Wire Cross Section Research Articles

Influence of cross-section geometry and wire orientation on the phonon shifts in ultra-scaled Si nanowires

Engineering of the cross-section shape and size of ultra-scaled Si nanowires (SiNWs) provides an attractive way for tuning their structural properties. The acoustic and optical phonon shifts of the free-standing circular, hexagonal, square, and triangular SiNWs are calculated using a modified valence force field (MVFF) model. The acoustic phonon blue shift (acoustic hardening) and the optical phonon red shift (optical softening) show a strong dependence on the cross-section shape and size of the SiNWs. The triangular SiNWs have the least structural symmetry as revealed by the splitting of the degenerate flexural phonon modes and these show the minimum acoustic hardening and the maximum optical hardening. The acoustic hardening, in all SiNWs, is attributed to the decreasing difference in the vibrational energy distribution between the inner and the surface atoms with decreasing cross-section size. The optical softening is attributed to the reduced phonon group velocity and the localization of the vibrational energy density on the inner atoms. While the acoustic phonon shift shows a strong wire orientation dependence, the optical phonon softening is independent of wire orientation.

One- and two-dimensional cavity modes in ZnO microwires

We demonstrate that one-dimensional (1D) Fabry–Pérot modes (FPM) and 2D whispering gallery modes (WGM) occur separately or simultaneously within a single, tapered ZnO microwire. Their observation is strongly correlated with the size and shape of the microwire cross-section. FPM can preferentially be observed in thick wires with an elongated wire cross-section without hexagonal symmetry. The formation of WGM otherwise requires hexagonal symmetry—they can be observed in thin wires having a regular hexagonal cross-section. All optical eigenmodes were unambiguously identified by their in- and out-of- (cross-sectional) plane photonic mode dispersion.

Energy effectiveness and electromagnetic compatibility of DC traction power supply systems with 24-kV grid voltage

A new DC traction power supply system is advanced with a grid voltage of 24 kV, which would enable one to reduce significantly the distance between substations, the power grid wire cross section, and the power losses in supplying devices. This makes the new system superior to the AC traction power supply systems taken together with the absence of the supply voltage asymmetry, weaker electromagnetic influence and induction losses.

Bend-imitating models of abruptly bent electron waveguides

The fundamentals of bend-imitating approach regarding the one-electron quantum mechanics in abruptly bent ideal electron waveguides are given. In general, the theory allows to model each particular circularlike bend of a continuous quantum wire as some effective multichannel scatterer being pointlike in longitudinal direction. Its scattering ability is determined by the bending angle, mean bending radius, lateral coordinate (or coordinates) in wire cross section, time (or electronic energy), and possibly by the applied magnetic field. In an equivalent formulation, the theory gives rise to rather simple matching rules for the electron wave function and its longitudinal derivative affecting only the straight parts of a wire and thereby permitting to bypass a detailed quantum mechanical consideration of elbow domains. The proposed technique is applicable for the analytical investigation of spectral and transport electronic properties related to the ideal abruptly bent 3D wirelike structures of fixed cross se...

Analysis of Transverse Resistance Measurements in ${\rm Nb}_{3}{\rm Sn}$ Superconducting Wires

The superconducting wires are generally made of several hundreds or thousands of fine superconducting filaments embedded in a metallic matrix. Several relevant properties of the superconducting wires depend on the transverse resistances between filament bundles. In Nb3Sn wires realized with Bronze Route or Internal Tin technology, the presence of the bronze matrix can determine a significant increase of the transverse interfilament resistance with respect to wires with copper matrix. This increased resistivity in turn plays a role in determining the ac losses, thermal stability, and sensitivity to mechanical bending of the wire. The direct measurements of the transverse electrical resistances give useful information both for stability computations and to analyze the mechanical performance of the wire. The complexity of these measurements is however remarkable, due to the current distribution phenomena that occur among superconducting filaments during these tests. This paper presents the application of a 2D FEM model of the wire cross section and of a 3D electrical circuit model of the wire sample to derive qualitative and quantitative information about the transverse electrical resistance matrix. The paper shows that a detailed qualitative and quantitative description of the measurement results can only be obtained by means of a 3D model, that allows computing the current distribution along and across the sample length during the measurements.

An Optimization of a NbTi Wire Cross Section to Attain Low AC-Losses and High Critical Current

Removing the heat generated by AC-losses in large-scale superconducting applications has high costs. This is also the case in semi-DC magnets such as the ones of large particle accelerators where magnets are ramped synchronously with the beam energy. Also, these magnets require large cables made of several individual strands. This makes even the AC-loss analysis of such magnets very difficult. However, to attain low-loss full-size magnets, it becomes necessary to use wire designs that provide low AC-losses and adequate stability. The design of individual wires includes at least the determination of filament sizes and locations and the selection of matrix material. At the same time a high critical current and good workability must be ensured. With numerical analysis it is possible to consider these factors and design new strands and cables having low AC-losses for specific applications. In this paper we consider how to employ a numerical tool for the optimization of the NbTi wire cross-section to achieve low AC-loss and high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

Fracture of thermally activated NiTi shape memory alloy wires

This paper presents a study on the fracture of NiTi SMA wire undergoing thermal cycling, activated through resistive heating, under a constant load referred to as thermo-mechanical cycling (TMC). In general, TMC results in initiation of a large number of surface cracks on the SMA wire perpendicular to the wire axis. After initiation, these cracks propagate simultaneously inside the material under cyclic strain. But, the important observation in this study is the generation of cracks in the bulk of the material during TMC, preferentially at the core region of the wire. It has been shown that generation of cracks at the core region is due to strain inhomogeneity during TMC as a consequence of variation in the volume fraction of austenite and martensite phases across the wire cross section. This strain inhomogeneity is attributed to temperature and stress gradients that can exist across the cross section of the wire during thermal cycling. Study shows that nucleation of cracks and their growth at the core region of the wire plays an important role in the fracture of thermally activated SMA wire.

Magnetic field effects in artificial dielectrics with arrays of magnetic wires at microwaves

A magnetic field tunable electromagnetic response in periodic lattices of conducting magnetic wires is demonstrated. The wire medium having a negative permittivity in the lower frequency band is customarily investigated as an important component of so-called double negative metamaterials. Here we are interested in a strong dispersion of the permittivity in these structures and a possibility to alter it by changing the losses in magnetic wires with an external magnetic field. The theoretical approach is based on calculating the relaxation parameter depending on the wire surface impedance, and hence, on the wire magnetic properties. Thus, in arrays of Co-based amorphous wires the application of a moderate magnetic field (of about 1–2 kA/m) which causes the magnetization reorientation is capable of few fold permittivity change in the frequency range of 1–2 GHz. Such efficient tuning for certain structural and magnetic parameters was confirmed experimentally by measuring the transmission and reflection spectra from lattices of Co66Fe3.5B16Si11Cr3.5 glass-coated amorphous wires with a different wire cross-section and a different lattice period. The chosen wires are also confirmed to show a large magnetoimpedance effect at GHz frequencies, which constitutes the underlying mechanism of magnetic field dependent permittivity in wire media.

Influence of Residual Stresses on Fatigue Crack Propagation in Pearlitic Cold-Drawn Steel Wires

The aim of the present paper is to evaluate the effect of residual stresses, due to cold-drawing process, on the fatigue crack propagation in a pearlitic steel wire with a V-shaped circumferential notch. In order to analyse the effect of the notch severity on the residual stress distribution, three different values of the notch root radius are examined. The residual stress distributions in the reduced cross-section of such wires are numerically evaluated through FE analyses which simulate the material removing operation in the notched region. The stress-intensity factors (SIFs) related to tension loading and residual stresses are computed. Then, the crack propagation under cyclic tension combined with the residual stresses is analysed by taking into account the above SIF values and the actual stress ratio, which is different from that due to cyclic tension only.

Negative Refraction and Focusing Properties of Silver Nanowires Array with Different Cross-Sections

A three-dimensional silver metallic nanowires array which can realize negative refraction and image focusing in the visible frequency is presented. Homogeneous effective medium theory is used to investigate the negative refraction properties when the cell size of the array is much smaller than the incident wavelength. The analytical results are confirmed by Finite Difference Time Domain (FDTD) numerical simulations. The imaging properties comparison among the nanowires arrays with triangle, circle, ellipse, hexagon, and square wire cross-sections which have the same filling factor show the structure shapes of the nanowires will not influence the negative refraction but the imaging properties because of the different loss from the metal nanowires.

A New Way to Reduce Flow Disturbance in Endovascular Stents: A Numerical Study

Traditional commercial stents are made of wires with square or semi-circular cross-sections that lead to flow disturbance, which plays an important role in the initiation and progression of restenosis. A new stent with streamlined cross-sectional wires was proposed and researched numerically for its hemodynamic performance. Simplified models of stents with square, semi-circular, or streamlined cross-sectional wires were constructed numerically. Blood flows in the three models were simulated using computational fluid dynamics methods, and compared in terms of flow pattern, wall shear stress (WSS), and oscillating shear index (OSI). The results showed that when compared with the two traditional stents, the new stent with streamlined cross-sectional wires induced almost no flow disturbance, significantly enhanced WSS, and reduced the value of OSI within the stent. The present preliminary study indicates that the optimization of the cross-sectional shape of stent wires ought to be considered in the structural design for endovascular stents.

A fast inversion method for highly conductive submicron wires on a substrate

A numerical method is presented for sizing of highly conductive penetrable and perfectly electrically conducting (PEC) submicron wires on substrates. For efficiency, the Method of Auxiliary Sources is used in the forward model of the inverse Kirsch-Kress Method. The radius of the circular cross section of PEC and silver wires positioned on a semi-infinite silicon substrate is estimated based on numerically simulated scattered far field. The illumination is monochromatic, transverse electric (TE) polarised, and with fixed angle of incidence. Average relative errors smaller than 1% and 5% are achieved for PEC and penetrable wires, respectively, in the dynamic ranges 0.2–1.3 and 0.8–1.3 times the operating free-space wavelength, respectively. In all cases, the inversion time is less than 1 sec.

Experimental calibration of transmission grating and theoretical calculation of diffraction efficiency

Transmission grating is widely used in measurement of soft X rays. In order to measure the diffraction efficiencies of the transmission grating which is used in laser fusion, the transmission grating was calibrated on Beijing Synchrotron Radiation Facility in the energy region from 200eV to 1600eV, and the experimental results have been obtained. The model for grating efficiency simulation has been developed and calculations using a new so called 7-side quasi-trapezoidal cross section model were carried out. The results from the new model are in good agreement with the experimental data. The exact grating wire cross section is described.

Quasi-simultaneous measurements of ionic currents by vibrating probe and pH distribution by ion-selective microelectrode

This work reports a new methodology to measure quasi-simultaneously the local electric fields and the distribution of specific ions in a solution via selective microelectrodes. The field produced by the net electric current was detected using the scanning vibrating electrode technique (SVET) with quasi-simultaneous measurements of pH with an ion-selective microelectrode (pH-SME). The measurements were performed in a validation cell providing a 48 μm diameter Pt wire cross section as a source of electric current. A time lag between acquiring each current density and pH data-point was 1.5 s due to the response time of pH-SME. The quasi-simultaneous SVET–pH measurements that correlate electrochemical oxidation–reduction processes with acid–base chemical equilibria are reported for the first time. No cross-talk between the vibrating microelectrode and the ion-selective microelectrode could be detected under given experimental conditions.

Modified valence force field approach for phonon dispersion: from zinc-blende bulk to nanowires

The correct estimation of the thermal properties of ultra-scaled CMOS and thermoelectric semiconductor devices demands for accurate phonon modeling in such structures. This work provides a detailed description of the modified valence force field (MVFF) method to obtain the phonon dispersion in zinc-blende semiconductors. The model is extended from bulk to nanowires after incorporating proper boundary conditions. The computational demands by the phonon calculation increase rapidly as the wire cross-section size increases. It is shown that nanowire phonon spectra differ considerably from the bulk dispersions. This manifests itself in the form of different physical and thermal properties in these wires. We believe that this model and approach will prove beneficial in the understanding of the lattice dynamics in the next generation ultra-scaled semiconductor devices.

Strain Measurements on ACSR Conductors During Fatigue Tests III—Strains Related to Support Geometry

A simple conductor bending model taking into account the geometry of the suspension clamp has been used to interpret the strains measured on top and bottom wires of two ACSR conductors outer layer. Taut Drake and Bersfort ACSR conductor specimens were fitted with a short commercial metallic suspension clamp and forced to vibrate at one of their normal modes. On each gauged wire, five equally-spaced cross-sections were monitored near the last point of contact of the conductor with the bed of the clamp or with the bolted keeper. Three strain gauges were used at each selected wire cross-section making it possible to obtain the wire traction strain as well as the binormal and normal bending strains. This more complex conductor-clamp model was found to yield theoretical strain values closer to measured values than the usual models where clamp geometry is ignored. Hence, this could be a step to a more precise estimate of a given conductor-clamp fatigue limit when undergoing Aeolian vibrations.

Experimental Analysis of Torque Characteristics of Orthodontic Wires

A major requirement for orthodontic wires is superior elasticity. The question arises whether today's nickel titanium wires display a distinctively superelastic plateau also under torsional loading, and whether typical torsion angles are sufficient to produce adequate torquing moments with superelastic wires. The objective of this study was to compare various nickel titanium and steel wires in a pure torsion experiment. To experimentally examine the torque characteristic of orthodontic wires, we used nickel titanium wires manufactured by Dentaurum (Tensic®) and ODS (Euro Arch NiTi) measuring 0.40 × 0.40 mm2, 0.40 × 0.56 mm2, 0.43 × 0.64 mm2, 0.46 × 0.64 mm2, 0.48 × 0.64 mm2, 0.51 × 0.51 mm2, and steel wires made by Dentaurum (remanium®), 3M Unitek (HI-T™ II Stainless Steel) measuring 0.40 × 0.40 mm2, 0.40 × 0.56 mm2, 0.43 × 0.56 mm2, 0.43 × 0.64 mm2, 0.46 × 0.64 mm2, 0.48 × 0.64 mm2, 0.51 × 0.51 mm2. Torque was measured at an ambient temperature of 37 ° C for the nickel titanium wires. The distance between the bearing points was 10 mm for all measurements. The steel wires' torquing moments were determined at a torsion angle of 20 °, the torquing moments of the nickel titanium wires were investigated on the plateau, and we compared the results of the means and the standard deviations of all wires. Starting and end points of the loading and unloading plateau were determined for all nickel titanium wires. The torquing moment/torsion angle diagrams of the nickel titanium wires by different manufacturers displayed the curves typical of superelastic wires. The torquing moments of the wires with a smaller cross-section yielded values below 5 Nmm and thus appear obviously too small (e.g. Dentaurum Tensic®, 0.40 × 0.40 mm2: 1.3 Nmm). The mean values of the loading plateau's starting point yielded values of about 20 °. As the torsional play in the bracket slot of the wires with a smaller cross-section is typically about 10 °, we doubt whether these wires reach the superelastic plateau. Moreover, we observed production-associated variations in the material properties of various nickel titanium wires. It is thus difficult for the practitioner to draw a correlation between a wire's crosssection and the actual torquing moment delivered.

Efficiency Optimization and Prediction in High‐Gradient Magnetic Centrifugation

AbstractIn order to separate small magnetizable particles down to the micro‐ and nanometer scale, high‐gradient magnetic separation is a well‐established process. The superposition of magnetic filtration with centrifugation, called magnetic field‐enhanced centrifugation, permits continuous separation. The separation efficiency of magnetic filters and the prediction of the efficiency is described. The separation efficiency of one single stage could be enhanced from 51 to 78 % by increasing the wire number and improving the wire cross section. The separation efficiency on different particle sizes at different filter stage numbers and comparison to the prediction of separation efficiency based on magnetic forces and the fluid drag force is demonstrated.

Hydrogen surface passivation of Si and Ge nanowires: A semiempirical approach

AbstractA semiempirical nearest‐neighbor tight‐binding approach, that reproduces the indirect band gaps of elemental semiconductors, has been applied to study the electronic and optical properties of Si and Ge nanowires (NWs). The calculations show that Si‐NWs keep the indirect bandgap whereas Ge‐NWs changes into the direct bandgap when the wire cross section becomes smaller. Also, the band gap enhancement of Si‐NWs showing to quantum confinement effects is generally larger than that of similar‐sized Ge‐NWs, confirming the larger quantum confinement effects in Si than in Ge when they are confined in two dimensions. Finally, the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes: intra‐atomic and interatomic optical matrix elements are applied. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2448–2454, 2010

Effect of cold work on the mechanical response of drawn ultra-fine gold wire

Effect of cold work on the mechanical response of drawn gold wire is studied using finite element (FE) simulations. The drawing simulations were conducted in a single stage as well as multi-stage, i.e. two steps for the equivalent area reduction on a micrometer size gold wire. The effect of wire drawing process parameters such as die angle, coefficient of friction and area reduction were considered for the simulations. A clear variation in residual stresses from tensile to compressive is seen across the wire cross-section. Mechanical properties are assessed via residual stress state and the hardness variation across the drawn wire cross-section; the hardness is determined using simulated micro-indentation tests. The effect of this stress is also observed in the indentation response. In the area of tensile residual stresses increasing pile-up was seen at the indenter edges, while in the area of compressive stresses the opposite was observed. The results clearly show the dominating role played by the residual compressive and tensile stresses across the wire section in its mechanical response.