2,231 research outputs found
Muon content of ultra-high-energy air showers: Yakutsk data versus simulations
We analyse a sample of 33 extensive air showers (EAS) with estimated primary
energies above 2\cdot 10^{19} eV and high-quality muon data recorded by the
Yakutsk EAS array. We compare, event-by-event, the observed muon density to
that expected from CORSIKA simulations for primary protons and iron, using
SIBYLL and EPOS hadronic interaction models. The study suggests the presence of
two distinct hadronic components, ``light'' and ``heavy''. Simulations with
EPOS are in a good agreement with the expected composition in which the light
component corresponds to protons and the heavy component to iron-like nuclei.
With SYBILL, simulated muon densities for iron primaries are a factor of \sim
1.5 less than those observed for the heavy component, for the same
electromagnetic signal. Assuming two-component proton-iron composition and the
EPOS model, the fraction of protons with energies E>10^{19} eV is
0.52^{+0.19}_{-0.20} at 95% confidence level.Comment: 8 pages, 3 figures; v2: replaced with journal versio
Neutrinos: the Key to UHE Cosmic Rays
Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely
determine both the injection spectrum and the evolution model for UHECR sources
- primarily because interactions during propagation obscure the early Universe
from direct observation. Detection of neutrinos produced in those same
interactions, coupled with UHECR results, would provide a full description of
UHECR source properties.Comment: three pages, three figures. corrected typo
Spin excitations of the correlated semiconductor FeSi probed by THz radiation
By direct measurements of the complex optical conductivity of
FeSi we have discovered a broad absorption peak centered at frequency
that develops at temperatures below 20 K.
This feature is caused by spin-polaronic states formed in the middle of the gap
in the electronic density of states. We observe the spin excitations between
the electronic levels split by the exchange field of . Spin
fluctuations are identified as the main factor determining the formation of the
spin polarons and the rich magnetic phase diagram of FeSi.Comment: 5 pages, 4 figure
On the Hierarchy of Block Deterministic Languages
A regular language is -lookahead deterministic (resp. -block
deterministic) if it is specified by a -lookahead deterministic (resp.
-block deterministic) regular expression. These two subclasses of regular
languages have been respectively introduced by Han and Wood (-lookahead
determinism) and by Giammarresi et al. (-block determinism) as a possible
extension of one-unambiguous languages defined and characterized by
Br\"uggemann-Klein and Wood. In this paper, we study the hierarchy and the
inclusion links of these families. We first show that each -block
deterministic language is the alphabetic image of some one-unambiguous
language. Moreover, we show that the conversion from a minimal DFA of a
-block deterministic regular language to a -block deterministic automaton
not only requires state elimination, and that the proof given by Han and Wood
of a proper hierarchy in -block deterministic languages based on this result
is erroneous. Despite these results, we show by giving a parameterized family
that there is a proper hierarchy in -block deterministic regular languages.
We also prove that there is a proper hierarchy in -lookahead deterministic
regular languages by studying particular properties of unary regular
expressions. Finally, using our valid results, we confirm that the family of
-block deterministic regular languages is strictly included into the one of
-lookahead deterministic regular languages by showing that any -block
deterministic unary language is one-unambiguous
- …