Rate Of Grain Research Articles

Modeling the Grain Size Distribution during Solid Phase Crystallization of Silicon

AbstractWe analyze the grain size distribution during solid phase crystallization of Silicon thin films. We use a model developed recently that offers analytical expressions for the time-evolution of the grain size distribution during crystallization of a d-dimensional solid. Contrary to the usual fit of the experimental results with a lognormal distribution, the theory describes the data from basic physical principles such as nucleation and growth processes. The theory allows for a good description of the grain size distribution except for early stages of crystallization. The latter case is expected and discussed. An important outcome of the model is that the distribution at full crystallization is determined by the time-dependence of the nucleation and growth rates of grains. In the case under consideration, the theory leads to an analytical expression that has the form of a lognormal-type distribution for the fully crystallized sample.

Effect of growth restricting factor on grain refinement of aluminum alloys

Grain structure is an important and readily observable feature in aluminum alloy castings. Depending on the constitutional and heat-flow conditions in a solidified aluminum alloy, various morphologies are possible. Grain refining is one of the predominant techniques in controlling the quality of castings. It plays a vital role in improving metallurgical characteristics and mechanical properties of aluminum alloys. Fine equiaxed grains ensure remarkable benefits. There are a number of techniques to achieve fine equiaxed grain structure, but grain refinement by the addition of grain refiners referred to as inoculation is the most popular due to its simplicity. Grain refinement has been studied extensively by researchers for several decades, not only for developing efficient grain refiners but also for achieving an understanding of the mechanism of grain refinement. In spite of its commercial importance, benefits and numerous scientific studies in this area, the grain refinement of aluminum and its alloys is still a controversial subject. Solute elements like titanium segregate to the inoculants/melt interface affecting the dendrites and also affect the constitutional undercooling at the solid–liquid interface. This segregating power of an element is quantified by the growth restricting factor (GRF). In the present investigation, the effect of GRF on grain refinement of aluminum-silicon alloys was studied by the addition of Al-5Ti-1B master alloy. It is evident from this investigation that the growth rate of grains is inversely proportional to the GRF.

Supernova Remnants in the AKARI IRC Survey of the Large Magellanic Cloud

Abstract We present a near- to mid-infared study of supernova remnants (SNRs) using the AKARI IRC Survey of the Large Magellanic Cloud (LMC). The LMC survey observed about a 10 square degree area of the LMC in five bands centered at 3, 7, 11, 15, and 24$\mu$m using the Infrared Camera (IRC) aboard AKARI. The number of SNRs in the survey area is 21, which is about a half of the known LMC SNRs. We systematically examined AKARI images and identified eight SNRs with distinguishable infrared emission. All of them were detected at $\gtrsim$10$\mu$m and some at 3 and 7$\mu$m, too. We present their AKARI images and fluxes. In the 11$/$15$\mu$m versus 15$/$24$\mu$m color-color diagram, the SNRs appear to be aligned along a modified blackbody curve, representing thermal emission from dust at temperatures of between 90 and 190K. There is a good correlation between the 24$\mu$m and X-ray fluxes of the SNRs. It was also found that there is a good correlation between the 24$\mu$m and radio fluxes even if there is no direct physical connection between them. We considered the origin of the detected mid-infrared emission in individual SNRs. We conclude that the mid-infrared emissions in five SNRs that show morphologies similar to the X-rays are dominated by thermal emission from hot dust heated by X-ray emitting plasma. Their 15$/$24$\mu$m color temperatures are generally higher than the Spitzer 24$/$70$\mu$m color temperatures, which suggests that a single-temperature dust model cannot describe the full spectral energy distribution (SED) of the SNRs. It also implies that our understanding of the full SED is essential for estimating the dust destruction rate of grains by SNR shocks.

Elastoviscoplastic micromechanical modeling of the transient creep of ice

A salient feature of the rheology of isotropic polycrystalline ices is the decrease of the strain rate by more than 2 orders of magnitude during transient creep tests to reach a secondary creep regime at a strain which is systematically of ∼1%. We use a recent (so‐called “affine”) version of the self‐consistent mean‐field theory to model the elastoviscoplastic behavior of ice. The model aims at bridging scales between the rheology of single grain and the one of polycrystals by evaluating the intergranular interactions. It takes into account the long‐term memory effects, which manifests itself by the fact that local stress and strain rate in grains depend on the whole mechanical history of the polycrystal. It is shown that the strong hardening amplitude during the transient creep is entirely explained by the stress redistribution within the specimen, from an almost uniform stress distribution upon instantaneous loading (purely elastic response) to strong interphase and intraphase heterogeneities in the stationary regime (purely viscoplastic response). The experimental hardening kinetic is much too slow to be explained by the same process; it is attributed to the hardening of hard glide slip systems (prismatic slip) in the transient regime. Moreover, the model very well reproduces the permanent creep rate of several highly anisotropic specimens of the Greenland Ice Core Project ice core (pronounced crystallographic textures), when accounting for a single‐grain rheology that well matches the experimental one. Our results are consistent with recent findings concerning dislocation dynamics in ice.

The flow rate of granular materials through an orifice

The flow rate of grains through large orifices is known to be dependent on its diameter to a 5/2 power law. This relationship has been checked for big outlet sizes, whereas an empirical fitting parameter is needed to reproduce the behavior for small openings. In this work, we provide experimental data and numerical simulations covering a wide span of outlet sizes, both in three and two dimensions. This allows us to show that the laws that are usually employed are satisfactory only if a small range of openings is considered. We propose a new law for the mass flow rate of grains that correctly reproduces the data for all the orifice sizes, including the behaviors for very large and very small outlet sizes.

Responses of ethylene and ACC in rice grains to soil moisture and their relations to grain filling

The objectives of this study were to investigate ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) in rice grains and root bleeding sap during the grain filling period and their relationship to the grain filling rate. Two high lodging-resistant rice (Oryza sativa L.) cultivars were grown in pots or tanks. Three treatments, including well watered (WW), moderate soil-drying (MD) and severe soil-drying (SD), were conducted from 9 days of post-anthesis until maturity. The effects of chemical regulators on the concentrations of ethylene and ACC in the grains were also studied. The results show that MD significantly increased the grainfilling rate and grain weight, whereas SD significantly reduced the grain-filling rate and grain weight. Concentrations of ethylene and ACC in the grains were very high at the early grain filling stage and then sharply decreased during the linear period of grain growth. MD reduced the ACC concentrations and ethylene evolution rate, whereas SD remarkably increased the ACC concentrations and ethylene evolution rate. Both the ethylene evolution rate in rice grains and the ACC concentrations in the root-bleeding sap were significantly and positively correlated with the ACC concentrations in rice grains. The ethylene evolution rate was significantly and negatively correlated with the grain-filling rate. The application of amino-ethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, at 9–13 days of postanthesis significantly reduced the ACC concentrations and ethylene evolution rate of grains, but significantly enhanced the activities of sucrose synthase, ADP glucose pyrophosphorylase and soluble starch synthase. The results were reversed when ethephon, an ethylenereleasing agent, was applied. The results suggest that moderate soil drying during the grain-filling period in rice could inhibit the production of ethylene and ACC and therefore accelerate grain filling and increase grain weight.

Seed Size Variation in Grain Crops: Allometric Relationships between Rate and Duration of Seed Growth

Genetic control and environmental modulation of seed size operate through their influences on rate and duration of seed filling, and their interaction. To account for this interaction, here we advance an allometric model centered on the scaling exponent α calculated as the slope of the linear regression between duration and rate of grain filling in a log‐log scale. The scaling exponent allows for three types of responses: seed size is stable as a result of full compensation between rate and duration (α = −1), seed size is variable as a result of rate (α > −1), or duration‐dominated growth (α < −1). The concept was tested with 45 data sets from the literature involving nine crop species, and sources of variation including genotype, environment, and their interaction. Relative variation in seed size ranged from 5 to 274%, and the scaling exponent was strongly concentrated in the range from 0 (large, rate‐driven seed size range) to −1 (narrow seed size range due to mutually cancelled effects of rate and duration). The range of seed size declined when the scaling exponent declined from approximately 0 to −1. An α ≈ −1 (rate and duration effects cancel each other) is necessary and sufficient for small variation in seed size, whereas α ≈ 0 is necessary but not sufficient for large seed size variation. The magnitude of seed size variation is dependent on the variation in the rate of seed growth when α ≈ 0. This double condition for seed size variability is summarized in a multiple regression model with α and range of rate of grain filling as independent variables, which accounted for 73% of the variation in range of seed size.

The parameters of grain filling and yield components in common wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum)

Abstract Final grain dry weight, a component of yield in wheat, is dependent on the duration and the rate of grain filling. The purpose of the study was to compare the grain filling patterns between common wheat, (Triticum aestivum L.), and durum wheat, (Triticum turgidum L. var. durum), and investigate relationships among grain filling parameters, yield components and the yield itself. The most important variables in differentiating among grain filling curves were final grain dry weight (W) for common wheat genotypes and grain filling rate (R) for durum wheat genotypes; however, in all cases the sets of variables important in differentiating among grain filling curves were extended to either two or all three parameters. Furthermore, in one out of three environmental conditions and for both groups of genotypes, the most important parameter in the set was grain filling duration (T). It indicates significant impact of environmental conditions on dry matter accumulation and the mutual effect of grain filling duration and its rate on the final grain dry weight. The medium early anthesis date could be associated with further grain weight and yield improvements in wheat. Grain filling of earlier genotypes occurs in more temperate environments, which provides enough time for gradual grain fill and avoids the extremes of temperature and the stress of dry conditions.

Breeding Effects on Grain Filling, Biomass Partitioning, and Remobilization in Mediterranean Durum Wheat

This work assesses the changes resulting from durum wheat (Triticum turgidum L. var. durum) breeding in Italy and Spain during the 20th century on grain filling, biomass production, and allocation at anthesis, and the remobilization of preanthesis photosynthates to the grain of main stems. Field experiments, involving 12 Italian and 12 Spanish cultivars released at different periods, were conducted at two Spanish sites during three growing seasons. Breeding activities did not modify final grain weight (WG), the maximum rate of grain filling (R), nor grain filling duration (D) of central grains of main spikes. Genetic variability existed for WG and R within countries and periods. Cycle length (expressed as days from sowing to anthesis [DSA]) was reduced by 2 and 8 d in Italian and Spanish cultivars, respectively. Crop dry weight (CDW) decreased by 21% (0.51% yr−1) and green area index (GAI) by 28% (–0.33% yr−1) in Spanish cultivars. Green area index at anthesis did not differ between old and modern Italian cultivars, while CDW decreased by 9%. Leaf area index (LAI) remained unchanged in cultivars from both countries, while the spike:stem ratio increased by 8 and 10% in Italian and Spanish cultivars, respectively. Changes over time in DSA were positively associated with changes in CDW and GAI. Dry matter translocation (DMT) efficiency switched from 9% in old cultivars to 20% in modern ones. The contribution of preanthesis assimilates to grain yield (CPA) increased to values of 31 and 27% in Italian and Spanish modern cultivars, respectively. Opportunities for further increases in genetic yield potential in Mediterranean‐type environments are discussed.

Effects of Soil Moisture and Irrigation Patterns during Grain Filling on Grain Yield and Quality of Rice and Their Physiological Mechanism

The objective of this study was to investigate whether a moderate soil-drying or an alternate wetting and moderate-drying irrigation during the grain filling period could improve the grain quality and increase yield in rice. Two rice cultivars, Wuyujing 3 (japonica) and Yangdao 6 (indica), were grown in pots and cement tanks. Three soil moisture treatments and three irrigation patterns, well-watered (WW, well-watered) and conventional irrigation (CI, continuous flooding), moderate soil-drying (MD, soil water potential at-10～-30 kPa) and alternate wetting and moderate-drying irrigation (W-MD, re-watered when soil water potential reached at-25 kPa), and severe soil-drying (SD, soil water potential at-40～-60 kPa) and alternate wetting and severe-drying irrigation (W-SD, re-watered when soil water potential reached at-50 kPa), were imposed during grain-filing. Compared with WW or CI, MD or W-MD significantly increased grain weight, peak viscosity, and breakdown values, and re-duced chalkiness and setback values. The results were reversed for SD or W-SD treatments. Activities of sucrose synthase (SuS), adenine diphosphoglucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE) in grains in mid-dle and late grain-filling stages were significantly enhanced, whereas ethylene revolution rate of grains decreased, under MD or W-MD. The SD or W-SD had the opposite effects. The results indicate that both MD and W-MD can improve rice quality, result-ing from the physiological mechanism of enhancing activities of SuS, AGP, StS, and SBE and decreasing ethylene production in grains.

Breeding Effects on Grain Filling, Biomass Partitioning, and Remobilization in Mediterranean Durum Wheat

This work assesses the changes resulting from durum wheat (Triticum turgidum L. var. durum) breeding in Italy and Spain during the 20th century on grain filling, biomass production, and allocation at anthesis, and the remobilization of preanthesis photosynthates to the grain of main stems. Field experiments, involving 12 Italian and 12 Spanish cultivars released at different periods, were conducted at two Spanish sites during three growing seasons. Breeding activities did not modify final grain weight (WG), the maximum rate of grain filling (R), nor grain filling duration (D) of central grains of main spikes. Genetic variability existed for WG and R within countries and periods. Cycle length (expressed as days from sowing to anthesis [DSA]) was reduced by 2 and 8 d in Italian and Spanish cultivars, respectively. Crop dry weight (CDW) decreased by 21% (0.51% yr−1) and green area index (GAI) by 28% (–0.33% yr−1) in Spanish cultivars. Green area index at anthesis did not differ between old and modern Italian cultivars, while CDW decreased by 9%. Leaf area index (LAI) remained unchanged in cultivars from both countries, while the spike:stem ratio increased by 8 and 10% in Italian and Spanish cultivars, respectively. Changes over time in DSA were positively associated with changes in CDW and GAI. Dry matter translocation (DMT) efficiency switched from 9% in old cultivars to 20% in modern ones. The contribution of preanthesis assimilates to grain yield (CPA) increased to values of 31 and 27% in Italian and Spanish modern cultivars, respectively. Opportunities for further increases in genetic yield potential in Mediterranean-type environments are discussed.

Grain filling duration, a crucial determinant of genotypic variation of grain yield in field-grown tropical irrigated rice

Grain filling, a crucial determinant of grain yield in cereal crops, is characterized by duration and rate of grain filling. This study aimed to (1) seek genotypic variations in grain filling duration and rate on area basis, (2) compare the contribution of grain filling duration and rate to grain yield and (3) examine the influence of temperature and solar radiation on grain filling duration and rate for effective grain filling period in the field-grown tropical irrigated rice. Six tropical genotypes were used in the 2004 dry season and wet season at the International Rice Research Institute (IRRI), Laguna, Philippines. Grain filling rate and duration exhibited highly significant genotypic variations in each crop season. Grain weight on area basis was positively associated with grain filling duration, irrespective of crop seasons, but negatively or not significantly associated with grain filling rate. Grain filling rate and duration were negatively correlated with each other. Final grain weight linearly increased with the rise in cumulative mean temperature and cumulative solar radiation. Longer grain filling duration resulted in higher cumulative mean temperature and cumulative solar radiation for effective grain filling. Higher daily mean temperature and radiation did not accelerate daily grain filling rates of different rice genotypes. It was concluded that longer grain filling duration, which provided rice plants with more cumulative mean temperature and cumulative solar radiation for effective grain filling period, was the main factor that determined grain yield on unit area basis in the field-grown tropical irrigated rice genotypes.

The flow rate of granular materials through an orifice

The flow rate of grains through large orifices is known to be dependent on its diameter to a 5/2 power law. This relationship has been checked for big outlet sizes, whereas an empirical fitting parameter is needed to reproduce the behavior for small openings. In this work, we provide experimental data and numerical simulations covering a wide span of outlet sizes, both in three- and two-dimensions. This allows us to show that the laws that are usually employed are satisfactory only if a small range of openings is considered. We propose a new law for the mass flow rate of grains that correctly reproduces the data for all the orifice sizes, including the behaviors for very large and very small outlet sizes.

Physiological analysis on pre-harvest sprouting in recombinant inbred rice lines

Pre-harvest sprouting (PHS) in rice production is usually caused by high temperature and humidity or continuous rains. It frequently happens in F1 in hybrid rice seed production. The PHS or “Physiologically germinated” seeds are of lower quality, by which the hybrid rice seed production is badly affected every three years at a loss of 20% or even 50% yield in seed production over the vast Yangtse River Valley and Southwest China. It is estimated that PHS causes an average decrease of seed activity by 10%. A recombinant inbred line population including 304 lines, derived from a cross between Indica rice (Oryza sativa L.) cultivars Zhong-156 and Gumei-2, was used to study the PHS physiology. Based on the data of sprouting rate in panicles and sprouting rate in grains, two kinds of lines, namely easy-to-sprout lines and hard-to-sprout lines, were selected to investigate their physiological differences when PHS happened. The experiment was conducted in a special field with a microclimate of higher temperature and humidity. The results indicated that it was easier to produce PHS from the female parent GM-2 than the male parent ZH-156, besides, the GA1 content and amylase activity in GM-2 grains were higher than those in ZH-156. However, the abscisic acid (ABA) content in GM-2 grains was lower than that in ZH-156. Higher temperature and higher humidity facilitated the GA1 increment from milk ripe stage to yellow ripe stage. GM-2 and the easily-sprouting lines showed an even higher increase in GA1 than ZH-156 and the hardly-sprouting lines, which enhanced the amylase activity and induced pre-harvest sprouting. This may be the physiological basis for pre-harvest sprouting induced by higher temperature and higher humidity, and these special characteristics must be inherited from their parents.

Effect of thermal diffusion and electrostatic force on evolution of wind-blown sand flow

A theoretical model is suggested to mathematically describe the effect of thermal diffusion from a sand-bed on evolution of a wind-blown sand flow. An upward wind field is engendered by the thermal diffusion and the coupling interaction among the horizontal and upward wind flow, saltating grains, and a kind of electrostatic force exerted on the grains are considered in this theoretical model. The numerical results show that the effect of the thermal diffusion on the evolution process of wind-bown grain flow is quite obvious and very similar to the effect of the electrostatic force on the evolution. Not only the time for the entire system to reach a steady state (called the duration time), the transport rate of grains, the mass-flux profiles and the trajectory of saltating grains are affected by the thermal diffusion and the electrostatic force exerted on saltating grains, but also the wind profiles and the temperature profiles at the steady state are affected by the wind-blown sand flow.

Activities of Enzymes for Sucrose-Starch Conversion in Developing Endosperm of Rice and Their Association with Grain Filling in Extra-Heavy Panicle Types

Rice cultivars with numerous spikelets per panicle (extra-heavy panicle types) frequently fail to exhibit their high yield potential due to low grain filling. Existing genetic variation in grain filling, however, opens possibilities for genetic improvement for this trait. We studied the correlation between grain filling and the activities of enzymes for sucrose-starch conversion in developing endosperm. The activity of sucrose synthase (EC 2.4.1.13, SuSy) and ADPglucose pyrophosphorylase (EC 2.7.7.27, AGPase), were measured in three extra-heavy panicle types and a standard cultivar grown at two locations under different environmental conditions. The proportions of grains with definite specific gravities and the rate of grain filling were adopted as the parameters related to grain filling. AGPase activity, but not that of SuSy, was consistently correlated to high proportions of high-density grains (specific gravity > 1.20) and high rates of grain growth in spikelets, particularly in those on secondary branches in which low grain filling is the rule. Such correlation was also detected in spikelets on primary branches which generally show better grain filling, but only early stages. Therefore, a high activity of AGPase might contribute to the reduction of the sucrose concentration by accelerating sucrose metabolism at the developing seed, a sink terminus of the phloem. Thus the sink-directed phloem transport of sucrose would be promoted, resulting in improved grain filling of extra-heavy panicle types. SuSy would play some roles in such a cultivar difference in grain filling, but depending on environments.

Microstructure Changes in Alloy AZ31B in Semisolid State and Its Mechanical Properties

The structural changes of the wrought magnesium alloy AZ31B in semisolid state were clarified using optical microscopy and hot-stage microscopy. The influence of heat treatment variables was assessed. Compression tests covering a range from room temperature to 673 K were carried out for mechanical property assessment; flow stress and breaking strain were determined. The following are the results: (1) The grain growth of the hot-extruded AZ31B without preprocessing sensitively reacted at temperature and retention time. (2) The hot-extruded AZ31B with 30 % preprocessing showed an almost perfectly spheroidized structure in a semisolid state under certain conditions. (3) Heating velocity markedly affected the spheroidizing rate of grains. (4) From the direct observation of the hot-extruded alloy AZ31B by hot-stage microscopy, spheroidization was observed in some crystal populations. (5) Spheroided materials in the semisolid temperature range had a lower flow stress and a larger breaking strain than nonspheroidized materials. These results indicate the possibility of manufacturing wrought magnesium alloy by cold working.

Influence of crystallographic orientation on dry etch properties of TiN

A study of the impact of physical vapor deposition conditions on the etch properties of TiN has been conducted using a transformer coupled plasma. This work focuses only on a Cl2-based etch plasma. It is shown that the crystallographic orientation of TiN, observed from x-ray diffraction spectra, has a major influence on the etch behavior. Etch yields at varying dry etch conditions of two types of TiN, with different crystallographic orientations, have been studied quantitatively. The high roughness which is created during plasma exposure was identified as being the result of different etch rates of grains and intergranular material at the grain boundaries. Moreover, it is shown that TiN(111) is more difficult to etch, resulting in more pronounced roughness, than TiN(200), which is easier to etch, resulting in smoother surfaces for certain process conditions.

The effect of drawing velocity and phase transformation on the structure of directionally annealed iron

Undeformed iron bars were directionally annealed under various processing parameters. Columnar grains having an aspect ratio as high as 50 were produced at optimum processing conditions of a hot zone temperature of 850 °C, a 200 °C/cm temperature gradient and a drawing velocity of 1 μm/s. Equiaxed grains were formed both when the drawing velocity was low, and when it exceed the maximum growth rate of grains. The ferrite to austenite phase transformation hindered the columnar grain growth. A novel microstructure with columnar grains in the outer region, whose longitudinal axis parallels to the drawing direction, and fine equiaxed grains at the center of the specimen was observed. The skin effect of high frequency induction heating during the directional annealing was used to explain the formation of this novel microstructure.

Grain growth and yield formation of durum wheat grown at contrasting latitudes and water regimes in a Mediterranean environment

A set of ten durum wheat genotypes was grown in experiments conducted under four contrasting Mediterranean conditions during three years to assess the effect of latitude and water regime on grain growth and grain yield formation. The relationship between grain weight and accumulated growing degree-days (GDD) from anthesis was described by a logistic equation and final grain weight (W) and maximum rate (R) and duration (D) of grain filling were calculated from the fitted curves. Thousand kernel weight (TKW) was positively related to grain yield at both latitudes and water regimes, although the contribution of the number of grains per m 2 to final yield was only significant in the south, where environmental constraints likely limited the achievement of a large grain set. Differences in final grain weight between latitudes could be mostly explained by differences in the grain filling rate, while changes on W between water regimes were due to altered grain filling durations. Under northern conditions grain yield was positively associated to grain filling duration but negatively related to the maximum rate of grain filling, while in the south the coefficients of the grain filling curves had little or no effect on final yield. Reductions in grain yield under rainfed conditions were due to the fall in the number of grains per m 2 since TKW was not significantly affected by drought.