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Research was conducted to examine the (C2H5O-) potential energy surface viva a modified Gaussian-2 methodology, the G2++ approximation. Eight stable isomers were found on the surface whose calculated heats of formation are in very good agreement with available experimental data. CH3CH2O- is the most stable among the isomers. Results are in total agreement with the experimental collision activated dissociation and infrared multiple photon induced elimination studies of the ethoxide anion.

A new Gaussian-2 method incorporating the energy correction due to spin contamination has been used in studying the structures and energetics of C2H2N and C(sub 2)H(sub 2)N(super +) isomers. The heat of reaction(sub f298) obtained with the new technique shows good agreement with existing data. However, the results for CH2NC and CH(sub 2)NC(super +) as well as for c-NCHCH and c-NCHCH+ do not agree with available experimental data. CH2NC may be the product of the reaction between the nitrogen atom and the vinyl radical based on the ionization energies of the C2H2N isomers.

We have applied a hybrid equilibration and sampling procedure for the atomic-level simulation of a hydrated lipid bilayer to systems consisting of dipalmitoyl phosphatidylcholine (DPPC) and cholesterol. The procedure is applied to a bilayer of 64 molecules of DPPC, 64 molecules of cholesterol, and 4116 waters (1:1 ratio), and to a bilayer of 108 molecules of DPPC, 54 molecules of cholesterol, and 5301 waters (2:1 ratio). After equilibration three separate continuous molecular dynamics runs, separated by 10 000 configurational bias Monte Carlo steps, were carried out for each system. Properties of the systems were calculated and averaged over the three separate runs. A striking result from the simulations is the overall similarity of lipid structure in the 1:1 and the 2:1 systems. The area per DPPC, lipid chain order parameter profiles, and atom distribution are all very similar for the two systems, in agreement with available experimental data. The calculated dipole potential profiles reveal differences in the electrostatic environment in the two systems. Based on simulation data we suggest that there is a critical lipid:cholesterol ratio above 2:1 but probably below 4:1 at which cholesterol forces DPPC chains into gel-like conformational order. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This study explores the effect of delayed differentiation on a multiproduct vendor-buyer integrated inventory system with rework to identify its potential benefits and provide managers with in-depth information for operational decision-making. The main considerations of the proposed study include a multiproduct fabrication plan to increase machine utilization, a rework process to ensure product quality, and a multi-shipment policy to distribute the end products. In addition, these products sharing an intermediate part for which a two-stage fabrication scheme is adopted, wherein the common parts are produced at the first stage and the end products are manufactured at the second stage. The aim is to reduce the overall system costs and shorten the replenishment cycle time. Mathematical modeling and optimization methods were employed to derive the closed-form optimal replenishment cycle time and delivery decisions. We demonstrated the applicability of our research results through numerical examples and revealed that for both linear and nonlinear relationships between the common intermediate part's completion rate α and its practical value at α, our proposed two-stage production scheme with delayed differentiation is considerably beneficial vis-à-vis single-stage schemes in saving overall system costs and reducing the replenishment cycle time. [ABSTRACT FROM AUTHOR]

In a turbulent and highly competitive business environment, management always pursues options to reduce overall operating costs. The vendor-buyer integrated system has recently drawn attention from managers, because it can benefit both parties of the supply chain and it is suitable to be applied to a so-called intra-supply chain system within the present-day globalized enterprise. This study attempts to simultaneously determine production and shipment decisions for a multi-product vendor-buyer integrated inventory system with a rework process, wherein multiple products are fabricated in sequence by a single machine under a rotation cycle time policy. All defective items produced in regular production are assumed repairable, and are reworked right after the regular production ends. Finished goods of each product are transported to sales offices/customers after rework. A multi-delivery policy is applied, wherein a fixed quantity of n instalments of the finished batch is delivered at fixed intervals during the delivery timeframe. Mathematical modelling and optimization techniques are used to help simultaneously determine the optimal production and shipment decisions that minimize the expected overall system costs. A numerical example is used to show the applicability of our research results. [ABSTRACT FROM AUTHOR]

An in vitro study was performed to determine the acute phytotoxicities and genotoxicity of DDE either spiked to soil or added to hydrophonic cultures on wheat Triticum aestivum . A 24-well plate was first used to determine toxicity on individual grains using conventional seed germination/seedling growth toxicity tests whereas a single cell electrophoresis system was applied to measure genotoxicity at single cell level for wheat. Hydrophonic cultures provide a simplified environment to screen for toxicities with high sensitivity. Inverse dose-response relationships were detected between exogenous DDE levels and one of the following parameters: seed germination, seedling growth, and genotoxicity. In contrast, soil reduced the stress on T. aestivum by lowering bioavailability leading to less DDE distributed in radicle and coleoptile, modulated growth, and enhanced tolerance. At all DDE doses spiked to soil including the reference safety level of 0.5 mg/kg, DNA breakage was detected in both radicle and coleoptile but their magnitudes did not correlate with the organ nor the soil DDE contents. Thus, although wheat is highly sensitive to the genotoxic effect of DDE, first demonstrated here, the seed germination test offers a simple quantitative measure of DDE's phytotoxicity in soil and hydrophonic cultures. This study also found that fungus Pleurotus pulmonarius , which secretes extracellular ligninolytic enzymes causing non-specific cleavage of lignin and organopollutants, remediated DDE spiked to soil. In 5 weeks, 78% of 10 mg/kg DDE was biodegraded, and the fungal-treated soil reduced acute toxicity on T. aestivum using the seed germination test. [ABSTRACT FROM AUTHOR]

A computational study on the structures, energetics, and reactions of the C2H3S− isomers has been carried out. The computational model used is a modified version of the ab initio Gaussian-2 (G2) method. This modified model, called G2++, is designed specifically for anionic systems. Twelve C2H3S− isomers/conformers have been identified. The thioformylmethyl anion (1−) is the most stable isomer and its ΔHf298 is −5.8 kJ mol−1. The next two most stable isomers are the thioacetyl anion (2−) and 1-thiovinyl anion (3−/4−), which are 156.7 and 167.0/175.9 kJ mol−1 higher in energy than 1−, respectively. A cyclic anion (12−) is the highest in energy among the C2H3S− isomers and its ΔHf298 is 440.7 kJ mol−1. The G2++ proton affinities (PAs) of 1− and thiiranyl anion (11−) are 1446.0 and 1642.2 kJ mol−1, respectively, which are in excellent agreement with the experimental data. The G2++ΔHf298 of 11−, 198.9 kJ mol−1, is in very good agreement with the experimental value (192.2 kJ mol−1), which is obtained by combining the experimental PA for 11− and the ΔHf298 data for H+and thiirane. Other isomers/conformers identified include CH2SCH− (9−/10−), and 2-thiovinyl anion (5−/6−/7−/8−). Four anions, 2−, 4−, 5−, and 11−, can rearrange to 1−, with barriers ranging from 40 to 117 kJ mol−1. Energy barriers for the ring opening processes 11−→10− and 12−→7− were calculated to be 182.2 and 5.2 kJ mol−1, respectively. Two other rearrangements, 8−→4− and 3−→2−, were found to have energy barriers over 180 kJ mol−1. [Copyright &y& Elsevier]