Values Of Magnetic Flux Research Articles

Bound states in the continuum in open Aharonov-Bohm rings

Using formalism of effective Hamiltonian we consider bound states in continuum (BIC). They are those eigen states of non-hermitian effective Hamiltonian which have real eigen values. It is shown that BICs are orthogonal to open channels of the leads, i.e. disconnected from the continuum. As a result BICs can be superposed to transport solution with arbitrary coefficient and exist in propagation band. The one-dimensional Aharonov-Bohm rings that are opened by attaching single-channel leads to them allow exact consideration of BICs. BICs occur at discrete values of energy and magnetic flux however it's realization strongly depend on a way to the BIC's point.

Control of chemical reaction involving dissolved oxygen using magnetic field gradient

This study investigated the control of dissolved oxygen concentration using magnetic forces from gradient magnetic fields near a Nd–Fe–B permanent magnet. Maximum values of magnetic flux density and the product of the magnetic flux density and its gradient were 0.63 T and 44 T 2/m, respectively. The magnet was placed under a Petri dish filled with 15 ml of 10% ammonia water. The Petri dish had a copper sheet in the center. Absorbance of tetraamminecopper(II) complex produced by the reaction in oxygen was measured using a spectrophotometer to observe oxygen concentration. Results showed that the magnetic field quantitatively enhanced tetraamminecopper(II) complex production. Moreover, remarkable enhancement of the copper complex production occurred in the magnetic field at less than 2 mm depth. The calculated magnetic force increase near the magnet surface supports this result. These results show that greater enhancement of the reaction rate occurs when the stronger magnetic force acts on oxygen molecules.

Macroscopic Aharonov–Bohm effect in superconductors

The problems of the influence of the vector-potential field produced by a finite-radius solenoid on a superconducting medium outside the solenoid and on a hollow superconducting cylinder inside of which the solenoid is located are solved in the framework of the Ginzburg–Landau theory for type-II superconductors. The dependence of the magnetic flux in the solenoid on the surface current density in its winding is found, and it is shown that there exist regions of magnetic flux values that cannot be realized at any current density in the solenoid. In the case when the solenoid radius is significantly greater than the magnetic field penetration depth, this dependence has the form of a step function with a step height equal to the magnetic flux quantum and a width that is a “quantum of surface current density.” The change of the superconducting transition temperature in a cylinder outside the solenoid is found as a function of the surface current density in the solenoid.

Detection of Fatigue Damage in SUS304 Steel Using the Residual Magnetization Method (Plane Bending Fatigue at a Temperature of Living Environment)

In order to detect the amount of fatigue damage in SUS304 steel, we were investigating the relationship between fatigue damage and the perpendicular leakage magnetic flux density caused by martensitic structure induced by cyclic stress. Plane bending fatigue tests were carried out at the temperate of 0°C, 30°C and 65°C. The main results obtained were as follows : (1) The magnetic flux density of the center in the specimen clearly increase with the increase of the bending stress and number of cycles. However it is difficult to estimate the fatigue damage with using method when the temperature changed during the test, since the martensitic transformation also depends on the temperature. (2) When repeating the stress below a fatigue limit, the value of magnetic flux density will not increase from a certain value. This indicates that fatigue damage is not advancing. (3) The final value of saturated magnetic flux density and σa/σω correlated each other even when the temperature differs.

Development of Computational Technique for Labeling Magnetic Flux-Surfaces

In recent Large Helical Device (LHD) experiments, radial profiles of ion temperature, electric field, etc. have been measured in the m/n = 1/1 magnetic island produced by island control coils, where m is the poloidal mode number and n the toroidal mode number. When the plasma transport in radial profiles is numerically analyzed, an average over a magnetic flux-surface in the island is a very useful concept to understand the transport. When averaging, a proper labeling of the flux-surfaces is necessary. In general, it is not easy to label the flux-surfaces in a magnetic field containing the island, compared with the case of a magnetic field configuration having nested flux-surfaces. In the present paper, we have developed a new computational technique to label the magnetic flux-surfaces. This technique uses an optimization algorithm called the simulated annealing method. The flux-surfaces are discerned by using two labels: one is classification of the magnetic field structure, i.e., core, island, ergodic, and outside regions, and the other depends on the value of the toroidal magnetic flux. We have applied this technique to an LHD configuration with the m/n = 1/1 island, and successfully discriminated of the magnetic field structure.

Influence of parity on the persistent currents of superconducting nanorings

We argue that at sufficiently low temperatures $T$ superconducting parity effect may strongly influence equilibrium persistent currents (PCs) in isolated superconducting nanorings containing a weak link with few conducting modes. An odd electron, being added to the ring, occupies the lowest available Andreev state and produces a countercurrent circulating inside the ring. For a single channel quantum point contact at $T=0$ this countercurrent exactly compensates the supercurrent ${I}_{e}$ produced by all other electrons and, hence, yields complete blocking of PCs for any value of the external magnetic flux. In superconducting nanorings with embedded normal metal the odd electron countercurrent can ``overcompensate'' ${I}_{e}$ and a novel ``$\ensuremath{\pi}∕N$-junction'' state occurs in the system. Changing the electron parity number from even to odd results in spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.

Evaluation of Residential Exposure to Intermediate Frequency Magnetic Fields

The authors measured the exposure to intermediate-frequency (IF: 10 kHz to 30 MHz) electromagnetic fields (EMF) in residential environments. They developed a system to acquire and record waveforms of IF magnetic fields (MFs) and set 5 nanotesla (nT) for the trigger level of acquisition. They operated the system near power lines, railroads, and electrical appliances as possible sources of IF-MFs. Most of the maximum values of magnetic flux density and the time derivative for each wave were below the upper limit of the measurable range of our system (i.e., 53 nT and 10 T/s); these values were much lower than the minimum amplitudes that can theoretically induce heating or membrane excitation within biological systems. Moreover, the amplitudes of the IF-MFs were not related to those of extremely low frequency (ELF) MF measured simultaneously, indicating that IF-MFs do not underlie the associations, observed in several epidemiological studies, between residential exposure to ELF-EMF and childhood cancer.

Semiclassical gravitational effects near a singular magnetic flux

We consider the backreaction of the vacuum polarization effect for a massive charged scalar field in the presence of a singular magnetic massless string on the background metric. Using semiclassical approach, we find the first-order (in ℏ units) metric modifications and the corresponding gravitational potential and deficit angle. It is shown that, in certain region of values of coupling constant and magnetic flux, the gravitational potential and deficit angle can be positive as well as negative over all distances from the string and can even change its sign. Unlike the case of massless scalar field, the gravitational corrections were found to have short-range behavior.

ELF magnetic field exposure in a neonatal intensive care unit.

In this paper, the magnetic flux density (MFD) distribution in a neonatal intensive care unit is described and MFD values inside a few open infant warming systems and incubators are reported. Typical measured values of the magnetic flux density at power frequency (50 Hz) in the "general environment" (the rooms of the unit) were lower than 0.2 microT, while higher MFD values were detected close to medical equipment and inside the open infant warming systems. In both cases, the magnetic flux density quickly decreases with increasing distance, so that measured values are reduced to "background" (i.e., general environment) levels 20-30 cm away from the sources. The total harmonic content over the 100-800 Hz frequency range was also evaluated. In the general environment, measured values in this band were negligible, while this was not the case close to medical equipment. Field levels inside the open and closed incubators depend on the position of the electronic control system, of the heating power generator and its winding conductor, and of the 220 V main plug. The magnetic flux density was also monitored for a prolonged period of time in a few types of open infant warming systems and incubators under standard intensive care unit operation with premature newborn present.

Quantitative magnetotail characteristics of different magnetospheric states

Abstract. Quantitative relationships allowing one to compute the lobe magnetic field, flaring angle and tail radius, and to evaluate magnetic flux based on solar wind/IMF parameters and spacecraft position are obtained for the middle magnetotail, X=(–15,–35)RE, using 3.5 years of simultaneous Geotail and Wind spacecraft observations. For the first time it was done separately for different states of magnetotail including the substorm onset (SO) epoch, the steady magnetospheric convection (SMC) and quiet periods (Q). In the explored distance range the magnetotail parameters appeared to be similar (within the error bar) for Q and SMC states, whereas at SO their values are considerably larger. In particular, the tail radius is larger by 1–3 RE at substorm onset than during Q and SMC states, for which the radius value is close to previous magnetopause model values. The calculated lobe magnetic flux value at substorm onset is ~1GWb, exceeding that at Q (SMC) states by ~50%. The model magnetic flux values at substorm onset and SMC show little dependence on the solar wind dynamic pressure and distance in the tail, so the magnetic flux value can serve as an important discriminator of the state of the middle magnetotail. Key words. Magnetospheric physics (solar windmagnetosphere- interactions, magnetotail, storms and substorms)

Quantum phase transitions and persistent currents in Josephson-junction ladders

In this work we study quantum phase transitions and persistent currents in capacitively coupled one-dimensional Josephson-junction arrays. We will focus particularly on the roles of exciton-like pairs in the strong coupling limit in the presence of external gate charges and magnetic fluxes. We use the numerical density-matrix renormalization group method for the study in the full range of values of gate charge and magnetic flux. To clarify the various effects, we report the pair correlation functions and the exciton densities as welll as the persistent current.

Resolvent convergence in norm for Dirac operator with Aharonov–Bohm field

We consider the Hamiltonian for relativistic particles moving in the Aharonov–Bohm magnetic field in two dimensions. The field has δ-like singularity at the origin, and the Hamiltonian is not necessarily essentially self-adjoint. The self-adjoint realization requires one parameter family of boundary conditions at the origin. We approximate the point-like field by smooth ones and study the problem of norm resolvent convergence to see which boundary condition is physically reasonable among admissible boundary conditions. We also study the effect of perturbations by scalar potentials. Roughly speaking, the obtained result is that the limit self-adjoint realization is different even for small perturbation of scalar potentials according to the values of magnetic fluxes. It changes at half-integer fluxes. The method is based on the resolvent analysis at low energy on magnetic Schrödinger operators with resonance at zero energy and the resonance plays an important role from a mathematical point of view. However it has been neglected in earlier physical works. The emphasis here is placed on this natural aspect.

D-branes in Melvin background

In this paper we discuss D-branes in the Melvin background and its supersymmetric generalizations. In particular we determine the D-brane spectra in these backgrounds by constructing their boundary states explicitly, where some of the D-branes are supersymmetric. The results sensitively depend on whether the value of magnetic flux in the Melvin background is rational or irrational. For the rational case the D-branes are regarded as the generalizations of fractional D-branes in abelian orbifolds n/N of type-II or type-0 string theory. For the irrational case we found a very limited spectrum. Since the background includes the non-trivial H-flux, the D-branes will provide interesting examples from the viewpoint of the non-commutative geometry.

Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives

AbstractIdentifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time‐varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel–chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques. Bioelectromagnetics 22:463–469, 2001. © 2001 Wiley‐Liss, Inc.

Errors in electromagnetic flow meter with magnetic particles

Magnetic admixtures change the magnitude and distribution of the magnetic field and virtual current in active fluid volume of electromagnetic flow meter, and measurement error appears. The value of error depends on the concentration, permeability and electric conductivity of magnetic admixtures and on the form of particles. The principles of error formation are investigated assuming that in the fluid with uniform properties there may be a small concentration of spherical particles, whose magnetic and electric properties are different from that of the fluid. An ideal electromagnetic flow meter with a rectangular duct and infinitely conductive large electrodes is assumed. The flat velocity profile is supposed. Measurement error is evaluated using the analogy between electrostatic, magnetic and electric current fields. The main causes of measurement error are examined. There is a deviation of densities of virtual current and magnetic flux inside particles, a deviation of mean values of magnetic flux and virtual current densities outside particles and a distortion of magnetic and virtual current fields in surroundings of particles. The magnetic particles with electric conductivity considerably greater than fluid conductivity are especially dangerous. A relative error in this case may exceed volume concentration of particles six times. For non-magnetic particles measurement error is absent independent of their conductivity.

Evaluation of the magnetic field within a BPSCCO cylinder superimposed by multi-layered soft-iron cylinders by use of an HTS DC-SQUID

The evaluation of the maximum shielded magnetic flux density B/sub s/ of a high-critical temperature superconducting (HTS) cylinder acting as a magnetic shielding vessel, is required to improve the value of B/sub s/ for practical use. The authors have improved the value of B/sub s/ by the superposition of multi-layered soft-iron cylinders over a Bi-Pb-Sr-Ca-Cu-O cylinder which is termed the superimposed cylinder. Little is known, however, of the characteristics and evaluation procedures for the magnetic flux density B/sub ia/ within the innermost of the superimposed cylinders when the value of the external magnetic flux density B/sub ex/ is less than that of B/sub s/. The present research has evaluated the shielding effect for the superimposed cylinder with the use of an HTS DC-SQUID magnetometer and spectrum analyzer. The present paper examines the magnetic step response of B/sub in/ to the applied B/sub ex/, the characteristics of B/sub in/ when exposed to a B/sub ex/ having a value less than that of B/sub s/, and the magnetic noise power spectra within the superimposed cylinder. In addition, a discussion is conducted on the relationship between the number of layers of the multi-layered soft-iron cylinder and the value of B/sub in/.

Superconductivity in a mesoscopic double square loop: Effect of imperfections

We have generalized the network approach to include the effects of short-range imperfections in order to analyze recent experiments on mesoscopic superconducting double loops. The presence of weakly scattering imperfections causes gaps in the phase boundary $B(T)$ or $\ensuremath{\Phi}(T)$ for certain intervals of T, which depend on the magnetic flux penetrating each loop. This is accompanied by a critical temperature ${T}_{c}(\ensuremath{\Phi}),$ showing a smooth transition between symmetric and antisymmetric states. When the scattering strength of imperfections increases beyond a certain limit, gaps in the phase boundary ${T}_{c}(B)$ or ${T}_{c}(\ensuremath{\Phi})$ appear for values of magnetic flux lying in intervals around half-integer ${\ensuremath{\Phi}}_{0}=hc/2e.$ The critical temperature corresponding to these values of magnetic flux is determined mainly by imperfections in the central branch. The calculated phase boundary is in good agreement with experiment.

Magnetic flux distribution in a three-dimensional inductive network of Josephson junctions

The magnetic response of three-dimensional Josephson junction networks to constant or slowly varying external magnetic fields is studied. General equations are written for complex networks made of n elementary cubic cells, each cell containing 12 resistively shunted ideal Josephson junctions. The magnetic-flux distribution in the network is calculated numerically as a function of the external magnetic field for different values of superconducting quantum interference device parameter, network size, and external magnetic-field direction. The magnetic-flux distribution in the network is graphically shown, first for increasing and then for decreasing values of the external magnetic flux.

High Volume Reduction and Group Separation of Simulated Fission Products by Cold Crucible.

An advanced technology of SHTM (Super High Temperature Treatment Method) using an induction cold crucible for the treatment of fission products generated after the reprocessing of spent fuel is proposed as the future stage of the current vitrification. Without adding any glass materials, 2000 g of simulated fission products consisting of 23 elements, including lanthanides oxides simulating highly active nuclides and corrosion products, together with the minimum amount of reducing agent were inductively heated up to 2000°C, followed by melting and solidification in a convergent type cold wall crucible. Internal diameter of the crucible, applied electric power and the frequency was 100 mm, less than 100 kW and 25 kHz, respectively. As a result, highly volume-reduced materials, approximately 1/20 of the current vitrification, was obtained. Platinum metal group, such as palladium and ruthenium, got together in the center and bottom of the crucible, surrounded with the titanium oxides immobilizing lanthanides elements. Validity of the process con-ceptwas confirmed experimentally. A cylindrical mathematical model with three phases coupled with electromagnetic field, heat conduction and mass balance has been developed to get better understanding of SHTM. The model predicts the presence of critical value of magnetic flux density and the initial dimension of the pretreated fission products that triggers the whole melting of the fission products in the crucible surrounded with the cold wall. Reaction free layer of fission products plays an important role for the melting. There exits an optimal intensity of the magnetic flux density sustaining high temperature of the material near the cold wall.

Four-terminal SQUID: Magnetic flux switching in bistable state and noise

The effect of thermal fluctuations on the behaviour of a 4-terminal SQUID is investigated. The studied system consists of the Josephson 4-terminal junction with two terminals short-circuited by a superconducting ring and the other two form the transport circuit. The behaviour of a 4-terminal SQUID is controlled by external parameters, the applied magnetic flux and the transport current. They determine the voltage in the transport channel and the magnetic flux embraced in the ring. Within the numerical model the noise-rounded current–voltage characteristics and the time dependence of the magnetic flux has been calculated. In some region of the control parameters the 4-terminal SQUID is in the bistable state with two magnetic flux values. The switching of the flux in bistable state produced by the thermal noise or by the transport current is studied.