114 research outputs found
Особенности строения сеноманской газоконденсатной залежи на Заполярном месторождении (ЯНАО)
By focusing fs-laser radiation in the volume of a transparent material the refractive index can be changed locally, leading to 3-dimensional waveguiding structures. Waveguides are written in phosphate glass (IOG from Schott) at a depth of 100 µm below the surface. The pulse energy and the scan velocity are varied. For the first time the optical path difference caused by the waveguides and therefore the refractive index distribution of the waveguides and their cross sections are determined using interference microscopy. The optical path difference measured in the written structures and their cross sections is analyzed by a phase-shift algorithm. Thus, the refractive index distribution both along a line perpendicular to the waveguide and in the plane of a cross section is determined. The results are visualized as 2-dimensional graphics. Several regions of opposite sign of the refractive index change are observed in the cross sections of waveguides generated by femtosecond laser pulses. The number and the size of these regions are increasing with increasing pulse energy and decreasing scan velocity
Anomalous coupling in radiation mediated shocks}
We summarize recent attempts to unravel the role of plasma kinetic effects in
radiation mediated shocks. Such shocks form in all strong stellar explosions
and are responsible for the early electromagnetic emission released from these
events. A key issue that has been overlooked in all previous works is the
nature of the coupling between the charged leptons, that mediate the radiation
force, and the ions, which are the dominant carriers of the shock energy. Our
preliminary investigation indicates that in the case of relativistic shocks, as
well as Newtonian shocks in multi-ion plasma, this coupling is driven by
either, transverse magnetic fields of a sufficiently magnetized upstream
medium, or plasma micro-turbulence if strong enough magnetic fields are absent.
We discuss the implications for the shock breakout signal, as well as abundance
evolution and kilonova emission in binary neutron star mergers.Comment: 8 pages, 2 figures, to appear in Journal of Plasma Physic
Computational General Relativistic Force-Free Electrodynamics: I. Multi-Coordinate Implementation and Testing
General relativistic force-free electrodynamics is one possible plasma-limit
employed to analyze energetic outflows in which strong magnetic fields are
dominant over all inertial phenomena. The amazing images of black hole shadows
from the galactic center and the M87 galaxy provide a first direct glimpse into
the physics of accretion flows in the most extreme environments of the
universe. The efficient extraction of energy in the form of collimated outflows
or jets from a rotating BH is directly linked to the topology of the
surrounding magnetic field. We aim at providing a tool to numerically model the
dynamics of such fields in magnetospheres around compact objects, such as black
holes and neutron stars. By this, we probe their role in the formation of high
energy phenomena such as magnetar flares and the highly variable
teraelectronvolt emission of some active galactic nuclei. In this work, we
present numerical strategies capable of modeling fully dynamical force-free
magnetospheres of compact astrophysical objects. We provide implementation
details and extensive testing of our implementation of general relativistic
force-free electrodynamics in Cartesian and spherical coordinates using the
infrastructure of the Einstein Toolkit. The employed hyperbolic/parabolic
cleaning of numerical errors with full general relativistic compatibility
allows for fast advection of numerical errors in dynamical spacetimes. Such
fast advection of divergence errors significantly improves the stability of the
general relativistic force-free electrodynamics modeling of black hole
magnetospheres.Comment: 19 pages, 15 figures, submitted to A&
Three-dimensional dynamics of strongly twisted magnetar magnetospheres: Kinking flux tubes and global eruptions
The origin of the various outbursts of hard X-rays from magnetars, highly
magnetized neutron stars, is still unknown. We identify instabilities in
relativistic magnetospheres that can explain a range of X-ray flare
luminosities. Crustal surface motions can twist the magnetar magnetosphere by
shifting the frozen-in footpoints of magnetic field lines in current-carrying
flux bundles. Axisymmetric (2D) magnetospheres exhibit strong eruptive
dynamics, as to say, catastrophic lateral instabilities triggered by a critical
footpoint displacement of . In contrast, our new
three-dimensional (3D) twist models with finite surface extension capture
important non-axisymmetric dynamics of twisted force-free flux bundles in
dipolar magnetospheres. Besides the well-established global eruption resulting
(as in 2D) from lateral instabilities, such 3D structures can develop helical,
kink-like dynamics, and dissipate energy locally (confined eruptions). Up to
of the induced twist energy is dissipated and available to power X-ray
flares in powerful global eruptions, with most of our models showing an energy
release in the range of the most common X-ray outbursts, erg.
Such events occur when significant energy builds up deeply buried in the dipole
magnetosphere. Less energetic outbursts likely precede powerful flares due to
intermittent instabilities and confined eruptions of a continuously twisting
flux tube. Upon reaching a critical state, global eruptions produce the
necessary Poynting-flux-dominated outflows required by models prescribing the
fast radio burst production in the magnetar wind, for example, via relativistic
magnetic reconnection or shocks.Comment: 21 pages, 11 figures, submitted to ApJ
First record of the neotropical subgenus Hylaeus (Gongyloprosopis) Snelling, 1982, for Brazil (Hymenoptera: Colletidae).
We report the first record of the neotropical bee subgenus Hylaeus (Gongyloprosopis) Snelling, 1982 (Colletidae) for Brazil. Additionally, an overview of the current geographic records for the three known species of the subgenus is presented. We expand the distribution of Hylaeus (Gongyloprosopis) orbicus (Vachal, 1910), the male is illustrated, and the first floral association with Vismia japurensis Reichardt (Hypericaeae) is reported for this species
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