Response Of Grains Research Articles

Impedance response and dielectric relaxation in co-precipitation derived ferrite (Ni,Zn)Fe2O4 ceramics

Dielectric spectra and magnetization hysteresis loops were used to investigate the grain size effect with temperature on the electrical and magnetic response of co-precipitation derived spinel (Ni0.5Zn0.5)Fe2O4 (NZFO) ceramics. Remarkable dielectric relaxation phenomena of non-Debye type have been observed in each NZFO ceramics as confirmed by two kinds of Cole-Cole plots of the 1100 °C sintered samples, mainly due to the electron-hopping mechanism between n-type and p-type carriers and interfacial ion effect when applied an increase of temperature. The high and low response of grain and grain-boundary regions were determined by modeling the impedance experimental results on two equivalent RC circuits taking into account grain deep trap states. By employing the modified Arrhenius equation, activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. In addition, the magnetization of various sintering temperature samples is dominated by cation distribution and surface effect in different particle ranges.

Optical and Electrical Properties of ZnO Thin Films Grown by Sol-Gel Method

The ZnO thin films have been produced on p-type Si and quartz substrates by the spin-coating method and after deposition were heated at different temperatures in the range from 650K to 850K. The photoluminescence (PL) and cathodoluminescence (CL) measurements were carried out at temperature range 12K-350K. I-V, C-V measurements were performed on the Al/ZnO/Si/Al structures at different temperatures. The structural properties of the ZnO thin films were carried out using x-ray and SEM method. The effects of the thickness variation and annealing temperature on the crystallinity parameters were observed. The electrical response of grains, grain boundaries, and contacts of the ZnO film was obtained.

Thermally driven asymmetric responses of grains versus spin-glass related distributions of blocking temperature in exchange biased Co/IrMn bilayers

Controlling ferromagnetic/antiferromagnetic blocking temperatures in exchange biased based devices appears crucial for applications. The blocking temperature is ascribed to the ability of both antiferromagnetic grains and interfacial spin-glass-like phases to withstand ferromagnetic magnetization reversal. To better understand the respective contributions of grains versus spin-glass, blocking temperature distributions were measured after various thermal treatments for cobalt/iridium-manganese bilayers. The high-temperature contribution linked to antiferromagnetic grains shifts towards lower temperatures above a threshold thermal annealing. In contrast, the occurrence and evolution of training effects for the low-temperature contribution only agree with its inferred interfacial spin-glass-like origin.

The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

Enhancement of giant dielectric response in Ga-doped CaCu3Ti4O12 ceramics

The influences of Ga3+ doping ions on the microstructure, dielectric and electrical properties of CaCu3Ti4O12 ceramics were investigated systematically. Addition of Ga3+ ions can cause a great increase in the mean grain size of CaCu3Ti4O12 ceramics. This is ascribed to the ability of Ga3+ doping to enhance grain boundary mobility. Doping CaCu3Ti4O12 with 0.25mol% of Ga3+ caused a large increase in its dielectric constant from 5439 to 31,331. The loss tangent decreased from 0.153 to 0.044. The giant dielectric response and dielectric relaxation behavior can be well described by the internal barrier layer capacitor model based on Maxwell−Wagner polarization at grain boundaries. The nonlinear coefficient, breakdown field, and electrostatic potential barrier at grain boundaries decreased with increasing Ga3+ content. Our results demonstrated the importance of ceramic microstructure and electrical responses of grain and grain boundaries in controlling the giant dielectric response and dielectric relaxation behavior of CaCu3Ti4O12 ceramics.

Electrical responses and dielectric relaxations in giant permittivity NaCu3Ti3TaO12 ceramics

Dielectric relaxations and electrical responses in NaCu3Ti3TaO12 ceramics were investigated as a function of temperature. NaCu3Ti3TaO12 ceramics exhibit giant dielectric constants with values of e′∼1.45–2.08×104. Two sets of thermally activated dielectric relaxations were observed in low and high temperature ranges. Sintering conditions have an insignificant influence on the microstructure of NaCu3Ti3TaO12 ceramics, and have a slight impact on their e′ values. Thermally activated electrical responses of grains and grain boundaries have been studied at different temperatures by using complex admittance and impedance spectroscopy analyses, respectively. The low temperature relaxation mechanism is found to correlate closely with electrical response of semiconducting grains; whereas the apparent high e′ values are attributed to electrical response of insulating grain boundaries. These results support the internal barrier layer capacitor model to explain the giant dielectric properties of NaCu3Ti3TaO12 ceramics. Additionally, high temperature relaxation may be attributed to the sample-electrode effect and/or defect ordering.

Quality Response of Grains in Different Spikelet Positions to Temperature Stress During Grain Filling of Rice

High temperature after anthesis may degrade the grain quality of rice ( Oryza sativa L.). To understand the effect of stress duration (initial and mid grain filling stages) and the influence to grain quality at different spikelet positions, an indica cultivar and a japonica cultivar, Yangdao 6 and Yangjing 9538, were used in a pot experiment under 35 °C during the initial (8–18 d after anthesis) and mid (18–28 d after anthesis) terms of grain filling. The treatment under normal atmospheric temperature (25–27 °C) served as the control. The high-temperature treatment at initial filling stage had larger influence on grain quality than the stress imposed at mid filling stage, and the grain quality varied with cultivars and spikelet positions. Both treatments with high temperature reduced milled rice rate and head milled rice rate, but increased crude protein content; grains on the primary branches received larger effect than those on the secondary branches. In the same branch, later-flowered grains were affected greater than early-flowered grains. When high temperature was imposed at initial grain filling stage, the chalkiness degree and chalky grain percentage were significantly increased in the early-flowered grains, whereas the amylose content was significantly decreased; such variations were larger in grains on the primary branches than those on the secondary branches. Besides, the 2 cultivars showed different responses of grain quality to high-temperature stress, which indicated the fact of phenotypic difference on temperature sensitivity. Generally, the influence of temperature on rice quality was greater when the stress imposed at the earlier stage of grain filling.

Response of grain amaranth (Amaranthus cruentus L.), to method and rate of cattle kraal manure application at Kadawa and Samaru in Nigeria

Field experiments were conducted between June and October 2010 wet season at two different locations. The first was at the Horticultural Research Garden of the Institute for Agricultural Research (IAR), Samaru in the Northern Guinea Savanna agro-ecological zone and the second experiment was conducted at the Research Farm of the Irrigation Research Sub-Station (IRS), Kadawa in the Sudan Savanna agro-ecological zone also of the Institute for Agricultural Research, Ahmadu Bello University, Zaria, Nigeria to evaluate the response of grain amaranth growth and green edible vegetable yield components to three methods of cattle kraal manure application (broadcasting, side banding and spot placement incorporated) and five rates of cattle kraal manure application (0, 5, 10, 15 and 20 t ha-1), using the variety ?Pure branch?. The experiment was laid out in a randomized complete block design (RCBD) and replicated three times. Cattle kraal manure application rates significantly (p > 0.05) increased growth of green edible vegetable yield characters of grain amaranth except stem girth at Samaru. Growth and green edible vegetable yield characters were generally not influenced by methods of cattle kraal manure application except for plant height, number of leaves per plant at 12 WAT at Samaru, and plant fresh weight at 12 WAT at Kadawa and dry weight at 4 and 12 WAT at Samaru and 12 WAT at Kadawa. Application of cattle kraal manure of 10 t ha-1 to Amaranthus cruenthus gave the highest mean values which were comparable to those of 15 and 20 t ha-1 rates for all the characters measured such as plant height, number of leaves, leaf area, fresh and dry weights. Thus, the finding suggests that 10 t ha-1 should be recommended to farmers growing Amaranthus in the Northern Guinea and Sudan Savanna of Nigerian agro-ecologies.

Oxygen-vacancy-related relaxation and scaling behaviors ofBi0.9La0.1Fe0.98Mg0.02O3ferroelectric thin films

Oxygen-vacancies-related dielectric relaxation and scaling behaviors of Bi0.9La0.1Fe0.98Mg0.02O3 (BLFM) thin film have been investigated by temperature-dependent impedance spectroscopy from 40 oC up to 200 oC. We found that hopping electrons and single-charged oxygen vacancies (VO.) coexist in the BLFM thin film and make contribution to dielectric response of grain and grain boundary respectively. The activation energy for VO. is shown to be 0.94 eV in the whole temperature range investigated, whereas the distinct activation energies for electrons are 0.136 eV below 110oC and 0.239 eV above 110oC in association with hopping along the Fe2+- VO.-Fe3+ chain and hopping between Fe2+-Fe3+, respectively, indicating different hopping processes for electrons. Moreover, it has been found that hopping electrons is in form of long rang movement, while localized and long range movement of oxygen vacancies coexist in BLFM film. The Cole-Cole plots in modulus formalism show a poly-dispersive nature of relaxation for oxygen vacancies and a unique relaxation time for hopping electrons. The scaling behavior of modulus spectra further suggests that the distribution of relaxation times for oxygen vacancies is temperature independent.

The effect of different nitrogen and irrigation levels on grain β-glucan content in some durum wheat cultivars

\beta-glucan is a non-starchy, water-soluble polysaccharide component of wheat grain that positively affects grain nutrient quality. High \beta-glucan content in wheat grain also has a cholesterol-lowering effect in humans. The aim of this study was to evaluate the effect of nitrogen and irrigation on durum wheat grain \beta-glucan content. Correlations between durum wheat grain \beta-glucan content, and grain yield and some quality characteristics were examined. Kunduru 1149, Kızıltan 91, and Çakmak 79 durum wheat cultivars were used as material, and 0-, 75-, and 150-mm irrigation levels with 0, 40, 80, and 120 kg ha^{-1} nitrogen rates were applied. Higher nitrogen levels generally increased durum wheat grain \beta-glucan content in both years of the study and the N3 nitrogen level had the greatest effect on the \beta-glucan content in durum wheat. Higher irrigation levels negatively affected the \beta-glucan content in the wheat grain. Non-irrigated treatments generally yielded the highest \beta-glucan content in both years of the study. The response of grain \beta-glucan content according to cultivar was significant and C_1 had the best grain \beta-glucan content of all the cultivars. Correlations between grain \beta-glucan content, and grain yield, protein content, 1000-grain weight, test weight, seed vitreousness, and the SDS sedimentation were significant. With the exception of protein content in 2005, strong positive correlations were observed between \beta-glucan content, and grain yield and quality characteristics. These results indicate that higher irrigation levels negatively affected grain \beta-glucan content in durum wheat, whereas higher nitrogen rates positively affected grain \beta-glucan content. Moreover, the effect of cultivar characteristics on the β-glucan content in durum wheat grain was statistically significant.

Spatially Resolved Characterization of Geometrically Necessary Dislocation Dependent Deformation in Microscale Laser Shock Peening

As the laser spot size in microscale laser shock peening is in the order of magnitude of several microns, the anisotropic response of grains will have a dominant influence on its mechanical behavior of the target material. Furthermore, conventional plasticity theory employed in previous studies needs to be re-examined due to the length scale effect. In the present work, the length scale effects in microscale laser shock peening have been investigated. The crystal lattice rotation underneath the shocked surface was determined via electron backscatter diffraction. From these measurements, the geometrically necessary dislocation (GND) density that the material contains has been estimated. The yield strength increment was then calculated from the GND distribution by using the Taylor model and integrated into each material point of the finite element method (FEM) simulation. Finite element simulations, based on single crystal plasticity, were performed for the process both with and without considering the GND hardening, and the comparison has been conducted.

Yield response of pea, lentil and chickpea to phosphorus addition in a clay loam soil of central Montana

Production of pea, lentil and chickpea, as a forage and food source, has increasingly become a popular agricultural practice in the northern Great Plains. While many local soils are rich in phosphorus (P), it has been commonly believed that P-fertilization still has potential to promote production. A two-year (2003–2004) field study was conducted to fine-tune P fertilization strategies in a clay loam soil (14 mg Olsen-P kg−1, sodium bicarbonate extractable soil P) of central Montana. Treatments included three varieties for each of the three crop species (pea: Majorest, Mozart and Delta; lentil: Vantage, Richlea and Brewer; and chickpea: Yuma, Myles and Chico), a control (0 P) and three P rates (7.3, 14.7 and 22.0 kg P ha−1) in triple super-phosphate (TSP), arranged in a randomized complete block design with four replicates. Responses of grain and forage yield to P addition varied depending on crop species and varieties within each species. Grain yields correlated quadratically to the rate of P applied for Majoret, Mozart and Brewer. Forage yield of Majoret, Mozart, Vantage and Richlea was significantly increased with P addition. P-addition enhanced vegetative growth as evidenced by the increased shoot-grain ratio. Chickpea varieties did not respond to P fertilization. The best yielding variety in this soil was Mozart, Vantage and Myles from each species, respectively. To facilitate decision making for producers, the relationship between the increased yield and the rate of P application was quantified. Averaged over two years, by growing Majoret, Mozart, Vantage and Richlea for forage at low rate of P application (7.3 kg P ha−1), income was about 1.8–2.3 times of the cost of P fertilizer applied.

Crop management systems and maize grain yield under narrow row spacing

Reduction in row spacing provides a more uniform distribution among plants that can increase grain yield. The benefits of narrow row spacing can depend on the plant architecture and on the kind of crop management system. The objective of this study was to assess the effects of narrow row spacing on the grain yield of maize hybrids growing under different management systems. Six experiments were carried out in Eldorado do Sul, State of Rio Grande do Sul, Brazil, during the 2003/04 and 2004/05 growing seasons. Each experiment corresponded to a crop management system. Treatments consisted of two row spacings (0.8 and 0.4 m), two hybrids (Penta and Flash) and two plant densities, which varied with the crop management system and growing season. Besides plant density, the crop management systems differed in the quantities of fertilizers applied at sowing, side-dress and use of irrigation. A complete randomized block design was used in each experiment, in a 2 × 2 × 2 treatment factorial scheme with four replications. The increases in grain yield with narrow row spacing were small, ranging from zero to 14%. They depended on the growing season and were manifested only with yields higher than 10 t ha-1, regardless of the hybrid. The number of grains per area was the component that best explained the response of grain to narrow row spacing, regardless of plant density, hybrid and crop management system. Narrow row spacing is a worth management strategy to enhance maize grain yield when high input cropping systems are used.

Nitrogen supply to the grain modifies the effects of temperature on starch and protein accumulation during grain filling in wheat

Effects of nutritional status on the responses to high temperature of 2 wheat cultivars that differed in their sensitivity to high temperature were investigated in plants grown in pots in environmentally controlled growth rooms. The availability of nitrogen to the grains was altered by changing the amount and timing of the nitrogen supplied to the plants, and also by trimming the ears. Single grain weight was significantly decreased in the plants grown at 30/25°C compared with those grown at 20/15°C. The effects of nitrogen level or trimming on the response of grain filling to temperature did not seem to be mediated through alterations in the availability of carbohydrates within the grains. Neither N level nor trimming had substantial effects on the deposition of starch, but both treatments altered the accumulation of protein, and the responses of protein accumulation to the effects of temperature. At the lower temperature, increasing the nitrogen supply resulted in greater single grain weight, more protein per grain, and higher grain protein percentage. At the higher temperature, raising the supply of N increased none of these attributes; the rate of protein accumulation was not accelerated by raising the temperature as much at high as at low N, and high N reduced the duration of protein deposition. There was a linear and positive relationship between the amounts of amino acids in the grain and the rate of accumulation of protein in the endosperm, and the effects of N level and trimming were associated with changes in the concentration of amino acids in the grains. High temperature conditions appear to lower the supply of amino acids to the grain in plants well supplied with nitrogen. There was a positive relationship between the rate of protein deposition and the amount of amino acids in the grain. Although raising the level of nitrogen resulted in an increase in amino acid levels in the grain at low temperature, there was no such increase at high temperature. Trimming, however, did increase grain protein and the rate of protein deposition at high temperature as well as the amino acid levels in the grain. One possible interpretation of this paradox arises from other work showing that under high temperature and/or water deficit there is an inadequate supply of soluble carbohydrates in the shoot to metabolise high levels of nitrogen. Differences in the responses of starch deposition and protein accumulation to N level, trimming, and temperature confirm that these two components accumulate in the grain independently of each other. Consequences of the interactions between nitrogen supply, temperature, and cultivar are discussed in relation to yield and quality.

Determination of Young’s modulus of grains in a gamma titanium aluminide alloy

An experimental and analytical process for determining the elastic response of grains in a gamma titanium aluminide alloy was developed. Three-dimensional finite element models were employed to deduce the transversely isotropic properties. The results are compared with those reported for polysynthetically twinned materials.

Dielectric spectroscopy of sedimentary rocks

A physiochemical model for the complex dielectric response of sedimentary rocks is used to invert broadband dielectric spectra for effective grain size distributions. The complex dielectric response of each grain within the “water‐wet” granular matrix is obtained by superimposing the polarization of the electrochemical double layer, which is assumed to surround each grain, with the complex dielectric response of the dry mineral grain. The effective complex dielectric response of the water‐wet matrix (grains and surface phase) is obtained by volume averaging over the entire distribution of particle sizes. The complex dielectric response of the total mixture (water‐wet matrix and bulk pore solution) is obtained using the Bruggeman‐Hanai‐Sen effective medium theory. Studies of Berea sandstone show that the grain size distribution, obtained by inverting the real part of the complex dielectric spectra, is similar to the grain size distribution obtained from optical images of the sample in thin section. The current model, however, does not account for surface roughness effects or the polarization of counterions over multiple grain lengths; therefore the grain size distribution obtained by dielectric spectroscopy is broader than the image‐derived distribution. The dielectric‐derived grain size distribution can be fit with two separate power laws that crossover at R ≅ 1 μm, which corresponds to a relaxation frequency of 2 kHz. The low‐frequency dielectric response (f < 2 kHz) is primarily controlled by the macroscopic grain fraction (mainly quartz grains), which has a fractal dimension of d = 1.84±0.05. The high‐frequency dielectric response (f > 2 kHz) is primarily controlled by the clay size grains and surface roughness, which has a fractal dimension of d = 2.48±0.07. At very low frequencies (f < 0.1 Hz) the dielectric response appears to be controlled by the electrochemical polarization of counterions over multiple grain lengths. A more general model should account for the effects of surface roughness and grain interactions on the dielectric response. It would also be useful to develop a simplified version of this model, perhaps similar in form to the empirically derived Cole‐Cole response, which could be more easily used to model and interpret electrical geophysical field surveys (e.g., induced‐polarization, ground‐penetrating radar, and time domain reflectometery measurements).

Barley yield and grain protein concentration as affected by assimilate and nitrogen availability

Two types of experiments were conducted with the malting barley cv. Grimmett to examine how assimilate and nitrogen (N) availability at different growth stages determined yield and grain protein concentration (GPC) in south-east Queensland. In one series of experiments, plants were sown in April, June, and August so that they would experience different growing conditions, and responses to N application rate were examined. Another experiment examined response of growth, yield, and GPC to variation of assimilate production pre and post anthesis, caused by the canopy manipulation treatments of opening, closure, and 50% shading at 3 different growth stages. Without N application all 3 sowings produced similar yields (1·9-2·3 t/ha), but when N was applied, yield was higher and responded more to applied N in the June sowing than in the other sowings.The different responses of grain yield to N application rate among the 3 sowing dates were not due to differences in N uptake but to the efficiency of N use; with favourable temperatures throughout crop growth, the crop sown in June utilised N most eciently to develop a large number of grainsand to produce sufficient as similates to fill these grains. When yield had a positive response to low N application rates, then there was generally no response of GPC, whereas when there was no response of grain yield to further rate of N application then GPC increased. The results of the second experiment show that N uptake depended on plant N demand at early stages of growth when N was still available in the soil, but total N content of tops at maturity was similar among canopy manipulation treatments. Canopy opening at any stage of growth tended to increase tiller number, leaf area index, and above-ground dry matter, but the effect was greater attillering stage which produced the highest yield because of the greatest number of heads. Shading reduced yield at all stages, but particularly at pre-anthesis. Shading and canopy closure during grain filling reduced grain yield, but with similar N uptake these treatments significantly increased GPC .These results indicate that GPC depends on both assimilate and N availability to grain, and GPC can increase sharply when grain yield is reduced with low assimilate availability as a result of adverse growing conditions. Responses of grain yield to applied N depended on environmental conditions, particularly the patterns of air temperature during growth, and the crop utilised N more efficiently to produce higher yield when it was not exposed to extreme temperatures during the latter stages of growth.

In-Situ Observation of Deformation Processes by OIM

The thermo-mechanical response of single crystals has been studied in detail since the discovery of X-ray and electron diffraction. While an extensive knowledge exists on the effect of crystallographic orientation on deformation and recrystallization behavior of single crystals, the thermo-mechanical response of grains of different orientations embedded in a polycrystalline matrix are not well understood. With the emergence of microstructure based models predicting the structure evolution during deformation or recrystallization, data validating the predicted structure changes are essential. This requires to study the evolution of microstructural attributes such as morphology or orientation of an individual grain within a specific grain neighborhood during mechanical or thermal exposure. Interrupted coupon scale testing, with a separation of testing and microstructural observation is not sufficient due to the small size of the objects to be observed. Thus, the structure evolution of selected grains has to be followed in-situ.

Pre-harvest sprouting in wheat. I. Influence of cultivar, rainfall and temperature during grain ripening

Tolerance to pre-harvest sprouting, measured by the response of grain in intact harvested ears to a standard wetting treatment, varied substantially from season to season and in all trials declined with time after harvest ripeness. The major factor associated with the observed variation in tolerance at harvest and the decline after harvest ripeness appeared to be the level of grain germinability. Statistical analyses of meteorological data relating to the 10- and 20-day periods prior to harvest and the period from harvest to wetting treatment, indicated that most of the seasonal variation in tolerance could be explained in terms of the amount of rain during the 20-day period prior to harvest. The potential to use this relationship to develop an early warning system for wheat growers together with implications for wheat breeding and cultivar improvement programs are discussed.

Microstructural and magnetic studies of sinter-forged (Bi, Pb) 2Sr 2Ca 2Cu 3O x superconductor

The microstructural and magnetic properties of sinter-forged BiPbSrCaCuO superconductors have been studied. The as-sinter-forged sample consisted of significant microcracks all through the bulk and first forms into a Bi 2-2-1-2 phase ( c = 3.08 nm). However, after heat treatment at 860°C in air for 10 days, the final sample transformed to microstructurally smooth grains of Bi 2-2-2-3 phase ( c = 3.70 nm). ac magnetic susceptibility data taken at 0.1, 1 and 10 Oe evidence the onset of diamagnetic response of grains at T c = 105 K with a rather narrow transition width, ΔT c = 3 K. TEM, SEM and XRD analyses reveal remarkable microstructural changes into a smooth laminar structure during the formation of Bi 2-2-2-3 phase.