Etiologic factors of urinary lithiasis in Tunisian children

Fifty-five Tunisian children with urinary stones, between the ages of 8 months and 15 years, underwent morphological and infrared spectrophotometric analysis of their stones. This study provides an approach to the aetiological profile of urinary stones in Tunisian children. The nucleus of the stones was composed of acidic ammonium urate in 48% of cases with a morphology suggestive of phosphorus deficiency associated with a history of diarrhoea. In 24% of cases, the nucleus contained struvite indicating the presence of urinary tract infection by urease-positive bacteria. The main growth factors of urinary stones were hyperoxaluria and urinary tract infection. In 5 cases, the stones were due to a hereditary lithogenic metabolic disease : cystinuria in 1 case and primary hyperoxaluria in 4 cases.     

The dielectric constants of CaWO4, Nd/CaWO4 and Gd/CaWO4

The dielectric constants and loss for pure single crystals of calcium tungstate and for neodymium- and gadolinium-doped crystals have been measured from 1 to 40 MHz. At 20? C the values for pure calcium tungstate areε _a′ = 11.3±0.4,ε _c′ = 9.1±0.4, at 1 MHz. These agree closely with Brower and Fang's data and increase very slightly with frequency. Doping at levels of less than 1.0 at.% produced no measurable change inε _a′ orε _c′. The dielectric loss, tanδ, which was isotropic, was about 5×10^?3 for all specimens at 1 MHz; at higher frequencies, tan? increased and, in the neodymium-doped crystals, the high frequency loss was found to be concentration dependent.     

On the Optimality of Cyclic Transmission in Teletext Systems

Teletext is a one-way information delivery system where pages of information are broadcast to all users in a continuous manner. System response time is an important consideration in the design of teletext systems. One factor contributing to response time is the order in which pages are transmitted. In this paper, we formulate the problem of determining the sequence of page transmissions as a Markovian decision process. Using this formulation we show that, from a response time point of view, a cyclic order of page transmissions is optimal. We also describe two algorithms for designing a teletext broadcast cycle.     

The use of multicast delivery to provide a scalable and interactivevideo-on-demand service

In typical proposals for video-on-demand (VoD) systems, customers are serviced individually by allocating and dedicating a transmission channel and a set of server resources to each customer. This approach leads to an expensive to operate, nonscalable system. We consider a VoD system that uses multicast delivery to service multiple customers with a single set of resources. The use of multicast communication requires that part of the on-demand nature of the system be sacrificed to achieve scalability and cost-effectiveness. One drawback to using multicast communication is that it complicates the provision or interactive VCR-style functions. Interactivity can be provided by either increasing the complexity of the customer set-top box (STB) or by modifying the semantics of the interactive functions to make them easier to provide. We describe a framework and mechanisms by which such interactive functions can be incorporated into a multicast delivery VoD system. Through the use of simulation, we evaluate and compare the performance of a unicast VoD system and multicast VoD systems offering various levels of interactivity     

Software engineering technology watch

Predicting the evolution of software engineering technology is, at best, a dubious proposition; it is fast paced and determined by an array of factors, many of them outside the software engineering arena. The authors discuss their first ventures in this domain and preliminary conclusions. The goal of watching software engineering trends means to determine what information we must gather and maintain to gain a comprehensive view of the discipline and its evolution. This information must be sufficiently rich to support discipline-wide assessments and trend-specific analysis. The authors identified a number of software engineering-specific and technology-related indicators, which they divided into seven categories which are presented.     

Analysis and optimization of transmission schedules for single-hopWDM networks

Considers single-hop lightwave networks with stations interconnected using wave division multiplexing. The stations are equipped with tunable transmitters and/or receivers. A predefined, wavelength-time oriented schedule specifies the slots and the wavelengths on which communication between any two pairs of stations is allowed to take place. The authors define a wide variety of schedules and develop a general framework for analyzing their throughput performance for any number of available wavelengths, any tunability characteristics, and general (potentially nonuniform) traffic patterns. They then consider the optimization of schedules given the traffic requirements and present optimization heuristics that give near-optimal results. They also investigate how the number of available wavelengths (channels) affects the system throughput, and develop techniques to efficiently share the available channels among the network stations. As a result, they obtain systems that are easy to scale while having very good performance     

Performance characterization of quorum-consensus algorithms forreplicated data

The authors develop a model and define performance measures for a replicated data system that makes use of a quorum-consensus algorithm to maintain consistency. They consider two measures: the proportion of successfully completed transactions in systems where a transaction aborts if data is not available, and the mean response time in systems where a transaction waits until data becomes available. Based on the model, the authors show that for some quorum assignment there is an optimal degree of replication beyond which performance degrades. There exist other quorum assignments which have no optimal degree of replication. The authors also derive optimal read and write quorums which maximize the proportion of successful transactions     

Performability of the hypercube [reliability]

The authors address the problem of modeling and evaluating the composite performance and reliability measures (performability) of a hypercube architecture running a specific application. A generalized stochastic Petri net (GSPN) is used to model the component failures and repairs in the hypercube. The GSPN model defines the dimension and number of subcubes available for the application. This model generalizes previously proposed models for hypercube reliability and automatically generates the underlying Markov chain needed for performability analysis. A novel performability analysis algorithm is presented that computes both the moments and the distribution of performability in O( N³). The algorithm is conceptually simpler than those previously reported. An example is given to illustrate the modeling process and demonstrate the importance of performability analysis for mission-critical systems     

Stability of the anodic film on aluminium in relation to the nature of some anions

Using a galvanostatic method of investigation the influence has been studied of various anions on the formation of anodic layers during anodization in borate solution. According to the results obtained sodium carbonate, phosphate, succinate and oxalate enhance the formation of the anodic oxide layer. Sulfite, sulfate, thiosulfate and nitrate lower the anode potential to a constant value which depends from the type of anion and may be extremely low in the case of halogen ions (chloride, bromide, iodide). This phenomenon is attributed in the case of the halides to a pitting type attack, while a duplex layer formation is assumed to take place with the other members of this group. The effect of the halides may be suppressed by the addition of phosphate ions, but rather high phosphate:halide ratios are required in order to achieve healing of the pits. The pores in the duplex layer may be sealed by a second anodization in borate, phosphate, benzoate or succinate solution.     

Étude de la génération d’impulsions brèves d’un laser DFB à trois contrôles de phases (3QWS-DFB)

The purpose of this paper is to study the generation of short pulses of the three quarter wave shift distributed feedback (3Qws-dfb) laser by using switching gain technique. We have used the temporal domain model (Tdm) which is a multimode spatio-temporal model that considers simultaneously all the modes of the overall intra-cavity field as well as the two following nonlinear effects, the spectral hole burning (Shb) and the gain saturation. Obtained results showed that a 3Qws-dfb laser can generate short pulses in accordance with Fourier criteria. These results show that 3Qws-dfb lasers are potential candidates as monomode optical sources for long distance high bit rate telecommunications.