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BACKGROUND: Posterior communicating artery (PcomA) aneurysms are more likely to recanalize than anterior communicating artery (AcomA) aneurysms. However, it is still unclear whether the recanalization rate of these aneurysms is a result of involvement from the fetal posterior cerebral artery (fPCA) in PcomA aneurysms and variation of the unilateral A1 segment in AcomA aneurysms. The purpose of this study is to retrospectively evaluate the different recanalization rates between PcomA aneurysms with fPCA and AcomA aneurysms with a variation of the unilateral A1 segment. METHODS: We retrospectively collected information regarding 214 patients, each with communicating segment aneurysms between January 2013 and January 2020. Follow-up documentation on clinical and imaging data was comparatively analyzed between variant types, and recanalization rates of the variant and normal types were analyzed by stratification. RESULTS: Of the 84 variant-type aneurysms (PcomA with fPCA and AcomA with a variation of the unilateral A1 segment, 41/43), complete recanalization occurred in 23 patients (27.4%), and it was significantly more likely to occur in PcomA aneurysms with fPCA (39.1%) than in AcomA aneurysms with a variation of the unilateral A1 segment (16.3%). Stent-assisted coil embolization (SACE) has been shown to reduce recanalization (OR =0.092, 95% CI: 0.011 to 0.790, P=0.03). Additionally, variant types and the normal type (non-fetal, 106, and bilateral A1 symmetry, 24) have different odds ratios (OR) of recanalization (P=0.04), and the OR of the variant subtypes was significant, unlike the normal type (P=0.49). CONCLUSIONS: This study suggests that PcomA aneurysms with fPCA are more likely to recanalize than AcomA aneurysms with a variation of the unilateral A1 segment.

Background: Symptomatic vertebral artery dissecting aneurysm (VADA) is a challenging disease with controversy on treatment strategy due to anatomic configuration and their nature. Moreover, the outcomes of reconstructive treatment have not been well established. Objective: To evaluate the safety and efficacy of reconstructive endovascular treatment (EVT) for symptomatic VADAs with Willis covered stent. Methods: We evaluated retrospectively 13 patients with symptomatic VADAs who treated with Willis covered stent, compared with stent-assisted coiling (SAC) on the characteristics, posttreatment course, angiographic and clinical follow-up outcomes at an average of 14.4 months (range, 3–48 months). Results: A total of 33 patients with symptomatic VADAs were reviewed, 23 of these patients with ruptured VADAs. The technical successful rate is 100% respectively in Willis covered stent (Group A) and SAC (Group B, n ​= ​20). The initial complete occlusion rate was significant higher in group A (100%) than group B (30%) (p ​ ​0.05). No obvious in-stent stenosis and no re-hemorrhage and delayed ischemic symptoms during the follow-up period. The final angiograms of all survived patients demonstrated the complete occlusion rate was higher in group A (100%) than group B (80%), but no significant statistical difference (p ​> ​0.05). Clinical outcomes were favorable in 31 (93.9%), severe disability occurred in one in group B, and only one death in group A. The final clinical outcomes were also not significant difference in the two groups (p ​> ​0.05). Conclusions: Our initial result demonstrated reconstructive EVT with Willis covered stent provides a viable approach for selected symptomatic VADAs involving the intracranial and extracranial segments, which is similar to favorable results with SAC. However, an expanded clinical experiences and larger cohort studies are needed.

We investigated lipidomic features from healthy controls (HCs), patients with unruptured cerebral aneurysms (UCAs) and ruptured CAs (RCAs) to analyze their lipidomic profiles and identify a lipid signature associated with CAs. Patients (n = 540) were enrolled from two centers. We identified significantly altered plasma lipids in 2 cohort with the total lipid intensity decreasing from HC to UCA to RCA. Triglycerides comprised the distinct profile of lipids in CAs. A four-lipid signatures showed good calibration and diagnostic prediction for CA vs. HC and UCA vs. RCA, but independent discriminate CA from HC, UCA from RCA, and RCA (RI and RII) or UCA (UI and UII) subtypes, in training and validation cohorts. Comprehensive lipidomic profiles identified decreased lipids as a prominent feature of CA development, and a four-lipid signature could not only better diagnose and predict UCAs/RCAs from HCs, but also predicted patients subtypes with severe RCA or high-risk UCA.

Purpose: To evaluate the safety and the clinical efficacy of percutaneous vertebroplasty (PVP) in treating malignant spinal tumors and malignant vertebral compression fractures with epidural involvement.Materials and methods: 43 patients with spinal metastatic tumors and malignant vertebral compression fractures with epidural involvement were treated using PVP. American Spinal Injury Association (ASIA) impairment scale results at presentation were used to divide patients into 2 groups. Patients in group A had no symptoms of neurological compression (n = 25); and patients in group B had symptoms of neurological compression (n = 28). A 13G bone puncture needle was placed across the pedicle of the fractured vertebra, and polymethyl methacrylate (PMMA) was injected into the fractured vertebral body under fluoroscopic control. Patients were seen in follow-up at 1, 3, and 6 months after the procedure and every six months thereafter.Results: PVP was technically successful and well-tolerated in all patients. Clinical assessment at the final follow-up found complete pain relief (n = 19) or good pain relief (n = 14) in 33 patients (62.3%, 95% CI: 49%, 76%). ASIA impairment scale assessment at the final follow-up demonstrated symptoms of neurologic compression in 31 patients and no symptoms of neurologic compression in 22 patients. Symptoms of neurologic compression were found in five group A patients and eight group B patients.Conclusions: PVP was a safe and moderately effective procedure in the treatment of malignant vertebral compression fractures with epidural involvement. Keywords: percutaneous vertebroplasty, pain, malignant spinal tumor, metastasis

DC collection network offers an attractive alternative to AC network for photovoltaic, as it avoids the charging current issues and reduces the size and weight. Variable voltage gain DC/DC converters play an important role in DC collection network. Two topologies suitable for photovoltaic DC collection are studied. Boost and LLC converter and active clamp isolated full-bridge boost converter are two converters with high and variable voltage conversion ratio suitable for the photovoltaic system. This work investigates the two converters comprehensively. The topologies are analysed so as to summarise and compare the characteristic of the converters. Soft switching condition is compared to help extend the zero voltage switching range. Voltage and current stress of the two converters are calculated. Loss comparison is made with the theoretical analysis. Advantages and disadvantages are summarised to get a deep insight into their application field.

With the development of NEMSs (nano-electro-mechanical systems), the size-dependent behavior has been an active topic. The scale parameter seems an essential factor dominating mechanical behavior at nanoscale. However, is it always dominant? This is a question deserving careful investigation. For this reason, the buckling of a bi-layered PE (piezoelectric) nanobeam is analyzed. The main purpose is to reveal and compare the effects of the nonlocal scale, imperfect interface, interlaminar van der Waals force and loading ratio. The imperfect interface is modeled by normal and shear springs, and the van der Waals force is represented by the Hamaker formula. Based on the principle of virtual work, the analytical solution of the critical buckling loading is derived by using the trigonometric shear deformation theory. After the verification in some degenerated cases, parametric studies are conducted. It is indicated that if the nonlocal parameter varies in the typical range [0, 4 nm^2], it only has quite limited effect on the buckling behavior, as compared with the other three factors. In this case, although the buckling relies on the nonlocal scale, it is far more dependent on the conventional non-nanoscale factors. The conclusions can provide references for optimal design of NEMSs.

Mg-based stent is a promising candidate of the next generation fully degradable vascular stents. The latest progress includes the CE approval of the Magmaris ® WE43 based drug eluting stent. However, so far, the long term (more than 1 year implantation) in vivo degradation and the physiological effects caused by the degradation products were still unclear. In this study, a 20 month observation was carried out after the bare Mg-Nd-Zn-Zr (abbr. JDBM) stent prototype was implanted into the common carotid artery of New Zealand white rabbit in order to evaluate its safety, efficacy and especially degradation behavior. The degradation of the main second phase Mg12Nd was also studied. Results showed that the bare JDBM stent had good safety and efficacy with a complete re-endothelialization within 28 days. The JDBM stent struts were mostly replaced in situ by degradation products in 4 month. The important finding was that the volume and Ca concentration of the degradation products decreased in the long term, eliminating the clinicians’ concern of possible vessel calcification. In addition, the alloying elements Mg and Zn in the stent could be safely metabolized as continuous enrichment in any of the main organs were not detected although Nd and Zr showed an abrupt increase in spleen and liver after 1 month implantation. Collectively, the long term in vivo results showed the rapid re-endothelialization of JDBM stent and the long term safety of the degradation products, indicating its great potential as the backbone of the fully degradable vascular stent. Statement of significance Mg-based stent is a promising candidate of the next generation fully degradable stents, especially after the recent market launch of one of its kind (Magmaris). However the fundamental question about the long term degradation and metabolic mechanism of Mg-based stent and its degradation products remain unanswered. We implanted our patented Mg-Nd-Zn-Zr bare stent into the common carotid artery of rabbits and conducted a 20 months observation. We found that the Ca containing degradation products could be further degraded in vivo. All the alloying elements showed no continuous enrichment in the main organs of rabbits. These findings eliminate the clinicians’ concern of possible vessel calcification and element enrichment after the implantation of Mg alloy based stents to some extent.

Although the cracking problems of multiferroic structures have been widely investigated, concentrated force-induced fracture still remains as an un-fully explored failure mode that has considerable significance in this field. The present article analyzes the interfacial crack in a layered multiferroic cylinder subjected to a concentrated axial shear force on its outer surface. The methods of infinite trigonometric-series and Cauchy singular integral equation are applied to solve the problem. The convergence behaviors of the dimensionless infinite trigonometric-series functions are clarified, and the numerical results of stress intensity factor (SIF) are verified by the analytical solution in a special case. Parametric studies are conducted, and the effects of structural parameters on the fracture behavior are revealed. Two structural optimization ways are suggested for reducing the harmful peak value of SIF. One is to decrease the radius of the interface when the total thickness is given, and the other is to increase the layer thickness when the radius of the interface is specified. The obtained conclusions can provide references for anti-fracture optimization of cylindrical multiferroic devices under a concentrated force.

Swarm robots have been an active topic in the field of intelligent machines in recent years. Self-assembly is an important function of swarm robots that provides an effective way for building different kinds of configurations by autonomous docking. For a self-assembly process, the path planning control is a key technique. The present paper proposes a CVT (Centroidal Voronoi Tessellation) based intelligent control algorithm for the self-assembly path planning. It can enable swarm robots to move from an initial virtual region into the target virtual region by a synchronous collaborative scheduling method. Matlab simulations are performed on the self-assembly control of three typical configurations including the line-shape, cross-shape and H-shape. The time consumption is compared under different error conditions, the effectiveness of the new algorithm is validated and its limitation is also pointed out. Overall, this algorithm provides a promising way for the intelligent control of self-assembly path planning of swarm robots.

Multiferroic devices often serve under harmonic vibration. Resonance induced cracking is a common failure of them. The present work studies the resonant fracture of a multiferroic cylindrical structure by the combined methods of variable separation, infinite series, singular integral equation and Lobatto–Chebyshev collocation. It is found that complex modulus and residual stress are two important factors governing the resonant fracture behavior. Generally, the loss factors only affect the resonant amplitude of the fracture parameter, but the residual stress affects both the resonant amplitude and frequency. The obtained conclusions can provide guidelines for the anti-fracture optimal designs of multiferroic devices.

Yi-Feng Gu,1 Qing-Hua Tian,1 Yong-Dong Li,1 Chun-Gen Wu,1 Yan Su,2 Hong-Mei Song,1 Cheng-Jian He,1 Dong Chen,2 1Institute of Diagnostic and Interventional Radiology, 2Department of Orthopaedics, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, People’s Republic of China Objective: The aim of this study was to compare the efficacy of percutaneous vertebroplasty (PVP) and interventional tumor removal (ITR), with PVP alone for malignant vertebral compression fractures and/or spinal metastatic tumor with epidural involvement. Patients and methods: A total of 124 patients were selected for PVP and ITR (n = 71, group A) and PVP alone (n = 53, group B). A 14G needle and guide wire were inserted into the vertebral body, followed by sequential dilatation of the tract until the last cannula reached the anterior portion of the pedicle. Tumors were then ablated with a radiofrequency probe. ITR was performed with marrow nucleus rongeurs, and then cement was injected into the extirpated vertebra. Outcomes were collected preoperatively and at 1, 3 and 6months and every subsequent 6months. Results: The rates of pain relief and increased mobility at the last follow-up were higher in group A than those in group B (P < 0.05). There were significant differences in visual analog scale (VAS) score and Oswestry disability index (ODI) score at 1, 3 and 6months, 1year and >1year in group A than in group B (P < 0.05). The rates of paraplegia recovery and vertebral stability in group A were higher than those in group B (P < 0.05). Conclusion: PVP and ITR proved to be an effective approach for patients with malignant vertebral compression fractures and/or spinal metastatic tumor and provided distinct advantages in pain relief, function recovery and vertebral stability that are comparable to that obtained with PVP alone. Keywords: percutaneous vertebroplasty, pain, malignant spinal tumor, removal, metastasis

Magneto-electro-elastic (MEE) interfacial regions may be formed in multiferroic composites consisting of alternate piezoelectric (PE) and piezomagnetic layers during the hot-pressing process. The existence of such an MEE region may have effects on the mechanical behavior of the composite, which is an interesting problem deserving studying. The present article proposes an interfacial fracture model for a multiferroic composite that contains an MEE interfacial region. The methods of Fourier integral transform and Green’s functions are employed to convert the crack problem with mixed boundary conditions into Cauchy singular integral equations, which are further numerically solved by the Lobatto–Chebyshev collocation method to determine the stress intensity factors. In the numerical computation, the PE volume fraction is chosen as the only characteristic parameter to calculate the material properties of the MEE interfacial region based on the linear rule of mixture. Finally, parametric studies are conducted to reveal the effects of the volume fraction on the fracture behavior, and two main conclusions are drawn: (a) The effects of the PE volume fraction reflect the effects of the material-property jumps across the interfaces, and (b) the interfacial fracture behavior is mainly dominated by the competition between the property jumps across the interfaces and the thickness of the interfacial region.

Crack interaction may give rise to local upward pulse of fracture parameter, which is harmful to structural safety. The method to be adopted to remove such pulse is significant but remains unclear. In addition, piezoelectric (PE) stiffening exists in multiferroic composites, but does its counterpart, PE softening, also exist? If yes, when do they occur? These problems deserve study. In the present article, a fracture analysis is performed on a multiferroic semicylinder consisting of a PE inner layer, a magnetoelectroelastic (MEE) interlayer, and a piezomagnetic (PM) outer one. This is the first study to consider the MEE interlayer in multiferroic composites. The combined methods of Green's functions, dislocation simulation, and Cauchy singular integral equations are used for solving the problem. Numerical results are provided for parametric studies, yielding two main conclusions: (a) bilateral clamping is an effective way for removing the upward pulse of the local SIF oscillation induced by crack interaction. (b) Besides the conventional PE stiffening effect, its counterpart effect of PE softening is also noted, both of which depend on the piling way of the PM, PE, and MEE layers. Specifically, PE stiffening always occurs on the PM–MEE interface, while PE softening invariably appears on the PE–MEE interface.

Sliding is a typical failure mode of composite interfaces. According to traditional theory, interfacial sliding can be represented by the linear shear-spring model (LSSM). Although the required driving interfacial shear stress has been characterized by LSSM, the relation between interfacial normal stress and sliding is not yet reflected by it. The present paper proposes an interfacial sliding-prevention/promotion model to consider the effect of interfacial normal stress on interfacial sliding. As an example of application, the intra-layer fracture problem is analyzed on a bi-layered multiferroic ceramics. Green’s functions are derived to construct the Cauchy singular integral equations, which are further numerically solved to get mechanical strain energy release rate (MSERR) and interfacial normal stress. Parametric studies yield a new finding that non-zero normal stress may be produced in local interfacial regions by intra-layer cracks under pure in-plane shear. Local positive normal stress gives rise to local sliding-promotion effect, while local negative normal stress leads to local sliding-prevention effect. The interfacial shear imperfection and local sliding-prevention/promotion constitute the mechanisms for the variation of MSERRs of the two intra-layer cracks.

A coupling model is proposed to characterize interfacial imperfections by generalizing the spring model and referring to the magneto-electro-elastic constitutive relations. As an application, in-plane fracture analysis is performed on a multiferroic composite, which consists of a ferromagnetic layer, a ferroelectric layer and an imperfect interfacial region. The methods of Fourier integral transform and Green’s function are employed to derive the Cauchy singular integral equations for the cracks. Numerical results of the mechanical strain energy release rate are provided to survey the effects of interfacial imperfections and their couplings. It is found that imperfection couplings affect the fracture behavior remarkably and so it is necessary to consider them in the mechanical problems of this kind of smart structures.

The purpose of the present paper is to answer the following open question given by Sederberg's research team: are there T-splines with linearly dependent blending functions that do not have multiple knots? First, the mathematical properties of the blending functions of T-splines without multiple knots are analyzed. Then, the linear independence of them is proved, and meanwhile a necessary condition is deduced for the linear dependence of T-spline blending functions. Finally, the answer to the open question is obtained: there are no T-splines with linearly dependent blending functions that do not have multiple knots.

Local refinement is widely applied in surface modeling. This paper proposes the concept of influence knot set, and uses it to establish a new algorithm for the local refinement of T-spline surfaces, whose effectiveness is demonstrated by several examples. Compared with existing algorithms, the present one may have two advantages: (a) it does not produce excessive propagation of control points because the number of additional control points is reduced; (b) it simplifies the process of judging whether an additional control point needs to be added or not, and so the final T-mesh topology can be obtained more easily.

Mode III fracture analysis is performed on the multiple unequal interfacial cracks in a tri-layered multiferroic semi-cylinder by the methods of dislocation simulation, Green’s function and Cauchy singular integral equation. Based on the parametric studies on the numerical results of stress intensity factor (SIF), the interaction laws of the cracks, especially the local oscillation phenomenon of the SIF curves, are revealed, and the boundary effect, the shielding effect and the interference effect are employed to interpret the underlying mechanisms. The obtained results can provide theoretical references to the anti-fracture optimal design of this kind of smart structures.

Magnesium alloy covered stents have rarely been used in the common carotid artery (CCA). We evaluated the long-term efficacy of magnesium alloy covered stents in a lateral aneurysm model in rabbit CCA. Magnesium alloy covered stents (group A, n = 7) or Willis covered stents (group B, n = 5) were inserted in 12 New Zealand White rabbits and they were followed up for 12 months. The long-term feasibility for aneurysm occlusion was studied through angiograms; the changes in vessel area and lumen area were assessed with IVUS. Complete aneurysmal occlusion was achieved in all aneurysms. Angiography showed that the diameter of the stented CCA in group A at 6 and 12 months was significantly greater than the diameter immediately after stent placement. On intravascular ultrasound (IVUS) examination, the mean lumen area of the stented CCA in group A was significantly greater at 6 and 12 months than that immediately after stent placement; the mean lumen area was also significantly greater in group A than in group B at the same time points. The magnesium alloy covered stents proved to be an effective approach for occlusion of lateral aneurysm in the rabbit CCA; it provides distinct advantages that are comparable to that obtained with the Willis covered stent.

The relativistic backward-wave oscillator has been considered to be one of the most promising high-power microwave devices. As the output microwave power is further increased, the breakdown phenomenon inside the relativistic backward-wave oscillator, including the collector pole, becomes more and more serious, which eventually leads to the pulse shortening, becoming a biggest obstacle to the development of the device with high power and high energy. Such a problem has also been one of the important issues which constrain its development. Based on the 2.5D particle-in-cell simulation software, i.e. UNIPIC-2D developed by our research group, in this paper the dynamic gassing model is used to study the effects of the relativistic backward-wave oscillator collector breakdown process and the guiding magnetic field under different outgassing coefficients. The result of particle simulation demonstrates that as the electrons continue to bombard the collector, the surface pressure of the collector is increased, and gas ionization occurs. The generated plasma enters into the slow-wave structure along the guiding magnetic field, thus affecting the beam-wave interaction process and causing the output power to drop. With the increase of the gas release coefficient, the pulse shortening phenomenon becomes more and more obvious. In the case of low guiding magnetic field, the breakdown and pulse shortening are alleviated.

The present work studies the interfacial fracture in a piezoelectric cylindrical shell patch. The problem is solved by the methods of infinite trigonometric series and Cauchy singular integral equation, and the numerical results of the stress intensity factor (SIF) are obtained. The effects of the interfacial radius and crack’s location on the SIF are explained through the effects of the free surface, interfacial curvature, crack length, and interface end, respectively. An optimal stiffness matching relationship between the piezoelectric layer and dielectric substrate is suggested. The effects of the piezoelectric and dielectric coefficients are explained through the mechanism of piezoelectric stiffening.

The purpose of the present work is to establish a set of real fundamental solutions for the differential governing equations of three dimensional axisymmetric problems in piezoelectric media. Firstly, conventional complex fundamental solutions are derived by analysis on the eigenvalue problem, and then, Euler’s formula is used to transform them into equivalent real fundamental solutions. As an example of application, the fracture problem of an axisymmetric penny-shaped crack in a piezoelectric layer is resolved by the real fundamental solutions based new method. Theoretical derivation and numerical computation are validated in the special case of a penny-shaped crack in an infinite piezoelectric body. Effects of geometrical parameters and electric-loading coefficient on energy release rates are surveyed and their agreement with the results of existing papers is also indicated. The advantage of such a real fundamental solutions based new method is that it can effectively help to avoid the difficult complex analysis in mixed boundary value problems.

The purpose of the present paper is to investigate the problem of interfacial fracture in a multiferroic composite under magnetostriction or electrostriction. Methods of distributed interfacial dislocations, Green’s function and Cauchy singular integral equations are employed to solve the problem of multiple cracks on the interface. Numerical results of the fracture parameter are discussed, and the magnetostrictive or electrostrictive interfacial fracture is explained via the physical phenomena of “active/passive deformation”, “magneto/electro-mechanical coupling” and “piezomagnetic/piezoelectric stiffening”.

In the present work, we investigate the problem of multiple cracks on the interface between a piezoelectric layer and an orthotropic substrate. The method of dislocation simulation and singular integral equation are used to solve the crack problem. The theoretical derivation is verified by the classical result in a special case. Numerical results of the stress intensity factor are obtained, and thereby the effects of geometrical parameters and material orthotropy are surveyed. The optimal stiffness ratio of the orthotropic substrate is suggested for the purpose of interfacial fracture prevention, which is significant for the design and assessment of such a kind of smart structures.

For the first time, real fundamental solutions are proposed for in-plane magnetoelectroelastic governing equations. Dislocation simulation method is used to derive singular integral equations for collinear unequal crack series under mode I loadings. Special cases of a single crack and two collinear equal cracks are used to validate the proposed solution. The effects of crack space, crack length and magnetic/electric loading are discussed. Real fundamental solutions have an advantage over complex fundamental solutions, because real analyses are more straightforward than complex analyses. Moreover, the model of collinear unequal cracks is more practical than that of collinear equal cracks.

Interface fracture of a multiferroic composite is studied by the methods of integral transform and singular integral equation. Parametric studies on the stress intensity factor yield three conclusions. (a) The multiferroic composite is more likely to fracture in electric field than in magnetic field. (b) Under magnetostriction, piezomagnetic stiffening does not affect the interface crack, but the influence of piezoelectric stiffening is notable. Under electrostriction, inverse results are obtained. (c) In magnetic loading cases, the piezomagnetic layer should be softer and the piezoelectric strip stiffer; however, if electric loading is applied instead, opposite conclusion should be expected.

The purpose of the present work is to study the fracture behavior of the arc-shaped interface in a cylindrical non-homogeneous magnetoelectroelastic structure. Fracture analysis is performed by the method of Cauchy singular integral equation. Parametric studies are conducted on the stress intensity factor, and practical guidelines are given for the optimization of fracture performance. (a) The ratio between the outer and inner radii should be at least 1.1. (b) A softer inner side plus a stiffer outer side is a good non-homogeneity design for the magnetoelectroelastic layer. (c) A soft central cylinder and a stiff outer magnetoelectroelastic layer constitute a good stiffness matching on the interface.

Fracture analysis is performed for the arc-shaped interface in a layered cylindrical piezoelectric sensor polarized along its axis. Parametric studies on the numerical results of the singular integral equation yield three guidelines for optimal designs of cylindrical piezoelectric sensors made for axial shear testing. (a) The optimal value of the radius ratio is from 1.1 to 1.5. (b) A stiff piezoelectric layer plus a soft central cylindrical substrate can generate good strength matching on the interface. (c) An unelectroded rather than electroded outer surface is beneficial to reducing the stress intensity factor of the interface crack.

In fracture analysis of piezoelectric devices, the structural dimension is often assumed to be infinite at least in one direction. However, all practical piezoelectric structures are finite and their dimensions in different directions are often comparable and cannot be simplified as infinite. The assumption of infinite dimension may lead to inexact theoretical results. The present work aims at studying the interfacial fracture behavior of a functionally graded piezoelectric layer on a dielectric substrate with finite dimension. The crack problem is solved by the methods of Fourier series and Cauchy singular integral equation. Parametric studies on the stress intensity factor (SIF) reveal the following: (a) when a crack tip is near to an interface end, its SIF is mainly governed by the end effect; (b) when a crack is far from the interface ends and the piezoelectric layer is thin, its SIF is principally affected by the thickness of the piezoelectric layer, and (c) only when a crack is far from the interface ends and meanwhile the piezoelectric layer is thick will its SIF be dominated by the non-homogeneity parameter, and in this case, the SIF increases with the increasing non-homogeneity parameter.

The mechanical model is established for a piezoelectric sensor with a mode III permeable crack parallel to the imperfect interface. Fracture analysis is performed by the standard methods of Fourier transform and singular integral equation. Three conclusions are drawn: (a) the imperfect interface has a shielding effect on the crack parallel and very near to it; (b) the shielding effect depends on the structural stiffness and the distance between the crack and interface; (c) for the electrically permeable crack, mechanical imperfection has more remarkable shielding effect than dielectric imperfection does.

The purpose of the present work is to study the effect of an imperfect interface on the fracture behavior of a layered piezoelectric sensor. For mathematical convenience, the problem is investigated under mode III-a simple case in fracture mechanics. Fracture analysis is performed by the methods of Fourier integral transform and Cauchy singular integral equation. Parametric studies on the numerical results of energy release rate reveal the crack tip shielding and anti-shielding effects of the imperfect interface. When the inclined angle of crack is less than 0.1 π , the imperfect interface may shield the crack, however, when it is larger than 0.2 π , the crack may be anti-shielded. If the distance between a crack tip and the imperfect interface is less than two times of the crack length, the shielding or anti-shielding effect is remarkable, and otherwise it is negligible. Finally, the crack tip shielding and anti-shielding effects of the mechanical imperfection are generally more remarkable than those of the dielectric imperfection.

To prospectively evaluate the long-term clinical safety and efficacy of a newly designed self-expanding metallic stent (SEMS) in the treatment of patients with achalasia. Seventy-five patients with achalasia were treated with a temporary SEMS with a 30-mm diameter. The SEMSs were placed under fluoroscopic guidance and removed by gastroscopy 4–5 days after stent placement. Follow-up data focused on dysphagia score, technique and clinical success, clinical remissions and failures, and complications and was performed at 6 months, 1 year, and within 3 to 5 years, 5 to 8 years, 8 to 10 years, and >10 years postoperatively. Stent placement was technically successful in all patients. Complications included stent migration (n = 4, 5.33%), chest pain (n = 28, 38.7%), reflux (n = 15, 20%), and bleeding (n = 9, 12%). No perforation or 30-day mortality occurred. Clinical success was achieved in all patients 1 month after stent removal. The overall remission rates at 6 months, 1, 1–3, 3–5, 5–8, 8–10, and >10 year follow-up periods were 100%, 96%, 93.9%, 90.9%, 100%, 100%, and 83.3%, respectively. Stent treatment failed in six patients, and the overall remission rate in our series was 92%. The median and mean primary patencies were 2.8 ± 0.28 years (95% CI: 2.25–3.35) and 4.28 ± 0.40 years (95% CI: 3.51–5.05), respectively. The use of temporary SEMSs with 30-mm diameter proved to be a safe and effective approach for managing achalasia with a long-term satisfactory clinical remission rate.

A new mechanical model is established for a non-homogeneous weldment with HAZs and fusion zones treated as functionally graded materials. The interface-perpendicular anti-plane fracture problems are analyzed for the HAZ and the weld metal, respectively, by the methods of Fourier integral transform and Cauchy singular integral equation. Lobatto–Chebyshev collocation method put forth by Erdogan and Gupta is employed to obtain numerical results of stress intensity factor (SIF). Parametric studies yield three conclusions: (1) overmatching is more beneficial than undermatching to the reduction of the SIF of a HAZ crack, however, the latter is more effective than the former in reducing the SIF of a weld-metal crack; (2) the optimum value of mismatch factor is 1.0, and values too greater or too smaller than this should be avoided in engineering design; (3) when the mismatch factor is unequal to 1.0, the SIF could be reduced by increasing the absolute value of the non-homogeneity parameters of HAZs.

The mechanical model is established for the dynamic fracture problem of a layered graded magnetoelectroelastic sensor subjected to harmonic waves. Fourier integral transform is employed to derive the system of Cauchy singular integral equations, numerical solutions of which are obtained by the Lobatto–Chebyshev collocation method put forth by Erdogan and Gupta. The energy release rate (ERR) is chosen as the fracture parameter. Parametric studies on ERRs yield some guidelines for engineering applications: (1) to avoid the peak value of ERR, the wave number of applied loading should be as large as possible; (2) smaller values for non-homogeneity parameters and larger thickness for the sensitive coating can be chosen to enhance the anti-fracture ability of the sensor; (3) cracks in the lower-half region of the guiding layer are more dangerous than those in the upper half, and the monitoring for the former should be specially strengthened.

The mechanical model was established for the anti-plane fracture problem of a functionally graded coating–substrate system with a coating crack inclined to the weak/micro-discontinuous interface. The Cauchy singular integral equation for the crack was derived using Fourier integral transform, and the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta was used to get its numerical solution. Finally, the effects of the weak/micro-discontinuity of the interface on SIFs were analyzed, the “affected regions” corresponding to the two crack tips have been obtained and their engineering significance was discussed. It was indicated that, for the crack tip in the corresponding “affected region”, to reduce the weak-discontinuity of the interface and to make the interface micro-discontinuous are the two effective ways to reduce the SIF, and the latter way always has more remarkable SIF-reduction effect. For the crack tip outside the “affected region”, its SIF is mainly influenced by material stiffness, and to prevent such a tip from growing toward the interface “softer coating and stiffer substrate” is a more advantageous combination than “stiffer coating and softer substrate”.

The mechanical model was established for the anti-plane interfacial fracture problem of a symmetrically bonded smart structure with linearly non-homogeneous magnetoelectroelastic properties. The system of Cauchy singular integral equations for the interfacial crack was derived by Fourier integral transform. The numerical solutions of the Cauchy singular integral equations were obtained by the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta. The mechanical strain energy release rate and the total energy release rate were chosen as fracture parameters to discuss the effect of the non-homogeneity parameter on the extension force of the crack. A conclusion was drawn that, to reduce the weak-discontinuity of the interface in the magnetoelectroelastic structure would be beneficial to decrease the extension force of the interfacial crack. Based on this conclusion, a new improved design was suggested for the symmetrically bonded linearly non-homogeneous magnetoelectroelastic composite. The enhancement of the capability of the improved structure to resist interfacial fracture was validated by comparison between the improved and unimproved structures for their fracture responses.

An elastic-viscoplastic mechanics model is used to investigate asymptotically the mode Ⅲ dynamically propagating crack tip field in elastic-viscoplastic materials. The stress and strain fields at the crack tip possess the same power-law singularity under a linear-hardening condition. The singularity exponent is uniquely determined by the viscosity coefficient of the material. Numerical results indicate that the motion parameter of the crack propagating speed has little effect on the zone structure at the crack tip. The hardening coefficient dominates the structure of the crack-tip field. However, the secondary plastic zone has little influence on the field. The viscosity of the material dominates the strength of stress and strain fields at the crack tip while it does have certain influence on the crack-tip field structure. The dynamic crack-tip field degenerates into the relevant quasi-static solution when the crack moving speed is zero. The corresponding perfectly-plastic solution is recovered from the linear-hardening solution when the hardening coefficient becomes zero.

A mechanical model was established for the antiplane dynamic fracture problem of a functionally graded coating–substrate structure with a coating crack perpendicular to the weak-discontinuous interface. The problem was reduced to a Cauchy singular integral equation by the methods of Laplace and Fourier integral transforms. Erdogan’s collocation method and the Laplace numerical inversion proposed by Miller and Guy were used to calculate the dynamic stress intensity factors. Three conclusions were drawn through parametric studies: (a) unlike the conclusion drawn for an interfacial crack, reducing the weak discontinuity of the interface will not necessarily decrease the dynamic stress intensity factor (DSIF) of the coating crack perpendicular to the interface; (b) increasing the stiffness of the substrate when that of the coating is fixed, or decreasing the stiffness of coating when that of the substrate is fixed, will be beneficial for the reduction of the DSIF of a coating crack perpendicular to the interface; and (c) the free surface has a greater influence on the DSIF than the interface does, and the effect of the interface on the DSIF is greater than that of the material stiffness in the crack-tip region.

The main idea of this paper is to study the effects of the transitional gradient of material property at interface on the mechanical behavior of a bi-interface structure with a sandwiched non-homogeneous interlayer. Four different types of transitional functions of material property are put forward and their influences are analyzed by the finite element method. It is indicated that, to diminish the value of the gradient of Young’s modulus at interface is beneficial to decreasing the stress concentration at interface. Under the mode-I loading, among all the mode-I and mode-II stress intensity factors at both interfaces, the dominant one is always the mode-I stress intensity factor at the more rigid interface. With the gradient of Young’s modulus at interface decreasing, the SIFs corresponding to the two different interfaces vary inversely, however, the dominant stress intensity factor decreases. To reduce the gradient of material property at interfaces, i.e., to reduce the weak-discontinuity of interfaces, will be beneficial to enhancing the ability of bi-interface structure against fracture.

The anti-plane impact fracture analysis was performed for a weak-discontinuous interface in a symmetrical functionally gradient composite strip. A new bi-parameter exponential function was introduced to simulate the continuous variation of material properties. Using Laplace and Fourier integral transforms, we reduced the problem to a dual integral equation and obtained asymptotic analytical solution of crack-tip stress field. Based on the numerical solution of the second kind of Fredholm integral equation transformed from the dual integral equation, the effects of the two non-homogeneity parameters on DSIF were discussed. It was indicated that the relative stiffness of the interface and the general stiffness of the whole structure are two important factors affecting the impact fracture behavior of the weak-discontinuous interface. The greater the relative stiffness of the interface is, the higher the value of the dynamic stress intensity factor will be. The greater the general stiffness of the whole structure is, the shorter the time for DSIF to arrive at the peak value and then to stabilize to the steady one. If the general stiffness of the whole structure is great enough, there will be an oscillation between the peak and steady values of DSIF.

Purpose The purpose of this study was to evaluate the initial clinical efficacy of a retrieval stent filter for the management of Budd Chiari syndrome complicated with inferior vena cava thrombosis. Description The retrieval stent filter consists of two parts (ie, the filter and the Z-stent). The filter was composed of seven legs arranged in the shape of a cone with a retrieval hook at its apex. The filter and the Z-stent were connected with each other, and the retrieval of the stent filter was performed with an Amplatz gooseneck snare (MicroVena [White Bear Lake, MN]). Eight consecutive patients were treated with the stent filters. Evaluation The stent filter placement was technically successful in all patients. Inferior vena cavography demonstrated that all of the inferior vena cavae were patent without incidental pulmonary embolism after deploying the stent filter. A 3∼11 months follow-up study showed that all of the stent filters were removed after approximately 5 to 24 days of placement. All patients were still alive with resolution of the symptoms. Conclusions The use of a retrieval stent filter proved to be expedient, safe, and effective in the treatment of Budd Chiari syndrome complicated with inferior vena cava thrombosis.