Phase noise in distributed oscillators

The phase noise of a distributed oscillator is evaluated very simply by identifying an effective capacitance equal to the total capacitance distributed along the transmission lines. The contributions of the various passive and active noise sources to the total phase noise are calculated revealing several guidelines for improved distributed oscillator designs

Room-temperature ballistic transport in narrow graphene strips

We investigate electron-phonon couplings, scattering rates, and mean free paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our calculations for these graphene nanostrips show both the expected similarity with single-wall carbon nanotubes (SWNTs) and the suppression of the electron-phonon scattering due to a Dirichlet boundary condition that prohibits one major backscattering channel present in SWNTs. Low-energy acoustic phonon scattering is exponentially small at room temperature due to the large phonon wave vector required for backscattering. We find within our model that the electron-phonon mean free path is proportional to the width of the nanostrip and is approximately 70 $\mu$m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure

The excess burden of cancer in men in the UK

In general men are at significantly greater risk than women from nearly all of the common cancers that occur in both sexes (with the exception of breast cancer) (White 2009, Wilkins 2006, DH 2007). This report will consider the current overall burden of cancer among men in the UK, estimated from the latest statistics, and outline the extent of the differences between the sexes. All figures and calculations reported here are based on data extracted from the Cancer Research UK CancerStats web pages extracted in June 2009 (Cancer Research UK, 2009)

ROSAT PSPC observations of the outer regions of the Perseus cluster of galaxies

We present an analysis of four off-axis ROSAT PSPC observations of the Perseus cluster of galaxies (Abell~426). We detect the surface brightness profile to a radius of 80 arcmin ($\sim 2.4 h_{50}^{-1}$ Mpc) from the X-ray peak. The profile is measured in various sectors and in three different energy bands. Firstly, a colour analysis highlights a slight variation of $N_{H}$ over the region, and cool components in the core and in the eastern sector. We apply the $\beta$-model to the profiles from different sectors and present a solution to the, so-called, $\beta$-problem. The residuals from an azimuthally-averaged profile highlight extended emission both in the East and in the West, with estimated luminosities of about 8 and 1 $\times 10^{43} erg/s$, respectively. We fit several models to the surface brightness profile, including the one obtained from the Navarro, Frenk and White (1995) potential. We obtain the best fit with the gas distribution described by a power law in the inner, cooling region and a $\beta$-model for the extended emission. Through the best-fit results and the constraints from the deprojection of the surface brightness profiles, we define the radius where the overdensity inside the cluster is 200 times the critical value, $r_{200}$, at $2.7 h_{50}^{-1}$ Mpc. Within $2.3 h_{50}^{-1}$ Mpc ($0.85 r_{200}$), the total mass in the Perseus cluster is $1.2 \times 10^{15} M_{\odot}$ and its gas fraction is about 30 per cent.Comment: 21 pages, 23 figures; accepted for publication in MNRAS; also available at http://www-xray.ast.cam.ac.uk/~settori/paper.htm

Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics

A sample of 197 X-ray emitting clusters of galaxies is considered in the context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the gas mass, extrapolated via an assumed $\beta$ model to a fixed radius of 3 Mpc, is correlated with the gas temperature as predicted by MOND ($M_g \propto T^2$). The observed temperatures are generally consistent with the inferred mass of hot gas; no substantial quantity of additional unseen matter is required in the context of MOND. However, modified dynamics cannot resolve the strong lensing discrepancy in those clusters where this phenomenon occurs. The prediction is that additional baryonic matter may be detected in the central regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro

Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.Comment: 9 page PDF, 550 kbyte

Moir\'e super-lattice structures in kicked Bose-Einstein condensates

Vortex lattices in rapidly rotating Bose-Einstein condensates lead to a periodic modulation of the superfluid density with a triangular symmetry. Here we show that this symmetry can be combined with an external perturbation in order to create super-lattice structures with two or more periodicities. Considering a condensate which is kicked by an optical lattice potential, we find the appearance of transient moir\'e lattice structures, which can be identified using the kinetic energy spectrum.Comment: 7 pages, 8 figure