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Hanoi, Vietnam

Tang T.D.,Hanoi University
CAD Computer Aided Design | Year: 2014

Five-axis CNC machine tools are more and more popular in machining area, because of their ability to machine parts with complex geometries efficiently as well as achieve higher dimensional accuracy. Since two additional rotational axes are introduced in five-axis machines, there are difficult geometric problems that need to be solved in order to take full advantages of five-axis machining, and the most complex problems are collision detection and avoidance. Due to its widespread importance, a lot of researches have been carried out to solve the collision detection and avoidance problems. These include the surface properties analysis based method, convex hull based method, C-space based method, accessibility based method, bounding volume and space partition method, distance calculation (vector) based method, rolling ball method, radial projection method, graphic-assisted method, and sweep plane approach. This paper aims at providing a state of the art review on algorithms for collision detection and avoidance in five-axis NC machining. In addition, a comparison of algorithms for collision detection and avoidance is considered. © 2014 Elsevier Ltd. All rights reserved. Source

Van Hieu N.,Hanoi University
Sensors and Actuators, B: Chemical | Year: 2010

A truly simple procedure was presented for highly reproducible synthesis of very large-scale SnO2 nanowires (NWs) on silicon and alumina substrates. The growth involves thermally evaporating SnO powder in a tube furnace with temperature, pressure, and O2 gas-flow controlled to 960 °C, 0.5-5 Torr, and 0.4-0.6 sccm, respectively. The scanning- and transmission-electron-microscopic studies show that the diameter and length of the nanowires vary from 50 to 150 nm and 1 to 10 μm, respectively. As-synthesized SnO2 NWs on alumina substrates were used to fabricate gas sensor by screen-printing method. A good ohmic contact of the screen-printed NWs sensor was obtained. Randomly selected gas-sensor devices were tested with various gases such as C2H5OH, CH3COCH3, C3H8, CO, and H2 for studying gas-sensing properties. The results reveal that as-fabricated sensors exhibit relatively reproducible and good response to ethanol gas. Typically, the response to 100 ppm ethanol in air is around 11.8, and response and recovery times are around 4 and 30 s, respectively. © 2009 Elsevier B.V. All rights reserved. Source

Nguyen H.H.,Hanoi University
Journal of Plastic, Reconstructive and Aesthetic Surgery | Year: 2012

Background: Total scalp avulsion is a rare and devastating event. Microsurgical replantation is the sole method to achieve an ideal cosmetic outcome. In the literature, most studies have reviewed limited sample sizes. Most authors report better outcomes when a greater number of microvascular anastomoses are used. This strategy remains controversial, as some authors have suggested that one artery may be sufficient. Methods: From 2005 to 2008, seven patients who sustained scalp avulsion underwent microsurgical replantation. All of the vascular anastomoses were made with a branch of the superficial temporal artery. We did not use vein grafts. The ischaemia time was 4-16 h. Results: In six cases, a single artery and one to two veins were anastomosed; in another case, two arteries and three veins were anastomosed. Six of the seven scalp replantations were successful and achieved normal hair regrowth. In five of the six successful cases, we performed a single-artery anastomosis. Conclusion: Scalp avulsion is rare around the world but occurs relatively frequently in our country due to the lack of safe and secure working conditions in agriculture and industry. In cases where multiple arterial anastomoses are not possible, the present findings suggest that one branch of the superficial temporal artery may be sufficient to reperfuse the replanted scalp and achieve excellent aesthetic results. © 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved. Source

Dong P.V.,Institute of Physics | Long H.N.,Institute of Physics | Hung H.T.,Hanoi University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We show that there is an infinite number of U(1) symmetries like Peccei-Quinn symmetry in the 3-3-1 model with minimal scalar sector-two scalar triplets. Moreover, all of them are completely broken due to the model's scalars by themselves (notice that these scalars as known to have been often used to break the gauge symmetry and to generate the masses for the model's particles). There is not any residual Peccei-Quinn symmetry. Because of the minimal scalar content, there are some quarks that are massless at tree level, but they can get consistent mass contributions at one loop due to this fact. Interestingly, axions as associated with the mentioned U(1)s breaking (including Majoron due to lepton-charge breaking) are all gauged away because they are also the Goldstone bosons responsible for the gauge symmetry breaking as usual. © 2012 American Physical Society. Source

Nga T.T.,Hanoi University
BMC pharmacology & toxicology | Year: 2014

The irrational overuse of antibiotics should be minimized as it drives the development of antibiotic resistance, but changing these practices is challenging. A better understanding is needed of practices and economic incentives for antibiotic dispensing in order to design effective interventions to reduce inappropriate antibiotic use. Here we report on both quantitative and qualitative aspects of antibiotic sales in private pharmacies in northern Vietnam. A cross-sectional study was conducted in which all drug sales were observed and recorded for three consecutive days at thirty private pharmacies, 15 urban and 15 rural, in the Hanoi region in 2010. The proportion of antibiotics to total drug sales was assessed and the revenue was calculated for rural and urban settings. Pharmacists and drug sellers were interviewed by a semi-structured questionnaire and in-depth interviews to understand the incentive structure of antibiotic dispensing. In total 2953 drug sale transactions (2083 urban and 870 rural) were observed. Antibiotics contributed 24% and 18% to the total revenue of pharmacies in urban and rural, respectively. Most antibiotics were sold without a prescription: 88% in urban and 91% in rural pharmacies. The most frequent reported reason for buying antibiotics was cough in the urban setting (32%) and fever in the rural area (22%). Consumers commonly requested antibiotics without having a prescription: 50% in urban and 28% in rural area. The qualitative data revealed that drug sellers and customer's knowledge of antibiotics and antibiotic resistance were low, particularly in rural area. Over the counter sales of antibiotic without a prescription remains a major problem in Vietnam. Suggested areas of improvement are enforcement of regulations and pricing policies and educational programs to increase the knowledge of drug sellers as well as to increase community awareness to reduce demand-side pressure for drug sellers to dispense antibiotics inappropriately. Source

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