BPH Sensor Network Optimization Based on Cellular Automata and Honeycomb Structure

Mobile Networks and Applications - The brown planthopper (BPH) is a crucial pest of rice in tropical zones like the Mekong Delta of Vietnam. It economically causes severe loss to the rice harvest...     

Color image segmentation using tensor voting based color clustering

A novel color image segmentation method using tensor voting based color clustering is proposed. By using tensor voting, the number of dominant colors in a color image can be estimated efficiently. Furthermore, the centroids and structures of the color clusters in the color feature space can be extracted. In this method, the color feature vectors are first encoded by second order, symmetric, non-negative definite tensors. These tensors then communicate with each other by a voting process. The resulting tensors are used to determine the number of clusters, locations of the centroids, and structures of the clusters used for performing color clustering. Our method is based on tensor voting, a non-iterative method, and requires only the voting range as its input parameter. The experimental results show that the proposed method can estimate the dominant colors and generate good segmented images in which those regions having the same color are not split up into small parts and the objects are separated well. Therefore, the proposed method is suitable for many applications, such as dominant colors estimation and multi-color text image segmentation.     

Use of ENVISAT/ASAR wide-swath data for timely rice fields mapping in the Mekong River Delta

Because of the importance of rice for the global food security and because of the role of inundated paddy fields in greenhouse gases emissions, monitoring the rice production world-wide has become a challenging issue for the coming years. Local rice mapping methods have been developed previously in many studies by using the temporal change of the backscatter from C-band synthetic aperture radar (SAR) co-polarized data. The studies indicated in particular the need of a high observation frequency. In the past, the operational use of these methods has been limited by the small coverage and the poor acquisition frequency of the available data (ERS-1/2, Radarsat-1). In this paper, the method is adapted for the first time to map rice at large scale, by using wide-swath images of the Advanced SAR (ASAR) instrument onboard ENVISAT. To increase the observation frequency, data from different satellite tracks are combined. The detection of rice fields is achieved by exploiting the high backscatter increase at the beginning of the growing cycle, which allows the production of rice maps early in the season (in the first 50 days). The method is tested in the Mekong delta in Vietnam. The mapping results are compared to existing rice maps in the An Giang province, with a good agreement (higher than 81%). The rice planted areas are retrieved from the maps and successfully validated with the official statistics available at each province (R² = 0.92). These results show that the method is useful for large scale early mapping of rice areas, using current and future C band wide-swath SAR data.     

Minimizing human-exoskeleton interaction force by using global fast sliding mode control

A critical issue in the model-based control of performance-augmenting exoskeleton systems is the unknown nonlinear dynamic properties of the systems or the uncertainties. An improper estimation of the system dynamics can cause instabilities in the system and generate considerable human-exoskeleton interaction forces during human motions. Thus, the controller of such exoskeleton systems needs to add robustness to stabilize it against the uncertainties. In this paper, we propose a global fast sliding mode control algorithm integrated in a hybrid controller for each exoskeleton leg to minimize human-exoskeleton interaction forces. By doing so, the proposed algorithm does not require an exact estimation of the dynamic properties of the exoskeleton system, but still minimizes the physical human-exoskeleton interaction (pHEI) forces. Finally, the performance of the proposed algorithm is verified by experiments on our lower exoskeleton system, which is used for human power augmentation and called “PRMI” exoskeleton. Our experimental results show that the proposed control algorithm provides a good control quality for the PRMI exoskeleton. The PRMI exoskeleton can support a wearer carrying heavy load while tracking the rapid movements of the wearer without obstructing them.     

Preparation of meso-structured silica–calcium mixed oxide (MSCMO) catalyst for converting Vietnamese rubber seed oil to biodiesel

This report covered some new contributions in catalyst preparation and characterization. Meso-structured silica–calcium mixed oxide catalyst possessed both acidic and basic sites was synthesized through co-condensation method in alkaline environment using tetraethylorthosilicate, CaO, and cetyltrimethylammoniumbromide. The co-condensation process was established at 90 °C for 24 h obtaining white-gel precipitate which was dried at 120 °C followed by calcination at 550 °C for 5 h. The as-synthesized catalyst was used in conversion of rich free fatty acid rubber seed oil (22 %wt) in Vietnam to fatty acid methyl esters (FAMEs) in mild conditions such as temperature of 120 °C, time of 4 h, catalyst dosage of 3 %wt, methanol/oil mass ratio of 2.5/1 and agitating speed of 550 rpm achieving the reaction yield of 95.4 %. The catalyst were characterized by various techniques such as X-ray diffraction, transmission electron spectroscopy, Nitrogen Adsorption–Desorption Analysis (BET), temperature programmed desorption (NH₃ and CO₂-TPD). Especially, X-ray absorption spectroscopies was applied to explain the occurrence of acid and base sites on catalysts surface. The analysis showed the sixfold coordinated calcium sites characterizing for the mixed oxide structure of CaO–SiO₂. The results helped to simulate the bonding structure around the Ca sites indicating the electrostatic charge differences along the Ca–O–Si connections and the ability for occurring the defect sites containing the O^2? moieties corresponding to the acidity and basicity of the catalysts respectively. Gas chromatography–mass spectroscopy was also used to determine the composition of the FAMEs showing high purity of these products.     

Organic nonvolatile memory transistors based on fullerene and an electron-trapping polymer

We report for the first time organic n-type nonvolatile memory transistors based on a fullerene (C₆₀) semiconductor and an electron-trapping polymer, poly(perfluoroalkenyl vinyl ether) (CYTOP). The transistors with a Si++/SiO₂/CYTOP/C₆₀/Al structure show good n-type transistor performance with a threshold voltage (V_th) of 2.8 V and an electron mobility of 0.4 cm² V⁻¹ s⁻¹. Applying gate voltages of 50 or −45 V for about 0.1 s to the devices induces the reversible shifts in their transfer characteristics, which results in a large memory window (ΔV_th) of 10 V. A memory on/off ratio of 10⁵ at a small reading voltage below 5 V and a retention time greater than 10⁵ s are achieved. The memory effect in the transistor is ascribed to electrons trapped at the CYTOP/SiO₂ interface. Because of the use of high-electron-mobility C₆₀, the switching voltages of our memory transistors become significantly lower than those of conventional memory transistors based on pentacene.     

Calibration of KVp meter used in quality control tests of diagnostic X-ray units

In diagnostic radiology, the tube voltage [peak kilovoltage (kV(p))] is one of the most important parameter affecting both radiation exposure and image contrast. So, an accurate kV(p) meter is necessary to control kV(p) in the medical radiography practice with the overall uncertainty less than ± 5 % according to IEC 61676. Therefore, both invasive and non-invasive calibration methods of kV(p) meter were established and applied to different kinds of commercial quality control instruments for diagnostic radiology. Calibration of kV(p) meter by the invasive method is the most accurate (with uncertainty of 1.67 %, k=2); however, the non-invasive method also provides good results (with uncertainty of 3.12 %, k=2). Due to their detailed design, the commercial kV(p) meters have various responses with X-ray beam, so the working regime of a particular device type must be appropriately selected with a specific X-ray machine used for calibration of kV(p) meter.