Self-assembly of organometallic Pd(II) complexes via CH3 center dot center dot center dot pi interactions: the first example of a cyclopalladated compound with herringbone stacking pattern

Two binuclear cyclometallated compounds [Pd(C-2,N-dmba)(mu-N-3)](2) (1) and [Pd-2(C-2,N-dmba)(2)(mu-N-3)(mu-Cl)] (2) (dmba = N,N-dimethylbenzylarnine) have been synthesized and characterized by elemental 3 analysis, IR and NMR spectroscopies and single crystal X-ray diffraction crystallography. The ability of CH3 groups to form C(sp(3))-H...pi hydrogen bonds with phenyl rings is responsible for the molecular self-assembly within the crystals of 1 and 2. Compound 1 crystallizes as one-dimensional supramolecular chains whereas the crystal packing of 2 consists of a herringbone of sandwiches composed by two inversely related [Pd-2(C-2,N-dmba)(2)(mu-N-3)(mu-Cl)] molecules. (c) 2007 Elsevier B.V. All rights reserved.

Grain-boundary segregation and precipitates in La2O3 and Pr2O3 doped SnO2 center dot CoO-based varistors

Structural heterogeneities in SnO2.CoO-based varistors were analyzed by transmission electron microscopy. In SnO2.CoO-based system doped with La2O3 and Pr2O3 two kinds of precipitate phases at grain boundary region were found. Using energy dispersive spectrometry they were found to be Co2SnO4 and Pr2Sn2O7, presenting a defined crystalline structure. It was also identified that such precipitate phases are mainly located in triple-junctions of the microstructure. HRTEM analysis revealed the existence of other two types of junctions, one as being homo-junctions of SnO2 grains and other due to twin grain boundaries inside the SnO2.CoO grain. The role of these types of junction in the overall nonlinear electrical features is also discussed. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Grain boundary electric characterization of Zn7Sb2O12 semiconducting ceramic: A negative temperature coefficient thermistor

The electrical properties of the grain boundary region of electroceramic sensor temperature based on inverse spinel Zn7Sb2O12 were investigated at high temperature. The zinc antimoniate was synthesized by a chemical route based on the modified Pechini method. The electric properties of Zn7Sb2O12 were investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz and from 250 up to 600 degreesC. The grain boundary conductivity follows the Arrhenius law, with two linear branches of different slopes. These branches exhibit activation energies with very similar values; the low-temperature (less than or equal to350 degreesC) and high-temperature (greater than or equal to400 degreesC) regions are equal to 1.15 and 1.16 eV, respectively. Dissimilar behavior is observed on the relaxation time (tau) curve as a function of temperature, where a single slope is identified. The negative temperature coefficient parameters and nature of the polarization phenomenon of the grain boundary are discussed. (C) 2003 American Institute of Physics.

Investigation of food grain drying with pulsating air flows

In this article we investigate experimentally the potential of using pulsating flows for drying of food grains. A Rijke type oscillator with an electrical heater was used to dry batches of soybean grains. Drying temperatures were 60 degreesC. We observed a decrease on the drying time for pulsating flows when compared with the conventional non-pulsating regime. This decrease depended on sample initial moisture content and weight, and on final sample moisture content. (C) 2004 Elsevier B.V. Ltd.

Temperature dependence of fractal dimension of grain boundary region in SnO2 based ceramics

Fractal dimensions of grain boundary region in doped SnO2 ceramics were determined based on previously derived fractal model. This model considers fractal dimension as a measure of homogeneity of distribution of charge carriers. Application of the derived fractal model enables calculation of fractal dimension using results of impedance spectroscopy. The model was verified by experimentally determined temperature dependence of the fractal dimension of SnO2 ceramics. Obtained results confirm that the non-Debye response of the grain boundary region is connected with distribution of defects and consequently with a homogeneity of a distribution of the charge carriers. Also, it was found that C-T-1 function has maximum at temperature at which the change in dominant type of defects takes place. This effect could be considered as a third-order transition.

Ferroelectric state analysis in grain boundary of Na0.85Li0.15NbO3 ceramic

The electric and dielectric properties of the grain boundary of Na0.85Li0.15NbO3 lead-free ferroelectric-semiconductor perovskite were investigated. The impedance spectroscopy was carried out as a function of a thermal cycle. The sodium lithium niobate was synthesized by a chemical route based on the evaporation method. Dense ceramic, relative density of 97%, was prepared at 1423 K for 2 h in air atmosphere. ac measurements were carried out in the frequency range of 5 Hz-13 MHz and from 673 to 1023 K. Theoretical adjust of the impedance data was performed to deriving the electric parameters of the grain boundary. The electric conductivity follows the Arrhenius law, with activation energy values equal to 1.55 and 1.54 eV for heating and cooling cycle, respectively. The nonferroelectric state of the grain boundary and its correlation with symmetry are discussed in the temperature domain. (C) 2003 American Institute of Physics.

Influence of low and high levels of grain defects on maize wet milling

Yields and starch pasting characteristics obtained from wet milling of maize samples with low and high levels of defect grains were compared to those from sound samples. Defect grain groups ere established taking into account the defect degree. Thus the first group consisted of fermented, molded, heated and sprouted grains and the second of insect damaged. hollow, fermented (up to 1/4) grains and those injured by other causes. The grain groups, if present at low levels in the samples, 10% for first group and 17% for second group did not affect the chemical composition of starch and its pasting properties. obtained by the rapid visco analyser. Samples with high levels of grain groups (up to 100%). affected wet milling yields and starch viscosity. Samples with 100% of grains in the first group decreased starch, germ yield and peak viscosity and increased gluten yield. Samples with 100% of grains in the second group decreased germ and fiber yield but increased starch yield. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

alpha-SiAlON ceramics with elongated grain morphology using an alternative sintering additive

In this work, the use of a natural yttrium oxide and rare earth oxide solid solution (CRE2O3) as stabilizers of the alpha-Si3N4 phase to form alpha-SiAlON has been investigated. This oxide mix is produced at FAENQUIL-DEMAR, at a cost of only 20% of pure commercial Y2O3. Two alpha-SiAlONs using pure Y2O3 or CRE2O3 have been prepared, using mixes of 20% by volume of a molar fraction of 9:1 of AlN to Y2O3 or AlN to CRE2O3, respectively, with 80% alpha-Si3N4. Samples were gas pressure-sintered at 1900 degreesC, under 1.5 MPa of N-2 for 60 min. Both compositions yielded alpha-SiAlON ceramics with high relative densities (98% t.d.), hardness of 18 GPa and fracture toughness of 5 Mpa m(1/2), with homogeneous microstructures composed of elongated alpha-SiAlON grains with aspect ratios of 5. It is concluded that the mixed rare earth concentrate (CRE2O3) can be used to produce alpha-SiAlON ceramics with similar microstructures and mechanical properties of alpha-SiAlON ceramics fabricated using pure Y2O3, but with the advantage of its lower production cost. (C) 2004 Elsevier B.V All rights reserved.

AMS and grain shape fabric of the Late Palaeozoic diamictites of the Southeastern Paran Basin, Brazil

Diamictites interbedded with marine shales and turbidites onlap the eastern border of the Parana Basin (Southern Brazil). These poorly sorted sediments were deposited during the Permo-Carboniferous glaciation, and their matrix-supported clasts show no preferred orientation. These massive rocks have been studied using anisotropy of magnetic susceptibility (AMS) and grain shape fabric. Hysteresis loops and thermomagnetic measurements show that AMS depends mostly on the paramagnetic clays, but fine ferromagnetic particles also contribute to the anisotropy. The coarse silt to sand grain preferred orientation study supports the use of AMS in describing the diamictite fabric, at least regarding the orientation of the foliation. AMS and grain shape data reveal subhorizontal to weakly inclined magnetic and grain shape foliation parallel to the regional bedding. The magnetic lineations are normally scattered within the foliation plane in agreement with the oblate AMS ellipsoids found in these rocks. Both fabric patterns are consistent with deposition by subaqueous mudflows that were resedimented downslope, with elastic supply from continental sources. The off-vertical grain shape foliation poles suggest that the deposition of diamictites was controlled by the depocentre topography of the Rio do Sul sub-basin.

Maternal antibody transfer to broiler progeny varies among strains and is affected by grain source and cage density

Two experiments were conducted to examine the effects of broiler breeder dietary grain source and cage density on maternal antibody (MatAb) transfer to progeny in 2 genetic strains (A and B). Broiler breeders were assigned to 16 litter floor pens and fed either corn- or wheat-based diets. Breeders were administered 4 live vaccines against Newcastle disease virus (NDV). At 23 wk of age, pullets and cocks, which reflected the full BW distribution from each treatment, were moved to a cage breeder house and placed at 1 or 2 hens/cage. Breeders were artificially inseminated at 44 wk (experiment 1) and 52 wk of age (experiment 2). Eggs were collected for 8 d, incubated, and placed in individual pedigree bags at d 19 of incubation. Blood samples from 5 chicks per treatment combination were collected at hatch in both experiments. Spleen and bursa were collected from the same chicks for histomorphometry analyses in experiment 2. In the second experiment, 12 chicks per treatment were placed in cages. Progeny were provided diets based on the same grain (corn or wheat) as their parents. Serum samples were collected at 5, 9, and 13 d of age and analyzed for anti-NDV MatAb. Data were analyzed as a 2 x 2 x 2 factorial design considering strain, dietary grain source, and cage density as main factors. Interaction effects were observed in breeders and progeny. Experiment 1 showed that strain A chicks had lower levels of MatAb when hens were housed at 2 hens/cage rather than 1 hen/cage. The MatAb levels of strain B chickens were not affected by cage density in either experiment. Experiment 2 demonstrated similar effects of cage density on MatAb levels and the area of bursa follicles for both strains. Progeny of breeders fed corn-based diets had smaller spleen white pulp only when hens were housed at 2 hens/cage compared with 1 hen/cage. The results of these experiments suggest that breeder strain and cage-density conditions affected MatAb transfer to progeny and embryo development of spleen and bursa.

Influence of Wood Moisture Content on the Modulus of Elasticity in Compression Parallel to the Grain

Brazilian Standard ABNT NBR7190:1997 for timber structures design, adopts a first degree equation to describe the influence of wood moisture content. Periodically, when necessary, the referred standard is revised in order to analyze inconsistencies and to adopt considerations according new realities verified. So, the present paper aims to examine the adequacy of its equation which corrects to 12% of moisture the values of rigidity properties obtained on experimental tests. To quantify the moisture influence on modulus of elasticity, it was applied tests of compression parallel to the grain for six specimens of different strength classes, considering nominal moisture of 12; 20; 25; 30%. As results, modulus of elasticity in the moisture range 25-30% showed statistically equivalents, and was obtained a first degree equation to correlate the studied variables which leads to statically equivalent estimations when compared with results by ABNT NBR7190:1997 equation. However, it was indicated to maintain the current expression for the next text of the referred document review, without prejudice to statistical significance of the estimates.

The dielectric suppress and the control of semiconductor non-Ohmic feature of CaCu3Ti4O12 by means of tin doping

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Parasitism of Greenbugs (Homoptera: Aphididae) by Lysiphlebus testaceipes (Hymenoptera: Braconidae) in Grain Sorghum: Implications for Augmentative Biological Control

Field cage studies were conducted to describe the relationship between the percentage of Lysiphlebus testaceipes (Cresson) parasitism (as measured by aphid mummies) and densities of greenbug, Schizaphis graminum Rondani, on grain sorghum, Sorghum bicolor L. In 1993 and 1994, a biotype E-susceptible grain sorghum hybrid was grown in field cages and L. testaceipes adults were released after each plant was infested with 20 biotype E greenbugs. The release rates were 0, 0.5, 1.0, and 2.0 wasps per plant in 1993, and 0, 0.16, 0.33, and 0.5 wasps per plant in 1994. Greenbugs and mummies were counted 1-2 times a week on all leaves of 2-4 randomly selected plants per cage. A release rate of 0.33-0.5 wasps per plant infested with 20 greenbugs maximized the number of mummies produced and prevented the greenbugs from reaching an economic threshold of 1,000 greenbugs per plant. Peak numbers of mummies occurred ≈400-500 DD (10°C base) after the initial wasp release. Regression analyses showed that the greenbug population started decreasing when the percentage of parasitism (as measured by mummies) reached 20-30 %. Greenbugs in the absence of wasps significantly reduced yield in 1994, but not in 1993.

Effect of atmosphere on the sintering and grain growth of tin oxide

High purity SnO 2 powder (>99.9%) was compacted in cylindrical pellets and sintered in atmospheres of dry argon, argon with water vapor, oxygen and CO 2 using 10 °C/min up to 1200 °C or isotherms in the range of 1000 to 1200 °C. Time, temperature and sintering atmosphere have large influence on grain growth and low influence on densification of this oxide. Surface diffusion is the dominant mechanism up to 1200 °C and evaporation-condensation is dominant above 1200 °C. The maximum linear shrinkage observed was about 2.0% and attributed to structural rearrangement of particles due to high capillary stresses developed with neighboring particles. © 1999 Trans Tech Publications.