19,506 research outputs found
Decay dynamics in the coupled-dipole model
Cooperative scattering in cold atoms has gained renewed interest, in
particular in the context of single-photon superradiance, with the recent
experimental observation of super-and subradiance in dilute atomic clouds.
Numerical simulations to support experimental signatures of cooperative
scattering are often limited by the number of dipoles which can be treated,
well below the number of atoms in the experiments. In this paper, we provide
systematic numerical studies aimed at matching the regime of dilute atomic
clouds. We use a scalar coupled-dipole model in the low excitation limit and an
exclusion volume to avoid density-related effects. Scaling laws for super-and
subradiance are obtained and the limits of numerical studies are pointed out.
We also illustrate the cooperative nature of light scattering by considering an
incident laser field, where half of the beam has a phase shift. The
enhanced subradiance obtained under such condition provides an additional
signature of the role of coherence in the detected signal
Efficient algorithm to study interconnected networks
Interconnected networks have been shown to be much more vulnerable to random
and targeted failures than isolated ones, raising several interesting questions
regarding the identification and mitigation of their risk. The paradigm to
address these questions is the percolation model, where the resilience of the
system is quantified by the dependence of the size of the largest cluster on
the number of failures. Numerically, the major challenge is the identification
of this cluster and the calculation of its size. Here, we propose an efficient
algorithm to tackle this problem. We show that the algorithm scales as O(N log
N), where N is the number of nodes in the network, a significant improvement
compared to O(N^2) for a greedy algorithm, what permits studying much larger
networks. Our new strategy can be applied to any network topology and
distribution of interdependencies, as well as any sequence of failures.Comment: 5 pages, 6 figure
Impact of Inter-Country Distances on International Tourism
Tourism is a worldwide practice with international tourism revenues
increasing from US\$495 billion in 2000 to US\$1340 billion in 2017. Its
relevance to the economy of many countries is obvious. Even though the World
Airline Network (WAN) is global and has a peculiar construction, the
International Tourism Network (ITN) is very similar to a random network and
barely global in its reach. To understand the impact of global distances on
local flows, we map the flow of tourists around the world onto a complex
network and study its topological and dynamical balance. We find that although
the WAN serves as infrastructural support for the ITN, the flow of tourism does
not correlate strongly with the extent of flight connections worldwide.
Instead, unidirectional flows appear locally forming communities that shed
light on global travelling behaviour inasmuch as there is only a 15%
probability of finding bidirectional tourism between a pair of countries. We
conjecture that this is a consequence of one-way cyclic tourism by analyzing
the triangles that are formed by the network of flows in the ITN. Finally, we
find that most tourists travel to neighbouring countries and mainly cover
larger distances when there is a direct flight, irrespective of the time it
takes
- …