Error and Attack Tolerance of Layered Complex Networks

Many complex systems may be described not by one, but by a number of complex networks mapped one on the other in a multilayer structure. The interactions and dependencies between these layers cause that what is true for a distinct single layer does not necessarily reflect well the state of the entire system. In this paper we study the robustness of three real-life examples of two-layer complex systems that come from the fields of communication (the Internet), transportation (the European railway system) and biology (the human brain). In order to cover the whole range of features specific to these systems, we focus on two extreme policies of system's response to failures, no rerouting and full rerouting. Our main finding is that multilayer systems are much more vulnerable to errors and intentional attacks than they seem to be from a single layer perspective.Comment: 5 pages, 3 figure

Large-eddy simulation of pulverized coal jet flame - Effect of oxygen concentration on NO<inf>x</inf> formation

Large-eddy simulation is applied to a laboratory-scale open-type pulverized coal flame generated by a triple stream burner, and the NO production and reduction in oxy- fuel condition are investigated for the first time. Pulverized Cerrejon coal which is classified as bituminous coal is used as a fuel. The results show that regardless of the equivalence ratio, as the O2 concentration increases from 21% to 40%, O2 consumption becomes marked because gas temperature rises and oxidation reaction is enhanced by the higher concentration of O2. Also, NO is formed rapidly due to the oxidation reaction of nitrogen from volatile matter of coal, and its concentration reaches a few hundred ppm further downstream. After the rapid formation, in the case of equivalence ratio larger than unity, NO decreases, because the reducing atmosphere becomes dominant due to the lack of O2. The trend becomes signi cant as the O2 concentration in the carrier gas increases from 21% to 40%. In the case of equivalence ratio less than unity, on the other hand, NO does not decrease clearly, because the oxidizing atmosphere contributes to the further formation of NO. Present study shows the usefulness of the large-eddy simulations for predicting the characteristics of pulverized coal flames.This research was partially supported by \Strategic Programs for Innovative Research (SPIRE) - Field No. 4: Industrial Innovations" from MEXT (Ministry of Education, Culture, Sports, Science, and Technology) using computational resources of the HPCI sys- tem provided by RIKEN Advanced Institute for Computational Science through the HPCI System Research Project (Project ID: hp120294, hp130018). See also (http:// www. uid.me.kyoto-u.ac.jp/members/kurose/hpci.html). Experiments at Cambridge were supported by EPSRC, within the Oxycap Oxyfuels Grant EP/G062153/1.This is the final version of the article. It was first published by Elsevier at http://www.sciencedirect.com/science/article/pii/S001623611401064

Evolution of Surface Density Function in an Open Turbulent Jet Spray Flame

A three-dimensional Direct Numerical Simulation of an open turbulent jet spray flame representing a laboratory-scale burner configuration has been used to analyse the statistical behaviours of the magnitude of reaction progress variable gradient |∇c| [alternatively known as the Surface Density Function (SDF)] and the strain rates, which affect its evolution. The flame has been found to exhibit fuel-lean combustion close to the jet exit, but fuel-rich conditions have been obtained further downstream due to the evaporation of fuel droplets, which leads to the reduction in the mean value of the SDF in the downstream direction. This change in mixture composition in the axial direction has implications on the statistical behaviours of the SDF and the strain rates affecting its evolution. The mean value of dilatation rate remains positive, whereas the mean normal strain rate assumes positive values where the effects of heat release are strong but becomes negative towards both unburned and burned gas sides. The mean values of dilatation rate, normal strain rate and tangential strain rate decrease downstream of the jet exit. However, the mean behaviours of displacement speed and its components do not change significantly away from the jet exit. The mean values of normal strain rate arising from flame propagation remain positive and thus act to thicken the flame. The mean tangential strain rate due to flame propagation (alternatively the curvature stretch rate) remains negative throughout the flame at all axial locations investigated. The mean effective normal strain rate assumes positive values throughout the flame and it increases in the downstream direction for the present case, which is consistent with the reduction in the peak mean value of the SDF in the axial direction. The mean effective tangential strain rate (alternatively stretch rate) assumes negative values throughout the flame at all axial locations

Controlling Window Protocols for Time-Constrained Communication in a Multiple Access Environment

For many time-constrained communication applications, such as packetized voice, a critical performance measure is the percentage of messages which are transmitted within a given amount of time after their arrival at a sending station. We examine the use of a group random access protocol based on time windows for achieving time-constrained communication in a multiple access environment. First, we formulate a policy for controlling protocol operation in order to minimize the percentage of messages with waiting times greater than some given bound. A semi-Markov decision model is then developed for protocol operation and three of the four optimal control elements of this policy are then determined. Although the semi-Markov decision model can also be used to obtain performance results, the procedure is too computationally expensive to be of practical use. Thus, an alternate performance model based on a centralized queueing system with impatient customers is developed. Protocol performance under the optimal elements of the control policy shows significant improvements over cases in which the protocol is not controlled in this manner. Simulation results are also presented to corroborate the analytic results

Priority diffusion model in lattices and complex networks

We introduce a model for diffusion of two classes of particles ($A$ and $B$) with priority: where both species are present in the same site the motion of $A$'s takes precedence over that of $B$'s. This describes realistic situations in wireless and communication networks. In regular lattices the diffusion of the two species is normal but the $B$ particles are significantly slower, due to the presence of the $A$ particles. From the fraction of sites where the $B$ particles can move freely, which we compute analytically, we derive the diffusion coefficients of the two species. In heterogeneous networks the fraction of sites where $B$ is free decreases exponentially with the degree of the sites. This, coupled with accumulation of particles in high-degree nodes leads to trapping of the low priority particles in scale-free networks.Comment: 5 pages, 3 figure

Supporting User-Defined Functions on Uncertain Data

Uncertain data management has become crucial in many sensing and scientific applications. As user-defined functions (UDFs) become widely used in these applications, an important task is to capture result uncertainty for queries that evaluate UDFs on uncertain data. In this work, we provide a general framework for supporting UDFs on uncertain data. Specifically, we propose a learning approach based on Gaussian processes (GPs) to compute approximate output distributions of a UDF when evaluated on uncertain input, with guaranteed error bounds. We also devise an online algorithm to compute such output distributions, which employs a suite of optimizations to improve accuracy and performance. Our evaluation using both real-world and synthetic functions shows that our proposed GP approach can outperform the state-of-the-art sampling approach with up to two orders of magnitude improvement for a variety of UDFs. 1

Variability in organ-specific EGFR mutational spectra in tumour epithelium and stroma may be the biological basis for differential responses to tyrosine kinase inhibitors

Organ-specific differences in epidermal growth factor receptor (EGFR) mutational spectra and frequencies were found in lung cancer and sporadic and BRCA1/2-related breast cancers. Additionally, we found a high frequency of EGFR mutations in the tumour stroma of these invasive breast carcinomas. Those organ-specific mutational spectra and potential targets in the cancer-associated stroma might influence the efficacy of TKI therapy

Flame self-interaction during turbulent boundary layer flashback of hydrogen-rich premixed combustion

A three-dimensional direct numerical simulation database of turbulent boundary layer flashback of a hydrogen-rich premixed flame with an equivalence ratio of 1.5 has been analyzed to investigate flame self-interaction (FSI) events. The nonreacting turbulence characteristics of the channel flow are representative of the friction-velocity-based Reynolds number, Reτ=120. A skeletal chemical mechanism with nine species and twenty reactions is employed for the representation of hydrogen-air combustion. Three definitions of the reaction progress variable, c, based on the mass fractions of H2, O2, and H2O, have been considered to define the progress variable. It is found that the FSI events predominantly occur close to the burned gas side for all definitions of c at all the wall normal distances. No FSI events adjacent to the wall have been identified for the c definition based on O2 and H2O mass fractions, whereas FSI events occur for c based on H2 in the near-wall region. In the regions further away from the wall, all c definitions show that tunnel formation and tunnel closure type FSI events remain predominant, which is consistent with the earlier findings by Griffiths et al. [Proc. Combust. Inst. 35, 1341 (2015)1540-748910.1016/j.proci.2014.08.003] involving hydrogen-air premixed flame under shear flow conditions. In this work for c based on H2 mass fraction, unburned gas pockets have also been identified at all wall normal distances and are a consequence of the hydrogen-rich nature of the flame. The reason for the variations in topologies with the change in the definition of c based on different species and wall normal distance is a consequence of several factors, including the changes in the level of turbulence within the turbulent boundary layer, heat loss to the isothermal wall in the near-wall region, and the differential diffusion induced by the nonunity Lewis number. The results from the current analysis show that the turbulent boundary layer and heat loss at the wall play important roles in determining the FSI topologies. The differences in the qualitative nature and distributions of the FSI events between different definitions of c have important implications on the possible extension of flame-surface-based modeling methodology for hydrogen-rich flames within turbulent boundary layers