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1.
VPLIV DODATKA »SELACID® GREEN GROWTH« NA PITOVNE LASTNOSTI BROJLERSKIH PIŠČANCEV
Eva Gačnik Hrastnik, 2009, diplomsko delo

Opis: V diplomski nalogi smo predstavili vpliv in delovanje krmnega dodatka »Selacid® Green Growth« na proizvodne lastnosti brojlerskih piščancev. Poskus se trajal 42 dni na Testni postaji za perutnino, Fakultete za kmetijstvo in biosistemske vede, Univerze v Mariboru. Piščanci petelinčki provenience ROSS 308, so bili krmljeni s krmnimi mešanicami iz redne proizvodnje , ki smo jih razdelili v 4 testne skupine po 300 živali. Testna skupina A je predstavljala kontrolno skupino, ki je prejemala krmo brez dodatka, piščanci testnih skupin B, C in D pa so v krmi prejemali dodatek »Selacid® Green Growth« v različnih odmerkih na tono krme. »Selacid® Green Growth« je koncentriran prehranski dodatek, s posebno kombinacijo kratkoverižnih organskih kislin in srednjeverižnih maščobnih kislin ter njihovih soli, s širokim spektrom delovanja na Gram- kot na tudi z Gram+ bakterije v prebavnem traktu perutnine. Osnovni namen in cilj raziskave je bil ugotoviti, ali krmni dodatek pozitivno vpliva na rentabilnost proizvodnje piščančjega mesa. Rezultati so pokazali, da so piščanci iz kontrolne skupine A pri tehtanjih dosegli nižjo telesno maso. Piščanci iz testnih skupin B, C in D so dosegli tudi nižjo konverzijo krme, prav tako pa so statistično značilno (P≤0,05) odstopali pri doseženem proizvodnem številu, ki je bilo višje kot pri kontrolni skupini A.S tem smo potrdili pozitiven učinek testiranega dodatka.
Ključne besede: brojlerski piščanec / prehrana / organske kisline / alternativni krmi dodatki / »Selacid® Green Growth«
Objavljeno: 30.11.2009; Ogledov: 2235; Prenosov: 177
.pdf Celotno besedilo (472,22 KB)

2.
Analysis of growth models for batch kefir grain biomass production in RC1 reaction system
Marko Tramšek, Andreja Goršek, 2008, izvirni znanstveni članek

Opis: This work describes the statistical analysis of three mathematical models, modified for describing the kefir grain biomass growth curve. Experimental data of time-dependent kefir grain mass increase were used. The propagation was performed in RC1 batch reaction system under optimal bioprocess parameters (temperature, rotational frequency of stirrer, glucose mass concentration) using traditional cultivation in fresh, high-temperature, pasteurized whole fat cow's milk. We compared values of biological parameters obtained by applying the nonlinear regression of experimental data in logistic, Gompertz and Richards models. The most statistically appropriate model was determined using the seven statistical indicators. We established that the kefir grain biomass growth curve during batch propagation under optimal bioprocess conditions can be most successfully described using the Gompertz growth model.
Ključne besede: chemical processing, milk products, kefir grain growth, process parameters, design of experiments, modeling, mathematical models, Gompertz growth model, RC1
Objavljeno: 31.05.2012; Ogledov: 1645; Prenosov: 36
URL Povezava na celotno besedilo

3.
Numerical analysis of the crack growth in a high loaded bolt connection
Marko Knez, Srečko Glodež, Janez Kramberger, 2007, izvirni znanstveni članek

Opis: The paper deals with the research on the crack growth in a bolt connection of a lug for crane counter weight bars. Counter weight bars are structural elements subjected to very heavy loads and therefore need special attention. The main purpose of this research is to determine the number of load cycles required for a crack to propagate from initial to criticakl crack length, whenthe final failure can be expected to occur. All required material parameters and experimental results were determined in our previous research. The influence of the initial crack siye upon the remaining life of the lug is reserched numericallu by means of FE analysis and analytically by use of the corrected analystical model.
Ključne besede: fracture mechanics, cyclic loading, fatigue crack growth, service life prediction, numerical analysis, bolt connection
Objavljeno: 31.05.2012; Ogledov: 1347; Prenosov: 31
URL Povezava na celotno besedilo

4.
Quantitative examination of process parameters during kefir grain biomass production
Andreja Goršek, Marko Tramšek, 2007, kratki znanstveni prispevek

Opis: This article examines the propagation of kefir grains in fresh HTP whole fat cows' milk, with some additions (glucose and bakers yeast). The objective of our work was an experimental determination of the various process parameters relative influence on the propagation and daily kefir grain increase mass, using the Taguchi method for experimental design. The effects of medium temperature, glucose mass concentration, bakers yeast mass concentration and the rotational frequency of the stirrer at four levels were studied. Orthogonal array layout of L16 was selected for the proposed experimental design. All experiments were performed in an automated laboratory reaction calorimeter RC1 (Mettler-Toledo) with the same milk (3.5 % fat). The gravimetric method was used to determine daily kefir grain mass increases. Relative contributions of the proposed influencing process parameters on the daily kefir grains increase mass were estimated by analysis of the variance (ANOVA). The highest increase (51.5 %) was found at the rotational frequency of the stirrer 90 (1/min), at glucose mass concentration 20 g/L, and at mediumtemperature 24 °C. Within the observed range of yeast mass concentrationthis process parameter was found to be insignificant compared to others. The rotational frequency of the stirrer has the highest relative influence on the daily kefir grains increase mass (37.3 %) while glucose mass concentration and medium temperature have lower ones, 18.8 % and 9.9 %, respectively. The remaining fraction represents error influence. The main reason for its relatively high value (34.0 %) is that kefir grains are bulky and awkward to handle. This fact confirms the importance of optimal kefir grains production management.
Ključne besede: chemical processing, milk products, kefir, kefir grain growth, process parameters, design of experiments, Taguchi method, RC1
Objavljeno: 31.05.2012; Ogledov: 1519; Prenosov: 30
URL Povezava na celotno besedilo

5.
A novel approach for assuring and following inoculum activity during kefir grains growth studies : application of dynamic pH profiles
Marko Tramšek, Andreja Goršek, 2007, izvirni znanstveni članek

Opis: The profiles of kefir grains growth curves strongly depend on bioprocess conditions and inoculum viability. Therefore, accurate growth curve studies require the use of optimally active kefir grains as inoculum. Accordingly, the main objective of our study was experimental optimization of classic kefir grains activation procedure and afterwards, comparison among growth curves of differently activated kefir grains. For this purpose some experiments were initially performed in computer-controlled RC1 reactor provided data of dynamic pH profiles during batch propagation of differently activated grains. Experimental data were mathematically analyzed and using the special methodology of minimizing the absolute deviation of pH(t) profiles the minimal time for grains activation was determined. We established that optimal inoculum activity could be ensured only by the kefir grains, which were previously activated at least over eleven successive days. In the second part of research the growth curve of optimally activated kefir grains was constructed using experimental measurements and fitted with Gompertz model. The present results were compared with the results obtained by our previous study, where classically activated grains were used. We established that, inspite of equal daily kefir grain mass increase, considerable difference in growth curves of differently activated kefir grains exist.
Ključne besede: chemical processing, kefir grains, growth curve, minimal activation time, dynamic pH profiles, Gompertz model
Objavljeno: 31.05.2012; Ogledov: 1028; Prenosov: 36
.pdf Celotno besedilo (384,93 KB)
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6.
Microcrack initiation and growth in heat-risistant 15Kh2MFA steel under cyclic loading
P. Yasniy, V.B. Hlado, V. Hutsaylyuk, Tomaž Vuherer, 2005, izvirni znanstveni članek

Opis: This paper presents the results of investigation of a nuclear reactor pressurevessel steel 15Kh2MFA of two strength levels under cyclic loading. Themechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found.
Ključne besede: material testing, nuclear reactor, pressure vessel, cyclic loading, cyclic deformation, dislocation structure, fatigue crack growth, TEM, fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 899; Prenosov: 12
URL Povezava na celotno besedilo

7.
Modelling of surface crack growth under lubricated rolling-sliding contact loading
Boštjan Zafošnik, Zoran Ren, Jože Flašker, Gennady Mishuris, 2005, izvirni znanstveni članek

Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno: 01.06.2012; Ogledov: 1484; Prenosov: 29
URL Povezava na celotno besedilo

8.
Effect of residual stresses on the fatigue crack propagation in welded joints
Nenad Gubeljak, Jožef Predan, Reinhard Pippan, Maks Oblak, 2005, izvirni znanstveni članek

Opis: The effect of residual stress on the fatigue crack growth was investigated forcyclic tension. Three-point bend specimens were used with through thicknessnotches at the center line of the welded joint. The experiments were performed for different load amplitudes and load ratios under conditions of small-scale yielding. The influence of the residual stresses on fatigue crack growth was estimated by experimentally observed fatigue crack growth rate and measurement of residual stresses at the surface of specimen. This paper describes an approach taken in two models to estimate the residual stress effect on fatigue crack propagation and to predict remaining service life of awelded structure.
Ključne besede: fracture mechnaics, fatigue crack, crack growth, residual stresses, fatigue crack growh rate, X-ray
Objavljeno: 01.06.2012; Ogledov: 1051; Prenosov: 21
URL Povezava na celotno besedilo

9.
Micromechanical analysis of constraint effect on fracture initiation in strength mis-matched welded joints
Miloš Dobrojević, Marko Rakin, Nenad Gubeljak, I. Cvijović, Milorad Zrilić, N. Krunich, Aleksandar Sedmak, 2007, izvirni znanstveni članek

Opis: In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect crack growth initiation in mismatched welded joints. The single edged- notched bend specimens (precrack length ▫$a_o/W=0.32$▫) were experimentally and numerically analysed. The coupled micromechanical model prposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18 mm). HSLA steel was used as the base metal in a quenched and tempered condition. The flux-cored arx-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smmoth specimen. The difference in fracture behaviour between over- and undermatched welded joints obtained in experimental results was followed by numerical computationsof void volume fraction in front of the crack tip.
Ključne besede: fracture mechanics, ductile fracture, high strength low alloyed steel, cracks, micromechanical model, mismatched welded joints, constraint effect, void growth
Objavljeno: 01.06.2012; Ogledov: 1008; Prenosov: 25
URL Povezava na celotno besedilo

10.
The influence of different parameters on surface pitting of contacting mechanical elements
Gorazd Fajdiga, Jože Flašker, Srečko Glodež, 2004, izvirni znanstveni članek

Opis: The paper describes a general computational model for simulation of surface pitting of mechanical elements subjected to contact loading conditions. In the model it is assumed that the initial crack of length 0.015 mm is initiated at the contacting surfaces due to previously thermal, mechanical treatment of the material or running in process. The discretised model with the initial crack is then subjected to normal contact pressure, which takes into account the EHD lubrication conditions and tangential loading due to friction between contacting surfaces. The model accounts also for the influence of fluid trapped in the crack on crack prppagation. The virtual crack extension VCE method within FEM analysis is then used for 2 dimensional simulation of fatigue crack propagation from the initial crack up to the formation of the surface pit. The pit shapes and relationships between the stress intensity factor and crack length are determined for various combinations of contacting surface curvatures and loadings. The comparison of computational and available experimental results shows that the proposed model reliably simulates the surface fatigue crack growth under contact loading and can be used for computational predictions of surface pitting for various contacting mechanical elements.
Ključne besede: machine elements, gears, contact problems, pitting, fatigue crack growth, simulation, model
Objavljeno: 01.06.2012; Ogledov: 1003; Prenosov: 28
URL Povezava na celotno besedilo

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