Generation Of Grains Research Articles

Alien Chromatin from Hordeeae Grasses Enhances the Compatibility of Epichloë Endophyte Symbiosis with the Hexaploid Wheat Triticum aestivum.

The inoculation of Epichloë endophytes into modern cereals, resulting in systemic infection, depends on the genetics of both the host and the endophyte strain deployed. Until very recently, the only modern cereal to have been infected with Epichloë, in which normal phenotype seed-transmitted associations were achieved, is rye (Secale cereale). Whilst minor in-roads have been achieved in infecting hexaploid wheat (Triticum aestivum), the phenotypes of these associations have all been extremely poor, including host death and stunting. To identify host genetic factors that may impact the compatibility of Epichloë infection in wheat, wheat-alien chromosome addition/substitution lines were inoculated with Epichloë, and the phenotypes of infected plants were assessed. Symbioses were identified whereby infected wheat plants were phenotypically like uninfected controls. These plants completed their full lifecycle, including the vertical transmission of Epichloë into the next generation of grain, and represent the first ever compatible wheat-Epichloë associations to be created.

Formation of Dusty Structures in Spherical Glow Discharge

We study, for the first time, plasma-dust structures in the spherical geometry of a discharge, which are formed either spontaneously or specially. High molecular gases, such as acetone and ethyl alcohol, are used for the generation of strata. Strata are required for the formation of structures of injected grains. The generation of grains in air plasma occurs spontaneously, and a structure is formed around the anode, when strata are not observed. Experiments were carried out in the range of pressures 30–100 Pa at a discharge current of 20–30 mA. To control the chemical composition of the gas environment, mass-spectrometry is used.

Experimental characterization and numerical analysis of additively manufactured mild steel under monotonic loading conditions

Additive Manufacturing (AM), for the case of metals, is a technology developed to create 3D products by following a layer-by-layer welding procedure. In this work, the tensile behavior of wire arc additively manufactured mild steel is studied experimentally and numerically. The microstructure of the metal is strongly influenced by the AM process that involves several heating and cooling cycles; therefore, it is first analyzed with optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction to identify the different phases and to extract the grain properties. With this information, two approaches are used to build the Representative Volume Element, which will be part of a multi-scale material model. The first approach constitutes a synthetic generation of grains according to a Voronoi Tessellation and the second one an image-based representation. Afterwards, a virtual tensile test for the determination of the stress–strain relation of the material is performed, which is later compared with the measurements of a real tensile test carried out on several specimens that were obtained using the wire arc additive manufacturing technique. It can be observed that the influence of the welding direction on the stiffness and the ductility of the additively manufactured steel product is rather low, yielding similar results in both parallel and perpendicular directions. Additionally, a softening behavior of the material is noticed.

Simultaneous X-ray radiography and diffraction topography imaging applied to silicon for defect analysis during melting and crystallization

One of the key issues to be resolved to improve the performance of silicon solar cells is to reduce crystalline defect formation and propagation during the growth-process fabrication step. For this purpose, the generation of structural defects such as grain boundaries and dislocations in silicon must be understood and characterized. Here, in situ X-ray diffraction imaging, historically named topography, is combined with radiography imaging to analyse the development of crystal defects before, during and after crystallization. Two individual indirect detector systems are implemented to record simultaneously the crystal structure (topographs) and the solid–liquid morphology evolution (radiographs) at high temperature. This allows for a complete synchronization of the images and for an increased image acquisition rate compared with previous studies that used X-ray sensitive films to record the topographs. The experiments are performed with X-ray synchrotron radiation at beamline ID19 at the European Synchrotron Radiation Facility. In situ observations of the heating, melting, solidification and holding stages of silicon samples are presented, to demonstrate that with the upgraded setup detailed investigations of time-dependent phenomena are now possible. The motion of dislocations is recorded throughout the experiment, so that their interaction with grain boundaries and their multiplication through the activation of Frank–Read sources can be observed. Moreover, the capability to record with two camera-based detectors allows for the study of the relationship between strain distribution, twinning and nucleation events. In conclusion, the simultaneous recording of topographs and radiographs has great potential for further detailed investigations of the interaction and generation of grains and defects that influence the growth process and the final crystalline structure in silicon and other crystalline materials.

Quantitative Studies of Machining-Induced Microstructure Alteration and Plastic Deformation in AISI 316 Stainless Steel Using EBSD

Surface machining can result in a heavily plastic deformed layer in the subsurface. The microstructure alterations and the extent of plastic deformation of a milled 316 austenitic stainless steel were investigated using electron backscatter diffraction (EBSD) technique in this study. The microstructure alteration of the deformed layer was characterized by the generation of grain and subgrain boundaries. The plastic deformation was evaluated by kernel average misorientation (KAM) and grain average misorientation (GAM). The local deformation within grains was assessed by the misorientation from adjacent point (MFAP). The EBSD results indicated gradients of microstructure and plastic deformation along the depth direction. High-angle grain boundaries were generated within the depth of 40 μm, and subgrain boundaries were produced up to the depth of 150 μm. Estimated by KAM and GAM, the plastic strain was about 0.7 at the depth of 25 μm and decreased to 0.1 at the depth of 115 μm The MFAP analysis revealed that the local deformation varied within individual grains. Additionally, the change of micro-hardness along the depth direction showed a strong correlation with KAM and GAM values.

The distributions and ages of refractory objects in the solar nebula

Refractory objects such as Calcium, Aluminum-rich Inclusions, Amoeboid Olivine Aggregates, and crystalline silicates, are found in primitive bodies throughout our Solar System. It is believed that these objects formed in the hot, inner solar nebula and were redistributed during the mass and angular momentum transport that took place during its early evolution. The ages of these objects thus offer possible clues about the timing and duration of this transport. Here we study how the dynamics of these refractory objects in the evolving solar nebula affected the age distribution of the grains that were available to be incorporated into planetesimals throughout the Solar System. It is found that while the high temperatures and conditions needed to form these refractory objects may have persisted for millions of years, it is those objects that formed in the first 10 5 years that dominate (make up over 90%) those that survive throughout most of the nebula. This is due to two effects: (1) the largest numbers of refractory grains are formed at this time period, as the disk is rapidly drained of mass during subsequent evolution and (2) the initially rapid spreading of the disk due to angular momentum transport helps preserve this early generation of grains as opposed to later generations. This implies that most refractory objects found in meteorites and comets formed in the first 10 5 years after the nebula formed. As these objects contained live 26Al, this constrains the time when short-lived radionuclides were introduced to the Solar System to no later than 10 5 years after the nebula formed. Further, this implies that the t = 0 as defined by meteoritic materials represents at most, the instant when the solar nebula finished accreting significant amounts of materials from its parent molecular cloud.

AN INTEGRATED CRYSTAL PLASTICITY FE SYSTEM FOR MICROFORMING SIMULATION

Based on Voronoi tessellation and the probability theory, a VGRAIN system is created for the generation of grains and grain boundaries for micromaterials. This system requires physical parameters obtained from microstructures of materials, such as the average, minimum and maximum grain sizes. Numerical procedures have been established to link the physical parameters of a material to the control variable in a gamma distribution equation and a method has been developed to solve the probability equation. These are the basis for the development of the VGRAIN system, which can be used to generate different grain structures and shapes that follow a certain pattern according to the probability theory. Statistical analyses have been carried out to investigate the distribution of generated virtual grains. The generated virtual microstructure is then implemented in the commercial FE code, ABAQUS, for mesh generation and micromechanics analysis using crystal plasticity (CP) equations for face-centered cubic (FCC) materials, which are implemented in the commercial FE solver, ABAQUS, through the user-defined subroutines, VUMAT/UMAT. FE analyses have been carried out to demonstrate the effectiveness of the integrated system for the investigation of localized straining and necking, encountered in microforming processes, such as extrusion of micropins, deformation of microfilms and hydroforming of microtubes.

AN INTEGRATED MICROMECHANICS MODELLING APPROACH FOR MICRO-FORMING SIMULATION

An effort has been made to create an integrated Crystal Plasticity FE (CPFE) system. This enables micro-forming process simulation to be carried out easily and the important features in forming micro-parts can be captured. Firstly, based on Voronoi tessellation and the probability theory, a VGRAIN system is created for the generation of grains and grain boundaries for micro-materials. Numerical procedures have been established to link the physical parameters of a material to the control variable in a gamma distribution equation. An interface has been created, so that the generated virtual microstructure of the material can be inputted in the commercial FE code, ABAQUS, for mesh generation. Secondly, FE analyses have been carried out to demonstrate the effectiveness of the integrated system for the investigation of uncontrollable curvature and localized necking in extrusion of micro-pins and hydro-forming of micro-tubes.

Optimized algebraic reconstruction technique for generation of grain maps based on three-dimensional x-ray diffraction (3DXRD)

Recently, an algebraic reconstruction method has been presented for generation of three-dimensional (3D) maps of the grain boundaries within polycrystals. The grains are mapped layer by layer in a nondestructive way by diffraction with hard x rays. We optimize the algorithm by means of simulations and discuss ways to automate the analysis. The use of generalized Kaiser-Bessel functions as basis functions is shown to be superior to a conventional discretization in terms of square pixels. The algorithm is reformulated as a block-iterative method in order to incorporate the instrumental point-spread function and, at the same time, to avoid the need to store the set of equations. The first reconstruction of a full layer and two neighboring 3D grains from experimental data are demonstrated.

Influence of deposition conditions on Ir/IrO2 oxygen barrier effectiveness

The influence of the deposition temperature during the reactive sputtering process on the microstructure of thin Ir and IrO2 films deposited on oxidized Si substrates was investigated and related to the oxygen barrier effectiveness. For this purpose differential thermal analysis combined with residual gas analysis by mass spectrometry was used for the investigation of the microstructural and chemical behavior of the as-sputtered IrO2 films upon heating. Moreover, in situ stress relaxation analyses up to 900 °C, in and ex situ x-ray diffraction measurements were done for various annealing conditions. The investigated polycrystalline IrO2 films exhibited a large compressive stress and a distorted lattice due to the sputter deposition process. It is demonstrated that a high deposition temperature involves a delayed relaxation of the IrO2 grains which is causing an extrinsic, enhanced defect controlled oxygen mobility for the annealing temperatures below the recrystallization. The well-known low intrinsic oxygen diffusivity was only found in those samples which show—in addition to the recovery process—a recrystallization at low temperatures and thus a formation and growth of a new generation of grains with a lattice spacing as in bulk IrO2. Moreover, the oxygen diffusion in Ir films was investigated and the oxygen was found to penetrate the Ir films very quickly at elevated temperatures. The microstructure of the films was investigated by cross sectional transmission electron microscopy and it is shown that the cold-sputtered columnar IrO2 films protect the underlying layers from oxidation during a 700 °C high temperature oxygen anneal with an optimized Ir/IrO2 oxygen barrier stack.

Modelling of interfacial viscoplastic slip coupled to damage in a polycrystalline microstructure

The mesomechanics behavior of a polycrystalline microstructure subjected to creep and constant strain rate loadings is investigated. The analysis is based on a Voronoi polygonization strategy for the generation of grains, that are bonded to each other via interfaces along the grain boundaries. A new constitutive model is proposed for the rate-dependent debonding along these interfaces, whereby damage is kinetically coupled to viscoplastic slip and dilatation. The paper may be viewed as generalizing the rate-independent model used in Cannmo et al. (1995).

Modelling of plasticity and damage in a polycrystalline microstructure

The mesomechanical behavior of a polycrystalline microstructure subjected to monotonic and cyclic loadings is investigated. The analysis is based on a Voronoi polygonization strategy for generation of grains embedded in a contiguous matrix. The main emphasis is to investigate the interaction between the microconstituents and the failure processes along grain boundaries. A rational interface theory based on damage development coupled to inelastic slip and dilatation is developed. The theory uses the interface width as a constitutive parameter, which regularizes the theory of LEMAITRE [1992], that is restricted to perfect bond between grain and matrix. In a series of FE-analyses parameter variations were performed: The unit cell size (as compared to the average grain diameter), the grain-matrix area ratio, the interface width and constitutive parameters. It appears that the composite behavior can be designed as brittle or ductile solely depending on the strength and rate of damage development in the interfaces. A localization band was detected, and its orientation is in the range that is predicted within continuum theory.

Grain growth in turbulent protoplanetary accretion disks

We have numerically studied the coagulation and transportation of grains in the turbulent accretion solar nebula. Compared with the case of laminer nebula, the turbulence enhances the growth rate. The grains diffuse radially through the nebula owing to turbulent diffusion. The accreted interstellar grains form the reservoir, from which the new generations of grains grow. The opacity calculation shows that the initial thermal convection terminates earlier in the inner region and that there is a possibility of restart of the convection due to the accreted grains, particularly in the outer region. We discuss about the implications of our calculations to the evolution of the grain and nebula, and the formation of planetesimals.

Grain growth in the turbulent accretion disk solar nebula

We have studied the coagulation of grains in the turbulent accretion disk solar nebula, considering turbulent diffusion, radial drift, and supply of interstellar grains by accreting interstellar cloud. The space-time dependent mass spectrum of grains and the Rosseland mean grain opacity have been calculated. Before the accretional effect becomes noticeable, the mass spectrum n( m) is well-described by n( m) ∝ m −1.31 for large grains and n( m) ∝ m −1.03 for small grains. The boundary is at the grains with the friction times comparable to the inner time scale of the turbulence. If the turbulence is fully developed, the growth time of grains is about 20 to 40 times shorter than that for the laminar nebula. In case of weak turbulence with velocity fluctuation of 0.03 × sound speed, the time scale is the same order as that in the laminar nebula. The accretion builds up the reservoir of interstellar grains, from which new generations of grains grow. Finally the spectrum reaches a steady state, crudely approximated by n( m) ∝ m −2. The grain opacity keeps constant as long as the mean grain radius of the first generation is smaller than the wavelength of radiation. The rapid increase is found at the end of this Rayleigh limit stage, and subsequently the opacity decreases as nearly (time) −2 owing to the grain growth. But the opacity increases again when the grains of the second generation grow as large as the wavelength and approaches a steady value. From these results, we have tried to describe the evolution of the nebula and the formation of planetesimals.

アルミニウムの再結晶に及ぼすけい素および鉄，けい素共存の影響

Precipitation of silicon during annealing also retards the recrystallization of aluminum, but its effect is smaller than that of precipitation of iron compound in Al-Fe alloy. Precipitated silicon particles due to precipitation treatment prior to annealing have a marked effect for particle stimulated nucleation same as primary inclusions of Al3Fe. The recrystallization of Al-Fe alloys is accelerated by the coexisting silicon, and generation of grain is also intensified. The grain growth at high temperature is prevented remarkably by the primary inclusions in Al-Fe alloys. Its grain growth, however, is rather intensified by the coexisting silicon.