Periodicity of superconducting shape resonances in thin films

The pairing temperature of superconducting thin films is expected to display, within the Bardeen-Cooper-Schrieffer theory, oscillations as a function of the film thickness. We show that the pattern of these oscillations switches between two different periodicities at a density-dependent value of the superconducting coupling. The transition is most abrupt in the anti-adiabatic regime, where the Fermi energy is less than the Debye energy. To support our numerical data, we provide new analytical expressions for the chemical potential and the pairing temperature as a function of thickness, which only differ from the exact solution at weak coupling by exponentially-small corrections.Comment: Published versio

Propagation of shear stress in strongly interacting metallic Fermi liquids enhances transmission of terahertz radiation

A highlight of Fermi-liquid phenomenology, as explored in neutral 3He, is the observation that in the collisionless regime shear stress propagates as if one is dealing with the transverse phonon of a solid. The existence of this “transverse zero sound” requires that the quasiparticle mass enhancement exceeds a critical value. Could such a propagating shear stress also exist in strongly correlated electron systems? Despite some noticeable differences with the neutral case in the Galilean continuum, we arrive at the verdict that transverse zero sound should be generic for mass enhancement higher than 3. We present an experimental setup that should be exquisitely sensitive in this regard: the transmission of terahertz radiation through a thin slab of heavy-fermion material will be strongly enhanced at low temperature and accompanied by giant oscillations, which reflect the interference between light itself and the “material photon” being the actual manifestation of transverse zero sound in the charged Fermi liquid

The baculovirus anti-apoptotic p35 protein promotes transformation of mouse embryo fibroblasts.

The baculovirus p35 protein is a potent inhibitor of programmed cell death induced by a variety of stimuli in insects, nematodes, and mammalian cell lines. The broad ability of p35 in preventing apoptosis has led us to investigate its effect on mouse embryo fibroblasts in vitro and in vivo. For this purpose, we have used R- cells (3T3-like fibroblasts derived from mouse embryos with a targeted disruption of the insulin-like growth factor I receptor (IGF-IR) genes) and R508 cells (derived from R- and with 15 x 10(3) IGF-IRs per cell). Both cell lines grow normally in monolayer, but they do not form colonies in soft agar, and they are non-tumorigenic in nude mice. We show here that, in addition to its anti-apoptotic effect, p35 causes transformation of R508 cells, as evidenced by the following: 1) decreased growth factor requirements, 2) ability to form foci in monolayer and colonies in soft agar, and 3) ability to form tumors in nude mice. Since R- cells stably transfected with p35 do not transform, our observations suggest that in addition to its effect as an inhibitor of apoptosis, the baculovirus p35 protein has transforming potential that requires the presence of the IGF-IR. The possibility that these two properties could be separated was confirmed by demonstrating that R508 cells expressing another anti-apoptotic protein, Bcl-2, could not form tumors in nude mice

Shape-resonant superconductivity in nanofilms: from weak to strong coupling

Ultrathin superconductors of different materials are becoming a powerful platform to find mechanisms for enhancement of superconductivity, exploiting shape resonances in different superconducting properties. Here we evaluate the superconducting gap and its spatial profile, the multiple gap components, and the chemical potential, of generic superconducting nanofilms, considering the pairing attraction and its energy scale as tunable parameters, from weak to strong coupling, at fixed electron density. Superconducting properties are evaluated at mean field level as a function of the thickness of the nanofilm, in order to characterize the shape resonances in the superconducting gap. We find that the most pronounced shape resonances are generated for weakly coupled superconductors, while approaching the strong coupling regime the shape resonances are rounded by a mixing of the subbands due to the large energy gaps extending over large energy scales. Finally, we find that the spatial profile, transverse to the nanofilm, of the superconducting gap acquires a flat behavior in the shape resonance region, indicating that a robust and uniform multigap superconducting state can arise at resonance.Comment: 7 pages, 4 figures. Submitted to the Proceedings of the Superstripes 2016 conferenc

Secondary headaches: secondary or still primary?

The second edition of the International Classification of Headache Disorders makes a distinction between primary and secondary headaches. The diagnosis of a secondary headache is made if the underlying disease is thought to cause headache or if a close temporal relationship is present together with the occurrence of the headache. At first glance, this may allow clearly secondary headaches to be distinguished from primary headaches. However, by reviewing the available literature concerning several selected secondary headaches, we will discuss the hypothesis that some secondary headaches can also be understood as a variation of primary headaches in the sense that the underlying cause (e.g. infusion of glyceryl trinitrate [ICHD-II 8.1.1], epilepsy [7.6.2], brain tumours [7.4], craniotomy [5.7], etc.) triggers the same neurophysiologic mechanisms that are responsible for the pain in primary headache attacks