A heuristic method for the minimum toll booth problem

This paper addresses the toll pricing problem in which the objective is to minimize the number of required toll facilities in a traffic network. The problem is shown to be NP-hard. To obtain a solution in a reasonable time, an effective metaheuristic algorithm is developed. The algorithm uses a local search technique in which the neighborhood function employs the dynamic slope scaling procedure to deal with the fixed charge nature of the objective function. Numerical results from 50 randomly generated and three real networks are reported.     

Permeation through homopolymer latex films

The helium permeabilities of homopolymer films cast from polymer solutions and latex dispersions have been measured as a function of time. The permeability coefficients of most polymer latex films started off at a value which was considerably higher than that of the corresponding solvent-cast film, but then dropped at a rate dependent on the polymer concerned. The permeability coefficients levelled off at a value which was closer to, but still higher than that of the equivalent solvent-cast film. Solvent-cast film permeabilities remained constant for the period of several months over which time they were examined. The reduction in the permeability of latex films is attributed to ageing processes occurring within the film after casting. The fact that latex film permeability coefficients are always higher than those of solvent-cast films suggests that latex films never become completely homogeneous. The effect on permeability of the latex type and characteristics, and preparation and storage conditions has been examined. The polymer molecular weight, particle size, and surface-change density did not appear to exert any influence, within experimental error. However, the time-dependent permeability behavior was affected by the film preparation and storage temperatures.     

Mechanism of emulsion polymerization of styrene in soap-free systems

The formation and growth of monodisperse polystyrene latex particles in the absence of added surfactant has been studied by sampling polymerization reactions at different times and determining the surface and bulk properties of the latex. A large number of nuclei in excess of 5 × 10¹²/ml were generated during the first minute of reaction, but this fell due to coagulation until a constant number (10¹¹?10¹²/ml) was reached. The rate of polymerization per particle was then found to be proportional to the particle radius. Gel-permeation chromatography has shown that the initial particles consist mainly of material of MW 1000 with a small amount of polymer up to MW 10⁶, and the presence of this low molecular weight polymer, which in many cases can still be detected after 100% conversion, is taken as being indicative of particle formation via a micellization-type mechanism involving short-chain (MW 500) free-radical oligomers. M?_n values determined for the latex particles throughout the course of reactions show that the molecular weight increases to a maximum of about 10⁵ as the particles grow. The presence of anomalous regions within the particles has been confirmed by transmission electron microscopy, scanning electron microscopy, and gas adsorption studies. It has also been found possible to re-expose these regions within apparently homogeneous particles by stirring with styrene monomer; this is indicative of a molecular weight heterogeneity within the latex particles. The presence of sulfate, carboxyl, and hydroxyl groups upon the latex particle surfaces has been determined by conductometric titration.     

Analysis of synthetic peptides by capillary electrophoresis: effect of organic solvent modifiers and variable electrical potentials on separation efficiencies

In this study, procedures based on volatile ammonium acetate buffer electrolytes of high pH value containing different organic solvent modifiers have been developed to achieve very high efficiency separations of histidine-containing synthetic peptides by high-performance capillary electrophoresis (HPCE) employing untreated fused silica capillaries. Different organic solvents, including acetonitrile, methanol and ethanol, at high volume fractions were used to modify the composition of the background buffer electrolyte. With the peptides investigated, it was found that methanol had the greatest effect in terms of enhancement of separation efficiency, as determined from the evaluation of theoretical plate numbers, N, of these HPCE systems. On the other hand, separation selectivities, e.g. the alpha(ij) values, did not change significantly as the volume fraction, psi, of the organic solvents was increased up to psi = 60% (v/v). Under these conditions, very rapid, e.g. 1-2 min, separation times could be still achieved. Compared to the effect of carrying out the separation of these peptides at constant voltage, a dramatic increase in the separation efficiency was also achieved by applying a linear voltage gradient during the HPCE experiment. Under optimal conditions of organic solvent composition and linear voltage gradient ramps, very high peak efficiencies for the studied set of synthetic peptides with N values of approximately 2-3 million theoretical plates per meter could be routinely obtained with fast analysis times. Moreover, these buffer electrolyte conditions are compatible with direct interfacing of the HPCE effluent to electrospray ionisation and ion trap mass spectrometers, thus expanding the analytical capabilities of these HPCE systems.     

High-performance liquid chromatography of amino acids, peptides and proteins. CIX. Investigations on the relation between the ligand density of cibacron blue immobilized porous and non-porous sorbents and protein-binding capacities and association constants.

A porous silica of nominal 5 microns particle diameter and 30 nm pore size (Nucleosil 300-5) and a non-porous silica of nominal 1.5 microns particle diameter were activated with 3-mercaptopropyltriethoxysilane (MPTS), followed by the immobilization of the triazine dye, Cibacron Blue F3GA. Various biomimetic dye sorbents with graduated ligand densities between 1 mumol/m2 and 0.01 mumol/m2 were prepared. The capacities and the association constants associated with the binding of lysozyme to these sorbents were determined by frontal analysis experiments [J. Chromatogr., 476 (1989) 205-225]. Due to the ability of the Cibacron Blue F3GA-modified silicas to act as mixed mode coulombic and hydrophobic interaction sorbents and the highly charged nature of the surface structure of lysozyme (pl 11), two mobile phase conditions were examined. In one case a 0.1 M phosphate buffer, pH 7.8, was used as the equilibration and loading buffer, in the second case 1 M sodium chloride-0.1 M phosphate buffer, pH 7.8 was employed as the equilibration and loading buffer to monitor the influence of ionic interactions. The elution was performed in each case with a 2.5 M potassium thiocyanate solution. With the porous silica dye sorbents and 1 M NaCl present in the loading buffer, the highest capacity was achieved when Cibacron Blue F3GA was immobilised to the level of 0.1 mumol/m2. In the case of the non-porous silica dye sorbents, the maximum protein capacity was achieved when 0.5 mumol/m2 dye were immobilised onto the support. Evaluation of the frontal breakthrough curves confirmed that the kinetics of adsorption of lysozyme onto the non-porous sorbent were substantially faster than the adsorption of lysozyme onto the porous sorbent due to the absence of pore diffusion effects in case of the non-porous support. Furthermore, the adsorption of lysozyme on both sorbents was faster when no salt was added to the loading buffer, indicating that there is either conformational or reorientation effects operating during the specific binding of the protein to the dye ligand, or that the interaction is proceeding through the participation of a second class of binding sites. The magnitude of the association constants, Ka, for the lysozyme-Cibacron Blue F3GA systems were found to be dependent on the ligand density of the sorbent. With decreasing ligand density, the protein-ligand interaction became stronger, e.g. Ka values became larger. These results confirm earlier observations on the effect of ligand steric compression on the affinate-ligand association constant, e.g. the protein needs sufficient space to interact with the ligand in an optimum way.(ABSTRACT TRUNCATED AT 400 WORDS)     

A divergent approach to the myriaporones and tedanolide: completion of the carbon skeleton of myriaporone 1

[reaction: see text] A linear but concise synthetic approach toward the structurally related natural products myriaporone and tedanolide is reported. The route is highlighted by a stereoselective homoallenylboration and a regio- and chemoselective nitrile oxide cycloaddition. Installation of the (Z)-olefin completed the carbon skeleton of myriaporone 1.     

Carbon-13 chemical shifts of some propargyl alcohol derivatives

The natural abundance ¹³C chemical shifts of a range of propargyl alcohol derivatives have been determined and individual resonances assigned. The shielding effects of the triple bond and hydroxyl group on neigbouring carbons have been characterised. The observed for these compounds are compared to those of alkyl or allyl alcohols.     

Rapid chromatographic isolation and immunoblot characterization of immunoreactive fibroblast growth factor-related polypeptides from various tissues

Procedures to rapidly isolate fibroblast growth factor (FGF)-like activity from a number of tissue sources (lung, plasma, brain, ovary, corpus luteum, pituitary, chondrosarcoma) of bovine, porcine or rat origin are described. In addition, immunoblotting experiments using well characterized and specific rabbit polyclonal anti-fibroblast growth factor beta (anti-FGF-beta) sera have been performed. Besides documenting the first report of the isolation of FGF-beta from bovine lung and plasma, these studies provide evidence for the existence of higher-molecular-mass proteins with FGF-beta-like immunoreactivity. For example, in addition to new truncated forms of the acidic and basic FGF (FGF-alpha and FGF-beta), respectively, other higher-molecular-mass immunoreactive proteins were detected in bovine, pig and rat brain, and in rat chondrosarcoma. The tissue distribution of these immunoreactive proteins and their competitive inhibition characteristics mitigate against the possibility that the polyclonal antisera are cross-reacting non-specifically with common cellular proteins. Rather, the data suggest that the immunoblotting technique is either detecting other proteins structurally related to FGF-beta or alternatively FGF-beta is strongly bound to specific carrier proteins (e.g. heparan sulphate proteoglycan fragments) associated with their transport and recognition at the cellular level.     

A new ring opening reaction of N-aminophthalimide hydrazones

Araldehyde hydrazones III of N-aminophthalimide underwent rapid ring opening reactions initiated by the addition of excess base to their refluxing methanolic solutions. The products were conveniently isolated through liquid-liquid extraction as the stable sodium salts V, and acidification precipitated the resulting phthalic acid congeners VI from aqueous solution. Compounds III readily exchanged one hydrazine moiety for another. For example, IIId reacted with 2,4-dinitrophenylhydrazine to give the 2,4-dinitrophenylhydrazone of 4-chlorobenzaldehyde (VIId, 93%). Nonetheless, IIIg reacted exclusively at the carboxaldehyde function to give products VIIIa and VIIIb.