Search

With the rapid development of aviation industry, the study of novel titanium (Ti) alloy with superior mechanical properties is of great significance. In this paper, a newly developed Ti-6Al-2Mo-2Sn-2Zr-2Cr-2V alloy was fabricated by laser directed energy deposition (L-DED), which exhibits coarse β columnar grains containing the basket-weave structure knitted with α phases and β phases. After solution and aging heat-treatment, the fine secondary α phase precipitates, which leads to the increase in microhardness. The as-deposited sample exhibits the tensile strength of 1025 MPa and the elongation of 6.0%. With solution temperature increasing, the strength increases but the plasticity first increases and then decreases. The fracture mechanism shows a mixed of ductile and brittle fracture. The average impact toughness of as-deposited sample in building direction is 40.9 J cm ^−2 higher than that (23.4 J cm ^−2 ) in direction perpendicular to building direction. After solution and aging heat-treatment, the impact toughness improves significantly.

This paper proposes a line-matching algorithm based on feature grouping and a line band descriptor (LBD) to address the insufficient reliability of individual line descriptors for line matching. First, the algorithm generates line-pairs according to geometrical relationships such as the distances and angles between line segments extracted from a single image. Subsequently, the algorithm employs the epipolar line of intersection between two lines in a reference line-pair to constrain candidate pairs corresponding to the reference line-pair. Thereafter, each line in the reference line-pair is considered individually, and its support region and the corresponding support region of each candidate line in the candidate pairs are established, following which an affine transformation is used for unifying the sizes of the reference support region and the candidate support region. Moreover, the LBD descriptor is then used for describing the reference and candidate lines. The Euclidean distances between the reference line and each candidate line descriptors are calculated, and the nearest neighbor distance ratio (NNDR) is used as a criterion for determining the final matching. Finally, the one-to-many and many-to-one line correspondences in matching results are transformed into one-to-one line correspondences by fitting multiple lines to the new line; simultaneously, incorrect matches are eliminated. The experimental results show that the proposed algorithm yields reliable line-matching performance for close-range images.

Two-dimensional (2D) bilayer Janus pellicle (denoted as BJP) of concurrent double aeolotropic electrical conduction, superparamagnetism and luminescence is designed and constructed via electrospinning by using one-dimensional (1D) nanofibers and Janus nanoribbons as constructive units. The BJP comprises top-down two layers tightly bonded together. The top layer is a left-right structured Janus film which consists of Janus nanoribbons array as left and right side, and further, arrangement orientations of Janus nanoribbons in the two sides are perpendicular, leading to double aeolotropic conduction, and the conduction ratio reaches 108 times. The down layer is a non-array luminescent film made of nanofibers. Under the excitation by 291 and 294 nm light, red luminescence of the left side of the top layer and green luminescence of down layer in BJP are respectively achieved. The maximum saturation magnetization of the top layer can reach 21.45 (emu/g). By rolling the 2D BJP into the tube respectively with the ways of rolling from left to right or from up to down, three-dimensional (3D) dual-wall Janus-type tube with the Janus-type tube as outer or inner and the homogeneous tube as inner or outer is obtained.

It is a difficult scientific problem of applied fluid mechanics that the flame is too long and does not match the furnace chamber in a small restricted heating space. This paper aims to investigate the effect of the air quantity distribution ratio on the flame height of a flue gas self-circulation burner. In order to obtain a better combustion emission effect and a shorter flame height, a burner head structure with a small flue gas self-circulation was designed. Numerical simulation was employed to investigate the effect of the different distributions of central air, swirling air and secondary air on flame height. The periodic boundary condition model was adopted and the numerical model was compared and validated by experiment. Correlation analysis was used to determine the influence of the air inlet ratio of each part on the flame height and recirculating flue gas ratio (RFGR). The results show that the influence of different air quantity distributions on flame length is very significant. A reasonable central air ratio is a necessary condition for the good combustion of this flue gas self-circulation burner. Secondary air can effectively increase the RFGR, and flame height was significantly shorter with the increase of RFGR, but when it increased to more than 12%, the flame length was basically no longer shortened. On the premise of stable combustion, when the ratio of central air, swirling air and secondary air are respectively 25%, 35% and 40%, the shortest flame length is achieved. This work reveals an influence mechanism of the flame height of a small burner with a flue gas circulation structure. These results can provide theoretical support and an engineering design basis for the short flame problem in a small restricted space.

We investigate the extreme X-ray variability of a z = 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In the first event, XID 403 brightened by a factor of >2.5 in ≲6.1 rest-frame days in the observed-frame 0.5–5 keV band. The event lasted for ≈5.0–7.3 days, and then XID 403 dimmed by a factor of >6.0 in ≲6.1 days. After ≈1.1–2.5 yr in the rest frame (including long observational gaps), it brightened again, with the 0.5–5 keV flux increasing by a factor of >12.6. The second event lasted over 251 days, and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index Γ = 2.8 ± 0.3) without obscuration during the second outburst, and the rest-frame 2–10 keV luminosity reaches ${1.5}_{-0.5}^{+0.8}\times {10}^{43}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ; there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and R -band (rest-frame ≈2500 Å) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events.

Abstract Background Lung cancer is the most common cancer in China. Previous studies have indicated that lung cancer incidence exhibits remarkable spatial heterogeneity, and lung cancer is related to outdoor air pollution. However, the non-linear spatial association between outdoor air pollution and lung cancer incidence in China remains unclear. Methods In this study, the relationships between the lung cancer incidence of males and females from 207 counties in China in 2013 with annual concentrations of PM2.5, PM10, SO2, NO2, CO and O3 were analysed. GeoDetector q statistic was used for examining the non-linear spatial association between outdoor air pollution and incidence of lung cancer. Results An apparent spatial and population gender heterogeneity was found in the spatial association between outdoor air pollution and lung cancer incidence. Among the six selected pollutants, SO2 has the greatest influence on lung cancer (q = 0.154 in females) in north China. In the south, each selected pollutant has a significant impact on males or females, and the mean q value in the south is 0.181, which is bigger than that in the north (q = 0.154). In addition, the pollutants have evident non-linear interaction effects on lung cancer. In north China, the interaction between SO2 and PM2.5 is the dominant interaction, with q values of 0.207 in males and 0.334 in females. In the south, the dominant interactive factors are between SO2 and O3 in males and between SO2 and CO in females, with q values of 0.45, 0.232 respectively. Smoking is a substantial contributor to lung cancer among men, either in South or North China, with q value of 0.143 and 0.129 respectively, and the interaction between smoking and air pollutants increases this risk. Conclusions This study implies that the influence of SO2 and PM2.5 on lung cancer should be focused on in north China, and in the south, the impact of O3 and CO as well as their interaction with SO2 need to be paid more attention. Smoking, particularly in men, remains a significant risk factor for lung cancer in both North and South China.

Soil moisture is an important parameter for agricultural production. Efficient and accurate monitoring of soil moisture is an important link to ensure the safety of agricultural production. Remote sensing technology has been widely used in agricultural moisture monitoring because of its timeliness, cyclicality, dynamic tracking of changes in things, easy access to data, and extensive monitoring. Vegetation index and surface temperature are important parameters for moisture monitoring. Based on NDVI, this paper introduces land surface temperature and average temperature for optimization. This article takes the soil moisture in winter wheat growing area in Henan Province as the research object, dividing Henan Province into three main regions producing winter wheat and dividing the growth period of winter wheat into the early, middle and late stages on the basis of phenological characteristics and regional characteristics. Introducing appropriate correction factor during the corresponding growth period of winter wheat, correcting the vegetation index in the corresponding area, this paper establishes regression models of soil moisture on NDVI and soil moisture on modified NDVI based on correlation analysis and compare models. It shows that modified NDVI is more suitable as a indicator of soil moisture because of the better correlation between soil moisture and modified NDVI and the higher prediction accuracy of the regression model of soil moisture on modified NDVI. The research in this paper has certain reference value for winter wheat farmland management and decision-making.

The cavitation erosion behavior of Ni foam/polyurethane (PU) co-continuous composites under different experimental conditions was investigated using an ultrasonic vibration cavitation erosion device. Experimental results showed that the Ni foam metal skeleton structure had severe effects on the cavitation resistance of the composites. The composites with thick metal arris and large pore size exhibited good resistance to cavitation erosion. Stress waves had greater influence on the cavitation erosion behavior of composites than micro-jets. In a synergistic way of buffering stress wave in the resin phase and absorbing stress waves in the metal phase, the composites could exhibit better cavitation resistance than pure PU.

Land subsidence in shanghai has been found for more than 70 years. In the early years, it was mainly caused by groundwater exploitation. In recent years, engineering dewatering in shallow ground (within 90 m) has become a major source for land subsidence in the rapid urbanization course. A management partition of land subsidence induced by foundation pit dewatering for the first confined aquifer was suggested.

As an insulating dielectric, polyimide is favorable for the application of optoelectronics, electrical insulation system in electric power industry, insulating, and packaging materials in space aircraft, due to its excellent thermal, mechanical and electrical insulating stability. The charge storage profile of such insulating dielectric is utmost important to its application, when it is exposed to electron irradiation, high voltage corona discharge or other treatments. These treatments could induce changes in physical and chemical properties of treated samples. To investigate the charge storage mechanism of the insulating dielectrics after high-voltage corona discharge, the relaxation processes responsible for corona charged polyimide films under different poling conditions were analyzed by the Thermally Stimulated Discharge Currents method (TSDC). In the results of thermal relaxation process, the appearance of various peaks in TSDC spectra provided a deep insight into the molecular status in the dielectric material and reflected stored space charge relaxation process in the insulating polymers after corona discharge treatments. Furthermore, the different space charge distribution status under various poling temperature and different discharge voltage level were also investigated, which could partly reflect the influence of the ambiance condition on the functional dielectrics after corona poling.

When an intense laser pulse is loaded upon solids, very high impact pressure can be generated on the surface. In this letter, we simulate this process through one-dimensional particle-in-cell simulation and find that the pressure as high as 0.13 TPa can be generated after the laser pulse with intensity 1015 W/cm2 and 5 picosecond duration is injected upon a nanometer solid-density plasma. The peak pressure is shown to be resulted from an energetic high-density plasma bunch, produced through plasma implosion under extremely high light pressure.

The steam exciting force has been proved to be great threat to the operation safety of steam turbines. The mechanism of steam exciting vibration cannot be profoundly revealed by simply analyzing the steam exciting force, especially in simplified models. Therefore, a full-circle stage of steam turbine with shroud and labyrinth seals was investigated by numerical simulator CFX. The instability of leakage flow and the pressure fluctuation were analyzed on the eccentric condition. The effects of leakage vortexes, the depth-width ratio of seal cavity, and the eccentricity on the steam exciting force were studied. Results show that the leakage flow is nonuniform in the circumferential direction with the change of front teeth vortexes, which causes the steam exciting force. The tangential and radial steam exciting force both increase with the eccentricity increasing. The effects of the depth-width ratio of seal cavity on the two forces are different. In addition, the pressure fluctuation caused by the leakage vortexes on the shroud surfaces is a main factor inducing the steam exciting force. This research provides a theoretical guidance for the operation safety and optimization of steam turbines.

Nitric oxide (NO), gibberellic acid (GA), and phosphorus (P) have been reported to regulate primary root (PR) growth, but interactions between them in the growth of Arabidopsis PR remain unknown. This work confirmed that low P availability significantly inhibited PR growth and that NO arrested PR growth in either high P or low P conditions. Moreover, NO counteracted the stimulatory effects of GA on PR growth under low P conditions. Finally, the dependence of low P and NO inhibition of PR growth on the DELLA-SLY pathway revealed that NO stabilized a major DELLA protein. We therefore conclude that antagonistic interactions between NO and GA regulate PR growth under both the high and low P conditions, and a DELLA-SLY module is the node where NO, GA, and P pathways converge and interact.

Homogeneous low phosphorus availability was reported to regulate root architecture in Arabidopsis via auxin, but the roles of auxin in root architecture plasticity to heterogeneous P availability remain unclear. In this study, we employed auxin biosynthesis-, transport- and signalling-related mutants. Firstly, we found that in contrast to low P (LP) content in the whole medium, primary root (PR) growth of Arabidopsis was partially rescued in the medium divided into two parts: upper with LP and lower with high P (HP) content or in the reverse arrangement. The down part LP was more effective to arrest PR growth as well as to decrease density of lateral roots (DLR) than the upper LP, and effects were dependent on polar auxin transport. Secondly, we verified that auxin receptor TIR1 was involved in the responses of PR growth and lateral root (LR) development to P supply and loss of function of TIR1 inhibited LR development. Thirdly, effects of heterogeneous P on LRD in the upper part of PR was dependent on PIN2 and PIN4, and in the down part on PIN3 and PIN4, whereas density of total LRs was dependent on auxin transporters PIN2 and PIN7. Finally, heterogeneous P availability altered the accumulation of auxin in PR tip and the expression of auxin biosynthesisrelated genes TAA1, YUC1, YUC2, and YUC4. Taken together, we provided evidences for the involvement of auxin in root architecture plasticity in response to heterogeneous phosphorus availability in Arabidopsis.

With the development of computers, network communications, scientific computing, mapping remote sensing and geographic information technologies, Discrete Global Grids (DGGs) and Earth System Spatial Grid（ESSG）have become the integrated spatial data model facing the large-scale and global-scale problems and the complex geo-computation. This paper discusses the property and character of the global spatial data at first. Then it introduces the grid division system based on large arc QTM octree and compares this scheme with degradation octree scheme. At last, it introduces the application of the scheme in land surface, underground and aerial geographic entity modeling. The study suggests that: the grid division system based on large arc QTM octree has the potential to integrate the whole spatial data of different layers of the geospatial. And it will have a broad application prospect in complex large-scale geographic computing.

We report the synthesis of CH3NH3Pb(Br3−yXy) (X=Cl and I) single crystals via a stepwise temperature control approach. High-quality CH3NH3Pb(Br3−yXy) crystals with a tunable bandgap from 1.92eV to 2.53eV have been prepared successfully in this way. And further experiments revealed the influence of halogen content and preparation temperature on the structural and optical properties of these crystals. It is observed that chlorine can lower the critical nucleation energy, which results in crystallizing at lower temperature with the chlorine content increasing, while the nucleation energy increases slowly with increasing iodine content. Moreover, in contrast to Frank–van der Merwe growth with low heating rate, high heating rate leads to a mass of small size single crystals and Stranski-Krastanov growth. The single crystals with tunable band gap and impressive characteristics enable us to fabricate high performance photodetectors for different wavelengths.

Silicon microwires with lateral dimension from 5 μm to 20 μm and depth as long as 20 μm are prepared by bilayer metal assisted chemical etching (MaCE). A bilayer metal configuration (Metal 1 / Metal 2) was applied to assist etching of Si where metal 1 acts as direct catalyst and metal 2 provides mechanical support. Different metal types were investigated to figure out the influence of metal catalyst on morphology of etched silicon. We find that silicon microwires with vertical side wall are produced when we use Ag/Au bilayer, while cone–like and porous microwires formed when Pt/Au is applied. The different micro-/nano-structures in as-etched silicon are demonstrated to be due to the discrepancy of work function of metal catalyst relative to Si. Further, we constructed a silicon microwire arrays solar cells in a radial p–n junction configurations in a screen printed aluminum paste p–doping process.