The Efficiency of a Microcolumn of Rice Bran for On‐line Trace Enrichment in FI‐AAS,a Highly Selective System for On‐line Preconcentration and Determination of Copper

A flow injection flame atomic absorption spectrometry system incorporating a microcolumn of rice bran was designed, and its capability for on‐line trace enrichment of copper, cadmium and lead was studied. Analytes were deposited on the microcolumn by processing a standard or solution of analytes on the column. Injection of 250 μL of nitric acid (1 mol/L) then served to elute the retained species to FAAS. The procedure was successfully applied for determination of copper in tap water, well water and multivitamin tablets. The accuracy was assessed through recovery experiments and independent analysis by furnace‐AAS. A sample volume of 20 mL of copper resulted in a preconcentration factor of 96; precision value at the 20 μg/L was 4.1%.     

On-line sample preconcentration with chemical derivatization of bacterial biomarkers by capillary electrophoresis: a dual strategy for integrating sample pretreatment with chemical analysis

Simple, selective yet sensitive methods to quantify low-abundance bacterial biomarkers derived from complex samples are required in clinical, biological, and environmental applications. In this report, a new strategy to integrate sample pretreatment with chemical analysis is investigated using on-line preconcentration with chemical derivatization by CE and UV detection. Single-step enantioselective analysis of muramic acid (MA) and diaminopimelic acid (DAP) was achieved by CE via sample enrichment by dynamic pH junction with ortho-phthalaldehyde/N-acetyl-L-cysteine labeling directly in-capillary. The optimized method resulted in up to a 100-fold enhancement in concentration sensitivity compared to conventional off-line derivatization procedures. The method was also applied toward the detection of micromolar levels of MA and DAP excreted in the extracellular medium of Escherichia coli bacterial cell cultures. On-line preconcentration with chemical derivatization by CE represents a unique approach for conducting rapid, sensitive, and high-throughput analyses of other classes of amino acid and amino sugar metabolites with reduced sample handling, where the capillary functions simultaneously as a concentrator, microreactor, and chiral selector.     

The ethnobotanical,phytochemistry and pharmacological activities of Psidium guajava L.

Psidium guajava L., commonly known as guava is an important tropical food plant with diverse medicinal values. In traditional medicine, it is used in the treatment of various diseases such as diarrhoea, diabetes, rheumatism, ulcers, malaria, cough, and bacterial infections. The aim of this review is to provide up-to-date information on the ethnomedicinal uses, bioactive compounds, and pharmacological activities of P. guajava with greater emphasis on its therapeutic potentials. The bioactive constituents extracted from P. guajava include phytochemicals (gallic acid, casuariin, catechin, chlorogenic acid, rutin, vanillic acid, quercetin, syringic acid, kaempferol, apigenin, cinnamic acid, luteolin, quercetin-3-O-α-L-arabinopyranoside, morin, ellagic acid, guaijaverin, pedunculoside, asiastic acid, ursolic acid, oleanolic acid, methyl gallate and epicatechin) and essential oils (limonene, trans-caryophyllene, α-humulene, γ-muurolene, selinene, caryophyllene oxide, bisabolol, isocaryophyllene, δ-cadinene, α-copaene, α-cedrene, β-eudesmol, α-pinene, β-pinene, β-myrcene, linalool, α-terpineol and eucalyptol). In vitro and in vivo studies demonstrated that P. guajava possesses pharmacological activities such as antidiabetic, antidiarrhoeal, hepatoprotective, anticancer, antioxidant, anti-inflammatory, antiestrogenic, and antibacterial activities which support its traditional uses. The exhibited pharmacological activities reported may be attributed to the numerous bioactive compounds present in different parts of P. guajava. Based on the beneficial effects of P. guajava as well as its bioactive constituents, it can be exploited in the development of pharmaceutical products and functional foods. However, there is a need for comprehensive studies in clinical trials to establish the safe doses and efficacy of P. guajava for the treatment of several diseases.     

混流装配线平衡问题的多目标优化方法研究

针对混流装配线存在的工序作业多、平衡难度大等问题,以U型布置的混装线为研究对象,兼顾工作站平均负荷和瞬时负荷平衡,在最小化工作站数的基础上均衡了工作站间和工作站内不同产品的作业负荷,建立U型混流装配线多目标平衡优化模型,同时提出目标法解决联合目标中的目标函数兼容性问题。设计并运用改进的自适应遗传算法求解模型,考虑到交叉、变异操作的随机性,在变异阶段加入强制规则,并对新生成的子代个体进行基因冲突检测,以提高可行解的比率。算例研究的结果表明本文所提的多目标优化方法能够较好地解决混装线平衡问题。     

磁绝缘传输线的有损线模型

 开发了一种磁绝缘传输线(MITL)的电路模拟方法。以传输线模拟方法TLCOD为基础,将MITL分成若干段有损传输线单元,每个单元由一段无损传输线及一个对地损失电阻组成。根据磁绝缘准则判断单元的磁绝缘状况并计算相关参量,推导丝阵负载条件下MITL末端界面电压的表达式,阐述模型的求解方法及步骤;用有损线模型计算阳加速器MITL得到的结果与实验结果基本吻合,表明模型正确有效。     

阳加速器水传输线及磁绝缘传输线的电路模拟

 根据阳加速器传输线的阻抗分区特性,建立电路模型,并对短路实验及丝阵内爆实验进行模拟。短路实验的模拟结果与实验测试结果非常接近;通过对丝阵具体条件的分析,合理地引入串联电阻,同样准确地模拟了丝阵内爆的传输线响应特性,并利用模型简单描述了丝阵内爆的一般特性。模拟结果表明,模拟方法正确有效、电路模型可用于变阻抗水传输线及MITL的设计分析及基本规律研究。     

Comparison of line search minimization algorithms for exploring topography of multidimensional potential energy surfaces: Mg+Arn case

The most robust numerical algorithms for unconstrained optimization that involve a line search are tested in the problem of locating stable structures and transition states of atomic microclusters. Specifically, the popular quenching technique is compared with conjugate gradient and variable metric algorithms in the Mg⁺Ar_n clusters. It is found that the variable metric method BFGS combined with an approximate line minimization routine is the most efficient, and it shows global convergence properties. This technique is applied to find a few hundred stationary points of Mg⁺Ar₁₂ and to locate isomerization paths between the two most stable icosahedral structures found for Mg⁺Ar₁₂. The latter correspond to a solvated and a nonsolvated ion, respectively. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 :1011–1022, 1997     

Internal conrotation and disrotation in H2BCH2BH2 and diborylmethane 1,3 H exchange

The paths of correlated internal disrotation (barrier less than 0.4 kcal/mol) and conrotation (barrier around 1.9 kcal/mol) of the two BH₂ groups in H₂BCH₂BH₂ have been computed employing ab initio [MP2(full)/6–31G**] and density functional theory (Becke3LYP/6–311+G**) methods. Two B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative interactions stabilize the C_s symmetric H₂BCH₂BH₂ isomer ( 1 ). The B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative stabilization, evaluated by homodesmotic reactions and using the orbital deletion procedure (which “deactivates” the “vacant” born p orbital), is less than 6 kcal/mol in diborylmethane. The B(SINGLE BOND)C(DOTTED BOND)B(p) stabilization is shown to be remarkably large in C₄B₆H₁₀ (Td). At MP2(fu)/6–31G**, disproportionation into 1 and methane is only 5.6 kcal/mol exothermic. The 1,3 H exchange in diborylmethane is an asynchronous process and proceeds via a doubly bridged cyclic intermediate with 9.3 kcal/mol barrier. Structures with “planar tetracoordinate” carbon are stabilized considerably by BH₂ substituents, but they are still high in energy. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1792–1803, 1997     

A construction of a perfect set of Euler tours of K2k + I

In this article we define a perfect set of Euler tours of K_2k + I, I a 1-factor of K_2k, to be a set of Euler tours of K_2k + I that partition the 2-paths of K_2k, with the added condition that if ab ∈ I, then each Euler tour contains either the digon a b a or b a b. We prove for all k > 1 that K_2k + I has a perfect set of Euler tours, and, as a corollary, that L(K_2k) has a Hamilton decomposition. © 1998 John Wiley & Sons, Inc. J Combin Designs 6: 183–211, 1998