An adaptive isogeometric analysis meshfree collocation method for elasticity and frictional contact problems

A collocation method has been recently developed as a powerful alternative to Galerkin's method in the context of isogeometric analysis, characterized by significantly reduced computational cost, but still guaranteeing higher-order convergence rates. In this work, we propose a novel adaptive isogeometric analysis meshfree collocation (IGAM-C) for the two-dimensional (2D) elasticity and frictional contact problems. The concept of the IGAM-C method is based upon the correspondence between the isogeometric collocation and reproducing kernel meshfree approach, which facilitates the robust mesh adaptivity in isogeometric collocation. The proposed method reconciles collocation at the Greville points via the discretization of the strong form of the equilibrium equations. The adaptive refinement in collocation is guided by the gradient-based error estimator. Moreover, the resolution of the nonlinear equations governing the contact problem is derived from a strong form to avoid the disadvantages of numerical integration. Numerical examples are presented to demonstrate the effectiveness, robustness, and straightforward implementation of the present method for adaptive analysis.     

Materials in harnessing solar power

Harnessing renewable solar energy through different technologies is greatly dependent on the advancement of solar grade materials’ science and engineering. In this article, the prominent solar energy technologies, namely solar photovoltaic and concentrated solar power and other relevant technologies, and aspects related to various solar grade materials, influence of nanomaterials on enhancement of solar energy harvest, technology–market relations, development of hybrid systems etc., are discussed. The inspiration to write this article is not only to review the existing technologies to harvest solar energy but also to highlight the pertinent and possible solutions thereof, especially from materials perspective.     

Synthesis of Composite Nanosheets of Graphene and Boron Nitride and Their Lubrication Application in Oil

Composite nanosheets of graphene and boron nitride have been produced in large quantities for the first time using high‐energy ball milling in ammonia gas as an exfoliation agent. The anti‐wear properties of the composite nanosheets as a lubricant additive are investigated via a four‐ball method. The results show that the composite nanosheets are exfoliated from the commercial graphite and h‐BN powders and combined into graphene/BN composite nanosheets during the ball milling process. The composite nanosheets formed have diameters larger than 200 nm and consist of heterostructures of approximately 10 monolayers of graphene and BN. The composite nanosheets exhibit better wear resistance and friction reduction properties than the homogeneous nanosheets because of the stronger interaction between graphene and BN nanosheets, which can effectively improve the anti‐wear properties of mineral base oil as a lubricant additive.

     

Performance analysis of IEEE 802.11 DCF with stochastic reward nets

In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11‐based wireless local area networks (WLANs). We consider the distributed co‐ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN‐based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on–off traffic model and taking into account the freezing of the back‐off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimal relay functionality for SNR maximization in memoryless relay networks

We explore the SNR-optimal relay functionality in a mernoryless relay network, i.e. a network where, during each channel use, the signal transmitted by a relay depends only on the last received symbol at that relay. We develop a generalized notion of SNR for the class of memoryless relay functions. The solution to the generalized SNR optimization problem leads to the novel concept of minimum mean squared uncorrelated error (MMSUE) estimation. For the elemental case of a single relay, we show that MMSUE estimate is a scaled version of the MMSE estimate. This scheme, that we call estimate and forward (EF), performs better than the best of amplify and forward (AF) and demodulate and forward (DF) in both parallel and serial relay networks. We determine that AF is near-optimal at low transmit power in a parallel network, while DF is near-optimal at high transmit power in a serial network. For hybrid networks that contain both serial and parallel elements, the advantage of EF over the best of AF and DF is found to be significant. Error probabilities are provided to substantiate the performance gain obtained through SNR optimality. We also show that, for Gaussian inputs, AF, DF and EF are identical     

Fuzzy database systems—challenges and opportunities of a new era

There have been significant theoretical advances in fuzzy database technology, yet commercially its successes have been negligible. This article examines the current state of this technology and suggests directions for future efforts. A framework for the analysis of fuzzy database technology is proposed and extant models are examined with reference to this framework. Fuzzy databases are studied in relation to the requirements of the database community. It is argued that new generation applications and object-oriented databases hold the key to the future commercial acceptability of this technology. © 1996 John Wiley & Sons, Inc.     

Antimicrobial susceptibility of starter culture bacteria used in Norwegian dairy products

Commercial starter culture bacteria are widely used in the production of dairy products and could represent a potential source for spread of genes encoding resistance to antimicrobial agents. To learn more about the antimicrobial susceptibility of starter culture bacteria used in Norwegian dairy products, a total of 189 isolates of lactic acid bacteria were examined for susceptibility to ampicillin, penicillin G, cephalothin, vancomycin, bacitracin, gentamicin, streptomycin, erythromycin, tetracycline, chloramphenicol, quinupristin/dalfopristin, ciprofloxacin, trimethoprim and sulphadiazine using Etest for MIC determination. Most of the isolates (140) originated from 39 dairy products (yoghurt, sour cream, fermented milk and cheese), while 49 were isolated directly from nine commercial cultures. The bacteria belonged to the genera Lactobacillus, Lactococcus, Leuconostoc and Streptococcus. Only one of the 189 isolates was classified as resistant to an antimicrobial agent included in the study. This isolate, a lactobacillus, was classified as high level resistant to streptomycin. The remaining isolates were not classified as resistant to the antimicrobial agents included other than to those they are known to have a natural reduced susceptibility to. Thus, starter culture bacteria in Norwegian dairy products do not seem to represent a source for spread of genes encoding resistance to antimicrobial agents.     

Diamond Synthesis from Graphite in the Presence of MnCO3

In order to investigate the catalytic effect of MnCO₃, a typical transition-metal carbonate, a graphite and MnCO₃ (60:40 by weight) mixture was subjected to temperature and pressure ranges of 6.5–7.7 GPa and 1700°–2100°C, respectively. Diamonds were synthesized from graphite in the presence of MnCO₃, at 2000°C and 7.7 GPa, where MnCO₃ was confirmed to be in a molten state. Although MnO was found to be decomposed from the samples that were subjected to the aforementioned PT conditions, no diamond formation was detected from an MnO and graphite system for identical experimental conditions. Therefore, it was concluded that MnCO₃ solvent catalyzed diamond formation from graphite.     

Structure–property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber

Amine functionalized multiwalled carbon nanotubes (a‐MWNT) based polypropylene (PP) composite fibers were prepared in the presence of polypropylene‐g‐maleic anhydride (PP‐g‐MA) by melt‐mixing followed by melt‐spinning with subsequent post‐drawing of the as‐spun fibers of varying draw ratio (DR). In order to enhance the interfacial interaction, a‐MWNT were utilized in combination with PP‐g‐MA during melt‐mixing. Fourier transform infrared spectroscopic analysis revealed the formation of imide bonds between MA functionality of PP‐g‐MA and amine functional group of a‐MWNT. Higher tensile properties of PP/a‐MWNT/PP‐g‐MA composite fibers were registered with varying DR of the as‐spun fiber. Orientation factors of a‐MWNT and PP chains along the fiber axis were correlated with the higher tensile modulus and tensile strength of PP/a‐MWNT/PP‐g‐MA composite fiber of varying DR. Crystallization studies indicated the role of hetero‐nucleating action of a‐MWNT in PP/a‐MWNT/PP‐g‐MA composite fiber. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Harnessing of bioelectricity in microbial fuel cell (MFC) employing aerated cathode through anaerobic treatment of chemical wastewater using selectively enriched hydrogen producing mixed consortia

The possibility of bioelectricity generation from anaerobic chemical wastewater treatment was evaluated in a microbial fuel cell (MFC) [dual-chambered; mediator less anode; aerated cathode; plain graphite electrodes] employing selectively enriched hydrogen producing (acidogenic) mixed culture. Performance of MFC was evaluated at two organic/substrate loading rates (OLR) (1.165 Kg COD/m³-day and 1.404 Kg COD/m³-day) in terms of bioelectricity production and wastewater treatment at ambient pressure and temperature under acidophilic microenvironment (pH 5.5) using non-coated plain graphite electrodes (mediatorless anode; air cathode). Experimental data demonstrated the feasibility of in situ bioelectricity generation along with wastewater treatment. The performance of MFC with respect to power generation and wastewater treatment was found to depend on the applied OLR. Maximum voltage of 716 mV (2.84 mA; OLR −1.165 kg COD/m³-day) and 731 mV (2.97 mA; OLR-1.404 kg COD/m³-day) was observed at stable operating conditions. Substrate degradation rate (SDR) of 0.519 Kg COD/m³-day and 0.858 Kg COD/m³-day was observed at two OLRs studied. Maximum power yield (0.73 W/Kg COD_R and 0.49 W Kg/COD_R) and current density (339.87 mA/m² and 355.43 mA/m²) was observed at applied 50 Ω resistance. Fuel cell performance was evaluated employing polarization curve (100 Ω-30 KΩ), Coulombic efficiency (€_cb) and cell potentials along with sustainable power yield at stable phase of fuel cell operation. Designed MFC configuration, adopted operating conditions and used parent inoculum showed positive response.