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The classical D-type expansion of spherical H II regions
Get PDFRecent numerical and analytic work has highlighted some shortcomings in our understanding of the dynamics of H II region expansion, especially at late times, when the H II region approaches pressure equilibrium with the ambient medium. Here we reconsider the idealized case of a constant radiation source in a uniform and spherically symmetric ambient medium, with an isothermal equation of state. A thick-shell solution is developed that captures the stalling of the ionization front and the decay of the leading shock to a weak compression wave as it escapes to large radii. An acoustic approximation is introduced to capture the late-time damped oscillations of the H II region about the stagnation radius. Putting these together, a matched asymptotic equation is derived for the radius of the ionization front which accounts for both the inertia of the expanding shell and the finite temperature of the ambient medium. The solution to this equation is shown to agree very well with the numerical solution at all times, and is superior to all previously published solutions. The matched asymptotic solution can also accurately model the variation of H II region radius for a time-varying radiation source
Seacht bpearsain fhichead uair mé: a poem on the optative subjunctive in a copy of Irish Grammatical Tracts III-IV
Get PDFAn edition of a poem found in TCD MS H 2.17 with a discussion of the optative subjunctive in Old, Middle and especially Classical Modern Irish, and remarks on Irish Grammatical Tracts III-IV
Review of Lynette Olson (ed.), St Samson of Dol and the Earliest History of Brittany, Cornwall and Wales
Get PDFBook review of Lynette Olson (ed.), St Samson of Dol and the Earliest History of Brittany, Cornwall and Wales (Woodbridge, 2017), in Studia Celtica
Magnetic monopoles in noncommutative quantum mechanics 2
Get PDFIn this paper we extend the analysis of magnetic monopoles in quantum mechanics in three dimensional rotationally invariant noncommutative space R^3_λ . We construct the model step-by-step and observe that physical objects known from previous studies appear in a very natural way. Nonassociativity became a topic of great interest lately, often in connection with magnetic monopoles. We show that this model does not possess this property
The (2,5) minimal model on degenerating genus two surfaces
Get PDFIn the (2, 5) minimal model, the partition function for genus g = 2 Riemann surfaces is expected to be given by a quintuplet of Siegel modular forms that extend the Rogers-Ramanujan functions on the torus. Their expansions around the g = 2 boundary components of the moduli space are obtained in terms of standard modular forms. In the case where a handle of the g = 2 surface is pinched, our method requires knowledge of the 2-point function of the fundamental lowest-weight vector in the non-vacuum representation of the Virasoro algebra, for which we derive a third order ODE
Seismic anisotropy in central North Anatolian Fault Zone and its implications on crustal deformation
No full textMapping the core of the Tarantula Nebula with VLT-MUSE
Get PDFWe introduce VLT-MUSE observations of the central 2'x2' (30x30 pc) of the Tarantula Nebula in the Large Magellanic Cloud. The observations provide an unprecedented spectroscopic census of the massive stars and ionised gas in the vicinity of R136, the young, dense star cluster located in NGC 2070, at the heart of the richest star-forming region in the Local Group. Spectrophotometry and radial-velocity estimates of the nebular gas (superimposed on the stellar spectra) are provided for 2255 point sources extracted from the MUSE datacubes, and we present estimates of stellar radial velocities for 270 early-type stars (finding an average systemic velocity of 271 +/- 41 km/s). We present an extinction map constructed from the nebular Balmer lines, with electron densities and temperatures estimated from intensity ratios of the [S II ], [N II ], and [S III ] lines. The interstellar medium, as traced by H-alpha and [N II ] 6583, provides new insights in regions where stars are probably forming. The gas kinematics are complex, but with a clear bi-modal, blue- and red-shifted distribution compared to the systemic velocity of the gas centred on R136. Interesting point-like sources are also seen in the eastern cavity, western shell, and around R136; these might be related to phenomena such as runaway stars, jets, formation of new stars, or the interaction of the gas with the population of Wolf–Rayet stars. Closer inspection of the core reveals red-shifted material surrounding the strongest X-ray sources, although we are unable to investigate the kinematics in detail as the stars are spatially unresolved in the MUSE data. Further papers in this series will discuss the detailed stellar content of NGC 2070 and its integrated stellar and nebular properties
A Higgs--Chern-Simons gravity model in 2+1 dimensions
Get PDFWe study a gravity model in 2+1 dimensions, arising from a generalized Chern-Simons (CS) density we call a Higgs-Chern-Simons (HCS) density. This generalizes the construction of gravitational systems resulting from non-Abelian CS densities in all odd dimensions. The new HCS densities employed here are arrived at by the usual one-step descent of new Higgs--Chern-Pontryagin (HCP) densities, the latter resulting from the dimensional reduction of Chern-Pontryagin (CP) densities in some even dimension, such that in any given dimension (including even) there is an infinite tower of such models. Here, we restrict our attention to the lowest dimension, 2+1, and to the simplest such model resulting from the dimensional reduction of the 3-rd CP density. We construct a black hole (BH) solution in closed form, generalizing the familiar BTZ BH. We also study the electrically charged BH solution of the same model augmented with a Maxwell term, and contrast this solution with the electrically charged BTZ BH, specifically concering their respective thermodynamic properties