STUDY OF NEGATIVE REFRACTIVE INDEX IN Rb FOUR-LEVEL N-TYPE ATOMIC GAS MEDIUM

In this work, we study the generation of a negative refractive index based on electromagnetically induced transparency (EIT) in a Rb four-level N-type atomic gas medium. We derive analytic expressions for the relative permittivity and relative permeability of the medium according to the parameters of the probe, pump, and signal laser fields. We then investigate the variation of the real parts of the relative permittivity and relative permeability with respect to the intensity and frequency of the pump and signal laser fields. In the presence of the pump laser beam, the medium becomes transparent to the probe laser beam even in the resonant region. At the same time, the real parts of the relative permittivity and relative permeability are simultaneously negative (i.e., the medium exhibits a negative refractive index) in the EIT spectral domain. In the presence of the signal laser beam, the EIT effect occurs over two different frequency domains of the probe beam, so a negative refractive index is also generated in these two frequency domains. The investigation of the real parts of the relative permittivity and relative permeability with intensity and frequency of the pump and signal laser fields allowed us to find the laser parameters for the appearance of the negative refractive index, which can be useful for experimental observations

Factors affecting the decision to choose a university of high school students: A study in An Giang Province, Vietnam

It is important to provide high school students with the necessary information for them to consult and make a decision to choose a university. The study aims to identify and evaluate the influence of factors in the decision to choose a university for high school students. The questionnaire survey method was used to collect data from 393 students from eight high schools in An Giang Province, Vietnam. Exploratory factor analysis and linear regression were used to analyze the data. The research results show that students are quite satisfied and quite certain with their decision to choose a university, while there are six important factors affecting the decision to choose a university. Influential factors with decreasing order of magnitude are: i) Factors consulted by teachers, family, friends, and relatives; ii) Factors of future job opportunities; iii) Factors of media activities; iv) Factors of learning conditions; v) Factors of university reputation; vi) Factors belong to the students themselves. The findings of the study show that there is no statistically significant difference between the group of males and females, between grades 10, 11, and 12. Besides, there is a statistically significant difference between students in high schools. The findings of this study have theoretical and practical implications for university admissions in Vietnam. Proposals made to university administrators were discussed. From the research results, we want to help students find the right university, and support universities to improve the efficiency of admissions

Research on Factors Affecting Credit Risk of Joint Stock Commercial Banks on Vietnam Stock Market

Design/methodology/approach: The article aims at identifying factors affecting credit risk of commercial banks in Vietnam. The study uses data collected from financial statements of 15 typical joint stock commercial banks out of a total of 27 joint stock commercial banks listed on the Vietnam stock exchange from 2012 to 2022 with panel data of 15 joint stock commercial banks for the period 2012 - 2022. The banks in the research data are the those with the largest total assets in the banking system. After collecting and processing data, research sample includes 165 observations and the study uses E-view software in quantitative analysis to build a regression model to determine the relationship and level of influence of Internal factors to credit risk of listed joint stock commercial banks.   Findings: Research results indicate that factors affecting credit risk of listed joint stock commercial banks include: Ratio of equity to total assets, capital structure of the bank, and operational performance of the banks.   Research, Practical & Social impications: These results confirm the importance of taking into account micro finance factors when making financing. Understanding the impact of these factors and relationships contributes to decision and risk management.   Originality/value: In order to limit credit risk it is necessary to focus on: Ensuring reasonable equity; Stricter control over loan capital; Optimal use of resources

A STUDY ON THE SYNTHESIS OF MgAl2O4 SPINEL BY STARCH ASSISTED SOL-GEL PROCESS

In this paper, the synthesis of ceramic spinel MgAl2O4 by starch assisted sol - gel process is presented. The gel mixture was prepared by using Mg(NO3)2.6H2O, Al(NO3)3.9H2O as precursors and starch as a gel agent. The study focused on relevant components of gel mixture and the calcinating temperature. The results showed that suitable molar proportion of Mg2+/Al3+; starch/(Mg2+ + Al3+) and H2O/starch were 0.5, 0.4 and 60, respectively. The calcination at               1100 oC for 60 minutes was suitable for forming phase of spinel. The product was a single phase of spinel MgAl2O4 with excellent crystallinity and uniform size in the range of 300 to 400 nm

INFLUENCE OF SYNTHESIS FACTORS ON PROPERTIES OF GEOPOLYMERS BASED ON RED MUD AND RICE HUSK ASH

In this paper, the effect of mixing ratio of raw materials, curing temperature and time on geopolymerization between red mud and rice husk ash were investigated. The results showed that the optimum conditions were SiO2/Al2O3 ratio of 4 and Na2O/Al2O3 ratio of 2.0, curing temperature of 100oC and curing time of 24 hours. The compressive strength, bulk density, total shrinkage of the obtained product were 22.8 MPa, 2.39 g.cm-3, 15%, respectively that met requirement of unsintered bricks using for construction

UV Light Induced Thermoluminescence of Rare Earth doped Nanomaterials Y2_2O3_3:Eu3+^{3+}, Gd2_2O3_3:Eu3+^{3+} and Gd2_2O3_3:Er3+^{3+}

Thermoluminescence  properties of ultraviolet irradiated Y2O3:Eu3+, Gd2O3:Eu3+ and Gd2O3:Er3+ nanophosphors have been reported. The materials were synthesized by gel- combustion method with EDTA- Na2 as organic agent. This method allows production of very fine white powder at low temperature with very high efficiency. XRD has been studied to determine the structure of the prepared nano powders. The obtained materials exhibit sufficient sensibility to UV radiation and may be useful in UV light measurements

Assessing status and habitat of siamese fireback (Lophura diardi) by using camera trap in Lo Go-Xa Mat National Park, Vietnam

Siamese fireback, Lophura diardi, belonging to Galliformes is at risk due to habitat loss and hunting, which are main challenges to conservation of the species. In order to provide scientific information to conserve the L. diardi, we implemented a camera-trap survey in Lo Go-Xa Mat National Park from 2017 to 2018. Occupancy and Poisson regression models were used to investigate presence of the species and potential factors influencing the occurrence of the species in the study area. Our results showed that the probability of occurrence of the species at locations within the park was high at 0.84 (0.69–0.92) and detection probability was relative low at 0.19 (0.16–0.23). The best models consistently suggested that the abundance of the species was high in closed canopy forest cover (β = 0.41), but appeared to be notably lower in areas far away from the ranger stations (β = -0.25) and in places with high frequency of human (β = -0.22). This research provided the first quantitative information of status and potential factors influencing occurrence of the L. diardi in the park, which is an essential data for developing practical actions to protect the species and monitoring program in the future for the park.         

TỔNG HỢP VẬT LIỆU Ni/UiO-66 THEO PHƯƠNG PHÁP TRỰC TIẾP VÀ GIÁN TIẾP

An archetypal metal-organic framework, UiO-6,6, synthesized with the solvo-thermal method, has a large specific surface area of 1071 m2·g–1. This material was modified with NiCl2 in the direct (Nix(tt)/UiO-66) and indirect (Nix(gt)/UiO-66) methods. The two modified materials were characterized by using powder X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. Their crystalline and chemical structure is not much different. However, the thermal and porous properties differ from each other.UiO-66 là họ vật liệu khung hữu cơ kim loại tổng hợp bằng phương pháp nhiệt dung môi có diện tích bề mặt riêng lớn (1071 m2·g–1). Vật liệu UiO-66 này được biến tính bằng NiCl2 theo phương pháp trực tiếp (Nix(tt)/UiO-66) và gián tiếp (Niy(gt)/UiO-66). Kết quả đặc trưng hai vật liệu biến tính này bằng nhiễu xạ tia X, hiển vi điện tử quét và phổ hồng ngoại khác nhau không đáng kể. Tuy nhiên, phân tích nhiệt trọng lượng và đẳng nhiệt hấp phụ – khử hấp phụ N2 cho thấy có sự khác nhau giữa các phương pháp tổng hợp

ẢNH HƯỞNG CỦA VITAMIN E BỔ SUNG VÀO THỨC ĂN ĐẾN HIỆU QUẢ SINH SẢN, CHẤT LƯỢNG TRỨNG VÀ ẤU TRÙNG CÁ KHOANG CỔ NEMO (Amphiprion ocellaris (CUVIER, 1830))

This study was carried out to determine the effects of vitamin E (a-tocopherol) in five levels (0, 125, 250, 375 and 500 mg vitamin E/kg feed) in broodfish diets on reproductive, egg and larval quality parameters of clownfish (Amphirion ocellaris). Each treatment was repeated in triplicate and the supplemental feeding trial was arranged for 13 months. The result showed that there were no significant differences in re-maturation and spawning periods, spawning frequency, fecundity, egg diameter and larval size of Nemo fish observed between the treatments. However, diets supplemented with vitamin E positively influenced the rate of egg loss, hatching rate of egg and survival rate of the 3 days post hatch. The overall result of this experiment indicated that the optimum vitamin E requirement of clownfish for reproductive performance was 375 mg vitamin E/kg feed.Thí nghiệm được thực hiện nhằm xác định ảnh hưởng của vitamin E (0, 125, 250, 375 và 500 mg/kg thức ăn) được bổ sung trong thức ăn cá bố mẹ đến các chỉ số sinh sản, chất lượng trứng và ấu trùng cá khoang cổ Nemo (Amphiprion ocellaris). Mỗi nghiệm thức được lặp lại 3 lần và thí nghiệm được tiến hành trong 13 tháng. Kết quả đã cho thấy thời gian tái thành thục và sinh sản, tần suất sinh sản, sức sinh sản thực tế, đường kính trứng và kích thước ấu trùng không bị ảnh hưởng bởi chế độ ăn bổ sung vitamin E ở các mức khác nhau. Tuy nhiên, chế độ ăn có bổ sung vitamin E đã ảnh hưởng tích cực đến tỷ lệ hao hụt của trứng, tỷ lệ trứng nở và tỷ lệ sống của ấu trùng 3 ngày tuổi. Kết quả nghiên cứu chỉ ra rằng nhu cầu vitamin E tối ưu của cá khoang cổ Nemo đạt được hiệu quả sinh sản là 375 mg vitamin E/kg thức ăn

CSA: Thực hành nông nghiệp thông minh với khí hậu ở Việt Nam

During the last five years, Vietnam has been one of the countries most affected by climate change. Severe typhoons, flooding, cold spells, salinity intrusion, and drought have affected agriculture production across the country, from upland to lowland regions. Fortunately for Vietnam, continuous work in developing climate-smart agriculture has been occurring in research organizations and among innovative farmers and entrepreneurs. Application of various CSA practices and technologies to adapt to the impact of climate change in agriculture production have been expanding. However, there is a need to accelerate the scaling process of these practices and technologies in order to ensure growth of agriculture production and food security, increase income of farmers, make farming climate resilient, and contribute to global climate change mitigation. This book aims to provide basic information to researchers, managers, and technicians and extentionists at different levels on what CSA practices and technologies can be up scaled in different locations in Vietnam