5,591 research outputs found
Algebraic structures with unbounded Chern numbers
We determine all Chern numbers of smooth complex projective varieties of
dimension at least four which are determined up to finite ambiguity by the
underlying smooth manifold. We also give an upper bound on the dimension of the
space of linear combinations of Chern numbers with that property and prove its
optimality in dimension four.Comment: 15 pages; final version, to appear in Journal of Topolog
Heterotic warped Eguchi-Hanson spectra with five-branes and line bundles
We consider heterotic strings on a warped Eguchi-Hanson space with five-brane
and line bundle gauge fluxes. The heterotic string admits an exact CFT
description in terms of an asymmetrically gauged SU(2)xSL(2,R) WZW model, in a
specific double scaling limit in which the blow-up radius and the string scale
are sent to zero simultaneously. This allows us to compute the perturbative 6D
spectra for these models in two independent fashions: i) Within the
supergravity approximation we employ a representation dependent index; ii) In
the double scaling limit we determine all marginal vertex operators of the
coset CFT. To achieve agreement between the supergravity and the CFT spectra,
we conjecture that the untwisted and the twisted CFT states correspond to the
same set of hyper multiplets in supergravity. This is in a similar spirit as a
conjectured duality between asymptotically linear dilaton CFTs and little
string theory living on NS-five-branes. As the five-brane charge is
non-vanishing, heterotic (anti-)five-branes have to be added in order to cancel
irreducible gauge anomalies. The local spectra can be combined in such a way
that supersymmetry is preserved on the compact resolved T^4/Z_2 orbifold by
choosing the local gauge fluxes appropriately.Comment: 1+36 pages LaTe
Numerical solution of scattering problems using a Riemann--Hilbert formulation
A fast and accurate numerical method for the solution of scalar and matrix
Wiener--Hopf problems is presented. The Wiener--Hopf problems are formulated as
Riemann--Hilbert problems on the real line, and a numerical approach developed
for these problems is used. It is shown that the known far-field behaviour of
the solutions can be exploited to construct numerical schemes providing
spectrally accurate results. A number of scalar and matrix Wiener--Hopf
problems that generalize the classical Sommerfeld problem of diffraction of
plane waves by a semi-infinite plane are solved using the approach
Channel cross-correlations in transport through complex media
Measuring transmission between four antennas in microwave cavities, we
investigate directly the channel cross-correlations of the cross sections
from antenna at to antenna . Specifically
we look for the and , where the only difference is that
has none of the four channels in common, whereas has
exactly one channel in common. We find experimentally that these two channel
cross-correlations are anti-phased as a function of the channel coupling
strength, as predicted by theory. This anti-correlation is essential to give
the correct values for the universal conductance fluctuations. To obtain a good
agreement between experiment and predictions from random matrix theory the
effect of absorption had to be included.Comment: 6 pages, 5 figure
Not All Wireless Sensor Networks Are Created Equal: A Comparative Study On Tunnels
Wireless sensor networks (WSNs) are envisioned for a number of application scenarios. Nevertheless, the few in-the-field experiences typically focus on the features of a specific system, and rarely report about the characteristics of the target environment, especially w.r.t. the behavior and performance of low-power wireless communication. The TRITon project, funded by our local administration, aims to improve safety and reduce maintenance costs of road tunnels, using a WSN-based control infrastructure. The access to real tunnels within TRITon gives us the opportunity to experimentally assess the peculiarities of this environment, hitherto not investigated in the WSN field. We report about three deployments: i) an operational road tunnel, enabling us to assess the impact of vehicular traffic; ii) a non-operational tunnel, providing insights into analogous scenarios (e.g., underground mines) without vehicles; iii) a vineyard, serving as a baseline representative of the existing literature. Our setup, replicated in each deployment, uses mainstream WSN hardware, and popular MAC and routing protocols. We analyze and compare the deployments w.r.t. reliability, stability, and asymmetry of links, the accuracy of link quality estimators, and the impact of these aspects on MAC and routing layers. Our analysis shows that a number of criteria commonly used in the design of WSN protocols do not hold in tunnels. Therefore, our results are useful for designing networking solutions operating efficiently in similar environments
An 826 MOPS, 210 uW/MHz Unum ALU in 65 nm
To overcome the limitations of conventional floating-point number formats, an
interval arithmetic and variable-width storage format called universal number
(unum) has been recently introduced. This paper presents the first (to the best
of our knowledge) silicon implementation measurements of an
application-specific integrated circuit (ASIC) for unum floating-point
arithmetic. The designed chip includes a 128-bit wide unum arithmetic unit to
execute additions and subtractions, while also supporting lossless (for
intermediate results) and lossy (for external data movements) compression units
to exploit the memory usage reduction potential of the unum format. Our chip,
fabricated in a 65 nm CMOS process, achieves a maximum clock frequency of 413
MHz at 1.2 V with an average measured power of 210 uW/MHz
How (non-) linear is the hydrodynamics of heavy ion collisions?
We provide evidence from full numerical solutions that the hydrodynamical
evolution of initial density fluctuations in heavy ion collisions can be
understood order-by-order in a perturbative series in deviations from a smooth
and azimuthally symmetric background solution. To leading linear order, modes
with different azimuthal wave numbers do not mix. Quadratic and higher order
corrections are small and can be understood as overtones with corresponding
wave numbers.Comment: 8 pages, 4 figure
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