867 research outputs found

    The Consequences of Structural Racism, Concentrated Poverty, and Violence on Young Men and Boys of Color

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    Defining violence broadly as "systemic injury directed against a group or geographic area," this research brief describes the scope of violence that black young men and boys face as a result of structural conditions. It recommends policy for addressing both the root causes of violence and the trauma that people are facing right now

    On equal-input and monotone Markov matrices

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    The classes of equal-input and of monotone Markov matrices are revisited, with special focus on embeddability, infinite divisibility, and mutual relations. Several uniqueness results for the embedding problem are obtained in the process. We employ various algebraic and geometric tools, including commutativity, permutation invariance and convexity. Of particular relevance in several demarcation results are Markov matrices that are idempotents.Comment: 30 page

    Lie Markov models with purine/pyrimidine symmetry

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    Continuous-time Markov chains are a standard tool in phylogenetic inference. If homogeneity is assumed, the chain is formulated by specifying time-independent rates of substitutions between states in the chain. In applications, there are usually extra constraints on the rates, depending on the situation. If a model is formulated in this way, it is possible to generalise it and allow for an inhomogeneous process, with time-dependent rates satisfying the same constraints. It is then useful to require that there exists a homogeneous average of this inhomogeneous process within the same model. This leads to the definition of "Lie Markov models", which are precisely the class of models where such an average exists. These models form Lie algebras and hence concepts from Lie group theory are central to their derivation. In this paper, we concentrate on applications to phylogenetics and nucleotide evolution, and derive the complete hierarchy of Lie Markov models that respect the grouping of nucleotides into purines and pyrimidines -- that is, models with purine/pyrimidine symmetry. We also discuss how to handle the subtleties of applying Lie group methods, most naturally defined over the complex field, to the stochastic case of a Markov process, where parameter values are restricted to be real and positive. In particular, we explore the geometric embedding of the cone of stochastic rate matrices within the ambient space of the associated complex Lie algebra. The whole list of Lie Markov models with purine/pyrimidine symmetry is available at http://www.pagines.ma1.upc.edu/~jfernandez/LMNR.pdf.Comment: 32 page

    The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary Studies of the Nova Outburst

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    The observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One of the more important sources of uncertainty is the nuclear reaction data used as input for the evolutionary calculations. A recent paper by Starrfield, Truran, Wiescher, & Sparks (1998) has demonstrated that changes in the reaction rate library used within a nova simulation have significant effects, not just on the production of individual isotopes (which can change by an order of magnitude), but on global observables such as the peak luminosity and the amount of mass ejected. We present preliminary results of systematic analyses of the impact of reaction rate uncertainties on nova nucleosynthesis.Comment: 4 pages, 3 figures. to appear in "Cosmic Explosions", proceeding of the 10th Annual October Astrophysics Conference in Maryland (ed. S.S. Holt and W. W. Zhang

    Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?

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    Subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet, and it is important to understand how they are linked offshore from river mouths. Previously, it was thought that slope failures or direct plunging of river floodwater (hyperpycnal flow) dominated the triggering of turbidity currents on delta fronts. Here we reanalyze the most detailed time‐lapse monitoring yet of a submerged delta; comprising 93 surveys of the Squamish Delta in British Columbia, Canada. We show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes, rather than landslides or hyperpycnal flows. Turbidity currents triggered by settling plumes occur frequently, run out as far as landslide‐triggered events, and cause the greatest changes to delta and lobe morphology. For the first time, we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

    FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs

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    We present medium-resolution z-, J-, and H-band spectra of four late-type dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine the origin of numerous weak absorption features throughout their near-infrared spectra, and motivated by the recent tentative identification of the E 4\Pi- A ^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have compared the dwarf spectra to a laboratory FeH emission spectrum. We have identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra of the dwarfs. In particular, we have identified 34 features which dominate the appearance of the H-band spectra of the dwarfs and which appear in the laboratory FeH spectrum. Finally, all of the features are either weaker or absent in the spectrum of the L7.5 dwarf which is consistent with the weakening of the known FeH bandheads in the spectra of the latest L dwarfs.Comment: accepted by Ap

    Panel: COVID-19 Challenges to Project Management

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    COVID-19 has presented many new challenges and new opportunities for project management professionals and IT leaders. This panel will address these challenges and identify project management best practices and processes which have been effective in meeting these challenges. The panelists will share specific instances and challenges explaining how Project Cost Management, Time Management, Risk Management, Human Resources Management, and Risk Management have enabled them to manage during the pandemic and as a part of “return-to-work” scenarios. Hearing from these leaders as they accomplish digital transformations for their businesses and organizations will be an opportunity to bridge the gap between research and practice and to establish a dialogue between academic leaders and IT industry leaders which will provide many new questions to come
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