X射线能量谱间接测量方法

X光机的X射线能量谱在CT图像硬化校正、散射校正和定量CT成像等技术中扮演着重要角色。提出了一种通过由质量衰减系数已知的材料构成的楔型模体的扫描数据来恢复X射线能量谱的方法。经GEANT4模拟数据及实采数据验证,该方法能够较好地恢复X光机的X射线能量谱。通过仿真实验,分析了在几个常用电压下模体材质和厚度对恢复X射线能量谱的影响。     

用于温差发生器的高精度温度测量与控制系统设计

讨论了用于温差发生器的高精度温度测量与控制的设计与实现。采用PT100铂电阻作为温度传感器,详细推导了非平衡电桥测量非线性的校正公式,采用24位的Σ-Δ型的模数转换器AD7714保证了0.005℃的温度测量分辨率。控温电路采用线性化电流方式,算法上对积分分离PID算法做出改良,并与不完全微分PID算法结合形成一种优化PID算法,能快速、精确的把温差稳定到目标值,控温精度达到0.01℃。     

Theoretical analysis and experimental verification of a cost-effective chromatic dispersion monitoring method in a 40-Gb/s optical fiber communication system

A cost-effective technique for in-service chromatic dispersion monitoring in a 40-Gb/s optical communication system is proposed. Microwave devices are adopted to detect the electrical power of a specific frequency band. A simplified theoretical model is proposed and discussed focusing on the relationship between electrical power and chromatic dispersion at different frequency bands. The dynamic monitoring of chromatic dispersion is achieved using devices such as PIN detector, microwave amplifier, narrow-band microwave filter, and electrical power detector. The maximum detectable chromatic dispersion is 130 ps/nm and a resolution of 5.2 ps/nm/dB has been achieved in the frequency band centered at 12 GHz.     

固体材料反斯托克斯荧光制冷的理论研究及其最新进展

本文首先回顾了反斯托克斯荧光制冷的历史发展,简单讨论了激光制冷的循环过程及其制冷条件;其次,概述了反斯托克斯Raman散射、反斯托克斯荧光制冷的热力学理论和热力学限制,重点介绍了适用于各种制冷材料(如稀土离子掺杂玻璃、半导体和晶体等)反斯托克斯荧光制冷研究的理论模型,并简单讨论了激光制冷实验中各种测量温度变化的实验方法及其基本原理。最后,就反斯托克斯荧光制冷的一种最新应用及其前景进行了简单介绍与展望。     

45kVA/2.4kV单相高温超导变压器的设计和试验

为了研究630kVA/10.5kV三相高温超导变压器突发短路情况下热稳定性以及机械稳定性的问题,开发了45kVA(2400V/160V,18.75A/281.25A)单相高温超导变压器.铁心为单相三柱式铁心;杜瓦为带有室温孔的玻璃钢杜瓦,可以保证铁心处在室温下并与绕组隔绝;导线采用Ag合金包套不锈钢加强Bi2223多芯高温超导带材,高压绕组为多层圆筒式绕组,各层间分别置有层间绝缘和冷却通道,低压绕组采用饼式结构;为减小引线的漏热,低压引线采用优化的气冷引线.采用有限单元法(FEM)分析了该变压器电磁、机械问题,并对其进行了基本的性能试验以及突发短路试验,得到重要意义的结果.     

Electroless gold deposition on silicon(100) wafer based on a seed layer of silver

This article describes a method of electroless gold deposition on a Si(100) wafer having a silver surface as seed layer. The seed layer was firstly deposited onto the surface of an etched wafer in an acidic solution of 0.005 mol/L AgNO₃+0.06 mol/LHF. The electroless gold deposition is performed by immersing the Ag-activated wafer in an electroless bath with a composition of 1.27×10^-3 mol/L[AuCl₄]^-+2.00×10^-2 mol/LNaH₂PO₂+8.32×10^-2 mol/L NH₂CH₂CH₂NH₂ (pH = 9.0–9.5). The bath temperature is 50–70 °C. The morphology of the seed layer and the gold film were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).PACS 82.45.Mp; 81.15.Pq; 81.10.Dn     

A Solvable Decorated Ising Lattice Model

A decorated lattice is suggested and the Ising model on it with three kinds of interactions K₁, K₂, and K₃ is studied. Using an equivalent transformation, the square decorated Ising lattice is transformed into a regular square Ising lattice with nearest-neighbor, next-nearest-neighbor, and four-spin interactions, and the critical fixed point is found at K₁=0.5769, K₂=-0.0671, and K₃=0.3428, which determines the critical temperature of the system. It is also found that this system and the regular square Ising lattice, and the eight-vertex model belong to the same universality class.     

Guided wave propagation in single and double layer hollow cylinders embedded in infinite media

Millions of miles of pipes are being used for the transportation, distribution, and local use of petroleum products, gas, water, and chemicals. Most of the pipes are buried in soil, leading to the significance of the study on the subject of guided wave propagation in pipes with soil influence. Previous investigations of ultrasonic guided wave propagation in an elastic hollow cylinder and in an elastic hollow cylinder coated with a viscoelastic material have led to the development of inspection techniques for bare and coated pipes. However, the lack of investigation on guided wave propagation in hollow cylinders embedded in infinite media like soil has hindered the development of pipe inspection methods. Therefore the influence of infinite media on wave propagation is explored in this paper. Dispersion curves and wave structures of both axisymmetric and nonaxisymmetric wave modes are developed. Due to the importance of the convergence of numerical calculations, the requirements of thickness and element number of the finite soil layer between hollow cylinder and infinite element layer are discussed, and an optimal combination is obtained in this paper. Wave structures are used for the mode identification in the non-monotonic region caused by the viscoelastic properties of coating and infinite media.     

A realization of digital wireless transmission for MRI signals based on 802.11b

In this paper, a digital wireless transmission system based on 802.11b standard for magnetic resonance imaging (MRI) application is designed and built for the first time to eliminate the interference aroused by coil array cables. The analysis shows that the wireless receiver has a very high sensitivity to detect MRI signals. The modulation technique of differential quadrature phase shift keyed (DQPSK) can be applied to MRI data transmission with rate of 2 Mbps and bandwidth of 2 MHz. The bench test verifies that this wireless link has a dynamic range over 86 dB supporting up to 3 T MRI system data transmission. The 2D spin echo imaging of phantom is performed and the SNR of the image obtained by the wireless transmission can be comparable with that got by the coaxial cables.     

Fat-water selective excitation in balanced steady-state free precession using short spatial-spectral RF pulses

Fat suppression is important but challenging in balanced steady-state free precession (bSSFP) acquisitions, for a number of clinical applications. In the present work, the practicality of performing fat-water selective excitations using spatial-spectral (SPSP) RF pulses in bSSFP sequence is examined. With careful pulse design, the overall duration of these SPSP pulses was kept short to minimize detrimental effects on TR, scan time and banding artifact content. Fat-water selective excitation using SPSP pulses was demonstrated in both phantom and human bSSFP imaging at 3T, and compared to results obtained using a two-point Dixon method. The sequence with SPSP pulses performed better than the two-point Dixon method, in terms of scan time and suppression performance. Overall, it is concluded here that SPSP RF pulses do represent a viable option for fat-suppressed bSSFP imaging.