Modeling of optical low coherence reflectometry recorded Braggreflectograms: evidence to a decisive role of Bragg spectral selectivity

This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP     

Increasing Reliability in Cable-Free Radio LANs Low Level Forwarding in HIPERLAN

Radio LANs are emerging in the computing world. They are supported by distinct configurations: on the one hand radio LANs with base stations and a wired backbone, on the other hand radio LANs implementing Intra-forwarding. Adding a new node in a radio LAN with Intra-forwarding, increases the reliability, while this reliability decreases with ad hoc or hub configurations. This advantage of Intra-forwarding is quantified. Intra-forwarding, as defined in the HIPERLAN standard, is based on a hop-by-hop policy and link check procedures. It is shown how point-to-point packets and broadcast packets are forwarded. The three basic components of Intra-forwarding needed to build and update the Intra-forwarding database are described. The originality of this approach is the use of multipoint relays which enable better scalability. The correctness of the Intra-forwarding protocol is proved and its cost is evaluated.     

Relationship between the enzymatic determination of starch and the starch iodine index in two varieties of cider apple

Monitoring the hydrolysis or disappearance of starch by the starch iodine test is a simple procedure for determining the maturity of cider apples, but it does not indicate the exact amount of starch present. So far, studies of starch in apples have dealt exclusively with dessert apples. In this paper the relationship between the visual starch index, the dark‐coloured surface area and the real starch content was studied in two varieties of cider apple commonly used in Normandy (France). Starch determination in cider apples required adapting the protocol provided by the Boehringer enzymatic kit. The work led to proposing a simplified index with five scales instead of 10. This index gives the correspondences between the new and old scales as well as the probable starch contents for each new scale. © 2002 Society of Chemical Industry     

ZnO/Al2O3 coatings for the photoprotection of polycarbonate

ZnO and ZnO/Al₂O₃ thin films were deposited by r.f. magnetron sputtering on polycarbonate (PC) films in order to protect this polymer against photodegradation. The composition, structure and optical properties of the ceramic coatings were characterised. CO₂-plasma treatments were applied to PC in order to improve the coating adhesion. The PC surface energy was characterised by wettability measurements and the chemical bonds were analysed by XPS.It was found that ZnO coatings improve the stability of PC to UV radiations and that an intermediate alumina coating inhibits the photocatalytic oxidation of PC at the PC/ZnO interface. Additionally an external alumina coating brings a high hardness to the coating.     

On Modeling Coordination via Asynchronous Communication and Enhanced Matching

The paper proposes a theoretical study of a coordination language embodying Linda's asynchronous communication primitive with a refined matching mechanism based on pairs composed of attribute names associated with their values. Computations in this language are described by means of an operational semantics, reporting the whole traces of executions. The non-compositionality of this intuitive operational semantics motivates the design of a compositional and fully abstract denotational semantics, which is then exploited for studying program equivalence in this setting.     

Preface: Volume 68, Number 3

Modern information systems rely more and more on combining concurrent, distributed, mobile and heterogenous components. This move from old systems, typically conceived in isolation, induces the need for new languages and software architectures. In particular, coordination languages have been proposed to cleanly separate computational aspects and communication. On the other hand, software architects face the problem of specifying and reasoning about non-functional requirements. All these issues are widely perceived as fundamental to improve software productivity, to enhance maintainability, to advocate modularity, to promote reusability, and to lead to systems more tractable and more amenable to verification and global analysis.The FOCLASA workshop was organized on August 24th 2002 as a satellite event of Concur'02 with the aim of bringing together researchers working on the foundations of component-based computing, coordination, and software architectures.This volume contains selected 12 papers presented at the workshop. They were reviewed by the program committee, consisting, besides the editors, of

• Rocco De Nicola (University of Firenze, Italy)

• Jos Luiz Fiadeiro (ATX Software and University of Lisbon, Portugal)

• Roberto Gorrieri (University of Bologna, Italy)

• Paola Inverardi (University L'Aquila, Italy)

• Joost Kok (University of Leiden, The Netherlands)

• Antonio Porto (New University of Lisbon, Portugal)

We would like to thank them together with the authors of the papers for their contribution to the meeting. We would also like to thank Michael Mislove for his help in editing this volume. Finally, we are grateful to L. Brim, M. Kretinsky, and A. Kucera for their help in organizing the workshop in Brno.     

Ultra-fast optical spectrum analyzer for DWDM applications

Dense wavelength division multiplexing optical networks use tunable devices such as distributed Bragg reflector laser diodes. These optical sources require a precise wavelength calibration according to the ITU grid, even with aged components. Some specific optical spectrum analyzers are commercially available. Unfortunately, measurements using those systems are generally relatively slow. We present and discuss in this paper a fast spectral measurement system that can easily be implemented in a laser diode package.     

Experimental determination of carrier-induced differential loss in 2-section GaInAsP/InP laser-waveguide

Measurements of threshold current density and external efficiency on broad-area laser-waveguide structure have led to the determination of the optical loss and differential loss d alpha /dN approximately=1.1-2.3 *10/sup -17/ cm/sup 2/ at lambda =1.53 mu m in a lambda /sub g/=1.30 mu m GaInAsP layer. This measurement will be useful for the design of tunable lasers.<>     

Markov types and minimax redundancy for Markov sources

Redundancy of universal codes for a class of sources determines by how much the actual code length exceeds the optimal code length. In the minimax scenario, one designs the best code for the worst source within the class. Such minimax redundancy comes in two flavors: average minimax or worst case minimax. We study the worst case minimax redundancy of universal block codes for Markovian sources of any order. We prove that the maximal minimax redundancy for Markov sources of order r is asymptotically equal to 1/2m/sup r/(m-1)log/sub 2/n+log/sub 2/A/sub m//sup r/-(lnlnm/sup 1/(m-1)/)/lnm+o(1), where n is the length of a source sequence, m is the size of the alphabet, and A/sub m//sup r/ is an explicit constant (e.g., we find that for a binary alphabet m=2 and Markov of order r=1 the constant A/sub 2//sup 1/=16/spl middot/G/spl ap/14.655449504 where G is the Catalan number). Unlike previous attempts, we view the redundancy problem as an asymptotic evaluation of certain sums over a set of matrices representing Markov types. The enumeration of Markov types is accomplished by reducing it to counting Eulerian paths in a multigraph. In particular, we propose exact and asymptotic formulas for the number of strings of a given Markov type. All of these findings are obtained by analytic and combinatorial tools of analysis of algorithms.     

1 W fibre coupled power InGaAsP/InP 14xx pump laser for Raman amplification

A 1 W record singlemode fibre coupled output power using 1460 nm InGaAsP/InP non-tapered buried ridge lasers has been demonstrated. The impact of the bandgap of the passive quaternary waveguide on internal loss was investigated. Optimised design allows internal losses as low as 3.3 cm/sup -1/, external efficiency of 0.46 W/A for a 3 mm-long laser and symmetrical (12/spl deg//spl times/12/spl deg/) far-field pattern.