Energy exchange between vibration modes of a graphene nanoflake oscillator: Molecular dynamics study

We investigated the oscillatory behaviors of a square graphene-nanoflake (GNF) on a rectangular GNF via classical molecular dynamics simulations, and analyzed the energy exchange and the oscillation frequencies for three different modes. The simulation results using a model structure show that the GNF oscillator can be considered as a high frequency oscillator. As its initial velocity increases, its telescoping region increases, then its structural asymmetry along the axis due to own small rotation exerted asymmetric van der Waals (vdW) force on it, and finally, this asymmetric vdW force enhances its rotational motions during its axial translational motions. So the initial kinetic energy of the axial translational motion is changed into the energy of the orthogonal vibrational and the rotational motions. Its resonance frequencies are dependent on the aspect ratio of the bottom rectangular GNF, the difference between the lengths of the GNF oscillator and the bottom rectangular GNF, and the initial velocity.     

Large eddy simulation of orientation and rotation of ellipsoidal particles in isotropic turbulent flows

The rotational motion and orientational distribution of ellipsoidal particles in turbulent flows are of significance in environmental and engineering applications. Whereas the translational motion of an ellipsoidal particle is controlled by the turbulent motions at large scales, its rotational motion is determined by the fluid velocity gradient tensor at small scales, which raises a challenge when predicting the rotational dispersion of ellipsoidal particles using large eddy simulation (LES) method due to the lack of subgrid scale (SGS) fluid motions. We report the effects of the SGS fluid motions on the orientational and rotational statistics, such as the alignment between the long axis of ellipsoidal particles and the vorticity, the mean rotational energy at various aspect ratios against those obtained with direct numerical simulation (DNS) and filtered DNS. The performances of a stochastic differential equation (SDE) model for the SGS velocity gradient seen by the particles and the approximate deconvolution method (ADM) for LES are investigated. It is found that the missing SGS fluid motions in LES flow fields have significant effects on the rotational statistics of ellipsoidal particles. Alignment between the particles and the vorticity is weakened; and the rotational energy of the particles is reduced in LES. The SGS-SDE model leads to a large error in predicting the alignment between the particles and the vorticity and over-predicts the rotational energy of rod-like particles. The ADM significantly improves the rotational energy prediction of particles in LES.     

Theory of molecule-surface scattering at thermal and hyperthermal energies

A theoretical model of molecule-surface scattering is developed which includes energy and momentum transfers between the surface and projectile for both translational and rotational motions and internal mode excitation for the projectile molecule. The translation and rotation motions are treated in the classical limit, while a quantum treatment for internal vibrational mode excitation is used. The results of calculations are compared with recent high-precision measurements of the scattering of a beam of C(2)H(2) molecules from a clean, ordered LiF(001) surface at energies of up to nearly 1 eV. The calculated results for angular distributions and rotational excitations are in good agreement with experiment.     

Light scattering from fluids. A semi-phenomenological calculation of the coupling constants between the orientational and translational motion

The coupling parameters X and Z between translational and orientational motions, which determine the lineshapes of the VH and HH depolarized light scattering spectra respectively, are calculated. By using a simple model that explains the connection between rotational and translational motions, it is shown that X and Z are proportional to k²η_r/ρ. The correct order of magnitude of the proportionality coefficient is obtained.     

A Depolarized Dynamic Light Scattering Method to Calculate Translational and Rotational Diffusion Coefficients of Nanorods

A new analysis of depolarized dynamic light scattering data is presented, which allows the unambiguous determination of rotational and translational diffusions coefficients of nanorods in suspension. By visualizing data scaling, purely translational diffusive motions can be isolated from vertically polarized scattering, allowing the unique determination of rotational diffusion from the depolarized scattering. The method is applied to nanorods with four different aspect ratios, and compared with theoretical predictions. Diffusion coefficients obtained show good agreement with calculations based on the direct measurements of rod length and diameter. Where the theories are shown to be valid, the method allows the measurement of statistically meaningful particle sizes and aspect ratios.     

Collision hamiltonian for non-linear molecules

A model hamiltonian which describes the non-reactive collision of two non-linear molecules has been constructed. This hamiltonian gives insight into the character of the complex translational, vibrational and rotational motions. The main features of the isolated molecule case are essentially disturbed by the non-adiabatic interaction between the macroscopic molecular motions and the vibrations. The usual angular momentum expressions are found to be the asymptotic limits of the true angular momenta in the case when these non-adiabaticities are switched off.     

Reciprocity in electrohydrodynamics

We consider a rigid body of arbitrary shape with a permanent charge distribution and a permanent dielectric profile immersed in a fluid with a frequency dependent dielectric constant. The body performs small oscillatory translational and rotational motions and the whole system is subjected to an applied electric field oscillating at the same frequency. The force and torque on the body and its external dipole moment are related by a resistance matrix to the translational and rotational velocity and the applied electric field. We show on the basis of the equations of linear electrohydrodynamics that the resistance matrix is symmetric. This may be regarded as an example of Onsager symmetry.     

Depolarization of second-order intensity correlation tensor of light scattered by random orientation of asymmetric particles

Investigation of second-order intensity correlation tensor elements (SOICT) by depolarization measurement of light scattered on orientational fluctuations of asymmetric particles is shown to yield new information on translational and rotational molecular motions.     

Molecular motions in liquid ethane studied by cold neutron scattering

In a previous work we report a comparative study of the molecular motions in gaseous and liquid methane and argon. In the present work we present the results of a study of the molecular motions in liquid ethane at three widely different temperatures. The aim is to study the rotational-translational motions of the rigid molecule. The unknown scattering from the librational and other motions of the CH₃ group is experimentally determined from a high-temperature run by a procedure of isolation of this scattering by use of successive approximations in which also the corrections for multiple scattering are involved.It is found that the translational motions are very nearly described by a cross section based on simple Langevin diffusion. The effects of encaging in ethane well below the critical point seem to influence the cross section only rather modestly. The scaling of the “encaging part” of the translational motion from liquid argon to ethane by use of the law of corresponding states is not successful. The rotational motions are equally well described by the Langevin rotational-diffusion model or by the step model. It is observed that certain degrees of rotational freedom tend to be frozen when the freezing point is approached.     

First quantum correction to the radial distribution function and to the thermodynamic properties for a fluid of hard spheres

Dealing with the positions and orientations of the molecules as independent stochastic processes, the authors investigate the influence of translational and rotational fluctuations of anisotropically polarizable microsystems on the evolution in time of the second-order intensity correlation tensor of Rayleigh scattered light as well as on its spectral density. The notion of second-order depolarization is introduced and is shown to be a useful quantity for obtaining information on the translational and rotational motions of microsystems and their optical anisotropy.     

Heterodyne-detected fifth-order nonresonant Raman scattering from room temperature CS2

Actively phase-locked heterodyne-detected fifth-order nonresonant Raman scattering from room temperature CS2 has been measured. The experimental signals have similar magnitudes, shapes, and sign changes as calculated responses obtained via molecular dynamics simulations [S. Saito and I. Ohmine, Phys. Rev. Lett. 88, 207401 (2002)]. The measured signals contain sign changes that appear to be associated with the coupling of rotational motions both to each other and to translational motions.     

Faxén theorems for a spherically symmetric polymer in time dependent compressible flow

We derive Faxén theorems for the force, the torque and the symmetric force dipole moment acting on a spherically symmetric polymer suspended in an arbitrary time dependent compressible flow. The translational and rotational motions of the polymer are allowed to be non-steady as well. These results extend the theorems already derived for the case of a polymer immersed in a creeping flow.     

Nuclear electric quadrupole interactions in liquids entrapped in cavities

Liquids entrapped in cavities and containing quadrupole nuclei are considered. The interaction of the quadrupole moment of a nucleus with the electric field gradient is studied. In such a system, molecules are in both rotational and translational Brownian motions which are described by the diffusion equation. Solving this equation, we show that the intra- and intermolecular nuclear quadrupole interactions are averaged to zero in cavities with the size larger than several angstroms.     

Calibration of a multiple axes 3-D laser scanning system consisting of robot, portable laser scanner and turntable

A multiple axes 3-D laser scanning system consisting of a portable 3-D laser scanner, a industrial robot and a turntable is demonstrated. By using a criterion sphere, a robot tool center point (TCP) calibration approach is proposed to calibrate the relation between the laser 3-D scanner and the robot end-effector. In this approach, two different translational motions of robot are first made to determine the rotation part, and then at least three different rotational motions are made to determine the translation part. Meanwhile, by using the criterion sphere, a turntable approach is proposed to calibrate the pose of the turntable relative to the robot. In this approach, several rotational angles of turntable and two different heights of the sphere are made to determine the rotational axis of turntable. Experiment is performed on a portable laser scanner mounted on an industrial robot ABB IRB4400 with a turntable. The experiment results show that the two proposed calibration algorithms are stable and flexible. The application of 3-D measurement is also given to demonstrate the effectiveness and stability of the multiple axes 3-D laser scanning system.     

RETRACTED ARTICLE: Quantum effects on translation and rotation of molecular chlorine in solid para-hydrogen

Structure and quantum effects of a Cl₂ molecule embedded in fcc and hcp para-hydrogen (pH₂) crystals are investigated in the zero-temperature limit. The interaction is modelled in terms of Cl₂–pH₂ and pH₂–pH₂ pair potentials from ab initio CCSD(T) and MP2 calculations. Translational and rotational motions of the molecules are described within three-dimensional anharmonic Einstein and Devonshire models, respectively, where the crystals are either treated as rigid or allowed to relax. The pH₂ molecules, as well as the heavier Cl₂ molecule, show large translational zero-point energies (ZPEs) and undergo large-amplitude translational motions. This gives rise to substantial reductions in the cohesive energies and expansions of the lattices, in agreement with experimental results for pure hydrogen crystals. The rotational dynamics of the Cl₂ impurity is restricted to small-amplitude librations, again with high librational ZPEs, which are described in terms of two-dimensional non-degenerate anharmonic oscillators. The lattice relaxation causes qualitative changes of the rotational energy surfaces, which finally favour librations around the crystallographic directions pointing towards the nearest neighbours, both for fcc and hcp lattices. Implications on the reactant orientation in the experimentally observed laser-induced chemical reaction, Cl + H₂ → HCl + H, are discussed.     

Tensor analysis of the refraction distortions dynamics of a sounding optical beam

The capabilities of dynamics analysis of the sounding-beam intensity profile at the output of an atmospheric path on the basis of the chronogram structure tensor are considered. The spatio–temporal structure of the velocity field of refraction distortions is investigated. The characteristic dimensions of the regions of the translational and rotational types of flow motions are determined. The profiles of local velocity projections are obtained, as well as their statistical properties under the conditions of weak variations of meteoparameters in the output flow recording interval. Comparison of the characteristic values of wind velocity that is recorded with an array of anemometers and those calculated with the suggested method allowed us to elaborate an approach to the rough estimation of the translational and fluctuation components of aerodynamic flows at the path.     

The effect of HF field on diffusion and convection in a plasma column

A cylindrical plasma model with both axial and azimuthal steady magnetic field is used. Nonlinear excitation of time averaged electric currents by the HF field is analyzed. Ponderomotive forces of the HF field also lead to translational and rotational plasma motions. Radial plasma diffusion can be modified by the presence of the HF field at sufficiently low frequencies. The analysis can be applied to problems of anomalous transport.     

Combined measurement of X‐ray photon correlation spectroscopy and diffracted X‐ray tracking using pink beam X‐rays

Combined X‐ray photon correlation spectroscopy (XPCS) and diffracted X‐ray tracking (DXT) measurements of carbon‐black nanocrystals embedded in styrene–butadiene rubber were performed. From the intensity fluctuation of speckle patterns in a small‐angle scattering region (XPCS), dynamical information relating to the translational motion can be obtained, and the rotational motion is observed through the changes in the positions of DXT diffraction spots. Graphitized carbon‐black nanocrystals in unvulcanized styrene–butadiene rubber showed an apparent discrepancy between their translational and rotational motions; this result seems to support a stress‐relaxation model for the origin of super‐diffusive particle motion that is widely observed in nanocolloidal systems. Combined measurements using these two techniques will give new insights into nanoscopic dynamics, and will be useful as a microrheology technique.     

Pumping of confined water in carbon nanotubes by rotation-translation coupling

Bidirectional single file water transport in a carbon nanotube is known to occur in "bursts" in short nanotubes. Here we show that in long carbon nanotubes, when the orientation of the water molecules is maintained along one direction, a net water transport along that direction can be attained due to coupling between rotational and translational motions. The rotations of the water molecules are correlated more with the translation of the neighboring water molecule with the acceptor oxygen than the neighbor with the donor hydrogen. This mechanism can be used to pump water through nanotubes.     

Lattice model for translational and rotational motions based on generalised diffusion equations: I. General formalism

A simple lattice model based on generalised diffusion equations and Gaussian statistics, aimed at describing diffusive translational and rotational motions, is presented. It is shown that it allows the generation of correlation functions relevant to spectroscopic techniques that are very similar to those experimentally observed in a large variety of complex systems. For some ranges of values of the model parameters, these functions, which can be expressed in closed mathematical forms, can be approximately represented by the sum of two exponentials or by “stretched" exponentials. Received 17 September 1999 and Received in final form 10 February 2000