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  • Chemistry  (1)
  • Dextran-modified poly(methyl methacrylate) latex particles  (1)
  • Production scheduling  (1)
  • (Acremonian)
  • 1995-1999  (3)
  • 1
    ISSN: 1435-1536
    Keywords: Key words Isothermal equilibrium adsorption ; Concanavalin A ; Dextran-modified poly(methyl methacrylate) latex particles ; Electrostatic/affinity interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Isothermal equilibrium adsorption experiments were carried out to study the adsorption of concanavalin A (Con A) on dextran-modified poly(methyl methacrylate) (PMMA) latex particles. Three PMMA particles with various levels of dextran modification were selected for study: 0% (designated as D0), 1.24% (D20), and 2.45% (D75) based on total polymer weight. The Langmuir model is applicable to both D0 and D20 systems, although the data for the D20 system are somewhat scattered. On the other hand, the amount of Con A adsorbed per gram polymer particles (q*) versus the Con A concentration in water (c*) curve for the D75 system cannot be described by the Langmuir model. The deviation is attributed to the formation of a crosslinked network structure, caused by specific binding of the dimeric Con A molecules onto two neighboring particles with grafted dextran. The ratio of the initial number of Con A molecules to the initial number of active binding sites on the dextran-modified particle surface plays an important role in determining the structure of flocs formed. The maximum amount of Con A adsorbed on the particle surface (q max) is of the order of 10−1 μmol per gram particles and q max in decreasing order is D75 〉 D20 〉 D0. The dissociation constant of the Con A-D20 (or Con A-D75) pair is of the order of 10−1 μmol dm−3 which is 1 order of magnitude smaller than that of the Con A-D0 pair. Thus, the electrostatic interaction between Con A and D0 is much weaker than the affinity interaction between Con A and D20 (or D75). An empirical model is proposed to qualitatively explain the q* versus c* data.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Thin (750 Å) plasma-polymerized films of acetylene were deposited onto polished steel substrates in an inductively coupled r.f. reactor. The films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) immediately after deposition and after aging in the atmosphere. The FTIR spectra of the as-deposited films were characterized by bands related to mono- and disubstituted acetylene groups and by bands related to methyl and methylene groups. During exposure to the atmosphere, bands related to acetylenic groups decreased in intensity while new bands due to carbonyl groups appeared. When XPS spectra were obtained from films that were exposed to the atmosphere, new components assigned to oxidation products were observed in the C 1s spectra that were not observed for as-deposited films, verifying that oxidation had occurred. Numerous peaks related to aromatic structures were observed in positive SIMS spectra of as-deposited films. Results obtained from AES showed that the plasma-polymerized films were continuous and that the oxide on the substrate surface was partially reduced during deposition.Plasma-polymerized acetylene films were excellent primers for rubber-to-steel bonding. Miniature lap joints were prepared by using rubber as an ‘adhesive’ to bond together pairs of polished steel adherends primed with plasma-polymerized acetylene films. The force required to break the as-prepared joints was ∼2000 N for a bonded area of 64 mm2 and failure was 100% cohesive in the rubber. Similar results were obtained for joints prepared using polished brass substrates.Because of the complexity of reactions between rubber and the plasma-polymerized primer, a model ‘rubber’ consisting of a mixture of squalene, zinc oxide, carbon black, sulfur, stearic acid, cobalt naphthenate, N,N-dicyclohexylbenzothiazole sulfenamide and diaryl-p-diphenyleneamine was used to simulate the cross-linking reaction. The results obtained using XPS, SIMS, AES and FTIR showed that sulfur diffused through the primer to form a layer of sulfide at the primer/substrate interface. Zinc and cobalt sulfides and perthiomercaptides, which formed at the interface between squalene and the plasma-polymerized acetylene primer, catalyzed the reaction between squalene and the primer. Cross-links between squalene and the primer were mostly mono-sulfidic, although some evidence for di- and trisulfidic cross-links was observed.
    Additional Material: 17 Ill.
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  • 3
    ISSN: 1436-6304
    Keywords: Production scheduling ; dynamic setup change ; Produktionsablaufplanung ; stochastisches Flow-Shop-Problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Wir betrachten ein zweistufiges Produktionssystem, in dem zwei Produkte mit konstanten produktspezifischen Produktionsgeschwindigkeiten und Rüstzeiten bearbeitet werden. Zwischen den beiden Maschinen sind zwei produktspezifische Puffer angeordnet. Die Nachfragerate für jedes Produkt ist abschnittsweise konstant. Jede Maschine unterliegt zeitabhängigen Störungen. Die fehlerfreien Laufzeiten und die Reparaturzeiten sind exponentialverteilte Zufallsvariablen, wobei Rüst- und Bearbeitungsvorgänge nach einer störungsbedingten Unterbrechung ohne Verlust fortgesetzt werden. Wir modellieren das Produktionssystem als zeit- und mengenkontinuierlichen Prozeß. Es wird das Problem der Bestimmung der optimalen Kontrollpolitik mit dem Ziel der Minimierung der diskontierten Kosten bei unendlichem Horizont formuliert. Zur Bestimmung der Struktur der optimalen Kontrollpolitik wird eine diskretisierte Version des Problems mit Hilfe der dynamischen Programmierung unter Berücksichtigung einer stückweise linearen Strafkostenfunktion gelöst. Anschließend wird ein Algorithmus entwickelt, mit dem geringe Lagerbestände bei gleichzeitiger Erfüllung der Nachfrage erreicht werden können. Der Algorithmus, der auf einer hierarchischen Kontrollstruktur basiert, dient zur Bestimmung der Produktionszeitpunkte, wobei in Echtzeit auf zufällige Störungen im System reagiert werden kann. Die Leistungsfähigkeit des Verfahrens wird anhand eines Simulationsmodells mit alternativen Politiken verglichen.
    Notes: Abstract In this paper, we study a manufacturing system consisting of two machines separated by two intermediate buffers, and capable of producing two different products. Each product requires a constant processing time on each of the machines. Each machine requires a constant non-negligible setup change time from one product to the other. The demand rate for each product is considered to be piecewise constant. Each machine undergoes failure and repair. The time-to-failure and time-to-repair are exponentially distributed random variables. The setup change and processing operations are resumable. We model our system as a continuous time, continuous flow process. An optimal control problem is formulated for the system to minimize the total expected discounted cost over an infinite horizon. To determine the optimal control policy structure, a discrete version of the problem is solved numerically using a dynamic programming formulation with a piecewise linear penalty function. A real-time control algorithm is then developed with the objective of maintaining low work-in-process inventory and keeping the production close to the demand. The algorithm uses a hierarchical control structure to generate the loading times for each product on each machine in real time and to respond to random disruptions in the system. The system is simulated using this algorithm to study its performance. The performance of the algorithm is also compared to alternative policies.
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