Search

Chang’e-5 (CE-5) mission is expected to land and sample in the Rumker region, north of the Oceanus Procellarum. To select optimal sampling points, the microwave radiation features in this mare unit are analyzed, and the dielectric constant and thickness of lunar regolith are retrieved based on Chang’e lunar microwave sounder (CELMS) data. According to the microwave brightness temperature (TB) maps, TB varying with frequency at noon and midnight are different, in which noon TB increases with frequency, but midnight TB does not follow this rule. Moreover, there are differences among TB distributions at the three higher frequencies, especially in the southern part. In addition, a great TB difference between noon and midnight can be seen in Rumker E that shows higher daytime temperature but lower nighttime temperature The inversion results reveal that the dielectric constant is lower in the west and north, higher in the middle and east, and the largest value occurs in Rumker E. As for the regolith thickness, most areas are uniform and no more than 4 m, with the thickest and thinnest regolith appearing in the northwest and Rumker E, no less than 6 m and about 2.5 m, respectively. Considering the safety and operability of landing and sampling, the northwest with thick regolith is recommended, while the Rumker E should be eluded.

In order to study the influence of different factors on the temperature field of the freezing wall of connecting passage, and to evaluate the effect of different influencing factors, four groups of analyses were carried out through three-dimensional finite element software, including the influence of brine temperature, the influence of freezing pipe diameter, the influence of freezing pipe spacing, and the influence of soil water content. The analysis shows that the finite element method based on the thermodynamics theory can better simulate the freezing temperature field and formation law of the freezing wall of each section. Among the influencing factors, the brine temperature and the freezing pipe spacing have the greatest influence on the temperature field of the freezing wall. The thickness of the freezing wall increases linearly with the increase in the freezing time. At the same time, the thickness of the freezing wall increases with the increase in the diameter of the freezing tube and the decrease in the spacing between the freezing tubes. With the decrease in brine temperature and water content, the difference of freezing wall thickness at different levels becomes larger and larger with the increase in freezing time. The influence of various factors on the freezing wall is in the order of brine temperature, freezing tube spacing, and freezing tube diameter. At present, the saltwater temperature in the freezing project of the metro shield tunnel is generally controlled at −28~−30 °C. Generally, from the perspective of actual engineering, it is better to control the spacing of freezing pipes at 1.0~1.3 m, and the diameter of the freezing pipe of the connecting channel is generally more than 89 mm. By comparing the numerical simulation value with monitoring data, the numerical calculation result is consistent with the monitoring temperature change rule.

As one of the main filled materials of the Lianghekou (LHK) rockfill dam, the strength and deformation characteristics of LHK rockfill is of great interest for hydraulic and geotechnical e...

A great number of bridges have been built in the world, which are very important for economic and society developments. Thus, the bridge monitoring is vital and is also a hot topic in recent years. Many bridge monitoring methods have been presented to monitor the bridge vibration. For example, some bridge monitoring methods require the sensors directly contact with the bridge, which might be difficult to install and maintain. In addition, some remote monitoring instruments are expensive and sensitive to the environment. In this paper, a bridge monitoring radar with a central frequency of 36.05 GHz is devised based on a millimeter-wave technology to measure the bridge vibration. It has a super-range resolution of 0.5 m and a high deformation measure precision of $56~\mu \text{m}$ . Experiments on a high-speed railway bridge and a large cable suspended bridge are performed to verify the effectiveness of the radar interferometry for accurate and precise monitoring of the vibration types and magnitudes of these bridges.

The effect of oxygen impurity on corrosion behavior of as-cast Zr61Ti2Cu25Al12 bulk metallic glasses (BMGs) is clarified using electrochemical measurements, microstructure characterization and surface analyses. We find unexpectedly that oxygen impurity (≤1200 ppm) improves pitting corrosion resistance when a fully amorphous structure is attained. The oxygen-induced annihilation of free volume enhances passive film protectiveness and hence accounts for the improved corrosion property. In contrast, adding more oxygen impurity (1800 ppm) deteriorates pitting corrosion resistance by assisting the formation of highly-reactive crystalline phases. The finding herein provides an avenue for designing new low-cost Zr-based BMGs with superior properties by oxygen microalloying.

In this paper, We introduce the Interferometric Imaging Radar Altimeter (InIRA), the first spaceborne wide-swath ocean radar altimeter on board Chinese Tiangong-2 space laboratory, which was launched on September 15, 2016. The major mission of InIRA is to validate the mechanism and design of new generation ocean radar altimeter, as well as conduct preliminary application researches. The in-orbit observation results of Tiangong-2 InIRA demonstrate that it is capable of measuring the dynamic sea surface height with wide swath, sea waves of different scales and sea winds, which help us greatly improve the observation and measurement efficiency compared with traditional nadir-looking radar altimeters. Besides, it can also be used to survey and monitor the inland waters, e.g. lakes and rivers, as well as acquire terrain digital surface model (DSM). Here, we will present some typical observation results over both ocean and land surfaces.

A wideband mm-wave antenna is proposed with a directional radiation pattern for micro-deformation monitoring radar applications. The devised antenna consists of a coplanar waveguide (CPW) feeding, a dipole-like radiating patch, a parasitic strip setting at the front of the radiating patch and a rounded ground plane with slots at the left and the right sides of the antenna. The parasitic strip is to enhance the bandwidth of the antenna, and it also used for improving the directional characteristic of the proposed antenna. The antenna is well designed and analyzed by using the HFSS, and the obtained results show that the antenna has a wideband bandwidth and good directional radiation patterns, making it suitable for micro-deformation monitoring radar applications.

The small-size unmanned aerial vehicle (UAV) is being used widely in many fields, especially in surveying, mapping and remote sensing. Due to the platform's size and load ability, its payload is strictly limited. Synthetic aperture radar(SAR) is a kind of microwave imaging instrument with high performance under all weather, day and night conditions. Highly miniaturized SAR can satisfy the requirement of observation on small UAV. Frequency modulation continuous wave (FMCW) technology provides a way for small volume, low cost, high reliability and high resolution SAR. FMCW SAR transmits frequency modulated signal continuously. This reduces the peak power, which is the important factor determining the size and cost of SAR. Meanwhile, due to transmitting and receiving signals simultaneously, increasing the isolation between the transmitter and receiver becomes associated problem. Two separated antennas solve the problem partly. There is another problem in processing algorithm. Long duration of signal makes the assumption of stop and go model ineffective. Frequency scaling algorithm has to be chosen to correct the phase variation during one period of frequency sweep. Procedure of development for prototype and practical systems and verification experiments are shown in this paper. The results of experiments with such radars prove the expected performance.

The ability of radar that can detect micro deformation of targets at hundreds of meters makes it useful in status assessment or critical monitoring for many scenes such as bridges, high buildings, dams, slopes, etc. FMCW (Frequency Modulation Continuous Wave) mode is utilized in micro deformation detection radar. Based on this, static measurements and dynamic measurements are used in different scenes. Static measurement means radar is fixed on the ground or somewhere more stable than targets when it works. Dynamic measurements observe the target with radar on a sliding rail track, which also called GBSAR (Ground Based Synthetic Aperture Radar). Then the detection of static measurement is point or line observation, while GBSAR is area observation.

FMCW (Frequency Modulation Continuous Wave) ISAR (Inverse Synthetic Aperture Radar) operating at Ka-band developed by us recently is a kind of portable, compact radar due to its relatively simple electronic and mechanical construction. For its short range detection performance, vehicles within tens of meters are taken as targets, which can be found easily to verify the function of system. In this paper, the Ka-band FMCW ISAR is introduced and discussed to monitoring moving vehicles. Compared with pulse mode, FMCW mode transmits less power and then saves the power amplifier. With its counterpart of transmitted signal as local oscillator, the receiver is simplified. When IF is produced by mixing transmitted signal and received signal, its frequency is low. Then, the A/D, processing and storage circuits are less complicated than those of the pulse-based ISAR systems. The results show that the designed Ka-band FMCW ISAR can give a high accuracy and resolution for monitoring the vehicles.

Water-soluble γ-Fe2O3/polyvinylpyrrolidone (PVP) nanoparticles were obtained by transferring oleic acid (OA) coated iron-oxide nanocrystals from hexane to water. The particle size of the γ-Fe2O3/PVP nanoparticles with excellent monodispersity is about 14 nm. Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results indicate that PVP anchors on the γ-Fe2O3 nanoparticles through its carbonyl group and provided sufficient hydrophilicity. The maghemite content in the γ-Fe2O3/PVP nanoparticles was about 81 wt-%. The saturation magnetisation of the superparamagnetic γ-Fe2O3/PVP nanoparticles is 57·7 emu g− 1 at 295 K. For in vivo magnetic resonance imaging (MRI) studies, the γ-Fe2O3/PVP nanoparticles can be guided to the target area by a permanent magnet and show negative contrast enhancement on the target area of laboratory mice.

Electromagnetic (EM) wave absorption properties of metallic perovskite lanthanum nickel oxide (LNO) powder and dielectric-modulated LNO–FeCo/C composites were investigated. Reflection loss (RL) of the LNO–paraffin composites depends on the mass ratio of LNO powder dispersion in the paraffin matrix, in which the optimal RL of −24.7 dB at 17.6 GHz with the absorbent layer thickness of 1.6 mm is obtained at the 10 wt% LNO–paraffin composite, just below the percolation threshold (PC) of the LNO dispersion in the paraffin matrix. Three absorption peaks in the frequency dependence of RL of the 10 wt% LNO–paraffin composite are ascribed to the dielectric relaxations which occurred at frequencies of about 3.3, 9.2 and 15.1 GHz. Dielectric-modulation by metal-conductive LNO powder significantly increases the relative complex permittivity of the (x)LNO–(y)FeCo/C–paraffin composites and a good impedance match coming from the dielectric-modulation by the LNO powder would be obtained just below the PC of the LNO powder dispersion in the paraffin matrix. The (8 wt%)LNO–(32 wt%)FeCo/C–paraffin composite exhibited an enhanced EM wave absorption performance, in which RL values less than −20 dB can be obtained in the 2–18 GHz range by choosing an appropriate thickness from 1.3 mm to 8 mm and the minimum RL is −50.6 dB at 9 GHz with the absorbent layer thickness of 2.4 mm.