Use of Ritz method for damage detection of reinforced and post-tensioned concrete beams

Damage-induced changes in modal characteristics can be detected using experimental modal analysis. In this article, based on changes in natural frequency, mode shapes, and damping ratios, a methodology for detecting damage location and severity is presented. The damage was induced by application of point load at half span location on the reinforced and post-tensioned concrete beams. The load was gradually increased to obtain different crack patterns to be used in simulation of damage scenarios. Experimental modal analysis was performed on the undamaged and damaged beams. The natural frequency and mode shapes were used to determine the location of damage. The approach is developed at an element level with a conventional finite element (FE) model by Ritz method, which is called Ritz damage detection method (RDDM). The mathematical model for both damped and undamped damaged structures have been established through the eigenvalue equations. The singular value decomposition (SVD) technique is used for determination of damage or sound index. These indexes are sensitive to the change of dynamic characteristics due to damages. This approach is applied to five simply supported post-tensioned concrete beams. The numerical results show that the exact location and severity of damage for different simulated damage scenarios could be efficiency found by the present methodology.     

Antibacterial magnetic nanoparticles for therapeutics: a review

Along with the extensive range of exotic nanoparticle (NPs) applications, investigation of magnetic NPs (MNPs) in vitro has ushered modern antibacterial studies into an increasingly attractive research area. A great number of microorganisms exist in the size scales from nanometre to micrometre regions. The enormous potential of engineered MNPs in therapeutic procedures against various drug‐resistant bacteria has declined the menace of fatal bacterial infections. Many biocompatible MNPs have been introduced that possess remarkable impacts on various bacterial strains. Conventional synthesis methods such as co‐precipitation or hydrothermal techniques have been widely adopted in the production of MNPs. The MNPs for antibacterial applications are mainly required to be superparamagnetic, recyclable and biocompatible. To implement novel strategies in developing new generation antimicrobial magnetic nanomaterials, it is essential to obtain a comprehensive preview of recent achievements in synthesis, proposed antibacterial mechanisms and characterisation techniques of these nanomaterials. This review highlights notable aspects of antibacterial activity in engineered MNPs and nanocomposites including their particle properties (size, shape and saturation magnetisation), antibacterial mechanisms, synthesis methods, testing methods, surface modifications and minimum inhibitory concentrations.Inspec keywords: nanocomposites, magnetic particles, biomedical materials, antibacterial activity, nanofabrication, nanoparticles, drugs, precipitation (physical chemistry), reviews, nanomagnetics, superparamagnetism, nanomedicineOther keywords: drug‐resistant bacteria, fatal bacterial infections, bacterial strains, conventional synthesis methods, antibacterial applications, antibacterial activity, exotic nanoparticle applications, antibacterial mechanisms, antimicrobial magnetic nanomaterials, antibacterial MNP, biocompatible MNP, in vivo magnetic nanoparticle, review, hydrothermal techniques, superparamagnetism, nanocomposites, surface modifications     

A theoretic framework for intelligent expert systems in medical encounter evaluation

Abstract: This paper describes a novel approach to implementation of a medical diagnosis expert system that can assist physicians with their daily practices. Differential artificial intelligence techniques are incorporated into a multi-stage expert system to best represent the various phases of the patient diagnosis process. A weighted scoring system is used to represent the subjective analysis stage, while a rule-based fuzzy expert system is employed to both interpret laboratory tests and imaging findings and suggest the final diagnosis. A model of various patient flow scenarios is presented to demonstrate the functionality of the proposed expert system. An actual example of patient walkthrough is used to demonstrate various computation steps from recording the patient chief complaint to arriving at the final diagnosis. It is shown that the conclusion arrived at by using the proposed system is consistent with a common diagnosis of a third party specialist who is asked to evaluate the performance of the system.     

A fast and reliable multi-sender algorithm for peer-to-peer networks

Due to special constraints in peer-to-peer (P2P) networks (such as bandwidth limitation) and because of their highly dynamic characteristics, a single node cannot provide a reliable multimedia stream to the receivers. Several multi-sender algorithms are proposed to reliably deliver a media stream to the receiver through the intrinsically unreliable P2P networks. Based on upload bandwidths and availability of peers as well as the bandwidths of the links connecting the senders and the receiver, PROMISE selects a set of active senders to maximize the expected bit-rate delivered to the receiver. By careful investigation of PROMISE, in this paper, we present why and how it deviates from finding the optimal solution. The proposed algorithm, we call IPROMISE, consistently provides a higher media quality to the receiver, with a computational complexity similar to PROMISE. We also introduce FastIPROMISE which provides the same quality as IPROMISE but requires much less computations. That is achieved by shrinking the search space.     

Compression-induced axial crack propagation in DCDC polymer samples: experiments and modeling

The fracture strength of PMMA is studied using columns with rectangular cross- section that contain a central hole and are subjected to axial compression. Samples with geometries such that the width is 2, 3, 4, and 5 times the diameter of the hole are investigated. Cracks are initiated by introducing sharp notches in the axial direction at the crowns of the hole in each sample. The sample is then subjected to axial compression such that the axial cracks grow in a stable manner until a critical compression is attained, after which the cracks extend rapidly in the sample but do not reach its ends. To predict the experimental results, we have first sought to use several published models, but discovered that none would produce results in accord with our data, as they seem not to address the essential features of our beam-column experiments. We have then developed a simple model that consists of a suitably modified version of an elasticity solution based on a short-crack in an infinite plate, combined with a beam-column solution for a long-crack. This model yields results in good accord with our data and also gives reasonable values for the fracture toughness of the material. A comparative discussion of several published models is presented at the end of the paper, pointing out that linear elasticity is not an appropriate tool for solving the present beam-column problem.     

TPU/PCL/nanomagnetite ternary shape memory composites: studies on their thermal, dynamic-mechanical, rheological and electrical properties

Shape memory polymer composites based on a blend of thermoplastic polyurethane (TPU) segmented block copolymer and poly(ε-caprolactone) (PCL) with weight ratio of 70/30 and various nanomagnetite contents (0–5 wt%) were prepared by melt blending of TPU and PCL, together with a masterbatch of TPU/nanomagnetite. The samples were compounded for 10 min at 200 °C using an internal mixer. Synthesized nanomagnetite powder was introduced to the masterbatch via a solution mixing method using a high-intensity ultrasonic horn. Subsequently, thermal, mechanical, rheological and electrical properties of the TPU/PCL/nanomagnetite shape memory composites were investigated through various tests. The degree of crystallization of the PCL component in the composite structure was inspected by differential scanning calorimetry (DSC) and X-ray diffraction measurements. The results revealed that the percentage of crystallinity and the melting temperature of the PCL component changed in the presence of magnetite nanoparticles, which was related to the nanoparticles acting as nucleants. Observing a single glass transition temperature (T _g) in DSC thermograms of the samples was indicative of good compatibility of the TPU and PCL components in the composite structure. This was also confirmed by dynamic-mechanical analysis in which the loss modulus curves showed a single glass transition temperature. Moreover, the loss modulus peak at glass transition was lowered and broadened by addition of nanomagnetite, by which it was assumed that introducing nanoparticles into the system changed the mechanism of glass transition due to particle–matrix interactions. The dynamic rheological and electrical resistivity experiments verified the existence of a low percolation threshold at about 2 wt% nanomagnetite. The state of nanomagnetite dispersion in the masterbatch and the microstructure of the ternary composites were characterized by scanning electron microscopy. Finally, adding nanomagnetite led to weakening of shape recovery of the polymer blend, with shape recovery dropping to 70 % at 5 % of nanomagnetite.     

Stability and extraction study of phenolic wastewater treatment by supported liquid membrane using tributyl phosphate and sesame oil as liquid membrane

Phenols pose a risk to the environment and to human health. Phenol and its derivatives are toxic pollutants, frequently found in surface and tap waters, and in aqueous effluents from various manufacturing processes. In this paper, an experimental study regarding transport of phenol through a supported liquid membrane (SLM) using tributyl phosphate (TBP) and sesame oil as liquid membrane (LM) was performed. Factors affecting permeation of phenol such as initial phenol concentration, carrier concentration, feed phase pH and stripping phase concentration were analyzed using Taguchi method. Optimal experimental condition of phenol transport was obtained using analysis of variance (ANOVA) after 7 h extraction (feed concentration: 200 mg/L; carrier concentration (%TBP): 40%; feed pH: 2; strip phase concentration: 1.1 M). Mass transfer coefficient for this system was evaluated, and compared with similar works, and it was shown that it has the highest mass transfer rate. In addition to transport study, stability of the membrane was investigated by examination of stripping phase concentration, carrier concentration and salt concentration effects.     

Regulation of the Stem Cell–Host Immune System Interplay Using Hydrogel Coencapsulation System with an Anti‐Inflammatory Drug

The host immune system is known to influence mesenchymal stem cell (MSC)‐mediated bone tissue regeneration. However, the therapeutic capacity of hydrogel biomaterial to modulate the interplay between MSCs and T‐lymphocytes is unknown. Here it is shown that encapsulating hydrogel affects this interplay when used to encapsulate MSCs for implantation by hindering the penetration of pro‐inflammatory cells and/or cytokines, leading to improved viability of the encapsulated MSCs. This combats the effects of the host pro‐inflammatory T‐lymphocyte‐induced nuclear factor kappaB pathway, which can reduce MSC viability through the CASPASE‐3 and CASPASE‐8 associated proapoptotic cascade, resulting in the apoptosis of MSCs. To corroborate rescue of engrafted MSCs from the insult of the host immune system, the incorporation of the anti‐inflammatory drug indomethacin into the encapsulating alginate hydrogel further regulates the local microenvironment and prevents pro‐inflammatory cytokine‐induced apoptosis. These findings suggest that the encapsulating hydrogel can regulate the MSC‐host immune cell interplay and direct the fate of the implanted MSCs, leading to enhanced tissue regeneration.     

The Horn Antenna as Gaussian Source in the mm-Wave Domain

Rising progress of mm-wave technology in spectroscopy, remote-sensing and its prospective application in communications requires accurate radiation beam characterization in quasi-optical systems. Gaussian approximation is a well-known practical model at optical and infrared wavelengths, and here we try to show the performance and limits of this method for the horn antenna as a classical mm-wave radiation source. This approach provides a compact and more practical analytical tool to design and optimize quasi-optical systems, compared to electromagnetic (EM) full-wave solutions. The radiation pattern (beam shape) and the phase distribution are studied analytically, both with the EM full-wave method and Gaussian approximation. Comparative results with measurements are presented to verify the analytical process and show the feasibility of the method for conventional horns.     

A micromechanical approach for the fatigue failure prediction of unidirectional polymer matrix composites in off-axis loading including the effect of viscoelasticity

A novel micromechanical approach is used to study the fatigue failure of unidirectional polymer matrix composites subject to off-axis loading. The main advantage of the present micromechanical model lies in its ability to give closed form solutions for the effective nonlinear response of unidirectional composites and to predict the material response to any combination of shear and normal loading. The fatigue failure criterion is expressed in terms of the fatigue failure functions of the constituent materials. The micromechanical model is also used to calculate these fatigue failure functions from the knowledge of the S–N diagrams of the composite material in longitudinal, transverse, and shear loadings; thus, eliminating the need for any further experimentation. Unlike previous works, the present study accounts for the viscoelasticity of the matrix material rendering it the capability of modeling creep damage accumulation in high-temperature composite materials. The results are found to be in good agreement with the literature. In particular, for higher off-axis angles, the results are seen to be in better concurrence with the experimental data compared to when the effect of viscoelasticity is overlooked. The present approach is also capable of accounting for the strain evolution due to viscoelasticity of the matrix material.