Chemistry of trifluoromethyl compounds : I. NMR evidence for bis(trifluoromethyl)zinc and methyl(trifluoromethyl)zinc

Bis(trifluoromethyl)zinc and methyl(trifluoromethyl)zinc have been identified by ¹⁹F and ^1H NMR methods. The compounds were formed in the following reactions: (1) dimethylzinc and bis(trifluoromethyl)mercury and (2) dimethylzinc and bis(trifluoromethyl)cadmium.     

Die Kristallstruktur der Verbindung Cd2Ge7O16

The crystal structure of Cd₂Ge₇O₁₆ has been determined by means of three-dimensional single-crystal data. A finalR-value of 6.3% was obtained by least squares refinement based on 230 observed reflexions. The tetragonal unit cell with the lattice parametersa=11.31 andc=4.63 Å contains two formula units Cd₂Ge₇O₁₆. The compound is built up by [GeO₄]-tetrahedra and [GeO₆]-octahedra forming a three-dimensional framework with the Cd atoms located in the cavities. The average interatomic distances are found to be: Ge–O=1.74 (tetrahedra), 1.89 (octahedra) and Cd–O=2.36 Å.

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Metal benzoylpivaloylmethanates. Part III. Manganese(III) and iron(III) chelates

Summary The synthesis and principle properties of several novel tris[1-(4-X-phenyl)-4,4-dimethylpenta-1, 3-dionato]-iron(III) and manganese(III) complexes, where X=MeO, Me, H, F, Cl and NO₂, are described. Magnetic susceptibility measurements in the 4.2–295 K range show a near Curie behaviour and a constant magnetic moment for manganese(III) complexes and for iron complexes, with X=F, Cl or NO₂. Iron complexes with ligands having substituents: X=MeO, Me and H, show weak antiferromagnetic interaction (J=ca.–8 cm^–1 for the two former compounds) and a decrease in magnetic moment with decreasing temperature. In both manganese(III) and iron(III) complexes the diketonate ligand can be easily replaced by chlorine. Equilibrium constants could be evaluated only for substitution of the third diketonate ligand by chloride in the iron complexes on the basis of spectrophotometric measurements. For manganese chelates, the replacement of the second diketonate by chloride is accompanied by reduction of manganese(III) manganese(II) and free organic radical formation is observed.     

Obtaining the key set of typical vectors by factor analysis and subsequent isolation of component spectra

The key set of typical rows (or typical columns), used to reproduce a data matrix, are obtained by finding the set of rows (or set of columns) most orthogonal to each other. If the data matrix consists of the spectra of a series of related mixtures, and there exists at least one data point unique to each of the components, the spectra of the pure components can be isolated. The method is applied to problems in nuclear magnetic resonance, gas—liquid chromatography and mass spectrometry.     

Biomineralization of unicellular organisms: an unusual membrane biochemistry for the production of inorganic nano- and microstructures

With evolution, Nature has ingeniously succeeded in giving rise to an impressive variety of inorganic structures. Every organism that synthesizes biogenic minerals does so in a form that is unique to that species. This biomineralization is apparently biologically controlled. It is thus expected that both the synthesis and the form of every specific biogenic mineral is genetically determined and controlled. An investigation of the mechanism of biomineralization has only become possible with the development of modern methods in molecular biology. Unicellular organisms such as magnetic bacteria, calcareous algae, and diatoms, all of which are amongst the simplest forms of life, are particularly suited to be investigated by these methods. Crystals and composites of proteins and amorphous inorganic polymers are formed as complex structures within these organisms; these structures are not known in conventional inorganic chemistry.     

A graph-based hyper-heuristic for educational timetabling problems

This paper presents an investigation of a simple generic hyper-heuristic approach upon a set of widely used constructive heuristics (graph coloring heuristics) in timetabling. Within the hyper-heuristic framework, a tabu search approach is employed to search for permutations of graph heuristics which are used for constructing timetables in exam and course timetabling problems. This underpins a multi-stage hyper-heuristic where the tabu search employs permutations upon a different number of graph heuristics in two stages. We study this graph-based hyper-heuristic approach within the context of exploring fundamental issues concerning the search space of the hyper-heuristic (the heuristic space) and the solution space. Such issues have not been addressed in other hyper-heuristic research. These approaches are tested on both exam and course benchmark timetabling problems and are compared with the fine-tuned bespoke state-of-the-art approaches. The results are within the range of the best results reported in the literature. The approach described here represents a significantly more generally applicable approach than the current state of the art in the literature. Future work will extend this hyper-heuristic framework by employing methodologies which are applicable on a wider range of timetabling and scheduling problems.     

A further note on the force discrepancy for wing theory in Euler flow

Uniform steady potential flow past a wing aligned at a small angle to the flow direction is considered. The standard approach is to model this by a vortex sheet, approximated by a finite distribution of horseshoe vortices. In the limit as the span of the horseshoe vortices tends to zero, an integral distribution of infinitesimal horseshoe vortices over the vortex sheet is obtained. The contribution to the force on the wing due to the presence of one of the infinitesimal horseshoe vortices in the distribution is focused upon. Most of the algebra in the force calculation is evaluated using Maple software and is given in the appendices. As in the two previous papers by the authors on wing theory in Euler flow [E Chadwick, A slender-wing theory in potential flow, Proc. R. Soc. A461 (2005) 415–432, and E Chadwick and A Hatam, The physical interpretation of the lift discrepancy in Lanchester-Prandtl lifting wing theory for Euler flow, leading to the proposal of an alternative model in Oseen flow, Proc. R. Soc. A463 (2007) 2257–2275], it is shown that the normal force is half that expected. In this further note, in addition it is demonstrated that the axial force is infinite. The implications and reasons for these results are discussed.     

Fuzzy job shop scheduling with lot-sizing

This paper deals with a problem of determining lot-sizes of jobs in a real-world job shop-scheduling in the presence of uncertainty. The main issue discussed in this paper is lot-sizing of jobs. A fuzzy rule-based system is developed which determines the size of lots using the following premise variables: size of the job, the static slack of the job, workload on the shop floor, and the priority of the job. Both premise and conclusion variables are modelled as linguistic variables represented by using fuzzy sets (apart from the priority of the job which is a crisp value). The determined lots’ sizes are input to a fuzzy multi-objective genetic algorithm for job shop scheduling. Imprecise jobs’ processing times and due dates are modelled by using fuzzy sets. The objectives that are used to measure the quality of the generated schedules are average weighted tardiness of jobs, the number of tardy jobs, the total setup time, the total idle time of machines and the total flow time of jobs. The developed algorithm is analysed on real-world data obtained from a printing company.     

Constraining the parameters of binary systems through time-dependent light deflection

A theory is derived relating the configuration of the cores of active galaxies, specifically candidates for presumed super-massive black hole binaries (SMBHBs), to time-dependent changes in images of those galaxies. Three deflection quantities, resulting from the monopole term, mass quadrupole term, and spin dipole term of the core, are examined. The resulting observational technique is applied to the galaxy 3C66B. This technique is found to under idealized circumstances surpass the technique proposed by Jenet et al. in accuracy for constraining the mass of SMBHB candidates, but is exceeded in accuracy and precision by Jenet’s technique under currently understood likely conditions. The technique can also under favorable circumstances produce results measurable by currently available astronomical interferometry such as very-long-baseline interferometry (VLBI).     

Antibacterial Activity of Polymers: Discussions on the Nature of Amphiphilic Balance

The purpose of this Viewpoint is to discuss the molecular design principles that guide development of synthetic antimicrobial polymers, especially those intended to mimic the structure of host defense peptides (HDPs). In particular, we focus on the principle of “amphiphilic balance” as it relates to some recently developed polyphosphoniums with somewhat atypical structure. We find that the fundamental concept of amphiphilic balance is still applicable to these new polymers, but that the method to achieve such balance is somewhat unique. We then briefly outline the future challenges and opportunities in this field.