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101.
Gian Luca Chiarello Davide Ferri Jan-Dierk Grunwaldt Lucio Forni Alfons Baiker 《Journal of Catalysis》2007,252(2):137-147
A 0.5 wt% Pd/LaCoO3, prepared by flame-spray pyrolysis (FP), was tested as catalyst for the low-temperature selective reduction of NO by H2 in the presence of excess O2. In particular, the effect of the precalcination and prereduction temperature on catalytic activity was compared with that of a similar Pd/LaCoO3 sample prepared by impregnation with a Pd solution of FP-prepared LaCoO3. The FP-made catalyst allowed full NO conversion at 150 °C, with 78% selectivity to N2, thus outperforming the catalytic behavior of the corresponding sample prepared by impregnation. The higher activity of the FP-made catalyst has been attributed to the formation of segregated Co metal particles, not present in the impregnated sample, formed during the precalcination at 800 °C, followed by reduction at 300 °C. Two reaction mechanisms can be deduced from the temperature-programmed experiments. The first of these, occurring at lower temperatures, indicates cooperation between the Pd and Co metal particles, with formation of active nitrates on cobalt, successively reduced by hydrogen spillover from Pd. The second, occurring at higher temperature, allows 50% conversion of NO, with >90% selectivity to N2, and involves N adatoms formed by dissociative NO adsorption over Pd. Prereduction at 600 °C led to a slight increase in catalytic activity, due to the formation of a PdCo alloy, which is more stable on reoxidization compared with Pd alone. Moreover, the cooperative reaction mechanism seems to be favored by the proximity of Co and Pd in metal particles. 相似文献
102.
103.
Walter Gsele Wolfgang Egel-Hess Klaus Wintermantel Friedrich Richard Faulhaber Alfons Mersmann 《化学,工程师,技术》1990,62(7):544-552
Formation of solids by crystallization and precipitation. Formation of solids from solutions can take place by crystallization or precipitation. The principal factor is the relationship between solubility and supersaturation. In crystallization, the solubility of the crystallising substance is so high that the formation of solids occurs largely in the metastable zone in the immediate vicinity of the solubility limits. Crystal growth and nucleation are functions of supersaturation. If a high supersaturation is required at low substance-specific growth rates for an adequate crystal growth, high nucleation rates and hence small crystals will result. On this basis, the authors present information for the specific design of crystallization processes. In contrast, the solubility of the precipitated product must be very low for precipitation. Direct crystal formation is possible only for substance systems of high solubility. As a rule, however, the precipitated substance is so insoluble that solids are formed via amorphous intermediates. The results of a large number of experiments show the influence of various parameters of the precipitation process on the filtrability of the precipitated product. 相似文献
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108.
Sasan?Amini Kristian?Beckers Markus?B?hm Fritz?Busch Nihan?Celikkaya Vittorio?Cozzolino Anne?Faber Michael?Haus Dominik?Huth Alfons?Kemper Andreas?Kipf Helmut?Krcmar Florian?MatthesEmail author J?rg?Ott Christian?Prehofer Alexander?Pretschner ?mer?Uluda? Wolfgang?W?rndl 《Informatik-Spektrum》2017,40(2):180-191
109.
A large number of different model checking approaches has been proposed during the last decade. The different approaches are
applicable to different model types including untimed, timed, probabilistic and stochastic models. This paper presents a new
framework for model checking techniques which includes some of the known approaches and enlarges the class of models to which
model checking can be applied to the general class of weighted automata. The approach allows an easy adaption of model checking
to models which have not been considered yet for this purpose. Examples for those new model types for which model checking
can be applied are max/plus or min/plus automata which are well established models to describe different forms of dynamic
systems and optimization problems. In this context, model checking can be used to verify temporal or quantitative properties
of a system. The paper first presents briefly our class of weighted automata, as a very general model type. Then Valued Computational
Tree Logic (CTL) is introduced as a natural extension of the well known branching time logic CTL. Afterwards, algorithms to check a weighted automaton with respect to a CTL) is introduced as a natural extension of the well known branching time logic CTL. Afterwards, algorithms
to check a weighted automaton with respect to a CTL formula are presented. As a last result, bisimulation equivalence is
extended to weighted automata and CTL$. 相似文献
110.
Experimental test of a robust formation controller for marine unmanned surface vessels 总被引:1,自引:0,他引:1
Daniel Schoerling Chris Van Kleeck Farbod Fahimi Charles Robert Koch Alfons Ams Peter Löber 《Autonomous Robots》2010,28(2):213-230
Experiments with two formation controllers for marine unmanned surface vessels are reported. The formation controllers are
designed using the nonlinear robust model-based sliding mode approach. The marine vehicles can operate in arbitrary formation
configurations by using two leader-follower control schemes. For the design of these controller schemes 3 degrees of freedom
(DOFs) of surge, sway, and yaw are assumed in the planar motion of the marine surface vessels. Each vessel only has two actuators;
therefore, the vessels are underactuated and the lack of a kinematic constraint puts them into the holonomic system category.
In this work, the position of a control point on the vessel is controlled, and the orientation dynamics is not directly controlled.
Therefore, there is a potential for an oscillatory yaw motion to occur. It is shown that the orientation dynamics, as the
internal dynamics of this underactuated system, is stable, i.e., the follower vehicle does not oscillate about its control
point during the formation maneuvers. The proposed formation controller relies only on the state information obtained from
the immediate neighbors of the vessel and the vessel itself. The effectiveness and robustness of formation control laws in
the presence of parameter uncertainty and environmental disturbances are demonstrated by using both simulations and field
experiments. The experiments were performed in a natural environment on a lake using a small test boat, and show robust performance
to parameter uncertainty and disturbance. This paper reports the first experimental verification of the above mentioned approach,
whose unique features are the use of a control point, the zero-dynamic stability analysis, the use of leader-follower method
and a nonlinear robust control approach. 相似文献