A study of the creep effect upon the response of a pressure sensor embedded in an ice sheet

A new numerical incremental analysis is presented for the viscoelastic bridging response of a pressure sensor embedded in an ice sheet. The analysis takes into account the effect of the time dependent creep response of both the ice sheet and pressure sensor upon the ratio between measured stress and undisturbed stress (called the registration ratio or inclusion factor). The effect of the sensor dimensions, sensor stiffness, elastic modulus of ice, creep properties of the sensor and ice, and rate of loading on the registration ratio is presented.A daily algorithm is also presented, which can be used to interpret the field data obtained using the pressure sensor by predicting the daily change in the base line (zero pressure) due to creep behaviour of the panel.     

Spermine Derivatives of Indole-3-carboxylic Acid,Indole-3-acetic Acid and Indole-3-acrylic Acid as Gram-Negative Antibiotic Adjuvants

The discovery of new antibiotic adjuvants is an attractive option for overcoming antimicrobial resistance. We have previously reported the discovery of a bis-6-bromoindolglyoxylamide derivative of spermine as being able to enhance the action of antibiotics against Gram-negative bacteria but suffers from being cytotoxic and red-blood cell haemolytic. A series of analogues was prepared exploring variation of the indolglyoxylamide unit, to include indole-3-acrylic, indole-3-acetic and indole-3-carboxylate units, and evaluated for antibiotic enhancing properties against a range of Gram-negative bacteria, and for intrinsic antimicrobial, cytotoxic and haemolytic properties. Two spermine derivatives, bearing 5-bromo-indole-3-acetic acid ( 17 ) and 5-methoxy-indole-3-acrylic acid ( 14 ) end groups were found to exhibit good to moderate antibiotic adjuvant activities for doxycycline towards the Gram-negative bacteria Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae, but with more modest intrinsic antimicrobial activity and greatly reduced cytotoxic and haemolytic properties. The mechanism of action of the latter derivative identified its ability to disrupt the outer membranes of bacteria and to inhibit the AcrAB-TolC efflux pump directly or by inhibiting the proton gradient.     

UV-waterborne polyurethane-acrylate nanocomposite coatings containing alumina and silica nanoparticles for wood: mechanical, optical, and thermal properties assessment

The effect of alumina and silica nanoparticles on mechanical, optical, and thermal properties of UV-waterborne nanocomposite coatings was investigated. The addition of nanoalumina and nanosilica was shown to decrease the hardness because of nanoparticle aggregation. In comparison to the neat coating and despite the presence of aggregates, the scratch resistance of nanocomposite coatings was significantly improved. As expected, the gloss of UV-waterborne coatings was reduced following the addition of nanoparticles due to an increase of the surface roughness. Alumina and silica nanoparticles were found to enhance the glass transition temperature of PUA nanocomposite coatings by hindering the mobility of macromolecular chains at the interface around the nanoparticles. Finally, the interest and efficiency of grafting trialkoxysilanes was demonstrated with the study of nanosilica behavior. Not only was the dispersion of nanosilica enhanced following trialkoxysilanes grafting onto silica nanoparticles, but also the scratch resistance and the adhesion of UV-waterborne coatings containing nanosilica markedly increased even with 1 wt% content. Silica which is recommended in the wooden furniture and kitchen cabinet manufacturing industry as nano-reinforcement provides improved properties well suited in surface coating applications to efficiently protect surface of wood substrates.     

Kinetic studies of UV-waterborne nanocomposite formulations with nanoalumina and nanosilica

UV-waterborne coatings are gaining in popularity because of their environment friendly advantages. Most of the mechanical properties of such coatings are lower in comparison with high solids content UV coatings. For these reasons a nanocomposite-based approach was followed and seems promising in order to promote the use of UV-waterborne coatings in the wood products industry. The kinetic study of coatings gives interesting information regarding the curing process and photodifferential scanning calorimetry (photo-DSC) has proved its efficiency. The aim of this work was to study the photopolymerization kinetics by photo-DSC of a typical UV-waterborne coating formulation containing different amounts of nanoparticles. Formulations were mainly based on a polyurethane–acrylate (PUA) resin and a photoinitiator. Nanoalumina and functionalized nanosilica were added to the formulation at three concentrations: 1, 3 and 5 wt%. UV-waterborne formulations were dried during 10 min at 80 °C before curing under a UV source (47 mW/cm²). DSC-exothermic curves demonstrated that photopolymerization was less efficient when nanoparticles were introduced but the UV-curing of coatings based on functionalized nanosilica were better than those containing nanoalumina. Finally the kinetic profile of UV-waterborne coating formulations were characterized using an autocatalytic model and kinetic parameters k, m and n were determined.     

Alumina and zirconia acrylate nanocomposites coatings for wood flooring: Photocalorimetric characterization

Radiation curable coatings are presently the standard in wood flooring industries, although important improvements can still be brought to these coatings. In this work, nanocomposites coatings for wood flooring were prepared from various acrylate reactives. Nanoparticles were added in the neat acrylate formulation prepared from two acrylate monomers, two acrylate oligomers, a defoaming agent and a photoinitiator. Particle size characterization was performed by a dynamic light scattering technique. Reinforcing agents and coupling agents addition effects on acrylate resin conversion were studied by photo-calorimetry (photo-DSC). For each nanocomposite sample, heat of reaction and induction time were determined from exotherms and these datas were used to study the effects of reinforcing agents and coupling agents on curing kinetics of radiation curable nanocomposite coatings. Photo-DSC studies show that nanoparticles and coupling agent clearly affect coatings polymerization. In fact, zirconia nanoparticles tend to decrease polymerization. Alumina nanoparticles do not affect negatively curing coatings. Silane coupling agent affects positively the curing of acrylate coatings, although zirconate coupling agent tends to decrease it.     

Triplet markov fields for the classification of complex structure data

We address the issue of classifying complex data. We focus on three main sources of complexity, namely the high dimensionality of the observed data, the dependencies between these observations and the general nature of the noise model underlying their distribution. We investigate the recent Triplet Markov Fields and propose new models in this class designed for such data and in particular allowing very general noise models. In addition, our models can handle the inclusion of a learning step in a consistent way so that they can be used in a supervised framework. One advantage of our models is that whatever the initial complexity of the noise model, parameter estimation can be carried out using state-of-the-art Bayesian clustering techniques under the usual simplifying assumptions. As generative models, they can be seen as an alternative, in the supervised case, to discriminative Conditional Random Fields. Identifiability issues underlying the models in the non supervised case, are discussed while the models performance is illustrated on simulated and real data exhibiting the mentioned various sources of complexity.     

Geometric effects in high‐temperature vapour‐phase lubrication using hydrocarbon feed gases

The effectiveness of ‘far‐field’ vapour‐phase lubrication, in which areas of a bearing surface that are cycled through the contact are exposed to vapour while outside the contact, has been demonstrated in both sliding and combined roll slide tests using acetylene vapours to deposit pyrolytic graphite. Friction coefficients as low as μ = 0.008 have been measured for steel at 540°C with far‐field acetylene concentrations as low as 5%. Effective vapour‐phase lubrication depends on solid lubricant deposition that exceeds the contact's capacity to remove solid lubricant through wear. While the rate of removal is increased by increasing the sliding velocity, in far‐field vapour‐phase lubrication the rate of lubricant deposition, and therefore the lubrication effectiveness, is augmented by increased areas available for far‐field deposition, such as those provided by performing wear tests with increased wear‐track diameters. These geometric concepts may be considered in rolling‐element bearing and gear set applications where vapour‐phase lubrication is to be employed.     

Thermodynamic evaluation of the carbon-hydrogen system at high temperatures

A theoretical study of the C-H system reveals that, at high temperatures, many polymeric species have to be taken into account. Free energy functions of the species involved have been calculated to permit the evaluation of the equilibrium compositions of the system in both the heterogeneous and homogeneous regions. Pressures ranging from 0.1 to 10 atm. and carbon to hydrogen ratios from 0.5 to 20 were investigated between 2,000 and 6,000°K. Since the reaction of carbon vapor with hydrogen is highly exothermic, a reaction scheme was also developed whereby the endothermic heat of cracking of various hydrocarbons could be balanced by the former reaction. Several conditions related to a global heat of reaction have been considered.     

Surface shear stress relaxation of silica glass

A constant angle of twist was applied to silica glass rods in order to produce a torsional shear strain and a reduction in torque representative of the stress state in the glass was measured as a function of time when rods were heat-treated in air at temperatures, 550-700°C, far below the glass transition temperature. The monotonic decrease of torque with time was explained by surface stress relaxation, which can be described by a relaxation of stress at the surface of glass which is promoted by water. The obtained surface stress relaxation diffusion coefficients were consistent with those obtained earlier from silica glass fiber bending under a similar water vapor pressure. The observed relaxation in torsion supports the mechanism of surface stress relaxation over the swelling-based mechanism for applications including glass fiber strengthening.     

Ion‐Exchanged Lithium Aluminosilicate Glass: Strength and Dynamic Fatigue

Sodium for lithium and potassium for lithium ion‐exchanges of a lithium aluminosilicate glass were conducted and the resulting strength and dynamic fatigue characteristics were studied. Four‐point bend mechanical tests revealed that greater strengthening can be achieved by the potassium for lithium ion‐exchange, compared to the sodium for lithium ion‐exchange, and that the dynamic fatigue tendency is strongly suppressed by both exchanges. This suppression of dynamic fatigue characteristics of ion‐exchange strengthened glass was explained by the ability of the surface compressive layer to delay the onset of slow crack growth. Bulk stresses continue to increase in magnitude while the crack is arrested in the surface compressive stress region. Upon offsetting the surface compressive stress, the crack rapidly propagates into a high‐magnitude tensile stress field until the fracture toughness is reached, resulting in minimal crack growth prior to material failure. A slow crack growth model utilizing a fracture mechanics weight function was developed to simulate the experiments. Dynamic fatigue characteristics of the as‐received glass, without ion‐exchange treatment, were also measured and simulated for comparison.