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  • Dextran-modified poly(methyl methacrylate) latex particles  (1)
  • Mechanical ventilation  (1)
  • Produktionsablaufplanung  (1)
  • (Acremonian)
  • Springer  (3)
  • 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.
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  • 2
    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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  • 3
    ISSN: 1432-1238
    Keywords: Key words Spontaneous variability ; Mechanical ventilation ; Arterial oxygenation ; Positive end-expiratory pressure ; Inverse ratio ventilation ; Venous admixture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To assess the magnitude of spontaneous variability of arterial oxygenation and oxygen tension-based indices over time in medical intensive care unit (ICU) patients and to study whether high positive end-expiratory pressure (PEEP) or inverse inspiratory-to-expiratory (I:E) ratio ventilation (IRV) results in a greater variability than low PEEP with conventiona l I:E ratio ventilation. Design: Prospective study. Setting: Medical ICU in a tertiary medical center. Participants: 23 patients requiring a pulmonary artery floating catheter for hemodynamic monitoring. Intervention: After being completely sedated, patients were randomized to receive pressure-control ventilation at setting A: high PEEP (15 cmH2O) with conventional I:E ratio (1:2) and setting B: inverse I:E ratio (2:1) with low PEEP (5 cmH2O) alternately, and then at setting C: low PEEP (5 cmH2O) with conventional I:E ratio (1:2). Each ventilation setting lasted 1 h. Measurements and results: The arterial and mixed venous blood samples were measured simultaneously at baseline (time 0), and at 15, 30, 45, and 60 min thereafter. The coefficient of variation (CV) of arterial oxygen tension (PaO2) over time was 5.9 % for setting A, 7.2 % for setting B, and 6.9 % for setting C. ANOVA showed no significant differences in CVs of PaO2 between the three settings. Oxygen tension-based indices, alveolar-arterial oxygen difference (A-aDO2) and PaO2/PAO2 (alveolar oxygen tension), displayed CV s equal to that of PaO2; the CV of A-aDO2/PaO2 was significantly greater than that of PaO2. Conclusions: In critically ill medical ICU patients, despite sedation, the spontaneous variability in PaO2 over time is substantial. A high PEEP or IRV does not contribute to the increased variation in PaO2.
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