| 1. |
- Carlson, Johan, et al.
(author)
-
Prediction of molar fractions in two-component gas mixtures using pulse-echo ultrasound and PLS regression
- 2006
-
In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 53:3, s. 606-613
-
Journal article (peer-reviewed)abstract
- The composition, and thus the energy content and monetary value of natural gas and biogas, vary considerably depending on the source. Present energy measurement techniques are riot suitable for online use. We show with experiments on mixtures of ethane (C/sub 2/H/sub 6/) and oxygen (O/sub 2/) how partial least squares regression (PLSR) can be used to predict the molar fraction of ethane in the mixtures, given spectral data from ultrasonic pulse-echo measurements. The PLSR technique is compared with the standard principal component regression (PCR), and we show that PLSR yields better predictive performance.
|
|
| 2. |
- Samuelsson, Olof, et al.
(author)
-
Monitoring of power system events at transmission and distribution level
- 2006
-
In: IEEE Transactions on Power Systems. - 0885-8950. ; 21:2, s. 1007-1008
-
Journal article (peer-reviewed)abstract
- Monitoring of events in the power system provides a great deal of insight into the behavior of the system. Events with impact on the entire power system typically occur in or near the transmission network and are therefore best monitored at transmission system substations. This puts great demands on the equipment and in general restricts the use of the data since it becomes property of the transmission system operator. An alternative is to measure at lower voltage levels. This paper documents the close agreement between voltage and frequency at low and high voltage levels during a remote and a nearby fault in the transmission network. The very high quality of the data suggests that valuable information about the transmission system can be obtained at lower voltages.
|
|
| 3. |
- Hagell, Peter, et al.
(author)
-
Measuring fatigue in Parkinson's disease : a psychometric study of two brief generic fatigue questionnaires.
- 2006
-
In: Journal of Pain and Symptom Management. - : Elsevier. - 0885-3924 .- 1873-6513. ; 32:5, s. 420-32
-
Journal article (peer-reviewed)abstract
- This study evaluated and compared the measurement properties of the 13-item Functional Assessment of Chronic Illness Therapy-Fatigue Scale (FACIT-F) and the 9-item Fatigue Severity Scale (FSS) in 118 consecutive Parkinson's disease (PD) patients, using traditional and Rasch measurement methodologies. Both questionnaires exhibited excellent data quality and reliability (coefficient alpha>or=0.9), and acceptable rating scale functionality, and both discriminated between fatigued and nonfatigued patients. Factor and Rasch analyses provided general support for unidimensionality of both FACIT-F and FSS, although they do not appear to measure identical aspects of fatigue. No signs of differential item functioning (DIF) were found for the FACIT-F, whereas potential age DIF was detected for two FSS items. These results support the measurement validity of both questionnaires in PD, although the FACIT-F displayed better measurement precision and modest psychometric advantages over the FSS. Availability of psychometrically sound fatigue measures that are applicable across disorders provides a sound basis for advancing the understanding of this common and distressing complaint.
|
|
| 4. |
- Hagell, Peter, et al.
(author)
-
Measuring fatigue in Parkinsons disease: A psychometric study of two brief generic fatigue questionnaires
- 2006
-
In: Journal of Pain and Symptom Management. - : Elsevier BV. - 0885-3924 .- 1873-6513. ; 32:5, s. 420-432
-
Journal article (peer-reviewed)abstract
- This study evaluated and compared the measurement properties of the 13-item Functional Assessment of Chronic Illness Therapy-Fatigue Scale (FACIT-F) and the 9-item Fatigue Severity Scale (FSS) in 118 consecutive Parkinsons disease (PD) patients, using traditional and Rasch measurement methodologies. Both questionnaires exhibited excellent data quality and reliability (coefficient alpha greater than= 0.9), and acceptable rating scale functionality, and both discriminated between fatigued and nonfatigued patients. factor and Rasch analyses provided general support for unidimensionality of both FACIT-F and FSS, although they do not appear to measure identical aspects of fatigue. No signs of differential item functioning (DIF) were found for the FACIT-F, whereas potential age DIF, was detected for two FSS items. These results support the measurement validity of both questionnaires in PD, although the FACIT-F displayed better measurement precision and modest psychometric advantages over the FSS. Availability of psychometrically sound fatigue measures that are applicable across disorders provides a sound basis for advancing the understanding of this common and distressing complaint.
|
|
| 5. |
- Abeywickrama, Nilanga, 1976, et al.
(author)
-
Exploring Possibilities for Characterization of POwer Transformer Insulation by Frequency Response Analysis (FRA)
- 2006
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 21:3, s. 1375-1382
-
Journal article (peer-reviewed)abstract
- This paper explores the possibility for using frequencyresponse analysis (FRA) technique to characterize thequality of transformer insulation. For this purpose, a single-phase and a three-phase lumped parameter circuit models were developed.The single-phase model represents a transformer without a laminated core, whereas the three-phase model represents a real transformer with core. Calculations of frequency dependent circuit parameters are presented and the effects imparted on the frequency response by different loss mechanisms (in insulation, inwindings and in core) are discussed. The simulations are compared with results of measurements on real objects. It is shown that FRA could be used for insulation diagnostics if the measurements were of high enough quality.
|
|
| 6. |
- Axelberg, P.G.V., et al.
(author)
-
An algorithm for determining the direction to a flicker source
- 2006
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 21:2, s. 755-760
-
Journal article (peer-reviewed)abstract
- This paper describes an algorithm for calculating the direction to a flicker source with respect to a monitoring point. The proposed algorithm is based on sampling of both the voltage and current. The low-frequency fluctuations in voltage and current are recovered from the input signals by demodulation, and passed through a bandpass filter as described in IEC 61000-4-15. A new quantity - flicker power - is defined from the output signals of the two filters. The direction to a flicker source is obtained from the sign of this flicker power. The proposed algorithm has been validated by simulations and several field measurements
|
|
| 7. |
- Bjurström, Johan, et al.
(author)
-
Synthesis of textured thin piezoelectric AlN films with a nonzero C-axis mean tilt for the fabrication of shear mode resonators
- 2006
-
In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 53:11, s. 2095-2100
-
Journal article (peer-reviewed)abstract
- A method for the deposition of thin piezoelectric aluminum nitride (AlN) films with a nonzero c-axis mean tilt has been developed. The deposition is done in a standard reactive magnetron sputter deposition system without any hardware modifications. In essence, the method consists of a two-stage deposition process. The resulting film has a distinct tilted texture with the mean tilt of the c-axis varying roughly in the interval 28 to 32 degrees over the radius of the wafer excluding a small exclusion zone at the center of the latter. The mean tilt angle distribution over the wafer has a circular symmetry. A membrane-type shear mode thickness-excited thin film bulk acoustic resonator together with a micro-fluidic transport system has been subsequently fabricated using the two stage AIN deposition as well as standard bulk micro machining of Si. The resonator consisted of a 2-mu m-thick AlN film with 200-nm-thick A1 top and bottom electrodes. The resonator was characterized with a network analyzer when operating in both air and water. The shear mode resonance frequency was about 1.6 GHz, the extracted device Q around 350, and the electromechanical coupling k(t)(2) 2% when the resonator was operated in air, whereas the latter two dropped down to 150 and 1.8%, respectively, when the resonator was operated in pure water.
|
|
| 8. |
- Lundberg, Angela, et al.
(author)
-
Snow density variations : consequences for ground-penetrating radar
- 2006
-
In: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 20:7, s. 1483-1495
-
Journal article (peer-reviewed)abstract
- Reliable hydrological forecasts of snowmelt runoff are of major importance for many areas. Ground-penetrating radar (GPR) measurements are used to assess snowpack water equivalent for planning of hydropower production in northern Sweden. The travel time of the radar pulse through the snow cover is recorded and converted to snow water equivalent (SWE) using a constant snowpack mean density from the drainage basin studied. In this paper we improve the method to estimate SWE by introducing a depth-dependent snowpack density. We used 6 years measurements of peak snow depth and snowpack mean density at 11 locations in the Swedish mountains. The original method systematically overestimates the SWE at shallow depths (+25% for 0·5 m) and underestimates the SWE at large depths (-35% for 2·0 m). A large improvement was obtained by introducing a depth-density relation based on average conditions for several years, whereas refining this by using separate relations for individual years yielded a smaller improvement. The SWE estimates were substantially improved for thick snow covers, reducing the average error from 162 ± 23 mm to 53 ± 10 mm for depth range 1·2-2·0 m. Consequently, the introduction of a depth-dependent snow density yields substantial improvements of the accuracy in SWE values calculated from GPR data.
|
|
| 9. |
- Matevosyan, Julija, et al.
(author)
-
Minimization of Imbalance Cost Trading Wind Power on the Short-Term Power Market
- 2006
-
In: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 21:3, s. 1396-1404
-
Journal article (peer-reviewed)abstract
- Present power markets are designed for trading conventional generation. For wind generation to participate in a short-term energy market, lengthy wind power production forecasts are required. Although wind speed forecasting techniques are constantly improving, wind speed forecasts are never perfect, and resulting wind power forecast errors imply imbalance costs for wind farm owners. In this paper, a new method for minimization of imbalance costs is. developed. Stochastic programming is used to generate optimal wind power production bids for a short-term power market. A Wind power forecast error is represented as a stochastic process. The imbalance costs resulting from this strategy are then compared to the case when wind power production bids on a short-term power market are based directly on a wind speed forecast.
|
|
| 10. |
- Norrga, Staffan
(author)
-
Experimental study of a soft-switched isolated bidirectional AC-DC converter without auxiliary circuit
- 2006
-
In: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 21:6, s. 1580-1587
-
Journal article (peer-reviewed)abstract
- An isolated ac-dc converter topology includes a capacitively snubbered. voltage source converter (VSC) and a cycloconverter, coupled by a medium frequency transformer. The topology offers the possibility of bilateral power flow as well as three-level pulse width modulation on the ac side. It is shown that by alternately commutating the VSC and the cycloconverter it is possible to achieve either zero-voltage or zero-current switching conditions for all semiconductor devices in all points of operation. This is the case without any need for auxiliary semiconductor devices. At low load the transformer current may be insufficient for recharging the VSC snubber capacitors. In this case, however, it is possible to utilize the cycloconverter for providing a current path by which a quasi-resonant commutation can be made. The design and operation of a 40-kVA prototype converter system is described. It is shown how the rather complex switching logic required for implementing the chosen algorithm for commutation and modulation can be realized by using modern programmable logic devices [field programmable gate array (FPGA)]. Measurement results from the prototype converter are presented and analyzed. The measurements indicate that the,studied commutation algorithm works well in practice.
|
|
