108 research outputs found
Narrow-band tunable extreme-ultraviolet laser source for lifetime measurements and precision spectroscopy
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
Extreme ultraviolet laser calibration of D-2 Lyman and Werner transitions
- X-1 Sigma(+)(g)(0,0) Werner band of the D-2 molecule were measured using a narrowband tunable extreme-ultraviolet laser source, at an unprecedented accuracy of Delta lambda/lambda = 6 x 10(-8). The results bear relevance for future use in the calibration of dense classical spectra obtained for the HD and D-2 hydrogen isotopologues
Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.This project is funded by a Leverhulme Trust Research Grant. WULTB wishes to acknowledge support from the LABEX Plas@par managed by the French ANR (ANR-11-IDEX-0004-02). J.D. Barrow is supported by the STFC of the UK
VUV spectroscopic study of the D1Piu state of molecular deuterium
The D^1\Pi_u - X^1\Sigma_g^+ absorption system of molecular deuterium has
been re-investigated using the VUV Fourier -Transform (FT) spectrometer at the
DESIRS beamline of the synchrotron SOLEIL and photon-induced fluorescence
spectrometry (PIFS) using the 10 m normal incidence monochromator at the
synchrotron BESSY II. Using the FT spectrometer absorption spectra in the range
72 - 82 nm were recorded in quasi static gas at 100 K and in a free flowing jet
at a spectroscopic resolution of 0.50 and 0.20 cm^{-1} respectively . The
narrow Q-branch transitions, probing states of \Pi^- symmetry, were observed up
to vibrational level v = 22. The states of \Pi^+ symmetry, known to be
broadened due to predissociation and giving rise to asymmetric Beutler-Fano
resonances, were studied up to v = 18. The 10 m normal incidence beamline setup
at BESSY II was used to simultaneously record absorption, dissociation,
ionization and fluorescence decay channels from which information on the line
intensities, predissociated widths, and Fano q-parameters were extracted.
R-branch transitions were observed up to v = 23 for J = 1-3 as well as several
transitions for J = 4 and 5 up to v = 22 and 18 respectively. The Q-branch
transitions are found to weakly predissociate and were observed from v = 8 to
the final vibrational level of the state v = 23. The spectroscopic study is
supported by two theoretical frameworks. Results on the \Pi^- symmetry states
are compared to ab initio multi-channel-quantum defect theory (MQDT)
calculations, demonstrating that these calculations are accurate to within 0.5
cm^-1.Comment: 16 pages, 10 figures, 2 tables, supplemental material with an
additional tabl
Antigen processing and presentation by dendritic cells is independent of coronin 1
Coronin 1, which is a member of the evolutionary conserved coronin protein family that is highly expressed in all leukocytes is involved in the activation of the Ca(2+)/calcineurin signaling pathway following cell surface stimulation in T cells, B cells as well as macrophages. Mice deficient for coronin 1 have strongly reduced peripheral T cell numbers as a result of a lack of pro-survival signals for naĂŻve T cells. Whether or not impaired antigen processing and presentation in the absence of coronin 1 expression contributes to this reduction of T cell numbers is unknown. We here show that coronin 1-deficient bone marrow-derived dendritic cells develop normally, and that wild type and coronin 1-deficient dendritic cells were equally able to induce antigen-specific proliferation of T cells. Furthermore, upon immunization, in vivo proliferation of adoptively transferred antigen-specific T cells was comparable in wild type and coronin 1-deficient mice. Finally, infection of wild type and coronin 1-deficient dendritic cells with an ovalbumin-expressing Listeria monocytogenes strain induced comparable levels of ovalbumin-specific T cells responses. Together these results suggest that coronin 1 is dispensable for antigen processing and presentation by dendritic cells
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