23,444 research outputs found
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
Coupling the solar surface and the corona: coronal rotation, Alfv\'en wave-driven polar plumes
The dynamical response of the solar corona to surface and sub-surface
perturbations depends on the chromospheric stratification, and specifically on
how efficiently these layers reflect or transmit incoming Alfv\'en waves. While
it would be desirable to include the chromospheric layers in the numerical
simulations used to study such phenomena, that is most often not feasible. We
defined and tested a simple approximation allowing the study of coronal
phenomena while taking into account a parametrised chromospheric reflectivity.
We addressed the problems of the transmission of the surface rotation to the
corona and that of the generation of polar plumes by Alfv\'en waves (Pinto et
al., 2010, 2011). We found that a high (yet partial) effective chromospheric
reflectivity is required to properly describe the angular momentum balance in
the corona and the way the surface differential rotation is transmitted
upwards. Alfv\'en wave-driven polar plumes maintain their properties for a wide
range of values for the reflectivity, but they become bursty (and eventually
disrupt) when the limit of total reflection is attained.Comment: Solar Wind 13: Proceedings of the Thirteenth International Solar Wind
Conferenc
Non-Invasive Measurement of Frog Skin Reflectivity in High Spatial Resolution Using a Dual Hyperspectral Approach
Background:Most spectral data for the amphibian integument are limited to the visible spectrum of light and have been collected using point measurements with low spatial resolution. In the present study a dual camera setup consisting of two push broom hyperspectral imaging systems was employed, which produces reflectance images between 400 and 2500 nm with high spectral and spatial resolution and a high dynamic range.Methodology/Principal Findings:We briefly introduce the system and document the high efficiency of this technique analyzing exemplarily the spectral reflectivity of the integument of three arboreal anuran species (Litoria caerulea, Agalychnis callidryas and Hyla arborea), all of which appear green to the human eye. The imaging setup generates a high number of spectral bands within seconds and allows non-invasive characterization of spectral characteristics with relatively high working distance. Despite the comparatively uniform coloration, spectral reflectivity between 700 and 1100 nm differed markedly among the species. In contrast to H. arborea, L. caerulea and A. callidryas showed reflection in this range. For all three species, reflectivity above 1100 nm is primarily defined by water absorption. Furthermore, the high resolution allowed examining even small structures such as fingers and toes, which in A. callidryas showed an increased reflectivity in the near infrared part of the spectrum.Conclusion/Significance:Hyperspectral imaging was found to be a very useful alternative technique combining the spectral resolution of spectrometric measurements with a higher spatial resolution. In addition, we used Digital Infrared/Red-Edge Photography as new simple method to roughly determine the near infrared reflectivity of frog specimens in field, where hyperspectral imaging is typically difficult. © 2013 Pinto et al
Thermal and non-thermal emission from reconnecting twisted coronal loops
Twisted magnetic fields should be ubiquitous in flare-producing active
regions where the magnetic fields are strongly non-potential. It has been shown
that reconnection in helical magnetic coronal loops results in plasma heating
and particle acceleration distributed within a large volume, including the
lower coronal and chromospheric sections of the loops. This scenario can be an
alternative to the standard flare model, where particles are accelerated only
in a small volume located in the upper corona. We use a combination of MHD
simulations and test-particle methods, which describe the development of kink
instability and magnetic reconnection in twisted coronal loops using resistive
compressible MHD, and incorporate atmospheric stratification and large-scale
loop curvature. The resulting distributions of hot plasma let us estimate
thermal X-ray emission intensities. The electric and magnetic fields obtained
are used to calculate electron trajectories using the guiding-centre
approximation. These trajectories combined with the MHD plasma density
distributions let us deduce synthetic HXR bremsstrahlung intensities. Our
simulations emphasise that the geometry of the emission patterns produced by
hot plasma in flaring twisted coronal loops can differ from the actual geometry
of the underlying magnetic fields. The twist angles revealed by the emission
threads (SXR) are consistently lower than the field-line twist present at the
onset of the kink-instability. HXR emission due to the interaction of energetic
electrons with the stratified background are concentrated at the loop
foot-points in these simulations, even though the electrons are accelerated
everywhere within the coronal volume of the loop. The maximum of HXR emission
consistently precedes that of SXR emission, with the HXR light-curve being
approximately proportional to the temporal derivative of the SXR light-curve.Comment: (accepted for publication on A&A
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