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Crystal Chemistry and Phase Equilibrium Studies of the Bao(baco3)‐r2o3‐cuo Systems. V. Melting Relations in ba2(y,nd,eu)cu3o6+x
- Winnie Wong‐Ng, Lawrence P. Cook, Michael D. Hill, Boris Paretzkin, E.R. Fuller, JR.
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- Journal:
- MRS Online Proceedings Library Archive / Volume 169 / 1989
- Published online by Cambridge University Press:
- 28 February 2011, 81
- Print publication:
- 1989
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The influence of the ionic size of the lanthanides R on melting relations of Ba2RCu3O6+x, where R=Y, Eu and Nd, was studied and compared with that of a high Tc superconductor mixed‐lanthanide phase Ba2(Y.75Eu.125Nd 125)Cu3O6+xThese materials have been characterized by a variety of methods including differential thermogravimetric analysis (DTA), scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy (EDX) and X‐ray powder diffraction. Single phase samples of Ba2(Y.75Eu.125Nd.125)Cu3O6+x were annealed at 1004, 1040, 1052, 1060, 1078, 1107 and 1160°C and quenched into a helium gas container cooled by liquid nitrogen. The SEM micrographs of these samples showed the progressive chnages in features of the microstructures from sintering and grain growth through melting and then recrystallization from the melt. The addition of the SEM technique in conjunction with X‐ray diffraction has been helpful in the study of phase equilibria in this system.
4 - THE NORTHERN HEMISPHERE
- Edited by M. K. Hughes, P. M. Kelly, J. R. Pilcher, V. C. LaMarche, Jr.
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- Book:
- Climate from Tree Rings
- Published online:
- 05 October 2010
- Print publication:
- 17 June 1982, pp 105-158
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Summary
INTRODUCTION
The Editors
The distribution of land and its relief differs markedly between the two hemispheres. This influences both the potential extent of the tree-ring data base and the nature of the climatic and atmospheric circulation features that are to be reconstructed. The atmospheric circulation of the Northern Hemisphere does not have the year-round vigour of the Southern Hemisphere. Pronounced seasonal changes in climate and the strength and position of the major circulation features occur, particularly in the continental interiors. Kelly discusses climatological points of relevance to dendroclimatic analysis.
The Arctic area, reported on by Jacoby, Brubaker and Garfinkel, and Lawson and Kuivinen, is of special interest as climatic variations in high latitudes are particularly marked and may indicate changes over a much wider region. As these authors show, there has been a considerable amount of work undertaken in high latitudes, particularly in Alaska where a clear climate signal in tree rings has been demonstrated. This region has its special problems related to access to sites and the properties of the tree-ring series themselves. It is an area with great potential and one especially requiring international cooperation.
Western North America, reported on by Brubaker, is one of the most heavily worked areas of the globe. It is the source of most climate reconstructions so far. The range of species, the altitudinal gradients, and the latitudinal range have all contributed to this success, although there is much still to be done.
5 - CLIMATE RECONSTRUCTIONS
- Edited by M. K. Hughes, P. M. Kelly, J. R. Pilcher, V. C. LaMarche, Jr.
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- Book:
- Climate from Tree Rings
- Published online:
- 05 October 2010
- Print publication:
- 17 June 1982, pp 159-198
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Summary
INTRODUCTION
The Editors
The aim of dendroclimatology is to extract the climate signal in the annual rings of trees and use it to provide a proxy record of climate for times and places where the instrumental record is absent or inadequate. These proxy records are used to produce reconstructions of one or more climate variables in the time, frequency, and sometimes the spatial domains. Reconstructions from tree rings are of potential value in four main fields. First, they may be used to provide an extended climate data base to be used in the testing of models of climate. Second, they may provide a longer and more representative data base for the calculation of climate and climate-related statistics. Third, they may provide detailed descriptions of climate in distant periods which may be used as analogues of possible future changes in climate. Fourth, they may be used in the verification of other proxy records of climate, including historical (or documentary) data, for pre-instrumental times.
The bases of the methods currently available for the preparation and testing of climate reconstructions from tree rings have been discussed in Chapters 1 and 2 of this book, whilst the existing data base, and the potential for its improvement, has been described in Chapters 3 and 4. In order that the reader may see the potential of dendroclimatology, short accounts of a number of dendroclimatic reconstructions are brought together in this chapter.
1 - DATA ACQUISITION AND PREPARATION
- Edited by M. K. Hughes, P. M. Kelly, J. R. Pilcher, V. C. LaMarche, Jr.
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- Book:
- Climate from Tree Rings
- Published online:
- 05 October 2010
- Print publication:
- 17 June 1982, pp 1-31
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Summary
INTRODUCTION
The Editors
Where trees form annual growth layers, there exists the likelihood that the characteristics of those layers reflect the conditions under which they were formed. Differences in annual growth layers, which are seen as tree rings, may be parallel in many trees within a region indicating that some common set of external factors is influencing growth. Such similarities in growth variation may be strong and spatially extensive. Where this is true, it is reasonable to assume that the external agents forcing the pattern of variability common to trees in a region relate to climate. There are no other environmental factors likely to act on the same range in the space, time, and frequency domains. It should be possible, therefore, to extract a record of the climate variables recorded in the rings of wood formed in the past. This is the basic assumption of dendroclimatology.
Many tree species in the temperate regions show patterns of common year-to-year variability in one or more measure describing the state of the tree ring. This phenomenon has been exploited by scientists in two main fields: dendrochronology (tree-ring dating of wood found in archaeological, geological, or other contexts) and dendroclimatology (the use of tree rings as proxy climate indicators). Both fields depend heavily on the identification and verification of patterns of common yearto- year variability in many wood samples from a site or region.