CRAFT TF中场线圈导体及内部接头电阻-温度特性研究

我国于2019年启动了国家大科学装置聚变堆主机关键系统综合研究设施(CRAFT)的建设,环向场(Toroidal Field, TF)线圈是聚变堆主机关键系统综合研究设施的重要组成部分.TF线圈绝缘制造采用真空压力浸渍工艺实现,因TF线圈体量巨大,为使线圈绝缘固化时温度均匀,减少绝缘树脂固化热应力,拟采用导体电流加热的方式进行加热.TF中场线圈有三个内部接头,因此需要同时知道导体和内部接头电阻与温度之间的关系,以防内部接头局部过热,导致绝缘固化失败.本文将中场内部接头样件加热到线圈绝缘工艺温度,用直流四线法测量导体和内部接头在不同温度下的电阻,得到在303～443 K温度区间内导体和内部接头电阻-温度关系式.发现相同温度下,导体电阻大于内部接头电阻,同时分析了内部接头铜套以及铬层对电阻的影响.并根据测得的电阻-温度关系式,可以得到在不同温度下超导缆及内部接头产生焦耳热的能力,从而为超导线圈绝缘固化温度控制提供重要的参考依据.     

一种新的信源、信道编码和差错隐藏的联合优化方法

本文提出了一种基于广义的率失真函数的信源编码,信道编码和差错隐藏联合优化的方法.这种广义的率失真函数综合反映了视频信源经信源编码,信道编码,差错隐藏后的率失真特性,因此可以用来进行视频通信系统收发端的联合优化.仿真结果表明,和传统的信源信道联合编码算法相比,这种基于广义的率失真特性的联合优化可以取得更好的结果.     

A NOTE ON n-PERINORMAL OPERATORS

The study of operators satisfying σja(T) = σa(T) is of significant interest. Does σja(T) = σa(T) for n-perinormal operator T ∈ B(H)ff This question was raised by Mecheri and Braha [Oper. Matrices 6(2012), 725–734]. In the note we construct a counterexample to this question and obtain the following result: if T is a n-perinormal operator in B(H), then σja(T)\{0} = σa(T)\{0}. We also consider tensor product of n-perinormal operators.     

Piecewise Phase Recovery Algorithm Using Block Turbo Codes for Next Generation Mobile Communications

This paper presents an efficient carrier recovery algorithm combined with a turbo‐coding technique in a mobile communication system. By using a block turbo code made up of independently decodable block codes, we can efficiently recover the fast time‐varying carrier phase as well as correct channel errors. Our simulation results reveal that the proposed scheme can accommodate mobiles with high speed, and at the same time can reduce the number of iterations to lock the phase.     

Characterization technique in phase distribution during sample preparation for applications to solder joints and wire-bonding chips

Characterization of solder joint microstructure is essential in evaluation of microelectronic packaging reliability. Analysis techniques and sample preparation play important roles in the material characterization. This study demonstrates several novel approaches in the microstructure evaluation of solder joints. By utilizing precision etching and coating techniques, the interface of the IC packaging chip between the solder and under-bump metallization (UBM) could be revealed much more precisely and the intermetallic compounds were distinctly visible in details by field-emission scanning electron microscopy (FE-SEM). At the Sn-Pb/Ni/Cu interface, the intermetallic compounds defined as Ni₃Sn₄ and Cu₆Sn₅ by electron probe microanalysis (EPMA) were formed between the nickel and the solder. Meanwhile, when the Au-Al wire bonding assembly was etched by the ion beam technique, the interface between gold and aluminum as well as the intermetallic compound could be clearly identified. By adjusting the operating variables, such as etching energy, etching period, and incident angle between the ion beam and sample, the time for sample preparation was significantly reduced. For example, when the cross-section surface of the Sn-Pb solder specimen was perpendicular to the incident ion beam, the highest quality SEM micrographs were obtained at 2.5 keV with an etching time of 7 min. and at 4.5 keV with an etching time of 3 min.     

High-Speed Cyclic Bend Tests and Board-Level Drop Tests for Evaluating the Robustness of Solder Joints in Printed Circuit Board Assemblies

This paper presents a comprehensive study of the resistance of solder joints to failure when subjected to strain rates that simulate the conditions of drop impact experienced by a portable electronic product. Two test methods are used in this study: the board-level drop-shock test (BLDST) and the board-level high-speed cyclic bend test (HSCBT). The performance of (i) 12 material combinations consisting of six solder alloys and two pad finishes, and (ii) 11 manufacturing variations covering three vendors, two finishes, three immersion gold thicknesses, and three thermal aging conditions were investigated using these two test methods. Correlations between the two test methods were performed. Quantitative correlation and sensitivity coefficients for the failure modes and the measured characteristic parameters—number of drops to failure for BLDST and number of cycles to failure for HSCBT—were evaluated. Finally, the potential of HSCBT as a test method for material selection and for bridging board-level and product-level tests was demonstrated through generation of board strain versus number of cycles to failure (S–N) curves of solder joints for six material systems, four bending frequencies, and two test temperatures.     

EFFECT OF Z-PINS'' DIAMETER, SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated.Overlap length of the single lap joint is 15 mm,20 mm,23 mm,37 mm,and 60 mm,respectively.The experimcntal results indicate that the final failure modes of the joints can be divided into twó groups,(a) the bond-line stops debonding until crack encounters Z-pins;and then the adherends break at the location of Z-pins,when overlap length is more than 20 mm;(b) the bond-line detaches entirely and Z-pins are drawn from adherends,when overlap length is equal to 15 mm.A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints.Here,the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line.The tractions are prescribed as functions of the crack displacement,which are available in simple forms that summarize the complex deformations to a reasonable accuracy.The resulting model can be used to track the evolution of complete failure mechanisms,for example,bond-line initial delamination and ultimate failure associated with Z-pin pullout,ultimate failure of the adherends.The paper simulates connecting performance of the single lap joints with different Z-pins' diameter,spacing and overlap length;the numerical results agree with the experimental results;the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints.By numerical analysis method,the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm,when Z-pins' diameter and spacing are 0.4 ram,5 ram,respectively.     

市区多径衰落信道中的TCM DS／SSMA系统性能分析

本文将网络编码调制（ＴＣＭ）应用于市区多径衰落信道下的直接序列扩频多址（ＤＳ／ＳＳＭＡ）系统中，应用ＤＳ条件下市区多径衰落信道的等效模型，提出了一种采用理论分析和数值模拟相结合分析ＴＣＭＤＳ／ＳＳＭＡ系统在该信道下性能的新方法，并将传统的Ｕｎｇｅｒｂｏｅｃｋ型ＴＣＭ才本文所构成的若干种低码率ＴＣＭＤＳ／ＳＳＭＡ系统的性能进行了比较。     

Finite element modeling of thermal fatigue and damage of solder joints in a ceramic ball grid array package

A nonlinear finite element model is presented for analyzing the cyclic and thermal fatigue loading and for viscoplastic damage characterization of the lead-tin (Pb-Sn) solder joints in a ceramic ball grid array (CBGA) surface mount package. An approach using a Δ ∈ _eq ⁱⁿ -modified Coffin-Manson equation is proposed to estimate the fatigue life of the solder joints. The Δ ∈ _eq ⁱⁿ represents a saturated equivalent inelastic strain range as determined by the finite element model. The present study shows that the predictied fatigue life and the associated damage mechanism of the solder joint agree reasonably well with the test data for the 18,25, and 32 mm CBGA packages run at a cyclic temperature load of 0°C/100°C with a frequency of 1.5 cycles per hour. Analysis also shows that a preferred failure site is expected to occur in and around the Pb37-Sn63 solder attachment of the solder joint. A time-dependent (creep induced) damage mechanism is found to be more pronounced than the time-independent (plastic deformation) mechanism.