Search

In the topology optimization analysis of continuum, the checkerboards, that is the fomation of regions of alternating solid and void elements ordered in a checkerboard-like fashion, often appear in the optimum solutions. In this paper, a nodeless hybrid element is proposed and this element is applied to the topology optimization analysis of continuum in order to solve the checkerboards problem. The proposed hybrid element is fomulated based on the idea of nodeless element proposed by Kawai et al. and the stress assumed element proposed by Sekiguchi and Kikuchi. The homogenization design method is used for the topology optimization analysis of continuum. Some examples of two-dimensional problems are shown to demonstrate the effectiveness of the proposed element in the topology optimization analysis of continuum.

Restoration of the ‘Force Method’ has been my dream since I began to study the Finite Element Method about 40 years ago. First of all, the Force Method was originally developed in structural frame analysis by the introduction of the concept of redundant forces. But it is only successful in analysis of simple frames. Furthermore in two- and three-dimensional problems concept of ‘redundancy’ loses its meaning, and consequently development of the Force Method should be made on a different point of view. In this paper revival of the traditional ‘Force Method’ is attempted based on the Hu-Washizu principle and using the stress function approach. Verification study is made solving the well-known in-plane bending problem of a cantilever rectangular plate due to vertical shearing force acting along the tip edge [1]. Copyright © 2000 John Wiley & Sons, Ltd.

Purpose To evaluate the usefulness of the fat suppression technique for magnetic resonance imaging of oral tongue cancer.

A unique case of desmoplastic ameloblastoma is reported from the clinical, radiographic, and histologic viewpoints. The patient was a 56-year-old man who complained of a painless swelling on the buccal aspect of the left mandible. Periapical and panoramic radiographs revealed a rounded, slightly radiolucent area with blurred osteosclerotic margins. Occlusal radiograph and computed tomography images disclosed buccal bone expansion outlined by thinned cortices. Computed tomography images exhibited an enhanced area in the anterior portion of the lesion. Interestingly, the coronal computed tomography images revealed a close relationship between the periodontal membrane of the left mandibular second premolar and the enhanced area. Biopsy specimens from the anterior portion of the lesion displayed typical histologic features of the desmoplastic variant of ameloblastoma. However, those from the posterior portion disclosed a large cystic formation. Oxytalan fibers were identified in the stromal tissue of the tumor, which suggested that the tumor arose from the epithelial rests of Malassez in the periodontal membrane of the related tooth. We also reviewed previously reported 41 cases. In 36 of 38 cases in which the location was specified, the tumor was found in the anterior to premolar region of the maxilla or mandible. A radiographic description was given in only 29 previous cases, 28 of which involved multilocular lesions. No cyst as large as the one in the present case was found among the previously reported desmoplastic ameloblastomas. Although the present case deviates from the usual desmoplastic variant of ameloblastoma in terms of locus, radiologic appearance, and cyst formation, it still meets the histologic criteria for this variant in both the stromal and epithelial components.

Objective. The aim of this study was to describe the radiographic patterns of cemento-osseous dysplasia. Study Design. Fifty-four patients affected with benign fibro-osseous jaw lesions that showed periapical radiopacities and /or radiolucencies in a focal or a multiplex form were studied. The clinical, radiographic, and histopathologic features of the patients with cemento-osseous dysplasia were retrospectively studied. Radiographic features of the cemento-osseous dysplasia lesions were classified according to the appearance of calcified bodies. Radiographic visibility of periodontal ligament spaces of related teeth was assessed. Results. Forty-nine (91%) of the 54 patients were women. The mean age of the total group was 50.8 years, and that of the male group was 64.6 years. The cemento-osseous dysplasia lesions could be classified into 6 types radiographically. Eighteen patients had at least 2 or more types of cemento-osseous dysplasia lesions. Of 147 related teeth, 142 had periodontal ligament spaces clearly visible. Six of 9 patients who had a total of 25 teeth with active hypercementosis showed concomitant occurrence of other types of cemento-osseous dysplasia lesions. Biopsy specimens showed various amounts of bonelike and cementumlike tissues. Conclusions. It is likely that cemento-osseous dysplasia consists of 3 variations of a single entity, all with the same unknown cause. In one variation, the entity originates from the periodontium; in another, it is of medullary bone origin; and in the third it results from the simultaneous involvement of both tissues.(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:107-14)

We report detailed clinical and imaging findings of two patients with recurrent maxillary ameloblastoma. In one patient the recurrent tumour presented at follow-up examination 5 years after the initial operation. The other patient had a far advanced recurrent tumour with maxillary destruction extending into the adjacent normal structures including the infratemporal fossa, infraorbital fissure, masticator space and the left ethmoid sinus. The findings on conventional radiography including panoramic, posteroanterior and Waters' projection, and the findings of computed tomography (CT) and magnetic resonance (MR) imaging were evaluated using the following three variables: artefact degradation, lesion detectability, and conspicuity. The results suggested that MR imaging was the best imaging method for visualization of the tumours, followed by contrast enhanced CT. These two cases show that maxillary ameloblastoma can be difficult to control when it extends to the adjacent normal structures after destroying the maxilla. MR imaging was essential to establish the exact extent of the advanced maxillary ameloblastoma.

The study aimed to find out the best time to undertake radiological follow-up examinations and remove fixation materials after fractures of the mandible through a retrospective study of radiographs. Serial radiographs of 325 fracture sites in 231 patients over a 10-year period were examined. Outcome was measured by radiographic features of healing at less than 2, 2-3, 3-4, and 4 or more months. Osteogenic change (osteogenesis and union) was the best radiographic criterion for evaluating follow-up radiographs. This change started to predominate 1-2 months after injury in patients less than 18 years of age (21/31, 68%) and 2-3 months after injury in older patients (21/25, 84%). Overall, union was noted in 98 of 115 patients (85%) 3 months or more after the fracture. We recommend follow-up radiographic examination to confirm clinical judgement during the fifth week after a mandibular fracture in patients less than 18 years of age, and the ninth week for older patients. The fixation materials should be removed during the fifth month after injury.

The findings of conventional radiography, computed tomography, and magnetic resonance imaging are reported for an odontogenic myxoma arising in the left anterior maxilla of a 50-year-old man. The magnetic resonance imaging characteristics of an intraosseous myxoma are described for the first time. The initial conventional radiographic examination disclosed a unilocular radiolucency with poorly delineated margins as typically seen in malignant tumors. Subsequently, acquired computed tomography scans displayed bony expansion and thinning of cortices on the labial aspect of the lesion. Magnetic resonance imaging revealed a well-defined, well-enhanced mass lesion with homogeneous signal intensity on every pulse sequence. The lesion showed intermediate signal intensity on the T1- and T2-weighted images. Magnetic resonance imaging of the present maxillary myxoma revealed a higher signal intensity on T1-weighted and a lower signal intensity on T2-weighted images than for previously reported myxomas of the soft tissues. This discrepancy might be related to the viscosity of the mucoid substance or the protein density of the tumor.

We present a case of mucus escape reaction in which we encountered difficulty in interpreting the images acquired by plain radiography, computed tomography, and magnetic resonance imaging. The 48-year-old male Japanese patient was referred for evaluation of a gradual swelling subjacent to the inferior border of the left mandible. At the early imaging examinations, magnetic resonance imaging provided information crucial to resolving the issue of whether the lesion consisted of a central malignant disease process or a malignant disease in the submandibular space or both of these two separate disease entities. Magnetic resonance imaging demonstrated no evidence of tumorous lesion, but rather showed a fluid-containing cavity that was also confirmed by the subsequent intrasurgical inspection. On further consideration of these imaging findings, we concluded that the entity was mucus escape reaction with simultaneous occurrence of an intraconnective tissue hemorrhage adjacent to the left submandibular gland, concomitant extensive bony defect of the left mandible and lingual cortical defect, and chronic sialoadenitis of the left submandibular gland.

Radiographic changes were observed in 45 patients who had undergone iliac bone grafting with either metal or wire fixation after resection of the mandible. Changes were generally not observed during the first month after surgery. Bony resorption was seen during the second or third month. Osteogenesis commenced at any stage, but was usually radiographically evident by 3 to 6 months. Union was not radiographically evident in most cases until more than 6 months had elapsed after surgery. For follow up, plain film radiographs 4 to 6 months after surgery are recommended in patients who receive bone grafts.

Panoramic radiographs of 1203 Japanese patients were examined to detect idiopathic radiopaque foci of dense bone. One hundred seventeen patients (9.7%) exhibited 134 such lesions. The majority (97%) of the opacities were found in the mandible, especially in the mandibular first premolar to second molar region (85.4%). The lesion was most prevalent in the first three decades of life.

The radiographic and clinical features of periostitis ossificans in 55 patients with mandibular osteomyelitis were studied. On the basis of whether the original mandibular contour was preserved or not, the lesions could be classified radiographically into two major types, each with two subtypes. Type 1 lesions were of shorter duration than Type II. Type 1-2 and Type II-1 periostitis ossificans were characteristically observed in patients under 25 years of age. Extraction of the lower third molar with pericoronitis was the most frequent cause of periostitis ossificans. An unerupted third molar tooth bud was found in close proximity to the area of periostitis ossificans in six patients. With adequate treatment there can be complete resolution of periostitis ossificans in Type I cases; however, when there has been loss of mandibular contour (Type II cases), mandibular deformity remains even when normal bony architecture has been restored.

The clinical and radiographic features of gigantic dense bone islands of the jaw were reviewed in 21 subjects to better determine the pathogenesis of this condition. Most of the islands were asymptomatic. They showed a striking predilection for occurrence in the premolar to molar region of the mandible. The greatest dimension of gigantic dense bone islands measured on panoramic radiographs ranged from 2.5 to 7.0 cm, and they were most commonly structureless radiopaque areas. None showed bony expansion buccolingually, nor did they displace adjacent teeth or bony anatomic structures. It is concluded that gigantic dense bone island is not a benign bone neoplasm and is perhaps merely a large counterpart of smaller dense bone islands or idiopathic osteosclerosis.

First of all, I was very much impressed by Dr. Kalos’ talk (Chap. 14). Indeed, the computer will change and reconstruct all fields of learning in the near future and play an important role in their development including both life sciences and social sciences.

The patient, a 14-year-old male, had noticed a painless swelling in his left cheek 7 months prior to visiting our university dental hospital, but ignored the symptoms until his visit. Conventional X-ray examination and CT scan revealed an expansive lesion with an a d m i x t u r e of r a d i o l u c e n c i e s a n d radiopacities in the region of the left mandibular molar to the ramus (Fig. 1). These radiopacities consisted of exuberant radiopaque bodies which varied in size from a few mm to a few cm, showing varying density. Biopsy specimens revealed that the stromal tissue consisted of a proliferation of cellular fibrous tissue throughout which islands of compact bone-like or cementumlike tissue were sparsely scattered. Areas of myxomatous degeneration were seen in the stromal tissue, where spherical calcifications were also visible surrounded by osteoblastic cells (Fig. 2). While these radiographic lea

The present patient, a healthy 48-yearold male, was referred to our university dental hospital for evaluation of a swelling of the left palatal region. The patient had noticed a swelling and a pulsing pain in the anterior region of the left palate two weeks before his first visit to our hospital. Ten days before this first visit, he had undergone the removal of cuspids of the left maxi l lary first molar and incision of the swelling. Intra-oral examination revealed a swelling, which fluctuated on palpation, of the left palate in the region of the left maxi l lary canine to the second premolar. The mucosal surface of the swelling appeared normal in color and texture. Percussion pain was noted in all erupted teeth of the maxilla. A panoramic radiograph revealed diffuse osteolyses in the region from the left maxillary canine to the left first molar on (Fig. 1, ar row heads). All teeth in the affected area, except the left maxi l lary molars, were free from carious lesions and periodontal diseases (Fig. 2). CT images revealed an extensive osteolysis perforating the cortical plate of the palatal in the region of the left maxi l lary canine (Fig. 3, arrow). These radiographic features are very similar to those of malignant lymphoma of the bone I~, which made it difficult to determine if the lesion was a benign reactive process or a malignant one or some interaction of the two. A purulent discharge was released upon incision of the swelling of the palatal aspect of the left maxi l lary canine. The patient 's prognosis has been uneventful for the past three years and the osteolytic areas caused by the osteomyelitis has been completely filled in with new bone trabeculae. In the present case, the extensive osteolysis of the lesion by itself may not be enough to d e t e r m i n e w h e t h e r it is osteomyelitis from malignant lymphoma. Periapical pathosis of the left maxi l lary first molar and fluctuation of the swelling suggested that the lesion migh t r a t he r be osteomyelitis than malignant lymphoma of the bone. However, the rar i ty of maxil lary osteomyelitis made it more difficult to determine w h e t h e r the p r e s e n t case is osteomyelitis or malignant lymphoma. In such cases as this, it is necessary to check for signs and/or causes of inflammatory conditions. Where no such conditions exist, a biopsy of the lesion should be taken.

This article describes a new approach to managing innovation by strategic organizational activation, and sets out the conditions necessary to realize such managerial innovation. There must be few levels in the hierarchy and sub-units must have substantial authority; and top management must provide strong leadership. Three case histories are cited, Asahi-Beer, Nissan and Matsushita Electric—to demonstrate the operation of the programmes.

Recently the finite element method for analysis of flow problems has been established and a number of important contributions are being reported every year all over the world.It is common practice to use the higher order shape functions for these finite element flow analysis. Use of the higher order shape functions, however, may present a serious problem on computing time and cost in practice and it is believed that this situation will be more critical in case of flow analysis than in case of nonlinear analysis of solid mechanics problems.In view of such a situation, use of the lower order shape functions will be proposed in the finite element analysis of flow problems in this paper. In this approach, the higher derivative of velocity components, for example, will be approximated by the finite difference expression of the lower order derivatives. Therefore, it is expected that computing time for matrix manipulation will be considerably reduced. So far, application of this method has been made to analysis of KdV equation in the shallow water wave, steady creep flow and the potential flow problems. Results of these analysis have duly proved validity of this method. In this paper application will be attempted to analysis of the Navier-Stokes equation and discussion will be presented in comparison with existing finite element method.

Rock mass usually have cracks and joints, and can be considered anisotropic. Many numerical and experimental studies have been made on the mechanical properties. However the method of numerical analysis which can fully express the behaviour of such anisotropic rock mass with such discontinuities has not yet been developed. Recently the necessity of large scale excurvations and consequently establishment of an effective method of analysis is considered urgent to clarify the mechanical properties of jointed and cracked rock media.This paper is based on the “rigid body spring models” proposed by Kawai, in which the elements themselves are assumed to be rigid and they are connected by two types of springs distributed over their interfase boundaries. Using the Mohr-Coulomb's failure criterion and considering the effect of contact as well as separation on the two points of interface boundaries of each elements, the perfect elasto-plastic analysis was carried out basing on the initial stress method.In this paper the following results were obtained.(1) Homogeneous and anisotropic mechanical characteristics of materials can be obtained by random or anisotropic discretization.(2) In some cases of cracked rock masses, the crack propagates by slow stable fracture, while such as in splitting tensile test, it causes an instantaneous unstable fracture. This two modes of fracture are verified by numerical analysis.(3) Fracture pattern results for jointed rock are good agreement with experimental and numerical results.

Geometric non-linearlity depends on the first derivative of the displacement field, so that it is very advantageous to use the lower displacement field with respect to cost and computing time.In this paper, a new discrete plate bending element with the first order shape function is proposed, and their higher order derivatives are approximated by the finite difference expression which results in substantial simplification of energy integrals.Furthermore, in this element a number of displacement parameter of one node is 1/3 of a well-known plate bending element and therefore considereable reduction of computing time can be expected.From the results of numerical analysis it can be concluded that this model might be very powerful in non-linear in-plane as well as bending analysis of plates.

The algorithm for the discrete limit analysis of general thin-walled structures proposed in the previous reports is applied to the dynamic collapse problems of impulsively loaded plates and shells. The present algorithm allows the discontinuity of displacements on the interelement boundaries and it enables us to solve the problems on the limit strength of arbitrarily shaped thin-walled plate and shell structures taking geometrical as well as material nonlinearities into consideration.In the impact dynamics of structures the static analysis by the present algorithm is a great help to the investigation on the relation of the external loading energy (or the internal plastic work) and the magnitude of permanent displacements as supposed from the conventional rigid-plastic analysis, however, in the present report the transient response analysis by the direct time-integration of the equation of motion is carried out in order to illustrate the usefulness of the present technique to the general nonlinear dynamic analysis.As numerical examples the dynamic collapse behaviors of the impulsively loaded strip, rectangular plates, circular cylindrical shells, hemispherical shell and cylindrical panel were simulated, the results of which were compared with the finite element and finite difference solutions, theoretical rigid-plastic solutions and experimental results presented in the literatures. These numerical studies made it clear that the present algorithm can give qualitatively satisfied solutions for the dynamic plastic problems and treat about 130 spring-time steps per CPU second on a HITAC M-280 H in the implicit time integration code.

For nonlinear problems in structural mechanics, finite element analysis based on the incremental theory has been well established. But a large computing time and cost make it difficult to use this method effectively in stractural analysis and design.In this paper the authors propose the application of classical Rayleigh-Ritz procedure to structural nonlinear problems including material and geometrical nonlinearities. By using this method, the size of the final stiffness matrix to be handled can be considerably reduced and therefore substantial cut of computing time may be expected, although it depends upon the selection of trial functions, a scheme of numerical energy integrals, and types of problems.As numerical examples ultimate strength analysis of uniaxially or biaxially loaded steel H-columns are shown. The present analysis is based on the incremental theory by the Lagrangian approach, and the most general displacement functions of beam-columns, derived on the assumptions that cross sections are rigid and shearing deformations can be neglected, are used as trial functions. Some initial imperfections, i. e. load eccentricities, initial deflections, and residual stresses are taken into account. The authors believe that the same procedure may be effectively applied to nonlinear dynamic problems of beam-columns.

In the present paper a nonlinear finite element code based on the updated Lagrangian approach will be developed for the analysis of the crushing behavior of structural elements and some numerical examples will be presented in order to show the validity of the present algorithm. Several features of the developed code are : 1. The bilinear degenerate shell element with reduced integration is employed.2. The hourglass control stiffness proposed by Flanagan and Belytschko and in-plane rotational stiffness due to Kanok-Nukulchai are added to the element stiffness.3. The virtual work equation is expressed in terms of the updated Green strains and the updated Kirchhoff stresses and the calculated Kirchhoff stress increments are transformed into the Jaumann stress increments at each incremental step. In this transformation the normal strain in the thickness direction is determined so as to maintain the plane stress condition.In numerical examples the post-buckling behavior of axially loaded elastic and elasto-plastic columns are analized and the calculated load-deflection curves are checked against the exact solution and experimental results. The crushing behavior of axially compressed circular cylindrical shells is also calculated, and the obtained results are compared with experimental results.

A method of discrete limit analysis which was proposed by Kawai in 1976 is extended to study structural behaviour of a set of solid blocks at the ultimate state of loading where the effect of finite rotation of these blocks should be taken into account. It is shown that Shanley's theory of plastic buckling can be simply demonstrated by using the present discrete models.

In order to break the present deadlock of finite element non-linear analysis in solid mechanics, the importance of consideration of slip phenomena in inelastic problems is pointed out and a series of new simplified elements are introduced which may be powerful in the discrete analysis of highly non-linear problems.