Pole-placement controllers for linear systems with point delays

This paper presents a robust control algorithm for plants involvingboth internal (i.e. in the state) and external (i.e. in theoutput or input) known point delays. Several stabilizing controllerstructures are given and analysed for the case of perfectlymodelled plants with known parameters. The parametrized partsof two of the controller structures involve delays, while thoseof the two remaining controllers are delay-free. However, auxiliarycompensating signals which weight the plant input and outputintegrals are incorporated in all the controller structuresfor stabilization and model matching purposes.     

氢原子在过渡金属修饰的Mg(0001)面扩散的第一性原理研究

基于密度泛函理论(DFY)的第一性原理计算方法,对氢原子在过渡金属(Sc、Ti、Cr、Mn、Fe、Co、Ni、Cu、V、Zn)修饰的Mg(0001)表面扩散性能进行了研究.研究发现过渡金属元素Sc、Ti、V、Cr、Mn、Fe、Co、Ni和Cu选择替代在镁表面第二层稳定,而Zn则选择替代在第一层稳定.当镁表面掺杂Zn和Cu时,氢原子选择停留在表面稳定;当掺杂Sc、Ti、V、Cr、Mn、Fe、Co和Ni时,氢原子选择进入镁块体内部.值得一提的是氢原子通过从过渡金属顶部通道扩散进入镁块体内部的势垒大大降低,笔者用差分电荷密度分析后发现氢原子与过渡金属原子成键使扩散势垒降低.当氢原子进入镁块体内部后靠近Sc、Ti、V、Cu和Zn原子时,将与这些过渡金属原子成键,从而阻碍了氢原子继续向内部扩散;而氢原子靠近Cr、Mn、Fe、Co、Ni原子时,选择离开过渡金属从而促进了氢原子向块体内扩散,可以大幅改善镁基储氢材料的吸氢动力性能.     

Baryon masses,chiral extrapolations,and all that<Superscript>⋆</Superscript>

We calculate the baryon octet masses to fourth order in chiral perturbation theory employing dimensional and cut-off regularization. We analyze the pion and kaon mass dependences of the baryon masses based on the MILC data. We show that chiral perturbation theory gives stable chiral extrapolation functions for pion (kaon) masses below 550 (600) MeV. For the pion-nucleon sigma term we find (0) = 39.5...46.7MeV.     

Prenatal stress and subsequent exposure to chronic mild stress influence dendritic spine density and morphology in the rat medial prefrontal cortex

Background  

Both prenatal stress (PS) and postnatal chronic mild stress (CMS) are associated with behavioral and mood disturbances in humans and rodents. The aim of this study was to reveal putative PS- and/or CMS-related changes in basal spine morphology and density of pyramidal neurons in the rat medial prefrontal cortex (mPFC).     

青海省唐古特铁线莲质量控制标准的研究

目的对青海省唐古特铁线莲质量控制标准进行研究。方法采用薄层色谱法对唐古特铁线莲进行定性鉴定,展开剂为氯仿与丙酮（95：5）,显色剂为10％硫酸甲醇;采用HPLC（Lc-2010HT）法测定唐古特铁线莲中齐墩果酸的含量,色谱柱为PhenomenexLunaCt8（250mm×4．6mm,5Ixm）,流动相为y（乙腈）＋V（0．2％磷酸水溶液）=35＋65,流量为1mL／min,柱温为室温（25℃）,检测波长为205nm。结果薄层色谱鉴定中,供试品色谱与对照品色谱相应的位置上,显示出相同颜色的荧光斑点;齐墩果酸在0．0233—0,7000mg／mL范围内呈良好的线性关系,线性回归方程为Y=2×10-6＋360803,r。=0．9917,RSD为1．61％,并对青海省野生和栽培唐古特铁线莲中齐墩果酸进行了定量分析,结果显示前者平均值为0．1184％、RSD为2．5113％,后者平均值为0．0651％、RSD为2．92％。结论该法操作简单、快速、准确、灵敏、重现性好,可有效控制青海省唐古特铁线莲的质量。     

Pt^＋（^2D）催化H2O和CH4制取水煤气循环反应的理论探究

采用密度泛函理论（DFT）B3LYP方法和非迭代三激发电子相关耦合簇CCSD（T）方法研究了二重态和四重态势能面上由Pt＋（2D,4F）催化H2O和CH4产生水煤气的循环反应.采用分子轨道（MO）理论和自然键轨道（NBO）理论对最低能量路径的反应势能面作了详细的分析说明.应用Kozuch撰写的能量跨度模型（energetic span model）确定了决定循环反应速率的决速过渡态（TDTS）和决速中间体（TDI）,最后计算了催化剂的转化频率（TOF）以评价催化剂的性能.     

Method development for the determination of wood preservatives in commercially treated wood using gas chromatography-mass spectrometry

Fungicides and insecticides are commonly used preservatives to protect wood products against microbiological degradations. Currently, there is a lack of analytical methods addressing the quantitative determination of a wide range of wood preserving species in wood matrices. In this study, a reliable method was developed for the determination of a mixture of wood preserving agents with differing chemical structures (i.e., properties), including tebuconazole (TAZ), propiconazole (PAZ), 3-iodo-2-propynyl butylcarbamate (IPBC), and permethrin (PER), in pine wood. The analyte recoveries obtained by Soxhlet and multiple-stage sonication extractions were compared. While both extraction methods yielded similar results (80–100%), Soxhlet extraction was found to be less labor-intensive and thus preferred providing also lower RSDs of 1–6%. In comparison to methanol, commonly used as an extraction solvent for triazoles, acetone yielded similar extraction efficiencies for all analytes while reducing the time of sample concentration. The solid phase extraction method for triazoles was adapted to allow for a separation of IPBC and PER from the wood matrix. As opposed to previous studies, three recovery standards were employed, which enabled the correction of individual analyte losses during the sample preparation. The matrix-affected limits of detection (LODs) using gas chromatography with mass spectrometric detection were nearly the same for triazoles 0.07 and 0.21 ng g⁻¹ for PAZ and TAZ in sapwood and 0.18 and 0.21 ng g⁻¹ in heartwood, respectively. Higher LODs were observed for IPBC and PER: 3.9 and 1.7 ng g⁻¹ in sapwood, and 2.0 and 6.0 ng g⁻¹ in heartwood, respectively. The recoveries in the wood submitted to commercial sample treatment showed gradient distribution of analytes depending on the penetration of the treatment.     

Supercritical carbon dioxide extraction of Usnea longissima (L.) Ach.: Optimization by Box-Behnken design (BBD)

Usnic acid (UA) was extracted from Usnea longissima (L.) Ach. in supercritical carbon dioxide (SC-CO₂) medium. The selected process parameters were extraction temperature (35–45 °C), amount of co-solvent (0%–5%) and extraction time (5–9 h). These parameters were applied to Box-Behnken design (BBD) belonging to response surface methodology (RSM) to determine optimum process parameters for the highest amount of UA in the extract. g UA/100g lichen, extraction yield % and UA content values were calculated in the range of 0.045–0.317, 2.77–5.4 and 71%–82% in different experimental conditions, respectively. The optimum conditions were predicted as 42 °C, 4.3% (ethanol) and 7.48 h. It was determined that the predicted and experimental values of g UA/100g lichen were compatible, and the suggested model was valid.