Composition of lime-cement and air-entrained cement mortar as a function of distance to the brick-mortar interface: consequences for masonry

The composition of a lime-cement mortar and an air-entrained cement mortar was studied as a function of distance to the brick-mortar interface. Both mortars had the same cement-to-sand ratio and the same water-to-cement ratio; in the lime-cement mortar the binder-to-sand ratio was highest. The measurements indicate that the mortar composition (i.e. the contents of sand, cured binder and voids) and the contents of chemical substances of the cured binder (i.e. the contents of calcite, portlandite and ettringite) change with distance to the brick-mortar interface. For the mortar composition the tendency of these changes is the same, but for the contents of the chemical substances of cured binder for the two mortar types the tendency of these changes is opposite and also the extent of the changes is significantly different. For the air-entrained cement mortar, the observations are explained by the enrichment of binder towards the brick-mortar interface, resulting from the compaction of fresh mortar. In the lime-cement mortar such an enrichment of binder hardly occurs and the observations are explained by the intense carbonation that takes place. As a result, the contents of the chemical substances in the mortars is very much different. In the air-entrained cement mortar, near the brick-mortar interface the enrichment of cement and the low water content (resulting from the low water retentivity of this mortar), lower the water-to-cement ratio and as a consequence the cement is not fully hydrated. In the lime-cement mortar, as the Ca(OH)₂ content and the water content is higher, near the brick-mortar interface, a carbonated zone is formed which is hardly permeable for CO₂ (and probably water). This does not occur in the air-entrained cement mortar, it remains permeable.     

Measurement and simulation of pollutant emissions from marine diesel combustion engine and their reduction by exhaust gas recirculation

Taking into account the complexity and cost of a direct experimental approach, the recourse to simulation, which can also predict inaccessible information by measurement, offers an effective and fast alternative to apprehend the problem of pollutant emissions from internal combustion engines. An analytical model based on detailed chemical kinetics employed to calculate the pollutant emissions of a marine Diesel engine in general gave satisfactory results compared to experimentally measured results. Especially, the nitric oxide (NO) emission values were found to be higher than the limiting values tolerated by the International Maritime Organization (IMO). Thus, this study was undertaken to reduce to the maximum these emissions. The reduction of pollutant emissions is apprehended with exhaust gas recirculation (EGR). This paper was recommended for publication in revised form by Associate Editor Kyoung Doug Min Nader Larbi, born on 28 of August 1973 in Tunis, received a Diploma of 2nd class from Merchant Navy of Sousse as an Engineer Officer, and went on to receive his Master and Ph.D. degrees from the Nation School of Engineers of Tunis.     

Chemical Synthesis of Organo-siloxene 2D Materials from Calcium Di-Silicide: Characterization,Dielectric and Electrochemical Studies

Silicon - Silicon is one of the most used materials in semiconductors and electronic devices. Its miniaturization in two-dimensional (2D) scale is now a great challenge to improve and/or extend its...     

Stabilization and decay estimate for distributed bilinear systems

In this paper, we consider the problem of feedback stabilization for the distributed bilinear system y′(t)=Ay(t)+u(t)By(t). Here A is the infinitesimal generator of a linear C⁰ semigroup of contractions on a Hilbert space H and B:H→H is a linear bounded operator. A sufficient condition for feedback stabilization is given and explicit decay estimate is established. Applications to vibrating systems are presented.     

Wideband slot antenna using a new feeding technique for wireless applications

This article presents a new wideband slot antenna for wireless applications at 5.8 GHz. To improve the antenna bandwidth, a new feeding mechanism based on a capacitively‐ and inductively‐coupled slot is proposed. To demonstrate this approach, an experimental antenna prototype operating at the 5.8‐GHz band was designed, fabricated, and measured. The obtained results indicate very good agreement between the numerical and experimental results. The proposed antenna achieves a 28.5% bandwidth, a 5.7‐dBi gain, and a ?15‐dB front‐to‐back ratio, which are very sufficient for broadband wireless applications. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Exploitation piscicole du barrage Guenitra (Oum Toub,Skikda, Algérie)

The breeding of the carp Cyprinus carpio L. in the Guenitra dam (Oum, Toub, Skikda, Algeria) began in 1989 with 800 larvae imported from Hungary. This pilot project in carp breeding aimed to provide a stock of protein resource at low cost, with the purpose of extending the scheme to other water bodies in the area. Studies of the dam and its fauna took place between 1995 and 1999. It was determined that the Guenitra dam is favourable to carp breeding. The experiment can be replicated with success in similar water bodies.

L’élevage de la carpe Cyprinus carpio L. dans le barrage Guenitra (Skikda, Algérie) a vu le jour en 1989 avec l’ensemencement de 800 alevins importés de la Hongrie. Ce projet pilote de carpiculture avait pour objectif la mise en place d’une ressource protéique à moindre coÛt avec l’ambition de sa généralisation à d’autres plans d’eau de la région. Pour cela, nous avons étudié entre 1995 et 1999, l’hydrobiologie du barrage et les réactions biotope‐biocénose‐ichthyofaune en estimant le stock de pêche s’évaluant entre : Carpe grosse tête Ctenopharyngodon idella Val., Carpe herbivore Aristichthys nobilis R et Carpe argentée Hypophtalmichthys molitrix Val. Les résultats obtenus, durant ces trois campagnes (1996/97, 97/98 et 98/99) englobent les paramètres climatologiques, les analyses physico‐chimiques in situ des sels minéraux et en laboratoire et enfin, l’âge et la biométrie des trois espèces de Carpes. Cette étude diagnostic préliminaire montre que le barrage Guenitra est un écosystème tout à fait favorable à la mise en place et l’exploitation d’une activité carpicole. D’autre part, elle permet de consolider l’idée de transfert de ce type d’élevage dans d’autres retenues d’eau ayant un environnement similaire.     

An improved Backstepping technique using sliding mode control for transient stability enhancement and voltage regulation of SMIB power system

The problem of transient stability and voltage regulation for a single machine infinite bus (SMIB) system is addressed in this paper. An improved Backstepping design method for transient stability enhancement and voltage regulation of power systems is discussed beginning with the classical Backstepping to designing the nonlinear excitation control of synchronous generator. Then a more refined version of this technique will be suggested incorporating the sliding mode control to enhance voltage regulation and transient stability. The proposed method is based on a standard third-order model of a synchronous generator connected to the grid (SMIB system). It is basically implemented on the excitation side of the synchronous generator and compared to the classical Backstepping controller as well as the conventional controllers which are the automatic voltage regulator and the power system stabiliser. Simulation results prove the effectiveness of the proposed method which ameliorates to a great extent the transient stability compared to the other methods.     

A bounded dynamic programming approach to schedule operations in a cross docking platform

Cross docking is a logistic technique employed to reduce the inventory holding, order picking, transportation costs as well as the delivery time. Products arriving to the cross dock are unloaded from inbound trailers, possibly reconsolidated with other products arriving from different destinations and loaded into outbound trailers within less than 24 h. In this study, we consider a multiple receiving and shipping door cross dock environment. The objective is to find optimal (for reasonably small cross docks) or near optimal (for larger cross docking facilities) scheduling policies which minimizes the total costs related to the transshipment operations at the facility.     

A Risk-Aware Reputation-Based Trust Management in Wireless Sensor Networks

Wireless sensor networks (WSNs) are susceptible to many security threats and are specifically prone to physical node capture in which the adversary can easily launch the so-called insider attacks such as node compromise, bypassing the traditional security mechanisms based on cryptography primitives. So, the compromised nodes can be modified to misbehave and disrupt the entire network and can successfully perform the authentication process with their neighbors, which have no way to distinguish fraudulent nodes from trustworthy ones. Trust and reputation systems have been recently suggested as a powerful tools and an attractive complement to cryptography-based schemes in securing WSNs. They provide ability to detect and isolate both faulty and malicious nodes. Considerable research has been done on modeling and managing trust and reputation. However, trust topic issue in WSNs remains an open and challenging field. In this paper, we propose a Risk-aware Reputation-based Trust (RaRTrust) model for WSNs. Our novel framework uses both reputation and risk to evaluate trustworthiness of a sensor node. Risk evaluation is used to deal with the dramatic spoiling of nodes, which makes RaRTrust robust to on–off attack and differ from other trust models based only on reputation. This paper contributes to model the risk as opinion of short-term trustworthiness combining with traditional reputation evaluation to derive trustworthiness in WSNs.

     

Sweet sorghum: A quality raw material for the manufacturing of chemical paper pulp

After the extraction of sugar in conditions adaptable to the industrial scale, sweet sorghum bagasse is used for the first time to manufacture chemical pulp. The quality of the pulp obtained is excellent for the paper industry. The pulp exhibits a degree of cohesion higher than 80%, a low kappa number indicating a good delignification, a high degree of polymerization, and exceptional physico-mechanical properties. Unexpectedly, the final results allow us to consider sweet sorghum as a major raw material for the paper industry in every region where it will be possible to grow it in association with sugar cane. These pulps can be used in sectors usually restricted to superior chemical pulps such as those obtained from softwood.