2,317 research outputs found
Plasma waves driven by gravitational waves in an expanding universe
In a Friedmann-Robertson-Walker (FRW) cosmological model with zero spatial
curvature, we consider the interaction of the gravitational waves with the
plasma in the presence of a weak magnetic field. Using the relativistic
hydromagnetic equations it is verified that large amplitude magnetosonic waves
are excited, assuming that both, the gravitational field and the weak magnetic
field do not break the homogeneity and isotropy of the considered FRW
spacetime.Comment: 14 page
Radiative Neutrino Decay in Media
In this letter we introduce a new method to determine the radiative neutrino
decay rate in the presence of a medium. Our approach is based on the
generalisation of the optical theorem at finite temperature and density.
Differently from previous works on this subject, our method allows to account
for dispersive and dissipative electromagnetic properties of the medium. Some
inconsistencies that are present in the literature are pointed-out and
corrected here. We shortly discuss the relevance of our results for neutrino
evolution in the early universe.Comment: 11 pages, 3 encapsulated figure
A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury
There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe
CHALLENGES IN FLYING QUADROTOR UNMANNED AERIAL VEHICLE FOR 3D INDOOR RECONSTRUCTION
Three-dimensional modelling plays a vital role in indoor 3D tracking, navigation, guidance and emergency evacuation. Reconstruction of indoor 3D models is still problematic, in part, because indoor spaces provide challenges less-documented than their outdoor counterparts. Challenges include obstacles curtailing image and point cloud capture, restricted accessibility and a wide array of indoor objects, each with unique semantics. Reconstruction of indoor environments can be achieved through a photogrammetric approach, e.g. by using image frames, aligned using recurring corresponding image points (CIP) to build coloured point clouds. Our experiments were conducted by flying a QUAV in three indoor environments and later reconstructing 3D models which were analysed under different conditions. Point clouds and meshes were created using Agisoft PhotoScan Professional. We concentrated on flight paths from two vantage points: 1) safety and security while flying indoors and 2) data collection needed for reconstruction of 3D models. We surmised that the main challenges in providing safe flight paths are related to the physical configuration of indoor environments, privacy issues, the presence of people and light conditions. We observed that the quality of recorded video used for 3D reconstruction has a high dependency on surface materials, wall textures and object types being reconstructed. Our results show that 3D indoor reconstruction predicated on video capture using a QUAV is indeed feasible, but close attention should be paid to flight paths and conditions ultimately influencing the quality of 3D models. Moreover, it should be decided in advance which objects need to be reconstructed, e.g. bare rooms or detailed furniture
Cosmological Magnetogenesis driven by Radiation Pressure
The origin of large scale cosmological magnetic fields remains a mystery,
despite the continuous efforts devoted to that problem. We present a new model
of magnetic field generation, based on local charge separation provided by an
anisotropic and inhomogeneous radiation pressure. In the cosmological context,
the processes we explore take place at the epoch of the reionisation of the
Universe. Under simple assumptions, we obtain results (i) in terms of the order
of magnitude of the field generated at large scales and (ii) in terms of its
power spectrum. The amplitudes obtained (B ~ 8.10^(-6) micro-Gauss) are
considerably higher than those obtained in usual magnetogenesis models and
provide suitable seeds for amplification by adiabatic collapse and/or dynamo
during structure formation.Comment: 9 pages, 2 figure
In-situ Magnesium Diboride Superconducting Thin Films grown by Pulsed Laser Deposition
Superconducting thin films of MgB2 were deposited by Pulsed Laser Deposition
on magnesium oxide and sapphire substrates. Samples grown at 450C in an argon
buffer pressure of about 10-2 mbar by using a magnesium enriched target
resulted to be superconducting with a transition temperature of about 25 K.
Film deposited from a MgB2 sintered pellet target in ultra high vacuum
conditions showed poor metallic or weak semiconducting behavior and they became
superconducting only after an ex-situ annealing in Mg vapor atmosphere. Up to
now, no difference in the superconducting properties of the films obtained by
these two procedures has been evidenced.Comment: 10 pages, 4 figure
Modelado de la extracción con hexano de molido de soja pretratado enzimáticamente
In this work, the influence of the variables which can affect oil extraction from soybean enzymatically pretreated grit using hexane, were studied. From the experimental results, a mathematical model for calculating the extraction yield was proposed. The statistical tests used to obtain this model showed that the yield does not depend on the enzymatic incubation pH but on the temperature and time of enzymatic treatment and on the interaction between time and temperature. The proposed model fit the experimental data well.En este trabajo se estudia la influencia de las variables de proceso que pueden tener efecto sobre el rendimiento de la extracciĂłn con hexano a partir de soja molida pretratada enzimáticamente.Se propone a partir de los resultados experimentales, un modelo matemático para el cálculo del rendimiento de la extracciĂłn. Los tests estadĂsticos utilizados para obtener este modelo demostraron que el rendimiento en aceite no depende del pH de la incubaciĂłn enzimática mientras que si depende tanto de la temperatura como del tiempo de ataque enzimático sobre el molido de soja. El modelo ajustĂł satisfactoriamente los datos experimentales
Pulsar kicks from neutrino oscillations
Neutrino oscillations can explain the observed motion of pulsars. We show
that two different models of neutrino emission from a cooling neutron star are
in good quantitative agreement and predict the same order of magnitude for the
pulsar kick velocity, consistent with the data.Comment: revtex; 4 page
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