External Field Interaction Research Articles

Molecular influence on nuclear-quadrupole-coupling effects in laser induced alignment.

We computationally studied the effect of nuclear-quadrupole interactions on the field-free impulsive alignment of different asymmetric-top molecules. Our analysis is focused on the influence of the hyperfine- and rotational-energy-level structures. These depend on the number of nuclear spins, the rotational constants, and the symmetry of the tensors involved in the nuclear spin and external field interactions. Comparing the prototypical large-nuclear-spin molecules iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, and 2,5-diiodobenzonitrile, we demonstrate that the magnitude of the hyperfine splittings compared to the rotational-energy splittings plays a crucial role in the spin-rotational dynamics after the laser pulse. Moreover, we point out that the impact of the quadrupole coupling on the rotational dynamics decreases when highly excited rotational states dominate the dynamics.

Effect of exchange, anisotropy, and external field interactions on the hysteresis and compensation of a two-dimensional ferrimagnet

We investigate the effects of exchange, anisotropy, and external field interactions on the of hysteresis and compensation behavior of a two-dimensional ferrimagnet with spins of values Q=7/2, and S=2 alternating on a square lattice, by means of the Monte Carlo (MC) and mean-field (MFT) simulation techniques. We analyze the temperature dependence of the magnetization and the hysteresis loops of the model for various values of the parameters in the Hamiltonian. The system experiences spin compensation, discontinuities, exchange bias, and multiple hysteresis loops when it is subjected to different values of exchange, anisotropy, and magnetic fields. The temperature range where the system experiences discontinuities in the magnetization increases with the decrease (increase) of the |D1′| modulus of the anisotropic field and with the change of direction of the h′ applied field, which is corroborated by the phase diagrams in the (D1′,T) and (h′,T) planes. We found that the exchange bias phenomenon occurs for a threshold value of the next-nearest-neighbor interaction of the S-spin (J2′=7.1). We compare our results with two investigations, one that does not include antiferromagnetic next-nearest-neighbor interactions nor external fields and another that does not consider the anisotropies of the sublattices, which are key parameters in the thermomagnetic behavior of the model.

Magnetic energy drives mass transfer processes to accelerate the degradation of Fe-based implant

The main obstacle of Fe towards the orthopedic application is the slow degradation rate. In this work, a FeGa alloy is developed by mechanical alloying and selective laser melting, and exposed to magnetic field to investigate the influence of magnetic energy on the degradation behavior of the alloy. The magnetic field magnetizes the FeGa alloy and establishes an induced magnetic field, which forms gradient magnetic energy around the corrosion pits during the degradation period. The gradient magnetic energy transfers the paramagnetism corrosion product particles like FexOy and GaOx to the edge of the corrosion pits and avoids the deposition of passive corrosion product layer, thereby maintaining the erosion of immersion solution to achieve a continuous corrosion process. Moreover, the magnetic field subjects Lorentz forces to oxygen and the corrosive ions in the medium, which provides driving forces for transferring them to the alloy surface, thereby accelerating the oxygen absorption degradation reaction. Results indicate that FeGa alloy coupled with magnetic field has a smaller charge transfer resistance of 3297.8 Ω than FeGa alloy (4877.2 Ω) and Fe (5951.1 Ω) in the absence of magnetic field, indicating a lower corrosion resistance of the corrosion product layer. Furthermore, the FeGa alloy in magnetic field exhibits high corrosion current density of 28.12 ± 0.35 μA/cm2 and fast corrosion rate of 0.25 ± 0.02 mm/year, which are significantly higher than FeGa alloy and Fe without magnetic field. The findings of this work suggest that combining component design with external field interactions can effectively regulate the degradation of Fe-based implants.

Lattice-layer entanglement in Bernal-stacked bilayer graphene

The complete lattice-layer entanglement structure of Bernal stacked bilayer graphene is obtained for the quantum system described by a tight-binding Hamiltonian which includes mass and bias voltage terms. Through a suitable correspondence with the parity-spin $SU(2)\otimes SU(2)$ structure of a Dirac Hamiltonian, when it brings up tensor and pseudovector external field interactions, the lattice-layer degrees of freedom can be mapped into such a parity-spin two-qubit basis which supports the interpretation of the bilayer graphene eigenstates as entangled ones in a lattice-layer basis. The Dirac Hamiltonian mapping structure simply provides the tools for the manipulation of the corresponding eigenstates and eigenenergies of the Bernal-stacked graphene quantum system. The quantum correlational content is then quantified by means of quantum concurrence, in order to have the influence of mass and bias voltage terms quantified, and in order to identify the role of the trigonal warping of energy in the intrinsic entanglement. Our results show that while the mass term actively suppresses the intrinsic quantum entanglement of bilayer eigenstates, the bias voltage term spreads the entanglement in the Brillouin zone around the Dirac points. In addition, the interlayer coupling modifies the symmetry of the lattice-layer quantum concurrence around a given Dirac point. It produces some distortion on the quantum entanglement profile which follows the same pattern of the isoenergy line distortion in the Bernal-stacked bilayer graphene.

Nonequilibrium Response of Nanosystems Coupled to Driven Quantum Baths.

Commonly, nanosystems are characterized by their response to time-dependent external fields in the presence of inevitable environmental fluctuations. The direct impact of the external driving on the environment is generally neglected. While this approach is satisfactory for macroscopic systems, on the nanoscale, an interaction of external fields with the environment is often unavoidable on principle. We extend the standard linear response theory of quantum dissipative systems to strongly driven baths. Significant modifications are found for two paradigm examples. First, we evaluate the polarizability of a molecule immersed in a strongly polarizable medium that responds to terahertz radiation. We find an increase of the molecular polarizability by about 30%. Second, we determine the response of a semiconductor quantum dot in close proximity to a metallic nanoparticle. Both are placed in a polarizable medium and exposed to electromagnetic irradiation. We show that the response of the quantum dot is qualitatively modified by the driven nanoparticle, including the generation of an additional channel of stimulated emission.

A New Information Soliton to Resist Decaying of the Excitation Based on the External Field Interaction

In this work, we reveal possibility using information soliton to resist senescence of certain important bio-excitations (such as Davydov solitons) which play a fundamental role in information processing of life. For this goal, a type of external field interaction with original system is introduced. This field enables the total system to be described by a nonlinear Master equation. Then we found that the nonlinear term in the equation drives the initial excitation to evolve as a kind of information soliton asymptotically. It is this information soliton to resist decaying of the excitations. This provides a constructive way to prolong age of biological excitations by exerting an external field, which forms a basis used in medical devices or treatments.

Molecular dynamics simulations of proton transverse relaxation times in suspensions of magnetic nanoparticles

In this work we have analyzed the influence of various factors on the transverse relaxation times T2 of water protons in suspension of magnetic nanoparticles. For that purpose we developed a full molecular dynamics force field which includes the effects of dispersion interactions between magnetic nanoparticles and water molecules, electrostatic interactions between charged nanoparticles and magnetic dipole–dipole and dipole–external field interactions. We also accounted for the magnetization reversal within the nanoparticles body frames due to finite magnetic anisotropy barriers. The force field together with the Langevin dynamics imposed on water molecules and the nanoparticles allowed us to monitor the dephasing of water protons in real time. Thus, we were able to determine the T2 relaxation times including the effects of the adsorption of water on the nanoparticles’ surfaces, thermal fluctuations of the orientation of nanoparticles’ magnetizations as well as the effects of the core–shell architecture of nanoparticles and their agglomeration into clusters. We found that there exists an optimal cluster size for which T2 is minimized and that the retardation of water molecules motion, due to adsorption on the nanoparticles surfaces, has some effect in the measured T2 times. The typical strengths of the external magnetic fields in MRI are enough to keep the magnetizations fixed along the field direction, however, in the case of low magnetic fields, we observed significant enhancement of T2 due to thermal fluctuations of the orientations of magnetizations.

NUMERICAL CALCULATION OF INTERNAL INDUCED FIELDS IN HUMANS DUE TO HIGH VOLTAGE TRANSMISSION LINES

Interaction of extremely low frequency (ELF) electromagnetic fields (EMF) with human has been a great concern over the previous years for researchers. ELF EMFs emanating from high voltage transmission lines interact with human by inducing electric fields internally in body. Various studies have shown the ill effects of this interaction on human organism. In this paper, numerical calculations of internally induced electric field and current density in human of different gender and age are done. Maximum values of external electric and magnetic fields are estimated from the detailed survey carried out on 132 kV high voltage transmission line. Human body is a complex structure comprising of several tissues with varying values of conductivity and relative permittivity. It is very difficult to describe the interaction of external fields with every single tissue and no direct method is available for measurement of internally induced fields. Internal fields are estimated with the help of homogeneous ellipsoid model. The total induced electric field and current density due to combined effect of external electric and magnetic field is calculated. Results obtained are compared with recommended exposure levels.

Comparisons of Cassini flybys of the Titan magnetospheric interaction with an MHD model: Evidence for organized behavior at high altitudes

Recent papers suggest the significant variability of conditions in Saturn’s magnetosphere at the orbit of Titan. Because of this variability, it was expected that models would generally have a difficult time regularly comparing to data from the Titan flybys. However, we find that in contrast to this expectation, it appears that there is underlying organization of the interaction features roughly above ∼1800 km (1.7 Rt) altitude by the average external field due to Saturn’s dipole moment. In this study, we analyze Cassini’s plasma and magnetic field data collected at 9 Titan encounters during which the external field is close to the ideal southward direction and compare these observations to the results from a 2-fluid (1 ion, 1 electron) 7-species MHD model simulations obtained under noon SLT conditions. Our comparative analysis shows that under noon SLT conditions the Titan plasma interaction can be viewed in two layers: an outer layer between 6400 and 1800 km where interaction features observed in the magnetic field are in basic agreement with a purely southward external field interaction and an inner layer below 1800 km where the magnetic field measurements show strong variations and deviate from the model predictions. Thus the basic features inferred from the Voyager 1 flyby seem to be generally present above ∼1800 km in spite of the ongoing external variations from SLT excursions, time variability and magnetospheric current systems as long as a significant southward external field component is present. At around ∼1800 km kinetic effects (such as mass loading and heavy ion pickup) and below 1800 km ionospheric effects (such as drag of ionospheric plasma due to coupling with neutral winds and/or magnetic memory of Titan’s ionosphere) complicate what is observed.

Polarized neutron reflectivity studies on granular Co 80Fe 20/Al 2O 3 multilayers

Polarized neutron reflectivity (PNR) studies have been performed on granular multilayers [Co 80Fe 20( t n )/Al 2O 3 (3 nm)] m . For a non-percolating superferromagnetic (SFM) sample ( t n =1.3 nm) no spin-flip (SF) scattering was observed, measured at various points of the hysteresis, confirming that the magnetization reversal is achieved merely by domain nucleation and growth. For a percolated sample ( t n =1.6 nm) an oscillating magnetization depth profile from FeCo layer to FeCo layer along the multilayer stack was observed around the coercive field. The competition between long-range dipolar, short-range Néel and external field interactions apparently give rise to such a modulated magnetization depth profile in these magnetic multilayers.

Relaxation and hysteresis in a two-dimensional dipolar lattice

The relaxation of polarization in time is studied for a two-dimensional dipolar lattice. Simulations are carried out integrating numerically the ordinary differential equations that result from considered dipole-dipole and dipole external field interaction for each dipole in a plane dipole arrangement. A potential law is found in the simulation of relaxation of polarization in time domain, in good agreement with experimental evidence. The influence of several parameters in system response is discussed. A hysteresis loop of polarization was obtained, showing ferroelectric behavior of the model.

A numerical study of relaxation in a two dimensional dipolar lattice

A dynamic model is proposed for ferroelectrics. The mathematical model is a system of nonlinear differential equations that results from considered dipole-dipole and dipole external field interaction for each dipole. All the simulations are carried out integrating numerically the system of ordinary differential equations for a plane dipole arrangement. On simulation of relaxation of polarization in time domain a potential law is found, in good agreement with experimental evidence. The influence of several parameters in system response is discussed. Finally, hysteresis loop was obtained and shows noise behavior.

人工物等粒子に及ぼす場の相互作用に関する実験例からの考察(ソフト人工物II)

人工物等粒子に及ぼす場の相互作用に関する実験例からの考察(ソフト人工物II)

A novel method for generating approximate wavefunctions

AbstractMolecular Hamiltonians are constituted by momentum operators (e.g., kinetic energy and interaction with electromagnetic radiation), local potential operators (e.g., electron–electron coulomb, electron–nucleus, and electron–external field interactions), and spin operators. In general, the effect of transformations that generate states from a reference state is to destroy this form. Here it is shown how one can generate all pure states by the action of a commutative semigroup of transformations that are diagonal in the space–spin coordinate representation that do not destroy this form and thus maintain the physical interpretability of effective Hamiltonians. Using such transformations, we formulate an approximation theory that has physical interpretation at all orders. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Break-up of dipolar rings under an external magnetic field

An experimental and theoretical study of the deformation and break-up process of rings, formed by magnetic microspheres, under the application of an external magnetic field is reported in this Letter. When the external magnetic field is applied parallel to the plane of the rings, we found that the break-up process has three different outcomes depending on the way of application and time history of the external field: (a) deformation into a compact set of dipoles with a triangular lattice structure, (b) opening into a single chain, and (c) break-up into two chains with various relative sizes. A thorough theoretical investigation of the break-up process has been carried out based on computer simulations, taking into account solely the dipole–dipole and dipole–external field interactions, without thermal noise. The experimental results and the simulations are in good agreement.

A higher order electron wave propagation method

A finite-difference propagation scheme for simulating electron currents through arbitrary quantum structures is presented in this paper. It is shown that due to the strong interaction of external fields and electrons, the trajectories predicted using higher order propagation operators are a significant improvement over that of lower order schemes, especially in cases where the longitudinal electron momentum is not accurately known. A novel boundary condition based on the popular transparent boundary condition is used for minimizing unphysical reflections off the computation boundaries even in the presence of strong lateral electric fields. The application of this scheme is illustrated through a few examples. >

Zeeman study of the phosphorescent state of palladium phthalocyanine in Shpol'skii matrices

Abstract The Zeeman splitting in the lowest phosphorescent state of palladium phthalocyanine (PdPc) in Shpol'skii matrices of mixed α-chloronaphthalene and n-octane as well as tetrahydrofuran and n-octane at 25 ± 5 K is reported. We believe this is the first study in which a randomly oriented large molecular system has ever been investigated with Zeeman spectroscopy without reliance on photoselection. The fact that we observed a Zeeman splitting in the randomly oriented sample arises from the dominance of the external field interaction over the internal molecular couplings. The evidence shows that the lowest phosphorescent state is the low-energy component of the lifted degeneracy of the 3Eu state of PdPc in the matrix crystal field and that this component is indeed an S = 1 triplet state. Spin-spin and spin-orbit interactions further split this triplet state into a doublet and a singlet with the doublet lying = 2.0 cm−1 lower than the singlet. The spectroscopic g value observed in the system is a statistical weighting of all molecules in the field, but with strongest weighting of the perpendicular ones (g⊥ ≈ 2.3).

Reducible relativistic wave equations

The relativistic wave equations considered in this study are of the form (-i Gamma . delta +m) psi (x)=0, and describe a unique mass m and spin s with 2(2s=1) independent components. Furthermore, their Gamma mu matrices form a reducible, but not necessarily decomposable, set over the representation space of the Lorentz group. It is shown that such reducible equations are dynamically equivalent to simpler irreducible equations: (-i beta . delta +m) phi (x)=0 where the beta mu can be constructed from the Gamma mu of the original equation. The beta mu form the irreducible 'core' of the original equation. The external field interactions for reducible wave equations in general are also studied. It will be shown that if the external fields do not introduce any new independent components into the equation and if the interactions are made up of the Gamma -matrices contracted over the external potentials, then such interactions can be studied as the same type of interactions of the irreducible beta -equation. Thus the dynamical equivalence of the free Gamma and beta equations extends to most interactions of interest. The results of the study show that the number of theories available which can lead to different physical predictions is significantly restricted.

Sakata-Taketani spin-0 theory with external field interactions: Lagrangian formalism and causal properties

To illustrate that a relativistic field theory need not be manifestly covariant, we construct Lorentz-invariant Lagrangian densities that yield the equation satisfied by an interacting (two-component) Sakata-Taketani spin-0 field. Six types of external field couplings are considered, two scalars, two vectors, an antisymmetric second-rank tensor, and a symmetric second-rank tensor, with the results specialized to electromagnetic interactions. For either of the two second-rank couplings, the equation is found to describe noncausal wave propagation, a property that is apparent from the dependence of the coefficients of the space derivatives on the external field; in contrast, the noncausality of the corresponding manifestly covariant Duffin-Kemmer-Petiau spin-0 equation is not so obvious. The possibilities for generalizing our results to higher spin theories involving only the essential 2(2 J + 1) components for a particle with a definite spin J and mass m are discussed in considerable detail.

Noncausal effects in relativistic wave equations

Manifestly covariant wave equations describing particles with a unique mass and spin can, for certain types of external-field interactions, possess noncausal solutions. The paper reports a procedure for applying Pierce decomposition of all six couplings expressed in the Duffin-Kemmer-Petiau spin-0 formula. This treatment converts the equation to a form in which the causal properties are apparent. The conditions under which the causal properties of higher-spin equations can be made manifest are discussed.