Nitrogen dry deposition to Lake Superior and Lake Michigan

Nitrate (NO₃^?) levels in Lake Superior have increased from historic levels of about 5?μM to its current concentration of about 25?μM. The atmosphere makes a substantial contribution to the nitrogen budgets for Lake Superior and Lake Michigan. This study provides a more well-defined estimate of nitrogen dry deposition rates derived from the measurement of over-water concentrations, and in situ meteorological measurements, which were input into the Resistance Model. We obtained a nitrogen dry deposition rate of [(3.41?±?2.26)?×?10⁷?kg?N/yr; (5.90?±?3.91)?kg?N/ha/yr] over Lake Michigan, and [(1.54?±?1.06)?×?10⁷?kg?N/yr; (1.87?±?1.27)?kg?N/ha/yr] over Lake Superior. Nitric acid (HNO₃), which originates from the combustion of fossil fuels, contributes 84% of the total nitrogen dry deposition to Lake Michigan; and 66% to Lake Superior. Ammonia (NH₃), which originates from agricultural activities and gasoline combustion, is the second highest contributor of nitrogen dry deposition to both lakes: contributing 13% to Lake Michigan and 32% to Lake Superior. The nitrogen dry deposition is approximately 68% of the nitrogen wet deposition over Lake Superior, and approximately 80% of wet deposition over Lake Michigan. The over-water dry deposition velocity of HNO₃ and NH₃ were also evaluated. We obtained morning deposition velocities of 0.099?cm/s for NH₃ and 0.095?cm/s for HNO₃; and afternoon values of 0.137?cm/s for NH₃ and 0.132?cm/s for HNO₃. Another key finding is that the atmospheric concentrations of nitrogen compounds near Lake Michigan and Lake Superior have decreased since 2003.     

分段沉积/雕铣成型的工艺规划

分段沉积/雕铣成型技术是快速原形结合传统加工方法的一种新的工艺,兼有快速原形的高柔性和传统加工的高精度。本文就分段沉积/雕铣成型技术中零件的分段、薄壁件的加工、尖角的加工、曲面的加工等一些特殊工艺进行合理的工艺规划,提出解决措施。     

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豫西地区中、下二叠统太原组、山西组、上石盒子组及下石盒子组煤成气资源丰富，但成煤环境纵向发育与横向变化较大，规律难于把握。因此，开展煤成气源岩沉积环境研究有利于该区煤成气资源的勘探与开发及合理的利用。通过露头、钻井、地震资料及分析、测试资料的综合研究认为：本区中、下二叠统主要沉积了一套浅海碳酸盐岩，海湾-泻湖、潮坪、沼泽、障壁岛(砂质滩、坝)及三角洲相陆源碎屑岩和煤层。从总的沉积特征来看，下二叠统太原组、山西组基本上发育滨、浅海相碳酸盐岩、陆源碎屑岩和煤的混合沉积。上二叠统上、下石盒子组则以海陆交互相陆源碎屑沉积为主，三角洲及三角洲平原沼泽十分发育；沉积环境具有自下而上，自南东向北西方向由海相逐步过渡为陆相的基本特点。其煤成气源岩沉积环境以早二叠世山西期潮坪、泻湖过渡带之滨岸沼泽环境为最佳，其次为中二叠世下石盒子期三角洲平原沉积之平原沼泽环境。     

Preparation of a tubular palladium membrane by photocatalytic deposition

A novel photocatalytic deposition method for the preparation of a thin tubular palladium membrane is presented in this paper. The membrane is prepared on a porous asymmetric TiO₂ support by photocatalytic reaction of palladium ion, followed by electroless plating. Gas permeation results show that the membrane exhibits increased hydrogen permeance with the increase of temperature. The hydrogen permeance and selectivity to nitrogen at 773 K are about 1.43×l0⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 17, respectively, when the pressure in the feed side is 0.1 MPa. The activation energy of hydrogen permeation is 11.06 kJ/mol at the temperature range of 573–773 K.     

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.     

Preventing chlorine deposition on heat transfer surfaces with aluminium-silicon rich biomass residue and additive

Biomass fuels often contain higher concentrations of easily vaporisable alkalis and chlorine than do coal and peat. The more vaporisable the alkalis or chlorine compounds the higher is the risk for ash-related problems. The presence of certain elements may reduce or remove these problems. This work shows how co-combusting of different biomass fuels in a fluidised bed boiler can result in useful interactions that decrease or totally inhibit Cl deposition and bed agglomeration. In a first set of experiments, fuel 1 contained easily vaporised chlorine that produces Cl-rich deposits on superheaters. Fuel 2 was enriched in aluminium silicate, but contained much ash, resulting in low heating value and high load of fly ash. In a second set of experiments, fuel 1 was enriched in Cl and alkalis, which lead to corrosive deposits, bed agglomeration and fouling. As a result of protecting reactions, the mixtures were free from the problems observed during their separate combustion.     

Colloid Transport through Natural Filter Media

In this project the use of natural media filtration (NMF) was evaluated for its ability to remove colloidal particles from the aqueous phase as a function of ionic strength and filter media type by determining first-order kinetic deposition rate coefficients. Mushroom compost (MC) and leaf compost (LC) were tested as natural filter media and the results were compared to those obtained using sand and granular activated carbon (GAC). The highest deposition rate coefficients were observed for GAC, followed by LC and MC, and the lowest deposition rate coefficients were found for sand. As predicted by the Derjaguin–Landau–Verwey–Overbeek theory, higher deposition rates were obtained at higher solution ionic strengths. Overall the experiments suggest that the NMF process can efficiently remove colloidal particles from surface waters.     

Hot wire chemical vapor deposition: limits and opportunities of protecting the tungsten catalyzer from silicide with a cavity

Hot Wire Chemical Vapor Deposition (HW-CVD) is one of the most promising techniques for depositing the intrinsic microcrystalline silicon layer for the production of micro-morph solar cells. However, the silicide formation at the colder ends of the tungsten wire drastically reduces the lifetime of the catalyzer, thus limiting its industrial exploitation. A simple but interesting strategy to decrease the silicide formation is to hide the electrical contacts of the catalyzer in a long narrow cavity which reduces the probability of the silane molecules to reach the colder ends of the wire. In this paper, the working mechanism of the cavity is elucidated. Measurements of the thickness profile of the silicon deposited in the internal walls of the cavity have been compared with those predicted using a simple diffusion model based on the assumption of Knudsen flow. A lifetime study of the protected and unprotected wires has been carried out. The different mechanisms which determine the deterioration of the catalyzer have been identified and discussed.     

Transport of Sulphur dioxide with deposition and wash out in wet and dry regions

Here we have investigated theoretically the average integrated ground level concentration of sulphur dioxide in wet and dry regions due to the emission from an elevated point source. The profiles of concentration distribution have been obtained in wet and dry regions on various rates of rainfall.     

Electrolytic deposition of magnesium-substituted hydroxyapatite crystals on titanium substrate

Electrolytic deposition of magnesium-substituted hydroxyapatite (Mg-HAp) coatings on titanium was investigated and Mg-HAp crystals with up to 2 wt.% Mg²⁺ were deposited in electrolytes with various Mg²⁺ concentration. The incorporation of Mg substantially changed the morphology of the HAp crystals and decreased the crystal size and crystallinity of the HAp. The similarity with natural dentin and bone in composition and the increased specific surface of the Mg-HAp coatings on the Ti substrates were believed to benefit the bioactivity and the drug-carrying properties of the coatings.