• Title/Summary/Keyword: cyclic service

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Performance of Multi-User MIMO/OFDM System using Cyclic Delay Diversity for Fading Channels (페이딩 채널에서 순환 지연 다이버시티를 적용한 다중 사용자 MIMO OFDM 시스템의 성능)

  • Park, In-Hwan;Kim, Yoon-Hyun;Kim, Jin-Young
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.10 no.6
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    • pp.263-268
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    • 2010
  • As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. In this paper, we propose a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with cyclic delay diversity and block diagonalization procoding method to improve bit error rate (BER) performance with wireless local area network (WLAN) channel model C and D for 802.11n WLAN system. The results of mathlab simulation show the improvement of BER performance in 802.11n wireless indoor channel environment.

Fatigue Crack and Delamination Behavior in the Composite Material Containing n Saw-cut and Circular Hole (I) - Aramid Fiber Reinforced Metal Laminates - (소컷 및 원공 주위의 피로균열 형태변화와 층간분리거동 (I) - 아라미드섬유 강화 금속적층재의 경우 -)

  • Song, Sam-Hong;Kim, Cheol-Woong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.1
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    • pp.58-65
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    • 2003
  • The aramid fiber reinforced metal laminates(AFRMLs) used for the wing part fair flight suffer the cyclic bending moment of variable amplitude during service. The fatigue crack propagation and delamination behavior in AFRMLs containing a saw-cut and circular hole was investigated using the average stress criterion(ASC) model. Mechanical tests were carried out using the cyclic bending moment of 4.9 N . m and delamination was observed by ultrasonic C-scan images. In case of AFRMLs containing a saw-cut fatigue crack propagated in aluminum matrix, inducing delamination. However, in case of AFRMLs containing a circular hole, delamination formed with two types under cyclic bending moment of 4.9 N . m. First, delamination formed along the fatigue crack in aluminum matrix. Second, delamination formed without any fatigue crack around the circular hole. Therefore, delamination was formed depending on the stress distribution near the circular hole.

Ageing assessment of zirconia implant prostheses by three different quantitative assessment techniques

  • Kyaw, Phyu Phyu;Pongprueksa, Pong;Anuchitolarn, Warangkana;Sirinukunwatta, Krongkarn;Suputtamongkol, Kallaya
    • The Journal of Advanced Prosthodontics
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    • v.11 no.5
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    • pp.253-261
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    • 2019
  • PURPOSE. To evaluate the influence of cyclic loading on phase transformation of zirconia abutments and to compare the effectiveness of three different quantitative ageing assessment techniques. MATERIALS AND METHODS. Thirty two Y-TZP prostheses fabricated from two brands, InCoris ZI and Ceramill ZI, were cemented to titanium bases and equally divided into two subgroups (n=8): control group without any treatment and aged group with cyclic loading between 20 N and 98 N for 100,000 cycles at 4 Hz in distilled water at $37^{\circ}C$. The tetragonal-to-monoclinic phase transformation was assessed by (i) conventional x-ray diffraction (XRD), (ii) micro x-ray diffraction (${\mu}XRD$), and (iii) micro-Raman spectroscopy. The monoclinic-phase fractions (M%) were compared by two-way ANOVA. RESULTS. InCoris Zi presented significantly higher M% than Ceramill Zi in both control and aged groups (P<.001). Both materials exhibited significant phase transformation with monoclinicphase of 1 to 3% more in aged groups than controls for all three assessment techniques. The comparable M% was quantified by both ${\mu}XRD$ and XRD. The highest M% was assessed with micro-Raman. CONCLUSION. Cyclic loading produced significant phase transformation in tested Y-TZP prostheses. The micro-Raman spectroscopy could be used as an alternative to XRD and ${\mu}XRD$.

The Delamination and Fatigue Crack Propagation Behavior in A15052/AFRP Laminates Under Cyclic Bending Moment (반복-굽힘 모멘트의 진폭에 따른 A15052/AFRP 적층재의 층간분리 영역과 피로균열진전 거동)

  • Song, Sam-Hong;Kim, Cheol-Ung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.8
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    • pp.1277-1286
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    • 2001
  • Aluminum 5052/Aramid Fiber Reinforced Plastic(Al5052/AFRP) laminates are applied to the fuselage-wing intersection. The Al5052/AFRP laminates suffer from the cyclic bending moment of variable amplitude during the service. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in Al5052/AFRP laminate was investigated in this study. Al5052/AFRP laminate composite consists of three thin sheets of Al5052 and two layers of unidirectional aramid fibers. The cyclic bending moment fatigue tests were performed with five different levels of bending moment. The shape and size of the delamination zone formed along the fatigue crack between Al5052 sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging mechanism and the delamination zone were studied. Fiber failures were not observed in the delamination zone in this study. It represents that the fiber bridging modification factor should turn out to increase and that the fatigue crack growth rate should decrease. The shape of delamination zone turns out to be semi-elliptic with the contour decreased non-linearly toward the crack tip.

Service Restoration In Distribution Networks Using Cyclic Best-First Search (순환적 최적우선탐색을 이용한 배전계통의 정전복구)

  • Choi, Sang-Yule
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.18 no.5
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    • pp.162-168
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    • 2004
  • Service restoration is an emergency control in distribution control centers to restore out-of-service area as soon as possible when a fault occurs in distribution networks. Therefore, it requires fast computation time and high quality solutions for load balancing. In this paper, a load balance index and heuristic guided best-first search are proposed for these problem. The proposed algorithm consists of two parts. One is to set up a decision tree to represent the various switching operations available. Another is to identify the most effective the set of switches using proposed search technique and a feeder load balance index. Test results on the KEPCO's 108 bus distribution system show that the performance is efficient and robust.

Cyclic Polling-Based Dynamic Bandwidth Allocation for Differentiated Classes of Service in Ethernet Passive Optical Networks (EPON망에서 차등 CoS 제공을 위한 주기적 폴링 기반의 동적 대역 할당 방법)

  • 최수일
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.7B
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    • pp.620-627
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    • 2003
  • Ethernet passive optical networks (EPONs) are an emerging access network technology that provide a low-cost method of deploying optical access lines between a carrier's central office and customer sites. Dynamic bandwidth allocation (DBA) provides statistical multiplexing between the optical network units for efficient upstream channel utilization. To support dynamic bandwidth distribution, 1 propose an cyclic polling-based DBA algorithm for differentiated classes of service in EPONs. And, I show that an interleaved polling scheme severely decreases downstream channel capacity for user traffics when the upstream network load is low. To obtain realistic simulation results, I used synthetic traffic that exhibits the properties of self-similarity and long-range dependence I then analyzed the network performance under various loads, specifically focusing on packet delays for different classes of traffic.

A Study on Fatigue Crack Propagation Behavior in Random Short-Fiber SMC Composites (비규칙 단섬유강화 SMC 복합재료의 피로균열 전파거동에 관한 연구)

  • Kim, Jae-Dong;Koh, Sung-Wi
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.26 no.2
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    • pp.204-212
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    • 1990
  • The SMC composite, now being considered in certain structural applications, is anticipated to experience repeated loading during service. Thus, understanding of the fatigue behavior is essential in proper use of the composite material. In this paper, using the SMC composite composed of E-glass chopped strand and unsaturated polyester resin three point bending fatigue tests are carried out to investigate the fatigue crack propagating behavior under various cyclic stresses and fatigue damage of various microcrack forms. The following results are obtained from this study; 1) Most of the total fatigue life of the SMC composite is consumed at the initial extension or the growth of the macroscopic crack. 2) A Paris' type power-law relationship between the crack propagation rate and stress intensity factor range is obtained, and the value of material constant m is much higher (m=9~11)than that of other metals. 3) In case of high cyclic stress the fatigue damage show high microcrack density and short crack length, but in case of low cyclic stress does it vice versa. 4) Fatigue damage is characterized by microcrack density, crack length and distribution of crack orientation.

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A Quantitative Estimation of Welding Residual Stress Relaxation for Fatigue Strength Analysis (피로강도해석을 위한 용접잔류응력 이완의 정량적 평가)

  • Han, Seung-Ho;Lee, Tak-Kee;Shin, Byung-Chun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.10
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    • pp.2018-2025
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    • 2002
  • It is well known that the strength and the fatigue life of welded steel components are affected extensively by welding residual stresses distributed around their weldments under not only monotonic but also cyclic loads. The externally applied loads are to be superimposed with the welding residual stresses, so that unexpected deformations and failures of the components might occur. These residual stresses are not kept constant, but relaxed or redistributed during in service. Under monotonic loads the relaxation takes place when the sum of external and welding residual stress exceeds locally the yield stress of material used. By the way, it is shown that under cyclic loads the welding residual stress is considerably relieved by the first or the early cycles of loads, and then gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon and mechanism of the stress relaxation are still not clear, and there are few comprehensive models to predict amount of relaxed welding residual stress. In this study, the characteristics of the welding residual stress relaxation under monotonic and cyclic loads were investigated, and a model to predict quantitatively amount of welding residual stress relaxation was proposed.

Mean Waiting Time Analysis of Cyclic Server System under N-Policy (N-정책하의 순환 서비스시스템의 평균대기시간 분석)

  • 홍정완;이창훈
    • Journal of the Korean Operations Research and Management Science Society
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    • v.18 no.3
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    • pp.51-63
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    • 1993
  • We consider a cyclid server system under N-policy. This system consists of multiple queues served in a cyclic order by a single server. In this paper, we consider the following control policy. Every time server polls one queue, the server inspects the state of the queue. If the total number of units is found to have reached or exceeded a pre-specified value, the server begins to serve the queue until it is empty. As soon as the queue becomes empty, the server polls next queue. An approximate analysis of this system is presented. Sever vacation model is used as an analytical tool. However, server vacation periods are considered to be dependent on the service times of respective queues. The results obtained from the approximate analysis are ompared with simulation results.

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Effects of Drying Methods on the Quality and Physiological Activities of Blueberry(Vaccinium ashei) (건조방법에 따른 블루베리의 품질 및 생리활성)

  • Park, Sung-Jin;Choi, Young-Bum;Ko, Jung-Rim;Rha, Young-Ah;Lee, Hyeon-Yong
    • Culinary science and hospitality research
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    • v.20 no.1
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    • pp.55-64
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    • 2014
  • This study was performed to determine the effects of drying methods on the quality and physiological activities of blueberry. Blueberries(Vaccinium ashei) were dried by hot-air ($60^{\circ}C$), cyclic low pressure ($50^{\circ}C$), and freeze drying methods. They contained high properties of carbohydrates(68.48~80.00%), crude protein(1.63~5.41%), crude fat(0.58~1.25%), and ash(0.71~1.11%) regardless of the drying methods. There were no differences in pH according to the drying methods. Browning index increased as the drying temperature increased. The L, a values of the freeze-dried sample were higher than those of the other dried samples, whereas the b value of the cyclic low pressure dried sample was higher than that of the other samples. The free sugar contents of the hot-air sample were higher than those of the other samples. Vitamin C content of the freeze dried sample was higher than that of either the hot-air or cyclic low pressure dried sample. The contents of total polyphenols and anthocyanins were higher in the freeze dried sample. The DPPH radical scavenging activity of freeze drying sample was higher than that of either the hot-air or cyclic low pressure dried sample. The result indicated that there were no differences in product quality depending on the freeze-drying and cyclic low pressure drying methods.