A size-dependent thermodynamic model for coke crystallites: The carbon–hydrogen system up to 2500 K

The development is presented of a model of the thermodynamic functions of enthalpy, entropy and Gibbs energy for the elements carbon and hydrogen in coke crystallites. It is applicable to varying degrees of graphitization, described by the crystallite length L_a and the crystallite height L_c. The model parameters are derived from known properties such as bond enthalpies and entropies of formation. Good agreement has been obtained between the predicted thermal dehydrogenation of petroleum cokes and experimental data. The removal of hydrogen from idealized coke crystallites is predicted to occur mostly between 1100 and 1300 K. Agreement has also been found in the comparison of the predicted thermodynamic stability of coke relative to graphite, in a previous experimental study. This stability has been determined as at ≈900 J g⁻¹ at temperatures between 950 and 1250 K and for L_a = 10 nm. The current predictive capacity of the present model is valid for temperatures up to 2500 K.     

Highly conductive multilayer-graphene paper as a flexible lightweight electromagnetic shield

A graphene-based porous paper made of multilayer graphene (MLG) microsheets is developed for application as a flexible electrically conducting shielding material at radio frequency. The production process is based on the thermal expansion of a graphite intercalated compound, the successive liquid-phase exfoliation of the resulting expanded graphite in a proper solvent, and finally the vacuum filtration of the MLG-suspension using a nanoporous alumina membrane. Enhancement of the electrical conductivity and electromagnetic shielding properties of the MLG paper is achieved by gentle annealing at 250 °C overnight, and by mechanical compression at 5 MPa. The obtained results show that the developed MLG papers are characterized by an electrical conductivity up to 1443.2 S/cm, porosity around 43%, high flexibility, shielding effectiveness up to 55 dB at 18 GHz with a thickness of 18 μm. Numerical simulations are performed in order to understand the main factors contributing to the shielding performance of the new material.     

基于马尔科夫状态转移的家居负荷预测模型

智能配电网的发展增强了家居负荷预测的重要性.基于状态转移的研究思路,提出基于相似日选择的蒙特卡洛马尔科夫单个设备负荷预测模型,采用自下而上的分析方法,获取单个家庭的综合负荷水平.对温控类型设备,采用皮尔逊相关系数研究了环境温度与设备运行周期之间的相关性,建立了隐马尔科夫模型,依据当天外界环境信息对温控类型设备的压缩机运行状态做出预测,进一步计算了不同时间段内的平均功率体现用户负荷水平.仿真结果表明,基于相似日选取的蒙特卡洛马尔科夫模型对不同设备的日平均负荷的预测误差约为2％～8％,而隐马尔科夫模型对温控类设备状态预测的精度约为70％.     

Theoretical study on the effect of low-temperature reforming on gasoline compression ignition (GCI) at low-load conditions

In this paper, the influence of reforming conditions on the reforming products of gasoline, as well as the effect of main reforming products on GCI combustion at low-load conditions has been studied by experiment and numerical simulation. The results show CO, H₂ and CH₄ are the major reforming products, and their production is improved by higher reforming temperature, oxygen concentration and reforming time. The production of CO and H₂ is mainly determined by the dehydrogenation reaction between fuel molecules and OH, while the one between iC₈H₁₈ and O₂ is essential for the CH₄ generation. The combustion efficiency rises sharply with more CO addition, but increases first and then decreases with increased H₂, while the peak value of 96.71% is achieved. Besides, higher combustion efficiency is obtained with more internal exhaust gas recirculation (i-EGR) used. The increased OH and H radicals can be attained by adding CH₄, which further improves combustion efficiency.     

Preparation and photoluminescence of γ-CuI nanoparticles

γ-CuI nanoparticles have been successfully prepared via a simple complex compound method, using a mixture of de-ionized water/ethanol as reaction medium at room temperature. X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy were used to characterize the samples. The results show that the diameter of the as-prepared CuI is about 30–40 nm and the fluorescence spectrum with a strong emission peak at 417 nm is observed. The possible mechanism of the formation of CuI nanoparticles is discussed.     

Anomalous activation of shallow B+ implants in Ge

The electrical activation of B⁺ implantation at 2 keV to doses of 5.0 × 10¹³–5.0 × 10¹⁵ cm^?2 in crystalline and pre-amorphized Ge following annealing at 400 °C for 1.0 h was studied using micro Hall effect measurements. Preamorphization improved activation for all samples with the samples implanted to a dose of 5.0 × 10¹⁵ cm^?2 displaying an estimated maximum active B concentration of 4.0 × 10²⁰ cm^?3 as compared to 2.0 × 10²⁰ cm^?3 for the crystalline sample. However, incomplete activation was observed for all samples across the investigated dose range. For the sample implanted to a dose of 5.0 × 10¹³ cm^?2, activation values were 7% and 30%, for c-Ge and PA-Ge, respectively. The results suggest the presence of an anomalous clustering phenomenon of shallow B⁺ implants in Ge.