In the present study, compressible low-Reynolds-number flow past a stationary isolated sphere was investigated by direct numerical simulations of the Navier–Stokes equations using a body-fitted grid with high-order schemes. The Reynolds number based on free-stream quantities and the diameter of the sphere was set to be between 250 and 1000, and the free-stream Mach number was set to be between 0.3 and 2.0. As a result, it was clarified that the wake of the sphere is significantly stabilized as the Mach number increases, particularly at the Mach number greater than or equal to 0.95, but turbulent kinetic energy at the higher Mach numbers conditions is higher than that at the lower Mach numbers conditions of similar flow regimes. A rapid extension of the length of the recirculation region was observed under the transitional condition between the steady and unsteady flows. The drag coefficient increases as the Mach number increases mainly in the transonic regime and its increment is almost due to the increment in the pressure component. In addition, the increment in the drag coefficient is approximately a function of the Mach number and independent of the Reynolds number in the continuum regime. Moreover, the effect of the Mach and Reynolds numbers on the flow properties such as the drag coefficient and flow regime can approximately be characterized by the position of the separation point.

In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.

The interaction of femtosecond ultra-intense laser pulses with clusters increases absorption of the incident laser light compared with the interaction with solid targets and leads to enhanced generation of different quantum beams with unique parameters. Future investigations of such interaction urgently need detailed modeling and optimization of cluster parameters, for instance, in order to obtain the clusters with desired size, or some specific spatial configuration of the target etc. A numerical model of gas-cluster targets production by the nozzle flows of gases and binary mixtures is presented. Some previous results of the model utilization are summarized, and some new results are given. Techniques of experimental verification of the numerical results are discussed.

Sustainable commercial use of native wildlife is an alternative economic means of land use by Indigenous people in remote rural areas. This situation applies within large tracts of land owned by Indigenous people across northern Australia. The commercial use of saltwater crocodiles Crocodylus porosus is a growing industry in Australia's Northern Territory. Although Indigenous people sell crocodile eggs and hatchlings, the majority of harvesting and incubation is done by non-indigenous people from less remote areas. One Indigenous community has been heavily involved in this industry and now manages its own harvest and incubation programme. We present a case study of this programme, which has transitioned from outside agencies managing the harvest, to complete local ownership and management. Egg harvests and incubation success rates declined by 40% following the switch to local management. Income increased, as did production costs; in particular, royalty payments made to Indigenous landowners. The declines reflect the community's motives for engaging in the industry, which have been socially rather than commercially driven, and damage to nesting habitat by feral animals. The increase in royalties reflects the need to compete with non-indigenous harvesters from outside the township, who are strictly commercially driven. Harvesting, incubation and trade in crocodile eggs and hatchlings can form a viable and sustainable enterprise for remote Indigenous communities. However, efficiency needs to be improved to fulfil the need for a reliable and dependable supply chain, and regulatory institutions should give Indigenous harvesters sufficient freedom to pursue innovative and viable livelihood options.

The superbubble (SB) 30 Dor C with the strong non-thermal X-ray emission is one of the best targets for study of the cosmic-ray (CR) acceleration. We investigated X-ray spectral properties of the SB with a high spatial resolution of ~10 pc. Consequently, the spectra in the east regions can be described with a combination of absorbed thermal and non-thermal models while the spectra in the west regions can be fitted with an absorbed non-thermal model. We found that the observed photon index and intensity in 2-10 keV show variations of 2.0-3.5 and (0.6-8.0) × 10−7 erg s−1 cm−2 str−1, respectively. The results are possibly caused by the spatial variation of the CR acceleration efficiency and/or the circumstellar environment.

We propose a fast method of calculating the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}p$-part of the class numbers in certain non-cyclotomic $\mathbb{Z}_p$-extensions of an imaginary quadratic field using elliptic units constructed by Siegel functions. We carried out practical calculations for $p=3$ and determined $\lambda $-invariants of such $\mathbb{Z}_3$-extensions which were not known in our previous paper.

King Abdul Aziz University of Saudi Arabia (KAU) and Tokai University in Japan have collaborated to design and manufacture a solar powered unmanned air vehicle (UAV), Sun Falcon, which has capability of continuous one day fight with intended design extension towards night flight. The project is a student-driven endeavour involving some 30 students. Both universities are equally involved in the actual design studies of the performance characteristics, aerodynamic design, propulsion and structural analysis. Tokai University is in charge of the actual on-site supervision and examination of on-going manufacturing processes and ultimate fabrication of the prototype model.

The conceptual design of the Sun Falcon was meticulously worked out in consideration of the operational mission, which included such flight characteristics as the cruising velocity, flight altitude, payload, flight time, rate of climb, power requirements and so on. The weather condition patterns in Saudi Arabia, which remained fairly supportive of the solar cell performance, were also deemed crucial in the design process. However, the design of a solar plane had other challenges in terms of power unit accommodation and payload consideration in comparison to other conventional UAVs. In this paper, an outline of the design features of the Sun Falcon is presented and other notable design features particular to solar UAVs are discussed. It was learnt in this exercise that the selection of the base aerofoil is perhaps one of the most important design items, as the Reynolds number for such UAVs understandably drops notably lower than conventional aeroplanes and such features as the camber curvature and wing area must cater for the installation of solar panels whose size, strength and quantity must respect local weather conditions. For the Sun Falcon, the actual design process examined two candidate aerofoils FX74-CL5-140 (FX74) and SD7037-092-88(SD7037) both of which were abundantly suitable for furnishing the required aerodynamic characteristics. SD7037 was ultimately chosen as it provided the best geometry and camber line in terms of accommodation and placement of the solar panels. Further scrutiny demonstrated that this latter aerofoil provided better take-off performance and superior L/D behaviour under cruise conditions. In order to check out the aerodynamic performance in general and overall stability and control characteristics, a preflight test under battery power (a 2,500 mAh li-po 4-cell 14·8v) was achieved on 4 June 2013. Other solar powered based tests are currently under way at present.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

In this work, we present a method able to fabricate thin GaN nanomembranes fit for device applications. Starting from commercial GaN on sapphire substrates, MBE was used to deposit a sacrificial layer, which comprises of a superlattice of InN/InGaN, after which thin a GaN film of hundreds of nanometers thickness was grown on top. Pulsed laser irridiation with photon energy of 2.3eV gives rise to the controlled decomposition of the sacrificial intermediate layer, which can be followed by easy separation of the top GaN membrane from the substrate. This process can be used to manufacture GaN membranes with low defect density and a wider range of thickness. We demonstrated that large area, free-standing GaN membranes, with a thickness from 200nm and up, could be made using this method, and the high crystal quality of the lift-off GaN layers is well preserved in this process.

Catastrophic degradation of high power laser diodes is due to the generation of extended defects during the laser operation. The stress necessary for is induced by temperature gradients generated by local enhancement of the temperature due to non radiative recombination and subsequent laser self absorption. The thermal stresses induced by such temperature gradient are calculated using finite element methods, showing that the yield strength can be surpassed. The thermal conductivity of the laser structure is shown to play a relevant role in the process.

Deep-level densities of p-GaAs1−xBix and at the GaAs/p-GaAs1−xBix heterointerface have been shown to be sufficiently low for device applications based on the results of deep-level transient spectroscopy, isothermal capacitance transient spectroscopy and admittance spectroscopy. Although the metastable alloy of GaAs1−xBix is grown by molecular beam epitaxy at low temperature (370 °C), the deep-level density of p-GaAs1−xBix is suppressed such that it is on the order of 1015 cm−3. The state density at the heterointerface was determined to be 8 · 1011 cm−2eV−1, which is comparable to other III–V heterointerfaces formed at high temperatures. The surfactant-like effect of Bi is believed to prevent defect formation during low-temperature growth.

Boron Phosphide (BP) is a promising material for use as a room temperature semiconductor detector of thermal neutrons. The absorption of a thermal neutron by a 10B nucleus in BP can yield 2.3MeV of energy which in solid state BP can yield ∼0.5 million electron-hole pairs that would be detectable with minimal amplification in a device. BP thin films are grown according to the net reaction below in a cold wall chemical vapor deposition (CVD) reactor: Thin film depositions are performed using diborane and phosphine with a balance of hydrogen gas at near atmospheric pressure with RF induction heating. The resultant BP films are characterized by Raman, XRD, SEM, TEM and TEM-EELS for chemical composition, surface and bulk morphology. BP growths on Si and SiC substrates are compared. SiC provides reduced lattice mismatch for growth of BP and growth of heteroepitaxial BP on SiC will be discussed.

By using aberration corrected scanning transmission electron microscopy we have found no small scale lateral In composition fluctuations exist in the In0.15Ga0.85N active region of a light emitting diode. Images were acquired at 2% of the electron dose known to create electron beam damage, so the acquired images reflect the intrinsic structure of the InGaN active region. Position averaged convergent beam electron diffraction reveals the local sample thickness where images were acquired is 4.8 nm, eliminating the possibility that the absence of composition variation was observed due to projection through a thick sample. In addition, 2-3 atomic layer steps were observed in the top surface of In0.08Ga0.92N layers and the In0.15Ga0.85N active layers, providing a possible mechanism for lateral carrier confinement.

Gallium nitride (GaN) is a robust piezoelectric semiconductor with excellent thermal and chemical stability, making it an attractive material for surface acoustic wave (SAW) sensors operating in high temperature and harsh environments. The sensitivity of SAW devices is proportional to the square of the operating frequency. Therefore, high operating frequencies into the GHz regime are desirable for SAW sensors. For GaN, this requires sub-micron interdigital transducers (IDTs) when devices are designed to operate at the fundamental Rayleigh mode frequency. The necessity for sub-micron IDTs can increase fabrication costs and complexity. By designing SAW devices to operate at harmonic frequencies, GHz operation can be realized with relatively large IDTs, resulting in simpler and more cost effective solutions for GaN based SAW sensors. Devices have previously been designed to operate at the 5th and higher harmonics on lithium niobate, but there are no reports of using this technique on GaN in the literature. In this study, GaN thin films have been grown via metal organic vapor phase epitaxy on sapphire substrates. SAW devices designed to operate at the fundamental frequency and higher harmonics have been fabricated and measured. Operating frequencies greater than 2 GHz have been achieved using IDTs with 5 μm fingers. In addition, reduction of electromagnetic feedthrough around the 5th and 7th harmonic is demonstrated through varying ground electrode geometries.

The insertion of nanostructured materials (such as quantum wells, wires, and dots) into the intrinsic region of p-i-n solar cells introduces an intermediate band within the bandgap of the host material. It has been shown that the sub-bandgap conversion provided by the nanostructured materials, enhances the short circuit current as well as the overall efficiency of InAs quantum dots (QD) imbedded in GaAs superlattice (SL) solar cells [1]. As a contender for space applications, it is necessary to subject these solar cell structures to temperatures encountered in the Low Earth Orbit (LEO), probing for any material degradation. Herein, we focus on temperature dependent characterization using high resolution X-ray diffraction (HRXRD) of InAs QD enhanced GaAs solar cell structures with varying growth parameters. The structures characterized can be classified into three groups: (1) GaP strain compensation coverage, (2) GaAs barrier coverage, and (3) InAs coverage for QD formation. HRXRD rocking curves of each structure focusing around the GaAs peak are analyzed at a range of temperatures up to 200˚C. Although no noticeable shifts in the SL peaks are detected, interfacial diffusion decreased the resolution of fringes produced by reflections at the SL interfaces in test structures with varying InAs QD coverage. Unbalanced strain in the same structures shows a distortion in the GaAs peaks.