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* old and bologna study programme


11 - 20 / 25
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Selestina Gorgieva, 2014, doctoral dissertation

Abstract: This work presents the methodological study, processing and optimization of novel, technologically acceptable procedure for in situ coating of polypropylene (PP) mesh (used for hernia treatment) with physico-chemically, mechanically and micro-structurally different gelatin (GEL) scaffolds to assess implant composite biocompatibility impact. In order to systematically follow the experimental work progress and respective achievements, whole research path is subdivided into three main sections. In the first section, the procedure for fabrication of gradiently micro-porous GELscaffolds on the cryo-unit’s cooling plate surface, using spatiotemporal and temperature- controlled gelation and freezing, followed by lyophylizaton was studied. Subsequently, cross-linking procedure using different molarities of reagents (EDC and NHS) and reaction media (100% PBS or 20/80% PBS/EtOH mixture) was performed for variable time extensions (1-24 h), rendering scaffolds physico-chemical properties. In this way, scaffolds with micro-structures having porosity gradient from 100 µm to 1000 µm and pores with rounded to ellipsoid morphology were formed, which, in combination with ethanol (EtOH) addition in cross-linking media modulates the swelling capacity towards twice lower percentages (~600%) comparing with scaffolds cross-linked in 100% PBS. Whilst the presence of EtOH reduce the cross-linking kinetic by retaining the scaffolds’ micro-structure formed during freezing, the 100% PBS and higher EDC molarity resulted in 40% cross-linking degree, being expressed as a thermal resistance up to 73 °C. The presented integral fabrication procedure was shown to allow tuning of both, the physical and micro-structural properties of scaffold, utilized in preparation of materials for specific biomedical applications. In the second part, the complex relation between surface and interface-related physico-chemical properties and gradient micro-structuring of 3D GELscaffolds, being fabricated by simultaneous temperature- controlled freeze-thawing cycles and in situ cross-linking using variable conditions (pH and molarity of carbodiimide reagent) and fibroblast cells viability (by tracking of their spreading and morphology) was established. Rarely- populated cells with rounded morphology and small elongations were observed on scaffolds with apparently negatively- charged surface with a lower cross-linking degree (CD) and consequently higher molecular mobility and availability of cell-recognition sequences, in comparison with the prominently- elongated and densely- populated cells on a scaffold’s with positively- charged surface, higher CD and lower mobility. Surface micro-structure effect was demonstrated by cell’s vacuolization and their pure inter-communication being present on scaffold’s bottom side with smaller pores (25±19 µm) and thinner pore walls (9±5 µm), over the air- exposed side with twice bigger pores (56±38 µm) and slightly thicker pore walls (12±6 µm). Strong correlation of preparation conditions (pH and reagents molarity) with CD (r2=0.96) and moderate correlation with local molecular mobility (r2 =-0.44), as well as micro-structure features being related to temperature gradient, imply on possibility to modulate scaffold’s properties in a direction to guide cell’s viability and most likely its genotype development. The third part presents an innovative strategy for the fabrication of bio-active PPmesh-GELscaffold composites with a potential for abdominal hernia treatment, where mesothelial cells in-growth have to be stimulated together with fibroblasts on-site proliferation, while formation of fibrin-developing, viscera-to-abdominal wall adhesions should be reduced, together with bacteria- related infections. In this respect, the plasma pre-activated PPmesh was coated with micro-structured GELscaffold, with pore size in 50 µm to 100 µm range at the upper-side and loosely- porous network at the composite bottom side, being modulated by sample thickness and freezing end- temperature applied. Simultaneously, the
Keywords: gelatin, targeted cross-linking, controlled freezing, gradiental micro-porosity, scaffold, surface and interface chemistry, physico-mechanical properties, polypropylene mesh, composite, biocompatibility.
Published: 07.05.2014; Views: 1076; Downloads: 80
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Vključitev tekstovnega prikazovalnika v sistem vodenja manipulatorja
Sebastjan Ribič, 2016, undergraduate thesis

Abstract: Na pnevmatski manipulator smo priključili dvovrstični prikazovalnik za upravljanje. Prikazovalnik TD-200 smo priključili na krmilnik SIEMENS S7-200, ki je upravljal z manipulatorjem. S pomočjo krmilne verige, diagrama stanj, pnevmatske sheme in z uporabo programa STEP 7-Micro/WIN smo spisali program in sporočila za izpisovanje dogodkov v sistemu manipulatorja. Komunikacija med krmilnikom in prikazovalnikom je delovala brez težav in testiranje na simulacijski plošči je pokazalo odlične rezultate.
Keywords: pnevmatski manipulator, dvovrstični prikazovalnik, TD 200, krmilnik S7-200, STEP 7-Micro/WIN
Published: 11.04.2016; Views: 463; Downloads: 49
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E-business in micro companies
Simona Sternad Zabukovšek, Irena Šišovska, Monika Mravljak, Samo Bobek, 2015, original scientific article

Abstract: E-business is entering its mature stage. E-business in large companies has been researched in several surveys, whereas SMEs and micro companies have been researched less often. Micro companies are, together with SMEs, a critical part of national economies worldwide; both are central to the EU%s development strategies. It is well known that, in an information society, business models are driven by e-business concepts, and e-business models are emerging. An in-depth understanding of e-business use in micro companies is crucial for the success of such companies. The main purpose of this paper is to research the intensity of e-business use, advantages and disadvantages of e-business, the biggest problems of e-business implementation/maintenance, and attitude toward trends of e-business in micro companies. The paper presents findings from a survey carried out on a sample of micro companies. Data were collected via an e-questionnaire, and results were calculated using SPSS. The data confirmed that e-business in micro companies is most often used in connection with e-banking; e-business with the government also appears to be very important.
Keywords: E-business, micro companies, e-business adoption, e-business CSFs
Published: 03.04.2017; Views: 299; Downloads: 62
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Roundabout arm capacity determined by microsimulation and discrete functions technique
Tomaž Tollazzi, Matjaž Šraml, Tone Lerher, 2008, original scientific article

Abstract: The paper demonstrates the influence of the multi-channel pedestrian flow on the actual capacity of a one-lane roundabout, using micro-simulation and discrete functions. The proposed model is based on the theory of the expected time gap between the units of pedestrian traffic flow, which have the priority when crossing the arm of the roundabout. The proposed model represents an upgrade of the previous research in the field of modelling traffic flows in the one-lane roundabout.Apart from the multi-channel pedestrian flow the disturbances caused by the circular traffic flow of motorised vehicles at the roundabout are also considered. In this way the model can better illustrate the real conditions in traffic. A simulation analysis has been performed on the roundabout arm at Koroška Street in Maribor. The results of the analysis have indicated a relatively high reserve of the actual throughput capacity for the main motorized traffic flow in the analysed roundabout arm. The presented model represents a practicable and adaptable tool for planning the roundabout capacity in practice and for the sensitivity analysis of individual variables on the throughput capacity of the roundabout.
Keywords: roundabouts, traffic flow analysis, micro-simulation modelling, capacity analysis
Published: 05.06.2017; Views: 531; Downloads: 46
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Reliable and accurate release of micro-sized objects with a gripper that uses the capillary-force method
Suzana Uran, Riko Šafarič, Božidar Bratina, 2017, original scientific article

Abstract: There have been recent developments in grippers that are based on capillary force and condensed water droplets. These are used for manipulating micro-sized objects. Recently, one-finger grippers have been produced that are able to reliably grip using the capillary force. To release objects, either the van der Waals, gravitational or inertial-forces method is used. This article presents methods for reliably gripping and releasing micro-objects using the capillary force. The moisture from the surrounding air is condensed into a thin layer of water on the contact surfaces of the objects. From the thin layer of water, a water meniscus between the micro-sized object, the gripper and the releasing surface is created. Consequently, the water meniscus between the object and the releasing surface produces a high enough capillary force to release the micro-sized object from the tip of the one-finger gripper. In this case, either polystyrene, glass beads with diameters between 5–60 µm, or irregularly shaped dust particles of similar sizes were used. 3D structures made up of micro-sized objects could be constructed using this method. This method is reliable for releasing during assembly and also for gripping, when the objects are removed from the top of the 3D structure—the so-called “disassembling gripping” process. The accuracy of the release was lower than 0.5 µm.
Keywords: micro-objects, one-finger gripper, gripping, releasing, capillary force
Published: 21.06.2017; Views: 354; Downloads: 314
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Monitoring the evaporation of fluids from fiber-optic micro-cell cavities
Eyal Preter, Borut Preložnik, Vlada Artel, Chaim Sukenik, Denis Đonlagić, Avi Zadok, 2013, original scientific article

Abstract: Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identificationof fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.
Keywords: fiber-optic sensors, opto-fluidics, evaporation monitoring, optical micro-cells, fiber cavities, droplet analysis
Published: 22.06.2017; Views: 252; Downloads: 165
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Fatigue crack initiation from microstructurally small Vickers indentations
Tomaž Vuherer, Andrej Godina, Zijah Burzić, Vladimir Gliha, 2007, original scientific article

Abstract: The resistivity of coarse grain steel against crack initiation in the presence of micro defects is discussed. Samples of material with martensitic microstructure were prepared by adequate thermal treatment. Microstructurally small Vickers indentations were used as an artificial micro defect. The compressive residual stresses are due to the irreversibility of plastic deformation. The moment of indenting enables to prepare samples with and without effects of residual stresses. The stress level for crack initiation depends on the actual indentation size. The location of initiated cracks is affected by the presence and character of residual stresses.
Keywords: welded joints, micro defect, coarse grain HAZ, crack initiation, crack growth, stress concentration, fatigue limit, Vickers, residual stresses
Published: 03.07.2017; Views: 292; Downloads: 56
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Quality and delivery of milk in Slovenia
Marjan Janžekovič, Maksimiljan Brus, Lidija Mužerlin, 2007, original scientific article

Abstract: Milk production represents the possibility of earning monthly income and assures social security to many farms in Slovenia. In Slovenia the European rules and regulations on the quality of the delivered milk have been introduced, relating to the hygienic quality of milk and the count of somatic cells. The purchase price of the milk depends also on the protein and fat content. The aim of the research was to establish, whether the quality of the delivered milk complies with the prescriptions regulated by the Slovene legislation. The quality of the delivered milk in the area of the Šentjur agricultural cooperative (ACŠ) and in the entire area of Slovenia (SLO) has been studied. The bacteriological data in the individual quality classes, the data on the total count of somatic cels and the data on the fat and protein contents have been analyzed. 36 monthly accounts have been included in statistical processing. It has been established that the delivered milk of the areas in question does not differ in the relevant quality values.
Keywords: cattle, milk quality, fats, proteins, micro-organisms, somatic cells
Published: 10.07.2017; Views: 280; Downloads: 52
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Compression pre-stress of tubular torsion springs
Vinko Močilnik, Nenad Gubeljak, Jožef Predan, Jože Flašker, 2010, original scientific article

Abstract: This paper reports the results of a series of biaxial static compression and torsion experiments performed to evaluate the effects of static compression stress on the fatigue life of those smooth tubes made of high strength spring steel. The fatigue life of biaxial loaded springs depends, among others, on biaxial compression and torsion loading. A high shear loading ratio leads to low-cycle fatigue behaviour rather than high-cycle fatigue, because it was found that a crack was initiated at a local highly deformed area on surface of the specimen.The experimentally obtained results show a significant extension of fatigue strain life as a result of combining axial compression loading with torsion. Cracking behaviour was observed and it was noted that compression pre-stresses contribute to retardation of the fatigue crack initiation process and, consequently, contribute to the extension of fatigue life.
Keywords: fatigue, fatigue life, micro crack, multi axial stress state, pre-stressing, torsion, torsion bar springs, twist angle
Published: 11.07.2017; Views: 225; Downloads: 50
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Influence of kinematic factors of friction stir welding on the characteristics of welded joints of forged plates made of EN AW 7049 A aluminium alloy
Milenko Perović, Sebastian Baloš, Dražan Kozak, Darko Bajić, Tomaž Vuherer, 2017, original scientific article

Abstract: In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min−1 to 850 min−1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow.
Keywords: dynamic recrystallization, friction stir welding, impact strength, micro hardness distribution
Published: 12.07.2017; Views: 342; Downloads: 200
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