微波消解MPT-AES测定催化剂中的铈

研究了微波等离子体炬原子发射光谱法(MPT-AES)测定催化剂中稀土元素铈的方法。详细考察了测定铈时的实验参数，进行了系统优化。催化剂处理采用了微波消解技术。方法的检出限为2．56μg／mL，相对标准偏差(n=11)为4．37％，线性范围为20～250μg／mL，回收率在90％～ll0％之间。实验结果表明微波消解和MPT-AES联用可成为测定催化剂中铈含量的简单、快速、准确的分析方法。     

微波消解-分光光度法测定催化裂化原料中铁和镍

采用微波消解技术处理催化裂化原料，用分光光度法测定样品中的铁和镍。详细考察了微波消解消化剂的种类和用量，消解时间，消解压力和消解功率对消解效果的影响，确定了最佳微波消解程序。将微波消解技术与常规分光光度法结合测定催化裂化原料中的铁和镍，与常压溶样方法测定结果相吻合。该方法的相对误差小于0．9％，相对标准偏差(n=5)小于2．7％，两种样品制备方法的加标回收率均在95．2％～102．4％之间。实验结果表明：该方法简便、快速、准确、节省试剂、无环境污染，在催化裂化原料质量检测方面切实可行。     

微波消解-紫外分光光度法测定水中总氮

研究了用微波消解-紫外分光光度法测定水样中的总氮，结果表明，所提出的消解方法具有操作简单、省时、消解完全的特点，精密度和准确度均令人满意．方法的线性范吲为0．0242～9．60mg／L，水样加标回收率为101％～103％，相对标准偏差为0．13％～0．44％。     

微波消解-分光光度法测定石油焦中的钒

研究了用微波消解分光光度法测定石油焦中的钒。在石油焦样品处理中采用了常规溶样及微波消解两种方法。重点研究了微波消解石油焦样品的方法，详细考察了微波消解时样品的最佳用量、消解压力、功率、时间，建立了最佳微波消解程序。结果表明两种方法测定结果基本吻合。样品测定的RSD小于4、02％，加标回收率均在98．6％～102．7％之间，但微波消解法的溶样速度是常规法的10倍。钒的线性范围为0～8．0g／L。结果表明，微波消解分光光度法测定石油焦中的钒是一种快速、准确且无环境污染的方法。     

控温消解-冷原子吸收方法测定水果蔬菜中微量汞

应用程序控温－湿法消解－氢化物发生－冷原子吸收光谱法对水果蔬菜中的汞的定量方法进行了研究和探讨。对程序控温消解仪的消解条件、氢化物－冷原子吸收的测定条件进行了探讨。在本文选择的条件下，回收率为86．99％－108．00％，相对偏差为4．6％－10．8％。该方法与国家标准方法相对照，无明显差异。     

催化剂中钨的测定溶样方法的改进

研究了新的溶样方法——微波消解法,并将其与常规光度法相结合测定催化剂中钨。考察了测定条件,研究了消解用酸的种类、用量和不同的消解程序对消解效果的影响,确定了微波消解催化剂的最佳消解程序。将经微波消解处理的催化剂样品用常规光度法测定钨的含量,其相对误差小于2．0%,相对标准偏差小于1．3%。将微波消解法与常压敞口消解法进行对比,测定结果基本一致。微波消解法酸用量减少了约5．0倍,消解速度提高了3．5～6．7倍。该方法具有省时、省酸、样品损失少、无环境污染、测定结果准确可靠等优点。     

氢化物发生原子荧光光谱法测定污泥中的砷

用氢化物发生原子荧光光谱法测定污泥中的砷.分别用微波消解、湿法消解两种方法处理污泥样品，微波消解效果优于湿法消解，在最佳实验条件下，砷的检出限为0.04μg/L，回收率为94．2％～104.8％，测定结果的相对标准偏差为2．22％～4．23％。     

消解氨溶-火焰原子发射光谱法测定丁苯橡胶中的钾、钠

和浓硝酸消解了丁苯橡胶样品，再用氨水溶解消解产物。取适量消解产物的氨溶液，加入消电离剂Li^ 配制成试液，以工作曲线法测定。对样品处理方法、消解产物的溶解性质、线性范围、干扰及检出限进行了考察。测定结果的相对标准偏差小于3．9％，加标回收率为97．3％－103．7％。建立了快速同时测定丁苯橡胶中钾、钠的火焰原子发射光谱法。     

微波消解-火焰原子吸收光谱法测定玉米面中的铜、锌和铁

实验采用微波消解系统消解玉米面样品,将样品置于密闭容器内,加入一定量的硝酸和过氧化氢,放在微波炉内进行消解。详细考察了微波消解溶剂、消解时间、消解功率和消解压力对消解效果的影响,采用正交实验设计确定了微波消解的最佳工作参数。用火焰原子吸收光谱法测定玉米面中铜、锌和铁的含量,其相对标准偏差分别为1．99％、0．92％和2．10％（n=6）,平均加标回收率分别为97．5％、102．9％和98．7％。与常压消解法的测定结果进行比较,测定值吻合,准确度和精密度均优于传统方法。     

高压釜消解-氢化物发生原子荧光光度法测定土壤中的砷、硒

对高压釜密封消解一氢化物发生原子荧光法测定土壤中砷、硒的方法进行了研究。采用HNO3-HClO4作消解剂，在最佳的消解条件和测定条件下，测定砷、硒的线性回归方程分别为I=244．1c 1．03、I=88．26c 2．86．线性范围均为0．50～10．00μg／L，相关系数均为0．9999，检出限均为0．0002μg/mL。测定土壤中砷、硒的回收率分别为90％～105％、89％～104％，RSD分别为2．2％～4．0％、1．9％～3．1％。     

The effect of trimethylamine N-oxide on RNase a stability

The thermal stability of bovine pancreatic ribonuclease (RNase A) has been investigated in the presence of trimethylamine N-oxide (TMAO), a naturally occurring osmolyte, by means of differential scanning calorimetry (DSC) and circular dichroism (CD) measurements at neutral and acid pH conditions. It is well known that compatible osmolytes such as TMAO are effective in stabilizing protein structure and counteracting the denaturing the effect of urea and guanidinium hydrochloride (GuHCl). Calorimetric results show that TMAO stabilizes RNase A at pH 7.0 and does not stabilize the protein at pH 4.0. RNase A thermal denaturation in the presence of TMAO is a reversible two-state N ⇆ D process. We also show that TMAO counteracts the urea and GuHCl denaturing effect at neutral pH, whereas the counteracting ability is lost at acid pH.     

The Role of Birth Control in the Survival of the Human Race

Analysis of the growth of the world's population shows that if no trenchant measures are taken, the number of the earth's inhabitants is likely to double to 8 billion people within as few as 35 years. Hormonal contraception is presently the best method available which would be capable of counteracting this trend. 6.5 tons of estrogen and 32 tons of progestogen would in theory be sufficient to protect the 500 million women of child-bearing age from unwanted pregnancies for one year.—In addition, the history, industrial methods of synthesis, mode of action and side effects of steroid contraceptives as well as the possible future developments are briefly mentioned.     

From the double-stranded helix to the chiral nematic phase of B-DNA: a molecular model

B-DNA solutions of suitable concentration form left-handed chiral nematic phases (cholesterics). Such phases have also been observed in solutions of other stiff or semiflexible chiral polymers; magnitude and handedness of the cholesteric pitch are uniquely related to the molecular features. In this work we present a theoretical method and a numerical procedure which, starting from the structure of polyelectrolytes, lead to the prediction of the cholesteric pitch. Molecular expressions for the free energy of the system are obtained on the basis of steric and electrostatic interactions between polymers; the former are described in terms of excluded volume, while a mean field approximation is used for the latter. Calculations have been performed for 130 base pair fragments of B-DNA. The theoretical predictions provide an explanation for the experimental behavior, by showing the counteracting role played by shape and charge chirality of the molecule.     

Horizontal chevron domain formation and smectic layer reorientation in SmC* liquid crystals stabilized by polymer networks

The influence of a polymer network, stabilizing an initial texture of horizontal chevron geometry, on the in-plane smectic C* layer reorientation process is studied for different applied electric field conditions. As expected, the reorientation of smectic layers is strongly slowed down and eventually suppressed by the network, even at rather low monomer concentrations. Polymer network formation in a uniformly reoriented smectic layer state reveals that the network acts in two ways: first it gives a biased elastic torque counteracting a field of such symmetry as to cause a change from the templated layer direction; second it introduces an increased effective viscosity counteracting the reorientation in both directions. The behaviour of samples stabilized by two different kinds of polymer networks, created in between the smectic layers (intra-layer) and across them (inter-layer), is then investigated and discussed.     

Horizontal chevron domain formation and smectic layer reorientation in SmC* liquid crystals stabilized by polymer networks

The influence of a polymer network, stabilizing an initial texture of horizontal chevron geometry, on the in-plane smectic C* layer reorientation process is studied for different applied electric field conditions. As expected, the reorientation of smectic layers is strongly slowed down and eventually suppressed by the network, even at rather low monomer concentrations. Polymer network formation in a uniformly reoriented smectic layer state reveals that the network acts in two ways: first it gives a biased elastic torque counteracting a field of such symmetry as to cause a change from the templated layer direction; second it introduces an increased effective viscosity counteracting the reorientation in both directions. The behaviour of samples stabilized by two different kinds of polymer networks, created in between the smectic layers (intra-layer) and across them (inter-layer), is then investigated and discussed.     

Tailoring the microstructure of particle-stabilized wet foams

Inorganic colloidal particles which are in situ hydrophobized upon adsorption of short-chain amphiphilic molecules can be used as foam stabilizers. In this study, we tailor the microstructure of particle-stabilized wet foams, namely, the foam air content, average bubble size, and bubble size distribution, by changing the composition of the initial colloidal suspension. Wet foams featuring average bubble sizes between 10 and 200 microm and air contents between 45% and 90% were obtained by adjusting the amphiphile and particle concentration, pH, ionic strength, and particle size in the initial suspension. The influence of these parameters on the bubble size was satisfactorily described in terms of a balance between the shear stress applied during mixing and the counteracting Laplace pressure of the air bubbles. This model, originally developed for oil droplets in emulsions, can therefore be used to deliberately tailor the microstructure of particle-stabilized wet foams.     

Recent Advances in the Semisynthesis,Modifications and Biological Activities of Ocotillol-Type Triterpenoids

Ginseng is one of the most widely consumed herbs in the world and plays an important role in counteracting fatigue and alleviating stress. The main active substances of ginseng are its ginsenosides. Ocotillol-type triterpenoid is a remarkably effective ginsenoside from Vietnamese ginseng that has received attention because of its potential antibacterial, anticancer and anti-inflammatory properties, among others. The semisynthesis, modification and biological activities of ocotillol-type compounds have been extensively studied in recent years. The aim of this review is to summarize semisynthesis, modification and pharmacological activities of ocotillol-type compounds. The structure–activity relationship studies of these compounds were reported. This summary should prove useful information for drug exploration of ocotillol-type derivatives.     

A new multiscale modeling method for simulating the loss processes in polymer solar cell nanodevices

The photoelectric power conversion efficiency of polymer solar cells is till now, compared to conventional inorganic solar cells, still relatively low with maximum values ranging from 7% to 8%. This essentially relates to the existence of exciton and charge carrier loss phenomena, reducing the performance of polymer solar cells significantly. In this paper we introduce a new computer simulation technique, which permits to explore the causes of the occurrence of such phenomena at the nanoscale and to design new photovoltaic materials with optimized opto-electronic properties. Our approach consists in coupling a mesoscopic field-theoretic method with a suitable dynamic Monte Carlo algorithm, to model the elementary photovoltaic processes. Using this algorithm, we investigate the influence of structural characteristics and different device conditions on the exciton generation and charge transport efficiencies in case of a novel nanostructured polymer blend. More specifically, we find that the disjunction of continuous percolation paths leads to the creation of dead ends, resulting in charge carrier losses through charge recombination. Moreover, we observe that defects are characterized by a low exciton dissociation efficiency due to a high charge accumulation, counteracting the charge generation process. From these observations, we conclude that both the charge carrier loss and the exciton loss phenomena lead to a dramatic decrease in the internal quantum efficiency. Finally, by analyzing the photovoltaic behavior of the nanostructures under different circuit conditions, we demonstrate that charge injection significantly determines the impact of the defects on the solar cell performance.     

Synergistic extraction of uranyl ion with acylpyrazolones and dicyclohexano-18-crown-6

Synergistic extraction of uranyl ion with acylpyrazolones such as 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5 (HPMTFP, pKa=2.7), 1-phenyl-3-methyl-4-acetylpyrazolone (HPMAP, pKa=3.8) or 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (HPMBP, pKa=4.2) in combination with dicyclohexano-18-crown-6 (DC-18-C6) has been studied at various fixed temperatures. The results indicate that the equilibrium constants of the organic phase addition reaction, log Ks, at 30°C are almost constant, viz., 2.72, 2.69 and 2.84, respectively, for the above three systems. The similarity and low log Ks values with DC-18-C6 as compared with TBP systems with these pyrazolones appears to arise due to the limitation to the approach of the large crown ether molecule in bonding with the uranyl chelate. This is in contrast to the fact that the relative basicities of the two donors (equilibrium constant for nitric acid uptake) are comparable. Thermodynamic data for chelate extraction with HPMTFP evaluated by the temperature coefficient method indicates that a hydrated chelate is extracted into the organic phase. Also, the organic phase addition reaction with DC-18-C6 is stabilized by exothermic enthalpy change, the entropy change counteracting in all the three cases.