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One of the key problems in the development of morphing aircraft is the morphing structure, which should be able to carry loads and change its geometry simultaneously. This paper investigates a compliant structure, which has the potential to change the dihedral angle of morphing wing-tip devices. The compliant structure is able to induce deformation by unsymmetrical stiffness allocation and carry aerodynamic loads if the total stiffness of the structure is sufficient.
The concept has been introduced by building a simplified model of the structure and deriving the analytical equations. However, a properly designed stiffness asymmetry, which is optimised, can help to achieve the same deformation with a reduced actuation force.
In this paper, round corrugated panels are used in the compliant structure and the stiffness asymmetry is introduced by changing the geometry of the corrugation panel. A new equivalent model of the round corrugated panel is developed, which takes the axial and bending coupling of the corrugated panel into account. The stiffness matrix of the corrugated panel is obtained using the equivalent model, and then the deflections of the compliant structure can be calculated. The results are compared to those from detailed finite element models built in the commercial software Abaqus. Samples with different geometries were manufactured for experimental tests.
After verifying the equivalent model, optimisation is performed to find the optimum geometries of the compliant structures. The actuation force of a single compliant structure is first optimised, and then the optimisation is performed for a compliant structure consisting of multiple units. A case study is used to show the performance improvement obtained.
Fatigue cracking in polycrystalline NiTi was investigated using a multiscale experimental framework for average grain sizes (GS) from 10 to 1500 nm for the first time. Macroscopic fatigue crack growth rates, measured by optical digital image correlation, were connected to microscopic crack opening and closing displacements, measured by scanning electron microscope DIC (SEM-DIC) using a high-precision external SEM scan controller. Among all grain sizes, the 1500 nm GS sample exhibited the slowest crack growth rate at the macroscale, and the largest crack opening level (stress intensity at first crack opening) and minimum crack opening displacements at the microscale. Smaller GS samples (10, 18, 42, and 80 nm) exhibited nonmonotonic trends in their fatigue performance, yet the correlation was strong between macroscale and microscale behaviors for each GS. The samples that exhibited the fastest crack growth rates (42 and 80 nm GS) showed a small crack opening level and the largest crack opening displacements. The irregular trends in fatigue performance across the nanocrystalline GS samples were consistent with nonmonotonic values in the elastic modulus reported previously, both of which may be related to the presence of residual martensite only evident in the small GS samples (10 and 18 nm).
Modulation of gamma-aminobutyric acid A (GABAA) receptor signalling by the neurosteroid allopregnanolone has a major role in late gestation neurodevelopment. The objective of this study was to characterize the mRNA levels of GABAA receptor subunits (α4, α5, α6 and δ) that are key to neurosteroid binding in the brain, following preterm birth. Myelination, measured by the myelin basic protein immunostaining, was used to assess maturity of the preterm brains. Foetal guinea pig brains were obtained at 62 days’ gestational age (GA, preterm) or at term (69 days). Neonates were delivered by caesarean section, at 62 days GA and term, and maintained until tissue collection at 24 h of age. Subunit mRNA levels were quantified by RT-PCR in the hippocampus and cerebellum of foetal and neonatal brains. Levels of the α6 and δ subunits were markedly lower in the cerebellum of preterm guinea pigs compared with term animals. Importantly, there was an increase in mRNA levels of these subunits during the foetal-to-neonatal transition at term, which was not seen following preterm birth. Myelination was lower in preterm neonatal brains, consistent with marked immaturity. Salivary cortisol concentrations, measured by EIA, were also higher for the preterm neonates, suggesting greater stress. We conclude that there is an adaptive increase in the levels of mRNA of the key GABAA receptor subunits involved in neurosteroid action after term birth, which may compensate for declining allopregnanolone levels. The lower levels of these subunits in preterm neonates may heighten the adverse effect of the premature decline in neurosteroid exposure.
The paper is an investigation into the withdrawal rates of seven Scottish Offices and covers the years 1972-76 with an appendix giving the results for 1977.
The rates were basically analysed by class and duration with further investigations mainly on the 1976 data by age at entry, sex, size of sum assured, premium paying term, premium payment frequency and by type of agent introducing the business. Comparisons were made of the level of withdrawal rates among the various Offices and also the variations from year to year separately. A graduation of the combined data for 1975 and 1976 for each of the five main classes was carried out.
Background: To date, no physical activity (PA) questionnaires intended for primary care have been compared against a criterion measure of PA and current (2008) aerobic PA recommendations of the American College of Sports Medicine/American Heart Association (ACSM/AHA). Aim: This study evaluated preliminary evidence for criterion validity of two brief (<1 min) PA questionnaires with accelerometry, and their ability to identify if individuals meet ACSM/AHA PA recommendations. Methods: 45 health clinic staff wore an accelerometer for seven consecutive days and afterwards completed two brief PA questionnaires, the Physical Activity Vital Sign (PAVS), and the Speedy Nutrition and Physical Activity Assessment (SNAP). Agreement and descriptive statistics were calculated between the PAVS or SNAP and accelerometry in order to measure each questionnaire’s ability to quantify the number of days participants achieved ⩾30 min of moderate–vigorous PA (MVPA) performed in bouts of ⩾10 continuous minutes. Participants with <5 days of ⩾30 bout-min of MVPA were considered insufficiently active according to PA recommendations. Findings: There was a significant positive correlation between number of days with ⩾30 bout-min MVPA and the PAVS (r=0.52, P<0.001), and SNAP (r=0.31, P<0.05). The PAVS had moderate agreement with accelerometry for identifying if individuals met or did not meet PA recommendations (κ=0.46, P<0.001), whereas SNAP had poor agreement (κ=0.12, P<0.05). Conclusions: This study provides preliminary evidence of criterion validity of the PAVS and SNAP with accelerometry and agreement identifying if respondents meet current (2008) ACSM/AHA aerobic PA recommendations. The PAVS and SNAP should be evaluated further for repeatability, and in populations varying in PA levels, age, gender, and ethnicity.
We have developed a chemical kinetics simulation that can be used as both an educational
and research tool. The simulator is designed as an accessible, open-source project that
can be run on a laptop with a student-friendly interface. The application can potentially
be scaled to run in parallel for large simulations. The simulation has been successfully
used in a classroom setting for teaching basic electrochemical properties. We have shown
that this can be used for simulating fundamental molecular and chemical processes and even
simplified models of predator–prey interactions. By giving the simulated entities spatial
extent in the lattice, the particles do not interpenetrate, and clusters of particles can
spatially exclude one another. Our simulation demonstrates that spatial inhomogeneity
leads to different results than those that are obtained by using standard ordinary
differential equation models, as previously reported.
A discussion of resonant tunneling physics in both diode and transistor heterojunction structures is presented. It is evident the In(GaAI)As/InP system is significantly superior for this application. We also present results on resonant tunneling in lower dimensional systems.
In this paper present experimental results on the quality of AIGaAs material after high concentrations of impurities have been introduced for the purpose of impurity induced disordering. A comparison between Zn and Si diffusion is presented, and the nature of the transition region between uniform alloy and as-grown periodic structure has been characterized both experimentally and theoretically. Device implications of these observations is discussed.
We have successfully used an ultrathin (20-50 Å) native oxide layer on the surface of InP as an etch mask for transferring patterns onto the substrate. The oxide mask is grown in situ in O2 atmosphere, and the mask pattern is created by locally removing the oxide with a focused ion beam. Depending on the thickness of the mask, the required ion dose varies from 2×1014 to 2×1015 Ga/cm2. C12 etches the exposed areas selectively. Features as deep as 3 microns have been produced with such an ultrathin mask. High quality InGaAs and InP epitaxial layers have been overgrown on such patterned substrate. We have studied the formation and desorption of the oxide mask with Auger analysis. We also demonstrate that the secondary charged particle emission from a substrate during ion exposure provides a useful signal for the determination of the required dose.
We have examined spectrally resolved photoconductivity and photoluminescence from InAs/Ga1–xInxSb strained-layer superlattices, which have been proposed as infrared detectors in the 8-14 μm region. Our measurements indicate that the energy gaps of the strained–layer superlattices are substantially smaller than those of InAs/GaSb superlattices with similar layer thicknesses, in agreement with previous theoretical predictions. Measurements on InAs/Ga1–xInxSb superlattices with x=0 and 0.25 and layer thicknesses of 25 – 45 A indicate superlattice band gaps of 3 – 15 μm, in excellent agreement with gaps calculated by a two band k · p model. Our results demonstrate that far-infrared energy gaps are compatible with the thin layers necessary for strong optical absorption in type-IT superlattices, and suggest that InAs/Ga1–xInxSb superlattices are promising candidates for far-infrared detection.
Sil−xGex alloy layers and ultra-short period SimGen superlattices on alloy buffer layers of the same concentration have been grown by MBE. The superlattices as a whole have been shown to have the lattice constant of the underlying alloy buffer layer, the individual Si and Ge layers being fully strained. Samples with a graded Ge content have been used to study the relaxation as a function of Ge content by means of X-ray diffraction and RBS and channeling.
Transmission electron spectroscopy reveals that interface roughness is not simply statistical in these superlattices. Rather, electron diffraction shows additional features from a period doubling in the (111) directions, indicating that a corresponding interfacial ordering occurs. These features show 2- or 3-dimensional behavior depending on the thickness of the Si and Ge layers in the superlattices. Annealing studies show these features to persist even for annealing temperatures where the superlattices disintegrate into alloys.
Buried single-crystal layers of CoSi2 were formed in 150Ω-cm, p-type (100) silicon by high dose implantation of Co followed by furnace annealing. Subsequently, epitaxial silicon layers were grown over these buried CoSi2 layers using SiCl2H2 /HCI/H2. The RBS channel yield of the buried CoSi2 and the epitaxial Si layer is less than 4% indicating good crystallinity of the layer. The defect density in the epitaxial silicon layer as revealed by a dilute Schimmel etch, was in excess of 108 dislocations/cm2 which appear to originate from <111> CoSi2 facets. However, both the substrate/CoSi2 and the CoSi2/epi interface are single crystal as revealed by lattice fringes in TEM. To our knowledge, this is the first report of such a structure.