Experimental flow study over a blunt-nosed axisymmetric body at incidence

The flowfield over a blunt-nosed cylinder was examined experimentally at a low subsonic speed for Re=1.88×10⁵ and angles of attack up to 40°. Velocity measurements were carried out (employing a seven-hole Pitot tube) as well as wall static pressure and wall shear-stress measurements. Surface flow visualization was applied using liquid crystals and a mixture of oil–TiO₂. For all the examined cases no flow asymmetries were found. For high angles of attack (20° and above) a separation “bubble” appears at the leeside of the nose area (streamwise flow separation). The basic feature of the circumferential pressure distribution at the after body area for these angles of attack is a plateau close to the suction peak and a fast recovery next to it. One streamwise vortex on each side of the symmetry plane is formed as well as a separation bubble about 90° far from this plane, where the cross-flow primary separation line is located. Each cross-flow primary separation line starts at the leeside nose area and moves towards the windward side along the cylindrical after body. The space between the two primary separation lines close to the wall is characterized by high flow fluctuations on the leeside, compared to the low fluctuations of the windward side.     

Decay kinetics of the green emission in tungstates and molybdates

Luminescence characteristics of a number of undoped and variously doped PbWO₄ crystals were studied at 0.4–400 K by the time-resolved spectroscopy and compared with those of ZnWO₄,CdWO₄ and PbMoO₄ crystals. Two types of green emission centres are detected in PbWO₄ crystals. The centres of the first type are responsible for the low-temperature 2.3–2.4 eV emission observed under excitation around 3.90–3.95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the first type could vary for different crystals. The centres of the second type with the emission around 2.5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb⁺-WO₃ centres at T>180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated.     

Rare earth photoionization study by the resonant microwave cavity technique

Photoconductivity spectra of rare earth-doped insulating materials are measured using the resonant microwave cavity method. This technique is based on the detection of the cavity Q-factor changes induced by irradiation of the sample (inserted in the cavity) by a pulsed tunable laser. Results obtained with Lu₂(SiO₄)O:Ce³⁺ and BaF₂:Eu²⁺ are presented and discussed. Photoionization thresholds at 400 nm (3.1 eV) and 310 nm (4.0 eV) are measured for Lu₂(SiO₄)O:Ce³⁺ and BaF₂:Eu²⁺, respectively.     

Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Strangeness saturation: Dependence on system-size, centrality and energy

The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic heavy-ion collisions.     

A realistic coronary artery phantom for particle image velocimetry

Myocardial infarction results from the rupture of an atherosclerotic plaque, which occurs in response to both mechanical stress and inflammatory processes. In order experimentally observe flow into atherosclerotic coronary artery morphologies, a novel technique for molding realistic compliant phantom featuring injection-molded inclusions and multiple layers has been developed. This transparent phantom allows for particle image velocimetry (PIV) flow analysis and can supply experimental data to validate computational fluid dynamics algorithms and hypothesis.     

The glow curve structure for the LiF:Mg,Cu,Na,Si TL detector with dopants concentrations and sintering temperatures

The glow curve structures for LiF:Mg,Cu,Na,Si TL detectors with various dopant concentrations and sintering temperatures were investigated for the improvement of the glow curve structure and sensitivity of the TL detector. The dopant concentrations were varied over the following ranges: Mg (0–0.25 mol%), Cu (0–0.07 mol%), Na and Si (0–1.5 mol%). With increasing Cu concentration, the intensity of the main peak was intensified and reached a maximum at a concentration of 0.05 mol%. The high-temperature peak was reduced. The dependency of the main peak intensity on the Mg concentration exhibits a sharp maximum at 0.2 mol%. The intensity of the high-temperature peak tends to rise slightly with increasing Mg concentration. It was found that the optimum concentrations of the dopants in the LiF:Mg,Cu,Na,Si TL material are Mg: 0.2 mol%, Cu: 0.05 mol%, Na and Si: 0.9 mol%. The dependency of the main peak intensity on sintering temperature exhibits a very sharp maximum at 830°C. The high-temperature peak was rapidly reduced after 825°C.     

Highly strained InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on In_xGa_(1−x)As−In_yAl_(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In_0.84Ga_0.16As/AlAs/In_0.52Al_0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In_0.84Ga_0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.     

Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in ⁶He and ⁶Be were investigated by using the ⁶Li(⁷Li, ⁷Be)⁶He reaction at 455 MeV and ⁶Li(³He, t)⁶Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at E _x =18.0±1.0 MeV in ⁶He and into ³He + ³He from one at E _x =18.0±1.2 MeV in ⁶Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for ⁶He and ⁶Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around E _x =18 MeV in ⁶He and ⁶Be.