Numerical Models of Binary Neutron Star System Mergers. I.: Numerical Methods and Equilibrium Data for Newtonian Models

The numerical modeling of binary neutron star mergers has become a subject of much interest in recent years. While a full and accurate model of this phenomenon would require the evolution of the equations of relativistic hydrodynamics along with the Einstein field equations, a qualitative study of the early stages on inspiral can be accomplished by either Newtonian or post-Newtonian models, which are more tractable. In this paper we offer a comparison of results from both rotating and non-rotating (inertial) frame Newtonian calculations. We find that the rotating frame calculations offer significantly improved accuracy as compared with the inertial frame models. Furthermore, we show that inertial frame models exhibit significant and erroneous angular momentum loss during the simulations that leads to an unphysical inspiral of the two neutron stars. We also examine the dependence of the models on initial conditions by considering initial configurations that consist of spherical neutron stars as well as stars that are in equilibrium and which are tidally distorted. We compare our models those of Rasio & Shapiro (1992,1994a) and New & Tohline (1997). Finally, we investigate the use of the isolated star approximation for the construction of initial data.Comment: 32 pages, 19 gif figures, manuscript with postscript figures available at http://www.astro.sunysb.edu/dswesty/docs/nspap1.p

Effects Of Sample Orientation On The Corrosion Of Zinc In Ammonium Sulfate And Sodium Hydroxide Solutions

The corrosion and electrochemical properties of three zinc single crystal surfaces with different orientations have been investigated. In near-neutral 1 M (NH4)2SO4, the corrosion rates on all three surfaces were found to be similar. However, the SEM morphologies of the corresponding corroded surfaces were markedly different from each other, but consistent with preferential attack of {1120} surfaces. In alkaline 0.5 N NaOH solution, the three sample orientations showed significantly different reactivities, with the (1120) surface exhibiting the highest reactivity and corrosion rate. Here, passivation ultimately occurred and the difference in the corrosion performance of the three surfaces, even for small overvoltages, is attributed to the presence of oxide or hydrated oxide films. © 1991

The electronic properties of bilayer graphene

We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energy. We take into account five tight-binding parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure

Supermassive black holes with high accretion rates in active galactic nuclei. XIII. Ultraviolet time lag of Hβ emission in Mrk 142

Funding: We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grant RGPIN/04157. V.C.K. acknowledges the support of the Ontario Graduate Scholarships. C.H. acknowledges support from the National Science Foundation of China (12122305). The research of V.C.K. was partially supported by the New Technologies for Canadian Observatories, an NSERC CREATE program.We performed a rigorous reverberation-mapping analysis of the broad-line region (BLR) in a highly accreting (L/LEdd = 0.74–3.4) active galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent observations of the inner accretion disk and the BLR to determine a time lag for the Hβ λ4861 emission relative to the ultraviolet (UV) continuum variations. We used continuum data taken with the Niel Gehrels Swift Observatory in the UVW2 band, and the Las Cumbres Observatory, Dan Zowada Memorial Observatory, and Liverpool Telescope in the g band, as part of the broader Mrk 142 multi-wavelength monitoring campaign in 2019. We obtained new spectroscopic observations covering the Hβ broad emission line in the optical from the Gemini North Telescope and the Lijiang 2.4-meter Telescope for a total of 102 epochs (over a period of eight months) contemporaneous to the continuum data. Our primary result states a UV-to-Hβ time lag of 8.68+0.75−0.72 days in Mrk 142 obtained from light-curve analysis with a Python-based Running Optimal Average algorithm. We placed our new measurements for Mrk 142 on the optical and UV radius-luminosity relations for NGC 5548 to understand the nature of the continuum driver. The positions of Mrk 142 on the scaling relations suggest that UV is closer to the “true” driving continuum than the optical. Furthermore, we obtain log(M•/M⊙) = 6.32 ± 0.29 assuming UV as the primary driving continuum.Publisher PDFPeer reviewe

W_{1+\infty} and W(gl_N) with central charge N

We study representations of the central extension of the Lie algebra of differential operators on the circle, the W-infinity algebra. We obtain complete and specialized character formulas for a large class of representations, which we call primitive; these include all quasi-finite irreducible unitary representations. We show that any primitive representation with central charge N has a canonical structure of an irreducible representation of the W-algebra W(gl_N) with the same central charge and that all irreducible representations of W(gl_N) with central charge N arise in this way. We also establish a duality between "integral" modules of W(gl_N) and finite-dimensional irreducible modules of gl_N, and conjecture their fusion rules.Comment: 29 pages, Latex, uses file amssym.def (a few remarks added, typos corrected

A Local Proinflammatory Signalling Loop Facilitates Adverse Age-Associated Arterial Remodeling

Background: The coincidence of vascular smooth muscle cells (VSMC) infiltration and collagen deposition within a diffusely thickened intima is a salient feature of central arterial wall inflammation that accompanies advancing age. However, the molecular mechanisms involved remain undefined. Methodology/Principal Findings: Immunostaining and immunoblotting of rat aortae demonstrate that a triad of proinflammatory molecules, MCP-1, TGF-b1, and MMP-2 increases within the aortic wall with aging. Exposure of VSMC isolated from 8-mo-old rats (young) to MCP-1 effects, via CCR-2 signaling, both an increase in TGF-b1 activity, up to levels of untreated VSMC from 30-mo-old (old) rats, and a concurrent increase in MMP-2 activation. Furthermore, exposure of young VSMC to TGF-b1 increases levels of MCP-1, and MMP-2 activation, to levels of untreated VSMC from old rats. This autocatalytic signaling loop that enhances collagen production and invasiveness of VSMC is effectively suppressed by si-MCP-1, a CCR2 antagonist, or MMP-2 inhibition. Conclusions/Significance: Threshold levels of MCP-1, MMP-2, or TGF-b1 activity trigger a feed-forward signaling mechanism that is implicated in the initiation and progression of adverse age-associated arterial wall remodeling. Intervention that suppressed this signaling loop may potentially retard age-associated adverse arterial remodeling