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Results 101-110 of 144 (Search time: 0.001 seconds).
  • Authors: Sungkyu Park; Sungwon Han; Jeongwook Kim; Mir Majid Molaie; Hoang Dieu Vu; Karandeep Singh; Jiyoung Han; Wonjae Lee; Meeyoung Cha;  Advisor: -;  Co-Author: - (2021)

    COVID-19, caused by SARS-CoV-2, has led to a global pandemic. The World Health Organization has also declared an infodemic (ie, a plethora of information regarding COVID-19 containing both false and accurate information circulated on the internet). Hence, it has become critical to test the veracity of information shared online and analyze the evolution of discussed topics among citizens related to the pandemic.

  • Authors: Luu, Thi Ha Thu; Nguyen, Tu; Dao, Duc Anh; Do, Quang Trung; Manh Trung, Tran; Tran, Thi Quynh Nhu; Nguyen, Thi Huyen; Nguyen, Van Quang; Nguyen, Duy Hung; Dao, Xuan Viet; Nguyen, Duc Trung Kien; Pham, Thanh Huy;  Advisor: -;  Co-Author: - (2021)

    Orange-red-emitting Eu3+-doped Ca9Gd(PO4)7 phosphors have been obtained by a sol-gel technique. These phosphors, excited by UV (270 nm) and near UV light (394 nm), emit orange-red light in the range of 580–710 nm. The Ca9Gd(PO4)7:7 mol% Eu3+ phosphor annealed at 1100 °C shows the highest PL intensity. Judd-Ofelt analysis reveals that the neighbor surroundings of Eu3+ ions are asymmetric, and the lowest asymmetry value is found at the dopant ratio of 7 mol%. The optimal phosphor excited by the wavelength of 394 nm displays an excellent thermal stability (∼76.4 % at 160 °C) with an activation energy of 0.163 eV. The corresponding CIE chromaticity coordinates (x; y) and color purity are calculated to be (0.5849; 0.3635) and 84.6 %, respectively. The quantum efficiency values of the Ca9...

  • Authors: Trung Thanh. Nguyen; Khaled Elbassioni;  Advisor: -;  Co-Author: - (2021)

    Binary non-linear programs belong to the class of  which are computationally hard even to approximate. This paper aims to explore some conditions on the problem structure, under which the resulting problem can be well approximated. Particularly, we consider a setting when both objective function and constraint are low-rank functions, which depend only on a few  of the input variables, and provide  approximation schemes. Our result generalizes and unifies some existing results in the literature.

  • Authors: Vu, Huu Nhu;  Advisor: -;  Co-Author: - (2021)

    In this paper, we consider a Levenberg–Marquardt method with general regularization terms that are uniformly convex on bounded sets to solve the ill-posed inverse problems in Banach spaces, where the forward mapping might not Gâteaux differentiable and the image space is unnecessarily reflexive. The method therefore extends the one proposed by Jin and Yang in (2016 Numer. Math. 133 655–684) for smooth inverse problem setting with globally uniformly convex regularization terms. We prove a novel convergence analysis of the proposed method under some standing assumptions, in particular, the generalized tangential cone condition and a compactness assumption. All these assumptions are fulfilled when investigating the identification of the heat source for semilinear elliptic boundary-valu...

  • Authors: Duy H. Nguyen; Tuyen M. Pham; Tuan Q. Do;  Advisor: -;  Co-Author: - (2021)

    In this paper, we study a non-canonical extension of a supergravity-motivated model acting as a vivid counterexample to the cosmic no-hair conjecture due to its unusual coupling between scalar and electromagnetic fields. In particular, a canonical scalar field is replaced by the string-inspired Dirac–Born–Infeld one in this extension. As a result, exact anisotropic inflationary solutions for this Dirac–Born–Infeld model are figured out under a constant-roll condition. Furthermore, numerical calculations are performed to verify that these anisotropic constant-roll solutions are indeed attractive during their inflationary phase.

  • Authors: Canh V. Pham;  Advisor: Dung V. Pham; Bao Q. Bui; Anh V. Nguyen;  Co-Author: - (2021)

    Misinformation detection in Online Social Networks has recently become a critical topic due to its important role in restraining misinformation. Recent studies have showed that machine learning methods can be used to detect misinformation/fake news/rumors by detecting user’s behaviour. However, we can not implement this strategy for all users on a social network due to the limitation of budget. Therefore, it is critical to optimize the monitor/sensor placement to effectively detect misinformation. In this paper, we investigate Minimum Budget for Misinformation Detection problem which aims to find the smallest set of nodes to place monitors in a social network so that detection function is at least a given threshold. Beside showing the inapproximability of the problem under the well-...

  • Authors: Nguyen Cong Luong;  Advisor: Xiao Lu; Dinh Thai Hoang; Dusit Tao Niyato; Dong In Kim;  Co-Author: - (2021)

    Joint radar and communication (JRC) has recently attracted substantial attention. The first reason is that JRC allows individual radar and communication systems to share spectrum bands and thus improves the spectrum utilization. The second reason is that JRC enables a single hardware platform, e.g., an autonomous vehicle or a UAV, to simultaneously perform the communication function and the radar function. As a result, JRC is able to improve the efficiency of resources, i.e., spectrum and energy, reduce the system size, and minimize the system cost. However, there are several challenges to be solved for the JRC design. In particular, sharing the spectrum imposes the interference caused by the systems, and sharing the hardware platform and energy resource complicates the design of th...