Beihang University

About: Beihang University is a education organization based out in Beijing, China. It is known for research contribution in the topics: Computer science & Control theory. The organization has 67002 authors who have published 73507 publications receiving 975691 citations. The organization is also known as: Beijing University of Aeronautics and Astronautics.

Automatic Change Detection in Synthetic Aperture Radar Images Based on PCANet

Abstract: This letter presents a novel change detection method for multitemporal synthetic aperture radar images based on PCANet. This method exploits representative neighborhood features from each pixel using PCA filters as convolutional filters. Thus, the proposed method is more robust to the speckle noise and can generate change maps with less noise spots. Given two multitemporal images, Gabor wavelets and fuzzy $c$ -means are utilized to select interested pixels that have high probability of being changed or unchanged. Then, new image patches centered at interested pixels are generated and a PCANet model is trained using these patches. Finally, pixels in the multitemporal images are classified by the trained PCANet model. The PCANet classification result and the preclassification result are combined to form the final change map. The experimental results obtained on three real SAR image data sets confirm the effectiveness of the proposed method.

Flexible two-dimensional Tin+1Cn (n = 1, 2 and 3) and their functionalized MXenes predicted by density functional theories.

Abstract: Two-dimensional (2D) transition metal carbides/nitrides Mn+1Xn labeled as MXenes are attracting increasing interest due to promising applications as Li-ion battery anodes and hybrid electro-chemical capacitors. To realize MXenes devices in future flexible practical applications, it is necessary to have a full understanding of the mechanical properties of MXenes under deformation. In this study, we extensively investigated the stress–strain curves and the deformation mechanisms in response to tensile stress by first principles calculations using 2D Tin+1Cn (n = 1, 2 and/or 3) as examples. Our results show that 2D Ti2C can sustain large strains of 9.5%, 18% and 17% under tensions of biaxial and uniaxial along x and y, respectively, which respectively increase to 20%, 28% and 26.5% for 2D Ti2CO2 due to surface functionalizing oxygen, which is much better than graphene (15% biaxial). The failure of 2D Tin+1Cn MXene is due to the significant collapse of the surface atomic layer; however, surface functionalization could slow down this collapse, resulting in the improvement of mechanical flexibility. We have also discussed the critical strains and Young's modulus of 2D Tin+1Cn and Tin+1CnO2. Our results provide an insight into the microscopic deformation mechanism of MXenes and hence benefit their applications in flexible electronic devices.

Tunable and Ultraefficient Microwave Absorption Properties of Trace N-Doped Two-Dimensional Carbon-Based Nanocomposites Loaded with Multi-Rare Earth Oxides

Abstract: A high efficiency and great tunability of bandwidth and absorption-range electromagnetic wave absorber is proposed without precedent. A series of 2D carbon-based nanocomposites with the loading of cerium oxide (CN-Ce) and other types of rare earth oxides (CN-REOs) can be successfully synthesized by a simple solvothermal-sintering method. As-synthesized 2D nanocomposites with local graphite-like C3 N4 structure and trace N-doped are identified by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. The CN-REOs and polyvinylidene fluoride composite absorbers with reflection loss values above -40 dB are obtained in C-band, X-band, and Ku-band, respectively. The empirical rules on effective bandwidth and frequency range are discovered and summarized, which can be successfully realized by simply tuning the doping amount or type of REO. The mechanism is explained by enhanced attenuation and tunable impedance matching. In addition co-filled samples by two types of CN-REOs nanocomposites are prepared to support these findings and inspire the preparation of absorber with desirable frequency band in the range of 2-18 GHz.

Fiber-Optic Fabry–Pérot Acoustic Sensor With Multilayer Graphene Diaphragm

Abstract: A fiber-optic Fabry-Perot acoustic sensor with a ~100-nm-thick multilayer graphene diaphragm is reported. Acoustic testing demonstrates a pressure-induced deflection of 1100 nm/kPa and a noise equivalent acoustic signal level of ~ 60 μPa/Hz1/2 at the frequency of 10 kHz. The sensor exhibits a flat frequency response from 0.2 to 22 kHz and may be useful for highly sensitive acoustic sensing.