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Characterization of Cu-Al-Ni melt-spun ribbons using a focussed ion beam (FIB)
Franc Zupanič, Elfride Unterweger, Albert C. Kneissl, Ivan Anžel, Gorazd Lojen, 2007, izvirni znanstveni članek

Opis: This work investigates the possibilities for applying a focussed ion beam (FIB) for the metallographic preparation and characterization of Cu-Al-Ni melt-spun ribbons. Two alloys were selected for this reason: CuAl13Ni4 and CuAl15Ni4. The microstructure of the first alloy was fully martensitic and the microstructure of the second consisted of two phases: martensite and ▫$\gamma_2$▫. It was discovered that with FIB-etching the microstructures of both alloys can be clearly revealed on polished cross-sections of the melt-spun ribbons, as well as on their wheel-side and air-side surfaces. However, better results were obtained when the etched surface was smoother, and finer details were visible when using smaller ion currents. In addition, a study was made into the influence of platinum deposition on the quality of 3D-cross sections. It was found that Pt-deposition is necessary when the edge of the trench should be straight and sharp, and the surface of the 3D cross-section smooth. However, in this case, the microstructure of the ribbons free surface cannot be seen.
Ključne besede: focussed ion beam, FIB, metallography, melt-spinning, shape memory alloy, Cu-Al-Ni
Objavljeno: 31.05.2012; Ogledov: 800; Prenosov: 15
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Metallographic sample preparation of orthodontic Ni-Ti wire
Lidija Zorko, Rebeka Rudolf, 2009, izvirni znanstveni članek

Opis: Shape memory alloys (SMA) has been at the forefront of research for the last several decades. In this field especially, Nickel-Titanium (Ni-Ti) alloys have been found to be the most useful of all SMA. The most important applications of SMA Ni-Ti alloys are namely in medicine and dentistry, where they are used as orthodontic wires. In this paper we describe the procedure of preparing metallographic samples of typical orthodontic Ni-Ti wires which are nowadays used in dentistry praxis. We prepared the samples for microstructure observation using a light microscope. Special attention is given to the metallographic preparation, which could result in damages and deformations of the sample surfaces if the procedure is incorrect. Finally, we illustrated the typical metallographic recipe for Ni-Ti SMA alloys for optical observation.
Ključne besede: shape memory alloys, Ni-Ti wire, metallographic preparation, microstructure
Objavljeno: 31.05.2012; Ogledov: 934; Prenosov: 14
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Microstructure of rapidly solidified Cu-Al-Ni shape memory alloy ribbons
Gorazd Lojen, Ivan Anžel, Albert C. Kneissl, Elfride Unterweger, Borut Kosec, Milan Bizjak, 2005, izvirni znanstveni članek

Opis: Cu-Al-Ni shape memory alloys (SMAs) are currently the only available high temperature SMAs, showing a good resistance against functional fatigue. In polycrystalline state, they are very brittle and exhibit, in general, only small reversible deformations. By melt spinning, thin Cu-Al-Ni ribbons can be manufactured directly from the melt. Appropriate casting parameters can ensurea single layer columnar structure with a fibre texture, which significantly increases the maximal reversible strain in longitudinal direction. Cu-Al-Ni ribbons, containing 13, 14 and 15 wt.% Al were cast by free jet melt spinning. Because of the alloys' low thermal conductivity, the cooling rate was surprisingly low - considering the crystal grain size - significantly below 103 K/s. Therefore, wide ribbons having a single layer columnar and (except the ribbons containing 13 wt.% Al) completely martensiticstructure could not be obtained. Regardless the chemical composition, the ribbons have a single layer columnar structure only if the thickness does not exceed approximately 50 m, otherwise the structure consists of at least two layers of equiaxed grains. In as-cast condition, only ribbons containing 13 wt.% Al seem to be completely martensitic. Heat treatments at temperatures up to 900 °C improved the structure of 13 and 14 wt.% Al ribbons. All ribbons exhibit one-way shape memory effect in as-cast condition. Heat-treated ribbons containing 13 wt.% Al exhibited two-way shape memory effect already after one bending and heating cycle.
Ključne besede: metallurgy, shape memory alloys, Cu-Al-Ni alloy, microstructure, melt spinning
Objavljeno: 01.06.2012; Ogledov: 960; Prenosov: 41
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Microstructure and properties of shape memory alloys
Albert C. Kneissl, Elfride Unterweger, Gorazd Lojen, Ivan Anžel, 2005, izvirni znanstveni članek

Opis: This work addresses three topics: the generation of two-way shape memory effects in NiTi, NiTiW and CuAlNi wire materials and the investigation of the long term stability of these effects; investigations on thin CuAlNi films produced by PVD; investigation on thin CuAlNi ribbons produced by melt-spinning.
Ključne besede: metallurgy, shape memory alloys, properties, microstructure
Objavljeno: 01.06.2012; Ogledov: 703; Prenosov: 27
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Competition between local disordering and global ordering fields in nematic liquid crystals
Matej Cvetko, Milan Ambrožič, Samo Kralj, 2010, izvirni znanstveni članek

Opis: We study the influence of external electric or magnetic field B on orientational ordering of nematic liquid crystals or of other rod-like objects (e.g. nanotubes immersed in a liquid) in the presence of random anisotropy field type of disorder. The Lebwohl-Lasher lattice type of semi-microscopic approach is used at zero temperature. Therefore, results are valid well below the transition into the isotropic phase. We calculate the correlation function of systems as a function of B, concentration p of impurities imposing random anisotropy field disorder, the disorder strength W and system dimensionality (2D and 3D systems). In order to probe memory effects we calculate correlation length ▫$xi$▫ for random and homogeneous initial configurations. We determine the crossover fields Bc(p) separating roughly the ordered and disordered regime. Memory effects are apparent only in the latter case, i.e. for B < Bc.
Ključne besede: disorder, Imry-Ma theorem, liquid crystals, memory effect, orientational order
Objavljeno: 07.06.2012; Ogledov: 681; Prenosov: 71
.pdf Celotno besedilo (747,18 KB)
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Memory effects in randomly perturbed systems exhibiting continuous symmetry breaking
Matej Cvetko, Milan Ambrožič, Samo Kralj, 2009, izvirni znanstveni članek

Opis: We studied pattern characteristics in randomly perturbed structures exhibitingcontinuous symmetry breaking. A Lebwohl-Lasher-type lattice model was used which described well the onset of orientational ordering of a system of rod-like objects. For example, such systems mimic the orientational ordering tendency in liquid crystals or in an ensemble of nanotubes. We set impurities to impose a random anisotropy type of disorder on the objects. Structural characteristics were studied as a function of concentration of impurities, interaction strength w between impurities and rod-like objects, external ordering strength and history of samples. We showed that the characteristic linear size of patterns and range of ordering strongly depend on the history of samples for weak enough strength w. The two-dimensional and three-dimensional simulations yielded qualitatively similar results.
Ključne besede: liquid crystals, memory effect, nanotubes, structural order, percolation
Objavljeno: 07.06.2012; Ogledov: 709; Prenosov: 49
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Spatial rotation and recognizing emotions : gender related differences in brain activity
Norbert Jaušovec, Ksenija Jaušovec, 2008, izvirni znanstveni članek

Opis: In three experiments, gender and ability (performance and emotional intelligence) related differences in brain activity - assessed with EEG methodology - while respondents were solving a spatial rotation tasks and identifying emotions in faces were investigated. The most robust gender related difference in brain activity was observed in the lower-2 alpha band. Males and females displayed an inverse IQ-activation relationship in just that domain in which they usually perform better: females in the emotional intelligence domain, and males in the visuospatial ability domain. A similar pattern of brain activity could also be observed for the male/female respondents with different levels of performance and emotional IQ. It was suggested that high ability representatives of both genders to some extent compensate for their inferior problem solving skills (males in emotional tasks and females in spatial rotation tasks) by increasing their level of attention.
Ključne besede: psychology, cognitive processes, emotional intelligence, EEG activities, problem complexity, brain, memory, spatial rotation, gender, event-related desynchronization
Objavljeno: 07.06.2012; Ogledov: 1143; Prenosov: 19
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David Satler, 2013, magistrsko delo

Opis: The main aim of this thesis was to examine verbal working memory in native and foreign language. In the theoretical part we mainly focused on the Baddeley’s (2002) multicomponent model of working memory. We also reviewed several studies that had aims similar to ours. Finally, we briefly discussed the importance of working memory for scholastic attainment and effectiveness of working memory training. For the empirical part, two versions of an experiment were designed. One version was in Slovene and the other in English. We tested verbal working memory of 76 participants which we divided into four groups. Two groups were tested in their native (Slovene) language, and two in foreign (English) language. The experiment consisted of twelve word sequences, each containing five words. English words were matched with their Slovene equivalents in meaning, frequency and number of syllables. The participants had to recall each word in a sequence in order in which it appeared. The groups were matched for age and level of education, but differed in language proficiency. Results of the experiments strongly support the view that verbal working memory interacts with language proficiency and that it is superior in native language. Furthermore, similar phenomena showed in both languages, suggesting universal nature of verbal working memory.
Ključne besede: working memory, verbal working memory, foreign language, native language, language proficiency
Objavljeno: 07.10.2013; Ogledov: 1246; Prenosov: 150
.pdf Celotno besedilo (1,37 MB)

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