Loop Area Research Articles

Cyclic bond behavior in reinforced concrete flexural members exposed to elevated temperatures

After enduring fire incidents, many reinforced concrete (RC) structures require assessment of their ability to withstand future seismic loads. A critical factor contributing to seismic behavior of such structures is residual bond between steel and concrete under cyclic loading. This paper examines cyclic bond-slip behavior in RC flexural members that have experienced elevated temperatures. Twenty-six modified beam-end specimens with different diameters of longitudinal reinforcement, concrete strengths, and confinement levels were fabricated. The specimens were subjected to a variety of heating regimes and a natural cool down before loading of their longitudinal rebar in a monotonic or cyclic pattern. The decrease in bond strength after 2-hr exposure to temperatures of 400, 600, and 700 °C were 23, 58, and 65 percent for monotonic loading but 30, 60, and 65 percent for cyclic loading, respectively. Elevated temperatures also caused a decrease in slope and area of hysteretic bond-slip loops. Cyclic bond strength was 25–45% less than monotonic bond strength and better correlated with the residual compressive strength of concrete, unlike monotonic bond strength, which was better correlated with the square root of this property. A model was proposed for backbone bond-slip curves of RC flexural members that are exposed to elevated temperatures.

Effects of mixed corrosion damage on constitutive relation and ductile fracture behavior of butt-welded joints under cyclic loading

The corrosion damage of welded connection regions posed a threat to the reliability and durability of welded steel structures. In this paper, the morphology scanning and cyclic loading tests of butt-welded joints exposed to the salt spray corrosion environment were conducted to investigate the effects of corrosion damage on surface characteristics and hysteresis behavior of butt-welded joints. Three-dimension scanning test results showed that the butt-welded joint under the salt spray environment suffered a kind of mixed corrosion damage. Compared with the thickness loss caused by uniform corrosion, pitting damage tended to cause serious local geometric defects, aggravating the geometric discontinuity problem. For the corroded butt-welded joint, the hysteresis loop area and cycles decreased significantly with the increase of corrosion damage, and the ductile fracture behavior under the cyclic loading gradually disappeared. The numerical comparative analysis of models with two different patterns of corrosion damage showed that the pitting damage caused a severer hysteresis behavior degradation of butt-welded joints compared to the uniform corrosion damage under the same volumetric loss ratio. Particularly, the pitting damage had a significant effect on reducing cyclic deformation and energy dissipation. According to the above experimental and numerical analysis, a modified cyclic plastic fracture criteria considering pitting damage and a nonlinear cyclic constitutive model considering mixed corrosion for the corroded butt-welded joint were proposed respectively to equivalently consider the influence of corrosion geometric damage by weakening the material properties.

Effect of CoFe2O4 mole percentage in the scaling behaviour of dynamic hysteresis loop in eco-friendly (1-x)(0.94Na0.5Bi0·5TiO3-0.06BaTiO3)–x(CoFe2O4) particulate composite

Many technological applications of ferroelectric materials are fundamentally connected to domain reversal under the electric field. Here the polarization reversible mechanism has been studied in (1-x)(0.94Na0·5Bi0·5TiO3-0.06BaTiO3)–x(CoFe2O4) (NBBT-CFO) (x = 0, 15, 25 and 35 mol%) particulate composites through the electric field and frequency-dependent scaling behavior of their hysteresis loop. Along with this, the role of the CFO on the polarization reversal processes of NBBT has been investigated systematically. Three-stage behaviour has been observed in the polarization reversal for all the systems. The observed scaling parameter β value for the composites is found to be less than parent NBBT, which has been discussed based on the pinning effect that arises due to the CFO phase. The induced pinning effect in the composites is due to the high leakage current which is confirmed by the leakage current density (J) measurement. The scaling relation of loop area <A> versus E0 and ƒ for the composites is followed by the power law <A>∝f−0.265E01.320 in the saturated region. The present findings may be useful in technological applications related to polarization reversal.

The silent impact of underground climate change on civil infrastructure

Urban areas increasingly suffer from subsurface heat islands: an underground climate change responsible for environmental, public health, and transportation issues. Soils, rocks, and construction materials deform under the influence of temperature variations and excessive deformations can affect the performance of civil infrastructure. Here I explore if ground deformations caused by subsurface heat islands might affect civil infrastructure. The Chicago Loop district is used as a case study. A 3-D computer model informed by data collected via a network of temperature sensors is used to characterize the ground temperature variations, deformations, and displacements caused by underground climate change. These deformations and displacements are significant and, on a case-by-case basis, may be incompatible with the operational requirements of civil structures. Therefore, the impact of underground climate change on civil infrastructure should be considered in future urban planning strategies to avoid possible structural damage and malfunction. Overall, this work suggests that underground climate change can represent a silent hazard for civil infrastructure in the Chicago Loop and other urban areas worldwide, but also an opportunity to reutilize or minimize waste heat in the ground.

Experimental study on cyclic-bend-over-sheave (CBOS) characteristics of an HMPE fibre rope under dynamic loading

Cyclic bending over sheave (CBOS) is one of the most typical usage scenarios of marine handling ropes, where the rope will be subjected to both tensile deformation and bending deflection. In this paper, the CBOS characteristics of a 24 mm high module polyethylene (HMPE) marine handling rope subjected to dynamic tension are investigated by a series of full-scale experimental tests at the diameter ratio of D/d=400/24, where D=400mm is the sheave diameter. The variations in useful life, strain, stiffness and surface temperature have been measured at different loading conditions. Two stages of temperature variation at the bending section of the rope are found, and those stages are associated with the variation in the area of hysteresis loop from the tension-strain figure. On the other hand, the CBOS lifetime is found to decrease with the increasing average, amplitude and period of the dynamic loading, while the nominal stiffness increases with the average magnitude and period of loading but decreases with increasing amplitude. On this basis, two empirical equations taking into account the loading conditions are proposed through regression analysis. The obtained coefficients have good agreement with the present experimental results.

Hysteresis Phenomena in the Relationship between the Cosmic Ray Cutoff Rigidity and Parameters of the Magnetosphere during a Storm on May 15, 2005

Variations in the cutoff rigidities of cosmic rays (ΔR) depending on the parameters of the solarwind, the interplanetary magnetic field (IMF), and geomagnetic activity were studied at different phases ofthe strong magnetic storm on May 15, 2005. We found that the trajectories ΔR, i.e., the successive values thatΔR takes depending on the parameters under study during the main phase of the storm did not coincide withthe trajectories in the recovery phase, which led to the formation of hysteresis loops. The clearest hysteresisloops are formed for the relationship between ΔR and the Bz component of the IMF, the density and pressureof the solar wind, and the Dst index of geomagnetic activity. The area of the hysteresis loops increases withthe latitude of the cosmic ray observation station.

Thixotropy of fresh cement pastes in presence of cationic polymer

Cationic polymer can effectively improve the clay tolerance of polycarboxylate superplasticizer in cement pastes, but the thixotropy of fresh cement pastes in presence of cationic polymer has not received sufficient attention. In this paper, the effect of cationic polymer on the thixotropy of fresh cement pastes containing Na-bentonite was studied. The hydration heat was considered and measured. Besides hysteresis loop areas, the destruction and reconstruction of flocs in thixotropic behaviors of cement pastes were also investigated. The results showed that the cationic polymer delayed the release of cement hydration and decreased the total hydration heat. Cement hydration improved the thixotropy of cement pastes. An obvious decrease of hysteresis loop areas of cement pastes was observed with the addition of cationic polymer, which indicated the decrease of the thixotropy. The equilibrium shear stress, characteristic time of destruction of flocs and incipient structural parameter in thixotropic behaviors were also decreased with the addition of cationic polymer. On the other hand, cationic polymer increased the reconstruction rate of flocculated structure in cement pastes.

Time-dependent thixotropy of dysphagia management-oriented polysaccharide solutions

During dysphagia management, the required foods are often thixotropic yield fluids (YSFs) in which polysaccharide gums are used as thickeners or gelling agents. Thixotropy is a prevalent hysteresis phenomenon in YSFs, so it always occurs as an apparently time-dependent stress or modulus response. The yielding behavior of the food bolus is inseparable from the mastication and swallowing process, among which time-dependent thixotropy is integral. Nevertheless, standardizing and generalizing the thixotropy levels has always been a challenge in the manufacturing application of YSFs. Moreover, the existing thixotropic approaches cannot guarantee the accuracy and comparability of the measurement process due to technicalities. Along these lines, in this work, the thixotropic stress-shear rate hysteresis loops were investigated based on the utilization of dysphagia management-oriented model polysaccharide solutions that exhibited different time-dependent thixotropy levels. More specifically, xanthan gum (XG), carboxymethylated curdlan (CMCD), and konjac glucomannan (KGM) solutions were selected to mimic dysphagia diet construction, whereas the relationship between their technically mechanical properties and structural changes was analyzed. Compared with the KGM solutions, both XG and CMCD solutions presented significant thixotropy levels with different timescale responses and concentration dependence. The recorded discrepancy in their loop area and shape were attributed to their different intermolecular association and networks.

Evaluation and assessment of clique arrangements for the estimation of omnipolar electrograms in high density electrode arrays: an experimental animal model study

High-density catheters combined with Orientation Independent Sensing (OIS) methods have emerged as a groundbreaking technology for cardiac substrate characterisation. In this study, we aim to assess the arrangements and constraints to reliably estimate the so-called omnipolar electrogram (oEGM). Performance was evaluated using an experimental animal model. Thirty-eight recordings from nine retrospective experiments on isolated perfused rabbit hearts with an epicardial HD multielectrode were used. We estimated oEGMs according to the classic triangular clique (4 possible orientations) and a novel cross-orientation clique arrangement. Furthermore, we tested the effects of interelectrode spacing from 1 to 4 mm. Performance was evaluated by means of several parameters that measured amplitude rejection ratios, electric field loop area, activation pulse width and morphology distortion. Most reliable oEGM estimations were obtained with cross-configurations and interelectrode spacings le 2 mm. Estimations from triangular cliques resulted in wider electric field loops and unreliable detection of the direction of the propagation wavefront. Moreover, increasing interelectrode distance resulted in increased pulse width and morphology distortion. The results prove that current oEGM estimation techniques are insufficiently accurate. This study opens a new standpoint for the design of new-generation HD catheters and mapping software.

Versatile and Accessible Magnetic Diagnosis Platform with Different Types of Magnetic Particles for Liquid and Solid Biopsies.

The diagnosis of liquid and solid biopsies by different instruments makes the clinic loading difficult in many aspects. Given the compositions of magnetic particles (MPs) with diverse characterizations and the innovative acoustic type of vibration sample magnetometer (VSM), the versatile, accessible magnetic diagnosis platform was proposed to meet clinical demands, such as low loading for multiple biopsies. In liquid biopsies of alpha-fetoprotein (AFP) standard solutions and subject serums, molecular concentration was analyzed from saturation magnetization by the soft type of Fe3O4 MPs with AFP bioprobe coating. In the phantom mixture simulated as bounded MPs in tissue, the bounded MPs was evaluated from the area of the hysteresis loop by hard type of cobalt MPs without bio-probes coating. Not only a calibration curve was founded for many hepatic cell carcinoma stages, but also microscale images verified the Ms increase due to magnetic protein clusters, etc. Hence, its wide populations in clinics could be expected.

Right ventricular myocardial work characterization in patients with pulmonary hypertension and association with pulmonary hypertension severity

Abstract Funding Acknowledgements Type of funding sources: None. Background Right ventricular myocardial work (RVMW) assessed by transthoracic echocardiography allows to study and analyze the right ventricular (RV) function non-invasively, using RV pressure-strain loops. The association between these novel indexes of RVMW and invasive hemodynamic parameters has not yet been extensively studied, namely in precapillary pulmonary hypertension (PH) population. Objectives To evaluate the relationship between RVMW and the severity of PH through invasive indices of right heart catheterization (RHC) in a cohort of patients with group I and group IV PH. Methods A prospective registry of pre-capillary PH patients evaluated in a single tertiary center was used. Echocardiography and right heart catheterization were performed in the same day. Dedicated software for left ventricle myocardial work was used for the RV. RV global myocardial work index (RVGWI) was calculated as the area of the RV pressure-strain loops. From RVGWI, RV global constructive work (RVGCW; work contributing to myocardial shortening during systole and lengthening during isovolumic relaxation), RV global wasted work (RVGWW; work contributing to myocardial lengthening during systole and shortening during isovolumic relaxation), and RV global work efficiency (RVGWE; relation between RVGCW and RVGWW) were estimated. Pearson’s correlation was applied to assess correlations between continuous variables. Results 17 pts (80% women, mean age 67 ± 10 years) were included. Conventional echocardiographic parameters for the evaluation of RV systolic function, such as TAPSE, annular tricuspid s’ velocity and fractional area change (FAC), did not correlate with mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR). Strong correlations were found between right ventricle-pulmonary artery (RV-PA) coupling and mPAP (r = -0,655, p = 0,006) and RVP(r = - 0,610, p = 0,017), as well as with RV GLS (r = 0,749, p = 0,001 and r = 0,622, p = 0,01, respectively). Of the RVMW indexes, RVGWI, RVGWW and RVGWE strongly correlated with mPAP and PVR: as these invasive parameters increase, RVGWI (r = -0,581, p = 0,015 and r = -0,536, p = 0,027, respectively) and RVGWE (r = -0,779, p &amp;lt; 0,001 and r = -0,773, p &amp;lt; 0,001, respectively) decline significantly, whereas RVGWW (r = 0,735, p = 0,001 and r = 0,800, p &amp;lt; 0,001) increases. In our population, only RVGCW didn’t correlate significantly with high afterload (r= −0,304, p = 0,235 for mPAP, and r = -0,181, p = 0,488 for RVP). Conclusions New methods to evaluate RV function are crucial in patients with RV hemodynamic overload, since conventional echocardiographic parameters do not perform well. Novel echocardiographic assessment of RVMW are associated with severity of PH in our population.

Right Ventricle Myocardial Work in ToF-repair survivors: no longer behind the scenes

Abstract Funding Acknowledgements Type of funding sources: None. Background Tetralogy of Fallot is the most common cyanotic CHD and survivors after ToF repair are growing rapidly. Children and, more frequently, young adults spToF develop late complications: life-threatening ventricular arrhythmias and SCD remain a great concern in these patients. This study has the aim to analyse advanced Right Ventricle echocardiographic and CMR features sp-ToF in the long-term follow-up, finding non-invasive predictors of adverse prognosis. Methods This is a retrospective cohort study. 240 patients sp-ToF were included (mean age 13 ± 11 years). The electrocardiographic, echocardiographic, CMR and CPET data were reviewed retrospectively. Non-invasive RV Global myocardial Work Index (RVGWI) was calculated as the area of the RV pressure-strain loops. RV Global Constructive Work (RVGCW), RV Global Wasted Work (RVGWW) and RV Global Work Efficiency (RVGWE) were estimated. Patients were screened according to age at surgery, time since the radical repair at the follow-up, increased estimated RV systolic pressure, differences in instrumental findings after PVrep. A composite end-point of MACEs (syncope, sustained and non-sustained ventricular tachycardia, sudden cardiac death) was used. Results Older patients at surgery (≥12 months) have significantly reduced VO2 max at CPET, larger RA and LA areas and larger RV basal diameter. CPET values are not significantly different in patients with more than 25 years since the corrective surgery but echo and CMR-LVEF measured are slightly but significantly reduced and RVGWE is significantly lower. Patients with RVSP ≥ 60 mmHg have significantly higher RVGWW, worst RV FWLS, lower RVGCW and RVGWE. Patients who have undergone PVrep show improvement in RV GLS, RV FWLS and RVGWE and a RVGWW reduction. As reguards the CMR RV volume evaluation sp-ToF, patients with RVESVi ≥80ml/m2 have lower RVGWE and show an inverse correlation between RVEDVi and RVGWE. Sp-ToF patients with borderline/impaired predicted VO2 max at CPET have a reduced RV FWLS, higher RVGWW and an inverse correlation between METs and RVGWW. Patients who have suffered MACEs (2 NS-TV, 3 S-TV, 7 syncopes, 8 sudden deaths) hadsignificant impairment of RV systolic function (FAC, RV FWLS, CMR-RVFE), significantly higher RVGWW, lower RVGWE and RVGWI. Conclusion Long-term survival and clinical condition sp-ToF in infancy are generally good and late functional status in survivors could be excellent up to 25 years after radical correction. However, older patients at surgery have relative reduced functional status compared with those undergoing early repair. The advanced echocardiographic and CMR evaluation of RV function sp-ToF are usually related to worse prognosis, VT and reduced functional status. RV myocardial work evaluation is feasible in patients with repaired ToF, it may be a more sensitive indicator of RV fuctional impairment compared with standard echocardiographic parameters and is able to predict exercise capacity.

Diagnostic performance of the non-invasive myocardial work indices in predicting subclinical myocardial work impairment in Fontan patients

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): public hospital sources. Background The Fontan procedure is an operation that has allowed many paediatric patients suffering from severe congenital heart disease to reach adulthood. More and more frequently we come to interface with the consequences of Fontan's circulation, such as cardiac function and exercise capacity deterioration. Recently the new non-invasive method for calculating myocardial work (MW) based on spackle tracking analysis with the estimation of left ventricular pressure and the measurement of non-invasive blood pressure has been introduced. Purpose Aim of this study was to evaluate the diagnostic performance of the non-invasive myocardial work indices in predicting subclinical myocardial work impairment in patients with Fontan circulation. Methods A total of 69 patients were included and compared with healthy age- and sex- matched controls (CTRL). Ventricular systolic function and global longitudinal strain (GLS) were assessed. Cardiopulmonary exercise test was performed. Global myocardial work index (MWI) was calculated as the area of the LV pressure strain loops. From MWI, global Constructive Work (MCW), Wasted Work (MWW) and Work Efficiency (MWE) were estimated. Results The two groups were comparable for blood pressure, weight end height. Mean age of Fontan patients was 21.0±9.2 years. MWI (1162 ± 364 mmHg% vs 1777 ± 240 mmHg%, p &amp;lt; 0.001), MCW (1554 ± 450 mmHg% vs 2102 ± 221 mmHg%, p = 0.001) and MWE (90 ± 6% vs 96 ± 2% p = 0.001) were significantly reduced in Fontan patients compared with healthy CTRL. Moreover, GLS (−13,9± 3,1 % vs −21,2 ± 1.5%, p &amp;lt; 0.001) and the ejection fraction (EF) (58,9 ± 4.5% vs 63.3 ± 3.9%, p &amp;lt; 0.002) were significantly lower in Fontan patients. Fontan patients with normal EF showed, however, significantly reduced values of MWI compared with CTRL (p&amp;lt;0.05). Fontan patients with functional right ventricle showed significantly reduced MWE compared with patients with functional left ventricle (p = 0.030).In univariate analysis, peak VO2 was significantly associated with age, SatO2, MWI. In multivariate regression, lower peak VO2 was associated with older age (p = 0.003) and lower MWI (p = 0.026). Conclusions Fontan's physiology is associated with impaired ventricular work. Estimation of myocardial work indices may be a more sensitive indicator of impaired myocardial work compared with ejection fraction and is able to predict exercise capacity.

Complex myocardial mechanics in adult patients with repaired TOF- A novel study assessing myocardial work and mechanical dispersion at rest and during exercise

Abstract Funding Acknowledgements Type of funding sources: None. Background Assessment of LV myocardial work (MW) and biventricular mechanical dispersion (MD) in patient with repaired TOF (rTOF) is novel. We sought to investigate the LV MW and biventricular MD response during stress echocardiography. Methods We analysed MW and MD at baseline and at low exercise intensity for 100 adult patients with repaired TOF, 60 patients with severe pulmonary regurgitation (SPR), and 40 patients with negligible PR (NPR). MW was derived as the area of pressure strain loop using speckle tracking echocardiography and blood pressure. MD was derived as the SD of time Q/R wave on ECG to peak longitudinal strain and expressed in millisecond. Results Reduced MW indices were observed in the entire population with mean global work efficiency (MWE) was 85±7%. Overall mean of global work index (GWI) was 1198±312mmHg%, 1701±303mmHg% for global constructive work (GCW), and 293±194mmHg% for global wasted work (GWW). The SPR group had lower MWE, lower GCW and higher GWW. During exercise, overall ΔMWE decreased by −2±10%, ΔGWI increased by 36±43%, ΔGCW increased by 68±40%, and ΔGWW increased by 120±110%. Overall resting mean value of RVMD was 46±18,ms, while 64±11,ms for LVMD, and higher values were observed during exercise. Changes in MWE, MWW, and LV and RVMD were closely associated with peak oxygen uptake (r=.33, r=.41, r=.36, r=.47, p&amp;lt;0.001). Conclusions LV MW indices are reduced and biventricular MD are pronounced in rTOF patients. Augmentation of MW parameters and timing were associated with objective exercise ability, suggesting that they are potential determinants of cardiopulmonary capability.

Research on Hysteretic Behavior of FRP-Confined Concrete Core-Encased Rebar.

FRP-confined concrete core-encased rebar (FCCC-R) is a novel composite structure that has recently been proposed to effectively delay the buckling of ordinary rebar and enhance its mechanical properties by utilizing high-strength mortar or concrete and an FRP strip to confine the core. The purpose of this study was to study the hysteretic behavior of FCCC-R specimens under cyclic loading. Different cyclic loading systems were applied to the specimens and the resulting test data were analyzed and compared, in addition to revealing the mechanism of elongation and mechanical properties of the specimens under the different loading systems. Furthermore, finite-element simulation was performed for different FCCC-Rs using the ABAQUS software. The finite-element model was also used for the expansion parameter studies to analyze the effects of different influencing factors, including the different winding layers, winding angles of the GFRP strips, and the rebar-position eccentricity, on the hysteretic properties of FCCC-R. The test result indicates that FCCC-R exhibits superior hysteretic properties in terms of maximum compressive bearing capacity, maximum strain value, fracture stress, and envelope area of the hysteresis loop when compared to ordinary rebar. The hysteretic performance of FCCC-R increases as the slenderness ratio is increased from 10.9 to 24.5 and the constraint diameter is increased from 30 mm to 50 mm, respectively. Under the two cyclic loading systems, the elongation of the FCCC-R specimens is greater than that of ordinary rebar specimens with the same slenderness ratio. For different slenderness ratios, the range of maximum elongation improvement is about 10% to 25%, though there is still a large discrepancy compared to the elongation of ordinary rebar under monotonic tension. Despite the maximum compressive bearing capacity of FCCC-R is improved under cyclic loading, the internal rebars are more prone to buckling. The results of the finite-element simulation are in good agreement with the experimental results. According to the study of expansion parameters, it is found that the hysteretic properties of FCCC-R increase as the number of winding layers (one, three, and five layers) and winding angles (30°, 45°, and 60°) in the GFRP strips increase, while they decrease as the rebar-position eccentricity (0.15, 0.22, and 0.30) increases.

Improvement in cardiac function and regional LV strain following intramyocardial injection of a theranostic hydrogel early postmyocardial infarction in a porcine model.

Myocardial infarction (MI) is often complicated by left ventricular (LV) remodeling and heart failure. We evaluated the feasibility of a multimodality imaging approach to guide delivery of an imageable hydrogel and assessed LV functional changes with therapy. Yorkshire pigs underwent surgical occlusions of branches of the left anterior descending and/or circumflex artery to create an anterolateral MI. We evaluated the hemodynamic and mechanical effects of intramyocardial delivery of an imageable hydrogel in the central infarct area (Hydrogel group, n = 8) and a Control group (n = 5) early post-MI. LV and aortic pressure and ECG were measured and contrast cineCT angiography was performed at baseline, 60 min post-MI, and 90 min post-hydrogel delivery. LV hemodynamic indices, pressure-volume measures, and normalized regional and global strains were measured and compared. Both Control and Hydrogel groups demonstrated a decline in heart rate, LV pressure, stroke volume, ejection fraction, and pressure-volume loop area, and an increase in myocardial performance (Tei) index and supply/demand (S/D) ratio. After hydrogel delivery, Tei index and S/D ratio were reduced to baseline levels, diastolic and systolic functional indices either stabilized or improved, and radial strain and circumferential strain increased significantly in the MI regions (ENrr: +52.7%, ENcc: +44.1%). However, the Control group demonstrated a progressive decline in all functional indices to levels significantly below those of Hydrogel group. Thus, acute intramyocardial delivery of a novel imageable hydrogel to MI region resulted in rapid stabilization or improvement in LV hemodynamics and function.NEW & NOTEWORTHY Our study demonstrates that contrast cineCT imaging can be used to evaluate the acute effects of intramyocardial delivery of a therapeutic hydrogel to the central MI region early post MI, which resulted in a rapid stabilization of LV hemodynamics and improvement in regional and global LV function.

Studying the rate-dependent specific absorption rate in magnetic hyperthermia through multiscale simulations

In this work, the issue of whether the dynamic magnetic properties of monodispersed magnetic colloids, modeled using micromagnetic simulations, can be extrapolated to analyze magnetic particle hyperthermia data, i.e., specific absorption rate (SAR) values acquired at high frequencies of excitation fields, is addressed. Micromagnetic finite difference simulations were performed using the Object Oriented Micromagnetic Framework (OOMMF) software package in order to obtain the dynamic hysteresis loops under a 24 kA/m alternating magnetic field amplitude and for various frequencies (50–765 kHz). In OOMMF, the finite difference method was used to find the solution of the nonlinear Landau–Lifshitz Gilbert (LLG) equation, which describes the nanoparticles’ magnetization motion when applying an effective magnetic field. To create a system of randomly oriented magnetite nanoparticles having a certain volume fraction (0.02%) that coincides with the experimentally utilized concentration of 1 mg/ml, we start with a perfect simple cubic lattice with a large lattice spacing so that the particle–particle distance is large enough to neglect dipolar interactions (non-interacting nanoparticles). The system under study is a set of 40-nm magnetite nanoparticles with a lognormal size distribution. The simulations were performed assuming quasistatic conditions, an approach that is reasonable for ferromagnetic-like behavior. It is worth noting that the code considers not only the uniaxial anisotropy Ku but also the cubic magnetocrystalline one Kc as well. Kc is usually neglected in literature because the uniaxial contribution dominates, but this is not the case for magnetite since Ku = 9 kJ/m3 and Kc = −11 kJ/m3. Moreover, such an inclusion seems quite reasonable since the magnetocrystalline anisotropy is always present yet with a relative contribution. The SAR values at each frequency were determined after calculating hysteresis losses via the area of the simulated hysteresis loops. Interestingly, SAR values at low frequencies followed an exponential increase trend with a frequency indicating a deviation from the linear behavior usually reported in the literature. To validate our approach, we employed a coupled electromagnetic-thermal model based on COMSOL Multiphysics simulations that provides an accurate estimation of the magnetic field and temperature distribution within the ferrofluid. The time-dependent temperature curves are obtained after 30 min of magnetic particle hyperthermia treatment for the same alternating magnetic field amplitude used in OOMMF simulations (30 mT) and for two representative frequency values. One in the low (300 kHz) and one in the high (765 kHz) frequency regimes. The numerical curves were compared to the corresponding experimental ones and found to be in good agreement. Our findings provide new insight into the validity of dynamic micromagnetic simulation to analyze the frequency behavior of SAR within the framework of LLG and indicate that anisotropy selection plays a key role in the reliability of simulations.

Investigation and Modeling of DC Bias Impact on Core Losses at High Frequency

This paper aims to study the core losses behavior at high frequency (MHz range) with superimposed DC bias in ferrite. Inductive compensation method is employed in the measurement circuit to reduce sensitivity to phase errors. An addition to the circuit is proposed in this work to make easier DC bias generation. Furthermore, a detailed measurement accuracy consideration is also discussed. The tested MnZn ferrite has a nominal relative permeability of 1500 and 800, which was tested at frequency from 500 kHz to 3 MHz. The measurement results are explained thoroughly with three controlling parameters: excitation frequency, peak AC flux density, and DC bias. There are several important findings. First, a higher DC bias creates higher losses at the same frequency and AC flux density. Secondly, at the same DC bias and AC flux density, higher frequency generates a lower relative losses increase. This second point has not been seen in previous literature and is elaborated more in Section III.B. Thirdly, the measurement result shows how DC bias increases the hysteresis loop area and coercivity. The first and third findings confirm the the existing literature findings. As a final step, an improved Steinmetz Premagnetization Graph and Artificial Neural Network are used to create core loss prediction model. The measurement data and the built model can be accessed online for use by other magnetics designer.

Study of the omnipolar EGM reconstruction for robustness against wavefront propagation in epicardial signals

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): National Research Program, Ministerio de Ciencia e Innovación, Spanish Government, Instituto de Salud Carlos III. Background Characterisation of electrophysiological substrate is commonly performed by examining cardiac tissue locally by using high-density (HD) arrays of equispaced electrodes – e.g. Advisor™ HD Grid Mapping Catheter, Sensor Enabled™ (SE). These allow creating activation maps of local tissue and substrate exploration. Recently, a novel operation mode arouse: the omnipole, which overcomes many limitations of bipolar and unipolar electrograms, as they are claimed to be orientation independent. Nevertheless, the current technique to reconstruct omnipolar EGMs has pitfalls as the estimation of some incidence angles of the propagation wavefront. We propose a novel reconstruction method to estimate omnipolar EGMs which overcomes the angle dependence weakness of the current one, providing a more robust EGM representation. We hypothesise that this technique will improve reconstruction of electrophysiological signals. Methods Prior electrophysiological experiments on isolated rabbit hearts were used [1], including recordings with a 128-electrode array 1mm apart over ventricular epicardium at 37ºC, with bipolar electrode stimulation. Four-electrodes cliques were designed from these experiments, with different inter-electrode distances as depicted in fig. 1A, reconstructing the current, and novel omnipolar configuration. Metrics to assess the quality of the EGM signals were designed, including the bipolar loop area, and the ratio of the bipolar components of the omnipole (ox and oy) – see fig. 1B. The bipoles were calculated from unipolar EGMs, the signal was corrected with the 45º offset in the cross, the propagation angle was then detected, and the local activation time (LAT) was estimated. Results In the bipole plots, it was observed that the morphology of the bipolar loop gets distorted with an increase in the interelectrode distance – thinner for distances &amp;lt;2mm. There is a direct relation between the areas in the bipolar loop and the inter-electrode distance (see fig. 2A). Furthermore, the values of the area in the cross are always comparable to the best performing triangular clique. For the ratio of bipoles, the relation is inversely to distance (see fig. 2B), similarly, the performance of the cross is comparable to the best performing triangular omnipole. Conclusion For reconstructing omnipolar EGMs, inter-electrode distances smaller than 2mm should be employed. Furthermore, if that condition is satisfied, the novel omnipolar reconstruction method proposed based on the cross configuration is more accurate and robust to wavefront propagation, given that the omnipolar EGM performs similarly or better than the best triangular configuration – and which triangle is fixed for the whole procedure, being the current reconstruction method less robust. Thus, a new standpoint to omnipolar reconstruction in high density electrode catheters is open, towards the design of new devices, and the practice in the clinic.

Circulation in Quasi-2D Turbulence: Experimental Observation of the Area Rule and Bifractality.

We present an experimental study of the velocity circulation in a quasi-two-dimensional turbulent flow. We show that the area rule of circulation around simple loops holds in both the forward cascade enstrophy inertial range (ΩIR) and the inverse cascade energy inertial range (EIR): When the side lengths of a loop are all within the same inertial range, the circulation statistics depend on the loop area alone. It is also found that, for circulation around figure-eight loops, the area rule still holds in EIR but is not applicable in ΩIR. In ΩIR, the circulation is nonintermittent; whereas in EIR, the circulation is bifractal: space filling for moments of the order of 3 and below and a monofractal with a dimension of 1.42 for higher orders. Our results demonstrate, as in a numerical study of 3D turbulence [K. P. Iyer et al., Circulation in High Reynolds Number Isotropic Turbulence is a Bifractal, Phys. Rev. X 9, 041006 (2019).PRXHAE2160-330810.1103/PhysRevX.9.041006], that, in terms of circulation, turbulent flows exhibit a simpler behavior than velocity increments, as the latter are multifractals.