4,657 research outputs found
Understanding the transmission dynamics of a large-scale measles outbreak in Southern Vietnam
No full textOBJECTIVES: Southern Vietnam experienced a large measles outbreak of over 26,000 cases during 2018-2020. We aimed to understand and quantify the measles spread in space-time dependence and the transmissibility during the outbreak. METHODS: Measles surveillance reported cases between January 2018 and June 2020, vaccination coverage, and population data at provinicial level were used. To illustrate the spatio-temporal pattern of disease spread, we employed the endemic-epidemic multivariate time series model decomposing measles risk additively into autoregressive, spatio-temporal, and endemic components. Likelihood-based estimation procedures were performed to determine the time-varying reproductive number Re of measles. RESULTS: Our analysis showed that the incidence of measles was associated with vaccination coverage heterogeneity and spatial interaction between provincial units. The risk of infections was dominated by between-province transmission (36.1% to 78.8%), followed by local endogenous transmission (4.1% to 61.5%). In contrast, the endemic behavior had a relatively small contribution (2.4% to 33.4%) across provinces. In the exponential phase of the epidemic, Re was above the threshold with a maximum value of 2.34 (95% CI: 2.20-2.46). CONCLUSION: Local vaccination coverage and human mobility are important factors contributing to the measles dynamics in Southern Vietnam, and the high risk of inter-provincial transmission is of most concern. Strengthening the disease surveillance is recommended, and further research is essential to understand the relative contribution of population immunity and control measures in measles epidemics.sponsorship: We would like to thank the VLIR-UOS for awarding T.H.T.N. a scholarship to study the Master of Epidemiology at the Univer-sity of Antwerp, Belgium. We are pleased to acknowledge the Pas-teur Institute in Ho Chi Minh City including the Board of Directors for supporting the research endeavor in terms of data use, col-leagues of the Outbreak Control Unit (Pham Duy Quang, Nguyen Thi Phuong Thuy, Tran Cong Kha, Doan Ngoc Minh Quan, Nguyen Quoc Kien, Tran Anh Tuan, Phan Thi Ngoc Uyen, Nguyen Viet Thinh, Hoang Thi Lien, and Phan Cong Hung), and the EPI Unit (Hoang Anh Thang, Chau Van Luom, Truong Cong Hieu, Vo Ngoc Quang, Nguyen Dieu Thuy, Nguyen Thi Huyen, Phan Thi Quynh Tram, Vien Dang Khanh Linh, Nguyen Thi Thu Trang, Nguyen Van Hoang, Tran Quang Trung, Trinh Trung Truc, Tran Thanh Hai) for their huge efforts and enthusiasm in case monitoring, surveillance and contact tracing, outbreak investigation, and launching the sup-plementary immunization activities during the measles outbreak. We would also like to acknowledge the large contribution of 20 Provincial Centers for Disease Control and Prevention in two cities and 18 provinces in Southern Vietnam in the EPI National Project. (VLIR-UOS)status: Publishe
Nguyen Van Thang, Ambiguity of Identity: The Mieu in North Vietnam
No full textRenard Ronald D. Nguyen Van Thang, Ambiguity of Identity: The Mieu in North Vietnam. In: Aséanie 20, 2007. pp. 206-207
Graph bisection algorithms
Full text linkThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaves 64-66.by Thang Nguyen Bui.Ph.D
A Greedy Algorithm for Subspace Approximation Problem
Full text linkIn the subspace approximation problem, given m points in R^{n} and an integer k <= n, the goal is to find a k-dimension subspace of R^{n} that minimizes the l_{p}-norm of the Euclidean distances to the given points. This problem generalizes several subspace approximation problems and has applications from statistics, machine learning, signal processing to biology. Deshpande et al. [Deshpande et al., 2011] gave a randomized O(sqrt{p})-approximation and this bound is proved to be tight assuming NP != P by Guruswami et al. [Guruswami et al., 2016]. It is an intriguing question of determining the performance guarantee of deterministic algorithms for the problem. In this paper, we present a simple deterministic O(sqrt{p})-approximation algorithm with also a simple analysis. That definitely settles the status of the problem in term of approximation up to a constant factor. Besides, the simplicity of the algorithm makes it practically appealing
Lagrangian Duality based Algorithms in Online Energy-Efficient Scheduling
Full text linkWe study online scheduling problems in the general energy model of speed scaling with power down. The latter is a combination of the two extensively studied energy models, speed scaling and power down, toward a more realistic one. Due to the limits of the current techniques, only few results have been known in the general energy model in contrast to the large literature of the previous ones.
In the paper, we consider a Lagrangian duality based approach to design and analyze algorithms in the general energy model. We show the applicability of the approach to problems which are unlikely to admit a convex relaxation. Specifically, we consider the problem of minimizing energy with a single machine in which jobs arrive online and have to be processed before their deadlines. We present an alpha^alpha-competitive algorithm (whose the analysis is tight up to a constant factor) where the energy power function is of typical form z^alpha + g for constants alpha > 2 and g non-negative. Besides, we also consider the problem of minimizing the weighted flow-time plus energy. We give an O(alpha/ln(alpha))-competitive algorithm; that matches (up to a constant factor) to the currently best known algorithm for this problem in the restricted model of speed scaling
Sliding mode control for systems with slow and fast modes
No full textThis dissertation addresses the problems of sliding mode control for systems with slow and fast dynamics. A system using a sliding mode control strategy can display robust performances against parametric and exogenous disturbances under the matching condition (Drazenovic's condition). We investigate the problem of output feedback sliding mode control for sampled-data systems with an unknown external disturbance. Given an output sliding surface, we construct a discrete-time control law. Since the external disturbance in the control law is unknown, we approximate it by system information from the previous time instant. The synthesized control law provides promising results with high robustness against the external disturbance. These results are further improved by a method which better approximate the disturbance by system information from two previous time instants. The stability and robustness of the closed-loop system are analyzed by studying a transformed singularly perturbed discrete-time system. The second topic is to study sliding mode control for singularly perturbed systems which exhibit slow and fast dynamics. A state feedback control law is designed for either slow or fast modes. Then, the system under that state feedback control law is put into a triangular form. In the new coordinates, a sliding surface is constructed for the remaining modes using Utkin and Young's method. A sliding mode control law is synthesized by a method which is an improved version of the unit control method by Utkin. Lastly, a composite control law is synthesized from the two components. The topic is also addressed by Lyapunov approaches. A state feedback composite control law is designed to stabilize the system. Accordingly, Lyapunov functions are constructed to synthesize a sliding surface. Two sliding surfaces and two sliding mode controllers are proposed. Asymptotic stability and disturbance rejection are achieved. Sliding mode control for singularly perturbed discrete-time systems with parametric uncertainties is also investigated. Proceeding along the same lines as in the continuous-time case, we propose two approaches to construct a composite control law. It is shown that the closed-loop system under the proposed control laws is asymptotically stable provided the perturbation parameter is small enough.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Thang Tien Nguye
TRAN Quyet Thang
No full text학위논문(박사)--아주대학교 일반대학원 :전자공학과,2017. 2CHAPTER 1: INTRODUCTION 1
1.1 Introduction to Light Modulating Devices 1
1.2 Introduction to Graphene 1
1.3 Overview of the Numerical Methods 3
1.4 Organization of Dissertation 7
CHAPTER 2: TUNABLE WIDE-ANGLE TUNNELING IN GRAPHENE-ASSISTED FRUSTRATED TOTAL INTERNAL REFLECTION 9
2.1 Introduction 9
2.2 Frustrated Total Internal Reflection (FTIR) Effect 10
2.3 Controllable Wide Angle Tunneling Effect with ENZ Effect in FTIR Configuration 11
2.4 Waveguide-type optical modulator based on a GA-FTIR structure 20
2.5 Chapter Summary 26
CHAPTER 3: LOW LOSS ELECTRICALLY CONTROLLABLE VERTICALLY COUPLED DIRECTIONAL COUPLER 28
3.1 Introduction 28
3.2 Vertically Coupled Directional Coupler 29
3.3 Chapter Summary 40
CHAPTER 4: OPTICAL PHASE MODULATOR BASED ON GRAPHENE EMBEDDED ALL PASS FILTER 42
4.1 Introduction 42
4.2 Phase Modulating All Pass Filter with Graphene 42
4.3 Chapter Summary 48
CHAPTER 5: COUPLED MODE THEORY OF PERFECT GRAPHENE ABSORBERS IN DUAL-MODE/SINGLE-MODE COUPLED RESONATORS SYSTEM 50
5.1 Introduction 50
5.2 Dual Mode - Single Mode Coupled Resonators System 51
5.3 Temporal Coupled Mode Theory of the "Triple-mode absorber" 52
5.4 Numerical verification of the CMT 59
5.5 Chapter Summary 66
CHAPTER 6: CONCLUSION AND FUTURE WORK 68
6.1 Conclusion 68
6.2 Future Work 68
REFERENCES 70
APPENDIX: AUTHOR'S PUBLICATIONS LIST 79DoctoralOne of the most important component of integrated photonics is a class of devices known as light modulation devices, which allow us to modulate and manipulate the flow of light, similar to the role transistor played in electronics. Only recently introduced, but graphene have shown incredible promises as a "miracle" material in electronics, with properties ranging from zero band gap, very high electrical mobility, ultra broadband optical responses, and the ability to drastically modify its optical properties through chemical or electrical doping.
In this dissertation, the author presented several unique nanostructures to exploit the aforementioned graphene characteristics to create light modulation devices with superior performance characteristics. Novel effects including wide angle extraordinary reflection causes by epsilon near zero effect and wide angle extraordinary transmission causes by coupling of plasmonic supermodes, phase modulation with near unity amplitude transmission with all pass filter, and graphene perfect absorber with a coupled system of dual mode/single mode resonator was thoroughly investigated, theoretically and numerically. The effects was also presented in practical nanostructures better suited for applications, which are also numerically investigated with various numerical methods
Erratum: Mott Transition in the Mass Imbalanced Ionic Hubbard Model at Half Filling
Full text linkErratum: Mott Transition in the Mass Imbalanced Ionic Hubbard Model at Half Filling[Nguyen Thi Hai Yen, Le Duc Anh, Hoang Anh Tuan, Nguyen Toan Thang and Tran Thi Thu Trang, Communications in Physics, Vol. 29, No. 3SI (2019), pp. 305-312]This paper was published on 22 October 2019 with an omission in the text of the author’s list. The author list should read asNGUYEN THI HAI YEN, LE DUC ANH, HOANG ANH TUAN, NGUYEN TOAN THANG, TRAN THI THU TRANG AND NGUYEN THI HUONGInstitute of Physics, Vietnam Academy of Science and Technology (VAST), Hanoi, Vietnam Hanoi National University of Education, Hanoi, Vietnam Graduate University of Science and Technology, VAST, Hanoi, Vietnam Ha Long University, Quang Ninh, Vietnam Thuy Loi University, Hanoi, VietnamE-mail: [email protected] author’s list has been corrected as of 29 November 2019. The author’s list has been corrected in the electronic version of the journal
sj-pdf-1-sgo-10.1177_21582440211040774 – Supplemental material for Estimate the Impact of Payments for Environmental Services on Local Livelihoods and Environment: An Application of Propensity Scores
No full textSupplemental material, sj-pdf-1-sgo-10.1177_21582440211040774 for Estimate the Impact of Payments for Environmental Services on Local Livelihoods and Environment: An Application of Propensity Scores by Thang Quyet Nguyen, Nguyen Tan Huynh and Wen-Kai K. Hsu in SAGE Open</p
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