Fracture toughness of foams with tetrakaidecahedral unit cells using finite element based micromechanics

Fracture toughness of open-cell foams consisting of tetrakaidecahedral unit cells is predicted by simulating crack propagation using a finite element (FE) based micromechanical model. The inputs to the model are the geometric parameters required to model the repeating unit cell and tensile strength of the foam ligament or strut. Cracks are created by removing certain number of cells pertaining to a crack length. The FE model consists of a local micro-scale region surrounding the crack tip. For an assumed stress intensity factor, the displacements along the boundary of the local model are calculated based on linear elastic fracture mechanics for orthotropic materials. The stresses in the ligaments ahead of the crack tip calculated from this micro-model in conjunction with the tensile strength of the strut material are used to predict fracture toughness. A parametric study with different micro-model sizes and different crack lengths is performed to check for convergence of predicted Mode-I, Mode-II and mixed mode fracture toughness values. The effect of applying rotations as additional boundary conditions along with translational displacement boundary conditions on the predicted fracture toughness values is also studied.     

Protection of simple series and parallel systems with components of different values

We apply game theory, optimization, and reliability analysis to identify optimal defenses against intentional threats to system reliability. The goals are to identify optimal strategies for allocating resources among possible defensive investments, and to develop qualitative guidelines that reflect those strategies. The novel feature of the approach is the use of reliability analysis together with game theory and optimization to study optimal management of intentional threats to system reliability. Thus, this work extends and adapts the existing body of game-theoretic work on security to systems with series or parallel structures. The results yield insights into the nature of optimal defensive investments that yield the best tradeoff between investment cost and security. In particular, the results illustrate how the optimal allocation of defensive investments depends on the structure of the system, the cost-effectiveness of infrastructure protection investments, and the adversary's goals and constraints.     

Set-membership adaptive equalization and an updator-sharedimplementation for multiple channel communications systems

This paper considers the problems of channel estimation and adaptive equalization in the novel framework of set-membership parameter estimation. Channel estimation using a class of set-membership identification algorithms known as optimal bounding ellipsoid (OBE) algorithms and their extension to tracking time-varying channels are described. Simulation results show that the OBE channel estimators outperform the least-mean-square (LMS) algorithm and perform comparably with the RLS and the Kalman filter. The concept of set-membership equalization is introduced along with the notion of a feasible equalizer. Necessary and sufficient conditions are derived for the existence of feasible equalizers in the case of linear equalization for a linear FIR additive noise channel. An adaptive OBE algorithm is shown to provide a set of estimated feasible equalizers. The selective update feature of the OBE algorithms is exploited to devise an updator-shared scheme in a multiple channel environment, referred to as updator-shared parallel adaptive equalization (USHAPE). U-SHAPE is shown to reduce the hardware complexity significantly. Procedures to compute the minimum number of updating processors required for a specified quality of service are presented     

Parametric sensitivity of fracture behaviour of concrete

The fictitious crack method (FCM) is applied to determine the load-deflection diagrams of notched plain concrete beams under three-point bending using various forms of strain softening in the stress-deformation relationship. The results indicate that there is a need to determine a more realistic relationship.     

Urinary pyrraline as a biochemical marker of non-oxidative Maillard reactions in vivo

The presence of pyrraline, a non-oxidative glucose-derived Maillard reaction product in plasma proteins has been established previously. In this study we have investigated the presence of pyrraline in human urine to determine whether pyrraline-containing proteins are metabolized or selectively retained. Pyrraline was detected by means of HPLC, and its presence was confirmed by UV and electrospray-mass spectrometry. The quantification of pyrraline in urine from healthy individuals showed 1.21 +/- 0.4 micrograms/mg creatinine. In urine from diabetic patients, pyrraline levels varied considerably, although the mean level was higher than in healthy subjects (1.37 +/- 0.6 micrograms/mg creatinine). These data further support the presence of a catabolic pathway for advanced non-oxidative Maillard reaction products in vivo and suggest their role in the pathogenesis of diabetes.     

Velocity and dispersion in porous media

A deterministic model for the longitudinal dispersion in a porous medium is attempted following the analysis of Taylor[1]. The results of the present model are in agreement with the cell model of Simpson[2] and the experimental observations of Harleman et al.[3]. The present model also gives, for the first time in the literature, the information about the behaviour of the diffusion coefficient with the particle size of a porous media.     

Improving power efficiency of coded OFDM with feedback

Coding with diversity is one of the keys to reliable wireless communication over fading channels. Adaptive modulation can provide additional performance improvement which may be significant when the channel diversity orders are small. In this letter, we propose adaptation algorithms for improving the power efficiency of coded orthogonal frequency division multiplexing (OFDM) on fading channels. We derive simple power-loading and bit-loading algorithms for achieving a fixed throughput and reliability with minimal transmitter power. We illustrate the performance of our schemes using simulations.     

Liquid Phase Sintered Solders with Indium as Minority Phase for Next Generation Thermal Interface Material Applications

Because of their high thermal conductivity (K), low melting point (T _m), and low shear strength, indium-based materials are excellent candidates for thermal interface material (TIM) applications. However, high In-content solders are expensive and possess low compressive creep strength, which may lead to structural instability following heat-sink attachment. Here, a radically different approach for producing microelectronic solder TIMs based on liquid phase sintering (LPS) is presented, which not only addresses the above problems, but also paves the way for the development of solder TIMs with even higher K than that of In for next generation packages. LPS Sn-In solders, the microstructure of which consists of particles of the high melting phase (HMP) Sn and a smaller amount of intergranular low melting phase (LMP) In, were processed and characterized. Flow stresses close to that of pure In, and electrical/thermal conductivities approximately half that of pure In, were obtained. LPS solder joints between Cu substrates were produced via a single step process combining LPS with joining. The contact thermal resistance of the internal grain boundaries was estimated, and it is inferred that, because of the numerous internal boundaries, the solder/substrate interfaces have a rela- tively small effect on the joint resistance. Based on the estimated boundary resistance, a previously developed model was utilized to predict the thermal conductivity of the LPS solder as a function of HMP type, volume fraction, and particle size. Preliminary results for LPS solders with Cu as the HMP phase are also presented.     

Symbol-level adaptive modulation for coded OFDM on block fading channels

It has recently been recognized by many researchers that adaptive modulation is most effective when the channel diversity order is small. In this letter, we propose a simple adaptive modulation scheme for orthogonal frequency division multiplexing (OFDM) systems on channels that provide a small order of diversity. The proposed adaptation algorithm is based on a novel and very simple analytical formula we derive for the performance of BICM on block fading channels. Simulation results show that the derived analytical formula is very tight when the targeted bit error probability is small. OFDM systems on indoor channels provide small orders of diversity and form an ideal scenario for adaptation. In order to keep system complexity and feedback requirements at a minimum, we will consider symbol-level adaptive modulation wherein all the subcarriers in an OFDM symbol use the same modulation.     

An extension to the ordered subcarrier selection algorithm (OSSA)

In this letter, we propose an extension to the ordered subcarrier selection algorithm (OSSA) for orthogonal frequency division multiplexing (OFDM) systems. The result is a simple algorithm for minimizing the bit error rate of the OFDM system at a fixed throughput. The proposed algorithm employs multiple modulations (non-uniform bit loading) within an OFDM symbol. However, unlike existing bit loading algorithms that have a very high computational complexity, the proposed algorithm is based only on the ordered statistics of the subcarrier gains and is consequently very simple. After ordering the subcarriers based on their gains, progressively higher order modulations are used with increasing gains. The key aspect here that greatly simplifies the algorithm is that the modulation used on a subcarrier depends only on the position of its gain in the ordered set and not on the actual values of the gains. We show an analytical approach for determining the parameters of the algorithm.