31. The response of saturated soils to a dynamic loadStanislav Lenart, 2008, izvirni znanstveni članek Opis: This paper presents the two most significant types of deformation behavior fordynamically loaded, saturated soil. Flow liquefaction and cyclic mobility deserve special attention because of the large deformations that accompany these two phenomena. The submergence of a railway-line embankment due to the newly built Sava-river accumulation reservoir in Boštanj and the large landslide that occurred in the Stože area in the Julian Alps are case histories in Slovenia where flow liquefaction and cyclic mobility were analyzed. The dynamic loading caused by railway traffic and possible seismic activity were taken into account. Material from these two sites, silty sand and lacustrine carbonate silt, were used in extensive laboratory research, with the objective to define a procedure for excess pore-water pressure-generation modeling in dynamically loaded saturated soil.
It has been found recently that the change of the pore-water pressure is related to the dissipated energy density calculated from the hysteresis loops caused by dynamic loading. Based on the experimental results an empirical equation defining the generation of pore pressure during dynamic loading has been proposed. The equation is divided into two parts: the first part describing the residual pore-water pressure generation, and the second part describing the increment and decrement of pore-water pressure within the load cycle, the so-called temporary pore-water pressure change. The proper effective stresses and thus the stress path of the dynamically loaded soil can be defined by using the proposed energy-based numerical model.
The proposed pore-pressure model can also be used in deformation-behavior modeling. It was observed from the experimental results that after a few cycles of dynamic loading the saturated soil starts to exhibit a very low stiffness at the beginning of a load cycle, after which it begins to strengthen. The strain developed during this softening phase represents the main share of the total strain. The occurrence and duration of this phase are related to the energy dissipated during the cyclic loading as well, and the relation between the dissipated energy, the excess pore pressure and the short-term flow during cyclic mobility, give us an opportunity for a simple response modeling of the dynamically loaded saturated soils.
Ključne besede: flow liquefaction, cyclic mobility, excess pore pressure, dissipated energy
Objavljeno v DKUM: 05.06.2018; Ogledov: 1106; Prenosov: 241
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32. The limit values and the distribution of three-dimensional passive earth pressuresStanislav 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: 1160; Prenosov: 173
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33. Determination of passive earth pressure using three-dimensional failure mechanismHelena Vrecl-Kojc, Stanislav Škrabl, 2007, izvirni znanstveni članek Opis: This paper presents a modified three-dimensional (3D) failure mechanism for determining the 3D passive earth pressure coefficient using the upper bound theorem within the framework of the limit analysis theory. The translational kinematically admissible failure mechanism generalized with a depth of h = 1.0 is considered in the analysis. The mechanism geometry presents a volume of rigid blocks composed of the central body and two lateral rigid bodies, which are connected by a common velocity field. The front surface of the central body interacts with the retaining wall, while the upper surface can be loaded by surcharge loading. The lateral body segments represent four- and three-sided polygons in the cross section of the central body; therefore, they define the polygonal failure surface of the central part. At the outer side, each segment of the lateral body is bounded by infinitesimally spaced rigid half-cones that describe the envelope of a family of half-cones. The numerical results of 3D passive earth pressure limit values are presented by non-dimensional coefficients of passive earth pressure influenced by the soil weight Kpg and a coefficient of passive earth pressure influenced by the surcharge Kpq. This research was intended to improve the lowest values obtained until now using the limit analysis theory. The results are presentedin a graphical form depending on the geometrical parameters and soil properties. A brief description of two world-recognized failure mechanisms based on the limit analysis approach, and the comparison of three failure mechanism results are also presented.
Ključne besede: soil mechanics, passive earth pressure, upper bound theorem, optimization, three-dimensional failure mechanism
Objavljeno v DKUM: 18.05.2018; Ogledov: 1324; Prenosov: 78
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34. Interactional approach of cantilever pile walls analysisStanislav Škrabl, 2006, izvirni znanstveni članek Opis: This paper proposes a new method for the geomechanical analysis and design of cantilever retaining structures. It is based on the limit equilibrium method, but it uses some additional conditions for interaction between the retaining structure and the ground, when referring to the distribution of the mobilized earth pressures on the structure. The greatest benefit of the proposed method is shown in the analysis of structures of layered ground (heterogeneous above the dredge level and homogeneous below it), embedded in frictional and cohesive materials, and in the possibility of considering the influence of surcharge loadings on the active or passive side of the retaining structure. When analyzing such cases in practice, the proposed method gives results which are in better agreement with the results of FEM based elasto-plastic interaction analyses than with the results of currently used methods. At the same time, its results are in accordance with those published for homogeneaus cohesionless ground. Since in practice almost all retaining structures are erected in layered ground (heterogeneaus above the dredge level and homogeneous below it), the proposed method is very convenient and applicable for the analyses and design of cantilever structures under arbitrary geomechanical conditions.
Ključne besede: geomechanics, soil-structure interaction, retaining walls, embedment, cantilevers, earth pressure, pressure distribution, friction soil - wall, limit analysis, shear forces
Objavljeno v DKUM: 17.05.2018; Ogledov: 1460; Prenosov: 101
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35. Cyclic liquefaction potential of lacustrine carbonate from Julian AlpsBojan Žlender, Stanislav Lenart, izvirni znanstveni članek Opis: This paper presents the liquefaction studies of lacustrine carbonate silt from the Julian Alp landslide Stože. Geological conditions of the region and geomechanical characteristics of the ground were investigated. The research project was performed with the intention to determine the effects of cyclic loading on lacustrine carbonate silt. Investigation with 77 cyclic triaxial tests was performed on universal triaxial apparatus Wykeham Farrance UP 100 TR, in the Laboratory of soil mechanics, Faculty of Civil Engineering, University of Maribor. The essential equipment comprises cylindrical triaxial apparatus with a cell, a press with appurtenant electro-mechanic equipment, measuring equipment, and computer hardware and software equipment. Specimens with dimensions of height = 140 mm and diameter = 70 mm were saturated, then subjected to the arbitrary initial isotropic stress state and consolidated with vertical and radial draining, and then loaded with distortional loading of chosen dynamical axial force (frequency f = 1 Hz). A set of tests with a spectrum of different stress states and cyclic loading were performed. This research showed that lacustrine carbonate silt is a highly sensitive material.The resistance to liquefaction was somewhat higher than that of typical clean sand, but a perceivable excess pore pressure generation, which causes the decrease of strength parameters, was noticed. Test results of cyclic triaxial tests indicate dynamic characteristics of lacustrine carbonate silt and wide applicability of the test method.
Ključne besede: civil engineering, geomechanics, soil investigations, lacustrine carbonate silt, cyclic triaxial tests, liquefaction potential, shear modulus, damping ratio, cyclic stress ratio, pore pressure ratio
Objavljeno v DKUM: 15.05.2018; Ogledov: 1697; Prenosov: 140
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37. Increased augmentation index and central systolic arterial pressure are associated with lower school and motor performance in young adolescentsBernarda Vogrin, Marjan Rupnik, Dušanka Mičetić-Turk, 2017, izvirni znanstveni članek Opis: Objective: In adults, improper arterial function has been linked to cognitive impairment. The pulse wave velocity (PWV), augmentation index (AIx) and other vascular parameters are useful indicators of arterial health. In our study, we monitored arterial properties, body constitution, school success, and motor skills in young adolescents. We hypothesize that reduced cognitive and motor abilities have a vascular origin in children.
Methods: We analysed 81 healthy school children aged 11-16 years. Anthropometry central systolic arterial pressure, body mass index (BMI), standard deviation scores (SDS) BMI, general school performance grade, and eight motor tests were assessed. PWV, AIx, and central systolic arterial pressure (SBPao) were measured.
Results: AIx and SBPao correlated negatively with school performance grades. Extremely high AIx, PWVand SBPao values were observed in 5% of children and these children had average to low school performance. PWV correlated significantly with weight, height, and waist and hip circumference. AIx, PWV, school success, and BMI correlated strongly with certain motor functions.
Conclusions: Increased AIx and SBPao are associated with lower school and motor performance in children. PWV is influenced by the body's constitution.
Ključne besede: augmentation index, pulse wave velocity, school success, motor functions, young adolescents, central systolic arterial pressure, body mass index
Objavljeno v DKUM: 13.07.2017; Ogledov: 1285; Prenosov: 360
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38. Determining the speed of sound, density and bulk modulus of rapeseed oil, biodiesel and diesel fuelBoban Nikolić, Breda Kegl, Saša Marković, Melanija Mitrović, 2012, izvirni znanstveni članek Opis: Modern tendencies in the development of diesel engines include the operation of the system for injecting diesel fuel at pressures higher than 100 MPa. Knowing the characteristics of liquid fuels such as speed of sound, bulk modulus and density depending on pressure, is important for predicting the behavior of fuel injection systems for diesel engines and optimization of the same. The paper presents an original method and apparatus (device) for determining the speed of sound and density of fluids depending on the pressures. With this method, values of these characteristics for rapeseed oil, biodiesel and conventional diesel fuel at pressures up to 160 MPa are determined. The method is non-destructive, it can also be applied to higher pressures than 160 MPa, as well as other liquid fluids that are used at high pressure - hydraulic oil, for example.
Ključne besede: biodiesel, rapeseed oil, speed of sound, bulk modulus, density, high pressure
Objavljeno v DKUM: 07.07.2017; Ogledov: 1258; Prenosov: 380
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39. Partial pressure of end-tidal carbon dioxide successful predicts cardiopulmonary resuscitation in the field - a prospective observational studyMiran Kolar, Miljenko Križmarić, Petra Klemen, Štefek Grmec, 2008, izvirni znanstveni članek Opis: Introduction: The prognosis among patients who suffer out-of-hospital cardiac arrest is poor. Higher survival rates have been observed only in patients with ventricular fibrillation who were fortunate enough to have basic and advanced life support initiated early after cardiac arrest. The ability to predict outcomes of cardiac arrest would be useful for resuscitation. Changes in expired end-tidal carbon dioxide levels during cardiopulmonary resuscitation may be a useful non-invasive predictor of successful resuscitation and survival from cardiac arrest, and help in the termination of cardiopulmonary resuscitation in the field.
Methods: This is a prospective observational study of 737 cases of victims who suffered sudden out-of-hospital cardiac arrest. The patients were intubated and the measurements of end-tidal carbon dioxide were performed. Data according to the Utstein criteria, demographic information, medical data and partial pressure of end-tidal carbon dioxide (petCO2) values were collected for each patient in cardiac arrest, by the emergency physician. We presumed that an end-tidal carbon dioxide level of 1.9 kPa (14.3 mmHg) or more after 20 minutes of standard advanced cardiac life support would predict restoration of spontaneous circulation (ROSC).
Results: Partial pressure of end-tidal carbon dioxide after 20 minutes of advanced life support averaged 0.92+/- 0.29 kPa (6.9mmHg +/- 2.2 mmHg) in patients who did not have ROSC and 4.36 +/-1.11 kPa (32.8 mmHg +/- 9.1 mmHg) in those who did (p<0,001). End-tidal carbon dioxide values of 1.9 kPa (14.3 mmHg) or less discriminated between the 402 patients with ROSC and 335 patients without ROSC. When a 20-minute end-tidal carbon dioxide value of 1.9 kPa (14.3 mmHg) or less was used as a screening test to predict ROSC, the sensitivity, specificity, positive predictive value, and negative predictive value were all 100 percent.
Conclusions: Measurements of end-tidal carbon dioxide levels of more than 1.9 kPa (14.3 mmHg) after 20 minutes should be used to accurately predict ROSC. End-tidal carbon dioxide levels should be monitored during cardiopulmonary resuscitation and considered a useful prognostic value for determining the outcome of resuscitative efforts and termination of cardio-pulmonary resuscitation in the field.
Ključne besede: out-of-hospital cardiac arrest, cardiopulmonary resuscitation, CPR, partial pressure of end-tidal carbon dioxide, PetCO2
Objavljeno v DKUM: 29.06.2017; Ogledov: 1968; Prenosov: 187
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40. Process design for flavour encapsulation into carbohydrate melts using high pressure homogenizerUrban Feguš, 2016, doktorska disertacija Opis: The aim of the research project was to develop encapsulated flavourings suitable for the final food applications such as chewing gums, instant teas and confectionary products. For this purpose that water soluble particles with particle size distribution 400-1500 µm and flavour loading up to 30 wt. % should be developed.
In order to produce encapsulates with desired physical properties research work was divided into three project phases. The scope of Phase 1 was to select suitable carrier materials and to perform preliminary experiments using laboratory scale process set-up. Different carbohydrates (maltodextrin, simple sugars and sugar syrups) were tested and selected according to their physical characteristics and their process performance. Afterwards preliminary experiments were performed by using laboratory scale set-up. Observations were used for defining process parameters for the design and construction of the pilot plant.
Phase 2 covered design and development of the pilot plant for flavour encapsulation while In Phase 3 different process parameters were tested. In the first part influence of the process parameters (processing temperature, homogenizing pressure, mass flow, temperature of the cooling media, retention time in the cooling media and ratio between cooling media and product) on the encapsulation efficiency was investigated. Experiments were performed according to the Design of Experiments (DoE) analysed using analysis of covariance (ANCOVA). Process temperature, pressure at second homogenization step and residence time in cooling media had significant effect on the encapsulation efficiency while pressure at first homogenizing step, mass flow, temperature of the cooling media and ratio between product and cooling media were nonsignificant. Increase in the process temperature (T>130 °C) resulted in paste-like product with increased moisture content up to 13,3 wt.% which was not suitable for further processing. On the other hand samples processed at lower temperature (T<130 °C) resulted in crystalline-like structure with low moisture content. Low flavour retention (<4,5 %) was observed within all samples. Results obtained by ANCOVA were used for further optimization of the process parameters (e.g. homogenizing pressure and the retention time in the cooling media). Maximum flavour load of 3,5 % was observed regardless the homogenizing pressure. Low encapsulation efficiency (η<35 %) was related to poor emulsion stability. Additionally, effect of expansion pressure on the particle size distribution was investigated. It was observed that particle size distribution was little affected by varying expansion pressure (nozzle diameter). All formulation showed similar particle size distribution in-between 40-440 µm. In the last section effect of the emulsifier, flavouring properties and carrier were studied. Emulsifiers with different HLB values were tested in order to increase encapsulation efficiency. Flavourings were selected on the basis of their composition (polarity and volatility). For the encapsulation experiments mentha arvensis oil, orange oil and compounded pineapple flavouring were used. As an alternative carrier material erythritol was used. Addition of emulsifier improved flavour retention for samples containing mentha arvensis oil, while no affect was observed within samples containing orange oil and pineapple flavouring due to the volatility and diffusion of active compounds from matrix to surrounding environment.
Ključne besede: encapsulation, carbohydrate melts, flavouring, high pressure homogenizer
Objavljeno v DKUM: 25.07.2016; Ogledov: 2378; Prenosov: 161
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