9,522 research outputs found

    Interactive simulation and visualization

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    Journal ArticleMost of us perform data analysis and visualization only after everything else is finished, which often means that we don't discover errors invalidating the results of our simulation until postprocessing. A better approach would be to improve the integration of simulation and visualization into the entire process so that you can make adjustments along the way. We call this approach computational steering. Computational steering is the capacity to control all aspects of the computational science pipeline-the succession of steps required to solve computational science and engineering problems. When you interactively explore a simulation in time and space, you steer it. In this sense, you can rely on steering to assist in debugging and to modify the computational aspects of your application

    Micro-CT Image-Derived Metrics Quantify Arterial Wall Distensibility Reduction in a Rat Model of Pulmonary Hypertension

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    We developed methods to quantify arterial structural and mechanical properties in excised rat lungs and applied them to investigate the distensibility decrease accompanying chronic hypoxia-induced pulmonary hypertension. Lungs of control and hypertensive (three weeks 11% O2) animals were excised and a contrast agent introduced before micro-CT imaging with a special purpose scanner. For each lung, four 3D image data sets were obtained, each at a different intra-arterial contrast agent pressure. Vessel segment diameters and lengths were measured at all levels in the arterial tree hierarchy, and these data used to generate features sensitive to distensibility changes. Results indicate that measurements obtained from 3D micro-CT images can be used to quantify vessel biomechanical properties in this rat model of pulmonary hypertension and that distensibility is reduced by exposure to chronic hypoxia. Mechanical properties can be assessed in a localized fashion and quantified in a spatially-resolved way or as a single parameter describing the tree as a whole. Micro-CT is a nondestructive way to rapidly assess structural and mechanical properties of arteries in small animal organs maintained in a physiological state. Quantitative features measured by this method may provide valuable insights into the mechanisms causing the elevated pressures in pulmonary hypertension of differing etiologies and should become increasingly valuable tools in the study of complex phenotypes in small-animal models of important diseases such as hypertension

    The road half traveled

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    This brief reviews the extensive evidence on agricultural market reforms in Sub-Saharan Africa and summarizes the impact reforms have had on market performance, agricultural production, use of modern inputs, and poverty. It offers eight recommendations for completing the reform process and developing a new agenda for agricultural markets in Sub-Saharan Africa.

    The road half traveled

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    During the past two decades, most countries in Sub-Saharan Africa undertook extensive economic reforms to reduce the role of the government and increase the role of the market in their economies. Because of the importance of the agricultural sector in the region, agricultural market reforms occupied a central place in these liberalization efforts. Agricultural reforms included the removal of price controls, deregulation of agricultural marketing, closure of state-owned enterprises that monopolized agricultural trade, and changes in the foreign exchange market to provide greater incentives for exports. The expectation was that improving price incentives for farmers and reducing government intervention in the agricultural sector would be enough to generate a supply response and allow well-functioning markets to emerge quickly. Almost two decades later, the general consensus is that the reform programs in Sub-Saharan Africa have not met expectations. At the beginning of the 21st century, Sub-Saharan Africa confronts a number of daunting problems: extensive hunger, malnutrition, poverty, resource degradation, and the spread of AIDS. Because the majority of the region's population remains dependent on agriculture for its livelihood, well-functioning and efficient agricultural markets continue to be key to improving Sub-Saharan Africa's economic health. This report reviews the extensive evidence on agricultural market reforms in Sub-Saharan Africa and summarizes the impact reforms have had on market performance, agricultural production, use of modern inputs,and poverty. The report offers eight recommmendations for completing the reform process and developing a new agenda for agricultural markets in Sub-Saharan Africa.

    Reforming agricultural markets in Africa

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    "Since the early 1980s, almost all African governments have embarked on economic reform programs to reduce state intervention in the economy and to allow markets to play a larger role. In the agricultural sector these programs were designed to eliminate price controls on agricultural commodities, disband or privatize state farms and state-owned enterprises, reduce the heavy taxation of agricultural exports, phase out subsidies on fertilizer and other inputs, and allow greater competition in agricultural markets. These measures have been highly controversial. Proponents argue that the reforms have improved market efficiency, reduced budget deficits, stimulated export production, and increased the share of the final price received by farmers. Opponents argue that the reforms have destabilized agricultural prices, widened the income distribution gap, and reduced access to low-cost inputs. Reforming Agricultural Markets in Africa by Mylène Kherallah, Christopher Delgado, Eleni Gabre-Madhin, Nicholas Minot, and Michael Johnson, published by The Johns Hopkins University Press for IFPRI, reviews the experience of the last 20 years. It evaluates the degree to which the reforms have actually been implemented, their impact on agricultural production and prices, and the net effect on the well-being of African households." Author's Introduction.

    Diverging volumetric trajectories following pediatric traumatic brain injury.

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    Traumatic brain injury (TBI) is a significant public health concern, and can be especially disruptive in children, derailing on-going neuronal maturation in periods critical for cognitive development. There is considerable heterogeneity in post-injury outcomes, only partially explained by injury severity. Understanding the time course of recovery, and what factors may delay or promote recovery, will aid clinicians in decision-making and provide avenues for future mechanism-based therapeutics. We examined regional changes in brain volume in a pediatric/adolescent moderate-severe TBI (msTBI) cohort, assessed at two time points. Children were first assessed 2-5 months post-injury, and again 12 months later. We used tensor-based morphometry (TBM) to localize longitudinal volume expansion and reduction. We studied 21 msTBI patients (5 F, 8-18 years old) and 26 well-matched healthy control children, also assessed twice over the same interval. In a prior paper, we identified a subgroup of msTBI patients, based on interhemispheric transfer time (IHTT), with significant structural disruption of the white matter (WM) at 2-5 months post injury. We investigated how this subgroup (TBI-slow, N = 11) differed in longitudinal regional volume changes from msTBI patients (TBI-normal, N = 10) with normal WM structure and function. The TBI-slow group had longitudinal decreases in brain volume in several WM clusters, including the corpus callosum and hypothalamus, while the TBI-normal group showed increased volume in WM areas. Our results show prolonged atrophy of the WM over the first 18 months post-injury in the TBI-slow group. The TBI-normal group shows a different pattern that could indicate a return to a healthy trajectory

    Inflatable nested toroid structure

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    An inflatable structure comprises at least two generally toroidal, inflatable modules. When in a deployed mode, the first, inner module has a major diameter less than that of a second, outer module and is positioned within the inner circumference of the outer module such that the first module is nested circumferentially alongside the second module. The inflatable structure, in a non-deployed, non-inflated mode, is of compact configuration and adapted to be transported to a site of deployment. When deployed, the inflatable structure is of substantially increased interior volume. In one embodiment, access between the interior of the first module and the second module is provided by at least one port or structural pass-through. In another embodiment, the inflatable structure includes at least one additional generally toroidal module external of and circumferentially surrounding the second module
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