Wire Of Circular Cross Section Research Articles

Exact solutions for isothermal cyclic torsional loading of a circular SMA bar exploiting the shape memory effect

Two simple and fully analytical models are presented for a SMA bar or wire of circular cross section subjected to fully-reversed cyclic torsional loading, by taking into consideration the reorientation of the martensitic variants occurring during unloading and reverse loading. The process is assumed to take place at constant temperature between the start temperatures of the martensitic and austenitic transformations. In the first part of this work, the same shear modulus is taken both for Martensite and Austenite. In the second part, different elastic shear moduli are considered for the two phases. The volume fractions of both positive and negative twisted Martensite are assumed to evolve linearly with the shear stress. The bar is initially in a state of Austenite. As the applied torque is increased the martensitic transformation starts from the outer surface and then it extends inwards. If the maximum applied torque is large enough, then the complete Martensitic transformation takes place in the outer region of the cross section. During unloading and subsequent reverse loading the martensitic reorientation process may occur starting from the boundary between the fully martensitic outer region and the intermediate transforming region. Particular attention is focused on modeling the unloading and reverse loading processes. At each stage, the radial distributions of shear stress and Martensite variant are calculated analytically. A closed form relation between the applied torque and the angle of twist is presented for the entire process in the case of equal shear moduli, and only for the loading and elastic unloading stages in the case of different shear moduli. The approach is then validated against analytical, numerical and experimental results available in the literature for the direct loading–unloading process. Application to the seismic response of dissipative systems based on SMA helical springs is also envisaged.

Analysis of residual stress in circular cross-section wires after drawing process

Residual stresses arising in the drawing process have a significant impact on the quality of the cold-drawn wire. Knowledge of residual stresses and their distribution makes it possible to predict the behavior of metal products under operating loads and to prevent their possible destruction. In this regard, it is necessary to adjust the main parameters of the drawing process, including the geometry of the die channel. The work is devoted to the study of residual stresses arising from inhomogeneity of plastic deformation depending on the reduction value and the die angle. Computer simulation of wire drawing process by finite element method is performed. The distributions of residual stress tensor components along the wire radius are calculated for different values of reduction and die angle. The analysis of the obtained relations is carried out. The influence of the die angle on the distribution of residual stresses is most noticeable at small reductions. After the maximum values of residual stresses are reached at the reduction values of 35-40%, they noticeable decrease occurs.

Degenerate critical coupling in all-dielectric metasurface absorbers.

We develop the theory of all-dielectric absorbers based on temporal coupled mode theory (TCMT), with parameters extracted from eigenfrequency simulations. An infinite square array of cylindrical resonators embedded in air is investigated, and we find that it supports two eigenmodes of opposite symmetry that are each responsible for half of the total absorption. The even and odd eigenmodes are found to be the hybrid electric (EH111) and hybrid magnetic (HE111) waveguide modes of a dielectric wire of circular cross section, respectively. The geometry of the cylindrical array is shown to be useful for individual tuning of the radiative loss rates of the eigenmodes, thus permitting frequency degeneracy. Further, by specifying the resonators' loss tangent, the material loss rate can be made to equal the radiative loss rate, thus achieving a state of degenerate critical coupling and perfect absorption. Our results are supported by S-parameter simulations, and agree well with waveguide theory.

Energy-loss rate of hot electrons due to confined acoustic phonon modes in a semiconductor quantum wire under transverse electric field

The hot-electron energy-loss rate via the acoustic-phonons in an embedded semiconductor quantum wire of circular cross section in the presence of external electric field has been investigated using deformation potential theory. Dimensional confinement effect on modifying acoustic-phonon modes are taken into account. The energy-loss rate as a function of electric field strength, electron density and electron temperature is obtained. Our calculations show that the electric field applied perpendicularly to the wire axis can be used as an important tool for the control of the energy-loss processes in nanowires.

Conduction of Electrons in Quantum Wires of Circular Cross-Section

Objectives: Quantum wires are one-dimensional (1-D) material that exhibit length to width ratios of about 1000 or more. The properties of quantum wire are due to the electrons in them have quantized energy levels perpendicular to their lengths. Such quantum confinement effect exhibits discrete values of electrical conductance which are integral multiples of (e2/h). Methods/ Analysis: In this paper we present a quantum mechanical analysis of evaluation of the electron energy eigen states and their corresponding eigen functions in a quantum wire of circular cross-section. Findings: The energy eigen values of quantum wires of different radii are calculated. Applications: On the basis of our preliminary analysis it has been observed that quantum wires can also be used as electronic energy filters.

The influence of boundary conditions on the electrical conductivity of a thin cylindrical wire

Within the kinetic approach, the high-frequency electrical conductivity of a thin semiconductor circular cross-section wire is calculated. The radius of the wire is assumed to be small compared with the characteristic skin depth that allows neglecting the skin effect. A model taking into account the dependence of the reflectivity coefficient on the surface roughness factor and the angle of incidence of the charge carriers at the inner border of the wire was used as the boundary conditions for the nonequilibrium distribution function of the charge carriers The extreme cases of a degenerate semiconductor and a nondegenerate one are considered. The results obtained are compared to the calculations for the model of Fuchs diffuse-specular boundary conditions.

Complex frequencies and field distributions of localized surface plasmon modes in graphene-coated subwavelength wires

In this work we study the modal characteristics of localized surface plasmons in graphene-coated, circular cross-section wires. Localized surface plasmons are represented in terms of cylindrical multipole partial waves characterized by discrete, complex frequencies that depend on the size of the wire and can be dynamically tuned via a gate voltage. We consider both intrinsically nonplasmonic wires and intrinsically plasmonic wires. In the first case the localized surface plasmons are introduced by the graphene coating, whereas in the second case the localized eigenmodes of the graphene coating are expected to hybridize those already existing in the bare wire. We show that the approach presented here, valid for particle sizes where the retardation effects can be significant, is in good agreement with analytical expressions obtained in the limit when particle size is very small compared to the wavelength of the eigenmode and with results indirectly determined from scattering cross-section spectra.

Geometry effects on magnetization dynamics in circular cross-section wires

Three-dimensional magnetic memory design based on circular-cross section nanowires with modulated diameter is the emerging field of spintronics. The consequences of the mutual interaction between electron spins and local magnetic moments in such non-trivial geometries are still open to debate. This paper describes the theoretical study of domain wall dynamics within such wires subjected to spin polarized current. We used our home-made finite element software to characterize the variety of domain wall dynamical regimes observed for different constriction to wire diameter ratios d/D. Also, we studied how sizeable geometry irregularities modify the internal micromagnetic configuration and the electron spin spatial distribution in the system, the geometrical reasons underlying the additional contribution to the system's nonadiabaticity, and the specific domain wall width oscillations inherent to fully three-dimensional systems.

Numerical investigation of leaky modes in helical structural waveguides embedded into a solid medium

Helical multi-wire cables are widely used in bridges (suspended or prestressed) and anchored retaining wall constructions. Such structures can be damaged or degraded due to corrosion and fatigue. Non destructive evaluation techniques are required to reveal defects inside cable structures. Among these numerous techniques, elastic guided waves are of potential interest owing to their ability to propagate over long distances. However in civil engineering, cables are often buried or grouted in large solid media that can be considered as unbounded. Waves can strongly attenuate along the guide axis due to the energy leakage into the surrounding medium, which reduces the propagating distance. This energy leakage can be enhanced in helical structures, which further complicates their inspection. Searching modes with low attenuation becomes necessary. The goal of this work is to propose a numerical approach to compute modes in embedded helical structures, combining the so-called semi analytical finite element method and a radial perfectly matched layer technique. Two types of radial perfectly matched layer, centered and off-centered, are considered. Both are implemented in a twisting coordinate system which preserves translational invariance. The centered configuration is validated thanks to the twisted cylinder test case. The effect of twist on the eigenspectrum is briefly discussed. Then, an embedded helical wire of circular cross-section is considered. The off-centered configuration is shown to give the same results as the centered one. The effect of twist on modal attenuation is investigated. Finally, computations are performed for a seven-wire strand embedded into concrete, widely used in civil engineering cables.

Comparison and experimental validation of two potential resonant viscosity sensors in the kilohertz range

Oscillating microstructures are well established and find application in many fields. These include force sensors, e.g. AFM micro-cantilevers or accelerometers based on resonant suspended plates. This contribution presents two vibrating mechanical structures acting as force sensors in liquid media in order to measure hydrodynamic interactions. Rectangular cross section microcantilevers as well as circular cross section wires are investigated. Each structure features specific benefits, which are discussed in detail. Furthermore, their mechanical parameters and their deflection in liquids are characterized. Finally, an inverse analytical model is applied to calculate the complex viscosity near the resonant frequency for both types of structures. With this approach it is possible to determine rheological parameters in the kilohertz range in situ within a few seconds. The monitoring of the complex viscosity of yogurt during the fermentation process is used as a proof of concept to qualify at least one of the two sensors in opaque mixtures.

On the estimate of eddy current losses in current carrying conductors

It is shown that ohmic losses in current carrying conductors at nonzero frequency can be decomposed into two parts. One part is due to a current distribution that would have existed within the conductor at zero frequency (dc current distribution). The other is due to excess current distribution defined to be the difference of the actual current distribution at nonzero frequency and the dc current distribution. An integral equation for the computation of excess current distribution is derived and an easily computable upper bound on the excess losses is found. This upper bound is used to estimate the total eddy current losses and the accuracy of this estimate is tested for long wires of circular cross section. This estimate is shown to be accurate if the wire radius is about the same or smaller than the skin depth.

Size effects in the magnetization of a superconducting wire

The size effects in the magnetization of a long cylindrical wire of circular cross section in the presence of an external magnetic field are investigated. For this study the London theory is used with boundary conditions appropriate for this geometry. Using the Monte Carlo simulated annealing method, the free energy of the mixed state is minimized with respect to the vortex positions. The ground state of the vortex lattice for n=1 up to 18 vortices for a given radius of the cylinder is obtained. It is found that the finite size of the sample provokes a matching effect in the magnetization, as found in experiments with superconducting samples of finite size but different geometry.

Vortex lattice and matching fields for a long superconducting wire

We investigate the flux penetration patterns and matching fields of a long cylindrical wire of circular cross section in the presence of an external magnetic field. For this study we write the London theory for a long cylinder both for the mixed and Meissner states, with boundary conditions appropriate for this geometry. Using the Monte Carlo simulated annealing method, the free energy of the mixed state is minimized with respect to the vortex position and we obtain the ground state of the vortex lattice for $N=3$ up to 18 vortices. The free energy of the Meissner and mixed states provides expressions for the matching fields. We find that, as in the case of samples of different geometry, the finite-size effect provokes a delay on the vortex penetration and a vortex accumulation in the center of the sample. The vortex patterns obtained are in good agreement with experimental results.

Bend-imitating approach to quantum wire-like nanostructures

The bend-imitating approach to arbitrarily bent 2D quantum wires is substantially improved to make it consistent with the actual additivity of bending angles when the distance between two bends of the same type tends to zero. Within the revised 2D bend-imitating model strict but rather simple analytical conditions for the full electronic transparency of quadruply-bent wire-like structures are formulated in terms of electron energy and geometric parameters of the structure. The model of an arbitrarily bent and twisted 3D quantum wire of circular cross section is elaborated. To demonstrate the power of the 3D bend-imitating model the energies of localized electronic states and their dependences on geometrical parameters for doubly-bent singly-twisted structure are analytically calculated.

Screening effects on the confined and interface polarons in cylindrical quantum wires.

We study the contribution of confined and interface phonons to the polaron energy in quantum-well wires. We use a dispersionless, macroscopic continuum model to describe the phonon confinement in quantum wires of circular cross section. Surface phonon modes of a free-standing wire and interface phonon modes of a wire embedded in a dielectric material are also considered. Polaron energy is calculated by variationally incorporating the dynamic screening effects. We find that the confined and interface phonon contribution to the polaron energy is comparable to that of bulk phonons in the density range N=${10}^{5}$--${10}^{7}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Screening effects within the random-phase approximation significantly reduce the electron-confined phonon interaction, whereas the exchange-correlation contribution tends to oppose this trend at lower densities. \textcopyright{} 1996 The American Physical Society.

Scattering by thin wire loaded with a ferrite ring

A coupled integral equation formulation and a method of moments (MoM) solution are presented for the problem of scattering by a thin conducting wire of circular cross section with ferrite loading. It is proved that ferrite loading can be used to reduce the radar cross section of long thin objects at their resonant frequency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Binding energies of on-axis hydrogenic and nonhydrogenic donors in GaAs/Ga1?x Al x As

In a previous work [Phys. Rev. B43(1991)9262], the binding energies of hydrogenic and nonhydrogenic on-axis donors in GaAs/Ga1−xA1 X As quantum-well wires of circular cross section have been calculated as functions of the radius of the quantum-well wire. In both the hydrogenic and nonhydrogenic cases, a variational trial wave function was chosen that could be written as the product of an “envelope function”, and a function containing the variational parameter. It was assumed in these calculations that the potential barrier that exists at the surface of the GaAs cylinder and the surrounding Ga1−xA1 X As matrix is infinite. For the envelope function, an ordinary Bessel function of the first kind and of order zero was chosen. This envelope function satisfies the boundary condition, the vanishing of the trial function at the surface of the quantum-well wire. The question arises: how sensitive are the calculated binding energies to the choice of the envelope function? In the present work, we attempt to provide a partial answer to this question by choosing another envelope function, a spherical Bessel function of order zero. This function also satisfies the boundary condition and makes the trial wave function vanish at the interface between the GaAs cylinder and the Ga1−xA1 X As matrix. Our calculations show that the binding energies of both the hydrogenic and the nonhydrogenic on-axis donors depend on the choice of the envelope function.

On the approach to criticality of a vibrating, macroscopic object in superfluid 3HeB

Abstract An intuitive picture of pair breaking by a vibrating wire is developed, which makes dear how quasi-particles can escape from the wire at critical velocities below the Landau critical velocity νL. Assuming strong gap suppression at the wire surface, a critical velocity of ν ∗ = ν L 5 is obtained, for ideal dipole flow around a wire of circular cross-section. In addition, a further transition to enhanced quasi-particle emission is predicted to occur at a velocity ν 1 ∗ = ν L 3 More generally, for non-dipole flow, ν ∗ = ν L (1 + 2α 1 ) and ν 1 ∗ = solν L (1 + α l where at αl characterizes the local superflow near the surface of the wire.

Fundamental experimental parameters in the direct wire-casting process

Direct wire casting by “in-rotating-water melt spinning” has opened up a new future for the production of rapidly solidified wires. The process is unique in that wires of circular cross-section are formed in a single-step process by ejecting the molten metal into a moving water layer. Experiments with a wide range of alloys have shown that the continuity and uniformity of diameter and the as-cast dimensions are a function of several interrelated process parameters, including the nozzle diameter, the ejection pressure, the melt superheat, the casting angle and the water velocity. An iron-based alloy (Fe 68Ni 20Si 10C 2) was used as a model system to optimize the process and to determine the product characteristics over a wide range of casting conditions. Continuous wires of excellent surface finish and small (less than 10%) variation in diameter have been produced. Model calculations of the process show good agreement between theoretical predictions and experimental observations for optimum conditions.

Thermoelectric effects in thin films and wires

Recently, a new theoretical evaluation of an angle-dependent reflectivity function for random rough surfaces has been developed. This theory is applied here to the calculation of the thermoelectric effects in thin metallic films and wires of circular cross-section, and is compared with earlier approximations of Soffer and Maradudin. It is found that, in the calculation of the Peltier coefficient and thermoelectric power, there is an additional term arising from the energy dependence of the surface specularity. This term gives rise to a size effect which is of the same order of magnitude as the other terms; although it is always negative and presents a minimum at intermediate values of the thickness divided by the mean free path. For simple metals the combined effect of these terms is small, but they can lead to a minimum in the thermoelectric power at low temperatures.