Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations     

Veltman K  Huijbregts MA  van den Heuvel-Greve MJ  Vethaak AD  Hendriks AJ 《Marine environmental research》2006,61(5):511-530

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.  相似文献   

澳大利亚——斑达岛弧碰撞力学     

Barb.  AJ 蓝晶 《地质科学译丛》1989,6(3):22-22

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西澳Connemarra和Kathleen金矿床蚀变和未蚀变岩石的识别     

Eggo  AJ 李月湘 《国外铀金地质》1991,(2):27-34

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Developing a Radiative Shock Experiment Relevant to Astrophysics     

Shigemori K  Ditmire T  Remington BA  Yanovsky V  Ryutov D  Estabrook KG  Edwards MJ  MacKinnon AJ  Rubenchik AM  Keilty KA  Liang E 《The Astrophysical journal》2000,534(2):L159-L162

We assume that internal shocks of gamma-ray bursts (GRBs) consist of multiple sub-jets with a collimation half-angle of about several times gamma-1i, where gammai is the Lorentz factor of each sub-jet. If by chance a sub-jet is first emitted off-axis from the line of sight, the observed peak energy can be in the X-ray region. Next, if by chance a subsequent sub-jet is emitted along the line of sight, then the peak energy will be in the gamma-ray region and the gamma ray may arrive after the X-ray precursor from the former sub-jet depending on parameters. This model predicts a new class of GRBs with extremely weak and short gamma-ray emission but X-ray precursors and/or postcursors as well as an afterglow.  相似文献   

Initial Time Dependence of Abundances in Solar Energetic Particle Events     

Reames DV  Ng CK  Tylka AJ 《The Astrophysical journal》2000,531(1):L83-L86

We compare the initial behavior of Fe/O and He/H abundance ratios and their relationship to the evolution of the proton energy spectra in "small" and "large" gradual solar energetic particle (SEP) events. The results are qualitatively consistent with the behavior predicted by the theory of Ng et al. published in 1999. He/H ratios that initially rise with time are a signature of scattering by non-Kolmogorov Alfvén wave spectra generated by intense beams of shock-accelerated protons streaming outward in large gradual SEP events.  相似文献   

答复Ballhaus等（1988）的讨论     

Nald.  AJ 杨合群 《西北地质》1990,(90):21-25

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白朴杂剧的艺术魅力扮亮了多个地名异彩     

白桦 《中国地名》2013,(10):74-75

白朴（1226～1306年）,字仁甫,一字太素,号兰谷。其父白华,曾任金朝枢密院经历官。当蒙古大军围攻金朝首都时,白华随金哀宗出奔,家眷则留在城内。不久城破,白朴的母亲死于浩劫,年仅8岁的白朴,幸得其父亲好友元好问携带抚养。  相似文献   

How to overcome inter-electrode variability and instability to quantify dissolved oxygen, Fe(II), mn(II), and S(?II) in undisturbed soils and sediments using voltammetry     

Slowey AJ  Marvin-Dipasquale M 《Geochemical transactions》2012,13(1):6-20

Background

Although uniquely capable of measuring multiple redox constituents nearly simultaneously with no or minimal sample pretreatment, voltammetry is currently underutilized in characterizing redox conditions in aquatic and terrestrial systems. Investigation of undisturbed media such as pore water requires a solid-state electrode, and such electrodes can be difficult to fabricate reproducibly. An approach to determine the concentrations of electroactive constituents using indirectly calibrated electrodes has been developed, but the protocol for and accuracy of this approach??the pilot ion method??has not been documented in detail.

Results

A detailed procedure for testing electrode quality is provided, and the application and limitations of the pilot ion method have been documented. To quantify Fe(II) and Mn(II), subtraction of non-linear baseline functions from voltammetric signals produced better calibration curves than did linear baselines, enabled lower detection limits and reliable deconvolution of overlapping signals, and was successfully applied to sediment pore water signals. We observed that electrode sensitivities often vary by tens of percent, and that the sensitivity declines over time. The ratio of calibration slopes of Mn(II) to Fe(II) varied by no more than 11% from one Hg/Au electrode to another and Fe(II) concentrations predicted by the Mn(II) pilot ion were, on average, 13% different from their actual values. However, concentration predictions by the pilot ion method were worse for less than 15???M Fe(II) (46% different on average). The ratio of calibration slopes of Mn(II) to S(?II) varied by almost 20% from one Hg/Au electrode to another, and S(?II) predicted concentrations were as much as 58% different from their actual values. These predictions of Fe(II) and S(?II) concentrations indicate that the accuracy of the pilot ion method depends on how independent calibration slope ratios are from the electrode used. At medium-to-high concentration for the ocean, naturally derived dissolved organic carbon did not significantly affect the baseline-corrected electrode response of Mn(II) and Fe(II), but did significantly affect the response of S(?II).

Conclusions

Despite their intrinsic variability, Hg/Au electrodes fabricated by hand can be used to quantify O₂, S(?II), Fe(II), and Mn(II) without calibrating every electrode for every constituent of interest. The pilot ion method can achieve accuracies to within 20% or less, provided that the underlying principle??the independence of slope ratios??is demonstrated for all voltammetric techniques used, and effects of the physicochemical properties of the system on voltammetric signals are addressed through baseline subtraction.  相似文献   

Weakly nonlinear approximation of periodic flow in phreatic aquifers     

Smith AJ 《Ground water》2008,46(2):228-238

Published frequency-domain solutions of periodic flow in aquifers apply strictly to mathematically linear systems that arise when aquifer diffusivity is assumed constant in space and time. This assumption can be invalid in phreatic aquifers that experience spatiotemporal variation in the free surface position and consequent variation in saturated thickness. A weakly nonlinear approach to formulating and solving periodic flow problems in the frequency domain can be applied in situations where conventional linearized approximations break down. The weakly nonlinear equations provide robust approximations of the true nonlinear response and require much less computational effort and time to solve than the full nonlinear problem. Nondimensional rules of thumb are presented for choosing between linear, weakly nonlinear and nonlinear solution strategies.  相似文献   

The Sea Empress oil spill (Wales, UK): effects on Common Scoter Melanitta nigra in Carmarthen Bay and status ten years later     

Banks AN  Sanderson WG  Hughes B  Cranswick PA  Smith LE  Whitehead S  Musgrove AJ  Haycock B  Fairney NP 《Marine pollution bulletin》2008,56(5):895-902

Carmarthen Bay, UK, regularly supports internationally important numbers (>16,000) of non-breeding Common Scoters Melanitta nigra. The spill of 72,000 tonnes of crude oil from the Sea Empress in 1996 affected birds both through direct mortality and likely pollution of key food resources. Numbers were greatly reduced following the spill, whilst changes in the distribution of birds within Carmarthen Bay suggested that potentially sub-optimal foraging zones were used. However, ten years after the incident, numbers of Common Scoter were no different to those recorded immediately before the spill. Compared to some other spills, rapid revival is evident. Numbers increased to pre-spill levels within three winters and distributional changes suggested a concurrent return to previously contaminated feeding areas, implying that the ecosystem had regenerated sufficiently to support its top predator. The importance of prolonged, standardised monitoring of bird numbers and distribution as indicators of ecological recovery from environmental damage is emphasised.  相似文献