Role of sintering on magneto-electric effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2Ti0.8Zr0.2O3 composite ceramics

Magnetoelectric composites containing CuFe_1.8Cr_0.2O₄–Ba_0.8Pb_0.2Ti_0.8Zr_0.2O₃ phases have been prepared by sintering them at different firing temperatures. The particle size for either phase of the composite was found to increase, whereas porosity decreases with increase in sintering temperature. This is due to the increase in the grain size with increase in sintering temperature. Resistivity of the composite decreases with increase in either sintering temperature or with increase in CuFe_1.8Cr_0.2O₄ content. The variation of dielectric constant (′) with temperature reflects DPT type behaviour. The peak value of dielectric constant (′_max) for a composite decreased with increase in its sintering temperature. The maximum value of the magnetoelectric conversion factor (dE/dH)_max equal to 182.7 μV/(cm*Oe) is obtained for 70% Ba_0.8Pb_0.2Ti_0.8Zr_0.2O₃–30% CuFe_1.8Cr_0.2O₄ composite when sintered at 1000°C.     

A State-Space Model of Fatigue Crack Growth

This paper proposes a nonlinear dynamic model of fatigue crack growth in the state-space setting based on the crack closure concept under cyclic stress excitation of variable amplitude and random loading. The model state variables are the crack length and the crack opening stress. The state-space model is capable of capturing the effects of stress overload and underload on crack retardation and acceleration, and the model predictions are in fair agreement with experimental data on the 7075-T6 aluminum alloy. Furthermore, the state-space model recursively computes the crack opening stress via a simple functional relationship and does not require a stacked array of peaks and valleys of stress history for its execution; therefore, savings in both computation time and memory requirement are significant. As such, the state space model is suitable for real-time damage monitoring and control in operating machinery. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Airflow distribution through perforated tiles in raised-floor data centers

Raised-floor data centers are the most commonly used facilities for housing computer and telecommunication equipment. To adequately cool this equipment, the cooling air through perforated tiles must be distributed properly. The airflow distribution depends on the pressure distribution or the flow field in the space under the raised floor (plenum); it is a complex function of a large number of variables, including the size of the plenum, the open area of the perforated tiles, the locations and flow rates of the computer room air conditioner (CRAC) units, and the size and location of the under-floor obstructions like cables and pipes. In this article, the effect of these parameters on the airflow distribution is studied using an idealized one-dimensional computational model. Within the one-dimensional framework, the airflow distribution is governed by two dimensionless parameters: one related to the pressure variation in the plenum and the other to the frictional resistance. Results, in terms of distributions of pressure in the plenum and flow rates through the perforated tiles, are presented over a range of values of these two parameters. These results provide an understanding of the fundamental fluid mechanical processes controlling the airflow distribution through the perforated tiles. The one-dimensional model is used to calculate flow rates for two possible arrangements of the CRAC units, and these results are compared with those given by a three-dimensional model.     

A Simulation Approach to Study the Effect of SiC Polytypism Factor on Sensitivity of Piezoresistive MEMS Pressure Sensor

Silicon - SiC is a well known wide band gap semiconductor explored for realizing the piezoresistive micro-electro-mechanical systems (MEMS) pressure sensors for harsh environments. In this work a...