Differential rotation on rapidly rotating stars

Theories of meridional circulation and differential rotation in stellar convective zones predict trends in surface flow patterns on main-sequence stars that are amenable to direct observational testing. Here I summarise progress made in the last few years in determining surface differential rotation patterns on rapidly-rotating young main-sequence stars of spectral types F, G, K and M. Differential rotation increases strongly with increasing effective temperature along the main sequence. The shear rate appears to increase with depth in the sub-photospheric layers. Tidal locking in close binaries appears to suppress differential rotation, but better statistics are needed before this conclusion can be trusted. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

近200 a来珠穆朗玛峰北坡远东绒布冰芯气候记录

１９９９年５月中美联合珠穆朗玛峰地区绒布冰川考察期间,在远东绒布冰川海拔６５００ｍ的北支冰流粒雪盆内钻取到一支４１ｍ长冰芯,通过数年层法并根据β活化度的参照年（１９５４年和１９６３年）,对远东绒布冰芯实施定年,冰芯底部为１８１４年,冰芯年平均净积累量为２２４ｍｍ（冰当量）。根据远东绒布冰芯δ＾１８Ｏ的变化,重建了珠穆良玛峰北坡地区近２００ａ气候变化,发现有５次冷期和５次暖期,且总趋势为变暖,这与本     

The origin of alluvial gold in the Leadhills area of Scotland: evidence from interpretation of internal chemical characteristics

A detailed chemical study has been carried out of 1794 gold grains from 55 sites within an area approximately 7 km by 18 km around Leadhills in the turbidite-facies, wacke-dominant Southern Uplands terrane of Scotland, formed as an accretionary thrust complex at the Laurentian continental margin during Ordovician and Silurian subduction of the Iapetus Ocean. The Leadhills area has had a long history of alluvial gold working, since at least 1510, and probably much earlier, but few bedrock sources of mineralisation have been located. Quantitative electron microprobe point analyses were obtained of sectioned and polished gold grains and of the associated microscopic inclusions, which in total comprised 35 types of opaque minerals. Microchemical X-ray maps were also obtained using a fully automated electron microprobe to show internal chemical compositional variation, to resolve the components of multiple and composite inclusions and to help in the identification of the smallest examples. Silver is present within most grains but Cu, Hg and Pd were only detected in about 3% of the grains. The shapes of cumulative frequency plots of the Ag contents of grains from different sites allow recognition of populations from different sources and enables comparison and differentiation between sites. In one of the main rivers, the Shortcleugh Water, the nature of the gold is generally similar, both in terms of Ag content and inclusion type, but a further type of gold, relatively rich in Ag and containing distinctive Ni and Sb-rich inclusions, is also present in 4 adjacent samples in one sector of the watercourse. This component of the samples reflects downstream dispersion, of up to 400 m, of gold grains from a mineralised structure cutting the river almost perpendicularly. Elsewhere abrupt changes in the nature of the alluvial gold within streams reflect a series of different sources and indicate limited glacial and alluvial dispersion. Four main types of gold which are considered to be derived from different varieties of source mineralisation can be recognised on the basis of composition and inclusion assemblage. The commonest type (ca. 70%) contains 8.4–13.1% Ag and inclusions, mostly of arsenopyrite, pyrrhotite, pyrite, chalcopyrite, galena, sphalerite and cobaltite, characteristics typical of mesothermal gold from shear-zones within a turbidite environment, suggesting sources within the local Lower Palaeozoic sedimentary rocks. The second type is richer in Ag (15.8–31.3%) with a basic igneous signature indicated from inclusions of Sb-rich gersdorffite, pyrite, Ni arsenide and other Ni-rich minerals, and shows some spatial association with discordant Tertiary basaltic dykes which cut the sedimentary rocks. The third type, mostly found in an area mantled by glacial drift, is poor in Ag (<1.2%) but frequently Cu-bearing and with inclusions of platinoids and Cu oxide. Associated with this type of gold are grains of the intermetallic compound Au₃Cu and platinoids such as isoferroplatinum and a complex Ir-rich phase. Its source is problematical and could partly reflect detrital material associated with ophiolitic debris, which is common in the northernmost turbidites, and partly a local source of lode gold. The fourth gold type is also Ag-poor (<3.2%), but frequently contains Pd, up to 6.3%, while the inclusions comprise selenides of Pb, Hg and Cu. In nearby areas this type of gold is associated with Permian red beds and associated basaltic volcanics and also structures in the Lower Palaeozoic into which oxidising solutions derived from the red bed sequence have penetrated.     

Leveling geochemical data between map sheets

Geochemical surveys are frequently assembled into larger, regional compilations. In some cases a boundary shift in the values for one or more elements may be observed at the join of adjacent surveys. This indicates that data for the affected elements are not consistent between the surveys. Where the same sampling medium has been used, the shift may be due to different crews/organizations, who varied in their sampling techniques. However, most commonly the shift is due to imperfect calibration of the analytical method used for samples from the different surveys. For example, there may have been a lack of proper analytical standardization between survey programs. To carry out leveling, bands are established on either side of the boundary between two surveys that show a shift. It is desirable that the bands have a close match in terms of geology and physiography. A quantitative method is presented to estimate the optimum width for these bands. Quantiles of the data within each band are calculated. The quantile pairs are plotted in X–Y space and a line fitted to express the relationship between the pairs of quantiles. The equation of this line is used to correct the shift between the two surveys. This method is tested on data for Mo in stream sediments, and pH of stream water, from two National Geochemical Reconnaissance Surveys in British Columbia.     

Coupling behavior of shear deformation and end rotation of elastomeric seismic isolation bearings

This paper presents a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to combined end rotations and shear deformation. The mechanical model consists of a series of axial springs at the top, mid‐height and bottom of the bearing to vertically reproduce asymmetric bending moment distribution in the bearings. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing and the imposed shear deformation. Static bending tests under various combinations of vertical load and shear deformation were performed to identify the mechanical characteristics of bearings. The test results indicate that bearing rotational stiffness increases with increasing vertical load but decreases with increasing shear deformation. Simulation analyses were conducted to validate the new mechanical model. The results of analyses using the new model show very good agreement with experimental observations. A series of seismic response analyses were performed to demonstrate the dynamic behavior of top‐of‐column isolated structures, a configuration where the end rotations of isolation bearings are typically expected to be larger. The results suggest that the end rotations of elastomeric bearings used in practical top‐of‐column isolated structures do not reduce the stability limit of isolation system. Copyright © 2016 John Wiley & Sons, Ltd.     

Resilience to change in two coastal communities: Using the maximum dexterity fleet

Using whole-ecosystem dynamic simulation models fitted to local data, two coastal communities are described (temperate, northern British Columbia, Canada; tropical, Raja Ampat, Indonesia) where relatively poor fishers’ livelihoods are threatened by climate change and overfishing. A novel theoretical minimum bycatch scenario, the ‘maximum dexterity fleet’, is combined with a search algorithm specifying optimal fisheries to achieve economic and biodiversity goals. Potential gains made by approaching an optimal fleet configuration prove robust against increased risks from climate variability. Although fish, gear and way of life differ greatly, in both communities it is suggested that dexterity (adroitness in adapting fishing gear) could lead to improved benefits from fishing.     

Variability of Sea-Ice Extent in Baffin Bay over the Last Millennium

Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.     

Climate,fire and vegetation history from subtropical North Stradbroke Island (Minjerribah), eastern Australia,during the last three interglacials

Records of Australian palaeoclimate beyond the last glacial cycle are rare, limiting detailed analysis of long-term climate trends and associated ecosystem responses. This study analyses a discontinuous pollen and charcoal record from Fern Gully Lagoon, North Stradbroke Island (Minjerribah), subtropical Queensland, Australia, which covers much of the last ~210 ,000 years. Climate variation is inferred from changes in vegetation, while analysis of micro- and macrocharcoal is used to infer fire activity. Pollen assemblages consist of ~40% rainforest taxa during marine isotope stage (MIS) 7a–c and early MIS 5. These are inferred to result from high rainfall in the Australian subtropics, which was also evident in north-east and central Australia. Human impact from 21 ,000 years ago likely supressed post-MIS 2 rainforest expansion to some extent. However, the increased Holocene abundance of herbs and grasses and reduced representation of aquatic taxa suggest that the Holocene was relatively dry when compared with early MIS 5 and MIS 7a–c. Similar MIS 5 and early MIS 7a–c climates, in contrast to a notably drier Holocene, suggest that the progressive interglacial drying trend most strongly recorded in central Australia was not a major feature of subtropical eastern Australian climates.