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

Early prediction of triple negative breast cancer response to cisplatin treatment using diffusion-weighted MRI and 18F-FDG-PET

学位記番号：医博甲1707

Vietnamese learners mastering english articles

The dissertation set out with the objective to find a solution to help Vietnamese learners address problems in using English articles

Single pion contribution to the hyperfine splitting in muonic hydrogen

A detailed discussion of the long-range one-pion exchange (Yukawa potential) contribution to the 2S hyperfine splitting in muonic hydrogen which had, until recently, been disregarded is presented. We evaluate the relevant vertex amplitudes, in particular $\pi^0\mu^+\mu^-$, combining low energy chiral expansions together with experimental data on $\pi^0$ and $\eta$ decays into two leptons. A value of $\Delta{E}^\pi_{HFS}= -(0.09 \pm 0.06)\ \mu\rm{eV}$ is obtained for this contribution.Comment: v2: Expanded and completed versio

Novel approach to measure the leptonic eta(')->mu+mu- decays via charmed meson decays

In this article, we propose a novel approach to measure the branching ratios of the leptonic eta(')-> mu+mu- decays by using charmed meson decays, namely, D+(s)->pi+ eta(')(->mu+mu-) and D0->K-pi+eta(')(->mu+mu-). We advocate that the data available at LHCb can already yield a new measurement of Br(eta->mu+mu-) with accuracy competitive with the current world average. We also estimate that using the data collected by LHCb between 2015 and 2018 in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.0/fb, the relative uncertainties to this branching ratio can be reduced down to ~10%. We also show that the first observation of Br(eta'->mu+mu-) may be possible with the Upgrade of the LHCb experiment.Comment: 12 pages, 3 figure

Inequality in Vietnamese Urban-Rural Living Standards, 1993-2006

Using data from five waves of the Vietnam Household Living Standard Survey, we find evidence of significant urban-rural expenditure inequality. Urban-rural inequality in Vietnam increased dramatically from 1993 to 1998, and peaked in 2002 before reducing slightly in 2004, and significantly in 2006. The urban-rural gap also monotonically increases across the expenditure distribution. We use a variant of the Oaxaca-Blinder decomposition method, applied to the unconditional quantile regression method of Firpo, Fortin and Lemieux (2009), to explain the components of the per capita expenditure differentials between urban and rural households at selected quantiles of the distribution. We also compare these estimates with those at mean obtained by OLS. Our results show a number of factors contributing significantly to the high urban-rural gap. These include inter-group differences in education, household demographic structure, industrial structure and their related returns. Adjusting the average characteristics of rural households to those of urban households will reduce about a half of the overall urban-rural expenditure gap. A significant part of the remaining unexplained component lies in the intercept differences; that is, the inter-group differences in other factors not captured in the model that favor urban households.urban-rural inequality, Vietnam, unconditional quantile regression, Oaxaca decomposition