Search results for "Modulus"
showing 10 items of 491 documents
Biocomposite PBAT/lignin blown films with enhanced photo-stability.
2022
Lignin can be obtained as a byproduct during cellulose-rich pulp fibers production and it is habitually treated as waste or intended for low-value destinations. However, due to UV absorption and mechanical properties, lignin can contribute to the fabrication of biodegradable blown films with superior performances. In this study, it was established the suitability of lignin for manufacturing biocomposite PBAT blown films with higher stiffness and photo-oxidation resistance. The effect of the filler concentration on the melt rheological behavior in non-isothermal elongational flow was investigated. The results allowed us to choose the correct filler concentration for producing films through a…
ORMOSIL thin films: Tuning mechanical properties via a nanochemistry approach
2006
The mechanical properties (hardness and elastic modulus) of organically modified silicate thin films can be finely tuned by varying the degree of alkylation and thus the fraction of six- and four-membered siloxane rings in the organosilica matrix. This opens the way to large tunability of parameters that are of crucial practical importance for films that are finding increasing application in numerous fields ranging from microelectronics to chemical sensing.
Correlation effects in the total energy, the bulk modulus, and the lattice constant of a transition metal: Combined local-density approximation and d…
2009
We present an accurate implementation of total-energy calculations into the local-density approximation plus dynamical mean-field theory $(\text{LDA}+\text{DMFT})$ method. The electronic structure problem is solved through the full-potential linear muffin-tin orbital and Korringa-Kohn-Rostoker methods with a perturbative solver for the effective impurity suitable for moderately correlated systems. We have tested the method in detail for the case of Ni, and investigated the sensitivity of the results to the computational scheme and to the complete self-consistency. It is demonstrated that the $\text{LDA}+\text{DMFT}$ method can resolve a long-standing controversy between the LDA/generalized …
Strain pattern in supercooled liquids
2016
Investigations of strain correlations at the glass transition reveal unexpected phenomena. The shear strain fluctuations show an Eshelby-strain pattern ($\,\sim \cos{(4\theta)}/r^2\,$), characteristic for elastic response, even in liquids at long times [1]. We address this using a mode-coupling theory for the strain fluctuations in supercooled liquids and data from both, video microscopy of a two-dimensional colloidal glass former and simulations of Brownian hard disks. We show that long-ranged and long-lived strain-signatures follow a scaling law valid close to the glass transition. For large enough viscosities, the Eshelby-strain pattern is visible even on time scales longer than the stru…
Thermodynamic formalism for transport coefficients with an application to the shear modulus and shear viscosity.
2016
We discuss Onsager's thermodynamic formalism for transport coefficients and apply it to the calculation of the shear modulus and shear viscosity of a monodisperse system of repulsive particles. We focus on the concept of extensive "distance" and intensive "field" conjugated via a Fenchel-Legendre transform involving a thermodynamic(-like) potential, which allows to switch ensembles. Employing Brownian dynamics, we calculate both the shear modulus and the shear viscosity from strain fluctuations and show that they agree with direct calculations from strained and non-equilibrium simulations, respectively. We find a dependence of the fluctuations on the coupling strength to the strain reservoi…
Theory of vibrational anomalies in glasses
2015
Abstract The theory of elasticity with spatially fluctuating elastic constants (heterogeneous-elasticity theory) is reviewed. It is shown that the vibrational anomalies associated with the boson peak can be qualitatively and quantitatively explained in terms of this theory. Two versions of a mean-field theory for solving the stochastic equation of motion are presented: the coherent-potential approximation (CPA) and the self-consistent Born approximation (SCBA). It is shown that the latter is included in the former in the Gaussian and weak-disorder limit. We are able to discuss and explain cases in which the change of the vibrational spectrum by varying an external parameter can be accounted…
High-frequency vibrational density of states of a disordered solid.
2013
We investigate the high-frequency behavior of the density of vibrational states in three-dimensional elasticity theory with spatially fluctuating elastic moduli. At frequencies well above the mobility edge, instanton solutions yield an exponentially decaying density of states. The instanton solutions describe excitations, which become localized due to the disorder-induced fluctuations, which lower the sound velocity in a finite region compared to its average value. The exponentially decaying density of states (known in electronic systems as the Lifshitz tail) is governed by the statistics of a fluctuating-elasticity landscape, capable of trapping the vibrational excitations.
CCD uvby-beta photometry of young open clusters. I. The double cluster h and chi Persei
2002
We present CCD uvby-beta photometry for stars in the nuclei of the young double cluster h and chi Persei. We find that the reddening is highly variable through the h Persei nucleus, increasing from west to east, with values ranging from E(b-y)=0.328+-0.022 in the western part to E(b-y)=0.465+-0.025 in the south-east. Towards chi Persei the reddening is fairly constant, with E(b-y)=0.398+-0.025. Both clusters share a common distance modulus of 11.7+-0.1 mag., and an age of log t=7.10+-0.05 years.
Elastic moduli, dislocation core energy and melting of hard disks in two dimensions
2000
Elastic moduli and dislocation core energy of the triangular solid of hard disks of diameter $\sigma$ are obtained in the limit of vanishing dislocation- antidislocation pair density, from Monte Carlo simulations which incorporates a constraint, namely that all moves altering the local connectivity away from that of the ideal triangular lattice are rejected. In this limit, we show that the solid is stable against all other fluctuations at least upto densities as low as $\rho \sigma^2 = 0.88$. Our system does not show any phase transition so diverging correlation lengths leading to finite size effects and slow relaxations do not exist. The dislocation pair formation probability is estimated …
CCDuvbyβ photometry of the young open cluster NGC 663
2004
NGC 663 is a young, moderately rich open cluster, known to contain one of the largest fractions of Be stars among all galactic clusters. In this work we present CCD uvby-beta photometry for stars in its central area. We have used these data to obtain the main cluster physical parameters. We find that the reddening is highly variable, with values ranging from E(b-y)=0.639+/-0.032 in the central part to E(b-y)=0.555+/-0.038 in the south-east. The distance modulus is found to be 11.6+/-0.1 mag.(2.1 Kpc), and the age log t=7.4+/-0.1 years (25+7/-5 Myr). The age obtained is consistent with the interpretation of the Be phenomenon as an evolutionary effect.