Essais saoudiens sur les ciments importés

Au fur et à mesure que le développement s'accélère en Arabie saoudite, les matériaux importés deviennent de plus en plus nombreux et entrent en concurrence les uns avec les autres. Le Materials Testing Laboratory de Riyad a procédé, il ny a pas très longtemps, à une étude comparative d'échantillons de ciments importés et de ciments fabriqués dans le pays. S'ils concernent avant tout les chimistes du ciment, les résultats n'en présentent pas moins un intérêt plus général.     

Single-Row Transformation of Complete Graphs

A complete graph is a fully-connected graph where every node is adjacent to all other nodes in the graph. Very often, many applications in science and engineering are reducible to this type of graph. Hence, a simplified form of a complete graph contributes in providing the solutions to these problems. In this paper, we present a technique for transforming a complete graph into a single-row routing problem. Single-row routing is a classical technique in the VLSI design that is known to be NP-complete. We solved this problem earlier using a method called ESSR, and, the same technique is applied to the present work to transform a complete graph into its single-row routing representation. A parallel computing model is proposed which contributes in making the problem modular and scalable. We also discuss the application of this work on the channel assignment problem in the wireless cellular telephone networks.     

Correlation of growth and aflatoxin production by Aspergillus flavus with some essential metals in gamma irradiated crushed corn

The effects of gamma irradiation and some essential metals on growth and aflatoxin B1 production by Aspergillus flavus in crushed corn were investigated. The production of aflatoxin by A. flavus was influenced by the addition of zinc, copper or iron and the effect gradually decreased with increasing metal concentration from 0 to 300 ppm. A. flavus grew and depleted zinc, copper and iron at initial concentration of 100, 200 or 300 ppm. Presence of 100 ppm zinc, copper or iron plus gamma irradiation (0.5, 1.0, 2.0 kGy) enhanced the growth of A. flavus and the production of aflatoxin in contrast with irradiated samples alone. A. flavus was able to metabolize and deplete elements in all gamma-irradiated samples. These results suggest that stricter control of element levels in gamma irradiated grains could control aflatoxin contamination.     

Polychromatic reflectance and transmittance of a slab with a randomly rough boundary

We investigated four different approximation models for describing the polychromatic reflectance and transmittance of a slab with a randomly rough boundary while taking into account the coherent and the incoherent scattering of the rough boundary. Comparisons with experiments (an etched-silicon wafer) show that approximation models that apply a two-scale roughness to the randomly rough boundary and that take into account the coherent and the incoherent scattering yield better agreement and extend the range of validity of the approximation to shorter wavelengths.     

Experimental study of inward freezing in circular and square pipes

This paper describes the results of an experimental study of the inward freezing of water in tubes of circular and square geometries. The temperature-time history is recorded using thermocouples, from which the progress of the freezing front is deduced. The results obtained pertain to the conditions of water not initially at freezing temperature, the outside surface temperature of the tube varying with time. Since the available theories assume liquid to be initially at freezing temperature and a constant sub-freezing temperature at the outside surface, a rigorous comparison is not possible. In order to make some sort of comparison, the sensible heat of water has been incorporated into the latent heat while the actual surface temperature variation has been replaced by its time-average value. Despite these approximations, the experimental results are in reasonable agreement with the theory.     

Data Converter for Multistandard Mobile Phones

This paper describes an analog to digital converter (ADC) for mobile communication systems using a direct down conversion architecture. The ADC can be programmed to meet the requirements of different communication standards, including GSM (Global System for Mobile communication) and WCDMA (Wideband Code Division Multiple Access). The ADC is realized with a pipeline ADC architecture for WCDMA and a Sigma-Delta architecture for GSM. In order to have an optimized area and power consumption, the basic building blocks (opamps) of the converters are shared between the two converter architectures. The entire ADC consumes about 5.5 mW and occupies an active area of about 0.36 mm². A test circuit has been developed and fabricated and measurements show that both the required programmability and the required performance can be obtained using the proposed configurations.     

SIVA: A System for Coverage-Directed State Space Search

We introduce SImulation Verification with Augmentation (SIVA), a tool for coverage-directed state space search on digital hardware designs. SIVA tightly integrates simulation with symbolic techniques for efficient state space search. Specifically, the core algorithm uses a combination of ATPG and BDDs to generate directed input vectors, i.e., inputs which cover behavior not excited by simulation. We also present approaches to automatically generate lighthouses that guide the search towards hard-to-reach coverage goals. Experiments demonstrate that our approach is capable of achieving significantly greater coverage than either simulation or symbolic techniques in isolation.     

Successful Delivery of Public-Private Partnerships for Infrastructure Development

Two common approaches have been used by governments for the implementation of public-private partnerships (PPPs): a finance-based approach that aims to use private financing to satisfy infrastructure needs, and a service-based approach that aims to optimize the time and cost efficiencies in service delivery. The implementation of PPPs, however, may suffer from legal, political, and cultural impediments. In the United States, the federal government enabled a number of acts to ease the impediments and promote PPPs for infrastructure development. Based on a detailed analysis of PPPs in the United Kingdom and British Columbia, Canada, this paper describes principles that would characterize the implementation of PPPs at the program level (e.g., whether the implementation is successful). The principles pertain to the: availability of a PPP legal framework and implementation units; perception of the private finance objectives, risk allocation consequences, and value-for-money objectives; maintenance of PPPs process transparency; standardization of procedures; and use of performance specifications. Guidelines for successful implementation are explained and discussed in the context of the United States PPPs experience and impediments.