Slowdown Of Dynamics Research Articles

Characterizing the Effects of the Alkyl Chain Length of Linear Organic Carbonates on Lithium Ion Electrolyte Structure and Dynamics: A Solvent Perspective

Lithium ion batteries have become the workhorse of the portable energy storage industry, yet there remains a strong need to improve their safety and efficiency. While many studies have focused on improving the electrodes or optimizing the electrolyte composition, few studies have focused on characterizing the electrolytes at the molecular level. In this work, we have utilized both steady-state and time-dependent infrared spectroscopies to characterize the structure and dynamics of the free carbonates both in neat solvents and within lithium-ion electrolytes. Time-resolved studies reveal similar dynamics of the bulk carbonates; however, a slowdown of the bulk carbonate dynamics occurs upon the addition of lithium salt. Thus, our studies reveal that the free carbonate molecules become significantly more ordered upon the addition of a lithium salt, which reveals further insight into the molecular-level structure of these electrolytes.

Surface Solvation Tunes Molecular-Recognition Plasticity in IDPs

Surface water dynamics is key to molecular-recognition in biomolecules. The role of such dynamics becomes more prominent for Intrinsically Disordered Proteins (IDPs); as molecular-recognition of IDPs is not the fallout of classical ‘structure-function’ paradigm and thus dynamics is what determines their binding characteristics. There exists great diversity in terms of binding modalities of IDPs, ranging from ultrafast transient interactions to very stable recognition, attributing multifarious functionality to IDPs. While recent experiments have linked IDP biophysics and hydration dynamics, the exact mechanism by which solvation dynamics govern such diverse molecular-recognition in IDPs remains largely unanswered.In this work, we combine site-selective fluorescent labelling with picosecond-resolved fluorescence and single-molecule FRET, to study the interplay between solvation dynamics and binding modes of IDPs. We probed dynamics of hydration water on IDP surfaces and perturbation of the same when IDPs bind their partners. We focused on two IDPs from the nucleocytoplasmic transport pathway, Nup153FG and IBB. Both these IDPs bind a nuclear transport receptor (NTR) Importinβ, albeit in very different ways. Nup153FG binds Importinβ through a set of ultrafast transient multivalent interactions without any major conformational change, retaining its disorder. We observed solvation fluctuations in the dynamic Nup153FG. Importinβ complex to be unperturbed relative to unbound Nup153FG. IBB forms a stable helix upon binding Importinβ. We detected a ∼2 fold relative slowdown of water dynamics in the IBB. Importinβ complex. Our results provide direct evidence showing interfacial water dynamics retardation to be an activation barrier, instrumental in tuning the plasticity of the complex from stable long lived to transient and dynamic. In the context of nucleocytoplasmic transport such differential behavior of these two IDPs can be linked to their functions; dynamic Nup153. NTR complex facilitate fast nucleocytoplasmic transport while stable IBB. Importinβ ensures integrity of the import-complex during a transport event.

Osmotic Pulsations of Lipid Vesicles under Hypotonic Stress

The response of lipid bilayers to osmotic stress is an important part of cellular function. It has been shown that cell-sized giant unilamellar vesicles (GUVs) exposed to hypotonic media, respond to the osmotic assault by undergoing a cyclical sequence of swelling and bursting events, coupled to the membrane's compositional degrees of freedom. In this work, we seek to establish a fundamental and quantitative understanding of the essential pulsatile behavior of GUVs under hypotonic conditions, by advancing a comprehensive theoretical model for vesicle dynamics. We combine experimental and theoretical approaches to characterize the swell-burst cycles of GUVs under hypotonic conditions. We first focus on the membrane rupture mechanism, and show that thermal fluctuations enable stochastic pore nucleations, leading to a dependence of the lytic strain on the load rates. Second, we emphasize the role of solute diffusion in the leak-out process, responsible for the slowdown of the pulsatile dynamics. Finally, we unravel new scaling relationships between the pulsatile dynamics and the GUV properties. Our findings provide a fundamental framework that has the potential to guide future investigations on the non-equilibrium dynamics of vesicles under osmotic stress.

ЕВРАЗИЙСКИЙ ЭКОНОМИЧЕСКИЙ СОЮЗ: В ПОПЫТКЕ ИЗБЕЖАТЬ ПОСТСОВЕТСКОЙ ИНТЕГРАЦИОННОЙ PATH DEPENDENCE

The article analyzes the issue of development of regional integration processes and for-mation of integration structures within post-Soviet space. Within the last decade one of the most dynamically evolving regional integration project is so called the “Eurasian project”? connected with the creation of Eurasian economic union (EAEU). At the moment this integration structure is not a full-fledged one and is susceptible to a number of specific risks. One of the major one is dependence on the deep-rooted “bad integration practices”, or post-Soviet integration path dependence. Previously it led to slowdown of in-tegration dynamics, decrease of effectiveness as well as decay of integration structures. In order to es-cape it, the EAEU should strive to increase its effectiveness on the basic of selecting valid integration model, working out straightforward integration strategy and proper usage of mechanisms of integration cooperation.

The study of diffusion mechanism in network-forming liquid: Silica liquid

Molecular dynamics simulation is employed to investigate the diffusion mechanism in silica melt, a typical network-forming liquid. From the analysis of SiOx→SiOx±1 and OSiy→OSiy±1 reactions we reveal two moving modes: fast hopping and slow collective moving. Accordingly the atoms diffuse in the melt by simple hopping or through displacing of super-molecule (SM). A cluster analysis is performed for several of atom sets. It is shown that the melt exhibits non-uniform spatial distribution of reaction which causes the dynamics heterogeneity (DH). Further, the network structure of the melt consists of main subnet and large defective subnets. These subnets differ strongly in local environment, chemical composition and atomic density. This result evidences two distinct phases, the structure heterogeneity in silica melt and supports the polymorphism of network-forming liquid. We also find out that the node transformation spreads non-uniformly through the network structure. It takes place mainly in large defective subnet. The strong localization of node transformation is responsible for dynamical slowdown.

Critical scaling of icosahedral medium-range order in CuZr metallic glass-forming liquids.

The temperature evolution of icosahedral medium-range order formed by interpenetrating icosahedra in CuZr metallic glassforming liquids was investigated via molecular dynamics simulations. Scaling analysis based on percolation theory was employed, and it is found that the size distribution of clusters formed by the central atoms of icosahedra at various temperatures follows a very good scaling law with the cluster number density scaled by S−τ and the cluster size S scaled by |1 − Tc/T|−1/σ, respectively. Here Tc is scaling crossover-temperature. τ and σ are scaling exponents. The critical scaling behaviour suggests that there would be a structural phase transition manifested by percolation of locally favoured structures underlying the glass transition, if the liquid could be cooled slowly enough but without crystallization intervening. Furthermore, it is revealed that when icosahedral short-range order (ISRO) extends to medium-range length scale by connection, the atomic configurations of ISROs will be optimized from distorted ones towards more regular ones gradually, which significantly lowers the energies of ISROs and introduces geometric frustration simultaneously. Both factors make key impacts on the drastic dynamic slow-down of supercooled liquids. Our findings provide direct structure-property relationship for understanding the nature of glass transition.

FOXO/DAF-16 Activation Slows Down Turnover of the Majority of Proteins in C. elegans

SummaryMost aging hypotheses assume the accumulation of damage, resulting in gradual physiological decline and, ultimately, death. Avoiding protein damage accumulation by enhanced turnover should slow down the aging process and extend the lifespan. However, lowering translational efficiency extends rather than shortens the lifespan in C. elegans. We studied turnover of individual proteins in the long-lived daf-2 mutant by combining SILeNCe (stable isotope labeling by nitrogen in Caenorhabditis elegans) and mass spectrometry. Intriguingly, the majority of proteins displayed prolonged half-lives in daf-2, whereas others remained unchanged, signifying that longevity is not supported by high protein turnover. This slowdown was most prominent for translation-related and mitochondrial proteins. In contrast, the high turnover of lysosomal hydrolases and very low turnover of cytoskeletal proteins remained largely unchanged. The slowdown of protein dynamics and decreased abundance of the translational machinery may point to the importance of anabolic attenuation in lifespan extension, as suggested by the hyperfunction theory.

The study of diffusion in network-forming liquids under pressure and temperature

In this paper, the molecular dynamics simulation is applied to investigate the diffusion in silica liquids under different temperature and pressure. We show that the diffusion is controlled by the rate of effective SiOx→SiOx±1 and OSiy→OSiy±1 reaction. With increasing the pressure, the rate of reaction increases and the Si–O bond is weaker. Moreover, the reactions are not uniformly distributed in the space, but instead they happen frequently or rarely in separate regions. We also reveal two motion types: free and correlation motion. The correlation motion concerns the moving of a group of atoms which is similar to that of the diffusion of a super-molecule in the liquid. A detailed analysis of the movement of atoms from specified set shows the clustering of them which indicates structure and dynamics heterogeneity. Further, we find that the correlation motion is very important for the diffusion in network-forming liquid. The observed phenomena such as diffusion anomaly, dynamics heterogeneity and dynamical slowdown are originated from the correlation motion of atom.

The study of dynamics heterogeneity and slow down of silica by molecular dynamics simulation

We have numerically studied the diffusion in silica liquids via the SiOx → SiOx±1, OSiy → OSiy±1 reactions and coordination cells (CC). Five models with temperatures from 1000 to 3500 K have been constructed by molecular dynamics simulation. We reveal that the reactions happen not randomly in the space. In addition, the reactions correlated strongly with the mobility of CC atom. Further we examine the clustering of atoms having unbroken bonds and restored bonds. The time evolution of these clusters under temperature is also considered. The simulation shows that both slow down and dynamic heterogeneity (DH) is related not only to the percolation of restored-rigid clusters near glass transition but also to their long lifetime.

Structural Interpretation of the Large Slowdown of Water Dynamics at Stacked Phospholipid Membranes for Decreasing Hydration Level: All-Atom Molecular Dynamics.

Hydration water determines the stability and function of phospholipid membranes as well as the interaction of membranes with other molecules. Experiments and simulations have shown that water dynamics slows down dramatically as the hydration decreases, suggesting that the interfacial water that dominates the average dynamics at low hydration is slower than water away from the membrane. Here, based on all-atom molecular dynamics simulations, we provide an interpretation of the slowdown of interfacial water in terms of the structure and dynamics of water–water and water–lipid hydrogen bonds (HBs). We calculate the rotational and translational slowdown of the dynamics of water confined in stacked phospholipid membranes at different levels of hydration, from completely hydrated to poorly hydrated membranes. For all hydrations, we analyze the distribution of HBs and find that water–lipids HBs last longer than water–water HBs and that at low hydration most of the water is in the interior of the membrane. We also show that water–water HBs become more persistent as the hydration is lowered. We attribute this effect (i) to HBs between water molecules that form, in turn, persistent HBs with lipids; (ii) to the hindering of the H-bonding switching between water molecules due to the lower water density at the interface; and (iii) to the higher probability of water–lipid HBs as the hydration decreases. Our interpretation of the large dynamic slowdown in water under dehydration is potentially relevant in understanding membrane biophysics at different hydration levels.

About the diffusion mechanism in the silica liquid

In this paper, we have numerically studied the diffusion mechanism in silica liquid based on the idea that the collective movement of particles is controlled by reactions [Formula: see text] and [Formula: see text]. Four models at temperatures from 2600 K to 3500 K have been constructed by molecular dynamic simulation. The simulation shows that the liquid has a small amount of defect-cells which are of importance for the diffusion. In particular, the majority of reactions happen via defect-cells SiO5 and OSi3. Moreover, the defect-cells do not uniformly distribute in the liquid, but they have a tendency to locate nearby forming large cluster. Further, it is revealed that the spatial distribution of reactions is heterogeneous. We found two distinct clusters. First cluster (none-reaction cluster) consists of particles on which no reaction happens. The second cluster (reaction cluster) includes particles where the reactions happen. The size of clusters found is dependent with temperature and diffusion time. Moreover, the mobility of particles in none-reaction cluster is significantly smaller than in reaction cluster. This indicates the dynamics heterogeneity in the liquid. We suggest that the dynamics slowdown is originated from the percolation of none-reaction cluster.

Efficient measurement of point-to-set correlations and overlap fluctuations in glass-forming liquids.

Cavity point-to-set correlations are real-space tools to detect the roughening of the free-energy landscape that accompanies the dynamical slowdown of glass-forming liquids. Measuring these correlations in model glass formers remains, however, a major computational challenge. Here, we develop a general parallel-tempering method that provides orders-of-magnitude improvement for sampling and equilibrating configurations within cavities. We apply this improved scheme to the canonical Kob-Andersen binary Lennard-Jones model for temperatures down to the mode-coupling theory crossover. Most significant improvements are noted for small cavities, which have thus far been the most difficult to study. This methodological advance also enables us to study a broader range of physical observables associated with thermodynamic fluctuations. We measure the probability distribution of overlap fluctuations in cavities, which displays a non-trivial temperature evolution. The corresponding overlap susceptibility is found to provide a robust quantitative estimate of the point-to-set length scale requiring no fitting. By resolving spatial fluctuations of the overlap in the cavity, we also obtain quantitative information about the geometry of overlap fluctuations. We can thus examine in detail how the penetration length as well as its fluctuations evolve with temperature and cavity size.

The Insurance Market in the Republic of Crimea and Sevastopol: The Issues of Adaptation to the Russain Law

The results of January-September 2013 point to the continued trend in economic growth slowdown. Within the above period, the industrial production index amounted to 100.1% on January-September 2012, including that of manufacturing industry which was equal to 99.7%. The index of agricultural industry happened to be below the expected mid-year values and was at the level of 101.8% as compared to January-September 2012. In the building and investment complex, a slump intensified by quarters of the current year. In January-September 2013, investments in capital assets decreased by 1.9%, while in the 3rd quarter, by 1.2% on the respective period of the previous year. A dramatic slowdown of the dynamics of GDP takes place with preservation of the trend towards growth in wages and salaries which situation increases the risks of downfall of financial indices of economic activities.

Pinning of the Contact Line during Evaporation on Heterogeneous Surfaces: Slowdown or Temporary Immobilization? Insights from a Nanoscale Study.

The question of the effect of surface heterogeneities on the evaporation of liquid droplets from solid surfaces is addressed through nonequilibrium molecular dynamics simulations. The mechanism behind contact line pinning which is still unclear is discussed in detail on the nanoscale. Model systems with the Lennard-Jones interaction potential were employed to study the evaporation of nanometer-sized cylindrical droplets from a flat surface. The heterogeneity of the surface was modeled through alternating stripes of equal width but two chemical types. The first type leads to a contact angle of 67°, and the other leads to a contact angle of 115°. The stripe width was varied between 2 and 20 liquid-particle diameters. On the surface with the narrowest stripes, evaporation occurred at constant contact angle as if the surface was homogeneous, with a value of the contact angle as predicted by the regular Cassie-Baxter equation. When the width was increased, the contact angle oscillated during evaporation between two boundaries whose values depend on the stripe width. The evaporation behavior was thus found to be a direct signature of the typical size of the surface heterogeneity domains. The contact angle both at equilibrium and during evaporation could be predicted from a local Cassie-Baxter equation in which the surface composition within a distance of seven fluid-particle diameters around the contact line was considered, confirming the local nature of the interactions that drive the wetting behavior of droplets. More importantly, we propose a nanoscale explanation of pinning during evaporation. Pinning should be interpreted as a drastic slowdown of the contact line dynamics rather than a complete immobilization of it during a transition between two contact angle boundaries.

Critical slowing down of the charge carrier dynamics at the Mott metal-insulator transition.

We report on the dramatic slowing down of the charge carrier dynamics in a quasi-two-dimensional organic conductor, which can be reversibly tuned through the Mott metal-insulator transition (MIT). At the finite-temperature critical end point, we observe a divergent increase of the resistance fluctuations accompanied by a drastic shift of spectral weight to low frequencies, demonstrating the critical slowing down of the order parameter (doublon density) fluctuations. The slow dynamics is accompanied by non-Gaussian fluctuations, indicative of correlated charge carrier dynamics. A possible explanation is a glassy freezing of the electronic system as a precursor of the Mott MIT.

Ultrafast 2D-IR and simulation investigations of preferential solvation and cosolvent exchange dynamics.

Using a derivative of the vitamin biotin labeled with a transition-metal carbonyl vibrational probe in a series of aqueous N,N-dimethylformamide (DMF) solutions, we observe a striking slowdown in spectral diffusion dynamics with decreased DMF concentration. Equilibrium solvation dynamics, measured with the rapidly acquired spectral diffusion (RASD) technique, a variant of heterodyne-detected photon-echo peak shift experiments, range from 1 ps in neat DMF to ∼3 ps in 0.07 mole fraction DMF/water solution. Molecular dynamics simulations of the biotin-metal carbonyl solute in explicit aqueous DMF solutions show marked preferential solvation by DMF, which becomes more pronounced at lower DMF concentrations. The simulations and the experimental data are consistent with an interpretation where the slowdown in spectral diffusion is due to solvent exchange involving distinct cosolvent species. A simple two-component model reproduces the observed spectral dynamics as well as the DMF concentration dependence, enabling the extraction of the solvent exchange time scale of 8 ps. This time scale corresponds to the diffusive motion of a few Å, consistent with a solvent-exchange mechanism. Unlike most previous studies of solvation dynamics in binary mixtures of polar solvents, our work highlights the ability of vibrational probes to sense solvent exchange as a new, slow component in the spectral diffusion dynamics.

On the interplay between the slowdown of dynamics and the kinetics of aggregation: The case study of a reactive binary mixture.

Modeling the kinetics of aggregation requires a proper strategy to take into account not only the reactivity of reagents but also the ability they have to diffuse. The lack of direct information about diffusion represents the most serious experimental obstacle to the use of diffusion-corrected mean-field equations, which is usually overcome by using information on the structural relaxation dynamics. A very accurate description of the entire kinetics of aggregation can be made by introducing a single time scale of diffusion, set by the structural relaxation time τ of the system according to ∼τ(ξ), with ξ a fractional exponent. Here, we apply this modeling to the case of a reactive binary mixture made of diglycidyl ether of bisphenol-A and 1,3-phenylenediamine, where the reaction proceeds along an autocatalyic (hydroxyl catalyzed) and a non-catalytic (impurity catalyzed) pathway and find that a very small value of the exponent ξ = 0.27 ± 0.03 is needed to reproduce all the data. Our results help revise some preconceived ideas: contrary to widely held assumptions, we find that (i) the time scale of diffusion neither increases proportionally to the structural relaxation time nor is related to τ by a power law with the same fractional exponent as that relating τ to conductivity; (ii) no direct connection exists between the transition to diffusion-control and the development of a gel network or formation of a glassy phase; and (iii) there is no significant difference in the enthalpy barrier for bond formation in the presence of hydroxyl or other than hydroxyl catalyst groups.

Quasi-isothermal and heat–cool protocols from MT-DSC

Understanding the evolution of the cooperative molecular mobility as a function of time and temperature remains an unsolved question in condensed matter physics. Many recent works concern the question of the molecular dynamic slowdown in a temperature domain ranging from the crossover temperature T c (beginning of cooperative relaxation) down to the calorimetric glass transition temperature T g. Recent studies have shown that the estimation of cooperativity length based on calorimetric investigations using Donth’s approach can be extended to a wider temperature range from T g to T c. To describe the relaxation time evolution and the characteristic length evolution of cooperative motions, besides the Donth’s fluctuation approach other models exist in the literature such as “4 points correlation function” model. Whatever the model used, calorimetric investigations are needed to estimate the heat capacity as a function of the temperature. In this work, we have focused our attention on the modulated temperature differential scanning calorimetry (MT-DSC) experiments and we have tested different MT-DSC protocols allowing the heat capacity determination. For this goal we decided to work on different amorphous glass formers in order to cover a large range of glass transition temperature. The influence of the protocol used on the cooperativity length calculation is discussed in detail. Lissajous figures were constructed to verify whether the steady state is reached.

Glassy slowdown and replica-symmetry-breaking instantons.

Glass-forming liquids exhibit a dramatic dynamical slowdown as the temperature is lowered. This can be attributed to relaxation proceeding via large structural rearrangements whose characteristic size increases as the system cools. These cooperative rearrangements are well modeled by instantons in a replica effective field theory, with the size of the dominant instanton encoding the liquid's cavity point-to-set correlation length. Varying the parameters of the effective theory corresponds to varying the statistics of the underlying free-energy landscape. We demonstrate that, for a wide range of parameters, replica-symmetry-breaking instantons dominate. The detailed structure of the dominant instanton provides a rich window into point-to-set correlations and glassy dynamics.

Tunable dielectric constant of water at the nanoscale.

Using molecular dynamics simulations, the influence of the surface charge density of a nanotube on the static dielectric permittivity ε of confined water was reported. Whereas the dielectric anisotropy between the radial and axial directions of water confined in hydrophilic and hydrophobic membranes and the increase in axial dielectric permittivity with respect to the bulk value have previously been described, we found that an increase in the surface charge density leads to a drastic decrease in ε into the axial direction. The decrease in ε is accompanied by a strong slowdown in the rotational dynamics of water molecules. We show that this effect is due to the strong orientation of water molecules induced by the surface charge. Thus, by controlling the surface charge in nanotubes and nanocavities, it is possible to tune the dielectric permittivity of confined fluids at the nanoscale.