SỰ LAN TRUYỀN SÓNG ĐIỆN TỪ TRONG SIÊU VẬT LIỆU HYPERBOLIC VỚI ĐỘ THẤM ĐIỆN MÔI GẦN BẰNG KHÔNG

In this paper, we investigated hyperbolic metamaterials based on a structure containing metallic nanowires embedded in a dielectric matrix with the utility environment theory method. Hyperbolic metamaterials with near-zero permittivity may exist simultaneously in type I and type II. The propagation of transverse electromagnetic waves in these two types of metamaterial was considered. The diverging incident light beam seems to convert into a well-collimated beam and transfers all its energy in the direction perpendicular to the surface of the hyperbolic metamaterial of type I in the region of special values ​​of the incidence angle from –5 to 5°. In the hyperbolic metamaterial of type II, the light wave entirely transmits through the material layers, while the transmittance remains constant in the range of incident angle values ​​from –40 to 40°. The radius of the metal nanowires and the material thickness also affect the characteristics of electromagnetic wave propagation.Trong bài báo này, chúng tôi nghiên cứu siêu vật liệu hyperbolic trên cơ sở cấu trúc chứa sợi kim loại kích thước nanomet nhúng trong nền điện môi bằng phương pháp lý thuyết môi trường hiệu dụng. Kết quả nghiên cứu cho thấy siêu vật liệu hyperbolic với độ thấm điện môi gần bằng 0 (ENZ) có thể tồn tại cùng lúc ở loại I và loại II. Điểm đặc biệt lan truyền sóng điện từ phân cực từ ngang được nghiên cứu trong hai loại siêu vật liệu này. Chùm ánh sáng đến phân kỳ dường như chuyển thành chùm sáng chuẩn trực tốt và chuyển toàn bộ năng lượng theo hướng vuông góc với bề mặt siêu vật liệu hyperbolic loại I trong vùng giá trị đặc biệt của góc tới từ –5 đến 5°. Trong siêu vật liệu hyperbolic loại II, sóng ánh sáng truyền hoàn toàn qua lớp cấu trúc vật liệu; đồng thời, giá trị hệ số truyền qua không đổi trong vùng giá trị góc tới từ –40 đến 40°. Sự thay đổi bán kính sợi kim loại trong cấu trúc và độ dày của lớp siêu vật liệu có ảnh hưởng đến đặc tính lan truyền sóng điện từ

Characteristics of Simulated Workplace Neutron Standard Fields

This paper presents the development of simulated workplace neutron standard fields at the Institute for Nuclear Science and Technology with the 241Am-Be source moderated by polyethylene spheres with diameters of 15 cm and 30 cm. The characterization of the standard fields (in terms of neutron fluence rates and neutron ambient dose equivalent rates) was performed using Bonner sphere spectrometer system together with MAXED and FRUIT unfolding codes. The related quantities such as neutron dose equivalent-averaged energies and fluence-to-ambient dose equivalent conversion coefficients were also determined. The discrepancies of values are satisfied the standard uncertainty criteria as recommended by the International Standard Organization 12789 series. It implies that the simulated workplace neutron standard fields can be applied in the practical works for calibration purposes

Species diversity of rotifers (Rotifera: Eurotatoria) of Phu Ninh Lake with five new records from Vietnam

A total of sixty-one taxa of rotifer, belonging to 15 families, 3 orders were identified from the Phu Ninh Lake, Vietnam. Of these, five species were recorded new to Vietnam Rotifera fauna, including Lecane acanthinula (Hauer, 1938), L. sola (Hauer, 1936), L. thailandensis Segers & Sanoamuang, 1994, L. pyriformis (Daday, 1905), and Mytilina bisulcata (Lucks, 1912). The result raised the total number of rotifers known from Vietnam to 227 species. Moreover, the results showed that the number of species recorded increased with the increase of sample size, which followed the equation y=12.85+14.12log(x) (R2 = 0.99). Based on the estimators, the α-diversity of rotifers in Phu Ninh Lake might be up to 67±4 taxa (according to the Bootstrap index), 71±8 taxa (according to the Chao index), or even up to 79 taxa (according to Jacknife 2 index)

The Role of Social Network Sites in English Language Teaching_Harnessing the Potential of Facebook and YouTube as Learning Tools

This paper provides a comprehensive review of the role of Social Network Sites (SNSs) in the context of English as a Second Language (ESL) and English as a Foreign Language (EFL) teaching and learning. It examines the definitions and potential applications of SNSs, with a specific focus on Facebook and YouTube. The paper discusses the educational and instructional implementations of these SNSs, as well as the challenges and drawbacks faced by both teachers and students when utilizing them. Furthermore, it explores the pedagogical implications of incorporating the cutting-edge features offered by SNSs, aiming to bridge the gap between traditional and technologically driven learning environment

Factors Influencing Intention to Use Social Insurance Application (VssID) in Vietnam Through Technology Acceptance Model

Technology is becoming more and more popular in public services in general and social insurance in particular in Vietnam. Although the social insurance software has been used since November 2020, the number of users is still limited so far. Therefore, this study aims at investigating determinants of the intention to use social insurance management applications of Vietnamese people. Applying a combination of three models (TAM, TRA and TPB), the study identifies five determinants of technology acceptance of users in their intention to use this application in Vietnam’s Social Insurance, including Perceived usefulness, Perceived ease of use, Subjective norm, Perceived behavioral control, and Attitude towards usage. Data for the study were collected through a survey in three big Vietnamese cities: Ho Chi Minh City, Hanoi and Da Nang. Research results show that users' technology acceptance intention in social insurance in Vietnam is positively influenced by all five factors. From the analysis results, the study proposes recommendations related to improving the performance of the application, propagandizing the high applicability of VssID to the public. Policies and guidelines for the government to promote user's habit of using the application are also recommended. Keywords: Social insurance, intention to use, technology acceptance, VssID DOI: 10.7176/JESD/14-6-02 Publication date:March 31st 202

LECTIN THỰC VẬT VÀ TIỀM NĂNG ỨNG DỤNG TRONG KIỂM SOÁT CÔN TRÙNG GÂY HẠI

Phytophagous insects is one of the major biological constraints in crop production. To cope with continuous threat from insects, plants produce insecticidal peptides or proteins. Plant lectins are carbohydrate binding proteins, one of the most important secondary metabolites which also serve as a defense tool against plant-eating organisms. Although most lectins have moderate effects to development, fecundity or growth of insect, several lectins are highly toxic to insects. In the last decade, many studies reported a role of lectins in pest management. In particular, several plant lectins respond to different kinds of stress such as drought, fire, wounding, high-salinity, hormone treatment and pathogen attack. This group of lectin is called as “inducible plants lectin”. This review summarized recent progresses in research on the application of lectin as a potential approach for integrated pest management. Côn trùng gây hại được biết đến như là yếu tố sinh học bất lợi gây ảnh hưởng trực tiếp đến sinh trưởng và phát triển của cây nông nghiệp. Thực vật tự bảo vệ bằng cách tổng hợp ra protein hay peptide đối kháng, trong đó lectin được xem như một nhóm protein gây độc hiệu quả đối với côn trùng. Hầu hết các lectin chỉ ảnh hưởng ở mức độ vừa phải đến sự sinh trưởng và phát triển nhưng một số lại có khả năng dẫn đến tỷ lệ tử vong cao đối với côn trùng. Trong  một thập kỷ trở lại, rất nhiều nghiên cứu đã được công bố liên quan đến khả năng kháng côn trùng hiệu quả của một số loại lectin trên cây trồng, đặc biệt là chúng có thể được cảm ứng sinh tổng hợp trong các điều kiện môi trường bất lợi. Bài viết này tóm tắt và thảo luận các thành tựu nghiên cứu về tiềm năng ứng dụng của lectin trong quản lý dịch hại trên đồng ruộng. Đây được coi là hướng nghiên cứu tiềm năng cho ngành trồng trọt, nhất là trong bối cảnh các điều kiện bất lợi gây ra bởi biến đổi khí hậu ngày càng ảnh hưởng nghiêm trọng đến tình hình sản xuất cây nông nghiệp như hiện nay

Optimization of Total Flavonoid Extraction From the Helicteres hirsuta Lour. Roots by Bath Ultrasound Assisted method and cytotoxic activities of these Flavonoids

This study was carried out to optimize the various approaches to analyze the effects of various variables on the total flavonoid content extraction from the roots of Helicteres hirsuta L. The existence of various compounds in the methanol fraction was accessed by using LC-MS/MS analysis. The results of the study identified the ideal parameters such as times (30 minutes); methanol solvent concentration (50%); ultrasonic frequency (12 Hz); and material/solvent ratio [1:30 (w/v)] for extracting the highest total flavonoids from the roots of H. Hirsuta. The study's results suggested that the total flavonoid value was 3.52684 (mg Catechin/g extract). The verified experiment obtained an actual value of 5.205 (mg Catechin/g extract). Further, the results of the study suggested the presence of 20 compounds of a flavonoid nature (66.667%) appearing in the purified methanol fractional extract. These compounds can inhibit DPPH free radicals at 50%, with an IC50 value of 536.760 g/mL, and they also have inhibitory activity on the growth of cancer cell lines with IC50 values ranging from 115.81 and 219.17g/mL. The human leukemia cell line (HL-60) exhibits the most significant cytotoxic response to a methanol extract from H. hirsuta root with an IC50 value of 115.81 g/mL

Risk Factors for Human Infection with Avian Influenza A H5N1, Vietnam, 2004

TOC Summary: Risk factors include direct or household contact with sick or dead poultry and absence of an indoor water source

Direct and indirect costs of smoking in Vietnam

This study was designed to overcome limitations of two previous investigations by calculating both direct and indirect health costs of five smoking-related diseases that are responsible for almost 75% of all smoking-related deaths in Vietnam: lung cancer, cancers of the upper aerodigestive tract, chronic obstructive pulmonary disease, ischaemic heart disease and stroke. Understanding the healthcare system is crucial for calculating the actual cost of smoking in Vietnam. The total estimated economic cost of smoking for five smoking-related diseases was 24 679.9 billion VND (US$1173.2 million), not taking into account exposure to second hand smoke