Tạp chí Kỹ thuật và Công nghệ Đại học Quốc gia Thành phố Hồ Chí Minh

Autoclaved Aerated Concrete (AAC) is a Lightweight, Load-bearing, High-insulating, Durable building product, which is produced in a wide range of sizes and strengths. AAC Blocks is lightweight and when compared to the red bricks, AAC blocks are three times lighter. AAC block is rapidly developing in Vietnam. The block has more advantages such as precast, and easy installation. AAC is produced from the common materials: lime, sand, cement and water, and a small amount of rising agent. After mixing and molding, it is then autoclaved under heat and pressure to create its unique properties. Then, the AAC block will be cut into block brick by steel wire. When cutting the ACC block, the block brick surface must be smooth so that it is unnecessary to mortar. Furthermore, the roughness of the surface must be smaller than 0.1mm to paint the wall easily. The block dimension also need high precision so that the wall will be straight when blocks are superposed. However, in this paper, the roughness of the block surface will be only researched because the roughness will decide the cost, and the dimension decide the estheticism of wall. The block is made by using steel wires to cut big AAC blocks into small blocks. Effects of processing parameters on the performance of the steel wire sawing processes are wire speed, feed rate and tension. Each parameter will affect surface quality with different effects. In addition, these parameters affect each other, which causes scratches on the AAC surface. Experiments will be made to measure the height of roughness with the change of wire speed, feed rate and tension. The best parameters will be found, which helps the AAC manufacturer to obtain the higher quality.

In dentistry, X-ray method has been considered as the gold standard for identifying different types of structural damage in teeth. However, X-rays not only have adverse effects on patients’ health but also have failed in detecting small and early-stage lesions due to the low sensitivity of the method to these types of lesion. In order to overcome the disadvantages of X-ray method, in recent years, the infrared and fluorescence techniques have been developed strongly due to the fact that the optical properties of damaged tissue under infrared and ultraviolet lights are significantly different from those of sound dental tissue because of the demineralization of damaged tissue. The aim of the present study was to apply the fluorescence and infrared techniques to diagnosis of dental lesions at early stages. In this study, the optical systems with 850-nm LEDs and 365-nm LEDs which were applied for infrared imaging and luminescence imaging, respectively, were designed and used for diagnosing in vitro different types of early-stage lesions such as white spot lesions, dental plaque and lesions under restoration. A number of 68 tooth samples were assayed with infrared technique, fluorescence technique and clinical observation combined with radiography at the same time. Cohen's Kappa coefficient which was obtained with Statistical Package for the Social Sciences program was used to evaluate the agreement in diagnosis between the mentioned methods. The statistical evaluation showed that Kappa coefficients between traditional methods (clinical examination combined with X-rays) with optical techniques including infrared and fluorescence techniques were 0.147 and 0.235, respectively. These results suggest that all the lesions analyzed in this study were at the early stages and could not be detected by both visual inspection and X-rays, whereas the infrared and fluorescence techniques could be more sensitive to these types of lesion due to the fact that the optical techniques are able to detect early signs of demineralization of damaged tissue.

In this paper, the authors propose a novel adaptive multilayer T-S fuzzy controller (AMTFC) with an optimized soft computing algorithm for a class of robust control uncertain nonlinear SISO systems. First, a new multilayer T-S fuzzy was created by combined multiple simple T-S fuzzy models with a sum function in the output. The multi-layer fuzzy model used in nonlinear identification has many advantages over conventional fuzzy models, but it cannot be created by the writer's experience or the trial and error method. It can only be created using an optimization algorithm. Then the parameters of the multilayer fuzzy model are optimized by the differential evolution DE algorithm is used to offline identify the nonlinear inverse system with uncertain parameters. The trained model was validated by a different dataset from the training dataset to guarantee the convergence of the training algorithm. Second, for robustly and adaptive purposes, the authors have proposed an additional adaptive fuzzy model based on Lyapunov stability theory combined with the optimized multilayer fuzzy. The adaptive fuzzy based on the sliding mode surface is designed to guarantee that the closed-loop system is asymptotically stable has been proved base on a Lyapunov stability theory. Furthermore, simulation tests are performed in the Matlab/Simulink environment that controlling a water level of a coupled tank with uncertain parameters are given to illustrate the effectiveness of the proposed control scheme. The proposed control algorithm is implemented in simulation with many different control parameters, and it is also compared with the conventional adaptive control algorithm and inverse controller. The simulation results also show the superior of the proposed controller than an adaptive fuzzy control or inverse controller when using the least mean square error standard.

For the first time, an environmentally friendly and effective procedure to produce high-value engineering aerogels from fly ash (FA) has been developed by dispersing FA particles into a mixture of biodegradable polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC), followed by freezedrying. The effect of FA content on the physical properties, morphology, mechanical strength, and thermal conductivity of FA aerogels is also studied comprehensively. The lightweight FA aerogels show a low density of 0.072 – 0.093 g/cm3 with high porosity of 94.94 – 95.78%. The morphology of aerogels shows the uniform distribution of FA particles in PVA-CMC matrixes that creates a porous structure with a pore size of 2-5 mm. Therefore, the FA aerogels exhibit good heat insulation with extremely low thermal conductivity of 0.040 – 0.047 W/m.K at ambient temperature and pressure that is comparable to some commercial insulation materials such as mineral wool, fiberglass, expanded polystyrene, and other silica-based aerogels from waste. Moreover, the compressive modulus of FA aerogels is about 67.73 – 254.75 kPa indicating their excellent mechanical properties under 1 kN vertical compression. The experimental results indicate the significant better durability of FA aerogels than that of previous aerogels from other wastes such as sugarcane bagasse (88 kPa), pineapple leaf fibers (1.64 – 5.34 kPa), recycled polyethylene terephthalate (1.16 – 2.87 kPa), spent coffee grounds (5.41 – 15.62 kPa), and silica – cellulose (86 – 169 kPa). It is concluded that FA aerogels are a promising candidate as a lightweight thermal insulating material.

Granular columns have been used to improve load bearing capacity and to reduce the settlement of the soft soils for the past three decades. However, for soft soils with less than 15 kPa of undrained shear strength, the use of granular columns is ineffective because the soft soil does not mobilize sufficiently lateral confinement stress to balance the column lateral stress, which leads to the laterally deformed column (bulging) at the top section of the column. To overcome this limitation, many researchers have developed a new method of soil improvement using granular columns with geosynthetic encasement, which are actually an extension of the granular columns. This new approach, which is more advantageous than the granular columns, is thanks to geosynthetic providing additional confinement stress in conjunction with the soil surrounding the column. In this paper, the authors apply analytical solutions based on “unit cell concept” model in order to compare the effect of settlement between stone columns and stone columns with geosynthetic encasement implementing to reinforce the soft soil ground of Vifon II plant in Long An. The authors also investigate the effect on the column settlement due to variables of the column diameter, column spacing and embankment height. The results show that in all cases, the settlement of stone column is about 50-80% higher than stone column with geosynthetic encasement, which have proved the superior efficiency of geosynthetic encased column (GEC) compared to conventional stone applied in soft soil improvement.  

Honey is a nutritious, sweet-tasting drink with the natural fragrance of flowers, so it is favored and widely used in many areas of life. Hard qualitative norms on honey quality are such as color, content of HMF, reducing sugar, microorganisms ... One of the causes of rapid change in bile quality during use is the amount of water in honey. The surveys of the methods for reducing the water content of honey with the results obtained are as follows: Using temperature to reduce water content in honey makes honey color darker. Although silica gel is very effective in reducing water content, it reduces honey amount and changes the original honey scent. In particular, the “hive model” industrial equipment reduces the water content (18.08%) compared to the raw honey (22.01%). Analyzing the sugar components: fructose, glucose, maltose, and saccharose almost unchanged. Nine volatile compounds have been identified in samples of raw honey and honey with low water content, especially aromatic compounds that characterize the fragrance of nectar such as furanoid linalool oxide, cis- and furanoid linalool oxide in honey with low water content are not significantly lower compared to raw honey. During the 2-month follow-up period, honey with low water content had lower sugar content (3%) and HMF increase (9%) compared to the raw honey (11% and 41%). The results show that the method of removing water from honey is a solution to help stabilize the quality of honey preservation.

This paper proposes a method of designing controller and building control algorithms for an industrial robot to establish laboratory lectures for education. The robot is used in this paper is SV3X robot, a product of MOTOMAN. In this research, we present how to design and manufacture a controller for an old robot. After that, we propose labortory lectures based on this controller. A new graphic user interface (GUI) is also built based on C# language. Next, we propose algorithms that can be done. Two algorithms suggested were controlling robot to follow a desired trajectory and controlling robot to grasp a know object from started point to goal point. Finally, these algorithms are verified by experiments. Repeatability of robot is also checked.

In 500 kV power systems, shunt reactors are usually used to control the reactive power balance and regulate the operating voltage within the permissible limits. Therefore, shunt reactors may be frequently switched daily. Using circuit breakers to switch shunt reactors will produce transient components during this period. When a shunt reactor is switched on, the inrush current will appear and when the shunt reactor is switched off, the transient recovery voltage (TRV) will occur between two terminal contacts in the circuit breaker. This paper will focus on analyzing TRV components that occur when opening the circuit breaker to interrupt inductive loads with small currents, namely the analysis of TRV that occurs when opening the circuit breaker of the shunt reactor 500 kV - 128 MVar at 500 kV O Mon substation by using ATP/EMTP transient analysis software. The simulation has indicated that the obtained results are suitable to the practical case and they are can be used a basis for a suggestion of solutions to reduce the TRV for other 500 kV substations with shunt reactors in Vietnam. This study also has significant technical and economic contributions. In the economy, the application of this model for shunt reactor circuit breakers will provide an evaluation of their TRV standing level in the practical operation, leading to reducing the maintenance and replacement costs of circuit breakers. In the technique, this solution will help to solve the problems of selecting appropriate circuit breakers, the best operation procedure, and effective reduction of TRV.

This paper presents the results of experimental research on key technology and equipment for cultivation of Spirulina platensis from the CO2 capture from the smoke of rice husk boiler with the climate conditions in Viet Nam. The experimental cultivation of Spirulina platensis in the Zarrouk medium were conducted in the 1 litter of volume’s photobioreactor which has stirred with aeration pump. Experimental results show that the temperature changes every day in a fairly wide range from 25 to 40 oC and get over the optimal temperature for growth of Spirulina platensis 30 to 38 oC but not much at noon time; when blowing from the smoke of steam boiler with the suitable temperature and stirring simultaneous by the circulating pump; at the same time the CO2 absorption process into water was occurred and converting it into HCO3-, as a suitable substrate for Spirulina platensis is easy to assimilate; the biomass concentration of Spirulina increases from 0.1 to 1.81 g/l and the pH of suspension increases from 8.5 to 10.2 after the stage’s first time of 7 days of cultivation with Zarrouk medium and since the eight days to 16th day of the cultivation is steaming stage from boiler with period of 30 minute into the above medium that containing 7.76 % CO2 for maintaining the pH of solution from 8.5 to 9.5. The smoke of steam boiler that has CO2 in which blow to supply the carbon nutrient source in the formation of HCO3-, to maintain the pH value in the range of 8.5 ¸ 9.7 and increase biomass productivity to 2.53 g/l simultaneously. The photosynthetic rate of algae biomass was compared with the cultivation of Spirulina platensis under the same conditions like that using the pure CO2 and non-using the pure CO2 and the results in two of the above conditions are equivalent. This research is basis for constructing equipment and building a technology process in which utilizing CO2 from exhaust gas for Spirulina platensis cyanobacteria’s cultivation with the aim of reducing green-house gas CO2 in industry.