7,454 research outputs found
Tectonic evolution of the Archaean high-grade terrain of South India
The southern Indian shield consists of three major tectonic provinces viz., (1) Dharwar Craton, (2) Eastern Ghat Mobile Belt, and (3) Pandyan Mobile Belt. An understanding of their mutual relations is crucial for formulating crustal evolution models. The tectonic evolution of these provinces is summarized
Increasing the number of fibered faces of arithmetic hyperbolic 3-manifolds
We exhibit a closed hyperbolic 3-manifold which satisfies a very strong form
of Thurston's Virtual Fibration Conjecture. In particular, this manifold has
finite covers which fiber over the circle in arbitrarily many ways. More
precisely, it has a tower of finite covers where the number of fibered faces of
the Thurston norm ball goes to infinity, in fact faster than any power of the
logarithm of the degree of the cover, and we give a more precise quantitative
lower bound. The example manifold M is arithmetic, and the proof uses detailed
number-theoretic information, at the level of the Hecke eigenvalues, to drive a
geometric argument based on Fried's dynamical characterization of the fibered
faces. The origin of the basic fibration of M over the circle is the modular
elliptic curve E=X_0(49), which admits multiplication by the ring of integers
of Q[sqrt(-7)]. We first base change the holomorphic differential on E to a
cusp form on GL(2) over K=Q[sqrt(-3)], and then transfer over to a quaternion
algebra D/K ramified only at the primes above 7; the fundamental group of M is
a quotient of the principal congruence subgroup of level 7 of the
multiplicative group of a maximal order of D. To analyze the topological
properties of M, we use a new practical method for computing the Thurston norm,
which is of independent interest. We also give a non-compact finite-volume
hyperbolic 3-manifold with the same properties by using a direct topological
argument.Comment: 42 pages, 7 figures; V2: minor improvements, to appear in Amer. J.
Mat
Complex order parameter symmetry and thermal conductivity
Thermal behaviour of superconductors with complex order parameter symmetry is
studied within a weak coupling theory. It is shown numerically, that the
thermal nature of the different components of complex order parametrs are
qualitatively different. Within the complex order parameter scenario, the
recent experimental observations by Krishna {\it et al.}, [Science {\bf 277},
83 (1997)] on magnetothermal conductivity and by J. Ma {\it et al.},
[Science {\bf 267}, 862 (1995)] on temperature dependent gap anisotropy for
high temperature superconductors can have natural explanation.Comment: 6 pages, 3 figures and macros attached, Europhysics Letters (1998) in
pres
Is Explicit Congestion Notification usable with UDP?
We present initial measurements to determine if ECN is usable with
UDP traffic in the public Internet. This is interesting because ECN
is part of current IETF proposals for congestion control of UDPbased
interactive multimedia, and due to the increasing use of UDP
as a substrate on which new transport protocols can be deployed.
Using measurements from the author’s homes, their workplace,
and cloud servers in each of the nine EC2 regions worldwide, we
test reachability of 2500 servers from the public NTP server pool,
using ECT(0) and not-ECT marked UDP packets. We show that
an average of 98.97% of the NTP servers that are reachable using
not-ECT marked packets are also reachable using ECT(0) marked
UDP packets, and that ~98% of network hops pass ECT(0) marked
packets without clearing the ECT bits. We compare reachability of
the same hosts using ECN with TCP, finding that 82.0% of those
reachable with TCP can successfully negotiate and use ECN. Our
findings suggest that ECN is broadly usable with UDP traffic, and
that support for use of ECN with TCP has increased
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