This article provides an overview of research on race-related stressors that can affect the mental health of socially disadvantaged racial and ethnic populations. It begins by reviewing the research ...on self-reported discrimination and mental health. Although discrimination is the most studied aspect of racism, racism can also affect mental health through structural/institutional mechanisms and racism that is deeply embedded in the larger culture. Key priorities for research include more systematic attention to stress proliferation processes due to institutional racism, the assessment of stressful experiences linked to natural or manmade environmental crises, documenting and understanding the health effects of hostility against immigrants and people of color, cataloguing and quantifying protective resources, and enhancing our understanding of the complex association between physical and mental health.
We say an algorithm on n × n matrices with integer entries in −M,M (or n-node graphs with edge weights from −M,M) is truly subcubic if it runs in O(n3 − δ poly(log M)) time for some δ > 0. We define ...a notion of subcubic reducibility and show that many important problems on graphs and matrices solvable in O(n3) time are equivalent under subcubic reductions. Namely, the following weighted problems either all have truly subcubic algorithms, or none of them do: *The all-pairs shortest paths problem on weighted digraphs (APSP). *Detecting if a weighted graph has a triangle of negative total edge weight. *Listing up to n2.99 negative triangles in an edge-weighted graph. *Finding a minimum weight cycle in a graph of non-negative edge weights. *The replacement paths problem on weighted digraphs. *Finding the second shortest simple path between two nodes in a weighted digraph. *Checking whether a given matrix defines a metric. *Verifying the correctness of a matrix product over the (min, +)-semiring. *Finding a maximum subarray in a given matrix. Therefore, if APSP cannot be solved in n3−ε time for any ε > 0, then many other problems also need essentially cubic time. In fact, we show generic equivalences between matrix products over a large class of algebraic structures used in optimization, verifying a matrix product over the same structure, and corresponding triangle detection problems over the structure. These equivalences simplify prior work on subcubic algorithms for all-pairs path problems, since it now suffices to give appropriate subcubic triangle detection algorithms. Other consequences of our work are new combinatorial approaches to Boolean matrix multiplication over the (OR,AND)-semiring (abbreviated as BMM). We show that practical advances in triangle detection would imply practical BMM algorithms, among other results. Building on our techniques, we give two improved BMM algorithms: a derandomization of the combinatorial BMM algorithm of Bansal and Williams (FOCS’09), and an improved quantum algorithm for BMM.
starbench: the D-type expansion of an H ii region Bisbas, T. G; Haworth, T. J; Williams, R. J. R ...
Monthly notices of the Royal Astronomical Society,
10/2015, Letnik:
453, Številka:
2
Journal Article
Recenzirano
Odprti dostop
starbench is a project focused on benchmarking and validating different star formation and stellar feedback codes. In this first starbench paper we perform a comparison study of the D-type expansion ...of an H ii region. The aim of this work is to understand the differences observed between the 12 participating numerical codes against the various analytical expressions examining the D-type phase of H ii region expansion. To do this, we propose two well-defined tests which are tackled by 1D and 3D grid- and smoothed particle hydrodynamics-based codes. The first test examines the ‘early phase’ D-type scenario during which the mechanical pressure driving the expansion is significantly larger than the thermal pressure of the neutral medium. The second test examines the ‘late phase’ D-type scenario during which the system relaxes to pressure equilibrium with the external medium. Although they are mutually in excellent agreement, all 12 participating codes follow a modified expansion law that deviates significantly from the classical Spitzer solution in both scenarios. We present a semi-empirical formula combining the two different solutions appropriate to both early and late phases that agrees with high-resolution simulations to ≲ 2 per cent. This formula provides a much better benchmark solution for code validation than the Spitzer solution. The present comparison has validated the participating codes and through this project we provide a data set for calibrating the treatment of ionizing radiation hydrodynamics codes.
Although electrospun nanofibers are expanding their potential commercial applications in various fields, the issue of energy savings, which are important for cost reduction and technological ...feasibility, has received little attention to date. In this study, a concentric spinneret with a solid Teflon-core rod was developed to implement an energy-saving electrospinning process. Ketoprofen and polyvinylpyrrolidone (PVP) were used as a model of a poorly water-soluble drug and a filament-forming matrix, respectively, to obtain nanofibrous films via traditional tube-based electrospinning and the proposed solid rod-based electrospinning method. The functional performances of the films were compared through in vitro drug dissolution experiments and ex vivo sublingual drug permeation tests. Results demonstrated that both types of nanofibrous films do not significantly differ in terms of medical applications. However, the new process required only 53.9% of the energy consumed by the traditional method. This achievement was realized by the introduction of several engineering improvements based on applied surface modifications, such as a less energy dispersive air-epoxy resin surface of the spinneret, a free liquid guiding without backward capillary force of the Teflon-core rod, and a smaller fluid-Teflon adhesive force. Other non-conductive materials could be explored to develop new spinnerets offering good engineering control and energy savings to obtain low-cost electrospun polymeric nanofibers.
We built and measured the dynamical current versus time behavior of nanoscale niobium oxide crosspoint devices which exhibited threshold switching (current-controlled negative differential ...resistance). The switching speeds of 110 × 110 nm(2) devices were found to be Δt(ON) = 700 ps and Δt(OFF) = 2:3 ns while the switching energies were of the order of 100 fJ. We derived a new dynamical model based on the Joule heating rate of a thermally driven insulator-to-metal phase transition that accurately reproduced the experimental results, and employed the model to estimate the switching time and energy scaling behavior of such devices down to the 10 nm scale. These results indicate that threshold switches could be of practical interest in hybrid CMOS nanoelectronic circuits.
Current hardware approaches to biomimetic or neuromorphic artificial intelligence rely on elaborate transistor circuits to simulate biological functions. However, these can instead be more faithfully ...emulated by higher-order circuit elements that naturally express neuromorphic nonlinear dynamics
. Generating neuromorphic action potentials in a circuit element theoretically requires a minimum of third-order complexity (for example, three dynamical electrophysical processes)
, but there have been few examples of second-order neuromorphic elements, and no previous demonstration of any isolated third-order element
. Using both experiments and modelling, here we show how multiple electrophysical processes-including Mott transition dynamics-form a nanoscale third-order circuit element. We demonstrate simple transistorless networks of third-order elements that perform Boolean operations and find analogue solutions to a computationally hard graph-partitioning problem. This work paves a way towards very compact and densely functional neuromorphic computing primitives, and energy-efficient validation of neuroscientific models.
For over 100 years, thyroid hormones have been known to be essential for neonatal neurodevelopment but whether they are required by the foetal brain remains a matter of controversy. For decades, the ...prevailing view was that thyroid hormones are not necessary until after birth because circulating levels in the foetus are very low and the placenta forms an efficient barrier to their transfer from the mother. Clinical observations of good neurological outcome following early treatment of congenital hypothyroidism were used to support the view that thyroid hormones are not required early in neurodevelopment. Nevertheless, the issue remained contentious because of findings that the severity of foetal neurological deficit due to maternal iodine deficiency correlated with the degree of maternal thyroxine (T4) deficiency. Furthermore, neurological damage in these cases could be prevented by correction of maternal T4 deficiency before mid‐gestation. This observation led to the opposing view, supported by epidemiological studies of neurological cretinism, that maternal thyroid hormones are important and necessary for early foetal neurodevelopment. It is now clear that thyroid hormones are essential for both foetal and post‐natal neurodevelopment and for the regulation of neuropsychological function in children and adults. In recent years, this controversial subject has progressed very rapidly following remarkable progress in understanding of the molecular mechanisms of thyroid hormone action. This article reviews the contributions of molecular biology and genetics to our new understanding of the physiological effects of thyroid hormones on neurodevelopment and in the adult brain.
•Place research has roots in several loosely related critiques of positivist epistemologies.•Place offers a framework for comparing pluralistic positions on knowledge and meaning.•Describes inherent, ...instrumental, sociocultural, and identity layers of place meaning.•Norms for sensible place-making may be grounded in place as bios, ethnos, and demos.•Understanding place requires access to both objective and subjective views of reality.
Drawing on critical pluralism and positionality, this essay offers a four-part framework for making sense of the manifold ways place has been studied and applied to landscape planning and management. The first element highlights how diverse intellectual origins behind place research have inhibited a trans-disciplinary understanding of place as an object of study in environmental planning and management. The second focuses on ontological pluralism as found in attempts to make sense of place meanings by (a) fleshing out four layers of place meaning that vary in terms of tangibility, commonality, and emotionality and (b) critiquing four methodological approaches to identifying place meanings. The third looks at making sense of place-making as a way to highlight ontological and epistemic pluralism in studies of the material and social-discursive practices that create, govern, and transform places. In particular it draws attention to the way place meanings, knowledge, and practices are always situated or positioned. The fourth highlights axiological or normative pluralism as reflected in various prescriptive notions of place-making as the outcome of deliberate efforts of people to try to shape, contest, and/or otherwise govern the landscape. These include place as bios, ethnos, and demos as normative ideals for prescribing what constitutes a good place and underscores the challenge of adjudicating across different conceptions of sensible places. This paper concludes by reiterating the ways that place research and practice can benefit from both a critical pluralist perspective and a heightened awareness of the diverse positionalities occupied by observers of and actors in the landscape.
PDF
