Characteristics of aluminium metal foam for automotive applications

Closed cell aluminium foam has been examined with respect to crash protection systems, stiff and strong light weight structures and sound absorbing panels / enclosures for use in automotive systems. Monotonic compression tests revealed that the crash box made from aluminium foam-filled steel tube showed twice the energy absorption compared to empty crash box. Flexural studies on foam-filled thin walled aluminium extruded section showed higher resistance to bending (7.5 kN) against empty Al-section (5.8 kN). Differences in the mechanisms of deformation between foam filled sections and their empty counterparts were studied in compression and bend loading conditions. Acoustic behaviour was evaluated in the as-received foam and in foams post processed to increase cell interconnectivity. High sound absorption coefficients were observed in most conditions. The optimum combination of high sound absorption coefficient and frequency range occurred in a crushed foam with good cell interconnectivity.     

THERMOELASTIC PLANE WAVES WITHOUT ENERGY DISSIPATION IN A HALF-SPACE DUE TO TIME-DEPENDENT HEATING OF THE BOUNDARY

The linear theory of thermoelasticity without energy dissipation for homogeneous and isotropic materials is used to study plane waves in a half-space. The waves are supposed to be caused by a time-dependent heating of the stressfree boundary, which includes (i) sudden heating to a constant temperature, (ii) smooth heating for all times, (iii) smooth heating followed by sudden cooling, and (iv) smooth heating that becomes constant after a lapse of time, among its particular cases. The Laplace transform method is used to solve the problem. Exact solutions, in closed form, for the displacement, temperature, and stress fields are obtained and analyzed. Numerical results that illustrate the theoretical analysis are presented     

Effect of crossflow regulation by varying jet diameters in streamwise direction on jet impingement heat transfer under maximum crossflow condition

Jet impingement heat transfer has been studied numerically for a maximum crossflow condition using a 3?×?9 array of jets. Five-hole configurations have been studied for jet average Reynolds numbers ranging from 10,000 to 20,000. Crossflow has been mitigated by varying the jet diameters in the streamwise direction to reduce the impact of crossflow on downstream jet impingement. The design criteria for all five configurations were to keep the average of the jet diameters equal to the constant jet diameter configuration (baseline). It has been found that the configuration with increasing and then decreasing jet diameters provided higher levels of heat transfer with more uniform cooling when compared to the traditional constant diameter configuration and other configurations.     

A novel cost-effective approach to fabricate diopside bioceramics: A promising ceramics for orthopedic applications

The objective of the present study is to prepare low temperature diopside (CaMgSi₂O₆) ceramics from natural waste (Rice husk ash & eggshells) and study the physico-mechanical and in vitro biological properties. X-ray powder diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) and energy-dispersive spectrometry (EDS) were used to assess the crystalline phase, thermal behavior, microstructure, functional groups and composition, respectively. Degradation as well as mechanical stability was studied by testing the weight loss and compressive strength in dynamic mode of simulated body fluid (SBF) according to ISO 10993-14. The bioactivity of diopside samples was tested by means of ability and rate of apatite mineralization on the surface in static mode of SBF. Cytocompatibility by human osteoblast-like cells and their proliferation were studied using MTT assay. Results revealed that the pure phase of diopside was successfully attained at significantly low temperature (800 °C) with good mechanical properties, which were nearly similar to that of human cortical bone, and with enhanced mechanical stability. Diopside ceramics possessed apatite growth on its surface in SBF and exhibits excellent biocompatibility with MG-63 cells. These results suggested that prepared diopside can be a cost-effective bioceramics for potential orthopedic applications.     

Probing magnetic anisotropy and spin polarization in spintronic materials

Magnetic anisotropy and spin polarization are fundamental parameters in ferromagnetic materials that have use in spintronic device applications. As the need for screening properties of new magnetic materials rises, it is important to have measurement probes for quantities such as anisotropy and spin polarization. We have developed two unconventional yet powerful techniques to study these parameters. A resonant RF transverse susceptibility method is used to map the characteristic anisotropy and switching fields over a wide range in temperature and magnetic fields. For studies of spin polarization, the phenomenon of Andreev reflection across ferromagnet-superconductor junctions is used to extract values of the transport spin polarization. The effectiveness of these approaches is demonstrated in candidate spintronic materials such as half-metallic CrO/sub 2/ thin films and arrays of monodisperse, single-domain Fe nanoparticles.     

Thermoelastic interactions without energy dissipation due to a line heat source

Summary The linear theory of thermoelasticity without energy dissipation is employed to study thermoelastic interactions due to a continuous line source of heat in a homogeneous and isotropic unbounded solid. Laplace and Hankel transforms are employed to solve the problem. Exact expressions, in closed form, for the temperature and stress fields are obtained. Numerical results for a hypothetical, copper-like material are presented with the view of illustrating the theoretical results.     

Superparamagnetic Polymer Nanocomposites with Uniform Fe3O4 Nanoparticle Dispersions

Magnetic nanoparticles embedded in polymer matrices are good examples of functional nanostructures with excellent potential for applications such as electromagnetic interference shielding, magneto‐optical storage, biomedical sensing, flexible electronics, etc. Control over the dispersion of the nanoparticle phase embedded in a polymer matrix is critical and often challenging. To achieve excellent dispersion, competition between polymer–polymer and polymer–particle interactions have to be balanced to avoid clustering of particles in polymer nanocomposites. We report the first deposition of magnetic nanocomposite poly(methyl methacrylate)/polypyrrole bilayers from solution using spin‐coating. Fe₃O₄ nanoparticles have been synthesized using a chemical co‐precipitation route. Using a combination of dissolving the polymer and mixing fatty acid surfactant coated Fe₃O₄ nanoparticles, we have demonstrated the formation of nanocomposites with uniform nanoparticle dispersion. Cross‐sectional scanning electron microscopy, transmission electron microscopy, and magnetic measurements confirm the excellent dispersion and superparamagnetic response. Low‐frequency impedance measurements on these bilayers are also presented and analyzed.     

Reducing the impact of false time out on TCP performance in TCP over OBS networks

Random burst contention losses plague the performance of Optical Burst Switched networks. Such random losses occur even in low load network condition due to the analogous behavior of wavelength and routing algorithms. Since a burst may carry many packets from many TCP sources, its loss can trick the TCP sources to conclude/infer that the underlying (optical) network is congested. Accordingly, TCP reduces sending rate and switches over to either fast retransmission or slow start state. This reaction by TCP is uncalled-for in TCP over OBS networks as the optical network may not be congested during such random burst contention losses. Hence, these losses are to be addressed in order to improve the performance of TCP over OBS networks. Existing work in the literature achieves the above laid objective at the cost of violating the semantics of OBS and/or TCP. Several other works make delay inducing assumptions. In our work, we introduce a new layer, called Adaptation Layer, in between TCP and OBS layers. This layer uses burst retransmission to mitigate the effect of burst loss due to contention on TCP by leveraging the difference between round trip times of TCP and OBS. We achieve our objective with the added advantage of maintaining the semantics of the layers intact.     

Amplified on-chip fluorescence detection of DNA hybridization by surface-initiated enzymatic polymerization

We describe the incorporation of multiple fluorophores into a single stranded DNA (ssDNA) chain using terminal deoxynucleotidyl transferase (TdT), a template-independent DNA polymerase that catalyzes the sequential addition of deoxynucleotides (dNTPs) at the 3'-OH group of an oligonucleotide primer; we term this methodology surface initiated enzymatic polymerization (SIEP) of DNA. We found that long (>1 Kb) ssDNA homopolymer can be grown by SIEP, and that the length of the ssDNA product is determined by the monomer to oligonucleotide initiator ratio. We observed efficient initiation (≥50%) and narrow polydispersity of the extended product when fluorescently labeled nucleotides are incorporated. TdT's ability to incorporate fluorescent dNTPs into a ssDNA chain was characterized by examining the effect of the molar ratios of fluorescent dNTP to natural dNTP on the degree of fluorophore incorporation and the length of the polymerized DNA strand. These experiments allowed us to optimize the polymerization conditions to incorporate up to ~50 fluorescent Cy3-labeled dNTPs per kilobase into a ssDNA chain. With the goal of using TdT as an on-chip labeling method, we also quantified TdT mediated signal amplification on the surface by immobilizing ssDNA oligonucleotide initiators on a glass surface followed by SIEP of DNA. The incorporation of multiple fluorophores into the extended DNA chain by SIEP translated to a ~45 fold signal amplification compared to the incorporation of a single fluorophore. SIEP was then employed to detect hybridization of DNA, by the posthybridization, on-chip polymerization of fluorescently labeled ssDNA that was grown from the 3'-OH of target strands that hybridized to DNA probes that were printed on a surface. A dose-response curve for detection of DNA hybridization by SIEP was generated, with a ~1 pM limit of detection and a linear dynamic range of 2 logs.