Evaluation of AM1-calculated radical cation ion-neutral complexes

AM1 semiempirical molecular orbital calculations are reported for 20 ion-neutral complexes, including hydrogen-bonded complexes, presumably involved in the gas-phase unimolecular decomposition of simple organic radical cations. The systems investigated are [C₂H₄O₂]^˙+, [C₂H₅NO]^˙+, [C₂H₆O]^˙+, [C₂H₆O₂]^˙+, [C₃H₆O]^˙+, [C₃H₆O₂]^˙+, [C₃H₈O]^˙+, and [C₃H₈O₂]^˙+. The AM1 results are compared with ab initio molecular orbital calculations at different levels of theory up to MP3/6-31G(d, p)//SCF/6-31G(d) + ZPVE and the available experimental data. AM1 fails to predict some local minima and the equilibrium geometries calculated for several complexes are found to be qualitatively different from those predicted by the ab initio calculations. However, reasonable agreement is generally found for the stabilization energies of the complexes toward dissociation into their loosely bound components. © John Wiley & Sons, Inc.     

Selecting and adapting weekly work schedules with working time accounts: A case of a retail clothing chain

A case of selection and adaptation of weekly work schedules is presented. Weekly work schedules in two franchises of an important retail clothing chain have to be established. Working time accounts are used: each week, an employee can owe the company a certain number of hours or vice versa. Nevertheless, over a certain threshold, the hours have to be paid for by the company and the account balance returns to zero. A minimum and desired level of capacity of employees is contemplated. Hierarchically, the planned capacity must attempt to reach the minimum level; then it must fit a desired level as much as possible. At present, the task of allocation and the final adjustment of schedules is done manually, which is difficult, ineffective and often inaccurate. The procedure proposed is divided into two phases. Firstly, a work schedule, selected from a list, is assigned to each worker; a mixed linear program, followed by a local optimization process, is used. In the second phase, the work schedules are modified according to predefined rules: if there is a surplus of capacity, work schedules are reduced, and if there is a shortage, work schedules are extended. The company considers the results to be satisfactory.     

Simulation of Gas Dipole Tests in Fractures at the Intermediate Scale Using a New Upscaling Method

A high-level radioactive waste disposal site may lead to gas generation by different physical mechanisms. As these sites are to be located in areas with low water flow, any small amount of gas can lead to relative high gas pressures, so that multiphase flow analysis becomes relevant. The movement of gas and water through the system has two important implications. Firstly, water flow takes place in unsaturated conditions, and thus travel times of the radioactive particles transported are affected; and secondly, gas can also carry radioactive particles. Therefore, one of the key points in such studies is the time when gas would break through the biosphere under a number of different flow conditions. In fractured zones, gas would flow preferentially through the most conductive features. We consider a two-dimensional system representing an isolated fracture. In each point we assign a local porosity and permeability and a local pressure-saturation relationship. A dipole (injector-producer) gas flow system is generated and the variation in water saturation is studied. A simple method is proposed for obtaining upscaled values for several parameters involved in two-phase flow. It is based on numerical simulation on a block scale assuming steady-state conditions and absence of capillary pressure gradients. The proposed method of upscaling is applied to simulate a dipole test using a coarser grid than that of the reference field. The comparison between the results in both scales shows an encouraging agreement.     

Deformation and Flow Driven by Osmotic Processes in Porous Materials: Application to Bituminised Waste Materials

This paper presents a coupled Chemo-Hydro-Mechanical (CHM) analysis of the behaviour of leached Bituminized Waste materials (BW). Under geological disposal conditions the main factor that affects the long-term behaviour of this kind of materials is water uptake. First, the long-term behavior of BW in contact with water has been studied. A formulation has been proposed for the analysis of deformation induced by dissolution of salts in porous media in contact with water. The equations include the effect of coupled transport phenomena and the formulation has been included as an extension in the coupled THM program CODE_BRIGHT. The impact of osmotic forces on the swelling of the material has been investigated by simulating water uptake swelling tests under confined conditions. The numerical analysis has proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour. A sensitivity analysis has also been carried out to examine the effect of various key parameters.     

Michael reactions of titanium enolates of glycolic acid derivatives with the Weinreb and morpholine amides of acrylic acid

The conjugate additions of titanium enolates of glycolate-derived chiral oxazolidin-2-ones to various Michael acceptors have been evaluated as an entry to enantiopure 1,2,5-trioxygenated and related synthons. alpha,beta-unsaturated Weinreb and morpholine amides do react under suitable conditions and their adducts can be converted to diverse C1-C5 chiral fragments.     

Hydrogen transfer between sulfuric acid and hydroxyl radical in the gas phase: competition among hydrogen atom transfer, proton-coupled electron-transfer, and double proton transfer

In an attempt to assess the potential role of the hydroxyl radical in the atmospheric degradation of sulfuric acid, the hydrogen transfer between H2SO4 and HO* in the gas phase has been investigated by means of DFT and quantum-mechanical electronic-structure calculations, as well as classical transition state theory computations. The first step of the H2SO4 + HO* reaction is the barrierless formation of a prereactive hydrogen-bonded complex (Cr1) lying 8.1 kcal mol(-1) below the sum of the (298 K) enthalpies of the reactants. After forming Cr1, a single hydrogen transfer from H2SO4 to HO* and a degenerate double hydrogen-exchange between H2SO4 and HO* may occur. The single hydrogen transfer, yielding HSO4* and H2O, can take place through three different transition structures, the two lowest energy ones (TS1 and TS2) corresponding to a proton-coupled electron-transfer mechanism, whereas the higher energy one (TS3) is associated with a hydrogen atom transfer mechanism. The double hydrogen-exchange, affording products identical to reactants, takes place through a transition structure (TS4) involving a double proton-transfer mechanism and is predicted to be the dominant pathway. A rate constant of 1.50 x 10(-14) cm(3) molecule(-1) s(-1) at 298 K is obtained for the overall reaction H2SO4 + HO*. The single hydrogen transfer through TS1, TS2, and TS3 contributes to the overall rate constant at 298 K with a 43.4%. It is concluded that the single hydrogen transfer from H2SO4 to HO* yielding HSO4* and H2O might well be a significant sink for gaseous sulfuric acid in the atmosphere.