A method for the design of MRI radiofrequency coils based on triangular and pulse basis functions

This paper presents a numerical technique for the design of an RF coil for asymmetric magnetic resonance imaging (MRI) systems. The formulation is based on an inverse approach where the cylindrical surface currents are expressed in terms of a combination of sub-domain basis functions: triangular and pulse functions. With the homogeneous transverse magnetic field specified in a spherical region, a functional method is applied to obtain the unknown current coefficients. The current distribution is then transformed to a conductor pattern by use of a stream function technique. Preliminary MR images acquired using a prototype RF coil are presented and validate the design method.     

Elasto-plastic and visco-elastic deformations of a polymer sphere measured using colloid probe and scanning electron microscopy

The adhesive interaction energy between a single 27 μm polystyrene sphere and a flat silica surface has been measured, as a function of applied load on the sphere, using an atomic force microscope (AFM). The pull-off force required to remove the sphere from the surface after application of a given load was found to increase as a function of the applied load. These data are indicative of a plastic or elasto-plastic deformation of the sphere. Simple analyses of these data using established elastic/plastic deformation theories indicate that, at the loads used, the system is most probably undergoing an elasto-plastic deformation. Further evidence for some plastic deformation of the sphere was obtained using scanning electron micrographs of the same sphere after an AFM experiment had been completed. Careful analysis of all these data indicated a significant time dependence of these adhesive interactions due to the viscoelastic nature of the polymer bead in question.     

Comparison of the long range polymer chain dynamics of polystyrene and cis-polyisoprene using polymers randomly labeled with pyrene

The ability of the Fluorescence Blob Model (FBM) to probe the chain dynamics of a polymer backbone was verified for the first time by investigating whether it responds to known differences in backbone flexibility for flexible cis-polyisoprene (PIP) and more sterically hindered polystyrene (PS), both randomly labeled with pyrene. For comparable pyrene contents, the steady-state fluorescence spectra indicated that Py-PIP formed considerably more excimer than the Py-PS samples. Analysis of the fluorescence decays with the FBM provided the rate constant for intramolecular excimer formation. This rate constant was much larger for Py-PIP than for Py-PS, in agreement with the enhanced excimer formation observed for Py-PIP. The enhanced ability of Py-PIP to form excimer is attributed to the PIP backbone being less sterically hindered than the PS backbone. This study is the first example of a comparison of the long range polymer chain dynamics for two different polymeric backbones randomly labeled with pyrene.     

GPU Accelerated Successive Interference Cancellation for NOMA Uplink with User Clustering

Wireless Personal Communications - Non-orthogonal multiple access (NOMA) can achieve high throughput by using the same time and frequency resources for multiple users. NOMA distinguishes multiple...     

开发高性能的无铅波峰焊料合金

无铅波峰焊已经发展为两个主要的合金体系:SnAgCu锡/银/铜体系通常含银量达3至4%和基于SnCu锡铜共晶体系。如果按照用户的价值方程式来衡量,二者都存在固有的缺陷。含银3%至4%的SnAgCu体系可提供良好的可靠性和工艺良率,但原材料的成本昂贵。作为替代品的SnCu共晶体系及其改性合金SnCuNi的原材料成本较低,但其工艺良率和焊接可靠性存在问题。为了克服现有焊料体系的缺点,确信电子开发出新型焊料合金SACX0307。研究SAC305、Sn99.3Cu0.7、改性Sn99.3Cu0.7SnCuNi和SACX0307四种合金系的测试结果,评估无铅焊接工艺的4个主要特性:工艺良率、铜浸出率、浮渣形成和热机械可靠性。波峰焊实验使用了测试电路板专门设计较复杂,以区分不同加工条件下的差异、三种助焊剂包括水基和醇基配方和两种电路板表面处理铜OSP和浸银处理。测试表明,SACX0307填补了SAC305合金与SnCu共晶合金系列之间的空白,就波峰焊的四个主要特性而言,其性能优于Sn99.3Cu0.7和SnCuNiSn99.3Cu0.7,而原材料成本低于SAC305。     

Giant Electric Field Tuning of Magnetic Properties in Multiferroic Ferrite/Ferroelectric Heterostructures

Multiferroic heterostructures of Fe₃O₄/PZT (lead zirconium titanate), Fe₃O₄/PMN‐PT (lead magnesium niobate‐lead titanate) and Fe₃O₄/PZN‐PT (lead zinc niobate‐lead titanate) are prepared by spin‐spray depositing Fe₃O₄ ferrite film on ferroelectric PZT, PMN‐PT and PZN‐PT substrates at a low temperature of 90 °C. Strong magnetoelectric coupling (ME) and giant microwave tunability are demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnetic resonance (FMR) field shift up to 600 Oe, corresponding to a large microwave ME coefficient of 67 Oe cm kV^?1, is observed in Fe₃O₄/PMN‐PT heterostructures. A record‐high electrostatically tunable FMR field range of 860 Oe with a linewidth of 330–380 Oe is demonstrated in Fe₃O₄/PZN‐PT heterostructure, corresponding to a ME coefficient of 108 Oe cm kV^?1. Static ME interaction is also investigated and a maximum electric field induced squareness ratio change of 40% is observed in Fe₃O₄/PZN‐PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability is brought forth to significantly enhance the microwave tunable range up to 1000 Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequencies provide great opportunities for electrostatically tunable microwave multiferroic devices.     

Exocrine Pancreatic Secretions in Young Pigs Fed Diets Containing Faba Beans (Vicia faba) and Peas (Pisum sativum): Nitrogen,Protein and Enzyme Secretions

Two experiments were carried out to investigate the effect of feeding diets containing faba beans and peas on pancreatic secretions in young pigs fitted with a pancreatic pouch re-entrant cannula. In Experiment 1, eight barrows, with an average initial weight of 8·5 kg, were fed one of two maize starch-based diets formulated to contain 200 g crude protein (CP) kg⁻¹ according to a completely randomised design. In one of the diets, soya bean meal was the sole protein source; in the other diet, soya bean meal and faba beans (cv Fibro; dark-flowering) each supplied 50% of the dietary CP. In Experiment 2, five barrows, with an average initial weight of 18·1 kg, were fed one of two diets according to a two-period change-over design. The diets were formulated to contain 150 g CP kg⁻¹ with peas (cv Ascona or cv Radley) as the sole protein source. In both experiments, the experimental periods consisted of 8 days: 6 days adaptation followed by a 2 day collection of pancreatic juice. The soya bean meal diet and the faba bean diet contained 0.04 and 0.21% tannins (catechin equivalents), respectively. The trypsin inhibitor activities of the Ascona and Radley pea diets were 0·76 and 3·24 mg of trypsin inhibited per gram, respectively. In both experiments, diet did not affect ( P> 0·05) the pancreatic secretions of nitrogen, protein, amylase, lipase and chymotrypsin. In Experiment 1, specific trypsin activity was higher ( P< 0·05) in pancreatic juice from pigs fed the diet containing soya bean meal and faba beans (53700 units litre⁻¹) than for those fed the soya bean meal diet (41200 units litre⁻¹). However, there was no effect ( P> 0·05) when trypsin activity was expressed as total activity (units 24 h⁻¹). It is concluded that the inclu-sion of faba beans and peas in diets for young pigs has only minor effects on exocrine pancreatic secretions.     

Pseudomorphic HEMT manufacturing technology for multifunctionalKa-band MMIC applications

We have demonstrated very good performance, high yield Ka-band multifunctional MMIC results using our recently developed 0.25-μm gate length pseudomorphic HEMT (PHEMT) manufacturing technology. Four types of MMIC transceiver components-low noise amplifiers, power amplifiers, mixers, and voltage controlled oscillators-were processed on the same PHEMT wafer, and all were fabricated using a common gate recess process. High performance and high producibility for all four MMIC components was achieved through the optimization of the device epitaxial structure, a process with wide margins for critical process steps and circuit designs that allow for anticipated process variations, resulting in significant performance margins. We obtained excellent results for the Ka-band power amplifier: greater than 26 dBm output power at center frequency with 4.0% standard deviation over the 3-in. wafer, 2-GHz bandwidth, greater than 20 pet-cent power-added efficiency, over 8 dB associated gain, and over 10 dB linear gain. The best performance for the Ka-band LNA was over 17 dB gain and 3.5 dB noise figure at Ka-band. In this paper, we report our device, process, and circuit approach to achieve the state-of-the-art performance and producibility of our MMIC chips     

Radiation-curable prepreg composites

Advanced composites, specifically carbon-fiber-reinforced epoxies, are used extensively for a variety of demanding structural applications, primarily because of their high strength-to-weight and stiffness-to-weight ratios, corrosion resistance, and damage tolerance characteristics. Electron beam (EB) treatment can be used to produce useful physical and/or chemical changes in plastics and composites by initiating various polymerization and crosslinking reactions. The advantages of using EB rather than thermal curing for carbon-fiber-reinforced epoxy composites include curing at ambient temperature, reduced curing times, and fewer volatiles. An EB-curable carbon fiber-acrylated epoxy composite is being developed for various applications. The tensile properties of the 14-ply EB-cured epoxy laminate were comparable with the properties of the thermally cured laminates used in the aircraft industry. Research is continuing to develop resin formulations and select coupling agents to improve the compression properties of EB-cured laminates.