53 research outputs found
Efficiency of attack strategies on complex model and real-world networks
We investigated the efficiency of attack strategies to network nodes when
targeting several complex model and real-world networks. We tested 5 attack
strategies, 3 of which were introduced in this work for the first time, to
attack 3 model (Erdos and Renyi, Barabasi and Albert preferential attachment
network, and scale-free network configuration models) and 3 real networks
(Gnutella peer-to-peer network, email network of the University of Rovira i
Virgili, and immunoglobulin interaction network). Nodes were removed
sequentially according to the importance criterion defined by the attack
strategy. We used the size of the largest connected component (LCC) as a
measure of network damage. We found that the efficiency of attack strategies
(fraction of nodes to be deleted for a given reduction of LCC size) depends on
the topology of the network, although attacks based on the number of
connections of a node and betweenness centrality were often the most efficient
strategies. Sequential deletion of nodes in decreasing order of betweenness
centrality was the most efficient attack strategy when targeting real-world
networks. In particular for networks with power-law degree distribution, we
observed that most efficient strategy change during the sequential removal of
nodes.Comment: 18 pages, 4 figure
An energy window study of light transmission-disorder relationship in 1D photonic structures
While the light transmission of photonic crystals is characterized by the
photonic band gap, the one of disordered photonic structures is typified by a
multiplicity of transmission depths. The total transmission over a range of
wavelengths is related to the width of such range, but also to the type of
disorder. Less homogeneous disordered structures transmit more light than the
ordered counterpart regardless of the wavelengths range width. More homogeneous
disordered structures transmit more light than the ordered counterpart only
above a certain value of the width. We studied this behaviour with a
statistical analysis over 5000 permutations of structures for each wavelength
width and for each homogeneity degree (Shannon-Wiener index).Comment: 8 pages, 4 figure
The influence of a power law distribution of cluster size on the light transmission of disordered 1D photonic structures
A better understanding of the optical properties of random photonic
structures is beneficial for many applications, such as random lasing, optical
imaging and photovoltaics. Here we investigated the light transmission
properties of disordered photonic structures in which the high refractive index
layers are aggregated in clusters. We sorted the size of the clusters from a
power law distribution tuning the exponent a of the distribution function. The
sorted high refractive layer clusters are randomly distributed within the low
refractive index layers. We studied the total light transmission, within the
photonic band gap of the corresponding periodic crystal, as a function of the
exponent in the distribution. We observed that, for a within the interval
[0,3.5], the trend can be fitted with a sigmoidal function.Comment: 9 pages, 7 Figures, 1 Tabl
New Betweenness Centrality Node Attack Strategies for Real-World Complex Weighted Networks
In this work, we introduce a new node attack strategy removing nodes with the highest conditional weighted betweenness centrality (CondWBet), which combines the weighted structure of the network and the node's conditional betweenness. We compare its efficacy with well-known attack strategies from literature over five real-world complex weighted networks. We use the network weighted efficiency (WEFF) like a measure encompassing the weighted structure of the network, in addition to the commonly used binary-topological measure, i.e., the largest connected cluster (LCC). We find that if the measure is WEFF, the CondWBet strategy is the best to decrease WEFF in 3 out of 5 cases. Further, CondWBet is the most effective strategy to reduce WEFF at the beginning of the removal process, whereas the Strength that removes nodes with the highest sum of the link weights first shows the highest efficacy in the final phase of the removal process when the network is broken into many small clusters. These last outcomes would suggest that a better attacking in weighted networks strategy could be a combination of the CondWBet and Strength strategies
Transmission of Light in Crystals with different homogeneity: Using Shannon Index in Photonic Media
Light transmission in inhomogeneous photonic media is strongly influenced by
the distribution of the diffractive elements in the medium. Here it is shown
theoretically that, in a pillar photonic crystal structure, light transmission
and homogeneity of the pillar distribution are correlated by a simple linear
law once the grade of homogeneity of the photonic structure is measured by the
Shannon index, widely employed in statistics, ecology and information entropy.
The statistical analysis shows that the transmission of light in such media
depends linearly from their homogeneity: the more is homogeneous the structure,
the more is the light transmitted. With the found linear relationship it is
possible to predict the transmission of light in random photonic structures.
The result can be useful for the study of electron transport in solids, since
the similarity with light in photonic media, but also for the engineering of
scattering layers for the entrapping of light to be coupled with photovoltaic
devices.Comment: 15 pages, 5 figure
Estinzione secondaria in reti trofiche
L' estinzione secondaria è un fenomeno di grande interesse nel campo della ricerca ecologica. Capire come un singolo evento di estinzione influenzi la stabilità della rete trofica è fondamentale nella comprensione dei meccanismi che governano la stabilità di questi sistemi complessi. In questo lavoro di tesi di dottorato sono stati analizzati i metodi capaci di prevedere l'estinzione secondaria in reti trofiche, in particolare traslando l'attenzione dalle reti qualitative verso nuove metodologie di previsione ad hoc per le reti quantitative
Role of the annealing parameters on the resistance of indium tin oxide nanocrystalline films
The optical and electrical properties of films made of nanoparticles of
indium tin oxide (ITO) are widely studied because of the significance of this
material for transparent electrodes, smart windows, and nonlinear optics
components. In this work, a systematic study of the resistance in ITO
nanocrystalline films, as a function of post fabrication parameters, such as
the temperature and time of annealing, has been performed. A tunability of the
resistance with the annealing parameters, in a range of three orders of
magnitude, has been demonstrated.Comment: 8 pages, 4 figure
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