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Journal Details
Format
Journal
eISSN
2255-8896
First Published
18 Mar 2008
Publication timeframe
6 times per year
Languages
English

Search

Volume 53 (2016): Issue 2 (April 2016)

Journal Details
Format
Journal
eISSN
2255-8896
First Published
18 Mar 2008
Publication timeframe
6 times per year
Languages
English

Search

8 Articles
Open Access

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

Published Online: 20 May 2016
Page range: 3 - 13

Abstract

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).

Keywords

  • forecasting error
  • short-term forecasting
  • system load
  • wind power
  • wind speed
Open Access

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

Published Online: 20 May 2016
Page range: 14 - 19

Abstract

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.

Keywords

  • radio telescope
  • antenna control system
  • time and frequency synchronization
Open Access

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

Published Online: 20 May 2016
Page range: 20 - 30

Abstract

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.

Keywords

  • experimental buildings
  • monitoring system
  • numerical simulation
  • OpenFOAM
  • thermal comfort
Open Access

Study of Copper Nitride Thin Film Structure

Published Online: 20 May 2016
Page range: 31 - 37

Abstract

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.

Keywords

  • copper nitride
  • thin film
  • x-ray diffraction
  • x-ray absorption spectroscopy
Open Access

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

Published Online: 20 May 2016
Page range: 38 - 47

Abstract

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.

Keywords

  • deconvolution
  • compressive sampling
  • ℓ minimization
  • numeric simulation
  • thin film coatings
Open Access

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

Published Online: 20 May 2016
Page range: 48 - 57

Abstract

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.

Keywords

  • Kelvin probe
  • contact potential difference
  • surface potential
Open Access

Hardware Design of the Energy Efficient Fall Detection Device

Published Online: 20 May 2016
Page range: 58 - 67

Abstract

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.

Keywords

  • 3-axis accelerometer
  • electronics
  • energy efficiency
  • fall detection
  • hardware
  • microcontroller
  • telecare
Open Access

The Influence of Wind Turbines on Radio Astronomical Observations in Irbene

Published Online: 20 May 2016
Page range: 68 - 74

Abstract

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.

Keywords

  • electromagnetic interferences
  • radio astronomy
8 Articles
Open Access

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

Published Online: 20 May 2016
Page range: 3 - 13

Abstract

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).

Keywords

  • forecasting error
  • short-term forecasting
  • system load
  • wind power
  • wind speed
Open Access

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

Published Online: 20 May 2016
Page range: 14 - 19

Abstract

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.

Keywords

  • radio telescope
  • antenna control system
  • time and frequency synchronization
Open Access

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

Published Online: 20 May 2016
Page range: 20 - 30

Abstract

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.

Keywords

  • experimental buildings
  • monitoring system
  • numerical simulation
  • OpenFOAM
  • thermal comfort
Open Access

Study of Copper Nitride Thin Film Structure

Published Online: 20 May 2016
Page range: 31 - 37

Abstract

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.

Keywords

  • copper nitride
  • thin film
  • x-ray diffraction
  • x-ray absorption spectroscopy
Open Access

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

Published Online: 20 May 2016
Page range: 38 - 47

Abstract

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.

Keywords

  • deconvolution
  • compressive sampling
  • ℓ minimization
  • numeric simulation
  • thin film coatings
Open Access

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

Published Online: 20 May 2016
Page range: 48 - 57

Abstract

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.

Keywords

  • Kelvin probe
  • contact potential difference
  • surface potential
Open Access

Hardware Design of the Energy Efficient Fall Detection Device

Published Online: 20 May 2016
Page range: 58 - 67

Abstract

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.

Keywords

  • 3-axis accelerometer
  • electronics
  • energy efficiency
  • fall detection
  • hardware
  • microcontroller
  • telecare
Open Access

The Influence of Wind Turbines on Radio Astronomical Observations in Irbene

Published Online: 20 May 2016
Page range: 68 - 74

Abstract

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.

Keywords

  • electromagnetic interferences
  • radio astronomy

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