8,590 research outputs found
Kleine Schriften von Franz Skutsch ; herausgegeben von Wilhelm Kroll. Pp. xxvi + 531. Leipzig: Teubner, 1914. M. 20.
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Sit down at the ball game: how trade barriers make the world less food secure
This paper analyses the impacts of trade policy responses to rising world food prices by carrying out a series of stylised experiments in the wheat market using a world trade model, GTAP. The sequence of events that is modelled comprises a negative wheat supply shock and subsequent implementation of an export tax by a major net exporter and a reduction in import tariffs by a small importer. The effects of trade policy responses are contrasted with those of full liberalisation of the wheat market. At the core are the (opposite) effects on producers and consumers, as well as the terms-of-trade and trade tax revenue effects. Food security is shown to depend crucially on changes in prices but also in incomes that are associated with changes in factor returns. The results reveal that major net exporters are generally better off when implementing export taxes for food security purposes. Large exporting countries export price instability causing world food prices to rise further. Net importing countries lose out and have limited leeway to reduce tariffs or subsidise imports. Liberalising wheat trade mitigates rising prices and contributes to food security, but to the detriment of production in Africa and Asia, making them more dependent on and vulnerable to changes in the world market. Concerted action at the WTO forum is required, notably clarifying and sharpening the rules regarding export measures.food security; world food crisis; international grain trade; trade measures; trade liberalisation; CGE modelling
Study of porous wall low density wind tunnel diffusers
Porous wall wind tunnel diffusers used with low density hypersonic nozzl
The Long-Run Impacts of Same-Race Teachers
Black primary-school students matched to a same-race teacher perform better on standardized tests and face more favorable teacher perceptions, yet little is known about the long-run, sustained impacts of student-teacher demographic match. We show that assigning a black male to a black teacher in the third, fourth, or fifth grades significantly reduces the probability that he drops out of high school, particularly among the most economically disadvantaged black males. Exposure to at least one black teacher in grades 3-5 also increases the likelihood that persistently low-income students of both sexes aspire to attend a four-year college. These findings are robust across administrative data from two states and multiple identification strategies, including an instrumental variables strategy that exploits within-school, intertemporal variation in the proportion of black teachers, family fixed-effects models that compare siblings who attended the same school, and the random assignment of students and teachers to classrooms created by the Project STAR class-size reduction experiment
NuSTAR hard X-ray observation of a sub-A class solar flare
We report a NuSTAR observation of a solar microflare, SOL2015-09-01T04.
Although it was too faint to be observed by the GOES X-ray Sensor, we estimate
the event to be an A0.1 class flare in brightness. This microflare, with only 5
counts per second per detector observed by RHESSI, is fainter than any hard
X-ray (HXR) flare in the existing literature. The microflare occurred during a
solar pointing by the highly sensitive NuSTAR astrophysical observatory, which
used its direct focusing optics to produce detailed HXR microflare spectra and
images. The microflare exhibits HXR properties commonly observed in larger
flares, including a fast rise and more gradual decay, earlier peak time with
higher energy, spatial dimensions similar to the RHESSI microflares, and a
high-energy excess beyond an isothermal spectral component during the impulsive
phase. The microflare is small in emission measure, temperature, and energy,
though not in physical size; observations are consistent with an origin via the
interaction of at least two magnetic loops. We estimate the increase in thermal
energy at the time of the microflare to be 2.4x10^27 ergs. The observation
suggests that flares do indeed scale down to extremely small energies and
retain what we customarily think of as "flarelike" properties.Comment: Status: Accepted by the Astrophysical Journal, 2017 July 1
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