نتایج جستجو برای: greenstone
تعداد نتایج: 587 فیلتر نتایج به سال:
The existence of a core dynamo during the first billion years Earth history is closely related to thermal state Earth's interior and composition early atmosphere. scarcity well-preserved rock units older than 3.5 (Ga) has motivated paleomagnetic analysis detrital zircons. Studies zircons from Jack Hills, Australia, however, have found pervasive occurrence secondary ferromagnetic minerals, casti...
Previous studies of tenancy and land reform programs suggest that these programs substantially increased agricultural productivity. However, these studies are limited to sharecropping environments. This paper investigates the productivity effect of the 1953 land ownership transfer program in Taiwan, where fixed-rental contracts predominated. This program transferred 27% of the paddy land to inc...
The Godthåbsfjord region of West Greenland contains the most extensive, best exposed and most intensely studied early Archean rocks on Earth. A geological record has been described of numerous magmatic events between ~3.9 and 3.6 Ga, and evidence of life at >3.85 Ga and ~3.8-3.7 Ga has been proposed from two widely-separated localities. Some of these claims have recently been questioned, and th...
This paper describes an experimental system that enhanced an iPod with digital library capabilities. Using the open source digital library software Greenstone as a base, this paper more specifically maps out the technical steps necessary to achieve this, along with an account of our subsequent experimentation. This included command-line usage of Greenstone’s basic runtime system on the device, ...
This paper uses historical fluctuations in temperature within countries to identify its effects on aggregate economic outcomes. We find three primary results. First, higher temperatures substantially reduce economic growth in poor countries. Second, higher temperatures appear to reduce growth rates, not just the level of output. Third, higher temperatures have wide-ranging effects, reducing agr...
This paper uses annual variation in climate to examine the impact of temperature and precipitation on national economies. We find three primary results. First, higher temperatures substantially reduce economic growth in poor countries. Second, higher temperatures appear to reduce growth rates, not just the level of output. Third, higher temperatures have wide-ranging effects, reducing agricultu...
Ballooning, the aerial displacement of a spider caused by friction between air and the spide r with its silk, has considerable ecological importance but remains poorly understood as a mechanical process . The studies reported here provide insight into the mechanics of ballooning by way of experiments involving (1 ) stroboscopic measurement of the rates of fall of spiders slowed by known lengths...
Abstract Trace element and isotopic data for basalts from the Isua greenstone belt, West Greenland, indicate that they were derived a range of mantle reservoirs included depleted lower mantle, transition zone, primitive reservoir probably located in shallow upper mantle. Modeling trace compositions indicates formed through mixing between refertilization these diverse sources their resultant mel...
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