71,177 research outputs found
New Optimal Binary Sequences with Period via Interleaving Ding-Helleseth-Lam Sequences
Binary sequences with optimal autocorrelation play important roles in radar,
communication, and cryptography. Finding new binary sequences with optimal
autocorrelation has been an interesting research topic in sequence design.
Ding-Helleseth-Lam sequences are such a class of binary sequences of period
, where is an odd prime with . The objective of this
letter is to present a construction of binary sequences of period via
interleaving four suitable Ding-Helleseth-Lam sequences. This construction
generates new binary sequences with optimal autocorrelation which can not be
produced by earlier ones
On -manifolds with free fundamental group and simple boundary links in
We classify compact oriented -manifolds with free fundamental group and
a torsion free abelian group in terms of the second homotopy group
considered as -module, the cup product on the second cohomology of the
universal covering, and the second Stiefel-Whitney class of the universal
covering. We apply this to the classification of simple boundary links of
-spheres in . Using this we give a complete algebraic picture of closed
-manifolds with free fundamental group and trivial second homology group.Comment: 20 page
Interaction Between Supernova Remnant G22.7-0.2 And The Ambient Molecular Clouds
We have carried out 12CO (J=1-0 and 2-1), 13CO (J=1-0), and C18O (J=1-0)
observations in the direction of the supernova remnant (SNR) G22.7-0.2. A
filamentary molecular gas structure, which is likely part of a larger molecular
complex with VLSR~75-79 km/s, is detected and is found to surround the southern
boundary of the remnant. In particular, the high-velocity wing (77-110 km/s) in
the 12CO (J=1-0 and J=2-1) emission shows convincing evidence of the
interaction between SNR G22.7-0.2 and the 75-79 km/s molecular clouds (MCs).
Spectra with redshifted profiles, a signature of shocked molecular gas, are
seen in the southeastern boundary of the remnant. The association between the
remnant and the 77 km/s MCs places the remnant at the near distance of 4.0-4.8
kpc, which agrees with a location on the Scutum-Crux arm. We suggest that SNR
G22.7-0.2, SNR W41, and HII region G022.760-0.485 are at the same distance and
are associated with GMC G23.0-0.4.Comment: 9 pages, 9 figures, 3 tables, accepted for publication in Ap
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