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In this article, experimental studies on the flexural behavior of concrete beams with corroded reinforcement were conducted. The beams were subjected to simultaneous different load levels and immersed in NaCl solution for 30 days with accelerated corrosion. A four-point bending test was subsequently carried out to determine the loading capacity of these beams. Experimental data show that the loading capacity of the beam decreases as the level of preload increases. The mass loss of steel bars in the beams increases as the level of preload increases. The loading capacity and steel mass loss of the beams subjected to 0.8 of failure load of the non-corroded beam decrease by 32.7 and 30.3%, respectively. The numerical investigation was also done to evaluate the loading capacity with various corrosion degrees of steel bars.

Mangrove forest in the Mekong Delta plays important roles in protecting coasts from soil erosion and strong waves, supplying seafood, and accumulating carbon. Despite these benefits, mangroves have been and continue to be severely damaged by the impacts of natural and socioeconomic activities. In recent years, large areas of mangrove forest have been restored through planting and other various management actions. In this study, we analyzed high-resolution WorldView-2 images to quantify changes in the mangrove forest in seven coastal provinces (Tien Giang, Ben Tre, Tra Vinh, Soc Trang, Bac Lieu, Ca Mau, and Kien Giang) of the Mekong Delta from 2015 to 2020. Our study is one of the first to analyze mangrove forest change at the commune scale, the smallest official administrative unit in Vietnam, to determine the area of restored mangroves. The potentials and challenges in future mangrove restoration were also assessed by analyzing satellite imagery and field survey data. In the study area, mangrove forest area increased by 11,184 ha (approximately 2,237 ha per year) from 79,593 ha in 2015 to 90,777 ha in 2020. A total area of 16,138 ha (approximately 20.3%) was lost due to mangrove conversion to other land uses, aquaculture activities and coastal erosion, etc., while 27,322 ha (approximately 34.1%) was restored or newly planted during state- and NGO-funded mangrove restoration projects and programs. These results confirmed that mangrove restoration projects and programs have played a significant role in maintaining and increasing mangrove forest cover in Mekong Delta. The results can also assist managers and decision makers in mangrove restoration evaluation, and suggest analyzing WorldView-2 images to monitor mangrove restoration over time in Vietnam.

To improve knowledge of this matter, the potential application of two gridded meteorological products (GMPs), the China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) and Climate Forecast System Reanalysis (CFSR), are compared for the first time with data from ground-based meteorological stations over 6 years, from 2008 to 2013, over the Cau River basin (CRB), northern Vietnam. Statistical indicators and the Soil and Water Assessment Tool (SWAT) model are employed to investigate the hydrological performances of the GMPs against the data of 17 rain gauges distributed across the CRB. The results show that there are strong correlations between the temperature reanalysis products in both CMADS and CFSR and those obtained from the ground-based observations (the correlation coefficients range from 0.92 to 0.97). The CFSR data overestimate precipitation (percentage bias approximately 99%) at both daily and monthly scales, whereas the CMADS product performs better, with obvious differences (compared to the ground-based observations) in high-terrain areas. Regarding the simulated river flows, CFSR-SWAT produced “unsatisfactory”, while CMADS-SWAT (R2 > 0.76 and NSE > 0.78) performs better than CFSR-SWAT on the monthly scale. This assessment of the applicative potential of GMPs, especially CMADS, may further provide an additional rapid alternative for water resource research and management in basins with similar hydro-meteorological conditions.

Located in the northern economic focal region, Hai Duong is one of the cultural and spiritual centers of Vietnam. Hai Duong is not only favored with beautiful natural sceneries such as Con Son, Kiep Bac, Kinh Chu, An Phu, ... but it also owns priceless cultural and historical assets such as traditional festivals, historical relics, and folk songs, etc… This diversity allows Hai Duong to develop different types of eco-tourism. However, there are many hinderances to Hai Duong in making tourism the key economic sector. The province has failed to determine its own direction of tourism development, leading to ineffective investment in tourist attraction sites. Insufficient promotion of local tourist attractions also make the tourism products offered non-unique. These problems reduce destination competitiveness of the province. Based on theories of destination competitiveness, this article evaluated the current status of tourism destination competitiveness in Hai Duong province on a number of criteria, then suggesting recommendations, solutions to improve the competitiveness of the province in the new development period.

River bank (RB) erosion is a global issue affecting livelihoods and properties of millions of people. However, it has not received enough attention in the Vietnamese Mekong Delta (VMD), i.e., the world’s third largest delta, compared to salinity intrusion and flooding. There have been several studies examining RB and coastal erosion in the VMD using remotely sensed satellite data, but the applied methodology was not adequately validated. Therefore, we developed a novel SRBED (Spectral RB Erosion Detection) method, in which the M-AMERL (Modified Automated Method for Extracting Rivers and Lakes) is proposed, and a new RB change detection algorithm using Landsat data. The results show that NDWI (Normalized Difference Water Index) and MNDWI (Modified Normalized Difference Water Index) using the M-AMERL algorithm (i.e., NDWIM-AMERL, MNDWIM-AMERL) perform better than other indices. Furthermore, the NDWIM-AMERL; SMA (i.e., NDWIM-AMERL using the SMA (Spectral Mixture Analysis) algorithm) is the best RB extraction method in the VMD. The NDWIM-AMERL; SMA performs better than the MNDWI, NDVI (Normalized Difference Vegetation Index), and WNDWI (Weighted Normalized Difference Water Index) indices by 35–41%, 70% and 30%, respectively. Moreover, the NDVI index is not recommended for assessing RB changes in the delta. Applying the developed SRBED method and RB change detection algorithm, we estimated a net erosion area of the RB of –1.5 km2 from 2008 to 2014 in the Tien River from Tan Chau to My Thuan, with a mean erosion width of –2.64 m and maximum erosion widths exceeding 60 m in places. Our advanced method can be applied in other river deltas having similar characteristics, and the results from our study are helpful in future studies in the VMD.

Observation of the Hau River distributary of the Mekong River delta in Vietnam, conducted in dry and flood season (2009, 2014, and 2015), is utilized to investigate the mechanism of formation, distribution of estuarine turbidity maxima (ETM), and links with sediment transport in the system. Additionally, 3D (three-dimensional) numerical models are applied to simulate the seasonal tidal variation (flood and dry seasons) of the water and suspended sediment transport processes of the Mekong River Delta. The 3D model, with a combination of hydrodynamic-wave and suspended sediment transport, was set up and validated with measured data in the study area. The mechanism that measures ETM is the process of suspended sediment from the river when it interacts with seawater and speeds up the flocculation, combined with the asymmetry of the tidal current, which will create the region with ETM by moving in/out with the tidal current’s ups and downs. As there is surface flow velocity towards the sea, the bottom baroclinic flow has a decisive role in deposition and erosion, and it causes the suspended sediment concentration (SSC) to be maximized. During the flood season, the salt wedge near the river’s mouth, at the peak of the tide, pushes towards the sea’s direction when there are ebbing tides, with a scope of about 20 km. In the dry season, there is estuary disturbance as well; the salt wedge forms, but is relatively weak or does not exist, depending on the time of the tide. The maximum turbidity zone in the flood season moves the subaqueous delta with a scope of about 20 km and SSC of about 0.1 to 0.6 g L−1, whereas in the dry season, the seawater has high salinity, and seaward SSC penetrates the estuaries to cause a disturbance and flocculation. The penetration scope is up to 50 km and creates a water mass that has high SSC, from 0.2 to 0.7 g L−1, to run in/off by the tidal current’s ups and downs for several kilometers in the tidal phase.

Plastic usage in tourism activities has increased significantly in Vietnam over the past decades, leading to the burden of plastic pollution and the threat to sustainable tourism development. The Vietnamese government has recognized the importance of plastic waste management in sustainable tourism. Laws and regulations on controlling pollution due to non-biodegradable plastic bags. Public education activities have been organized to encourage people replace plastic products with natural materials, reuse plastic bags and reduce plastic wastes. Many tourism businesses have found ways to limit plastic consumption, such as replacing disposal plastic products with eco-friendly products. Vietnamese tourism has taken the first steps in reducing plastic waste pollution in tourism activities. This article proposed some solutions to limit and restrain plastic wastes from tourism in Vietnam.

Xylocarpus granatum J. Koenig is one of the most widespread core component species of mangrove forests in the Indo-West Pacific (IWP) region, and as such is suitable for examining how genetic structure is generated across spatiotemporal scales. We evaluated the genetic structure of this species using maternally inherited chloroplast (cp) and bi-parentally inherited nuclear DNA markers, with samples collected across the species range. Both cp and nuclear DNA showed generally similar patterns, revealing three genetic groups in the Indian Ocean, South China Sea (with Palau), and Oceania, respectively. The genetic diversity of the Oceania group was significantly lower, and the level of population differentiation within the Oceania group was significantly higher, than in the South China Sea group. These results revealed that in addition to the Malay Peninsula—a common land barrier for mangroves—there is a genetic barrier in an oceanic region of the West Pacific that prevents gene flow among populations. Moreover, demographic inference suggested that these patterns were generated in relation to sea level changes during the last glacial period and the emergence of Sahul Shelf which lied northwest of Australia. We propose that the three genetic groups should be considered independent conservation units, and that the Oceania group has a higher conservation priority.

Patterns of genetic structure are essential for a comprehensive understanding of the evolution and biogeography of a species. Here, we investigated the genetic patterns of one of the most widespread and abundant mangrove species in the Indo-West Pacific, Sonneratia alba J. Sm., in order to gain insights into the ecological and evolutionary drivers of genetic structure in mangroves. We employed 11 nuclear microsatellite loci and two chloroplast regions to genotyped 25 S. alba populations. Our objectives were to (1) assess the level of genetic diversity and its geographic distribution; and (2) determine the genetic structure of the populations. Our results revealed significant genetic differentiation among populations. We detected a major genetic break between Indo-Malesia and Australasia, and further population subdivision within each oceanic region in these two major clusters. The phylogeographic patterns indicated a strong influence of vicariance, oceanic barriers and geographic distance on genetic structure. In addition, we found low genetic diversity and high genetic drift at range edge. This study advances the scope of mangrove biogeography by demonstrating a unique scenario whereby a widespread species has limited dispersal and high genetic divergence among populations.

This paper deals with an analytical approach to the static behavior of Steel Concrete Composite (SCC) slabs. The Classical Plate Theory (CPT) and Refined Plate Theory (RPT) are considered when constructing governing equations describing the behavior of steel concrete plates. The displacement fields are represented by trigonometric series to find the exact solution by applying Navier's approach. Various numerical examples have been compared with the considered ones showing their high accuracy. The influence of plate parameters such as the thickness of steel and concrete layers on displacement was investigated in detail. [ABSTRACT FROM AUTHOR]

As targeted mutagenesis techniques become more prevalent for various filamentous fungi, the use of physical mutagen to induce random genetic variations across whole-genome remains an ideal option for genetic improvement. The aim of this study was to investigate the use of gamma radiation to enhance the antagonistic ability of Trichoderma against plant pathogenic fungi. The spore suspensions of Trichoderma koningiopsis VTCC 31435 was irradiated at doses ranging from 0 to 2500 Gy using a gamma Co-60 source at the Hanoi Irradiation Center. The results showed that the number of surviving spores depends on the irradiation dose. Spore numbers decreased sharply in the dose range of 100 to 1200 Gy, at higher doses, the variation in spore numbers was less pronounced. The required radiation dose to kill 90% of the total number of fungal spores (D10) of the T. koningiopsis VTCC 31435 strain was approximately 250 Gy. At a dose of 2500 Gy, the number of fungal but surviving spores decreased by about 7 Log units compared to the non-irradiated. After irradiation, morphological changes, as well as growth characteristics, were observed in some of the radiation-resistant obtained colonies. Using cellophane membrane assay and dual culture methods, five potential radiation-resistant mutants with better antagonistic ability against the fungus Rhizoctonia solani, which causes sheath blight in rice, were identified Notably, among these, the potential mutant VTCC(a) I-1 exhibited the highest antifungal activity of media-permeable metabolites (ICMA) and mycelial growth inhibition activity (IMG) against R. solani. The ICMA and IMG values of this mutant increased by 154.12% and 148.68%, respectively, compared to the wild-type strain and remained stable for at least six consecutive generations. The research results suggest that gamma irradiation may have potential applications in enhancing the antagonistic abilities against pathogenic fungi and other beneficial biological properties in Trichoderma sp. [ABSTRACT FROM AUTHOR]

This paper develops a finite element method for double beams subjected to static loading. The double beam consists of two Euler-Bernoulli beams connected continuously by an elastic spring connection. The finite element for a double beam is formulated with eight degrees of freedom based on the Euler-Bernoulli beam theory. The finite element method is implemented in MATLAB software to analyze the behavior of the double beams. The MATLAB code calculates the displacements of both the upper and lower beams. Numerical examples are compared with the analytical solution to demonstrate the high accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This study applied finite element analysis to a steel-concrete composite plate resting on the axial bar, using a four-node quadrilateral finite element for a steel-concrete composite plate combined with a truss element. Plate displacements and deformations were used to formulate the finite element method based on the first-order plate theory, also known as the Mindlin plate theory. The finite element analysis to combine steel-concrete composite plates and axial bars was implemented in MATLAB. Numerical examples were used in detail, showing a very small difference between the current study and the SAP2000 results. [ABSTRACT FROM AUTHOR]

Metaheuristic algorithms have been applied to tackle challenging optimization problems in various domains, such as health, education, manufacturing, and biology. In particular, the field of Structural Health Monitoring (SHM) has received significant interest, particularly in the area of damage identification in structures. Popular optimization algorithms such as Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Cuckoo Search (CS), Teaching Learning Based Optimization (TLBO), Artificial Hummingbird Algorithm (AHA), Moth Flame Optimizer (MFO), among others, have been employed to address this problem. However, notwithstanding the wide recognition of the current algorithms, their constraints are commonly acknowledged. Hence, this article advocates for the adoption of innovative hunting-inspired algorithms, namely the Ant Lion Optimizer (ALO), African Vulture Optimization Algorithm (AVOA), Grey Wolf Optimizer (GWO), Marine Predator Algorithm (MPA), and Whale Optimization Algorithm (WOA), which emulate the behaviors of wildlife species, to discern the areas and magnitudes of deterioration in a suspension footbridge. Moreover, in order to reduce computational time, only natural frequencies are applied as objective functions. The obtained results indicate that all the utilized algorithms can accurately detect the damages in the considered structure. [ABSTRACT FROM AUTHOR]