Membranes of semicrystalline aliphatic polyamide nylon 4,6: Formation by diffusion-induced phase separation

The preparation of membranes of nylon 4,6 by diffusion-induced phase separation (DIPS) using formic acid as a solvent and water as a nonsolvent was studied. Nylon 4,6 is a semi-crystalline polymer; phase separation from a solution can occur by solid-liquid (s-l) de-mixing as well as by liquid-liquid (l-l) demixing. Upon quenching films of solutions with low polymer concentration (< 17 wt %) in a nonsolvent bath containing water, the morphology of the membranes show a foam-like structure typical for l-l demixing. When phase separation is induced by water vapor a transition in structure occurs from the cellular type to a morphology typical for s-l phase separated films. At higher polymer concentrations membranes exhibit structures consisting of spheres or smaller crystal-like units resulting from an s-l phase separation process. The addition of 2 wt % or more of water to polymer solutions with low concentration (up to 15 wt %) resulted in s-l demixing as well. In a DIPS process s-l demixing is kinetically competitive with l-l demixing if nuclei are already present in the starting solutions (heterogeneous nucleation), or if a relatively long time is available for crystal nuclei to be formed. The morphology resulting from s-l demixing is a result of spherulitic crystallization. A certain concentration of nuclei or of precursor particles already present results in a small nucleation density during precipitation and thus large spherulites can be grown; at higher polymer and/or water concentrations the nucleation density increases resulting in an axialitic morphology of the membranes

Resources for Sale: Corruption, Democracy and the Natural Resource Curse

A puzzling piece of empirical evidence suggests that resource-abundant countries tend to grow slower than their resource-poor counterparts. We attempt to explain this phenomenon by developing a lobbying game in which rent seeking firms interact with corrupt governments. The presence or absence of political competition, as well as the potential costs of political transitions, turn out to be key elements in generating the `resource curse.¿ These variables define the degree of freedom that incumbent governments have in pursuing development policies that maximize surplus in the lobbying game, but put the economy off its optimal path. We test our predictions by adding measures of democracy and authoritarianism to existing regression models of the resource curse, and obtain support for our hypothese

Compensation for Wildlife Damage: Habitat Conversion, Species Preservation and Local Welfare

We study the environmental and economic consequences of introducing a program to compensate peasants of a small economy for the damage caused by wildlife. We show that the widely held belief that compensation induces wildlife conservation may be erroneous. In a partially open economy, compensation can lower the wildlife stock and result in a net welfare loss for local people. In an open economy, compensation can trigger wildlife extinction and also reduce welfare. The conditions leading to a reduction of the wildlife stock are identified and the implications for current and planned compensation programs are discussed.compensation, crop damage, wildlife, endangered species preservation, bushmeat trade

Resources for Sale: Corruption, Democracy and the Natural Resource Curse

A puzzling piece of empirical evidence suggests that resource-abundant countries tend to grow slower than their resource-poor counterparts. We attempt to explain this phenomenon by developing a lobbying game in which rent seeking firms interact with corrupt governments. The presence or absence of political competition, as well as the potential costs of political transitions, turn out to be key elements in generating the ‘resource curse.’ These variables define the degree of freedom that incumbent governments have in pursuing development policies that maximize surplus in the lobbying game, but put the economy off its optimal path. We test our predictions by adding measures of democracy and authoritarianism to existing regression models of the resource curse, and obtain support for our hypotheses.Resource endowment and economic growth, development, rent seeking, bribing, corruption.

Contesting Resources - Rent Seeking, Conflict and the Natural Resource Curse

A growing empirical literature links natural resource abundance and "pointiness" to impeded economic growth and civil strife. We develop rent seeking and conflict models that capture the most salient features of contests for resource rents, and show how both resource abundance and geographical clustering can be associated with intense contests and sub-optimal economic performance. However, we also show that these relationships are not necessarily monotonous { pointiness can trigger more intense contests but can also facilitate the coordination on peaceful outcomes. Finally we show that contesting resources through violent conflict may yield superior outcomes (from an economy-wide perspective) than contests through rent seeking. --point resources,civil war,economic growth and resources