DESIGN OF A MULTI-BAND FRACTAL ANTENNA

In recent years, the demand for compact and multi-function handheld communication devices has grown significantly. Devices having internal antennas have appeared to fill this need. Antenna frequency band and size are major factors. In the past few decades, fractal antenna theory develops rapidly, basing on fractal geometry to maximize the length of material. Fractal surface is a function of roughness, by increasing roughness, polarization changes. For this reason, fractal antennas are very compact, are multi-band and have useful applications which require small, cheap and effective antenna such as cellular telephones and microwave communications. Anotable fractal antenna to be mounted on wireless devices such as mobile phones, laptops is presented in this thesis. The proposed multi-band fractal antenna simultaneously operates in the IEEE 802.11a, IEEE 802.1 lb/g and WiMax frequency bands. The multi-band behavior is obtained by using Sierpinski Gasket fractal structures. The overall size of the antenna renders it suitable to be installed at the back of the mobile phone or the top of the display of a notebook. Simulation results are obtained by CST Microwave studio

DESIGN OF A MULTI-BAND FRACTAL ANTENNA

In recent years, the demand for compact and multi-function handheld communication devices has grown significantly. Devices having internal antennas have appeared to fill this need. Antenna frequency band and size are major factors. In the past few decades, fractal antenna theory develops rapidly, basing on fractal geometry to maximize the length of material. Fractal surface is a function of roughness, by increasing roughness, polarization changes. For this reason, fractal antennas are very compact, are multi-band and have useful applications which require small, cheap and effective antenna such as cellular telephones and microwave communications. Anotable fractal antenna to be mounted on wireless devices such as mobile phones, laptops is presented in this thesis. The proposed multi-band fractal antenna simultaneously operates in the IEEE 802.11a, IEEE 802.1 lb/g and WiMax frequency bands. The multi-band behavior is obtained by using Sierpinski Gasket fractal structures. The overall size of the antenna renders it suitable to be installed at the back of the mobile phone or the top of the display of a notebook. Simulation results are obtained by CST Microwave studio

Linear Query Approximation Algorithms for Non-monotone Submodular Maximization under Knapsack Constraint

This work, for the first time, introduces two constant factor approximation algorithms with linear query complexity for non-monotone submodular maximization over a ground set of size $n$ subject to a knapsack constraint, $\mathsf{DLA}$ and $\mathsf{RLA}$. $\mathsf{DLA}$ is a deterministic algorithm that provides an approximation factor of $6+\epsilon$ while $\mathsf{RLA}$ is a randomized algorithm with an approximation factor of $4+\epsilon$. Both run in $O(n \log(1/\epsilon)/\epsilon)$ query complexity. The key idea to obtain a constant approximation ratio with linear query lies in: (1) dividing the ground set into two appropriate subsets to find the near-optimal solution over these subsets with linear queries, and (2) combining a threshold greedy with properties of two disjoint sets or a random selection process to improve solution quality. In addition to the theoretical analysis, we have evaluated our proposed solutions with three applications: Revenue Maximization, Image Summarization, and Maximum Weighted Cut, showing that our algorithms not only return comparative results to state-of-the-art algorithms but also require significantly fewer queries

Neoarchean and Paleoproterozoic K-rich granites in the Phan Si Pan Complex, north Vietnam : constraints on the early crustal evolution of the Yangtze Block

This study was financially supported by projects from the China Natural Science Foundation (41672222) and State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Wuhan (MSFGPMR201802). PAC acknowledges support from Australian Research Council grant FL160100168. This study was also supported by the Ministry of Natural Resources and Environment of Vietnam, Project BĐKH.29/16-20 to Dung My Tran.Precambrian igneous and metamorphic rocks of the Phan Si Pan Complex, North Vietnam, constitute the southern extension of the Yangtze Block, and provide a valuable record of the early evolution of the continental crust. We present results of U-Pb zircon geochronology and geochemistry for Precambrian granites in this complex to constrain their emplacement age and genesis. Granites from three plutonic bodies yielded ages of 2848 ± 15 Ma, 2768 ± 19 Ma and 1869 ± 30 Ma, which represent newly-recognized late Archean to Paleoproterozoic potassic granite plutonism in the southern Yangtze Block. The average εHf(t) values range from −6.2 to 0.1 for the 2.85–2.77 Ga granitic rocks and -13.1 to -9.2 for the ca. 1.86 Ga granitic rocks, with two-stage model ages of 3.64 to 3.20 Ga and 3.31 to 3.07 Ga, respectively, suggesting derivation from partial melting of Paleoarchean and Mesoarchean crust. The late Archean potassic granites exhibit high K2O, and high Sr/Y and (La/Yb)N ratios with negligible Eu anomalies, indicating derivation from melting of the thickened lower crust, which is inferred to have occurred in an active margin setting. The late Paleoproterozoic alkali feldspar granites are characterized by high FeOT/(FeOT + MgO)(0.96–0.99) and 10000∗Ga/Al (2.75–2.94) ratios, showing an affinity of A-type granite. These A-type granites exhibit flat chondrite-normalized HREE patterns and strong negative Eu anomalies, and low Sr/Y and (La/Yb)N ratios, corresponding to melting at a shallow depth, probably in a post-collisional extension setting. Comparison of the rock units and events recorded by the Phan Si Pan complex with other Archean to Paleoproterozoic complexes (Houhe, Dongchuan, Yudongzi, Douling, Zhongxiang and Kongling complexes) in the Yangtze Block indicate spatially distinct histories of crustal growth, and thus may reflect independent terranes. The ca. 1.86 Ga post-collisional magmatism, which succeeds a 2.0–1.9 Ga metamorphic event, is distributed throughout the Yangtze Block, including the Phan Si Pan Complex, suggesting assembly of the disparate terranes and final cratonization of the Yangtze Block overlaps with, and may be related to, assembly of the Nuna supercontinent.PostprintPeer reviewe

Early Paleoproterozoic magmatism in the Yangtze Block : evidence from zircon U-Pb ages, Sr-Nd-Hf isotopes and geochemistry of ca. 2.3 Ga and 2.1 Ga granitic rocks in the Phan Si Pan Complex, north Vietnam

This study was financially supported by projects from the China Natural Science Foundation (41672222) and State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Wuhan (MSFGPMR201802). PAC acknowledges support from Australian Research Council grant FL160100168. This study was also supported by the Ministry of Natural Resources and Environment of Viet Nam, Project BĐKH.29/16-20 to Dung My Tran.Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207Pb/206Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have εHf(t) values ranging from -4.1 to -2.1, corresponding to TDM2 model ages of 3002–2890 Ma, whereas zircons in the gneissic granite have εHf(t) values between -0.95 and +1.72 and corresponding TDM2 model ages of 2660–2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics.PostprintPeer reviewe

HIỆU QUẢ KINH TẾ CỦA NÔNG HỘ THAM GIA HỢP ĐỒNG SẢN XUẤT LÚA HỮU CƠ: NGHIÊN CỨU TRƯỜNG HỢP XÃ PHONG HIỀN, HUYỆN PHONG ĐIỀN, TỈNH THỪA THIÊN HUẾ

A random survey of 85 farmers engaging in organic rice contract farming was conducted in Phong Hien Commune, Phong Dien District, Thua Thien Hue Province. The economic accounting and quantile regression methods are applied to quantify the economic efficiency of households and the factors that affect annual revenue in the various quantiles. The findings show that the average annual profit of farmers is 0.709 million VND/ 500 m2. The revenue-to-total cost ratio in all cropping seasons is greater than 1, indicating that farmers are profitable and their profit margin is 17%. Moreover, an average family labor contribution generates a profit of 179 thousand VND/ 500 m2. The results of quantile regression at 75% show that the annual revenue of households is positively affected by two factors: education and the interaction of cultivated area and family labor cost. Improving the economic effeciency of farming household hinges on their ability to effectively utilize and allocate expenses, optimize the costs of purchasing organic fertiliser, and harmonizing production scale with labor utilization sourced from within the family. This research contributes empirical evidence in support of planning the  development of organic rice production in Thua Thien Hue Province. Nghiên cứu khảo sát ngẫu nhiên 85 hộ trồng lúa hữu cơ theo hình thức hợp đồng sản xuất ở xã Phong Hiền, huyện Phong Điền, tỉnh Thừa Thiên Huế. Phương pháp hạch toán kinh tế và hồi quy phân vị được áp dụng nhằm đánh giá hiệu quả kinh tế của nông hộ và ảnh hưởng của các yếu tố đến doanh thu hằng năm ở các mức phân vị khác nhau. Kết quả cho thấy, lợi nhuận bình quân hằng năm của hộ là 0,709 triệu đồng/ sào. Tỷ suất doanh thu trên tổng chi phí ở các vụ lớn hơn 1 cho thấy nông hộ đang có lãi và khả năng sinh lời là 17%. Ngoài ra, công lao động gia đình trung bình mang lại 179 nghìn đồng lợi nhuận/ sào. Kết quả hồi quy ở mức phân vị 75% cho thấy, doanh thu cả năm của hộ chịu ảnh hưởng tích cực bởi yếu tố học vấn và tương tác giữa quy mô sản xuất và lao động gia đình. Để nâng cao hiệu quả kinh tế, điều quan trọng là hộ cần kết hợp sử dụng và phân bổ tốt các khoản chi phí, tối ưu chi phí mua phân hữu cơ, kết hợp tốt giữa quy mô sản xuất và sử dụng công lao động gia đình. Nghiên cứu đóng góp bằng chứng thực nghiệm ủng hộ phát triển quy hoạch vùng sản xuất lúa hữu cơ trên địa bàn tỉnh Thừa Thiên Huế

Determinants Influencing Entrepreneurial Intention in Hanoi, Vietnam

This research employed survey data from 204 students between two groups of  economics and technical majors in Hanoi city for assessing the impact levels of determinants on entrepreneurial intention. The results show that a number of determinants including Need for achievement, Self-efficacy, and Instrumental readiness have positive impacts on student’s entrepreneurial intention. Besides, this study is also to create a basis for  comparative students among different economics and technical majors, work exoperience, and gender. These findings are the basis to recommend policies and solutions to promote entrepreneurship movement in Vietnam. Keywords: Entrepreneurial intention, need for achievement, self-efficacy, instrumental readiness. DOI: 10.7176/EJBM/12-15-10 Publication date:May 31st 2020

Tin Dioxide Nanocrystals as an Effective Sensitizer for Erbium Ions in Er-Doped SnO 2

Undoped SnO2 and erbium-doped SnO2 powders were successfully prepared by precipitation method. The effect of the heat treatment and doping contents on the structure of tin oxide and optical properties was also studied. The XRD data and Raman spectra indicate that the SnO2 crystals have formed after being heat-treated at 400°C and the average size of grains is about 8 nm for doping content of 1 mol%. An increase of doping concentration has controlled the growth of nanocrystals. The principle of the visible and infrared emissions of SnO2 and SnO2:Er is also discussed. All photoluminescence study shows that the Er3+ ions can be located in SnO2 nanocrystals and that there is energy transfer from defect levels of SnO2 nanoparticles to neighboring Er3+ ions of crystals

In and Ga Codoped ZnO Film as a Front Electrode for Thin Film Silicon Solar Cells

Doped ZnO thin films have attracted much attention in the research community as front-contact transparent conducting electrodes in thin film silicon solar cells. The prerequisite in both low resistivity and high transmittance in visible and near-infrared region for hydrogenated microcrystalline or amorphous/microcrystalline tandem thin film silicon solar cells has promoted further improvements of this material. In this work, we propose the combination of major Ga and minor In impurities codoped in ZnO film (IGZO) to improve the film optoelectronic properties. A wide range of Ga and In contents in sputtering targets was explored to find optimum optical and electrical properties of deposited films. The results show that an appropriate combination of In and Ga atoms in ZnO material, followed by in-air thermal annealing process, can enhance the crystallization, conductivity, and transmittance of IGZO thin films, which can be well used as front-contact electrodes in thin film silicon solar cells