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On helical behavior of turbulence in the ship wake

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Journal of Hydrodynamics 2013年第1期25卷 83-90页

作者： GOLBRAIKH Ephim EIDELMAN alexander SOLOVIEV Alex Physics Department Ben-Gurion University of the Negev Mechanical Engineering Department Ben-Gurion University of the Negev Oceanographic Center NOVA South eastern University

Turbulent ship wake conservation at a long distance is among unsolved problems at present. It is well known that far wakes have a vortical structure and slowly expand with distance. As was obtained by Dubrovin et al., slow expansion of the wake may be related to the distribution of turbulent viscosity in it. In our work we study the effect of helicity in the wake on the behavior of turbulent viscosity. Taking into account the helical nature of the wake, we can clarify the difference between turbulence inside and outside the wake on the one hand and slowing down of its expansion with time on the other hand.

关键词： ship wake turbulent ship wake helical turbulence

Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants： A review

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Frontiers of Chemical Science and Engineering 2018年第3期12卷 564-576页

作者： Wenjin Ding alexander Bonk Thomas Bauer Institute of Engineering Thermodynamics German Aerospace Center (DLR) 70569 Stuttgart Germany Institute of Engineering Thermodynamics German Aerospace Center (DLR) 51147 Cologne Germany

Recently, more and more attention is paid on applications of molten chlorides in concentrated solar power （CSP） plants as high-temperature thermal energy storage （TES） and heat transfer fluid （HTF） materials due to their high thermal stability limits and low prices, compared to the commercial TES/HTF materials in CSP- nitrate salt mixtures. A higher TES/HTF operating temperature leads to higher efficiency of thermal to electrical energy conversion of the power block in CSP, however causes additional challenges, particularly increased corrosiveness of metallic alloys used as contain- ers and structural materials. Thus, it is essential to study corrosion behaviors and mechanisms of metallic alloys in molten chlorides at operating temperatures （500-800℃） for realizing the commercial application of molten chlorides in CSE The results of studies on hot corrosion of metallic alloys in molten chlorides are reviewed to understand their corrosion behaviors and mechanisms under various conditions （e.g., temperature, atmosphere）. Emphasis has also been given on salt purification to reduce corrosive impurities in molten chlorides and development of electrochemical techniques to in-situ monitor corrosive impurities in molten chlorides, in order to efficiently control corrosion rates of metallic alloys in molten chlorides to meet the requirements of industrial applications.

关键词： corrosion mechanisms impurities metallic corrosion salt purification electrochemical techniques

Biomimetic flexible plate actuators are faster and more efficient with a passive attachment

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Acta Mechanica Sinica 2016年第6期32卷 1001-1011页

作者： Peter D.Yeh alexander Alexeev George W.Woodruff School of Mechanical Engineering Georgia Institute of Technology

Using three-dimensional computer simulations, we probe biomimetic free swimming of an internally actuated flexible plate in the regime near the first natural frequency. The plate is driven by an oscillating internal moment approximating the actuation mechanism of a piezoelectric macro fiber composite (MFC) bimorph. We show in our simulations that the addition of a passive attachment increases both swimming velocity and efficiency. Specifically, if the active and passive sections are of similar size, the overall performance is the best. We determine that this optimum is a result of two competing factors. If the passive section is too large, then the actuated portion is unable to generate substantial deflection to create sufficient thrust. On the other hand, a large actuated section leads to a bending pattern that is inefficient at generating thrust especially at higher frequencies.

关键词： Flexible plate Biomimetic Lattice Boltzmann Fluid-structure interaction Robotic fish Piezoelectric actuator

OpenStreetMap data quality enrichment through awareness raising and collective action tools——experiences from a European project

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Geo-Spatial Information Science 2018年第3期21卷 234-246页

作者： Amin Mobasheri alexander Zipf Louise Francis GIScience Research Group Institute of GeographyHeidelberg UniversityHeidelbergGermany Mapping for Change(Co.Ltd.) LondonUnited Kingdom

Nowadays,several research projects show interest in employing volunteered geographic information(VGI)to improve their systems through using up-to-date and detailed *** European project CAP4Access is one of the successful examples of such international-wide research projects that aims to improve the accessibility of people with restricted mobility using crowdsourced *** this project,OpenStreetMap(OSM)is used to extend OpenRouteService,a well-known routing ***,a basic challenge that this project tackled was the incompleteness of OSM data with regards to certain information that is required for wheelchair accessibility(*** information,kerb data,etc.).In this article,we present the results of initial assessment of sidewalk data in OSM at the beginning of the project as well as our approach in awareness raising and using tools for tagging accessibility data into OSM database for enriching the sidewalk data *** experiments have been carried out in different European cities,and discussion on the results of the experiments as well as the lessons learned are *** lessons learned provide recommendations that help in organizing better mapping party events in the *** conclude by reporting on how and to what extent the OSM sidewalk data completeness in these study areas have benefited from the mapping parties by the end of the project.

关键词： Accessibility OpenStreetMap(OSM) data quality data completeness sidewalk wheel map

Do people communicate about their whereabouts? Investigating the relation between user-generated text messages and Foursquare check-in places

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Geo-Spatial Information Science 2018年第3期21卷 159-172页

作者： Ming Li Rene Westerholt alexander Zipf Institute of Geography Heidelberg UniversityHeidelbergGermany

The social functionality of places(***,restaurant)partly determines human behaviors and reflects a region’s functional *** descriptions of places are thus valuable to a range of studies of humans and geographic *** their potential impacts on human verbalization behaviors,one possibility is to link the functions of places to verbal representations such as users’postings in location-based social networks(LBSNs).In this study,we examine whether the heterogeneous user-generated text snippets found in LBSNs reliably reflect the semantic concepts attached with check-in *** investigate Foursquare because its available categorization hierarchy provides rich a-priori semantic knowledge about its check-in places,which enables a reliable verification of the semantic concepts identified fromuser-generated text snippets.A latent semantic analysis is conducted on a large Foursquare check-in *** results confirm that attached text messages can represent semantic concepts by demonstrating their large correspondence to the official Foursquare venue *** further elaborate the representativeness of text messages,this work also performs an investigation on the textual terms to quantify their abilities of representing semantic concepts(i.e.,representativeness),and another investigation on semantic concepts to quantify how well they can be represented by text messages(i.e.,representability).The results shed light on featured terms with strong locational characteristics,as well as on distinctive semantic concepts with potentially strong impacts on human verbalizations.

关键词： Text mining latent semantic analysis semantic concepts Foursquare location-based social network(LBSN)

New characterizations of finite supersoluble groups

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Science China Mathematics 2008年第5期51卷 827-841页

作者： alexander N SKIBA Department of Mathematics Gomel State University of F.Skorina

Let A be a subgroup of a group G and X a nonempty subset of G. A is called an X-semipermutable subgroup of G if A has a supplement T in G such that for every subgroup T 1 of T there exists an element x ∈ X such that ... 详细信息

关键词： finite groups supplement 2-maximal subgroups X-semipermutable supersoluble groups 20D10

An exploratory analysis of usability of Flickr tags for land use/land cover attribution

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Geo-Spatial Information Science 2019年第1期22卷 12-22页

作者： Yingwei Yan Michael Schultz alexander Zipf Institute of Geography Heidelberg UniversityHeidelbergGermany

This study explored the land use/land cover(LULC)separability by the machine-generated and user-generated Flickr photo tags(*** auto-tags and the user-tags,respectively),based on an authoritative LULC dataset for San Diego County in the United *** types of LULCs were derived from the authoritative *** was observed that certain types of the reclassified LULCs had abundant tags(*** parks)or a high tag density(*** commercial lands),compared with the less populated ones(*** agricultural lands).Certain highly weighted terms of the tags derived based on a term frequency–inverse document frequency weighting scheme were helpful for identifying specific types of the LULCs,especially for the commercial recreation lands(*** zoos).However,given the 10 sets of tags retrieved from the corresponding 10 types of LULCs,one set of tags(all the tags located at one specific type of the LULCs)could not fully delineate the corresponding LULC due to semantic overlaps,according to a latent semantic analysis.

关键词： Land use/land cover Flickr quantitative semantics volunteered geographic information

Texture-based latent space disentanglement for enhancement of a training dataset for ANN-based classification of fruit and vegetables

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Information Processing in Agriculture 2023年第1期10卷 85-105页

作者： Khurram Hameed Douglas Chai alexander Rassau School of Engineering Edith Cowan University270 Joondalup DriveJoondalup WA 6027PerthAustralia

The capability of Convolutional Neural Networks(CNNs)for sparse representation has significant application to complex tasks like Representation Learning(RL).However,labelled datasets of sufficient size for learning this representation are not easily *** unsupervised learning capability of Variational Autoencoders(VAEs)and Generative Adversarial Networks(GANs)provide a promising solution to this issue through their capacity to learn representations for novel data samples and classification *** this research,a texture-based latent space disentanglement technique is proposed to enhance learning of representations for novel data samples.A comparison is performed among different VAEs and GANs with the proposed approach for synthesis of new data *** different VAE architectures are considered,a single layer dense VAE and a convolution based VAE,to compare the effectiveness of different architectures for learning of the *** GANs are selected based on the distance metric for disjoint distribution divergence estimation of complex representation learning *** proposed texture-based disentanglement has been shown to provide a significant improvement for disentangling the process of representation learning by conditioning the random noise and synthesising texture rich images of fruit and vegetables。

关键词： Information Maximisation(IM) Fruit and vegetables classification Representation Learning(RL) Variational Autoencoder(VAE) Generative Adversarial Network (GAN) Latent space disentanglement

Varicocele and testicular function

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Asian Journal of Andrology 2015年第4期17卷 659-667页

作者： alexander W Pastuszak Center for Reproductive Medicine Baylor College of Medicine Houston TX USA Scott Department of Urology Bay or Co ege of Medicine Houston TX USA Divisionof Urology University of Texas Med ca School at Houston Houston TX USA Department of Urology University of Texas MD Anderson Cancer Center HoustonTX USA

Testicular varicocele, a dilation of the veins of the pampiniform plexus thought to increase testicular temperature via venous congestion, is commonly associated with male infertility. Significant study has clarified the negative impact of varicocele on semen parameters and more recent work has shed light on its detrimental effects on the molecular and ultrastructural features of sperm and the testicular microenvironment, as well as more clearly defined the positive impacts of treatment on couples＇ fertility. The relationship between varicocele and testicular endocrine function, while known for some time based on histologic evaluation, has become more apparent in the clinical setting with a growing link between varicocele and hypogonadism. Finally, in the pediatric setting, while future study will clarify the impact of varicocele on fertility and testicular function, recent work supports a parallel effect of varicocele in adolescents and adults, suggesting a re-evaluation of current treatment approaches in light of the progressive nature of the condition and potential increased risk of future disease.

关键词： hypogonadism Leydig cell male fertility oxidative stress Sertoli cell ultramorphology varicocele