Vec-Liepaja, Latvia
Vec-Liepaja, Latvia

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Freimanis J.,Ventspils University College | Freimanis J.,Liepaja University
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2011

The differential operator of polarized radiative transfer equation is examined in case of homogeneous medium in Euclidean three-dimensional space with arbitrary curvilinear coordinate system defined in it. This study shows that an apparent rotation of polarization plane along the light ray with respect to the chosen reference plane for Stokes parameters generally takes place, due to purely geometric reasons. Analytic expressions for the differential operator of transfer equation dependent on the components of metric tensor and their derivatives are found, and the derivation of differential operator of polarized radiative transfer equation has been made a standard procedure. Considerable simplifications take place if the coordinate system is orthogonal. © 2011 Elsevier Ltd.

Trinite B.,Liepaja University | Sokolovs J.,Riga Stradins University
Journal of Voice | Year: 2014

Objectives To establish psychometric indicators of the Voice Handicap Index (VHI) (Latvian version) and their relationship to the psychometric indicators of the original items. Study Design Parallel group design. Methods The VHI was translated and adapted to Latvian. The translated version of the VHI (Lat-VHI) was completed by 54 patients with voice disorders and by 73 subjects without voice disorders forming the control group. A test-retest group included 54 subjects without voice problems, able to complete the questionnaire twice. The test-retest stability, internal consistency of items of the Lat-VHI, and content and convergent validity of the Latvian version of the VHI were analyzed. Results The interclass correlation coefficient ratio of all scales indicated statistically significant (P < 0.001) test-retest reliability for the Lat-VHI. High internal consistency was observed among the Lat-VHI total scale (α =.96), functional (α =.92), physical (α =.86), and emotional scale (α =.91) in the patient group. The Pearson moment correlation coefficient indicates a high correlation among the Lat-VHI total scale and subscales (r > 0.94), as well as a high correlation among subscales (r > 0.81) in the patient group. Convergent validity of the Lat-VHI was determined by comparing the Lat-VHI results with the Voice Disorder Severity scale results. Statistically significant correlation (r = 0.78, P < 0.001) was discovered in the patient group. Conclusions The Latvian version of the VHI is a psychometrically validated instrument whose indicators correspond to the psychometric indicators of the original sample. © 2014 The Voice Foundation.

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.

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.

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.

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.

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.

Stepanov I.A.,Liepaja University
Materials Letters | Year: 2016

It is shown from experimental data that the isochoric heat capacity of the negative thermal expansion substances ZrW2O8 and Sc2W3O12 is larger than their isobaric one. This is in agreement with the theory developed earlier by the author. Their isentropic compressibility is also larger than their isothermal compressibility. It is possible that this result is valid also for Y2Mo3O12. © 2016 Elsevier B.V. All rights reserved.

Liepaja University | Date: 2015-07-01

The invention is related to biogas production and namely - to the systems anticipated for control and maintenance of anaerobic bacteria processes in the solid domestic waste layer. A system is proposed, which contains: humidity, pressure and temperature sensors placed in the layer of the solid household wastes; the data monitoring and analysis unit; the command unit; the water and auxiliary substance supply system, which contains the liquid feeder and the system of pipes, located in the layer of solid household wastes; the humidity, pressure and temperature sensors are connected to the data monitoring and analysis unit having a possibility to send and receive electronic signals, which is connected to the command unit having also a possibility to send and receive electronic signals, which, in its turn, is connected to the liquid feeder having a possibility to send and receive electronic signals; the liquid feeder is designed with a possibility, when receiving a command from the command unit, to selectively supply liquid into the system of watering pipes for watering a segment of the solid household waste polygon, whereas the watering pipe system is designed with a possibility to provide uniform watering of a segment of the solid household waste polygon, where each mentioned segment of the waste polygon contains humidity sensors, which are placed at the borders of the segment, at least one temperature sensor and at least one pressure sensor, which are placed in the centre of the segment; the position of the humidity sensor is chosen in such a way that the coordinates (x, y, z) of the humidity, pressure and temperature sensors would correspond to the existing formulas, where the reference point is the south-eastern corner of the solid household waste polygon.

Benders J.,Liepaja University
International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM | Year: 2015

Paper aims to analyse the principal aspects of ecodesign development process, putting attention to current problems, necessary preconditions and development measures in Latvia. Ecodesign development had been defined by EC Integrated product policy, comprising ecodesign, green procurement and environmental technology issues. The current research is based on literature analysis, thus composing theoretical framework, as well as, sociological research methods – deep interviews and questionnaires representing principal target groups (state institutions, entrepreneurships, consumers, retail sector). The integration of ecodesign related strategies into strategic planning documents in economy sectors, improvement of ecodesign competences in enterprises, better cooperation with science and technology are issues, recognized as principal measures for ecodesign development in country. Environmental information and communication measures should comprise the main three target groups - state institutions, employers and consumers. These issues cover the necessary legal measures and voluntary measures. The latter is based on environmental competence and motivation and precisely the voluntary part of ecodesign development measures are issues, which are not enough accepted in enterprises. Research confirmed the importance of life cycle assessment end stages, which are related with product distribution and consumption, where the retail industry also plays role; the ecodesign development possibilities in retail industry had been considered. © SGEM 2015.

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