Experimental determination of the local heat transfer coefficient in a closely packed pin arrangement

The determination of the heat transfer coefficient of the pins of the Spallation Neutron Source is a very important problern for the development of this facility, as data for thermal and structural studies. Forthis purpose, a test apparatus was built, in scale 1 : 1, for the simulation of the thermal and hydraulical conditions of the Neutron Source. This apparatus is a pin bank, with one of the pins electrically heated. Performance of measurements gave the values for the heat transfer coefficient, here presented in the Nusselt Nurober form, and its local distribution. Results show the linear dependence of Nusselt Nurober on Reynolds Number, for a constant heat production

Spectroscopy of the heaviest nuclei (theory)

Recent progress in the applications of covariant density functional theory (CDFT) to the description of the spectroscopy of the heaviest nuclei is reviewed. The analysis of quasiparticle spectra in actinides and the heaviest A ~ 250 nuclei provides a measure of the accuracy of the description of single-particle energies in CDFT and an additional constraint for the choice of effective interactions for the description of superheavy nuclei. The response of these nuclei to the rotation is rather well described by cranked relativistic Hartree+Bogoliubov theory and it serves as a supplementary tool in configuration assignment in odd-mass nuclei. A systematic analysis of the fission barriers with allowance for triaxial deformation shows that covariant density functional theory is able to describe fission barriers on a level of accuracy comparable with the best phenomenological macroscopic+microscopic approaches.Comment: 10 pages, 7 figures, invited talk of A.V. Afanasjev at the International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July 4-9, 2010, to be published in Journal of Physics G: Conference Series (JPCS

Cotunneling thermopower of single electron transistors

We study the thermopower of a quantum dot weakly coupled to two reservoirs by tunnel junctions. At low temperatures the transport through the dot is suppressed by charging effects (Coulomb blockade). As a result the thermopower shows an oscillatory dependence on the gate voltage. We study this dependence in the limit of low temperatures where the transport through the dot is dominated by the processes of inelastic cotunneling. We also obtain a crossover formula for intermediate temperatures which connects our cotunneling results to the known sawtooth behavior in the sequential tunneling regime. As the temperature is lowered, the amplitude of thermopower oscillations increases, and their shape changes qualitatively.Comment: 9 pages, including 4 figure

EVALUATION OF THE APPLICABILITY OF A TURBULENT WAKE INLET BOUNDARY CONDITION

With the objective of reducing the computational cost of the iterative processes of aerodynamic components design, tests were carried out to study under what conditions, and with what difference, only part of the calculation domain can be solved using as input information obtained from complete simulations already solved. An experimental study of an airfoil exposed to the wake interference of an upstream airfoil at a Reynolds number of 150,000 was used to verify the solutions of the Reynolds-Averaged Navier-Stokes equations solved applying the k-ω Shear Stress Transport model for turbulence closure. A Grid Convergence Index study was performed to verify if the solution of the equations for the adopted discretization leads to results within the asymptotic range. With the physical coherence of the numerical methodology verified, comparisons between the simulations with the domain comprising the two airfoils and the domain comprising only the downstream airfoil were performed. Computational time reductions in the order of 40% are observed. The differences in the aerodynamic coefficients for the two types of simulation are presented as a function of distances non-dimensionalized by the characteristic length of the body that disturbs the flow forming the wake, showing that the difference between the two methods was inversely proportional to the distance between the two bodies. Behavior that was maintained until a point where the simulation diverges, equivalent to 25% of the characteristic length of the body that generates the wake

Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion