A Manpower Allocation Model of Job Specialization

A major copier machine company in Hong Kong presently faces the problem of providing effective servicing and repairing support to its four service regions. Due to the shortage of skilled technicians and the variety of jobs to be handled by technicians of differing skill levels, its Service Department appears to be understaffed, experiencing substantial daily backlogs. This study concentrates on a new perspective of operation: the assignment of technicians at each skill level to specialize in a single type of job in one of the four regions. The objective is to maximize the overall daily number of completed service calls. A mathematical model is developed to handle this specialized allocation problem, where the average travel time (forming part of the coefficient of one of the model's variables) of a technician servicing a type of job in a region is dependent on the decision variables – the composition of the whole team. This results in what we call a mixed integer non-linear programme with variable coefficients. An exact solution is obtained by an iterative algorithm with an overall dynamic programming approach. Sample numerical results are also reported.     

Orlik-Solomon Algebras and Tutte Polynomials

The OS algebra A of a matroid M is a graded algebra related to the Whitney homology of the lattice of flats of M. In case M is the underlying matroid of a hyperplane arrangement A in ^r , A is isomorphic to the cohomology algebra of the complement ^r A. Few examples are known of pairs of arrangements with non-isomorphic matroids but isomorphic OS algebras. In all known examples, the Tutte polynomials are identical, and the complements are homotopy equivalent but not homeomorphic.We construct, for any given simple matroid M ₀, a pair of infinite families of matroids M _n and M _n , n 1, each containing M ₀ as a submatroid, in which corresponding pairs have isomorphic OS algebras. If the seed matroid M ₀ is connected, then M _n and M _n have different Tutte polynomials. As a consequence of the construction, we obtain, for any m, m different matroids with isomorphic OS algebras. Suppose one is given a pair of central complex hyperplane arrangements A ₀ and A ₁ . Let S denote the arrangement consisting of the hyperplane {0} in ₁ . We define the parallel connection P(A ₀, A ₁), an arrangement realizing the parallel connection of the underlying matroids, and show that the direct sums A ₀ A ₁ and S P (A ₀, A ₁) have diffeomorphic complements.     

Clickable Poly(ionic liquids): A Materials Platform for Transfection

The potential applications of cationic poly(ionic liquids) range from medicine to energy storage, and the development of efficient synthetic strategies to target innovative cationic building blocks is an important goal. A post‐polymerization click reaction is reported that provides facile access to trisaminocyclopropenium (TAC) ion‐functionalized macromolecules of various architectures, which are the first class of polyelectrolytes that bear a formal charge on carbon. Quantitative conversions of polymers comprising pendant or main‐chain secondary amines were observed for an array of TAC derivatives in three hours using near equimolar quantities of cyclopropenium chlorides. The resulting TAC polymers are biocompatible and efficient transfection agents. This robust, efficient, and orthogonal click reaction of an ionic liquid, which we term ClickabIL, allows straightforward screening of polymeric TAC derivatives. This platform provides a modular route to synthesize and study various properties of novel TAC‐based polymers.     

Mass spectrometric determination of cadmium in i.a.e.a. fish solubles

The cadmium content of the I.A.E.A Fish Solubles [A-6 (1975)] was determined by the isotope dilution method. After dry-ashing and dissolution of the specimen, the cadmium was equilibrated with a known amount of ¹⁰³Cd spike, isolated by ion exchange, purified by dithizone extraction, and converted to the sulfide form in 1% H₃PO₄ solution. The CdS precipitate was loaded onto a baked single rhenium filament for mass spectrometric analysis. The ¹⁰³Cd/¹¹⁰Cd ratio was measured to compute the cadmium content of 0.278 ± 0.032 ppm (dry weight basis) in the Fish Solubles.     

Fluorescence Assay Based on Aptamer-Quantum Dot Binding to <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Spores

A novel assay was developed for the detection of Bacillus thuringiensis (BT) spores. The assay is based on the fluorescence observed after binding an aptamer-quantum dot conjugate to BT spores. The in vitro selection and amplification technique called SELEX (Systematic Evolution of Ligands by EXponential enrichment) was used in order to identify the DNA aptamer sequence specific for BT. The 60 base aptamer was then coupled to fluorescent zinc sulfide-capped, cadmium selenide quantum dots (QD). The assay is semi-quantitative, specific and can detect BT at concentrations of about 1,000 colony forming units/ml.     

A simple method to remove contaminating salt from IPG strips prior to IEF

In this study, Saccharomyces cerevisiae yeast lysate is used to demonstrate how a simple wash procedure can improve IEF of IPG strips passively rehydrated in the presence of NaCl. By performing three 10 min washes after IPG strip rehydration and before IEF, corresponding second-dimensional gels from strips containing NaCl look similar to control strips while the second-dimensional gels of unwashed strips contains streaks and spaces devoid of protein. Up to 500 mM NaCl was added to the yeast lysate and successfully focused following this wash regime. Protein loss due to the washes was determined to be minimal by comparing replicates of washed and unwashed strips and analyzing the densities of their corresponding second-dimensional gel spots. In the event of unknown salt contamination, indicated by low voltage during focusing, it is possible to stop focusing, wash the strips, and then continue focusing with acceptable second dimension results.