A raw material shortage model of the Finnish chemical industry

At the beginning of 1975 the Federation of the Finnish Chemical Industry and the University of Helsinki, Department of Computer Science, set up a project to develop a mathematical model to be used as a planning tool during accidental raw material shortages in the Finnish chemical industry. The model has been designed, programmed, and tested. The main part of the system consists of a linear programming model, which is used to answer “what-if” questions.This paper describes the model, the programs and the main problems encountered in the design process. The present version of the system can solve problems involving at most 100 firms, 400 products, 400 types of raw materials and 200 technical or policy constraints.     

Dimethylmercury in mixtures of thermotropic nematogens

Abstract

The geometry of dimethylmercury was studied in several mixtures of the liquid crystals ZLI 1167 and phase 4. The variation of the geometry is not very large but systematic changes can be detected as a function of the liquid crystal composition. The anisotropics, δ[sgrave], of the ¹H, ¹³C and ¹⁹⁹Hg shielding tensors were investigated by applying two methods based on mixing liquid crystals with opposite diamagnetic anisotropies and by applying various referencing methods. Apart from these, the anisotropy, δJ _HgC, of the ¹⁹⁹Hg–¹³C spin–spin coupling tensor was studied in four mixtures of these liquid crystals, and was found to vary with the solvent.     

Effect of ligand on the synthesis of star polymers by resorcinarene‐based ATRP initiators

The effect of the steric hindrance on the initiating properties of two multifunctional resorcinarene‐based initiators in atom transfer radical polymerization (ATRP) was studied by using Cu(I)‐complexes of three multidentate amine ligands in the polymerization of tert‐butyl acrylate and methyl methacrylate. These ligands are less sterically hindered and have higher activities in the catalysis of ATRP of (meth)acrylates than 2,2′‐bipyridine. The polymerizations were faster and more controlled than with the 2,2′‐bipyridyl catalyst, but the tendency for bimolecular coupling increased. Even though the initiator was octafunctional, the resulting star polymers had only four arms. This indicates that the steric hindrance arising from the conformations of the initiators determines the structure of the polymer, but the ligand noticeably affects the controllability of the polymerization © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3349–3358, 2005     

Variable order spherical harmonic expansion scheme for the radiative transport equation using finite elements

We propose the P_N approximation based on a finite element framework for solving the radiative transport equation with optical tomography as the primary application area. The key idea is to employ a variable order spherical harmonic expansion for angular discretization based on the proximity to the source and the local scattering coefficient. The proposed scheme is shown to be computationally efficient compared to employing homogeneously high orders of expansion everywhere in the domain. In addition the numerical method is shown to accurately describe the void regions encountered in the forward modeling of real-life specimens such as infant brains. The accuracy of the method is demonstrated over three model problems where the P_N approximation is compared against Monte Carlo simulations and other state-of-the-art methods.     

Quantification of human brain metabolites from in vivo 1H NMR magnitude spectra using automated artificial neural network analysis

Long echo time (TE=270 ms) in vivo proton NMR spectra resembling human brain metabolite patterns were simulated for lineshape fitting (LF) and quantitative artificial neural network (ANN) analyses. A set of experimental in vivo 1H NMR spectra were first analyzed by the LF method to match the signal-to-noise ratios and linewidths of simulated spectra to those in the experimental data. The performance of constructed ANNs was compared for the peak area determinations of choline-containing compounds (Cho), total creatine (Cr), and N-acetyl aspartate (NAA) signals using both manually phase-corrected and magnitude spectra as inputs. The peak area data from ANN and LF analyses for simulated spectra yielded high correlation coefficients demonstrating that the peak areas quantified with ANN gave similar results as LF analysis. Thus, a fully automated ANN method based on magnitude spectra has demonstrated potential for quantification of in vivo metabolites from long echo time spectroscopic imaging.     

Atomic oxygen adsorption on Pb(1 0 0)

We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO.     

Exploring the 2,2′-Diamino-5,5′-bipyrimidine Hydrogen-Bonding Motif: A Modular Approach to Alkoxy-Functionalized Hydrogen-Bonded Networks

The programmed self-association of 2,2′-diamino-4,4′-dialkoxy-5,5′-bipyrimidines allows for the de novo construction of alkoxy-functionalized H-bonded ribbons and sheets as evidenced by X-ray crystallographic analysis. The data provide insight into the interplay of the different structural and interactional features of the molecular components to the generation of the supramolecular assembly. Hydrophobicity of the didodecyl side chains of 4c leads to the dominance of the H-bonding factor, resulting in the formation of a fully interconnected array. These results define the utility of the of 2,2′-diamino-4,4′-dialkoxy-5,5′-bipyrimidines as a potential scaffold for the attachment of electro- or photochemically active alkoxy residues for self-assembled functional supramolecular materials.