936 research outputs found
Core structure of EAS in 10(15) to 10(17) eV
With the use of Akeno calorimeter, the attenuation of particles in concrete is analyzed as the function of the shower size of 10 to the 5th power to 10 to the 7th power. The attenuation length does not depend much on the shower size but depends a little on the shower age. The average value is approx. 150 g/sq cm for s = 0.5 to 0.85 and approx. 40 g/sq cm for s = 0.85 to 1.15. These values and their fluctuations are consistent with the equi-intensity curves of extensive air showers (EAS)
Vortex Tubes in Turbulence Velocity Fields at Reynolds Numbers 300-1300
The most elementary structures of turbulence, i.e., vortex tubes, are studied
using velocity data obtained in a laboratory experiment for boundary layers
with microscale Reynolds numbers 295-1258. We conduct conditional averaging for
enhancements of a small-scale velocity increment and obtain the typical
velocity profile for vortex tubes. Their radii are of the order of the
Kolmogorov length. Their circulation velocities are of the order of the
root-mean-square velocity fluctuation. We also obtain the distribution of the
interval between successive enhancements of the velocity increment as the
measure of the spatial distribution of vortex tubes. They tend to cluster
together below about the integral length and more significantly below about the
Taylor microscale. These properties are independent of the Reynolds number and
are hence expected to be universal.Comment: 8 pages, to appear in Physical Review
Constructing new optimal entanglement witnesses
We provide a new class of indecomposable entanglement witnesses. In 4 x 4
case it reproduces the well know Breuer-Hall witness. We prove that these new
witnesses are optimal and atomic, i.e. they are able to detect the "weakest"
quantum entanglement encoded into states with positive partial transposition
(PPT). Equivalently, we provide a new construction of indecomposable atomic
maps in the algebra of 2k x 2k complex matrices. It is shown that their
structural physical approximations give rise to entanglement breaking channels.
This result supports recent conjecture by Korbicz et. al.Comment: 9 page
Computing Storyline Visualizations with Few Block Crossings
Storyline visualizations show the structure of a story, by depicting the
interactions of the characters over time. Each character is represented by an
x-monotone curve from left to right, and a meeting is represented by having the
curves of the participating characters run close together for some time. There
have been various approaches to drawing storyline visualizations in an
automated way. In order to keep the visual complexity low, rather than
minimizing pairwise crossings of curves, we count block crossings, that is,
pairs of intersecting bundles of lines.
Partly inspired by the ILP-based approach of Gronemann et al. [GD 2016] for
minimizing the number of pairwise crossings, we model the problem as a
satisfiability problem (since the straightforward ILP formulation becomes more
complicated and harder to solve). Having restricted ourselves to a decision
problem, we can apply powerful SAT solvers to find optimal drawings in
reasonable time. We compare this SAT-based approach with two exact algorithms
for block crossing minimization, using both the benchmark instances of
Gronemann et al. and random instances. We show that the SAT approach is
suitable for real-world instances and identify cases where the other algorithms
are preferable.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Magnetic monopole search by 130 m(2)sr He gas proportional counter
A search experiment for cosmic ray magnetic monopoles was performed by means of atomic induction mechanism by using He mixture gas proportional counters of the calorimeter (130 square meters sr) at the center of the Akeno air shower array. In 3,482 hours operation no monopole candidate was observed. The upper limit of the monopole flux is 1.44 x 10 to the minus 13th power cm-z, sec -1, sr-1 (90% C.L.) for the velocity faster than 7 x 0.0001 c
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Scale locality of the energy cascade using real space quantities
The classical energy cascade in turbulence as described by Richardson and Kolmogorov is predominantly a conjecture relying on the locality of interactions between scales of turbulence. This picture is generally accepted and assumes that energy and enstrophy transfers occur between neighbouring scales of turbulence and that vortex stretching plays a major role in the dynamics of this energy cascade. Direct numerical simulation data for Re_λ ranging from 37 to 1131 is used to gather evidence for the cascade by investigating the energy and enstrophy fluxes between scales and the interplay between vorticity at one scale and strain at an adjacent scale. This is achieved by using a bandpass filter to educe the turbulent structures at various length scales allowing one to determine the fluxes between these scales and to interrogate the role of non-local (in physical-space) vortex stretching. It is shown that the structures of a length scale L mostly transfer their energy to structures of size 0.3L and that most of the enstrophy flux goes from structures of scale L to 0.3L. Furthermore, vortical structures of a length scale L_ω are stretched mostly by straining structures of size 3 to 5L_ω and the stretching by eddies of sizes larger than 10L_ω is negligible. The stretching is dominated by the most extensive principal strain rate of the straining structures. These observations are found to be independent of Re_λ for the range investigated in this study. These results provide strong evidence for the classical view of an energy cascade transferring energy from large to small scales through a hierarchy of steps, each step consisting of the stretching of vortices by somewhat larger structures.Qualcomm European Research Studentship Fund in Technolog
Probing the size of extra dimension with gravitational wave astronomy
In Randall-Sundrum II (RS-II) braneworld model, it has been conjectured
according to the AdS/CFT correspondence that brane-localized black hole (BH)
larger than the bulk AdS curvature scale cannot be static, and it is
dual to a four dimensional BH emitting the Hawking radiation through some
quantum fields. In this scenario, the number of the quantum field species is so
large that this radiation changes the orbital evolution of a BH binary. We
derived the correction to the gravitational waveform phase due to this effect
and estimated the upper bounds on by performing Fisher analyses. We
found that DECIGO/BBO can put a stronger constraint than the current table-top
result by detecting gravitational waves from small mass BH/BH and BH/neutron
star (NS) binaries. Furthermore, DECIGO/BBO is expected to detect 10 BH/NS
binaries per year. Taking this advantage, we found that DECIGO/BBO can actually
measure down to m for 5 year observation if we know that
binaries are circular a priori. This is about 40 times smaller than the upper
bound obtained from the table-top experiment. On the other hand, when we take
eccentricities into binary parameters, the detection limit weakens to m due to strong degeneracies between and eccentricities. We also
derived the upper bound on from the expected detection number of extreme
mass ratio inspirals (EMRIs) with LISA and BH/NS binaries with DECIGO/BBO,
extending the discussion made recently by McWilliams. We found that these less
robust constraints are weaker than the ones from phase differences.Comment: 19 pages, 10 figures. Published in PRD, typos corrected, references
and footnotes adde
Hawking temperature for near-equilibrium black holes
We discuss the Hawking temperature of near-equilibrium black holes using a
semiclassical analysis. We introduce a useful expansion method for slowly
evolving spacetime, and evaluate the Bogoliubov coefficients using the saddle
point approximation. For a spacetime whose evolution is sufficiently slow, such
as a black hole with slowly changing mass, we find that the temperature is
determined by the surface gravity of the past horizon. As an example of
applications of these results, we study the Hawking temperature of black holes
with null shell accretion in asymptotically flat space and the AdS-Vaidya
spacetime. We discuss implications of our results in the context of the AdS/CFT
correspondence.Comment: 13 pages, 7 figures, REVTeX4; published in PR
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