Influence Of Atomic Motion Research Articles

A new insight into the influence of atomic motion on the mechanical properties of polyethylene chains

To investigate the potential mechanism affecting the mechanical properties of polyethylene (PE) are beneficial to its practical application. In this paper, the atomic motion is decomposed to reveal the underlying mechanisms of how PE mechanical properties are affected by temperature, strain rate, and inter-chain interaction, using molecular dynamics (MD) simulations. It is found that the underlying mechanism of temperature affecting mechanical properties of PE chains is further demonstrated to closely relate with the radial motion of PE atoms. The increasing motion range of PE atoms in the radial direction would result in a decrease of breaking stress and breaking strain of PE chains in the axial direction. In addition, the strain rates would suppress the radial movement range of the PE atoms, which strengthens the mechanical properties of the PE chain. In contrast, the introduction of interaction between PE chains by increasing the chain number causes the radial motion of atoms to be more intense, which reduces the strength of the polyethylene chains. These simulation results are highly expected to provide novel insight to understand the mechanism of materials' mechanical properties.

Peculiarities of Joint Influence of Atomic Motion and Hyperfine Splitting of an Excited State on the Shape of Resonance of Coherent Population Trapping in a Rarefied Gas

Peculiarities of Joint Influence of Atomic Motion and Hyperfine Splitting of an Excited State on the Shape of Resonance of Coherent Population Trapping in a Rarefied Gas

Influence of atomic motion on the collective effects in dense and cold atomic ensembles

We show that atomic motion leads not only to noticeable quantitative, but in some cases also to qualitative modification of collective effects in dense and cold atomic ensembles even in the case when the characteristic Doppler shifts are tens of times smaller than the natural linewidth. The observed influence is explained as a result of the suppression of the impact of sub-radiant collective states caused by the displacement of the atoms.

Thermofluctuational Fracture Mechanism in Solids in the Presence of an Active Medium

The paper addresses an approach to the physical notion of failure of solids in the presence of an active medium (a destructive compound), which is based on two successive steps. The first one is to go from considering a body as an elastic or viscoelastic continuum to studying it as an atomic-molecular system. The second step that follows the investigation of the atomic structure is to take into account the influence of atomic motion in a solid during the study of mechanical properties of solids (at high temperatures, in a wide range of loading speeds, under cyclic and vibrational loads), which is based on the experimental data on ultimate strength and yield stress of metals. A mechanism of crack initiation in a loaded metal under the action of destructive compounds is discussed. The capillary and diffusional propagation of a molten liquid-metal compound along grain boundaries and structural defects in a solid metal in combination with the viscous flow of the melt over its surface are shown to dictate the crack propagation into metal structure. The pattern of the affecting destructive factor has been clarified.

Noise spectroscopy with large clouds of cold atoms

Noise measurement is a powerful tool to investigate many phenomena from laser characterization to quantum behavior of light. In this paper, we report on intensity noise measurements obtained when a laser beam is transmitted through a large cloud of cold atoms. While this measurement could possibly investigate complex processes such as the influence of atomic motion, one is first limited by the conversion of the intrinsic laser frequency noise to intensity noise via the atomic resonance. This conversion is studied here in details. We show that, while experimental intensity noise spectra collapse onto the same curve at low Fourier frequencies, some differences appear at higher frequencies when the probe beam is detuned from the center of the resonance line. A simple model, based on a mean-field approach, which corresponds to describing the atomic cloud by a dielectric susceptibility, is sufficient to understand the main features. Using this model, the noise spectra allow extracting some quantitative informations on the laser noise as well as on the atomic sample.

Nonclassical feature of the field in the two-atom Tavis-Cummings model with atomic motion

We study the nonclassical feature of the field in the two-atom Tavis-Cummings model with atomic motion using the quantum theory. The influence of atomic motion, the field mode structure and the field initial states on the properties of the light squeezing and the photon antibunching are discussed.

Influence of atomic motion on squeezing of double-mode field in interaction with a moving V-type three-level atom

The influence of atomic motion on squeezing of the double-mode field in the interaction with a moving V-type three level atom is investigated by means of the quantum theory and the method of numerical analysis. The results show, on the one hand, when the initial photon field is in non-correlative coherent state of double-mode, only the quadrature U1 is squeezed and the squeezed degree of U1 increases with the increasing of the parameter β which describes the atomic motion and structure of the field mode. On the other hand, when the initial field is in the vacuum squeezed state of double-mode, the quadrature U2 is squeezed principally and we can obtain a steady squeezed light by choosing an appropriate parameter β.

Influence of atomic motion on the population and dipole squeezing of a cascade three-level atom in cavity field

The dynamical property of a cascade three-level atom is investigated in the condition of atomic motion. The influence of atomic motion on the population and dipole squeezing is discussed. The results show that atomic motion makes the amplitude of atomic population be steady and increasing the parameter ep which denotes the atomic motion and the structure of field mode can shorten the period of collapse–revivals. By choosing an appropriate parameter ep, we can obtain a dipole squeezed atom of long standing.

Influence of Atomic Motion on a Microlaser in an OpticalStanding-Wave Cavity

We study the microlaser in an optical standing-wave cavityinjected with two-level atoms. The results have shown the obvious influence ofatomic centre-of-mass motion on the microlaser, such as the photondistribution, the linewidth and the frequency shift. It was found that whenthe momentum of atoms is comparable to that of photons, the influence ofatomic motion is dominated and the number of photons in the microlaser can begreatly enhanced, owing to part of the atomic kinetic energy beingtransferred to the resonator. This work provides a comparison of the relatedstudies on the atomic motion under special assumptions.

Influence of atomic motion on the shape of two-photon resonance in gas

A gas of three-level atoms with Λ configuration of energy levels was taken as an example to demonstrate that the influence of particle motion on the two-photon resonances extends further than the residual Doppler shift (k1−k2)v. In particular, a narrow dip in the absorption spectrum (“dark” resonance) undergoes substantial narrowing, as compared to the atoms at rest. The width of this resonance is studied nonperturbatively as a function of the intensities of probe and strong fields.

Vibrations of surface atoms studied by NRRA

The motion of the target nuclei in the surface of a solid affects the shape of yield curves of narrow nuclear resonances. We measured yield curves for the 272 keV resonance in 21Ne(p,γ) 22Na with frozen neon. The in-situ preparation of the targets and the measurements were carried out under UHV conditions. The targets were cooled by a He evaporation cryostat to temperatures below 10 K. This temperature could be maintained even with beam currents of about 1 μA. The measurements were carried out with the 400 kV high energy resolution accelerator at the University of Münster. The measured yield curves showed a huge Lewis peak with a peak-to-plateau ratio of 2.5. The influence of atomic motion on the width of the Lewis peak was calculated with two different theoretical models. The calculated values are in good agreement with the experimental width.

Resonance line shape and filling factor in an alkali vapor maser: Influence of atomic motion

Resonance line shape and filling factor are two important parameters that condition the gain, oscillation threshold, output power, and short-term frequency stability of optically pumped alkali vapor masers. Both quantities are calculated using density matrix formalism and taking atomic motion into account. Some experimental verifications and methods for measuring the filling factor in a given configuration are indicated.