Vietnam Journal of Science and Technology

This paper presents the new numerical results of vibration response analysis of cracked FGM plate based on phase-field theory and finite element method. Effects of geometrical and material properties on the vibration behaviors of the plate are investigated in this work. The computed results show that the crack and stiffener have a strong influence on both the vibration responses and vibration mode shapes of the structure. The computed results can be used as a good reference to study some related mechanical problems.

Nanomaterials hold great promise of improved plant disease resistance, controlled release of agro-chemicals, enhanced plant growth, etc. In this study, the effect of nanosilica (10 – 30 nm) prepared from rice husk on the growth promotion of chili plant in green house was carried out. The experiment of nanosilica treatment by foliar spraying was arranged in a factorial design with 3 replications at various nanosilica concentrations of 0, 40, 60 and 100 ppm. Plant growth characteristics and chlorophyll content were assessed. Results showed that the fresh weight, dry weight, and chlorophyll content increased with the treatment of nanosilica. The optimal concentration of nanosilica was found to be of 60 ppm. Thus, treatment of nanosilica was beneficial in enhancing the growth of the chili plants.

This paper is the following part of our project to predict the penetration rate for percussive drilling with rotary in very hard rock. As results in [1] have been shown that the rate of penetration was strong influent by Brazilian tensile strength and it was exist the correlation between the rate of penetration and the rock properties. Yet, the study was valid on six hard rocks in experimental result of test tricone and rotary with percussive. All relationships have been shown but the coefficient R2 is still very low. This paper will present a new relationship with high value of R2 based on previous data and also establish a mathematical relationship, numerical model to predict the penetration rate.

In this study, rice husk was used as a precursor to prepare activated carbon using steam as a physical activation agent. Steam for activation can be used to activate almost all raw materials. A variety of methods have been developed but all of these share the same basic principle of initial carbonization followed by an activation step with steam. The study also investigates the effects of preparation parameters on the surface characteristics of the carbon. These parameters include the range of temperature and time in the carbonization and activation. The initial carbonization, done at temperatures up to 500°C in 60 min, is a highly exothermic process where the temperature is strictly controlled. The creation of the internal surface is done during the activation step with steam at temperatures 800°C in 30 min., for which the BET surface area is up to 710.8m2/g. Besides, the iodine and methylene blue adsorption capacity of rice-husk carbon are the best that reach 865.98±6.5 and 217.86±1.0 (mg/g), respectively. The entire synthetic procedure was simple, environmental-friendly and economical-effectively. The application prospect of the activated carbon prepared in this work was much more promising due to its high adsorptive capacity.

This paper reports a novel curve developed from non - circular gearing theory, which can be applied in rotor profile design of the two - lobe Roots blower. The formulas for calculating the volumetric efficiency and specific flow rate of the blower have also been established. To evaluate this type of the Roots blower, the volumetric efficiency and specific flow rate are being compared with those parameters of the two traditional designs and one recent variant.

In the search for bioactive constituents from Vietnamese plants,  the leaves and stems of Callistemon citrinus (Curtis) Skeels were selected for chemical investigation. Phytochemical analysis of plant led to the isolation of eight phenolic compounds including two flavonoids (eucalyptine (1) and 8-demethyleucalyptine (2)), two alcohols (blumenol A (3), n-tetratriacontanol (4)), three benzoic acid derivatives (acid gallic (5), methyl gallate (6) protocatechuic acid (7)), one sterol (b-sitosterol (8)), and along with one sesquiterpene (2,6,10-bisabolatriene (9)). The structures of the natural compounds were determined by spectroscopic evidences including 1D- and 2D-NMR and ESI-MS.

Silver nanoparticles (SNPs) are one of metallic nanoparticles widely applied in many fields. Research of SNPs application in plant tissue culture has been gaining attention in recent years. Moreover, novel plant tissue culture systems have been researched and developed for improving SNPs uptake capability in medium. In this study, we investigated effects of SNPs on Chrysanthemum morifolium ramat. cv. "JIMBA" growth and its ability in 3 culture systems: in vitro solid medium system, in vitro liquid medium system and microponic (combined of micropropagation and hydroponic). The 3 cm Chrysanthemum shoots and silver nanoparticles of diameter smaller than 20 nm were used in the experiments. After 4 weeks, the results showed that the SNPs concentration was suitable for growth of Chrysanthemum in vitro solid medium system, in vitro liquid medium system and microponic was 1.5, 1.5 and 5 ppm, respectively. Microponic system not only improved plant growth but also reduced the succulent phenomenon. SNP uptake was likely dependent on concentrations and culture systems. At low concentrations (1, 5, and 10 ppm), SNPs were completely absorbed after 4 weeks of culture in all systems, but not at high concentrations (20 ppm). The amount of absorbed silver nanoparticles was directly proportional to the culture period and inversely proportional to the concentration of SNPs supplemented to the medium. In all of our investigated systems, the hydroponic system showed the highest capability of SNPs absorption.

The chemical examination of ethanolic extract of manglicolous lichen Graphis ajarekarii (Ga-Et) resulted in isolation of three known metabolites – chiodectonic acid (1), graphenone (2) and graphisquinone (3). All the isolates (1-3) and Ga-Et were screened against DPPH and superoxide free radicals, six different cancer cell lines and one normal human cell line (NHME). This work is the first report of antioxidant and cytotoxicity studies on the isolated metabolites (1-3).

Nematodes communities in Ba Lai river, Ben Tre province were investigated in September of 2015 (eight stations from estuary to upstream). The results showed that the nematodes communities have characterized by high density and biodiversity, providing useful information of nematodes assemblages in freshwater habitas, in particular inland river. Also the results indicated that the distribution of nematodes communities in Ba Lai river was strongly discriminated between in and outside of dam with two groups. The Ba Lai dam may be reasons for cause  the nematodes distribution discontinuity. Present study is a pioneering attempt to record the impact of the dam on benthic-invertebrate in Vietnam.

Desalination of seawater using membrane distillation (MD) can be a practical approach to mitigating the fresh water scarcity in Vietnam. This paper provides a comprehensive review of the seawater MD desalination process. The fundamentals of the MD process including configurations, membrane modules, membrane properties, and heat and mass transfer mechanisms together with approaches to enhancing heat and mass transfer are first systematically reviewed and analyzed. Then, the potential and challenges of the seawater MD desalination process are thoroughly discussed.