6,167 research outputs found
Biofuel scenarios in a water perspective: the global blue and green water footprint of road transport in 2030
The trend towards substitution of conventional transport fuels by biofuels requires additional water. The EU aims In the last two centuries, fossil fuels have been our major source of energy. However, issues concerning energy security and the quality of the environment have given an impulse to the development of alternative, renewable fuels. Particularly the transport sector is expected to steadily switch from fossil fuels to a larger fraction of biofuels - liquid transport fuels derived from biomass. Many governments believe that biofuels can replace substantial volumes of crude oil and that they will play a key role in diversifying the sources of energy supply in the coming decades. The growth of biomass requires water, a scarce resource. The link between water resources and (future) biofuel consumption, however, has not been analyzed in great detail yet. Existing scenarios on the use of water resources usually only consider the changes in food and livestock production, industry and domestic activity. The aim of this research is to assess the change in water use related to the expected increase in the use of biofuels for road transport in 2030, and subsequently evaluate the contribution to potential water scarcity. The study builds on earlier research on the relation between energy and water and uses the water footprint (WF) methodology to investigate the change in water demand related to a transition to biofuels in road transport. Information about this transition in each country is based on a compilation of different energy scenarios. The study distinguishes between two different bio-energy carriers, bio-ethanol and biodiesel, and assesses the ratio of fuel produced from selected first-generation energy crops per country. For ethanol these crops are sugar cane, sugar beet, sweet sorghum, wheat and maize. For biodiesel they are soybean, rapeseed, jatropha, and oil palm
Overschooling and unemployment
Although overschooling is regarded as the result of imperfect allocation in the labour market, hardly any attention has been given to the influence of another imperfection, unemployment. Several researchers report about an increasing incidence of overschooling in the Netherlands. Although a lot of research has been done in the Netherlands on overschooling, this is not a phenomenon restricted to the Netherlands. Overschooling was found and measured in the United States, Germany, Spain, Portugal the United Kingdom and may be around in other Western European countries as well. Remarkably, however, is that in this line of research no attention has been paid to the effect of unemployment on overschooling. Because it can be argued that almost all unemployed are overschooled, the incidence and amount of overschooling and its rate of return should be directly affected by the unemployment rate in a country. However for the Netherlands we cannot find a relation between the unemployment rate and the amount of overschooling. The amount of overschooling is in 1998, a year with low unemployment, as high as in 1985, a year with high unemployment. After correcting the selectivity bias, caused by the unemployed, we also do not find changes in the rate of return on education, suggesting that wages in the Netherlands are rather sticky. Therefore efficiency wage theory seems to be a better candidate in explaining overschooling than a matching model as propesed by Hartog.
Micromorphological Observations on Till Samples from Shackleton Range and North Victoria Land, Antarctica
Initial surface deformations during impact on a liquid pool
A tiny air bubble can be entrapped at the bottom of a solid sphere that
impacts onto a liquid pool. The bubble forms due to the deformation of the
liquid surface by a local pressure buildup inside the surrounding gas, as also
observed during the impact of a liquid drop on a solid wall. Here we perform a
perturbation analysis to quantitatively predict the initial deformations of the
free surface of the liquid pool as it is approached by a solid sphere. We study
the natural limits where the gas can be treated as a viscous fluid (Stokes
flow) or as an inviscid fluid (potential flow). For both cases we derive the
spatio-temporal evolution of the pool surface, and recover some of the recently
proposed scaling laws for bubble entrapment. When inserting typical
experimental values for the impact parameters, we find that the bubble volume
is mainly determined by the effect of gas viscosity
Nonmonotonic settling of a sphere in a cornstarch suspension\ud
Cornstarch suspensions exhibit remarkable behavior. Here, we present two unexpected observations for a sphere settling in such a suspension: In the bulk of the liquid the velocity of the sphere oscillates around a terminal value, without damping. Near the bottom the sphere comes to a full stop, but then accelerates again toward a second stop. This stop-go cycle is repeated several times before the object reaches the bottom. We show that common shear thickening or linear viscoelastic models cannot account for the observed phenomena, and propose a minimal jamming model to describe the behavior at the botto
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