• Steel and Composite Structures
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• 제49권6호
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• pp.667-684
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• 2023

In the context of finite element method, a computational simulation is presented to study and analyze the dynamic behavior of regularly perforated functionally graded rotating beam for the first time. To investigate the effect of perforation configurations, both regular circular and squared perforation patterns are studied. To explore impacts of graded material distributions, both axial and transverse gradation profiles are considered. The material characteristics of graded materials are assumed to be smoothly and continuously varied through the axial or the thickness direction according the nonlinear power gradation law. A computational finite elements procedure is presented. The accuracy of the numerical procedure is verified and compared. Resonant frequencies, axial displacements as well as internal stress distributions throughout the perforated graded rotating cantilever beam are studied. Effects of material distributions, perforation patterns, as well as the rotating beam speed are investigated. Obtained results proved that the graded material distribution has remarkable effects on the dynamic performance. Additionally, circular perforation pattern produces more softening effect compared with squared perforation configuration thus larger values of axial displacements and maximum principal stresses are detected. Moreover, squared perforation provides smaller values of nondimensional frequency parameters at most of vibration modes compared with circular pattern.

• 대한기관식도과학회지
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• 제5권1호
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• pp.30-35
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• 1999

Between 1994 to 1998, 7 patients had taken emergency operations by iatrogenic esophageal perforation. To evaluate patterns of injury, clinical presentation, and treatment options for patients, we reviewed all the 7 patients who had gotten transmural injury to the esophagus during dilatations or stenting procedures at our hospital. The primary diagnosis of the patients were as followings , two were achalagia and remaining five were corrosive esophageal strictures. Chest pain, fever, tachycardia were the early signs after esophageal perforation. The sites of perforation were thoracic esophagus in all cases and all of them underwent operation within 8 hours of initial injury. There were no postoperative mortality. Complications were developed three cases： stricture of anastomotic site, mediastinitis due to graft failure of colon and pleural empyema.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
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• pp.114-117
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• 2005

In the reactive concentric resonator, perforated inner tubes are widely used for various purposes related to noise reduction, flow guiding, and structural aspects. Perforation distribution patterns influence both the acoustic performance and mechanical performance. In this study, the influence of distribution patterns on acoustic performance are explained by adopting the concept of extended inlet/outlet length. Predicted transmission with varying extended inlet/outlet length is compared with prediction by varying distribution patterns. The transmission loss difference due to perforation distribution patterns can be explained by changing the extended inlet/outlet length of the uniformly perforated resonator.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.223-243
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• 2023

There is a burgeoning demand for minimizing the mass of satellites because of its direct impact on reducing launch-to-orbit cost. This must be done without compromising the structure's efficiency. The present paper introduces a relatively low-cost and easily implementable approach for optimizing structural mass to a maximum natural frequency. The natural frequencies of the satellite are of utmost pertinence to the application requirements, as the sensitive electronic instrumentation and onboard computers should not be affected by the vibrations of the satellite structure. This methodology is applied to a realistic model of Al-Azhar University micro-satellite in partnership with the Egyptian Space Agency. The procedure used in structural design can be summarized in two steps. The first step is to select the most favorable primary structural configuration among several different candidate variants. The nominated variant is selected as the one scoring maximum relative dynamic stiffness. The second step is to use perforation patterns reduce the overall mass of structural elements in the selected variant without changing the weight. The results of the presented procedure demonstrate that the mass reduction percentage was found to be 39% when compared to the unperforated configuration that had the same plate thickness. The findings of this study challenge the commonly accepted notion that isogrid perforations are the most effective means of achieving the goal of reducing mass while maintaining stiffness. Rather, the study highlights the potential benefits of exploring a wider range of perforation unit cells during the design process. The study revealed that rectangular perforation patterns had the lowest efficiency in terms of modal stiffness, while triangular patterns resulted in the highest efficiency. These results suggest that there may be significant gains to be made by considering a broader range of perforation shapes and configurations in the design of lightweight structures.

• Imaging Science in Dentistry
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• 제47권4호
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• pp.261-267
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• 2017

Purpose: Analyzing different patterns of maxillary sinus septa in cone-beam computed tomography (CBCT) images and predicting maxillary sinus membrane perforations. Materials and Methods: In this cross-sectional study, CBCT images of 222 patients ranging from 20 to 81 years old were evaluated. One hundred fifty-two patients (93 females and 59 males) who had maxillary sinus septa in axial views were included in this study. Cross-sectional images were used to determine classifications of sinus septa and the risk of membrane perforation using a method modified from Al-Faraje et al. Variables of sex, age, and dental status were considered. Chi-squared and Kruskal-Wallis tests were used for data analysis(P<.05). Results: In this study, 265 maxillary sinus septal patterns were found. The mean age of the patients was $44.1{\pm}14.7$ years old. The Class I and VII-div II patterns had the greatest and least prevalence, respectively. Furthermore, there was a significant relationship between the location of septa and the frequency of membrane perforation risk (P<.05). In this study, the relationship of different patterns of septa with dental status did not differ significantly (P>0.05). Conclusion: A higher prevalence of moderate risk of membrane perforation in the molar region relative to the premolar region was observed. Furthermore, maxillary sinus septa occur most frequently in the molar region, demonstrating the importance of paying attention to this region during sinus lift surgery. This study did not show any relationship between tooth loss and the presence of septa.

• Earthquakes and Structures
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• 제20권4호
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• pp.377-388
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• 2021

Thin perforated Steel Plate Shear Walls (SPSWs) are among the most common types of seismic energy dissipation systems to protect the main boundary components of SPSWs from fatal fractures in the high-risk zones. In this paper, the cyclic behavior of the different circular hole patterns under cyclic loading is reported. Based on the experimental results, it can be concluded that a change in the perforation pattern of the circular holes leads to a change in the locations of the fracture tendency over the web plate, especially at the plate-frame interactions. Accordingly, the cyclic responses of the tested specimens were simulated by finite element method using the ABAQUS package. Likewise, perforated shear panels with a new perforation pattern obtained by implementing Topology Optimization (TO) were proposed. It was found that the ultimate shear strength of the specimen with the proposed TO perforation pattern was higher than that of the other specimens. In addition, theoretical equations using the Plate-Frame Interaction (PFI) method were used to predict the shear strength and initial stiffness of the considered specimens. The theoretical results showed that the proposed reduced coefficients relationships cannot accurately predict the shear strength and initial stiffness of the considered perforated shear panels. Therefore, the reduced coefficients should be adopted in the theoretical equations based on the obtained experimental and numerical results. Finally, with the results of this study, the shear strength and initial stiffness of these types of perforated shear panels can be predicted by PFI method.

• 한국기계가공학회지
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• 제12권4호
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• pp.55-60
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• 2013

In this study, mechanical properties of versatile light weight plywood(manufacturing using piercing) are studied. A credibility evaluation was carried out for different perforation patterns including octagonal shape, rectangular shape and circular shape. A static structural analysis is conducted to find the stresses produced. Circular perforations are found to have better strength to weight ratio. Results of each type of perforation are discusses and compared.

• 대한의생명과학회지
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• 제25권4호
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• pp.367-371
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• 2019

In this study, the author observed the fungal characteristics of T. verrucosum which is commonly known as the cattle ringworm fungus in the farms of Hoengseong, Gangwon-do. After isolating 20 strains of T. verrucosum from cattle, they were cultured on SDA, PDA media and the fungal characteristics were concluded through visual observation of the colonies, microscopic findings, hair perforation test and urease test. The size of the colonies cultured on SDA media at 37 C was on an average 5 mm at 1 week, 33 mm at 2 weeks, 42 mm at 3 weeks and 58 mm after 4 weeks. Observing the characteristics of the colonies, 17 strains of T. album showing central bold radial folds, 2 strains of T. ochraceum having l throughout the colonies and 1 strain of T. discoides with rapid growth rate and gray-white cotton patterns were found. On microscopic observations of the cultured colonies on SDA, PDA media, macroconidia and microconidia were not found in T. verrucosum and hyphae and chlamydospore were only seen in T. album types. Out of 20 strains of T. verrucosum, hair perforation test was positive on only 3 strains and urease test was positive on all of the 20 strains.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.765-779
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• 2020

This article presents a nonclassical size dependent model based on the modified couple stress theory to study and analyze the bending behavior of perforated microbeams under different loading patterns. Modified equivalent material and geometrical parameters for perforated beam are presented. The modified couple stress theory with one material length scale parameter is adopted to incorporate the microstructure effect into the governing equations of perforated beam structure. The governing equilibrium equations of the perforated Timoshenko as well as the perforated Euler Bernoulli are developed based on the potential energy minimization principle. The Poisson's effect is included in the governing equilibrium equations. Regular square perforation configuration is considered. Based on Fourier series expansion, closed forms for the bending deflection and the rotational displacements are obtained for simply supported perforated microbeams. The proposed methodology is validated and compared with the available results in the literature and an excellent agreement is detected. Numerical results demonstrated the applicability of the proposed methodology to investigate the bending behavior of regularly squared perforated beams incorporating microstructure effect under different excitation patterns. The obtained results are significantly important for the design and production of perforated microbeam structures.

• 복식문화연구
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• 제16권4호
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• pp.722-734
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• 2008

This study focuses on the trend of modern society that places importance on health and happiness. By using gilsang (signs that brings good fortunes) patterns that wishes for fortune and health, the objective of this study is to design a distinct but universal fashion good that is unique to Korea and is used not only as a piece of artwork, but as part of development of new and assorted cultural products that is competitive in the international society. This study was conducted first by studying related documents for the theoretical background. In addition, in order to satisfy consumer demands, a jacquard that can procure international competitiveness was designed and fashion goods fitting to this was planned. Through this, the various possibilities of using the jacquard designs were suggested. The development process of fashion goods using jacquard was divided into 10 stages: theme setting, gilsang pattern setting, sketching, textile plan, design organization, input, simulation process, perforation and sewing, selection of design for the fashion good and goods production. Fashion materials are a very important element in creating variations and uniqueness in the fashion industry. Development of new materials has made the aesthetic and ornamental elements, together with the practical and functional aspects of textiles possible. A major issue today is rising out of the past mass production method of OEM (Original Equipment Manufacturing), and developing various artistic patterns that can be used in mass-produced products and assorted production in small quantities in order to develop specialized fashion goods.