Temporal signatures of advective versus diffusive radon transport at a geothermal zone in Central Nepal

Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m⁻² d⁻¹. Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO₂ concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m⁻³, but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO₂ advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m⁻³, remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S₁ and semi-diurnal S₂ periodic components. At the advection-dominated points, radon concentration did not exhibit S₁ or S₂ components. At the reference points, however, the S₂ component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S₁ component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle.     

水体中常见无机阳离子对TiO_2薄膜光催化还原Cr(Ⅵ)的影响

选择了6种水体中常见的阳离子(Na+、Mg2+、Ca2+、Al3+、Cu2+、Ni2+),分别考查了其对TiO2薄膜光催化还原Cr(Ⅵ)的影响;从光吸收、无机离子本身的性质对光生电子的捕获及传递等讨论了上述离子影响TiO2薄膜光催化还原Cr(Ⅵ)的反应速率的原因。结果表明:由于其不能捕获光生电子,Na+、Mg2+、Ca2+本身对TiO2薄膜光催化还原Cr(Ⅵ)的反应速率影响不大;Al3+吸引电子能力较强,成为光生电子和Cr(Ⅵ)之间的桥梁,促进了Cr(Ⅵ)的还原;浓度为1 mmmol/L时,Cu2+显著地促进了Cr(Ⅵ)的光催化还原,其主要原因是Cu2+捕获光生电子的能力很强,起到了催化剂的作用,而浓度大于10 mmol/L时,Cu2+形成单质Cu以及对紫外光的吸收都使促进作用降低;Ni2+未充满的d轨道具有获得并传递光生电子的能力,也促进了Cr(Ⅵ)的还原;在浓度同为1mmol/L时,对Cr(Ⅵ)光催化还原的促进作用依次为:Cu2+Al3+Ni2+Na+、Ca2+、Mg2+。     

Diffusive gradient in thin FILMS (DGT) compared with soil solution and labile uranium fraction for predicting uranium bioavailability to ryegrass

The usefulness of uranium concentration in soil solution or recovered by selective extraction as unequivocal bioavailability indices for uranium uptake by plants is still unclear. The aim of the present study was to test if the uranium concentration measured by the diffusive gradient in thin films (DGT) technique is a relevant substitute for plant uranium availability in comparison to uranium concentration in the soil solution or uranium recovered by ammonium acetate. Ryegrass (Lolium perenne L. var. Melvina) is grown in greenhouse on a range of uranium spiked soils. The DGT-recovered uranium concentration (C_DGT) was correlated with uranium concentration in the soil solution or with uranium recovered by ammonium acetate extraction. Plant uptake was better predicted by the summed soil solution concentrations of UO₂²⁺, uranyl carbonate complexes and UO₂PO₄⁻. The DGT technique did not provide significant advantages over conventional methods to predict uranium uptake by plants.     

Dissipation gradients of phenanthrene and pyrene in the Rice rhizosphere

An experiment was conducted to reveal the effects of rice cultivation as well as polycyclic aromatic carbohydrates (PAHs) degrading bacterium (Acinetobacter sp.) on the dissipation gradients of two PAHs (PHE and PYR) in the rhizosphere. The results showed that the presence of rice root and bacteria significantly accelerated the dissipation rate of PHE and PYR. The root exudates contributed to the formation of dissipation gradients of PHE and PYR along the vertical direction of roots, with a higher dissipation rate in the rhizosphere and near rhizosphere zone than the soil far away the rhizosphere.     

Nano-textured polysilicon solar absorption films

Nano-textured polysilicon (poly-Si) solar absorption films are to be applied to the solar receiver of solar thermal electricity Stirling engine. These films were fabricated by deposition of hydrogenated amorphous silicon films (a-Si:H) into poly-Si films, using the pulse-wave modulation plasma and furnace annealing of the a-Si:H films. This is followed by wet etching of poly-Si films into nano-textured structures. The films are then coated with a-SiN_x:H films as the antireflection and protection layers. It was observed that increasing the pulsed plasma turn-on (t_on) time leads to deposition of less dense a-Si:H film with high hydrogen content and void density. This results in films having low dielectric constant and refractive index, and high optical bandgap. Less-dense a-Si:H film can be transferred into large grain size poly-Si film, using annealing. Also, highly rough nano-textured surface structure can be produced, by etching. The denser a-Si:H film, large grain size poly-Si film, and nano-textured surface poly-Si film can enhance the absorbance of sunlight and reduce the emissivity of far infrared light. The nano-textured poly-Si film coated with an a-SiN_x:H layer can effectively increase the absorbance of sunlight to approximately 85% and reduce the emissivity of far infrared light to 49%. The nano-textured poly-Si/a-SiN_x:H films can be used as efficient solar absorption films for solar thermal electricity Stirling engine.     

Chemical Valorization of Forest and Agricultural By-Products. Obtention,Chemical Characteristics,and Mechanical Behavior of a Novel Family of Hydrophobic Films

Abstract

Esterification of hemicelluloses of the xylan family was performed in order to produce hydrophobic films. Acylation reactions were carried out with lauroyl chloride in the N,N-dimethylacetamide/lithium chloride homogeneous system using 4-dimethylaminopyridine as activator and were induced by microwave irradiation. In the experimental conditions used, 108 and 172% mass ratios were obtained for the dodecyl-grafted xylan and heteroxylan, respectively. The degrees of substitution (DS) were 1.3 (maximum 2) for xylan and 1.2 (maximum 2.1) for heteroxylan. These products were further characterized by FT-IR spectroscopy. The mechanical and thermomechanical behavior of this new family of hydrophobic films were analyzed and compared to those obtained from cellulose with a similar DS by the means of tensile tests. Our results indicate that the dodecyl-grafted xylan film presents the best rigidity—resistance to traction ratio.     

Representative measurement of two-dimensional reactive phosphate distributions and co-distributed iron(II) and sulfide in seagrass sediment porewaters

The high degree of heterogeneity within sediments can make interpreting one-dimensional measurements difficult. The recent development and use of in situ techniques that measure two-dimensional distributions of porewater solutes have facilitated investigation of the role of spatial heterogeneity in sediment biogeochemistry. A colourimetric diffusive equilibration in thin films method has been developed that allows two-dimensional, high-resolution measurement of reactive phosphate in sediment porewaters. A method detection limit of 0.22 μM, an effective upper limit of ∼1000 μM and relative standard deviations typically below 5% were achieved. This method was evaluated by deployment in seagrass (Zostera capricorni) colonised sediments, as part of combined probes with similar colourimetric methods for sulfide and iron(II). The two-dimensional, high resolution distributions obtained provide a highly representative measurement of the co-distributions of porewater solutes, allowing heterogeneous features and biogeochemical processes to be observed and interpreted. Microniches of high phosphate concentration >100 μM were observed throughout the distributions and were interpreted to be due to localised zones of rapid organic matter mineralisation, possibly using electron acceptors other than iron(III) oxyhydroxides (e.g. aerobic respiration) as often they did not correspond with microniches of higher Fe(II) concentration.     

高效薄层析进行农药吸附态光解的研究

研究了绿麦隆和消草醚２种除草剂在硅胶Ｇ高效薄层上的光稳定性,提出应用高效薄层析技术作为农药吸附态光解的一种试验方法。在高效薄层上直接点样,同一薄层上包括照光、黑暗对照和定量曲线样品,原始剂量４００—８００ｎｇ·１×５ｍｍ斑点－１,照光后直接展开和扫描定量测定,最低检测量可达２０ｎｇ·斑点－１。本方法无须对样品进行提取、净化等处理,具有快速高效、重复性好,且可直观光解产物等优点。     

航空煤油薄油层燃烧特性实验研究

为研究薄油层燃烧特性,开展航空煤油薄层油池火实验,分析油品燃烧的整个过程、燃烧速率、火焰高度和辐射反馈等参数随时间的变化规律。结果表明:整个薄层燃烧过程除发展、稳定和熄灭阶段外,还存在薄层燃烧衰减阶段。稳定阶段的燃烧速率与初始油层厚度相关,但随着厚度的增加其逐渐趋于稳定;薄层燃烧衰减阶段,燃烧速率会随着实时油层厚度的下降逐渐降低。对比火焰高度的实测值和模型预测值发现,Heskestad模型的预测更接近实际结果;燃烧发展阶段后,火焰辐射反馈基本维持稳定,受初始厚度的影响较小,但辐射透射强度会随着油层厚度的降低而增加,且增速逐渐加快,表明辐射透射在薄层燃烧衰退阶段中起到关键作用。结合辐射透射的变化规律,将辐射反馈分为可吸收和不可吸收2部分,并提出用于预测辐射透射大小的经验模型。     

The Impact of Climate Change on Mammal Diversity in Canada

Current large-scale mammalian diversity patterns in Canada can be accurately explained using various measurements of heat energy. Unfortunately, climatic change is predicted to alter the fundamental climatic basis for contemporary diversity gradients, with the expected consequence that much of the Canadian biota will need to migrate in order to remain within climatically suitable regions. We make predictions regarding future mammal diversity patterns in Canada, and therefore provide a preliminary indication of where management intervention should be directed in order to conserve mammal diversity as climate changes. We also examine the current distributions of individual mammal species in Canada in order to determine which taxa cannot migrate farther north because of the Arctic Ocean barrier. Of the 25 species that fall into this category, we examine the predicted loss of habitat in one keystone species – Dicrostonyx groenlandicus, the collared lemming – and find that this taxon is likely to lose approximately 60% of its habitat with unpredictable but likely detrimental consequences for the arctic biota. We discuss the implications of our findings briefly.