Analysis of an interfacial crack in a piezoelectric bi-material via the extended Green’s functions and displacement discontinuity method

Based on the extended Stroh formalism, we first derive the extended Green’s functions for an extended dislocation and displacement discontinuity located at the interface of a piezoelectric bi-material. These include Green’s functions of the extended dislocation, displacement discontinuities within a finite interval and the concentrated displacement discontinuities, all on the interface. The Green’s functions are then applied to obtain the integro-differential equation governing the interfacial crack. To eliminate the oscillating singularities associated with the delta function in the Green’s functions, we represent the delta function in terms of the Gaussian distribution function. In so doing, the integro-differential equation is reduced to a standard integral equation for the interfacial crack problem in piezoelectric bi-material with the extended displacement discontinuities being the unknowns. A simple numerical approach is also proposed to solve the integral equation for the displacement discontinuities, along with the asymptotic expressions of the extended intensity factors and J-integral in terms of the discontinuities near the crack tip. In numerical examples, the effect of the Gaussian parameter on the numerical results is discussed, and the influence of different extended loadings on the interfacial crack behaviors is further investigated.     

Crack problem for superconducting strip with finite thickness

The inclined crack problems are considered for a thin strip and a strip with finite thickness in a perpendicular magnetic field. The critical current density is assumed to be a constant. The crack orientation is varied and the effect of crack on the magnetic field distribution is neglected. Based on the analytical results and variational inequality, the field and current distributions are computed for both thin strip and strip with finite thickness cases, respectively. Then, the stress intensity factors at the crack tip are determined using the finite element method for magnetic field loads. The numerical results are presented for different inclined crack angles, magnetization processes and geometry parameters of the strip. The results show that the fracture behavior of the strip with finite thickness is more complicated than that of the thin strip. With the numerical results, we can predict the largest possibility of cracking as the strip is in an external field.     

Influence of screw length and diameter on tibial strain energy density distribution after anterior cruciate ligament reconstruction

Postoperative tunnel enlargement has been frequently reported after anterior cruciate ligament（ACL）reconstruction.Interference screw,as a surgical implant in ACL reconstruction,may influence natural loading transmission and contribute to tunnel enlargement.The aims of this study are（1）to quantify the alteration of strain energy density（SED）distribution after the anatomic single-bundle ACL reconstruction;and（2）to characterize the influence of screw length and diameter on the degree of the SED alteration.A validated finite element model of human knee joint was used.The screw length ranging from 20 to 30 mm with screw diameter ranging from 7 to 9 mm were investigated.In the post-operative knee,the SED increased steeply at the extra-articular tunnel aperture under compressive and complex loadings,whereas the SED decreased beneath the screw shaft and nearby the intra-articular tunnel aperture.Increasing the screw length could lower the SED deprivation in the proximal part of the bone tunnel;whereas increasing either screw length or diameter could aggravate the SED deprivation in the distal part of the bone tunnel.Decreasing the elastic modulus of the screw could lower the bone SED deprivation around the screw.In consideration of both graft stability and SED alteration,a biodegradable interference screw with a long length is recommended,which could provide a beneficial mechanical environment at the distal part of the tunnel,and meanwhile decrease the bone-graft motion and synovial fluid propagation at the proximal part of the tunnel.These findings together with the clinical and histological factors could help to improve surgical outcome,and serve as a preliminary knowledge for the following study of biodegradable interference screw.     

An electrically conducting interface crack with a contact zone in a piezoelectric bimaterial

A plane problem for an electrically conducting interface crack in a piezoelectric bimaterial is studied. The bimaterial is polarized in the direction orthogonal to the crack faces and loaded by remote tension and shear forces and an electrical field parallel to the crack faces. All fields are assumed to be independent of the coordinate co-directed with the crack front. Using special presentations of electromechanical quantities via sectionally-analytic functions, a combined Dirichlet–Riemann and Hilbert boundary value problem is formulated and solved analytically. Explicit analytical expressions for the characteristic mechanical and electrical parameters are derived. Also, a contact zone solution is obtained as a particular case. For the determination of the contact zone length, a simple transcendental equation is derived. Stress and electric field intensity factors and, also, the contact zone length are found for various material combinations and different loadings. A significant influence of the electric field on the contact zone length, stress and electric field intensity factors is observed. Electrically permeable conditions in the crack region are considered as well and matching of different crack models has been performed.     

磁电弹性体中螺型位错与唇口裂纹的相互作用

研究磁电弹性体中螺型位错与唇口裂纹的相互作用。结合Muskhelishvili方法和干扰技术, 在假定裂纹面具有不可渗透条件下得到磁电弹性体中由位错和唇口裂纹所诱导的应力场、电场和磁场的解析解。应用广义Peach-Koehler公式,得到作用在位错上的影像力。通过数值算例,得到场强度因子的变化规律及影像力和广义力随位错位置的变化规律。     

DC and analog/RF performance optimisation of source pocket dual work function TFET

We investigate a systematic study of source pocket tunnel field-effect transistor (SP TFET) with dual work function of single gate material by using uniform and Gaussian doping profile in the drain region for ultra-low power high frequency high speed applications. For this, a n⁺ doped region is created near the source/channel junction to decrease the depletion width results in improvement of ON-state current. However, the dual work function of the double gate is used for enhancement of the device performance in terms of DC and analog/RF parameters. Further, to improve the high frequency performance of the device, Gaussian doping profile is considered in the drain region with different characteristic lengths which decreases the gate to drain capacitance and leads to drastic improvement in analog/RF figures of merit. Furthermore, the optimisation is performed with different concentrations for uniform and Gaussian drain doping profile and for various sectional length of lower work function of the gate electrode. Finally, the effect of temperature variation on the device performance is demonstrated.     

基于分离粒子随机扩散理论的色谱模拟

为了对扩散分子的轨迹实施动态追踪与模拟, 深入理解分子扩散对色谱动力学的影响, 本文利用微尺度受限空间随机行走的模拟方法对色谱填充柱中的分子扩散过程进行了模拟. 重点考察了固定相的填充率、固定相的形状和柱长对色谱动力学行为的影响. 模拟结果表明短柱和大填充率具有较高的柱效; 在相同的密堆排列下, 固定相形状对分子扩散过程影响微弱; 待分离粒子的运动表现出微尺度空间限域的扩散特征, 但粒子的流动行为会随外部压力的增大而增加. 本论文提出的模拟方法对于发展高效能色谱, 开发新型分离技术等具有参考意义.     

The deformation-stability fundamental length and deviations from c

A fundamental length (or time) is conjectured in many contexts. The “stability of physical theories principle” provides an unambiguous derivation of the stable structures that Nature might have chosen for its algebraic framework. 1/c$1/c$ and ? are the deformation parameters that stabilize the Galilean and Poisson algebras. The stability principle applied to the Poincaré–Heisenberg algebra, yields two deformation parameters defining two length (or time) scales. One of the scales is probably related to Planck?s length but the other might be much larger. This is used as working hypothesis to compute deviations from c in speed measurements of massless particles.     

On relativistic electron bremsstrahlung in thin targets

The simple model of relativistic electron bremsstrahlung in a thin target is presented for conditions when its thickness less then a photon formation length. Results of our calculations obtained with account of an influence of target dielectric properties are in agreement with data at 25 GeV electron bremsstrahlung in thin layers of different media.