Effect of A-site ionic size variation on TCR and electrical transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 with x = 0, 0.1 and 0.2

In this work, the structural and transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 manganites with x 0, 0.1 and 0.2 prepared by solid state reaction route are studied. These compounds are found to be crystallized in orthorhombic structural form. Experimental results showing a shift in the metal to semiconductor/insulator transition temperature (TMI) towards room temperature (289 K) with the substitution of Nd by La, as the value of x is varied in the sequence (0,0.1,0.2), have been provided. The shift in the TMI, from 239 K (for x=0) to near the room temperature 289 K (for x=0.2), is attributed to the fact that the average radius of site-A increases with the percentage of La. The maximum temperature coefficients of resistance (TCR) of (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0.1 and 0.2) are found to be higher compared to its parent compound Nd0.7Sr0.3MnO3. The electrical transport mechanisms for (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0 to 0.2) are explored by using different theoretical models, for temperatures below and above TMI. An appropriate enlightenment for the observed behavior is discussed in detail

Critical Shock Energy and Shock and Detonation Parameters of an Explosive

The present study deals with the connection between critical shock energy and detonation properties of an explosive. A relation for critical shock energy has been derived in terms of detonation velocity, width of reaction zone, initial density of the explosive, specific heat ratio of detonation products and either constants of linear relation between shock and particle velocity of the explosive or the constants of the Murnaghans type of equation of state of the explosive. These relations have been used to calculate the critical shock energy of RDX, HMX, RDX/TNT (60/40) and TNT explosives. The values of critical shock energies obtained in this study are in close agreement with those reported in the literature.Defence Science Journal, 2009, 59(4), pp.436-440, DOI:http://dx.doi.org/10.14429/dsj.59.154

Study of structural effect on Eu-substituted LSMO manganite for high temperature coefficient of resistance

n this work, Eu substituted La0.7Sr0.3MnO 3 (LSMO) is studied to achieve high temperature coefficient of resistance (TCR). The compounds La0.7-xEuxSr 0.3MnO3 with x=0, 0.1 0.2 and 0.3 are prepared by solid state reaction route and their structural and transport properties are examined by different characterization techniques. The metal-semiconductor/insulator transition temperature (TMI) decreases from 390 K (for x=0) to 240 K (for x=0.3) with decrease in average ionic radius 〈rA〉 of A-site. The maximum TCR percentage of La0.7-xEuxSr 0.3MnO3 compound is found to be increased for x=0.2 (1.9%) and for x=0.3 (3.36%) compared to its parent compound La0.7Sr 0.3MnO3 (1.1%). The substitution of Eu increases the lattice distortion, which enhances the TCR value from 1.1% to 3.36%. The robustness of distortion increases with decreasing 〈rA〉 which is well correlated with the high magneto-resistance, and high TCR findings

Computational Fluid Dynamics Modelling to design and optimise Power Kites for Renewable Power Generation

Power kites provide the potential rewards of obtaining the disused energy supply from high altitude wind. This paper aims to provide a design of Power kite and optimise the potential for renewable power generation. The Power kite was modelled using Computational Fluid Dynamics (CFD) to study its characteristics. The numerical modelling results were compared against the wind tunnel experimental study and two 3D printed Power kites. The design was optimised using several variables, including aerofoil choice, surface roughness, wind speed and operating parameters. Attempts at optimising the kite design were implemented. The results suggest that operating the kites at minimum 15 m horizontal separation is favourable, with the trailing kite operating below the leading, removing the potential for this kite to operate in the wake turbulence of the first. As the wind speed is generally very low at low altitudes, it is recommended to use a symmetrical aerofoil for the kite design, as these tend to produce greater lift with low Reynolds airflow. This paper presents relevant, applicable data which can be used for predicting the performance, and potentially optimising further Power kite designs

Vocal cord palsy in an infant with myelomeningocoele

In this article we describe the case of a four-month-old male infant with myelomeningocoele, who presented with inspiratory stridor and vocal cord palsy (VCP). Hindbrain dysfunction is a leading cause of mortality and morbidity in children with neural tube defects. It is important to consider the above in the differential diagnosis of infants with breathing difficulties. A discussion of myelodysplasia, Arnold-Chiari malformations, bilateral VCP and anaesthesia management is presented.South Afr J Anaesth Analg, 2011;17(6):394-39

Metallised Fuel rich Propellants for Solid Rocket Ramjet: A Review

This paper reviews the research work carried out in the field of metallised fuel-rich propellants (FRP). Limitations and merits of various potential metals (Al, Mg, B, Be, or Zr) as a component of FRP are discussed. The paper also includes a discussion on the combustion mechanism of metallised propellants, including problem areas and probable remedial measures. Zirconium and Ti appear to have potential to offer FRP with efficient combustion. Ideal performance is not achieved with current systems based on Al and B and further work is needed to develop FRP having all three desirable attributes, viz., ease of ignition, stable combustion and high specific impulse (I/sub sp/) in a single composition

Strength Degradation of Sapphire Fibers During Pressure Casting of a Sapphire-Reinforced Ni-Base Superalloy

Transient-liquid-phase (TLP) bonding was used to fabricate a Haynes 230 Ni-base superalloy/sapphire fiber composite for high-temperature applications. Boron was used as a melting-point depressant for the Ni, to aid superalloy infiltration of the fibers. Preliminary study of the composite indicated an incomplete TLP bonding cycle. Therefore, microstructural and microchemical analyses were carried out to determine the TLP bonding mechanism. It was found that the TLP process did not occur under local thermodynamic equilibrium conditions at the solid/liquid interfaces, contrary to the primary assumption of conventional models, so a modified model for TLP bonding is proposed. The main differences between the proposed and the conventional models are: (a) the concentration of the melting-point depressant increases with time during isothermal solidification, (b) extensive boride segregation at grain boundaries and boride precipitation occurs within grains adjacent to the interlayer in the initial composite assembly, (c) because of the relatively high boron concentration in the interlayer, the TLP bonding cycle was incomplete, resulting in residual-liquid borides. To achieve ideal TLP bonding, four modifications are recommended: (i) use less boron, (ii) use finer sapphire fibers, (iii) create smaller initial grain sizes in the matrix and (iv) increase the homogenization time

Impact, Friction, Shock Sensitivities and DDT Behaviour of Advanced CMDB Propellants

This paper reports results of impact, friction and shock sensitivities of CMDB propellants containing AP, RDX, PETN and their combinations. Results of impact and friction sensitivities indicate that CMDB propellants containing AP are highly sensitive and AP-based compositions are more impact and friction sensitive than RDX and PETN-based compositions, qnd that these sensitivities are proportionalto oxygen balance of the composition, which is in agreement withearlier findings. Inclusion of high explosives like RDX and PETN increases the shock sensitivity of CMDB formulations, whereas AP-based compositions are least shock sensitive. There exists are lationship between shock sensitivity and VOD of the individual oxidiser/high energy ingredient incorporated in the formulation. Shockamplitude values of 87 and 46 k bar in CMDB and DBP, as determinedby NOL card gap test, suggest that CMDB propellants are much more shock sensitive than DBP. Composite propellants are insensitive toshock, as they did not undergo detonation even at zero card gap.Results of DDT behaviour of CMDB propellants show that they aremore prone to deflagration to detonation transition under adverse conditions