Molecular dynamics calculation of the J-integral fracture criterion for nano-sized crystals

The critical J-integral is recognized as a valuable criterion for evaluating elastic-plastic fracture behavior of materials. It is, however, computationally complicated at the atomic scale for a nano-sized crystal when using the traditional integral method to reckon the traction force, strain, strain energy, etc. atom by atom. This paper attempts to propose an effective J-integral calculation method based on molecular dynamics (MD) simulations. The proposed method takes advantage of the potential energy interpretation of the J-integral, the main task in which is to calculate the potential energy difference of two identical crystal models with the neighboring crack length. As the potential energy of crystals at the atomic scale can be obtained easily from molecular dynamics simulations, the proposed method is thus computationally simple and especially applicable to complex crystal structures. A nickel crystal having an opening model I crack is investigated using this method. The critical J-integral in the ductile fracture plane (1\bar10) is calculated to be 4.424 Jm^–2. It is also found in this study that the onset of crack propagation does not coincide with the occurrence of the maximum tension stress for nano-sized crystals, which is different from conventional fracture mechanics observation.     

Synthesis,characterization, DC-electrical conductivity and γ-ray effect on Ag1+, Y3+ double doped nano lithium manganates (LiMn2−2x Ag x Y x O4) for rechargeable batteries

Pristine lithium manganate (LiMn₂O₄) and Ag¹⁺, Y³⁺ double doped nano lithium manganate [LiMn_2?2x Ag _x Y _x O₄, (x = 0.025, 0.05)] spinels were synthesized via a coprecipitation method for rechargeable batteries applications. The synthesized LiMn_1.9Ag_0.05Y_0.05O₄ was exposed to different doses of γ-irradiation (10 and 30 kGy). The resulting spinel products were characterized by using thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), electronic (UV-Vis) and electron spin resonance (ESR) spectra. LiMn₂O₄ exhibited a discharge capacity of 124 mAhg^?1 while LiMn_1.9Ag_0.05Y_0.05O₄ had discharge capacities of 129 and 137 mAhg^?1 for non irradiated and γ-irradiated (30 kGy) samples, respectively. The effects of the dopant cations and γ-irradiation on the discharge capacity and DC-electrical conductivity of some synthesized spinels were studied.     

Thermal behavior of an elliptic inhomogeneity surrounded by a compliant interphase layer

Summary This paper examines the thermal behavior of a plane elastic compliant interphase layer surrounding an elliptic inhomogeneity which is embedded within an infinite matrix. To allow continuity of traction but discontinuity of displacements, the compliant interphase is modeled as a spring layer with a vanishing thickness. Furthermore, to obtain the resulting thermal stresses, the complex variable method was used, together with a series solution. A commerical finite element package was used to validate the theoretical predictions. The results reveal that thermal stresses vary with the aspect ratio of the inhomogeneity and the parameterh describing the spring constant of the interphase layer for four different types of inhomogeneous materials: aluminum, copper, gold and silver. In all these cases, the matrix was assumed to be made of silicon and the thermal stresses were assumed to result from a uniform change in temperature.     

Hesitant Fuzzy-Sets Based Decision-Making Model for Security Risk Assessment

Security is an important component in the process of developing healthcare web applications. We need to ensure security maintenance; therefore the analysis of healthcare web application's security risk is of utmost importance. Properties must be considered to minimise the security risk. Additionally, security risk management activities are revised, prepared, implemented, tracked, and regularly set up efficiently to design the security of healthcare web applications. Managing the security risk of a healthcare web application must be considered as the key component. Security is, in specific, seen as an add-on during the development process of healthcare web applications, but not as the key problem. Researchers must ensure that security is taken into account right from the earlier developmental stages of the healthcare web application. In this row, the authors of this study have used the hesitant fuzzy-based AHP-TOPSIS technique to estimate the risks of various healthcare web applications for improving security-durability. This approach would help to design and incorporate security features in healthcare web applications that would be able to battle threats on their own, and not depend solely on the external security of healthcare web applications. Furthermore, in terms of healthcare web application's security-durability, the security risk variable is measured, and vice versa. Hence, the findings of our study will also be useful in improving the durability of several web applications in healthcare.     

Hybrid Sine Cosine and Stochastic Fractal Search for Hemoglobin Estimation

The sample's hemoglobin and glucose levels can be determined by obtaining a blood sample from the human body using a needle and analyzing it. Hemoglobin (HGB) is a critical component of the human body because it transports oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues to the lungs. Calculating the HGB level is a critical step in any blood analysis job. The HGB levels often indicate whether a person is anemic or polycythemia vera. Constructing ensemble models by combining two or more base machine learning (ML) models can help create a more improved model. The purpose of this work is to present a weighted average ensemble model for predicting hemoglobin levels. An optimization method is utilized to get the ensemble's optimum weights. The optimum weight for this work is determined using a sine cosine algorithm based on stochastic fractal search (SCSFS). The proposed SCSFS ensemble is compared to Decision Tree, Multilayer perceptron (MLP), Support Vector Regression (SVR) and Random Forest Regressors as model-based approaches and the average ensemble model. The SCSFS results indicate that the proposed model outperforms existing models and provides an almost accurate hemoglobin estimate.     

Numerical simulation of normal and oblique ballistic impact on ceramic composite armours

This paper presents three-dimensional finite element models that investigate the performance of ceramic–composite armours when subjected to normal and oblique impacts by 7.62 AP rounds. The finite element results are compared with experimental data from different sources both for normal and oblique impact, respectively. Simulation of the penetration processes as well as the evaluation of energy and stresses distributions within the impact zones highlight the difference between normal and oblique ballistic impact phenomena. The findings show that the distributions of global kinetic, internal and total energy versus time are similar for normal and oblique impact. However, the interlaminar stresses at the ceramic–composite interface and the forces at the projectile–ceramic interface for oblique impact are found to be smaller than those for normal impact. Finally, it is observed that the projectile erosion in oblique impact is slightly greater than that in normal impact.     

Towards more reliable and secure source routing in mobile ad hoc and sensor networks

Routing protocols in mobile ad hoc and sensor networks discover a multi-hop route between source and destination nodes. A highly reliable path is an important component for enhancing the security of communication. This paper presents RAS: a Reliable routing protocol for enhanced reliability and security of communication in mobile Ad hoc and Sensor networks. Enhanced reliability and security are achieved by the maintenance of a reliability factor by the nodes, which is increased when nodes participate successfully in data transmissions. This is determined through the use of positive and passive acknowledgements. Additional optimizations are included in order to increase the efficiency and performance of the network. Simulation experiments are performed in order to verify the operation of the proposed protocol and evaluate its performance. The results show an improvement in the reliability of the discovered path with the proper choice of certain important reliability parameters.     

Diversity‐multiplexing tradeoff over correlated Rayleigh fading channels: a non‐asymptotic analysis

In this paper, we present a finite‐signal‐to‐noise ratio (finite‐SNR) framework to establish tight bounds on the diversity‐multiplexing tradeoff of a multiple input multiple output (MIMO) system. We focus on a more realistic propagation environment where MIMO channel fading coefficients are correlated and where SNR values are finite. The impact of spatial correlation on the fundamental diversity‐multiplexing tradeoff is investigated. We present tight lower bounds on the outage probability of both spatially uncorrelated and correlated MIMO channels. Using these lower bounds, accurate finite‐SNR estimates of the diversity‐multiplexing tradeoff are derived. These estimates allow to gain insight on the impact of spatial correlation on the diversity‐multiplexing tradeoff at finite‐SNR. As expected, the diversity‐multiplexing tradeoff is severely degraded as the spatial correlation increases. For example, a MIMO system operating at a spectral efficiency of R bps/Hz and at an SNR of 5 dB in a moderately correlated channel, achieves a better diversity gain than a system operating at the same spectral efficiency and at an SNR of 10 dB in a highly correlated channel, when the multiplexing gain r is greater than 0.8. Another interesting point is that provided that the spatial correlation channel matrix is of full rank, the maximum diversity gain is not affected by the spatial correlation. Copyright © 2009 John Wiley & Sons, Ltd.     

0.2 mu m gate length pseudomorphic HIGFET using novel selfaligned TiPtAu/WN T-gate technology for high-speed digital and millimetre wave applications

A selfaligned refractory gate HIGFET technology is described. A three-layer resist process has been used for gate TiPtAu thickening, making high-speed digital structures compatible with low noise microwave applications. Pseudomorphic HIGFETs with 0.2 mu m gate length exhibit a maximum transconductance of 600 mS/mm and a maximum oscillation frequency f/sub max/ of 100 GHz.<>