10,299 research outputs found
Comparison of X-ray and gamma-ray dose-response curves for pink somatic mutations in Tradescantia clone 02
Microdosimetric data indicate that the mean specific energy,zeta, produced by individual charged particles from X rays and gamma rays is different for the two radiation qualities by nearly a factor of two. In order to test whether this influences the initial, linear component in the dose-effect relations, a comparison was made between dose-response curves for pink somatic mutations inTradescantia clone 02 stamen hairs following X and gamma irradiations. Absorbed doses ranged from 2.66 to 300 rad. The results are in agreement with predictions made on the basis of microdosimetric data. At low doses gamma rays are substantially less effective than X rays. The RBE of gamma rays vs. X rays at low doses was approximately 0.6, a value lower than those usually reported in other experimental systems
Simple methods for assessing groundwater resources in low permeability areas of Africa
In many areas throughout Africa, a staggering proportion of
wells and boreholes fail. Failure can occur for a number of
reasons – inadequate maintenance and community
involvement, poor engineering or a lack of water. Often it
can be difficult to work out the exact reason after the event.
However, in many geological environments the impacts of
poorly sited and designed boreholes and wells are a major
concern to funding agencies, implementing institutions and
local communities. In such areas, good supplies of
groundwater cannot be found everywhere, and boreholes
and wells must be sited and designed carefully to make use
of the available groundwater. To appropriately site and
design water sources, the groundwater resources of an area
need first to be investigated to understand how water occurs
in the ground.
In this manual we present some techniques that allow a
quick assessment of groundwater resources without
requiring much expertise or expense. Some of the
techniques are old and established while others are new.
However, all techniques have been tested by BGS (and
others) in assessing groundwater resources in Africa. This
manual does not claim to be a detailed textbook for
hydrogeologists – there are enough already (see reading list
at the end of the chapter). Rather it is meant as a practicalaid for those involved in the practice of rural water supply, particularly in Africa. Little training or equipment is required for the tests and they can all be carried out in a short space of time.
The manual is divided into six sections. The first gives
an overview of the groundwater resources of sub-Saharan
Africa (SSA) and discusses the scope and detail of
investigations required in different geological
environments. The remaining chapters describe simple
techniques for assessing groundwater resources, from basic
reconnaissance to assessing the yield of a borehole. In the
appendix are summary sheets of the most common
techniques which can be photocopied and used in the field
Methodology of mechanical characterization of coated spherical materials
The aim of this work was to develop a methodology for the mechanical characterization of catalyst beads with a core-shell structure and more especially for coated spherical granules. Supports composed of an alpha
alumina core coated by gamma alumina shell were shaped by pan coating to this purpose. The proposed methodology started with the characterization of the microstructure of the coating and the highlight of potential macro defects within. Thereafter three tests simulating mechanical stress, such as impact, compression (bulk crushing test), and shear (drum attrition test) are used. The operational parameters of these tests were also optimised in order to stress preferentially the shell of the coated materials. Among the evaluated tests, drum attrition seems to be most efficient for characterizing coated spherical granules
Shale problems and water-based drilling fluid optimisation in the Hassi Messaoud Algerian oil field
Drilling fluid formulation and properties play a fundamental role in drilling operations. Clay minerals behave initially as a beneficial rheological adjuvant in drilling muds. Nevertheless, the contamination of oil reservoirs by clay minerals present in the drilled geological formation (shales) may generate major problems during drilling as plug formation. In this context, our study deals with the optimisation of drilling conditions in the Hassi Messaoud Algerian field. The mineralogical heterogeneity of this field is first discussed. The rheological and filtration characteristics of water-based muds with different polymer and electrolyte concentrations are investigated. The physical and chemical changes of both drilled formation and drilling fluid during the drilling process are studied. Therefore, depending on the clay present in the geological formation, an optimised drilling fluid system using a new filtration procedure is proposed. A good correlation is found between filtration/rheological properties and inhibition
Experimental evidence for the essential identity of the selective and normal photo-electric effects
In the fall of 1913, while studying the photo-electric properties of freshly cut surfaces of the alkali metals in extreme vacua, we observed that immediately after first cutting, the fresh surface of sodium showed very large photo-sensitiveness when tested with monochromatic light of wave length 5461 A., even when the vacuum was of the order 10(-6) mm. as measured by a McLeod gauge. But after several weeks of experimenting and many cuttings a condition was reached in which a freshly cut surface was completely insensitive when illuminated with this wave length. The lost sensitiveness reappeared, however, in the course of not more than two minutes after cutting, and grew rapidly to a very large value in fifteen or twenty minutes. When the gas pressure was of the order of 0.01 mm. the same phenomenon occurred but the rise to a maximum value was less rapid. From these results we began to surmise that photo-electric currents must be due to the influence of some active gas, which diffused from the walls to the metal and whose action upon the surface was retarded by the presence of an inert gas
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