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Feng J.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Jiang Y.,National University of Defense Technology | Zhao N.,Northwest Institute of Nuclear Technology
ACS Applied Materials and Interfaces | Year: 2011

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m -1 K -1 at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system. © 2011 American Chemical Society. Source

Chen J.,Xian Jiaotong University | Wang J.,Xian Jiaotong University | Wang J.,Northwest Institute of Nuclear Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2013

In this paper, a pseudospectral (PS) scheme is introduced into the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method for solving the shielding effectiveness (SE) of thin slots. The maximum time-step size in this method is only determined by two spatial discretizations and the spatial discretization only needs two cells per wavelength. The 3-D formula of the method is presented and the time stability condition of the method is demonstrated. When this method is applied to simulate thin slots, high computational efficiency is obtained and less computer memory is used, which is demonstrated through numerical examples by comparing with the finite-difference time-domain (FDTD) method, HIE-FDTD method, and alternating-direction implicit (ADI)-FDTD method. © 2013 IEEE. Source

Wu G.,Northwest Institute of Nuclear Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2014

Double exponential function and its modified forms are widely used in high-power electromagnetics such as high-altitude electromagnetic pulse and ultrawide-band pulse study. Physical parameters of the pulse, typically the rise time tr, full width at half maximum tw, and/or fall time tf, usually need to be transformed into mathematical characteristic parameters of the functions, commonly denoted as α and β. This paper discusses the dependences of pulse shape properties, represented by ratios of tw/tr and tf/tr, on a dimensionless parameter A = β/α or B = α/β; and focuses on their limit correlations associated with the mathematical forms. It has been proven that pulses with tw/tr < 4.29 cannot be expressed by the commonly used difference of double exponentials function. This limit can be mitigated partially by the latest proposed p-power of double exponentials function with a well-chosen p parameter. A novel form, difference of double Gaussian functions is also proposed to describe pulses with low t w/tr ratios better. Quotient of double exponentials, however, is shown to be the most flexible function for describing transient pulses with arbitrary tw/tr ratios, despite of its intrinsic drawbacks. All these functions are applied for several examples and further compared in both time and frequency domains. © 2014 IEEE. Source

Duan L.,Northwest Institute of Nuclear Technology | Yan X.,Max Planck Institute of Colloids and Interfaces | Wang A.,CAS Beijing National Laboratory for Molecular | Jia Y.,CAS Beijing National Laboratory for Molecular | Li J.,CAS Beijing National Laboratory for Molecular
ACS Nano | Year: 2012

Seeking safe and effective artificial blood substitutes based on hemoglobin (Hb) as oxygen carriers is an important topic. A significant challenge is to enhance the loading content of Hb in a well-defined structure. Here we report a facile and controllable avenue to fabricate Hb spheres with a high loading content by templating decomposable porous CaCO 3 particles in collaboration with covalent layer-by-layer assembly technique. The surface of the Hb spheres was further chemically modified by biocompatible polyethylene glycol to protect and stabilize the system. Multiple characterization techniques were employed to reveal the loading and density of Hb in an individual CaCO 3 particle. The results demonstrate that the strategy developed in this work is effective and flexible for construction of the highly loaded Hb spheres. More importantly, such Hb spheres retain their carrying-releasing oxygen function. It may thus have great potential to develop Hb spheres with highly loaded content as realistic artificial blood substitutes in the future. © 2012 American Chemical Society. Source

Zeng Z.,Northwest Institute of Nuclear Technology
Qiangjiguang Yu Lizishu/High Power Laser and Particle Beams | Year: 2011

Approximate series solutions of the output pulse waveforms and transmission efficiencies of transmission line with exponential impedance profile have been developed based on distributed-parameter model for typical incident pulses suitable for next generation of Z -pinch plasma drivers. The transmission efficiencies are studied computationally with these solutions for petawatt-class Z-pinch driver's exponential transmission line taking account of the line's length and ratio of output impedance to the input as well as the pulse's shape and parameter. The voltage transmission efficiency increases with the increase of the ratio of output impedance to the input, line length and pulse frequencies; the power transmission efficiency increases with the increase of pulse frequencies and with the decrease of steepness of the line's impedance variation. Source

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