Real-Space Approach for the Electronic Calculation of Twisted Bilayer Graphene Using the Orthogonal Polynomial Technique

We discuss technical issues involving the implementation of a computational method for the electronic structure of material systems of arbitrary atomic arrangement. The method is based on the analysis of time evolution of electron states in the real lattice space. The Chebyshev polynomials of the first kind are used to approximate the time evolution operator.  We demonstrate that the developed method is powerful and efficient since the computational scaling law is linear. We invoked the method to study the electronic properties of special twisted bilayer graphene whose atomic structure is quasi-crystalline. We show the density of states of an electron in this graphene system as well as the variation of the associated time auto-correlation function. We find the fluctuation of electron density on the lattice nodes forming a typical pattern closely related to the typical atomic pattern of the quasi-crystalline bilayer graphene configuration

Secrecy performance analysis on spatial modeling of wireless communications with unmanned aerial vehicle and ground devices

In this paper, the secrecy performance of the spatial modeling for ground devices with randomly placed eavesdroppers when an unmanned aerial vehicle (UAV) acted as two hops decode and forward (DF) was investigated. We characterize the secrecy outage probability (SOP) and intercept probability (IP) expressions. Our capacity performance analysis is based on the Rayleigh fading distributions. After analytical results by Monte Carlo simulation, and the Gauss-Chebyshev parameter was selected to yield a close approximation, the results demonstrate the SOP with the average signal-to-noise ratio (SNR) between UAV and ground users among the eavesdroppers and the IP relationship with the ability to intercept the information of the ground users successfully

Factors Effect on Tourist Loyalty: A Case Study of Homestay Tourism in Ben Tre (Southern Vietnam).

The purpose of this paper is to measure the effects of homestay service quality, tourist satisfaction, and cultural contact on tourist loyalty: a case of homestay tourism in Ben Tre (Southern Vietnam). This study has used qualitative and quantitative researches: (i) qualitative research was carried out through focus group discussions with 10 tourists, and (ii) quantitative research was conducted through direct interviews with 294 tourists in Ben Tre Province (Southern Vietnam). The results show that: (i) tourist loyalty is affected by 04 components of homestay service quality (reliability, responsiveness, assurance, and tangibles), tourist satisfaction; and (ii) tourist satisfaction is affected by 05 components of homestay service quality (reliability, responsiveness, assurance, tangibles, and empathy), and cultural contact. However, the research subject has certain limitations: (i) due to limited resources in conducting research, the sample size consisted of 294 tourists, (ii) This study conducted the sampling technique of using direct interview methods from respondents using homestay services in Ben Tre Province, Vietnam

AN INVESTIGATION INTO DIFFICULTIES IN ENGLISH LISTENING OF FRESHMEN MAJORING IN ENGLISH AT A UNIVERSITY IN THE MEKONG DELTA, VIETNAM

English is a very popular language in the world. However, learning a foreign language is not an easy process for learners, especially the English listening process. In fact, most learners believe that it is hard for them to master this skill. Therefore, the research “An Investigation into Difficulties in English Listening of Freshmen Majoring in English at a University in the Mekong Delta” was conducted with the purpose of helping these students to recognize clearly their own problems in English listening. Statistical data were collected from eighty-five English-majored freshmen. The main instrument of the study was a questionnaire. The findings of the research would point out the students’ difficulties in linguistics, including vocabulary, grammar, pronunciation, intonation and accent; background knowledge; and difficulties from their own minds. One more notable purpose of this research is that thanks to the results, students can now solve their own problems, so that they can study better. Article visualizations

Optimization of Weld Parameters in Wire and Arc-Based Directed Energy Deposition of High Strength Low Alloy Steels

This paper aims to investigate the fabrication of high strength low alloy (HSLA) steels by wire and arc-based directed energy deposition (WADED). Firstly, the relationship between the process variables (including the travel speed-V, the current-C, and the voltage-U) and the geometrical characteristics of weld beads (including the bead height (BH), bead width (BW), and melting pool length (MPL)) was investigated. Secondly, the optimal process variables were identified using the desirability approach. The results indicate that voltage-U has the highest impact on BW and MPL, meanwhile the travel speed-V is the most impacting factor on BH. The optimal variables for the WADED process of HSAL steels are V = 0.3 m/min, C = 160 A, and U = 19 V. The component fabricated with the optimal variables is fully dense without spatters and defects, confirming the efficiency of the WADED process for HSLA steels

PROBLEMS IN VIETNAMESE-ENGLISH TRANSLATION OF RELATIVE CLAUSES FOR ENGLISH-MAJORED JUNIORS AT TAY DO UNIVERSITY, VIETNAM

Realistically, Vietnamese-English translation is not easy for Vietnamese students to master, and relative clauses are not typical in Vietnamese. Therefore, learners cannot avoid mistakes in their translation practice. Concerned researchers carried out a study to identify common Vietnamese-English translation errors in terms of English relative clauses. The participants were 60 juniors from the Bachelor of English course at Tay Do University. Test papers and interviews were employed as the instruments. The collected data from the two instruments mentioned above were all analyzed carefully afterward. The results of the study showed that the students suffered from a variety of grammar and vocabulary problems hindering them from translating Vietnamese into English correctly. Article visualizations

Using Solvent Vapor Annealing for the Enhancement of the Stability and Efficiency of Monolithic Hole-conductor-free Perovskite Solar Cells

In the last few years, perovskite solar cells have attracted enormous interest in the photovoltaic community due to their low cost of materials, tunable band gap, excellent photovoltaic properties and easy process ability at low temperature. In this work, we fabricated hole-conductor-free carbon-based perovskite solar cells with the monolithic structure: glass/FTO/bl-TiO$_{2}$/(mp-TiO$_{2}$/mp-ZrO$_{2}$/mp-carbon) perovskite. The mixed 2D/3D perovskite precursor solution composed of PbI$_{2}$, methylammonium iodide (MAI), and 5-ammoniumvaleric acid iodide (5-AVAI) was drop-casted through triple mesoporous TiO$_{2}$/ZrO$_{2}$/carbon electrode films. We found that the isopropyl alcohol (IPA) solvent vapor annealing strongly influenced on the growth of mixed 2D/3D perovskite on triple mesoscopic layers. It resulted in the better pore filling, better crystalline quality of perovskite layer, thus the improved stability and efficiency of perovskite solar cell was attributed to lower defect concentration and reduced recombination

ĐẶC TRƯNG KHAI THÁC NGUỒN LỢI ĐỘNG VẬT ĐÁY CÓ GIÁ TRỊ KINH TẾ CHỦ YẾU Ở THỦY VỰC NHA PHU, KHÁNH HÒA

The exploitation characteristics of zoobenthos resources with economic value at the Nha Phu waters were determined by five field trips carried out from 2011 - 2016. The results shows that Nha Phu waters have had great exploitation pressure, with high density of boats (11.9 motorboats/100 ha, 7.7 boats/100 ha and 16.2 people/100 ha), average days of fishery exploitation being high (185 days/fishery/year) and concentrating mainly in the dry season (70% of total average days of fishery/year), specially the destructive artisanal fisheries, (56% of total time of fishery). The average yeild of fishery was dominant in the dry season (73% of total commercial yield and 93% of total number of benthic animal seeds), in which the destructive artisanal fisheries possess 73% of the entire yield of benthic animal. Yields of zoobenthos have decreased seriously, specially for crustaceans (17%). It may be due to greater pressure of fishery exploitation, especially the destructive artisanal fisheries. The results of this study will contribute the scientific basis and data to planning for effective exploitation and management of fisheries resources.Đặc trưng khai thác nguồn lợi động vật đáy có giá trị kinh tế chủ yếu ở thủy vực Nha Phu, Việt Nam được xác định thông qua 5 chuyến điều tra khảo sát từ năm 2011 - 2016. Kết quả nghiên cứu cho thấy, thủy vực Nha Phu có áp lực khai thác lớn, với mật độ phương tiện (11,9 ghe/100 ha, 7,7 sỏng/100 ha và 16,2 người/100 ha), số nghề (13 nghề) và thời gian khai thác trung bình nghề khá cao (185 ngày/nghề/năm) và tập trung chủ yếu vào mùa khô (chiếm gần 70% tổng thời gian hoạt động trung bình nghề/năm), đặc biệt nghề khai thác hủy diệt tận thu như xiết điện, lưới lồng, cào máy, giã cào (chiếm trên 56% tổng thời gian năm). Sản lượng của các nghề khai thác chiếm ưu thế vào mùa khô (chiếm trên 73% tổng sản lượng khai thác thương phẩm (423,9 tấn/năm) và trên 93% tổng con giống (161.000 con giống/năm) động vật đáy cả năm), trong đó các nghề hủy diệt, tận thu chiếm chiếm trên 73% tổng sản lượng động vật đáy. Thành phần và sản lượng nguồn lợi động vật đáy có chiều hướng suy giảm nghiêm trọng, đặc biệt nguồn lợi giáp xác (giảm 17%). Nguyên nhân có thể do thời gian hoạt động trung bình/năm và doanh thu của các loại nghề khá cao, đặc biệt nghề khai thác mang tính hủy diệt, tận thu. Kết quả nghiên cứu này cung cấp cơ sở khoa học và dữ liệu cho quy hoạch khai thác và quản lý nguồn lợi thủy sản hợp lý

Studying the thermo-gas-dynamic process in a muzzle brake compensator

To reduce the recoil and improve the stability of small arms, a muzzle brake compensator is attached to the muzzle of the barrel. This device uses the kinetic energy of the powder gas escaping from the bore after the bullet is fired. In this paper, the authors present the determination of the thermo-gas-dynamic model of the operation of a muzzle brake compensator and an example of calculating this type of muzzle device for the AK assault rifle using 7.62x39 mm ammunition. The results of the calculation allowed for obtaining the parameters of the powder gas flow in the process of flowing out of the muzzle device, as well as the change in the momentum of the powder gas's impact on the muzzle device. The model proposed in the article provides the basis for a quantitative evaluation of the effectiveness of using the muzzle device in stabilizing infantry weapons when firing

Determining the optimal range of vitamin C for early red drum (Sciaenops ocellatus) juveniles

Vitamin C plays an important role for fish survival, growth and disease resistance. However, the optimal vitamin C for rearing red drum Sciaenops ocellatus juveniles in Vietnam is not known. To address this issue, a 70-day feeding trial was conducted to evaluate the optimal dietary vitamin C requirements for red drum juveniles. Seven isonitrogenous (55.35% protein) and isolipidic (9.07% lipid) diets were formulated to include graded vitamin C concentrations of 23.2, 124.5, 235.2, 423.8, 626.7, 824.6, and 1,027.3 mg/kg, respectively. The results showed that fish fed on 423.8 mg/kg vitamin C diet had the highest growth rate, which can be linked to the increased feed utilization. Broken-line analysis indicated that the optimal dietary vitamin C requirements of red drum juveniles were 342.92 and 405.80 mg/kg for growth parameters, feed utilization, body composition and biochemical parameters of serum. Based on these parameters the optimal vitamin C supplementation level for red drum juveniles was estimated in the range of 342.92–405.80 mg/kg vitamin C in the diets with direct applications in producing artificial feed for rearing juveniles of this species in Vietnam