Zeitschriften und Ausgaben

Volumen 59 (2022): Heft 4 (August 2022)

Volumen 59 (2022): Heft 3 (June 2022)

Volumen 59 (2022): Heft s3 (June 2022)

Volumen 59 (2022): Heft 2 (April 2022)

Volumen 59 (2022): Heft 1 (February 2022)

Volumen 58 (2021): Heft 6 (December 2021)

Volumen 58 (2021): Heft 5 (October 2021)

Volumen 58 (2021): Heft 4 (August 2021)

Volumen 58 (2021): Heft 3 (June 2021)

Volumen 58 (2021): Heft 2 (April 2021)

Volumen 58 (2021): Heft 1 (February 2021)

Volumen 57 (2020): Heft 6 (December 2020)

Volumen 57 (2020): Heft 5 (October 2020)

Volumen 57 (2020): Heft 4 (August 2020)

Volumen 57 (2020): Heft 3 (June 2020)

Volumen 57 (2020): Heft 1-2 (April 2020)

Volumen 56 (2019): Heft 6 (December 2019)

Volumen 56 (2019): Heft 5 (October 2019)

Volumen 56 (2019): Heft 4 (August 2019)

Volumen 56 (2019): Heft 3 (June 2019)

Volumen 56 (2019): Heft 2 (April 2019)

Volumen 56 (2019): Heft 1 (February 2019)

Volumen 55 (2018): Heft 6 (December 2018)

Volumen 55 (2018): Heft 5 (October 2018)

Volumen 55 (2018): Heft 4 (August 2018)

Volumen 55 (2018): Heft 3 (June 2018)

Volumen 55 (2018): Heft 2 (April 2018)

Volumen 55 (2018): Heft 1 (February 2018)

Volumen 54 (2017): Heft 6 (December 2017)

Volumen 54 (2017): Heft 5 (October 2017)

Volumen 54 (2017): Heft 4 (August 2017)

Volumen 54 (2017): Heft 3 (June 2017)

Volumen 54 (2017): Heft 2 (April 2017)

Volumen 54 (2017): Heft 1 (February 2017)

Volumen 53 (2016): Heft 6 (December 2016)

Volumen 53 (2016): Heft 5 (October 2016)

Volumen 53 (2016): Heft 4 (August 2016)

Volumen 53 (2016): Heft 3 (June 2016)

Volumen 53 (2016): Heft 2 (April 2016)

Volumen 53 (2016): Heft 1 (February 2016)

Volumen 52 (2015): Heft 6 (December 2015)

Volumen 52 (2015): Heft 5 (October 2015)

Volumen 52 (2015): Heft 4 (August 2015)

Volumen 52 (2015): Heft 3 (June 2015)

Volumen 52 (2015): Heft 2 (April 2015)

Volumen 52 (2015): Heft 1 (February 2015)

Volumen 51 (2014): Heft 6 (December 2014)

Volumen 51 (2014): Heft 5 (October 2014)

Volumen 51 (2014): Heft 4 (August 2014)

Volumen 51 (2014): Heft 3 (June 2014)

Volumen 51 (2014): Heft 2 (April 2014)

Volumen 51 (2014): Heft 1 (February 2014)

Volumen 50 (2013): Heft 6 (December 2013)

Volumen 50 (2013): Heft 5 (October 2013)

Volumen 50 (2013): Heft 4 (August 2013)

Volumen 50 (2013): Heft 3 (June 2013)

Volumen 50 (2013): Heft 2 (April 2013)

Volumen 50 (2013): Heft 1 (February 2013)

Volumen 49 (2012): Heft 6-II (December 2012)

Volumen 49 (2012): Heft 6-I (December 2012)

Volumen 49 (2012): Heft 5 (October 2012)

Volumen 49 (2012): Heft 4 (August 2012)

Volumen 49 (2012): Heft 2 (April 2012)

Volumen 49 (2012): Heft 1 (February 2012)

Volumen 48 (2011): Heft 6 (December 2011)

Volumen 48 (2011): Heft 5 (October 2011)

Volumen 48 (2011): Heft 4 (August 2011)

Volumen 48 (2011): Heft 3 (June 2011)

Volumen 48 (2011): Heft 2 (April 2011)

Volumen 48 (2011): Heft 1 (February 2011)

Volumen 47 (2010): Heft 6 (December 2010)

Volumen 47 (2010): Heft 5 (October 2010)

Volumen 47 (2010): Heft 4 (August 2010)

Volumen 47 (2010): Heft 3 (June 2010)

Volumen 47 (2010): Heft 2 (April 2010)

Volumen 47 (2010): Heft 1 (February 2010)

Volumen 46 (2009): Heft 6 (December 2009)

Volumen 46 (2009): Heft 5 (October 2009)

Volumen 46 (2009): Heft 4 (August 2009)

Volumen 46 (2009): Heft 3 (June 2009)

Volumen 46 (2009): Heft 2 (April 2009)

Volumen 46 (2009): Heft 1 (February 2009)

Volumen 45 (2008): Heft 6 (December 2008)

Volumen 45 (2008): Heft 5 (October 2008)

Volumen 45 (2008): Heft 4 (August 2008)

Volumen 45 (2008): Heft 3 (June 2008)

Volumen 45 (2008): Heft 2 (April 2008)

Volumen 45 (2008): Heft 1 (February 2008)

Zeitschriftendaten
Format
Zeitschrift
eISSN
2255-8896
Erstveröffentlichung
18 Mar 2008
Erscheinungsweise
6 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 53 (2016): Heft 2 (April 2016)

Zeitschriftendaten
Format
Zeitschrift
eISSN
2255-8896
Erstveröffentlichung
18 Mar 2008
Erscheinungsweise
6 Hefte pro Jahr
Sprachen
Englisch

Suche

8 Artikel
Uneingeschränkter Zugang

Short-Term Forecasting of Loads and Wind Power for Latvian Power System: Accuracy and Capacity of the Developed Tools

Online veröffentlicht: 20 May 2016
Seitenbereich: 3 - 13

Zusammenfassung

Abstract

The paper analyses the performance results of the recently developed short-term forecasting suit for the Latvian power system. The system load and wind power are forecasted using ANN and ARIMA models, respectively, and the forecasting accuracy is evaluated in terms of errors, mean absolute errors and mean absolute percentage errors. The investigation of influence of additional input variables on load forecasting errors is performed. The interplay of hourly loads and wind power forecasting errors is also evaluated for the Latvian power system with historical loads (the year 2011) and planned wind power capacities (the year 2023).

Schlüsselwörter

  • forecasting error
  • short-term forecasting
  • system load
  • wind power
  • wind speed
Uneingeschränkter Zugang

Time and Frequency Synchronization on the Virac Radio Telescope RT-32

Online veröffentlicht: 20 May 2016
Seitenbereich: 14 - 19

Zusammenfassung

Abstract

One of the main research directions of Ventspils International Radio Astronomy Centre (VIRAC) is radio astronomy and astrophysics. The instrumental base for the centre comprised two fully steerable parabolic antennas, RT-16 and RT-32 (i.e. with the mirror diameter of 16 m and 32 m). After long reconstruction, radio telescope RT-32 is currently equipped with the receiving and data acquisition systems that allow observing in a wide frequency range from 327 MHz to 9 GHz. New Antenna Control Unit (ACU) allows stable, fast and precise pointing of antenna. Time and frequency distribution service provide 5, 10 and 100 MHz reference frequency, 1PPS signals and precise time stamps by NTP protocol and in the IRIG-B format by coaxial cable.

For the radio astronomical observations, main requirement of spatially Very Long Base Line Interferometric (VLBI) observations for the observatory is precise synchronization of the received and sampled data and linking to the exact time stamps. During October 2015, radio telescope RT-32 performance was tested in several successful VLBI experiments. The obtained results confirm the efficiency of the chosen methods of synchronization and the ability to reproduce them on similar antennas.

Schlüsselwörter

  • radio telescope
  • antenna control system
  • time and frequency synchronization
Uneingeschränkter Zugang

Experimental and Numerical Analysis of Air Flow, Heat Transfer and Thermal Comfort in Buildings with Different Heating Systems

Online veröffentlicht: 20 May 2016
Seitenbereich: 20 - 30

Zusammenfassung

Abstract

Monitoring of temperature, humidity and air flow velocity is performed in 5 experimental buildings with the inner size of 3×3×3 m3 located in Riga, Latvia. The buildings are equipped with different heating systems, such as an air-air heat pump, air-water heat pump, capillary heating mat on the ceiling and electric heater. Numerical simulation of air flow and heat transfer by convection, conduction and radiation is carried out using OpenFOAM software and compared with experimental data. Results are analysed regarding the temperature and air flow distribution as well as thermal comfort.

Schlüsselwörter

  • experimental buildings
  • monitoring system
  • numerical simulation
  • OpenFOAM
  • thermal comfort
Uneingeschränkter Zugang

Study of Copper Nitride Thin Film Structure

Online veröffentlicht: 20 May 2016
Seitenbereich: 31 - 37

Zusammenfassung

Abstract

X-ray diffraction and x-ray absorption spectroscopy at the Cu K-edge were used to study the atomic structure in copper nitride (Cu3N) thin films. Textured nanocrystalline films are obtained upon dc magnetron sputtering on substrates heated at about 190 °C, whereas amorphous films having strongly disordered structure already in the second coordination shell of copper are deposited in the absence of heating.

Schlüsselwörter

  • copper nitride
  • thin film
  • x-ray diffraction
  • x-ray absorption spectroscopy
Uneingeschränkter Zugang

Development of Mathematical Models for Detecting Micron Scale Volumetric Defects in Thin Film Coatings

Online veröffentlicht: 20 May 2016
Seitenbereich: 38 - 47

Zusammenfassung

Abstract

The focus of the present research is to investigate possibilities of volumetric defect detection in thin film coatings on glass substrates by means of high definition imaging with no complex optical systems, such as lenses, and to determine development and construction feasibility of a defectoscope employing the investigated methods. Numerical simulations were used to test the proposed methods. Three theoretical models providing various degrees of accuracy and feasibility were studied.

Schlüsselwörter

  • deconvolution
  • compressive sampling
  • ℓ minimization
  • numeric simulation
  • thin film coatings
Uneingeschränkter Zugang

Determination of Contact Potential Difference by the Kelvin Probe (Part I) I. Basic Principles of Measurements

Online veröffentlicht: 20 May 2016
Seitenbereich: 48 - 57

Zusammenfassung

Abstract

Determination of electric potential difference using the Kelvin probe, i.e. vibrating capacitor technique, is one of the most sensitive measuring procedures in surface physics. Periodic modulation of distance between electrodes leads to changes in capacitance, thereby causing current to flow through the external circuit. The procedure of contactless, non-destructive determination of contact potential difference between an electrically conductive vibrating reference electrode and an electrically conductive sample is based on precise control measurement of Kelvin current flowing through a capacitor. The present research is devoted to creation of a new low-cost miniaturised measurement system to determine potential difference in real time and at high measurement resolution. Furthermore, using the electrode of a reference probe, the Kelvin method leads to both the indirect measurement of an electronic work function, or a contact potential of sample, and of a surface potential for insulator type samples.

In the article, the first part of the research, i.e., the basic principles and prerequisites for establishment of such a measurement system are considered.

Schlüsselwörter

  • Kelvin probe
  • contact potential difference
  • surface potential
Uneingeschränkter Zugang

Hardware Design of the Energy Efficient Fall Detection Device

Online veröffentlicht: 20 May 2016
Seitenbereich: 58 - 67

Zusammenfassung

Abstract

Health issues for elderly people may lead to different injuries obtained during simple activities of daily living. Potentially the most dangerous are unintentional falls that may be critical or even lethal to some patients due to the heavy injury risk. In the project “Wireless Sensor Systems in Telecare Application for Elderly People”, we have developed a robust fall detection algorithm for a wearable wireless sensor. To optimise the algorithm for hardware performance and test it in field, we have designed an accelerometer based wireless fall detector. Our main considerations were: a) functionality – so that the algorithm can be applied to the chosen hardware, and b) power efficiency – so that it can run for a very long time. We have picked and tested the parts, built a prototype, optimised the firmware for lowest consumption, tested the performance and measured the consumption parameters. In this paper, we discuss our design choices and present the results of our work.

Schlüsselwörter

  • 3-axis accelerometer
  • electronics
  • energy efficiency
  • fall detection
  • hardware
  • microcontroller
  • telecare
Uneingeschränkter Zugang

The Influence of Wind Turbines on Radio Astronomical Observations in Irbene

Online veröffentlicht: 20 May 2016
Seitenbereich: 68 - 74

Zusammenfassung

Abstract

The reflection and diffraction of external communication and navigational transmitters from tall constructions and moving blades of wind turbines produce some short-pulse additional electromagnetic interference strong enough to fully disturb radio astronomical observations. The problem of short-pulse electromagnetic interference is distinctive to all radio telescopes surrounded by wind turbines. This problem became significant for Ventspils International Radio Astronomy Centre (VIRAC) after new wind park “Platene” of Winergy Ltd. was built in 2012 and radio telescopes RT-16 and RT-32 renovated and equipped with cryogenic high sensitive receivers. The paper deals with the analysis and evaluation of intensities and probabilities of short-pulse interferences produced by wind park “Platene” and its possible impact on radio astronomical observations at VIRAC radio telescopes.

Schlüsselwörter

  • electromagnetic interferences
  • radio astronomy
8 Artikel
Uneingeschränkter Zugang

Short-Term Forecasting of Loads and Wind Power for Latvian Power System: Accuracy and Capacity of the Developed Tools

Online veröffentlicht: 20 May 2016
Seitenbereich: 3 - 13

Zusammenfassung

Abstract

The paper analyses the performance results of the recently developed short-term forecasting suit for the Latvian power system. The system load and wind power are forecasted using ANN and ARIMA models, respectively, and the forecasting accuracy is evaluated in terms of errors, mean absolute errors and mean absolute percentage errors. The investigation of influence of additional input variables on load forecasting errors is performed. The interplay of hourly loads and wind power forecasting errors is also evaluated for the Latvian power system with historical loads (the year 2011) and planned wind power capacities (the year 2023).

Schlüsselwörter

  • forecasting error
  • short-term forecasting
  • system load
  • wind power
  • wind speed
Uneingeschränkter Zugang

Time and Frequency Synchronization on the Virac Radio Telescope RT-32

Online veröffentlicht: 20 May 2016
Seitenbereich: 14 - 19

Zusammenfassung

Abstract

One of the main research directions of Ventspils International Radio Astronomy Centre (VIRAC) is radio astronomy and astrophysics. The instrumental base for the centre comprised two fully steerable parabolic antennas, RT-16 and RT-32 (i.e. with the mirror diameter of 16 m and 32 m). After long reconstruction, radio telescope RT-32 is currently equipped with the receiving and data acquisition systems that allow observing in a wide frequency range from 327 MHz to 9 GHz. New Antenna Control Unit (ACU) allows stable, fast and precise pointing of antenna. Time and frequency distribution service provide 5, 10 and 100 MHz reference frequency, 1PPS signals and precise time stamps by NTP protocol and in the IRIG-B format by coaxial cable.

For the radio astronomical observations, main requirement of spatially Very Long Base Line Interferometric (VLBI) observations for the observatory is precise synchronization of the received and sampled data and linking to the exact time stamps. During October 2015, radio telescope RT-32 performance was tested in several successful VLBI experiments. The obtained results confirm the efficiency of the chosen methods of synchronization and the ability to reproduce them on similar antennas.

Schlüsselwörter

  • radio telescope
  • antenna control system
  • time and frequency synchronization
Uneingeschränkter Zugang

Experimental and Numerical Analysis of Air Flow, Heat Transfer and Thermal Comfort in Buildings with Different Heating Systems

Online veröffentlicht: 20 May 2016
Seitenbereich: 20 - 30

Zusammenfassung

Abstract

Monitoring of temperature, humidity and air flow velocity is performed in 5 experimental buildings with the inner size of 3×3×3 m3 located in Riga, Latvia. The buildings are equipped with different heating systems, such as an air-air heat pump, air-water heat pump, capillary heating mat on the ceiling and electric heater. Numerical simulation of air flow and heat transfer by convection, conduction and radiation is carried out using OpenFOAM software and compared with experimental data. Results are analysed regarding the temperature and air flow distribution as well as thermal comfort.

Schlüsselwörter

  • experimental buildings
  • monitoring system
  • numerical simulation
  • OpenFOAM
  • thermal comfort
Uneingeschränkter Zugang

Study of Copper Nitride Thin Film Structure

Online veröffentlicht: 20 May 2016
Seitenbereich: 31 - 37

Zusammenfassung

Abstract

X-ray diffraction and x-ray absorption spectroscopy at the Cu K-edge were used to study the atomic structure in copper nitride (Cu3N) thin films. Textured nanocrystalline films are obtained upon dc magnetron sputtering on substrates heated at about 190 °C, whereas amorphous films having strongly disordered structure already in the second coordination shell of copper are deposited in the absence of heating.

Schlüsselwörter

  • copper nitride
  • thin film
  • x-ray diffraction
  • x-ray absorption spectroscopy
Uneingeschränkter Zugang

Development of Mathematical Models for Detecting Micron Scale Volumetric Defects in Thin Film Coatings

Online veröffentlicht: 20 May 2016
Seitenbereich: 38 - 47

Zusammenfassung

Abstract

The focus of the present research is to investigate possibilities of volumetric defect detection in thin film coatings on glass substrates by means of high definition imaging with no complex optical systems, such as lenses, and to determine development and construction feasibility of a defectoscope employing the investigated methods. Numerical simulations were used to test the proposed methods. Three theoretical models providing various degrees of accuracy and feasibility were studied.

Schlüsselwörter

  • deconvolution
  • compressive sampling
  • ℓ minimization
  • numeric simulation
  • thin film coatings
Uneingeschränkter Zugang

Determination of Contact Potential Difference by the Kelvin Probe (Part I) I. Basic Principles of Measurements

Online veröffentlicht: 20 May 2016
Seitenbereich: 48 - 57

Zusammenfassung

Abstract

Determination of electric potential difference using the Kelvin probe, i.e. vibrating capacitor technique, is one of the most sensitive measuring procedures in surface physics. Periodic modulation of distance between electrodes leads to changes in capacitance, thereby causing current to flow through the external circuit. The procedure of contactless, non-destructive determination of contact potential difference between an electrically conductive vibrating reference electrode and an electrically conductive sample is based on precise control measurement of Kelvin current flowing through a capacitor. The present research is devoted to creation of a new low-cost miniaturised measurement system to determine potential difference in real time and at high measurement resolution. Furthermore, using the electrode of a reference probe, the Kelvin method leads to both the indirect measurement of an electronic work function, or a contact potential of sample, and of a surface potential for insulator type samples.

In the article, the first part of the research, i.e., the basic principles and prerequisites for establishment of such a measurement system are considered.

Schlüsselwörter

  • Kelvin probe
  • contact potential difference
  • surface potential
Uneingeschränkter Zugang

Hardware Design of the Energy Efficient Fall Detection Device

Online veröffentlicht: 20 May 2016
Seitenbereich: 58 - 67

Zusammenfassung

Abstract

Health issues for elderly people may lead to different injuries obtained during simple activities of daily living. Potentially the most dangerous are unintentional falls that may be critical or even lethal to some patients due to the heavy injury risk. In the project “Wireless Sensor Systems in Telecare Application for Elderly People”, we have developed a robust fall detection algorithm for a wearable wireless sensor. To optimise the algorithm for hardware performance and test it in field, we have designed an accelerometer based wireless fall detector. Our main considerations were: a) functionality – so that the algorithm can be applied to the chosen hardware, and b) power efficiency – so that it can run for a very long time. We have picked and tested the parts, built a prototype, optimised the firmware for lowest consumption, tested the performance and measured the consumption parameters. In this paper, we discuss our design choices and present the results of our work.

Schlüsselwörter

  • 3-axis accelerometer
  • electronics
  • energy efficiency
  • fall detection
  • hardware
  • microcontroller
  • telecare
Uneingeschränkter Zugang

The Influence of Wind Turbines on Radio Astronomical Observations in Irbene

Online veröffentlicht: 20 May 2016
Seitenbereich: 68 - 74

Zusammenfassung

Abstract

The reflection and diffraction of external communication and navigational transmitters from tall constructions and moving blades of wind turbines produce some short-pulse additional electromagnetic interference strong enough to fully disturb radio astronomical observations. The problem of short-pulse electromagnetic interference is distinctive to all radio telescopes surrounded by wind turbines. This problem became significant for Ventspils International Radio Astronomy Centre (VIRAC) after new wind park “Platene” of Winergy Ltd. was built in 2012 and radio telescopes RT-16 and RT-32 renovated and equipped with cryogenic high sensitive receivers. The paper deals with the analysis and evaluation of intensities and probabilities of short-pulse interferences produced by wind park “Platene” and its possible impact on radio astronomical observations at VIRAC radio telescopes.

Schlüsselwörter

  • electromagnetic interferences
  • radio astronomy

Planen Sie Ihre Fernkonferenz mit Scienceendo