Dependence Of Magnetic Field Strength Research Articles

Probing the magnetic field strength dependence of the chiral magnetic effect

The article presents a study aimed at probing the dependence of the Chiral Magnetic Effect (CME) on the magnetic field strength using the Anomalous Viscous Fluid Dynamics (AVFD) model in Pb–Pb at LHC energies. The results demonstrate the quadratic dependence of the correlators used for the study of the CME in heavy ion collisions on the number of spectators, a proxy of the magnitude of the magnetic field. The article also presents the extension of this approach to a two dimensional space, formed by both the aforementioned proxy of the magnetic field strength but also a proxy of the final state ellipticity, a key ingredient of the background in these measurements, for each centrality interval. This provides an exciting possibility to experiments to isolate the background contributions from the potential CME signal.

Mathematical modeling of the magnetic field in the vicinity of narrow capillaries

A mathematical model of the magnetic field, which is generated by negative charges located on the outer side of the red blood cell (RBC) membrane, has been constructed. When modeling, the geometric (area, volume) and physical (speed, number of revolutions per second, charge, number of charges on the membrane) characteristics of a red blood cell in a narrow capillary are taken into account. Computer calculations made it possible to find the magnetic field strength near a single RBC rolling along a narrow capillary. Calculations were also carried out to determine the magnetic field strength in the vicinity of a capillary through which several RBCs move. The dependence of the maximum magnetic field strength on the distances between RBCs (hematocrit) was found. In particular, it is shown that at distances from the capillary equal to 8 capillary diameters, the maximum magnetic field intensity changes on average by 1.3 times with an increase in hematocrit by 1.5 times (from 12.27% to 18.25%).

Calculation of specific loss power of magnetic fluids by mean spherical approximation (MSA) model

According to various theoretical models the heating performance, i.e. the volumetric power dissipation of magnetic fluids under alternating magnetic field is proportional to the imaginary part of the complex susceptibility. However, the magnetic field strength dependence of the susceptibility is usually taken into account only by the Langevin theory. The main goal of our work was to propose a theoretical model based on the series expansion of the mean spherical approximation (MSA) theory to calculate the magnetic properties, and derive the power dissipation by including the dipole-dipole interactions. The predictions of the theory for the field strength dependence of the power dissipation was verified by comparison with experimental data. It was shown that compared to the MSA theory the generally used Langevin limiting case underestimates the power dissipation. The contribution of the higher-order terms in the approximated dynamic susceptibility at different field strengths was also investigated.

Density and magnetic field strength dependence of radio pulses induced by energetic air showers

We have studied the effect of changing the density and magnetic field strength in the coherent pulses that are emitted as energetic showers develop in the atmosphere. For this purpose we have developed an extension of ZHS, a program to calculate coherent radio pulses from electromagnetic showers in homogeneous media, to account for the Lorentz force due to a magnetic field. This makes it possible to perform quite realistic simulations of radio pulses from air showers in a medium similar to the atmosphere but without variations of density with altitude. The effects of independently changing the density, the refractive index and the magnetic field strength are studied in the frequency domain for observers in the Cherenkov direction at far distances from the shower. This approach is particularly enlightening providing an explanation of the spectral behavior of the induced electric field in terms of shower development parameters. More importantly, it clearly displays the complex scaling properties of the pulses as density and magnetic field strength are varied. The usually assumed linear behavior of electric field amplitude with magnetic field strength is shown to hold up to a given magnetic field strength at which the extra time delays due to the deflection in the magnetic field break it. Scaling properties of the pulses are obtained as the density of air decreases relative to sea level. A remarkably accurate scaling law is obtained that relates the spectra of pulses obtained when reducing the density and increasing the magnetic field.

Experimental Study of the Working Process in Liquid Rocket Engines by an Electrophysical Diagnostic Method

An experimental study of the self electromagnetic field generated by the low-temperature plasma of the fuel combustion products of a model liquid-propellant rocket engine is carried out. The fuel components were gaseous oxygen and ethyl alcohol. When modeling emergency situations in the operation of the model rocket engine, the intensity of its self electromagnetic field generated by the ionized products of fuel combustion was recorded. A linear dependence of the self magnetic field strength on the pressure in the combustion chamber in the range 2.2–3.5 MPa was established. The feasibility of noncontact electrophysical methods for diagnosing the working process in aircraft power plants using as a useful signal the value of the magnetic field strength is shown.

Curie-temperature dependence of microwave heating behavior of NixZn(1−x)Fe2O4 powders

Recently, the microwave well absorber goes noticed as a heating aid to establish a microwave chemical plant. We determine the mechanism of the rapid and selective heating of magnetic conductive particles by electric and magnetic microwave fields. Furthermore, we investigate the dependencies of the Curie temperature of NixZn(1−x)Fe2O4 powders on their heating behaviors by employing a conventional microwave oven. In these experiments, the maximum microwave heating temperature increases with the Curie temperature of ferrites. To investigate the dependence of the microwave magnetic field strength on the heating behavior, we focus a pure magnetic field separated from 2.45 GHz microwaves onto these ferrites, and the magnetic field enhanced by a single-mode cavity is used to heat the ferrites at higher Curie temperatures. Our results indicate that there are two types of energy interactions between the ferrites and the microwave magnetic field with two different mechanisms: magnetic loss and eddy current heating. Furthermore, the heating performance of the ferrites as microwave absorbers is evaluated in comparison with SiC, which is a typical microwave absorber used in microwave processing. We believe that our findings can contribute to further advancements in microwave chemistry and related fields.

Complex vibration modes in magnetorheological fluid-based sandwich beams

The study investigates the complex vibration modes of sandwich beams filled with magnetorheological fluids (MRFs). An approach is suggested involving both experiments and calculation procedures to determine the complex modes of the beams’ free vibrations. Testing was done on three-layered cantilever beam filled with MRF and exposed to the magnetic field generated by an electromagnet. The purpose of the work is to analyse the influence of MRF on the beam motion and to determine the complex modes. Measurements of free vibrations of two beams filled with MRFs differing in the iron particle content by volume were taken in a purpose-built experimental set-up. Vibrations of the beam were registered under magnetic field varying in strength and for varied electromagnet’s positions with respect to the beam fixed end. Thus obtained measurement data were utilised to derive the dependence of magnetic field strength and electromagnet position on beam stiffness and damping. Complex modes were obtained with the use of finite element (FE) proposed by the authors for the investigated beams. Results are given as plots of modulus and argument of the complex vibration mode against the co-ordinate defining the position along the beam axis. Results revealed major discrepancies between the values of real and imaginary parts of the beams’ vibrations modes.

Collision-induced stimulated photon echo generated at transition 0–1 on broad spectral line conditions

For the first time, the collision induced stimulated photon echo generated at transition 1SP1 of 174Yb (type 0–1) in the mixture of gases Yb + Xe was investigated in the presence of weak longitudinal magnetic field, with experimental parameters corresponding to broad spectral line conditions. Comparison of the experimental echo amplitude versus magnetic field strength dependence with the theoretical curve shows a very good agreement, giving rise to an improved estimate for the difference between alignment and orientation decay rates.

Coronal flux ropes and their interplanetary counterparts

We report on a study comparing coronal flux ropes inferred from eruption data with their interplanetary counterparts constructed from in situ data. The eruption data include the source-region magnetic field, post-eruption arcades, and coronal mass ejections (CMEs). Flux ropes were fit to the interplanetary CMEs (ICMEs) considered for the 2011 and 2012 Coordinated Data Analysis Workshops (CDAWs). We computed the total reconnected flux involved in each of the associated solar eruptions and found it to be closely related to flare properties, CME kinematics, and ICME properties. By fitting flux ropes to the white-light coronagraph data, we obtained the geometric properties of the flux ropes and added magnetic properties derived from the reconnected flux. We found that the CME magnetic field in the corona is significantly higher than the ambient magnetic field at a given heliocentric distance. The radial dependence of the flux-rope magnetic field strength is faster than that of the ambient magnetic field. The magnetic field strength of the coronal flux ropes is also correlated with that in interplanetary flux ropes constructed from in situ data, and with the observed peak magnetic field strength in ICMEs. The physical reason for the observed correlation between the peak field strength in ICMEs is the higher magnetic field content in faster coronal flux ropes and ultimately the higher reconnected flux in the eruption region. The magnetic flux ropes constructed from the eruption data and coronagraph observations provide a realistic input that can be used by various models to predict the magnetic properties of ICMEs at Earth and other destination in the heliosphere.

Towards a universal master curve in magnetorheology

We demonstrate that inverse ferrofluids behave as model magnetorheological fluids. A universal master curve is proposed, using a reduced Mason number, under the frame of a structural viscosity model where the magnetic field strength dependence is solely contained in the Mason number and the particle concentration is solely contained in the critical Mason number (i.e. the yield stress). A linear dependence of the critical Mason number with the particle concentration is observed that is in good agreement with a mean (average) magnetization approximation, particle level dynamic simulations and micromechanical models available in the literature.

Linking brain vascular physiology to hemodynamic response in ultra-high field MRI

Functional MRI using blood oxygenation level-dependent (BOLD) contrast indirectly probes neuronal activity via evoked cerebral blood volume (CBV) and oxygenation changes. Thus, its spatio-temporal characteristics are determined by vascular physiology and MRI parameters. In this paper, we focus on the spatial distribution and time course of the fMRI signal and their magnetic field strength dependence. Even though much is still unknown, the following consistent picture is emerging: a) For high spatial resolution imaging, fMRI contrast-to-noise increases supra-linearly with field strength. b) The location and spacing of penetrating arteries and ascending veins in the cortical tissue are not correlated to cortical columns, imposing limitations on achievable point-spread function (PSF) in fMRI. c) Baseline CBV distribution may vary over cortical layers biasing fMRI signal to layers with high CBV values. d) The largest CBV change is in the tissue microvasculature, less in surface arteries and even less in pial veins. e) Venous CBV changes are only relevant for longer stimuli, and oxygenation changes are largest in post-capillary blood vessels. f) The balloon effect (i.e. slow recovery of CBV to baseline) is located in the tissue, consistent with the fact that the post-stimulus undershoot has narrower spatial PSF than the positive BOLD response. g) The onset time following stimulation has been found to be shortest in middle/lower layers, both in optical imaging and high-resolution fMRI, but we argue and demonstrate with simulations that varying signal latencies can also be caused by vascular properties and, therefore, may potentially not be interpreted as neural latencies. With simulations, we illustrate the field strength dependency of fMRI signal transients, such as the adaptation during stimulation, initial dip and the post-stimulus undershoot. In sum, vascular structure and function impose limitations on the achievable PSF of fMRI and give rise to complex fMRI transients, which contain time-varying amount of excitatory and inhibitory neuronal information. Nevertheless, non-invasive fMRI at ultra-high magnetic fields not only provides high contrast-to-noise but also an unprecedented detailed view on cognitive processes in the human brain.

Magnetic fields of young solar twins

The goal of this work is to study the magnetic fields of six young solar-analogue stars both individually, and collectively, to search for possible magnetic field trends with age. If such trends are found, they can be used to understand magnetism in the context of stellar evolution of solar-like stars and, the past of the Sun and the solar system. This is also important for the atmospheric evolution of the inner planets, Earth in particular. We used Stokes IV data from two different spectropolarimeters, NARVAL and HARPSpol. The least-squares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a modern Zeeman-Doppler imaging code in order to reconstruct the magnetic topology of all stars and the brightness distribution of one of our studied stars. Our results show a significant decrease in the magnetic field strength and energy as the stellar age increases from 100Myr to 250Myr while there is no significant age dependence of the mean magnetic field strength for stars with ages 250-650Myr. The spread in the mean field strength between different stars is comparable to the scatter between different observations of individual stars. The meridional field component has the weakest strength compared to the radial and azimuthal field components in 15 out of the 16 magnetic maps. It turns out that 89-97% of the magnetic field energy is contained in l=1-3. There is also no clear trend with age and distribution of field energy into poloidal/toroidal and axisymmetric/non-axisymmetric components within the sample. The two oldest stars in this study do show a twice as strong octupole component compared to the quadrupole component. This is only seen in one out of 13 maps of the younger stars. One star, chi1 Ori displays two field polarity switches during almost 5 years of observations suggesting a magnetic cycle length of either 2, 6 or 8 years.

Pion and σ-meson Properties in a Strong Magnetic Field**Supported by the National Natural Science Foundation of China under Grant Nos. 10935001, 11175004, and 11435001, and the National Key Basic Research Program of China under Grant Nos. G2013CB834400 and G2015CB856900

With the Nambu–Jona-Lasinio (NJL) model we calculate the properties of pion and σ-meson at finite temperature and finite magnetic field. The obtained temperature and magnetic field strength dependence of the constituent quark mass M, the pion and σ-meson masses and the neutral pion decay constant indicates that, in the simple four fermion interaction model, there exists the magnetic catalysis effect. It also shows that the Gell-Mann–Oakes–Renner relation is violated obviously with the increasing of the temperature, and the effect of the magnetic field becomes pronounced only around the critical temperature. The deviation of the critical temperatures obtained with different criteria indicates that the chiral phase transition driven by the temperature in the magnetic field strength region we have considered is in fact a crossover.

Interplanetary coronal mass ejections from MESSENGER orbital observations at Mercury

AbstractWe use observations from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, in orbit around Mercury, to investigate interplanetary coronal mass ejections (ICMEs) near 0.3 AU. MESSENGER is the first spacecraft since Helios 1 and 2 in the 1980s to make in situ measurements of the interplanetary medium at heliocentric distances < 0.5 AU. As such, it presents a unique opportunity for observing the innermost heliosphere. It also allows for observations of ICMEs well within 1 AU to study their evolution as they expand and propagate outward, interacting with the solar wind. We catalog ICME events observed by the MESSENGER Magnetometer between 2011 and 2014 and present statistical analyses of ICME properties at Mercury. In addition, using existing data sets of ICMEs at 1 AU, we investigate key ICME property changes from Mercury to 1 AU. We find good agreement with previous studies for the magnetic field strength dependence on distance, and we also find evidence that ICME deceleration continues past the orbit of Mercury. This paper describes the database of ICMEs from MESSENGER orbital observations around Mercury, which is publicly available through the supporting information (Table S1) associated with this manuscript and the Virtual Energetic Particle Observatory. Our ICME database will prove particularly useful for multipoint spacecraft studies of recent ICMEs, as well as for model validation of ICME properties.

19F spin–lattice relaxation of perfluoropolyethers: Dependence on temperature and magnetic field strength (7.0–14.1 T)

Fluorine (19F) MRI of perfluorocarbon-labeled cells has become a powerful technique to track the migration and accumulation of cells in living organisms. It is common to label cells for 19F MRI with nanoemulsions of perfluoropolyethers that contain a large number of chemically equivalent fluorine atoms. Understanding the mechanisms of 19F nuclear relaxation, and in particular the spin–lattice relaxation of these molecules, is critical to improving experimental sensitivity. To date, the temperature and magnetic field strength dependence of spin–lattice relaxation rate constant (R1) for perfluoropolyethers has not been described in detail. In this study, we evaluated the R1 of linear perfluoropolyether (PFPE) and cyclic perfluoro-15-crown-5 ether (PCE) at three magnetic field strengths (7.0, 9.4, and 14.1T) and at temperatures ranging from 256–323K. Our results show that R1 of perfluoropolyethers is dominated by dipole–dipole interactions and chemical shift anisotropy. R1 increased with magnetic field strength for both PCE and PFPE. In the temperature range studied, PCE was in the fast motion regime (ωτc<1) at all field strengths, but for PFPE, R1 passed through a maximum, from which the rotational correlation time was estimated. The importance of these measurements for the rational design of new 19F MRI agents and methods is discussed.

Spectroscopic Study and Motion Analysis of Arc Spot Initiated on Nanostructured Tungsten

Arcing on the nanostructured tungsten surface has been examined recently because it gives rise to the erosion of materials and impurity transport toward the core plasma in a nuclear fusion reactor. Arcing was initiated on a helium-exposed tungsten surface, on which nanostructured tungsten was formed, by irradiation with ruby laser pulses of 0.08 MJ·m-2. The motion of an arc spot was observed with a fast-framing camera. The magnetic field strength and arc current dependences of velocity were discussed on the basis of experimental observation. Arc trails were observed using a digital fine scope to determine the relationship between the grouping width of an arc trail and arc velocity; the changes in grouping width and condition of the specimen surface are discussed. Spectroscopic measurements were performed to determine the electron temperature by the Boltzmann plot method.

Measurements on the Temperature, Dynamic Strain Amplitude and Magnetic Field Strength Dependence of the Dynamic Shear Modulus of Magnetosensitive Elastomers in a Wide Frequency Range

A measurement study is conducted to investigate how changes in temperature, dynamic strain amplitude, and magnetic field strength influence the behavior of a magnetosensitive material. During the measurements seven temperatures, four magnetic fields, and three dynamic strain amplitudes are used over a 200 to 800 Hz frequency range. The results indicate a decrease in shear modulus magnitude as the dynamic strain amplitude is increased. As the frequency and magnetic field strength increases the magnitude increases. However, the measurements indicate that the temperature is the most influential of the parameters as the material stiffens significantly when the temperature reaches the transition phase. Understanding the temperature dependence increases the knowledge of magnetosensitive materials.

Detailing magnetic field strength dependence and segmental artifact distribution of myocardial effective transverse relaxation rate at 1.5, 3.0, and 7.0 T

Realizing the challenges and opportunities of effective transverse relaxation rate (R2 *) mapping at high and ultrahigh fields, this work examines magnetic field strength (B0 ) dependence and segmental artifact distribution of myocardial R2 * at 1.5, 3.0, and 7.0 T. Healthy subjects were considered. Three short-axis views of the left ventricle were examined. R2 * was calculated for 16 standard myocardial segments. Global and mid-septum R2 * were determined. For each segment, an artifactual factor was estimated as the deviation of segmental from global R2 * value. The global artifactual factor was significantly enlarged at 7.0 T versus 1.5 T (P = 0.010) but not versus 3.0 T. At 7.0 T, the most severe susceptibility artifacts were detected in the inferior lateral wall. The mid-septum showed minor artifactual factors at 7.0 T, similar to those at 1.5 and 3.0 T. Mean R2 * increased linearly with the field strength, with larger changes for global heart R2 * values. At 7.0 T, segmental heart R2 * analysis is challenging due to macroscopic susceptibility artifacts induced by the heart-lung interface and the posterior vein. Myocardial R2 * depends linearly on the magnetic field strength. The increased R2 * sensitivity at 7.0 T might offer means for susceptibility-weighted and oxygenation level-dependent MR imaging of the myocardium.

Observation of exponential spectra and Lorentzian pulses in the TJ-K stellarator

An experimental investigation of the low-frequency density fluctuations in the plasma edge region of the TJ-K stellarator [N. Krause et al., Rev. Sci. Inst. 73, 3474 (2002)] finds that the ensemble-averaged frequency spectra exhibit a near exponential frequency dependence whose origin can be traced to individual pulses having a Lorentzian temporal shape. Similar features have been previously observed [D. C. Pace et al., Phys. Plasmas 15, 122304 (2008)] in a linear magnetized device under conditions in which cross-field pressure gradients are present. The reported observation of such features within the turbulent environment of a toroidal confinement device provides support for the conjecture that the underlying processes are a general feature of pressure gradients. Also presented is the magnetic field strength dependence of the pulse widths and the waiting time distribution between pulses.

Dynamic rheology of sphere- and rod-based magnetorheological fluids

The effect of particle shape in the small amplitude oscillatory shear behavior of magnetorheological (MR) fluids is investigated from zero magnetic field strengths up to 800 kA/m. Two types of MR fluids are studied: the first system is prepared with spherical particles and a second system is prepared with rodlike particles. Both types of particles are fabricated following practically the same precipitation technique and have the same intrinsic magnetic and crystallographic properties. Furthermore, the distribution of sphere diameters is very similar to that of rod thicknesses. Rod-based MR fluids show an enhanced MR performance under oscillatory shear in the viscoelastic linear regime. A lower magnetic field strength is needed for the structuration of the colloid and, once saturation is fully achieved, a larger storage modulus is observed. Existing sphere- and rod-based models usually underestimate experimental results regarding the magnetic field strength and particle volume fraction dependences of both storage modulus and yield stress. A simple model is proposed here to explain the behavior of microrod-based MR fluids at low, medium and saturating magnetic fields in the viscoelastic linear regime in terms of magnetic interaction forces between particles. These results are further completed with rheomicroscopic and dynamic yield stress observations.