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Signal-in-space (SIS) continuity and availability are important indicators of performance assessment for Global Navigation Satellite Systems (GNSSs). The BeiDou Navigation Satellite System (BDS) Open Service Performance Standard (BDS-OS-PS-1.0) has been released, and the corresponding public performance indicators have been provided, but the actual SIS performance is uncertain to users. SIS continuity and availability are primarily related to unscheduled outages (failures). Therefore, based on the existing failure classification system and actual operation modes, four types of failure modes are first analysed: long-term failure related to satellite service period, maintenance failure related to satellite manoeuvring, short-term failure associated with random repairable anomalies and equivalent failure corresponding to a combination of the above three types of failures. Second, based on the failure classification and selected precise and broadcast ephemerides from 2015–2016, the Mean Time Between Failure (MTBF) and Mean Time To Repair (MTTR) of each failure type are obtained using appropriate detection methods. Finally, using a corresponding assessment model, the SIS continuity and availability of BeiDou are calculated for individual and equivalent failure cases, and these are compared with the provided index in the BDS Open Service Performance Standard.
Although the streaked optical pyrometer (SOP) system has been widely adopted in shock temperature measurements, its reliability has always been of concern. Here, two calibrated Planckian radiators with different color temperatures were used to calibrate and verify the SOP system by comparing the two calibration standards using both multi-channel and single-channel methods. A high-color-temperature standard lamp and a multi-channel filter were specifically designed for the measurement system. To verify the reliability of the SOP system, the relative deviation between the measured data and the standard value of less than 5% was calibrated out, which demonstrates the reliability of the SOP system. Furthermore, a method to analyze the uncertainty and sensitivity of the SOP system is proposed. A series of laser-induced shock experiments were conducted at the ‘Shenguang-II’ laser facility to verify the reliability of the SOP system for temperature measurements at tens of thousands of kelvin. The measured temperature of the quartz in our experiments agreed fairly well with previous works, which serves as evidence for the reliability of the SOP system.
This paper presents a lower-limb exoskeleton that is actuated by pneumatic muscle actuators (PMAs). This exoskeleton system is composed of the mechanical structures, a treadmill, and a weight support system. With the cooperative work of the three parts, the system aims to assist either the elderly for muscle strengthening by conducting walking activities or the stroke patients during a rehabilitation training program. A mechanism is developed to separate the PMAs from the wearer’s legs to reduce the subject’s physical exertion. Furthermore, considering the difficulty in the modeling of proposed PMAs-driven exoskeleton, a safe and model-free control strategy called proxy-based sliding mode control (PSMC) is used to ensure proper control of the exoskeleton. However, the favorable performances are strongly dependent on the appropriate control parameters, which may be difficult to obtain with blind tuning. Therefore, we propose a global parameters optimization algorithm called switch-mode firefly algorithm (SMFA) to automatically calculate the pre-defined object function and attain the most applicable parameters. Experimental studies are conducted, and the results show the effectiveness of the proposed method.
Owing to the development of new technologies, the epigenome, a second dimensional method for genome analysis has emerged. Epigenetic mechanisms, including DNA methylation, histone modifications and noncoding RNAs, regulate gene expression without changing the genetic sequence. These epigenetic mechanisms normally modulate gene expression, trans-generational effects and inherited expression states in various biological processes. Abnormal epigenetic patterns typically cause pathological conditions, including cancers, age-related diseases, and specific cartilage and bone diseases. Facing the rapidly developing epigenetic field, we reviewed epigenetic mechanisms and their involvement with the skeletal system and their role in skeletal development, homeostasis and degeneration. Finally, we discuss the prospects for the future of epigenetics.
Oedaleus asiaticus Bey. Bienko is a significant grasshopper pest species occurring in north Asian grasslands. Outbreaks often result in significant loss in grasses and economic losses. Interestingly, we found this grasshopper was mainly restricted to Stipa-dominated grassland. We suspected this may be related to the dominant grasses species, Stipa krylovii Roshev, and hypothesized that S. krylovii contributes to optimal growth performance and population distribution of O. asiaticus. A 4 year investigation showed that O. asiaticus density was positively correlated to the above-ground biomass of S. krylovii and O. asiaticus growth performance variables (survival rate, size, growth rate) were significantly higher in Stipa-dominated grassland. A feeding trial also showed that O. asiaticus had a higher growth performance when feeding exclusively on S. krylovii. In addition, the choice, consumption and the efficiency of conversion of ingested food (ECI) by O. asiaticus was highest for S. krylovii compared with other plant species found in the Asian grasslands. These ecological and biological traits revealed why O. asiaticus is strongly associated with Stipa-dominated grasslands. We concluded that the existence of S. krylovii benefited the growth performance and explained the distribution of O. asiaticus. These results are useful for improved pest management strategies and developing guidelines for the monitoring of grasshopper population dynamics against the background of vegetation succession and changing plant communities in response to activities such as grazing, fire and climate change.
Usually, humanoid walking gaits are only roughly distinguished between stable and
unstable. The evaluation of a stable humanoid walking gait is difficult to
quantify in scales. And, it is extremely hard to adjust humanoid robots in
suitable a walking gait for different movement objectives such as fast walking,
uneven floor walking, and so on. This paper proposes a stability margin
constructed by center of pressure (COP) to evaluate the gait stability of
humanoid walking. The stability margin is modeled by the COP regions that a
humanoid robot needs for stable standing. We derive the mathematical model for
COP position by dividing the walking gait into single and double support phases
in order to measure the stability of the COP regions. An actual measuring system
for the stable COP regions is designed and implemented. The measured COP
trajectory of a walking gait is eventually evaluated with respect to the stable
COP regions for the stability margins. The evaluation focuses on weak stability
areas to be improved for robust walking gaits. To demonstrate the robustness of
the improved walking gait, we replicate the experiment on three different
terrains. The experiments demonstrate that the walking gaits developed based on
stable COP region can be applied for different movement objectives.
At the end of 2013, China reported a countrywide outbreak of measles. From January to May 2014, we investigated the clinical and immunological features of the cases of the outbreak admitted to our hospital. In this study, all 112 inpatients with clinically diagnosed measles were recruited from the 302 Military Hospital of China. The virus was isolated from throat swabs from these patients, and cytokine profiles were examined. By detecting the measles virus of 30 of the 112 patients, we found that this measles outbreak was of the H1 genotype, which is the major strain in China. The rates of complications, specifically pneumonia and liver injury, differed significantly in patients aged <8 months, 8 months to 18 years, and >18 years: pneumonia was more common in children, while liver injury was more common in adults. Pneumonia was a significant independent risk factor affecting measles duration. Compared to healthy subjects, measles patients had fewer CD4+IL-17+, CD4+IFN-γ+, and CD8+IFN-γ+ cells in both the acute and recovery phases. In contrast, measles patients in the acute phase had more CD8+IL-22+ cells than those in recovery or healthy subjects. We recommend that future studies focus on the age-related distribution of pneumonia and liver injury as measles-related complications as well as the association between immunological markers and measles prognosis.
Investigation of customer participation in new product development (NPD) performance has yielded conflicting results. This study explores the idea that intensive customer participation is not always better. Instead, the usefulness of customer participation in NPD is determined by the fit between product innovativeness and customer participation as information providers and as co-developers. An empirical study of 196 NPD projects of Taiwanese high-tech firms is analyzed by structural equation modeling. The findings show that product innovativeness negatively moderates the impact of customer participation as information providers on NPD outcome. Thus, the greater the involvement of customer participation as information providers in radical innovation projects, the lower the NPD outcome. Moreover, our results also indicate that product innovativeness positively affects the relationship between customer participation as a co-developer and NPD outcome, which suggest that the more customer participation as a co-developer in a radical innovation project, the better the NPD outcome.
The crystal structure of a-plane GaN/ZnO heterostructures on r-plane sapphire was investigated by using the XRD and TEM measurment. It was found the formation of (220) ZnGa2O4 and crystal orientation of semipolar (10
3) GaN at GaN/ZnO interface. The epitaxial relation of normal surface direction are the sapphire (1
02) // a-GaN (11
0) and ZnGa2O4 (220) // semi-polar GaN (10
). Beside, the emission peak energy of ZnO appears shift about 60 meV in the GaN/ZnO/GaN heterostructures due to the re-crystallization of ZnO layer with Ga or N atom and the formation of the localized state.
We propose a direct solver for the three-dimensional Poisson equation with a variable coefficient, and an algorithm to directly solve the associated sparse linear systems that exploits the sparsity pattern of the coefficient matrix. Introducing some appropriate finite difference operators, we derive a second-order scheme for the solver, and then two suitable high-order compact schemes are also discussed. For a cube containing N nodes, the solver requires arithmetic operations and memory to store the necessary information. Its efficiency is illustrated with examples, and the numerical results are analysed.
We have investigated TiN/TiSi2 films as diffusion barriers between copper and silicon. The TiN/TiSi2 films were formed by annealing Ti/Si via rapid thermal process at a temperature of 850'C for 30 seconds in N2 ambient. The contact resistance and leakage current of the Cu/TiN/TiSi 2/n+-p Si contact system were measured after sintering at 350-600°C for 30 minutes in an N2 ambient. We found an abrupt increase of contact resistance occurred at a sintering temperature of 600°C. From the leakage current of n+-p diode, we observed that the thermally stable temperature was about 475ycC. Meanwhile, XTEM photographs showed small Cu3Si crystallites with size of about 0.25 μm precipitated in the n+Si substrate at a sintering temperature 500°C. The formation of Cu3Si increases the occupied volume, generates the gap between TiSi2 and n+Si, and gradually increases the specific contact resistance. SIMS profiles also showed that a certain amount of Cu atoms diffused into the n+-p Si junction and that Si atoms existed in the Cu film. The Cu3Si formation across the n+-p junction can explain the abrupt increase in the leakage current measurement at 500°C. So the failure mechanisms for contact resistance and leakage current are different.
High-Tc superconducting Bi-Pb-Sr-Ca-Cu oxide with zero resistance temperature at above lOOK has been synthesized via the use of ethylenediamine-tetra-acetate(EDTA) colloid and corresponding metal nitrates. Remarkable sinterability of the precursor requires shorter time to achieve superconducting phases than conventional solid-state reactions. Superconducting properties were measured electrically and magnetically. The thermal decomposition, X-ray diffraction and microstructural characteristics of the precursor and the sintered samples were also discussed.
The characteristics of YBa2Cu3O7−x (YBCO) thin films by laser ablation on MgO bicrystals have been investigated. The bicrystals were fabricated by hot pressing two single crystals with the configuration of  tilt boundaries. The YBCO films were epitaxial grown with C-axis normal to the both adjacent grains of bicrystals. The FWHM about (005) reflection was 0.4–0.5 degree, indicating the high degree of the oriention for the film with small mosaic spread. Our preliminary study showed that the typical value of Jc on either side of the bicrystal boundary was 0.4–10×106 A/cm2 at 15K, while that across the 10° tilt boundaries was 0.3–9×105 A/cm2 at 15K. These results implied that the artificial grain boundaries effectively weakened the supercurrent, and therefore, the weak-link properties of artificial boundaries were more easily controllable than those of naturally occuring grain boundaries.
Effect of heat treatment on the properties and microstructure of non-stoichiometric Ti-Mn based hydrogen storage alloys were investigated. The results were presented that the hydrogen storage capacity was increased and the width of P-C-T Plateau extended, but the slope of plateau increased after heat treatment. Through SEM, EDS and XRD analysis, it was found that the crystal parameters and cell volume was increased, meanwhile the composition homogeneity effectively enhanced and the content of C15 phase decreased after heat treatment. The accretion of slope of plateau would be related to the ratio of valence electron/atom of the alloys.
A new method of epitaxial growth of CoSi2 film on Si substrate by ternary solid state interaction is investigated. XRD, RBS and TEM show that single-crystalline CoSi2 can be formed on both Si (111) and (100) substrates by using Co/Ti/Si or TiN/Co/Ti/Si multilayer. The evolution of multilayer structure and its resistivity is studied and epitaxy mechanism is discussed. Experimental results indicate strong affinity between Co and Si. During the ternary interaction the epitaxial CoSi2 can be grown directly on Si and its growth may behave as a diffusion controlled process. The thickness of Ti layer and the annealing procedure have important effect on CoSi2 epitaxial growth.
A single crystal GaAs/Si heterostructure has been fabricated using the “two step” version of the traditional halogenide VPE technique. The X-ray diffraction spectroscopy, the high resolution electron microscopy observation and the Raman scattering spectroscopy have been used to analyze the structure of the GaAs epitaxial film on Si, while the X-ray photoelectron energy spectroscopy has been used to determine the chemical structure of the GaAs epilayer. The results indicate that the epilayer is a stoichiometric GaAs single crystal film.
Silicon implantation has been found to dramatically enhance the grain size of polysilicon crystallized from LPCVD a-Si by retarding the nucleation process at the substrate interface. Corresponding improvement in TFT device performance was also observed, resulting in field effect mobilities as high as 109 cm2/Vs in devices with 1000 Å thick Si active layer. This effect is more significant in device fabrication processes with higher temperature, possibly due to increasingly efficient removal of implant related defects.
Supersaturated high-conductivity polycrystalline silicon (polysilicon) formed by rapid thermal processing (RTP) is a promising new material for emitters, contacts and diffusion sources in advanced high-speed bipolar and MOS IC technologies.
A matrix of processing conditions was used to evaluate the effect of polysilicon thickness, implant dose, RTP conditions and the nature of the substrate on the dopant diffusion in both the polysilicon and single crystal substrate and also on the interface properties.
Results of conductivity measurements, spreading resistance profiling (SRP), secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS)/channeling are presented. The results have proved the formation of shallow, defect-free junctions and epitaxial emitters with low series resistance and improved contact properties.
An electron-beam-induced voltage (EBIV) technique has been developed to measure the barrier height of Schottky diodes. The principle of this technique is described and is compared with the conventional electron-beam-induced current (EBIC) technique. Applications of both techniques are illustrated in a study of composite silicide Schottky diodes with mixed high and low barrier areas formed using bilayer and co-evaporated Pd-Ti and Pt-Ti films on silicon substrates. The difficulty of using EBIC for quantitative studies of diode characteristics is discussed and contrasted with the advantages of the EBIV technique. The extension of the EBIV technique to contactless measurements of barrier height variation with good lateral resolution is described.
The cyclic voltammetry stripping (CVs) behavior of the tin-doped indium oxide (ITO) on SiO2 in 0.3M HCl is reported. The CVs result showed an obvious reduction-current peak that occurred during the first cathodic potential scanning. Smaller reduction current and more negative potential of the reduction-current peak were also observed for the ITO that was annealed at 500 °C. The result was attributed to the replenished oxygen-deficient site and the oxygen anion density is decreased in the ITO. The present study has proved that CVs is a useful method to differentiate the carrier concentration in ITO film controlled by different pretreatments. Many spherical In-Sn particles were formed on the ITO when the reduction current took place. During precipitation of these spherical particles, the grain boundaries of the ITO were dissolved and the ITO surface nearby the grain boundaries offered a preferred nucleation site for the formation of these spherical In-Sn particles. Based on the microstructure observed and the result derived from the short potential range scanning, the formation mechanism of the spherical particle is proposed.