| 1. |
- Nguyen Van, Toan, et al.
(författare)
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Fabrication of highly sensitive and selective H2 gas sensor based on SnO2 thin film sensitized with microsized Pd islands
- 2016
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 301, s. 433-442
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Tidskriftsartikel (refereegranskat)abstract
- Ultrasensitive and selective hydrogen gas sensor is vital component in safe use of hydrogen that requires a detection and alarm of leakage. Herein, we fabricated a H2 sensing devices by adopting a simple design of planar–type structure sensor in which the heater, electrode, and sensing layer were patterned on the front side of a silicon wafer. The SnO2 thin film–based sensors that were sensitized with microsized Pd islands were fabricated at a wafer–scale by using a sputtering system combined with micro–electronic techniques. The thicknesses of SnO2 thin film and microsized Pd islands were optimized to maximize the sensing performance of the devices. The optimized sensor could be used for monitoring hydrogen gas at low concentrations of 25–250 ppm, with a linear dependence to H2 concentration and a fast response and recovery time. The sensor also showed excellent selectivity for monitoring H2 among other gases, such as CO, NH3, and LPG, and satisfactory characteristics for ensuring safety in handling hydrogen. The hydrogen sensing characteristics of the sensors sensitized with Pt and Au islands were also studied to clarify the sensing mechanisms.
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| 2. |
- Tran, Thi-Thuy-Quynh, et al.
(författare)
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Network Coding with Multimedia Transmission and Cognitive Networking: An Implementation based on Software-Defined Radio
- 2020
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Ingår i: REV Journal on Electronics and Communications. ; 10:3-4, s. 72-84
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Tidskriftsartikel (refereegranskat)abstract
- Network coding (NC) is considered a breakthrough to improve throughput, robustness, and security of wireless networks. Although the theoretical aspects of NC have been extensively investigated, there have been only few experiments with pure NC schematics. This paper presents an implementation of NC under a two-way relay model and extends it to two non-straightforward scenarios: (i) multimedia transmission with layered coding and multiple-description coding, and (ii) cognitive radio with Vandermonde frequency division multiplexing (VFDM). The implementation is in real time and based on software-defined radio (SDR). The experimental results show that, by combining NC and source coding, we can control the quality of the received multimedia content in an on-demand manner. Whereas in the VFDM-based cognitive radio, the quality of the received content in the primary receiver is low (due to imperfect channel estimation) yet retrievable. Our implementation results serve as a proof for the practicability of network coding in relevant applications.
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| 3. |
- Hoang-Minh, Thao, et al.
(författare)
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Mineralogical Characterization of Di Linh Bentonite, Vietnam: A Methodological Approach of X-ray Diffraction and Transmission Electron Microscopy
- 2014
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Ingår i: Proceedings of 13th International Symposium on Mineral Exploration (ISME-XIII). - Hanoi : Vietnam National University Press, Hanoi. - 9786046215400 ; , s. 143-148
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Konferensbidrag (refereegranskat)abstract
- Vietnam has decided to establish nuclear power as further energy option. In order to develop a Vietnamese reference bentonite as potential barrier in a final repository for high radioactive waste, a detailed mineralogical investigation of Di Linh bentonite (Lam Dong province), lacustrine clay, was carried out by different methods especially transmission electron microscopy (TEM) linked with energy-dispersive X-ray (EDX). From a sample homogenized from 5 tones of the bentonite, mineral formulae of clay particles was calculated The calculation also focuses on randomly interstratifications of two and three members. The fraction <2 μm of Di Linh bentonite is composed mainly by montmorillonite (Ca0.06Mg0.03Na0.09K0.03Al1.39Fe0.25Mg0.26(OH)2 Si3.96Al0.04O10) and regular ordering (R1) illite-smectite interstratifications with K- and charge-deficiency (Ca0.04Mg0.07Na0.18K0.16Al1.76Fe0.08Mg0.16(OH)2Si3.62Al0.38O10). Additionally, Fe-poor kaolinite-smectite-vermiculite interstratifications and trace of Fe-rich chloritesmectite- vermiculite interstatifications were identified. TEM-investigations showed analytical proofs of the sedimentary character of smectite formation in the Di Linh deposit. Parent muscovite was weathered in several steps in two different environments: (i) K-leaching and layer-wise alteration into kaolinite; (ii) further edge- controlled alteration of mica into lathlike montmorillonite particles under dissolution of kaolinite layers from former kaolinite-mica intergrowths. Mineralogical composition of the Di Linh bentonite with mainly montmorillonite and illite-rich illite-smectite interstratifications shows that the Di Linh bentonite can be a suitable barrier candidate in final repositories.
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| 4. |
- Hoang-Minh, Thao, et al.
(författare)
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Use of TEM-EDX for structural formula identification of clay minerals : a case study of Di Linh bentonite, Vietnam
- 2019
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Ingår i: Journal of applied crystallography. - : International Union of Crystallography (IUCr). - 0021-8898 .- 1600-5767. ; 52:1, s. 133-147
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Tidskriftsartikel (refereegranskat)abstract
- Transmission electron microscopy linked with energy-dispersive X-ray spectroscopy (TEM-EDX) was applied to characterize mineralogical signals ofweathering processes in the Di Linh bentonite deposit (Vietnam) and to visualize the effects of Na activation on the smectitic phases. Modelling of X ray diffraction patterns (oriented mount) was applied in order to refine the computed structural formula. X-ray diffraction, X-ray fluorescence and Fouriertransform infrared spectroscopy (FT-IR) methods were also applied to verify the TEM-EDX results. An Excel-based routine has been developed in this research to allow fast computation of structural formulae and classification of the investigated clay particles. This routine supports the acquirement of 100 300 TEM-EDX analyses as a representative set of individual particles for each sample. The Excel-based routine involves end members of different clay mineral groups and interstratifications with two or three members (e.g. illite smectite interstratifications – IS-ml; dioctahedral vermiculite–smectite interstratifications – diVS-ml; and kaolinite–montmorillonite–dioctahedral vermiculite interstratifications – KSV-ml). The routine is now freely available. According to the identification procedure, the <2 mm fraction of the Di Linh bentonite (Vietnam) is composed mainly of K- and charge-deficient illite smectite interstratifications (or diVS-ml): montmorillonite-rich randomly ordered (R0) type and illite-rich regularly ordered (R1) type. Additionally, Fe-poor KSV-ml was identified.Industrial Na activation of the Di Linh bentonite resulted in an increase of theR1 diVS-ml portion and dissolution of a large part of the smectite-rich phases.The TEM-EDX approach also gave analytical proof of a sedimentary processfor Di Linh smectite. The parent muscovite was altered in two different environments: (i) K-leaching and layer-wise alteration into kaolinite (weathering), and (ii) further edge-controlled alteration of mica into lath-like montmorillonite particles associated with a dissolution of kaolinite layers from the former kaolinite–mica intergrowths by heat impact (basalt flow).
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| 5. |
- Nguyen, C. T., et al.
(författare)
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A Comprehensive Survey of Enabling and Emerging Technologies for Social Distancing : Part I Fundamentals and Enabling Technologies
- 2020
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 8, s. 153479-153507
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Tidskriftsartikel (refereegranskat)abstract
- Social distancing plays a pivotal role in preventing the spread of viral diseases illnesses such as COVID-19. By minimizing the close physical contact among people, we can reduce the chances of catching the virus and spreading it across the community. This two-part paper aims to provide a comprehensive survey on how emerging technologies, e.g., wireless and networking, artificial intelligence (AI) can enable, encourage, and even enforce social distancing practice. In this Part I, we provide a comprehensive background of social distancing including basic concepts, measurements, models, and propose various practical social distancing scenarios. We then discuss enabling wireless technologies which are especially effect- in social distancing, e.g., symptom prediction, detection and monitoring quarantined people, and contact tracing. The companion paper Part II surveys other emerging and related technologies, such as machine learning, computer vision, thermal, ultrasound, etc., and discusses open issues and challenges (e.g., privacy-preserving, scheduling, and incentive mechanisms) in implementing social distancing in practice.
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| 6. |
- Nguyen, C. T., et al.
(författare)
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A Comprehensive Survey of Enabling and Emerging Technologies for Social Distancing - Part II : Emerging Technologies and Open Issues
- 2020
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 8, s. 154209-154236
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Tidskriftsartikel (refereegranskat)abstract
- This two-part paper aims to provide a comprehensive survey on how emerging technologies, e.g., wireless and networking, artificial intelligence (AI) can enable, encourage, and even enforce social distancing practice. In Part I, an extensive background of social distancing is provided, and enabling wireless technologies are thoroughly surveyed. In this Part II, emerging technologies such as machine learning, computer vision, thermal, ultrasound, etc., are introduced. These technologies open many new solutions and directions to deal with problems in social distancing, e.g., symptom prediction, detection and monitoring quarantined people, and contact tracing. Finally, we discuss open issues and challenges (e.g., privacy-preserving, scheduling, and incentive mechanisms) in implementing social distancing in practice. As an example, instead of reacting with ad-hoc responses to COVID-19-like pandemics in the future, smart infrastructures (e.g., next-generation wireless systems like 6G, smart home/building, smart city, intelligent transportation systems) should incorporate a pandemic mode in their standard architectures/designs.
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| 7. |
- Nguyen, Nhan Thanh, et al.
(författare)
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Joint Communications and Sensing Design for Multi-Carrier MIMO Systems
- 2023
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Ingår i: IEEE Workshop on Statistical Signal Processing Proceedings. ; 2023-July, s. 110-114
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Konferensbidrag (refereegranskat)abstract
- In conventional joint communications and sensing (JCAS) designs for multi-carrier multiple-input multiple-output (MIMO) systems, the dual-functional waveforms are often optimized for the whole frequency band, resulting in limited communications-sensing performance tradeoff. To overcome the limitation, we propose employing a subset of subcarriers for JCAS, while the communications function is performed over all the subcarriers. This offers more degrees of freedom to enhance the communications performance under a given sensing accuracy. We first formulate the rate maximization under the sensing accuracy constraint to optimize the beamformers and JCAS subcarriers. The problem is solved via Riemannian manifold optimization and closed-form solutions. Numerical results for an 8 × 4 MIMO system with 64 subcarriers show that compared to the conventional subcarrier sharing scheme, the proposed scheme employing 16 JCAS subcarriers offers 60% improvement in the achievable communications rate at the signal-to-noise ratio of 10 dB. Meanwhile, this scheme generates the sensing beampattern with the same quality as the conventional JCAS design.
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| 8. |
- Duong, Quang Trung, et al.
(författare)
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Pairwise Error Probability of Distributed Space--Time Coding Employing Alamouti Scheme in Wireless Relays Networks
- 2009
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Ingår i: Wireless personal communications. - : Springer. - 0929-6212 .- 1572-834X. ; 51:2, s. 231-244
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze the pairwise error probability (PEP) of distributed space-time codes, in which the source and the relay generate Alamouti space--time code in a distributed fashion. We restrict our attention to the space-time code construction for Protocol III in [1]. In particular, we derive two closed-form approximations for PEP when the relay is either close to the destination or source and an upper bound for any position of the relay. Using the alternative definition of $Q$-function, we can express these PEPs in terms of finite integral whose integrand is composed of trigonometric functions. We further show that with only one relay assisted source-destination link, system still achieves diversity order of two, assuming single-antenna terminals. We also perform Monte-Carlo simulations to verify the analysis.
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| 9. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Low-Latency and Secure Computation Offloading Assisted by Hybrid Relay-Reflecting Intelligent Surface
- 2021
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Ingår i: International Conference on Advanced Technologies for Communications. - 2162-1020 .- 2162-1039. ; 2021-October, s. 306-311
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Konferensbidrag (refereegranskat)abstract
- Recently, the hybrid relay-reflecting intelligent surface (HRRIS) has been introduced as a spectral-and energy-efficient architecture to assist wireless communication systems. In the HRRIS, a single or few active relay elements are deployed along with a large number of passive reflecting elements, allowing it to not only reflect but also amplify the incident signals. In this work, we investigate the potential of the HRRIS in aiding the computation offloading in a single-user mobile edge computing system. The objective is to minimize the offloading latency while ensuring the secrecy of user data against a malicious eavesdropper. We develop efficient solutions to this latency minimization problem based on alternating optimization. Through numerical results, we show that the deployment of the HRRIS can result in a considerable reduction in latency. Furthermore, the latency reduction gain offered by the HRRIS is much more significant than that of the conventional reconfigurable intelligent surface (RIS).
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| 10. |
- Pham, Binh Thai, et al.
(författare)
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Performance Evaluation of Machine Learning Methods for Forest Fire Modeling and Prediction
- 2020
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Ingår i: Symmetry. - Switzerland : MDPI. - 2073-8994. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Predicting and mapping fire susceptibility is a top research priority in fire-prone forests worldwide. This study evaluates the abilities of the Bayes Network (BN), Naïve Bayes (NB), Decision Tree (DT), and Multivariate Logistic Regression (MLP) machine learning methods for the prediction and mapping fire susceptibility across the Pu Mat National Park, Nghe An Province, Vietnam. The modeling methodology was formulated based on processing the information from the 57 historical fires and a set of nine spatially explicit explanatory variables, namely elevation, slope degree, aspect, average annual temperate, drought index, river density, land cover, and distance from roads and residential areas. Using the area under the receiver operating characteristic curve (AUC) and seven other performance metrics, the models were validated in terms of their abilities to elucidate the general fire behaviors in the Pu Mat National Park and to predict future fires. Despite a few differences between the AUC values, the BN model with an AUC value of 0.96 was dominant over the other models in predicting future fires. The second best was the DT model (AUC = 0.94), followed by the NB (AUC = 0.939), and MLR (AUC = 0.937) models. Our robust analysis demonstrated that these models are sufficiently robust in response to the training and validation datasets change. Further, the results revealed that moderate to high levels of fire susceptibilities are associated with ~19% of the Pu Mat National Park where human activities are numerous. This study and the resultant susceptibility maps provide a basis for developing more efficient fire-fighting strategies and reorganizing policies in favor of sustainable management of forest resources.
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