733 research outputs found
Dynamic Community Discovery Method Based on Phylogenetic Planted Partition in Temporal Networks
As most of the community discovery methods are researched by static thought, some community discovery algorithms cannot represent the whole dynamic network change process efficiently. This paper proposes a novel dynamic community discovery method (Phylogenetic Planted Partition Model, PPPM) for phylogenetic evolution. Firstly, the time dimension is introduced into the typical migration partition model, and all states are treated as variables, and the observation equation is constructed. Secondly, this paper takes the observation equation of the whole dynamic social network as the constraint between variables and the error function. Then, the quadratic form of the error function is minimized. Thirdly, the LevenbergâMarquardt (LâM) method is used to calculate the gradient of the error function, and the iteration is carried out. Finally, simulation experiments are carried out under the experimental environment of artificial networks and real net-works. The experimental results show that: compared with FaceNet, SBM + MLE, CLBM, and Pi-sCES, the proposed PPPM model improves accuracy by 5% and 3%, respectively. It is proven that the proposed PPPM method is robust, reasonable, and effective. This method can also be applied to the general social networking community discovery field
Framework for Designing 3D Virtual Environments
The process of design and development of virtual environments can be supported by tools and frameworks, to save time in technical aspects and focusing on the content. In this paper we present an
academic framework which provides several levels of abstraction to ease
this work. It includes state-of-the-art components we devised or integrated adopting open-source solutions in order to face specific problems.
Its architecture is modular and customizable, the code is open-source
Disrupting resilient criminal networks through data analysis: The case of sicilian mafia
Compared to other types of social networks, criminal networks present particularly hard challenges, due to their strong resilience to disruption, which poses severe hurdles to LawEnforcement Agencies (LEAs). Herein, we borrow methods and tools from Social Network Analysis (SNA) to (i) unveil the structure and organization of Sicilian Mafia gangs, based on two real-world datasets, and (ii) gain insights as to how to efficiently reduce the Largest Connected Component (LCC) of two networks derived from them. Mafia networks have peculiar features in terms of the links distribution and strength, which makes them very different from other social networks, and extremely robust to exogenous perturbations. Analysts also face difficulties in collecting reliable datasets that accurately describe the gangs' internal structure and their relationships with the external world, which is why earlier studies are largely qualitative, elusive and incomplete. An added value of our work is the generation of two realworld datasets, based on raw data extracted from juridical acts, relating to a Mafia organization that operated in Sicily during the first decade of 2000s. We created two different networks, capturing phone calls and physical meetings, respectively. Our analysis simulated different intervention procedures: (i) arresting one criminal at a time (sequential node removal); and (ii) police raids (node block removal). In both the sequential, and the node block removal intervention procedures, the Betweenness centrality was the most effective strategy in prioritizing the nodes to be removed. For instance, when targeting the top 5% nodes with the largest Betweenness centrality, our simulations suggest a reduction of up to 70% in the size of the LCC. We also identified that, due the peculiar type of interactions in criminal networks (namely, the distribution of the interactions' frequency), no significant differences exist between weighted and unweighted network analysis. Our work has significant practical applications for perturbing the operations of criminal and terrorist networks
Criminal networks analysis in missing data scenarios through graph distances
Data collected in criminal investigations may suffer from issues like: (i) incompleteness, due to the covert nature of criminal organizations; (ii) incorrectness, caused by either unintentional data collection errors or intentional deception by criminals; (iii) inconsistency, when the same information is collected into law enforcement databases multiple times, or in different formats. In this paper we analyze nine real criminal networks of different nature (i.e., Mafia networks, criminal street gangs and terrorist organizations) in order to quantify the impact of incomplete data, and to determine which network type is most affected by it. The networks are firstly pruned using two specific methods: (i) random edge removal, simulating the scenario in which the Law Enforcement Agencies fail to intercept some calls, or to spot sporadic meetings among suspects; (ii) node removal, modeling the situation in which some suspects cannot be intercepted or investigated. Finally we compute spectral distances (i.e., Adjacency, Laplacian and normalized Laplacian Spectral Distances) and matrix distances (i.e., Root Euclidean Distance) between the complete and pruned networks, which we compare using statistical analysis. Our investigation identifies two main features: first, the overall understanding of the criminal networks remains high even with incomplete data on criminal interactions (i.e., when 10% of edges are removed); second, removing even a small fraction of suspects not investigated (i.e., 2% of nodes are removed) may lead to significant misinterpretation of the overall network. Copyright
Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects
We analyze the influence of spatial orientation on the optical response of
hydrogenated silicon quantum wires. The results are relevant for the
interpretation of the optical properties of light emitting porous silicon. We
study (111)-oriented wires and compare the present results with those
previously obtained within the same theoretical framework for (001)-oriented
wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In
analogy with the (001)-oriented wires and at variance with crystalline bulk
silicon, we find that the (111)-oriented wires exhibit a direct gap at whose value is largely enhanced with respect to that found in bulk
silicon because of quantum confinement effects. The imaginary part of the
dielectric function, for the external field polarized in the direction of the
axis of the wires, shows features that, while being qualitatively similar to
those observed for the (001) wires, are not present in the bulk. The main
conclusion which emerges from the present study is that, if wires a few
nanometers large are present in the porous material, they are
optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte
Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves
The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a \blue{dissipative} plasmonic material. Correspondingly, the ESWs transmute from Dyakonov--Tamm surface waves into surface--plasmon--polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results
Analytical Solution for the Deformation of a Cylinder under Tidal Gravitational Forces
Quite a few future high precision space missions for testing Special and
General Relativity will use optical resonators which are used for laser
frequency stabilization. These devices are used for carrying out tests of the
isotropy of light (Michelson-Morley experiment) and of the universality of the
gravitational redshift. As the resonator frequency not only depends on the
speed of light but also on the resonator length, the quality of these
measurements is very sensitive to elastic deformations of the optical resonator
itself. As a consequence, a detailed knowledge about the deformations of the
cavity is necessary. Therefore in this article we investigate the modeling of
optical resonators in a space environment. Usually for simulation issues the
Finite Element Method (FEM) is applied in order to investigate the influence of
disturbances on the resonator measurements. However, for a careful control of
the numerical quality of FEM simulations a comparison with an analytical
solution of a simplified resonator model is beneficial. In this article we
present an analytical solution for the problem of an elastic, isotropic,
homogeneous free-flying cylinder in space under the influence of a tidal
gravitational force. The solution is gained by solving the linear equations of
elasticity for special boundary conditions. The applicability of using FEM
codes for these simulations shall be verified through the comparison of the
analytical solution with the results gained within the FEM code.Comment: 23 pages, 3 figure
Ternary Quarter Wavelength Coatings for Gravitational Wave Detector Mirrors: Design Optimization via Exhaustive Search
Multimaterial optical coatings are a promising viable option to meet the
challenging requirements (in terms of transmittance, absorbance and thermal
noise) of next generation gravitational wave detector mirrors. In this paper we
focus on ternary coatings consisting of quarter-wavelength thick layers, where
a third material (H') is added to the two presently in use, namely Silica (L)
and Titania-doped Tantala (H), featuring higher dielectric contrast (against
Silica), and lower thermal noise (compared to Titania-doped Tantala), but
higher optical losses. We seek the optimal material sequences, featuring
minimal thermal (Brownian) noise under prescribed transmittance and absorbance
constraints, by exhaustive simulation over all possible configurations, for
different values (in a meaningful range) of the optical density and extinction
coefficient of the third material. In all cases studied, the optimal designs
consist of a stack of (H'|L) doublets topped by a stack of (H|L) doublets,
confirming previous heuristic assumptions, and the achievable coating noise
power spectral density reduction factor is \sim 0.5. The robustness of the
found optimal designs against layer thickness deposition errors and
uncertainties and/or fluctuations in the optical losses of the third material
is also investigated. Possible margins for further thermal noise reduction by
layer thickness optimization, and strategies to implement it, are discussed.Comment: (twocolum style) 13 pages, 8 figures, 4 table (updated version 5)
Appearing on Physical Review Researc
Signatures of thermal hysteresis in Tamm-wave propagation
We numerically solved the boundary-value problem for Tamm waves (which may
also be classified as Uller-Zenneck waves here) guided by the planar interface
of a homogeneous isotropic dissipative dielectric (HIDD) material and a
periodically multilayered isotropic dielectric material. The HIDD material was
chosen to be VO which, at optical wavelengths, has a
temperature-dependent refractive index with a hysteresis feature, i.e., the
temperature-dependence of its refractive index varies depending upon whether
the temperature is increasing or decreasing. A numerical code was implemented
to extract solutions of the dispersion equation at a fixed wavelength for both
- and -polarization states over the temperature range [50,80] degrees. A
multitude of Tamm waves of both linear polarization states were found,
demonstrating a clear demarcation of the heating and cooling phases in terms of
wavenumbers and propagation distances. Thereby, the signatures of thermal
hysteresis in Tamm-wave propagation were revealed
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