Some applications of the WKB method to the wrinkling of bi-annular plates in tension

An application of WKB methods is proposed here for a stretched annular thin plate with piecewise-constant mechanical properties (also known as a bi-annular plate). Unlike the classical scenario involving only a simple annular such plate, in certain cases the neutral stability curve fails to be convex and the critical eigenmodes behave rather differently as the plate becomes progressively thinner (equivalent to ${\mu \to \infty}$ in our notations). On one side of this curve, the corresponding eigenmodes are localised near the inner rim of the annulus, while in the remaining part these functions are concentrated along the interface separating the two annular sub-regions. By using the asymptotic reduction technique proposed by Coman and Haughton in (Acta Mech 185:179–200, 2006), the original fourth-order three-point boundary-value problem is formally reduced to a pair of second-order differential equations coupled through a set of matching conditions at the interface. It is shown that for ${\mu \gg 1}$ the critical eigenvalues for both cases mentioned above can be approximated by solving a couple of simple transcendental equations and that the results predicted compare well with the direct numerical simulations of the original problem.     

On a class of non-smooth oscillators

The aim of this paper is to provide a unifying framework for several models of non-smooth oscillators with hysteresis which have attracted considerable interest in the engineering literature over the past three decades. By using the theory of maximal monotone operators in conjunction with a relatively recent result of Haraux and Ôtani (1990, Journal of the Mathematical Society of Japan , 42 : 277-294) we are able to characterize the attractors of these systems; in particular, it is shown that the study of their bounded orbits lies at the heart of understanding their possible dynamics. The interplay between material nonlinearity and viscous damping is analysed for a special case of the original model and some new features of this problem are revealed.     

Adsorption and Thermal Desorption of Volatile Organic Compounds in a Fixed Bed – Experimental and Modeling

Adsorption and thermal desorption dynamics of acetone in fixed-bed silica gel were studied experimentally and theoretically. The effect of process factors on adsorption and desorption performances was established. Acetone adsorption from air stream was performed by the dynamic (flowing gas) method in a laboratory setup at two levels of air superficial velocity (0.7 and 1.7 cm s^?1), temperature (30 and 40°C), and adsorbent particle diameter (0.21 and 0.54 cm). The values of saturation adsorption capacity (0.147–0.270 g g^?1) increased up to 78% and 36%, respectively, with a decrease in air velocity and adsorption temperature. Acetone thermal desorption from spent silica gel was studied in a thermobalance at three levels of process temperature (60, 70, and 80°C) and two values of particle size (0.21 and 0.54 cm). Equilibrium desorption efficiency (63–81%) was up to 14% larger for finer particles and increased with the desorption temperature. Kinetic models with relevant parameters adjusted based on experimental data were adopted to predict the dynamics of acetone adsorption and thermal desorption. The models simulated well the real conditions and could be applied to scale up and operate the adsorption columns used for air remediation.     

A new fabrication method of low stress PECVD SiNx layers for biomedical applications

A new fabrication method to produce low residual stress PECVD SiN_x layers at high deposition rates was developed and their biomedical applications were reported in this paper. This new method employed up to 600 W high power to fabricate low stress SiN_x layers in high frequency (13.56 MHz). By adjusting the composition of reactant gases, the residual stress can be lowered to 4 MPa and high deposition rate up to 320 nm/min can be achieved. In addition, this paper also investigated the influence of other important parameter, such as pressure, power and gases flow rates. Moreover, by using this optimized process, an 11 μm thick low stress SiN_x layer was produced, which will be used to fabricate large window area for cell culture. Finally, a successful cell culture test involving cultivating mouse stem cells onto the porous membrane made of these low stress PECVD SiN_x layers indicated that these layers are biocompatible and are suitable for biomedical applications.     

Implementing a New Group of TPW Cells as National Standard: Impact on Calibration Services

The definition of the kelvin is based on the triple-point temperature of highly pure water having the isotopic composition of ocean water (more specifically, the isotopic composition is equivalent to that of VSMOW). Belgian national metrology realizes the triple point of water (TPW) as the mean of temperatures measured in three sealed cells. In order to take into account the isotopic composition effect on TPW temperature, the ensemble of cells was replaced in 2006. Three new cells, with isotopic analysis of the contained water, were bought from different manufacturers. The new group of cells was compared to the old TPW national realization in order to quantify the effect of moving towards a new reference. Two different standard thermometers were used in all the cells to take 10 daily measurements on two different ice mantles. The measured resistances were corrected for hydrostatic head, self-heating, and isotopic composition (when available) before calculating the difference. A difference of about 87 μK was found between the old and the new national references. This difference is transferred to customers’ thermometers and cells through calibrations, and the change has to be documented in each new calibration certificate. An additional consequence of the new ensemble cell implementation is the significant reduction in the spread of deviations of individual cells from the mean temperature. The maximum difference between two cells of the ensemble is 96 μK for the old reference cells and 46 μK for the new reference cells corrected for isotopic composition effects.     

Edge-wave buckling of rolled elastic strips: asymptotic results

The problem considered in this paper concerns the edge-wave buckling phenomenon commonly encountered in forming processes such as rolling and levelling. Due to the combined action of global tensile forces and residual stresses, the elastic strips involved in these scenarios experience a symmetric short-wave deformation pattern that tends to be confined near their long edges. We use boundary-layer techniques to provide simple estimates for the critical load and the wavelength of the buckling waves. A number of complementary asymptotic features of the marginal stability curves are also reported.     

Audio based solutions for detecting intruders in wild areas

This paper presents an overview of the work that has been done in the field of wildlife intruder detection using only acoustic sensors. The motivation of such an application is related to protection of large wildlife regions, such as forests, lakes, and other natural reservations. The sounds of interest are represented by humans, engines, birds and animals. In order to simulate various environmental situations, different types of noisy environments have been considered. Both low complexity and standard audio classification methods are presented. Standard audio classification methods prove to be more robust, but at an expense of significantly increased complexity. Since low complexity systems are more feasible for monitoring remote areas, the complexity issue is discussed and solutions are proposed.     

Heating characteristics of western hemlock (Tsuga heterophylla) in a high frequency field

The research aimed to establish whether dielectric heating of wood at high frequency could be accomplished fast, without excessive temperature fluctuations and no wood degrade. The intention was to develop optimized dielectric heating schedules in order to effectively pasteurize green timbers and logs for export—an eco-friendly substitute to currently used toxic chemical method. Data analysis revealed that the electric field distribution within the specimen was a strong function of its dielectric properties. Specifically, homogeneous moisture contents generated constant electric field values while heterogeneous distributions generated sudden drops and raises of the electric field strength with heating uniformly dispersed due to a fast redistribution from hot to colder areas. Convection losses through air contact may reduce the average heating rate of the timber shell by about 50%.     

Modeling Shrinkage Response to Tensile Stresses in Wood Drying III. Stress—Tensile Set Correlation in Short Pieces of Lumber

This article reports on the correlation between tensile stresses, temperature, and target moisture content in short pieces of lumber based on relationships developed on experiments made on small wood strips subjected to different types of restraints. Linear motion position sensors were placed around a tested specimen using a frame connected to a support body. A wireless moisture and temperature monitoring system was used to record wood moisture and temperature changes. All measurements were performed perpendicular to fiber grain while drying at 40, 60, and 80°C in an environment set for a target moisture content of 5%; the experiments were stopped when the average moisture content of the lumber was around 10%. High stress values were obtained for specimens dried at 60°C and a low relative humidity, whereas a high reduction in stress level could be obtained for 80°C. The findings are intended to be used in further studies of the shrinkage process as an indicator of the tensile stresses generated in the early stages of wood drying.