Importance Of Tunneling Research Articles

Temperature Distribution Curve Analysis on Concrete through LS-DYNA

The development and importance of tunnels are increasing worldwide, and countries like Korea, where about 70% of the total land is covered with mountain regions, need more tunnel constructions to connect different routes of roads for safe and efficient transport. This study applied fire to the 200 mm × 200 mm × 200 mm concrete specimens, similar to the Rijkswaterstaat (RWS) fire, through an electric furnace. Thermocouples were placed inside the specimens to analyze the temperature during the occurrence of fire. Experimental and simulation thermal analysis during the occurrence of fire was analyzed. The experimental temperature at different depths agreed with the simulation results. Different international fire curves were applied to study the temperature inside the concrete through simulation by LS-DYNA. Concrete with different thicknesses of fireproof board was analyzed through simulation, and using fireproof board reduces the inside temperature during fire occurrence. Among the studied international fire curves, modified hydrocarbon fire curves had a high-temperature effect on concrete.

3D Monitoring & its Significance in Tunneling: Special Emphasis on Tunnel T-74R of USBRL Project, India

Nowadays, Tunnels are the major transportation network throughout the world. The importance of tunnel and its associated system also increases as the demand of Tunnel construction increases day by day. It has its significant importance in water conveyance networks as well as communication networks. As it is spreading fast over the world, the assessments of deformations are becoming an important part of tunneling system. The paper deals with the 3D monitoring system for the safety perspective and to make proper judgement about the condition of tunnels related to the information obtained in the measuring equipments. It also enables to react under various rock setting with the precise and reliable monitoring results. As we observed in the T-74R tunnel, where deformation of the tunnel’s support system is a natural occurrence, the T-74R’s main support system was also affected. The groundmass is prone to deformation due to its poor state and proximity to the principal thrust. The finding of the T-74R tunnel utilising 3D monitoring devices is important. They have provided the information about actual ground behaviour conditions.

Thermal Decomposition of CH3O: A Curious Case of Pressure-Dependent Tunneling Effects.

The thermal unimolecular decomposition of a methoxy radical (CH3O), a key intermediate in the combustion of methane, methanol, and other hydrocarbons, was studied using high-level coupled-cluster calculations, followed by E,J-resolved master equation analyses. The experimental results available for a wide range of temperature and pressure are in striking agreement with the calculations. In line with a previous theoretical study that used a one-dimensional master equation, the tunneling correction is found to exhibit a marked pressure dependence, being the largest at low pressure. This curious effect on the tunneling enhancement also affects the calculated kinetic isotope effect, which falls initially with pressure but is predicted to rise again at high pressures. These findings serve to reconcile a set of conflicting results regarding the importance of tunneling in this prototype unimolecular reaction and also motivate further experimental investigation. This study also exemplifies how changes in the energy redistribution due to collisions manifest in the tunneling rates.

A theoretical study on the dynamics of gas-phase reaction of methyl cation with atomic oxygen

The dynamics and kinetics of the reaction of CH3+ cation with atomic oxygen in its lowest triplet and singlet states in the presence of N2 molecules as the bath gas is theoretically investigated. The potential energies over both surfaces at the CCSD(T)/aug-cc-pVTZ level of theory are explored. Both singlet and triplet surfaces characterize by barrierless initiation step. The entrance channel to form the energized adducts are governed by the capture probability once the centrifugal barrier is surmounted. Multiwell-multichannel mechanisms are found for both singlet and triplet potential energy surfaces. One-dimensional chemical master equation is solved to explore the dynamics and kinetics of the title reaction. The fractional populations of the stationary points as function of time are analyzed to determine the role of the energized intermediates on the dynamics of the title reaction. No significant temperature or pressure dependence for the title reaction was observed over a wide range of temperature (300–3000 K) and pressure (0.1–4.5 atm). The results indicate cis and trans-HCOH+, CH2O+, and H atom are the major products for both surfaces. CVT method was used to explore the importance of tunneling in hydrogen transfer isomerization reactions of CH2O+ to trans-HCOH+ and HOC+ to HCO+ using small-curvature approximation.

Unimolecular Decay of the Dimethyl-Substituted Criegee Intermediate in Alkene Ozonolysis: Decay Time Scales and the Importance of Tunneling.

We used the steady-state master equation to model unimolecular decay of the Criegee intermediate formed from ozonolysis of 2,3-dimethyl-2-butene (tetramethylethylene, TME). Our results show the relative importance and time scales for both the prompt and thermal unimolecular decay of the dimethyl-substituted Criegee intermediate, (CH3)2COO. Calculated reactive fluxes show the importance of quantum mechanical tunneling for both prompt and thermal decay to OH radical products. We constrained the initial energy distribution of chemically activated (CH3)2COO formed in TME ozonolysis by combining microcanonical rates k(E) measured experimentally under collision-free conditions and modeled using semiclassical transition-state theory (SCTST) with pressure-dependent yields of stabilized Criegee intermediates measured with scavengers in flow-tube experiments. Thermal decay rates under atmospheric conditions k(298 K, 1 atm) increase by more than 1 order of magnitude when tunneling is included. Accounting for tunneling has important consequences for interpreting pressure dependent yields of stabilized Criegee intermediates, particularly with regard to the fraction of Criegee intermediates formed in the zero-pressure limit.

Importance of tunneling in H-abstraction reactions by OH radicals

We present a combined experimental and theoretical study focussing on the quantum tunneling of atoms in the reaction between CH4 and OH. The importance of this reaction pathway is derived by investigating isotope substituted analogs. Quantitative reaction rates needed for astrochemical models at low temperature are currently unavailable both in the solid state and in the gas phase. Here, we study tunneling effects upon hydrogen abstraction in CH4 + OH by focusing on two reactions: CH4 + OD -> CH3 + HDO and CD4 + OH -> CD3 + HDO. The experimental study shows that the solid-state reaction rate R(CH4 + OD) is higher than R(CD4 + OH) at 15 K. Experimental results are accompanied by calculations of the corresponding unimolecular and bimolecular reaction rate constants using instanton theory taking into account surface effects. From the work presented here, the unimolecular reactions are particularly interesting as these provide insight into reactions following a Langmuir-Hinshelwood process. The resulting ratio of the rate constants shows that the H abstraction (k(CH4 + OD)) is approximately ten times faster than D-abstraction (k(CD4 + OH)) at 65 K. We conclude that tunneling is involved at low temperatures in the abstraction reactions studied here. The unimolecular rate constants can be used by the modeling community as a first approach to describe OH-mediated abstraction reactions in the solid phase. For this reason we provide fits of our calculated rate constants that allow the inclusion of these reactions in models in a straightforward fashion.

Communication: ab initio simulations of hydrogen-bonded ferroelectrics: collective tunneling and the origin of geometrical isotope effects.

Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains - facilitated by quantum mechanical tunneling - is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.

직광에 의한 눈부심 현상이 터널 출구부 안전성에 미치는 영향 연구

PURPOSES : In Korea, over 70 percent of the land consists of mountainous and rolling area. Thus, tunnels continue its upward trend as road network are extended. In these circumstances, the importance of tunnel has been increased nowadays and then its safety investigation and research should be performed. This study is focus on confirming and improving the safety of tunnel. On tunnel hood, sunglare effect can irritate driver`s behavior instantly and this can result in incident. METHODS : The study of this phenomenon is rarely conducted in domestic and foreign papers, so there is no proper measure for this. This study analyzes the driving environment of the effect of sunglare effect on tunnel hood. RESULTS : Traffic accidents stem from complex set of factors. This study build the Traffic Accident Prediction Models to find out the effect of sunglare effect on tunnel`s hood. The independent variables are traffic volume, geometric design of road, length of tunnel and road side environment. Using these variables, this model estimates accident frequency on tunnel hood by Poisson regression model and Negative binomial regression model. Although Poisson regression model have more proper goodness of fit than Negative binomial regression model, Poisson regression model has overdipersion problem. So the Negative binomial regression model is used in this analysis. CONCLUSIONS : Consequently, the model shows that sunglare effect can play a role in driving safety on tunnel hood. As a result, the information of sunglare effect should be noticed ahead of tunnel hood so this can prevent drivers from being in hazard situation.

Tunnelling in the O + CO reaction

The importance of tunnelling in the formation of CO2 from O( 3 P) + CO at very low temperatures is studied with harmonic quantum transition state theory. To optimize the quantum transition state, we have used both fitted potential energy surfaces and direct dynamics, where forces and energies are calculated by a quantum chemistry code on the fly as they are needed. Whilst tunnelling does increase the classical reaction rate for the O( 3 P) + CO addition reaction at very low temperatures, the onset of tunnelling is at too low temperatures for the reaction to significantly contribute to the formation of interstellar CO2. Instead, it is more likely that an oxygen atom impinging on an interstellar ice would form a loosely bound complex with adsorbed CO, which may subsequently react with a hydrogen atom to ultimately yield CO2.

Ionization of the hydrogen atom by short half-cycle pulses: dependence on the pulse duration

A theoretical study of the ionization of hydrogen atoms by short external half-cycle pulses (HCPs) as a function of the pulse duration, using different quantum and classical approaches, is presented. Total ionization probability and energy distributions of ejected electrons are calculated in the framework of the singly-distorted Coulomb-Volkov (SDCV) and the doubly-distorted Coulomb-Volkov (DDCV) approximations. We also performed quasiclassical calculations based on a classical trajectory Monte Carlo method which includes the possibility of tunneling (CTMC-T). Quantum and classical results are compared to the numerical solution of the time-dependent Schrodinger equation (TDSE). We find that for high momentum transfers the DDCV shows an improvement compared to the SDCV, especially in the low-energy region of the electron emission spectra, where SDCV fails. In addition, DDCV reproduces successfully the TDSE electron energy distributions at weak momentum transfers. CTMC-T results reveal the importance of tunneling in the ionization process for relative long pulses and strong momentum transfers but fails to overcome the well-known classical suppression observed for weak electric fields.

The importance of tunneling in the first hydrogenation step in ammonia synthesis over a Ru(0001) surface

The hydrogenation of nitrogen (N(ads)+H(ads)-->NH(ads)) on metal surfaces is an important step in ammonia catalysis. We investigate the reaction dynamics of this hydrogenation step by time independent scattering theory and variational transition state theory (VTST) including tunneling corrections. The potential energy surface is derived by hybrid density functional theory on a model cluster composed of 12 ruthenium atoms resembling a Ru(0001) surface. The scattering calculations are performed on a reduced dimensionality potential energy hypersurface, where two dimensions are treated explicitly and all others are included implicitly by the zero-point correction. The VTST calculations include quantum effects along the reaction coordinate by applying the small curvature tunneling scheme. Even at room temperature (where ruthenium already shows catalytic activity) we find rate enhancement by tunneling by a factor of approximately 70. Inspection of the reaction probabilities shows that the major contribution to reactivity comes from the vibrational ground state of the reactants into vibrationally excited product states. The reaction rates are higher than determined in previous studies, and are compatible with experimental overall rates for ammonia synthesis.

Unraveling the dissociation of dimethyl sulfoxide following absorption at 193 nm

We have studied the photodissociation of dimethyl sulfoxide, DMSO-h6 and DMSO-d6, at 193 nm using the technique of photofragment translational spectroscopy with a tunable vacuum ultraviolet product probe provided by undulator radiation on the Chemical Dynamics Beamline at the Advanced Light Source. In contrast to previous investigations we have found the dissociation to proceed via a stepwise mechanism involving multiple reaction channels. The primary dissociation, S–C bond cleavage to eliminate a methyl radical, was found to have two competing channels with distinct translational energy distributions. The translational energy distribution for the major primary dissociation channel suggests that it proceeds in a statistical manner on the ground electronic surface following internal conversion. In competition with this channel is a primary dissociation that exhibits a translational energy distribution suggestive of dissociation on an excited electronic surface with most of the available energy partitioned into translational and electronic degrees of freedom. Secondary decomposition of the CD3SO intermediate was found to proceed exclusively via C–S bond cleavage, CD3SO→CD3+SO. However, secondary decomposition of the CH3SO intermediate was found to exhibit competition between CH3SO→CH3+SO and CH3SO→CH2SO+H. The dissociation to CH3 and SO was the major secondary decomposition channel with the translational energy distribution indicating a barrier to recombination of >8 kcal/mol. While a minor hydrogen atom elimination channel was found to play a role in secondary decomposition of CH3SO intermediates, no analogous secondary C–D bond cleavage was detected from the CD3SO intermediates indicating the importance of tunneling in the secondary decomposition of CH3SO.

Degeneracy in one dimension: Role of singular potentials

That the bound energy eigenstates of one-dimensional quantum systems can be degenerate in the presence of specific singular or supersingular potentials is demonstrated by choosing a family of bistable and other oscillators. Relevance of our study to spectroscopic observations is noted. Quasi-degeneracy is found even in the absence of any singularity in the potential and the importance of tunneling is highlighted in this context to analyze the general nature of such potentials leading to double degeneracy. Additionally, the case of spiked oscillators is discussed with particular reference to the “Klauder phenomenon,” revealing clearly that the mere presence of singularity in the potential is not a sufficient criterion for the occurrence of degeneracy. © 1996 John Wiley & Sons, Inc.

Kinetic isotope effects and tunneling in CH bond activation of ethylene and ethylidyne on Pt(111)

The importance of tunneling in the dehydrogenation of ethylene on Pt(111) was assessed with temperature programmed reaction spectroscopy. Rate constants for hydrogen (deuterium) evolution during the formation and decomposition of ethylidyne were quantified, and the kinetic isotope effects measured. At low ethylene coverage hydrogen is evolved in a desorption-limited step near 340 K. At higher coverage a first-order process gives rise to ethylidyne formation near 300 K with rate constants of 3 × 10 16 exp(− 22.4(kcal/mol)/ RT) s −1 and 2 × 10 16 exp(−23.0(kcal/mol)/ RT) s −1 for C 2H 4 and C 2D 4, respectively, yielding a normal kinetic isotope effect of 4.0 at 300 K. The rate constants for rate-limiting C-H(D) bond activation in CCH 3 and CCD 3 are 2.9 × 10 16 exp(−37.3(kcal/mol)/ RT) s −1 and 1 × 10 16 exp(−37.8(kcal/mol)/ RT) s −1, respectively, giving a kinetic isotope effect of 3.1 at 300 K. All of the criteria normally applied to judge the importance of tunneling indicate that tunneling is unimportant for these reactions.

Reactions of trapped electrons in methanol-isopropanol glasses irradiated at 77 K

Trapped electron (eT−) reactivity in methanol-isopropanol glasses irradiated at 77 K has been studied as a function of trap-depth, the variation in the trap depth being achieved by varying the methanol:isopropanol ratio. Benzyl chloride and carbon disulfide have been used as scavengers. In the case of the glasses containing benzyl chloride, the observed yield of the benzyl radical has been correlated with the trapping efficiency of the matrix. The data has been interpreted with the aim of assessing the relative importance of tunnelling in the scavenging of electrons in low temperature glassy matrices.

Influence of steric hindrance in molecules of substituted 2-phenyl-1,1,3,3-tetramethylguanidines on the kinetics and isotope effects of their proton transfer reactions with 4-nitrophenylnitromethane in acetonitrile solvent

Rate constants have been determined for the proton and deuteron transfer reactions of 4-nitrophenylnitromethane, NO2C6H4CH2NO2, with three phenyl substituted derivatives of 2-phenyl-1,1,3,3-tetramethylguanidine, X—C6H4—N=C[N(CH3)2]2, where X = 4-Cl, 2-Cl, and 2-Br, in the temperature range 278–308 K in acetonitrile solvent. In the concentration ranges used, the reaction to form an ion-paired product is first order in acid and first order in base. The reaction was followed spectrophotometrically using the stopped-flow technique. The reaction is fastest for the 4-Cl substituted base and slowest for the 2-Br analogue. The observed deuterium kinetic isotope effects show a clear dependence on the position and the size of the substituent in the base molecule. Kinetic isotope effects at 25 °C, kH/kD = 9.7 ± 0.3, 12.5 ± 0.3, and 15.6 ± 0.3, were observed for 4-Cl, 2-Cl, and 2-Br substituted bases respectively. The appropriate ratios of Arrhenius preexponential factors, AH/AD = 0.98 ± 0.10, 0.87 ± 0.10, and 0.77 ± 0.10, may indicate increasing importance of tunnelling of the proton when the substituent is moved from the para to the ortho position or when the size of ortho substituent increases. Values of tunnelling correction factors were calculated using Bell's equation by means of the Caldor and Saunders method.

Quantum tunnelling of vacancies in light metals

The usefulness of the WKB method is illustrated by calculating characteristic tunnelling rates in several elemental solids and establishing the temperatures at which the tunnelling becomes of comparable importance to the thermally activated processes. In this way we have verified the importance of tunnelling which dominates the low-temperature region, while it becomes negligible above a temperature value depending on the mass and the barrier thickness. In studying vacancy migration in lithium metal we have considered various pathways in the configuration space of Li atoms. A (1, 1, 1)-jump of the vacancy, accompanied by the simultaneous outward movement of between 4 to 12 lithium atoms, is shown to be most efficient. In this model the lithium motion achieves a 104-fold increase in the jump probability and a reduction of the activation energy from ∼0.25 to ∼0.16 eV.

The importance of tunnelling in chemical reactions of muonium

The importance of tunnelling in chemical reactions of muonium

Model Computations on Transition States in the Proton Abstraction from Carbon Acids. Influence of Coupling of Atomic Motions on the Importance of Tunnelling and on the Reduced Mass Along the Reaction Co-ordinate.

Model Computations on Transition States in the Proton Abstraction from Carbon Acids. Influence of Coupling of Atomic Motions on the Importance of Tunnelling and on the Reduced Mass Along the Reaction Co-ordinate.

Kinetic isotope effects in some reactions of tri-(4-nitrophenyl)-methane with alkoxide bases in various alcoholic media

Rate constants and Arrhenius parameters have been determined for proton-transfer and deuteron-transfer reactions of tri-(4-nitrophenylmethane) with alkoxide ions in alcohol + toluene mixtures. The kinetic isotope effects (kH/kD) at 25°C are considerable (8.4 in ethanol + toluene, 8.9 in propan-2-ol + toluene, 23 in t-butanol + toluene) and indicate that the rate-limiting step is a proton transfer. For the forward reactions, the results suggest that the importance of tunnelling increases with the size of the alkoxide group. For the backward reactions, the rates for proton- and deuteron-transfer are different, although they would be expected to be equal by reason of rapid exchange with the solvent; this suggests that in the product the proton remains firmly bonded to the carbanion.