A Physical Model for Inception and Propagation of Upward Lightning Leader from a 1200 kV AC Power Transmission Line

UHV power transmission lines have high probability of shielding failure due to their higher height, larger exposure area and high operating voltage. Lightning upward leader inception and propagation is an integral part of lightning shielding failure analysis and need to be studied in detail. In this paper a model for lightning attachment has been proposed based on the present knowledge of lightning physics. Leader inception is modeled based on the corona charge present near the conductor region and the propagation model is based on the correlation between the lightning induced voltage on the conductor and the drop along the upward leader channel. The inception model developed is compared with previous inception models and the results obtained using the present and previous models are comparable. Lightning striking distances (final jump) for various return stroke current were computed for different conductor heights. The computed striking distance values showed good correlation with the values calculated using the equation proposed by the IEEE working group for the applicable conductor heights of up to 8 m. The model is applied to a 1200 kV AC power transmission line and inception of the upward leader is analyzed for this configuration.

Dynamics of history-dependent epidemics in temporal networks

The structural properties of temporal networks often influence the dynamical processes that occur on these networks, e.g., bursty interaction patterns have been shown to slow down epidemics. In this paper, we investigate the effect of link lifetimes on the spread of history-dependent epidemics. We formulate an analytically tractable activity-driven temporal network model that explicitly incorporates link lifetimes. For Markovian link lifetimes, we use mean-field analysis for computing the epidemic threshold, while the effect of non-Markovian link lifetimes is studied using simulations. Furthermore, we also study the effect of negative correlation between the number of links spawned by an individual and the lifetimes of those links. Such negative correlations may arise due to the finite cognitive capacity of the individuals. Our investigations reveal that heavy-tailed link lifetimes slow down the epidemic, while negative correlations can reduce epidemic prevalence. We believe that our results help shed light on the role of link lifetimes in modulating diffusion processes on temporal networks.

Accelerating Information Diffusion in Social Networks Under the Susceptible-Infected-Susceptible Epidemic Model

Standard Susceptible-Infected-Susceptible (SIS) epidemic models assume that a message spreads from the infected to the susceptible nodes due to only susceptible-infected epidemic contact. We modify the standard SIS epidemic model to include direct recruitment of susceptible individuals to the infected class at a constant rate (independent of epidemic contacts), to accelerate information spreading in a social network. Such recruitment can be carried out by placing advertisements in the media. We provide a closed form analytical solution for system evolution in the proposed model and use it to study campaigning in two different scenarios. In the first, the net cost function is a linear combination of the reward due to extent of information diffusion and the cost due to application of control. In the second, the campaign budget is fixed. Results reveal the effectiveness of the proposed system in accelerating and improving the extent of information diffusion. Our work is useful for devising effective strategies for product marketing and political/social-awareness/crowd-funding campaigns that target individuals in a social network.

QEP Based Solution for Power Allocation in Amplify and Forward Networks

The problem of cooperative beamforming for maximizing the achievable data rate of an energy constrained two-hop amplify-and-forward (AF) network is considered. Assuming perfect channel state information (CSI) of all the nodes, we evaluate the optimal scaling factor for the relay nodes. Along with individual power constraint on each of the relay nodes, we consider a weighted sum power constraint. The proposed iterative algorithm initially solves a set of relaxed problems with weighted sum power constraint and then updates the solution to accommodate individual constraints. These relaxed problems in turn are solved using a sequence of Quadratic Eigenvalue Problems (QEP). The key contribution of this letter is the generalization of cooperative beamforming to incorporate both the individual and weighted sum constraint. Furthermore, we have proposed a novel algorithm based on Quadratic Eigenvalue Problem (QEP) and discussed its convergence.

Secure Communication in Amplify-and-Forward Networks with Multiple Eavesdroppers: Decoding with SNR Thresholds

The problem of secure unicast communication over a two hop Amplify-and-Forward wireless relay network with multiple eavesdroppers is considered. Assuming that a receiver (destination or eavesdropper) can decode a message only if the received SNR is above a predefined threshold, we consider this problem in two scenarios. In the first scenario, we maximize the SNR at the legitimate destination, subject to the condition that the received SNR at each eavesdropper is below the target threshold. Due to the non-convex nature of the objective function and eavesdroppers' constraints, we transform variables and obtain a quadratically constrained quadratic program (QCQP) with convex constraints, which can be solved efficiently. When the constraints are not convex, we consider a semidefinite relaxation (SDR) to obtain computationally efficient approximate solution. In the second scenario, we minimize the total power consumed by all relay nodes, subject to the condition that the received SNR at the legitimate destination is above the threshold and at every eavesdropper, it is below the corresponding threshold. We propose a semidefinite relaxation of the problem in this scenario and also provide an analytical lower bound.

Continuum in the X-Z-Y Weak Bonds: Z= Main Group Elements

The Continuum in the variation of the X-Z bond length change from blue-shifting to red-shifting through zero-shifting in the X-Z---Y complex is inevitable. This has been analyzed by ab-initio molecular orbital calculations using Z= Hydrogen, Halogens, Chalcogens, and Pnicogens as prototypical examples. Our analysis revealed that, the competition between negative hyperconjugation within the donor (X-Z) molecule and Charge Transfer (CT) from the acceptor (Y) molecule is the primary reason for the X-Z bond length change. Here, we report that, the proper tuning of X-and Y-group for a particular Z-can change the blue-shifting nature of X-Z bond to zero-shifting and further to red-shifting. This observation led to the proposal of a continuum in the variation of the X-Z bond length during the formation of X-Z---Y complex. The varying number of orbitals and electrons available around the Z-atom differentiates various classes of weak interactions and leads to interactions dramatically different from the H-Bond. Our explanations based on the model of anti-bonding orbitals can be transferred from one class of weak interactions to another. We further take the idea of continuum to the nature of chemical bonding in general. (C) 2015 Wiley Periodicals, Inc.

Quasi-geostrophic dynamics in the presence of moisture gradients

The derivation of a quasi-geostrophic system from the rotating shallow-water equations on a midlatitude -plane coupled with moisture is presented. Condensation is prescribed to occur whenever the moisture at a point exceeds a prescribed saturation value. It is seen that a slow condensation time-scale is required to obtain a consistent set of equations at leading order. Further, since the advecting wind fields are geostrophic, changes in moisture (and hence precipitation) occur only via non-divergent mechanisms. Following observations, a saturation profile with gradients in the zonal and meridional directions is prescribed. A purely meridional gradient has the effect of slowing down the dry Rossby waves, through a reduction in the equivalent gradient' of the background potential vorticity. A large-scale unstable moist mode results on the inclusion of a zonal gradient by itself, or in conjunction with a meridional moisture gradient. For gradients that are are representative of the atmosphere, the most unstable moist mode propagates zonally in the direction of increasing moisture, matures over an intraseasonal time-scale and has small phase speed.

Experimental solubilities of two lipid derivatives in supercritical carbon dioxide and new correlations based on activity coefficient models

The solubilities of two lipid derivatives, geranyl butyrate and 10-undecen-1-ol, in SCCO2 (supercritical carbon dioxide) were measured at different operating conditions of temperature (308.15 to 333.15 K) and pressure (10 to 18 MPa). The solubilities (in mole fraction) ranged from 2.1 x 10(-3) to 23.2 x 10(-3) for geranyl butyrate and 2.2 x 10(-3) to 25.0 x 10(-3) for 10-undecen-1-ol, respectively. The solubility data showed a retrograde behavior in the pressure and temperature range investigated. Various combinations of association and solution theory along with different activity coefficient models were developed. The experimental data for the solubilities of 21 liquid solutes along with geranyl butyrate and 10-undecen-1-ol were correlated using both the newly derived models and the existing models. The average deviation of the correlation of the new models was below 15%.

Campaigning in Heterogeneous Social Networks: Optimal Control of SI Information Epidemics

We study the optimal control problem of maximizing the spread of an information epidemic on a social network. Information propagation is modeled as a susceptible-infected (SI) process, and the campaign budget is fixed. Direct recruitment and word-of-mouth incentives are the two strategies to accelerate information spreading (controls). We allow for multiple controls depending on the degree of the nodes/individuals. The solution optimally allocates the scarce resource over the campaign duration and the degree class groups. We study the impact of the degree distribution of the network on the controls and present results for Erdos-Renyi and scale-free networks. Results show that more resource is allocated to high-degree nodes in the case of scale-free networks, but medium-degree nodes in the case of Erdos-Renyi networks. We study the effects of various model parameters on the optimal strategy and quantify the improvement offered by the optimal strategy over the static and bang-bang control strategies. The effect of the time-varying spreading rate on the controls is explored as the interest level of the population in the subject of the campaign may change over time. We show the existence of a solution to the formulated optimal control problem, which has nonlinear isoperimetric constraints, using novel techniques that is general and can be used in other similar optimal control problems. This work may be of interest to political, social awareness, or crowdfunding campaigners and product marketing managers, and with some modifications may be used for mitigating biological epidemics.

Cost effective campaigning in social networks

Campaigners are increasingly using online social networking platforms for promoting products, ideas and information. A popular method of promoting a product or even an idea is incentivizing individuals to evangelize the idea vigorously by providing them with referral rewards in the form of discounts, cash backs, or social recognition. Due to budget constraints on scarce resources such as money and manpower, it may not be possible to provide incentives for the entire population, and hence incentives need to be allocated judiciously to appropriate individuals for ensuring the highest possible outreach size. We aim to do the same by formulating and solving an optimization problem using percolation theory. In particular, we compute the set of individuals that are provided incentives for minimizing the expected cost while ensuring a given outreach size. We also solve the problem of computing the set of individuals to be incentivized for maximizing the outreach size for given cost budget. The optimization problem turns out to be non trivial; it involves quantities that need to be computed by numerically solving a fixed point equation. Our primary contribution is, that for a fairly general cost structure, we show that the optimization problems can be solved by solving a simple linear program. We believe that our approach of using percolation theory to formulate an optimization problem is the first of its kind. (C) 2016 Elsevier B.V. All rights reserved.

Social optimum in social groups with give-and-take criterion

We consider a Social Group' of networked nodes, seeking a universe' of segments. Each node has a subset of the universe and access to an expensive resource for downloading data. Nodes can also acquire the universe by exchanging copies of segments among themselves, at low cost, using inter-node links. While exchanges over inter-node links ensure minimum cost, some nodes in the group try to exploit the system. We term such nodes as non-reciprocating nodes' and prohibit such behavior by proposing the give-and-take' criterion, where exchange is allowed if each node has segments unavailable with the other. Under this criterion, we consider the problem of maximizing the number of nodes with the universe at the end of local exchanges. First, we present a randomized algorithm that is shown to be optimal in the asymptotic regime. Then, we present greedy links algorithm, which performs well for most of the scenarios and yields an optimal result when the number of nodes is four. The polygon algorithm is proposed, which yields an optimal result when each of the nodes has a unique segment. After presenting some intuitive algorithms (e.g., greedy incremental algorithm and rarest first algorithm), we compare the performances of all proposed algorithms with the optimal. Copyright (c) 2015 John Wiley & Sons, Ltd.

Experimental Investigations on the Pulsed Power Switch of a HIRA based UWB System

The Ultra Wide Band (UWB) system has been a subject of research in the last few years due to its utility in various high power electromagnetic applications. Due to its simplicity in design and fabrication, the Half Impulse Radiating Antenna (HIRA) based UWB system has attracted many researchers. Effectiveness of a UWB system, in terms of the bandwidth of the radiated pulse depends on the duration of the radiated field which is typically of sub nanosecond regime. This duration in turn depends on the closure time of the switch used in the UWB pulsed power source. This paper presents the work carried out on the pressurised gas switch of a 50 kV pulsed power system of a HIRA based UWB system. The aim of the present work is to establish the relationship between the pulser switch breakdown voltage and gas pressure, rise time and gas pressure as well as the dependency of the Pulse Repetition Rate (PRR) on the switch breakdown voltage.

Electromagnetic Shielding Properties of Nano Carbon Filled Silicone Rubber Composites

Electromagnetic shielding has become important for various electrical systems because of the electromagnetic pollution caused by the large scale use of electronic devices operating at different frequencies and power levels. Traditionally used metallic shields lack flexibility and hence may not be the right choice for certain applications. In such situations, filled polymer composites provide a good alternative for electromagnetic shielding applications. Being polymer based, they are easy to manufacture and can be molded into the required geometry and shape. In this study, the shielding properties of multiwalled carbon nanotubes and carbon nanofibers filled silicone rubber are studied. The conductivity and the shielding effectiveness of the composites were measured at different filler loadings. Both the fillers are able to make the base polymer conducting even at very low filler loadings. The conductivity and the shielding effectiveness improved when the filler loading was above the percolation threshold.

La teología pastoral de Evangelii Gaudium en el proyecto misionero de Francisco

Resumen: Este ensayo teológico comprende y expone el pensamiento pastoral del Papa Francisco, primer obispo de Roma y Papa latinoamericano, elegido desde las periferias del orbe para guiar al Pueblo de Dios en el corazón de la urbe. Francisco es un pastor misionero y un pastoralista lúcido, que ha enseñado teología pastoral y, lo sigue haciendo, de otra forma, desde el ministerio petrino. La exhortación Evangelii gaudium (2013) condensa de una forma orgánica su mirada a la evangelización en la huella de la exhortación Evangelii nuntiandi de Pablo VI (1975) y del Documento Conclusivo de Aparecida del Episcopado latinoamericano y caribeño (2007). La novedad de su pontificado reformador y misionero hunde sus raíces en la figura singular del jesuita argentino Jorge Mario Bergoglio; en su arraigo en la Iglesia latinoamericana y en el proyecto misionero de Aparecida; y en la incipiente pero promisoria teología argentina postconciliar. El autor hace un pormenorizado estudio sistemático y contextualizado de la exhortación La alegría del Evangelio desde el propio documento y en relación a otros textos de Jorge Bergoglio y, ahora, del Papa Francisco. Articula su discurso en dos momentos mostrando sus interrelaciones. El primero, breve, presenta al sucesor de Pedro como un icono de la fisonomía regional y la reflexión pastoral de la Iglesia latinoamericana. El segundo analiza nueve claves de la Evangelii gaudium: la alegría de evangelizar, síntesis de la mística misionera; la figura de la Iglesia centrada en la misión; la influencia del proyecto misionero de Aparecida; la conversión misionera para la reforma eclesial desde el Concilio Vaticano II; la Iglesia, Pueblo de Dios y Madre de los pueblos, como sujeto de la misión; la fuerza evangelizadora de la piedad católica popular; la revolución de la ternura comunicada en el Evangelio de la misericordia; la dimensión social del Evangelio y de la evangelización; la opción por los pobres desde el corazón de Dios.

“Evangelización con espíritu” (EG 261) : la unidad de la teología, la espiritualidad y la pastoral al servicio del anuncio del evangelio: una lectura de la exhortación pastoral Evangelii Gaudium desde la Teología Espiritual

Resumen: Uno de los grandes “maestros en teología” en la Argentina de los últimos tiempos, Lucio Gera (+07.08.2012), cuyo segundo aniversario de fallecido honramos en este número de la revista Teología, hablaba de la ineludible exigencia posconciliar de integrar teología, espiritualidad y pastoral. El capítulo V de Evangelii gaudium, “Evangelizadores con Espíritu” (cf. EG 259ss), se ubica especialmente en este horizonte de convicciones porque tiene un inconfundible contenido teológico, un marcado acento espiritual y una clara orientación y lenguaje pastoral, pero sobre todo en razón de expresar una íntima compenetración entre estas tres dimensiones. En este artículo, que reelabora y amplía una presentación oral en la Jornada Evangelii gaudium, organizada por la Facultad de Teología de la UCA el pasado 5 de junio, se asume el vigor de la propuesta de una “evangelización con espíritu” (EG 261) y se reflexiona, en diálogo con nuestra iglesia local, sobre cuatro aspectos relacionados con ella: 1. una teología de la “evangelización con espíritu”, es decir, “con Espíritu Santo”; 2. una espiritualidad contemplativa: amar la Palabra y gustar ser pueblo; 3. el estilo pastoral mariano de la evangelización; y 4. la danza de la teología, la espiritualidad y la pastoral al servicio de la alegría de evangelizar.