875 research outputs found
The influence of the radiative non-symmetric ion-atom collisions on the stellar atmospheres in VUV region
The aim of this work is to draw attention to the processes of radiative
charge exchange in non-symmetric ion-atom collisions as a factor of influence
on the opacity of stellar atmospheres in VUV region. For that purpose
calculations of the spectral absorption coefficients for several ion-atom
systems, namely: He + H and H + X, where X = Na and Li have been
performed. On chosen examples it has been established that the examined
processes generate rather wide molecular absorption bands in the VUV region,
which should be taken into account for the interpretation of data obtained from
laboratory measurements or astrophysical observations. In this paper the
potential significance is discussed of the considered radiative processes for
DB white dwarfs and solar atmospheres, as well as for the atmospheres of the
so-called lithium stars
The ion-atom absorption processes as one of the factors of the influence on the sunspot opacity
As a continuation of the previous investigations of the symmetric and
strongly non-symmetric ion-atom absorption processes in the far UV region
within the models of the quiet Sun photosphere, these processes are studied
here within a model of the sunspot. Here we mean the absorption processes in
the H+H and H collisions and the processes of the
photo-dissociation of the H and H molecular ions, where is
one of the metal atoms: Na, Ca, Mg, Si and Al. Obtained results show that
the influence of the considered ion-atom absorption processes on the opacity of
sunspots in the considered spectral region (110 nm
230 nm) is not less and in some parts even larger than the influence of the
referent electron-atom processes. In such a way, it is shown that the
considered ion-atom absorption processes should be included \emph{ab initio} in
the corresponding models of sunspots of solar-type and near solar-type stars.
Apart of that, the spectral characteristics of the considered non-symmetric
ion-atom absorption processes (including here the case = Li), which can be
used in some further applications, have been determined and presented within
this work.Comment: Accepted in Monthly Notices of the Royal Astronomical Societ
Excitation and deexcitation processes in atom-Rydberg atom collisions in helium-rich white dwarf atmospheres
We aim to show the importance of non-elastic excitation and deexcitation
processes in collisions with the
principal quantum number for helium-rich white dwarf atmospheres. We
compare the efficiencies of these processes with those of the known non-elastic
electron- atom processes in the atmospheres of some DB
white dwarfs. We show that in significant parts of the considered atmospheres,
which contain weakly ionized layers (the ionization degree ),
the influence of the studied atom-Rydberg atom processes on excited helium atom
populations is dominant or at least comparable to the influence of the
concurrent electron--atom processes.Comment: Astronomy & Astrophysics, Accepted: 14 February 201
Ion-atom radiative processes in the solar atmosphere: quiet Sun and sunspots
In the previous works the significance of the symmetric and non-symmetric
ion-atom absorption processes in far UV and EUV regions within a model of the
quiet Sun atmosphere, has been studied. The considered processes were the
processes of the photo-dissociation of the molecular ions H and
H and absorption processes in H+H and H collisions, where
denotes the metal atom. As the continuation of the previous investigation,
these processes are considered also within the corresponding sunspot model. In
this work the non-symmetric ion-atom absorption processes are considered with
Mg, Si, etc. It was analyzed the significance of such processes in far UV
and EUV regions in comparison with the concurrent absorption processes,
especially with the processes of the photo-ionization of the metal atoms (Na,
Mg, Ca, etc.) which were not included in the consideration in the case of the
quiet Sun atmosphere. From our analysis it follows that the non-symmetric
ion-atom absorption processes considered here, are significant not only for
quiet Sun modeling but also for sunspots and should be included {\it ab initio}
in both cases.Comment: accepted in Advances in Space Researc
Stark Broadening of in III Lines in Astrophysical and Laboratory Plasma
Besides the need of Stark broadening parameters for a number of problems in
physics, and plasma technology, in hot star atmospheres the conditions exist
where Stark widths are comparable and even larger than the thermal Doppler
widths. Using the semiclassical perturbation method we investigated here the
influence of collisions with charged particles for In III spectral lines. We
determined a number of Stark broadening parameters important for the
investigation of plasmas in the atmospheres of A-type stars and white dwarfs.
Also, we have compared the obtained results with existing experimental data.
The results will be included in the STARK-B database, the Virtual Atomic and
Molecular Data Center and the Serbian Virtual Observatory
Noncommutative field theory from angular twist
We consider a noncommutative field theory with space-time -commutators
based on an angular noncommutativity, namely a solvable Lie algebra: the
Euclidean in two dimension. The -product can be derived from a twist
operator and it is shown to be invariant under twisted Poincar\'e
transformations. In momentum space the noncommutativity manifests itself as a
noncommutative -deformed sum for the momenta, which allows for an
equivalent definition of the -product in terms of twisted convolution of
plane waves. As an application, we analyze the field theory at
one-loop and discuss its UV/IR behaviour. We also analyze the kinematics of
particle decay for two different situations: the first one corresponds to a
splitting of space-time where only space is deformed, whereas the second one
entails a non-trivial -multiplication for the time variable, while one
of the three spatial coordinates stays commutative.Comment: 23 pages 1 figur
Sustainable reuse of modern movement heritage buildings : problems and solutions in Scotland and Italy
Many buildings which were built in the 20th century, and due to their exceptional architectural value included in the lists of built heritage, are sometimes standing vacant for different reasons. This paper investigates the problems that need to be resolved to enable a sustainable reuse of various types of modern heritage buildings. The investigation is undertaken through case studies of some modern heritage buildings in Scotland and Italy in order to identify common problems and regional differences in enabling the reuse of those buildings. In addition, some examples of the reuse of modern built heritage are presented to highlight what has contributed to the reuse, and whether and how that meets the current environmental requirements, and the local social and economic needs. The research indicates how public and private organisations have contributed to the successful reuse of modern built heritage and what problems they encounter in the efforts to provide new uses for the remaining vacant buildings. The investigation examines how economic, social, environmental, functional, structural and design aspects impact on defining new uses for modern heritage buildings. The analysis of the above requirements through the selected case studies leads to the recommendations on the key issues, strategies and tactics that should be considered to enable an appropriate and timely reuse of the 20th century built heritage
Jordanian Quantum Deformations of D=4 Anti-de-Sitter and Poincare Superalgebras
We consider a superextension of the extended Jordanian twist, describing
nonstandard quantization of anti-de-Sitter () superalgebra in
the form of Hopf superalgebra. The super-Jordanian twisting function and
corresponding basic coproduct formulae for the generators of are
given in explicit form. The nonlinear transformation of the classical
superalgebra basis not modifying the defining algebraic relations but
simplifying coproducts and antipodes is proposed. Our physical application is
to interpret the new super-Jordanian deformation of superalgebra as
deformed D=4 supersymmetries. Subsequently we perform suitable
contraction of quantum Jordanian superalgebra and obtain new
-deformation of D=4 Poincare superalgebra, with the bosonic sector
describing the light cone -deformation of Poincare symmetries.Comment: LaTeX,13 pages, comments and references added, to be published in
Eur.Phys.J.
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