Handling preferences in student-project allocation

Annals of Operations Research - We consider the problem of allocating students to project topics satisfying side constraints and taking into account students’ preferences. Students rank...     

Microplate-based microbial assay for risk assessment and (eco)toxic fingerprinting of chemicals

We have developed a multi-species microbial assay, MARA, for assessing the (eco)toxic risks of chemical compounds and for the determination of their toxic fingerprints. The main advantages with MARA are (1) the simultaneous testing on several microbial strains; (2) the concept of toxic fingerprinting; (3) the simple and inexpensive handling and reading of the test. The toxic activity is measured in parallel on 11 different micro-organisms lyophilised in a microplate. A concentration gradient of the chemical to be tested is added and growth is indicated through the reduction of tetrazolium red (TTC). The microplates are read by a common flatbed scanner or a microplate spectrophotometer. The array of the 11 different inhibition values constitute a toxic fingerprint, characteristic for each type of chemical compound, and it is shown that the assay can distinguish between 12 standard chemicals. Both the reproducibility (CV≈20%) and the sensitivity are similar to other toxicity tests based on micro-organisms.     

Water-alcohol interactions in the two-phase system water-alcohol-alkane

The system water-alcohol-alkane has been studied at 25°C as a possible model system for micelles. The solubility of water in pure alcohols and in octane in the presence of alcohol has been determined. The data suggest that water may enter the octane phase hydrogen bonded to the hydroxyl group of the alcohol. If this system has any bearing on aqueous micellar solutions, it seems possible that solubilized alcohol molecules may carry water into the micellar interior. Addition of 1,2-propanediol does not increase the water content in octane, probably because dimerization of the diol in octane is energetically more favorable than diol-water interactions.     

Nucleoside Phosphoramidate Analogues with Modification in the Bridging Positions of the Phosphodiester Linkage

Abstract

Phosphoramidate modified DNA oligomersl[1] have recently been shown to have promising properties for antisensdantigene applications. An eficient method, for the preparation of nucleoside P3′ → N5′ and N3′ → P5′ phosphoramidates and their thio analogues 3 was developedl'l. I t consists of the oxidative generation of a pyridine adducr of type 2 of nucleoside metaphosphate from the corresponding nucleoside H-phosphonate, nucleoside H-phosphonothioate or nucleoside H-phosphondithioatc monoester, and its consecutive clean reaction with 5′- or 3′-aminonucleosides in the presence of triethylamine.     

Spectrophotometric determination of chloride,bromide, and iodide with an improved mercury-iron-thiocyanate method

Stable reagents for the spectrophotometric mercury-iron-thiocyanate method for the determination of halide have been developed. The molar absorptivity for concentrations up to 170 μmole/liter of halide is for chloride 3.4 × 10³, for bromide 3.9 × 10³, and for iodide 4.0 × 10³. Above this concentration there is a slight decrease of the absorptivity for chloride and a slight increase for bromide and iodide.     

Études sur la détection,la caractérisation et le dosage des aldéhydes: Méthodes d'oximation

Five methods for the estimation of aldehydes by oximation have been compared. In all the methods, a single or double branching in position α in the case of aliphatic aldehydes, and in positions 2 and 6 in the case of aromatic aldehydes, tends to lessen the accuracy (steric hindrance). Of the methods examined those of Bryant and Smith¹ and Smith and Mitchell³ are the most common.Three new oximes are described. For one of these, two modifications have been isolated, both of which are converted to acetate by the action of acetic anhydride and sodium carbonate. The question is discussed whether this is a case of the syn and anti forms of the oximo or of two polymorphic modifications.     

On the curvature of compressible boundary layer flows near separation

Summary Oswatitsch's analytical expression for the slope of a viscous flow separation or reattachment streamline is shown to be consistent with detailed experimental data on a supersonic boundary layer flow past a compression corner. An extension of his analysis is then given which yields a comparable new relation for the streamlinecurvature just above separation in either laminar or turbulent two-dimensional compressible boundary layer flows. This result is applied to examine the possible occurrence of Görtler streamwise vortices due to such curvature.

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Zusammenfassung Es wird gezeigt, daß die analytische Beziehung von Oswatitsch für den Neigungswinkel einer zähflüssigen Strömungsablösung (oder das Wiederanlegen), in Übereinstimmung ist mit detaillierten Versuchsergebnissen an einer Überschall-Grenzschichtströmung längs einer Kompressionsecke. Darüber hinaus wird eine Erweiterung dieser Theorie angegeben, welche eine vergleichbare Beziehung für die Stromlinienkrümmung im Bereich über dem Ablösepunkt, sowohl für laminare als auch turbulente zweidimensionale Grenzschichtströmung gibt. Dieses Ergebnis wird zu einer Abschätzung möglichen Auftretens von Görtlerschen Wirbeln in Strömungsrichtung infolge dieser Krümmung verwendet.

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Based on work supported partially by the US Air Force Office of Scientific Research under Contract F49620-76-C-0013 and by the Alexander Humboldt Foundation.     

Determination of the temperature—time profile of the sample in pyrolysis—gas chromatography

The mean temperature-time profile in a sample has been determined in order to establish whether it is possible to equate the temperature of the pyrolyzer with that of the sample being pyrolyzed. This was done by studying the degradation of cis-1,4-polybutadiene be sequential pyrolysis. The rate of degradation was determined for different amounts (0.5–20 μg) of sample. The temperature dependence of the degradation rate was determined from an Arrhenius plot. The experimental results were combined with theoretically derived expressions for the heating of samples subjected to pyrolysis. The temperature–time profiles of different amounts of sample could then be calculated.It was found that samples thinner than 1 μm were heated to a mean temperature of 95% of the temperature of the pyrolyzer in 40 ms or faster. Too thin samples can give rise to noticeable catalytic effects.By choosing the appropriate pyrolysis conditions of sample thickness, time and temperature it is possible to assume that the temperature of the sample is nearly the same as that of the pyrolyzer.     

Temperature-programmed packed capillary liquid chromatography coupled to evaporative light-scattering detection and electrospray ionization time-of-flight mass spectrometry for characterization of high-molecular-mass hindered amine light stabilizers

High-molecular weight-hindered amine light stabilizers (HMW-HALSs) are of utmost importance in modern polyolefin stabilization technology and in-depth knowledge about their chemical composition, particularly the oligomers, is essential for development of new and more efficient stabilizers. In the present study, the applicability of temperature-programmed packed capillary LC coupled to miniaturized ELSD and positive mode ESI-TOF-MS for analysis of HMW-HALSs is demonstrated through extensive characterization of two state-of-the-art stabilizers, i.e., HALS-1 and HALS-2. Both stabilizers were individually separated on a 320 microm i.d. x 35 cm long Hypersil 3 microm ODS-100 column using a temperature program from 30 to 120 degrees C and a quaternary mixture of ethylacetate, acetonitrile, triethylamine (TEA) and acetic acid (45.0:44.9:10.0:0.1 (v/v/v/v)) as the mobile phase. The effect of using various amounts of ethylacetate, acetonitrile and triethylamine in the mobile phase on the chromatographic separation is demonstrated. Furthermore, the LC-ESI-TOF-MS analyses revealed that HALS-1 (oligomeric) was highly complex and consisted of at least five different mass series, while HALS-2, which was assumed to be monomeric, contained two different mass series. Chemical structures for nearly all species of both stabilizers are proposed.