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Propagation and dispersion of hydromagnetic and ion cyclotron waves in plasmas immersed in magnetic fields
The dispersion properties of surface dust ion-acoustic waves in a self-gravitating magnetized dusty plasma slab are investigated. The dispersion relation is derived by using the low-frequency magnetized dusty dielectric function and the surface wave dispersion integral for the slab geometry. We find that the self-gravitating effect suppresses the frequency of surface dust ion-acoustic wave for the symmetric mode in the long wavelength regime, whereas it hardly changes the frequency for the anti-symmetric mode. As the slab thickness and the wave number increase, the surface wave frequency slowly decreases for the symmetric mode but increases significantly for the anti-symmetric mode. The influence of external magnetic field is also investigated in the case of symmetric mode. We find that the strength of the magnetic field enhances the frequency of the symmetric-mode of the surface plasma wave. The increase of magnetic field reduces the self-gravitational effect and thus the self-gravitating collapse may be suppressed and the stability of dusty objects in space is enhanced.
Here, in this work, hydrophobic magnetic deep eutectic solvents (HMDESs) were used in the development of a simple and rapid dispersive liquid-liquid microextraction (DLLME) approach coupled to high performance liquid chromatography with UV detection (HPLC-UV) for the determination of ten organic contaminants including five polycyclic aromatic hydrocarbons, four UV filters, and a pesticide from water at trace levels. The HMDESs were prepared by mixing a hydrogen bond acceptor, metal halide salt, and hydrogen bond donor in suitable molar ratios. Two HMDESs, 2 tetraoctylammonium bromide ([N 8888 + ][Br - ]): cobalt chloride (CoCl 2 ): 4 octanoic acid (OA) and 3 trioctylphosphine oxide (TOPO): neodymium chloride (NdCl 3 ): 3 OA, offered the highest analyte extraction efficiency overall and were chosen as suitable solvents for validation of the microextraction method. Under optimized extraction conditions, the method required 30 µL of HMDES as extraction solvent, acetone (87.5 µL) as disperser solvent, a NaCl concentration of 30% (w/v), and an extraction time of 120 s at 20°C. Enrichment factors of the analytes ranged from 44.6 for 3-(4-methylbenzylindene) camphor to 66.0 for 2-ethylhexyl-4-(dimethyl)aminobenzoate. The method provided low limits of detection (LODs) ranging from 0.5 to 4.5 µg L -1 , and acceptable precision, with RSD values lower than 9.6%. Furthermore, the validated method was successfully applied for tap and lake water analysis, resulting in relative recoveries of spiked samples ranging between 94.7 and 119.2%.
A current issue with the LHC collimation system is single-diffractive, off-energy protons from the primary collimators that pass completely through the secondary collimation system and are absorbed immediately downbeam in the cold magnets of the dispersion suppressor section. Simulations suggest that the high impact rate could result in quenching of these magnets. We have studied replacing the 60 cm primary graphite collimators, which remove halo mainly by inelastic strong interactions, with 5.25 mm tungsten, which remove halo mainly by multiple coulomb scattering and thereby reduce the rate of single-diffractive interactions that cause losses in the dispersion suppressor.
The total energy shift of a polarized massive Dirac neutrino in an electron–positron plasma in a constant magnetic field is investigated. The calculation in the Feynman gauge is performed for the first time by using the Matsubara temperature Green functions. The dependence of the dispersion relation and the anomalous magnetic moment of the neutrino on the magnetic field strength, spin, energy, direction of motion, neutrino mass, and the plasma parameters is analyzed. The results of investigations for the massive neutrino in the limiting case are compared with those obtained earlier by other authors for the massless left neutrino.
Structural characterization, exploiting X-ray scattering differences at elemental absorption edges, is developed to quantitatively determine crystallographic site-specific metal disorder. We apply this technique to the problem of Zn-Cu chemical disorder in ZnCu{sub 3}(OH){sub 6}Cl{sub 2}. This geometrically frustrated kagome antiferromagnet is one of the best candidates for a spin-liquid ground state, but chemical disorder has been suggested as a mundane explanation for its magnetic properties. Using anomalous scattering at the Zn and Cu edges, we determine that there is no Zn occupation of the intralayer Cu sites within the kagome layer; however there is Cu present on the Zn intersite, leading to a structural formula of (Zn{sub 0.85}Cu{sub 0.15})Cu{sub 3}(OH){sub 6}Cl{sub 2}. The lack of Zn mixing onto the kagome lattice sites lends support to the idea that the electronic ground state in ZnCu{sub 3}(OH){sub 6}Cl{sub 2} and its relatives is nontrivial.
We report on an investigation of the temperature-dependent magnetic properties of magnetorheological elastomers (MREs). These are a class of composites that consist of magnetically permeable particles dispersed in a nonmagnetic polymeric matrix. Under the application of an external magnetic field, a large deformation occurs altering the mechanical properties of these materials. Due to their magnetoelastic coupling response, these materials are finding an increasing interest among the scientific community. These polymer-based composites’ performance depends on many factors, which temperature is one of the biggest influencing factors requiring further investigation. In this work, the magnetic properties of isotropic and anisotropic polyurethane-based MRE with different iron (Fe) particle loading fractions (50, 60, 70, and 80% by weight) were investigated under different temperatures. From the analysis, the magnetization curves of these materials are observed to overlap for the different measured temperature values. The variation of various magnetic properties including saturation magnetization and differential susceptibility with temperature was also determined. Furthermore, the results show ~ 2.5% decrement in the saturation magnetization for each of the loading fractions, between the lowest (300K) and the highest (400K) measured temperature. On the other hand, the initial differential susceptibility exhibits different trends with increasing temperature. Generally, the magnetization response of these materials is seen to be only slightly sensitive to temperature changes. Additionally, the magnetization response is observed to be highly dependent on particle loading fractions and particle orientation within the elastomer.
Lunar breccias of low metamorphic grade offer a unique opportunity to investigate the magnetic properties of dispersed fine-grained iron. These rocks exhibit a pronounced time-dependent magnetization whose acquisition and decay are well explained by Neel's single-domain theory. The effect is due to iron grains in the range from 120 to 150 A in diameter, which covers the transition from superparamagnetic to stable single-domain behavior.
In a fluid description, we study space-time evolution of lower hybrid modes in a cold quasi-neutral homogeneous plasma in presence of a background inhomogeneous magnetic field. Within a linear analysis, a dispersion relation with inhomogeneous magnetic field shows 'phase mixing' of such oscillations. A manifestation of 'phase mixing' is shown in 'mode coupling.' By using Lagrangian variables, an exact solution is presented in parametric form of this nonlinear time dependent problem. It is demonstrated that initially excited lower hybrid modes always break via phase mixing phenomenon in presence of an inhomogeneous magnetic field. Breaking of such oscillations is revealed by the appearance of spikes in the plasma density profile.
Critical applications of spin polarized low energy electron microscopy (SPLEEM) employ this technique's vector imaging capability to resolve domain wall (DW) spin textures. Studying several thin film systems including Co/W(110), Co/Cu(001) and (Co/Ni) n /W(110), we demonstrate that an additional contrast can appear at magnetic DWs. By imaging the magnetization as a function of electron landing energy, electron energies are selected at which the magnetic domain contrast vanishes. Surprisingly, under such conditions of zero contrast between magnetic domains, we observe the appearance of magnetic contrast outlining the DWs. This DW contrast fails to depend on the DW spin texture. Instead, our measurements show that this DW contrast results from a combination of the energy-dependence of the spin reflectivity asymmetry of the magnetic film, the finite energy width of the spin polarized electron source, and the dispersion of the magnetic prism array that separates the illumination and imaging columns of the instrument. Awareness of this DW contrast mechanism is useful to aid correct interpretation of SPLEEM images.
Here we present a technique using magnetic nanofluid to induce bidispersed suspension of nonmagnetic particles to assemble into colloidal chain, triangle, rectangle, ring-flower configurations. By changing the amplitude and direction of the magnetic field, we could tune the structure of nonmagnetic particles in magnetic nanofluid. The structures are assembled using magneto static interactions between effectively nonmagnetic particles dispersed in magnetizable magnetic nanofluid. The assembly of complex structures out of simple colloidal building blocks is of practical interest in photonic crystals and DNA biosensors.
We present details on a new measurement of the muon magnetic anomaly, a μ =(g μ −2)/2. The result is based on positive muon data taken at Fermilab’s Muon Campus during the 2019 and 2020 accelerator runs. The measurement uses 3.1 GeV/c polarized muons stored in a 7.1-m-radius storage ring with a 1.45 T uniform magnetic field. The value of a μ is determined from the measured difference between the muon spin precession frequency and its cyclotron frequency. This difference is normalized to the strength of the magnetic field, measured using nuclear magnetic resonance. The ratio is then corrected for small contributions from beam motion, beam dispersion, and transient magnetic fields. We measure a μ =116592057(25)×10 −11 (0.21 ppm). This is the world’s most precise measurement of this quantity and represents a factor of 2.2 improvement over our previous result based on the 2018 dataset. In combination, the two datasets yield a μ (FNAL)=116592055(24)×10 −11 (0.20 ppm). Combining this with the measurements from Brookhaven National Laboratory for both positive and negative muons, the new world average is a μ (exp)=116592059(22)×10 −11 (0.19 ppm).
The laminar wave train structure of collisionless magnetic slow shocks is investigated using two fluid hydromagnetics with ion cyclotron radius dispersion. For shock strengths less than the maximally strong switch-off shock, in the shock leading edge dispersive steepening forms a magnetic field gradient, while in the downstream flow dispersive propagation forms a trailing wave train; dispersion scale lengths are the ion inertial length if beta is smaller than 1 and the ion cyclotron radius if beta is greater than 1. In the switch-off slow shock leading edge, dispersion only produced rotations of the magnetic field direction; the gradient of the magnetic field magnitude, and hence the shock steepening length, is determined solely by resistive diffusion. The switch-off shock structure consists of a long trailing of magnetic rotations which are gradually damped by resistivity.
A theoretical analysis is presented for dispersion relation and growth rate in a Cherenkov free electron laser with finite axial magnetic field. It is shown that the growth rate and the resonance frequency of Cherenkov free electron laser increase with increasing axial magnetic field for low axial magnetic fields, while for high axial magnetic fields, they go to a saturation value. The growth rate and resonance frequency saturation values are exactly the same as those for infinite axial magnetic field approximation. The effects of electron beam self-fields on growth rate are investigated, and it is shown that the growth rate decreases in the presence of self-fields. It is found that there is an optimum value for electron beam density and Lorentz relativistic factor at which the maximum growth rate can take place. Also, the effects of velocity spread of electron beam are studied and it is found that the growth rate decreases due to the electron velocity spread.
The dispersion equation of a strongly anisotropic one-dimensional magnet catena-[Fe{sup II}(ClO{sub 4}){sub 2}(Fe{sup III}(bpca){sub 2})]ClO{sub 4} containing alternating high-spin (HS) (S = 2) and low-spin (LS) (S = 1/2) iron ions is obtained by the diagram technique for Hubbard operators. The analysis of this equation yields six branches in the excitation spectrum of this magnet. It is important that the crystal field for ions with spin S = 2 is described by the Hamiltonian of single-ion easy-plane anisotropy, whose orientation is changed by 90° when passing from one HS iron ion to another. The U(N) transformation technique in the atomic representation is applied to diagonalize a single-ion Hamiltonian with a large number of levels. It is shown that the modulation of the orientation of easy magnetization planes leads to a model of a ferrimagnet with easy-axis anisotropy and to the formation of energy spectrum with a large gap. For HS iron ions, a decrease in the mean value of the spin projection due to quantum fluctuations is calculated. The analysis of the specific features of the spectrum of elementary excitations allows one to establish a correspondence to a generalized Ising model for which the magnetic susceptibility is calculated in a wide range of temperatures by the transfer-matrix method. The introduction of a statistical ensemble that takes into account the presence of chains of different lengths and the presence of iron ions with different spins allows one to describe the experimentally observed modification of the magnetic susceptibility of the magnet under optical irradiation.
Drying sessile droplets is a promising route to transform colloidal dispersions into surface coatings, which are widely used in material design and biochemical detection. However, directing the assembly of the particles within drying droplets and achieving surface patterns beyond the well-known coffee-ring formation remain a challenge. Here, we present a new principle of directing the assembly of nonmagnetic colloidal particles dispersed in a magnetic fluid and generating unusual surface patterns. We use the ability of ferrofluids to change phases with the application of magnetic fields to program the assembly of nonmagnetic microparticles present in drying sessile droplets. We show that in the absence of external magnetic field, the superparamagnetic nanoparticles in the magnetic fluid are spontaneously transported to the droplet edge because of solvent evaporation. This nanoparticle transport leads to the formation of nanoparticle-rich edge and nanoparticle-depleted center of the drying droplet. Upon the application of a uniform external magnetic field, the asymmetry in the magnetic nanoparticle distribution drives a magnetostatic convection and finger-like instability from the droplet edge to the center. This magnetic microconvection from droplet edge-to-center reverses the particle transport from center-to-edge, well-known for drying droplets in the absence of external field. We use this magnetostatic microconvection to assemble secondary nonmagnetic microspheres in droplets, overwriting ring formation and direct their assembly into four distinct kinetically stable states. As a result, the method presented here offers an active control over the colloidal assembly achieved by drying sessile droplets and thus enables a new route for fabricating complex patterns and functional surface coating.