Formation of Modularity in a Model of Evolving Networks

Modularity structures are common in various social and biological networks. However, its dynamical origin remains an open question. In this work, we set up a dynamical model describing the evolution of a social network. Based on the observations of real social networks, we introduced a link-creating/deleting strategy according to the local dynamics in the model. Thus the coevolution of dynamics and topology naturally determines the network properties. It is found that for a small coupling strength, the networked system cannot reach any synchronization and the network topology is homogeneous. Interestingly, when the coupling strength is large enough, the networked system spontaneously forms communities with different dynamical states. Meanwhile, the network topology becomes heterogeneous with modular structures. It is further shown that in a certain parameter regime, both the degree and the community size in the formed network follow a power-law distribution, and the networks are found to be assortative. These results are consistent with the characteristics of many empirical networks, and are helpful to understand the mechanism of formation of modularity in complex networks.Comment: 6 pages, 4 figur

Interdiffused AlGaAs-GaAs quantum well for improved electroabsorptive modulation

This is a theoretical study of the effects of two asgrown structural parameters on the modulation properties of Al xGa 1-xAs-GaAs quantum wells (QW's), which are the Al concentration in barrier and the thickness of the well layer serving as initial conditions before interdiffusion. The results show that, with a larger Al concentration and a wider well width, the range of interdiffusion for an enhanced electroabsorption (EA) change increases with both of these parameters, while insertion loss increases with the former and decreases with the latter. However, the increase in loss is lower than that of the rectangular QW for the same magnitude of absorption change. The range of a tunable absorption-peak wavelength produced by interdiffussion increases with increasing Al concentration and decreases with increasing well width. Moreover, in a moderately interdiffused QW, the required bias reduces for the same level of EA modulation. For the best device operation, interdiffused QW's with the Al concentration between 0.3 and 0.4 and well width between 10 and 12 nm are must suitable for developing a general-purpose electroabsorptive modulator. When applied in high-speed modulators, the EA of a wide and shallow QW active-region structure can be further enhanced by the use of corresponding interdiffusion.published_or_final_versio

Electro-absorptive properties of interdiffused InGaAsP/InP quantum wells

The effects of Group III and Group V interdiffusions with a varied as-grown well width and P concentration in the quaternary InGaAsP quantum well material have been theoretically studied. Interesting features of multiple mini-well profiles, generated by interdiffusion induced compressive and tensile strains, have been obtained and varying envelope overlapping of the electron-hole wave functions has been observed. The results show that the interdiffusion of the Group III elements with a well width of 10 nm offers a wide adjustability of the operation wavelength, enhances Stark shift, and reduces absorption loss, although they bear the shortcomings of low electro-absorption and contrast ratio. Several methods are proposed here to recover the contrast ratio with a maximum improvement of 66%. For the Group V interdiffusion of a 10-nm-wide as-grown well, a low absorption loss and a large Stark shift will result, while that of a narrowed well can widen the band-edge wavelength adjustability with a large electro-absorption. These results are important for the development of electro-absorptive InGaAsP/InP diffused quantum well modulators. © 1997 American Institute of Physics.published_or_final_versio

Improved performance of vertical-cavity modulator through the use of diffused quantum wells

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The applications of an interdiffused quantum well in a normally on electroabsorptive fabry-perot reflection modulator

A Fabry-Perot reflection-type modulator which uses interdiffused AlGaAs/GaAs quantum wells as the active cavity material has been studied and optimized theoretically. An asymmetric Bragg reflector structure (modeled by transfer matrices), with a doped depletion layer in the heterostructure, has been considered. This is the first study to model such a material system in this type of modulator, and the results show improvement in modulation property over its as-grown rectangular quantum-well modulator. In particular, the change of reflectance in the diffused quantum-well modulator is almost 0.6 to 0.7, which is higher than that of the typically available values (∼0.5 to 0.6), while the OFF-state on-resonance reflectance is almost close to zero. The operation voltage is also reduced by more than half as the interdiffusion becomes extensive. The finesse of the more extensively diffused quantum well also increases. Both of these features contribute to an improvement of the change of reflectance in the modulator. The operation wavelengths can be adjusted over a range of 100 nm. However, the absorption coefficient change of the diffused quantum well increases only when there is a small amount of interdiffusion.published_or_final_versio

Scene Graph Generation by Iterative Message Passing

Understanding a visual scene goes beyond recognizing individual objects in isolation. Relationships between objects also constitute rich semantic information about the scene. In this work, we explicitly model the objects and their relationships using scene graphs, a visually-grounded graphical structure of an image. We propose a novel end-to-end model that generates such structured scene representation from an input image. The model solves the scene graph inference problem using standard RNNs and learns to iteratively improves its predictions via message passing. Our joint inference model can take advantage of contextual cues to make better predictions on objects and their relationships. The experiments show that our model significantly outperforms previous methods for generating scene graphs using Visual Genome dataset and inferring support relations with NYU Depth v2 dataset.Comment: CVPR 201

Electrooptic and electroabsorptive modulation properties in interdiffusion-modified AlGaAs-GaAs quantum wells

The electric field induced refractive index change and absorption coefficient change in TE polarization are analyzed at room temperature for several interdiffusion modified Al0.3Ga0.7As-GaAs quantum-well structures. The results show that for the small and medium interdiffusion lengths with fields of 100 and 50 kV/cm, respectively, improved chirping and electroabsorption can be obtained. Further, in a selected set of interdiffusion lengths and fields, the material can be used for an electroabsorption modulator with reduced chirping in a wide range of operation wavelengths (758-874 nm).published_or_final_versio

Polarization-insensitive electroabsorptive modulation using interdiffused InGaAs(P)-InP quantum wells

This is a theoretical study to demonstrate the use of interdiffusion in the realization of polarization insensitivity at the band-edge. Two InGaAs-InP quantum well as-grown structures have been investigated: one with lattice-matched condition and the other with small as-grown tensile strain (0.15%). The interdiffusion is considered to take place on the Group V (As and P) sublattice only. As a result, a tensile strain is produced which merges the heavy- and light-hole states in order to achieve polarization insensitivity. Criteria to develop polarization-insensitive quantum wells (QW's) using interdiffusion are presented here. When the two-phase interdiffusion mechanism is modeled, the results show that the well barrier interfaces of the QW maintain an abrupt profile while the well width remains constant after interdiffusion. The two interdiffused QW structures considered here can produce polarization insensitive electroabsorption at operation wavelengths around 1.55 μm. The one with lattice-matched condition is particularly attractive since it only requires an easy (high-yield) fabrication process with a simple postprocessing thermal annealing to achieve polarization insensitivity.published_or_final_versio

Electro -absorptive and electro -optic quantum well modulators using surface acoustic wave

The characteristics of Al0.3Ga0.7As/GaAs QW acousto-absorption and acousto-optic modulators using the interaction between Surface Acoustic Wave (SAW) and quantum well (QW) optical waveguide structures are analyzed here theoretically. The QW structures are optimized by maximizing the optical confinement of modal field in the active region and the piezoelectric effect of SAW on QWs. The electric field induced by SAW reduces non-uniformly in depth, which limits in the development of high efficiency modulators, especially for devices with a large number of QWs in the active region. We present the results of the analysis of a range of QW SQW modulators using between one and 25 QWs in the active region. For devices with thin active regions, the QW structures are designed so that at the top surface strong SAW effects can be obtained while for the 25 periods structure, the QWs located at a depth of 2/3 SAW wavelength in order to obtain an uniform SAW induced electric field. The results show that the single and five QW devices are suitable for absorptive modulation and optical modulation respectively while the 25-QW modulators can shorten the modulation interaction length and thus increase modulation bandwidth. The effective index change of these devices are at least 10 times larger than the conventional surface acoustic wave devices. These results make the quantum-well modulators more attractive for the development of acousto-optic device applications.published_or_final_versio