PRELIMINARY STUDY ON THE OPHIOLITIC MELANGE IN THE YALU TSANGPU GRAND CANYON AREA

PRELIMINARY STUDY ON THE OPHIOLITIC MELANGE IN THE YALU TSANGPU GRAND CANYON AREA     

FORMATION AND EUOLUTION OF TETHYS IN THE TIBETAN PLATEAU

FORMATION AND EUOLUTION OF TETHYS IN THE TIBETAN PLATEAU     

TAKE ANOTHER VISION TO THE UPLIFT OF THE QING—ZANG (TIBETAN) PLATEAU BASED ON CENOZOIC VOLCANISM

TAKE ANOTHER VISION TO THE UPLIFT OF THE QING—ZANG (TIBETAN) PLATEAU BASED ON CENOZOIC VOLCANISM     

SEDIMENTARY PROCESS OF THE CENOZOIC BASIN AND ITS RESPONSE TO THE SLIP-HISTORY OF THE ALTYN TAGH FAULT, NW CHINA

SEDIMENTARY PROCESS OF THE CENOZOIC BASIN AND ITS RESPONSE TO THE SLIP-HISTORY OF THE ALTYN TAGH FAULT, NW CHINAtheprogramsof ( 1)theYoungGeologistsFoundationoftheMGMR (No .Qn979812 ) ;;( 2 )theNational (No .G19980 4 0 80 0 ) ;;and ( 3)the     

THE PALEOCURRENT PATTERN OF EARLY TERTIARY REDBEDS IN THE HOH XIL BASIN,NORTHERN TIBET PLATEAU:IMPLICATIONS FOR AN EARLY UPLIFT AND UNROOFING

THE PALEOCURRENT PATTERN OF EARLY TERTIARY REDBEDS IN THE HOH XIL BASIN,NORTHERN TIBET PLATEAU:IMPLICATIONS FOR AN EARLY UPLIFT AND UNROOFING     

TECTONIC EVOLUTION OF THE GARZE—LITANG PLATE JUNCTION, WITH PARTICULAR REFERENCE TO THE GOLD DEPOSITS

TECTONIC EVOLUTION OF THE GARZE—LITANG PLATE JUNCTION, WITH PARTICULAR REFERENCE TO THE GOLD DEPOSITS     

THE EARLY UPLIFT IN NORTHERN TIBETAN PLATEAU: EVIDENCE FROM THE STUDY ON CENOZOIC VOLCANIC ROCKS IN QIANGTANG REGION

THE EARLY UPLIFT IN NORTHERN TIBETAN PLATEAU: EVIDENCE FROM THE STUDY ON CENOZOIC VOLCANIC ROCKS IN QIANGTANG REGION     

Ultramafic Xenoliths From a Kamafugite Lava in Cenozoic Volcanic Field of West Qinling, China and Its Geological Implication

ULTRAMAFIC XENOLITHS FROM A KAMAFUGITE LAVA IN CENOZOIC VOLCANIC FIELD OF WEST QINLING, CHINA AND ITS GEOLOGICAL IMPLICATION     

Simulations of Titan's brightness by a two-dimensional haze model

We have used a 2-D microphysics model to study the effects of atmospheric motions on the albedo of Titan's thick haze layer. We compare our results to the observed variations of Titan's brightness with season and latitude. We use two wind fields; the first is a simple pole-to-pole Hadley cell that reverses twice a year. The second is based on the results of a preliminary Titan GCM. Seasonally varying wind fields, with horizontal velocities of about 1 cm sec-1 at optical depth unity, are capable of producing the observed change in geometric albedo of about 10% over the Titan year. Neither of the two wind fields can adequately reproduce the latitudinal distribution of reflectivity seen by Voyager. At visible wavelengths, where only haze opacity is important, upwelling produces darkening by increasing the particle size at optical depth unity. This is due to the suspension of larger particles as well as the lateral removal of smaller particles from the top of the atmosphere. At UV wavelengths and at 0.89 micrometers the albedo is determined by the competing effects of the gas the haze material. Gas is bright in the UV and dark at 0.89 micrometers. Haze transport at high altitudes controls the UV albedo and transport at low altitude controls the 0.89 micrometers albedo. Comparisons between the hemispheric contrast at UV, visible, and IR wavelengths can be diagnostic of the vertical structure of the wind field on Titan.     

A fertility transition in Sub-Saharan Africa?

This paper documents and summarizes data on the recent fertility decline in sub-Saharan Africa and reviews the critical theoretical, methodological, and policy issues and controversies that the African situation provokes. After an introduction, African fertility change for the period 1960-94 is described through a discussion of fertility trends and of the proximate determinants of the fertility change. This discussion is illustrated with tables on the total fertility rate for countries of sub-Saharan Africa for the periods 1975-85 and 1986-93, and total fertility rates for countries participating in the Demographic and Health Surveys (DHS) for the periods 0-3 and 4-7 years prior to the survey. Figures show maps of Africa displaying total fertility rates in sub-Saharan Africa for 1975-85 and 1986- 93, and graphs of absolute and percentage change in total fertility rates for DHS countries between periods 0-3 and 4-7 years prior to the survey. The next section deals with theoretical issues such as whether the classic model of demographic transition is applicable to Africa and Jack Caldwell's views that cultural values make Africa different. It is seen that existing theory is of limited value in explaining the recent fertility decline in the region and that the two theories are beginning to converge to some degree. Consideration of methodological issues centers on the limited usefulness of fertility data collected by the large-scale, standardized demographic surveys to aid in the identification of patterns and processes. The discussion of policy issues is concerned with how survey data have been used and interpreted to formulate policy. The paper closes by reviewing the east Asian, South African, and Caribbean models of fertility decline and discussing problems in predicting the nature and extent of future fertility change in sub-Saharan Africa in light of recent findings.