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71.
机械结构结合部精确建模是对含结合部的机械结构进行动态分析和优化设计的关键问题之一。文章主要研究块体结构和平板由螺栓联接后构成的固定结合部的动力学建模问题。将结合部区域的刚度特性用结合部的材料机械特性参数等效表达,提出了虚拟接触材料的结合部刚度表达模型。通过模态实验和模型修正识别出不同结合面工况下虚拟接触材料的弹性模量,建立了含结合部动力特性的有限元模型。该模型可方便用于含结合部结构的有限元计算,经试验验证满足实际工程应用要求。 相似文献
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73.
Hyunkyu Park Sojung Kim Yujin Jeong Tim Minshall 《Creativity & Innovation Management》2021,30(1):96-115
Drawing on the mixed methods of qualitative research and agent‐based simulation, this study examines: (a) how end‐users use digital platforms to become customer–entrepreneurs undertaking commercial activities on platforms; and (b) how platform providers can convert this customer entrepreneurship into a revenue stream. Considering that end‐users have traditionally been defined as passive and uncharged actors in platform business models, an in‐depth understanding of their commercial activities and the viable revenue model to monetize this emerging customer practice is warranted. Our qualitative study reveals that customer–entrepreneurs make substantial use of platform offerings to advertise their products; communicate with end‐consumers; and accept payments. These commercial activities are largely exercised for free on platforms, even though they could otherwise serve as a source of revenue. On this point, our simulation results identify two pricing models achieving the generation of nearly identical revenues over time. First, platform providers may charge both advertising and transaction fees, which maximize the survival of professional customer–entrepreneurs. Second, platform businesses may levy advertising fees only, which maximizes the survival of informal customer–entrepreneurs operating on a micro‐scale and part‐time basis. This study offers theoretical, methodological, and managerial implications for platform studies. 相似文献
74.
Current applications of electronic performance monitoring based on job design theories that consider worker performance rather than stress issues are likely to generate unsatisfying and stressful jobs (Smith et al, 1986). This study examines critical job design elements that could influence worker stress responses in an electronic monitoring context. A questionnaire survey of employees in telecommunications companies representative of each region in the United States examined job stress in directory assistance, service representative and clerical jobs with specific emphasis on the influence of electronic monitoring of job performance, satisfaction and employee health. Useable surveys were received from 745 employees representing seven operating companies and AT & T; a response rate of about 25%. The results of this survey indicated that employees who had their performance electronically monitored perceived their working conditions as more stressful, and reported higher levels of job boredom, psychological tension, anxiety, depression, anger, health complaints and fatigue. It is postulated that these effects may be related to changes in job design due to electronic performance monitoring. 相似文献
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76.
Yeonsil Moon Changmok Lim Yeahoon Kim Won-Jin Moon 《International journal of molecular sciences》2021,22(6)
The role of the blood–brain barrier (BBB) breakdown has been recognized as being important in Alzheimer’s disease pathogenesis. We aimed to evaluate whether regional BBB integrity differed according to sex and whether differences in BBB integrity changed as a consequence of aging or cognitive decline, using dynamic contrast-enhanced (DCE)-magnetic resonance imaging (MRI). In total, 75 participants with normal cognition (NC) or mild cognitive impairment (MCI) underwent cognitive assessments and MRI examination including DCE-MRI. Regional Ktrans was calculated in cortical regions and the Patlak permeability model was used to calculate BBB permeability (Ktrans, min−1). Females had a lower median Ktrans in the cingulate and occipital cortices. In the “older old” group, sex differences in Ktrans were only observed in the occipital cortex. In the MCI group, sex differences in Ktrans were only observed in the occipital cortex. Age was the only predictor of cognitive assessment scores in the male MCI group; however, educational years and Ktrans in the occipital cortex could predict cognitive scores in the female MCI group. Our study revealed that females may have better BBB integrity in cingulate and occipital cortices. We also found that sex-related differences in BBB integrity are attenuated with aging or cognitive decline. 相似文献
77.
Kin Kit Fong Inn Shi Tan Henry Chee Yew Foo Man Kee Lam Adrian Chiong Yuh Tiong Steven Lim 《中国化学工程学报》2021,33(5):297-305
The rising production of produced water from oilfields had been proven to bring detrimental environmental effects. In this study, an efficient, recyclable, and environmental-friendly reduced graphene oxide immobilized κ-Carrageenan hydrogel composite(κCa GO) was fabricated as an alternative sorbent for crude oil-in-water demulsification. Polyethyleneimine(PEI) was employed to form a stable hydrogel composite. The conditions for the immobilization of graphene oxide(GO) on PEI-modified κ-Carrageenan(κC) beads were optimized appropriately. An immobilization yield of 77% was attained at 2% PEI, 2 h immobilization activation time, and p H6.5. Moreover, the synthesized κCa GO is capable of demulsification with an average demulsification efficiency of 70%. It was found that the demulsification efficiency increases with salinity and κCa GO dosage, and it deteriorates under alkaline condition. These phenomena can be attributed to the interfacial interactions between κCa GO and the emulsion. Furthermore, the κCa GO can be recycled to use for up to six cycles without significant leaching and degradation. As such, the synthesized κCa GO could be further developed as a potential sorbent substitute for the separation of crude oil from produced water. 相似文献
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80.
Jeung -Soo Huh Jae -Chang Kim Jeong -Ok Lim K. F. Jensen 《Metals and Materials International》1997,3(2):103-107
The growth of high quality ZnSe by organometallic vapor phase epitaxy (OMVPE) has been investigated fortertiary-butyl allyl selenide (tBASe), combined with dimethylzinc-triethylamine (DMZn : NEt3). Single crystalline ZnSe films were grown on GaAs at temperature as low as 350°C with a reasonable growth rate (~1 µm/h). Secondary ion mass spectrometry (SIMS) spectra show a negligible carbon incorporation in ZnSe films from tBASe even at high VI/II ratio, in contrast the carbon concentration of 1021 cm-3 in ZnSe films grown from diallyl selenide (DASe)and methylallylselenide (MASe). Good surface morphology, crystalline and interface quality of ZnSe on (001) GaAs are confirmed by scanning electron microscopy, double crystal diffractometry (DCD) and Rutherford backscattering spectrometry (RBS). Photoluminescence at 10K shows sharp near-band-edge excitonic spectra. 相似文献