591 research outputs found
Wave scattering on a domain wall in a chain of PT-symmetric couplers
We study wave propagation in linear arrays composed of pairs of conjugate
waveguides with balanced gain and loss, i.e. arrays of the PT-symmetric
couplers, where the linear spectrum is known to feature high-frequency and
low-frequency branches. We introduce a domain wall by switching the gain and
loss in a half of the array, and analyze the scattering of linear waves on this
defect. The analysis reveals two major effects: amplification of both reflected
and transmitted waves, and excitation of the reflected and transmitted
low-frequency and high-frequency waves by the incident high-frequency and
low-frequency waves, respectively.Comment: 7 pages, 9 figures, Physical Review A, in pres
Solitons in a chain of PT-invariant dimers
Dynamics of a chain of interacting parity-time invariant nonlinear dimers is
investigated. A dimer is built as a pair of coupled elements with equal gain
and loss. A relation between stationary soliton solutions of the model and
solitons of the discrete nonlinear Schrodinger (DNLS) equation is demonstrated.
Approximate solutions for solitons whose width is large in comparison to the
lattice spacing are derived, using a continuum counterpart of the discrete
equations. These solitons are mobile, featuring nearly elastic collisions.
Stationary solutions for narrow solitons, which are immobile due to the pinning
by the effective Peierls-Nabarro potential, are constructed numerically,
starting from the anti-continuum limit. The solitons with the amplitude
exceeding a certain critical value suffer an instability leading to blowup,
which is a specific feature of the nonlinear PT-symmetric chain, making it
dynamically different from DNLS lattices. A qualitative explanation of this
feature is proposed. The instability threshold drops with the increase of the
gain-loss coefficient, but it does not depend on the lattice coupling constant,
nor on the soliton's velocity.Comment: 9 pages, 9 figure
Open questions in the study of population III star formation
The first stars were key drivers of early cosmic evolution. We review the
main physical elements of the current consensus view, positing that the first
stars were predominantly very massive. We continue with a discussion of
important open questions that confront the standard model. Among them are
uncertainties in the atomic and molecular physics of the hydrogen and helium
gas, the multiplicity of stars that form in minihalos, and the possible
existence of two separate modes of metal-free star formation.Comment: 15 pages, 2 figures. To appear in the conference proceedings for IAU
Symposium 255: Low-Metallicity Star Formation: From the First Stars to Dwarf
Galaxie
Impact of climate changes on indicator specie and predicted socio-economical effects
Impact of the above-mentioned factors can be seen on particular representatives of flora and fauna, communities, landscape elements and elementary associations, and is demonstrated on the example of model species and communities
Definition of Time Induction of Self-Ignition of the Substance on the Prognostic Extrapolation Depending on the Basis of Indicators Fire and Explosion Hazard
In this article the research directed on development of a technique of definition of time of induction of the self-ignition of substances and materials which is an indicator of the beginning of development of an emergency is conducted. The experiment consisting in supervision over process of self-ignition of coal and oil deposits was the basis for research. On the basis of experimental data the curve expressing analytic - expected dependence of size of temperature of ignition on induction time was constructed. Proceeding from graphical representation of process, functional dependence of time of induction on a temperature indicator was received: y=16920•x{0.537}. By means of known indicators of such substances as bitumen oil oxidized (the combustible solid substance received by oxidation of residual product of oil refining) and tar oil (the combustible solid substance which is residual product of oil refining) and the received algorithm, verification of reliability of the received dependence and a technique of definition of time of induction of spontaneous ignition of deposits of oil in general was carried out. The practical importance of the conducted research is that having data on time of induction of process of self-ignition, by means of preventive measures becomes possible to avoid and prevent accidents in oil and oil processing branches, at the same time loss of property and loss of human life
Three-Dimensional Simulations of a Starburst-Driven Galactic Wind
We have performed a series of three-dimensional simulations of a
starburst-driven wind in an inhomogeneous interstellar medium. The introduction
of an inhomogeneous disk leads to differences in the formation of a wind, most
noticeably the absence of the ``blow-out'' effect seen in homogeneous models. A
wind forms from a series of small bubbles that propagate into the tenuous gas
between dense clouds in the disk. These bubbles merge and follow the path of
least resistance out of the disk, before flowing freely into the halo.
Filaments are formed from disk gas that is broken up and accelerated into the
outflow. These filaments are distributed throughout a biconical structure
within a more spherically distributed hot wind. The distribution of the
inhomogeneous interstellar medium in the disk is important in determining the
morphology of this wind, as well as the distribution of the filaments. While
higher resolution simulations are required in order to ascertain the importance
of mixing processes, we find that soft X-ray emission arises from gas that has
been mass-loaded from clouds in the disk, as well as from bow shocks upstream
of clouds, driven into the flow by the ram pressure of the wind, and the
interaction between these shocks.Comment: 37 pages, 16 figures, mpg movie can be obtained at
http://www.mso.anu.edu.au/~jcooper/movie/video16.mpg, accepted for
publication in Ap
Remote Prophylaxis of Social and Educational Adaptation of University International Entrants in Total Pandemic
The relevance of the study is due to the trends of the global pandemic, which provoked an extremal transition of all areas of higher education to distance learning, as the only possible way to work with domestic and international entrants and students. In addition, the trends of the pandemic in the current educational environment also determine the special need to develop remote mechanisms for a prophylaxis approach to solving the problems of social and educational adaptation of international entrants – future University students. In this regard, this article is aimed at identifying the features of remote prophylaxis of social and educational adaptation of entrants. The article reveals the transformation of social and educational adaptation of international entrants in the global pandemic; defines the structure and content of remote prophylaxis of social and educational adaptation of international University entrants in the global pandemic. Based on the results of the research, the authors of the article substantiate the prophylaxis model of the educational and software complex for remote prophylaxis of social and educational adaptation of University international entrants. The effectiveness of the model is proved by the results of its use in the process of remote social and educational adaptation of University international entrants in the context of a global pandemic. The materials of the article have practical application and can be useful in the development and implementation of various methods and practices of social and educational adaptation of international entrants – future University students in the context of a global pandemic. It is recommended for University teachers and students, methodologists, curators, Tutors
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