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2. Inter-person differences in isometric coactivations of triceps surae and tibialis anterior decrease in young, but not in older adults after 14 days of bed restMatjaž Divjak, Gašper Sedej, Nina Murks, Mitja Gerževič, Uroš Marušič, Rado Pišot, Boštjan Šimunič, Aleš Holobar, 2022, original scientific article Abstract: We examined activation patterns of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SO), and tibialis anterior (TA) muscles in eight older (58.4 ± 3.3 years) and seven young (23.1 ± 2.9 years) participants, before and after 14 days of horizontal bed rest. Visual feedback on the exerted muscle torque was provided to the participants. The discharge patterns of individual motor units (MUs) were studied in three repetitions of isometric plantar flexion at 30 and 60% of Maximum Voluntary Contraction (MVC), before, and 1 day after the 14-day bed rest, respectively. In the GL and GM muscles, the older participants demonstrated higher MU discharge rates than the young, regardless of the contraction level, both before and after the bed rest. In the TA and SO muscles, the differences between the older and young participants were less consistent. Detailed analysis revealed person-specific changes in the MU discharge rates after the bed rest. To quantify the coactivation patterns we calculated the correlation coefficients between the cumulative spike trains of identified MUs from each muscle, and measured the root mean square difference of the correlation coefficients between the trials of the same session (intra-session variability) and between different sessions (inter-session variability) in each participant (intra-person comparison) and across participants (inter-person comparison). In the intra-person comparison, the inter-session variability was higher than the intra-session variability, either before or after the bed rest. At 60% MVC torque, the young demonstrated higher inter-person variability of coactivation than the older participants, but this variability decreased significantly after the bed rest. In older participants, inter-person variability was consistently lower at 60% than at 30% MVC torque. In young participants, inter-person variability became lower at 60% than at 30% MVC torque only after the bed rest. Precaution is required when analyzing the MU discharge and coactivation patterns, as individual persons demonstrate individual adaptations to aging or bed rest.
Keywords: mišičnoskeletni sistem, mišice, bed rest, staranje, elektromiografija, high density electromyography, muscle disuse, motor units, discharge rate, aging
Published in DKUM: 07.07.2023; Views: 262; Downloads: 35
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3. Sustainable processing of materials using supercritical fluids : doktorska disertacijaDragana Borjan, 2022, doctoral dissertation Abstract: Supercritical fluids (SCFs) are powerful solvents with many unique properties. They have great potential for many processes, from extraction to chemical reactions and recycling. Accordingly, phase equilibrium data and thermodynamic and transport properties measurements in systems with a supercritical phase, as well as reliable and versatile mathematical models of the phase equilibrium thermodynamics, are needed for the process design and economic feasibility studies. The dissertation focuses on the benefits of supercritical fluid technology and consists of three main sections.
The first section includes studies of the phase equilibria of the binary gas-alcohol and gas-urea derivatives. The influence of pressure and temperature on the system behaviour (solubility, viscosity, density, interfacial tension, melting point curve) was investigated. Most of the experiments were carried out with a high-pressure optical view cell, with minor modifications of the apparatus and measurement principle to determine mentioned thermodynamic and transport properties.
The second part of the dissertation deals with the recovery of extracts from natural materials. Special interest is oriented towards supercritical fluid extracts, characterised by strong biological activities, especially antimicrobial and antioxidant properties. Supercritical fluid extraction has been performed on a semi-continuous apparatus (at pressures of 150 bar and 250 bar and temperatures of 313.15 K and 333.15 K for oregano extraction; and at pressures of 100 bar and 300 bar and temperatures of 313.15 K and 333.15 K for red beetroot extraction) and various methods such as the microdilution method and the DPPH method were used to determine antimicrobial and antioxidant activity.
In the third part, an overview of different methods for recycling carbon fibre reinforced composites is given, including chemical recycling with supercritical fluids. This field has not been well explored, and the approach is relatively new but very interesting from a sustainable point of view. For an economically feasible process design, the thermodynamic and mass transfer data have to be determined. The principles of the future lab- and pilot-scale operations demand these supporting data be known.
The results obtained in the frame of this study represent the high added value in the scientific field. They are essential to design and modify processes that yield products that cannot be achieved with conventional production processes.
Keywords: supercritical fluids, alcohols, urea, phase equilibria, viscosity, density, interfacial tension, modified capillary method, isolation methods, supercritical fluid extraction, pharmacological activity, carbon fiber reinforced composites, recycling techniques
Published in DKUM: 11.10.2022; Views: 581; Downloads: 111
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4. Electrodynamics in organic dimer insulators close to mott critical pointMarko Pinterić, David Rivas Góngora, Željko Rapljenović, Tomislav Ivek, Matija Čulo, B. Korin-Hamzić, Ognjen Milat, Branko Gumhalter, Predrag Lazić, Miriam Sanz Alonso, Weiwu Li, Andrej Pustogow, Guilherme Gorgen Lesseux, Martin Dressel, Silvija Tomić, 2018, original scientific article Keywords: strongly correlated systems, Mott insulators, quantum spin liquid, dielectric properties, vibrational properties, density functional theory
Published in DKUM: 27.06.2018; Views: 1448; Downloads: 430
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5. Shear modulus of a saturated granular soil derived from resonant-column testsH. Patiño, E. Martínez, Jesús González, A. Soriano, 2017, original scientific article Abstract: This paper presents the results of 120 determinations of the shear modulus (G) of a saturated granular soil (20–40 Ottawa sand) in different conditions of relative density (Dr), effective consolidation pressure (σ’ c) and level of torsional excitation (Te). The equipment used was a resonant-column apparatus manufactured by Wykeham Farrance and the tests were performed with relative density values of 20, 40, 60 and 80%, effective consolidation pressures of 50, 100, 150, 200, 250 and 300 kPa, and torsional excitations of 0.025, 0.05, 0.1, 0.2 and 0.4 volts (V), leading to shear strains (γ) between 0.002% and 0.023%. The results led to very simple empirical expressions for the shear modulus as a function of the angular strain for different effective consolidation pressures and void-ratio values.
Keywords: resonant column, resonant frequency, shear modulus, relative density, effective consolidation pressure, dynamic shear modulus
Published in DKUM: 18.06.2018; Views: 1081; Downloads: 80
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6. Effect of the initial structure on the behaviour of Chlef sandNoureddine Della, Ahmed Arab, Mostefa Belkhatir, Hanifi Missoum, Claude Bacconnet, Daniel Boissier, 2010, original scientific article Abstract: It has been known for many years that initial structure, plays an important part in the results of laboratory testing of natural of silty sands. For this purpose, a series of monotonic undrained triaxial compression tests were carried out on samples composed of Chlef sand with 0.5% non-plastic silt content using two depositional methods (dry funnel pluviation and wet deposition) at different initial relative density (RD= 29%, 50% and 80%). All specimens were subjected to isotropic consolidation of 50 kPa, 100 kPa and 200 kPa. It was found that the initial structure of the soil influences considerably the undrained shear response in terms of maximal deviatoric stress, peak strength and excess pore water pressure.
Keywords: liquefaction, sand, dry funnel pluviation, wet deposition, density, deviatoric stress, pore pressure
Published in DKUM: 11.06.2018; Views: 777; Downloads: 75
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7. Determining the speed of sound, density and bulk modulus of rapeseed oil, biodiesel and diesel fuelBoban Nikolić, Breda Kegl, Saša Marković, Melanija Mitrović, 2012, original scientific article Abstract: 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.
Keywords: biodiesel, rapeseed oil, speed of sound, bulk modulus, density, high pressure
Published in DKUM: 07.07.2017; Views: 1064; Downloads: 346
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8. Determination of pressure losses in hydraulic pipeline systems by considering temperature and pressureVladimir Savić, Darko Knežević, Darko Lovrec, Mitar Jocanović, Velibor Karanović, 2009, original scientific article Abstract: Generally accepted methods for calculating pressure losses within flat pipelines, as presented in literature and used in praxis, are based on the Reynolds number, which considers the viscosity and density of fluid, internal pipe friction coefficient, pipe geometry, and oil circulation velocity. Such an approach contains serious inconsequentiality. Namely, only nominal values for viscosity and density are considered in the calculation, which differs substantially from real conditions. It often leads to inaccurate calculations of pressure losses. A numerical model has been developed within the work prescribed in the paper, which takes into account actual changes in density and viscosity under the current oil pressure and temperature in order to overcome the above weaknesses of standard calculation procedures. Such an approach is novel and provides new capacity for an accurate pressure drop analysis of advanced hydraulic systems.
Keywords: tlačne izgube, ravne cevi, viskoznost, gostota, temperatura, pressure loss, float pipelines, viscosity, density, temeprature
Published in DKUM: 11.08.2015; Views: 1169; Downloads: 72
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9. Temperature and pressure dependence of volumetric properties for binary mixtures of n-heptane and n-octaneDarja Pečar, Valter Doleček, 2007, original scientific article Abstract: The densities of n-heptane, n-octane and their binary mixtures were measured at 298.15, 323.15 and 348.15 K and within the pressure range 0.1 to 40 MPa using a vibrating tube densimeter. The reliability of this technique has been verified in our previous works. The partial molar volumes, excess molar volumes, isothermal compressibilities, isobaric thermal expansivities and internal pressures were calculated from the obtained densities. This study presents the dependence of densities, partial molar volumes, excess molar volumes, isothermal compressibilities, isobaric thermal expansivities and internal pressures on composition, temperature and pressure.
Keywords: density measurements, partial molar volume, excess molar volume, isothermal compressibility, isobaric thermal expansivity, internal pressure, n-heptane, n-octane
Published in DKUM: 10.07.2015; Views: 1410; Downloads: 114
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10. On automorphisms of Banach algebrasMatej Brešar, 2002, original scientific article Abstract: Podana je razširitev Jacobsonovega izreka o gostoti na Banachove algebre z avtomorfizmi. Zatem so obravnave aplikacije tega izreka. Med drugim so karakterizirani avtomorfizmi ▫$alpha$▫ na Banachovi algebri z lastnostjo, da je preslikava ▫$alpha-1$▫ spektralno omejena.
Keywords: matematika, funkcionalna analiza, teorija operatorjev, avtomorfizem, Banachova algebra, izrek o gostoti, spektralno omejena preslikava, mathematics, functional analysis, operator theory, automorphism, Banach algebra, density theorem, spectrally bounded map
Published in DKUM: 10.07.2015; Views: 1052; Downloads: 103
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