Search

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]

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]

Magnetic nanoparticles (MNPs) are physically immobilized in some biomedical applications. In this case, dynamic ac magnetization that determines MNPs’ performance has strong dependence on the relative direction between the magnetic easy axes of MNPs and the applied excitation field. To study this dependence, we prepared immobilized MNP samples with different degrees of easy axes’ alignment. The degree of alignment was changed by setting the strength of a dc field that is applied during the immobilization process. The magnetic properties of these samples, such as ac magnetization, coercive field, amplitude of third-harmonic signal, and hysteresis loss, are compared with those of a randomly oriented easy axes’ sample. It was shown that these values are significantly affected by the degree of easy axes’ alignment when the strength of the ac excitation field, $H_{0}$ , is relatively small. The alignment effect gradually becomes smaller when $H_{0}$ is increased. These findings are important for immobilized MNP applications in hyperthermia and magnetic particle imaging. [ABSTRACT FROM AUTHOR]

Highlights • Procedure for magnetic parameters evaluation of magnetic nanoparticles is presented. • Suspended sample M-H curve, immobilized sample M-H curve and AC susceptibility are used. • Parameters of Resovist MNP sample and its two fractionated samples were evaluated. • Resovist sample parameters were given by volume-weighted average of the two fractionated samples. Abstract We present a procedure for the comprehensive evaluation of parameters of magnetic nanoparticles (MNPs), such as saturation magnetization, core-size distribution, anisotropy energy constant, and characteristic time for Néel relaxation for use in biomedical applications and fundamental MNPs research. The static magnetization curve of suspended and immobilized MNP samples and the AC susceptibility of immobilized samples were used for the evaluation of these parameters. The magnetic properties reconstructed from the obtained parameters agreed with the experimental results, indicating the accuracy of the estimation procedure. Using the procedure, the parameters of the commercial Resovist MNP sample were evaluated. Then, the Resovist sample was magnetically fractionated into two MNP samples with large and small core sizes, and the parameters of the two fractionated samples were evaluated. It was demonstrated that the parameters of the Resovist sample are given by the volume-weighted average for those of the fractionated samples. [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]

The magnetic core-size distribution of magnetic nanoparticles (MNPs) was estimated from three independent measurements, i.e., magnetization, ac susceptibility (ACS), and magnetic relaxation (MRX). First, distribution of magnetic moment m in MNP sample was estimated by analyzing the static magnetization ( M – H) curve of the MNP sample in suspension. Next, distribution of anisotropy energy E was estimated by analyzing the ACS of immobilized MNP sample measured from 10 Hz to 1 MHz. The ACS measurement in much lower frequency range was substituted by the MRX measurement. MRX of immobilized MNP sample was measured from 2 to 10^4 s, corresponding to the frequency range from 10^-4 to 0.5 Hz in ACS measurement. The relaxation curve was analyzed using a newly developed analytical method to estimate the E distribution of the MNPs in the range of large E values. Then, the estimated distributions of m and E were transferred to the distributions of magnetic core size. Core-size distributions obtained from m and E distributions reasonably agreed with each other. Namely, we obtained similar core-size distribution from static and dynamic properties of MNP sample, confirming the validity of the present method. Therefore, the present method can be useful to estimate the core-size distribution of MNP sample. [ABSTRACT FROM AUTHOR]

A novel method for constructing an integrated gradiometer and a magnetometer is proposed based on fundamental mode orthogonal fluxgate operation. In the integrated sensor construction, the summation of both sensor head outputs is used for the magnetometer operation and the subtraction of them is used for the gradiometer operation. The baseline separation distance between the sensor heads is adjustable. The sensor heads pair can be configured either axially or in parallel. Experiments were conducted with axial configuration of 5 cm baseline to show the selective detection capability to gradient and homogeneous magnetic field. The sensing system presented can be used to measure the average and the gradient of input magnetic field and its interesting applications are the gradiometric sensing of magnetic field distribution anomalies in a relatively large homogenous magnetic field interference. [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]

Abstract: The fatigue performance of reinforced concrete beams strengthened with externally post-tensioned carbon fiber-reinforced polymer (CFRP) tendons was examined in an experimental and analytical study. Five unstrengthened and 13 strengthened reinforced concrete beams were tested under various fatigue load ranges until failure. The strengthened beams were post-tensioned with two external CFRP tendons on a double-harped profile. The results demonstrated that external post-tensioning significantly decreased the stresses in the internal reinforcement at all stages of loading, and hence extended the fatigue life of the strengthened beams. All beams failed due to the fatigue fracture of the internal steel reinforcing bars. The CFRP tendons demonstrated excellent fatigue performance, with no indication of distress at the deviated points or at the anchors. A fatigue model based on a strain-life approach was proposed to predict the fatigue life of the strengthened beams. The model allows the effect of strengthening on the fatigue life of the beams to be explicitly evaluated during the strengthening design process. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental study to examine the fatigue performance of a novel wedge-type anchor for carbon fiber reinforced polymer (CFRP) post-tensioning tendons. The CFRP tendon–anchor systems were tested under different cyclic loading conditions. Two minimum stress levels, representing 40% and 47% of the ultimate strength of the CFRP tendon, were considered. Four stress ranges varying between 7% and 17% of the ultimate strength of the tendon were applied. The anchor system successfully met the Post-Tensioning Institute provisions for cyclic loading. The fatigue life of the system was primarily affected by the applied stress range with little effect by the minimum stress. The fatigue limit of the CFRP tendon–anchor system could be taken at a stress range of 10% for a maximum stress of 50% of its ultimate capacity. Below this stress level, the assembly is expected to withstand an infinite fatigue life. [Copyright &y& Elsevier]

• Studied the effect of viscosity on amplitude and phase of harmonic signals from magnetic nanoparticles. • Viscosity dependences are related to co-existence of Néel and Brownian relaxation. • Viscosity dependences are discussed in terms of field dependent relaxation time of MNP. • Investigated frequency dependence of the viscosity effect on harmonic signals. • Discussed viscosity dependence of different parameters used for MNP thermometry. We studied effect of viscosity on harmonic signals of magnetic nanoparticles (MNP). Harmonic signals are measured when an excitation field with amplitude (~3 mT) and frequency (~10 kHz) is applied, where the relaxation mechanism of the used MNP is affected by the coexistence of Brownian and Néel processes. Viscosity dependence of amplitude and phase of fundamental, third and fifth harmonics are measured when viscosity changed from 0.89 mPa·s to 12.6 mPa·s. The measured viscosity dependences are discussed in terms of field dependent relaxation time of MNP. We also discuss a method to determine temperature and viscosity from the measured harmonic signals. [ABSTRACT FROM AUTHOR]

This report describes the intraoperative course of a pediatric patient with neuromuscular scoliosis who died of massive fat and marrow emboli during posterior instrumentation for scoliosis surgery. In addition, the report describes the incidence and consequences of embolic events during spine surgery as well as the most common clinical sequelae. This patient's unique presentation is highlighted. [ABSTRACT FROM AUTHOR]

• Studied the effect of viscosity on the harmonic signals from magnetic nanoparticles. • First harmonic decreased with increase in viscosity while third and fifth increased. • First and third harmonics had negative correlation, whereas the third and fifth had positive correlation. • Viscosity dependences are related to co-existence of Néel and Brownian relaxation. • Proposed a method for estimation of viscosity and temperature of MNP samples. We studied the effect of viscosity on the harmonic signals of magnetic nanoparticles (MNPs) for thermometry application. Although thermometry is based on the temperature dependence of MNPs harmonic signals, they are also affected by the viscosity of the surrounding media. Therefore, we first perform numerical calculation to qualitatively show the effect of viscosity on the first (M 1), third (M 3) and fifth (M 5) harmonic signals when an excitation field with medium amplitude (3 mT) and high frequency (10 kHz) is applied. We then present the experimental results for Resovist MNPs samples when viscosity is changed from 0.89 to 5.2 mPa·s. We obtained qualitative agreement between numerical calculation and experimental results on the viscosity dependences. Next, we study the correlation between the changes in harmonic signals caused by viscosity variation. The M 1 and M 3 had negative correlation in their change, while M 3 and M 5 had positive correlation. Due to the positive correlation, the ratio M 5 / M 3 became almost independent of viscosity when appropriate amplitude and frequency were chosen for the excitation field. We also proposed a method to accurately estimate both viscosity and temperature of the MNPs sample from the measured harmonic signals even when the viscosity is not known in advance, which will be useful for precise thermometry. [ABSTRACT FROM AUTHOR]

Abstract This research investigates experimentally and analytically a novel one-way slab system reinforced with either basalt fiber-reinforced polymer (BFRP) or glass fiber-reinforced polymer (GFRP) longitudinal bars embedded in fiber-reinforced concrete (FRC) incorporating basalt macro-fibers (BMF). Twelve one-way concrete slab strips were prepared and tested to failure under four-point loading configuration. The investigated parameters included the type of fiber-reinforced polymer bars (BFRP and GFRP), the longitudinal reinforcement ratio ρ f (1.4 and 2.8 ρ bf , where ρ bf is the balanced reinforcement ratio), and the volume fraction of the fibers added (0, 0.5, 1, and 2% per volume). The test results demonstrated the promise of BMF to enhance the flexural performance of the tested slab strips in terms of ductility and load-carrying capacities. The formulations of different available codes and design guidelines were used to predict the test results. Comparison between the experimental and predicted results showed the adequacy of the models to predict the flexural performance of the tested slab strips. The findings of this study demonstrated the potential of using the BMF as alternatives to conventional fibers in flexural concrete members. [ABSTRACT FROM AUTHOR]

This paper presents the recent development in Structural Health Monitoring (SHM) applications for monitoring the dynamic behavior of structures using the Global Positioning Systems (GPS) technique. GPS monitoring systems for real-time kinematic (RTK), precise point positioning (PPP) and the sampling frequency development of GPS measurements are summarized for time series analysis. Recent proposed time series GPS monitoring systems, errors sources and mitigation, as well as system analysis and identification, are presented and discussed. [ABSTRACT FROM AUTHOR]

• We showed wash-free detection of C-reactive proteins based on the Brownian relaxation of magnetic markers. • Brownian relaxation time was prolonged by using cluster formation of bound markers. • Two types of magnetic properties, i.e., third-harmonic signal and magnetic relaxation, were used for the measurement. • We also discussed the relationship between the signals that was measured with the two measurement methods. We demonstrate the wash-free detection of biological targets based on the Brownian relaxation of magnetic markers. The Brownian relaxation time of bound markers was prolonged by using a cluster (or agglomerate) of bound markers that was formed via the binding reaction between markers and targets. Thus, bound and free markers were differentiated magnetically by using the difference in their relaxation times. Two types of magnetic properties, i.e., third-harmonic signal and magnetic relaxation, were used for measurement. The concentration of target was detected from the decrease in the third-harmonic signal and the increase in the magnetic-relaxation signal. We demonstrated the detection of C-reactive proteins using these two properties. In both cases, a good correlation was obtained between the measured signal and the concentration of target. It was also shown that the two methods had different concentration dependences, which will be caused mainly by the distribution of cluster size of the bound markers. [ABSTRACT FROM AUTHOR]