scholarly journals Molecular Dynamics Investigated by Temporally Two-Dimensional Coherent Raman Spectroscopy

1999 ◽  
Vol 19 (1-4) ◽  
pp. 35-40 ◽  
Author(s):  
A. Lau ◽  
M. Pfeiffer ◽  
V. Kozich ◽  
A. Kummrow
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Time Delays ◽  
Additional Contribution ◽  
Raman Resonance ◽  
Additional Information ◽  
Low Viscosity ◽  
Fast Relaxation ◽  
Coherent Raman ◽  
Set Up

A six-wave set-up is described to determine molecular dynamics in the condensed phase. Applying two independent time delays between excitation and probe pulses additional information on the dynamics should be obtainable. We show experimentally that such investigations can be carried out with noisy light having intensity fluctuations in the femtosecond region. As first result we found a fast relaxation time in neat nitrobenzene of 100 fs, becoming even faster in mixtures with low viscosity liquids. Switching on a Raman resonance yields a longer relaxation time, which could be explained by an additional contribution by that vibration.

Defects and Ion Transport Properties of Yttrium Doped Zirconia

1996 ◽  
Vol 453 ◽  
Author(s):  
P. J. Chaba ◽  
P. E. Ngoepe
Keyword(s):  
Molecular Dynamics ◽  
Oxygen Vacancy ◽  
Ion Transport ◽  
Transport Properties ◽  
Temperature Variation ◽  
Yttrium Oxide ◽  
Elastic Constants ◽  
Oxygen Transport ◽  
Solid Oxide ◽  
Set Up

AbstractA comparison of calculated and experimental temperature variation of elastic constants were used to predict types of oxygen—vacancy dopant clusters in yttria stabilised cubic zirconia, which serves as an electrolyte in solid oxide fuelcells. Such clusters were incorporated in supercells set up for molecular dynamics studies, where oxygen transport properties were investigated at concentrations of 9.4 and 24 mol % of yttrium oxide and up to 1600K.

scholarly journals Swap-Driven Self-Adhesion and Healing of Vitrimers

Coatings ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 114 ◽  
Author(s):  
Simone Ciarella ◽  
Wouter Ellenbroek
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Stress Relaxation ◽  
Healing Process ◽  
Star Polymers ◽  
Coarse Grained ◽  
Self Healing ◽  
Central Question ◽  
Trade Off ◽  
Dynamics Simulations

Vitrimers are covalent network materials, comparable in structure to classical thermosets. Unlike normal thermosets, they possess a chemical bond swap mechanism that makes their structure dynamic and suitable for activated welding and even autonomous self-healing. The central question in designing such materials is the trade-off between autonomy and material stability: the swap mechanism facilitates the healing, but it also facilitates creep, which makes the perfectly stable self-healing solid a hard goal to reach. Here, we address this question for the case of self-healing vitrimers made from star polymers. Using coarse-grained molecular dynamics simulations, we studied the adhesion of two vitrimer samples and found that they bond together on timescales that are much shorter than the stress relaxation time. We showed that the swap mechanism allows the star polymers to diffuse through the material through coordinated swap events, but the healing process is much faster and does not depend on this mobility.

scholarly journals Tribological properties of surface microtexture friction pairs under different lubrication conditions

2019 ◽  
Vol 11 (10) ◽  
pp. 168781401988156
Author(s):  
Lili Wang ◽  
Xingtang Zhao ◽  
Shaohui Guo ◽  
Min Wang
Keyword(s):  
Friction Pair ◽  
Element Model ◽  
High Viscosity ◽  
Navier Stokes ◽  
Solid Mixture ◽  
Low Viscosity ◽  
Frictional Performance ◽  
Friction Performance ◽  
Set Up ◽  
Lubrication Conditions

In the field of journal bearings, the microtexture processing technology of the bush inner surface has become an effective way to improve the performance of journal bearing. The two-dimensional finite element model of microtexture surface with different shapes of friction pairs is established based on the Navier–Stokes (N-S) equation, and the effect of lubrication conditions on the frictional performance of friction pairs is analyzed. Four microtextures that are radial grooves, circular pits, local reticulation, and circumferential grooved microtexture are processed by laser microcarving on the surface of specimen, and three different lubricating medium conditions are set up with high-viscosity oil, low-viscosity oil, and oil–solid mixture, and the effect of lubrication condition and texture shape on the wear reduction of the microtexture friction pair is studied. Results show that the concave microtexture and the radial groove can improve effectively the friction performance of the friction pair. The microtexture can effectively store the lubricating medium and wear abrasive particles in the mixed lubrication, and avoid effectively the second wear, and its average friction coefficient of radial groove microtexture is 22%, 30% lower than that of high- and low-viscosity lubricating media, respectively. Both theory and experiment have proved that the effect of microtexture on high-viscosity lubricant is better than that of low-viscosity lubricant.

Molecular Dynamics of Cellulose-Water Systems Investigated by NMR Relaxation Method

Holzforschung ◽  
2000 ◽  
Vol 54 (5) ◽  
pp. 501-504 ◽  
Author(s):  
K. Banas ◽  
B. Blicharska ◽  
W. Dietrich ◽  
M. Kluza
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Nmr Relaxation ◽  
Relaxation Method ◽  
Water Systems ◽  
Motion Model ◽  
Cellulose Pulp ◽  
Time Dependencies ◽  
Nmr Relaxation Time ◽  
Different Origin

Summary On the basis of the proton NMR relaxation time dependencies on temperature and frequency in cellulose pulp a simple two-motion model of molecular dynamics has been proposed. The parameters, activation energies and correlation times, describing the model may be correlated with structure features such as level of crystallinity of cellulose with different origin, as well as degree of paper devastation.

A theoretical model for the collective motion of proteins by means of principal component analysis

Open Physics ◽  
2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Hiqmet Kamberaj
Keyword(s):  
Molecular Dynamics ◽  
Principal Component Analysis ◽  
Relaxation Time ◽  
Friction Coefficient ◽  
Principal Component ◽  
Component Analysis ◽  
Dynamics Simulation ◽  
Coarse Grained ◽  
Dynamical Friction ◽  
Collective Coordinates

AbstractA coarse grained model in the frame work of principal component analysis is presented. We used a bath of harmonic oscillators approach, based on classical mechanics, to derive the generalized Langevin equations of motion for the collective coordinates. The dynamics of the protein collective coordinates derived from molecular dynamics simulations have been studied for the Bovine Pancreatic Trypsin Inhibitor. We analyzed the stability of the method by studying structural fluctuations of the Ca atoms obtained from a 20 ns molecular dynamics simulation. Subsequently, the dynamics of the collective coordinates of protein were characterized by calculating the dynamical friction coefficient and diffusion coefficients along with time-dependent correlation functions of collective coordinates. A dual diffusion behavior was observed with a fast relaxation time of short diffusion regime 0.2–0.4 ps and slow relaxation time of long diffusion about 1–2 ps. In addition, we observed a power law decay of dynamical friction coefficient with exponent for the first five collective coordinates varying from −0.746 to −0.938 for the real part and from −0.528 to −0.665 for its magnitude. It was found that only the first ten collective coordinates are responsible for configuration transitions occurring on time scale longer than 50 ps.

Proton NMR Study of Molecular Dynamics in Hydrazinium Perchlorate

1990 ◽  
Vol 45 (2) ◽  
pp. 102-106
Author(s):  
K. Ganesan ◽  
R. Damle ◽  
J. Ramakrishna
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Minimum ◽  
Second Moment ◽  
Spin Lattice ◽  
Nmr Study

AbstractThe proton spin-lattice relaxation time T1 (at 5.4, 10 and 15 MHz) and second moment M2 (at 9.8 MHz) have been measured in hydrazinium Perchlorate (N2H5ClO4). The temperature dependence of T, shows two minima. The low temperature T, minimum has been explained in terms of NH3 reorientation about the N-N axis while the high temperature minimum is attributed to the exchange of protons within the NH2 group (180° flip about the H - N - H bisectrix). The activation energies for NH3 and NH: motions are found to be 20.5 kJ mol-1 and 39.8 kJ mol-1 , respectively. The second moment variation with temperature shows two transitions around 120 K and 210 K and has been discussed in terms of NH3/NH2 motions.

scholarly journals Recovery of Shear-Modified Polybutadiene Solutions

2006 ◽  
Vol 79 (2) ◽  
pp. 267-280 ◽  
Author(s):  
C. M. Roland ◽  
C. G. Robertson
Keyword(s):  
Relaxation Time ◽  
Dynamic Modulus ◽  
Viscoelastic Relaxation ◽  
Newtonian Viscosity ◽  
Low Viscosity ◽  
Stress Coefficient ◽  
Linear Viscoelastic ◽  
Recoverable Compliance ◽  
Transient Viscosity ◽  
Nonlinear Shear

Abstract We have investigated the recovery of the overshoot in the transient viscosity, the first normal stress coefficient, and the dynamic modulus for entangled polybutadiene solutions subjected to nonlinear shear flow. The molecular-weight dependences of the various time scales (linear viscoelastic relaxation time, entanglement recovery time, and timescale for decay of stress following cessation of shearing) are all consistent with the usual 3.4 power law. Nevertheless, the time for recovery of the stress overshoot and plateau value of the dynamic modulus were substantially longer (by as much as two orders of magnitude) than the linear viscoelastic relaxation time calculated from the Newtonian viscosity and the equilibrium recoverable compliance. These results indicate that complete entanglement recovery requires cooperative chain motions over a length scale exceeding that associated with linear relaxation. This persistence of a disentangled state means that a state of low viscosity and reduced elasticity is retained for an extended time, suggesting that shear modification can be used to facilitate the processing of polymers.

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