Heating plasma loops in the solar corona

We find a new heat source term for hot coronal loops and include it in the energy equation. This term requires the loop to be hotter than the ambient corona and depends on the combined effect of electron fluid shear and the temperature gradient. Under certain circumstances, the shear drives the heat up the radial temperature gradient into a cross section of the magnetic flux tube from which it leaves by radiation and by conduction down the axial temperature gradient in the usual manner. The heat source is thus a surface term applied over the whole of the loop rather than a volume-distributed term, and its strength is proportional to the cube of the temperature. We apply it to the usual scaling law and obtain an expression for the radius of the flux tube for thermal equilibrium to hold. The temperature distribution around the plasma loop is determined and compared with recent observations and is found to be in satisfactory agreement with them

On the magnetic structure of the solar transition region

We examine the hypothesis that ``cool loops'' dominate emission from solar transition region plasma below temperatures of $2\times10^5$K. We compare published VAULT images of H L$\alpha$, a lower transition region line, with near-contemporaneous magnetograms from Kitt Peak, obtained during the second flight (VAULT-2) on 14 June 2002. The measured surface fields and potential extrapolations suggest that there are too few short loops, and that L$\alpha$ emission is associated with the base regions of longer, coronal loops. VAULT-2 data of network boundaries have an asymmetry on scales larger than supergranules, also indicating an association with long loops. We complement the Kitt Peak data with very sensitive vector polarimetric data from the Spectro-Polarimeter on board Hinode, to determine the influence of very small magnetic concentrations on our analysis. From these data two classes of behavior are found: within the cores of strong magnetic flux concentrations ($> 5\times10^{18}$ Mx) associated with active network and plage, small-scale mixed fields are absent and any short loops can connect just the peripheries of the flux to cell interiors. Core fields return to the surface via longer, most likely coronal, loops. In weaker concentrations, short loops can connect between concentrations and produce mixed fields within network boundaries as suggested by Dowdy and colleagues. The VAULT-2 data which we examined are associated with strong concentrations. We conclude that the cool loop model applies only to a small fraction of the VAULT-2 emission, but we cannot discount a significant role for cool loops in quieter regions. We suggest a physical picture for how network L$\alpha$ emission may occur through the cross-field diffusion of neutral atoms from chromospheric into coronal plasma.Comment: Accepted by ApJ, 9 May 200

Uptake of hypobromous acid (HOBr) by aqueous sulfuric acid solutions: low-temperature solubility and reaction

International audienceHypobromous acid (HOBr) is a key species linking inorganic bromine to the chlorine and odd hydrogen chemical families. We have measured the solubility of HOBr in 45-70wt% sulfuric acid solutions representative of upper tropospheric and lower stratospheric aerosol composition. Over the temperature range 201-252 K, HOBr is quite soluble in sulfuric acid, with an effective Henry's law coefficient, H*=104-107mol L-1atm-1. H* is inversely dependent on temperature, with ?H=-45.0±5.4 kJ mol-1 and ?S=-101±24 J mol-1K-1 for 55-70wt% H2SO4 solutions. Our study includes temperatures which overlap both previous measurements of HOBr solubility. For uptake into 55-70wt% H2SO4, the solubility is described by log H*=(2349±280)/T-(5.27±1.24). At temperatures colder than ~213K, the solubility of HOBr in 45wt% H2SO4 is at least a factor of five larger than in 70wt% H2SO4, with log H*=(3665±270)/T-(10.63±1.23). The solubility of HOBr is comparable to that of HBr, indicating that upper tropospheric and lower stratospheric aerosols should contain equilibrium concentrations of HOBr which equal or exceed those of HBr. Upon uptake of HOBr into aqueous sulfuric acid in the presence of other brominated gases, particularly for 70wt% H2SO4 solution, our measurements demonstrate chemical reaction of HOBr followed by evolution of gaseous products including Br2O and Br2

Can extreme black holes have (long) Abelian Higgs hair?

It has been argued that a black hole horizon can support the long range fields of a Nielsen-Olesen string, and that one can think of such a vortex as black hole ``hair''. In this paper, we examine the properties of an Abelian Higgs vortex in the presence of a charged black hole as we allow the hole to approach extremality. Using both analytical and numerical techniques, we show that the magnetic field lines (as well as the scalar field) of the vortex are completely expelled from the black hole in the extreme limit. This was to be expected, since extreme black holes in Einstein-Maxwell theory are known to exhibit such a ``Meissner effect'' in general. This would seem to imply that a vortex does not want to be attached to an extreme black hole. We calculate the total energy of the vortex fields in the presence of an extreme black hole. When the hole is small relative to the size of the vortex, it is energetically favoured for the hole to remain inside the vortex region, contrary to the intuition that the hole should be expelled. However, as we allow the extreme horizon radius to become very large compared to the radius of the vortex, we do find evidence of an instability. This proves that it is energetically unfavourable for a thin vortex to interact with a large extreme black hole. This would seem to dispel the notion that a black hole can support `long' abelian Higgs hair in the extreme limit. We show that these considerations do not go through in the near extreme limit. Finally, we discuss whether this has implications for strings that end at black holes.Comment: 21 pages REVTeX plus 9 figures. Additional figures and mpeg movies available at http://www.damtp.cam.ac.uk/user/ats25/strhole.html We have made several cosmetic changes, and we have revised and extended the discussion of strings which end on extreme horizon

Black hole pairs and supergravity domain walls

We examine the pair creation of black holes in the presence of supergravity domain walls with broken and unbroken supersymmetry. We show that black holes will be nucleated in the presence of non- extreme, repulsive walls which break the supersymmetry, but that as one allows the parameter measuring deviation from extremality to approach zero the rate of creation will be suppressed. In particular, we show that the probability for creation of black holes in the presence of an extreme domain wall is identically zero, even though an extreme vacuum domain wall still has repulsive gravitational energy. This is consistent with the fact that the supersymmetric, extreme domain wall configurations are BPS states and should be stable against quantum corrections. We discuss how these walls arise in string theory, and speculate about what string theory might tell us about such objects.Comment: 21 pages LaTeX, special style files (psfrag.sty, efsf_psfrag.sty, a4local.sty, epsf.tex), minor revisions and amended reference

Abelian Higgs hair for extreme black holes and selection rules for snapping strings

It has been argued that a black hole horizon can support the long range fields of a Nielsen-Olesen string, and that one can think of such a vortex as black hole ``hair''. We show that the fields inside the vortex are completely expelled from a charged black hole in the extreme limit (but not in the near extreme limit). This would seem to imply that a vortex cannot be attached to an extreme black hole. Furthermore, we provide evidence that it is energetically unfavourable for a thin vortex to interact with a large extreme black hole. This dispels the notion that a black hole can support `long' Abelian Higgs hair in the extreme limit. We discuss the implications for strings that end at black holes, as in processes where a string snaps by nucleating black holes.Comment: 4 pages REVTeX plus 3 figures. Additional figures and mpeg movies available at http://www.damtp.cam.ac.uk/user/ats25/strhole.html This paper is a condensed version of gr-qc/9706004, and is essentially the talk presented at The Eighth Marcel Grossmann Meeting on General Relativity, 22-27 June 1997, The Hebrew University, Jerusalem, Israe

From O'Shaughnessy to opportunity: Innovating Hepatology Trials in the UK

Developing new treatments that improve outcomes for patients with decompensated cirrhosis remains an unmet area of clinical need. The UK has a rich history of being on the forefront of clinical trials for this patient group. However, there have been challenges in achieving this goal in the past decade, with several negative studies as well as trials struggling to achieve recruitment. This has been further exacerbated by the changed clinical landscape following the COVID-19 pandemic. In response to this, the O'Shaughnessy report was commissioned to identify potential opportunities to improve clinical trial performance in the UK. In this review article, we identify critical areas for the UK hepatology community to collaborate and develop sustainable partnerships for clinical trial delivery which will ensure that outcomes are representative, inclusive and patient-centred

Kinetics of excited hydrogen-like atoms in high-temperature plasmas

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN019200 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Audio Technology, Music, and Media: From Sound Wave to Resproduction

Buku ini menyediakan A hingga Z suara yang direkam sejati, dari awal hingga saat ini, menguraikan bagaimana teknologi, teknik, dan sikap sosial telah mengubah hal-hal, mencatat apa yang baik dan apa yang kurang baik. Penulis memulai dengan membahas fisika generasi suara dan perambatan. Dia kemudian melanjutkan untuk menguraikan sejarah suara yang direkam dan teknik dan teknologi awal, seperti munculnya perekam pita multi-saluran dan dampaknya pada suara yang direkam. Dia melanjutkan debat suara langsung versus suara yang direkam dan mengapa ada perbedaan, terutama dengan musik klasik. Topik lain yang dibahas adalah suara instrumen nyata dan bagaimana suara itu diproduksi dan cara merekamnya; teknik mikrofon dan suara stereo sejati; stasiun kerja digital, pengambilan sampel, dan media digital; dan reproduksi musik di rumah dan bagaimana hal itu telah berubah. Penulis membungkus buku dengan membahas di mana kita harus menuju rekaman musik populer dan klasik dan reproduksi, peran Insinyur Audio pada abad ke-21, dan melihat sekilas teknologi hari ini dan di mana ia menuju. Buku ini sangat ideal bagi siapa saja yang tertarik dengan suara yang direkam