• ETRI Journal
• /
• 제21권1호
• /
• pp.1-27
• /
• 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.

• 대한인간공학회지
• /
• 제34권4호
• /
• pp.313-326
• /
• 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.

• 한국건설관리학회논문집
• /
• 제14권4호
• /
• pp.84-96
• /
• 2013

최근 건설 산업의 디지털화로 인하여 건축 디자인이 정형에서 자유로운 비정형 형태로 변화하고 있다. 특히, 국내에서는 최근 비정형이 디자인 경향으로 도입되어 현상설계, 턴키 등에서 설계 당선을 위한 디자인 요소로 많이 적용되고 있다. 그러나 기존의 정형 건축물의 외벽공법을 비정형 건축물의 외피에 그대로 적용함으로써 누수 및 크랙 등 다양한 하자가 발생하고 있다. 이러한 문제점을 개선하고 공사기간과 공사비를 최소화할 수 있는 비정형 건축물의 설계와 시공이 새로운 기술로 도입되고 있다. 이에 본 연구는 비정형 외피시스템 구현을 위한 공법을 국내외 비정형 건축물의 외피시스템 사례 분석을 통하여 실증적으로 시사점을 도출하고 비정형 건축물 외피시스템의 설계와 시공시 고려해야 할 사항을 다음과 같이 제시하였다. 첫째, 시공성을 고려한 비정형 형태의 설계가 되도록 하여야 한다. 둘째, 2방향 곡면을 정확히 구현할 수 있는 단위 패널 생산 기술의 개발이 필요하다. 셋째, 비정형 콘크리트 외피용 노출 콘크리트 거푸집을 개발하여야 한다. 넷째, 외피 시스템을 부위별로 구분하여 우수처리와 방수를 위한 재료와 공법 특성과 유지관리 방안을 고려하여야 한다.

• 한국인터넷방송통신학회논문지
• /
• 제10권6호
• /
• pp.107-111
• /
• 2010

차량 주행 중에 타이어에서 발생하는 초음파를 이용하여 손상 물질에 의한 타이어의 손상을 검출하는 방법에 대해 연구하였다. 손상이 있는 타이어는 회전 주기성이 있는 초음파 신호가 발생하므로 주기성을 검출하기 위해 포락선 검출 전처리 과정을 거친 후 자기상관함수를 사용하였다. 실험에서는 손상된 타이어의 1회전 시간과 자기상관함수를 이용해 구한 주기가 같은 것으로 나타났다. 이로 인해 타이어의 손상 유무를 분별할 수 있는 결과를 도출하였다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
• /
• pp.118-121
• /
• 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.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1997년도 하계학술대회 논문집 C
• /
• pp.1427-1429
• /
• 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.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
• /
• pp.87-90
• /
• 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.

• Advanced Composite Materials
• /
• 제17권4호
• /
• pp.319-332
• /
• 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.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1996년도 추계학술대회 논문집
• /
• pp.245-248
• /
• 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%.

• Composites Research
• /
• 제18권2호
• /
• pp.30-37
• /
• 2005

본 논문에서는 평직구조를 갖는 성층권 비행선 기낭의 하중막재에 대한 비선형 유한요소 해석 결과를 기술하였다. 평직구조를 갖는 하중막재의 미세구조를 3차원적으로 구현하였고, Updated Lagrangian 방법을 사용하여 기하학적 비선형성을 고려하였다 계산결과, 큰 변형률에서 비선형해석으로부터 얻은 응력-변형률 곡선은 선형해석의 결과와 큰 차이를 보였다. 또한 응력-변형률 곡선으로부터 얻은 비선형 탄성계수 값은 선형 탄성계수보다 큰 값을 보였는데 그 차이는 섬유의 굴곡도가 작은 경우 더욱 두드러지게 나타났다