31,898 research outputs found
Quantum random number generation for 1.25 GHz quantum key distribution systems
Security proofs of quantum key distribution (QKD) systems usually assume that
the users have access to source of perfect randomness. State-of-the-art QKD
systems run at frequencies in the GHz range, requiring a sustained GHz rate of
generation and acquisition of quantum random numbers. In this paper we
demonstrate such a high speed random number generator. The entropy source is
based on amplified spontaneous emission from an erbium-doped fibre, which is
directly acquired using a standard small form-factor pluggable (SFP) module.
The module connects to the Field Programmable Gate Array (FPGA) of a QKD
system. A real-time randomness extractor is implemented in the FPGA and
achieves a sustained rate of 1.25 Gbps of provably random bits.Comment: 6 pages, 8 figure
Learning Points and Routes to Recommend Trajectories
The problem of recommending tours to travellers is an important and broadly
studied area. Suggested solutions include various approaches of
points-of-interest (POI) recommendation and route planning. We consider the
task of recommending a sequence of POIs, that simultaneously uses information
about POIs and routes. Our approach unifies the treatment of various sources of
information by representing them as features in machine learning algorithms,
enabling us to learn from past behaviour. Information about POIs are used to
learn a POI ranking model that accounts for the start and end points of tours.
Data about previous trajectories are used for learning transition patterns
between POIs that enable us to recommend probable routes. In addition, a
probabilistic model is proposed to combine the results of POI ranking and the
POI to POI transitions. We propose a new F score on pairs of POIs that
capture the order of visits. Empirical results show that our approach improves
on recent methods, and demonstrate that combining points and routes enables
better trajectory recommendations
Properties of kinematic singularities
The locally rotationally symmetric tilted perfect fluid Bianchi type V
cosmological model provides examples of future geodesically complete spacetimes
that admit a `kinematic singularity' at which the fluid congruence is
inextendible but all frame components of the Weyl and Ricci tensors remain
bounded. We show that for any positive integer n there are examples of Bianchi
type V spacetimes admitting a kinematic singularity such that the covariant
derivatives of the Weyl and Ricci tensors up to the n-th order also stay
bounded. We briefly discuss singularities in classical spacetimes.Comment: 13 pages. Published version. One sentence from version 2 correcte
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