Parametrizations of equation of state parameter as a function of the scale factor or redshift are frequently used in dark energy modeling. The question investigated in this paper is if parametrizations proposed in the literature are compatible with the dark energy being a barotropic fluid. The test of this compatibility is based on the functional form of the speed of sound squared, which for barotropic fluid dark energy follows directly from the function for the Equation of state parameter. The requirement that the speed of sound squared should be between 0 and speed of light squared provides constraints on model parameters using analytical and numerical methods. It is found that this fundamental requirement eliminates a large number of parametrizations as barotropic fluid dark energy models and puts strong constraints on parameters of other dark energy parametrizations.

The paper brings a novel approach to unification of dark matter and dark energy in terms of a cosmic fluid. A model is introduced in which the cosmic fluid speed of sound squared is defined as a function of its equation of state (EoS) parameter. It is shown how logarithmic part of this function results in dynamical regimes previously not observed in cosmic fluid models. It is shown that in a particular dynamical regime the model behaves as a unification of dark matter and phantom dark energy. Further, it is shown that the model may describe dark matter -dark energy unification in which dark energy asymptotically behaves as dark energy with a constant EoS parameter larger than -1. In a specific parameter regime the unified fluid model also reproduces global expansion similar to ΛCDM model with fluid speed of sound vanishing for small scale factor values and being small, or even vanishing, for large scale factor values. Finally, it is shown how the model may be instrumental in describing the cosmic fluid dark matter-dark energy-dark matter unification. Physical constraints on model parameters yielding such transient dark energy behavior are obtained.

The formalism of dark energy based on modeling speed of sound as a function of equation of state parameter is elaborated. A specific model which allows detailed study of cosmological constant boundary crossing is introduced and analytical solutions for the model dynamics are obtained. It is shown how in specific parameter regimes dark energy can be a transient phenomenon. It is further demonstrated how the model reproduces specific features of recent fits of dark energy w(z) to observational data.

Purely kinetic k-essence models have been shown in the literature to be a field theory equivalent of barotropic fluid models of dark energy or dark matter-dark energy unification. In the modeling framework where the speed of sound squared of a barotropic fluid is modeled as a function of its Equation of State parameter, a systematic procedure of obtaining the Lagrangian density of an equivalent purely kinetic k-essence model is presented. As this modeling approach starts from the speed of sound, purely kinetic k-essence models can be constructed for which the speed of sound is in agreement with the observational constraints. Depending on the chosen functional form for the barotropic fluid speed of sound squared, analytically tractable examples of solutions for the purely kinetic k-essence Lagrangian density in parametric and closed form are obtained.

Zdravstveno veleučilište Zagreb SažetakFizika je jedna od ključnih prirodnih znanosti u fizioterapijskoj praksi. Cilj ovoga istraživanja bio je ispitati poznavanje i primjenu fizikalnih zakonitosti u fizioterapijskom procesu kod studenata preddiplomskog studija fizioterapije. U istraživanju su sudjelovala 92 studenta druge i treće godine, koji su položili ispit iz predmeta Fizika na prvoj godini studija. Za potrebe ovog istraživa-nja konstruiran je test čiji su zadaci tematski povezani s primjenom fizikalnih zakonitosti u kreiranju fizioterapijskog procesa.Prema rezultatima, najviše studenata ima vrlo dobar (39,1 %) ili izvrstan (43,5 %) uspjeh postignut na predmetu Fizika. Percipiranu razinu znanja o utjecaju fizikalnih zakonitosti u svrhu objektivizacije i poboljšanja kvalitete fizioterapijskog procesa studenti ocjenjuju ocjenom dobar. Na ukupnom uzorku dvije trećine studenata smatra da je poznavanje fizikalnih zakonitosti važno ili vrlo važno u kreiranju fizioterapijskog procesa. Ukupno 60 % studenata točno je odgovorilo na dva ili tri od mogućih pet pitanja na testu. Iz rezultata je vidljivo da u broju točnih odgovora postoji statistički značajna razlika s obzirom na godinu studija, pri čemu su studenti druge godine studija fizioterapije dali više točnih odgovora u odnosu na studente treće godine. Rezultati istraživanja ukazuju da ne postoji statistički značajna povezanost točnih odgovara studenata s njihovom završnom ocjenom, samoprocjenom znanja iz područja fizike te dostupnošću stručne i znanstvene literature.Rezultati ovog istraživanja omogućuju izradu smjernica povezanih s oblikovanjem strategija za unaprjeđenje kvalitete nastavnog plana i programa predmeta Fizika na studiju fizioterapije u cilju primjene fizikalnih zakonitosti u fizioterapijskom procesu.Ključne riječi: fizikalne zakonitosti, fizioterapijski proces, fizika Datum primitka: 14.09.2017.