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  • 1
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    Effects of lunar cumulate mantle overturn and megaregolith on the expansion and contraction history of the Moon (2013)
    Wiley
    Details
    Publication Date: 2013-10-01
    Description: [1]  Gravity anomalies derived from recent GRAIL data suggest the presence of early volume expansion of the Moon. The absence of identifiable thrust faults limits the total net contraction that has occurred. These observations provide constraints on the lunar thermal evolution which raise questions for giant impact origin of the Moon. To study the lunar expansion/contraction history, we perform 3D thermochemical mantle evolution models, with solidifying core overlain by a layer of ilmenite-bearing cumulates (IBC) resulting from mantle overturn after magma ocean solidification. Our models focus on the effects of the overturn-produced density stratification with a deep heat-producing element (HPE) distribution and a top insulating megaregolith layer. The deep HPE can cause an early expansion up to 1.5 km radius due to the heating of the deep mantle. This HPE distribution also reduces the present-day contraction by ~7 km. Compared to the models without overturn, an end-member model with a stable IBC-rich layer on the core-mantle boundary shows an overall present-day contraction as small as 1.1 km. The low thermal conductivity of megaregolith also affects the present-day contraction, reducing it by ~ 3 km.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Recent Tectonic Activity on Pluto Driven by Phase Changes in the Ice Shell (2016)
    Wiley
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    Publication Date: 2016-06-17
    Description: The New Horizons spacecraft has found evidence for geologic activity on the surface of Pluto, including extensional tectonic deformation of its water ice bedrock (see Moore et al. [2016]). One mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean. We use updated physical properties for Pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean. For thermal conductivities of rock less than 3 W m −1 K −1 , an ocean forms and at least partially freezes, leading to recent extensional stresses in the ice shell. In scenarios where the ocean freezes and the ice shell is thicker than 260 km, ice II forms and causes global volume contractions. Since there is no evidence for recent compressional tectonic features, we argue that ice II has not formed and that Pluto's ocean has likely survived to present day.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    A high-order numerical study of reactive dissolution in an upwelling heterogeneous mantle—I. Channelization, channel lithology and channel geometry (2011)
    Oxford University Press
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    Publication Date: 2011-06-14
    Description: SUMMARY High-porosity channels are important pathways for melt migration in the mantle. To better understand the lithology and geometry of high-porosity melt channels, we conduct high-order accurate numerical simulations of reactive dissolution along a solubility gradient in an upwelling and viscously deformable porous column. In contrast to earlier studies, we assume the dissolution reaction to be at equilibrium, consider a finite soluble mineral abundance, and employ a high-order accurate numerical scheme. Using sustained perturbations in porosity and soluble mineral abundance at the inflow boundary, we explore the structure of steady-state high-porosity melt channels and their associated lithologies over a range of parameters, including soluble mineral abundance, solubility gradient, amplitude and lateral variation in inflow melt flux, melt fraction and upwelling rate. In general, high-porosity dunite channels are transient and shallow parts of pathways for melt migration in the mantle. The lower parts of a high-porosity channel are orthopyroxene-bearing dunite, harzburgite and possibly lherzolite. A wide orthopyroxene-free dunite channel may contain two or three high-porosity melt channels. The depth of dunite channel initiation depends on the solubility gradient, soluble mineral abundance, inflow melt flux, melt suction rate and upwelling rate. The amplitude and length scale of lateral variation in porosity and orthopyroxene abundance at the base of the upwelling column are important in determining the size and dimension of dunite channels, the strength of melt focusing and the melt suction rate, the presence of compacting boundary layer, as well as the number of high-porosity melt branches within a dunite channel. The spatial relations among the high-porosity melt channels, dunite and harzburgite channels documented in our numerical simulations may shed new light on a number of field, petrological and geochemical observations related to melt migration in the mantle.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    Waves, channels, and the preservation of chemical heterogeneities during melt migration in the mantle (2011)
    Wiley
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    Publication Date: 2011-10-25
    Description: The style of melt migration in the mantle is important to the interpretation of basalts erupted on the surface. Both grain-scale diffuse porous flow and channelized melt migration have been proposed. Through high-order accurate numerical simulations, we show that strong nonlinear interactions between compaction and dissolution in an upwelling mantle give rise to porosity waves and high-porosity melt channels that have well organized but time-dependent structures. Only the upper part of the channel is pyroxene-free dunite. The lower part is harzburgite. Transient melt flow in the wave regime results in significant lateral mixing and chromatographic fractionation even when mantle source compositions are independent of time. Caution must be exercised when inferring the geometry and spatial distribution of mantle heterogeneity based on spatial and temporal variations in isotopic ratios recorded in basalts.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Compaction–dissolution waves in an upwelling mantle column (2011)
    Oxford University Press
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    Publication Date: 2011-10-19
    Description: SUMMARY Compaction–dissolution waves in porosity and melt pressure form spontaneously in numerical simulations of melt migration in an upwelling, viscously compacting, porous column in a solubility gradient. The melt fraction is assumed to be small and the solid comprises olivine and orthopyroxene. The solubility of orthopyroxene in the melt is assumed to increase linearly with height and induces a gradient reaction, assumed to be at local equilibrium. Approximations for the vertical, 1-D, steady-state solutions are derived assuming negligible resistance to compaction. The linear stability of the steady-state solutions is characterized by complex eigenvalues and an oscillatory instability with strong wavenumber selection. This instability leads to the formation of checkerboard compaction–dissolution waves observed in the non-linear numerical simulations. The phase velocity of these waves is larger than the solid velocity but smaller than the melt velocity. The oscillatory instability is realized over a range of parameters and the variation in wave properties is explored. A power-law bulk-viscosity formulation, ξ=η/ϕ m f , is shown to decrease growth rates linearly in the exponent, m. For small perturbations, the growth rates and phase velocities measured from high-resolution numerical simulations are predicted by the linear theory as well as the dominant wavenumber in the non-linear regime. We present a regime diagram for reaction infiltration instabilities in viscously compacting porous media and show that compaction–dissolution waves are favoured by increasing solid upwelling and small solubility gradients relative to high-porosity channels. The regime diagram suggests that the formation of compaction–dissolution waves is a feasible new physical mechanism for melt transport beneath mid-ocean ridges.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Unresponsiveness to cannabinoids and reduced addictive effects of opiates in CB1 receptor knockout mice (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-01-15
    Description: The function of the central cannabinoid receptor (CB1) was investigated by invalidating its gene. Mutant mice did not respond to cannabinoid drugs, demonstrating the exclusive role of the CB1 receptor in mediating analgesia, reinforcement, hypothermia, hypolocomotion, and hypotension. The acute effects of opiates were unaffected, but the reinforcing properties of morphine and the severity of the withdrawal syndrome were strongly reduced. These observations suggest that the CB1 receptor is involved in the motivational properties of opiates and in the development of physical dependence and extend the concept of an interconnected role of CB1 and opiate receptors in the brain areas mediating addictive behavior.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ledent, C -- Valverde, O -- Cossu, G -- Petitet, F -- Aubert, J F -- Beslot, F -- Bohme, G A -- Imperato, A -- Pedrazzini, T -- Roques, B P -- Vassart, G -- Fratta, W -- Parmentier, M -- New York, N.Y. -- Science. 1999 Jan 15;283(5400):401-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉IRIBHN, Universite libre de Bruxelles, B-1070 Brussels, Belgium.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9888857" target="_blank"〉PubMed〈/a〉
    Keywords: Analgesics, Opioid/pharmacology ; Animals ; Behavior, Animal/drug effects ; Blood Pressure/drug effects ; Body Temperature/drug effects ; Cannabinoids/metabolism/*pharmacology ; Dronabinol/*pharmacology ; Heart Rate/drug effects ; Mice ; Mice, Knockout ; Morphine/pharmacology ; Motor Activity/drug effects ; Narcotics/*pharmacology ; Opioid-Related Disorders/*physiopathology ; Pain Threshold/drug effects ; Receptors, Cannabinoid ; Receptors, Drug/genetics/*physiology ; Receptors, Opioid, kappa/agonists/physiology ; Reinforcement (Psychology) ; Substance Withdrawal Syndrome/physiopathology
    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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  • 7
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    Selective amplification and cloning of four new members of the G protein-coupled receptor family (1989)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1989-05-05
    Description: An approach based on the polymerase chain reaction has been devised to clone new members of the family of genes encoding guanosine triphosphate-binding protein (G protein)-coupled receptors. Degenerate primers corresponding to consensus sequences of the third and sixth transmembrane segments of available receptors were used to selectively amplify and clone members of this gene family from thyroid complementary DNA. Clones encoding three known receptors and four new putative receptors were obtained. Sequence comparisons established that the new genes belong to the G protein-coupled receptor family. Close structural similarity was observed between one of the putative receptors and the 5HT1a receptor. Two other molecules displayed common sequence characteristics, suggesting that they are members of a new subfamily of receptors with a very short nonglycosylated (extracellular) amino-terminal extension.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Libert, F -- Parmentier, M -- Lefort, A -- Dinsart, C -- Van Sande, J -- Maenhaut, C -- Simons, M J -- Dumont, J E -- Vassart, G -- New York, N.Y. -- Science. 1989 May 5;244(4904):569-72.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut de Recherche Interdisciplinaire, Faculte de Medecine, Universite Libre de Bruxelles, Campus Erasme, Belgium.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2541503" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Base Sequence ; *Cloning, Molecular ; DNA/genetics ; DNA-Directed DNA Polymerase ; GTP-Binding Proteins/*metabolism ; *Gene Amplification ; Humans ; Molecular Sequence Data ; Receptors, Adrenergic, alpha/genetics ; Receptors, Adrenergic, beta/genetics ; Receptors, Muscarinic/genetics ; Receptors, Neurokinin-2 ; Receptors, Neurotransmitter/*genetics ; Receptors, Serotonin/genetics ; Sequence Homology, Nucleic Acid ; Thyroid Gland/analysis ; Transcription, Genetic
    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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  • 8
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    Molecular cloning of the thyrotropin receptor (1989)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1989-12-22
    Description: The pituitary hormone thyrotropin, or thyroid-stimulating hormone (TSH), is the main physiological agent that regulates the thyroid gland. The thyrotropin receptor (TSHR) was cloned by selective amplification with the polymerase chain reaction of DNA segments presenting sequence similarity with genes for G protein-coupled receptors. Out of 11 new putative receptor clones obtained from genomic DNA, one had sequence characteristics different from all the others. Although this clone did not hybridize to thyroid transcripts, screening of a dog thyroid complementary DNA (cDNA) library at moderate stringency identified a cDNA encoding a 4.9-kilobase thyroid-specific transcript. The polypeptide encoded by this thyroid-specific transcript consisted of a 398-amino acid residue amino-terminal segment, constituting a putative extracellular domain, connected to a 346-residue carboxyl-terminal domain that contained seven putative transmembrane segments. Expression of the cDNA conferred TSH responsiveness to Xenopus oocytes and Y1 cells and a TSH binding phenotype to COS cells. The TSHR and the receptor for luteinizing hormone-choriogonadotropin constitute a subfamily of G protein-coupled receptors with distinct sequence characteristics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Parmentier, M -- Libert, F -- Maenhaut, C -- Lefort, A -- Gerard, C -- Perret, J -- Van Sande, J -- Dumont, J E -- Vassart, G -- R01-DK21732/DK/NIDDK NIH HHS/ -- New York, N.Y. -- Science. 1989 Dec 22;246(4937):1620-2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut de Recherche Interdisciplinaire, Faculte de Medecine, Universite Libre de Bruxelles, Belgium.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2556796" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Blotting, Northern ; Cell Line ; *Cloning, Molecular ; Cyclic AMP ; Dogs ; Female ; *Genes ; Molecular Sequence Data ; Oocytes/drug effects/metabolism ; Organ Specificity ; Polymerase Chain Reaction/methods ; RNA, Messenger/genetics ; Receptors, Thyrotropin/*genetics ; Thyrotropin/pharmacology ; Transcription, Genetic ; Xenopus
    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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  • 9
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    Mars' paleomagnetic field as the result of a single-hemisphere dynamo (2008)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2008-09-27
    Description: Mars' crustal magnetic field was most likely generated by dynamo action in the planet's early history. Unexplained characteristics of the field include its strength, concentration in the southern hemisphere, and lack of correlation with any surface features except for the hemispheric crustal dichotomy. We used numerical dynamo modeling to demonstrate that the mechanisms proposed to explain crustal dichotomy formation can result in a single-hemisphere dynamo. This dynamo produces strong magnetic fields in only the southern hemisphere. This magnetic field morphology can explain why Mars' crustal magnetic field intensities are substantially stronger in the southern hemisphere without relying on any postdynamo mechanisms.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stanley, Sabine -- Elkins-Tanton, Linda -- Zuber, Maria T -- Parmentier, E Marc -- New York, N.Y. -- Science. 2008 Sep 26;321(5897):1822-5. doi: 10.1126/science.1161119.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of Toronto, Toronto, ON M5S1A7, Canada. stanley@physics.utoronto.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18818355" target="_blank"〉PubMed〈/a〉
    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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  • 10
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    The Effect of Ilmenite Viscosity on the Dynamics and Evolution of an Overturned Lunar Cumulate Mantle (2017)
    Wiley
    Details
    Publication Date: 2017-06-16
    Description: Lunar cumulate mantle overturn and the subsequent upwelling of overturned mantle cumulates provides a potential framework for understanding the first-order thermochemical evolution of the Moon. Upwelling of ilmenite-bearing cumulates (IBC) after the overturn has a dominant influence on the dynamics and long-term thermal evolution of the lunar mantle. An important parameter determining the stability and convective behaviour of the IBC is its viscosity, which was recently constrained through rock-deformation experiments. To examine the effect of IBC viscosity on the upwelling of overturned lunar cumulate mantle, here we conduct three-dimensional mantle convection models with an evolving core superposed by an IBC-rich layer, which resulted from mantle overturn after magma ocean solidification. Our modelling shows that a reduction of mantle viscosity by one order of magnitude, due to the presence of ilmenite, can dramatically change convective planform and long-term lunar mantle evolution. Our model results suggest a relatively stable partially molten IBC layer that has surrounded the lunar core to the present day.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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