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Wind-induced instabilities and monitoring of wind turbine

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Earthquake Engineering and Engineering Vibration 2019年第2期18卷 475-485页

作者： isaac Wait Zhaohui (Joey) Yang Gang Chen Benjamin Still College of IT & Engineering Marshall University Department of Civil Engineering University of Alaska Anchorage

This paper presents real-time monitoring data and analysis results of the non-stationary vibrations of an operational wind turbine. The advanced time-frequency spectrum analysis reveals varied non-stationary vibrations with timevarying frequencies, which are correlated with certain system natural modes characterized by finite element analysis. Under the effects of strong wind load, the wind turbine system exhibits certain resonances due to blade passing excitations. The system also exhibits certain instabilities due to the coupling of the tower bending modes and blade flapwise mode with blade passing excitations under the variation of wind speed. An analytical model is used to elaborate the non-stationary and instability phenomena observed in experimental results. The properties of the nonlinear instabilities are evaluated by using Lyapunov exponent estimation.

关键词： wind turbine condition monitoring non-stationary vibrations instabilities whirl modes warm permafrost

Multimodal label-free microscopy

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Journal of Innovative Optical Health Sciences 2014年第5期7卷 17-38页

作者： Nicolas Pavillon Katsumasa Fujita Nicholas isaac Smith Biophotonics LaboratoryImmunology Frontier Research Center(IFReC Department of Applied Physics Osaka UniversitySuitaOsaka 565-0871Japan

This paper reviews the different multimodal applications based on a large ext ent of label-freeinaging modalities,ranging from linear to nonlinear optics,while also inchuding *** put specific emphasis on multimodal measurements going across the usual boundaries between imaging modalities,whereas most multimodal platforms combine techniquesbased on similar light interactions or similar hardware *** this review,we limitthe scope to focus on applications for biology such as live cells or tissues,since by their nat ure ofbeing alive or fragile,we are often not free to take liberties with the image acquisition times andare forced to gather the maximum amount of information possible at one *** such samples,imaging by a given label-free method usually presents a challenge in obt aining suficient opticalsignal or is limited in terms of the types of observable *** imaging is thenparticularly attractive for these samples in order to maximize the amount of measured *** multimodal imaging is always useful in the sense of acquiring additional infor-mation from additional modes,at times it is possible to attain information that could not bediscovered using any single mode alone,which is the essence of the progress that is possible usinga multimodal approach.

关键词： Optical microscopy nonlinear optics microspectroscopy

Design and Implementation of Smart Power Voltage and Frequency Synchroniser in Power Distribution System

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Journal of Power and Energy Engineering 2023年第4期11卷 1-16页

作者： isaac Kofi Mensah Prah Joseph Cudjoe Attachie Electrical and Electronic Engineering Department University of Mines and Technology Tarkwa Ghana

Voltage and frequency are usually considered and assessed independently in the design and operation of electrical networks. However, these two are linked. Each and every malfunctioning electrical system has an impact on both voltage and frequency. This paper presents the opportunity for monitoring the distributed electrical energy by means of a system that monitors, controls, and provides a breakpoint based on high or low voltage and frequency tripping mechanism that avoids any damage to the load. The designed system comprised a switch mode power supply (SMPS), a direct digital synthesizer (DDS), and PIC16F876A microcontroller techniques for stable voltage and frequency outputs. Proteus design suite version 8.11 software and Benchcope SDS1102CN were used for modeling and simulation. The hardware prototype was implemented at a telecom cell site for data capturing and analysis. Test results showed that the implementation of the prototype provided stable and constant outputs of 222 V/50 Hz and 112 V/60 Hz which constituted 99% and 99.8% efficiency for voltage and frequency performance respectively. The paper also discusses different technologies that can be adopted by the system to mitigate voltage and frequency effects on customer appliances.

关键词： Switch Mode Power Supply Direct Digital Synthesis Pulse Width Modulation H-Bridge Mosfet Microcontroller Filtering and Rectification

A Cytogenetic Analysis of Enteromius parablabes (Daget, 1957) from Aho Stream, Ile-Ife, Nigeria

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Open Journal of Genetics 2022年第3期12卷 25-32页

作者： Michael Olaoluwa Popoola Oluwatomisin Awe Idowu isaac Adeniran Department of Zoology Obafemi Awolowo University Ile-Ife Nigeria

In this study, Enteromius parablabes [1] was analyzed with the aim of providing baseline information regarding the diploid chromosome number and karyotype differences of both sexes. The diploid chromosome number (2n) was 50 for both sexes, and this corresponds to the diploid chromosome number reported for most small African Barbus species. The fundamental number (NFa) of the male and female was 81 and 98 respectively. The first pair of metaphase chromosomes which has been suggested to be a marker for the small African Barbus group was conspicuously larger in the female karyotype. The karyotype of the female consisted more of metacentric (39m + 7sm + 2st + 2t) which is common in the group while the karyotype of the male which consisted more of telocentric chromosomes (10m + 21st + 19T) is scarce. The chromosomal number obtained for E. parablabes demonstrates its diploid status in the context of the ploidy lines characteristic of the African Barbus assemblage.

关键词： Karyotype Barbus Taxonomy Africa Chromosome

The Hydration Kinetics of Selected Ghanaian Maize (<i>Zea mays</i>L.) Hybrids

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Open Journal of Applied Sciences 2022年第1期12卷 99-110页

作者： isaac Godfred Antwi Ahmad Addo Ato Bart-Plange Department of Agricultural and Biosystems Engineering Kwame Nkrumah University of Science and Technology Kumasi Ghana

Water absorption characteristics of maize (Abotem, Abeleehi, and Dorke SR) hybrids grown in Ghana were investigated using models obtained from Fick’s law of diffusion. The maize kernels were soaked in water at four different temperatures of 30ºC, 40ºC, 50ºC and 60ºC to evaluate their water absorption behaviours. The results indicated that temperature and variety were the major factors controlling water absorption patterns. The diffusion coefficients of the hybrids were found to differ in the order of Dorke SR > Abeleehi > Abotem and increased as the soaking temperature increased. The calculated water diffusivities varied from (2.54 - 3.49) × 10-10 m2/s for Abotem, (2.64 - 3.59) × 10-10 m2/s for Abeleehi, (3.21 - 4.20) × 10-10/s for Dorke SR. The Arrhenius- type equation was able to describe the strong effect of temperature on the diffusion coefficient of the hybrids. The activation energy values obtained were7.50 kJ/mol for Abeleehi, 6.27 kJ/mol for Dorke SR and 9.09 kJ/mol for Abotem. Results indicated that temperature and variety were the major factors controlling water a

关键词： Maize Water Absorption Diffusion Coefficient Activation Energy

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新能源高渗透率电力系统的频率响应

新能源高渗透率电力系统的频率响应

作者： isaac Adjei Nketsiah 华北电力大学(北京)

学位级别：硕士

发电厂排放物是生产过程中重要的污染源。由于传统发电厂消耗大量化石燃料的同时产生大量污染,因此采用可再生清洁能源替代化石燃料是必要的。但是高渗透率可再生能源（RES）接入弱电网中,会威胁系统的整体稳定性和可靠性。由于大量使... 详细信息

发电厂排放物是生产过程中重要的污染源。由于传统发电厂消耗大量化石燃料的同时产生大量污染,因此采用可再生清洁能源替代化石燃料是必要的。但是高渗透率可再生能源（RES）接入弱电网中,会威胁系统的整体稳定性和可靠性。由于大量使用基于逆变器的电力电子设备,在转动惯量不存在或很小的情况下,系统阻尼特性和维持频率支撑等稳定性考虑更具挑战性。惯性不足对电网的稳定性构成了许多威胁,其中一个关键的问题是频率不稳定。频率稳定性受到系统惯性和频率储备的功率不平衡的不利影响,需要针对频率响应展开研究以确保频率稳定性。人们对于低惯量互联电力系统能够保留足够的PFR储备以响应可信事件并保持一定运行可靠性的能力表示非常关注。本工作旨在为电网发生突发事件后提供合适的解决方案。虚拟惯性由储能系统（ESS）提供,向电网提供大量惯性以确保稳定性。模糊逻辑控制器被用于观察VSC内的扰动。飞轮储能系统（FESS）被用于在突发事件后提供快速的频率响应。

关键词：可再生能源(RES) 储能系统(ESS) 模糊逻辑控制(FLC) 电压源变换器(VSC) 飞轮储能系统(FESS)

Occupational Health Hazards among Large-Scale Gold Mineworkers in Ghana

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Occupational Diseases and Environmental Medicine 2022年第3期10卷 149-166页

作者： Emmanuel Dartey isaac Monney Kofi Sarpong Collins Kuffour Department of Chemistry Education Akenten Appiah-Menka University of Skills Training and Entrepreneurial Development Mampong Ashanti Ghana Department of Environmental Health and Sanitation Education Akenten Appiah-Menka University of Skills Training and Entrepreneurial Development Mampong Ashanti Ghana

Introduction: The mining industry ranks among the most hazardous occupations globally owing to the high prevalence of workplace accidents. To better protect workers in the industry, there is a need for a comprehensive understanding of risk factors, common illnesses and provision of PPE. Objective: This study examined the prevalence and underlying risk factors to work-related injuries, common illnesses, and Personal Protective Equipment (PPE) usage among mineworkers in two large-scale mining companies in Ghana that consented to participation. Methodology: Two hundred mineworkers were selected through stratified sampling in these companies using a semi-structured questionnaire. Chi-square test and binomial logistic regression were employed to determine the relationship between the incidence of occupational injury and selected risk factors using R studio. Results: The results showed that more than a tenth (16%;n = 31) of mineworkers had sustained physical injuries since being employed—mostly lacerations (53%). Out of those injured, (85%;n = 22) reportedly sustain an injury annually. A little more than half (57%;n = 112) of the mineworkers work for more than 40 hours per week. Injuries were significantly associated with the type of profession at the mine (p = 0.04;χ2 = 4.3)—Technicians and Mechanics were more likely to be injured. Although not statistically significant, working for more than 40 hours/week doubled the odds of being injured at the workplace (aOR = 1.77;95% CI: -0.27 - 1.48). The topmost illnesses among mineworkers were musculoskeletal pains (MSPs) [53%] and headaches (35%). About two-thirds (65%) had all the needed PPEs for their work. Safety goggles were the predominant PPE reportedly lacking among the mineworkers (16%;n = 31). Conclusion: There is a need for targeted training/intervention programmes and adoption of assistive ergonomic devices to protect mineworkers.

关键词： Occupational Health Safety Gold Mining Injury Illnesses Ghana

平稳过程下的股票交易与风险对冲策略——乌干达证券交易所案例研究

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平稳过程下的股票交易与风险对冲策略——乌干达证券交易所案例研...

作者： WATANDA ODOI isaac 大连海事大学

学位级别：硕士

风险是投资领域中不可避免的变量,因为投资者寻求如何有效地对冲风险。在股市中,风险是不可避免的,因为股票往往波动很大。本研究旨在确定可用于对冲风险的最合适的风险措施。该研究是根据USE Local股票指数从7/3/2017到21/02/2022期间... 详细信息

风险是投资领域中不可避免的变量,因为投资者寻求如何有效地对冲风险。在股市中,风险是不可避免的,因为股票往往波动很大。本研究旨在确定可用于对冲风险的最合适的风险措施。该研究是根据USE Local股票指数从7/3/2017到21/02/2022期间使用从八家上市公司的非洲金融网站获得的乌干达证券交易所的历史数据进行的.然后(?)历史数据收集到excel工作簿中,并使用excel电子表格进行进一步分析。该研究通过构建最优投资组合,采用多元化作为风险对冲策略。马科维茨的现代投资组合理论运用了通过资产的最优投资组合构建实现多元化的原则。这是因为投资者专注于其资产的最佳投资组合构建,他们能够对冲非系统性风险。由于该研究考虑了USE的研究,它由不同种类的股票组成,投资者在这些股票中采用不同的最优投资组合的构建作为对冲持续市场风险的一种方式。投资组合由传统的MAD、Mean-CVaR和MV模型构建而成,这些模型经过优化以构建最优投资组合。研究构建的最优投资组合以确定最适合股票市场的投资组合。最佳投资组合的风险度量是使用风险价值、方差、协方差和CVaR来衡量的。MV、MAD的最佳模型显示出不同的结果,但Mean-CVaR模型除外,其风险是使用CVaR测量的,因为它给出了最低值0.586风险作为其适当的风险测量。Mean-CVaR模型在所有三个模型中的性能最高,为111.8%,因为它具有最低的风险0.5816和最高的期望值0.65。因此,股票交易中的风险可以通过多元化来对冲,这保证了最佳性能,就像在USE Mean-CVaR模型中为投资者提供最佳回报一样。

关键词：多元化股市固定过程风险协方差风险价值

Capital Adequacy,Deposits and Lending Behavior of Banking Systems——A Country Level Study in Sub-saharan Africa

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Capital Adequacy,Deposits and Lending Behavior of Banking Sy...

作者： isaac AKPEMAH BATHUURE 江苏大学

学位级别：硕士

资本充足率是保障商业银行稳健运行的主要基础。银行系统故障有可能使一个国家的经济增长停滞,包括非洲经济在内的许多经济体并未免受银行系统脆弱系统的灾难性影响。本研究的主要目的是研究银行的资本充足率如何影响国家级研究中非洲... 详细信息

资本充足率是保障商业银行稳健运行的主要基础。银行系统故障有可能使一个国家的经济增长停滞,包括非洲经济在内的许多经济体并未免受银行系统脆弱系统的灾难性影响。本研究的主要目的是研究银行的资本充足率如何影响国家级研究中非洲背景下银行系统存款和贷款的决策。论文采用固定效应和随机效应回归模型测度资本要求和银行存款/贷款的影响,其中以银行存款和贷款作为因变量。同时使用Pearson相关性检验,对25个非洲国家样本银行在2000年至2017年期间资本充足率对银行系统存款和贷款的影响方向和影响强度进行分析。论文具体分析了利率、金融稳定性、资本充足率等各自变量对以银行存贷款为代表的银行存贷款行为的影响,包括涉及低GDP国家、高GDP国家和所有国家的存款和银行贷款模型。分析表明,无论是高GDP还是低GDP国家,CAR都与银行存款呈正相关。这一研究表明,这些国家的银行存款并不是银行的主要资金来源。但另一方面,CAR对银行贷款有积极影响,也被用作银行存贷款的衡量指标之一。论文研究揭示了一个有趣的现象,决策者需要通过衡量决策进行战略性考虑。这是因为已有研究表明,在低GDP和高GDP国家,CAR与银行存款呈负相关。这一发现的主要意义是,这些国家的银行存款并不是银行的主要资金来源。为了让政策制定者在不影响贷款或存款的情况下充分了解银行在CAR方面的行为,应就CAR做出战略性和审慎的决策。最重要的是,鉴于不同环境下资本要求的不同结果;低GDP和高GDP,在设定适当的资本要求水平时应考虑经济规模。

关键词：借贷行为资本充足率存款行为银行规模撒哈拉以南非洲