• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.65-73
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• 2004

Composites are a material class for which nondestructive material property characterization is as important as flaw detection. Laminates of fiber reinforced composites often possess strong in-plane elastic anisotropy attributable to the specific fiber orientation and layup sequence when waves are propagating in the thickness direction of composite laminates. So the layup orientation greatly influences its properties in a composite laminate. It could result in the part being .ejected and discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Therefore a ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. This model decomposes the transmission of a linearly polarized ultrasound wave into orthogonal components through each ply of a laminate. Also in order to develop these methods into practical inspection tools, motorized system have been developed for different measurement modalities for acquiring ultrasonic signals as a function of in-plane angle. It is found that high probability shows between the model and tests developed in characterizing cured layups of the laminates.

• Applied Microscopy
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• 제27권3호
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• pp.321-332
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• 1997

The dermal papilla is known to playa major role in influencing the form and dynamics of the hair follicle, which probably involves regulatory substances crossing the basal lamina. But little is known about the junctions between the dermal papilla and the surrounding epithelial cells of the hair bulb, or between the connective tissue and the epithelial cells on the outside of the hair follicle. This study was performed to identify the ultrastructural differences between dermoepidermal junction of the skin and connective tissue-epithelial junctions on the outside of the hair follicle and around the dermal papilla of normal anagen hair follicles in the human fetal scalp skin. Electron microscopic findings of dermoepidermal junction in scalp skin showed that basal lamina was very irregular and undulated, and it contained many attachment plaques of hemidesmosomes with sub-basal dense plates, tonofilaments, and anchoring filaments. Also invaginations of plasma membrane of basal keratinocytes were seen. There were clear differences both on the outside of the follicle and around the dermal papilla as compared with similar junction in the skin. In particular, neither hemidesmosomes nor tonofilaments, as seen in dermoepidermal junction, were observed in the dermal papilla. Also attachment plaque, sub-basal dense plate and anchoring filaments were not observed at the junction on the outside of the follicle and the dermal papilla. There were some differences between connective tissue-epithelial junctions on the outside of the hair follicle and around the dermal papilla, ie, smoothness of basal lamina and orthogonal arrangement of collagen fibers were seen in the outside of hair follicle, but not in the dermal papilla. These results indicate that the mechanical connection between the hair follicle and the connective tissue component is much weaker than that between the corresponding components in skin, and it reflects the dynamic processes during the anagen phase of the hair follicle compared to the relatively permanent state of the epidermis.

• 분석과학
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• 제33권2호
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• pp.98-107
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• 2020

Methamphetamine (MA) is currently the most abused illicit drug in Korea. MA is produced by chemical synthesis, and the final target drug that is produced contains small amounts of the precursor chemicals, intermediates, and by-products. To identify and quantify these trace compounds in MA seizures, a practical and feasible approach for conducting chromatographic fingerprinting with a suite of traditional chemometric methods and recently introduced machine learning approaches was examined. This was achieved using gas chromatography (GC) coupled with a flame ionization detector (FID) and mass spectrometry (MS). Following appropriate examination of all the peaks in 71 samples, 166 impurities were selected as the characteristic components. Unsupervised (principal component analysis (PCA), hierarchical cluster analysis (HCA), and K-means clustering) and supervised (partial least squares-discriminant analysis (PLS-DA), orthogonal partial least squares-discriminant analysis (OPLS-DA), support vector machines (SVM), and deep neural network (DNN) with Keras) chemometric techniques were employed for classifying the 71 MA seizures. The results of the PCA, HCA, K-means clustering, PLS-DA, OPLS-DA, SVM, and DNN methods for quality evaluation were in good agreement. However, the tested MA seizures possessed distinct features, such as chirality, cutting agents, and boiling points. The study indicated that the established qualitative and semi-quantitative methods will be practical and useful analytical tools for characterizing trace compounds in illicit MA seizures. Moreover, they will provide a statistical basis for identifying the synthesis route, sources of supply, trafficking routes, and connections between seizures, which will support drug law enforcement agencies in their effort to eliminate organized MA crime.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.1911-1932
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• 2013

Orthogonal frequency-division multiplexing (OFDM) has become a popular modulation scheme for wireless protocols because of its spectral efficiency and robustness against multipath interference. Although the components of various OFDM protocols are functionally similar, they remain distinct because of the characteristics of the environment. Recently, graphics processing units (GPUs) have been used to accelerate the signal processing of the physical layer (PHY) because of their great computational power, high development efficiency, and flexibility. In this paper, we describe the implementation of parameterized baseband modules using GPUs for two different OFDM protocols, namely, 802.11a and 802.16. First, we introduce various modules in the modulator/demodulator parts of the transmitter and receiver and analyze the computational complexity of each module. We then describe the integration of the GPU-based baseband modules of the two protocols using the parameterized method. GPU-based implementations are addressed to explain how to accelerate the baseband processing to archive real-time throughput. Finally, the performance results of each signal processing module are evaluated and analyzed. The experiments show that the GPU-based 802.11a and 802.16 PHY meet the real-time requirement and demonstrate good bit error ratio (BER) performance. The performance comparison indicates that our GPU-based implemented modules have better flexibility and throughput to the current ones.

• 대한기계학회논문집
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• 제16권6호
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• pp.1156-1162
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• 1992

본 연구에서는 종횡비가 다른 3가지의 날카로운 모서리를 가진 타원 슬롯노즐 (AR=1,2,4)을 풍동 수축부 끝에 장착하여 타원제트의 유동특성 및 축교차현상을 3-D LDV 시스템을 이용하여 조사하였다.

• 한국산림과학회지
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• 제95권6호
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• pp.768-777
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• 2006

이 연구는 지리산 국립공원 방문자를 대상으로 경관선호 모델을 형성하기 위하여, 지리산 경관과 영국의 케이른고럼스 경관의 선택적 상황에서 경관선호를 결정하게 하는 요소로서 시각적 경관 요소와 더불어 경관자체의 효과를 검증하는 조건부 로짓모델을 제시하는데 그 목적이 있다. 선택적 상황에 따른 경관선호를 측정하기 위하여 지리산 국립공원을 방문한 탐방객에 대하여 영국의 케이른고럼스 국립공원의 경관사진과 지리산 경관사진을 쌍체로 배열한 사진설문조사를 실시하였다. 시각적 경관의 구성요소는 디지털사진측정의 과정을 거쳐 상호 수직적인 주요인들로 축약되어, 모델의 설명변수로 사용되었다. 연구의 결과, 시각적 경관의 구성요소만으로 형성되는 일반조건부로짓모델은 비유관대안도립성(IIA)의 가정을 충족하지 못하고, 모델의 설명력이 낮게 나타났다(${\rho}^2=0.06$). 반면, 대안특성상수(ASC)로서 표현되는 경관자체의 효과를 포함하는 혼합조건부로짓모델은 비유관대안독립성(IIA)의 가정을 충족하였고, 모델의 적합성 또한 양호하게 나타났다(${\rho}^2=0.25$). 이는 경관선호모델에 있어서 선호의 요인으로써 시각적 경관의 구성요소 뿐만 아니라, 경관자체의 효과를 포함하는 혼합조건부로짓모델이 적합한 것으로 해석된다.

• 대한기계학회논문집
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• 제18권1호
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• pp.139-149
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• 1994

A numerical simulation of unsteady axisymmetric turbulent flow was performed for a reciprocating engine including port/valve assembly. The governing equations based on a nonorthogonal coordinate formulation with Cartesian velocity components were used and discretised by the finite volume method with non-staggered variable arrangements. The modified $\kappa-\xi$. turbulence model which included the effect of compressibility was used. The results of twodimensional transient calculation for the axisymmetric configuration were compared with the experimental data. Although slightly low rms velocity was predicted compared to the experimental data, predicted velocity distributions at the valve exit and in-cylinder region showed good agreements with the experimental data. The flow at the valve exit was separated at the same valve lift position with the experimental data. Two vortices incylinder region were generated during the initial intake process. The clockwise main vortex became strong and moved upward to the top wall. The counter-clockwise second vortex became weak and stick to the upper left corner of the cylinder. After middle intake process, new vortex adjacent to upper cylinder wall appeared by the piston motion and therefore, the in-cylinder flow was formed into three vortices. The cylinder pressure just before bottom dead center of piston was higher than inlet pressure and then the reverse flow occured at the valve exit. The in-cylinder flow characteristics were strongly dependent on piston motion, but insensitive to valve motion.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 제11차 KACG 학술발표회 Crystalline Particle Symposium (CPS)
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• pp.285-309
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• 1996

Non oxide ceramics such as nitrides of transition metals have shown significant potential for future economic impact, in diverse applications in ceramic, aerospace and electronic industries, as refractory products, abrasives and cutting tools, aircraft components, and semi-conductor substrates amid others. Combustion synthesis has become an attractive alternative to the conventional furnace technology to produce these materials cheaply, faster and at a higher level of purity. However he process os highly exothermic and manifests complex dynamics due to its strongly non-linear nature. In order to develop an understanding of this process and to study the effect of operational parameters on the final outcome, numerical modeling is necessary, which would generated essential knowledge to help scale-up the process. the model is based on a system of parabolic-hyperbolic partial differential equations representing the heat, mass and momentum conservation relations. The model also takes into account structural change due to sintering and volumetric expansion, and their effect on the transport properties of the system. The solutions of these equations exhibit steep moving spatial gradients in the form of reaction fronts, propagating in space with variable velocity, which gives rise to varying time scales. To cope with the possibility of extremely abrupt changes in the values of the solution over very short distances, adaptive mesh techniques can be applied to resolve the high activity regions by ordering grid points in appropriate places. To avoid a control volume formulation of the solution of partial differential equations, a simple orthogonal, adaptive-mesh technique is employed. This involves separate adaptation in the x and y directions. Through simple analysis and numerical examples, the adaptive mesh is shown to give significant increase in accuracy in the computations.

• Journal of the Korean Wood Science and Technology
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• 제48권5호
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• pp.591-607
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• 2020

This study was aimed to investigate the changes of chemical composition of the volatile organic compounds (VOCs) emitted from red pine needles in the process of needle abscission or senescence. The VOCs in intact, senescent, and litter red pine needle samples were analyzed by headspace-solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC/MS). And then, multivariate statistical interpretation of the processed data sets was conducted to investigate similarities and dissimilarities of the needle samples. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used to investigate the dataset structure and discrimination between samples, respectively. From the data preview, the levels of major components of VOCs from needles were not significantly different between needle samples. By PCA investigation, the data reduction according to classification based on the chlorophyll a / chlorophyll b (Ca/Cb) ratio were found to be ideal for differentiating intact, senescent, and litter needles. The following OPLS-DA taking Ca/Cb ratio as y-variables showed that needle samples were well grouped on score plot and had the significant discriminant compounds, respectively. Several compounds had significantly correlated with Ca/Cb ratio in a bivariate correlation analysis. Notably, the litter needles had a higher content of oxidized compounds than the intact needles. In summary, we found that chemical compositions of VOCs between intact, senescent, and litter needles are different each other and several compounds reflect characteristic of needle.

• Earthquakes and Structures
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• 제2권4호
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• pp.357-376
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• 2011

Ground motion models predict the mean and standard deviation of the logarithm of spectral acceleration, as a function of predictor variables such as earthquake magnitude, distance and site condition. Such models have been developed for a variety of seismic environments throughout the world. Some calculations, such as the Conditional Mean Spectrum calculation, use this information but additionally require knowledge of correlation coefficients between logarithmic spectral acceleration values at multiple periods. Such correlation predictions have, to date, been developed primarily from data recorded in the Western United States from active shallow crustal earthquakes. This paper describes results from a study of spectral acceleration correlations from Japanese earthquake ground motion data that includes both crustal and subduction zone earthquakes. Comparisons are made between estimated correlations for Japanese response spectral ordinates and correlation estimates developed from Western United States ground motion data. The effect of ground motion model, earthquake source mechanism, seismic zone, site conditions, and source to site distance on estimated correlations is evaluated and discussed. Confidence intervals on these correlation estimates are introduced, to aid in identifying statistically significant differences in correlations among the factors considered. Observed general trends in correlation are similar to previous studies, with the exception of correlation of spectral accelerations between orthogonal components, which is seen to be higher here than previously observed. Some differences in correlations between earthquake source zones and earthquake mechanisms are observed, and so tables of correlations coefficients for each specific case are provided.