116,833 research outputs found
Economic causes and consequences of migrations within the context of under-development in West Africa
African Studies Center Working Paper No. 6INTRODUCTION:
In recent discussions of development and inequality in
Africa, at least three positions can be identified concerning
relationships between rural-urban migration and inequality.
The most simplistic and journalistic view is that migrants
come to the cities only to find unemployment and
miserable living conditions. The story, as usually depicted,
identifies the problem as misguided persistence in migrating
explanations based on the inappropriateness of educational
curricula, lures of brights lights, and misinformation. Despite
little evidence to support this view, many African
politicians have identified persistent migration as the
cause of urban poverty and have attempted to stop the flow
of migrants through exhortation, administrative controls, and
coercion. Actions seem to have been based on the notion that
the problems of urban poverty will disappear if only the poor... [TRUNCATED
The Botswana National Migration Study: a conceptual framework
African Studies Center Working Paper No. 4
Holding fixture for a hot stamping press
A hand held guide for manually positioning a work piece between the anvil rib and tool of a hot die stamping press is described. A groove completed by interchangeable cover plates attached at one end of the guide conforms to a cross sectional dimension common to similar workpieces and, with a force fit, retentively holds each of the workpieces
Changing patterns of global-scale vegetation photosynthesis, 1982-1999
The primary objective of this research was to assess changes in global vegetation photosynthesis between 1982 and 1999. Global-scale Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) data from the Pathfinder AVHRR Land (PAL) and Global Inventory Modeling and Mapping Studies (GIMMS) datasets were analysed for 96% of the non-Antarctic land area of the Earth. The results showed that between 1982 and 1999 over 30% of the Earth's land surface increased and less than 5% decreased in annual average photosynthesis greater than 4%. Although both the PAL and GIMMS datasets produced broadly similar patterns of change, there were distinct differences between the two datasets. Changes in vegetation photosynthesis were occurring in spatial clusters across the globe and were being driven by climate change, El Nino-Southern Oscillation (ENSO) events and human activity
Disordered asymmetric simple exclusion process: mean-field treatment
We provide two complementary approaches to the treatment of disorder in a
fundamental nonequilibrium model, the asymmetric simple exclusion process.
Firstly, a mean-field steady state mapping is generalized to the disordered
case, where it provides a mapping of probability distributions and demonstrates
how disorder results in a new flat regime in the steady state current--density
plot for periodic boundary conditions. This effect was earlier observed by
Tripathy and Barma but we provide treatment for more general distributions of
disorder, including both numerical results and analytic expressions for the
width of the flat section. We then apply an argument based on
moving shock fronts to show how this leads to an increase in the high current
region of the phase diagram for open boundary conditions. Secondly, we show how
equivalent results can be obtained easily by taking the continuum limit of the
problem and then using a disordered version of the well-known Cole--Hopf
mapping to linearize the equation. Within this approach we show that adding
disorder induces a localization transformation (verified by numerical scaling),
and maps to an inverse localization length, helping to give a new
physical interpretation to the problem.Comment: 13 pages, 16 figures. Submitted to Phys. Rev.
Men of Color: A Role for Policymakers in Improving the Status of Black Male Students in U.S. Higher Education
This report calls for greater involvement by federal and state policymakers and others to improve black male college readiness and completion. It presents policy-relevant trends concerning black male college students, highlights promising practices on campuses across the country, and proposes suggestions for policymakers and other stakeholders
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Automated Design of Tissue Engineering Scaffolds by Advanced CAD
The design of scaffolds with an intricate and controlled internal structure represents a
challenge for Tissue Engineering. Several scaffold manufacturing techniques allow the
creation of complex and random architectures, but have little or no control over geometrical
parameters such as pore size, shape and interconnectivity- things that are essential for tissue
regeneration. The combined use of CAD software and layer manufacturing techniques allow
a high degree of control over those parameters, resulting in reproducible geometrical
architectures. However, the design of the complex and intricate network of channels that are
required in conventional CAD, is extremely time consuming: manually setting thousands of
different geometrical parameters may require several days in which to design the individual
scaffold structures. This research proposes an automated design methodology in order to
overcome those limitations. The combined use of Object Oriented Programming and
advanced CAD software, allows the rapid generation of thousands of different geometrical
elements. Each has a different set of parameters that can be changed by the software, either
randomly or according to a given mathematical formula, so that they match the different
distribution of geometrical elements such as pore size and pore interconnectivity.
This work describes a methodology that has been used to design five cubic scaffolds with
pore size ranging from about 200 to 800 µm, each with an increased complexity of the
internal geometry.Mechanical Engineerin
Analytic solution of nonlinear fractional Burgers-type equation by invariant subspace method
In this paper we study the analytic solutions of Burgers-type nonlinear
fractional equations by means of the Invariant Subspace Method. We first study
a class of nonlinear equations directly related to the time-fractional Burgers
equation. Some generalizations linked to the forced time-fractional Burgers
equations and variable-coefficient diffusion are also considered. Finally we
study a Burgers-type equation involving both space and time-fractional
derivatives
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