Development of a detailed model for process-based simulation of nitrification in waterbodies and integration into a hydrodynamic water quality model

Nitrifikation ist ein Zweistufenprozess, der unter geeigneten Bedingungen durch zwei unterschiedliche chemolithotrophe Bakterien hervorgerufen wird. Geeignete Bedingungen sind vor allem ausreichend vorhandener Sauerstoff und geeignete pH-Werte für das Wachstum der Bakterien. Wenn eine der Bedingungen nicht gegeben ist, wird die Nitrifikation gehemmt und kann nicht vollständig stattfinden. Dies kann zu hohen Gehalten an Nitrit bzw. Ammoniak im Gewässer führen und sich toxisch auf die Fauna des Gewässers auswirken. Viele vorhandene Gewässergütemodelle betrachten die Nitrifikation vereinfacht als einstufigen Prozess. Die getrennte Oxidation von Ammonium zu Nitrit und weiter zu Nitrat wird vernachlässigt, ebenso die Abhängigkeit der Nitrifikation von der Bakterienanzahl, dem pH-Wert und der Substratverfügbarkeit. Ziel dieser Arbeit war es, am Beispiel des Tay Ninh Flusses in Vietnam die Hemmung der Nitrifikation zunächst experimentell zu untersuchen, darauf aufbauend umfassende Prozessgleichungen zur Simulation der Nitrifikation zu entwickeln und diese an die Versuchsergebnisse anzupassen. Im Anschluss waren die Prozessgleichungen in ein renommiertes vorhandenes Gewässergütemodell zu integrieren. Mit dem Modell waren die Wasserqualität und die Hemmung aussagekräftig als Zeitreihe zu simulieren und zu bewerten. In der Arbeit wurde zunächst die Nitrifikation des Flusses näher untersucht. Es wurde eine Hemmung der Ammoniumoxidation festgestellt, die auf die niedrigen pH-Werte des Flusses zurückzuführen war. Dahingegen war die Nitritoxidation kaum gehemmt. Um den pH-Einfluss auf die Nitrifikation des Flusses genauer zu quantifizieren, wurde ein Nitrifikationsversuch durchgeführt. Anschließend wurde ein detailliertes mathematisches Modell mit dem Namen DYSIN zur umfassenden prozessbasierten Simulation der Nitrifikation von Gewässern entwickelt. Das Modell enthält fünf miteinander verknüpfte Differentialgleichungen. Mit Hilfe des oben beschriebenen Experiments wurde DYSIN verifiziert, der in-situ-Nitrifikationsversuch konnte sehr gut nachgebildet werden. Die Prozessgleichungen von DYSIN wurden anschließend in das Gewässergütemodell CE-QUAL-W2 implementiert. Die guten Simulationsergebnisse deuten auf die Fähigkeit des erweiterten CE-QUAL-W2 hin, aussagekräftigere Prognosen als mit dem alten Modell zu liefern. Das erweiterte CE-QUAL-W2 kann an allen Gewässern eingesetzt werden. DYSIN kann auch in andere hydrodynamische Gewässergütemodelle eingebaut werden.Nitrification is a two-step process, which is induced under appropriate conditions by two groups of chemolithotrophic bacteria. Appropriate conditions are above all sufficiently available dissolved oxygen and appropriate pH-values for bacterial growth. Should any of the conditions be missing, the nitrification process will be inhibited and not be completed, which causes high nitrite and ammonia concentration in water body, which in turn has a toxic impact on the fauna in the water body. In many of the already existing models, the two-step nitrification is simplified to a one-step process. The separate oxidation of ammonium to nitrite und further to nitrate is omitted. The dependency of the nitrification on the amount of bacteria, as well as on the pH-value and the availability of substrate are also not taken into account. The objective of the dissertation was firstly to investigate the nitrification inhibition of the Tay Ninh river in Vietnam by means of an experiment. After that detailed process equations to simulate the nitrification were developed and fitted to the results of the experiment. These equations were integrated into a well-known water quality model which was then used to produce and evaluate a time series that describes the water quality and the nitrification inhibition. In the dissertation, the nitrification in the river was firstly examined in detail by means of monitoring. An inhibition of the ammonium oxidation process was observed, which could be due to the low pH of the river. On the contrary, the nitrite oxidation was only minimally inhibited. In order to better quantify the impact of pH on the nitrification process in river, a nitrification experiment was carried out. After that, a detailed and process-based mathematical model named DYSIN was developed to comprehensively simulate the nitrification in water bodies. The model contains five coupled differential equations. The DYSIN model was verified using data obtained from the experiment mentioned above and could very well reproduce the in-situ nitrification experiment. The process equations of DYSIN were then implemented in the well-known model CE-QUAL-W2. The extended model gave more realistic simulation results, which indicates that it can be used to provide more accurate prognoses than what the old version could give. In principle, the extended model can be applied to all water bodies. DYSIN can also be implemented in other hydrodynamic water quality models

Theoretical Framework on the Role of Knowledge Management for Students on Academic Performance

Knowledge management is a developing sector that has received lots of consideration and support from the community which is industrial. Knowledge management is a young academic field which has not been built up a systematized and unified framework. This paper reviews the role of knowledge management for students on academic performance by using the structural equation modeling. Through applying knowledge management in the study process can help students to gain better results. As a result, it can be expected to shed light on the relative importance of knowledge management on students’ academic performance. Keywords: Knowledge management, Academic performance, digital economy DOI: 10.7176/IKM/11-2-05 Publication date:March 31st 202

A Review of Salary Policies for Vietnamese Civil Servants from 2010 to 2019

The public- sector salary policy is an important part of the socio-economic policy system, directly related to the balances of the economy, state budget and the life of the salary earners. This paper rests on secondary data that are legal documents on salary policy, related data and literature officially published to describe and analyse the salary system for Vietnamese civil servants in governmental agencies from 2010 to 2019. Some issues are outlined for consideration. First, how civil servants are ranked and salary policies for them from 2010 to 2019 are. The salary policy includes salary formula, base pay, minimum wage, allowances, components of the pay scale, pay rise rules. Second, their four characteristics are drawn out consisting of the stable and unified legal system; career-based grade pay system; many allowances; the salary system tends to pay for performance, be market-oriented but not really achieved. Third, some comments, pros and cons of the salary system in this period are explored. Finally, it is summarized that some suggestions, recommendations to improve Vietnamese civil service salary system through minimizing its disadvantages and promoting inherent advantages. Keywords: Vietnam, salary policy, salary system, public sector, civil servants, career-based system DOI: 10.7176/PPAR/9-11-03 Publication date: November 30th 201

Determining the Price of Software Products in Software Manufacturing Firms in Vietnam

From the early 2000s to the present, Vietnam has made efforts to facilitate the development of information technology industry and to promote the growth of it market in general and software in particular. Many policies and measures to encourage the development of software firms have been issued by the government. However, despite enjoying favorable conditions from the State's support policy, software firms still face many difficulties in product consumption. In addition to illegally copying software and copyrighted software that have been severely damaged, causing great harm to manufacturers, there are also situations where products are not sold with the right value. Currently, in Vietnam there is not yet a method of calculation, as well as a complete unified accounting for the determination of software product price, each firm follows its experience. Based on data collected, both primary and secondary, we synthesize, evaluate, compare and analyze the research topic. The results show that the determination of software product price at software manufacturing firms is not very reasonable; the recognition and allocation of core software value has not been proper. So based on the findings, some recommendations are given for improving the determination of product prices at software manufacturing firms in the context of developing countries like Vietnam. Keywords: Software, core software, intangible fixed asset, license. DOI: 10.7176/EJBM/11-14-12 Publication date:May 31st 201

Performance implications of exploratory and exploitative innovation: the role of management control systems

Drawing on prominent theories of innovation, this study investigates the inter-relationships between the use of management control systems (MCS), exploratory innovation, exploitative innovation, and firm performance in Vietnam, an emerging market. The research hypotheses were empirically tested using a partial least squares-structural equation model. Data were collected by survey questionnaires from a sample of 238 top-level and middle-level managers in Vietnamese firms. The results confirm that the diagnostic use of MCS has a significant positive effect on exploitative innovation and the interactive use of MCS has a significant positive effect on both exploratory innovation and exploitative innovation. The results also reveal that exploitative innovation and exploratory innovation partially mediate the relationship between the interactive use of MCS and firm performance. Understanding these relationships can assist Vietnamese firms to invest appropriately in MCS that is able to promote innovation actions, thereby achieving outstanding performance

Using metagenomics tool to evaluate the enrichment efficiency of methanogens in marine sediment in Truong Sa archipelage, Khanh Hoa province, Vietnam

Methanogens (archaea bacteria that produce methan) play an important role in the anaerobic digestion of organic waste, however, in marine environment, the low density of methanogens makes anaerobic digestion very slow. In this study, we used methagenomics tool to evaluate the enrichment efficiency of methanogens communities in marine sediments as a basis for building a anaerobic microbial formulation to treat organic waste in marine environment. The results of determination of methanogen density by MPN method have shown that methanogen has been accumulated with higher density (up to 3.2.107 MNP/ml) through 2 times of enrichment in artificial seawater with CH3COONa 10 mM substrate. In addition, metagenomics data have also shown a decrease in the number of archaea species through each enrichment, indicating that methanogenic species have gradually dominated the microbial community. This is the first study on using metagnenomics tools to evaluate the enrichment of methanogens in marine sediment samples in Truong Sa archipelago, Vietnam. Metagenomics data help provide more reliable evidence in microbial studies, especially in obligate anaerobes such as methanogens

Multivariate statistical assessment of a polluted river under nitrification inhibition in the tropics.

A large complex water quality data set of a polluted river, the Tay Ninh River, was evaluated to identify its water quality problems, to assess spatial variation, to determine the main pollution sources, and to detect relationships between parameters. This river is highly polluted with organic substances, nutrients, and total iron. An important problem of the river is the inhibition of the nitrification. For the evaluation, different statistical techniques including cluster analysis (CA), discriminant analysis (DA), and principal component analysis (PCA) were applied. CA clustered 10 water quality stations into three groups corresponding to extreme, high, and moderate pollution. DA used only seven parameters to differentiate the defined clusters. The PCA resulted in four principal components. The first PC is related to conductivity, NH4-N, PO4-P, and TP and determines nutrient pollution. The second PC represents the organic pollution. The iron pollution is illustrated in the third PC having strong positive loadings for TSS and total Fe. The fourth PC explains the dependence of DO on the nitrate production. The nitrification inhibition was further investigated by PCA. The results showed a clear negative correlation between DO and NH4-N and a positive correlation between DO and NO3-N. The influence of pH on the NH4-N oxidation could not be detected by PCA because of the very low nitrification rate due to the constantly low pH of the river and because of the effect of wastewater discharge with very high NH4-N concentrations. The results are deepening the understanding of the governing water quality processes and hence to manage the river basins sustainably

Genetic Diversity and Population Structure of Canarium tramdenum Dai and Yakovl. in Northern Vietnam

Canarium tramdenum occurs naturally in subtropical and tropical regions of Indochina and China. The wood is used for making high quality furniture and the fruit and leaves are used in traditional medicine. However, a lack of information on genetic diversity and population structure has handicapped the genetic conservation and domestication of this high-value species. This study evaluated genetic variation within and among four C. tramdenum populations. Sixty individuals were collected from four natural populations in Vietnam in the provinces of Ninhbinh, Bacgiang, Nghean, and Backan. Genetic diversity and genetic structure were determined using 20 ISSR markers. A total of 192 DNA fragments with sizes ranging from 110 bp to 3,000 bp were detected, of which 154 segments (80.2%) were polymorphic and 38 segments (19.8%) were monomorphic. The ISSR data indicated a moderate degree of genetic diversity for the species (h = 0.252). The four populations were separated into three genetic clusters with low levels of genetic distance between them. AMOVA result showed that most (78%) of the genetic variation was within the populations. The moderate to high genetic diversity of C. tramdenum and the low genetic differentiation among populations suggested that all existing natural populations in the particular regions needed to be preserved to protect the genetic diversity of this species

TỔNG HỢP VẬT LIỆU Ni/UiO-66 THEO PHƯƠNG PHÁP TRỰC TIẾP VÀ GIÁN TIẾP

An archetypal metal-organic framework, UiO-6,6, synthesized with the solvo-thermal method, has a large specific surface area of 1071 m2·g–1. This material was modified with NiCl2 in the direct (Nix(tt)/UiO-66) and indirect (Nix(gt)/UiO-66) methods. The two modified materials were characterized by using powder X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. Their crystalline and chemical structure is not much different. However, the thermal and porous properties differ from each other.UiO-66 là họ vật liệu khung hữu cơ kim loại tổng hợp bằng phương pháp nhiệt dung môi có diện tích bề mặt riêng lớn (1071 m2·g–1). Vật liệu UiO-66 này được biến tính bằng NiCl2 theo phương pháp trực tiếp (Nix(tt)/UiO-66) và gián tiếp (Niy(gt)/UiO-66). Kết quả đặc trưng hai vật liệu biến tính này bằng nhiễu xạ tia X, hiển vi điện tử quét và phổ hồng ngoại khác nhau không đáng kể. Tuy nhiên, phân tích nhiệt trọng lượng và đẳng nhiệt hấp phụ – khử hấp phụ N2 cho thấy có sự khác nhau giữa các phương pháp tổng hợp

LEARNING IDIOMS FOR ENGLISH MAJORS: VIETNAMESE STUDENTS’ PERCEPTIONS OF DIFFICULTIES AND LEARNING STRATEGIES

Learning idioms play an influential role in language generally and in English notably. Comprehending idioms assists language learners in integrating culture, enhancing skills, and ameliorating English levels. Numerous studies have analyzed the function of idioms in second language acquisition (Cieślicka, 2015). This study investigates the difficulties and strategies used in learning idioms by English-majored students at a regional public university (PU) in the south of Vietnam. This paper furnishes data showing learners’ perceptions of facing complications and learning methods. The samples consisted of 150 undergraduate EFL students from English-medium instruction programs. The data was analyzed by utilizing descriptive and inferential statistics. The findings reveal that students struggle to understand idiomatic terms without specific, understandable contexts. Furthermore, the results indicate that the most frequently employed strategies are guessing the meaning of idioms, learning idioms through keywords, and learning from a range of sources, particularly via media. The findings also mentioned that low-proficiency and high-proficiency students encounter identical challenges, with no significant differences. The study's results revealed that the majority of students have difficulty acquiring, recognizing, and interpreting idioms. The findings indicated that guessing the implication of idioms is the most used strategy.  Article visualizations