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Background and objective: To investigate the use of high-resolution magnetic resonance imaging (HR-MRI) to identify the characteristics of culprit plaques in intracranial arteries, and to evaluate the predictive value of the characteristics of culprit plaques combined with the modified Essen score for the recurrence risk of high-risk non-disabling ischemic cerebrovascular events (HR-NICE) patients. Methods: A retrospective analysis was conducted on 180 patients with HRNICE at the First Affiliated Hospital of Xinxiang Medical University, including 128 patients with no recurrence (non-recurrence group) and 52 patients with recurrence (recurrence group). A total of 65 patients with HR-NICE were collected from the Sixth Affiliated Hospital of Shanghai Jiaotong University as a validation group, and their modified Essen scores, high-resolution magnetic resonance vessel wall images, and clinical data were collected. The culprit plaques were analyzed using VesselExplorer2 software. Univariate and multivariate logistic regression analyses were used to identify independent risk factors for recurrence, and a nomogram was constructed using R software to evaluate the discrimination of the model. The area under the curve (AUC) of the receiver operating characteristic curve (ROC) was used to evaluate the model performance. Calibration curves and Decision Curve Analysis (DCA) were used to evaluate the model efficacy. Results: Intra-plaque hemorrhage (OR  =  3.592, 95% CI  =  1.474–9.104, p  =  0.006), homocysteine (OR  =  1.098, 95% CI  =  1.025–1.179, p  =  0.007), and normalized wall index (OR  =  1.114, 95% CI  =  1.027–1.222, p  =  0.015) were significantly higher in the recurrent stroke group than in the non-recurrent stroke group, and were independent risk factors for recurrent stroke. The performance of the nomogram model (AUC  =  0.830, 95% CI: 0.769–0.891; PR-AUC  =  0.628) was better than that of the modified Essen scoring model (AUC  =  0.660, 95% CI: 0.583–0.738) and the independent risk factor combination model (AUC  =  0.827, 95% CI: 0.765–0.889). The nomogram model still had good model performance in the validation group (AUC  =  0.785, 95% CI: 0.671–0.899), with a well-fitting calibration curve and a DCA curve indicating good net benefit efficacy for patients. Conclusion: High-resolution vessel wall imaging combined with a modified Essen score can effectively assess the recurrence risk of HR-NICE patients, and the nomogram model can provide a reference for identifying high-risk populations with good clinical application prospects. [ABSTRACT FROM AUTHOR]

Background: The role of complement component 1q (C1Q) related genes on human atherosclerotic plaques (HAP) is less known. Our aim is to establish C1Q associated hub genes using single-cell RNA sequencing (scRNA-seq) and bulk RNA analysis to diagnose and predict HAP patients more effectively and investigate the association between C1Q and HAP (ischemic stroke) using bidirectional Mendelian randomization (MR) analysis. Methods: HAP scRNA-seq and bulk-RNA data were download from the Gene Expression Omnibus (GEO) database. The C1Q-related hub genes was screened using the GBM, LASSO and XGBoost algorithms. We built machine learning models to diagnose and distinguish between types of atherosclerosis using generalized linear models and receiver operating characteristics (ROC) analyses. Further, we scored the HALLMARK_COMPLEMENT signaling pathway using ssGSEA and confirmed hub gene expression through qRTPCR in RAW264.7 macrophages and apoE-/- mice. Furthermore, the risk association between C1Q and HAP was assessed through bidirectional MR analysis, with C1Q as exposure and ischemic stroke (IS, large artery atherosclerosis) as outcomes. Inverse variance weighting (IVW) was used as the main method. Results: We utilized scRNA-seq dataset (GSE159677) to identify 24 cell clusters and 12 cell types, and revealed seven C1Q associated DEGs in both the scRNA-seq and GEO datasets. We then used GBM, LASSO and XGBoost to select C1QA and C1QC from the seven DEGs. Our findings indicated that both training and validation cohorts had satisfactory diagnostic accuracy for identifying patients with HPAs. Additionally, we confirmed SPI1 as a potential TF responsible for regulating the two hub genes in HAP. Our analysis further revealed that the HALLMARK_COMPLEMENT signaling pathway was correlated and activated with C1QA and C1QC. We confirmed high expression levels of C1QA, C1QC and SPI1 in ox-LDL-treated RAW264.7 macrophages and apoE-/- mice using qPCR. The results of MR indicated that there was a positive association between the genetic risk of C1Q and IS, as evidenced by an odds ratio (OR) of 1.118 (95%CI: 1.013–1.234, P = 0.027). Conclusion: The authors have effectively developed and validated a novel diagnostic signature comprising two genes for HAP, while MR analysis has provided evidence supporting a favorable association of C1Q on IS. [ABSTRACT FROM AUTHOR]

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. Themethods 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. [ABSTRACT FROM AUTHOR]

Background The ability to diagnose sidewall cerebral aneurysms (SCAs) on an angle measurement basis may be useful in clinical practice. A study was undertaken to evaluate the effect of an outflow angle (OA)-assisted approach. Methods MR angiography (MRA) images of 438 patients with suspected SCAs and other cerebrovascular diseases were separately evaluated using the subjective approach and the OA approach. The approaches were then exchanged for confirmation of unclear cases. An OA of ≥90° was considered to represent SCA positivity. The accuracy, sensitivity, and specificity of the OA-assisted approach were determined using patient-based, aneurysm-based, and size-based evaluations. Results Digital subtraction angiography (DSA) detected 301 SCAs in 267 patients and no SCAs in 171. An OA of ≥90° was observed for 271 aneurysms in 244 patients (true positives); the OA approach misinterpreted OA as <90° for 29 aneurysms in 29 patients (false negatives) and missed one aneurysm. The subjective approach detected 309 SCAs in 273 patients. This approach misdiagnosed 10 patients (false positives) and missed two aneurysms in two patients (false negatives). The OA-assisted approach detected 300 SCAs in 267 patients and no SCAs in 171, overlooking one aneurysm. Patient-based evaluation yielded high accuracy, sensitivity, specificity, and positive and negative predictive values for the OA-assisted approach. Conclusions The OA-assisted approach for SCA diagnosis effectively reduced the false-positive rate obtained with the subjective approach with high accuracy, sensitivity, and specificity, suggesting that MRA based on this approach can be a reliable alternative to DSA in SCA screening and diagnosis. [ABSTRACT FROM AUTHOR]

Objective To evaluate whether the aneurysm outflow angle (OA) at MR angiography (MRA) might serve as discriminant for accurate diagnosis of, and differentiation between, small sidewall cerebral aneurysms (SCAs) and infundibula. Methods Between June 2007 and July 2015, 426 consecutive patients with SCAs completed both an MRA and DSA examination. Of these, 156 patients with small SCAs and 52 patients with infundibula were included in this study. A patient with an OA ≥90° was defined as having a SCA, while those with OA <90° were defined as having an infundibulum. Results DSA identified 172 SCAs in 156 patients and 55 infundibula in 52 patients. The average OA on MRA was 102.96°±13.36° (range 60°-151°) in 172 SCAs of 156 patients. An OA of ≥90° was seen for 159 (92.4%) small SCAs in 147 patients, while an OA of <90° was observed for 13 SCAs. The average OA on MRA was 69.05°±14.26° (range 35-107°) in 55 infundibula of 52 patients. An OA of ≥90° was seen in one patient with one infundibulum; while an OA of <90° was observed for 54 infundibula (98.2%) in 51 patients. The average OA in SCAs (n=172) was greater than the average OA in infundibula (n=55; 102.96° vs 69.05°, p<0.001). Conclusions The OA at MRA could serve as discriminant for accurate diagnosis of, and differentiation between, small SCAs and infundibula. [ABSTRACT FROM AUTHOR]

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 14 G 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 6 months and every subsequent 6 months. 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 6 months, 1 year and >1 year 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. [ABSTRACT FROM AUTHOR]

Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain method and the particle tracing method, such an algorithm is self-consistent and accurate since the interaction between electromagnetic fields and particles is properly modeled. In the time domain aspect, the generation of multipactor can be easily visualized, which makes it possible to gain a deeper insight into the physical mechanism of this effect. In addition to the classic secondary electron emission model, the measured practical secondary electron yield is used, which increases the accuracy of the algorithm. In order to validate the method, the impedance transformer and ridge waveguide filter are studied. By analyzing the evolution of the secondaries obtained by our method, multipactor thresholds of these components are estimated, which show good agreement with the experimental results. Furthermore, the most sensitive positions where multipactor occurs are determined from the phase focusing phenomenon, which is very meaningful for multipactor analysis and design. [ABSTRACT FROM AUTHOR]

ABSTRACT AIM The azygous anterior cerebral artery (Az) is a rarely observed anomaly of the anterior cerebral artery, and its associated aneurysm is even rarer. Our aim was to evaluate 3-dimensional time-of-flight magnetic resonance angiography (3-D-TOF MRA) in the diagnosis of Az and associated aneurysms. MATERIALS AND METHODS Three thousand five hundred seventy-two consecutive patients underwent 3-D-TOF MRA at 3.0 T. Postprocessing techniques, including volume rendering (VR) and single artery highlighting, were performed by a 3-D specialist. All MRA data and clinical information were recorded and stored in a database for further analysis. RESULTS Fourteen patients (.39%) were identified as having an Az. Among these cases, 3 males (21.43%) had an aneurysm located at the distal bifurcation of the Az, with a mean size of 9.43 ± 3.33 mm. In MRA, the common trunk of the Az was slightly larger in diameter than the A1 segment (2.62 ± .35 mm vs. 2.54 ± .35 mm; P = .008). CONCLUSIONS With the VR technique, 3-D-TOF MRA is feasible and valuable in detecting an Az and associated aneurysm. Our MRA-based study has proved that the Az is a rare anomaly but has a relatively high incidence of associated aneurysms. [ABSTRACT FROM AUTHOR]

Background: The reported prevalence of unruptured cerebral aneurysms (UCAs) varies widely. Objective: To measure the prevalence of UCAs by using 3-dimensional time-of-flight magnetic resonance angiography in adults aged 35 to 75 years. Design: Cross-sectional study done between June 2007 and June 2011. Setting: Two communities chosen at random from 2 districts (1 urban and 1 suburban) in Shanghai, China. Participants: 4813 adults aged 35 to 75 years. Measurements: Three-dimensional time-of-flight magnetic resonance angiography, interpreted by 3 observers blinded to the participants' information, was used to identify the location and size of UCAs and to estimate the overall, age-specific, and sex-specific prevalence. Results: 369 UCAs were found in 336 participants (130 men and 206 women); 4477 participants had no evidence of UCAs. The prevalence was 7.0% overall (95% CI, 6.3% to 7.7%), with 5.5% for men (CI, 4.6% to 6.4%) and 8.4% for women (CI, 7.3% to 9.5%). The overall prevalence of UCAs was higher in women than in men (P < 0.001) and peaked at ages 55 to 64 years in men and women. The UCAs were mostly located in the internal carotid artery (81%), and 90.2% had a maximum diameter less than 5 mm. Mean diameter was larger in women than in men (3.7 mm vs. 3.2 mm; P < 0.009). Limitation: Participants were from 2 communities selected from 2 districts in Shanghai, and adults older than 75 years were not studied. Conclusion: The overall prevalence of UCAs was 7.0% in Chinese adults aged 35 to 75 years, and most lesions had a diameter less than 5 mm. Primary Funding Source: National Natural Science Foundation of China. [ABSTRACT FROM AUTHOR]

With the development of bionic engineering, research into bionic robots has become a popular topic. In this field, the design of robotic mechanisms to realize the locomotion of insects forms a significant research branch. The current paper presents a caterpillar robotic mechanism that is composed of our newly-developed self-assembly modular robots (Sambot). A trapezoidal wave locomotion gait is planned for the caterpillar mechanism and the kinematics equations are established and solved analytically for such locomotion. The variations of the kinematics quantities are illustrated and discussed. The variation of the jump of the angular acceleration indicates that it is better to apply the trapezoidal wave gait to low velocity situations. Finally, the obtained data of the kinematics quantities is used to perform the gait control locomotion experiment and the errors of the experimental data are analysed in depth. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the use of a biodegradable nanofiber-covered stent (BDNCS) in the treatment of a canine carotid artery aneurysm. Materials and Methods: Seventeen beagle dogs, each with one lateral saccular aneurysm created using a venous pouch, were selected to test the BDNCS. The BDNCS consists of three parts: A bare stent, a biodegradable nanofiber membrane, and a balloon catheter . The bare stent was sculpted by a laser from a cobalt chromium superalloy, and the biodegradable nanofiber membrane was constructed from polylactic acid (PLA) and polycaprolactone [PCL, P (LLA-CL)] by the electro-spinning method. The biodegradable nanofiber stent was premounted on a balloon catheter to form a BDNCS. Angiographic assessments were categorized as complete or incomplete occlusion. Data regarding technical success, initial and final angiographic results, mortality and morbidity were collected, and follow-up was performed at 1 and 3 months after the procedure. Results: BDNCS placement was successful in 17 canines with 17 aneurysms. The initial angiographies showed that a complete occlusion was achieved in 13 canines (76.5%) and an incomplete occlusion in 4 (23.5%). One canine died 1 week later . The angiographies obtained at 3-month follow-up exhibited complete occlusion in 14 canines (87.5%) and an incomplete occlusion in 2 canines, with mild in-stent stenosis in 5 canines. Conclusions: Our results suggest that BDNCS may be a feasible approach for aneurysm occlusion, although the occurrence of mild in-stent stenosis was relatively high. Longer-term follow-up investigations are needed to validate these findings. [ABSTRACT FROM AUTHOR]

Aims: To evaluate the feasibility of using the Willis covered stent in the management of patients with traumatic carotid-cavernous fistulas (CCFs). Materials and Methods: Twelve consecutive patients with 14 post-traumatic CCFs referred for treatment with Willis covered stents were enrolled in this prospective study. Data on technical success, initial and final angiographic results, mortality, morbidity and final clinical outcome were collected. Follow-u p was at one, three, six, and 12 months, and yearly thereafter. Results: Deployment of covered stents was technically successful in all the patients without complications. One covered stent was placed in eight patients and two covered stents in four. Angiographic results following stent placement showed a complete occlusion in nine patients with 11 CCFs, and an incomplete occlusion in three patients. Angiographic follow-up (mean, 14.00 ± 6.93 months; range, 6-24 months) revealed complete occlusion and no obvious in-stent stenosis in all the patients. Clinical follow-up (mean, 17.75 ± 7.05 months; range, 7-28 months) demonstrated full recovery in 11 patients, and improvement in one. Conclusion: This initial experience indicates that the use of the Willis covered stent is a feasible procedure and may be an alternative treatment option for CCFs. [ABSTRACT FROM AUTHOR]

Background and Purpose: The aim of this study was to evaluate the anatomical changes and investigate the prevalence in intracranial aneurysm with fenestrations using magnetic resonance angiography (MRA). Materials and Methods: Between June 2008 and October 2010, 4652 patients (aged 23-73 years) with suspected intracranial aneurysm or other cerebrovascular diseases underwent MRA examination. MRA was performed using a threedimensional time-of-flight technique (3D-TOF) with volume rendering (VR) and maximum intensity projection reconstruction methods. The presence and location of fenestrations and aneurysms was reviewed. When fenestrations were present in combination with aneurysms, we noted the relationship of the locations. The classification of fenestration accompanied by intracranial aneurysm was divided into three types according to the anatomical relationship as follows: Type I, aneurysm adjacent to but not on a fenestration; Type II, aneurysm located on the fenestration; type III, aneurysm located at a position remote from a fenestration. Results: Among the 4652 patients examined, 409 patients were defined with 412 intracranial aneurysms, and the prevalence of aneurysms was 8.8%. One hundred and forty-one patients were identified with fenestrations; 24 of these patients were confirmed with intracranial aneurysms. Seven cases were classified as type I, three as type II and 14 as type III. The prevalence of intracranial aneurysm with fenestrations was 17.0%, with significant statistical difference compared with aneurysms unaccompanied with fenestrations (P=0.0064). Conclusion: The anatomical relationship between fenestrations and intracranial aneurysms was visualized by MRA with VR, which displayed pathologies with sufficient clarity to enable diagnosis. Furthermore, the results of this study suggest that physicians should be alerted to the occurrence of intracranial aneurysm following the detection of fenestrations by MRA. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to study collinear unequal crack series in magnetoelectroelastic materials, which are of more practical significance than the widely studied collinear equal cracks. Fracture analysis is performed by the combined methods of distributed generalized dislocations, Green's function and singular integral equations (SIEs). The theoretical derivation is validated by the degeneration of SIEs in special cases. Parametric studies on the numerical results of mechanical strain energy release rate (MSERR) yield the following conclusions. (a) As two unequal cracks approach each other, interference occurs in crack tip fields, resulting in an obvious increase of MSERR. The ratio between the crack space and the length of the shorter crack is a main factor affecting the interference. (b) Negative or positive electric loading may shield or enhance crack growth, respectively. In the case of positive magnetic permeability, the effect of magnetic loading is analogous to that of electric loading; however, if magnetic permeability is negative, the result is completely opposite. (c) Positive values of magnetic permeability are found to be more reasonable than the negative values. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to evaluate the feasibility, safety and efficacy of endovascular treatment of large or giant intracranial aneurysms with the Willis covered stent. Methods: Nineteen patients, each with a large or giant intracranial aneurysm, were treated with the Willis covered stent. Of these 19 aneurysms, 6 were giant and 13 were large; 18 were located in the cranial internal carotid artery and 1 in the vertebral artery. Results of the procedure, technical events and complications were recorded. Clinical and imaging follow-ups were performed at 3 and 6-12 months after the procedure. Results: Placement of Willis covered stent was successful in all patients. Complete aneurysm exclusion was achieved in 13 of the 19 aneurysms immediately after the procedure. No mortality or morbidity developed during the treatment or the follow-up period. During the follow-up period, complete aneurysm exclusion was achieved in 18 of the 19 patients; 11 aneurysms were totally involuted, 3 decreased to 25% of the original diameter, 4 decreased to 50% and 1 remained unchanged. Nine patients experienced full recovery, 9 improved and 1 was unchanged. No obvious in-stent stenosis was noted. Conclusions: Endovascular treatment of large or giant intracranial aneurysm with the Willis covered stent is feasible, safe and efficacious in selected cases. Endoleak is a frequent issue after initial covered stent placement, but can be eliminated or dramatically reduced to minimal endoleak by additional covered stent placement and/or balloon reinflation. Minor endoleak is likely to spontaneously resolve over time. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Purpose: Whether an infundibular dilation (ID) is an anatomical variant or a pre-aneurysm has not been clearly determined. The aim of the present study was to evaluate the anatomical change of IDs by use of three-dimensional rotational angiography (3DRA) with volume rendering (VR). Methods: One-hundred thirty-eight patients with known or suspected aneurysms, treated consecutively, underwent both two-dimensional digital subtraction angiography (2DDSA) and 3DRA with VR. Two readers evaluated the IDs or aneurysms blindly, using 2DDSA and 3DRA, according to the same diagnostic criteria. A 5-point scale of observer confidence was used to determine the presence of IDs or aneurysms. For 3DRA with VR, the relationship between IDs and aneurysms was classified as one of the three types: type I, protrusion or bulge from side wall of IDs; type II, aneurysms involving or enclosing IDs; or type III, aneurysms and IDs coexisting near each other but with some distance between them. Results: The number of IDs found by 2DDSA and 3DRA with VR was 41 and 48, respectively. Five anterior choroidal arteries and two posterior communicating arteries IDs were missed by 2DDSA. According to 3DRA with VR, there were five IDs of type I, nine of type II, and 22 of type III. Conclusions: The 3DRA with VR appears superior to 2DRA for both diagnosing IDs and displaying the anatomical relationship between IDs and aneurysms. The findings also suggest that some IDs might progress to aneurysms or become a part of them, which should be carefully evaluated prior to operation. [ABSTRACT FROM AUTHOR]

The effect of surface/interface stress on mechanical behaviors may become remarkable when the characteristic size of a structure decreases to nanoscale. Various problems have been analyzed to reveal the size-dependent mechanical behaviors of nano structures with curved surfaces/interfaces. In this work, the problem of planar surfaces/interfaces is addressed. The generalized Young-Laplace equation is presented for a planar interface and the propagation behavior of Love wave in a nanocoating is discussed. Parametric studies indicate that if the surface effect of the nanocoating is considered the phase velocity of Love wave shows notable size-dependency on both the nanocoating thickness and the wavelength. When these two sizes are both in nanoscale, the phase velocity further depends on the relative size between them. In addition, increasing the residual surface stress may reduce the phase velocity of Love wave. [ABSTRACT FROM AUTHOR]

Aims: The advent of three-dimensional (3D) rotational angiography (3D DSA) challenged the role of digital subtraction angiography (DSA) as a "gold standard" in the diagnosis of intracranial aneurysms. In this study, we report our experiences in diagnosing intracranial aneurysms by using 3D DSA with volume rendering (VR) technique, particularly focusing on its role in depicting additional aneurysms missed by 2D DSA. Materials and Methods: One hundred and thirty-eight consecutive patients with known or suspected aneurysms (54 men, 84 women; median age, 55 years; age range, 18-83 years) underwent both conventional DSA and 3D DSA with VR examination simultaneously. The images of 2D DSA or 3D DSA with VR were evaluated by two observers independently for the presence of aneurysms. Then additional aneurysms were decided and depicted. Results: 3D DSA with VR showed 146 aneurysms in 123 (89.1%) of 138 patients and no aneurysms in 15 patients. 2D DSA showed 115 aneurysms in 110 of 137 patients, with one aneurysm in 106 patients each, 2 in 3 patients each and 3 in 1 patient. After reaching a consensus, there were 31 additional aneurysms detected by 3D DSA with VR. 30 aneurysms were <3 mm in maximum diameter with 3 aneurysms ruptured. These additional aneurysms were located in internal carotid artery (ICA, n = 28, 90.32%), anterior cerebral artery (ACA, n = 3, 9.68%). No additional aneurysms were found in either middle cerebral artery (MCA) or vertebrobasilar and posterior cerebral artery (PCA) systems. Conclusions: 3D DSA, especially VR images, not only clearly reveals aneurysms and aneurysmal morphology, but also detects additional aneurysms missed by 2D DSA, especially small aneurysms less than 3 mm. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to study the problem of two collinear unequal cracks in a piezoelectric plane under mode I electromechanical loadings via a new approach. For the first time, real fundamental solutions are derived for in-plane piezoelectric governing equations. The cracks are simulated by continuously distributed generalized dislocations and Cauchy singular integral equations are established from the solution of a generalized point dislocation. Both the theorectical derivation and numerical computations are validated by the exact solution in a special case. Parametric studies are conducted to reveal the effects of crack space, crack length, electric loading and remanent electric displacement on energy release rate. It is found that negative electric displacement loading can decrease both the total energy release rate (TERR) and the mechanical strain energy release rate (MSERR), implying that it has a shielding effect on cracks definitely. Positive electric displacement loading can enhance MSERR, but meanwhile it can enhance or reduce TERR depending on the magnitude of the electric loading factor. The effect of a remanent electric displacement along the poling direction is equivalent to that of a positive electric field loading and should be considered in engineering design. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Monte Carlo collision (MCC) model is widely adopted to simulate discharge plasmas using the particle-in-cell (PIC) method; however, it has low efficiency in high-pressure plasmas because of the small time steps required due to the constraint of high collision frequency. To relax this time step constraint, a compensated Monte Carlo collision model (CMCC) is proposed which considers multiple collisions in a time step as a series of single collisions to compensate for the neglected collisions. The electron motion in a high-pressure He gas for various reduced electric fields E/N and the streamer formation process in a laser-triggered spark gap were simulated using the CMCC model. Simulation results showed that the CMCC model with long time step obtained reasonable electron velocity distribution, temperature, drift velocity, plasma density, and space-charge field. It was demonstrated that the CMCC model had high accuracy and high efficiency, particularly for PIC simulation in high-pressure plasmas. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract  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”. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Micropolar elasticity theory links together the macro mechanical behavior and the micro geometrical scales and makes it possible to study the macro and micro fracture of micro-structural materials by classical methods. The present work aims at comparing the effects of micropolarity on the fracture parameters of a micro-crack and a macro-crack. Through Fourier integral transform, the problem of a mode-I crack in an infinite micropolar plane is reduced as a system of Cauchy singular integral equations, which are further solved numerically by the Lobatto–Chebyshev collocation method. Parametric studies on the numerical solutions of the force stress and couple stress intensity factors indicate that: the fracture behavior of the micropolar material depends on not only micropolar parameters but also the loading; when the force traction is applied, the micropolar material with a micro-crack behaves more softly than classical elastic materials, but the micropolar material with a macro-crack behaves more stiffly than the classical case. It is concluded that the micropolarity is beneficial to reducing the driving force of a micro-crack, but it may also enhance the driving force of a macro-crack meanwhile. [ABSTRACT FROM AUTHOR]

Abstract  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. [ABSTRACT FROM AUTHOR]

Abstract  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. [ABSTRACT FROM AUTHOR]

Anti-plane fracture analysis is performed for a micropolar material. The crack problem is reduced as Cauchy singular integral equations by Fourier integral transform. Numerical solutions of the stress intensity factors are obtained by the Lobatto–Chebyshev collocation method. Parametric studies indicate that the fracture behavior of the micropolar material depends on the coupling factor and the internal length scale. Larger coupling factor and internal length scale lead to stronger micropolar effect. The micropolarity is beneficial to reducing the driving force of a micro-crack, however, it may also prompt the propagation of a macro-crack. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aim of this retrospective study was to evaluate the clinical efficacy and limitations of different endovascular modalities in the treatment of very large and giant intracranial aneurysms. A group of 20 patients with very large and giant intracranial aneurysms treated by endovascular approaches were retrospectively analyzed. Of the 20 patients, 9 had been treated by parent artery occlusion, 8 by coil embolization, and 3 with an intracranial covered stent. Two recurrent aneurysms initially treated with coil embolization were retreated with an intracranial covered stent. Patients were followed for 9–83 months after the procedure. Endovascular treatment was technically feasible in all 20 patients. One patient died 7 days after the procedure from rebleeding caused by incomplete aneurysmal occlusion. Immediate postprocedural angiograms showed that complete occlusion was achieved in 11 aneurysms, subtotal occlusion in 7, and incomplete occlusion in 2. The final angiographic results in the other 19 surviving patients confirmed complete occlusion of 15 aneurysms, subtotal occlusion in 3, and incomplete occlusion in 1. Clinical evaluations performed at the final follow-up visit showed an excellent outcome in 11 patients and a good outcome in 8. Endovascular treatment of giant intracranial aneurysms with coil embolization is often associated with a low complete occlusion rate and a high recanalization rate, and parent artery occlusion remains a practical option in selected patients. Based on our limited experience, the use of an intracranial covered stent appears to be a relatively simple and safe procedure for occluding very large and giant aneurysms while still maintaining the patency of the parent artery. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the preliminary clinical efficacy and retrievability of a covered, retrievable, metallic hinged stent in the treatment of bronchial stump fistula (BPF).Material and Methods: Between April 2003 and March 2005, eight patients with bronchial stump fistula after pneumonectomy or lobectomy were treated with two types of covered, retrievable, metallic hinged stents. Type A stent was placed in six patients and type B in two under fluoroscopic guidance. The stent was removed with a retrieval set when BPF was healed or complications occurred.Results: Stent placement in the bronchial tree was technically successful in all patients, without procedure‐related complications. Immediate closure of the BPF was achieved in all patients after the procedure. Stents were removed from all patients but one. Removal of the stents was difficult in two patients due to tissue hyperplasia. Patients were followed for 4–16 months. Placement of the stents remained stable in all patients except one due to severe cough. Permanent closure of BPF was achieved in seven (87.5%) of eight patients.Conclusion: Use of a covered, retrievable, expandable, metallic hinged stent is a simple, safe, and effective procedure for the closure of bronchial stump fistula. Retrieval of the stent seems feasible. [ABSTRACT FROM AUTHOR]

Vascular diseases like aneurysms, pseudoaneurysms and direct high-flow carotid-cavernous fistulas on the intracranial segment of the internal carotid artery are usually managed through transarterial embolization with detachable coils or balloons. Utility of covered stents has been reported with good results in the treatment of selective cases. But the current generation of covered stents for coronary use is rather stiff and difficult to navigate in tortuous vessels particularly in the intracranial vasculature. Herein, we report on the use and technical respects of balloon-expanded covered stents specially designed for intracranial vasculature in the treatment of two pseudoaneurysms secondary to the successful obliteration of direct CCFs on the intracranial segment of the internal carotid artery. This is the first report of covered stents specially developed for use in intracranial vasculature. [ABSTRACT FROM AUTHOR]

An elastic-viscoplastic constitutive model was adopted to analyze asymptotically the tip-field of moving crack in linear-hardening materials under plane strain condition. Under the assumption that the artificial viscosity coefficient was in inverse proportion to power law of the rate of effective plastic strain, it is obtained that stress and strain both possess power law singularity and the singularity exponent is uniquely determined by the power law exponent of the rate of effective plastic strain. Variations of zoning structure according to each material parameter were discussed by means of numerical computation for the tip-field of mode II dynamic propagating crack, which show that the structure of crack tip field is dominated by hardening coefficient rather than viscosity coefficient. The secondary plastic zone can be ignored for weak hardening materials while the secondary plastic zone and the secondary elastic zone both have important influence on crack tip field for strong hardening materials. The dynamic solution approaches to the corresponding quasi-static solution when the crack moving speed goes to zero, and further approaches to the HR (Hui-Riedel) solution when the hardening coefficient is equal to zero. [ABSTRACT FROM AUTHOR]

A mechanical model was established for mode II interfacial crack static growing along an elastic-elastic power law creeping bimaterial interface. For two kinds of boundary conditions on crack faces, traction free and frictional contact, asymptotic solutions of the stress and strain near tip-crack were given. Results derived indicate that the stress and strain have the same singularity, there is not the oscillatory singularity in the field; the creep power-hardening index n and the ratio of Young’s module notably influence the crack-tip field in region of elastic power law creeping material and n only influences distribution of stresses and strains in region of elastic material. When n is bigger, the creeping deformation is dominant and stress fields become steady, which does not change with n. Poisson’s ratio does not affect the distributing of the crack-tip field. [ABSTRACT FROM AUTHOR]

An expression for loss-front velocity of magnetically insulated ion flow in a vacuum transmission line is developed. It agrees well with the results from particle-in-cell simulations at high voltage. [ABSTRACT FROM AUTHOR]

The article presents a letter to the editor in response to the article "Prevalence of unruptured cerebral aneurysms in Chinese adults aged 35 to 75 years: a cross-sectional study" by M. H. Li and colleagues in 2013 issue and its response from the author.