Optimization of the visibility of graphene on poly-Si film by thin-film optics engineering

A multilayer optical system containing poly-Si film, SiO 2 film, and Si substrate (poly-Si substrate) has been designed to enhance the visibility of graphene in contact with poly-Si. Film thicknesses of poly-Si and SiO 2 have been optimized by parametric study of the integral contrast of single layer graphene using transfer matrix theory. The multilayer poly-Si substrate and the most commonly used 285 nm SiO 2 /Si substrate (SiO 2 substrate) have been fabricated. Graphene grown by chemical vapor deposition on Ni catalyst has been transferred to the substrates and the visibility of the graphene on the different substrates has been compared. The samples have been characterized by optical microscope, illuminated with light from halogen lamp, and/or filtered with a 600 nm narrow band optical filter. The contrast of graphene on poly-Si substrate has been increased to near 8.7 under 600 nm narrow band illumination from nearly invisible under ordinary illumination, while the contrast of graphene on SiO 2 remains almost the same. Raman spectroscopy has been used to verify the presence of the single layer graphene on the poly-Si substrate.</p

A Mass Bound for Spherically Symmetric Black Hole Spacetimes

Requiring that the matter fields are subject to the dominant energy condition, we establish the lower bound $(4\pi)^{-1} \kappa {\cal A}$ for the total mass $M$ of a static, spherically symmetric black hole spacetime. (${\cal A}$ and $\kappa$ denote the area and the surface gravity of the horizon, respectively.) Together with the fact that the Komar integral provides a simple relation between $M - (4\pi)^{-1} \kappa A$ and the strong energy condition, this enables us to prove that the Schwarzschild metric represents the only static, spherically symmetric black hole solution of a selfgravitating matter model satisfying the dominant, but violating the strong energy condition for the timelike Killing field $K$ at every point, that is, $R(K,K) \leq 0$. Applying this result to scalar fields, we recover the fact that the only black hole configuration of the spherically symmetric Einstein-Higgs model with arbitrary non-negative potential is the Schwarzschild spacetime with constant Higgs field. In the presence of electromagnetic fields, we also derive a stronger bound for the total mass, involving the electromagnetic potentials and charges. Again, this estimate provides a simple tool to prove a ``no-hair'' theorem for matter fields violating the strong energy condition.Comment: 16 pages, LATEX, no figure

Observation of second flexural mode enhancement in graphene resonators

The enhancement of the second flexural mode in a monolayer graphene resonator by an inhomogeneous electrostatic actuation force has been observed. The devices have been fabricated by transferring the graphene onto a poly-Si/SiO2/Si substrate whereby the poly-Si has been released to produce graphene resonators. Enhancement of the second harmonic has been demonstrated by varying the actuation voltage, achieving an amplitude enhancement of up to 95% of the fundamental mode. The reported findings open new perspectives for graphene resonant sensors with enhanced sensitivity.</p

Leukaemogenic effects of Ptpn11 activating mutations in the stem cell microenvironment

Germline activating mutations of the protein tyrosine phosphatase SHP2 (encoded by PTPN11), a positive regulator of the RAS signalling pathway, are found in 50% of patients with Noonan syndrome. These patients have an increased risk of developing leukaemia, especially juvenile myelomonocytic leukaemia (JMML), a childhood myeloproliferative neoplasm (MPN). Previous studies have demonstrated that mutations in Ptpn11 induce a JMML-like MPN through cell-autonomous mechanisms that are dependent on Shp2 catalytic activity. However, the effect of these mutations in the bone marrow microenvironment remains unclear. Here we report that Ptpn11 activating mutations in the mouse bone marrow microenvironment promote the development and progression of MPN through profound detrimental effects on haematopoietic stem cells (HSCs). Ptpn11 mutations in mesenchymal stem/progenitor cells and osteoprogenitors, but not in differentiated osteoblasts or endothelial cells, cause excessive production of the CC chemokine CCL3 (also known as MIP-1α), which recruits monocytes to the area in which HSCs also reside. Consequently, HSCs are hyperactivated by interleukin-1β and possibly other proinflammatory cytokines produced by monocytes, leading to exacerbated MPN and to donor-cell-derived MPN following stem cell transplantation. Remarkably, administration of CCL3 receptor antagonists effectively reverses MPN development induced by the Ptpn11-mutated bone marrow microenvironment. This study reveals the critical contribution of Ptpn11 mutations in the bone marrow microenvironment to leukaemogenesis and identifies CCL3 as a potential therapeutic target for controlling leukaemic progression in Noonan syndrome and for improving stem cell transplantation therapy in Noonan-syndrome-associated leukaemias

Uniqueness Theorem for Static Black Hole Solutions of sigma-models in Higher Dimensions

We prove the uniqueness theorem for self-gravitating non-linear sigma-models in higher dimensional spacetime. Applying the positive mass theorem we show that Schwarzschild-Tagherlini spacetime is the only maximally extended, static asymptotically flat solution with non-rotating regular event horizon with a constant mapping.Comment: 5 peges, Revtex, to be published in Class.Quantum Gra