21 research outputs found
Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding
Crossover from Collective to Incoherent Spin Excitations in Superconducting Cuprates Probed by Detuned Resonant Inelastic X-Ray Scattering
Spin excitations in the overdoped high temperature superconductors Tl2Ba2CuO6+δ and (Bi,Pb)2(Sr,La)2CuO6+δ were investigated by resonant inelastic x-ray scattering (RIXS) as functions of doping and detuning of the incoming photon energy above the Cu-L3 absorption peak. The RIXS spectra at optimal doping are dominated by a paramagnon feature with peak energy independent of photon energy, similar to prior results on underdoped cuprates. Beyond optimal doping, the RIXS data indicate a sharp crossover to a regime with a strong contribution from incoherent particle-hole excitations whose maximum shows a fluorescencelike shift upon detuning. The spectra of both compound families are closely similar, and their salient features are reproduced by exact-diagonalization calculations of the single-band Hubbard model on a finite cluster. The results are discussed in the light of recent transport experiments indicating a quantum phase transition near optimal doping
Evaluating the SERCA2 and VEGF mRNAs as Potential Molecular Biomarkers of the Onset and Progression in Huntington's Disease
Abnormalities of intracellular Ca2+ homeostasis and signalling as well as the down-regulation
of neurotrophic factors in several areas of the central nervous system and in peripheral
tissues are hallmarks of Huntington\u2019s disease (HD). As there is no therapy for this hereditary,
neurodegenerative fatal disease, further effort should be made to slow the progression
of neurodegeneration in patients through the definition of early therapeutic interventions.
For this purpose, molecular biomarker(s) for monitoring disease onset and/or progression
and response to treatment need to be identified. In the attempt to contribute to the research
of peripheral candidate biomarkers in HD, we adopted a multiplex real-time PCR approach
to analyse the mRNA level of targeted genes involved in the control of cellular calcium homeostasis
and in neuroprotection. For this purpose we recruited a total of 110 subjects possessing
the HD mutation at different clinical stages of the disease and 54 sex- and agematched
controls. This study provides evidence of reduced transcript levels of sarco-endoplasmic
reticulum-associated ATP2A2 calcium pump (SERCA2) and vascular endothelial
growth factor (VEGF) in peripheral blood mononuclear cells (PBMCs) of manifest and premanifest
HD subjects. Our results provide a potentially new candidate molecular biomarker
for monitoring the progression of this disease and contribute to understanding some early
events that might have a role in triggering cellular dysfunctions in HD
A new X ray diffractometer ETA for surface gradient investigations in phase, texture and stress analysis
The Use of High-Energy Synchrotron Diffraction for Residual Stress Analyses
The application of high-energy synchrotron diffraction (HESD) for residual stress analysis was studied at the high-energy beam line ID15A in Grenoble, France. The measurements were performed using an 80 μm slit in the incoming beam and two 100 μm slits in the reflected beam. The main advantages of HESD are illustrated in three examples, namely: a ceramic matrix composites (CMC); a thermal barrier coating (TBC); and a cold-forward-extruded steel sample. From the examples of HESD residual stress analysis on a CMC, a TBC, and a textured sample demonstrated that the method has strong advantages with respect to the high penetration depth and the high local resolution achievable, as well as to the simultaneous investigation of residual stresses and texture