Absence Of Magnetic Field Research Articles

Ultrathin films of three-dimensional topological insulators by vapor-phase epitaxy: Surface dominant transport in a wide temperature range as revealed by measurements of the Seebeck effect

Realization of intrinsic surface dominant transport in a wide temperature region for a topological insulators (TIs) is an important frontier research in order to promote the progresses of TIs towards the future electronics. We report here systematic measurements of longitudinal electrical transport, Shubnikov-de-Haas (SdH) quantum oscillations, Hall coefficient (R_H^2D), and Seebeck coefficient as a function of film thickness (d) and temperature using high quality Bi2-xSbxTe3-ySey (BSTS) single crystal thin films grown by physical vapor-phase deposition. The thickness dependence of sheet conductance and Seebeck coefficient clearly show the suppression of semiconducting hole carriers of bulk states by reducing film thickness, reaching to the surface dominant transport at below dc=14 nm. Quantitative arguments are made as to how the contribution of itinerant carrier number (n) can be suppressed, using both R_H^2D (n_Hall^2D) and SdH (n_SdH). Intriguingly, the value of n_Hall^2D approaches to be twice of n_SdH below dc. While R_H^2D shows a negative sign in whole temperature region, a change from negative to positive polarity is clearly observed for S at high temperatures when d is thick. We point out that this inconsistency observed between R_H^2D and S is intrinsic in 3D-TIs and its origin is the large difference in carrier mobility between the bulk and the topological surface. We propose that Seebeck coefficient can become a convenient and powerful tool to evaluate the intrinsic carrier concentration for the topological surface in 3D-TIs even in the absence of magnetic field.

Traveling electromagnetic waves in annular Josephson tunnel junctions

It is well known that long Josephson tunnel junctions (JTJs) act as active transmission lines for the slow-mode propagation of magnetic flux-quanta (in the form of solitary waves) that is at the base of many superconducting circuits. At the same time, they support the propagation of quasi-TEM dispersive waves with which the magnetic flux non-linearly interact. In this work, we study the properties of the electromagnetic resonances, under different conditions of practical interest, in annular JTJs (AJTJs), in which the wavelengths are limited to the length of the circumference divided by an integer. Our analysis is based on perturbed sine–Gordon equations the (1+1)-dimensional space with periodic boundary conditions. We discuss the discrete modes of the traveling EM waves in circular AJTJs in the presence of an in-plane magnetic field, as well as in the recently introduced confocal AJTJs (in the absence of magnetic field). In both cases, a variable-separation method leads to quantitatively different Mathieu equations characterized by even and odd spatially periodic solutions with different eigenfrequencies. It implicates that a single mode circulating wave is given by the superposition of two standing waves with the same wavelengths but different frequencies, and so has a periodically inverting direction of propagation. The control parameters of this frequency splitting are the in-plane magnetic field amplitude for the circular AJTJ and the aspect ratio for the confocal AJTJs. In the appropriate limits, the previously known solutions are recovered.

CPN -Rosochatius system, superintegrability, and supersymmetry

We propose new superintegrable mechanical system on the complex projective space $\mathbb{CP}^N$ involving a potential term together with coupling to a constant magnetic fields. This system can be viewed as a $\mathbb{CP}^N$-analog of both the flat singular oscillator and its spherical analog known as "Rosochatius system". We find its constants of motion and calculate their (highly nonlinear) algebra. We also present its classical and quantum solutions. The system belongs to the class of "K\"ahler oscillators" admitting $SU(2|1)$ supersymmetric extension. We show that, in the absence of magnetic field and with the special choice of the characteristic parameters, one can construct $\mathcal{N}=4, d=1$ Poinacar\'e supersymmetric extension of the system considered.

Involvement of the EGF Receptor in MAPK Signaling Activation by a 50 Hz Magnetic Field in Human Neuroblastoma Cells.

Previous studies have shown that a 63-hour, intermittent exposure to a 50 Hz, 100 μT magnetic field (MF) induces in the NB69 line of human neuroblastoma a proliferative response that is mediated by activation of the MAPK pathways ERK1/2 and p38. The present study aims to investigate the potential involvement of the epidermal growth factor receptor (EGFR) in the field-induced cell proliferation and activation of MAPK pathways. NB69 cultures were MF- or sham-exposed for 5 to 30 minute intervals and 63 hours. Cell proliferation and activation of MAPK-ERK1/2, -p38 and -JNK was analyzed in the presence or absence of erlotinib, an effective inhibitor of EGFR tyrosine kinase. The expression of p-EGFR and MMP-9 in the presence or absence of MF was also studied. Between 3 and 7 replicates of each experiment were performed, using between 3 and 4 samples per experimental condition and replicate. At the end of each replicate, the samples were analyzed at short times (5-30 min) through immunofluorescence and Western blotting, and the growth response was assessed (63 hours interval) through dye exclusion with Trypan blue. The results confirmed that field exposure induces cell proliferation and activation of ERK1/2, p38 and JNK, and revealed that these effects were blocked with erlotinib. The data also showed that, compared to shamexposed controls, the MF exposure induces early and transient increases in the expression of p-EGFR and MMP-9 at 15 and 5 min from the exposure onset, respectively. The obtained results reveal that the activation of the MAPK-ERK1/2 and -p38 pathways by the MF is mediated by the EGF receptor. Taken together with our previously published results, this dataset suggests that the proliferative response induced in NB69 by a 63-hour exposure to a weak, power frequency MF, is mediated by early transient activation of EGFR in which MMP-9 would be involved.

Effect of Material Composition on Tunable Surface Roughness of Magnetoactive Elastomers.

We investigated magnetic-field-induced modifications of the surface roughness of magnetoactive elastomers (MAEs) with four material compositions incorporating two concentrations of ferromagnetic microparticles (70 wt% and 80 wt%) and exhibiting two shear storage moduli of the resulting composite material (about 10 kPa and 30 kPa). The analysis was primarily based on spread optical reflection measurements. The surfaces of all four materials were found to be very smooth in the absence of magnetic field (RMS roughness below 50 nm). A maximal field-induced roughness modification (approximately 1 μm/T) was observed for the softer material with the lower filler concentration, and a minimal modification (less than 50 nm/T) was observed for the harder material with the higher filler concentration. All four materials showed a significant decrease in the total optical reflectivity with an increasing magnetic field as well. This effect is attributed to the existence of a distinct surface layer that is depleted of microparticles in the absence of a magnetic field but becomes filled with particles in the presence of the field. We analyzed the temporal response of the reflective properties to the switching on and off of the magnetic field and found switching-on response times of around 0.1 s and switching-off response times in the range of 0.3–0.6 s. These observations provide new insight into the magnetic-field-induced surface restructuring of MAEs and may be useful for the development of magnetically reconfigurable elastomeric optical surfaces.

MHD flow of fractional Newtonian fluid embedded in a porous medium via Atangana-Baleanu fractional derivatives

The novelty of this research is to utilize the modern approach of Atangana-Baleanu fractional derivative to electrically conducting viscous fluid embedded in porous medium. The mathematical modeling of the governing partial differential equations is characterized via non-singular and non-local kernel. The set of governing fractional partial differential equations is solved by employing Laplace transform technique. The analytic solutions are investigated for the velocity field corresponding with shear stress and expressed in term of special function namely Fox-H function, moreover a comparative study with an ordinary and Atangana-Baleanu fractional models is analyzed for viscous flow in presence and absence of magnetic field and porous medium. The Atangana-Baleanu fractional derivative is observed more reliable and appropriate for handling mathematical calculations of obtained solutions. Finally, graphical illustration is depicted via embedded rheological parameters and comparison of models plotted for smaller and larger time on the fluid flow.

Effect of gravity, magnetic field and internal heat source on a fiber-reinforced medium with two temperatures

In the present paper, the Lord–Shulman theory with one relaxation time, Green–Lindsay theory with two relaxation times and the classical dynamical coupled theory as well as Green–Naghdi theory without energy dissipation are applied to study the total deformation of a magneto-thermoelastic fiber-reinforced medium under the gravitational. The normal mode analysis is used to obtain the exact expressions for the thermodynamic temperature, the conductive temperature, the force stresses and the displacements. Comparisons are made with the results in the four theories in the presence and absence of magnetic field, the gravity, as well as the internal heat source. The effect of the gravity, magnetic field and the internal heat source is observed on all the quantities.

Unpaired Weyl Nodes from Long-Ranged Interactions: Fate of Quantum Anomalies.

We study the effect of long-ranged interactions on Weyl semimetals. Such interactions can give rise to unpaired Weyl nodes, which we demonstrate by explicitly constructing a system with just a single node-a situation that is fundamentally forbidden by fermion doubling in noninteracting band structures. Adding a magnetic field, we investigate the fate of the chiral anomaly. Remarkably, as long as a system exhibits a single Weyl node in the absence of magnetic fields, arbitrarily weak fields qualitatively restore the lowest Landau level structure of a noninteracting Weyl semimetal. This underlines the universality of the chiral anomaly in the context of Weyl semimetals. We furthermore demonstrate how the topologically protected Fermi-arc surface states are modified by long-ranged interactions.

Colossal magnetoresistance in low-doped EuTi1−xNbxO3 (x = 0.003 and 0.005)

We studied the magnetization (M), magnetostriction (λ||), resistivity (ρ), magnetoresistance (MR), and thermoelectric properties of low-doped EuTi1−xNbxO3 (x = 0.003 and 0.005). In both the samples, Eu2+(4f7) spins order antiferromagnetically at TN≅5.5K, and the paramagnetic to antiferromagnetic transition is accompanied by a spontaneous contraction of the length in the absence of magnetic field and a positive magnetostriction under external magnetic fields. ρ(T) shows non-metallic behavior in the temperature range 400–2.5 K but a weak kink at TN in a zero magnetic field. The application of an external magnetic field induces the semimetal-metal transition and negative MR. The magnitude of negative MR has a maximum value of 82% (57%) under 7 T for x = 0.003 (0.005) at T = 2.5 K, and the MR monotonously decreases with increasing temperature. Thermopower data indicate that the doped carriers are electrons. It is suggested that scattering of 4d1 electrons doped in the impurity band by 4f spin fluctuations is responsible for the colossal magnetoresistance.

Magneto-rotation-fibre-reinforced thermoelastic with gravity and energy dissipation

In this article, two theories of the generalized thermoelasticity Green-Naghdi theory (of type II and III) are applied, as well as the coupled theory to study the effect of magnetic field and rotation under influence of gravity on 2D problem of a fibre-reinforced thermoelastic. The normal mode analysis is used to obtain the expressions for the temperature, displacement components and the thermal stresses distributions. The resulting formulation is applied for two different concrete problems. The first concerns the case of a punch moving across the surface of semi-infinite thermoelastic half-space subjected to appropriate boundary conditions. The second deals with a thick plate subjected to a time-dependent heat source on each face. Numerical results are illustrated graphically for each problem considered. A comparison is made with the results predicted obtained by the two theories in the presence and absence of magnetic field, rotation and gravity field.

Numerical investigations of Richtmyer-Meshkov instability in different magnetic field configurations and the corresponding dynamic mode decomposition

Based on magnetohydrodynamics(MHD), the evolution of the Richtmyer-Meshkov instability in different magnetic field configurations are studied. To ensure the zero magnetic divergence, an unsplit integration algorithm is adopted by combining corner transport upwind and constrained transport (CTU+CT) algorithm. The second order Godunov flux is obtained by using piecewise parabolic method(PPM) to construct conserved variables. The numerical results show that the evolution of complex wave patterns is not affected by magnetic fields, but the interface instability is compressed by magnetic field, especially in the case of transverse magnetic fields. Specifically, whether there exists magnetic field or not, irregular reflections occur outside the cylinder. Meanwhile, the central part of incident shock wave interacts with the density interface and generates the transmitted shock wave. Subsequently, the transmitted shock wave oscillates back and forth inside the cylinder, forming a transmission-reflection structure multiple times. Besides, in the absence of magnetic field, the density interface rolls up with a series of vortex sequences and an SF<sub>6</sub> jet surrounded by vortex pairs appears. Then the SF<sub>6</sub> jet passes through the downstream interface. In a longitudinal magnetic field, although density interface is smooth, a few vortex sequences still exist in the downstream interface and SF<sub>6</sub> jet can still pass through downstream interface. However, in the case of transverse magnetic field, the interface is much smoother than in the other cases and the SF<sub>6</sub> jet cannot pass through the downstream interface. The quantitative study also indicate that the increase of characteristic sizes is suppressed by the magnetic field. In addition, because of the influence of Richtmyer-Meshkov instability, magnetic lines are distorted near density interfaces. More distortions can be observed in the upstream interfaces, resulting in strong Lorentz forces in that area, which leads to the long distance between two vortex sheets distributed along two sides of the interface. In the downstream interfaces Lorentz forces are rather small, but the forces are even smaller in the longitudinal magnetic field, as a result vortex sheets interact with each other in that area. Furthermore, the dynamic mode decomposition(DMD) is primarily used in this paper and the results illustrate that even controlled by magnetic fields, vortex sequences can still exist, especially in the case of longitudinal magnetic field. For all cases, the first DMD modes all illustrate that a stable mode is the dominated feature of fluid field, and the following second to fourth mode show that the strength of vortex sequences decreases while their frequencies increase continually. Besides, for the same modes, the frequency of vortex sequences is reduced by magnetic fields, especially by the transverse magnetic field.

Spin Supercurrent in Phenomena of Quantum Non-Locality (Quantum Correlations, Magnetic Vector Potential) and in Near-Field Antenna Effect

It is shown that such phenomena as quantum correlations (interaction of space-separated quantum entities), the action of magnetic vector potential on quantum entities in the absence of magnetic field, and near-field antenna effect (the existence of superluminally propagating electromagnetic fields) may be explained by action of spin supercurrents. In case of quantum correlations between quantum entities, spin supercurrent emerges between virtual particles pairs (virtual photons) created by those quantum entities. The explanation of magnetic vector potential and near-field antenna effect is based on contemporary principle of quantum mechanics: the physical vacuum is not an empty space but the ground state of the field consisting of quantum harmonic oscillators (QHOs) characterized by zero-point energy. Using the properties of the oscillators and spin supercurrent, it is proved that magnetic vector potential is proportional to the moment causing the orientation of spin of QHO along the direction of magnetic field. The near-field antenna effect is supposed to take place as a result of action of spin supercurrent causing secondary electromagnetic oscillations. In this way, the electromagnetic field may spread at the speed of spin supercurrent. As spin supercurrent is an inertia free process, its speed may be greater than that of light, which does not contradict postulates of special relativity that sets limits to the speed of inertial systems only.

Влияние дисперсии магнитной анизотропии кластеров Ge-=SUB=-3-=/SUB=-Mn-=SUB=-5-=/SUB=- на температурные зависимости намагниченности тонких пленок Ge:Mn

AbstractThe temperature dependences of magnetization M ( T ) of thin ion-implanted Ge:Mn (4 at % Mn) films containing Ge_3Mn_5 clusters were measured on samples cooled in the absence of magnetic field (zero field cooled, ZFC) and in a magnetic field of 10 kOe (field-cooled, FC). It has been established that the shape of ZFC–FC differential M ( T ) curves is determined by lognormal distribution of the size-dependent magnetic anisotropy energy of Ge_3Mn_5 clusters. Analysis of the observed ZFC–FC magnetization curves allowed the magnetic anisotropy dispersion (variance) and magnetic anisotropy constant to be estimated.

Influence of the Magnetic Anisotropy Dispersion in Ge3Mn5 Clusters on the Temperature Dependences of Magnetization in Thin Ge:Mn Films

The temperature dependences of magnetization M(T) of thin ion-implanted Ge:Mn (4 at % Mn) films containing Ge3Mn5 clusters were measured on samples cooled in the absence of magnetic field (zero field cooled, ZFC) and in a magnetic field of 10 kOe (field-cooled, FC). It has been established that the shape of ZFC–FC differential M(T) curves is determined by lognormal distribution of the size-dependent magnetic anisotropy energy of Ge3Mn5 clusters. Analysis of the observed ZFC–FC magnetization curves allowed the magnetic anisotropy dispersion (variance) and magnetic anisotropy constant to be estimated.

Dynamic measurement of ferrofluid thermal conductivity under an external magnetic field

An experimental investigation is conducted to study the thermal conductivity of ferrofluid in the dynamic condition. Effect of magnetic field strength on thermal conductivity of Fe3O4/water ferrofluid flowing in a tube with constant heat flux at different Reynolds numbers (400–800) and volume fractions (1–2 Vol.%) is examined. A set of thermocouples arranged in the radial direction is used to obtain the ferrofluid temperature profile and consequently the thermal conductivity. The data show that the thermal conductivity increases with the nanofluid concentration. Moreover, in the absence of magnetic field, an enhancement in thermal conductivity is observed with increasing Reynolds number while an opposite trend is observed under magnetic field. Compared to the water thermal conductivity, the maximum thermal conductivity enhancement of 32.3% was obtained for the ferrofluid with concentration of 2 Vol.% at Reynolds number of 400 and under magnetic field of 800 G. Our insights into the thermal conductivity of the ferrofluid under dynamic condition provide a new data and can be used to promote the accuracy of heat transfer calculations.

MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material

PurposeThe purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters.Design/methodology/approachFinite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied.FindingsIt was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10.Originality/valueSuch configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects.

MHD boundary layer bionanoconvective non‐Newtonian flow past a needle with Stefan blowing

AbstractThe purpose of the article is to present a transport model for magnetohydrodynamics‐forced convective non‐Newtonian boundary flow from a thin needle in a nanofluid in the presence of microorganisms and Stefan blowing. The governing equations are reduced to ordinary differential equations with the help of similarity transformations and then numerically solved by using the Matlab bvp4c function. The effect of various emerging parameters on the flow field, heat, mass, and density of motile microorganisms transfer was computed and studied. It was found that some of the parameters have an important effect on the boundary layer thickness. Justification with earlier simpler model in the absence of magnetic field is included. The model finds applications in various transdermal delivery system, biomedical electromagnetic treatments and to design new medical devices for cell delivery to the central nervous system.

Uniaxial pressure control of competing orders in a high-temperature superconductor.

Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.

بررسی تجربی تأثیر سطح شیاردار و میدان مغناطیسی بر جوشش استخری نانوسیال گاما-اکسیدآهن/ آب

Use of nanoparticle, heater surface expansion and magnetic field applying are important and effective elements on boiling heat transfer. In this article, pool boiling of deionized water and γ-Fe2O3/water nanofluid have been analyzed on smooth and copper grooved surface at one atmosphere pressure in the presence and absence of magnetic field, experimentally. The result showed that the boiling heat transfer coefficient of deionized water has increased in circular and rectangular grooved surfaces and has decreased in triangular grooved surface toward the smooth surface. The boiling heat transfer coefficient of nanofluid has increased 24% in circular grooved surface and has decreased 8% and 37% in rectangular and 37% in triangular grooved surfaces. The corners existence and wettability reduction in vertical wall of rectangular and triangular grooves and the bubbles slipping cause thermal resistance increasing toward circle groove. Two flat constant magnets have been used in two sides of boiling reservoir for magnetic field creation. By applying magnetic field with negative gradient, the boiling heat transfer coefficient of nanofluid has enhanced in circular and rectangular grooved surfaces and has reduced in triangular grooved surface. The upward magnetic force causes the formed bubbles diameter decreasing, but groove type is effective on result, too.

Strain-Induced Topological Insulator in Methyl-Decorated SiGe Films

Since the discovery of topological insulators (TIs), there has been much research into prediction and experimentally discovering distinct classes of these materials, in which the bulk insulating but helical edge states are conducting in the absence of magnetic field. Herein, using first-principle calculations along with tight-binding model, methyl-decorated SiGe film is shown to undergo a topological phase transition under external tensile strain. The band gap can be tuned by the tensile strain, and at critical strain (e = 8%) at Γ-point opens a gap Eg = 0.35 eV due to band inversion. The nonzero topological invariant and helical edge states are further confirmed by topological invariant, Z2 = 1, for stretched SiGeCH3. Thus, a large energy gap induced by spin–orbit coupling and tensile strain indicates that methyl-decorated SiGe film is quite promising to design two-dimensional TIs materials for practical application. Moreover, for design and fabrication of topological electronic devices, we propose a bil...