18,760 research outputs found

    A Comment on "The Far Future of Exoplanet Direct Characterization" - the Case for Interstellar Space Probes

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    Following on from ideas presented in a recent paper by Schneider et al. (2010) on "The Far Future of Exoplanet Direct Characterization", I argue that they have exaggerated the technical obstacles to performing such 'direct characterization' by means of fast (order 0.1c) interstellar space probes. A brief summary of rapid interstellar spaceflight concepts that may be found in the literature is presented. I argue that the presence of interstellar dust grains, while certainly something which will need to be allowed for in interstellar vehicle design, is unlikely to be the kind of 'show stopper' suggested by Schneider et al. Astrobiology as a discipline would be a major beneficiary of developing an interstellar spaceflight capability, albeit in the longer term, and I argue that astrobiologists should keep an open mind to the possibilities.Comment: Accepted for publication in Astrobiolog

    Crime Prevention and Community Safety

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    This chapter traces and evaluates both the historic emergence of the modern ‘preventive turn’ as well as the elaboration and institutionalisation of crime prevention and community safety over the last thirty years or so. Focusing on the UK, the evolution and changes over time are situated, where relevant, in a broader international context. The chapter identifies three distinct periods of developments that structure the shifts in crime prevention policy and practices from the 1980s to the present day. It explores the conceptualisation, take-up and advancement of a preventive mentality and practices in relation to situational, social and developmental crime prevention as well as community safety. It goes on to assess the institutionalisation of preventive partnerships and early intervention as distinct forms of governance and their implications for ‘responsibilisation’ and ‘securitisation’. In conclusion, it reflects upon the journey travelled thus far as well as possible future directions in an age of austerity

    Biological basis of child health 2: introduction to fertilisation, prenatal development and birth

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    This article is the second in a series called the biological basis of child health. It considers the period of development from fertilisation to birth, outlining the three stages of prenatal development - the germinal, embryonic and fetal stages. The article details how tissues and organs typically develop at each stage, and explains how and when deviations in development and congenital anomalies are likely to occur. It also describes some of the common congenital anomalies, their potential effects and their detection before or after birth. Information is also provided about the delivery of full-term infants, including the stages of labour

    Universal trapping scaling on the unstable manifold for a collisionless electrostatic mode

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    An amplitude equation for an unstable mode in a collisionless plasma is derived from the dynamics on the two-dimensional unstable manifold of the equilibrium. The mode amplitude ρ(t)\rho(t) decouples from the phase due to the spatial homogeneity of the equilibrium, and the resulting one-dimensional dynamics is analyzed using an expansion in ρ\rho. As the linear growth rate γ\gamma vanishes, the expansion coefficients diverge; a rescaling ρ(t)γ2r(γt)\rho(t)\equiv\gamma^2\,r(\gamma t) of the mode amplitude absorbs these singularities and reveals that the mode electric field exhibits trapping scaling E1γ2|E_1|\sim\gamma^2 as γ0\gamma\rightarrow0. The dynamics for r(τ)r(\tau) depends only on the phase eiξe^{i\xi} where dϵk/dz=ϵkeiξ/2d\epsilon_{{k}} /dz=|{\epsilon_{{k}}}|e^{-i\xi/2} is the derivative of the dielectric as γ0\gamma\rightarrow0.Comment: 11 pages (Latex/RevTex), 2 figures available in hard copy from the Author ([email protected]); paper accepted by Physical Review Letter

    AXJ1749+684: a narrow emission-line galaxy with a flat X-ray spectrum

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    We report the serendipitous detection of an X-ray source, AXJ1749+684, with the ASCA Gas Imaging Spectrometer. AXJ1749+684 is identified with a LINER/starburst-type spiral galaxy KUG 1750+683A at a redshift z = 0.05. It has a hard X-ray spectrum, consistent with that of the X-ray background (XRB) in the 1-10 keV band. Despite the optical classification, the X-ray luminosity cannot be explained by starburst activity. Combined with spatial variations in the optical emission line ratios, this suggests the presence of an obscured Seyfert nucleus embedded within a starforming galaxy. Similar behaviour could explain the ambiguous properties of the faint narrow-line X-ray galaxies (NLXGs) emerging from deep X-ray surveys.Comment: MNRAS Letters in press, 6 pages, 7 figures in MNRAS LaTex styl
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