4,674 research outputs found
Non-stationary Rayleigh-Taylor instability in supernovae ejecta
The Rayleigh-Taylor instability plays an important role in the dynamics of
several astronomical objects, in particular, in supernovae (SN) evolution. In
this paper we develop an analytical approach to study the stability analysis of
spherical expansion of the SN ejecta by using a special transformation in the
co-moving coordinate frame. We first study a non-stationary spherical expansion
of a gas shell under the pressure of a central source. Then we analyze its
stability with respect to a no radial, non spherically symmetric perturbation
of the of the shell. We consider the case where the polytropic constant of the
SN shell is and we examine the evolution of a arbitrary shell
perturbation. The dispersion relation is derived. The growth rate of the
perturbation is found and its temporal and spatial evolution is discussed. The
stability domain depends on the ejecta shell thickness, its acceleration, and
the perturbation wavelength.Comment: 16 page
Production of vector resonances at the LHC via WZ-scattering: a unitarized EChL analysis
In the present work we study the production of vector resonances at the LHC
by means of the vector boson scattering and explore the
sensitivities to these resonances for the expected future LHC luminosities. We
are assuming that these vector resonances are generated dynamically from the
self interactions of the longitudinal gauge bosons, and , and work
under the framework of the electroweak chiral Lagrangian to describe in a model
independent way the supposedly strong dynamics of these modes. The properties
of the vector resonances, mass, width and couplings to the and gauge
bosons are derived from the inverse amplitude method approach. We implement all
these features into a single model, the IAM-MC, adapted for MonteCarlo, built
in a Lagrangian language in terms of the electroweak chiral Lagrangian and a
chiral Lagrangian for the vector resonances, which mimics the resonant behavior
of the IAM and provides unitary amplitudes. The model has been implemented in
MadGraph, allowing us to perform a realistic study of the signal versus
background events at the LHC. In particular, we have focused our study on the
type of events, discussing first on the potential of the hadronic
and semileptonic channels of the final , and next exploring in more detail
the clearest signals. These are provided by the leptonic decays of the gauge
bosons, leading to a final state with ,
, having a very distinctive signature, and showing clearly the
emergence of the resonances with masses in the range of 1.5-2.5 TeV, which we
have explored.Comment: Revised version accepted for publication in JHEP. Enlarged analysis.
References added. 44 pages, 23 figures, 3 table
Understanding chemical reactions within a generalized Hamilton-Jacobi framework
Reaction paths and classical and quantum trajectories are studied within a
generalized Hamilton-Jacobi framework, which allows to put on equal footing
topology and dynamics in chemical reactivity problems. In doing so, we show how
high-dimensional problems could be dealt with by means of Caratheodory plots or
how trajectory-based quantum-classical analyses reveal unexpected
discrepancies. As a working model, we consider the reaction dynamics associated
with a Mueller-Brown potential energy surface, where we focus on the
relationship between reaction paths and trajectories as well as on reaction
probability calculations from classical and quantum trajectories.Comment: 22 pages, 5 figures, 1 tabl
Linear and non-linear amplification of high-mode perturbations at the ablation fronts in HIPER targets.
The linear and non-linear sensitivity of the 180 kJ baseline HiPER target to high-mode perturbations, i.e. surface roughness, is addressed using two-dimensional simulations and a complementary analysis by linear and non-linear ablative Rayleigh–Taylor models. Simulations provide an assessment of an early non-linear stage leading to a significant deformation of the ablation surface for modes of maximum linear growth factor. A design using a picket prepulse evidences an improvement in the target stability inducing a delay of the non-linear behavior. Perturbation evolution and shape, evidenced by simulations of the non-linear stage, are analyzed with existing self-consistent non-linear theory
European Federation of Periodontology Survey of Postgraduate and Specialist Training in Europe in 2020:Periodontal specialist training in Europe
AIMS: The survey's aim was to establish which universities and other educational organisations deliver postgraduate and specialist training in Periodontology in the 31 countries who are members of the European Federation of Periodontology (EFP) and to obtain details of how these programmes are organised, funded, regulated and evaluated. METHODS: A questionnaire and covering letter were emailed to all national periodontal societies. The questions were on the name of country, official recognition, training programmes, entry to specialist training, specialist training assessment and recognition after completion of training. RESULTS: Twenty‐nine (93%) of national periodontal societies responded. Key findings included the following: Periodontology was reported as being recognised at a national level in 17 countries, there was a three‐year full‐time programme in 12 countries, no fees were charged for specialist training in 10 countries, in 14 countries trainees received annual salaries, end of training (summative) assessments varied from country to country, 12 countries reported that they had a requirement for specialists in Periodontology to complete continuing education to maintain registration as specialists. CONCLUSIONS: This survey has established which universities and other educational organisations deliver postgraduate and specialist training in Periodontology and how these programmes are organised, funded, regulated and evaluated. To provide uniformly high‐quality periodontal care for patients in all European countries, further harmonisation of postgraduate and specialty training in Periodontology would be advantageous
Studies on phase motion in the process
We propose a measurement on the elastic scattering phase shift
difference through
process in future high statistics BES-III experiment. The decay amplitude is
constructed with seven Lorentz invariant form-factors and is compared with
their theoretical estimation. It is found that the phase shift difference can
be obtained, based on a Monte Carlo study and it is expected the phase shift in
the energy region between 350 MeV to 550 MeV can be measured at future BES-III.Comment: 16 pages, 1 figur
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Wideband Dual-Polarized Filtering Antenna for Base Station Applications
For the purpose of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission.A compact wideband dual-polarized filtering antenna based on tightly coupled cross dipoles is presented in this letter. The enhancement of impedance bandwidth is realized by introducing four impedance equalizers to equalize the input resistances of the two inherent resonant modes of tightly coupled cross dipole antenna. The enhancement of the selectivity is realized by introducing two radiation nulls in 5G sub-6 GHz n77 and n79 bands. The radiation null in n77 band is obtained by introducing the cross strips in the center of the antenna. The radiation null in the n79 band is achieved by the introduction of open-end branches. The manipulation of their key parameters allows for independent control over both radiation nulls. The validity of the antenna's design principle was confirmed by carrying out fabrication and measurements. The results obtained showcase the antenna's broad fractional bandwidth of 63.4 exceptional port isolation of 31 dB. High out-of-band rejection levels in n77 and n79 bands are also obtained. In addition, since the whole radiator of the presented antenna is coplanar, it offers the advantage of a simple structure and convenient manufacturing, making it highly suitable for the use in base stations operating across multiple bands.Royal Society - International Exchanges 2019 Cost Share (NSFC);
Huawei Technologies Ltd, in part by Engineering and Physical Sciences Research Council (EPSRC) (Grant Number: EP/S005625/1 and EP/N032497/1)
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