Thermal conductivity of micro/nano-porous polymers: Prediction models and applications

Micro/nano-porous polymeric material is considered a unique industrial material due to its extremely low thermal conductivity, low density, and high surface area. Therefore, it is necessary to establish an accurate thermal conductivity prediction model suiting their applicable conditions and provide a theoretical basis for expanding their applications. In this work, the development of the calculation model of equivalent thermal conductivity of micro/nano-porous polymeric materials in recent years is summarized. Firstly, it reviews the process of establishing the overall equivalent thermal conductivity calculation model for micro/nanoporous polymers. Then, the predicted calculation models of thermal conductivity are introduced separately according to the conductive and radiative thermal conductivity models. In addition, the thermal conduction part is divided into the gaseous thermal conductivity model, solid thermal conductivity model and gas–solid coupling model. Finally, it is concluded that, compared with other porous materials, there are few studies on heat transfer of micro/ nanoporous polymers, especially on the particular heat transfer mechanisms such as scale effects at the micro/nanoscale. In particular, the following aspects of porous polymers still need to be further studied: micro scaled thermal radiation, heat transfer characteristics of particular morphologies at the nanoscales, heat transfer mechanism and impact factors of micro/nanoporous polymers. Such studies would provide a more accurate prediction of thermal conductivity and a broader application in energy conversion and storage systems.     

Single-channel color image encryption using phase retrieve algorithm in fractional Fourier domain

A single-channel color image encryption is proposed based on a phase retrieve algorithm and a two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and then permuted by a sequence of chaotic pairs generated by the two-coupled logistic map. Secondly, the permutation image is decomposed into three new components, where each component is encoded into a phase-only function in the fractional Fourier domain with a phase retrieve algorithm that is proposed based on the iterative fractional Fourier transform. Finally, an interim image is formed by the combination of these phase-only functions and encrypted into the final gray scale ciphertext with stationary white noise distribution by using chaotic diffusion, which has camouflage property to some extent. In the process of encryption and decryption, chaotic permutation and diffusion makes the resultant image nonlinear and disorder both in spatial domain and frequency domain, and the proposed phase iterative algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.     

Convergence to nonlinear diffusion waves for solutions of Euler equations with time-depending damping

In this paper, we are concerned with the asymptotic behavior of solutions to the system of Euler equations with time-depending damping, in particular, include the constant coefficient damping. We rigorously prove that the solutions time-asymptotically converge to the diffusion wave whose profile is self-similar solution to the corresponding parabolic equation, which justifies Darcy's law. Compared with previous results about Euler equations with constant coefficient damping obtained by Hsiao and Liu (1992) [2], and Nishihara (1996) [9], we obtain a general result when the initial perturbation belongs to the same space, i.e. $H^3(\mathbb{R})\times H^2(\mathbb{R})$. Our proof is based on the classical energy method.     

Effect of energy dependent cross-section on flow velocity measurements with charge exchange spectroscopy in magnetized plasma

Charge exchange spectroscopy (CXS) is widely used to measure plasma flow velocity. Accurate measurement is heavily affected by energy dependent cross section between neutral atoms and impurity ions. One symmetric layout of poloidal CXS is applied on Large Helical Device. Correction velocity due to the cross section is exacted from total velocity when actual plasma flow velocity is acquired with the benefit of this layout. A linear relationship between correction velocity and ion temperature is observed. Abundant discharges with wide plasma conditions are investigated and the ratio of correction velocity to ion temperature with the same beam energy shows the normal distribution. The impact of beam energy on the ratio of correction velocity to ion temperature of the carbon system and the hydrogen system is discovered based upon the statistics. Effective emission coefficient (Q) from Atomic Data and Analysis Structure (ADAS) is utilized to study the dependence of correction velocity on Q. The relationship in which the ratio of correction velocity to ion temperature increases linearly with the increasing normalized effective emission coefficient ((1/Q)dQ/dv) is observed. Experimental (1/Q)dQ/dv is obtained according to this observation, and comparison with different fractions of n?=?2 excited state is also discussed. The influence of different receivers (carbon and hydrogen) is also presented. The experimental (1/Q)dQ/dv from the carbon system decreases with beam energy decreasing when beam energy is less than 30 keV/amu. This tendency of (1/Q)dQ/dv at low beam energy indicates the existence of the contribution of n?=?2 excited state donors to the cross section.     

扩散场重建格林函数检测钢轨近表面缺陷*

利用超声相控阵全矩阵捕获功能获取后期时间的扩散场信息,实现钢轨近表面缺陷成像。对扩散场信号进行互相关,重建阵元之间的格林函数,获取阵元之间未延时的响应,恢复被噪声湮没的早期缺陷信息,将波数成像方法用于近表面缺陷的快速成像。采用两种超声相控阵探头在钢轨表面采集实验数据,说明格林函数恢复效果与相控阵阵元的个数和激励频率有关。实验结果清晰地显示了距钢轨表面5～10 mm处的缺陷,证实了互相关方法重建格林函数对近表面缺陷检测的有效性。     

关于GB型空间的若干结果

本文对GB型空间进行了若干讨论,得到了一些结果。 设X为Banach空间,X为X的共轭空间,B(X,X)为X到X的所有有界线性算子组成的空间。如果X中的弱收敛序列为弱收敛序列,则称X为GB型空间。Grothendieck.A于1953年证明了l~∞是GB型空间。显然自反空间是GB型空间。     

高超声速飞行器高温流场对激光武器毁伤效应的影响

以美国ABL系统激光武器为例,分析了高超声速飞行器高温流场气体影响激光武器毁伤效应的一些主要因素,包括气体击穿、等离子体屏蔽效应、烧蚀产物颗粒的影响。结果表明:通常情况下,流场电子数密度小于1017cm-3,流场本身等离子体特性不会引起对激光的等离子体屏蔽效应;只有在0.5 km射程以内和宽脉冲激光引起的高压流场(约10 MPa以上)气体击穿,才会导致明显的等离子体屏蔽效应,但在实际战场条件下这种情况一般不会发生;对采用烧蚀手段进行防热的飞行器而言,飞行高度大于10 km,并且基于自由来流流量的无量纲化烧蚀流量小于10-2左右时,烧蚀产物颗粒不会引起激光的衰减。     

High‐order compact schemes for fractional differential equations with mixed derivatives

In this article, we consider two‐dimensional fractional subdiffusion equations with mixed derivatives. A high‐order compact scheme is proposed to solve the problem. We establish a sufficient condition and show that the scheme converges with fourth order in space and second order in time under this condition.© 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 2141–2158, 2017     

A Renal‐Clearable Duplex Optical Reporter for Real‐Time Imaging of Contrast‐Induced Acute Kidney Injury

Despite its high morbidity and mortality, contrast‐induced acute kidney injury (CIAKI) remains a diagnostic dilemma because it relies on in vitro detection of insensitive late‐stage blood and urinary biomarkers. We report the synthesis of an activatable duplex reporter (ADR) for real‐time in vivo imaging of CIAKI. ADR is equipped with chemiluminescence and near‐infrared fluorescence (NIRF) signaling channels that can be activated by oxidative stress (superoxide anion, O₂^.?) and lysosomal damage (N‐acetyl‐β‐d ‐glucosaminidase, NAG), respectively. By virtue of its high renal clearance efficiency (80 % injected doses after 24 h injection), ADR detects sequential upregulation of O₂^.? and NAG in the kidneys of living mice prior to a significant decrease in glomerular filtration rate (GFR) and tissue damage in the course of CIAKI. ADR outperforms the typical clinical assays and detects CIAKI at least 8 h (NIRF) and up to 16 h (chemiluminescence) earlier.     

Validated liquid chromatography–tandem mass spectrometry method for quantification of ticagrelor and its active metabolite in human plasma

A rapid, simple and sensitive LC–MS/MS method was established and validated for simultaneous quantification of ticagrelor and its active metabolite AR‐C124910XX in human plasma. After plasma samples were deproteinized with acetonitrile, the post‐treatment samples were chromatographed on a Dikma C₁₈ column interfaced with a triple quadrupole tandem mass spectrometer. Electrospray negative ionization mode and multiple reaction monitoring were adopted to assay ticagrelor and AR‐C124910XX. Acetonitrile and 5 mΜ ammonium acetate was used as the mobile phase with a gradient elution at a flow rate of 0.5 mL/min. The method was linear in the range of 0.781–800 ng/mL for both ticagrelor and AR‐C124910XX with a correlation coefficient ≥0.994. The intra‐ and inter‐day precisions were within 12.61% in terms of relative standard deviation and the accuracy was within ±7.88% in terms of relative error. The LC–MS/MS method was fully validated for its sensitivity, selectivity, stability, matrix effect and recovery. This convenient and specific LC–MS/MS method was successfully applied to the pharmacokinetic study of ticagrelor and AR‐C124910XX in healthy volunteers after an oral dose of 90 mg ticagrelor.