Heterostructures based on layering of two-dimensional (2D) materials such as graphene and hexagonal boron nitride represent a new class of electronic devices. Realizing this potential, however, ...depends critically on the ability to make high-quality electrical contact. Here, we report a contact geometry in which we metalize only the ID edge of a 2D graphene layer. In addition to outperforming conventional surface contacts, the edge-contact geometry allows a complete separation of the layer assembly and contact metallization processes. In graphene heterostructures, this enables high electronic performance, including low-temperature ballistic transport over distances longer than 15 micrometers, and room-temperature mobility comparable to the theoretical phonon-scattering limit. The edge-contact geometry provides new design possibilities for multilayered structures of complimentary 2D materials.
At interfaces between complex oxides, electronic systems with unusual electronic properties can be generated. We report on superconductivity in the electron gas formed at the interface between two ...insulating dielectric perovskite oxides, LaAlO₃ and SrTiO₃. The behavior of the electron gas is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The superconducting transition temperature of congruent with 200 millikelvin provides a strict upper limit to the thickness of the superconducting layer of congruent with 10 nanometers.
The realization of high-transition-temperature (high-Tc) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications and the opportunity ...to study quantum phenomena in reduced dimensions. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas Tc is high and the coherence length very short, which provides an opportunity-but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation. In these bilayers, Tc is either ∼15 K or ∼30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2-3 nm of the interface. If such a bilayer is exposed to ozone, Tc exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1-2 unit cells thick. Enhancement of Tc in bilayer systems was observed previously but the essential role of the interface was not recognized at the time.
We report the discovery of a new monomeric peptide that reduces body weight and diabetic complications in rodent models of obesity by acting as an agonist at three key metabolically-related peptide ...hormone receptors: glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon receptors. This triple agonist demonstrates supraphysiological potency and equally aligned constituent activities at each receptor, all without cross-reactivity at other related receptors. Such balanced unimolecular triple agonism proved superior to any existing dual coagonists and best-in-class monoagonists to reduce body weight, enhance glycemic control and reverse hepatic steatosis in relevant rodent models. Various loss-of-function models, including genetic knockout, pharmacological blockade and selective chemical knockout, confirmed contributions of each constituent activity in vivo. We demonstrate that these individual constituent activities harmonize to govern the overall metabolic efficacy, which predominantly results from synergistic glucagon action to increase energy expenditure, GLP-1 action to reduce caloric intake and improve glucose control, and GIP action to potentiate the incretin effect and buffer against the diabetogenic effect of inherent glucagon activity. These preclinical studies suggest that, so far, this unimolecular, polypharmaceutical strategy has potential to be the most effective pharmacological approach to reversing obesity and related metabolic disorders.
Small-scale cogeneration of heat and power using solid biomass fuels is a promising option for the decentralization of the energy supply in the future. In this context, numerous research activities ...and commercial developments focus on combined systems with Stirling engines and thermochemical conversion of biomass. However, only few of the reviewed concepts and developments achieved to provide commercially successful products. The main problems are ash melting issues and fouling on heat exchanger surfaces as a consequence of the required high temperature levels at the hot side of the Stirling engine. The systems reveal short operation and maintenance intervals as well as mechanical issues due to still insufficiently technically mature Stirling engine technologies. Recent research therefore focuses on the combination of Stirling engines with fluidized bed combustion as homogeneous temperature distribution, enhanced heat transfer and fuel flexibility provide theoretically advantages. Nevertheless, due to the thermodynamic boundary conditions and constraints the electrical efficiency of biomass-fired Stirling engines is limited to 15–20%. However, with the additional utilization of thermal energy at an overall fuel utilization efficiency above 80%, such a system can provide an attractive small-scale CHP solution.
•Review on concepts combining Stirling engines and thermochemical biomass conversion.•Developments often fail due to slagging issues of heat exchanger surfaces.•Crucial high combustion and low ash melting temperatures state a central trade-off.•The electrical efficiency for biomass-fired Stirling engines is limited to 15–20%.•Fluidized bed combustion avoids fouling and allows enhanced heat transfer.
We have combined hard X-ray photoelectron spectroscopy with angular dependent O K-edge and V L-edge X-ray absorption spectroscopy to study the electronic structure of metallic and insulating end ...point phases in 4.1 nm thick (14 units cells along the c-axis of VO2) films on TiO2(001) substrates, each displaying an abrupt MIT centered at ∼300 K with width <20 K and a resistance change of ΔR/R > 103. The dimensions, quality of the films, and stoichiometry were confirmed by a combination of scanning transmission electron microscopy with electron energy loss spectroscopy, X-ray spectroscopy, and resistivity measurements. The measured end point phases agree with their bulk counterparts. This clearly shows that, apart from the strain induced change in transition temperature, the underlying mechanism of the MIT for technologically relevant dimensions must be the same as the bulk for this orientation.
The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of ...future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity.
Introduction Dans les contextes du diabète de type 1, de type 2, et de la greffe d'îlots de Langerhans, les molécules clés pour la médiation de l'inflammation au sein des cellules bêta sont des ...cibles majeures pour des stratégies thérapeutiques innovantes. Nous avons testé l'hypothèse selon laquelle la MAP3 Kinase 8 Tpl2 (Tumor progression locus 2) pouvait être un acteur important dans le réseau de signalisation impliqué dans les effets délétères de plusieurs cytokines pro-inflammatoires sur la fonction et la survie des cellules bêta. Matériels et Méthodes La fonction et la survie des cellules bêta INS-1E, des îlots pancréatiques murins et humains sont mesurées par activation de cas-pase-3/fragmentation de l'ADN, et la sécrétion d'insuline en incubations statiques. Les niveaux d'expression/phosphorylation des protéines sont mesurés par western blot. La tolérance au glucose, ainsi que les taux plas-matiques de glucose et d'insuline sont mesurés chez les souris db/db. Résultats Nous montrons que la kinase Tpl2 est exprimée dans les cellules INS-1E et les îlots pancréatiques murins et humains. Tpl2 est activée et surexprimée par l'IL-1bêta et l'association de plusieurs cytokines (IL-1bêta + TNFalpha + IFNgamma). Son inhibition ne modifie pas les effets bénéfiques du glucose sur la survie des cellules bêta, la sécrétion d'insuline, et l'activation des ERK1/2, mais bloque l'activation des MAP kinases p38, JNK, et ERK1/2 induite par les cytokines. L'inhibition de Tpl2 réduit les effets pro-apoptotiques de l'IL-1bêta et de l'association de cytokines pro-inflammatoires. La sécrétion d'insuline et la survie des îlots murins et humains traités avec l'inhibiteur pharmacologique de Tpl2 sont protégées des effets délétères de l'inflammation. In vivo, l'administration de l'inhibiteur de Tpl2 à des souris diabétiques db/db améliore la tolérance au glucose, réduit l'hyperglycémie et l'hyperinsulinémie. Conclusions Cette étude identifie Tpl2 comme un nouvel acteur moléculaire majeur contrôlant spécifiquement les effets délétères des cytokines pro-inflammatoires, et propose Tpl2 comme cible thérapeutique visant à protéger les cellules bêta de la dysfunction et destruction induites par l'inflammation.
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