Guidelines for the Application of Vacuum Contactors

The overvoltage phenomena associated with switching currents in vacuum and their effects on motor insulation are described in some detail, and a practical guideline for the application of overvoltage protective devices is presented.     

An analysis of the mechanical behavior of Al-Al3Ni composites

Commercial purity Al-Al₃Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10^-3 to 1.0 mm/s. The composites were tested in tension and in compression and the results were analyzed using a simple model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing, and discontinuity and premature fracture of fibers. The theoretically predicted values of the tangent modulus and strength in tension and compression were shown to closely fit the experimental results up to a growth rate of about 0.3 mm/s. Beyond this value, the excessive misalignment of the fibers caused some deterioration in the mechanical properties and a change in the mode of fracture. It has been concluded that the elastic constrained matrix exerts considerable effect on the mechanical properties thus providing an effective means of improving them by increasing the surface area of the fiber-matrix interface.     

Molecular Detection of Mycotoxigenic Fungi in Foods: The Case for Using PCR-DGGE

Among the toxin-producing microbes, those that produce mycotoxins are especially problematic due to their broad distribution in the environments and in foods. Several species of Aspergillus, Penicillium, and Fusarium are sources of potent mycotoxins such as aflatoxins, ochratoxins, patulin, deoxynivalenol, and fumonisins. It is, therefore, vital that mycotoxigenic fungi contaminants in food are rapidly and accurately identified for ensuring the safety of consumers. Most of the current methods are based on PCR using gene-specific or species-specific primers. However, contaminating microbes often compose a complex community and PCR-DGGE may provide a better approach than traditional single-gene and/or single-species based methods. It provides “fingerprints” for each microbial flora and has been widely used to analyze environmental and food-associated microbial communities. This review shows the advantages and disadvantages of different molecular methods for the detection of mycotoxigenic fungi including PCR-DGGE as a potent and applicable method that could overcome the difficulties associated with other methods.     

Flow patterns in a pilot plant-scale turbulent fluidized bed reactor: Concurrent application of tracers and fiber optic sensors

Hydrodynamics of a turbulent fluidized bed is studied by means of the concurrent application of fiber optic sensors and a helium tracer. It is observed that in the vicinity of the column wall there is a high bubble activity region. Low bubble activity and negative bubble velocities are reported for the dense phase near the column centre-line region. A temperature increase from 22 to 145°C results in a more homogeneous turbulent fluidized bed with smaller bubbles and more gas flowing through an expanded dense bed emulsion phase. Mass transfer coefficients between bubble-emulsion (k_be) and bubble-annulus (k_ba) are evaluated. The dominant mass transfer path was the one from the bubbles to the annular region with k_ba being several times greater than k_be.     

Novel composite sandwich structure from green materials: Mechanical,physical, and biological evaluation

Flax and Jute fabrics were used as reinforcements with polyester resin to form composite skins while poplar particleboard was used as a core for making composite sandwich structures by applying vacuum assisted resin transfer molding (VARTM) technique. Mechanical, physical, and biological properties of these novel composite sandwich structures were evaluated. The results showed that the proposed engineered panels have superior mechanical properties that are suitable for different structural applications compared with conventional particleboards. When compared with the control panels, significant enhancement on Modulus of elasticity (MOE) and Modulus of rupture (MOR) were achieved. On the other hand, the results indicated that the proposed panel composites exhibit better dimensional stability compared with poplar particleboard control panels. In addition, the proposed composite sandwich structures proved resistant against the decay fungi after 12 weeks of fungal exposure. Obviously, the developed composite panels could be used in a wide variety of applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42253.     

Computer-aided modeling of dielectric and ferroelectric properties

In this article the concept of charges fluctuating in double well potentials is used as a basis for a quantitative computer calculation of interactions between permanent dipoles. Numerical calculations are of advantage, because the dipole-dipole interaction energy can exceed the thermal energy. In this case nonlinearities can arise, which are difficult to treat analytically. Furthermore, a numerical recalculation of the Lorentz field resulting from induced dipoles has been carried out. Within the Lorentz calculation of the local field, two models are used in juxtaposed position: a discrete model, which takes account of dipoles inside a conceptual sphere, and a continuum model, which treats the dipoles outside this sphere as a continuum. Using both models the local field at the center dipole of the sphere is calculated. It is shown that several dielectric and ferroelectric properties can be calculated using very simple model assumptions     

Digitally programmable switched-current FIR filter for low-voltageapplications

In this paper, we describe a switched-current (SI) finite-impulse response (FIR) filter, suitable for equalizer architectures. The basic cell of the FIR filter is a SI sample-hold (S/H) circuit, appropriate for low-voltage operation. The programmability of the FIR filter structure is achieved via MOSFET-only current dividers. The FIR filter has been designed and implemented using a 0.8 μm CMOS process and operates at a power-supply voltage of 2 V     

Effect of grain size on the primary and secondary creep behavior of Sn–3 wt.% Bi alloy

The effect of grain size as well as creep temperature on the primary and secondary creep parameters of Sn–3 wt.% Bi alloy has been studied. It was found that the creep parameters α, β, and έ _s were decreased with increasing grain size. This was explained in view of the dislocation interaction with the defects and different inclusions in the matrix. For both the primary and secondary creep, the activation energies estimated indicate that the rate-controlling mechanism is the grain boundary-sliding mechanism.     

Fabrication and electrical characterization of n-InSb on porous Si heterojunctions prepared by liquid phase epitaxy

Thin films of InSb were grown on p-type porous silicon (PSi) (1 1 1) substrates by liquid phase epitaxy (LPE) to obtain monocrystalline InSb epilayer on a PSi substrate for low cost device applications. The structural characterization of the devices was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction measurements indicate that InSb monocrystalline epilayer was successfully grown onto PSi. The current-voltage (I-V) characteristics of n-InSb/p-PSi heterojunction devices were measured in the temperature range of 298-398 K. The measurements indicate that these heterojunctions have good rectifying characteristics. The estimated zero-bias barrier height φ_BO and the ideality factor η show strong temperature dependence. The conventional Richardson plot exhibits linear behavior in the entire temperature range indicating that the conduction seems to be predominantly due to thermionic emission mechanism. In addition, the capacitance-voltage characteristics are investigated at frequency of 1 MHz. The built-in potential of the heterojunction is determined after eliminating the effect of the capacitance effect of the interface state caused by the lattice mismatch.