Routing and wavelength assignment of scheduled lightpath demands

We present algorithms that compute the routing and wavelength assignment (RWA) for scheduled lightpath demands in a wavelength-switching mesh network without wavelength conversion functionality. Scheduled lightpath demands are connection demands for which the setup and teardown times are known in advance. We formulate separately the routing problem and the wavelength assignment problem as spatio-temporal combinatorial optimization problems. For the former, we propose a branch and bound algorithm for exact resolution and an alternative tabu search algorithm for approximate resolution. A generalized graph coloring approach is used to solve the wavelength assignment problem. We compared the proposed algorithms to an RWA algorithm that sequentially computes the route and wavelength assignment for the scheduled lightpath demands.     

On the improvement of network resource utilization efficiency for the establishment of static dependable connections in SRLG-constrained WDM translucent networks

In this paper, we investigate the problem of establishing static connections with fault-tolerant requirements, also known as dependable connections, taking into account quality of transmission constraints. To the best of our knowledge, this is the first study that tackles the aforementioned problem under shared risk link group (SRLG) constraints in translucent WDM optical mesh networks where typically a set of strategically localized network nodes are equipped with regeneration capability to overcome physical-layer impairment effects. A novel cross-layer heuristic approach is introduced to solve the problem for an heterogeneous networked scenario relying on a cost-effective two-stage protection procedure which combines the well-known path protection and partial path protection schemes in order to ensure instantaneous recovery from any SRLG-failure event. The proposed heuristic integrates a generic auxiliary graph model that incorporates various network heterogeneity factors such as the number of transceivers at each network node, the number of wavelengths on each fiber link, and the regeneration capability of each node, represented by different edges in the constructed graph. Moreover, the integrated auxiliary graph can be applied efficiently to model either single- or mixed-line-rate translucent WDM optical networks wherein different modulation formats are employed in order to support the transmission at different line rates. Our solution approach aims at maximizing the total number of accommodated requests by reducing network resource consumption through the simultaneous use of the backup–backup and primary–backup multiplexing techniques. We, here, present extended versions of these two techniques that generalize the sharing concept to some other important node resources—specifically, regeneration equipments which constitute the major cost factor in optical transport networks—in addition to link resources (i.e., wavelength channels). As far as we know, this is the first attempt to deploy simultaneously generalized versions of the backup–backup and primary–backup multiplexing techniques when considering static traffic patterns without compromising the 100 % fault-recoverability guarantee. The performances of the proposed heuristic are evaluated and discussed through extensive numerical experiments carried out on different network topologies. Significant improvements are demonstrated, either in terms of network blocking performance or in terms of resource utilization efficiency, in comparison with previously proposed approaches.     

Modified spontaneous emission in oligo (p-phenylene vinylene) planar microcavities

This paper reports on the photoluminescence properties of phenylene vinylene oligomers films (OPV) the emission of which was modified by microcavity effect. Films with 4 and 6 vinyl groups (respectively denoted OPV-4 and OPV-6) were investigated. A strong blue luminescence at 470 nm is observed for OPV-4. OPV-6 shows an emission spectrum quite similar to that of poly phenylene vinylene (PPV). Photoluminescence excitation measurements (PLE) give similar behaviors for the two samples and do not show any change in the shape of the spectra. Ageing under UV irradiation (380 nm) of the unencapsulated OPV-4 layers was evidenced by an exponential decrease of the photoluminescence intensity of about 40% after 3 h a continuous illumination. OPV-6 samples, aged on shelf, for weeks does only show a small decrease (15%) of the PL level over more than 7 h under continuous UV irradiation. Microcavity related effects were observed by inserting the films between two mirrors. These are generally a TiO₂/SiO₂ distributed Bragg reflectors (DBR) as bottom mirror and a Ag film as top mirror. However best results were obtained with two dielectric DBR. As expected, a strong enhancement of the emission at the cavity resonance and pronounced angular effects (emission peaking in the direction normal to the surface of the device) were observed. The importance of the position of the emitting material within the microcavity is evidenced with a thin tris(8-hydroxy) quinoline aluminum (Alq) embedded in SiO₂ with various cavity configurations.     

Quantitative proteomic analysis of bacterial enzymes released in cheese during ripening

Due to increasingly available bacterial genomes in databases, proteomic tools have recently been used to screen proteins expressed by micro-organisms in food in order to better understand their metabolism in situ. While the main objective is the systematic identification of proteins, the next step will be to bridge the gap between identification and quantification of these proteins. For that purpose, a new mass spectrometry-based approach was applied, using isobaric tagging reagent for quantitative proteomic analysis (iTRAQ), which are amine specific and yield labelled peptides identical in mass. Experimental Swiss-type cheeses were manufactured from microfiltered milk using Streptococcus thermophilus ITG ST20 and Lactobacillus helveticus ITG LH1 as lactic acid starters. At three ripening times (7, 20 and 69 days), cheese aqueous phases were extracted and enriched in bacterial proteins by fractionation. Each sample, standardised in protein amount prior to proteomic analyses, was: i) analysed by 2D-electrophoresis for qualitative analysis and ii) submitted to trypsinolysis, and labelled with specific iTRAQ tag, one per ripening time. The three labelled samples were mixed together and analysed by nano-LC coupled on-line with ESI-QTOF mass spectrometer. Thirty proteins, both from bacterial or bovine origin, were identified and efficiently quantified. The free bacterial proteins detected were enzymes from the central carbon metabolism as well as stress proteins. Depending on the protein considered, the quantity of these proteins in the cheese aqueous extract increased from 2.5 to 20 fold in concentration from day 7 to day 69 of ripening.     

Original features of cell-envelope proteinases of Lactobacillus helveticus. A review

Lactobacillus helveticus is a lactic acid bacterium very used in fermented milks and cheese. The rapid growth of L. helveticus in milk is supported by an efficient cell envelope proteinase (CEP) activity, due to subtilisin-like serine proteases. These enzymes play also crucial roles in texture and flavor formation in dairy products as well as in generating in situ bioactive peptides. In L. helveticus, several genes encoding putative CEPs were detected and characterized by a large intraspecific diversity; little is known about regulation of expression of CEP-encoding genes. Anchored at the bacterial surface, CEPs are large-sized enzymes (> 150 kDa) hydrolyzing β- and α_s1-casein as well. Substrate cleavages occur after almost all types of amino acids residues, but mass spectrometry analysis revealed L. helveticus strains with specific profiles of substrate hydrolysis, which could explain identification of strains associated with interesting technological properties. In this review, the most recent data regarding CEP-encoding genes, CEP activities toward caseins and L. helveticus strain diversity are discussed.     

An efficient media access protocol for packet-switched wavelength-division multiplexed photonic networks

A reservation-based protocol based on a Pipelining Cyclic Scheduling Algorithm (PCSA) is proposed for packet-switched single-hop photonic networks. This protocol contains a mechanism to avoid contention at the receivers. Packets arrive in order and the transmission delay and its variations are optimized. The effects of propagation delay and processing time are almost compensated for by a pipelining technique. Analytical models and analysis are developed. The transmission delay is calculated as a function of the offered load, the number of nodes, propagation delay and processing time. Finally, the results of the analysis and simulations are compared.     

Isolation and characterisation of a Lactobacillus helveticus ITG LH1 peptidase-rich sub-proteome

Lactobacillus helveticus strains, one of the most nutritionally fastidious lactic acid bacteria, have a potent proteolytic system that makes them very interesting for different uses in the dairy industry. Its applications concern from cheese ripening to the preparation of fermented milk products with biologically active peptides. The cell-free extract (CFE) of Lactobacillus helveticus strain ITG LH1 was analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), using IPG immobiline dry strips (pH 4-7). With the aim to study the proteolytic enzymes expressed by Lactobacillus helveticus ITG LH1 grown in milk medium, a two step-chromatography methodology, based on ion exchange and affinity chromatography, was developed for the preparation of a peptidase-rich sub-proteome from the CFE of stationary growing cells. Several affinity chromatography columns were tested and among them a HiTrap Chelating column was selected as it provided the best performance for the enrichment in peptidases. Peptidase activities were studied using different beta-Naphtylamide (beta-NA) derivatives and specific activities were increased 50- to 100-fold by this chromatographic procedure. Sub-proteome characterisation was performed by 2D-PAGE, pH 4-7, followed by protein digestion with trypsin, analysis by MALDI-TOF mass spectrometry and subsequent database searches using peptide mass fingerprints. Among the most abundant proteins seven peptidases were present, namely the two general aminopeptidases (PepN, PepC), three dipeptidases (PepDA, PepV, PepQ) and two endopeptidases (PepO, PepO3), all of them corresponding to the catalytic classes of metallo- or cysteine-peptidases. Several stress proteins (such as heat shock proteins DnaK and GroEL) and other enzymes implied in bacterial metabolism, namely in the carbohydrate pathways (such as LDH), were also identified in the peptidase-rich sub-proteome.     

Translucent network design from a CapEx/OpEx perspective

Translucent wdm network design has been widely investigated during the last 10 years. Translucent networks stand halfway between opaque and transparent networks improving the signal budget while reducing the network cost. On one hand, opaque networks provide satisfying quality from source to destination by the use of electrical reg regeneration (Re-amplifying, Re-shaping, and Re-timing) at each network node. In addition to their high cost inherent to numerous 3R regenerations, opaque networks are also constrained by the bit-rate dependence of electrical components. Transparent networks, on the other hand, do not include any electrical regeneration; therefore, the signal quality is degraded due to the accumulation of linear and non-linear effects along the signal’s route. Translucent networks include electrical regeneration at some network nodes. Among the different possible strategies for translucent network design, sparse regeneration inserts regenerators whenever needed to help establish connection requests. In this context the objective of translucent network design is to judiciously choose the regeneration sites in order to guarantee a certain quality of transmission while minimizing the network cost. In this paper, we propose to solve the translucent network design problem by introducing a heuristic for routing, wavelength assignment, and regenerator placement. This heuristic, called COR2P (Cross-Optimization for RWA and Regenerator Placement) aims not only to minimize the number of required regenerators, but also to minimize the number of regeneration sites. In this perspective, we introduce an original cost function that contributes to the optimization of CapEx/OpEx expenditures in translucent network design. In fact, the CapEx-to-OpEx ratio strongly depends on the pricing and management strategy of the carrier. In this respect, COR2P is designed in a way that its parameters can be adjusted according to carriers’ strategies. In order to discuss its different features, we compare COR2P performance with two other algorithms proposed in the literature for translucent network design.     

Organic thin film transistors with HfO2 high-k gate dielectric grown by anodic oxidation or deposited by sol–gel

We report here on pentacene based organic field effect transistors (OFETs) with a high-k HfO₂ gate oxide. HfO₂ layers were prepared by two different methods: anodic oxidation and sol–gel. A comparison of the two processes on the electrical properties of OFETs is given. Ultra thin nanoporous (20 nm) sol–gel deposited oxide films were obtained following an annealing at 450 °C. They lead to high mobility and stable devices (μ = 0.12 cm²/V s). On the other hand, devices with anodic HfO₂ revealed a little bit more leaky and show some hysteresis. Anodization, however, presents the advantage of being a fully room temperature process, compatible with plastic substrates. Stability and response to a bias stress are also reported.