Controlling Tokamak Geometry with 3D Magnetic Perturbations

It is shown that small externally applied magnetic perturbations can significantly alter important geometric properties of magnetic flux surfaces in tokamaks. Through 3D shaping, experimentally relevant perturbation levels are large enough to influence turbulent transport and MHD stability in the pedestal region. It is shown that the dominant pitch-resonant flux surface deformations are primarily induced by non-resonant 3D fields, particularly in the presence of significant axisymmetric shaping. The spectral content of the applied 3D field can be used to control these effects

Very fast X-ray spectral variability in Cygnus X-1: Origin of the hard and soft-state emission components

The way in which the X-ray photon index, {\Gamma}, varies as a function of count rate is a strong diagnostic of the emission processes and emission geometry around accreting compact objects. Here we present the results from a study using a new, and simple, method designed to improve sensitivity to the measurement of the variability of {\Gamma} on very short time-scales. We have measured {\Gamma} in ~2 million spectra, extracted from observations with a variety of different accretion rates and spectral states, on time-scales as short as 16 ms for the high mass X-ray binary Cygnus X-1, and have cross-correlated these measurements with the source count rate. In the soft-state cross-correlation functions (CCFs) we find a positive peak at zero lag, stronger and narrower in the softer observations. Assuming that the X-rays are produced by Compton scattering of soft seed photons by high energy electrons in a corona, these results are consistent with Compton cooling of the corona by seed photons from the inner edge of the accretion disc, the truncation radius of which increases with increasing hardness ratio. The CCFs produced from the hard-state observations, however, show an anti-correlation which is most easily explained by variation in the energy of the electrons in the corona rather than in variation of the seed photon flux. The hard-state CCFs can be decomposed into a narrow anti-correlation at zero lag, which we tentatively associate with the effects of self-Comptonisation of cyclo-synchrotron seed photons in either a hot, optically thin accretion flow or the base of the jet, and a second, asymmetric component which we suggest is produced as a consequence of a lag between the soft and hard X-ray emission. The lag may be caused by a radial temperature/energy gradient in the Comptonising electrons combined with the inward propagation of accretion rate perturbations.Comment: 12 pages, 14 figures; accepted for publication in Monthly Notices of the Royal Astronomical Society, 2013 June

Angiotensin-Converting Enzyme 2 (ACE2) Is a Key Modulator of the Renin Angiotensin System in Health and Disease

Angiotensin-converting enzyme 2 (ACE2) shares some homology with angiotensin-converting enzyme (ACE) but is not inhibited by ACE inhibitors. The main role of ACE2 is the degradation of Ang II resulting in the formation of angiotensin 1–7 (Ang 1–7) which opposes the actions of Ang II. Increased Ang II levels are thought to upregulate ACE2 activity, and in ACE2 deficient mice Ang II levels are approximately double that of wild-type mice, whilst Ang 1–7 levels are almost undetectable. Thus, ACE2 plays a crucial role in the RAS because it opposes the actions of Ang II. Consequently, it has a beneficial role in many diseases such as hypertension, diabetes, and cardiovascular disease where its expression is decreased. Not surprisingly, current therapeutic strategies for ACE2 involve augmenting its expression using ACE2 adenoviruses, recombinant ACE2 or compounds in these diseases thereby affording some organ protection

Black Hole - Neutron Star Mergers as Central Engines of Gamma-Ray Bursts

Hydrodynamic simulations of the merger of stellar mass black hole - neutron star binaries (BH/NS) are compared with mergers of binary neutron stars (NS/NS). The simulations are Newtonian, but take into account the emission and backreaction of gravitational waves. The use of a physical nuclear equation of state allows us to include the effects of neutrino emission. For low neutron star to black hole mass ratios the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted, whereas for ratios near unity the neutron star is already distroyed during its first approach. A gas mass between about 0.3 and about 0.7 solar masses is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several 10^{53} erg/s during an estimated accretion time scale of about 0.1 s. The emitted neutrinos and antineutrinos annihilate into electron-positron pairs with efficiencies of 1-3% percent and rates of up to 2*10^{52} erg/s, thus depositing an energy of up to 10^{51} erg above the poles of the black hole in a region which contains less than 10^{-5} solar masses of baryonic matter. This could allow for relativistic expansion with Lorentz factors around 100 and is sufficient to explain apparent burst luminosities of up to several 10^{53} erg/s for burst durations of approximately 0.1-1 s, if the gamma emission is collimated in two moderately focussed jets in a fraction of about 1/100-1/10 of the sky.Comment: 8 pages, LaTex, 4 postscript figures, 2 tables. ApJ Letters, accepted; revised and shortened version, Fig. 2 change

The speed of range shifts in fragmented landscapes

Peer reviewedPublisher PD

Inverse modeling of global and regional energy and water cycle fluxes using Earth observation data

The NASA Energy and Water Cycle Study (NEWS) climatology is a self-consistent coupled annual and seasonal cycle solution for radiative, turbulent and water fluxes over the Earth's surface using Earth observation data covering 2000-2009. Here we seek to improve the NEWS solution, particularly over the ocean basins, by considering spatial covariances in the observation errors (some evidence for which is found by comparing five turbulent flux products over the oceans) and by introducing additional horizontal transports from ocean reanalyses as weak constraints. By explicitly representing large error covariances between surface heat flux components over the major ocean basins we retain the flux contrasts present in the original data and infer additional heat losses over the North Atlantic, more consistent with a strong Atlantic overturning. This change does not alter the global flux balance but if only the errors in evaporation and precipitation are correlated then those fluxes experience larger adjustments (e.g. the surface latent heat flux increases to 85 +- 2 Wm). Replacing SeaFlux v1 with J-OFURO v3 ocean fluxes also leads to a considerable increase in the global latent heat loss as well as a larger North Atlantic heat loss. Furthermore, including a weak constraint on the horizontal transports of heat and freshwater from high-resolution ocean reanalyses improves the net fluxes over the North Atlantic, Caribbean and Arctic Oceans, without any impact on the global flux balances. These results suggest that better characterised flux uncertainties can greatly improve the quality of the optimised flux solution