Triangle Evolution-A Hybrid Heuristic for Global Optimization

Abstract This paper presents a hybrid heuristic{triangle evolution (TE) for global optimization. It is a real coded evolutionary algorithm. As in di®erential evolution (DE), TE targets each individual in current population and attempts to replace it by a new better individual. However, the way of generating new individuals is di®erent. TE generates new individuals in a Nelder- Mead way, while the simplices used in TE is 1 or 2 dimensional. The proposed algorithm is very easy to use and e±cient for global optimization problems with continuous variables. Moreover, it requires only one (explicit) control parameter. Numerical results show that the new algorithm is comparable with DE for low dimensional problems but it outperforms DE for high dimensional problems.

Investigation of Vaporized Kerosene Injection and Combustion in a Supersonic Model Combustor

Injection and combustion of vaporized kerosene was experimentally investigated in a Mach 2.5 model combustor at various fuel temperatures and injection pressures. A unique kerosene heating and delivery system, which can prepare heated kerosene up to 820 K at a pressure of 5.5 MPa with negligible fuel coking, was developed. A three-species surrogate was employed to simulate the thermophysical properties of kerosene. The calculated thermophysical properties of surrogate provided insight into the fuel flow control in experiments. Kerosene jet structures at various preheat temperatures injecting into both quiescent environment and a Mach 2.5 crossflow were characterized. It was shown that the use ofvaporized kerosene injection holds the potential of enhancing fuel-air mixing and promoting overall burning. Supersonic combustion tests further confirmed the preceding conjecture by comparing the combustor performances of supercritical kerosene with those of liquid kerosene and effervescent atomization with hydrogen barbotage. Under the similar flow conditions and overall kerosene equivalence ratios, experimental results illustrated that the combustion efficiency of supercritical kerosene increased approximately 10-15% over that of liquid kerosene, which was comparable to that of effervescent atomization.

Performance of a Supersonic Model Combustor using Vaporized Kerosene Injection

Characteristics of supersonic combustion by injecting kerosene vapor into a Mach 2.5 crossflow at various preheat temperatures and pressures were investigated experimentally. A two-stage heating system has been designed and tested, which can prepare heated kerosene of 0.8 kg up to 820 K at pressure of 5.5 Mpa with minimum/negligible fuel coking. In order to simulate the thermophysical properties of kerosene over a wide range of thermodynamic conditions, a three-component surrogate that matches the compound class of the parent fuel was employed. The flow rate of kerosene vapor was calibrated using a sonic nozzle. Computed flow rates using the surrogate fuel are in agreement with the experimental data. Kerosene jets at various preheat temperatures injecting into both quiescent environment and Mach 2.5 crossflow were visualized. It was found that at injection pressure of 4 Mpa and preheat temperature of 550 K the kerosene jet was completely in vapor phase, while keeping almost the same penetration depth as compared to the liquid kerosene injection. Supersonic combustion tests were also carried out to compare the combustor performance for the cases of vaporized kerosene injection, liquid kerosene injection, and effervescent atomization with hydrogen barbotage, under the similar stagnation conditions. Experimental results demonstrated that the use of vaporized kerosene injection leads to better combustor performance. Further parametric study on vaporized kerosene injection in a supersonic model combustor is needed to assess the combustion efficiency as well as to identify the controlling mechanism for the overall combustion enhancement.

Investigation of Vaporized Kerosene Injection and Combustion in a Supersonic Model Combustor

Injection and combustion of vaporized kerosene was experimentally investigated in a Mach 2.5 model combustor at various fuel temperatures and injection pressures. A unique kerosene heating and delivery system, which can prepare heated kerosene up to 820 K at a pressure of 5.5 MPa with negligible fuel coking, was developed. A three-species surrogate was employed to simulate the thermophysical properties of kerosene. The calculated thermophysical properties of surrogate provided insight into the fuel flow control in experiments. Kerosene jet structures at various preheat temperatures injecting into both quiescent environment and a Mach 2.5 crossflow were characterized. It was shown that the use ofvaporized kerosene injection holds the potential of enhancing fuel-air mixing and promoting overall burning. Supersonic combustion tests further confirmed the preceding conjecture by comparing the combustor performances of supercritical kerosene with those of liquid kerosene and effervescent atomization with hydrogen barbotage. Under the similar flow conditions and overall kerosene equivalence ratios, experimental results illustrated that the combustion efficiency of supercritical kerosene increased approximately 10-15% over that of liquid kerosene, which was comparable to that of effervescent atomization.

Heat Transfer of Aviation Kerosene at Supercritical Conditions

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass How rate range of 10-100 g/s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency.

reducing symmetries to generate easier sat instances

Finding countermodels is an effective way of disproving false conjectures. In first-order predicate logic, model finding is an undecidable problem. But if a finite model exists, it can be found by exhaustive search. The finite model generation problem in the first-order logic can also be translated to the satisfiability problem in the propositional logic. But a direct translation may not be very efficient. This paper discusses how to take the symmetries into account so as to make the resulting problem easier. A static method for adding constraints is presented, which can be thought of as an approximation of the least number heuristic (LNH). Also described is a dynamic method, which asks a model searcher like SEM to generate a set of partial models, and then gives each partial model to a propositional prover. The two methods are analyzed, and compared with each other.

可满足性问题研究

数理逻辑是计算机科学的基础，而逻辑公式的可满足性问题是计算机科学和人工智能领域中的一个著名而又重要的问题。它在计算机科学和人工智能研究中有广泛的应用。本文将重点介绍实际可用的判定算法及其相关技术。 本文的研究分两大方向，分别是命题逻辑的可满足性问题研究和一阶逻辑的可满足性问题研究。命题逻辑的可满足性问题（Satisfiability Problem）是一个历史悠久的问题，一般简称为 SAT问题。SAT 问题的求解算法有两大类，分别是确定性算法和非确定性算法。本文只研究确定性算法的相关内容，尤其是如何进行剪枝。我们充分调研了SAT求解算法和求解工具的相关知识，在此基础上，提出了local Lemma 这个剪枝技术，该技术可以更加充分地挖掘剪枝信息，达到进行更多剪枝的目的。 在一阶逻辑的可满足性问题研究方面，本文采取直接搜索可行的一阶逻辑模型的方法研究有限论域上的一阶逻辑的可满足性问题。该方法本质上就是深度优先的回溯搜索。因此，我们的研究重点就是如何找到问题的更高效的一阶逻辑的表示以及如何采用启发式的方式进行剪枝。在这个问题上，我的主要工作有两个：一个是模型搜索中适用于谓词的同构消去技术，包括Row by Row策略和Ramsey Number 策略两个技术；另一个是 DASH（Decision Assignment Scheme Heuristic），用来在生成有限模型的时候边搜索边消除同构子空间。DASH 能用近乎零代价保证输出的模型都是互不同构的。这两个技术都是基于有限论域中的元素的固有对称性，换言之，就是需要有限论域中的元素是两两可交换的。 在已有的成果的基础上，我们又尝试使用它们去求解一些数学中的实际问题，如拟群拉丁方，有限射影平面，正交拉丁方（组）等。我们给出了在这几个方面的一些尝试和初步结果，包括一个重要的定理和若干效率提高了几个数量级的改进。 值得一提的是，和马菲菲共同提出的横截矩阵（Transversal Matrix）概念是一个新颖的成果，使得正交拉丁方的表示和求解取得了明显的改进。在这个概念的基础上，进一步给出了几个定理，进行了理论上的拓展。实验数据表明，我们的求解途径和技术能有效解决拉丁方相关的问题。

constructing finite algebras with falcon

The generation of models and counterexamples is an important form of reasoning. In this paper, we give a formal account of a system, called FALCON, for constructing finite algebras from given equational axioms. The abstract algorithms, as well as some implementation details and sample applications, are presented. The generation of finite models is viewed as a constraint satisfaction problem, with ground instances of the axioms as constraints. One feature of the system is that it employs a very simple technique, called the least number heuristic, to eliminate isomorphic (partial) models, thus reducing the size of the search space. The correctness of the heuristic is proved. Some experimental data are given to show the performance and applications of the system.

参数化系统安全性的启发式符号验证

参数化系统(paramterized system)是指包含特定有限状态进程多个实例的并发系统,其中的参数是指系统内进程实例的数目,即系统的规模.反向可达性分析(backward reachability analysis)已被广泛用于验证参数化系统是否满足以向上封闭(upward-closed)集合表示的安全性(safety property).与有限状态系统验证相类似,参数化系统的验证同样也面临着状态爆炸(state explosion)问题,并且模型检测算法的有效性依赖于如何采用有效的数据结构表示状态集合.针对表示无穷状态的向上封闭集合,研究人员提出了多种基于约束(constraint-based)的符号表示方法.但这些方法依然面临着符号状态爆炸(symbolic state explosion)问题或者其包含判定问题,即判断一个约束条件集合符号化表示的实际状态集合是否为另一约束条件集合所对应的状态集合的子集,是Co-NP完全问题.因此,虽然有限状态验证技术能够验证一些具有一定规模的问题,但现有针对参数化系统的验证方法所能解决的问题的规模较为有限,需要近一步提高模型检测算法的效率.针对参数化系统提出了加快反向可达性分析的多个启发式规则,实验结果表明,这些启发式规则可以使算法的效率提高几个数量级,从而有助于解决现有参数化系统验证方法所存在的问题.

一种任务类型敏感的J2EE事务调度算法

J2EE(Java 2 platform enterprise edition)是构建分布式企业应用的基础中间件平台,当前的J2EE事务对资源的访问调度仍然是简单的先来先服务策略,导致服务器负载很重时,次要任务和关键任务争夺有限的资源,降低了关键任务的性能与成功率.为此,有必要识别任务类型,在资源不足时优先保证关键任务事务的执行.但提交给J2EE的事务基于交互方式执行,且缺乏必要的调度信息,因而不能简单地沿用已有的优先级驱动调度算法.提出一种新的事务调度算法TMPBP(threaded multi-queue priority-based protocol),该算法能够安全、有效地提高系统重负载情况下关键事务的服务质量,防止饥饿和优先级倒置.TMPBP包含了一种新的启发式优先级分派算法HRS(heuristic resource statistics),可以在调度信息缺乏的J2EE环境下动态识别关键事务.结果表明,通过合理地选择参数,TMPBP算法能够显著地提高关键事务的服务质量.

OpenOffice.org对非BMP平面字符支持的实现

Unicode标准中的非BMP平面字符多用于古籍研究或者少数民族语言文字,由于这些字符的使用面特别窄,多数软件系统包括办公软件都不支持对这些字符的处理。本文以开源办公套件OpenOffice.org为基础,分析了它对非BMP平面支持的现状,然后着重探讨了实现对非BMP平面字符的全面支持所需要解决的一系列问题,并分别给出了合理的改进方案,最后以CJK和藏文为例展示了改进后的效果。

安达市碱性草地土壤颗粒的分维特征

运用土壤颗粒质量分形模型计算松嫩平原低平地安达试区植被分布区和碱斑区样点土壤颗粒的分形维数,并建立分形维数与土壤颗粒不同粒级间的回归关系,以探讨土地碱化后土壤粒径分布的分形特征及其与土壤物理性状的关系。结果表明:安达试区土壤颗粒分形维数较高,平均分别仅有48.7×10-5cm/s(Pit A)和4.30×10-6cm/s(Pit B),反映了该区土壤细颗粒含量高、土壤大孔隙数量少、土壤饱和导水率低的特征;土壤颗粒分形维数与黏粒含量呈对数正相关关系,而与粉粒和砂粒含量相关性不显著,说明在安达试区,影响土壤颗粒分形维数的主要因素是黏粒含量;羊草地土壤颗粒分形维数在土壤垂直剖面上的变异较大,说明植被生长促进了土壤质地的变异;碱斑地土壤颗粒分形维数明显大于羊草地,细颗粒含量高,饱和导水率低,说明碱斑的形成恶化了土壤物理性质;土壤颗粒分形维数可以反映安达市土壤物理性质的好坏,能作为土壤退化和生态环境恶化的评价指标。研究结果可为安达市以及松嫩平原盐碱地生态环境的修复和治理提供科学依据。