6,764 research outputs found
Partial Match Queries in Two-Dimensional Quadtrees : a Probabilistic Approach
We analyze the mean cost of the partial match queries in random
two-dimensional quadtrees. The method is based on fragmentation theory. The
convergence is guaranteed by a coupling argument of Markov chains, whereas the
value of the limit is computed as the fixed point of an integral equation
Space-time coding techniques with bit-interleaved coded modulations for MIMO block-fading channels
The space-time bit-interleaved coded modulation (ST-BICM) is an efficient
technique to obtain high diversity and coding gain on a block-fading MIMO
channel. Its maximum-likelihood (ML) performance is computed under ideal
interleaving conditions, which enables a global optimization taking into
account channel coding. Thanks to a diversity upperbound derived from the
Singleton bound, an appropriate choice of the time dimension of the space-time
coding is possible, which maximizes diversity while minimizing complexity.
Based on the analysis, an optimized interleaver and a set of linear precoders,
called dispersive nucleo algebraic (DNA) precoders are proposed. The proposed
precoders have good performance with respect to the state of the art and exist
for any number of transmit antennas and any time dimension. With turbo codes,
they exhibit a frame error rate which does not increase with frame length.Comment: Submitted to IEEE Trans. on Information Theory, Submission: January
2006 - First review: June 200
Generation of 3rd and 5th harmonics in a thin superconducting film by temperature oscillations and isothermal nonlinear current response
The generation of harmonics of the voltage response is considered when an AC
current is applied through a superconducting film above T_c. It is shown that
almost at all temperatures the mechanism of the temperature oscillations
created by the AC current and the temperature dependence of the resistance
dominates over the isothermal nonlinear electric conductivity. Only in a narrow
critical region close to T_c the latter is essential for the generation of the
harmonics. A detailed investigation of harmonics generation provides an
accurate method for measuring the thermal boundary conductance between the film
and the insulating substrate. The critical behaviour of the third harmonic will
give a new method for the determination of the lifetime of metastable Cooper
pairs above T_c. The comparison of the calculated fifth harmonics of the
voltage with the experiment is proposed as an important test for the
applicability of the employed theoretical models.Comment: 8 pages, LaTeX, submitted to European Journal of Physics
Forward Physics at the LHC: within and beyond the Standard Model
We review the detection capabilities in the forward direction of the various
LHC experiments together with the associated physics programme. A selection of
measurements accessible with near-beam instrumentation in various sectors (and
extensions) of the Standard Model (SM) is outlined, including QCD (diffractive
and elastic scattering, low-x parton dynamics, hadronic Monte Carlos for
cosmic-rays), electroweak processes in gamma-gamma interactions, and Higgs
physics (vector-boson-fusion and central exclusive production).Comment: 9 pages, 18 figs. Lectures given at the LAWHEP'07 School (Sao Miguel
das Missoes, Brazil, 3-7 Dec 2007) to appear in Braz. J. Phys. Also presented
in HLPW08 (Spa, Belgium, 6-8 Mar 2008) AIP Conf. Proceeds, to appear; and in
HANUC European Grad. School (Jyvaskyla, Finland, 25-29 Aug. 2008
Incompatible quantum measurements admitting a local hidden variable model
The observation of quantum nonlocality, i.e. quantum correlations violating a
Bell inequality, implies the use of incompatible local quantum measurements.
Here we consider the converse question. That is, can any set of incompatible
measurements be used in order to demonstrate Bell inequality violation? Our
main result is to construct a local hidden variable model for an incompatible
set of qubit measurements. Specifically, we show that if Alice uses this set of
measurements, then for any possible shared entangled state, and any possible
dichotomic measurements performed by Bob, the resulting statistics are local.
This represents significant progress towards proving that measurement
incompatibility does not imply Bell nonlocality in general.Comment: A few small changes, closer to the published versio
Genuine hidden quantum nonlocality
The nonlocality of certain quantum states can be revealed by using local
filters before performing a standard Bell test. This phenomenon, known as
hidden nonlocality, has been so far demonstrated only for a restricted class of
measurements, namely projective measurements. Here we prove the existence of
genuine hidden nonlocality. Specifically, we present a class of two-qubit
entangled states, for which we construct a local model for the most general
local measurements (POVMs), and show that the states violate a Bell inequality
after local filtering. Hence there exist entangled states, the nonlocality of
which can be revealed only by using a sequence of measurements. Finally, we
show that genuine hidden nonlocality can be maximal. There exist entangled
states for which a sequence of measurements can lead to maximal violation of a
Bell inequality, while the statistics of non-sequential measurements is always
local.Comment: 5 pages, no figure
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