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  • Author or Editor: G. Chen x
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Abstract  

The heats of hydration reactions for MgCl2⋅4H2O and MgCl2⋅2H2O include two parts, reaction enthalpy and adsorption heat of aqueous vapor on the surfaces of magnesium chloride hydrates. The hydration heat for the reactions MgCl2⋅4H2O+2H2O→MgCl2⋅6H2O and MgCl2⋅2H2O+2H2O→MgCl2⋅4H2O, measured by DSC-111, is –30.36 and –133.94 kJ mol–1,respectively. The adsorption heat of these hydration processes, measured by head-on chromatography method, is –13.06 and –16.11 kJ mol–1, respectively. The molar enthalpy change for the above two reactions is –16.64 and –118.09 kJ mol–1, respectively. The comparison between the experimental data and the theoretical values for these hydration processes indicates that the results obtained in this study are quite reliable.

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Abstract  

A novel approach is implemented to alleviate some persistent problems in neutron capture prompt gamma activation analysis (PGAA). Detection sensitivities of PGAA are often restricted by the following factors: poor signal to noise ratios, interferences from background signals, and, in some cases, overlapping energy lines from different origins, namely ultra short-lived decay lines interfering with prompt decay. Timing the gamma-ray acquisition with the actual capture events using a pulsed beam of cold neutrons allows discrimination between prompt and delayed emissions from a sample source as well as against background events. Coincidence gating selects the prompt gamma-ray emissions. Contributions of background capture gamma-rays are suppressed because of different flight times of neutrons to the sources of background radiation, providing a reduction in direct gamma-ray interferences. Anti-coincidence gating allows measurement of only decay radiation that originates from short-lived activated states of the nuclides after capture. Spectra of decaying nuclides are free of interfering prompt activities, as well as have lower continuum background from Compton scattering of high-energy prompt gamma-rays in the detector. The measurements provide the opportunity to use ultra-short half-life nuclides for analytical purposes, no sample transfer times are lost, and repetitive activation and counting cycles are achieved with the use of pulsed neutron beams.

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The relationship between plant communities and elevation in the Guandi mountainous area was studied. Data from 89 sampling units, each of 10 m x 20 m size, taken along an elevation gradient were analyzed by TWINSPAN, DECORANA and diversity and evenness indices. The samples were clustered into 23 groups by TWINSPAN, representing 23 vegetation types. The composition and distribution of communities varied greatly along the altitude gradient, suggesting that community diversity is closely related to elevation in the Guandi Mountains. This is due to the change of temperature and water-conditions along the elevation gradient. Species heterogeneity and evenness were significantly correlated with elevation along the entire gradient, but showing first a trend of increases and then decreases, corresponding to the hypothesis of maximum diversity at medium elevation. Species richness varied greatly in the study area, and was not significantly correlated with elevation.

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Effects of hydrocolloids (arabic gum, guar gum, and xanthan gum) on the physicochemical and rheological properties of whole-barley fortified cracker flour were determined using solvent retention capacity, alveograph, and Mixolab profiles. Results showed that the water absorption of whole-barley fortified cracker flour was reduced by the additional arabic gum. Besides, arabic gum was more effective in reducing the resistance to inflation and improving the extensibility of whole-barley fortified dough. Mixolab parameters indicated that the weakening of gluten proteins and the rate of starch retrogradation in whole-barley fortified cracker dough were reduced by the presence of arabic gum. Guar gum and xanthan gum promoted the rate of protein breakdown, but slowed down the starch gelatinization and retrogradation rate during the Mixolab heating-cooling cycle. In conclusion, involved arabic gum rather than guar gum or xanthan gum is benefit to improve the baking quality of wholebarley fortified saltine crackers.

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Summary A ternary solid complex Gd(Et2dtc)3(phen) has been obtained from reactions of sodium diethyldithiocarbamate (NaEt2dtc), 1,10-phenanthroline (phen) and hydrated gadolinium chloride in absolute ethanol. The title complex was described by chemical and elemental analyses, TG-DTG and IR spectrum. The enthalpy change of liquid-phase reaction of formation of the complex, Δr H Θ m(l), was determined as (-11.628±0.0204) kJ mol-1 at 298.15 K by a RD-496 III heat conduction microcalorimeter. The enthalpy change of the solid-phase reaction of formation of the complex, Δr H Θ m(s), was calculated as (145.306±0.519) kJ mol-1 on the basis of a designed thermochemical cycle. The thermodynamics of reaction of formation of the complex was investigated by changing the temperature of liquid-phase reaction. Fundamental parameters, the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A), the reaction order (n), the activation enthalpy (Δr H Θ ), the activation entropy (Δr S Θ ), the activation free energy (Δr G Θ ) and the enthalpy (Δr H Θ ), were obtained by combination of the thermodynamic and kinetic equations for the reaction with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, Δc U, was determined as (-18673.71±8.15) kJ mol-1 by a RBC-II rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δc H Θ m, and standard enthalpy of formation, Δf H Θ m, were calculated to be (-18692.92±8.15) kJ mol-1 and (-51.28±9.17) kJ mol-1, respectively.

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Summary

1,7-Dihydroxy-3,8-dimethoxyxanthone (X1) and 1,8-dihydroxy-3,7-dimethoxyxanthone (X2) are two important xanthones of the Tibetan medicinal plant Gentianopsis paludosa (Hook. f.) Ma. They are very similar in structure, the only difference being exchange of OH and OCH3 at the 7 and 8 positions. By calculations based on the geometry of the molecules using the MM+ force field, the different distances between the hydroxyl groups of the two xanthones were obtained (4.64774 Å for X2 and 7.19412 Å for X1), therefore, the two hydroxyl groups of X1 should freely interact with more water molecules than those of X2 in aqueous solution. In other words, X2 is more hydrophobic than X1. Micellar electrokinetic capillary chromatography (MEKC) was therefore chosen for separation of the compounds. The optimum separation conditions were: 20 mm borate + 20 mm SDS (pH 9.8) as running buffer, 17.5 kV applied potential, and detection wavelength 260 nm. The two xanthones were well separated in 9.0 min, with Gaussian peak shapes. The repeatability of the MEKC method (expressed as RSD) for X1 and X2 was 0.9 and 1.1%, respectively, for migration time, and 3.1 and 1.4% for peak area. The limits of detection (S/N = 3) were 0.41 μg mL−1 for X1 and 0.82 μg mL−1 for X2. The recovery of the MEKC method for the two xanthones was also satisfactory.

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The Avenin-like gene (EU096532) was cloned from Aegilops biuncialis (2n = 4X, UUMM) in our previously study, the encoded gluten protein contained 19 cysteine residues, much more than that in all other glutenin subunits characterized so far. In present study, the protein was expressed in E. coli in large scale and purified in high purity through His-binding affinity chromatography. The purified protein was simply added or incorporated into a base flour and conducted with a 2 g Mixograph in order to investigate the functional properties including mixing time (MT), peak dough resistance (PR) and breakdown in resistance (RBD). Both 10 mg and 15 mg Avenin-like protein could cause significant increases in MT and PR, and decrease in RBD, compared to the control, when incorporated into dough. But the latter showed larger effect on functional properties. Size exclusion high-performance liquid chromatography (SE-HPLC) analysis confirmed that Avenin-like protein was chemically incorporated into polymeric subunits by intermolecular disulphide bonds.

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Chlorophyll content is positively correlated with photosynthetic rate. However, little is known about the genetic correlation between grain yield and chlorophyll content in the same wheat mapping population. The primary goal of the study was to detect the genetic basis of grain yield and chlorophyll content and their possible roles in the genetic improvement of grain yield in wheat. Here, quantitative trait loci (QTLs) for grain yield and chlorophyll content were studied using a set of 168 doubled haploid (DH) lines derived from a cross between two elite Chinese wheat cultivars, Huapei 3×Yumai 57. The DH population and parents were evaluated for grain yield and chlorophyll content in three environments. A total of 11 additive QTLs and 6 pairs of epistatic QTLs were detected for grain yield and chlorophyll content. Loci, such as Xcfd53, Xwmc718 , and Xwmc215 on chromosomes (e.g. 2D, 4A, and 5D) simultaneously controling grain yield and chlorophyll content, showed tight linkages or pleiotropisms. Three novel major QTLs, qGY5D, qChla5D , and qChlb5D , closely linked with the PCR marker Xwmc215 on chromosome 5D, accounted for 10.32%, 12.95%, and 23.29% of the phenotypic variance, respectively. The favorable alleles came from Yumai 57.

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With the continuous expansion of the global dairy trade market, the quality and safety of the Chinese dairy market have a wide and far-reaching impact on the world. Based on the development of the dairy scandal in the past few years in China, this study illustrates the serious damage of melamine on human health and the negative impact on the dairy industry in China.

This study shows that the lack of effective government regulations is a key reason for dairy market failure. Consumers are lacking confidence in the quality of Chinese dairy products and the government's market regulations. The Chinese dairy market will continue to rely on imported dairy products. By analyzing the typical cases of the dairy market in China, this study aims to provide a guide for dairy industries in other countries.

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