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| 2. |
- Bax, Gerhard, et al.
(författare)
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GIS BASED STUDY OF ROCK SLOPE INSTABILITIES IN MOUNTAINOUS KARST AREAS AND THE CONSEQUENCES ON HIGHWAY CONSTRUCTION, GUIZHOU PROVINCE, CHINA
- 2004
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The Guizhou Province in southwest central China is characterized by complex geological fold belts resulting in a varying geomorphologic pattern with steep valleys and ridges. The dominating carbonate rocks cause a karst environment with rough topography and bedrock outcrops lacking soil cover, leading to a fragmentation of the natural ecology environment. Soil erosion is another major problem of this densely populated area.During intense exploitation of the area due to extended highway construction projects, there are risks for further fragmentation of the landscape. The construction process furthermore is triggering the establishment of rock falls and rock landslides endangering natural ecosystems and human lives. For the prediction and prevention of larger rock falls and rock landslides it is necessary to measure dip and strike of bedding and joints in the involved geological strata in relation to road directions. These data, together with elevation data and its derivates (slope, aspect) are put together in a GIS system enabling risk assessment for geohazards. The elevation data for this study are derived from freely available SRTM data with a 90 m grid. Landsat TM and ETM+ is use as ancillary data. The lithological and tectonic information is based on the Geological Map of Guizhou province, scale 1 : 500 000, dip and strike from local measurements.Based on the derived information we hope to establish recommendations for the design and construction of prevention measures.
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| 3. |
- Chen, Jun, et al.
(författare)
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Antioxidant capacity of bovine milk as assayed by spectrophotometric and amperometric methods
- 2003
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Ingår i: International Dairy Journal. - 0958-6946. ; 13:12, s. 927-935
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Tidskriftsartikel (refereegranskat)abstract
- The total antioxidant capacity (TAC) of bovine milk, whey, and low-molecular-weight (LMW) fractions of whey was investigated using spectrophotometric methods including an ABTS-based method (reduction of the cation radical of 2,2′-azinobis(3-ethylenebenzothiazoline-6-sulfonic acid)) and a FRAP method (reduction of Fe3+). Significant antioxidant capacity in milk and whey was demonstrated by the ABTS method (TAC(ABTS)), and it apparently increased with increasing pH. TAC (ABTS) was several-fold higher in milk than in whey, which had a slightly higher TAC than a LMW fraction prepared from it. Also the FRAP method could be used to demonstrate TAC in whey, although the low pH necessary for this method led to some protein precipitation. Most of the ferric-reducing activity of whey was found in the LMW fraction. The TAC values obtained using these methods were also compared to those obtained using a newly developed flow-injection amperometric (FIAmp) procedure for LMW fractions. High correlations were found for the TAC values of LMW samples obtained by the ABTS, FRAP and FIAmp methods (R2>0.8, P<0.001). Furthermore, to identify the major antioxidants in the LMW fraction, it was treated by uricase. Since most of the TAC (using ABTS, FRAP and FIAmp methods) was removed by uricase treatment, it could be concluded that urate is the major antioxidant in the LMW fraction. Also the effect of heat treatment on TAC in milk and whey was monitored. After heating of whey at 63°C for 1 h, TAC(ABTS) tended to increase by at least 20%, while TAC(FRAP) was not significantly changed. In milk, TAC(ABTS) remained constant during the same heat treatment. It is concluded that the methods tested gave the most reliable results for the LMW fraction of whey and that the use of several methods is necessary to characterise the antioxidant capacity of milk.
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| 4. |
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| 5. |
- Chen, Jun, et al.
(författare)
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Electrochemical studies on antioxidants in bovine milk
- 2002
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Ingår i: Analytica Chimica Acta. - 1873-4324. ; 474:1-2, s. 137-146
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic voltammetry (CV), rotating disk electrode (RDE) linear sweep voltammetry and flow-injection amperometry (FIAmp) were used to investigate the possibility to determine antioxidants in bovine milk, whey and low-molecular-weight (LMW) fractions of whey. Using CV one major current wave was found in all types of samples at oxidation potentials between +600 and +700 mV against Ag | AgCl|0.1 mol l−1 KCl. The wave registered for the LMW fraction disappeared after treatment with uricase as shown by CV and RDE, indicating that the major antioxidant in the LMW fraction may be urate. The antioxidant capacities of the LMW fractions were also measured by the FIAmp method using an oxidation potential of +700 mV with Trolox as standard, and values between 100 and 130 mol l−1 Trolox equivalents were obtained. It is concluded that different electrochemical methods can be used to measure antioxidants in milk.
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| 6. |
- Chen, Jun
(författare)
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Selenium Compounds and Antioxidant Capacity in Bovine Milk. Studies on Glutathione Peroxidase, Bioavailability and Electrochemical Techniques
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The efficacy and function of antioxidants have been intensively studied in foods and other biological systems in recent decades. This thesis concerns different aspects of the antioxidant properties of bovine milk, with emphasis on measurement of the total antioxidant capacity (TAC), the activity of the selenium-containing glutathione peroxidase (GSHPx), and the bioavailability of selenium from bovine milk in humans. The TAC measurements were based on the scavenging of the cation radical of 2,2?-azinobis(3-ethylenebenzothiazoline-6-sulphonic acid) (the ABTS method), the reduction of the complex of ferric ion and 2,4,6-tripyridyl-s-triazine (the FRAP method), or the amperometric signal registered at a glassy carbon electrode at an oxidation potential of +700 mV (versus AgôAgCl) in a flow-injection assay (the FIAmp method). Milk, whey, high-molecular-weight (HMW, >10 kDa) fraction and low-molecular-weight (LMW, <10 kDa) fraction of whey were all found to have antioxidant capacity. High correlations were found for the TAC values in the LMW fraction as detected by the three methods (R2 > 0.8, P< 0.001). The major antioxidant in the LMW fraction was identified as urate by specific enzyme treatment. Other electrochemical techniques such as cyclic voltammetry (CV) and rotating disk electrode (RDE) linear sweep voltammetry were also employed to characterise the antioxidant capacity in milk. Extracellular glutathione peroxidase (eGSHPx) is one of the antioxidant enzymes in bovine milk, and a coupled enzymatic assay has been optimised for measuring its activity. The activity of GSHPx was monitored during heat treatment of milk and whey. The activity of GHSPx in milk and whey was maintained at 72°C for 2 min, implying that the enzyme was stable at this common pasteurisation temperature used in dairy industry. The activity of purified cellular glutathione peroxidase (cGSHPx) was less stable than that of purified eGSHPx, and both purified enzymes were less stable than the GSHPx activity in milk. Selenium is an integral part of GSHPx, as well as of other selenoproteins with redox enzymatic activities and it is probably also related to the antioxidant status in humans. Therefore, the bioavailability of selenium from bovine milk was studied in humans using the ileostomy model. It was found that the fractional absorption of selenium was significantly higher for milk than for fermented milk, 73.3 (16.1) versus 64.1 (11.2) %, mean (SD), and selenium from bovine milk was thus highly bioavailable to humans.
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| 7. |
- Ji, Xiaoyan, et al.
(författare)
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Determination of dissolution kinetics of K2SO4 crystal with ion selective electrode
- 2001
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Ingår i: Chemical Engineering Science. - 0009-2509 .- 1873-4405. ; 56, s. 7017-7024
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution kinetics of potassium sulfate crystals was studied and the effects of hydrodynamic situation and temperature on the dissolution were investigated. The dissolution was determined by measuring the change of electromotive force (E) with the potassium ion selective electrode. From the values of E, the concentration of K+ was calculated combined with an activity coefficient model. The results are accurate and rapid, the maximum deviation is less than 2%. Theory, developed for constant bulk concentration in a rotating disk system, was modified in order to analyze the general grain dissolution process. Normal distribution was introduced in calculating the area of crystals in order to obtain reliable dissolution rate. Using the modified theory diffusion rate constant, equilibrium exchange rate constant and thickness of diffusion layer were obtained. It is found that the diffusion rate constants increase while the thickness of diffusion layer decreases with the increase of temperature and stirring speed; the equilibrium exchange rate is dependent on bulk concentration.
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