39,758 research outputs found
Supersymmetric partners of the trigonometric Poschl-Teller potentials
The first and second-order supersymmetry transformations are used to generate
Hamiltonians with known spectra departing from the trigonometric Poschl-Teller
potentials. The several possibilities of manipulating the initial spectrum are
fully explored, and it is shown how to modify one or two levels, or even to
leave the spectrum unaffected. The behavior of the new potentials at the
boundaries of the domain is studied.Comment: 20 pages, 4 figure
Understanding open-charm mesons
We present a theoretical framework that accounts for the new and
mesons measured in the open-charm sector. These resonances are
properly described if considered as a mixture of conventional wave
quark-antiquark states and four-quark components. The narrowest states are
basically wave quark-antiquark mesons, while the dominantly four-quark
states are shifted above the corresponding two-meson threshold. We study the
electromagnetic decay widths as basic tools to scrutiny their nature.Comment: 4 pages, to appear in the proceedings of 9th International Workshop
on Meson Production, Properties and Interaction (Meson2006), Kracow (Poland),
9 - 13 June 200
Valence fluctuations in a lattice of magnetic molecules: application to iron(II) phtalocyanine molecules on Au(111)
We study theoretically a square lattice of the organometallic Kondo adsorbate
iron(II) phtalocyanine (FePc) deposited on top of Au(111), motivated by recent
scanning tunneling microscopy experiments. We describe the system by means of
an effective Hubbard-Anderson model, where each molecule has degenerate
effective orbitals with and symmetry, which we solve for
arbitrary occupation and arbitrary on-site repulsion . To that end, we
introduce a generalized slave-boson mean-field approximation (SBMFA) which
correctly describes both the non-interacting limit (NIL) and the
strongly-interacting limit , where our formalism
reproduces the correct value of the Kondo temperature for an isolated FePc
molecule. Our results indicate that while the isolated molecule can be
described by an SU(4) Anderson model in the Kondo regime, the case of the
square lattice corresponds to the intermediate-valence regime, with a total
occupation of nearly 1.65 holes in the FePc molecular orbitals. Our results
have important implications for the physical interpretation of the experiment.Comment: 7 pages, 2 figure
Empirical studies of open source evolution
Copyright @ 2008 Springer-VerlagThis chapter presents a sample of empirical studies of Open Source Software (OSS) evolution. According to these studies, the classical results from the studies of proprietary software evoltion, such as Lehman’s laws of software evolution, might need to be revised, if not fully, at least in part, to account for the OSS observations. The book chapter also summarises what appears to be the empirical
status of each of Lehman’s laws with respect to OSS and highlights the threads to
validity that frequently emerge in these empirical studies. The chapter also discusses
related topics for further research
Low optical polarisation at the core of the optically-thin jet of M87
We study the optical linear and circular polarisation in the optically-thin
regime of the core and jet of M87. Observations were acquired two days before
the Event Horizon Telescope (EHT) campaign in early April 2017. A high degree
( per cent) of linear polarisation (P) is detected in the
bright jet knots resolved at to
(-) from the centre, whereas the nucleus and inner jet
show P per cent. The position angle of the linear
polarisation shifts by degrees from each knot to the adjacent ones,
with the core angle perpendicular to the first knot. The nucleus was in a low
level of activity (P- per cent), and no emission was
detected from HST-1. No circular polarisation was detected either in the
nucleus or the jet above a level of P per cent,
discarding the conversion of P into P. A disordered
magnetic field configuration or a mix of unresolved knots polarised along axes
with different orientations could explain the low P. The latter
implies a smaller size of the core knots, in line with current interferometric
observations. Polarimetry with EHT can probe this scenario in the future. A
steep increase of both P and P with increasing
frequency is expected for the optically-thin domain, above the turnover point.
This work describes the methodology to recover the four Stokes parameters using
a wave-plate polarimeter.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure
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