Function Of Magnetic Field Strength Research Articles

Studies of magnetic fields in the solar photosphere using the line-ratio method

The longitudinal magnetic field measured using the Fe I λ 525 and Fe I λ 524.7 nm lines and global magnetic field of the sun differ depending on the observatory. To study the cause of these discrepancies, we calculate the H ‖(525)/H ‖(524.7) ratios for various combinations of magnetic elements and compare them with the corresponding observed values. We use the standard quiet model of the solar photosphere suggesting that there are magnetic fields of different polarities in the range between zero and several kilogauss. The magnetic element distribution is found as a function of magnetic field strength and the parameters of this distribution are determined for which the calculated H ‖(525)/H ‖(524.7) ratio agrees with the observed one. The sigma-components are found to be shifted differently for various points of the Fe I λ 525 nm profile calculated for the inhomogeneous magnetic field. The farther the point is from the line center, the larger the sigma-components shift. Such a peculiarity of the profiles may be responsible for the discrepancies in the measured values of the global magnetic field obtained at different observatories. The increase in modulus of the global magnetic field during the maxima of solar activity can be due to a larger fraction of magnetic elements with kilogauss magnetic fields.

Synthesis and magnetic properties of poly(amic acid) complexes containing 1,10-phenanthroline

AbstractA novel poly(amic acid) containing 1,10-phenanthroline (PPHPA) was first synthesized by the polycondensation of 4,4'-oxydiphthalic dianhydride (ODPA) with 5,6-diamine-1,10-phenanthroline (DAPH). Three polymeric complexes were first prepared by the reaction of polymer (PPHPA) with NiSO4, CuSO4, and NdCl3, respectively. The structures of the polymer and the complexes were characterized by IR, 1H-NMR, and elemental analysis. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0-50 kOe) at 5 K and as a function of temperature (5-300 K) at a magnetic field strength of 30 kOe. The results show that PPHPA-Ni2+ and PPHPA-Nd3+ were soft ferromagnets, whereas PPHPA-Cu2+ exhibited the features of an antiferromagnet.

Synthesis and Magnetic Properties of Poly(Schiff Base) Complex Containing 4,7-Disubstituted-1,10-Phenanthroline

A novel poly(Schiff base) containing 4,7-disubstituted-1,10-phenanthroline (BAPcBDA) was synthesized by the polycondensation of 4,7-Bis(4-aminophenoxy)-l, l0-phenanthroline (BAP) with 4,4'-Biphenyldicarboxaldehyde (BDA). The polymeric complex was first prepared by the reaction of polymer (BAPcBDA) with NiSO4. The structures of the monomer and polymer were characterized by IR,1H-NMR, and elemental analysis. The magnetic behaviors of the complex were measured as a function of magnetic field strength (0-50 kOe) at 5 K and as a function of temperature (5-300 K) at a magnetic field strength of 30 KOe. The results show that BAPcBDA-Ni2+exhibited the features of an antiferromagnet.

K-space reconstruction with anisotropic kernel support (KARAOKE) for ultrafast partially parallel imaging.

Partially parallel imaging (PPI) greatly accelerates MR imaging by using surface coil arrays and under-sampling k-space. However, the reduction factor (R) in PPI is theoretically constrained by the number of coils (N(C)). A symmetrically shaped kernel is typically used, but this often prevents even the theoretically possible R from being achieved. Here, the authors propose a kernel design method to accelerate PPI faster than R = N(C). K-space data demonstrates an anisotropic pattern that is correlated with the object itself and to the asymmetry of the coil sensitivity profile, which is caused by coil placement and B(1) inhomogeneity. From spatial analysis theory, reconstruction of such pattern is best achieved by a signal-dependent anisotropic shape kernel. As a result, the authors propose the use of asymmetric kernels to improve k-space reconstruction. The authors fit a bivariate Gaussian function to the local signal magnitude of each coil, then threshold this function to extract the kernel elements. A perceptual difference model (Case-PDM) was employed to quantitatively evaluate image quality. A MR phantom experiment showed that k-space anisotropy increased as a function of magnetic field strength. The authors tested a K-spAce Reconstruction with AnisOtropic KErnel support ("KARAOKE") algorithm with both MR phantom and in vivo data sets, and compared the reconstructions to those produced by GRAPPA, a popular PPI reconstruction method. By exploiting k-space anisotropy, KARAOKE was able to better preserve edges, which is particularly useful for cardiac imaging and motion correction, while GRAPPA failed at a high R near or exceeding N(C). KARAOKE performed comparably to GRAPPA at low Rs. As a rule of thumb, KARAOKE reconstruction should always be used for higher quality k-space reconstruction, particularly when PPI data is acquired at high Rs and/or high field strength.

Extreme-Values Statistics and Dynamics of Water at Protein Interfaces

Immobilized proteins present a unique interface with water. The water translational diffusive motions affect the high-frequency dynamics and the nuclear spin-lattice relaxation as with all surfaces; however, rare binding sites for water in protein systems add very low-frequency components to the dynamics spectrum. Water binding sites in protein systems are not identical, thus distributions of free energies and consequent dynamics are expected. (2)H(2)O spin-lattice relaxation rate measurements as a function of magnetic field strength characterize the local rotational fluctuations for protein-bound water molecules. The measurements are sensitive to dynamics down to the kilohertz range. To account for the data, we show that the extreme-values statistics of rare events, i.e., water dynamics in rare binding sites, implies an exponential distribution of activation energies for the strongest binding events. In turn, for an activated dynamical process, the exponential energy distribution leads to a Pareto distribution for the reorientational correlation times and a power law in the Larmor frequency for the (2)H(2)O spin-lattice relaxation rate constants at low field strengths. The most strongly held water molecules escape from rare binding sites in times on the order of microseconds, which interrupts the intramolecular correlations and causes a plateau in the spin-lattice relaxation rate at very low magnetic field strengths. We examine the magnetic relaxation dispersion (MRD) data using two simple but related models: a protein-bound environment for water characterized by a single potential well and a protein-bound environment characterized by a double potential well where the potential functions for the local motions of the bound-state water are of different depth. This analysis is applied to D(2)O deuterium spin-lattice relaxation on cross-linked albumin and lysozyme, which is dominated by the intramolecular relaxation driven by the dynamical modulation of the nuclear electric quadrupole coupling. We also separate the intramolecular from the intermolecular contribution to water proton spin-lattice relaxation by isotope dilution and show that the intramolecular proton data map onto the deuterium relaxation by a scale factor implied by the relative strength of the quadrupole and dipolar couplings. The temperature and pH dependence of the magnetic relaxation dispersion are complex and accounted for by changing only the weighting factors in a superposition of contributions from single-well and double-well contributions. These experiments show that the reorientational dynamics spectrum for water, in and on a protein, is characterized by a strongly asymmetric distribution with a long-time tail that extends at least to microseconds.

Circular Rydberg States of Atomic Hydrogen in an Arbitrary Magnetic Field

We report a theoretical scheme using a B-spline basis set to improve the poor computational accuracy of circular Rydberg states of hydrogen atoms in the intermediate magnetic field. This scheme can produce high accuracy energy levels and valid for an arbitrary magnetic field. Energy levels of hydrogen are presented for circular Rydberg states with azimuthal quantum numbers |m| = 10–70 as a function of magnetic field strengths ranging from zero to 2.35 × 109 T. The variation of spatial distributions of electron probability densities with magnetic field strengths is discussed and competition between Coulomb and magnetic interactions is illustrated.

The Work Function Associated with Ultra-relativistic Electron Emission from Strongly Magnetized Neutron Star Surface

Following an extremely interesting idea \cite{R1}, published long ago, the work function at the outer crust region of a strongly magnetized neutron star is obtained using relativistic version of Thomas-Fermi type model. In the present scenario, the work function becomes anisotropic; the longitudinal part is an increasing function of magnetic field strength, whereas the transverse part diverges. An approximate estimate of the electron density in the magnetosphere due to field emission and photo emission current, from the polar cap region are obtained.

Interaction of chlorobenzene with gelator in methyl-4,6- O-( p-nitrobenzylidene)-α- d-glucopyranoside gel probed by proton fast field cycling NMR relaxometry

The solvent–gelator interactions in the gel composed of the low molecular mass gelator methyl-4,6- O-benzylidene- α- d-glucopyranoside with chlorobenzene is the subject of the studies. The interaction causes a significant slowing down of the motion of chlorobenzene molecules at the gelator surfaces when compared to bulk chlorobenzene. The motion manifests itself through the low frequency dispersion of the proton spin-lattice relaxation time of chlorobenzene in gel observed below 10 5 Hz. The relaxation time was measured with the Fast Field Cycling relaxometry method in the function of magnetic field strength and temperature. The data were interpreted in terms of two-fraction fast-exchange model.

The Landau level-superfluid modified factor and the overal soft X/γ-ray efficiency coefficient of a magnetar

As soon as the energy of electrons near the Fermi surface are higher than $Q$, the threshold energy of inverse $\beta-$ decay, the electron capture process will dominate. The resulting high-energy neutrons will destroy anisotropic ${}^3P_2$ neutron superfluid Cooper pairs. By colliding with the neutrons produced in the process $n+ (n\uparrow n\downarrow)\longrightarrow n+ n+ n$, the kinetic energy of the outgoing neutrons will be transformed into thermal energy. The transformed thermal energy would transported from the star interior to the star surface by conduction, then would be transformed into radiation energy as soft X-rays and gamma-rays. After a highly efficient modulation within the pulsar magnetosphere, the surface thermal emission (mainly soft X/$\gamma$-ray emission) has been shaped into a spectrum with the observed characteristics of magnetars. By introducing two important parameters: Landau level-superfluid modified factor and effective X/$\gamma$-ray coefficient, we numerically simulate the process of magnetar cooling and magnetic field decay, and then compute magnetars' soft X/$\gamma$-ray luminosities $L_{X}$. Further, we obtain aschematic diagrams of $L_{X}$ as a function of magnetic field strength $B$. The observations are compared with the calculations.

SYNTHESIS AND MAGNETIC PROPERTIES OF POLY(SCHIFF BASE) COMPLEXES CONTAINING 1,10-PHENANTHROLINE AND PYRIDINE UNIT

A novel poly(Schiff base) containing 1,10-phenanthroline(DAPcPYA) was synthesized by the polycondensation of 2,6-pyridinedicarboxaldehyde(PYA) with 5,6-diamine-1,10-phenanthroline(DAP).Three polymeric complexes were first prepared by the reaction of polymer(DAPcPYA) with NiSO4,FeSO4,and NdCl3,respectively.The structures of the polymer and the complexes were characterized by IR,1H-NMR,and elemental analysis.The magnetic behaviors of these complexes were measured as a function of magnetic field strength(0～4.0×106 A/m) at 5 K and as a function of temperature(5～300 K) at a magnetic field strength of 2.4×106 A/m.The results show that DAPcPYA-Ni2+ and DAPcPYA-Nd3+ were soft ferromagnets,whereas DAPcPYA-Fe2+ exhibited the features of an antiferromagnet.

A novel hyperbranched aromatic polyamide containing bithiazole: Synthesis, metal complexation and magnetic properties

Based on the polycondensation of bifunctional 2,2′-diamino-4, 4′-bithiazole(DABT) and trifunctional 1,3,5-benzenetricarbonyl trichloride (BTC), a novel hyperbranched aromatic polyamide PBD was synthesized with excellent solubility and good thermal stability. The structure of the polymer was confirmed by FT-IR and 1H NMR spectrum. The calculated degree of branching of our product was 52%. By exploring the influence of several different solvent systems, the yield of the polymer increased in the solvent system of DMAc/LiCl. Two kinds of metal complexes were obtained by chelation of the polyamide with Cu2+ and Ni2+, and the metal contents of the complexes were determined by complexometric titration. The magnetic behaviors of the complexes were examined as a function of magnetic field strength at 5 K, and as a function of temperature (5–300 K) at a magnetic field strength of 2.4 × 106 A/m. The results indicated that the complexes were soft ferromagnetic materials with Curie-Weiss temperature at 102 K and 53 K, respectively.

Steady shear magnetorheology of inverse ferrofluids

Silica-based inverse ferrofluids (IFFs) are synthesized and their pre-yield and post-yield rheological properties are investigated as a function of magnetic field strength (8.8–276 kA/m), volume fraction (12.6–26.1 vol %), silica particle size (104–378 nm radius), and ferrofluid Newtonian viscosity (44–559 mPa s). The Mason number (Mn) provides a good scaling of the data in the steady simple shear flow regime. Special emphasis is made on the low and moderate Mason number region. At low Mn values, two different behaviors are observed depending on the IFF formulation and magnetic field strength applied: (i) either the viscosity monotonically increases with decreasing shear rate suggesting the existence of a yield stress (ii) or a low-shear plateau is reached. At medium Mn values, a power law behavior is found η/η∞∝MnΔ with −1<Δ<−2/3. Yielding behavior is modeled by using both macroscopic and microscopic approaches under the assumption of spheroidal, cylindrical, and single-width particle chain models.

Optimization of Yb+fluorescence and hyperfine-qubit detection

Fluorescence of single, trapped $^{171}\mathrm{Yb}$${}^{+}$ ions has been experimentally studied as a function of laser polarization, power, and detuning and as a function of magnetic field strength. The suppression of efficient fluorescence by coherent population trapping and the counteracting effect of the magnetic field are found to agree with theoretical predictions. For comparison, a fluorescence study has also been made of the isotope $^{174}\mathrm{Yb}$${}^{+}$ for which coherent population trapping is absent on the main fluorescence and laser cooling transition. Finally, state-sensitive fluorescence detection of the $^{171}\mathrm{Yb}$${}^{+}$ hyperfine qubit is studied, including the role of coherent population trapping in the optimization of detection parameters. A qubit detection fidelity of greater than $97%$ is achieved.

Magnetic carbonyl iron suspension with organoclay additive and its magnetorheological properties

Soft magnetic carbonyl iron (CI) based magnetorheological (MR) fluids containing three different loadings of submicron-sized organoclay were prepared. The MR characteristics were measured via rotational and oscillatory tests, in which the flow curves exhibited a non-Newtonian behaviour for all investigated samples. The dynamic yield stress change was measured as a function of magnetic field strength by adopting a linear fit of the relation of log ( τ y) proportional to log ( H), which was originally applied for electrorheological fluids. The viscoelastic performances of the pure CI suspension and the CI/organoclay suspensions showed the existence of a solid-like character. The sedimentation ratio was also investigated to confirm the role of sub-micron organoclay particles on the MR properties, in which the dispersion stability of pure CI was improved with increasing the content of organoclay in the CI suspension.

Field and temperature induced colossal strain in Gd 5(Si xGe 1− x) 4

Gd 5(Si x Ge 1− x ) 4, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic–structural phase transition, which occurs near room temperature for the compositions 0.41≤ x≤0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd 5Si 2Ge 2 ( x=0.5), and polycrystalline Gd 5Si 1.95Ge 2.05 ( x=0.487) and Gd 5Si 2.09Ge 1.91 ( x=0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd 5Si 2.09Ge 1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.

Scaling the energy conversion rate from magnetic field reconnection to different bodies

Magnetic field reconnection is often invoked to explain electromagnetic energy conversion in planetary magnetospheres, stellar coronae, and other astrophysical objects. Because of the huge dynamic range of magnetic fields in these bodies, it is important to understand energy conversion as a function of magnetic field strength and related parameters. It is conjectured theoretically and shown experimentally that the energy conversion rate per unit area in reconnection scales as the cube of an appropriately weighted magnetic field strength divided by the square root of an appropriately weighted density. With this functional dependence, the energy release in flares on the Sun, the large and rapid variation of the magnetic flux in the tail of Mercury, and the apparent absence of reconnection on Jupiter and Saturn, may be understood. Electric fields at the perihelion of the Solar Probe Plus mission may be tens of V/m.

Obtaining true transverse relaxation time distributions in high-field NMR measurements of saturated porous media: Removing the influence of internal gradients

It is well known that nuclear magnetic resonance (NMR) transverse relaxation measurements of porous media at high magnetic field strengths provide only an effective relaxation time T(2,eff), as opposed to the true T(2), due to molecular diffusion through magnetic field gradients induced by the magnetic susceptibility contrast between the adsorbent and the adsorbate. Here, we deconvolve the diffusion and surface relaxation contributions to measurements of T(2,eff) and thus obtain the true T(2) relaxation time distribution. This technique is applicable within the short time diffusion regime where the diffusion exponent varies as t(E) (3), while the surface relaxation exponent varies as t(E), where t(E) is the echo time in a standard Carr-Purcell Meiboom-Gill measurement. We demonstrate this technique on measurements of water in contact with glass spheres across a range of magnetic field strengths from B(0)=50 mT to 7.4 T. A direct measurement of T(2,eff) suggests that the transverse relaxation rate increases with field strength, in contrast to theoretical predictions. We show that when the effects of the susceptibility induced gradients, which are known to increase with magnetic field strength, are deconvolved from the T(2,eff) measurement, the true T(2) relaxation rate does indeed decrease with increasing field strength. We also apply the T(2) correction in multidimensional NMR experiments using the example of a T(1)-T(2) relaxation correlation. Here, the correction is essential in order to obtain the true T(1)/T(2) ratio as a function of magnetic field strength, which provides a measure of mobility for surface-adsorbed species; without this correction, we see surface residence times overestimated by up to two orders of magnitude. This novel approach enables the accurate determination of T(2) distributions, and hence T(1)/T(2) ratios, on high-field spectrometers that would have previously been deemed inappropriate for the study of liquids in porous media because of the intrinsic susceptibility effects.

An oscillatory system with a magnetic-fluid viscoinertial element

Results of measuring the damping factor of an oscillatory system the viscoinertial element of which is represented by a magnetic fluid filling a U-shaped glass tube are considered. The role of elasticity is played by an air-filled cavity that is formed in one of the tube legs under the piezoelectric plate attached to its end and serving for oscillation reception. A method of measuring the oscillation damping factor is proposed, and the results of these measurements are used to determine the shear viscosity of magnetic fluid samples as a function of magnetic field strength.

Parameter space region in the collisional magnetized electronegative plasma

The influence of the elastic collisions on the structure of a magnetized electronegative discharge is investigated. For a constant magnetic field, the profiles of the velocities of positive ions, the density of species, and electric potential are obtained. Furthermore, the positive ion flux is obtained as a function of magnetic field strength for different values of the collision frequency. The results show that in the absence of collision in a constant magnetic field, the discharge structure is uniform while by taking the collision into account, the structure becomes multilayer stratified. By increasing the collision frequency the discharge leaves the multilayer structure, and related oscillations in the plasma potential and space charge vanish. The parameter space region is obtained for collisionless and collisional cases. In this paper it is shown that a combined effect of collision and magnetic field determines the presheath-sheath structure.

Magnetorheology of soft magnetic carbonyl iron suspension with single-walled carbon nanotube additive and its yield stress scaling function

The serious dispersion problem of carbonyl iron (CI) based magnetorheological (MR) fluid, due to the large density mismatch between CI particles and continuous medium, has hampered its MR applications. To resolve this undesirable sedimentation, we introduced fibrous single-walled carbon nanotube (SWNT) into CI suspension as additives. The dynamic yield stress change measured as a function of magnetic field strength was examined by adopting a universal equation which was originally applied for electrorheological (ER) fluids. In addition, the viscoelastic performances of CI/SWNT suspension were compared to investigate the influence of additives on the pristine CI suspension. The sedimentation ratio was also examined to confirm the role of submicron SWNT bundles.