Tunneling Motion Research Articles

Gate-controlled valley transport and Goos–Hänchen effect in monolayer WS2

Based on a Dirac-like Hamiltonian and coherent scattering formalism, we study the spin-valley transport and Goos–Hänchen-like (GHL) effect of transmitted and reflected electrons in a gated monolayer WS2. Our results show that the lateral shift of spin-polarized electrons is strongly dependent on the width of the gated region and can be positive or negative in both Klein tunneling and classical motion regimes. The absolute values of the lateral displacements at resonance positions can be considerably enhanced when the incident angle of electrons is close to the critical angle. In contrast to the time reversal symmetry for the transmitted electrons, the GHL shift of the reflected beams is not invariant under simultaneous interchange of spins and valleys, indicating the lack of spin-valley symmetry induced by the tunable potential barrier on the WS2 monolayer. Our findings provide evidence for electrical control of valley filtering and valley beam splitting by tuning the incident angle of electrons in nanoelectronic devices based on monolayer transition metal dichalcogenides.

Multidimensional Large Amplitude Dynamics in the Pyridine-Water Complex.

Aqueous pyridine plays an important role in a variety of catalytic processes aimed at harnessing solar energy. In this work, the pyridine-water interaction is studied by microwave spectroscopy and density functional theory calculations. Water forms a hydrogen bond to the nitrogen with the oxygen tilted slightly toward either of the ortho-hydrogens of the pyridine, and a tunneling motion involving in-plane rocking of the water interconverts the resulting equivalent structures. A pair of tunneling states with severely perturbed rotational spectra is identified and their energy separation, ΔE, is inferred from the perturbations and confirmed by direct measurement. Curiously, values of ΔE are 10404.45 and 13566.94 MHz for the H2O and D2O complexes, respectively, revealing an inverted isotope effect upon deuteration. Small splittings in some transitions suggest an additional internal motion making this complex an interesting challenge for theoretical treatments of large amplitude motion. The results underscore the significant effect of the ortho-hydrogens on the intermolecular interaction of pyridine.

A butterfly motion of formic acid and cyclobutanone in the 1 : 1 hydrogen bonded molecular cluster.

Upon supersonic expansion, formic acid and cyclobutanone (CBU) form a molecular cluster in which the two constituent molecules, linked by OHO and CHO hydrogen bonds, undergo a rapid interconversion between two equivalent forms. The tunneling motion takes place through the rupture and reformation of the C-HO hydrogen bond between the carbonyl oxygen of HCOOH and one of the two hydrogen atoms of the methylenic group adjacent to the cyclobutanone keto group. From the microwave spectra, tunneling energy splittings (ΔE01) have been determined for the parent (1122.756(3) MHz), DCOOHCBU (1084.538(1) MHz) and HCOODCBU (1180.282(4) MHz) isotopic species. From these splittings, the potential barrier to interconversion has been calculated to be B2 = 39.7(5) cm-1. The tunneling pathway is an asymmetric butterfly-like motion between the two moieties of the adduct, with a barrier at a configuration in which the ring plane of cyclobutanone is coplanar with formic acid.

Tunnelling and barrier-less motions in the 2-fluoroethanol-water complex: a rotational spectroscopic and ab initio study.

The pure rotational spectrum of the 2-fluoroethanol (2-FE)water complex was measured using a chirped pulse Fourier-transform microwave spectrometer and a cavity-based Fourier-transform microwave spectrometer. In the detected 2-FEwater conformer, 2-FE serves as a proton donor, in contrast to its role in the observed ethanolwater conformer, while water acts simultaneously as a hydrogen bond donor and acceptor, forming a hydrogen-bonded ring with an OHO and an OHF hydrogen bond. Comparison to the calculated dipole moment components suggests that the observed structure sits between the two most stable minima identified theoretically. This conclusion is supported by extensive deuterium isotopic data. Further analysis shows that these two minima are connected by a barrier-less wagging motion of the non-bonded hydrogen of the water subunit. The observed narrow splitting with a characteristic 3 : 1 intensity ratio is attributed to an exchange of the bonded and non-bonded hydrogen atoms of water. The tunneling barrier of a proposed tunneling path is calculated to be as low as 5.10 kJ mol-1. A non-covalent interaction analysis indicates that the water rotation motion along the tunneling path has a surprisingly small effect on the interaction energy between water and 2-FE.

Rotational spectroscopy of the methyl glycidate-water complex: conformation and water and methyl rotor tunnelling motions.

Methyl glycidate is a chiral epoxy ester whose structure and characteristic functional groups can be used to model biological events involving much larger chiral esters on the molecular scale. Since biological molecules function in aqueous solution, it is of interest to obtain detailed knowledge of the initial few steps of solvation using high resolution spectroscopy. In the current study, rotational spectra of methyl glycidate monohydrate were investigated by using a chirped-pulse and a cavity-based Fourier transform microwave spectrometer. Quantum theory of atoms in molecules and non-covalent interaction analyses were performed for the observed monohydrate to characterize non-covalent interactions in the system. In the observed monohydrate, methyl glycidate takes on its most stable monomeric form, while water serves as a hydrogen bond donor to the carbonyl group and as a hydrogen bond acceptor to the hydrogen atom of the CH2 group on the epoxide ring, and additionally forms a close contact to the epoxide oxygen atom. Unexpectedly, water tunnelling splittings on the order of tens to hundreds of kHz were detected. A water tunnelling path was proposed and a surprisingly low tunnelling barrier of about 2 kJ mol-1 was calculated. The proposed tunnelling path is asymmetric in the forward and backward tunnelling directions, demonstrating the complicated dynamics of water motions in the system. In addition, splittings due to the methyl internal rotation were observed and analyzed.

Femoral and tibial tunnel placement correlate with graft tunnel motion: A quantitative clinical imaging study

Femoral and tibial tunnel placement correlate with graft tunnel motion: A quantitative clinical imaging study

Is There a Difference in Graft Motion for Bone-Tendon-Bone and Hamstring Autograft ACL Reconstruction at 6 Weeks and 1 Year?

Background: Bone–patellar tendon–bone (BTB) grafts are generally believed to heal more quickly than soft tissue grafts after anterior cruciate ligament (ACL) reconstruction, but little is known about the time course of healing or motion of the grafts within the bone tunnels. Hypothesis: Graft-tunnel motion will be greater in hamstring (HS) grafts compared with BTB grafts and will be less at 1 year than at 6 weeks. Study Design: Controlled laboratory study. Methods: Twelve patients underwent anatomic single-bundle ACL reconstruction using HS or BTB autografts (6 per group) with six 0.8-mm tantalum beads embedded in each graft. Dynamic stereo x-ray images were collected at 6 weeks and 1 year during treadmill walking and stair descent and at 1 year during treadmill running. Tibiofemoral kinematics and bead positions were evaluated. Graft-tunnel motion was based on bead range of motion during the loading response phase (first 10%) of the gait cycle. Results: During treadmill walking, there was no difference in femoral tunnel or tibial tunnel motion between BTB or HS grafts at 6 weeks (BTB vs HS: 2.00 ± 1.05 vs 1.25 ± 0.67 mm [femoral tunnel]; 1.20 ± 0.63 vs 1.27 ± 0.71 mm [tibial tunnel]), or 1 year (BTB vs HS: 1.62 ± 0.76 vs 1.08 ± 0.26 mm [femoral tunnel]; 1.58 ± 0.75 vs 1.68 ± 0.53 mm [tibial tunnel]). During stair descent, there was no difference in femoral or tibial tunnel motion between BTB and HS grafts at 6 weeks or 1 year. With running, there was no difference between graft types at 1 year. For all results, P values were > .05. Knee kinematics were consistent with the literature. Conclusion: During walking and stair descent, ACL reconstruction using suspensory fixation yielded no difference between graft types in femoral or tibial tunnel motion at 6 weeks or 1 year. All subjects were asymptomatic with knee kinematics similar to that of the literature. The significance of persistent, small (1 to 3 mm) movements at 1 year for healing or graft performance is unknown. Clinical Relevance: These study results may have significant implications for graft choice, rehabilitation strategies, and timing for return to sports.

Communication: Isotopic effects on tunneling motions in the water trimer.

We present results of ring polymer molecular dynamics simulations that shed light on the effects of nuclear quantum fluctuations on tunneling motions in cyclic [H2O]3 and [D2O]3, at the representative temperature of T = 75 K. In particular, we focus attention on free energies associated with two key isomerization processes: The first one corresponds to flipping transitions of dangling OH bonds, between up and down positions with respect to the O-O-O plane of the cluster; the second involves the interchange between connecting and dangling hydrogen bond character of the H-atoms in a tagged water molecule. Zero point energy and tunneling effects lead to sensible reductions of the free energy barriers. Due to the lighter nature of the H nuclei, these modifications are more marked in [H2O]3 than in [D2O]3. Estimates of the characteristic time scales describing the flipping transitions are consistent with those predicted based on standard transition-state-approximation arguments.

Character tables of n-dimensional hyperoctahedral groups and their applications

ABSTRACTWe have shown that powerful matrix-type-based multinomial generators together with combinatorial techniques can be applied to derive the conjugacy classes, irreducible representations and the character tables of n-dimensional hyperoctahedral or hypercube groups of order n! × 2n, which are generalisations of non-rigid molecular theory formulated by Longuet-Higgins. The hyperoctahedral groups appear in the symmetry groups of non-rigid molecules, non-rigid water clusters, and other weakly bound van der Waals complexes that exhibit rapid tunnelling motion among various low-lying surmountable potential energy minima. These groups also have applications in quantum chromodynamics in the classification of states of quarks. The associated combinatorics has applications in enumerations, nuclear spin statistics and NMR spectroscopy. Finally, the groups enhance understanding of chirality in biosystems, that is, the functionality of intrinsically disordered proteins. We have derived the character tables of hyperoctahedral groups of sixth dimension, and techniques have been outlined to generalise for higher dimensions in the form of matrix generators.

Microwave measurements of the tropolone-formic acid doubly hydrogen bonded dimer.

The microwave spectrum was measured for the doubly hydrogen bonded dimer formed between tropolone and formic acid. The predicted symmetry of this dimer was C2v(M), and it was expected that the concerted proton tunneling motion would be observed. After measuring 25 a- and b-type rotational transitions, no splittings which could be associated with a concerted double proton tunneling motion were observed. The calculated barrier to the proton tunneling motion is near 15,000 cm(-1), which would likely make the tunneling frequencies too small to observe in the microwave spectra. The rotational and centrifugal distortion constants determined from the measured transitions were A = 2180.7186(98) MHz, B = 470.873 90(25) MHz, C = 387.689 84(22) MHz, DJ = 0.0100(14) kHz, DJK = 0.102(28) kHz, and DK = 13.2(81) kHz. The B3LYP/aug-cc-pVTZ calculated rotational constants were within 1% of the experimentally determined values.

Rotational spectra and gas phase structure of the maleimide – Formic acid doubly hydrogen bonded dimer

Rotational transitions were measured for the maleimide – formic acid doubly hydrogen bonded dimer using a Flygare–Balle type pulsed-beam Fourier transform microwave spectrometer. No splittings caused by possible concerted double proton tunneling motion were observed. Experimental rotational constants (MHz), quadrupole coupling constants (MHz), and centrifugal distortion constants (kHz) were determined for the parent and three deuterium substituted isotopologues. The values for the parent are A=2415.0297(10), B=784.37494(38), C=592.44190(33), DJ=0.0616(64), DJK=−0.118(35), DK=−1.38(15), 1.5χaa=2.083(14), and 0.25(χbb–χcc)=1.1565(29). The hydrogen bond lengths were determined using a nonlinear least squares structure fitting program. Rotational constants for this complex are consistent with a planar structure, with an inertial defect of Δ=−0.528amuÅ2. The B3LYP calculation yielded rotational constants within 0.1% of the experimental values.

Microscopic modeling of mass and charge distributions in the spontaneous fission ofPu240

We propose a methodology to calculate microscopically the mass and charge distributions of spontaneous fission yields. We combine the multidimensional minimization of collective action for fission with stochastic Langevin dynamics to track the relevant fission paths from the ground-state configuration up to scission. The nuclear potential energy and collective inertia governing the tunneling motion are obtained with nuclear density functional theory in the collective space of shape deformations and pairing. We obtain a quantitative agreement with experimental data and find that both the charge and mass distributions in the spontaneous fission of $^{240}\mathrm{Pu}$ are sensitive both to the dissipation in collective motion and to adiabatic fission characteristics.

固体表面に存在する水素原子が示す量子効果

Quantum effect is manifest for hydrogen atoms on surfaces as well as for those in solution and solids. The excited states of a hydrogen atom directly adsorbed on metal surfaces are beyond the diffusion barrier, thus being delocalized to the next sites, and even spread over the entire surface in the low-coverage limit. In addition, water and hydroxyl group on the surfaces show significant quantum effect, due to tunneling and zero-point motion of the hydrogen atom. We briefly review some experimental and theoretical studies that revealed the quantum effect of the hydrogen atom on the surfaces.

Classification of hydrogen bond flips in small water polyhedra applied to concerted proton tunneling.

Recently a new mechanism of proton tunneling in a prism-like water hexamer was revealed [Richardson et al., Science, 2016, 351, 1310]. The tunneling motion involves the concerted breaking of two hydrogen bonds and rotations of two nearest water molecules. Eventually, this structural transformation means flipping one of the hydrogen bonds without the creation of defects in the hydrogen bond network. On the surface of polyhedral water clusters, there are five essentially different types of hydrogen bonds, and only two of them can be changed in this manner. In this article, the topological classification of such transformations for five small water polyhedra: triangular, pentagonal, and hexagonal prisms as well as cube and polyhedron 4454, consisting of four square and four pentagonal faces, is presented. Our classification includes the enumeration of all possible one-bond-flips with consideration of the types of hydrogen bonds on the polyhedral surface. Attention is paid to the most stable proton configurations which can be studied in experiments. It was established that a number of one-bond-flip transitions between the low energy configurations are possible in clusters in the shape of triangular and pentagonal prisms.

The Design of Angle Auto Direction-adjusting System for Wind Tunnel Motion Mechanism

In this article a motion mechanism angle self direction-adjusting controlling system is designed. The main function of this system is to achieve the angle following control with the variation of inflow direction. This article describes the construction and working principle of the angle self direction-adjusting system, aiming to the controlling target the self-adapting fuzzy controller is designed, the controller is then simulated and analyzed after adding square wave signals. It is validated that the self-adapting fuzzy PID controller has a good dynamic, static and robust characteristics.

Microwave spectra and structure of the cyclopropanecarboxylic acid-formic acid dimer.

The rotational spectrum of the cyclopropanecarboxylic acid-formic acid doubly hydrogen bonded dimer has been measured in the 4-11 GHz region using a Flygare-Balle type pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, four unique singly substituted (13)C isotopologues, and a singly deuterated isotopologue. Splittings due to a possible concerted double proton tunneling motion were not observed. Rotational constants (A, B, and C) and centrifugal distortion constants (DJ and DJK) were determined from the measured transitions for the dimer. The values of the rotational (in MHz) and centrifugal distortion constants (in kHz) for the parent isotopologue are A = 4045.4193(16), B = 740.583 80(14), C = 658.567 60(23), DJ = 0.0499(16), and DJK = 0.108(14). A partial gas phase structure of the dimer was derived from the rotational constants of the measured isotopologues, previous structural work on each monomer units and results of the calculations.

Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube

In single electron tunneling through clean, suspended carbon nanotube devices at low temperature, distinct switching phenomena have regularly been observed. These can be explained via strong interaction of single electron tunneling and vibrational motion of the nanotube. We present measurements on a highly stable nanotube device, subsequently recorded in the vacuum chamber of a dilution refrigerator and immersed in the 3He/ 4He mixture of a second dilution refrigerator. The switching phenomena are absent when the sample is kept in the viscous liquid, additionally supporting the interpretation of dc-driven vibration. Transport measurements in liquid helium can thus be used for finite bias spectroscopy where otherwise the mechanical effects would dominate the current.

Rotational Spectra of Two Hydrogen-Bonded Methyl Salicylate Monohydrates: Relative Stability and Tunneling Motions

The mechanism for the dual fluorescence of methyl salicylate (MS) is a long-standing research topic. Two distinctly different hydrogen-bonded MS–water complexes, one with the carbonyl O and the other with the hydroxy O serving as the hydrogen-bond acceptor, were detected using chirped pulse and cavity-based Fourier transform microwave spectroscopy and found to be of comparable stability. This observation provides direct experimental evidence for the previously undetected hydroxy O-bonded isomer, supporting the recently proposed new mechanism for the dual fluorescence of MS in protic solvents. An interesting interplay between the methyl internal rotation and water tunneling motions was also investigated. The existence of an unconventional O···H–C hydrogen-bond was verified using the atoms-in-molecules theory. Thorough searches for the elusive ketoA, a higher energy form of MS, were unsuccessful. This result supports recent theoretical reports that only one MS species exists in the ground state.

ACL Reconstruction

Objectives:It has often been suggested that bone-patellar tendon-bone (BTB) grafts heal more quickly to graft tunnels than soft-tissue grafts after ACL reconstruction, due to rapid bone-to-bone healing. Little is known, however, about the motion of the grafts under functional, dynamic loads, or the actual time course for graft-tunnel healing in humans. The goal of this study was to assess the motion of both hamstrings (HS) and BTB grafts during gait at two time points (6 and 52 weeks) after surgery. It was hypothesized that there would be greater graft-tunnel motion in HS than BTB grafts, and that graft motion would be less at 1 year when compared with 6 weeks.Methods:Twelve human subjects underwent anatomic single-bundle ACL reconstruction using either hamstrings (HS) or bone-patellar tendon-bone (BTB) autografts (6 in each group) and extra-cortical fixation. Six 0.8 mm tantalum beads were embedded into the grafts prior to implantation, with pairs of beads located within each bone tunnel and in the mid-substance region. At six weeks and one year after surgery, dynamic stereo X-ray (DSX) images were collected at 100 frames/s while subjects walked on an instrumented treadmill (1.3 m/s). 3D femur and tibia bone models were generated from CT scans. Tibiofemoral kinematics and graft bead positions were analyzed by combining the 3D models with DSX data. Graft-tunnel motion was assessed by determining the maximum range of motion of the most proximal femoral tunnel and most distal tibial tunnel beads along the direction of the bone tunnels during the stance phase of gait. Effects of graft type and time were assessed with a 2-factor ANOVA, with alpha = 0.05.Results:Femoral tunnel motion (mean±s.d.) at 6 weeks was 2.47±0.96 mm (range 0.95-3.44 mm) for BTB and 1.51±0.68 mm (range 0.88-2.41 mm) for HS grafts, decreasing slightly to 2.09±0.84 mm for BTB and 1.37±0.41 for HS grafts by one year. Tibial tunnel motion was 1.45±0.57 mm (range 0.74-2.44 mm) for BTB and 1.43±0.59 mm (range 0.89-2.30 mm) for HS grafts at 6 weeks, and changed little by one year (1.58±0.46 mm for BTB and 1.52±0.57 for HS grafts). Across all time points, femoral graft-tunnel motion was significantly greater for BTB than HS grafts (p=0.004). In the tibial tunnel, there were no significant differences in motion between BTB and HS at 6 weeks or 1 year. For both graft types, there was no significant change in motion between 6 weeks and 1 year.Conclusion:Contrary to the study hypothesis, there was a greater motion relative to the femoral tunnel wall in BTB than HS grafts during walking. Significant graft-tunnel motion also persisted one year after reconstruction. These data suggest that the graft-to-tunnel healing process may occur more slowly then widely believed, especially for BTB grafts. However, all subjects were asymptomatic one year after surgery, and the implications of persistent, small (1-3 mm) movements of the grafts are unknown. These results, however, may have significant implications for graft choice, rehabilitation strategies and timing for return to sports.

Gas phase measurements of mono-fluoro-benzoic acids and the dimer of 3-fluoro-benzoic acid

The microwave spectrum of the mono-fluoro-benzoic acids, 2-fluoro-, 3-fluoro-, and 4-fluoro-benzoic acid have been measured in the frequency range of 4-14 GHz using a pulsed beam Fourier transform microwave spectrometer. Measured rotational transition lines were assigned and fit using a rigid rotor Hamiltonian. Assignments were made for 3 conformers of 2-fluorobenzoic acid, 2 conformers of 3-fluorobenzoic acid, and 1 conformer of 4-fluorobenzoic acid. Additionally, the gas phase homodimer of 3-fluorobenzoic acid was detected, and the spectra showed evidence of proton tunneling. Experimental rotational constants are A(0(+)) = 1151.8(5), B(0(+)) = 100.3(5), C(0(+)) = 87.64(3) MHz and A(0(-)) = 1152.2(5), B(0(-)) = 100.7(5), C(0(-)) = 88.85(3) MHz for the two ground vibrational states split by the proton tunneling motion. The tunneling splitting (ΔE) is approximately 560 MHz. This homodimer appears to be the largest carboxylic acid dimer observed with F-T microwave spectroscopy.