Engineering Journal (Faculty of Engineering, Chulalongkorn University, Bangkok)
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X-Band Front-end Module of FMCW RADAR for Collision Avoidance Application
Get PDFA frequency modulated continuous wave (FMCW) radar front-end module is developed as a laboratory prototype of NECTEC, NSTDA. The performance of proposed prototype is verified by the reflection test of aluminum plates in outdoor environment. The frequency domain data from a spectrum analyzer was measured at every 20 meters of the distance between the front-end prototype and the aluminum plate until the maximum distance of 200 meters is reached. The calculation of the beat frequencies at different range of reflecting aluminum plates is presented. The maximum error between measured and calculated distances does not exceed 5.02 percent. The effect of different radar cross section (RCS) of reflecting objects of 0.3, 0.8 and 1.5 m2 plate area are analyzed. The low value of different received power ratio per one squared meter unit area of 0.66 percent is obtained to prove the consistency of reflected power level over the different size of object under test.
Development of a Suture Pad for Medical Training from Silk Fiber Reinforced Polydimethylsiloxane Composite
Get PDFThe aim of this research is to develop a suture pad simulating human skin for suturing practice. The suture pad was fabricated with layers of artificial dermis and subcutis which reproduced the mechanical properties of skin. The main focus of this study was to reinforce polydimethylsiloxane with silk fiber to create a realistic dermis. The effects of silk fiber amount and aspect ratio on the mechanical properties of the suture pads were investigated. Results revealed that the tensile strength and modulus of the composite increased in relation to fiber content and aspect ratio. Composites with silk fiber exhibited higher tear resistance to suture thread compared with pure polydimethylsiloxane. Furthermore, the hardness of the composites was improved with the addition of silk fiber. It was found that polydimethylsiloxane composite reinforced with 2 phr of silk fiber with an aspect ratio of 1000 showed a hardness value similar to that of human skin. These results indicate that silk fiber reinforced polydimethylsiloxane composites can realistically simulate human skin and have the potential to be used as suture pads for medical training
Influence of Formwork Structure on Heat Treatment of Precast Concrete Elements by Solar Energy
Get PDFThe present paper aims to study the influence of the formwork structure on the efficiency of heat treatment (HT) of precast concrete elements (PCE) by solar energy in various climatic conditions. The objects of the study were different types of formworks composed of solar energy equipment for HT of PCE. In total, six types of formworks, made of steel sheet, laminated plywood and timber, with and without insulation were studied. Calculation and experimental study were carried out for humid continental, and subtropical climates. Experimental study was carried out in the laboratory and in the open air. According to the obtained results, the heat insulation material in the formwork structure contributes to increase the strength of concrete. Formwork with heat insulation layer of 40 mm gave the best results. However, the level of the contribution depends on climatic conditions. Heat insulation material in the formwork structure is necessary in humid continental climate. Even the thickness of the insulation layer of 20 mm gives good results and the difference between the concrete strength with thickness of 20 mm and 40 mm is insignificant. On the contrary, in humid subtropical climate, the heat insulation material in the formwork structure is favorable, but not compulsory, since the difference between the concrete strengths is not significant and the strength values, obtained in all six types of formwork, allow it to be removed after 24 hours of curing
Hydrogen Production from Methane in Atmospheric Non-Equilibrium Plasma
Get PDFThe instability of supplied power is a serious problem for chemical plants in developing countries. An easy start-up/shut-down system is important in this situation. The present report describes a hydrocarbon decomposition system using nonequilibrium plasma for hydrogen production. A microwave oven was used as a preliminary microwave reactor, which contained a quartz glass tube that passed through the top panel to the bottom panel of the microwave oven. Argon and methane flow were directed into the reactor, where the argon gas became plasma in the tube. A carbon stick was set in the tube as the excitation material of argon to plasma. Initially, the reaction was conducted under a methane partial pressure of 200 hPa. The main products were hydrogen and acetylene, with a small amount of ethylene also produced. Conversion and yields decreased with increasing methane partial pressure. Hydrogen production rate initially increased with methane partial pressure, but then decreased. The optimum methane partial pressure was determined. Gas flow rate had no effect on conversion or yield. The reactant and products reached an equilibrium state as soon as the reactant was introduced to the plasma. Pure hydrogen, 95%, was obtained by adjusting the experimental conditions
Low-Pressure Measurement using an Extrinsic Fiber-Based Fabry-Perot Interferometer for Industrial Applications
Get PDFThe development of an extrinsic fiber-based Fabry-Perot interferometer (EFFPI) for low-pressure measurement in the industry applications has been studied in this work. Monochromatic light from a laser diode with a wavelength of 1310 nm is operated as a source for illuminating the EFFPI sensor. A 30 mm diameter PVC pipe is utilized as a target, of which one end is sealed with a rubber balloon and the end is connected to the air pressure flow controlling system. Furthermore, the center point of the balloon is secured with a reflective thin film, which has a reflectance of ~55%. For the performance validation of the fiber sensor, a low-pressure range from 5 to 50 mBar is released onto the target. With 12 rounds repeatability, the experimental results reported that the average measured pressure values from the EFFPI sensor are 4.915 – 50.988 mBar. When compared to the reference instrument, the maximum and average errors in percentage terms are, however, 3.77% and 1.45%, respectively. In addition, results showed that the measured pressure value is directly proportional to the number of interference fringes, giving a sensitivity in the pressure measurement of the EFFPI sensor of 0.248 mBar/fringe
Three-Dimensional Data Quality Assessment: Unmanned Aerial Vehicle Photogrammetry and Mobile Laser Scanner
Get PDFWith significantly rapid in acquiring data and sufficient data quality, unmanned aerial vehicle (UAV) photogrammetry and land based mobile laser scanner are actively implemented in three-dimensional (3D) data acquisition that involve with large area. Considering the final data provided by both measurement approaches are point clouds, accuracy assessment using several well-distributed control points are less significant. With intention to robustly evaluate the accuracies of both measurement approaches using point clouds, this study has established reference point clouds using terrestrial laser scanner (TLS) and tacheometry techniques. At the similar test site, fourteen (14) images were captured using UAV photogrammetry approach and georeferenced point clouds were directly acquired from MLS measurement. To produce quality point clouds from photogrammetry approach, six (6) ground control points (GCP) have been well-distributed at the test area to aid geometry correction in image processing phase. Obtained point clouds from both measurement approaches were deviated with the reference point clouds to determine values of mean deviations with the precisions. Based on law of propagation of variance (LOPOV) algorithm, final accuracy of the tested UAV photogrammetry and MLS were computed by propagating the accuracy of reference point clouds and yielded mean deviations of both approaches. Consider the theories and constraints for both approaches, it is found that the yielded accuracies are meet the measurement principles
Semi-supervised Thai Sentence Segmentation Using Local and Distant Word Representations
Get PDFA sentence is typically treated as the minimal syntactic unit used to extract valuable information from long text. However, in written Thai, there are no explicit sentence markers. Some prior works use machine learning; however, a deep learning approach has never been employed. We propose a deep learning model for sentence segmentation that includes three main contributions. First, we integrate n-gram embedding as a local representation to capture word groups near sentence boundaries. Second, to focus on the keywords of dependent clauses, we combine the model with a distant representation obtained from self-attention modules. Finally, due to the scarcity of labeled data, for which annotation is difficult and time-consuming, we also investigate two techniques that allow us to utilize unlabeled data: Cross-View Training (CVT) as a semi-supervised learning technique, and a pre-trained language model (ELMo) to improve word representation. In the experiments, our model reduced the relative error by 7.4% and 18.5% compared with the baseline models on the Orchid and UGWC datasets, respectively. Ablation studies revealed that the main contributing factor was adopting n-gram features, which were further analyzed using the interpretation technique and indicated that the model utilizes the features in the same way that humans do
3D-printed Guided Mode Resonance Readout System for Biomedical and Environmental Applications
Get PDFThis paper demonstrates design and development of an open-source platform-based reflection spectroscopy readout system for guided mode resonance (GMR) sensing applications. The GMR dimensions, reflection grating period, imaging system and components orientations are optimized to enhance the angular resolution while sustaining resonance excitation within the visible range. To achieve the needed arrangement of the multiple components, 3D printing is utilized to build the mechanical mounting. The reflection spectra are extracted from the webcam images and processed using a software written on raspberry-pi computational unit. This ensures the compactness and portability of the system. The system performance of the transducer is tested by measuring the changes in the refractive index of the environment at the GMR chip interface
Influential Factors on Aerosol Change During COVID-19 in Ayutthaya, Thailand
Get PDFVarious interventions were made by the Thai government to prevent the COVID-19 spread by controlling socioeconomic activities, but the effectiveness of these interventions and other factors have not yet been fully clarified. Thus, this study aims to provide further scientific evidence on those potential factors which affect the socioeconomic activities changes during the pandemic, by using spatial analysis on atmospheric composition. By taking Phra Nakhon Si Ayutthaya Province, Thailand as the case area. Results of the government's COVID-19 measures and statuses of industries were compared with changes in aerosols, including PM 2.5 which was analyzed by Google Earth Engine with nine open datasets including meteorological and hydrological factors. The analysis revealed that the aerosol index in ueban area of the province decreased at 28.03% in 2020 compared in 2019. Besides, PM 2.5 drastically decreased from March 2020, even without the influence of wind speed which as the highest causal relationship, and kept low level compared with previous years. The reason of the tendency would be explained that other than government interventions including national-level state of the emergency decree, reduction of factories’ activities at Rojana Industrial Park and reduction of the number of tourists had significant influence to reduce the mean value of PM 2.5
Comparative Study of Scheduling Algorithms in LTE HetNets with Almost Blank Subframe
Get PDFThe trend and human lifestyle have been changing, which lead to the tremendously increasing demand for data usage over wireless communication systems even on the go. Traffic offload has been used for LTE Heterogeneous Networks (HetNets) to optimize overall system capacity via load balancing mechanisms among network tiers. In this work, the two main techniques used for interference coordination in the multi-tier systems i.e. Almost Blank Subframe (ABS) and Cell Range Expansion (CRE) have been focused on. Resource scheduling is one of the major issues in LTE HetNets aimed at efficient radio resource allocation. Based on the implementation of ABS and CRE mechanisms, this work investigates the system performance while different scheduling schemes are implemented. Five scheduling schemes including Round Robin (RR), Best-Channel Quality Identification (Best-CQI), Maximum Throughput (Max-TP), Proportional Fairness (PF), and Resource Fairness (RF) are considered here. The simulation studies include a comparison of the LTE HetNet system performance under different ABS and CRE configured parameters as well as employing different scheduling mechanisms. System performance is observed in terms of the average throughput, the peak throughput, the edge throughput, and the fairness index. The results provide recommendations on the system configurations as well as the choice of a scheduler that can be considered or suitable for different scenarios and network planning objectives. Coined from these results, the Best-CQI and the Max-TP mechanism offer the highest peak throughput and the high average throughput. The RR, PF, and RF provide the high cell edge throughput and fairness index, however, the peak throughput has been compromised