Blocking models of optical burst switches with shared wavelength converters: exact formulations and analytical approximations

Loss modeling of asynchronous optical burst switches with shared wavelength converters is considered. An exact analysis based on continuous time Markov chains is proposed and validated by comparison with simulation for balanced and unbalanced traffic. A computationally efficient approximated analysis is also proposed and compared with the exact model to find applicability conditions. Approximate loss performance evaluation is presented for ranges of values which are not tractable either by simulation or exact analysis.

A decrease of reelin expression as a putative vulnerability factor in schizophrenia

Postmortem prefrontal cortices (PFC) (Brodmann's areas 10 and 46), temporal cortices (Brodmann's area 22), hippocampi, caudate nuclei, and cerebella of schizophrenia patients and their matched nonpsychiatric subjects were compared for reelin (RELN) mRNA and reelin (RELN) protein content. In all of the brain areas studied, RELN and its mRNA were significantly reduced (approximately 50%) in patients with schizophrenia; this decrease was similar in patients affected by undifferentiated or paranoid schizophrenia. To exclude possible artifacts caused by postmortem mRNA degradation, we measured the mRNAs in the same PFC extracts from gamma-aminobutyric acid (GABA)A receptors alpha1 and alpha5 and nicotinic acetylcholine receptor alpha7 subunits. Whereas the expression of the alpha7 nicotinic acetylcholine receptor subunit was normal, that of the alpha1 and alpha5 receptor subunits of GABAA was increased when schizophrenia was present. RELN mRNA was preferentially expressed in GABAergic interneurons of PFC, temporal cortex, hippocampus, and glutamatergic granule cells of cerebellum. A protein putatively functioning as an intracellular target for the signal-transduction cascade triggered by RELN protein released into the extracellular matrix is termed mouse disabled-1 (DAB1) and is expressed at comparable levels in the neuroplasm of the PFC and hippocampal pyramidal neurons, cerebellar Purkinje neurons of schizophrenia patients, and nonpsychiatric subjects; these three types of neurons do not express RELN protein. In the same samples of temporal cortex, we found a decrease in RELN protein of approximately 50% but no changes in DAB1 protein expression. We also observed a large (up to 70%) decrease of GAD67 but only a small decrease of GAD65 protein content. These findings are interpreted within a neurodevelopmental/vulnerability "two-hit" model for the etiology of schizophrenia.     

Variability in the classification of radiographs using the 1980 International Labor Organization Classification for Pneumoconioses

This study describes the extent of agreement in classification of chest radiographs using the International Labor Organization (ILO) classification among six readers from the United States and Canada. A set of 119 radiographs was created and read by three Canadian and three US readers. The two ratings of interest were profusion (scored from 0/- to 3/+) and pleural abnormalities consistent with pneumoconiosis (scored with the ILO system, then collapsed into a yes/no). We used a number of approaches to evaluate interreader agreement on profusion and pleural changes, determining concordance, observed agreement, kappa statistic, and a new measure to approximate sensitivity and specificity. This study found that five of six readers had good fair to good agreement for pleural findings and for profusion as a dichotomous variable (> or = 1/0 vs < or = 0/1) using the kappa statistic, while a sixth reader had poor agreement. We found that concordance, expressed as percent agreement, was higher for normal radiographs than for ones that showed disease, and describe the use of the kappa statistic to control for this finding. This analysis adds to the existing literature with the use of the kappa statistic, and by presenting a new measure for "underreading" and "overreading" tendencies.     

Clustering strategies for multicast precoding in multibeam satellite systems

Next generation multibeam SatCom architectures will heavily exploit full frequency reuse schemes along with interference management techniques, eg, precoding or multiuser detection, to drastically increase the system throughput. In this framework, we address the problem of the user selection for multicast precoding by formulating it as a clustering problem. By introducing a novel mathematical framework, we design fixed/variable size clustering algorithms that group users into simultaneously precoded and served clusters while maximising the system throughput. Numerical simulations are used to validate the proposed algorithms and to identify the main system‐level trade‐offs.     

Two New Nonlinear Nonlocal Diffusions for Noise Reduction

Two new nonlocal nonlinear diffusion models for noise reduction are proposed, analyzed and implemented. They are both a close relative of the celebrated Perona-Malik equation. In a way, they can be viewed as a new regularization paradigm for Perona-Malik. They do preserve and enhance the most cherished features of Perona-Malik while delivering well-posed equations which admit a stable natural discretization. Unlike other regularizations, however, certain piecewise smooth functions are (meta)stable equilibria and, as a consequence, their dynamical behavior and that of their discrete implementations can be fully understood and do not lead to any “paradox”. The presence of nontrivial equilibria also explains why blurring is kept in check. One of the models has been proved to be well-posed. Numerical experiments are presented that illustrate the main features of the new models and that provide insight into their interesting dynamical behavior as well as demonstrate their effectiveness as a denoising tool.

The effect of silylation on titanium-containing silica catalysts for the epoxidation of functionalised molecules

The epoxidation of functionalised substrates of interest as fine chemicals using mesoporous titanium-containing silicas is here reported and the role of silylation in changing the surface hydrophilic character of these catalysts is investigated. The silylation procedure was carried out on two titanium-grafted silicas with different morphologies. An ordered MCM-41 and a non-ordered commercial mesoporous silica were used as supports. The reactivity of bulky substrates with different characteristics (limonene, -terpineol, carveol and methyl linoleate) is studied and compared. The effect of silylation is more pronounced on Ti–MCM-41 than with low-surface area Ti–SiO₂ and it is shown that the catalytic performances are strongly dependent on the nature of the reactant. Purely alkenic molecules show better reactivity over silylated catalysts than over non-silylated ones. On the other hand, a hydrophilic environment around the titanium active sites has often a beneficial effect in the epoxidation of richly functionalised substrates.     

A Modular Ligation Strategy for Asymmetric Bivalent Nucleosomes Trimethylated at K36 and K27

In nature, individual histones in the same nucleosome can carry identical (symmetric) or different (asymmetric) post-translational modification (PTM) patterns, increasing the combinatorial complexity. Embryonic stem cells exhibit “bivalent” nucleosomes, some of which are marked by an asymmetric arrangement of H3K36me3 (an activating PTM) and H3K27me3 (a repressive PTM). Here we describe a modular synthetic method to access such asymmetrically modified nucleosomes and show that H3K36me3 inhibits the activity of the methyltransferase PRC2 locally while still prolonging its chromatin binding time.