• Title/Summary/Keyword: Envelope material

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Envelope-Function Equation and Motion of Wave Packet in a Semiconductor Superlattice Structure

  • Kim, Byoung-Whi;Jun, Young-Il;Jung, Hee-Bum
    • ETRI Journal
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    • v.21 no.1
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    • pp.1-27
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    • 1999
  • We present a new description of envelope-function equation of the superlattice (SL). The SL wave function and corresponding effective-mass equation are formulated in terms of a linear combination of Bloch states of the constituent material with smaller band gap. In this envelope-function formalism, we review the fundamental concept on the motion of a wave packet in the SL structure subjected to steady and uniform electric fields F. The review confirms that the average of SL crystal momentums K = ($k_x,k_y,q$), where ($K_x,k_y$) are bulk inplane wave vectors and q SL wave vector, included in a wave packet satisfies the equation of motion = $_0+Ft/h$; and that the velocity and acceleration theorems provide the same type of group velocity and definition of the effective mass tensor, respectively, as in the Bulk. Finally, Schlosser and Marcus's method for the band theory of metals has been by Altarelli to include the interface-matching condition in the variational calculation for the SL structure in the multi-band envelope-function approximation. We re-examine this procedure more thoroughly and present variational equations in both general and reduced forms for SLs, which agrees in form with the proposed envelope-function formalism. As an illustration of the application of the present work and also for a brief investigation of effects of band-parameter difference on the subband energy structure, we calculate by the proposed variational method energies of non-strained $GaAs/Al_{0.32}Ga_{0.68}As$ and strained $In_{0.63}Ga_{0.37}As/In_{0.73}Ga_{0.27}As_{0.58}P_{0.42}SLs$ with well/barrier widths of $60{\AA}/500{\AA}$ and 30${\AA}/30{\AA}$, respectively.

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Dynamic Electromyography Analysis of Shoulder Muscles for One-handed Manual Material Handling

  • Mo, Seung-Min;Jung, Myung-Chul
    • Journal of the Ergonomics Society of Korea
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    • v.34 no.4
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    • pp.313-326
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    • 2015
  • Objective: The objective of this research is to quantitatively analyze muscle activities of arm and shoulder, according to direction in various types of one-handed manual material handling, based on surface electromyography. Background: Workers in industrial sites frequently carry out one-handed manual material handling using arm and shoulder muscles. Therefore, chronic load and accumulated fatigue occur to arm and shoulder muscles, which becomes a main cause of upper arm and shoulder musculoskeletal disorders. The shoulder muscles have widely range of motion, and complex interactions take place among various muscles including rotator cuff muscles. In this regard, research on interactions among should muscles, according to such various dynamic motions, is required. Method: Ten male subjects in their 20s participated in this research. This research considered upward, downward, leftward, rightward, forward and backward directions and fourteen muscles around arm and shoulder (biceps brachii and trapezius, etc.) as independent variables. The mean muscle activity was set as the dependent variable. This research extracted $4^{th}{\sim}7^{th}$ repetition signals according to ten times of repetitive muscle contraction, and analyzed the muscle activity concerned using the envelope detection technique. Results: The mean muscle activity of upward direction was analyzed highly statistically significant. The reason is that the effect of gravity works to arm and shoulder muscles. Also, it is conjectured that deformation of coracoacromial ligament was caused, and its contact pressure increased, due mainly to the shoulder flexion, and therefore load was analyzed high. Muscle activity was analyzed significantly low, according to concentric ballistic motion used in the concentric contraction phase by storing elastic energy in the eccentric contraction phase with a motion to bring the weight to the front of subject's body as to downward, leftward and backward directions. Because, elbow joint's flexion-extension motions mainly occurred, biceps brachii was analyzed high muscle activity as the prime mover. Conclusion: The information on the quantitative load of muscles can be applied to ergonomic work design for one-handed manual material handling to minimize muscle load. Application: This research has effectively identified muscle activity according to dynamic contraction by applying an envelope detection technique. The results can be used for ergonomic work design to minimize muscle load during the one-handed manual material handling, according to each direction. The research results are expected to be used for musculoskeletal disorder prevention and physiotherapy in the rehabilitation medical field, based on the muscle load of arm and shoulder in various directions.

Deduction of Considerations During Design and Construction by Analysing Domestic and Abroad Case Analysis of Freeform Building Envelope (국내외 비정형 건축물 외피시스템 사례 분석을 통한 설계 및 시공시 고려사항 도출)

  • Ryu, Han-Guk
    • Korean Journal of Construction Engineering and Management
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    • v.14 no.4
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    • pp.84-96
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    • 2013
  • Recently, architectural design has been changing from formal design to freeform design due to the digitalization of construction industry. Especially, the formal design has been accepted as a design trend recently and applied many times as a design concept in the architectural design competitions such as turn-key. However, various deflects such as water leak and cracks have been occurred because the traditional construction methods had been applied without any revision or adaptation of the formal construction method for the freeform building construction. Design and construction of freeform building has been developed as an new method in order to solve the problems and minimize the construction duration and cost for the freeform building. Therefore this research deduced the positive implications for developing freefrom envelope by analyzing the domestic and abroad cases and proposed the considerations during design and construction of the freeform envelope as follows. First, the freeform design should consider the constructability for the freeform envelope. Second, manufacturing technology for the two-way curvature of the unit panel should be developed. Third, exposed concrete form method should be developed for the freeform envelope of concrete. Forth, material characteristics, construction method and facility management should be considered in order to manage precipitation and keep water-proof according to the classification of the freeform envelope area.

The Damage Classification by Periodicity Detection of Ultrasonic Wave Signal to Occur at the Tire (타이어에서 발생하는 초음파 신호의 주기성 검출에 의한 손상 분별)

  • Oh, Young-Dal;Kang, Dae-Soo
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.10 no.6
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    • pp.107-111
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    • 2010
  • The damage of tire by damage material classification method is researched as used ultrasonic wave signal to occur at a tire during vehicle driving. Auto-correlation function after having passed through an envelope detecting preprocess is used for detecting periodicity because of occurring periodic ultrasonic waves signal with tire revolution. One revolution cycle time of a damaged tire and period that calculated auto-correlation function appeared equally in experiment. The result that can classification whether or not there was a tire damage is established.

W/C Ratio Effects on Mechanical Properties of High Performance hybrid SC and PE Fibers Reinforced Cement Composites (물-시멘트비에 따른 하이브리드 섬유보강 고인성 시멘트 복합체의 역학적 특성)

  • Yun, Hyun-Do;Kim, Sun-Woo;Cheon, Esther;Lee, Sang-Soo
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05a
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    • pp.118-121
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    • 2006
  • The research reported here is concerned with the effects of the fiber combination condition and water/cement ratio on the mechanical properties of high performance fiber-reinforced cementitious composites(HPFRCC). An experimental investigation of the behavior of steel cords(SC) and SC and Polyethylene(PE) hybrid fiber reinforced cementitious material under compressive and tensile loading is presented. In this experimental research, the tensile and compressive strength and strain capacity of HPFRCC were selected using the cylindrical specimens. The results show that W/C ratio is a significant effect factor on the compressive and tensile performance of HPFRCC. The envelope curve concept applies to hybrid fiber-reinforced cementitious composites in tension just as it does to compressive stress-strain curve of fiber-reinforced cement composites. For practical purposes, the tensile envelope curve may be taken to be the same as the monotonic tensile stress-strain curve.

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The study on Properties of PZT-5A Probe (PZT-5A 탐촉자의 특성 분석)

  • Kim, Cheol-Su;Kim, Sang-Su;Song, Jun-Tea;Park, Young-Kwan;Lee, Jong-Duck
    • Proceedings of the KIEE Conference
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    • 1997.07d
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    • pp.1427-1429
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    • 1997
  • In this study, piezoelectric transducer were designed and manufactured using PZT-5A which have relatively high electromechanical coefficient. A epoxy is a good material as matching and backing layers. The envelope was reduced 60% as using matching layer and 76% as using matching and backing layer. NDT was successfully carried out for aluminum test pieces. Distance error and resolution of PZT-5A probe were improved as increasing frequency. Envelope was effectively reduced by backing layer but sensitiveness was poor.

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Non-Linear Behavior Analysis for Stratospheric Airship Envelope (성층권 비행선 기낭 막재료에 대한 비선형 거동 연구)

  • Suh Young Wook;Woo Kyeongsik
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2004.04a
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    • pp.87-90
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    • 2004
  • In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load­bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis with much higher non-linear elastic moduli. The difference was more distinguishable when the tow waviness was smaller.

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Thermoelastic Behaviors of Fabric Membrane Structures

  • Roh, Jin-Ho;Lee, Han-Geol;Lee, In
    • Advanced Composite Materials
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    • v.17 no.4
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    • pp.319-332
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    • 2008
  • The thermoelastic behaviors of an inflatable fabric membrane structure for use in a stratospheric airship envelope are experimentally and numerically investigated. Mechanical tensile properties of the membrane material at room, high, and low temperatures are measured using an $Instron^{(R)}$ universal testing machine and an $Instron^{(R)}$ thermal chamber. To characterize the nonlinear behavior of the inflated membrane structure due to wrinkling, the bending behavior of an inflated cylindrical boom made of a fabric membrane is observed at various pressure levels. Moreover, the envelope of a stratospheric airship is numerically modeled based on the thermoelastic properties of the fabric membrane obtained from experimental data, and the wrinkled deformed shape induced by a thermal load is analyzed.

A Study on PZT-5A Probe for Nondestructive Inspection (비파괴검사를 위한 PZT 5A 탐촉자에 관한 연구)

  • 황현석;정규원;이종덕;송준태
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1996.11a
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    • pp.245-248
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    • 1996
  • In this study, piezoelectric transducers were designed and manufactured using PZT-5A which had relatively high electromechanical coefficient, NDT system was developed with was able to inspect automatically using stepping motors, PC-Lab, and PC-Scope The optimum design conditions for NDT were presented and verified comparing PZT-5A probes with comercial probes. It was proved with comercial probes. It was proved by simulation and experiments that Epoxy is good as material of matching and backing layers. The envelope was reduced 60% with matching layer and 76% with matching and backing layer. NDT was successfully carried out for aluminum test pieces. Distance error of PZT-5A probe was 2.8%.

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Non-Linear Behavior Analysis for Stratospheric Airship Envelope (성층권 비행선 기낭 막재료에 대한 비선형 거동 연구)

  • Suh Young Wook;Woo Kyeongsik
    • Composites Research
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    • v.18 no.2
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    • pp.30-37
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    • 2005
  • In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load-bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis. And non-linear elastic moduli were much higher than linear elastic moduli. The difference was more distinguishable when the tow waviness ratio was smaller.