C++ lambda expressions and closures

A style of programming that uses higher-order functions has become common in C++, following the introduction of the Standard Template Library (STL) into the standard library. In addition to their utility as arguments to STL algorithms, function parameters are useful as callbacks on GUI events, defining tasks to be executed in a thread, and so forth. C++’s mechanisms for defining functions or function objects are, however, rather verbose, and they often force the function’s definition to be placed far from its use. As a result, C++ frustrates programmers in taking full advantage of its own standard libraries. The effective use of modern C++ libraries calls for a concise mechanism for defining small one-off functions in the language, a need that can be fulfilled with lambda expressions.This paper describes a design and implementation of language support for lambda expressions in C++. C++’s compilation model, where activation records are maintained in a stack, and the lack of automatic object lifetime management make safe lambda functions and closures challenging: if a closure outlives its scope of definition, references stored in a closure dangle. Our design is careful to balance between conciseness of syntax and explicit annotations to guarantee safety. The presented design is included in the draft specification of the forthcoming major revision of the ISO C++ standard, dubbed C++0x. In rewriting typical C++ programs to take advantage of lambda functions, we observed clear benefits, such as reduced code size and improved clarity.     

Optimizing content-based routers: posets and forests

Event-based systems are seen as good candidates for supporting distributed applications in dynamic and ubiquitous environments because they support decoupled and asynchronous one-to-many and many-to-many information dissemination. Event systems are widely used because asynchronous messaging provides a flexible alternative to RPC. They are typically implemented using an overlay network of routers. A content-based router forwards event messages based on filters that are installed by subscribers and other routers. This paper addresses the optimization of content-based routing tables organized using the covering relation and presents novel configurations for improving local and distributed operation. We present the poset-derived forest data structure and variants that perform considerably better under frequent filter additions and removals than existing data structures. The results offer a significant performance increase to currently known covering-based routing mechanisms. Sasu Tarkoma received his M.Sc. and Ph.Lic degrees in Computer Science from the University of Helsinki, Department of Computer Science. He has over 20 scientific publications and has also contributed to several books on mobile middleware. His research interests include distributed computing and middleware. Jaakko Kangasharju is a PhD student at the University of Helsinki and working as a researcher at the Helsinki Institute for Information Technology. His research is concentrated on XML messaging and processing in the mobile wireless environment. He has participated in related standardization efforts at the Object Management Group and the World Wide Web Consortium.     

Heat and mass transfer in calcination of limestone particles

The heat and mass‐transfer phenomena occurring during the calcination of limestone particles was studied by means of modeling. The applicability of two modeling methods for calcination was compared under different conditions. An unsteady numerical particle model with mass, momentum, energy balance, and shrinking core models were chosen for the study. The influence of different phenomena (chemical kinetics, advective and diffusive mass transfer, and heat transfer) in different conditions was evaluated with the aid of dimensionless parameters, and their relative importance was shown in a regime chart. Especially, the significance of advection was studied and its importance in high CO₂ concentration was observed. Local temperatures inside the particle were obtained by solving a dynamic energy balance in each particle layer including calcination reaction energy and conduction heat transfer. Noticeable temperature differences between constant ambient conditions and the particle were observed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2563–2572, 2012     

Drying of Solid Furl Particlbs in Hot Gases

Drying of solid fuel particles in hot gases ( 50-200c) is studied both theoretically and experimentally. The measurements are carried out by using a thermobalance reactor constructed for drying and pyrolysis studies of particles up to 30 mm by diameter. The model is based on the solution of the conservation equations for mass and energy. The drying is considered to consist of three successive periods: a short initial heating period, period of constant rate of drying and period of falling rate of drying. It is assumed that the particle moisture distribution is uniform during the constant rate of drying. Shrinking core model is assumed for the falling rate period. esides fuel particles, the model is applicable also for other solid particle drying processes. Model calculations are compared to measurements for wood chips. The model can predict the efFect of the main parameters reasonably well. These main parameters affecting the drying rate are: particle size, particle shape, initial particle moisture content, gas temperature and gas moisture content, emperature of the reactor walls and slip velocity. The irregular shape of practical fuel particles can approximately be simulated as one-dimensional case ( plate, cylinder, sphere) by using an equivalent volumc to surface area ratio.     

Spray deposition and compression of TiO2 nanoparticle films for dye-sensitized solar cells on plastic substrates

Spray deposition of powder suspensions followed by room temperature compression was studied as a method for preparing nanostructured TiO₂ films for dye-sensitized solar cells. The structure of the films was analyzed with optical and scanning electron microscopy and the films were applied to dye-sensitized solar cells. Continuous and fast deposition of crack-free 7–14 μm thick films was achieved by heating the substrates during the deposition. Scanning electron microscopy revealed small amount of structural imperfections in the compressed films due to the nature of the deposition method. An energy conversion efficiency of 2.8% was achieved at 100 mW/cm² light intensity.     

Non-uniform electric field in poling of structurally graded monolithic piezoactuator

In this paper the effect of a non-uniform electric poling field and its optimisation for structurally graded piezoelectric actuators are investigated. The two compared actuator structures were both based on commercial PZT 5H bulk discs with thicknesses of 375 µm (Ø 25 mm), where one was machined into a graded structure with a step-like decrease of the thickness towards the centre and one intact. The hysteresis loops of the pre-stressed concave shaped actuators were measured under 0.5–5.0 kV/mm electric fields at 25–100°C temperatures, and the remanent polarization and coercive electric field were determined. The graded structured actuator obtained ～10% higher coercive field compared to the non-graded actuator, when measured at 25°C and 5.0 kV/mm. On the other hand the remanent polarisation values of the graded actuator were slightly lower than non graded bulk values. However the maximum decrease was only 9.6% under 5.0 kV/mm. The results show that strain and stress gradients in the structure are generated when exposed to an electric field. Furthermore, as a consequence of the restricted dimension changes, an inherent bending of the monolithic ceramic structure was obtained which can be utilised, for example, in miniaturised micro-machined actuators or in larger pre-stressed benders.     

Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine

This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modeling of gas flow and heat transfer in an annular channel. Velocity and temperature profiles are modeled in the air gap of a high-speed test machine. Friction and heat transfer coefficients are presented in a large velocity range. The goals are reached acceptably using numerical and experimental research. The velocity field by the numerical method does not match in every respect the estimated flow mode. The absence of secondary Taylor vortices is evident when using time averaged numerical simulation.     

多层柔性衬底电路板的低成本丝网印刷

当大批量生产多层聚合物基厚膜电路板时需要低成本的印刷技术.对于有超过6层导电层且不平滑的表面来说,丝网印刷是一个便宜、便捷的选择.为了研究丝网印刷技术的可行性,本研究在不同衬底材料的表面,如聚碳酸酯(PC)、聚酯(PET)、聚酰亚胺(PI)和液晶聚合物(LCP),使用同样的印刷分辨率,常规的厚膜网版印刷,通过丝网的网孔在衬底上形成精细图形.最后,研究在双层PI衬底(拥有2层导体层,在导体层的两侧有1层绝缘层覆盖板基孔)上的印刷.丝网印刷的导体材料是银基纳米颗粒油墨,介质层是聚酰亚胺基材料.许多变量是妨碍这种经济适用技术大规模生产应用的影响因素.例如,如果固化温度超过200℃,聚酰亚胺基板的稳定性就成为大问题.在本实验中,如果印刷面积小,层与层之间的对齐公差是允许的.然而,在印刷进行一段时间后,层与层之间的平整度会变差.测试用纳米粒子油墨是一种很好的导电系统,但是,当固化温度从230℃降低到200℃时,生产效率会受到极大影响.另一种实现多层结构的方法是层压法.本研究选择PET和PC层,重点是处理沉积胶层的PET层和片材的复合过程.多层结构中的板基孔和导线通过常规厚膜网印解决.先打孔,然后采用厚膜网印填补,最后印刷表面.层与层之间的黏合精度和对准精度<±15μm.