Soliton surfaces

We find dispersion laws for the photon propagating in the presence of mutually orthogonal constant external electric and magnetic fields in the context of the $\theta $-expanded noncommutative QED. We show that there is no birefringence to the first order in the noncommutativity parameter $% \theta .$ By analyzing the group velocities of the photon eigenmodes we show that there occurs superluminal propagation for any direction. This phenomenon depends on the mutual orientation of the external electromagnetic fields and the noncommutativity vector. We argue that the propagation of signals with superluminal group velocity violates causality in spite of the fact that the noncommutative theory is not Lorentz-invariant and speculate about possible workarounds.

view Abstract Citations (753) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Does the missing mass problem signal the breakdown of Newtonian gravity? Bekenstein, J. ; Milgrom, M. Abstract A nonrelativistic potential theory for gravity is considered which differs from the Newtonian theory. The theory is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass. The theory involves a modification of the Poisson equation and can be derived from a Lagrangian. The total momentum, angular momentum, and (properly defined) energy of an isolated system are conserved. The center-of-mass acceleration of an arbitrary bound system in a constant external gravitational field is independent of any property of the system. In other words, all isolated objects fall in exactly the same way in a constant external gravitational field (the weak equivalence principle is satisfied). However, the internal dynamics of a system in a constant external field is different from that of the same system in the absence of the external field, in violation of the strong principle of equivalence. These two results are consistent with the phenomenological requirements of the modified dynamics. A toy relativistic theory is sketched which has a nonrelativistic limit satisfying the requirements of the modified dynamics. Publication: The Astrophysical Journal Pub Date: November 1984 DOI: 10.1086/162570 Bibcode: 1984ApJ...286....7B Keywords: Galactic Rotation; Gravitation Theory; Mass Distribution; Missing Mass (Astrophysics); Newton Theory; Nonrelativistic Mechanics; Potential Theory; Computational Astrophysics; Cosmology; Equivalence; Poisson Equation; Astrophysics full text sources ADS |

1. The impulse activity of single nerve fibers supplying the ampullae of Lorenzini in hyoid group of the Black Sea skate, was recorded to study the response of these receptors to various modifications of stimulation with the vertical component of a magnetic field. 2. When the animal was at rest in motionless water an impulse reaction was observed only with changes in magnetic field, a constant field had no effect. The intensity of response was determined by the rate of magnetic field change (dB/dt). 3. The nature of responses to magnetic field changes depended on the orientation of the ampullary canals relative to induced currents in the animal's body and in the surrounding sea water (Figs. 1, 2 and 3). 4. The intensity of response of a single receptor to magnetic field changes decreased with the shortening of the ampullary canal under study (Fig. 4); cutting of the other canals or dissection of the capsule of the ampullary cluster appeared to have no effect. 5. The receptors of the ampullae of Lorenzini were shown to respond to a constant magnetic field when the fish moved in water, or when water was moved with respect to the fish (Figs. 5 and 6). 6. The character of impulse responses to a constant magnetic field depended on the direction of the field and the direction of movement of either the fish or the water. The relationship between the response intensity and magnetic field, or velocity of water flow is roughly linear (Figs. 7 and 8). 7. Symmetrical receptors on the right and left sides of the animal's body responded oppositely to stimulation by either increasing or constant magnetic field (Figs. 1 and 6). 8. Experiments involving compensation for the Earth's magnetic field with Helmholtz coils revealed a statistically significant reaction to the vertical component of the geomagnetic field (0.35 Gs in the region of the Karadag Biological Station, the Crimea). 9. The mechanisms and functional role of the detection of changing and constant magnetic field by the ampullae of Lorenzini are discussed.

This work explores the conditions that allow the injection and pinning of different magnetic domain walls (DWs) in Permalloy nanostripes with notches of different shapes. The injection is done under a constant external field by applying a 10 ns current pulse through an adjacent current line. The type of DW is identified by its anisotropic magnetoresistance (AMR). We find that, while a quasi-static pinning (nucleating at zero field and propagating the DW to the notch by slowly increasing the external field) would allow to distinguish different types of DWs pinned at the notch, a dynamic pinning (nucleating, propagating, and pinning the DW under a constant non-zero magnetic field) makes the discrimination of different DWs very difficult. Micromagnetic simulations indicate that the AMR of the different types of DWs become quite similar to each other as the injection field increases. This might explain why at large injection fields, usually only one or two values of resistance are detected, depending on the shape of the notch. Therefore, caution should be taken when establishing a one-to-one relationship between a type of DW and a value of resistance, especially if the injection is done under a non-zero external magnetic field.

The exact solution for the chiral field superpropagator in a constant external Abelian field is given.

A comparative study of magnetoplasticity in two types of NaCl crystals differing in impurity content only by a small Ni addition (0.06 ppm) in one of them, NaCl(Ni), has been carried out. Two methods of sample magnetic exposure were used: in a constant field B = 0–0.6 T and in crossed fields in the EPR scheme—the Earth’s field BEarth (50 μT) and a variable pumping field \(\tilde B( \sim 1 \mu T)\) at frequencies ν ~ 1 MHz. In the experiments in the EPR scheme, the change of the field orientation from \(\tilde B \bot B_{Earth}\) to \(\left. {\tilde B} \right\|B_{Earth}\) led to almost complete suppression of the effect in the NaCl(Ni) crystals and reduced only slightly (approximately by 20%) the height of the resonance peak of dislocation mean paths in the crystals without Ni, with the amplitude of the mean paths in NaCl(Ni) in the orientation \(\tilde B \bot B_{Earth}\) having been appreciably lower than that in NaCl. In contrast, upon exposure to a constant magnetic field, a more intense effect was observed in the crystal with Ni. The threshold pumping field amplitude \(\tilde B\), below which the effect is absent under resonance conditions, for the NaCl(Ni) crystals turned out to be a factor of 5 smaller than that for NaCl, while the thresholds of a constant magnetic field coincide for both types of crystals. All these differences are discussed in detail and interpreted.

Paramagnetic relaxation in strongly anisotropic materials is analytically investigated in zero and weak constant magnetic fields. The objectives of the microscopic analytical investigation are (i) the weak-field electron paramagnetic resonance (EPR) linewidth and (ii) the electron spin relaxation rates given by a calorimetric Gorter type experiment in the zero constant field at the arbitrary low-frequency field directions, respectively, to the sample crystallographic axes. The EPR linewidth is calculated under the suggestion of its spin-phonon nature at the one-phonon mechanism of the spin-lattice relaxation in the case of the strong isotropic exchange interaction for the arbitrary direction Z of the constant magnetic field. The EPR linewidth is presented as the half sum of the zero-field relaxation rates, measured by the Gorter experiment with the low-frequency field oriented along the X, Y axes. With the help of the macroscopic consideration, it is shown that the zero-field relaxation rates describe the relaxation of the X and Y magnetization components in a zero or weak constant magnetic field. The relaxation rates of the magnetizations created along a,b,c crystallographic axes by a low-frequency field in a Gorter type experiment follow the obtained expressions in the particular cases and are in the experimentally confirmed relations with the EPR linewidth.

Objective To investigate the growth inhibiting action of PEG modified magnetic 5-Fluorouracil albumin microspheres (PEG-5-FU-MAMS) combined with constant external magnetic fields on human colorectal carcinoma LoVo cells in vitro and the mechanism. Methods The PEG-5-FU-MAMS were prepared by emulsification/solidification method.The cultured LoVo cells were divided into four groups.Group A was processed with PEG-5-FU-MAMS combined with external magnetic fields, group B was PEG-5-FU-MAMS without magnetic fields, group C was free 5-FU, group D was pure magnetic field.The growth of LoVo cells was observed under an inverted microscopy, and the inhibitory rate (IR) was assayed by methyl thiazol tetrazolium (MTT) assay. Results The obtained microspheres (MS) were spherical and about (1.32±0.50)μm in size.The drug loading was (5.31±0.13)% and the MS had good magnetic responsibility.The release rate of 5-Fu in vitro showed that PEG-5-FU-MAMS had pronounced sustained-release effect.LoVo cells grew well and had good refraction after 24 h. Under the microscope, tumor cells were completely adherent.After different treatment, the tumor growth showed no difference on tumor cells in pure magnetic group.The IR of pure PEG-5-FU-MAMS group and free 5-FU group at same drug concentration were similar, there were no significant differences between them(q=2.02, 2.11, 2.74; P>0.05). Compared with pure PEG-5-FU-MAMS and free 5-FU group, when the concentration of 5-FU exceeded 10.0 mg/L, IR was significantly increased after PEG-5-FU-MAMS combined with constant external magnetic fields(F=62.09, 66.74, 56.62, 66.13; P<0.05). Conclusions PEG-5-FU-MAMS is characterized with good shape, particle size, drug loading, magnetic responsibility and drug release.The growth inhibiting action is significantly enhanced after PEG-5-FU-MAMS combined with constant external magnetic fields. Key words: Fluorouracil; Albumins; Microspheres; LoVo cells

The susceptibility for the brownian motion in a cosine potential is proportional to the one sided Fourier transform of the velocity autocorrelation function whereas the polarizability for the rotation of a dipole in a constant external field is proportional to the one sided Fourier transform of the time derivative of the sin- and cos-autocorrelation function. The one sided Fourier transform of these autocorrelation functions can be expressed by matrix continued fractions. They are evaluated for large, medium and even for very small damping constants, thus obtaining various susceptibilities practically in the whole region of friction constants. Furthermore the connection to the zero friction limit case is discussed.

Quantum electrodynamics in an external constant field

Massive scalar and spin 1/2 fields are considered on a two-dimensional space-time with constant background curvature and in the presence of an external constant field. For each case, the Euler–Heisenberg effective action and the pair creation rate and their dependence on both the curvature and external field is determined exactly.

The response of a QCD-like gauge theory, holographically dual to a deformed $\mathrm{AdS}_5$ model, to constant electromagnetic fields is thoroughly investigated. The calculations in this paper are performed for three different cases, i.e., with only a quadratic correction, with only a logarithmic correction, and with both quadratic and logarithmic corrections, for which the parameters are chosen as the ones found in \cite{quadlog} by fitting to experimental and lattice results. The critical electric fields of the system are found by analyzing its total potential. Comparing the total potential for the three cases, we observe that the quarks can be liberated easier in quadratic and then logarithmic case, for a given electric field. Then, by calculating the expectation value of a circular Wilson loop, the pair production rate is evaluated while a constant electric field as well as a constant magnetic field are present. The aforementioned result obtained from the potential analysis is also confirmed here when no magnetic fields are present. We moreover find that the presence of a magnetic field perpendicular to the direction of the electric field suppresses the rate of producing the quark pairs and accordingly increases the critical electric field below which the Schwinger effect does not occur. Interestingly, the presence of a parallel magnetic field alone does not change the response of the system to the external electric field, although it enhances the creation rate when a perpendicular magnetic field is also present.

We analyze the influence of constant magnetic constituents on the radiation of high-energy electrons in a planar undulator. Broadening and spectrum shift effect of the constant field is compared with other common spectrum distortions in undulator radiation (UR) sources. Analytical formulation of the effect of the constant magnetic field enables us to obtain and study exact expressions for the UR intensity. They reveal the possibilities to influence off-the-axis effects and give practical recommendations for the undulators with radiation properties, best profitable for free-electron lasers.

This paper describes the design and implementation of a new DC current sensor based on T-T mode disk-type magnetoelectric (ME) laminate composite, in which two layers of transversely magnetized magnetostrictive Terfenol-D and one layer of transversely polarized piezoelectric PZT are epoxy-bonded. Compared to traditional applications for AC magnetic or current sensing under constant DC magnetic field, we exploit DC current measurement of the ME laminate under constant AC magnetic field drive. A ferrite magnetic concentrator is applied to centralize magnetic flux. A pair of Nd-Fe-B magnets and the measured DC current Idc are used to provide the DC bias magnetic field for the ME composite. The DC current sensitivity calculation is performed on the base of equivalent circuit modeling and magnetic circuit analysis. The theoretical prediction and the experimental result are thoroughly compared. The difference between them is rectified by a correction factor. Under resonant AC drive, a stable induced voltage, more than 9 V, changes with the variation of the measured DC current Idc over the range of 0 ∼ 500 A, indicating that this sensor is applicable for DC current measurement. The DC current sensitivity over the range of 0 ∼ 500 A is 2.42 mV/A with 1 A AC current at the resonant frequency fr = 84.9 kHz. Several measures for enhancing the current sensitivity are also discussed in this paper.

Understanding how a magnetic field affects the interaction of magnetic nanoparticles (MNPs) with cells is fundamental to any potential downstream applications of MNPs as gene and drug delivery vehicles. Here, we present a quantitative analysis of how a pulsed magnetic field influences the manner in which MNPs interact with and penetrate across a cell monolayer. Relative to a constant magnetic field, the rate of MNP uptake and transport across cell monolayers was enhanced by a pulsed magnetic field. MNP transport across cells was significantly inhibited at low temperature under both constant and pulsed magnetic field conditions, consistent with an active mechanism (i.e., endocytosis) mediating MNP transport. Microscopic observations and biochemical analysis indicated that, in a constant magnetic field, transport of MNPs across the cells was inhibited due to the formation of large (>2 μm) magnetically induced MNP aggregates, which exceeded the size of endocytic vesicles. Thus, a pulsed magnetic field enhances the cellular uptake and transport of MNPs across cell barriers relative to a constant magnetic field by promoting accumulation while minimizing magnetically induced MNP aggregation at the cell surface.