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Abstract: The coil to globule transition of the polypeptide chain is the physical phenomenon behind the folding of globular proteins. Globular proteins with a single domain usually consist of about 30 to 100 amino acid residues, and this finite size extends the transition interval of the coil-globule phase transition. Based on the pedantic derivation of the two-state model, we introduce the number of amino acid residues of a polypeptide chain as a parameter in the expressions for two cooperativity measures and reveal their physical significance. We conclude that the k2 measure, defined as the ratio of van ’t Hoff and calorimetric enthalpy is related to the degeneracy of the denatured state and describes the number of cooperative units involved in the transition; additionally, it is found that the widely discussed k2=1 is just the necessary condition to classify the protein as the two-state folder. We also find that Ωc, a quantity not limited from above and growing with system size, is simply proportional to the square of the transition interval. This fact allows us to perform the classical size scaling analysis of the coil-globule phase transition. Moreover, these two measures are shown to describe different characteristics of protein folding
Keywords: protein folding, two-state model, size scaling, thermodynamic cooperativity
Published in RUNG: 24.02.2021; Views: 2086; Downloads: 65
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Abstract: The interest in developing new materials intended for food packaging based on bacterial cellulose is growing in the recent years. Flexible and transparent films from bacterial cellulose-chitosan-polyvinyl alcohol have shown excellent UV-barrier properties. However, this composite material interacts with ambient moisture modifying its water activity due to its hydrophilic nature. In this work, an extensive study was carried out to evaluate the changes in the properties of these films as a function of water activity. Moisture adsorption isotherm were described by the GAB method. Results showed the plasticizing effect of water molecules increasing the water vapour permeability of the samples from 1.86·10-12 to 1.17·10-11 g/m·s·Pa, the percentage of elongation from 3.25 to 36.55% and the distance to burst from 0.64 to 5.12 mm. The increase of the water activity dropped the tensile strength values from 74.76 to 38.56 MPa, Young’s modulus values from 3133.46 to 30.71 MPa and burst strength to 703.87 g. The values of the UV-barrier were maintained at the wide range of water activity. Consequently, water molecules do not affect the UV-barrier properties of the films.
Keywords: GAB model, moisture adsorption isotherms, plasticization, bacterial cellulose, mechanical properties, UV-barrier properties, moisture content
Published in RUNG: 09.12.2020; Views: 2469; Downloads: 0
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Abstract: Biodegradable films based on bacterial cellulose, glycerol and polyvinyl alcohol are a new alternative to develop food packaging with the capac- ity to retard or inhibit the effect of UV radiation. However, these compounds are sensitive to moisture. Therefore, the purpose of this study was to evaluate the modifications of the mechanical, water vapor permeability and optical properties of these composite films depending on their water activity. Results showed that water molecules acted as a plasticizer agent, modifying the mechanical, water vapor perme- ability and optical properties of the developed films. However, an overplastification process took place at higher activity water, resulting in a weakness of film structure and decreasing drastically the elongation. The transmittance in the UV–VIS light region decreased when the activity water increased. No significant variations were observed in color, trans- parency or opacity properties.
Keywords: GAB model, Moisture adsorption isotherms, Plasticization, Bacterial cellulose, Mechanical properties, UV-barrier properties
Published in RUNG: 09.12.2020; Views: 2404; Downloads: 90
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Keywords: graphene, chitosan, polysaccharide, fuel cell, alkaline, ethanol, photoconductivity, ionic conductivity, mixed-conductor model
Published in RUNG: 03.12.2020; Views: 2542; Downloads: 0
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Abstract: V magistrskem delu je predstavljena sistemska ureditev področja skladiščenja in interne logistike s poudarkom na prenovi poslovno informacijske rešitve za podjetje Plastik SI d.o.o. Družba, katere osnovna dejavnost je proizvodnja plastične embalaže, se je v preteklih letih soočila s težavami obravnavanega področja. Ugotovili so, da je bilo neurejeno stanje posledica številnih dejavnikov kot so: slaba prostorska organiziranost skladišč, omejena funkcionalnost informacijske rešitve, nezadostno izvajanje operativnih nalog skladiščenja in interne logistike ter v zadnjem obdobju porast aktivnosti zaradi povečanega obsega proizvodnje. Vodstvo družbe je za rešitev nastalega problema rezerviralo potrebne vire in sredstva ter postavilo jasne in končne cilje v obliki učinkovite podpore procesni funkciji skladiščenja in interne logistike. Pri tem je določilo časovni okvir za izvedbo naloge. Ker so ocenili, da je obravnavano področje kompleksno in obsežno, so nalogo opredelili kot razvojni projekt in na ta način izboljšali možnosti uspeha in doseganja pričakovanih učinkov. Namen projekta, opisanega v magistrskem delu, je bil razviti in implementirati sistemsko rešitev, ki bo temeljila na prenovljeni in nadgrajeni informacijski platformi. Poudarek je bil na upoštevanju dolgoročne vzdržnosti, da bo načrtovana rešitev omogočala kasnejšo razširljivost in morebitne nadgradnje. Rezultat projekta je učinkovita informacijska podpora za skladiščenje in interno logistiko.
Keywords: Skladišče, interna logistika, projekt, informacijski sistem, model, metodologija, agilnost.
Published in RUNG: 20.07.2020; Views: 3040; Downloads: 104
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