40,639 research outputs found
Flux-ratio anomalies from discs and other baryonic structures in the Illustris simulation
The flux ratios in the multiple images of gravitationally lensed quasars can
provide evidence for dark matter substructure in the halo of the lensing galaxy
if the flux ratios differ from those predicted by a smooth model of the lensing
galaxy mass distribution. However, it is also possible that baryonic structures
in the lensing galaxy, such as edge-on discs, can produce flux-ratio anomalies.
In this work, we present the first statistical analysis of flux-ratio anomalies
due to baryons from a numerical simulation perspective. We select galaxies with
various morphological types in the Illustris simulation and ray-trace through
the simulated halos, which include baryons in the main lensing galaxies but
exclude any substructures, in order to explore the pure baryonic effects. Our
ray-tracing results show that the baryonic components can be a major
contribution to the flux-ratio anomalies in lensed quasars and that edge-on
disc lenses induce the strongest anomalies. We find that the baryonic
components increase the probability of finding high flux-ratio anomalies in the
early-type lenses by about 8% and by about 10 - 20% in the disc lenses. The
baryonic effects also induce astrometric anomalies in 13% of the mock lenses.
Our results indicate that the morphology of the lens galaxy becomes important
in the analysis of flux-ratio anomalies when considering the effect of baryons,
and that the presence of baryons may also partially explain the discrepancy
between the observed (high) anomaly frequency and what is expected due to the
presence of subhalos as predicted by the CDM simulations.Comment: 16 pages, 11 figures, accepted by MNRA
ROBAST: Development of a ROOT-Based Ray-Tracing Library for Cosmic-Ray Telescopes and its Applications in the Cherenkov Telescope Array
We have developed a non-sequential ray-tracing simulation library, ROOT-based
simulator for ray tracing (ROBAST), which is aimed to be widely used in optical
simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written
in C++, and fully utilizes the geometry library of the ROOT framework. Despite
the importance of optics simulations in CR experiments, no open-source software
for ray-tracing simulations that can be widely used in the community has
existed. To reduce the dispensable effort needed to develop multiple
ray-tracing simulators by different research groups, we have successfully used
ROBAST for many years to perform optics simulations for the Cherenkov Telescope
Array (CTA). Among the six proposed telescope designs for CTA, ROBAST is
currently used for three telescopes: a Schwarzschild-Couder (SC) medium-sized
telescope, one of SC small-sized telescopes, and a large-sized telescope (LST).
ROBAST is also used for the simulation and development of hexagonal light
concentrators proposed for the LST focal plane. Making full use of the ROOT
geometry library with additional ROBAST classes, we are able to build the
complex optics geometries typically used in CR experiments and ground-based
gamma-ray telescopes. We introduce ROBAST and its features developed for CR
experiments, and show several successful applications for CTA.Comment: Accepted for publication in Astroparticle Physics. 11 pages, 10
figures, 4 table
Test particle acceleration in a numerical MHD experiment of an anemone jet
To use a 3D numerical MHD experiment representing magnetic flux emerging into
an open field region as a background field for tracing charged particles. The
interaction between the two flux systems generates a localised current sheet
where MHD reconnection takes place. We investigate how efficiently the
reconnection region accelerates charged particles and what kind of energy
distribution they acquire. The particle tracing is done numerically using the
Guiding Center Approximation on individual data sets from the numerical MHD
experiment. We derive particle and implied photon distribution functions having
power law forms, and look at the impact patterns of particles hitting the
photosphere. We find that particles reach energies far in excess of those seen
in observations of solar flares. However the structure of the impact region in
the photosphere gives a good representation of the topological structure of the
magnetic field.Comment: 9 pages, 7 figures, accepted for publication in A&
Uniform white light distribution with low loss from coloured LEDs using polymer doped polymer mixing rods
Colour mixing of red, green and blue (RGB) LEDs is demonstrated for a 6 cm long PMMA cylindrical rod with a transparent refractive index matched micro particle (TRIMM) diffuser sheet at the output end. Ray tracing simulations have been performed, and the output light distributions, transmittances and losses modelled and compared with experiment. Photographed and modelled colour mixing results are presented for rods with and without TRIMM sheet mixers. The TRIMM particles homogenize the light output of plain PMMA rods to form white light, with negligible backscattering. A simple method for measuring the concentration of the particles in the diffuser sheet is described, and computer modeling and analysis of TRIMM particle systems is discussed
ROBAST: Development of a Non-Sequential Ray-Tracing Simulation Library and its Applications in the Cherenkov Telescope Array
We have developed a non-sequential ray-tracing simulation library, ROot-BAsed
Simulator for ray Tracing (ROBAST), which is aimed for wide use in optical
simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written
in C++ and fully utilizes the geometry library of the ROOT analysis framework.
Despite the importance of optics simulations in CR experiments, no open-source
software for ray-tracing simulations that can be widely used existed. To reduce
the unnecessary effort demanded when different research groups develop multiple
ray-tracing simulators, we have successfully used ROBAST for many years to
perform optics simulations for the Cherenkov Telescope Array (CTA). Among the
proposed telescope designs for CTA, ROBAST is currently being used for three
telescopes: a Schwarzschild--Couder telescope, one of the Schwarzschild--Couder
small-sized telescopes, and a large-sized telescope (LST). ROBAST is also used
for the simulations and the development of hexagonal light concentrators that
has been proposed for the LST focal plane. By fully utilizing the ROOT geometry
library with additional ROBAST classes, building complex optics geometries that
are typically used in CR experiments and ground-based gamma-ray telescopes is
possible. We introduce ROBAST and show several successful applications for CTA.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
General relativistic Poynting-Robertson effect to diagnose wormholes existence: static and spherically symmetric case
We derive the equations of motion of a test particle in the equatorial plane
around a static and spherically symmetric wormhole influenced by a radiation
field including the general relativistic Poynting-Robertson effect. From the
analysis of this dynamical system, we develop a diagnostic to distinguish a
black hole from a wormhole, which can be timely supported by several and
different observational data. This procedure is based on the possibility of
having some wormhole metrics, which smoothly connect to the Schwarzschild
metric in a small transition surface layer very close to the black hole event
horizon. To detect such a metric-change, we analyse the emission proprieties
from the critical hypersurface (stable region where radiation and gravitational
fields balance) together with those from an accretion disk in the Schwarzschild
spacetime toward a distant observer. Indeed, if the observational data are well
fitted within such model, it immediately implies the existence of a black hole;
while in case of strong departures from such description it means that a
wormhole could be present. Finally, we discuss our results and draw the
conclusions.Comment: 17 pages, 11 figures, 1 Table. Paper accepted on April 30, 2020 on
Physical Review
3D Particle Tracking Velocimetry Method: Advances and Error Analysis
A full three-dimensional particle tracking system was developed and tested. By using three separate CCDs placed at the vertices of an equilateral triangle, the threedimensional location of particles can be determined. Particle locations measured at two different times can then be used to create a three-component, three-dimensional velocity field. Key developments are: the ability to accurately process overlapping particle images, offset CCDs to significantly improve effective resolution, allowance for dim particle images, and a hybrid particle tracking technique ideal for three-dimensional flows when only two sets of images exist. An in-depth theoretical error analysis was performed which gives the important sources of error and their effect on the overall system. This error analysis was verified through a series of experiments, which utilized a test target with 100 small dots per square inch. For displacements of 2.54mm the mean errors were less than 2% and the 90% confidence limits were less than 5.2 μm in the plane perpendicular to the camera axis, and 66 μm in the direction of the camera axis. The system was used for flow measurements around a delta wing at an angle of attack. These measurements show the successful implementation of the system for three-dimensional flow velocimetry
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