2,581 research outputs found
Exploring the Micro-Structure of the Proton: from Form Factors to DVCS
For a long time people made the mistake of thinking the proton was
understood. New experiments, ranging from form factors to deeply virtual
Compton scattering, promise a new era of highly informative studies. Among the
controversial topics of the future may be such basic features as the physical
size of the proton, the role of quark orbital angular momentum, and the
possibility of making "femto-photographic" images of hadronic micro-structure.Comment: 19 pages, 2 figures, presented by John Ralston at the Workshop on
"Testing QCD through Spin Observables in Nuclear Targets", University of
Virginia, Charlottesville, Virginia, April 18-2
Eruption of a plasma blob, associated M-class flare, and large-scale EUV wave observed by SDO
We present a multiwavelength study of the formation and ejection of a plasma
blob and associated EUV waves in AR NOAA 11176, observed by SDO/AIA and STEREO
on 25 March 2011. SDO/AIA images clearly show the formation and ejection of a
plasma blob from the lower solar atmosphere at ~9 min prior to the onset of the
M1.0 flare. This onset of the M-class flare happened at the site of the blob
formation, while the blob was rising in a parabolic path with an average speed
of ~300 km/s. The blob also showed twisting and de-twisting motion in the lower
corona, and the blob speed varied from ~10-540 km/s. The faster and slower EUV
wavefronts were observed in front of the plasma blob during its impulsive
acceleration phase. The faster EUV wave propagated with a speed of ~785 to 1020
km/s, whereas the slower wavefront speed varied in between ~245 and 465 km/s.
The timing and speed of the faster wave match the shock speed estimated from
the drift rate of the associated type II radio burst. The faster wave
experiences a reflection by the nearby AR NOAA 11177. In addition, secondary
waves were observed (only in the 171 \AA channel), when the primary fast wave
and plasma blob impacted the funnel-shaped coronal loops. The HMI magnetograms
revealed the continuous emergence of new magnetic flux along with shear flows
at the site of the blob formation. It is inferred that the emergence of twisted
magnetic fields in the form of arch-filaments/"anemone-type" loops is the
likely cause for the plasma blob formation and associated eruption along with
the triggering of M-class flare. Furthermore, the faster EUV wave formed ahead
of the blob shows the signature of fast-mode MHD wave, whereas the slower wave
seems to be generated by the field line compression by the plasma blob. The
secondary wave trains originated from the funnel-shaped loops are probably the
fast magnetoacoustic waves.Comment: A&A (in press), 22 pages, 13 figure
Friedmann model with viscous cosmology in modified gravity theory
In this paper, we introduce bulk viscosity in the formalism of modified
gravity theory in which the gravitational action contains a general function
, where and denote the curvature scalar and the trace of the
energy-momentum tensor, respectively within the framework of a flat
Friedmann-Robertson-Walker model. As an equation of state for prefect fluid, we
take , where and viscous term as a
bulk viscosity due to isotropic model, of the form , where and are constants, and
is the Hubble parameter. The exact non-singular solutions to the
corresponding field equations are obtained with non- viscous and viscous
fluids, respectively by assuming a simplest particular model of the form of
, where ( is a constant). A big-rip
singularity is also observed for at a finite value of cosmic time
under certain constraints. We study all possible scenarios with the possible
positive and negative ranges of to analyze the expansion history of
the universe. It is observed that the universe accelerates or exhibits
transition from decelerated phase to accelerated phase under certain
constraints of and . We compare the viscous models with the
non-viscous one through the graph plotted between scale factor and cosmic time
and find that bulk viscosity plays the major role in the expansion of the
universe. A similar graph is plotted for deceleration parameter with
non-viscous and viscous fluids and find a transition from decelerated to
accelerated phase with some form of bulk viscosity.Comment: 19 pages, 3 figures, the whole paper has been revised to improve the
quality of paper. Some references added. arXiv admin note: text overlap with
arXiv:1307.4262 by other author
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