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  • 1
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    Brownian motion of massive black hole binaries and the final parsec problem (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-02
    Description: Massive black hole binaries (BHBs) are expected to be one of the most powerful sources of gravitational waves in the frequency range of the pulsar timing array and of forthcoming space-borne detectors. They are believed to form in the final stages of galaxy mergers, and then harden by slingshot ejections of passing stars. However, evolution via the slingshot mechanism may be ineffective if the reservoir of interacting stars is not readily replenished, and the binary shrinking may come to a halt at roughly a parsec separation. Recent simulations suggest that the departure from spherical symmetry, naturally produced in merger remnants, leads to efficient loss cone refilling, preventing the binary from stalling. However, current N -body simulations able to accurately follow the evolution of BHBs are limited to very modest particle numbers. Brownian motion may artificially enhance the loss cone refilling rate in low- N simulations, where the binary encounters a larger population of stars due its random motion. Here we study the significance of Brownian motion of BHBs in merger remnants in the context of the final parsec problem. We simulate mergers with various particle numbers (from 8k to 1M) and with several density profiles. Moreover, we compare simulations where the BHB is fixed at the centre of the merger remnant with simulations where the BHB is free to random walk. We find that Brownian motion does not significantly affect the evolution of BHBs in simulations with particle numbers in excess of one million, and that the hardening measured in merger simulations is due to collisionless loss cone refilling.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    The mass spectrum of compact remnants from the PARSEC stellar evolution tracks (2015)
    Oxford University Press
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    Publication Date: 2015-07-02
    Description: The mass spectrum of stellar mass black holes (BHs) is highly uncertain. Dynamical mass measurements are available only for few (~10) BHs in X-ray binaries, while theoretical models strongly depend on the hydrodynamics of supernova (SN) explosions and on the evolution of massive stars. In this paper, we present and discuss the mass spectrum of compact remnants that we obtained with sevn , a new public population-synthesis code, which couples the parsec stellar evolution tracks with up-to-date recipes for SN explosion (depending on the carbon–oxygen mass of the progenitor, on the compactness of the stellar core at pre-SN stage and on a recent two-parameter criterion based on the dimensionless entropy per nucleon at pre-SN stage). sevn can be used both as a stand-alone code and in combination with direct-summation N -body codes ( starlab , higpus ). The parsec stellar evolution tracks currently implemented in sevn predict significantly larger values of the carbon–oxygen core mass with respect to previous models. For most of the SN recipes we adopt, this implies substantially larger BH masses at low metallicity (≤2  x  10 –3 ), than other population synthesis codes. The maximum BH mass found with sevn is ~25, 60 and 130 M at metallicity Z  = 2  x  10 –2 , 2  x  10 –3 and 2  x  10 –4 , respectively. Mass loss by stellar winds plays a major role in determining the mass of BHs for very massive stars (≥90 M ), while the remnant mass spectrum depends mostly on the adopted SN recipe for lower progenitor masses. We discuss the implications of our results for the transition between neutron star and BH mass, and for the expected number of massive BHs (with mass 〉25 M ) as a function of metallicity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Dynamics of stellar black holes in young star clusters with different metallicities - II. Black hole-black hole binaries (2014)
    Oxford University Press
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    Publication Date: 2014-06-05
    Description: In this paper, we study the formation and dynamical evolution of black hole–black hole (BH–BH) binaries in young star clusters (YSCs), by means of N -body simulations. The simulations include metallicity-dependent recipes for stellar evolution and stellar winds, and have been run for three different metallicities ( Z = 0.01, 0.1 and 1 Z ). Following recent theoretical models of wind mass-loss and core-collapse supernovae, we assume that the mass of the stellar remnants depends on the metallicity of the progenitor stars. We find that BH–BH binaries form efficiently because of dynamical exchanges: in our simulations, we find about 10 times more BH–BH binaries than double neutron star binaries. The simulated BH–BH binaries form earlier in metal-poor YSCs, which host more massive black holes (BHs) than in metal-rich YSCs. The simulated BH–BH binaries have very large chirp masses (up to 80 M ), because the BH mass is assumed to depend on metallicity, and because BHs can grow in mass due to the merger with stars. The simulated BH–BH binaries span a wide range of orbital periods (10 –3 –10 7  yr), and only a small fraction of them (0.3 per cent) is expected to merge within a Hubble time. We discuss the estimated merger rate from our simulations and the implications for Advanced VIRGO and LIGO.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Do open star clusters evolve towards energy equipartition? (2016)
    Oxford University Press
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    Publication Date: 2016-05-26
    Description: We investigate whether open clusters (OCs) tend to energy equipartition, by means of direct N -body simulations with a broken power-law mass function. We find that the simulated OCs become strongly mass segregated, but the local velocity dispersion does not depend on the stellar mass for most of the mass range: the curve of the velocity dispersion as a function of mass is nearly flat even after several half-mass relaxation times, regardless of the adopted stellar evolution recipes and Galactic tidal field model. This result holds both if we start from virialized King models and if we use clumpy sub-virial initial conditions. The velocity dispersion of the most massive stars and stellar remnants tends to be higher than the velocity dispersion of the lighter stars. This trend is particularly evident in simulations without stellar evolution. We interpret this result as a consequence of the strong mass segregation, which leads to Spitzer's instability. Stellar winds delay the onset of the instability. Our simulations strongly support the result that OCs do not attain equipartition, for a wide range of initial conditions.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Hierarchical black hole triples in young star clusters: impact of Kozai-Lidov resonance on mergers (2016)
    Oxford University Press
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    Publication Date: 2016-10-08
    Description: Mergers of compact-object binaries are one of the most powerful sources of gravitational waves (GWs) in the frequency range of second-generation ground-based GW detectors (advanced LIGO and Virgo). Dynamical simulations of young dense star clusters (SCs) indicate that ~27 per cent of all double compact-object binaries are members of hierarchical triple systems (HTs). In this paper, we consider 570 HTs composed of three compact objects (black holes or neutron stars) that formed dynamically in N -body simulations of young dense SCs. We simulate them for a Hubble time with a new code based on the Mikkola's algorithmic regularization scheme, including the 2.5 post-Newtonian term. We find that ~88 per cent of the simulated systems develop Kozai–Lidov (KL) oscillations. KL resonance triggers the merger of the inner binary in three systems (corresponding to 0.5 per cent of the simulated HTs), by increasing the eccentricity of the inner binary. Accounting for KL oscillations leads to an increase of the total expected merger rate by 50 per cent. All binaries that merge because of KL oscillations were formed by dynamical exchanges (i.e. none is a primordial binary) and have chirp mass 〉20 M . This result might be crucial to interpret the formation channel of the first recently detected GW events.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Dynamical age differences among coeval star clusters as revealed by blue stragglers (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-12-22
    Description: Globular star clusters that formed at the same cosmic time may have evolved rather differently from the dynamical point of view (because that evolution depends on the internal environment) through a variety of processes that tend progressively to segregate stars more massive than the average towards the cluster centre. Therefore clusters with the same chronological age may have reached quite different stages of their dynamical history (that is, they may have different 'dynamical ages'). Blue straggler stars have masses greater than those at the turn-off point on the main sequence and therefore must be the result of either a collision or a mass-transfer event. Because they are among the most massive and luminous objects in old clusters, they can be used as test particles with which to probe dynamical evolution. Here we report that globular clusters can be grouped into a few distinct families on the basis of the radial distribution of blue stragglers. This grouping corresponds well to an effective ranking of the dynamical stage reached by stellar systems, thereby permitting a direct measure of the cluster dynamical age purely from observed properties.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ferraro, F R -- Lanzoni, B -- Dalessandro, E -- Beccari, G -- Pasquato, M -- Miocchi, P -- Rood, R T -- Sigurdsson, S -- Sills, A -- Vesperini, E -- Mapelli, M -- Contreras, R -- Sanna, N -- Mucciarelli, A -- England -- Nature. 2012 Dec 20;492(7429):393-5. doi: 10.1038/nature11686.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy. francesco.ferraro3@unibo.it〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23257880" 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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  • 7
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    The Drosophila TNF receptor Grindelwald couples loss of cell polarity and neoplastic growth (2015)
    Nature Publishing Group (NPG)
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    Publication Date: 2015-04-16
    Description: Disruption of epithelial polarity is a key event in the acquisition of neoplastic growth. JNK signalling is known to play an important part in driving the malignant progression of many epithelial tumours, although the link between loss of polarity and JNK signalling remains elusive. In a Drosophila genome-wide genetic screen designed to identify molecules implicated in neoplastic growth, we identified grindelwald (grnd), a gene encoding a transmembrane protein with homology to members of the tumour necrosis factor receptor (TNFR) superfamily. Here we show that Grnd mediates the pro-apoptotic functions of Eiger (Egr), the unique Drosophila TNF, and that overexpression of an active form of Grnd lacking the extracellular domain is sufficient to activate JNK signalling in vivo. Grnd also promotes the invasiveness of Ras(V12)/scrib(-/-) tumours through Egr-dependent Matrix metalloprotease-1 (Mmp1) expression. Grnd localizes to the subapical membrane domain with the cell polarity determinant Crumbs (Crb) and couples Crb-induced loss of polarity with JNK activation and neoplastic growth through physical interaction with Veli (also known as Lin-7). Therefore, Grnd represents the first example of a TNFR that integrates signals from both Egr and apical polarity determinants to induce JNK-dependent cell death or tumour growth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Andersen, Ditte S -- Colombani, Julien -- Palmerini, Valentina -- Chakrabandhu, Krittalak -- Boone, Emilie -- Rothlisberger, Michael -- Toggweiler, Janine -- Basler, Konrad -- Mapelli, Marina -- Hueber, Anne-Odile -- Leopold, Pierre -- England -- Nature. 2015 Jun 25;522(7557):482-6. doi: 10.1038/nature14298. Epub 2015 Apr 15.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] University of Nice-Sophia Antipolis, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [2] CNRS, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [3] INSERM, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [4] Genetics and Physiology of Growth laboratory, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France. ; Department of Experimental Oncology, European Institute of Oncology, Via Adamello 16, 20139 Milan, Italy. ; 1] University of Nice-Sophia Antipolis, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [2] CNRS, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [3] INSERM, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France [4] Death receptors Signalling and Cancer Therapy laboratory, Institute of Biology Valrose, Parc Valrose, 06108 Nice, France. ; Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25874673" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Apoptosis/genetics ; Cell Adhesion Molecules/metabolism ; Cell Division/genetics ; *Cell Polarity/genetics ; Cell Transformation, Neoplastic/genetics ; Disease Models, Animal ; Drosophila Proteins/chemistry/deficiency/genetics/*metabolism ; Drosophila melanogaster/*cytology/enzymology/genetics/*metabolism ; Female ; Humans ; JNK Mitogen-Activated Protein Kinases/metabolism ; MAP Kinase Signaling System ; Male ; Matrix Metalloproteinase 1/metabolism ; Membrane Proteins/chemistry/deficiency/genetics/*metabolism ; Molecular Sequence Data ; Neoplasm Invasiveness/genetics ; Neoplasms/enzymology/genetics/*metabolism/*pathology ; Receptors, Tumor Necrosis Factor/chemistry/genetics/*metabolism ; ras Proteins/genetics/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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    The Virgo O3 run and the impact of the environment (2022)
    IOP
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    Publication Date: 2024-05-03
    Description: Sources of geophysical noise (such as wind, sea waves and earthquakes) or of anthropogenic noise impact ground-based gravitational-wave interferometric detectors, causing transient sensitivity worsening and gaps in data taking. During the one year-long third observing run (O3: from April 01, 2019 to March 27, 2020), the Virgo Collaboration collected a statistically significant dataset, used in this article to study the response of the detector to a variety of environmental conditions. We correlated environmental parameters to global detector performance, such as observation range, duty cycle and control losses. Where possible, we identified weaknesses in the detector that will be used to elaborate strategies in order to improve Virgo robustness against external disturbances for the next data taking period, O4, currently planned to start at the end of 2022. The lessons learned could also provide useful insights for the design of the next generation of ground-based interferometers.
    Description: Published
    Description: 235009
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Keywords: Gravitational waves ; ambient noise ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Inscuteable and NuMA proteins bind competitively to Leu-Gly-Asn repeat-enriched protein (LGN) during asymmetric cell divisions (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-12-14
    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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  • 10
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    Increasing the Astrophysical Reach of the Advanced Virgo Detector via the Application of Squeezed Vacuum States of Light (2019)
    American Physical Society
    Details
    Publication Date: 2019-12-05
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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