Equivalent cyclic polygon of a euclidean travelling salesman problem tour and modified formulation

Central European Journal of Operations Research - We define a geometric transformation of Euclidean Travelling Salesman Problem (TSP) tours that leads to a new formulation of the TSP. For every...     

The interaction between poly(N-isopropylacrylamide) and salts in aqueous media: The “salting-out” phenomenon as studied by attenuated total reflection/fourier transform infrared spectroscopy

The effect of two strong salting-out salts (Na₂SO₄ and K₂SO₄) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 33–46, 2004     

Classical versus Jennings model for the ground state of H near a metallic surface

We show that, contrary to earlier reports, application of the one-parameter variational technique to the classical (image) model for H in front of an Al surface leads to energy shifts for the ground state which are very close to those obtained numerically with a more sophisticated model of the system.     

A parametric study of surface-discharge nitrogen lasers

A parametric study of sandwich-type discharge chamber nitrogen lasers has been carried out. A non-monotonic dependence of the energy emitted by the laser and the discharge chamber thickness is found. Discharge chambers with = 1 have the best electro-optical efficiency. The ratio between the electrode gap,d, and is found to be a scaling parameter. The possible influence of wall ablation in the comportment is also discussed.     

Multiresidue determination of fluoroquinolones in shrimp by liquid chromatography-fluorescence-mass spectrometry

An efficient multiresidue method for analysis of fluoroquinolones in shrimp has been developed in which quantitation by fluorescence and confirmation by Multiple Stage Mass Spectrometry (MS) is achieved simultaneously. In this method, shrimp tissue is extracted with ammoniacal acetonitrile and the extract is defatted and then evaporated. After dissolution in basic phosphate buffer, fluoroquinolones in the extract are separated by liquid chromatography and quantitated, taking advantage of their intense fluorescence. Eluate from the fluorescence detector enters the MS, which allows for confirmation by monitoring ratios of 2 prominent product ions in the MS3 or MS2 spectrum. Using this method, 8 fluoroquinolones have been analyzed in shrimp samples fortified at 10, 25, 50, or 100 ppb levels. Recoveries for desethyleneciprofloxacin, norfloxacin, ciprofloxacin, danofloxacin, enrofloxacin, orbifloxacin, sarafloxacin, and difloxacin ranged from 75 to 92%, with relative standard deviation values of <6%. The limits of quantitation ranged from 0.1 to 1 ng/g. Enrofloxacin and ciprofloxacin were also successfully determined in enrofloxacin-incurred shrimp using this method.     

Highly enantioselective synthesis of 2H-1-benzothiopyrans by a catalytic domino reaction

A highly enantioselective catalytic asymmetric synthesis of 2H-1-benzothiopyrans is presented. The organocatalytic asymmetric domino reactions between 2-mercaptobenzaldehyde and α,β-unsaturated aldehydes proceed with excellent chemo- and enantioselectivities to give the corresponding pharmaceutically valuable benzothiopyrans in high yields with 91-98% ee.     

Synthesis and Structural Characterization of [Mn(ethyl isonicotinate)(2)(N(3))(2)](n)(), a Two-Dimensional Alternating Ferromagnetic-Antiferromagnetic Compound. Magnetostructural Correlations for the End-to-End Pseudohalide-Manganese System

Three compounds with formula [Mn(L)(2)(N(3))(2)](n)(), in which L is 4-acpy = 4-acetylpyridine (1), Etinc = ethyl isonicotinate (2), and py = pyridine (3), have been studied from the magnetic point of view. The new compound [Mn(L)(2)(N(3))(2)](n)() (2) crystallizes in the monoclinic system, space group P2(1)/a (No. 14), formula [C(16)H(18)MnN(8)O(4)], with a = 15.176(5) ?, b = 9.060(3) ?, c = 15.760(6) ?, beta = 111.62(3) degrees, and Z = 4. Compounds 1 and 2 are two-dimensional systems, whereas 3 is a 3-D compound. Compound 2 shows ferromagnetic Mn(2)(N(3))(2) dimeric entities linked antiferromagnetically to the four neighboring dimeric entities by four end-to-end azido bridges, leading to an alternate ferromagnetic-antiferromagnetic two-dimensional compound. MO calculations have been performed to study the superexchange pathway for the manganese 1,3-azido system.     

A simple one-pot, three-component, catalytic, highly enantioselective isoxazolidine synthesis

The highly chemo- and enantioselective organocatalytic three-component reaction between N-arylhydroxylamines, aldehydes and α,β-unsaturated aldehydes is presented; the reaction gives access to isoxazolidines in high yields with >25:1 dr and 91-99% ee.     

LCAO–MO similarity measures and taxonomy

Similarity measures between pairs of molecular wave functions are described. They are based on the geometrical structure of the LCAO–MO framework and upon multivariate analysis ideas. The theoretical framework is presented, and formulae for some integrals needed are given. Two main measures, distance and correlation coefficients, are used. Distance and correlation matrices induce relationships in the whole MO set, which can be depicted through minimal spanning tree techniques. Furthermore, principal component analysis allows a two-dimensional visualization of the Mo manifold geometrical relationships. Various examples are given in order to obtain information on how basis set, environment, excitation, bending, stretching, and electronegativity affect the induced order. For this purpose “ab initio” SCF–LCAO–MO calculations with double- and single-zeta quality basis sets have been used for various simple molecular structures: H₂O, NH₃, CH₄, N₂, O₂, C₂, NO, CN, and CO. The results obtained can open the way to LCAO–MO taxonomy. Using this information, other areas of interest are connected with similarity measures (SCF and CI , localization procedures, etc.), proving in this manner their potential utility.