6,707 research outputs found
On the slope conjecture of Barja and Stoppino for fibred surfaces
Let be a locally non-trivial relatively minimal fibration of
genus with relative irregularity . It was conjectured by Barja
and Stoppino that the slope . We prove the
conjecture when is small with respect to ; we also construct
counterexamples when is odd and .Comment: any comment is welcom
On the slope of hyperelliptic fibrations with positive relative irregularity
Let be a locally non-trivial relatively minimal fibration of
hyperelliptic curves of genus with relative irregularity . We
show a sharp lower bound on the slope of . As a consequence, we
prove a conjecture of Barja and Stoppino on the lower bound of as
an increasing function of in this case, and we also prove a conjecture of
Xiao on the ampleness of the direct image of the relative canonical sheaf if
.Comment: final version, accepted by Trans. Amer. Math. So
On the Severi type inequalities for irregular surfaces
Let be a minimal surface of general type and maximal Albanese dimension
with irregularity . We show that if , and also obtain the
characterization of the equality. As a consequence, we prove a conjecture of
Manetti on the geography of irregular surfaces if or
, and we also prove a conjecture that surfaces
of general type and maximal Albanese dimension with
are exactly the resolution of double covers of abelian surfaces branched over
ample divisors with at worst simple singularities.Comment: Any comment is welcom
A Trust-based Pollution Attack Prevention Scheme in Peer-to-Peer Streaming Networks
Nowadays, peer-to-peer (P2P) streaming systems have become a popular way to
deliver multimedia content over the internet due to their low bandwidth
requirement, high video streaming quality, and flexibility. However, P2P
streaming systems are vulnerable to various attacks, especially pollution
attacks, due to their distributed and dynamically changing infrastructure. In
this paper, by exploring the features of various pollution attacks, we propose
a trust management system tailored for P2P streaming systems. Both direct trust
and indirect trust are taken into consideration when designing the trust
management system. A new direct trust model is proposed. A dynamic confidence
factor that can dynamically adjust the weight of direct and indirect trust in
computing the trust is also proposed and studied. A novel double-threshold
trust utilization scheme is given. It is shown that the proposed trust
management system is effective in identifying polluters and preventing them
from further sharing of polluted data chunks.Comment: to appear in Computer Network
On Shimura curves in the Torelli locus of curves
Oort has conjectured that there do not exist Shimura curves lying generically
in the Torelli locus of curves of genus . We show that there do not
exist one-dimensional Shimura families of semi-stable curves of genus
of Mumford type. We also show that there do not exist Shimura curves lying
generically in the Torelli locus of hyperelliptic curves of genus .
The first result proves a slightly weaker form of the conjecture for the case
of Shimura curves of Mumford type. The second result proves the conjecture for
the Torelli locus of hyperelliptic curves. We also present examples of Shimura
curves contained generically in the Torelli locus of curves of genus and
.Comment: 42 pages. Some typos are corrected. comments are welcom
The Oort conjecture on Shimura curves in the Torelli locus of curves
Oort has conjectured that there do not exist Shimura curves contained
generically in the Torelli locus of genus- curves when is large enough.
In this paper we prove the Oort conjecture for Shimura curves of Mumford type
and Shimura curves parameterizing principally polarized -dimensional abelian
varieties isogenous to -fold self-products of elliptic curves for . We
also prove that there do not exist Shimura curves contained generically in the
Torelli locus of hyperelliptic curves of genus . As a consequence, we
obtain a finiteness result regarding smooth genus- curves with completely
decomposable Jacobians, which is related to a question of Ekedahl and Serre.Comment: 52 pages. Comments are welcome. Text subsumes arxiv.org/abs/1311.585
Incentive Mechanism Design for Heterogeneous Peer-to-Peer Networks: A Stackelberg Game Approach
With high scalability, high video streaming quality, and low bandwidth
requirement, peer-to-peer (P2P) systems have become a popular way to exchange
files and deliver multimedia content over the internet. However, current P2P
systems are suffering from "free-riding" due to the peers' selfish nature. In
this paper, we propose a credit-based incentive mechanism to encourage peers to
cooperate with each other in a heterogeneous network consisting of wired and
wireless peers. The proposed mechanism can provide differentiated service to
peers with different credits through biased resource allocation. A Stackelberg
game is formulated to obtain the optimal pricing and purchasing strategies,
which can jointly maximize the revenue of the uploader and the utilities of the
downloaders. In particular, peers' heterogeneity and selfish nature are taken
into consideration when designing the utility functions for the Stackelberg
game. It is shown that the proposed resource allocation scheme is effective in
providing service differentiation for peers and stimulating them to make
contribution to the P2P streaming system.Comment: to appear in IEEE Transactions on Mobile Computin
Localize energy in random media: A new phase state
This Letter reports a new wave phenomenon. We show that wave energy can be
stored in random media. Associated with such energy storage is a global
collective behavior. The features depicted are so general that they may be
observed in many random systems.Comment: 3 pages revtex file, 1 eps figure
A note on Shimura subvarieties in the hyperelliptic Torelli locus
We prove the non-existence of Shimura subvarieties of positive dimension
contained generically in the hyperelliptic Torelli locus for curves of genus at
least 8, which is an analogue of Oort's conjecture in the hyperelliptic case
A note on the characteristic nonabelian Hodge theory in the geometric case
We provide a construction of associating a de Rham subbundle to a Higgs
subbundle in characteristic in the geometric case. As applications, we
obtain a Higgs semistability result and a -unliftable result.Comment: 16 pages. The assumption (n\rank(E)-1)\leq p-2 in the Higgs
semistability result has been removed in the current versio
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