• ALGAE
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• 제39권2호
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• pp.109-127
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• 2024

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO₂ and O₂. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydae production gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000-8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0-4.0 L min^-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

• Advances in Computational Design
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• 제1권2호
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• pp.155-173
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• 2016

This paper presents a method of design for the energy harvesting of a piezoelectric cantilever beam. Vibration modes have strain nodes where the strain distribution changes in the direction of the beam length. Covering the strain nodes of the vibration modes with continuous electrodes effects a cancellation of the voltages outputs. The use of segmented electrodes avoids cancellations of the voltage for multi-mode vibration. The resistive load affects the voltage and generated power. The optimum resistive load is considered for segmented and continuous electrodes, and then the power output is verified. One of the effective parameters on energy harvesting performance is the existence of concentrated mass. This topic is studied in this paper. Resonance and off-resonance cases are considered for the harvester. In this paper, both theoretical and experimental methods are used for satisfactory results.

• Journal of Communications and Networks
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• 제14권2호
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• pp.130-139
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• 2012

Energy harvesting has emerged as a powerful technology for complementing current battery-powered communication systems in order to extend their lifetime. In this paper a general framework is introduced for the optimization of communication systems in which the transmitter is able to harvest energy from its environment. Assuming that the energy arrival process is known non-causally at the transmitter, the structure of the optimal transmission scheme, which maximizes the amount of transmitted data by a given deadline, is identified. Our framework includes models with continuous energy arrival as well as battery constraints. A battery that suffers from energy leakage is studied further, and the optimal transmission scheme is characterized for a constant leakage rate.

• International Journal of Reliability and Applications
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• 제3권2호
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• pp.61-80
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• 2002

Tree-harvesting worker data of 508 separate worker accidents are analyzed and an exploratory approach taken. The worker accident data cover a sample of five years. The scope of the study was the southeastern United States of America. As might be hypothesized, the chainsaw was the most hazardous type of tree-harvesting equipment. It accounted for 55％ of the tree-harvesting accidents. Most chainsaw accidents resulted in injuries to the lower extremities and were more frequent among younger employees. The probability of one or more chainsaw accidents occurring in any 30-day period was approximately 0.856. Chainsaw accidents were more likely to occur in late morning and early afternoon. We used statistical tools such as Pareto charts, c-charts and Ishikawa diagrams. Such tools are useful in diagnosing the root-cause of tree-harvesting worker accidents and help in developing preventive safety programs. Recommendations to help improve the quality of information of accident data collected by insurance companies and others are briefly given. The strategy and culture of continuous process improvements are stressed.

• 전력전자학회논문지
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• 제25권4호
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• pp.243-250
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• 2020

Energy harvesting is a recent technology involving the harvest and utilization of extremely small surrounding energy. Energy harvesting research is conducted in various fields. Triboelectric nanogenerators (TENGs) are energy harvesting technologies that use static electricity generated by physical movement or friction. Although TENGs generate output power in microwatt levels, they experience high internal impedance compared with other energy harvesting generators, thereby making the continuous transfer of electric power to loads difficult. This study proposes a power management system for TENGs that consists of three stages, that is, an AC/DC rectifier, an impedance coupler switch with a capacitor bank, and a DC/DC converter. In addition, the selection method of the AC/DC rectifier and DC/DC converter is proposed to maximize the amount of power transferred from energy harvesting areas. Furthermore, the impedance coupler switch and capacitor bank are discussed in detail. The validity and performance of the proposed three-stage power management system for TENGs are verified using a prototype system.

• Composites Research
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• 제34권6호
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• pp.400-405
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• 2021

본 연구에서는 인장 시 에너지 하베스팅을 하는 Polyvinylidene Fluoride(PVDF) 리본 하베스터를 신발에 접목한 스마트 슈즈의 에너지 하베스팅 효율을 증가시키기 위한 복합재료 프레임을 설계하였다. 프레임의 하중방향 변형량을 최소화하기 위해 이방성 재료인 탄소 연속 섬유를 사용하여 설계하고 3D 프린터를 이용하여 복잡한 형상을 제작하였다. 보행 시 발생하는 하중에 의한 안창과 중창의 변형량을 계산하기 위해 스프링 요소를 이용하여 안창과 중창을 모델링 하였다. 유한요소 해석을 사용하여 보행 시 스마트 슈즈에 장착된 리본형 하베스터의 인장량을 계산하였다. 예측된 하베스터의 최종 인장 길이 정보는 스마트 슈즈의 에너지 하베스팅 효율 증대에 활용할 수 있을 것으로 기대된다.

• Journal of applied mathematics & informatics
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• 제19권1_2호
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• pp.311-326
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• 2005

The paper deals with the problem of selective harvesting in a prey-predator model with predator self limitation. Criteria for local stability and global stability for both the exploited and unexploited system are derived. The effort has been considered as a dynamic variable and taxation as a control instrument to protect the fish populations from over exploitation. Finally, the optimal taxation policy is discussed with the help of control theory.

• 농업과학연구
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• 제49권4호
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• pp.785-793
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• 2022

In this study, tomato maturity was estimated based on deep learning for a harvesting robot. Tomato images were obtained using a RGB camera installed on a monitoring robot, which was developed previously, and the samples were cropped to 128 × 128 size images to generate a dataset for training the classification model. The classification model was constructed based on convolutional neural networks, and the mean-variance loss was used to learn implicitly the distribution of the data features by class. In the test stage, the tomato maturity was estimated as a continuous index, which has a range of 0 to 1, by calculating the expected class value. The results show that the F1-score of the classification was approximately 0.94, and the performance was similar to that of a deep learning-based classification task in the agriculture field. In addition, it was possible to estimate the distribution in each maturity stage. From the results, it was found that our approach can not only classify the discrete maturation stages of the tomatoes but also can estimate the continuous maturity.

• 농약과학회지
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• 제17권4호
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• pp.293-301
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• 2013

본 실험은 작물의 농약잔류성 포장시험 결과를 다른 소면적 작물로 외삽 할 수 있는지 알아보기 위하여 온실에서 재배되는 엽채소류를 대상으로 경엽살포 후 작물간 농약잔류 경향을 비교하였다. 배추속에 속하는 겨자채(Brassica juncea L.), 케일(Brassica oleracea L.), 다청채(a kind of pak-choi (Brassica rapa subsp. chinensis L.)), 잎 브로콜리(Brassica oleracea var alboglabra) 4종과 배추속이 아닌 들깻잎(Perilla frutescens Britt.), 상추(Lactuca sativa L.), 적근대(Beta vulgaris L. subsp. vulgaris) 및 적치커리(Cichorium intybus L. var. foliosum Hegi) 4종을 대상으로 하였다. 이들은 온실이나 노지에서 연중 재배되며 일정한 수확기 동안 연속적으로 잎을 따서 수확하는 작물들로서 시금치처럼 포기 형태로 일시에 수확하는 작물들과 구별된다. 무게 대비 엽면적 비율이 58 $cm^2/g$으로 가장 높은 들깻잎에서 imidacloprid 등 7종 농약의 잔류량이 살포 당일부터 5일 후 까지 가장 높았다. 따라서 식품의 일일섭취량 통계에 따른 섭취량이 일정 수준을 차지하면서 시험대상 8작물중 농약 잔류량이 상대적으로 높은 들깻잎을 농약잔류성시험의 대표작물로 선정하여 외삽 적용을 위한 작물 그룹을 제안한다.

• 한국전자통신학회논문지
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• 제14권1호
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• pp.225-234
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• 2019

마찰 나노 발전을 활용한 TENG(: Triboelectric nanogenerators)는 작은 진동에서 높은 변환 효율과 지속적인 전력을 얻을 수 있는 장점이 있다. 하지만, 마찰 전기 에너지 수집을 위해서는 비선형 에너지 추출 기술이 요구되며, 연결 인터페이스 회로를 통한 동기화 기반의 능동적인 스위치회로가 요구된다. 본 연구는 사람으로의 움직임으로부터 발생한 비선형(non-linear) 에너지를 효율적으로 저장하는 기법을 제시하였다. 또한, 개발된 보드는 서로 다른 방향으로 움직이는 동작으로부터 발생하는 에너지를 효율적으로 수확하고 저장할 수 있다. 본 연구에서 개발된 실리콘기반 압전기반의 TENG 셀과 다중모듈이 연결 가능한 에너지 하베스팅 보드의 측정하였다. 결과적으로, 다중입력 에너지 수집환경에서 안정적인 에너지의 저장 유지를 통해 약 49.2mW/count를 발전하였다.