Narrow Results

Recent breakthroughs in nanomaterial synthesis have led to continuous development of an expanding library of novel, complex, and shape-controlled structures with unique properties. Such anisotropic Janus particles (JPs) are colloids that provide asymmetry and can impart different chemical and physical properties and directionality within a single particle. The fabrication of such asymmetric particles has attracted tremendous interest amongst research scientists and this interest arises from their fascinating properties and the exciting range of potential application opportunities. JPs are typically divided into three categories, namely, polymeric, inorganic, and polymeric-inorganic. Each of this kind of JPs can be of a range of shapes such as spherical, snowman-shaped, rod-shaped, or cylindrical. Herein, this chapter focuses mainly on JPs with a magnetic component, with emphasis on the fabrication methods and also the unique properties and applications of magnetic JPs in recent years.

Although progress of radiation therapy in recent years is rapid, medical accidents like the irradiation of over and under dose occur frequently in Japan. To eradicate these accidents and to increase accuracy of radiation therapy, we are developing an implantable real time micro dosimeter system. CdTe semiconductor is used as an ideal detector. And the doses of radiation are monitored by measuring the magnetic field converted from the current. We investigated the relationship between dose rate and current value from CdTe semiconductor(4mm×4mm×0.5mm). The data showed that 70 to 90 nA of electric current is proportionally generated from the CdTe semiconductor when it is irradiated by a LINAC under an air condition by the dose rate of 1 ~ 6Gy/min. In addition, the proportion of irradiated dose and the current was confirmed under a subaqueous condition(15cm in depth). To investigate the influence of a magnetic field on a human body, we calculated the tolerance frequency for human body using FEM simulation method. The data showed that the sending and receiving of data as a frequency of magnetic field should be set 100MHz or less. We are now miniaturizing the dosimeter circuit up to the size of inserted level by a fine needle.

Recent progress of radiation therapy is rapid. However, medical accidents like the irradiation of over and under dose occur frequently. To reduce these accidents and to increase accuracy of radiation therapy, we are developing an implantable real time microdosimeter system. CdTe semiconductor is used as a detector. And the doses of radiation are monitored by measuring the magnetic field converted from the current. We investigated the relationship between dose rate and current value from CdTe semiconductor(4mm×4mm×0.5mm). The data showed that 70 to 90 nA of electric current is proportionally generated from the CdTe semiconductor when the LINAC is working in air by the dose rate of 1 ~6Gy/min. In addition, the proportion of irradiate dose and the current was confirmed in subaqueous condition(15cm in depth). To investigate the influence of a magnetic field on a human body, we calculated the tolerance frequency to human body using FEM simulation method. The data showed that the sending and receiving of data as a frequency of magnetic field should be set 100MHz or less. We are now miniaturizing the dosimeter circuit based on these data.

Detecting cracks in a power distribution line nondestructively will be possible through proposed evaluation of the magnetic field distribution around the line when it is energized. We have examined and simulated the distribution of the magnetic field around a conducting wire. We confirmed the feasibility of this method and suggested that the optimum search coil width is about 2 mm when the crack is 1.0-mm wide and 1.5-mm deep from the results of the simulation.

We discuss the possibility of diffusive conduction and thus of suppression of shot noise by a factor 1/3 in mesoscopic semiconductor devices with two-dimensional and one-dimensional potential disorder, for which existing experimental data do not provide a conclusive result. On the basis of our numerical analysis, we conclude that it is quite difficult to achieve diffusive transport over a reasonably wide parameter range, unless the device dimensions are increased up to the macroscopic scale where, however, shot noise disappears because the device length exceeds the Debye length. In addition, in the case of one-dimensional disorder, some mechanism capable of mode-mixing has to be present in order to reach or even approach the diffusive regime.

We model the propagation of pulsars through the inhomogeneous ISM using nonrelativistic axisymmetric magneto-hydrodynamic (MHD) simulations. We take into account the wind from the star, which carries predominantly azimuthal magnetic field, and investigate the PWN at different levels of magnetization (the ratio of magnetic to matter energy-densities) in the wind. We consider the interaction of PWN with large-scale and small-scale imhomogeneities in the ISM at different values of magnetization. We conclude that the inhomogeneities in the ISM can change the shapes of the bow shocks and magnetotails at different values of the magnetization.

In this work we consider the effects of vertical self-gravity on a magnetized neutrino-dominated accretion disk, which is supposed to be a candidate for central engine of gamma-ray bursts (GRBs). We study some of the physical timescales that are considered to play a crucial role in the disk’s late-time activity, such as viscous, cooling, and diffusion timescales. We are also interested to probe the emission of X-ray flares’ probability, observed in GRBs’ extended emission by an investigation on the “magnetic barrier” and “fragmentation”. Our results approve the self-gravity as an amplifier for Blandford–Payne luminosity (BP power) and the magnetic field produced through the accretion process, but a suppressor for neutrino luminosity and magnetic barrier. The latter takes place as a result of the fragmentation enhancement in the outer disk, which is more likely to happen for the higher mass accretion rates.

The persistent emission of the anomalous X-ray pulsar 4U 0142+61 extends over a broad range of energy, from mid-infrared up to hard X-rays. In particular, this object is unique among soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) in presenting simultaneously mid-infrared emission and also pulsed optical emission. In spite of having many propositions to explain this wide range of emission, it is still lacking one that reproduces simultaneously all the observations. Filling this gap, we present a model that is able, for the first time, to reproduce simultaneously the entire spectral energy distribution of 4U 0142+61 using plausible physical components and parameters. We propose that the persistent emission comes from an accreting white dwarf (WD) surrounded by a debris disk. This model is thoroughly discussed at Ref. 2 and assumes that: (i) the hard X-rays are due to the bremsstrahlung emission from the post-shock region of the accretion column; (ii) the soft X-rays are originated by hot spots on the WD surface; and (iii) the optical and infrared emissions are caused by an optically thick dusty disk, the WD photosphere, and the tail of the post-shock region emission. In this scenario, 4U 0142+61 harbors a fast-rotator near-Chandrasekhar WD, which is highly magnetized. Such a WD can be formed by a merger of two less massive WDs.

Many neutron stars propagate through the interstellar medium with supersonic velocities, and their magnetospheres interact with the interstellar medium (ISM), forming bow shocks and magnetotails. Using numerical MHD simulations, we investigated the propagation of a magnetized neutron stars through a non-uniform ISM, the interaction of the magnetospheres with the ISM and the influence of ISM density on the shape of the magnetosphere tail. We consider the interaction of magnetized neutron stars with small-scale and large-scale inhomogeneities in the ISM. We conclude that the inhomogeneities in the ISM can change the shapes of the bow shocks and magnetotails at different values of the magnetization.

A solution of the Boltzmann equation is obtained for a magnetized plasma with arbitrary degenerate electrons and nondegenerate nuclei. For the arbitrary and non-degenerate electrons kinetic coefficients are obtained by solving Boltzmann equation by Chapman-Enskog method of successive approximations. The expressions have a considerably more complicated dependence on magnetic field than analogous dependences derived in previous publications on this subject.

We generalize the relativistic accretion thick disc model to the background of a spinning charged accelerating black hole described by the C-metric to study the effects of this background on the disc model. We show the properties of this accretion disc model and its dependence on the initial parameters. This background can be distinguishable from the Kerr space-time by analyzing the observing features of accretion discs.

QED’s predictions that photons propagating in a magnetized vacuum should feel the vacuum birefringence are still standing. Magnetars have strong magnetic fields and may give us signals of this effect through the delay of photons travelling from this source to detectors and the polarization position or by the angle and degree of polarization of the radiation emitted. Starting from non linear electrodynamics, we analyze and discuss for weak and strong field approximations the theoretical predictions for both using a toy model of rotating neutron stars with dipolar magnetic field shape and photon trajectories that lie radial.

We discuss some aspects of Sousa et al. [1, 2] concerning two mechanisms of gravitational wave (GW) emission in fast-spinning white dwarfs (WDs): accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter in the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii and RX J0648.0-4418. In addition, we applied the magnetic deformation mechanism for SGRs/AXPs described as WD pulsars. We found that, for the first mechanism, the systems AE Aquarii and RX J0648.0-4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of δm ≥ 10⁻⁵M_⊙. For the second mechanism, the three systems studied require that the WD has a magnetic field above ∼ 10⁹ G to emit GWs that can be detected by BBO. Furthermore, we found that some SGRs/AXPs as WD pulsars can be detected by BBO and DECIGO, whereas SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of these detectors.

Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars, limiting in particular the stability of white dwarfs. Despite considerable progress in the determination of the equation of state of dense Coulomb plasmas, the threshold electron Fermi energies are still generally estimated from the corresponding Q values in vacuum. Moreover, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields reaching 10⁹ G. Even more extreme magnetic fields might exist in super Chandrasekhar white dwarfs, the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. The roles of the dense stellar medium and magnetic fields on the onset of electron captures and on the structure of white dwarfs are briefly reviewed. New analytical formulas are derived to evaluate the threshold density for the onset of electron captures for arbitrary magnetic fields. Their influence on the structure of white dwarfs is illustrated by simple analytical formulas and numerical calculations.

We study the role of many-body correlations in the ultrafast dynamics of quantum well magnetoexcitons. In linear response, inter-Landau level transitions are suppressed if magnetic field is stronger than magnetoexciton binding energy. However, in nonlinear response, two-electron Auger processes remain unsuppressed even at very strong field. We show that Auger scattering plays a dominant role in the coherent exciton dynamics in strong magnetic field. We perform numerical calculations of four-wave-mixing (FWM) polarization which incorporate Auger processes nonperturbatively, and find a strong amplitude enhancement of the FWM signal accompanied with polarization oscillations at negative time delays. We identify these oscillations as quantum beats between dark two-exciton states related to each other via Auger processes.

We present a fabrication of polarity sensing superconducting magnetometer of Wheatstone bridge type. Superconducting sensor was field cooled in the magnetic field of a 0.15T permanent magnet by placing near the N or S pole. Two variable resistors were used to balance the bridge circuit. Passing a current along the superconductor in a transverse magnetic field, a voltage develops between the ends as the current varied. The magnetic field dependence of the induced output voltage of the HTS magnetometer has been tested in the the 10⁻⁵ to 10⁻⁴T range by changing the distance between the pole of a permanent magnet to the S pole of the superconducting magnetometer. The positive voltage increased, when the S pole of the magnet approached the N pole of the sensor.

We study the one-dimensional S = 1/2 Heisenberg model with an uniform and a staggered magnetic fields, using the dynamical density-matrix renormalization group (DDMRG) technique. The DDMRG enables us to investigate the dynamical properties of chain with lengths up to a few hundreds, and the results are numerically exact in the same sense as ‘exact diagonalization’ results are. Thus, we can analyze the low-energy spectrum almost in the thermodynamic limit. In this work, we calculate the dynamical spin structure factor and demonstrate the performance of the DDMRG method applying the open-end boundary conditions as well as the periodic boundary conditions.

Magnetorheological Elastomers (MREs) are composites where magnetic particles are suspended in a nonmagnetic solid or gel-like matrix. Solid MREs are shown to have a controllable, field-dependent shear modulus. Up to now, most of conventional MREs models are based on the magnetic dipole interactions between two adjacent particles of the chain. These models can express the field-dependent properties of MREs with simple chain-like structure. In this paper, a effective permeability model is proposed to predict the field-induced modulus of MREs. This model is based on effective permeability rule instead of dipole interaction rule, which take into account the particle's saturation and can predict the mechanical performances of MREs with complex structure and components. A novel MREs is also designed to improve the magnetic energy density and field-dependent performance by using the iron particles with magnetizable soft shell.

In this work we consider three-dimensional Schrödinger operators with constant magnetic fields and random ergodic electric potentials. We study the strong-magnetic-field asymptotic behaviour of the integrated density of states in two energy regimes: far from the Landau levels and near a given Landau level. These energy regimes are defined by the threshold distribution in the absolutely continuous spectrum of the unperturbed operator.

Single protein crystals are indispensable in the determination of the three-dimensional structure of proteins and other biological macromolecules by X-ray crystallography. The quality of the crystals governs the resolution limit or accuracy of the atomic positions calculated. The purpose of this chapter is to describe the idea of using magnetic fields to grow better quality protein crystals. The possibilities as well as limitations will be discussed.