Non-adiabatic effects in the phonon dispersion of Mg 1--x Al x B 2

Superconducting MgB$\_2$ shows an E$\_{2g}$ zone center phonon, as measured by Raman spectroscopy, that is very broad in energy and temperature dependent. The Raman shift and lifetime show large differences with the values elsewhere in the Brillouin Zone measured by Inelastic X-ray Scattering (IXS), where its dispersion can be accounted for by standard harmonic phonon theory, adding only a moderate electron-phonon coupling. Here we show that the effects rapidly disappear when electron-phonon coupling is switched off by Al substitution on the Mg sites. Moreover, using IXS with very high wave-vector resolution in MgB$\_2$, we can follow the dispersion connecting the Raman and the IXS signal, in agreement with a theory using only electron-phonon coupling but without strong anharmonic terms. The observation is important in order to understand the effects of electron-phonon coupling on zone center phonons modes in MgB$\_2$, but also in all metals characterized by a small Fermi velocity in a particular direction, typical for layered compounds

The Endosomal Network: Mediators and Regulators of Endosome Maturation

Endocytosis is a means for the cell to sample its environment for nutrients and regulate plasma membrane (PM) composition and area. Whereas the majority of internalized cargo is recycled back to the cell surface, select material is sent to the lysosome for degradation. Endosomes further play major roles in central cell activities as diverse as establishment of cell polarity and signaling, lysosomal storage and immunity. The complexity of endosomal functions is reflected by the extensive changes to endosome properties as they mature. The identity of individual endosomes is influenced by the presence of specific Rab GTPases and phosphoinositides (PIPs), which coordinate membrane traffic and facilitate endosomal functions. Motors and tethers direct the endosomes to the required locations and moderate fusion with other organelles. The maintenance of the elaborate endosomal network is supported by the ER and the trans-Golgi network (TGN), which promote the exchange of membrane components, provide enzymes, and assist with signaling. Additionally, V-ATPase is emerging as an underappreciated coordinator of endosome maturation and cell signaling. The inputs of the various mediators of endosome maturation are tightly regulated and coordinated to ensure appropriate maintenance and functioning of endosomes at each stage of the maturation process. Perturbations in endosome maturation are implicated in devastating diseases, such as neurodegeneration and cancer, and the endosome maturation processes are manipulated and exploited by intracellular pathogens to meet their own needs. A greater understanding of coordination and fine-tuning of endosome maturation will help us address various pathologies more effectively