9,524 research outputs found
Coarsening Dynamics of Granular Heaplets in Tapped Granular Layers
A semi-continuum model is introduced to study the dynamics of the formation
of granular heaplets in tapped granular layers. By taking into account the
energy dissipation of collisions and screening effects due to avalanches, this
model is able to reproduce qualitatively the pattern of these heaplets. Our
simulations show that the granular heaplets are characterised by an effective
surface tension which depends on the magnitude of the tapping intensity. Also,
we observe that there is a coarsening effect in that the average size of the
heaplets, V grows as the number of taps k increases. The growth law at
intermediate times can be fitted by a scaling function V ~ k^z but the range of
validity of the power law is limited by size effects. The growth exponent z
appears to diverge as the tapping intensity is increased.Comment: 4 pages, 4 figure
EVN Observations of HESS J1943+213: Evidence for an Extreme TeV BL Lac Object
We report on the 1.6 GHz (18 cm) VLBI observations of the unresolved, steady
TeV source HESS J1943+213 located in the Galactic plane, performed with the
European VLBI Network (EVN) in 2014. Our new observations with a nearly full
EVN array provide the deepest image of HESS J1943+213 at the highest resolution
ever achieved, enabling us to resolve the long-standing issues of the source
identification. The milliarcsecond-scale structure of HESS J1943+213 has a
clear asymmetric morphology, consisting of a compact core and a diffuse
jet-like tail. This is broadly consistent with the previous e-EVN observations
of the source performed in 2011, and re-analyzed in this work. The core
component is characterized by the brightness temperature of K, which is typical for low-luminosity blazars in general. Overall, radio
properties of HESS J1943+213 are consistent with the source classification as
an "extreme high-frequency-peaked BL Lac object". Remarkably, we note that
since HESS J1943+213 does not reveal any optical or infrared signatures of the
AGN activity, it would never be recognized and identified as a BL Lac object,
if not its location close to the Galactic plane where the High Energy
Stereoscopic System has surveyed, and the follow-up dedicated X-ray and radio
studies triggered by the source detection in the TeV range. Our results suggest
therefore a presence of an unrecognized, possibly very numerous population of
particularly extreme HBLs, and simultaneously demonstrate that the
low-frequency VLBI observations with high-angular resolution are indispensable
for a proper identification of such objects.Comment: 8 pages, 3 figures, accepted to ApJ
Determining All Universal Tilers
A universal tiler is a convex polyhedron whose every cross-section tiles the
plane. In this paper, we introduce a certain slight-rotating operation for
cross-sections of pentahedra. Based on a selected initial cross-section and by
applying the slight-rotating operation suitably, we prove that a convex
polyhedron is a universal tiler if and only if it is a tetrahedron or a
triangular prism.Comment: 18 pages, 12 figure
Gain in a quantum wire laser of high uniformity
A multi-quantum wire laser operating in the 1-D ground state has been
achieved in a very high uniformity structure that shows free exciton emission
with unprecedented narrow width and low lasing threshold. Under optical pumping
the spontaneous emission evolves from a sharp free exciton peak to a
red-shifted broad band. The lasing photon energy occurs about 5 meV below the
free exciton. The observed shift excludes free excitons in lasing and our
results show that Coulomb interactions in the 1-D electron-hole system shift
the spontaneous emission and play significant roles in laser gain.Comment: 4 pages, 4 figures, prepared by RevTe
Comparison between Magnetic Configuration and Rotational Transform Profile during ETB formation on CHS
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