The Post-Starburst Evolution of Tidal Disruption Event Host Galaxies

We constrain the recent star formation histories of the host galaxies of eight optical/UV-detected tidal disruption events (TDEs). Six hosts had quick starbursts of <200 Myr duration that ended 10 to 1000 Myr ago, indicating that TDEs arise at different times in their host's post-starburst evolution. If the disrupted star formed in the burst or before, the post-burst age constrains its mass, generally excluding O, most B, and highly massive A stars. If the starburst arose from a galaxy merger, the time since the starburst began limits the coalescence timescale and thus the merger mass ratio to more equal than 12:1 in most hosts. This uncommon ratio, if also that of the central supermassive black hole (SMBH) binary, disfavors the scenario in which the TDE rate is boosted by the binary but is insensitive to its mass ratio. The stellar mass fraction created in the burst is 0.5-10% for most hosts, not enough to explain the observed 30-200x boost in TDE rates, suggesting that the host's core stellar concentration is more important. TDE hosts have stellar masses 10^9.4 - 10^10.3 Msun, consistent with the SDSS volume-corrected, quiescent Balmer-strong comparison sample and implying SMBH masses of 10^5.5 - 10^7.5 Msun. Subtracting the host absorption line spectrum, we uncover emission lines; at least five hosts have ionization sources inconsistent with star formation that instead may be related to circumnuclear gas, merger shocks, or post-AGB stars.Comment: ApJ, 835, 176 (2017

Reactions of isonitriles with [Fe₃(CO)₁₂] and [Ru₃(CO)₁₂] monitored by electrospray mass spectrometry: structural characterisation of [Fe₃(CO)₁₀(CNPh)₂] and [Ru₄(CO)₁₁(μ₃-η²-CNPh)₂(CNPh)]

The reactions of [Fe₃(CO)₁₂] or [Ru₃(CO) ₁₂] with RNC (R=Ph, C₆H₄OMe-p or CH₂SO₂C₆H₄Me-p) have been investigated using electrospray mass spectrometry. Species arising from substitution of up to six ligands were detected for [Fe₃(CO)₁₂], but the higher-substituted compounds were too unstable to be isolated. The crystal structure of [Fe₃(CO)₁₀(CNPh)₂] was determined at 150 and 298 K to show that both isonitrile ligands were trans to each other on the same Fe atom. For [Ru₃(CO)₁₂] substitution of up to three COs was found, together with the formation of higher-nuclearity clusters. [Ru₄(CO)₁₁(CNPh)₃] was structurally characterised and has a spiked-triangular Ru₄ core with two of the CNPh ligands coordinated in an unusual μ₃-η² mode. The substitution reactions of [M₃(CO)₁₂] by RNC have been investigated by electrospray mass spectrometry showing up to six COs can be replaced. [Fe₃(CO)₁₀(CNPh)₂] has both PhNC axially on the same Fe atom, and [Ru₄(CO)₁₁(μ₃-η²-CNPh)₂(CNPh)] has a spiked-triangular cluster core with two PhNC ligands in an unusual coordination mode

Strategic or Status quo-Preserving Business Exit: (How) Do CEO Turnover and Succession Matter?

Business exit has implications for a firm’s corporate strategy. Two types of exit events are distinguished: those that involve strategic change and those that are status quo-preserving. This study investigates the impact of CEO turnover and succession on strategic versus status quo-preserving business exits. Based on a sample of CEO turnover and succession events and subsequent business exits of German corporations from different industries, our results suggest that neither voluntary nor involuntary CEO turnover is relevant to business exit. In contrast, outsider succession significantly affects the likelihood of strategic business exit, while a corporation’s performance does not moderate this relationship

How Much Might Universal Health Insurance Reduce Socioeconomic Disparities in Health? A Comparison of the US and Canada

A strong association between lower socioeconomic status (SES) and worse health-- the SES-health gradient-- has been documented in many countries, but little work has compared the size of the gradient across countries. We compare the size of the income gradient in self-reported health in the US and Canada. We find that being below median income raises the likelihood that a middle aged person is in poor or fair health by about 15 percentage points in the U.S., compared to less than 8 percentage points in Canada. We also find that the 7 percentage point gradient difference between the two countries is reduced by about 4 percentage points after age 65, the age at which the virtually all U.S. citizens receive basic health insurance through Medicare. Income disparities in the probability that an individual lacks a usual source of care are also significantly larger in the US than in Canada before the age of 65, but about the same after 65. Our results are therefore consistent with the availability of universal health insurance in the U.S, or at least some other difference that occurs around the age of 65 in one country but not the other, narrowing SES differences in health between the US and Canada.

Parallelization of implicit finite difference schemes in computational fluid dynamics

Implicit finite difference schemes are often the preferred numerical schemes in computational fluid dynamics, requiring less stringent stability bounds than the explicit schemes. Each iteration in an implicit scheme involves global data dependencies in the form of second and higher order recurrences. Efficient parallel implementations of such iterative methods are considerably more difficult and non-intuitive. The parallelization of the implicit schemes that are used for solving the Euler and the thin layer Navier-Stokes equations and that require inversions of large linear systems in the form of block tri-diagonal and/or block penta-diagonal matrices is discussed. Three-dimensional cases are emphasized and schemes that minimize the total execution time are presented. Partitioning and scheduling schemes for alleviating the effects of the global data dependencies are described. An analysis of the communication and the computation aspects of these methods is presented. The effect of the boundary conditions on the parallel schemes is also discussed

APPALACHIAN BRIDGES TO THE BACCALAUREATE: HOW COMMUNITY COLLEGES AFFECT TRANSFER SUCCESS

Statement of the problem. Too few community college students who intend to transfer and earn a baccalaureate degree actually do. This is a problem because postsecondary education is a key factor in economic mobility, and community colleges enroll a disproportionate number of nontraditional, part-time and low-income students. Although individual factors must be considered by community colleges, they often are out of the control of the institution. This study focused on the institutional factors, including the ways that organizational structures contribute to the success of a community college’s transfer program. Design. This companion study was conducted by a four-member research team. In order to describe the transfer population and institutional characteristics, a quantitative analysis was conducted for the student population, which included 338 spring and summer 2009 Associate in Arts and/or Associate in Science (AA/AS) graduates from four Appalachian community colleges. This analysis indicated that individual student characteristics did not explain the differences in institutional transfer rates. Two of the institutions were identified as statistically significant institutions promoting transfer success. Students from these high-impact community colleges were found to be at least two times more likely to transfer than students attending the low-impact institutions. Each member of the research team looked at a different aspect of the transfer experiences of the cohort. Two components explored institutional perspectives by interviewing 27 faculty, staff, and leaders from the four community colleges. The other two components examined student perceptions of their community college transfer experiences. Major conclusions. One component of the companion study examined the interplay of informal and formal organizational structures of community colleges in the context of successful transfer. A typology model was created to illustrate the interface of structural elements that plays a role in the differentiation between high-impact and low-impact institutions. Findings indicated that two elements seem to make a difference in a community college’s ability to impact successful transfer: (a) the existence of strong internal and external ties, and (b) the level of integration of transfer services

Proof of Luck: an Efficient Blockchain Consensus Protocol

In the paper, we present designs for multiple blockchain consensus primitives and a novel blockchain system, all based on the use of trusted execution environments (TEEs), such as Intel SGX-enabled CPUs. First, we show how using TEEs for existing proof of work schemes can make mining equitably distributed by preventing the use of ASICs. Next, we extend the design with proof of time and proof of ownership consensus primitives to make mining energy- and time-efficient. Further improving on these designs, we present a blockchain using a proof of luck consensus protocol. Our proof of luck blockchain uses a TEE platform's random number generation to choose a consensus leader, which offers low-latency transaction validation, deterministic confirmation time, negligible energy consumption, and equitably distributed mining. Lastly, we discuss a potential protection against up to a constant number of compromised TEEs.Comment: SysTEX '16, December 12-16, 2016, Trento, Ital