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For years, archaeologists, climatologists, and ecologists have used stable oxygen isotope values (δIn this study, we have evaluated the effects of the cooking methods on the otolith δThere were no morphological changes between the cooked and uncooked otoliths. The δThis study suggests that cooking processes do not change otolith stable isotopic compositions and will therefore allow for future research to use the otolith δ

RATIONALE Otoliths are usually used to estimate the age of fish and the chemical composition such as nitrogen stable isotope ratios (δ15 N values) may record environmental information and ecological role of the fish. However, the isotopic fractionation of δ15 N values between diets and otoliths has rarely been investigated and remains unclear. METHODS Nitrogen isotopic fractionation between five different diets (δ15 Ndiet values) and otoliths (δ15 Noto values) were elucidated in tilapia Oreochromis mossambica reared in controlled feeding experiments. The otoliths were dissolved with hydrogen chloride and peroxodisulfate was used to oxidize the total organic materials to nitrate, which was further converted into N2 O gas by denitrification bacteria before the measurement of δ15 Noto values by isotope ratio mass spectrometry. The δ15 N values of muscles, gills, scales and livers of the tilapias were also measured by isotope ratio mass spectrometry. RESULTS The peroxodisulfate oxidation-bacterial conversion method reduced the minimum mass of the otoliths required for analysis to as low as 2 mg, unlike past methods, which have required masses of 8-155 mg. The δ15 Noto values were not significantly different from the δ15 Ndiet values of the five diets. Furthermore, the somatic growth rate had no effect on the δ15 Noto values. Nevertheless, the δ15 N values of metabolically active tissues were significantly different from each other and higher than the δ15 Ndiet values, due to the deamination of these tissues. CONCLUSIONS These results suggest that diet was the main source of amino acids for the otolith organic matrix and there was no biochemical transamination during the assimilation of dietary amino acids to otoliths. The δ15 Noto value can be used as a proxy of nitrogen sources of fishes and may have potential application in ecological studies such as the detection of diet shift, migration, trophic levels and environmental changes experienced by the fish population.

High-strength ZrC ceramics with relative density above 98% were prepared by reactive hot pressing of ZrC and Al at 1900°C. The reaction between ZrC and Al resulted in the formation of ZrC1−x, Zr3Al3C5 and Zr–Al compound such as AlZr3 and Al–C–Zr. The intermediate product AlZr3 below 1600°C and remained Al–C–Zr phase could form liquid phase and promoted the first stage of densification process. The improvement in densification behavior at higher temperatures (1800°C–1900°C) could be attributed to the formation of nonstoichiometric ZrC1−x. Adding 5 wt% and 7.5 wt% Al to ZrC, the formed ZrC0.85–Zr3Al3C5 and ZrC0.80–Zr3Al3C5 based ceramics had 3-point bending strength as high as 757 ± 79 MPa and 967 ± 50 MPa, respectively, with hardness and fracture toughness being 16.2–18.3 GPa and 3.3–3.5 MPa m1/2, respectively.

In cooperative learning, students work together as a team to maximize the academic success of all the team members. The failure of even a single member can compromise the success of the entire team. Thus, to evaluate the functioning of the team reliably, it is necessary to consider both the performance of the individual team members and the interactions among them. In this study, a method was developed for identifying dysfunctional teams and troubled individuals by examining the correlation between the team scores obtained in sequential tests and the correlation between the scores obtained by the different team members. The effectiveness of the proposed method was evaluated via field experiments. Forty-eight students were randomly assigned to cooperative learning teams and their learning performance assessed by four-unit tests. The results indicated that the proposed method can identify the most troubled individuals in a team even when the team performance/grouping information is not taken explicitly into account. Furthermore, when the team information is considered, the method can identify both the dysfunctional teams and the troubled individuals within the teams. Therefore, the proposed method provides a useful basis for the development of computer-assisted solutions for assessing the performance of cooperative learning teams. [ABSTRACT FROM AUTHOR]

Composites of ZrC–SiC with relative densities in excess of 98% were prepared by reactive hot pressing of ZrC and Si at temperature as low as 1600°C. The reaction between ZrC and Si resulted in the formation of ZrC1−x, SiC, and ZrSi. Low-temperature densification of ZrC−SiC ceramics is attributed to the formed nonstoichiometric ZrC1−x and Zr–Si liquid phase. Adding 5 wt% Si to ZrC, the three-point bending strength of formed ZrC0.8–13.4 vol%SiC ceramics reached 819 ± 102 MPa with hardness and toughness being 20.5 GPa and 3.3 MPa·m1/2, respectively.

Transmission electron microscopy study of pressureless sintered ZrB2–20 vol% SiC composites with WC (5–10 vol%) additions was carried out in this work. Two independent chemical reactions in which the ZrO2 impurities were removed from ZrB2 grain surface were confirmed. Three new formed phases, (W, Zr)ssB, (Zr, W)ssC, and (W, Zr)ssSi2, apart from the plate-like ZrB2 and SiC grains, were identified in the samples. Microstructure observations strongly suggest that the liquid phases in terms of (W, Zr)ssB and (W, Zr)ssSi2, appear in this system during the sintering process below 2200°C, and the former could well wet the ZrB2 grain boundaries. The mass transport process between ZrB2 and (W, Zr)ssB was also confirmed by scanning-transmission electron microscope analysis. The above results supports that the densification at 2200°C is assisted by liquid phase and the elongation of ZrB2 platelets resulted from the Ostwald ripening during the dissolution–diffusion–precipitation process.

WC powder was synthesized by a nitridation–carburization method with WO3 prepared by the citrate sol–gel route as the starting material, and the reaction mechanism was investigated. It was found that WO3 was converted to nanosized W2N after the nitridation process in NH3. Then, the W2N was transformed to W metal, W2C, and WC in sequence when it was carburized in CH4–H2 gas mixture. The WC powder obtained possessed a high specific surface area of 24.6 m2/g, and showed a particle size of 20–30 nm, which was much finer than the WC powder prepared by direct carburization of WO3 in CH4–H2 gas mixture. The reason was also discussed.

Alterable roles of VC addition on the densification, microstructure development, and mechanical properties of the ZrB2–SiC ultrahigh temperature ceramics (UHTCs) were comprehensively investigated based on utilizing the thermodynamic analysis and experimental results. Chemical reactions of VC with the inevitably existed oxide (ZrO2) impurity on the particle surfaces of the ZrB2 starting powder, or with the ZrB2 matrix phase could be controlled by adjusting the atmospheres during hot pressing. Different chemical reactions during hot pressing also resulted in much different material microstructures and then different material properties. Benefiting the VC addition and proper sintering atmosphere, refined grain size of ZrB2 and improved mechanical properties were developed in ZrB2–SiC systems. By properly controlling these reactions, the microstructures and mechanical properties of ZrB2–SiC based UHTCs could be tailored.

This work reported the microstructural evolution and grain growth kinetics of ZrB2–SiC composites containing 10, 20, and 30 vol% SiC during heat treatment at 2000°C. The coarsening of ZrB2 occurred in the three systems, whereas the obvious coarsening for SiC appeared only in the composite with 30 vol% SiC. The kinetics analysis showed the ZrB2 grain growth rate in the ZrB2–30 vol% SiC was 25 times lower than that for ZrB2–10 vol% SiC during heat treatment. Furthermore, the grain growth controlling mechanisms of ZrB2 and SiC were discussed. In addition, it was found that the heat treatment had little effect on Vickers hardness and fracture toughness of ZrB2–SiC.

The perovskite-like layer-structured (PLS) Nd2Ti2O7 and La2Ti2O7 have possibly the highest Curie points of any materials. To pole these ceramics, highly textured, dense ceramics with high DC electrical resistivity are required. The ferroelectric and piezoelectric properties of lead-free Nd2Ti2O7 and La2Ti2O7 grain-oriented ceramics prepared by spark plasma sintering using a two-step method are reported. The Tc of Nd2Ti2O7 and La2Ti2O7 are 1482±5° and 1461±5°C, respectively. The measured piezoelectric constant of the textured La2Ti2O7 was d33=2.6 pC/N. These results now open up the possibility of studying the ferroelectric/piezoelectric properties of the PLS family of ceramics with super-high Curie points.

Phase pure hafnium diboride (HfB 2 ) powder was synthesized by borothermal reduction of hafnium dioxide using amorphous boron at relatively low temperature (1600°C) in vacuum. The synthesized HfB 2 powder had an average particle size of 1.37 μm with an equiaxed shape, and a low oxygen content of 0.79 wt%. Using the as-synthesized HfB 2 powder and a commercial SiC, HfB 2 monolithic, and HfB 2 -20 vol%SiC composite were hot pressed at 2000°C to relative densities of 95.7% and 99.2%, respectively. With the addition of SiC, the grain size decreased and the fracture behavior changed from intergranular to a mixed mode, which resulted in a high flexural strength of 993 ± 90 MPa for the composite. Fracture toughness of the composite was 6.29 ± 0.65 MPa m 1/2 , which was significantly higher than that of the HfB 2 monolithic and the reported values in literature.

Fine hafnium diboride (HfB2) powders have been prepared by modified carbothermal/borothermal reduction of hafnium dioxide (HfO2) at relatively low temperatures (1500°–1600°C) for 1–2 h. The XRD patterns could be indexed as hexagonal HfB2 and no evidence of HfC, HfO2, or other impurities was observed. Glow discharge mass spectrometer analysis indicates that the synthesized HfB2 powders had high purity. The synthesized HfB2 powders had small average crystallite size (around 1 μm) and low oxygen content (

A ZrB 2 -SiC-ZrC ceramic was produced by reactive hot pressing using Zr, Si, and B 4 C as raw materials. The kinetics of the reaction process was studied. The reduction of powders by ball milling is of crucial importance for the sintering. The self-propagating high-temperature synthesis reaction between the raw powders can be ignited by controlling the sintering conditions, which leads to a sintering temperature as low as 1600°C, the lowest sintering temperature reported thus far. The relative density is 97.3%, with an open porosity of 0.6%, and the mechanical properties are comparable to the composites that sintered at higher temperatures. The depletion of oxygen impurities during the sintering was discussed.

Powders of Nd/V-doped Bi4Ti3O12 with a composition Bi3.74Nd0.26Ti2.98V0.02O12.01 (BNTV), prepared by the molten salt synthesis, using chlorides as the fluxes, were successfully obtained. The influences of the molar ratio of KCl to NaCl, temperature, and soak time on the formation and morphology of BNTV were investigated. The results indicated that Na+ can enter the lattice of Bi4Ti3O12 (BIT), leading to a decrease in the cell dimensions of BIT phase. The grain size and morphology of BNTV powders were considerably affected by the molar ratio of KCl to NaCl in the fluxes, in which the platelets showed the morphology of a rectangle and no regular shape in KCl and NaCl fluxes, respectively. The grain size of BNTV increased with increasing amount of NaCl in the fluxes, but the thickness decreased. The platelets prepared in the NaCl flux were faceted along (0 0 1) plane.

Dense and predominantly single-phase samples of Cr2AlC, together with a trace amount of Cr7C3, were fabricated by hot pressing of a mixture of chromium, aluminum, and graphite powders at 1400°C for 1 h. The hardness, Young's modulus, flexural strength, and compressive strength of Cr2AlC samples were 5.2, 288 GPa, 483±29, and 1159±23 MPa, respectively, which are comparable with those of Ti3AlC2 and Nb2AlC. The material exhibits good damage tolerance. For indentation loads up to 50 N, the post-indentation flexural strengths decrease by approximately 10% and by 31% for a load of 100 N. The flexural strengths of Cr2AlC samples quenched from 300°C to room temperature decrease from 483 to 455 MPa, while the retained strengths decrease quickly to 199 MPa when the quench temperature increases to 500°C. A further increase in quench temperature to 700°, 900°, and 1100°C results in a small reduction of strength.

The phase and microstructure relationship of 12 mol% CeO2-stabilized ZrO2 ceramics prepared from coated powder was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersed Xray spectroscopy (EDS). As compared with the sample prepared with co-precipitated method, which exhibited a similar grain size distribution, the EDS analysis revealed that the powder coating induced a wide distribution of CeO2 solubility, which decreases monotonically with the increase of grain size. This variation of stabilizer content from grain to grain rendered many large grains in the monoclinic phase. Stronger cerium segregation to grain boundaries was observed between large grains, which often form thin amorphous films there. The inhomogeneous; CeO2 distribution keeps more tetragonal ZrO2 grains close to the phase boundary to facilitate the transforming toughness. Addition of an Al2O3 precursor in coated powders effectively raises the overall CeO2 stabilizer content in the grains and preserves more transformable tetragonal phase in the microstructure, which further enhanced the fracture toughness. The dependence of CeO2 solubility on grain size may be explained in a simple coating-controlled diffusion and growth process that deserves further investigation.

The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α′ and β′), were hot-pressed at 1800°C for 1 h. The results showed that Pr α′ phase would transfer to β′ with the appearance of JEM phase (Pr(Si6−zAlz)(N10−zOz)) after sintering, thus resulting in the increase of β′ phase to 86 wt%. The addition of Y2O3 into SHS-ed Pr α′ powders as the starting materials restrains the transformation of α′ to β′ and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α′ grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α′ grains were found, i.e., nucleating on the undissolved Pr α′ grains and on the nuclei of (Pr, Y) α′ grains precipitated from liquid phase.

Effective grain alignment in Bi4Ti3O12 ceramics by superplastic-deformation-induced directional dynamic ripening

Two calcium-doped α-SiAlON compositions (Ca 0.6 Si 10.2 Al 1.8 -O 0.6 N 15.4 and Ca 1.8 Si 6.6 Al 5.4 O 1.8 N 14.2 ) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from α-Si 3 N 4 to α-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of α-SiAlON. Elongated α-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the α-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.

ZrB2–LaB6 powder was obtained by reactive synthesis using ZrO2, La2O3, B4C, and carbon powders. Then ZrB2–20 vol% SiC–10 vol% LaB6 (ZSL) ceramics were prepared from commercially available SiC and the synthesized ZrB2–LaB6 powder via hot pressing at 2000°C. The phase composition, microstructure, and mechanical properties were characterized. Results showed that both LaB6 and SiC were uniformly distributed in the ZrB2 matrix. The hardness and bending strength of ZSL were 17.06±0.52 GPa and 505.8±17.9 MPa, respectively. Fracture toughness was 5.7±0.39 MPa·m1/2, which is significantly higher than that reported for ZrB2–20 vol% SiC ceramics, due to enhanced crack deflection and crack bridging near SiC particles.

The purpose of this study was to evaluate heart rate and blood pressure responses to a commercially available source of ma-haung, a natural source of the sympathomimetic substance, ephedrine, and to evaluate the pharmacokinetic properties of the product in normotensive, healthy adults. On day 1, twelve study participants were monitored with an ambulatory blood pressure device between hours 7 and 20. On day 2, they ingested four capsules of powdered ma-huang at hours 8 and 17 while again wearing the monitor between hours 7 and 20. Serial plasma samples were obtained and concentrations of ephedrine were analyzed by high-performance liquid chromatography. Pharmacokinetic parameters of ephedrine were determined from plasma concentration-time profiles. The ephedrine alkaloid content of each capsule was also determined by high-performance liquid chromatography. Six participants experienced a statistically significant increase in heart rate, but the effects on blood pressure were variable. The half-life, volume of distribution, clearance, and maximum concentration in plasma of ephedrine in the ma-huang product were similar to values previously reported for a 20 mg, immediate-release ephedrine tablet. Values for the absorption rate were considerably lower and time to reach maximum concentration was longer for the capsules, compared with the standard tablet. Variability in alkaloid content of ephedrine was low and yielded a mean dose of ephedrine at 19.4 mg; pseudoephedrine at 4.9 mg; and methylephedrine at 1.2 mg for a four-capsule dose. In summary, ma-haung had variable effects on blood pressure and increased heart rate in healthy, normotensive adults. Pharmacokinetic parameters for ephedrine were in agreement with those previously reported; however, the absorption rate was much slower after ingestion of ma-huang.

Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi4Ti3O12) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi3+ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi4Ti3O12 ceramics.

Thick translucent and luminescent Gd–α-sialon ceramic disks (0.7–1.06 mm in thickness) were prepared by hot pressing. The effect of carbon atmosphere on their optical properties during sintering was explored by change packing methods. The results show that the sample with a lower carbon contamination has a higher translucence in the visible band and IR band (450–3500 nm), increasing transmission around 10% even if it is thicker. When excited at 350 nm, Gd–α-sialon with the lower carbon contamination can produce a visible light at 450–500 nm bands, but the luminescence is very weak in the sample containing more carbon contamination. These indicate that carbon contamination causes a severe degradation of the optical properties of α-sialon ceramics, and reduction of carbon contamination of α-sialon ceramics is very important for the optical property improvement.

Well-developed acicular Ba2NaNb5O15 (BNN) seed crystals have been successfully prepared by the reaction between BaCO3, Nb2O5 and molten NaCl salt. The effects of the calcination temperature, time, and weight ratio of the oxide mixture to salt on the morphology of BNN particles were investigated. Uniform acicular seeds with high aspect ratio could be achieved at 1200°C for 4 h with the salt-to-oxide mixture of 2:1.

The effects of sintering cycles and doping elements on the microstructures of Ln-α-sialon were studied. The results showed that microstructures with an elongated α-sialon morphology could be obtained through high-temperature post-heat treatment (1800–1900°C) or by prolonging soaking times during sintering. Different rare-earth elements had a profound effect on the microstructure of the resulting α-sialon. The Ln-α-sialon doped with low-Z-value elements could easily develop elongated grains with higher aspect ratio.

Self-propagating high-temperature synthesis (SHS) was applied to synthesize α-SiAlON powders doped by RE (RE = Eu,Pr,Ce) and codoped by RE and yttrium. The results showed that the weight ratio of α-SiAlON to (α-SiAlON +β-SiAlON) decreased from 70%, 55%, and 25% for europium-, praseodymium-, and cerium-doped α-SiAlON compositions, respectively, and the weight percentage of α-SiAlON phase increased to 100% for both (Eu,Y) and (Pr,Y) systems and 94% for the (Ce,Y) system, indicating SHS is a promising approach for synthesizing α-SiAlONs stabilized by the cations that could not be incorporated into the α-SiAlON structure by conventional sintering methods.

The single-phase α-sialon ceramics with high optical transmittance have been prepared by hot pressing. The maximum transmittance reached 65.2% and 52.2% in the infrared wavelength region, 58.5% and 40% in the visible region for the samples 1.0 and 1.5 mm thickness, respectively. The material also exhibited good mechanical properties of high hardness (20 GPa) and better fracture toughness (5.1 MPa.m 1/2 ). Both high optical transmittance and improved toughness of α-sialon ceramics were attributed to the less-grain-boundary glassy phase and the homogeneous microstructure, which was obtained by a proper process and confirmed by SEM and TEM observation, compared to that prepared by ordinary sintering. It is, therefore, expected that the translucent α-sialon ceramics could be a promising optical window material.

The properties of an aqueous Bi4Ti3O12 suspension stabilized by an acrylic acid/acrylic ester copolymer have been investigated. The adsorption of a copolymer on Bi4Ti3O12 surface resulted in a dramatic increase in the absolute zeta potential at pH 3–11. Coincidentally, the rheological property of the suspension was significantly improved. The adsorption quantity increased with increasing copolymer concentration at first, then decreased as the copolymer concentration was beyond 1.5 wt%. The viscosity varied in a complicated manner with copolymer concentration, due to the variations in the adsorption quantity and adsorption configuration of the copolymer molecules on Bi4Ti3O12 particle surface. High-quality tapes were prepared through tape casting.

A phenomenon of bilevel solubility was observed in a TiO2-doped (2.0 wt%) alumina with bimodal microstructure sintered in N2. Surface contributions to dopant signals in individual grains were identified and removed, using a spatially resolved energy dispersive spectroscopy analysis. Two levels of solubility, 1.005 ± 0.166 and 0.504 ± 0.082 mol% of TiO2 in Al2O3, were obtained for anisotropic and equiaxed grains, respectively. No grain size dependence of solubility was found, but segregation of SiO2 to boundaries with the anisotropic grains was observed. This phenomenon was explained by the incorporation of Ti3+ into the Al2O3 lattice during the abnormal grain growth caused by SiO2 liquid under a reducing atmosphere.

Terra Nova, 22, 251–256, 2010 Abstract The continuously distributed, well-preserved fracture-filling carbonates were collected from the cores retrieved from the Taiwan Chelungpu-fault Drilling Program between 400 and 2000 m depth for carbon and oxygen isotope analyses to constrain the fluid compositions and processes associated with brittle deformation within the accretionary wedge. The isotope analyses of fracture-filling carbonates yielded δ18O values steadily increasing with depth. The δ13C values exhibited a pattern similar to that of δ18O values at shallower depths, but an opposite trend at greater depths. Such variations in the isotopic compositions could be best explained by a mixing of shallow, meteoric water and deeply rooted fluid carrying isotopic signatures of various microbial processes. The notable excursion of δ18O values might infer a conduit for the lateral fluid transport along the high vein density zone. Overall, the isotopic patterns preclude the substantial influence of early diagenesis and suggest pervasive fluid percolation through the fracture network.

Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si 3 N 4 /BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of α-Si 3 N 4 , β-Si 3 N 4 , and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, α-Si 3 N 4 nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60-300 nm. The composites show compressive strength of 16.6 ± 1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies.

Dy-α-sialon and β-Si3N4 materials containing Dy-oxynitride glass were hot pressed at 1800°C for 1 h. The luminescence spectra of Dy3+ in these samples were compared when excited at 350 nm. The results showed that two strong emission bands in the region 470–500 nm and 570-600 nm, associated with the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions, were observed in Dy-α-sialon. However, no emission peak was detected from the β-Si3N4 sample, despite it containing the same amount of Dy3+ cations. This proved that only the Dy3+ cations in the α-sialon structure, not those in the oxynitride glass, produce the luminescence spectrum.

A ZrB 2 -SiC-ZrC composite was prepared from a mixture of zirconium, silicon, and B 4 C via reactive hot pressing at a relatively low temperature (1800°C) for 60 min under 20 MPa in an argon atmosphere. The relative density was 96.8%, the micro-hardness (Hv10) was 16.7 GPa, and the fracture toughness was 5.1 MPa·m 1/2 . The presence of ZrC was helpful for the densification process and improved the mechanical properties of the composite. A model of the microstructure development of the composite was proposed to explain the phase distribution.