A modified NiS fire-assay neutron activation method is developed for the determination of all platinum-group elements (PGEs) in mantle-derived xenoliths. This method is characterized by sub-ppb detection limits, <0.1~0.002 ppb procedural blanks and 7~15% analytical precision for PGEs. Analyses of PGE standard rocks indicate that this modified NiS fire-assay neutron activation method is as reliable as the method previously proposed for a large scale of samples. The capability of the method for the measurement of PGEs in the upper mantle is also illustrated by some exciting results obtained from mantle-derived xenoliths of Eastern China.
It is widely reported that the productivity-richness relation (PRR) is highly variable, and several field studies suggest that the PRR varies with observational scale. Here we provide the first experimental study to test whether the PRR is scale-dependent when all replicate ecosystems have similar initial conditions. We also test the relation between productivity and compositional dissimilarity, and whether the PRR varies with ecosystem size. Moderately complex replicated microcosms were assembled consisting of a range of protozoa, algae, and a diverse bacterial flora. We found that the PRR of protozoan and algal communities varied with observational scale, but was unrelated to ecosystem size. Specifically, protozoan and algal richness increased monotonically with productivity at the local scale, but became flattened at the regional scale. This varying PRR at different scales occurred because dissimilarity among replicates decreased with productivity. Thus, in this model system, our experimental approach found a different form of scale dependence than previous field research. We speculate that this difference results from different processes governing extinctions at low levels of productivity.
This investigation is one of the first to adopt quantile regression (QR) technique to examine covariance risk dynamics in international stock markets. Feasibility of the proposed model is demonstrated in G7 stock markets. Additionally, two conventional random-coefficient frameworks, including time-varying betas derived from GARCH models and state-varying betas implied by Markov-switching models, are employed and subjected to comparative analysis. The empirical findings of this work are consistent with the following notions. First, the beta smile (beta skew) curve for the Italian, U.S. and U.K. (Canadian, French and German) markets. That is, covariance risk among global stock markets in extremely bull and/or bear market states is significantly higher than in stable periods. Additionally, the Japanese market provides a special case, and its beta estimate at extremely bust state is significantly lower, not higher than that at the middle region. Second, the quantile-varying betas are identified as possessing two key advantages. Specifically, the comparison of the system with quantile-varying betas against that with time-varying betas implied by GARCH models provides meaningful implications for correlation-volatility relationship among international stock markets. Furthermore, the quantile-varying beta design in this study relaxes a simple dual beta setting implied by Markov-switching models of Ramchand — Susmel (1998) and can identify dynamics of asymmetry in betas.
SOFM (self-organizing feature map) clustering is powerful in analyzing and solving complicated and non-linear problems. This method was used and compared with fuzzy C-means clustering and TWINSPAN, the most common classification methods, in analysis of plant communities in the Guancen Mts., China. The dataset consisted of importance values of 112 species in 53 quadrats of 10 m × 20 m. All the three methods classified the 53 quadrats into eight groups, representing eight associations of vegetation. They were all effective in the analysis of ecological data. The consistency of SOFM clustering with fuzzy C-means clustering (FCM) and TWINSPAN classification was 81.1% and 94.3%, respectively. SOFM clustering has some advantages and more potentiality in application to studies of ecology.
An efficient method used to separate five bioactive compounds from Gelidium amansii was optimized by the HCI software. The optimum composition of mobile phase for high-performance liquid chromatographic (HPLC) separation was obtained. The elution profiles were calculated by the polynomial theory based on the retention factor ln k = A + BF + CF2 (F was the volume percentage of acetonitrile with 1.0% acetic acid); then, the theory was applied to calculate the elution profile in both isocratic and gradient modes by modifying different mobile phase conditions with HCI program. The calculated results of mobile phase condition suggested that acetonitrile-water (containing 1.0% acetic acid) with a linear gradient elution of 0∼30 min from 15:85 to 50:50 (v/v) was the optimized component. In the experimental conditions, the agreement between the experimental elution profiles and the calculated values of eluted concentration was relatively good.
Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount
of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (Tp) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk
crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength
and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated
with crystallization and morphology of glass ceramics.
The decomposition kinetics of reference calcite and three ultra-fine samples with different morphologies are investigated.
The kinetic parameters and rate equation are obtained according to the methods reported in our previous studies. Compared
with the reference calcite, a considerable diminution of the activation energy Ea up to 70–80 kJ mol−1 is observed in the case of three ultra-fine samples. There are also some distinct differences concerning the activation energy
of each of the ultra-fine sample. This may have something to do with the particle morphology revealed by TEM and SEM measurements.
XRD measurements of four calcite samples show that large strain exists in the crystal lattice in the case of ultra-fine calcite
samples. This may give a reason to their abnormal decomposition behavior.
A micellar high-performance liquid chromatography (HPLC) method has been described for simultaneous determination of ephedrine, pseudoephedrine, and methylephedrine in Ephedra Herb and two traditional Chinese preparations. The separation and determination of ephedrine, pseudoephedrine, and methylephedrine were performed using a mobile phase containing 1.75 × 10−1 mol·L−1 sodium dodecyl sulphate and 0.02 mol·L−1 potassium hydrogen phosphate with 10% (v/v) methanol at pH 3.0, running at 1.5 mL·min−1 by a Venusil XBP C18 (250 × 4.6 mm, 5 μm) column at 40 °C. The detected wavelength was set at 210 nm. The method was validated according to the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines. The main analytical parameters were linearity (r > 0.9990), intra- and inter-day precisions (relative standard deviation [RSD %], 0.33–1.63, and RSD %, 1.26–2.20, respectively), limit of quantifications [LOQs], and limit of detections [LODs] (2.6 × 10−4 and 7.8 × 10−5 mg·mL−1 for ephedrine, 6.8 × 10−4 and 2.0 × 10−4 mg·mL−1 for pseudoephedrine, and 5.0 × 10−4 and 1.5 × 10−4 mg·mL−1 for methylephedrine). RSDs of recoveries were <5.5% in the three samples. Based on the optimized chromatographic conditions and the eluted orders, a model of separation mechanism for the analytes was established. The results indicated that the proposed method was an accurate, “green” and cheap method.
Authors:J. Jia, G. Li, C. Liu, M. Lei, and Z. Yang
Wheat yellow rust resistance gene Yr17 was originated from the wheat-Aegilops ventricosa introgression, and still effective on the adult plant in Southern China. The previous studies located the gene Yr17 on the translocation of 2NS-2AS using the molecular and cytological markers. In the present study, we screened new PCR-based markers to map the gene Yr17 region from the investigation of a segregating 120 F2 population. All markers including four EST-PCR markers, a SCAR (sequence characterized amplified region) and a PLUG (PCR based landmark unique gene) marker specific to Yr17 gene were mapped on the chromosome 2AS, and located on the chromosomal deletion bin 2AS5-0.8–1.00 region. Based on the wheat-rice collinearity, we found that the sequences of the Yr17 gene linked markers were comparatively matched at rice chromosome 4 and chromosome 7. However, the identified closely linked genomic sequence of Yr17 gene is most likely collinear with genomic region of rice chromosome 4. The newly produced PCR based markers closely linked to Yr17 gene will be useful for the marker-assisted selection in wheat breeding for rust resistance.