Beijing University of Technology

About: Beijing University of Technology is a education organization based out in Beijing, Beijing, China. It is known for research contribution in the topics: Microstructure & Laser. The organization has 31929 authors who have published 31987 publications receiving 352112 citations. The organization is also known as: Běijīng Gōngyè Dàxué & Beijing Polytechnic University.

Effect of chromium concentration on microstructure and properties of Fe–3.5B alloy

Abstract: The cast low carbon Fe–3.5B alloys containing various chromium concentrations were prepared in a 10 kg medium frequency induction furnace and the effects of chromium concentration on microstructure and properties of Fe–3.5B alloys have been examined by means of optical microscope (OM), scanning electron microscope (SEM), back-scattered electron microscope (BSE), electron probe microanalyzer (EPMA), energy dispersive spectrum (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Vickers hardness. As a result, the as-cast structures of Fe–3.5B– X Cr ( X = 0, 2, 5, 8, 12, 18, mass fraction) alloys are mainly composed of dendrite ferrite, martensite, pearlite and boride. The boride in the alloy without chromium addition comprises the eutectic Fe 2 B, which is continuous netlike or fish-bone structure distributed over the metallic matrix. With the increase of chromium concentration in Fe–3.5B alloy, matrix structure turns into the supersaturated α -Fe solid solution while the morphology of boride becomes dispersed due to the transformation of boride from simple Fe 2 B to (Fe,Cr) 2 B when the chromium concentration in Fe–3.5B alloy exceeds 8 wt.%. Meanwhile, some primary M 2 B-type borides may precipitate under this condition. The bulk hardness of the as-cast alloy ranges from 41.8 to 46.8 HRC. However, the bulk hardness of the heat treated alloy rises first and falls later mainly because of the morphology variation of structure. Fracture toughness of boride is improved gradually owing to the entrance of chromium into Fe 2 B, which may be attributed to the change of spatial structure of boride.

Mesoporous Chromia with Ordered Three-Dimensional Structures for the Complete Oxidation of Toluene and Ethyl Acetate

Abstract: Mesoporous chromia with ordered three-dimensional (3D) hexagonal polycrystalline structures were fabricated at 130, 180, 240, 280, and 350 °C in an autoclave through a novel solvent-free route using KIT-6 as the hard template. The as-obtained materials were characterized (by means of X-ray diffraction, transmission electron microscopy, N2 adsorption−desorption, temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques) and tested as a catalyst for the complete oxidation of toluene and ethyl acetate. We found that with a high surface area of 106 m2/g and being multivalent (Cr3+, Cr5+, and Cr6+), the chromia (meso-Cr-240) fabricated at 240 °C is the best among the five in catalytic performance. According to the results of the temperature-programmed reduction and X-ray photoelectron spectroscopy investigations, it is apparent that the coexistence of multiple chromium species promotes the low-temperature reducibility of chromia. The excellent performance of meso-Cr-240 is because of go...

Role of electronic excitation in the amorphization of Ge-Sb-Te alloys.

Abstract: First-principles molecular dynamics simulation reveals the effects of electronic excitation in the amorphization of Ge-Sb-Te. The excitation makes the phase change an element-selective process, lowers the critical amorphization temperature considerably, for example, to below 700 K at a 9% excitation, and reduces the atomic diffusion coefficient with respect to that of melt by at least 1 order of magnitude. Noticeably, the resulting structure has fewer wrong bonds and significantly increased phase-change reversibility. Our results point to a new direction in manipulating ultrafast phase-change processes with improved controllability.

Computer-aided design of high-efficiency GeTe-based thermoelectric devices

Abstract: Driven by materials science development, the thermoelectric performance has been enhanced. However, only increasing the figure of merit to enhance the thermoelectric efficiency becomes more challenging. Here, we combine an enhanced figure of merit and geometry optimization of a device by computer-aided design to achieve a record-high thermoelectric efficiency of 16%. A figure of merit over 2.2 in p-type Ge1−x−yCrxSbyTe alloys is achieved resulting from the convergence of three valence edges induced by Cr doping to enhance the power factor and superlattice precipitates to lower the thermal conductivity. Using finite element analysis simulations, we optimize the geometry of a segmented thermoelectric device made of the as-developed Ge1−x−yCrxSbyTe and other reported materials, leading to a record high efficiency. Furthermore, our simulations on over 70 existing n-type thermoelectric materials can serve as a library to bridge the gap between materials science and device engineering to achieve high-efficiency thermoelectric devices.

Small Object Detection in Unmanned Aerial Vehicle Images Using Feature Fusion and Scaling-Based Single Shot Detector With Spatial Context Analysis

Abstract: Objects in unmanned aerial vehicle (UAV) images are generally small due to the high-photography altitude. Although many efforts have been made in object detection, how to accurately and quickly detect small objects is still one of the remaining open challenges. In this paper, we propose a feature fusion and scaling-based single shot detector (FS-SSD) for small object detection in the UAV images. The FS-SSD is an enhancement based on FSSD, a variety of the original single shot multibox detector (SSD). We add an extra scaling branch of the deconvolution module with an average pooling operation to form a feature pyramid. The original feature fusion branch is adjusted to be better suited to the small object detection task. The two feature pyramids generated by the deconvolution module and feature fusion module are utilized to make predictions together. In addition to the deep features learned by the FS-SSD, to further improve the detection accuracy, spatial context analysis is proposed to incorporate the object spatial relationships into object redetection. The interclass and intraclass distances between different object instances are computed as a spatial context, which proves effective for multiclass small object detection. Six experiments are conducted on the PASCAL VOC dataset and the two UAV image datasets. The experimental results demonstrate that the proposed method can achieve a comparable detection speed but an accuracy superior to those of the six state-of-the-art methods.