Hydrogen-diesel fuel co-combustion strategies in light duty and heavy duty CI engines

The co-combustion of diesel fuel with H₂ presents a promising route to reduce the adverse effects of diesel engine exhaust pollutants on the environment and human health. This paper presents the results of H₂-diesel co-combustion experiments carried out on two different research facilities, a light duty and a heavy duty diesel engine. For both engines, H₂ was supplied to the engine intake manifold and aspirated with the intake air. H₂ concentrations of up to 20% vol/vol and 8% vol/vol were tested in the light duty and heavy duty engines respectively. Exhaust gas circulation (EGR) was also utilised for some of the tests to control exhaust NO_x emissions.The results showed NO_x emissions increase with increasing H₂ in the case of the light duty engine, however, in contrast, for the heavy duty engine NO_x emissions were stable/reduced slightly with H₂, attributable to lower in-cylinder gas temperatures during diffusion-controlled combustion. CO and particulate emissions were observed to reduce as the intake H₂ was increased. For the light duty, H₂ was observed to auto-ignite intermittently before diesel fuel injection had started, when the intake H₂ concentration was 20% vol/vol. A similar effect was observed in the heavy duty engine at just over 8% H₂ concentration.     

Microstructure and transport properties of porous building materials

To successfully predict the performance of building materials exposed to a degradative environment, transport properties must be either measured or estimated. The development of relationships between microstructure and transport properties for these materials should allow accurate prediction of the latter and an increased understanding of how microstructure influences transport. Here, two microstructural characterization techniques, mercury intrusion porosimetry and scanning electron microscopy, are combined with computer modelling techniques to compute the vapor diffusivity and air permeability of three building materials commonly exposed in building facades, two types of brick and a natural sandstone. In general, the computed values compare favorably to those measured experimentally, thus demonstrating the capability of employing microstructural characterization to predict transport properties.

---

Résumé Pour obtenir une prédiction fiable des performances des matériaux de construction exposés à un environnement agressif, leurs propriétés de transport doivent être soit mesurées soit estimées. Le développement de relations entre la microstructure et les propriétés de transport devrait permettre une prédiction exacte de ces dernières et une meilleure compréhension de l’influence de la microstructure sur le transfert. Dans cet article, deux techniques de caractérisation de la microstructure (porosimétrie au mercure et microscopie électronique à balayage) sont combinées avec des techniques de simulation par ordinateur pour calculer la diffusivité à la vapeur d’eau et la perméabilité à l’air de trois matériaux de construction traditionnellement utilisés en facades: deux types de brique et un grès naturel. En général, les valeurs calculées sont proches de celles mesurées expérimentalement. Ces résultats démontrent les possibilités des outils de caractérisation de la structure pour prédire les propriétés de transport.

---

---

Editorial note: Mr. Daniel Quenard is a RILEM Senior Member and a member of TC 123-MME on the Use of Microstructural Models and Expert systems for Cemenitious Materials. He and Mr. K. Xu work at the CSTB (Centre Scientifique et Technique du Batiment), France, a RILEM Titular Member. Mr. Dale P. Bentz is a RILEM Senior Member and participates in the work of TC 159-ETC (Engineering of the Interfacial Transition Zone in Cementitious Composites). He and Mr. Nicos Martys work at the National Institute of Standards and Technology (NIST), USA, a RILEM Titular Member.     

Capacitated Clustering Problems by Hybrid Simulated Annealing and Tabu Search

The capacitated clustering problem (CCP) is the problem in which a given set of weighted objects is to be partitioned into clusters so that the total weight of objects in each cluster is less than a given value (cluster ‘capacity’). The objective is to minimize the total scatter of objects from the ‘centre’ of the cluster to which they have been allocated. A simple constructive heuristic, a R-interchange generation mechanism, a hybrid simulated annealing (SA) and tabu search (TS) algorithm which has computationally desirable features using a new non-monotonic cooling schedule, are developed. A classification of the existing SA cooling schedules is presented. The effects on the final solution quality of the initial solutions, the cooling schedule parameters and the neighbourhood search strategies are investigated. Computational results on randomly generated problems with size ranging from 50 to 100 customers indicate that the hybrid SA/TS algorithm out-performs previous simulated annealing algorithms, a simple tabu search and local descent algorithms.     

Automatically performing weak mutation with the aid of symbolic execution,concolic testing and search-based testing

Automating software testing activities can increase the quality and drastically decrease the cost of software development. Toward this direction, various automated test data generation tools have been developed. The majority of existing tools aim at structural testing, while a quite limited number aim at a higher level of testing thoroughness such as mutation. In this paper, an attempt toward automating the generation of mutation-based test cases by utilizing existing automated tools is proposed. This is achieved by reducing the killing mutants’ problem into a covering branches one. To this extent, this paper is motivated by the use of state of the art techniques and tools suitable for covering program branches when performing mutation. Tools and techniques such as symbolic execution, concolic execution, and evolutionary testing can be easily adopted toward automating the test input generation activity for the weak mutation testing criterion by simply utilizing a special form of the mutant schemata technique. The propositions made in this paper integrate three automated tools in order to illustrate and examine the method’s feasibility and effectiveness. The obtained results, based on a set of Java program units, indicate the applicability and effectiveness of the suggested technique. The results advocate that the proposed approach is able to guide existing automating tools in producing test cases according to the weak mutation testing criterion. Additionally, experimental results with the proposed mutation testing regime show that weak mutation is able to speedup the mutant execution time by at least 4.79 times when compared with strong mutation.     

The design of economic policy under model uncertainty

This paper examines how considerations of model uncertainty can affect policy design. Without such considerations one may expect that choice of policy control rules for a macroeconomic model would depend on some welfare criterion based on the model as given. However if there is uncertainty in the structure of the model or in the values of particular model parameters then it is argued that choice of policy should take this into account.We introduce and define some measures ofrobustness which describe how well a particular control rule performs when the model is uncertain. These can only be evaluated using Monte-Carlo simulations; in that sense they are ex post. Then we define a number of indicators which may be of use in predicting robustness, and which do not require simulations to calculate. In that sense they are ex ante.Lastly we evaluate the ex ante indicators on a small macromodel by comparing their predictions with the actual robustness outturn for the range of possible control rules. We find that use of the indicators in choosing rules yields some improvement on the ordinary welfare criterion, especially when the shocks hitting the system are unknown.     

An integrated semantic framework supporting universal accessibility to ICT

As we are moving rapidly to a digital economy, accessing and effectively using Information and Communication Technologies (ICT) in everyday life is widely recognized as an important requirement. However, the accessibility technologies that we have up to date are meeting the needs of only some, at a very high cost and, as a consequence, accessible ICT for all people still remains a major research and development goal. This work presents an integrated ontological framework for the semantic representation of terms and concepts (i.e., related to user needs and preferences (N&P) with respect to ICT use, as well as solutions, platforms and devices) that are required for addressing the universal accessibility in the scope of the Cloud4all project and the Global Public Inclusive Infrastructure (GPII). Cloud4all aims at advancing and building upon the concept of GPII through the development of the necessary tools and models for making ICT accessible for all by exploiting the cloud computing paradigm. The main goal of the proposed framework lays in the separation between generalized accessibility concepts, user interaction mechanisms and N&P with the particular details of different ICT artifacts. Thus, the framework aims at integrating concepts related with user N&P, as well as ICT solutions, platforms, devices and their customizable settings along with information concerning their vendors or implementers, in order to (a) offer the necessary expressiveness for defining/representing personal N&P across applications, platforms and devices, (b) link N&P with the conditions/context according to which these shall be applicable for (e.g., considering the user activity and the physical environment), (c) link interaction requirements (originated from user characteristics) with N&P and (d) support the Cloud4all matchmaking process through the mapping between N&P and application-specific settings based on semantic rules and automatic reasoning techniques.     

Rocking Response of Free-Standing Blocks under Cycloidal Pulses

This paper examines in depth the transient rocking response of free-standing rigid blocks subjected to physically realizable trigonometric pulses. First, the expressions for the dynamic horizontal and vertical reactions at the pivot point of a rocking block are derived and it is shown that the coefficient of friction needed to sustain pure rocking motion is, in general, an increasing function of the acceleration level of the pulse. Subsequently, this paper shows that under cycloidal pulses a free-standing block can overturn with two distinct modes: (1) by exhibiting one or more impacts; and (2) without exhibiting any impact. The existence of the second mode results in a safe region that is located on the acceleration-frequency plane above the minimum overturning acceleration spectrum. The shape of this region depends on the coefficient of restitution and is sensitive to the nonlinear nature of the problem. This paper concludes that the sensitive nonlinear nature of the problem, in association with the presence of the safe region that embraces the minimum overturning acceleration spectrum, complicates further the task of estimating peak ground acceleration by only examining the geometry of free-standing objects that either overturned or survived a ground shaking.     

Rocking Response of Anchored Blocks under Pulse-Type Motions

This paper examines the transient rocking response of anchored blocks subjected to physically realizable horizontal pulse-type motion. Restrainers with elastic-brittle and elastic-plastic behavior are considered. Under one-sine pulse, anchored blocks can overturn with two distinct modes of overturning: (1) by exhibiting one impact; and (2) without exhibiting any impact. It is found that restrainers are more efficient in preventing overturning of small slender blocks subjected to low frequency pulses. This study uncovers that, although for most of the frequency range anchored blocks survive higher accelerations than free-standing blocks, there is a finite frequency range where the opposite happens. This paper examines this counterintuitive behavior and explains the destructive effect that increased strength and increased ductility of restrainers have on the rocking stability of rigid structures when excited by certain ground motions.