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Search Results: 1 - 10 of 4796 matches for " Kinh Nguyen Viet "
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Full-Filling Subcarrier Power Allocation in OFDMA-Based Cognitive Radio Systems  [PDF]
Tuan Le Van, Hieu Dinh Chi, Kinh Nguyen Viet, Hieu Nguyen Thanh
Wireless Engineering and Technology (WET) , 2014, DOI: 10.4236/wet.2014.51002

When implementing an appropriate windowing, the interference from a Cognitive Radio (CR) system to licensed systems (primary users) will be significantly reduced. Consequently, power allocated to subcarriers can be increased, especially subcarriers having far spectral distance to primary user bands can be allocated full of its maximum possible power. In this paper, we propose a new class of sub-optimal subcarrier power allocation algorithm that significantly reduces complexity of OFDMA-based CR systems. Two sub-optimal proposals, called Pre-set Filling Range (PFR) and Maximum Filling Range (MFR) are studied. Investigations show that this new power allocating algorithm allows CR systems obtain high throughput while retaining low complexity.

Consideration of Viscoelasticity in Time Step FEM-Based Restraint Analyses of Hardening Concrete  [PDF]
Dirk Schlicke, Nguyen Viet Tue
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.410A2002

Concrete structures may suffer considerable restraint stresses during their hardening period. This is caused by several deformation impacts, especially temperature field changings due to hydration heat and volume changes due to autogenous shrinkage. Mainly affected are massive concrete members, but also the application of new concrete types or the erection of outstanding constructions requires further investigations in this context. 3D-FEM analyses of hydration heat induced temperature development in combination with the well known shrinkage give sufficient results for the deformation impact. The according elastic restraint stresses can be determined with consideration of the concrete’s rising elastic modulus and the restraint degree of the system. But due to duration of the heat flow process, the height of restraint stresses is strongly dependent from the viscoelasticity of the concrete. The viscoelastic effects consist of many components constituted by changing material properties influencing themselves. In practice, different simplified approaches are available for considering this in calculations. Their implementation in time step analyses is not generally admitted and requires expertise. In contrast, present research develops material models needing specific input parameters for every use case. This contribution focuses on a practicable approach considering the superposition of the viscoelastic behaviour of every stress increment in time step FEM analysis. The differentiation between the pure viscoelastic material behaviour (as it is given in the codes for idealistic conditions like creep or relaxation) and the according viscoelastic system response (addicted to the systems variable restraint degree) allows the transfer of this model into practice. As one application example of this approach,

Impacts of Exchange Rate Volatility and FDI on Technical Efficiency—A Case Study of Vietnamese Agricultural Sector  [PDF]
Nguyen Khac Minh, Pham Van Khanh, Nguyen Viet Hung
American Journal of Operations Research (AJOR) , 2015, DOI: 10.4236/ajor.2015.54025
Abstract: The objective of this research is to examine impacts of exchange rate volatility and FDI on efficiency of the Vietnamese agricultural sector at the provincial level for the period 1998-2011. Due to the characteristic of high uncertainty in agricultural production, the chance-constrained programming model would be used to estimate efficiency of the agricultural production sector. In order to study impacts of exchange rate volatility and FDI, we employ the two-stage model. In the first stage, we use the chance-constrained programming model to measure technical efficiency and ARIMA model to quantify exchange rate volatility. In the second stage, we use the fixed effect model to evaluate impacts of exchange rate volatility and FDI on efficiency of agricultural production in poor and rich provinces. The estimated results show that fluctuation in exchange rate volatility would reduce efficiency in agricultural production but FDI has an insignificant impact on the efficient production in Vietnam agricultural sector.
Forest Change and Its Effect on Biomass in Yok Don National Park in Central Highlands of Vietnam Using Ground Data and Geospatial Techniques  [PDF]
Nguyen Viet Luong, Ryutaro Tateishi, Nguyen Thanh Hoan, To Trong Tu
Advances in Remote Sensing (ARS) , 2015, DOI: 10.4236/ars.2015.42010
Abstract: This paper assesses the changes in forest cover in Yok Don National Park of Vietnam between 2004 and 2010, and the implications of such changes on the biomass stocks of this national park. Remote sensing and GIS tools along with the ground truth data collected from the field were employed for classifying the forest types of the study area from SPOT HRV satellite imagery for years 2004 and 2010. The total area considered in this study is 115.5 thousand ha. Five different categories of forests were identified. The results demonstrated that between 2004 and 2010, the Evergreen broad leaved rich quality forest decreased by 11.2 thousand ha (3.5 Mega tons of biomass) and the Dry open dipterocarps medium quality forest decreased by 15.3 thousand ha (2.5 Mega tons of biomass). In that time period, the Evergreen broad leaved medium quality forest increased by 3.2 thousand ha (0.8 Mega tons of biomass), the Evergreen broad leaved poor quality forest increased by 2.5 thousand ha (0.24 Mega tons of biomass), and the Dry open dipterocarps poor quality forest increased by 3.2 thousand ha (0.69 Mega tons of biomass). Total biomass of the study area decreased by 4.3 Mega tons.
POEMS Syndrome Diagnosed 10?Years after Disabling Peripheral Neuropathy
Viet H. Nguyen
Case Reports in Medicine , 2011, DOI: 10.1155/2011/126209
Abstract: Peripheral neuropathy is characterized as a generalized, relatively homogeneous process affecting many peripheral nerves and predominantly affecting distal nerves. The epidemiology of peripheral neuropathy is limited since the disease presents with varying etiology, pathology, and severity. Toxic, inflammatory, hereditary, and infectious factors can cause damage to the peripheral nerves resulting in peripheral neuropathy. Peripheral neuropathy is most commonly caused by diabetes, alcohol, HIV infection, and malignancy. We report a case of a 42-year-old female with 10-year history of progressively worsening peripheral neuropathy, hypothyroidism, and skin changes who presents with dyspnea secondary to recurrent pleural and pericardial effusions. Prior to her arrival, her peripheral neuropathy was believed to be secondary to chronic demyelinating inflammatory polyneuropathy (CDIP) given elevated protein in the cerebral spinal fluid (CSF) which was treated with intravenous immunoglobulin (IVIG) and corticosteroids. Unfortunately, her peripheral neuropathy did not have any improvement. Incidentally, patient was found to have splenomegaly and papilledema on physical exam. Serum protein electrophoresis showed a monoclonal pattern of IgA lambda. Patient met the diagnostic criteria for POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes) syndrome. An underlying diagnosis of POEMS syndrome should be considered in patients with chronic debilitating neuropathy and an elevated protein in the CSF.
Approximating the Minimum Tour Cover of a Digraph
Viet Hung Nguyen
Algorithms , 2011, DOI: 10.3390/a4020075
Abstract: Given a directed graph G with non-negative cost on the arcs, a directed tour cover T of G is a cycle (not necessarily simple) in G such that either head or tail (or both of them) of every arc in G is touched by T. The minimum directed tour cover problem (DToCP), which is to find a directed tour cover of minimum cost, is NP-hard. It is thus interesting to design approximation algorithms with performance guarantee to solve this problem. Although its undirected counterpart (ToCP) has been studied in recent years, in our knowledge, the DToCP remains widely open. In this paper, we give a 2 log2( n)-approximation algorithm for the DToCP.
Toward an Adaptive Learning System Framework: Using Bayesian Network to Manage Learner Model
Viet Anh Nguyen
International Journal of Emerging Technologies in Learning (iJET) , 2012, DOI: 10.3991/ijet.v7i4.2290
Abstract: This paper represents a new approach to manage learner modeling in an adaptive learning system framework. It considers developing the basic components of an adaptive learning system such as the learner model, the course content model and the adaptation engine. We use the overlay model and Bayesian network to evaluate learners’ knowledge. In addition, we also propose a new content modeling method as well as adaptation engine to generate adaptive course based on learner’s knowledge. Based on this approach, we developed an adaptive learning system named is ACGS-II, that teaches students how to design an Entity Relationship model in a database system course. Empirical testing results for students who used the application indicate that our proposed model is very helpful as guidelines to develop adaptive learning system to meet learners’ demands.
Mother Tongue Use in Task-Based Language Teaching Model
Nguyen Viet Hung
English Language Teaching , 2012, DOI: 10.5539/elt.v5n8p23
Abstract: Researches of English language teaching (ELT) have focused on using mother tongue (L1) for years. The proliferation of task-based language teaching (TBLT) has been also occurred. Considerable findings have been made in the existing literature of the two fields; however, no mentions have been made in the combination of these two ELT aspects, i.e., the use of L1 in English as a Second and Foreign Language (L2) classrooms in which TBLT is adopted. Hence, this paper is to make an argumentation in the appropriateness of this combination. Firstly, terminologies related to Tasks and TBLT framework are shortly revised. Secondly, the controversies with for and against views in monolingual approach in second and foreign language teaching (L2 teaching) is mentioned. Lastly, the paper makes an argumentation on why and how to use mother tongue in a modern teaching model as TBLT.
A Mixed Approaches Method Used to Investigate Teacher Cognition of English Language Teaching
Nguyen Viet Hung
English Language Teaching , 2012, DOI: 10.5539/elt.v5n11p161
Abstract: This paper is a part in a bigger research project related to ELT quality in secondary schools in Vietnam since the implementation of the new series of English textbooks was officially passed by in 2006, and the innovated direction was paid to task-based language teaching (TBLT). The purpose of this paper is to make argumentation on why, what and how to use mixed approaches method to investigate two subdomains of teacher cognition - teacher perception and teacher belief. Firstly, an introduction in the research project and research questions about secondary school teacher perception of TBLT and teacher belief of textbooks is shortly made. Secondly, the question what the mixed approaches method are like is dealt with. Next, the question why the mixed approaches method should be used in investigating teacher cognition in general and teacher perception as well as teacher belief in particular is answered and illustrated by writer’s framework of research paradigm for the suitability and applicability. Lastly, the question how the mixed approaches method should be implemented to answer the research project questions is clarified and argued for its suitability.
Heavy diquark effective theory and supersymmetry of hadrons containing a single heavy quark
Nguyen Ai Viet
Physics , 1993,
Abstract: A new supersymmetry is proposed for hadrons containing a single heavy quark. This supersymmetry is based on a new approximation to those hadrons, which we would consider as a further step beyond the spectator light diquark model of baryons. The heavy diquark effective theory is constructed by the techniques introduced in a different context by Georgi and Wise$^1$ and by Carone$^2$. This theory can be incorporated into a supersymmetric theory together with Heavy Quark Effective Theory, and leads to a common universal Isgur-Wise function for mesons and baryons./.
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