Dynamic Transitions in Small World Networks: Approach to Equilibrium

We study the transition to phase synchronization in a model for the spread of infection defined on a small world network. It was shown (Phys. Rev. Lett. {\bf 86} (2001) 2909) that the transition occurs at a finite degree of disorder $p$, unlike equilibrium models where systems behave as random networks even at infinitesimal $p$ in the infinite size limit. We examine this system under variation of a parameter determining the driving rate, and show that the transition point decreases as we drive the system more slowly. Thus it appears that the transition moves to $p=0$ in the very slow driving limit, just as in the equilibrium case.Comment: 8 pages, 2 figure

A bibliometric analysis of automatic and semi-automatic ontology construction processes

Through a bibliometric analysis, the paper reveals the current state and the global research trend in the areas of automatic ontology construction process (AOCP) and semi-automatic ontology construction process (SOCP) during the period of 2000-2016. Scopus, GoogleScholar, and Scitepress digital library were used to extract the data for analysis. The study revealed that the majority of the works were published in conference proceedings. China was found to be the most contributing country in this area followed by USA, France, and Spain. The University of Karlsruhe contributed the maximum publications in both AOCP and SOCP whereas Peking University contributed largely to AOCP and Jozef StefanInstitute contributed largely only to SOCP. The majority of the researchers were from computer science background but a significant number of researchers were also from other disciplines including engineering and allied operations, library and information science, management and auxiliary services, making this research area truly interdisciplinary

Intermediate states in bivalent ion induced shrinking of polyacrylate coils on surfaces and in solution: Intermediate states in bivalent ion induced shrinking of polyacrylate coils on surfaces and in solution

Specifically binding ions induce the transition of anionic polyacrylate coils from extended conformation to collapsed globules passing through a cascade of intermediate states when solution conditions approach the L-type precipitation threshold. It is the conformation of these intermediate states on surfaces and in solution which is at the focus of this thesis. In comparing the surface and solution conformations of intermediate states, we were able to qualitatively and quantitatively underline the effects of sample history. Two types of quantitative comparisons have been emphasized. In real space, the radius of gyration values of adsorbed molecules have been evaluated incorporating fully the x, y and z axes. These values have been compared with radius of gyration values of the very same sample solution obtained using SLS. In reciprocal space, a novel image processing protocol has been used to generate the 2D form factor curve wherein the correlation maxima have been compared with corresponding maxima obtained for the very same sample solution using small angle scattering techniques like the SANS. The influence of bivalent ions, respectively, Strontium, Lead and Calcium, on the shape of polyacrylate coils is studied. In the last case, temperature has been introduced as a secondary parameter to shed further light on the mechanism by which polyelectrolytebivalent ion complexation takes place. Both scattering and AFM experiments reveal formation of necklace-like structures as intermediates for NaPA-Sr2+ system. Since the mol. wt. of the NaPA coils used was relatively large in this case, adsorption on mica surfaces was strong. Under such conditions, the molecules undergo a z collapse upon flux drying but do not get altered in x and y directions. The ratio Rg(AFM)/Rg(SLS) was found to be in the range 0.7-0.9. The remaining (insignificant) differences in the Rg Abstract ii values arise due to the fact that AFM gives the square root of number averaged mean squared radius of gyration while SLS gives the square root of z-averaged mean squared radius of gyration. The differences in radius of gyration values observed in solution and on surfaces were more prominent for NaPA-Pb2+ system. Again, although both scattering and AFM reveal necklace-like structures as intermediates, the ratio Rg(AFM)/Rg(SLS) was now found to be nearly 0.6. The fact that Rg(AFM) is the square root of number averaged and Rg(SLS) is the square root of z-averaged mean squared radius of gyration, alone cannot explain this low value. Since the mol. wt. of NaPA coils used in this case was quite low, adsorption on mica surfaces was weak. Under such conditions, the molecule does not only undergo a z collapse upon flux drying, but also shrinks in the x and y directions due to capillary forces. Finally, with NaPA-Ca2+ system, the picture did not show a one-to-one correspondence between solution and surface conformations at all. In fact, it showed a one-step-ahead correspondence. As already stated, the coil to globule transition was induced by increasing the equilibration temperature from 15°C to 30°C in this case. SANS could not identify any necklace-like intermediates in solution at the equilibration temperature of 15°C while AFM scans at this temperature showed the beginning of formation of pearls. Likewise, at the equilibration temperature of 30°C, SANS could identify necklace-like intermediates in solution with a large majority of dumbbells while AFM scans at this temperature showed a mix of dumbbells, sausage-like structures and globules. Indeed, we were witnessing an accelerated coil to globule transition on surfaces as compared to the situation in solution resulting in a pre-emption in the formation of intermediate states on surfaces. Since the ratio Rg(AFM)/Rg(SLS) (given the square root of number averaged and the square root of z-averaged mean Abstract iii squared values respectively) at the equilibration temperature of 30°C showed a range of 0.7-0.9 indicating strong adsorption of the relatively high mol. wt. NaPA coil on mica surfaces, our suspect were the substrate-sample interaction forces. The AFM scans were therefore analysed with 2D form factor curves, a better protocol when no assumptions about the shape of adsorbed molecules are made a priori, to trace the effects of sample history. The thesis establishes the general utility of AFM to capture the essential features of a collapsing coil which the very coil exhibits in solution. The shape of the coil on surface and in solution may not be exactly the same, yet reveal the same characteristics. The comparative advantages and disadvantages of salt pre-treated mica surfaces and chemically modified mica surfaces have been brought out. Finally, a definitive new insight is gained as regards the mechanism of coil collapse induced by specifically binding ions. The entropic nature of the process as well as the visualized shape of the collapsing intermediates does not support a mechanism along an electrostatically driven shrinking with linear, rod-like arrays of pearls as intermediates. On a molecular level, it is the liberation of water molecules and Na+ ions which promotes binding of bivalent ions to COO- residues. This binding in turn increases the hydrophobicity of the polyacrylate chains. As a consequence, the chains shrink due to an increased propensity for polymerpolymer contacts (and finally precipitate)

Dynamic Selection of Symmetric Key Cryptographic Algorithms for Securing Data Based on Various Parameters

Most of the information is in the form of electronic data. A lot of electronic data exchanged takes place through computer applications. Therefore information exchange through these applications needs to be secure. Different cryptographic algorithms are usually used to address these security concerns. However, along with security there are other factors that need to be considered for practical implementation of different cryptographic algorithms like implementation cost and performance. This paper provides comparative analysis of time taken for encryption by seven symmetric key cryptographic algorithms (AES, DES, Triple DES, RC2, Skipjack, Blowfish and RC4) with variation of parameters like different data types, data density, data size and key sizes.Comment: 8 pages, 4 figures, Fifth International Conference on Communications Security & Information Assurance (CSIA 2014) May 24~25, 2014, Delhi, Indi

Emergence of Power Law in a Market with Mixed Models

We investigate the problem of wealth distribution from the viewpoint of asset exchange. Robust nature of Pareto's law across economies, ideologies and nations suggests that this could be an outcome of trading strategies. However, the simple asset exchange models fail to reproduce this feature. A yardsale(YS) model in which amount put on the bet is a fraction of minimum of the two players leads to condensation of wealth in hands of some agent while theft and fraud(TF) model in which the amount to be exchanged is a fraction of loser's wealth leads to an exponential distribution of wealth. We show that if we allow few agents to follow a different model than others, {\it i.e.} there are some agents following TF model while rest follow YS model, it leads to distribution with power law tails. Similar effect is observed when one carries out transactions for a fraction of one's wealth using TF model and for the rest YS model is used. We also observe a power law tail in wealth distribution if we allow the agents to follow either of the models with some probability.Comment: 18 pages and 9 figure

Breast Cancer Detection on Automated 3D Ultrasound with Co-localized 3D X-ray.

X-ray mammography is the gold standard for detecting breast cancer while B-mode ultrasound is employed as its diagnostic complement. This dissertation aimed at acquiring a high quality, high-resolution 3D automated ultrasound image of the entire breast at current diagnostic frequencies, in the same geometry as mammography and its 3D equivalent, digital breast tomosynthesis, and to extend and help test its utility with co-localization. The first objective of this work was to engineer solutions to overcome some challenges inherent in acquiring complete automated ultrasound of the breast and minimizing patient motion during scans. Automated whole-breast ultrasound that can be registered to X-Ray imaging eliminates the uncertainty associated with hand-held ultrasound. More than 170 subjects were imaged using superior coupling agents tested during the course of this study. At least one radiologist rated the usefulness of X-Ray and ultrasound co-localization as high in the majority of our study cases. The second objective was to accurately register tomosynthesis image volumes of the breast, making the detection of tissue growth and deformation over time a realistic possibility. It was found for the first time to our knowledge that whole breast digital tomosynthesis image volumes can be spatially registered with an error tolerance of 2 mm, which is 10% of the average size of cancers in a screening population. The third and final objective involved the registration and fusion of 3D ultrasound image volumes acquired from opposite sides of the breast in the mammographic geometry, a novel technique that improves the volumetric resolution of high frequency ultrasound but poses unique problems. To improve the accuracy and speed of registration, direction-dependent artifacts should be eliminated. Further, it is necessary to identify other regions, usually at greater depths, that contain little or misleading information. Machine learning, principal component analysis and speckle reducing anisotropic diffusion were tested in this context. We showed that machine learning classifiers can identify regions of corrupted data accurately on a custom breast-mimicking phantom, and also that they can identify specific artifacts in-vivo. Initial registrations of phantom image sets with many regions of artifacts removed provided robust results as compared to the original datasets.Ph.D.Biomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78947/1/sumedha_1.pd

Power-law persistence characterizes traveling waves in coupled circle maps with repulsive coupling

We study persistence in coupled circle maps with repulsive (inhibitory) coupling, and find that it offers an effective way to characterize the synchronous, traveling wave and spatiotemporally chaotic states of the system. In the traveling wave state, persistence decays as a power law and, in contrast to earlier observations in dynamical systems, this power-law scaling does not occur at the transition point alone, but over the entire dynamical phase (with the same exponent). We give a cellular automata model displaying the qualitative features of the traveling wave regime and provide an argument based on the theory of Motzkin numbers in combinatorics to explain the observed scaling

Synchronization in a network of model neurons

We study the spatiotemporal dynamics of a network of coupled chaotic maps modelling neuronal activity, under variation of coupling strength ε and degree of randomness in coupling p. We find that at high coupling strengths (ε > εfixed) the unstable saddle point solution of the local chaotic maps gets stabilized. The range of coupling where this spatiotemporal fixed point gains stability is unchanged in the presence of randomness in the connections, namely εfixed is invariant under changes in p. As coupling gets weaker (ε < εfixed), the spatiotemporal fixed point loses stability, and one obtains chaos. In this regime, when the coupling connections are completely regular (p=0), the network becomes spatiotemporally chaotic. Interestingly however, in the presence of random links (p > 0) one obtains spatial synchronization in the network. We find that this range of synchronized chaos increases exponentially with the fraction of random links in the network. Further, in the space of fixed coupling strengths, the synchronization transition occurs at a finite value of p, a scenario quite distinct from the many examples of synchronization transitions at p→0. Further we show that the synchronization here is robust in the presence of parametric noise, namely in a network of nonidentical neuronal maps. Finally we check the generality of our observations in networks of neurons displaying both spiking and bursting dynamics