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  • Lunar and Planetary Science and Exploration  (46)
  • LUNAR AND PLANETARY EXPLORATION  (38)
  • Animals  (15)
  • 1
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    Evidence for Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Even though the Early Noachian (EN) used in geologic mapping is undefined at the early end, it is often assumed in absolute chronologies to extend back to 4.6 BYA. We explored this assumption by searching for evidence of buried impact basins, in the largest occurrences of Early Noachian terrain. The hypothesis is that if such basins exist, they indicate crust which must predate the surface units mapped as the oldest on Mars, and those units must then be less than 4.6 BY old. Alternatively, if no such buried features are seen, then the surface units may represent crust of the same age below, which could in principle be as old as Mars. Here we show the former alternative is true. There must be crust older than the oldest mapped surface units. We also show that a number of Noachian terrains on Mars appear to have a common total (visible + buried) crater retention age. This might be either the age of the original (planet-wide?) crust of Mars, or may indicate crater saturation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXIV; LPI-Contrib-1156
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    NASA TECHNICAL REPORTS
  • 2
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    Evidence for Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noachian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science Conference; Houston, TX; United States
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    NASA TECHNICAL REPORTS
  • 3
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    A Preliminary Relationship Between the Depth of Martian Gullies and the Abundance of Hydrogen on Near-Surface Mars (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: Recent compelling evidence has been presented to suggest the presence of near-surface water or water ice on Mars. The Mars Orbiter Camera (MOC) has photographed relatively young fluvial features in the form of gullies which have been attributed to groundwater seepage. The Gamma Ray Spectrometer (GRS) from the Mars Odyssey spacecraft has detected large amounts of hydrogen in the Martian soil, inferred to come from water or water ice within the upper meter of the surface. We explore the model of groundwater seepage as the mechanism of gully formation as opposed to other mechanisms. We investigate the abundance of hydrogen to the depth at which gully-like features form. We see a positive correlation, which implies the presence of a groundwater system for Mars.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Mars: Hydrology, Drainage, and Valley Systems; LPI-Contrib-1197
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    NASA TECHNICAL REPORTS
  • 4
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    A Very Large Population of Likely Buried Impact Basins in the Northern Lowlands of Mars Revealed by MOLA Data (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: High resolution Mars Orbiter Laser Altimeter (MOLA) data have revealed a large number of subdued quasi-circular depressions (QCDs) 〉50 km diameter in the northern lowlands of Mars which are generally not visible in Viking imagery and which may be buried ancient impact basins. Additional information is contained in the original extended abstract.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXII; LPI-Contrib-1080
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  • 5
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    Evidence for the Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noa-chian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science Conference; Mar 16, 2003 - Mar 20, 2003; Houston, TX; United States
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    NASA TECHNICAL REPORTS
  • 6
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    Polar patterns of driven filaments (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-09-03
    Description: The emergence of collective motion exhibited by systems ranging from flocks of animals to self-propelled microorganisms to the cytoskeleton is a ubiquitous and fascinating self-organization phenomenon. Similarities between these systems, such as the inherent polarity of the constituents, a density-dependent transition to ordered phases or the existence of very large density fluctuations, suggest universal principles underlying pattern formation. This idea is followed by theoretical models at all levels of description: micro- or mesoscopic models directly map local forces and interactions using only a few, preferably simple, interaction rules, and more macroscopic approaches in the hydrodynamic limit rely on the systems' generic symmetries. All these models characteristically have a broad parameter space with a manifold of possible patterns, most of which have not yet been experimentally verified. The complexity of interactions and the limited parameter control of existing experimental systems are major obstacles to our understanding of the underlying ordering principles. Here we demonstrate the emergence of collective motion in a high-density motility assay that consists of highly concentrated actin filaments propelled by immobilized molecular motors in a planar geometry. Above a critical density, the filaments self-organize to form coherently moving structures with persistent density modulations, such as clusters, swirls and interconnected bands. These polar nematic structures are long lived and can span length scales orders of magnitudes larger than their constituents. Our experimental approach, which offers control of all relevant system parameters, complemented by agent-based simulations, allows backtracking of the assembly and disassembly pathways to the underlying local interactions. We identify weak and local alignment interactions to be essential for the observed formation of patterns and their dynamics. The presented minimal polar-pattern-forming system may thus provide new insight into emerging order in the broad class of active fluids and self-propelled particles.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schaller, Volker -- Weber, Christoph -- Semmrich, Christine -- Frey, Erwin -- Bausch, Andreas R -- England -- Nature. 2010 Sep 2;467(7311):73-7. doi: 10.1038/nature09312.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lehrstuhl fur Biophysik-E27, Technische Universitat Munchen, 85748 Garching, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20811454" target="_blank"〉PubMed〈/a〉
    Keywords: Actin Cytoskeleton/*metabolism ; Animals ; Cytoskeleton/*chemistry ; Microtubules/chemistry ; *Models, Biological ; Myosin Subfragments/*metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 7
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    A genetically encoded photoactivatable Rac controls the motility of living cells (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-08-21
    Description: The precise spatio-temporal dynamics of protein activity are often critical in determining cell behaviour, yet for most proteins they remain poorly understood; it remains difficult to manipulate protein activity at precise times and places within living cells. Protein activity has been controlled by light, through protein derivatization with photocleavable moieties or using photoreactive small-molecule ligands. However, this requires use of toxic ultraviolet wavelengths, activation is irreversible, and/or cell loading is accomplished via disruption of the cell membrane (for example, through microinjection). Here we have developed a new approach to produce genetically encoded photoactivatable derivatives of Rac1, a key GTPase regulating actin cytoskeletal dynamics in metazoan cells. Rac1 mutants were fused to the photoreactive LOV (light oxygen voltage) domain from phototropin, sterically blocking Rac1 interactions until irradiation unwound a helix linking LOV to Rac1. Photoactivatable Rac1 (PA-Rac1) could be reversibly and repeatedly activated using 458- or 473-nm light to generate precisely localized cell protrusions and ruffling. Localized Rac activation or inactivation was sufficient to produce cell motility and control the direction of cell movement. Myosin was involved in Rac control of directionality but not in Rac-induced protrusion, whereas PAK was required for Rac-induced protrusion. PA-Rac1 was used to elucidate Rac regulation of RhoA in cell motility. Rac and Rho coordinate cytoskeletal behaviours with seconds and submicrometre precision. Their mutual regulation remains controversial, with data indicating that Rac inhibits and/or activates Rho. Rac was shown to inhibit RhoA in mouse embryonic fibroblasts, with inhibition modulated at protrusions and ruffles. A PA-Rac crystal structure and modelling revealed LOV-Rac interactions that will facilitate extension of this photoactivation approach to other proteins.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2766670/" 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/PMC2766670/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wu, Yi I -- Frey, Daniel -- Lungu, Oana I -- Jaehrig, Angelika -- Schlichting, Ilme -- Kuhlman, Brian -- Hahn, Klaus M -- GM057464/GM/NIGMS NIH HHS/ -- GM64346/GM/NIGMS NIH HHS/ -- R01 GM057464/GM/NIGMS NIH HHS/ -- R01 GM057464-09/GM/NIGMS NIH HHS/ -- U54 GM064346/GM/NIGMS NIH HHS/ -- U54 GM064346-089026/GM/NIGMS NIH HHS/ -- England -- Nature. 2009 Sep 3;461(7260):104-8. doi: 10.1038/nature08241. Epub 2009 Aug 19.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina 27599, USA. yiwu@med.unc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19693014" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Avena/genetics ; Cell Line ; *Cell Movement/radiation effects ; Cell Surface Extensions ; Cell Survival ; Cryptochromes ; Crystallization ; Crystallography, X-Ray ; Embryo, Mammalian/cytology ; Enzyme Activation/radiation effects ; Fibroblasts ; Flavoproteins/chemistry/genetics/metabolism ; Fluorescence Recovery After Photobleaching ; Genetic Engineering/*methods ; HeLa Cells ; Humans ; Mice ; Models, Molecular ; Myosins/metabolism ; Protein Conformation ; rac1 GTP-Binding Protein/chemistry/*genetics/*metabolism/radiation effects ; rho GTP-Binding Proteins/antagonists & inhibitors/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Deciphering the splicing code (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-05-07
    Description: Alternative splicing has a crucial role in the generation of biological complexity, and its misregulation is often involved in human disease. Here we describe the assembly of a 'splicing code', which uses combinations of hundreds of RNA features to predict tissue-dependent changes in alternative splicing for thousands of exons. The code determines new classes of splicing patterns, identifies distinct regulatory programs in different tissues, and identifies mutation-verified regulatory sequences. Widespread regulatory strategies are revealed, including the use of unexpectedly large combinations of features, the establishment of low exon inclusion levels that are overcome by features in specific tissues, the appearance of features deeper into introns than previously appreciated, and the modulation of splice variant levels by transcript structure characteristics. The code detected a class of exons whose inclusion silences expression in adult tissues by activating nonsense-mediated messenger RNA decay, but whose exclusion promotes expression during embryogenesis. The code facilitates the discovery and detailed characterization of regulated alternative splicing events on a genome-wide scale.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barash, Yoseph -- Calarco, John A -- Gao, Weijun -- Pan, Qun -- Wang, Xinchen -- Shai, Ofer -- Blencowe, Benjamin J -- Frey, Brendan J -- Canadian Institutes of Health Research/Canada -- England -- Nature. 2010 May 6;465(7294):53-9. doi: 10.1038/nature09000.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Biomedical Engineering, Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto M5S 3G4, Canada.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20445623" target="_blank"〉PubMed〈/a〉
    Keywords: Alternative Splicing/*genetics ; Animals ; *Gene Expression Regulation ; Gene Silencing ; Genetic Code/*genetics ; Humans ; Mice ; *Models, Genetic ; RNA, Messenger/*metabolism ; Reproducibility of Results
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 9
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    A major ecosystem shift in the northern Bering Sea (2006)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2006-03-11
    Description: Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grebmeier, Jacqueline M -- Overland, James E -- Moore, Sue E -- Farley, Ed V -- Carmack, Eddy C -- Cooper, Lee W -- Frey, Karen E -- Helle, John H -- McLaughlin, Fiona A -- McNutt, S Lyn -- New York, N.Y. -- Science. 2006 Mar 10;311(5766):1461-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Marine Biogeochemistry and Ecology Group, Department of Ecology and Evolutionary Biology, 10515 Research Drive, Building A, Suite 100, University of Tennessee, Knoxville, TN 37932, USA. jgrebmei@utk.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16527980" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arctic Regions ; Ducks ; *Ecosystem ; Fishes ; Geologic Sediments/chemistry ; *Ice Cover ; Oxygen/analysis ; Pacific Ocean ; Population Dynamics ; Temperature ; Walruses ; Whales
    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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  • 10
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    Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-09-23
    Description: Protein aggregation is an established pathogenic mechanism in Alzheimer's disease, but little is known about the initiation of this process in vivo. Intracerebral injection of dilute, amyloid-beta (Abeta)-containing brain extracts from humans with Alzheimer's disease or beta-amyloid precursor protein (APP) transgenic mice induced cerebral beta-amyloidosis and associated pathology in APP transgenic mice in a time- and concentration-dependent manner. The seeding activity of brain extracts was reduced or abolished by Abeta immunodepletion, protein denaturation, or by Abeta immunization of the host. The phenotype of the exogenously induced amyloidosis depended on both the host and the source of the agent, suggesting the existence of polymorphic Abeta strains with varying biological activities reminiscent of prion strains.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Meyer-Luehmann, Melanie -- Coomaraswamy, Janaky -- Bolmont, Tristan -- Kaeser, Stephan -- Schaefer, Claudia -- Kilger, Ellen -- Neuenschwander, Anton -- Abramowski, Dorothee -- Frey, Peter -- Jaton, Anneliese L -- Vigouret, Jean-Marie -- Paganetti, Paolo -- Walsh, Dominic M -- Mathews, Paul M -- Ghiso, Jorge -- Staufenbiel, Matthias -- Walker, Lary C -- Jucker, Mathias -- NS45357/NS/NINDS NIH HHS/ -- RR-00165/RR/NCRR NIH HHS/ -- Wellcome Trust/United Kingdom -- New York, N.Y. -- Science. 2006 Sep 22;313(5794):1781-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Cellular Neurology, Hertie-Institute for Clinical Brain Research, University of Tubingen, D-72076 Tubingen, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16990547" target="_blank"〉PubMed〈/a〉
    Keywords: Aged ; Aged, 80 and over ; Aging ; Alzheimer Disease/metabolism ; Amyloid beta-Peptides/*administration & dosage/*analysis/chemistry/pharmacology ; Amyloid beta-Protein Precursor/*administration & dosage/pharmacology ; Amyloidosis/*metabolism/pathology ; Animals ; Brain/pathology ; Brain Chemistry ; Brain Diseases/*metabolism/pathology ; Female ; Hippocampus/*chemistry/pathology ; Humans ; Male ; Mice ; Mice, Transgenic ; Protein Denaturation ; Time Factors ; Tissue Extracts
    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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