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Nguyen V.-G.,Le Quy Don Technical University
Optical Engineering | Year: 2016

Geometric parameters that define the geometry of imaging systems are crucial for image reconstruction and image quality in X-ray computed tomography (CT). The problem of determining geometric parameters for an offset flat-panel cone beam CT (CBCT) system, a recently introduced modality with a large field of view, with the assumption of an unstable mechanism and geometric parameters that vary in each view, is considered. To accurately and rapidly find the geometric parameters for each projection view, we use the projection matrix method and design a dedicated phantom that is partially visible in all projection views. The phantom consists of balls distributed symmetrically in a cylinder to ensure the inclusion of the phantom in all views, and a large portion of the phantom is covered in the projection image. To efficiently use calibrated geometric information in the reconstruction process and get rid of approximation errors, instead of decomposing the projection matrix into actual geometric parameters that are manually corrected before being used in reconstruction, as in conventional methods, we directly use the projection matrix and its pseudo-inverse in projection and backprojection operations of reconstruction algorithms. The experiments illustrate the efficacy of the proposed method with a real offset flat-panel CBCT system in dental imaging. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). Source


Nguyen V.H.,Le Quy Don Technical University | Pham P.X.,University of Sydney
Fuel | Year: 2015

Biodiesels, renewable fuels derived from biomass, animal fat, algae, wastes or residues, are amongst potential candidates to improve energy security and to reduce greenhouse gas emissions. Different from fossil diesel which mainly consists of hydrocarbons, biodiesels are oxygenated fuels. Oxygen contained in biodiesels, as an oxidizing enhancer, plays a crucial role in improving the auto-ignition quality. The oxygen enrichment coming from biodiesels causes the fuel-air mixture in the auto-ignition zone where the mixture is quite rich to become leaner, consequently improving combustion and emission quality. As such, a quantitative analysis of the impact of oxygen content in biodiesel-diesel blends in engine combustion and emission concentrations is crucial in giving key clues to fuel manufacturing as well as to internal combustion engine modeling. This study aims to establish a link between the oxygen content and engine performance as well as emission concentrations when using biodiesel blends B0, B10 and B20 (0%, 10% and 20% of biodiesel by volume in biodiesel-diesel mixtures, respectively). The biodiesel was derived from residues of the manufacturing process of palm cooking oil using methanol transesterification with the aid of a high hardness solid ceramic metal catalyst. The engine used in this test is a modern common-rail, single-cylinder engine operating under a fixed injection condition (injection timing, pressure and duration) but with a wide range of engine speeds. The results show that the oxygen enrichment coming from the fuel blends tested in this study lowers the engine power which is attributable to lower heating values of the biodiesel blends compared with that of the fossil diesel. However, the oxygen contained in the blends suppresses particle formation and decreases hydrocarbon and carbon monoxide concentrations. © 2015 Elsevier Ltd. All rights reserved. Source


Pham V.-B.,Le Quy Don Technical University
Transactions on Emerging Telecommunications Technologies | Year: 2015

The number of time slot (or symbols per slot in 3rd Generation Partnership Project language) in the long-term evolution frame structure for data transmission is not guaranteed to be an even number, so the Alamouti orthogonal space-time block code (STBC) can not be applied. Recently, Lei et al. (Institute of Electrical and Electronics Engineers Transactions on Wireless Communications, 2011) introduced a quasi-orthogonal space time block code (QOSTBC) for two transmit antennas and three time slots (which is named as L-QOSTBC in this paper). This code achieves two desirable properties as full rate and full diversity. However, the main disadvantage of the L-QOSTBC is high decoding complexity due to pair-symbol maximum likelihood decoding. In this paper, we propose a novel three-time-slot STBC (TTS-STBC) for two transmit antennas. The proposed TTS-STBC can achieve full-rate full-diversity transmission with single-symbol maximum likelihood decoding. In comparison to L-QOSTBC, the proposed TTS-STBC has lower decoding complexity and higher coding gain. In addition, a new decoding strategy for the proposed TTS-STBC that named as single-symbol quasi-maximum likelihood is also developed to overcome the performance degradation caused by time-varying fading channels. Simulation results show that the proposed TTS-STBC outperforms the L-QOSTBC in both quasi-static and time-varying fading channels. © 2014 John Wiley & Sons, Ltd. Source


Hiep P.T.,Yokohama National University | Hiep P.T.,Le Quy Don Technical University
Ad-Hoc and Sensor Wireless Networks | Year: 2016

Since the elderly population is increasing all over the world, health care market keeps growing and there is a need for monitoring of health issues. Body area networks (BANs) consist of wireless sensors attached on or inside human body for monitoring vital health related problems, i.e. Electro Cardiogram (ECG), ElectroEncephalogram (EEG), Electronystagmogram(ENG) etc. Moreover, the quick development in entertainment devices, e.g. music/video players, games using vital data, wireless earphones and so on, requests high data rate communications and low energy consumption. In order to improve the energy-efficiency, cluster-based wireless sensor networks (WSN), included multiple hops cluster-based WSN have been analyzed. Since the network topology in IEEE802.15.6 is defined as one hop star plus one, the conventional cluster-based with CSMA/CA scheme is taken into considered. We focus on the system throughput and propose a spatial reuse superframe to increase the throughput. The performance of spatial reuse superframe is analyzed and compared to the conventional cluster-based scenario. The calculation result indicates that the spatial reuse superframe outperforms the conventional cluster-based when the access probability and/or the total number of sensors are high. There are optimal the number of clusters, the access probability and the total number of sensors that obtain the highest throughput. However, the number of spatial reuse superframes (k) that achieves the highest throughput depends on the system model. The optimization method of k is proposed to obtain the higher throughput and k increases when system parameters increase, excepted the payload. k is constant while the payload is varying. The proposed method can be applied to not only IEEE802.15.6 WBAN but also another WSN. ©2016 Old City Publishing, Inc. Source


Ngo L.T.,Le Quy Don Technical University
Journal of Intelligent and Fuzzy Systems | Year: 2013

Triangulated irregular network (TIN) has used to represent 3-dimensional surfaces by dividing domain into irregular sub-triangles and approximately represent using piecewise linear functions. Hence, TIN are also used to approximately represent membership functions of general type-2 fuzzy sets for reducing computational complexity. To support speed-up in computation of operations of type-2 fuzzy sets, a refinement CTIN is proposed by combining contour model and constraint Delaunay criteria. So a type-2 fuzzy set is also represented by RCTIN in the same way. The paper deals with the use RCTIN to represent general type-2 fuzzy sets. On the basis of RCTIN representation theorem, algorithms for operations and general type-2 fuzzy logic systems (GT2FLS) are proposed. A T2FLS is designed and implemented in comparing previous approaches under an application of obstacle avoidance of robot navigation. © 2013 - IOS Press and the authors. All rights reserved. Source

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