A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution
A broad class of astronomical accretion disks is presently shown to be dynamically unstable to axisymmetric disturbances in the presence of a weak magnetic field, an insight with consequently broad applicability to gaseous, differentially-rotating systems. In the first part of this work, a linear analysis is presented of the instability, which is local and extremely powerful; the maximum growth rate, which is of the order of the angular rotation velocity, is independent of the strength of the magnetic field. Fluid motions associated with the instability directly generate both poloidal and toroidal field components. In the second part of this investigation, the scaling relation between the instability's wavenumber and the Alfven velocity is demonstrated, and the independence of the maximum growth rate from magnetic field strength is confirmed. 25 refs.
Comparison of Magnetic Properties of MRI Contrast Media Solutions at Different Magnetic Field Strengths
Rationale and Objectives:To characterize and compare commercially available contrast media (CM) for magnetic resonance imaging (MRI) in terms of their relaxivity at magnetic field strengths ranging from 0.47 T to 4.7 T at physiological temperatures in water and in plasma. Relaxivities also were quantified in whole blood at1.5 T. Methods:Relaxivities of MRI-CM were determined by nuclear magnetic resonance (NMR) spectroscopy at 0.47 T and MRI phantom measurements at 1.5 T, 3 T, and 4.7 T, respectively. Both longitudinal (T1) and transverse relaxation times (T2) were measured by appropriate spin-echo sequences. Nuclear magnetic resonance dispersion (NMRD) profiles were also determined for all agents in water and in plasma. Results:Significant dependencies of relaxivities on the field strength and solvents were quantified. Protein binding leads to both increased field strength and solvent dependencies and hence to significantly altered T1 relaxivity values at higher magnetic field strengths. Conclusions:Awareness of the field strength and solvent associated with relaxivity data is crucial for the comparison and evaluation of relaxivity values. Data observed at 0.47 T can thus be misleading and should be replaced by relaxivities measured at 1.5 T and at 3 T in plasma at physiological temperature.
Magnetic Fields in Molecular Clouds: Observations Confront Theory
This paper presents a summary of all 27 available sensitive Zeeman measurements of magnetic field strengths in molecular clouds together with other relevant physical parameters. From these data input parameters to magnetic star formation theory are calculated, and predictions of theory are compared with observations. Results for this cloud sample are the following: (1) Internal motions are supersonic but approximately equal to the Alfv?n speed, which suggests that supersonic motions are likely MHD waves. (2) The ratio of thermal to magnetic pressures ?p ? 0.04, implying that magnetic fields are important in the physics of molecular clouds. (3) The mass-to-magnetic flux ratio is about twice critical, which suggests but does not require that static magnetic fields alone are insufficient to support clouds against gravity. (4) Kinetic and magnetic energies are approximately equal, which suggests that static magnetic fields and MHD waves are roughly equally important in cloud energetics. (5) Magnetic field strengths scale with gas densities as |B| ?? with ? ? 0.47; this agrees with the prediction of ambipolar diffusion driven star formation, but this scaling may also be predicted simply by Alfv?nic motions. The measurements of magnetic field strengths in molecular clouds make it clear that magnetic fields are a crucial component of the physics governing cloud evolution and star formation.
Magnetic clouds and force‐free fields with constant alpha
Magnetic clouds observed at 1 AU are modeled as cylindrically symmetric, constant alpha force-free magnetic fields. The model satisfactorily explains the types of variations of the magnetic field direction that are observed as a magnetic cloud moves past a spacecraft in terms of the possible orientations of the axis of a magnetic cloud. The model also explains why the magnetic field strength is observed to be higher inside a magnetic cloud than near its boundaries. However, the model predicts that the magnetic field strength profile should be symmetric with respect to the axis of the magnetic cloud, whereas observations show that this is not generally the case.
Electrodynamics of Magnetars: Implications for the Persistent X-Ray Emission and Spin-down of the Soft Gamma Repeaters and Anomalous X-Ray Pulsars
We consider the structure of neutron star magnetospheres threaded by large-scale electrical currents and the effect of resonant Compton scattering by the charge carriers (both electrons and ions) on the emergent X-ray spectra and pulse profiles. In the magnetar model for the soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs), these currents are maintained by magnetic stresses acting deep inside the star, which generate both sudden disruptions (SGR outbursts) and more gradual plastic deformations of the rigid crust. We construct self-similar force-free equilibria of the current-carrying magnetosphere with a power-law dependence of magnetic field on radius, ∝ r-(2+p), and show that a large-scale twist of field lines softens the radial dependence of the magnetic field to p < 1. The spin-down torque acting on the star is thereby increased in comparison with an orthogonal vacuum dipole. We comment on the strength of the surface magnetic field in the SGR and AXP sources, as inferred from their measured spin-down rates, and the implications of this model for the narrow measured distribution of spin periods. A magnetosphere with a strong twist [B/Bθ = O(1) at the equator] has an optical depth ~1 to resonant cyclotron scattering, independent of frequency (radius), surface magnetic field strength, or charge/mass ratio of the scattering charge. When electrons and ions supply the current, the stellar surface is also heated by the impacting charges at a rate comparable to the observed X-ray output of the SGR and AXP sources, if Bdipole ~ 1014 G. Redistribution of the emerging X-ray flux at the cyclotron resonance will strongly modify the emerging pulse profile and, through the Doppler effect, generate a nonthermal tail to the X-ray spectrum. We relate the sudden change in the pulse profile of SGR 1900+14 following the 1998 August 27 giant flare to an enhanced optical depth at the electron cyclotron resonance resulting from a sudden twist imparted to the external magnetic field during the flare. The self-similar structure of the magnetosphere should generate frequency-independent profiles; more complicated pulse profiles may reflect the presence of higher multipoles, ion cyclotron scattering, or possibly nonresonant Compton scattering of O-mode photons by pair-loaded currents.
Influence of molecular parameters and increasing magnetic field strength on relaxivity of gadolinium- and manganese-based T1 contrast agents.
Simulations were performed to understand the relative contributions of molecular parameters to longitudinal (r(1)) and transverse (r(2)) relaxivity as a function of applied field, and to obtain theoretical relaxivity maxima over a range of fields to appreciate what relaxivities can be achieved experimentally. The field-dependent relaxivities of a panel of gadolinium and manganese complexes with different molecular parameters, water exchange rates, rotational correlation times, hydration state, etc. were measured to confirm that measured relaxivities were consistent with theory. The design tenets previously stressed for optimizing r(1) at low fields (very slow rotational motion; chelate immobilized by protein binding; optimized water exchange rate) do not apply at higher fields. At 1.5 T and higher fields, an intermediate rotational correlation time is desired (0.5-4 ns), while water exchange rate is not as critical to achieving a high r(1). For targeted applications it is recommended to tether a multimer of metal chelates to a protein-targeting group via a long flexible linker to decouple the slow motion of the protein from the water(s) bound to the metal ions. Per ion relaxivities of 80, 45, and 18 mM(-1) s(-1) at 1.5, 3 and 9.4 T, respectively, are feasible for Gd(3+) and Mn(2+) complexes.
Magnetic field decay in isolated neutron stars
We investigate three mechanisms that promote the loss of magnetic flux from an isolated neutron star. Ohmic decay produces a diffusion of the magnetic field with respect to the charged particles. It proceeds at a rate that is inversely proportional to the electric conductivity and independent of the magnetic field strength. Ohmic decay occurs in both the fluid core and solid crust of a neutron star, but it is too slow to directly affect magnetic fields of stellar scale. Ambipolar diffusion involves a drift of the magnetic field and charged particles relative to the neutrons. The drift speed is proportional to the second power of the magnetic field strength if the protons form a normal fluid. Variants of ambipolar diffusion include both the buoyant rise and the dragging by superfluid neutron vortices of magnetic flux tubes. Ambipolar diffusion operates in the outer part of the fluid core where the charged particle composition is homogeneous, protons and electrons being the only species. The charged particle flux associated with ambipolar diffusion decomposes into a solenoidal and an irrotational component. Both components are opposed by frictional drag. The irrotational component perturbs the chemical equilibrium between neutrons, protons, and electrons, thus generating pressure gradients that effectively choke it. The solenoidal component is capable of transporting magnetic flux from the outer core to the crust on a short time scale. Magnetic flux that threads the inner core, where the charged particle composition is inhomogeneous, would be permanently trapped unless particle interactions could rapidly smooth departures from chemical equilibrium. Magnetic fields undergo a Hall drift related to the Hall component of the electric field. The drift speed is proportional to the magnetic field strength. Hall drift occurs throughout a neutron star. Unlike ohmic decay and ambipolar diffusion which are dissipative, Hall drift conserves magnetic energy. Thus, it cannot by itself be responsible for magnetic field decay. However, it can enhance the rate of ohmic dissipation. In the solid crust, only the electrons are mobile and the tangent of the Hall angle is large. There, the evolution of the magnetic field resembles that of vorticity in an incompressible fluid at large Reynolds number. This leads us to speculate that the magnetic field undergoes a turbulent cascade terminated by ohmic dissipation at small scales. The small-scale components of the magnetic field are also transported by Hall drift waves from the inner crust where ohmic dissipation is slow to the outer crust where it is rapid. The diffusion of magnetic flux through the crust takes ~ 5 x 10^8/B_(12) yr, where B_(12) is the crustal magnetic field strength measured in units of 10^(12) G.
Cosmological magnetic fields: their generation, evolution and observation
We review the possible mechanisms for the generation of cosmological magnetic fields, discuss their evolution in an expanding Universe filled with the cosmic plasma and provide a critical review of the literature on the subject. We put special emphasis on the prospects for observational tests of the proposed cosmological magnetogenesis scenarios using radio and gamma-ray astronomy and ultra-high-energy cosmic rays. We argue that primordial magnetic fields are observationally testable. They lead to magnetic fields in the intergalactic medium with magnetic field strength and correlation length in a well defined range.We also state the unsolved questions in this fascinating open problem of cosmology and propose future observations to address them.
MR imaging of the menisci and cruciate ligaments: a systematic review.
PURPOSE To systematically review and synthesize published data on the diagnostic performance of magnetic resonance (MR) imaging of the menisci and cruciate ligaments and to assess the effect of study design characteristics and magnetic field strength on diagnostic performance. MATERIALS AND METHODS Articles published between 1991 and 2000 were included if at least 30 patients were studied, arthroscopy was the reference standard, the magnetic field strength was reported, positivity criteria were defined, and the absolute numbers of true-positive, false-negative, true-negative, and false-positive results were available or derivable. Pooled weighted and summary receiver operating characteristic (ROC) analyses were performed for tears of both menisci and both cruciate ligaments separately and for the four lesions combined, by using random effects models. Differences were assessed according to lesion type. RESULTS Twenty-nine of 120 retrieved articles were included. Pooled weighted sensitivity was higher for medial meniscal tears than that for lateral meniscal tears. However, pooled weighted specificity for the medial meniscus was lower than that for the lateral meniscus. In summary ROC analyses performed per lesion, various study design characteristics were found to influence diagnostic performance. Higher magnetic field strength significantly improved discriminatory power only for anterior cruciate ligament tears. When all lesions were combined in one overall summary ROC analysis, magnetic field strength was a significant but modest predictor of diagnostic performance. CONCLUSION Diagnostic performance of MR imaging of the knee is different according to lesion type and is influenced by various study design characteristics. Higher magnetic field strength modestly improves diagnostic performance, but a significant effect was demonstrated only for anterior cruciate ligament tears.
Free radical mechanism for the effects of environmental electromagnetic fields on biological systems.
The radical pair mechanism is discussed as a possible route whereby a magnetic field of environmental strength might affect a biological system. It is well established as the origin of reproducible field effects in chemistry, and these can be observed even at very low magnetic field strengths, including that of the geomagnetic field. Here it is attempted to give a description which might assist experimentalists working in biological laboratories to devize tests of its relevance to their work. The mechanism is well understood and a specific theoretical approach is taken to explore and emphasize the importance of the lifetime of the radical pair and the precise chemical natures of the radicals which comprise it in affecting the size of the low-field effects. Further subsequent processes are likely necessary to cause this primary effect to attain biological significance. Arguments are provided to suggest that the encounters of freely diffusing pairs (F-pairs) of radicals are unlikely to produce significant effects in biology.
Anisotropy and magnetic field effects on the entanglement of a two qubit Heisenberg XY chain.
We investigate the entanglement of a two-qubit anisotropic Heisenberg XY chain in thermal equilibrium at temperature T in the presence of an external magnetic field B along the z axis. By means of the combined influences of anisotropic interactions and a magnetic field B, one is able to produce entanglement for any finite T, by adjusting the magnetic field strength. This contrasts with the isotropic interaction or the B = 0 cases, for which there is no entanglement above a critical temperature T(c) that is independent of the external B field.
Toward a Universal Scaling Relation between Jet Power and Radio Power
We present an analysis of the energetics and particle content of the lobes of 24 radio galaxies at the cores of cooling clusters. The radio lobes in these systems have created visible cavities in the surrounding hot, X-ray-emitting gas, which allow direct measurement of the mechanical jet power of radio sources over six decades of radio luminosity, independently of the radio properties themselves. We find that jet (cavity) power increases with radio synchrotron power approximately as P-jet similar to L-radio(beta), where 0.35 <= beta <= 0.70 depending on the bandpass of measurement and state of the source. However, the scatter about these relations caused by variations in radiative efficiency spans more than 4 orders of magnitude. A number of factors contribute to this scatter, including aging, entrainment, variations in magnetic field strengths, and the partitioning of energy between electrons and nonradiating heavy particles. After accounting for variations in synchrotron break frequency (age), the scatter is reduced by approximate to 50%, yielding the most accurate scaling relation available between the lobe radio power and the jet (cavity) power. Furthermore, we place limits on the magnetic field strengths and particle content of the radio lobes using a variety of X-ray constraints. We find that the lobe magnetic field strengths vary between a few to several tens of microgauss depending on the age and dynamical state of the lobes. If the cavities are maintained in pressure balance with their surroundings and are supported by internal fields and particles in equipartition, the ratio of energy in electrons to heavy particles (k) must vary widely from approximately unity to 4000, consistent with heavy (hadronic) jets.
Magnetic Field Dependence of Nitrogen−Proton J Splittings in 15N-Enriched Human Ubiquitin Resulting from Relaxation Interference and Residual Dipolar Coupling
One-bond 1JNH couplings have been measured in 15N-enriched human ubiquitin and range from 91.1 to 95.6 Hz. Measurements have been carried out using two different methods and at 1H frequencies of 360, 500, and 600 MHz. The best method yields a precision of ca 0.02 Hz, and permits reliable measurement of the small changes (<0.3 Hz) in 1JNH splitting that occur when the magnetic field strength is increased from 8.5 to 14 T. The dependence of the 1JNH splittings on the strength of the static magnetic field originates from two sources: a dynamic frequency shift caused by interference of the 15N chemical shift anisotropy and the 15N−1H dipolar coupling relaxation mechanisms, and a dipolar contribution caused by a small degree of alignment resulting from the anisotropic magnetic susceptibility of the diamagnetic protein. Best fitting of the measured data yields an orientation-independent decrease of 0.11 Hz in the 1JNH splittings at 600 MHz relative to 360 MHz, in perfect agreement with theoretical predictions ...
High magnetic field water and metabolite proton T1 and T2 relaxation in rat brain in vivo
Comprehensive and quantitative measurements of T1 and T2 relaxation times of water, metabolites, and macromolecules in rat brain under similar experimental conditions at three high magnetic field strengths (4.0 T, 9.4 T, and 11.7 T) are presented. Water relaxation showed a highly significant increase (T1) and decrease (T2) with increasing field strength for all nine analyzed brain structures. Similar but less pronounced effects were observed for all metabolites. Macromolecules displayed field‐independent T2 relaxation and a strong increase of T1 with field strength. Among other features, these data show that while spectral resolution continues to increase with field strength, the absolute signal‐to‐noise ratio (SNR) in T1/T2‐based anatomical MRI quickly levels off beyond ∼7 T and may actually decrease at higher magnetic fields. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Magnetic nanoparticles for interstitial thermotherapy – feasibility, tolerance and achieved temperatures
Background: The concept of magnetic fluid hyperthermia is clinically evaluated after development of the whole body magnetic field applicator MFH® 300F and the magnetofluid MFL 082AS. This new system for localized thermotherapy is suitable either for hyperthermia or thermoablation. The magnetic fluid, composed of iron oxide nanoparticles dispersed in water, must be distributed in the tumour and is subsequently heated by exposing to an alternating magnetic field in the applicator. We performed a feasibility study with 22 patients suffering from heavily pretreated recurrences of different tumour entities, where hyperthermia in conjunction with irradiation and/or chemotherapy was an option. The potential to estimate (by post-implantation analyses) and to achieve (by improving the technique) a satisfactory temperature distribution was evaluated in dependency on the implantation technique. Material and methods: Three implantation methods were established: Infiltration under CT fluoroscopy (group A), TRUS (transrectal ultrasound) – guided implantation with X-fluoroscopy (group B) and intra-operative infiltration under visual control (group C). In group A and B the distribution of the nanoparticles can be planned prior to implantation on the basis of three-dimensional image datasets. The specific absorption rates (SAR in W/kg) can be derived from the particle distribution imaged via CT together with the actual H-field strength (in kA/m). The temperature distribution in the tumour region is calculated using the bioheat-transfer equation assessing a mean perfusion value, which is determined by matching calculated temperatures to direct (invasive or endoluminal) temperature measurements in reference points in or near the target region. Results: Instillation of the magnetic fluid and the thermotherapy treatments were tolerated without or with only moderate side effects, respectively. Using tolerable H-field-strengths of 3.0–6.0 kA/m in the pelvis, up to 7.5 kA/m in the thoracic and neck region and >10.0 kA/m for the head, we achieved SAR of 60–380 W/kg in the target leading to a 40°C heat-coverage of 86%. However, the coverage with ≥42°C is unsatisfactory at present (30% of the target volume in group A and only 0.2% in group B). Conclusion: Further improvement of the temperature distribution is required by refining the implantation techniques or simply by increasing the amount of nanofluid or elevation of the magnetic field strength. From the actual nanoparticle distribution and derived temperatures we can extrapolate, that already a moderate increase of the H-field by only 2 kA/m would significantly improve the 42°C coverage towards 100% (98%). This illustrates the great potential of the nanofluid-based heating technology.
Guided Neurite Elongation and Schwann Cell Invasion into Magnetically Aligned Collagen in Simulated Peripheral Nerve Regeneration
High-strength magnetic fields were used to align collagen gel formed into 4-mm-diameter rods during the self-assembly of type I collagen monomers into fibrils. We developed an in vitro assay to study neurite elongation into the magnetically aligned collagen gel rods from dorsal root ganglia (DRG) explants placed onto one end of the rods. The depth of neurite elongation from chick embryo DRG neurons into these rods was found to be substantially greater than that observed in controls and increased with an increase in magnetic field strength, as did the collagen gel rod birefringence, indicative of collagen fibril alignment along the rod axis. Moreover, the axial bias of neurite elongation became more pronounced with an increase in magnetic field strength, presumably due to a contact guidance response of growth cones at the neurite tips. Coinvasion of Schwann cells from neonatal rat DRG was also studied in these assays using double immunolabeling. In the absence of serum, Schwann cells were highly associated with, and often trailed, elongating neurites. In the presence of serum, Schwann cells showed significantly higher rates of invasion and formed axially aligned chords reminiscent of bands of Büngner. These results may translate into an improved method of entubulation repair of transected peripheral nerves by directing and stimulating axonal growth through a tube filled with magnetically aligned collagen gel.
Solution of the Field Problem of the Germanium Gyrator
A mathematical solution is obtained of a two‐dimensional boundary‐value problem involving flow of electricity in a solid when Hall effect is present, it being assumed that only one type of carrier is involved and that there is no surface recombination. The solution is used to calculate the efficiency of a Hall‐effect ``gyrator,'' a four‐terminal circuit element which violates the reciprocity law, as function of relative electrode size, shape of boundary, and magnetic field strength. It is also shown how corrections must be applied in measurements of Hall voltage and magnetoresistance in short samples.Some of the results have been checked experimentally with fields up to 22 000 gauss. The calculations have been carried out for much higher fields as well and should prove useful in studies of materials such as indium antimonide which have higher mobilities than germanium.
Measuring the Magnetic Field on the Classical T Tauri Star BP Tauri
We examine several theories that describe how stellar magnetic fields on classical T Tauri stars (CTTSs) interact with their surrounding accretion disks. We demonstrate that these theories require magnetic field strengths ranging from a few hundred to several thousand gauss, depending on which model is used and more importantly on the properties of individual systems. For example, the CTTS BP Tau is predicted to have a relatively strong magnetic field (1.4-4.1 kG), which should be detectable. We present infrared (IR) and optical echelle spectra of BP Tau and several reference stars of similar spectral class. Using detailed spectrum synthesis and the latest model atmospheres, we fitted 12 absorption features in the optical spectrum, including the strong titanium oxide (TiO) band head at 7055 Å. For BP Tau we determine key stellar parameters: effective temperature (Teff=4055 ± 112 K), gravity (log g=3.67 ± 0.50), metallicity ([M/H]=0.18 ± 0.11), projected rotational velocity (v sin i=10.2 ± 1.8 km s-1), and optical veiling (r=0.00-0.15). A similar analysis of 61 Cyg B (K7 V) is used to validate the methodology. We then use the IR spectra to look for Zeeman broadening, which has a more pronounced effect at longer wavelengths. A Zeeman sensitive Ti I line at 2.2233 μm appears significantly broadened in BP Tau, relative to several rotationally broadened standard stars. The observed line is also significantly broader than predictions based on our optical analysis. Interpreting this excess broadening as Zeeman splitting of the Ti I line, we fitted the spectrum and find a distribution of field strengths whose surface averaged mean is B̄=2.6 ± 0.3 kG. We did not use the Zeeman sensitive Fe I line at 8468.4 Å when determining stellar or magnetic parameters for BP Tau, so this line provides a test of our results. The observed line profile is indeed broader than the nonmagnetic prediction, but the 8468.4 Å line gives a magnetic flux lower than what was obtained in the IR, perhaps indicating that strong fields are concentrated into cool spots. Finally, we investigate an ad hoc model in which the IR line is assumed to form in the accretion disk itself. We discuss several reasons why the magnetic model is preferred, but the disk atmosphere example illustrates that our magnetic field measurement must still be tested using several IR lines with a range of Zeeman sensitivities.
Magnetic processes in a collapsing dense core I. Accretion and ejection
Context. To understand the star formation process, it is important to study the collapse of a prestellar dense core. Aims. We investigate the effect of the magnetic field during the first collapse up to the formation of the first core, focusing particularly on the magnetic braking and the launching of outflows. Methods. We perform 3D AMR high resolution numerical simulations of a magnetically supercritical collapsing dense core using the RAMSES MHD code and develop semi-analytical models that we compare with the numerical results. Results. We study in detail the various profiles within the envelope of the collapsing core for various magnetic field strengths. Even modest values of magnetic field strength modify the collapse significantly. This is largely due to the amplification of the radial and toroidal components of the magnetic field by the differential motions within the collapsing core. For a weak magnetic intensity corresponding to an initial mass-to-flux over critical mass-to-flux ratio, μ equals 20 a centrifugally supported disk forms. The strong differential rotation triggers the growth of a slowly expanding magnetic tower. For higher magnetic field strengths corresponding to μ = 2, the collapse occurs primarily along the field lines, therefore delivering weaker angular momentum into the inner part whereas at the same time, strong magnetic braking occurs. As a consequence no centrifugally supported disk forms. An outflow is launched from the central thermally supported core. Detailed comparisons with existing analytical predictions indicate that it is magneto-centrifugally driven. Conclusions. For cores having a mass-to-flux over critical mass-to-flux radio μ < 5, the magnetic field appears to have a significant impact. The collapsing envelope is denser and flatter than in the hydrodynamical case and no centrifugally supported disk forms. For values μ < 20, the magnetic field drastically modifies the disk evolution. In a companion paper, the influence of the magnetic field on the dense core fragmentation is studied.
The heliospheric plasma sheet
High-resolution magnetic field and plasma data gathered by ISEE 3/ICE during several sector boundary crossings are used to investigate the narrow heliospheric current sheet (approximately equal 3 x 10 (exp 3) km to 10 (exp 4) km thick), together with the heliospheric plasma sheet in which it is embedded. The heliospheric plasma sheet region is identified by a significantly enhanced plasma beta caused by density enhancements and diminished magnetic field strength and is about 20 to 30 times the thickness of the current sheet. The thickness of the heliospheric plasma sheet is found to increase exponentially with its average proton density. The heliospheric current sheet is often displaced to one edge or the other of the heliospheric plasma sheet. Further, the point of maximum plasma beta in the plasma sheet, where the magnetic field strength is at a broad local minimum, is not colocated with the heliospheric current sheet. Within the plasma sheet, changes in the magnetic pressure are balanced by corresponding changes in the plasma thermal pressure as expected for a convected solar wind feature. In addition, observations show small pressure differences between the regions upstream and downstream of the plasma sheet, which are interpreted as causing the plasma sheet to move across the spacecraft.
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