Investigation of sodium sulfate phase transitions in a porous material using humidity- and temperature-controlled X-ray diffraction

Crystals growing in confined spaces can generate stress and are a major cause of damage in porous materials. To investigate such deleterious processes, appropriate in situ techniques are required. This paper describes the use of X-ray diffractometry under controlled conditions of temperature and relative humidity (RH-XRD) for the direct observation of phase transition reactions in a porous substrate. An improved environmental chamber without temperature gradients is presented and applied to the investigation of phase transformations in the system Na2SO4 + H2O. This salt is generally considered as particularly damaging and frequently used in accelerated weathering tests. It is demonstrated that RH-XRD can be successfully applied for the direct observation of several relevant phase transitions in glass frits used as porous substrates. The conversion of Na2SO4(III) to Na2SO4(V) and the hydration of Na2SO4(V) both proceed fairly rapidly as true solid-state reactions without deliquescence of the educt phases. In contrast, crystallization from solution is kinetically hindered as there is a strong tendency of aqueous Na2SO4 to form supersaturated solutions also in narrow pores. The important implications of this behavior of the salt are also briefly discussed in the paper.     

Linear programming based approximation algorithms for feedback set problems in bipartite tournaments

We consider the feedback vertex set and feedback arc set problems on bipartite tournaments. We improve on recent results by giving a 2-approximation algorithm for the feedback vertex set problem. We show that this result is the best that we can attain when using optimal solutions to a certain linear program as a lower bound on the optimal value. For the feedback arc set problem on bipartite tournaments, we show that a recent 4-approximation algorithm proposed by Gupta (2008) [8] is incorrect. We give an alternative 4-approximation algorithm based on an algorithm for the feedback arc set on (non-bipartite) tournaments given by van Zuylen and Williamson (2009) [14].     

UML在流程工业优化调度工艺描述系统中的应用

结合建模工具Rational Rosc说明如何在系统开发过程中运用UML建模。通过流程工业优化调度工艺描述系统的实际建模，对UML建模应用作了进一步说明。     

Metacomputing in practice: a distributed compute server for pharmaceutical industry

We describe a distributed high-performance compute server that has been implemented for running compute-intensive applications on a mixture of HPC systems interconnected by Inter-and Intranet. With a practical industrial background, our work focusses on high availability, efficient job load balancing, security, and the easy integration of HPC computing into the daily work-flow at pharmaceutical companies.

The work was done in the course of the ESPRIT project P A Distributed Pharmaceutical Application Server The client software is implemented in Java. All results are displayed in a web browser and can be forwarded to the next stage of applications used in the drug design cycle. The server software handles the job load balancing between the participating HPC nodes and is capable of managing multi-site applications.

Our environment currently supports four key applications that are used in rational drug design and drug target identification. They range from the automatic functional annotation of protein sequences to three-dimensional protein structure prediction tools and protein comparison applications.     

线性调节器盼抗干扰设计

本文给出了一种扰动情况下线性调节器的设计方法。主导思想是,在最优控制律中附加干扰成份,以抵消扰动信号的影响,使系统保持希望的平衡态,并在规定的性能指标下为最优。文中还给出了一个轧机控制系统的设计实例及仿真结果。     

Effects of Zwitterionic buffers on sorption of ferrous iron at goethite and its oxidation by CCl4

A major factor which controls sorption and oxidation of Fe(II) at the mineral-water interface is pH, hence buffers are commonly used to control pH in experimental studies. Here, we examined the effects of widely used organic buffers (3-morpholinopropane-1-sulfonic acid (MOPS) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)) on Fe(II) uptake and oxidation by CCl(4) in aqueous suspensions of goethite. Significant sorption of these zwitterionic buffers occurred only at Fe(II)-loaded goethite but not at native goethite. The addition of MOPS and HEPES caused substantial release of Fe(II) from goethite, retarded the oxidation of surface-bound Fe(II) by CCl(4) and changed the reaction pathway as indicated by lower yields of CHCl(3). To explore electrostatic and steric contributions of MOPS and HEPES to the observed phenomena we studied sorption and competitive effects of model sorbates (Ca(2+), sulfonates) which suggest the formation of a complex between surface-bound Fe(II) and MOPS or HEPES. Our study shows for the first time that these frequently used zwitterionic organic buffers may interfere significantly with the surface chemistry and thus with redox reactions of Fe(II) at goethite. Hence, kinetic or mechanistic information obtained in such systems requires careful interpretation.