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An improved variational optimization approach is established to optimize and analyse the propulsion efficiency of the high-altitude contra-rotating propellers for high-altitude airships based on the Vortex Lattice Lifting Line Method. The optimum radial circulation distribution, chord and pitch distribution are optimized under the maximum lift-to-drag ratio of aerofoils. To consider the effects of the actual Reynolds number and the Mach number of each aerofoil section, aerodynamics such as lift coefficient, drag coefficient and lift-to-ratio are obtained by interpolating a CFD database, which is established by numerical simulations under different Reynolds number, Mach number and angles-of-attack. The improved method is verified by validation cases on a high-altitude CRP using the three-dimensional steady Reynolds-averaged Navier-Stokes solver and moving reference frames technique. The optimization results of thrust, torque and efficiency for both the individual front/rear propeller and CRP are shown to agree reasonably well with the CFD results. Using the improved approach, the influence of blade numbers, diameter, rotation speeds, axial distance and torque ratio on the optimum efficiency of CRPs is illustrated in detail by conducting parametric studies.
Rabies is one of the major public health problems in China, and the mortality rate of rabies remains the highest among all notifiable infectious diseases. A meta-analysis was conducted to investigate the post-exposure prophylaxis (PEP) vaccination rate and risk factors for human rabies in mainland China. The PubMed, Web of Science, Chinese National Knowledge Infrastructure, Chinese Science and Technology Periodical and Wanfang databases were searched for articles on rabies vaccination status (published between 2007 and 2017). In total, 10 174 human rabies cases from 136 studies were included in this meta-analysis. Approximately 97.2% (95% confidence interval (CI) 95.1–98.7%) of rabies cases occurred in rural areas and 72.6% (95% CI 70.0–75.1%) occurred in farmers. Overall, the vaccination rate in the reported human rabies cases was 15.4% (95% CI 13.7–17.4%). However, among vaccinated individuals, 85.5% (95% CI 79.8%–83.4%) did not complete the vaccination regimen. In a subgroup analysis, the PEP vaccination rate in the eastern region (18.8%, 95% CI 15.9–22.1%) was higher than that in the western region (13.3%, 95% CI 11.1–15.8%) and this rate decreased after 2007. Approximately 68.9% (95% CI 63.6–73.8%) of rabies cases experienced category-III exposures, but their PEP vaccination rate was 27.0% (95% CI 14.4–44.9%) and only 6.1% (95% CI 4.4–8.4%) received rabies immunoglobulin. Together, these results suggested that the PEP vaccination rate among human rabies cases was low in mainland China. Therefore, standardised treatment and vaccination programs of dog bites need to be further strengthened, particularly in rural areas.
A nonlinear station-keeping control method for a multi-vectored propeller airship under unknown wind field with thrust saturation is developed, which is composed of three modules: nonlinear model predictive controller (NMPC), disturbance observer (DOB) and tracking differentiator (TD). The nonlinear kinematics and dynamics models are introduced, and the wind effect is considered by the wind-induced aerodynamic force. Based on both models, an explicit NMPC is designed. Then a nonlinear DOB is introduced to estimate the wind disturbance. A TD, showing the relationship between the maximum propulsion force and the maximum flight acceleration, is proposed to handle the thrusts’ amplitude saturation. Stability analysis shows that the closed-loop system is globally asymptotically stable. Simulations for a multi-vectored propeller airship are conducted to demonstrate the robustness and effectiveness of the proposed method.
Nutraceuticals have generated interest as a way to mitigate the cognitive decline in older adults. The aim of this systematic review was to determine the evidence for these claims from the scientific literature in randomised, double-blinded, controlled trials (duration: ≥1 year; participants: n≥100; age(mean): ≥65 years). Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched four electronic databases (PubMed, Scopus, CINAHL and Web of Science) and identified twenty-five studies published between the 15·June·2006 and 14·June·2016. Interventions included B-vitamins, n-3 fatty acids, antioxidant vitamins and herbs. Of the B-vitamin studies, four found benefits to cognition with supplementation. The first of these B-vitamin studies, in individuals with mild cognitive impairment (n 266; duration=2 years), included benefit to executive function (P=0·015) and improvements in the Mini-Mental State Examination (MMSE) among participants with baseline homocysteine above 11·3 µmol/l (P<0·001). In the same sample, the second study found cognitive benefits of B-vitamins dependent on the higher baseline plasma n-3 fatty acid status. The third B-vitamin study (n 900; duration=2 years) reported improved performance in immediate (P=0·046) and delayed recall (P=0·013), whereas the fourth study (n 856; duration=2 years) reported slower rate of cognitive decline in the MMSE (P=0·05). One study investigating DHA treatment (n 402; duration=1·5 years) revealed the slower rate of cognitive change in apoE e4 non-carriers (P=0·03). As only five included studies revealed notable benefits, presently based on the specific compounds explored here, there is not compelling evidence to support the use nutraceuticals to improve cognition in the elderly. Future long-term trials of nutraceuticals should investigate interactions with lifestyle, blood biomarkers and genetic risk factors.
In general, an airship is equipped with hybrid-heterogeneous actuators: the aerodynamic surfaces, the vectored propellers and the buoyant ballonets. The aerodynamic surfaces have high efficiency in attitude control at high speed. However, vectored propellers are also introduced here for attitude control under the special working condition of low airspeed. Due to the lower thrust-to-weight ratio, the composite control of hybrid-heterogeneous actuators is the primary object in controller design for an airship. In composite attitude control, first the attitude moment allocation between aerodynamic control surfaces and vectored propellers is designed according to different dynamic airspeed, to achieve the smooth motion transition from low to high airspeed, then the weighted generalised inverse (WGI) is used to design the reconfigurable actuator allocation among the homogeneous multi-actuators, where the authority of every actuator can be decided by setting the corresponding value of the weight matrix, thus the control law is unchanged under different actuator configurations. Taking the mid-altitude airship as an example, the simulations of position control, trace tracking and altitude control are provided. Simulation results demonstrate that the attitude moments allocation obtains moment distribution between the aerodynamic surfaces and the vectored propellers under different airspeeds; the reconfigurable actuator allocation achieves a good distribution and reconfiguration among homogeneous actuators, thereby enhancing the reliability of the control system.
In the theory research and engineering practice, more basic inflatable models are essential for the mechanical property analysis of inflatable structures. Firstly, this paper presents a model of the tapered inflatable cantilever beam based on Timoshenko's theory and analyzes its deformation under a concentrated force. Moreover, the following forces resulting from internal pressure and taper ratio are introduced into the equilibrium equations of the deformed configuration. Thus, the model is optimized compared to the existing one for a straight beam. To verify the effectiveness and the superiority of the established model, the theoretical method based on the model and FEM method are compared by adopting an example about the tapered beams. Finally, the theoretical method is applied in analyzing the influence of geometry and estimating a valid range of taper ratio. By the criterion of the same amount material area, the optimum taper ratio is obtained.
In spite of its frustrated lattice, the multiferroic
Lu0.5Sc0.5FeO3 exhibits two consecutive
magnetic transitions at TN1 ≈ 175 K and TN2 ≈ 70 K determined from neutron diffraction. In the ordered
state, magnetic fluctuations are present, most likely arising from the in-plane
frustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover of
the magnetic intensity is observed from elastic to inelastic upon warming,
indicating that magnetic fluctuations persist well above TN1, a common feature in hexagonal multiferroics.
CMOS-compatible fabrication and etching processes are often used in subwavelength grating structures manufacturing, it normally generates tapered sidewall profile of the gratings. In this work, we have studied the impacts on resonance mode characteristics of subwavelength grating structures due to the tapered sidewall profile, as well as grating with high aspect ratio. Our simulation results have revealed that both of these two factors play important roles on the resonance mode behavior of subwavelength grating devices. We also discussed the mechanism between the guided mode resonance and the grating cavity mode resonance. Our study will provide guidance for a series of integrated photonics devices applications, such as compact optical filter, photonics amplifier, and lasers, while the realistic subwavelength grating structure is considered.
One main difference between practical device and ideal design for subwavelength grating structure is the tapered sidewall profile of grating, which is normally obtained by the practical CMOS-compatible fabrication and etching process. Our work has investigated the impacts of tapered sidewall profile on the subwavelength grating wideband reflector characteristics. Both zero-contrast gratings (ZCG) and high- contrast gratings (HCG) are numerically investigated in detail and the results show a distinct differences of the impacts of tapered sidewall profile of grating. The simulation results reveal that this factor play a critical role in determining the reflection bandwidth, average reflectance, and the band edge. Our study has potential in guiding the utilization of subwavelength grating wideband reflector on application of a variety of nanophotonic devices and their integration, as well as to facilitate the design of the fabrication process on the control of tapered sidewall profile.
Nitrogen (N) supply is essential for achieving high grain yield in maize production, but excessive N application can lead to lodging risks and potential yield loss. The main objective of the present study was to investigate the effect of ethephon application under different N fertilizer rates in reducing maize lodging. Field experiments were conducted to determine the interactive effects of ethephon (0 and 180 g/ha) and N rate (0, 75, 150 and 225 kg N/ha) on the morphological and chemical characteristics of basal internode and yield across two summer maize-growing seasons (2011/12) in Wuqiao of the North China Plain. Findings showed that ethephon significantly increased the maximum diameter of the 7th to 14th internodes, and decreased the internode lengths, which led to a decrease in plant and ear heights under different N rates. Significant ethephon × N interaction effects were observed on the diameter and length of internode, dry weight per unit internode length and breaking resistance. Ethephon significantly increased N, cellulose and hemicellulose contents of the basal internode, but cellulose and hemicellulose contents decreased as the rate of N application increased. Internode diameter, dry weight per unit internode length, and N content of the basal internode were significantly positively correlated with breaking resistance. Ethephon significantly increased grain yield and harvest index in 2011, but not in 2012. Grain yield and above-ground biomass were increased with increasing N application in both growing seasons, showing linear and quadratic responses. These results suggested that ethephon could increase stalk strength by improving the morphological and chemical characteristics of the basal internode, and maintain high yield and biomass under high N rates.
In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven “MW-like” halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~ 103–4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs — precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~ 6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD–generating dwarf models) to recover the luminosity function of infalling dwarf galaxies — and the detailed accretion history of the halo — across cosmic time.
Computed tomography (CT) is an important tool in clinical diagnostic imaging enabling three-dimensional anatomic imaging at high spatial resolution with short scan times. However, X-ray attenuation differences in physiological fluids and soft tissues are relatively small, requiring the use of contrast agents to achieve sufficient imaging contrast. Recent advances in energy-sensitive X-ray detectors have made spectral (color) CT commercially feasible by unmixing the energy-dependent attenuation profile of different materials and will potentially enable molecular imaging in CT. In order to leverage these capabilities for diagnostic imaging, we are developing a spectral library of nanoparticle contrast agents with K-shell absorption edges spaced at least 10 keV apart. The objective of this study was to demonstrate the ability of spectral CT to simultaneously detect up to three different contrast agents and unmixed their signals to create color images. Gadolinium oxide (Gd), hafnium oxide (Hf) and gold (Au) were chosen due to exhibiting K-edges spaced 10-20 keV apart. Core-shell nanoparticles of each composition were synthesized by various methods to have a core diameter of 15-20 nm and were coated with a silica shell at least 2-4 nm in thickness to create a common platform for surface functionalization. The contrast agents were imaged in a soft tissue equivalent phantom using source-side method for spectral CT imaging. The source-side approach utilized monochromatic synchrotron radiation at the Argonne National Laboratory which, while not clinically applicable, served as a gold standard due to providing the highest spectral resolution. The nanoparticles designed for this study have broad applications in biomedical imaging due to their modular assembly, potential for enabling multi-modal detection, and surface functionalization with biomolecules (e.g., antibodies, peptides or enzymes) for active targeting.
A stratospheric airship flies at a working altitude of 20km when it takes off from the ground. During ascent and descent, the wind field and thermal environment are highly complex. The thermal environment affects altitude, whereas wind influences the horizontal position of the airship. At a low altitude, this horizontal position cannot be controlled by thrusts given the low thrust-to-weight ratio, especially under a large wind field. However, it may be controlled indirectly by the pitch angle during ascent and descent with a certain vertical velocity. This study therefore proposes ascending and descending schemes for a stratospheric airship based on the thermal model. In this model, altitude is determined by the net lift/weight, whereas the horizontal position is controlled by the thrust and pitch. The pitch angle is determined by ballonets and an elevator. To allocate pitch control between the ballonets and the elevator under different airspeeds, pseudo-inverse dynamics of varied weight are introduced. In horizontal position control, the method of chain allocation is then applied between a pitch angle and vectored thrust to control the position of a stratospheric airship during ascent/descent.
We investigated the seasonality of tuberculosis (TB) in Wuhan, China, to evaluate the increased risk of disease transmission during each season and to develop an effective TB control strategy. We applied spectral analysis to the weekly prevalence data of sputum smear positive (SSP) and sputum smear negative (SSN) pulmonary TB reported from 2006 to 2010. Cases of both SSP and SSN feature 1·0- and 0·5-year periodic modes. The least squares method was used to fit curves to the two periodic modes for SSP and SSN data. The curves demonstrated dominant peaks in spring similar to cases reported previously for other locations. Notably for SSP, dominant peaks were also observed in summer. The spring peaks of SSP and SSN were explained in terms of poorly ventilated and humid rooms and vitamin D deficiency. For the summer peaks of SSP, summer influenza epidemics in Wuhan may contribute to the increase in TB prevalence.
The “pad-in-a-bottle” (PIB) approach to planarization is a non-traditional chemical mechanical polishing (CMP) process in which slurry containing polymer beads is used. The approach is hypothesized to be able to perform polishing by mixing polymer beads with similar chemical and mechanical properties as pad asperities into the slurry to provide force application and polishing contacts, so that a traditional CMP pad is not needed. Pad-in-a-bottle could provide predictable and controllable mechanical contacts through bead size control, which could substantially reduce process variability. Pad-in-a-bottle also has the potential to reduce the CMP consumable cost. In this work, we propose a physical model to understand the behavior of the pad-in-a-bottle approach and estimate the relationship of applied pressure and material removal rate in this variant of CMP. Two specific cases of polymer bead formation are considered in our modeling work, bead packing and bead stacking. Model prediction shows that the two bead formation cases generate distinctly different polishing mechanisms: material removal is applied pressure driven in bead packing, but contact event driven in bead stacking. The physical model suggests that in future experiments or applications of pad-in-a-bottle, a polymer bead size distribution or shape variation may be needed to achieve efficient material removal.
Under the FP7 HELIOS project a 16 channel 10G transceiver based on a separate integrated transmitter incorporating hybrid lasers and modulators on silicon and a separate receiver both for 1550nm wavelength range has been demonstrated. An MZM (ITLMZ) chip consisting of a single mode hybrid III-V/silicon laser, a silicon Mach-Zehnder (MZ) modulator and an optical output coupler exhibited 10G operation with high BER. A 200GHz 16 channel receiver with polarization management was obtained with a 2D grating coupler, 2xAWGs and 16 Ge photodiodes. Polarization Dispersion Loss (PDL) was below 1dB, Bandwidth (BW) above 20GHz, receiver sensitivity in the order of 0.08 A/W
Because of the huge volume and inflated membrane structure of stratosphere airship, the deformation of stratosphere airship is very sensitive to the change of environment conditions such as wind, temperature and so on. The influence of deformation on manipulation and control is very remarkable. So, during the course of building flight dynamic model of the flexible airship, the added-mass matrix of deformation is very important part in the state equations of dynamic models. For obtaining the accurate added-mass matrix of different flexible airship, we proposed an approach that can calculate the added-mass matrix of a flexible airship with arbitrary geometry shape by the panel method. Through the comparison of results of computation and theory for ellipsoid of revolution and the flexible Skyship-500 airship, the proposed method can calculate the added-mass matrix for arbitrary geometric shape very accurately.