Anomalous NMR relaxation in cartilage matrix components and native cartilage: fractional-order models

We present a fractional-order extension of the Bloch equations to describe anomalous NMR relaxation phenomena (T(1) and T(2)). The model has solutions in the form of Mittag-Leffler and stretched exponential functions that generalize conventional exponential relaxation. Such functions have been shown by others to be useful for describing dielectric and viscoelastic relaxation in complex, heterogeneous materials. Here, we apply these fractional-order T(1) and T(2) relaxation models to experiments performed at 9.4 and 11.7 Tesla on type I collagen gels, chondroitin sulfate mixtures, and to bovine nasal cartilage (BNC), a largely isotropic and homogeneous form of cartilage. The results show that the fractional-order analysis captures important features of NMR relaxation that are typically described by multi-exponential decay models. We find that the T(2) relaxation of BNC can be described in a unique way by a single fractional-order parameter (α), in contrast to the lack of uniqueness of multi-exponential fits in the realistic setting of a finite signal-to-noise ratio. No anomalous behavior of T(1) was observed in BNC. In the single-component gels, for T(2) measurements, increasing the concentration of the largest components of cartilage matrix, collagen and chondroitin sulfate, results in a decrease in α, reflecting a more restricted aqueous environment. The quality of the curve fits obtained using Mittag-Leffler and stretched exponential functions are in some cases superior to those obtained using mono- and bi-exponential models. In both gels and BNC, α appears to account for micro-structural complexity in the setting of an altered distribution of relaxation times. This work suggests the utility of fractional-order models to describe T(2) NMR relaxation processes in biological tissues.     

Quantum tunnelling of higher-dimensional Kerr-anti-de Sitter black holes beyond semi-classical approximaton

Based on the theory of Klein-Gordon scalar field particles,the Hawking radiation of a higher-dimensional Kerr-anti-de Sitter black hole with one rotational parameter is investigated using the beyond semi-classical approximation method.The corrections of quantum tunnelling probability,Hawking temperature and Bekenstein-Hawking entropy are also included.     

Phase transition behavior and piezoelectric properties of low-Li and high-Sb modified KNN based piezoceramics

(Na_0.5K_0.5)_0.975Li_0.025Nb_0.82−xSb_xTa_0.18O₃ lead-free piezoceramics were prepared by the conventional solid-state sintering method. All samples possess a pure perovskite phase, and no secondary phase could be certified. The crystal structure changes from tetragonal to pseudo-cubic with increasing amount of Sb. The ferroelectric Curie temperature (T_c) shifts to lower temperature while the tetragonal to orthorhombic phase transition temperature (T_o-t) shows no obvious change with increasing Sb⁵⁺. Enhanced piezoelectric and electromechanical properties are obtained with x=0.06: d₃₃=352 pC/N, k_p=47% and k_t=38%, showing that they could be promising candidates as lead-free piezoelectric materials.     

Surfactant-free hydrothermal synthesis of?submicron?BiFeO3?powders

Submicron BiFeO₃ powders were successfully synthesized via a simple hydrothermal process with the assistance of mineralizer (NaOH) at 150–190°C, using FeCl₃ and Bi(NO₃)₃⋅5H₂O as reactants. The effects of mineralizer concentration, reaction temperature and time on the phase evolution and crystal morphology of the resulting samples were investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry and differential scanning calorimetry (TG-DSC), and vibrating sample magnetometry (VSM) were used to characterize the as-synthesized samples. The experimental results revealed that a pure BiFeO₃ phase could be formed at a temperature ranging from 170 to 190°C for 4–20 h in the presence of 0.03–0.12 M NaOH. It was found that the mineralizer concentration, reaction temperature and time played a key role in controlling the growing speed of nuclei and formation of BiFeO₃ crystallites. The possible formation mechanisms of submicron BiFeO₃ powders with different morphologies were presented. The magnetization of BiFeO₃ powders showed a weak ferromagnetic behavior at room temperature.     

铕与4-(4-吡啶甲酰基)苯甲酸配合物的合成与荧光性能研究

以Eu3+为中心离子,4-(4-吡啶甲酰基)苯甲酸(HPFBA)、1,10-菲罗啉(Phen)和三苯基氧膦(TPPO)为配体,合成了新型配合物Eu(PFBA)3(H2O)4,Eu(PFBA)3Phen(H2O)3和Eu(PFBA)3TPPO(H2O)3(PFBA=4-(4-吡啶甲酰基)苯甲酸根).红外光谱表明,形成配合...     

不同功率下无工质微波推力器的推力预估

基于经典电动力学理论,从麦克斯韦方程组和麦克斯韦张量出发,推导出无工质微波推力器的推力计算方程. 应用有限元分析软件,计算了特定谐振模式下的特定圆台谐振腔在不同功率条件下的电磁场分布;根据推导出的理论计算公式,计算了不同功率条件下推力器的总推力. 计算结果表明:推力与功率成正比,而且磁场力决定着总推力的大小;圆台谐振腔消耗20–200 W电磁波功率时所产生的推力在20–250 mN范围内. 关键词： 电磁波 麦克斯韦张量     

水平层状介质中电磁场并矢Green函数的一种快速新算法

本文利用提取直射波并结合自适应数字滤波等技术提出一种计算水平层状介质中电磁场并矢Green函数的快速算法. 首先将谱域Green函数中表征均匀介质作用的直射波提取出来并对其积分进行解析计算,这种处理降低了谱域Green函数的奇异性,可在很大程度上缩短其积分收敛区间. 然后在将谱域Green函数剩余部分对应积分转化为三个快速下降积分的基础上,引入一种自适应数字滤波算法对其进行快速求解. 最后通过具体算例验证了本文所述算法的有效性. 关键词： 并矢Green函数 快速算法 水平层状介质     

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl₂O₄) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.     

Eigenspace-based source number estimation for direction-of-arrival estimation

A eigenspace-based source number estimation was presented.It projects the estimated covariance matrix of array signal into signal eigen-subspace and noise eigen-subspace, respectively.Using the orthogonality between signal eigen-subspace and noise eigen-subspace, it is easy to differentiate the contribution of signal and noise by using the criterion value,or the magnitude of projection.Like the Direction-of-Arrival(DOA) estimation algorithm,the estimator uses the eigenvalue decomposition of covariance matrix with order M×M,where M is the number of elements,and hence can save much computational burden.To reduce more computational burden,the estimation can be implemented by the decomposition in the real-value space.Computer simulation demonstrates the distribution of criterion value and the performance of the estimation method.The estimation method was also tested with the sonar data,which shows good performances.