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High inductive helical support provides a solution to controlling the alignment error of inner electrodes in magnetically insulated transmission lines (MITLs). Three-dimensional particle-in-cell simulations were performed to examine the current loss mechanism and the effects of structural parameters on electron flow in an MITL with a helical inductor. An empirical expression related to the ratio of electron current loss to anode current and the ratio of anode current to self-limited current was obtained. Electron current loss caused by helical inductor with different structures was displayed. The results indicate that the current loss in an MITL, near an inductive helical support, comprises both the inductor current and the electron current loss. The non-uniform structure and current of a helical inductor cause an abrupt change in the magnetic field near the helical support, which leads to anomalous behavior and current loss of electron flow. In addition, current loss in the inductive helical-supported MITL is negligible when the inductance of the support is sufficiently high. This work facilitates the estimation of electron current loss caused by the inductive helical support in MITLs.
High-power orbital angular momentum (OAM) beams have distinct advantages in improving capacity and data receiving for free-space optical communication systems at long distances. Utilizing the coherent combination of a beam array technique and helical phase approximation by a piston phase array, we have proposed a generating system for a novel high-power beam carrying OAM, which could overcome the power limitations of a common vortex phase modulator and a single beam. The characteristics of this generating method and the orthogonality of the generated OAM beams with different eigenstates have been theoretically analyzed and verified. Also a high-power OAM beam produced by coherent beam combination (CBC) of a six-element hexagonal fiber amplifier array has been experimentally implemented. Results show that the CBC technique utilized to control the piston phase differences among the array beams has a high efficiency of 96.3%. On the premise of CBC, we have obtained novel vortex beams carrying OAM of
by applying an additional piston phase array modulation on the corresponding beam array. The experimental results agree approximately with the theoretical analysis. This work could be beneficial to areas that need high-power OAM beams, such as ultra-long distance free-space optical communications, biomedical treatments, and powerful trapping and manipulation under deep potential wells.
We present a high-peak-power, near-infrared laser system based on optical parametric chirped pulse amplification pumped by a home-built picosecond pumping laser, which can generate over 40 mJ energy at 1450 nm center wavelength and operate at 100 Hz repetition rate. Subsequently, the chirped laser pulses are compressed down to 60 fs with 26.5 mJ energy, corresponding to a peak power of 0.44 TW. This high-energy, long-wavelength laser source is highly suitable for driving various nonlinear optical phenomena, such as high-order harmonic generation and high-flux coherent extreme ultraviolet/soft X-ray radiation.
High-peak-power transform-limited narrow-linewidth nanosecond all-fiber lasers are desired in a range of applications. However, their linewidths will be broadened by self-phase modulation (SPM). We propose a novel concept that generates transform-limited laser pulses by temporally shaping the pulse seed. The impact of the pulse shape on SPM-induced spectral broadening was studied numerically and experimentally. It was found theoretically that the square-shape pulsed laser is immune to SPM-induced spectral broadening. Based on this principle, we built a high-peak-power, linearly polarized, square-shape nanosecond all-fiber laser in a master oscillator power amplifier (MOPA) configuration. Stimulated Brillouin scattering (SBS) limited peak powers of 4.02 kW, 5.06 kW, 6.52 kW and 9.30 kW were obtained at pulse widths of 8 ns, 7 ns, 6 ns and 5 ns. Thanks to the square-shape pulsed seed, the linewidths at maximum peak power remained at 129.5 MHz, 137.6 MHz, 156.2 MHz and 200.1 MHz, respectively, close to the transform-limited values of 110.8 MHz, 126.6 MHz, 147.7 MHz and 177.3 MHz.
Conventional underwater navigation and positioning methods for Autonomous Underwater Vehicles (AUVs) either require the installation of acoustic arrays, which make AUVs less independent, or result in cumulative errors. This paper proposes an Underwater Terrain Positioning Method (UTPM) using Maximum a Posteriori (MAP) estimation and a Pulse Coupled Neural Network (PCNN) model for highly accurate navigation by AUVs. The PCNN model is used as a secondary discriminant to effectively identify pseudo-anchor points in flat terrain feature areas and to find the true positioning point, which significantly improves the matching positioning accuracy in these areas. Simulation results show that the proposed method effectively corrects Inertial Navigation System (INS) cumulative errors and has high matching positioning accuracy, which satisfy the requirements of AUV underwater navigation and positioning.
Findings from observational studies on the associations between vitamin E intake and stroke risk remain controversial, and the dose–response relationship between vitamin E intake and risk of stroke remains to be determined. We conducted a meta-analysis of prospective studies aiming to clarify the relationships between vitamin E intake and risk of stroke. Relevant studies were identified by searching online databases through to June 2018. We computed summary relative risks (RR) with corresponding 95 % CI. Among 3156 articles retrieved from online databases and relevant bibliographies, nine studies involving 3284 events and 220 371 participants were included in the final analyses. High dietary vitamin E intake was inversely associated with the risk of overall stroke (RR=0·83, 95 % CI 0·73, 0·94), and with the risk of stroke for individuals who were followed-up for <10 (RR=0·84, 95 % CI 0·72, 0·91). There was a non-linear association between dietary vitamin E intake and stroke risk (P=0·0249). Omission of any single study did not alter the summary result. In conclusion, this meta-analysis suggests that there is a significant inverse relationship between dietary vitamin E intake and stroke risk. This meta-analysis provides evidence that a higher dietary vitamin E intake is associated with a lower stroke risk.
The microstructure evolution of the directionally solidified NiAl–Cr(Mo) planar eutectic lamellar structure was studied at 1150 °C and times of up to 400 h. The planar eutectic lamellar structure is obtained at the withdrawal rate range of 2.5–7.5 μm/s. The interlamellar spacing decreases gradually with increasing the withdrawal rate. The lamellar termination (like angular or smooth) commonly exists in the as-DS alloy. After high temperature treatment, the lamellar structure at 2.5 μm/s (interlamellar spacing, 3.7 μm) is almost stable, only a little migration of termination occurs at 400 h. When the withdrawal rate increases to 4.5 μm/s, the coarsening and migration of termination occur at 200 h. The adjacently coarsened terminations assemble when the coarsening processes to a certain degree, thus resulting in the formation of the blocky Cr(Mo) phase. Similarly, the above instable phenomenon occurs at 7.5 μm/s. The relevant instability mechanisms are discussed.
DNA nanostructures are a set of materials with well-defined physical, chemical, and biological properties that can be used on their own or incorporated with other materials for many applications. Herein, the practical aspects of utilizing DNA nanostructures (structural or dynamic) as materials are comprehensively covered. This article first summarizes properties of DNA molecules and practical considerations and then discusses the fundamental design principles of structural DNA nanostructures. Finally, various aspects of dynamic DNA nanostructure-based actuation and computation are included.
To better stabilize the hydrogen-terminated surface, a diamond based metal-insulator-semiconductor field-effect transistor with Zr-Si-N dielectric layer has been investigated. On the diamond epitaxial layer grown by microwave plasma chemical vapor deposition system, Pd films were patterned as the source and drain electrodes by photolithography and electron beam evaporation methods. Then, a Zr-Si-N dielectric layer and W metal film were fabricated as the gate structure by radio frequency magnetron sputtering technique. The device illustrates p-type depletion mode, in which the threshold voltage, maximum transconductance, drain current maximum, capacitance and dielectric constant were calculated to be 3.0V, 1.27mS/mm, -5.16 mA/mm, 0.275μF/cm2 and 7.8, respectively. The result suggest that Zr-Si-N dielectric layer is shown to have the ability to protect the two-dimensional hole gas.
Hydrogels have been widely used in many applications from tissue engineering to drug delivery systems. For both tissue engineering and drug delivery, the mechanical properties are important because they would affect cell-materials interactions and injectability of drugs encapsulated in hydrogel carriers. Therefore, it is important to study the mechanical properties of these hydrogels, particularly at physiological temperature (37°C). This study adopted strain sweep and frequency sweep rotational rheological tests to investigate the rheological characteristics of various tissue engineering relevant hydrogels with different concentrations at 37°C. These hydrogels include alginate, RGD-alginate, and copolymerized collagen/alginate/fibrin. It has revealed that the addition of RGD has negligible effect on the elastic modulus and viscosity of alginate. Alginate gels have demonstrated shear thinning behavior which indicates that they are suitable candidates as carriers for cells or drug delivery. The addition of collagen and fibrin would reinforce the mechanical properties of alginate which makes it a strong scaffold material.
To describe nutrient intakes, characterize dietary patterns and analyse their associations with sociodemographic characteristics among pregnant women in Shaanxi, China.
Population-based cross-sectional survey.
Twenty counties and ten districts in Shaanxi Province of Northwest China, 2013.
Women (n 7462) were recruited using a stratified multistage random sampling method to report diets during pregnancy, at 0–12 months (median 3 months; 10th–90th percentile, 0–7 months) after delivery.
Pregnant women had higher intakes of fat, niacin and vitamin E than the nutrient reference values, while most micronutrients such as vitamin A, folate, Ca and Zn were reportedly low. Women in the highest education, occupation and household income groups had higher nutrient intakes than those in the lowest groups. Nutrient intake differences also existed by geographic area, residence and maternal age at delivery. Three dietary patterns were identified: balanced pattern, vegetarian pattern and snacks pattern. Participants with high balanced pattern scores tended to be better educated, wealthier, 25–29 years old at delivery, working outside and living in urban areas and central Shaanxi. Women with high scores on the vegetarian pattern and snacks pattern tended to be in low balanced pattern score groups, and had lower nutrient intakes than those in the high balanced pattern score groups.
The study suggested that pregnant women in Shaanxi, China had low intakes of most nutrients such as vitamin A, folate and Ca. Dietary patterns and most nutrient intakes varied by sociodemographic characteristics. Targeted programmes are needed to improve dietary intakes and dietary patterns among sociodemographically disadvantaged groups.
To determine the breast-feeding pattern of four main ethnic groups (the Han, Uygur, Tibetan and Zhuang) living in rural western China.
The study utilized a cross-sectional design.
Forty-five counties in ten provinces in western China in 2005.
A sample of 11 783 children younger than 36 months old (8960 Han, 1281 Uygur, 792 Tibetan and 750 Zhuang) and their mothers were recruited using a stratified, multistage, cluster random sampling method.
The rates of exclusive breast-feeding of children at 6 months of age in the Han, Uygur, Tibetan and Zhuang ethnic groups were 11·6 %, 0·8 %, 4·4 % and 13·8 %, respectively. The rates of any breast-feeding for children at 24 months of age were 8·5 %, 25·7 %, 3·0 % and 4·3 % in the four ethnic groups, respectively. After adjusting for related factors, Zhuang children had a higher odds ratio of exclusive breast-feeding to 6 months compared with Han children, whereas Uygur and Tibetan children had lower odds ratio (Zhuang: OR=1·291; 95 % CI 1·006, 1·657; Uugur: OR=0·062; 95 % CI 0·032, 0·121; Tibetan: OR=0·323; 95 % CI 0·220, 0·475). Uygur children had a lower hazard ratio of discontinued breast-feeding compared with Han children, whereas Tibetan children had a higher hazard ratio (Uygur: HR=0·368; 95 % CI 0·333, 0·408; Tibetan: HR=1·366; 95 % CI 1·244, 1·500).
The breast-feeding pattern differed among the Han, Uygur, Tibetan and Zhuang ethnic groups. The results suggest that health education regarding the benefits of breast-feeding is needed in rural western China.