Elliptical Defect Research Articles

A new simple laparoscopic-extracorporeal technique for the repair of a Morgagni diaphragmatic hernia.

We used a new technique to treat a right-sided Morgagni hernia in a symptomatic adult with a transverse colon that was herniated in the chest. Three trocars were required. The herniated viscera were easily reduced in the abdomen, and the diaphragmatic border that was mobilized from the liver showed the elliptical diaphragmatic defect (9 x 5 cm); however, the hernial sac was not resected. Four transversal 1-cm cutaneous incisions were made just below the costal arch. Using a Reverdin needle holder, we introduced eight ligatures under laparoscopic control through the abdominal wall and through the free diaphragmatic border. Each suture was then held by the grasper and freed from the Reverdin. After the Reverdin was extracted and reintroduced more caudally, the intraabdominal suture was placed into it and finally extracted again. Before knotting, all the sutures were pulled together to achieve perfect closure of the defect. A suction drain was placed in the hernial sac. The duration of the procedure was 12 min. The patient was discharged on the 5th postoperative day. A review of 20 other patients treated via a video-assisted approach is also included here. We found this original technique to be extremely simple, rapid, and effective. It can also be performed by surgeons who are not specially trained in intracorporeal suturing and knotting and can probably also be used for the repair of other types of diaphragmatic defects. The use of laparoscopy and magnification allows the surgeon to achieve a better point of control for simpler solutions.

Electrode Potential on the Boundary of a Medium in an Elliptic Notch Made in a Stressed Conducting Body

We determine the dependences of the distribution of the electrode potential along the contour of a medium-filled elliptic defect in a stressed conducting body on the physical and chemical characteristics of the material and medium and the relations between the geometric parameters of the defect. We also indicate the points of separation of the anode and cathode zones on the contour of the defect.

Vascular surgical society of great britain and ireland: new technique of in situ autogenous venous valve construction using varicose vein and bench hydrostatic testing of its properties in vitro

BACKGROUND: Long-term results of valve transposition and autogenous valve grafts (from axillary and brachial vein) for chronic venous insufficiency due to post-thrombotic valve destruction are poor. Attempts at constructing in situ autogenous venous valves using varicose veins have been ongoing since 1953 but have been unsuccessful. A technique has been developed to create new autogenous in situ valve. METHODS: Varicose long saphenous veins were obtained following stripping during routine varicose vein surgery. A longitudinal elliptical segment of vein wall was excised from opposite sides; this effectively reduces the diameter of the vein. Polypropylene sutures were applied on each side, starting at the centre of the elliptical defect, and brought out proximally. After closing the elliptical defects, gentle traction was applied to the initial sutures and they were tied causing invagination of the vein wall. Both ends of the vein were connected to pressure transducers and a standard pressure monitoring device. Normal saline was pumped at various pressures through the valve-bearing segment while pressures were recorded simultaneously. RESULTS: Fourteen constructed valves were tested for their bench hydrostatic properties. Mean(s.d.) minimum opening pressure of the valves was 5. 3(2.4) mmHg. The valves were competent at a minimum pressure of 2. 7(0.6) mmHg. They sustained sudden pressures of up to 139.0(13.8) mmHg and remained competent at a maximum pressure of 260 mmHg. CONCLUSION: This technique produces a competent one-way valve capable of sustaining high back pressures, while allowing forward flow with minimal resistance.

Analysis of Anisotropic Piezoelectric Materials with Elliptical Cavity or Rigid Inclusion under In-Plane Loadings and Their Numerical Examples.

Piezoelectric materials are gradually used in industrial areas from the excellent charactaristics of the mechanical and electrical couplings such as the expectation to reduce stress concentrations by electrical controls. Contrary to this expectation, piezoelectric materials may have some tendencies to develop critical crack growth because of stress concentrations induced by both mechanical and electrical loads. Therefore, it is necessary to study the behavior of stresses and displacements at the vicinity of the stress concentrated region like a cavity or crack as well as a rigid inclusion. In this paper, a two-dimensional electroelastic analysis is performed on a anisotropic piezoelectric material containing elliptical defect under the cases of in-plane load at infinity. General solutions are provided in terms of complex functions, with emphasis being placed on stress concentrations. Several numerical examples are given for both mechanical and electrical loads.

A Simple Mathematical Formula for Custom-made Croissant Tissue Expanders

The popularity of croissant-type tissue expanders has increased steadily during the past 5 years. Croissant-shaped expansion offers the advantage of creating a tailored skin flap that is advanced easily into an elliptical skin defect without the formation of dog-ears or without the need for backcuts in the expanded flap. Because the majority of lesions can be considered elliptical in shape, surgical removal is performed easily with an adapted croissant expander. We present a simple mathematical formula for calculating the exact dimensions of the required croissant expander. A good clinical result was obtained using this formula to design large custom-made croissant tissue expanders in a patient with a giant nevus.

Simulation of the growth of near-surface defects

The growth of near-surface circular and elliptical defects is simulated by using an eigenstrain-based solution for the crack front stress intensity factor. From these results the crack growth rate at all points is inferred from Paris' law, and the crack front is advanced. The stress intensity factors are re-evaluated, and the new crack front shape implied by Paris' law found. This process, which allows the crack front shape to evolve freely, is repeated until final fracture occurs. The results are then compared with predictions of component life based on simplified “engineering” analysis, where the crack shape at each stage during its life is idealised as an ellipse (if buried) or a semi-ellipse (if surface-breaking).

Analyses of Piezoelectric Isotropic Materials with Elliptical Cavity, Rigid Boundary or Elastic Inclusion under Out-of-Plane Shear Loadings and their Numerical Examples.

Piezoelectric materials are widely used in industrial areas from the excellent results of the mechanical and electrical couplings such as the expectation to reduce stress concentrations by electrical controls. Contrary to this expectation, piezoelectric materials may have some tendencies to develop critical crack growth because of stress concentrations induced by both mechanical and electrical loads. Therefore, it is necessary to study the behavior of stresses and displacements at the vicinity of the stress concentrated region like a cavity or crack as well as elliptical inclusion. In this paper, a two-dimensional electroelastic analysis is performed on a isotropic piezoelectric material containing elliptical defect under the cases of out of plane shear loadings at infinity. General solutions are provided in terms of complex functions, with emphasis being placed on stress concentrations. Several numerical examples are given for both mechanical and electrical loads.

AN IMPROVED NUMERICAL TECHNIQUE FOR SIMULATING THE GROWTH OF PLANAR FATIGUE CRACKS

Abstract— This paper describes a versatile technique for simulating the fatigue growth of a wide range of planar cracks of practical significance. Crack growth is predicted on a step‐by‐step basis from the Paris law using stress intensity factors calculated by the finite element method. The crack front is defined by a cubic spline curve from a set of nodes. Both the 1/4‐node crack opening displacement and the three‐dimensional J‐integral (energy release rate) methods are used to calculate the stress intensity factors. Automatic remeshing of the finite element model to a new position which defines the new crack front enables the crack propagation to be followed. The accuracy and capability of this finite element simulation technique are demonstrated in this paper by the investigation of various problems of both theoretical and practical interest. These include the shape growth trend of an embedded initially penny‐shaped defect and an embedded initially elliptical defect in an infinite body, the growth of a semi‐elliptical surface crack in a finite thickness plate under tension and bending, the propagation of an internal crack in a round bar and the shape change of an external surface crack in a pressure vessel.

Improving defects search in structure by boundary element and genetic algorithm scan method

An inverse technique has been used to estimate the geometry for defects in elastic structures and the elastic properties of the structure from additional information such as experimental data of displacements, strain and velocity of the structure subjected to any mechanical loading or constraint. In the present paper, a newly developed inverse technique using a genetic algorithm (GA) is presented for identifying several circular and elliptical defects in a square plate subjected to a uni-directional load with various loading directions. In the present paper, the position, size and number of internal defects are unknown and are estimated by using displacement data at the outer surface of the plate. The influence of some parameters, mutation ratio and method, in GA upon the final results of inverse analysis is investigated. An inverse technique using GA leads to several candidates of solution for each loading direction owing to different sensitivities of deformation. A new method referred to as a GA scan method is presented to reconstruct defect image from solution candidates.

Stress intensity factors of embedded elliptical cracks and an assessment of the ASME XI defect recharacterisation criteria

This paper considers aspects related to the calculation of the stress intensity factors of planar embedded defects in a solid under tension. The determination of stress intensity factor solutions using a modified body force method is described, this technique having certain advantages over existing finite element, boundary element and ordinary body force methods. Furthermore, comprehensive modified body force solutions are presented and discussed for a range of elliptical defect geometries. These solutions have then been used to asses the conservation of the recharacterisation procedure for defects of complex geometry described in Section XI of the ASME Boiler and Pressure Vessel Code. Maximum stress intensity factor values calculated using both the modified body force method and the ASME XI rules in conjunction with standard solutions are compared and contrasted. The results of this analysis show that, by and large, ASME XI is conservative and hence safe. However, geometries for which ASME XI provides non-conservative estimates have been encountered and, in certain circumstances, this may be a cause for concern.

Development of subchondral cystic lesions after articular cartilage and subchondral bone damage in young horses.

The objective of this study was to determine if damage to the articular cartilage alone or articular cartilage plus subchondral bone of the distal medial femoral condyle of young, exercised horses resulted in the formation of subchondral cystic lesions. Twelve Quarter Horses (age 1-2 years), free of clinical and radiographic signs of osteochondrosis and lameness were used. In 6 horses (Group 1), a 15 times 1 mm linear full thickness defect in the articular cartilage was made arthroscopically on the weightbearing surface of the distal aspect of the medial femoral condyle. In the other 6 horses (Group 2), a 15 times 3 mm full thickness elliptical cartilage defect was made, followed by burring a 5 mm diameter, 4 mm deep hole into the subchondral bone. Three weeks after surgery, all horses were hand walked and trotted for 2 weeks and then exercised for 6 min daily, 5 days a week for the next 14 weeks on a treadmill. They were then turned onto a small paddock for 6 weeks (6 months total). The development of subchondral cystic lesions was determined using radiography. Bone activity in the femoral condyle was monitored with nuclear scintigraphy. All horses that developed subchondral cystic lesions radiographically were subjected to euthanasia for gross and histological examination of the lesions. No subchondral cystic lesions and no clinical abnormalities were detected in the horses in Group 1. Subchondral cystic lesions developed radiographically in 5 of 6 horses in (Group 2). Scintigraphic findings of horses with subchondral cystic lesions were inconsistent. Histological examination of lesions revealed variable quantities of fibrous connective tissue, fibrocartilage and bone, with evidence of bone remodelling adjacent to the subchondral cystic lesion. The results suggest that damage to articular cartilage plus subchondral bone, but not articular cartilage alone, of the distal medial femoral condyle may lead to the development of subchondral cystic lesions. These findings indicate that all subchondral cystic lesions in horses may not be osteochondrosis-type lesions and that trauma to weightbearing articular surfaces of young horses may be a predisposing factor.

Magnetic leakage field due to sub-surface defects in ferromagnetic specimens

This paper describes analytical expressions for the magnetic leakage field of two types of internal defects: two dimensional rectangular and elliptical defects as functions of the applied magnetic field strength, the defect size and the distance below the surface. In this study, the magnetic image effects from the spatial boundary and the defect boundary are taken into consideration. That is, the leakage field of rectangular-like defects or elliptically shaped defects ‘below the surface’ are derived by using the modified dipole model and image theory. The profiles and strengths of leakage fields calculated from the proposed analytical forms are presented under various conditions and compared with experimentally measured ones.

Unknown defect identification in elastic field by boundary element method with filtering procedure

A new solution procedure in solving inverse problems in computational mechanics is developed. The basis of the procedure is a new filtering algorithm instead of the well-known Kalman filtering algorithm for a stochastic dynamic system. The boundary element method in connection with the new filtering algorithm is applied to unknown defect identification problems in an elastic field. The effectiveness of the procedure is demonstrated on the inverse analyses of identification problems of a circular or an elliptic defect in a 2-D elastic field, and a sphere defect in a 3-D field.

A Surgical Technique for the Treatment of Central Corneal Perforations

Generally, corneal perforations of 2 mm in diameter or greater are treated using graft material for tectonic support. A surgical technique for the primary repair of such perforations without the use of any additional tissue is presented. This procedure is demonstrated by a case report. The technique involves creation of an elliptical defect out of a circular one, thus allowing for primary closure, with the addition of glue. A definitive penetrating keratoplasty was subsequently performed with several important modifications described herein. A water-tight closure was obtained with this technique for 1 month while the inflammation subsided. Preoperative visual acuity was light perception. One year postoperatively, it was count fingers at 8 feet with mild irregular astigmatism. This technique is useful for perforations which are central, larger than 2 mm in diameter, and when corneal or scleral material is not readily available for patch grafting.

Probing the interface fluctuations in semiconductor superlattices using a magneto-transport technique

We have analysed the vertical transport properties of a GaAs/AlAs short period superlattice as the crossed magnetic field is rotated in the plane of the layers. The rotation of the magnetic field has been used to probe the interface roughness along the different in-plane crystallographic directions. Two maxima separated by 180° in the current intensity have been observed when the magnetic field is rotated through 360°. We interpret our results in terms of anisotropic scattering from elliptical interface defects of which the great axis is along [11̄0] and the minor one along [110].

Transient thermal stress analysis of a near-edge elliptical defect in a semi-infinite plate subjected to a moving heat source

In this paper, the maximum transient thermal stresses on the boundary of a near-edge elliptical defect in a semi-infinite thin plate were determined by the digital photoelastic technique, when the plate edge experiences a moving heat source. The relationships between the maximum transient thermal stresses and the size and inclination of the elliptical defect, the minimum distance from the elliptical defect to the plate edge as well as the speed of the moving heat source were also studied. Finally, by using a statistical analysis package, the variations of the maximum transient thermal stresses were then correlated with the time, the minimum distance between the edge and the elliptical defect, temperature difference, and speed of the moving heat source.

Kalmanフィルタと境界要素法による構造要素に内在する未知空洞欠陥の形状同定解析

An approach in solving defect shape identification problems is proposed in this paper. This approach is developed with the boundary element method in conjunction with the Kalman filtering technique, especially the extended Kalman filtering technique. The boundary element approach is utilized by reason of easyness on lemeshing of the defect shape in identification process. Applicability and effectiveness of the proposed method are examined with numerical simulation of several identification examples on a circular or an elliptic defect in 2-D elastostatics.

Defects Search with Boundary Element Method by Applying Genetic Algorithm. Proposal of Optimization Technique and GA Scan Method.

Inverse analysis for an elastic structure is used to estimate the geometry or the shape for defects and the elastic properties of the structure from additional information such as experimental data of displacements, strain and velocity of the structure subjected to any mechanical loading or constraint. In the present paper, a newly developed inverse technique using genetic algorithm (GA) is presented for identifying several elliptical defects in a square plate subjected to a uni-directional load with various loading directions. The position, the size and the number of internal defects are estimated by using displacement data of the plate and GA. The influence of some parameters in GA upon the final results of inverse analysis is investigated and a new method for estimation of defects is presented.

Surface defects of GaAs epitaxial layers grown by low-pressure OMVPE

We have investigated the surface defects of GaAs epitaxial layers grown by low-pressure organometallic vapor phase epitaxy on GaAs substrates oriented (100)±0.5°, at growth temperatures of 630 to 650°C, at V/III ratios of 20 to 100, and at growth pressures of 0.1 to 76 Torr. We have observed the shapes and internal structures of the surface defects in detail by using scanning electron microscopy and transmission electron microscopy. Elliptic cone-shaped surface defects formed at lower growth pressure below 1 Torr are convex to the epilayer surface, like the so-called “hillocks” in chloride vapor phase epitaxy, and certainly have one dislocation near each of the centers. These results form strong evidence for the formation of the elliptic cone-shaped surface defects by spiral growth at the dislocations propagated from the substrates. Four corner-shaped surface defects generated at higher growth pressure above 1 Torr are concave to the epilayer surface, and they have usually one dislocation near each of the centers and sometimes stacking faults. Four corner-shaped surface defects seem to be formed by vapor etching at threading dislocations and/or stacking faults. The reason the shape of these surface defects changes with growth pressure is also discussed.

Kinetic instabilities during the propagation of a branch crack: effects of loading conditions and internal pressure

In order to understand the physical processes controlling the formation of various branch features stemming from pre-existing defects in rocks, this paper presents a model based on fracture mechanics concepts. We examine the consequences of the elastic stress field around an open oblique elliptical defect subjected to constant uniaxial or biaxial stress on the kinetics of the classical branch crack. Assuming that propagation does not fundamentally change the elastic stress field, the strain energy release rate, G, is computed for each branch crack length, L, by integrating the values of the principal stress acting perpendicular to the stress trajectory of the other principal stress, starting exactly from the point of maximum tensile stress at the edge of the elliptical defect. The propagation regime depends on the slope of the G( L) curve and on its position with respect to the equilibrium value G o and the critical value G c for which catastrophic rupture occurs. Without internal pressure, the unimodal curves predict three possible successive propagation regimes: (1) stable propagation with increasing velocity; (2) catastrophic propagation with velocity jump and associated acoustic emission; and (3) stable propagation with decreasing velocity. The catastrophic regime is limited to high load values. Experimentally, the triggering of the propagation can be very difficult to predict, as it depends on slight variations in the length of pre-existing microcracks stemming from the elliptical defect at the root of the branch crack path. With internal pressure, the stress field is modified so that the maximum tensile stress is present at some distance from the edge of the elliptical defect. This can result in a change in the shape of G( L) curves which indicates that two independent velocity jumps may occur: the first one is mainly linked to the local influence of the defect, the second (leading to a large extension) is due to the general influence of the internal pressure.