Internal Tunnel Research Articles

Structural analysis of a hormone-bound Striga strigolactone receptor.

Strigolactones (SLs) regulate many aspects of plant development, but ambiguities remain about how this hormone is perceived because SL-complexed receptor structures do not exist. We find that when SL binds the Striga receptor, ShHTL5, a series of conformational changes relative to the unbound state occur, but these events are not sufficient for signalling. Ligand-complexed receptors, however, form internal tunnels that posit an explanation for how SL exits its receptor after hydrolysis.

Analytical stress and displacement of twin noncircular tunnels in elastic semi-infinite ground

In general, twin noncircular tunnels may cause high stress concentrations and large settlements because of the strong interaction between tunnels and their noncircular shape. In this study, new analytical solutions are presented to efficiently predict the elastic stresses and displacements around shallow twin noncircular tunnels in rocks. The key factors, i.e., the real interactions between tunnels, arbitrary tunnel shapes, arrangements and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account.The Schwartz alternating method is used to reduce the twin noncircular tunnels problem to a series of problems where only one noncircular tunnel is contained in the half-plane. Then, the solutions to the problem of a noncircular tunnel in the half-plane are obtained by complex variable theory combined with conformal mapping. Finally, convergent and highly accurate analytical solutions of twin noncircular tunnels are achieved by superposing the solutions of the reduced single tunnel problems. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. The proposed analytical solution can help to reveal the mechanical mechanisms of ground responses due to twin tunnelling in an elastic semi-infinite ground.

An Ab Initio RRKM-Based Master Equation Study for Kinetics of OH-Initiated Oxidation of 2-Methyltetrahydrofuran and Its Implications in Kinetic Modeling

Cyclic ethers (CEs) can be promising future biofuel candidates. Most CEs possess physico-chemical and combustion indicators comparable to conventional fuels, making them suitable for internal combustion engines. This work computationally investigates the kinetic behaviors of hydrogen abstraction from 2-methyl tetrahydrofuran (2MTHF), one of the promising CEs, by hydroxyl radicals under combustion and atmospheric relevant conditions. The various reaction pathways were explored using the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory. The Rice–Ramsperger–Kassel–Marcus-based master equation (RRKM-ME) rate model, including treatments for hindered internal rotation and tunneling, was employed to describe time-dependent species profiles and pressure and temperature-dependent rate coefficients. Our kinetic model revealed that the H-abstraction proceeds via an addition-elimination mechanism forming reaction complexes at both the entrance and exit channels. Eight different reaction channels yielding five radical products were located. The reaction exhibited complex kinetics yielding a U-shaped Arrhenius behavior. An unusual occurrence of negative temperature dependence was observed at low temperatures, owing to the negative barrier height for the hydrogen abstraction reaction from the C-H bond at the vicinity of the O-atom. A shift in the reaction mechanism was observed with the dominance of the abstraction at Cα-H of 2MTHF ring (causing negative-T dependence) and at CH3 (positive-T dependence) at low and high temperatures, respectively. Interestingly, the pressure effect was observed at low temperatures, revealing the kinetic significance of the pre-reaction complex. Under atmospheric pressure, our theoretical rate coefficients showed excellent agreement with the available literature data. Our model nicely captured the negative temperature-dependent behaviors at low temperatures. Our predicted global rate coefficients can be expressed as k (T, 760 Torr) = 3.55 × 101 × T−4.72 × exp [−340.0 K/T] + 8.21 × 10−23 × T3.49 × exp [918.8 K/T] (cm3/molecule/s). Our work provides a detailed kinetic picture of the OH-initiated oxidation kinetics of 2MTHF. Hence, this information is useful for building a kinetic me chanism for methylated cyclic ethers.

Infrared Spectra of the Water-CO2 Complex in the 4.3-3.6 μm Region and Determination of the Ground State Tunneling Splitting for HDO-CO2.

Spectra of water─CO2 dimers are studied using a tunable mid-infrared source to probe a pulsed slit jet supersonic expansion. H2O-CO2 and D2O-CO2 are observed in the CO2 ν3 fundamental region (≈2350 cm-1), D2O-CO2 is also observed in the D2O ν3 fundamental region (≈2790 cm-1), and HDO-CO2 is observed in the HDO O-D stretch fundamental region (≈2720 cm-1), all for the first time in these regions. Analysis of the spectra yields excited state rotational parameters and vibrational shifts. They also yield the first experimental values of the ground state internal rotation tunneling splittings for D2O-CO2 (0.003 cm-1) and HDO-CO2 (0.0234 cm-1). The latter value is a direct determination made possible by the reduced symmetry of HDO-CO2. These results provide stringent and easily interpreted tests for theoretical water-CO2 potential energy surface calculations.

Nanomechanical damping via electron-assisted relaxation of two-level systems

We report on measurements of dissipation and frequency noise at millikelvin temperatures of nanomechanical devices covered with aluminum. A clear excess damping is observed after switching the metallic layer from superconducting to the normal state with a magnetic field. Beyond the standard model of internal tunneling systems coupled to the phonon bath, here we consider the relaxation to the conduction electrons together with the nature of the mechanical dispersion laws for stressed/unstressed devices. With these key ingredients, a model describing the relaxation of two-level systems inside the structure due to interactions with electrons and phonons with well-separated timescales captures the data. In addition, we measure an excess $1/f$-type frequency noise in the normal state, which further emphasizes the impact of conduction electrons.

In silico анализ особенностей пространственной организации молекул целлюлаз из различных продуцентов

The spatial structure of the enzyme largely determines the mechanism of its functioning. In particular, changes in the number, structure, and localization of internal cavities, tunnels, and pores in an enzyme molecule can change its thermal stability, the mechanism of substrate diffusion to the active site, and the features of interaction with the microenvironment. The composition, localization, and structure of internal cavities, tunnels, and pores in Thermotoga maritima cellulases associated with various ligands and having amino acid substitutions have been studied. The parameters of pores, tunnels, and cavities were calculated using the Mole software. An assumption was put forward about the effect of these modifications on the change in the structure of the enzymes presented in the work. The data analyzed in this work are of significant value for understanding the processes of conformational rearrangements in the molecules of cellulases from Thermotoga maritima when they are bound to various ligands and in the presence of point mutations, which can be useful in designing industrial catalysts based on these proteins and studying their physiological role within the producer organism.

Weave technologies and impact performance of varied shaped cellular textile composites

Cellular structural composites have been widely used in aerospace, radar satellite, rocket missile, automobile, ship, rail transit, construction, and packaging engineering etc. Textile reinforced composite is a niche market of the composites family with its advantages of light weight and good mechanical properties. In this article, textile reinforced cellular composites are fabricated and tested under low velocity impact to investigate their energy absorption performances by experimental method. Cellular structure fabric with internal tunnels of triangle, hexagon, trapezoid, and mixed shapes are weaved and consolidated by epoxy resin. The cellular structure composites are impacted under low velocity impact and it is verified that the four types of composites are show different impact performances. The triangle cell composite is sensitive to the out-coming penetration, while the trapezoid cell material is flexible to deform to absorb the energy. The other two structure cell composites are easily damaged by the output impact. The outcomes of this research study provide experimental results for the future investigation of similar composite materials.

Design of deep rock tunnels using hyperstatic reaction and convergence confinement methods

Tunnel lining is usually installed with delay behind the tunnel face excavation, which requires that a displacement is considered at the tunnel boundary before the support structure installation. This delayed installation comes with a release and redistribution of stress in the rock mass. Internal tunnel lining forces significantly rely on the stress relaxation process taking place in the rock mass surrounding the excavated tunnel. One of the difficulties when designing tunnel supports is, therefore, to analyse the rock–support interaction considering the tunnel lining convergence caused by the stress redistribution. Here, a simple and effective calculation process based on the combination of two methods, the hyperstatic reaction method (HRM) and convergence confinement method, is presented to analyse the interaction of rock mass and support structure. The rock mass is assumed to obey the Hoek–Brown criterion. The stress release is also taken into consideration. The present method is validated by comparing results of the HRM in terms of tunnel lining forces against the analytical ones. Thereafter, the effect of the stress release coefficient, the tunnel depth and the Hoek–Brown criterion parameters (the geological strength index and σci) on the lining internal forces are presented and discussed.

Evacuation speed of human beings in road tunnels at different altitudes

There is an increasing number of road tunnels constructed in high-altitude areas of China. Generally, a tunnel is long and narrow. Therefore, when a fire breaks out in a tunnel, it is difficult to get rid of the smoke and the heat, which poses a threat to stranded people. The walking speed of people is the critical factor determining the evacuation time, particularly in high-altitude areas where the ambient pressure is low. In this study, a series of field tests were conducted by considering the environmental parameters to explore the effects of altitude on the people’s walking speed, and the considered parameters include the blood oxygen saturation of people, their heart rate and its variability parameters, ratings of perceived exertion, and walking speed. The results show that ambient pressure, which is about 97 kPa at an altitude of 500 m, decreases to approximately 64 kPa at an altitude of around 3850 m. In other words, the ambient pressure decreases with the increase in the altitude, and the difference in illumination between the internal tunnel and open environment is obvious. More specifically, several factors, including gender, age, tunnel environment, and altitude influence the walking speed, and corresponding reduction coefficients are introduced to reflect the influence of the factors on the walking speed. Finally, based on the field data, a reliable formula is proposed to predict the walking speed at different altitudes.

Conductive, Strong and Tough Reduced Graphene Oxide-based composite film for infrared camouflage application

For graphene-based film, versatility is essential for its potential multi-functional applications. In order to obtain graphene-based films with superior mechanical and electrical properties, a “brick and mortar” structure has been proposed by previous researchers. In this structure, the graphene or reduced graphene oxide (rGO) layers are the “bricks”, while the “mortar” is various, which is critical to the performance of the films. In this work, the mixture of carbon nanotube (CNT)/polyurethane (PU) was introduced as the mortar to bind rGO layers, forming a dense layered film. The PU builds strong interactions between rGO layers through covalent bonds, while the CNTs help to highly reduce the inter-layer electrical resistance. Hence, the CNT/PU/rGO film shows an optimized tensile strength of 1193 MPa and an electrical conductivity of 687 S cm−1. More remarkably, the PU has good compatibility with ionic liquid (IL), and can build internal transport tunnels for IL in the films. IL was further introduced into the composite film. By applying voltage upon the two sides of the film, ion transport across the two sides of the film can be fast and precisely guided. The interaction between IL and the nano-carbon assemblies can tune the infrared emissivity of the composite film, which “function” proposes the film for potential application as a flexible infrared camouflage device. The performance of the infrared camouflage film is investigated in this work.

Kuramoto synchronization of quantum tunneling polarons for describing the dynamic structure in cuprate superconductors

A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by Extended X-ray Absorption Fine Structure experiments (EXAFS), anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic many-body Hamiltonian on a relevant six-atom cluster and show that the EXAFS results can be understood as a Kuramoto synchronization between coupled internal quantum tunneling polarons associated with the two-site distribution of the copper-apical-oxygen ($Cu-O_{ap}$) pair in the dynamic structure. Furthermore, we find that this first order, anti-phase synchronization transition can be fine tuned by temperature and anharmonicity of the lattice vibrations, and promotes the pumping of charge, initially stored at the apical oxygen reservoirs, into the copper-oxide planes. Simultaneously, the internal quantum tunneling polaron extends to the copper-planar-oxygen ($Cu-O_{pl}$) pair. All these findings support an interpretation of the EXAFS data in terms of an effective, quantum mechanical triple-well-potential, which accurately represents the anti-phase synchronization of apical oxygens displacements and lattice-assisted charge transfer to the $CuO_2$ plane.

Application of a technique for reducing supersonic starting loads on internal wind tunnel balances

Higher than anticipated supersonic starting loads in the VTI T-38 wind tunnel were a consequence of higher than designed minimum start pressures. Initially, high starting loads limited the usefulness of the facility at high supersonic Mach numbers. Over time, it was established that several procedures and techniques had to be used cooperatively to diminish the problem. One of the techniques is the establishment of additional points of contact of the model and the support sting for the duration of the starting loads, so that a part of the aerodynamic loads is transferred to the sting through the added path, relieving the sensitive force balance. Some applications of this technique require dedicated mechanisms to operate, which was impractical for the VTI T-38 wind tunnel. To the contrary, the implementation of the idea in the VTI T-38 wind tunnel relies on using suitable inserts to make the clearance between the model and the sting such that model-sting contact is forced to occur during the start and stop phenomena, but not during the measurement phase of the test. For typical model configurations, transient starting and stopping loads can be reduced by more than 50%.

Study on oxygen concentration distribution of Sejila mount tunnel construction based on fluent

Sichuan-Tibet Railway is a major construction project to ensure national defense security and support social and economic development in the west. Due to the geographical environment at high altitudes in the Sichuan-Tibet region, for every 1000 m increase in the average altitude, the atmospheric pressure decreases by about 11.55 %, and the oxygen partial pressure decreases accordingly, forming a low-pressure and low-oxygen environment, which affects the construction safety. The oxygen consumption of mechanical equipment in the tunnel and the discharge of pollutants make the construction personnel’s hypoxia problem more serious. Based on the project of the Sejila Mountain Tunnel, this paper divides the tunnel into the working face and the construction section along the tunnel according to different construction procedures. Based on the numerical simulation by CFD software, the distribution law of oxygen concentration in the tunnel construction process before the implementation of the environmental control scheme under different factors is proposed, and the relationship between various influencing factors and oxygen concentration distribution is obtained. It is concluded that oxygen consumption and emission of internal combustion engines and tunnel excavation length are important factors affecting oxygen concentration in the tunnel construction environment.

Comprehensive Test and Evaluation Analysis of Permeable Concrete (PC) Clogging by Using Steel Slag

In recent decade, researchers have more attention to water resource protection and forward the concept of sponge city construction. PC is becoming more and more popular as a rainwater management tool because of fast climate changes worldwide. In this experiment, PC specimens were prepared with steel slag as aggregate, and the targeted porosity of specimens was 15%, 20%, and 25% respectively, and the ratio of water to cement was 0.38, 0.4, and 0.42. The PC specimens under the 200 mm high head are the most severely blocked; 0.283 m/s high‐speed horizontal runoff appears after the rapid plugging stage later in the other two types of speed tests. With time, the plugging effect of the test specimen is almost the same; the clogging degree of the PC sample with the porosity of 25% is more obvious than that of other porosity test specimens. The PC with large porosity is more serious to clogging because the higher seepage velocity will enter the internal tunnel with higher penetration force, which increases the possibility of clogging. Tests have shown that, at different rainwater runoff head heights, the PC specimens under the 200 mm high head are the most severely blocked; 0.283 m/s high‐speed horizontal runoff appears after the rapid plugging stage later in the other two types of speed tests but over time. With time, the plugging effect of the test specimen was almost the same; the clogging degree of the permeable concrete sample with the porosity of 25% is more obvious than that of other porosity test specimens. While it is noticed that the compressive strength of the PC after clogging has decreased in the freeze‐thaw environment, the destruction process is faster than the unblocked test specimen.

Ab Initio Kinetics of Initial Thermal Pyrolysis of Isopropyl Propionate: A Revisited Study.

This work reports a detailed mechanism of the initial thermal pyrolysis of isopropyl propionate, (C2H5C(=O)OCH(CH3)2), an important biodiesel additive/surrogate, for a wide range of T = 500–2000 K and P = 7.6–76 000 Torr. The detailed kinetic behaviors of the title reaction on the potential energy surface constructed at the CBS-QB3 level were investigated using the RRKM-based master equation (RRKM-ME) rate model, including hindered internal rotation (HIR) and tunneling corrections. It is revealed that the C3H6 elimination occurring via a six-centered retro-ene transition state is dominant at low temperatures, while the homolytic fission of the C–C bonds becomes more competitive at higher temperatures. The tunneling treatment is found to slightly increase the rate constant at low temperatures (e.g., ∼1.59 times at 563 K), while the HIR treatment, being important at high temperatures, decreases the rate (e.g., by 5.9 times at 2000 K). Showing a good agreement with experiments in low-temperature kinetics, the kinetic model reveals that the pressure effect should be taken into account at high temperatures. Finally, the temperature- and pressure-dependent kinetic mechanism, consisting of the calculated thermodynamic and kinetic data, is provided for further modeling and simulation of any related systems.

Evolution of Charge-Lattice Dynamics across the Kuramoto Synchronization Phase Diagram of Quantum Tunneling Polarons in Cuprate Superconductors

Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to hole-doped cuprate superconductors, EXAFS has revealed the presence of internal quantum tunneling polarons (IQTPs). An IQTP arises in EXAFS as a two-site distribution for certain Cu–O pairs, which is also duplicated in inelastic scattering but not observed in standard diffraction measurements. The Cu–Sr pair distribution has been found to be highly anharmonic and strongly correlated to both the IQTPs and to superconductivity, as, for example, in YSr2Cu2.75Mo0.25O7.54(Tc=84 K). In order to describe such nontrivial, anharmonic charge-lattice dynamics, we have proposed a model Hamiltonian for a prototype six-atom cluster, in which two Cu-apical-O IQTPs are charge-transfer bridged through Cu atoms by an O atom in the CuO2 plane and are anharmonically coupled via a Sr atom. By applying an exact diagonalization procedure to this cluster, we have verified that our model indeed produces an intricate interplay between charge and lattice dynamics. Then, by using the Kuramoto model for the synchronization of coupled quantum oscillators, we have found a first-order phase transition for the IQTPs into a synchronized, phase-locked phase. Most importantly, we have shown that this transition results specifically from the anharmonicity. Finally, we have provided a phase diagram showing the onset of the phase-locking of IQTPs as a function of the charge-lattice and anharmonic couplings in our model. We have found that the charge, initially confined to the apical oxygens, is partially pumped into the CuO2 plane in the synchronized phase, which suggests a possible connection between the synchronized dynamic structure and high-temperature superconductivity (HTSC) in doped cuprates.

Analytical solutions of noncircular tunnels in viscoelastic semi-infinite ground subjected to surcharge loadings

The construction of noncircular tunnels at shallow depths has become increasingly common in urban areas to efficiently utilize underground space. In general, noncircular tunnels may cause high stress concentrations and large settlements. In addition, the stability of shallow tunnels affected by the structural loads/surcharge loads on the surface is too significant to ignore. This study presents new analytical solutions to efficiently predict the stresses and displacements around shallow noncircular tunnels in rheological rock. The key factors, i.e., any viscoelastic characteristics of the surrounding rock, arbitrarily distributed loads exerted on the ground surface, arbitrary tunnel shapes and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account. A noncircular tunnel in the half-plane was mapped into an anulus by employing the conformal mapping function. Then, the elastic solutions of the problem are obtained by complex variable theory combined with the mapping function. Based on the elastic solutions and the extended corresponding principle for the viscoelastic problem, time-dependent analytical solutions are obtained for the ground assuming any viscoelastic models. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. Then, a parametric study is finally performed to investigate the influence of the location or range of the surcharge, tunnel burial depth and lateral pressure coefficient on the ground stresses and displacements. The proposed analytical solution can provide insight into the mechanical behavior of shallow noncircular tunnels under surcharge loads, as well as an alternative method in the preliminary designs of future shallow tunnels.

A method to estimate the damage of Diabrotica speciosa larvae on potato tubers

ABSTRACT The marketable value of potato tubers is affected by damage caused by Diabrotica speciosa, whose larvae create holes on the tubers’ skin and internal feeding tunnels. The estimation of potato tuber damage is usually performed by assessing the external damage to the detriment of feeding tunnels caused by larvae. Thus, we propose a method to estimate the damage caused by D. speciosa larvae, considering the external and internal aspects of the tubers separately. For that, potato plants cv. Agata were grown under different infestations of larvae, measuring the area occupied by the holes and the volume of internal feeding tunnels, relating these data to the total area and volume of the tuber. The methodology used allowed us to characterize an increase in damage in tubers with the highest infestation of larvae. The correlation between internal and external damage caused by D. speciosa larvae was not significant, indicating that external damage alone is not an adequate parameter for the diagnosis of overall tuber quality. However, the method proposed here provides information regarding the volume of pulp consumed by the larvae, the extent of the galleries formed, and the relative volume of damage concerning the total tuber. Moreover, the method proposed here contemplates a more precise analysis of the external area damaged by herbivory relative to the total area of the tuber, which is not commonly considered in studies of underground plant structures.

Structures of guaiacol and the guaiacol-argon van der waals complex from rotational spectroscopy of guaiacol isotopologues

High-resolution rotational spectra were recorded for guaiacol and eight isotopologues as well as the guaiacol-argon van der Waals complex using a resonant-cavity Fourier transform microwave spectrometer. The monomer spectra were assigned to an anti-syn conformation with an internal hydrogen bond from the hydroxyl group to the methoxy oxygen. Atomic coordinates of the carbon and hydroxyl hydrogen atoms were determined from the experimental moments of inertia using the Kraitchman method, and these coordinates are in excellent agreement with the corresponding coordinates in the MP2/6-311++G(d,p) model structure. The recorded rotational transitions showed no evidence for methyl internal rotation tunneling, and a potential energy scan (ωB97XD/6-311++G(d,p)) identified a 1006.0 cm−1 barrier to methyl internal rotation. The rotational spectrum of guaiacol-argon was used determine the location of the argon with respect to the anti-syn monomer conformation: RCM = 3.533 Å, θ = 105.4 °, and χ = -100.0 °. The argon is positioned towards the hydroxyl and methoxy groups because of relatively strong van der Waals interactions between argon and the oxygen atoms.

Probing the transport of Ni(II) ions through the internal tunnels of the Helicobacter pylori UreDFG multimeric protein complex

The survival of several pathogenic bacteria, such as Helicobacter pylori (Hp), relies on the activity of the nickel-dependent enzyme urease. Nickel insertion into urease is mediated by a multimeric chaperone complex (HpUreDFG) that is responsible for the transport of Ni(II) from a conserved metal binding motif located in the UreG dimer (CPH motif) to the catalytic site of the enzyme. The X-ray structure of HpUreDFG revealed the presence of water-filled tunnels that were proposed as a route for Ni(II) translocation. Here, we probe the transport of Ni(II) through the internal tunnels of HpUreDFG, from the CPH motif to the external surface of the complex, using microsecond-long enhanced molecular dynamics simulations. The results suggest a “bucket-brigade” mechanism whereby Ni(II) can be transported through a series of stations found along these internal pathways.