Magnetic fields measured by Voyager 1 (V1) show that the spacecraft crossed the boundary of an unexpected region five times between days 210 and ~238 in 2012. The magnetic field strength B increased ...across this boundary from ≈0.2 to ≈0.4 nanotesla, and B remained near 0.4 nanotesla until at least day 270, 2012. The strong magnetic fields were associated with unusually low counting rates of >0.5 mega–electron volt per nuclear particle. The direction of B did not change significantly across any of the five boundary crossings; it was very uniform and very close to the spiral magnetic field direction, which was observed throughout the heliosheath. The observations indicate that V1 entered a region of the heliosheath (the heliosheath depletion region), rather than the interstellar medium.
Optimization of phosphorus ((31) P) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T1 relaxation times and the Nuclear Overhauser Effect (NOE) of ...phosphorus-containing metabolites.
Twelve patients with prostate cancer and one healthy volunteer were scanned on a 7 T whole-body system using a (31) P endorectal coil combined with an eight-channel (1) H body array coil. T1 relaxation times were measured using progressive saturation in a two-dimensional localization sequence. (31) P MRSI was performed twice: once without NOE and once with NOE using low-power continuous wave (1) H irradiation to determine NOE enhancements.
T1 relaxation times of (31) P metabolites in the human prostate at 7 T varied between 3.0 and 8.3 s. Positive but variable NOE enhancements were measured for most metabolites. Remarkably, the (31) P MR spectra showed two peaks in chemical shift range of inorganic phosphate.
Knowledge of T1 relaxation times and NOE enhancements enables protocol optimization for (31) P MRSI of the prostate at 7 T. With a strongly reduced (31) P flip angle (≤ 45°), a (31) P MRSI dataset with optimal signal-to-noise ratio per unit time can be obtained within 15 minutes. The NOE enhancement can improve fitting accuracy, but its variability requires further investigation.
•Mechanical properties of MRF were studied using the theory of electromagnetic-thermal effects.•Testing of the coupling effect of multiple physical fields.•Temperature affects magnetic field strength ...and magnetization rate of magnetic particles.•Magnetic field strength and temperature influences the shear yield stress of MR fluid.
The mechanical properties of magnetorheological fluid are influenced by multiple factors in multi-physical field environments. To precisely characterize the mechanical properties and variations under the influence of multi-physical field coupling, this study analyzes the mechanism of electromagnetic-thermal multi-physical field coupling based on the principles of electromagnetic thermal effects. Furthermore, it derives formulas to describe the changes in resistance of the excitation coil, electric current, and magnetic field strength resulting from the influence of temperature. A physical model of the excitation coil is constructed for conducting numerical simulations, and a test bench is assembled to validate the magnetic field strength generated by the excitation coil. By considering the impact of temperature on both the magnetic field strength and the magnetization rate of the particles in the magnetorheological fluids, an analytical calculation is performed to determine the shear yield stress of the fluid under multi-physical field conditions. The results showed that the magnetic field strength generated by the excitation coil as temperature decreased with increasing, and with an increase in temperature from 30 °C to 80 °C, the magnetic induction strength decreased by 17.1 % from 22.88 mT to 18.96 mT, while the shear yield stress decreases by 29.2 % from 35.9 kPa to 25.4 kPa. These findings have a significant effect on the performance of magnetorheological fluids materials, underscoring the necessity of considering multi-physical field effects when researching their performance and verifying the performance degradation and failure of magnetorheological devices under high-temperature conditions.
The Sun's meridional flow is an axisymmetric flow that is generally directed from its equator toward its poles at the surface. The structure and strength of the meridional flow determine both the ...strength of the Sun's polar magnetic field and the intensity of sunspot cycles. We determine the meridional flow speed of magnetic features on the Sun using data from the Solar and Heliospheric Observatory. The average flow is poleward at all latitudes up to 75°, which suggests that it extends to the poles. It was faster at sunspot cycle minimum than at maximum and substantially faster on the approach to the current minimum than it was at the last solar minimum. This result may help to explain why this solar activity minimum is so peculiar.
•We studied the effect of different MRI scanner parameters on breast radiomics.•We extracted 529 radiomic features from 272 breast cancer patients in our cohort.•The radiomic features were ...categorized into relevant groups.•Scanner parameters affected tissue radiomics more compared to tumor radiomics.
To assess the impact of varying magnetic resonance imaging (MRI) scanner parameters on the extraction of algorithmic features in breast MRI radiomics studies.
In this retrospective study, breast imaging data for 272 patients were analyzed with magnetic resonance (MR) images. From the MR images, we assembled and implemented 529 algorithmic features of breast tumors and fibrograndular tissue (FGT). We divided the features into 10 groups based on the type of data used for the feature extraction and the nature of the extracted information. Three scanner parameters were considered: scanner manufacturer, scanner magnetic field strength, and slice thickness. We assessed the impact of each of the scanner parameters on each of the feature by testing whether the feature values are systematically diverse for different values of these scanner parameters. A two-sample t-test has been used to establish whether the impact of a scanner parameter on values of a feature is significant and receiver operating characteristics have been used for to establish the extent of that effect.
On average, higher proportion (69% FGT versus 20% tumor) of FGT related features were affected by the three scanner parameters. Of all feature groups and scanner parameters, the feature group related to the variation in FGT enhancement was found to be the most sensitive to the scanner manufacturer (AUC= 0.81 ± 0.14).
Features involving calculations from FGT are particularly sensitive to the scanner parameters.
The purpose of this chapter is the mathematical study of the perturbation of a homogeneous static magnetic field caused by the embedding of a red blood cell. Analytical expressions for the magnetic ...potential and the magnetic strength vector are derived. From the obtained results, it emerges that the magnetic field inside the red blood cell is not uniform and the magnitude depends on the orientation of the erythrocyte. The expressions for the magnetic field quantities are significant in applications such as the magnetic resonance imaging and in the magnetic resonance spectroscopy.
•For measuring the magnetic field strength of the micro-coil in the WP-μMS (structure: transmitting coil-micro-coil).•The calculation of the magnetic field strength is obtained through the mutual ...inductance coefficient.•Increase the mutual inductance measurement to nH-scale by using magnetically coupled resonance.•The magnetic field of the micro-coil is measured by eliminating magnetic field interference from the transmitting coil.
In recent years, the wireless passive micro-magnetic stimulator (WP-μMS) has emerged as a focal for implantable neuromagnetism modulation research. However, accurately measuring the magnetic field strength of the micro-coil presents a significant challenge due to its small size and low mutual inductance (M). Firstly, this paper establishes a theoretical model of magnetic coupling with a three-stage structure of transmitting coil-micro-coil-detecting coil. The calculation method of detecting the coil to measure the magnetic field is determined by calculating the M between each pair of coils. Secondly, the magnetic coupling resonance method enhances the measured value M to the nH-scale. This approach also eliminates the influence of the M between the transmitting coil-detecting coil on the measurement of the transmitting coil-micro-coil M, thereby achieving accurate measurement of the mT-scale magnetic field strength of the WP-μMS micro-coil. Finally, the effectiveness of the measured mT-scale magnitude magnetic stimulation is validated biologically.
This research studies the influence of static magnetic fields on the structure of calcium carbonate (CaCO3) crystals. Experiments were conducted by exposing Ca2+ and CO32− solutions to magnetic ...fields. The solutions were then combined to form CaCO3 particles. Three characteristics of CaCO3 formation reaction have been investigated, namely absorbance differentiation, vibrational modes and crystal structure. Absorbances were measured using ultraviolet–visible spectrophotometer, while vibrational modes were measured using Flourier transform (FT) infrared and FT Raman spectroscopies. X-ray diffractometer was used to determine the crystal structure. Experimental results show that the nucleation of CaCO3 crystals was inhibited when starting solutions were exposed to magnetic fields. The effect of magnetic fields was mainly attributed to CO32− solution and remained for more than 144 h after starting solutions were combined. As various magnetic field strengths were applied to the solutions, aragonite was formed, and aragonite/calcite ratios were proportional to magnetic field strengths. Using the X-ray technique, the measured crystal structure indicated that the aragonite/calcite ratio increased from 10 to 82% when the magnetic field strength was increased from 60 to 460 mT for the duration of 8 min.
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•Influence of magnetic fields on the structure of calcium carbonate crystals.•Confirmation of two-structured phases of calcium carbonate crystals.•First detailed report on the quantitative analysis of calcium carbonate phases.•Two-structured phase ratio changes with magnetic strength and exposure time.
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