Tạp chí Khoa học Tự nhiên Đại học Quốc gia Thành phố Hồ Chí Minh

High voltage cathode LiCoPO4 has been taken great interest for high power Li-ion batteries (LIBs). Though Co enhance the cyclability, capacity of materials, Co concentration should be reduced in electrode materials due to its high cost and toxic. In this work, the solvo-thermal reaction following by pyrolysis in inert Ar was investigated to synthesize the electrode materials LiFexCo1-xPO4 (0.1 <= x <= 0.5) for LIBs. The structure of the materials after calcinated at 600 oC, 700 oC and 800 oC was analyzed by X-ray diffraction (XRD). The results indicated that the olivine structure was obtained for all Fe contents, except for x = 0.5. At the content of 0.1 and 0.5, the intensity of impurity peaks in the samples increased with the pyrolysis temperature. Meanwhile, other samples did not display the obvious change of olivine structure. Electrochemical properties of the materials were evaluated via cyclic voltammetry (CV) and Galvanostatic charging-discharging. CV curves of the samples with Fe content of 0.2x0.4 all displayed high intensity and reversible redox peak of Co3+/Co2+ locating at 4.8 V and another peak of Fe3+/Fe2+ locating at 3.5 V. As the Fe content increased, the former peaks decreased while the latter increased due to the change of active species concentrations. Unfortunately, the specific capacities obtained for Fe-substituted materials were lower than the pristine material (70 mAh/g versus 120 mAh/g) and gradually declined during cycling. The results could be due to the electrolyte decomposition in the first charging. However, the sample with x = 0.1 exhibited the best performance with discharge capacity of 70 mAh/g and 73% capacity retention obtained after 25 cycles, which was better than the sample with x = 0.2 and unsubstituted sample.

In the carbonyl sampling of 2, 4- dinitrophenylhydrazine (DNPH) impregnated cartridge, the ozone removal was necessary because ozone reacted with the DNPH derivatives. A commercial ozone scrubber was usually used to remove O3. However, high humidity leaded to carbonyl compounds being trapped on the ozone scrubber before passing through the DNPH cartridge. The purpose of this study was to assess the ozone removal by KI-denuder under the climatic conditions of Ho Chi Minh City. Several parameters including air sampling flow rate and denuder length were optimized to achieve the highest removal efficiency. The optimum parameters of the KI denuder were the sampling flow rate of less than 1 L/min, and the denuder length of 20 cm. The effect of the initial O3 concentration on the removal efficiency was also investigated. Finally, the ozone removal efficiency of KI-denuder was compared to that of ozone scrubber when two devices were applied for the carbonyl sampling during field measurement. The results show that KI-denuder could be used to replace the ozone scrubber with high removal efficiency, particularly in high humidity condition. In conclusion, KI-denuder was effective, simple, easy to use and cheap. Therefore, it was encouraged to use in carbonyl sampling.

One of the most effective methods for type 2 diabetes treatments is inhibition of enzyme α-glucosidase in the intestines to slow down the release of glucose from carbohydrates in the diet, reduce plasma glucose levels and prevent hyperglycemia after meals. Therefore, seeking α-glucosidase inhibitors used in the treatment of diabetes from plant is the attention of many scientists. Based on the potential of the hairy root culture technology in increasing valuable chemical compounds accumulating, this study aimed to induce hairy roots from six plants of the Malvaceae family including Urena lobata, Abutilon indicum, Hibiscus Sabdariffa, Hibiscus rosa-sinensis, Sida acuta, Sida rhombifolia, and screening which materials has the highest in α-glucosidase inhibitory activity. We have successfully induced hairy roots from six plant species by using the Agrobacterium rhizogenes ATCC 15834 strain. The highest rates of hairy root induction were observed in Hibiscus Sabdariffa and Urena lobata. The stable introduction of rolB and rolC genes to plant genomes was confirmed by PCR. Under liquid-shake culture conditions on MS medium, hairy roots of Hibiscus sabdariffa, Urena lobata and Sida acuta showed better development than other species, and therefore, they are selected for the study of α-glucosidase inhibitory activity. This study proved that Urena lobata was stronger in inhibiting α-glucosidase activity than other studied plants, with the IC50 value of 7.65 μg/ml. The results of this study demonstrated Urena lobata hairy root might be considered as a potential supply of medicinal plants for the treatment of type 2 diabetes.  

In order to find an effective halogen-free flame retardant for acrylonitrile-butadienestyrene copolymer (ABS), organo-phosphorus compounds were studied and their flame retarding performances were determined by UL 94 vertical test. It is found that the flame retardancy strongly depends on phosphorus (P) content of organophosphorus compounds. Only the mixture of ABS with 2-(6-oxido-6Hdibenz< c,e><1,2>oxaphosphorin-6-yl) methyl diethyl phosphinate (ODOPM-DE), which has the highest P content, i.e., 17.68 % gives V-0 rating for the 70/30 composition.

In this study, LiFePO4/carbon (LFP/C) nanocomposite was successfully prepared by hydrothermal method in which sucrose was used as carbon precursor. The obtained composite was characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results showed that this nanocomposite possessed a high-crystallized LFP with a olevin structure and rod-type particles morphology with the size of 100-500 nm. The LFP/C cathode yields showed good capacity of 110 mAh g-1 at 0.1 C as well as high columbic efficiency of 95% in term of using 1.0 M LiPF6 in EC/DMC (1/1). In the case of using an additional 2% VC in the electrolyte system, the specific capacity was 136 mAh g-1 and columbic efficiency was nearly 100%. The superior electrochemical performances can be attributed to the formation of SEI layers on the electrode surface by VC decompostion, leading to suppressed the additional SEI formation from the other solvent, reduced charge-transferred resistance and improving cell capacity as well as long-term capacity retention.

M cells are specialized intestinal epithelial cells found in the follicle-associated epithelium (FAE) of Payer’s patches (PPs). M cells play a vital role, which is known as the gateway and initiator of mucosal immune responses in the gastrointestinal tract. Mature M cells, derived from intestinal stem cells, are randomly located throughout the gastrointestinal tract. The morphology of M cells is characterized by the lack of microvilli and a thin glycocalyx layer in comparison with other intestinal epithelial cells. Glycoprotein 2 (GP2) is highly expressed on the M-cells surface, to enable the uptake of pathogens in the lumen via ligand-receptor interactions. Then, antigens are transported to the subepithelial dome (SED) region to initiate IgA production. Therefore, applications targeting M cells have been attracting researchers’ attention. In this review, the origin, characteristics, and maturation of M cell were summarized, followed by discussion on the development of oral vaccines targeting M cells to solve the disadvantages of antigen dispersion in the intestine and immune tolerance in order to effectively stimulate the mucosal immunity in preventing intestinal pathogens. Furthermore, the combination of targeting M cell strategy and vaccine delivery system can not only effectively stimulate the mucosal immune but also protect the antigenic activity laying the base for research and development of oral vaccines in the future.

Ground penetrating radar method (GPR) is common place in imaging buried objects, such as: supply water and drainage systems, electric and telecom cables. For shallow geology, GPR method has provided high-resolution sections containing subsurface information. In processing data, the velocity of GPR wave is the most important parameter. It helps to exactly specify the structure of a geology sections. Defining a wrong velocity may lead to an erroneous result. In this research, we are going to present two processing steps to define the electromagnetic wave velocity and the position of object from GPR data that was acquired by using a shield antenna machine prototype. The first step is application of Kirchhoff migration and energy difference graphs to calculate the electromagnetic wave velocity. In the second step, the result of migrated sections consisting of hyperbole diffraction was evaluated. If migrated using the right velocity, the diffracted hyperbola will focus on its peak and have the maximum energy. Finally, we used the workflow to define the velocity, the position and the size of the object from real GPR data collected at Go Vap district, Ho Chi Minh City, Vietnam.

Remote sensing techniques have been widely used to measure the qualitative parameters of waterbodies. Total suspended solid (TSS) is an important water quality parameter and a surrogate for the water clarity. It can be used as the indicator of sediment in the reservoir, which usually consists of silt, fine sand and microorganisms. This study aimed to utilize the remote sensing technology, in particular Landsat 8 Operational Land Imager (Landsat 8 OLI), to determine the amount of TSS concentration as well as the spatial distribution of TSS concentration in the surface water of the Tri An reservoir. The relationship between field TSS data collected in March, 2020 and the reflectance values of the the Landsat 8 Oli images was investigated. Results showed that there was a strong linear relationshiop between TSS concentration and the reflectance of the red and near infrared reflectance bands from the Landsat 8 Oli (r ranged from 0.58–0.93), in which the ratio of the red band produced the best correlation with the TSS (r = 0.93, with a standard error of 0.6–1.39 mg/L). Based on the linear regression equation, the TSS concentration calculated from the red reflectance values was used for mapping the spatial distribution of TSS in the surface water of the Tri An reservoir. Our results confirmed the accuracy and potential of using the single band from Landsat 8 OLI for mapping the spatial distribution of TSS in the Tri An reservoir.

In recent years, drought stress was strongly affected on the development and yield of tomatoes. There are increasing interests in the study of physiological transformations in adaption to stress in plants In this study, effects of drought stress (mannitol at different concentration) on the development of tomato shoot were studied. Morphological and physiological changes during the development of shoot under drought stress conditions were analyzed. Based on the analysis results, the combination of cytokinin and gibberellin was treated to increase the drought stress tolerance of plants. Results showed that mannitol at 20 g/L induced tomato drought stress. Shoot height, number of leaves, leaf area, and the number of roots significantly decreased in the drought stress condition compared to the control. The formation superoxide (O2-) and hydrogen peroxide (H2O2) occurred in the meristem, elongation region and cap of the roots in the drought stress condition instead of only cap root in the control. In the drought stress condition, there was an increase in respiration intensity, proline and carotenoid content, and abscisic acid activity. In contrast, the content of chlorophyll, photosynthesis intensity, cytokinin and gibberellin activity decreased in comparison with the control. The combination treatment of zeatin 0.5 mg/L and GA3 0.5 mg/L improved the drought stress tolerance of plants. The shoot height, number of leaves, leaf area and number of roots of the treated plants were higher than those of the control plants.

A nanostructured hybrid material prepared from eco-friendly natural materials such as nanosilica (nSiO2) extracted from rice husk and oligochitosan (OS) isolated from shrimp shells is material of high promise with special properties to be applied in various fields, especially in agriculture. In this study, hybrid nanosilica material based on oligochitosan (SOS) with a concentration of 50 mg/L as nutrient source was supplied to the lettuce (Lactuca sativa) at different stages of growth. The two-week-old lettuce (H2W2) supplied with the hybrid material had an increase in leaf length by 17.24% and root length by 5.26% in comparison with those of the control lettuce. Additionally, the fresh weight and leaf number of the hybrid-supplied plant were 20.39% heavier and 9.09% higher than those of the control samples, respectively. Moreover, the chlorophyll measurement indicated that the total chlorophyll content of H2W2 was 7.61% higher than that of the control, and the plant growth characteristics also increased by 20.39% compared with the control plant. The SOS hybrid material could be seen as a green agrochemical with a great promise of being applied in the modern agriculture. This kind of renewable material also contributes to replacing and declining the numbers of the type of toxic chemical fertilizers and plant protection products used on the market today.