Viscoelastic and mechanical properties of multi walled carbon nanotube/epoxy composites with different nanotube content

The viscoelastic and mechanical properties of composites multi walled carbon nanotube (MWNT)/epoxy at different weight fractions (0.1, 0.5, 1 and 2 wt.%) were evaluated by performing tensile and dynamic-mechanical thermal analysis (DMTA) tests. The MWNT/epoxy composite were fabricated by sonication and a cast molding process. The results showed that addition of nanotubes to epoxy had significant effect on the viscoelastic and mechanical properties. However, the use of 0.5 wt.% increased the viscoelastic properties more significantly. Concerning viscoelastic modeling, the COLE–COLE diagram has been plotted by the results of DMTA test. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite.     

Heat transfer enhancement by metal screens and metal spheres in phase change energy storage systems

This study focuses on heat transfer enhancement in double pipe energy storage system. Enhancement is achieved by use of metal screens/spheres placed inside the phase change material (PCM), which is paraffin wax and results in increasing the effective thermal conductivity of the combined media of PCM and metal screens/spheres. The experiments are conducted as a function of the diameter and number of spheres inserted in the phase change material. Also, the experiments investigate the effect of increasing the temperature of the heat transfer fluid (HTF). Results are presented in terms of variations in the PCM Nusselt number and the melting Fourier number. Results indicate three-fold decrease in the Fourier number and similar increase in the Nusselt number. Replacing 2-volume percentage of the wax material by the metal spheres results in this large enhancement.     

Sparsity-motivated automatic target recognition

We present an automatic target recognition algorithm using the recently developed theory of sparse representations and compressive sensing. We show how sparsity can be helpful for efficient utilization of data for target recognition. We verify the efficacy of the proposed algorithm in terms of the recognition rate and confusion matrices on the well known Comanche (Boeing-Sikorsky, USA) forward-looking IR data set consisting of ten different military targets at different orientations.     

CdTe quantum dots and polymer nanocomposites for x-ray scintillation and imaging

Investigations are reported on the x-ray scintillation and imaging application of CdTe quantum dots (QDs) and their polymer nanocomposites. Aqueous CdTe QDs with emissions ranging between 510 and 680 nm were prepared and incorporated into polyvinyl alcohol or polymethyl methacrylate polymer matrices. The x-ray luminescent properties were evaluated and a resolution of 5 lines∕mm was obtained from the nanocomposite films. Additionally, the fast decay time, nonafterglow, and superior spectral match to conventional charge coupled devices, show that CdTe QD nanocomposites have high promise for x-ray imaging applications.     

Sand Control Measures and Sand Drift Fences

Sand drift and sand dune movements are typical logistic problems facing civilian and industrial cities in arid and semiarid countries like Saudi Arabia. Some of these countries are considered active when it comes to sand drift and sand dune movement, due to the high annual sand drift rate. Urban cities have extensive facilities in the middle of these active areas that require good protection and innovative solutions?to this problem. This paper briefly reviews sand movement control measures and highlights sand drift fence design guidelines for the first time.     

The PecT repressor interacts with regulatory regions of pectate lyase genes in Erwinia chrysanthemi

Erwinia chrysanthemi is a broad host range phytopathogenic enterobacterium responsible for soft-rot disease of many plant species. The pecT gene encodes a repressor that negatively regulates the expression of virulence factors, such as pectinases, motility or exopolysaccharide synthesis. The cloned pecT gene was overexpressed using a phage T7 system. The purification of PecT involved the use of a TSK-heparin column and delivered the PecT protein that was purified to near homogeneity. The purified repressor displayed a 34 kDa apparent molecular mass. Gel-filtration experiments revealed that the PecT protein is a dimer. Band-shift assays demonstrated that the tetramer of the PecT protein could specifically bind in vitro to the regulatory regions of the pectate lyase genes with variable affinities. In addition, we demonstrated that PecT represses its own synthesis by interacting independently with two 200 bp regions, R1 and R2, located from -382 to -632 and -17 to -234, respectively, from the distal P1 promoter and from -465 to -715 and -100 to -317 from the P2 proximal promoter. We propose a model that explains the regulation exerted by PecT on its target genes and that integrates the phenotype obtained with a PecT overproducing pec-1 mutant or a pecT mutant.     

Synthesis of poly(methylmethacrylate)/montmorillonite nanocomposites via in situ intercalative suspension and emulsion polymerization

Summary Na-montmorillonite (MMT) with cation exchange capacity (CEC) of 90 mEq/100g was converted to MMT-CTAB and MMT-CPC forms by the intercalation of Cetyltrimethylammonium bromide (CTAB) and Cetylpyridinium chloride (CPC), respectively. The intercalation of these surfactants onto the basal space of the montmorillonite was evidenced by fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). The intercalation of the CPC expanded the basal space from 12.19 A^o to 21.47 A^o while in case of CTAB it was expanded to 19.35 A^o only. The (MMT-CPC) was subsequently used as a host for the preparation of PMMA nanocomposites via intercalative suspension and emulsion polymerization of methylmethacrylate (MMA) using benzoyl peroxide (BPO) and potassium persulphate (PPS) individually and simultaneously. The use of BPO and PPS together invoked better exfoliation but the yield did not change appreciably in comparison with using either of the initiators alone. Different structures were obtained with the variation of the preparation conditions; exfoliated and intercalated nanocomposites which were characterized by XRD, transmission electron microscope (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The resultant nanocomposites exhibited improved thermal stability relative to the equivalent macrocomposites. No glass transition temperature (Tg) could be detected for the prepared nanocomposites which was assumed to result from the restricted molecular motion of the polymer chains.     

Extending electrical resistivity measurements in micro-scratching of silicon to determine thermal conductivity of the metallic phase Si-II

The aim of this work to analyse the relationships between parameters of concrete surface geometry determined with various methods as well as their relations to adhesion in repair systems. Several types of concrete preparation techniques were selected to obtain different levels of surface roughness of concrete substrates. Four measurement techniques, corresponding to different levels of observation, have been used to characterize the surface geometry: laser profilometry, mechanical profilometry, a microscopic method and a “sand” (macroscopic) method. The correlations between parameters describing surface geometry are determined. The relationships between bond strength and selected parameters of surface geometry are also discussed.