46,601 research outputs found

    Condensed Surfaces of Magnetic Neutron Stars, Thermal Surface Emission, and Particle Acceleration Above Pulsar Polar Caps

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    For sufficiently strong magnetic fields and/or low temperatures, the neutron star surface may be in a condensed state with little gas or plasma above it. Such surface condensation can significantly affect the thermal emission from isolated neutron stars, and may lead to the formation of a charge-depleted acceleration zone ("vacuum gap") in the magnetosphere above the stellar polar cap. Using the latest results on the cohesive property of magnetic condensed matter, we quantitatively determine the conditions for surface condensation and vacuum gap formation in magnetic neutron stars. We find that condensation can occur if the thermal energy kT of the neutron star surface is less than about 8% of its cohesive energy Q_s, and that a vacuum gap can form if the neutron star's rotation axis and magnetic moment point in opposite directions and kT is less than about 4% of Q_s. Thus, vacuum gap accelerators may exist for some neutron stars. Motivated by this result, we also study the physics of pair cascades in the vacuum gap model for photon emission by accelerating electrons and positrons due to both curvature radiation and resonant/nonresonant inverse Compton scattering. Our calculations of the condition of cascade-induced vacuum breakdown and the related pulsar death line/boundary generalize previous works to the superstrong field regime. We find that inverse Compton scatterings do not produce a sufficient number of high energy photons in the gap and thus do not lead to pair cascades for most neutron star parameters. We discuss the implications of our results for the recent observations of neutron star thermal radiation as well as for the detection/non-detection of radio emission from high-B pulsars and magnetars.Comment: 25 pages, 11 figures. Minor changes. MNRAS in pres

    Bioelectric signal analysis and measurement

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    Nonstationary time series techniques are used to analyze EEG signals for the estimation of alertness. A time varying order is extracted in sequential time series measurement of these data and strategies are devised for obtaining optimal representation of the EEG signal

    Resonant Tidal Excitations of Inertial Modes in Coalescing Neutron Star Binaries

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    We study the effect of resonant tidal excitation of inertial modes in neutron stars during binary inspiral. For spin frequencies less than 100 Hz, the phase shift in the gravitational waveform associated with the resonance is small and does not affect the matched filtering scheme for gravitational wave detection. For higher spin frequencies, the phase shift can become significant. Most of the resonances take place at orbital frequencies comparable to the spin frequency, and thus significant phase shift may occur only in the high-frequency band (hundreds of Hertz) of gravitational wave. The exception is a single odd-paity m=1m=1 mode, which can be resonantly excited for misaligned spin-orbit inclinations, and may occur in the low-frequency band (tens of Hertz) of gravitational wave and induce significant (>> 1 radian) phase shift.Comment: Minor changes. 6 pages. Phys. Rev. D. in press (volume 74, issue 2

    Drell-Yan plus missing energy as a signal for extra dimensions

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    We explore the search sensitivity for signals of large extra dimensions at hadron colliders via the Drell-Yan process pp -> l+ l- + E_T(miss) X (l = e,mu) where the missing transverse energy is the result of escaping Kaluza-Klein gravitons. We find that one is able to place exclusion limits on the gravity scale up to 560 GeV at the Fermilab Tevatron, and to 4.0 (3.3) TeV at the CERN LHC, for n = 3 (4) extra dimensions.Comment: 5 pages, 2 PS figs, revised verseion to be published in Physics Letters

    Working within the preference of people with dementia

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    Section A: Preferred music interventions’ effect on psychological and behavioural outcomes for people with dementia: a systematic review. A previous review concluded that preferred music is an effective intervention for managing agitation in people with dementia; however, the majority of the research articles included were pilot studies. A systematic review is carried out in this work to investigate the effect of preferred music on people with dementia. Six search engines yielded 240 papers, of which 12 were eligible. The report reviewed studies that investigated outcomes including agitation, anxiety, depression and overall emotional state. Inconsistent results are found across studies of most outcomes. Methodological issues mean that some studies are prone to bias. Consequently, it is difficult to draw conclusions from the review. The results suggest the need for further investigation into this area of research. Section B: Development of the video analysis scale of engagement (vase) tool for people with advanced dementia. The current study sought to develop a valid, reliable and unobtrusive tablet computer-based observational tool to appraise a continuous scale of engagement with people with advanced dementia. VASE was designed to enable the rating of moment-by-moment changes in engagement during an intervention, which would be useful for process evaluation in research. An initial version of the Video Analysis Scale of Engagement (VASE) was tested. Face validity and content validity were conducted to validate an operational definition of engagement and develop an acceptable protocol for the tool. Thirty-seven non-professional and professional volunteers were recruited to view and rate people with dementia’s level of engagement in the music activities using the VASE. An inter-class coefficient (ICC) test gave a high level of rating agreement across professionals and non-professionals. However, the ICC results of within-professionals were mixed. Mixed-linear modelling suggested there that the types of interventions (active or passive music listening), the particular intervention session being rated, five second “stages” of each video and the age of those doing the rating could affect the ratings. Results suggested that raters used the VASE in a dynamic fashion, and that the tool was able to distinguish between interventions. Further investigation and adjustments are warranted for this to be considered a valid and reliable tool in the measurement of engagement of people with advanced dementia in a group activity setting

    Radiative transitions of the helium atom in highly magnetized neutron star atmospheres

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    Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree-Fock calculations of the polarization-dependent photoionization cross sections of the He atom in strong magnetic fields ranging from 10^12 G to 10^14 G. Convenient fitting formulae for the cross sections are given as well as related oscillator strengths for various bound-bound transitions. The effects of finite nucleus mass on the radiative absorption cross sections are examined using perturbation theory.Comment: 14 pages, 7 figures. Minor changes. MNRAS in pres

    Transitional Justice and Its Discontents:Socioeconomic Justice in Bosnia and Herzegovina and the Limits of International Intervention

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    The incorporation of socioeconomic concerns into transitional justice has traditionally, as a result of prevailing liberal notions about dealing with the past, been both conceptually and practically difficult. This article demonstrates and accounts for these difficulties through the case of Bosnia and Herzegovina, a country which has been characterized by a complex transition process and a far-reaching international intervention, encompassing transitional justice and peacebuilding as well as political and economic reforms. Examining the limits of international intervention in Bosnia and the marginalization of socioeconomic justice issues, the article analyses the events surrounding the protests that broke out in February 2014, and the ensuing international engagement with the protest movement. Faced with a broad-based civic movement calling for socioeconomic justice, the international community struggled to understand its claims as justice issues, framing them instead as problems to be tackled through reforms aimed at completing Bosnia’s transition towards a market economy. The operation of peacebuilding and transitional justice within the limits of neoliberal transformation is thus instrumental in explaining how and why socioeconomic justice issues become marginalized, as well as accounting for the expression of popular discontent where justice becomes an object of contestation and external intervention

    Dynamical evolution and leading order gravitational wave emission of Riemann-S binaries

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    An approximate strategy for studying the evolution of binary systems of extended objects is introduced. The stars are assumed to be polytropic ellipsoids. The surfaces of constant density maintain their ellipsoidal shape during the time evolution. The equations of hydrodynamics then reduce to a system of ordinary differential equations for the internal velocities, the principal axes of the stars and the orbital parameters. The equations of motion are given within Lagrangian and Hamiltonian formalism. The special case when both stars are axially symmetric fluid configurations is considered. Leading order gravitational radiation reaction is incorporated, where the quasi-static approximation is applied to the internal degrees of freedom of the stars. The influence of the stellar parameters, in particular the influence of the polytropic index nn, on the leading order gravitational waveforms is studied.Comment: 31 pages, 7 figures, typos correcte

    How strong are the Rossby vortices?

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    The Rossby wave instability, associated with density bumps in differentially rotating discs, may arise in several different astrophysical contexts, such as galactic or protoplanetary discs. While the linear phase of the instability has been well studied, the nonlinear evolution and especially the saturation phase remain poorly understood. In this paper, we test the non-linear saturation mechanism analogous to that derived for wave-particle interaction in plasma physics. To this end we perform global numerical simulations of the evolution of the instability in a two-dimensional disc. We confirm the physical mechanism for the instability saturation and show that the maximum amplitude of vorticity can be estimated as twice the linear growth rate of the instability. We provide an empirical fitting formula for this growth rate for various parameters of the density bump. We also investigate the effects of the azimuthal mode number of the instability and the energy leakage in the spiral density waves. Finally, we show that our results can be extrapolated to 3D discs.Comment: Accepted for publication in MNRA
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