Inherent structure switching patterns for glass-forming liquids

Gradient-descent mapping on the potential energy hypersurface locates the relevant inherent structures (local minima) during the course of MC or MD simulation runs for continuum models. Observing temporal sequences of such inherent structures is proposed as a way to clarify relaxation processes near the glass transition. Also, the importance to execute parallel MC and MD runs on the same glass model is stressed to establish a quantitative time scaling for the two to permit comparison of relaxation results.     

Viscous behaviour of glass-forming liquids: a thermodynamic approach

The temperature dependence of the viscosity of the undercooled melts exhibits an important role in the study of nucleation, crystal growth and the glass-forming ability of materials. Several attempts have been made to study the viscous behaviour of the glass-forming melts and these investigations are mainly based on free volume theory as well as on the configurational entropy model. In the present investigation, an attempt has been made to correlate the thermodynamic parameters with the viscosity of the glass-forming melts and to study the temperature dependence of the viscosity of undercooled liquids on the basis of the free volume theory as well as on the basis of the configurational entropy model of Adam and Gibbs. The entire study is confined on the expression for thermodynamic parameters reported by the authors recently. The expression obtained has been successfully applied to study the temperature dependence of the viscosity of the metallic, molecular and oxide glass-forming liquids.     

On the accuracy of direct integration methods for structural dynamics

Abstract

This paper presents a method of eigen analysis to evaluate the accuracy of the time integration method in the structural dynamic analysis of both transient and steady state responses. Accuracy measure for transient response is evaluated by period elongation and amplitude decay after a complete cycle of response of an undamped system. The proposed method is a unique measure, independent of the initial conditions. Accuracy measure for steady state response is evaluated by the amplitude decay and phase angle of a frequency response. The accuracy measure proposed by this method can be applied to all ranges of ?t/T. The significance of the large range ?t/T is discussed. The proposed method is used to evaluate the accuracy of three commonly used time integration methods: the Wilson method, the Newmark method and the Houbolt method.     

Microfluidic rheology of non-Newtonian liquids

We investigate the rheological properties of a non-Newtonian glass-former liquid within lithographically defined microchannels in the range of temperatures above the vitrification region. The non-Newtonian behavior of the fluid, as evidenced by rotational rheology, is well described by a power law dependence of the viscosity on the shear rate. Taking into account such non-Newtonian character in the equations for the microfluidic motion, we relate the penetration dynamics into capillaries with the liquid rheological properties. The temperature dependence of the viscosity, determined over 1 order of magnitude in the temperature range 286-333 K and for shear rates between 0.07 and 1 s-1, can be described by a Vogel-Fulcher-Tamman law, consistent with the fragile nature of the investigated compound. Microfluidics is a promising analytical approach for the investigation of the rheology of non-Newtonian fluids within confined microenvironments.     

Viscous and thermodynamic behaviour of glass-forming organic liquids

The free energy difference (ΔG) between an undercooled liquid and its corresponding equilibrium solid has been evaluated on the basis of a method involving Taylor series expansion of ΔG around its value at the equilibrium melting temperature. The resultant expression is shown to be capable of correctly estimating ΔG at temperatures as low as the glass transition temperature. The method is then enlarged to obtain the configurational entropy and used in conjunction with the Adam and Gibbs model to derive a novel expression for the viscosity of undercooled liquids. Most commonly used expressions for the temperature dependence of viscosity are shown to be approximations of the equation obtained in this study.     

Shear-accelerated crystallization of glass-forming metallic liquids in high-pressure die casting

As one of the most important forming technologies for industrial bulk metallic glass(BMG) parts with complex shapes, high-pressure die casting(HPDC) can fill a die cavity with a glass-forming metallic liquid in milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior in the HPDC process has never been established. In this study, we report on the solidification behavior of Zr₅₅Cu₃₀Ni₅Al₁₀ glass forming liquid un...     

Microfluidic flow-flash: method for investigating protein dynamics

We report a new method, microfluidic flow-flash, for measuring protein reaction kinetics. The method couples a microscope imaging detection system with a microfluidic flow cell to reduce data acquisition times and sample consumption. This combination allows for the simultaneous collection of spectral and temporal information. The microfluidic flow cell design utilizes three-dimensional sheath flow to reduce sample dispersion and minimize sample consumption. The ability to alter the flow rates in the microfluidic flow cells allows a variety of time scales to be studied with submillisecond time resolution. The imaging detection system can be coupled with several spectroscopic probes including fluorescence and UV/visible absorbance spectroscopy. Here, we utilize the microfluidic flow-flash method to probe the kinetics of CO recombination or O2 binding to myoglobin after the laser-induced photolysis of CO from myoglobin by UV/visible absorbance spectral imaging.     

Structural origin of enhanced slow dynamics near a wall in glass-forming systems

Spatial confinement is known to induce a drastic change in the viscosity, relaxation times, and flow profile of liquids near the glass (or jamming) transition point. The essential underlying question is how a wall affects the dynamics of densely packed systems. Here we study this fundamental problem, using experiments on a driven granular hard-sphere liquid and numerical simulations of polydisperse and bidisperse colloidal liquids. The nearly hard-core nature of the particle-wall interaction provides an ideal opportunity to study purely geometrical confinement effects. We reveal that the slower dynamics near a wall is induced by wall-induced enhancement of 'glassy structural order', which is a manifestation of strong interparticle correlations. By generalizing the structure-dynamics relation for bulk systems, we find a quantitative relation between the structural relaxation time at a certain distance from a wall and the correlation length of glassy structural order there. Our finding suggests that glassy structural ordering may be the origin of the slow glassy dynamics of a supercooled liquid.     

Simulation of glasses and glass-forming liquids after two decades: some perspectives

We comment on the current status of molecular dynamics and ion dynamics computer simulation studies with respect to advances in understanding of glass formation from viscous liquids, and suggest a classification of current glass and viscous liquid problems in terms of their accessibility to study by computer simulation methods, giving examples in each class. In class C are the problems which are accessible with modest computing facilities and one case, in which the fragility of alternative polymorphic forms of vitreous SiO₂ is assessed, is treated in some detail.     

Experimental investigation of the dynamics of the phase transition boundary in the motion of a heated non-Newtonian fluid in a channel

The process of growth of the boundary crystallized phase in the motion of a heated non-Newtonian fluid in a channel with a cold wall has been studied experimentally. As the fluid, polypropylene with pseudoplastic properties was used. Experimental curves of the growth of the wall crystallized phase as a function of time were obtained for different values of the initial fluid melt temperature. The experimental value of the Nusselt number at the solid-liquid interface has been computed.     

大块非晶形成合金液体的热物理性能与玻璃形成能力

大块非晶合金由于其优异的性能而成的具有很大潜力的新材料，而合金的玻璃形成能力（GFA）的大小是能否获得大块非晶合金的根本所在。因此研究合金的玻璃形成能力成为材料科学领域重要的研究课题。本文从液体热物理性能出发，结合在这些方面所做的研究工作对大块非晶形成合金液体的玻璃形成能力做了一些探讨，希望对大块非晶合的研究有所裨益。     

An investigation of the motion of homogeneous and stratified liquids in rectangular cavities by the method of photochromic visualization

A method of photochromic visualization has been developed for investigating thermogravitational flows in homogeneous and stratified fluids in a closed volume.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 5, pp. 760–766, May, 1990.     

Conservative Eulerian method for numerical investigation of the hydrodynamics of liquids with a free surface

An effective numerical method is suggested for investigation of the hydrodynamics of liquids with a free surface. The method is a conservative Eulerian method that is useful for investigation of processes with turbulent behavior of the surface of the liquid that are accompanied by generation of waves, splash, spatter, etc. In the present method, apart from hydrodynamic equations, a transfer equation is used to describe transfer of the liquid phase. A method of numerical solution free from grid diffusion is suggested for this equation. It is proved that the conservative Eulerian method is adequate quantitatively for modeling the motions of a liquid with a slight deformation on its surface and adequate qualitatively for complicated motions.Dneprodzerzhinsk Industrial Institute, Dneprodzerzhinsk, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 228–234, September–October, 1994.     

Wind modes for structural dynamics: a continuous approach

Load on structural systems is often represented by a multi-dimensional and/or multi-variate random process. The cross-correlation often existing between loading components acting in different points of the structure introduces conceptual and computational difficulties in many practical problems. It is the case, for example, of the projection of the external load on the vibration modes in the modal analysis of linear systems or of the simulation of multi-correlated time series for a Monte Carlo-based analysis of non-linear structures. The use of the proper orthogonal decomposition (POD) introduces some formal simplifications in the solution of the aforementioned problems, but requires the evaluation of the eigenquantities of some statistical representations of the loading process. The knowledge of such quantities in analytic form yields computational advantages and enables important physical interpretations. In the present paper, an analytic expression of POD is developed for a class of processes, which includes models usually adopted to represent the atmospheric turbulence. Examples of linear analysis of a wind-excited slender structure and of simulation of turbulence fields are presented.     

A solution method for problems of free convective motion in liquids

The solution of the problem of free convective motion of liquids with high Prandtl and Schmidt numbers is obtained in the form of inner and outer asymptotic solutions which are joined together. Boundary conditions of the first or second kind are considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 5, pp. 857–863, November, 1975.     

Molecular dynamics investigation of temperature dependent structural and fracture properties of amorphous silicon nitride

Abstract

Silicon nitride presents good mechanical properties and thermal stability at high temperature. As the experiments have limitations in the micro-/nanoscale characterisation of structural and fracture properties at high temperatures, atomistic simulation is the proper way to investigate the mechanism of this unique feature. In the present paper, the structural and fracture properties of amorphous silicon nitride (a-Si₃N₄) were studied at temperatures up to 1500 K. The simulation results consist of experiments on radial distribution function, temperature dependent yield stress and Young’s modulus. Based on the structural and mechanical results of α-Si₃N₄ at different temperatures, the structure–property correlations were discussed.     

Microfluidic device for the detection of glucose using a micro direct methanol fuel cell as an amperometric detection power source

We designed and prepared a novel microbiosensing system consisting of a microbioreactor fabricated using photosensitive sheets intercalated between Pyrex wafers as a dam structure, together with a micro fuel cell as a power source device between the electrodes for amperometric detection. The dam structure retains enzyme (glucose oxidase, GOx)-immobilized microbeads in a microchannel. Microelectrodes are used as an integrated detector within a microchannel located downstream of the dam structure, and these are used to detect the oxidation current of hydrogen peroxide produced from a glucose sample and GOx. A micro direct methanol fuel cell (mu-DMFC, i.d. 500 microm) was fabricated on a polymeric substrate and was used to supply a potential for the electrochemical detector. In this case, two mu-DMFCs were stacked on one substrate to increase the voltage for the oxidation of hydrogen peroxide. A linear response curve was obtained in range from 0.1 to 10 mM glucose for the designed microbiosensing system. These results show that a microfluidic biosensing system designed with a mu-DMFC device is useful and has the potential to assist minuaturization and simplification of the sensing system, in addition to increasing disposability of the device.     

Accuracy of a composite implicit time integration scheme for structural dynamics

A comprehensive study of the two sub‐steps composite implicit time integration scheme for the structural dynamics is presented in this paper. A framework is proposed for the convergence accuracy analysis of the generalized composite scheme. The local truncation errors of the acceleration, velocity, and displacement are evaluated in a rigorous procedure. The presented and proved accuracy condition enables the displacement, velocity, and acceleration achieving second‐order accuracy simultaneously, which avoids the drawback that the acceleration accuracy may not reach second order. The different influences of numerical frequencies and time step on the accuracy of displacement, velocity, and acceleration are clarified. The numerical dissipation and dispersion and the initial magnitude errors are investigated physically, which measure the errors from the algorithmic amplification matrix's eigenvalues and eigenvectors, respectively. The load and physically undamped/damped cases are naturally accounted. An optimal algorithm‐Bathe composite method (Bathe and Baig, 2005; Bathe, 2007; Bathe and Noh, 2012) is revealed with unconditional stability, no overshooting in displacement, velocity, and acceleration, and excellent performance compared with many other algorithms. The proposed framework also can be used for accuracy analysis and design of other multi‐sub‐steps composite schemes and single‐step methods under physical damping and/or loading. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental investigation of a direct driven radial compressor for domestic heat pumps

The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a.     

Dielectric spectroscopy of a glass-forming emulsion

The dielectric behaviour of an aqueous solution-in-oil emulsion in which the liquid within the particles forms a glassy structure on being taken below its glass transition temperature is reported. Measurements have been made for a single concentration of oil/solution/surfactant which gave a stable emulsion structure over the temperature range 225–340 K, indicating a glass transition at 218 K. The principal features of the low-frequency dielectric response are considered in terms of the model response discussed earlier by the authors and the physical bases of the individual response components are established.