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Relevance. Despite the use of alkali stripping technology for processing monazite concentrate in industry, this method has a number of limitations, such as low efficiency of concentrate stripping, the need to use a large excess of alkali and a long process time. Aim. Improvement of existing technology to overcome these limitations. Methods. Fusion with NaOH under pressure and fusion with NaOH combined with ball milling, as well as fusion with NaOH using high intensity ultrasound. High-intensity ultrasound has long been studied and used in industry to intensify leaching/alloying in various applications to increase efficiency and speed in leaching for copper, vanadium, nickel, bauxite and uranium ores. This article is devoted to studying the influence of high-intensity ultrasound on the efficiency of opening monazite concentrate with NaOH solutions. Experimental data were obtained using mass spectrometric, X-ray diffraction and ICP-OES analysis methods. Results and conclusions. The optimal conditions for leaching batches of samples weighing from 100 g to 1 kg were determined. The authors have carried out the research on the separation of radioactive elements and impurities in a solution of rare earth chlorides, obtaining a solution of rare earth chlorides purified from radioactive components and impurities. It was shown that ultrasonic exposure eliminates the disadvantages of traditional fusion technology with NaOH, which can be used for deep processing of Vietnamese monazite concentrate. The conditions for obtaining REE chlorides from a previously opened monazite concentrate are given.

Irradiation is known as a handful measure to inhibit potato sprouting, kill harmful bacteria, and increase preservation. The absorbed dose is one of the essential characteristics of the irradiation process. In this study, the depth-dose distributions in potatoes and polymethyl methacrylate were investigated under low-energy X-ray irradiation by using the Fricke dosimeter and Gafchromic film dosimeter. The dose rates required for the rays to penetrate in polymethyl methacrylate were compared with those in potatoes. Polymethyl methacrylate could be used as a phantom in measuring the depth dose delivered in potatoes. The difference in depth-dose distribution in potatoes between one-sided and double-sided irradiation was also investigated. The calculated dose uniformity ratio values are 5.8 and 1.9 for potatoes irradiating one-sided and double-sided.

Background: The Ho-Chi-Minh-city Heart Institute in Vietnam took part in the Optimize Heart Failure (OHF) Care Program, designed to improve outcomes following heart failure (HF) hospitalization by increasing patient awareness and optimizing HF treatment. Methods: HF patients hospitalized with left ventricular ejection-fraction (LVEF)

In Vietnam, a great number of toxic substances, including carcinogens and procarcinogens, from industrial and agricultural activities, food production, and healthcare services are daily released into the environment. In the present study, we report the development of novel yeast-based biosensor systems to determine both genotoxic carcinogens and procarcinogens by cotransformation with two plasmids. One plasmid is carrying human CPR and CYP (CYP3A4, CYP2B6, or CYP2D6) genes, while the other contains the RAD54-GFP reporter construct. The three resulting coexpression systems bearing both CPR-CYP and RAD54-GFP expression cassettes were designated as CYP3A4/CYP2B6/CYP2D6 + RAD54 systems, respectively and used to detect and evaluate the genotoxic potential of carcinogens and procarcinogens by selective activation and induction of both CPR-CYP and RAD54-GFP expression cassettes in response to DNA damage. Procarcinogens were shown to be predominantly, moderately or not bioactivated by one of the CYP enzymes and thus selectively detected by the specific coexpression system. Aflatoxin B1 and benzo(a)pyrene were predominantly detected by the CYP3A4 + RAD54 system, while N-nitrosodimethylamine only moderately activated the CYP2B6 + RAD54 reporter system and none of them was identified by the CYP2D6 + RAD54 system. In contrast, the genotoxic carcinogen, methyl methanesulfonate, was detected by all systems. Our yeast-reporter system can be performed in 384-well microplates to provide efficient genotoxicity testing to identify various carcinogenic compounds and reduce chemical consumption to about 53% as compared with existing 96-well genotoxicity bioassays. In association with a liquid handling robot, this platform enables rapid, cost-effective, and high-throughput screening of numerous analytes in a fully automated and continuous manner without the need for user interaction.

The present study contributes information to the testicular development and reproductive aspects of Glossogobius giuris (Hamilton 1822), one of the target fishes in the Mekong Delta. Trawl nets were used to monthly collect fish specimens from January to December 2020 in four sites along Bassac River, from Cai Rang, Can Tho (CRCT) to Long Phu, Soc Trang (LPST), Hoa Binh, Bac Lieu (HBBL) and Dam Doi, Ca Mau (DDCM). Data analysis of 632 Glossogobius giuris individuals showed that five-stage of sperm development was found in testis histological slides. At stage IV of the testis, different phases of the sperm were observed, indicating that it is a multi-spawner, releasing sperms many times during the breeding season. Further analyses of the testis about apparent frequency and gonadosomatic index showed that this goby can release sperms monthly with a peak in the main wet season. The length at first maturity was observed at 7.24, 7.18, 7.43, and 6.57 cm of TL in CRCT, LPST, HBBL, and DDCM, respectively. The findings contribute essential information to fish population management and sustainable exploitation.

Glossogobius sparsipapillus is one of the gobies that inhabits brackish and freshwater regions in the Mekong Delta. However, data on the biological parameters of this species population are limited. Therefore, the present study aims to provide the necessary knowledge on the fishing status of this goby living in freshwater (Cai Rang, Can Tho: CR) and brackish water regions (Long Phu, Soc Trang: LP). Data analysis results of 1379 individuals showed that males outnumbered females in LP (374 males: 288 females); the reverse case was found in CR (351 males: 366 females). There were five-six classes of length frequency, with the highest values between 8 and 12 cm (1122 individuals, 81.36%). The von Bertalanffy curve was L = 15.75(1 − e−0.62(t + 0.30)) in CR and L = 15.85(1 − e−0.83(t + 0.23)) in LP. Its longevity was 4.84 yrs in CR and 3.61 yrs in LP. The growth performance was 2.19 in CR and 2.32 in LP. The total, natural, and fishing mortalities were 2.17 yr−1, 1.49 yr−1, and 0.68 yr−1 in CR; 3.46 yr−1, 1.68 yr−1, and 1.78 yr−1 in LP, respectively. The fish stock has not been overexploited as E (0.31 in CR and 0.51 in LP) were lower than E0.1 (0.465 in CR and 0.652 in LP) 0.3.46 yr−1, 1.68 yr−1, and 1.78 yr−1 in LP, respectively. The fish stock has not been overexploited as E (0.31 in CR and 0.51 in LP) were lower than E0.1 (0.465 in CR and 0.652 in LP).

This study supplies knowledge on the reproductive traits of Glossogobius aureus, one of the commercial fishes living in brackish water and freshwater. A collection of 742 G. aureus specimens was caught using gill nets from January to December 2020. The results of the gonadal breeding frequency and gonadosomatic indices showed that G. aureus spawned year-round, but with higher activity during four months, from August to October, of the wet season. Size at first maturity (Lm) of males was higher than that of females in all study sites. The batch fecundity (F) was 1044–27,349 eggs/female and increased with fish size, as shown by the high determination values (r2 > 0.6). The study results provide new references on the reproductive biology of the population of Glossogobius aureus which will help in the sustainable management of its fisheries in the studied areas.

Periophthalmodon septemradiatus (Hamilton, 1822) is a unique mudskipper living in the mudbanks from estuarine to riverine regions in the Vietnamese Mekong Delta (VMD), but there is no data on its growth patterns and condition factors that are helpful for fish resource assessment and adaptation understanding. This study was conducted at five sites, from the lower (Soc Trang province) to middle (Can Tho city) and upper (An Giang province) reaches of Bassac River in VMD, to provide knowledge on growth patterns and condition factors to this mudskippers. Fish samples were caught using traps and hands for 24 months, from July 2017 to June 2019, at these five sites. The total length and weight of 3,417 individuals (1,340 females and 2,077 males) varied by sex, season and site (p < 0.001 for all cases). This species exhibited a positive allometric type as the slope (b = 3.06 ± 0.01) of the length-weight relationship (LWR) was >3 (p < 0.001) for both sexes. The growth pattern changed with sex as mudskipper showed isometry in females but positive allometry in males. Maturity also affected fish growth type since it shifted from negative allometry in immature groups to positive allometry in mature groups. The growth pattern of fish changed from isometry in the dry season to positive allometry in the wet season. The mudskipper showed isometry at the lower reaches in Soc Trang but positive allometry at the middle and upper reaches in Can Tho and An Giang. The condition factor (CF) did not change according to sex, size and season, but with month and site variables. The present environmental condition in these studied sites tended to be not good enough for this fish as CF (0.95 ± 0.01) was less than 1 (p < 0.001). The findings provided basic information on the growth and adaptation of P. septemradiatus being helpful in fish adaptation understanding and resource conservation in VMD.

Growth pattern and condition factor (CF) are essential to fish resource assessment but limited to Periophthalmus gracilis—an amphibious fish living in the mudflats along the Indo-Pacific regions, including the Mekong Delta (MD), Vietnam. This study lasted from April 2020 to March 2021 to verify if their growth pattern and CF change with sex, size, season, month and site. The total length and weight of 486 individuals (236 females and 250 males) were 2.9–5.9 cm and 0.13–1.66 g, respectively. The mudskipper displayed negative allometry as the slope value (b = 2.69 ± 0.06) obtained from length and weight (LWR) was significantly less than 3 (p < 0.01), indicating that most fish specimens were caught in the immature stage. The fish growth pattern did not change with sex as both males and females displayed negative allometry but varied by size since the mudskipper showed negative allometry in the immature group and isometry in the mature group. Likewise, growth type changed with season since fish showed negative allometry in the dry season but isometry in the wet season. As the slope value (b) varied by site and month, the mudskipper displayed spatiotemporal growth patterns, ranging from negative to positive allometry. The CF was impacted by sex as this value of females (1.09 ± 0.02) was higher than that of males (0.96 ± 0.01, p < 0.01). Besides, CF was regulated by fish length since this value was higher in the mature group (1.12 ± 0.03) than in the immature group (1.01 ± 0.01, p < 0.01). Likewise, CF was affected by season as this value was higher in the wet season (1.05 ± 0.02) than in the dry season (0.99 ± 0.01, p < 0.01). Although the CF varied with site and month variables (p < 0.01), this value (1.02 ± 0.01) was generally higher than 1, showing fish adapted well to their habitat. The fish length at first capture should be increased to exploit this species sustainably.

Length-weight relationship (LWR), growth pattern and condition factor (CF) play a vital role in fish resource evaluation and management but data on this is limited for Periophthalmus variabilis. This is an amphibious fish that lives in the mudflats of the mangrove forests in the Western Pacific regions, including the Vietnamese Mekong Delta (VMD). This paper contributes to the understanding of the LWR, growth pattern and CF of P. variabilis. Fish specimens were collected by hand at four sites in the VMD from April 2020 to March 2021. The analysis of 495 individual fish (259 females and 236 males) showed that fish weight could be estimated from a given fish length due to high determination values (r2 = 0.70 − 0.97). Dusky-gilled mudskippers of the VMD exhibited positive allometry, as indicated by their larger than 3 b value (b = 3.094 ± 0.045, p = 0.04). However, the growth pattern of the mudskipper between the sex and maturation stage (immature versus mature) showed isometry. These fish displayed positive allometry in the dry season (b = 3.138 ± 0.065) (>3, p = 0.04) but isometry in the wet season (b = 3.058 ± 0.061) (≈3, p = 0.34). Fish growth ranged from isometry to positive allometry and varied by site (b = 2.850 ± 0.103–3.370 ± 0.114) and month (b = 2.668 ± 0.184–3.588 ± 0.299) based on the b value. The CF of P. variabilis was not affected by sex (p = 0.29), body size (p = 0.64) or season (p = 0.43), but was affected by site (p = 0.01) and month (p = 0.01). The CF of this species (1.05 ± 0.02) was higher than 1 (p

Abstract Populations of Periophthalmus chrysospilos, the Gold‐spotted mudskipper, within the Mekong Delta are facing extirpation risks due to indiscriminate harvesting for the growing aquarium and food‐fish trade. This study provides some of the first information on reproductive ecology—such as spawning type and season, length at first maturity, and batch fecundity—of this species, to be used in their management. The sex ratio of wild populations, based on 1031 individuals (523 males and 508 females) is 1:1. The gonadosomatic index (GSI) values are exhibit a non‐normal distribution and changed with gender, season, and site. A combination of GSIs and the monthly appearance of mature gonads suggest that this species reproduces throughout the year, with peak from July to October. This species exhibits sexual and spatial variation in size at first maturity (Lm) as Lm is 6.2–8.6 cm in males and 6.4–7.3 cm in females. The batch fecundity (F = 2614 to 23,465 eggs/female) exhibits non‐normal distribution and varies with site, with the highest values at Dam Doi, Ca Mau (13,336 ± 1,279 SE) and the lowest at Tran De, Soc Trang (6654 ± 851 SE). In addition, batch fecundity is directly proportional to body size due to high determination relationships between batch fecundity and fish size (r2 > 0.64 for all cases). Information derived on the reproductive biology of this species can inform its conservation, sustainable exploitation, and ex situ propagation.

The food composition and feeding ecology of fishes living in the intertidal zone play an essential role in understanding the energetic connectivity between terrestrial and aquatic systems. Periophthalmus chrysospilos is an amphibious fish species occurring in the intertidal zone, but data on its diet and foraging ecology is still poorly known. This study on Ps. chrysospilos was carried out from April 2020 to March 2021 at four sites within the Mekong Delta estuary to define the influence of spatio-temporal factors on the diet of this species. The diet composition and relative gut lengths (RGLs) of Ps. chrysospilos were analysed in relation to four parameters—sex, size, site, and season. A total of 1,031 individuals were collected, and their digestive tract lengths were used to calculate the RGL. The digestive tracts of only 546 individuals were with food items (approximately 1:1 of empty vs full digestive tract) and were subsequently used for further analyses. The ranges in total length and weight in both adult and juvenile individuals were 3.4–10.6 cm and 0.38–14.13 g, respectively. The RGL values varied with season, fish size and site, but was always lower than 1, indicating a predominantly carnivorous diet. The variability of food items found within the digestive tracts demonstrated its adaptability in pursuing prey items within the limits of the littoral zone, and its importance as a conduit of terrestrial-marine connectivity. This species is characterised as an opportunistic mesopredator feeding primarily on Acetes spp., Uca spp., Dolichoderus sp., and rarely on Polychaeta and Actinopterygii. Other items found within the digestive tract are Mollusca, and detritus. The diet composition of Ps. chrysospilos did not vary with season and size, but changed with sex and site parameters. Uca spp. contributed to the sexual variation in dietary component, whereas Mollusca, Uca spp., Dolichoderus sp. and detritus, were drivers for spatial variation in the dietary component. The research provides fundamental information on diet composition and feeding strategy, as well as contributes towards knowledge on foraging ecology and resource use by intertidal animal communities.

In this study, an integrated forecasting model was developed by combining the ensemble empirical mode decomposition (EEMD) model and gated recurrent unit (GRU) neural network to accurately predict the rooftop solar power output at a specific power unit located in Tay Ninh province, Vietnam. The EEMD method was employed to decompose the solar power signals into multiple frequencies, allowing for a more comprehensive analysis. Subsequently, the GRU network, known for its ability to capture long-term dependencies, was utilized to forecast future values for each decomposition series. By merging the forecasted values obtained from the decomposition series, the final prediction for the solar power output was generated. To evaluate the efficacy of our proposed approach, a comparative analysis was undertaken against other forecasting models, including a single artificial neural network, long short-term memory network, and GRU, all of which solely considered the solar power series as input features. The experimental results provided compelling evidence of the superior performance of the EEMD-GRU model, especially when incorporating weather variables into the forecasting process, achieving the best results in all three forecasting scenarios (1-step, 2-step, and 3-step). For both forecasting targets, Inverter 155 and 156, the n-RMSE indices were 1.35%, 3.5%, and 4.8%, respectively, significantly lower than the compared single models. This integration of weather variables enhances the model's accuracy and reliability in predicting rooftop solar power output, establishing it as a valuable tool for efficient energy management in the region. [ABSTRACT FROM AUTHOR]

Offshore wind energy is a renewable energy source that is developing fast. It is considered to be the most promising energy source in the next decade. Besides, the expanding trend for this technology requires the consideration of diversified seabeds. In deep seabeds, floating offshore wind technology (FOWT) is needed. For this latter technology, such as for conventional WT, we need to consider aspects related to performance, aerodynamic force, and forces during operation. In this paper, a two-bladed downwind wind turbine model is utilized to conduct experiments. The collective pitch and cyclic pitch angle are adjusted using swashplated equipment. The fluid forces and moments acting on the rotor surface are measured by a six-component balancing system. By changing the pitch angle of the wind turbine blades, attempts are made to manage the fluid forces generated on the rotor surface. Under varied uniform wind velocities of 7, 8, 9, and 10 m/s, the effect of collective pitch control and cyclic pitch control on the power coefficient and thrust coefficient of FOWT is then discussed. Furthermore, at a wind speed of 10 m/s, both the power coefficient and loads are investigated as the pitch angle and yaw angle change. Experimental results indicate that the combined moment magnitude can be controlled by changing the pitch-angle amplitude. The power coefficient is adjusted by the cyclic pitch-angle controller when the pitch-angle phase changes. In addition, the thrust coefficient fluctuated when the pitch angle changed in the oblique inflow wind condition. [ABSTRACT FROM AUTHOR]

Glossogobius aureus (Gobiiformes: Gobiidae) is a target fish and widely distributed in the Mekong Delta, from fresh to brackish waters. However, knowledge on its food and feeding ecology is scarce. Therefore, this research was carried out in four sampling sites along the estuarine of Hau River in order to fill this information gap. A total of 742 individual fish was collected monthly using trawl nets from January to December 2020. A combined analysis of the fullness index and Costello graph suggested that this fish species displayed high feeding intensity. The results revealed that G. aureus is a carnivore and its food composition comprised Acetes spp., Actinopterygii, zooplankton, and other preys (e.g. snails and detritus). Acetes spp. is the main food of this species. The diet composition varied with sites but not genders, fish sizes, and seasons. Acetes spp., Actinopterygii and other preys contributed to the spatial variation of food composition. The findings revealed knowledge about the fish feeding ecology, which may propose suitable foods for its aquaculture development. [ABSTRACT FROM AUTHOR]

The development of lightweight automotive parts is an important issue for improving the efficiency of vehicles. Polymer composites have been widely applied to reduce weight and improve mechanical properties by mixing polymers with carbon fibers, glass fibers, and carbon nanotubes. Polypropylene (PP) has been added to carbon fiber-reinforced nylon-6 (CF/PA6) composite to achieve further weight reduction and water resistance. However, the mechanical properties were reduced by the addition of PP. In this research, multiwalled carbon nanotubes (CNTs) were added to compensate for the reduced mechanical properties experienced when adding PP. Tensile testing and bending tests were carried out to evaluate the mechanical properties. A small amount of CNTs improved the mechanical properties of carbon fiber-reinforced PA6/PP composites. For example, the density of CF/PA6 was reduced from 1.214 to 1.131 g/cm3 (6.8%) by adding 30 wt % PP, and the tensile strength of 30 wt % PP composite was improved from 168 to 173 MPa (3.0%) by adding 0.5 wt % CNTs with small increase of density (1.135 g/cm3). The developed composite will be widely used for lightweight automotive parts with improved mechanical properties.

This present study provides an overview of the reproductive traits, including ovarian development, spawning season, size at maturity (Lm), and fecundity of Acentrogobius viridipunctatus - a high economic value fish in the Vietnamese Mekong Delta (VMD). A total of 432 females were collected using trawl nets from January to December 2020 at four sites, including Long Huu-Tra Vinh (LHTV), Trung Binh-Soc Trang (TBST), Dien Hai-Bac Lieu (DHBL), and Tan Thuan-Ca Mau (TTCM). The ovarian diameter was seen to increase from 2.09 (stage I) to 6.57 mm (stage V). Histological analysis showed that the goby was a multi-spawner due to the different oocyte stages found in stages IV and V of ovaries. It can release eggs all year-round due to the monthly appearance of ovarian stages IV and V during the study period, with the main peak in the 2-4 months of the wet season noted with the highest value of gonadosomatic index at that time. The Lm increased from 6.6 cm at TBST to 9.4 cm at TTCM. This species displayed relatively high fecundity, ranging from 5,481 to 130,683 eggs/female. The average fecundity of this fish was 27,698 ± 7,983 eggs/female at LHTV, 46,592 ± 7,264 eggs/female at TBST, 23,271 ± 4,985 eggs/female at DHBL, and 31,408 ± 2,515 eggs/female at TTCM. Egg diameter ranged from 0.45 ± 0.01 at DHBL to 0.50 ± 0.01 at TBST. For sustainable exploitation, local governments should ask the fishers to avoid catching fish during the main spawning period, and the fish length at first capture should be >Lm. [ABSTRACT FROM AUTHOR]

This study provides new knowledge of length-weight relationship (LWR), growth pattern and condition factor (CF) of Butis humeralis, one of target catching gobies for food supply in the Mekong Delta, based on a collection of 1,439 fish (580 females and 859 males). Gill nets are used to catch fish samples for twelve months, from April 2019 to March 2020, at six sites in estuaries in the Mekong Delta. The analyses show that the weight of males and females of different fish sizes, seasons and sites are determined by a given total length since the determination coefficients of LWRs are high (r²>0.8 for all cases). As the slope coefficient values (b) are higher than the threshold of three, both males and females display positive allometric growth patterns. Likewise, fishes caught at two fish sizes in two seasons and five sites (except in Vinh Hau, b=2.97±0.12 SE) exhibit positive allometry. The CF of Butis humeralis fluctuates around the well-being parameter of one, ranging from 0.95±0.01 SE to 1.08±0.02 SE, which indicates that these six sites are suitable environments for fish growth. The results yield reliable biological data for further research on manageable and conservable strategies of this species. [ABSTRACT FROM AUTHOR]

Periophthalmus chrysospilos is an amphibious fish living in mudflats from eastern India to Indonesia, including the Vietnamese Mekong Delta. Population biological traits play an important role in fishery assessment, but understanding is limited for this species. In total 1,031 specimens were caught in two regions covering four provinces, including the TVST (Duyen Hai, Tra Vinh and Tran De, Soc Trang) and BLCM (Dong Hai, Bac Lieu and Dam Doi, Ca Mau). Results found that the sex ratio was close to 1:1. The parameters of the von Bertalanffy in TVST were L∞ = 12.8 cm, K = 0.41 yr−1, t0 = −0.10 yr and in BLCM were 12.7 cm, 0.38 yr−1 and −0.08 yr, respectively. Although the growth coefficient (Φ′) in BLCM (1.79), was lower than that in TVST (1.83), the species shared a similar size at first capture (7.9 cm in TVST and 7.9 cm in BLCM). The species suffered from heavy pressure of fishing in TVST as fishing mortality in TVST (2.32 yr−1 ) was higher than that in BLCM (1.38 yr−1 ), leading to the higher total mortality (Z = 3.60 yr−1 ) in TVST compared to BLCM (Z = 2.59 yr−1 ). By contrast, the species showed similar natural mortality over both sites (1.20 yr−1 in TVST and 1.22 yr−1 in BLCM). The Periophthalmus chrysospilos population was reasonably exploited because E values (0.64 in TVST and 0.53 in BLCM) were lower than E10 (0.706 in BTTV and 0.705 in STBL). Nonetheless, to avoid the consequences of overfishing, some sustainable fisheries practices should be implemented, such as protecting mangrove forests, restricting fishing during the recruitment period, using appropriate fishing tools and increasing mesh size. [ABSTRACT FROM AUTHOR]

Length-weight relationship (LWR), growth pattern and condition factor (CF) play a vital role in fish resource evaluation and management but data on this is limited for Periophthalmus variabilis. This is an amphibious fish that lives in the mudflats of the mangrove forests in the Western Pacific regions, including the Vietnamese Mekong Delta (VMD). This paper contributes to the understanding of the LWR, growth pattern and CF of P. variabilis. Fish specimens were collected by hand at four sites in the VMD from April 2020 to March 2021. The analysis of 495 individual fish (259 females and 236 males) showed that fish weight could be estimated from a given fish length due to high determination values (r² = 0.70 - 0.97). Dusky-gilled mudskippers of the VMD exhibited positive allometry, as indicated by their larger than 3 b value (b = 3.094 ± 0.045, p = 0:04). However, the growth pattern of the mudskipper between the sex and maturation stage (immature versus mature) showed isometry. These fish displayed positive allometry in the dry season (b = 3.138 ± 0.065) (>3, p = 0:04) but isometry in the wet season (b = 3.058 ± 0.061) (≈3, p= 0.34). Fish growth ranged from isometry to positive allometry and varied by site (b = 2.850 ± 0.103-3.370 ± 0.114) and month (b = 2.668 ± 0.184-3.588 ± 0.299) based on the b value. The CF of P. variabilis was not affected by sex (p = 0.29), body size (p = 0.64) or season (p = 0.43), but was affected by site (p = 0:01) and month (p=0.01). The CF of this species (1.05 ± 0.02) was higher than 1 (p<0:001), indicating that the fish adapted well to their habitat. [ABSTRACT FROM AUTHOR]

In Vietnam and in other developing countries, twowheeled electric vehicles are potential alternatives to gasolinepowered motorbikes. The growth in the number of Electric TwoWheelers (E2Ws) requires a large power demand of charging load. In addition, the increasing spread in the appearance and penetration of rooftop photovoltaic (PV) power systems, with their intermittence and uncertain nature, poses technical challenges that need to be addressed. The coordination of PV rooftop operation and EV charging may be an effective solution to meet the emerging load demand from EVs, increasing solar power penetration while minimizing the cost of grid reinforcement or possible upgrades. In this paper, a two-level desired load profile tracking algorithm for PV integrated electric bicycles/electric motorcycle charging stations is proposed with the purposes of load leveling, valley filling, and peak shaving. The simulation results show that the proposed algorithm is an effective solution, significantly improving the load profile, especially when compared with uncontrolled charging and constant charging power scheme. [ABSTRACT FROM AUTHOR]

The present study was conducted in four sampling sites, from fresh to brackish waters, to contribute knowledge on the length-weight relationship, growth, and body condition factor of the commercial fish Glossogobius aureus (Gobiiformes: Gobiidae) in the Mekong Delta. Fish specimens were caught using gill nets from January to December 2020. Data analyzed results of 742 specimens (382 males and 360 females) showed that weights of males and females in various sizes, seasons, and sites are able to estimate from a fish given length due to high determination coefficients (r²> 0.8, in all cases). The growth pattern of Glossogobius aureus fluctuated monthly from negative allometry to isometry and positive allometry as its slope (b) obtained from LWRs ranged from 2.583±0.119 SE to 3.123±0.066 SE. Likewise, b of this fish changes with fish size and site, but not season and gender. Albeit the growth pattern showed intraspecific and spatio-temporal variations, this goby displayed negative allometry since b (2.859±0.030) was lower than three. Likely, fish body condition factors, ranging from 0.937±0.022 SE to 1.218±0.030 SE, varied between fish sizes, sites, and months. The present findings contributed valuable data to understand fish adaptation and fishery management. [ABSTRACT FROM AUTHOR]

This article first provided information on otolith shapes, the variation of otolith weight by sex, fish size, season, and sampling site, and the linear relationship between otolith weight and fish size. A total of 815 Periophthalmus chrysospilos specimens from Duyen Hai, Tra Vinh; Tran De, Soc Trang; Dong Hai, Bac Lieu; and Dam Doi, Ca Mau in the Mekong Delta ranged from 4.20 to 12.50 cm total length and from 1.26 to 16.88 g weight were analysed. The analysis results revealed that Ps. chrysospilos had a square otolith, deeply notched at the anterior apex and flat at the posterior apex. The weight of the left otolith showed a statistical difference according to survey factors, including gender, fish size, season, and sampling site. The otolith weight had a proportional relationship with to the total length, body weight, and head length of mudskippers (r2 =0.7~0.9), which meant that fish size could be predicted from the otolith weight and about 70-90% of the otolith weight of Ps. chrysospilos varied corresponded the growth of the fish.

Increasing offshore wind farms are rapidly installed and planned. However, this will pose a bottle neck challenge for long-distance transmission as well as inherent variation of their generating power outputs to the existing AC grid. VSC-HVDC links could be an effective and flexible method for this issue. With the growing use of voltage source converter high-voltage direct current (VSC-HVDC) technology, the hybrid VSC-HVDC and AC system will be a next-generation transmission network. This paper analyzes the contribution of the multi VSC-HVDC system on the AC voltage stability of the hybrid system. A key contribution of this research is proposing a novel adaptive control approach of the VSC-HVDC as a so-called dynamic reactive power booster to enhance the voltage stability of the AC system. The core idea is that the novel control system is automatically providing a reactive current based on dynamic frequency of the AC system to maximal AC voltage support. Based on the analysis, an adaptive control method applied to the multi VSC-HVDC system is proposed to realize maximum capacity of VSC for reactive power according to the change of the system frequency during severe faults of the AC grid. A representative hybrid AC-DC network based on Germany is developed. Detailed modeling of the hybrid AC-DC network and its proposed control is derived in PSCAD software. PSCAD simulation results and analysis verify the effective performance of this novel adaptive control of VSC-HVDC for voltage support. Thanks to this control scheme, the hybrid AC-DC network can avoid circumstances that lead to voltage instability. [ABSTRACT FROM AUTHOR]

In Vietnam's major urban areas, private motorcycles are the main means of transportation that are suitable for socio-economic conditions, current transport infrastructure, and people's habits. However, in recent years, the negative effects of a large number and high density of motorcycles in urban areas such as traffic congestion and noise and air pollution have resulted in a gradual change in the public's opinion of private vehicle adoption, especially motorcycles. The public has also urged the authorities to issue policies of limiting or curving the growth in the number of private vehicles powered by fossil fuels in big cities. However, in order to achieve the goal, other alternative means of transport should be proposed to encourage people to move to a more sustainable and eco-friendly form of mobility. The alternatives also should be consistent with the average income level as well as social characteristics. In recent years, along with the development of a highly connected public transport network, efficient and less-polluting vehicles including electric two-wheelers have been emerging, thriving, and drawing more attraction from Vietnamese people and policy makers. The spread in the number of electric two-wheelers in Vietnam's major cities may be a sign of the transition to a more sustainable and less-polluting means of transport as an alternative to gasoline-powered motorcycles. In this paper, the authors aim to analyze the current road traffic status in Vietnam's major cities, as well as shed a light on the transition to the greener and more efficient alternative vehicles to motorcycles in Vietnam's urban traffic. Several recommendations for encouraging this vehicle type development are also important outcomes of this paper. [ABSTRACT FROM AUTHOR]

Abstract The Squaretail mullet, Ellochelon vaigiensis, is a commercial fish species distributed throughout the Indo‐Pacific region. This species tolerates wide variations in salinity, having been reported from both freshwater and marine habitats. Although economically significant, there is little information on its reproduction, especially in the Vietnamese Mekong Delta (VMD), where it is heavily extracted. Our study elucidates the breeding pattern, seasonality, first length at maturity, as well as potential and relative fecundity of this species. Fish specimens were collected by trawl nets from November 2020 to October 2021 at four estuarine sites within the VMD. We found this species to be a synchronous spawner, with peaks in reproductive activity from June to September. In the populations we surveyed, there was significant dominance of males (1.26:1.00) based on 942 fish samples (526 males and 416 females). The length at 50% maturity for females was significantly higher than for males at all sites and ranged from 10.6 to 19.3 cm. The diameter of the eggs examined for this species exhibited slight variation, from 0.43 to 0.54 mm. The potential fecundity ranged from 246,254 ± 35,878 to 411,970 ± 54,370 eggs, corresponding to female length and weight of 26.7–32.6 cm and 102.97–234.19 g, respectively. Relative fecundity values were highest at Thanh Phu, Ben Tre (6388 ± 605 eggs), and Dong Hai, Bac Lieu (6461 ± 637 eggs), followed by Tran De, Soc Trang (4729 ± 408), and were found to be lowest at Duyen Hai, Tra Vinh (3117 ± 223 eggs). Information on reproductive behavior in this species has far‐reaching impacts on sustainable extractions, stock conservation, and aquaculture.

Glossogobius aureus (Gobiiformes: Gobiidae) is a target fish and widely distributed in the Mekong Delta, from fresh to brackish waters. However, knowledge on its food and feeding ecology is scarce. Therefore, this research was carried out in four sampling sites along the estuarine of Hau River in order to fill this information gap. A total of 742 individual fish was collected monthly using trawl nets from January to December 2020. A combined analysis of the fullness index and Costello graph suggested that this fish species displayed high feeding intensity. The results revealed that G. aureus is a carnivore and its food composition comprised Acetes spp., Actinopterygii, zooplankton, and other preys (e.g. snails and detritus). Acetes spp. is the main food of this species. The diet composition varied with sites but not genders, fish sizes, and seasons. Acetes spp., Actinopterygii and other preys contributed to the spatial variation of food composition. The findings revealed knowledge about the fish feeding ecology, which may propose suitable foods for its aquaculture development.

Dusky-gilled mudskipper Periophthalmus variabilis, a member of the family Gobiidae, is a potential aquarium pet in the Mekong Delta (MD), Vietnam; however, data on its feeding habit and intensity has been limited. Therefore, this study aims to evaluate the relative gut length (RGL) and gastro-somatic index (GI) of Periophthalmus variabilis in order to determine the feeding habit and intensity of this mudskipper and its variation regarding sex, size, season, site, and their interaction. One thousand one hundred seventy mudskipper samples were collected monthly in four locations: Duyen Hai-Tra Vinh, Tran De-Soc Trang, Hoa Binh-Bac Lieu, and Dam Doi-Ca Mau from January 2022 to December 2022. The analysis showed that Periophthalmus variabilis was a carnivorous fish with an average RGL value of 0.52±0.01 SE (

Butis genus is characterised by their small body size and morphological variability, allowing them to adapt to different habitats. This paper analyses the mitochondrial cytochrome C oxidase subunit I gene sequences and morphology of Butis for identification purposes and to understand genetic relationships. The morphological characteristics of Butis koilomatodon differed obviously from Butis humeralis and Butis butis. After classification based on morphology, the total deoxyribonucleic acid of fish samples was isolated, and the mitochondrial cytochrome C oxidase subunit I genes were successfully amplified using the polymerase chain reaction method. At approximately 617bp, the obtained mitochondrial cytochrome C oxidase subunit I gene sequences were highly similar to the reference sequences on Genbank (85.90–100%). The phylogenetic graphic was divided into five distinct groups, where B. koilomatodon was grouped in one group; and B. humeralis and B. butis were grouped together. The results suggest that B. humeralis was an entirely different species from B. butis, with a mean genetic divergence of up to 14%. However, further studies using a combination of other types of deoxyribonucleic acid barcoding together with morphological features should be undertaken to confirm these findings.

This study provided data on gastrointestinal morphology and feeding intensity of slender mudskipper Periophthalmus gracilis distributed in some coastal provinces in the Mekong Delta, Vietnam (VMD). Fish specimens were sampled monthly by hand-catching, from 01/2022 to 12/2022, in four provinces in the VMD: Tra Vinh, Soc Trang, Bac Lieu, and Ca Mau. After sexing, the fish total length and weight, gut length, and gastrointestinal morphology were measured and described. The study showed that Periophthalmus gracilis had a protruding upper jaw with a longer upper jaw bone length. The teeth are large and sharp, with pointed molars and unevenly distributed in a row on the upper jaw. The tongue was short and had a round tip. The gastrointestinal had an elastic tube-shaped esophagus, a short sac-shaped stomach, and long, straight, curving tube intestines. The feeding intensity of the mudskipper varied by season and month, with differences between males and females. These findings provided new information on the mudskipper’s gastrointestinal morphology and feeding habit.

This study contributed to investigating the changes in morphometric and meristic variations in Mystus albolineatus at two different sites in the Mekong Delta (VMD). This is a high economic-value fish species in the region. The study was conducted for 12 months (03/2022 - 02/2023) at two sites along the Hau River (a branch of the Mekong River) with different environmental characteristics, including a freshwater site year-round at Cai Rang (Can Tho City) and a site affected by saltwater intrusion during the dry season at Long Phu (Soc Trang province). Fish samples were collected using different fishing gear of various sizes. The results obtained 825 individuals (443 females and 382 males) at both sites (408 at Cai Rang and 417 at Long Phu). Through the analysis process, it was found that the total length (TL) and weight (W) of this fish species were significantly influenced by gender and season. Both parameters were significantly higher in females (TL:11.13±0.09 SE cm; W: 10.17±0.06 SE g) than in males (TL: 10.68±0.10 SE cm; W: 9.95±0.07 SE g). Meanwhile, during the dry season (TL: 10.15±0.10 SE cm; W: 9.58±0.08 SE g), the fish had lower length and weight compared to the wet season (TL: 11.42±0.08 SE cm; W: 10.39±0.05 SE g). The interaction between gender and season also significantly affected the TL of Mystus albolineatus. In addition, eye diameter (ED), eye distance (DE), body height (BH), head length (HL), ED/HL, DE/HL, BH/TL, and HL/TL all showed significant differences by gender and season. The results of this study on the morphological characteristics of this fish species indicate that it adapts well to the environment at both research sites. The findings of this study provide basic data on the variation in morphological characteristics of Mystus albolineatus in the VMD region.

The Glossogobius species play an essential role in food supply and are distributed widely from the marine to freshwater, especially in the Mekong Delta, Vietnam (VMD). Some of their morphometrics and meristics are observed to vary with species and sampling sites. Therefore, the present study aims to verify if their mitochondrial Cytochrome b (Cytb) gene, one of the popular gene sequences used in fish phylogenic variation assessment, varies with species and sampling sites in the VMD. The Cytb gene size was 1300 bp for GcytbH/GcytbL primer pair and 1045 bp for GluMuq1-F/Mixcyto937-2R. The genetic distances within and among these three fish species groups were 0–11%. The Cytb gene sequences’ similarity between this study and the NCBI database was 85.84–100%. The Glossogobius specimens were observed to disperse in small branches of the phylogenetic tree with a low K2P value, suggesting that the Cytb genetic diversity may be low among species.

This study aims to provide a procedure for performing microscopy in fish gonads. Specimens used in this study were the ovaries and testes of fish collected in the Mekong Delta from April to July 2022. Organs at five different stages for each sex (ovary diameter from 1.16 cm in stage I to 4.04 cm in stage V; testis diameter from 0.42 in stage I to 2.39 in stage V) were studied in this procedure. The results showed that both ovaries and testes needed to be fixed at 4% formol for 24 h and under running water for eight hours. Ovaries and testes were then immersed in 500 ethanol for 24 h to initiate dehydration. Results showed that the time for dehydration and paraffin infiltration was longer in the ovary (26 to 55 h across stages) than in the testis (25 to 26 h across stages). The mean staining time of the ovary was 1.5 min (stage I) to 3.5 min (stage V) in Hematoxylin and 50 s (stage I) to 140 s (stage V) in Eosin. Whereas the staining time of testis was shorter, 1 min (stage I) to 3 min (stage V) in Hematoxylin and 30 s (stage I) to 90 s (stage V) in Eosin. This study provides a reference for further studies on the histological structure of fish gonads. These results could be applied to fish species inside and outside the Mekong Delta.

Periophthalmus chrysospilos is an amphibious fish and considered candidates of typical aquarium fish in the Mekong Delta (MD), Vietnam. It is a species that is facing overfishing. Unfortunately, the data on its length-weight relationship (LWR), growth pattern, and condition factor are limited. The present study lasted from April 2020 to March 2021 to contribute knowledge of these data. A collection of 1,031 specimens (508 females and 523 males) was obtained from estuarine and coastal regions. The results showed that the fish total length (TL) and weight (W) were significantly different between sexes, seasons, and sites. In order to determine LWRs, weights of males and females in two sizes, seasons, four sites, and twelve months were estimated from the fish given lengths. The species displayed temporal variation in growth patterns as b values ranged from 2.87 ± 0.12 SE to 3.46 ± 0.07 SE. It generally showed positive allometric growth as b (3.22 ± 0.02 SE) was higher than the threshold of three. The fish body conditional factor was close to the well-being value of one and was not influenced by sex, but by season, site and month variations. The findings concluded that the species was well adapted to its habitat.

Ellochelon vaigiensis is widely distributed and plays a vital role in the fisheries in the Mekong Delta (MD), but data on its population biological traits have not been known. Consequently, this study was conducted to provide data on its population biology used for fishing status assessment and fish resources management. Fish specimens were collected using trawl nets in two regions of the Hau River mouth, including northern in Ben Tre and Tra Vinh (BTTV) and southern in Soc Trang and Bac Lieu (STBL). Fish population biological parameters were estimated using FiSAT II software based on the fish length-frequency data. The male and female length-frequency data in each ecoregion were pooled together. Data analysis of 1,383 individual fish showed the sex ratio of the species was 1.00:1.30 at BTTV (309 females and 402 males) and 1.00:1.25 STBL (299 females and 373 males). Most fish specimens were caught at 12–22 cm total length (914 individuals), accounting for 66.09% of the fish collection. The difference in salinity between these two regions could affect the population biological parameters of E. vaigiensis. There were five cohorts (e.g., five growth curves) in the BTTV and STBL. The von Bertalanffy curves of fish populations at BTTV and STBL were L = 33.6 (1 −e−0.46(t + 0.34)) L = 31.5 (1 −e−0.56(t + 0.29)), respectively. The growth index (Φ′) of this species at STBL (2.74) was higher than that at BTTV (2.72), whereas its longevity at BTTV (6.52 yrs) was higher than at STBL (5.36 yrs). The biomass and relative yield parameters, including E0.1, E0.5 and Emax were 0.358, 0.265 and 0.436 at BTTV; and 0.418, 0.293, and 0.513 at STBL, respectively. The fishing (F), natural (M), and total (Z) mortalities were 0.35/yr, 1.06/yr, and 1.41/yr at BTTV; and 0.55/yr, 1.24/yr, and 1.78/yr at STBL, respectively. The BTTV and STBL population was not overexploited because the exploitation rate (EBTTV = 0.25, ESTBL = 0.31) was lower than E0.1 (0.358 in BTTV and 0.418 in STBL).

The Squaretail mullet Ellochelon vaigiensis is widely found from marine to brackish and freshwater, including the Vietnamese Mekong Delta (VMD). Data on the length-weight relationships (LWRs), growth pattern, and condition factor (CF) play an essential role in fisheries assessment but are limited to E. vaigiensis – a commercial fish in VMD. To better understand the growth pattern of this fish, the study collected samples at four sites, including Thanh Phu, Ben Tre (BT); Duyen Hai, Tra Vinh (TV); Tran De, Soc Trang (ST); and Dong Hai, Bac Lieu (BL). Each month, fish samples were collected using bottom nets at each sampling site during high tide in both the dry season (January to May 2021) and the wet season (November to December 2020 and June to October 2021). This study qualified whether LWRs, growth pattern, and CF of E. vaigiensis vary with sexual, intraspecific, and spatiotemporal variables. The analysis results of 942 specimens showed that fish total length (TL = 17.86 ± 0.13 cm) and weight (W = 54.29 ± 1.05 g) changed with sex, season, month and site. The W could be appraised from a given TL due to high coefficients (r2) of LWRs that were regulated by fish size and season but not sex. The species showed negative allometry as its slope value of LWRs (b = 2.34 ± 0.30) was

Spotted green goby Acentrogobius viridipunctatus is one of the commercial gobies living from brackish to freshwater globally, including the Southwest of Viet Nam, but there is no data on population biological traits used for assessing status of stock. Consequently, the research aimed to provide life history parameters of this fish like asymptotic length (L∞), growth coefficient indicator (K), exploitation rate (E), length at first capture (L50), the maximum age (tmax), growth coefficient (Φ′), and mortalities. A total 960 individuals (528 males and 432 females) were caught using trawls at two ecoregions, including Tra Vinh-Soc Trang (TVST) and Bac Lieu-Ca Mau (BLCM), from January to December 2020. Results showed that average fish length was 8.0–11.0 cm, and L∞ was 14.70 cm at TVST and BLCM. The von Bertalanffy growth curve was Lt = 14.70 (1 − e−0.73(t+0.27)) at TVST and Lt = 14.70 (1 − e−0.84 (t+0.23)) at BLCM, respectively. The Φ′ at BLCM (2.26) was higher than that at TVST (2.20), but tmax at BLCM (3.57 yrs) was lower than that at TVST (4.11 yrs). The total mortality (Z), fishing mortality (F), and natural mortality (M) at TVST were 2.09 yr−1, 0.29 yr−1, and 1.80 yr−1, respectively. These parameters at BLCM were larger than those at TVST, with values of 3.47 yr−1, 0.34 yr−1, and 3.14 yr−1, respectively. The fishing status at TVST and BLCM was not subjected to overfishing as E in these regions (0.14 and 0.10) were lower than E0.1 (0.76 and 0.72). Local authorities should ask fishers to increase fishing mesh size for sustainable exploitation.

Glossogobius sparsipapillus is a potential candidate for aquaculture in the Mekong Delta, but information on its food and feeding habit is still fragmented and deficient. This study, therefore, aims to contribute diet and feeding ecology to this fish based on 661 specimens (331 males and 330 females) caught in estuarine areas from December 2019 to November 2020. Data analysis showed that fish diet composition comprised five categories such as Acetes spp., small fish, Polychaeta, Uca spp., and others (e.g., fish scales and detritus). This goby is a generalist feeder, feeding preliminarily on Acetes spp. but rarely on Polychaeta. Feeding intensity is high and does not change with sexes but varies according to fish sizes, seasons, and sites. Moreover, a similar meal size was observed in different sexes, fish sizes, seasons, and sites. The findings supply the fundamental knowledge on the food and feeding of this species, being used for artificially cultivating study.

This study provided knowledge on testicular development, spawning reference and length at first maturity (Lm) of Acentrogobius viridipunctatus—a target catching fish for food supply in the southwest Viet Nam. A total of 528 individuals were collected using trawl nets from January to December 2020 at Long Huu-Tra Vinh (LHTV), Trung Binh-Soc Trang (TBST), Dien Hai-Bac Lieu (DHBL) and Tan Thuan-Ca Mau (TTCM). Five developmental stages of testis were found, and testis diameter increased from ∼1.07 (stage I) to ∼4.82 mm (stage V). Testis stage I consisted of spermatogonia (S) which shifted to primary spermatocytes (SC1) in stage II. In testis stage III, SC1 was divided into secondary spermatocytes (SC2). At this stage, testis consisted of S, SC1, SC2 and some spermatid (ST). At stages IV and V, testis comprised mainly spermatozoa (SZ) besides S, SC1, SC2 and ST, showing that this goby was a multi-spawner. Testis frequency and gonadosomatic index analyses showed that this species released sperms yearly, with a prominent peak in the wet season. The Lm decreased from 9.3 ± 0.3 cm at TBST to 9.0 ± 0.3 cm at LHTV, 8.9 ± 0.2 cm at TTCM and 6.5 ± 0.5 cm at DHBL. Findings provided fundamental data to set up suitable fishing and conserving strategies for this species.

Objective: Knowledge of diet composition and feeding habits are essential to our understanding of fish ecological adaptation and aquaculture studies. This study aims to gain knowledge on diet composition, feeding intensity and habits for Glossogobius giuris – a commercial goby residing in brackish to freshwater regions of the Vietnamese Mekong Delta. Methods: A collection of 1,291 samples (632 males and 659 females) were caught monthly from January 2020 to December 2020 at four sites using trawl nets. A combined analysis of prey occurrence and weight was used to calculate the diet composition of this fish. Results: This fish displayed high feeding intensity, and its diet composition was seen to be comprised of small fish, Acetes spp., Uca spp., molluscs, and others (e.g., detritus and fish scales). Although males and females of two fish size groups, two seasons and at the four sites displayed the same feeding trends as Costello graphical analysis showed, the diet composition was seen to vary with season and site. It suggested that the difference in salinity between seasons and the four sites regulated food composition within this fish. Conclusion: These findings advance the understanding of fish adaptation capacities and food flexibility.