141,054 research outputs found
On cost-effective communication network designing
How to efficiently design a communication network is a paramount task for
network designing and engineering. It is, however, not a single objective
optimization process as perceived by most previous researches, i.e., to
maximize its transmission capacity, but a multi-objective optimization process,
with lowering its cost to be another important objective. These two objectives
are often contradictive in that optimizing one objective may deteriorate the
other. After a deep investigation of the impact that network topology, node
capability scheme and routing algorithm as well as their interplays have on the
two objectives, this letter presents a systematic approach to achieve a
cost-effective design by carefully choosing the three designing aspects. Only
when routing algorithm and node capability scheme are elegantly chosen can
BA-like scale-free networks have the potential of achieving good tradeoff
between the two objectives. Random networks, on the other hand, have the
built-in character for a cost-effective design, especially when other aspects
cannot be determined beforehand.Comment: 6 pages, 4 figure
Automorphisms of finite order on Gorenstein del Pezzo surfaces
In this note we shall determine all actions of groups of prime order p with p
> 3 on Gorenstein del Pezzo (singular) surfaces Y of Picard number 1. We show
that every order-p element in Aut(Y) (= Aut(Y'), Y' being the minimal
resolution of Y) is lifted from a projective transformation of the projective
plane. We also determine when Aut(Y) is finite in terms of the self
intersection of the canonical divisor of Y, Sing(Y) and the number of singular
members in the anti-canonical linear system of Y. In particular, we show that
either |Aut(Y)| = 2^a 3^b for some 0 3 there
is at least one element g_p of order p in Aut(Y) (hence |Aut(Y)| is infinite).Comment: 18 pages, Transactions of the American Mathematical Society, to
appea
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