scholarly journals Rheological Properties of Cement Paste with Nano-Fe3O4 under Magnetic Field: Flow Curve and Nanoparticle Agglomeration

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5164
Author(s):  
Dengwu Jiao ◽  
Karel Lesage ◽  
Mert Yucel Yardimci ◽  
Khadija El Cheikh ◽  
Caijun Shi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Rheological Properties ◽  
Cement Paste ◽  
High Rate ◽  
Parallel Plates ◽  
Nanoparticle Agglomeration ◽  
High Magnetic Field Strength ◽  
Concrete Pumping ◽  
Underlying Mechanisms ◽  
Nano Fe3o4

Understanding the influence of magnetic fields on the rheological behavior of flowing cement paste is of great importance to achieve active rheology control during concrete pumping. In this study, the rheological properties of cementitious paste with water-to-cement (w/c) ratio of 0.4 and nano-Fe3O4 content of 3% are first measured under magnetic field. Experimental results show that the shear stress of the cementitious paste under an external magnetic field of 0.5 T is lower than that obtained without magnetic field. After the rheological test, obvious nanoparticle agglomeration and bleeding are observed on the interface between the cementitious paste and the upper rotating plate, and results indicate that this behavior is induced by the high magnetic field strength and high-rate shearing. Subsequently, the hypothesis about the underlying mechanisms of nanoparticles migration in cementitious paste is illustrated. The distribution of the nanoparticles in the cementitious paste between parallel plates is examined by the magnetic properties of the powder as determined by a vibrating sample magnetometer. It is revealed that the magnetization of cementitious powders at different sections and layers provides a solid verification of the hypothesis.

scholarly journals Structural evolution of cement paste with nano-Fe3O4 under magnetic field - Effect of concentration and particle size of nano-Fe3O4

2021 ◽  
Vol 120 ◽  
pp. 104036
Author(s):  
Dengwu Jiao ◽  
Karel Lesage ◽  
Mert Yucel Yardimci ◽  
Khadija El Cheikh ◽  
Caijun Shi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Cement Paste ◽  
Field Effect ◽  
Magnetic Field Effect ◽  
Structural Evolution ◽  
Nano Fe3o4

The rheological properties of magnetic field excited magnetic powders sheared between two parallel plates

2013 ◽  
Vol 22 (11) ◽  
pp. 115036 ◽  
Author(s):  
Kaikai Chen ◽  
Yu Tian ◽  
Lei Shan ◽  
Xiangjun Zhang ◽  
Yonggang Meng
Keyword(s):  
Magnetic Field ◽  
Rheological Properties ◽  
Parallel Plates

scholarly journals Rheological behavior of cement paste with nano-Fe3O4 under magnetic field: Magneto-rheological responses and conceptual calculations

2021 ◽  
Vol 120 ◽  
pp. 104035 ◽  
Author(s):  
Dengwu Jiao ◽  
Karel Lesage ◽  
Mert Yucel Yardimci ◽  
Khadija El Cheikh ◽  
Caijun Shi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cement Paste ◽  
Rheological Behavior ◽  
Nano Fe3o4 ◽  
Magneto Rheological

scholarly journals Preparation of Electric- and Magnetic-Activated Water and Its Influence on the Workability and Mechanical Properties of Cement Mortar

2021 ◽  
Vol 13 (8) ◽  
pp. 4546
Author(s):  
Kaiyue Zhao ◽  
Peng Zhang ◽  
Bing Wang ◽  
Yupeng Tian ◽  
Shanbin Xue ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Compressive Strength ◽  
Flexural Strength ◽  
Cement Paste ◽  
Cement Mortar ◽  
Environmental Issues ◽  
Chemical Admixtures ◽  
Untreated Water ◽  
Alternating Voltage

Cement-based materials prepared with activated water induced by a magnetic field or electric field represent a possible solution to environmental issues caused by the worldwide utilization of chemical admixtures. In this contribution, electric- and magnetic-activated water have been produced. The workability and mechanical properties of cement mortar prepared with this activated water have been investigated. The results indicate that the pH and absorbance (Abs) values of the water varied as the electric and magnetic field changed, and their values increased significantly, exhibiting improved activity compared with that of the untreated water. In addition, activated water still retains activity within 30 min of the resting time. The fluidity of the cement paste prepared with electric-activated water was significantly larger than that of the untreated paste. However, the level of improvement differed with the worst performance resulting from cement paste prepared with alternating voltage activated water. In terms of mechanical properties, both compressive strength and flexural strength obtained its maximum values at 280 mT with two processing cycles. The compressive strength increased 26% as the curing time increased from 7 days to 28 days and flexural strength increased by 31%. In addition, through the introduction of magnetic-activated water into cement mortar, the mechanical strength can be maintained without losing its workability when the amount of cement is reduced.

scholarly journals Characteristics of intracerebral haemorrhage associated with COVID-19: a systematic review and pooled analysis of individual patient and aggregate data

2021 ◽  
Author(s):  
R. Beyrouti ◽  
J. G. Best ◽  
A. Chandratheva ◽  
R. J. Perry ◽  
D. J. Werring
Keyword(s):  
Intracerebral Haemorrhage ◽  
Pooled Analysis ◽  
Aggregate Data ◽  
High Rate ◽  
Individual Data ◽  
Aggregate Level ◽  
Level Data ◽  
Pooled Prevalence ◽  
Underlying Mechanisms ◽  
Different Characteristics

Abstract Background and purpose There are very few studies of the characteristics and causes of ICH in COVID-19, yet such data are essential to guide clinicians in clinical management, including challenging anticoagulation decisions. We aimed to describe the characteristics of spontaneous symptomatic intracerebral haemorrhage (ICH) associated with COVID-19. Methods We systematically searched PubMed, Embase and the Cochrane Central Database for data from patients with SARS-CoV-2 detected prior to or within 7 days after symptomatic ICH. We did a pooled analysis of individual patient data, then combined data from this pooled analysis with aggregate-level data. Results We included data from 139 patients (98 with individual data and 41 with aggregate-level data). In our pooled individual data analysis, the median age (IQR) was 60 (53–67) years and 64% (95% CI 54–73.7%) were male; 79% (95% CI 70.0–86.9%) had critically severe COVID-19. The pooled prevalence of lobar ICH was 67% (95% CI 56.3–76.0%), and of multifocal ICH was 36% (95% CI 26.4–47.0%). 71% (95% CI 61.0–80.4%) of patients were treated with anticoagulation (58% (95% CI 48–67.8%) therapeutic). The median NIHSS was 28 (IQR 15–28); mortality was 54% (95% CI 43.7–64.2%). Our combined analysis of individual and aggregate data showed similar findings. The pooled incidence of ICH across 12 cohort studies of inpatients with COVID-19 (n = 63,390) was 0.38% (95% CI 0.22–0.58%). Conclusions Our data suggest that ICH associated with COVID-19 has different characteristics compared to ICH not associated with COVID-19, including frequent lobar location and multifocality, a high rate of anticoagulation, and high mortality. These observations suggest different underlying mechanisms of ICH in COVID-19 with potential implications for clinical treatment and trials.

scholarly journals The Influence of Chosen Factors on the Rheological Properties of Cement Paste

2015 ◽  
Vol 108 ◽  
pp. 568-574 ◽  
Author(s):  
Alina Kaleta ◽  
Stefania Grzeszczyk
Keyword(s):  
Rheological Properties ◽  
Cement Paste

Magnetohydrodynamic Squeeze Film Characteristics Between Parallel Circular Plates Containing a Single Central Air Bubble in the Inertial Flow Regime

1999 ◽  
Vol 66 (4) ◽  
pp. 1021-1023 ◽  
Author(s):  
R. Usha ◽  
P. Vimala
Keyword(s):  
Magnetic Field ◽  
Differential Equation ◽  
Nonlinear Differential Equation ◽  
Bubble Radius ◽  
Fluid Film ◽  
Squeeze Film ◽  
Parallel Plates ◽  
Circular Plates ◽  
Air Bubble ◽  
Approximate Analytical Solutions

In this paper, the magnetic effects on the Newtonian squeeze film between two circular parallel plates, containing a single central air bubble of cylindrical shape are theoretically investigated. A uniform magnetic field is applied perpendicular to the circular plates, which are in sinusoidal relative motion, and fluid film inertia effects are included in the analysis. Assuming an ideal gas under isothermal condition for an air bubble, a nonlinear differential equation for the bubble radius is obtained by approximating the momentum equation governing the magnetohydrodynamic squeeze film by the mean value averaged across the film thickness. Approximate analytical solutions for the air bubble radius, pressure distribution, and squeeze film force are determined by a perturbation method for small amplitude of sinusoidal motion and are compared with the numerical solution obtained by solving the nonlinear differential equation. The combined effects of air bubble, fluid film inertia, and magnetic field on the squeeze film force are analyzed.

COMPARISON OF CARDIAC MAGNETIC FIELD DISTRIBUTIONS DURING DEPOLARIZATION AND REPOLARIZATION

2003 ◽  
Vol 13 (12) ◽  
pp. 3783-3789 ◽  
Author(s):  
F. E. SMITH ◽  
P. LANGLEY ◽  
L. TRAHMS ◽  
U. STEINHOFF ◽  
J. P. BOURKE ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Distribution ◽  
Normal Subjects ◽  
The Body ◽  
Magnetic Field Distribution ◽  
T Wave ◽  
High Magnetic Field Strength ◽  
The Magnetic Field

Multichannel magnetocardiography measures the magnetic field distribution of the human heart noninvasively from many sites over the body surface. Multichannel magnetocardiogram (MCG) analysis enables regional temporal differences in the distribution of cardiac magnetic field strength during depolarization and repolarization to be identified, allowing estimation of the global and local inhomogeneity of the cardiac activation process. The aim of this study was to compare the spatial distribution of cardiac magnetic field strength during ventricular depolarization and repolarization in both normal subjects and patients with cardiac abnormalities, obtaining amplitude measurements by magnetocardiography. MCGs were recorded at 49 sites over the heart from three normal subjects and two patients with inverted T-wave conditions. The magnetic field intensity during depolarization and repolarization was measured automatically for each channel and displayed spatially as contour maps. A Pearson correlation was used to determine the spatial relationship between the variables. For normal subjects, magnetic field strength maps during depolarization (R-wave) showed two asymmetric regions of magnetic field strength with a high positive value in the lower half of the chest and a high negative value above this. The regions of high R-wave amplitude corresponded spatially to concentrated asymmetric regions of high magnetic field strength during repolarization (T-wave). Pearson-r correlation coefficients of 0.7 (p<0.01), 0.8 (p<0.01) and 0.9 (p<0.01) were obtained from this analysis for the three normal subjects. A negative correlation coefficient of -0.7 (p<0.01) was obtained for one of the subjects with inverted T-wave abnormalities, suggesting similar but inverted magnetic field and current distributions to normal subjects. Even with the high correlation values in these four subjects, the MCG was able to identify differences in the distribution of magnetic field strength, with a shift in the T-wave relative to the R-wave. The measurement of cardiac magnetic field distribution during depolarization and repolarization of normal subjects and patients with clinical abnormalities should enable the improvement of theoretical models for the explanation of the cardiac depolarization and repolarization processes.

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