Modelling of Strains During SAW Surfacing Taking into Heat of the Weld in Temperature Field Description and Phase Transformations

NASA Astrophysics Data System (ADS)

Winczek, J.; Makles, K.; Gucwa, M.; Gnatowska, R.; Hatala, M.

2017-08-01

In the paper, the model of the thermal and structural strain calculation in a steel element during single-pass SAW surfacing is presented. The temperature field is described analytically assuming a bimodal volumetric model of heat source and a semi-infinite body model of the surfaced (rebuilt) workpiece. The electric arc is treated physically as one heat source. Part of the heat is transferred by the direct impact of the electric arc, while another part of the heat is transferred to the weld by the melted material of the electrode. Kinetics of phase transformations during heating is limited by temperature values at the beginning and at the end of austenitic transformation, while the progress of phase transformations during cooling is determined on the basis of TTT-welding diagramand JMA-K law for diffusive transformations, and K-M law for martensitic transformation. Totalstrains equal to the sum ofthermaland structuralstrainsinduced by phasetransformationsin weldingcycle.

Heat storage in alloy transformations

NASA Technical Reports Server (NTRS)

Birchenall, C. E.; Gueceri, S. I.; Farkas, D.; Labdon, M. B.; Nagaswami, N.; Pregger, B.

1981-01-01

The feasibility of using metal alloys as thermal energy storage media was determined. The following major elements were studied: (1) identification of congruently transforming alloys and thermochemical property measurements; (2) development of a precise and convenient method for measuring volume change during phase transformation and thermal expansion coefficients; (3) development of a numerical modeling routine for calculating heat flow in cylindrical heat exchangers containing phase change materials; and (4) identification of materials that could be used to contain the metal alloys. Several eutectic alloys and ternary intermetallic phases were determined. A method employing X-ray absorption techniques was developed to determine the coefficients of thermal expansion of both the solid and liquid phases and the volume change during phase transformation from data obtained during one continuous experimental test. The method and apparatus are discussed and the experimental results are presented. The development of the numerical modeling method is presented and results are discussed for both salt and metal alloy phase change media.

Preliminary Reports, Memoranda and Technical Notes of the Materials Research Council Summer Conference La Jolla, California,

DTIC Science & Technology

1980-07-01

are many possible sources of acoustic emission. Some examples are, fracture of brittle particles , martensitic phase transformations , twinning, grain...Model for Some Martensitic Phase Transformations B. Budiansky .............. ........ . .... 374 ! TITLE PAGE S Fracture Toughness and Tensile Strength...the stress-induced phase transformation of a second phase of embedded particles such as zirconia. In a way which is not clearly understood, the zone of

Computer simulations of austenite decomposition of microalloyed 700 MPa steel during cooling

NASA Astrophysics Data System (ADS)

Pohjonen, Aarne; Paananen, Joni; Mourujärvi, Juho; Manninen, Timo; Larkiola, Jari; Porter, David

2018-05-01

We present computer simulations of austenite decomposition to ferrite and bainite during cooling. The phase transformation model is based on Johnson-Mehl-Avrami-Kolmogorov type equations. The model is parameterized by numerical fitting to continuous cooling data obtained with Gleeble thermo-mechanical simulator and it can be used for calculation of the transformation behavior occurring during cooling along any cooling path. The phase transformation model has been coupled with heat conduction simulations. The model includes separate parameters to account for the incubation stage and for the kinetics after the transformation has started. The incubation time is calculated with inversion of the CCT transformation start time. For heat conduction simulations we employed our own parallelized 2-dimensional finite difference code. In addition, the transformation model was also implemented as a subroutine in commercial finite-element software Abaqus which allows for the use of the model in various engineering applications.

Differential scanning calorimetry study and computer modeling of β ⇒ α phase transformation in a Ti-6Al-4V alloy

NASA Astrophysics Data System (ADS)

Malinov, S.; Guo, Z.; Sha, W.; Wilson, A.

2001-04-01

The relationship between heat-treatment parameters and microstructure in titanium alloys has so far been mainly studied empirically, using characterization techniques such as microscopy. Calculation and modeling of the kinetics of phase transformation have not yet been widely used for these alloys. Differential scanning calorimetry (DSC) has been widely used for the study of a variety of phase transformations. There has been much work done on the calculation and modeling of the kinetics of phase transformations for different systems based on the results from DSC study. In the present work, the kinetics of the β ⇒ α transformation in a Ti-6Al-4V titanium alloy were studied using DSC, at continuous cooling conditions with constant cooling rates of 5 °C, 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C/min. The results from calorimetry were then used to trace and model the transformation kinetics in continuous cooling conditions. Based on suitably interpreted DSC results, continuous cooling-transformation (CCT) diagrams were calculated with lines of isotransformed fraction. The kinetics of transformation were modeled using the Johnson-Mehl-Avrami (JMA) theory and by applying the “concept of additivity.” The JMA kinetic parameters were derived. Good agreement between the calculated and experimental transformed fractions is demonstrated. Using the derived kinetic parameters, the β ⇒ α transformation in a Ti-6Al-4V alloy can be described for any cooling path and condition. An interpretation of the results from the point of view of activation energy for nucleation is also presented.

Transformative occupational therapy: We are wired to be transformers.

PubMed

Dubouloz, Claire-Jehanne

2014-10-01

Transformative learning involves critical self-reflection as the motor for transforming values, beliefs, knowledge, and feelings and discovering the new meaning of daily life following a catastrophic injury or illness. Transformation has been conceptualized in various disciplines as a transcendent experience, rebirth process, and meaning-making process and within occupational therapy as a meaning perspective process. This Muriel Driver lecture explores the concept of transformation and presents the newly developed Meaning Perspectives Transformation model, constructed from research conducted with several different rehabilitation client groups. The model is characterized by three phases: trigger, changing, and outcomes. A client's critical self-reflection acts as a catalyst for moving between the phases and is represented in the model as a moment of readiness for change leading to the development of alternative ways of performing. The Meaning Perspectives Transformation model provides a tool for being an effective occupational therapist, encouraging therapists to listen closely to their clients to identify their weakening and emerging meaning perspectives and enable their occupational evolution and transformation.

Effect of lattice-mismatch-induced strains on coupled diffusive and displacive phase transformations

NASA Astrophysics Data System (ADS)

Bouville, Mathieu; Ahluwalia, Rajeev

2007-02-01

Materials which can undergo slow diffusive transformations as well as fast displacive transformations are studied using the phase-field method. The model captures the essential features of the time-temperature-transformation (TTT) diagrams, continuous cooling transformation (CCT) diagrams, and microstructure formation of these alloys. In some material systems there can exist an intrinsic volume change associated with these transformations. We show that these coherency strains can stabilize mixed microstructures (such as retained austenite-martensite and pearlite-martensite mixtures) by an interplay between diffusive and displacive mechanisms, which can alter TTT and CCT diagrams. Depending on the conditions there can be competitive or cooperative nucleation of the two kinds of phases. The model also shows that small differences in volume changes can have noticeable effects on the early stages of martensite formation and on the resulting microstructures.

A uniaxial constitutive model for superelastic NiTi SMA including R-phase and martensite transformations and thermal effects

NASA Astrophysics Data System (ADS)

Helbert, Guillaume; Saint-Sulpice, Luc; Arbab Chirani, Shabnam; Dieng, Lamine; Lecompte, Thibaut; Calloch, Sylvain; Pilvin, Philippe

2017-02-01

The well-known martensitic transformation is not always the unique solid-solid phase change in NiTi shape memory alloys (SMA). For this material, R-phase can occur from both austenite and martensite. In some applications, macroscopic strain of the material can be limited to 2%. In these cases, R-phase contribution can not be neglected anymore when compared with martensite. Furthermore, different thermomechanical couplings have to be taken into account to carefully predict strain rate effects and to better describe application conditions. In this paper, a new model taking into account various phase transformations with thermomechanical couplings is presented. This model is based on several transformation criteria. In most applications, SMA are used as wires, submitted to tensile-tensile loadings, in the superelasticity working range. Consequently, a uniaxial reduction of the model is presented for its simplicity. A thermodynamic framework is proposed. It enables to describe the internal variables evolution laws. The simple and fast identification process of model parameters is briefly presented. To verify the validity of the proposed model, simulation results are compared with experimental ones. The influences of testing temperature and strain amplitude on the material behavior is discussed. The damping capacity is also studied, using an energy-based criterion.

Prediction of Continuous Cooling Transformation Diagrams for Dual-Phase Steels from the Intercritical Region

NASA Astrophysics Data System (ADS)

Colla, V.; Desanctis, M.; Dimatteo, A.; Lovicu, G.; Valentini, R.

2011-09-01

The purpose of the present work is the implementation and validation of a model able to predict the microstructure changes and the mechanical properties in the modern high-strength dual-phase steels after the continuous annealing process line (CAPL) and galvanizing (Galv) process. Experimental continuous cooling transformation (CCT) diagrams for 13 differently alloying dual-phase steels were measured by dilatometry from the intercritical range and were used to tune the parameters of the microstructural prediction module of the model. Mechanical properties and microstructural features were measured for more than 400 dual-phase steels simulating the CAPL and Galv industrial process, and the results were used to construct the mechanical model that predicts mechanical properties from microstructural features, chemistry, and process parameters. The model was validated and proved its efficiency in reproducing the transformation kinetic and mechanical properties of dual-phase steels produced by typical industrial process. Although it is limited to the dual-phase grades and chemical compositions explored, this model will constitute a useful tool for the steel industry.

Two-dimensional lithium diffusion behavior and probable hybrid phase transformation kinetics in olivine lithium iron phosphate

DOE PAGES

Hong, Liang; Li, Linsen; Chen-Wiegart, Yuchen-Karen; ...

2017-10-30

Olivine lithium iron phosphate is a technologically important electrode material for lithium-ion batteries and a model system for studying electrochemically driven phase transformations. Despite extensive studies, many aspects of the phase transformation and lithium transport in this material are still not well understood. Here we combine operando hard X-ray spectroscopic imaging and phase-field modeling to elucidate the delithiation dynamics of single-crystal lithium iron phosphate microrods with long-axis along the [010] direction. Lithium diffusivity is found to be two-dimensional in microsized particles containing ~3%lithium-iron anti-site defects. Our study provides direct evidence for the previously predicted surface reaction-limited phase-boundary migration mechanism andmore » the potential operation of a hybrid mode of phase growth, in which phase-boundary movement is controlled by surface reaction or lithium diffusion in different crystallographic directions. These findings uncover the rich phase-transformation behaviors in lithium iron phosphate and intercalation com-pounds in general and can help guide the design of better electrodes.« less

Two-dimensional lithium diffusion behavior and probable hybrid phase transformation kinetics in olivine lithium iron phosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Liang; Li, Linsen; Chen-Wiegart, Yuchen-Karen

Olivine lithium iron phosphate is a technologically important electrode material for lithium-ion batteries and a model system for studying electrochemically driven phase transformations. Despite extensive studies, many aspects of the phase transformation and lithium transport in this material are still not well understood. Here we combine operando hard X-ray spectroscopic imaging and phase-field modeling to elucidate the delithiation dynamics of single-crystal lithium iron phosphate microrods with long-axis along the [010] direction. Lithium diffusivity is found to be two-dimensional in microsized particles containing ~3%lithium-iron anti-site defects. Our study provides direct evidence for the previously predicted surface reaction-limited phase-boundary migration mechanism andmore » the potential operation of a hybrid mode of phase growth, in which phase-boundary movement is controlled by surface reaction or lithium diffusion in different crystallographic directions. These findings uncover the rich phase-transformation behaviors in lithium iron phosphate and intercalation com-pounds in general and can help guide the design of better electrodes.« less

Two-dimensional lithium diffusion behavior and probable hybrid phase transformation kinetics in olivine lithium iron phosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Liang; Chen-Wiegart, Yu-Chen K.

2017-10-30

Olivine lithium iron phosphate is a technologically important electrode material for lithium-ion batteries and a model system for studying electrochemically driven phase transformations. Despite extensive studies, many aspects of the phase transformation and lithium transport in this material are still not well understood. Here we combine operando hard X-ray spectroscopic imaging and phase-field modeling to elucidate the delithiation dynamics of single-crystal lithium iron phosphate microrods with long-axis along the [010] direction. Lithium diffusivity is found to be two-dimensional in microsized particles containing ~3%lithium-iron anti-site defects. Our study provides direct evidence for the previously predicted surface reaction-limited phase-boundary migration mechanism andmore » the potential operation of a hybrid mode of phase growth, in which phase-boundary movement is controlled by surface reaction or lithium diffusion in different crystallographic directions. These findings uncover the rich phase-transformation behaviors in lithium iron phosphate and intercalation com-pounds in general and can help guide the design of better electrodes.« less

Finite size effects in phase transformation kinetics in thin films and surface layers

NASA Astrophysics Data System (ADS)

Trofimov, Vladimir I.; Trofimov, Ilya V.; Kim, Jong-Il

2004-02-01

In studies of phase transformation kinetics in thin films, e.g. crystallization of amorphous films, until recent time is widely used familiar Kolmogorov-Johnson-Mehl-Avrami (KJMA) statistical model of crystallization despite it is applicable only to an infinite medium. In this paper a model of transformation kinetics in thin films based on a concept of the survival probability for randomly chosen point during transformation process is presented. Two model versions: volume induced transformation (VIT) when the second-phase grains nucleate over a whole film volume and surface induced transformation (SIT) when they form on an interface with two nucleation mode: instantaneous nucleation at transformation onset and continuous one during all the process are studied. At VIT-process due to the finite film thickness effects the transformation profile has a maximum in a film middle, whereas that of the grains population reaches a minimum inhere, the grains density is always higher than in a volume material, and the thinner film the slower it transforms. The transformation kinetics in a thin film obeys a generalized KJMA equation with parameters depending on a film thickness and in limiting cases of extremely thin and thick film it reduces to classical KJMA equation for 2D- and 3D-system, respectively.

Phase-field modeling of the beta to omega phase transformation in Zr–Nb alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeddu, Hemantha Kumar; Lookman, Turab

A three-dimensional elastoplastic phase-field model is developed, using the Finite Element Method (FEM), for modeling the athermal beta to omega phase transformation in Zr–Nb alloys by including plastic deformation and strain hardening of the material. The microstructure evolution during athermal transformation as well as under different stress states, e.g. uni-axial tensile and compressive, bi-axial tensile and compressive, shear and tri-axial loadings, is studied. The effects of plasticity, stress states and the stress loading direction on the microstructure evolution as well as on the mechanical properties are studied. The input data corresponding to a Zr – 8 at.% Nb alloy aremore » acquired from experimental studies as well as by using the CALPHAD method. Our simulations show that the four different omega variants grow as ellipsoidal shaped particles. Our results show that due to stress relaxation, the athermal phase transformation occurs slightly more readily in the presence of plasticity compared to that in its absence. The evolution of omega phase is different under different stress states, which leads to the differences in the mechanical properties of the material. The variant selection mechanism, i.e. formation of different variants under different stress loading directions, is also nicely captured by our model.« less

Atomistic to Continuum Multiscale and Multiphysics Simulation of NiTi Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Gur, Sourav

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process (transformation temperature, phase fraction evolution kinetics due to temperature) are also demonstrated herein. Next, to couple and transfer the statistical information of length scale dependent phase transformation process, multiscale/ multiphysics methods are used. Here, the computational difficulty from the fact that the representative governing equations (i.e. different sub-methods such as molecular dynamics simulations, phase field simulations and continuum level constitutive/ material models) are only valid or can be implemented over a range of spatiotemporal scales. Therefore, in the present study, a wavelet based multiscale coupling method is used, where simulation results (phase fraction evolution kinetics) from different sub-methods are linked via concurrent multiscale coupling fashion. Finally, these multiscale/ multiphysics simulation results are used to develop/ modify the macro/ continuum scale thermo-mechanical constitutive relations for NiTi SMA. Finally, the improved material model is used to model new devices, such as thermal diodes and smart dampers.

Prediction and Optimization of Phase Transformation Region After Spot Continual Induction Hardening Process Using Response Surface Method

NASA Astrophysics Data System (ADS)

Qin, Xunpeng; Gao, Kai; Zhu, Zhenhua; Chen, Xuliang; Wang, Zhou

2017-09-01

The spot continual induction hardening (SCIH) process, which is a modified induction hardening, can be assembled to a five-axis cooperating computer numerical control machine tool to strengthen more than one small area or relatively large area on complicated component surface. In this study, a response surface method was presented to optimize phase transformation region after the SCIH process. The effects of five process parameters including feed velocity, input power, gap, curvature and flow rate on temperature, microstructure, microhardness and phase transformation geometry were investigated. Central composition design, a second-order response surface design, was employed to systematically estimate the empirical models of temperature and phase transformation geometry. The analysis results indicated that feed velocity has a dominant effect on the uniformity of microstructure and microhardness, domain size, oxidized track width, phase transformation width and height in the SCIH process while curvature has the largest effect on center temperature in the design space. The optimum operating conditions with 0.817, 0.845 and 0.773 of desirability values are expected to be able to minimize ratio (tempering region) and maximize phase transformation width for concave, flat and convex surface workpieces, respectively. The verification result indicated that the process parameters obtained by the model were reliable.

An "unreasonable effectiveness" of Hilbert transform for the transition phase behavior in an Aharonov-Bohm two-path interferometer

NASA Astrophysics Data System (ADS)

Englman, R.

2016-08-01

The recent phase shift data of Takada et al. (Phys. Rev. Lett. 113 (2014) 126601) for a two level system are reconstructed from their current intensity curves by the method of Hilbert transform, for which the underlying Physics is the principle of causality. An introductory algebraic model illustrates pedagogically the working of the method and leads to newly derived relationships involving phenomenological parameters, in particular for the sign of the phase slope between the resonance peaks. While the parametrization of the experimental current intensity data in terms of a few model parameters shows only a qualitative agreement for the phase shift, due to the strong impact of small, detailed variations in the experimental intensity curve on the phase behavior, the numerical Hilbert transform yields a satisfactory reproduction of the phase.

Multiphase model for transformation induced plasticity. Extended Leblond's model

NASA Astrophysics Data System (ADS)

Weisz-Patrault, Daniel

2017-09-01

Transformation induced plasticity (TRIP) classically refers to plastic strains observed during phase transitions that occur under mechanical loads (that can be lower than the yield stress). A theoretical approach based on homogenization is proposed to deal with multiphase changes and to extend the validity of the well known and widely used model proposed by Leblond (1989). The approach is similar, but several product phases are considered instead of one and several assumptions have been released. Thus, besides the generalization for several phases, one can mention three main improvements in the calculation of the local equivalent plastic strain: the deviatoric part of the phase transformation is taken into account, both parent and product phases are elastic-plastic with linear isotropic hardening and the applied stress is considered. Results show that classical issues of singularities arising in the Leblond's model (corrected by ad hoc numerical functions or thresholding) are solved in this contribution excepted when the applied equivalent stress reaches the yield stress. Indeed, in this situation the parent phase is entirely plastic as soon as the phase transformation begins and the same singularity as in the Leblond's model arises. A physical explanation of the cutoff function is introduced in order to regularize the singularity. Furthermore, experiments extracted from the literature dealing with multiphase transitions and multiaxial loads are compared with the original Leblond's model and the proposed extended version. For the extended version, very good agreement is observed without any fitting procedures (i.e., material parameters are extracted from other dedicated experiments) and for the original version results are more qualitative.

Length scale effects and multiscale modeling of thermally induced phase transformation kinetics in NiTi SMA

NASA Astrophysics Data System (ADS)

Frantziskonis, George N.; Gur, Sourav

2017-06-01

Thermally induced phase transformation in NiTi shape memory alloys (SMAs) shows strong size and shape, collectively termed length scale effects, at the nano to micrometer scales, and that has important implications for the design and use of devices and structures at such scales. This paper, based on a recently developed multiscale model that utilizes molecular dynamics (MDs) simulations at small scales and MD-verified phase field (PhF) simulations at larger scales, reports results on specific length scale effects, i.e. length scale effects in martensite phase fraction (MPF) evolution, transformation temperatures (martensite and austenite start and finish) and in the thermally cyclic transformation between austenitic and martensitic phase. The multiscale study identifies saturation points for length scale effects and studies, for the first time, the length scale effect on the kinetics (i.e. developed internal strains) in the B19‧ phase during phase transformation. The major part of the work addresses small scale single crystals in specific orientations. However, the multiscale method is used in a unique and novel way to indirectly study length scale and grain size effects on evolution kinetics in polycrystalline NiTi, and to compare the simulation results to experiments. The interplay of the grain size and the length scale effect on the thermally induced MPF evolution is also shown in this present study. Finally, the multiscale coupling results are employed to improve phenomenological material models for NiTi SMA.

Mathematical model of phase transformations and elastoplastic stress in the water spray quenching of steel bars

NASA Astrophysics Data System (ADS)

Nagasaka, Y.; Brimacombe, J. K.; Hawbolt, E. B.; Samarasekera, I. V.; Hernandez-Morales, B.; Chidiac, S. E.

1993-04-01

A mathematical model, based on the finite-element technique and incorporating thermo-elasto-plastic behavior during the water spray quenching of steel, has been developed. In the model, the kinetics of diffusion-dependent phase transformation and martensitic transformation have been coupled with the transient heat flow to predict the microstructural evolution of the steel. Furthermore, an elasto-plastic constitutive relation has been applied to calculate internal stresses resulting from phase changes as well as temperature variation. The computer code has been verified for internal consistency with previously published results for pure iron bars. The model has been applied to the water spray quenching of two grades of steel bars, 1035 carbon and nickel-chromium alloyed steel; the calculated temperature, hardness, distortion, and residual stresses in the bars agreed well with experimental measurements. The results show that the phase changes occurring during this process affect the internal stresses significantly and must be included in the thermomechanical model.

Combining phase-field crystal methods with a Cahn-Hilliard model for binary alloys

NASA Astrophysics Data System (ADS)

Balakrishna, Ananya Renuka; Carter, W. Craig

2018-04-01

Diffusion-induced phase transitions typically change the lattice symmetry of the host material. In battery electrodes, for example, Li ions (diffusing species) are inserted between layers in a crystalline electrode material (host). This diffusion induces lattice distortions and defect formations in the electrode. The structural changes to the lattice symmetry affect the host material's properties. Here, we propose a 2D theoretical framework that couples a Cahn-Hilliard (CH) model, which describes the composition field of a diffusing species, with a phase-field crystal (PFC) model, which describes the host-material lattice symmetry. We couple the two continuum models via coordinate transformation coefficients. We introduce the transformation coefficients in the PFC method to describe affine lattice deformations. These transformation coefficients are modeled as functions of the composition field. Using this coupled approach, we explore the effects of coarse-grained lattice symmetry and distortions on a diffusion-induced phase transition process. In this paper, we demonstrate the working of the CH-PFC model through three representative examples: First, we describe base cases with hexagonal and square symmetries for two composition fields. Next, we illustrate how the CH-PFC method interpolates lattice symmetry across a diffuse phase boundary. Finally, we compute a Cahn-Hilliard type of diffusion and model the accompanying changes to lattice symmetry during a phase transition process.

On a phase field approach for martensitic transformations in a crystal plastic material at a loaded surface

NASA Astrophysics Data System (ADS)

Schmitt, Regina; Kuhn, Charlotte; Müller, Ralf

2017-07-01

A continuum phase field model for martensitic transformations is introduced, including crystal plasticity with different slip systems for the different phases. In a 2D setting, the transformation-induced eigenstrain is taken into account for two martensitic orientation variants. With aid of the model, the phase transition and its dependence on the volume change, crystal plastic material behavior, and the inheritance of plastic deformations from austenite to martensite are studied in detail. The numerical setup is motivated by the process of cryogenic turning. The resulting microstructure qualitatively coincides with an experimentally obtained martensite structure. For the numerical calculations, finite elements together with global and local implicit time integration scheme are employed.

Rate-independent dissipation in phase-field modelling of displacive transformations

NASA Astrophysics Data System (ADS)

Tůma, K.; Stupkiewicz, S.; Petryk, H.

2018-05-01

In this paper, rate-independent dissipation is introduced into the phase-field framework for modelling of displacive transformations, such as martensitic phase transformation and twinning. The finite-strain phase-field model developed recently by the present authors is here extended beyond the limitations of purely viscous dissipation. The variational formulation, in which the evolution problem is formulated as a constrained minimization problem for a global rate-potential, is enhanced by including a mixed-type dissipation potential that combines viscous and rate-independent contributions. Effective computational treatment of the resulting incremental problem of non-smooth optimization is developed by employing the augmented Lagrangian method. It is demonstrated that a single Lagrange multiplier field suffices to handle the dissipation potential vertex and simultaneously to enforce physical constraints on the order parameter. In this way, the initially non-smooth problem of evolution is converted into a smooth stationarity problem. The model is implemented in a finite-element code and applied to solve two- and three-dimensional boundary value problems representative for shape memory alloys.

Modelling a single phase voltage controlled rectifier using Laplace transforms

NASA Technical Reports Server (NTRS)

Kraft, L. Alan; Kankam, M. David

1992-01-01

The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

Coupled gamma/alpha phase transformations in low-carbon steels

NASA Astrophysics Data System (ADS)

Mizutani, Yasushi

Since steels have been the most prevalently utilized materials for many years, the desire for steels with low alloying components with a well-balanced combination of high strength and toughness is increasing. Low carbon steels consisting of bainitic microstructures are ideally suited to meeting such technological and economic requirements. Thus it is extremely important to fully clarify the mechanism of bainite formation in order to produce this type of engineering steel by optimized alloy and process design. This research focuses on understanding the mechanism of coupled displacive/diffusional gamma/alpha transformation in low-carbon steels including bainitic and martensitic transformation, and establishing a more comprehensive and physically rational computational model for predictive control of coupled gamma/alpha transformation phenomena. Models for coupled gamma/alpha phase transformation proposed in this study are based on a mechanistic and unified theory and the following assumptions: (1) The energy dissipation due to interface motion can be linearly combined with the energy dissipation due to carbon diffusion. (2) The carbon concentrations at the interface in both gamma and alpha phases are constrained by an interface solute trapping law. (3) Interface motion during nucleation is also governed by the carbon diffusion field velocity. (4) The response function of glissile interface motion can be expressed in the form of thermally activated dislocation glide. In contrast to the conventional semi-empirical models of the previous literature, the computational model proposed in this study is demonstrated to successfully provide a comprehensive and quantitative prediction of the effects of temperature, composition, microstructure, and the interactions among them. This includes the effects of substitutional solutes, morphology of the parent gamma phase, density of nucleation sites, temperature dependent variation of flow stress of matrix, and dynamic recovery of forest dislocations on the kinetics of coupled gamma/alpha phase transformation.

A High-Rate, Single-Crystal Model for Cyclotrimethylene Trinitramine including Phase Transformations and Plastic Slip

DOE PAGES

Addessio, Francis L.; Luscher, Darby Jon; Cawkwell, Marc Jon; ...

2017-05-14

A continuum model for the high-rate, thermo-mechanical deformation of single-crystal cyclotrimethylene trinitramine (RDX) is developed. The model includes the effects of anisotropy, large deformations, nonlinear thermo-elasticity, phase transformations, and plastic slip. A multiplicative decomposition of the deformation gradient is used. The volumetric elastic component of the deformation is accounted for through a free-energy based equation of state for the low- (α) and high-pressure (γ) polymorphs of RDX. Crystal plasticity is addressed using a phenomenological thermal activation model. The deformation gradient for the phase transformation is based on an approach that has been applied to martensitic transformations. Simulations were conducted andmore » compared to high-rate, impact loading of oriented RDX single crystals. The simulations considered multiple orientations of the crystal relative to the direction of shock loading and multiple sample thicknesses. Thirteen slip systems, which were inferred from indentation and x-ray topography, were used to model the α-polymorph. It is shown that by increasing the number of slip systems from the previously considered number of six (6) to thirteen (13) in the α-polymorph, better comparisons with data may be obtained. Simulations of impact conditions in the vicinity of the α- to γ-polymorph transformation (3.8 GPa) are considered. Eleven of the simulations, which were at pressures below the transformation value (3.0 GPa), were compared to experimental data. Comparison of the model was also made with available data for one experiment above the transformation pressure (4.4 GPa). Also, simulations are provided for a nominal pressure of 7.5 GPa to demonstrate the effect of the transformation kinetics on the deformation of a high-rate plate impact problem.« less

A High-Rate, Single-Crystal Model for Cyclotrimethylene Trinitramine including Phase Transformations and Plastic Slip

DOE Office of Scientific and Technical Information (OSTI.GOV)

Addessio, Francis L.; Luscher, Darby Jon; Cawkwell, Marc Jon

A continuum model for the high-rate, thermo-mechanical deformation of single-crystal cyclotrimethylene trinitramine (RDX) is developed. The model includes the effects of anisotropy, large deformations, nonlinear thermo-elasticity, phase transformations, and plastic slip. A multiplicative decomposition of the deformation gradient is used. The volumetric elastic component of the deformation is accounted for through a free-energy based equation of state for the low- (α) and high-pressure (γ) polymorphs of RDX. Crystal plasticity is addressed using a phenomenological thermal activation model. The deformation gradient for the phase transformation is based on an approach that has been applied to martensitic transformations. Simulations were conducted andmore » compared to high-rate, impact loading of oriented RDX single crystals. The simulations considered multiple orientations of the crystal relative to the direction of shock loading and multiple sample thicknesses. Thirteen slip systems, which were inferred from indentation and x-ray topography, were used to model the α-polymorph. It is shown that by increasing the number of slip systems from the previously considered number of six (6) to thirteen (13) in the α-polymorph, better comparisons with data may be obtained. Simulations of impact conditions in the vicinity of the α- to γ-polymorph transformation (3.8 GPa) are considered. Eleven of the simulations, which were at pressures below the transformation value (3.0 GPa), were compared to experimental data. Comparison of the model was also made with available data for one experiment above the transformation pressure (4.4 GPa). Also, simulations are provided for a nominal pressure of 7.5 GPa to demonstrate the effect of the transformation kinetics on the deformation of a high-rate plate impact problem.« less

Hydrostatic, uniaxial, and triaxial compression tests on unpoled "Chem-prep" PZT 95/5-2Nb ceramic within temperature range of -55 to 75 degrees C.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeuch, David Henry; Montgomery, Stephen Tedford; Lee, Moo Yul

Sandia is currently developing a lead-zirconate-titanate ceramic 95/5-2Nb (or PNZT) from chemically prepared ('chem-prep') precursor powders. Previous PNZT ceramic was fabricated from the powders prepared using a 'mixed-oxide' process. The specimens of unpoled PNZT ceramic from batch HF803 were tested under hydrostatic, uniaxial, and constant stress difference loading conditions within the temperature range of -55 to 75 C and pressures to 500 MPa. The objective of this experimental study was to obtain mechanical properties and phase relationships so that the grain-scale modeling effort can develop and test its models and codes using realistic parameters. The stress-strain behavior of 'chem-prep' PNZTmore » under different loading paths was found to be similar to that of 'mixed-oxide' PNZT. The phase transformation from ferroelectric to antiferroelectric occurs in unpoled ceramic with abrupt increase in volumetric strain of about 0.7 % when the maximum compressive stress, regardless of loading paths, equals the hydrostatic pressure at which the transformation otherwise takes place. The stress-volumetric strain relationship of the ceramic undergoing a phase transformation was analyzed quantitatively using a linear regression analysis. The pressure (P{sub T1}{sup H}) required for the onset of phase transformation with respect to temperature is represented by the best-fit line, P{sub T1}{sup H} (MPa) = 227 + 0.76 T (C). We also confirmed that increasing shear stress lowers the mean stress and the volumetric strain required to trigger phase transformation. At the lower bound (-55 C) of the tested temperature range, the phase transformation is permanent and irreversible. However, at the upper bound (75 C), the phase transformation is completely reversible as the stress causing phase transformation is removed.« less

Role of Oxidative Stress in Transformation Induced by Metal Mixture

PubMed Central

Martín, Silva-Aguilar; Emilio, Rojas; Mahara, Valverde

2011-01-01

Metals are ubiquitous pollutants present as mixtures. In particular, mixture of arsenic-cadmium-lead is among the leading toxic agents detected in the environment. These metals have carcinogenic and cell-transforming potential. In this study, we used a two step cell transformation model, to determine the role of oxidative stress in transformation induced by a mixture of arsenic-cadmium-lead. Oxidative damage and antioxidant response were determined. Metal mixture treatment induces the increase of damage markers and the antioxidant response. Loss of cell viability and increased transforming potential were observed during the promotion phase. This finding correlated significantly with generation of reactive oxygen species. Cotreatment with N-acetyl-cysteine induces effect on the transforming capacity; while a diminution was found in initiation, in promotion phase a total block of the transforming capacity was observed. Our results suggest that oxidative stress generated by metal mixture plays an important role only in promotion phase promoting transforming capacity. PMID:22191014

Modal analysis of untransposed bilateral three-phase lines -- a perturbation approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faria, J.A.B.; Mendes, J.H.B.

1997-01-01

Model analysis of three-phase power lines exhibiting bilateral symmetry leads to modal transformation matrices that closely resemble Clarke`s transformation. The authors develop a perturbation theory approach to justify, interpret, and gain understanding of this well known fact. Further, the authors show how to find new frequency dependent correction terms that once added to Clarke`s transformation lead to improved accuracy.

Phase transformation of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} and its disordered crystal structure at 1073 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurokawa, Daisuke; R and D Center, Taiheiyo Cement Corporation, Chiba 285-8655; Takeda, Seiya

The phase transformation of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} and the crystal structure of its high-temperature phase were investigated by differential thermal analysis, temperature-dependent Raman spectroscopy and high-temperature X-ray powder diffraction (CuKα{sub 1}). We determined the starting temperature of the orthorhombic-to-cubic transformation during heating (=711 K) and that of the reverse transformation during cooling (=742 K). The thermal hysteresis was negative (=−31 K), suggesting the thermoelasticity of the transformation. The space group of the high temperature phase is I4{sup ¯}3m with the unit-cell dimensions of a=0.92426(2) nm and V=0.78955(2) nm{sup 3} (Z=2) at 1073 K. The initial structural model wasmore » derived by the direct methods and further refined by the Rietveld method. The final structural model showed the orientational disordering of SO{sub 4} tetrahedra. The maximum-entropy method-based pattern fitting method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. At around the transformation temperature during heating, the vibrational spectra, corresponding to the Raman-active SO{sub 4} internal stretching mode, showed the continuous and gradual change in the slope of full width at half maximum versus temperature curve. This strongly suggests that the orthorhombic-to-cubic phase transformation would be principally accompanied by the statistical disordering in orientation of the SO{sub 4} tetrahedra, without distinct dynamical reorientation. - Graphical abstract: (Left) Three-dimensional electron-density distributions of the SO{sub 4} tetrahedron with the split-atom model, and (right) a bird's eye view of electron densities on the plane parallel to (111). - Highlights: • Crystal structure of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} at 1073 K is determined by powder XRD. • The atom arrangements are represented by the split-atom model. • The MPF method is used to confirm the validity of the model. • The phase transition is accompanied by orientational disordering of SO{sub 4} tetrahedra.« less

Status on Iterative Transform Phase Retrieval Applied to the GBT Data

NASA Technical Reports Server (NTRS)

Dean, Bruce; Aronstein, David; Smith, Scott; Shiri, Ron; Hollis, Jan M.; Lyons, Richard; Prestage, Richard; Hunter, Todd; Ghigo, Frank; Nikolic, Bojan

2007-01-01

This slide presentation reviews the use of iterative transform phase retrieval in the analysis of the Green Bank Radio Telescope (GBT) Data. It reviews the NASA projects that have used phase retrieval, and the testbed for the algorithm to be used for the James Webb Space Telescope. It shows the comparison of phase retrieval with an interferometer, and reviews the two approaches used for phase retrieval, iterative transform (ITA) or parametric (non-linear least squares model fitting). The concept of ITA Phase Retrieval is reviewed, and the application to Radio Antennas is reviewed. The presentation also examines the National Radio Astronomy Observatory (NRAO) data from the GBT, and the Fourier model that NRAO uses to analyze the data. The challenge for ITA phase retrieval is reviewed, and the coherent approximation for incoherent data is shown. The validity of the approximation is good for a large tilt. There is a review of the proof of concept of the Phase Review simulation using the input wavefront, and the initial sampling parameters estimate from the focused GBT data.

Interaction of lysozyme protein with different sized silica nanoparticles and their resultant structures

NASA Astrophysics Data System (ADS)

Yadav, Indresh; Aswal, V. K.; Kohlbrecher, J.

2016-05-01

The interaction of model protein-lysozyme with three different sized anionic silica nanoparticles has been studied by UV-vis spectroscopy, dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The surface area and curvature of the nanoparticles change with size, which significantly influence their interaction with protein. The lysozyme adsorbs on the surface of the nanoparticles due to electrostatic attraction and leads to the phase transformation from one phase (clear) to two-phase (turbid) of the nanoparticle-protein system. The dominance of lysozyme induced short-range attraction over long-range electrostatic repulsion between nanoparticles is responsible for phase transformation and modeled by the two-Yukawa potential. The magnitude of the attractive interaction increases with the size of the nanoparticles as a result the phase transformation commences relatively at lower concentration of lysozyme. The structure of the nanoparticle-protein system in two-phase is characterized by the diffusion limited aggregate type of mass fractal morphology.

Interaction of lysozyme protein with different sized silica nanoparticles and their resultant structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Indresh, E-mail: iykumarindresh288@gmail.com; Aswal, V. K.; Kohlbrecher, J.

The interaction of model protein-lysozyme with three different sized anionic silica nanoparticles has been studied by UV-vis spectroscopy, dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The surface area and curvature of the nanoparticles change with size, which significantly influence their interaction with protein. The lysozyme adsorbs on the surface of the nanoparticles due to electrostatic attraction and leads to the phase transformation from one phase (clear) to two-phase (turbid) of the nanoparticle-protein system. The dominance of lysozyme induced short-range attraction over long-range electrostatic repulsion between nanoparticles is responsible for phase transformation and modeled by the two-Yukawa potential. Themore » magnitude of the attractive interaction increases with the size of the nanoparticles as a result the phase transformation commences relatively at lower concentration of lysozyme. The structure of the nanoparticle-protein system in two-phase is characterized by the diffusion limited aggregate type of mass fractal morphology.« less

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.

2015-12-11

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/ discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surfacemore » layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. In conclusion, our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments.« less

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

NASA Astrophysics Data System (ADS)

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.; Harder, R.; Maxey, E.; Wingert, J.; Singer, A.; Hy, S.; Mulvaney, P.; Zapol, P.; Shpyrko, O. G.

2015-12-01

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surface layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. Our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments.

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

PubMed Central

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.; Harder, R.; Maxey, E.; Wingert, J.; Singer, A.; Hy, S.; Mulvaney, P.; Zapol, P.; Shpyrko, O. G.

2015-01-01

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surface layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. Our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments. PMID:26655832

In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys

DOE PAGES

Tan, L.; Yang, Y.

2015-11-01

For an in situ phase transformation of the Chi (χ) phase to the Laves phase we observed in a Fe–Cr–Ni–Mo model alloy. The morphology, composition, and crystal structure of the χ and Laves phases, and their orientation relationship with the matrix austenite phase were investigated. The resulted Laves phase has larger lattice mismatch with the matrix phase than the χ phase, leading to the increase of local strain fields and the formation of dislocations. Moreover, this finding is helpful to understand the precipitation behavior of the intermetallic phases in the Mo-containing austenitic stainless steels.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Y.B.; Yang, L.H.; Duan, J.L.

The kinetics of the β → α phase transformation in the 47Zr–45Ti–5Al–3V (wt.%) alloy with different initial β grain sizes under isothermal conditions was investigated by X-ray diffraction. The results showed that the volume fraction of α phase first increased with increasing aging time, and then reached an equilibrium value. The equilibrium value of α phase decreased with increased aging temperature. At the same aging temperature and time, the volume fraction of α phase in the 47Zr–45Ti–5Al–3V alloy solution-treated at 850 °C was higher than at 1050 °C, and the size of α phase in the 47Zr–45Ti–5Al–3V alloy solution-treated atmore » 850 °C was larger than that at 1050 °C. The kinetics of the β → α phase transformation was modeled under isothermal conditions in the theoretical frame of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. The Avrami index (n) increased with increasing aging temperature, while the reaction rate constant (k) decreased. - Highlights: • The kinetics of the β → α phase transformation in the ZrTiAlV alloy was investigated. • The volume fraction of α phase first increased and then reached an equilibrium value. • The kinetics of the β → α phase transformation was modeled by the JMAK theory. • The n increased with increasing aging temperature, while the k decreased.« less

Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

NASA Astrophysics Data System (ADS)

Srivastava, Ankit; Ghassemi-Armaki, Hassan; Sung, Hyokyung; Chen, Peng; Kumar, Sharvan; Bower, Allan F.

2015-05-01

The micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructure-based simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of 980 MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite-martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite-martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

Theoretical modelling of residual and transformational stresses in SMA composites

NASA Astrophysics Data System (ADS)

Berman, J. B.; White, S. R.

1996-12-01

SMA composites are a class of smart materials in which shape memory alloy (SMA) actuators are embedded in a polymer matrix composite. The difference in thermal expansion between the SMA and the host material leads to residual stresses during processing. Similarly, the SMA transformations from martensite to austenite, or the reverse, also generate stresses. These stresses acting in combination can lead to SMA/epoxy interfacial debonding or microcracking of the composite phase. In this study the residual and transformational stresses are investigated for a nitinol wire embedded in a graphite/epoxy composite. A three-phase micromechanical model is developed. The nitinol wire is assumed to behave as a thermoelastic material. Nitinol austenitic and martensitic transformations are modelled using linear piecewise interpolation of experimental data. The interphase is modelled as a thermoelastic polymer. A transversely isotropic thermoelastic composite is used for the outer phase. Stress-free conditions are assumed immediately before cool down from the cure temperature. The effect of nitinol, coating and composite properties on residual and transformational stresses are evaluated. Fiber architectures favoring the axial direction decrease the magnitude of all residual stresses. A decrease in stresses at the composite/coating interface is also predicted through the use of thick, compliant coatings. Reducing the recovery strain and moving the transformation to higher temperatures were found to be most effective in reducing residual stresses.

Effectiveness of Discovery Learning-Based Transformation Geometry Module

NASA Astrophysics Data System (ADS)

Febriana, R.; Haryono, Y.; Yusri, R.

2017-09-01

Development of transformation geometry module is conducted because the students got difficulties to understand the existing book. The purpose of the research was to find out the effectiveness of discovery learning-based transformation geometry module toward student’s activity. Model of the development was Plomp model consisting preliminary research, prototyping phase and assessment phase. The research was focused on assessment phase where it was to observe the designed product effectiveness. The instrument was observation sheet. The observed activities were visual activities, oral activities, listening activities, mental activities, emotional activities and motor activities. Based on the result of the research, it is found that visual activities, learning activities, writing activities, the student’s activity is in the criteria very effective. It can be concluded that the use of discovery learning-based transformation geometry module use can increase the positive student’s activity and decrease the negative activity.

Martensitelike spontaneous relaxor-normal ferroelectric transformation in Pb(Zn1/3Nb2/3)O3-PbLa(ZrTi)O3 system

NASA Astrophysics Data System (ADS)

Deng, Guochu; Ding, Aili; Li, Guorong; Zheng, Xinsen; Cheng, Wenxiu; Qiu, Pingsun; Yin, Qingrui

2005-11-01

The spontaneous relaxor-normal ferroelectric transformation was found in the tetragonal composition of Pb(Zn1/3Nb2/3)O3-PbLa(ZrTi)O3 (0.3PZN-0.7PLZT) complex ABO3 system. The corresponding dielectric permittivities and losses of different compositions located near the morphotrophic phase boundary were analyzed. By reviewing all of the results about this type of transformation in previous references, the electric, compositional, structural, and thermodynamic characteristics of the spontaneous relaxor-normal transformation were proposed. Additionally, the adaptive phase model for martensite transformation proposed by Khachaturyan et al. [Phys. Rev. B 43, 10832 (1991)] was introduced into this ferroelectric transformation to explain the unique transformation pathway and associated features such as the tweedlike domain patterns and the dielectric dispersion under the critical transition temperature. Due to the critical compositions near the MPB, the ferroelectric materials just fulfill the condition, in which the adaptive phases can form in the transformation procedure. The formation of the adaptive phases, which are composed of stress-accommodating twinned domains, makes the system bypass the energy barrier encountered in conventional martensite transformations. The twinned adaptive phase corresponds to the tweedlike domain pattern under a transmission electronic microscope. At lower temperature, these precursor phases transform into the conventional ferroelectric state with macrodomains by the movement of domain walls, which causes a weak dispersion in dielectric permittivity.

Thermokinetic Modeling of Phase Transformation in the Laser Powder Deposition Process

NASA Astrophysics Data System (ADS)

Foroozmehr, Ehsan; Kovacevic, Radovan

2009-08-01

A finite element model coupled with a thermokinetic model is developed to predict the phase transformation of the laser deposition of AISI 4140 on a substrate with the same material. Four different deposition patterns, long-bead, short-bead, spiral-in, and spiral-out, are used to cover a similar area. Using a finite element model, the temperature history of the laser powder deposition (LPD) process is determined. The martensite transformation as well as martensite tempering is considered to calculate the final fraction of martensite, ferrite, cementite, ɛ-carbide, and retained austenite. Comparing the surface hardness topography of different patterns reveals that path planning is a critical parameter in laser surface modification. The predicted results are in a close agreement with the experimental results.

Transformation in the pharmaceutical industry: transformation-induced quality risks--a survey.

PubMed

Shafiei, Nader; Ford, James L; Morecroft, Charles W; Lisboa, Paulo J; Taylor, Mark J; Mouzughi, Yusra

2013-01-01

This paper is the fourth in a series that explores ongoing transformation in the pharmaceutical industry and its impact on pharmaceutical quality from the perspective of risk identification. The aim of this paper is to validate proposed quality risks through elicitation of expert opinion and define the resultant quality risk model. Expert opinion was obtained using a questionnaire-based survey with participants with recognized expertise in pharmaceutical regulation, product lifecycle, or technology. The results of the survey validate the theoretical and operational evidence in support of the four main pharmaceutical transformation triggers previously identified. The quality risk model resulting from the survey indicated a firm relationship between the pharmaceutical quality risks and regulatory compliance outcomes during the marketing approval and post-marketing phases of the product lifecycle and a weaker relationship during the pre-market evaluation phase. In this paper through conduct of an expert opinion survey the proposed quality risks carried forward from an earlier part of the research are validated and resultant quality risk model is defined. The survey results validate the theoretical and operational evidence previously identified. The quality risk model indicates that transformation-related risks have a larger regulatory compliance impact during product approval, manufacturing, distribution, and commercial use than during the development phase.

Phase transformation and sustained load crack growth in ZrO[sub 2] + 3 mol% Y[sub 2]O[sub 3]: Experiments and kinetic modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, H.; Gao, M.; Wei, R.P.

1995-01-01

To better understand environmentally assisted crack growth (SCG) in yttria stabilized zirconia, experimental studies were undertaken to characterize the kinetics of crack growth and the associated stress/moisture induced phase transformation in ZrO[sub 2] + 3 mol% Y[sub 2]O[sub 3] (3Y-TZP) in water, dry nitrogen and toluene from 3 to 70 C. The results showed that crack growth in water depended strongly on stress intensity factor (K[sub 1]) and temperature (T) and involved the transformation of a thin layer of material near the crack tip from the tetragonal (t) to the monoclinic (m) phase. These results, combined with literature data onmore » moisture-induced phase transformation, suggested that crack growth enhancement by water is controlled by the rate of this transformation and reflects the environmental cracking susceptibility of the transformed m-phase. A model was developed to link subcritical crack growth (SCG) rate to the kinetics of t [yields] m phase transformation. The SCG rate is expressed as an exponential function of stress-free activation energy, a stress-dependent contribution in terms of the mode 1 stress intensity factor K[sub I] and actuation volume, and temperature. The stress-free activation energies for water and the inert environments were determined to be 82 [+-] 3 and 169 [+-] 4 kJ/mol, respectively, at the 95% confidence level, and the corresponding activation volumes were 14 and 35 unit cells. The decreases in activation energy and activation volume may be attributed to a change in surface energy by water.« less

A level set approach for shock-induced α-γ phase transition of RDX

NASA Astrophysics Data System (ADS)

Josyula, Kartik; Rahul; De, Suvranu

2018-02-01

We present a thermodynamically consistent level sets approach based on regularization energy functional which can be directly incorporated into a Galerkin finite element framework to model interface motion. The regularization energy leads to a diffusive form of flux that is embedded within the level sets evolution equation which maintains the signed distance property of the level set function. The scheme is shown to compare well with the velocity extension method in capturing the interface position. The proposed level sets approach is employed to study the α-γphase transformation in RDX single crystal shocked along the (100) plane. Example problems in one and three dimensions are presented. We observe smooth evolution of the phase interface along the shock direction in both models. There is no diffusion of the interface during the zero level set evolution in the three dimensional model. The level sets approach is shown to capture the characteristics of the shock-induced α-γ phase transformation such as stress relaxation behind the phase interface and the finite time required for the phase transformation to complete. The regularization energy based level sets approach is efficient, robust, and easy to implement.

A High-Rate, Single-Crystal Model including Phase Transformations, Plastic Slip, and Twinning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Addessio, Francis L.; Bronkhorst, Curt Allan; Bolme, Cynthia Anne

2016-08-09

An anisotropic, rate-­dependent, single-­crystal approach for modeling materials under the conditions of high strain rates and pressures is provided. The model includes the effects of large deformations, nonlinear elasticity, phase transformations, and plastic slip and twinning. It is envisioned that the model may be used to examine these coupled effects on the local deformation of materials that are subjected to ballistic impact or explosive loading. The model is formulated using a multiplicative decomposition of the deformation gradient. A plate impact experiment on a multi-­crystal sample of titanium was conducted. The particle velocities at the back surface of three crystal orientationsmore » relative to the direction of impact were measured. Molecular dynamics simulations were conducted to investigate the details of the high-­rate deformation and pursue issues related to the phase transformation for titanium. Simulations using the single crystal model were conducted and compared to the high-­rate experimental data for the impact loaded single crystals. The model was found to capture the features of the experiments.« less

α-Phase transformation kinetics of U – 8 wt% Mo established by in situ neutron diffraction

DOE PAGES

Garlea, Elena; Steiner, M. A.; Calhoun, C. A.; ...

2016-05-08

The α-phase transformation kinetics of as-cast U - 8 wt% Mo below the eutectoid temperature have been established by in situ neutron diffraction. α-phase weight fraction data acquired through Rietveld refinement at five different isothermal hold temperatures can be modeled accurately utilizing a simple Johnson-Mehl-Avrami-Kolmogorov impingement-based theory, and the results are validated by a corresponding evolution in the γ-phase lattice parameter during transformation that follows Vegard’s law. Neutron diffraction data is used to produce a detailed Time-Temperature-Transformation diagram that improves upon inconsistencies in the current literature, exhibiting a minimum transformation start time of 40 min at temperatures between 500 °Cmore » and 510 °C. Lastly, the transformation kinetics of U – 8 wt% Mo can vary significantly from as-cast conditions after extensive heat treatments, due to homogenization of the typical dendritic microstructure which possesses non-negligible solute segregation.« less

Parameters of Models of Structural Transformations in Alloy Steel Under Welding Thermal Cycle

NASA Astrophysics Data System (ADS)

Kurkin, A. S.; Makarov, E. L.; Kurkin, A. B.; Rubtsov, D. E.; Rubtsov, M. E.

2017-05-01

A mathematical model of structural transformations in an alloy steel under the thermal cycle of multipass welding is suggested for computer implementation. The minimum necessary set of parameters for describing the transformations under heating and cooling is determined. Ferritic-pearlitic, bainitic and martensitic transformations under cooling of a steel are considered. A method for deriving the necessary temperature and time parameters of the model from the chemical composition of the steel is described. Published data are used to derive regression models of the temperature ranges and parameters of transformation kinetics in alloy steels. It is shown that the disadvantages of the active visual methods of analysis of the final phase composition of steels are responsible for inaccuracy and mismatch of published data. The hardness of a specimen, which correlates with some other mechanical properties of the material, is chosen as the most objective and reproducible criterion of the final phase composition. The models developed are checked by a comparative analysis of computational results and experimental data on the hardness of 140 alloy steels after cooling at various rates.

Motion compensation via redundant-wavelet multihypothesis.

PubMed

Fowler, James E; Cui, Suxia; Wang, Yonghui

2006-10-01

Multihypothesis motion compensation has been widely used in video coding with previous attention focused on techniques employing predictions that are diverse spatially or temporally. In this paper, the multihypothesis concept is extended into the transform domain by using a redundant wavelet transform to produce multiple predictions that are diverse in transform phase. The corresponding multiple-phase inverse transform implicitly combines the phase-diverse predictions into a single spatial-domain prediction for motion compensation. The performance advantage of this redundant-wavelet-multihypothesis approach is investigated analytically, invoking the fact that the multiple-phase inverse involves a projection that significantly reduces the power of a dense-motion residual modeled as additive noise. The analysis shows that redundant-wavelet multihypothesis is capable of up to a 7-dB reduction in prediction-residual variance over an equivalent single-phase, single-hypothesis approach. Experimental results substantiate the performance advantage for a block-based implementation.

Chirality Switching by Martensitic Transformation in Protein Cylindrical Crystals: Application to Bacterial Flagella

NASA Astrophysics Data System (ADS)

Komai, Ricardo Kiyohiro

Martensitic transformations provide unique engineering properties that, when designed properly, become important parts of new technology. Martensitic transformations have been studied for many years in traditional alloys (iron, steel, titanium, etc.), however there is still much to be learned in regards to these transformations in biological materials. Olson and Hartman showed in 1982 that these transformations are also observed in bacterial flagella and T4 bacteriophage viral sheaths, allowing for propulsion of bacteria in a fluid environment and, for the virus, is responsible for the infection mechanism. This work demonstrates, using the bacterial flagella as an example, that these transformations can be modelled using thermodynamic methods that are also used to model the transformations in alloys. This thesis work attempts to explain the transformations that occur in bacterial flagella, which are capable of small strain, highly reversible martensitic transformations. The first stress/temperature phase diagrams of these flagella were created by adding the mechanical energy of the transformation of the flagella to limited chemical thermodynamics information of the transformation. Mechanical energy is critical to the transformation process because the bacterial body applies a torque to the radius of the flagella. Finally, work has begun and will be completed in regards to understanding the kinetics of the transformation of the flagella. The motion of the transformation interface can be predicted by using a Landau-Ginzburg model. The crystallography of the transformation in bacterial flagella is also being computed to determine the invariant lines of transformation that occur within this cylindrical crystal. This work has shown that it is possible to treat proteins in a similar manner that alloys are treated when using thermodynamic modelling. Much can be learned from translating what is known regarding phase transformations in hard material systems to soft, organic systems.

Berry phase in Heisenberg representation

NASA Technical Reports Server (NTRS)

Andreev, V. A.; Klimov, Andrei B.; Lerner, Peter B.

1994-01-01

We define the Berry phase for the Heisenberg operators. This definition is motivated by the calculation of the phase shifts by different techniques. These techniques are: the solution of the Heisenberg equations of motion, the solution of the Schrodinger equation in coherent-state representation, and the direct computation of the evolution operator. Our definition of the Berry phase in the Heisenberg representation is consistent with the underlying supersymmetry of the model in the following sense. The structural blocks of the Hamiltonians of supersymmetrical quantum mechanics ('superpairs') are connected by transformations which conserve the similarity in structure of the energy levels of superpairs. These transformations include transformation of phase of the creation-annihilation operators, which are generated by adiabatic cyclic evolution of the parameters of the system.

A Semiempirical Model for Sigma-Phase Precipitation in Duplex and Superduplex Stainless Steels

NASA Astrophysics Data System (ADS)

Ferro, P.; Bonollo, F.

2012-04-01

Sigma phase is known to reduce the mechanical properties and corrosion resistance of duplex and superduplex stainless steels. Therefore, heat treatments and welding must be carefully performed so as to avoid the appearance of such a detrimental phase, and clearly, models suitable to faithfully predict σ-phase precipitation are very useful tools. Most fully analytical models are based on thermodynamic calculations whose agreement with experimental results is not always good, so that such models should be used for qualitative purposes only. Alternatively, it is possible to exploit semiempirical models, where time-temperature-transformation (TTT) diagrams are empirically determined for a given alloy and the continuous-cooling-transformation (CCT) diagram is calculated from the TTT diagram. In this work, a semiempirical model for σ-phase precipitation in duplex and superduplex stainless steels, under both isothermal and unisothermal conditions, is proposed. Model parameters are calculated from empirical data and CCT diagrams are obtained by means of the additivity rule, whereas experimental measurements for model validation are taken from the literature. This model gives a satisfactory estimation of σ-phase precipitates during both isothermal aging and the continuous cooling process.

Effect of a core-softened O-O interatomic interaction on the shock compression of fused silica

NASA Astrophysics Data System (ADS)

Izvekov, Sergei; Weingarten, N. Scott; Byrd, Edward F. C.

2018-03-01

Isotropic soft-core potentials have attracted considerable attention due to their ability to reproduce thermodynamic, dynamic, and structural anomalies observed in tetrahedral network-forming compounds such as water and silica. The aim of the present work is to assess the relevance of effective core-softening pertinent to the oxygen-oxygen interaction in silica to the thermodynamics and phase change mechanisms that occur in shock compressed fused silica. We utilize the MD simulation method with a recently published numerical interatomic potential derived from an ab initio MD simulation of liquid silica via force-matching. The resulting potential indicates an effective shoulder-like core-softening of the oxygen-oxygen repulsion. To better understand the role of the core-softening we analyze two derivative force-matching potentials in which the soft-core is replaced with a repulsive core either in the three-body potential term or in all the potential terms. Our analysis is further augmented by a comparison with several popular empirical models for silica that lack an explicit core-softening. The first outstanding feature of shock compressed glass reproduced with the soft-core models but not with the other models is that the shock compression values at pressures above 20 GPa are larger than those observed under hydrostatic compression (an anomalous shock Hugoniot densification). Our calculations indicate the occurrence of a phase transformation along the shock Hugoniot that we link to the O-O repulsion core-softening. The phase transformation is associated with a Hugoniot temperature reversal similar to that observed experimentally. With the soft-core models, the phase change is an isostructural transformation between amorphous polymorphs with no associated melting event. We further examine the nature of the structural transformation by comparing it to the Hugoniot calculations for stishovite. For stishovite, the Hugoniot exhibits temperature reversal and associated phase transformation, which is a transition to a disordered phase (liquid or dense amorphous), regardless of whether or not the model accounts for core-softening. The onset pressures of the transformation predicted by different models show a wide scatter within 60-110 GPa; for potentials without core-softening, the onset pressure is much higher than 110 GPa. Our results show that the core-softening of the interaction in the oxygen subsystem of silica is the key mechanism for the structural transformation and thermodynamics in shock compressed silica. These results may provide an important contribution to a unified picture of anomalous response to shock compression observed in other network-forming oxides and single-component systems with core-softening of effective interactions.

Dynamic Diffraction Studies on the Crystallization, Phase Transformation, and Activation Energies in Anodized Titania Nanotubes.

PubMed

Albetran, Hani; Vega, Victor; Prida, Victor M; Low, It-Meng

2018-02-23

The influence of calcination time on the phase transformation and crystallization kinetics of anodized titania nanotube arrays was studied using in-situ isothermal and non-isothermal synchrotron radiation diffraction from room temperature to 900 °C. Anatase first crystallized at 400 °C, while rutile crystallized at 550 °C. Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 °C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation. The Avrami equation was used to model the titania crystallization mechanism and the Arrhenius equation was used to estimate the activation energies of the titania phase transformation. Activation energies of 22 (10) kJ/mol for the titanium-to-anatase transformation, and 207 (17) kJ/mol for the anatase-to-rutile transformation were estimated.

Effects of Phase Transformations and Dynamic Material Strength on Hydrodynamic Instability Evolution in Metals

NASA Astrophysics Data System (ADS)

Opie, Saul

Hydrodynamic phenomena such as the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities can be described by exponential/linear growth of surface perturbations at a bimaterial interface when subjected to constant/impulsive acceleration. A challenge in designing systems to mitigate or exploit these effects is the lack of accurate material models at large dynamic strain rates and pressures. In particular, little stress-strain constitutive information at large strain rates and pressures is available for transient material phases formed at high pressures, and the continuum effect the phase transformation process has on the instability evolution. In this work, a phase-aware isotropic strength model is developed and partially validated with a novel RM-based instability experiment in addition to existing data from the literature. With the validated material model additional simulations are performed to provide insight into to the role that robust material constitutive behavior (e.g., pressure, temperature, rate dependence) has on RM instability and how RM instability experiments can be used to characterize and validated expected material behavior. For phase aware materials, particularly iron in this work, the simulations predict a strong dependence on the Atwood number that single phase materials do not have. At Atwood numbers close to unity, and pressures in the high pressure stability region, the high pressure phase dominates the RM evolution. However, at Atwood numbers close to negative one, the RM evolution is only weakly affected by the high-pressure phase even for shocks well above the phase transformation threshold. In addition to RM evolution this work looks at the closely related shock front perturbation evolution. Existing analytical models for isentropic processes in gases and liquids are modified for metal equation of states and plastic behavior for the first time. It is found that the presence of a volume collapsing phase transformation with increased pressure causes shock front perturbations to decay sooner, while plastic strength has the opposite effect which is significantly different from the effect viscosity has. These results suggest additional experimental setups to validate material models, or relevant material parameters that can be optimized for system design objectives, e.g., minimize feed through perturbations in inertial confinement fusion capsules.

Shock induced polymorphic transition in quartz, carbon, and boron nitride

NASA Technical Reports Server (NTRS)

Tan, Hua; Ahrens, Thomas J.

1990-01-01

The model proposed by Ahrens (1988) to explain the mechanism of the polymorphism in silicates is revised, and the revised model is applied to the quartz/stishovite, graphite/diamond, and graphite-boron nitride (g-BN) phase transformations. In this model, a key assumption is that transformation to a high-density amorphous or possibly liquid phase which rapidly crystallized to the high-pressure phase is triggered by the high temperatures in the shear band and upon crossing the metastable extension of a melting curve. Good agreement between the calcualted results and published data is obtained. The present theory predicts the standard entropy for cubic BN to be 0.4-0.5 J/g K.

Analysis of thermomechanical states in single-pass GMAW surfaced steel element

NASA Astrophysics Data System (ADS)

Winczek, Jerzy; Gawronska, Elzbieta; Murcinkova, Zuzana; Hatala, Michal; Pavlenko, Slavko; Makles, Krzysztof

2017-03-01

In the paper the model of temperature field, phase changes and stress states calculation during single-pass arc weld surfacing have been presented. In temperature field solution the temperature changes caused by the heat of weld and by electric arc have been taken into consideration. Kinetics of phase changes during heating is limited by temperature values at the beginning and at the end of austenitic transformation, while progress of phase transformations during cooling has been determined on the basis of time-temperature-transformation (TTT) - welding diagram. The analysis of stress state has been presented for S235 steel flat assuming planar section hypothesis and using integral equations of stress equilibrium. It has enabled a clear interpretation of influence of temperature field and phase transformation on stresses caused by surfacing using Gas Metal Arc Welding (GMAW) method.

Characterization of Titan III-D Acoustic Pressure Spectra by Least-Squares Fit to Theoretical Model

DTIC Science & Technology

1980-01-01

P(f) for a set value of P0 and f0" Mhe inverse transform was taken and the result multiplied by a decaying exponential which modelled the envelope of...0 FORWARD TRANSFORM C IF=1 INVERSE TRANSFORM c C M 0 XREAL AND XIMAG RETURNED AS REAL AND IMAG. FOR FORWARD Xr"RM9; C M= " " " MAGNITUDE AND PHASE...34 .. .. C (PHASE IN DEGREE9) C M=2 XREAL RETURNED AS ’PSD’ XIMAG =0. C HERE ’DSD’ MEANS SUM OF N VALUES OF XREAL = MEAN SQU\\Riz OF INPUT C C FOR INVERSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devaraj, Arun; Jana, Saumyadeep; McInnis, Colleen A.

During eutectoid transformation of U-10Mo alloy, uniform metastable γ UMo phase is expected to transform to a mixture of α-U and γ’-U 2Mo phase. The presence of transformation products in final U-10Mo fuel, especially the α phase is considered detrimental for fuel irradiation performance, so it is critical to accurately evaluate the extent of transformation in the final U-10Mo alloy. This phase transformation can cause a volume change that induces a density change in final alloy. To understand this density and volume change, we developed a theoretical model to calculate the volume expansion and resultant density change of U-10Mo alloymore » as a function of the extent of eutectoid transformation. Based on the theoretically calculated density change for 0 to 100% transformation, we conclude that an experimental density measurement system will be challenging to employ to reliably detect and quantify the extent of transformation. Subsequently, to assess the ability of various methods to detect the transformation in U-10Mo, we annealed U-10Mo alloy samples at 500°C for various times to achieve in low, medium, and high extent of transformation. After the heat treatment at 500°C, the samples were metallographically polished and subjected to optical microscopy and x-ray diffraction (XRD) methods. Based on our assessment, optical microscopy and image processing can be used to determine the transformed area fraction, which can then be correlated with the α phase volume fraction measured by XRD analysis. XRD analysis of U-10Mo aged at 500°C detected only α phase and no γ’ was detected. To further validate the XRD results, atom probe tomography (APT) was used to understand the composition of transformed regions in U-10Mo alloys aged at 500°C for 10 hours. Based on the APT results, the lamellar transformation product was found to comprise α phase with close to 0 at% Mo and γ phase with 28–32 at% Mo, and the Mo concentration was highest at the α/γ interface.« less

Gyrator transform of Gaussian beams with phase difference and generation of hollow beam

NASA Astrophysics Data System (ADS)

Xiao, Zhiyu; Xia, Hui; Yu, Tao; Xie, Ding; Xie, Wenke

2018-03-01

The optical expression of Gaussian beams with phase difference, which is caused by gyrator transform (GT), has been obtained. The intensity and phase distribution of transform Gaussian beams are analyzed. It is found that the circular hollow vortex beam can be obtained by overlapping two GT Gaussian beams with π phase difference. The effect of parameters on the intensity and phase distributions of the hollow vortex beam are discussed. The results show that the shape of intensity distribution is significantly influenced by GT angle α and propagation distance z. The size of the hollow vortex beam can be adjusted by waist width ω 0. Compared with previously reported results, the work shows that the hollow vortex beam can be obtained without any model conversion of the light source.

Gyrator transform of Gaussian beams with phase difference and generation of hollow beam

NASA Astrophysics Data System (ADS)

Xiao, Zhiyu; Xia, Hui; Yu, Tao; Xie, Ding; Xie, Wenke

2018-06-01

The optical expression of Gaussian beams with phase difference, which is caused by gyrator transform (GT), has been obtained. The intensity and phase distribution of transform Gaussian beams are analyzed. It is found that the circular hollow vortex beam can be obtained by overlapping two GT Gaussian beams with π phase difference. The effect of parameters on the intensity and phase distributions of the hollow vortex beam are discussed. The results show that the shape of intensity distribution is significantly influenced by GT angle α and propagation distance z. The size of the hollow vortex beam can be adjusted by waist width ω 0. Compared with previously reported results, the work shows that the hollow vortex beam can be obtained without any model conversion of the light source.

Unraveling the Age Hardening Response in U-Nb Alloys

DOE PAGES

Hackenberg, Robert Errol; Hemphill, Geralyn M. Sewald; Forsyth, Robert Thomas; ...

2016-11-15

Complicating factors that have stymied understanding of uranium-niobium’s aging response are briefly reviewed, including (1) niobium inhomogeneity, (2) machining damage effects on tensile properties, (3) early-time transients of ductility increase, and (4) the variety of phase transformations. A simple Logistic-Arrhenius model was applied to predict yield and ultimate tensile strengths and tensile elongation of U-4Nb as a function of thermal age. Lastly, fits to each model yielded an apparent activation energy that was compared with phase transformation mechanisms.

Phase equilibrium modeling for high temperature metallization on GaAs solar cells

NASA Technical Reports Server (NTRS)

Chung, M. A.; Davison, J. E.; Smith, S. R.

1991-01-01

Recent trends in performance specifications and functional requirements have brought about the need for high temperature metallization technology to be developed for survivable DOD space systems and to enhance solar cell reliability. The temperature constitution phase diagrams of selected binary and ternary systems were reviewed to determine the temperature and type of phase transformation present in the alloy systems. Of paramount interest are the liquid-solid and solid-solid transformations. Data are being utilized to aid in the selection of electrical contact materials to gallium arsenide solar cells. Published data on the phase diagrams for binary systems is readily available. However, information for ternary systems is limited. A computer model is being developed which will enable the phase equilibrium predictions for ternary systems where experimental data is lacking.

THERMODYNAMICS AND KINETICS OF PHASE TRANSFORMATIONS IN PLUTONIUM ALLOYS - PART I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turchi, P A; Kaufman, L; Liu, Z

2004-08-18

In this report we investigate order, stability, and phase transformations for a series of actinide-based alloys. The statics and kinetics of precipitation and ordering in this class of alloys are modeled with a scheme that couples fundamental information on the alloy energetics obtained from experimental and assessed thermo-chemical data to the CALPHAD approach commonly used in industry for designing alloys with engineering specificity with the help of the Thermo-Calc software application. The CALPHAD approach is applied to the study of the equilibrium thermodynamic properties of Pu-based alloys, Pu-X, where X=Al, Fe, Ga. The assessment of the equilibrium phase diagrams inmore » the whole range of alloy composition has been performed with the PARROT module of the Thermo-Calc application software. Predictions are made on the low temperature and Pu-rich side of the phase diagrams of Pu-Ga and Pu-Al for which controversy has been noted in the past. The validity of the assessed thermo-chemical database will be discussed by comparing predicted heats of transformation for pure Pu with measured values from differential scanning calorimetry analysis. An overall picture for the stability properties of Pu-Ga and Pu-Al that reconciles the results of past studies carried out on these alloys is proposed. Results on phase stability in the ternary Fe-Ga-Pu and Al-Fe-Pu alloys are discussed. The information collected in this study is then used to model metastability, long-term stability and aging for this class of alloys by coupling Thermo-Calc with DICTRA, a series of modules that allow the analysis of DIffusion Controlled TRAnsformations. Kinetics information is then summarized in so-called TTT (temperature-time-transformations) diagrams for the most relevant phases of actinide alloys. Specifically, results are presented on kinetics of phase transformations associated with the eutectoid-phase decomposition reaction occurring at low temperature, and with the martensitic transformation that takes place at low Ga content in Pu-Ga alloys. Finally, after a summary of the most salient results, suggestions are made for further studies at the micro- and mesoscales.« less

Computationally efficient method for Fourier transform of highly chirped pulses for laser and parametric amplifier modeling.

PubMed

Andrianov, Alexey; Szabo, Aron; Sergeev, Alexander; Kim, Arkady; Chvykov, Vladimir; Kalashnikov, Mikhail

2016-11-14

We developed an improved approach to calculate the Fourier transform of signals with arbitrary large quadratic phase which can be efficiently implemented in numerical simulations utilizing Fast Fourier transform. The proposed algorithm significantly reduces the computational cost of Fourier transform of a highly chirped and stretched pulse by splitting it into two separate transforms of almost transform limited pulses, thereby reducing the required grid size roughly by a factor of the pulse stretching. The application of our improved Fourier transform algorithm in the split-step method for numerical modeling of CPA and OPCPA shows excellent agreement with standard algorithms.

Dilatometric investigation of α(orthorhombic)→β(tetragonal) transformation in U-15 wt.% Cr alloy

NASA Astrophysics Data System (ADS)

Rameshkumar, Santhosh; Raju, Subramanian; Saibaba, Saroja

2018-04-01

The α→β transformation characteristics in U-15wt.% Cr alloy have been investigated by dilatometry at slow heating rates (3-10 K min-1). The starting microstructure of U-15Cr alloy consists of a mixture of metastable βm-U(body centred tetroganal), α-U(orthorhombic) and elemental Cr(bcc) phases. Upon heating, the metastable βmU phase has progressively transformed to equilibrium α-U structure; before, finally undergoing equilibrium α→β transformation with further increase in temperature. The measured α→β transformation temperature, when extrapolated to 0 K min-1 heating rate has been found to be higher than the currently accepted equilibrium phase diagram estimate. This is due to the kinetic difficulty associated with Cr-diffusion in U-15Cr alloy. The kinetics of α→β transformation upon continuous heating has been modeled in terms of a suitable framework for diffusional transformations, and the effective activation energy for overall transformation has been estimated to be in the range 160-180 kJ mol-1.

Thermomechanical Characterization and Modeling of Superelastic Shape Memory Alloy Beams and Frames

NASA Astrophysics Data System (ADS)

Watkins, Ryan

Of existing applications, the majority of shape memory alloy (SMA) devices consist of beam (orthodontic wire, eye glasses frames, catheter guide wires) and framed structures (cardiovascular stents, vena cava filters). Although uniaxial tension data is often sufficient to model basic beam behavior (which has been the main focus of the research community), the tension-compression asymmetry and complex phase transformation behavior of SMAs suggests more information is necessary to properly model higher complexity states of loading. In this work, SMA beams are experimentally characterized under general loading conditions (including tension, compression, pure bending, and buckling); furthermore, a model is developed with respect to general beam deformation based on the relevant phenomena observed in the experimental characterization. Stress induced phase transformation within superelastic SMA beams is shown to depend on not only the loading mode, but also kinematic constraints imposed by beam geometry (such as beam cross-section and length). In the cases of tension and pure bending, the structural behavior is unstable and corresponds to phase transformation localization and propagation. This unstable behavior is the result of a local level up--down--up stress/strain response in tension, which is measured here using a novel composite-based experimental technique. In addition to unstable phase transformation, intriguing post-buckling straightening is observed in short SMA columns during monotonic loading (termed unbuckling here). Based on this phenomenological understanding of SMA beam behavior, a trilinear based material law is developed in the context of a Shanley column model and is found to capture many of the relevant features of column buckling, including the experimentally observed unbuckling behavior. Due to the success of this model, it is generalized within the context of beam theory and, in conjunction with Bloch wave stability analysis, is used to model and design SMA honeycombs.

Comparison of Austenite Decomposition Models During Finite Element Simulation of Water Quenching and Air Cooling of AISI 4140 Steel

NASA Astrophysics Data System (ADS)

Babu, K.; Prasanna Kumar, T. S.

2014-08-01

An indigenous, non-linear, and coupled finite element (FE) program has been developed to predict the temperature field and phase evolution during heat treatment of steels. The diffusional transformations during continuous cooling of steels were modeled using Johnson-Mehl-Avrami-Komogorov equation, and the non-diffusion transformation was modeled using Koistinen-Marburger equation. Cylindrical quench probes made of AISI 4140 steel of 20-mm diameter and 50-mm long were heated to 1123 K (850 °C), quenched in water, and cooled in air. The temperature history during continuous cooling was recorded at the selected interior locations of the quench probes. The probes were then sectioned at the mid plane and resultant microstructures were observed. The process of water quenching and air cooling of AISI 4140 steel probes was simulated with the heat flux boundary condition in the FE program. The heat flux for air cooling process was calculated through the inverse heat conduction method using the cooling curve measured during air cooling of a stainless steel 304L probe as an input. The heat flux for the water quenching process was calculated from a surface heat flux model proposed for quenching simulations. The isothermal transformation start and finish times of different phases were taken from the published TTT data and were also calculated using Kirkaldy model and Li model and used in the FE program. The simulated cooling curves and phases using the published TTT data had a good agreement with the experimentally measured values. The computation results revealed that the use of published TTT data was more reliable in predicting the phase transformation during heat treatment of low alloy steels than the use of the Kirkaldy or Li model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garlea, Elena; Steiner, M. A.; Calhoun, C. A.

The α-phase transformation kinetics of as-cast U - 8 wt% Mo below the eutectoid temperature have been established by in situ neutron diffraction. α-phase weight fraction data acquired through Rietveld refinement at five different isothermal hold temperatures can be modeled accurately utilizing a simple Johnson-Mehl-Avrami-Kolmogorov impingement-based theory, and the results are validated by a corresponding evolution in the γ-phase lattice parameter during transformation that follows Vegard’s law. Neutron diffraction data is used to produce a detailed Time-Temperature-Transformation diagram that improves upon inconsistencies in the current literature, exhibiting a minimum transformation start time of 40 min at temperatures between 500 °Cmore » and 510 °C. Lastly, the transformation kinetics of U – 8 wt% Mo can vary significantly from as-cast conditions after extensive heat treatments, due to homogenization of the typical dendritic microstructure which possesses non-negligible solute segregation.« less

Experimental and Numerical Simulations of Phase Transformations Occurring During Continuous Annealing of DP Steel Strips

NASA Astrophysics Data System (ADS)

Wrożyna, Andrzej; Pernach, Monika; Kuziak, Roman; Pietrzyk, Maciej

2016-04-01

Due to their exceptional strength properties combined with good workability the Advanced High-Strength Steels (AHSS) are commonly used in automotive industry. Manufacturing of these steels is a complex process which requires precise control of technological parameters during thermo-mechanical treatment. Design of these processes can be significantly improved by the numerical models of phase transformations. Evaluation of predictive capabilities of models, as far as their applicability in simulation of thermal cycles thermal cycles for AHSS is considered, was the objective of the paper. Two models were considered. The former was upgrade of the JMAK equation while the latter was an upgrade of the Leblond model. The models can be applied to any AHSS though the examples quoted in the paper refer to the Dual Phase (DP) steel. Three series of experimental simulations were performed. The first included various thermal cycles going beyond limitations of the continuous annealing lines. The objective was to validate models behavior in more complex cooling conditions. The second set of tests included experimental simulations of the thermal cycle characteristic for the continuous annealing lines. Capability of the models to describe properly phase transformations in this process was evaluated. The third set included data from the industrial continuous annealing line. Validation and verification of models confirmed their good predictive capabilities. Since it does not require application of the additivity rule, the upgrade of the Leblond model was selected as the better one for simulation of industrial processes in AHSS production.

Transformation-Induced, Geometrically Necessary, Dislocation-Based Flow Curve Modeling of Dual-Phase Steels: Effect of Grain Size

NASA Astrophysics Data System (ADS)

Ramazani, Ali; Mukherjee, Krishnendu; Prahl, Ulrich; Bleck, Wolfgang

2012-10-01

The flow behavior of dual-phase (DP) steels is modeled on the finite-element method (FEM) framework on the microscale, considering the effect of the microstructure through the representative volume element (RVE) approach. Two-dimensional RVEs were created from microstructures of experimentally obtained DP steels with various ferrite grain sizes. The flow behavior of single phases was modeled through the dislocation-based work-hardening approach. The volume change during austenite-to-martensite transformation was modeled, and the resultant prestrained areas in the ferrite were considered to be the storage place of transformation-induced, geometrically necessary dislocations (GNDs). The flow curves of DP steels with varying ferrite grain sizes, but constant martensite fractions, were obtained from the literature. The flow curves of simulations that take into account the GND are in better agreement with those of experimental flow curves compared with those of predictions without consideration of the GND. The experimental results obeyed the Hall-Petch relationship between yield stress and flow stress and the simulations predicted this as well.

Dynamic Diffraction Studies on the Crystallization, Phase Transformation, and Activation Energies in Anodized Titania Nanotubes

PubMed Central

Albetran, Hani; Vega, Victor

2018-01-01

The influence of calcination time on the phase transformation and crystallization kinetics of anodized titania nanotube arrays was studied using in-situ isothermal and non-isothermal synchrotron radiation diffraction from room temperature to 900 °C. Anatase first crystallized at 400 °C, while rutile crystallized at 550 °C. Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 °C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation. The Avrami equation was used to model the titania crystallization mechanism and the Arrhenius equation was used to estimate the activation energies of the titania phase transformation. Activation energies of 22 (10) kJ/mol for the titanium-to-anatase transformation, and 207 (17) kJ/mol for the anatase-to-rutile transformation were estimated. PMID:29473854

Experiment and Modeling of Simultaneous Creep, Plasticity and Transformation of High Temperature Shape Memory Alloys During Cyclic Actuation

NASA Technical Reports Server (NTRS)

Kumar, Parikshith K.; Desai, Uri; Chatzigeorgiou, George; Lagoudas, Dimitris C.; Monroe, James; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glen

2010-01-01

The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary creep effects. The model calibration is based on the test results. The creep tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.

High pressure phase-transformation induced texture evolution and strengthening in zirconium metal: Experiment and modeling

DOE PAGES

Yu, Xiaohui; Zhang, Ruifeng; Weldon, David; ...

2015-07-28

We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can bemore » attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.« less

Large tensile superelasticity from intermartensitic transformations in Ni49Mn28Ga23 single crystal

NASA Astrophysics Data System (ADS)

Chernenko, V. A.; Villa, E.; Salazar, D.; Barandiaran, J. M.

2016-02-01

A multistep superelastic behavior, with up to a 12% strain, is reported in a <001>P-oriented Ni49Mn28Ga23 single crystal. The observed behavior is produced by intermartensitic transformations during the tensile stress-strain measurements at temperatures between -140 °C and +60 °C. The tensile stress-temperature phase diagram and the stress dependence of the intermartensitic transformation entropies have been obtained. These results provide important input for theoretical modeling of the phase transformations in these alloys and show promising mechanical properties of the classical Ni-Mn-Ga ferromagnetic shape memory alloys.

Nanowire growth by an electron beam induced massive phase transformation

DOE PAGES

Sood, Shantanu; Kisslinger, Kim; Gouma, Perena

2014-11-15

Tungsten trioxide nanowires of a high aspect ratio have been synthesized in-situ in a TEM under an electron beam of current density 14A/cm² due to a massive polymorphic reaction. Sol-gel processed pseudocubic phase nanocrystals of tungsten trioxide were seen to rapidly transform to one dimensional monoclinic phase configurations, and this reaction was independent of the substrate on which the material was deposited. The mechanism of the self-catalyzed polymorphic transition and accompanying radical shape change is a typical characteristic of metastable to stable phase transformations in nanostructured polymorphic metal oxides. A heuristic model is used to confirm the metastable to stablemore » growth mechanism. The findings are important to the control electron beam deposition of nanowires for functional applications starting from colloidal precursors.« less

Behaviour of rippled shocks from ablatively-driven Richtmyer-Meshkov in metals accounting for strength

DOE PAGES

Opie, S.; Gautam, S.; Fortin, E.; ...

2016-05-26

While numerous continuum material strength and phase transformation models have been proposed to capture their complex dependences on intensive properties and deformation history, few experimental methods are available to validate these models particularly in the large pressure and strain rate regime typical of strong shock and ramp dynamic loading. In the experiments and simulations we present, a rippled shock is created by laser-ablation of a periodic surface perturbation on a metal target. The strength of the shock can be tuned to access phase transitions in metals such as iron or simply to study high-pressure strength in isomorphic materials such asmore » copper. Simulations, with models calibrated and validated to the experiments, show that the evolution of the amplitude of imprinted perturbations on the back surface by the rippled shock is strongly affected by strength and phase transformation kinetics. Increased strength has a smoothing effect on the perturbed shock front profile resulting in smaller perturbations on the free surface. Lastly, in iron, faster phase transformations kinetics had a similar effect as increased strength, leading to smoother pressure contours inside the samples and smaller amplitudes of free surface perturbations in our simulations.« less

Disorder trapping by rapidly moving phase interface in an undercooled liquid

NASA Astrophysics Data System (ADS)

Galenko, Peter; Danilov, Denis; Nizovtseva, Irina; Reuther, Klemens; Rettenmayr, Markus

2017-08-01

Non-equilibrium phenomena such as the disappearance of solute drag, the origin of solute trapping and evolution of disorder trapping occur during fast transformations with originating metastable phases [D.M. Herlach, P.K. Galenko, D. Holland-Moritz, Metastable solids from undrercooled melts (Elsevier, Amsterdam, 2007)]. In the present work, a theoretical investigation of disorder trapping by a rapidly moving phase interface is presented. Using a model of fast phase transformations, a system of governing equations for the diffusion of atoms, and the evolution of both long-range order parameter and phase field variable is formulated. First numerical solutions are carried out for a congruently melting binary alloy system.

Reduction of the allotropic transition temperature in nanocrystalline zirconium: Predicted by modified equation of state (MEOS) method and molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Salati, Amin; Mokhtari, Esmail; Panjepour, Masoud; Aryanpour, Gholamreza

2013-04-01

The temperature at which polymorphic phase transformation occurs in nanocrystalline (NC) materials is different from that of coarse-grained specimens. This anomaly has been related to the role of grain boundary component in these materials and can be predicted by a dilated crystal model. In this study, based on this model, a modified equation of state (MEOS) method (instead of equation of state, EOS, method) is used to calculate the total Gibbs free energy of each phase (β-Zr or α-Zr) in NC Zr. Thereupon, the change in the total Gibbs free energy for β-Zr to α-Zr phase transformation (ΔGβ→α) via the grain size is calculated by this method. Similar to polymorphic transformation in other NC materials (Fe, Nb, Co, TiO2, Al2O3 and ZnS), it is found that the estimated transformation temperature in NC Zr (β→α) is reduced with decreasing grain size. Finally, a molecular dynamics (MD) simulation is employed to confirm the theoretical results.

Size effects in martensitic microstructures: Finite-strain phase field model versus sharp-interface approach

NASA Astrophysics Data System (ADS)

Tůma, K.; Stupkiewicz, S.; Petryk, H.

2016-10-01

A finite-strain phase field model for martensitic phase transformation and twinning in shape memory alloys is developed and confronted with the corresponding sharp-interface approach extended to interfacial energy effects. The model is set in the energy framework so that the kinetic equations and conditions of mechanical equilibrium are fully defined by specifying the free energy and dissipation potentials. The free energy density involves the bulk and interfacial energy contributions, the latter describing the energy of diffuse interfaces in a manner typical for phase-field approaches. To ensure volume preservation during martensite reorientation at finite deformation within a diffuse interface, it is proposed to apply linear mixing of the logarithmic transformation strains. The physically different nature of phase interfaces and twin boundaries in the martensitic phase is reflected by introducing two order-parameters in a hierarchical manner, one as the reference volume fraction of austenite, and thus of the whole martensite, and the second as the volume fraction of one variant of martensite in the martensitic phase only. The microstructure evolution problem is given a variational formulation in terms of incremental fields of displacement and order parameters, with unilateral constraints on volume fractions explicitly enforced by applying the augmented Lagrangian method. As an application, size-dependent microstructures with diffuse interfaces are calculated for the cubic-to-orthorhombic transformation in a CuAlNi shape memory alloy and compared with the sharp-interface microstructures with interfacial energy effects.

The Riesz transform and simultaneous representations of phase, energy and orientation in spatial vision.

PubMed

Langley, Keith; Anderson, Stephen J

2010-08-06

To represent the local orientation and energy of a 1-D image signal, many models of early visual processing employ bandpass quadrature filters, formed by combining the original signal with its Hilbert transform. However, representations capable of estimating an image signal's 2-D phase have been largely ignored. Here, we consider 2-D phase representations using a method based upon the Riesz transform. For spatial images there exist two Riesz transformed signals and one original signal from which orientation, phase and energy may be represented as a vector in 3-D signal space. We show that these image properties may be represented by a Singular Value Decomposition (SVD) of the higher-order derivatives of the original and the Riesz transformed signals. We further show that the expected responses of even and odd symmetric filters from the Riesz transform may be represented by a single signal autocorrelation function, which is beneficial in simplifying Bayesian computations for spatial orientation. Importantly, the Riesz transform allows one to weight linearly across orientation using both symmetric and asymmetric filters to account for some perceptual phase distortions observed in image signals - notably one's perception of edge structure within plaid patterns whose component gratings are either equal or unequal in contrast. Finally, exploiting the benefits that arise from the Riesz definition of local energy as a scalar quantity, we demonstrate the utility of Riesz signal representations in estimating the spatial orientation of second-order image signals. We conclude that the Riesz transform may be employed as a general tool for 2-D visual pattern recognition by its virtue of representing phase, orientation and energy as orthogonal signal quantities.

A unified analysis of solidification in Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Lu, Ming-Fang

2012-04-01

The simulation of multiphase solidification process can be handled by combining the VOF (Volume of Fluid) transport equation, in which the continuum mechanics model is used to simulate the melt/solid interface and the conservation of mass, momentum, and energy. Because the melt phase, the solid phase, and the melt/solid interface are controlled by a single control equation; if the enthalpy model based on porosity concept represents the processing of the phase transformation range, it is possible to solve the problem of phase transformation in the same way as solving the single-phase problem. Once the energy field of enthalpy for each step in time is resolved, the position of the interface can be precisely calculated with the use of VOF equation. This type of novel VOF method can be applied to find out the conditions of vertical Bridgman crystal growing located on the earth or under microgravity.

A unified analysis of solidification in Bridgman crystal growth

NASA Astrophysics Data System (ADS)

Lu, Ming-Fang

2011-11-01

The simulation of multiphase solidification process can be handled by combining the VOF (Volume of Fluid) transport equation, in which the continuum mechanics model is used to simulate the melt/solid interface and the conservation of mass, momentum, and energy. Because the melt phase, the solid phase, and the melt/solid interface are controlled by a single control equation; if the enthalpy model based on porosity concept represents the processing of the phase transformation range, it is possible to solve the problem of phase transformation in the same way as solving the single-phase problem. Once the energy field of enthalpy for each step in time is resolved, the position of the interface can be precisely calculated with the use of VOF equation. This type of novel VOF method can be applied to find out the conditions of vertical Bridgman crystal growing located on the earth or under microgravity.

Constitutive modeling of the dynamic-tensile-extrusion test of PTFE

NASA Astrophysics Data System (ADS)

Resnyansky, A. D.; Brown, E. N.; Trujillo, C. P.; Gray, G. T.

2017-01-01

Use of polymers in defense, aerospace and industrial applications under extreme loading conditions makes prediction of the behavior of these materials very important. Crucial to this is knowledge of the physical damage response in association with phase transformations during loading and the ability to predict this via multi-phase simulation accounting for thermodynamical non-equilibrium and strain rate sensitivity. The current work analyzes Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) experiments on polytetrafluoroethylene (PTFE). In particular, the phase transition during loading and subsequent tension are analyzed using a two-phase rate sensitive material model implemented in the CTH hydrocode. The calculations are compared with experimental high-speed photography. Deformation patterns and their link with changing loading modes are analyzed numerically and correlated to the test observations. It is concluded that the phase transformation is not as critical to the response of PTFE under Dyn-Ten-Ext loading as it is during the Taylor rod impact testing.

Heating- and pressure-induced transformations in amorphous and hexagonal ice: A computer simulation study using the TIP4P/2005 model

NASA Astrophysics Data System (ADS)

Engstler, Justin; Giovambattista, Nicolas

2017-08-01

We characterize the phase behavior of glassy water by performing extensive out-of-equilibrium molecular dynamics simulations using the TIP4P/2005 water model. Specifically, we study (i) the pressure-induced transformations between low-density (LDA) and high-density amorphous ice (HDA), (ii) the pressure-induced amorphization (PIA) of hexagonal ice (Ih), (iii) the heating-induced LDA-to-HDA transformation at high pressures, (iv) the heating-induced HDA-to-LDA transformation at low and negative pressures, (v) the glass transition temperatures of LDA and HDA as a function of pressure, and (vi) the limit of stability of LDA upon isobaric heating and isothermal decompression (at negative pressures). These transformations are studied systematically, over a wide range of temperatures and pressures, allowing us to construct a P-T phase diagram for glassy TIP4P/2005 water. Our results are in qualitative agreement with experimental observations and with the P-T phase diagram obtained for glassy ST2 water that exhibits a liquid-liquid phase transition and critical point. We also discuss the mechanism for PIA of ice Ih and show that this is a two-step process where first, the hydrogen-bond network (HBN) is distorted and then the HBN abruptly collapses. Remarkably, the collapse of the HB in ice Ih occurs when the average molecular orientations order, a measure of the tetrahedrality of the HBN, is of the same order as in LDA, suggesting a common mechanism for the LDA-to-HDA and Ih-to-HDA transformations.

Heating- and pressure-induced transformations in amorphous and hexagonal ice: A computer simulation study using the TIP4P/2005 model.

PubMed

Engstler, Justin; Giovambattista, Nicolas

2017-08-21

We characterize the phase behavior of glassy water by performing extensive out-of-equilibrium molecular dynamics simulations using the TIP4P/2005 water model. Specifically, we study (i) the pressure-induced transformations between low-density (LDA) and high-density amorphous ice (HDA), (ii) the pressure-induced amorphization (PIA) of hexagonal ice (I h ), (iii) the heating-induced LDA-to-HDA transformation at high pressures, (iv) the heating-induced HDA-to-LDA transformation at low and negative pressures, (v) the glass transition temperatures of LDA and HDA as a function of pressure, and (vi) the limit of stability of LDA upon isobaric heating and isothermal decompression (at negative pressures). These transformations are studied systematically, over a wide range of temperatures and pressures, allowing us to construct a P-T phase diagram for glassy TIP4P/2005 water. Our results are in qualitative agreement with experimental observations and with the P-T phase diagram obtained for glassy ST2 water that exhibits a liquid-liquid phase transition and critical point. We also discuss the mechanism for PIA of ice I h and show that this is a two-step process where first, the hydrogen-bond network (HBN) is distorted and then the HBN abruptly collapses. Remarkably, the collapse of the HB in ice I h occurs when the average molecular orientations order, a measure of the tetrahedrality of the HBN, is of the same order as in LDA, suggesting a common mechanism for the LDA-to-HDA and I h -to-HDA transformations.

Molecular dynamics study of dual-phase microstructure of Titanium and Zirconium metals during the quenching process

NASA Astrophysics Data System (ADS)

Miyazaki, Narumasa; Sato, Kazunori; Shibutani, Yoji

Dual-phase (DP) transformation, which is composed of felite- and/or martensite- multicomponent microstructural phases, is one of the most effective tools to product functional alloys. To obtain this DP structure such as DP steels and other materials, we usually apply thermal processes such as quenching, tempering and annealing. As the transformation dynamics of DP microstructure depends on conditions of temperature, annealing time, and quenching rate, physical properties of materials are able to be tuned by controlling microstructure type, size, their interfaces and so on. In this study, to understand the behavior of DP transformation and to control physical properties of materials by tuning DP microstructures, we analyze the atomistic dynamics of DP transformation during the quenching process and the detail of DP microstructures by using the molecular dynamics simulations. As target metals of DP transformation, we focus on group 4 transition metals, such as Ti and Zr described by EAM interatomic potentials. For Ti and Zr models we perform molecular dynamics simulations by assuming melt-quenching process from 3000 K to 0 K under the isothermal-isobaric ensemble. During the process for each material, we observe liquid to HCP like transition around the melting temperature, and continuously HCP-BCC like transition around martensitic transformation temperature. Furthermore, we clearly distinguish DP microstructure for each quenched model.

Effects of lateral diffusion on morphology and dynamics of a microscopic lattice-gas model of pulsed electrodeposition.

PubMed

Frank, Stefan; Roberts, Daniel E; Rikvold, Per Arne

2005-02-08

The influence of nearest-neighbor diffusion on the decay of a metastable low-coverage phase (monolayer adsorption) in a square lattice-gas model of electrochemical metal deposition is investigated by kinetic Monte Carlo simulations. The phase-transformation dynamics are compared to the well-established Kolmogorov-Johnson-Mehl-Avrami theory. The phase transformation is accelerated by diffusion, but remains in accord with the theory for continuous nucleation up to moderate diffusion rates. At very high diffusion rates the phase-transformation kinetic shows a crossover to instantaneous nucleation. Then, the probability of medium-sized clusters is reduced in favor of large clusters. Upon reversal of the supersaturation, the adsorbate desorbs, but large clusters still tend to grow during the initial stages of desorption. Calculation of the free energy of subcritical clusters by enumeration of lattice animals yields a quasiequilibrium distribution which is in reasonable agreement with the simulation results. This is an improvement relative to classical droplet theory, which fails to describe the distributions, since the macroscopic surface tension is a bad approximation for small clusters.

Final Report, Fundamental Mechanisms of Transient States in Materials Quantified by DTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, G. H.; McKeown, J. T.

At the project’s inception, there was growing evidence that the time domain for in situ observations of material evolution held great promise for allowing measurements to be made in never previously contemplated regimes. Also, central to the development of the project was the knowledge that phase transformations are of central importance to the development of materials microstructure and hence properties. We addressed this opportunity by developing a transmission electron microscope that could be operated in the pulsed mode (DTEM), with exposure times down to 20 ns and interframe times down to 20 ns in the nine-frame movie mode, designed withmore » the intent of performing in situ experiments. This unprecedented capability allowed us to investigate structural phase transformations, intermetallic formation reactions, crystallization from the amorphous phase, rapid solidification of liquid metals, transformations in phase change materials, and catalyst nanoparticles. The ability of the electron microscope to create images with high spatial resolution allows for the accurate measurement of position. Common to all of the transformations mentioned above is the presence of a distinct interface between the old phase and the growing new phase. Measuring the position of the interface as a function of time, combined with the ability to count nucleation sites as a function of time, allowed for the exceptionally accurate measure of transformation kinetics. These measurements were used to guide and constrain the development of models and simulation methods for the classes of transformations studied.« less

Two-Phase Model of Combustion in Explosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuhl, A L; Khasainov, B; Bell, J

2006-06-19

A two-phase model for Aluminum particle combustion in explosions is proposed. It combines the gas-dynamic conservation laws for the gas phase with the continuum mechanics laws of multi-phase media, as formulated by Nigmatulin. Inter-phase mass, momentum and energy exchange are prescribed by the Khasainov model. Combustion is specified as material transformations in the Le Chatelier diagram which depicts the locus of thermodynamic states in the internal energy-temperature plane according to Kuhl. Numerical simulations are used to show the evolution of two-phase combustion fields generated by the explosive dissemination of a powdered Al fuel.

About the choice of Gibbs' potential for modelling of FCC ↔ HCP transformation in FeMnSi-based shape memory alloys

NASA Astrophysics Data System (ADS)

Evard, Margarita E.; Volkov, Aleksandr E.; Belyaev, Fedor S.; Ignatova, Anna D.

2018-05-01

The choice of Gibbs' potential for microstructural modeling of FCC ↔ HCP martensitic transformation in FeMn-based shape memory alloys is discussed. Threefold symmetry of the HCP phase is taken into account on specifying internal variables characterizing volume fractions of martensite variants. Constraints imposed on model constants by thermodynamic equilibrium conditions are formulated.

Stability of phase transformation models for Ti-6Al-4V under cyclic thermal loading imposed during laser metal deposition

NASA Astrophysics Data System (ADS)

Klusemann, Benjamin; Bambach, Markus

2018-05-01

Processing conditions play a crucial role for the resulting microstructure and properties of the material. In particular, processing materials under non-equilibrium conditions can lead to a remarkable improvement of the final properties [1]. Additive manufacturing represents a specific process example considered in this study. Models for the prediction of residual stresses and microstructure in additive manufacturing processes, such as laser metal deposition, are being developed with huge efforts to support the development of materials and processes as well as to support process design [2-4]. Since the microstructure predicted after each heating and cooling cycle induced by the moving laser source enters the phase transformation kinetics and microstucture evolution of the subsequent heating and cooling cycle, a feed-back loop for the microstructure calculation is created. This calculation loop may become unstable so that the computed microstructure and related properties become very sensitive to small variations in the input parameters, e.g. thermal conductivity. In this paper, a model for phase transformation in Ti-6Al-4V, originally proposed by Charles Murgau et al. [5], is adopted and minimal adjusted concerning the decomposition of the martensite phase are made. This model is subsequently used to study the changes in the predictions of the different phase volume fractions during heating and cooling under the conditions of laser metal deposition with respect to slight variations in the thermal process history.

A theoretical study of the omega-phase transformation in metals

NASA Astrophysics Data System (ADS)

Sanati, Mahdi

I have studied the formation of o-phase from electronic and mesoscopic (domain wall) points of view. To study the formation of domain walls, I have extended the Landau model of Cook for the o-phase transition by including a spatial gradient (Ginzburg) term of the scalar order parameter. In general, the Landau free energy is an asymmetric double-well potential. From the variational derivative of the total free energy I obtained a static equilibrium condition. By solving this equation for different physical parameters and boundary conditions, I obtained different quasi-one-dimensional soliton-like solutions. These solutions correspond to three different types of domain walls between the o-phase and the beta-matrix. These results are used to model the formation of the o-phase in bcc Ti. Canonical band model and first principles calculations confirmed the instability of the bcc-phase of group III and IV transition metals with respect to the o-phase transformation. I showed that the d-electron density is the controlling parameter for this type of the transformation. Also the possibility of formation of the o-phase for rare earth metals is discussed. First-principles full-potential linear muffin-tin orbital method (FPLMTO) calculations are performed for o-type displacement of the atoms to study the formation of the o-phase in TiAl and Ti 3Al2Nb alloys. The results of my calculations showed an instability in ordered B2 TiAl structure with respect to the o-phase when one third of the Al atoms are replaced by Nb atoms. These phenomena are explained, first by symmetry arguments; then a pair potential model is used to illustrate this instability based on interactions between different pair of atoms derived from the electronic structure. In addition, importance of the atomic arrangements on the structural stability of the Ti3Al2 Nb system is discussed.

Small strain multiphase-field model accounting for configurational forces and mechanical jump conditions

NASA Astrophysics Data System (ADS)

Schneider, Daniel; Schoof, Ephraim; Tschukin, Oleg; Reiter, Andreas; Herrmann, Christoph; Schwab, Felix; Selzer, Michael; Nestler, Britta

2018-03-01

Computational models based on the phase-field method have become an essential tool in material science and physics in order to investigate materials with complex microstructures. The models typically operate on a mesoscopic length scale resolving structural changes of the material and provide valuable information about the evolution of microstructures and mechanical property relations. For many interesting and important phenomena, such as martensitic phase transformation, mechanical driving forces play an important role in the evolution of microstructures. In order to investigate such physical processes, an accurate calculation of the stresses and the strain energy in the transition region is indispensable. We recall a multiphase-field elasticity model based on the force balance and the Hadamard jump condition at the interface. We show the quantitative characteristics of the model by comparing the stresses, strains and configurational forces with theoretical predictions in two-phase cases and with results from sharp interface calculations in a multiphase case. As an application, we choose the martensitic phase transformation process in multigrain systems and demonstrate the influence of the local homogenization scheme within the transition regions on the resulting microstructures.

Gas uptake and chemical aging of semisolid organic aerosol particles

PubMed Central

Shiraiwa, Manabu; Ammann, Markus; Koop, Thomas; Pöschl, Ulrich

2011-01-01

Organic substances can adopt an amorphous solid or semisolid state, influencing the rate of heterogeneous reactions and multiphase processes in atmospheric aerosols. Here we demonstrate how molecular diffusion in the condensed phase affects the gas uptake and chemical transformation of semisolid organic particles. Flow tube experiments show that the ozone uptake and oxidative aging of amorphous protein is kinetically limited by bulk diffusion. The reactive gas uptake exhibits a pronounced increase with relative humidity, which can be explained by a decrease of viscosity and increase of diffusivity due to hygroscopic water uptake transforming the amorphous organic matrix from a glassy to a semisolid state (moisture-induced phase transition). The reaction rate depends on the condensed phase diffusion coefficients of both the oxidant and the organic reactant molecules, which can be described by a kinetic multilayer flux model but not by the traditional resistor model approach of multiphase chemistry. The chemical lifetime of reactive compounds in atmospheric particles can increase from seconds to days as the rate of diffusion in semisolid phases can decrease by multiple orders of magnitude in response to low temperature or low relative humidity. The findings demonstrate that the occurrence and properties of amorphous semisolid phases challenge traditional views and require advanced formalisms for the description of organic particle formation and transformation in atmospheric models of aerosol effects on air quality, public health, and climate. PMID:21690350

Investigations on solid-solid phase transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile.

PubMed

Li, Hui; Stowell, Joseph G; He, Xiaorong; Morris, Kenneth R; Byrn, Stephen R

2007-05-01

Solid-solid transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile from the dark-red to the red form was investigated. By controlled crystallization, the dark-red form was prepared and the crystals were sieved into fractions: coarse (>250 microm), medium (125-177 microm), and fine (<88 microm). The transformation rate order (fastest to slowest) of the different fractions is coarse > medium > fine. However, milling accelerates the transformation, that is, smaller particles generated by milling transforms faster. Furthermore, ethanol vapor annealing slows both the transformation of the coarse and medium fractions, especially the latter. Therefore, the mechanism of transformation is not directly related to the crystal-size and most likely related to the amount and activity of the defects in the crystals. The three-dimensional (3-D) Avrami-Erofe'ev model, know as "random nucleation and growth" model, fits the kinetics of coarse fraction best. Higher relative humidity accelerates the transformation dramatically even though the compound is highly-hydrophobic. With minimal hydrogen bonding interaction involved, it appears even small amounts of water can serve as a nucleation catalyst by binding to the crystal surface, especially at defect sites, thus increasing the molecular mobility of these sites, promoting the transformation to the second phase and thereby increasing the transformation rate. (c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association.

Transforming Primary Care Practice and Education: Lessons From 6 Academic Learning Collaboratives.

PubMed

Koch, Ursula; Bitton, Asaf; Landon, Bruce E; Phillips, Russell S

Adoption of new primary care models has been slow in academic teaching practices. We describe a common framework that academic learning collaboratives are using to transform primary care practice based on our analysis of 6 collaboratives nationally. We show that the work of the collaboratives could be divided into 3 phases and provide detail on the phases of work and a road map for those who seek to emulate this work. We found that learning collaboratives foster transformation, even in complex academic practices, but need specific support adapted to their unique challenges.

Negative pressure driven phase transformation in Sr doped SmCoO₃.

PubMed

Arshad Farhan, M; Javed Akhtar, M

2010-02-24

Atomistic computer simulation techniques based on energy minimization procedures are utilized for the structural investigation of perovskite-type SmCoO(3). A reliable potential model is derived which reproduces both cubic as well as orthorhombic phases of SmCoO(3). We observe a negative chemical pressure induced structural phase transformation from distorted perovskite (orthorhombic) to perfect perovskite (cubic) due to the substitution of Sr(2 + ) at the Sm(3 + ) sites. However, external hydrostatic pressure shows isotropic compression and no pressure-induced structural transformation is observed up to 100 GPa. To maintain the electroneutrality of the system, charge compensation is through oxygen vacancies which results in the brownmillerite-type structure. A defect model is proposed, which is consistent with experimental results. The solution energies for divalent and trivalent cations are also calculated. These results show that the cations having ionic radii less than 0.75 Å will occupy the Co sites and those with ionic radii larger than 0.75 Å will substitute at the Sm sites.

Pressure-induced transformations in computer simulations of glassy water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2013-11-14

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Pressure-induced transformations in computer simulations of glassy water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2013-11-01

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

A Thin Lens Model for Charged-Particle RF Accelerating Gaps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Christopher K.

Presented is a thin-lens model for an RF accelerating gap that considers general axial fields without energy dependence or other a priori assumptions. Both the cosine and sine transit time factors (i.e., Fourier transforms) are required plus two additional functions; the Hilbert transforms the transit-time factors. The combination yields a complex-valued Hamiltonian rotating in the complex plane with synchronous phase. Using Hamiltonians the phase and energy gains are computed independently in the pre-gap and post-gap regions then aligned using the asymptotic values of wave number. Derivations of these results are outlined, examples are shown, and simulations with the model aremore » presented.« less

Ice polyamorphism in the minimal Mercedes-Benz model of water.

PubMed

Cartwright, Julyan H E; Piro, Oreste; Sánchez, Pedro A; Sintes, Tomás

2012-12-28

We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism.

Ice polyamorphism in the minimal Mercedes-Benz model of water

NASA Astrophysics Data System (ADS)

Cartwright, Julyan H. E.; Piro, Oreste; Sánchez, Pedro A.; Sintes, Tomás

2012-12-01

We investigate ice polyamorphism in the context of the two-dimensional Mercedes-Benz model of water. We find a first-order phase transition between a crystalline phase and a high-density amorphous phase. Furthermore, we find a reversible transformation between two amorphous structures of high and low density; however, we find this to be a continuous and not an abrupt transition, as the low-density amorphous phase does not show structural stability. We discuss the origin of this behavior and its implications with regard to the minimal generic modeling of polyamorphism.

Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution

PubMed Central

Esmaeeli, Hadi S.; Farnam, Yaghoob; Bentz, Dale P.; Zavattieri, Pablo D.; Weiss, Jason

2016-01-01

This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to −35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained. PMID:28082830

Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution.

PubMed

Esmaeeli, Hadi S; Farnam, Yaghoob; Bentz, Dale P; Zavattieri, Pablo D; Weiss, Jason

2017-02-01

This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to -35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained.

Transformation kinetics for the shock wave induced phase transition in cadmium sulfide crystals

NASA Astrophysics Data System (ADS)

Knudson, M. D.; Gupta, Y. M.

2002-06-01

Initial stage kinetics of the cadmium sulfide (CdS) phase transition was investigated using picosecond time-resolved electronic spectroscopy in plate-impact shock wave experiments. Real-time changes in the electronic spectra were observed, with 100 ps time resolution, in CdS single crystals shocked along a and c axes to stresses ranging between 35 and 90 kbar, which is above the phase-transition threshold stress of approximately 30 kbar. Significant difference in the transformation kinetics was observed for the two crystal orientations. At sufficiently high instantaneous stress, above approximately 60 to 70 kbar for a axis and 50 kbar for c axis, transformation to a metastable state appears to reach a constant state within the 100 ps time resolution. At lower instantaneous stresses, an incubation period on the order of several nanoseconds is observed prior to the onset of electronic changes that mark the onset of the structural change. The subsequent increase in absorbance was quite rapid, with a constant state being reached within the first few nanoseconds after the onset of the structural changes. These results suggest that the nucleation process determines the transformation rate. This insight into transformation kinetics, along with the transformation mechanism obtained from the high-stress experiments, was used to develop a phenomenological model, incorporating ideas of nucleation and growth in martensitic transformations, to simulate the time-dependent extinction of light observed in our experiments. The calculational results incorporating both extinction due to light absorption by the daughter phase volumes and scattering of light by small volumes of the daughter phase were in good agreement with experimental observations. Finally, the orientational differences observed in the transformation kinetics were interpreted in terms of the differences in the elastic-plastic response for the two orientations.

Sensitivity analysis of simulated SOA loadings using a variance-based statistical approach: SENSITIVITY ANALYSIS OF SOA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrivastava, Manish; Zhao, Chun; Easter, Richard C.

We investigate the sensitivity of secondary organic aerosol (SOA) loadings simulated by a regional chemical transport model to 7 selected tunable model parameters: 4 involving emissions of anthropogenic and biogenic volatile organic compounds, anthropogenic semi-volatile and intermediate volatility organics (SIVOCs), and NOx, 2 involving dry deposition of SOA precursor gases, and one involving particle-phase transformation of SOA to low volatility. We adopt a quasi-Monte Carlo sampling approach to effectively sample the high-dimensional parameter space, and perform a 250 member ensemble of simulations using a regional model, accounting for some of the latest advances in SOA treatments based on our recentmore » work. We then conduct a variance-based sensitivity analysis using the generalized linear model method to study the responses of simulated SOA loadings to the tunable parameters. Analysis of SOA variance from all 250 simulations shows that the volatility transformation parameter, which controls whether particle-phase transformation of SOA from semi-volatile SOA to non-volatile is on or off, is the dominant contributor to variance of simulated surface-level daytime SOA (65% domain average contribution). We also split the simulations into 2 subsets of 125 each, depending on whether the volatility transformation is turned on/off. For each subset, the SOA variances are dominated by the parameters involving biogenic VOC and anthropogenic SIVOC emissions. Furthermore, biogenic VOC emissions have a larger contribution to SOA variance when the SOA transformation to non-volatile is on, while anthropogenic SIVOC emissions have a larger contribution when the transformation is off. NOx contributes less than 4.3% to SOA variance, and this low contribution is mainly attributed to dominance of intermediate to high NOx conditions throughout the simulated domain. The two parameters related to dry deposition of SOA precursor gases also have very low contributions to SOA variance. This study highlights the large sensitivity of SOA loadings to the particle-phase transformation of SOA volatility, which is neglected in most previous models.« less

Kinetics of Phase Transition from Lamellar to Hexagonally Packed Cylinders for a Triblock Copolymer in a Selective Solvent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu,Y.; Li, M.; Bansil, R.

2007-01-01

We examined the kinetics of the transformation from the lamellar (LAM) to the hexagonally packed cylinder (HEX) phase for the triblock copolymer, polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) in dibutyl phthalate (DBP), a selective solvent for polystyrene (PS), using time-resolved small-angle X-ray scattering (SAXS). We observe the HEX phase with the EB block in the cores at a lower temperature than that observed for the LAM phase due to the solvent selectivity of DBP for the PS block. Analysis of the SAXS data for a deep temperature quench well below the LAM-HEX transition shows that the transformation occurs in a one-step process. Wemore » calculate the scattering using a geometric model of rippled layers with adjacent layers totally out of phase during the transformation. The agreement of the calculations with the data further supports the continuous transformation mechanism from the LAM to HEX for a deep quench. In contrast, for a shallow quench close to the order-order transition, we find agreement with a two-step nucleation and growth mechanism.« less

In-Situ Phase Mapping and Direct Observations of Phase Transformations During Arc Welding of 1045 Steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmer, J; Palmer, T

2005-09-13

In-situ Spatially Resolved X-Ray Diffraction (SRXRD) experiments were performed during gas tungsten arc (GTA) welding of AISI 1045 C-Mn steel. Ferrite ({alpha}) and austenite ({gamma}) phases were identified and quantified in the weld heat-affected zone (HAZ) from the real time x-ray diffraction data. The results were compiled along with weld temperatures calculated using a coupled thermal fluids weld model to create a phase map of the HAZ. This map shows the {alpha} {yields} {gamma} transformation taking place during weld heating and the reverse {gamma} {yields} {alpha} transformation taking place during weld cooling. Superheating is required to complete the {alpha} {yields}more » {gamma} phase transformation, and the amount of superheat above the A3 temperature was shown to vary with distance from the centerline of the weld. Superheat values as high as 250 C above the A3 temperature were observed at heating rates of 80 C/s. The SRXRD experiments also revealed details about the {gamma} phase not observable by conventional techniques, showing that {gamma} is present with two distinct lattice parameters as a result of inhomogeneous distribution of carbon and manganese in the starting pearlitic/ferritic microstructure. During cooling, the reverse {gamma} {yields} {alpha} phase transformation was shown to depend on the HAZ location. In the fine grained region of the HAZ, at distances greater than 2 mm from the fusion line, the {gamma} {yields} {alpha} transformation begins near the A3 temperature and ends near the A1 temperature. In this region of the HAZ where the cooling rates are below 40 C/s, the transformation occurs by nucleation and growth of pearlite. For HAZ locations closer to the fusion line, undercoolings of 200 C or more below the A1 temperature are required to complete the {gamma} {yields} {alpha} transformation. In this region of the HAZ, grain growth coupled with cooling rates in excess of 50 C/s causes the transformation to occur by a bainitic mechanism.« less

Structural transition in lanthanum gallate and transformation of the fine structure of the EPR spectrum of a Gd3+ impurity center

NASA Astrophysics Data System (ADS)

Vazhenin, V. A.; Guseva, V. B.; Fokin, A. V.; Potapov, A. P.; Artyomov, M. Yu.

2011-04-01

Abrupt changes in resonance positions, hysteretic temperature behavior, and coexistence of phases, which indicate a first-order phase transition, have been revealed from measurements of temperature dependences of the EPR spectra of Gd3+ and Mn4+ centers in the vicinity of the structural transition of lanthanum gallate. The transformation of monoclinic Gd3+ centers into trigonal Gd3+ centers upon the phase transition has been used to estimate the adequacy of two approximations of the superposition model for parameters of the zero-field splitting of the ground state.

Molecular Dynamics Modeling and Simulation of Diamond Cutting of Cerium.

PubMed

Zhang, Junjie; Zheng, Haibing; Shuai, Maobing; Li, Yao; Yang, Yang; Sun, Tao

2017-12-01

The coupling between structural phase transformations and dislocations induces challenges in understanding the deformation behavior of metallic cerium at the nanoscale. In the present work, we elucidate the underlying mechanism of cerium under ultra-precision diamond cutting by means of molecular dynamics modeling and simulations. The molecular dynamics model of diamond cutting of cerium is established by assigning empirical potentials to describe atomic interactions and evaluating properties of two face-centered cubic cerium phases. Subsequent molecular dynamics simulations reveal that dislocation slip dominates the plastic deformation of cerium under the cutting process. In addition, the analysis based on atomic radial distribution functions demonstrates that there are trivial phase transformations from the γ-Ce to the δ-Ce occurred in both machined surface and formed chip. Following investigations on machining parameter dependence reveal the optimal machining conditions for achieving high quality of machined surface of cerium.

Molecular Dynamics Modeling and Simulation of Diamond Cutting of Cerium

NASA Astrophysics Data System (ADS)

Zhang, Junjie; Zheng, Haibing; Shuai, Maobing; Li, Yao; Yang, Yang; Sun, Tao

2017-07-01

The coupling between structural phase transformations and dislocations induces challenges in understanding the deformation behavior of metallic cerium at the nanoscale. In the present work, we elucidate the underlying mechanism of cerium under ultra-precision diamond cutting by means of molecular dynamics modeling and simulations. The molecular dynamics model of diamond cutting of cerium is established by assigning empirical potentials to describe atomic interactions and evaluating properties of two face-centered cubic cerium phases. Subsequent molecular dynamics simulations reveal that dislocation slip dominates the plastic deformation of cerium under the cutting process. In addition, the analysis based on atomic radial distribution functions demonstrates that there are trivial phase transformations from the γ-Ce to the δ-Ce occurred in both machined surface and formed chip. Following investigations on machining parameter dependence reveal the optimal machining conditions for achieving high quality of machined surface of cerium.

Deformation of olivine during phase transformation to wadsleyite

NASA Astrophysics Data System (ADS)

Mohiuddin, A.; Girard, J.; Karato, S. I.

2017-12-01

The strength of subducting slabs in the transition zone is critical in controlling the style of mantle convection. However, rheological properties of a subducted slab are elusive: low temperatures of a slab would make slabs strong, but in many regions there is evidence of intense deformation of slabs in the transition zone. One potential cause of intense deformation of subducting slabs is grain size reduction and accompanied microstructural changes during phase transformation of olivine to its higher-pressure polymorphs. There have been no experimental studies to quantify the influence of grain-size evolution. In addition to grain size reduction, distribution of small grains during phase transformation governs the degree of weakening during phase transformation (for e.g. load bearing framework vs. inter-connected layered framework). We conducted laboratory studies on the size and spatial distribution of new grains of wadsleyite after the transformation from olivine. Our results under static conditions show that an interconnected microstructure develops during the initial stage of phase transformation and that the grain size of the interconnected phase (wadsleyite) depends on the temperature at which the phase transformation occurs (smaller grains at lower temperatures). Development of an interconnected microstructure may lead to strain localization in the weaker phase, i.e. the fine-grained interconnected network accommodates most of the strain and therefore weakening of the entire composite. We will test this model through a series of two synchrotron in-situ deformation experiments: (i) Olivine aggregate will be deformed during slow pressure increase from deep upper mantle pressure ( 10 GPa) to transition zone pressure ( 15 GPa) at a given temperature simulating the deformation of a slab penetrating into the transition zone (ii) olivine is partially transformed to wadsleyite in a multi anvil apparatus at Yale and will be deformed within the stability field where olivine and wadsleyite coexist. We will use the Rotational Drickamer Apparatus (RDA) at a synchrotron facility (Argonne National Lab, 6-BM-B beamline, white beam and x-ray radiography) and characterize the stresses acting on olivine and wadsleyite during such simulations. We plan to present our preliminary results.

Probing heat transfer, fluid flow and microstructural evolution during fusion welding of alloys

NASA Astrophysics Data System (ADS)

Zhang, Wei

The composition, geometry, structure and properties of the welded joints are affected by the various physical processes that take place during fusion welding. Understanding these processes has been an important goal in the contemporary welding research to achieve structurally sound and reliable welds. In the present thesis research, several important physical processes including the heat transfer, fluid flow and microstructural evolution in fusion welding were modeled based on the fundamentals of transport phenomena and phase transformation theory. The heat transfer and fluid flow calculation is focused on the predictions of the liquid metal convection in the weld pool, the temperature distribution in the entire weldment, and the shape and size of the fusion zone (FZ) and heat affected zone (HAZ). The modeling of microstructural evolution is focused on the quantitative understanding of phase transformation kinetics during welding of several important alloys under both low and high heating and cooling conditions. Three numerical models were developed in the present thesis work: (1) a three-dimensional heat transfer and free surface flow model for the gas metal arc (GMA) fillet welding considering the complex weld joint geometry, (2) a phase transformation model based on the Johnson-Mehl-Avrami (JMA) theory, and (3) a one-dimensional numerical diffusion model considering multiple moving interfaces. To check the capabilities of the developed models, several cases were investigated, in which the predictions from the models were compared with the experimental results. The cases studied are the follows. For the modeling of heat transfer and fluid flow, the welding processes studied included gas tungsten arc (GTA) linear welding, GTA transient spot welding, and GMA fillet welding. The calculated weldment geometry and thermal cycles was validated against the experimental data under various welding conditions. For the modeling of microstructural evolution, the welded materials investigated included AISI 1005 low-carbon steel, 1045 medium-carbon steel, 2205 duplex stainless steel (DSS) and Ti-6Al-4V alloy. The calculated phase transformation kinetics were compared with the experimental results obtained using an x-ray diffraction technique by Dr. John W. Elmer of Lawrence Livermore National Laboratory. (Abstract shortened by UMI.)

Direct Visualisation of the Structural Transformation between the Lyotropic Liquid Crystalline Lamellar and Bicontinuous Cubic Mesophase.

PubMed

Tran, Nhiem; Zhai, Jiali; Conn, Charlotte E; Mulet, Xavier; Waddington, Lynne J; Drummond, Calum J

2018-05-29

The transition between the lyotropic liquid crystalline lamellar and the bicontinuous cubic mesophase drives multiple fundamental cellular processes involving changes in cell membrane topology including endocytosis and membrane budding. While several theoretical models have been proposed to explain this dynamic transformation, experimental validation of these models has been challenging due to the short lived nature of the intermediates present during the phase transition. Herein, we report the direct observation of a lamellar to bicontinuous cubic phase transition in nanoscale dispersions using a combination of cryogenic transmission electron microscopy and static small angle X-ray scattering. The results represent the first experimental confirmation of a theoretical model which proposed that the bicontinuous cubic phase originates from the centre of a lamellar vesicle, then propagates outward via the formation of inter-lamellar attachments and stalks. The observation was possible due to the precise control of the lipid composition to place the dispersion systems at the phase boundary of a lamellar and a cubic phase, allowing for the creation of long-lived structural intermediates. By surveying the nanoparticles using cryogenic transmission electron microscopy, a complete phase transition sequence was established.

Dehydration and dehydroxylation of C-S-H phases synthesized on silicon wafers

NASA Astrophysics Data System (ADS)

Giraudo, Nicolas; Bergdolt, Samuel; Laye, Fabrice; Krolla, Peter; Lahann, Joerg; Thissen, Peter

2018-03-01

In this work, the synthesis of specific ultrathin Calcium-Silicate-Hydrate (C-S-H) phases on silicon wafers and their transformation into C-S phases is achieved. Specific mineral phases are identified, and the synthesis is successful controlled. Samples are investigated by means of Fourier Transform Infrared (FTIR) spectroscopy and X-ray Diffraction (XRD) and the results are analyzed based on first-principles calculations. When C-S-H phases are transformed into C-S phases, only a few reflexes are detected on XRD, and the coherent scattering domains decrease with the increment of the temperature and time of exposure. This behavior is explained by the Ca/Si changes, which are identified by changes in the FTIR spectra. A thermodynamic analysis is performed with the help of first-principles calculations to underline the influence of the calcium-to-silicon (Ca/Si) ratio in the process of dehydroxylation. To increase the Ca/Si ratio water is partially substituted by methanol at the synthesis. This is observed in the FTIR spectra and is confirmed by lower temperatures of dehydroxylation. The catalytic nature of calcium towards the dehydroxylation is confirmed. The core of this work lies in the preparation of a model, which perfection makes possible to model reactivity, stability and mechanical properties using first-principles calculations, and is the starting point for the synthesis of many others.

Martensitic and austenitic transformations in core-surface cubic nanoparticles

NASA Astrophysics Data System (ADS)

Özüm, S.; Yalçın, O.; Erdem, R.; Bayrakdar, H.; Eker, H. N.

2015-01-01

As a continuation of our recently published work, we have used the pair approximation in Kikuchi version to investigate martensitic and austenitic transformations in homogeneous (HM) and composite (CM) cubic nanoparticles (CNPs) based on the Blume-Emery-Griffiths model. A single cubic nanoparticle made of a core surrounded by a surface is considered as shaped in two dimensional (2D) square arrays instead of hexagonal array. From the phase diagrams of HM and CM-CNPs it has been observed that the martensitic-austenitic transformations (MT-AT) occurred. The influence of the exchange coupling and single-ion anisotropy parameters in the model Hamiltonian on the MT-AT is studied and analyzed in comparison with the results for hexagonal nanoparticles. Significant changes of the phase transition points and hysteresis behaviours depending upon the particle structure have been discussed.

Phase transformation in multiferroic Bi5Ti3FeO15 ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

NASA Astrophysics Data System (ADS)

Jiang, P. P.; Duan, Z. H.; Xu, L. P.; Zhang, X. L.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2014-02-01

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi5Ti3FeO15 ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200-873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property.

Modeling of phase transformations of Ti6Al4 V during laser metal deposition

NASA Astrophysics Data System (ADS)

Suárez, A.; Tobar, M. J.; Yáñez, A.; Pérez, I.; Sampedro, J.; Amigó, V.; Candel, J. J.

The low density, excellent high temperature mechanical properties and good corrosion resistance of titanium and its alloys have led to a diversified range of successful applications. As a consequence, there is a demand of increasing the capabilities of processing such alloys. The laser cladding technique allows direct metal deposition with an excellent metallurgical bond and a pore free fine grained microstructure. A nonlinear transient thermo-metallurgical model was developed to study the technique with titanium alloys to get a better understanding of the thermal and metallurgical underlying aspects. The calculated temperatures and phase transformations are compared with experimental tests.

A comparison of hydrological deformation using GPS and global hydrological model for the Eurasian plate

NASA Astrophysics Data System (ADS)

Li, Zhen; Yue, Jianping; Li, Wang; Lu, Dekai; Li, Xiaogen

2017-08-01

The 0.5° × 0.5° gridded hydrological loading from Global Land Surface Discharge Model (LSDM) mass distributions is adopted for 32 GPS sites on the Eurasian plate from January 2010 to January 2014. When the heights of these sites that have been corrected for the effects of non-tidal atmospheric and ocean loading are adjusted by the hydrological loading deformation, more than one third of the root-mean-square (RMS) values of the GPS height variability become larger. After analyzing the results by continuous wavelet transform (CWT) and wavelet transform coherence (WTC), we confirm that hydrological loading primarily contributes to the annual variations in GPS heights. Further, the cross wavelet transform (XWT) is used to investigate the relative phase between the time series of GPS heights and hydrological deformation, and it is indicated that the annual oscillations in the two time series are physically related for some sites; other geophysical effect, GPS systematic errors and hydrological modeling errors could result in the phase asynchrony between GPS and hydrological loading signals for the other sites. Consequently, the phase asynchrony confirms that the annual fluctuations in GPS observations result from a combination of geophysical signals and systematic errors.

Phase Transformations and Microstructural Evolution: Part II

DOE PAGES

Clarke, Amy Jean

2015-10-30

The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance. In this issue, aspects of liquid–solid and solid-state phase transformations and microstructural evolution are highlighted. Many papers in thismore » issue are highlighted by this paper, giving a brief summary of what they bring to the scientific community.« less

Learning a force field for the martensitic phase transformation in Zr

NASA Astrophysics Data System (ADS)

Zong, Hongxiang; Pilania, Ghanshyam; Ramprasad, Rampi; Lookman, Turab

Atomic simulations provide an effective means to understand the underlying physics of martensitic transformations under extreme conditions. However, this is still a challenge for certain phase transforming metals due to the lack of an accurate classical force field. Quantum molecular dynamics (QMD) simulations are accurate but expensive. During the course of QMD simulations, similar configurations are constantly visited and revisited. Machine Learning can effectively learn from past visits and, therefore, eliminate such redundancies. In this talk, we will discuss the development of a hybrid ML-QMD method in which on-demand, on-the-fly quantum mechanical (QM) calculations are performed to accelerate calculations of interatomic forces at much lower computational costs. Using Zirconium as a model system for which accurate atomisctic potentials are currently unvailable we will demonstrate the feasibility and effectiveness of our approach. Specifically, the computed structural phase transformation behavior within the ML-QMD approach will be compared with available experimental results. Furthermore, results on phonons, stacking fault energies, and activation barriers for the homogeneous martensitic transformation in Zr will be presented.

Pressure-induced transformations in glassy water: A computer simulation study using the TIP4P/2005 model

NASA Astrophysics Data System (ADS)

Wong, Jessina; Jahn, David A.; Giovambattista, Nicolas

2015-08-01

We study the pressure-induced transformations between low-density amorphous (LDA) and high-density amorphous (HDA) ice by performing out-of-equilibrium molecular dynamics (MD) simulations. We employ the TIP4P/2005 water model and show that this model reproduces qualitatively the LDA-HDA transformations observed experimentally. Specifically, the TIP4P/2005 model reproduces remarkably well the (i) structure (OO, OH, and HH radial distribution functions) and (ii) densities of LDA and HDA at P = 0.1 MPa and T = 80 K, as well as (iii) the qualitative behavior of ρ(P) during compression-induced LDA-to-HDA and decompression-induced HDA-to-LDA transformations. At the rates explored, the HDA-to-LDA transformation is less pronounced than in experiments. By studying the LDA-HDA transformations for a broad range of compression/decompression temperatures, we construct a "P-T phase diagram" for glassy water that is consistent with experiments and remarkably similar to that reported previously for ST2 water. This phase diagram is not inconsistent with the possibility of TIP4P/2005 water exhibiting a liquid-liquid phase transition at low temperatures. A comparison with previous MD simulation studies of SPC/E and ST2 water as well as experiments indicates that, overall, the TIP4P/2005 model performs better than the SPC/E and ST2 models. The effects of cooling and compression rates as well as aging on our MD simulations results are also discussed. The MD results are qualitatively robust under variations of cooling/compression rates (accessible in simulations) and are not affected by aging the hyperquenched glass for at least 1 μs. A byproduct of this work is the calculation of TIP4P/2005 water's diffusion coefficient D(T) at P = 0.1 MPa. It is found that, for T ≥ 210 K, D(T) ≈ (T - TMCT)-γ as predicted by mode coupling theory and in agreement with experiments. For TIP4P/2005 water, TMCT = 209 K and γ = 2.14, very close to the corresponding experimental values TMCT = 221 K and γ = 2.2.

Pressure-induced transformations in glassy water: A computer simulation study using the TIP4P/2005 model.

PubMed

Wong, Jessina; Jahn, David A; Giovambattista, Nicolas

2015-08-21

We study the pressure-induced transformations between low-density amorphous (LDA) and high-density amorphous (HDA) ice by performing out-of-equilibrium molecular dynamics (MD) simulations. We employ the TIP4P/2005 water model and show that this model reproduces qualitatively the LDA-HDA transformations observed experimentally. Specifically, the TIP4P/2005 model reproduces remarkably well the (i) structure (OO, OH, and HH radial distribution functions) and (ii) densities of LDA and HDA at P = 0.1 MPa and T = 80 K, as well as (iii) the qualitative behavior of ρ(P) during compression-induced LDA-to-HDA and decompression-induced HDA-to-LDA transformations. At the rates explored, the HDA-to-LDA transformation is less pronounced than in experiments. By studying the LDA-HDA transformations for a broad range of compression/decompression temperatures, we construct a "P-T phase diagram" for glassy water that is consistent with experiments and remarkably similar to that reported previously for ST2 water. This phase diagram is not inconsistent with the possibility of TIP4P/2005 water exhibiting a liquid-liquid phase transition at low temperatures. A comparison with previous MD simulation studies of SPC/E and ST2 water as well as experiments indicates that, overall, the TIP4P/2005 model performs better than the SPC/E and ST2 models. The effects of cooling and compression rates as well as aging on our MD simulations results are also discussed. The MD results are qualitatively robust under variations of cooling/compression rates (accessible in simulations) and are not affected by aging the hyperquenched glass for at least 1 μs. A byproduct of this work is the calculation of TIP4P/2005 water's diffusion coefficient D(T) at P = 0.1 MPa. It is found that, for T ≥ 210 K, D(T) ≈ (T - T(MCT))(-γ) as predicted by mode coupling theory and in agreement with experiments. For TIP4P/2005 water, T(MCT) = 209 K and γ = 2.14, very close to the corresponding experimental values T(MCT) = 221 K and γ = 2.2.

Numerical tests of local scale invariance in ageing q-state Potts models

NASA Astrophysics Data System (ADS)

Lorenz, E.; Janke, W.

2007-01-01

Much effort has been spent over the last years to achieve a coherent theoretical description of ageing as a non-linear dynamics process. Long supposed to be a consequence of the slow dynamics of glassy systems only, ageing phenomena could also be identified in the phase-ordering kinetics of simple ferromagnets. As a phenomenological approach Henkel et al. developed a group of local scale transformations under which two-time autocorrelation and response functions should transform covariantly. This work is to extend previous numerical tests of the predicted scaling functions for the Ising model by Monte Carlo simulations of two-dimensional q-state Potts models with q=3 and 8, which, in equilibrium, undergo temperature-driven phase transitions of second and first order, respectively.

Potential Energy Landscape of the Liquid-Liquid Phase Transition in Water and the transformation between Low-Density and High-Density Amorphous Ice

NASA Astrophysics Data System (ADS)

Giovambattista, N.; Sciortino, F.; Starr, F. W.; Poole, P. H.

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics for describing supercooled liquids and glasses. We use the PEL formalism and computer simulations to study the transformation between low-density (LDL) and high-density liquid (HDL) water, and between low-density (LDA) and high-density amorphous ice (HDA). We employ the ST2 water model that exhibits a LDL-HDL first-order phase transition and a sharp LDA-HDA transformation, as observed in experiments. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that LDL configurations are located in the same megabasin as LDA, and that HDL configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid and the amorphous ice differ. We also study the liquid-to-ice-VII first-order phase transition. The PEL properties across this transition are qualitatively similar to the changes found during the LDA-HDA transformation, supporting the interpretation that the LDA-HDA transformation is a first-order-like phase transition between out-of-equilibrium states.

A Lagging Model for Describing Drawdown Induced by a Constant-Rate Pumping in a Leaky Confined Aquifer

NASA Astrophysics Data System (ADS)

Lin, Ye-Chen; Yeh, Hund-Der

2017-10-01

This study proposes a generalized Darcy's law with considering phase lags in both the water flux and drawdown gradient to develop a lagging flow model for describing drawdown induced by constant-rate pumping (CRP) in a leaky confined aquifer. The present model has a mathematical formulation similar to the dual-porosity model. The Laplace-domain solution of the model with the effect of wellbore storage is derived by the Laplace transform method. The time-domain solution for the case of neglecting the wellbore storage and well radius is developed by the use of Laplace transform and Weber transform. The results of sensitivity analysis based on the solution indicate that the drawdown is very sensitive to the change in each of the transmissivity and storativity. Also, a study for the lagging effect on the drawdown indicates that its influence is significant associated with the lag times. The present solution is also employed to analyze a data set taken from a CRP test conducted in a fractured aquifer in South Dakota, USA. The results show the prediction of this new solution with considering the phase lags has very good fit to the field data, especially at early pumping time. In addition, the phase lags seem to have a scale effect as indicated in the results. In other words, the lagging behavior is positively correlated with the observed distance in the Madison aquifer.

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 1: thermodynamics of spontaneous amorphization.

PubMed

Qian, Ken K; Bogner, Robin H

2011-07-01

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal molecules in the presence of mesoporous materials has been observed, for which pathway was suggested to be via the vapor phase, that is, sublimation of the crystalline molecules followed by adsorption on the porous media. The objective of this paper is to rigorously evaluate this amorphization pathway and to study the thermodynamics of spontaneous amorphization. Mesoporous silicon dioxide (SiO(2)) was used as a model system. Physical mixtures of SiO(2) and crystalline compounds were prepared and stored at 0% relative humidity (RH) and 40 °C. Loss of crystallinity of the model compounds was confirmed using powder X-ray diffraction and polarized light microscopy. Adsorption chamber was set up, in which naphthalene and SiO(2) were stored, without physical contact, under reduced pressure at 0% RH and 40 °C. Data confirmed that the rate and extent of sublimation and adsorption of naphthalene were significant for amorphization to occur on a pharmaceutically relevant timescale. Furthermore, a thermodynamic model has been developed to explain spontaneous amorphization. This unique phase transformation phenomenon can be a simple and effective method to improve the aqueous solubility and bioavailability of poorly soluble drug molecules. Copyright © 2011 Wiley-Liss, Inc. and the American Pharmacists Association

Phase Transformations and Microstructural Evolution: Part I

DOE PAGES

Clarke, Amy Jean

2015-08-29

The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance, including in extreme environments, of structural metal alloys. In this paper, aspects of phase transformations and microstructural evolution aremore » highlighted from the atomic to the microscopic scale for ferrous and non-ferrous alloys. Many papers from this issue are highlighted with small summaries of their scientific achievements given.« less

Effect of grain boundaries on shock-induced phase transformation in iron bicrystals

NASA Astrophysics Data System (ADS)

Zhang, Xueyang; Wang, Kun; Zhu, Wenjun; Chen, Jun; Cai, Mengqiu; Xiao, Shifang; Deng, Huiqiu; Hu, Wangyu

2018-01-01

Non-equilibrium molecular-dynamic simulations with a modified analytic embedded-atom model potential have been performed to investigate the effect of three kinds of grain boundaries (GBs) on the martensitic transformation in iron bicrystals with three different GBs under shock loadings. Our results show that the phase transition was influenced by the GBs. All three GBs provide a nucleation site for the α → ɛ transformation in samples shock-loaded with up = 0.5 km/s, and in particular, the elastic wave can induce the phase transformation at Σ3 ⟨110⟩ twist GB, which indicates that the phase transformation can occur at Σ3 ⟨110⟩ twist GB with a much lower pressure. The effect of GBs on the stress assisted transformation (SAT) mechanisms is discussed. All variants nucleating at the vicinity of these GBs meet the maximum strain work (MSW) criterion. Moreover, all of the variants with the MSW nucleate at Σ5 ⟨001⟩ twist GB and Σ3 ⟨110⟩ tilt GB, but only part of them nucleate at Σ3 ⟨110⟩ twist GB. This is because the coincident planes between both sides of the GB would affect the slip process, which is the second stage of the martensitic transformation and influences the selection of variant. We also find that the martensitic transformation at the front end of the bicrystals would give rise to stress attenuation in samples shock-loaded with up = 0.6 km/s, which makes the GBs seem to be unfavorable to the martensitic transformation. Our findings have the potential to affect the interface engineering and material design under high pressure conditions.

Kinetics of phase transformation in glass forming systems

NASA Technical Reports Server (NTRS)

Ray, Chandra S.

1994-01-01

The objectives of this research were to (1) develop computer models for realistic simulations of nucleation and crystal growth in glasses, which would also have the flexibility to accomodate the different variables related to sample characteristics and experimental conditions, and (2) design and perform nucleation and crystallization experiments using calorimetric measurements, such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA) to verify these models. The variables related to sample characteristics mentioned in (1) above include size of the glass particles, nucleating agents, and the relative concentration of the surface and internal nuclei. A change in any of these variables changes the mode of the transformation (crystallization) kinetics. A variation in experimental conditions includes isothermal and nonisothermal DSC/DTA measurements. This research would lead to develop improved, more realistic methods for analysis of the DSC/DTA peak profiles to determine the kinetic parameters for nucleation and crystal growth as well as to assess the relative merits and demerits of the thermoanalytical models presently used to study the phase transformation in glasses.

Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material.

PubMed

Lim, Jin-Myoung; Hwang, Taesoon; Kim, Duho; Park, Min-Sik; Cho, Kyeongjae; Cho, Maenghyo

2017-01-03

Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 layered oxide cathodes have been highlighted for large-scale energy applications due to their high energy density. Although its specific capacity is enhanced at higher voltages as Ni ratio increases, its structural degradation due to phase transformations and lattice distortions during cycling becomes severe. For these reasons, we focused on the origins of crack generation from phase transformations and structural distortions in Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 using multiscale approaches, from first-principles to meso-scale phase-field model. Atomic-scale structure analysis demonstrated that opposite changes in the lattice parameters are observed until the inverse Li content x = 0.75; then, structure collapses due to complete extraction of Li from between transition metal layers. Combined-phase investigations represent the highest phase barrier and steepest chemical potential after x = 0.75, leading to phase transformations to highly Li-deficient phases with an inactive character. Abrupt phase transformations with heterogeneous structural collapse after x = 0.81 (~220 mAh g -1 ) were identified in the nanodomain. Further, meso-scale strain distributions show around 5% of anisotropic contraction with lower critical energy release rates, which cause not only micro-crack generations of secondary particles on the interfaces between the contracted primary particles, but also mechanical instability of primary particles from heterogeneous strain changes.

Theory of the amplitude-phase retrieval in any linear-transform system and its applications

NASA Astrophysics Data System (ADS)

Yang, Guozhen; Gu, Ben-Yuan; Dong, Bi-Zhen

1992-12-01

This paper is a summary of the theory of the amplitude-phase retrieval problem in any linear transform system and its applications based on our previous works in the past decade. We describe the general statement on the amplitude-phase retrieval problem in an imaging system and derive a set of equations governing the amplitude-phase distribution in terms of the rigorous mathematical derivation. We then show that, by using these equations and an iterative algorithm, a variety of amplitude-phase problems can be successfully handled. We carry out the systematic investigations and comprehensive numerical calculations to demonstrate the utilization of this new algorithm in various transform systems. For instance, we have achieved the phase retrieval from two intensity measurements in an imaging system with diffraction loss (non-unitary transform), both theoretically and experimentally, and the recovery of model real image from its Hartley-transform modulus only in one and two dimensional cases. We discuss the achievement of the phase retrieval problem from a single intensity only based on the sampling theorem and our algorithm. We also apply this algorithm to provide an optimal design of the phase-adjusted plate for a phase-adjustment focusing laser accelerator and a design approach of single phase-only element for implementing optical interconnect. In order to closely simulate the really measured data, we examine the reconstruction of image from its spectral modulus corrupted by a random noise in detail. The results show that the convergent solution can always be obtained and the quality of the recovered image is satisfactory. We also indicated the relationship and distinction between our algorithm and the original Gerchberg- Saxton algorithm. From these studies, we conclude that our algorithm shows great capability to deal with the comprehensive phase-retrieval problems in the imaging system and the inverse problem in solid state physics. It may open a new way to solve important inverse source problems extensively appearing in physics.

Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO 4 [Accommodation of High Transformation Strain in Battery Electrodes via Formation of Nanoscale Intermediate Phases: Operando Structure Investigation of Olivine Sodium Iron Phosphate

DOE PAGES

Xiang, Kai; Xing, Wenting; Ravnsbaek, Dorthe B.; ...

2017-02-21

Virtually all intercalation compounds used as battery electrodes exhibit significant changes in unit cell volume during use. Na xFePO 4 (0 < x < 1, NFP) olivine, of interest as a cathode for sodium-ion batteries, is a model for topotactic, high strain systems as it exhibits one of the largest discontinuous volume changes (~17% by volume) during its first-order transition between two otherwise isostructural phases. Using synchrotron radiation powder X-ray diffraction (PXD) and pair distribution function (PDF) analysis, we discover a new strain-accommodation mechanism wherein a third, <10 nm scale nanocrystalline phase forms to buffer the large lattice mismatch betweenmore » primary phases. The new phase has a and b lattice parameters matching one crystalline endmember phase and c lattice parameter matching the other, and is not detectable by powder diffraction alone. Finally, we suggest that this strain-accommodation mechanism may apply to systems with large transformation strains but in which true “amorphization” does not occur.« less

Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO 4 [Accommodation of High Transformation Strain in Battery Electrodes via Formation of Nanoscale Intermediate Phases: Operando Structure Investigation of Olivine Sodium Iron Phosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, Kai; Xing, Wenting; Ravnsbaek, Dorthe B.

Virtually all intercalation compounds used as battery electrodes exhibit significant changes in unit cell volume during use. Na xFePO 4 (0 < x < 1, NFP) olivine, of interest as a cathode for sodium-ion batteries, is a model for topotactic, high strain systems as it exhibits one of the largest discontinuous volume changes (~17% by volume) during its first-order transition between two otherwise isostructural phases. Using synchrotron radiation powder X-ray diffraction (PXD) and pair distribution function (PDF) analysis, we discover a new strain-accommodation mechanism wherein a third, <10 nm scale nanocrystalline phase forms to buffer the large lattice mismatch betweenmore » primary phases. The new phase has a and b lattice parameters matching one crystalline endmember phase and c lattice parameter matching the other, and is not detectable by powder diffraction alone. Finally, we suggest that this strain-accommodation mechanism may apply to systems with large transformation strains but in which true “amorphization” does not occur.« less

Electron-beam-induced structure transformation of the quasicrystalline phases of the Al 62Cu 20Co 15Si 3 alloy

NASA Astrophysics Data System (ADS)

Reyes-Gasga, J.; R. Garcia, G.; Jose-Yacaman, M.

1995-02-01

Some details on the phase transformation experienced by the quasicrystalline phases of the Al 62Cu 20Co 15Si 3 alloy under a 400 kV electron beam are given. The transition is observed in situ with a high resolution electron microscope and recorded on video tape. The results show that the electron beam radiation produces a sequence of changes similar to the ones observed in an ion-beam-induced amorphization process. Considering electron radiation damage analysis, the results agree well with the "flip-flop" model [Coddens, Bellisent, Calvayrac and Ambroise (1991) Europhys. Lett.16, 271] where the transition from a quasicrystalline phase to a crystalline phase is produced by atomic displacements but not in a cascade way.

Martensitic phase transformations in the nanostructured surface layers induced by mechanical attrition treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ni Zhichun; Wang Xiaowei; Wu Erdong

2005-12-01

Conversion electron Moessbauer spectroscopy (CEMS) and x-ray diffraction (XRD) analysis have been used to investigate the relationship between characteristics of phase transformation and the treatment time in surface nanocrystallized 316L stainless steel induced by surface mechanical attrition treatment (SMAT). A similar trend of development of the martensitic phase upon the treatment time has been observed from both CEMS and XRD measurements. However, in the CEMS measurement, two types of martensite phase with different magnetic hyperfine fields are revealed. Based on a random distribution of the non-iron coordinating atoms, a three-element theoretical model is developed to illustrate the difference of twomore » types of martensite phase. The calculated results indicate the segregation of the non-iron atoms associated with SMAT treatment.« less

EFFECT OF REDOX ZONATION ON THE REDUCTIVE TRANSFORMATION OF P-CYANONITROBENZENE IN A LABORATORY SEDIMENT COLUMN

EPA Science Inventory

The reductive transformation of a model compound, p-cyanonitrobenzene (pCNB), was investigated in a laboratory sediment column that had been characterized with respect to redox zonation. Characterization of the redox zones was assessed by measurement of the solution phase concent...

Implications of Low Volatility SOA and Gas-Phase Fragmentation Reactions on SOA Loadings and their Spatial and Temporal Evolution in the Atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrivastava, ManishKumar B.; Zelenyuk, Alla; Imre, Dan

2013-04-27

Recent laboratory and field measurements by a number of groups show that secondary organic aerosol (SOA) evaporates orders of magnitude slower than traditional models assume. In addition, chemical transport models using volatility basis set (VBS) SOA schemes neglect gas-phase fragmentation reactions, which are known to be extremely important. In this work, we present modeling studies to investigate the implications of non-evaporating SOA and gas-phase fragmentation reactions. Using the 3-D chemical transport model, WRF-Chem, we show that previous parameterizations, which neglect fragmentation during multi-generational gas-phase chemistry of semi-volatile/inter-mediate volatility organics ("aging SIVOC"), significantly over-predict SOA as compared to aircraft measurements downwindmore » of Mexico City. In sharp contrast, the revised models, which include gas-phase fragmentation, show much better agreement with measurements downwind of Mexico City. We also demonstrate complex differences in spatial SOA distributions when we transform SOA to non-volatile secondary organic aerosol (NVSOA) to account for experimental observations. Using a simple box model, we show that for same amount of SOA precursors, earlier models that do not employ multi-generation gas-phase chemistry of precursors ("non-aging SIVOC"), produce orders of magnitude lower SOA than "aging SIVOC" parameterizations both with and without fragmentation. In addition, traditional absorptive partitioning models predict almost complete SOA evaporation at farther downwind locations for both "non-aging SIVOC" and "aging SIVOC" with fragmentation. In contrast, in our revised approach, SOA transformed to NVSOA implies significantly higher background concentrations as it remains in particle phase even under highly dilute conditions. This work has significant implications on understanding the role of multi-generational chemistry and NVSOA formation on SOA evolution in the atmosphere.« less

Computation and projection of spiral wave trajectories during atrial fibrillation: a computational study.

PubMed

Pashaei, Ali; Bayer, Jason; Meillet, Valentin; Dubois, Rémi; Vigmond, Edward

2015-03-01

To show how atrial fibrillation rotor activity on the heart surface manifests as phase on the torso, fibrillation was induced on a geometrically accurate computer model of the human atria. The Hilbert transform, time embedding, and filament detection were compared. Electrical activity on the epicardium was used to compute potentials on different surfaces from the atria to the torso. The Hilbert transform produces erroneous phase when pacing for longer than the action potential duration. The number of phase singularities, frequency content, and the dominant frequency decreased with distance from the heart, except for the convex hull. Copyright © 2015 Elsevier Inc. All rights reserved.

Estimation in a semi-Markov transformation model

PubMed Central

Dabrowska, Dorota M.

2012-01-01

Multi-state models provide a common tool for analysis of longitudinal failure time data. In biomedical applications, models of this kind are often used to describe evolution of a disease and assume that patient may move among a finite number of states representing different phases in the disease progression. Several authors developed extensions of the proportional hazard model for analysis of multi-state models in the presence of covariates. In this paper, we consider a general class of censored semi-Markov and modulated renewal processes and propose the use of transformation models for their analysis. Special cases include modulated renewal processes with interarrival times specified using transformation models, and semi-Markov processes with with one-step transition probabilities defined using copula-transformation models. We discuss estimation of finite and infinite dimensional parameters of the model, and develop an extension of the Gaussian multiplier method for setting confidence bands for transition probabilities. A transplant outcome data set from the Center for International Blood and Marrow Transplant Research is used for illustrative purposes. PMID:22740583

Single Channel Quantum Color Image Encryption Algorithm Based on HSI Model and Quantum Fourier Transform

NASA Astrophysics Data System (ADS)

Gong, Li-Hua; He, Xiang-Tao; Tan, Ru-Chao; Zhou, Zhi-Hong

2018-01-01

In order to obtain high-quality color images, it is important to keep the hue component unchanged while emphasize the intensity or saturation component. As a public color model, Hue-Saturation Intensity (HSI) model is commonly used in image processing. A new single channel quantum color image encryption algorithm based on HSI model and quantum Fourier transform (QFT) is investigated, where the color components of the original color image are converted to HSI and the logistic map is employed to diffuse the relationship of pixels in color components. Subsequently, quantum Fourier transform is exploited to fulfill the encryption. The cipher-text is a combination of a gray image and a phase matrix. Simulations and theoretical analyses demonstrate that the proposed single channel quantum color image encryption scheme based on the HSI model and quantum Fourier transform is secure and effective.

Numerical Study of the Plasticity-Induced Stabilization Effect on Martensitic Transformations in Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hempel, Philipp

2017-12-01

It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-based material model by including a non-linear isotropic hardening plasticity model. An implementation of this material model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

High-pressure x-ray diffraction study on lithium borohydride using a synchrotron radiation

NASA Astrophysics Data System (ADS)

Nakano, S.; Nakayama, A.; Kikegawa, T.

2008-07-01

Lithium borohydride (LiBH4) was compressed up to 10 GPa using a diamond-anvil-cell to investigate its high-pressure structure. In-situ x-ray diffraction profiles indicated a pressure-induced transformation at 1.1 GPa, which was consistent with the previous experimental observation such as Raman scattering spectroscopy. The high-pressure phase was indexed on a tetragonal symmetry of P42/mmc, which was not corresponding some structural models proposed by previous calculation studies. An unknown substance (presumably another Li-B-H compound), which was contained in the starting material, also transformed into its high-pressure phase at 0.6 GPa without any relation to the transformation of LiBH4.

Phase Transformation of Droplets into Particles and Nucleation in Atmospheric Pressure Discharges

NASA Astrophysics Data System (ADS)

Iqbal, M. M.; Stallard, C. P.; Dowling, D. P.; Turner, M. M.

2013-09-01

We investigate the mechanism of phase transformation of liquid precursor droplets into nano-particulates in an atmospheric pressure discharge (APD). This phase transformation is possible when the solid to a liquid mass ratio of slurry droplet reaches a threshold value. The behaviour of phase transformation of a single slurry droplet of HMDSO is described by developing a numerical model under the saturation condition of evaporation. It is observed from the temporal evolution of inner radius (Ri) of a single slurry droplet that its value approaches zero before the entire shifting of a liquid phase and which explains with an expansion in the crust thickness (Ro - Ri) . The solid traces of nano-particles are observed experimentally on the surface coating depositions because the time for transferring the slurry droplet of HMDSO into solid state is amplified with an increment in the radii of droplets and the entire phase transition occurs within residence time for the nano-sized liquid droplets. The GDE coupled with discharge plasma is numerically solved to describe the mechanism of nucleation of nano-sized particles in APD plasma under similar conditions of the experiment. The growth of nucleation in APD plasma depends on the type of liquid precursor, such as HMDSO, TEOS and water, which is verified with a sharp peak in the nucleation rate and saturation ratio. Science Foundation Ireland under Grant No. 08/SRC/I1411.

Transformer overload characteristics---Bubble evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woods, E.E.; Wendel, R.C.; Dresser, R.D.

1988-08-01

Project RP1289-3 explores significant parameters affecting bubble evolution from transformer oil under high temperature operating conditions to address the question: Does ''real life'' operation of a transformer cause harmful bubbling conditions. Studies outlined in the project are designed to determine when bubbling occurs in transformers and if bubbling can be harmful during the normal operation of these transformers. Data obtained from these studies should provide a basis for utilities to perform risk assessments in relation to their loading practices. The program is designed to demonstrate those conditions under which bubbling occurs in transformers by using controlled models and actual signalmore » phase transformers that were designed to give access to both high and low voltage windings for the purpose of viewing bubble generation. Results and observations from tests on the full-size transformers, thermal models, and electrical models have led to the conclusion that bubbles can occur under operating conditions. The electrical models show that dielectric strength can be reduced by as much as 40 percent due to the presence of bubbles. Because of factory safety considerations, the transformers could not be tested at hot spot temperatures greater than 140/degree/C. Therefore, there is no information on the dielectric strength of the full-size transformers under bubbling conditions. 4 refs., 28 figs., 45 tabs.« less

Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite-ferrite phase transformation in steels

NASA Astrophysics Data System (ADS)

Fang, H.; van der Zwaag, S.; van Dijk, N. H.

2018-07-01

The magnetic configuration of a ferromagnetic system with mono-disperse and poly-disperse distribution of magnetic particles with inter-particle interactions has been computed. The analysis is general in nature and applies to all systems containing magnetically interacting particles in a non-magnetic matrix, but has been applied to steel microstructures, consisting of a paramagnetic austenite phase and a ferromagnetic ferrite phase, as formed during the austenite-to-ferrite phase transformation in low-alloyed steels. The characteristics of the computational microstructures are linked to the correlation function and determinant of depolarisation matrix, which can be experimentally obtained in three-dimensional neutron depolarisation (3DND). By tuning the parameters in the model used to generate the microstructure, we studied the effect of the (magnetic) particle size distribution on the 3DND parameters. It is found that the magnetic particle size derived from 3DND data matches the microstructural grain size over a wide range of volume fractions and grain size distributions. A relationship between the correlation function and the relative width of the particle size distribution was proposed to accurately account for the width of the size distribution. This evaluation shows that 3DND experiments can provide unique in situ information on the austenite-to-ferrite phase transformation in steels.

Infinite number of solvable generalizations of XY-chain, with cluster state, and with central charge c = m/2

NASA Astrophysics Data System (ADS)

Minami, Kazuhiko

2017-12-01

An infinite number of spin chains are solved and it is derived that the ground-state phase transitions belong to the universality classes with central charge c = m / 2, where m is an integer. The models are diagonalized by automatically obtained transformations, many of which are different from the Jordan-Wigner transformation. The free energies, correlation functions, string order parameters, exponents, central charges, and the phase diagram are obtained. Most of the examples consist of the stabilizers of the cluster state. A unified structure of the one-dimensional XY and cluster-type spin chains is revealed, and other series of solvable models can be obtained through this formula.

Automated red blood cells extraction from holographic images using fully convolutional neural networks.

PubMed

Yi, Faliu; Moon, Inkyu; Javidi, Bahram

2017-10-01

In this paper, we present two models for automatically extracting red blood cells (RBCs) from RBCs holographic images based on a deep learning fully convolutional neural network (FCN) algorithm. The first model, called FCN-1, only uses the FCN algorithm to carry out RBCs prediction, whereas the second model, called FCN-2, combines the FCN approach with the marker-controlled watershed transform segmentation scheme to achieve RBCs extraction. Both models achieve good segmentation accuracy. In addition, the second model has much better performance in terms of cell separation than traditional segmentation methods. In the proposed methods, the RBCs phase images are first numerically reconstructed from RBCs holograms recorded with off-axis digital holographic microscopy. Then, some RBCs phase images are manually segmented and used as training data to fine-tune the FCN. Finally, each pixel in new input RBCs phase images is predicted into either foreground or background using the trained FCN models. The RBCs prediction result from the first model is the final segmentation result, whereas the result from the second model is used as the internal markers of the marker-controlled transform algorithm for further segmentation. Experimental results show that the given schemes can automatically extract RBCs from RBCs phase images and much better RBCs separation results are obtained when the FCN technique is combined with the marker-controlled watershed segmentation algorithm.

Automated red blood cells extraction from holographic images using fully convolutional neural networks

PubMed Central

Yi, Faliu; Moon, Inkyu; Javidi, Bahram

2017-01-01

In this paper, we present two models for automatically extracting red blood cells (RBCs) from RBCs holographic images based on a deep learning fully convolutional neural network (FCN) algorithm. The first model, called FCN-1, only uses the FCN algorithm to carry out RBCs prediction, whereas the second model, called FCN-2, combines the FCN approach with the marker-controlled watershed transform segmentation scheme to achieve RBCs extraction. Both models achieve good segmentation accuracy. In addition, the second model has much better performance in terms of cell separation than traditional segmentation methods. In the proposed methods, the RBCs phase images are first numerically reconstructed from RBCs holograms recorded with off-axis digital holographic microscopy. Then, some RBCs phase images are manually segmented and used as training data to fine-tune the FCN. Finally, each pixel in new input RBCs phase images is predicted into either foreground or background using the trained FCN models. The RBCs prediction result from the first model is the final segmentation result, whereas the result from the second model is used as the internal markers of the marker-controlled transform algorithm for further segmentation. Experimental results show that the given schemes can automatically extract RBCs from RBCs phase images and much better RBCs separation results are obtained when the FCN technique is combined with the marker-controlled watershed segmentation algorithm. PMID:29082078

Localizing sources of acoustic emission during the martensitic transformation

NASA Astrophysics Data System (ADS)

Niemann, R.; Kopeček, J.; Heczko, O.; Romberg, J.; Schultz, L.; Fähler, S.; Vives, E.; Mañosa, L.; Planes, A.

2014-06-01

Acoustic avalanches are a general feature of solids under stress, e.g., evoked by external compression or arising from internal processes like martensitic phase transformations. From integral measurements, it is usually concluded that nucleation, phase boundary pinning, or interface incompatibilities during this first-order phase transition all may generate acoustic emission. This paper studies the local sources of acoustic emission to enlight the microscopic mechanisms. From two-dimensional spatially resolved acoustic emission measurement and simultaneous optical observation of the surface, we can identify microstructural events at the phase boundary that lead to acoustic emission. A resolution in the 100-μm range was reached for the location of acoustic emission sources on a coarse-grained Ni-Mn-Ga polycrystal. Both, the acoustic activity and the size distribution of the microstructural transformation events, exhibit power-law behavior. The origin of the acoustic emission are elastically incompatible areas, such as differently oriented martensitic plates that meet each other, lamellae growing up to grain boundaries, and grain boundaries in proximity to transforming grains. Using this result, we propose a model to explain the decrease of the critical exponent under a mechanical stress or magnetic field.

Dual Transformer Model based on Standard Circuit Elements for the Study of Low- and Mid-frequency Transients

NASA Astrophysics Data System (ADS)

Jazebi, Saeed

This thesis is a step forward toward achieving the final objective of creating a fully dual model for transformers including eddy currents and nonlinearities of the iron core using the fundamental electrical components already available in the EMTP-type programs. The model is effective for the study of the performance of transformers during power system transients. This is very important for transformer designers, because the insulation of transformers is determined with the overvoltages caused by lightning or switching operations. There are also internally induced transients that occur when a switch is actuated. For example switching actions for reconfiguration of distribution systems that offers economic advantages, or protective actions to clear faults and large short-circuit currents. Many of the smart grid concepts currently under development by many utilities rely heavily on switching to optimize resources that produce transients in the system. On the other hand, inrush currents produce mechanical forces which deform transformer windings and cause malfunction of the differential protection. Also, transformer performance under ferroresonance and geomagnetic induced currents are necessary to study. In this thesis, a physically consistent dual model applicable to single-phase two-winding transformers is proposed. First, the topology of a dual electrical equivalent circuit is obtained from the direct application of the principle of duality. Then, the model parameters are computed considering the variations of the transformer electromagnetic behavior under various operating conditions. Current modeling techniques use different topological models to represent diverse transient situations. The reversible model proposed in this thesis unifies the terminal and topological equivalent circuits. The model remains invariable for all low-frequency transients including deep saturation conditions driven from any of the two windings. The very high saturation region of the iron core magnetizing characteristic is modified with the accurate measurement of the air-core inductance. The air-core inductance is measured using a non-ideal low-power rectifier. Its dc output serves to drive the transformer into deep saturation, and its ripple provides low-amplitude variable excitation. The principal advantage of this method is its simplicity. To model the eddy current effects in the windings, a novel equivalent circuit is proposed. The circuit is derived from the principle of duality and therefore, matches the electromagnetic physical behavior of the transformer windings. It properly models the flux paths and current distribution from dc to MHz. The model is synthesized from a non-uniform concentric discretization of the windings. Concise guidelines are given to optimally calculate the width of the sub-divisions for various transient simulations. To compute the circuit parameters only information about the geometry of the windings and about their material properties is needed. The calculation of the circuit parameters does not require an iterative process. Therefore, the parameters are always real, positive, and free from convergence problems. The proposed model is tested with single-phase transformers for the calculation of magnetizing inrush currents, series ferroresonance, and Geomagnetic Induced Currents (GIC). The electromagnetic transient response of the model is compared to laboratory measurements for validation. Also, 3D finite element simulations are used to validate the electromagnetic behavior of the transformer model. Large manufacturer of transformers, power system designers, and electrical utility companies can benefit from the new model. It simplifies the design and optimization of the transformers' insulation, thereby reducing cost, and enhancing reliability of the system. The model could also be used for inrush current and differential protection studies, geomagnetic induced current studies, harmonic penetration studies, and switching transient studies.

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2014-03-21

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2014-03-01

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Applications of squeezed states: Bogoliubov transformations and wavelets to the statistical mechanics of water and its bubbles

NASA Technical Reports Server (NTRS)

Defacio, Brian; Kim, S.-H.; Vannevel, A.

1994-01-01

The squeezed states or Bogoliubov transformations and wavelets are applied to two problems in nonrelativistic statistical mechanics: the dielectric response of liquid water, epsilon(q-vector,w), and the bubble formation in water during insonnification. The wavelets are special phase-space windows which cover the domain and range of L(exp 1) intersection of L(exp 2) of classical causal, finite energy solutions. The multiresolution of discrete wavelets in phase space gives a decomposition into regions of time and scales of frequency thereby allowing the renormalization group to be applied to new systems in addition to the tired 'usual suspects' of the Ising models and lattice gasses. The Bogoliubov transformation: squeeze transformation is applied to the dipolaron collective mode in water and to the gas produced by the explosive cavitation process in bubble formation.

Generalized thermoelastic problem of an infinite body with a spherical cavity under dual-phase-lags

NASA Astrophysics Data System (ADS)

Karmakar, R.; Sur, A.; Kanoria, M.

2016-07-01

The aim of the present contribution is the determination of the thermoelastic temperatures, stress, displacement, and strain in an infinite isotropic elastic body with a spherical cavity in the context of the mechanism of the two-temperature generalized thermoelasticity theory (2TT). The two-temperature Lord-Shulman (2TLS) model and two-temperature dual-phase-lag (2TDP) model of thermoelasticity are combined into a unified formulation with unified parameters. The medium is assumed to be initially quiescent. The basic equations are written in the form of a vector matrix differential equation in the Laplace transform domain, which is then solved by the state-space approach. The expressions for the conductive temperature and elongation are obtained at small times. The numerical inversion of the transformed solutions is carried out by using the Fourier-series expansion technique. A comparative study is performed for the thermoelastic stresses, conductive temperature, thermodynamic temperature, displacement, and elongation computed by using the Lord-Shulman and dual-phase-lag models.

In Situ TEM Nanoindentation Studies on Stress-Induced Phase Transformations in Metallic Materials

DOE PAGES

Liu, Y.; Wang, H.; Zhang, X.

2015-11-30

Though abundant phase transformations are in general thermally driven processes, there are many examples wherein stresses can induce phase transformations. We applied numerous in situ techniques, such as in situ x-ray diffraction and neutron diffraction in order to reveal phase transformations. Recently, an in situ nanoindentation technique coupled with transmission electron microscopy demonstrated the capability to directly correlating stresses with phase transformations and microstructural evolutions at a submicron length scale. We briefly review in situ studies on stress-induced diffusional and diffusionless phase transformations in amorphous CuZrAl alloy and NiFeGa shape memory alloy. Moreover, in the amorphous CuZrAl, in situ nanoindentationmore » studies show that the nucleation of nanocrystals (a diffusional process) occurs at ultra-low stresses manifested by a prominent stress drop. In the NiFeGa shape memory alloy, two distinctive types of martensitic (diffusionless) phase transformations accompanied by stress plateaus are observed, including a reversible gradual phase transformation at low stress levels, and an irreversible abrupt phase transition at higher stress levels.« less

Accounting for inherent variability of growth in microbial risk assessment.

PubMed

Marks, H M; Coleman, M E

2005-04-15

Risk assessments of pathogens need to account for the growth of small number of cells under varying conditions. In order to determine the possible risks that occur when there are small numbers of cells, stochastic models of growth are needed that would capture the distribution of the number of cells over replicate trials of the same scenario or environmental conditions. This paper provides a simple stochastic growth model, accounting only for inherent cell-growth variability, assuming constant growth kinetic parameters, for an initial, small, numbers of cells assumed to be transforming from a stationary to an exponential phase. Two, basic, microbial sets of assumptions are considered: serial, where it is assume that cells transform through a lag phase before entering the exponential phase of growth; and parallel, where it is assumed that lag and exponential phases develop in parallel. The model is based on, first determining the distribution of the time when growth commences, and then modelling the conditional distribution of the number of cells. For the latter distribution, it is found that a Weibull distribution provides a simple approximation to the conditional distribution of the relative growth, so that the model developed in this paper can be easily implemented in risk assessments using commercial software packages.

Invariant Deformation Element Model Interpretation to the Crystallography of Diffusional Body-Centered-Cube to Face-Centered-Cube Phase Transformations

NASA Astrophysics Data System (ADS)

Liu, Hongwei; Liu, Jiangwen; Su, Guangcai; Li, Weizhou; Zeng, Jianmin; Hu, Zhiliu

2012-10-01

The crystallography of body-centered-cube to face-centered cube (bcc-to-fcc) diffusion phase transformations in a duplex stainless steel and a Cu-Zn alloy, including long axis, orientation relationship (OR), habit plane (HP), and dislocation spacing, is successfully interpreted with one-step rotation from the Bain lattice relationship by applying a simplified invariant line (IL) analysis. It is proposed that the dislocation slipping direction in the matrix plays an important role in controlling the crystallography of precipitation.

Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material

PubMed Central

Lim, Jin-Myoung; Hwang, Taesoon; Kim, Duho; Park, Min-Sik; Cho, Kyeongjae; Cho, Maenghyo

2017-01-01

Ni-rich LiNi0.8Co0.1Mn0.1O2 layered oxide cathodes have been highlighted for large-scale energy applications due to their high energy density. Although its specific capacity is enhanced at higher voltages as Ni ratio increases, its structural degradation due to phase transformations and lattice distortions during cycling becomes severe. For these reasons, we focused on the origins of crack generation from phase transformations and structural distortions in Ni-rich LiNi0.8Co0.1Mn0.1O2 using multiscale approaches, from first-principles to meso-scale phase-field model. Atomic-scale structure analysis demonstrated that opposite changes in the lattice parameters are observed until the inverse Li content x = 0.75; then, structure collapses due to complete extraction of Li from between transition metal layers. Combined-phase investigations represent the highest phase barrier and steepest chemical potential after x = 0.75, leading to phase transformations to highly Li-deficient phases with an inactive character. Abrupt phase transformations with heterogeneous structural collapse after x = 0.81 (~220 mAh g−1) were identified in the nanodomain. Further, meso-scale strain distributions show around 5% of anisotropic contraction with lower critical energy release rates, which cause not only micro-crack generations of secondary particles on the interfaces between the contracted primary particles, but also mechanical instability of primary particles from heterogeneous strain changes. PMID:28045118

Ferroelectric Phase Transformations for Energy Conversion and Storage Applications

NASA Astrophysics Data System (ADS)

Jo, Hwan Ryul

Ferroelectric materials possess a spontaneous polarization and actively respond to external mechanical, electrical, and thermal loads. Due to their coupled behavior, ferroelectric materials are used in products such as sensors, actuators, detectors, and transducers. However, most current applications rely on low-energy conversion that involves low magnitude fields. They utilize the low-field linear properties of ferroelectric materials (piezoelectric, pyroelectric) and do not take full advantage of the large-field nonlinear behavior (irreversible domain wall motion, phase transformations) that can occur in ferroelectric materials. When external fields exceed a certain critical level, a structural transformation of the crystal can occur. These phase transformations are accompanied by a much larger response than the linear piezoelectric and pyroelectric responses, by as much as a multiple of ten times in the magnitude. This makes the non-linear behavior in ferroelectric materials promising for energy harvesting and energy storage technologies which will benefit from large-energy conversion. Yet, the ferroelectric phase transformation behavior under large external fields have been less studied and only a few studies have been directed at utilizing this large material response in applications. This dissertation addresses the development ferroelectric phase transformation-based applications, with particular focus on the materials. Development of the ferroelectric phase transformation-based applications was approached in several steps. First, the phase transformation behavior was fully characterized and understood by measuring the phase transformation responses under mechanical, electrical, thermal, and combined loads. Once the behavior was well characterized, systems level applications were addressed. This required assessing the effect of the phase transformation behavior on system performance. The performance of ferroelectric devices is strongly dependent on material properties and phase transformation behavior which can be tailored by modifying the chemical composition, processing conditions, and the loading history (poling). This results in optimization of system performance by tailoring material properties and phase transformation behavior. This approach applied to three ferroelectric phase transformation-based applications: 1. Ferroelectric energy generation 2. Ferroelectric high-energy storage capacitor 3. Ferroelectric thermal energy harvesting. This dissertation has addressed tuning the large field properties for phase transformation-based systems.

Role of valence electrons in phase transformation kinetics of thallium and its dilute alloys

NASA Technical Reports Server (NTRS)

Ahmed, R.; Ahmed, S.

1991-01-01

The kinetics of the phase transformation of thallium and its dilute alloys were investigated using XRD and calorimetry. Pure thallium exhibits a beta(bcc) to alpha(hcp) phase transformation on cooling at 508 K. With alloying additions, the crystal structure for each phase does not change, although the size of the unit cell increases. The enthalpy and the temperature of phase transformation of each alloy have been determined. The chemical free energy change associated with the phase transformation of each alloy was calculated. The valence electrons make an outstanding contribution to the chemical free energy change required for the phase change.

Effect of Co on Discontinuous Precipitation Transformation with TCP Phase in Ni-based Alloy Containing Re

NASA Astrophysics Data System (ADS)

Shi, Qianying; An, Ning; Huo, Jiajie; Zheng, Yunrong; Feng, Qiang

2017-05-01

The effect of Co on discontinuous precipitation (DP) transformation involving the formation of topologically close-packed (TCP) phase was investigated in three Ni-Cr-Re model alloys containing different levels of Co. One typical TCP phase, σ, was generated within DP cellular colonies along the migrating grain boundaries in experimental alloys during aging treatment. As a result of the increased solubility of Re in the γ matrix and enlarged interlamellar spacing of σ precipitates inside of growing DP colonies, Co addition suppressed the formation of σ phase and associated DP colonies. This study suggests that Co could potentially serve as a microstructural stabilizer in Re-containing Ni-base superalloys, which provides an alternative method for the composition optimization of superalloys.

Intercalation Dynamics in Lithium-Ion Batteries

DTIC Science & Technology

2009-09-01

When applied to strongly phase-separating, highly anisotropic materials such as LiFePO4 , this model predicts phase-transformation waves between the...new findings relevant to batteries: Defect Interactions: When applied to strongly phase-separating, highly anisotropic mate- rials such as LiFePO4 ...93 6.3.5 Relevance to LiFePO4 . . . . . . . . . . . . . . . . . . . . . . . . . . 93 6.3.6 Wave propagation

Heat storage in alloy transformations

NASA Technical Reports Server (NTRS)

Birchenall, C. E.; Gueceri, S. I.

1980-01-01

The theory of eutectic transformation was examined to find guidelines to the best material combinations to examine. The heats of transformation were measured calorimetrically, and the volume changes of expanding solid mixtures and homogeneous liquid solutions, especially during the transformation between the two states at fixed temperature, were measured by changes in X-ray absorption. Heat flow models appropriate to storage in phase change materials were developed along with efficient calculating procedures so that the relative importance of the problems associated with energy storage density, heat conduction, and similar properties could be assessed.

High pressure phase transformations revisited

NASA Astrophysics Data System (ADS)

Levitas, Valery I.

2018-04-01

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum theories, and (d) to couple experimental, theoretical, and computational studies of the behavior of a tested sample to extract information about fields of stress and strain tensors and concentration of high pressure phase, transformation criteria and kinetics. The ideal characterization should contain complete information which is required for simulation of the same experiments.

High pressure phase transformations revisited.

PubMed

Levitas, Valery I

2018-04-25

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum theories, and (d) to couple experimental, theoretical, and computational studies of the behavior of a tested sample to extract information about fields of stress and strain tensors and concentration of high pressure phase, transformation criteria and kinetics. The ideal characterization should contain complete information which is required for simulation of the same experiments.

Estimation of Transformation Temperatures in Ti-Ni-Pd Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Narayana, P. L.; Kim, Seong-Woong; Hong, Jae-Keun; Reddy, N. S.; Yeom, Jong-Taek

2018-03-01

The present study focused on estimating the complex nonlinear relationship between the composition and phase transformation temperatures of Ti-Ni-Pd shape memory alloys by artificial neural networks (ANN). The ANN models were developed by using the experimental data of Ti-Ni-Pd alloys. It was found that the predictions are in good agreement with the trained and unseen test data of existing alloys. The developed model was able to simulate new virtual alloys to quantitatively estimate the effect of Ti, Ni, and Pd on transformation temperatures. The transformation temperature behavior of these virtual alloys is validated by conducting new experiments on the Ti-rich thin film that was deposited using multi target sputtering equipment. The transformation behavior of the film was measured by varying the composition with the help of aging treatment. The predicted trend of transformational temperatures was explained with the help of experimental results.

Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals.

PubMed

Bardhan, Rizia; Hedges, Lester O; Pint, Cary L; Javey, Ali; Whitelam, Stephen; Urban, Jeffrey J

2013-10-01

A quantitative understanding of nanocrystal phase transformations would enable more efficient energy conversion and catalysis, but has been hindered by difficulties in directly monitoring well-characterized nanoscale systems in reactive environments. We present a new in situ luminescence-based probe enabling direct quantification of nanocrystal phase transformations, applied here to the hydriding transformation of palladium nanocrystals. Our approach reveals the intrinsic kinetics and thermodynamics of nanocrystal phase transformations, eliminating complications of substrate strain, ligand effects and external signal transducers. Clear size-dependent trends emerge in nanocrystals long accepted to be bulk-like in behaviour. Statistical mechanical simulations show these trends to be a consequence of nanoconfinement of a thermally driven, first-order phase transition: near the phase boundary, critical nuclei of the new phase are comparable in size to the nanocrystal itself. Transformation rates are then unavoidably governed by nanocrystal dimensions. Our results provide a general framework for understanding how nanoconfinement fundamentally impacts broad classes of thermally driven solid-state phase transformations relevant to hydrogen storage, catalysis, batteries and fuel cells.

Transformation of Context-dependent Sensory Dynamics into Motor Behavior

PubMed Central

Latorre, Roberto; Levi, Rafael; Varona, Pablo

2013-01-01

The intrinsic dynamics of sensory networks play an important role in the sensory-motor transformation. In this paper we use conductance based models and electrophysiological recordings to address the study of the dual role of a sensory network to organize two behavioral context-dependent motor programs in the mollusk Clione limacina. We show that: (i) a winner take-all dynamics in the gravimetric sensory network model drives the typical repetitive rhythm in the wing central pattern generator (CPG) during routine swimming; (ii) the winnerless competition dynamics of the same sensory network organizes the irregular pattern observed in the wing CPG during hunting behavior. Our model also shows that although the timing of the activity is irregular, the sequence of the switching among the sensory cells is preserved whenever the same set of neurons are activated in a given time window. These activation phase locks in the sensory signals are transformed into specific events in the motor activity. The activation phase locks can play an important role in motor coordination driven by the intrinsic dynamics of a multifunctional sensory organ. PMID:23459114

Nested sparse grid collocation method with delay and transformation for subsurface flow and transport problems

NASA Astrophysics Data System (ADS)

Liao, Qinzhuo; Zhang, Dongxiao; Tchelepi, Hamdi

2017-06-01

In numerical modeling of subsurface flow and transport problems, formation properties may not be deterministically characterized, which leads to uncertainty in simulation results. In this study, we propose a sparse grid collocation method, which adopts nested quadrature rules with delay and transformation to quantify the uncertainty of model solutions. We show that the nested Kronrod-Patterson-Hermite quadrature is more efficient than the unnested Gauss-Hermite quadrature. We compare the convergence rates of various quadrature rules including the domain truncation and domain mapping approaches. To further improve accuracy and efficiency, we present a delayed process in selecting quadrature nodes and a transformed process for approximating unsmooth or discontinuous solutions. The proposed method is tested by an analytical function and in one-dimensional single-phase and two-phase flow problems with different spatial variances and correlation lengths. An additional example is given to demonstrate its applicability to three-dimensional black-oil models. It is found from these examples that the proposed method provides a promising approach for obtaining satisfactory estimation of the solution statistics and is much more efficient than the Monte-Carlo simulations.

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

PubMed Central

Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

2016-01-01

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

Synthesis, Characterization, and Self-Controlled Orthorhombic to Tetragonal Polymorphic Transformation in BaTiO3 Nanoparticles

NASA Astrophysics Data System (ADS)

Ram, S.; Jana, A.; Kundu, T. K.

The phase formation and thermal-induced phase transformation are studied in BaTiO3 nanoparticles. 2 h of heating a polymer precursor at 550°C in air formed a single phase BaTiO3 of 15 nm average crystallite size D. The X-ray diffraction peaks are analyzed assuming a Pnma orthorhombic (o) crystal structure of lattice parameters a = 0.6435 nm, b = 0.5306 nm, and c = 0.8854 nm. The lattice volume V = 0.3023 nm3, with z = 4 formula units, yields a density ρ = 5.124 g/cm3. This is a new polymorph in comparison to well-known Pm3m tetragonal (t) structure, V = 0.0644 nm3 or ρ = 6.016 g/cm3 (z = 1). An o ↦ t transformation appears on heating at temperature as high as 650°C in air. A proposed model explains the transformation above a certain D value in terms of the Gibbs free energy. Unless heating above 750°C, the two phases coexist in a composite structure (D≤27 nm), with as much residual o-phase trace as ~28 vol%. As a function of temperature both the phases decrease in the V values up to 0.2975 and 0.0643 nm3 at 750°C respectively (0.0650 nm3 at 650°C). This is an important parameter for designing useful ferroelectric and other properties in a hybrid composite structure.

Phase transformation pathways of ultrafast-laser-irradiated Ln2O3 (Ln =Er -Lu )

NASA Astrophysics Data System (ADS)

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung; Solomon, Jonathan M.; Asta, Mark; Mao, Wendy L.; Yalisove, Steven M.; Ewing, Rodney C.

2018-01-01

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln2O3 (Ln =Er -Lu ), and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln =Tm -Lu , consistent with the material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln =Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.

Phase transformation pathways of ultrafast-laser-irradiated Ln 2 O 3 ( Ln = Er – Lu )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln 2O 3 ( Ln = Er – Lu ) , and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln = Tm – Lu , consistent with themore » material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln = Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.« less

Phase transformation pathways of ultrafast-laser-irradiated Ln 2 O 3 ( Ln = Er – Lu )

DOE PAGES

Rittman, Dylan R.; Tracy, Cameron L.; Chen, Chien-Hung; ...

2018-01-10

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln 2O 3 ( Ln = Er – Lu ) , and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln = Tm – Lu , consistent with themore » material's phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln = Er , revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.« less

CHEMICAL TRANSFORMATION MODULES FOR EULERIAN ACID DEPOSITION MODELS. VOLUME 1. THE GAS-PHASE CHEMISTRY

EPA Science Inventory

This study focuses on the review and evaluation of mechanistic and kinetic data for the gas-phase reactions that lead to the production of acidic substances in the environment. A master mechanism is designed that treats oxides, sulfur dioxide, ozone, hydrogen peroxide, ammonia, t...

An introduction to wavelet analysis in oceanography and meteorology - With application to the dispersion of Yanai waves

NASA Technical Reports Server (NTRS)

Meyers, Steven D.; Kelly, B. G.; O'Brien, J. J.

1993-01-01

Wavelet analysis is a relatively new technique that is an important addition to standard signal analysis methods. Unlike Fourier analysis that yields an average amplitude and phase for each harmonic in a dataset, the wavelet transform produces an instantaneous estimate or local value for the amplitude and phase of each harmonic. This allows detailed study of nonstationary spatial or time-dependent signal characteristics. The wavelet transform is discussed, examples are given, and some methods for preprocessing data for wavelet analysis are compared. By studying the dispersion of Yanai waves in a reduced gravity equatorial model, the usefulness of the transform is demonstrated. The group velocity is measured directly over a finite range of wavenumbers by examining the time evolution of the transform. The results agree well with linear theory at higher wavenumber but the measured group velocity is reduced at lower wavenumbers, possibly due to interaction with the basin boundaries.

Phase transformation dependence on initial plastic deformation mode in Si via nanoindentation

DOE PAGES

Wong, Sherman; Haberl, Bianca; Williams, James S.; ...

2016-09-30

Silicon in its diamond-cubic phase is known to phase transform to a technologically interesting mixture of the body-centred cubic and rhombohedral phases under nanoindentation pressure. In this study, we demonstrate that during plastic deformation the sample can traverse two distinct pathways, one that initially nucleates a phase transformation while the other initially nucleates crystalline defects. These two pathways remain distinct even after sufficient pressure is applied such that both deformation mechanisms are present within the sample. Here, it is further shown that the indents that initially nucleate a phase transformation generate larger, more uniform volumes of the phase transformed materialmore » than indents that initially nucleate crystalline defects.« less

Modelling the effect of acoustic waves on the thermodynamics and kinetics of phase transformation in a solution: Including mass transportation

NASA Astrophysics Data System (ADS)

Haqshenas, S. R.; Ford, I. J.; Saffari, N.

2018-01-01

Effects of acoustic waves on a phase transformation in a metastable phase were investigated in our previous work [S. R. Haqshenas, I. J. Ford, and N. Saffari, "Modelling the effect of acoustic waves on nucleation," J. Chem. Phys. 145, 024315 (2016)]. We developed a non-equimolar dividing surface cluster model and employed it to determine the thermodynamics and kinetics of crystallisation induced by an acoustic field in a mass-conserved system. In the present work, we developed a master equation based on a hybrid Szilard-Fokker-Planck model, which accounts for mass transportation due to acoustic waves. This model can determine the kinetics of nucleation and the early stage of growth of clusters including the Ostwald ripening phenomenon. It was solved numerically to calculate the kinetics of an isothermal sonocrystallisation process in a system with mass transportation. The simulation results show that the effect of mass transportation for different excitations depends on the waveform as well as the imposed boundary conditions and tends to be noticeable in the case of shock waves. The derivations are generic and can be used with any acoustic source and waveform.

Modelling the effect of acoustic waves on the thermodynamics and kinetics of phase transformation in a solution: Including mass transportation.

PubMed

Haqshenas, S R; Ford, I J; Saffari, N

2018-01-14

Effects of acoustic waves on a phase transformation in a metastable phase were investigated in our previous work [S. R. Haqshenas, I. J. Ford, and N. Saffari, "Modelling the effect of acoustic waves on nucleation," J. Chem. Phys. 145, 024315 (2016)]. We developed a non-equimolar dividing surface cluster model and employed it to determine the thermodynamics and kinetics of crystallisation induced by an acoustic field in a mass-conserved system. In the present work, we developed a master equation based on a hybrid Szilard-Fokker-Planck model, which accounts for mass transportation due to acoustic waves. This model can determine the kinetics of nucleation and the early stage of growth of clusters including the Ostwald ripening phenomenon. It was solved numerically to calculate the kinetics of an isothermal sonocrystallisation process in a system with mass transportation. The simulation results show that the effect of mass transportation for different excitations depends on the waveform as well as the imposed boundary conditions and tends to be noticeable in the case of shock waves. The derivations are generic and can be used with any acoustic source and waveform.

Two-dimensional Coupled Petrological-tectonic Modelling of Extensional Basins

NASA Astrophysics Data System (ADS)

Kaus, B. J. P.; Podladchikov, Y. Y.; Connolly, J. A. D.

Most numerical codes that simulate the deformation of a lithosphere assume the den- sity of the lithosphere to be either constant or depend only on temperature and pres- sure. It is, however, well known that rocks undergo phase transformations in response to changes in pressure and temperature. Such phase transformations may substantially alter the bulk properties of the rock (i.e., density, thermal conductivity, thermal ex- pansivity and elastic moduli). Several previous studies demonstrated that the density effects due to phase transitions are indeed large enough to have an impact on the litho- sphere dynamics. These studies were however oversimplified in that they accounted for only one or two schematic discontinuous phase transitions. The current study there- fore takes into account all the reactions that occur for a realistic lithospheric composi- tion. Calculation of the phase diagram and bulk physical properties of the stable phase assemblages for the crust and mantle within the continental lithosphere was done ac- counting for mineral solution behaviour using a free energy minimization program for natural rock compositions. The results of these calculations provide maps of the varia- tions in rock properties as a function of pressure and temperature that are easily incor- porated in any dynamic model computations. In this contribution we implemented a density map in the two-dimensional basin code TECMOD2D. We compare the results of the model with metamorphic reactions with a model without reactions and define some effective parameters that allow the use of a simpler model that still mimics most of the density effects of the metamorphic reactions.

Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice.

PubMed

Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W; Poole, Peter H

2016-12-14

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.

Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice

NASA Astrophysics Data System (ADS)

Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W.; Poole, Peter H.

2016-12-01

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.

Fault tolerant vector control of induction motor drive

NASA Astrophysics Data System (ADS)

Odnokopylov, G.; Bragin, A.

2014-10-01

For electric composed of technical objects hazardous industries, such as nuclear, military, chemical, etc. an urgent task is to increase their resiliency and survivability. The construction principle of vector control system fault-tolerant asynchronous electric. Displaying recovery efficiency three-phase induction motor drive in emergency mode using two-phase vector control system. The process of formation of a simulation model of the asynchronous electric unbalance in emergency mode. When modeling used coordinate transformation, providing emergency operation electric unbalance work. The results of modeling transient phase loss motor stator. During a power failure phase induction motor cannot save circular rotating field in the air gap of the motor and ensure the restoration of its efficiency at rated torque and speed.

A thermodynamically consistent model of magneto-elastic materials under diffusion at large strains and its analysis

NASA Astrophysics Data System (ADS)

Roubíček, Tomáš; Tomassetti, Giuseppe

2018-06-01

A theory of elastic magnets is formulated under possible diffusion and heat flow governed by Fick's and Fourier's laws in the deformed (Eulerian) configuration, respectively. The concepts of nonlocal nonsimple materials and viscous Cahn-Hilliard equations are used. The formulation of the problem uses Lagrangian (reference) configuration while the transport processes are pulled back. Except the static problem, the demagnetizing energy is ignored and only local non-self-penetration is considered. The analysis as far as existence of weak solutions of the (thermo) dynamical problem is performed by a careful regularization and approximation by a Galerkin method, suggesting also a numerical strategy. Either ignoring or combining particular aspects, the model has numerous applications as ferro-to-paramagnetic transformation in elastic ferromagnets, diffusion of solvents in polymers possibly accompanied by magnetic effects (magnetic gels), or metal-hydride phase transformation in some intermetallics under diffusion of hydrogen accompanied possibly by magnetic effects (and in particular ferro-to-antiferromagnetic phase transformation), all in the full thermodynamical context under large strains.

Design of Fatigue Resistant Heusler-strengthened PdTi-based Shape Memory Alloys for Biomedical Applications

NASA Astrophysics Data System (ADS)

Frankel, Dana J.

The development of non-surgical transcatheter aortic valve implantation (TAVI) techniques, which utilize collapsible artificial heart valves with shape memory alloy (SMA)-based frames, pushes performance requirements for biomedical SMAs beyond those for well-established vascular stent applications. Fatigue life for these devices must extend into the ultra-high cycle fatigue (UHCF) regime (>600M cycles) with zero probability of failure predicted at applied strain levels. High rates of Ni-hypersensitivity raise biocompatibility concerns, driving the development of low-Ni and Ni-free SMAs. This work focuses on the development of biocompatible, precipitation-strengthened, fatigue-resistant PdTi-based SMAs for biomedical applications. Functional and structural fatigue are both manifestations of cyclic instability resulting in accumulation of slip and eventual structural damage. While functional fatigue is easily experimentally evaluated, structural fatigue is more difficult to measure without the proper equipment. Therefore, in this work a theoretical approach using a model well validated in steels is utilized to investigate structural fatigue behavior in NiTi in the UHCF regime, while low cycle functional fatigue is evaluated in order to monitor the core phenomena of the cyclic instability. Results from fatigue simulations modeling crack nucleation at non-metallic inclusions in commercial NiTi underscore the importance of increasing yield strength for UHCF performance. Controlled precipitation of nanoscale, low-misfit, L21 Heusler aluminides can provide effective strengthening. Phase relations, precipitation kinetics, transformation temperature, transformation strain, cyclic stability, and mechanical properties are characterized in both Ni-free (Pd,Fe)(Ti,Al) and low-Ni high-strength "hybrid" (Pd,Ni)(Ti,Zr,Al) systems. Atom probe tomography is employed to measure phase compositions and particle sizes used to calibrate LSW models for coarsening kinetics and Gibbs-Thompson models for composition trajectories for systems under evolving unstable equilibrium. Mechanical and thermal cyclic stability are investigated using compression testing and differential scanning calorimetry. Mechanical properties are characterized using room temperature and high temperature Vickers microhardness as well as nanoindentation. A superelastic Ni-free (Pd,Fe)(Ti,Al) alloy with near-ambient transformation temperatures, low hysteresis, a highly stable cyclic response, and reversible transformation strains of 3.2% was designed. Due to Pd softening, the addition of Zr is considered to improve strength in a low-Ni "hybrid" (Pd,Ni)(Ti,Zr,Al) alloy. Aging studies at 600°C result in unusually fast coarsening kinetics, while low-temperature aging studies at 500-530°C reveal the presence of a Zr-rich phase in association with the matrix and Heusler phase. A strengthening study on a nontransforming hybrid prototype shows lower than expected precipitation strengthening at 600°C but significant strengthening when aged at 500°C due to the Zr-rich phase. Transformation temperatures, transformation strain, and cyclic stability are characterized in a set of transforming hybrid prototypes.

Chaotic oscillations and noise transformations in a simple dissipative system with delayed feedback

NASA Astrophysics Data System (ADS)

Zverev, V. V.; Rubinstein, B. Ya.

1991-04-01

We analyze the statistical behavior of signals in nonlinear circuits with delayed feedback in the presence of external Markovian noise. For the special class of circuits with intense phase mixing we develop an approach for the computation of the probability distributions and multitime correlation functions based on the random phase approximation. Both Gaussian and Kubo-Andersen models of external noise statistics are analyzed and the existence of the stationary (asymptotic) random process in the long-time limit is shown. We demonstrate that a nonlinear system with chaotic behavior becomes a noise amplifier with specific statistical transformation properties.

Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

NASA Technical Reports Server (NTRS)

Benafan, Othmane

2012-01-01

The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

Possible existence of two amorphous phases of d-mannitol related by a first-order transition

NASA Astrophysics Data System (ADS)

Zhu, Men; Wang, Jun-Qiang; Perepezko, John H.; Yu, Lian

2015-06-01

We report that the common polyalcohol d-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature Tg (284 K), the supercooled liquid (SCL) of d-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity. On fast heating, Phase X transforms back to the SCL near Tg + 50 K, enabling a determination of their equilibrium temperature. The presence of d-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from d-mannitol's SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near Tg with substantial enthalpy decrease toward the crystalline phases; the processes in water and d-mannitol both strengthen the hydrogen bonds. In contrast to TPP, d-mannitol's Phase X forms more rapidly and can transform back to the SCL. These features make d-mannitol a valuable new model for understanding polyamorphism.

Pressure, temperature, and electric field dependence of phase transformations in niobium modified 95/5 lead zirconate titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Wen D.; Carlos Valadez, J.; Gallagher, John A.

2015-06-28

Ceramic niobium modified 95/5 lead zirconate-lead titanate (PZT) undergoes a pressure induced ferroelectric to antiferroelectric phase transformation accompanied by an elimination of polarization and a volume reduction. Electric field and temperature drive the reverse transformation from the antiferroelectric to ferroelectric phase. The phase transformation was monitored under pressure, temperature, and electric field loading. Pressures and temperatures were varied in discrete steps from 0 MPa to 500 MPa and 25 °C to 125 °C, respectively. Cyclic bipolar electric fields were applied with peak amplitudes of up to 6 MV m{sup −1} at each pressure and temperature combination. The resulting electric displacement–electric field hysteresis loops weremore » open “D” shaped at low pressure, characteristic of soft ferroelectric PZT. Just below the phase transformation pressure, the hysteresis loops took on an “S” shape, which split into a double hysteresis loop just above the phase transformation pressure. Far above the phase transformation pressure, when the applied electric field is insufficient to drive an antiferroelectric to ferroelectric phase transformation, the hysteresis loops collapse to linear dielectric behavior. Phase stability maps were generated from the experimental data at each of the temperature steps and used to form a three dimensional pressure–temperature–electric field phase diagram.« less

Comparison of the quench and fault current limiting characteristics of the flux-coupling type SFCL with single and three-phase transformer

NASA Astrophysics Data System (ADS)

Jung, Byung Ik; Cho, Yong Sun; Park, Hyoung Min; Chung, Dong Chul; Choi, Hyo Sang

2013-01-01

The South Korean power grid has a network structure for the flexible operation of the system. The continuously increasing power demand necessitated the increase of power facilities, which decreased the impedance in the power system. As a result, the size of the fault current in the event of a system fault increased. As this increased fault current size is threatening the breaking capacity of the circuit breaker, the main protective device, a solution to this problem is needed. The superconducting fault current limiter (SFCL) has been designed to address this problem. SFCL supports the stable operation of the circuit breaker through its excellent fault-current-limiting operation [1-5]. In this paper, the quench and fault current limiting characteristics of the flux-coupling-type SFCL with one three-phase transformer were compared with those of the same SFCL type but with three single-phase transformers. In the case of the three-phase transformers, both the superconducting elements of the fault and sound phases were quenched, whereas in the case of the single-phase transformer, only that of the fault phase was quenched. For the fault current limiting rate, both cases showed similar rates for the single line-to-ground fault, but for the three-wire earth fault, the fault current limiting rate of the single-phase transformer was over 90% whereas that of the three-phase transformer was about 60%. It appears that when the three-phase transformer was used, the limiting rate decreased because the fluxes by the fault current of each phase were linked in one core. When the power loads of the superconducting elements were compared by fault type, the initial (half-cycle) load was great when the single-phase transformer was applied, whereas for the three-phase transformer, its power load was slightly lower at the initial stage but became greater after the half fault cycle.

Reverse Shape Memory Effect Related to α → γ Transformation in a Fe-Mn-Al-Ni Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Peng, Huabei; Huang, Pan; Zhou, Tiannan; Wang, Shanling; Wen, Yuhua

2017-05-01

In this study, we investigated the shape memory behavior and phase transformations of solution-treated Fe43.61Mn34.74Al13.38Ni8.27 alloy between room temperature and 1173 K (900 °C). This alloy exhibits the reverse shape memory effect resulting from the phase transformation of α (bcc) → γ (fcc) between 673 K and 1073 K (400 °C and 800 °C) in addition to the shape memory effect resulting from the martensitic reverse transformation of γ' (fcc) → α (bcc) below 673 K (400 °C). There is a high density of hairpin-shaped dislocations in the α phase undergoing the martensitic reverse transformation of γ' → α. The lath γ phase, which preferentially nucleates and grows in the reversed α phase, has the same crystal orientation with the reverse-transformed γ' martensite. However, the vermiculate γ phase, which is precipitated in the α phase between lath γ phase, has different crystal orientations. The lath γ phase is beneficial to attaining better reverse shape memory effect than the vermiculate γ phase.

From the S U (2 ) quantum link model on the honeycomb lattice to the quantum dimer model on the kagome lattice: Phase transition and fractionalized flux strings

NASA Astrophysics Data System (ADS)

Banerjee, D.; Jiang, F.-J.; Olesen, T. Z.; Orland, P.; Wiese, U.-J.

2018-05-01

We consider the (2 +1 ) -dimensional S U (2 ) quantum link model on the honeycomb lattice and show that it is equivalent to a quantum dimer model on the kagome lattice. The model has crystalline confined phases with spontaneously broken translation invariance associated with pinwheel order, which is investigated with either a Metropolis or an efficient cluster algorithm. External half-integer non-Abelian charges [which transform nontrivially under the Z (2 ) center of the S U (2 ) gauge group] are confined to each other by fractionalized strings with a delocalized Z (2 ) flux. The strands of the fractionalized flux strings are domain walls that separate distinct pinwheel phases. A second-order phase transition in the three-dimensional Ising universality class separates two confining phases: one with correlated pinwheel orientations, and the other with uncorrelated pinwheel orientations.

Transformation of the θ-phase in Mg-Li-Al alloys: a density functional theory study.

PubMed

Zhang, Caili; Han, Peide; Zhang, Zhuxia; Dong, Minghui; Zhang, Lili; Gu, Xiangyang; Yang, Yanqing; Xu, Bingshe

2012-03-01

In Mg-Li-Al alloys, θ-phase MgAlLi(2) is a strengthening and metastable phase which is liable to be transformed to the equilibrium phase AlLi on overaging. While the structural details of the θ-phase MgAlLi(2) and the microscopic transformation are still unknown. In this paper, the structure of MgAlLi(2) unit cell was determined through X-ray powder diffraction simulation. Microscopic transformation process of θ-phase MgAlLi(2) was discussed in detail using first principles method.

Local Mechanical Response of Superelastic NiTi Shape-Memory Alloy Under Uniaxial Loading

NASA Astrophysics Data System (ADS)

Xiao, Yao; Zeng, Pan; Lei, Liping; Du, Hongfei

2015-11-01

In this paper, we focus on the local mechanical response of superelastic NiTi SMA at different temperatures under uniaxial loading. In situ DIC is applied to measure the local strain of the specimen. Based on the experimental results, two types of mechanical response, which are characterized with localized phase transformation and homogenous phase transformation, are identified, respectively. Motivated by residual strain accumulation phenomenon of the superelastic mechanical response, we conduct controlled experiments, and infer that for a given material point, all (or most) of the irreversibility is accumulated when the transformation front is traversing the material point. A robust constitutive model is established to explain the experimental phenomena and we successfully simulate the evolution of local strain that agrees closely with the experimental results.

Abiotic transformation of high explosives by freshly precipitated iron minerals in aqueous Fe¹¹ solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boparai, Hardiljeet K.; Comfort, Steve; Satapanajaru, Tunlawit

Zerovalent iron barriers have become a viable treatment for field-scale cleanup of various ground water contaminants. While contact with the iron surface is important for contaminant destruction, the interstitial pore water within and near the iron barrier will be laden with aqueous, adsorbed and precipitated FeII phases. These freshly precipitated iron minerals could play an important role in transforming high explosives (HE). Our objective was to determine the transformation of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), and TNT (2,4,6-trinitrotoluene) by freshly precipitated iron FeII/FeIII minerals. This was accomplished by quantifying the effects of initial FeII concentration, pH, and the presence of aquifermore » solids (FeIII phases) on HE transformation rates. Results showed that at pH 8.2, freshly precipitated iron minerals transformed RDX, HMX, and TNT with reaction rates increasing with increasing FeII concentrations. RDX and HMX transformations in these solutions also increased with increasing pH (5.8-8.55). By contrast, TNT transformation was not influenced by pH (6.85-8.55) except at pH values <6.35. Transformations observed via LC/MS included a variety of nitroso products (RDX, HMX) and amino degradation products (TNT). XRD analysis identified green rust and magnetite as the dominant iron solid phases that precipitated from the aqueous FeII during HE treatment under anaerobic conditions. Geochemical modeling also predicted FeII activity would likely be controlled by green rust and magnetite. These results illustrate the important role freshly precipitated FeII/FeIII minerals in aqueous FeII solutions play in the transformation of high explosives.« less

From the Mountains to the Valleys: Theorizing Gender in Sport through McIntosh's Interactive Phases.

ERIC Educational Resources Information Center

Fairchild, David L.

1994-01-01

This paper uses Peggy McIntosh's (1983) interactive phase typology as a descriptive model within which to characterize contemporary sport with respect to certain gender issues, accepting gender as dynamically and culturally constituted. The paper discusses possibilities for transforming sport by enhancing the appreciation of sport and enriching…

78 FR 12269 - Wireline Competition Bureau Seeks Updates and Corrections to TelcoMaster Table for Connect...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-22

... Competition Bureau Seeks Updates and Corrections to TelcoMaster Table for Connect America Cost Model AGENCY... centers to particular holding companies for purposes of Connect America Phase II implementation. DATES... companies for purposes of Connect America Phase II implementation. 2. The USF/ICC Transformation Order, 76...

Intergranular fracture in UO{sub 2}: derivation of traction-separation law from atomistic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yongfeng; Millett, P.C.; Tonks, M.R.

2013-07-01

In this study, the intergranular fracture behavior of UO{sub 2} was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt Σ5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at themore » propagating crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior. (authors)« less

Intergranular fracture in UO2: derivation of traction-separation law from atomistic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yongfeng Zhang; Paul C Millett; Michael R Tonks

2013-10-01

In this study, the intergranular fracture behavior of UO2 was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt E5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at the propagatingmore » crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior.« less

The WS transform for the Kuramoto model with distributed amplitudes, phase lag and time delay

NASA Astrophysics Data System (ADS)

Lohe, M. A.

2017-12-01

We apply the Watanabe-Strogatz (WS) transform to a generalized Kuramoto model with distributed parameters describing the amplitude of oscillation, phase lag, and time delay at each node of the system. The model has global coupling and identical frequencies, but allows for repulsive interactions at arbitrary nodes leading to conformist-contrarian phenomena together with variable amplitude and time-delay effects. We show how to determine the initial values of the WS system for any initial conditions for the Kuramoto system, and investigate the asymptotic behaviour of the WS variables. For the case of zero time delay the possible asymptotic configurations are determined by the sign of a single parameter μ which measures whether or not the attractive nodes dominate the repulsive nodes. If μ>0 the system completely synchronizes from general initial conditions, whereas if μ<0 one of two types of phase-locked synchronization occurs, depending on the initial values, while for μ=0 periodic solutions can occur. For the case of arbitrary non-uniform time delays we derive a stability condition for completely synchronized solutions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haslam, J J; Wall, M A; Johnson, D L

We have measured and modeled the change in electrical resistivity due to partial transformation to the martensitic {alpha}{prime}-phase in a {delta}-phase Pu-Ga matrix. The primary objective is to relate the change in resistance, measured with a 4-probe technique during the transformation, to the volume fraction of the {alpha}{prime} phase created in the microstructure. Analysis by finite element methods suggests that considerable differences in the resistivity may be anticipated depending on the orientational and morphological configurations of the {alpha}{prime} particles. Finite element analysis of the computed resistance of an assembly of lenticular shaped particles indicates that series resistor or parallel resistormore » approximations are inaccurate and can lead to an underestimation of the predicted amount of {alpha}{prime} in the sample by 15% or more. Comparison of the resistivity of a simulated network of partially transformed grains or portions of grains suggests that a correction to the measured resistivity allows quantification of the amount of {alpha}{prime} phase in the microstructure with minimal consideration of how the {alpha}{prime} morphology may evolve. It is found that the average of the series and parallel resistor approximations provide the most accurate relationship between the measured resistivity and the amount of {alpha}{prime} phase. The methods described here are applicable to any evolving two-phase microstructure in which the resistance difference between the two phases is measurable.« less

Phase transformation in the alumina-titania system during flash sintering experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jha, S. K.; Lebrun, J. M.; Raj, R.

2016-02-01

We show that phase transformation in the alumina–titania system, which produces aluminum-titanate, follows an unusual trajectory during flash sintering. The experiments begin with mixed powders of alumina–titania and end in dense microstructures that are transformed into aluminum-titanate. The sintering and the phase transformation are separated in time, with the sintering occurs during Stage II, and phase transformation during Stage III of the flash sintering experiment. Stage III is the steady-state condition of flash activated state that is established under current control, while Stage II is the period of transition from voltage to current control. The extent of phase transformation increasesmore » with the current density and the hold time in Stage III.« less

A novel attack method about double-random-phase-encoding-based image hiding method

NASA Astrophysics Data System (ADS)

Xu, Hongsheng; Xiao, Zhijun; Zhu, Xianchen

2018-03-01

By using optical image processing techniques, a novel text encryption and hiding method applied by double-random phase-encoding technique is proposed in the paper. The first step is that the secret message is transformed into a 2-dimension array. The higher bits of the elements in the array are used to fill with the bit stream of the secret text, while the lower bits are stored specific values. Then, the transformed array is encoded by double random phase encoding technique. Last, the encoded array is embedded on a public host image to obtain the image embedded with hidden text. The performance of the proposed technique is tested via analytical modeling and test data stream. Experimental results show that the secret text can be recovered either accurately or almost accurately, while maintaining the quality of the host image embedded with hidden data by properly selecting the method of transforming the secret text into an array and the superimposition coefficient.

Current harmonics elimination control method for six-phase PM synchronous motor drives.

PubMed

Yuan, Lei; Chen, Ming-liang; Shen, Jian-qing; Xiao, Fei

2015-11-01

To reduce the undesired 5th and 7th stator harmonic current in the six-phase permanent magnet synchronous motor (PMSM), an improved vector control algorithm was proposed based on vector space decomposition (VSD) transformation method, which can control the fundamental and harmonic subspace separately. To improve the traditional VSD technology, a novel synchronous rotating coordinate transformation matrix was presented in this paper, and only using the traditional PI controller in d-q subspace can meet the non-static difference adjustment, the controller parameter design method is given by employing internal model principle. Moreover, the current PI controller parallel with resonant controller is employed in x-y subspace to realize the specific 5th and 7th harmonic component compensation. In addition, a new six-phase SVPWM algorithm based on VSD transformation theory is also proposed. Simulation and experimental results verify the effectiveness of current decoupling vector controller. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Interfaces between hexagonal and cubic oxides and their structure alternatives

DOE PAGES

Zhou, Hua; Wu, Lijun; Wang, Hui-Qiong; ...

2017-11-14

Multi-layer structure of functional materials often involves the integration of different crystalline phases. The film growth orientation thus frequently exhibits a transformation, owing to multiple possibilities caused by incompatible in-plane structural symmetry. Nevertheless, the detailed mechanism of the transformation has not yet been fully explored. Here we thoroughly probe the heteroepitaxially grown hexagonal zinc oxide (ZnO) films on cubic (001)-magnesium oxide (MgO) substrates using advanced scanning transition electron microscopy, X-ray diffraction and first principles calculations, revealing two distinct interface models of (001) ZnO/(001) MgO and (100) ZnO/(001) MgO. Here we have found that the structure alternatives are controlled thermodynamically bymore » the nucleation, while kinetically by the enhanced Zn adsorption and O diffusion upon the phase transformation. Finally, this work not only provides a guideline for the interface fabrication with distinct crystalline phases but also shows how polar and non-polar hexagonal ZnO films might be manipulated on the same cubic substrate.« less

Temperature-modulated DSC provides new insight about nickel-titanium wire transformations.

PubMed

Brantley, William A; Iijima, Masahiro; Grentzer, Thomas H

2003-10-01

Differential scanning calorimetry (DSC) is a well-known method for investigating phase transformations in nickel-titanium orthodontic wires; the microstructural phases and phase transformations in these wires have central importance for their clinical performance. The purpose of this study was to use the more recently developed technique of temperature-modulated DSC (TMDSC) to gain insight into transformations in 3 nickel-titanium orthodontic wires: Neo Sentalloy (GAC International, Islandia, NY), 35 degrees C Copper Ni-Ti (Ormco, Glendora, Calif) and Nitinol SE (3M Unitek, Monrovia, Calif). In the oral environment, the first 2 superelastic wires have shape memory, and the third wire has superelastic behavior but not shape memory. All wires had cross-section dimensions of 0.016 x 0.022 in. Archwires in the as-received condition and after bending 135 degrees were cut into 5 or 6 segments for test specimens. TMDSC analyses (Model 2910 DSC, TA Instruments, Wilmington, Del) were conducted between -125 degrees C and 100 degrees C, using a linear heating and cooling rate of 2 degrees C per min, an oscillation amplitude of 0.318 degrees C with a period of 60 seconds, and helium as the purge gas. For all 3 wire alloys, strong low-temperature martensitic transformations, resolved on the nonreversing heat-flow curves, were not present on the reversing heat-flow curves, and bending appeared to increase the enthalpy change for these peaks in some cases. For Neo Sentalloy, TMDSC showed that transformation between martensitic and austenitic nickel-titanium, suggested as occurring directly in the forward and reverse directions by conventional DSC, was instead a 2-step process involving the R-phase. Two-step transformations in the forward and reverse directions were also found for 35 degrees C Copper Ni-Ti and Nitinol SE. The TMDSC results show that structural transformations in these wires are complex. Some possible clinical implications of these observations are discussed.

Transformer modeling for low- and mid-frequency electromagnetic transients simulation

NASA Astrophysics Data System (ADS)

Lambert, Mathieu

In this work, new models are developed for single-phase and three-phase shell-type transformers for the simulation of low-frequency transients, with the use of the coupled leakage model. This approach has the advantage that it avoids the use of fictitious windings to connect the leakage model to a topological core model, while giving the same response in short-circuit as the indefinite admittance matrix (BCTRAN) model. To further increase the model sophistication, it is proposed to divide windings into coils in the new models. However, short-circuit measurements between coils are never available. Therefore, a novel analytical method is elaborated for this purpose, which allows the calculation in 2-D of short-circuit inductances between coils of rectangular cross-section. The results of this new method are in agreement with the results obtained from the finite element method in 2-D. Furthermore, the assumption that the leakage field is approximately 2-D in shell-type transformers is validated with a 3-D simulation. The outcome of this method is used to calculate the self and mutual inductances between the coils of the coupled leakage model and the results are showing good correspondence with terminal short-circuit measurements. Typically, leakage inductances in transformers are calculated from short-circuit measurements and the magnetizing branch is calculated from no-load measurements, assuming that leakages are unimportant for the unloaded transformer and that magnetizing current is negligible during a short-circuit. While the core is assumed to have an infinite permeability to calculate short-circuit inductances, and it is a reasonable assumption since the core's magnetomotive force is negligible during a short-circuit, the same reasoning does not necessarily hold true for leakage fluxes in no-load conditions. This is because the core starts to saturate when the transformer is unloaded. To take this into account, a new analytical method is developed in this dissertation, which removes the contributions of leakage fluxes to properly calculate the magnetizing branches of the new models. However, in the new analytical method for calculating short-circuit inductances (as with other analytical methods), eddy-current losses are neglected. Similarly, winding losses are omitted in the coupled leakage model and in the new analytical method to remove leakage fluxes to calculate core parameters from no-load tests. These losses will be taken into account in future work. Both transformer models presented in this dissertation are based on the classical hypothesis that flux can be discretized into flux tubes, which is also the assumption used in a category of models called topological models. Even though these models are physically-based, there exist many topological models for a given transformer geometry. It is shown in this work that these differences can be explained in part through the concepts of divided and integral fluxes, and it is explained that divided approach is the result of mathematical manipulations, while the integral approach is more "physically-accurate". Furthermore, it is demonstrated, for the special case of a two-winding single-phase transformer, that the divided leakage inductances have to be nonlinear for both approaches to be equivalent. Even between models of the divided or integral approach models, there are differences, which arise from the particular choice of so-called flux paths" (tubes). This arbitrariness comes from the fact that with the classical hypothesis that magnetic flux can be confined into predefined flux tubes (leading to classical magnetic circuit theory), it is assumed that flux cannot leak from the sides of flux tubes. Therefore, depending on the transformer's operation conditions (degree of saturation, short-circuit, etc.), this can lead to different choices of flux tubes and different models. In this work, a new theoretical framework is developed to allow flux to leak from the sides of the tube, and generalized to include resistances and capacitances in what is called electromagnetic circuit theory. Also, it is explained that this theory is actually equivalent to what is called finite formulations (such as the finite element method), which bridges the gap between circuit theory and discrete electromagnetism. Therefore, this enables not only to develop topologically-correct transformer models, where electric and magnetic circuits are defined on dual meshes, but also rotating machine and transmission lines models (wave propagation can be taken into account).

Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

NASA Astrophysics Data System (ADS)

Kirby, Stephen H.; Stein, Seth; Okal, Emile A.; Rubie, David C.

1996-05-01

Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine → spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes should cease at depths near 700 km, because the seismogenic phase transformations in the slab are completed or can no longer occur. Substantial metastability is expected only in old, cold slabs, consistent with the observed restriction of deep earthquakes to those settings. Earthquakes should be restricted to the cold cores of slabs, as in any model in which the seismicity is temperature controlled, via the distribution of metastability. However, the geometries of recent large deep earthquakes pose a challenge for any such models. Transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics, including focal mechanisms indicating localized shear failure rather than implosive deformation, are so similar to those of shallow earthquakes. Finally, metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab. Such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and/or are detached from subducting slabs. Metastability in downgoing slabs could have considerable geodynamic significance. Metastable wedges would reduce the negative buoyancy of slabs, decrease the driving force for subduction, and influence the state of stress in slabs. Heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage, causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity. Because wedge formation should occur only for fast subducting slabs, it may act as a "parachute" and contribute to regulating plate speeds. Wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel, favoring the subsequent sinking of the slab into the lower mantle.

Color image encryption based on gyrator transform and Arnold transform

NASA Astrophysics Data System (ADS)

Sui, Liansheng; Gao, Bo

2013-06-01

A color image encryption scheme using gyrator transform and Arnold transform is proposed, which has two security levels. In the first level, the color image is separated into three components: red, green and blue, which are normalized and scrambled using the Arnold transform. The green component is combined with the first random phase mask and transformed to an interim using the gyrator transform. The first random phase mask is generated with the sum of the blue component and a logistic map. Similarly, the red component is combined with the second random phase mask and transformed to three-channel-related data. The second random phase mask is generated with the sum of the phase of the interim and an asymmetrical tent map. In the second level, the three-channel-related data are scrambled again and combined with the third random phase mask generated with the sum of the previous chaotic maps, and then encrypted into a gray scale ciphertext. The encryption result has stationary white noise distribution and camouflage property to some extent. In the process of encryption and decryption, the rotation angle of gyrator transform, the iterative numbers of Arnold transform, the parameters of the chaotic map and generated accompanied phase function serve as encryption keys, and hence enhance the security of the system. Simulation results and security analysis are presented to confirm the security, validity and feasibility of the proposed scheme.

Single-phase power distribution system power flow and fault analysis

NASA Technical Reports Server (NTRS)

Halpin, S. M.; Grigsby, L. L.

1992-01-01

Alternative methods for power flow and fault analysis of single-phase distribution systems are presented. The algorithms for both power flow and fault analysis utilize a generalized approach to network modeling. The generalized admittance matrix, formed using elements of linear graph theory, is an accurate network model for all possible single-phase network configurations. Unlike the standard nodal admittance matrix formulation algorithms, the generalized approach uses generalized component models for the transmission line and transformer. The standard assumption of a common node voltage reference point is not required to construct the generalized admittance matrix. Therefore, truly accurate simulation results can be obtained for networks that cannot be modeled using traditional techniques.

Martensitic transformation and phase diagram in ternary Co-V-Ga Heusler alloys

NASA Astrophysics Data System (ADS)

Xu, Xiao; Nagashima, Akihide; Nagasako, Makoto; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke

2017-03-01

We report the martensitic transformation behavior in Co-V-Ga Heusler alloys. Thermoanalysis and thermomagnetization measurements were conducted to observe the martensitic transformation. By using a transmission electron microscope and an in situ X-ray diffractometer, martensitic transformation was found to occur from the L21 Heusler parent phase to the D022 martensite phase. Phase diagrams were determined for two pseudo-binary sections where martensitic transformation was detected. Magnetic properties, including the Curie temperatures and spontaneous magnetization of the parent phase, were also investigated. The magnetic properties showing behaviors different from those of NiMn-based alloys were found.

Simulation investigation of thermal phase transformation and residual stress in single pulse EDM of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Tang, Jiajing; Yang, Xiaodong

2018-04-01

The thermal phase transformation and residual stress are ineluctable in the electrical discharge machining (EDM) process, and they will greatly affect the working performances of the machined surface. This paper presents a simulation study on the thermal phase transformation and residual stress in single-pulse EDM of Ti-6Al-4V, which is the most popular titanium alloy in fields such as aircraft engine and some other leading industries. A multi-physics model including thermal, hydraulic, metallography and structural mechanics was developed. Based on the proposed model, the thickness and metallographic structure of the recast layer and heat affected layer (HAZ) were investigated. The distribution and characteristics of residual stress around the discharge crater were obtained. The recast layer and HAZ at the center of crater are found to be the thinnest, and their thicknesses gradually increase approaching the periphery of the crater. The recast layer undergoes a complete α‧ (martensitic) transformation, while the HAZ is mainly composed by the α  +  β  +  α‧ three-phase microstructure. Along the depth direction of crater, the Von Mises stress increases first and then decreases, reaching its maximal value near the interface of recast layer and HAZ. In the recast layer, both compressive stress component and tensile stress component are observed. ANOVA results showed that the influence of discharge current on maximal tensile stress is more significant than that of pulse duration, while the pulse duration has more significant influence on average thickness of the recast layer and the depth location of the maximal tensile stress. The works conducted in this study will help to evaluate the quality and integrity of EDMed surface, especially when the non-destructive testing is difficult to achieve.

Use of glancing angle X-ray powder diffractometry to depth-profile phase transformations during dissolution of indomethacin and theophylline tablets.

PubMed

Debnath, Smita; Predecki, Paul; Suryanarayanan, Raj

2004-01-01

The purpose of this study was (i) to develop glancing angle x-ray powder diffractometry (XRD) as a method for profiling phase transformations as a function of tablet depth; and (ii) to apply this technique to (a) study indomethacin crystallization during dissolution of partially amorphous indomethacin tablets and to (b) profile anhydrate --> hydrate transformations during dissolution of theophylline tablets. The intrinsic dissolution rates of indomethacin and theophylline were determined after different pharmaceutical processing steps. Phase transformations during dissolution were evaluated by various techniques. Transformation in the bulk and on the tablet surface was characterized by conventional XRD and scanning electron microscopy, respectively. Glancing angle XRD enabled us to profile these transformations as a function of depth from the tablet surface. Pharmaceutical processing resulted in a decrease in crystallinity of both indomethacin and theophylline. When placed in contact with the dissolution medium, while indomethacin recrystallized, theophylline anhydrate rapidly converted to theophylline monohydrate. Due to intimate contact with the dissolution medium, drug transformation occurred to a greater extent at or near the tablet surface. Glancing angle XRD enabled us to depth profile the extent of phase transformations as a function of the distance from the tablet surface. The processed sample (both indomethacin and theophylline) transformed more rapidly than did the corresponding unprocessed drug. Several challenges associated with the glancing angle technique, that is, the effects of sorbed water, phase transformations during the experimental timescale, and the influence of phase transformation on penetration depth, were addressed. Increased solubility, and consequently dissolution rate, is one of the potential advantages of metastable phases. This advantage is negated if, during dissolution, the metastable to stable transformation rate > dissolution rate. Glancing angle XRD enabled us to quantify and thereby profile phase transformations as a function of compact depth. The technique has potential utility in monitoring surface reactions, both chemical decomposition and physical transformations, in pharmaceutical systems.

Phase Boundary Propagation in Li-Alloying Battery Electrodes Revealed by Liquid-Cell Transmission Electron Microscopy

DOE PAGES

Leenheer, Andrew J.; Jungjohann, Katherine L.; Zavadil, Kevin R.; ...

2016-05-31

Battery cycle life is directly influenced by the microstructural changes occurring in the electrodes during charge and discharge cycles. In this study, we image in situ the nanoscale phase evolution in negative electrode materials for Li-ion batteries using a fully enclosed liquid cell in a transmission electron microscope (TEM) to reveal early degradation that is not evident in the charge–discharge curves. To compare the electrochemical phase transformation behavior between three model materials, thin films of amorphous Si, crystalline Al, and crystalline Au were lithiated and delithiated at controlled rates while immersed in a commercial liquid electrolyte. This method allowed formore » the direct observation of lithiation mechanisms in nanoscale negative electrodes, revealing that a simplistic model of a surface-to-interior lithiation front is insufficient. For the crystalline films, a lithiation front spread laterally from a few initial nucleation points, with continued grain nucleation along the growing interface. The intermediate lithiated phases were identified using electron diffraction, and high-resolution postmortem imaging revealed the details of the final microstructure. Lastly, our results show that electrochemically induced solid–solid phase transformations can lead to highly concentrated stresses at the laterally propagating phase boundary which should be considered for future designs of nanostructured electrodes for Li-ion batteries.« less

Length-Scale-Dependent Phase Transformation of LiFePO4 : An In situ and Operando Study Using Micro-Raman Spectroscopy and XRD.

PubMed

Siddique, N A; Salehi, Amir; Wei, Zi; Liu, Dong; Sajjad, Syed D; Liu, Fuqiang

2015-08-03

The charge and discharge of lithium ion batteries are often accompanied by electrochemically driven phase-transformation processes. In this work, two in situ and operando methods, that is, micro-Raman spectroscopy and X-ray diffraction (XRD), have been combined to study the phase-transformation process in LiFePO4 at two distinct length scales, namely, particle-level scale (∼1 μm) and macroscopic scale (∼several cm). In situ Raman studies revealed a discrete mode of phase transformation at the particle level. Besides, the preferred electrochemical transport network, particularly the carbon content, was found to govern the sequence of phase transformation among particles. In contrast, at the macroscopic level, studies conducted at four different discharge rates showed a continuous but delayed phase transformation. These findings uncovered the intricate phase transformation in LiFePO4 and potentially offer valuable insights into optimizing the length-scale-dependent properties of battery materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Phase transformations involving the [alpha][sub 2] and O phases in Ti-Al-Nb alloys. [Ti-28. 5Al-13Nb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muraleedharan, K.; Banerjee, D.

1993-08-15

An orthorhombic (O) phase with Cmcm space group and Ti[sub 2]AlNb composition has ben established in the Ti-Al-Nb system. Efforts to develop alloys with this orthorhombic phase as a major phase, in place of the [alpha][sub 2] (Ti[sub 3]Al) phase, resulted in compositions with superior combinations of strength and toughness. The determination of phase diagrams for the Ti-Al-Nb system is a continuing effort. Bendersky et al. considered possible transformation paths and the hierarchy of structures in going from the [beta] phase to [alpha][sub 2] or O phases through displacive or replacive reactions. Microstructures predicted by these considerations have been documentedmore » in the particularly well investigated [beta]-->O transformation. Very little work has however been carried out on the [alpha][sub 2]-->O phase transformation. In this paper, the authors report preliminary results of isothermal aging study of this transformation.« less

Time Series of Tropical-Forest Structure from TanDEM-X, Transformed to Time Series of Biomass by MODIS

NASA Astrophysics Data System (ADS)

Treuhaft, R. N.; Baccini, A.; Goncalves, F. G.; Lei, Y.; Keller, M.; Walker, W. S.

2017-12-01

Tropical forests account for about 50% of the world's forested biomass, and play a critical role in the control of atmospheric carbon dioxide. Large-scale (1000's of km) changes in forest structure and biomass bear on global carbon source-sink dynamics, while small-scale (< 100 m) changes bear on deforestation and degradation monitoring. After describing the interferometric SAR (InSAR) phase-height observation, we show forest phase-height time series from the TanDEM-X radar interferometer at X-band (3 cm), taken with monthly and sub-hectare temporal and spatial resolution, respectively. The measurements were taken with more than 30 TanDEM-X passes over Tapajós National Forest in the Brazilian Amazon between 2011 and 2014. The transformation of phase-height rates into aboveground biomass (AGB) rates is based on the idea that the change in AGB due to a change in phase-height depends on the plot's AGB. Plots with higher AGB will produce more AGB for a given increase in height or phase-height. Postulating a power-law dependence of plot-level mass density on physical height, we previously found that the best conversion factors for transforming phase-height rate to AGB rate were indeed dependent on AGB. For 78 plots, we demonstrated AGB rates from InSAR phase-height rates using AGB from field measurements. For regional modeling of the Amazon Basin, field measurements of AGB, to specify the conversion factors, is impractical. Conversion factors from InSAR phase-height rate to AGB rate in this talk will be based on AGB derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). AGB measurement from MODIS is based on the spectral reflectance of 7 bands from the visible to short wave infrared, and auxiliary metrics describing the variance in reflectance. The mapping of MODIS reflectance to AGB is enabled by training a machine learning algorithm with lidar-derived AGB data, which are in turn trained by field measurements for small areas. The performance of TanDEM-X AGB rate from MODIS-derived conversion factors will be compared to that derived from field-based conversion factors. We will also attempt to improve phase-height rate to AGB rate transformation by deriving improved models of mass density dependences on height, based on the aggregation of single-stem allometrics.

Measurement of the internal stress and electric field in a resonating piezoelectric transformer for high-voltage applications using the electro-optic and photoelastic effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

VanGordon, James A.; Kovaleski, Scott D., E-mail: kovaleskis@missouri.edu; Norgard, Peter

The high output voltages from piezoelectric transformers are currently being used to accelerate charged particle beams for x-ray and neutron production. Traditional methods of characterizing piezoelectric transformers (PTs) using electrical probes can decrease the voltage transformation ratio of the device due to the introduction of load impedances on the order of hundreds of kiloohms to hundreds of megaohms. Consequently, an optical diagnostic was developed that used the photoelastic and electro-optic effects present in piezoelectric materials that are transparent to a given optical wavelength to determine the internal stress and electric field. The combined effects of the piezoelectric, photoelastic, and electro-opticmore » effects result in a time-dependent change the refractive indices of the material and produce an artificially induced, time-dependent birefringence in the piezoelectric material. This induced time-dependent birefringence results in a change in the relative phase difference between the ordinary and extraordinary wave components of a helium-neon laser beam. The change in phase difference between the wave components was measured using a set of linear polarizers. The measured change in phase difference was used to calculate the stress and electric field based on the nonlinear optical properties, the piezoelectric constitutive equations, and the boundary conditions of the PT. Maximum stresses of approximately 10 MPa and electric fields of as high as 6 kV/cm were measured with the optical diagnostic. Measured results were compared to results from both a simple one-dimensional (1D) model of the piezoelectric transformer and a three-dimensional (3D) finite element model. Measured stresses and electric fields along the length of an operating length-extensional PT for two different electrical loads were within at least 50 % of 3D finite element simulated results. Additionally, the 3D finite element results were more accurate than the results from the 1D model for a wider range of electrical load impedances under test.« less

Measurement of the internal stress and electric field in a resonating piezoelectric transformer for high-voltage applications using the electro-optic and photoelastic effects.

PubMed

VanGordon, James A; Kovaleski, Scott D; Norgard, Peter; Gall, Brady B; Dale, Gregory E

2014-02-01

The high output voltages from piezoelectric transformers are currently being used to accelerate charged particle beams for x-ray and neutron production. Traditional methods of characterizing piezoelectric transformers (PTs) using electrical probes can decrease the voltage transformation ratio of the device due to the introduction of load impedances on the order of hundreds of kiloohms to hundreds of megaohms. Consequently, an optical diagnostic was developed that used the photoelastic and electro-optic effects present in piezoelectric materials that are transparent to a given optical wavelength to determine the internal stress and electric field. The combined effects of the piezoelectric, photoelastic, and electro-optic effects result in a time-dependent change the refractive indices of the material and produce an artificially induced, time-dependent birefringence in the piezoelectric material. This induced time-dependent birefringence results in a change in the relative phase difference between the ordinary and extraordinary wave components of a helium-neon laser beam. The change in phase difference between the wave components was measured using a set of linear polarizers. The measured change in phase difference was used to calculate the stress and electric field based on the nonlinear optical properties, the piezoelectric constitutive equations, and the boundary conditions of the PT. Maximum stresses of approximately 10 MPa and electric fields of as high as 6 kV/cm were measured with the optical diagnostic. Measured results were compared to results from both a simple one-dimensional (1D) model of the piezoelectric transformer and a three-dimensional (3D) finite element model. Measured stresses and electric fields along the length of an operating length-extensional PT for two different electrical loads were within at least 50 % of 3D finite element simulated results. Additionally, the 3D finite element results were more accurate than the results from the 1D model for a wider range of electrical load impedances under test.

Efficient Text Encryption and Hiding with Double-Random Phase-Encoding

PubMed Central

Sang, Jun; Ling, Shenggui; Alam, Mohammad S.

2012-01-01

In this paper, a double-random phase-encoding technique-based text encryption and hiding method is proposed. First, the secret text is transformed into a 2-dimensional array and the higher bits of the elements in the transformed array are used to store the bit stream of the secret text, while the lower bits are filled with specific values. Then, the transformed array is encoded with double-random phase-encoding technique. Finally, the encoded array is superimposed on an expanded host image to obtain the image embedded with hidden data. The performance of the proposed technique, including the hiding capacity, the recovery accuracy of the secret text, and the quality of the image embedded with hidden data, is tested via analytical modeling and test data stream. Experimental results show that the secret text can be recovered either accurately or almost accurately, while maintaining the quality of the host image embedded with hidden data by properly selecting the method of transforming the secret text into an array and the superimposition coefficient. By using optical information processing techniques, the proposed method has been found to significantly improve the security of text information transmission, while ensuring hiding capacity at a prescribed level. PMID:23202003

Modelling Metamorphism by Abstract Interpretation

NASA Astrophysics Data System (ADS)

Dalla Preda, Mila; Giacobazzi, Roberto; Debray, Saumya; Coogan, Kevin; Townsend, Gregg M.

Metamorphic malware apply semantics-preserving transformations to their own code in order to foil detection systems based on signature matching. In this paper we consider the problem of automatically extract metamorphic signatures from these malware. We introduce a semantics for self-modifying code, later called phase semantics, and prove its correctness by showing that it is an abstract interpretation of the standard trace semantics. Phase semantics precisely models the metamorphic code behavior by providing a set of traces of programs which correspond to the possible evolutions of the metamorphic code during execution. We show that metamorphic signatures can be automatically extracted by abstract interpretation of the phase semantics, and that regular metamorphism can be modelled as finite state automata abstraction of the phase semantics.

Micromechanics of composites with shape memory alloy fibers in uniform thermal fields

NASA Technical Reports Server (NTRS)

Birman, Victor; Saravanos, Dimitris A.; Hopkins, Dale A.

1995-01-01

Analytical procedures are developed for a composite system consisting of shape memory alloy fibers within an elastic matrix subject to uniform temperature fluctuations. Micromechanics for the calculation of the equivalent properties of the composite are presented by extending the multi-cell model to incorporate shape memory alloy fibers. A three phase concentric cylinder model is developed for the analysis of local stresses which includes the fiber, the matrix, and the surrounding homogenized composite. The solution addresses the complexities induced by the nonlinear dependence of the in-situ martensite fraction of the fibers to the local stresses and temperature, and the local stresses developed from interactions between the fibers and matrix during the martensitic and reverse phase transformations. Results are presented for a nitinol/epoxy composite. The applications illustrate the response of the composite in isothermal longitudinal loading and unloading, and in temperature induced actuation. The local stresses developed in the composite under various stages of the martensitic and reverse phase transformation are also shown.

Design of two-way reversible bending actuator based on a shape memory alloy/shape memory polymer composite

NASA Astrophysics Data System (ADS)

Taya, Minoru; Liang, Yuanchang; Namli, Onur C.; Tamagawa, Hirohisa; Howie, Tucker

2013-10-01

The design of a reversible bending actuator based on a SMA/SMP composite is presented. The SMA/SMP composite is made of SMA NiTi wires with a bent ‘U’-shape in the austenite phase embedded in an epoxy SMP matrix which has a memorized flat shape. The bending motion is caused by heating the composite above TAf to activate the NiTi recovery. Upon cooling, the softening from the austenite to R-phase transformation results in a relaxation of the composite towards its original flat shape. In the three-point bending measurement the composite was able to exhibit a reversible deflection of 1.3 mm on a support with a 10 mm span. In addition, a material model for predicting the composite’s deflection is presented and predicts the experimental results reasonably well. The model also estimates the in-plane internal force and the degree of the SMA phase transformation.

Superintegrability of geodesic motion on the sausage model

NASA Astrophysics Data System (ADS)

Arutyunov, Gleb; Heinze, Martin; Medina-Rincon, Daniel

2017-06-01

Reduction of the η-deformed sigma model on AdS_5× S5 to the two-dimensional squashed sphere (S^2)η can be viewed as a special case of the Fateev sausage model where the coupling constant ν is imaginary. We show that geodesic motion in this model is described by a certain superintegrable mechanical system with four-dimensional phase space. This is done by means of explicitly constructing three integrals of motion which satisfy the sl(2) Poisson algebra relations, albeit being non-polynomial in momenta. Further, we find a canonical transformation which transforms the Hamiltonian of this mechanical system to the one describing the geodesic motion on the usual two-sphere. By inverting this transformation we map geodesics on this auxiliary two-sphere back to the sausage model. This paper is a tribute to the memory of Prof Petr Kulish.

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

PubMed

Cao, Shi-Gu; Li, Yunsong; Wu, Hong-Hui; Wang, Jie; Huang, Baoling; Zhang, Tong-Yi

2017-08-09

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO 3 ) with a special thermomechanical treatment (TMT), where BaTiO 3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

Fundamental Studies on Phase Transformations and Mechanical Properties of Fusion Welds in Advanced Naval Steels

DTIC Science & Technology

2017-07-31

Studies on Phase Transformations and Mechanical Properties of Fusion Welds in Advanced Naval Steels Sb. GRANT NUMBER N00014-12-1-0475 Sc. PROGRAM...naval and structural applications. However, prior to this research project, a fundamental understanding of the phase transformation behavior under the...Steel, Phase Transformations 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER a. REPORT b.ABSTRACT c. THIS PAGE ABSTRACT OF PAGES u u

Phase Stability and Stress-Induced Transformations in Beta Titanium Alloys

NASA Astrophysics Data System (ADS)

Kolli, R. Prakash; Joost, William J.; Ankem, Sreeramamurthy

2015-06-01

In this article, we provide a brief review of the recent developments related to the relationship between phase stability and stress-induced transformations in metastable body-centered-cubic β-phase titanium alloys. Stress-induced transformations occur during tensile, compressive, and creep loading and influence the mechanical response. These transformations are not fully understood and increased understanding of these mechanisms will permit future development of improved alloys for aerospace, biomedical, and energy applications. In the first part of this article, we review phase stability and discuss a few recent developments. In the second section, we discuss the current status of understanding stress-induced transformations and several areas that require further study. We also provide our perspective on the direction of future research efforts. Additionally, we address the occurrence of the hcp ω-phase and the orthorhombic α″-martensite phase stress-induced transformations.

The Modeling of Vibration Damping in SMA Wires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, D R; Kloucek, P; Seidman, T I

Through a mathematical and computational model of the physical behavior of shape memory alloy wires, this study shows that localized heating and cooling of such materials provides an effective means of damping vibrational energy. The thermally induced pseudo-elastic behavior of a shape memory wire is modeled using a continuum thermodynamic model and solved computationally as described by the authors in [23]. Computational experiments confirm that up to 80% of an initial shock of vibrational energy can be eliminated at the onset of a thermally-induced phase transformation through the use of spatially-distributed transformation regions along the length of a shape memorymore » alloy wire.« less

Shear-driven phase transformation in silicon nanowires

NASA Astrophysics Data System (ADS)

Vincent, L.; Djomani, D.; Fakfakh, M.; Renard, C.; Belier, B.; Bouchier, D.; Patriarche, G.

2018-03-01

We report on an unprecedented formation of allotrope heterostructured Si nanowires by plastic deformation based on applied radial compressive stresses inside a surrounding matrix. Si nanowires with a standard diamond structure (3C) undergo a phase transformation toward the hexagonal 2H-allotrope. The transformation is thermally activated above 500 °C and is clearly driven by a shear-stress relief occurring in parallel shear bands lying on {115} planes. We have studied the influence of temperature and axial orientation of nanowires. The observations are consistent with a martensitic phase transformation, but the finding leads to clear evidence of a different mechanism of deformation-induced phase transformation in Si nanowires with respect to their bulk counterpart. Our process provides a route to study shear-driven phase transformation at the nanoscale in Si.

Shear-driven phase transformation in silicon nanowires.

PubMed

Vincent, L; Djomani, D; Fakfakh, M; Renard, C; Belier, B; Bouchier, D; Patriarche, G

2018-03-23

We report on an unprecedented formation of allotrope heterostructured Si nanowires by plastic deformation based on applied radial compressive stresses inside a surrounding matrix. Si nanowires with a standard diamond structure (3C) undergo a phase transformation toward the hexagonal 2H-allotrope. The transformation is thermally activated above 500 °C and is clearly driven by a shear-stress relief occurring in parallel shear bands lying on {115} planes. We have studied the influence of temperature and axial orientation of nanowires. The observations are consistent with a martensitic phase transformation, but the finding leads to clear evidence of a different mechanism of deformation-induced phase transformation in Si nanowires with respect to their bulk counterpart. Our process provides a route to study shear-driven phase transformation at the nanoscale in Si.

Variational formulation and stability analysis of a three dimensional superelastic model for shape memory alloys

NASA Astrophysics Data System (ADS)

Alessi, Roberto; Pham, Kim

2016-02-01

This paper presents a variational framework for the three-dimensional macroscopic modelling of superelastic shape memory alloys in an isothermal setting. Phase transformation is accounted through a unique second order tensorial internal variable, acting as the transformation strain. Postulating the total strain energy density as the sum of a free energy and a dissipated energy, the model depends on two material scalar functions of the norm of the transformation strain and a material scalar constant. Appropriate calibration of these material functions allows to render a wide range of constitutive behaviours including stress-softening and stress-hardening. The quasi-static evolution problem of a domain is formulated in terms of two physical principles based on the total energy of the system: a stability criterion, which selects the local minima of the total energy, and an energy balance condition, which ensures the consistency of the evolution of the total energy with respect to the external loadings. The local phase transformation laws in terms of Kuhn-Tucker relations are deduced from the first-order stability condition and the energy balance condition. The response of the model is illustrated with a numerical traction-torsion test performed on a thin-walled cylinder. Evolutions of homogeneous states are given for proportional and non-proportional loadings. Influence of the stress-hardening/softening properties on the evolution of the transformation domain is emphasized. Finally, in view of an identification process, the issue of stability of homogeneous states in a multi-dimensional setting is answered based on the study of second-order derivative of the total energy. Explicit necessary and sufficient conditions of stability are provided.

Aging Wire Insulation Assessment by Phase Spectrum Examination of Ultrasonic Guided Waves

NASA Technical Reports Server (NTRS)

Anastasi, Robert F.; Madaras, Eric I.

2003-01-01

Wire integrity has become an area of concern to the aerospace community including DoD, NASA, FAA, and Industry. Over time and changing environmental conditions, wire insulation can become brittle and crack. The cracks expose the wire conductor and can be a source of equipment failure, short circuits, smoke, and fire. The technique of using the ultrasonic phase spectrum to extract material properties of the insulation is being examined. Ultrasonic guided waves will propagate in both the wire conductor and insulation. Assuming the condition of the conductor remains constant then the stiffness of the insulator can be determined by measuring the ultrasonic guided wave velocity. In the phase spectrum method the guided wave velocity is obtained by transforming the time base waveform to the frequency domain and taking the phase difference between two waveforms. The result can then be correlated with a database, derived by numerical model calculations, to extract material properties of the wire insulator. Initial laboratory tests were performed on a simple model consisting of a solid cylinder and then a solid cylinder with a polymer coating. For each sample the flexural mode waveform was identified. That waveform was then transformed to the frequency domain and a phase spectrum was calculated from a pair of waveforms. Experimental results on the simple model compared well to numerical calculations. Further tests were conducted on aircraft or mil-spec wire samples, to see if changes in wire insulation stiffness can be extracted using the phase spectrum technique.

Hamiltonian theory of guiding-center motion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Littlejohn, R.G.

1980-05-01

A Hamiltonian treatment of the guiding center problem is given which employs noncanonical coordinates in phase space. Separation of the unperturbed system from the perturbation is achieved by using a coordinate transformation suggested by a theorem of Darboux. As a model to illustrate the method, motion in the magnetic field B=B(x,y)z is studied. Lie transforms are used to carry out the perturbation expansion.

Deformation mode and strain path dependence of martensite phase transformation in a medium manganese TRIP steel

DOE PAGES

Wu, Wei; Wang, Yu-wei; Makrygiannis, Panagiotis; ...

2017-11-06

The martensite phase transformation dependence upon deformation modes and strain paths in a medium manganese (10 wt%) TRIP steel stamped into a T-shape panel was quantified through combination of 3D digital image correlation and synchrotron X-ray diffraction. The T-shape emulates a portion of a common anti-intrusion component. The stamping speed was kept intentionally slow (1 mm/s) so as to avoid excessive heat generation. The steel, which belongs to the third generation advanced high strength steel (3GAHSS) family, was chosen for two reasons: (1) it is two-phase, i.e. austenite and ferrite, with martensite resulting from deformation-induced phase transformation; (2) the 66more » vol.% initial retained austenite volume fraction (RAVF) enabled a thorough examination of the martensite phase transformation at large deformation levels without exhaustion. Strain fields were coupled with measured RAVF values of small specimens extracted from specific locations on a formed T-shape panel. This enabled an exploration of the effects of linear, bilinear, and non-linear strain paths as well as deformation modes such as tension, plane strain, biaxial tension, and equibiaxial tension. Results suggest a significant martensite phase transformation dependence on deformation mode and strain path in the absence of fracture and when martensite phase transformation is unaffected by heat generated during forming. In general, the uniaxial and biaxial tension deformation modes facilitate the martensite phase transformation, while the smallest amount of martensite phase transformation occurs under plane strain. Some discussion as to further application of the experimental methods detailed in this study to other 3GAHSS and the effects of fracture on martensite phase transformation is provided.« less

Deformation mode and strain path dependence of martensite phase transformation in a medium manganese TRIP steel

DOE PAGES

Wu, Wei; Wang, Yu -Wei; Makrygiannis, Panagiotis; ...

2017-11-06

The martensite phase transformation dependence upon deformation modes and strain paths in a medium manganese (10 wt%) TRIP steel stamped into a T-shape panel was quantified through combination of 3D digital image correlation and synchrotron X-ray diffraction. The T-shape emulates a portion of a common anti-intrusion component. The stamping speed was kept intentionally slow (1 mm/s) so as to avoid excessive heat generation. The steel, which belongs to the third generation advanced high strength steel (3GAHSS) family, was chosen for two reasons: (1) it is two-phase, i.e. austenite and ferrite, with martensite resulting from deformation-induced phase transformation; (2) the 66more » vol.% initial retained austenite volume fraction (RAVF) enabled a thorough examination of the martensite phase transformation at large deformation levels without exhaustion. Strain fields were coupled with measured RAVF values of small specimens extracted from specific locations on a formed T-shape panel. This enabled an exploration of the effects of linear, bilinear, and non-linear strain paths as well as deformation modes such as tension, plane strain, biaxial tension, and equibiaxial tension. Results suggest a significant martensite phase transformation dependence on deformation mode and strain path in the absence of fracture and when martensite phase transformation is unaffected by heat generated during forming. In general, the uniaxial and biaxial tension deformation modes facilitate the martensite phase transformation, while the smallest amount of martensite phase transformation occurs under plane strain. In conclusion, some discussion as to further application of the experimental methods detailed in this study to other 3GAHSS and the effects of fracture on martensite phase transformation is provided.« less

Deformation mode and strain path dependence of martensite phase transformation in a medium manganese TRIP steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei; Wang, Yu -Wei; Makrygiannis, Panagiotis

The martensite phase transformation dependence upon deformation modes and strain paths in a medium manganese (10 wt%) TRIP steel stamped into a T-shape panel was quantified through combination of 3D digital image correlation and synchrotron X-ray diffraction. The T-shape emulates a portion of a common anti-intrusion component. The stamping speed was kept intentionally slow (1 mm/s) so as to avoid excessive heat generation. The steel, which belongs to the third generation advanced high strength steel (3GAHSS) family, was chosen for two reasons: (1) it is two-phase, i.e. austenite and ferrite, with martensite resulting from deformation-induced phase transformation; (2) the 66more » vol.% initial retained austenite volume fraction (RAVF) enabled a thorough examination of the martensite phase transformation at large deformation levels without exhaustion. Strain fields were coupled with measured RAVF values of small specimens extracted from specific locations on a formed T-shape panel. This enabled an exploration of the effects of linear, bilinear, and non-linear strain paths as well as deformation modes such as tension, plane strain, biaxial tension, and equibiaxial tension. Results suggest a significant martensite phase transformation dependence on deformation mode and strain path in the absence of fracture and when martensite phase transformation is unaffected by heat generated during forming. In general, the uniaxial and biaxial tension deformation modes facilitate the martensite phase transformation, while the smallest amount of martensite phase transformation occurs under plane strain. In conclusion, some discussion as to further application of the experimental methods detailed in this study to other 3GAHSS and the effects of fracture on martensite phase transformation is provided.« less

Deformation mode and strain path dependence of martensite phase transformation in a medium manganese TRIP steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei; Wang, Yu-wei; Makrygiannis, Panagiotis

The martensite phase transformation dependence upon deformation modes and strain paths in a medium manganese (10 wt%) TRIP steel stamped into a T-shape panel was quantified through combination of 3D digital image correlation and synchrotron X-ray diffraction. The T-shape emulates a portion of a common anti-intrusion component. The stamping speed was kept intentionally slow (1 mm/s) so as to avoid excessive heat generation. The steel, which belongs to the third generation advanced high strength steel (3GAHSS) family, was chosen for two reasons: (1) it is two-phase, i.e. austenite and ferrite, with martensite resulting from deformation-induced phase transformation; (2) the 66more » vol.% initial retained austenite volume fraction (RAVF) enabled a thorough examination of the martensite phase transformation at large deformation levels without exhaustion. Strain fields were coupled with measured RAVF values of small specimens extracted from specific locations on a formed T-shape panel. This enabled an exploration of the effects of linear, bilinear, and non-linear strain paths as well as deformation modes such as tension, plane strain, biaxial tension, and equibiaxial tension. Results suggest a significant martensite phase transformation dependence on deformation mode and strain path in the absence of fracture and when martensite phase transformation is unaffected by heat generated during forming. In general, the uniaxial and biaxial tension deformation modes facilitate the martensite phase transformation, while the smallest amount of martensite phase transformation occurs under plane strain. Some discussion as to further application of the experimental methods detailed in this study to other 3GAHSS and the effects of fracture on martensite phase transformation is provided.« less

CMS-Wave

DTIC Science & Technology

2014-10-27

a phase-averaged spectral wind-wave generation and transformation model and its interface in the Surface-water Modeling System (SMS). Ambrose...applications of the Boussinesq (BOUSS-2D) wave model that provides more rigorous calculations for design and performance optimization of integrated...navigation systems . Together these wave models provide reliable predictions on regional and local spatial domains and cost-effective engineering solutions

Choice of optical system is critical for the security of double random phase encryption systems

NASA Astrophysics Data System (ADS)

Muniraj, Inbarasan; Guo, Changliang; Malallah, Ra'ed; Cassidy, Derek; Zhao, Liang; Ryle, James P.; Healy, John J.; Sheridan, John T.

2017-06-01

The linear canonical transform (LCT) is used in modeling a coherent light-field propagation through first-order optical systems. Recently, a generic optical system, known as the quadratic phase encoding system (QPES), for encrypting a two-dimensional image has been reported. In such systems, two random phase keys and the individual LCT parameters (α,β,γ) serve as secret keys of the cryptosystem. It is important that such encryption systems also satisfy some dynamic security properties. We, therefore, examine such systems using two cryptographic evaluation methods, the avalanche effect and bit independence criterion, which indicate the degree of security of the cryptographic algorithms using QPES. We compared our simulation results with the conventional Fourier and the Fresnel transform-based double random phase encryption (DRPE) systems. The results show that the LCT-based DRPE has an excellent avalanche and bit independence characteristics compared to the conventional Fourier and Fresnel-based encryption systems.

In- Situ Synchrotron Diffraction Studies on Transformation Strain Development in a High-Strength Quenched and Tempered Structural Steel—Part II. Martensitic Transformation

NASA Astrophysics Data System (ADS)

Dutta, R. K.; Huizenga, R. M.; Petrov, R. H.; Amirthalingam, M.; King, A.; Gao, H.; Hermans, M. J. M.; Richardson, I. M.

2014-01-01

In-situ synchrotron diffraction studies on the kinetics of phase transformation and transformation strain development during bainitic transformation were presented in part I of the current article. In the current article, in-situ phase transformation behavior of a high-strength (830 MPa yield stress) quenched and tempered S690QL1 [Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt. pct)] structural steel, during continuous cooling and under different mechanical loading conditions to promote martensitic transformation, has been studied. Time-temperature-load resolved 2D synchrotron diffraction patterns were recorded and used to calculate the phase fractions and lattice parameters of the phases during heating and cooling cycles under different loading conditions. In addition to the thermal expansion behavior, the effects of the applied stress on the elastic strains during the martensitic transformation were calculated. The results show that small tensile stresses applied at the transformation temperature do not change the kinetics of the phase transformation. The start temperature for the martensitic transformation increases with the increasing applied tensile stress. The elastic strains are not affected significantly with the increasing tensile stress. The variant selection during martensitic transformation under small applied loads (in the elastic region) is weak.

Vibration mode and vibration shape under excitation of a three phase model transformer core

NASA Astrophysics Data System (ADS)

Okabe, Seiji; Ishigaki, Yusuke; Omura, Takeshi

2018-04-01

Structural vibration characteristics and vibration shapes under three-phase excitation of a archetype transformer core were investigated to consider their influences on transformer noise. Acoustic noise and vibration behavior were measured in a three-limb model transformer core. Experimental modal analysis by impact test was performed. The vibration shapes were measured by a laser scanning vibrometer at different exciting frequencies. Vibration amplitude of the core in out-of-plane direction were relatively larger than those in other two in-plane directions. It was consistent with the result that the frequency response function of the core in out-of-plane direction was larger by about 20 dB or more than those in in-plane directions. There were many vibration modes having bending deformation of limbs in out-of-plane direction. The vibration shapes of the core when excited at 50 Hz and 60 Hz were almost the same because the fundamental frequencies of the vibration were not close to the resonance frequencies. When excitation frequency was 69 Hz which was half of one of the resonance frequencies, the vibration shape changed to the one similar to the resonance vibration mode. Existence of many vibration modes in out-of-plane direction of the core was presumed to be a reason why frequency characteristics of magnetostriction and transformer noise do not coincide.

A numerical simulation of the full two-dimensional electrothermal de-icer pad. Ph.D. Thesis Final Report

NASA Technical Reports Server (NTRS)

Masiulaniec, Konstanty C.

1988-01-01

The ability to predict the time-temperature history of electrothermal de-icer pads is important in the subsequent design of improved and more efficient versions. These de-icer pads are installed near the surface of aircraft components, for the specific purpose of removing accreted ice. The proposed numerical model can incorporate the full 2-D geometry through a section of a region (i.e., section of an airfoil), that current 1-D numerical codes are unable to do. Thus, the effects of irregular layers, curvature, etc., can now be accounted for in the thermal transients. Each layer in the actual geometry is mapped via a body-fitted coordinate transformation into uniform, rectangular computational grids. The relevant heat transfer equations are transformed and discretized. To model the phase change that might occur in any accreted ice, in an enthalpy formulation the phase change equations are likewise transformed and discretized. The code developed was tested against numerous classical numerical solutions, as well as against experimental de-icing data on a UH1H rotor blade obtained from the NASA Lewis Research Center. The excellent comparisons obtained show that this code can be a useful tool in predicting the performance of current de-icer models, as well as in the designing of future models.

Modeling of the Effect of Path Planning on Thermokinetic Evolutions in Laser Powder Deposition Process

NASA Astrophysics Data System (ADS)

Foroozmehr, Ehsan; Kovacevic, Radovan

2011-07-01

A thermokinetic model coupling finite-element heat transfer with transformation kinetics is developed to determine the effect of deposition patterns on the phase-transformation kinetics of laser powder deposition (LPD) process of a hot-work tool steel. The finite-element model is used to define the temperature history of the process used in an empirical-based kinetic model to analyze the tempering effect of the heating and cooling cycles of the deposition process. An area is defined to be covered by AISI H13 on a substrate of AISI 1018 with three different deposition patterns: one section, two section, and three section. The two-section pattern divides the area of the one-section pattern into two sections, and the three-section pattern divides that area into three sections. The results show that dividing the area under deposition into smaller areas can influence the phase transformation kinetics of the process and, consequently, change the final hardness of the deposited material. The two-section pattern shows a higher average hardness than the one-section pattern, and the three-section pattern shows a fully hardened surface without significant tempered zones of low hardness. To verify the results, a microhardness test and scanning electron microscope were used.

Tunable arbitrary unitary transformer based on multiple sections of multicore fibers with phase control.

PubMed

Zhou, Junhe; Wu, Jianjie; Hu, Qinsong

2018-02-05

In this paper, we propose a novel tunable unitary transformer, which can achieve arbitrary discrete unitary transforms. The unitary transformer is composed of multiple sections of multi-core fibers with closely aligned coupled cores. Phase shifters are inserted before and after the sections to control the phases of the waves in the cores. A simple algorithm is proposed to find the optimal phase setup for the phase shifters to realize the desired unitary transforms. The proposed device is fiber based and is particularly suitable for the mode division multiplexing systems. A tunable mode MUX/DEMUX for a three-mode fiber is designed based on the proposed structure.

Possible existence of two amorphous phases of D-mannitol related by a first-order transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Men; Yu, Lian, E-mail: lian.yu@wisc.edu; Wang, Jun-Qiang

2015-06-28

We report that the common polyalcohol D-mannitol may have two amorphous phases related by a first-order transition. Slightly above its glass transition temperature T{sub g} (284 K), the supercooled liquid (SCL) of D-mannitol transforms to a low-energy, apparently amorphous phase with stronger hydrogen bonds. The enthalpy of this so-called Phase X is approximately halfway between those of the known amorphous and crystalline phases, a position low for glass aging and high for crystal polymorphs. Similar to the SCL, Phase X is transparent with broad X-ray diffraction and Raman scattering; upon temperature cycling, it exhibits a glass-transition-like change of heat capacity.more » On fast heating, Phase X transforms back to the SCL near T{sub g} + 50 K, enabling a determination of their equilibrium temperature. The presence of D-sorbitol as a plasticizer enables observation of a first-order transition from the SCL to Phase X entirely in the liquid state (liquid-liquid transition). The transition from D-mannitol’s SCL to Phase X has intriguing similarities with the formation of the glacial phase of triphenyl phosphite (TPP) and the conversion from high-density to low-density amorphous ice, both studied intensely in the context of polyamorphism. All three processes occur near T{sub g} with substantial enthalpy decrease toward the crystalline phases; the processes in water and D-mannitol both strengthen the hydrogen bonds. In contrast to TPP, D-mannitol’s Phase X forms more rapidly and can transform back to the SCL. These features make D-mannitol a valuable new model for understanding polyamorphism.« less

The development and testing of a linear induction motor being fed from the source with limited electric power

NASA Astrophysics Data System (ADS)

Tiunov, V. V.

2018-02-01

The report provides results of the research related to the tubular linear induction motors’ application. The motors’ design features, a calculation model, a description of test specimens for mining and electric power industry are introduced. The most attention is given to the single-phase motors for high voltage switches drives with the usage of inexpensive standard single-phase transformers for motors’ power supply. The method of the motor’s parameters determination, when the motor is being fed from the transformer, working in the overload mode, was described, and the results of it practical usage were good enough for the engineering practice.

Study of microwave drying of wet materials based on one-dimensional two-phase model

NASA Astrophysics Data System (ADS)

Salomatov, Vl V.; Karelin, V. A.

2017-11-01

Currently, microwave is one of the most interesting ways to conduct drying of dielectric materials, in particular coal. In this paper, two processes were considered - heating and drying. The temperature field of the coal semi-mass in the heating mode is found analytically strictly with the use of integral transformations. The drying process is formulated as a nonlinear Stephen problem with a moving boundary of the liquid-vapor phase transformation. The temperature distribution, speed and drying time in this mode are determined approximately analytically. Parametric analysis of the influence of the material and boundary conditions on the dynamics of warming up and drying is revealed.

Mechanisms of kinetic trapping in self-assembly and phase transformation

PubMed Central

Hagan, Michael F.; Elrad, Oren M.; Jack, Robert L.

2011-01-01

In self-assembly processes, kinetic trapping effects often hinder the formation of thermodynamically stable ordered states. In a model of viral capsid assembly and in the phase transformation of a lattice gas, we show how simulations in a self-assembling steady state can be used to identify two distinct mechanisms of kinetic trapping. We argue that one of these mechanisms can be adequately captured by kinetic rate equations, while the other involves a breakdown of theories that rely on cluster size as a reaction coordinate. We discuss how these observations might be useful in designing and optimising self-assembly reactions. PMID:21932884

Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere

USGS Publications Warehouse

Kirby, S.H.; Stein, S.; Okal, E.A.; Rubie, David C.

1996-01-01

Earth's deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km. This depth interval closely brackets the mantle transition zone, characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher-pressure phases. Deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal, thermodynamic, and mechanical ferment inside slabs. Numerical simulations of reaction rates show that the olivine ??? spinel transformation should be kinetically hindered in old, cold slabs descending into the transition zone. Thus wedge-shaped zones of metastable peridotite probably persist to depths of more than 600 km. Laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting. This instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser, finer-grained phase. Hence in cold slabs, such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite. It is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs. This consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features. It explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone, where minerals in downgoing slabs should transform to spinel and ilmenite structures. The onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab. Even if a slab penetrates into the lower mantle, earthquakes should cease at depths near 700 km, because the seismogenic phase transformations in the slab are completed or can no longer occur. Substantial metastability is expected only in old, cold slabs, consistent with the observed restriction of deep earthquakes to those settings. Earthquakes should be restricted to the cold cores of slabs, as in any model in which the seismicity is temperature controlled, via the distribution of metastability. However, the geometries of recent large deep earthquakes pose a challenge for any such models. Transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics, including focal mechanisms indicating localized shear failure rather than implosive deformation, are so similar to those of shallow earthquakes. Finally, metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab. Such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and/or are detached from subducting slabs. Metastability in downgoing slabs could have considerable geodynamic significance. Metastable wedges would reduce the negative buoyancy of slabs, decrease the driving force for subduction, and influence the state of stress in slabs. Heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage, causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity. Because wedge formation should occur only for fast subducting slabs, it may act as a "parachute" and contribute to regulating plate speeds. Wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge tra

About the Transformation Phase Zones of Shape Memory Alloys' Fracture Tests on Single Edge-Cracked Specimen

NASA Astrophysics Data System (ADS)

Taillebot, V.; Lexcellent, C.; Vacher, P.

2012-03-01

The thermomechanical behavior of shape memory alloys is now well mastered. However, a hindrance to their sustainable use is the lack of knowledge of their fracture behavior. With the aim of filling this partial gap, fracture tests on edge-cracked specimens in NiTi have been made. Particular attention was paid to determine the phase transformation zones in the vicinity of the crack tip. In one hand, experimental kinematic fields are observed using digital image correlation showing strain localization around the crack tip. In the other hand, an analytical prediction, based on a modified equivalent stress criterion and taking into account the asymmetric behavior of shape memory alloys in tension-compression, provides shape and size of transformation outset zones. Experimental results are relatively in agreement with our analytical modeling.

Spatial Modeling of Iron Transformations Within Artificial Soil Aggregates

NASA Astrophysics Data System (ADS)

Kausch, M.; Meile, C.; Pallud, C.

2008-12-01

Structured soils exhibit significant variations in transport characteristics at the aggregate scale. Preferential flow occurs through macropores while predominantly diffusive exchange takes place in intra-aggregate micropores. Such environments characterized by mass transfer limitations are conducive to the formation of small-scale chemical gradients and promote strong spatial variation in processes controlling the fate of redox-sensitive elements such as Fe. In this study, we present a reactive transport model used to spatially resolve iron bioreductive processes occurring within a spherical aggregate at the interface between advective and diffusive domains. The model is derived from current conceptual models of iron(hydr)oxide (HFO) transformations and constrained by literature and experimental data. Data were obtained from flow-through experiments on artificial soil aggregates inoculated with Shewanella putrefaciens strain CN32, and include the temporal evolution of the bulk solution composition, as well as spatial information on the final solid phase distribution within aggregates. With all iron initially in the form of ferrihydrite, spatially heterogeneous formation of goethite/lepidocrocite, magnetite and siderite was observed during the course of the experiments. These transformations were reproduced by the model, which ascribes a central role to divalent iron as a driver of HFO transformations and master variable in the rate laws of the considered reaction network. The predicted dissolved iron breakthrough curves also match the experimental ones closely. Thus, the computed chemical concentration fields help identify factors governing the observed trends in the solid phase distribution patterns inside the aggregate. Building on a mechanistic description of transformation reactions, fluid flow and solute transport, the model was able to describe the observations and hence illustrates the importance of small-scale gradients and dynamics of bioreductive processes for assessing bulk iron cycling. As HFOs are ubiquitous in soils, such process-level understanding of aggregate-scale iron dynamics has broad implications for the prediction of the subsurface fate of nutrients and contaminants that interact strongly with HFO surfaces.

A poroelastic medium saturated by a two-phase capillary fluid

NASA Astrophysics Data System (ADS)

Shelukhin, V. V.

2014-09-01

By Landau's approach developed for description of superfluidity of 2He, we derive a mathematical model for a poroelastic medium saturated with a two-phase capillary fluid. The model describes a three-velocity continuum with conservation laws which obey the basic principles of thermodynamics and which are consistent with the Galilean transformations. In contrast to Biot' linear theory, the equations derived allow for finite deformations. As the acoustic analysis reveals, there is one more longitudinal wave in comparison with the poroelastic medium saturated with a one-phase fluid. We prove that such a result is due to surface tension.

Self-Assembly through Noncovalent Preorganization of Reactants: Explaining the Formation of a Polyfluoroxometalate.

PubMed

Schreiber, Roy E; Avram, Liat; Neumann, Ronny

2018-01-09

High-order elementary reactions in homogeneous solutions involving more than two molecules are statistically improbable and very slow to proceed. They are not generally considered in classical transition-state or collision theories. Yet, rather selective, high-yield product formation is common in self-assembly processes that require many reaction steps. On the basis of recent observations of crystallization as well as reactions in dense phases, it is shown that self-assembly can occur by preorganization of reactants in a noncovalent supramolecular assembly, whereby directing forces can lead to an apparent one-step transformation of multiple reactants. A simple and general kinetic model for multiple reactant transformation in a dense phase that can account for many-bodied transformations was developed. Furthermore, the self-assembly of polyfluoroxometalate anion [H 2 F 6 NaW 18 O 56 ] 7- from simple tungstate Na 2 WO 2 F 4 was demonstrated by using 2D 19 F- 19 F NOESY, 2D 19 F- 19 F COSY NMR spectroscopy, a new 2D 19 F{ 183 W} NMR technique, as well as ESI-MS and diffusion NMR spectroscopy, and the crucial involvement of a supramolecular assembly was found. The deterministic kinetic reaction model explains the reaction in a dense phase and supports the suggested self-assembly mechanism. Reactions in dense phases may be of general importance in understanding other self-assembly reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model

DOE PAGES

Chen, Cheng-Chien; Muechler, Lukas; Car, Roberto; ...

2016-08-25

We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1/2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site. In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices. On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying d-density wave charge order in the original Hubbard model. On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection. The ground state of the Hubbard model on the decorated honeycomb lattice is thus a 2D fermionicmore » symmetry-protected topological phase. This state—protected by time-reversal and reflection symmetries—cannot be connected adiabatically to a free-fermion topological phase.« less

Interruption of a dry-type transformer in no-load by a vacuum circuit-breaker

NASA Astrophysics Data System (ADS)

Vandenheuvel, W. M. C.; Daalder, J. E.; Boone, M. J. M.; Wilmes, L. A. H.

1983-08-01

Overvoltages generated during interruption of a dry type delta-star connected transformer in no load by a vacuum breaker were studied. During interruption of inrush current 37% of the phase-to-ground overvoltages were 5 pu, and 6% 7 pu. Comparison of experimental and theoretical results using Boyle's model shows no discrepancy for inrush currents and clean overvoltages from the steady-state interruption. Overvoltages due to repetitive reignitions (not covered by Boyle's model) are higher than the calculated values during steady-state switching.

A stress-induced phase transition model for semi-crystallize shape memory polymer

NASA Astrophysics Data System (ADS)

Guo, Xiaogang; Zhou, Bo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2014-03-01

The developments of constitutive models for shape memory polymer (SMP) have been motivated by its increasing applications. During cooling or heating process, the phase transition which is a continuous time-dependent process happens in semi-crystallize SMP and the various individual phases form at different temperature and in different configuration. Then, the transformation between these phases occurred and shape memory effect will emerge. In addition, stress applied on SMP is an important factor for crystal melting during phase transition. In this theory, an ideal phase transition model considering stress or pre-strain is the key to describe the behaviors of shape memory effect. So a normal distributed model was established in this research to characterize the volume fraction of each phase in SMP during phase transition. Generally, the experiment results are partly backward (in heating process) or forward (in cooling process) compared with the ideal situation considering delay effect during phase transition. So, a correction on the normal distributed model is needed. Furthermore, a nonlinear relationship between stress and phase transition temperature Tg is also taken into account for establishing an accurately normal distributed phase transition model. Finally, the constitutive model which taking the stress as an influence factor on phase transition was also established. Compared with the other expressions, this new-type model possesses less parameter and is more accurate. For the sake of verifying the rationality and accuracy of new phase transition and constitutive model, the comparisons between the simulated and experimental results were carried out.

Microstructural evolution during the homogenization heat treatment of 6XXX and 7XXX aluminum alloys

NASA Astrophysics Data System (ADS)

Priya, Pikee

Homogenization heat treatment of as-cast billets is an important step in the processing of aluminum extrusions. Microstructural evolution during homogenization involves elimination of the eutectic morphology by spheroidisation of the interdendritic phases, minimization of the microsegregation across the grains through diffusion, dissolution of the low-melting phases, which enhances the surface finish of the extrusions, and precipitation of nano-sized dispersoids (for Cr-, Zr-, Mn-, Sc-containing alloys), which inhibit grain boundary motion to prevent recrystallization. Post-homogenization cooling reprecipitates some of the phases, changing the flow stress required for subsequent extrusion. These precipitates, however, are deleterious for the mechanical properties of the alloy and also hamper the age-hardenability and are hence dissolved during solution heat treatment. Microstructural development during homogenization and subsequent cooling occurs both at the length scale of the Secondary Dendrite Arm Spacing (SDAS) in micrometers and dispersoids in nanometers. Numerical tools to simulate microstructural development at both the length scales have been developed and validated against experiments. These tools provide easy and convenient means to study the process. A Cellular Automaton-Finite Volume-based model for evolution of interdendritic phases is coupled with a Particle Size Distribution-based model for precipitation of dispersoids across the grain. This comprehensive model has been used to study the effect of temperature, composition, as-cast microstructure, and cooling rates during post-homogenization quenching on microstructural evolution. The numerical study has been complimented with experiments involving Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-Ray Diffraction and Differential Scanning Calorimetry and a good agreement has with numerical results has been found. The current work aims to study the microstructural evolution during homogenization heat treatment at both length scales which include the (i) dissolution and transformation of the as-cast secondary phases; (ii) precipitation of dispersoids; and (iii) reprecipitation of some of the secondary phases during post-homogenization cooling. The kinetics of the phase transformations are mostly diffusion controlled except for the eta to S phase transformation in 7XXX alloys which is interface reaction rate controlled which has been implemented using a novel approach. Recommendations for homogenization temperature, time, cooling rates and compositions are made for Al-Si-Mg-Fe-Mn and Al-Zn-Cu-Mg-Zr alloys. The numerical model developed has been applied for a through process solidification-homogenization modeling of a Direct-Chill cast AA7050 cylindrical billet to study the radial variation of microstructure after solidification, homogenization and post-homogenization cooling.

Transformation and bioaccessibility of lead induced by steamed bread feed in the gastrointestinal tract.

PubMed

Kan, Junhong; Sima, Jingke; Cao, Xinde

2017-03-01

Accidental ingestion of contaminated soil has been recognized as an important pathway of human exposure to lead (Pb), especially for children through hand-to-mouth activities. Intake of food following the soil ingestion may affect the bioaccessibility of Pb in the gastrointestinal tract. In this study, the effect of steamed bread on the transformation and subsequent bioaccessibility of Pb in two soils was determined by the physiologically based extraction test (PBET). Two compounds, Pb(NO 3 ) 2 and PbCO 3 , were included in the evaluation for comparison. In the gastric phase, Pb bioaccessibility decreased as the steamed bread increased due to the sorption of Pb on the undissolved steamed bread, especially in PbCO 3 , Pb bioaccessibility decreased from 95.03% to 85.40%. Whereas in the intestinal phase, Pb bioaccessibility increased from 1.85% to 5.66% and from 0.89% to 1.80% for Pb(NO 3 ) 2 and PbCO 3 , respectively. The increase was attributed to the transformation of formed Pb carbonates into soluble organic-Pb complexes induced by the dissolved steamed bread at neutral pH as indicated by MINTEQ modeling. For the PbCO 3 -contaminated soil, the change in Pb bioaccessibility in both gastric and intestinal phases behaved like that in the pure PbCO 3 compound, the steamed bread increased the bioaccessibility of Pb in the intestinal phase, but the decreased bioaccessibility of Pb was observed in the gastric phase after the steamed bread was added. However, in the soil contaminated with free Pb 2+ or sorbed Pb forms, the steamed bread increased the Pb bioaccessibility in both gastric and intestinal phases. This was probably due to the higher dissolved organic carbon induced transformation of sorbed Pb (Pb sorbed by Fe/Mn oxides) into soluble Pb-organic complex. Results from this study indicated that steamed bread had an influence on the Pb speciation transformation, correspondingly affecting Pb bioaccessibility in the gastrointestinal tract. Copyright © 2016. Published by Elsevier Inc.

Room-Temperature Deformation and Martensitic Transformation of Two Co-Cr-Based Alloys

NASA Astrophysics Data System (ADS)

Cai, S.; Schaffer, J. E.; Huang, D.; Gao, J.; Ren, Y.

2018-05-01

Deformation of two Co-Cr alloys was studied by in situ synchrotron X-ray diffraction. Both alloys show stress-induced martensite transformation, which is affected by phase stabilities and transformation strains. Crystal structure of WC in Co-20Cr-15W-10Ni is identified. Compared with other phases present, it is elastically isotropic, exhibits high strength, and can elastically withstand strains exceeding 1 pct. Texture change during phase transformation is explained based on the crystal orientation relationship between γ- and ɛ-phases.

Room-Temperature Deformation and Martensitic Transformation of Two Co-Cr-Based Alloys

NASA Astrophysics Data System (ADS)

Cai, S.; Schaffer, J. E.; Huang, D.; Gao, J.; Ren, Y.

2018-07-01

Deformation of two Co-Cr alloys was studied by in situ synchrotron X-ray diffraction. Both alloys show stress-induced martensite transformation, which is affected by phase stabilities and transformation strains. Crystal structure of WC in Co-20Cr-15W-10Ni is identified. Compared with other phases present, it is elastically isotropic, exhibits high strength, and can elastically withstand strains exceeding 1 pct. Texture change during phase transformation is explained based on the crystal orientation relationship between γ- and ɛ-phases.

Biological applications of phase-contrast electron microscopy.

PubMed

Nagayama, Kuniaki

2014-01-01

Here, I review the principles and applications of phase-contrast electron microscopy using phase plates. First, I develop the principle of phase contrast based on a minimal model of microscopy, introducing a double Fourier-transform process to mathematically formulate the image formation. Next, I explain four phase-contrast (PC) schemes, defocus PC, Zernike PC, Hilbert differential contrast, and schlieren optics, as image-filtering processes in the context of the minimal model, with particular emphases on the Zernike PC and corresponding Zernike phase plates. Finally, I review applications of Zernike PC cryo-electron microscopy to biological systems such as protein molecules, virus particles, and cells, including single-particle analysis to delineate three-dimensional (3D) structures of protein and virus particles and cryo-electron tomography to reconstruct 3D images of complex protein systems and cells.

The behavior of commensurate-incommensurate transitions using the phase field crystal model

NASA Astrophysics Data System (ADS)

Zhang, Tinghui; Lu, Yanli; Chen, Zheng

2018-02-01

We study the behavior of the commensurate-incommensurate (CI) transitions by using a phase field crystal model. The model is capable of modeling both elastic and plastic deformation and can simulate the evolution of the microstructure of the material at the atomic scale and the diffusive time scale, such as for adsorbed monolayer. Specifically, we study the behavior of the CI transitions as a function of lattice mismatch and the amplitude of substrate pinning potential. The behavior of CI phase transitions is revealed with the increase of the amplitude of pinning potential in some certain lattice mismatches. We find that for the negative lattice mismatch absorbed monolayer undergoes division, reorganization and displacement as increasing the amplitude of substrate pinning potential. In addition, for the positive mismatch absorbed monolayer undergoes a progress of phase transformation after a complete grain is split. Our results accord with simulations for atomic models of absorbed monolayer on a substrate surface.

FIBER AND INTEGRATED OPTICS: Efficiency of nonstationary transformation of the spatial coherence of pulsed laser radiation in a multimode optical fibre upon self-phase modulation

NASA Astrophysics Data System (ADS)

Kitsak, M. A.; Kitsak, A. I.

2007-08-01

The model scheme of the nonlinear mechanism of transformation (decreasing) of the spatial coherence of a pulsed laser field in an extended multimode optical fibre upon nonstationary interaction with the fibre core is theoretically analysed. The case is considered when the spatial statistics of input radiation is caused by phase fluctuations. The analytic expression is obtained which relates the number of spatially coherent radiation modes with the spatially energy parameters on the initial radiation and fibre parameters. The efficiency of decorrelation of radiation upon excitation of the thermal and electrostriction nonlinearities in the fibre is estimated. Experimental studies are performed which revealed the basic properties of the transformation of the spatial coherence of a laser beam in a multimode fibre. The experimental results are compared with the predictions of the model of radiation transfer proposed in the paper. It is found that the spatial decorrelation of a light beam in a silica multimode fibre is mainly restricted by stimulated Raman scattering.

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

Phase structure of completely asymptotically free SU(Nc) models with quarks and scalar quarks

NASA Astrophysics Data System (ADS)

Hansen, F. F.; Janowski, T.; Langæble, K.; Mann, R. B.; Sannino, F.; Steele, T. G.; Wang, Z. W.

2018-03-01

We determine the phase diagram of completely asymptotically free SU (Nc) gauge theories featuring Ns complex scalars and Nf Dirac quarks transforming according to the fundamental representation of the gauge group. The analysis is performed at the maximum known order in perturbation theory. We unveil a very rich dynamics and associated phase structure. Intriguingly, we discover that the completely asymptotically free conditions guarantee that the infrared dynamics displays long-distance conformality, and in a regime when perturbation theory is applicable. We conclude our analysis by determining the quantum corrected potential of the model and summarizing the possible patterns of radiative symmetry breaking. These models are of potential phenomenological interest as either elementary or composite ultraviolet finite extensions of the standard model.

Visualization of anisotropic-isotropic phase transformation dynamics in battery electrode particles

DOE PAGES

Wang, Jiajun; Karen Chen-Wiegart, Yu-chen; Eng, Christopher; ...

2016-08-12

Anisotropy, or alternatively, isotropy of phase transformations extensively exist in a number of solid-state materials, with performance depending on the three-dimensional transformation features. Fundamental insights into internal chemical phase evolution allow manipulating materials with desired functionalities, and can be developed via real-time multi-dimensional imaging methods. In this paper, we report a five-dimensional imaging method to track phase transformation as a function of charging time in individual lithium iron phosphate battery cathode particles during delithiation. The electrochemically driven phase transformation is initially anisotropic with a preferred boundary migration direction, but becomes isotropic as delithiation proceeds further. We also observe the expectedmore » two-phase coexistence throughout the entire charging process. Finally, we expect this five-dimensional imaging method to be broadly applicable to problems in energy, materials, environmental and life sciences.« less

Cyclic phase change in a cylindrical thermal energy storage capsule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, M.; Mujumdar, A.S.; Weber, M.E.

1983-12-01

This paper is concerned with a practical melting/freezing problem in conjunction with the more realistic case of a cyclic phase change thermal energy storage device. In this model the phase change medium is encapsulated in long cylindrical tubes, the surface temperature of which is allowed to vary sinusoidally with time about the discrete freezing temperature. Initial temperature of the medium is assumed to be constant at a temperature above or below the freezing/melting temperature. Natural convection in the melt is assumed to be negligible and the variations in the depth of freezing and/or melting in each half cycle is ignored.more » Depending on the half-cycle parameters the problem is simplified to either freezing or melting. The governing one-dimensional heat diffusion equations for both phases are solved by the Finite Integral Transform techniques. The kernels for the transformation are the time-dependent eigen functions separately defined for each phases. This extended transform method can accomodate any time-dependent surface temperature variation. The application of the transform generated a series of coupled, nonlinear first order differential equations, which are solved by Runge Kutta-Verner fifth and sixth order method. Dimensionless solutions of temperature variations in both phases, fusion front position and the fraction solidified (or melted) are displayed graphically to aid in practical calculations. For the special case of a constant surface temperature, comparisons are made between the present results and the existing integral and purely numerical results. The results are found to compare favourably. Results for fractional solidification (or melting and interface position are also compared with the simple Conduction Shape Factor method, after allowing for the time-dependent boundary conditions. Once again the results agree reasonably well.« less

Critical Behavior of Spatial Evolutionary Game with Altruistic to Spiteful Preferences on Two-Dimensional Lattices

NASA Astrophysics Data System (ADS)

Yang, Bo; Li, Xiao-Teng; Chen, Wei; Liu, Jian; Chen, Xiao-Song

2016-10-01

Self-questioning mechanism which is similar to single spin-flip of Ising model in statistical physics is introduced into spatial evolutionary game model. We propose a game model with altruistic to spiteful preferences via weighted sums of own and opponent's payoffs. This game model can be transformed into Ising model with an external field. Both interaction between spins and the external field are determined by the elements of payoff matrix and the preference parameter. In the case of perfect rationality at zero social temperature, this game model has three different phases which are entirely cooperative phase, entirely non-cooperative phase and mixed phase. In the investigations of the game model with Monte Carlo simulation, two paths of payoff and preference parameters are taken. In one path, the system undergoes a discontinuous transition from cooperative phase to non-cooperative phase with the change of preference parameter. In another path, two continuous transitions appear one after another when system changes from cooperative phase to non-cooperative phase with the prefenrence parameter. The critical exponents v, β, and γ of two continuous phase transitions are estimated by the finite-size scaling analysis. Both continuous phase transitions have the same critical exponents and they belong to the same universality class as the two-dimensional Ising model. Supported by the National Natural Science Foundation of China under Grant Nos. 11121403 and 11504384

Comparison between thermochemical and phase stability data for the quartz-coesite-stishovite transformations

NASA Technical Reports Server (NTRS)

Weaver, J. S.; Chipman, D. W.; Takahashi, T.

1979-01-01

Phase stability and elasticity data have been used to calculate the Gibbs free energy, enthalpy, and entropy changes at 298 K and 1 bar associated with the quartz-coesite and coesite-stishovite transformations in the system SiO2. For the quartz-coesite transformation, these changes disagree by a factor of two or three with those obtained by calorimetric techniques. The phase boundary for this transformation appears to be well determined by experiment; the discrepancy, therefore, suggests that the calorimetric data for coesite are in error. Although the calorimetric and phase stability data for the coesite-stishovite transformation yield the same transition pressure at 298 K, the phase-boundary slopes disagree by a factor of two. At present, it is not possible to determine which of the data are in error. Thus serious inconsistencies exist in the thermodynamic data for the polymorphic transformations of silica.

Visualisation and Reasoning in Explaining the Phases of the Moon

ERIC Educational Resources Information Center

Subramaniam, K.; Padalkar, Shamin

2009-01-01

In this study, we examine how subjects set up, transform, and reason with models that they establish on the basis of known facts as they seek to explain a familiar everyday phenomenon--the phases of the moon. An interview schedule was designed to elicit subjects' reasoning, and in the case where explanations were mistaken, to induce a change in…

Symmetric convolution of asymmetric multidimensional sequences using discrete trigonometric transforms.

PubMed

Foltz, T M; Welsh, B M

1999-01-01

This paper uses the fact that the discrete Fourier transform diagonalizes a circulant matrix to provide an alternate derivation of the symmetric convolution-multiplication property for discrete trigonometric transforms. Derived in this manner, the symmetric convolution-multiplication property extends easily to multiple dimensions using the notion of block circulant matrices and generalizes to multidimensional asymmetric sequences. The symmetric convolution of multidimensional asymmetric sequences can then be accomplished by taking the product of the trigonometric transforms of the sequences and then applying an inverse trigonometric transform to the result. An example is given of how this theory can be used for applying a two-dimensional (2-D) finite impulse response (FIR) filter with nonlinear phase which models atmospheric turbulence.

Numerical Solution of Moving Phase Boundary and Diffusion-Induced Stress of Sn Anode in the Lithium-Ion Battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Chun-Hao; Chason, Eric; Guduru, Pradeep R.

Here, we have previously observed a large transient stress in Sn film anodes at the beginning of the Sn-Li 2Sn 5 phase transformation. To understand this behavior, we use numerical modeling to simulate the kinetics of the 1-D moving boundary and Li diffusion in the Sn anodes. A mixture of diffusion-controlled and interface-controlled kinetics is found. The Li concentration in the Li 2Sn 5 phase remains near a steady-state profile as the phase boundary propagates, whereas the Li diffusion in Sn is more complicated. Li continuously diffuses into the Sn layer and produces a supersaturation; the Li can then diffusemore » toward the Sn/Li 2Sn 5 interface and contribute to further phase transformation. Finally, the evolution of Li concentration in the Sn induces strain which involves rate-dependent plasticity and elastic unloading, resulting in the complex stress evolution that is observed. In the long term, the measured stress is dominated by the stress in the growing Li 2Sn 5 phase.« less

Numerical Solution of Moving Phase Boundary and Diffusion-Induced Stress of Sn Anode in the Lithium-Ion Battery

DOE PAGES

Chen, Chun-Hao; Chason, Eric; Guduru, Pradeep R.

2017-08-02

Here, we have previously observed a large transient stress in Sn film anodes at the beginning of the Sn-Li 2Sn 5 phase transformation. To understand this behavior, we use numerical modeling to simulate the kinetics of the 1-D moving boundary and Li diffusion in the Sn anodes. A mixture of diffusion-controlled and interface-controlled kinetics is found. The Li concentration in the Li 2Sn 5 phase remains near a steady-state profile as the phase boundary propagates, whereas the Li diffusion in Sn is more complicated. Li continuously diffuses into the Sn layer and produces a supersaturation; the Li can then diffusemore » toward the Sn/Li 2Sn 5 interface and contribute to further phase transformation. Finally, the evolution of Li concentration in the Sn induces strain which involves rate-dependent plasticity and elastic unloading, resulting in the complex stress evolution that is observed. In the long term, the measured stress is dominated by the stress in the growing Li 2Sn 5 phase.« less

Design of electromagnetic refractor and phase transformer using coordinate transformation theory.

PubMed

Lin, Lan; Wang, Wei; Cui, Jianhua; Du, Chunlei; Luo, Xiangang

2008-05-12

We designed an electromagnetic refractor and a phase transformer using form-invariant coordinate transformation of Maxwell's equations. The propagation direction of electromagnetic energy in these devices can be modulated as desired. Unlike the conventional dielectric refractor, electromagnetic fields at our refraction boundary do not conform to the Snell's law in isotropic materials and the impedance at this boundary is matched which makes the reflection extremely low; and the transformation of the wave front from cylindrical to plane can be realized in the phase transformer with a slab structure. Two dimensional finite-element simulations were performed to confirm the theoretical results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Meng-Zheng; School of Physics and Electronic Information, Huaibei Normal University, Huaibei 235000; Ye, Liu, E-mail: yeliu@ahu.edu.cn

An efficient scheme is proposed to implement phase-covariant quantum cloning by using a superconducting transmon qubit coupled to a microwave cavity resonator in the strong dispersive limit of circuit quantum electrodynamics (QED). By solving the master equation numerically, we plot the Wigner function and Poisson distribution of the cavity mode after each operation in the cloning transformation sequence according to two logic circuits proposed. The visualizations of the quasi-probability distribution in phase-space for the cavity mode and the occupation probability distribution in the Fock basis enable us to penetrate the evolution process of cavity mode during the phase-covariant cloning (PCC)more » transformation. With the help of numerical simulation method, we find out that the present cloning machine is not the isotropic model because its output fidelity depends on the polar angle and the azimuthal angle of the initial input state on the Bloch sphere. The fidelity for the actual output clone of the present scheme is slightly smaller than one in the theoretical case. The simulation results are consistent with the theoretical ones. This further corroborates our scheme based on circuit QED can implement efficiently PCC transformation.« less

An optical Fourier transform coprocessor with direct phase determination.

PubMed

Macfaden, Alexander J; Gordon, George S D; Wilkinson, Timothy D

2017-10-20

The Fourier transform is a ubiquitous mathematical operation which arises naturally in optics. We propose and demonstrate a practical method to optically evaluate a complex-to-complex discrete Fourier transform. By implementing the Fourier transform optically we can overcome the limiting O(nlogn) complexity of fast Fourier transform algorithms. Efficiently extracting the phase from the well-known optical Fourier transform is challenging. By appropriately decomposing the input and exploiting symmetries of the Fourier transform we are able to determine the phase directly from straightforward intensity measurements, creating an optical Fourier transform with O(n) apparent complexity. Performing larger optical Fourier transforms requires higher resolution spatial light modulators, but the execution time remains unchanged. This method could unlock the potential of the optical Fourier transform to permit 2D complex-to-complex discrete Fourier transforms with a performance that is currently untenable, with applications across information processing and computational physics.

Transformation of a Spatial Map across the Hippocampal-Lateral Septal Circuit.

PubMed

Tingley, David; Buzsáki, György

2018-05-15

The hippocampus constructs a map of the environment. How this "cognitive map" is utilized by other brain regions to guide behavior remains unexplored. To examine how neuronal firing patterns in the hippocampus are transmitted and transformed, we recorded neurons in its principal subcortical target, the lateral septum (LS). We observed that LS neurons carry reliable spatial information in the phase of action potentials, relative to hippocampal theta oscillations, while the firing rates of LS neurons remained uninformative. Furthermore, this spatial phase code had an anatomical microstructure within the LS and was bound to the hippocampal spatial code by synchronous gamma frequency cell assemblies. Using a data-driven model, we show that rate-independent spatial tuning arises through the dynamic weighting of CA1 and CA3 cell assemblies. Our findings demonstrate that transformation of the hippocampal spatial map depends on higher-order theta-dependent neuronal sequences. Copyright © 2018 Elsevier Inc. All rights reserved.

A Fusion Algorithm for GFP Image and Phase Contrast Image of Arabidopsis Cell Based on SFL-Contourlet Transform

PubMed Central

Feng, Peng; Wang, Jing; Wei, Biao; Mi, Deling

2013-01-01

A hybrid multiscale and multilevel image fusion algorithm for green fluorescent protein (GFP) image and phase contrast image of Arabidopsis cell is proposed in this paper. Combining intensity-hue-saturation (IHS) transform and sharp frequency localization Contourlet transform (SFL-CT), this algorithm uses different fusion strategies for different detailed subbands, which include neighborhood consistency measurement (NCM) that can adaptively find balance between color background and gray structure. Also two kinds of neighborhood classes based on empirical model are taken into consideration. Visual information fidelity (VIF) as an objective criterion is introduced to evaluate the fusion image. The experimental results of 117 groups of Arabidopsis cell image from John Innes Center show that the new algorithm cannot only make the details of original images well preserved but also improve the visibility of the fusion image, which shows the superiority of the novel method to traditional ones. PMID:23476716

In Vitro versus In Vivo Phase Instability of Zirconia-Toughened Alumina Femoral Heads: A Critical Comparative Assessment

PubMed Central

Pezzotti, Giuseppe; Affatato, Saverio; Rondinella, Alfredo; Yorifuji, Makiko; Marin, Elia; Zhu, Wenliang; McEntire, Bryan; Bal, Sonny B.; Yamamoto, Kengo

2017-01-01

A clear discrepancy between predicted in vitro and actual in vivo surface phase stability of BIOLOX®delta zirconia-toughened alumina (ZTA) femoral heads has been demonstrated by several independent research groups. Data from retrievals challenge the validity of the standard method currently utilized in evaluating surface stability and raise a series of important questions: (1) Why do in vitro hydrothermal aging treatments conspicuously fail to model actual results from the in vivo environment? (2) What is the preponderant microscopic phenomenon triggering the accelerated transformation in vivo? (3) Ultimately, what revisions of the current in vitro standard are needed in order to obtain consistent predictions of ZTA transformation kinetics in vivo? Reported in this paper is a new in toto method for visualizing the surface stability of femoral heads. It is based on CAD-assisted Raman spectroscopy to quantitatively assess the phase transformation observed in ZTA retrievals. Using a series of independent analytical probes, an evaluation of the microscopic mechanisms responsible for the polymorphic transformation is also provided. An outline is given of the possible ways in which the current hydrothermal simulation standard for artificial joints can be improved in an attempt to reduce the gap between in vitro simulation and reality. PMID:28772828

Analysis of geometric phase effects in the quantum-classical Liouville formalism.

PubMed

Ryabinkin, Ilya G; Hsieh, Chang-Yu; Kapral, Raymond; Izmaylov, Artur F

2014-02-28

We analyze two approaches to the quantum-classical Liouville (QCL) formalism that differ in the order of two operations: Wigner transformation and projection onto adiabatic electronic states. The analysis is carried out on a two-dimensional linear vibronic model where geometric phase (GP) effects arising from a conical intersection profoundly affect nuclear dynamics. We find that the Wigner-then-Adiabatic (WA) QCL approach captures GP effects, whereas the Adiabatic-then-Wigner (AW) QCL approach does not. Moreover, the Wigner transform in AW-QCL leads to an ill-defined Fourier transform of double-valued functions. The double-valued character of these functions stems from the nontrivial GP of adiabatic electronic states in the presence of a conical intersection. In contrast, WA-QCL avoids this issue by starting with the Wigner transform of single-valued quantities of the full problem. As a consequence, GP effects in WA-QCL can be associated with a dynamical term in the corresponding equation of motion. Since the WA-QCL approach uses solely the adiabatic potentials and non-adiabatic derivative couplings as an input, our results indicate that WA-QCL can capture GP effects in two-state crossing problems using first-principles electronic structure calculations without prior diabatization or introduction of explicit phase factors.

Analysis of geometric phase effects in the quantum-classical Liouville formalism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryabinkin, Ilya G.; Izmaylov, Artur F.; Chemical Physics Theory Group, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6

2014-02-28

We analyze two approaches to the quantum-classical Liouville (QCL) formalism that differ in the order of two operations: Wigner transformation and projection onto adiabatic electronic states. The analysis is carried out on a two-dimensional linear vibronic model where geometric phase (GP) effects arising from a conical intersection profoundly affect nuclear dynamics. We find that the Wigner-then-Adiabatic (WA) QCL approach captures GP effects, whereas the Adiabatic-then-Wigner (AW) QCL approach does not. Moreover, the Wigner transform in AW-QCL leads to an ill-defined Fourier transform of double-valued functions. The double-valued character of these functions stems from the nontrivial GP of adiabatic electronic statesmore » in the presence of a conical intersection. In contrast, WA-QCL avoids this issue by starting with the Wigner transform of single-valued quantities of the full problem. As a consequence, GP effects in WA-QCL can be associated with a dynamical term in the corresponding equation of motion. Since the WA-QCL approach uses solely the adiabatic potentials and non-adiabatic derivative couplings as an input, our results indicate that WA-QCL can capture GP effects in two-state crossing problems using first-principles electronic structure calculations without prior diabatization or introduction of explicit phase factors.« less

Phase transition kinetics in DIET of vanadium pentoxide. I. Experimental results

NASA Astrophysics Data System (ADS)

Ai, R.; Fan, H.-J.; Marks, L. D.

1993-01-01

Experimental results of the kinetics of phase transformation in vanadium pentoxide during surface loss of oxygen from electron irradiation are described. Phase transformations under three different regimes were examined: (a) low flux; (b) intermediate flux and (c) high flux. Different phase transformation routes were observed under different fluxes. In a companion paper, numerical calculations are presented demonstrating that these results are due to a mixed interface/diffusion controlled phase transition pumped by surface oxygen loss.

Influence of Temperature on Fatigue-Induced Martensitic Phase Transformation in a Metastable CrMnNi-Steel

NASA Astrophysics Data System (ADS)

Biermann, Horst; Glage, Alexander; Droste, Matthias

2016-01-01

Metastable austenitic steels can exhibit a fatigue-induced martensitic phase transformation during cyclic loading. It is generally agreed that a certain strain amplitude and a threshold of the cumulated plastic strain must be exceeded to trigger martensitic phase transformation under cyclic loading. With respect to monotonic loading, the martensitic phase transformation takes place up to a critical temperature—the so-called M d temperature. The goal of the present investigation is to determine an M d,c temperature which would be the highest temperature at which a fatigue-induced martensitic phase transformation can take place. For this purpose, fatigue tests controlled by the total strain were performed at different temperatures. The material investigated was a high-alloy metastable austenitic steel X3CrMnNi16.7.7 (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si) produced using the hot pressing technique. The temperatures were set in the range of 283 K (10 °C) ≤ T ≤ 473 K (200 °C). Depending on the temperature and strain amplitude, the onset of the martensitic phase transformation shifted to different values of the cumulated plastic strain, or was inhibited completely. Moreover, it is known that metastable austenitic CrMnNi steels with higher nickel contents can exhibit the deformation-induced twinning effect. Thus, at higher temperatures and strain amplitudes, a transition from the deformation-induced martensitic transformation to deformation-induced twinning takes place. The fatigue-induced martensitic phase transformation was monitored during cyclic loading using a ferrite sensor. The microstructure after the fatigue tests was examined using the back-scattered electrons, the electron channeling contrast imaging and the electron backscatter diffraction techniques to study the temperature-dependent dislocation structures and phase transformations.

Grain boundary phase transformations in PtAu and relevance to thermal stabilization of bulk nanocrystalline metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

O’Brien, C. J.; Barr, C. M.; Price, P. M.

There has recently been a great deal of interest in employing immiscible solutes to stabilize nanocrystalline microstructures. Existing modeling efforts largely rely on mesoscale Monte Carlo approaches that employ a simplified model of the microstructure and result in highly homogeneous segregation to grain boundaries. However, there is ample evidence from experimental and modeling studies that demonstrates segregation to grain boundaries is highly non-uniform and sensitive to boundary character. This work employs a realistic nanocrystalline microstructure with experimentally relevant global solute concentrations to illustrate inhomogeneous boundary segregation. Furthermore, experiments quantifying segregation in thin films are reported that corroborate the prediction thatmore » grain boundary segregation is highly inhomogeneous. In addition to grain boundary structure modifying the degree of segregation, the existence of a phase transformation between low and high solute content grain boundaries is predicted. In order to conduct this study, new embedded atom method interatomic potentials are developed for Pt, Au, and the PtAu binary alloy.« less

Grain boundary phase transformations in PtAu and relevance to thermal stabilization of bulk nanocrystalline metals

DOE PAGES

O’Brien, C. J.; Barr, C. M.; Price, P. M.; ...

2017-10-31

There has recently been a great deal of interest in employing immiscible solutes to stabilize nanocrystalline microstructures. Existing modeling efforts largely rely on mesoscale Monte Carlo approaches that employ a simplified model of the microstructure and result in highly homogeneous segregation to grain boundaries. However, there is ample evidence from experimental and modeling studies that demonstrates segregation to grain boundaries is highly non-uniform and sensitive to boundary character. This work employs a realistic nanocrystalline microstructure with experimentally relevant global solute concentrations to illustrate inhomogeneous boundary segregation. Furthermore, experiments quantifying segregation in thin films are reported that corroborate the prediction thatmore » grain boundary segregation is highly inhomogeneous. In addition to grain boundary structure modifying the degree of segregation, the existence of a phase transformation between low and high solute content grain boundaries is predicted. In order to conduct this study, new embedded atom method interatomic potentials are developed for Pt, Au, and the PtAu binary alloy.« less

In situ Observation of Phase Transformation in MnAl(C) Magnetic Materials

PubMed Central

Si, Ping-Zhan; Qian, Hui-Dong; Choi, Chul-Jin; Park, Jihoon; Han, Sangho; Ge, Hong-Liang; Shinde, Kiran P.

2017-01-01

The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was observed by in situ transmission electron microscopy. The exact temperature range for different phase transformation modes was determined by magnetic measurements. The displacive growth of ε→τ in Mn54Al46 (or Mn54Al46C2.44) occurs at temperatures below 650 K (or 766 K), above which both modes coexist. One-third or less of the ε-phase can be transformed into τ-phase via displacive mode while the remaining two-thirds or more via massive mode. In bulk τ-phase, most τ-nanocrystals formed via displacive mode are distributed in the matrix of large τ-grains that formed via massive mode. The typical massive growth rate of the τ-phase is 8–60 nm/s, while the displacive growth rate is low. A more complete understanding of the ε→τ phase transformations in the MnAl-based magnets was provided in this work, based on which the annealing process for ε→τ was optimized and thus high purity τ-phase with high saturation magnetization was obtained. PMID:28858231

Mantle structure and composition to 800-km depth beneath southern Africa and surrounding oceans from broadband body waves

NASA Astrophysics Data System (ADS)

Simon, R. E.; Wright, C.; Kwadiba, M. T. O.; Kgaswane, E. M.

2003-12-01

Average one-dimensional P and S wavespeed models from the surface to depths of 800 km were derived for the southern African region using travel times and waveforms from earthquakes recorded at stations of the Kaapvaal and South African seismic networks. The Herglotz-Wiechert method combined with ray tracing was used to derive a preliminary P wavespeed model, followed by refinements using phase-weighted stacking and synthetic seismograms to yield the final model. Travel times combined with ray tracing were used to derive the S wavespeed model, which was also refined using phase-weighted stacking and synthetic seismograms. The presence of a high wavespeed upper mantle lid in the S model overlying a low wavespeed zone (LWZ) around 210- to ˜345-km depth that is not observed in the P wavespeed model was inferred. The 410-km discontinuity shows similar characteristics to that in other continental regions, but occurs slightly deeper at 420 km. Depletion of iron and/or enrichment in aluminium relative to other regions are the preferred explanation, since the P wavespeeds throughout the transition zone are slightly higher than average. The average S wavespeed structure beneath southern Africa within and below the transition zone is similar to that of the IASP91 model. There is no evidence for discontinuity at 520-km depth. The 660-km discontinuity also appears to be slightly deeper than average (668 km), although the estimated thickness of the transition zone is 248 km, similar to the global average of 241 km. The small size of the 660-km discontinuity for P waves, compared with many other regions, suggests that interpretation of the discontinuity as the transformation of spinel to perovskite and magnesiowüstite may require modification. Alternative explanations include the presence of garnetite-rich material or ilmenite-forming phase transformations above the 660-km discontinuity, and the garnet-perovskite transformation as the discontinuity.

Hypergeometric continuation of divergent perturbation series: II. Comparison with Shanks transformation and Padé approximation

NASA Astrophysics Data System (ADS)

Sanders, Sören; Holthaus, Martin

2017-11-01

We explore in detail how analytic continuation of divergent perturbation series by generalized hypergeometric functions is achieved in practice. Using the example of strong-coupling perturbation series provided by the two-dimensional Bose-Hubbard model, we compare hypergeometric continuation to Shanks and Padé techniques, and demonstrate that the former yields a powerful, efficient and reliable alternative for computing the phase diagram of the Mott insulator-to-superfluid transition. In contrast to Shanks transformations and Padé approximations, hypergeometric continuation also allows us to determine the exponents which characterize the divergence of correlation functions at the transition points. Therefore, hypergeometric continuation constitutes a promising tool for the study of quantum phase transitions.

Deformation and Failure Mechanisms of Shape Memory Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daly, Samantha Hayes

2015-04-15

The goal of this research was to understand the fundamental mechanics that drive the deformation and failure of shape memory alloys (SMAs). SMAs are difficult materials to characterize because of the complex phase transformations that give rise to their unique properties, including shape memory and superelasticity. These phase transformations occur across multiple length scales (one example being the martensite-austenite twinning that underlies macroscopic strain localization) and result in a large hysteresis. In order to optimize the use of this hysteretic behavior in energy storage and damping applications, we must first have a quantitative understanding of this transformation behavior. Prior resultsmore » on shape memory alloys have been largely qualitative (i.e., mapping phase transformations through cracked oxide coatings or surface morphology). The PI developed and utilized new approaches to provide a quantitative, full-field characterization of phase transformation, conducting a comprehensive suite of experiments across multiple length scales and tying these results to theoretical and computational analysis. The research funded by this award utilized new combinations of scanning electron microscopy, diffraction, digital image correlation, and custom testing equipment and procedures to study phase transformation processes at a wide range of length scales, with a focus at small length scales with spatial resolution on the order of 1 nanometer. These experiments probe the basic connections between length scales during phase transformation. In addition to the insights gained on the fundamental mechanisms driving transformations in shape memory alloys, the unique experimental methodologies developed under this award are applicable to a wide range of solid-to-solid phase transformations and other strain localization mechanisms.« less

Nanocantilevers with Adjustable Static Deflection and Significantly Tunable Spectrum Resonant Frequencies for Applications in Nanomechanical Mass Sensors

PubMed Central

Stachiv, Ivo; Sittner, Petr

2018-01-01

Nanocantilevers have become key components of nanomechanical sensors that exploit changes in their resonant frequencies or static deflection in response to the environment. It is necessary that they can operate at a given, but adjustable, resonant frequency and/or static deflection ranges. Here we propose a new class of nanocantilevers with a significantly tunable spectrum of the resonant frequencies and changeable static deflection utilizing the unique properties of a phase-transforming NiTi film sputtered on the usual nanotechnology cantilever materials. The reversible frequency tuning and the adjustable static deflection are obtained by intentionally changing the Young’s modulus and the interlayer stress of the NiTi film during its phase transformation, while the usual cantilever elastic materials guarantee a high frequency actuation (up to tens of MHz). By incorporating the NiTi phase transformation characteristic into the classical continuum mechanics theory we present theoretical models that account for the nanocantilever frequency shift and variation in static deflection caused by a phase transformation of NiTi film. Due to the practical importance in nanomechanical sensors, we carry out a complete theoretical analysis and evaluate the impact of NiTi film on the cantilever Young’s modulus, static deflection, and the resonant frequencies. Moreover, the importance of proposed NiTi nanocantilever is illustrated on the nanomechanical based mass sensors. Our findings will be of value in the development of advanced nanotechnology sensors with intentionally-changeable physical and mechanical properties. PMID:29462996

Benefits Estimation Model for Automated Vehicle Operations: Phase 2 Final Report

DOT National Transportation Integrated Search

2018-01-01

Automated vehicles have the potential to bring about transformative safety, mobility, energy, and environmental benefits to the surface transportation system. They are also being introduced into a complex transportation system, where second-order imp...

Phase transformations in Ln2O3 materials irradiated with swift heavy ions

NASA Astrophysics Data System (ADS)

Tracy, Cameron L.; Lang, Maik; Zhang, Fuxiang; Trautmann, Christina; Ewing, Rodney C.

2015-11-01

Phase transformations induced in the cubic C-type lanthanide sesquioxides, Ln2O3 (Ln = Sm, Gd, Ho, Tm, and Lu), by dense electronic excitation are investigated. The structural modifications resulting from exposure to beams of 185 MeV Xe and 2246 MeV Au ions are characterized using synchrotron x-ray diffraction and Raman spectroscopy. The formation of a B-type polymorph, an X-type nonequilibrium phase, and an amorphous phase are observed. The specific phase formed and the transformation rate show dependence on the material composition, as well as the ion beam mass and energy. Atomistic mechanisms for these transformations are determined, indicating that formation of the B-type phase results from the production of anti-Frenkel defects and the aggregation of anion vacancies into planar clusters, whereas formation of the X-type and amorphous phases requires extensive displacement of both anions and cations. The observed variations in phase behavior with changing lanthanide ionic radius and deposited electronic energy density are related to the energetics of these transformation mechanisms.

Pressure-induced transformations in amorphous silicon: A computational study

NASA Astrophysics Data System (ADS)

Garcez, K. M. S.; Antonelli, A.

2014-02-01

We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

Low Temperature Phase Transformations in Copper-Quenched Ti-44.5Al-8Nb-2.5V Alloy

PubMed Central

Cao, Shouzhen; Xiao, Shulong; Chen, Yuyong; Xu, Lijuan; Wang, Xiaopeng; Han, Jianchao

2017-01-01

In this study, an easily controlled transformation similar to the β + α → β + α + γ and the analysis of metastable phases in a β solidifying Ti-44.5Al-8Nb-2.5V alloy were investigated. Therefore, a liquid alloy copper-quenching followed by annealing at an application temperature (850 °C) has been carried out. Following quenching, a microstructure composed of several supersaturated phases—the basket-weave β0 (βbv) phase, the plate-like α2 (αp) phase and the stripe-like γ (γs) phase—was obtained. In the annealing processes, phase transformations in the prior βbv and αp phases domain corresponded nicely to the β + α → β + α + γ transformation during solidification. Also, in the annealed γs phase, the kinetics of the phase transformations involving the metastable L12 phase was firstly detected by transmission electron microscopy (TEM). The L12 phase had a lattice structure similar to the γ phase, whereas the composition of the phase was similar to the α2 phase. The formation of the γ pre-twin phase with an anti-phase boundary (APB) was detected in the γs phase of the matrix. The orientation relationships between the γs and precipitated: γ (γp) phase are <101]γs//<114]γp, (101¯)γs//(1¯10)γp and (01¯0)γs//(221¯)γp. PMID:28772561

Ground-state information geometry and quantum criticality in an inhomogeneous spin model

NASA Astrophysics Data System (ADS)

Ma, Yu-Quan

2015-09-01

We investigate the ground-state Riemannian metric and the cyclic quantum distance of an inhomogeneous quantum spin-1/2 chain in a transverse field. This model can be diagonalized by using a general canonical transformation to the fermionic Hamiltonian mapped from the spin system. The ground-state Riemannian metric is derived exactly on a parameter manifold ring S1, which is introduced by performing a gauge transformation to the spin Hamiltonian through a twist operator. The cyclic ground-state quantum distance and the second derivative of the ground-state energy are studied in different exchange coupling parameter regions. Particularly, we show that, in the case of exchange coupling parameter Ja = Jb, the quantum ferromagnetic phase can be characterized by an invariant quantum distance and this distance will decay to zero rapidly in the paramagnetic phase. Project supported by the National Natural Science Foundation of China (Grant Nos. 11404023 and 11347131).

A hybrid silicon membrane spatial light modulator for optical information processing

NASA Technical Reports Server (NTRS)

Pape, D. R.; Hornbeck, L. J.

1984-01-01

A new two dimensional, fast, analog, electrically addressable, silicon based membrane spatial light modulator (SLM) was developed for optical information processing applications. Coherent light reflected from the mirror elements is phase modulated producing an optical Fourier transform of an analog signal input to the device. The DMD architecture and operating parameters related to this application are presented. A model is developed that describes the optical Fourier transform properties of the DMD.

Digital signal processing based on inverse scattering transform.

PubMed

Turitsyna, Elena G; Turitsyn, Sergei K

2013-10-15

Through numerical modeling, we illustrate the possibility of a new approach to digital signal processing in coherent optical communications based on the application of the so-called inverse scattering transform. Considering without loss of generality a fiber link with normal dispersion and quadrature phase shift keying signal modulation, we demonstrate how an initial information pattern can be recovered (without direct backward propagation) through the calculation of nonlinear spectral data of the received optical signal.

Solid-state transformation of Fe-rich intermetallic phases in Al–5.0Cu–0.6Mn squeeze cast alloy with variable Fe contents during solution heat treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Bo; School of Mechanical Engineering, Gui Zhou University, Guiyang 550000; Zhang, Weiwen, E-mail: mewzhang@scut.edu.cn

2015-06-15

The Al–5.0 wt.% Cu–0.6 wt.% Mn alloys with a variable Fe content were prepared by squeeze casting. Optical microscopy (OM), Deep etching technique, scanning electron microscopy(SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to examine the solid-state transformation of Fe-rich intermetallics during the solution heat treatment. The results showed that the Chinese script-like α-Fe, Al{sub 6}(FeMn) and needle-like Al{sub 3}(FeMn) phases transform to a new Cu-rich β-Fe (Al{sub 7}Cu{sub 2}(FeMn)) phase during solution heat treatment. The possible reaction and overall transformation kinetics of the solid-state phase transformation for the Fe-rich intermetallics were investigated. - Graphical abstract: Displaymore » Omitted - Highlights: • The α-Fe, Al{sub 6}(FeMn) and Al{sub 3}(FeMn) phases change to the β-Fe phases. • Possible reactions of Fe phases during solution heat treatment are discussed. • The overall fractional transformation rate follows an Avrami curve.« less

Theta phase precession and phase selectivity: a cognitive device description of neural coding

NASA Astrophysics Data System (ADS)

Zalay, Osbert C.; Bardakjian, Berj L.

2009-06-01

Information in neural systems is carried by way of phase and rate codes. Neuronal signals are processed through transformative biophysical mechanisms at the cellular and network levels. Neural coding transformations can be represented mathematically in a device called the cognitive rhythm generator (CRG). Incoming signals to the CRG are parsed through a bank of neuronal modes that orchestrate proportional, integrative and derivative transformations associated with neural coding. Mode outputs are then mixed through static nonlinearities to encode (spatio) temporal phase relationships. The static nonlinear outputs feed and modulate a ring device (limit cycle) encoding output dynamics. Small coupled CRG networks were created to investigate coding functionality associated with neuronal phase preference and theta precession in the hippocampus. Phase selectivity was found to be dependent on mode shape and polarity, while phase precession was a product of modal mixing (i.e. changes in the relative contribution or amplitude of mode outputs resulted in shifting phase preference). Nonlinear system identification was implemented to help validate the model and explain response characteristics associated with modal mixing; in particular, principal dynamic modes experimentally derived from a hippocampal neuron were inserted into a CRG and the neuron's dynamic response was successfully cloned. From our results, small CRG networks possessing disynaptic feedforward inhibition in combination with feedforward excitation exhibited frequency-dependent inhibitory-to-excitatory and excitatory-to-inhibitory transitions that were similar to transitions seen in a single CRG with quadratic modal mixing. This suggests nonlinear modal mixing to be a coding manifestation of the effect of network connectivity in shaping system dynamic behavior. We hypothesize that circuits containing disynaptic feedforward inhibition in the nervous system may be candidates for interpreting upstream rate codes to guide downstream processes such as phase precession, because of their demonstrated frequency-selective properties.

Modeling solvent evaporation during thin film formation in phase separating polymer mixtures

DOE PAGES

Cummings, John; Lowengrub, John S.; Sumpter, Bobby G.; ...

2018-02-09

Preparation of thin films by dissolving polymers in a common solvent followed by evaporation of the solvent has become a routine processing procedure. However, modeling of thin film formation in an evaporating solvent has been challenging due to a need to simulate processes at multiple length and time scales. In this paper, we present a methodology based on the principles of linear non-equilibrium thermodynamics, which allows systematic study of various effects such as the changes in the solvent properties due to phase transformation from liquid to vapor and polymer thermodynamics resulting from such solvent transformations. The methodology allows for themore » derivation of evaporative flux and boundary conditions near each surface for simulations of systems close to the equilibrium. We apply it to study thin film microstructural evolution in phase segregating polymer blends dissolved in a common volatile solvent and deposited on a planar substrate. Finally, effects of the evaporation rates, interactions of the polymers with the underlying substrate and concentration dependent mobilities on the kinetics of thin film formation are studied.« less

Modeling solvent evaporation during thin film formation in phase separating polymer mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cummings, John; Lowengrub, John S.; Sumpter, Bobby G.

Preparation of thin films by dissolving polymers in a common solvent followed by evaporation of the solvent has become a routine processing procedure. However, modeling of thin film formation in an evaporating solvent has been challenging due to a need to simulate processes at multiple length and time scales. In this paper, we present a methodology based on the principles of linear non-equilibrium thermodynamics, which allows systematic study of various effects such as the changes in the solvent properties due to phase transformation from liquid to vapor and polymer thermodynamics resulting from such solvent transformations. The methodology allows for themore » derivation of evaporative flux and boundary conditions near each surface for simulations of systems close to the equilibrium. We apply it to study thin film microstructural evolution in phase segregating polymer blends dissolved in a common volatile solvent and deposited on a planar substrate. Finally, effects of the evaporation rates, interactions of the polymers with the underlying substrate and concentration dependent mobilities on the kinetics of thin film formation are studied.« less

2D non-separable linear canonical transform (2D-NS-LCT) based cryptography

NASA Astrophysics Data System (ADS)

Zhao, Liang; Muniraj, Inbarasan; Healy, John J.; Malallah, Ra'ed; Cui, Xiao-Guang; Ryle, James P.; Sheridan, John T.

2017-05-01

The 2D non-separable linear canonical transform (2D-NS-LCT) can describe a variety of paraxial optical systems. Digital algorithms to numerically evaluate the 2D-NS-LCTs are not only important in modeling the light field propagations but also of interest in various signal processing based applications, for instance optical encryption. Therefore, in this paper, for the first time, a 2D-NS-LCT based optical Double-random- Phase-Encryption (DRPE) system is proposed which offers encrypting information in multiple degrees of freedom. Compared with the traditional systems, i.e. (i) Fourier transform (FT); (ii) Fresnel transform (FST); (iii) Fractional Fourier transform (FRT); and (iv) Linear Canonical transform (LCT), based DRPE systems, the proposed system is more secure and robust as it encrypts the data with more degrees of freedom with an augmented key-space.

Alpha phase precipitation from phase-separated beta phase in a model Ti-Mo-Al alloy studied by direct coupling of transmission electron microscopy and atom probe tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devaraj, Arun; Nag, Soumya; Banerjee, Rajarshi

2013-10-19

The benefit of direct coupling of APT with TEM dark field imaging to investigate early stages of phase transformation in multicomponent alloys is demonstrated by analyzing alpha phase precipitated in a model Ti-10 at% Mo-10 at% Al alloy during annealing at 400oC. Through such a direct coupling approach a thermodynamically unexpected solute partitioning trend between beta matrix and alpha precipitate is observed in the early stages of precipitation, which is explained based on possible nucleation of alpha phase in the Ti rich (Mo and Al depleted regions) created as a result of phase separation in beta matrix. On further highermore » temperature annealing at 600oC for 1 hour, the alpha precipitates were shown to grow and get enriched in Al and further depleted in Mo reaching the thermodynamic equilibrium.« less

Tamoxifen-model membrane interactions: an FT-IR study

NASA Astrophysics Data System (ADS)

Boyar, Handan; Severcan, Feride

1997-06-01

The temperature- and concentration-induced effects of tamoxifen (TAM) on dipalmitoyl phosphatidylcholine (DPPC) model membranes were investigated by the Fourier transform-infrared (FT-IR) spectroscopic technique. An investigation of the C-H stretching region and the CO mode reveals that the inclusion of TAM changes the physical properties of the DPPC multibilayers by (i) shifting the main phase transition to lower temperatures; (ii) broadening the transition profile slightly; (iii) disordering the system in the gel and in the liquid crystalline phases; (iv) increasing the dynamics in the gel phase and decreasing the dynamics of the acyl chains in the liquid crystalline phase; (v) increasing the mobility of the terminal methyl group region of the bilayer in the gel phase and decreasing it in the liquid crystalline phase; (vi) increasing the frequency of the CO stretching mode both in the gel and in the liquid crystalline phases, i.e. non-bonding with carbonyl groups.

Relationships Between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Stainless Steel Under Biaxial Loading Conditions: Synchrotron X-ray and Electron Backscatter Diffraction Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cakmak, Ercan; Choo, Hahn; Kang, Jun-Yun

2015-02-11

The relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a function of the applied strains.more » The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.« less

High-Throughput Study of Diffusion and Phase Transformation Kinetics of Magnesium-Based Systems for Automotive Cast Magnesium Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Alan A; Zhao, Ji-Cheng; Riggi, Adrienne

The objective of the proposed study is to establish a scientific foundation on kinetic modeling of diffusion, phase precipitation, and casting/solidification, in order to accelerate the design and optimization of cast magnesium (Mg) alloys for weight reduction of U.S. automotive fleet. The team has performed the following tasks: 1) study diffusion kinetics of various Mg-containing binary systems using high-throughput diffusion multiples to establish reliable diffusivity and mobility databases for the Mg-aluminum (Al)-zinc (Zn)-tin (Sn)-calcium (Ca)-strontium (Sr)-manganese (Mn) systems; 2) study the precipitation kinetics (nucleation, growth and coarsening) using both innovative dual-anneal diffusion multiples and cast model alloys to provide largemore » amounts of kinetic data (including interfacial energy) and microstructure atlases to enable implementation of the Kampmann-Wagner numerical model to simulate phase transformation kinetics of non-spherical/non-cuboidal precipitates in Mg alloys; 3) implement a micromodel to take into account back diffusion in the solid phase in order to predict microstructure and microsegregation in multicomponent Mg alloys during dendritic solidification especially under high pressure die-casting (HPDC) conditions; and, 4) widely disseminate the data, knowledge and information using the Materials Genome Initiative infrastructure (http://www.mgidata.org) as well as publications and digital data sharing to enable researchers to identify new pathways/routes to better cast Mg alloys.« less

Structure and Stoichiometry of MgxZny in Hot-Dipped Zn-Mg-Al Coating Layer on Interstitial-Free Steel

NASA Astrophysics Data System (ADS)

Kim, Jaenam; Lee, Chongsoo; Jin, Youngsool

2018-03-01

Correlations of stoichiometry and phase structure of MgxZny in hot-dipped Zn-Mg-Al coating layer which were modified by additive element have been established on the bases of diffraction and phase transformation principles. X-ray diffraction (XRD) results showed that MgxZny in the Zn-Mg-Al coating layers consist of Mg2Zn11 and MgZn2. The additive elements had a significant effect on the phase fraction of Mg2Zn11 while the Mg/Al ratio had a negligible effect. Transmission electron microscope (TEM) assisted selected area electron diffraction (SAED) results of small areas MgxZny were indexed dominantly as MgZn2 which have different Mg/Zn stoichiometry between 0.10 and 0.18. It is assumed that the MgxZny have deviated stoichiometry of the phase structure with additive element. The deviated Mg2Zn11 phase structure was interpreted as base-centered orthorhombic by applying two theoretical validity: a structure factor rule explained why the base-centered orthorhombic Mg2Zn11 has less reciprocal lattice reflections in the SAED compared to hexagonal MgZn2, and a phase transformation model elucidated its reasonable lattice point sharing of the corresponding unit cell during hexagonal MgZn2 (a, b = 0.5252 nm, c = 0.8577 nm) transform to intermediate tetragonal and final base-centered orthorhombic Mg2Zn11 (a = 0.8575 nm, b = 0.8874 nm, c = 0.8771 nm) in the equilibrium state.

Influence of Al content on non-equilibrium solidification behavior of Ni-Al-Ta model single crystal alloys

NASA Astrophysics Data System (ADS)

Ai, Cheng; Zhou, Jian; Zhang, Heng; Zhao, Xinbao; Pei, Yanling; Li, Shusuo; Gong, Shengkai

2016-01-01

The non-equilibrium solidification behaviors of five Ni-Al-Ta ternary model single crystal alloys with different Al contents were investigated by experimental analysis and theoretical calculation (by JMatPro) in this study. These model alloys respectively represented the γ' phase with various volume fractions (100%, 75%, 50%, 25% and 0%) at 900 °C. It was found that with decreasing Al content, liquidus temperature of experimental alloys first decreased and then increased. Meanwhile, the solidification range showed a continued downward trend. In addition, with decreasing Al content, the primary phases of non-equilibrium solidified model alloys gradually transformed from γ' phase to γ phase, and the area fraction of which first decreased and then increased. Moreover, the interdendritic/intercellular precipitation of model alloys changed from β phase (for 100% γ') to (γ+γ')Eutectic (for 75% γ'), (γ+γ')Eutectic+γ' (for 50% γ' and 25% γ') and none interdendritic precipitation (for 0% γ'), and the last stage non-equilibrium solidification sequence of model alloys was determined by the nominal Al content and different microsegregation behaviors of Al element.

Thermally coupled moving boundary model for charge-discharge of LiFePO4/C cells

NASA Astrophysics Data System (ADS)

Khandelwal, Ashish; Hariharan, Krishnan S.; Gambhire, Priya; Kolake, Subramanya Mayya; Yeo, Taejung; Doo, Seokgwang

2015-04-01

Optimal thermal management is a key requirement in commercial utilization of lithium ion battery comprising of phase change electrodes. In order to facilitate design of battery packs, thermal management systems and fast charging profiles, a thermally coupled electrochemical model that takes into account the phase change phenomenon is required. In the present work, an electrochemical thermal model is proposed which includes the biphasic nature of phase change electrodes, such as lithium iron phosphate (LFP), via a generalized moving boundary model. The contribution of phase change to the heat released during the cell operation is modeled using an equivalent enthalpy approach. The heat released due to phase transformation is analyzed in comparison with other sources of heat such as reversible, irreversible and ohmic. Detailed study of the thermal behavior of the individual cell components with changing ambient temperature, rate of operation and heat transfer coefficient is carried out. Analysis of heat generation in the various regimes is used to develop cell design and operating guidelines. Further, different charging protocols are analyzed and a model based methodology is suggested to design an efficient quick charging protocol.

Comb model for the anomalous diffusion with dual-phase-lag constitutive relation

NASA Astrophysics Data System (ADS)

Liu, Lin; Zheng, Liancun; Fan, Yu; Chen, Yanping; Liu, Fawang

2018-10-01

As a development of the Fick's model, the dual-phase-lag constitutive relationship with macroscopic and microscopic relaxation characteristics is introduced to describe the anomalous diffusion in comb model. The Dirac delta function in the formulated governing equation represents the special spatial structure of comb model that the horizontal current only exists on the x axis. Solutions are obtained by analytical method with Laplace transform and Fourier transform. The dependence of concentration field and mean square displacement on different parameters are presented and discussed. Results show that the macroscopic and microscopic relaxation parameters have opposite effects on the particle distribution and mean square displacement. Furthermore, four significant results with constant 1/2 are concluded, namely the product of the particle number and the mean square displacement on the x axis equals to 1/2, the exponent of mean square displacement is 1/2 at the special case τq= τP, an asymptotic form of mean square displacement (MSD∼t1/2 as t→0, ∞) is obtained as well at the short time behavior and the long time behavior.

Semianalytical solutions for transport in aquifer and fractured clay matrix system

NASA Astrophysics Data System (ADS)

Huang, Junqi; Goltz, Mark N.

2015-09-01

A three-dimensional mathematical model that describes transport of contaminant in a horizontal aquifer with simultaneous diffusion into a fractured clay formation is proposed. A group of semianalytical solutions is derived based on specific initial and boundary conditions as well as various source functions. The analytical model solutions are evaluated by numerical Laplace inverse transformation and analytical Fourier inverse transformation. The model solutions can be used to study the fate and transport in a three-dimensional spatial domain in which a nonaqueous phase liquid exists as a pool atop a fractured low-permeability clay layer. The nonaqueous phase liquid gradually dissolves into the groundwater flowing past the pool, while simultaneously diffusing into the fractured clay formation below the aquifer. Mass transfer of the contaminant into the clay formation is demonstrated to be significantly enhanced by the existence of the fractures, even though the volume of fractures is relatively small compared to the volume of the clay matrix. The model solution is a useful tool in assessing contaminant attenuation processes in a confined aquifer underlain by a fractured clay formation.

Evaluation of Potential Energy Loss Reduction and Savings for U. S. Army Electrical Distribution Systems

DTIC Science & Technology

1993-09-01

Different Size Transformers (Per Transformer ) 41 15 Additional Energy Losses for Mis-Sized Transformers (Per Transformer ) 42 16 Power System ...directly affects the amount of neutral line power loss in the system . Since most Army three-phase loads are distribution transformers spread out over a...61 Balancing Three-Phase Loads Balancing Feeder Circuit Loads Power Factor Correction Optimal Transformer Sizing Conductor Sizing Combined

Holotransformations of bacterial colonies and genome cybernetics

NASA Astrophysics Data System (ADS)

Ben-Jacob, Eshel; Tenenbaum, Adam; Shochet, Ofer; Avidan, Orna

1994-01-01

We present a study of colony transformations during growth of Bacillus subtilis under adverse environmental conditions. It is a continuation of our pilot study of “Adaptive self-organization during growth of bacterial colonies” (Physica A 187 (1992) 378). First we identify and describe the transformations pathway, i.e. the excitation of the branching modes from Bacillus subtilis 168 (grown under diffusion limited conditions) and the phase transformations between the tip-splitting phase (phase T) and the chiral phase (phase C) which belong to the same mode. This pathway shows the evolution of complexity as the bacteria are exposed to adverse growth conditions. We present the morphology diagram of phases T and C as a function of agar concentration and pepton level. As expected, the growth of phase T is ramified (fractal-like or DLA-like) at low pepton level (about 1 g/1) and turns compact at high pepton level (about 10 g/1). The growth of phase C is also ramified at low pepton level and turns denser and finally compact as the pepton level increases. Generally speaking, the colonies develop more complex patterns and higher micro-level organization for more adverse environments. We use the growth velocity as a response function to describe the growth. At low agar concentration (and low pepton level) phase C grows faster than phase T, and for a high agar concentration (about 2%) phase T grows faster. We observe colony transformations between the two phases (phase transformations). They are found to be consistent with the “fastest growing morphology” selection principle adopted from azoic systems. The transformations are always from the slower phase to the faster one. Hence, we observe T→ C transformations at low agar concentrations and C→ T transformations at high agar concentrations. We have observed both localized and extended transformations. Usually, the transformations are localized for more adverse growth conditions, and extended for growth conditions close to the boundaries between morphologies. We have observed also transformations between different branching modes, as well as transformations via virtual states. Motivated by the contemporary knowledge about phages and plasmids, we postulate a theoretical framework to comply with our experimental findings. We explain our observations using these assumptions as well as our proposal of co-mutations and auto-catalytic mutations as presented in the above mentioned pilot paper. This theoretical framework is a part of the new evolving picture of genome cybernetics. We also discuss the concept of adaptive genome changes which are based on pre-existing knowledge as well as the concept of genetic learning. i.e. changes (in response to a new problem) which develop the potential for adaptive genome changes. These concepts follow naturally if the picture of genome cybernetics is accepted. We conclude with a discussion of the implications and with further predictions (to be tested experimentally) derived from our assumptions.

Electron backscatter diffraction studies of focused ion beam induced phase transformation in cobalt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, H.G., E-mail: helen.jones@npl.co.uk

A focused ion beam microscope was used to induce cubic to hexagonal phase transformation in a cobalt alloy, of similar composition to that of the binder phase in a hardmetal, in a controlled manner at 0°, 45° and 80° ion incident angles. The cobalt had an average grain size of ~ 20 μm, allowing multiple orientations to be studied, exposed to a range of doses between 6 × 10{sup 7} and 2 × 10{sup 10} ions/μm{sup 2}. Electron backscatter diffraction (EBSD) was used to determine the original and induced phase orientations, and area fractions, before and after the ion beammore » exposure. On average, less phase transformation was observed at higher incident angles and after lower ion doses. However there was an orientation effect where grains with an orientation close to (111) planes were most susceptible to phase transformation, and (101) the least, where grains partially and fully transformed at varying ion doses. - Highlights: •Ion-induced phase change in FCC cobalt was observed at multiple incidence angles. •EBSD was used to study the relationship between grain orientation and transformation. •Custom software analysed ion dose and phase change with respect to grain orientation. •A predictive capability of ion-induced phase change in cobalt was enabled.« less

ECHMERIT: A new on-line global mercury-chemistry model

NASA Astrophysics Data System (ADS)

Jung, G.; Hedgecock, I. M.; Pirrone, N.

2009-04-01

Mercury is a volatile metal, that is of concern because when deposited and transformed to methylmercury accumulates within the food-web. Due to the long lifetime of elemental mercury, which is the dominant fraction of mercury species in the atmosphere, mercury is prone to long-range transport and therefore distributed over the globe, transported and hence deposited even in regions far from anthropogenic emission sources. Mercury is released to the atmosphere from a variety of natural and anthropogenic sources, in elementary and oxidised forms, and as particulate mercury. It is then transported, but also transformed chemically in the gaseous phase, as well as in aqueous phase within cloud and rain droplets. Mercury (particularly its oxidised forms) is removed from the atmosphere though wet and dry deposition processes, a large fraction of deposited mercury is, after chemical or biological reduction, re-emitted to the atmosphere as elementary mercury. To investigate mercury chemistry and transport processes on the global scale, the new, global model ECHMERIT has been developed. ECHMERIT simulates meteorology, transport, deposition, photolysis and chemistry on-line. The general circulation model on which ECHMERIT is based is ECHAM5. Sophisticated chemical modules have been implemented, including gas phase chemistry based on the CBM-Z chemistry mechanism, as well as aqueous phase chemistry, both of which have been adapted to include Hg chemistry and Hg species gas-droplet mass transfer. ECHMERIT uses the fast-J photolysis routine. State-of-the-art procedures simulating wet and dry deposition and emissions were adapted and included in the model as well. An overview of the model structure, development, validation and sensitivity studies is presented.

The correlation of local deformation and stress-assisted local phase transformations in MMC foams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berek, H., E-mail: harry.berek@ikgb.tu-freiberg.de; Ballaschk, U.; Aneziris, C.G.

2015-09-15

Cellular structures are of growing interest for industry, and are of particular importance for lightweight applications. In this paper, a special case of metal matrix composite foams (MMCs) is investigated. The investigated foams are composed of austenitic steel exhibiting transformation induced plasticity (TRIP) and magnesia partially stabilized zirconia (Mg-PSZ). Both components exhibit martensitic phase transformation during deformation, thus generating the potential for improved mechanical properties such as strength, ductility, and energy absorption capability. The aim of these investigations was to show that stress-assisted phase transformations within the ceramic reinforcement correspond to strong local deformation, and to determine whether they canmore » trigger martensitic phase transformations in the steel matrix. To this end, in situ interrupted compression experiments were performed in an X-ray computed tomography device (XCT). By using a recently developed registration algorithm, local deformation could be calculated and regions of interest could be defined. Corresponding cross sections were prepared and used to analyze the local phase composition by electron backscatter diffraction (EBSD). The results show a strong correlation between local deformation and phase transformation. - Graphical abstract: Display Omitted - Highlights: • In situ compressive deformation on MMC foams was performed in an XCT. • Local deformation fields and their gradient amplitudes were estimated. • Cross sections were manufactured containing defined regions of interest. • Local EBSD phase analysis was performed. • Local deformation and local phase transformation are correlated.« less

A phase-field approach to nonequilibrium phase transformations in elastic solids via an intermediate phase (melt) allowing for interface stresses.

PubMed

Momeni, Kasra; Levitas, Valery I

2016-04-28

A phase-field approach for phase transformations (PTs) between three different phases at nonequilibrium temperatures is developed. It includes advanced mechanics, thermodynamically consistent interfacial stresses, and interface interactions. A thermodynamic Landau-Ginzburg potential developed in terms of polar order parameters satisfies the desired instability and equilibrium conditions for homogeneous phases. The interfacial stresses were introduced with some terms from large-strain formulation even though the small-strain assumption was utilized. The developed model is applied to study the PTs between two solid phases via a highly disordered intermediate phase (IP) or an intermediate melt (IM) hundreds of degrees below the melting temperature. In particular, the β ↔ δ PTs in HMX energetic crystals via IM are analyzed. The effects of various parameters (temperature, ratios of widths and energies of solid-solid (SS) to solid-melt (SM) interfaces, elastic energy, and interfacial stresses) on the formation, stability, and structure of the IM within a propagating SS interface are studied. Interfacial and elastic stresses within a SS interphase and their relaxation and redistribution with the appearance of a partial or complete IM are analyzed. The energy and structure of the critical nucleus (CN) of the IM are studied as well. In particular, the interfacial stresses increase the aspect-ratio of the CN. Although including elastic energy can drastically reduce the energy of the CN of the IM, the activation energy of the CN of the IM within the SS interface increases when interfacial tension is taken into account. The developed thermodynamic potential can also be modified to model other multiphase physical phenomena, such as multi-variant martensitic PTs, grain boundary and surface-induced pre-melting and PTs, as well as developing phase diagrams for IPs.

Thermodynamic Modelling of Phase Transformation in a Multi-Component System

NASA Astrophysics Data System (ADS)

Vala, J.

2007-09-01

Diffusion in multi-component alloys can be characterized by the vacancy mechanism for substitutional components, by the existence of sources and sinks for vacancies and by the motion of atoms of interstitial components. The description of diffusive and massive phase transformation of a multi-component system is based on the thermodynamic extremal principle by Onsager; the finite thickness of the interface between both phases is respected. The resulting system of partial differential equations of evolution with integral terms for unknown mole fractions (and additional variables in case of non-ideal sources and sinks for vacancies), can be analyzed using the method of lines and the finite difference technique (or, alternatively, the finite element one) together with the semi-analytic and numerical integration formulae and with certain iteration procedure, making use of the spectral properties of linear operators. The original software code for the numerical evaluation of solutions of such systems, written in MATLAB, offers a chance to simulate various real processes of diffusional phase transformation. Some results for the (nearly) steady-state real processes in substitutional alloys have been published yet. The aim of this paper is to demonstrate that the same approach can handle both substitutional and interstitial components even in case of a general system of evolution.

Probing microstructure and phase evolution of α-MoO 3 nanobelts for sodium-ion batteries by in situ transmission electron microscopy

DOE PAGES

Xia, Weiwei; Xu, Feng; Zhu, Chongyang; ...

2016-07-15

The fundamental electrochemical reaction mechanisms and the phase transformation pathways of layer-structured α-MoO 3 nanobelt during the sodiation/desodiation process to date remain largely unknown. In this study, to observe the real-time sodiation/desodiaton behaviors of α-MoO 3 during electrochemical cycling, we construct a MoO 3 anode sodium-ion battery inside a transmission electron microscope (TEM). Utilizing in situ TEM and electron diffraction pattern (EDP) observation, α-MoO 3 nanobelts are found to undergo a unique multi-step phase transformation. Upon the first sodiation, α-MoO 3 nanobelts initially form amorphous Na xMoO3 phase and are subsequently sodiated into intermediate phase of crystalline NaMoO 2, finallymore » resulting in the crystallized Mo nanograins embedded within the Na 2O matrix. During the first desodiation process, Mo nanograins are firstly re-oxidized into intermediate phase NaMoO 2 that is further transformed into amorphous Na 2MoO 3, resulting in an irreversible phase transformation. Upon subsequent sodiation/desodiation cycles, however, a stable and reversible phase transformation between crystalline Mo and amorphous Na2MoO 3 phases has been revealed. In conclusion, our work provides an in-deepth understanding of the phase transformation pathways of α-MoO 3 nanobelts upon electrochemical sodiation/desodiation processes, with the hope of assistance in designing sodium-ion batteries with enhanced performance.« less

Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule.

PubMed

Politi, Yael; Metzler, Rebecca A; Abrecht, Mike; Gilbert, Benjamin; Wilt, Fred H; Sagi, Irit; Addadi, Lia; Weiner, Steve; Gilbert, P U P A; Gilbert, Pupa

2008-11-11

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40-200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.

Modeling coupled sorption and transformation of 17β-estradiol-17-sulfate in soil-water systems

NASA Astrophysics Data System (ADS)

Bai, Xuelian; Shrestha, Suman L.; Casey, Francis X. M.; Hakk, Heldur; Fan, Zhaosheng

2014-11-01

Animal manure is the primary source of exogenous free estrogens in the environment, which are known endocrine-disrupting chemicals to disorder the reproduction system of organisms. Conjugated estrogens can act as precursors to free estrogens, which may increase the total estrogenicity in the environment. In this study, a comprehensive model was used to simultaneously simulate the coupled sorption and transformation of a sulfate estrogen conjugate, 17β-estradiol-17-sulfate (E2-17S), in various soil-water systems (non-sterile/sterile; topsoil/subsoil). The simulated processes included multiple transformation pathways (i.e. hydroxylation, hydrolysis, and oxidation) and mass transfer between the aqueous, reversibly sorbed, and irreversibly sorbed phases of all soils for E2-17S and its metabolites. The conceptual model was conceived based on a series of linear sorption and first-order transformation expressions. The model was inversely solved using finite difference to estimate process parameters. A global optimization method was applied for the inverse analysis along with variable model restrictions to estimate 36 parameters. The model provided a satisfactory simultaneous fit (R2adj = 0.93 and d = 0.87) of all the experimental data and reliable parameter estimates. This modeling study improved the understanding on fate and transport of estrogen conjugates under various soil-water conditions.

Kinetics of lisinopril intramolecular cyclization in solid phase monitored by Fourier transform infrared microscopy.

PubMed

Widjaja, Effendi; Tan, Wei Jian

2008-08-01

The solid-state intramolecular cyclization of lisinopril to diketopiperazine was investigated by in situ Fourier transform infrared (FT-IR) microscopy. Using a controllable heating cell, the isothermal transformation was monitored in situ at 147.5, 150, 152.5, 155, and 157.5 degrees C. The collected time-dependent FT-IR spectra at each isothermal temperature were preprocessed and analyzed using a multivariate chemometric approach. The pure component spectra of the observable component (lisinopril and diketopiperazine) were resolved and their time-dependent relative contributions were also determined. Model-free and various model fitting methods were implemented in the kinetic analysis to estimate the activation energy of the intramolecular cyclization reaction. Arrhenius plots indicate that the activation energy is circa 327 kJ/mol.

Transformation-Induced Diffraction Peak Broadening During Bainitic and Martensitic Transformations Under Small External Loads in a Quenched and Tempered High Strength Steel

NASA Astrophysics Data System (ADS)

Dutta, R. K.; Huizenga, R. M.; Amirthalingam, M.; Hermans, M. J. M.; King, A.; Richardson, I. M.

2013-09-01

In situ phase transformation behavior of a high strength S690QL1 steel during continuous cooling under different mechanical loading conditions has been used to investigate the effect of small external loads on the transformation-induced plasticity during bainitic and martensitic transformations. The results show that during phase transformations, the untransformed austenite undergoes plastic deformation, thereby retarding further transformation to bainite/martensite. This occurs independent of external load.

Impurities block the alpha to omega martensitic transformation in titanium.

PubMed

Hennig, Richard G; Trinkle, Dallas R; Bouchet, Johann; Srinivasan, Srivilliputhur G; Albers, Robert C; Wilkins, John W

2005-02-01

Impurities control phase stability and phase transformations in natural and man-made materials, from shape-memory alloys to steel to planetary cores. Experiments and empirical databases are still central to tuning the impurity effects. What is missing is a broad theoretical underpinning. Consider, for example, the titanium martensitic transformations: diffusionless structural transformations proceeding near the speed of sound. Pure titanium transforms from ductile alpha to brittle omega at 9 GPa, creating serious technological problems for beta-stabilized titanium alloys. Impurities in the titanium alloys A-70 and Ti-6Al-4V (wt%) suppress the transformation up to at least 35 GPa, increasing their technological utility as lightweight materials in aerospace applications. These and other empirical discoveries in technological materials call for broad theoretical understanding. Impurities pose two theoretical challenges: the effect on the relative phase stability, and the energy barrier of the transformation. Ab initio methods calculate both changes due to impurities. We show that interstitial oxygen, nitrogen and carbon retard the transformation whereas substitutional aluminium and vanadium influence the transformation by changing the d-electron concentration. The resulting microscopic picture explains the suppression of the transformation in commercial A-70 and Ti-6Al-4V alloys. In general, the effect of impurities on relative energies and energy barriers is central to understanding structural phase transformations.

A New Multiphase Equation of State for SiO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maerzke, Katie A.; Gammel, J. Tinka

SiO 2 is found as α-quartz at ambient conditions. Under shock compression, it transforms into a much higher density stishovite-like phase around 20 GPa, then into a liquid phase above 100 GPa. The SESAME library contains older equations of state for α-quartz, polycrystalline quartz, and fused quartz. These equations of state model the material as a single phase; i.e., there is no high pressure phase transition. Somewhat more recently (in 1992), Jon Boettger published equations of state for α-quartz, coesite, and stishovite, along with a phase transition model to mix them. However, we do not have a multiphase EOS thatmore » captures the phase transitions in this material. Others are working on a high-accuracy model for very high pressure SiO 2, since liquid quartz is used as an impedance matching standard above 100 GPa; however, we are focused on the 10-50 GPa range. This intermediate pressure range is most relevant for modeling the decomposition products of silicone polymers such as Sylgard 184 and SX358.« less

Performance of Four-Leg VSC based DSTATCOM using Single Phase P-Q Theory

NASA Astrophysics Data System (ADS)

Jampana, Bangarraju; Veramalla, Rajagopal; Askani, Jayalaxmi

2017-02-01

This paper presents single-phase P-Q theory for four-leg VSC based distributed static compensator (DSTATCOM) in the distribution system. The proposed DSTATCOM maintains unity power factor at source, zero voltage regulation, eliminates current harmonics, load balancing and neutral current compensation. The advantage of using four-leg VSC based DSTATCOM is to eliminate isolated/non-isolated transformer connection at point of common coupling (PCC) for neutral current compensation. The elimination of transformer connection at PCC with proposed topology will reduce cost of DSTATCOM. The single-phase P-Q theory control algorithm is used to extract fundamental component of active and reactive currents for generation of reference source currents which is based on indirect current control method. The proposed DSTATCOM is modelled and the results are validated with various consumer loads under unity power factor and zero voltage regulation modes in the MATLAB R2013a environment using simpower system toolbox.

Security analysis of quadratic phase based cryptography

NASA Astrophysics Data System (ADS)

Muniraj, Inbarasan; Guo, Changliang; Malallah, Ra'ed; Healy, John J.; Sheridan, John T.

2016-09-01

The linear canonical transform (LCT) is essential in modeling a coherent light field propagation through first-order optical systems. Recently, a generic optical system, known as a Quadratic Phase Encoding System (QPES), for encrypting a two-dimensional (2D) image has been reported. It has been reported together with two phase keys the individual LCT parameters serve as keys of the cryptosystem. However, it is important that such the encryption systems also satisfies some dynamic security properties. Therefore, in this work, we examine some cryptographic evaluation methods, such as Avalanche Criterion and Bit Independence, which indicates the degree of security of the cryptographic algorithms on QPES. We compare our simulation results with the conventional Fourier and the Fresnel transform based DRPE systems. The results show that the LCT based DRPE has an excellent avalanche and bit independence characteristics than that of using the conventional Fourier and Fresnel based encryption systems.

Modeling deformation behavior of Cu-Zr-Al bulk metallic glass matrix composites

NASA Astrophysics Data System (ADS)

Pauly, S.; Liu, G.; Wang, G.; Das, J.; Kim, K. B.; Kühn, U.; Kim, D. H.; Eckert, J.

2009-09-01

In the present work we prepared an in situ Cu47.5Zr47.5Al5 bulk metallic glass matrix composite derived from the shape memory alloy CuZr. We use a strength model, which considers percolation and a three-microstructural-element body approach, to understand the effect of the crystalline phase on the yield stress and the fracture strain under compressive loading, respectively. The intrinsic work-hardenability due to the martensitic transformation of the crystalline phase causes significant work hardening also of the composite material.

Isotropic scalar image visualization of vector differential image data using the inverse Riesz transform.

PubMed

Larkin, Kieran G; Fletcher, Peter A

2014-03-01

X-ray Talbot moiré interferometers can now simultaneously generate two differential phase images of a specimen. The conventional approach to integrating differential phase is unstable and often leads to images with loss of visible detail. We propose a new reconstruction method based on the inverse Riesz transform. The Riesz approach is stable and the final image retains visibility of high resolution detail without directional bias. The outline Riesz theory is developed and an experimentally acquired X-ray differential phase data set is presented for qualitative visual appraisal. The inverse Riesz phase image is compared with two alternatives: the integrated (quantitative) phase and the modulus of the gradient of the phase. The inverse Riesz transform has the computational advantages of a unitary linear operator, and is implemented directly as a complex multiplication in the Fourier domain also known as the spiral phase transform.

Isotropic scalar image visualization of vector differential image data using the inverse Riesz transform

PubMed Central

Larkin, Kieran G.; Fletcher, Peter A.

2014-01-01

X-ray Talbot moiré interferometers can now simultaneously generate two differential phase images of a specimen. The conventional approach to integrating differential phase is unstable and often leads to images with loss of visible detail. We propose a new reconstruction method based on the inverse Riesz transform. The Riesz approach is stable and the final image retains visibility of high resolution detail without directional bias. The outline Riesz theory is developed and an experimentally acquired X-ray differential phase data set is presented for qualitative visual appraisal. The inverse Riesz phase image is compared with two alternatives: the integrated (quantitative) phase and the modulus of the gradient of the phase. The inverse Riesz transform has the computational advantages of a unitary linear operator, and is implemented directly as a complex multiplication in the Fourier domain also known as the spiral phase transform. PMID:24688823

Multiphase-field model of small strain elasto-plasticity according to the mechanical jump conditions

NASA Astrophysics Data System (ADS)

Herrmann, Christoph; Schoof, Ephraim; Schneider, Daniel; Schwab, Felix; Reiter, Andreas; Selzer, Michael; Nestler, Britta

2018-04-01

We introduce a small strain elasto-plastic multiphase-field model according to the mechanical jump conditions. A rate-independent J_2 -plasticity model with linear isotropic hardening and without kinematic hardening is applied exemplary. Generally, any physically nonlinear mechanical model is compatible with the subsequently presented procedure. In contrast to models with interpolated material parameters, the proposed model is able to apply different nonlinear mechanical constitutive equations for each phase separately. The Hadamard compatibility condition and the static force balance are employed as homogenization approaches to calculate the phase-inherent stresses and strains. Several verification cases are discussed. The applicability of the proposed model is demonstrated by simulations of the martensitic transformation and quantitative parameters.

Determination of the continuous cooling transformation diagram of a high strength low alloyed steel

NASA Astrophysics Data System (ADS)

Kang, Hun Chul; Park, Bong June; Jang, Ji Hun; Jang, Kwang Soon; Lee, Kyung Jong

2016-11-01

The continuous cooling transformation diagram of a high strength low alloyed steel was determined by a dilatometer and microscopic analysis (OM, SEM) as well as thermodynamic analysis. As expected, Widmanstätten ferrite, bainite and martensite coexisted for most cooling rates, which made it difficult to determine the transformation kinetics of individual phases. However, peaks were clearly observed in the dilatometric {d( {LVDT} )}/{dT} curves. By overlapping the {d( {LVDT} )}/{dT} curves, which were determined using various cooling rates, peaks were separated and the peak rate temperatures, as well as the temperature at the start of transformation (5%) and the end of transformation (95%) of an individual phase, were determined. A SEM analysis was also conducted to identify which phase existed and to quantify the volume fraction of each phase. It was confirmed that the additional {d( {LVDT} )}/{dT} curve analysis described the transformation behavior more precisely than the conventional continuous cooling transformation diagram, as determined by the volume measured from the microstructure analysis.

Fresnel transform phase retrieval from magnitude.

PubMed

Pitts, Todd A; Greenleaf, James F

2003-08-01

This report presents a generalized projection method for recovering the phase of a finite support, two-dimensional signal from knowledge of its magnitude in the spatial position and Fresnel transform domains. We establish the uniqueness of sampled monochromatic scalar field phase given Fresnel transform magnitude and finite region of support constraints for complex signals. We derive an optimally relaxed version of the algorithm resulting in a significant reduction in the number of iterations needed to obtain useful results. An advantage of using the Fresnel transform (as opposed to Fourier) for measurement is that the shift-invariance of the transform operator implies retention of object location information in the transformed image magnitude. As a practical application in the context of ultrasound beam measurement we discuss the determination of small optical phase shifts from near field optical intensity distributions. Experimental data are used to reconstruct the phase shape of an optical field immediately after propagating through a wide bandwidth ultrasonic pulse. The phase of each point on the optical wavefront is proportional to the ray sum of pressure through the ultrasound pulse (assuming low ultrasonic intensity). An entire pressure field was reconstructed in three dimensions and compared with a calibrated hydrophone measurement. The comparison is excellent, demonstrating that the phase retrieval is quantitative.

Nano-scale phase transformation in Ti-implanted austenitic 301 stainless steel.

PubMed

Gustiono, Dwi; Sakaguchi, Norihito; Shibayama, Tamaki; Kinoshita, Hiroshi; Takahashi, Heishichiro

2003-01-01

Phase-transformation behaviours were investigated for austenitic 301 stainless steel during implantation at room temperature with 300 keV Ti ions to fluences of 8 x 10(19) to approximately 3 x 10(21) ions m(-2) by means of transmission electron microscopy. The cross-sectional specimen was prepared using a focused ion beam. Plan observation of the implanted specimen showed that phase transformation from gamma-phase to alpha-phase was induced by implantation to a fluence of 3 x 10(20) Ti ions m(-2). The nucleation of the irradiation (implantation)-induced phase increased with the increase of the dose. The orientation relationship between the gamma matrix and the induced alpha martensitic phase was identified as (011)alpha//(111)gamma and [11-1]alpha//[10-1], close to the Kurdjumov-Sachs relationship. Cross-sectional observation after implantation to a fluence of 5 x 10(20) ions m(-2) showed that phase transformation mostly nucleated near the surface and occurred in the higher the concentration gradient of the implanted ion, i.e. a higher stress concentration takes place and this stress introduced by the implanted ions acts as a driving force for the transformation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cong, Daoyong; Rule, Kirrily Clair; Li, Wen-Hsien

Here we describe insights into the phase transformation kinetics and lattice dynamics associated with the newly discovered confined martensitic transformation, which are of great significance to the in-depth understanding of the phase transformation behavior responsible for the rich new physical phenomena in shape memory alloys and could shed light on the design of novel multifunctional properties through tuning the confined martensitic transformation.

Implications of male circumcision for women in Papua New Guinea: a transformational grounded theory study.

PubMed

Redman-MacLaren, Michelle; Mills, Jane; Tommbe, Rachael; MacLaren, David; Speare, Rick; McBride, William J H

2017-07-27

Male circumcision reduces the risk of female-to-male transmission of human immunodeficiency virus (HIV) and is being explored for HIV prevention in Papua New Guinea (PNG). PNG has a concentrated HIV epidemic which is largely heterosexually transmitted. There are a diverse range of male circumcision and penile modification practices across PNG. Exploring the implications of male circumcision for women in PNG is important to inform evidence-based health policy that will result in positive, intended consequences. The transformational grounded theory study incorporated participatory action research and decolonizing methodologies. In Phase One, an existing data set from a male circumcision study of 861 male and 519 female participants was theoretically sampled and analyzed for women's understanding and experience of male circumcision. In Phase Two of the study, primary data were co-generated with 64 women in seven interpretive focus group discussions and 11 semi-structured interviews to develop a theoretical model of the processes used by women to manage the outcomes of male circumcision. In Phase Three participants assisted to refine the developing transformational grounded theory and identify actions required to improve health. Many women know a lot about male circumcision and penile modification and the consequences for themselves, their families and communities. Their ability to act on this knowledge is determined by numerous social, cultural and economic factors. A transformational grounded theory was developed with connecting categories of: Women Know a Lot, Increasing Knowledge; Increasing Options; and Acting on Choices. Properties and dimensions of each category are represented in the model, along with the intervening condition of Safety. The condition of Safety contextualises the overarching lived realty for women in PNG, enables the inclusion of men in the transformational grounded theory model, and helps to explain relationships between men and women. The theory presents the core category as Power of Choice. This transformational grounded theory provides a means to explore how women experience male circumcision and penile modification in PNG, including for HIV prevention. Women who have had opportunities for education have a greater range of choices and an increased opportunity to act upon these choices. However, women can only exercise their power of choice in the context of safety. The concept of Peace drawn from the Social Determinants of Health is applied in order to extend the explanatory power of the transformational grounded theory. This study shows that women's ambivalence about male circumcision is often related to lack of safety, a consequence of gender inequality in PNG.

Nanoclusters first: a hierarchical phase transformation in a novel Mg alloy

NASA Astrophysics Data System (ADS)

Okuda, Hiroshi; Yamasaki, Michiaki; Kawamura, Yoshihito; Tabuchi, Masao; Kimizuka, Hajime

2015-09-01

The Mg-Y-Zn ternary alloy system contains a series of novel structures known as long-period stacking ordered (LPSO) structures. The formation process and its key concept from a viewpoint of phase transition are not yet clear. The current study reveals that the phase transformation process is not a traditional spinodal decomposition or structural transformation but, rather a novel hierarchical phase transformation. In this transformation, clustering occurs first, and the spatial rearrangement of the clusters induce a secondary phase transformation that eventually lead to two-dimensional ordering of the clusters. The formation process was examined using in situ synchrotron radiation small-angle X-ray scattering (SAXS). Rapid quenching from liquid alloy into thin ribbons yielded strongly supersaturated amorphous samples. The samples were heated at a constant rate of 10 K/min. and the scattering patterns were acquired. The SAXS analysis indicated that small clusters grew to sizes of 0.2 nm after they crystallized. The clusters distributed randomly in space grew and eventually transformed into a microstructure with two well-defined cluster-cluster distances, one for the segregation periodicity of LPSO and the other for the in-plane ordering in segregated layer. This transformation into the LPSO structure concomitantly introduces the periodical stacking fault required for the 18R structures.

Finite-deformation phase-field chemomechanics for multiphase, multicomponent solids

NASA Astrophysics Data System (ADS)

Svendsen, Bob; Shanthraj, Pratheek; Raabe, Dierk

2018-03-01

The purpose of this work is the development of a framework for the formulation of geometrically non-linear inelastic chemomechanical models for a mixture of multiple chemical components diffusing among multiple transforming solid phases. The focus here is on general model formulation. No specific model or application is pursued in this work. To this end, basic balance and constitutive relations from non-equilibrium thermodynamics and continuum mixture theory are combined with a phase-field-based description of multicomponent solid phases and their interfaces. Solid phase modeling is based in particular on a chemomechanical free energy and stress relaxation via the evolution of phase-specific concentration fields, order-parameter fields (e.g., related to chemical ordering, structural ordering, or defects), and local internal variables. At the mixture level, differences or contrasts in phase composition and phase local deformation in phase interface regions are treated as mixture internal variables. In this context, various phase interface models are considered. In the equilibrium limit, phase contrasts in composition and local deformation in the phase interface region are determined via bulk energy minimization. On the chemical side, the equilibrium limit of the current model formulation reduces to a multicomponent, multiphase, generalization of existing two-phase binary alloy interface equilibrium conditions (e.g., KKS). On the mechanical side, the equilibrium limit of one interface model considered represents a multiphase generalization of Reuss-Sachs conditions from mechanical homogenization theory. Analogously, other interface models considered represent generalizations of interface equilibrium conditions consistent with laminate and sharp-interface theory. In the last part of the work, selected existing models are formulated within the current framework as special cases and discussed in detail.

Phase transformation in tantalum under extreme laser deformation

DOE PAGES

Lu, C. -H.; Hahn, E. N.; Remington, B. A.; ...

2015-10-19

The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centeredmore » cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. In conclusion, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).« less

Phase Transformation in Tantalum under Extreme Laser Deformation

PubMed Central

Lu, C.-H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

2015-01-01

The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear). PMID:26478106

Toward the Characterization of Mixed-Phase Clouds Using Remote Sensing

NASA Astrophysics Data System (ADS)

Andronache, C.

2015-12-01

Mixed-phase clouds consist of a mixture of ice particles and liquid droplets at temperatures below 0 deg C. They are present in all seasons in many regions of the world, account for about 30% of the global cloud coverage, and are linked to cloud electrification and aircraft icing. The mix of ice particles, liquid droplets, and water vapor is unstable, and such clouds are thought to have a short lifetime. A characteristic parameter is the phase composition of mixed-phase clouds. It affects the cloud life cycle and the rate of precipitation. This parameter is important for cloud parameters retrievals by radar, lidar, and satellite and is relevant for climate modeling. The phase transformation includes the remarkable Wegener-Bergeron-Findeisen (WBF) process. The direction and the rate of the phase transformations depend on the local thermodynamic and microphysical properties. Cloud condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and the dynamic response of clouds to aerosols. The complexity of dynamics and microphysics involved in mixed-phase clouds requires a set of observational and modeling tools that continue to be refined. Among these techniques, the remote sensing methods provide an increasing number of parameters, covering large regions of the world. Thus, a series of studies were dedicated to stratiform mixed-phase clouds revealing longer lifetime than previously thought. Satellite data and aircraft in situ measurements in deep convective clouds suggest that highly supercooled water often occurs in vigorous continental convective storms. In this study, we use cases of convective clouds to discuss the feasibility of mixed-phase clouds characterization and potential advantages of remote sensing.

The Investigation on Strain Strengthening Induced Martensitic Phase Transformation of Austenitic Stainless Steel: A Fundamental Research for the Quality Evaluation of Strain Strengthened Pressure Vessel

NASA Astrophysics Data System (ADS)

Li, Bo; Cai Ren, Fa; Tang, Xiao Ying

2018-03-01

The manufacture of pressure vessels with austenitic stainless steel strain strengthening technology has become an important technical means for the light weight of cryogenic pressure vessels. In the process of increasing the strength of austenitic stainless steel, strain can induce the martensitic phase transformation in austenite phase. There is a quantitative relationship between the transformation quantity of martensitic phase and the basic mechanical properties. Then, the martensitic phase variables can be obtained by means of detection, and the mechanical properties and safety performance are evaluated and calculated. Based on this, the quantitative relationship between strain hardening and deformation induced martensite phase content is studied in this paper, and the mechanism of deformation induced martensitic transformation of austenitic stainless steel is detailed.

Vapor-crystal phase transition in synthesis of paracetamol films by vacuum evaporation and condensation

NASA Astrophysics Data System (ADS)

Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.; Zarembo, V. I.

2014-03-01

We report on the structural and technological investigations of the vapor-crystal phase transition during synthesis of paracetamol films of the monoclinic system by vacuum evaporation and condensation in the temperature range 220-320 K. The complex nature of the transformation accompanied by the formation of a gel-like phase is revealed. The results are interpreted using a model according to which the vapor-crystal phase transition is not a simple first-order phase transition, but is a nonlinear superposition of two phase transitions: a first-order transition with a change in density and a second-order phase transition with a change in ordering. Micrographs of the surface of the films are obtained at different phases of formation.

New Density Functional Approach for Solid-Liquid-Vapor Transitions in Pure Materials

NASA Astrophysics Data System (ADS)

Kocher, Gabriel; Provatas, Nikolas

2015-04-01

A new phase field crystal (PFC) type theory is presented, which accounts for the full spectrum of solid-liquid-vapor phase transitions within the framework of a single density order parameter. Its equilibrium properties show the most quantitative features to date in PFC modeling of pure substances, and full consistency with thermodynamics in pressure-volume-temperature space is demonstrated. A method to control either the volume or the pressure of the system is also introduced. Nonequilibrium simulations show that 2- and 3-phase growth of solid, vapor, and liquid can be achieved, while our formalism also allows for a full range of pressure-induced transformations. This model opens up a new window for the study of pressure driven interactions of condensed phases with vapor, an experimentally relevant paradigm previously missing from phase field crystal theories.

Toughening Mechanisms in Nanolayered MAX Phase Ceramics—A Review

PubMed Central

Chen, Xinhua; Bei, Guoping

2017-01-01

Advanced engineering and functional ceramics are sensitive to damage cracks, which delay the wide applications of these materials in various fields. Ceramic composites with enhanced fracture toughness may trigger a paradigm for design and application of the brittle components. This paper reviews the toughening mechanisms for the nanolayered MAX phase ceramics. The main toughening mechanisms for these ternary compounds were controlled by particle toughening, phase-transformation toughening and fiber-reinforced toughening, as well as texture toughening. Based on the various toughening mechanisms in MAX phase, models of SiC particles and fibers toughening Ti3SiC2 are established to predict and explain the toughening mechanisms. The modeling work provides insights and guidance to fabricate MAX phase-related composites with optimized microstructures in order to achieve the desired mechanical properties required for harsh application environments. PMID:28772723

Relationships Between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Stainless Steel Under Biaxial Loading Conditions: Synchrotron X-ray and Electron Backscatter Diffraction Studies

DOE PAGES

Cakmak, Ercan; Choo, Hahn; Kang, Jun-Yun; ...

2015-02-11

Here we report that the relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a functionmore » of the applied strains. The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.« less

Early diagenesis and recrystallization of bone

NASA Astrophysics Data System (ADS)

Keenan, Sarah W.; Engel, Annette Summers

2017-01-01

One of the most challenging problems in paleobiology is determining how bone transforms from a living tissue into a fossil. The geologic record is replete with vertebrate fossils preserved from a range of depositional environments, including wetland systems. However, thermodynamic models suggest that bone (modeled as hydroxylapatite) is generally unstable in a range of varying geochemical conditions and should readily dissolve if it does not alter to a more thermodynamically stable phase, such as a fluorine-enriched apatite. Here, we assess diagenesis of alligator bone from fleshed, articulated skeletons buried in wetland soils and from de-fleshed bones in experimental mesocosms with and without microbial colonization. When microbial colonization of bone was inhibited, bioapatite recrystallization to a more stable apatite phase occurred after one month of burial. Ca-Fe-phosphate phases in bone developed after several months to years due to ion substitutions from the protonation of the hydroxyl ion. These rapid changes demonstrate a continuum of structural and bonding transformations to bone that have not been observed previously. When bones were directly in contact with sediment and microbial cells, rapid bioerosion and compositional alteration occurred after one week, but slowed after one month because biofilms reduced exposed surfaces and subsequent bioapatite lattice substitutions. Microbial contributions are likely essential in forming stable apatite phases during early diagenesis and for enabling bone preservation and fossilization.

High reliability megawatt transformer/rectifier

NASA Technical Reports Server (NTRS)

Zwass, Samuel; Ashe, Harry; Peters, John W.

1991-01-01

The goal of the two phase program is to develop the technology and design and fabricate ultralightweight high reliability DC to DC converters for space power applications. The converters will operate from a 5000 V dc source and deliver 1 MW of power at 100 kV dc. The power weight density goal is 0.1 kg/kW. The cycle to cycle voltage stability goals was + or - 1 percent RMS. The converter is to operate at an ambient temperature of -40 C with 16 minute power pulses and one hour off time. The uniqueness of the design in Phase 1 resided in the dc switching array which operates the converter at 20 kHz using Hollotron plasma switches along with a specially designed low loss, low leakage inductance and a light weight high voltage transformer. This approach reduced considerably the number of components in the converter thereby increasing the system reliability. To achieve an optimum transformer for this application, the design uses four 25 kV secondary windings to produce the 100 kV dc output, thus reducing the transformer leakage inductance, and the ac voltage stresses. A specially designed insulation system improves the high voltage dielectric withstanding ability and reduces the insulation path thickness thereby reducing the component weight. Tradeoff studies and tests conducted on scaled-down model circuits and using representative coil insulation paths have verified the calculated transformer wave shape parameters and the insulation system safety. In Phase 1 of the program a converter design approach was developed and a preliminary transformer design was completed. A fault control circuit was designed and a thermal profile of the converter was also developed.

Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule

PubMed Central

Politi, Yael; Metzler, Rebecca A.; Abrecht, Mike; Gilbert, Benjamin; Wilt, Fred H.; Sagi, Irit; Addadi, Lia; Weiner, Steve; Gilbert, P. U. P. A.

2008-01-01

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism. PMID:18987314

FAST TRACK COMMUNICATION: Field dependence of temperature induced irreversible transformations of magnetic phases in Pr0.5Ca0.5Mn0.975Al0.025O3 crystalline oxide

NASA Astrophysics Data System (ADS)

Lakhani, Archana; Kushwaha, Pallavi; Rawat, R.; Kumar, Kranti; Banerjee, A.; Chaddah, P.

2010-01-01

Glass-like arrest has recently been reported in various magnetic materials. As in structural glasses, the kinetics of a first order transformation is arrested while retaining the higher entropy phase as a non-ergodic state. We show visual mesoscopic evidence of the irreversible transformation of the arrested antiferromagnetic-insulating phase in Pr0.5Ca0.5Mn0.975Al0.025O3 to its equilibrium ferromagnetic-metallic phase with an isothermal increase of magnetic field, similar to its iso-field transformation on warming. The magnetic field dependence of the non-equilibrium to equilibrium transformation temperature is shown to be governed by Le Chatelier's principle.

Method for distinguishing normal and transformed cells using G1 kinase inhibitors

DOEpatents

Crissman, Harry A.; Gadbois, Donna M.; Tobey, Robert A.; Bradbury, E. Morton

1993-01-01

A G.sub.1 phase kinase inhibitor is applied in a low concentration to a population of normal and transformed mammalian cells. The concentration of G.sub.1 phase kinase inhibitor is selected to reversibly arrest normal mammalian cells in the G.sub.1 cell cycle without arresting growth of transformed cells. The transformed cells may then be selectively identified and/or cloned for research or diagnostic purposes. The transformed cells may also be selectively killed by therapeutic agents that do not affect normal cells in the G.sub.1 phase, suggesting that such G.sub.1 phase kinase inhibitors may form an effective adjuvant for use with chemotherapeutic agents in cancer therapy for optimizing the killing dose of chemotherapeutic agents while minimizing undesirable side effects on normal cells.

Method for distinguishing normal and transformed cells using G1 kinase inhibitors

DOEpatents

Crissman, H.A.; Gadbois, D.M.; Tobey, R.A.; Bradbury, E.M.

1993-02-09

A G[sub 1] phase kinase inhibitor is applied in a low concentration to a population of normal and transformed mammalian cells. The concentration of G[sub 1] phase kinase inhibitor is selected to reversibly arrest normal mammalian cells in the G[sub 1] cell cycle without arresting growth of transformed cells. The transformed cells may then be selectively identified and/or cloned for research or diagnostic purposes. The transformed cells may also be selectively killed by therapeutic agents that do not affect normal cells in the G[sub 1] phase, suggesting that such G[sub 1] phase kinase inhibitors may form an effective adjuvant for use with chemotherapeutic agents in cancer therapy for optimizing the killing dose of chemotherapeutic agents while minimizing undesirable side effects on normal cells.

Rapid calculation of acoustic fields from arbitrary continuous-wave sources.

PubMed

Treeby, Bradley E; Budisky, Jakub; Wise, Elliott S; Jaros, Jiri; Cox, B T

2018-01-01

A Green's function solution is derived for calculating the acoustic field generated by phased array transducers of arbitrary shape when driven by a single frequency continuous wave excitation with spatially varying amplitude and phase. The solution is based on the Green's function for the homogeneous wave equation expressed in the spatial frequency domain or k-space. The temporal convolution integral is solved analytically, and the remaining integrals are expressed in the form of the spatial Fourier transform. This allows the acoustic pressure for all spatial positions to be calculated in a single step using two fast Fourier transforms. The model is demonstrated through several numerical examples, including single element rectangular and spherically focused bowl transducers, and multi-element linear and hemispherical arrays.

Iterative-Transform Phase Retrieval Using Adaptive Diversity

NASA Technical Reports Server (NTRS)

Dean, Bruce H.

2007-01-01

A phase-diverse iterative-transform phase-retrieval algorithm enables high spatial-frequency, high-dynamic-range, image-based wavefront sensing. [The terms phase-diverse, phase retrieval, image-based, and wavefront sensing are defined in the first of the two immediately preceding articles, Broadband Phase Retrieval for Image-Based Wavefront Sensing (GSC-14899-1).] As described below, no prior phase-retrieval algorithm has offered both high dynamic range and the capability to recover high spatial-frequency components. Each of the previously developed image-based phase-retrieval techniques can be classified into one of two categories: iterative transform or parametric. Among the modifications of the original iterative-transform approach has been the introduction of a defocus diversity function (also defined in the cited companion article). Modifications of the original parametric approach have included minimizing alternative objective functions as well as implementing a variety of nonlinear optimization methods. The iterative-transform approach offers the advantage of ability to recover low, middle, and high spatial frequencies, but has disadvantage of having a limited dynamic range to one wavelength or less. In contrast, parametric phase retrieval offers the advantage of high dynamic range, but is poorly suited for recovering higher spatial frequency aberrations. The present phase-diverse iterative transform phase-retrieval algorithm offers both the high-spatial-frequency capability of the iterative-transform approach and the high dynamic range of parametric phase-recovery techniques. In implementation, this is a focus-diverse iterative-transform phaseretrieval algorithm that incorporates an adaptive diversity function, which makes it possible to avoid phase unwrapping while preserving high-spatial-frequency recovery. The algorithm includes an inner and an outer loop (see figure). An initial estimate of phase is used to start the algorithm on the inner loop, wherein multiple intensity images are processed, each using a different defocus value. The processing is done by an iterative-transform method, yielding individual phase estimates corresponding to each image of the defocus-diversity data set. These individual phase estimates are combined in a weighted average to form a new phase estimate, which serves as the initial phase estimate for either the next iteration of the iterative-transform method or, if the maximum number of iterations has been reached, for the next several steps, which constitute the outerloop portion of the algorithm. The details of the next several steps must be omitted here for the sake of brevity. The overall effect of these steps is to adaptively update the diversity defocus values according to recovery of global defocus in the phase estimate. Aberration recovery varies with differing amounts as the amount of diversity defocus is updated in each image; thus, feedback is incorporated into the recovery process. This process is iterated until the global defocus error is driven to zero during the recovery process. The amplitude of aberration may far exceed one wavelength after completion of the inner-loop portion of the algorithm, and the classical iterative transform method does not, by itself, enable recovery of multi-wavelength aberrations. Hence, in the absence of a means of off-loading the multi-wavelength portion of the aberration, the algorithm would produce a wrapped phase map. However, a special aberration-fitting procedure can be applied to the wrapped phase data to transfer at least some portion of the multi-wavelength aberration to the diversity function, wherein the data are treated as known phase values. In this way, a multiwavelength aberration can be recovered incrementally by successively applying the aberration-fitting procedure to intermediate wrapped phase maps. During recovery, as more of the aberration is transferred to the diversity function following successive iterations around the ter loop, the estimated phase ceases to wrap in places where the aberration values become incorporated as part of the diversity function. As a result, as the aberration content is transferred to the diversity function, the phase estimate resembles that of a reference flat.

Optimization of the transition path of the head hardening with using the genetic algorithms

NASA Astrophysics Data System (ADS)

Wróbel, Joanna; Kulawik, Adam

2016-06-01

An automated method of choice of the transition path of the head hardening in heat treatment process for the plane steel element is proposed in this communication. This method determines the points on the path of moving heat source using the genetic algorithms. The fitness function of the used algorithm is determined on the basis of effective stresses and yield point depending on the phase composition. The path of the hardening tool and also the area of the heat affected zone is determined on the basis of obtained points. A numerical model of thermal phenomena, phase transformations in the solid state and mechanical phenomena for the hardening process is implemented in order to verify the presented method. A finite element method (FEM) was used for solving the heat transfer equation and getting required temperature fields. The moving heat source is modeled with a Gaussian distribution and the water cooling is also included. The macroscopic model based on the analysis of the CCT and CHT diagrams of the medium-carbon steel is used to determine the phase transformations in the solid state. A finite element method is also used for solving the equilibrium equations giving us the stress field. The thermal and structural strains are taken into account in the constitutive relations.

Universality class of non-Fermi-liquid behavior in mixed-valence systems

NASA Astrophysics Data System (ADS)

Zhang, Guang-Ming; Su, Zhao-Bin; Yu, Lu

1996-01-01

A generalized Anderson single-impurity model with off-site Coulomb interactions is derived from the extended three-band Hubbard model, originally proposed to describe the physics of the copper oxides. Using the Abelian bosonization technique and canonical transformations, an effective Hamiltonian is derived in the strong-coupling limit, which is essentially analogous to the Toulouse limit of the ordinary Kondo problem. In this limit, the effective Hamiltonian can be exactly solved, with a mixed-valence quantum critical point separating two different Fermi-liquid phases, i.e., the Kondo phase and the empty orbital phase. In the mixed-valence quantum critical regime, the local moment is only partially quenched and x-ray edge singularities are generated. Around the quantum critical point, a type of non-Fermi-liquid behavior is predicted with an extra specific heat Cimp~T1/4 and a singular spin susceptibility χimp~T-3/4. At the same time, the effective Hamiltonian under single occupancy is transformed into a resonant-level model, from which the correct Kondo physical properties (specific heat, spin susceptibility, and an enhanced Wilson ratio) are easily rederived. Finally, a brief discussion is given to relate these theoretical results to observations in UPdxCu5-x (x=1,1.5) alloys, which show single-impurity critical behavior consistent with our predictions.

Understanding metastable phase transformation during crystallization of RDX, HMX and CL-20: experimental and DFT studies.

PubMed

Ghosh, Mrinal; Banerjee, Shaibal; Shafeeuulla Khan, Md Abdul; Sikder, Nirmala; Sikder, Arun Kanti

2016-09-14

Multiphase growth during crystallization severely affects deliverable output of explosive materials. Appearance and incomplete transformation of metastable phases are a major source of polymorphic impurities. This article presents a methodical and molecular level understanding of the metastable phase transformation mechanism during crystallization of cyclic nitramine explosives, viz. RDX, HMX and CL-20. Instantaneous reverse precipitation yielded metastable γ-HMX and β-CL-20 which undergo solution mediated transformation to the respective thermodynamic forms, β-HMX and ε-CL-20, following 'Ostwald's rule of stages'. However, no metastable phase, anticipated as β-RDX, was evidenced during precipitation of RDX, which rather directly yielded the thermodynamically stable α-phase. The γ→β-HMX and β→ε-CL-20 transformations took 20 and 60 minutes respectively, whereas formation of α-RDX was instantaneous. Density functional calculations were employed to identify the possible transition state conformations and to obtain activation barriers for transformations at wB97XD/6-311++G(d,p)(IEFPCM)//B3LYP/6-311G(d,p) level of theory. The computed activation barriers and lattice energies responsible for transformation of RDX, HMX and CL-20 metastable phases to thermodynamic ones conspicuously supported the experimentally observed order of phase stability. This precise result facilitated an understanding of the occurrence of a relatively more sensitive and less dense β-CL-20 phase in TNT based melt-cast explosive compositions, a persistent and critical problem unanswered in the literature. The crystalline material recovered from such compositions revealed a mixture of β- and ε-CL-20. However, similar compositions of RDX and HMX never showed any metastable phase. The relatively long stability with the highest activation barrier is believed to restrict complete β→ε-CL-20 transformation during processing. Therefore a method is suggested to overcome this issue.

Phase synchronization based on a Dual-Tree Complex Wavelet Transform

NASA Astrophysics Data System (ADS)

Ferreira, Maria Teodora; Domingues, Margarete Oliveira; Macau, Elbert E. N.

2016-11-01

In this work, we show the applicability of our Discrete Complex Wavelet Approach (DCWA) to verify the phenomenon of phase synchronization transition in two coupled chaotic Lorenz systems. DCWA is based on the phase assignment from complex wavelet coefficients obtained by using a Dual-Tree Complex Wavelet Transform (DT-CWT). We analyzed two coupled chaotic Lorenz systems, aiming to detect the transition from non-phase synchronization to phase synchronization. In addition, we check how good is the method in detecting periods of 2π phase-slips. In all experiments, DCWA is compared with classical phase detection methods such as the ones based on arctangent and Hilbert transform showing a much better performance.

Analysis on ultrashort-pulse laser ablation for nanoscale film of ceramics

NASA Astrophysics Data System (ADS)

Ho, C. Y.; Tsai, Y. H.; Chiou, Y. J.

2017-06-01

This paper uses the dual-phase-lag model to study the ablation characteristics of femtosecond laser processing for nanometer-sized ceramic films. In ultrafast process and ultrasmall size where the two lags occur, a dual-phase-lag can be applied to analyse the ablation characteristics of femtosecond laser processing for materials. In this work, the ablation rates of nanometer-sized lead zirconate titanate (PZT) ceramics are investigated using a dual-phase-lag and the model is solved by Laplace transform method. The results obtained from this work are validated by the available experimental data. The effects of material thermal properties on the ablation characteristics of femtosecond laser processing for ceramics are also discussed.

Quantum phase transition and quench dynamics in the anisotropic Rabi model

NASA Astrophysics Data System (ADS)

Shen, Li-Tuo; Yang, Zhen-Biao; Wu, Huai-Zhi; Zheng, Shi-Biao

2017-01-01

We investigate the quantum phase transition (QPT) and quench dynamics in the anisotropic Rabi model when the ratio of the qubit transition frequency to the oscillator frequency approaches infinity. Based on the Schrieffer-Wolff transformation, we find an anti-Hermitian operator that maps the original Hamiltonian into a one-dimensional oscillator Hamiltonian within the spin-down subspace. We analytically derive the eigenenergy and eigenstate of the normal and superradiant phases and demonstrate that the system undergoes a second-order quantum phase transition at a critical border. The critical border is a straight line in a two-dimensional parameter space which essentially extends the dimensionality of QPT in the Rabi model. By combining the Kibble-Zurek mechanism and the adiabatic dynamics method, we find that the residual energy vanishes as the quench time tends to zero, which is a sharp contrast to the universal scaling where the residual energy diverges in the same limit.

M3FT-15OR0202212: SUBMIT SUMMARY REPORT ON THERMODYNAMIC EXPERIMENT AND MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

McMurray, Jake W.; Brese, Robert G.; Silva, Chinthaka M.

2015-09-01

Modeling the behavior of nuclear fuel with a physics-based approach uses thermodynamics for key inputs such as chemical potentials and thermal properties for phase transformation, microstructure evolution, and continuum transport simulations. Many of the lanthanide (Ln) elements and Y are high-yield fission products. The U-Y-O and U-Ln-O ternaries are therefore key subsystems of multi-component high-burnup fuel. These elements dissolve in the dominant urania fluorite phase affecting many of its properties. This work reports on an effort to assess the thermodynamics of the U-Pr-O and U-Y-O systems using the CALPHAD (CALculation of PHase Diagrams) method. The models developed within this frameworkmore » are capable of being combined and extended to include additional actinides and fission products allowing calculation of the phase equilibria, thermochemical and material properties of multicomponent fuel with burnup.« less

Nanoscale phase transition behavior of shape memory alloys — closed form solution of 1D effective modelling

NASA Astrophysics Data System (ADS)

Li, M. P.; Sun, Q. P.

2018-01-01

We investigate the roles of grain size (lg) and grain boundary thickness (lb) on the stress-induced phase transition (PT) behaviors of nanocrystalline shape memory alloys (SMAs) by using a Core-shell type "crystallite-amorphous composite" model. A non-dimensionalized length scale lbarg(=lg /lb) is identified as the governing parameter which is indicative of the energy competition between the crystallite and the grain boundary. Closed form analytical solutions of a reduced effective 1D model with embedded microstructure length scales of lg and lb are presented in this paper. It is shown that, with lbarg reduction, the energy of the elastic non-transformable grain boundary will gradually become dominant in the phase transition process, and eventually bring fundamental changes of the deformation behaviors: breakdown of two-phase coexistence and vanishing of superelastic hysteresis. The predictions are supported by experimental data of nanocrystalline NiTi SMAs.

First-principles study of the α-ω phase transformation in Ti and Zr coupled to slip modes

NASA Astrophysics Data System (ADS)

Kumar, Anil; Bronkhorst, Curt A.; Lookman, Turab

2018-01-01

We present first-principles density functional theory calculations to study the α-ω phase transformation in Ti and Zr and its coupling to slip modes of the two phases. We first investigate the relative energetics of all possible slip systems in the α and ω phases to predict the dominant slip system that is activated during a plastic deformation under an arbitrary load. Using this and the crystallographic orientation relationships between α and ω phases, we construct low energy α/ω interfaces and study the energetics of the slip system at the interface between α and ω to compare to the slip systems in the bulk phases. We find that for a particular crystallographic orientation relationship, where (basal) α∥(prismatic-II)ω , and [a] α∥[c] ω , the slip at the interface is preferred compared to its bulk counterparts. This implies that the plastically deformed α/ω phase with this orientation relationship prefers to retain the interface (or coexisting phases) than transforming back to the pure phase after unloading. This is consistent with the observation that the ω-phase is retained in samples loaded in flyer plate experiments or under high-pressure torsion. Furthermore, calculation of the energy barrier for α to ω phase transformation as a function of glide at the α/ω interface shows significant coupling between the α-ω phase transformation and slip modes in Ti and Zr.

76 FR 52945 - Notice of Supplemental Filing; International Transmission Company, d/b/a ITC Transmission.

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-24

... replace a failed 675-MVA transformer with two 700-MVA phase-shifting transformers connected in series at... facilities with the installation of the new transformers, also known as phase angle regulators (PARs). On... further notice so that the transformers can be placed into service and benefits from controlling the Lake...

Phase-Field Modeling of Sigma-Phase Precipitation in 25Cr7Ni4Mo Duplex Stainless Steel

NASA Astrophysics Data System (ADS)

Malik, Amer; Odqvist, Joakim; Höglund, Lars; Hertzman, Staffan; Ågren, John

2017-10-01

Phase-field modeling is used to simulate the formation of sigma phase in a model alloy mimicking a commercial super duplex stainless steel (SDSS) alloy, in order to study precipitation and growth of sigma phase under linear continuous cooling. The so-called Warren-Boettinger-McFadden (WBM) model is used to build the basis of the multiphase and multicomponent phase-field model. The thermodynamic inconsistency at the multiple junctions associated with the multiphase formulation of the WBM model is resolved by means of a numerical Cut-off algorithm. To make realistic simulations, all the kinetic and the thermodynamic quantities are derived from the CALPHAD databases at each numerical time step, using Thermo-Calc and TQ-Interface. The credibility of the phase-field model is verified by comparing the results from the phase-field simulations with the corresponding DICTRA simulations and also with the empirical data. 2D phase-field simulations are performed for three different cooling rates in two different initial microstructures. A simple model for the nucleation of sigma phase is also implemented in the first case. Simulation results show that the precipitation of sigma phase is characterized by the accumulation of Cr and Mo at the austenite-ferrite and the ferrite-ferrite boundaries. Moreover, it is observed that a slow cooling rate promotes the growth of sigma phase, while a higher cooling rate restricts it, eventually preserving the duplex structure in the SDSS alloy. Results from the phase-field simulations are also compared quantitatively with the experiments, performed on a commercial 2507 SDSS alloy. It is found that overall, the predicted morphological features of the transformation and the composition profiles show good conformity with the empirical data.

Phase retrieval of singular scalar light fields using a two-dimensional directional wavelet transform and a spatial carrier.

PubMed

Federico, Alejandro; Kaufmann, Guillermo H

2008-10-01

We evaluate a method based on the two-dimensional directional wavelet transform and the introduction of a spatial carrier to retrieve optical phase distributions in singular scalar light fields. The performance of the proposed phase-retrieval method is compared with an approach based on Fourier transform. The advantages and limitations of the proposed method are discussed.

Magnetic Field-Induced Phase Transformation in Magnetic Shape Memory Alloys with High Actuation Stress and Work Output

DTIC Science & Technology

2010-05-03

Mechanisms for Advanced Properties in Phase Transforming Materials , Materials Science & Technology 2009 Conference, October 25-29, 2009, Pittsburgh, PA...Advanced Properties in Phase Transforming Materials , Materials Science & Technology 2009 Conference, October 25-29, 2009, Pittsburgh, PA, 2009. 11...observed materials behavior. Indeed, measured materials properties were found not to be the exact indication of the materials real response

The role of microstructure and phase distribution in the failure mechanisms and life prediction model for PSZ coatings

NASA Technical Reports Server (NTRS)

Sisson, R. D., Jr.; Sone, Ichiro; Biederman, R. R.

1985-01-01

Partially Stabilized Zirconia (PSZ) may become widely used for Thermal Barrier Coatings (TBC). Failure of these coatings can occur due to thermal fatigue in oxidizing atmospheres. The failure is due to the strains that develop due to thermal gradients, differences in thermal expansion coefficients, and oxidation of the bond coating. The role of microstructure and the cubic, tetragonal, and monoclinic phase distribution in the strain development and subsequent failure will be discussed. An X-ray diffraction technique for accurate determination of the fraction of each phase in PSZ will be applied to understanding the phase transformations and strain development. These results will be discussed in terms of developing a model for life prediction in PSZ coatings during thermal cycling.

Constitutive Modeling of the Dynamic-Tensile-Extrusion Test of PTFE

NASA Astrophysics Data System (ADS)

Resnyansky, Anatoly; Brown, Eric; Trujillo, Carl; Gray, George

2015-06-01

Use of polymers in the defence, aerospace and industrial application at extreme conditions makes prediction of behaviour of these materials very important. Crucial to this is knowledge of the physical damage response in association with the phase transformations during the loading and the ability to predict this via multi-phase simulation taking the thermodynamical non-equilibrium and strain rate sensitivity into account. The current work analyses Dynamic-Tensile-Extrusion (DTE) experiments on polytetrafluoroethylene (PTFE). In particular, the phase transition during the loading with subsequent tension are analysed using a two-phase rate sensitive material model implemented in the CTH hydrocode and the calculations are compared with experimental high-speed photography. The damage patterns and their link with the change of loading modes are analysed numerically and are correlated to the test observations.

Thermally induced phase transformation in multi-phase iron oxide nanoparticles on vacuum annealing

NASA Astrophysics Data System (ADS)

Anupama, A. V.; Keune, W.; Sahoo, B.

2017-10-01

The evolution of magnetic phases in multi-phase iron oxide nanoparticles, synthesized via the transferred arc plasma induced gas phase condensation method, was investigated by X-ray diffraction, vibrating sample magnetometry and 57Fe Mössbauer spectroscopy. The particles are proposed to be consisting of three different iron oxide phases: α-Fe2O3, γ-Fe2O3 and Fe3O4. These nanoparticles were exposed to high temperature (∼935 K) under vacuum (10-3 mbar He pressure), and the thermally induced phase transformations were investigated. The Rietveld refinement of the X-ray diffraction data corroborates the least-squares fitting of the transmission Mössbauer spectra in confirming the presence of Fe3O4, γ-Fe2O3 and α-Fe2O3 phases before the thermal treatment, while only Fe3O4 and α-Fe2O3 phases exist after thermal treatment. On thermal annealing in vacuum, conversion from γ-Fe2O3 to Fe3O4 and α-Fe2O3 was observed. Interestingly, we have observed a phase transformation occurring in the temperature range ∼498 K-538 K, which is strikingly lower than the phase transformation temperature of γ-Fe2O3 to α-Fe2O3 (573-623 K) in air. Combining the results of Rietveld refinement of X-ray diffraction patterns and Mössbauer spectroscopy, we have attributed this phase transformation to the phase conversion of a metastable "defected and strained" d-Fe3O4 phase, present in the as-prepared sample, to the α-Fe2O3 phase. Stabilization of the phases by controlling the phase transformations during the use of different iron-oxide nanoparticles is the key factor to select them for a particular application. Our investigation provides insight into the effect of temperature and chemical nature of the environment, which are the primary factors governing the phase stability, suitability and longevity of the iron oxide nanomaterials prepared by the gas-phase condensation method for various applications.

Solidification and solid-state transformation sciences in metals additive manufacturing

DOE PAGES

Kirka, Michael M.; Nandwana, Peeyush; Lee, Yousub; ...

2017-02-11

Additive manufacturing (AM) of metals is rapidly emerging as an established manufacturing process for metal components. Unlike traditional metals fabrication processes, metals fabricated via AM undergo localized thermal cycles during fabrication. As a result, AM presents the opportunity to control the liquid-solid phase transformation, i.e. material texture. But, thermal cycling presents challenges from the standpoint of solid-solid phase transformations. We will discuss the opportunities and challenges in metals AM in the context of texture control and associated solid-solid phase transformations in Ti-6Al-4V and Inconel 718.

Optical joint transform correlation on the DMD. [deformable mirror device

NASA Technical Reports Server (NTRS)

Knopp, Jerome; Juday, Richard D.

1989-01-01

Initial experimental investigation of the deformable mirror device (DMD) in a joint optical transform correlation is reported. The inverted cloverleaf version of the DMD, in which form the DMD is phase-mostly but of limited phase range, is used. Binarized joint Fourier transforms were calculated for similar and dissimilar objects and written onto the DMD. Inverse Fourier transform was done in a diffraction order for which the DMD shows phase-mostly modulation. Matched test objects produced sharp correlation, distinct objects did not. Further studies are warranted and they are outlined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hou, Huilong; Hamilton, Reginald F., E-mail: rfhamilton@psu.edu; Horn, Mark W.

NiTi shape memory alloy (SMA) thin films were fabricated using biased target ion beam deposition (BTIBD), which is a new technique for fabricating submicrometer-thick SMA thin films, and the capacity to exhibit shape memory behavior was investigated. The thermally induced shape memory effect (SME) was studied using the wafer curvature method to report the stress-temperature response. The films exhibited the SME in a temperature range above room temperature and a narrow thermal hysteresis with respect to previous reports. To confirm the underlying phase transformation, in situ x-ray diffraction was carried out in the corresponding phase transformation temperature range. The B2more » to R-phase martensitic transformation occurs, and the R-phase transformation is stable with respect to the expected conversion to the B19′ martensite phase. The narrow hysteresis and stable R-phase are rationalized in terms of the unique properties of the BTIBD technique.« less

Applications of wavelets in interferometry and artificial vision

NASA Astrophysics Data System (ADS)

Escalona Z., Rafael A.

2001-08-01

In this paper we present a different point of view of phase measurements performed in interferometry, image processing and intelligent vision using Wavelet Transform. In standard and white-light interferometry, the phase function is retrieved by using phase-shifting, Fourier-Transform, cosinus-inversion and other known algorithms. Our novel technique presented here is faster, robust and shows excellent accuracy in phase determinations. Finally, in our second application, fringes are no more generate by some light interaction but result from the observation of adapted strip set patterns directly printed on the target of interest. The moving target is simply observed by a conventional vision system and usual phase computation algorithms are adapted to an image processing by wavelet transform, in order to sense target position and displacements with a high accuracy. In general, we have determined that wavelet transform presents properties of robustness, relative speed of calculus and very high accuracy in phase computations.

Elucidating the Role of Electron Shuttles in Reductive Transformations in Anaerobic Sediments

EPA Science Inventory

Model studies have demonstrated that electron shuttles (ES) such as dissolved organic matter (DOM) can participate in the reduction of organic contaminants; however, much uncertainty exists concerning the significance of this solution phase pathway for contaminant reduction in na...

Effect of impurity on high pressure behavior of nano indium titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chitnis, Abhishek, E-mail: abhishekchitnis87@gmail.com; Garg, Nandini; Mishra, A. K.

2015-06-24

Angle dispersive x-ray diffraction studies were carried out on a mixture of nano particles of indium titanate, indium oxide, and disordered TiO{sub 2} upto pressures of ∼ 45 GPa. Our studies show that indium titanate undergoes a partial decomposition to its constituent high pressure oxides. However, concomitantly a very small fraction of indium titanate transforms to a denser phase at ∼ 27.5 GPa. This transformation to new phase was found to be irreversible. At this pressure even cubic In{sub 2}O{sub 3} transformed to the In{sub 2}O{sub 3} (II) (iso-structural to Rh{sub 2}O{sub 3} (II)) phase, without any signature of themore » intermediate corundum phase. The high pressure In{sub 2}O{sub 3} (II) phase transforms to the corundum structure on release of pressure. These studies indicate that the presence of a large fraction of seed impurities could have facilitated the decomposition of indium titanate into its constituent oxides at the cost of its incomplete transformation to the high pressure denser phase.« less

Smart vortex generator transformed by change in ambient temperature and aerodynamic force

NASA Astrophysics Data System (ADS)

Ikeda, Tadashige; Masuda, Shinya; Ueda, Tetsuhiko

2007-04-01

A Smart Vortex Generator (SVG) concept has been proposed, where the SVG is autonomously transformed between an upright vortex-generating position in take-off and landing and a flat drag-reducing position in a cruise. This SVG is made of a Shape Memory Alloy (SMA), which is in the austenite phase and memorizes the upright position at high temperatures of the take-off and landing. At low temperatures during ascent the SVG is transformed into a martensite phase, and it lies flat against a base structure due to external or/and internal forces. In this paper, we examine whether the SVG can be transformed into the drag-reducing position by an aerodynamic force. To this end, numerical simulations are carried out with a simple line element model. The aerodynamic force applied on the SVG is calculated by a commercial CFD program. Result reveals that this SVG can be transformed from the upright vortex-generating position into the drag-reducing position by just an airplane climbing, and vice versa, if the SMA applied to the SVG has the two-way shape memory effect. If the SMA has the one-way shape memory effect, it is necessary to reduce the stiffness of the SVG or/and use a counter spring.

Second amorphous-to-crystalline phase transformation in Cu(60)Ti(20)Zr(20) bulk metallic glass.

PubMed

Cao, Q P; Li, J F; Zhang, P N; Horsewell, A; Jiang, J Z; Zhou, Y H

2007-06-20

The second amorphous-to-crystalline phase transformation in Cu(60)Ti(20)Zr(20) bulk metallic glass was investigated by differential scanning calorimetry and x-ray diffractometry. The difference of the Gibbs free energies between the amorphous phase and the crystalline products during the transformation is estimated to be about 2.46 kJ mol(-1) at 753 K, much smaller than the 61 kJ mol(-1) obtained assuming that it is a polymorphic transformation. It was revealed that the phase transformation occurs through a eutectic crystallization of Cu(51)Zr(14) and Cu(2)TiZr, having an effective activation energy of the order of 400 kJ mol(-1). The average Avrami exponent n is about 2.0, indicating that the crystallization is diffusion controlled.

Broadband CARS spectral phase retrieval using a time-domain Kramers–Kronig transform

PubMed Central

Liu, Yuexin; Lee, Young Jong; Cicerone, Marcus T.

2014-01-01

We describe a closed-form approach for performing a Kramers–Kronig (KK) transform that can be used to rapidly and reliably retrieve the phase, and thus the resonant imaginary component, from a broadband coherent anti-Stokes Raman scattering (CARS) spectrum with a nonflat background. In this approach we transform the frequency-domain data to the time domain, perform an operation that ensures a causality criterion is met, then transform back to the frequency domain. The fact that this method handles causality in the time domain allows us to conveniently account for spectrally varying nonresonant background from CARS as a response function with a finite rise time. A phase error accompanies KK transform of data with finite frequency range. In examples shown here, that phase error leads to small (<1%) errors in the retrieved resonant spectra. PMID:19412273

Laterally structured ripple and square phases with one and two dimensional thickness modulations in a model bilayer system.

PubMed

Debnath, Ananya; Thakkar, Foram M; Maiti, Prabal K; Kumaran, V; Ayappa, K G

2014-10-14

Molecular dynamics simulations of bilayers in a surfactant/co-surfactant/water system with explicit solvent molecules show formation of topologically distinct gel phases depending upon the bilayer composition. At low temperatures, the bilayers transform from the tilted gel phase, Lβ', to the one dimensional (1D) rippled, Pβ' phase as the surfactant concentration is increased. More interestingly, we observe a two dimensional (2D) square phase at higher surfactant concentration which, upon heating, transforms to the gel Lβ' phase. The thickness modulations in the 1D rippled and square phases are asymmetric in two surfactant leaflets and the bilayer thickness varies by a factor of ∼2 between maximum and minimum. The 1D ripple consists of a thinner interdigitated region of smaller extent alternating with a thicker non-interdigitated region. The 2D ripple phase is made up of two superimposed square lattices of maximum and minimum thicknesses with molecules of high tilt forming a square lattice translated from the lattice formed with the thickness minima. Using Voronoi diagrams we analyze the intricate interplay between the area-per-head-group, height modulations and chain tilt for the different ripple symmetries. Our simulations indicate that composition plays an important role in controlling the formation of low temperature gel phase symmetries and rippling accommodates the increased area-per-head-group of the surfactant molecules.

Mechanical properties and microstructural change of W–Y2O3 alloy under helium irradiation

PubMed Central

Tan, Xiaoyue; Luo, Laima; Chen, Hongyu; Zhu, Xiaoyong; Zan, Xiang; Luo, Guangnan; Chen, Junling; Li, Ping; Cheng, Jigui; Liu, Dongping; Wu, Yucheng

2015-01-01

A wet-chemical method combined with spark plasma sintering was used to prepare a W–Y2O3 alloy. High-temperature tensile tests and nano-indentation microhardness tests were used to characterize the mechanical properties of the alloy. After He-ion irradiation, fuzz and He bubbles were observed on the irradiated surface. The irradiation embrittlement was reflected by the crack indentations formed during the microhardness tests. A phase transformation from α-W to γ-W was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Polycrystallization and amorphization were also observed in the irradiation damage layer. The W materials tended to exhibit lattice distortion, amorphization, polycrystallization and phase transformation under He-ion irradiation. The transformation mechanism predicted by the atomic lattice model was consistent with the available experimental observations. These findings clarify the mechanism of the structural transition of W under ion irradiation and provide a clue for identifying materials with greater irradiation resistance. PMID:26227480

Dopant concentration dependent growth of Fe:ZnO nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahai, Anshuman; Goswami, Navendu, E-mail: navendugoswami@gmail.com

2016-05-23

Systematic investigations of structural properties of 1-10% Fe doped ZnO nanostructure (Fe:ZnO NS) prepared via chemical precipitation method have been reported. Structural properties were probed thoroughly employing scanning electron microscope (SEM) and transmission electron microscope (TEM), energy dispersive X-ray (EDAX) analysis and X-ray diffraction (XRD). Morphological transformation of nanostructures (NS) with Fe incorporation is evident in SEM/TEM images. Nanoparticles (NP) obtained with 1% Fe, evolve to nanorods (NR) for 3% Fe; NR transform to nanocones (NC) (for 5% and 7% Fe) and finally NC transform to nanoflakes (NF) at 10% Fe. Morover, primary phase of Zn{sub 1-x}Fe{sub x}O along withmore » secondary phases of ZnFe{sub 2}O{sub 4} and Fe{sub 2}O{sub 3} were also revealed through XRD measurements. Based on collective XRD, SEM, TEM, and EDAX interpretations, a model for morphological evolution of NS was proposed and the pivotal role of Fe dopant was deciphered.« less

Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

NASA Astrophysics Data System (ADS)

Niemann, R.; Hahn, S.; Diestel, A.; Backen, A.; Schultz, L.; Nielsch, K.; Wagner, M. F.-X.; Fähler, S.

2016-06-01

Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

The self-healing of defects induced by the hydriding phase transformation in palladium nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulvestad, A.; Yau, A.

Nanosizing can dramatically alter material properties by enhancing surface thermodynamic contributions, shortening diffusion lengths, and increasing the number of catalytically active sites per unit volume. These mechanisms have been used to explain the improved properties of catalysts, battery materials, plasmonic materials, etc. Here we show that Pd nanoparticles also have the ability to self-heal defects in their crystal structures. Using Bragg coherent diffractive imaging, we image dislocations nucleated deep in a Pd nanoparticle during the forward hydriding phase transformation that heal during the reverse transformation, despite the region surrounding the dislocations remaining in the hydrogen-poor phase. We show that defectivemore » Pd nanoparticles exhibit sloped isotherms, indicating that defects act as additional barriers to the phase transformation. Our results resolve the formation and healing of structural defects during phase transformations at the single nanoparticle level and offer an additional perspective as to how and why nanoparticles differ from their bulk counterparts.« less

Analysis on Behaviour of Wavelet Coefficient during Fault Occurrence in Transformer

NASA Astrophysics Data System (ADS)

Sreewirote, Bancha; Ngaopitakkul, Atthapol

2018-03-01

The protection system for transformer has play significant role in avoiding severe damage to equipment when disturbance occur and ensure overall system reliability. One of the methodology that widely used in protection scheme and algorithm is discrete wavelet transform. However, characteristic of coefficient under fault condition must be analyzed to ensure its effectiveness. So, this paper proposed study and analysis on wavelet coefficient characteristic when fault occur in transformer in both high- and low-frequency component from discrete wavelet transform. The effect of internal and external fault on wavelet coefficient of both fault and normal phase has been taken into consideration. The fault signal has been simulate using transmission connected to transformer experimental setup on laboratory level that modelled after actual system. The result in term of wavelet coefficient shown a clearly differentiate between wavelet characteristic in both high and low frequency component that can be used to further design and improve detection and classification algorithm that based on discrete wavelet transform methodology in the future.

Single and two-shot quantitative phase imaging using Hilbert-Huang Transform based fringe pattern analysis

NASA Astrophysics Data System (ADS)

Trusiak, Maciej; Micó, Vicente; Patorski, Krzysztof; García-Monreal, Javier; Sluzewski, Lukasz; Ferreira, Carlos

2016-08-01

In this contribution we propose two Hilbert-Huang Transform based algorithms for fast and accurate single-shot and two-shot quantitative phase imaging applicable in both on-axis and off-axis configurations. In the first scheme a single fringe pattern containing information about biological phase-sample under study is adaptively pre-filtered using empirical mode decomposition based approach. Further it is phase demodulated by the Hilbert Spiral Transform aided by the Principal Component Analysis for the local fringe orientation estimation. Orientation calculation enables closed fringes efficient analysis and can be avoided using arbitrary phase-shifted two-shot Gram-Schmidt Orthonormalization scheme aided by Hilbert-Huang Transform pre-filtering. This two-shot approach is a trade-off between single-frame and temporal phase shifting demodulation. Robustness of the proposed techniques is corroborated using experimental digital holographic microscopy studies of polystyrene micro-beads and red blood cells. Both algorithms compare favorably with the temporal phase shifting scheme which is used as a reference method.

76 FR 59668 - Notice of Extension of Comment Period; International Transmission Company, d/b/a ITC Transmission

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-27

... transformer with two 700-MVA phase-shifting transformers connected in series at ITC's Bunce Creek Station in... installation of the new transformers, also known as phase angle regulators (PARs). On August 9, 2011, DOE... further notice so that the transformers can be placed into service and benefits from controlling the Lake...

Ion-beam-induced magnetic transformation of CO-stabilized fcc Fe films on Cu(100)

NASA Astrophysics Data System (ADS)

Shah Zaman, Sameena; Oßmer, Hinnerk; Jonner, Jakub; Novotný, Zbyněk; Buchsbaum, Andreas; Schmid, Michael; Varga, Peter

2010-12-01

We have grown 22-ML-thick Fe films on a Cu(100) single crystal. The films were stabilized in the face-centered-cubic (fcc) γ phase by adsorption of carbon monoxide during growth, preventing the transformation to the body-centered-cubic (bcc) α phase. A structural transformation of these films from fcc to bcc can be induced by Ar+ ion irradiation. Scanning-tunneling microscopy images show the nucleation of bcc crystallites, which grow with increasing Ar+ ion dose and eventually result in complete transformation of the film to bcc. Surface magneto-optic Kerr effect measurements confirm the transformation of the Fe film from paramagnetic (fcc) to ferromagnetic (bcc) with an in-plane easy axis. The transformation can also be observed by low-energy electron diffraction. We find only very few nucleation sites of the bcc phase and argue that nucleation of the bcc phase happens under special circumstances during resolidification of the molten iron in the thermal spike after ion impact. Intermixing with the Cu substrate impedes the transformation. We also demonstrate the transformation of films coated with Au to protect them from oxidation at ambient conditions.

Insight into the Effects of Reinforcement Shape on Achieving Continuous Martensite Transformation in Phase Transforming Matrix Composites

NASA Astrophysics Data System (ADS)

Zhang, Xudong; Ren, Junqiang; Wang, Xiaofei; Zong, Hongxiang; Cui, Lishan; Ding, Xiangdong

2017-12-01

A continuous martensite transformation is indispensable for achieving large linear superelasticity and low modulus in phase transforming metal-based composites. However, determining how to accurately condition the residual martensite in a shape memory alloy matrix though the reinforcement shape to achieve continuous martensite transformation has been a challenge. Here, we take the finite element method to perform a comparative study of the effects of nanoinclusion shape on the interaction and martensite phase transformation in this new composite. Two typical samples are compared: one reinforced by metallic nanowires and the other by nanoparticles. We find that the residual martensite within the shape memory alloy matrix after a pretreatment can be tailored by the reinforcement shape. In particular, our results show that the shape memory alloy matrix can retain enough residual martensite phases to achieve continuous martensite transformation in the subsequent loading when the aspect ratio of nanoreinforcement is larger than 20. In contrast, the composites reinforced with spherical or low aspect ratio reinforcement show a typical nonlinear superelasticity as a result of a low stress transfer-induced discontinuous martensite transformation within the shape memory alloy matrix.

Shock Condition Forensics and Cryptic Phase Transformations from Crystallographic Orientation Relationships in Zircon

NASA Astrophysics Data System (ADS)

Timms, N. E.; Erickson, T. M.; Cavosie, A. J.; Pearce, M. A.; Reddy, S. M.; Zanetti, M.; Tohver, E.; Schmieder, M.; Nemchin, A. A.; Wittmann, A.

2016-08-01

We present an approach to constrain pressure and temperature conditions during impact events involving identification of cryptic histories of phase transformations from orientation relationships in shocked zircon, linked to new P-T phase diagrams.

Transformation Paths from Cubic to Low-Symmetry Structures in Heusler Ni2MnGa Compound.

PubMed

Zelený, Martin; Straka, Ladislav; Sozinov, Alexei; Heczko, Oleg

2018-05-08

In order to explain the formation of low-temperature phases in stoichiometric Ni 2 MnGa magnetic shape memory alloy, we investigate the phase transformation paths from cubic austenite with Heusler structure to low-symmetry martensitic structures. We used ab initio calculations combined with the generalized solid state nudged elastic band method to determine the minimum energy path and corresponding changes in crystal lattice. The four-, five-, and seven-layered modulated phases of martensite (4O, 10M, and 14M) are built as the relaxed nanotwinned non-modulated (NM) phase. Despite having a total energy larger than the other martensitic phases, the 10M phase will spontaneously form at 0 K, because there is no energy barrier on the path and the energy decreases with a large negative slope. Moreover, a similar negative slope in the beginning of path is found also for the transformation to the 6M premartensite, which appears as a local minimum on the path leading further to 10M martensite. Transformation paths to other structures exhibit more or less significant barriers in the beginning hindering such a transformation from austenite. These findings correspond to experiment and demonstrates that the kinetics of the transformation is decisive for the selection of the particular low-symmetry structure.

Hybrid grating-prism dispersion eraser

NASA Astrophysics Data System (ADS)

Wang, Cheng; Li, Shuai; Liu, Yanqi; Liu, Xingyan; Leng, Yuxin; Li, Ruxin

2018-03-01

A hybrid grating-prism dispersion eraser is proposed to achieve broadband dispersion compensation. A ray-tracing model is built up for its phase spectrum and derivatives. The numerical calculation shows that the eraser can compensate dispersion up to fourth-order. When it is used in chirped-pulse amplifiers, it can obtain aberration-free phase with above 120 nm bandwidth at 0 . 8 μm central wavelength and support near-Fourier-transform-limited femtosecond pulses output.

Feasibility study for automatic reduction of phase change imagery

NASA Technical Reports Server (NTRS)

Nossaman, G. O.

1971-01-01

The feasibility of automatically reducing a form of pictorial aerodynamic heating data is discussed. The imagery, depicting the melting history of a thin coat of fusible temperature indicator painted on an aerodynamically heated model, was previously reduced by manual methods. Careful examination of various lighting theories and approaches led to an experimentally verified illumination concept capable of yielding high-quality imagery. Both digital and video image processing techniques were applied to reduction of the data, and it was demonstrated that either method can be used to develop superimposed contours. Mathematical techniques were developed to find the model-to-image and the inverse image-to-model transformation using six conjugate points, and methods were developed using these transformations to determine heating rates on the model surface. A video system was designed which is able to reduce the imagery rapidly, economically and accurately. Costs for this system were estimated. A study plan was outlined whereby the mathematical transformation techniques developed to produce model coordinate heating data could be applied to operational software, and methods were discussed and costs estimated for obtaining the digital information necessary for this software.

Theoretical model of a polarization diffractive elements for the light beams conversion holographic formation in PDLCs

NASA Astrophysics Data System (ADS)

Sharangovich, Sergey N.; Semkin, Artem O.

2017-12-01

In this work a theoretical model of the holographic formation of the polarization diffractive optical elements for the transformation of Gaussian light beams into Bessel-like ones in polymer-dispersed liquid crystals (PDLC) is developed. The model is based on solving the equations of photo-induced Fredericks transition processes for polarization diffractive elements formation by orthogonally polarized light beams with inhomogeneous amplitude and phase profiles. The results of numerical simulation of the material's dielectric tensor changing due to the structure's formation process are presented for various recording beams' polarization states. Based on the results of numerical simulation, the ability to form the diffractive optical elements for light beams transformation by the polarization holography methods is shown.

[Study of the phase transformation of TiO2 with in-situ XRD in different gas].

PubMed

Ma, Li-Jing; Guo, Lie-Jin

2011-04-01

TiO2 sample was prepared by sol-gel method from chloride titanium. The phase transformation of the prepared TiO2 sample was studied by in-situ XRD and normal XRD in different gas. The experimental results showed that the phase transformation temperatures of TiO2 were different under in-situ or normal XRD in different kinds of gas. The transformation of amorphous TiO2 to anatase was controlled by kinetics before 500 degrees C. In-situ XRD showed that the growth of anatase was inhibited, but the transformation of anatase to rutile was accelerated under inactive nitrogen in contrast to air. Also better crystal was obtained under hydrogen than in argon. These all showed that external oxygen might accelerate the growth of TiO2, but reduced gas might partly counteract the negative influence of lack of external oxygen. The mechanism of phase transformation of TiO2 was studied by in-situ XRD in order to control the structure in situ.

QR code-based non-linear image encryption using Shearlet transform and spiral phase transform

NASA Astrophysics Data System (ADS)

Kumar, Ravi; Bhaduri, Basanta; Hennelly, Bryan

2018-02-01

In this paper, we propose a new quick response (QR) code-based non-linear technique for image encryption using Shearlet transform (ST) and spiral phase transform. The input image is first converted into a QR code and then scrambled using the Arnold transform. The scrambled image is then decomposed into five coefficients using the ST and the first Shearlet coefficient, C1 is interchanged with a security key before performing the inverse ST. The output after inverse ST is then modulated with a random phase mask and further spiral phase transformed to get the final encrypted image. The first coefficient, C1 is used as a private key for decryption. The sensitivity of the security keys is analysed in terms of correlation coefficient and peak signal-to noise ratio. The robustness of the scheme is also checked against various attacks such as noise, occlusion and special attacks. Numerical simulation results are shown in support of the proposed technique and an optoelectronic set-up for encryption is also proposed.

Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

DOE PAGES

Hudak, Bethany M.; Depner, Sean W.; Waetzig, Gregory R.; ...

2017-05-12

High-temperature phases of hafnium dioxide have exceptionally high dielectric constants and large bandgaps, but quenching them to room temperature remains a challenge. Scaling the bulk form to nanocrystals, while successful in stabilizing the tetragonal phase of isomorphous ZrO 2, has produced nanorods with a twinned version of the room temperature monoclinic phase in HfO 2. Here we use in situ heating in a scanning transmission electron microscope to observe the transformation of an HfO 2 nanorod from monoclinic to tetragonal, with a transformation temperature suppressed by over 1000°C from bulk. When the nanorod is annealed, we observe with atomic-scale resolutionmore » the transformation from twinned-monoclinic to tetragonal, starting at a twin boundary and propagating via coherent transformation dislocation; the nanorod is reduced to hafnium on cooling. Unlike the bulk displacive transition, nanoscale size-confinement enables us to manipulate the transformation mechanism, and we observe discrete nucleation events and sigmoidal nucleation and growth kinetics.« less

Thermal and magnetic hysteresis associated with martensitic and magnetic phase transformations in Ni52Mn25In16Co7 Heusler alloy

NASA Astrophysics Data System (ADS)

Madiligama, A. S. B.; Ari-Gur, P.; Ren, Y.; Koledov, V. V.; Dilmieva, E. T.; Kamantsev, A. P.; Mashirov, A. V.; Shavrov, V. G.; Gonzalez-Legarreta, L.; Grande, B. H.

2017-11-01

Ni-Mn-In-Co Heusler alloys demonstrate promising magnetocaloric performance for use as refrigerants in magnetic cooling systems with the goal of replacing the lower efficiency, eco-adverse fluid-compression technology. The largest change in entropy occurs when the applied magnetic field causes a merged structural and magnetic transformation and the associated entropy changes of the two transformations works constructively. In this study, magnetic and crystalline phase transformations were each treated separately and the effects of the application of magnetic field on thermal hystereses associated with both structural and magnetic transformations of the Ni52Mn25In16Co7 were studied. From the analysis of synchrotron diffraction data and thermomagnetic measurements, it was revealed that the alloy undergoes both structural (from cubic austenite to a mixture of 7M &5M modulated martensite) and magnetic (ferromagnetic to a low-magnetization phase) phase transformations. Thermal hysteresis is associated with both transformations, and the variation of the thermal hystereses of the magnetic and structural transformations with applied magnetic field is significantly different. Because of the differences between the hystereses loops of the two transformations, they merge only upon heating under a certain magnetic field.

Thin film characterization by laser interferometry combined with SIMS

NASA Astrophysics Data System (ADS)

Kempf, J.; Nonnenmacher, M.; Wagner, H. H.

1988-10-01

Thin film properties of technologically important materials (Si, GaAs, SiO2, WSix) have been measured by using a novel technique that combines secondary ion mass spectrometry (SIMS) and laser interferometry. The simultaneous measurement of optical phase and reflectance as well as SIMS species during ion sputtering yielded optical constants, sputtering rates and composition of thin films with high depth resolution. A model based on the principle of multiple reflection within a multilayer structure, which considered also transformation of the film composition in depth and time during sputtering, was fitted to the reflectance and phase data. This model was applied to reveal the transformation of silicon by sputtering with O{2/+} ions. Special attention was paid to the preequilibrium phase of the sputter process (amorphization, oxidation, and volume expansion). To demonstrate the analytical potential of our method the multilayer system WSix/poly-Si/SiO2/Si was investigated. The physical parameters and the stoichiometry of tungsten suicide were determined for annealed as well as deposited films. A highly sensitive technique that makes use of a Fabry-Perot etalon integrated with a Michelson type interferometer is proposed. This two-stage interferometer has the potential to profile a sample surface with subangstroem resolution.

In situ X-ray diffraction strain-controlled study of Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys: crystal lattice and transformation features

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubinskiy, S.; National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049; Prokoshkin, S.

2014-02-15

Phase and structure transformations in biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) shape memory alloys (at.%) under and without load in the − 150 to 100 °S temperature range are studied in situ using an original tensile module for a low-temperature chamber of an X-ray diffractometer. Alpha″- and beta-phase lattice parameters, the crystallographic resource of recovery strain, phase and structure transformation sequences, and microstress appearance and disappearance are examined, compared and discussed. For both alloys, the crystallographic resource of recovery strain decreases with temperature increase to become 4.5% for TNZ and 2.5% for TNT alloy (at RT). Loading at low temperaturesmore » leads to additional α″-phase formation and reorientation. Heating under load, as compared to strain-free heating, affects the reverse transformation sequence of both alloys in different ways. For TNZ alloy, strain-free heating results in simultaneous ω→β and α″→β transformations, whereas during heating under stress, they are sequential: β + ω→α″ precedes α″→β. For TNT alloy, strain-free heating results in reverse α″→β transformation, whereas during heating under stress, α″→β transformation is preceded by α″-phase reorientation. - Highlights: • Comparative in situ XRD analysis of Ti–Nb–Zr(Ta) shape memory alloys is realized. • Lattice parameters of β- and α″-phases are calculated in the − 150 to + 100 °C range. • The higher the temperature, the lower the α″→β transformation strain. • Loading at low temperatures results in α″-phase formation and reorientation. • Transformation sequences upon heating with and without loading are different.« less

Experimental dynamic metamorphism of mineral single crystals

USGS Publications Warehouse

Kirby, S.H.; Stern, L.A.

1993-01-01

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a-?? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ??? clinoenstatite and w u ??rtzite ??? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO ?? nAl2O3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates. ?? 1993.

Randomly displaced phase distribution design and its advantage in page-data recording of Fourier transform holograms.

PubMed

Emoto, Akira; Fukuda, Takashi

2013-02-20

For Fourier transform holography, an effective random phase distribution with randomly displaced phase segments is proposed for obtaining a smooth finite optical intensity distribution in the Fourier transform plane. Since unitary phase segments are randomly distributed in-plane, the blanks give various spatial frequency components to an image, and thus smooth the spectrum. Moreover, by randomly changing the phase segment size, spike generation from the unitary phase segment size in the spectrum can be reduced significantly. As a result, a smooth spectrum including sidebands can be formed at a relatively narrow extent. The proposed phase distribution sustains the primary functions of a random phase mask for holographic-data recording and reconstruction. Therefore, this distribution is expected to find applications in high-density holographic memory systems, replacing conventional random phase mask patterns.

Grain boundary engineering to control the discontinuous precipitation in multicomponent U10Mo alloy

DOE PAGES

Devaraj, Arun; Kovarik, Libor; Kautz, Elizabeth; ...

2018-03-30

Here, we demonstrate here that locally stabilized structure and compositional segregation at grain boundaries in a complex multicomponent alloy can be modified using high temperature homogenization treatment to influence the kinetics of phase transformations initiating from grain boundaries during subsequent low temperature annealing. Using aberration-corrected scanning transmission electron microscopy and atom probe tomography of a model multicomponent metallic alloy —uranium-10 wt% molybdenum (U-10Mo) a nuclear fuel, that is highly relevant to worldwide nuclear non-proliferation efforts, we demonstrate the ability to change the structure and compositional segregation at grain boundary, which then controls the subsequent discontinuous precipitation kinetics during sub-eutectoid annealing.more » A change in grain boundary from one characterized by segregation of Mo and impurities at grain boundary to a phase boundary with a distinct U 2MoSi 2C wetting phase precipitates introducing Ni and Al rich interphase complexions caused a pronounced reduction in area fraction of subsequent discontinuous precipitation. The broader implication of this work is in highlighting the role of grain boundary structure and composition in metallic alloys on dictating the fate of grain boundary initiated phase transformations like discontinuous precipitation or cellular transformation. This work highlights a new pathway to tune the grain boundary structure and composition to tailor the final microstructure of multicomponent metallic alloys.« less

Grain boundary engineering to control the discontinuous precipitation in multicomponent U10Mo alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devaraj, Arun; Kovarik, Libor; Kautz, Elizabeth

Here, we demonstrate here that locally stabilized structure and compositional segregation at grain boundaries in a complex multicomponent alloy can be modified using high temperature homogenization treatment to influence the kinetics of phase transformations initiating from grain boundaries during subsequent low temperature annealing. Using aberration-corrected scanning transmission electron microscopy and atom probe tomography of a model multicomponent metallic alloy —uranium-10 wt% molybdenum (U-10Mo) a nuclear fuel, that is highly relevant to worldwide nuclear non-proliferation efforts, we demonstrate the ability to change the structure and compositional segregation at grain boundary, which then controls the subsequent discontinuous precipitation kinetics during sub-eutectoid annealing.more » A change in grain boundary from one characterized by segregation of Mo and impurities at grain boundary to a phase boundary with a distinct U 2MoSi 2C wetting phase precipitates introducing Ni and Al rich interphase complexions caused a pronounced reduction in area fraction of subsequent discontinuous precipitation. The broader implication of this work is in highlighting the role of grain boundary structure and composition in metallic alloys on dictating the fate of grain boundary initiated phase transformations like discontinuous precipitation or cellular transformation. This work highlights a new pathway to tune the grain boundary structure and composition to tailor the final microstructure of multicomponent metallic alloys.« less

Kinematic Thermal Model for Tonga Descending Slab: A Case Study on the Influence of Velocity Boundary Layers

NASA Astrophysics Data System (ADS)

Zhang, K.; Wei, D.

2009-12-01

Within the core of a colder slab (e.g., the Tonga slab), the existence of metastable olivine (MO), extending deeper than the 410 km, has several important implications for understanding both the mechanism of deep earthquakes (>300 km) and the slab dynamics. The effect of subduction kinematics on the slab thermal structure has been widely investigated by prescribing Constant Velocity field for the subducting Slab (CVS-model), which may result in artificial computational interferences along the slab interfaces by accelerating the heating of subducting slabs. For the purpose of moderating the CVS effect and investigating the influence of metastable phase transformations on deep seismicity, we construct a 2-dimensional finite element thermal model for a 120 Ma-old 50° dipping oceanic lithosphere descending at 10 cm/yr with Velocity Boundary Layers (VBL-model), within which the velocities decrease from v to zero with the distance to the interface. The density anomalies for the VBL-model show significant variations (~100 kg/m3) at depths of both ~230 and ~410 km, whereas CVS-model shows anomalies above ~410 km. Thus, the VBL-model result is in better agreement with our knowledge of the subducting evolution that the density anomalies are primarily controlled by the conductive cooling and the phase transitions for the shallow depths of the slab and the transition zone, respectively. The VBL-model pressure anomalies also indicate that the negative buoyancy force causes the downdip tensional (DDT) earthquakes occurring above depth of ~230 km. At depths >410 km, the zonal distributed pressures of the VBL-model show negative and positive anomalies within the core and the outermost portion of slab, respectively, whereas the CVS-model produces negative pressure anomalies. The seismicity shows that down-dip compressional (DDC) and DDT deep earthquakes occur along the lower and upper interfaces of Tonga slab, whereas the P- and T-axes for the earthquakes in-between portion are interchangeable. The VBL model rather than CVS model produces MO wedge extending to depth as the deepest (>660 km) earthquakes. If there really exists MO at depths >660 km, these deepest earthquakes will be in agreement with the suggestion that the MO associated transformational faulting can occur for the exothermic Ol-Sp transition but not for the endothermic Sp-Pv+Mw change (Green, 2007), otherwise, other mechanisms should be responsible for them. Therefore, the phase boundaries are important for the buoyancy and stresses within slabs (e.g. Bina, 2001) and the VBL-model is more credible. Moreover, VBL-model results also indicate that MO within the transition zone in Tonga increases the positive buoyancy force acting on the slab and facilitates slab stagnation at 660 km depth, in agreement with the tomographic (van der Hilst et al., 1995) and seismological observations (Chen and Brudzinski, 2001). As the subducting materials accumulated over 660 km, the MO begins to transform to Sp and deepest earthquakes occur. If Sp further transforms to Pv+Mw, the flattened ‘slab’ would penetrate the 660 km due to the density increment of Sp transformation.

Understanding Strain-Induced Phase Transformations in BiFeO3 Thin Films.

PubMed

Dixit, Hemant; Beekman, Christianne; Schlepütz, Christian M; Siemons, Wolter; Yang, Yongsoo; Senabulya, Nancy; Clarke, Roy; Chi, Miaofang; Christen, Hans M; Cooper, Valentino R

2015-08-01

Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO 3 thin films, which comprises a tetragonal-like ( T ') and an intermediate S ' polymorph. It exhibits a relatively large piezoelectric response when switching between the coexisting phase and a uniform T ' phase. This strain-induced phase transformation is investigated through a synergistic combination of first-principles theory and experiments. The results show that the S ' phase is energetically very close to the T ' phase, but is structurally similar to the bulk rhombohedral ( R ) phase. By fully characterizing the intermediate S ' polymorph, it is demonstrated that the flat energy landscape resulting in the absence of an energy barrier between the T ' and S ' phases fosters the above-mentioned reversible phase transformation. This ability to readily transform between the S ' and T ' polymorphs, which have very different octahedral rotation patterns and c / a ratios, is crucial to the enhanced piezoelectricity in strained BiFeO 3 films. Additionally, a blueshift in the band gap when moving from R to S ' to T ' is observed. These results emphasize the importance of strain engineering for tuning electromechanical responses or, creating unique energy harvesting photonic structures, in oxide thin film architectures.

Circular carrier squeezing interferometry: Suppressing phase shift error in simultaneous phase-shifting point-diffraction interferometer

NASA Astrophysics Data System (ADS)

Zheng, Donghui; Chen, Lei; Li, Jinpeng; Sun, Qinyuan; Zhu, Wenhua; Anderson, James; Zhao, Jian; Schülzgen, Axel

2018-03-01

Circular carrier squeezing interferometry (CCSI) is proposed and applied to suppress phase shift error in simultaneous phase-shifting point-diffraction interferometer (SPSPDI). By introducing a defocus, four phase-shifting point-diffraction interferograms with circular carrier are acquired, and then converted into linear carrier interferograms by a coordinate transform. Rearranging the transformed interferograms into a spatial-temporal fringe (STF), so the error lobe will be separated from the phase lobe in the Fourier spectrum of the STF, and filtering the phase lobe to calculate the extended phase, when combined with the corresponding inverse coordinate transform, exactly retrieves the initial phase. Both simulations and experiments validate the ability of CCSI to suppress the ripple error generated by the phase shift error. Compared with carrier squeezing interferometry (CSI), CCSI is effective on some occasions in which a linear carrier is difficult to introduce, and with the added benefit of eliminating retrace error.

78 FR 76789 - Additional Connect America Fund Phase II Issues

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-19

... inspection and copying during normal business hours in the FCC Reference Information Center, Portals II, 445... Phase I to Phase II. 2. Timing of Phase II Support Disbursements. In the USF/ICC Transformation Order... language in paragraph 180 of the USF/ICC Transformation Order. We now seek to more fully develop the record...

Multiple pathways in pressure-induced phase transition of coesite

NASA Astrophysics Data System (ADS)

Liu, Wei; Wu, Xuebang; Liang, Yunfeng; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-12-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture.

Is Ishtar Terra a thickened basaltic crust?

NASA Technical Reports Server (NTRS)

Arkani-Hamed, Jafar

1992-01-01

The mountain belts of Ishtar Terra and the surrounding tesserae are interpreted as compressional regions. The gravity and surface topography of western Ishtar Terra suggest a thick crust of 60-110 km that results from crustal thickening through tectonic processes. Underthrusting was proposed for the regions along Danu Montes and Itzpapalotl Tessera. Crustal thickening was suggested for the entire Ishtar Terra. In this study, three lithospheric models with total thicknesses of 40.75 and 120 km and initial crustal thicknesses of 3.9 and 18 km are examined. These models could be produced by partial melting and chemical differentiation in the upper mantle of a colder, an Earth-like, and a hotter Venus having temperatures of respectively 1300 C, 1400 C, and 1500 C at the base of their thermal boundary layers associated with mantle convection. The effects of basalt-granulite-eclogite transformation (BGET) on the surface topography of a thickening basaltic crust is investigated adopting the experimental phase diagram and density variations through the phase transformation.

The construction phase’s influence to the moving ability of cross-sections of woven structure

NASA Astrophysics Data System (ADS)

Inogamdjanov, D.; Daminov, A.; Kasimov, O.

2017-10-01

The purpose of this study is to work out bases to predict properties for single layer flat woven fabrics depending on changes of construction phases. A structural model of cross-section of single layered fabric is described based on the Pierce’s model. Form transformation of the yarn like straight, semi-arch and arch yarn is considered according to the alteration of yarn tension under the theory of Novikov. The value contributions to movement index of warp and weft yarn and their total moving ability in cross-sections at all structure phases of fabric are summarized.

Analysis and Modeling of a Two-Phase Jet Pump of a Thermal Management System for Aerospace Applications

NASA Technical Reports Server (NTRS)

Sherif, S.A.; Hunt, P. L.; Holladay, J. B.; Lear, W. E.; Steadham, J. M.

1998-01-01

Jet pumps are devices capable of pumping fluids to a higher pressure by inducing the motion of a secondary fluid employing a high speed primary fluid. The main components of a jet pump are a primary nozzle, secondary fluid injectors, a mixing chamber, a throat, and a diffuser. The work described in this paper models the flow of a two-phase primary fluid inducing a secondary liquid (saturated or subcooled) injected into the jet pump mixing chamber. The model is capable of accounting for phase transformations due to compression, expansion, and mixing. The model is also capable of incorporating the effects of the temperature and pressure dependency in the analysis. The approach adopted utilizes an isentropic constant pressure mixing in the mixing chamber and at times employs iterative techniques to determine the flow conditions in the different parts of the jet pump.

Phase and microstructural development in alumina sol-gel coatings on CoCr alloy.

PubMed

Bae, I J; Standard, O C; Roger, G J; Brazil, D

2004-09-01

Phase transformation of gamma-Al(2)O(3) to alpha-Al(2)O(3) in alumina sol gel coatings on biomedical CoCr alloy was studied as function of heat treatment temperature and time. Transformation in unseeded coatings was significant only above approximately 1200 degrees C. Addition of alpha-Al(2)O(3) seed particles having an average size of approximately 40 nm lowered the phase transformation temperature to around 800 degrees C. These particles were considered to act as heterogeneous nucleation sites for epitaxial growth of the alpha-Al(2)O(3) phase. The kinetics and activation energy (420 kJ/mol) for the phase transformation in the seeded coatings were similar to those reported for seeded monolithic alumina gels indicating that the transformation mechanism is the same in the two material configurations. Avrami growth parameters indicated that the mechanism was diffusion controlled and invariant over the temperature range studied but that growth was possibly constrained by the finite size of the seed particles and/or coating thickness. The phase transformation occurred by the growth of alpha-Al(2)O(3) grains at the expense of the precursor fine-grained gamma-Al(2)O(3) matrix and near-complete transformation coincided with physical impingement of the growing grains. The grain size at impingement was approximately 100 nm which agreed well with that predicted from the theoretical linear spacing of seed particles in the initial sol.

Calculations of single crystal elastic constants for yttria partially stabilised zirconia from powder diffraction data

NASA Astrophysics Data System (ADS)

Lunt, A. J. G.; Xie, M. Y.; Baimpas, N.; Zhang, S. Y.; Kabra, S.; Kelleher, J.; Neo, T. K.; Korsunsky, A. M.

2014-08-01

Yttria Stabilised Zirconia (YSZ) is a tough, phase-transforming ceramic that finds use in a wide range of commercial applications from dental prostheses to thermal barrier coatings. Micromechanical modelling of phase transformation can deliver reliable predictions in terms of the influence of temperature and stress. However, models must rely on the accurate knowledge of single crystal elastic stiffness constants. Some techniques for elastic stiffness determination are well-established. The most popular of these involve exploiting frequency shifts and phase velocities of acoustic waves. However, the application of these techniques to YSZ can be problematic due to the micro-twinning observed in larger crystals. Here, we propose an alternative approach based on selective elastic strain sampling (e.g., by diffraction) of grain ensembles sharing certain orientation, and the prediction of the same quantities by polycrystalline modelling, for example, the Reuss or Voigt average. The inverse problem arises consisting of adjusting the single crystal stiffness matrix to match the polycrystal predictions to observations. In the present model-matching study, we sought to determine the single crystal stiffness matrix of tetragonal YSZ using the results of time-of-flight neutron diffraction obtained from an in situ compression experiment and Finite Element modelling of the deformation of polycrystalline tetragonal YSZ. The best match between the model predictions and observations was obtained for the optimized stiffness values of C11 = 451, C33 = 302, C44 = 39, C66 = 82, C12 = 240, and C13 = 50 (units: GPa). Considering the significant amount of scatter in the published literature data, our result appears reasonably consistent.

Complexion-mediated martensitic phase transformation in Titanium

PubMed Central

Zhang, J.; Tasan, C. C.; Lai, M. J.; Dippel, A. -C.; Raabe, D.

2017-01-01

The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a–ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a–ω is stable only at the hetero-interface. PMID:28145484

Complexion-mediated martensitic phase transformation in Titanium.

PubMed

Zhang, J; Tasan, C C; Lai, M J; Dippel, A-C; Raabe, D

2017-02-01

The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a-ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a-ω is stable only at the hetero-interface.

Annealing effect on the magnetic induced austenite transformation in polycrystalline freestanding Ni-Co-Mn-In films produced by co-sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crouïgneau, G., E-mail: guillaume.crouigneau@neel.cnrs.fr; Univ. Grenoble Alpes, CRETA, F-38000 Grenoble; CNRS, Inst. NEEL, F-38000 Grenoble

2015-01-21

Ni-Co-Mn-In freestanding films, with a magneto-structural transformation at room temperature were successfully produced by co-sputtering and post-annealing methods leading to film composition mastering. For a post-annealing temperature of 700 °C, the phase transformation occurs slightly above room temperature, with a twisted martensitic microstructure phase observed at 300 K by Field Emission Scanning Electron Microscopy. Magnetization measurements on a polycrystalline film showed a phase transformation from a weakly magnetic martensite to a magnetic austenite phase. Moreover, an inverse magnetocaloric effect with an entropy variation of 4 J/kg K under 5 T was also measured. A simple magneto-actuation experiment based on the magnetic induced austenite transformation wasmore » also successfully completed. The possibility to insert such films in microsystems is clearly demonstrated in this work.« less

Method for utilizing properties of the sinc(x) function for phase retrieval on nyquist-under-sampled data

NASA Technical Reports Server (NTRS)

Dean, Bruce H. (Inventor); Smith, Jeffrey Scott (Inventor); Aronstein, David L. (Inventor)

2012-01-01

Disclosed herein are systems, methods, and non-transitory computer-readable storage media for simulating propagation of an electromagnetic field, performing phase retrieval, or sampling a band-limited function. A system practicing the method generates transformed data using a discrete Fourier transform which samples a band-limited function f(x) without interpolating or modifying received data associated with the function f(x), wherein an interval between repeated copies in a periodic extension of the function f(x) obtained from the discrete Fourier transform is associated with a sampling ratio Q, defined as a ratio of a sampling frequency to a band-limited frequency, and wherein Q is assigned a value between 1 and 2 such that substantially no aliasing occurs in the transformed data, and retrieves a phase in the received data based on the transformed data, wherein the phase is used as feedback to an optical system.

Reconstruction of networks from one-step data by matching positions

NASA Astrophysics Data System (ADS)

Wu, Jianshe; Dang, Ni; Jiao, Yang

2018-05-01

It is a challenge in estimating the topology of a network from short time series data. In this paper, matching positions is developed to reconstruct the topology of a network from only one-step data. We consider a general network model of coupled agents, in which the phase transformation of each node is determined by its neighbors. From the phase transformation information from one step to the next, the connections of the tail vertices are reconstructed firstly by the matching positions. Removing the already reconstructed vertices, and repeatedly reconstructing the connections of tail vertices, the topology of the entire network is reconstructed. For sparse scale-free networks with more than ten thousands nodes, we almost obtain the actual topology using only the one-step data in simulations.

Parallel Grand Canonical Monte Carlo (ParaGrandMC) Simulation Code

NASA Technical Reports Server (NTRS)

Yamakov, Vesselin I.

2016-01-01

This report provides an overview of the Parallel Grand Canonical Monte Carlo (ParaGrandMC) simulation code. This is a highly scalable parallel FORTRAN code for simulating the thermodynamic evolution of metal alloy systems at the atomic level, and predicting the thermodynamic state, phase diagram, chemical composition and mechanical properties. The code is designed to simulate multi-component alloy systems, predict solid-state phase transformations such as austenite-martensite transformations, precipitate formation, recrystallization, capillary effects at interfaces, surface absorption, etc., which can aid the design of novel metallic alloys. While the software is mainly tailored for modeling metal alloys, it can also be used for other types of solid-state systems, and to some degree for liquid or gaseous systems, including multiphase systems forming solid-liquid-gas interfaces.

Effect of cell-surface hydrophobicity on bacterial conversion of water-immiscible chemicals in two-liquid-phase culture systems.

PubMed

Hamada, Takahiro; Maeda, Yusuke; Matsuda, Hiroyuki; Sameshima, Yuka; Honda, Kohsuke; Omasa, Takeshi; Kato, Junichi; Ohtake, Hisao

2009-08-01

The effect of bacterial cell-surface hydrophobicity on the bioconversion of water-immiscible chemicals in an aqueous-organic (A/O) two-liquid-phase culture system was investigated. Escherichia coli JM109 and Rhodococcus opacus B-4 were used as hydrophilic and hydrophobic whole-cell catalysts, respectively. Hydroxylation reactions of monoaromatics, including toluene (log P(ow)=2.9), ethylbenzene (3.1), n-propylbenzene (3.4), and sec-butylbenzene (3.7), were employed as model conversions. When the todC1C2BA genes encoding Pseudomonas putida toluene dioxygenase were expressed in E. coli JM109, the yield of hydroxylated monoaromatics decreased with increasing substrate hydrophobicity. By contrast, R. opacus transformants, which expressed the todC1C2BA genes, showed high performance in the hydroxylation of monoaromatics, irrespective of substrate hydrophobicity. When the R. opacus transformants were examined for their ability to hydroxylate monoaromatics in an aqueous single-liquid-phase culture, the reaction velocity was markedly lower than that observed in the A/O two-liquid-phase culture. These results suggested that R. opacus B-4 accessed the hydrophobic substrates in the oil phase, thus making it more effective for the bioconversion reactions.

Anomalous behaviour of thermodynamic properties at successive phase transitions in (NH4)3GeF7

NASA Astrophysics Data System (ADS)

Bogdanov, Evgeniy V.; Kartashev, Andrey V.; Pogoreltsev, Evgeniy I.; Gorev, Mikhail V.; Laptash, Natalia M.; Flerov, Igor N.

2017-12-01

Heat capacity, thermal dilatation, susceptibility to hydrostatic pressure and dielectric properties associated with succession of three phase transitions below room temperature in double fluoride salt (NH4)3GeF7 were studied. A possible transformation into the parent Pm-3m cubic phase was not observed up to the decomposition of compound. Nonferroelectric nature of structural distortions was confirmed. The DTA under pressure studies revealed a high temperature stability of two phases: P4/mbm and Pbam. The entropies of the phase transitions agree well with the model of structural distortions. Analysis of the thermal properties associated with the individual phase transitions in the framework of thermodynamic equations has shown a high reliability of the data obtained.

Transient Control of Synchronous Machine Active and Reactive Power in Micro-grid Power Systems

NASA Astrophysics Data System (ADS)

Weber, Luke G.

There are two main topics associated with this dissertation. The first is to investigate phase-to-neutral fault current magnitude occurring in generators with multiple zero-sequence current sources. The second is to design, model, and tune a linear control system for operating a micro-grid in the event of a separation from the electric power system. In the former case, detailed generator, AC8B excitation system, and four-wire electric power system models are constructed. Where available, manufacturers data is used to validate the generator and exciter models. A gain-delay with frequency droop control is used to model an internal combustion engine and governor. The four wire system is connected through a transformer impedance to an infinite bus. Phase-to-neutral faults are imposed on the system, and fault magnitudes analyzed against three-phase faults to gauge their severity. In the latter case, a balanced three-phase system is assumed. The model structure from the former case - but using data for a different generator - is incorporated with a model for an energy storage device and a net load model to form a micro-grid. The primary control model for the energy storage device has a high level of detail, as does the energy storage device plant model in describing the LC filter and transformer. A gain-delay battery and inverter model is used at the front end. The net load model is intended to be the difference between renewable energy sources and load within a micro-grid system that has separated from the grid. Given the variability of both renewable generation and load, frequency and voltage stability are not guaranteed. This work is an attempt to model components of a proposed micro-grid system at the University of Wisconsin Milwaukee, and design, model, and tune a linear control system for operation in the event of a separation from the electric power system. The control module is responsible for management of frequency and active power, and voltage and reactive power. The scope of this work is to • develop a mathematical model for a salient pole, 2 damper winding synchronous generator with d axis saturation suitable for transient analysis, • develop a mathematical model for a voltage regulator and excitation system using the IEEE AC8B voltage regulator and excitation system template, • develop mathematical models for an energy storage primary control system, LC filter and transformer suitable for transient analysis, • combine the generator and energy storage models in a micro-grid context, • develop mathematical models for electric system components in the stationary abc frame and rotating dq reference frame, • develop a secondary control network for dispatch of micro-grid assets, • establish micro-grid limits of stable operation for step changes in load and power commands based on simulations of model data assuming net load on the micro-grid, and • use generator and electric system models to assess the generator current magnitude during phase-to-ground faults.

Modeling development of converter topologies and control for BTB voltage source converters. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, L.

1998-08-01

This report presents the results of an investigation into the merits of using a back-to-back voltage source converter (BTB-VSC) as an alternative to a conventional back-to-back high voltage DC link (HVDC). The report presents the basic benefits of the new technology along with the basic control blocks needed to implement the design. The report also describes a model of the BTB-VSC implemented in EMTDC{trademark} and discusses the use of the model. Simulation results, showing how the model responds to various control actions and system disturbances, are presented. This modeling work developed a detailed EMTDC{trademark} model using the appropriate converter technologymore » and magnetic interface configuration. Various possible converter and magnetic interface configurations were examined and the most promising configuration was used for the model. The chosen configuration minimizes the number of high voltage transformers needed and minimizes the complexity non-standard interfacing transformers. There is no need for transformers with phase shifts other than zero or thirty degrees (wye-wye or wye-delta). The only non-standard feature is the necessity of bringing the neutral side of the high voltage winding on the wye-wye unit out through bushings and to insulate the wye-wye transformer for the system voltage which is twice the transformer winding voltage. The developed EMTDC{trademark} model was used to demonstrate the possibility of achieving independent control of the real power transmitted and the voltages at the AC terminals. The model also demonstrates the ability to interconnect weak AC systems without the necessity of additional voltage support equipment as is the case with the conventional back-to-back DC interconnection. The model has been shown to work with short circuit ratios less than 2 based on the total rating of the high voltage transformers.« less

Thermal stability of intermetallic phases in Fe-rich Fe-Cr-Ni-Mo alloys

DOE PAGES

Yang, Ying; Tan, Lizhen; Busby, Jeremy T.

2015-06-12

Understanding the stability of precipitate phases in the Fe-rich Fe-Cr-Ni-Mo alloys is critical to the alloy design and application of Mo-containing Austenitic steels. Coupled with thermodynamic modeling, stability of the chi and Laves phases in two Fe-Cr-Ni-Mo alloys were investigated at 1000, 850 and 700 °C for different annealing time. The morphologies, compositions and crystal structures of the matrix and precipitate phases were carefully examined by Scanning Electron Microscopy, Electron Probe Microanalysis, X-ray diffraction and Transmission Electron Microscopy. The two key findings resulted from this work. One is that the chi phase is stable at high temperature and transformed intomore » the Laves phase at low temperature. The other is that both the chi and Laves phases have large solubilites of Cr, Mo and Ni, among which the Mo solubility has a major role on the relative stability of the precipitate phases. The developed thermodynamic models were then applied to evaluating the Mo effect on the stability of precipitate phases in AISI 316 and NF709 alloys.« less

Phase Transformations and Formation of Ultra-Fine Microstructure During Hydrogen Sintering and Phase Transformation (HSPT) Processing of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Sun, Pei; Fang, Zhigang Zak; Koopman, Mark; Xia, Yang; Paramore, James; Ravi Chandran, K. S.; Ren, Yang; Lu, Jun

2015-12-01

The hydrogen sintering and phase transformation (HSPT) process is a novel powder metallurgy method for producing Ti alloys, particularly the Ti-6Al-4V alloy, with ultra-fine microstructure in the as-sintered state. The ultra-fine microstructure is obtained as a direct result of the use of H2 gas during sintering. The refinement of the microstructure during HSPT is similar to that of thermal hydrogen processing (THP) of bulk Ti alloys. For both THP and HSPT of Ti-6Al-4V alloy, the mechanisms of the grain refinement depend on the phase equilibria and phase transformations in the presence of hydrogen, which are surprisingly still not well established to date and are still subjected to research and debate. In recent work by the present authors, a pseudo-binary phase diagram of (Ti-6Al-4V)-H has been determined by using in situ synchrotron XRD and TGA/DSC techniques. Aided by this phase diagram, the current paper focuses on the series of phase transformations during sintering and cooling of Ti-6Al-4V in a hydrogen atmosphere and the mechanisms for the formation of the ultra-fine microstructures obtained. Using experimental techniques, including in situ synchrotron XRD, SEM, EBSD, and TEM, the microstructural refinement was found to be the result of (1) the precipitation of ultra-fine α/α2 within coarse β grains during an isothermal hold at intermediate temperatures, and (2) the eutectoid transformation of β → α + δ at approximately 473 K (200 °C).

Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi: Simulations vs. Experiment

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell; Benafan, Othmane; Noebe, Ronald; Vaidyanathan, Raj; Anderson, Peter M.

2011-01-01

A recent microstructure-based FEM model that couples crystal-based plasticity, the B2<-> MB190 phase transformation and anisotropic elasticity at the grain scale is calibrated to recent data for polycrystalline NiTi (49.9 at.% Ni). Inputs include anisotropic elastic properties, texture and differential scanning calorimetry data, as well as a subset of recent isothermal deformation and load-biased thermal cycling data. The model is assessed against additional experimental data. Several experimental trends are captured - in particular, the transformation strain during thermal cycling monotonically increases and reaches a peak with increasing bias stress. This is achieved, in part, by modifying the martensite hardening matrix proposed by Patoor et al. [Patoor E, Eberhardt A, Berveiller M. J Phys IV 1996;6:277]. Some experimental trends are underestimated - in particular, the ratcheting of macrostrain during thermal cycling. This may reflect a model limitation that transformation-plasticity coupling is captured on a coarse (grain) scale but not on a fine (martensitic plate) scale.

Effect of phase transformations on microstructures in deep mantle materials

NASA Astrophysics Data System (ADS)

Merkel, Sébastien; Langrand, Christopher; Rosa, Angelika; Hilairet, Nadège

2017-04-01

Phase transformations induce microstructural changes in deep Earth materials, including changes in grain size and orientation distribution. The effect of phase transformations on mineral microstructures is usually studied using electron microscopy on quench products from high P/T experiments. The method allows for a precise evaluation of the microscopic mechanisms involved. It is limited, however, to samples that can be quenched to ambient conditions and allows for investigations at a single P/T point for each experiment. In recent years, we extended the use of multigrain crystallography to samples inside diamond anvil cells under mantle P/T conditions. The method allows for monitoring the orientations of hundreds of grains and grain size variations during various physical processes, such as plastic deformation and successions of phase transformations (Rosa et al 2015, Langrand et al 2017). Here, we will show results concerning hydrous Mg2SiO4 during the series of α-β-γ phase transformations up to 40 GPa and 850 °C. Such results are important to understand the descending behaviour of subducted slabs, observations of seismic anisotropy, and polarity changes for seismic waves reflected of deep Earth interfaces. The data is used to asses the effect of the transformation on grain orientation and grain sizes. In particular, we do not observe orientation relationships between the parent α-phase and the daughter β-phase phase, suggesting an incoherent growth. We also observe significant grain size reductions and only little grain growth within the newly formed phases (Rosa et al 2016). These new results are important for understanding the mechanical behavior of subducting slabs, seismic anisotropy in the Earth's mantle, and phase transformation mechanisms in olivine. Now that it is validated, the method can also be applied to other phases that can not be studied using electron microscopy, such as perovskite and post-perovskite. Langrand, Hilairet, Nisr, Roskosz, Ribárik, Vaughan, Merkel, Reliability of Multigrain Indexing for Orthorhombic Polycrystals above 1 Mbar: Application to MgSiO3-Post-Perovskite, J Appl Cryst 50, in press (2017) Rosa, Hilairet, Ghosh, Garbarino, Jacobs, Perrillat, Vaughan, Merkel, In situ monitoring of phase transformation microstructures at Earth's mantle pressure and temperature using multi-grain XRD, J Appl Cryst 48, 1346-1354 (2015) Rosa, Hilairet, Ghosh, Perrillat, Garbarino, Merkel, Evolution of grain sizes and orientations during phase transitions in hydrous Mg2SiO4, J Geophys Res 121, 7161-7176 (2016)

Prediction of Microstructure in HAZ of Welds

NASA Astrophysics Data System (ADS)

Khurana, S. P.; Yancey, R.; Jung, G.

2004-06-01

A modeling technique for predicting microstructure in the heat-affected zone (HAZ) of the hypoeutectoid steels is presented. This technique aims at predicting the phase fractions of ferrite, pearlite, bainite and martensite present in the HAZ after the cool down of a weld. The austenite formation kinetics and austenite decomposition kinetics are calculated using the transient temperature profile. The thermal profile in the weld and the HAZ is calculated by finite-element analysis (FEA). Two kinds of austenite decomposition models are included. The final phase fractions are predicted with the help of a continuous cooling transformation (CCT) diagram of the material. In the calculation of phase fractions either the experimental CCT diagram or the mathematically calculated CCT diagram can be used.

Extreme wave formation in unidirectional sea due to stochastic wave phase dynamics

NASA Astrophysics Data System (ADS)

Wang, Rui; Balachandran, Balakumar

2018-07-01

The authors consider a stochastic model based on the interaction and phase coupling amongst wave components that are modified envelope soliton solutions to the nonlinear Schrödinger equation. A probabilistic study is carried out and the resulting findings are compared with ocean wave field observations and laboratory experimental results. The wave height probability distribution obtained from the model is found to match well with prior data in the large wave height region. From the eigenvalue spectrum obtained through the Inverse Scattering Transform, it is revealed that the deep-water wave groups move at a speed different from the linear group speed, which justifies the inclusion of phase correction to the envelope solitary wave components. It is determined that phase synchronization amongst elementary solitary wave components can be critical for the formation of extreme waves in unidirectional sea states.

A new phase transformation path from nanodiamond to new-diamond via an intermediate carbon onion

NASA Astrophysics Data System (ADS)

Xiao, J.; Li, J. L.; Liu, P.; Yang, G. W.

2014-11-01

The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onions and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure; it is called ``new diamond'' because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has so far been challenging due to n-diamond's higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When a laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are first transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high temperature and high pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in a liquid. This phase transformation not only provides new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onions.The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onions and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure; it is called ``new diamond'' because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has so far been challenging due to n-diamond's higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When a laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are first transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high temperature and high pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in a liquid. This phase transformation not only provides new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05246c

Experimental and theoretical studies on the gas/solid/gas transformation cycle in extraterrestrial environments

NASA Astrophysics Data System (ADS)

Cottin, Hervé; Gazeau, Marie-Claire; Chaquin, Patrick; Raulin, François; Bénilan, Yves

2001-12-01

The ubiquity of molecular material in the universe, from hydrogen to complex organic matter, is the result of intermixed physicochemical processes that have occurred throughout history. In particular, the gas/solid/gas phase transformation cycle plays a key role in chemical evolution of organic matter from the interstellar medium to planetary systems. This paper focuses on two examples that are representative of the diversity of environments where such transformations occur in the Solar System: (1) the photolytic evolution from gaseous to solid material in methane containing planetary atmospheres and (2) the degradation of high molecular weight compounds into gas phase molecules in comets. We are currently developing two programs which couple experimental and theoretical studies. The aim of this research is to provide data necessary to build models in order to better understand (1) the photochemical evolution of Titan's atmosphere, through a laboratory program to determine quantitative spectroscopic data on long carbon chain molecules (polyynes) obtained in the SCOOP program (French acronym for Spectroscopy of Organic Compounds Oriented for Planetology), and (2) the extended sources in comets, through a laboratory program of quantitative studies of photochemical and thermal degradation processes on relevant polymers (e.g., Polyoxymethylene) by the SEMAPhOrE Cometaire program (French acronym for Experimental Simulation and Modeling Applied to Organic Chemistry in Cometary Environment).

Reaction process of {alpha} {yields} {gamma} massive transformation in Ti-rich TiAl alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumagai, T.; Abe, E.; Nakamura, M.

1995-08-01

Reaction sequence of the massive transformation from the high-temperature {alpha}-Ti phase to the {gamma}-TiAl phase ({gamma}{sub m}) in a Ti-48at.% Al alloy has been examined in terms of optical and transmission electron microscopes. Both transformed and untransformed regions were macroscopically observed in the sample quenched from the high-temperature {alpha} phase field, when the sample was held there for a extended period of time prior to quenching. The transformed region consists of randomly oriented fine {gamma} single phase grains, in which many thermal anti-phase domains (TAPDs), together with a number of stacking faults were observed. In contrast, the untransformed region comprisesmore » extremely fine lamellae of the {gamma} and {alpha}{sub 2}-Ti{sub 3}Al phases, and the {gamma} plates were found to run through the TAPDs caused by {alpha} {yields} {alpha}{sub 2} ordering. Subsequent aging at 1,273 K causes the microstructure change in the untransformed region from {alpha}{sub 2}/{gamma} lamellae to {gamma}/{gamma} lamellae spontaneously and expands the {gamma}{sub m} region. These observations suggest that the {alpha} {yields} {gamma}{sub m} transformation proceeds through formation of fine {gamma} plates.« less

Transformation of topologically close-packed β-W to body-centered cubic α-W: Comparison of experiments and computations.

PubMed

Barmak, Katayun; Liu, Jiaxing; Harlan, Liam; Xiao, Penghao; Duncan, Juliana; Henkelman, Graeme

2017-10-21

The enthalpy and activation energy for the transformation of the metastable form of tungsten, β-W, which has the topologically close-packed A15 structure (space group Pm3¯n), to equilibrium α-W, which is body-centered cubic (A2, space group Im3¯m), was measured using differential scanning calorimetry. The β-W films were 1 μm-thick and were prepared by sputter deposition in argon with a small amount of nitrogen. The transformation enthalpy was measured as -8.3 ± 0.4 kJ/mol (-86 ± 4 meV/atom) and the transformation activation energy as 2.2 ± 0.1 eV. The measured enthalpy was found to agree well with the difference in energies of α and β tungsten computed using density functional theory, which gave a value of -82 meV/atom for the transformation enthalpy. A calculated concerted transformation mechanism with a barrier of 0.4 eV/atom, in which all the atoms in an A15 unit cell transform into A2, was found to be inconsistent with the experimentally measured activation energy for any critical nucleus larger than two A2 unit cells. Larger calculations of eight A15 unit cells spontaneously relax to a mechanism in which part of the supercell first transforms from A15 to A2, creating a phase boundary, before the remaining A15 transforms into the A2 phase. Both calculations indicate that a nucleation and growth mechanism is favored over a concerted transformation. More consistent with the experimental activation energy was that of a calculated local transformation mechanism at the A15-A2 phase boundary, computed as 1.7 eV using molecular dynamics simulations. This calculated phase transformation mechanism involves collective rearrangements of W atoms in the disordered interface separating the A15 and A2 phases.

Constitutive modeling and structural analysis considering simultaneous phase transformation and plastic yield in shape memory alloys

NASA Astrophysics Data System (ADS)

Hartl, D. J.; Lagoudas, D. C.

2009-10-01

The new developments summarized in this work represent both theoretical and experimental investigations of the effects of plastic strain generation in shape memory alloys (SMAs). Based on the results of SMA experimental characterization described in the literature and additional testing described in this work, a new 3D constitutive model is proposed. This phenomenological model captures both the conventional shape memory effects of pseudoelasticity and thermal strain recovery, and additionally considers the initiation and evolution of plastic strains. The model is numerically implemented in a finite element framework using a return mapping algorithm to solve the constitutive equations at each material point. This combination of theory and implementation is unique in its ability to capture the simultaneous evolution of recoverable transformation strains and irrecoverable plastic strains. The consideration of isotropic and kinematic plastic hardening allows the derivation of a theoretical framework capturing the interactions between irrecoverable plastic strain and recoverable strain due to martensitic transformation. Further, the numerical integration of the constitutive equations is formulated such that objectivity is maintained for SMA structures undergoing moderate strains and large displacements. The implemented model has been used to perform 3D analysis of SMA structural components under uniaxial and bending loads, including a case of local buckling behavior. Experimentally validated results considering simultaneous transformation and plasticity in a bending member are provided, illustrating the predictive accuracy of the model and its implementation.

On Mutual Transform Between Number-Difference State and Phase State Corresponding to Operational Phase Operator

NASA Astrophysics Data System (ADS)

Fan, Hong-Yi; Hu, Hai-Peng

2005-09-01

In the mutual transform between the number-difference state and the phase state corresponding to the operational phase operator we find that there exists an end-point ambiguousness. This problem can be avoided by Lighthill's method. The project supported by the Ph. D Tutoring Programme of the Educational Ministry of China

Nanoscale Properties of Rocks and Subduction Zone Rheology: Inferences for the Mechanisms of Deep Earthquakes

NASA Astrophysics Data System (ADS)

Riedel, M. R.

2007-12-01

Grain boundaries are the key for the understanding of mineral reaction kinetics. More generally, nanometer scale processes involved in breaking and establishing bonds at reaction sites determine how and at which rate bulk rock properties change in response to external tectonic forcing and possibly feed back into various geodynamic processes. A particular problem is the effects of grain-boundary energy on the kinetics of the olivine-spinel phase transformation in subducting slabs. Slab rheology is affected in many ways by this (metastable) mineral phase change. Sluggish kinetics due to metastable hindrance is likely to cause particular difficulties, because of possible strong non-linear feedback loops between strain-rate and change of creep properties during transformation. In order to get these nanoscale properties included into thermo-mechanical models, reliable kinetic data is required. The measurement of grain-boundary energies is, however, a rather difficult problem. Conventional methods of grain boundary surface tension measurement include (a) equilibrium angles at triple junction (b) rotating ball method (c) thermal groove method, and others (Gottstein & Shvindlerman, 1999). Here I suggest a new method that allows for the derivation of grain-boundary energies for an isochemical phase transformation based on experimental (in-situ) kinetic data in combination with a corresponding dynamic scaling law (Riedel and Karato, 1997). The application of this method to the olivine-spinel phase transformation in subducting slabs provides a solution to the extrapolation problem of measured kinetic data: Any kinetic phase boundary measured at the laboratory time scale can be "scaled" to the correct critical isotherm at subduction zones, under experimentelly "forbidden" conditions (Liou et al., 2000). Consequences for the metastability hypothesis that relates deep seismicity with olivine metastability are derived and discussed. References: Gottstein G, Shvindlerman LS (1999) Grain Boundary Migration in Metals, CRC Press, 385 pp., New York. Riedel MR, Karato S (1997) Grain-Size Evolution in Subducted Oceanic Lithosphere Associated with the Olivine- Spinel Transformation and Its Effects on Rheology. EPSL 148: 27-43. Liou JG, Hacker BR, Zhang RY (2000) Into the forbidden zone. Science 287, 1215-1216.

Comparison of vapor formation of water at the solid/water interface to colloidal solutions using optically excited gold nanostructures.

PubMed

Baral, Susil; Green, Andrew J; Livshits, Maksim Y; Govorov, Alexander O; Richardson, Hugh H

2014-02-25

The phase transformation properties of liquid water to vapor is characterized by optical excitation of the lithographically fabricated single gold nanowrenches and contrasted to the phase transformation properties of gold nanoparticles located and optically excited in a bulk solution system [two and three dimensions]. The 532 nm continuous wave excitation of a single gold nanowrench results in superheating of the water to the spinodal decomposition temperature of 580 ± 20 K with bubble formation below the spinodal decomposition temperature being a rare event. Between the spinodal decomposition temperature and the boiling point liquid water is trapped into a metastable state because a barrier to vapor nucleation exists that must be overcome before the thermodynamically stable state is realized. The phase transformation for an optically heated single gold nanowrench is different from the phase transformation of optically excited colloidal gold nanoparticles solution where collective heating effects dominates and leads to the boiling of the solution exactly at the boiling point. In the solution case, the optically excited ensemble of nanoparticles collectively raises the ambient temperature of water to the boiling point where liquid is converted into vapor. The striking difference in the boiling properties of the single gold nanowrench and the nanoparticle solution system can be explained in terms of the vapor-nucleation mechanism, the volume of the overheated liquid, and the collective heating effect. The interpretation of the observed regimes of heating and vaporization is consistent with our theoretical modeling. In particular, we explain with our theory why the boiling with the collective heating in a solution requires 3 orders of magnitude less intensity compared to the case of optically driven single nanowrench.

Phase Transformations of an Fe-0.85 C-17.9 Mn-7.1 Al Austenitic Steel After Quenching and Annealing

NASA Astrophysics Data System (ADS)

Cheng, Wei-Chun

2014-09-01

Low-density Mn-Al steels could potentially be substitutes for commercial Ni-Cr stainless steels. However, the development of the Mn-Al stainless steels requires knowledge of the phase transformations that occur during the steel making processes. Phase transformations of an Fe-0.85 C-17.9 Mn-7.1 Al (wt.%) austenitic steel, which include spinodal decomposition, precipitation transformations, and cellular transformations, have been studied after quenching and annealing. The results show that spinodal decomposition occurs prior to the precipitation transformation in the steel after quenching and annealing at temperatures below 1023 K and that coherent fine particles of L12-type carbide precipitate homogeneously in the austenite. The cellular transformation occurs during the transformation of high-temperature austenite into lamellae of austenite, ferrite, and kappa carbide at temperatures below 1048 K. During annealing at temperatures below 923 K, the austenite decomposes into lamellar austenite, ferrite, κ-carbide, and M23C6 carbide grains for another cellular transformation. Last, when annealing at temperatures below 873 K, lamellae of ferrite and κ-carbide appear in the austenite.

From Majorana fermions to topological order.

PubMed

Terhal, Barbara M; Hassler, Fabian; DiVincenzo, David P

2012-06-29

We consider a system consisting of a 2D network of links between Majorana fermions on superconducting islands. We show that the fermionic Hamiltonian modeling this system is topologically ordered in a region of parameter space: we show that Kitaev's toric code emerges in fourth-order perturbation theory. By using a Jordan-Wigner transformation we can map the model onto a family of signed 2D Ising models in a transverse field where the signs, ferromagnetic or antiferromagnetic, are determined by additional gauge bits. Our mapping allows an understanding of the nonperturbative regime and the phase transition to a nontopological phase. We discuss the physics behind a possible implementation of this model and argue how it can be used for topological quantum computation by adiabatic changes in the Hamiltonian.

Metastable phase transformation and hcp-ω transformation pathways in Ti and Zr under high hydrostatic pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Lei; Ding, Xiangdong, E-mail: dingxd@mail.xjtu.edu.cn, E-mail: ekhard@esc.cam.ac.uk; Sun, Jun

2016-07-18

The energy landscape of Zr at high hydrostatic pressure suggests that its transformation behavior is strongly pressure dependent. This is in contrast to the known transition mechanism in Ti, which is essentially independent of hydrostatic pressure. Generalized solid-state nudged elastic band calculations at constant pressure shows that α-Zr transforms like Ti only at the lowest pressure inside the stability field of ω-phase. Different pathways apply at higher pressures where the energy landscape contains several high barriers so that metastable states are expected, including the appearance of a transient bcc phase at ca. 23 GPa. The global driving force for the hcp-ωmore » transition increases strongly with increasing pressure and reaches 23.7 meV/atom at 23 GPa. Much of this energy relates to the excess volume of the hcp phase compared with its ω phase.« less

Driving forces of redistribution of elements during quasicrystalline phase formation under heating of mechanically alloyed Al65Cu23Fe12 powder

NASA Astrophysics Data System (ADS)

Tcherdyntsev, V. V.; Kaloshkin, S. D.; Shelekhov, E. V.; Principi, G.; Rodin, A. O.

2008-02-01

Al65Cu23Fe12 alloys were prepared by ball milling of the elemental powders mixture. Phase and structural transformations at heating of as-milled powders were investigated by X-ray diffraction analysis. Precision analysis of Mössbauer spectra was performed to check the adequacy of the fitting of X-ray diffraction patterns. The results were compared with the data of differential scanning and solution calorimetry, as well as with the thermodynamic literature data, in order to estimate the driving forces of redistribution of elements that preceded the formation of single-phase quasicrystalline structure. The heat of elements mixing, which is positive for Cu-Fe system and negative for Al-Fe and Al-Cu systems, was supposed to be a decisive factor for phase transformations during heating of the alloy. The correlation between sequence of phase transformations during heating and the thermodynamic data was discussed and the scheme describing phase transformations observed was proposed.

Compressive Sensing Cluster Expansion Studies of Lithium Intercalation and Phase Transformation in MoS2 for Energy Storage

NASA Astrophysics Data System (ADS)

Liu, Chi-Ping; Zhou, Fei; Ozolins, Vidvuds; University of California, Los Angeles Collaboration; Lawrence livermore national laboratory Collaboration

2015-03-01

Bulk molybdenum disulfide (MoS2) is a good electrode material candidate for energy storage applications, such as lithium ion batteries and supercapacitors due to its high theoretical energy and power density. First-principles density-functional theory (DFT) calculations combined with cluster expansion are an effective method to study thermodynamic and kinetic properties of electrode materials. In order to construct accurate models for cluster expansion, it is important to effectively choose clusters with significant contributions. In this work, we employ a compressive sensing based technique to select relevant clusters in order to build an accurate Hamiltonian for cluster expansion, enabling the study of Li intercalation in MoS2. We find that the 2H MoS2 structure is only stable at low Li content while 1T MoS2 is the preferred phase at high Li content. The results show that the 2H MoS2 phase transforms into the disordered 1T phase and the disordered 1T structure remains after the first Li insertion/deinsertion cycle suggesting that disordered 1T MoS2 is stable even at dilute Li content. This work also highlights that cluster expansion treated with compressive sensing is an effective and powerful tool for model construction and can be applied to advanced battery and supercapacitor electrode materials.

Heat transfer and phase transitions of water in multi-layer cryolithozone-surface systems

NASA Astrophysics Data System (ADS)

Khabibullin, I. L.; Nigametyanova, G. A.; Nazmutdinov, F. F.

2018-01-01

A mathematical model for calculating the distribution of temperature and the dynamics of the phase transfor-mations of water in multilayer systems on permafrost-zone surface is proposed. The model allows one to perform calculations in the annual cycle, taking into account the distribution of temperature on the surface in warm and cold seasons. A system involving four layers, a snow or land cover, a top layer of soil, a layer of thermal-insulation materi-al, and a mineral soil, is analyzed. The calculations by the model allow one to choose the optimal thickness and com-position of the layers which would ensure the stability of structures built on the permafrost-zone surface.

Acanthite–argentite transformation in nanocrystalline silver sulfide and the Ag{sub 2}S/Ag nanoheterostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gusev, A. I., E-mail: gusev@ihim.uran.ru; Sadovnikov, S. I.

Nanocrystalline acanthite-structured silver sulfide of the monoclinic structure and a Ag{sub 2}S/Ag nanoheterostructure are produced. The high-temperature X-ray diffraction technique is applied to the in situ study of the (acanthite α-Ag{sub 2}S)–(argentite β-Ag{sub 2}S) phase transformation in nanocrystalline silver sulfide. The crystal structure of argentite is refined, and it is found that the content of vacant sites in the metal sublattice of argentite exceeds 92%. A model of a resistive switch, whose operation is based on the reversible acanthite–argentite transformation in a Ag{sub 2}S/Ag heterostructure, is considered.

Phase recovery in temporal speckle pattern interferometry using the generalized S-transform.

PubMed

Federico, Alejandro; Kaufmann, Guillermo H

2008-04-15

We propose a novel approach based on the generalized S-transform to retrieve optical phase distributions in temporal speckle pattern interferometry. The performance of the proposed approach is compared with those given by well-known techniques based on the continuous wavelet, the Hilbert transforms, and a smoothed time-frequency distribution by analyzing interferometric data degraded by noise, nonmodulating pixels, and modulation loss. The advantages and limitations of the proposed phase retrieval approach are discussed.

High-pressure transformation in the cobalt spinel ferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blasco, J., E-mail: jbc@posta.unizar.es; Subías, G.; García, J.

2015-01-15

We report high pressure angle-dispersive x-ray diffraction measurements on Co{sub x}Fe{sub 3−x}O{sub 4} (x=1, 1.5, 1.75) spinels at room temperature up to 34 GPa. The three samples show a similar structural phase transformation from the cubic spinel structure to an analogous post-spinel phase at around 20 GPa. Spinel and post-spinel phases coexist in a wide pressure range (∼20–25 GPa) and the transformation is irreversible. The equation of state of the three cubic spinel ferrites was determined and our results agree with the data obtained in related oxide spinels showing the role of the pressure-transmitting medium for the accurate determination ofmore » the equation of state. Measurements releasing pressure revealed that the post-spinel phase is stable down to 4 GPa when it decomposes yielding a new phase with poor crystallinity. Later compression does not recover either the spinel or the post-spinel phases. This phase transformation induced by pressure explains the irreversible lost of the ferrimagnetic behavior reported in these spinels. - Graphical abstract: Pressure dependence of the unit cell volume per formula unit for Co{sub 1.5}Fe{sub 1.5}O{sub 4} spinel. Circles and squares stand for spinel and postspinel phases, respectively. Dark (open) symbols: determination upon compression (decompression). - Highlights: • The pressure induces similar phase transformation in Co{sub 3−x}Fe{sub x}O{sub 4} spinels (1≤x≤2). • The postspinel phases decompose after releasing pressure. • The irreversibility of this phase transformation explains the disappearance of magnetism in these spinels after applying pressure. • Accurate equation of state can be obtained up to 10 GPa using an alcohol mixture as pressure transmitting medium. • The equation of state suggests similar elastic properties for these spinels in this composition range.« less

500 keV Ar2+ ion irradiation induced anatase to brookite phase transformation and ferromagnetism at room temperature in TiO2 thin films

NASA Astrophysics Data System (ADS)

Bharati, B.; Mishra, N. C.; Kanjilal, D.; Rath, Chandana

2018-01-01

In our earlier report, where we have demonstrated ferromagnetic behavior at room temperature (RT) in TiO2 thin films deposited through electron beam evaporation technique followed by annealing either in Ar or O2 atmosphere [Mohanty et al., Journal of Magnetism and Magnetic Materials 355 (2014) 240-245], here we have studied the evolution of structure and magnetic properties after irradiating the TiO2 thin films with 500 keV Ar2+ ions. The pristine film while exhibits anatase phase, the films become amorphous after irradiating at fluence in the range 1 × 1014 to 1 × 1016 ions/cm2. Increasing the fluence up to 5 × 1016 ions/cm2, amorphous to crystalline phase transformation occurs and the structure becomes brookite. Although anatase to rutile phase transformation is usually reported in literatures, anatase to brookite phase transformation is an unusual feature which we have reported here for the first time. Such anatase to brookite phase transformation is accompanied with grain growth without showing any change in film thickness evidenced from Rutherford's Back Scattering (RBS) measurement. From scanning probe micrographs (SPM), roughness is found to be more in amorphous films than in the crystalline ones. Anatase to brookite phase transformation could be realized by considering the importance of intermediate amorphous phase. Because due to amorphous phase, heat deposited by energetic ions are localized as dissipation of heat is less and as a result, the localized region crystallizes in brookite phase followed by grain growth as observed in highest fluence. Further, we have demonstrated ferromagnetic behavior at RT in irradiated films similar to pristine one, irrespective of their phase and crystallinity. Origin for room temperature ferromagnetism (RTFM) is attributed to the presence of oxygen vacancies which is confirmed by carrying out XPS measurement.

Investigation of electrical and magnetic properties of ferro-nanofluid on transformers

PubMed Central

2011-01-01

This study investigated a simple model of transformers that have liquid magnetic cores with different concentrations of ferro-nanofluids. The simple model was built on a capillary by enamel-insulated wires and with ferro-nanofluid loaded in the capillary. The ferro-nanofluid was fabricated by a chemical co-precipitation method. The performances of the transformers with either air core or ferro-nanofluid at different concentrations of nanoparticles of 0.25, 0.5, 0.75, and 1 M were measured and simulated at frequencies ranging from 100 kHz to 100 MHz. The experimental results indicated that the inductance and coupling coefficient of coils grew with the increment of the ferro-nanofluid concentration. The presence of ferro-nanofluid increased resistance, yielding to the decrement of the quality factor, owing to the phase lag between the external magnetic field and the magnetization of the material. PMID:21711784

Investigation of electrical and magnetic properties of ferro-nanofluid on transformers.

PubMed

Tsai, Tsung-Han; Chen, Ping-Hei; Lee, Da-Sheng; Yang, Chin-Ting

2011-03-28

This study investigated a simple model of transformers that have liquid magnetic cores with different concentrations of ferro-nanofluids. The simple model was built on a capillary by enamel-insulated wires and with ferro-nanofluid loaded in the capillary. The ferro-nanofluid was fabricated by a chemical co-precipitation method. The performances of the transformers with either air core or ferro-nanofluid at different concentrations of nanoparticles of 0.25, 0.5, 0.75, and 1 M were measured and simulated at frequencies ranging from 100 kHz to 100 MHz. The experimental results indicated that the inductance and coupling coefficient of coils grew with the increment of the ferro-nanofluid concentration. The presence of ferro-nanofluid increased resistance, yielding to the decrement of the quality factor, owing to the phase lag between the external magnetic field and the magnetization of the material.

Effect of Slag Composition on the Crystallization Kinetics of Synthetic CaO-SiO2-Al2O3-MgO Slags

NASA Astrophysics Data System (ADS)

Esfahani, Shaghayegh; Barati, Mansoor

2018-04-01

The crystallization kinetics of CaO-SiO2-Al2O3-MgO (CSAM) slags was studied with the aid of single hot thermocouple technique (SHTT). Kinetic parameters such as the Avrami exponent ( n), rate coefficient ( K), and effective activation energy of crystallization ( E A ) were obtained by kinetic analysis of data obtained from in situ observation of glassy to crystalline transformation and image analysis. Also, the dependence of nucleation and growth rates of crystalline phases were quantified as a function of time, temperature, and slag basicity. Together with the observations of crystallization front, they facilitated establishing the dominant mechanisms of crystallization. In an attempt to predict crystallization rate under non-isothermal conditions, a mathematical model was developed that employs the rate data of isothermal transformation. The model was validated by reproducing an experimental continuous cooling transformation diagram purely from isothermal data.

Phase transformation and magnetic properties of MnAl powders prepared by elemental-doping and salt-assisted ball milling

NASA Astrophysics Data System (ADS)

Qian, Hui-Dong; Si, Ping-Zhan; Choi, Chul-Jin; Park, Jihoon; Cho, Kyung Mox

2018-05-01

The effects of elemental doping of Si and Fe on the ɛ→τ phase transformation and the magnetic properties of MnAl were studied. The magnetic powders of Si- and Fe-doped MnAl were prepared by using induction melting followed by water-quenching, annealing, and salt-assisted ball-milling. The Fe-doped MnAl powders are mainly composed of the L10-structured τ-phase, while the Si-doped MnAl are composed of τ-phase and a small fraction of γ2- and β-phases. A unique thin leaves-like morphology with thickness of several tens of nanometers and diameter size up to 500 nm were observed in the Si-doped MnAl powders. The Fe-doped MnAl powders show irregular shape with much larger dimensions in the range from several to 10 μm. The morphology difference of the samples was ascribed to the variation of the mechanical properties affected by different doping elements. The phase transformation temperatures of the ɛ-phase of the samples were measured. The doping of Fe decreases the onset temperature of the massive phase transformation in MnAl, while the Si-doping increases the massive phase transformation temperature. Both Fe and Si increase the Curie temperature of MnAl. A substantially enhanced coercivity up to 0.45 T and 0.42 T were observed in the ball-milled MnAl powders doped with Si and Fe, respectively.

Influence of ignition process on mineral phase transformation in municipal solid waste incineration (MSWI) fly ash: Implications for estimating loss-on-ignition (LOI).

PubMed

Mu, Yue; Saffarzadeh, Amirhomayoun; Shimaoka, Takayuki

2017-01-01

This research focused on the mineral phase transformation under varied ignition conditions with the objective of estimating loss-on-ignition (LOI) parameter in municipal solid waste incineration (MSWI) fly ash residues. LOI is commonly used to measure the volatile species, unburned carbon and moisture in the solid materials. There are criteria for LOI measurement in some research fields, while there is no standard protocol for LOI measurement in MSWI fly ash. Using thermogravimetry technique, the ignition condition candidates were proposed at 440/700/900°C for 1 and 2h. Based on X-ray diffractometry results, obvious mineral phase transformation occurred as a function of ignition temperature variation rather than ignition time. Until 440°C, only some minor phases disappeared comparing with the original state. Significant mineral phase transformations of major phases (Ca- and Cl-based minerals) occurred between 440 and 700°C. The mineral phase transformation and the occurrence of newly-formed phases were determined not only by the ignition condition but also by the content of the co-existing components. Mineral phase components rarely changed when ignition temperature rose from 700 to 900°C. Consequently, in order to prevent critical damages to the original mineralogical composition of fly ash, the lowest ignition temperature (440°C) for 2h was suggested as an ideal measurement condition of LOI in MSWI fly ash. Copyright © 2016 Elsevier Ltd. All rights reserved.

Introduction to Phase-Resolving Wave Modeling with FUNWAVE

DTIC Science & Technology

2015-07-01

Boussinesq wave models have become a useful tool for modeling surface wave transformation from deep water to the swash zone, as well as wave-induced...overlapping area of ghost cells, three rows deep , as required by the fourth-order MUSCL-TVD scheme. The MPI with nonblocking communication was used to...implemented ERDC/CHL CHETN-I-87 July 2015 12 SPONGE LAYER SPONGE_ON Sponge_west_width Sponge_east_width Sponge_south_width

Finite element analysis of the tetragonal to monoclinic phase transformation during oxidation of zirconium alloys

NASA Astrophysics Data System (ADS)

Platt, P.; Frankel, P.; Gass, M.; Howells, R.; Preuss, M.

2014-11-01

Corrosion is a key limiting factor in the degradation of zirconium alloys in light water reactors. Developing a mechanistic understanding of the corrosion process offers a route towards improving safety and efficiency as demand increases for higher burn-up of fuel. Oxides formed on zirconium alloys are composed of both monoclinic and meta-stable tetragonal phases, and are subject to a number of potential mechanical degradation mechanisms. The work presented investigates the link between the tetragonal to monoclinic oxide phase transformation and degradation of the protective character of the oxide layer. To achieve this, Abaqus finite element analysis of the oxide phase transformation has been carried out. Study of the change in transformation strain energy shows how relaxation of oxidation induced stress and fast fracture at the metal-oxide interface could destabilise the tetragonal phase. Central to this is the identification of the transformation variant most likely to form, and understanding why twinning of the transformed grain is likely to occur. Development of transformation strain tensors and analysis of the strain components allows some separation of dilatation and shear effects. Maximum principal stress is used as an indication of fracture in the surrounding oxide layer. Study of the stress distributions shows the way oxide fracture is likely to occur and the differing effects of dilatation and shape change. Comparison with literature provides qualitative validation of the finite element simulations.

A new problem in mathematical physics associated with the problem of coherent phase transformation

NASA Astrophysics Data System (ADS)

Grinfeld, M. A.

1985-06-01

The description of heterogeneous coherent phase equilibria in an elastic single component system is shown to lead, in the approximation of small intrinsic deformation, to a new problem in mathematical physics with an unknown bound. The low order terms of the resulting system of equilibrium equations coincide with the equations of the classical linear theory of elasticity (generally speaking, anisotropic); however, the problem remains strongly nonlinear overall, inasmuch as it contains an unknown bound and a boundary condition on it which is quadratic with respect to translation. The formulas obtained are used to find certain explicit solutions to the boundary problems. As an example, the problem of heterogeneous equilibria in an infinite rectangular isotropic beam with free faces and constant loading on the surfaces x squared = const can be examined. A modeling problem for the asymptote of small intrinsic deformation during coherent phase transformation is presented as a scalar analog of the vector problem considered initially.

Human Data Supporting Glyburide in Ischemic Stroke

PubMed Central

Sheth, Kevin N.; Simard, J. Marc; Elm, Jordan; Kronenberg, Golo; Kunte, Hagen; Kimberly, W. Taylor

2016-01-01

The SUR1-TRPM4 channel is a critical determinant of edema and hemorrhagic transformation after focal ischemia. Blockade of this channel by the small molecule glyburide results in improved survival and neurological outcome in multiple preclinical models of ischemic stroke. A robust, compelling body of evidence suggests that an intravenous (IV) formulation of glyburide, RP-1127, can prevent swelling and improve outcome in patients with stroke. Retrospective studies of diabetic stroke patients show improved outcomes in patients who are continued on sulfonylureas after stroke onset. Early phase II study of MRI and plasma biomarkers support the conclusion that RP-1127 may decrease swelling and hemorrhagic transformation. Finally, the ongoing phase II RP-1127 development program has demonstrated continued safety as well as feasibility of enrollment and tolerability of the intervention. Continued efforts to complete the ongoing phase IIb study and definitive efficacy studies are urgently needed to bring a candidate pharmacotherapy to a population of severe stroke patients that currently have no alternative. PMID:26463916

Human Data Supporting Glyburide in Ischemic Stroke.

PubMed

Sheth, Kevin N; Simard, J Marc; Elm, Jordan; Kronenberg, Golo; Kunte, Hagen; Kimberly, W Taylor

2016-01-01

The SUR1-TRPM4 channel is a critical determinant of edema and hemorrhagic transformation after focal ischemia. Blockade of this channel by the small molecule glyburide results in improved survival and neurological outcome in multiple preclinical models of ischemic stroke. A robust, compelling body of evidence suggests that an intravenous formulation of glyburide, RP-1127, can prevent swelling and improve outcome in patients with stroke. Retrospective studies of diabetic stroke patients show improved outcomes in patients who are continued on sulfonylureas after stroke onset. An early phase II study using magnetic resonance imaging and plasma biomarkers supports the conclusion that RP-1127 may decrease swelling and hemorrhagic transformation. Finally, the ongoing phase II RP-1127 development program has demonstrated continued safety as well as feasibility of enrollment and tolerability of the intervention. Continued efforts to complete the ongoing phase II study and definitive efficacy studies are needed to bring a candidate pharmacotherapy to a population of severe stroke patients that currently have no alternative.

The effects of Nitinol phases on corrosion and fatigue behavior

NASA Astrophysics Data System (ADS)

Denton, Melissa

The purpose of these studies was to provide a detailed understanding of Nitinol phases and their effects on corrosion and fatigue life. The two primary phases, austenite and martensite, were carefully evaluated with respect to material geometry, corrosion behavior, wear, and fatigue life. Material characterization was performed using several techniques that include metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray photoelectron spectrum (XPS), and Auger electron spectroscopy (AES). Uniaxial tensile tests were conducted to determine the mechanical properties such as elongation, ultimate tensile strength, modulus, transformation strain, and plateau stress. In addition, accelerated wear testing and four point bend fatigue testing were completed to study the fatigue life and durability of the material. The corrosion of Nitinol was found to be dependent on various surface conditions. Electrochemical corrosion behavior of each phase was investigated using cyclic potentiodyamic polarization testing. The corrosion response of electropolished Nitinol was found to be acceptable, even after durability testing. Stress-induced martensite had a lower breakdown potential due to a rougher surface morphology, while thermally induced martensite and austenite performed similarly well. The surface conditioning also had a significant effect on Nitinol mechanical properties. Electropolishing provided a smooth mirror finish that reduced localized texture and enhanced the ductility of the material. Quasi-static mechanical properties can be good indicators of fatigue life, but further fatigue testing revealed that phase transformations had an important role as well. The governing mechanisms for the fatigue life of Nitinol were determined to be both martesitic phase transformations and surface defects. A new ultimate dislocation strain model was proposed based on specific accelerated step-strain testing.

[Study on phase correction method of spatial heterodyne spectrometer].

PubMed

Wang, Xin-Qiang; Ye, Song; Zhang, Li-Juan; Xiong, Wei

2013-05-01

Phase distortion exists in collected interferogram because of a variety of measure reasons when spatial heterodyne spectrometers are used in practice. So an improved phase correction method is presented. The phase curve of interferogram was obtained through Fourier inverse transform to extract single side transform spectrum, based on which, the phase distortions were attained by fitting phase slope, so were the phase correction functions, and the convolution was processed between transform spectrum and phase correction function to implement spectrum phase correction. The method was applied to phase correction of actually measured monochromatic spectrum and emulational water vapor spectrum. Experimental results show that the low-frequency false signals in monochromatic spectrum fringe would be eliminated effectively to increase the periodicity and the symmetry of interferogram, in addition when the continuous spectrum imposed phase error was corrected, the standard deviation between it and the original spectrum would be reduced form 0.47 to 0.20, and thus the accuracy of spectrum could be improved.

Tissue Inhibitor of Metalloproteinase 1 Expression Associated with Gene Demethylation Confers Anoikis Resistance in Early Phases of Melanocyte Malignant Transformation1

PubMed Central

Ricca, Tatiana I; Liang, Gangning; Suenaga, Ana Paula M; Han, Sang W; Jones, Peter A; Jasiulionis, Miriam G

2009-01-01

Although anoikis resistance has been considered a hallmark of malignant phenotype, the causal relation between neoplastic transformation and anchorage-independent growth remains undefined. We developed an experimental model of murine melanocyte malignant transformation, where a melanocyte lineage (melan-a) was submitted to sequential cycles of anchorage blockade, resulting in progressive morphologic alterations, and malignant transformation. Throughout this process, cells corresponding to premalignant melanocytes and melanoma cell lines were established and show progressive anoikis resistance and increased expression of Timp1. In melan-a melanocytes, Timp1 expression is suppressed by DNA methylation as indicated by its reexpression after 5-aza-2′-deoxycytidine treatment. Methylation-sensitive single-nucleotide primer extension analysis showed increased demethylation in Timp1 in parallel with its expression along malignant transformation. Interestingly, TIMP1 expression has already been related with negative prognosis in some human cancers. Although described as a MMP inhibitor, this protein has been associated with apoptosis resistance in different cell types. Melan-a cells overexpressing Timp1 showed increased survival in suspension but were unable to form tumors in vivo, whereas Timp1-overexpressing melanoma cells showed reduced latency time for tumor appearance and increased metastatic potential. Here, we demonstrated for the first time an increment in Timp1 expression since the early phases of melanocyte malignant transformation, associated to a progressive gene demethylation, which confers anoikis resistance. In this way, Timp1 might be considered as a valued marker for melanocyte malignant transformation. PMID:19956395

Twinning induced by the rhombohedral to orthorhombic phase transition in lanthanum gallate (LaGaO3)

NASA Astrophysics Data System (ADS)

Wang, W. L.; Lu, H. Y.

2006-10-01

Phase-transformation-induced twins in pressureless-sintered lanthanum gallate (LaGaO3) ceramics have been analysed using the transmission electron microscopy (TEM). Twins are induced by solid state phase transformation upon cooling from the rhombohedral (r, Rbar{3}c) to orthorhombic ( o, Pnma) symmetry at ˜145°C. Three types of transformation twins {101} o , {121} o , and {123} o were found in grains containing multiple domains that represent orientation variants. Three orthorhombic orientation variants were distinguished from the transformation domains converged into a triple junction. These twins are the reflection type as confirmed by tilting experiment in the microscope. Although not related by group-subgroup relation, the transformation twins generated by phase transition from rhombohedral to orthorhombic are consistent with those derived from taking cubic Pm {bar {3}}m aristotype of the lowest common supergroup symmetry as an intermediate metastable structure. The r→ o phase transition of first order in nature may have occurred by a diffusionless, martensitic-type or discontinuous nucleation and growth mechanism.

Hydrothermal synthesis of Nd3+-doped heterojunction ms/tz-BiVO4 and its enhanced photocatalytic performance

NASA Astrophysics Data System (ADS)

Chen, Ruizhi; Wang, Weixuan; Jiang, Dongmei; Chu, Xiaoxuan; Ma, Xueming; Zhan, Qingfeng

2018-06-01

BiVO4 photocatalysts with different Nd3+ doping content were prepared by a hydrothermal method with varied hydrothermal reaction time. The effects of Nd3+ doping on phase transformation, morphology, chemical valence, optical properties and photocatalytic activities were investigated. With different reaction time, phase transformation from tetragonal zircon (tz-BiVO4) to monoclinic scheelite (ms-BiVO4) could be found, and Nd3+ doping played a suppressive role in this process. Scanning electron microscopy showed the morphology evolved from irregular structure to rod-like shapes with phase transformation. The photoluminescence induced by Nd3+ doping could be confirmed by UV-vis diffuse reflectance spectra. Photocatalytic performance tests had been performed under simulated solar conditions and sample with 1 at% Nd3+ doping and 5 h reaction time showed the best performance (89% degradation rate in 90 min). The pH also showed great influence on morphology and phase transformation of samples. Finally, the phyotocatalytic mechanism and effects of Nd3+ in phase transformation were discussed.

a Thermal Conduction Switch Based on Low Hysteresis Nitife Shape Memory Alloy Helical Springs

NASA Astrophysics Data System (ADS)

Krishnan, V. B.; Bewerse, C.; Notardonato, W. U.; Vaidyanathan, R.

2008-03-01

Shape memory alloy (SMA) actuators possess an inherent property of sensing a change in temperature and delivering significant force against external loads through a shape change resulting from a temperature-induced phase transformation. The utilization of a reversible trigonal (R-phase) to cubic phase transformation in NiTiFe SMAs allows for this strain recovery to occur with reduced hysteresis between the forward and reverse transformations. However, the magnitude of the strain recovery associated with the R-phase transformation is lower than that of the monoclinic to cubic phase transformation. The use of helical springs can compensate for this design constraint as they produce significant stroke when compared to straight elements such as thin strips and wires. This work reports on the development and implementation of NiTiFe helical springs in a low-hysteresis thermal conduction switch for advanced spaceport applications associated with NASA's requirements for future lunar and Mars missions. Such a low-hysteresis thermal conduction switch can provide on-demand heat transfer between two reservoirs at different temperatures.

Phase Transformation and Shape Memory Effect of Ti-Pd-Pt-Zr High-Temperature Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Yamabe-Mitarai, Yoko; Takebe, Wataru; Shimojo, Masayuki

2017-12-01

To understand the potential of high-temperature shape memory alloys, we have investigated the phase transformation and shape memory effect of Ti-(50 - x)Pt- xPd-5Zr alloys ( x = 0, 5, and 15 at.%), which present the B2 structure in the austenite phase and B19 structure in the martensite phase. Their phase transformation temperatures are very high; A f and M f of Ti-50Pt are 1066 and 1012 °C, respectively. By adding Zr and Pd, the phase transition temperatures decrease, ranging between 804 and 994 °C for A f and 590 and 865 °C for M f. Even at the high phase transformation temperature, a maximum recovery ratio of 70% was obtained for one cycle in a thermal cyclic test. A work output of 1.2 J/cm3 was also obtained. The recovery ratio obtained by the thermal cyclic test was less than 70% because the recovery strain was < 1% and a large irrecoverable strain was obtained. The shape recovery was explained by the austenite strength. The training effect was also investigated.

Phase transformation as the single-mode mechanical deformation of silicon

DOE PAGES

Wong, Sherman; Haberl, Bianca; Williams, James S.; ...

2015-06-25

The mixture of the metastable body-centered cubic (bc8) and rhombohedral (r8) phases of silicon that is formed via nanoindentation of diamond cubic (dc) silicon exhibits properties that are of scientifc and technological interest. This letter demonstrates that large regions of this mixed phase can be formed in crystalline Si via nanoindentation without signifcant damage to the surrounding crystal. Cross-sectional transmission electron microscopy is used to show that volumes 6 μm wide and up to 650 nm deep can be generated in this way using a spherical tip of ~21.5 μm diameter. The phase transformed region is characterised using both Ramanmore » microspectroscopy and transmission electron microscopy. It is found that uniform loading using large spherical indenters can favor phase transformation as the sole deformation mechanism as long as the maximum load is below a critical level. We suggest that the sluggish nature of the transformation from the dc-Si phase to the metallic (b-Sn) phase normally results in competing deformation mechanisms such as slip and cracking but these can be suppressed by controlled loading conditions.« less

Effect of V-Nd co-doping on phase transformation and grain growth process of TiO2

NASA Astrophysics Data System (ADS)

Khatun, Nasima; Amin, Ruhul; Anita, Sen, Somaditya

2018-05-01

The pure and V-Nd co-doped TiO2 samples are prepared by the modified sol-gel process. The phase formation is confirmed by XRD spectrum. Phase transformation is delayed in V-Nd co-doped TiO2 (TVN) samples compared to pure TiO2. The particle size is comparatively small in TVN samples at both the temperature 450 °C and 900 °C. Hence the effect of Nd doping is dominated over V doping in both phase transformation and grain growth process of TiO2.

Protection relay of phase-shifting device with thyristor switch for high voltage power transmission lines

NASA Astrophysics Data System (ADS)

Lachugin, V. F.; Panfilov, D. I.; Akhmetov, I. M.; Astashev, M. G.; Shevelev, A. V.

2014-12-01

Problems of functioning of differential current protection systems of phase shifting devices (PSD) with mechanically changed coefficient of transformation of shunt transformer are analyzed. Requirements for devices of protection of PSD with thyristor switch are formulated. Based on use of nonlinear models of series-wound and shunt transformers of PSD modes of operation of major protection during PSD, switching to zero load operation and to operation under load and during short circuit operation were studied for testing PSD with failures. Use of the principle of duplicating by devices of differential current protection (with realization of functions of breaking) of failures of separate pares of PSD with thyristor switch was substantiated. To ensure protection sensitivity to the shunt transformer winding short circuit, in particular, to a short circuit that is not implemented in the current differential protection for PSD with mechanical switch, the differential current protection reacting to the amount of primary ampere-turns of high-voltage and low-voltage winding of this transformer was designed. Studies have shown that the use of differential current cutoff instead of overcurrent protection for the shunt transformer wndings allows one to provide the sensitivity during thyristor failure with the formation of a short circuit. The results of simulation mode for the PSD with switch thyristor designed to be installed as switching point of Voskhod-Tatarskaya-Barabinsk 220 kV transmission line point out the efficiency of the developed solutions that ensure reliable functioning of the PSD.

Long-term batch study of sorption, transformation and extractability to characterize the fate of the veterinary antibiotic sulfadiazine

NASA Astrophysics Data System (ADS)

Sittig, Stephan; Kasteel, Roy; Groeneweg, Joost; Vereecken, Harry

2010-05-01

The occurrence of veterinary antibiotic substances in various environmental compartments is of growing concern. Once released into the environment (e.g. via manure), these organic substances can cause changes in the composition of microbial populations, provoke the development and spreading of resistance genes and finally reach the food chain. The substance under study is the veterinary antibiotic sulfadiazine (SDZ), which belongs to the chemical group of the sulfonamides. These compounds are widely applied in animal husbandry. There are hardly any studies on the macroscopic sorption and desorption behaviour in combination with transformation processes, particularly investigating the sorbed fraction. We are conducting long-term batch sorption experiments to characterize the partitioning between the liquid and the solid phases as well as formation of transformation products. A sequential extraction procedure enables us to analyse the composition of the various sorbed fractions. We applied 14C-labelled SDZ in aqueous solution to fresh soil, originating from an agricultural field (silty loam). Adsorption and desorption studies are conducted for the duration of 60 d and 80 d, respectively. Unique setups for single time-steps allow us to trace the development of the partition process between the liquid and the solid phase and also partitioning within the solid phase. The composition of these liquid phases concerning the parent substance and the transformation products is analyzed. Using Radio-HPLC we find at least five transformation products: 4-hydroxy-sulfadiazine (4-OH-SDZ), 4-(2-iminopyrimidin-1(2H)-yl)-aniline (An-SDZ) and additionally three yet unknown products. By means of a sequential extraction, differently strong bound fractions of the compound can be distinguished. Extractions consist of a mild method (0.01 M CaCl2-solution; 24 h) followed by a methanol extraction (4 h). Finally, a residual fraction is gained by microwave extraction at an elevated temperature (150°C) and pressure (mixture of water and acetonitril, 4:1). Bound residues are determined by combustion. The course of the kinetic adsorption/desorption processes as well as the partitioning of the compound over the various solid phase fractions is observed. Sorption is time-dependent and strongly non-linear. The topsoil shows a significantly higher sorption affinity than the subsoil. While the amount of radioactivity sorbed to the soil matrix increases with time, the extractability decreases significantly, i. e. at the end of the experimental time there is no yield with mild extraction methods. On the contrary, after 60 d, there is still a considerably mass gained with the microwave extraction. Desorption is very slow due to hysteresis. In the topsoil transformation occurs with higher rates, leading to more detectable transformation products as in the subsoil. With our experimental setup it will be possible to set up a kinetic modell for the partitioning of the solute between the liquid and the solid phase. This description will also include an estimation of the transformation parameters.

In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paranjape, Harshad M.; Paul, Partha P.; Amin-Ahmadi, Behnam

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. In this paper, we characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented by electron microscopy. We simulated the local stress state in the specimen using a microstructural model informed by the experimental data. Using these combined microstructure, deformation, andmore » stress data, we report three phenomena, and relate them to specific sources of constraint. During initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of martensite habit plane variants that produce less than theoretical maximum transformation strain. Large Ni 4Ti 3 precipitates potentially contributed to the poor transformation response. Under load, proportional gradients in local rotation and elastic stretch developed in the martensite phase, because of the constraint at phase interfaces. Finally, this combined ff-HEDM, electron microscopy, microstructural simulation toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in other alloys with hierarchical microstructure.« less

In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

DOE PAGES

Paranjape, Harshad M.; Paul, Partha P.; Amin-Ahmadi, Behnam; ...

2017-11-20

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. In this paper, we characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented by electron microscopy. We simulated the local stress state in the specimen using a microstructural model informed by the experimental data. Using these combined microstructure, deformation, andmore » stress data, we report three phenomena, and relate them to specific sources of constraint. During initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of martensite habit plane variants that produce less than theoretical maximum transformation strain. Large Ni 4Ti 3 precipitates potentially contributed to the poor transformation response. Under load, proportional gradients in local rotation and elastic stretch developed in the martensite phase, because of the constraint at phase interfaces. Finally, this combined ff-HEDM, electron microscopy, microstructural simulation toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in other alloys with hierarchical microstructure.« less

Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

PubMed

Bazant, Martin Z

2013-05-21

Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal-air, and lead-acid batteries, as well as metal electrodeposition-dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler-Volmer equation, based on a dilute solution approximation. The Marcus theory of charge transfer likewise considers isolated reactants and neglects elastic stress, configurational entropy, and other nonidealities in condensed phases. The limitations of existing theories recently became apparent for the Li-ion battery material LixFePO4 (LFP). It has a strong tendency to separate into Li-rich and Li-poor solid phases, which scientists believe limits its performance. Chemists first modeled phase separation in LFP as an isotropic "shrinking core" within each particle, but experiments later revealed striped phase boundaries on the active crystal facet. This raised the question: What is the reaction rate at a surface undergoing a phase transformation? Meanwhile, dramatic rate enhancement was attained with LFP nanoparticles, and classical battery models could not predict the roles of phase separation and surface modification. In this Account, I present a general theory of chemical kinetics, developed over the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells.

Phase transformations during the growth of paracetamol crystals from the vapor phase

NASA Astrophysics Data System (ADS)

Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.

2014-07-01

Phase transformations during the growth of paracetamol crystals from the vapor phase are studied by differential scanning calorimetry. It is found that the vapor-crystal phase transition is actually a superposition of two phase transitions: a first-order phase transition with variable density and a second-order phase transition with variable ordering. The latter, being a diffuse phase transition, results in the formation of a new, "pretransition," phase irreversibly spent in the course of the transition, which ends in the appearance of orthorhombic crystals. X-ray diffraction data and micrograph are presented.

Basilar-membrane responses to broadband noise modeled using linear filters with rational transfer functions.

PubMed

Recio-Spinoso, Alberto; Fan, Yun-Hui; Ruggero, Mario A

2011-05-01

Basilar-membrane responses to white Gaussian noise were recorded using laser velocimetry at basal sites of the chinchilla cochlea with characteristic frequencies near 10 kHz and first-order Wiener kernels were computed by cross correlation of the stimuli and the responses. The presence or absence of minimum-phase behavior was explored by fitting the kernels with discrete linear filters with rational transfer functions. Excellent fits to the kernels were obtained with filters with transfer functions including zeroes located outside the unit circle, implying nonminimum-phase behavior. These filters accurately predicted basilar-membrane responses to other noise stimuli presented at the same level as the stimulus for the kernel computation. Fits with all-pole and other minimum-phase discrete filters were inferior to fits with nonminimum-phase filters. Minimum-phase functions predicted from the amplitude functions of the Wiener kernels by Hilbert transforms were different from the measured phase curves. These results, which suggest that basilar-membrane responses do not have the minimum-phase property, challenge the validity of models of cochlear processing, which incorporate minimum-phase behavior. © 2011 IEEE

Optical Hilbert transform using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Ge, Jing; Wang, Chinhua; Zhu, Xiaojun

2010-11-01

In this paper, we demonstrate that a simple and practical phase-shifted fiber Bragg grating (PSFBG) operated in reflection can provide the required spectral response for implementing an all-optical Hilbert transformer (HT), including both integer and fractional orders. The PSFBG consists of two concatenated identical uniform FBGs with a phase shift between them. It can be proved that the phase shift of the FBG and the apodizing profile of the refractive index modulation determine the order of the transform. The device shows a good accuracy in calculating the Hilbert transform of the complex field of an arbitrary input optical waveforms when compared with the theoretical results.

Fourier transform magnitudes are unique pattern recognition templates.

PubMed

Gardenier, P H; McCallum, B C; Bates, R H

1986-01-01

Fourier transform magnitudes are commonly used in the generation of templates in pattern recognition applications. We report on recent advances in Fourier phase retrieval which are relevant to pattern recognition. We emphasise in particular that the intrinsic form of a finite, positive image is, in general, uniquely related to the magnitude of its Fourier transform. We state conditions under which the Fourier phase can be reconstructed from samples of the Fourier magnitude, and describe a method of achieving this. Computational examples of restoration of Fourier phase (and hence, by Fourier transformation, the intrinsic form of the image) from samples of the Fourier magnitude are also presented.