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Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviour
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek

Opis: In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.
Ključne besede: mechanics, cellular materials, honeycomb structure, gas filler, thermal properties, mechanical properties, dynamic loading, LS-DYNA, computational simulations
Objavljeno: 31.05.2012; Ogledov: 1025; Prenosov: 19
URL Povezava na celotno besedilo

The synthesis of iron-nickel alloy nanoparticles using a reverse micelle technique
Irena Ban, Mihael Drofenik, Darko Makovec, 2006, izvirni znanstveni članek

Opis: Nanosized Fe0.2Ni0.8 particles were prepared by reducing their salts with sodium borohydride (NaBH4) in cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB) and n-butanol/isooctane at 25 °C.According to the TEM and X-ray diffraction analyses, the synthesized particles were around 4-12 nm in size. Due to their nanodimensions, the particles had a primitive cubic (pc) structure rather than the body-centered cubic (BCC) structure of the bulk material. An examination of the synthesis from the reverse micelle reveals that the morphology of the iron-nickel alloy nanoparticles depends mainly on the microemulsion`s composition. The magnetization of the nanoparticles was much lower than that of the bulk material, reflecting the influence of the nanodimensions on the particlesć magnetizations.
Ključne besede: magnetic materials, nickel/iron alloys, nanoparticles, synthesis, microemulsions, magnetic properties, reverse micelles
Objavljeno: 31.05.2012; Ogledov: 1196; Prenosov: 64
URL Povezava na celotno besedilo

Charpy toughness and microstructure of vibrated weld metal
Bogdan Pučko, Vladimir Gliha, 2006, izvirni znanstveni članek

Opis: Vibration during welding can be used to obtain certain changes in mechanical properties of weld metal. Research work on the influence of vibration on the secondary microstructure of welds and hence on the Charpy toughness was performed. Vibration during welding exhibits positive effects on the microstructure constituent formation. Multipass welding was simulated with reheating of the original single pass weld in order to obtain similar microstructure to multipass welds. Microstructures were examined with an optical microscope. Additionally, fractographic examination of the rupture of Charpy specimens was performed. Changes in the microstructure according to vibration were observed which affect toughness of the weld metal. Vibration during welding was rated more effective in the case of reheating the weld metal, which is the case in multipass welding.
Ključne besede: welding, welded joints, mechanical properties of metals, ferrite, vibration, microstructure, toughness, notched bar testing, weld metal
Objavljeno: 31.05.2012; Ogledov: 1428; Prenosov: 66
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Calculation of the thermal conductivity of nanofluids containing nanoparticles and carbon nanotubes
Jurij Avsec, Maks Oblak, 2003, izvirni znanstveni članek

Opis: A mathematical model for the calculation of thermal conductivity of nanofluids containing nanoparticles and nanotubes on the basis of statistical mechanics is presented. This appears to be the first such attempt published in the scientific literature. We focus on the influence of the liquid layer structure around nanoparticles as the reason for enhancement of the thermal conductivity of nanofluids. Analytical results of both the current analysis and statistical mechanics are compared with experimental data reported in the scientific literature, which show good agreement.
Ključne besede: statistical thermodynamics, mathematical models, thermal conductivity, nanofluids, transport properties, statistical nano-mechanics
Objavljeno: 31.05.2012; Ogledov: 1127; Prenosov: 60
URL Povezava na celotno besedilo

Characterisation of a new dental alloy with high Au content
Rebeka Rudolf, Tjaša Zupančič Hartner, Ivan Anžel, Primož Mrvar, Jože Medved, Dragoslav Stamenković, 2007, izvirni znanstveni članek

Opis: The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. This new Au dental alloy is based on the ternary system of Au-Pt-Zn with a nominal composition of 88.5Au-8.7Pt-1.5Zn-0.5In-0.4Ir-0.3Rh. The alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. Casting was followed with subsequent thermo-mechanical treatment (procedures of profile and polish milling, thermal treatment) and cutting-off strips to form a regular shape. The heat treatments of Au alloy samples were carried out in a tube furnace under different temperatures, and over different times. Testing of the new Au dental alloy included examining the initial cast, and the different heat treated conditions of the Au alloy. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done.Osnovo razvoja nove dentalne zlitine z visoko vsebnostjo Au predstavljata pravilna določitev kemijske sestave in tehnologije izdelave. Nova dentalna zlitina temelji na ternarnem sistemu of Au-Pt-Zn z nominalno kemijsko sestavo 88,5Au-8,7Pt-1,5Zn-0,5In-0,4Ir-0,3Rh. Izdelava dentalne zlitine je potekala s pretaljevanjem zelo čistih komponent v vakuumski indukcijski peči v Zlatarni Celje. Temu je sledilo odlivanje taline v ustrezno formo, postopek termo-mehanske obdelave odlitka in razrez zlitine v ustrezno obliko. Toplotna obdelava je bila izvedena pri različnih temperaturah in za različne čase. Testiranje dentalne zlitine je vključevalo določitev lastnosti začetnega stanja in stanja po različnih toplotnih obdelavah. Optične lastnosti dentalne zlitine so bile raziskane s spektro-fotometrično kolorimetrijo. Na novi Au dentalni zlitini so bili narejeni še testi citotoksičnosti z uporabo standardain vitro analize za testiranje biokompatibilnosti z uvajanjem novih, bolj občutljivih in vitro testov na celični liniji.
Ključne besede: dental alloy, characterisation, microstructure, properties
Objavljeno: 31.05.2012; Ogledov: 1244; Prenosov: 25
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The influence of thread twist on alterations in fibers` mechanucl properties
Andreja Rudolf, Jelka Geršak, 2006, izvirni znanstveni članek

Opis: In order to design high-quality threads, it is necessary to know the properties of threads and fibers, as well as the loadings and deformations which may occur during the sewing process. Thread properties depend on the mechanical properties of the fiber and the constructional parameters of the thread and its surface treatment, which directly influence sewing performance.The mechanical properties of a thread primarily depend on the fiber mechanical properties and the amount of twist. Knowledge of the thread dynamic loadings during the sewing process, depending on the number of turns and the lubrication method, is important for planning the required processing properties of the thread. This paper presents research into the influence of thread twist and the lubrication method on the mechanical properties and dynamic load of PES core-spun thread and its fibers. Research into the mechanical properties of the different twisted and surface treated threads, and separated fibers was carried out for this purpose. The influence of threaddynamic load during a sewing process was also researched regarding any alterations in the mechanical properties of the threads and separated fibers. Analyses of the results show that the amount of twist depends on the mechanical properties of the thread and its constituent fibers, whilst the method of surface treatment is based on the specific mechanical properties of the thread. A dynamic load causes greater or smaller thread deformations, which is reflected in changes in the thread and fiber mechanical properties. The occurred changes depend on dynamic load, amount of twist, and the lubrication method, which is confirmed with statistical analysis of the measured results.
Ključne besede: garment manufacturing, sewing, threads, textile fibres, surface treatment, dynamic loads, mechanical properties, amount of twist
Objavljeno: 30.05.2012; Ogledov: 1516; Prenosov: 18
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Development of a mathematical model for the heat transfer of the system man - clothing - environment
Jelka Geršak, Milan Marčič, 2007, izvirni znanstveni članek

Opis: The paper presents the development of a mathematical model of the heat transfer from the human body to the environment air that can be solved on a PC. The advantage of the presented heat transfer model is the ability of a fast evaluation of the heat transfer for various textile materials incorporated ino the clothing system under different ambient conditions.
Ključne besede: textiles, garment properties, heat transfer, mathematical model
Objavljeno: 31.05.2012; Ogledov: 1395; Prenosov: 64
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Antioxidant and antimicrobial activity of guarana seed extracts
Lucija Majhenič, Mojca Škerget, Željko Knez, 2007, izvirni znanstveni članek

Opis: The antioxidant and antibacterial activities of guarana (Paullinia cupana) seed extracts were determined. The seeds were extracted with water, methanol, 35% acetone and 60% ethanol at room (TR) and at boiling (TB) temperature of solvent.Extracts were analyzed for the contents of caffeine and catechins, epicatechin (EC), catechin (C) and epicatechin gallate (ECG), by high performance liquid chromatography (HPLC). The contents of total phenols (according to the Folin-Ciocalteu procedure) and proanthocyanidins were analysed by UV spectrophotometry. The guarana seed water extract obtained at room temperature contained higher amounts of caffeine and catechins than did alcoholic guarana seed extracts. The antioxidant and radical-scavenging activities of guarana seed extracts were evaluated using the ß-carotene-linoleic acid emulsion system and the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH ). All tested guarana seed extracts displayed strong antioxidant and radical-scavenging properties. The guarana seed extracts were tested against three food-borne fungi: Aspergillus niger, Trichoderma viride and Penicillium cyclopium, and three health-damaging bacteria: Escherichia coli, Pseudomonas fluorescens and Bacillus cereus by theagar well diffusion and broth dilution assay. The alcoholic guarana seed extracts displayed stronger antimicrobial activity against all tested microorganisms than did water extracts. Results presented here may suggest that seed extracts of guarana possess strong antimicrobial and antioxidant properties, and they can therefore be used as a natural additive in food, cosmetic and pharmaceutical industries.
Ključne besede: chemical processing, guarana extract, Paullinia cupana, seed extracts, antimicrobial properties, antioxidative properties
Objavljeno: 31.05.2012; Ogledov: 1210; Prenosov: 77
URL Povezava na celotno besedilo

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