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排序方式: 共有382条查询结果,搜索用时 15 毫秒
61.
Aleksandar Vencl Ilija Bobić Milan T. Jovanović Miroslav Babić Slobodan Mitrović 《Tribology Letters》2008,32(3):159-170
In the present study, the effect of the Al2O3 particles (average size of 12 μm, 3 and 10 wt.%) reinforcement on the microstructure and tribological properties of Al–Si
alloy (A356) was investigated. Composites were produced by applying compocasting process. Tribological properties of unreinforced
alloy and composites were studied, using pin-on-disc tribometer, under dry sliding conditions at different specific loads
and sliding speed of 1 m/s. Microhardness measurements, optical microscope and scanning electron microscope were used for
microstructural characterization and investigation of worn surfaces and wear debris. During compocasting of A356 alloy, a
transformation from a typical dendritic primary α phase to a non-dendritic rosette-like structure occurred. Composites exhibited
better wear resistance compared with unreinforced alloy. Presence of 3 wt.% Al2O3 particles in the composite material affected the wear resistance only at specific loads up to 1 MPa. The wear rate of composite
with 10 wt.% Al2O3 particles was nearly two order of the magnitude lower than the wear rate of the matrix alloy. Dominant wear mechanism for
all materials was adhesion, with others mechanisms: oxidation, abrasion and delamination as minor ones. 相似文献
62.
Stefan Dačić Aleksandar M. Veselinović Aleksandar Mitić Marija Nikolić Milica Cenić Dragica Dačić‐Simonović 《Microscopy research and technique》2016,79(11):1031-1037
In the present research, different adhesive techniques were used to set up fillings with composite resins. After the application of etch and rinse or self etch adhesive technique, marginal adaptation of composite fillings was estimated by the length of margins without gaps, and by the microretention of resin in enamel and dentin. The study material consisted of 40 extracted teeth. Twenty Class V cavities were treated with 35% phosphorous acid and restored after rinsing by Adper Single Bond 2 and Filtek Ultimate‐ASB/FU 3M ESPE composite system. The remaining 20 cavities were restored by Adper Easy One‐AEO/FU 3M ESPE composite system. Marginal adaptation of composite fillings was examined using a scanning electron microscope (SEM). The etch and rinse adhesive technique showed a significantly higher percentage of margin length without gaps (in enamel: 92.5%, in dentin: 57.3%), compared with the self‐etch technique with lower percentage of margin length without gaps, in enamel 70.4% (p < .001), and in dentin‐22.6% (p < .05). In the first technique, microretention was composed of adhesive and hybrid layers as well as resin tugs in interprismatic spaces of enamel, while the dentin microretention was composed of adhesive and hybrid layers with resin tugs in dentin canals. In the second technique, resin tugs were rarely seen and a microgap was dominant along the border of restoration margins. The SEM analysis showed a better marginal adaptation of composite resin to enamel and dentin with better microretention when the etch and rinse adhesive procedure was applied. 相似文献
63.
Nataša Maleš-Ilić Aleksandar Atanasković Kurt Blau Matthias Hein 《International Journal of Electronics》2016,103(8):1318-1331
This paper considers the linearisation of an asymmetrical two-way Doherty amplifier by the method that uses the second harmonics and fourth-order non-linear signals for linearisation. These even-order signals for linearisation are extracted at the output of the peaking amplifier, adjusted in amplitude and phase and injected at the input and output of the carrier amplifier transistor in the Doherty configuration. The effect of linearisation has been experimentally confirmed on a fabricated asymmetrical Doherty amplifier with the additional circuit for linearisation. The suppression of the third-order intermodulation products has been carried out for two-tone test, 64QAM and WCDMA digitally modulated signals in a range of signal power. 相似文献
64.
Aleksandar Ranković Milan S. Savić 《Electrical Engineering (Archiv fur Elektrotechnik)》2010,92(2):69-77
This paper deals with the calculation of the electric field strength in high voltage (HV) substations comprising complex geometrical
structures. Generalized charge simulation method is proposed for improving the precision of the calculation of the electric
field strength. The objective of this analysis is to examine the influence of towers, HV apparatus and fences on the spatial
electric field distribution. For this purpose, a three-dimensional generalized model of HV substation has been developed,
including phase conductors, bypass busbars, HV apparatus, fences and towers (denoted as Full model). The obtained results
of the calculation of the electric field strength are compared with the Simplified model, which only includes phase conductors
connected to HV network. Verification of the proposed Full model performed by comparing the calculated and in-field measured
values of the electric field strength within HV substations and in their vicinity gives very promising results. 相似文献
65.
Aleksandar Mitrašinovi? 《Renewable & Sustainable Energy Reviews》2011,15(8):3603-3607
With the possible depletion of fossil fuels in just one generation and the risk of eventual nuclear incidents, the question is whether renewable energy sources have the capacity to replace traditional ones. The availability of solar energy is significantly higher than any other renewable source and silicon is currently the major photo-catalytic material in the solar industry. Conversion efficiency and payback time are noted as key factors, besides atmospheric imperviousness, all of which affect usability of photo-catalytic material. The status and future of Si as a major candidate to take over from traditional sources of energy relies on cost reduction of the high purity Si used as feedstock for solar cell industry, reduced installation costs and network maintenance and development of the next generation of Si solar cells. 相似文献
66.
Perica Paunovi? Dafinka Stoevska GogovskaOrce Popovski Antonia StoyanovaEvelina Slavcheva Elefteria LefterovaPeter Iliev Aleksandar T. DimitrovSvetomir Had?i Jordanov 《International Journal of Hydrogen Energy》2011,36(16):9405-9414
The subject of this study is preparation and characterization of hypo-hyper d-electrocatalysts with reduced amount of precious metals aimed for water electrolysis. The studied electrocatalysts contain 10% mixed metallic phase (Co:Ru = 1:1 wt., Co:Ru = 4:1 wt. and Co:Ru:Pt = 4:0.5:0.5 wt.), 18% TiO2 as a crystalline anatase deposited on multiwalled carbon nanotubes (MWCNTs). Previously, MWCNTs were activated in 28% nitric acid. As a reference electrocatalyst for hydrogen evolution reaction, corresponding electrocatalysts with pure Pt metallic phase and mixed CoPt (Co:Pt = 1:1 wt.) metallic phase were prepared. Also, as a reference electrocatalyst for oxygen evolution reaction, electrocatalyst with pure Ru metallic phase was prepared.The prepared electrocatalysts were structurally characterized by means of XPS, XRD, TEM, SEM and FTIR analysis.Electrochemical characterization was performed by means of cyclic voltammetry and potentiodynamic method in the PEM hydrogen electrolyzer. The range of the catalytic activity for hydrogen evolution of studied electrocatalysts was the following: CoRuPt (4:0.5:0.5) > CoPt (1:1) > Pt > CoRu (1:1) > CoRu (4:1). The order of the catalytic activity for oxygen evolution was the following: CoRu (1:1) > Ru > CoRu (4:1) > Pt > CoRuPt (4:0.5:0.5) > CoPt (1:1). 相似文献
67.
Lutich AA Mauser C Da Como E Huang J Vaneski A Talapin DV Rogach AL Feldmann J 《Nano letters》2010,10(11):4646-4650
CdSe/CdS semiconductor nanocrystal heterostructures are currently of high interest for the peculiar electronic structure offering unique optical properties. Here, we show that nanorods and tetrapods made of such material combination enable efficient multiexcitonic emission, when the volume of the nanoparticle is maximized. This condition is fulfilled by tetrapods with an arm length of 55 nm and results in a dual emission with comparable intensities from the CdS arms and CdSe core. The relative intensities of the dual emission, originating from exciton phase-space filling and reduced Auger recombination, can be effectively modulated by the photon fluence of the pump laser. The results, obtained under steady-state detection conditions, highlight the properties of tetrapods as multiexciton dual-color emitters. 相似文献
68.
Preliminary investigation of mineral content of pollen collected from different Serbian maize hybrids – is there any potential nutritional value? 下载免费PDF全文
69.
Vladimir D. Stevanovic Aleksandar Gajic Ljubodrag Savic Vladan Kuzmanovic Dusan Arnautovic Tina Dasic Blazenka Maslovaric Sanja Prica Bojan Milovanovic 《Applied Energy》2011
The hydro energy of the gravity water flow from the coal-fired thermal power plant units to the river in an open cooling system of turbine condensers is determined. On the basis of statistical data for a long time period, the water net head duration curve due to the river annual level change, as well as the reduction of the hydro energy potential due to the thermal power plant overhauls periods, are evaluated in the case study of the Thermal Power Plant “Nikola Tesla B” in Serbia. A small hydro power plant is designed for the utilization of this hydro energy, and the economic benefits of the project are calculated. The internal rate of returns and pay back periods are calculated in dependence of the electricity price and total investment costs. The increase of profitability is assessed, bearing in mind that the plant might be realized as the Clean Development Mechanism project according to the Kyoto protocol. The obtained results show that the project is economically attractive, and it can be carried out with standard matured solutions of hydro turbines available at the market. Even for the relatively low electricity price from small hydro power plants in Serbia of 0.08 €/kW h the internal rate of return and the pay back period are 17.5% and 5.5 years. 相似文献
70.
The effects of heat treatment on the microstructure, hardness, tensile properties, and tribological behavior of ZA27 alloy
were examined. The alloys were prepared by conventional melting and casting route. The heat treatment of samples included
the heating up to 370 °C for 3 or 5 h, quenching in water, and natural aging. Lubricated sliding wear test were conducted
on as-cast and heat-treated ZA27 samples using block-on-disc machine. The friction and wear behavior of alloys were tested
in contact with steel discs using combinations of three levels of load (10, 30, and 50 N) and three levels of linear sliding
speeds (0.26, 0.50, and 1.00 m/s). To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning
electron microscopy (SEM). The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation.
The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, under all combinations of sliding
speeds and contact loads. The rate of improvement increased with duration of solutionizing process before quenching in water.
Obtained tribological results were related to the effects of heat treatment on microstructure changes of alloy. 相似文献