On the mechanism of crystalline polymorph selection by polymer heteronuclei

The phase-selective crystallization of acetaminophen (ACM) using insoluble polymers as heteronuclei was investigated in a combined experimental and computational effort to elucidate the mechanism of polymer-induced heteronucleation (PIHn). ACM heteronucleates from supersaturated aqueous solution in its most thermodynamically stable monoclinic form on poly(n-butyl methacrylate), whereas the metastable orthorhombic form is observed on poly(methyl methacrylate). When ACM crystals were grown through vapor deposition, only the monoclinic polymorph was observed on each polymer. Each crystallization condition leads to a unique powder X-ray diffraction pattern with the major preferred orientation corresponding to the crystallographic faces in which these crystal phases nucleate from surfaces of the polymers. The molecular recognition events leading to these outcomes are elucidated with the aid of computed polymer-crystal binding energies using docking simulations. This investigation illuminates the mechanism by which phase selection occurs during the crystallization of ACM using polymers as heteronuclei, paving the way for the improvement of methods for polymorph selection and discovery based on heterogeneous nucleation promoters.     

?therische ?le

Ohne Zusammenfassung     

Neutron activation analysis of wear products in a Diesel engine fueled with coal-oil slurries

The technique described is a stable tracer method and has the advantage of eliminating the use of radioactive engine components during the wear tests. The results obtained clearly show that the use of these slurries comprising pulverized coal and fuel oil is not acceptable due to excessive wear rates.     

The role of the interactive Kerr effect in two-photon optical multistability

We show that bistable behaviour in a two-photon resonant system within a cavity may be attributed to interactive mode-pulling via the two-photon optical Kerr effect and also to absorptive bleaching (atomic saturation). The interactive Kerr process may be regarded as giving rise to a new category of optical bistability. Moreover, a mechanism for the recently-predicted tristability can be found in terms of simultaneous competition between the interactive Kerr effect and bleaching.     

Vehicle Scheduling with Timed and Connected Calls: A Case Study

A manual method was developed for scheduling the vehicle fleet of a contract transport undertaking. The main requirements were observance of time limits on individual calls and the ability to allocate pairs or groups of related calls to the same vehicle. These objectives were achieved by introducing an initial allocation of calls to vehicles prior to sequential routing of the calls. The allocation was based on a model relating work density (calls per unit area) to vehicle loading (calls per unit of vehicle time), and on fact-finding research on the main parameters of calling time, travelling speed and distance. This relationship was embodied in a visual scheduling aid for use by the route planners. Implementation was successful and resulted in about 15 per cent of vehicle time being made available for additional revenue-earning work without increase in fleet size. When utilized this represented an effective saving in operating costs of about 12 per cent.