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Time-frequency based coherence analysis of red and green flickering visual stimuli for EEG-controlled applications
(2017-03-23)
Tantisatirapong, Suchada
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Dechwechprasit, Panisa
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Senavongse, Wongwit
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Phothisonothai, Montri
The stimulus flickering at specific frequencies, or as known as steady-state visually evoked potential (SSVEP), can be recorded on an occipital area of the brain. SSVEP is used to interpret the EEG signal to detect the desired goal of the experiment. In this paper, we aim to investigate SSVE signal by means of magnitude-squared coherence (MSC) analysis between the red and green visual stimuli. In the experimental paradigm, we considered two parameters that are chromatic color and flickering frequency where an epoch interval was 10 seconds. The obtained results showed the statistically significant frequency-domain response and its maximum MSC coefficient in the theta and alpha bands for green and red flickers, respectively.
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Automated detection of plasmodium falciparum from Giemsa-stained thin blood films
(2016-03-23)
Preedanan, Wongsakorn
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Phothisonothai, Montri
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Senavongse, Wongwit
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Tantisatirapong, Suchada
This paper investigates automated detection of malaria parasites in images of Giemsa-stained thin blood films. We aim to determine parasitemia based on automatic segmentation, feature extraction and classification methods. Segmentation relies on adaptive thresholding and watershed methods. Statistical features are then computed for each cell and classified using SVM binary classifier. Accuracy of classification is validated based on the leave-one-out cross-validation technique. This processing pipeline is applied on total 15 images of Giemsa-stained thin blood films and yields 92.71% sensitivity, 97.35% specificity and 97.17% accuracy.
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A study of performance and comparison of VSI with improved current waveshape for three-phase rectifier
(2008-10-30)
Tangsiriworakul, Chanwit
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Manop, Chalermchat
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Rojviroon, Wanchanai
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Senavongse, Wongwit
This paper studies and compares the efficiency of voltage source inverter with traditional 3-phase rectifier direct current circuit on the front end, with passive filter, and with improved current wave shape. The efficiency evaluation is tested using THD, power factor and under changing modulation index, switching frequency and changing load. There is also a comparison of the effect of delta modulation switching technique and SPWM method on direct current circuit. ©2008 IEEE.
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Biomechanical study of patellofemoral joint instability
(2005-12-12)
Senavongse, Wongwit
Patellofemoral joint instability is a complex clinical problem. It may be a consequence of pre-existing anatomical abnormality or trauma. The objectives of this study were to use experimental mechanics to measure patellar stability and to quantify the effects of pathological abnormalities on patellar stability in vitro. Eight fresh-frozen cadaver knees were studies. The patellar stability was measured using an Instron material testing machine. A total load of 175N was applied to the quadriceps muscles. Patellar force-displacement was tested at different knee flexion angles as the patella was cyclically displaced 10mm laterally and medially. Three pathological abnormalities were applied; VMO malfunction, flat lateral trochlea, and medial retinacular structure rupturing. For the first time, this study has shown comparative and quantitative influence of pathological abnormalities on patellar stability. It was found that a flat lateral trochlea has greater effect than the medial retinacular rupturing whereas the medial retinacular rupturing has greater effect than VMO malfunction on patellar lateral stability. These results are important for future investigations on the treatment of patellofemoral instability.
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Laboratory digital signal analysis with virtual spectrum analyzer
(2005-12-01)
Hengkietisak, Siriporn
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Tipyakanont, Surapol
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Tangsiriworakul, Chanwit
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Manop, Chalermchat
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Senavongse, Wongwit
This paper present laboratory digital signal analysis with virtual spectrum analyzer which is created using LabVIEW program on digital oscilloscope TDS 5054. This research aims to develop a knowledge-base on digital signal analysis and the working of virtual instrumentation, a topic which is currently attracting wide interest due to its many good attributes including flexibility, modularity, and low cost. It also aims to make a good use of expensive digital oscilloscope TDS 5054. In this study, laboratory spectrum analysis is performed with variable sampling rate, effect of windows filter etc. The results are displayed by both time domain and frequency domain. There are samples of signal waveforms such as Sinusoidal Waveform, Square waveform, Six-step waveform, and PWM (pulse width modulation) waveform. These waveforms are important in the study of power electronics. The data are obtained using special module program to extract information from the digital oscilloscope. © 2005 IEEE.
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A low cost prototype for testing stator winding shorted turns in 3-phase induction motors
(2005-12-01)
Manop, Chalermchat
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Senavongse, Wongwit
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Kinnares, Vijit
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Tangsiriworakul, Chanwit
This paper presents a prototype of stator winding shorted turns detector for three-phase induction motors. The focus condition is turn-to-turn short circuit, because this condition is the initial problem. The diagnosis technique is detectable from the voltage sum of the three instantaneous line to star-point voltage. In the testing, the supply is sinusoidal waveform and the motor must be star connected with floating neutral. Before diagnosis, this instrument will also determine the level of supply voltage imbalance, if it is over the limit, the test instrument will not diagnose shorted turns. From experimental results, 3-hp and 5-hp induction motors were used for testing this equipment which is capable of accurately identifying percentage of stator winding shorted turns. © 2005 IEEE.

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