An anomalous magnetic phase transition at 10 K in Nd7Rh3

The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has been shown recently by us to exhibit a signature of magnetic phase-coexistence phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric intermetallic compounds, bearing a relevance to the trends in the field of electronic phase-separation. In order to characterize this compound further, we have carried out dc magnetic susceptibility (chi), electrical resistivity, magnetoresistance and heat-capacity measurements as a function temperature (T= 1.8 to 300 K). The results reveal that this compound exhibits another unusual finding at the 10K-transition in the sense that the plot of chi(T) shows a sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve shows a downturn below the transition. In addition, the sign of magnetoresistance is negative and the magnitude is large over a wide temperature range in the vicinity of magnetic ordering temperature, with a sharp variation at 10 K. The results indicate that the transition below 10 K is first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40

Vibrational branching ratios in photoionization of CO and N2

We report results of experimental and theoretical studies of the vibrational branching ratios for CO 4sigma(-1) photoionization from 20 to 185 eV. Comparison with results for the 2sigma(u)(-1) channel of the isoelectronic N-2 molecule shows the branching ratios for these two systems to be qualitatively different due to the underlying scattering dynamics: CO has a shape resonance at low energy but lacks a Cooper minimum at higher energies whereas the situation is reversed for N-2

Rotating Water Table for the Determination of Non-Steady Forces in a Turbine Stage Through Modified Hydraulic Analogy

Determination of non-steady forces in a real turbine stage is difficult due to the local flow conditions, for example high pressures, high temperatures and in-accessibility to the region etc. Experimentation in a real turbine is also prohibitive due to the costs involved. An alternate method of arriving at these non-steady forces through the use of modified hydraulic analogy is discussed. A rotating water table facility, developed and fabricated based on the principles of modified hydraulic analogy ia described. A flat plate stage is simulated on the rotating water table, and the results obtalned are presented

Derived Properties of Surface Tension for Hard Sphere Liquids from an Equation of State

Analytical expressions for surface tension, derived by using the equation of state from the scaled particle theory and that from sound propagation through liquids, have boon subjected to arrive at Eotvos constant and compressibility coefficient by forming the derivatives of surface energy and pressure coefficient of surface tension respectively. It is gratifying to note that value so obtained are in fair agreement with experiment, especially when it is noted that they are obtained as the second derivatives of Helmholtz free energy

Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)

All the three series of manganates showsaturation magnetization characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2 respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably smaller showing a small increase around TM, the value of TM decreasing slightly with increase in x or decrease in . The ferromagnetic compositions (x xc) show insulator-metal (IM) transitions, while the compositions with x > xc are insulating. The magnetic and electrical resistivity behavior of these manganates is consistent with the occurrence of phase separation in the compositions around xc, corresponding to a critical average radius of the A-site cation, , of 1.18 A. Both Tc and TIM increase linearly when < rA > > or x xc as expected of a homogenous ferromagnetic phase. Both Tc and TM decrease linearly with the A-site cation size disorder at the A-site as measured by the variance s2. Thus, an increase in s2 favors the insulating AFM state. Percolative conduction is observed in the compositions with > < rAc >. Electron transport properties in the insulating regime for x > xc conforms to the variable range hopping mechanism. More interestingly, when x > xc, the real part of dielectric constant (e') reaches a high value (104-106) at ordinary temperatures dropping to a very small (~500) value below a certain temperature, the value of which decreases with decreasing frequency.Comment: 27 pages; 11 figures, Submitted to J.Phys:Condens Matte

Torque Ripple Minimization of a Switched Reluctance Motor using Fuzzy Logic Control

Switched Reluctance Motors (SRMs) are attractive for industrial applications because of their simple construction and low cost, ruggedness, the capability to cover a wide speed range and relatively high torque-to-mass ratio. The primary disadvantage of an SRM is the higher torque ripple compared with conventional machines, which contributes to acoustic noise & vibration. The origin of torque pulsations in an SRM is due to the highly nonlinear & discrete nature of torque production mechanism. The total torque in an SRM is the sum of torques generated by each of the stator phases, which are controlled independently. Torque-ripple reduction in switched reluctance motors (SRM) has become a major research theme. In servo control applications or when smooth control is required at low speeds, reduction of the torque ripple becomes the main issue in an acceptable control strategy. In this paper intelligent controller such as Fuzzy Logic Controller current compensating technique is employed for minimizing the torque ripples in switched reluctance motor. For the purpose of comparison, the performance of conventional Proportional- Integral (PI) controller and PID controller are also considered. The statistical parameters like minimum, maximum, mean of total torque and torque ripple coefficient are reported. DOI: 10.17762/ijritcc2321-8169.15070