Properties of poly(vinyl alcohol)–borax gel doped with neodymium and praseodymium

Neodymium and praseodymium ions, singly and in combination, have been doped into a poly(vinyl alcohol)–borax matrix. X-ray diffraction shows structural correlations from 2 to 6 Å and 15 Å, while small angle neutron scattering indicates that the rare-earth ions do not affect the nanoscale structures of the gels. Differential scanning calorimetry shows the glass transition temperature to increase with concentration of Pr in the gel. Excitation in the ultraviolet region leads to luminescent emission in the visible region. Simultaneous absorption in the visible region then leads to luminescent emission in the near infra-red region. The spectral qualities of the emission bands can be varied by choosing appropriate relative ratios of rare-earth species.     

Si-C-N三元系统的新陶瓷相

固体化学合成的氮化物较其他氧化物研究相对较少,然而过去20年来,该研究领域得到重视.超硬C3N4相所类似的碳氮化物目前已获得深入研究,相比较而言,Si-C-N化合物的研究依旧比较少.在大气条件下首先合成的三元晶体相为Si(NCN)2和Si2C2(NCN).本文回顾了近年来采用高温高压反应工艺合成C-N二元和Si-C-N三元系材料的研究现状.这类新型材料因具有一些独特的性能,如高硬度、磁性、光电性能,而具有重大研究前景.     

Hedonic Differences as a Function of Number of Samples Evaluated

SUMMARY: This study investigated the limit of the number of samples that can reliably evaluated for preference in a single laboratory test session. Multiple samples were presented to 200 subjects randomly assigned to five conditions. Two critical samples were included under each condition and the number of other samples varied from zero to four. Two replications of each set were evaluated by each subject in a single session without his knowledge that samples were repeated. The total number of samples for the five experiments were 4, 6, 8, 10 and 12. The experiment was run separately with milk, soup and gravy base and maple syrup. There was no evidence that serving up to 12 samples in a single session adversely affected preference discrimination.     

Negatively Buoyant Flow Along Vertical Cylinders at High Rayleigh Numbers

Conditions that must be satisfied before the launch of a Space Transportation System (STS) include combinations of ambient temperature and wind speed that are intended to prevent ice formation on the External Tank (ET) and a local air temperature around the STS of 33°F (0.56°C) or less. Nineteen effluent gases are purged or vented from the STS into the launch pad environment, the most significant of these being the cold and negatively buoyant boil-off gaseous oxygen (GOX) from the oxygen tank. Vented into the ambient, this GOX can be wind-carried toward the STS, where it will cool the launch pad environment. This article described a combined three-dimensional (3D) and two-dimensional (2D) computational fluid dynamics (CFD) analysis that investigated this cooling effect. The results of this analysis for a 6-knot (3.09 m/s) west wind and an ambient temperature of 38°F (3.33°C) indicate that the GOX could cool, relative to the ambient, the local air in the vicinity of the STS and the surface of the east Redesigned Solid Rocket Motor (RSRM) by as much as 28°F (15.56°C) and 5 to 6°F (2.78 to 3.33°C), respectively. The large lengths associated with the ET and the east RSRM resulted in Rayleigh numbers that were one to three orders of magnitude larger than those found in literature.     

发展表面增强激光解吸电离飞行时间质谱技术用于评估职业性暴露于丙烯酰胺环境的生物标记物

表面增强激光解吸电离飞行时间质谱技术(SELDI-TOF-MS)是一种用来检测生物样品中蛋白质的生物分析技术.血液或尿液中的蛋白质如果受毒性试剂的影响可能会发生变化.丙烯酰胺是一种广泛使用的工业化学品,很可能是一种致癌物,因此人们很担心暴露在丙烯酰胺中会产生健康问题.丙烯酰胺及其代谢产物环氧丙酰胺很容易与蛋白质结合.目前有多种分析技术评估内烯酰胺对尿液和血红蛋白的影响,但是这些分析方法耗时而且昂贵.本文考察了SELDI-TOF-MS能否作为一种筛查工具以鉴定受丙烯酰胺影响而发生修饰的尿液蛋白质或血红蛋白.     

Observations on the introduction of the DEFT for the routine assessment of bacteriological quality

In the light of experiences gained and observations made in the dairy industry, the critical control points and factors that affect the operation of the DEFT (Direct Epifluorescent Filter Technique) in a routine laboratory were determined. Recommendations are made for the optimization of both the test protocol and the instrumentation, and the need for adequate operator training is strongly emphasized.     

Analysis of the DNA Sequence of a 34 038 bp Region on the Left Arm of Yeast Chromosome XV

We report the DNA sequence of a 34 038 bp segment of Saccharomyces cerevisiae chromosome XV. Subsequent analysis revealed 20 open reading frames (ORFs) longer than 300 bp and two tRNA genes. Five ORFs correspond to genes previously identified in S. cerevisiae, including RPLA2, PRE6, MSE1, IFM1 and SCM2 (TAT2, TAP2, LTG3). Two putative proteins share considerable homology with other proteins in the current data libraries. ORF O2145 shows 41·2% identity with the glycophospholipid-anchored surface glycoprotein Gas1p of S. cerevisiae and ORF O2197 has 53·2% identity to chromosome segregation protein Dis3p of Schizosaccharomyces pombe. Accession Numbers for these sequences are provided in Table 1.©1997 John Wiley & Sons, Ltd.     

APPLICATION OF A NEW CONTINUOUS FLOW SPECTROPHOTOMETRIC METHOD FOR THE CHARACTERIZATION OF POLYPHENOL OXIDASE NATURALLY IMMOBILIZED ON COCONUT FIBER

The association of continuous flow injection and spectrophotometry affords a simple, novel and rapid way of monitoring continuously the activity of naturally immobilized enzymes in their natural environment, thus eliminating cumbersome purification. The method was applied to determine the activity of polyphenol oxidase (PPO) enzymes naturally immobilized on coconut (Cocus nucifera, L.) fiber tissues. Maximum enzyme activity occurred at a temperature of 25C and at pH 6.0 using catechol as substrate. Thermal stability was assayed in a temperature range of 20 to 75C. The PPO exhibited excellent thermal stability, with only 50% loss in its activity at 75C after 4.3 min exposure. For catechol apparent Michaelis‐Menten constant (apparent Km), apparent Vmax and the apparent activation energy were 9.1 × 10^?3 mol L^?1, 0.20 abs min^?1 and 10.5 kcal mol^?1, respectively. The immobilized PPO showed high activity for o‐diphenols. The reactivity order was caffeic acid > pyrogallol > catechol. Complete inhibition of the enzyme was observed with 1 × 10^?3 mol L^?1 concentration of cyanide, thiourea, L‐cysteine, ascorbic acid, sodium sulfite, nitrates of cadmium, zinc and mercury, individually. Benzoic acid, 3‐hydroxy‐benzoic acid, 4‐acetamidephenol, sodium azide, resorcinol, L‐cystine and EDTA at equal concentrations inhibited PPO partially.