The main purpose of this study is to analyze the natural frequencies of space frames using dynamic stiffness matrix method. The paper is going to present how to establish the dynamic stiffness matrix of the linear frame element bearing axial, torsion and bending in two planes on the basic of inertia to find the exact root of the dynamic balance equation using Euler - Bernoulli beam theory. Then, the matrix above was employed to establish the dynamic stiffness matrix of space frame elements and applied to analysis the natural frequencies of space frames. Comparing the analysis results of the dynamic stiffness method with those of the finite element method showed the accuracy of the dynamic stiffness method. The dynamic stiffness method gave accurate results as soon as the frame was viewed as a single element while the finite element method failed to perform the similar task.

System identification is one of the first things that must be done when solving an automatic control problem because it is impossible to analyze and synthesize the system without the mathematical model that describes the system. This paper presents and simulates the identification method of six phase induction motors using RBF (Radial Basis Function) neural network, identification parameters include speed, torque and the rotor flux on the fixed  shaft system. The RBF neural network is built and trained online based on input and output data of the object. Simulation results using Matlab/Simulink software show that the error of the identification coverges to 0. Identifying parameters follow the object parameters during the engine starting time, after load and is active white noise, the match between output response and recognition response is between 98%-99%. This study is a prerequisite to high performance control methods such as DTC (Direct Torque Control), FOC (Field Oriented Control), Fuzzy Logic be more advantageous.

In this paper, the effects of hydrothermal and calcination conditions on the structure of nano-hydroxyapatite synthesized from Thunnus tonggol bone were studied. The characteristics of samples were determined by various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and optical X-ray fluorescence spectroscopy (XRF). XRD results showed that the hydrothermal and calcination conditions affect the crystallinity and purity of nano-hydroxyapatite product. The suitable conditions for the synthesis of nano-hydroxyapatite have been proposed such as hydrothermal at 120°C in 7 hours and calcination at 800°C in 1 hour. Under the conditions, the hydroxyapatite had the nanoparticle size in a range of 30–100 nm, and reached a BET surface area of 15.8 m2/g, a pore volume of 0.018 cm3/g, and a pore diameter of 23.0 Å. The molar ratio of Ca/P in the nano-hydroxyapatite was 1.67, which would be the expected ratio for hydroxyapatite. The nano-hydroxyapatite product has high crystallinity and biological compatibility when tested in Simulated Body Fluid (SBF).

Voice control is an important function in many mobile devices and smart home systems, especially it is also a solution to help disabled people controlling common devices in their life. This paper indicates a short-controlled speech recognition method using MFCC (Mel frequency cepstral coefficients) and convolutional neural network (CNN) models. The input audio data are wave files that are assumed to be exactly 1 second in duration. A sliding window of size 30 ms with a step of 10 ms slides in turn over the input data to calculate the MFCC parameters. Each input file will obtain 98 MFCC features, each MFCC feature is a 40-dimensional vector (corresponding to 40 coefficients of Mel-scales filters). The research has used 3 Neural Network models to classify these control speech files: 1-layer Vanilla Neural Network model (1 softmax layer), Deep Neural Network - DNN (with 3 fully connected hidden layers) enough and 1 output layer) and the Convolution Neural Network model - CNN. Experiments were performed on Google's "Speech Commands Dataset" dataset. (https://ai.googleblog.com/2017/08/launching-speech-commands-dataset.html) consisting of 65,000 samples divided into 30 classes. Experimental results show that the CNN model achieves the highest classification accuracy of 94.5%.

This study aims to evaluate treatment ability of methyl blue (MB) dyes in water with Fe3O4@SiO2 attached Fe0 particles. The X-ray diffraction (XRD) technique was employed to characterize the structure of nanoparticles. The as-synthesized nanoparticles were analyzed by Fourier transform infrared spectroscopy (FTIR) technique to determine the presence of functional groups and bonds in the molecule. Surface morphology of as-synthesized Fe3O4@SiO2 nanoparticles was studied by scanning electron microscopy (TEM). The magnetic properties of Fe3O4 nanoparticles and Fe3O4@SiO2 attached Fe0 nanoparticles were evaluated by vibrating sample magnetometer technique (VSM). The as-synthesized material was in spherical shape with diameter of 100-500 nm, and its magnetism was 56.29 emu.g-1. The treatment of MB was conducted with 92.8% yield at pH 6.0 followed and fitted to pseudo-second order model and Langmuir isotherm adsoprtion model.

The study aims to assess the possibility of using the Leaf Area Index (LAI) MODIS product and IOT weather data to estimate rice yield at pixel level. MODIS LAI images (product MCD15A2Hv006) acquired at 30 to 40 days after-sowing were aggregated to construct the LAI map for each rice season cropping. The LAI values were converted to relative leaf growth values (RGRL) which were used in the Oryza2000 v3 model to simulate rice yield. The model was calibrated using the data from the season Summer-Autumn 2018. The estimated results were then compared with the statistics-based yield data of the Autumn-Winter 2018, Winter-Spring 2018-2019 and Summer-Autumn 2019 cropping seasons with RMSE values of 0.44 ton, 0.38 ton and 0.31 ton accordingly with nRMSE values of 5.61%, 4.22% và 5.40%. In general, the results obtained show that MODIS LAI product could help to build detailed pixel-level yield estimation maps through a simple image processing method that can be applied for agricultural managers.

Domestic wastewater usually contains a large amount of nitrate and phosphate causing eutrophication and water pollution. Microalgae often accumulate nitrogen and phosphorus from nitrate and orthophosphate to produce their biomass. Therefore, the screening of microalgae that are capable of efficiently absorbing nitrate and phosphate is necessary for initial wastewater treatment. This study investigated the ability to absorb nitrate and phosphate of 6 microalgal strains isolated from domestic wastewater. The results showed that two microalgae strains of phylum Chlorophyta, Chlorella sp.1 and Chlorella sp.2, can remove nitrate and phosphate in the experimental scale with absorption efficiency of > 90% and 88%, respectively. The result of this study suggests that these two Chlorella sp.1 and sp.2 can be used as potential agents for management of nitrate and phosphate in domestic wastewater in the upcoming experiments.

The coral reef fish survey and sampling activities were implemented in the Hai Tac archipelago (Ha Tien city, Kien Giang Province) from 2018 to 2019 using the SCUBA Line Intercept Method. The results showed that the total of 57 reef fish species belonging to 36 genera, 24 families, 6 orders, 1 class were identified. Two coral reef fish species, which are listed in the Vietnam Red Book, were recorded in Hai Tac archipelago. The species diversity in the Northeast monsoon was 8 species higher than in the Southwest monsoon. There were a higher number of fish species in coral reef habitat than in seagrass habitat. The diversity index was on a good level (H' = 2.25). The average density was 608.3±443.0 individuals/ 500 m2 and the density in the Southwest monsoon was lower than in the Northeast monsoon. The fish size < 10 cm in the total body length was accounted for the 80% of the number of observed individuals. This study supplements the data of coral reef fish species diversity in the Southwest Islands of Vietnam.

Cellulose-degrading bacteria and fungi become more important due to their applications in life, especially in degradation of cellulose rich waste and in production of organic fertilizer. From six termite nests collected in Binh Tan district, Vinh Long province, 28 bacteria strains and 7 fungi strains were isolated. All strains isolated were capable of degrading CMC (carboxymethyl cellulose). In which, some the strains that can degrade CMC with high efficiency include 1BTL6 (61.7%), 3BTT6 (65.8%), 2BTNT5 (61.5%) and 1BTNT3 (60.4%). In addition, strain 2BTNT5 has ability to degrade cellulose from straw for glucose production (0.14 mg/L) after 15 days.

The increasing saline intrusion in coastal areas of the Vietnamese Mekong Delta has affected the management of surface water resources for agriculture and aquaculture. This study evaluated the effectiveness in dealing with saline intrusion during the dry season from late 2019 to early 2020 in Ben Tre, based on the principle of clear roles and responsibilities of stakeholders in the OECD (Organization for Economic Co-operation and Development) water resources governance framework. The data were collected through interviews with relevant staff from district authorities and analyzed by descriptive statistics, and GIS tools were used to edit and publish maps. The duration of salinity intrusion in the dry season from 2019 to 2020 was longer, and the spatial range of saline intrusion was wider than the 40-year average, resulting in severe freshwater scarcity and significant agricultural and aquaculture losses. The promulgation of guiding documents to cope with saline intrusion in agriculture and aquaculture was promptly implemented to eliminate saline intrusion driven damages. However, horizontal coordination among local stakeholders could still be limited.

Phytase is widely used in animal raising to help controlling anti-nutritional factors and absorbing effectively phosphor. Among four studied fungi, Trichoderma asperellum showed that the highest phytase productivity in the semi-solid medium that contain 60% of corn powder and 40% of soya meal. The effect of the added mineral solution ratio and the cultured time was optimized by Response Surface Methodology (RSM). At 40% of added mineral solution and in 3.75 days of cultured time, the phytase activity of product get 5.31 UI/g. The highest phytate hydrolysis productivity of product in chicken feed pellets was determined at pH 5.0 with the inorganic phosphor content increase 25.6% for 2 hours. Adding 1% (w/w) of rich-phytase product to the portion showed the inorganic phosphor content in the free-range chicken dungs decreased from 14.5% to 39.1% while the weight of chicken was not different as compared with the control treatment.

Durian (Durio zibethinus) is one of the special fruits in Vietnam favored with high trade in the world. Currently, there are many varieties of durians grown in the Mekong Delta, and it is challenged to distinguish them through morphology. This study was aimed to examine genetic diversity based on DNA barcode and the ISSR molecular marker. The DNA sequences of three barcode DNA candidates, including ITS, matK, rpoC1 of nine varieties (Ri-6, Monthong, Kho Qua Xanh, Chin Hoa, Sua Hat Lep, Chuong Bo, Bi, Musang King, and Sau Huu) collected from Can Tho, Tien Giang, Ben Tre and Vinh Long were sequenced and analyzed. Six SNPs were identified from the ITS sequence between individuals Ri-6-Ben Tre, Monthong-Tien Giang, Chuong Bo-Tien Giang, Sua Hat Lep-Can Tho, and Sau Huu-Tien Giang. For the matK gene, nine SNPs were found to distinguish Ri-6 individuals (Can Tho and Southern Fruit Research Institute), Chin Hoa-Ben Tre, Sua Hat Lep-Ben Tre and Sau Huu-Tien Giang. The rpoC1 gene was highly conservative between varieties in this study. The ISSR molecular markers classified such durian varieties into five groups and showed clear differences between the exotic varieties of Musang King-Vinh Long and Monthong-Tien Giang.

Soursop (Annona murica L.) is known as a fruit that has a delicious and nutritious flavor but is easy to spoil and difficult to preserve. The study was carried out to isolate and select a yeast strain with good fermentation ability in the soursop fruit juice for application in soursop wine production. Thirty yeast strains were isolated and classified belonging to the two genera of Saccharomyces and Pichia. Of which, 4 yeast strains were selected and investigated the fermentation ability of soursop fruit juice (treated with 0.3% of pectinase for 1 hour and adjusted pH to 4 and 25oBrix) for 9 days. The yeast strain FBY015 was selected based on the best fermentation ability with the highest achieved alcohol concentration (10.70% v/v). This yeast strain was identified as Saccharomyces cerevisiae.

Nowadays, the economy is better, consumers' demand for rice has also changed, they prefer rice with high quality such as soft and aroma cooked rice. To meet the demand of consumers about rice, the application of functional markers for selection high quality of rice was carried out to assess quality traits in imported rice varieties from rice GeneBank, Can Tho University for selection high quality rice varieties that cope with the above objectives. DRR-GL marker was used to identify the gene controlling GS3 grain length; while the Wx-in1 marker was used  the Wx gene that controls the amylose trait, and the BADH2 gene control the aroma in rice.  The results showed  that 1 line (IR 86385-172-1-1-B) was with good quality such as elongated rice grain, 7.12mm grain length, amylose content is low 17.51%, very soft gelconsistency (level 1) 86.67mm, medium gelatinization temperature (level 5). This report was the prelimary step to select imported rice lines that may be used as starting materials for the quality breeding program in the future.

Pleurotus spp. mushrooms are very perishable, the shelf life of oyster mushrooms cannot prolong after 24 hours of the storage at room temperature. The objective of this study was to evaluate the effects of soaking fresh oyster mushrooms, including (i) CaCl2 and (ii) citric acid (at concentrations of 0.5; 1; 1.5 and 2% for 5, 10, 15 and 20 minutes, respectively) on the hardness and color of oyster mushrooms. It as well as is to determine (iii) the type and condition of packaging (paper, High-density polyethlene (HDPE), polyethylene terephthalate (PET), perforated-paper, perforared-HDPE and perforated-PET bags) (diameter of hole 7 mm and 8-9 holes /100 cm2) and (iv) storage temperature (3-5oC and 28-30oC) (with 60-62% and 76-78% of air humidity, respectively) to maintain the quality of fresh mushrooms through physical parameters. The results indicated that the hardness and color of oyster mushrooms improved by soaking for 10 minutes in 1.5% CaCl2 and 10 minutes in 1% citric acid. Furthermore, fresh oyster mushrooms packed HDPE bag can prolong the shelf life at 28-30oC for 3 days and at 3-5oC for 18-21 days.

In this study, the next generation sequencing technology was used to resequence the geneome of Doc Phung rice varieties (salt-tolerant variety) and Nep Mo (salt-susceptible variety) to identify functional markers that are involved in salt tolerance mechanisms in Doc Phung rice variety. In comparision with the reference geneome, the result showed that Doc Phung geneome was consisted of 1,918,726 variations of SNP and 163.409 InDels (81,435 insertions, and 81,974 deletion). Whereas in Nep Mo variety, there were 1,931,380 SNPs and 171.663 InDels (88,473 insertions and 83,190 deletion). Most of the variants are located in non-functional regions including upstreams, downstream, and intergeneic, accounting for over 75%. The variation of OsTZF1 (LOC_Os05g10670.1) gene that regulates the expression of those gene related to biological and abiotic stress factors, showed that there were 7 SNPs and 9 nucleotides insertion (encode 3 amino acid arginine) in Doc Phung variety when being compared to Nep Mo based on reference geneome. This information will help the breeders to apply as a molecular marker, using salt-tolerant rice breeding program in the future.

The study was conducted with the main objective of investigating the ability to store fried snakehead fish cakes at low temperatures using edible chitosan film. The contents of the study include (i) determining the appropriate concentration of chitosan used to wrap fried snakehead fish cakes, (ii) studying the ability to preserve fried snakehead fish cakes of different types of chitosan films at cold temperatures, and (iii) assessing the ability to preserve fried snakehead fish cakes of chitosan films under frozen conditions. The study results showed that a chitosan solution of 1.5% concentration is most suitable for wrapping fried snakehead fish cakes. Also, preserving with 1.5% chitosan film combined with sodium tripolyphosphate at a concentration of 0.2%, with a 2-minute dip time, can help improve the ability to inhibit the growth of microorganisms and maintain the quality of fish cake compared to using chitosan films. With the coating support, the preservation time of fried snakehead fish was 8 weeks of cold storage and 12 weeks of frozen storage, respectively with product quality not changing significantly and microbiological safety.

This study was carried out to evaluate the nitrogen conversion of selected nitrifying bacteria from shrimp ponds used for the recirculating system in shrimp culture tanks. The experiment consisted of 4 treatments: Control: no addition of bacteria; Treatment 1: added bacteria AOB TB7.2; Treatment 2: added NOB TV4.2 and Treatment 3: added a mixture of bacteria AOB TB7.2 and NOB TV4.2; each treatment was repeated 3 times. The results showed that the addition of bacteria AOB TB7.2 and NOB TV4.2 to the biofilter of circulatory system reduced the concentration of toxic gases such as ammonia and nitrite in the culture tank, and significantly increased shrimp survival. Moreover, there was no discharged water throughout the culture cycle could minimize the impact on the outside environment. Adding a combination of AOB TB7.2 and NOB TV4.2, the nitrification process took place faster than single supplementation. Nitrification and nitrification rate increased with bacteria addition treatments compared to the control (7 and 14 versus 14 and 35 days, respectively).

Research on morphology and histomorphology development of the digestive tract was carried out from hatching larvae to 35 days old to determine the suitable food for snakehead in this period. Larvae at 3-days old were fed with Moina sp. till the 10th day after hatching (AH) then replaced with trash fish. From day 17th AH, formualated feed was applied.  Fish samples were collected in the morning before feeding on days 1, 3, 5, 7, 9, 12, 15, 18, 21, 25, 30 and 35 for analysis of changes in the gastrointestinal tract. The result showed that, at day 3rd AH, the digestive tract was only a straight and undifferentiated tube. The digestive tract was divided into buccopharynx, esophagus, stomach and intestine distinctly on the 5th AH. The intestine started to fold and the lipid vacuoles in intestine were observed on day 7 AH. The gastric glands appeared on day 12 AH revealing that the development of digestive tract was completed in both morphology and function. The main change afterwards was an increase in folding of gastrointestinal mucosa, mainly in the stomach and the posterior intestines of snakehead fish. After day 18th AH, the stomach muscularis became two-layered and snakehead could digest formulated feed well. This is the appropriate time for weaning to formulated feed.

Disease is one of the most common and impactful risks for aquaculture farmers. A total number of 108 intensive white leg shrimp farmers in Ben Tre province were interviewed to evaluate the financial impact and adopted solutions to disease risk of shrimp farmers. Around 98% of farms reported multiple risks in production, of which disease accounts for 30.77%. White spots, hepatic disease and intestinal disease were reported the most. The disease reduced 279.01 million VND/ha/crop of profit. White spot caused the highest losses (546.33 million VND/ha/crop) and 26% of the households had profit losses. Disease arising in the first stage caused damage to 224.15 million VND/ha/crop. Reacted solutions to disease risk were divided into coping solutions (use of drugs, urgent harvest, destroying the crop, etc.) and preventive solutions (training on farming techniques, water monitoring, high quality and pathogen-free post larve, etc.). The coping solutions were chosen more frequently; the preventive solutions were assessed to be more effective. Therefore, farmers need provisions of high quality seeds and regular trainings to improve techniques in disease prevention and treatment.

This study was conducted under in vitro conditions to assess the effect of culture conditions on the protease production of Streptomyces DH3.4. Experiments were conducted in various pH levels (4, 5, 6, 7, 8 9) and different concentrations of NaCl (0; 0.5; 1; 1,5; 2; 2.5; 3 and 3.5%). The incubation time in the experiment was observed at intervals of 24, 48, 72, 96, 120, 144 and 168 hours. The sources of carbon used in the experiment were glycerol, D-glucose, sucrose, D-maltose, D-xylose, soluble starch with a concentration of 1%. Organic nitrogen sources were chosen such as casein, malt extract, peptone, tryptone, soybean meal, and yeast extract with a concentration of 0.5%. The sources of inorganic nitrogen including KNO3, (NH4NO3), (NH4)2SO4 and NH4Cl were designed with a concentration of 0.1%. Each experiment was run in triplicates. The results showed that the maximum protease production from Streptomyces strain DH3.4 was found under culture conditions adjusted to pH7.0, 1.5% NaCl and 144 hours of incubation. Starch performed the sole source of carbon, whereas malt extract and (NH4)2SO4 were the superior organic and inorganic substrates, respectively.

The remarkable development of computer science had a strong influence on the methods of linguistic research in the mid-twentieth and early twenty-first centuries. With the building of corpora including electronic documents representing a certain language, linguists can quickly access and search authentic language materials for their research topics on the basis of linguistic corpora with huge capacity. Various research teams have also designed the learner corpora as they regconized the potential of corpora for teaching and learning foreign languages. This article provides an overview of corpus linguistics, learner corpora and its applicability in research and teaching of foreign languages ​​through examples for German.

In this paper, Logistic models were used to estimate the impact of determinants on the decision to apply high technologies into coffee production in Central Highlands. The estimated results indicate that there are four important determinants affecting the decision to apply high technologies into coffee production, including age of famer, academic level, years of experience and institutions (access to information, extension services, and credit). Of which the institutions is the most significant factor decision to apply high technologies into coffee production. Based on the quantitative results, the empirical is foudation for some policy on access to technology information, extension services and human training; policies on high-tech human resource training. Contribute to apply high technologies into coffee production in the region. Particularly, high-tech human resource training should be a priority.

The paper is to determine the economic value of U Minh Ha forest ecosystems by estimating the willingness of residents in Tran van Thoi district, Ca Mau province to contribute to the forest conservation project by using the choice modeling (CM) approach. The results showed that residents were willing to pay more for the benefits that U Minh Ha forest offers, such as increasing forest products, reducing forest land loss, and developing ecotourism services. Respondents were willing to contribute an average of 0.5kg of rice monthly to increase the supply of forest products by 10 years, to contribute about 0.9kg of rice monthly if the project can reduce forest land loss by 50%. To increase the ecotourism services by 15%, the respondents were willing to contribute about 1kg of rice every month. These results are very useful to assess the status and affordability of residents in the development of U Minh Ha forest ecosystem.

This study is aimed to analyze the impact of destination attractiveness and place satisfaction on tourists’ environmentally responsible behavior in Da Nang city. Based on survey data of 393 tourists, the methods of exploratory factor analysis, confirmatory factor analysis, and structural equation modeling are used. The results showed that the attractiveness of the destination's core attributes and augmented attributes has positively impacted on place satisfaction and driving tourists’ responsible behavior in Da Nang city. The research contributes to helping local managers understand the factors affecting tourists’ environmentally responsible behavior, thereby proposing strategies to improve tourists’ environmentally responsible behavior when they visit the city.

The objective of this study is to analyze the factors affecting the students' satisfaction with e-learning services. Technology adoption model and successful information system theory are applied to propose model and test hypotheses. The data were collected from 267 students who studied via e-learning platform at some universities in Ho Chi Minh City. The results show that perceived ease of use, perceived usefulness, information quality, system quality, instructor, support services, subjective norm, and perceived behavior control positively affects learners' satisfaction. In addition, implications were proposed for educational institutions to enhance students’ satisfaction through enhancing the quality of e-learning services.

Value chain analysis of exported wooden furniture using Acacia wood in the South of Viet Nam aims to propose value chain upgrading strategies which will enhance competitiveness, expand markets and improve production efficiency. The study methodology were applied the value chain approach of Kaplinsky & Morris (2001), the ValueLinks method of GTZ (2007) and 123 chain actors and stakeholders participated through the use of analytical tools such as value chain description, chain economic analysis and SWOT analysis. The results indicated that there were six basic functions, 15 supported actors, 04 market channels in this value chain. In the most popular channel, one cubic meter of Acacia log wood material created 7,026,500 VND of value added, 1,585,600 VND of net value added of whole chain. Currently, the value chain has 11 advantages and 13 disadvantages. Four solutions were proposed for upgrading value chain of exported wooden furniture using Acacia wood in the South of Viet Nam, including (1) upgrading product standards and quality, (2) reducing production and operational costs, (3) investing to increase output and reduce labor intensity and (4) improving distribution system.

This study was conducted to analyze factors influencing the number of preventative measures against African swine fever that pig raising households in Dong Nai province had been implemented from collected data from 140 households using convenience sampling. The KAP framework (Knowledge-Attitude-Practice) and Poisson regression model were used. Research results showed that the number of households whose swines were infected accounted for 70% of the surveyed sample, and the scale of damage was mostly below 200 swines per household. Pig raising farmers can recognize several symptoms of the disease, but there remained some warning signs that were not compeletely noticed. Most of the households implemented 9 to 12 preventative measures at their farms, accounting for 65% of the sample. The regression results revealed that variables having statistically significant and positive correlation with the amount of implemented preventative measures were knowledge, the level of anxiety about risks of infection, and experience in dealing with previous diseases. Thus, if swine households have better knowledge of the disease, have more experience from dealing with previous infectious diseases, and worry about the infectious risks of their swines, they will be more active in implementing preventative measures.