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  • 1
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    Detonations in white dwarf dynamical interactions (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-22
    Description: In old, dense stellar systems collisions of white dwarfs are a rather frequent phenomenon. Here, we present the results of a comprehensive set of smoothed particle hydrodynamics simulations of close encounters of white dwarfs aimed to explore the outcome of the interaction and the nature of the final remnants for different initial conditions. Depending on the initial conditions and the white dwarf masses, three different outcomes are possible. Specifically, the outcome of the interaction can be either a direct or a lateral collision or the interaction can result in the formation of an eccentric binary system. In those cases in which a collision occurs, the infalling material is compressed and heated such that the physical conditions for a detonation may be reached during the most violent phases of the merger. While we find that detonations occur in a significant number of our simulations, in some of them the temperature increase in the shocked region rapidly lifts degeneracy, leading to the quenching of the burning. We thus characterize under which circumstances a detonation is likely to occur as a result of the impact of the disrupted star on the surface of the more massive white dwarf. Finally, we also study which interactions result in bound systems, and in which ones the more massive white dwarf is also disrupted as a consequence of the dynamical interaction. The sizeable number of simulations performed in this work allows us to find how the outcome of the interaction depends on the distance at closest approach, and on the masses of the colliding white dwarfs, and which is the chemical pattern of the nuclearly processed material. Finally, we also discuss the influence of the masses and core chemical compositions of the interacting white dwarfs and the different kinds of impact in the properties of the remnants.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Proline isomerization electrostatic mechanism [Biophysics and Computational Biology] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-07-16
    Description: Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions. Different families of enzymes, known as “peptidyl-prolyl isomerases” (PPIases), catalyze this reaction, which involves the interconversion between the cis and trans isomers of the N-terminal amide bond...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 3
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    A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes (2010)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2010-05-14
    Description: NGC 6791 is a well studied open cluster that it is so close to us that can be imaged down to very faint luminosities. The main-sequence turn-off age ( approximately 8 Gyr) and the age derived from the termination of the white dwarf cooling sequence ( approximately 6 Gyr) are very different. One possible explanation is that as white dwarfs cool, one of the ashes of helium burning, (22)Ne, sinks in the deep interior of these stars. At lower temperatures, white dwarfs are expected to crystallize and phase separation of the main constituents of the core of a typical white dwarf ((12)C and (16)O) is expected to occur. This sequence of events is expected to introduce long delays in the cooling times, but has not hitherto been proven. Here we report that, as theoretically anticipated, physical separation processes occur in the cores of white dwarfs, resolving the age discrepancy for NGC 6791.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Garcia-Berro, Enrique -- Torres, Santiago -- Althaus, Leandro G -- Renedo, Isabel -- Loren-Aguilar, Pablo -- Corsico, Alejandro H -- Rohrmann, Rene D -- Salaris, Maurizio -- Isern, Jordi -- England -- Nature. 2010 May 13;465(7295):194-6. doi: 10.1038/nature09045.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels, Spain. garcia@fa.upc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20463732" target="_blank"〉PubMed〈/a〉
    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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  • 4
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    Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J (2014)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2014-08-29
    Description: A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon-oxygen white dwarf or a pair of merging white dwarfs. The explosion fuses a large amount of radioactive (56)Ni (refs 1-3). After the explosion, the decay chain from (56)Ni to (56)Co to (56)Fe generates gamma-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of (56)Co lines at energies of 847 and 1,238 kiloelectronvolts and a gamma-ray continuum in the 200-400 kiloelectronvolt band from the type Ia supernova 2014J in the nearby galaxy M82. The line fluxes suggest that about 0.6 +/- 0.1 solar masses of radioactive (56)Ni were synthesized during the explosion. The line broadening gives a characteristic mass-weighted ejecta expansion velocity of 10,000 +/- 3,000 kilometres per second. The observed gamma-ray properties are in broad agreement with the canonical model of an explosion of a white dwarf just massive enough to be unstable to gravitational collapse, but do not exclude merger scenarios that fuse comparable amounts of (56)Ni.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Churazov, E -- Sunyaev, R -- Isern, J -- Knodlseder, J -- Jean, P -- Lebrun, F -- Chugai, N -- Grebenev, S -- Bravo, E -- Sazonov, S -- Renaud, M -- England -- Nature. 2014 Aug 28;512(7515):406-8. doi: 10.1038/nature13672.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Space Research Institute (IKI), Profsouznaya 84/32, Moscow 117997, Russia [2] Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany. ; Institute for Space Sciences (ICE-CSIC/IEEC), 08193 Bellaterra, Spain. ; 1] Universite de Toulouse, UPS-OMP, IRAP, Toulouse, France [2] CNRS, IRAP, 9 Avenue colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France. ; APC, Universite Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cite, 75205 Paris Cedex 13, France. ; Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya Street, 119017 Moscow, Russia. ; Space Research Institute (IKI), Profsouznaya 84/32, Moscow 117997, Russia. ; ETSAV, Universitat Politecnica de Catalunya, Carrer Pere Serra 1-15, 08173 Sant Cugat del Valles, Spain. ; 1] Space Research Institute (IKI), Profsouznaya 84/32, Moscow 117997, Russia [2] Moscow Institute of Physics and Technology, Institutsky pereulok 9, 141700 Dolgoprudny, Russia. ; LUPM, Universite Montpellier 2, CNRS/IN2P3, CC 72, Place Eugene Bataillon, F-34095 Montpellier Cedex 5, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25164750" target="_blank"〉PubMed〈/a〉
    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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  • 5
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    Neuropathy of haematopoietic stem cell niche is essential for myeloproliferative neoplasms (2014)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2014-07-22
    Description: Myeloproliferative neoplasms (MPNs) are diseases caused by mutations in the haematopoietic stem cell (HSC) compartment. Most MPN patients have a common acquired mutation of Janus kinase 2 (JAK2) gene in HSCs that renders this kinase constitutively active, leading to uncontrolled cell expansion. The bone marrow microenvironment might contribute to the clinical outcomes of this common event. We previously showed that bone marrow nestin(+) mesenchymal stem cells (MSCs) innervated by sympathetic nerve fibres regulate normal HSCs. Here we demonstrate that abrogation of this regulatory circuit is essential for MPN pathogenesis. Sympathetic nerve fibres, supporting Schwann cells and nestin(+) MSCs are consistently reduced in the bone marrow of MPN patients and mice expressing the human JAK2(V617F) mutation in HSCs. Unexpectedly, MSC reduction is not due to differentiation but is caused by bone marrow neural damage and Schwann cell death triggered by interleukin-1beta produced by mutant HSCs. In turn, in vivo depletion of nestin(+) cells or their production of CXCL12 expanded mutant HSC number and accelerated MPN progression. In contrast, administration of neuroprotective or sympathomimetic drugs prevented mutant HSC expansion. Treatment with beta3-adrenergic agonists that restored the sympathetic regulation of nestin(+) MSCs prevented the loss of these cells and blocked MPN progression by indirectly reducing the number of leukaemic stem cells. Our results demonstrate that mutant-HSC-driven niche damage critically contributes to disease manifestation in MPN and identify niche-forming MSCs and their neural regulation as promising therapeutic targets.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arranz, Lorena -- Sanchez-Aguilera, Abel -- Martin-Perez, Daniel -- Isern, Joan -- Langa, Xavier -- Tzankov, Alexandar -- Lundberg, Pontus -- Muntion, Sandra -- Tzeng, Yi-Shiuan -- Lai, Dar-Ming -- Schwaller, Jurg -- Skoda, Radek C -- Mendez-Ferrer, Simon -- Howard Hughes Medical Institute/ -- England -- Nature. 2014 Aug 7;512(7512):78-81. doi: 10.1038/nature13383. Epub 2014 Jun 22.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Stem Cell Niche Pathophysiology Group, Centro Nacional de Investigaciones Cardiovasculares (CNIC), 28029 Madrid, Spain. ; University Hospital Basel, CH-4031 Basel, Switzerland. ; Department of Haematology, IBSAL-Hospital Universitario de Salamanca, 37007 Salamanca, Spain. ; National Taiwan University, Taipei 10002, Taiwan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25043017" target="_blank"〉PubMed〈/a〉
    Keywords: Adrenergic beta-3 Receptor Agonists/pharmacology/therapeutic use ; Animals ; Apoptosis/drug effects ; Disease Progression ; Female ; Hematopoietic Stem Cells/drug effects/*pathology ; Humans ; Interleukin-1beta/metabolism ; Janus Kinase 2/genetics ; Mesenchymal Stromal Cells/drug effects/pathology ; Mice ; Myeloproliferative Disorders/drug therapy/*pathology ; Neoplasms/drug therapy/*pathology ; Neoplastic Stem Cells/drug effects/pathology ; Nerve Fibers/drug effects/*pathology ; Nestin/metabolism ; Neuroprotective Agents/pharmacology/therapeutic use ; Receptors, Adrenergic, beta-3/metabolism ; Schwann Cells/drug effects/pathology ; *Stem Cell Niche ; Sympathetic Nervous System/drug effects/*pathology/physiopathology
    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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  • 6
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    Global ocean current reconstruction from altimetric and microwave SST measurements (2014)
    Wiley
    Details
    Publication Date: 2014-05-15
    Description: Ocean currents are a key component to understanding many oceanic and climatic phenomena and knowledge of them is crucial for both navigation and operational applications. Currently, they are derived from Sea Surface Height (SSH) measurements provided by altimeters. However, distances between tracks and the limited number of available altimeters lead to errors in the accurate location of oceanic currents. In this study, we investigate the capability of Sea Surface Temperature (SST) observations to reconstruct surface currents at a global scale. The methodology we use consists of estimating the stream function by taking the phase from SST and the spectrum of SSH and then comparing it with altimetric measurements. Results reveal that SST provided by microwave radiometers can be used to retrieve ocean currents during winter near the major extratropical current systems, which are characterized by an intense mesoscale activity and the presence of strong thermal gradients. We have also found that surface ocean current reconstruction based on Surface Quasi-Geostrophic approach can be improved if the information about the energy spectrum provided by altimeters is used. This points to the development of a new method of reconstructing ocean currents based on the combination of the phase of SST images with the energy spectrum derived from along-track altimetric measurements.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Diagnosis of high resolution upper ocean dynamics from noisy Sea Surface Temperatures (2013)
    Wiley
    Details
    Publication Date: 2013-12-17
    Description: The noise present in infrared satellite measurements of Sea Surface Temperature (SST) hampers the use of Surface Quasi-Geostrophic (SQG) equations to diagnose ocean dynamics at high resolutions. Here, we propose a methodology to reduce the contribution of noise when diagnosing surface vorticity, divergence and vertical velocity from SST able to retain the dynamics at scales of a few kilometers. It is based on the use of denoising techniques with curvelets as basis functions and the application of a selective low-pass filters to improve the reconstruction of surface upwelling/downwelling patterns. First, it is tested using direct numerical simulations of SQG turbulence and then applied to diagnose low-frequency vertical velocity patterns from real MODIS images. The methodology here presented, which is not tied to the validity of SQG equations nor to the use of SST, is quite general and can be applied to a wide range of measurements and dynamical frameworks.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Electronic Resource
    Electronic Resource
    The Origin of Neutron Stars in Binary Systems (1990)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 28 (1990), S. 183-214 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.28.090190.001151
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  • 9
    Electronic Resource
    Electronic Resource
    Radiative transfer in explosive phenomena in compact objects
    Amsterdam : Elsevier
    Advances in Space Research 8 (1988), S. 699-702 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0273-1177(88)90479-6
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  • 10
    Electronic Resource
    Electronic Resource
    Cold C + O white dwarfs and neutron stars
    Amsterdam : Elsevier
    Advances in Space Research 8 (1988), S. 703-706 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0273-1177(88)90480-2
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