Slice-Selective Transmit Array Pulses for Improvement in Excitation Uniformity and Reduction of SAR

To overcome challenges of inhomogeneous transmit B1 distribution and high specific energy absorption rate (SAR) in MRI, we compare slice-selective array-optimized composite pulse and RF shimming designed to both improve B1 uniformity and reduce SAR using an 8-channel transmit head array loaded with a head model at various RF pulse excitation times, and compare results with standard quadrature voltage distribution at 3T (128 MHz) and 7T (300 MHz). The excitation uniformity was estimated throughout the 3D brain region and SAR was calculated for the whole head. The optimized composite pulse could produce significantly better homogeneity and significantly better homogeneity when SAR was not constrained, and both significantly better homogeneity and lower SAR when the pulse duration was allowed to be twice that of the quadrature or RF shimmed pulse. When the total pulse durations were constrained to the same length, the relative advantages of the optimized composite pulse for producing better homogeneity and lower SAR simultaneously were diminished. Using the optimization results, the slice-selective composite pulse sequence was implemented on a 3D MRI simulator currently under development, and showed both effective slice selection and improvement in excitation uniformity compared to a conventional quadrature driving method.

Species profile and reactivity of volatile organic compounds emission in solvent uses,industry activities and from vehicular tunnels

A survey was conducted of the volatile organic compounds(VOCs)released from sources of solvent use,industry activities and vehicle emissions in Guiyang,a capital city of China.Samples were collected by canisters and analyzed by GC-MS-FID.The species profiles of VOCs emitted from sources were obtained.Results showed that xylenes,ethylbenzene,acetone and dichloromethane were the characteristics species for painting,2-propanol and ethyl acetate for printing,α-pinene for solid wood furniture manufacturing,and 2-butanone for biscuit baking.These characteristics species could be as tracers for the sources respectively.In most of samples from the solvent use,the benzene/toluene(B/T)ratio was less than 0.3,indicating that the ratio could be as the indicator for tracing the solvent use related sources.The results also suggested that the toluene/xylene(T/X)ratio be as the indicator to distinguish the VOCs sources of painting(<2)from the printing(>2).Aromatics contributed the most to ozone formation potential(OFP)of most painting and non-paper printing sources,and oxygen-containing VOCs(OVOCs)were major species contributing to OFP of the sources from food production and paper printing.The OFP of the VOCs emissions from vehicle in tunnels and from other manufactures were dominated by both aromatics and alkenes.Theα-pinene could explain 56.94%and 32.54%of total OFP of the VOCs sources from filing cabinet and solid wood furniture manufacturing,which was rarely been involved in previous studies of VOCs source profiles,indicating that the species of concern for VOCs sources are still insufficient at present.

电极上气泡分离行为及其强化技术研究进展

电解水作为大规模生产氢气的途径,增强电解水效率对于氢能源的生产具有十分重要的意义。而如何提高电解水工艺的电解效率是一个被广泛关注的问题。在电解过程中,电极两端产生的气体有三种去向:逸出电解槽、溶解于电解质中、附着在电极上。但在电解过程中,附着在电极上的气泡会严重影响电极与电解质之间的接触面积,直接降低了电解效率。降低气泡在电极上的停留时间能够有效增加电解质与电极的接触时间,提高产氢效率。本工作主要综述了近年来促进电解过程中极板上氢氧气泡从电极分离行为的研究,分别从极板属性、电流、溶液浓度和外加物理场这几个方面对气泡成核、生长、聚结和分离行为进行了具体的归纳总结,讨论了各种强化气泡分离方法的特点,并展望了未来的发展方向和路线,为未来的电解气泡脱离技术的研究提供参考。

Mercury enrichment in Brassica napus in response to elevated atmospheric mercury concentrations

响应在强奸(Brassica 马来麝) 的机关的提高的大气的水银集中的水银丰富用一个开的最高的房间忿恨实验被调查，土壤水银充实耕作实验。结果显示在叶子和茎的水银集中在水银的不同集中下面显示出一个重要变化在大气并且当在根，种子和种子上衣的水银的集中没在不同大气的水银集中下面显示出重要变化时，玷污实验。用实验建立的功能关系，结果因为在强奸领域生物资源的大气的水银来源证明大气的来源在强奸叶子说明了至少 81.81%of 水银并且在茎的 32.29% 水银。因此，水银在未葬生物资源主要源于大气的水银的吸收。

亚稳Fe40Co20Cr20Mn10Ni10高熵合金中马氏体的拉伸压缩不对称性

本文系统研究了具有面心立方结构的亚稳态Fe40Co20Cr20-Mn10Ni10高熵合金在拉伸和压缩变形下的微观结构演变.结果表明,从FCC到HCP的马氏体相变在压缩条件下比在拉伸条件下要高得多,具有明显的拉伸-压缩不对称性.与拉伸试验相比,压缩试验的真应力更大,为马氏体相变的开启提供了更大的驱动力.除马氏体相变外,位错的平面滑移以及少量的变形孪晶在拉伸和压缩过程中均有发现.位错滑移在整个拉伸变形过程中起主导作用,而在压缩变形中位错运动和马氏体相变都起到了关键作用.由于该高熵合金具有中等的层错能(20mJm^-2),因此马氏体相变更倾向于在晶界或亚晶界等高能区域处成核.我们发现了六方马氏体相可以通过从小角晶界发射不全位错来形成,这为马氏体相变提供了新的路径.本研究对于理解亚稳态高熵合金的变形机制具有重要的意义.

Assessment of the maximum allowed acid deposition load at current stage in China

Soil acidification caused by acid deposition has been significant in some forests in southern China. We present an approach for assessing the current stage maximum allowed load （SML） of acid deposition for terrestrial system in the country. The main idea was that soil base cation exchange as a finite buffer to acidity was included in the soil acidity mass balance calculation at current acidification stage. We calculated the SML for five forests in southern China. The usual critical loads for the same forests were also calculated by the steady state mass balance model for comparison. The results showed that the SML is a more tolerant limit than the critical load for the forests with soils not acidified seriously at current stage. However, the SML become a more stringent limit to acid deposition when the forest soils have acidified seriously to very low base cation saturation. In this case the SML assessment is beneficial for the soils recovering from a serious acidified state. Based on a national scale database, the SML mapping for non-agricultural soil system in China was carried out.

Dissolved organic sulfur in streams draining forested catchments in southern China

Dissolved organic sulfur （DOS） is an important fraction for sulfur mobilization in ecosystem. In this work stream waters were sampled in 25 forested sites in southern China to study the dissolved sulfur fractions. Dissolved sulfur was fractionated into dissolved organic sulfur （DOS） and inorganic sulfate （SO]-） for 95 stream water samples. The results showed that the concentration of DOS ranged from 0 to 13.1 mg/L （average 1,3 mg/L） in all the streams, High concentrations of DOS in stream waters were found in the sites with high concentrations of sulfate. DOS constituted less than 60.1% of dissolved sulfur （average 17.9%）. Statistical analysis showed that DOS concentration was correlated with SO42- in streams waters and total sulfur in surface layer soils. The results also showed that DOS concentration in stream waters had a seasonal variation, but no trends were found with it. The implication was that the long term sulfur deposition had led the increase of the concentration and fraction of DOS in stream waters in acid rain prevailing regions

Distribution of eight heavy metals in the inner shelf sediments of East China Sea:Risk assessments and sources analysis

Although numerous studies on heavy metals(HMs)in sediments have been carried out in the East China Sea(ECS),the knowledge on the recent pollution levels of HMs in coastal region remains not well understood due to the rapid developments of urbanization in eastern China.In this study,23 surface samples and 4 core samples are collected in the inner shelf of the ECS.The average dry-weight concentrations follow the descending order of Zn,Cr,Ni,Pb,Cu,As,Cd,and Hg(103.6±26.0,42.8±12.4,37.0±9.1,34.7±11.1,19.5±10.3,15.7±11.6,0.056±0.017,and 0.041±0.017μg g^(−1),respectively).HMs concentrations share a similar spatial distribution pattern of TOC content with a decreasing trend from coastline to outer sea.Additionally,HMs concentrations exhibit a decreasing trend from top to bottom sediments,especially for Hg at the open sites due to the wet and dry deposition of atmospheric Hg besides the riverine inputs.The potential ecological risk indices(PERI)values in coastal sediments were about 2-4 times higher than those in open sea.Although the Hg and Cd concentrations were lower by 2-3 orders of magnitude than those of other six metals,the PERI values of Hg(65.5)and Cd(52.1)were 3-40 times higher than those of others.The hierarchical cluster result is consistent with the PCA result,suggesting that Hg,Cd,and As have similar sources and probably mainly originated from anthropogenic emissions.

The soil displacement measurement of mercury emission flux of the sewage irrigation farmlands in Northern China

Mercury fate of sewage irrigation in farmlands deserves attention with increasing scarcity of freshwater resources for agriculture in the worldwide.Soil-air total gaseous mercury(TGM)fluxes from four-sewage and one-fresh water irrigated farmlands were determined simultaneously.During maize-wheat rotation,soil-air TGM fluxes showed patterns of both emission and deposition during different growth stages.It enhanced one-order of magnitude emission with increased Hg contamination from historical sewage irrigation.A linear response relationship of TGM fluxes with soil Hg concentration was found,which showed greater TGM emission potential comparing with those from forest and urban soils.However,the ratio of soil-air TGM flux in daytime to nighttime were 3.94 in maize-season and 3.41 in wheat-season,respectively,which were little related to the change in soil Hg concentration.Furthermore,soil temperature and moisture,ambient-air TGM concentration all effected TGM evasion from sewage-irrigated soils.The data presented here suggest that evasion of TGMfromhistorical sewage irrigation farmlands with high Hg concentrations may be potential hotspots for Hg emission in atmosphere,and it was likely to underestimate Hg emissions from farmlands in existing emissions inventory.Additional regionalinvestigations and process-level researches are needed to better understand role of sewage irrigation farmlands in local-global Hg-biogeochemical-cycles.