Study of vibration and its effect on health of the motorcycle rider

The motorcycle riders are subjected to extreme vibrations due to the vibrations of its engine, improper structural design of the motorcycle and the bad road conditions. The literature review reveals that the vibrations are most hazardous to the health if it exceeds the limit. The experiments were conducted to measure the magnitude of the vibrations acting on the rider during motorcycle riding under various road conditions. Experimental values of accelerations and frequencies which are beyond permissible limits according to the literature confirm that vibration certainly affects health of the motorcycle rider

Mixed valency and anionogenic magnetism in alkali metal oxides

Magnetische eigenschappen alkali metaaloxides In zijn proefschrift beschrijft Shirakumara Giriyapura een onderzoek naar de magnetische eigenschappen van alkali metaaloxides. Het magnetisme in deze materialen is afkomstig van de zuurstof-atomen en niet, zoals gebruikelijk, van metaal-atomen. Giriyapura laat zien dat er veel overeenkomsten bestaan tussen het op zuurstof gebaseerd magnetisme en de veel bestudeerde magnetische overgangsmetalen. Het onderzoek concentreert zich op de synthese en eigenschappen van nieuwe alkali metaaloxides met gemengd superoxide (O2-) en peroxide (O22-) anionen. Dit verschil in ladingstoestand staat bekend als 'gemengde valentie' en is tot nu toe niet bestudeerd voor zuurstof. Gemengde valentie in overgangsmetalen is verantwoordelijk voor belangrijke eigenschappen zoals kolossaal magnetoweerstandsgedrag en supergeleiding. Nieuwe materialen zijn gesynthetiseerd door kationen te kiezen met een verschillende valentie zoals Ba2+ en K+ in Ba1-xKxO2, of door het zuurstofgehalte te variëren in b.v. AO2-x (A = alkali metaal). De koppeling tussen nabuur-superoxide en -peroxide anionen is in sommige verbindingen aanzienlijk en gaat gepaard met dynamische ladingsoverdracht. De ladingsoverdracht kan worden versterkt met externe stimuli zoals licht. Deze ladingsoverdracht is sterk gerelateerd aan de kristalstructuur en kan worden beïnvloed door het type kation en het zuurstofgehalte. Dit onderzoek opent nieuwe wegen voor de synthese van andere nieuwe gemengd valente zuurstofverbindingen met mogelijke eigenschappen die net zo rijk zijn als voor de overgangsmetaaloxides. This thesis investigates the magnetic properties of alkali metal oxides. These are unusual magnetic materials because the magnetism arises from oxygen rather than the metal atoms, as is usually the case. It is shown that oxygen-based magnetism shares many characteristics with much more widely studied transition metal-based materials. The main focus of the thesis is on the synthesis and properties of novel alkali oxides containing mixed superoxide (O2-) and peroxide (O22-) anions. This difference in charge is known as mixed valency and is a topic that until now has not been studied for magnetic oxygen. However, in transition metal materials mixed valency is often responsible for important physical phenomena, such as colossal magnetoresistance and superconductivity. Novel compounds with mixed oxygen valency have been synthesized by using mixed cations with different charges, such as Ba2+ and K+ in Ba1-xKxO2, or by varying the oxygen content in AO2-x (A = alkali metal). The coupling between neighboring superoxide and peroxide anions in some of these new compounds is significant and involves dynamic transfer of charge. This charge transfer can be enhanced by external stimuli such as light. The type of magnetism and degree of charge transfer in alkali oxides is closely linked to the crystal structure and can thus be varied via the type of alkali cation and the oxygen content. This work opens new possibilities for the synthesis of further novel magnetic oxygen compounds with as rich a variety of magnetic properties as transition metal materials.

Simulation of three dimensional double-diffusive throughflow in internally heated anisotropic porous media

A model for double-diffusive convection in an anisotropic porous layer with a constant throughflow is explored, with penetrative convection being simulated via an internal heat source. The validity of both the linear instability and global nonlinear energy stability thresholds are tested using three dimensional simulation. Our results show that the linear threshold accurately predicts on the onset of instability in the steady state throughflow. However, the required time to arrive at the steady state increases significantly as the Rayleigh number tends to the linear threshold. © 2014 Elsevier Ltd. All rights reserved

On the stability of natural convection in a porous vertical slab saturated with an Oldroyd-B fluid

The stability of the conduction regime of natural convection in a porous vertical slab saturated with an Oldroyd-B fluid has been studied. A modified Darcy�s law is utilized to describe the flow in a porous medium. The eigenvalue problem is solved using Chebyshev collocation method and the critical Darcy�Rayleigh number with respect to the wave number is extracted for different values of physical parameters. Despite the basic state being the same for Newtonian and Oldroyd-B fluids, it is observed that the basic flow is unstable for viscoelastic fluids�a result of contrast compared to Newtonian as well as for power-law fluids. It is found that the viscoelasticity parameters exhibit both stabilizing and destabilizing influence on the system. Increase in the value of strain retardation parameter � 2 portrays stabilizing influence on the system while increasing stress relaxation parameter � 1 displays an opposite trend. Also, the effect of increasing ratio of heat capacities is to delay the onset of instability. The results for Maxwell fluid obtained as a particular case from the present study indicate that the system is more unstable compared to Oldroyd-B fluid. © 2016, Springer-Verlag Berlin Heidelberg