A novel non‐linearly explicit second‐order accurate L‐stable methodology for finite deformation: hypoelastic/hypoelasto‐plastic structural dynamics problems

A novel non‐linearly explicit second‐order accurate L‐stable computational methodology for integrating the non‐linear equations of motion without non‐linear iterations during each time step, and the underlying implementation procedure is described. Emphasis is placed on illustrative non‐linear structural dynamics problems employing both total/updated Lagrangian formulations to handle finite deformation hypoelasticity/hypoelasto‐plasticity models in conjunction with a new explicit exact integration procedure for a particular rate form constitutive equation. Illustrative numerical examples are shown to demonstrate the robustness of the overall developments for non‐linear structural dynamics applications. Copyright © 2004 John Wiley & Sons, Ltd.     

A computational approach for multi‐scale analysis of heterogeneous elasto‐plastic media subjected to short duration loads

The asymptotic expansion homogenization (AEH) approach has found wide acceptance for the study of heterogeneous structures due to its ability to account for multi‐scale features. The emphasis of the present study is to develop consistent AEH numerical formulations to address elasto‐plastic material response of structures subjected to short‐duration transient loading. A second‐order accurate velocity‐based explicit time integration method, in conjunction with the AEH approach, is currently developed that accounts for large deformation non‐linear material response. The approach is verified under degenerate homogeneous conditions using existing experimental data in the literature and its ability to account for heterogeneous conditions is demonstrated for a number of test problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Design spaces,measures and metrics for evaluating quality of time operators and consequences leading to improved algorithms by design—illustration to structural dynamics

For the first time, for time discretized operators, we describe and articulate the importance and notion of design spaces and algorithmic measures that not only can provide new avenues for improved algorithms by design, but also can distinguish in general, the quality of computational algorithms for time‐dependent problems; the particular emphasis is on structural dynamics applications for the purpose of illustration and demonstration of the basic concepts (the underlying concepts can be extended to other disciplines as well). For further developments in time discretized operators and/or for evaluating existing methods, from the established measures for computational algorithms, the conclusion that the most effective (in the sense of convergence, namely, the stability and accuracy, and complexity, namely, the algorithmic formulation and algorithmic structure) computational algorithm should appear in a certain algorithmic structure of the design space amongst comparable algorithms is drawn. With this conclusion, and also with the notion of providing new avenues leading to improved algorithms by design, as an illustration, a novel computational algorithm which departs from the traditional paradigm (in the sense of LMS methods with which we are mostly familiar with and widely used in commercial software) is particularly designed into the perspective design space representation of comparable algorithms, and is termed here as the forward displacement non‐linearly explicit L‐stable (FDEL) algorithm which is unconditionally consistent and does not require non‐linear iterations within each time step. From the established measures for comparable algorithms, simply for illustration purposes, the resulting design of the FDEL formulation is then compared with the commonly advocated explicit central difference method and the implicit Newmark average acceleration method (alternately, the same conclusion holds true against controllable numerically dissipative algorithms) which pertain to the class of linear multi‐step (LMS) methods for assessing both linear and non‐linear dynamic cases. The conclusions that the proposed new design of the FDEL algorithm which is a direct consequence of the present notion of design spaces and measures, is the most effective algorithm to‐date to our knowledge in comparison to the class of second‐order accurate algorithms pertaining to LMS methods for routine and general non‐linear dynamic situations is finally drawn through rigorous numerical experiments. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of seven quantitative assays to assess lymphocyte cell death during HIV infection: measurement of induced apoptosis in anti-Fas-treated Jurkat cells and spontaneous apoptosis in peripheral blood mononuclear cells from children infected with HIV

The study of apoptosis in relation to various human disease states, particularly HIV infection, has seen a tremendous increase in activity. In this article, values obtained by seven different assays, designed to quantify apoptosis and applicable to the study of HIV infection, are compared in two cell systems: (1) stimulus-induced apoptosis in Jurkat cells treated with anti-Fas antibody and (2) spontaneous apoptosis in PBMCs isolated from HIV-infected children. The methods used included measurement of cells with subdiploid DNA content, labeling of DNA strand breaks by the TUNEL reaction, annexin V surface labeling for the detection of exposed phosphatidylserine, cytoplasmic antigen labeling with the apoptosis-specific antibody Apo 2.7, detection of changes in flow cytometric light-scattering properties, trypan blue dye exclusion by light microscopy, and detection of changes in cellular chromatin by fluorescence microscopy. These methods produced well-correlated values in the Jurkat system, whereas the same set of methods produced more discrepant values in the PBMC analyses, especially in those patients with low CD4 counts. Specifically, our results showed that the trypan blue test was unacceptable for quantification of apoptosis during HIV infection, whereas TUNEL, of all the methods tested, showed excellent overall correlation in both cell systems, was highly specific, and matched microscopic observation of the cells. Although many of the methods were suited to the study of a homogeneous cell line, caution must be exercised when examining cell death in a heterogeneous cell mixture from an HIV-infected individual.     

Adaptive p-version based finite element formulations for thermal modeling/analysis of structural configurations

Adaptive p-version based hierarchial finite element formulations in conjunction with a posteriori error estimation concepts are described with emphasis on applicability for thermal modeling/analysis of structural configurations. The basic concepts and formulations of hierarchical p-version finite elements for thermal analysis are first described. A posteriori error estimation features are utilized to steer the process of adaptive refinement. Several configurations comprised of one-dimensional structures are evaluated to validate the applicability of the proposed formulations and to demonstrate the potential of the p-version adaptive formulations for thermal modeling/analysis. The methodology offers potential and promises to be an attractive to conventional finite element thermal modeling/analysis approaches.     

On Efficient Scheduling of H2H Traffic and Reducing Signaling Overhead due to Uplink Small Data M2M Traffic in LTE-A Networks

Wireless Personal Communications - Large coverage and global connectivity makes cellular networks as preferred choice for internet of things (IoT). Machine-to-machine (M2M) communications deal with...     

Design of order‐preserving algorithms for transient first‐order systems with controllable numerical dissipation

Using a new design procedure termed as Algorithms by Design, which we have successfully introduced in our previous efforts for second‐order systems, alternatively, we advance in this exposition, the design and development of a computational framework that permits order‐preserving second‐order time accurate, unconditionally stable, zero‐order overshooting behavior, and features with controllable numerical dissipation and dispersion via a family of algorithms for effectively solving transient first‐order systems. The key feature is the incorporation of a spurious root to introduce controllable numerical dissipation while preserving second‐order accuracy (order‐preserving feature) resulting in a two‐root system, namely, the principal root (ρ_1∞) and a spurious root (ρ_2∞). In contrast to the classical Trapezoidal family of algorithms which are the most popular, the present framework has the same order of computational complexity, but a higher payoff that is a significant advance to the field for tackling a wide class of applications dealing with first‐order transient systems. We also present the special case with selection of ρ_1∞ = 1 and any ρ_2∞ leading to the design of a family of generalized single‐step single‐solve [GS4‐1] algorithms recovering the Crank–Nicolson method at one end (ρ_2∞ = 1) and the Midpoint Rule at the other end (ρ_2∞ = 0) and anything in between, all of which have spectral radius features resembling that of the Crank–Nicolson method. More interestingly, with the particular choice of ρ_1∞ = ρ_2∞ = 0, the developed framework additionally inherits L‐stable features. We illustrate the successful design of the developed GS4‐1 framework using two simple illustrative numerical examples. Copyright © 2011 John Wiley & Sons, Ltd.