcanism was a globally extensive process in the post-heavy bombardment history of Mercury [1]. No specific effusive vent structures, constructional volcanic edifices, or lava distributary features (leveed flow fronts or sinuous rilles) have been identified in the contiguous plains, although vent structures and evidence of high-effusion-rate flood eruptions are seen in adjacent areas [1]. Subsequent to the identification and mapping of the extensive north polar smooth plains, data from the Mercury Laser Altimeter (MLA) on MESSENGER revealed the presence of a broad topographic rise in the northern smooth plains that is ~1,000 km across and rises more than 1.5 km above the surrounding smooth plains [2] (Fig. 2). The purpose of this contribution is to characterize the northern plains rise and to outline a range of hypotheses for its origin.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC.CP.00112.2012 , 43rd Lunar and Planetary Science Conference (2012); Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
    Format: application/pdf
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  • 7
    Publikationsdatum: 2019-07-19
    Beschreibung: The Lunar Reconnaissance Orbiter spacecraft (LRO), launched on June 18, 2009, began with the goal of seeking safe landing sites for future robotic missions or the return of humans to the Moon as part of NASA's Exploration Systems Mission Directorate (ESMD). In addition, LRO's objectives included the search for surface resources and to investigate the Lunar radiation environment. After spacecraft commissioning, the ESMD phase of the mission began on September 15, 2009 and completed on September 15, 2010 when operational responsibility for LRO was transferred to NASA's Science Mission Directorate (SMD). The SMD mission was scheduled for 2 years and completed in September, 2012. The LRO mission has been extended for two years under SMD. The extended mission focuses on a new set of goals related to understanding the geologic history of the Moon, its current state, and what it can tell us about the evolution Of the Solar System. Here we will review the major results from the LRO mission for both exploration and science and discuss plans and objectives going forward including plans for the extended science phase out to 2014. Results from the LRO mission include but are not limited to the development of comprehensive high resolution maps and digital terrain models of the lunar surface; discoveries on the nature of hydrogen distribution, and by extension water, at the lunar poles; measurement of the day and night time temperature of the lunar surface including temperature down below 30 K in permanently shadowed regions (PSRs); direct measurement of Hg, H2, and CO deposits in the PSRs, evidence for recent tectonic activity on the Moon, and high resolution maps of the illumination conditions as the poles. The objectives for the second and extended science phases of the mission under SMD include: 1) understanding the bombardment history of the Moon, 2) interpreting Lunar geologic processes, 3) mapping the global Lunar regolith, 4) identifying volatiles on the Moon, and 5) measuring the Lunar atmosphere and radiation environment.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: GSFC.ABS.6464.2012 , Lunar Science Forum; Jul 16, 2012 - Jul 20, 2012; Mountain View, CA; United States
    Format: application/pdf
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  • 8
    Publikationsdatum: 2019-07-17
    Beschreibung: The first MOLA data were acquired in Sept. 1997 shortly after the arrival of Mars Global Surveyor (MGS) at Mars and before the start of aerobraking. Subsequently, data were obtained during several months in the spring and summer of 1998. All these data were obtained over the northern hemisphere. At the beginning of March 1999 the mapping phase of the MGS mission began in the designed 400 km near circular, near polar orbit and MOLA began collecting continuous global data. By the end of 1999 MOLA had acquired over 250 million altimeter measurements of the radius of the planet at accuracies of the order of a few meters radially and about 100 meters horizontally. These observations revealed the detailed structure of the Martian surface, the form of the polar caps, as well as the shape of the planet. The early results provided a unique view of the north polar cap and subsequently of the south polar cap from which an estimate of the total volume of present-day surface water ice of 3.2 to 4.7 million cubic km was obtained. To obtain full coverage of the polar caps it was necessary for MOLA to be pointed off nadir approximately 20 degrees and on several occasions MGS has performed a roll maneuver to make these observations. It is hoped that these off-nadir observations of the central region of the cap (MGS only reaches to latitudes plus or minus 86.5) will assist in the detection of the seasonal deposition of CO2 since it is believed that these high latitudes regions may be the accumulation zone.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: 31st Lunar and Planetary Science Conference; Mar 13, 2000 - Mar 17, 2000; Houston, TX; United States
    Format: text
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  • 9
    Publikationsdatum: 2019-07-13
    Beschreibung: No abstract available
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: KSC-E-DAA-TN57365 , Planetary and Terrestrial Mining Sciences Symposium; Jun 12, 2018 - Jun 15, 2018; Golden, CO; United States
    Format: application/pdf
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  • 10
    Publikationsdatum: 2019-07-12
    Beschreibung: From May of 1973 to February of 1974, the National Aeronautics and Space Administration conducted a series of three manned missions to the Skylab space station, a voluminous vehicle largely descendant of Apollo hardware, and America s first space station. The crewmembers of these three manned missions spent record breaking durations of time in microgravity (28 days, 59 days and 84 days, respectively) and gave the U.S. space program its first experiences with long-duration space flight. The program overcame a number of obstacles (including a significant crippling of the Skylab vehicle) to conduct a lauded scientific program that encompassed life sciences, astronomy, solar physics, materials sciences and Earth observation. Skylab has more to offer than the results of its scientific efforts. The operations conducted by the Skylab crews and ground personnel represent a rich legacy of operational experience. As we plan for our return to the moon and the subsequent manned exploration of Mars, it is essential to utilize the experiences and insights of those involved in previous programs. Skylab and SMEAT (Skylab Medical Experiments Altitude Test) personnel have unique insight into operations being planned for the Constellation Program, such as umbilical extra-vehicular activity and water landing/recovery of long-duration crewmembers. Skylab was also well known for its habitability and extensive medical suite; topics which deserve further reflection as we prepare for lunar habitation and missions beyond Earth s immediate sphere of influence. The Skylab Medical Operations Summit was held in January 2008. Crewmembers and medical personnel from the Skylab missions and SMEAT were invited to participate in a two day summit with representatives from the Constellation Program medical operations community. The purpose of the summit was to discuss issues pertinent to future Constellation operations. The purpose of this document is to formally present the recommendations of the Skylab and SMEAT participants.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: JSC-CN-18276
    Format: application/pdf
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