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Magnetic nanoparticles (MNPs) have been widely studied for bio-sensing applications, where suspended and immobilized MNPs can be magnetically distinguished using their different magnetic properties. We study magnetic properties of suspended and immobilized MNPs when the Néel relaxation time is much shorter than the Brownian. We show in both numerical simulation and experiment that they have different magnetic properties such as AC magnetization curves and harmonic spectra even though the dynamic behavior of both MNP types is primarily dominated by Néel relaxation. This difference is caused by the partial alignment of the easy axes in suspended MNPs when an AC magnetic field is applied. We introduce a distribution function for the angle of easy axis alignment. We also show a method to evaluate the distribution function from the measured AC magnetization curve and clarify the relationship between easy axis alignment and the AC field strength. Using the distribution function, we can quantitatively discuss the effect of easy axis alignment on the magnetic properties of suspended MNPs. The obtained results provide a basis for using MNPs in bio-sensing. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) have been widely studied for use in biomedical applications such as magnetic particle imaging and magnetic hyperthermia. We studied the effect of easy axis alignment on dynamic magnetization of both immobilized and suspended MNPs. For immobilized samples, easy axes of magnetization were aligned by applying a dc field during immobilization. For suspended samples, the applied ac field was set so that the alignment of the easy axes was caused by the ac field. Magnetization (M–H) curves of MNPs with different degrees of easy axis alignment were measured with an applied ac field. We found that the easy axis alignment of MNPs considerably affects their M–H curve and harmonic spectra, which indicates the importance of this alignment for their biomedical applications. The experimental results were quantitatively explained with numerical simulation that took account of easy axis alignment and core size distribution in the sample. We can express the degree of easy axis alignment using a distribution function of the easy axis angle for both immobilized and suspended cases. The distribution function will be useful for quantitatively evaluating MNP performance in biomedical applications. [ABSTRACT FROM AUTHOR]

We estimated the effective magnetic anisotropy constant K of magnetic nanoparticles (MNPs) from the temperature dependence of the coercive field Hc of the M–H curve for use in biosensing applications. For this purpose, a previous analytical expression for Hc was extended so that it can be applied to nanoparticles with a size distribution. Using the extended expression for Hc, we estimated the K value of multi-core based MNP sample that consists of crystalline aggregates of elementary particles. We prepared three MNP samples. One is Resovist, in which elementary particles and aggregates are mixed. The Resovist sample was magnetically divided into two fractions called MS1 and MS3, which included mainly aggregates and elementary particles, respectively. We discuss the K value of elementary particles and aggregates from the comparison among the three samples. It is suggested that the K value of the aggregates is much smaller than that of the elementary particles. The temperature dependence of K of the aggregates is also discussed. [ABSTRACT FROM AUTHOR]

This paper aims at investigating the efficiency of strengthening pre‐damaged circular reinforced concrete (RC) columns with Polyparaphenylene Benzobisoxazole fabric‐reinforced cementitious matrix (PBO‐FRCM). The investigated parameters were the degree of pre‐damage (non‐damaged, damaged monotonically up to yielding, or fatigue damaged), the number of PBO‐FRCM layers (0, 2, or 4), and the tie spacing (180 or 90 mm). The experimental results of testing 12 short columns under axial compression showed that PBO‐FRCM systems enhanced the capacity of the non‐damaged columns and successfully restored and further enhanced the capacity of the pre‐damaged columns. Columns strengthened with two and four PBO‐FRCM layers showed a gain in the capacity of up to 40% and 75%, respectively. Furthermore, PBO‐FRCM wrapping enhanced the ductility of both the non‐damaged and the pre‐damaged columns, in which ductility improvement was more noticeable in columns with the larger tie spacing. Finally, the theoretical load‐carrying capacity calculated using ACI 549 provisions showed a good agreement with the experimental capacity of all tested columns. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental and analytical study of the fatigue performance of reinforced concrete beams strengthened with externally post-tensioned carbon-fibre-reinforced polymer (CFRP) tendons. Two loading conditions prior to strengthening the beams were investigated: in-service loading and overloading. A total of 18 beams were tested to failure: three under monotonic loading and fifteen under fatigue loads. The CFRP tendons were post-tensioned to 40% of their ultimate capacity. The results demonstrated that overloading the beams had no discernable effect on the fatigue life of the strengthened beams. The strain-reduction approach for unbonded steel tendons was modified to account for using CFRP tendons and for the permanent deformations resulting from the overloading process. The loading history of the beams prior to and after post-tensioning was incorporated into a strain-life fatigue model to predict the fatigue life of the strengthened beams. Key words: concrete beams, overloading, damage, post-tensioning, fatigue, fiber-reinforced polymer, strain life. Cet article presente les resultats d'une etude experimentale et analytique de la resistance a la fatigue de poutres en beton arme renforcees d'une armature externe post tensionnee en polymeres renforces de fibres de carbone (<< PRFC >>). Deux conditions de chargement avant le renforcement des poutres ont ete examinees : en service et en surcharge. Dix-huit poutres ont ete mises a l'epreuve jusqu'a defaillance, trois sous un chargement monotone et 15 sous des charges de fati gue. Les armatures en << PRFC >> ont ete post tensionnees a 40 % de leur capacite maximale. Les resultats ont montre que la surcharge des poutres n'avait aucun effet evident sur la duree de vie en fatigue des poutres renforcees. L'approche de reduction des contraintes pour les armatures en acier non adherentes a ete modifiee pour tenir compte de l'utilisation d'armatures en << PRFC >> et des deformations permanentes decoulant du processus de surcharge. L'historique des chargements des poutres avant et apres le post-tensionnement a ete incorpore dans un modele de fatigue contrainte-duree de vie afin de predire la duree de vie en fatigue des poutres renforcees. Mots-cles : poutres en beton, surcharge, dommage, post-tensionnement, fatigue, polymere renforce de fibres, contrainteduree de vie. [Traduit par la Redaction], Introduction and background Strengthening of reinforced concrete structures can be achieved by various techniques, usually governed by the type of the structure and its functionality. External posttensioning is a proven [...]

A new detection system for magnetic particles, which can operate in an unshielded environment, is developed using a fundamental mode orthogonal fluxgate gradiometer. The proposed detection system offers the advantages of cost, size, and weight reduction as compared to contamination detection systems using superconducting quantum interference device sensor. The detection system can be used to detect metallic contamination in foods or lithium ion battery production lines. The system has been investigated numerically to optimize various design parameters of the system. Experimental setup has been developed to evaluate some of the numerically predicted results. Steel balls were successfully detected down to the diameter of 50 μm. [ABSTRACT FROM AUTHOR]

We studied the magnetization (M-H) curve of immobilized magnetic nanoparticles (MNPs) used for biomedical applications. First, we performed numerical simulation on the DC M-H curve over a wide range of MNPs parameters. Based on the simulation results, we obtained an empirical expression for DC M-H curve. The empirical expression was compared with the measured M-H curves of various MNP samples, and quantitative agreements were obtained between them. We can also estimate the basic parameters of MNP from the comparison. Therefore, the empirical expression is useful for analyzing the M-H curve of immobilized MNPs for specific biomedical applications. [ABSTRACT FROM AUTHOR]