单模螺旋光纤的本地场

本文从麦克斯韦方程出发,在螺旋光纤的本地坐标系中推导了电场满足的标量本地场波动方程,近似地求解了该波动方程,得到两个基本结果：１）单模螺旋光纤的本地模是圆偏振模;２）在两基模之间的传播常数之差是２τ。上述的理论结果和已知的实验结果相一致。     

反冲塞效应的热弹性理论分析(Ⅰ)──温度场分析*

本文对我们新近发现的长脉冲激光束对金属薄片材料的一种新的破坏方式──“反冲塞”效应进行了温度场分析,用Hankel变换和Laplace变换,得到了温度场的精确解,以激光束的空间分布为均匀分布和高斯分布为例对温度场进行了计算,结果表明激光束的空间均匀分布是产生反冲塞效应的主要原因。     

Reissner板切口尖端应力应变场

本文利用双重幂级数展开法推导出Reissner板切口特征方程,进而应用Muller迭代法求得不同切口张角下特征值序列解答,最后获得Reissner板切口尖端应力应变场.     

CAUSAL DOMAIN OF MINKOWSKI-SPACETIME TANGENT BUNDLE

The geometry of the causal domain of the spacetime tangent bundle is examined for Finslerian quantum fields in Minkowski spacetime. The Planck-scale structure of the boundary of the causal domain is elaborated. The geometry indicates that at the Planck scale, causal connectivity of Finslerian quantum fields may occur between spacelike separated points, and also at larger scales for extremely large relative four-velocities.     

磁共振成像的安全性

对磁共振成像(MRI)的安全性进行了综述,主要涉及五个方面:静磁场、梯度场、射频场、噪声和造影剂.在没有铁磁性外源性物质的条件下,静磁场对人体没有明显的损害,有较高的安全系数.随时间变化的梯度场(dB/dt)可在受试者体内诱导出电场而兴奋神经或肌肉.当梯度上升时间只有数毫秒时,外周神经兴奋是梯度场安全的上限指标.在MRI测定过程中,射频场发射的功率在患者组织内转化成热能,使组织温度升高.MRI运行过程中可产生各种噪声,可能使某些患者的听力受到损伤,使用耳塞仍是削弱噪声最简单和最经济的方法.目前使用的造影剂主要为含钆的化合物,副作用发生率在2%~4%.     

Synthesis and microwave properties of TI2Ba2CaCu2O8 superconducting films grown by MOCVD

We report on the synthesis, structural and electrical characterization of high quality Tl₂Ba₂Ca₁Cu₂O₈ (Tl-2212) superconducting films. The samples have been grown ex-situ on mm² LaAlO₃ (100) substrates by a combined approach of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion. The morphological and compositional nature of the c-axis oriented films has been investigated by SEM and X-ray analyses. Typical values of K and MA/cm² at 77 K have been measured. Microwave measurements have been performed at f = 87 GHz inserting the film in a copper cavity and at f =1.5 GHz on patterned samples using a microstrip resonator technique. A penetration depth nm is evaluated by fitting the microwave data with phenomenological equations. The minimum value of the surface resistance measured at 4.2 K is 60 and 6 m at 1.5 GHz and 87 GHz respectively. The microwave data are described in the context of a modified two fluid model. An evaluation of the temperature dependence of the scattering rate has been performed through the simultaneous measurement of the surface resistance and the penetration depth. Received 16 December 1999 and Received in final form 17 March 2000     

The contribution of Gd and Mn neighbours to the Gd hyperfine field in GdMn6Ge6

With the help of ^155,157Gd NMR in we derive the contribution of Gd and Mn neighbours to the hyperfine field at the rare earth site in the spiral spin phase of the intermetallic compound GdMn₆Ge₆. The substitution of Gd for Y atoms allows the determination of the separate contribution of remote Gd neighbours. The different temperature dependence of the hyperfine contributions of the Gd and Mn neighbours gives the possibility to estimate the transferred hyperfine field of Mn at the rare earth site both in magnitude and sign. Received 31 May 2000 and Received in final form 26 September 2000     

Universal octonary diagonal forms over some real quadratic fields

In this paper, we will prove there are infinitely many integers n such that n ²— 1 is square-free and admits universal octonary diagonal quadratic forms. Received: November 2, 1998.     

Initial-boundary Value Problem for the Landau-Lifshitz System with Applied Field

In this paper, the existence and partial regularity of weak solution to the initial-boundary value problem of Landau-Lifshitz equations with applied fields in a 2D bounded domain are obtained by the penalty method.     

A General Polynomial Sieve

An important component of the index calculus methods for finding discrete logarithms is the acquisition of smooth polynomial relations. Gordon and McCurley (1992) developed a sieve to aid in finding smooth Coppersmith polynomials for use in the index calculus method. We discuss their approach and some of the difficulties they found with their sieve. We present a new sieving method that can be applied to any affine subspace of polynomials over a finite field.