Bicomponents and the robustness of networks to failure

We study bicomponents in networks, sets of nodes such that each pair in the set is connected by at least two independent paths, so that the failure of no single node in the network can cause them to become disconnected. We show that standard network models predict there to be essentially no small bicomponents in most networks, but there may be a giant bicomponent, whose presence coincides with the presence of the ordinary giant component, and we find that real networks seem by and large to follow this pattern, although there are some interesting exceptions. We also study the size of the giant bicomponent as nodes in the network fail and find in some cases that our networks are quite robust to failure, with large bicomponents persisting until almost all vertices have been removed.     

Excess Diffusion of a Driven Colloidal Particle in a Convection Array

We numerically investigate the transport of a passive colloidal particle in a periodic array of planar counterrotating convection rolls,at high Peclet numbers.It is shown that an external bias,oriented parallel to the array,produces a huge excess diffusion peak,in cases where bias and advection drag become comparable.This effect is not restricted to one-dimensional convection geometries,and occurs independently of the array's boundary conditions.     

Electron transfer in proton-hydrogen collisions in nonideal classical plasmas

Effects of nonideality of classical plasma on the reaction: p + H(1s) → H(nlm) + p has been investigated by carrying out fully quantum mechanical calculations within the framework of a first-order distorted wave method. Scattering amplitude is calculated conveniently by employing a simple, variationally determined wave function of hydrogen atom embedded in nonideal classical plasma. A detailed study is made on the changes in electron transfer cross sections due to the nonideality of plasma varying from 0 to 4 and the incident proton energy lying between 10 and 500 keV. It has been found that nonideality of plasma causes substantial change in capture cross section.     

Vertical Sediment Concentration Distribution in High-Concentrated Flows:An Analytical Solution Using Homotopy Analysis Method

Transport of suspended sediment in open channel flow has an enormous impact on real life situations,viz. control and management of reservoir sedimentation, geomorphic evolution such as dunes, rivers, and coastlines etc. Transport entails advection and diffusion. Turbulent diffusion is governed by the concept of Fick’s law, which is based on the molecular diffusion theory, and the equation that represents the distribution of sediment concentration is the advection-diffusion equation. The study uses the existing governing equation which considers different phases for solid and fluid, and then couples the two phases. To deal with high-concentrated flow, sediment and turbulent diffusion coefficients are taken to be different from each other. The effect of hindered settling on sediment particles is incorporated in the governing equation, which makes the equation highly non-linear. This study derives an explicit closed-form analytical solution to the generalized one-dimensional diffusion equation representing the vertical sediment concentration distribution with an arbitrary turbulent diffusion coefficient profile. The solution is obtained by Homotopy Analysis Method, which does not rely on the small parameters present in the equation. Finally, the solution is validated by comparing it with the implicit solution and the numerical solution. A relevant set of laboratory data is selected to check the applicability of the model, and a close agreement shows the potential of the model in the context of application to high-concentrated sediment-laden open channel flow.     

Finite element modeling and optimization to prevent wire breakage in electro-discharge machining

One of the most important problems in wire electrical discharge machining is related to wire breakage. This research develops a simple finite element model and a new approach to predict the thermal distribution in the wire fairly accurately. The model can be used to optimize the different parameters of the system to prevent wire breakage. At any instant of time, the spatial heat distribution profile of the wire can be mapped on the transient analysis of any point on the wire traversing through all the heat zones from the top spool to the bottom end. Based on this principle, the finite element model and optimization algorithm are used to determine that the heat generated is the critical variable responsible for wire breakage. The model successfully predicts the thermal distribution profile accurately for various wire materials, for increased wire velocity and for reduction in heat transfer coefficient. This simple model is a precursor of development for 3-D finite element models that can describe the cross-sectional wire erosion as the workpiece cutting progresses. The modeling may lead to the development of a smart electro-discharge machining system with a sensor and feedback control to increase the cutting speed and minimize breakage.     

Wave propagation in circular cylindrical shells with periodic axial curvature

The propagation of longitudinal and flexural waves in axisymmetric circular cylindrical shells with periodic circular axial curvature is studied using a finite element method previously developed by the authors. Of primary interest is the coupling of these wave modes due to the periodic axial curvature which results in the generation of two types of stop bands not present in straight circular cylinders. The first type is related to the periodic spacing and occurs independently for longitudinal and flexural wave modes without coupling. However, the second type is caused by longitudinal and flexural wave mode coupling due to the axial curvature. A parametric study is conducted where the effects of cylinder radius, degree of axial curvature, and periodic spacing on wave propagation characteristics are investigated. It is shown that even a small degree of periodic axial curvature results in significant stop bands associated with wave mode coupling. These stop bands are broad and conceivably could be tuned to a specific frequency range by judicious choice of the shell parameters. Forced harmonic analyses performed on finite periodic structures show that strong attenuation of longitudinal and flexural motion occurs in the frequency ranges associated with the stop bands of the infinite periodic structure.     

The Effect of TiO2 and MgO on the Thermoluminescence Properties of a Lithium Potassium Borate Glass System

The influence of dopant TiO₂ and co-dopant MgO on the thermoluminescence (TL) properties of lithium potassium borate glass (LKB) is reported in this paper. The glow curve exhibits a prominent peak (T_m) at 230 °C. The TL intensity was enhanced by a factor of ~3 due to the incorporation of MgO, and this was attributed to the creation of extra electron traps mediated by radiative recombination energy transfer. We achieved good linearity of the TL yield with dose, low fading, excellent reproducibility and a promising effective atomic number (Z_eff=8.89), all of which are highly suitable for dosimetry. The effect of heating rate, sunlight and dose rate on the TL are also examined. These attractive features demonstrate that our dosimeter is useful in medical radiation therapy.     

Spherically confined hydrogenic atoms under classical non-ideal plasmas: Scaling law for the critical cage size

An elegant calculation is carried out to investigate the effects of the non-ideality of classical plasma on the energy levels of the hydrogenic atoms held in a spherical cage. Organized effect of the non-ideal classical plasma is described by an analytical pseudopotential which contains the Debye length $D$ and non-ideality parameter $\gamma$ as parameters. Convergent results for the bound states are obtained variationally by utilizing a large trail function containing cosine term which automatically takes care of the requisite boundary conditions. For the plasma-free case, our results are in excellent agreement with the most accurate results available in the literature. An inclusive study is made to explore the changes emerging in the energy levels due to the variation of the plasma parameters and cage size. Special emphasis is made on the determination of critical cage size precisely. The present study specifically reveals that the increasing plasma non-ideality leads to the elongation of the critical cage size. Moreover, it is empirically found that the critical cage size for a given hydrogenic atom can be obtained from a scaling law.