Lattice and Energy Band Engineering in AlInGaN/Ga Heterostructures

We report on structural, optical, and electrical properties of AlxInyGa1−x−yNGaNheterostructures grown on sapphire and 6H–SiC substrates. Our results demonstrate that incorporation of In reduces the lattice mismatch, Δa, between AlInGaN and GaN, and that an In to Al ratio of close to 1:5 results in nearly strain-free heterostructures. The observed reduction in band gap,ΔEg, determined from photoluminescence measurements, is more than 1.5 times higher than estimated from the linear dependencies of Δa and ΔEg on the In molar fraction. The incorporation of In and resulting changes in the built-in strain in AlInGaN/GaN heterostructures strongly affect the transport properties of the two-dimensional electron gas at the heterointerface. The obtained results demonstrate the potential of strain energy band engineering for GaN-based electronic applications

Forced Convection Heat Transfer from a Finite-Height Cylinder

[EN] This paper presents a large eddy simulation of forced convection heat transfer in the flow around a surface-mounted finite-height circular cylinder. The study was carried out for a cylinder with height-to-diameter ratio of 2.5, a Reynolds number based on the cylinder diameter of 44 000 and a Prandtl number of 1. Only the surface of the cylinder is heated while the bottom wall and the inflow are kept at a lower fixed temperature. The approach flow boundary layer had a thickness of about 10% of the cylinder height. Local and averaged heat transfer coefficients are presented. The heat transfer coefficient is strongly affected by the free-end of the cylinder. As a result of the flow over the top being downwashed behind the cylinder, a vortex-shedding process does not occur in the upper part, leading to a lower value of the local heat transfer coefficient in that region. In the lower region, vortex-shedding takes place leading to higher values of the local heat transfer coefficient. The circumferentially averaged heat transfer coefficient is 20 % higher near the ground than near the top of the cylinder. The spreading and dilution of the mean temperature field in the wake of the cylinder are also discussed.The simulation was carried out using the supercomputing facilities of the Steinbuch Centre for Computing (SCC) of the Karlsruhe Institute of Technology. MGV has been partially supported by grant TRA2012-37714 of the Spanish Ministry of Economy and Competitiveness.García Villalba, M.; Palau-Salvador, G.; Rodi, W. (2014). Forced Convection Heat Transfer from a Finite-Height Cylinder. Flow, Turbulence and Combustion. 93(1):171-187. https://doi.org/10.1007/s10494-014-9543-7S171187931Ames, F., Dvorak, L.: Turbulent transport in pin fin arrays: experimental data and predictions. J. Turbomach. 128(1), 71–81 (2006)Armstrong, J., Winstanley, D.: A review of staggered array pin fin heat transfer for turbine cooling applications. J. 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Development of methods for the preparation of radiopure ⁸²Se sources for the SuperNEMO neutrinoless double-beta decay experiment

A radiochemical method for producing 82Se sources with an ultra-low level of contamination of natural radionuclides (40K, decay products of 232Th and 238U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities. It includes chromatographic separation (purification), reduction, conditioning (which includes decantation, centrifugation, washing, grinding, and drying), and 82Se foil production. The conditioning stage, during which highly dispersed elemental selenium is obtained by the reduction of purified selenious acid (H2SeO3) with sulfur dioxide (SO2) represents the crucial step in the preparation of radiopure 82Se samples. The natural selenium (600 g) was first produced in this procedure in order to refine the method. The technique developed was then used to produce 2.5 kg of radiopure enriched selenium (82Se). The produced 82Se samples were wrapped in polyethylene (12 μm thick) and radionuclides present in the sample were analyzed with the BiPo-3 detector. The radiopurity of the plastic materials (chromatographic column material and polypropylene chemical vessels), which were used at all stages, was determined by instrumental neutron activation analysis. The radiopurity of the 82Se foils was checked by measurements with the BiPo-3 spectrometer, which confirmed the high purity of the final product. The measured contamination level for 208Tl was 8-54 μBq/kg, and for 214Bi the detection limit of 600 μBq/kg has been reached.</p

Measurement of the 2 nu beta beta decay half-life and search for the 0 nu beta beta decay of Cd-116 with the NEMO-3 detector

The NEMO-3 experiment measured the half-life of the 2 ν β β decay and searched for the 0 ν β β decay of 116 Cd . Using 410 g of 116 Cd installed in the detector with an exposure of 5.26 y, ( 4968 ± 74 ) events corresponding to the 2 ν β β decay of 116 Cd to the ground state of 116 Sn have been observed with a signal to background ratio of about 12. The half-life of the 2 ν β β decay has been measured to be T 2 ν 1 / 2 = [ 2.74 ± 0.04 ( stat ) ± 0.18 ( syst ) ] × 1 0 19     y . No events have been observed above the expected background while searching for 0 ν β β decay. The corresponding limit on the half-life is determined to be T 0 ν 1 / 2 ≥ 1.0 × 1 0 23     y at the 90% C.L. which corresponds to an upper limit on the effective Majorana neutrino mass of ⟨ m ν ⟩ ≤ 1.4 – 2.5     eV depending on the nuclear matrix elements considered. Limits on other mechanisms generating 0 ν β β decay such as the exchange of R-parity violating supersymmetric particles, right-handed currents and majoron emission are also obtained

Search for Neutrinoless Quadruple-beta Decay of Nd-150 with the NEMO-3 Detector

We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-β decay of 150Nd using a total exposure of 0.19 kg·y recorded with the NEMO-3 detector at the Modane Underground Laboratory (LSM). We find no evidence of this decay and set lower limits on the half-life in the range T1/2 > (1.1–3.2) × 1021 y at the 90% CL, depending on the model used for the kinematic distributions of the emitted electrons

Measurement of the beta beta Decay Half-Life of Te-130 with the NEMO-3 Detector

We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of Te-130 in the form of enriched and natural tellurium foils. The beta beta decay rate of Te-130 is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T-1/2(2v)=[7.0 +/- 0.9(stat) +/- 1: 1(syst)] x 10(20) yr. This represents the most precise measurement of this half- life yet published and the first real-time observation of this decay

Calorimeter development for the SuperNEMO double beta decay experiment

SuperNEMO is a double-β decay experiment, which will employ the successful tracker–calorimeter technique used in the recently completed NEMO-3 experiment. SuperNEMO will implement 100 kg of double-β decay isotope, reaching a sensitivity to the neutrinoless double-β decay (0νββ) half-life of the order of 1026 yr, corresponding to a Majorana neutrino mass of 50–100 meV. One of the main goals and challenges of the SuperNEMO detector development programme has been to reach a calorimeter energy resolution, ΔE∕E, around 3%∕E(MeV) σ, or 7%∕E(MeV) FWHM (full width at half maximum), using a calorimeter composed of large volume plastic scintillator blocks coupled to photomultiplier tubes. We describe the R&D programme and the final design of the SuperNEMO calorimeter that has met this challenging goal