The geography of highly skilled international migration   总被引：1，自引：0，他引：1  

Koser K  Salt J 《International journal of population geography : IJPG》1997,3(4):285-303

"The present paper provides a research review of recent literature on international migration by the highly skilled. Its principal aim is to identify the themes which are being discussed, and suggest where research into the subject might best proceed.... [The authors outline] the two most important perspectives in extant research, economic and socio-cultural, [and review] what is known about the geography of migration by the highly skilled.... The paper proposes...a reconceptualisation of migration by the highly skilled as one element in the international movement of expertise."  相似文献   

Study of annual mass balance(2011–2013) of Rikha Samba Glacier,Hidden Valley,Mustang, Nepal     

Sanjaya Gurung  Bikas C. Bhattarai  Rijan B. Kayasth  Dorothea Stumm  Sharad P. Joshi  Pradeep K. Mool 《寒旱区科学》2016,8(4):311-318

Although Himalayan glaciers are of particular interest in terms of future water supplies, regional climate changes, and sea-level rises, little is known about them due to lack of reliable and consistent data. There is a need for monitoring these glaciers to bridge this knowledge gap and to provide field measurements necessary to calibrate and validate the results from different remote sensing operations. Therefore, glaciological observations have been carried out by the Cryosphere Monitoring Project(CMP) since September 2011 on Rikha Samba Glacier in Hidden valley, Mustang district in western Nepal in order to study its annual mass balance. This paper presents the first results of that study. There are 10 glaciers in Hidden Valley, named G1, G2, G3, up to G10. Of these, G5 is the Rikha Samba Glacier, which has the largest area(5.37 km2) in this valley and the highest and lowest altitudes(6,476 and 5,392 m a.s.l., respectively). The glacier mass balance discussed in this paper was calculated using the glaciological method and the equilibrium line altitude(ELA). The glacier showed a negative annual point mass balance along the longitudinal profile of its lower part from September 10, 2011 to October 3, 2012. Stake measurements from October 4, 2012 to September 30, 2013 indicated a negative areal average of annual mass balance-0.088±0.019 m w.e. for the whole glacier. Based on these observations, the ELA of the Rikha Samba Glacier is estimated at 5,800 m a.s.l. in 2013. This negative balance may be due to rising air temperatures in the region, which have been incrementally rising since 1980 accompanied by little or no significant increase in precipitation in that period. The negative mass balance confirms the general shrinking trend of the glacier.  相似文献   

http://www.sciencedirect.com/science/article/pii/S167498711500095X   总被引：5，自引：3，他引：2  

Richard M.Palin  Owen M.Weller  David J.Waters  Brendan Dyck 《地学前缘(英文版)》2016,7(4):591-607

Pseudosection modelling is rapidly becoming an essential part of a petrologist's toolkit and often forms the basis of interpreting the tectonothermal evolution of a rock sample,outcrop,or geological region.Of the several factors that can affect the accuracy and precision of such calculated phase diagrams, "geological" uncertainty related to natural petrographic variation at the hand sample- and/or thin section-scale is rarely considered.Such uncertainty influences the sample's bulk composition,which is the primary control on its equilibrium phase relationships and thus the interpreted pressure-temperature(P-T) conditions of formation.Two case study examples-a garnet-cordierite granofels and a garnet-staurolite-kyanite schist-are used to compare the relative importance that geological uncertainty has on bulk compositions determined via(1) X-ray fluorescence(XRF) or(2) point counting techniques.We show that only minor mineralogical variation at the thin-section scale propagates through the phase equilibria modelling procedure and affects the absolute P-T conditions at which key assemblages are stable.Absolute displacements of equilibria can approach ±1 kbar for only a moderate degree of modal proportion uncertainty,thus being essentially similar to the magnitudes reported for analytical uncertainties in conventional thermobarometry.Bulk compositions determined from multiple thin sections of a heterogeneous garnet-staurolite-kyanite schist show a wide range in major-element oxides,owing to notable variation in mineral proportions.Pseudosections constructed for individual point count-derived bulks accurately reproduce this variability on a case-by-case basis,though averaged proportions do not correlate with those calculated at equivalent peak P-T conditions for a whole-rock XRF-derived bulk composition.The main discrepancies relate to varying proportions of matrix phases(primarily mica) relative to porphyroblasts(primarily staurolite and kyanite),indicating that point counting preserves small-scale petrographic features that are otherwise averaged out in XRF analysis of a larger sample.Careful consideration of the size of the equilibration volume,the constituents that comprise the effective bulk composition,and the best technique to employ for its determination based on rock type and petrographic character,offer the best chance to produce trustworthy data from pseudosection analysis.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987115001322   总被引：5，自引：1，他引：4  

Christopher J.Spencer  Christopher L.Kirkland  Richard J.M.Taylor 《地学前缘(英文版)》2016,7(4):581-589

Zircon U-Pb geochronology has become a keystone tool across Earth science,arguably providing the gold standard in resolving deep geological time.The development of rapid in situ analysis of zircon（via laser ablation and secondary ionization mass spectrometry） has allowed for large amounts of data to be generated in a relatively short amount of time and such large volume datasets offer the ability to address a range of geological questions that would otherwise remain intractable（e.g.detrital zircons as a sediment fingerprinting method）.The ease of acquisition,while bringing benefit to the Earth science community,has also led to diverse interpretations of geochronological data.In this work we seek to refocus U-Pb zircon geochronology toward best practice by providing a robust statistically coherent workflow.We discuss a range of data filtering approaches and their inherent limitations（e.g.discordance and the reduced chi-squared;MSWD）.We evaluate appropriate mechanisms to calculate the most geologically appropriate age from both ²³⁸U/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb ratios and demonstrate the cross over position when chronometric power swaps between these ratios.As our in situ analytical techniques become progressively more precise,appropriate statistical handing of U-Pb datasets will become increasingly pertinent.  相似文献   

Trilobite Biostratigraphy of the lower Paleozoic (Cambrian–Ordovician) Joseon Supergroup, Taebaeksan Basin, Korea   总被引：1，自引：0，他引：1  

CHOI Duck K.  LEE Jeong Gu  LEE Seung-Bae  PARK  Tae-Yoon S.  HONG Paul S. 《《地质学报》英文版》2016,90(6):1976-1999

In Korea,trilobites are among the most intensively studied fossil groups in the past century and provide invaluable information about lower Paleozoic stratigraphy,paleogeography,and tectonics of the Korean Peninsula. Trilobites occur in the lower Paleozoic Joseon Supergroup of the Taebaeksan Basin which was part of the Sino-Korean Craton in the Paleozoic. The Joseon Supergroup is divided into the Taebaek,Yeongwol,and Mungyeong groups. The Taebaek and Yeongwol groups are richly fossiliferous,while the Mungyeong Group is poorly fossiliferous. Contrasting trilobite faunal contents of the Taebaek and Yeongwol groups resulted in two separate biostratigraphic schemes for the Cambrian–Ordovician of the Taebaeksan Basin. A total of 22 biozones or fossiliferous horizons were recognized in the Taebaek Group; 19 zones were established in the Yeongwol Group; and four biozones were known from the Mungyeong Group. These trilobite biozones of the Taebaeksan Basin indicate the Joseon Supergroup ranges in age from the Cambrian Series 2 to Middle Ordovician and can be correlated well with the formations of North China,South China,and Australia.  相似文献   

Neoarchaean-Palaeoproterozoic Mafic Dyke Swarms from the Singhbhum Granite Complex,Singhbhum Craton,Eastern India: Implications for Identification of Large Igneous Provinces and Their Possible Continuation on Other Formerly Adjacent Crustal Blocks     

Rajesh K. Srivastav  Ulf S?derlun  Richard E. Ernst  Sisir K. Mondal  Amiya K. Samal 《《地质学报》英文版》2016,90(Z1):17-18

正The Singhbhum craton of the eastern India consists of the Singhbhum Granite Complex(SGC)and the Chotanagpur Gneissic Complex(CGC)separated by the Singhbhum Mobile Belt(SMB).The CGC is intruded by Mesoproterozoic as well as Cretaceous mafic dykes;in  相似文献   

Role of Multi-Generation Dyke Emplacements in Moyar-Bhavani Shear Zone,South India     

P. Pratheesh  V. Prasannakumar  K. R. Praveen  C. Vikas 《《地质学报》英文版》2016,90(Z1):112-112

正The Moyar-Bhavani Shear Zone(MBSZ)of the South Indian Granulite Terrain(SIGT),a complex continental block formed by the accretion of various crustal units during the Archaean to Neoproterozoic,bear evidences of  相似文献   

Mineralogy,Geochemistry and Palaeomagnetism of Mafic Dykes from Kumaun Lesser Himalaya: Implication on Petrogenesis,Tectonic Setting and Timing of Mafic Magmatism in Northern Part of Indian Lithosphere     

Santosh Kumar  N. Surdas Singh  S. K. Patil 《《地质学报》英文版》2016,90(Z1):120-121

正Occurrence of mafic dykes in Himalaya has been intriguing and debated since long because of its difficulty to ascent and emplacement through a thickened crust.Mafic dykes in Kumaun Lesser Himalaya(KLH)of central Indian  相似文献   

Relic Oceanic Crust at Sub-arc Depth: an Example from UHP Eclogites Enclosed in Serpentinites from the Southwestern Tianshan Mountains,China     

SHEN T. T.  ZHANG L. F.  LIU F. L  HERMANN J. 《《地质学报》英文版》2016,90(Z1):238-238

正Ultra-high pressure(UHP)eclogites that derive from subducted oceanic crust are rarely found at the Earth’s surface because they need to be enclosed in a buoyant host rock such as serpentinites that facilitate exhumation  相似文献   

使用威斯特波克射电望远镜对古代东方“客星”射电遗迹的探测     

G.G.C.帕伦博  P.斯基沃·卡姆波  G.K.迈利 《天文学报》1980,(4)

作者使用威斯特波克射电望远镜在610兆赫频率上对古代东方天文学家观测到的“客星”的七个视场区(1~o.5×1~o.5)进行了射电遗迹的巡天探测,结果没有发现弥漫射电辐射。本文给出了在这些视场区中的分立射电源的表,表中列出作者提出的这些射电源|b|<15°以內的光学证认。  相似文献