Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

Molybdenum disulphide is a layered transition metal dichalcogenide that has recently raised considerable interest due to its unique semiconducting and opto-electronic properties. Although several theoretical studies have suggested an electronic phase transition in molybdenum disulphide, there has been a lack of experimental evidence. Here we report comprehensive studies on the pressure-dependent electronic, vibrational, optical and structural properties of multilayered molybdenum disulphide up to 35 GPa. Our experimental results reveal a structural lattice distortion followed by an electronic transition from a semiconducting to metallic state at similar to 19 GPa, which is confirmed by ab initio calculations. The metallization arises from the overlap of the valance and conduction bands owing to sulphur-sulphur interactions as the interlayer spacing reduces. The electronic transition affords modulation of the opto-electronic gain in molybdenum disulphide. This pressure-tuned behaviour can enable the development of novel devices with multiple phenomena involving the strong coupling of the mechanical, electrical and optical properties of layered nanomaterials.

Active guests in the MoS2/MoSe2 host lattice: efficient hydrogen evolution using few-layer alloys of MoS2(1-x)Se2x

Few-layer transition metal dichalcogenide alloys based on molybdenum sulphoselenides MoS2(1-x)Se2x] possess higher hydrogen evolution (HER) activity compared to pristine few-layer MoS2 and MoSe2. Variation of the sulphur or selenium content in the parent dichalcogenides reveals a systematic structure-activity relationship for different compositions of alloys, and it is found that the composition MoS1.0Se1.0 shows the highest HER activity amongst the catalysts studied. The tunable electronic structure of MoS2/MoSe2 upon Se/S incorporation probably assists in the realization of high HER activity.

Water-responsive carbon nanotubes for selective detection of toxic gases

Ammonia plays an important role in our daily lives and hence its quantitative and qualitative sensing has become necessary. Bulk structure of carbon nanotubes (CNTs) has been employed to detect the gas concentration of 10 ppm. Hydrophobic CNTs were turned to hydrophilic via the application of a ramp electric field that allowed confinement of a controlled amount of water inside CNT microstructure. These samples were then also used to detect different gases. A comparative study has been performed for sensing three reducing gases, namely, ammonia, sulphur-di-oxide, and hydrogen sulphide to elaborate the selectivity of the sensor. A considerable structural bending in the bulk CNT was observed on evaporation of the confined water, which can be accounted to the zipping of individual nanotubes. However, the rate of the stress induced on these bulk microstructures increased on the exposure of ammonia due to the change in the surface tension of the confined solvent. A prototype of an alarm system has been developed to illustrate sensing concept, wherein the generated stress in the bulk CNT induces a reversible loss in electrical contact that changes the equivalent resistance of the electrical circuit upon exposure to the gas. (C) 2015 AIP Publishing LLC.

Modification of metal-InGaAs Schottky barrier behaviour by atomic layer deposition of ultra-thin Al2O3 interlayers

The effect of inserting ultra-thin atomic layer deposited Al2O3 dielectric layers (1 nm and 2 nm thick) on the Schottky barrier behaviour for high (Pt) and low(Al) work function metals on n- and p-doped InGaAs substrates has been investigated. Rectifying behaviour was observed for the p-type substrates (both native oxide and sulphur passivated) for both the Al/p-InGaAs and Al/Al2O3/p-InGaAs contacts. The Pt contacts directly deposited on p-InGaAs displayed evidence of limited rectification which increased with Al2O3 interlayer thickness. Ohmic contacts were formed for both metals on n-InGaAs in the absence of an Al2O3 interlayer, regardless of surface passivation. However, limited rectifying behaviour was observed for both metals on the 2 nm Al2O3/n-InGaAs samples for the sulphur passivated InGaAs surface, indicating the importance of both surface passivation and the presence of an ultra-thin dielectric interlayer on the current-voltage characteristics displayed by these devices. (C) 2015 Elsevier B.V. All rights reserved.

Tetrahedrites as thermoelectric materials: an overview

Tetrahedrites are natural earth-abundant minerals consisting of environmentally-friendly elements of copper and sulphur. Recently, research has been focused on the natural and synthetic minerals of tetrahedrite materials for thermoelectric applications. The thermoelectric figure of merit zT of around unity at similar to 723 K for many doped and natural tetrahedrite materials in the past 2-3 years was determined and this value is comparable to conventional p-type TE materials. In this review, a brief history of tetrahedrite materials is followed by information about its crystal structure and chemical bonding, electronic band structure and transport properties. Different synthesis approaches have been summarized. Also, this review outlines the effect of different doping elements on the thermoelectric properties of tetrahedrite materials, and the natural mineral tetrahedrite that can be used as thermoelectric materials.

Docking, molecular dynamics and QM/MM studies to delineate the mode of binding of CucurbitacinE to F-actin

CucurbitacinE (CurE) has been known to bind covalently to F-actin and inhibit depolymerization. However, the mode of binding of CurE to F-actin and the consequent changes in the F-actin dynamics have not been studied. Through quantum mechanical/molecular mechanical (QM/MM) and density function theory (DFT) simulations after the molecular dynamics (MD) simulations of the docked complex of F-actin and CurE, a detailed transition state (TS) model for the Michael reaction is proposed. The TS model shows nucleophilic attack of the sulphur of Cys257 at the beta-carbon of Michael Acceptor of CurE producing an enol intermediate that forms a covalent bond with CurE. The MD results show a clear difference between the structure of the F-actin in free form and F-actin complexed with CurE. CurE affects the conformation of the nucleotide binding pocket increasing the binding affinity between F-actin and ADP, which in turn could affect the nucleotide exchange. CurE binding also limits the correlated displacement of the relatively flexible domain 1 of F-actin causing the protein to retain a flat structure and to transform into a stable ``tense'' state. This structural transition could inhibit depolymerization of F-actin. In conclusion, CurE allosterically modulates ADP and stabilizes F-actin structure, thereby affecting nucleotide exchange and depolymerization of F-actin. (C) 2015 Elsevier Inc. All rights reserved.

The diversity and ecological role of protozoa in fresh waters

Protozoa feed on and regulate the abundance of most types of aquatic microorganisms, and they are an integral part of all aquatic microbial food webs. Being so small, aerobic protozoa thrive at low oxygen tensions, where they feed (largely unaffected by metazoan grazing) on the abundance of other microorganisms. In anaerobic environments, they are the only phagotrophic organisms, and they live in unique symbiotic consortia with methanogens, sulphate reducers and non-sulphur purple bacteria. The number of extant species of protozoa may be quite modest (the global number of ciliate species is estimated at 3000), and most of them probably have cosmopolitan distributions. This will undoubtedly make it easier to carry out further tasks, e.g. understanding the role of protozoan species diversity in the natural environment.

Revisión bibliográfica del tratamiento de biogás por biofiltración.

[ES]En el siguiente trabajo se ha realizado una revisión bibliográfica en la que se muestran los resultados obtenidos al llevar a cabo la purificación del biogás y/o la eliminación del metano, en los casos en los que su valorización no sea posible, mediante métodos biológicos (biofiltración). Se recogen asimismo las diversas fuentes desde las que se genera el biogás (generación incontrolada o producción controlada) junto con las concentraciones típicas de todos los compuestos que pueden formar su composición. En la purificación del biogás se ha estudiado la eliminación de compuestos perjudiciales para el aprovechamiento energético del biogás, como son el sulfuro de hidrógeno (H2S), los mercaptanos y los siloxanos. Para el estudio de los compuestos a eliminar se ha diferenciado entre distintas configuraciones de biorreactores (biofiltros, biofiltros percoladores y biolavadores) y para cada una de ellas se han recogido datos representativos como la temperatura óptima de operación, las diferencias entre operar a pH ácido o básico (teniendo en cuenta que el pH natural de operación es ácido pero que en estas condiciones la solubilidad del H2S es menor y el relleno se deteriora con mayor rapidez). También se ha analizado la influencia de la cantidad de oxígeno necesario para garantizar la degradación total de los contaminantes y evitar la acumulación de depósitos de azufre, llegando incluso a necesitarse proporciones de O2/H2S de 49.2 para la oxidación completa del H2S. Se ha estudiado también la cantidad necesaria de nitrógeno (nutriente) en los procesos llevados a cabo en condiciones anaerobias (cercana a 200 mgN-NO3 -/L), así como el efecto que tienen los compuestos producidos en la oxidación parcial (azufre elemental (S0), metanol, formaldehido, etc.) en el funcionamiento del sistema.

Estudo dos compostos reduzidos de enxofre na formação do ozônio troposférico na cidade do Rio de Janeiro

O petróleo é uma complexa mistura de compostos orgânicos e inorgânicos em que predominam os hidrocarbonetos e que apresentam contaminações variadas, entre essas os compostos de enxofre. Esses além de gerarem inconvenientes durante os processos de refino do petróleo, como corrosão nos equipamentos e envenenamento de catalisadores dos processos de craqueamento, também representam um grande problema para o meio ambiente e para a saúde da população, principalmente em relação à poluição atmosférica. Além das emissões de compostos de enxofre oriundas da própria refinaria, com destaque para os óxidos de enxofre e o sulfeto de hidrogênio, os compostos de enxofre, que não são retirados durante o refino e estão presentes nos derivados do petróleo, provocam a emissão de uma grande quantidade de poluentes na atmosfera durante o processo de queima dos combustíveis. Os efeitos dos CRE na atmosfera urbana ainda não são muito conhecidos, o que justifica um estudo mais profundo desses compostos, que além de causarem danos a saúde da população, podem influenciar na formação do ozônio troposferico

Compostos de enxofre em misturas de diesel e biodiesel

É difundido na literatura especializada que o uso de misturas de biodiesel e diesel de petróleo reduz as emissões dos compostos de enxofre. Esses compostos são responsáveis por inúmeras enfermidades respiratórias, além de provocar danos ao catalisador automotivo, contribuindo desta forma para a emissão de outros poluentes. Neste trabalho fez-se uma identificação dos compostos de enxofre, antes da queima no motor, presentes no diesel e em misturas de biodiesel/diesel de diferentes fontes. A metodologia empregada foi a cromatografia de fase gasosa e inicialmente empregou-se um detector de ionização por chama de hidrogênio para ajuste das condições operacionais, por ser um detector considerado universal e capaz de identificar tanto os majoritários hidrocarbonetos como os compostos de enxofre. Em seguida aplicou-se os parâmetros operacionais obtidos a um cromatógrafo à gás acoplado a um detector seletivo para enxofre, o SCD (sulphur chemiluminescence detector) para a identificação apenas dos compostos de enxofre. Após a obtenção dos dados teóricos em laboratório, foi realizada a análise de compostos mercaptídicos produzidas pelas emissões de um ônibus do Rio de Janeiro abastecido com diesel puro e misturas diesel/biodiesel nas proporções (v/v) 2% (B2), 5% (B5), 10% (B10), and 20% (B20). Os resultados indicaram uma redução dos compostos de enxofre proporcional à adição do biodiesel tanto na teoria quanto na prática

北京市土壤--植物系统重金属硫的分布迁移相互间关系和主成份分析

本文选择了北京市香山北京植物园、北京动物园、长安街和北京化工厂4个功能区和国槐（Sophora japonica (L) Beauv)、毛白杨 (populus tomentosa Carr)、丁香(Syringa Oblata)、野牛草(Buohloe dactyloides (Nutt) Engelm)4种植物;采集植物样品105个、土壤样品40个;测定了各样品的镍(Ni)、锌(Zn)、铜(Cu)、镉(Cd)、铅(Pb)、铬 (Cr)、硫(S)7种元素含量;通过对样品元素含量的直观分析、回归分析、主成份分析(PCA)，得出以下结论：各样品各元素含量的最高值或异常值多出现在化工厂内，其次是长安街、动物园、北京植物园无;各功能区各样品各元素含量大小顺序多是：化工厂><长安街>动物园><北京植物园：表明化工厂内土壤、植物受污染的程度较重，其次是长安街，动物园稍轻，北京植物园则较洁净。土壤中7种元素分布特征是：S > Zn > Pb > Cr > Cu > Ni > Cd;植物中7种元素分布特征是：S > Zn >< Cu > Pb > Cr >< Ni >< Cd。7种植物样品对S、Zn、Cu、 Cd具较大的富集系数;对Ni、Pb、Cr具较小的富集系数;说明前者比后者在土壤—植系统中较易迁移。7种植物样品对S均具积累效应;毛白杨叶对zn，毛白杨叶、枝、国槐皮对Cd，野牛草对Cu也都具积累效应。国槐各器官元素含量分配是：皮含量>叶含量>枝含量;毛白杨各器官元素含量分配是：叶含量>枝含量;表明植物各器官中，枝元素含量较低。对元素含量回归分析，发现植物各器官元素含量间具显著性正相关系;植物中元素含量与土壤中元素含量绝大多数呈正相关。前者说明植物各器官生长发育的正相关性;后者说明土壤条件与植物生长发育的正相关性。对元素含量的主成份分析和样品排序，揭示出采自同一功能区的样品大都可形成一集团，但尚存在交叉、重叠和过渡的样品;化工厂集团多处在排序图Z1轴左边，长安街集团多处在Z2轴上方，北京植物园集团多处在Z1轴右边或Z2轴下方。可明确得出，化工厂土壤、植物污染较重（元素含量较高），其次是长安街;动物园污染稍轻，北京植物园较洁净的结论。还可知，化工厂、长安街某些样点污染较轻;而北京植物园、动物园某些样点污染较重。

木本植物对大气污染指示与监测作用研究

本文研究了木本植物的不同部位即叶片、枝条和树皮以及植物的生理指标如气孔阻力对大气S02、TSP和重金属污染的指示和监测作用，并用树木年轮指示大气污染的历史和程度。结果认为： 承德市大气污染自1703年城市化以来开始出现，但达到严重污染水平则出现在本世纪50年代以来尤其是最近10-20年城市化与工业化的加剧，主要污染物以S02为主，从避暑山庄修建前的<0.1μg m-3达到目前的30μg m-3，重金属污染Fe自1927-45大庙铁矿开采后出现，Mn、Ni、Pb等出现在工业化以来的最近40-50年中，上述污染物含量在木质部年轮中明显升高，如S增加了10倍以上，Pb增加了560% (P<0.00l)。 不同城市功能区树皮pH和气孔阻力不同，主要与大气中的S02和TSP有关，据此可监测大气S02和TSP污染。前者以榆树、加拿大杨、垂柳和国槐最佳，相关系数分别可达-0.8384 (P<0.0l)，-0.7447、-0.6904和-0.6552 (P<0.05);后者则以白腊和旱柳下表皮最好，相关系数达0.9968和0.9951 (P<0.00l)。在扫描电镜下发现气孔受大气TSP影响出现不同程度的堵塞现象，主要有2种途径，小型颗粒物(<5μm)进入气孔腔，大型颗粒物(>30μm)可将气孔封盖。 植物不同器官部位污染物含量以树皮为最高，其次是枝条或叶，因而适宜的指示或监测部位是叶或枝条。主分量分析认为：承德市大气污染物以S为主，重金属Fe、Zn、Mn也有一定的贡献，Pb仅出现在繁忙道路区。不同季节污染物含量变化以休眠期最高，生长初期次之，生长旺盛期最低，如S和Pb分别从0.75 mg g-1和0.7 mg g-1上升到1.5 mg g-1和2.0 mg g-1(P<0.001)。植物不同季节污染物含量的变化反应了大气污染物季节变化特点，因而可以指示或监测大气污染尤其是S02污染。其中刺槐多部位复相关模型监测效果最佳，复相关系数可达0.987;某些植物单一部位的监测作用也较好，叶以珍珠梅最佳，相关系数为0.8695 (P<0.001)，枝以油松、珍珠梅、垂柳为好(r≥0.8，P <0.001)，树皮以刺槐为佳，r=0.8615 (P<0.0l)。植物不同部位的污染物含量还可用来评价大气环境质量，其中复合污染指数可以 评价总的大气环境质量，S污染指数和重金属污染指数可以评价S02、重金属和TSP污染，与直接利用污染物浓度法基本一致。油松不同部位对于大气S02的指示作用可表现为年轮对大气污染历史的指示或监测，针叶对现状S02污染的预测，并利用针叶对于S02的监测结果，绘制了大气S02污染分布图。 总之，本文利用古松年轮和现状城市植物的枝条、叶和树皮中的污染物含量以及树皮酸度等不同方面的指标，对承德市大气污染的历史和现状进行了指示与监测，即承德市大气污染从过去到现在均以S02为主，植物不同部位可以非常有效地进行大气S02污染的监测与评价，其中多部位的复相关模型预测效果极佳。另外，由植物监测而绘制的大气S02分布图，较准确地揭示了承德市大气S02现状分布规律。

Studies on phenolase enzyme in prawns. II. The inhibitory action on the enzyme by certain chemical agents

The effect of certain chemical agents on dopa oxidation by phenolases has been examined. Sulphur containing amino carboxylic acids are inhibitory agents for dopa oxidation. Tyrosine, a substrate for the enzyme also acts as an inhibitor for dopa oxidation by the enzyme. The possible mode of action has been discussed. The function of diethyl dithiocarbamate in suppressing the display of enzyme activity has been detailed and its behaviour has been compared to the other chemical agents studied.

Photosynthetic bacteria in the marine environment at Porto-Novo

Sediment and water samples were collected from mangrove and estuarine biotopes at fortnightly intervals. The physico-chemical characters of the overlying water were studied. In the mangrove biotope maximum temperature (31.5°C) and in the estuarine biotope maximum salinity (35.6‰) were recorded during the summer season, whereas in post-monsoon period the sulphate content was increased to 516 p.p.m. and the pH was reduced to 7.4. Invariably both in the enriched sediment and water samples four major peaks (at wavelengths 460, 705, 772 and 850 nm) and two minor peaks (at wavelengths 580 and 663 nm) of absorption spectra were noticed. A pure culture of Chromatium sp., isolated from mangroves sediment, showed three peaks of absorption spectra at wavelengths, 500, 580 and 850 nm. The effect of sodium chloride on the growth of Chromatium sp., was also studied and it was observed that maximum growth occurred in the range 1-3% sodium chloride concentration. This isolate was also capable of utilizing various sulphur and carbon compounds. Glycerol and glucose did not show any specific effect whereas pyruvate, malate and acetate increased the growth.

Embodied Energy and Gas Emissions of Retaining Wall Structures

The embodied energy (EE) and gas emissions of four design alternatives for an embankment retaining wall system are analyzed for a hypothetical highway construction project. The airborne emissions considered are carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2O), sulphur oxides (SO X), and nitrogen oxides (NO X). The process stages considered in this study are the initial materials production, transportation of construction machineries and materials, machinery operation during installation, and machinery depreciations. The objectives are (1) to determine whether there are statistically significant differences among the structural alternatives; (2) to understand the relative proportions of impacts for the process stages within each design; (3) to contextualize the impacts to other aspects in life by comparing the computed EE values to household energy consumption and car emission values; and (4) to examine the validity of the adopted EE as an environmental impact indicator through comparison with the amount of gas emissions. For the project considered in this study, the calculated results indicate that propped steel sheet pile wall and minipile wall systems have less embodied energy and gas emissions than cantilever steel tubular wall and secant concrete pile wall systems. The difference in CO 2 emission for the retaining wall of 100 m length between the most and least environmentally preferable wall design is equivalent to an average 2.0 L family car being driven for 6.2 million miles (or 62 cars with a mileage of 10,000 miles/year for 10 years). The impacts in construction are generally notable and careful consideration and optimization of designs will reduce such impacts. The use of recycled steel or steel pile as reinforcement bar is effective in reducing the environmental impact. The embodied energy value of a given design is correlated to the amount of gas emissions. © 2011 American Society of Civil Engineers.