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Vec-Liepaja, Latvia

Kaupuzs J.,University of Latvia | Kaupuzs J.,Liepaja University
Progress of Theoretical Physics | Year: 2010

We have extended our method of grouping Feynman diagrams (GFD theory) to study the transverse and longitudinal correlation functions G⊥(k) and G∥(k) in φ4 model below the critical point (T < T c) in the presence of an infinitesimal external field. Our method allows a qualitative analysis without cutting the perturbation series. The long-wave limit k → 0 has been studied at T < Tc, showing that G⊥(k) ≃ak-λ⊥ and G∥ (k) ≃ bk -λ∥ with exponents d/2 < λ⊥. < 2 and λ⊥= 2λ⊥- d are the physical solutions of our equations at the spatial dimensionality 2 < d < 4, which coincides with the asymptotic solution at T → Tc as well as with a nonperturbative renormalization group (RG) analysis provided in our paper. This has been confirmed also by recent Monte Carlo simulations. The exponents as well as the ratio bM2 /a2 (where M is magnetization) are universal. The results of the perturbative RG method are reproduced by formally setting λ⊥. = 2, although our analysis yields λ⊥ < 2. Source

Stepanov I.A.,Liepaja University
Materials Letters | Year: 2015

Thermodynamics suggests that substances with positive thermal expansion express heat under compression but those with negative thermal expansion absorb heat. Experiments show, however, that substances with negative thermal expansion do express heat. In this paper, an attempt is made to explain this paradox. It is also shown that the third Maxwell relation can be used for study of phase transitions together with the Clausius-Clapeyron equation. It is shown that water and ice have negative isothermal compressibility in some temperature interval about 273 K at low pressure. © 2015 Elsevier B.V. Source

Stepanov I.A.,Liepaja University
Results in Physics | Year: 2014

In some papers, dependences of the isobaric heat capacity of water versus pressure and temperature were obtained. It is shown that these dependences contradict both the dependence of heat capacity on temperature for supercooled water, and an important thermodynamic equation for the dependence of heat capacity on pressure. A possible explanation for this contradiction is proposed. © 2014 The Authors. Source

Grickus A.,Liepaja University
Engineering for Rural Development | Year: 2015

In circumstances, when it is important to replace insulation materials with high content of emissions during production, it is necessary to create a new heat and sound insulation material, which eliminates CO2 emissions, develop its production techniques and technological machinery - raw material chopper, pulp mixer, termopress, dryer chamber, formatting knives, determine technical control parameters and control equipment, develop a mathematical model of the material and calculation methods for design works. It is necessary to design, manufacture and experimentally test the respective technological equipment for insulation production pilot plant. To get exact physical parameters it is necessary to design, manufacture and test unique laboratory equipment for determining the properties of the insulation material. Source

Kaupuzs J.,University of Latvia | Kaupuzs J.,Liepaja University
Canadian Journal of Physics | Year: 2012

Power law singularities and critical exponents in n-vector models are considered within a theoretical approach called GFD (grouping of Feynman diagrams) theory. It is discussed how possible values of the critical exponents can be related to specific n-vector models in this approach. A good agreement with the estimates of the perturbative renormalization group (RG) theory can be obtained. Predictions for corrections to scaling of the perturbative RG and GFD approaches are different. A nonperturbative proof is provided, supporting corrections to scaling of the GFD theory. Highly accurate experimental data very close to the λ-transition point in liquid helium, as well as the Goldstone mode singularities in n-vector spin models, evaluated from Monte Carlo simulation results, are discussed with an aim to test the theoretical predictions. Our analysis shows that in both cases the data can be well interpreted within GFD theory. © 2012 Published by NRC Research Press. Source

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