Evaluation of alternatives for the broadcast operation in Kademlia under churn

During recent years, considerable effort has been devoted to the enhancement of Distributed Hash Table (DHT) systems with broadcasting capabilities. Such systems typically provide individual node routing but a broadcast primitive is required for functionalities such as information dissemination or data aggregation. Broadcasting can also be used as the basis for partial keyword searches. Little work has however specifically addressed Kademlia, a well known DHT, used in real applications. Our work exposes the particularities of this system, notably its XOR-based distance metrics, and analytically studies what broadcasting techniques can be applied to it. A model that estimates node coverage as a function of the probability that individual messages reach their destination has been also developed. For validation, several broadcasting algorithms have been implemented and comprehensively evaluated, considering node coverage, messages to nodes ratio, latency and imbalance factor. Moreover, several techniques are proposed to enhance the bare protocols when adverse circumstances such as churn and failure rate conditions are present. These include redundancy, resubmissions or flooding, and also combinations of those. All have been implemented and fully tested. An analysis of the strengths and weaknesses of algorithms and additional techniques, and a discussion on the choices and compromises to make, depending on system characteristics or application priorities, is finally presented.     

Stability and mechanical evaluation of bovine pericardium cross-linked with polyurethane prepolymer in aqueous medium

The present study investigates the potential use of non-catalyzed water-soluble blocked polyurethane prepolymer (PUP) as a bifunctional cross-linker for collagenous scaffolds. The effect of concentration (5, 10, 15 and 20%), time (4, 6, 12 and 24 h), medium volume (50, 100, 200 and 300%) and pH (7.4, 8.2, 9 and 10) over stability, microstructure and tensile mechanical behavior of acellular pericardial matrix was studied. The cross-linking index increased up to 81% while the denaturation temperature increased up to 12 °C after PUP crosslinking. PUP-treated scaffold resisted the collagenase degradation (0.167 ± 0.14 mmol/g of liberated amine groups vs. 598 ± 60 mmol/g for non-cross-linked matrix). The collagen fiber network was coated with PUP while viscoelastic properties were altered after cross-linking. The treatment of the pericardial scaffold with PUP allows (i) different densities of cross-linking depending of the process parameters and (ii) tensile properties similar to glutaraldehyde method.     

Chitosan impregnated gutta-percha points: antimicrobial in vitro evaluation and mechanical properties

Chitosan-impregnated gutta-percha points (ChitGPP) were tested for their ability to inhibit the growth of microorganisms usually involved in root canal infections. Their mechanical properties were also studied and compared with the commonly used commercial points in endodontics. ChitGPP were more efficient in reducing the microbial load than those without chitosan. ChitGPP also possess better tensile and elastic properties than commercial ones. After six months of storage, ChitGPP’s were still able to reduce the bacterial load by 1 log, suggesting that impregnation of gutta-percha points with chitosan could be a good alternative to obtain gutta-percha points with improved antimicrobial properties.     

Augmented reality annotations to assist persons with Alzheimers and their caregivers

Persons with Alzheimer’s disease (AD) and their caregivers implement diverse strategies to cope with memory loss. A common strategy involves placing tags on drawers or removing cabinet doors to make their contents visible. This study describes the Ambient aNnotation System (ANS), aimed at assisting people suffering from AD and their caregivers with this task. The system has two main modules: The tagging subsystem allows caregivers to create and manage ambient annotations in order to assist people with memory problems. The second subsystem allows people with AD to use a mobile phone to recognize tags in the environment and to receive relevant information in the form of audio, text, or images. The identification of these tags is performed in real time by uploading images from the mobile phone to a server, which uses the SURF algorithm for object recognition. We describe the design and implementation of the system as well as results of the evaluation of its performance and efficiency. ANS can process query images approximately every 2 s and is able to locate users in their homes with a precision of 0.93. A usability study conducted with six subjects determined that audio notifications are more effective than vibrating notifications to alert the user about tags in the environment.     

Two-dimensional numerical simulations of detonation cellular structures in H2O2Ar mixtures with OpenFOAM®

In the present work, the solver rhoCentralRfFoam, developed using the finite volume framework provided by OpenFOAM^®, is employed to perform numerical simulations of two-dimensional detonations. This solver uses the central scheme of Kurganov, Noelle, and Petrova for dealing with convective terms. Also, the detailed kinetic model for hydrogen oxidation of Marinov, Westbrook, and Pitz was used for properly defining chemically induced source terms, and the semi-implicit Bulirsh Stöer (SIBS) method was employed for solving the stiff ODE system required to compute the species' rates. The present study intends to investigate the solver's capability for computing cellular structures, which develop when non-planar detonations are propagating in confined mixtures. Interactions between waves, resulting from several ignition points, are used as perturbation sources for the onset of cellular structures. Numerical simulations allowed us to identify a well-shaped cellular structure and other different structures that are not clearly defined, close to the ignition sources. However, after extending the computational domain, convergence towards a unique cellular pattern is attained. Such cellular pattern compares with most of the available data. Also, in order to improve the presentation of cellular structures and their dynamic behavior, a numerical schlieren technique is utilized for some flow variables (e.g. vorticity and density).     

Synthesis of AlN nanopowder coated with a thin layer of C,using a thermal plasma reactor

High-purity nanocrystalline aluminum nitride powders were synthesized by using a 12?kW non-transferred arc plasma. The synthesis was conducted in a versatile, new designed, one-chamber thermal plasma reactor (TPR). The novel experimental assembly incorporated better working conditions like: high temperature gradient between the crucible and reactor's wall, and high super-saturation of the system by nitrogen and carbon. Thermodynamic modelling of the synthesis was conducted in order to achieve the best conditions for AlN formation. In this study, aluminum discs of Al 1100 were used as precursor material and pure nitrogen was the only gas used as reagent and plasmogenic gas.Nanopowders collected from reactor's wall were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-Ray diffraction (XRD). Synthesized h-AlN nano-powders were found to be free of oxides and aluminum metal. A thin carbon-layer around the particles was detected. TEM results indicated that the carbon-layer was around 5 and 10?nm. This outcome could make a significant difference with other synthesis reported in the literature since the occurrence of the carbon-layer, could delay AlN oxidation, prevent hydration, and could avoid the agglomeration of the particles.     

Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry