A double focusing inductively coupled plasma mass spectrometer with an ultrasonic nebulizer and a desolvation unit was used to measure lead-206 lead-207, lead-206 lead-208 and lead-207 lead-208 ...ratios in lead standard SRM981, diluted to total lead concentrations of 1 to 1000 ng per litre. At lead concentrations down to 10 ng per litre, it was possible to determine isotope ratios with sufficient precision, accuracy and reproducibility for many environmental studies. At 1 ng per litre, the procedural blanks were a problem. The method was used to obtain lead isotope ratios for synthetic (SRM1643d) and natural (SLRS-3) standard waters. Reproducibility was excellent for the synthetic water, but lower for the natural water, probably due to matrix effects. Isotope measurements at the sub-ng per litre level will require further work to reduce procedural blanks. In particular, instrument contamination and memory effects for lead will need to be solved.
Elemental and isotopic analyses of lead present at ultra-trace levels were obtained with a double focusing inductively coupled plasma mass spectrometer on a Pyrenean springwater. The sampling was ...carried out across a time series of 598 days encompassing an earthquake of magnitude 5.2. Lead concentrations show a tenfold increase and isotopic compositions shift toward anthropogenic values four days prior to the quake. The time lag between these geochemical anomalies and the earthquake, combined with hydrogeological constraints, are then used to infer where and when strain changes during earthquake preparation processes went beyond the threshold required to temporarily mix waters from normally independent aquifers. The occurrence of pre-seismic centrifugal strain waves propagating from the epicenter area is proposed on the basis of the observed geochemical anomalies.
The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow ...depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at 1370 K in the solar nebula could have produced the observed Si isotope variations. Nebular fractionation of forsterite should be accompanied by correlated variations between the Si isotopic composition and Mg/Si ratio following a slope of 1, which is observed in meteorites. Consideration of this nebular process leads to a revised Si concentration in the Earth's core of 3.6 (+6.0/-3.6) wt% and provides estimates of Mg/Si ratios of bulk planetary bodies.
In the periphery, Foxp3 expression is considered sufficient to maintain natural regulatory CD4+ T‐cell suppressive function. In this study, we challenge this model. Indeed, in mouse chimeras in which ...major histocompatibility complex (MHC) class II expression is restricted to the thymus, peripheral regulatory CD4+ T cells lack suppressive activity. In addition, regulatory CD4+ T cells recovered 5 days after transfer into recipient mice lacking expression of MHC class II molecules (self‐deprived) are unable to inhibit the proliferative response of conventional CD4+ T cells both in vitro and in vivo. Disruption of TCR/MHC class II interactions rapidly leads to alterations in the regulatory CD4+ T‐cell phenotype, the ability to respond to stimulation and to produce interleukin‐10, and the transcriptional signature. Interestingly, self‐deprivation does not affect Foxp3 expression indicating that in regulatory CD4+ T cells, self‐recognition induces unique transcriptional and functional features that do not rely on Foxp3 expression.
I
n the periphery,
F
oxp3 expression is considered sufficient to maintain natural regulatory
CD
4
+
T
‐cell suppressive function. In this study, we challenge this model. Indeed, in mouse chimeras in ...which major histocompatibility complex (
MHC
) class II expression is restricted to the thymus, peripheral regulatory
CD
4
+
T
cells lack suppressive activity. In addition, regulatory
CD
4
+
T
cells recovered 5 days after transfer into recipient mice lacking expression of
MHC
class II molecules (self‐deprived) are unable to inhibit the proliferative response of conventional CD4
+
T cells both in vitro and in vivo. Disruption of
TCR
/
MHC
class II interactions rapidly leads to alterations in the regulatory
CD
4
+
T
‐cell phenotype, the ability to respond to stimulation and to produce interleukin‐10, and the transcriptional signature. Interestingly, self‐deprivation does not affect Foxp3 expression indicating that in regulatory CD4
+
T cells, self‐recognition induces unique transcriptional and functional features that do not rely on Foxp3 expression.
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