Speciation of selenium in plant water extracts by ion exchange chromatography-hydride generation atomic absorption spectrometry

Determination of selenium (Se) speciation in plants is important in studying the bioavailability and toxicity of Se in Se-contaminated soil/sediment. In this study, we used an anion exchange resin (Dowex 1-10X) to separate Se into non-amino acid organic Se, Se-amino acids, selenite (Se [IV]) and selenate (Se [VI]) in a plant (Stanleya pinnata) extract. The hydride generation atomic absorption spectrometry (HGAAS) was used to determine concentrations of these Se compounds in plant extracts. Results showed that Se compounds can be quantitatively separated by the resin column. Recovery of five spiked standard Se compounds (trimethylselenonium ion (TMSe+), dimethylselenoxide (DMSeO), selenomethionine (Semet), Se [IV] and Se [VII]) in the plant extract ranged from 92.9 to 103%. Water extractable Se accounted for 60.4-72.6% of the total Se in the plant. Among the soluble Se compounds in the plant extract, Se-amino acids were 73-85.5%, Se [VI] ranged from 7.5 to 19.5% and non-amino acid organic Se was less than 7%. Se [IV] in most samples was below the detection limit (1 microg/g). This study showed that considerable amounts of the accumulated Se [VI] in the plant was metabolized to Se-amino acids during growth of the plant.     

The long-term evolutions and the regional characteristics of atmospheric methane concentrations in Nagoya, 1983-1997

This study provides information on the long-term evolutions of the atmospheric methane (CH4) concentrations in Nagoya City, Japan, which were analyzed by using the continuous monitoring data observed at the eight observatory stations for 1983-1997. The 15-year records of the atmospheric CH4 concentrations were examined by means of a time-series analysis using a fast Fourier transform with a low-pass filter to elucidate the seasonal cycles and the long-term trends. The annual averages of the CH4 concentrations in Nagoya were 1.85 ppmv (parts per million by volume), 1.91 ppmv, and 1.90 ppmv in 1988, 1995 and 1997, respectively. Moreover, the annual average growth rate showed a drastic decrease from 17 ppbv (parts per billion by volume) year(-1) in 1992 to 2 ppbv year(-1) in 1993, and further down to 7 ppbv year(-1) in 1997. Comparison of the atmospheric CH4 records in Nagoya with those in global air of the northern hemisphere observed at Mauna Loa observatory in Hawaii, USA, allows us to estimate the excess concentration of CH4 in the urban atmosphere of Nagoya, which was 0.17 ppmv in 1988 and 0.15 ppmv in 1997. On a local scale, the atmospheric CH4 concentrations in the northern part of Nagoya City increased until 1992 and then gradually decreased from 1993 to 1997, although those in the south-western urban areas constantly increased at the averaged growth rate of 13 ppbv year(-1) for 1988-1997. The variation of the long-term trends of the CH4 concentrations in Nagoya may be ascribed to the emission changes from the CH4 sources due to the human activities such as waste dumping and landfills.     

The uptake of chemical elements from coal ash and settling basin effluent by primary producers II. Relation between concentrations in ash deposits and tissues of grasses growing on the ash

A number of reports of biomagnification of trace metals by plants indicate that elements are selectively concentrated within certain tissues when plants grow on coal ash. This study determined the uptake by, and tissue bioaccumulation of, 15 chemical elements within broom sedge and nut grass growing in the drainage system of a coal ash basin. Biomagnification of these elements by the grasses was compared to concentrations of these elements found in duckweed within the same system.Aluminium, arsenic, barium, cadmium, cobalt, chromium, copper, iron, mercury, manganese, molybdenum, selenium, strontium, titanium, and zinc were measured by neutron activation analysis in roots, stems, leaves and fruit of the grasses which grew in sediments within the effluent. Mercury and zinc were biomagnified in both grasses and duckweed to a level exceeding the concentration in sediment. All elements were biomagnified above the water concentration in all parts of the plants. Bioaccumulation of elements in the leaves and fruit of these plants provides a concentrated source of potentially toxic chemical elements for passage to animals which may consume these plants. The mechanisms of movement of potentially toxic elements from coal ash or water into food webs need additional study as utilization of coal is increased.     

A computer technique for predicting smoke movement in tall buildings

An approach to the analysis of stack effect has been developed which allows the prediction of internal air flow quantities and associated pressure differentials for specific buildings prior to construction. An example of the application of this analysis is presented for a hypothetical 75-story office building. Note: The authors presented this paper at a symposium on “The Control of Smoke Movement on Escape Routes in Buildings,” sponsored by the Joint Fire Research Organization and held on April 9 and 10, 1969 in Hertfordshire, England.     

Radon and 'King Solomon's Miners': Faynan Orefield, Jordanian Desert

Concentrations of 222Rn were measured in ancient copper mines which exploited the Faynan Orefield in the South-Western Jordanian Desert. The concentrations of radon gas detected indicate that the ancient metal workers would have been exposed to a significant health risk and indicate that any future attempt to exploit the copper ores must deal with the hazard identified. Seasonal variations in radon concentrations are noted and these are linked to the ventilation of the mines. These modern data are used to explore the differential exposure to radon and the health of ancient mining communities.     

A preliminary note on the sequential decomposition of pectin by aquatic bacteria

In a eutrophic lake, an inverse relationship was observed between total aerobic heterotrophic bacteria and their pectolytic share which consisted mainly of Flavobacterium-Cytophaga species. When grown in a medium containing pectin and yeast extract as organic compounds pure cultures of the most abundant type of this bacterial group showed a diauxic characteristic of growth. Short time before entering the first lag phase of growth, production of pectolytic enzymes increased until the end of the second log phase of growth. This phenomenon may be due to the mechanism of a catabolic repression and derepression.     

Finite element analysis of optimized brace angle for the diagrid structural system

International Journal of Steel Structures - The Diagrid structural system is considered to be the best structural system for constructing free form structures, but it is also a very effective...     

Ultrafast terahertz responses in monolayer graphene

ABSTRACT

We theoretically investigate the ultrafast terahertz (THz) properties of monolayer graphene. The analytical formulations of the photon carrier, electric polarization and optical current are obtained by solving the Bloch-equations in present of the ultrafast THz Gaussian pulse. Graphene shows a large nonlinear and ultrafast optical response at THz frequencies due to the gapless and relativistic Dirac particles with nearly linear energy dispersion. It is found that the photon carrier density, electric polarization and optical current density increase with increasing the frequency of the THz pulse. These theoretical results are in agreement with recent experimental findings. This study confirms further that graphene exhibits important features and is relevant to the applications in the ultrafast THz fields.