17,804 research outputs found
Formation of Wormholes by Dark Matter in the Galaxy Dragonfly 44
Recently, ultra diffuse galaxy (UDG) of Dragonfly 44 in the Coma Cluster was
observed and observations of the rotational speed suggest that its mass is
almost same as the mass of the Milky Way. On the other hand, interestingly, the
galaxy emits only 1 \% of the light emitted by the Milky Way. Then, astronomers
reported that Dragonfly 44 may be made almost entirely of dark matter. In this
study we try to show that the dark matter that constitutes Dragonfly 44 can
form the wormhole or not. Two possible dark matter profiles are used, namely,
ultra diffuse galaxy King's model and generalized Navarro-Frenk-White (NFW)
dark matter profile. We have shown that King's model dark matter profile does
not manage to provide wormhole whereas generalized Navarro-Frenk-White (NFW)
dark matter profile is managed to find wormholes.Comment: 8 pages, two columns. Accepted for publication in Canadian Journal of
Physic
Structural Analysis of a Dragonfly Wing
Dragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in a lightweight structure with good aerodynamic performance. How insect wings carry aerodynamic and inertial loads, and how the resonant frequency of the flapping wings is tuned for carrying these loads, is however not fully understood. To study this we made a three-dimensional scan of a dragonfly (Sympetrum vulgatum) fore- and hindwing with a micro-CT scanner. The scans contain the complete venation pattern including thickness variations throughout both wings. We subsequently approximated the forewing architecture with an efficient three-dimensional beam and shell model. We then determined the wingâs natural vibration modes and the wing deformation resulting from analytical estimates of 8 load cases containing aerodynamic and inertial loads (using the finite element solver Abaqus). Based on our computations we find that the inertial loads are 1.5 to 3 times higher than aerodynamic pressure loads. We further find that wing deformation is smaller during the downstroke than during the upstroke, due to structural asymmetry. The natural vibration mode analysis revealed that the structural natural frequency of a dragonfly wing in vacuum is 154 Hz, which is approximately 4.8 times higher than the natural flapping frequency of dragonflies in hovering flight (32.3 Hz). This insight in the structural properties of dragonfly wings could inspire the design of more effective wings for insect-sized flapping micro air vehicles: The passive shape of aeroelastically tailored wings inspired by dragonflies can in principle be designed more precisely compared to sail like wings âwhich can make the dragonfly-like wings more aerodynamically effective
Sustainable control of Anopheles mosquito population
Despite the widespread use of insecticides, community engagement programmes and preventive measures mosquito borne diseases are growing and new tools to prevent the spread of disease are urgently needed. An alternative control measure for the eradication of Anopheles mosquitoes is suggested by the use of a Sustainable Control Model, which demonstrates the capability of Odonata, a natural beneficial predator, to exercise control over Anopheles mosquitoes in less than 140 days
Future Prospects: Deep Imaging of Galaxy Outskirts using Telescopes Large and Small
The Universe is almost totally unexplored at low surface brightness levels.
In spite of great progress in the construction of large telescopes and
improvements in the sensitivity of detectors, the limiting surface brightness
of imaging observations has remained static for about forty years. Recent
technical advances have at last begun to erode the barriers preventing
progress. In this Chapter we describe the technical challenges to low surface
brightness imaging, describe some solutions, and highlight some relevant
observations that have been undertaken recently with both large and small
telescopes. Our main focus will be on discoveries made with the Dragonfly
Telephoto Array (Dragonfly), which is a new telescope concept designed to probe
the Universe down to hitherto unprecedented low surface brightness levels. We
conclude by arguing that these discoveries are probably only scratching the
surface of interesting phenomena that are observable when the Universe is
explored at low surface brightness levels.Comment: 27 pages, 10 figures, Invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Network unfairness in dragonfly topologies
Dragonfly networks arrange network routers in a two-level hierarchy, providing a competitive cost-performance solution for large systems. Non-minimal adaptive routing (adaptive misrouting) is employed to fully exploit the path diversity and increase the performance under adversarial traffic patterns. Network fairness issues arise in the dragonfly for several combinations of traffic pattern, global misrouting and traffic prioritization policy. Such unfairness prevents a balanced use of the resources across the network nodes and degrades severely the performance of any application running on an affected node. This paper reviews the main causes behind network unfairness in dragonflies, including a new adversarial traffic pattern which can easily occur in actual systems and congests all the global output links of a single router. A solution for the observed unfairness is evaluated using age-based arbitration. Results show that age-based arbitration mitigates fairness issues, especially when using in-transit adaptive routing. However, when using source adaptive routing, the saturation of the new traffic pattern interferes with the mechanisms employed to detect remote congestion, and the problem grows with the network size. This makes source adaptive routing in dragonflies based on remote notifications prone to reduced performance, even when using age-based arbitration.Peer ReviewedPostprint (author's final draft
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