Metakaolin as an Additive in Composite Cement

Metakaolin made from kaolin is used around the world but rarely in Vietnam where abundant deposits of kaolin is found. The first studies of producing metakaolin were conducted with high quality Vietnamese kaolins. The results showed the potential to produce metakaolin, and its effect has on strength development of mortars and concretes. However, utilisation of a low quality kaolin for producing Vietnamese metakaolin has not been studied so far. The objectives of this study were to produce a good quality metakaolin made from low quality Vietnamese kaolin and to facilitate the utilisation of Vietnamese metakaolin in composite cements. In order to reach such goals, the optimal thermal conversion of Vietnamese kaolin into metakaolin was carried out by many investigations, and as such the optimal conversion is found using the analysis results of DSC/TGA, XRD and CSI. During the calcination in a range of 500 – 800 oC lasting for 1 – 5 hours, the characterisation of calcinated kaolin was also monitored for mass loss, BET surface, PSD, density as well as the presence of the residual water. It is found to have a well correlation between residual water and BET surface. The pozzolanic activity of metakaolin was tested by various methods regarding to the saturated lime method, mCh and TGA-CaO method. The results of the study showed which method is the most suitable one to characterise the real activity of metakaolin and can reach the greatest agreement with concrete performance. Furthermore, the pozzolanic activity results tested using methods were also analysed and compared to each other with respect to the BET surface. The properties of Vietnam metakaolin was established using investigations on water demand, setting time, spread-flowability, and strength. It is concluded that depending on the intended use of composite cement and weather conditions of cure, each Vietnamese metakaolin can be used appropriately to produce (1) a composite cement with a low water demand (2) a high strength of composite cement (3) a composite cement that aims to reduce CO2 emissions and to improve economics of cement products (4) a high performance mortar. The durability of metakaolin mortar was tested to find the needed metakaolin content against ASR, sulfat and sulfuric acid attacks successfully

Topological Lifshitz phase transition in effective model of QCD with chiral symmetry non-restoration

The topological Lifshitz phase transition is studied systematically within an effective model of QCD, in which the chiral symmetry, broken at zero temperature, is not restored at high temperature and/or baryon chemical potential. It is found that during phase transition the quark system undergoes a first-order transition from low density fully-gapped state to high density state with Fermi sphere which is protected by momentum-space topology. The Lifshitz phase diagram in the plane of temperature and baryon chemical potential is established. The critical behaviors of various equations of state are determined.Comment: 8 pages, 10 figure

Estimation of errors in determination of main parameters of earthquake hypocenter, recorded by the national seismic network of Vietnam

In this paper the authors present the error estimation in determining main parameters of earthquake hypocenter based on solving the system of linear equations, expressing the relationship between earthquake coordinates and the coordinates of the seismic stations. The results of the error estimation in determining the epicenter coordinates and the focus depth of the earthquakes recorded by the system of 30 seismic stations in Vietnam are presented, interpreted and compared with the results of the previous studies.The results show that the operation of the seismic network of Vietnam is not really optimal, particularly when determining the epicenter coordinates and the focus depth of the earthquakes in the East Vietnam Sea region.The national seismic network of Vietnam allows determination of the epicenter coordinates and the focal depth of earthquakes for most of the Vietnam territory with the errors ∆h ≤ 20 km, ∆φ ≤ 4 km, ∆ ≤ 5 km. The errors of the determination of the epicenter coordinates and the focal depth of the earthquakes are increasing to the south and southwest areas of the territory of Vietnam and reach the maximum in these areas. Particularly, errors of the determination of the epicenter coordinates (∆φ, ∆λ) and the focal depth (∆h) of earthquakes increase very rapidly toward the East Sea of Vietnam and reach the maximum in the region between the longitudes of 116-118°E.The Vietnam seismic network allows determining the epicenter coordinates and the focal depth of earthquakes in the Northern Vietnam with the smaller errors than in Central and Southern Vietnam, and this fact proves that the distribution of seismic network in Northern Vietnam is more optimal than the station networks in the Central and Southern Vietnam. Therefore, in order to improve the effectiveness of the Vietnam seismic network, more seismic stations need to be added to the Central and Southern Vietnam.References Aranovich Z.I., 1980. On the method of selecting the optimal positions of seismic stations in the local network. //Methodologies and assessment results of the effectiveness of the regional seismic network. Tbilisi: Mesnhiereba, 150-157 (in Russian).Aranovich Z.I., Akhalbedasvili А.М., Gosadze О.D. et al., 1977. The methodologies of evaluating the effectiveness of regional seismic network, in case of the Caucasus region.//The issues of optimization and automation of seismic observations. Tbilisi: Mesnhiereba, 27-57 (in Russian). Bui Van Duan, Nguyen Cong Thang, Nguyen Van Vuong, Pham Dinh Nguyen, 2013. The magnitude of the largest possible earthquake in the Muong La-Bac Yen fault zone. J. Sci. of the Earth, 35, 53-49.Burmin V. Yu.,  1976. The task of experimental planning and the estimation of the system of linear algebraic equations.//The USSR Academy of Sciences Publishing House. Cybernetics, 2, 195-200. Burmin V. Yu., 1986. The optimal distribution of seismic stations when recording near earthquakes.//The USSR Academy of Sciences Publishing House. Geophysics. Moscow, 5, 34-42 (in Russian).Burmin V. Yu., Akhmechiev V.M., 1994. The errors in determining parameters of near earthquake hypocenter and the effectiveness of seismic network.//Journal of Volcanology and Seismology. Moscow, 2, 109-128 (in Russian).Burmin V. Yu., Ngo TL., Kondorskaia N.V. and Akhmechiev V.M., 1992. The geometric analysis of existing seismic network in the Northern Vietnam.//The news from Russian Academy of Sciences. Journal of Geophysics. Moscow, 6, 123-128 (iIn Russian).Burmin V. Yu., Ngo T.L., Tran V.P., 2009. Estimation of efficiency of seismic stations modern network and design of an optimal one on the territory of Vietnam.// Journal “Seismic Instruments”, 45(1), 27-35.Burmin V. Yu., Nguyen VP., 2001. Planning to optimum regional network of the seismological observations for South- East Asia.//Journal “Volcanology and Seismology”, 1, 68-75.Iosif T. and Iosif S., 1974. Optimization of seismic stations distribution in Romania.//Studii si cercetari de geofisica, 12, 51-88.Iosif T., Skoko D. and Sato Y., 1972. Optimum distribution of seismic stations in Romania.//Bull. Int. seism. Earthq. Eng, 9, 121p.Kijko A., 1975. On optimal extensions of regional networks of seismic stations - Publs. Inst. Geophys. Pol. Acad. Sci., 96, 57-119.Kijko A., 1978. Method of the optimal planning of regional seismic networks.//Polish Academy of Sci. publication of the inst. Of geoph. A-7 (119). Panctwowe wydawnictwo naukowe. Warszawa; Lodz, 63p.Kijko A., 1980. Optimum seismic networks in the Ostrova coal basin.//Czechoslovakia. Acta montana UGG CSAV. Praha, 55, 73-95.Marshall A.W., Olkin I., 1965. Norms and inequalities for condition numbers.//Pacific J. Math, 15, 241-247.Marshall A.W., Olkin I., 1969. Norms and inequalities for condition numbers.//Linear Algebra and Application, 2(2), 167-172.Marshall A.W., Olkin I., 1973. Norms and inequalities for condition numbers.//Linear Algebra and Application, 3(7), 191-300.Ngo TL., 1990. Kinetic and dynamic parameters of earthquake hypocenter in the Northern Vietnam. The Candidate of Sciences Thesis on Mathematics-Physics, Speciality Geophysics. Institute of Geophysics, the USSR Academy of Sciences. Moscow, 133p (in Russian).Ngo T.L., 1999. The characteristics of seismicity and the main features of earthquake hypocenter in the Southeast Asia from the viewpoint of clarifying the new tectonic structures. The Doctor of Science Thesis on Mathematics-Physics, Speciality Geophysics. Institute of Geophysics, the USSR Academy of Sciences. Moscow, 342p (in Russian).Ngo T.L., 2005. The algorithm for improvement of velocity model of Earth’s crust and hodographs of travel times of seismic waves in the territory of Vietnam. J. Sci. of the Earth, 27(1), 23-26.Ngo T.L., 2005. The analysis of the seismic data for accounting hodographs of travel times of P-wave. J. Sci. of the Earth, 27, 374-377.Ngo T.L., Tran V.P., Vu T.H., Le T.T., 2014. The establishment of velocity model and hodographs of travel times of seismic waves in the Earth’s crust in the Northern, Central and Southern regions of Vietnam. Journal of Geology, Hanoi, Series A, 341-345, 355-365.Nguyen Quy Hy, et al., 1979. Optimal addition of seismic network in the Vietnam territory by the method of seismic experimental planning.//The research results of “Earth Sciences” 1977-1978. Series Geophysics. Vietnam Academy of Science and Technology. Hanoi, 9-31 (in Vietnamese).Nguyen Van Hung., Hoang Quang Vinh, Nguyen Van Huong, 2016. Tectono-structural system and geodynamic features of Northwest Vietnam in the late Cenozoic period. Vietnam J. Earth Sci., 38(1), 38-45. Doi: 10.15625/0866-7187/38/1/8408.Sato Y., 1965. Optimum distribution of seismic observation points.//Zisin J. Seism. Soc. Japan, 18(1), 9-14.Sato Y., Skoko D., 1965. Optimum distribution of seismic observation points II.//Bull. Earthquake. Res. Inst., 43(3), 451-458.Sato Y., Ochi I., 1967. Accuracy of the determination of earthquake source parameters in and around Japan.//Bull. Earthq. Res. Inst., 45(1), 1-17.Savarenski E.F., Shafronov V.V., Peskov A.B. et al., 1979. Optimal planning of seismic stations from the viewpoint of minimizing error in the epicenter determination.//The USSR Academy of Sciences Publishing House, 8, 64-71 (in Russian).Skoko D., Kotake Y., Sato Y., 1968. Optimum distribution of seismic observation points. V//Bull. Earthquake. Res. Inst., 46(4), 821-840.Skoko D., Sato Y., Ochi I., Dutta T.K., 1966. Accuracy of the determination of earthquake source parameters as determined by Monte Carlo method: Observation on Indian Network.//Bull. Earthquake. Res. Inst., 44(3), 893-900.  

Reduced Need of Infiltration Anesthesia Accompanied With Other Positive Outcomes in Diode Laser Application for Frenectomy in Children

Introduction: The abnormal maxillary labial frenum is common in children during the primary or mixed dentition stage. A conventional surgery for this abnormality usually requires infiltration anesthesia which leads to fear in children and consequent noncooperation during the surgery. The aim of present study was to evaluate the reduction in the need of infiltration anesthesia, intraoperative bleeding control and postoperative pain and wound healing in children when using the diode laser for abnormal labial frenum in the maxilla.Methods: The present study was carried out among 30 children attending the Hanoi Medical University, Vietnam. A Diode Laser with 810 nm wavelength and power of 0.8 W was used for frenectomy.Results: The proportion of procedures without any need of infiltration anesthesia was 70%, while 93.34% of children demonstrated positive and very positive behavior. Proportion of indolence on the first day after surgery was 83.3%. While 83.3% of children did not take any analgesics, not a single child complained of any pain 3 days after surgery.Conclusion: Our results indicated that the use of diode laser showed several benefits in maxillary labial frenectomy in children. These included reducing the need of infiltration anesthesia, increasing the children’s cooperation as well as decreasing the postoperative pain

Combating the COVID-19 Epidemic: Experiences from Vietnam.

The COVID-19 pandemic is spreading fast globally. Vietnam's strict containment measures have significantly reduced the spread of the epidemic in the country. This was achieved through the use of emergency control measures in the epidemic areas and integration of resources from multiple sectors including health, mass media, transportation, education, public affairs, and defense. This paper reviews and shares specific measures for successful prevention and control of COVID-19 in Vietnam, which could provide useful learning for other countries

A Multi-Center Randomised Controlled Trial of Gatifloxacin versus Azithromycin for the Treatment of Uncomplicated Typhoid Fever in Children and Adults in Vietnam

BACKGROUND: Drug resistant typhoid fever is a major clinical problem globally. Many of the first line antibiotics, including the older generation fluoroquinolones, ciprofloxacin and ofloxacin, are failing. OBJECTIVES: We performed a randomised controlled trial to compare the efficacy and safety of gatifloxacin (10 mg/kg/day) versus azithromycin (20 mg/kg/day) as a once daily oral dose for 7 days for the treatment of uncomplicated typhoid fever in children and adults in Vietnam. METHODS: An open-label multi-centre randomised trial with pre-specified per protocol analysis and intention to treat analysis was conducted. The primary outcome was fever clearance time, the secondary outcome was overall treatment failure (clinical or microbiological failure, development of typhoid fever-related complications, relapse or faecal carriage of S. typhi). PRINCIPAL FINDINGS: We enrolled 358 children and adults with suspected typhoid fever. There was no death in the study. 287 patients had blood culture confirmed typhoid fever, 145 patients received gatifloxacin and 142 patients received azithromycin. The median FCT was 106 hours in both treatment arms (95% Confidence Interval [CI]; 94-118 hours for gatifloxacin versus 88-112 hours for azithromycin), (logrank test p = 0.984, HR [95% CI] = 1.0 [0.80-1.26]). Overall treatment failure occurred in 13/145 (9%) patients in the gatifloxacin group and 13/140 (9.3%) patients in the azithromycin group, (logrank test p = 0.854, HR [95% CI] = 0.93 [0.43-2.0]). 96% (254/263) of the Salmonella enterica serovar Typhi isolates were resistant to nalidixic acid and 58% (153/263) were multidrug resistant. CONCLUSIONS: Both antibiotics showed an excellent efficacy and safety profile. Both gatifloxacin and azithromycin can be recommended for the treatment of typhoid fever particularly in regions with high rates of multidrug and nalidixic acid resistance. The cost of a 7-day treatment course of gatifloxacin is approximately one third of the cost of azithromycin in Vietnam. TRIAL REGISTRATION: Controlled-Trials.com ISRCTN67946944

Sex differences in total cholesterol of Vietnamese adults

Background The mid-life emergence of higher levels of total cholesterol (TC) for women than for men has been observed in different Western and Asian populations. The aim of this study was to investigate whether there is evidence of this in Vietnam and, if so, whether it can be explained by ageing, by body size and fatness, or by socio-demographic characteristics and behavioural factors.Methods Participants (n = 14706, 50.9% females) aged 25-64 years were selected by multi-stage stratified cluster sampling from eight provinces each representing one of the eight geographical regions of Vietnam. Measurements were made using the World Health Organization STEPS protocols. Linear regression was used to assess the independent contributions of potential explanatory factors to mean levels of TC. Data were analysed using complex survey methods.Results Men and women had similar mean levels of body mass index (BMI), and men had modestly higher mean levels of waist circumference (WC), in each 5-year age category. The mean TC of women increased more or less continuously across the age range but with a step-up at age 50 years to reach higher concentrations on average than those of their male counterparts. The estimated step-up was not eliminated by adjustment for anthropometric indices including BMI or WC, or by adjustment for socio-demographic characteristics or behavioural factors. The estimated step-up was least for women with the greatest weight.Conclusion There is a marked step-up in TC at age 50 years for Vietnamese women that cannot be explained by their age, or by their body fatness or its distribution, or by their socio-demographic characteristics or behavioural factors, and which results in greater mean levels of TC for middle-aged women than for their male counterparts in Vietnam.</p

The Characteristics of Aftershock Activities of Dien Bien Earthquake on 19 February 2001 and Their Relation to the Local Geomorphological, Tectonic Features

This article examines in detail the characteristics of Dien Bien earthquake on 19 February 2001 and its aftershocks. On the basis of the temporal development of aftershocks and the spatial distribution of tectonic faults, five aftershock series have been determined. The analysis of spatial distribution and temporal evolution of these five aftershock series has clarified the development in the source zone of Dien Bien earthquake, which is closely related to the active and recent activities of tectonic faults in the area, especially Lai Chau Dien Bien fault. The comparison between characteristics of aftershock activities of Dien Bien earthquake and geomorphological features as well as tectonic activities in the area has indicated that the magnitude of these aftershocks and their temporal evolution (early or late) depend not only on the closer or further distance compared to the mainshock and the active faults that cause them but also on terrain elevation, slope index, lineament density and their positions relative to other tectonic faults in the studied area

Seroprevalence of Helicobacter pylori Infection in Urban and Rural Vietnam

Helicobacter pylori-associated diseases, such as peptic ulcer and gastric cancer, are common in Vietnam, but the prevalence of the infection is largely unknown. A validated enzyme-linked immunosorbent assay was used for seroepidemiology with 971 samples from the general population, ages 0 to 88 years, with 546 samples from an urban population (Hanoi), and with 425 samples from a poor, rural province (Hatay). The overall seroprevalence of the infection was 746 per 1,000, with a prevalence of 788 per 1,000 in Hanoi and 692 per 1,000 in Hatay (P = 0.0007). The risk for infection in the rural area of Hatay was 40% lower than in the urban population of Hanoi, with the odds ratio being 0.59 (95% confidence interval, 0.43 to 0.81). The study shows that the prevalence of H. pylori infection is high in Vietnam and especially high in a large urban area, such as the city of Hanoi

Health staff perceptions of patient safety and associated factors in hospitals in Vietnam

Abstract: IntroductionPatient safety is a global challenge of preventing and mitigating medical errors which might harm patients during their course of treatment and care. This study was employed to contribute to the existing literature aimed to assess patient safety culture among health staff and to determine predictors of health staff perceptions of patient safety in hospitals in Vietnam.MethodsA cross-sectional study was conducted in three hospitals of Vietnam with a total of 763 participants. This study used the Hospital Patient Safety Scale developed by the American Health and Quality Research Organization.ResultsIn general, 8 of 12 patient safety dimensions in two hospital; and 10 of 12 dimensions in a third hospital had average scores of 60% and above positive responses. The communication openness and organizational learning dimensions were found to be significant different when comparing hospitals. Regarding sample characteristics, department (subclinical department) and health staff positions (nurses/technicians, pharmacists) were significant predictors in the total model including three hospitals (R2 = 0.07).ConclusionThis study reported that communication openness and organization learning are two aspects that need to be improved they are strongly related to patient safety culture and to knowledge exchange among health staff. It has been suggested that hospitals should deliver patient safety training courses and establish a supportive learning environment to improve these challenges