Purpose
To develop an experimental approach for determining in vivo transverse relaxation rates (T2) of metabolites that are detected by spectral editing without using simulations, and to demonstrate this approach to measure the T2 of γ-aminobutyric acid (GABA).
Materials and Methods
The proposed method first determines the TE-dependence of the edited signals using measurements in a pure phantom solution (10 mM γ-aminobutyric acid; GABA); the phantom T2 is also determined. Once the editing echo time (TE) -modulation pattern is known, it can then be used to determine T2 in vivo. The method was applied to measure GABA T2 in the occipital lobe of five healthy adult subjects at 3T, using a J-difference editing method. Unwanted macromolecular contributions to the GABA signal were also measured.
Results
The in vivo T2 of edited GABA signal was 88 ± 12 ms; this preliminary result is somewhat shorter than other metabolite T2 values in the literature at this field strength.
Conclusion
Spectral editing methods are now widely used to detect low concentration metabolites, such as GABA, but to date no edited acquisition methods have been proposed for the measurement of transverse relaxation times (T2). The method described has been successfully applied to measuring the T2 of GABA.
The COVID-19 outbreak greatly limited
human activities and reduced
primary emissions particularly from urban on-road vehicles but coincided
with Beijing experiencing “pandemic haze,” raising the
public concerns about the effectiveness of imposed traffic policies
to improve the air quality. This paper explores the relationship between
local vehicle emissions and the winter haze in Beijing before and
during the COVID-19 lockdown based on an integrated analysis framework,
which combines a real-time on-road emission inventory, in situ air
quality observations, and a localized numerical modeling system. We
found that traffic emissions decreased substantially during the COVID-19
pandemic, but its imbalanced emission abatement of NO
x
(76%, 125.3 Mg/day) and volatile organic compounds
(VOCs, 53%, 52.9 Mg/day) led to a significant rise of atmospheric
oxidants in urban areas, resulting in a modest increase in secondary
aerosols due to inadequate precursors, which still offset reduced
primary emissions. Moreover, the enhanced oxidizing capacity in the
surrounding regions greatly increased the secondary particles with
relatively abundant precursors, which was transported into Beijing
and mainly responsible for the aggravated haze pollution. We recommend
that mitigation policies should focus on accelerating VOC emission
reduction and synchronously controlling regional sources to release
the benefits of local traffic emission control.
Particulate matter
and NOx emissions
from diesel exhaust remains one of the most pressing environmental
problems. We explore the use of hierarchically ordered mixed Fe–Ce–Zr
oxides for the simultaneous capture and oxidation of soot and reduction
of NOx by ammonia in a single step. The
optimized material can effectively trap the model soot particles in
its open macroporous structure and oxidize the soot below 400 °C
while completely removing NO in the 285–420 °C range.
Surface characterization and DFT calculations emphasize the defective
nature of Fe-doped ceria. The isolated Fe ions and associated oxygen
vacancies catalyze facile NO reduction to N2. A mechanism
for the reduction of NO with NH3 on Fe-doped ceria is proposed
involving adsorbed O2. Such adsorbed O2 species
will also contribute to the oxidation of soot.
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