The epidemiology of trichinellosis in northern Vietnam

Trichinellosis is a meat-borne zoonotic disease caused by nematodes of the genus Trichinella. Typically, it is acquired by eating undercooked meat from pigs that are raised in non-controlled management conditions or from wildlife. The parasite is transmitted both in the domestic and sylvatic lifecycles. In the last decade, several outbreaks of trichinellosis have been observed in Northern Vietnam, where the disease was previously practically unknown. In chapter 1 a general review of the literature is given on Trichinella spp and trichinellosis, with special focus on the epidemiology, the diagnosis and the situation in SE Asia, particularly in Vietnam. This chapter is followed by the objectives of the thesis that introduce the research chapters. The 2nd chapter describes data on trichinellosis in domestic animals. In the 1st part the seroprevalence of anti-Trichinella IgG was measured in free-roaming pigs in Son La province of NW Vietnam where an outbreak of trichinellosis occurred in 2008. Of the 1035 pigs from which serum samples were collected, 206 (19.9%) were positive in ELISA. In Muscle samples from serologically positive pigs were tested by artificial digestion. Trichinella larvae were detected in 14.5% of them and identified by multiplex PCR as T. spiralis. In the 2nd part, the seroprevalence of Trichinella infection was determined in 558 pigs, 125 dogs and 98 cats in two provinces of NW Vietnam. The overall seroprevalence was 5.6%, 4% and 0% in pigs, dogs and cats, respectively. In pigs, positive cases were distributed in 8/20 districts of the two provinces. The results indicate that pigs and dogs act as a reservoir and play an important role in the maintenance of the domestic cycle of T. spiralis in NW Vietnam. In the 3rd chapter the occurrence of trichinellosis in wild boars and synanthropic rats was studied in NW Vietnam. The results showed prevalences of T. spiralis of 3.2% and 2,8% in hunted wild boars and rats, respectively. Trichinella-infected rats were found in 7 of the 20 districts of Dien Bien and Son La provinces. These results indicate that the local population and health centers should be made aware of the risks of eating raw or undercooked meat dishes prepared from wild animals. The 4th chapter describes studies on human trichinellosis. In the 1st part an outbreak of trichinellosis in Thanh Hoa province is described (2012), involving 24 patients who consumed raw meat from a wild boar. Six of these patients were treated in hospitals in Hanoi. ELISA and muscle biopsies were positive in all six patients. Trichinella sp. larvae were identified as T. spiralis by molecular analysis of the cox3 gene. In the 2nd part a post-outbreak cross-sectional study in the same community was described. A total of 100 inhabitants were identified with suspected trichinellosis, of which, 30% had antibodies to Trichinella. Serologically confirmed cases had fever, myalgia, facial oedema, diarrhoea, and/or pain of the masseter muscles. Clinical symptoms resolved in all patients after albendazole treatment. The results suggest that only a proportion of the trichinellosis cases had sought health care during the outbreak. In the 3rd part the presence of anti-Trichinella IgG in the serum of persons from ethnic minorities from NW Vietnam with clinical signs and symptoms that are compatible with trichinellosis was assessed. A total of 645 persons were enrolled, of which 200 lived in two villages where previously outbreaks of human trichinellosis had occurred, and 445 people who were hospitalized in the provincial hospitals without a definitive diagnosis. Seven (3.5%) persons from the villages and seven (1.6%) hospitalized patients, tested positive by both ELISA and Western Blot. The concomitant occurrence of facial edema and myalgia among the enrolled persons from the villages, accounted for 75% of the positive predictive value (PPV) and 99.5% of the negative predictive value (NPV), suggesting that they could be used for suspecting trichinellosis when serology is not available. In the 5th chapter we discuss the findings of our research in the context of the emergence of trichinellosis in Northern Vietnam. The high prevalence (1.6–3.5%) of anti-Trichinella IgG in persons from Northern Vietnamese provinces where T. spiralis is circulating in pigs and wildlife strongly supports the need to develop control programs to eliminate the infection from pigs and for consumers’ education and protection. There is a need to implement surveillance and better diagnosis for trichinellosis in humans and of Trichinella infections in slaughter animals and wildlife and to set up educational programs to prevent infection in Northern Vietnam

Population genomics of the giant black tiger shrimp Penaeus monodon to understand wild fishery and aquaculture production

Nga Vu investigated the genetic structure of black tiger shrimp within the Indo-Pacific using genome-wide markers. She found evidence for the existence of genetic adaptation within and among populations as a consequence of geographic distance and/or environmental conditions. Her research will be used by the aquaculture industry to identify populations to use as foundation animals for genetic improvement programs

LMI based antiswing adaptive controller for uncertain overhead cranes

This paper proposes an adaptive anti-sway controller for uncertain overhead cranes. The state-space model of the 2D overhead crane with the system parameter uncertainties is shown firstly. Next, the adaptive controller which can adapt with the system uncertainties and input disturbances is established. The proposed controller has ability to move the trolley to the destination in short time and with small oscillation of the load despite the effect of the uncertainties and disturbances. Moreover, the controller has simple structure so it is easy to execute. Also, the stability of the closed-loop system is analytically proven. The proposed algorithm is verified by using Matlab/Simulink simulation tool. The simulation results show that the presented controller gives better performances (i.e., fast transient response, position tracking, and low swing angle) than the state feedback controller when there exist system parameter variations as well as input disturbances

Adaptive sliding mode control for uncertain wheel mobile robot

In this paper a simple adaptive sliding mode controller is proposed for tracking control of the wheel mobile robot (WMR) systems. The WMR are complicated systems with kinematic and dynamic model so the error dynamic model is built to simplify the mathematical model. The sliding mode control then is designed for this error model with the adaptive law to compensate for the mismatched. The proposed control scheme in this work contains only one control loop so it is simple in both implementation and mathematical calculation. Moreover, the requirement of upper bounds of disturbance that is popular in the sliding mode control is cancelled, so it is convenient for real world applications. Finally, the effectiveness of the presented algorithm is verified through mathematical proof and simulations. The comparison with the existing work is also executed to evaluate the correction of the introduced adaptive sliding mode controller. Thoroughly, the settling time, the peak value, the integral square error of the proposed control scheme reduced about 50% in comparison with the compared disturbance observer based sliding mode control

Etude des phénomènes de charges d'espace dans des matériaux de câbles et câbles modèles destinés à des applications au transport d'énergie en Haute Tension Continue (HVDC)

Ce travail s'inscrit dans le cadre général du développement de câbles haute tension continue (HVDC) à isolation synthétique et se focalise sur l'étude des phénomènes d'accumulation de charges d'espace et de leurs conséquences sur la distribution de champ électrique dans les câbles et jonctions de câbles sous gradient thermique. Dans cette étude, des mesures de courant de conduction ont été réalisées sur deux matériaux polymères: le polyéthylène réticulé (XLPE), majoritairement utilisé comme isolant des câbles à haute tension, et un élastomère (EPDM) servant de matériau de raccordement. Ces résultats issus d'échantillons plans sont utilisés pour établir des modèles semi-empiriques de conductivité fonction de la température et du champ électrique. L'incorporation de ces modèles dans un logiciel de simulation numérique a permis par la suite de prédire les distributions de densité de charge et de champ dans différentes structures à géométrie plus complexe telles que les câbles et les associations d'isolants, modèles d'accessoires de câbles, soumis à diverses contraintes électriques et thermiques, en régime transitoire. Des mesures de charge d'espace, réalisées sur des bicouches d'isolants XLPE/EPDM, sur des câbles maquettes moyenne tension (MV) et mini-câbles, ont été effectuées par la méthode électro-acoustique pulsée. Les résultats obtenus dans les bicouches, modèles de jonctions, sous différentes conditions de température et de champ montrent que le signe de la charge d'interface dans les bicouches dépend de la température et du champ électrique. A ce comportement est associée une discontinuité du champ électrique dans les bicouches. Pour les câbles soumis à un gradient thermique, les résultats montrent le déplacement au cours du temps de la contrainte électrique maximale du semi-conducteur interne au semi-conducteur externe dû au gradient de conductivité électrique associé au gradient thermique selon le rayon du câble. Les résultats obtenus par simulation sur les structures bicouches (signe et densité de charge d'interface) et câbles MV sont compatibles avec les profils de densité de charges issus de la mesure sous différentes contraintes électriques et thermiques. Les écarts observés entre les résultats de simulation et de mesure sont attribués à la présence d'autres phénomènes d'accumulation de charges non pris en compte dans la simulation, liés entre autres à la présence de sous-produits de réticulation. L'effet des sous-produits de réticulation sur la réponse des isolants est considéré dans des mesures de charges d'espace sur mini-câbles et par l'évaluation des paramètres pertinents sur l'accumulation de charges appliquée à diverses formulations d'échantillons plans. Des distorsions très significatives du profil de champ électrique ont été mesurées, attestant de la tendance manifeste des sous-produits à se dissocier sous l'effet du champ et/ou à assister l'injection de charges.This work contributes to the development of polymer-insulated high voltage direct current (HVDC) cables, focusing on the investigation of space charge build-up phenomena and their consequences on electric field distribution within cables and cable joints under thermal gradient. In this study, conduction current measurements were realized on two different materials often used for HVDC cable construction, being cross-linked polyethylene (XLPE) used as cable insulation and an elastomer (EPDM) used in accessories. These data were used to build semi-empirical models of conductivity versus temperature and electric field. These models were incorporated in a commercial simulation tool in order to predict charge density and field distributions in more complex geometries such as cylindrical geometry and insulations association, submitted to various thermal and electrical stresses, in non-stationary conditions. Space charge measurements were carried out on bi-layers of XLPE/EPDM, and on medium voltage (MV) model cables and mini-cables, using the pulsed electro acoustic method. Results obtained on bi-layers as models of joints under various conditions of temperature and field show that the sign of the interfacial charges in the bi-layers depends on temperature and electric field. This makes non-homogeneous field distribution in bi-layers. For cables under thermal gradient, results show a switching in time of the position of field maximum from the inner semi-conductor to the outer semi-conductor due to the electrical conductivity gradient resulting from the thermal gradient along cable radius. Simulation results obtained on bi-layers (sign and density of charges) and within MV cables are consistent with charge density profiles obtained experimentally under various electrical and thermal stresses. Deviations between simulation and measurements are attributed to charge accumulation processes not accounted for in the model, involving notably cross-linking by-products. The effect of cross-linking by-products on the response of insulations is investigated through measurements on mini-cables and through the evaluation of parameters relevant to the accumulation of charges applied to various formulations of samples in plaque form. Substantial distortions of the electric field profile were measured, testifying for the evident propensity of by-products to dissociate under the electric field and/or assist charge injection

Trichinellosis in Vietnam

Trichinellosis is a zoonotic parasitic disease with a worldwide distribution. The aim of this work was to describe the epidemiological and clinical data of five outbreaks of trichinellosis, which affected ethnic minorities living in remote mountainous areas of northwestern Vietnam from 1970 to 2012. Trichinellosis was diagnosed in 126 patients, of which 11 (8.7%) were hospitalized and 8 (6.3%) died. All infected people had consumed raw pork from backyard and roaming pigs or wild boar at wedding, funeral, or New Year parties. The short incubation period (average of 9.5 days), the severity of the symptoms, which were characterized by diarrhea, abdominal pain, fever, myalgia, edema, weight loss, itch, and lisping, and the high mortality, suggest that patients had ingested a high number of larvae. The larval burden in pigs examined in one of the outbreaks ranged from 70 to 879 larvae/g. These larvae and those collected from a muscle biopsy taken from a patient from the 2012 outbreak were identified as Trichinella spiralis. Data presented in this work show that the northern regions of Vietnam are endemic areas for Trichinella infections in domestic pigs and humans

Asymptotic behavior of solutions of quasilinear differential-algebraic equations

This paper is concerned with the asymptotic behavior of solutions of linear differential-algebraic equations (DAEs) under small nonlinear perturbations. Some results on the asymptotic behavior of solutions which are well known for ordinary differential equations are extended to DAEs. The main tools are the projector-based decoupling and the contractive mapping principle. Under certain assumptions on the linear part and the nonlinear term, asymptotic behavior of solutions are characterized. As the main result, a Perron type theorem that establishes the exponential growth rate of solutions is formulated

Robust adaptive controller for wheel mobile robot with disturbances and wheel slips

In this paper an observer based adaptive control algorithm is built for wheel mobile robot (WMR) with considering the system uncertainties, input disturbances, and wheel slips. Firstly, the model of the kinematic and dynamic loops is shown with presence of the disturbances and system uncertainties. Next, the adaptive controller for nonlinear mismatched disturbance systems based on the disturbances observer is presented in detail. The controller includes two parts, the first one is for the stability purpose and the later is for the disturbances compensation. After that this control scheme is applied for both two loops of the system. In this paper, the stability of the closed system which consists of two control loops and the convergence of the observers is mathematically analysed based on the Lyapunov theory. Moreover, the proposed model does not require the complex calculation so it is easy for the implementation. Finally, the simulation model is built for presented method and the existed one to verify the correctness and the effectiveness of the proposed scheme. The simulation results show that the introduced controller gives the good performances even that the desired trajectory is complicated and the working condition is hard

Feature selection methods and sampling techniques to financial distress prediction for Vietnamese listed companies

The research is taken to integrate the effects of variable selection approaches, as well as sampling techniques, to the performance of a model to predict the financial distress for companies whose stocks are traded on securities exchanges of Vietnam. A firm is financially distressed when its stocks are delisted as requirement from Vietnam Stock Exchange because of making a loss in 3 consecutive years or having accumulated a loss greater than the company’s equity. There are 12 models, constructed differently in feature selection methods, sampling techniques, and classifiers. The feature selection methods are factor analysis and F-score selection, while 3 sets of data samples are chosen by choice-based method with different percentages of financially distressed firms. In terms of classifying technique, logistic regression together with SVM are used in these models. Data are collected from listed firms in Vietnam from 2009 to 2017 for 1, 2 and 3 years before the announcement of their delisting requirement. The experiment’s results highlight the outperformance of the SVM model with F-score selection method in a data sample containing the highest percentage of non-financially distressed firms