6,017 research outputs found
Black holes in the low mass gap: Implications for gravitational wave observations
Binary neutron-star mergers will predominantly produce black-hole remnants of
mass , thus populating the putative \emph{low mass gap}
between neutron stars and stellar-mass black holes. If these low-mass black
holes are in dense astrophysical environments, mass segregation could lead to
"second-generation" compact binaries merging within a Hubble time. In this
paper, we investigate possible signatures of such low-mass compact binary
mergers in gravitational-wave observations. We show that this unique population
of objects, if present, will be uncovered by the third-generation
gravitational-wave detectors, such as Cosmic Explorer and Einstein Telescope.
Future joint measurements of chirp mass and effective spin
could clarify the formation scenario of compact objects in the
low mass gap. As a case study, we show that the recent detection of GW190425
(along with GW170817) favors a double Gaussian mass model for neutron stars,
under the assumption that the primary in GW190425 is a black hole formed from a
previous binary neutron star merger.Comment: 8 pages, 4 figures, 1 table. v4: matches the version accepted for
publication in Phys. Rev.
Spazio pubblico e attrattivitĂ urbana. L'Isola e le sue piazze
LâIsola e le sue piazze è un progetto di valorizzazione urbana
integrata promosso nel gennaio 2015 da Comune di Milano,
Regione Lombardia e Distretto urbano del commercio Isola,
volto a promuovere lâidentitĂ del quartiere Isola, attraverso
la realizzazione di arredi temporanei, eventi e un piano di
comunicazione.
Entro tale contesto, un gruppo multidisciplinare di ricerca
del Politecnico di Milano afferente ai dipartimenti di
Architettura e Studi Urbani e di Design, attraverso mappature
e rilievi, osservazione diretta e interviste, ha condotto
un lavoro di accompagnamento e monitoraggio della proposta
risultata vincitrice del bando pubblico.
Il volume restituisce gli esiti della ricerca: descrive lo sfondo
entro cui è maturato il progetto, racconta le specificità del
quartiere, la qualitĂ del suo spazio pubblico, le geografie
dellâofferta economica. I testi degli autori della ricerca si
intrecciano alle voci di abitanti, di testimoni privilegiati, di
rappresentanti delle istituzioni e dellâassociazionismo
locale che a vario titolo sono stati coinvolti dal progetto, con
lâobiettivo di riflettere sulle molteplici dimensioni dello
spazio pubblico e dellâattrattivitĂ urbana: dagli usi formali e
informali ai servizi commerciali di prossimitĂ , dagli eventi
che hanno avuto luogo nel periodo osservato alle dinamiche
che hanno innescato, fino agli esiti di un inedito bando e alle
opportunitĂ della sua replicabilitĂ
Spin alignment and differential accretion in merging black hole binaries
Interactions between a supermassive black hole binary and the surrounding
accretion disc can both assist the binary inspiral and align the black hole
spins to the disc angular momentum. While binary migration is due to
angular-momentum transfer within the circumbinary disc, the spin-alignment
process is driven by the mass accreting on to each black hole. Mass transfer
between different disc components thus couples the inspiral and the alignment
process together. Mass is expected to leak through the cavity cleared by the
binary, and preferentially accretes on to the lighter (secondary) black hole
which orbits closer to the disc edge. Low accretion rate on to the heavier
(primary) black hole slows the alignment process down. We revisit the problem
and develop a semi-analytical model to describe the coupling between gas-driven
inspiral and spin alignment, finding that binaries with mass ratio q<~0.2
approach the gravitational-wave driven inspiral in differential misalignment:
light secondaries prevent primaries from aligning. Binary black holes with
misaligned primaries are ideal candidates for precession effects in the
strong-gravity regime and may suffer from moderately large (~1500 km/s) recoil
velocities.DG is supported by the UK Science and Technology Facility Council and the Isaac Newton Studentship of the University of Cambridge; partial support is also acknowledged from FP7-PEOPLE-2011-CIG Grant No. 293412, FP7-PEOPLE-2011-IRSES Grant No.295189, SDSC and TACC through XSEDE Grant No. PHY-090003 by the NSF, Finis Terrae through Grant No. ICTS-CESGA-249, ERC-2013-ADG Grant No. 341137, STFC Roller Grant No. ST/L000636/1 and DiRACâs Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv121
Detection and attribution of an anomaly in terrestrial photosynthesis in Europe during the COVID-19 lockdown
Carbon dioxide (CO2) uptake by plant photosynthesis, referred to as gross primary production (GPP) at the ecosystem level, is sensitive to environmental factors, including pollutant exposure, pollutant uptake, and changes in the scattering of solar shortwave irradiance (SWin) â the energy source for photosynthesis. The 2020 spring lockdown due to COVID-19 resulted in improved air quality and atmospheric transparency, providing a unique opportunity to assess the impact of air pollutants on terrestrial ecosystem functioning. However, detecting these effects can be challenging as GPP is influenced by other meteorological drivers and management practices. Based on data collected from 44 European ecosystem-scale CO2 flux monitoring stations, we observed significant changes in spring GPP at 34 sites during 2020 compared to 2015â2019. Among these, 14 sites showed an increase in GPP associated with higher SWin, 10 sites had lower GPP linked to atmospheric and soil dryness, and seven sites were subjected to management practices. The remaining three sites exhibited varying dynamics, with one experiencing colder and rainier weather resulting in lower GPP, and two showing higher GPP associated with earlier spring melts. Analysis using the regional atmospheric chemical transport model (LOTOS-EUROS) indicated that the ozone (O3) concentration remained relatively unchanged at the research sites, making it unlikely that O3 exposure was the dominant factor driving the primary production anomaly. In contrast, SWin increased by 9.4 % at 36 sites, suggesting enhanced GPP possibly due to reduced aerosol optical depth and cloudiness. Our findings indicate that air pollution and cloudiness may weaken the terrestrial carbon sink by up to 16 %. Accurate and continuous ground-based observations are crucial for detecting and attributing subtle changes in terrestrial ecosystem functioning in response to environmental and anthropogenic drivers
Accuracy of dielectric-dependent hybrid functionals in the prediction of optoelectronic properties of metal oxide semiconductors: a comprehensive comparison with many-body GW and experiments
Understanding the electronic structure of metal oxide semiconductors is crucial to their numerous technological applications, such as photoelectrochemical water splitting and solar cells. The needed experimental and theoretical knowledge goes beyond that of pristine bulk crystals, and must include the effects of surfaces and interfaces, as well as those due to the presence of intrinsic defects (e.g. oxygen vacancies), or dopants for band engineering. In this review, we present an account of the recent efforts in predicting and understanding the optoelectronic properties of oxides using ab initio theoretical methods. In particular, we discuss the performance of recently developed dielectric-dependent hybrid functionals, providing a comparison against the results of many-body GW calculations, including G 0 W 0 as well as more refined approaches, such as quasiparticle self-consistent GW. We summarize results in the recent literature for the band gap, the band level alignment at surfaces, and optical transition energies in defective oxides, including wide gap oxide semiconductors and transition metal oxides. Correlated transition metal oxides are also discussed. For each method, we describe successes and drawbacks, emphasizing the challenges faced by the development of improved theoretical approaches. The theoretical section is preceded by a critical overview of the main experimental techniques needed to characterize the optoelectronic properties of semiconductors, including absorption and reflection spectroscopy, photoemission, and scanning tunneling spectroscopy (STS)
Homologation of the Fischer Indolization: A Quinoline Synthesis via HomoâDiazaâCope Rearrangement
We disclose a new Brønsted acid promoted quinoline synthesis, proceeding via homoâdiazaâCope rearrangement of NâarylâNâ˛âcyclopropyl hydrazines. Our strategy can be considered a homologation of Fischer's classical indole synthesis and delivers 6âmembered Nâheterocycles, including previously inaccessible pyridine derivatives. This approach can also be used as a pyridannulation methodology toward constructing polycyclic polyheteroaromatics. A computational analysis has been employed to probe plausible activation modes and to interrogate the role of the catalyst
Fatigue behavior of foreign object damaged 7075 heat treated aluminum alloy coated with PVD WC/C
AbstractThe effect of a physically vapor deposited (PVD) WC/C coating on the fatigue behavior of as produced and foreign object damaged (FOD) solution heat treated and aged 7075 aluminum alloy was studied. Coated and uncoated samples were tested under rotating bending to determine the fatigue strengths between 104 and 106 cycles in both damaged and smooth condition. FOD was produced with single shots of small hard steel spheres impacting at 100 m/s in the minimum cross section. SEM was used to characterize the features of the fracture surfaces
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