5,760 research outputs found
Zircon geochronology of Archaean felsic sequences in the Zimbabwe craton: a revision of greenstone stratigraphy and a model for crustal growth
No full textU-Pb ion-microprobe (SHRIMP) work on zircon populations from 13 Zimbabwean Archaean felsic rocks are presented and interpreted. Samples were extracted from felsic volcanic sequences from most of the major greenstone belts and represent the first zircon geochronological data from within the greenstone belts themselves. The data demonstrate a Late Archaean volcanicity spanning 250 Ma which began at least 2900 Ma ago and ended at 2650 Ma. Theintrusion of extensive granitoid sills of the Chilimanzi suite at c. 2.6 Ga marks the widespread stabilization of the craton. Based on the new zircon data and a re-evaluation of published mapping, a new stratigraphic subdivision is presented for the Late (< 2.9 Ga) Archaean of Zimbabwe. A feature of the stratigraphic model is the cyclicity of magmatism which begins with ultramafic-mafic rocks, progresses through felsic volcanism and ends with a granitoid event. These cycles are repeated at least three or four times in the 250 Ma time span. An important characteristic of the felsic volcanic rocks is that the bulk of the material examined contains inherited, xenocrystic zircons whose ages range from 1000 Ma to 20 Ma older than the host rocks. The oldest xenocrystic zircons (c. 3.6 Ga) are restricted to volcanic rocks which erupted through the Tokwe segment; itself the only known > 3.3 Ga fragment of Archaean crust in Zimbabwe. These data suggest that the Early Archaean crust is restricted to the Tokwe segment in the south of the country. Since even the oldest of the felsic volcanics (2.90 Ga, Lower Belingwean) have zircons which are 50 Ma older, it is suggested that remnants of earlier cyclic greenstone--granitoid events must underlie the present craton and that all of the currently exposed greenstone belts of Zimbabwe were developed on sialic crust
[Portrait of R. W. Wilson ]
No full textFrom Sleeve: R.W. Wilson Chevrolet Motor Co. 5/4/28. 52714. N1106.Title supplied by cataloger.Positive digital file from original glass negative.Glass plate is chipped in a few places around the edges
Wilson, Lena (Death, 1886-06-05)
No full textAddress: Children's Hosp.Age at death: 3 yrs64/Pg. 194/1886/F N S/City/Dr. R.W. Stewart/Habig/Union BaptistOriginal record filed in drawer labeled 'WILSON-WINMIL'
A Validated Framework for Measuring Interface Support for Interactive Information Seeking
No full textIn this paper we present the validation of an evaluation framework that models the support provided by search systems for different types of user and their expected types of seeking behavior. Factors determining the types of users include previous knowledge and goals. After an overview is presented, the framework is validated in two ways. First, the novel integration of the two existing information-seeking models used in the framework is validated by the correlation of multiple expert and novice analysis. Second, the framework is validated against the results produced by two separated user studies. Further, the refinements made by the first validation technique are shown to increase the accuracy of the framework through the second technique. The successful validation process has shown that the framework can identify both strong and weak areas of search interface design in only a few hours. The results produced can be used to either revise and strengthen designs or inform the structure of a user study
Leading causes of death by age, sex, race, and Hispanic origin : United States, 1992
No full textThis report presents leading cause of death data using alternative age classifications. Rankings are shown separately for white, black, and Hispanic males and females.[P. Gardner, H.M. Rosenberg, R.W. Wilson].by Paula Gardner, MPH, and Harry M. Rosenberg, Ph.D., Division of Vital Statistics, and Ronald W. Wilson, Office of Analysis, Epidemiology, and Health Promotion
Investigation into bulk optical Bragg deflectors based on an electro-optically induced grating in periodically poled lithium niobate
No full textMany solutions exist for making laser modulators including acousto-optic (AO) and bulk electro-optic (EO) devices. However, another class of modulators based on Bragg diffraction in periodically poled materials offers the potential to overcome disadvantages inherent in the more conventional types, such as low efficiency in the infra-red and high drive voltages. These devices are an extension of early work on grating based EO devices, for example those by Hammer and Barros & Wilson, but by making use of periodic poling they allow additional design freedom. This in turn allows fast switching, high efficiency and simple construction as demonstrated in periodically poled lithium niobate at 633nm
Keyword Search: Quite Exploratory Actually
No full textThis short position paper describes some evidence found that counters the argument that there are better ways to support exploratory search than keyword search. Instead, this paper suggests that keyword search actually provides people with the freedom to search in relation to their own current state of understanding, rather than in the terms controlled by a search system. The challenge for future exploratory search systems, therefore, may be to maintain and enhance such freedoms
The Jan Mayen microplate complex and the Wilson cycle
No full textThe opening of the North Atlantic region was one of the most important geodynamic events that shaped the present day passive margins of Europe, Greenland and North America. Although well-studied, much remains to be understood about the evolution of the North Atlantic, including the role of the Jan Mayen microplate complex. Geophysical data provide an image of the crustal structure of this microplate and enable a detailed reconstruction of the rifting and spreading history. However, the mechanisms that cause the separation of microplates between conjugate margins are still poorly understood. We assemble recent models of rifting and passive margin formation in the North Atlantic and discuss possible scenarios that may have led to the formation of the Jan Mayen microplate complex. This event was probably triggered by regional plate tectonic reorganizations rejuvenating inherited structures. The axis of rifting and continental break-up and the width of the Jan Mayen microplate complex were controlled by old Caledonian fossil subduction/suture zones. Its length is related to east–west-oriented deformation and fracture zones, possibly linked to rheological heterogeneities inherited from the pre-existing Precambrian terrane boundaries
What remains of monetarism?
No full textIn October 1979 the Federal Reserve, in an attempt to curb double-digit inflation, announced that it would place more weight on monetary aggregates in policy deliberations. This policy shift helped reduce inflation but sent the economy into a recession. Three years later the Fed abandoned monetary targets and returned to targeting the federal funds rate. ; Monetary growth targets currently play no official role in the setting of U.S. monetary policy. Is such disregard justified by the data any more today than it was twenty years ago? This article provides a historical perspective on the development and apparent failure of monetarism as a policy guide. ; The author also explores whether the basic monetarist propositions still hold true for a sample of fifteen countries. The analysis suggests that it is premature to dismiss monetary aggregates as uninformative. The data from the economies studied indicate that, in general, nominal income growth and inflation are positively related to money growth. While these results do not support short-term manipulation of the monetary aggregates to deliver precise control over movements in income and prices, they also do not reject the notion that changes in money growth have important long-term effects on the economy. What the results suggest, therefore, is that failure to acknowledge this empirical fact could lead to undesirable policy consequences.Monetary policy ; Monetary theory
The Tetris model of the information seeking process
No full textAlthough many attempts have been made to model the information seeking process, so that we might better understand it and improve search systems, previous models have typically tried to flatten the dynamic and repetitive sequence of actions into a single set of stages. Some have surpassed the linear models with circular connections to show that users may, for example, search, examine results, and then refine their search, and repeat. Here we argue that simply adding circular attributes to the model does not fully capture the variability in the search process. Instead, we present the Tetris model of the information seeking process, as a means to more completely capture both the activities and the dynamic process involved in searching. After presenting the model, and related work, we continue by describing the additional benefits provided and how it may better inform design of information seeking systems
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