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https://www.readbyqxmd.com/read/29341767/dynamics-of-dwarf-galaxies-disfavor-stellar-mass-black-holes-as-dark-matter
#1
Savvas M Koushiappas, Abraham Loeb
We study the effects of black hole dark matter on the dynamical evolution of stars in dwarf galaxies. We find that mass segregation leads to a depletion of stars in the center of dwarf galaxies and the appearance of a ring in the projected stellar surface density profile. Using Segue 1 as an example we show that current observations of the projected surface stellar density rule out at the 99.9% confidence level the possibility that more than 6% of the dark matter is composed of black holes with a mass of few tens of solar masses...
July 28, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29341737/superradiant-instability-and-backreaction-of-massive-vector-fields-around-kerr-black-holes
#2
William E East, Frans Pretorius
We study the growth and saturation of the superradiant instability of a complex, massive vector (Proca) field as it extracts energy and angular momentum from a spinning black hole, using numerical solutions of the full Einstein-Proca equations. We concentrate on a rapidly spinning black hole (a=0.99) and the dominant m=1 azimuthal mode of the Proca field, with real and imaginary components of the field chosen to yield an axisymmetric stress-energy tensor and, hence, spacetime. We find that in excess of 9% of the black hole's mass can be transferred into the field...
July 28, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29341709/probing-primordial-black-hole-dark-matter-with-gravitational-waves
#3
Ely D Kovetz
Primordial black holes (PBHs) have long been suggested as a candidate for making up some or all of the dark matter in the Universe. Most of the theoretically possible mass range for PBH dark matter has been ruled out with various null observations of expected signatures of their interaction with standard astrophysical objects. However, current constraints are significantly less robust in the 20  M_{⊙}≲M_{PBH}≲100  M_{⊙} mass window, which has received much attention recently, following the detection of merging black holes with estimated masses of ∼30  M_{⊙} by LIGO and the suggestion that these could be black holes formed in the early Universe...
September 29, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29341674/stochastic-and-resolvable-gravitational-waves-from-ultralight-bosons
#4
Richard Brito, Shrobana Ghosh, Enrico Barausse, Emanuele Berti, Vitor Cardoso, Irina Dvorkin, Antoine Klein, Paolo Pani
Ultralight scalar fields around spinning black holes can trigger superradiant instabilities, forming a long-lived bosonic condensate outside the horizon. We use numerical solutions of the perturbed field equations and astrophysical models of massive and stellar-mass black hole populations to compute, for the first time, the stochastic gravitational-wave background from these sources. In optimistic scenarios the background is observable by Advanced LIGO and LISA for field masses m_{s} in the range ∼[2×10^{-13},10^{-12}] and ∼5×[10^{-19},10^{-16}]  eV, respectively, and it can affect the detectability of resolvable sources...
September 29, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29338907/new-photodynamic-molecular-beacons-pmb-as-potential-cancer-targeted-agents-in-pdt
#5
Aurélie Stallivieri, Ludovic Colombeau, Jérôme Devy, Nicolas Etique, Carine Chaintreuil, Bauyrzhan Myrzakhmetov, Mathilde Achard, Francis Baros, Philippe Arnoux, Régis Vanderesse, Céline Frochot
Further improvements in Photodynamic therapy (PDT) necessitate that the dye targets more selectively tumour tissues or neovascularization than healthy cells. Different enzymes such as matrix metalloproteinases (MMPs) are overexpressed in tumour areas. Among these MMPs, gelatinases (MMP-2 and MMP-9) and its activator MMP-14 are known to play a key role in tumour angiogenesis and the growth of many cancers such as glioblastoma multiforme (GBM), an aggressive malignant tumour of the brain. These last years, the concept of photodynamic molecular beacons (PMB) became interesting for controlling the photosensitizer's ability to generate singlet oxygen (1O2) close to target biomolecules as MMPs...
December 24, 2017: Bioorganic & Medicinal Chemistry
https://www.readbyqxmd.com/read/29337944/the-first-monster-black-holes
#6
Priyamvada Natarajan
No abstract text is available yet for this article.
January 16, 2018: Scientific American
https://www.readbyqxmd.com/read/29328736/dynamical-formation-of-kerr-black-holes-with-synchronized-hair-an-analytic-model
#7
Carlos A R Herdeiro, Eugen Radu
East and Pretorius have successfully evolved, using fully nonlinear numerical simulations, the superradiant instability of the Kerr black hole (BH) triggered by a massive, complex vector field. Evolutions terminate in stationary states of a vector field condensate synchronized with a rotating BH horizon. We show that these end points are fundamental states of Kerr BHs with synchronized Proca hair. Motivated by the "experimental data" from these simulations, we suggest a universal (i.e., field-spin independent), analytic model for the subset of BHs with synchronized hair that possess a quasi-Kerr horizon, applicable in the weak hair regime...
December 29, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29328720/real-time-dynamics-and-phase-separation-in-a-holographic-first-order-phase-transition
#8
Romuald A Janik, Jakub Jankowski, Hesam Soltanpanahi
We study the fully nonlinear time evolution of a holographic system possessing a first order phase transition. The initial state is chosen in the spinodal region of the phase diagram, and it includes an inhomogeneous perturbation in one of the field theory directions. The final state of the time evolution shows a clear phase separation in the form of domain formation. The results indicate the existence of a very rich class of inhomogeneous black hole solutions.
December 29, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29328688/astrometric-search-method-for-individually-resolvable-gravitational-wave-sources-with-gaia
#9
Christopher J Moore, Deyan P Mihaylov, Anthony Lasenby, Gerard Gilmore
Gravitational waves (GWs) cause the apparent position of distant stars to oscillate with a characteristic pattern on the sky. Astrometric measurements (e.g., those made by Gaia) provide a new way to search for GWs. The main difficulty facing such a search is the large size of the data set; Gaia observes more than one billion stars. In this Letter the problem of searching for GWs from individually resolvable supermassive black hole binaries using astrometry is addressed for the first time; it is demonstrated how the data set can be compressed by a factor of more than 10^{6}, with a loss of sensitivity of less than 1%...
December 29, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29327284/treatment-of-multiple-sclerosis-relapses-with-high-dose-methylprednisolone-reduces-the-evolution-of-contrast-enhancing-lesions-into-persistent-black-holes
#10
Maria Di Gregorio, Lorenzo Gaetani, Paolo Eusebi, Piero Floridi, Antonella Picchioni, Giovanni Rosi, Andrea Mancini, Chiara Floridi, Francesca Baschieri, Lucia Gentili, Paola Sarchielli, Paolo Calabresi, Massimiliano Di Filippo
INTRODUCTION: The MRI evidence of persistent black holes (pBHs) on T1-weighted images reflects brain tissue loss in multiple sclerosis (MS). The evolution of contrast-enhancing lesions (CELs) into pBHs probably depends on the degree and persistence of focal brain inflammation. The aim of our retrospective study was to evaluate the effect of a single cycle of intravenous methylprednisolone (IVMP), as for MS relapse treatment, on the risk of CELs' evolution into pBHs. PATIENTS AND METHODS: We selected 57 patients with CELs on the baseline MRI scan...
January 11, 2018: Journal of Neurology
https://www.readbyqxmd.com/read/29324930/characteristics-socioeconomic-status-and-ethnic-variations-of-primary-idiopathic-macular-hole-repair-in-vitreoretinal-centers-in-the-united-kingdom
#11
M Vasalaki, E Papavasileiou, S Velissaris, C Garnavou-Xirou, V Zygoura, O Theodorou, R Zakir, G Duguid, T Sandinha, D Steel, T L Jackson
OBJECTIVE: The purpose of this multicentre retrospective study was to investigate the characteristics and role of ethnicity and socioeconomic status amongst patients with idiopathic macular holes (IMH) and the surgical outcome. SUBJECTS AND METHOD: Consecutive patients undergoing primary IMH surgery at three vitreoretinal units in the UK (King's College Hospital, London, UK, Western Eye Hospital, London, UK, Sunderland Eye Infirmary, Sunderland, UK) between January 2007 and May 2017 were included...
September 2017: Hellenic Journal of Nuclear Medicine
https://www.readbyqxmd.com/read/29324418/niqsv-a-no-reference-synthesized-view-quality-assessment-metric
#12
Shishun Tian, Lu Zhang, Luce Morin, Olivier Deforges
Benefiting from multi-view video plus depth and depth-image-based-rendering technologies, only limited views of a real 3-D scene need to be captured, compressed, and transmitted. However, the quality assessment of synthesized views is very challenging, since some new types of distortions, which are inherently different from the texture coding errors, are inevitably produced by view synthesis and depth map compression, and the corresponding original views (reference views) are usually not available. Thus the full-reference quality metrics cannot be used for synthesized views...
April 2018: IEEE Transactions on Image Processing: a Publication of the IEEE Signal Processing Society
https://www.readbyqxmd.com/read/29323686/negative-poisson-s-ratio-and-high-mobility-transport-anisotropy-in-sic6-siligraphene
#13
Xiaobiao Liu, Xiaofei Shao, Bo Yang, Mingwen Zhao
The diverse forms of silicon carbides lead to versatile properties, but an auxetic allotrope at zero pressure has never been reported. Here, using first-principles calculations we propose a two-dimensional (2D) auxetic silicon carbide material, namely SiC6 siligraphene. The plausibility of the SiC6 siligraphene is verified by the low formation energy, positive phonon spectrum and high mechanical stability. The unique framework of sp2 carbon and sp3 silicon atoms leads to unusual in-plane negative Poisson's ratios and electronic properties superior to both graphene and silicene...
January 11, 2018: Nanoscale
https://www.readbyqxmd.com/read/29323456/tuning-the-carrier-confinement-in-ges-phosphorene-van-der-waals-heterostructures
#14
Chan Wang, Lei Peng, Qi Qian, Jinyan Du, Sufan Wang, Yucheng Huang
Van der Waals (vdW) heterostructures, which have the advantage of integrating excellent properties of the stacked 2D materials by vdW interactions, have gained increasing attention recently. In this work, within the framework of density functional theory calculations, the electronic properties of vdW heterostructure composed of phosphorene (BP) in black phosphorus phase and GeS monolayer are systematically explored. The results show that the carriers are not separated for both lattice-match and lattice-mismatch heterostructures...
January 11, 2018: Small
https://www.readbyqxmd.com/read/29323297/an-extreme-magneto-ionic-environment-associated-with-the-fast-radio-burst-source-frb-121102
#15
D Michilli, A Seymour, J W T Hessels, L G Spitler, V Gajjar, A M Archibald, G C Bower, S Chatterjee, J M Cordes, K Gourdji, G H Heald, V M Kaspi, C J Law, C Sobey, E A K Adams, C G Bassa, S Bogdanov, C Brinkman, P Demorest, F Fernandez, G Hellbourg, T J W Lazio, R S Lynch, N Maddox, B Marcote, M A McLaughlin, Z Paragi, S M Ransom, P Scholz, A P V Siemion, S P Tendulkar, P Van Rooy, R S Wharton, D Whitlow
Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin. The only known repeating fast radio burst source-FRB 121102-has been localized to a star-forming region in a dwarf galaxy at redshift 0.193 and is spatially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1...
January 10, 2018: Nature
https://www.readbyqxmd.com/read/29318984/a-brief-history-of-shigella
#16
Keith A Lampel, Samuel B Formal, Anthony T Maurelli
The history of Shigella, the causative agent of bacillary dysentery, is a long and fascinating one. This brief historical account starts with descriptions of the disease and its impact on human health from ancient time to the present. Our story of the bacterium starts just before the identification of the dysentery bacillus by Kiyoshi Shiga in 1898 and follows the scientific discoveries and principal scientists who contributed to the elucidation of Shigella pathogenesis in the first 100 years. Over the past century, Shigella has proved to be an outstanding model of an invasive bacterial pathogen and has served as a paradigm for the study of other bacterial pathogens...
January 2018: EcoSal Plus
https://www.readbyqxmd.com/read/29314299/quasi-monolayer-black-phosphorus-with-high-mobility-and-air-stability
#17
Sherman Jun Rong Tan, Ibrahim Abdelwahab, Leiqiang Chu, Sock Mui Poh, Yanpeng Liu, Jiong Lu, Wei Chen, Kian Ping Loh
Black phosphorus (BP) exhibits thickness-dependent band gap and high electronic mobility. The chemical intercalation of BP with alkali metal has attracted attention recently due to the generation of universal superconductivity regardless of the type of alkali metals. However, both ultrathin BP, as well as alkali metal-intercalated BP, are highly unstable and corrode rapidly under ambient conditions. This study demonstrates that alkali metal hydride intercalation decouples monolayer to few layers BP from the bulk BP, allowing an optical gap of ≈1...
January 3, 2018: Advanced Materials
https://www.readbyqxmd.com/read/29303345/implications-of-the-neutron-star-merger-gw170817-for-cosmological-scalar-tensor-theories
#18
Jeremy Sakstein, Bhuvnesh Jain
The LIGO and VIRGO Collaborations have recently announced the detection of gravitational waves from a neutron star-neutron star merger (GW170817) and the simultaneous measurement of an optical counterpart (the γ-ray burst GRB 170817A). The close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about 1 part in 10^{15}. This has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to the Λ cold dark matter model...
December 22, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29303335/light-ring-stability-for-ultracompact-objects
#19
Pedro V P Cunha, Emanuele Berti, Carlos A R Herdeiro
We prove the following theorem: axisymmetric, stationary solutions of the Einstein field equations formed from classical gravitational collapse of matter obeying the null energy condition, that are everywhere smooth and ultracompact (i.e., they have a light ring) must have at least two light rings, and one of them is stable. It has been argued that stable light rings generally lead to nonlinear spacetime instabilities. Our result implies that smooth, physically and dynamically reasonable ultracompact objects are not viable as observational alternatives to black holes whenever these instabilities occur on astrophysically short time scales...
December 22, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29303299/impact-of-bayesian-priors-on-the-characterization-of-binary-black-hole-coalescences
#20
Salvatore Vitale, Davide Gerosa, Carl-Johan Haster, Katerina Chatziioannou, Aaron Zimmerman
In a regime where data are only mildly informative, prior choices can play a significant role in Bayesian statistical inference, potentially affecting the inferred physics. We show this is indeed the case for some of the parameters inferred from current gravitational-wave measurements of binary black hole coalescences. We reanalyze the first detections performed by the twin LIGO interferometers using alternative (and astrophysically motivated) prior assumptions. We find different prior distributions can introduce deviations in the resulting posteriors that impact the physical interpretation of these systems...
December 22, 2017: Physical Review Letters
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