• Title/Summary/Keyword: D-D Diagram

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Study of dynamic mechanical behavior of aluminum 7075-T6 with respect to diameters and L/D ratios using Split Hopkinson Pressure Bar (SHPB)

  • Kim, Eunhye;Changani, Hossein
    • Structural Engineering and Mechanics
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    • v.55 no.4
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    • pp.857-869
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    • 2015
  • The aluminum 7075-T6 is known as an alloy widely used in aircraft structural applications, which does not exhibit strain rate sensitivity during dynamic compressive tests. Despite mechanical importance of the material, there is not enough attention to determine appropriate sample dimensions such as a sample diameter relative to the device bar diameter and sample length to diameter (L/D) ratio for dynamic tests and how these two parameters can change mechanical behaviors of the sample under dynamic loading condition. In this study, various samples which have different diameters of 31.8, 25.4, 15.9, and 9.5 mm and sample L/D ratios of 2.0, 1.5, 1.0, 0.5, and 0.25 were tested using Split Hopkinson Pressure Bar (SHPB), as this testing device is proper to characterize mechanical behaviors of solid materials at high strain rates. The mechanical behavior of this alloy was examined under ${\sim}200-5,500s^{-1}$ dynamic strain rate. Aluminum samples of 2.0, 1.5 and 1.0 of L/D ratios were well fitted into the stress-strain curve, Madison and Green's diagram, regardless of the sample diameters. Also, the 0.5 and 0.25 L/D ratio samples having the diameter of 31.8 and 25.4 mm followed the stress-strain curve. As results, larger samples (31.8 and 25.4 mm) in diameters followed the stress-strain curve regardless of the L/D ratios, whereas the 0.5 and 0.25 L/D ratios of small diameter sample (15.9 and 9.5 mm) did not follow the stress-strain diagram but significantly deviate from the diagram. Our results indicate that the L/D ratio is important determinant in stress-strain responses under the SHPB test when the sample diameter is small relative to the test bar diameter (31.8 mm), but when sample diameter is close to the bar diameter, L/D ratio does not significantly affect the stress-strain responses. This suggests that the areal mismatch (non-contact area of the testing bar) between the sample and the bar can misrepresent mechanical behaviors of the aluminum 7075-T6 at the dynamic loading condition.

Analysis of haline channel formed in the East China Sea and the Atlantic Ocean using the T-S gradient diagram

  • Kim, Juho;Kim, Hansoo;Paeng, Dong-Guk
    • Journal of Advanced Marine Engineering and Technology
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    • v.38 no.2
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    • pp.208-216
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    • 2014
  • In case of any coastal ocean near the mouth of huge rivers, low salinity water can be formed due to its large amount of freshwater discharge. For the acoustic analysis on the low salinity environment, some oceanographic data of the East China Sea and the Atlantic Ocean were collected through KODC (Korea Oceanographic Data Center) and NODC (National Oceanographic Data Center) online service. In this paper, the T-S gradient diagram is introduced to show a relation between the gradients of temperature and salinity in view of acoustic surface channel formation. Existence of haline channel, quantitative contribution of gradients of salinity and temperature, effectiveness of the channel formation can be known by the T-S gradient diagram. After applying the collected data into the diagram, tropical regions of the Atlantic Ocean show strong haline channel due to its nearly invariant temperature and drastic change of salinity with depth. The averaged transmission loss in the channel is about 5.7 ~ 7.5 dB less than that out of the channel by the results of acoustic propagation model (RAM: Range independent Acoustic Model). On the other hand, the East China Sea and temperate region of the Atlantic ocean have weaker haline channel with less difference of the averaged transmission loss between in and out of the channel as 3.2 ~ 6.0 dB. Although data samples used in this study have limitation to represent the general physical structures of the three ocean regions, the T-S gradient diagram is shown to be useful and acoustic field affected by low salinity environment is investigated in this study.

Approximate voronoi diagrams for planar geometric models

  • Lee, Kwan-Hee;Kim, Myung-Soo
    • 제어로봇시스템학회:학술대회논문집
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    • 1991.10b
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    • pp.1601-1606
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    • 1991
  • We present an algorithm to approximate the Voronoi diagrams of 2D objects bounded by algebraic curves. Since the bisector curve for two algebraic curves of degree d can have a very high algebraic degree of 2 * d$^{4}$, it is very difficult to compute the exact algebraic curve equation of Voronoi edge. Thus, we suggest a simple polygonal approximation method. We first approximate each object by a simple polygon and compute a simplified polygonal Voronoi diagram for the approximating polygons. Finally, we approximate each monotone polygonal chain of Voronoi edges with Bezier cubic curve segments using least-square curve fitting.

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ON CERTAIN CLASSES OF LINKS AND 3-MANIFOLDS

  • Kim, Soo-Hwan;Kim, Yang-Kok
    • Communications of the Korean Mathematical Society
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    • v.20 no.4
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    • pp.803-812
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    • 2005
  • We construct an infinite family of closed 3-manifolds M(2m+ 1, n, k) which are identification spaces of certain polyhedra P(2m+ 1, n, k), for integers $m\;\ge\;1,\;n\;\ge\;3,\;and\;k\;\ge\;2$. We prove that they are (n / d)- fold cyclic coverings of the 3-sphere branched over certain links $L_{(m,d)}$, where d = gcd(n, k), by handle decomposition of orbifolds. This generalizes the results in [3] and [2] as a particular case m = 2.

Non-linearity Testing of D/A Converters Applying Walsh Function (Walsh 함수를 적용한 D/A 컨버터의 비선형 시험)

  • Lee, Hae-Ki;Lee, Chun-Mo
    • Proceedings of the KIEE Conference
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    • 2002.06a
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    • pp.161-165
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    • 2002
  • The paper presents a diagnostic tool for analyzing the bit intermodulation in D/A converter. Bit intermodulation cause linearity errors which degrade the performance of the converter. A linear transformation of the Walsh transform of the integrated non-linearity diagram is shown to be sufficient to extract the bit intermodulation terms and their noise sensitivity. Practical applicability of the proposed method is shown by measurement.

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Theoretical Studies on the Methanolysis of a Cephalosporin; Mimicking Acylation of the Active Site Serine of D-Ala-D-Ala Transpeptidases

  • Nahm, Kee-Pyung
    • Bulletin of the Korean Chemical Society
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    • v.12 no.6
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    • pp.674-678
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    • 1991
  • Methanolysis of a ${\beta}$-lactam ring of a cephalosporin was simulated with AM1 semiempirical quantum mechanical calculation. The tetrahedral intermediate TD1 from an O-protonated cephalosporin and a methanol transfers the proton intramolecularly to the C-4 carboxylate to generate an oxyanion, i.e., second tetrahedral intermediate TD2, which undergoes the amide bond cleavage without further protonation on the N-5. For this cleavage a low-energy barrier TS2 was located. According to the energy diagram, tetrahedral intermediates easily undergo ring cleavage even without the protonation on the amide nitrogen.

Formulation of forming limit diagram based on strain-rate potential (소성 변형률 포텐셜에 기초한 성형 한계도의 정식화)

  • Kim D.;Chung K.;Kim K. J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.10a
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    • pp.156-159
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    • 2004
  • Most formulations for a forming limit diagram (FLD) have been based on yield stress potentials defined in the stress field. Nevertheless, there are formulations where potentials defined in the stain-rate field are especially convenient to formulate the rigid plastic material. Based on a strain-rate potential proposed for materials exhibiting planar anisotropic, the formulations for the forming limit diagram has been developed applying M-K theory. As verification example, the formulation is applied for anisotropic AA5182-O sheet. The good verification results show that the formulation for the forming limit diagram has been successfully developed.

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Dynamic Relationship in Creative Manpower, R&D Technology Level, and Tolerance in the Culture Industry (문화산업에서 창조인력, R&D 기술수준 및 관용성의 역동적인 관계성)

  • Choi, Hae-Ok;Lee, Man-Hyung
    • Korean System Dynamics Review
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    • v.10 no.2
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    • pp.81-102
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    • 2009
  • Based on various employment and technology data in the cultural sector from the mid-1990s to the mid-2000s in Seoul, Korea, this research examines whether technology- and human resource-oriented programs exert significant impact on creative manpower, R&D technology level and tolerance. After briefly introducing Seoul's trends in the culture industry, it tries to explain major reinforcing and balancing loops. The stock-flow diagram of the culture industry in Seoul is applied to estimate relative effectiveness of technology- and human resource-oriented cultural programs cultural programs. Judging from a series of simulated experiments, technology-oriented cultural programs are essential to increase creative manpower and R&D technology level in the short term. For the first half of research period, this research finds that human resource-oriented cultural programs put forth minimal impact, if they even exist at all. The trends, however, are reversed in the long term: Both size of creative manpower and R&D technology level absolutely depend on human resource-oriented cultural programs in the second half.

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Development of 750MHz CATV amplifier module using PHEMTs (PHEMT를 이용한 750MHz CATV증폭 모듈 개발)

  • 유주형;구경헌;조삼열
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.22 no.1
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    • pp.72-80
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    • 1997
  • A 750 MHz CATV amplifier module has been designed and fabricated using PHEMT chips on alumina board. Developed 2-stage push-pull amplifier using wire bounded PHEMT chips shows 19dB gain, 15dB return loss and 4. 2dB noise figure over 50-750MHz frequency range. These results are superior to the characteristics of the commer-cially abailable 750MHz amplifier module. In this paper, brief background of the amplifier design, the circuit diagram and the test result have been presented.

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