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Numerical simulation of the pile integrity test on defected piles
Mladen Ćosić, Boris Folić, Radomir Folić, 2014, izvirni znanstveni članek

Opis: This paper deals with the development of a discrete numerical 2D and 3D solid pile model with a discontinuity and defects to simulate non-destructive testing using the pile integrity test (PIT). The pile discontinuity and defects were modelled by reducing the specific finite elements and the elastic modulus of concrete. The wave-propagation response of the pile was analyzed based on a step-by-step numerical integration using the Hilber-Hughes-Taylor (HHT) method in the time domain. The concept of a system-response analysis was originally formulated based on the integration of individual reflectograms into a reflectogram surface, which is generated in a 3D cylindrical coordinate system. The use of reflectogram surfaces enables an understanding of wave propagation based on their velocity to a higher level than is usually the case with standard, one-dimensional reflectograms. Changes in the velocity responses on the reflectogram, shifting from a positive to a negative value, point to the locations of discontinuities and defects in the discrete 3D pile model, and there is a clear difference in the reflectograms, depending on the position of the measuring point. The study defines the typological models of the reflectogram: without discontinuities and defects, pile-head defect, defect in the middle of the pile length or a reduced modulus of elasticity in the middle of the pile length, pile-base defect or reduced modulus of elasticity in the pile-base zone and reduced modulus of elasticity in the pile-head zone.
Ključne besede: reflectogram surface, numerical pile model, solid finite elements
Objavljeno v DKUM: 14.06.2018; Ogledov: 705; Prenosov: 68
.pdf Celotno besedilo (769,91 KB)
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Atterberg limits in relation to other properties of fine-grained soils
Bojana Dolinar, Stanislav Škrabl, 2013, izvirni znanstveni članek

Opis: In soil mechanics the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure. As they depend on the same physical factors as the other mechanical properties of soils, the values of the liquid and plastic limits would be a very convenient basis for their prediction. There are many studies concerning the use of the Atterberg limits in soil mechanics; however, their results vary considerably and are not generally applicable. This paper explains the main reasons for the different conclusions in these studies, which do not take into account the following: a) the water in fine-grained soils appears as interparticle and interaggregate pore water as well as adsorbed water onto the surfaces of clay minerals; b) the physical properties of fine-grained soils depend on the quantity of pore water only, because the adsorbed water is tightly tied on the clayʼs external and internal surfaces and thus cannot influence to them; c) the quantity of adsorbed water on the external surfaces of the clay minerals in soils depends mostly on the size and the quantity of the clay minerals, while the interlayer water quantity depends mostly on the quantity and the type of the swelling clay minerals in the soil composition and their exchangeable cations. From this it follows that for swelling and non-swelling soils, the uniform relationships between the Atterberg limits (which represent the total quantity of pore water and the adsorbed water onto the external and internal surfaces of clay minerals) and other physical properties does not exist. This paper presents some possibilities for the use of the Atterberg limits in predicting the soilʼs other properties for non-swelling and limited-swelling soils.
Ključne besede: Atterberg limits, specific surface area, undrained shear strength, compressibility, hydraulic conductivity
Objavljeno v DKUM: 14.06.2018; Ogledov: 669; Prenosov: 57
.pdf Celotno besedilo (133,59 KB)
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The stability of the excavation face of shallow civil and mining tunnels
Pierpaolo Oreste, 2011, izvirni znanstveni članek

Opis: The stability of the excavation face of shallow tunnels excavated in difficult ground conditions is currently a relevant problem in the sector for tunnelling and mining. Even though face-reinforcement interventions with fibreglass dowels have proved to be efficient, there is still no reliable analysis and dimensioning method available. A new calculation procedure is illustrated in this paper for the analysis of the face static condition in shallow tunnels, also when reinforcement interventions with fibreglass dowels are used. The procedure is based on the limit-equilibrium method applied to the ground core ahead of the face. The main result of the calculation is that the safety factor of the excavation face is also obtained in the presence of reinforcements and from this it is then possible to proceed with the dimensioning of the intervention. The procedure has been applied to two real cases and satisfactory results have been obtained.
Ključne besede: fibreglass dowels, face reinforcement, surface tunnel, limit equilibrium method, factor of safety
Objavljeno v DKUM: 13.06.2018; Ogledov: 766; Prenosov: 78
.pdf Celotno besedilo (213,90 KB)
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The limit values and the distribution of three-dimensional passive earth pressures
Stanislav Škrabl, 2008, izvirni znanstveni članek

Opis: This paper presents a novel approach to the determination of the critical distribution and limit values of three-dimensional passive soil pressures acting on flexible walls following the upper-bound method within the framework of the limit-analysis theory. The method of limit analysis with a set of three-dimensional kinematically admissible hyperbolic translational failure mechanisms is used to determine the critical distribution of the passive pressures along the retaining structurećs height. The intensity of thepassive pressures is gradually determined with the mentioned translational failure mechanisms in the top-down direction. Thus, the critical distribution,the trust point and the resultant of the passive pressures that can be activated at the limit state for the chosen kinematic model are obtained. The results of the analyses show that the total sum of passive pressures, considering the critical distribution, is lower than the comparable values published in the literature. Furthermore, the trust point of the passive pressure resultant is independent of the friction between the retaining structures and the soil.
Ključne besede: limit analysis, earth pressure, passive pressure, failure surface, soil-structure interaction
Objavljeno v DKUM: 05.06.2018; Ogledov: 692; Prenosov: 56
.pdf Celotno besedilo (331,84 KB)
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Innovative solution principles of wave problems in horizontaly layered medias
Andrej Štrukelj, Andrej Umek, Tomaž Pliberšek, 2006, izvirni znanstveni članek

Opis: The paper presents engineeringly reasonable transformation of surface displacements of horizontally layered half-space. The latter shows in the half-space present types of waves. It is shown that surface waves are expressed through residuums in poles of the integrand and the volume waves are expressed as integrals along corresponding branch cuts. The singularity which always appears in the basic singular solution in elastodynamics is in this case exactly excluded. In the second part of the paper the behaviour of Stonely waves is investigated in greater detail. It is shown that in the case of layers of finite thickness their appearance and velocities depends not onlyon the material characteristics of neighbouring layers but also on their thickness.
Ključne besede: geomechanics, horizontally layered halfspace, volume waves, surface waves, Green`s function, Stonely waves
Objavljeno v DKUM: 17.05.2018; Ogledov: 954; Prenosov: 52
.pdf Celotno besedilo (613,03 KB)
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Undrained shear strength of saturated cohesive soils depending on consolidation pressure and mineralogical properties
Bojana Dolinar, 2004, izvirni znanstveni članek

Opis: The relationship between the water content and the undrained shear strength of finely grained soils can be described with a nonlinear function in which the type of soils is determined by two parameters. These parameters depend primarily on the size of clay minerals, their quantity in soil composition and the interlayer water quantity in expanding clay minerals. This article asserts that there exists also the exactly defined relationship also between the water content and consolidation pressure. In the function describing this relationship, the type of soil is determined by two parameters. They can be expressed depending on the same mineralogical properties of soils as the values of parameters in the function showing the relationship between the water content and the undrained shear strength. These findings allow us to express the ratio between undrained shear strength and consolidation pressure depending on mineralogical properties of soils.
Ključne besede: soil mechanics, properties of soils, clays, specific surface, undrained shear strenght, compressibility
Objavljeno v DKUM: 15.05.2018; Ogledov: 1020; Prenosov: 88
.pdf Celotno besedilo (103,26 KB)
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Modification of polyamide knitted fabric using different zeolites
Alenka Ojstršek, Tomaž Fakin, Karin Stana-Kleinschek, Darinka Fakin, 2017, izvirni znanstveni članek

Opis: The aim of this research was to apply three different types of zeolites and the combination thereof in the form of a very fine powder, together with different chemicals and additives on polyamide knitted fabric according to an industrially acceptable exhaustion procedure in order to study changes in the morphology, optical properties and wettability of surfaces. Zeolites were analysed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and gas physiosorption. Additionally, the morphology of zeolite-coated surfaces was examined closely using SEM, while changes in molecular-chemical level were examined by means of IR spectroscopy. Optical properties were studied using CIE colour measurement and diff use reflectance profi le determination, while the hydrophilic/hydrophobic character was examined using goniometry. The obtained results show the suitability of the employed exhaustion procedure, depending on the type of zeolite and the composition of the treatment bath. The results also provided evidence of the enhanced wettability of PA fabrics using 4A and 13X zeolites in combination with selected additives.
Ključne besede: zeolites, polyamide fibres, exhaustion, surface modification, wettability
Objavljeno v DKUM: 31.08.2017; Ogledov: 961; Prenosov: 386
.pdf Celotno besedilo (577,72 KB)
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The LexA regulated genes of the Clostridium difficile
Beata Maria Walter, Maja Rupnik, Vesna Hodnik, Gregor Anderluh, Bruno Dupuy, Nejc Paulič, Darja Žgur-Bertok, Matej Butala, 2014, izvirni znanstveni članek

Opis: Background: The SOS response including two main proteins LexA and RecA, maintains the integrity of bacterial genomes after DNA damage due to metabolic or environmental assaults. Additionally, derepression of LexA-regulated genes can result in mutations, genetic exchange and expression of virulence factors. Here we describe the first comprehensive description of the in silico LexA regulon in Clostridium difficile, an important human pathogen. Results: We grouped thirty C. difficile strains from different ribotypes and toxinotypes into three clusters according to lexA gene/protein variability. We applied in silico analysis coupled to surface plasmon resonance spectroscopy (SPR) and determined 16 LexA binding sites in C. difficile. Our data indicate that strains within the cluster, as defined by LexA variability, harbour several specific LexA regulon genes. In addition to core SOS genes: lexA, recA, ruvCA and uvrBA, we identified a LexA binding site on the pathogenicity locus (PaLoc) and in the putative promoter region of several genes involved in housekeeping, sporulation and antibiotic resistance. Conclusions: Results presented here suggest that in C. difficile LexA is not merely a regulator of the DNA damage response genes but also controls the expression of dozen genes involved in various other biological functions. Our in vitro results indicate that in C. difficile inactivation of LexA repressor depends on repressor`s dissociation from the operators. We report that the repressor`s dissociation rates from operators differentiate, thus the determined LexA-DNA dissociation constants imply on the timing of SOS gene expression in C. difficile.
Ključne besede: Clostridium difficile, antibiotic resistance, toxin regulation, SOS system, surface plasmon resonance, SPR, LexA repressor
Objavljeno v DKUM: 29.06.2017; Ogledov: 1021; Prenosov: 347
.pdf Celotno besedilo (1,16 MB)
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Protein adsorption on various plasma-treated polyethylene-terephthalate substrates
Nina Recek, Morana Jaganjac, Metod Kolar, Lidija Milković, Miran Mozetič, Karin Stana-Kleinschek, Alenka Vesel, 2013, izvirni znanstveni članek

Opis: Protein adhesion and cell response to plasma-treated polymer surfaces were studied. The polymer polyethylene terephthalate (PET) was treated in either an oxygen plasma to make the surface hydrophilic, or a tetrafluoromethane CF4 plasma to make the surface hydrophobic. The plasma source was radiofrequency (RF) discharge. The adsorption of albumin and other proteins from a cell-culture medium onto these surfaces was studied using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The cellular response to plasma-treated surfaces was studied as well using an MTT assay and scanning electron microscopy (SEM). The fastest adsorption rate was found on the hydrophilic oxygen plasma-treated sample, and the lowest was found on the pristine untreated sample. Additionally, the amount of adsorbed proteins was higher for the oxygen-plasma-treated surface, and the adsorbed layer was more viscoelastic. In addition, cell adhesion studies support this finding because the best cell adhesion was observed on oxygen-plasma-treated substrates.
Ključne besede: oxygen and fluorine plasma treatment, polymer surface modification, protein adsorption, cell adhesion, quartz crystal microbalance, QCM
Objavljeno v DKUM: 22.06.2017; Ogledov: 867; Prenosov: 363
.pdf Celotno besedilo (2,39 MB)
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