Forward acoustic performance of a model turbofan designed for a high specific flow (QF-14)

Forward noise and overall aerodynamic performance are presented for a high-tip-speed fan having an exceptionally high average axial Mach number at the rotor inlet. This high Mach number is intended to attenuate forward noise at both the design-speed takeoff point, and at the unconventional low-pressure-ratio, design-speed approach point. As speed was increased near design, all forward noise components were reduced, and rear noise in the discharge duct was increased, indicating that the high Mach number flow at the rotor face is attenuating forward noise at takeoff. The fan at takeoff is some 5.5 to 11 dB quieter than several reference fans. Data at the point closest to approach indicated tentatively that the design-speed approach mode was 3 dB quieter than the conventional mode

Ageing effects around the glass and melting transitions in poly(dimethylsiloxane) visualized by resistance measurements

The process of ageing in rubbers requires monitoring over long periods (days to years). To do so in non-conducting rubbers, small amounts of carbon-black particles were dispersed in a fractal network through the rubber matrix, to make the rubber conducting without modifying its properties. Continuous monitoring of the resistance reveals the structural changes around the glass and melting transitions and especially details about the hysteresis and ageing processes. We illustrate the method for the semicrystalline polymer poly(dimethylsiloxane) (PDMS).Comment: 4 pages, 4 figure

Analytical study of hydrogen turbopump cycles for advanced nuclear rockets Progress report, Sep. 15, 1964 - Sep. 15, 1965

Hydrogen turbopump cycles for obtaining high engine inlet pressures in advanced nuclear rockets, and data on gaseous nuclear reactors and heavy gas containmen

Lie Symmetry Analysis for Cosserat Rods

We consider a subsystem of the Special Cosserat Theory of Rods and construct an explicit form of its solution that depends on three arbitrary functions in (s,t) and three arbitrary functions in t. Assuming analyticity of the arbitrary functions in a domain under consideration, we prove that the obtained solution is analytic and general. The Special Cosserat Theory of Rods describes the dynamic equilibrium of 1-dimensional continua, i.e. slender structures like fibers, by means of a system of partial differential equations.Comment: 12 Pages, 1 Figur

Anti-pheromone as a tool for better exploration of search space

Many animals use chemical substances known as pheromones to induce behavioural changes in other members of the same species. The use of pheromones by ants in particular has lead to the development of a number of computational analogues of ant colony behaviour including Ant Colony Optimisation. Although many animals use a range of pheromones in their communication, ant algorithms have typically focused on the use of just one, a substance that encourages succeeding generations of (artificial) ants to follow the same path as previous generations. Ant algorithms for multi-objective optimisation and those employing multiple colonies have made use of more than one pheromone, but the interactions between these different pheromones are largely simple extensions of single criterion, single colony ant algorithms. This paper investigates an alternative form of interaction between normal pheromone and anti-pheromone. Three variations of Ant Colony System that apply the anti-pheromone concept in different ways are described and tested against benchmark travelling salesman problems. The results indicate that the use of anti-pheromone can lead to improved performance. However, if anti-pheromone is allowed too great an influence on ants' decisions, poorer performance may result

Mesoscale simulations of surfactant dissolution and mesophase formation

The evolution of the contact zone between pure surfactant and solvent has been studied by mesoscale simulation. It is found that mesophase formation becomes diffusion controlled and follows the equilibrium phase diagram adiabatically almost as soon as individual mesophases can be identified, corresponding to times in real systems of order 10 microseconds.Comment: 4 pages, 2 figures, ReVTeX

Covalency effects on the magnetism of EuRh2P2

In experiments, the ternary Eu pnictide EuRh2P2 shows an unusual coexistence of a non-integral Eu valence of about 2.2 and a rather high Neel temperature of 50 K. In this paper, we present a model which explains the non-integral Eu valence via covalent bonding of the Eu 4f-orbitals to P2 molecular orbitals. In contrast to intermediate valence models where the hybridization with delocalized conduction band electrons is known to suppress magnetic ordering temperatures to at most a few Kelvin, covalent hybridization to the localized P2 orbitals avoids this suppression. Using perturbation theory we calculate the valence, the high temperature susceptibility, the Eu single-ion anisotropy and the superexchange couplings of nearest and next-nearest neighbouring Eu ions. The model predicts a tetragonal anisotropy of the Curie constants. We suggest an experimental investigation of this anisotropy using single crystals. From experimental values of the valence and the two Curie constants, the three free parameters of our model can be determined.Comment: 9 pages, 5 figures, submitted to J. Phys.: Condens. Matte

Avascular Necrosis of the Foot and Ankle in a Patient with Systemic Sclerosis: A Case Based Review

This review describes a case of atraumatic avascular necrosis in the foot and ankle in a patient with systemic sclerosis who did not receive corticosteroid therapy. Both avascular necrosis and systemic sclerosis are uncommon disease entities. This case demonstrates that vasculitis and secondary vasoconstriction in the pathogenesis of systemic sclerosis are important risk factors for the development of avascular necrosis of the foot and ankle. Therefore, if these patients develop chronic foot and ankle pain, avascular necrosis should be included in the differential diagnosis, even if they do not receive corticosteroids. For the diagnosis and follow-up of avascular necrosis MRI remains the gold standard. Thus, MRI should be used to diagnose avascular necrosis in an early stage. Level of Clinical Evidence: 4.This review describes a case of atraumatic avascular necrosis in the foot and ankle in a patient with systemic sclerosis who did not receive corticosteroid therapy. Both avascular necrosis and systemic sclerosis are uncommon disease entities. This case demonstrates that vasculitis and secondary vasoconstriction in the pathogenesis of systemic sclerosis are important risk factors for the development of avascular necrosis of the foot and ankle. Therefore, if these patients develop chronic foot and ankle pain, avascular necrosis should be included in the differential diagnosis, even if they do not receive corticosteroids. For the diagnosis and follow-up of avascular necrosis MRI remains the gold standard. Thus, MRI should be used to diagnose avascular necrosis in an early stage. Level of Clinical Evidence: 4