Scheduling Parts in a Combined Production-transportation Work Cell

This paper is concerned with a combined production-transportation scheduling problem. The problem comprises a simple, two-machine, automated manufacturing cell, which either stands alone or is a subunit of a complete flexible manufacturing system. The cell consists of two machines in series with a dedicated part-handling device such as a crane or robotic arm for transferring parts from the first machine to the second. The loading of a new piece on the first machine and the ejection of a finished piece from the second machine are performed by dedicated automated mechanisms. The introduction of parts into the system is done n at a time, whereby the parts are reshuffled into a sequence that minimizes completion time. All processing and transfer times are considered deterministic—a reasonable assumption for a cell comprising a robotic transfer device and two CNC machining units. What complicates the problem is the assumption of a non-negligible time for the transfer device to return (empty) from the second machine to the first. The operation is a generalization of a two-machine flowshop problem, and is formulated as a specially structured, asymmetric travelling salesman problem. An approximate polynomial time 0(n log n) algorithm is proffered. The procedure incorporates a lower bound using the Gilmore–Gomory algorithm for the no-wait, two-machine flowshop problem.     

Formation of spanning water networks on protein surfaces via 2D percolation transition

The formation of spanning hydrogen-bonded water networks on protein surfaces by a percolation transition is closely connected with the onset of their biological activity. To analyze the structure of the hydration water at this important threshold, we performed the first computer simulation study of the percolation transition of water in a model protein powder and on the surface of a single protein molecule. The formation of an infinite water network in the protein powder occurs as a 2D percolation transition at a critical hydration level, which is close to the values observed experimentally. The formation of a spanning 2D water network on a single rigid protein molecule can be described by adapting the cluster analysis of conventional percolation studies to the characterization of the connectivity of the hydration water on the surface of finite objects. Strong fluctuations of the surface water network are observed close to the percolation threshold. Our simulations also furnish a microscopic picture for understanding the specific values of the experimentally observed hydration levels, where different steps of increasing mobility in the hydrated powder are observed.     

The Nature of the vibronic intensity borrowing mechanism in the 1B3u(n)1Ag(X) transition of pyrazine

The transition intensities of the S₀S₁ gas phase absorption spectra of pyrazine-d₀ and -d₄ were carefully measured. A discussion of the various aspects of vibronic intensity borrowing for this unique case is presented using our new experimental results.     

Glass transition in the lower homologues of polyethyleneoxide

Experimental measurements of T_g for two series of lower homologues of polyethyleneoxide. differing in their end-groups, are discussed in terms of existing theories. Simple free-volume considerations predicting linear dependence of T_g on (molecular weight)^?1 are inadequate in systems with end-groups capable of specific interactions (hydrogen bonding). Thermodynamic arguments show that the true T_g of infinitely long PEO chain is 220 ± 5°K. Suitable modification of parameters of the Gibbs-DiMarzio equations to account for the dependence of the free volume fraction on the concentration of end-groups results in good fit of the experimental data for hydroxyl-terminated samples and correctly predicts T_g(∞). Analysis of the data for chlorine-substituted oligomers suggests the existence of specific intermolecular interactions in the latter, involving chlorine atoms.     

Über die Silicatanionenkonstitution in Tetraethylammoniumsilicaten und ihren wäßrigen Lösungen

On the Constitution of Silicate Anions in Tetraethylammonium Silicates and their Aqueous Solutions Investigations by paperchromatography, ²⁹Si-NMR spectroscopy and trimethylsilylation method show that concentrated solutions of tetraethylammonium (TEA) silicates with molar TEA:Si ratios from 2.8 to 1 contain mainly double three-ring silicate anions. Besides of these small amount of mono-, di-, tri-, tetra-, cyclotri-, cyclotetra-, double four-ring- and other polycyclic silicate anions are present. From these solutions a crystalline double three-ring silicate of the formula [N(C₂H₅)₄]₆[Si₆O₁₅] · 57 H₂O could be obtained by crystallization at low temperature. Concentrated solutions with TEA:Si ratios of 0.8 to 0.6 contain mainly double three-, double four-, double five- an probably double six-ring silicate anions. From such solutions always the solid TEA-double four-ring silicate is obtained by crystallization. The reasons for the prefered formation of double ring silicate anions in TEA-silicate solutions and their crystallization are discussed.     

A comparative investigation of the fatty acid compositions of the seeds of a number of lines of a genetic collection of Gossypium hirsutum

A comparative analysis has been made of the amounts of lipids and their fatty-acid compositions in the seeds of the lines of agenetic collection of cotton plants of the speciesGossypium hirsutum and their hybrids and the variety Tashkent-1. The results obtained on the fatty-acid compositions of some hybrids make it possible to recommend the use of individual lines of cotton plants as donors for improving the food-value indices of cottonseed oil.Institute of Chemsitry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–176, March–April, 1991.     

Theoretical study of the visible photodissociation spectrum of Ar 3 +

The photodissociation of Ar ₃ ⁺ is studied following a consistent theoretical approach from the Potential Energy Surfaces to the dynamics. Six P.E.S. are computed according to a D.I.M.-like model Hamiltonian. Transition dipole moments are determined using a similar method. The 4-D dynamics of this system is obtained with the H.W.D. method (Hemiquantal dynamic with the Whole DIM basis). All the 4 nuclear degrees of freedom and all the 6 electronic states are involved in the dynamical calculations, allowing for very general investigations. The main theoretical results are:

1. the spectrum essentially results from a Σ → Σg transition to the second excited electronic state along with a symmetric stretching motion
2. excited Ar ₃ ⁺ molecules almost all dissociate in Ar⁺ + 2 Ar
3. dissociation in Ar ₂ ⁺ + Ar requires special conditions such as low laser excitation and is predicted to increase with a specific excitation of the bending mode
4. the dominant symmetric stretching motion induces a bimodal kinetic energy distribution of the fragments.

All these points are in close agreement with experimental results.     

The adsorption of cationic and amphoteric copolymers on glass surfaces: zeta potential measurements,adsorption isotherm determination,and FT Raman characterization

The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed.     

The behavior of thermoresponsive star-shaped poly-2-isopropyl-2-oxazoline in saline media

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Calorimetric study of poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K

For the first time, the heat capacity $ C_{\text{p}}^{^\circ } $ of poly(2-ethylhexyl acrylate) has been studied in an adiabatic vacuum calorimeter between 7 and 350 K, the standard thermodynamic functions: heat capacity $ C_{\text{p}}^{^\circ } $ (T), enthalpy H°(T) ? H°(0), entropy S°(T) ? S°(0), Gibbs function G°(T) ? H°(0) have been calculated from T → 0 to 350 K. The energy of combustion Δ_c U of the compound under study has been measured in a calorimeter with a stationary bomb and an isothermal shell. The standard enthalpy of combustion Δ_c H° and thermodynamic parameters of formation—enthalpy Δ_f H°, entropy Δ_f S°, Gibbs function Δ_f G°—at T = 298.15 K have been calculated. The results have been used to calculate the thermodynamic characteristics of 2-ethylhexyl acrylate bulk polymerization into poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K.