The distribution, occurrence and environmental effect of mercury in Chinese coals

Mercury (Hg) is a toxic, persistent, and globally distributed pollutant due to its characteristic properties such as low melting and boiling points, conversion between chemical forms and participation in biological cycles. During combustion mercury in coal is almost totally emitted to the atmosphere. With a huge amount of coal consumed, coal combustion is one of the main anthropogenic sources of this element in the environment. In this study, Hg data of 1699 coal samples of China has been compiled, and the concentration, distribution, modes of occurrence, and the impact of Hg emissions on the environment are investigated. Most Chinese coals have Hg content in the range of 0.1 to 0.3 ppm, with an average of 0.19 ppm, which is slightly higher than the average Hg content of world coals and is close to that of the U.S. coals. The Hg content in coals varies in different coal basins, geological ages and coal ranks. The most likely mode of occurrences of Hg in high-sulfur and high Hg content coals is as solid solution in pyrite. But in low-sulfur coals, modes of occurrence of Hg are variable, and the organic-bound and sulfide-bound Hg may dominate. Silicate-bound Hg may be the main form in some coals because of magmatic intrusion. Mercury emissions during coal combustion have resulted in serious environmental contamination in China, particularly in the northeastern and southwestern China, where a high Hg content in the atmosphere occurs.     

A techno-economic review of biomass gasification for production of chemicals

Gasification is a thermochemical process which can be used as a low-emission and highly efficient method to produce syngas and chemicals such as biomethanol and dimethyl ether (DME). In this paper, a review of technologies and methods for economic production of chemicals through gasification of biomass and other fuels has been carried out. A variety of techno-economic studies and analysis have been proposed in order to better understand the technical and economic assessments during the biomass gasification. Results showed that the methanol production cost for biomass (wood) is from 195 to 935 €/t, for waste residues is from 200 to 930 €/t, for coal is from 160 to 480 €/t, and for natural gas is from 90 to 290 €/t. It also concluded that fuel (wood) cost has positive linear relationship with ethanol production cost, meaning as the feedstock cost increases from 30 to 50 $/day-ton, the ethanol production cost enhances from 1.66 to 1.95 $/gal.     

基于TEE的主动可信TPM/TCM设计与实现

可信技术正在从被动可信度量向着下一代的主动可信监控方向发展，要求TPM/TCM模块有能力主动度量和干预主机系统，传统的TPM/TCM从架构和运行机制等方面都无法满足这种能力.TEE（trusted executionenvironment）技术提供了可信执行环境和主动访控能力，为构建下一代TPM/TCM提供了基本平台，但还存在系统结构、存储以及通信等多方面挑战.提出基于ARM平台TrustZone机制的TZTCM方案，通过分核异步系统架构解决TZTCM独立可信运行和主动可信安全监控问题，基于PUF（physical unclonable functions）安全存储机制和基于UUID（universally unique identifier）的TEE安全通信机制，解决了TEE环境下可信平台模块的存储安全和通信安全问题，为设计实现主动可信TPM/TCM给出了理论和实践参考.通过实验验证了所提关键机制的有效性，实验结果表明，TZTCM在密码计算能力上较常见TPM也有很大提升.TZTCM只需要在系统中增加或修改相应的软/固件，除了主动可信监控能力，还具有低成本、高性能、低功耗、易升级等特点，相对传统TPM/TCM具有非常明显的优势.     

基于机器学习的软件漏洞挖掘方法综述

软件复杂性的增加给软件安全性带来极大的挑战.随着软件规模不断增大以及漏洞形态多样化,传统漏洞挖掘方法由于存在高误报率和高漏报率的问题,已无法满足复杂软件的安全性分析需求.近年来,随着人工智能产业的兴起,大量机器学习方法被尝试用于解决软件漏洞挖掘问题.首先,本文通过梳理基于机器学习的软件漏洞挖掘的现有研究工作,归纳了其技术特征与工作流程.接着,从其中核心的原始数据特征提取切入,以代码表征形式作为分类依据对现有研究工作进行分类阐述,并系统地进行了对比分析.最后依据对现有研究工作的整理总结,探讨了基于机器学习的软件漏洞挖掘领域面临的挑战,并展望了该领域的发展趋势.     

Minimal gated unit for recurrent neural networks

Recurrent neural networks (RNN) have been very successful in handling sequence data. However, understanding RNN and finding the best practices for RNN learning is a difficult task, partly because there are many competing and complex hidden units, such as the long short-term memory (LSTM) and the gated recurrent unit (GRU). We propose a gated unit for RNN, named as minimal gated unit (MGU), since it only contains one gate, which is a minimal design among all gated hidden units. The design of MGU benefits from evaluation results on LSTM and GRU in the literature. Experiments on various sequence data show that MGU has comparable accuracy with GRU, but has a simpler structure, fewer parameters, and faster training. Hence, MGU is suitable in RNN's applications. Its simple architecture also means that it is easier to evaluate and tune, and in principle it is easier to study MGU's properties theoretically and empirically.     

Airfoil sampling of a pulsed Laval beam with tunable vacuum ultraviolet synchrotron ionization quadrupole mass spectrometry: application to low-temperature kinetics and product detection

A new pulsed Laval nozzle apparatus with vacuum ultraviolet (VUV) synchrotron photoionization quadrupole mass spectrometry is constructed to study low-temperature radical-neutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets. A design for the sampling geometry of a pulsed Laval nozzle expansion has been developed that operates successfully for the determination of rate coefficients by time-resolved mass spectrometry. The new concept employs airfoil sampling of the collimated expansion with excellent sampling throughput. Time-resolved profiles of the high Mach number gas flow obtained by photoionization signals show that perturbation of the collimated expansion by the airfoil is negligible. The reaction of C(2)H with C(2)H(2) is studied at 70 K as a proof-of-principle result for both low-temperature rate coefficient measurements and product identification based on the photoionization spectrum of the reaction product versus VUV photon energy. This approach can be used to provide new insights into reaction mechanisms occurring at kinetic rates close to the collision-determined limit.     

Characteristics of coal quality and their relationship with coal-forming environment: A case study from the Zhuji exploration area,Huainan coalfield,Anhui, China

The comprehensive information of coal quality and its relationship with coal-forming environment in Zhuji exploration area, Huainan coalfield Anhui, China, have been studied. The data of coal quality including proximate and ultimate analysis, calorific values, sulfur forms, petrography and selected trace elements (Ga, Ge, V, U, Th, Cl and As) are based on 614 samples of 13 minable coal seams from 88 drilling holes collected during exploration periods. These data were designed to provide information on the technological performance of coal. Characteristics of coal quality deposited in three different sedimentary environments, namely in coal-bearing strata of the Shanxi Formation, Lower Shihezi Formation and Upper Shihezi Formation, were analyzed. Results show that moisture, volatile matter, and ash yield all increase stratigraphically upward, which is opposite to the variation of calorific values. The correlation between ash yield and calorific value shows negatively higher relevance that than of moisture and ash yield. The coal quality parameters of the boreholes along the divided faults were rarely controlled by geological setting. It was suggested that other factors such as magmatic activity and underground water cycling may modify the parameters of coal quality to some extent and cause their redistribution.     

不同存放条件的保鲜膜预防冰箱冷藏食物细菌污染的效果比较

目的 研究不同存放条件下的保鲜膜对预防冰箱冷藏食物细菌污染的效果。方法 取9个培养基平板, 分成3组, 每组敞口、覆盖盒装保鲜膜、覆盖非盒装保鲜膜各1个, 放置在冰箱冷藏室, 3组分别在24、48、72 h后取出, 进行细菌培养计数。同时对2种保鲜膜表面细菌培养计数。所有实验进行3次, 计算平均值。结果 2种保鲜膜表面采样后均有细菌生长, 但培养菌落数无显著性差异(P>0.05); 敞口培养基平板均有细菌生长, 与其他培养基平板有显著性差异(P<0.05); 2种保鲜膜覆盖下的培养基平板细菌培养计数均为0, 无显著性差异(P>0.05)。在冰箱不同位置放置的敞口培养基平板表面生长的菌落数无显著性差异(P>0.05)。结论 冰箱冷藏条件下, 不同存放条件的保鲜膜均可达到预防食物空气污染效果。     

Light Extraction Efficiency Enhancement of GaN Blue LED by Liquid-Phase-Deposited ZnO Rods

We investigate the light extraction efficiency of a GaN light-emitting diode (LED) by using liquid-phase-deposited ZnO rods at near-room temperature. Zinc nitrate and hexamethylenetetramine were used as the deposition precursors. Compared with the conventional GaN LED, the optical power output of the GaN LED with crystalline ZnO rods on its surface has about 1.6 times enhancement.     

Application of fractional order theory of thermoelasticity to a bilayered structure with interfacial conditions

In this work, fractional order theory of thermoelasticity is applied to a bilayered structure being in imperfect thermal and mechanical contact. The model is subjected to a sudden heating at the traction-free end, assumed to be undisturbed at infinity. The heat conduction in each medium is described by the time-fractional heat conduction equations with two fractional order parameters, respectively. An analytical technique based on Laplace transform is adopted. Numerical results are computed and represented graphically, from which the effects of fractional derivative parameters of both media, thermal contact resistance, elastic wave impedance ratio on the responses are discussed.