Characterization of non-contact torque transfer and switching system for superconducting flywheel

Superconducting flywheel energy storage system can store the energy for a long duration, in that the main body of a flywheel is placed in a vacuum chamber to minimize rotational loss, and is separated from a generation motor. The superconducting flywheel device need a non-contact system which can transfer the rotational torque without contact. A combination of two permanent magnets can transmit the power without contact. We calculated the torque forces and the field distributions of two types of magnetic arrays; repulsive type and Halbach type. Both magnetic circuits have respective inner and outer diameters of 61.5 and 144 mm and consist of eight poles of Fe–Nd–B permanent magnets 30 mm in thickness. We also studied the effects of the number of poles and the size on the transferable torque forces and found that a practical torque transfer and switching systems can be constructed with a combination of permanent magnetic circuits.     

Effect of neutrino trapping on the three flavor FFLO phase of QCD

We compute the effect of a non-zero lepton chemical potential on the structure of the three flavor Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase of QCD at finite temperature. We show that, as in the BCS case, the lepton chemical potential favors two-species color superconductivity and disfavors the three species pairing. We stress that this study could be relevant for the cooling of a proto-neutron star with a FFLO core, if the temperatures are higher than the un-trapping temperature.     

The electromagnetic energy with the truncation method for a five-dimensional rotating black hole in a uniform magnetic field

We consider a charged five-dimensional Myers–Perry black hole in a uniform magnetic (test) field. Using the Komar mass formula, we calculate the total energy of the electromagnetic field within the truncation three-sphere for a five-dimensional rotating black hole with two equal-rotation parameters and two equal-magnetic field strengths. We show that the total electromagnetic energy takes the minimum value when the five-dimensional rotating black hole acquires a non-zero net electric charge Q.     

The analysis of space–time structure in QCD vacuum II: Dynamics of polarization and absolute X-distribution

We propose a framework for quantitative evaluation of dynamical tendency for polarization in an arbitrary random variable that can be decomposed into a pair of orthogonal subspaces. The method uses measures based on comparisons of given dynamics to its counterpart with statistically independent components. The formalism of previously considered X-distributions is used to express the aforementioned comparisons, in effect putting the former approach on solid footing. Our analysis leads to the definition of a suitable correlation coefficient with clear statistical meaning. We apply the method to the dynamics induced by pure-glue lattice QCD in local left–right components of overlap Dirac eigenmodes. It is found that, in finite physical volume, there exists a non-zero physical scale in the spectrum of eigenvalues such that eigenmodes at smaller (fixed) eigenvalues exhibit convex X-distribution (positive correlation), while at larger eigenvalues the distribution is concave (negative correlation). This chiral polarization scale thus separates a regime where dynamics enhances chirality relative to statistical independence from a regime where it suppresses it, and gives an objective definition to the notion of “low” and “high” Dirac eigenmode. We propose to investigate whether the polarization scale remains non-zero in the infinite volume limit, in which case it would represent a new kind of low energy scale in QCD.     

Spontaneous symmetry breaking in QCD

We study dynamical chiral symmetry breaking in massless QCD by the use of the generalized Hartree-Fock method. As the order parameter of chiral symmetry we choose the dynamical quark mass in the zero momentum limit which we call low energy quark mass. We calculate the low energy mass to the second order of diagrammatic expansion around shifted perturbative vacuum. We then show that the mass is finite and renormalization group invariant. After the improvement of the result by the method of effective charges we estimate the mass in the true vacuum under the gap and stationarity conditions and demonstrate that both of them produce non-zero mass proportional to a conventional scale, which breaks down the chiral symmetry.     

Experimental limits on neutron disappearance into another braneworld

Recent theoretical works have shown that matter swapping between two parallel braneworlds could occur under the influence of magnetic vector potentials. In our visible world, galactic magnetism possibly produces a huge magnetic potential. As a consequence, this Letter discusses the possibility to observe neutron disappearance into another braneworld in certain circumstances. The setup under consideration involves stored ultracold neutrons – in a vessel – which should exhibit a non-zero probability p to disappear into an invisible brane at each wall collision. An upper limit of p is assessed based on available experimental results. This value is then used to constrain the parameters of the theoretical model. Possible improvements of the experiments are discussed, including enhanced stimulated swapping by artificial means.     

Streaming instability of a dusty plasma in the presence of mass and charge variation

We study the effect of the mass and charge dynamics on the collective behaviour of a dusty plasma. It is shown that the finite non-zero streaming velocity of the dust grains leads to a novel coupling of the dust mass fluctuation with other dynamic variables of the plasma and the grains. The mass fluctuations causes a collisionless dissipation and provides an alternate channel for the beam mode instability to occur. Physically the negative energy wave associated with the beam mode couples to the mass fluctuation induced dissipative medium to produce the instability. We conclude that the higher value of the ion mass density to the dust mass density ratio reduces the threshold value for the onset of the instability. Its application in the astrophysical context is discussed.     

Topological self-dual configurations in a Maxwell–Higgs model with a CPT-odd and Lorentz-violating nonminimal coupling

We have studied the existence of topological self-dual configurations in a nonminimal CPT-odd and Lorentz-violating (LV) Maxwell–Higgs model, where the LV interaction is introduced by modifying the minimal covariant derivative. The Bogomol’nyi–Prasad–Sommerfield formalism has been implemented, revealing that the scalar self-interaction implying self-dual equations contains a derivative coupling. The CPT-odd self-dual equations describe electrically neutral configurations with finite total energy proportional to the total magnetic flux, which differ from the charged solutions of other CPT-odd and LV models previously studied. In particular, we have investigated the axially symmetrical self-dual vortex solutions altered by the LV parameter. For large distances, the profiles possess general behavior similar to the vortices of Abrikosov–Nielsen–Olesen. However, within the vortex core, the profiles of the magnetic field and energy can differ substantially from ones of the Maxwell–Higgs model depending if the LV parameter is negative or positive.     

Effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets

The effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets has been investigated. The magnetic flux loss of two kinds of magnets before and after irradiation was measured. Results show that the effect of γ-ray irradiation on the magnetic properties of sintered NdFeB is not so obvious as that on Fe–Cr–Co magnet. Irradiation-induced damage from γ-ray for the Fe–Cr–Co magnets was characterized for the first time. The decline of permanent magnetic properties of Fe–Cr–Co magnet induced by γ-ray irradiation is reversible except for the maximum energy product (BH)_max. The difference of coercivity mechanism between these two kinds of permanent magnets is responsible for the different dependence of magnetic properties loss induced by γ-ray irradiation.     

Iron-based soft magnetic composites with Mn–Zn ferrite nanoparticles coating obtained by sol–gel method

This paper focuses on iron-based soft magnetic composites which were synthesized by utilizing Mn–Zn ferrite nanoparticles to coat iron powder. The nanocrystalline iron powders, with an average particle diameter of 20 nm, were obtained via the sol–gel method. Scanning electron microscopy, energy dispersive X-ray spectroscopy and distribution maps show that the iron particle surface is covered with a thin layer of Mn–Zn ferrites. Mn–Zn ferrite uniformly coated the surface of the powder particles, resulting in a reduced imaginary permeability, increased electrical resistivity and a higher operating frequency of the synthesized magnets. Mn–Zn ferrite coated samples have higher permeability and lower magnetic loss when compared with the non-magnetic epoxy resin coated compacts. The real part of permeability increases by 33.5% when compared with the epoxy resin coated samples at 10 kHz. The effects of heat treatment temperature on crystalline phase formation and on the magnetic properties of the Mn–Zn ferrite were investigated via X-ray diffraction and a vibrating sample magnetometer. Ferrites decomposed to FeO and MnO after annealing above 400 °C in nitrogen; thus it is the optimum annealing temperature to attain the desired permeability.     

Diagrammatic weak-coupling expansion for the magneto-polaron energy

The problem of a Pekar-Fröhlich polaron in a magnetic field is considered for weak electron-phonon interaction. A diagrammatic technique for zero temperature is developed. Previously obtained results for two dimensions are reproduced. For three dimensions the polaron ground-state energy and the longitudinal effective mass are derived in the first orders of the electron-phonon coupling constant for non-zero values of a magnetic field. In a strong magnetic field the bulk polaron is shown to be equivalent to a one-dimensional polaron with a renormalized electron-phonon coupling constant. This leads to exact results in the strong-coupling limit.     

Deconfinement in dense two-color QCD

We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential μ and low temperature on a 8³×16 system. We identify three régimes along the μ-axis. For μ≲m_π/2 the system remains in the vacuum phase and all physical observables considered remain essentially unchanged. The intermediate régime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose–Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined régime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of μ exhibits a minimum in the deconfined régime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter.     

High-frequency properties of thin amorphous ribbons

Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies.     

Magnetic properties of the ferrimagnetic glass-ceramics for hyperthermia

Magnetic materials play a key-role in magnetic induction hyperthermia for the treatment of cancer. In this paper, we analyse the magnetic properties of ferrimagnetic glass-ceramics with the composition in the system SiO₂–Na₂O–CaO–P₂O₅–FeO–Fe₂O₃, as a function of the melting temperature. These materials were obtained by melting of commercial reagents in the temperature range of 1400–1550 °C. Room-temperature magnetic measurements were performed by means of a vibrating sample magnetometer at room temperature. The power loss was determined from calorimetric measurements, using a magnetic induction furnace. The highest power loss (61 W/g) has been obtained for samples melted at 1500 °C. The heat generation of the ferrimagnetic glass-ceramics prepared by two different synthesis methods (traditional melting and coprecipitation-derived) will be compared. These materials are expected to be useful in the localised treatment of cancer.     

Exotic electron states and tunable magneto-transport in a fractal Aharonov–Bohm interferometer

A Sierpinski gasket fractal network model is studied in respect of its electronic spectrum and magneto-transport when each ‘arm’ of the gasket is replaced by a diamond shaped Aharonov–Bohm interferometer, threaded by a uniform magnetic flux. Within the framework of a tight binding model for non-interacting, spinless electrons and a real space renormalization group method we unravel a class of extended and localized electronic states. In particular, we demonstrate the existence of extreme localization of electronic states at a special finite set of energy eigenvalues, and an infinite set of energy eigenvalues where the localization gets ‘delayed’ in space (staggered localization). These eigenstates exhibit a multitude of localization areas. The two terminal transmission coefficient and its dependence on the magnetic flux threading each basic Aharonov–Bohm interferometer is studied in details. Sharp switch on–switch off effects that can be tuned by controlling the flux from outside, are discussed. Our results are analytically exact.     

Exponentially Growing Finite Energy Solutions for the Klein–Gordon Equation on Sub-Extremal Kerr Spacetimes

For any sub-extremal Kerr spacetime with non-zero angular momentum, we find an open family of non-zero masses for which there exist smooth, finite energy, and exponentially growing solutions to the corresponding Klein–Gordon equation. If desired, for any non-zero integer m, an exponentially growing solution can be found with mass arbitrarily close to \({\frac{\left|am\right|}{2Mr_+}}\) . In addition to its direct relevance for the stability of Kerr as a solution to the Einstein–Klein–Gordon system, our result provides the first rigorous construction of a superradiant instability. Finally, we note that this linear instability for the Klein–Gordon equation contrasts strongly with recent work establishing linear stability for the wave equation.     

Electromagnetic and microwave absorption properties of Fe3O4 magnetic films plated on hollow glass spheres

Magnetic hollow spheres of low density were prepared by plating Fe₃O₄ magnetic films on hollow glass spheres using ferrite plating. The complex permeability and permittivity of spheres–wax composites were measured in the range of 2–18 GHz. The complex permeability and permittivity increased, and the dielectric and magnetic losses were improved as the volume fraction of the magnetic spheres in the composites increased from 60% to 80%, which also resulted in a great improvement of microwave absorption properties. For composites with volume fraction 80%, its magnetic resonance frequency was at about 13 GHz and it appeared three loss peaks in the calculated reflection loss curves; the bandwidth less than −10 dB was almost 4 GHz which was just in the Ku-band frequencies (12–18 GHz) and a minimum reflection loss of −20 dB was obtained when the thickness was 2.6 mm; the microwave absorbing properties were mainly due to the magnetic loss. The results showed that the magnetic spheres composites were good and light microwave absorbers in the Ku-band frequencies.     

More about neutron–mirror neutron oscillation

It was pointed out recently that oscillation of the neutron n into a mirror neutron n′, a sterile twin of the neutron with exactly the same mass, could be a very fast process with baryon number violation, even faster than the neutron decay itself. This process is sensitive to magnetic fields and it could be observed by comparing the neutron loss rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of the n−n′ oscillation in the case when a mirror magnetic field B′ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field B, depending on its strength and on its orientation with respect to B′. The recent experimental data, under this hypothesis, still allow for an n−n′ oscillation time of order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation of the magnetic field. If these hints will be confirmed in future experiments, this would point to the presence of a mirror magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of other origin that makes a difference between the neutron and mirror neutron states.     

Preparation and characterization of biodegradable magnetic carriers by single emulsion-solvent evaporation

This paper describes a single emulsion-solvent evaporation protocol to prepare PEGylated biodegradable/biocompatible magnetic carriers by utilizing hydrophobic magnetite and a mixture of poly(D,L lactide-co-glycolide) (PLGA) and poly(lactic acid-block-polyethylene glycol) (PLA-PEG) (26:1 by mass) polymers. We characterized the magnetic microspheres in terms of morphology, composite microstructure, size and size distribution, and magnetic properties. Results show that the preparation produces magnetic microspheres with a good spherical morphology, small size (mean diameter of 1.2–1.5 μm) by means of large size distributions, and magnetizations up to 20–30 emu/g of microspheres.