Study of the dimensional instabilities of laminated polypropylene films during heating treatments

Ensuring the geometrical stability of organic coatings is a key challenge for steel/polymer composites produced by the automotive industry to reduce the cars' weight. During the thermal treatment of painting, which exceeds the melting temperature of the organic part of the laminated film, polymer shrinkage may occur. It induces uncovered parts of the steel sheet which would present negative corrosion behavior in use. Two original and innovative experiments were presented. They enable to measure the deformation induced by the shrinkage and then to identify the microstructural mechanisms responsible for its appearance. Main results show strong influences of the macromolecular chains orientation induced by the film extrusion process and of the postheating parameters used to perform the painting curing. Raman spectroscopy and differential scanning calorimetry are used both to perform analysis of the microstructure evolution during heating treatments in terms of crystals melting, crystalline macromolecular chains disorientation, and volume damage healing. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Role of the Initiation Factors in mRNA Start Site Selection and fMet-tRNA Recruitment by Bacterial Ribosomes

Translation initiation is a complex, multi-step process of fundamental importance in all kingdoms of life, during which the start site of the genetic message transmitted in the form of an RNA molecule (mRNA) is selected, and the level of translation determined. Being the slowest step of protein synthesis, initiation is the phase most often subject to regulation. Here we review, in a historical perspective and focusing mainly on results from our laboratory, the development of our perception of the mechanisms by which the most relevant steps of this pathway occur in bacteria. In particular, we describe: (a) the mechanistics and kinetics of translation initiation; (b) properties of mRNAs with and without Shine–Dalgarno sequence relevant for initiation site selection and translational efficiency; c) ribosomal binding and dissociation of the initiation factors, formation and properties of translation initiation intermediates; (d) the mechanisms by which translation initiation fidelity is ensured. Finally, we provide a short survey of the known translation initiation inhibitors.     

Elastic moduli and damage evolution of three-axis woven fabric composites

Three-axis orthogonal woven fabric composites composed of carbon fibres and epoxy resin have been fabricated. Examined from micrographs, the fabric weaving yarns were found to be very slender with aspect ratios ranging from 11–13.6. Based upon the observed geometry, the composite has been modelled by a unit cell comprising wavy yarns. Both elliptical and lenticular cross-sections were adopted to simulate the slender weaving yarns. Taking into account one-dimensional stress concentration and yarn undulation, an iso-phase approach has been developed to analyse the composite elastic moduli. A higher weaving yarn aspect ratio was found to result in a lower modulus. Modulus reduction due to yarn undulation was more significant in weaving directions. Material characterization has been conducted based upon monotonic tensile and three-point flexural tests, and detailed damage mechanisms for both loadings have been examined. The onset of damage under tensile loading was found to be z-axis yarn debonding, followed by debonding and splitting in y-axis yarns. When subjected to flexural loading, yarn debonding, transverse cracking, and interyarn matrix cracking were the dominant damage mechanisms which appeared on specimen tensile sides. Stress transfer among yarns and how it relates to the composite damage have been discussed in detail. This revised version was published online in November 2006 with corrections to the Cover Date.     

Kinetics of azo‐initiated 1‐vinyl‐2‐pyrrolidone polymerizations at low conversions in aqueous media

The free‐radical polymerization behavior of 1‐vinyl,2‐pyrrolidone (NVP) was studied at low conversions, using capillary dilatometry. The aqueous media were kept at neutral pH and the studies were conducted isothermally, at 40 or 45°C. The azo‐type initiators used were 4,4′‐azobis‐4‐cyanopentanoic acid (ACPA), 2,2′‐azobisisobutyronitrile (AZBN), and 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)propane dihydrochloride] (ABDH). The monomer concentration and initiator concentration ranges were 1.17–2.34 mol L⁻¹ and 1–8 mmol L⁻¹, respectively. The rates of polymerization (R_p) and orders of reaction with respect to NVP and the initiator were evaluated and the kinetic equations were found to be R_p ∝ [NVP] [ACPA]^1.2; R_p ∝ [NVP] [AZBN]^1.1; and R_p ∝ [NVP]^2.2 [ABDH]^1.1. The polymers obtained were characterized by their viscosity numbers and correlation of the viscosity average molecular weights made with the type and amount of the azo initiator. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 239–246, 2000     

Intermetallic growth of wire-bond at 175°C high temperature aging

Two types of samples were applied in this wire-bond evaluation work for an Al-pad diffusion process. One was finished product for the cross-section examination of wire-bond and the other was without compound encapsulant used for the plane view examination of wire-bond interface. These samples were aged at 175 C in air from 0 h to 1008 h. It is found that the normal product which was ready on board existed ∼1 μm Au₂Al and Au₅Al₂ phases. The Au₂Al phase was then transformed to Au₅Al₂ phase in a 4 ∼ 72 h aging period. The Au₄Al phase formed along with the Au₅Al₂ phase in 72 h to 240 h aging period showing some porosity within the reacted phases. The total phase thickness increased to ∼4μm after 240 h aging. The Au₄Al phase became the major phase after 336 aging h. The reacted phase layer thickness increased to ∼6 μm and reached the steady state. A titanium-rich thin layer was also induced within the reacted phase layer. Three ternary phases as AlAu₂Ti, AlAuTi, and Al₂Au₂Ti are found in this titanium-rich layer. In particular, Al₂Au₂Ti could be a new phase.     

Computer code to predict the heat of explosion of high energy materials

The computational approach to the thermochemical changes involved in the process of explosion of a high energy materials (HEMs) vis-à-vis its molecular structure aids a HEMs chemist/engineers to predict the important thermodynamic parameters such as heat of explosion of the HEMs. Such a computer-aided design will be useful in predicting the performance of a given HEM as well as in conceiving futuristic high energy molecules that have significant potential in the field of explosives and propellants. The software code viz., LOTUSES developed by authors predicts various characteristics of HEMs such as explosion products including balanced explosion reactions, density of HEMs, velocity of detonation, CJ pressure, etc. The new computational approach described in this paper allows the prediction of heat of explosion (DeltaH(e)) without any experimental data for different HEMs, which are comparable with experimental results reported in literature. The new algorithm which does not require any complex input parameter is incorporated in LOTUSES (version 1.5) and the results are presented in this paper. The linear regression analysis of all data point yields the correlation coefficient R(2)=0.9721 with a linear equation y=0.9262x+101.45. The correlation coefficient value 0.9721 reveals that the computed values are in good agreement with experimental values and useful for rapid hazard assessment of energetic materials.     

Hydroquinone-O,O'-diacetic acid ('Q-linker') as a replacement for succinyl and oxalyl linker arms in solid phase oligonucleotide synthesis

When hydroquinone-O,Ooffiacetic acid is used as a linker arm in solid phase oligonucleotide synthesis, the time for NH4OH cleavage of oligodeoxy- or oligoribonucleotides is reduced to only 2 min. This allows increased productivity on automated DNA synthesizers without requiring any other modifications to existing reagents or synthesis and deprotection methods. The Q-linker may also be rapidly cleaved by milder reagents such as 5% NH4OH, potassium carbonate, anhydrous ammonia, t-butylamine or fluoride ion. However, the Q-linker is sufficiently stable for long-term storage at room temperature without degradation and no loss of material occurs during synthesis. The linker is also reasonably resistant to 20% piperidine/DMF, 0.5 M DBU/pyridine and 1:1 triethylamine/ethanol. The Q-linker can therefore serve as a general replacement for both succinyl and oxalyl linker arms.     

On the topography of fracture surfaces in bending–torsion fatigue

Fracture surfaces generated under combined bending–torsion fatigue loading in both the low-cycle fatigue and the high-cycle fatigue regions of specimens made of high-strength low-alloy Cr–Al–Mo steel are analysed in terms of topographical characteristics. Parameters reported here are the root mean square roughness, the number of peaks per unit length and the Hurst exponent quantifying various aspects of surface topography. As a main result of the analysis, the critical portion of torque beyond which the character of fracture topography significantly changes is estimated to be within the range of 40–50% of a total loading.     

Construction of XVCS for (k,n,t)∗ access structure

XOR-based Visual Cryptography System (XVCS) is developed to achieve high contrast and good resolution of the recovered secret image. In general (k,n) VCS, the secret image can be visualized only if k or more than k shares are stacked together. In (k,n,t)^? access structure, t number of participants are considered as the essential participants(t ≤ k ≤ n) whose shares are absolutely necessary to reconstruct the secret image. Several methods have been already proposed for the construction of (k,n)^? VCS for black and white images. The major focus of this work is to design an XVCS for (k,n,t)^? access structure for both black and white images and color images with maximum contrast. The experimental outcome shows that the proposed method has better results than other techniques proposed so far. Also, numerical examples are provided for (k,n,t)^? XVCS for t =?1 and 2. The XVCS designed for (k,n,t)^? access structure can be used for any real time application and is demonstrated with an example of user authentication in banking system.

     

Dynamic reblocking RSA-based multisignatures scheme for computerand communication networks

This investigation utilized dynamic reblocking to enhance the RSA-based multisignatures scheme and solve the moduli clashes problem. In contrast to other RSA-based multisignature schemes, the proposed scheme has fewer modular exponentiations operations, overcomes the signing order problem, and minimizes the keys requirements. Consequently, the proposed scheme is suitable for application to all computer communication network environments