143 research outputs found
Investigation of ultrafast laser photonic material interactions: challenges for directly written glass photonics
Currently, direct-write waveguide fabrication is probably the most widely
studied application of femtosecond laser micromachining in transparent
dielectrics. Devices such as buried waveguides, power splitters, couplers,
gratings and optical amplifiers have all been demonstrated. Waveguide
properties depend critically on the sample material properties and writing
laser characteristics. In this paper we discuss the challenges facing
researchers using the femtosecond laser direct-write technique with specific
emphasis being placed on the suitability of fused silica and phosphate glass as
device hosts for different applications.Comment: 11 pages, 87 references, 11 figures. Article in revie
Discrete soliton mobility in two-dimensional waveguide arrays with saturable nonlinearity
We address the issue of mobility of localized modes in two-dimensional
nonlinear Schr\"odinger lattices with saturable nonlinearity. This describes
e.g. discrete spatial solitons in a tight-binding approximation of
two-dimensional optical waveguide arrays made from photorefractive crystals. We
discuss numerically obtained exact stationary solutions and their stability,
focussing on three different solution families with peaks at one, two, and four
neighboring sites, respectively. When varying the power, there is a repeated
exchange of stability between these three solutions, with symmetry-broken
families of connecting intermediate stationary solutions appearing at the
bifurcation points. When the nonlinearity parameter is not too large, we
observe good mobility, and a well defined Peierls-Nabarro barrier measuring the
minimum energy necessary for rendering a stable stationary solution mobile.Comment: 19 pages, 4 figure
Two-dimensional discrete solitons in dipolar Bose-Einstein condensates
We analyze the formation and dynamics of bright unstaggered solitons in the
disk-shaped dipolar Bose-Einstein condensate, which features the interplay of
contact (collisional) and long-range dipole-dipole (DD) interactions between
atoms. The condensate is assumed to be trapped in a strong optical-lattice
potential in the disk's plane, hence it may be approximated by a
two-dimensional (2D) discrete model, which includes the on-site nonlinearity
and cubic long-range (DD) interactions between sites of the lattice. We
consider two such models, that differ by the form of the on-site nonlinearity,
represented by the usual cubic term, or more accurate nonpolynomial one,
derived from the underlying 3D Gross-Pitaevskii equation. Similar results are
obtained for both models. The analysis is focused on effects of the DD
interaction on fundamental localized modes in the lattice (2D discrete
solitons). The repulsive isotropic DD nonlinearity extends the existence and
stability regions of the fundamental solitons. New families of on-site,
inter-site and hybrid solitons, built on top of a finite background, are found
as a result of the interplay of the isotropic repulsive DD interaction and
attractive contact nonlinearity. By themselves, these solutions are unstable,
but they evolve into robust breathers which exist on an oscillating background.
In the presence of the repulsive contact interactions, fundamental localized
modes exist if the DD interaction (attractive isotropic or anisotropic) is
strong enough. They are stable in narrow regions close to the anticontinuum
limit, while unstable solitons evolve into breathers. In the latter case, the
presence of the background is immaterial
Phase transformation under direct laser writing in a YAG single crystal
The transformation from Y3Al5O12 to perovskite YAlO3 crystal phase was observed during ultrafast laser writing in the bulk of a Y3Al5O12 single crystal. The control of the phase transformation was demonstrated by tuning parameters of laser writing. The phenomenon is interpreted in terms of structural changes in the overheated garnet melt under laser heating followed by rapid solidification, and at least 1-ms dwell time of overheated melt is required to start spontaneous crystallization. The appearance of the perovskite phase was confirmed by Raman spectroscopy, quantitative phase and polarization microscopies
Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters
We investigate the interaction between the magnetized stellar wind plasma and
the partially ionized hydrodynamic hydrogen outflow from the escaping upper
atmosphere of non- or weakly magnetized hot Jupiters. We use the well-studied
hot Jupiter HD 209458b as an example for similar exoplanets, assuming a
negligible intrinsic magnetic moment. For this planet, the stellar wind plasma
interaction forms an obstacle in the planet's upper atmosphere, in which the
position of the magnetopause is determined by the condition of pressure balance
between the stellar wind and the expanded atmosphere, heated by the stellar
extreme ultraviolet (EUV) radiation. We show that the neutral atmospheric atoms
penetrate into the region dominated by the stellar wind, where they are ionized
by photo-ionization and charge exchange, and then mixed with the stellar wind
flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced
magnetic field forms in front of the planetary obstacle, which appears to be
much stronger compared to those produced by the solar wind interaction with
Venus and Mars. Depending on the stellar wind parameters, because of the
induced magnetic field, the planetary obstacle can move up to ~0.5-1 planetary
radii closer to the planet. Finally, we discuss how estimations of the
intrinsic magnetic moment of hot Jupiters can be inferred by coupling
hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models
together with UV observations. In particular, we find that HD 209458b should
likely have an intrinsic magnetic moment of 10-20% that of Jupiter.Comment: 8 pages, 6 figures, 2 tables, accepted to MNRA
KTM TOKAMAK OPERATION SCENARIOS SOFTWARE INFRASTRUCTURE
One of the largest problems for tokamak devices such as Kazakhstan Tokamak for Material Testing (KTM) is the operation scenarios' development and execution. Operation scenarios may be varied often, so a convenient hardware and software solution is required for scenario management and execution. Dozens of diagnostic and control subsystems with numerous configuration settings may be used in an experiment, so it is required to automate the subsystem configuration process to coordinate changes of the related settings and to prevent errors. Most of the diagnostic and control subsystems software at KTM was unified using an extra software layer, describing the hardware abstraction interface. The experiment sequence was described using a command language.The whole infrastructure was brought together by a universal communication protocol supporting various media, including Ethernet and serial links. The operation sequence execution infrastructure was used at KTM to carry out plasma experiments
Modeling the Ly transit absorption of the hot Jupiter HD 189733b
Hydrogen-dominated atmospheres of hot exoplanets expand and escape due to the
intense heating by the X-ray and extreme ultraviolet (XUV) irradiation of their
host stars. Excess absorption of neutral hydrogen has been observed in the
Ly line during transits of several close-in exoplanets, indicating such
extended atmospheres. For the hot Jupiter HD 189733b, this absorption shows
temporal variability. Variations in stellar XUV emission and/or stellar wind
conditions have been invoked to explain this effect. We apply a 1D hydrodynamic
upper atmosphere model and a 3D MHD stellar wind flow model to study the effect
of variations of the stellar XUV and wind conditions on the neutral hydrogen
distribution, including the production of energetic neutral atoms (ENAs), and
the related Ly transit signature. We obtain comparable, albeit slightly
higher Ly absorption as observed in 2011 with a stellar XUV flux of
erg cm s, rather typical activity conditions for
this star. Flares similar to the one observed 8 h before the transit are
unlikely to have caused a significant modulation of the transit signature. The
resulting Ly absorption is dominated by atmospheric broadening, whereas
the contribution of ENAs is negligible, as they are formed inside the bow shock
from decelerated wind ions that are heated to high temperatures. Thus, within
our modeling framework and assumptions, we find an insignificant dependence on
the stellar wind parameters. Since the transit absorption can be modeled with
typical stellar XUV and wind conditions, it is possible that the non-detection
of the absorption in 2010 was affected by less typical stellar activity
conditions, such as a very different magnitude and/or shape of the star's
spectral XUV emission, or temporal/spatial variations in Ly affecting
the determination of the transit absorption.Comment: 22 pages, 19 figures, 4 tables; A&A, publishe
Peculiarities of Spatial Structure of the Central Caucasian High-Mountain Natural Plague Focus
Within the limits of Central Caucasian high-mountain natural plague focus discovered are two zones of natural focality. The first natural focality zone in the mountain steppe of the eastern part of the focus has a parasitic complex similar in structural organization and functioning to lowland foci of the souslik type. Another one, situated in the western part of the focus, is compatible with Tuva mountain natural plague focus, where fleas
Neopsylla setosaare absent, and epizootic activity is characterized by a single-humped curve with an apex for July-August period. The similarities stated above can be used for optimization of epidemiological surveillance techniques, preventive measures, and methodology of studying mountain natural plague foci of the souslik type
Landscape-Epidemiological Zoning of the Krasnodar Territory and the Republic of Adygea by Tularemia
Objective of the study was epizootic-epidemiological zoning of the area of Krasnodar Territory and the Republic of Adygea by manifestations of tularemia to determine the level of epidemic hazard of each zone.Materials and methods. Utilized were archival data of the Black Sea Plague Control station over the period of 1946–2017 and plague Control Center of the Rospotrebnadzor. With the help of GIS software packages, MapINFO 10.5 and ArcGIS 10.2, the data bases containing the point-like layers of the sites of infection with tularemia (49), isolation of tularemia agent (195), and the layer of landscape-geographical regions in the Krasnodar Territory and the Republic of Adygea were created.Results and discussion. Usage of the geo-information technologies allowed for detailed consideration of tularemia manifestations in different parts of the region. The prospects of applying Arc GIS and MapINFO for geoencoding, processing and creation of geo-information pool of tularemia manifestations over a long period was shown. Vector data of landscapes and sites of epidemics and epizootic manifestations of tularemia on different species of mammals and ticks were generated. The conversion of the database to Microsoft Excel made it possible to make full use of statistical capabilities for epidemiological analysis. The work on epidemiological zoning carried out in the Krasnodar region and the Republic of Adygea starkly illustrated the feasibility of using GIS technologies for those purposes. The results of the analysis allowed for optimization of the mode of epizootiological survey in different parts of the studied region. Advisability of epizootiological inspection and monitoring of the territories with identification of geographical coordinates for epizootic manifestation sites was proved
Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment
We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100-420ms-1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical-numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 - f1 in the altitude ranges 0-0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1-20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere-ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling
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