A Survey on Advanced Multiple Access Techniques for 5G and Beyond Wireless Communications

Wireless Personal Communications - This paper summarizes the ongoing research initiatives based on the advanced multiple access techniques towards the fifth generation (5G) wireless communication...     

Influence of Hydrostatic Pressure and Humidity on Superplastic Ductility of Two β-Spodumene Glass-Ceramics

The extent of superplastic deformation in two lithium aluminosilicate glass-ceramics was found to be limited either by intergranular cavitation or by the initiation and growth of surface cracks. Tensile tests were performed under a superimposed hydrostatic pressure to distinguish between the two failure mechanisms. Two materials, one with a high flow stress and the other with a low flow stress, were studied. Cavitation was substantially suppressed by hydrostatic pressure in both materials. The strain-to-fracture, however, was enhanced only in the material with the lower flow stress. (In at least one instance the tensile ductility became almost infinite.) In the material with the higher flow stress, failure was caused by the initiation and propagation of cracks from the surface. The crack-propagation mode of failure was found to be sensitive to humidity, raising the possibility of stress-corrosion cracking at high temperatures in glass-ceramic materials.     

SIMULATION OF FILLING AND EMPTYING IN A HEXAGONAL-SHAPE SOLAR GRAIN SILO

ABSTRACT

A new silo design for grain-storage is examined using a numerical procedure to model its 3D granular flows during the filling and emptying processes. The authors in Hemández-Cordero, et al. Korea-Australia Rheol. J. 12(1)269-281(2000)] have previously presented the design of the new silo and its observed flow behavior. Its main characteristic is the almost complete elimination of excessive dynamics stresses. Since the required computational resources to model the transient phenomena in these experiments are enormous, here, we present basic numerical results related to packing and dynamics of grains considering this complex design. Especial emphasis is given to simulate in great detail collisions of spherical grains with the walls, between themselves, as well as the complex geometry of the new silo, such as filling and unloading openings, inclined walls, etc. The interactions include compressive normal forces between grains as well as tangential forces involved in sliding and rolling between two kernels. Virtual contact mechanics valid in the vicinity of the symmetry plane of the silo are also prescribed, permitting predictions closer to experimentally observed behavior. In spite of the complexity of interactions, steady flow patterns results obtained with reasonable computational times are presented.     

Efficient strategy for checkpointing in a transaction oriented database and its performance evaluation

A new efficient checkpointing strategy for a transaction oriented database system that operates in a stable on-line environment is proposed. Detailed experimental results are reported to evaluate the performance of the proposed scheme in terms of different system parameters.     

A new semi-empirical sea spectrum for estimating the scattering coefficient

A large data base comprising SEASAT A satellite scatterometer measurements and quasi-concurrent high quality sea wind data, as represented by Britt and Schroeder (1984) in the form of a multivariate regression, has been used to tune the overall magnitude of the assumed sea spectrum by inverting the two scale scattering theory. Scattering coefficient values computed for the derived spectrum have been compared with those computed for the spectrum suggested by earlier authors, and an improvement is found in the surface wind-scattering coefficient relationship as verified by comparison with the independent AAFE RADSCAT data set.     

Kinetics of Precipitation of α-Al2O3 in Polycrystalline Supersaturated MgO - 2Al2O3 Spinel Solid Solution

Supersaturated polycrystals of solid-solution spinel were heat-treated below the solvus temperature. Precipitation of α-alumina was examined by X-ray diffraction, microprobe, and scanning transmission electron microscopy. Precipitation kinetics followed classical time-temperature-transformation behavior: the precipitation rate was growth controlled at large undercoolings and nucleation controlled at low undercoolings. Scanning transmission electron microscopy and microprobe analysis revealed that the growth of precipitates was limited by interface reaction. Nucleation occurred throughout the polycrystal and was probably promoted by the grain boundaries. Precipitation was accompanied by the growth of pores at interfaces, presumably to accommodate the change in volume required by the phase transformation. Our observations in polycrystals contrast sharply with single-crystal work, where it has been reported that nucleation occurs at the free surface and that the formation of α-alumina is preceded by metastable phases.     

Antibacterial and dye degradation potential of zero‐valent silver nanoparticles synthesised using the leaf extract of Spondias dulcis

The present study reports a simple and low cost synthesis of zero‐valent silver nanoparticles (ZVSNPs) from silver nitrate using the leaf extract of Spondias dulcis. The ZVSNPs showed a unique peak at 420 nm in UV–vis spectrum. The SEM image portrayed cuboidal shaped particles. The EDX spectrum designated the elemental silver peak at 3 keV. In XRD, a sharp peak at 32.47° denoted the existence of (1 0 1) lattice plane and the average crystallite size was calculated as 48.61 nm. The lattice parameter was determined as 0.39 nm. The FTIR spectra of the leaf extract and ZVSNPs showed shifts in the specific functional group bands which ascertained the involvement of phytoconstituents in the formation and capping of nanoparticles. The average hydrodynamic size was measured as 59.66 nm by DLS method. A low PDI, 0.187 witnessed the monodispersity. A negative zeta potential value of −15.7 mV indicated the negative surface charges of the nanoparticles. The bactericidal action of ZVSNPs was demonstrated against two pathogens S.typhimurium and E.coli during which a dosage dependent zone of inhibition results was observed. Additionally, the catalytic potential of ZVSNPs was examined for the degradation of methylene blue dye in which an accelerated degradation of the dye was observed.Inspec keywords: antibacterial activity, crystallites, electrokinetic effects, scanning electron microscopy, nanoparticles, particle size, ultraviolet spectra, X‐ray chemical analysis, microorganisms, light scattering, nanofabrication, materials preparation, X‐ray diffraction, visible spectra, silver, dyes, Fourier transform infrared spectraOther keywords: wavelength 420.0 nm, Ag, voltage ‐15.7 mV, size 59.66 nm, size 0.39 nm, size 48.61 nm, electron volt energy 3.0 keV, Fourier transform infrared spectra, methylene blue dye, bactericidal action, dynamic light scattering, lattice parameter, Escherichia coli, Salmonella typhimurium, Spondias dulcis, negative zeta potential, polydispersity index, crystallite size, leaf extract, X‐ray diffraction, energy dispersive X‐ray spectrum, cuboidal‐shaped particles, scanning electron microscopy image, ultraviolet–visible spectrum, silver nitrate, zero‐valent silver nanoparticles     

INVITED REVIEW STABILITY OF COLLOIDAL DISPERSIONS

The stability of colloidal dispersions has traditionally attracted considerable attention in the chemical literature because of its origins in the physical chemistry of electrostatic and steric interactions between surfaces immersed in liquids. Moreover, progress in the physics and chemistry of stability phenomena has a direct impact on chemical engineering research, since stability of dispersions plays an important role in the rheology and transport properties of charged particles in liquids, separation processes (such as membrane filtration and solid/liquid separation), deposition and particulale fouling phenomena and numerous other processing operations. This paper presents a discussion of physical and chemical factors that affect colloidal stability and, in addition, presents an overview of the status of current research needs in this area. In addition to electrostatic and steric effects, some recent studies on the role of bulk motion of the supporting liquid on stability are also discussed. The emphasis throughout is on the stability of dilute dispersions, in which simultaneous interactions between more than two particles are negligible. Some major research needs in the above areas are also identified.