National University of Defense Technology

About: National University of Defense Technology is a education organization based out in Changsha, China. It is known for research contribution in the topics: Computer science & Radar. The organization has 39430 authors who have published 40181 publications receiving 358979 citations. The organization is also known as: Guófáng Kēxuéjìshù Dàxué & NUDT.

Review of cavity-stabilized combustion for scramjet applications:

Abstract: Cavities are widely used as flameholders in supersonic combustors due to their outstanding potential to stabilize combustion without excessive total pressure loss. A review of cavity-stabilized combustion for scramjet applications is provided in this article. The topics cover the fundamental problems and recent advances regarding cavity-organized combustion in high-speed flows, including combustion stabilization modes and mechanisms, flame stability analyses and correlations, combustion oscillations, and other related issues. Remarkable questions such as cavity-coupled fuel injection, flow and combustion coupling, optimal cavity geometry and scale, auto-ignition and flame propagation interactions, and unsteady effects are discussed. Then, an attempt is made to provide some guidelines for the future research of cavity flameholders.

Hybrid approach for solving systems of nonlinear equations using chaos optimization and quasi-Newton method

Abstract: Solving systems of nonlinear equations is one of the most difficult numerical computation problems. The convergences of the classical solvers such as Newton-type methods are highly sensitive to the initial guess of the solution. However, it is very difficult to select good initial solutions for most systems of nonlinear equations. By including the global search capabilities of chaos optimization and the high local convergence rate of quasi-Newton method, a hybrid approach for solving systems of nonlinear equations is proposed. Three systems of nonlinear equations including the ''Combustion of Propane'' problem are used to test our proposed approach. The results show that the hybrid approach has a high success rate and a quick convergence rate. Besides, the hybrid approach guarantees the location of solution with physical meaning, whereas the quasi-Newton method alone cannot achieve this.

Giant nonvolatile manipulation of magnetoresistance in magnetic tunnel junctions by electric fields via magnetoelectric coupling

Abstract: Electrically switchable magnetization is considered a milestone in the development of ultralow power spintronic devices, and it has been a long sought-after goal for electric-field control of magnetoresistance in magnetic tunnel junctions with ultralow power consumption. Here, through integrating spintronics and multiferroics, we investigate MgO-based magnetic tunnel junctions on ferroelectric substrate with a high tunnel magnetoresistance ratio of 235%. A giant, reversible and nonvolatile electric-field manipulation of magnetoresistance to about 55% is realized at room temperature without the assistance of a magnetic field. Through strain-mediated magnetoelectric coupling, the electric field modifies the magnetic anisotropy of the free layer leading to its magnetization rotation so that the relative magnetization configuration of the magnetic tunnel junction can be efficiently modulated. Our findings offer significant fundamental insight into information storage using electric writing and magnetic reading and represent a crucial step towards low-power spintronic devices. Electric field controlled magnetism provides an energy efficient way for the operations in the spintronic devices. Here the authors show strain induced, reversible, nonvolatile electric field control of magnetization and magnetoresistance in a magnetic tunnel junction on a ferroelectric substrate at room temperature and zero magnetic field.

ZrB2/SiC as a protective coating for C/SiC composites: Effect of high temperature oxidation on mechanical properties and anti-ablation property

Abstract: C/SiC composites are raising great interest as a thermal shielding for aerospace applications, provided that they are protected from oxidation by suitable coatings Conversely, ultra high temperature ceramics, and in particular ZrB 2 , is among the best oxidation resistant materials as known A new type of oxidation protective coating (ZrB 2 /SiC coating) was produced on C/SiC composites The composites were produced by precursor infiltration and pyrolysis (PIP), which is a simple and low cost method; the coating was ZrB 2 mixed with SiC, which was fabricated by painting slurry on the surface of the composite followed by chemical vapor deposition (CVD) SiC on the top Mechanical tests were conducted before and after oxidation test Anti-ablation property was tested under oxy-acetylene torch Oxidation test shows that the uncoated samples are oxidized quickly and the weight loss reaches 292% and the reservation of original flexural strength is only 674%, while the weight loss of ZrB 2 /SiC coated samples is only 519%, and the reservation of original flexural strength is 374% ZrB 2 /SiC coating can provide longtime protection for C/SiC composites at 1973 K Compared with the uncoated composites, the linear and mass ablation rates of the coated composites decreased by 621% and 461%, respectively, after ablation for 30 s The formation of zirconia and silicon dioxide from the oxidation of ZrB 2 /SiC improved the ablation resistance of the composites, because of the evaporation at elevated temperature, which absorbed heat from the flame and reduced the erosive attack to carbon fibers and SiC matrix

Broadband Phototransistor Based on CH3NH3PbI3 Perovskite and PbSe Quantum Dot Heterojunction

Abstract: Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FEpTs) based on CH3NH3PbI3 perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm2V–1s–1 for holes and 0.16 cm2V–1s–1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH3NH3PbI3 perovskite–PbSe quantum dot as a promising material for future photoelectronic app...