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Search Results: 1 - 10 of 1687 matches for " Luu Hoang Duc "
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A new concept of local metric entropy for finite-time nonautonomous dynamical systems
Luu Hoang Duc,Stefan Siegmund
Mathematics , 2014,
Abstract: We introduce a new concept of finite-time entropy which is a local version of the classical concept of metric entropy. Based on that, a finite-time version of Pesin's entropy formula and also an explicit formula of finite-time entropy for $2$-D systems are derived. We also discuss about how to apply the finite-time entropy field to detect special dynamical structures such as Lagrangian coherent structures.
Generation of random dynamical systems from fractional stochastic delay differential equations
Luu Hoang Duc,Bj?rn Schmalfuss,Stefan Siegmund
Mathematics , 2013,
Abstract: In this note we prove that a fractional stochastic delay differential equation which satisfies natural regularity conditions generates a continuous random dynamical system on a subspace of a H\"older space which is separable.
Asymptotic Behavior of Linear Almost Periodic Differential Equations
Bui Xuan Dieu,Luu Hoang Duc,Stefan Siegmund,Nguyen Van Minh
Mathematics , 2012,
Abstract: The present paper is concerned with strong stability of solutions of non-autonomous equations of the form $\dot u(t)=A(t)u(t)$, where $A(t)$ is an unbounded operator in a Banach space depending almost periodically on $t$. A general condition on strong stability is given in terms of Perron conditions on the solvability of the associated inhomogeneous equation.
HIV-Associated TB in An Giang Province, Vietnam, 2001–2004: Epidemiology and TB Treatment Outcomes
Trinh Thanh Thuy, N. Sarita Shah, Mai Hoang Anh, Do Trong Nghia, Duong Thom, Truong Linh, Dinh Ngoc Sy, Bui Duc Duong, Luu Thi Minh Chau, Phung Thi Phuong Mai, Charles D. Wells, Kayla F. Laserson, Jay K. Varma
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000507
Abstract: Background Mortality is high in HIV-infected TB patients, but few studies from Southeast Asia have documented the benefits of interventions, such as co-trimoxazole (CTX), in reducing mortality during TB treatment. To help guide policy in Vietnam, we studied the epidemiology of HIV-associated TB in one province and examined factors associated with outcomes, including the impact of CTX use. Methodology/Principal Findings We retrospectively abstracted data for all HIV-infected persons diagnosed with TB from 2001–2004 in An Giang, a province in southern Vietnam in which TB patients receive HIV counseling and testing. We used standard WHO definitions to classify TB treatment outcomes. We conducted multivariate analysis to identify risk factors for the composite outcome of death, default, or treatment failure during TB treatment. From 2001–2004, 637 HIV-infected TB patients were diagnosed in An Giang. Of these, 501 (79%) were male, 321 (50%) were aged 25–34 years, and the most common self-reported HIV risk factor was sex with a commercial sex worker in 221 (35%). TB was classified as smear-positive in 531 (83%). During TB treatment, 167 (26%) patients died, 9 (1%) defaulted, and 6 (1%) failed treatment. Of 454 patients who took CTX, 116 (26%) had an unsuccessful outcome compared with 33 (70%) of 47 patients who did not take CTX (relative risk, 0.4; 95% confidence interval [CI], 0.3–0.5). Adjusting for male sex, rural residence, TB smear status and disease location, and the occurrence of adverse events during TB treatment in multivariate analysis, the benefit of CTX persisted (adjusted odds ratio for unsuccessful outcome 0.1; CI, 0.1–0.3). Conclusions/Significance In An Giang, Vietnam, HIV-associated TB was associated with poor TB treatment outcomes. Outcomes were significantly better in those taking CTX. This finding suggests that Vietnam should consider applying WHO recommendations to prescribe CTX to all HIV-infected TB patients.
NIDE: A Novel Improved Differential Evolution for Construction Project Crashing Optimization
Nhat-Duc Hoang
Journal of Construction Engineering , 2014, DOI: 10.1155/2014/136397
Abstract: In the field of construction management, project crashing is an approach to shortening the project duration by reducing the duration of several critical project activities to less than their normal activity duration. The goal of crashing is to shorten the project duration while minimizing the crashing cost. In this research, a novel method for construction project crashing is proposed. The method is named as novel improved differential evolution (NIDE). The proposed NIDE is developed by an integration of the differential evolution (DE) and a new probabilistic similarity-based selection operator (PSSO) that aims at improving the DE’s selection process. The PSSO has the role as a scheme for preserving the population diversity and fending off the premature convergence. The experimental result has demonstrated that the newly established NIDE can successfully escape from local optima and achieve a significantly better optimization performance. 1. Introduction In the field of construction management, a construction project can be typically defined as a set of individual activities with their technical/managerial constraints. The nature of construction projects, which is characterized by constant changes in the environment, pressures to maintain schedules/costs with increasingly complex construction techniques, makes the task of project management a significant challenge [1]. Due to the complexity of construction projects, schedule management is proved to be very challenging [2]. Therefore, schedule overrun is not unusual in the construction field. Moreover, there can be a great motivation for the construction contractor and the project owner to reduce the project time [3]. The reason is that as a project progresses, it consumes indirect costs, consisting of the cost of facilities, equipment, and machinery, interest on investment, utilities, labor, and the loss of skills and labor of the project team who are not working at their regular jobs [4]. There also may be severe financial penalties for not completing a project on time; many construction and government contracts have penalty clauses for exceeding the project completion date. In addition, the project owner may desire to reduce the completion time in order to put the facility into operation sooner. In practice, to shorten the project schedule, the manager may accelerate some of the activities at an additional cost, that is, by allocating more or better resources, such as labor and equipment. Minimizing the sum of activity direct costs while meeting a specified deadline is of practical need and this has
The local criteria for blowup of the Dullin-Gottwald-Holm equation and the two-component Dullin-Gottwald-Holm system
Duc-Trung Hoang
Mathematics , 2014,
Abstract: We investigate wave breaking for the Dullin-Gottwald-Holm equation and the two-component Dullin-Gottwald-Holm system. We establish a new blow-up criterion for the general case $\gamma+c_0\alpha^2 \geq 0$ involving local-in-space conditions on the initial data.
On the Alternate Direction Implicit (ADI) Method for Solving Heat Transfer in Composite Stamping  [PDF]
Arthur Levy, Duc Anh Hoang, Steven Le Corre
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.81004
Abstract: Thermostamping of thermoplastic matrix composites is a process where a preheated blank is rapidly shaped in a cold matching mould. Predictive modelling of the main physical phenomena occurring in this process requires an accurate prediction of the temperature field. In this paper, a numerical method is proposed to simulate this heat transfer. The initial three-dimensional heat equation is handled using an additive decomposition, a thin shell assumption, and an operator splitting strategy. An adapted resolution algorithm is then presented. It results in an alternate direction implicit decomposition: the problem is solved successively as a 2D surface problem and several one-dimensional through thickness problems. The strategy was fully validated versus a 3D calculation on a simple test case and the proposed strategy is shown to enable a tremendous calculation speed up. The limits of applicability of this method are investigated with two parametric studies, one on the thickness to width ratio and the other one on the effect of curvature. These conditions are usually fulfilled in industrial cases. Finally, even though the method was developed under linear assumption (constant material properties), the strategy validity is extended to multiply, temperature dependant (nonlinear) case using an industrial test case. Because of the standard methods involved, the proposed ADI method can readily be implemented in existing software.
Decision Criteria and Their Subjectivity in Construction Procurement Selection
Thomas Ng,Duc Luu,Swee Chen
Australasian Journal of Construction Economics and Building , 2012,
Abstract: Employing a suitable construction procurement system is crucial to project success. However,many clients select procurement systems in a cursory manner and some clientseven use a specific procurement system by default without deliberate choice. A systematicmethod for procurement selection would help clients to arrive at more informed decisions.The first step towards a systematic procurement selection method is to identify decisioncriteria pertinent to assessing the alternatives. This paper identifies the commonly consideredcriteria for procurement selection through a qualitative survey in Australia. The subjectivityof the identified criteria is considered and the effects on procurement selectionare examined. The results indicate that speed, complexity, flexibility, responsibility, qualitylevel, risk allocation, and price competition cannot be easily gauged by objective means,and a misperception of the degree of fulfilment of any of these criteria could affect theoutcome of procurement selection.
Powdered Milk Consumers’ Buying Behavior
Luu Trong Tuan,Nguyen Thi Truc Phuong,Luu Thi Bich Ngoc,Luu Hoang Mai
International Journal of Business and Management , 2012, DOI: 10.5539/ijbm.v8n2p29
Abstract: Following the storm of melamine in milk and lower protein milk index than the published standard, consumers are more and more cautious when they choose powdered milk for their children. More especially, the Vietnamese prefer to buy imported powdered milk rather than domestic powdered milk. Accordingly, this research is conducted to investigate which factors influence consumer-buying behavior toward imported milk powdered in Ho Chi Minh City through a quantitative survey of 110 consumers. Through multiple regression analysis, the findings indicate that product brand, advertisement, and country of origin are significant predictors of consumer-buying behaviors towards imported powdered milk. Sponsorship turned out to be insignificant factor in predicting the dependent variable. Among demographic characteristics only income was found to affect the consumer-buying behavior.
Hilbert polynomials of non-standard bigraded algebras
Nguyen Duc Hoang,Ngo Viet Trung
Mathematics , 2002,
Abstract: This paper is a systematic study of the Hilbert polynomial of a bigraded algebra R which are generated by elements of bidegrees (1,0), (d_1,1),...,(d_r,1), where d_1,...,d_r are non-negative integers. The obtained results can be applied to study Rees algebras of homogeneous ideals and their diagonal subalgebras. The Hilbert polynomial is computed explicitly in the following cases: (1) R is a bigraded polynomial ring of the above type; (2) R is the Rees algebra of an ideal generated by a homogeneous regular sequence; (3) R is the Rees algebra of the ideal generated by the maximal minors of a generic (r-1) by r matrix.
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