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1.
Development of an experimental Dead-End microfiltration layout and process repeatability analysis
Gorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, original scientific article

Abstract: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Keywords: filtration, pressure oscillations, repeatability, processes, parameters
Published in DKUM: 01.02.2024; Views: 92; Downloads: 7
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2.
The external bias-dependent electric field at hole-injecting electrode/[alpha]-NPD junction and its relationship to Gaussian disordered interface states
Bruno Cvikl, 2019, original scientific article

Abstract: An alternative interpretation of two different sets of published temperature-dependent current-voltage a-NPD (i.e. N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,11-biphenyl)-4,4'-diamine) organic semiconductor data is presented. The measurements are described in terms of the hole drift current density expressed with two parameters: the electric field at the hole-injecting interface, Eint, and, ?max, the hole mobility determined by the measured current density at the maximum value of the externally applied electric field, Ea, in a given experiment. The former parameter, depending on the contact résistance, may be a function of Ea but the latter is Ea independent, The fixed value of Eint signifies the occurrence of the space charge limited current, SCLC, within the electrode/a-NPD structures and the contact is ohmic. Then, the calculated weak bias-dependent hole drift mobility, a function of Eint, equals the well%known exponential bias-dependent mobility, and saturates. The data not displaying SCLC characteristics are used for the calculation of Eint dependence on the applied field, Ea. It is shown that the quasi-ohmic contacts cause Eint to become a strong double-valued function of the externally applied electric field, Ea, described in terms of the distorted, inverted, high order parabola. The corresponding bias-dependent hole drift mobility is non-exponential and evolves on a considerably lower level than in SCLC cases. It is found that a sufficiently increased Ea alters the quasi-ohmic contact/a-NPD region into the ohmic one. A simple model of a thin, net hole charged, electrode/a-NPD interface enables the relationship between the deduced interfacial electric field, Eint, and the Ea dependent Gaussian width, as well as the energy shift of its peak along the negative binding energy is to be investigated. The currentvoltage method appears to be a helpful expedient for the investigation of the electric field at hole-injecting electrode/organic interfaces.
Keywords: electrode/organic electric field, contact affected hole mobility, organic interface disorder parameters
Published in DKUM: 22.12.2023; Views: 312; Downloads: 6
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3.
Audio-visual effects of a collaborative robot on worker efficiency
Aljaž Javernik, Klemen Kovič, Iztok Palčič, Robert Ojsteršek, 2023, original scientific article

Abstract: Collaborative workplaces are increasingly used in production systems. The possibility of direct collaboration between robots and humans brings many advantages, as it allows the simultaneous use of human and robotic strengths. However, collaboration between a collaborative robot and a human raises concerns about the safety of the interaction, the impact of the robot on human health, human efficiency, etc. Additionally, research is unexplored in the field of the collaborative robot’s audio-visual effects on the worker’s efficiency. Our study results contribute to the field of studying collaborative robots’ audio-visual effects on the worker’s behavior. In this research, we analyze the effect of the changing motion parameters of the collaborative robot (speed and acceleration) on the efficiency of the worker and, consequently, on the production process. Based on the experimental results, we were able to confirm the impact of robot speed and acceleration on the worker’s efficiency in terms of assembly time. We also concluded that the sound level and presence of a visual barrier between the worker and robot by themselves have no effect on the worker’s efficiency. The experimental part of the paper clearly identifies the impact of visualization on work efficiency. According to the results, the robot’s audio-visual effects play a key role in achieving high efficiency and, consequently, justifying the implementation of a collaborative workplace.
Keywords: collaborative robot, worker efficiency, motion parameters, visual contact, sound, human-robot symmetry, repeated measures ANOVA
Published in DKUM: 11.12.2023; Views: 150; Downloads: 13
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5.
Analysis of the influence of parameters when charging and discharging a capacitor using differential equations
Matic Krašovic, Peter Virtič, 2022, original scientific article

Abstract: Two different electrical circuits were analysed in this paper. The first was an RC circuit consisting of a resistor R, a capacitor C, and a DC voltage u, while the second was an RLC circuit consisting of a resistor R, a capacitor C, a DC voltage u and an inductor L. Both circuits were described using the state space mathematical model and, on this basis, graphs for charging and discharging a capacitor were plotted. Both circuits were described using differential equations for electrical current through a capacitor and voltage over a capacitor. Finally, different values of the R (resistance), L (inductance) and C (capacitance) parameters were taken, and graphs were plotted for voltage over capacitor. The purpose of the study was to explore how different values of parameters influence capacitor charging and discharging.
Keywords: RC circuit, RLC circuit, state space, transfer function, differential equations, parameters R, L, C, damping
Published in DKUM: 30.10.2023; Views: 136; Downloads: 8
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Vpliv izdelovalnih parametrov na lastnosti izdelkov iz Ti-6Al-4V, narejenih s selektivnim laserskim taljenjem in plastenje površine z bioaktivnim polimerom
Snehashis Pal, 2019, doctoral dissertation

Abstract: Technological parameters included in energy density (ED) are the more powerful tools in selective laser melting (SLM) technology which can be used in the time of fabrication to regulate chemical, metallurgical, and mechanical properties of a product. The volumetric Energy Density (ED) depends on the energy input employed by the laser power, scanning speed, hatch spacing, and the layer thickness. Density, microstructure, surface morphology, dimension accuracy, strength and porosity including the number of pores, place of the pore, size of a pore shape of a pore, inclusions of pores of an SLM product depends on the processing parameters. As the powder material fusion process is done by track by track and layer by layer, the architecture of the microstructure in a product is oriented as the direction of building up too. The research has emphasized on metallurgical properties, tensile properties, and producing the non-porous products from Ti-6Al-4V alloy powder and surface modification using bioactive polymer for orthopedic application. The research has followed four steps to study the metallurgical properties and finding out the combinations of technological parameters in producing non-porous products. The purpose of the first step of the study was to examine the effects of ED on the product properties and to obtain an optimum ED as well as the optimal range of scanning speed. The second step of the study has focused on the influences of laser power. The third step of the study has investigated the effect of amounts of track overlapping and hatch spacing. Almost a zero-porosity product has been able to produce by following these three steps of the ongoing research. The fourth step has studied the metallurgical properties emphasizing on re-melting of every layer. High-density products have been found in the fourth step where a small amount of very small sized pores are present as a result of keyhole effect and gaseous bubble entrapment mainly. Four buildup orientations have been selected for each ED in the first step of the study to examine the tensile properties of the products. The best buildup orientation has been seen in longitudinally vertical tensile specimens considering tensile properties. The tensile properties have also been studied in the second and third step of the study with best build up orientation of the tensile specimens. The alterations of metallurgical and tensile properties have also been investigated after heat-treatment of the specific samples. Dimensional accuracies were also invigilated on the cubic, and tensile specimens over the studies and consequently, inaccuracies have been noticed. The fifth step of the study has observed the pore properties, adhesion properties, the compressive strength of gelatin coating manufactured using unidirectional freezing and the freeze-drying process of three different gelatin concentrations on four different surfaced Ti-6Al-4V alloy substrates. The results indicate that the coating properties depend on the substrate’s surface texture as well as the concentration of gelatin. Above 80% of porosity, interconnected and well-aligned pores of 75-200 μm have been obtained which is required to stimulate bone ingrowth histologically.
Keywords: selective laser melting, unidirectional freezing, fabricating parameters, porosity, microstructure, mechanical strength
Published in DKUM: 01.04.2019; Views: 1651; Downloads: 137
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8.
Growth performance, haematology and serum biochemistry of West African dwarf sheep fed cassava peel-oil palm leaf meal based diets in a hot humid tropics
Peter-Damian Chukwunomso Jiwuba, Lydia Chidimma Jiwuba, Moses Udoha Onyekwere, 2017, original scientific article

Abstract: The growth performance, haematological and serum biochemical characteristics of thirty-six West African Dwarf (WAD) sheep of about 10 - 12 months of age and averaged 8.53kg in weight were sourced from the College flock. Four dietary treatments designated as T1, T2, T3 and T4 were formulated to contain 0%, 10%, 20% and 30% oil palm leaf meal (OPLM) respectively were randomly assigned to the animals. The experimental animals were divided into four groups of nine animals each, with each group replicated thrice with three animals per replicate. Each group was allotted to one of the diets in a completely randomized design. The animals were weighed at the beginning of the trial and weekly subsequently and data for growth performance were generated. Blood samples were obtained from one animal in each replicate, and data generated were analyzed statistically. Average daily feed intake, total dry matter intake and average daily weight gain were significantly (P<0.05) influenced by the dietary treatment, with animals on T4 group having higher and better values. Feed conversion ratio (FCR) also differed significantly (P<0.05) with sheep on T3 and T4 (11.82 and 11.49 respectively) having the best FCR. The haematology showed that the packed cell volume (PCV), red blood cell (RBC), and mean cell haemoglobin concentration (MCV) were significantly (P < 0.05) improved at 10%, 20% and 30% inclusion levels of OPLM, respectively. Sheep in treatment groups had improved (P < 0.05) white blood cell (WBC) count than those on the control group. Serum biochemistry results showed that total protein, albumin and globulin were significantly influenced (P < 0.05) and tended to increase with increasing levels of test ingredient. Sheep in treatment groups had higher (P < 0.05) urea values than those on control. Creatinine values at 20% and 30% inclusion differed significantly (P < 0.05) with the control value. Cholesterol was significantly influenced (P < 0.05) and followed an irregular trend across the treatment groups. The results showed that inclusion of OPLM had a beneficial effect on the general performance of the WAD sheep. Therefore, 30% OPLM supplementation was recommended for optimum performance in WAD sheep.
Keywords: sheep, supplemental diets, proximate composition, oil palm leaf meal, casava peel, blood parameters
Published in DKUM: 10.10.2018; Views: 1214; Downloads: 314
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9.
Use of a Perth sand penetrometer (PSP) device to determine the engineering parameters of sands
S. D. Mohammadi, 2016, original scientific article

Abstract: Determining the in-situ engineering parameters of sandy soils has always been a challenge for geotechnical engineers, resulting in several methods having been developed so far. The Perth Sand Penetrometer (PSP) test is one of the most versatile of these methods. It is a considerably faster and cheaper tool than boring equipment, especially when the depth of the exploration is moderate. In the present research, a methodology for the use of a PSP device to evaluate the engineering parameters of sandy soils in laboratory conditions is discussed and the repeatability of the test results is studied. First of all, the tests were performed on typical Tehran young alluvial deposits (poorly graded sandy soil, SP) consistently prepared to 5 densities using the sand raining or pluviation technique. Next, the normal and logNormal distributions of the test data using the Kolmogorov-Smirnov normality test were examined. After that, based on the obtained results, the relationship types between the dynamic point resistance index (qd) and other parameters, such as the relative density (Dr), the modulus of elasticity (E), the shear modulus (G) and the friction angle of the soil, were determined. The results show that the obtained relationships were semi-logarithmic and logarithmic, and most of the obtained experimental formulas had a high coefficient of determination (>90%). To evaluate the accuracy of the results, 95% confidence and prediction bands were also used and the results show that all the obtained experimental relationships were appropriate. Finally, the repeatability of the test results was evaluated by calculating the coefficient of variations, which was less than 30% for all the tests.
Keywords: dynamic-point resistance index (qd), engineering parameters, repeatability, statistical methods
Published in DKUM: 18.06.2018; Views: 965; Downloads: 166
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10.
Analysis of a dilatometer test in over-consolidated sediments, basin of the Duero river, Spain
Félix Escolano Sánchez, Manuel Bueno Aguado, 2015, original scientific article

Abstract: A dilatometer test is a useful method for in-situ geotechnical surveys. It can be compared with the results obtained using a mathematical model. The mathematical model of concentric rings shown in this article is governed by the constitutive equation of the “Hardening Soil Model”. A large number of tests made on the Dueñas Geological Facies, with a consistency ranging from firm clays to soft rocks, are compared to the model results. In this way, the “Hardening Soil Model” parameters are adjusted to the Dueñas Facies materials.
Keywords: Dueñas, geotechnical parameters, hardening soil model, soft rocks and clays deformation
Published in DKUM: 14.06.2018; Views: 1133; Downloads: 90
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