乙酰化淀粉/DL-丙交酯接枝共聚物的合成及降解性能研究

用醋酸乙烯酯和玉米淀粉反应制备出了不同取代度乙酰化淀粉，再用乙酰化淀粉同DL－丙交酯接枝共聚合成乙酰化淀粉／DL－丙交酯接枝共聚物。研究了原料配比，淀粉取代度对接枝反应单体转化率（C％），接枝率（G％）接枝效率（GE％）和接枝支链数均分子量（Mn)的影响，结果表明在给定的试验条件下接枝共聚反应的C％，G％，GE％和Mn可分别达到40％，225％，80％和1．4万。接枝共聚物在磷酸缓冲溶液和户外土壤掩埋降解实验表明，在160天内样品失重率分别为71％和60％，表明合成的乙酰化淀粉／DL－丙交酯接枝共聚物具有很好的降解性能。     

Simultaneous determination of trace uranium(VI) and zinc(II) by adsorptive cathodic stripping voltammetry with aluminon ligand

Uranium(VI) complexed with aluminon (3-[bis(3-carboxy-4-hydroxy-phenyl)methylene]-6-oxo-1,4-cyclohexadiene-1-carboxylic acid triammonium salt) was determined by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode. Trace uranium(VI) and zinc(II) can be simultaneously determined in a single scan in the presence of aluminon and urea. Optimal conditions were found to be: accumulation time; 180–200 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s⁻¹, supporting electrolyte; 0.1 M sodium acetate buffer at pH 6.5–7.0, and concentration of aluminon; 1×10⁻⁶ M. The linear range of uranium(VI) and zinc(II) were observed over the concentration range 2–33 and 30–120 ng ml⁻¹, respectively. The detection limit (S/N=3) are 0.2 ng ml⁻¹ (uranium) and 30 ng ml⁻¹ (zinc). A good reproducibility shows RSDs of 2.5–4.0% (n=10). The procedure offers high selectivity, with the presence of urea masking some metal ions.     

Buffers for the Physiological pH Range: Thermodynamics of the Second Dissociation of N-(2-Hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic Acid From 5 to 55°C

The second acidic dissociation constants pK ₂ of the ampholyte N-(2-hydroxyethyl) piperazine-N-2-hydroxypropanesulfonic acid (HEPPSO) have been determined at seven temperatures from 5 to 55°C from emf measurements utilizing hydrogen and silver–silver chloride cells without liquid junction. The thermodynamic quantities, G°, H°,S°, and C _p ^o have been calculated from the temperature coefficient of pK ₂. At 25°C, the pK ₂ = 8.042 and at 37°C, pK ₂ = 7.876; hence, buffer solutions of HEPPSO and NaHEPPSOate are important for pH control in the region close to that of clinical fluids (blood serum). Conventional pH values from 5 to 55°C as well as those obtained from liquid junction correction at 25 and 37°C have been reported for three buffer solutions with the compositions (molality scale): (1) equimolal mixture of HEPPSO (0.04 m) + NaHEPPSOate (0.04 m) + NaCl (0.12 m); (2) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m); and (3) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m) + NaCl (0.08 m).     

有机溶剂/缓冲液两相体系中全细胞催化拆分环氧氯丙烷

研究了有机溶剂/缓冲液两相体系中重组大肠杆菌E.coli BL21 (DE3)全细胞水解动力学拆分外消旋环氧氯丙烷制备(R)-环氧氯丙烷的过程.结果表明,最适反应条件为:最适有机溶剂异辛烷与缓冲液的体积比7:3,最适缓冲液pH 8.0,底物浓度574mmol/L,全细胞加入量0.07g湿菌体/ml溶液,温度30℃.在此条件下于1L反应器中反应45min,(R)-环氧氯丙烷的摩尔产率、光学纯度和时空产率分别达到37.5%,99.3%ee和0.286mol/(L·h).与单一水相体系相比,异辛烷/缓冲液两相体系中底物浓度和(R)-环氧氯丙烷时空产率分别提高了55.2%和98.6%.     

Continuous flow electrolytic cold vapor generation atomic fluorescence spectrometric determination of Hg in water samples

The determination of trace concentrations of Hg in water samples by the use of electrolytic cold vapor generation (ECVG) system and AFS was studied. Several buffer solutions were used and the detection limits with these systems were found to be by a factor of 1–2 lower than in the conventional electrolytic cold vapor generation system. Comparing with the traditional inorganic acid, phosphate buffer solution (PBS) increased the signal intensity of Hg vapor from electrolytic generation on Pt cathode and reduced the impact of cathode erosion on the stability of signal intensity. Moreover, buffer solution has better interference tolerance. The effects of the electrolytic conditions and interference ions on the ECVG have been studied. Under optimized conditions and with PBS as catholyte the detection limit for Hg was found to be 0.27 ng L⁻¹. The relative standard deviation was 2.8% for 11 consecutive measurements of 1 μg L⁻¹ Hg. This method has been applied in the determination of inorganic Hg in Yangtze River water.     

Ni基带上的氧化物过渡层制备

本文采用溅射沉积方法在双轴织构的Ni—W5％基带上制备了CeO2和Y2O3薄膜．研究表明CeO2薄膜在Ni基带上的外延方式受生长速率、生长温度的控制．在快速沉积情况下，CeO2薄膜为（111）取向，在沉积速率较低时，以（001）取向为主．CeO2薄膜沉积过程中，可以有效避免Ni的氧化．在Y2O3的沉积过程中，Ni基带的氧化不可避免，但其氧化物也有良好的取向．     

Optimal buffer size for a stochastic processing network in heavy traffic

We consider a one-dimensional stochastic control problem that arises from queueing network applications. The state process corresponding to the queue-length process is given by a stochastic differential equation which reflects at the origin. The controller can choose the drift coefficient which represents the service rate and the buffer size b>0. When the queue length reaches b, the new customers are rejected and this incurs a penalty. There are three types of costs involved: A “control cost” related to the dynamically controlled service rate, a “congestion cost” which depends on the queue length and a “rejection penalty” for the rejection of the customers. We consider the problem of minimizing long-term average cost, which is also known as the ergodic cost criterion. We obtain an optimal drift rate (i.e. an optimal service rate) as well as the optimal buffer size b ^*>0. When the buffer size b>0 is fixed and where there is no congestion cost, this problem is similar to the work in Ata, Harrison and Shepp (Ann. Appl. Probab. 15, 1145–1160, 2005). Our method is quite different from that of (Ata, Harrison and Shepp (Ann. Appl. Probab. 15, 1145–1160, 2005)). To obtain a solution to the corresponding Hamilton–Jacobi–Bellman (HJB) equation, we analyze a family of ordinary differential equations. We make use of some specific characteristics of this family of solutions to obtain the optimal buffer size b ^*>0. A.P. Weerasinghe’s research supported by US Army Research Office grant W911NF0510032.     

Influence of Buffer-Layer Thickness on Performance of Waveguide Modulators

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Effect of citrate impurities on the reference pH value of potassium dihydrogen buffer solution

Solutions of potassium dihydrogen citrate, KH₂C₆H₅O₇, exhibit reference pH values close to those of the primary standard pH buffer solutions of tartrate and phthate. Nevertheless, as opposed to all other recommended primary buffer standards, the citrate reagent is not commercially available as a standard reference material (SRM).In this work, experiments have been performed on solid reagent from different sources, which revealed the presence of the various citrate species in variable amounts. This may arise from the sensitivity of the system to the purification strategy, owing to the proximity of the acidity constants of the triprotic citric acid, H₃C₆H₅O₇.An experimental procedure has been developed which leads to a satisfactory preparation of the citrate reagent, to an extent that its solutions, independently of batch on supplier, exhibit reproducible pH values, in agreement with the conventionally assigned pH (S) = 3.776 at 25 °C for 0.05 m KH₂C₆H₅O₇.Comparison of expected and experimental values is used as a quantitative test for the quality of reagent, eventually indicating the need for purification according to recommendations.     

Cyclodextrin-modified micellar electrokinetic chromatography for separation of norgestrel enantiomers

A simple method for the separation of highly hydrophobic neutral enantiomers by cyclodextrin-modified micellar electrokinetic chro-matography (MEKC) is presented and strongly supported by experiments. The separation depends on the ratio between the concentrations of cyclodextrin (CD) and sodium dodecylsulfate (SDS) micelles and there is an optimum value of the ratio for the separation of the enantiomers of norgestrel and 4-androstene-3,17-dione. At the optimum value of the ratio, obtained by adjusting the absolute concentrations of CD and SDS. The electrophoretic mobility difference between two enantiomers can be maintained nearly constant.