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51.
The Boussinesq equations for the Rayleigh-Bénard problem have been solved by analytical and numerical methods. Two different sequences of Hopf bifurcations, leading from, stationary two-dimensional rolls to non-periodic motion, have been identified. For one of the sequences the first bifurcation results in transverse oscillations of the rolls. The next bifurcation gives quasiperiodic flow, and the sequence ends in chaotic motion after the third instability. The second route is characterized by waves in the periodic regime, travelling along the rolls. Thereafter two quasiperiodic regimes follow with two and three frequencies, respectively. Both types of sequences have been detected in the experiments reported by Gollub and Benson (1980). The regime of travelling waves is also analysed by a perturbation method.  相似文献   
52.
Miconazole and miconazolenitrate are antifungal drugs with poor solubilities in water and saliva. The low solubilities meant that only small amounts of the drugs-incorporated by a conventional method in chewing gum-were released during mastication. The experiments were performed on a mastication device.

In this study it was shown that application of a 20% miconazole - 80% polyethyleneglycol 6000 solid dispersion drastically improved the in vitro release of miconazole from cheving gum, when a medium similar to saliva was used. In addition to polyethyleneglycol 6000, polyvinylpyrrolidone 40000, xylitol and urea were tested as carriers. It was also shown that the release rate of miconazole from chewing gum was much greater than the release rate of miconazolenitrate.

No certain correlation could be shown between the dissolution rates of the solid dispersions measured by a stirring paddle method and the release rates of miconazole from solid dispersions in chewing gum.

The solid dispersion systems were characterized by differential scanning calorimetry. The systems containing polyethyleneglycol 6000 and xylitol were eutectic. Polyvinylpyrrolidone 40000 prevented crystallisation of miconazole when the percentage of drug in the solid dispersion was less than 50%.  相似文献   
53.
In this study, two colloidal dispersions of pure amorphous silicon dioxide particles, acetylated, and heat‐treated samples were tested for a possible application as a wood protection agents. The silicon, acetylated, and heat‐treated samples were exposed to an accelerated weathering experiment, and their dimensional stability was assessed. The weathering experiment comprised cycles of 2 h UV‐light irradiation followed by water spray for 18 min. The surface changes of the weathered samples were characterized by FT‐IR spectroscopy and color measurements. According to results, the silicon treatments showed lower color changes than untreated ones. However, acetylated and heat‐treated samples provided the lowest color changes. The resistance of the silicon, acetylated, and heat‐treated wood to decay was studied by means of brown and white rot fungi in laboratory decay tests. Decay test results revealed that acetylated and heat‐treated wood samples showed better decay resistance against P. placenta and C. versicolor than silicon treatments. Samples modified with silicon were exposed in above ground standard lap‐joint test in Ultuna, Sweden. The dispersions of pure amorphous silicon dioxide impregnated in wood did not significantly influence its hygroscopic and dimensional behavior. However, the silicon treatment reduced the color changes caused by weathering. The silicon impregnated samples showed a weak fungal discoloration similar to that of chromated copper arsenate impregnated controls in above ground standard lap‐joint test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4506–4513, 2006  相似文献   
54.
A laboratory scale setup was used for characterization of gravitational drainage of waste activated sludge. The aim of the study was to assess how time of drainage and cake dry matter depended on volumetric load, SS content and sludge floc properties. It was demonstrated that activated sludge forms compressible cakes, even at the low pressures found in gravitational drainage. The values of specific cake resistance were two to three orders of magnitude lower than those obtained in pressure filtration. Despite the compressible nature of sludge, key macroscopic parameters such as time of drainage and cake solid content showed simple functional dependency of the volumetric load and SS of a given sludge. This suggests that the proposed method may be applied for design purposes without the use of extensive numerical modeling. The possibilities for application of this new technique are, among others, the estimation of sludge drainability prior to mechanical dewatering on a belt filter, or the application of surplus sludge on reed beds, as well as adjustments of sludge loading, concentration or sludge pre-treatment in order to optimize the drainage process.  相似文献   
55.
Biochemistry in general and enzyme kinetics in particular have been heavily influenced by the model of biochemical reactions known as Michaelis–Menten kinetics. Assuming that the complex concentration is approximately constant after a short transient phase leads to the usual Michaelis–Menten (MM) approximation (or standard quasi-steady-state approximation (sQSSA)), which is valid when the enzyme concentration is sufficiently small. This condition is usually fulfilled for in vitro experiments, but often breaks down in vivo. The total QSSA (tQSSA), which is valid for a broader range of parameters covering both high and low enzyme concentrations, has been introduced in the last two decades. We extend the tQSSA to more complex reaction schemes, like fully competitive reactions, double phosphorylation, Goldbeter–Koshland switch and we show that for a very large range of parameters our tQSSA provides excellent fitting to the solutions of the full system, better than the sQSSA and the single reaction tQSSA. Finally, we discuss the need for a correct model formulation when doing “reverse engineering”, which aims at finding unknown parameters by fitting the model to experimentally obtained data. We show that the estimated parameters are much closer to the real values when using the tQSSA rather than the sQSSA, which overestimates the parameter values greatly.  相似文献   
56.
Investigations have been carried out on the electrical properties of nickel-based films prepared from air-fireable pastes on alumina substrates. In particular, magnetoresistive effects have been studied as a function of temperature, strength and direction of the magnetic field. These properties were determined in films at different stages of formation, i.e. prepared at various peak firing temperatures and dwell times, and compared with those displayed by nickel foils. These results provide the basis for the development of magnetoresistive thick-film sensors.  相似文献   
57.
Gas diffusion electrodes for high-temperature PEMFC based on acid-doped polybenzimidazole membranes were prepared by a tape-casting method. The overall porosity of the electrodes was tailored in a range from 38% to 59% by introducing porogens into the supporting and/or catalyst layers. The investigated porogens include volatile ammonium oxalate, carbonate and acetate and acid-soluble zinc oxide, among which are ammonium oxalate and ZnO more effective in improving the overall electrode porosity. Effects of the electrode porosity on the fuel cell performance were investigated in terms of the cathodic limiting current density and minimum air stoichiometry, anodic limiting current and hydrogen utilization, as well as operations under different pressures and temperatures.  相似文献   
58.
59.
Factor-VII-activating protease (FSAP) is involved in the regulation of hemostasis and inflammation. Extracellular histones play a role in inflammation and the conversion of latent pro-FSAP into active FSAP. FSAP has been shown to regulate endothelial permeability, but the mechanisms are not clear. Here, we have investigated the effects of FSAP on endothelial permeability in vitro. A mixture of histones from calf thymus stimulated permeability, and the wild-type (WT) serine protease domain (SPD) of FSAP blocked this effect. WT–SPD–FSAP did not influence permeability on its own, nor that stimulated by thrombin or vascular endothelial growth factor (VEGF)-A165. Histones induced a large-scale rearrangement of the junction proteins VE-cadherin and zona occludens-1 from a clear junctional distribution to a diffuse pattern. The presence of WT–SPD–FSAP inhibited these changes. Permeability changes by histones were blocked by both TLR-2 and TLR4 blocking antibodies. Histones upregulated the expression of TLR-2, but not TLR-4, in HUVEC cells, and WT–SPD–FSAP abolished the upregulation of TLR-2 expression. An inactive variant, Marburg I (MI)–SPD–FSAP, did not have any of these effects. The inhibition of histone-mediated permeability may be an important function of FSAP with relevance to sepsis, trauma, and stroke and the need to be investigated further in in vivo experiments.  相似文献   
60.
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Model predictive control (MPC) is a well‐known and widely used advanced control technique, which is model‐based and capable of handling both input and state/output constraints via receding horizon optimization methods. Fundamentally, MPC is a nondynamic or memoryless state feedback control. Because of its use of a model, MPC should be amenable to adaptive implementation and to on‐line tuning of the model. Such an approach requires guaranteeing signal properties, known as ‘persistent excitation’, to ensure uniform identifiability of the model, often expressed in terms of spectral content or ‘sufficient richness’ of a periodic input. We propose an approach to augment the input constraint set of MPC to provide this guarantee. This, in turn, requires equipping the controller with its own state to capture the control signal history. The feasibility of periodic signals for this condition is established. A computational example is presented illustrating the technique and its properties. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
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