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Détails du magazine
Format
Magazine
eISSN
2255-8896
ISSN
0868-8257
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

Volume 49 (2012): Edition 6-I (December 2012)

Détails du magazine
Format
Magazine
eISSN
2255-8896
ISSN
0868-8257
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

6 Articles
Accès libre

Capacitance and Leakage Current Balancing for Supercapacitive Energy Storage System / Kapacitāšu Un Noplūdes Strāvu Balansēšana Superkondensatoru Enerģijas Uzkrājējsistēmai

Publié en ligne: 01 Feb 2013
Pages: 3 - 12

Résumé

Abstract

In the paper, the problem of voltage imbalance in supercapacitor bank caused by different capacitances and leakage resistances is considered. The authors propose capacitance balancing in combination with passive resistor voltage balancing as an efficient method for decreasing the cell voltage imbalance and increasing the effective energy capacity of supercapacitor bank. The efficiency of the method is demonstrated theoretically and verified experimentally on eight supercapacitor cells.

Keywords

  • energy storage
  • supercapacitors
  • voltage balancing
  • capacitancebalancing
  • leakage current balancing
  • capacitance measurement
Accès libre

Choice of the Optimum Cross-Sections for 20–110–330 kV Overhead Lines Under Market Conditions / 20–110–330 Kv Gaisvadu Līniju Optimālo Šķērsgriezumu Izvēle Tirgus Apstākļos

Publié en ligne: 01 Feb 2013
Pages: 13 - 22

Résumé

Abstract

Approach is proposed to the choice of overhead line cross-sections that would be optimal under market conditions. For this purpose, in the design practice and at network reconstruction two methods exist: of the economic current density, and of the economic intervals. As of now, none of them works properly, since the cost of electrical materials, of building and construction as well as the total investments in a line are determined by the market prices. Therefore, a modified economic intervals’ method has been developed that can work under market conditions. The method allows also considering the discrete character of standard cross-sections for the lines and concrete technical and technically-economic parameters. For practical application of the proposed method, universal economic nomograms for 20-110-330 kV overhead lines have been calculated and constructed. In the paper, a user interface is proposed for realization of the modified method in Matlab environment.

Mots clés

  • overhead lines
  • optimum cross-section
  • annual costs
  • nomograms
  • user interface
Accès libre

Heat and Moisture Transport in Multi-Layer Walls: Interaction and Heat Loss at Varying Outdoor Temperatures / Siltuma Un Mitruma Pārnese Caur Daudzslāņainām Būvkonstrukcijām: Āra Temperatūras Izmaiņu Ietekme Uz Siltuma Zudumiem Iekštelpā

Publié en ligne: 01 Feb 2013
Pages: 32 - 43

Résumé

Abstract

The heat and moisture transport in multi-layer walls is analysed for five building units. Using the developed program, a typical of Latvian conditions temperature and relative humidity profiles in multi-layered constructions has been obtained and the indoor heat losses estimated. Consideration is also given to the risk of condensate formation and to the influence of moisture on the U-value. The created mathematical model allows forecasting the energy efficiency and sustainability of different technical solutions as refer to the heat and moisture transport in buildings.

Mots clés

  • moisture
  • temperature
  • transport
  • multi-layer wall
Accès libre

Photoluminescence of Eu and Ce Activated Oxyfluoride Glass And Glass Ceramics/ Eu Un Ce Jonu Luminiscence Oksifluorīdu Stiklos Un Stikla Keramikā

Publié en ligne: 01 Feb 2013
Pages: 44 - 48

Résumé

Abstract

The photoluminescence of SiO2-Al2O3-LiO2-LaF3 oxyfluoride glass and glass ceramic samples doped with Ce3+, Eu2+ and Ce3+/Eu2+ is investigated, and the spectra and fluorescence intensities are compared. The luminescence of samples activated by Eu ions is found to be more intensive than of the samples doped with Ce or Ce/Eu. The luminescence of glass ceramics is higher than that of the corresponding glass, which indicates that a proportion of the activator ions are embedded in the fluoride crystallites.

Mots clés

  • photoluminescence
  • oxyfluoride glass
  • glass ceramics
  • Ce3+
  • Eu2+ ions
  • luminescence intensities
  • spectra
Accès libre

Epr Spectrum Angular Dependences In Liyf4 Crystal / Epr Spektru Leņķiskās Atkarības Liyf4 Kristālā

Publié en ligne: 01 Feb 2013
Pages: 49 - 54

Résumé

Abstract

Electron paramagnetic resonance (EPR) measurements have been made for two perpendicular planes in a LiYF4 crystal before and after x-ray irradiation at room temperature. Analysis of the EPR spectrum angular dependence shows the presence of two defects - an impurity ion, which was embedded during the crystal growth process, and an x-ray induced defect with the g-factor of approx. 2.0. Spectral parameters and possible defect models are discussed.

Keywords

  • EPR spectrum
  • LiYF4 crystal
Accès libre

Epr Hyperfine Structure Of Radiation Defect In Oxyfluoride Glass Ceramics/ Radiācijas Defekta Epr Hipersīkstruktūra Oksifluorīdu Stikla Keramikā

Publié en ligne: 01 Feb 2013
Pages: 55 - 59

Résumé

Abstract

We have investigated the samples of thermally treated oxyfluoride glass ceramics 50SiO2-25LiO2-20YF3-3ErF3-2YbF2 by means of electron paramagnetic resonance (EPR) techniques. After irradiation of the samples with X-rays, in the EPR spectra a hyperfine structure characteristic of F-centres could be observed in different fluoride crystals. The structure of F-centre in the oxyfluoride glass ceramics containing LiYF4 crystallites is discussed.

Mots clés

  • electron paramagnetic resonance
  • defects
  • glass ceramics
6 Articles
Accès libre

Capacitance and Leakage Current Balancing for Supercapacitive Energy Storage System / Kapacitāšu Un Noplūdes Strāvu Balansēšana Superkondensatoru Enerģijas Uzkrājējsistēmai

Publié en ligne: 01 Feb 2013
Pages: 3 - 12

Résumé

Abstract

In the paper, the problem of voltage imbalance in supercapacitor bank caused by different capacitances and leakage resistances is considered. The authors propose capacitance balancing in combination with passive resistor voltage balancing as an efficient method for decreasing the cell voltage imbalance and increasing the effective energy capacity of supercapacitor bank. The efficiency of the method is demonstrated theoretically and verified experimentally on eight supercapacitor cells.

Keywords

  • energy storage
  • supercapacitors
  • voltage balancing
  • capacitancebalancing
  • leakage current balancing
  • capacitance measurement
Accès libre

Choice of the Optimum Cross-Sections for 20–110–330 kV Overhead Lines Under Market Conditions / 20–110–330 Kv Gaisvadu Līniju Optimālo Šķērsgriezumu Izvēle Tirgus Apstākļos

Publié en ligne: 01 Feb 2013
Pages: 13 - 22

Résumé

Abstract

Approach is proposed to the choice of overhead line cross-sections that would be optimal under market conditions. For this purpose, in the design practice and at network reconstruction two methods exist: of the economic current density, and of the economic intervals. As of now, none of them works properly, since the cost of electrical materials, of building and construction as well as the total investments in a line are determined by the market prices. Therefore, a modified economic intervals’ method has been developed that can work under market conditions. The method allows also considering the discrete character of standard cross-sections for the lines and concrete technical and technically-economic parameters. For practical application of the proposed method, universal economic nomograms for 20-110-330 kV overhead lines have been calculated and constructed. In the paper, a user interface is proposed for realization of the modified method in Matlab environment.

Mots clés

  • overhead lines
  • optimum cross-section
  • annual costs
  • nomograms
  • user interface
Accès libre

Heat and Moisture Transport in Multi-Layer Walls: Interaction and Heat Loss at Varying Outdoor Temperatures / Siltuma Un Mitruma Pārnese Caur Daudzslāņainām Būvkonstrukcijām: Āra Temperatūras Izmaiņu Ietekme Uz Siltuma Zudumiem Iekštelpā

Publié en ligne: 01 Feb 2013
Pages: 32 - 43

Résumé

Abstract

The heat and moisture transport in multi-layer walls is analysed for five building units. Using the developed program, a typical of Latvian conditions temperature and relative humidity profiles in multi-layered constructions has been obtained and the indoor heat losses estimated. Consideration is also given to the risk of condensate formation and to the influence of moisture on the U-value. The created mathematical model allows forecasting the energy efficiency and sustainability of different technical solutions as refer to the heat and moisture transport in buildings.

Mots clés

  • moisture
  • temperature
  • transport
  • multi-layer wall
Accès libre

Photoluminescence of Eu and Ce Activated Oxyfluoride Glass And Glass Ceramics/ Eu Un Ce Jonu Luminiscence Oksifluorīdu Stiklos Un Stikla Keramikā

Publié en ligne: 01 Feb 2013
Pages: 44 - 48

Résumé

Abstract

The photoluminescence of SiO2-Al2O3-LiO2-LaF3 oxyfluoride glass and glass ceramic samples doped with Ce3+, Eu2+ and Ce3+/Eu2+ is investigated, and the spectra and fluorescence intensities are compared. The luminescence of samples activated by Eu ions is found to be more intensive than of the samples doped with Ce or Ce/Eu. The luminescence of glass ceramics is higher than that of the corresponding glass, which indicates that a proportion of the activator ions are embedded in the fluoride crystallites.

Mots clés

  • photoluminescence
  • oxyfluoride glass
  • glass ceramics
  • Ce3+
  • Eu2+ ions
  • luminescence intensities
  • spectra
Accès libre

Epr Spectrum Angular Dependences In Liyf4 Crystal / Epr Spektru Leņķiskās Atkarības Liyf4 Kristālā

Publié en ligne: 01 Feb 2013
Pages: 49 - 54

Résumé

Abstract

Electron paramagnetic resonance (EPR) measurements have been made for two perpendicular planes in a LiYF4 crystal before and after x-ray irradiation at room temperature. Analysis of the EPR spectrum angular dependence shows the presence of two defects - an impurity ion, which was embedded during the crystal growth process, and an x-ray induced defect with the g-factor of approx. 2.0. Spectral parameters and possible defect models are discussed.

Keywords

  • EPR spectrum
  • LiYF4 crystal
Accès libre

Epr Hyperfine Structure Of Radiation Defect In Oxyfluoride Glass Ceramics/ Radiācijas Defekta Epr Hipersīkstruktūra Oksifluorīdu Stikla Keramikā

Publié en ligne: 01 Feb 2013
Pages: 55 - 59

Résumé

Abstract

We have investigated the samples of thermally treated oxyfluoride glass ceramics 50SiO2-25LiO2-20YF3-3ErF3-2YbF2 by means of electron paramagnetic resonance (EPR) techniques. After irradiation of the samples with X-rays, in the EPR spectra a hyperfine structure characteristic of F-centres could be observed in different fluoride crystals. The structure of F-centre in the oxyfluoride glass ceramics containing LiYF4 crystallites is discussed.

Mots clés

  • electron paramagnetic resonance
  • defects
  • glass ceramics

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