Decomposition of alkyl dixanthogens in aqueous solutions

Alkyl dixanthogens, (ROCSS)₂, decompose in aqueous solution in the presence of nucleophiles in many ways.It is proposed here that in alkaline solution the principal methods of decomposition of ethyl dixanthogen are by simultaneous attack of OH^? ions on the sulphur-sulphur bond to give products which include xanthate ion (ROCSS^?) and peroxide (H₂O₂) and on the carbon-sulphur bond to give products which include monothiocarbonate ion (ROSCO^?), sulphide ion (S^2?), and sulphur (S⁰). Above pH 12 reaction is complete in a few minutes, and more monothiocarbonate than xanthate is formed. At pH 9 the reaction takes over 20 h and more xanthate than monothiocarbonate is formed.The primary products react further to give various ions which depend in part on the pH of the system. In alkaline solution some of the xanthate and peroxide react to give perxanthate (ROCSSO^?). In acid solution both xanthate and monothiocarbonate decompose rapidly; CS₂ is formed from xanthate and OCS from monothiocarbonate.In the presence of other nucleophiles at pH 9.2, dissolved dixanthogen decomposes much more quickly than with OH^? alone, and other reactions occur. With thiosulphate a higher proportion of xanthate is formed together with some xanthyl thiosulphate and monothiocarbonate but no perxanthate. With sulphite (in the absence of oxygen) or cyanide the products include xanthate and monothiocarbonate but no perxanthate. With sulphite in the presence of oxygen, perxanthate is also formed.Suspensions of dixanthogens react slowly but in a similar fashion to dissolved dixanthogens.Longer-chain dixanthogens are much less soluble than ethyl dixanthogen but, in general, react in a similar way. Higher temperatures increase the rate of decomposition by OH^?.This work has various implications in operating plants.     

A structural and geophysical approach to the study of fractured aquifers in the Scansano-Magliano in Toscana Ridge, southern Tuscany, Italy

Fresh water availability has recently become a serious concern in the Italian Apennines, as various activities rely on a predictable supply. Along the ridge between Scansano and Magliano in Toscana, in southern Tuscany, the situation is further complicated by contamination of the nearby alluvial aquifers. Aquifers locally consist of thin fractured reservoirs, generally within low-permeability formations, and it can be difficult to plan the exploitation of resources based on conventional techniques. An integrated study based on geological data investigated the link between tectonics and groundwater circulation, to better define the hydrological model. After the regional identification of fault and fracture patterns, a major structure was investigated in detail to accurately map its spatial position and to understand the geometry and properties of the associated aquifer and assess its exploitation potential. The subsurface around the fault zone was clearly imaged using ground probing radar, two-dimensional and three-dimensional resistivity tomography, and three-dimensional shallow seismic surveys. The vertical and horizontal contacts between the different geological units of the Ligurian and Tuscan series were resolved with a high degree of spatial accuracy. Three-dimensional high-resolution geophysical imaging proved to be a very effective means of characterising small-scale fractured reservoirs.     

Fluxes of Sr into the headwaters of the Ganges

Himalayan weathering is recognized as an important agent in modifying sea water chemistry, but there are significant uncertainties in our understanding of Himalayan riverine fluxes. This paper examines causes of the variability, including that of the seasons, by analysis of downstream variations in Sr, ⁸⁷Sr, and major ions in the mainstream, in relation to the composition of tributary streams from subcatchments with differing geologic substrates.Water samples were collected over four periods spanning the premonsoon, monsoon, and postmonsoon seasons. Uncertainties in the relative fluxes have been estimated, using Monte Carlo techniques, from the short-term variability of mainstream chemistry and the scatter of tributary compositions. The results show marked seasonal variations in the relative inputs related to high monsoon rainfall in the High and Lesser Himalaya, contrasting with the major contribution from glacial melt waters from the Tibetan Sedimentary Series (TSS) at times of low rainfall. Much of the spread in previously published estimates of the sources of Sr in Himalayan rivers may result from these seasonal variations in Sr fluxes.The annual fluxes of Sr into the headwaters of the Ganges are derived from the three main tectonic units in the proportions 35 ± 1% from the TSS, 27 ± 3% from the High Himalayan Crystalline Series (HHCS), and 38 ± 8% from the Lesser Himalaya. The particularly elevated ⁸⁷Sr/⁸⁶Sr ratios characteristic of the HHCS and the Lesser Himalaya enhance their influence on seawater Sr-isotope composition. The TSS contributes 13 ± 1%, the HHCS 30 ± 3%, and the Lesser Himalaya 57 ± 11% of the ⁸⁷Sr flux in excess of the seawater ⁸⁷Sr/⁸⁶Sr ratio of 0.709.     

空间尺度转换与跨尺度信息链接:区域生态水文模拟研究空间尺度转换方法综述

空间尺度转换是近年来区域生态水文研究领域的一个基本研究问题。其需要主要是源于模型的输入数据与所能提供的数据空间尺度不一致以及模型所代表的地表过程空间尺度与所观测的地表过程空间尺度不吻合。综述了目前区域生态水文模拟研究中常用的空间尺度转换研究方法,包括向上尺度转换和向下尺度转换。详细论述了2种向下尺度转换方法: 统计学经验模型和动态模型。前者是通过将GCM大尺度数据与长期的历史观测数据比较从而建立统计学相关模型, 然后利用这个统计学经验模型进行向下的空间尺度转换. 然而动态模型并不直接对GCM数据进行向下尺度的转换,而是对与GCM进行动态耦合的区域气候模型(RCM) 的输出数据进行空间尺度转换. 通常后者所获得的数据精度要比前者高,但是一个主要缺点就是并不是全球所有的研究区域都有对应的RCM。还详细论述了2种向上尺度转换方法: 统计学经验模型和斑块模型。前者是建立一个能代表小尺度信息在大尺度上分布的密度分布概率函数, 然后利用这个函数在所需的大尺度上进行积分而求得大尺度所需的信息。而后者是根据相似性最大化原则将大尺度划分为若干个可操作的小尺度斑块,然后将计算的每个小尺度斑块的信息平均化得到大尺度所需的信息。通常在计算这种斑块化的小尺度信息的时候,对每个小尺度也会采用统计学经验模型来计算代表整个斑块小尺度的信息。建议用斑块模型与统计学经验模型相集合的方法来实现向上的空间尺度转换     

Rapid Eocene erosion,sedimentation and burial in the eastern Himalayan syntaxis and its geodynamic significance

The lower Bomi Group of the eastern Himalayan syntaxis comprises a lithological package of sedimentary and igneous rocks that have been metamorphosed to upper amphibolite-facies conditions. The lower Bomi Group is bounded to the south by the Indus–Yarlung Suture and to the north by unmetamorphosed Paleozoic sediments of the Lhasa terrane. We report U–Pb zircon dating, geochemistry and petrography of gneiss, migmatite, mica schist and marble from the lower Bomi Group and explore their geological implications for the tectonic evolution of the eastern Himalaya. Zircons from the lower Bomi Group are composite. The inherited magmatic zircon cores display ²⁰⁶Pb/²³⁸U ages from ~ 74 Ma to ~ 41.5 Ma, indicating a probable source from the Gangdese magmatic arc. The metamorphic overgrowth zircons yielded ²⁰⁶Pb/²³⁸U ages ranging from ~ 38 Ma to ~ 23 Ma, that overlap the anatexis time (~ 37 Ma) recorded in the leucosome of the migmatites. Our data indicate that the lower Bomi Group do not represent Precambrian basement of the Lhasa terrane. Instead, the lower Bomi Group may represent sedimentary and igneous rocks of the residual forearc basin, similar to the Tsojiangding Group in the Xigaze area, derived from denudation of the hanging wall rocks during the India–Asia continental collision. We propose that following the Indian–Asian collision, the forearc basin was subducted, together with Himalayan lithologies from the Indian continental slab. The minimum age of detrital magmatic zircons from the supracrustal rocks is ~ 41.5 Ma and their metamorphism had happened at ~ 37 Ma. The short time interval (< 5 Ma) suggests that the tectonic processes associated with the eastern Himalayan syntaxis, encompassing uplift and erosion of the Gangdese terrane, followed by deposition, imbrication and subduction of the forearc basin, were extremely rapid during the Late Eocene.     

Shark interactions in pelagic longline fisheries

Substantial ecological, economic and social problems result from shark interactions in pelagic longline fisheries. Improved understanding of industry attitudes and practices towards shark interactions assists with managing these problems. Information on fisher knowledge and new strategies for shark avoidance may benefit sharks and fishers. A study of 12 pelagic longline fisheries from eight countries shows that incentives to avoid sharks vary along a continuum, based on whether sharks represent an economic disadvantage or advantage. Shark avoidance practices are limited, including avoiding certain areas, moving when shark interaction rates are high, using fish instead of squid for bait and deeper setting. Some conventionally employed fishing gear and methods used to target non-shark species contribute to shark avoidance. Shark repellents hold promise; more research and development is needed. Development of specifically designed equipment to discard sharks could improve shark post release survival prospects, reduce gear loss and improve crew safety. With expanding exploitation of sharks for fins and meat, improved data collection, monitoring and precautionary shark management measures are needed to ensure that shark fishing mortality levels are sustainable.     

The Longmyndian Rocks of the Old Radnor Inlier,Welsh Borderland

Two formations are named in the presumed Precambrian sedimentary rocks of the Old Radnor Inlier. The Strinds Formation comprises fine- to medium-grained sandstones and pebbly sandstones. Grain-size, texture, clast types, and lithological invariance support correlation with the homogeneous and cross-bedded sandstone facies of the Bayston-Oakswood Formation of the Longmyndian, assigned to a braided alluvial plain environment. The Yat Wood Formation comprises fine-grained sandstones, siltstones, and laminated mudstones. It may be equivalent to some part of the Burway, Synalds, or Lightspout Formation. The Strinds and Yat Wood Formations are petrographically similar to each other and to the type Lonmyndian, and were sourced either directly or indirectly from a magmatic arc. The Strinds and Yat Wood Formations are seen only in faulted contact, and the inlier itself is partly or wholly bounded by strands of the Church Stretton fault zone. Similar faulted relationships are seen further northeast along the system at Pedwardine and in the Church Stretton area. A fault explanation for the juxtaposition of contrasting facies is favoured over that of an original unconformity of Strinds on Yat Wood Formation.