Reasoning from last conflict(s) in constraint programming

Constraint programming is a popular paradigm to deal with combinatorial problems in artificial intelligence. Backtracking algorithms, applied to constraint networks, are commonly used but suffer from thrashing, i.e. the fact of repeatedly exploring similar subtrees during search. An extensive literature has been devoted to prevent thrashing, often classified into look-ahead (constraint propagation and search heuristics) and look-back (intelligent backtracking and learning) approaches. In this paper, we present an original look-ahead approach that allows to guide backtrack search toward sources of conflicts and, as a side effect, to obtain a behavior similar to a backjumping technique. The principle is the following: after each conflict, the last assigned variable is selected in priority, so long as the constraint network cannot be made consistent. This allows us to find, following the current partial instantiation from the leaf to the root of the search tree, the culprit decision that prevents the last variable from being assigned. This way of reasoning can easily be grafted to many variations of backtracking algorithms and represents an original mechanism to reduce thrashing. Moreover, we show that this approach can be generalized so as to collect a (small) set of incompatible variables that are together responsible for the last conflict. Experiments over a wide range of benchmarks demonstrate the effectiveness of this approach in both constraint satisfaction and automated artificial intelligence planning.     

An experimental investigation on oil mist characterization used in MQL milling process

In this study, a method is developed to determine the oil mist characteristics for the minimal quantity lubricant process. The oil mist is characterized by the size, velocity, and volume flow rate of its particles. In each case, a specific measurement process is used: the laser diffraction granulometry method, the particle image velocimetry, and the gravimetric method. These methods are used in the case of static and simple models with different inner channels. Experimental tests have been done with the same inner channel as the existing spindle inner channel. Different output models with different inner canalizations have been tested, using these experimental processes. The main goal is to control the characteristics of output oil mist as a function of the input oil mist device parameters.     

Effect of surfactants and biomass on the gas/liquid mass transfer in an aqueous‐silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove VOCs from gaseous effluents

BACKGROUND: The two‐phase partitioning bioreactor (TPPB) has become a new strategy for waste gas treatment. However, the impact of biomass and surfactants on gas/liquid (G/L) mass transfer needs to be better evaluated because the effects on the mass transfer coefficient K_L and the interfacial area a, respectively, remains misunderstood. RESULTS: This study showed that, first, the surfactant extract produced by Rhodococcus erythropolis reduced the surface hydrophobicity of the biomass. Secondly, an optimal concentration appeared to exist for both components, respectively 0.5 g L^?1 and 0.7 g L^?1 for biomass (B) and surfactant extract (SE) when the global mass transfer coefficient (K_La) of oxygen was measured in a silicone oil/water TPPB. However, the combination of B and SE was found to induce a negative synergism. In particular, SE improved the interfacial area a by increasing the bubble diameter, while B reduced it as soon as a concentration of 1 g L^?1 was exceeded. In contrast, the SE acted negatively on the K_L, while B improved it overall. CONCLUSION: Better consideration is needed of the effect of biotic components in order to understand the phenomenon of G/L mass transfer in a TPPB. The behaviour of biomass growth and surfactants may strongly influence the mathematical models proposed in the literature. Copyright © 2009 Society of Chemical Industry     

Spice:IC 设计中的模拟程序

在开关电源(SMPS)的系列产品中,回扫转换器广泛用于中小型电源(1-100W)应用,如墙适配器、离线电池充电器、传真机等等。安森美半导体新推出的NCP1200使回扫电路设计变得非常简单:在集成电路周围加上两个无源元件和一个MOSFET就可以了!然而要研究环境对系统的影响,则要花     

射频便携式系统用低压降稳压器

由于低压降(LDO)稳压器的插入损耗较小，它们在电池驱动的便携式装置中占有一席之地。如果在过去的若干年中，电压降一直是主要问题，那么日益增长的对新一代便携式装置的市场要求，使低压降稳压器的其它特性尤为突出。在该领域中，设计师最关心的问题是输出噪声、脉冲波动抑制和静态电流。作为串联电阻的低压降稳压器线性稳压器的输出电压总是低于它的输入电压。有多种实现这类装置的方法，最普通的方法是采用一个相当于可变电阻的元件。该电阻串联连接在输入源与负载之间，构成一个串联稳压器。当所输出功率需量增加时，R镇流减小。与此…     

Influence of Residual Impurities on Phase Partitiioning and Grain Growth Processes of Y-TZP Materials

Microstructural evolution at 1450°C of two 3 mol% Y₂O₃─ZrO₂ tetragonal polycrystals (Y-TZP) containing different residual impurity amounts has been investigated by analytical and scanning electron microscopy in order to clarify the role of the amorphous intergranular phases. Phase partitioning is interpreted as a process based on dissolution/reprecipitation reactions involving mass transport via the liquid impurity phase. Grain growth is inhibited by yttria migration before the phase equilibrium is reached, then increases drastically.     

通过项目执行战略（下）

5原型和项目管理：如何面对复杂性和不确定性的挑战 过去十年期间，项目和大型项目计划管理文献内曾大篇幅报道有关核心战略的问题，但多数都未真正考虑使用一种认识论的方法(Bredillet，2004a)。项目管理分类(Shenhar et al.，2002；Turner．2000；Crawford et al．，2002；2004)也可反映组织理论核心逻辑所反映的趋势(Crawford et al．，2002：NASA，2004)。虽然分类标准和类别之间存在细微的差异，