scholarly journals Translational and rotational critical-like behaviors in the glass transition of colloidal ellipsoid monolayers

2021 ◽  
Vol 7 (3) ◽  
pp. eabd1958
Author(s):  
Zhongyu Zheng ◽  
Ran Ni ◽  
Yuren Wang ◽  
Yilong Han
Keyword(s):  
Glass Transition ◽  
Degrees Of Freedom ◽  
Glass Transition Point ◽  
Nonspherical Particles ◽  
Correlation Lengths ◽  
Dynamic Correlation ◽  
Glassy Systems ◽  
Different Temperatures ◽  
Rotational Degrees Of Freedom ◽  
Polycrystalline Structures

Critical-like behaviors have been found in translational degrees of freedom near the glass transition of spherical particle systems mainly with local polycrystalline structures, but it is not clear if criticality exists in more general glassy systems composed of nonspherical particles without crystalline structures. Here, through experiments and simulations, we show critical-like behaviors in both translational and rotational degrees of freedom in monolayers of monodisperse colloidal ellipsoids in the absence of crystalline orders. We find rich features of the Ising-like criticality in structure and slow dynamics at the ideal glass transition point ϕ0, showing the thermodynamic nature of glass transition at ϕ0. A dynamic criticality is found at the mode-coupling critical point ϕc for the fast-moving clusters whose critical exponents increase linearly with fragility, reflecting a dynamic glass transition. These results cast light on the glass transition and explain the mystery that the dynamic correlation lengths diverge at two different temperatures.

scholarly journals A Study on Physical Aging of Semicrystalline Polyethylene Terephthalate below the Glass Transition Point

2012 ◽  
Vol 10 (5) ◽  
Author(s):  
M. Farhoodi ◽  
S. M. Mousavi ◽  
R. Sotudeh-Gharebagh ◽  
Z. Emam-Djomeh ◽  
A. Oromiehie ◽  
...  
Keyword(s):  
Glass Transition ◽  
Aging Time ◽  
Polyethylene Terephthalate ◽  
Physical Aging ◽  
Degree Of Crystallinity ◽  
Glass Transition Point ◽  
Scanning Calorimetry ◽  
Different Temperatures ◽  
Dsc Method ◽  
Final Degree

Physical aging of semicrystalline polyethylene terephthalate was studied using differential scanning calorimetry(DSC). PET samples with crystallinity content of 0.28 were aged at two different temperatures, 25 and 45°C. Thesamples were stored for several days and periodically tested using DSC method. The glass transition temperature forthe samples aged at 25°C was about 73-74°C, and the position and intensity of endothermic peaks wereapproximately constant. Higher glass transition of the samples aged at 45°C, 73-86°C, was attributed to the enthalpyrelaxation process of amorphous regions of semicrystalline PET. For the samples aged at 45°C, the endothermicpeaks shifted to higher temperatures with increasing aging time. The position of the endothermic peaks determined bythe temperature of the maximum, Tmax, tended to increase with aging time for samples aged at 45°C, and theintensity of the peaks continuously increased with time; however, the results showed that the aging of PET samples at45°C even after 120 days continued the enthalpic relaxation of semicrystalline PET and that the process could bestudied by DSC method. The results also showed that the aging process could affect the final degree of crystallinity ofc-PET samples and the samples stored at 45°C showed higher degree of crystallinity than the samples aged at 25°C.

scholarly journals Configuration correlation governs slow dynamics of supercooled metallic liquids

2018 ◽  
Vol 115 (25) ◽  
pp. 6375-6380 ◽  
Author(s):  
Yuan-Chao Hu ◽  
Yan-Wei Li ◽  
Yong Yang ◽  
Peng-Fei Guan ◽  
Hai-Yang Bai ◽  
...  
Keyword(s):  
Glass Transition ◽  
Slow Dynamics ◽  
Theoretical Understanding ◽  
Correlation Lengths ◽  
Dynamic Correlation ◽  
Slowing Down ◽  
Metallic Liquids ◽  
Intrinsic Correlation ◽  
Scaling Analyses ◽  
Dynamics Simulations

The origin of dramatic slowing down of dynamics in metallic glass-forming liquids toward their glass transition temperatures is a fundamental but unresolved issue. Through extensive molecular dynamics simulations, here we show that, contrary to the previous beliefs, it is not local geometrical orderings extracted from instantaneous configurations but the intrinsic correlation between configurations that captures the structural origin governing slow dynamics. More significantly, it is demonstrated by scaling analyses that it is the correlation length extracted from configuration correlation rather than dynamic correlation lengths that is the key to determine the drastic slowdown of supercooled metallic liquids. The key role of the configuration correlation established here sheds important light on the structural origin of the mysterious glass transition and provides an essential piece of the puzzle for the development of a universal theoretical understanding of glass transition in glasses.

On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

2019 ◽  
Author(s):  
Riccardo Spezia ◽  
Hichem Dammak
Keyword(s):  
Degrees Of Freedom ◽  
Molecular Simulations ◽  
Zero Point ◽  
Thermal Bath ◽  
Unimolecular Dissociation ◽  
Point Energy ◽  
Rotational Degrees Of Freedom ◽  
The Difference ◽  
Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

scholarly journals Dislocation interactions in olivine control postseismic creep of the upper mantle

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
David Wallis ◽  
Lars N. Hansen ◽  
Angus J. Wilkinson ◽  
Ricardo A. Lebensohn
Keyword(s):  
Upper Mantle ◽  
Stress Transfer ◽  
Transient Creep ◽  
Slip Systems ◽  
Stress Distributions ◽  
Correlation Lengths ◽  
Mantle Viscosity ◽  
Dislocation Interactions ◽  
Different Temperatures ◽  
New Generation

AbstractChanges in stress applied to mantle rocks, such as those imposed by earthquakes, commonly induce a period of transient creep, which is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at temperatures ≤600 °C, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25 °C or 1150–1250 °C both preserve stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 μm. The similar stress distributions formed at these different temperatures indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle.

Effect of Rotational Degrees of Freedom on Molecular Mobility

2013 ◽  
Vol 117 (13) ◽  
pp. 6800-6806 ◽  
Author(s):  
M. Jafary-Zadeh ◽  
C. D. Reddy ◽  
Yong-Wei Zhang
Keyword(s):  
Molecular Mobility ◽  
Degrees Of Freedom ◽  
Rotational Degrees Of Freedom

Spin clusters and low-energy excitations in rare earth kagome systems

2017 ◽  
Vol 31 (01) ◽  
pp. 1630010
Author(s):  
M. J. R. Hoch
Keyword(s):  
Rare Earth ◽  
Muon Spin ◽  
Correlation Lengths ◽  
Dynamic Correlation ◽  
The Past ◽  
Spin Resonance ◽  
Muon Spin Resonance ◽  
Spin Clusters ◽  
Dependent Correlation ◽  
Model Approach

The rare earth kagome systems R3Ga5SiO[Formula: see text] (R = Nd or Pr), which are weakly frustrated antiferromagnets, do not exhibit long-range order at temperatures down to 40 mK as revealed by neutron scattering. The neutron experiments provide evidence for the emergence at low temperatures of correlated spins in nanoscale cluster regions with magnetic field-dependent correlation lengths. A variety of techniques have been used to determine the magnetic and thermal properties of these systems. In particular, high-field electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin resonance ([Formula: see text]SR) experiments have established that dynamic correlation of spins remains significant at temperatures well above 1 K. ESR provides evidence for spin wave excitations in spin clusters and the spectra have been interpreted using a Heisenberg model approach. While Nd[Formula: see text] (J = 9/2) is a Kramers ion Pr[Formula: see text] (J = 4) is not. This difference leads to contrasts in the magnetic properties of the two systems. This review surveys the information that has been obtained on the properties of these kagome materials over the past decade.

Dynamic Modeling of a High-Dynamic Flight Simulator

2014 ◽  
Vol 687-691 ◽  
pp. 610-615 ◽  
Author(s):  
Hui Liu ◽  
Li Wen Guan
Keyword(s):  
Dynamic Modeling ◽  
Degrees Of Freedom ◽  
Flight Simulator ◽  
Inverse Dynamic ◽  
Dynamic Formulation ◽  
Time Histories ◽  
Rotational Degrees Of Freedom ◽  
High Dynamic ◽  
Euler Approach ◽  
Simulation Results

High-dynamic flight simulator (HDFS), using a centrifuge as its motion base, is a machine utilized for simulating the acceleration environment associated with modern advanced tactical aircrafts. This paper models the HDFS as a robotic system with three rotational degrees of freedom. The forward and inverse dynamic formulations are carried out by the recursive Newton-Euler approach. The driving torques acting on the joints are determined on the basis of the inverse dynamic formulation. The formulation has been implemented in two numerical simulation examples, which are used for calculating the maximum torques of actuators and simulating the time-histories of kinematic and dynamic parameters of pure trapezoid Gz-load command profiles, respectively. The simulation results can be applied to the design of the control system. The dynamic modeling approach presented in this paper can also be generalized to some similar devices.

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