Efficiency Performance of Hospitals and Medical Centers in Vietnam

The purpose of this paper is to analyze the efficiency performance of the hospitals and medical centers in Vietnam by using a non-parametric approach, namely the data envelopment analysis (DEA) model. The data from the Economic Census for Enterprises by the General Statistics Office of Vietnam (GSO) consists of 44 observations, which include 17 hospitals and 27 medical centers in different provinces and cities in 2002. The results indicate that the average scale efficiency of the hospitals was 77.4 percent, while that of the medical centers was 58.7 percent. Further, hospitals were clearly more efficient than medical centers due to some possible factors. Locations in Hanoi and Ho Chi Minh city had no influence on either overall technical efficiency or scale efficiency. Despite differences in the results of testing the impact of net capital-labor ratio on efficiency for hospitals and medical centers, these organizations appear to operate in labor-intensive ways

Efficiency of Construction Firms in Vietnam

This paper uses both parametric and non-parametric approaches to estimate technical efficiency for 2,298 construction firms in Vietnam in the database of the 2002 Economic Census for Enterprises by the General Statistics Office of Vietnam (GSO). It is found that results from both approaches are consistent, and they could help explain the performance efficiency of these firms. Estimates from the non-parametric approach (data envelopment analysis [DEA] model) and the parametric approach (stochastic frontier production function [SFPF] model) indicate that the average pure technical efficiency of these firms was about 60 percent (58.6% and 57.8% for DEA and SFPF, respectively). Models to test the factors influencing efficiency scores in both approaches show relatively similar results that state firms were more efficient than non-state ones, and location in Hanoi and Ho Chi Minh city did have impacts on efficiency scores. However, exploration of the net capital-labor ratio variable show that it did not influence efficiency scores in the DEA model, while it had clear influence in the SFPF model

Numerical modeling of three-dimensional open elastic waveguides combining semi-analytical finite element and perflectly matched layer methods

Among the numerous techniques of non destructive evaluation, elastic guided waves are of particular interest to evaluate defects inside industrial and civil elongated structures owing to their ability to propagate over long distances. However for guiding structures buried in large solid media, waves can be strongly attenuated along the guide axis due to the energy radiation into the surrounding medium, usually considered as unbounded. Hence, searching the less attenuated modes become necessary in order to maximize the inspection distance. In the numerical modeling of embedded waveguides, the main difficulty is to account for the unbounded section. This paper presents a numerical approach combining a semi-analytical finite element method and a perfectly matched layer (PML) technique to compute the so-called trapped and leaky modes in three-dimensional embedded elastic waveguides of arbitrary cross-section. Two kinds of PML, namely the Cartesian PML and the radial PML, are considered. In order to understand the various spectral objects obtained by the method, the PML parameters effects upon the eigenvalue spectrum are highlighted through analytical studies and numerical experiments. Then, dispersion curves are computed for test cases taken from the literature in order to validate the approach

SCREENING ANTIBACTERIAL ACTIVITY OF VIETNAMESE PLANT EXTRACTS AGAINST HUMAN PATHOGENIC BACTERIA

Objectives: Infectious diseases caused by bacteria are a leading cause of death worldwide. Hence, the objectives of the study are aimed to evaluate the antibacterial activity against five human pathogenic bacteria of methanolic extracts from 66 plants collected from Vietnam. Methods: The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of methanol extracts of 66 plant species against five bacterial strains. Results: In this study, all the plant extracts were active against at least one train with MIC values ranging from 24 to 2048 μg/mL. Twenty-five plant extracts were active against all three Gram-positive bacteria (Bacillus cereus, Bacillus subtilis, and Staphylococcus aureus). Of these, the extracts of Macaranga trichocarpa (Rchb. f. and Zoll.) Mull. Arg. (Euphorbiaceae), Calophyllum inophyllum L. (Clusiaceae) and Caryodaphnopsis baviensis (Lecomte) Airy Shaw (Lauraceae) exhibited the highest antibacterial activity (MIC =24–128 μg/mL), followed by extracts of Betula alnoides Buch.- Ham. e × . D. Don (Betulaceae), Acronychia pedunculata (L.) Miq. (Rutaceae), Croton alpinus A. Chev. ex Gagnep. (Euphorbiaceae) (MIC =64–256 μg/mL). Furthermore, the extract of Rhus chinensis Mill. (Anacardiaceae) and Annona reticulata L. (Annonaceae) exhibited potent antibacterial activity against the two Bacillus species (MIC =32–64 μg/mL). Conclusion: Results of this study reveal that plant extracts from Vietnam have highly antibacterial activity against Gram-positive bacteria. These results suggest that Vietnamese plant extracts may be a rich source of antibacterial drugs

Modélisation numérique des guides d’onde ouverts : cas des structures élastiques courbes

National audiencePour le contrôle non destructif des matériaux et structures, les ondes élastiques guidées sont intéressantes en raison de leur longue distance de propagation. Cependant pour les guides enfouis dans un milieu infini, les modes peuvent devenir à fuite. Ces modes s'atténuent selon l'axe du guide en raison du rayonnement de l'énergie, ce qui réduit leur distance de propagation. La recherche des modes les moins atténués est donc nécessaire. Le calcul numérique des modes dans les guides enfouis présente une difficulté: les amplitudes des modes à fuite croissent dans la direction transversale. Une technique consiste à combiner la méthode des éléments finis semi-analytique (SAFE) et la méthode des couches parfaitement adaptées (PML). Cette méthode a été implémentée récemment par les auteurs pour simuler des plaques multi-couches enfouies et des guides enrobés de section arbitraire. Néanmoins, ces travaux ne considèrent que des guides droits, sans courbure. Nous nous intéressons ici à la modélisation par méthode SAFE-PML des structures courbes, plus particulièrement hélicoïdales, enrobées dans un solide. La motivation de ce travail est le contrôle non destructif des torons, structures multi-brins hélicoïdales, constituant les câbles de génie civil. Dans le vide, on peut simuler les guides hélicoïdaux par méthode SAFE grâce à des coordonnées hélicoïdales. Notre travail consiste à appliquer des PML selon des directions transversales twistées pour calculer les modes à fuite. Deux cas tests sont étudiés. Le premier cas test correspond à un cylindre "twisté" dans une matrice solide et permet de valider la méthode SAFE-PML twistée. L'effet du twist sur le spectre des modes propres est présenté. Le deuxième cas consiste à simuler un brin hélicoïdal enrobé. L'effet de la courbure du guide sur l'atténuation axiale des modes est étudié. Enfin, la simulation d’un toron plongé dans un coulis de ciment sera présentée

Computation of leaky modes in three-dimensional open elastic waveguides

International audienceElastic guided waves are of interest for inspecting structures due to their ability to propagate over long distances. When the guiding structure is embedded into a solid matrix, waveguides are open and waves can be trapped or leaky. With numerical methods, one of the difficulty is that leaky modes attenuate along the axis (complex wavenumber) and exponentially grow along the transverse direction. The goal of this work is to propose a numerical approach for computing modes in open elastic waveguides combining the so-called semi-analytical finite element method (SAFE) and a perfectly matched layer (PML) technique

Finite element computation of trapped and leaky elastic waves in open stratified waveguides

International audienceElastic guided waves are of interest for inspecting structures due to their ability to propagate over long distances. In numerous applications, the guiding structure is surrounded by a solid matrix that can be considered as unbounded in the transverse directions. The physics of waves in such an open waveguide significantly differs from a closed waveguide, i.e. for a bounded cross-section. Except for trapped modes, part of the energy is radiated in the surrounding medium, yielding attenuated modes along the axis called leaky modes. These leaky modes have often been considered in non destructive testing applications, which require waves of low attenuation in order to maximize the inspection distance. The main difficulty with numerical modeling of open waveguides lies in the unbounded nature of the geometry in the transverse direction. This difficulty is particularly severe due to the unusual behavior of leaky modes: while attenuating along the axis, such modes exponentially grow along the transverse direction. A simple numerical procedure consists in using absorbing layers of artificially growing viscoelasticity, but large layers may be required. The goal of this paper is to explore another approach for the computation of trapped and leaky modes in open waveguides. The approach combines the so-called semi-analytical finite element method and a perfectly matched layer technique. Such an approach has already been successfully applied in scalar acoustics and electromagnetism. It is extended here to open elastic waveguides, which raises specific difficulties. In this paper, two-dimensional stratified waveguides are considered. As it reveals a rich structure, the numerical eigenvalue spectrum is analyzed in a first step. This allows to clarify the spectral objects calculated with the method, including radiation modes, and their dependency on the perfectly matched layer parameters. In a second step, numerical dispersion curves of trapped and leaky modes are compared to analytical results

Computation of Dispersion Curves in Elastic Waveguides of Arbitrary Cross-section embedded in Infinite Solid Media

International audienceElastic guided waves are of interest for inspecting structures due to their ability to propagate over long distances. However, guiding structures are often buried in a large domain, considered as unbounded. Waveguides are then open and waves can be trapped or leaky. Analytical tools have been developed to model open solid waveguides but these tools are limited for simple geometries (plates, cylinders). With numerical methods, a difficulty is due to the unbounded geometry. Another issue is due to the presence of leaky modes, which grow exponentially along the transverse directions. The goal of this work is to implement a numerical approach to calculate modes in three dimensional elastic open waveguides, which combines the semi-analytical finite element method and the perfectly matched layers (PML) technique. Both Cartesian and cylindrical PML are implemented

Nonlinear rotordynamics of a drillstring in curved wells: models and numerical techniques

International audienceThe drilling operations for oil or geothermic extraction use a slender structure introduced inside the drill well, hanging from a derrick and driven by a rotary table at the surface. The drilling structure consists in a series of drill-pipes and some heavy pipes at the well bottom. The drilling process involves nonlinear dynamic phenomena such as bit-bounce, stick-slip due to the well-drillstring multi-contacts and the pulsating mud flow. The drillstring vibrations may yield, the rate of penetration decrease, the premature wears and damages of drilling equipment. Many numerical models have been proposed to study the dynamics of drillstring to improve the reliability of drilling operations. However, the numerical models of drilling structures representing several kilometers length require a huge amount of computer memory storage and yield a too long computational time. The reduction technique proposed by Craig-Bampton (CB) has been developed for modelling the nonlinear dynamics of rotating machines to save the computational time but still limited in the context of rotordynamics. The paper focuses on the implementation of the CB method in the case of long drillstring assembly modelled by beam finite elements. The pre-loaded states of the drillstring due to the well curvature, well-structure contacts and fluid-structure interactions are determined and taken into account in the dynamic computation. The drillstring transient dynamics is simulated and the orbital motion of several nodes are analyzed. The result convergence and the reduction of computational time obtained by the CB method are investigated and discussed

Finite element computation of leaky modes in straight and helical elastic waveguides

International audienceElastic guided waves are of interest for inspecting structures due to their ability to propagate over long distances. However, waveguides are often embedded in a large solid domain, considered as unbounded. The waves can attenuate strongly along the guide axis due to the energy leakage into the surrounding medium, which reduces the propagating distance. Searching modes with low attenuation becomes necessary. The goal of this work is to propose a numerical approach to compute modes in embedded elastic waveguides (straight and helical structures), combining the so-called semi-analytical finite element method (SAFE) and a perfectly matched layer (PML) method. The application of this work is the non destructive evaluation of multi-wire strands, which constitute cables in civil structures