Tunneling Process Research Articles

Failure mechanism and deformation prediction of soft rock tunnels based on a combined finite–discrete element numerical method

The large deformation mechanisms and predictions of soft rock tunnels have always been important but difficult to solve problems in the field of geotechnical engineering. A combined finite–discrete element numerical simulation method (FDEM) was used to study large deformation mechanism, classification and prediction. The deformations or failure mechanisms of tunnel surrounding rock were revealed, and the failure modes and displacement value prediction of surrounding rock with different strength-stress ratios were also investigated. The following conclusions were obtained: (1) Critical hysteresis damping can be adopted to simulate the progressive large deformation process of soft rock tunnels, which can obtain the final deformation of unsupported tunnels and avoid a dynamic response. (2) Under concentrated tangential stress, the surrounding rock undergoes X-shaped conjugate shear fracture, and this type of fracture network continues to propagate toward the depth of the surrounding rock until the model reaches a stable state; the reduction in tunnel cross-section is mainly caused by the macroscopic movement and volume expansion of rock fragments, and the latter is due to the generation of a large number of macroscopic voids. (3) As the strength-stress ratio decreases, the deformation or failure modes of the surrounding rock can be divided into four categories: elastic–plastic deformation, closed fracturing, shear dilation and broken expansion. (4) Finally, a prediction equation for isotropic and homogeneous soft rock unsupported tunnel deformation with general size driven by hydrostatic in situ stress is obtained, which indicates that with an increasing strength-stress ratio, the surrounding rock displacement decreases as an exponential function, with a correlation coefficient of R2 = 0.997. In addition, the robustness and reliability of the prediction equation is verified.

Advanced stability analysis method for the tunnel face in jointed rock mass based on DFN-DEM

An advanced stability analysis of surrounding rock can assure safe construction in tunnels. However, in traditional analysis methods, geometric information on the rock mass discontinuities is obtained by a geological compass and treated as an infinitely expanded plane in a numerical simulation, which is inaccurate in both geometric and numerical models. To solve this problem, this paper studied a control network and an image stitch method to assess the accuracy of a geometric model and proposed a more accurate method to obtain the geometric information of rock mass discontinuities based on digital photogrammetry. Based on discrete fracture network and discrete element method (DFN-DEM), this paper treated the rock mass discontinuities obtained by digital photogrammetry as finite disk planes and simulated the excavation process of the Qianyu tunnel. According to the simulation results, this paper determined the specific location of the collapse disaster on the tunnel face, which is of great significance to tunnel support design. Comparing the deformation of the surrounding rock mass on the tunnel face in the simulation results with the actual situation, this paper verified the feasible accuracy of this method in analysing the stability of the surrounding rock mass on a tunnel face in advance.

Exciton-assisted electron tunnelling in van der Waals heterostructures.

The control of elastic and inelastic electron tunnelling relies on materials with well-defined interfaces. Two-dimensional van der Waals materials are an excellent platform for such studies. Signatures of acoustic phonons and defect states have been observed in current-to-voltage measurements. These features can be explained by direct electron-phonon or electron-defect interactions. Here we use a tunnelling process that involves excitons in transition metal dichalcogenides (TMDs). We study tunnel junctions consisting of graphene and gold electrodes separated by hexagonal boron nitride with an adjacent TMD monolayer and observe prominent resonant features in current-to-voltage measurements appearing at bias voltages that correspond to TMD exciton energies. By placing the TMD outside of the tunnelling pathway, we demonstrate that this tunnelling process does not require any charge injection into the TMD. The appearance of such optical modes in electrical transport introduces additional functionality towards van der Waals material-based optoelectronic devices.

A Numerical Study on the Lateral Pile–Soil Interaction During the Tunneling Process in Clay

A Numerical Study on the Lateral Pile–Soil Interaction During the Tunneling Process in Clay

Analytical solutions of ground settlement induced by yaw in a space curved shield tunnel

This paper aims to provide the analytical solutions of the ground settlement for a space curved shield tunnel in the case of yaw construction. Settlement inducements include ground loss and construction loads, and two corresponding analytical models have been proposed in this study. Three-dimensional image theory has been adopted to calculate the ground settlement due to ground loss. Yaw-related parameters are introduced into the calculation model to deduce the relevant laws of the ground settlement. Based on modified Mindlin solutions, analytical models are established to calculate the ground settlement induced by construction loads, such as the frontal additional thrust, axial friction of shield shell, and the grouting pressure. The method of calculating the position of the shield machine in the ground is refined, and the influence area of construction loads from the shield machine is optimized. Subsequently, the obtained solutions are validated by a numerical model and field data. Besides, a comparison reveals that the proposed model is the composition of three classical analytical models, thus it excels them in solving the problem mentioned. Finally, parametric analyses of yaw are conducted to examine yaw angle and pitch angle on ground settlement. The proposed model can effectively predict ground settlement caused by the spatial linear shield tunneling process.

Ionization transition rates in the intermediate regime of the Keldysh parameter for a (0,1)*LG spiral amplitude modulated laser field

The mechanisms of the tunnel and multiphoton ionization transitions of hydrogen-like atoms and noble gas atoms are discussed. Atoms potassium and argon, with ionization energy of 4.34 and 15.76 eV, were chosen as the target. The atoms are exposed to Ti:Sapphire, (0,1)*LG, spiral amplitude modulated, laser beam at λ = 800 nm wavelength in a broad intensity range 1012 to 1015 W/cm2. The computational approach to describe tunnel and multiphoton processes was based on using the ADK theory. Stark and ponderomotive effects are also included to study their influence on the transition rate. Obtained results show that, for the lower γ values, the contribution of multiphoton ionization was less significant than the tunnel ionization contribution. In comparison, for higher γ values, multiphoton ionization dominated over tunnel ionization in a total transition rate. It is found that, in this particular case of spiral amplitude modulated mode, the intermediate regime, where both processes equally contribute, strongly depends on the atom selection and laser field intensity. Ionization in the intermediate regime occurs for γ ≈ 10 and 12 for low laser intensities, as γ ≈ 2 and 2.5 for the higher values, in the case of potassium and argon respectively. Our analysis indicated that the Stark and ponderomotive effects have a significant influence on the total transition rate. It is shown that these effects decrease the transition rate value and move the intermediate regime’s position toward lower values of the γ parameter, mainly in the case of higher laser field intensity.

Nonsinusoidal current-phase relations in semiconductor–superconductor– ferromagnetic insulator devices

Coherent tunneling processes of multiple Cooper pairs across a Josephson junction give rise to high harmonics in the current phase relation. In this work, we propose and study Josephson junctions based on semiconductor--superconductor--ferromagnetic insulator heterostructures to engineer nonsinusoidal current-phase relations. The gate-tunability of the charge carriers' density in the semiconductor, together with the adjustable magnetization of the ferromagnetic insulator, provides control over the content of the supercurrent harmonics. At finite exchange field, hybrid junctions can undergo a $0 -- \ensuremath{\pi}$ phase transition, resulting in a supercurrent reversal. Close to the transition, single-pair tunneling is suppressed and the current-phase relation is dominated by the second-harmonic, indicating transport primarily by pairs of Cooper pairs. Finally, we demonstrate that noncollinear magnetization or spin-orbit coupling in the leads and the junction can lead to a gate-tunable Josephson diode effect with efficiencies of up to $\ensuremath{\sim}30%$.

Theoretical analysis and fracture process of elliptical tunnel with symmetric cracks subjected to water pressure and ground stress

The water diversion tunnel played an important role in the allocation of water resources in the water diversion project. In the process of actual use, some cracks or joints at the edge of the tunnel could produce further cracking under the action of internal water pressure and in-situ stress, which was dangerous to the safety of the tunnel. The analytical solution formulas of stress intensity factors (SIFs) of the elliptical tunnel with two cracks were derived by using the complex function method, and the external factors affecting the stability of the elliptical tunnel were analyzed. The failure process of the specimens was analyzed by using the high-speed camera and digital image correlation (DIC) method to obtain the evolution laws of crack initiation behavior and tunnel fracture modes. The results can conclude that both sides of the elliptical tunnel and the crack tip were stress concentration areas. As the inclination angle α of the elliptical tunnel is varied from 0° to 45°, tensile cracks occur at the top and bottom of the elliptical tunnel caused by tensile stress, and the compressive strength is smallest when the elliptical tunnel with α is 45°. As the inclination angle α is 75°, two penetrating cracks appear at the edge of the elliptical tunnel and crack tips. The initiation pressure increases with the inclination angle α. The SIF of mode II rises with the ellipse major semi axis and the crack length.

Single-electron charge transfer into putative Majorana and trivial modes in individual vortices

Majorana bound states are putative collective excitations in solids that exhibit the self-conjugate property of Majorana fermions—they are their own antiparticles. In iron-based superconductors, zero-energy states in vortices have been reported as potential Majorana bound states, but the evidence remains controversial. Here, we use scanning tunneling noise spectroscopy to study the tunneling process into vortex bound states in the conventional superconductor NbSe2, and in the putative Majorana platform FeTe0.55Se0.45. We find that tunneling into vortex bound states in both cases exhibits charge transfer of a single electron charge. Our data for the zero-energy bound states in FeTe0.55Se0.45 exclude the possibility of Yu–Shiba–Rusinov states and are consistent with both Majorana bound states and trivial vortex bound states. Our results open an avenue for investigating the exotic states in vortex cores and for future Majorana devices, although further theoretical investigations involving charge dynamics and superconducting tips are necessary.

A General Framework for the Impact of Shield Tunnel Construction on Existing Tunnel in Soil

During the excavation process of shield tunneling, it is inevitable that the surrounding soil mass is disturbed, which will affect the adjacent structures. This paper proposes a general framework for the impact of shield tunneling construction on existing tunnels. First, the impact partition of shield tunneling construction regarding adjacent tunnels and buildings is established by a three-dimensional numerical analysis method. Then, the displacement of adjacent tunnels and buildings is predicted using fuzzy gray theory. Finally, based on the results of a numerical simulation and experiment, the risk classification standard of adjacent buildings is established. This framework has certain reference significance and value for the deformation prediction and safety evaluation of adjacent buildings.

2-D tunneling structures and increased peak to valley current ratio in double barrier quantum systems under perpendicular electric and magnetic bias

Tunneling across an electrically biased double barrier system (with potential V along the z-axis) in a transverse magnetic field B (along the x-axis) is studied. The magnetic field-induced coupling of the transverse momentum (ky) with the z-direction motion of the electron selects the minimum value of ky depending on the incident energy εz below which the wave becomes evanescent in nature and is restricted from participating in the tunneling process. With the increase in B, resonant tunneling across the DBS occurs for an increasing range of resonant energy εzr albeit at a particular transverse momentum kyr for each εzr. Thus, the one-dimensional resonant tunneling feature at the quasi-resonant energy εzr0 for the entire spectrum of ky in absence of the magnetic field changes to a two-dimensional resonance structure in the εy and εz plane with the application of the magnetic field. The lower and upper bound of εzr and the corresponding limits on kyr for resonant tunneling based on B and V is spelt out. A formula for current density based on these observations is developed and the current–voltage relation for the DBS in presence of the transverse magnetic field is studied. With the application of the magnetic field the Peak to Valley current ratio (PVCR) calculated on the basis of tunneling current increases by many folds. The effect of Zeeman splitting due to interaction of spin moment of conduction electrons with magnetic field on the tunnel current is discussed.

Multiple Fano Resonances in Dynamic Resonant Tunneling Processes

The existence of Fano resonances in dynamic resonant tunneling (RT) systems has been investigated. Fano resonances are characterized by the appearance of a 100% reflection coefficient in proximity to a high transmission coefficient. For a Fano resonance to appear, a bound state must exist. On the other hand, a resonant tunneling process is characterized by a high transmission and the existence of a quasi-bound state (QBS) instead of a bound one. It has been shown that, by narrowing the width of the barrier, the resonance energy of the QBS gradually decreases and eventually turns into a bound state. Consequently, in a dynamic RT process, there are two scenarios: either a bound state exists, in which case, Fano resonances exist for any barrier width, or a QBS exists, and the barrier should be narrow enough for the Fano resonance to appear. In both cases, the incoming particle’s frequency must be lower than the oscillating well’s frequency. In this work, these resonances are investigated in detail, and both exactly numerically and approximated analytical expressions are derived for both the weak and strong oscillating amplitude regimes. One of the conclusions is that, when the oscillating frequency is low enough, multiple Fano resonances can appear by varying the barrier’s width. Since these resonances are very sharp and zero transmission can easily be detected, this property can be used as a very accurate method for measuring the barrier’s width, even when the particle’s de-Broglie wavelength is much larger than the barrier’s width.

Resistive Switching: Physics, Devices and Applications

Resistive Switching: Physics, Devices and Applications

Characterization of just one atom using synchrotron X-rays.

Since the discovery of X-rays by Roentgen in 1895, its use has been ubiquitous, from medical and environmental applications to materials sciences1-5. X-ray characterization requires a large number of atoms and reducing the material quantity is a long-standing goal. Here we show that X-rays can be used to characterize the elemental and chemical state of just one atom. Using a specialized tip as a detector, X-ray-excited currents generated from an iron and a terbium atom coordinated to organic ligands are detected. The fingerprints of a single atom, the L2,3 and M4,5 absorption edge signals for iron and terbium, respectively, are clearly observed in the X-ray absorption spectra. The chemical states of these atoms are characterized by means of near-edge X-ray absorption signals, in which X-ray-excited resonance tunnelling (X-ERT) is dominant for the iron atom. The X-ray signal can be sensed only when the tip is located directly above the atom in extreme proximity, which confirms atomically localized detection in the tunnelling regime. Our work connects synchrotron X-rays with a quantum tunnelling process and opens future X-rays experiments for simultaneous characterizations of elemental and chemical properties of materials at the ultimate single-atom limit.

RETRACTED: Non-Hermiticity of tunneling time in a spacetime-symmetric extension of nonrelativistic quantum mechanics

Time continues to be an intriguing physical property in the modern era. On the one hand, we have the classical and relativistic notions of time, where space and time have the same hierarchy, which is essential in describing events in spacetime. On the other hand, in quantum mechanics time appears as a classical parameter, meaning that it does not have an uncertainty relation with its canonical conjugate. In this work, we use a recent spacetime-symmetric proposal [Phys. Rev. A 95, 032133 (2017)] that tries to solve the unbalance in nonrelativistic quantum mechanics by extending the usual Hilbert space, having the time parameter $t$ and the position operator $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}$ in one subspace and the position parameter $x$ and time operator $\mathbb{T}$ in the other subspace. Time as an operator is better suitable for describing tunneling processes. We then solve the $1/2$-fractional integrodifferential equation for a particle subjected to strong and weak potential limits and obtain an analytical expression for the tunneling time through a rectangular barrier. Using a Gaussian energy distribution, we demonstrate that, for wavepackets well resolved in time, the expectation value of the operator $\mathbb{T}$ is the energy average of the classical time ${T}_{\text{class}}=\ensuremath{\partial}S/\ensuremath{\partial}E$, where $S$ is the classical action, which can be real or imaginary. For wavepackets not well resolved in time, the contribution of ${T}_{\text{class}}$ consistently vanishes, and solely properties of the energy distribution contribute to $\mathbb{T}$. We show that the time of travel for nontunneling particles is purely real. When tunneling is involved, complex arrival times emerge, becoming a signature of tunneling. Furthermore, we apply our results to a constant energy distribution, obtaining pure imaginary times for energies below the barrier while obtaining complex times for particles with a wavepacket spreading energies below and above the barrier, and show a comparison to previous works.

Experimental study on the collapse evolution law of unlined tunnel in Boulder-Cobble mixed formation

The construction of shallow tunnels has become increasingly challenging due to the complex geological conditions encountered, particularly in boulder-cobble mixed (BCM) formations found in river terraces. To understand the deformation characteristics of these formations, it is necessary to study the instability and failure evolution process of unlined tunnels in BCM formations. This research systematically investigates the failure evolution process and the variation laws of surrounding rock stress and displacement through a physical model test under 1 g conditions, focusing on the two most common external disturbance factors: excavation and rainfall. The study findings reveal a grouped pattern of movement in the collapsing movement. During the evolution process of instability, the surrounding rocks formed pressure arches multiple times, resulting in a clear development of staged deformation. The instability of the pressure arch zone leads to an expansion of the loose zone in the surrounding rocks, particularly in the tunnel vault area. To prevent the collapse of surrounding rocks effectively, it is suggested to control the stability of the first-formed pressure arch. Based on the instability evolution characteristics of the surrounding rock, strategies for preventing and controlling collapse are summarized and refined. Finally, a practical project is presented to demonstrate the positive impact of optimizing the excavation method and support system. The conclusions of this research have guiding significance for the prevention and control of tunnel collapse in BCM formations.

Electrical transport phenomena and modulus behavior in lead-free Ba0.85Sr0.15Ti0.85Zr0.15O3 compound

In this work, the ceramic Ba0.85Sr0.15Ti0.85Zr0.15O3 is prepared using the conventional solid-state reaction method. The frequency dependence of the electrical conductivity, impedance, and electric modulus of Ba0.85Sr0.15Ti0.85Zr0.15O3 are investigated using numerous theoretical laws over a large temperature range. The X-ray diffraction (XRD) study confirms that this composition crystallizes in pseudo-cubic symmetry. In addition, it shows the good crystallization of our material. The appearance of semiconductor behavior is attributed to the activation of the small polaron hopping process. AC conductivity analysis confirms the presence of complex behaviors. Indeed, we found the contribution of several hopping and tunneling processes to the conduction properties. The Nyquist plots (Z” vs. Z’) confirm the important contribution of the microstructure to the transport and relaxation phenomena. The complex modulus analysis confirms the strong correlation between the movements of the mobile charge carriers and shows the thermal activation of the relaxation process in Ba0.85Sr0.15Ti0.85Zr0.15O3. As a result, the long-distance movement of the load carriers essentially determines the relaxation process at low frequencies. From the electric modulus results, it is observed that the system under study reveals a non-Debye character.

Photo-assisted spin transport in double quantum dots with spin–orbit interaction

We investigate the effect of spin–orbit interaction on the intra- and interdot particle dynamics of a double quantum dot (QD) under ac electric fields. The former is modeled as an effective ac magnetic field that produces electric-dipole spin resonance transitions, while the latter is introduced via spin-flip tunneling amplitudes. We observe the appearance of non-trivial spin-polarized dark states (DSs), arising from an ac-induced interference between photo-assisted spin-conserving and spin-flip tunneling processes. These DSs can be employed to precisely measure the spin–orbit coupling in QD systems. Furthermore, we show that the interplay between photo-assisted transitions and spin-flip tunneling enables the system to operate as a highly tunable spin filter. Finally, we investigate the operation of the system as a resonant flopping-mode qubit for arbitrary ac voltage amplitudes, allowing for high tunability and enhanced qubit control possibilities.

Fracturing process and initiation mechanism of hard rock tunnels with different shapes: particle flow modeling and analytical study

Fracturing process and initiation mechanism of hard rock tunnels with different shapes: particle flow modeling and analytical study

Quantum phase slips in a resonant Josephson junction

We investigate the consequences of resonant tunneling of Cooper pairs on the quantum phase slips occurring in a Josephson junction. The amplitude for quantum tunneling under the Josephson potential barrier is modified by the Landau-Zener amplitude of adiabatic passage through an Andreev level crossing, resulting in the suppression of $2\pi$ phase slips. As a consequence, close to resonance, $4\pi$ phase slips become the dominant tunneling process. We illustrate this crossover by determining the energy spectrum of a transmon circuit, showing that a residual charge dispersion persists even at perfect transparency.