Adhesive and thermal characteristics of maleimide-functional novolac resins

A novel, addition-curable maleimide-functional novolac phenolic resin was evaluated for adhesive properties such as lap shear strength and T-peel strength using aluminium adherends, when thermally self-cured and cocured with epoxy resins. The adhesive properties of the self-cured resin, although inferior at ambient temperature, improved at high temperature and were found to depend on the cure conditions. When cocured with epoxy resin, the adhesive properties improved significantly and showed a strong dependence on the nature of the epoxy resin used, on the stoichiometry of the reactants, on the concentration of imide groups in the phenolic resin, and on the extent of polymerization of the maleimide groups. Optimum adhesive properties were obtained for novolac resins with a moderate concentration of maleimide groups, taken on a 1 : 1 hydroxyl–epoxy stoichiometry with a novolac epoxy resin. In comparison to the conventional novolac, the imide–novolac contributed to improved adhesion and better adhesive property retention at higher temperature when cured with the novolac–epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 695–705, 1999     

A modified mechanical activation synthesis for carbon-coated LiFePO4 cathode in lithium batteries

An efficient synthesis based on mechanical activation (MA) was developed for carbon-coated lithium iron phosphate (LiFePO₄/C). The conventional MA process was modified by introducing two initial steps of slurry phase blending of the ingredients and solvent removal by rotary evaporation, so as to get an intimate mixing and homogenous dispersion of conductive carbon in the sample. Phase-pure, nanometer-sized particles of the active material covered with a porous, nanometer-sized web of carbon were obtained. LiFePO₄/C exhibited remarkably good electrochemical properties when evaluated as cathodes in room temperature lithium cells. An initial discharge capacity of 166 mAh/g (corresponding to 97.6% of theoretical capacity) was achieved at 0.1 C-rate. A very stable cycle performance was also realized; good capacity retention up to 100 cycles was achieved at different current densities.     

Improved Cycle Properties of FeS2 Cathode Material with Metallic Additives

Iron disulfide （FeS2） cathode active material was prepared from iron and sulfur at room temperature by high energy mechanical alloying. Modified FeS2 composites containing Co or Ni transition metal powders as additives were also prepared by the same method. Lithium cells with these FeS2 cathodes were studied for charge-discharge properties at room temperature using 0 .5M LiTFSI in tetra （ethylene glycol） dimethyl ether （TEGDME） solvent. Cyclic voltammetry showed two anodic oxidation peaks at 1.8 and 2.5V and two cathodic reduction peaks at 2.0 and 1.3 V for FeS2 with metal additives. The addition of 5wt% Co and 3wt% Ni resulted in an enhancement of the first discharge capacity giving 571 and 844mAh/g respectively at 0.1C-rate. The cycle performance was also enhanced remarkably by the addition of these electrically conductive transition metals in the active material. FeS2 with 5wt% Co exhibited a stable cycle performance delivering a reversible capacity of 338mAh/g （37.8% of theoretical capacity） after 20 cycles.     

A ψ–ω finite element formulations for the Navier-Stokes equations

A new method of solving the two-dimensional Navier–Stokes equations by using the finite element method is proposed. The flow is represented by the stream function–vorticity formulation and the no-slip boundary conditions are explicitly introduced in the nonlinear equations. This formulation coupled with the Newton-Raphson method enables the study of stationary flows for high Reynolds number, without any convergence problem. A number of flow problems are analysed in order to demonstrate the efficiency of the present formulation.     

In Situ synthesis of inorganic filler‐filled polyethylene using polyethersulfone‐supported TiCl4 catalyst system

In situ ethylene polymerizations with inorganic fillers were performed using catalyst based on titanium tetrachloride supported on polyethersulfone. The inorganic fillers used were MgO, TiO₂, and CaCO₃, which were pretreated with cocatalyst (methylaluminoxine) for better dispersion onto the polymer matrix. The formation of polyethylene (PE) within the whole matrix was confirmed by Fourier transform infrared studies. The wide‐angle X‐ray diffraction profile of the synthesized PEs indicated the presence of crystalline region. It was found that the nature of inorganic filler did not have any remarkable effect on the melting characteristics of the polymer, but the degree of crystallinity of PE was found to be higher for TiO₂‐filled PE. The amount of filler incorporated into the matrix was also evaluated through thermogravimetric analysis, where TiO₂‐filled PE showed ～ 49% of filler material, which was also reflected in the higher productivity obtained by this system. The morphology of the filler‐filled PEs was different, whereas the elemental dispersion was found to be uniform on the surface as elucidated through energy‐dispersive X‐ray spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

PriMa: a comprehensive approach to privacy protection in social network sites

With social networks (SNs) allowing their users to host large amounts of personal data on their platforms, privacy protection mechanisms are becoming increasingly important. The current privacy protection mechanisms offered by SNs mostly enforce access control policies based on users’ privacy settings. The task of setting privacy preferences may be tedious and confusing for the average user, who has hundreds of connections (e.g., acquaintances, colleagues, friends, etc.) and maintains an extensive profile on his main SN. Hence, users often end up with policies that do not sufficiently protect their personal information, thus facilitating potential privacy breaches and information misuse. In this paper, we propose PriMa (Privacy Manager), a privacy protection mechanism that supports semiautomated generation of access rules for users’ profile information, filling the gap between the privacy management needs of SN users and the existing SNs’ privacy protection mechanisms. PriMa access rules are generated using a multicriteria algorithm, so as to account for an extensive set of criteria to be considered when dealing with access control in SN sites. The resulting rules are simple yet powerful specifications, indicating the adequate level of protection for each user, and are dynamically adapted to the ever-changing requirements of the users’ preferences and SN configuration. We have implemented PriMa on a Drupal platform and as a third-party Facebook application. We have evaluated the performance of the PriMa application with respect to access rule generation.     

Synthesis and electrochemical characterisation of electrospun lithium titanate ultrafine fibres

The phase pure spinel lithium titanate (Li₄Ti₅O₁₂) in the form of ultrafine fibre was synthesised by the combination of sol–gel and electrospinning techniques. The electrospinning process for the preparation of Li₄Ti₅O₁₂ precursor was optimised to get bead-free fibrous mat with uniform thickness. Crystalline Li₄Ti₅O₁₂ in the form of ultrafine fibre was synthesised by the calcination of the precursor at 800 °C in air for 4 h. The material was characterised by X-ray diffraction, Raman spectroscopy and scanning electron microscopy and subsequently evaluated as an electrode active material using Li metal as a counter electrode. The material exhibited a first cycle specific capacity of 154 mAh g^?1 with good rate capability and cyclability.     

A Low-Complexity Uniform and Non-uniform Digital Filter Bank Based on an Improved Coefficient Decimation Method for Multi-standard Communication Channelizers

It has been shown in literature that the coefficient decimation (CD) techniques can be efficiently used to realize low-complexity finite impulse response (FIR) filters with flexible frequency responses. In this paper, we propose a novel filter bank (FB) design technique based on the combination of the conventional coefficient decimation method (CDM) and the modified coefficient decimation method recently proposed by us. In the proposed FB, subbands of desired bandwidths are obtained by the spectral subtraction of the lowpass and highpass frequency responses obtained after performing CD operations on the prototype filter, using appropriate decimation factors. The proposed FB that provides uniform as well as non-uniform subbands can be used for multi-standard channelization in wireless communication receivers. We show that the proposed FB has a significantly lower complexity along with superior stopband and transition band characteristics when compared with the conventional CDM-based progressive decimation filter bank (PDFB). The design example shows that the proposed FB offers 74 % reduction in multiplication complexity over the PDFB, when used for non-uniform multi-standard channelization with a fixed frequency channel distribution. If the same FB is used for multi-standard channelization with variable locations of the frequency channels, a substantial 95.67 % reduction in multiplication complexity is achieved over the PDFB.     

STUDY OF A LABORATORY-SCALE FROTH FLOTATION PROCESS USING ARTIFICIAL NEURAL NETWORKS

A three-layer feed-forward artificial neural network (ANN) model, trained using the error back propagation algorithm, has been established to simulate the froth flotation process for the beneficiation of coal fines. The network model validates the experimentally observed qualitative and quantitative trends. The optimal model parameters in terms of network weights have been estimated and can be used to compute the parameters of the coal flotation process over wide-ranging experimental conditions.