Wire Confinement Research Articles

Experimental investigations of concrete-filled steel tubular columns confined with high-strength steel wire

The use of high-strength steel wires is proposed to provide external confinement for concrete-filled steel tubular columns. This article presents an experimental study on high-strength steel-wire-confined concrete-filled steel tubular columns with various high-strength steel wire spacings and steel tube thicknesses and diameters. As observed from the experimental results, high-strength steel wires can effectively constrain and delay the local buckling of the steel tube in concrete-filled steel tubular columns. As a result, the load-carrying capacity and the post-peak stiffness of concrete-filled steel tubular columns are significantly increased by the high-strength steel wire confinement. When the spacing of the high-strength steel wires decreases, the load–axial strain response can evolve from a softening behavior to a hardening behavior for the concrete-filled steel tubular columns. Moreover, theoretical models were developed to predict the load-carrying capacity of the externally confined concrete-filled steel tubular columns, taking into account the mechanical mechanism and the triaxial stress state of the inner concrete. The analytical results are generally in reasonable agreement with the experimental results.

Axial Behavior of Concrete Cylinders Confined with FRP Wires

콘크리트 공시체의 압축강도와 연성성능을 향상시키기 위하여 FRP 와이어의 적용을 실험적으로 연구하였다. 와이어 보강겹수와 콘크리트 압축강도의 변화가 고려된 와이어 보강 공시체의 압축실험을 실시하였다. FRP 와이어 보강 공시체 압축실험에서 측정된 축방향변형률, 원주방향변형률, 체적변형률에 의한 와이어 내부 콘크리트의 손상상태를 분석하여 와이어 보강효과를 평가하였다. FRP 와이어 보강 공시체의 응력-변형률 선도는 두 개의 직선구간과 변환구간으로 구성된 것으로 측정되었으며, 균열이후구간에서 응력상승거동하였다. 와이어 보강 공시체의 균열강도와 최대강도는 와이어 보강겹수에 비례하여 증가하는 것으로 평가되었다. 와이어가 3겹 보강된 35 MPa 공시체의 최대강도는 무보강 공시체의 압축강도보다 286% 높게 측정되었다. FRP 와이어 보강 공시체의 내부 콘크리트 파괴형태는 i) 수직균열 또는 경사균열파괴; ii) 수평균열파괴로 구분되었다. 특히, 수평균열파괴는 와이어에 의한 구속약화로 인하여 갑자기 내부 콘크리트가 팽창하는 부분과 와이어가 아직 내부 콘크리트를 효과적으로 구속하는 부분의 전단효과로 발생하였으며, 수평균열은 공시체의 중앙부를 기준으로 여러 면으로 발생하였으며, 와이어에 의한 구속효과가 우수한 공시체에 발생하였다. FRP 와이어 보강 공시체 압축실험에서 와이어 최대파단변형률에 대한 인장파단변형률의 비가 55-90%로 측정되었으며, 평균 69.5%로 나타났다. 이는 일반 FRP 시트 보강 공시체 실험에서 측정된 시트 파단변형률보다 다소 높은 값으로 FRP 와이어 보강 공법의 우수성을 입증한다. The application of FRP wire as a mean of improving strength and ductility capacity of concrete cylinders under axial compressive load through confinement is investigated experimentally in this study. An experimental investigation involves axial compressive test of three confining amounts of FRP wire and three concrete compressive strengths. The effectiveness of FRP wire confinement on the concrete microstructure were examined by evaluating the internal concrete damage using axial, circumferential, and volumetric strains. The axial stress-strain relations of FRP wire confined concrete showed bilinear behavior with transition region. It showed strain-hardening behavior in the post-cracking region. The load carrying capacity was linearly increased with increasing of the amount of FRP wire. The ultimate strength of the 35 MPa specimen confined with 3 layer of FRP wire was increased by 286% compared to control one. When the concrete were effectively confined with FRP wire, horizontal cracks were formed by shearing. It was developed from sudden expansion of the concrete due to confinement ruptures at one side while the FRP wire was still working in hindering expansion of concrete at the other side of the crack. The FRP wire failure strains obtained from FRP wire confined concrete tests were 55~90%, average 69.5%, of the FRP wire ultimate uniaxial tensile strain. It was as high as any other FRP confined method. The magnitude of FRP wire failure strain was related to the FRP wire effectiveness.

Low-Frequency Spin Fluctuations in Skyrmions Confined by Wires: Measurements of Local Nuclear Spin Relaxation

We investigate low-frequency electron spin dynamics in a quantum Hall system with wire confinement by nuclear spin relaxation measurements. We developed a technique to measure the local nuclear spin relaxation rate T(1)(-1). T(1)(-1) is enhanced on both sides of the local filling factor ν(wire)=1, reflecting low-frequency fluctuations of electron spins associated with Skyrmions inside the wire. As the wire width is decreased, the fast nuclear spin relaxation is suppressed in a certain range of Skyrmion density. This suggests that the multi-Skyrmion state is modified and the low-frequency spin fluctuations are suppressed by the wire confinement.

Cohesive‐frictional model for bond and splitting action of prestressing wire

AbstractThis paper presents a numerical procedure for bond between indented wires and concrete, and the coupled splitting process of the surrounding concrete. The bond model is an interface, non‐associative, plasticity model. It is coupled with a cohesive fracture model for concrete to take into account the splitting of such concrete. Bond between steel and concrete is fundamental for the transmission of stresses between both materials in precast prestressed concrete. Indented wires are used to improve the bond in these structural elements. The radial component of the prestressing force, increased by Poisson's effect, may split the surrounding concrete, decreasing the wire confinement and diminishing the bonding. The combined action of the bond and the splitting is studied with the proposed model. The results of the numerical model are compared with the results of a series of tests, such as those which showed splitting induced by the bond between wire and concrete. Tests with different steel indentation depths were performed. The numerical procedure accurately reproduces the experimental records and improves knowledge of this complex process. Copyright © 2010 John Wiley & Sons, Ltd.

Splitting failure of precast prestressed concrete during the release of the prestressing force

Bond between steel and concrete is fundamental for the transmission of stresses between both materials in precast prestressed concrete. Indented wires are used to improve the bond in these structural elements. The radial component of the prestressing force, increased by Poisson’s effect, may split the surrounding concrete, decreasing the wire confinement and diminishing the bonding. This work presents a testing procedure to obtain the bond–slip curves, between steel and concrete, during the releasing of the prestressing force. The experimental procedure allows study of the splitting failure of the concrete, induced by the action of the indented wire. The influence of the distance between wires, the thickness of concrete cover and the depth of the wire indentations on the bond and splitting are examined. Specimens with three depths of the wire indentations and three thicknesses of concrete cover were tested. Moreover, a numerical procedure is presented for modelling the bond–slip, taking into account the possible failure of concrete by splitting. The numerical procedure accurately reproduces the experimental records and improves knowledge of this complex process.

Effect of spin-orbit interaction on the plasma excitations in a quantum wire

Incorporating the spin-orbit interaction into the Hamiltonian of a quantum wire, we have calculated the plasma excitation energies. We include both the Rashba term ($\ensuremath{\alpha}$ coupling) arising from the asymmetry of the heterostructure forming the two-dimensional electron gas, and the $\ensuremath{\beta}$ coupling due to the quantum wire confinement which we model with a harmonic potential. The $\ensuremath{\alpha}$ coupling lifts the degeneracy of the spin states and the $\ensuremath{\beta}$ coupling causes the quantized transverse single-particle energy to have negative dispersion. Our model yields several interesting features which may be observed with the use of inelastic light scattering and electron energy loss spectroscopy (EELS). The collective excitations for the quantum wire are determined by the allowed transitions between subbands. The collective plasma excitations split off from each branch of allowed particle-hole modes. The subband structure gives rise to a plasmon mode with a negative group velocity.

Excitons in quantum wires

This paper deals with excitons in quantum wires. We first study these excitons as the limit of excitons in D dimensions when $D \rightarrow 1$ . In order to do it, we have had to find a new resolution of the hydrogen atom Schrodinger equation: besides the fact that the usual resolution found in textbooks is not valid for D exactly equal to 1, it is, surprisingly enough, inconsistent since it relies on two hypergeometric functions which are not independent for the parameters of physical interest! In a second part, we write down the exact potential felt by the exciton relative motion along the wire in terms of the wire confinement. This allows a quite precise determination of the effective Coulomb potential for this 1D motion, which is of crucial importance to obtain a meaningfull finite value for the exciton ground state energy. In a last part, we study the dependence of the exciton energies on the wire area and anisotropy. While the quantitative results are here given for cylindrica l and rectangular wires with infinite barriers, we show how they can easily be extended to any particular wire shape and barrier height.

Rashba spin splitting in semiconductor quantum wires

A general three-dimensional model for asymmetric semiconductor quantum wires is introduced with exact and analytical solutions for the spin-dependent electronic structure. Simple expressions are obtained for the eigenvalues, wave functions, and spin expectation values, valid in both strong and weak Rashba spin-orbit coupling regimes. For III-V quantum wires, the Rashba interaction is shown to be typically in the weak coupling regime and to lead to considerable spin mixing only near the anticrossings, seen only in narrow-gap quantum wires. For realistic wires, the Rashba splitting is shown to decrease with increasing wire confinement.

The Wall Potential in the Pores of Vycor Glass Experienced by 3He Quasiparticles in a Dilute 3He-4He Solution

We have studied the Fermi fluid, 3He in 3He-4He solution, confined within the narrow channels of Vycor glass. Continuous wave NMR signals were observed in two almost identical coils, one containing bulk solution and the other the solution in Vycor glass. Three different solutions (0.1, 1.6, and 6%) have been studied over the temperature range 3mK to above 1K. The measurements relate to two exclusion effects of 3He from Vycor glass. One concerns potential energy, and we demonstrate the partial exclusion of 3He independent of concentration as the temperature is lowered from high temperatures down to around 200mK, thus giving an experimental measure of the van der Waals forces between the wall and the helium. The second effect is the additional quantum exclusion which arises from the influence of quantum wire confinement on the kinetic energy, as the temperature is progressively lowered below 50mK in the very dilute (0.1%) solution.

Carrier localization and photoluminescence in porous silicon

We show that the optical absorption and emission energies in porous silicon can be accounted for in a quantum wire confinement model where both the electron and the hole are localized by lateral surface wire undulations. Localization energies for both the particles have been numerically calculated within the effective mass approximation showing that there exists a limited class of wire geometries which are consistent with porous silicon optical and structure analysis data.

Exciton and biexciton correlations for weakly confined semiconductor quantum wires

The contributions of excitons and biexcitons to the four-wave mixing (FWM) signal are calculated for semiconductor quantum wells with an additional weak wire confinement. In contrast to the giant oscillator model, in our description the biexciton is formed from two singlet excitons by the Coulomb interactions. The matrix elements of the repulsive and attractive interactions between two excitons are calculated explicitly using 2D quantum well wave functions and quantized center-of-mass envelop functions. By calculating the excitonic polarization in the FWM direction, we obtain coherent exciton–biexciton quantum beats as function of the delay between the two pulses and of their intensity. Quantum beat oscillations are found not only on the rising side of the FWM-signal as in spatially homogeneous χ 3-theories, but also on the falling side, as it is observed experimentally. With increasing intensities the quantum beats develop into irregular signals.

Highly confined T-shaped quantum wires

A systematic approach to enhance the one-dimensional confinement energy of AlxGa1-xAs/Al0.3Ga0.7As T-shaped quantum wires is demonstrated. The design of the sample structures is derived from a calculation of the confined T-wire states. The samples are grown by molecular beam epitaxy cleaved edge overgrowth. We present experimental results, which show a T-wire confinement energy of 54 meV for an optimized sample structure. The temperature dependence of the wire luminescence intensity and decay time is dominated by exciton scattering into the cleaved multiple quantum well structure, with an activation energy comparable to the wire confinement energy.

Exciton trapping, binding and diamagnetic shift in T-shaped quantum wires

We determine the exciton states of T-shaped quantum wires. We use anisotropic effective-mass models to describe the electron and hole states. Pair correlation along the wire axis and in the lateral directions is included. We accurately model the measured redshifts between exciton photoluminescence in quantum wells and T-shaped wires. This redshift arises from enhanced exciton binding and the difference between well and wire confinement energy. We predict a large enhancement of binding energy only when lateral correlation is included, indicating that T-shaped wires are quasirather than quantum1D wires. We calculate exciton shapes and diamagnetic shifts to determine how the exciton is distorted when confined in a T-wire.

Optimization of the confinement energy of quantum-wire states in T-shaped GaAs/AlxGa1-xAs structures.

We report on an optimization of the wire confinement energies of the confined electronic states at the T-shaped intersection of GaAs and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells. These structures can be produced by the cleaved edge overgrowth technique. We present an analytical model for the confinement to give insight into the basic mechanism. The optimization of the confinement energy is done by calculations in a six-band k\ensuremath{\cdot}p approximation for the valence band and in an isotropic effective-mass approximation for the conduction band. The confined valence-band states are only weakly bound at the T-shaped intersection due to the large and anisotropic hole effective masses. Employing optimized sample parameters, confinement energies for the free-electron-hole pairs are nearly doubled compared to symmetric structures, and 34 meV are predicted for a 3-nm overgrown GaAs well. This is expected to be further enhanced by the Coulomb interaction, that is neglected in the numerical model. The experimental structures grown using the optimized geometry show wire confinement energies of up to 54 meV, which is significantly larger than KT at room temperature and larger than previously reported. \textcopyright{} 1996 The American Physical Society.

Electronic structure of dual gate quantum wire

The electronic structure of a novel nanometer scale semiconductor quantum wire structure [S. Y. Chou and Y. Wang, Appl. Phys. Lett. 63, 788 (1993)] has been calculated self-consistently. The structure has two control parameters, the voltage applied to a split gate and the voltage applied to a wire gate. The influences of both the split gate and the narrow wire gate which is placed inside the gap of the split gate, on the electronic structure of the system are examined. We show that varying the voltage on either the split gate or the wire gate changes the induced quantum wire confinement potential profile, the energy level spacing, the channel electron density, and the effective channel width. Results for the ballistic conductance of the device as a function of the two control voltages are extracted from the electronic structure calculations and are found to be in satisfactory agreement with experimental data.

Excitons in quantum well wires: V-shaped wire, T-shaped wire and strain-induced lateral confinement

We calculated the energy and the wave function of the exciton for i) a V-shaped quantum wire, ii) a T-shaped quantum wire and iii) a quantum wire resulting from strain-induced lateral confinement. The full Luttinger and Bir-Pikus Hamiltonian are taken into account in the three calculations. We used different parameters inside the well and at the barrier. The basis states |3/2m> are defined with respect to [110], the direction of the wire in the three kinds of structures, instead of the usual [001] direction. The hole dispersion curve allows one to define an effective mass which is to be introduced in the variational calculation of the exciton binding energy. We show that the hole is confined in a wire only in case i).

Voltage tunable potential wells for wire confinement of excitons

We use applied voltage to modulate lateral strain in a quantum well, thereby achieving tunable confinement of excitons. A capacitor structure is fabricated by attaching a flexible film containing a quantum well and a conducting layer to a doped Si substrate patterned with raised ribs. The film conforms to the ribs, creating a potential well for excitons where the quantum well is in tension. The film is pulled toward the substrate through electrostatic force, increasing the confinement. Modulation of strain confinement by over 50% is reported. The effect is reversible with voltage and polarity independent, as expected for electrostatic attraction.

Effects of the Coulomb interaction on the optical spectra of quantum wires.

We investigate theoretically excitonic effects on the optical properties of quantum-wire structures. The spatial nonlocal optical susceptibility is expressed in terms of electron-hole pair wave functions and energies. The corresponding two-particle equation is numericllay solved assuming a complete vertical confinement. The resulting exciton energies and the oscillator strengths are studied versus the wire confinement. The interplay of Coulomb attraction, center-of-mass quantization, and confinement of the internal motion is discussed. Very recent luminescence spectra for quantum-wire arrays fabricated by means of laser-induced cation interdiffusion, which show a variety of narrow exciton lines, can be interpreted.

Center-of-mass and internal motion of excitons in quantum wires

The properties of excitons, which are optically excited in single or coupled quantum wires, are studied within the effective-mass approximation. The two-particle wave functions and energies obey a Schrödinger equation with screened Coulomb interaction of electron and hole and their corresponding wire confinement potentials. This equation is approximately separated into an equation for the center-of-mass motion and another one more or less for the internal motion of the electron hole pairs. This allows a representation of absorption and luminescence spectra near a quantum-well exciton transition by a generalized Elliott formula.