http://nopr.niscair.res.in/handle/123456789/8819 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/9306 Title: Investigation on magnetic fluids as lubricant <br/> <br/>Authors: Burcan, Jan; Piotrowicz, Ewa Burcan; Sławińska, Anna <br/> <br/>Abstract: Experimental data were obtained for the lubricated bearings of precision and fine mechanisms, operating in the conditions of boundary friction or, at best, of mixed friction. The use of magnetically active lubricant in the thrust bearing with the spinning point contact, where the spherical surface rotation in relation to the axially-symmetrical seat (spherical bowl or plane), makes the fluid film lubrication possible. It is possible because the addition of new potential field, that means magnetic field, changes the energetic state of equilibrium occurring in spinning friction of slides. <br/> <br/>Page(s): 338-342 http://nopr.niscair.res.in/handle/123456789/9305 Title: Verwey type transition in nano-particle spinel ferrite Fe_2.2Co_0.8O₄ <br/> <br/>Authors: Chander, Subhash; Krishnamurthy, Anjali; Srivastava, Bipin K; Gupta, Ajay; Nigam, Arun Kumar <br/> <br/>Abstract: Results are presented on magnetization and Mössbauer measurements on two multi-disperse nano-particle samples of Co substituted spinel ferrite Fe_2.2Co_0.8O₄ with average particle sizes of ~ 50 Ǻ and ~ 80 Ǻ. In these nono-particle samples Co occupies the octahedral site B with ~ 60% preference. The 50 Ǻ average particle sized sample Co50 is largely in super-paramagnetic state at 300 K and its blocking temperature <i style="">T</i>_Bis~ 260 K. 80 Ǻ average particle sized sample Co80 has its <i style="">T</i>_Babove 300 K. The two samples exhibit magnetic relaxation. Much smaller moments of the two samples than saturation magnetization for the bulk particle sample and a loop shift observed in <i style="">M</i>-<i style="">H</i> curves of Co50 recorded in zero field and field cooling modes are suggestive of spin disordered surfaces. The nano-particle sample Co80, of the ferrite Fe_2.2Co_0.8O₄ which in its bulk particle state is known to have more than an order of magnitude higher magneto-crystalline anisotropy than Fe₃O₄, shows signature of a ‘Verwey’ type transition with enhanced magnetic anisotropy below ~ 90 K. Co50 does not show a ‘Verwey’ type transition. A weak hump in <i style="">M</i>-<i style="">T</i> curve at a lower temperature of ~ 50 K in Co50 is attributed to disordered spin freezing. <br/> <br/>Page(s): 343-348 http://nopr.niscair.res.in/handle/123456789/9304 Title: Ferroconvection induced by point heat source <br/> <br/>Authors: Sekar, R; Vaidyanathan, G; Vasanthakumari, R <br/> <br/>Abstract: A mathematical model is proposed to study the onset of the free convection in ferrofluid at low Rayleigh number from an instantaneous point heat source. In this work, the leading term of series expansion of the dependent variable in terms of Rayleigh number is considered and is valid in small Rayleigh number regime only. The rate of heat generation is assumed to be not very high, so that Stoke’s flow approximation could be used. The flow field is explained by the streamlines at different times. In the absence of field, the results are compared for the thermal convection due to the instantaneous point heat source. <br/> <br/>Page(s): 331-337 http://nopr.niscair.res.in/handle/123456789/9303 Title: Rheology of transformer oil based ferrofluids <br/> <br/>Authors: Patel, Rajesh; Upadhyay, Kinnari Parekh R V; Mehta, R V <br/> <br/>Abstract: In the present study we report results of rheological properties of temperature sensitive transformer oil based ferrofluids as a function of external magnetic field and temperature. The field induced viscosity is analyzed using Shliomis model. The variation of magnetic moment and domain magnetization with temperature has been deduced from this measurement which agrees with the reported values deduced from magnetization technique. <br/> <br/>Page(s): 301-304