Article

1998 ◽  
Vol 76 (12) ◽  
pp. 911-920
Author(s):  
M Grigorescu
Keyword(s):  
Potential Barrier ◽  
Exponential Decay ◽  
Quantum Dynamics ◽  
Driving Forces ◽  
Thermal Fluctuations ◽  
61.16 Di ◽  
73.40 Gk ◽  
Surface Phonons ◽  
Atom Dynamics ◽  
Transfer Probability

The quantum dynamics of a Xe atom placed on the STM surfaceis studied considering two important types of nonstationary externalforces. These are the driving forces appearing during the application of avoltage pulse, and the fluctuating forces determined by the coupling to anOhmic environment. The localization probability on the tipduring voltage pulses of 20 and 7 ns with symmetric triangular andtrapezoidal shapes is calculated neglecting the environmental interactions.The results indicate that the atom dynamics in this case is reversible, andafter the pulse the transfer probability is small.The effects of the fluctuating forces produced by the coupling to thesurrounding electrons and surface phonons are studied in a static potential.It is shown that the thermal fluctuations at the environmental temperaturecan lead to irreversible atom tunneling through the potential barrier,described by an exponential decay law.PACS Nos.: 61.16.Di, 73.40.Gk, 05.40.+j

scholarly journals Quantum dynamics of wave packets in a non-stationary parabolic potential and the Kramers escape rate theory

2016 ◽  
Vol 01 (02) ◽  
pp. 1650010 ◽  
Author(s):  
Vladimir I. Dubinko ◽  
Alexander S. Mazmanishvili ◽  
Denis V. Laptev ◽  
Juan F. R. Archilla
Keyword(s):  
Quantum Dynamics ◽  
Thermal Fluctuations ◽  
Reaction Rates ◽  
Strong Increase ◽  
Rate Theory ◽  
Driving Frequency ◽  
Rate Of Escape ◽  
System Temperature ◽  
Analytical Expressions ◽  
Time Periodic

At sufficiently low temperatures, the reaction rates in solids are controlled by quantum rather than by thermal fluctuations. We solve the Schrödinger equation for a Gaussian wave packet in a non-stationary harmonic oscillator and derive simple analytical expressions for the increase of its mean energy with time induced by the time-periodic modulation. Applying these expressions to the modified Kramers theory, we demonstrate a strong increase of the rate of escape out of a potential well under the time-periodic driving, when the driving frequency of the well position equals its eigenfrequency, or when the driving frequency of the well width exceeds its eigenfrequency by a factor of [Formula: see text]. Such regimes can be realized near localized anharmonic vibrations (LAVs), in which the amplitude of atomic oscillations greatly exceeds that of harmonic oscillations (phonons) that determine the system temperature. LAVs can be excited either thermally or by external triggering, which can result in strong catalytic effects due to amplification of the Kramers rate.

Fractal Dimensions in Tunneling Processes and Effects of Environmental Fluctuations

Fractals ◽  
1998 ◽  
Vol 06 (01) ◽  
pp. 59-66
Author(s):  
Vassilios Kovanis ◽  
Paolo Grigolini ◽  
V. M. Kenkre ◽  
G. P. Tsironis
Keyword(s):  
Wave Packet ◽  
Time Evolution ◽  
Exponential Decay ◽  
Electron Tunneling ◽  
Fractal Dimensions ◽  
Thermal Fluctuations ◽  
Gaussian Wave Packet ◽  
Relaxation Processes ◽  
Weierstrass Function ◽  
Quartic Potential

We study electron tunneling between two infinte potential square wells connected via an opaque barrier and find that time evolution of the probability of the presence of a Gaussian wave packet, localized initially in one of the wells, shares the fractal behavior of tunneling in a quartic potential, discovered by Dekker (H. Dekker, Phys. Rev.A35, 1825 (1987). However, the fractal dimensions are found to be closer to those of a conventional Weierstrass function than those appropriate to the quasi-Weierstrass behavior of Dekker. It is argued that the usual exponential decay predicted by conventional relaxation processes can be recovered only as an effect of thermal fluctuations.

scholarly journals Evolution of a Non-Hermitian Quantum Single-Molecule Junction at Constant Temperature

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 147
Author(s):  
Andrea Grimaldi ◽  
Alessandro Sergi ◽  
Antonino Messina
Keyword(s):  
Constant Temperature ◽  
Single Molecule ◽  
Quantum Dynamics ◽  
Numerical Study ◽  
Thermal Fluctuations ◽  
Theoretical Description ◽  
Level System ◽  
Different Temperatures ◽  
Molecule Junction ◽  
Single Molecule Junction

This work concerns the theoretical description of the quantum dynamics of molecular junctions with thermal fluctuations and probability losses. To this end, we propose a theory for describing non-Hermitian quantum systems embedded in constant-temperature environments. Along the lines discussed in [A. Sergi et al., Symmetry 10 518 (2018)], we adopt the operator-valued Wigner formulation of quantum mechanics (wherein the density matrix depends on the points of the Wigner phase space associated to the system) and derive a non-linear equation of motion. Moreover, we introduce a model for a non-Hermitian quantum single-molecule junction (nHQSMJ). In this model the leads are mapped to a tunneling two-level system, which is in turn coupled to a harmonic mode (i.e., the molecule). A decay operator acting on the two-level system describes phenomenologically probability losses. Finally, the temperature of the molecule is controlled by means of a Nosé-Hoover chain thermostat. A numerical study of the quantum dynamics of this toy model at different temperatures is reported. We find that the combined action of probability losses and thermal fluctuations assists quantum transport through the molecular junction. The possibility that the formalism here presented can be extended to treat both more quantum states (∼10) and many more classical modes or atomic particles (∼103−105) is highlighted.

Propagation of waves in high Brillouin zones: Chaotic branched flow and stable superwires

2021 ◽  
Vol 118 (40) ◽  
pp. e2110285118
Author(s):  
Alvar Daza ◽  
Eric J. Heller ◽  
Anton M. Graf ◽  
Esa Räsänen
Keyword(s):  
Periodic Structure ◽  
Potential Barrier ◽  
Quantum Dynamics ◽  
Periodic Potential ◽  
Dynamical Stability ◽  
Length Scale ◽  
Propagation Of Waves ◽  
Typical Length

We report unexpected classical and quantum dynamics of a wave propagating in a periodic potential in high Brillouin zones. Branched flow appears at wavelengths shorter than the typical length scale of the ordered periodic structure and for energies above the potential barrier. The strongest branches remain stable indefinitely and may create linear dynamical channels, wherein waves are not confined directly by potential walls as electrons in ordinary wires but rather, indirectly and more subtly by dynamical stability. We term these superwires since they are associated with a superlattice.

scholarly journals Local thermal energy as a structural indicator in glasses

2017 ◽  
Vol 114 (28) ◽  
pp. 7289-7294 ◽  
Author(s):  
Jacques Zylberg ◽  
Edan Lerner ◽  
Yohai Bar-Sinai ◽  
Eran Bouchbinder
Keyword(s):  
Thermal Energy ◽  
Driving Forces ◽  
Normal Modes ◽  
Low Frequency ◽  
General System ◽  
Thermal Fluctuations ◽  
Exact Expression ◽  
Internal Stresses ◽  
Vibrational Modes ◽  
Physical Observable

Identifying heterogeneous structures in glasses—such as localized soft spots—and understanding structure–dynamics relations in these systems remain major scientific challenges. Here, we derive an exact expression for the local thermal energy of interacting particles (the mean local potential energy change caused by thermal fluctuations) in glassy systems by a systematic low-temperature expansion. We show that the local thermal energy can attain anomalously large values, inversely related to the degree of softness of localized structures in a glass, determined by a coupling between internal stresses—an intrinsic signature of glassy frustration—anharmonicity and low-frequency vibrational modes. These anomalously large values follow a fat-tailed distribution, with a universal exponent related to the recently observed universal ω4 density of states of quasilocalized low-frequency vibrational modes. When the spatial thermal energy field—a “softness field”—is considered, this power law tail manifests itself by highly localized spots, which are significantly softer than their surroundings. These soft spots are shown to be susceptible to plastic rearrangements under external driving forces, having predictive powers that surpass those of the normal modes-based approach. These results offer a general, system/model-independent, physical/observable-based approach to identify structural properties of quiescent glasses and relate them to glassy dynamics.

Solute redistribution during in-situ irradiation of alloys in the high voltage electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 370-371
Author(s):  
P. R. Okamoto ◽  
N.Q. Lam ◽  
R. L. Lyles
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Driving Forces ◽  
Solute Diffusion ◽  
Solute Redistribution ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Thin Foils ◽  
Solute Atoms

During irradiation of thin foils in a high voltage electron microscope (HVEM) defect gradients will be set up between the foil surfaces and interior. In alloys defect gradients provide additional driving forces for solute diffusion since any preferential binding and/or exchange between solute atoms and mobile defects will couple a net flux of solute atoms to the defect fluxes. Thus, during irradiation large nonequilibrium compositional gradients can be produced near the foil surfaces in initially homogeneous alloys. A system of coupled reaction-rate and diffusion equations describing the build up of mobile defects and solute redistribution in thin foils and in a semi-infinite medium under charged-particle irradiation has been formulated. Spatially uniform and nonuniform damage production rates have been used to model solute segregation under electron and ion irradiation conditions.An example calculation showing the time evolution of the solute concentration in a 2000 Å thick foil during electron irradiation is shown in Fig. 1.

Chronic Pain: Fundamental Scientific Considerations, Specifically for Legal Claims

2013 ◽  
Vol 18 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Robert J. Barth
Keyword(s):  
Health Outcomes ◽  
Pain Perception ◽  
Driving Forces ◽  
Psychological Treatment ◽  
Dominant Role ◽  
Meta Analysis ◽  
General Medicine ◽  
Pain Syndrome ◽  
Problematic Relationship

Abstract Scientific findings have indicated that psychological and social factors are the driving forces behind most chronic benign pain presentations, especially in a claim context, and are relevant to at least three of the AMA Guides publications: AMA Guides to Evaluation of Disease and Injury Causation, AMA Guides to Work Ability and Return to Work, and AMA Guides to the Evaluation of Permanent Impairment. The author reviews and summarizes studies that have identified the dominant role of financial, psychological, and other non–general medicine factors in patients who report low back pain. For example, one meta-analysis found that compensation results in an increase in pain perception and a reduction in the ability to benefit from medical and psychological treatment. Other studies have found a correlation between the level of compensation and health outcomes (greater compensation is associated with worse outcomes), and legal systems that discourage compensation for pain produce better health outcomes. One study found that, among persons with carpal tunnel syndrome, claimants had worse outcomes than nonclaimants despite receiving more treatment; another examined the problematic relationship between complex regional pain syndrome (CRPS) and compensation and found that cases of CRPS are dominated by legal claims, a disparity that highlights the dominant role of compensation. Workers’ compensation claimants are almost never evaluated for personality disorders or mental illness. The article concludes with recommendations that evaluators can consider in individual cases.

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