Polarization modulation by vanadium dioxide on metallic substrates

Vanadium dioxide (VO2) undergoing phase transition is known alters the polarization state of light in reflection owing to large changes in complex refractive indices. While this effect is promising for optical modulation applications, the usual VO2 films on dielectric substrates tend to offer limited tunability for polarization modulation. In this paper, we show that metallic under-layers greatly enhance the performance by widening the spectral range and include visible wavelengths, by increasing the polarization modulation amplitude, and by widening the range of workable incidence angles. The imaginary part of the refractive index in the metallic layer is found to increase the relative phase shifts between s- and p-components of polarization as well as increasing the reflectance

The Status of Educational Sciences In Vietnam: A Bibliometric Analysis From Clarivate Web Of Science Database Between 1991 And 2018

Since 2013, Vietnam has implemented a plan to reform the whole education sector. However, there is little understanding on the status of educational research in Vietnam, which may lay the foundation for such plan. Thus, this research aims to analyze the whole picture of educational research from Vietnam, as seen from the Clarivate Web of Science (WOS) database: 215 publications were recorded, ranging from 1991 to 2018. These 215 publications were further analyzed from five perspectives: 1) number of publications by year; 2) research fields and levels of education; 3) top institutions with the highest number of publications; 4) international collaboration; and 5) quality. Some of the most notable results are: 1) the educational sciences in Vietnam have been still under-developed until recently; 2) among different research topics research among educational sciences, some (e.g., Vocational Education and Training or Early Childhood Education) seemed to be overlooked whereas others (e.g., Higher Education and Teaching and Learning) seemed to receive more attention from educational scholars; 3) all the most major education – specialized universities did not appear among the top five institutions with highest number of publications; 4) Australia, Thailand, the USA, New Zealand and China were the countries with the highest number of co-publications with Vietnamese researchers; and 5) The majority of publications belonged to low-ranked journals. Implications would be withdrawn for Vietnamese policymakers, education leaders, educational researchers and teachers in order to adjust their policies and/or action plans; thus, enhancing the performance and impacts of educational research in the future

An Analytical Framework Considering the Effects of Online Teaching Quality on Student Satisfaction

COVID-19 spreads across the world in late 2019 has affected to several aspects of social life. One of the most important sectors, which face difficulties was education, thus most universities have transferred from traditional education to online education through the internet to make their academic year going. This study aims to review the effects of online teaching quality on student satisfaction, a positive attitude resulting from an evaluation of students’ online teaching experience in higher education. Through applying the SERVQUAL model to measure the effects of online teaching quality on students’ satisfaction, it can be expected to get better the online teaching quality of higher education institutions in Vietnam. Keywords: Online teaching, student satisfaction, higher education, COVID-19, educational institution. DOI: 10.7176/EJBM/13-6-08 Publication date:March 31st 202

ẢNH HƯỞNG CỦA TỈ LỆ Ba/Ti LÊN ĐẶC TRƯNG CỦA HẠT NANO BaTiO3 TỔNG HỢP BẰNG PHƯƠNG PHÁP THỦY NHIỆT

Highly dispersed BaTiO3 nanospheres with a uniform particle size were synthesized with the hydrothermal method. The influence of Ba/Ti molar ratios on the formation of BaTiO3 nanospheres was studied by analyzing the XRD and SEM data. The TiO2·H2O synthesized with the sulfuric acid method assisted by ultrasonication was used as a starting material. Highly dispersed BaTiO3 nanospheres with an average size of about 100 nm were obtained at 200 °C in 12 hours with a Ba/Ti ratio of 1.5. The Ba/Ti ratios have a strong influence on the formation of nano BaTiO3 and the phase transition. The particle size increases with the Ba/Ti ratio, while the uniformity decreases.Vật liệu BaTiO3 nano hình cầu phân tán cao với kích thước đồng đều được tổng hợp bằng phương pháp thủy nhiệt. Ảnh hưởng của tỉ lệ mol Ba/Ti lên sự hình thành vật liệu được nghiên cứu bằng cách phân tích dữ liệu XRD và SEM. TiO2·nH2O tổng hợp bằng phương pháp axit sunfuric với sự hỗ trợ sóng siêu âm được sử dụng làm nguyên liệu ban đầu. Vật liệu nano BaTiO3 hình cầu với độ phân tán cao và kích thước trung bình khoảng 100 nm đã thu được tại 200 °C trong 12 giờ với tỉ lệ Ba/Ti = 1,5. Tỷ lệ Ba/Ti ảnh hưởng mạnh đến sự hình thành BaTiO3 nano hình cầu với quá trình chuyển pha. Khi tăng tỉ lệ Ba/Ti, kích thước hạt tăng và tính đồng nhất giảm

Carrot hairy roots (Daucus carota L.) characterisation and optimisation for high β‐carotene extraction

Hairy roots are widely known as a biological system for the production of highly diverse biomolecules. β‐carotene – a precursor for vitamin A – is known to be an anti‐oxidant and anti‐gastric cancer and protection agent against cardiovascular disease, heart disease and stroke. β‐carotene has been chemically synthesised and consumed by humans. However, the chemical process often produces a by‐product that may be harmful to human health. Therefore, this study established a protocol to induce hairy roots (HRs) from a Vietnamese carrot variety and produce natural β‐carotene. The Rhizobium rhizogenes ATCC15834 harbouring Ri plasmid and a Vietnamese carrot variety were used as materials for genetic transformation and HR induction studies. The result showed that approximately 50 HR lines were obtained. Culture medium supplemented with 30 mg/L of sucrose that gave the highest biomass of HR was shown in carrot HR line 30, which had a doubling time of 6.5 days. The highest content of β‐carotene extraction, at 128 mg/100g hairy roots, was achieved with a ratio volume (v/v) of 2‐propanol and plant samples of 20:1, followed by two hours’ incubation with 2‐propanol at 60 °C. Our study reveals a highly efficient protocol for Vietnamese carrot hairy root establishment and multiplication. A very efficient protocol for β‐carotene extraction from the hairy root was established to produce natural β‐carotene that achieves the same β‐carotene quantity as that produced by normal roots. This study provides new insight into the production of high‐content and natural β‐carotene for therapeutic application

Investigation of Sodium Manganese Oxide Nanowires Synthesized by Hydrothermal Method for Alkaline Ion Battery

Sodium Manganese Oxide (NaxMnO2) has attracted much attention as cathode materials for alkaline ion battery due to the ability of fast charge and discharge ion Na+, in particular in nanoscale. We report on the synthesis of NaxMnO2 nanowires via hydrothermal synthesis route from Mn2O3 and NaOH solution. The morphological observation indicates that the obtained Na0.44MnO2 nanowires with diameters of about 20-30 nm, length up to several micrometers were formed by this process. The electrochemical properties of fabricated materials were investigated by means of cyclic voltammetry technique and show that Sodium Manganese Oxide (NaxMnO2) is a promising material in the field of research and fabrication alkaline ion battery

MÀNG DẪN ĐIỆN TỪ SỢI NANO BẠC TỔNG HỢP BẰNG PHƯƠNG PHÁP POLYOL

In this paper, silver nanowires were prepared with the polyol method under ultrasonication. The optimal concentration of polyvinyl pyrrolidone in the reaction mixture was also determined. These nanowires were characterized with the XRD, SEM, and UV-Vis techniques. The conductive solution possesses a low resistance, good adhesion, high flexibility, and thermal stability. The solution was utilized to fabricate a conductive film, which might open up new technology applications.Trong bài báo này, sợi nano bạc đã được tổng hợp bằng phương pháp polyol dưới tác động của siêu âm. Đã xác định được nồng độ tối ưu của polyvinyl pyrrolidone cho quá trình chế tạo dung dịch. Sản phẩm sợi nano được khảo sát bằng kỹ thuật XRD, SEM và UV-Vis. Dung dịch dẫn điện có điện trở thấp, bám dính tốt, tính linh hoạt cao và ổn định nhiệt. Dung dịch này đã được sử dụng để chế tạo màng dẫn điện. Sản phẩm có thể mở ra một hướng mới cho các ứng dụng công nghệ sau này

Observation of High Doppler Velocity Wings in the Nascent Wind of R Doradus

We study the morpho-kinematics in the nascent wind of AGB star R Doradus in the light of high Doppler velocity wings observed in the spectral lines of several species. We probe distances from the star between ∼10 and ∼100 au using ALMA observations of the emission of five different molecular lines. High Doppler velocity enhancements of the line emission are observed in the vicinity of the line of sight crossing the star, reminiscent of those recently interpreted as gas streams in the nascent wind of a similar AGB star, EP Aqr. They are present in both blue-shifted and red- shifted hemispheres but are not exactly back-to-back. They are accelerated at a typical rate of 0.7 km s$^{−1}$ au$^{−1}$ up to some 20 km s$^{−1}$. Important differences are observed between the emissions of different molecules. We exclude an effect of improper continuum subtraction. However, in contrast to EP Aqr, the line of sight plays no particular role in the R Dor morpho-kinematics, shedding doubt on the validity of a gas stream interpretation. We discuss possible interpretations in terms of stellar pulsations or of rotation of the gas in the environment of the star. We conclude that, in the state of current knowledge, no fully convincing picture of the physics governing the production of such high velocities, typically twice as large as the terminal velocity, can be reliably drawn. New high resolution analyses of observations of the nascent wind of oxygen-rich AGB stars are needed to clarify the issue