Understanding N-nitrosodimethylamine Formation in Water: Chloramine Chemistry, Kinetics, and A Proposed Reaction Pathway

The formation of N-nitrosodimethylamine (NDMA) in drinking water systems is a concern because of its potential carcinogenicity and occurrence at toxicologically relevant levels. The postulated mechanism for NDMA formation involves a substitution between dichloramine and amine-based precursors to form an unsymmetrical dimethylhydrazine (UDMH), which is then oxidized by ground-state molecular oxygen to form NDMA. However, this latter reaction is spin forbidden, thus likely occurs at a slow rate. It is hypothesized that the reaction between monochloramine and hydroxylamine (a nitrification product) may form an intermediate, which is involved in the NDMA formation pathway. This intermediate may also be generated from dichloramine decay, in the absence of hydroxylamine. In this study, a series of batch kinetic experiments were conducted to investigate the decomposition of chloramine species at pH 8.0 to 10.0 and the concomitant formation of NDMA. Chloramine species were quantified using UV/Vis spectroscopy (Direct UV) and colorimetric methods (Hach) and compared to simulations from the unified chloramine model. NDMA was quantified using GC-MS following liquid-liquid extraction. The model captured the decay of monochloramine and dichloramine adequately, with the exception of monochloramine at pH 10.0, possibly due to an interference from a previously reported unidentified chloramine decomposition compound (UC1). NDMA formation was pH dependent with the maximum yields at pH 9.0 and the fastest kinetics at pH 10.0. A second unidentified compound (UC2), with a mass spectrum identified as UDMH, was detected only at pH 9.0 and 10.0 in batch reactors with DMA and dichloramine. Importantly, NDMA formation appeared to be insensitive to the presence or absence of UC2, suggesting UC2 was not involved in NDMA formation. Hydroxylamine accelerates the decomposition of monochloramine. The reaction between DMA and hydroxylamine formed a third unidentified compound (UC3), preliminarily identified as acetoxime, which was not observed in the presence of monochloramine. Upon addition of hydroxylamine, NDMA yields decreased by more than half in batch reactors with DMA and monochloramine. On balance, the findings suggest the existence of a NDMA formation pathway that may not involve UDMH, and points to the need for studies with scavengers and donors of short-lived species from chloramine decay

Formation of Reactive Nitrogen Species During Dichloramine Decay and Their Impact on N Nitrosodimethylamine Formation Under Drinking Water Conditions

NDMA occurrence and formation pathways in drinking water systems are reviewed and NDMA yields are compared on the basis of disinfectant type, water chemistry, and precursor category. In chloramination, despite monochloramine being the predominant species between pH 7-9, evidence suggests that dichloramine is the primary species involved in NDMA formation. This is somewhat confounding as NDMA yields are maximal at pH 9, yet at pH 9 dichloramine decays faster than it forms and hence is present at trace levels; additionally, the proposed mechanism involves a spin-forbidden incorporation of dissolved oxygen as a triplet, which is presumably kinetically slow. This review reveals that kinetic data for NDMA formation is lacking, and its influence on chloramine chemistry has not been carefully considered. In pH 7-10 waters amended with 10 μM total dimethylamine and 800 μeq Cl2.L–1 dichloramine (NHCl2), NDMA, nitrous oxide (N2O), dissolved oxygen (DO), NHCl2, and monochloramine (NH2Cl) were kinetically quantified. NHCl2, N2O, and DO profiles indicated reactive nitrogen species (RNS) formed during NHCl2 decomposition, including nitroxyl/nitroxyl anion (HNO/NO−) and peroxynitrous acid/peroxynitrite anion (ONOOH/ONOO–). Experiments with uric acid (an ONOOH/ONOO– scavenger) implicated ONOOH/ONOO– as a central node for NDMA formation, which was further supported by concomitant N-nitrodimethylamine formation. A kinetic model accurately simulated NHCl2, NH2Cl, NDMA, and DO concentrations and included (1) the unified model of chloramine chemistry revised with HNO as a direct product of NHCl2 hydrolysis, (2) HNO/NO− then reacting with (i) HNO to form N2O, (ii) DO to form ONOOH/ONOO–, or (iii) NHCl2 or NH2Cl to form nitrogen gas, and (3) NDMA formation via ONOOH/ONOO– or their decomposition products reacting with (i) dimethylamine (DMA) and/or (ii) chlorinated unsymmetrical dimethylhydrazine (UDMH-Cl), the product of NHCl2 and DMA. The role of DO was further examined at pH 9 by assessing kinetic profiles of NHCl2 and NDMA under ambient DO (~280 μM) and low-DO (\u3c 20 μM) conditions in the presence and absence of 10 μM TOTDMA. Uric acid completely shut down NDMA formation under the low-DO condition, validating ONOOH/ONOO− as the central node in NDMA formation. Yield experiments with initial NHCl2 of 200-, 400-, and 800 μeq Cl2.L–1 tracked the formation of NH3/NH4+, NH2Cl, N2O, N2, NO2−, and NO3−. NH3/NH4+ yields were 20–40% greater under the low-DO condition, implying a reaction occurred between NH3/NH4+ and ONOOH/ONOO− or its decomposition products. NH2Cl yields were 16–20% lower under the low-DO condition, revealing a previously unknown NH2Cl formation reaction. Under ambient DO conditions, about 80% of the nitrogen was accounted for compared to the low-DO conditions in which nitrogen recoveries were 90- and 100% in the absence and presence of 10 μM TOTDMA, respectively. An existing mechanistic model accurately predicted NH3/NH4+, NH2Cl, and N2 under ambient conditions but underpredicted N2O and overpredicted NO2− and NO3−. The results provide a framework to guide future experiments with ONOOH/ONOO− generators and revise the mechanistic model to better capture the nitrogenous end-products

Penalized Spline Joint Models for Longitudinal and Time-To-Event Data

The joint models for longitudinal data and time-to-event data have recently received numerous attention in clinical and epidemiologic studies. Our interest is in modeling the relationship between event time outcomes and internal time-dependent covariates. In practice, the longitudinal responses often show non-linear and fluctuated curves. Therefore, the main aim of this chapter is to use penalized splines with a truncated polynomial basis to parameterize the non-linear longitudinal process. Then, the linear mixed effects model is applied to subject-specific curves and to control the smoothing. The association between the dropout process and longitudinal outcomes is modeled through a proportional hazard model. Two types of baseline risk functions are considered, namely a Gompertz distribution and a piecewise constant model. The resulting models are referred to as penalized spline joint models; an extension of the standard linear joint models

OPORTUNIDADES E DESAFIOS DA TRANSFORMAÇÃO DIGITAL NA EDUCAÇÃO NO DESASTRE DE COVID NO VIETNÃ

Coronavirus affects the education system in the world. Schools, colleges, and universities are closed to control the spread of the coronavirus. School closure brings difficulties for students, teachers, and parents. So, online learning is a solution to continue the education system. However, the lack of network infrastructures, computers, and internet access is challenging. This paper aims to review the impact of the COVID-19 pandemic on the education and status of digital transformation in education in Vietnam. Verify the opportunities and challenges in the digital transformation in education and recommend some issues that need to do be concerned to promote the transformation process in education in Vietnam.O coronavírus afeta o sistema educacional no mundo. Escolas, faculdades e universidades são fechadas para controlar a disseminação do coronavírus. O fechamento de escolas traz dificuldades para alunos, professores e pais. Portanto, o aprendizado online é uma solução para dar continuidade ao sistema educacional. No entanto, a falta de infraestruturas de rede, computadores e acesso à Internet é um desafio. Este artigo tem como objetivo revisar o impacto da pandemia COVID-19 sobre a educação e a situação da transformação digital na educação no Vietnã. Verifique as oportunidades e desafios na transformação digital na educação e recomende algumas questões que precisam se preocupar para promover o processo de transformação na educação no Vietnã

A Hybrid of Adaptation and Dynamic Routing based on SDN for Improving QoE in HTTP Adaptive VBR Video Streaming

Recently, HTTP Adaptive Streaming HAS has received significant attention from both industry and academia based on its ability to enhancing media streaming services over the Internet. Recent research solutions that have tried to improve HAS by adaptation at the client side only may not be completely effective without interacting with routing decisions in the upper layers. In this paper, we address the aforementioned issue by proposing a dynamic bandwidth allocation and management architecture for streaming video flows to improve users satisfaction. We also introduce an initial cross layer hybrid method that combines quality adaptation of variable bitrate video streaming over the HTTP protocol at the client side and SDN based dynamical routing. This scheme is enabled by the Software Defined Networking architecture that is now being considered as an emerging paradigm that disassociates the forwarding process from the routing process. SDN brings flexibility and the ability to flexibly change routing solutions, in turn resulting in dynamically improving the services provided in the application layer. Our experimental results show that the proposed solution offers significantly higher overall bitrates as well as smoother viewing experience than existing methods.Comment: 14 pages, 17 figures, IJCSNS International Journal of Computer Science and Network Security, http://paper.ijcsns.org/07_book/201907/20190708.pd

Theoretical basis for reasonable population distribution in Tho Chu archipelago

Tho Chu archipelago is one of administrative units of Kien Giang province, Hon Nhan- one of its islands - is selected to become A1 base point of baseline for Vietnam territorial waters. If Tho Chau district is established, it will contribute to identifying sovereignty of Vietnam Southwest sea area following the United Nations Convention on the Law of the Sea, creating favourable conditions for islands’ socio-economic development, developing culture, enhancing effects of administration work and life quality of population in this island, firmly protecting sea border, securing island and sea sovereignty… However, the establishment of Tho Chu district appears in the context of streamlining administrative apparatus and limitation of capital for infrastructure construction in district level. This article focuses on the analysis of some factors affecting a reasonable population distribution in order to meet the requirement of building the Tho Chu into a district-level administrative unit in Kien Giang province

The revolution in online learning and implication in Vietnamese universities

Online education has rapidly become popular worldwide in higher education. There are massive open online courses which could be found in Coursera and EDX. These courses ensure the availability and the accessibility of the online learning through videos with subtitles. Online learning not only gives students unprecedented opportunities to learn, but also reduces the cost of higher education. However, online learning presents unit challenges compared to traditional learning, especially in Vietnamese education. In this paper, we present the advantages and disadvantages of online learning. In particular, we will show the advantages and disadvantages of taking online courses of Vietnamese students. We will also share our experience as a tutor of Funix University which is the first online university in Vietnam. In addition, we will give feasible suggestions to improve the quality of online learning in Vietnamese universities, especially the quality of assessment in online learning. These suggestions could be applied in building new online courses in the universities

Examining the factors of burden among family caregivers of older adults with diabetes mellitus regarding a development model

13301甲第415号博士（保健学）金沢大学博士論文要旨Abstract 以下に掲載：Journal of Wellness and Health Care 44(1) pp.19-21 2020. Wellness and Health Care Society = ウェルネス・ヘルスケア学会. 共著者：Huong Thi Thu Pham, Kato Mayumi, Shogenji Miho, Tsujiguchi Hiromasa, Taniguchi Yoshim