Grammar Engineering Support for Precedence Rule Recovery and Compatibility Checking

A wide range of parser generators are used to generate parsers for programming languages. The grammar formalisms that come with parser generators provide different approaches for defining operator precedence. Some generators (e.g. YACC) support precedence declarations, others require the grammar to be unambiguous, thus encoding the precedence rules. Even if the grammar formalism provides precedence rules, a particular grammar might not use it. The result is grammar variants implementing the same language. For the C language, the GNU Compiler uses YACC with precedence rules, the C-Transformers uses SDF without priorities, while the SDF library does use priorities. For PHP, Zend uses YACC with precedence rules, whereas PHP-front uses SDF with priority and associativity declarations.The variance between grammars raises the question if the precedence rules of one grammar are compatible with those of another. This is usually not obvious, since some languages have complex precedence rules. Also, for some parser generators the semantics of precedence rules is defined operationally, which makes it hard to reason about their effect on the defined language. We present a method and tool for comparing the precedence rules of different grammars and parser generators. Although it is undecidable whether two grammars define the same language, this tool provides support for comparing and recovering precedence rules, which is especially useful for reliable migration of a grammar from one grammar formalism to another. We evaluate our method by the application to non-trivial mainstream programming languages, such as PHP and C.     

Advanced methods for container stacking

In this paper, we study stacking policies for containers at an automated container terminal. It is motivated by the increasing pressure on terminal performance put forward by the increase in the size of container ships. We consider several variants of category stacking, where containers can be exchanged during the loading process. The categories facilitate both stacking and online optimization of stowage. We also consider workload variations for the stacking cranes.     

A nonlinear set‐membership filter for on‐line applications

A guaranteed estimator for a general class of nonlinear systems and on‐line usage is developed and analysed. This filter bounds the linearization error, then applies a linear set‐membership filter such that stability guarantees hold for nonlinear systems. A tight bound on the linearization error is found using interval analysis. This filter recursively estimates an ellipsoidal set in which the true state lies. General assumptions include the use of bounded noises and twice continuously differentiable dynamics. When the system is uniformly observable, it is proven that the nonlinear set‐membership filter is stable. In addition, if no noise is present and the initial error is small, the error between the centre of the estimated set and the true value converges to zero. The result is an estimator which is computationally attractive and can be implemented robustly in real‐time. The proposed method is applied to a two‐state example to demonstrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd.     

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.     

Optimisation of sulphate reduction in a methanol-fed thermophilic bioreactor

Several methods were tested to optimise sulphate reduction and minimise methane formation in thermophilic (65 degrees) expanded granular sludge bed reactors fed with a medium containing sulphate and methanol. Lowering the pH from 7.5 to 6.75 resulted in a rapid decrease of methane formation and a concomitant increase in sulphate reduction. The inhibition of methane formation was irreversible on the short-term. Lowering the COD/SO4(2-) ratio (COD: chemical oxygen demand) from 6 to 0.34 (g/g) rapidly favoured sulphate reduction over methanogenesis. Continuous addition of 2 g L(-1) 2-bromoethanesulphonate was ineffective as complete inhibition of methanogenesis was obtained only for two days. Inhibition of methanogens by sulphide at pH 7.5 was only effective when the total sulphide concentration was above 1200 mg S L(-1). For practical applications, a relatively short exposure to a slightly acidic pH in combination with operating the reactor at a volumetric methanol-COD loading rate close to the maximum volumetric sulphide-COD formation rate.     

Preventing injection attacks with syntax embeddings

Software written in one language often needs to construct sentences in another language, such as SQL queries, XML output, or shell command invocations. This is almost always done using unhygienic string manipulation, the concatenation of constants and client-supplied strings. A client can then supply specially crafted input that causes the constructed sentence to be interpreted in an unintended way, leading to an injection attack. We describe a more natural style of programming that yields code that is impervious to injections by construction. Our approach embeds the grammars of the guest languages (e.g. SQL) into that of the host language (e.g. Java) and automatically generates code that maps the embedded language to constructs in the host language that reconstruct the embedded sentences, adding escaping functions where appropriate. This approach is generic, meaning that it can be applied with relative ease to any combination of context-free host and guest languages.     

Stereoselective Monoamine Oxidase‐Catalyzed Oxidative Aza‐Friedel–Crafts Reactions of meso‐Pyrrolidines in Aqueous Buffer

We disclose the highly diastereoselective combination of monoamine oxidase‐catalyzed oxidation of meso‐pyrrolidines and aza‐Friedel–Crafts reactions in aqueous buffer to give valuable enantioenriched 2‐substituted pyrrolidines in a formal double C H activation process. A range of secondary as well as tertiary amines were shown to be suitable substrates for the biocatalytic oxidation and subsequent addition of a variety of C‐nucleophiles.

     

西安植物学家花园

<正>在风景园林中反映自然界是其文化和审美建构中最明确的一个方面。最初风景园林主要是视觉艺术。无论在中国和西方,景观概念的起源都来自于自然风景画。这些绘画作品成为风景园林设计直接的灵感来源。21世纪数字化的景观是一种将景观视觉化并创造变化的视角的新方法新技术。电脑屏幕是我们的画布,屏