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101.
B. Jeremic D. Vukelic P. M. Todorovic I. Macuzic M. Pantic D. Dzunic B. Tadic 《Journal of Friction and Wear》2013,34(2):114-119
The problem of measuring static friction at high temperatures and low contact pressures is theoretically analyzed, as well as the instruments for the accurate determination of the coefficient of static friction at high temperatures for contact pairs made of steel and bronze. The results of experimental investigation show that at low contact pressure and temperature above 120°C coefficient of static friction dramatically increases. This increase in the coefficient of friction can be of great practical value with regard to the load capacity of contacts where external forces are balanced with friction forces. 相似文献
102.
Mechanical and thermal properties of UV cured mixtures of linear and hyperbranched urethane acrylates 总被引:2,自引:0,他引:2
Enis S. Džunuzović Srba V. Tasić Branislav R. Božić Jasna V. Džunuzović Branko M. Dunjić Katarina B. Jeremić 《Progress in Organic Coatings》2012
The properties of urethane acrylate resin mixtures based on the linear and hyperbranched aliphatic polyesters were examined. Linear polyester was synthesized from neopentil glycol and adipic acid. Hyperbranched polyester of the third generation was synthesized from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylol propane. The modification of 60% of hyperbranched aliphatic polyester OH end groups was carried out with isononanoic acid or with soybean fatty acids. Two hyperbranched urethane acrylates, with the same degree of acrylation, and one linear urethane acrylate were obtained by reaction of appropriate polyester and isophorone diisocyanate and 2-hydroxyethyl acrylate. The influence of added amount of HUA and nature of non-acrylic end groups on the rheological, mechanical and thermal properties of the uncured and UV cured mixtures diluted with 20 wt.% hexanediol diacrylate was examined. The nature of non-acrylic end groups have great effect on the interaction between linear and hyperbranched urethane acrylates, which further has a crucial influence on the examined properties of uncured and UV cured mixture samples. 相似文献
103.
Ljiljana Kljajević Snežana Nenadović Miloš Nenadović Devendraprakash Gautam Tatjana Volkov-Husović Aleksandar Devečerski Branko Matović 《Ceramics International》2013,39(5):5467-5476
Spark plasma sintering (SPS) of ZrC–SiC composite powders in the presence of LiYO2 sintering additive was studied. The starting powders were obtained by a carbothermal reduction (CTR) of natural mineral zircon (ZrSiO4), which provided an intimate mixing of in-situ created ZrC and SiC powders. This composite powder and LiYO2 as additive were densified by spark plasma sintering. Microstructural features of the composite were investigated by XRD, SEM/EDS and AFM analysis. The sintered composite material possesses promising mechanical properties and excellent cavitation resistance which was observed with a cavitation erosion test. The values of Vickers microhardness and fracture toughness of the composite material are 20.7 GPa and 5.07 MPam1/2, respectively. 相似文献
104.
Bojana Balanč Ana Kalušević Ivana Drvenica Maria Teresa Coelho Verica Djordjević Vitor D Alves Isabel Sousa Margarida Moldão‐Martins Vesna Rakić Viktor Nedović Branko Bugarski 《Journal of food science》2016,81(1):E65-E75
Carqueja (Pterospartum tridentatum) is an endemic species and various bioactive compounds have been identified in its aqueous extract. The aim of this study was to protect the natural antioxidants from the aqueous extract of carqueja by encapsulation in Ca–alginate microbeads and Ca–alginate microbeads containing 10% and 20% (w/v) of inulin. The microbeads produced by electrostatic extrusion technique had an average diameter from 625 μm to 830 μm depending on the portion of inulin. The sphericity factor of the hydrogel microbeads had values between 0.014 and 0.026, while freeze dried microbeads had irregular shape, especially those with no excipient. The reduction in microbeads size after freeze drying process (expressed as shrinkage factor) ranged from 0.338 (alginate microbeads with 20% (w/v) of inulin) to 0.523 (plain alginate microbeads). The expressed radical scavenging activity against ABTS and DPPH radicals was found to be between 30% and 40% for encapsulated extract, while the fresh extract showed around 47% and 57% of radical scavenging activity for ABTS and DPPH radicals, respectively. The correlation between antioxidant activity and the total phenolic content were found to be positive (in both assay methods, DPPH and ABTS), which indicate that the addition of inulin didn't have influence on antioxidant activity. The presence of inulin reduced stiffness of the hydrogel, and protected bead structure from collapse upon freeze‐drying. Alginate–inulin beads are envisaged to be used for delivery of aqueous P. tridentatum extract in functional food products. 相似文献
105.
Branko N. Popov Xuguang LiGang Liu Jong-Won Lee 《International Journal of Hydrogen Energy》2011,36(2):1794-1802
This paper provides an overview on the development of advanced fuel cell cathode catalysts at University of South Carolina (USC) with the emphasis on the stability of non-precious metal and Pt alloy catalysts. Nitrogen-modified carbon composite (NMCC) catalysts were developed for the oxygen reduction reaction (ORR) through the pyrolysis of cobalt (iron)-nitrogen chelate followed by the treatment combination of pyrolysis, acid leaching, and re-pyrolysis. A promising stability was observed for 1050 h fuel cell operation under current density of 200 mA cm−2 as evidenced by a potential decay rate as low as 40 μV h−1. The performance degradation mechanism of the NMCC-based fuel cell is discussed. Pt and PtPd hybrid catalysts are developed that use a NMCC, which is itself active for the ORR, instead of a conventional carbon black support. The stability test at 1 A cm−2 indicated that the Pt/NMCC hybrid catalyst (new Pt-Co/C) is more stable than the conventional Pt-Co/C without the Co leaching out. The PEM fuel cell accelerated stress test (AST) for supports and catalysts demonstrated that their stability changes in the order: Pt3Pd1/NMCC hybrid catalyst > Pt/NMCC hybrid catalyst > conventional Pt/C catalyst. Moreover, the hybrid catalysts exhibit higher mass activity than the Pt/C catalysts. 相似文献
106.
Zhongwei Niu Saswat Kabisatpathy Jinbo He L. Andrew Lee Jianhua Rong Lin Yang Godfrey Sikha Branko N. Popov Todd S. Emrick Thomas P. Russell Qian Wang 《Nano Research》2009,2(6):474-483
A sol-gel process has been developed to incorporate bionanoparticles, such as turnip yellow mosaic virus, cowpea mosaic virus,
tobacco mosaic virus, and ferritin into silica, while maintaining the integrity and morphology of the particles. The structures
of the resulting materials were characterized by transmission electron microscopy, small angle X-ray scattering, and N2 adsorption-desorption analysis. The results show that the shape and surface morphology of the bionanoparticles are largely
preserved after being embedded into silica. After removal of the bionanoparticles by calcination, mesoporous silica with monodisperse
pores, having the shape and surface morphology of the bionanoparticles replicated inside the silica, was produced,. This study
is expected to lead to both functional composite materials and mesoporous silica with structurally well-defined large pores.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
107.
The α-Fe2O3/SiO2 nanocomposite containing 45 wt.% of hematite was prepared by the sol-gel method and characterized by using X-ray diffractometer (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometer. TEM microscopy showed spherical particles with average size about 10 nm, whereas XRD diffraction confirmed the formation of the hematite phase. The magnetic measurements showed anomalous behavior of the hysteresis loops including decrease of high field isothermal magnetization and overlap of initial, remagnetization and magnetization curves. This anomalous behavior represents a novel effect for α-Fe2O3/SiO2 nanocomposites. We conjecture that a field-induced antiferromagnetic coupling between nanoparticles may produce this effect. 相似文献
108.
Radoslava Stojanovic Ana Belscak‐Cvitanovic Verica Manojlovic Drazenka Komes Viktor Nedovic Branko Bugarski 《Journal of the science of food and agriculture》2012,92(3):685-696
BACKGROUND: Encapsulation of Thymus serpyllum L. aqueous extract within calcium alginate beads was studied in order to produce dosage formulations containing polyphenolic compounds. Electrostatic extrusion was applied for encapsulation of thyme aqueous extract in alginate gel beads. In addition to hydrogel beads, heat‐dried and freeze‐dried forms of beads were examined. METHODS: Encapsulation systems were examined and compared in order to choose the optimal one with respect to entrapment efficiency, preservation of antioxidant activity and thermal behaviour under heating conditions simulating the usual food processing. RESULTS: The beads obtained with approximately 2 mg g?1 of gallic acid equivalents encapsulated in 0.015 g mL?1 of alginate were spheres of a uniform size of about 730 µm. Encapsulation efficiency varied in the range 50‐80% depending on the encapsulation method. Besides, the analysis reveals that the encapsulation process and the material used did not degrade the bioactive compounds, as the total antioxidant content remained unchanged. This was verified by Fourier transform infrared analysis, which proved the absence of chemical interactions between extracted compounds and alginate. Addition of a filler substance, such as sucrose and inulin, in the dried product reduced its collapse and roundness distortion during drying process. CONCLUSION: This study demonstrates the potential of using hydrogel material for encapsulation of plant poplyphenols to improve their functionality and stability in food products. Copyright © 2011 Society of Chemical Industry 相似文献
109.
110.
During the last 20 years numerous water supply, hydroelectric and other large structures have been built along the Drava River and in its catchment area in Slovenia, Croatia, Hungary and Austria. Their construction has greatly influenced the water regime of the Drava River, especially during low water periods. The changes in the low flow regime along the stretch from Varazdin (285 km) to its confluence with the Danube (0 km) are examined. The analysis includes changes in the water levels, discharges and the amounts of suspended sediment and bed load. The intensity of changes, the time of their occurrence and their trends are examined. 相似文献