Tạp chí Phát triển Khoa học và Công nghệ Đại học Quốc gia Thành phố Hồ Chí Minh

In this study, we have synthesized polyurethane based on monoglyceride and 4.4 '-diphenyl methanediisocyanate (MDI) – an environmentally friendly polymer. Graphene oxite (GO) was used to reinforce for polyurethane forming polyurethane/graphene oxide (PU/GO) nanocomposite. The synthesis of PU and PU/GO was performed directly on the twinscrew extruder. This is a simple, time saving, economical and environmentally friendly method. Nanocomposites were manufactured with GO phase changed from 0.5% to 1.5% by weight. Structural analysis results of PU/GO showed a good dispersion through TEM figure (transmission electron microscopy). In addition, the mechanical and thermal properties of the nanocomposite were improved as compared to the original polyurethane. This study is a new step for the synthesis of polyurethane and nanocomposite based on polyurethane by the melt intercalation method.

Today, enterprise resource planning system (ERP) becomes popular and it is implemented in most business (in all fields and sizes) all over the world as well as in Vietnam. However, according to consultant experts, ERP projects, though on a large scale with high cost, entail low success rate. For Vietnamese contexts, those findings above are all the more true, because most of Vietnamese enterprises are on a small scale with short-time computerization access, lack of understanding of enterprise systems, and lack of financial resources. This research focuses on exploring key factors affecting the success of ERP projects in Vietnam. Through case studies and data collection, using SPSS for data analysis, key factors affecting the success of ERP projects are listed on such a descending order as follows: Characteristics of ERP team, Quality of consultancy, Characteristics of end-users and Characteristics of business. From the abovementioned analysis, suggestions for ensuring success of ERPs in Vietnam are also proposed.

The transparent electrode films SnO2: Sb were prepared by reactive magnetron sputtering method on glass substrate with various substrate temperatures. The material of target is alloy of Sn (99,5% purity) doped Sb (5% Sb by weight). The deposition processes were carried out in mixture of Ar (99,99% purity) and 02 (99,999% purity) gas. The vacuum inside the deposition chamber can get to about 10-5 torr. The substrate temperatures during the depositing processes were kept at fixed values between the room temperature and 450ºC. The dependence of crystal size and conductivity of films on substrate temperature were also investigated.

This article deals with optimal nesting problem when parts are cut from rectangular sheet in the footwear industry. The objective of the research is minimizing the waste of material or maximizing the number of parts to be cut from sheet materials. By generating the mathematical models and building up their algorithms, the software for solving problem dedicates to a number of industries for saving time and minimizing waste of material, and increasing the cutting productivity.

The aim of this work is to describe the source rocks in Cuu long Basin mainly consisting Cenozoic sediments (lower Oligocene + upper Eocene, upper Oligocene and lower Miocene) that are poor to rich in organic matter. The organic carbon (TOC%) in lower Oligocene + upper Eocene source rocks contains mostly kerogen type II, sometimes type I, III is 1.19-2.87%; in upper Oligocene source rocks containing mostly kerogen type II, sometimes type I and III is 1.14-4.0%; and in lower Miocene source rocks contains mostly kerogen type III is 0.64-1.32%. The Oligocene sediments are mostly deposited in lagoonal, estuarial and mixed environment. The depostitional environment of the organic matter in the lower Miocene sediments is terrestry.

Basing on collecting and classifying the researches in soil mixing column method, and applying soil mixing column method at Sai Gon East West highway, this article wants to state and analysis the factors that effect strength and stability of mixing column. It also has some comments of applying this method in soil improvement.

Water is a resource needed in all aspects of life and is regarded as a decisive factor for Earth's ecosystems survival. However, water resource has also become a limiting factor of social and economic development. For cities of the developing world, water is increasingly playing a vital role in sustainable urban development. Since economic reform known as “Doi Moi" (renovation) in 1986, Ho Chi Minh City, Vietnam, has undergone the rapid growth of urbanization and industrialization. As a result, the City has experie critical environmental challenges in which water use and management have placed constraints on its sustainable development. These striking challenges include water shortage, pollution and depletion of surface and groundwater sources. The underlying reasons can be attributed to inadequate management practices. The purpose of this paper is to provide an overview of rapid urbanization and growing water resource problems. It also examines the management practices and analyze the root causes of water resource issues in the course of sustainable development.

By finite difference method, the Schrödinger equation with different effective masses in different layers of some quantum well systems is solved. From this, the effect of number of wells, barrier width, well width, electric field on energies in quantum well systems are investigated.

This paper presents a 10-b ADC designed in a 0.18-μm CMOS technology. The ADC achieves 10-b resolution by using the cascaded folding technique in both the fine and coarse converters. Folding stages are pipelined to improve the settling time. As a result, this ADC can achieve the sampling rate up to 100MS/s. Moreover, instead of using a costly single track-and-hold circuit, a distributed track-and-hold circuit is used to reduce the chip area and the power consumption. This also allows utilizing the open-loop architecture of the folding technique, thus improving the performance of the system. The simulation results show that with a 49 MHz sine-wave input, the ADC consumes 66 mW and the effective number of bit (ENOB) is 9.28-b. Taking into account of process variations by using a Monte Carlo simulation, the DNL varies from ±0.45LSB to ±0.25LSB. The layout of the ADC occupies 1.2 mm2 die area.

This paper proposes an outage analysis framework for cooperative cognitive networks with proactive relay selection and selection combining (SC) under licensed outage constraint, maximum transmit power constraint, independent non-identical (i.n.i) fading distributions, erroneous channel information, and licensed users’ interference. Towards this end, we firstly suggest power allocation for unlicensed transmitters to satisfy power constraints and account for erroneous channel information and licensed users’ interference. Then, we propose an exact closed-form outage probability formula for the unlicensed network to promptly evaluate system performance and provide useful insights into performance limits. Multiple results show performance trade-off between the unlicensed network and the licensed network, error floor in the unlicensed network, considerable system performance degradation owing to erroneous channel information and licensed users’ interference, and significant performance enhancement due to the increase in the number of relays.