Papers by Keyword: Free Energy

Abstract: Expansion of single Shockley stacking faults (SSFs) during forward current operation is an important issue, because it decreases the reliability of 4H-SiC bipolar devices. In this paper, we propose a method for analyzing SSF dynamics based on free energy under current conduction, temperature, and resolved shear stress conditions. The driving force for dislocation dissociation reactions and formation of SSFs is incorporated into the free energy function, including chemical potential, stacking fault energy, crystallographic energy, gradient energy and elastic strain energy. The net energy gain of the chemical potential was calculated as a function of temperature and current conduction through use of the a TCAD device simulator based on the Boltzmann equation, Poisson equation and the current continuity equation concerning electron and hole distributions with self-consistency. It was confirmed that SSF dynamics can be simulated by the proposed method. It was also found that SSF formation can be attributed to quantum well variation in which electrons in n-type 4H–SiC enter SSF-induced quantum well states to lower the energy of the dislocation system.

Abstract: We develop a phase field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibility constraints for the internal strain field. The long-range elastic response of the material is obtained by minimization of the free energy that accounts for higher order terms of the order parameters and symmetry-adapted strain gradients. To demonstrate the performance of the model, a minimal version of continuum dislocation dynamics is used to investigate the simultaneous evolution of the network of geometrically necessary dislocations and the internal strain field.

Abstract: Mechanical alloying (MA) is a potential processing method for various equilibrium and non-equilibrium alloy phases such as supersaturated solid solution, metastable crystalline, amorphous, quasi-crystalline phases, nanostructures. Compared to conventional high temperature material processing such as melting and casting, improvement of solid solubility limit results from mechanical alloying at room temperature. The solid solubility increases with increase in milling time due to enhanced stress assisted atomic diffusion during particle refinement and reaches a saturation level at higher milling time. The extension of solid solubility is attributed to thermodynamic, dynamic or kinetic factors such as high dislocation density due to severe plastic deformation during particle refinement and enhanced diffusivity during MA. The review aims to discuss the insight of MA than other non-equilibrium processing in terms of achieving higher solubility, reasoning and mechanism of solubility improvement during MA of different alloy systems.

Abstract: The objective of this work is to increase the power of the two wheeler miniature engines (100cc to 250cc) by supercharging the vehicle using the suspension system. For this purpose a design is made to extract compressed air from the suspension system. It has been successfully shown that the air can be extracted from the suspension system, stored and then fed into the engine similar to supercharger or turbocharger, and the engine power can be improved using this free energy.

Abstract: The effect of magnetic fields on the swelling of liquid crystal elastomers (LCE) dissolved in liquid crystal (LC) solvent have been studied. The Flory-Huggins model used to calculate the free energy of an isotropic mixing and the Maier-Saupe model used to calculate the free energy of a nematic mixing. Numerical integration method used to calculate the orientational order parameter and the total free energy of system (consists of : nematic free energy, elastic free energy, isotropic mixing free energy and magnetic free energy) and the calculation results graphed as a function of temperatures for various magnetic fields and as function of magnetic fields for various of temperatures. We find that the magnetic field shifts the transition points towards higher temperatures, increases the energy transition, and induces an isotropic phase to paranematic phase.

Abstract: This paper examines the free energy potentials of damaged solids for the construction of damage mechanics constitutive models. The physical meaning of free energy in solid mechanics is analyzed in contrast with that in traditional fields of thermodynamics; 1D stress-strain curves are used to show the relationships between various thermodynamic state functions in isothermal loading processes; and the role of plastic free energy in damage evolution is discussed both macroscopically and microscopically. It is concluded that plastic free energy, which is a macroscopic representation of some additional microscopic elastic energy, cannot do work during unloading but get released when damage takes place, constituting part of the driving force for damage evolution.

Abstract: Bainite or the mixture of bainite and martensite is required to reach high strength levels in low carbon high strength steel. However, the bainite reaction rarely goes to completion, resulting in mixed structures of predominately bainitic ferrite and minor amounts of retained austenite, cementite or martensite mainly located at the ferrite grain boundaries. The exact nature of this minor transformation product depends on several factors including bulk composition, segregation and cooling rate. When the minor phase is largely martensite, the non-bainitic microstructure is called martensite-austenite microconstituent or MA. Interestingly, MA is believed to be one of the main factors causing the deterioration of toughness of steels. MA is also often associated with hydrogen-related cracking. In this current study, the formation of martensite-austenite constituents was studied experimentally and the results analyzed theoretically.

Abstract: The algorithm for fast evaluation of the hysteresis loops of uniaxial or textured ferroelectric microcrystal or grains with long-range interactions is developed. Two types of ceramic microstructures are considered: 1. Random ceramics with complete isotropic distribution function of the crystallographic orientations of grains; and 2. Textured ceramics with anisotropic distribution function of the crystallographic orientations of grains. The qualitative analysis of the hysteretic behavior in terms of the grain distribution function is successfully demonstrated. Comparison of the calculated results with experimental data for Pb (Mg_1/3Nb_2/3)O₃ PbTiO₃ ceramics is presented.

Abstract: Pseudoknots are complicated and stable RNA structure. Based on the idea of iteratively forming stable stems, and the character that the stems in RNA molecules are relatively stable, an algorithm is presented to predict RNA secondary structure including pseudoknots, it is an improvement from the previously used algorithm ,the algorithm takes O(n³) time and O(n²) sapce , in predicting accuracy, it outperforms other known algorithm of RNA secondary structure prediction, its performance is tested with the RNA sub-sequences in PseudoBase. The experimental results indicate that the algorithm has good specificity and sensitivity.

Abstract: This paper presents a transformation kinetics model of NiTi shape memory alloy (SMA) wires based on electrical resistivity (ER) derivative study under the assumption that the derivative of electrical resistivity with respect to temperature is in linear relationship with the derivative of free energy change with respect to temperature. Free energy change and electrical resistivity properties of SMA are analyzed based on differential scanning calorimetry (DSC) experiments during phase transformation. The simulated evolution of electrical resistivity during thermomechanical transformation is presented using the proposed model.