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  • Lunar and Planetary Science and Exploration  (365)
  • Models, Molecular  (160)
  • Astrophysics  (133)
  • 2005-2009  (658)
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  • 1
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    Detection of GRB 060927 at zeta = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: We report on follow-up observations of the gamma-ray burst GRB 060927 using the robotic ROTSE-IIIa telescope and a suite of larger aperture groundbased telescopes. An optical afterglow was detected 20 s after the burst, the earliest rest-frame detection of optical emission from any GRB. Spectroscopy performed with the VLT about 13 hours after the trigger shows a continuum break at lambda approx. equals 8070 A, produced by neutral hydrogen absorption at zeta = 5.6. We also detect an absorption line at 8158 A which we interpret as Si II lambda 1260 at zeta = 5.467. Hence, GRB 060927 is the second most distant GRB with a spectroscopically measured redshift. The shape of the red wing of the spectral break can be fitted by a damped Ly(alpha) profile with a column density with log(N(sub HI)/sq cm) = 22.50 +/- 0.15. We discuss the implications of this work for the use of GRBs as probes of the end of the dark ages and draw three main conclusions: i) GRB afterglows originating from zeta greater than or approx. equal to 6 should be relatively easy to detect from the ground, but rapid near-infrared monitoring is necessary to ensure that they are found; ii) The presence of large H I column densities in some GRBs host galaxies at zeta 〉 5 makes the use of GRBs to probe the reionization epoch via spectroscopy of the red damping wing challenging; iii) GRBs appear crucial to locate typical star-forming galaxies at zeta 〉 5 and therefore the type of galaxies responsible for the reionization of the universe.
    Keywords: Astrophysics
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  • 2
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    Scientific Goals and Objectives for the Human Exploration of Mars: 1. Biology and Atmosphere/Climate (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: To prepare for the exploration of Mars by humans, as outlined in the new national vision for Space Exploration (VSE), the Mars Exploration Program Analysis Group (MEPAG), chartered by NASA's Mars Exploration Program (MEP), formed a Human Exploration of Mars Science Analysis Group (HEM-SAG), in March 2007. HEM-SAG was chartered to develop the scientific goals and objectives for the human exploration of Mars based on the Mars Scientific Goals, Objectives, Investigations, and Priorities.1 The HEM-SAG is one of several humans to Mars scientific, engineering and mission architecture studies chartered in 2007 to support NASA s plans for the human exploration of Mars. The HEM-SAG is composed of about 30 Mars scientists representing the disciplines of Mars biology, climate/atmosphere, geology and geophysics from the U.S., Canada, England, France, Italy and Spain. MEPAG selected Drs. James B. Garvin (NASA Goddard Space Flight Center) and Joel S. Levine (NASA Langley Research Center) to serve as HEMSAG co-chairs. The HEM-SAG team conducted 20 telecons and convened three face-to-face meetings from March through October 2007. The management of MEP and MEPAG were briefed on the HEM-SAG interim findings in May. The HEM-SAG final report was presented on-line to the full MEPAG membership and was presented at the MEPAG meeting on February 20-21, 2008. This presentation will outline the HEM-SAG biology and climate/atmosphere goals and objectives. A companion paper will outline the HEM-SAG geology and geophysics goals and objectives.
    Keywords: Lunar and Planetary Science and Exploration
    Type: 39th Lunar and Planetary Sciences Conference; Mar 10, 2008 - Mar 14, 2008; Houston, TX; United States
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  • 3
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    Structural basis of transcription: backtracked RNA polymerase II at 3.4 angstrom resolution (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-05-30
    Description: Transcribing RNA polymerases oscillate between three stable states, two of which, pre- and posttranslocated, were previously subjected to x-ray crystal structure determination. We report here the crystal structure of RNA polymerase II in the third state, the reverse translocated, or "backtracked" state. The defining feature of the backtracked structure is a binding site for the first backtracked nucleotide. This binding site is occupied in case of nucleotide misincorporation in the RNA or damage to the DNA, and is termed the "P" site because it supports proofreading. The predominant mechanism of proofreading is the excision of a dinucleotide in the presence of the elongation factor SII (TFIIS). Structure determination of a cocrystal with TFIIS reveals a rearrangement whereby cleavage of the RNA may take place.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2718261/" 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/PMC2718261/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Dong -- Bushnell, David A -- Huang, Xuhui -- Westover, Kenneth D -- Levitt, Michael -- Kornberg, Roger D -- GM036559/GM/NIGMS NIH HHS/ -- GM041455/GM/NIGMS NIH HHS/ -- GM049985/GM/NIGMS NIH HHS/ -- K99 GM085136/GM/NIGMS NIH HHS/ -- K99 GM085136-01/GM/NIGMS NIH HHS/ -- R00 GM085136/GM/NIGMS NIH HHS/ -- R01 GM036659/GM/NIGMS NIH HHS/ -- R01 GM041455/GM/NIGMS NIH HHS/ -- R01 GM049985/GM/NIGMS NIH HHS/ -- R01 GM049985-16/GM/NIGMS NIH HHS/ -- R37 GM036659/GM/NIGMS NIH HHS/ -- R37 GM036659-22/GM/NIGMS NIH HHS/ -- R37 GM041455/GM/NIGMS NIH HHS/ -- R37 GM041455-20/GM/NIGMS NIH HHS/ -- U54 GM072970/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2009 May 29;324(5931):1203-6. doi: 10.1126/science.1168729.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19478184" target="_blank"〉PubMed〈/a〉
    Keywords: Base Pair Mismatch ; Crystallography, X-Ray ; Guanosine Monophosphate/chemistry/metabolism ; Models, Molecular ; Nucleic Acid Conformation ; Oligoribonucleotides/chemistry/*metabolism ; Protein Conformation ; Protein Structure, Secondary ; Protein Structure, Tertiary ; RNA/chemistry/*metabolism ; RNA Polymerase II/*chemistry/*metabolism ; Saccharomyces cerevisiae/*enzymology ; *Transcription, Genetic ; Transcriptional Elongation Factors/chemistry/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    Solution nuclear magnetic resonance structure of membrane-integral diacylglycerol kinase (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-06-27
    Description: Escherichia coli diacylglycerol kinase (DAGK) represents a family of integral membrane enzymes that is unrelated to all other phosphotransferases. We have determined the three-dimensional structure of the DAGK homotrimer with the use of solution nuclear magnetic resonance. The third transmembrane helix from each subunit is domain-swapped with the first and second transmembrane segments from an adjacent subunit. Each of DAGK's three active sites resembles a portico. The cornice of the portico appears to be the determinant of DAGK's lipid substrate specificity and overhangs the site of phosphoryl transfer near the water-membrane interface. Mutations to cysteine that caused severe misfolding were located in or near the active site, indicating a high degree of overlap between sites responsible for folding and for catalysis.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2764269/" 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/PMC2764269/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Van Horn, Wade D -- Kim, Hak-Jun -- Ellis, Charles D -- Hadziselimovic, Arina -- Sulistijo, Endah S -- Karra, Murthy D -- Tian, Changlin -- Sonnichsen, Frank D -- Sanders, Charles R -- R01 GM047485/GM/NIGMS NIH HHS/ -- R01 GM047485-17/GM/NIGMS NIH HHS/ -- R01 GM47485/GM/NIGMS NIH HHS/ -- T32 NS007491/NS/NINDS NIH HHS/ -- T32 NS007491-09/NS/NINDS NIH HHS/ -- New York, N.Y. -- Science. 2009 Jun 26;324(5935):1726-9. doi: 10.1126/science.1171716.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19556511" target="_blank"〉PubMed〈/a〉
    Keywords: Adenosine Triphosphate/metabolism ; Amino Acid Sequence ; Biocatalysis ; Catalytic Domain ; Cell Membrane/enzymology ; Diacylglycerol Kinase/*chemistry/metabolism ; Escherichia coli/*enzymology ; Escherichia coli Proteins/*chemistry/metabolism ; Models, Molecular ; Molecular Sequence Data ; Nuclear Magnetic Resonance, Biomolecular ; Protein Conformation ; Protein Folding ; Protein Multimerization ; Protein Structure, Quaternary ; Protein Structure, Secondary ; Protein Structure, Tertiary
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
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    Structural basis of immune evasion at the site of CD4 attachment on HIV-1 gp120 (2009)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2009-12-08
    Description: The site on HIV-1 gp120 that binds to the CD4 receptor is vulnerable to antibodies. However, most antibodies that interact with this site cannot neutralize HIV-1. To understand the basis of this resistance, we determined co-crystal structures for two poorly neutralizing, CD4-binding site (CD4BS) antibodies, F105 and b13, in complexes with gp120. Both antibodies exhibited approach angles to gp120 similar to those of CD4 and a rare, broadly neutralizing CD4BS antibody, b12. Slight differences in recognition, however, resulted in substantial differences in F105- and b13-bound conformations relative to b12-bound gp120. Modeling and binding experiments revealed these conformations to be poorly compatible with the viral spike. This incompatibility, the consequence of slight differences in CD4BS recognition, renders HIV-1 resistant to all but the most accurately targeted antibodies.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2862588/" 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/PMC2862588/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, Lei -- Kwon, Young Do -- Zhou, Tongqing -- Wu, Xueling -- O'Dell, Sijy -- Cavacini, Lisa -- Hessell, Ann J -- Pancera, Marie -- Tang, Min -- Xu, Ling -- Yang, Zhi-Yong -- Zhang, Mei-Yun -- Arthos, James -- Burton, Dennis R -- Dimitrov, Dimiter S -- Nabel, Gary J -- Posner, Marshall R -- Sodroski, Joseph -- Wyatt, Richard -- Mascola, John R -- Kwong, Peter D -- Z99 AI999999/Intramural NIH HHS/ -- New York, N.Y. -- Science. 2009 Nov 20;326(5956):1123-7. doi: 10.1126/science.1175868.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19965434" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Antibodies, Neutralizing/chemistry/*immunology/metabolism ; Antigens, CD4/chemistry/*metabolism ; Binding Sites ; Binding Sites, Antibody ; Crystallography, X-Ray ; Epitopes ; HIV Antibodies/*chemistry/*immunology/metabolism ; HIV Envelope Protein gp120/*chemistry/*immunology/metabolism ; Hiv-1 ; Humans ; Hydrophobic and Hydrophilic Interactions ; *Immune Evasion ; Models, Molecular ; Molecular Sequence Data ; Peptide Fragments/chemistry/immunology/metabolism ; Protein Conformation
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    Volatile Analysis by Pyrolysis of Regolith (Vapor) on the Moon using Mass Spectrometry (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The identification of lunar resources such as water is a fundamental component of the the NASA Vision for Space Exploration. The Lunar Prospector mission detected high concentrations of hydrogen at the lunar poles that may indicate the presence of water or other volatiles in the lunar regolith [1]. One explanation for the presence of enhanced hydrogen in permanently shadowed crater regions is long term trapping of water-ice delivered by comets, asteroids, and other meteoritic material that have bombarded the Moon over the last 4 billion years [2]. It is also possible that the hydrogen signal at the lunar poles is due to hydrogen implanted by the solar wind which is delayed from diffusing out of the regolith by the cold temperatures [3]. Previous measurements of the lunar atmosphere by the LACE experiment on Apollo 17, suggested the presence of cold trapped vola'tiles that were expelled by solar heating [4]. In situ composition and isotopic analyses of the lunar regolith will be required to establish the abundance, origin, and distribution of water-ice and other volatiles at the lunar poles. Volatile Analysis by Pyrolysis of Regolith (VAPoR) on the Moon using mass spectrometry is one technique that should be considered. The VAPoR pyrolysis-mass spectrometer (pyr-MS) instrument concept study was selected for funding in 2007 by the NASA Lunar Sortie Science Opportunities (LSSO) Program. VAPoR is a miniature version of the Sample Analysis at Mars (SAM) instrument suite currently being developed at NASA Goddard for the 2009 Mars Science Laboratory mission (Fig. 1).
    Keywords: Lunar and Planetary Science and Exploration
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  • 7
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    Surface Clutter Removal in Airborne Radar Sounding Data from the Dry Valleys, Antarctica (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: We have collected roughly 1,000 line-km of airborne radar sounding data over glaciers, rock/ice glaciers, permafrost, subsurface ice bodies, ice-covered saline lakes, and glacial deposits in Taylor and Beacon Valley. These data are being analyzed in order to develop techniques for discriminating between subsurface and off-nadir echoes and for detecting and characterizing subsurface interfaces. The identification of features on Mars exhibiting morphologies consistent with ice/rock mixtures, near-surface ice bodies and near-surface liquid water, and the importance of such features to the search for water on Mars, highlights the need for appropriate terrestrial analogs and analysis techniques in order to prepare for radar sounder missions to Mars. Climatic, hydrological, and geological conditions in the Dry Valleys of Antarctica are analogous in many ways to those on Mars. A crucial first step in the data analysis process is the discrimination of echo sources in the radar data. The goal is to identify all returns from the surface of off-nadir topography in order to positively identify subsurface echoes. This process will also be critical for radar data that will be collected in areas of Mars exhibiting significant topography, so that subsurface echoes are identified unambiguously. The positive detection and characterization of subsurface (including sub-ice) water is a primary goal of NASA's Mars exploration program. Our data over the Dry Valleys provides an opportunity to implement techniques we are developing to accomplish these goals.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Workshop on Radar Investigations of Planetary and Terrestrial Environments; 45-46; LPI-Contrib-1231
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  • 8
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    The Miniaturized Moessbauer Spectrometers MIMOS II on MER: Four Years of Operation - A Summary (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The two Miniaturized Moessbauer Spectrometers (MIMOS II) on board the two Mars Exploration Rovers Spirit and Opportunity have now been collecting important scientific data for more than four years. The spectrometers provide information about Fe-bearing mineral phases and determine Fe oxidation states. The total amount of targets analized exceeds 600, the total integration time exceeds 260 days for both rovers. Since landing, more than five half-lives of the Co-57 MB sources have past (intensity at the time of landing approx. 150 mCi). Current integration times are about 50 hours in order to achieve reasonable statistics as opposed to 8 hours at the beginning of the mission. In total, 13 different mineral phases were detected: Olivine, pyroxene, hematite, magnetite and nanophase ferric oxide were detected at both landing sites. At Gusev, ilmenite, goethite, a ferric sulfate phase and a yet unassigned phase (in the rock Fuzzy Smith) were detected. At Meridiani, jarosite, metallic iron in meteoritic samples (kamacite), troilite, and an unassigned ferric phase were detected. Jarosite and goethite are of special interest, as these minerals are indicators for water activity. In this abstract, an overview of Moessbauer results will be given, with a focus on data obtained since the last martian winter. The MER mission has proven that Moessbauer spectroscopy is a valuable tool for the in situ exploration of extraterrestrial bodies and for the study of Febearing samples. The experience gained through the MER mission makes MIMOS II a obvious choice for future missions to Mars and other targets. Currently, MIMOS II is on the scientific payload of two approved future missions: Phobos Grunt (Russian Space Agency; 2009) and ExoMars (European Space Agency; 2013).
    Keywords: Lunar and Planetary Science and Exploration
    Type: 39th Lunar and Planetary Science Conference; Mar 10, 2008 - Mar 14, 2008; League City, TX; United States
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  • 9
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    90 GHz and 150 GHz Observations of the Orion M42 Region. A Submillimeter to Radio Analysis (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We have used the new 90GHz MUSTANG camera on the Robert C. Green Bank Telescope (GBT)to map the bright Huygens region of the star-forming region M42 with a resolution of 9" and a sensitivity of 2.8 mJy/beam. Ninety GHz is an interesting transition frequency, as MUSTANG detects both the free-free emission characteristic of the H II region created by the Trapezium stars, normally seen at lower frequencies, and thermal dust emission from the background OMCI molecular cloud, normally mapped at higher frequencies. We also present similar data from the 150 GHz GISMO camera taken on the IRAM 30 m telescope. This map has 15" resolution. By combining the MUSTANG data with 1.4, 8. and 31 GHz radio data from the VLA and GBT, we derive a new estimate of the emission measure averaged electron temperature of T(sub e) = 11376+/-1050 K by an original method relating free-free emission intensities at optically thin and optically thick frequencies. Combining Infrared Space Observatory-long wavelength spectrometer (ISO-LWS) data with our data, we derive a new estimate of the dust temperature and spectral emissivity index within the 80" ISO-LWS beam toward Orion KL/BN, T(sub d) = 42+/-3 K and Beta(sub d) = 1.3+/-0.1. We show that both T(sub d) and Beta(sub d) decrease when going from the H II region and excited OMCI interface to the denser UV shielded part OMCI (Orion KL/BN, Orion S). With a model consisting of only free-free and thermal dust emission, we are able to fit data taken at frequencies from 1.5 GHz to 854 GHz (350 micrometers).
    Keywords: Astrophysics
    Type: The Astrophysical Journal; 705; 1; 226-236
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  • 10
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    Noble Gas Analysis for Mars Robotic Missions: Evaluating K-Ar Age Dating for Mars Rock Analogs and Martian Shergottites (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The purpose of this noble gas investigation was to evaluate the possibility of measuring noble gases in martian rocks and air by future robotic missions such as the Mars Science Laboratory (MSL). The MSL mission has, as part of its payload, the Sample Analysis at Mars (SAM) instrument, which consists of a pyrolysis oven integrated with a GCMS. The MSL SAM instrument has the capability to measure noble gas compositions of martian rocks and atmosphere. Here we suggest the possibility of K-Ar age dating based on noble gas release of martian rocks by conducting laboratory simulation experiments on terrestrial basalts and martian meteorites. We provide requirements for the SAM instrument to obtain adequate noble gas abundances and compositions within the current SAM instrumental operating conditions, especially, a power limit that prevents heating the furnace above approx.1100 C. In addition, Martian meteorite analyses from NASA-JSC will be used as ground truth to evaluate the feasibility of robotic experiments to constrain the ages of martian surface rocks.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-18017 , Lunar Planetary Science Conference; Mar 23, 2009 - Mar 27, 2009; Houston, TX; United States
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