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Search Results: 1 - 10 of 5006 matches for " Nguyen Quang Huy "
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Sharp Strichartz estimates for water waves systems
Quang-Huy Nguyen
Mathematics , 2015,
Abstract: Water waves are well-known to be dispersive at the linearization level. Considering the fully nonlinear systems, we prove for reasonably smooth solutions the optimal Strichartz estimates for pure gravity waves and the semi-classical Strichartz estimates for gravity-capillary waves; for both 2D and 3D waves. Here, by optimal we mean the gains of regularity (over the Sobolev embedding from Sobolev spaces to H\"older spaces) obtained for the linearized systems. Our proofs combine the paradifferential reductions of Alazard-Burq-Zuily \cite{ABZ1, ABZ3} with a dispersive estimate using a localized wave package type parametrix of Koch-Tataru \cite{KT}.
Pseudo-local property of gravity water waves system
Quang-Huy Nguyen
Mathematics , 2015,
Abstract: By proving a weighted contraction estimate for the flow of gravity water waves, we show that this nonlocal system is in fact pseudo-local in the following sense: locally in time, the dynamic far away from a given bounded region has a small effect on that region (again, in a sense that we will make precise in the article). Our estimate on the flow also implies a new spatial decay property of the waves.
Hadamard well-posedness of the gravity water waves system
Quang-Huy Nguyen
Mathematics , 2015,
Abstract: We consider in this article the system of (pure) gravity water waves in any dimension and in fluid domains with general bottoms. The unique solvability of the problem was established by Alazard-Burq-Zuily \cite{ABZ} at a low regularity level where the initial surface is $C^{3/2+\varepsilon}$ in term of Sobolev embeddings. Our result states that the solutions obtained above depend continuously on initial data in the strong topology where the solutions are constructed. This completes a well-posedness result in the sense of Hadamard.
Fabrication and Characterization of CTS/Coconut Composite Membranes Crosslinked with Glutaraldehyde for Elimination of Heavy Metal in Aqueous Solution  [PDF]
Truong Thi Cam Trang, Nguyen Quang Huy, Takaomi Kobayashi
Journal of Agricultural Chemistry and Environment (JACEN) , 2019, DOI: 10.4236/jacen.2019.82006
Abstract: Chitosan/coconut (CTS/coconut) composite membranes were successfully prepared by the cross-linking reaction with glutaraldehyde and they were applied in eliminating heavy metals from aqueous solutions. The cross-linked membranes were obtained at the ratios of 1/1, 1/1.5 and 1/2 and the coconut fiber was chemically treated by NaOCl/NaOH. The best ratio of CTS/coconut fiber is found to be 1/1.5 which has a relatively high stability with the degree of swelling (DS) and solvent content (SC) of membrane to be 13.33% and 69.88%, respectively. The results also indicate that the CTS membranes showed preferential separation of heavy metals for blend CTS/coconut membranes.
Strichartz estimates and local existence for the capillary water waves with non-Lipschitz initial velocity
Thibault de Poyferre,Quang Huy Nguyen
Mathematics , 2015,
Abstract: We consider the gravity-capillary waves in any dimension and in fluid domains with general bottoms. Using the paradiferential reduction established in the companion paper, we prove Strichartz estimates for solutions to this problem, at a low regularity level such that initially, the velocity field can be non-Lipschitz up to the free surface. We then use those estimates to solve the Cauchy problem at this level of regularity.
A paradifferential reduction for the gravity-capillary waves system at low regularity and applications
Thibault De Poyferré,Quang-Huy Nguyen
Mathematics , 2015,
Abstract: We consider in this article the system of gravity-capillary waves (in any dimension) under the Zakharov/Craig-Sulem formulation. Using a paradifferential approach introduced by Alazard-Burq-Zuily we symmetrize this system into a quasilinear equation whose principal term is of order 3/2. The main novelty compare to earlier studies is that this reduction is performed at the Sobolev regularity of quasilinear pdes: $H^s(R^d)$ with $s \textgreater{} 3/2+d/2$ ($d$ is the horizontal dimension). From this reduction, we deduce a blow-up criterion and then an a priori estimate for the solution and the Lipschitz continuity of the solution map in terms of the Sobolev norm and the Strichartz norm.
Using lot quality-assurance sampling and area sampling to identify priority areas for trachoma control: Viet Nam
Myatt,Mark; Mai,Nguyen Phuong; Quynh,Nguyen Quang; Nga,Nguyen Huy; Tai,Ha Huy; Long,Nguyen Hung; Minh,Tran Hung; Limburg,Hans;
Bulletin of the World Health Organization , 2005, DOI: 10.1590/S0042-96862005001000012
Abstract: objective: to report on the use of lot quality-assurance sampling (lqas) surveys undertaken within an area-sampling framework to identify priority areas for intervention with trachoma control activities in viet nam. methods: the lqas survey method for the rapid assessment of the prevalence of active trachoma was adapted for use in viet nam with the aim of classifying individual communes by the prevalence of active trachoma among children in primary school. schoolbased sampling was used; school sites to be sampled were selected using an area-sampling approach. a total of 719 communes in 41 districts in 18 provinces were surveyed. findings: survey staff found the lqas survey method both simple and rapid to use after initial problems with area-sampling methods were identified and remedied. the method yielded a finer spatial resolution of prevalence than had been previously achieved in viet nam using semiquantitative rapid assessment surveys and multistage cluster-sampled surveys. conclusion: when used with area-sampling techniques, the lqas survey method has the potential to form the basis of survey instruments that can be used to efficiently target resources for interventions against active trachoma. with additional work, such methods could provide a generally applicable tool for effective programme planning and for the certification of the elimination of trachoma as a blinding disease.
Deterministic Compressive Sampling for High-Quality Image Reconstruction of Ultrasound Tomography
Tran Quang-Huy,Tran Duc-Tan,Huynh Huu Tue,Nguyen Linh-Trung
Physics , 2015,
Abstract: A well-known diagnostic imaging modality, termed ultrasound tomography, was quickly developed for the detection of very small tumors whose sizes are smaller than the wavelength of the incident pressure wave without ionizing radiation, compared to the current gold-standard X-ray mammography. Based on inverse scattering technique, ultrasound tomography uses some material properties such as sound contrast or attenuation to detect small targets. The Distorted Born Iterative Method (DBIM) based on first-order Born approximation is an efficient diffraction tomography approach. Compressed Sensing (CS) technique was applied to the detection geometry configuration of ultrasound tomography as a powerful tool for improved image reconstruction quality. However, this configuration is very difficult to implement in practice. Inspired of easier hardware implementation of deterministic CS, in this paper, we propose the chaos measurements in the detection geometry configuration and the image reconstruction process is implemented using L1 regularization. The simulation results of the proposed method have demonstrated the high performance of the proposed approach, the normalized error is approximately 90% reduced, compared to the conventional approach. Furthermore, with the same quality, we can save half of number of measurements and only use two iterations when using the proposed method.
Integrated Science, Technology, Engineering and Mathematics (STEM) Education through Active Experience of Designing Technical Toys in Vietnamese Schools
Le Xuan Quang,Le Huy Hoang,Vu Dinh Chuan,Nguyen Hoai Nam,Nguyen Thi Tu Anh,Vu Thi Hong Nhung
Computer Science , 2015, DOI: 10.9734/BJESBS/2015/19429
Abstract: STEM has attracted great consideration. The purpose of research is: (1) study STEM education, (2) explore STEM education with the creative and experiential activity, (3) suggest applying STEM education by designing technical toys for the middle school student. This study used a qualitative approach to carry out teaching integration for STEM education. The study applied to teaching the technological field in Vietnamese middle schools. The design performed at the Faculty of Technology Education, Hanoi National University of Education, Vietnam in April 2015. This study used the integrated approach to design subjects for STEM education. Two procedures for integration undertook with analysis. A sample of producing technical toy was consistent with developing students competencies. Integrated approach to STEM education through designing technical toys is possible. Recently, there has been a booming interest in Integrated Science, Technology, Engineering and Mathematics (STEM) education, but the approaches to STEM still remains controversial in diverse educational contexts. This study addressed this issue by exploring STEM education with the use of creative and experiential activities in a Vietnamese educational context. It also proposed a practical model for integrating STEM into teaching technology in secondary schools by designing technical toys. The implementation of the practical model suggests the possibility in using the integrated approach to STEM education through designing technical toys for middle school students in Vietnam. By applying the subject knowledge domains to solve real world problems and settings, the students can experience the benefits of a concrete and active learning in a meaningful and practical context. The multidisciplinary and interdisciplinary integration approaches are consistent with the development of the students competencies.
Effect of an Excess of Loss Reinsurance on Upper Bounds of Ruin Probabilities  [PDF]
Nguyen Quang Chung
Journal of Mathematical Finance (JMF) , 2017, DOI: 10.4236/jmf.2017.74053
Abstract: In this paper, discrete time risk models under an excess of loss reinsurance are studied. Adjustment coefficients of the cedent and the reinsurer are established as functions of quota share level and retention level. By the martingale method, ruin probabilities of the cedent and the reinsurer still have exponential form. Finally, numerical examples are provided to illustrate the results obtained in this paper.
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