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Field topologies in ideal and near-ideal magnetohydrodynamics and vortex dynamics

Science china(Physics,Mechanics & Astronomy) 2015年第1期58卷 12-31页

作者： LOW B.c. High Altitude Observatory National Center for Atmospheric Research

Magnetic field topology frozen in ideal magnetohydrodynamics （MHD） and its breakage in near-ideal MHD are reviewed in two parts, clarifying and expanding basic concepts. The first part gives a physically complete description of the frozen field topology derived from magnetic flux conservation as the fundamental property, treating four conceptually related topics： Eulerian and La- grangian descriptions of three dimensional （3D） MHD, chandrasekhar-Kendall and Euler-potential field representations, magnetic helicity, and inviscid vortex dynamics as a fluid system in physical contrast to ideal MHD. A corollary of these developments clar- ifies the challenge of achieving a high degree of the frozen-in condition in numerical MHD. The second part treats field-topology breakage centered around the Parker Magnetostatic Theorem on a general incompatibility of a continuous magnetic field with the dual demand of force-free equilibrium and an arbitrarily prescribed, 3D field topology. Preserving field topology as a global con- straint readily results in formation of tangential magnetic discontinuities, or, equivalently, electric current-sheets of zero thickness. A similar incompatibility is present in the steady force-thermal balance of a heated radiating fluid subject to an anisotropic thermal flux conducted strictly along its frozen-in magnetic field in the low-fl limit. In a weakly resistive fluid the thinning of current sheets by these general incompatibilities inevitably results field notwithstanding the small resistivity. Strong Faraday in sheet dissipation, resistive heating and topological changes in the induction drives but also macroscopically limits this mode of energy dissipation, trapping or storing free energy in self-organized ideal-MHD structures. This property of MHD turbulence captured by the Taylor hypothesis is reviewed in relation to the Sun＇s corona, calling for a basic quantitative description of the breakdown of flux conservation in the low-resistivity li

关键词： magnetic topology magnetic reconnection current sheets magnetic helicity thermal conduction solar corona magnetohy-drodynamics interstellar clouds

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Atomistic simulations of plasma catalytic processes

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Frontiers of chemical Science and Engineering 2018年第1期12卷 145-154页

作者： Erik c. Neyts Research Group PLASMANT Department of Chemistry University of Antwerp Universiteitsplein 1 2610 Wilrijk-Antwerp Belgium

There is currently a growing interest in the realisation and optimization of hybrid plasma/catalyst systems for a multitude of applications, ranging from nanotechnology to environmental chemistry. In spite of this interest, there is, however, a lack in fundamental understanding of the underlying processes in such systems. While a lot of experimental research is already being carded out to gain this understanding, only recently the first simulations have appeared in the literature. In this contribution, an overview is presented on atomic scale simulations of plasma catalytic processes as carried out in our group. In particular, this contribution focusses on plasma-assisted catalyzed carbon nanostructure growth, and plasma catalysis for greenhouse gas conversion. Attention is paid to what can routinely be done, and where challenges persist.

关键词： atomic scale simulation plasma-catalyst

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Effect of Rotational and Sliding Motions on Friction and Degeneration of Articular cartilage under Dry and Wet Friction

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Journal of Bionic Engineering 2015年第3期12卷 464-472页

作者： Ahmet c. cilingir Department of Mechanical Engineering Sakarya University 54187 Sakatya Turkey

Understanding the tribological properties of articular cartilage allows scientists to evaluate degenerative joint diseases and develop new treatment techniques. The objectives of this study are to demonstrate the detrimental effect of rotational motion under both dry and wet friction and to evaluate the friction and wear behavior of bovine articular cartilage with sliding and rotational testing configurations that represent fluid film and boundary lubrication mechanisms, respectively. The articular cartilage pin and plate samples were harvested from healthy adult bovine and then tested on a self-made friction and wear simulator. cartilage samples were subjected to sliding and rotational motions under constant load. Friction coefficients and wear factors were calculated under three conditions： using bovine serum, phosphate buffered saline and with no lubricant present. The friction coefficient and wear factor of the articular cartilage were significantly increased with rotational motion under both dry and wet friction. Using bovine serum as lubricant in the sliding testing configuration the friction coefficient and wear factor of articular cartilage were both decreased. A similar decrease in the tribological properties of cartilage was initially observed for the rotational testing configuration with bovine serum; however, the friction coefficient and wear factor were increased after 150,000 cycles. In the absence of lubricant, the articular cartilage was entirely worn on contact area in both sliding and rotational testing configurations. Bovine serum proved an effective fluid film lubricant for articular cartilage surfaces.

关键词： articular cartilage rotational motion sliding motion dry friction wet friction wear

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Energy and economic analysis of a point-focus concentrating photovoltaic system when its installation site varies

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Frontiers in Energy 2021年第2期15卷 384-395页

作者： c.RENNO A.PERONE Department of Industrial Engineering University of SalernoVia Giovanni Paolo II13284084 Fisciano(Salerno)Italy

The concentrating photovoltaic (cPV) systems are a promising technology to obtain clean energy. However, these systems are not equally convenient worldwide due to different climatic conditions. The main aim of this paper is to analyze energy and economic performances of a point-focus cPV system for a residential user when its installation site varies. Three locations, Riyadh, copenhagen, and Palermo, characterized by very different weather conditions are chosen. A model that links the electrical power of a triple-junction (TJ) cell with its temperature and concentrated radiation incident on it is experimentally developed to evaluate the energy performance of the cPV system. A comparison of the three localities for typical winter and summer sunny days indicates that the higher values of the TJ cell temperature are reached in summer, over 70°c at Riyadh, and its electrical power is reduced compared to a winter day. In winter, a TJ cell in Riyadh supplies an electric power of about 20% higher than that in other two cities, while in summer, the maximum power is observed at copenhagen. On the contrary, the electrical producibility also depends on the sunlight daily hours number during the year. Hence, considering the real distribution of direct normal irradiance (DNI) and the environmental temperature for each locality, a cPV system composed of modules of 90 cells adopted for a residential user is sized. The electric producibility of the cPV system, by varying its module number, is evaluated for different localities together with the optimal number of the modules which is able to maximize the investment profitability.

关键词： cPV system point-focus experimental model energy and economic analysis

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A reference evapotranspiration map for Bosnia and Herzegovina

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International Soil and Water conservation Research 2019年第1期7卷 89-101页

作者： Sabrija(c)adro Salwa cherni-(c)adro Mihajlo Markovi(c) Jasminka(Z)urovec University of Sarajevo(UNSA) Faculty of Agriculture and Food Sciences(PPF)Bosnia and Herzegovina Hydro-Engineering Institute Sarajevo(HEIS) Bosnia and Herzegovina University of Banja Luka(UNIBL) Faculty of AgricultureBosnia and Herzegovina

There are three major challenges for climatic data availability for Reference Evapotranspiration (ET0) calculations in Bosnia and Herzegovina:limited data availability,discontinuity of data records,and low station *** main objective of this study was to apply reliable methods to calculate and spatially distribute ET0,while considering the impact of the elevation.A 20 m spatial resolution map was created for mean ET0 values at monthly,vegetation period (April-September) and annual temporal resolution at municipality (143 municipalities),regional (4 regions) and national spatial resolutions.108 weather stations for the period 1961-2016 (56 years) were utilized for spatial interpolation of ET0 using kriging with external drift *** required elevation for ET0 estimation at each grid node was ext'acted from the digital elevation model of Bosnia and ***0 was calculated using FAO-56 PenmanMonteith,and in cases where only minimum and maximum temperature data were available the Hargreaves-Samani equation adjusted with locally appropriate empirical radiation coefficient was used.A gradual decrease of mean ET0 values from the southern to central and northern to central part of the country is *** the all seasons (monthly,vegetation and annually),the southern region has greater ET0 than the other three regions (north,west and central-east),which are *** long-term mean annual ET0 for Bosnia and Herzegovina is 716 mm,approximately 78% (559 mm) of which occurs during in the vegetation period.

关键词： Reference evapotranspiration Interpolation Penman-Monteith Limited data calibration

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Integration of hepatitis B virus DNA into chromosomal DNA during acute hepatitis B

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World Journal of Gastroenterology 2005年第41期11卷 6416-6421页

作者： Gerald c Kimbi Anna Kramvis Michael c Kew MRc/University Molecular Hepatology Research Unit Department of Medicine University of the WitwatersrandParktown 2193JohannesburgSouth Africa

AIM： To examine the serum from black African patients with acute hepatitis B to ascertain if integrants of viral DNA can be detected in fragments of cellular DNA leaking from damaged hepatocytes into the circulation. METHODS： DNA was extracted from the sera of five patients with uncomplicated acute hepatitis B and one with fulminant disease. Two subgenomic PcRs designed to amplify the complete genome of HBV were used and the resulting amplicons were cloned and sequenced. RESULTS： HBV and chromosomal DNA were amplified from the sera of all the patients. In one patient with uncomplicated disease, HBV DNA was integrated into host chromosome 7 q11.23 in the WBScR1 gene. The viral DNA comprised 200 nucleotides covering the S and X genes in opposite orientation, with a 1 169 nucleotide deletion. The right virus/host junction was situated at nucleotide 1 774 in the cohesive overlap region of the viral genome, at a preferred topoisomerase I cleavage motif. The chromosomal DNA was not rearranged. The patient made a full recovery and seroconverted to anti-HBs- and anti-HBe-positivity. Neither HBV nor chromosomal DNA could be amplified from his serum at that time. cONcLUSION： Integration of viral DNA into chromosomal DNA may occur rarely during acute hepatitis B and, with clonal propagation of the integrant, might play a role in hepatocarcinogenesis.

关键词： Hepatocellular chronic hepatitis B infection clonal propagation

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Inaccuracies in the history of a well-known introduction:a case study of the Australian House Sparrow(Passer domesticus)

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chinese Birds 2016年第2期7卷 95-109页

作者： Samuel c.Andrew Simon c.Griffith Department of Biological Sciences Macquarie University

Background:Modern ecosystems contain many invasive species as a result of the activity of acclimatisation societies that operated in the second half of the nineteenth century,and these species provide good opportunities for studying invasion ***,to gain insight into the ecological and genetic mechanisms that determine the rate of colonization and adaptation to new environments,we need a good understanding of the history of the introduced species,and a knowledge of the source population,timing,and number of individuals introduced is particularly ***,any inaccuracies in the history of an introduction will affect subsequent assumptions and ***:Focusing on a single well-known species,the House Sparrow(Passer domesticus),we have documented the introduction into Australia using primary sources(*** records and newspaper articles).Results:Our revised history differs in a number of significant ways from previous *** evidence indicates that the House Sparrow was not solely introduced from source populations in England but also from Germany and most strikingly also from India—with the latter birds belonging to a different *** also clarify the distinction between the number released and the number of founders,due to pre-release captive breeding programs,as well as identifying inaccuracies in a couple of well-cited sources with respect to the range expansion of the introduced ***:Our work suggests that caution is required for those studying introductions using the key sources of historical information and ideally should review original sources of information to verify the accuracy of published accounts.

关键词： Acclimatisation Bottlenecks Propagule size Range expansion Hybridisation

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Energy storage and harvesting in BaTiO_(3)/epoxy nanodielectrics

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High Voltage 2016年第4期1卷 151-157页

作者： Georgia c.Manika Georgios c.Psarras Department of Materials Science University of Patras26504PatrasGreece

composite nanodielectrics consisted of an epoxy resin and barium titanate nanoparticles were developed and *** measurements were performed via broadband dielectric *** results reveal the presence of three relaxation processes,which are attributed to(a)glass to rubber transition of the polymer matrix(α-mode),(b)re-arrangement of polar side groups(β-mode)and(c)interfacial polarisation between system’s *** ability of the examined nanodielectrics to store and harvest energy was also examined in dc *** dc voltage varied in the range of 10–240 *** data indicate that increasing the applied dc field results to higher values of the stored and harvested *** energy efficiency was also investigated in all *** filler content enhances the coefficient of energy efficiency(neff)up to 58.2%for the 7 phr BaTiO_(3)nanocomposite at 200 V and 10 s charging/discharging time.

关键词： spectroscopy. rubber arrangement

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Sources and Deficiency Diseases of Mineral Nutrients in Human Health and Nutrition:A Review

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Pedosphere 2014年第1期24卷 13-38页

作者： U.c.GUPTA S.c.GUPTA Agriculture and Agri-canada canada Crops and Livestock Research Centre The Department of Plastic Surgery Loma Linda University

Mineral nutrients are fundamentally metals and other inorganic compounds. The life cycle of these mineral nutrients begins in soil, their primary source. Soil provides minerals to plants and through the plants the minerals go to animals and humans; animal products are also the source of mineral nutrients for humans. Plant foods contain almost all of the mineral nutrients established as essential for human nutrition. They provide much of our skeletal structure, e.g., bones and teeth. They are critical to countless body processes by serving as essential co-factors for a number of enzymes. Humans can not utilize most foods without critical minerals and enzymes responsible for digestion and absorption. Though mineral nutrients are essential nutrients, the body requires them in small, precise amounts. We require them in the form found in crops and they can be classified into three different categories： major, secondary, and micro or trace minerals. This classification is based upon their requirement rather than on their relative importance. Major minerals such as potassium （K） and phosphorus （P） are required in amounts of up to 10 g d-1. The daily requirement of secondary and micro minerals ranges from 400 to 1 500 mg d-1 and 45 ~tg d-1 to 11 mg d-1, respectively. To protect humans from mineral nutrient deficiencies, the key is to consume a variety of foods in modest quantities, such as different whole grains, low fat dairy, and different meats, vegetables and fruits. For insurance purposes, a supplement containing various mineral nutrients can be taken daily.

关键词： deficiency diseases deficiency symptoms origin recommended daily dose toxicity

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3D FINITE ELEMENT ANALYSIS OF THE DAMAGE EFFEcTS ON THE DENTAL cOMPOSITE SUBJEcT TO WATER SORPTION

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Acta Mechanica Solida Sinica 2006年第3期19卷 212-222页

作者： Tsui c.P. chow c.L. Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hong Kong ChinaDepartment of Mechanical EngineeringThe University of Michigan-DearbornDearbornMichiganUSA

The damage effects of water sorption on the mechanical properties of the hydroxyapatite particle reinforced Bis-GMA/TEGDMA copolymer （HA/Bis-GMA/TEGDMA） h-ave been predicted using 3D finite cell models. The plasticizer effect on the polymer matrix was considered as a variation of its Young＇s modulus. Three different cell models were used to determine the influence of varying particle contents, interphase strength and moisture concentration on the debonding damage. The stress distribution pattern has been examined and the stress transfer mode clarified. The Young＇s modulus and fracture strength of the Bis-GMA/TEGDMA composite were also predicted using the model with and without consideration of the damage. ine Iormer results with consideration of the debonding damage are in good agreement with existing literature experimental data. The shielding effect of our proposed model and an alternative approach were discussed. The Fcc cell model has also been extended to predict the critical load for the damaged and the undamaged composite subject to the 3-point flexural test.

关键词： water sorption dental composite interphase debonding finite element method (FEM) unit cell model

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