Self-diffusion of polystyrene in solution 1. Experimental results of the NMR pulsed field gradient technique

We report self-diffusion measurements for polystyrene dissolved in benzene and chloroform using the NMR pulsed field gradient technique. The observed echo attenuations point to dynamic exchange processes or cluster formation in the semidilute solution. The experimental results are compared with theoretical predictions from the reptation mechanism and the blob theory. There is qualitative agreement, but a more comprehensive analysis of the data and results from experiments with polymer mixtures show that polymer self diffusion in semidilute solutions cannot be explained by the reptation mechanism in its simple form.     

反相高效液相色谱法快速测定7种四环素类抗生素

建立了一种反相高效液相色谱梯度洗脱分离测定四环素类药物的新方法。采用DiamonsilTM C1 8ODS(2 5 0mm× 4 .6mmi.d ,5 μm)色谱柱 ,以甲醇 乙腈 0 .0 1mol/L草酸为流动相 ,流速 1.0mL/min ,2 70nm检测 ,在10min内分离检测四环素等 7种化合物。同时还研究了流动相组成、梯度条件、pH值、草酸浓度等因素对分离效果的影响。     

Computer-aided optimization of stepwise gradient profiles in thin-layer chromatography

Summary Two mixtures, one containing model coloured solutes and the other glycosides from the Digitalis species were separated by stepwise gradient thin-layer chromatography, the first in the system silica-toluene + ethyl acetate, the second in the system silica-ethyl acetate + methanol. The optimal gradient programs (i.e., for which maximal spread of spots along the plate is observed) were determined using a computer program reported in an earlier paper. Good separation and satisfactory agreement of predicted and experimental R_F values were obtained; the non-aqueous system for the separation of lanatosides permits considerable shortening of elution time owing to the lower viscosity of ethyl acetate-methanol mixtures.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

STUDIES ON THE SELF-DIFFUSION OF WATER ETHANOL MIXTURE IN CHITOSAN PERVAPORATION MEMBRANE WITH PULSED FIELD GRADIENT NMR DATA

The self-diffesion of water, ethanol and water-ethanol mixtures in chitosan (CS) membranes crosslinked byaqueous H_2SO_4 solution and uncrosslinked membrane was measured using pulsed-field gradient (PFG) nuclear magneticresonance (NMR) spectroscopy to obtain the partial solubilities and self-diffusion coefficients. An attempt was made toexplain the transport properties of water and ethanol through the CS membrane. It was concluded that there are two types ofchannel water and ethanol diffesate transfer. The water was localized in the hydrophilic ionic region formed by the ionizedgroups, and the ethanol was localized in the hydrophobic amorphous network of the polymer. There was a good agreementbetween the separation fastors estimated from PFG-NMR data and those obtained by pervaporation testing.     

高效毛细管线性聚丙烯酰胺凝胶电泳柱的制备、柱性能表征及操作条件考察

发展一种简便快速的线性聚丙烯酰胺毛细管凝胶电泳（ＣＧＥ）柱的新型制备方法，用于分离Ｐｏｌｙ ｄＡ（４０～６０）和双链ＤＮＡ，柱效达 ６百万理论板／米。提出“筛分能力”作为 ＣＧＥ柱评价指标，对样品迁移行为随操作条件的变化规律进行考察，为毛细管凝胶电泳的理论研究和实验条件优化奠定了基础。     

The hydrodynamic limit of a one-dimensional nearest neighbor gradient system

We study the hydrodynamic behavior of a one-dimensional nearest neighbor gradient system with respect to a positive convex potential . In the hydrodynamic limit the density distribution is shown to evolve according to the nonlinear diffusion equation ,(q)/t= (²/dq²){F([1/₁(q)]), with F= –.     

A preliminary cost analysis of the biotreatment of refinery spent-sulfidic caustic

Caustics are used in petroleum refining to remove hydrogen sulfide from various hydrocarbon streams. Spent-sulfidic caustics from three refineries have been successfully biotreated on the bench and pilot scale, resulting in neutralization and removal of active Sulfides. Sulfides were completely oxidized to sulfate byThiobacillus denitrificans strain F. Microbial oxidation of sulfide produced acid, which at least partially neutralized the caustic. A commercial-scale treatment system has been designed that features a bioreactor with a suspended culture of flocculatedT. denitrificans, a settler and acid and nutrient storage and delivery systems. A cost analysis has been performed for nine cases representing a range of spent caustic sulfide and hydroxide concentrations at a base treatment rate of 10 gpm. This analysis shows that refinery spent-sulfidic caustic can be biotreated for 4-8.3￠/gal.     

Scanning the beta-globin gene for mutations in large populations by denaturing capillary and gel electrophoresis

Separation of mutant from nonmutant DNA sequences of 100 bp may be accomplished by using defined denaturing conditions of chemical denaturant and/or elevated temperature during electrophoresis on either polyacrylamide slab gels (denaturing gradient gel electrophoresis, DGGE) or capillary gels (constant denaturant capillary electrophoresis, CDCE). In analysis of mutant directly from a polymerase chain reaction (PCR) product mixture, both have detection sensitivities of approximately 1%. CDCE that facilitates an intermediate mutant enrichment step permits detection of mutants at fractions as low as 2 x 10(-6). Here we report the successful application of both approaches to scan for mutations of the human beta-globin gene (HBB) in two human population samples of approximately 5000 persons in the HBB. Using DGGE, the coding region and flanking intronic splice sites of HBB were scanned in a population of 4949 Han Chinese individuals in pool sizes of 48 individual DNA samples. Four point mutations ranging in mutant frequency from 0.5 to 0.0002 were identified. Using CDCE with a mutant enrichment step, these same sequences were scanned in a population of 5028, predominantly African-American juveniles (<9 years) as a single pooled DNA sample. Three point mutations were identified ranging in mutant frequency from 0.13 to 0.0005. This study shows that both the DGGE/small pool and the CDCE/large pool approaches offer the means to define the fine structure map of genetic variation in large population samples, and with appropriately engineered facilities to provide high throughput, should be useful in pangenomic scans to discover genes carrying casual mutations for common diseases.     

Immobilized pH gradients as a first dimension in shotgun proteomics and analysis of the accuracy of pI predictability of peptides

In this work, we demonstrate the potential use of immobilized pH gradient isoelectric focusing as a first dimension in shotgun proteomics. The high resolving power and resulting reduction in matrix ionization effects due to analyzing peptides with almost the exact same physiochemical properties, represents a significant improvement in performance over traditional strong cation-exchange first-dimensional analysis associated with the shotgun proteomics approach. For example, using this technology, we were able to identify more than 6000 peptides and > 1200 proteins from the cytosolic fraction of Escherichia coli from approximately 10 microg of material analyzed in the second-dimensional liquid chromatography-tandem mass spectrometry experiment. Sample loads on the order of 1 mg can be resolved to 0.25 isoelectric point (pI) units, which make it possible to analyze organisms with significantly larger genomes/proteomes. Accurate pI prediction can then be employed using currently available algorithms to very effectively filter data for peptide/protein identification, and thus lowering the false-positive rate for cross-correlation-based peptide identification algorithms. By simplifying the protein mixture problem to tryptic peptides, the effect of specific amino acids on pI prediction can be evaluated as a function of their position in the peptide chain.     

Stochastic scheduling problems II-set strategies-

The paper introduces the finite class of set strategies for stochastic scheduling problems. It is shown that the knownstable classes of strategies such as ES and MES strategies are of this type, as arelist-scheduling strategies such as LEPT and SEPT and other, more complicatedpriority-type strategies. Roughly speaking, set strategies are characterized by the fact that the decision as to which jobs should be started at timet depends only on the knowledge of the two sets of jobs finished up to timet and being processed at timet. Contrary to list scheduling strategies, set strategies may involve deliberate idleness of machines, i.e. may not be greedy and can therefore not generally be induced by priority rules. It is demonstrated that set strategies have useful properties. They are e.g. ⁿ -almost everywhere continuous and therefore show satisfactorystability behaviour w.r.t. weak convergence of the joint distribution of job durations. Furthermore, the optimum w.r.t.all strategies is already attained on this class if job durations are independent and exponentially distributed and the performance measure fulfills a certainshift condition. This shift property is a quite natural concept and generalizes aspects of the notion ofadditivity in semi-Markov decision theory and stochastic dynamic optimization. Its complete analytical characterization is a major object of this paper. Typical additive cost criteria such as makespan and flowtime are of course covered, which yields simultaneously a first step towards generalization of optimality of LEPT and SEPT rules, as known for special cases. In fact, in view of the obtained optimality result, the question of when deliberate idleness of machines can be avoided, gains considerable interest, as it characterizes stochastic environments in whichpriority strategies are optimal. This provides a major link with current research on the analysis of networks of queues in the context of computer systems.The work of the first two authors was supported by the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen, while the work of the last author was supported by DAAD.