Search Results

You are looking at 1 - 10 of 1,705 items for :

  • "variations" x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All

] F. Chen , A. Wu , C. Chen , The influence of different treatments on the free radical scavenging activity of burdock and variations of its active components , Food Chem. 86 ( 2004 ) 479 – 484

Restricted access

A new method is proposed for the derivation of kinetic parameters of reactions in homogeneous systems, by carrying out kinetic measurements under conditions of programmed temperature variations, instead of performing them under isothermal conditions at different temperatures. The basic relations are given for simple, paralle and complex reactions, without specifying the analytical shape of the temperature programme function.

Restricted access

Chon, H. T., Ahn, J. S. & Ch. Jung, M. , 1998. Seasonal variations and chemical forms of heavy metals in soils and dusts from the satellite cities of Seoul, Korea. Environmental Geochemistry and Health. 20 . 77

Restricted access

Abstract  

Seasonal variations of radionuclide concentration in pine needles (Pinus Thunbergii) were examined. The seasonal variations were classified roughly into two types, one represented by the periodical variation of137Cs concentration and the other represented by a linear decrease of103Ru concentration when plotted on a semi-log scale. Weathering half-lives for the latter type of nuclides were estimated and a fairly good consistency in the half-lives for different nuclides was observed irrelevant to their radioactive half-lives.

Restricted access

Abstract  

A system has been designed and applied to study variations of the photofraction with distance. A137Cs and a54Mn gamma-source have been used; their distances to the detector were varied and the variations of the photofraction have been studied in the range of 1 to 300 mm.

Restricted access

Abstract  

Experiments were designed to evaluate, in a controlled way, some of the variations that can be expected in radon concentration in soil due mainly to meteorological factors and to close spacing monitoring in the field. Electronic continuous radon monitoring and the track-etch method were used to record the radon -decay. The radon emanation in daily measurements and in long term surveys showed a general effect modulated by temperature and pressure variations. Radon monitoring in soil for nearby stations showed that a 10% range of variation can be expected with the track-etch method and as a result of non-homogeneous emanation pattern of the soil.

Restricted access

Abstract  

INAA with thermal and epithermal irradiation has been applied for determination of 40 chemical elements in soils and different organs of plants. The time and spatial variations of elemental composition of plants and soils are studied.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Narazaki, K. Fujitaka, S. Igarashi, Y. Ishikawa, and N. Fujinami

Abstract  

Seasonal variations of 7Be deposition in regions throughout Japan (26°18'N-43°05'N, 127°54'E-141°27'E) were observed during the period of 1989-1995. The observation indicated that 7Be deposition peaked in spring all over Japan except in the inland central basin. However, spring peak was not always the annual maximum. Along the coastal side of the Japan Sea, especially around Hokuriku region, 7Be deposition was at its maximum in winter. In addition, September peak also was observed in some regions, which was presumably caused by high precipitation or blowing in of northern air stream. Variations were classified into 4 types according to meteorological factors and local geographical conditions: winter peak, double peaks (spring and September peaks), spring peak and non-peak. A correlation between 7Be deposition and precipitation was observed in winter.

Restricted access

Abstract  

Pyrrolidyl triazenes prepared by interception of the diazonium transient in the Sandmeyer reaction of amines can serve as useful intermediates in the iodination and radioiodination of aryl rings. Decomposition of such triazenes in the presence of iodide is acid-catalyzed and is sensitive to choice of solvent, acid, and triazene structure. A condition variation study by HPLC of four different solvent systems and two non-nucleophilic acids was carried out on the123I iodination of the triazenes of p-nitroaniline, p-anisidine and p-toluidine. This method has proven useful in radiolabeling of two pharmaceutical analogs which were not amenable to labeling through the classic Sandmeyer method.

Restricted access

Abstract  

Leaf and aerosol samples were monthly collected in Mt. Sefuri (Fukuoka Prefecture). Radioactivities of 7Be, 210Pb and 40K were determined with gamma-ray spectrometry. The concentrations of some elements in the leaf samples were determined by neutron activation analysis. Similar seasonal variation of 7Be and 210Pb was observed between leaf and aerosol samples, high in spring and winter and low in summer. Correlation factors for trace elements contained in the leaf show large variations. This indicates that the contribution of two sources (atmospheric deposition and uptake from soil) is very variable.

Restricted access