Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

Various sorption phenomena, such as aging, hysteresis and irreversible sorption, can cause differences between contaminant (ad)sorption and desorption behavior and lead to apparent sorption ‘asymmetry’. We evaluate the relevance of these characteristics for neptunium(V) (Np(V)) sorption/desorption on goethite using a 34-day flow-cell experiment and kinetic modeling. Based on experimental results, the Np(V) desorption rate is much slower than the (ad)sorption rate, and appears to decrease over the course of the experiment. The best model fit with a minimum number of fitting parameters was achieved with a multi-reaction model including (1) an equilibrium Freundlich site (site 1), (2) a kinetically-controlled, consecutive, first-order site (site 2), and (3) a parameter ψ_2,de, which characterizes the desorption rate on site 2 based on a concept related to transition state theory (TST). This approach allows us to link differences in adsorption and desorption kinetics to changes in overall reaction pathways, without assuming different adsorption and desorption affinities (hysteresis) or irreversible sorption behavior a priori. Using modeling as a heuristic tool, we determined that aging processes are relevant. However, hysteresis and irreversible sorption behavior can be neglected within the time-frame (desorption over 32 days) and chemical solution conditions evaluated in the flow-cell experiment. In this system, desorption reactions are very slow, but they are not irreversible. Hence, our data do not justify an assumption of irreversible Np(V) sorption to goethite in transport models, which effectively limits the relevance of colloid-facilitated Np(V) transport to near-field environments. However, slow Np(V) desorption behavior may also lead to a continuous contaminant source term when metals are sorbed to bulk mineral phases. Additional long-term experiments are recommended to definitely rule out irreversible Np(V) sorption behavior at very low surface loadings and environmentally-relevant time-scales.     

The audacity of the ocean: Gendered politics of positionality in the Pacific

Throughout the contemporary Pacific, relationships that indigeneity makes possible are emerging as celebrated resistance to post-colonial development anxieties. In the process, lived experience heightens the commitment to decolonize thinking, language and practice in teaching and research. Not only because these imperatives are highly personalized but also because they are gendered and heavy with generational trauma. These gendered dynamics circulate around popular culture and imaginaries of Pacific paradise but also problematically around the challenges of long-standing intolerances especially around gender and race. The paper asks how a gendered politics of positionality engages with emerging positionalities that uncritically allow for such intolerances. I touch on two ways in which colonial continuities of belittlement are often reinforced, but are also offering hopeful and careful decolonial scholarly futures. The first is the naming of the Pacific and the second is supervising women doctoral candidates from the Pacific. In this paper, the audacity of the ocean offers a metaphorical opportunity to carefully reconcile these tensions and provide trajectories for decolonial knowledge-making. However, it also offers a material way of understanding the on-going work with ‘tensions’ and disruptions in their ever present but changeable forms. Oceanic tropes and a feminist Oceanic audacity of embodied engagement in the Pacific offer dynamic and gendered intellectual agility which runs counter to the tropical imageries of languid indifference.

black/is a state of mind like the colour of an island Teaiwa (2017) we sweat and cry salt water, so we know that the ocean is really in our blood Teaiwa (2008)

     

侧扫声纳系统姿态参数平滑方法研究

针对侧扫声纳系统姿态参数采样率低于声纳Ping值采样率的问题,采用窗口移动多项式最小二乘平滑方法（Savitzky—Golay平滑法）,对阶梯状姿态数据进行平滑。结果证明了该法的可行性。在选取窗口宽度和多项式阶数时,通过实测数据比较表明,采用窗口为11的二阶多项式平滑后结果与原数据符合程度高。     

Field Tracer Test for the Design of LNAPL Source Zone Surfactant Flushing

A field tracer test was carried out in a light nonaqueous phase liquid (LNAPL) source zone using a well pattern consisting of one injection well surrounded by four extraction wells (5‐spot well pattern). Multilevel sampling was carried out in two observation wells located inside the test cell characterized by heterogeneous lithology. Tracer breakthrough curves showed relatively uniform flow within soil layers. A numerical flow and solute transport model was calibrated on hydraulic heads and tracer breakthrough curves. The model was used to estimate an average accessible porosity of 0.115 for the swept zone and an average longitudinal dispersivity of 0.55 m. The model was further used to optimize the relative effects of viscous forces versus capillary forces under realistic imposed hydraulic gradients and to establish optimal surfactant solution properties. Maximum capillary number (N_Ca) values between injection and extraction wells were obtained for an injection flow rate of 16 L/min, a total extraction flow rate of 20 L/min, and a surfactant solution with a viscosity of 0.005 Pa?s. The unconfined nature of the aquifer limited further flow rate or viscosity increases that would have led to unrealistic hydraulic gradients. An N_Ca range of 3.8 × 10^?4 to 7.6 × 10^?3 was obtained depending on the magnitude of the simulated LNAPL‐water interfacial tension reduction. Finally, surfactant and chase water slug sizing was optimized with a radial form of the simplified Ogata‐Banks analytical solution (Ogata and Banks 1961) so that injected concentrations could be maintained in the entire 5‐spot cell.     

Crop area mapping in West Africa using landscape stratification of MODIS time series and comparison with existing global land products

In Africa, food security early warning systems use satellite-derived data concerning crop conditions and agricultural production. Such systems can be improved if they are provided with a more reliable estimation of the cultivated area at national scale. This paper evaluates the potential of using time series from the MODerate resolution Imaging Spectroradiometer MOD13Q1 (16-day composite of normalized difference vegetation index at 250 m resolution) to extract cultivated areas in the fragmented rural landscapes of Mali. To this end, we first stratified Southern Mali into 13 rural landscapes based on the spatio-temporal variability of NDVI and textural indices, using an object-oriented classification scheme.The accuracy of the resulting map (MODIS_crop) and how it compares with existing coarse-resolution global land products (GLC2000 Africa, GLOBCOVER, MODIS V05 and ECOCLIMAP-II), was then assessed against six crop/non-crop maps derived from SPOT 2.5 m resolution images used as references. For crop areal coverage, the MODIS_crop cultivated map was successful in assessing the overall cultivated area at five out of the six validation sites (less than 6% of the absolute difference), while in terms of crop spatial distribution, the producer accuracy was between 33.1% and 80.8%. This accuracy was linearly correlated with the mean patch size index calculated on the SPOT crop maps (r² = 0.8). Using the Pareto boundary as an accuracy assessment method at the study sites, we showed that (i) 20-40% of the classification crop error was due to the spatial resolution of the MODIS sensor (250 m), and that (ii) compared to MODIS V05, which otherwise performed better than the other existing products, MODIS_crop generally minimized omission-commission errors. A spatial validation of the different products was carried out using SPOT image classifications as reference. In the corresponding error matrices, the fraction of correctly classified pixels for our product was 70%, compared to 58% for MODIS V05, while it ranged between 40% and 51% for the GLC2000, the ECOCLIMAP-II and the GLOBCOVER.     

藏南洛扎地区洛扎断裂构造特征及其地质意义

藏南洛扎地区洛扎断裂属于区域上定日—洛扎断裂的东段部分,是喜马拉雅造山带中一条重要的断裂,但其总体研究程度较低。运用地质填图和构造解析的方法研究了洛扎断裂的几何形态、运动表现和活动历史等,讨论其在喜马拉雅造山带构造格局形成中的意义。主要认识如下:(1)洛扎断裂现今主要表现为一条规模大的脆性-脆韧性断层,SWW—NEE走向,高角度倾向NNW。断层带内发育劈理带、断层泥、构造角砾岩等。运动性质主体表现为正断层。(2)洛扎断裂的南北两侧地块具有显著不同的变形特征,南侧为平缓的大型背斜-向斜构造,北侧为近NWW—SEE走向的倒转褶皱-断层构造。(3)洛扎断裂经历了多期活动,中生代正断活动,古近纪逆冲活动,中新世韧性伸展,中新世晚期逆冲活动以及上新世—第四纪正断活动。现今断层展示的更多是最后一期活动的形迹。(4)依据其规模大、多期活动性、两盘构造变形与沉积的系统差异性等肯定了其作为构造分区断层而存在。(5)洛扎断裂和藏南拆离断层(STD)在研究区均有出露,局部二者出露线近于重合,但洛扎断裂以高角度断面切割了平缓的STD。洛扎断裂是比STD具有更悠久地质历史的区域性断层,只是后者中新世以来的活动性更多受到关注。     

Modeling of cadmium speciation and dynamics in the Seine estuary (France)

A complexation model (MOCO) was used to describe cadmium (Cd) speciation during estuarine transit in the Seine estuary. This model was developed from field data. Laboratory experiments based on the use of¹⁰⁹Cd enabled checking of certain model simplifications and hypotheses and evaluation of parameters which could not be measured directly. MOCO was coupled with a 3D multivariable hydrosedimentary model (SAM3D) to simulate Cd dynamics in the estuary. These results were compared with measurements (dissolved and particulate Cd) obtained during cruises representative of various hydrodynamic conditions. The purpose of this article is to present the modeling approach used, and its expected applications and limits.     

238U-206Pb, 235U-207Pb,systematics on Pyrenean basement

U-Pb ages for zircons of pyreneean gneisses and associated granites are comparable to whole rock Rb-Sr ages of 580, 320 m.y. and recent. Inherited radiogenic Pb in the granites limits the dating accuracy but points out an important contribution of crustal material in their formation.     

Assimilation of continental crust by komatiites in the Precambrian basement of the Carswell structure (Saskatchewan,Canada)

The isotope geochemistry (Sm-Nd, Pb-Pb and Rb-Sr) of mafic gneisses from the basement of the Carswell structure (Saskatchewan, Canada), rich both in Mg and incompatible elements (K, Rb, REE) has been investigated. A good Sm-Nd alignment gives a slope corresponding to an age of 3.7 Ga. However, comparison with major elements data strongly suggests that this alignment is a mixing line between Mg-rich, high CaO/Al₂O₃ magmas and the local felsic crust older than 2.9 Ga. The mafic magmas were probably of komatiitic affinity (MgO > 20 percent) but, nevertheless, were extracted from a source with nearly chondritic to slightly enriched light REE distribution. The age of the komatiite emplacement (1.9–2.9 Ga) is only loosely constrained by the oldest crustal residence age in the series and the subsequent metamorphic events. The granulite facies climax is dated at ca. 1.9 Ga by concordant whole rock Pb-Pb and Sm-Nd garnet-whole rock isochrons. The Rb-Sr systematics have been disturbed by later event(s) younger than 1.5–1.7 Ga, but do not permit a more precise assessment of the perturbation age.     

Electrochemical measurements bearing on the oxidation state of the Skaergaard Layered Intrusion

The oxygen fugacities (fO₂'s) of magnetically-concentrated fractions (MCF) of three rock samples from the Skaergaard Layered Intrusion were measured between 800–1150° C using oxygen-specific, solid zirconia electrolytes at atmospheric pressure. Two of the bulk rock samples (an oxide cumulate and an oxide-bearing gabbro) are from the Middle Zone (MZ) and the other (an olivine plagioclase orthocumulate) is from the Lower Zone (LZ). All MCF define fO₂ versus T arrays that lie 1.5–0.5 log units above the fayalite-magnetite-quartz (FMQ) buffer. Experiments with different cell-imposed initial redox states (one from a reduced direction and one from an oxidized direction) were run on each sample in an attempt to achieve experimental reversibility. This was accomplished by imposing a known redox memory on the galvanic cell prior to loading each sample. Reversibility for each sample agreed to better than 0.2 of a log unit. Irreversible autoreduction of 0.2 of a log unit was observed on the two MZ samples at temperatures exceeding 1065° C. Scanning electron microscope and electron microprobe study of pre- and post-run products shows that reaction and textural re-equilibration occurred among the oxide phase assemblages under the experimental conditions employed. Careful characterization of pre- and post-run assemblages is clearly necessary before adequate interpretation of the experimental results can be made in these types of electrochemical studies. Different approaches to investigations of the fO₂ of the Skaergaard Intrusion, be it thermodynamic calculations or experimental methods, should yield concordant results or at least understandable discrepancies. Calculated fO₂'s using thermobarometry applied to the ilmenite-magnetite pairs in the post-experimental assemblages agree with the experimentally determined fO₂'s to within one log unit at a given temperature. These results are also consistent with previously calculated fO₂ values (Buddington and Lindsley 1964; Morse et al. 1980), but are considerably more oxidized than a previous electrolyte-based fO₂ study of a different sample suite from the Skaergaard (Sato and Valenza 1980) that include values close to the iron-wustite (IW) buffer from both MZ and LZ oxide separates. Differences between this electrochemical study and that of Sato and Valenza (1980) may be due to variations in the level of indigenous (or curatorially-introduced) carbon in the samples studied. Despite a number of experimental difficulties, electrochemical cells can provide an accurate and precise method of determining the oxygen fugacity of naturally occurring, complex oxide assemblages. Tight experimental reversals and reproducible values obtained in heating and cooling cycles are an indication of the precision and accuracy of the data recoverable with electrochemical cells.