Polarization mode dispersion tolerance of Miller and Manchester signals

Polarization mode dispersion (PMD) which is the time space varying nature of two parallel splitting rays polarized perpendicularly in single mode fiber, causes a serious problem in high bit rate transmission. We evaluated the PMD induced system penalty by means of simulations for Miller and Manchester signals under similar conditions and found that Miller is more tolerant to PMD than Manchester.     

Numerical study of a separated-reattaching flow

The flow over a normal plate with a long, downstream splitter plate is numerically studied with fine spatial and temporal resolutions. The time-dependent two-dimensional Navier-Stokes equations are integrated in time using a high-order, upwind-biased finite-difference scheme. Calculations are performed at several Reynolds numbers to study the evolution of the unsteady nature of the flow. Steady separated flow has been observed for Reynolds numbers up to 150, after which unsteady vortical structures are seen to develop from the shear layer. The time-mean flow characteristics in the steady and unsteady regimes are described. The calculations are seen to agree fairly well with experimental data at high Reynolds numbers.This work was supported by the Office of Naval Research under Grant N-00014-92-J-1640.     

Application of β-cyclodextrin in polymeric solid phase for separation and determination of lead in different environmental matrices

Immobilization of β-cyclodextrin on Dowex resin as an insoluble polymeric matrix by covalent bond presents a new solid-phase medium for preconcentration of Pb (II) at trace level in environmental samples prior to its flame atomic absorption spectrometric determination. The method is based on the sorption of lead after passing on modified Dowex sorbent in a column. The effect of several parameters such as pH, flow rate of sample, eluent kind and volume was investigated. The sorption capacity of the matrix has been found to be 0.4996?mg?g^?1 of adsorbent with the preconcentration factor of 250 for Pb (II). Nitric acid (3 M) as an eluent was sufficient to obtain quantitative recovery (>95%) for Pb (II). The optimum flow rate was 10?ml?min ^?1. The calibration curve was linear in the range of (3–250?ng?mL^?1) with a correlation coefficient of 0.9995. The limit of detection (LOD) based on three times the standard deviation of the blank was 1.37?ng?mL^?1. The relative standard deviation (RSD) for determination of 10?ng?mL^?1 and 100?ngmL^?1 of Pb (II) was 3.00 % and 0.58 % (n?=?10), respectively. The method was successfully applied to determination of lead in some environmental samples such as tap water, river water, soil and rice.     

Isolation and Characterization of Putative Endophytic Bacteria Antagonistic to Phoma tracheiphila and Verticillium albo-atrum

A collection of 200 bacterial isolates recovered from citrus plants (Citrus limon, Citrus sinensis, and Citrus reticulata), Medicago truncatula and Laurus nobilis, was established. In vitro screening indicated that 28 isolates exhibited an inhibitory activity against the vascular pathogens Phoma tracheiphila and Verticillium albo-atrum. Isolates were screened according to their hydrolytic activities, plant growth-promoting bacteria (PGPB) abilities, as well as for the presence of nonribosomal peptide synthetase (NRPS) genes responsible of the lipopeptide biosynthesis. The results were positive for 16 isolates which exhibited at least two PGPB activities and a single NRPS gene. Genetic diversity of the selected isolates was studied using random amplified polymorphic DNA (RAPD) and repetitive element PCR (REP) tools that showed clustering of strains into three major groups (I, II, and III) (i, ii, and iii), respectively. Clustering was further confirmed by the 16S rDNA sequencing that assigned nine isolates to Bacillus velezensis, four isolates to Bacillus methyltrophicus, one isolate to Bacillus amyloliquefaciens, and two isolates to Bacillus mojavensis. Organ-bacterial genotype interaction as well as positive correlation with NRPS genes are discussed.     

Combinatorial auctions

Combinatorial auctions are an important class of market mechanisms in which participants are allowed to bid on bundles of multiple heterogeneous items. In this paper, we discuss several complex issues that are encountered in the design of combinatorial auctions. These issues are related to the formulation of the winner determination problem, the expression of combined bids, the design of progressive combinatorial auctions that require less information revelation, and the need for decision support tools to help participants make profitable bidding decisions. For each issue, we survey the existing literature and propose avenues for further research. An earlier version of this paper appeared in 4OR 2, 1–33, 2004.     

Strong lift-and-project cutting planes for the stable set problem

A great deal of research has been focusing, since the early seventies, on finding strong relaxations for the stable set problem. Polyhedral combinatorics techniques have been at first developed to strengthen the natural linear formulation. Afterward, strong semidefinite programming relaxations have been deeply investigated. Nevertheless, the resulting integer programming (IP) algorithms cannot be regarded as being quite successful in practice, as most of the relaxations give rise to one out of two extreme situations: either provide weak bounds at low computational cost or give good bounds (sometimes excellent) but too demanding to compute. In this paper we present a method to bridge such a gap. In particular, a new lift-and-project relaxation is obtained by a problem-specific variant of the lifting operator M(K, K) by Lovász and Schrijver, combined with Benders decomposition. This yields strong cutting planes, generated by solving a cut generating linear program. An extensive computational experience shows that embedding these cuts in a branch-and-cut framework significantly reduces the size of the enumeration trees as well as the CPU times with respect to state-of-the-art IP algorithms.     

Local and medium range structure of erbium containing glasses: A molecular dynamics study

Erbium containing glasses cover an important role in optical communications and laser technology. The local environment of the ions constituting the three dimensional network exerts a strong influence on the chemical and physical properties of the glasses. In particular the network modifier cations strongly influence the short and intermediate range order of the glass structure. The structural modifications induced by the alumina addition in the glass matrix, as a function of the erbium oxide concentration, have been studied using molecular dynamics (MD) simulations. While at low Er₂O₃ concentration the network former action of the Al³⁺ leads to a more polymerized glass network, at higher Er₂O₃ content the influence of the alumina on the erbium local structure is limited. Further investigation points out micro-heterogeneity in the Na⁺ and Ca²⁺ distribution as a function of the alumina concentration.     

An application of the Lovász–Schrijver <Emphasis Type="Italic">M</Emphasis>(<Emphasis Type="Italic">K</Emphasis>, <Emphasis Type="Italic">K</Emphasis>) operator to the stable set problem

Although the lift-and-project operators of Lovász and Schrijver have been the subject of intense study, their M(K, K) operator has received little attention. We consider an application of this operator to the stable set problem. We begin with an initial linear programming (LP) relaxation consisting of clique and non-negativity inequalities, and then apply the operator to obtain a stronger extended LP relaxation. We discuss theoretical properties of the resulting relaxation, describe the issues that must be overcome to obtain an effective practical implementation, and give extensive computational results. Remarkably, the upper bounds obtained are sometimes stronger than those obtained with semidefinite programming techniques.      

Large diaphragmatic defect as the cause of hydrothorax in a cirrhotic patient: demonstration with peritoneal scintigraphy and magnetic resonance imaging

A 52-year-old man with history of post-hepatitic cirrhosis presented with ascitis and respiratory distress. Chest X-ray on admission showed a large right hydrothorax. Thoracentesis yielded a large volume of a clear transudate fluid. Peritoneal scintigraphy showed rapid migration of radiotracer into the right pleural cavity, confirming the abdominal origin of the pleural fluid and suspecting a large diaphragmatic defect. MR imaging study using ultrafast sequences confirmed the large diaphragmatic defect.