Tunneling Transport Research Articles

Quantitative assessment of rock mass stress–strain behavior at Severomuysky Tunnel

The article presents the selected geotechnical engineering studies accomplished in 2021–2022 by the Research Center for Applied Geomechanics and Convergent Technologies in Mining, College of Mining, NUST MISIS for the reconstruction project of Severomuysky Tunnel (ST) of the Baikal–Amur Mainline. The studies included the quantitative and qualitative geotechnical assessment of rock mass, its stress–strain analysis and susceptibility to rock bursts. Within the rock mass quality rating of ST, using the geological logs on 441 sample boreholes, the lab-scale test data on the physical and mechanical properties of 1820 rock samples were processed. The average values of the rock mass quality rating are presented for three geotechnical elements. The stress–strain analysis of ST rock mass and the lab-scale tests of rock brittleness made it possible to detect sites susceptible to rock bursts along the transportation tunnel, and to develop appropriate geotechnical monitoring activities. The recommendations are given to implement the described geotechnical surveys in construction and reconstruction of analogous objects and facilities, and in solid mineral mining.  The geotechnical research and other operations were carried out under guidance of RSRS GmbH Railway Infrastructure Projects CEO E. V. Dorot and the Company’s experts. The authors appreciate participation of the Project Engineers of the Research Center for Applied Geomechanics and Convergent Technologies in Mining, College of Mining, NUST MISIS N. G. Vysotin, A. M. Yanbekov, M. A. Kosyreva and S. S. Shermatova.

Use of One-Stage Detector and Feature Detector in Infrared Video on Transport Infrastructure and Tunnels

This article presents the use of the combination of the object detection method and feature detector in an infrared video on traffic infrastructure and in tunnels. The theme of the paper is the validation of vehicle detection and its classification using infrared video streams. In addition, the article focuses on the use of a feature detector and object detection to distinguish between vehicles with electric and combustion motors. The method suggests the use of a low-resolution thermal camera as an inexpensive extension of installed thermal camera technologies. The developed system has been verified for the applicability of vehicle detection and classification using object detection methods and their application in transport infrastructure and tunnels. It also presents a method for distinguishing propulsion units into electric and internal combustion; both systems’ conclusions are then statistically verified. The application of the system is evident in regional traffic management systems, including safety applications for traffic control in tunnels. Categorizing vehicles provides valuable information for higher levels of traffic management, toll systems, and municipal database systems, as well as for a preventive system for estimating vehicle conditions and their potential of fire in tunnels.

Self-consistent computation of spin torques and magneto-resistance in tunnel junctions and magnetic read-heads with metallic pinhole defects

A three-dimensional self-consistent spin transport model is developed, which includes both tunnelling transport, leading to tunnelling magneto-resistance, as well as metallic transport, leading to giant magneto-resistance. An explicit solution to the drift-diffusion model is also derived, which allows analysing the effect of both the reference and free layer thickness on the spin-transfer torque polarization and field-like coefficient. It is shown the model developed here can be used to compute the signal-to-noise ratio in realistic magnetic read-heads, where spin torque-induced fluctuations and instabilities limit the maximum operating voltage. The effect of metallic pinhole defects in the insulator layer is also analysed. Increasing the area covered by pinholes results in a rapid degradation of the magneto-resistance, following an inverse dependence. Moreover, the spin torque angular dependence becomes skewed, similar to that obtained in fully metallic spin valves, and the spin-transfer torque polarization decreases. The same results are obtained when considering tunnel junctions with a single pinhole defect, but decreasing cross-sectional area, showing that even a single pinhole defect can significantly degrade the performance of tunnel junctions and magnetic read-heads below the 40 nm node.

Large-bias spectroscopy of Yu-Shiba-Rusinov states in a double quantum dot

We have performed tunnel transport spectroscopy on a quantum dot (QD) molecule proximitized by a superconducting contact. In such a system, the scattering between QD spins and Bogoliubov quasiparticles leads to the formation of Yu-Shiba-Rusinov (YSR) states within the superconducting gap. In this work, we investigate interactions appearing when one- and two-electron spin states in a double-QD energetically align with the superconducting gap edge. We find that the inter-dot spin-triplet state interacts considerably stronger with the superconductor than the corresponding singlet, pointing to stronger screening. By forming a ring molecule with a significant orbital contribution to the effective g-factor, we observe interactions of all four spin-orbital one-electron states with the superconductor under a weak magnetic field.

In-plane ferroelectric tunnel junctions based on 2D α-In2Se3/semiconductor heterostructures

Ferroelectric tunnel junctions (FTJs) have great potential for application in high-density non-volatile memories. Recently, α-In2Se3 was found to exhibit robust in-plane and out-of-plane ferroelectric polarizations at a monolayer thickness, which is ideal to serve as a ferroelectric component in miniaturized electronic devices. In this work, we design two-dimensional van der Waals heterostructures composed of an α-In2Se3 ferroelectric and a hexagonal IV–VI semiconductor and propose an in-plane FTJ based on these heterostructures. Our first-principles calculations show that the electronic band structure of the designed heterostructures can be switched between insulating and metallic states by ferroelectric polarization. We demonstrate that the in-plane FTJ exhibits two distinct transport regimes, tunneling and metallic, for OFF and ON states, respectively, leading to a giant tunneling electroresistance effect with the OFF/ON resistance ratio exceeding 1 × 104. Our results provide a promising approach for the high-density ferroelectric memory based on the 2D ferroelectric/semiconductor heterostructures.

Experimental analysis on the interaction between underground structures and sand layer under groundwater level change

Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures. Global warming and active underground construction cause conspicuous changes in the groundwater level, which further leaves an impact on the underground structures’ serviceability. To reveal the interaction between underground structure and soil under groundwater level change in the sand layer, model tests of circular transportation tunnel and rectangular utility tunnel were carried out. With the self-designed experimental equipment and innovative experimental methods, the changes in tunnel stress, bending moment, buoyancy, and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied. The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level, indicating critical locations that should be strengthened. Meanwhile, both tunnels showed the same movement trend: settling first, floating afterwards and settling at last. And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure. Conclusions can provide a notable reference for future related research and engineering designs.

Effects of Crowd Density on Radio Propagation at 24 GHz in a Pedestrian Tunnel for 5G Communications

In this paper, we report the results of radio propagation characterisation in a pedestrian tunnel with different crowd densities at 24 GHz using commercial ray-tracing software called Wireless InSite. The 3D empty tunnel and human body models we created using computer-aided design software and imported into Wireless InSite. The tunnel model is based on a pedestrian tunnel connecting Suria and KLCC, which is located in the heart of Kuala Lumpur. Five three-dimensional (3D) human body models with different levels of detail were developed and tested. The crowd densities investigated were 0, 0.05, 0.1, 0.15 and 0.2 people/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> which correspond to 0, 25, 50, 75, and 100 people, respectively, in the study area. The results show that the path loss exponent, log-normal shadowing’s standard deviation, and fluctuation in received power increase as the number of people increases. When the crowd density is above 0.1 people/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the path loss exponent of the large-scale path loss model is higher than that of the empty tunnel. The results of this study are also useful for understanding the effects of human crowds on millimetre wave propagation in indoor tunnel-like environments such as hallways, enclosed corridors, mines, and transportation tunnels. The findings contribute to increasing the effectiveness of network planning and deployment for 5G communication, especially in pedestrian tunnels.

Study results of a stress-strain state of a pylon station construction from monolithic reinforced concrete in the engineering and geological conditions of St. Petersburg

In recent years, structures made from monolithic reinforced concrete have been increasingly developed in the field of underground construction. This has been made possible by the development of modern tunneling technologies such as NATM and ADECO&amp;RS, which have proven themselves abroad. Being low-sedimentation methods of underground structures construction, they have found wide application not only in mountain transport tunneling but also in construction in an urban environment, where precipitation and negative impact on the surrounding infrastructure has a decisive role in the choice of one or another technology. Foreign experience of construction in the same physical and mechanical characteristics of soils gives reason to assert the possibility of using new technologies in our country. However, this task requires a comprehensive approach to its solution. This article presents an experimental and theoretical substantiation of a pylon station lining made from monolithic reinforced concrete in the engineering and geological conditions of St. Petersburg on the example of the planned St. Petersburg Metro station “Chernigovskaya” of the “Krasnoselsko-Kalininskaya” line being built from “Obvodniy Kanal-2” station to “Yugo-Zapadnaya” station.

CARBON FOOTPRINT OF A CONCRETE TRANSPORT STRUCTURE - A DEEP TUNNEL

The research object of this scientific work is the massive concrete structures of underground low-deep transport tunnels, reinforced with steel and non-metallic composite reinforcement. Circular-section tunnels with the frame nominal diameters of 5, 10 and 15 m are considered. The subject of the research study is the assessment of the averaged carbon footprint in both types of the constructive solution throughout their entire life cycle. The presented research is due to the need to implement the European Climate Law (the European Green Agreement. At the same time the Paris Agreement (2016) recommends to stop producing and using carbon steel in construction by 2030. The ecological impact of both types of transport tunnels is expressed in the form of carbon footprint, as the equivalent of carbon dioxide emissions, which is calculated separately for each stage of their existence in accordance with the current European Codes, including the recommendations of the proprietary methodology. To determine the required sizes of the tunnels concrete frames and their reinforcement, the numerical routine (B3) experiment was carried out in PLAXIS software complex in accordance with the current regulations. Averaged according to three different diameters and generalized carbon dioxide emissions during the life cycle of the reference structure (type 1) and proposed one (type 2) of the underground transport tunnel with the length of 1 m.p. were, respectively, 15.97 t СО2 eq and 11.551 t СО2 eq, i.e. decreased by almost 1.4 times. The conducted research made it possible to analyze the carbon dioxide emissions into the atmosphere, to systematize the existing factors and impact factors of the specified building on the environment, and to determine the ways of their reduction. The possibility and expediency of using basalt-plastic reinforcement instead of steel in monolithic concrete structures, incl. transport tunnels, according to the criterion of reducing greenhouse gas emissions are proved. Keywords: carbon footprint, carbon dioxide emissions, underground transport tunnel, monolithic heavy concrete, steel and non-metallic composite reinforcement, construction life cycle, stage, information group (module).

Construction risk control technology of a large tunnel complex in urban area

The stability of the surrounding rock analysis and evaluation during tunnel construction is the basis of tunnel construction risk control. In this paper, we focus on the stability of a large-scale transportation tunnel complex during its construction in a densely-populated urban area. The tunnel complex includes seven shallow-buried tunnels with large cross-sections. In order to gain insight into the excavation influence of the different tunnels, stability analyses were first carried out using FLAC3D numerical simulation. Results showed that the tunnels were subjected to heave and crown settlement induced by adjacent excavation. Also, stress concentrated in the rock blocks connecting different tunnels. Subsequently, a bench-scale model test was performed to understand the failure of the rock blocks and to examine the accuracy of the numerical simulation. The test results agreed well with the numerical simulation. Based on the numerical and test results, the mechanism of the rock blocks failure was explained and construction risk control technology to stabilize the rock blocks was proposed. The construction risk analyses revealed: 1) tunnels are subjected to significant heave due to the excavation of tunnels located above; 2) the stability of the rock blocks is the paramount determinant for stabilizing the whole tunnel complex; 3) ensuring rock blocks to be in a state of triaxial stress is conducive to its stability and hence the stability of multiple tunnels.

Divide-and-conquer approach to study protein tunnels in long molecular dynamics simulations

Nowadays, molecular dynamics (MD) simulations of proteins with hundreds of thousands of snapshots are commonly produced using modern GPUs. However, due to the abundance of data, analyzing transport tunnels present in the internal voids of these molecules, in all generated snapshots, has become challenging. Here, we propose to combine the usage of CAVER3, the most popular tool for tunnel calculation, and the TransportTools Python3 library into a divide-and-conquer approach to speed up tunnel calculation and reduce the hardware resources required to analyze long MD simulations in detail. By slicing an MD trajectory into smaller pieces and performing a tunnel analysis on these pieces by CAVER3, the runtime and resources are considerably reduced. Next, the TransportTools library merges the smaller pieces and gives an overall view of the tunnel network for the complete trajectory without quality loss.

Andreev-like Reflection in the Pfaffian Fractional Quantum Hall Effect

We study tunnel transport between the edge of a Pfaffian fractional quantum Hall state and that of an integer quantum Hall state. Based on the duality argument between strong and weak tunnelings, we find that Andreev-like reflection appears for a strong tunneling regime. We calculate charge conductance in the weak and strong tunneling regimes for the low-voltage limit. In the weak tunneling limit, $\mathrm{d}I/\mathrm{d}V$ is proportional to $V^{1/\nu}$ with bias voltage $V$ and $\nu=1/2$. On the other hand, in the strong tunneling limit, $\mathrm{d}I/\mathrm{d}V$ is expressed by $(e^{2}/h)2\nu/(1+\nu)$ with correction term.

Variable-Barrier Quantum Coulomb Blockade Effect in Nanoscale Transistors.

Current-voltage characteristics of a quantum dot in double-barrier configuration, as formed in the nanoscale channel of silicon transistors, were analyzed both experimentally and theoretically. Single electron transistors (SET) made in a SOI-FET configuration using silicon quantum dot as well as phosphorus donor quantum dots were experimentally investigated. These devices exhibited a quantum Coulomb blockade phenomenon along with a detectable effect of variable tunnel barriers. To replicate the experimental results, we developed a generalized formalism for the tunnel-barrier dependent quantum Coulomb blockade by modifying the rate-equation approach. We qualitatively replicate the experimental results with numerical calculation using this formalism for two and three energy levels participated in the tunneling transport. The new formalism supports the features of most of the small-scaled SET devices.

Life-saving problems during fire in road tunnels

One of the main risk factors for the safe operation of tunnels, according to the design solutions of Georgian road tunnels, is the possibility of fire initiation with relevant negative consequences. The report will discuss the fire development scenarios under the ground based on the results of numerical modeling, as well as the recommendations for training and raising awareness of fire service personnel and rescuers depending on fire capacity, tunnel geometry, location and other factors, which will be applicable to the safe operation of transport tunnels and the survival of fire in the event of a fire.

Light‐Enhanced Negative Differential Resistance and Multi‐Level Resistive Switching in Glutamine‐Functionalized MoS2 Quantum Dots for Resistive Random‐Access Memory Devices

AbstractNegative differential resistance (NDR) with multi‐level resistive switching has been investigated for realizing multi‐level memory devices. However, achieving a high peak‐to‐valley ratio of NDR is a formidable challenge for a reliable multi‐level switch. Here, a new type of a light‐enhanced NDR device accompanied with resistive switching based on glutamine‐functionalized MoS2 quantum dots has been demonstrated. By increasing the illuminated light power on the device, the NDR effect can be greatly enhanced and a peak‐to‐valley ratio as high as 15.5 has been achieved. The tunneling transport and carrier trapping of the interface states are responsible for the mechanism of the light‐enhanced NDR. Multi‐level resistive switching can be realized in the same device by adjusting the illuminated light power. A high on/off resistance ratio of ≈103 and good endurance in multi‐valued switching have been achieved, exhibiting potential applications in multi‐level memory devices.

Microscopic formation mechanism of Si/Tl5Al1/TiN ohmic contact on non-recessed i-InAlN/GaN heterostructures with ultra-low resistance

In this work, we use Si/Tl5Al1/TiN for a source/drain ohmic contact to demonstrate an ultra-low contact resistance of 0.11 Ω mm (ρc = 2.62 × 10−7 Ω cm2) on non-recessed i-InAlN/GaN heterostructures. The Ti5Al1 alloy was used to suppress the out-diffusion of Al and extract N from the InAlN layer, which aided the formation of ohmic contact by improving the tunneling efficiency of electrons, as we have reported in the past work. A thin Si inter-layer combined with the Ti5Al1 alloy is proposed to further reduce contact resistance. A heavy n-type InAlN layer was obtained through doping with Si atoms to improve the tunneling transport of electrons. Furthermore, the TiN inclusions penetrated into the GaN channel because the in-diffused Si promoted the decomposition of GaN at a high annealing temperature and the in-diffused Ti reacted with GaN. These TiN inclusions provided direct contact with two-dimensional electron gas, offering an additional path for the injection of electrons into the channel. The tunneling and spike mechanism worked alternately to lower the contact resistance at different annealing temperatures (dividing at 900 °C), implying that the joint effect of tunneling and the spike mechanism was initially promoted in the formation of ohmic contact. The mechanism of this Si/Ti5Al1/TiN ohmic contact was fully understood through microscopic and thermodynamic analyses. These results shed light on the mechanism for the formation of ohmic contact in a gold-free metal stack for GaN-based HEMTs.

The Relation of the Method Used in Tunneling Operations with the Geological Structure Example of the Black Sea Coastal Road

Transportation tunnels are the most preferred method to facilitate transportation in mountainous and rough terrains. The excavation method and the choice of fortification tools in tunnel construction depend on the geological structure of the tunnel route. Correct formation determination and determination will reduce the cost and eliminate many risks. The Black Sea region has a very mountainous and rugged terrain. The most obvious method used to overcome rough terrain is road tunnels. The rock classification of the tunnel route and the support to be formed accordingly are very important in the selection of the method to be applied in the highway tunnel constructions. Within the scope of this study, Trabzon-Akyazi region, which is an important part of the Black Sea coastal road, was studied. The geological formations on the route of the 3-lane and double-tube tunnel with a length of approximately 2476 meters, which is planned to be built within the highway passing through this region, were examined and the method used in the tunnel construction was determined. As a result of the analyzes and calculations, it has been determined that the dominant unit along the tunnel routes is the agglomerate of the Besirli formation and the New Austrian Tunneling (NATM) method is applicable. The rock classes found were determined to be B3 and C2 classes according to NATM. Excavations in the tunnel were carried out by drilling and blasting method in the form of the upper half and the lower half.

NaCdSb: An Orthorhombic Zintl Phase with Exceptional Intrinsic Thermoelectric Performance

AbstractMany Zintl phases are promising thermoelectric materials owning to their features like narrow band gaps, multiband behaviors, ideal charge transport tunnels, and loosely bound cations. Herein we show a new Zintl phase NaCdSb with exceptional intrinsic thermoelectric performance. Pristine NaCdSb exhibits semiconductor behaviors with an experimental hole concentration of 2.9×1018 cm−3 and a calculated band gap of 0.5 eV. As the temperature increases, the hole concentration rises gradually and approaches its optimal one, leading to a high power factor of 11.56 μW cm−1 K−2 at 673 K. The ultralow thermal conductivity is derived from the small phonon group velocity and short phonon lifetime, ascribed to the structural anharmonicity of Cd−Sb bonds. As a consequence, a maximum zT of 1.3 at 673 K has been achieved without any doping optimization or structural modification, demonstrating that NaCdSb is a remarkable thermoelectric compound with great potential for performance improvement.

NaCdSb: An Orthorhombic Zintl Phase with Exceptional Intrinsic Thermoelectric Performance.

Many Zintl phases are promising thermoelectric materials owning to their features like narrow band gaps, multiband behaviors, ideal charge transport tunnels, and loosely bound cations. Herein we show a new Zintl phase NaCdSb with exceptional intrinsic thermoelectric performance. Pristine NaCdSb exhibits semiconductor behaviors with an experimental hole concentration of 2.9×1018 cm-3 and a calculated band gap of 0.5 eV. As the temperature increases, the hole concentration rises gradually and approaches its optimal one, leading to a high power factor of 11.56 μW cm-1 K-2 at 673 K. The ultralow thermal conductivity is derived from the small phonon group velocity and short phonon lifetime, ascribed to the structural anharmonicity of Cd-Sb bonds. As a consequence, a maximum zT of 1.3 at 673 K has been achieved without any doping optimization or structural modification, demonstrating that NaCdSb is a remarkable thermoelectric compound with great potential for performance improvement.

A light-controllable topological transistor based on quantum tunneling of anomalous topological edge states

Motivated by the recent observation of anomalous Hall effects in graphene [Nat. Phys. 16, 38–41 (2020)], we study the tunneling transport properties of topological edge states in irradiated graphene and graphene-like materials. We investigate the quantum tunneling transport in a structure: laser-irradiated graphene/gapped graphene/laser-irradiated graphene. We find that electrons cannot transport through the device because of the band gap, but electrons will tunnel through the device when anomalous topological edge states are induced by a laser. We predict a topological transistor based on the tunneling transport of topological edge states in irradiated graphene-like materials.