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排序方式: 共有97条查询结果,搜索用时 15 毫秒
21.
Henneken H Lindahl R Ostin A Vogel M Levin JO Karst U 《Journal of environmental monitoring : JEM》2003,5(1):100-105
A diffusive sampling method for the determination of methyl isocyanate (MIC) in air is introduced. MIC is collected using a glass fiber filter impregnated with 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ). The urea derivative formed is desorbed from the filter with acetonitrile and analyzed by means of high-performance liquid chromatography (HPLC) using fluorescence detection (FLD) with lambdaex = 471 nm and lambdaex = 540 nm. Additionally, a method was developed using tandem mass spectrometric (MS-MS) detection, which was performed as selected reaction monitoring (SRM) on the transition [MIC-NBDPZ + H]+ (m/z 307) to [NBDPZ + H]+ (m/z 250). The diffusive sampler was tested with MIC concentrations between 1 and 35 microg m(-3). The sampling periods varied from 15 min to 8 h, and the relative humidity (RH) was set from 20% up to 80%. The sampling rate for all 15 min experiments was determined to be 15.0 mL min(-1) (using HPLC-FLD) with a relative standard deviation of 9.9% for 56 experiments. At 80% RH, only 15 min sampling gave acceptable results. Further experiments revealed that humidity did not affect the MIC derivative but the reagent on the filter prior to and during sampling. The sampling rate for all experiments (including long term sampling) performed at 20% RH was found to be 15.0 mL min(-1) with a relative standard deviation of 6.3% (N = 42). The limit of quantification was 3 microg m(-3) (LC-MS-MS: 1.3 microg m(-3)) for 15 min sampling periods and 0.2 microg m(-3) (LC-MS-MS: 0.15 microg m(-3)) for 8 h sampling runs applying fluorescence detection. 相似文献
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Der Beitrag umfa?t eine übersicht über die Entwicklung wesentlicher Segmente des in Deutschland und international zug?nglichen
Angebots an Umweltdatenbanken. Anschlie?end werden wichtige Umweltdatenbanken im Angebot von STN International dargestellt.
Anhand ausgew?hlter Beispiele aus der Recherchepraxis werden schlie?lich Ablauf (Stufen der Vorbereitung, Durchführung und
Nachbereitung) sowie Ergebnisse der Online-Recherche in wichtigen STN-Umweltdatenbanken dargestellt. 相似文献
25.
Hartmut Follmann 《Die Naturwissenschaften》1982,69(2):75-81
DNA replication requires monomeric deoxyribonucleotides, which cannot be regarded as primary products of organic syntheses on a primitive earth. However, the present biosynthetic pathway — reductive elimination of the 2′-OH group from ribonucleotides, catalyzed by ribonucleotide reductases and thioredoxins — suggests an early, polyphyletic combination of protein-nucleotide interactions and metal catalysis. That key process had to precede the upcome of RNA-DNA dualism on the way from RNA-protein protocells to true organisms. 相似文献
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Hartmut Koehler Jürgen Warrelmann Peter Behrend Ingo Dobner Tobias Frische Wolfgang Heyser Bernd Jastorff Ulrich Walter 《Environmental Sciences Europe》2001,13(6):359-368
The final article of a series of three evaluates the in situ-remediation of TNT(trinitrotoluene)-contaminated soil from ‘Werk Tanne’. The multidisciplinary approach allows a differentiated assessment. Grading with large-scale machinery leads to a depletion of TNT for almost 90% within the first 6 months, while ADNT(amino-dinitrotoluene)-content decreases more or less steadily over 1,5 years. Grading reduces the heterogenous distribution of the contamination only slightly. Results from field-monitoring and biotest-battery indicate residual toxicities of ecotoxicological relevance and a reduced capacity for biological regeneration, in comparison with the uncontamined site. Mycorrhized plants safe-guard the site and improve the soilecological conditions. Their role in reducing lower level residual toxicity requires further investigation. There is need for future research (1) on the dynamics and mechanisms of the initial decrease of TNT followed by stagnation, (2) on the fate of the primary metabolites, (3) on long-term effects of the phytoremediation, and (4) on the establishment of the complex monitoring for routine work. 相似文献
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Vetterlein D Szegedi K Ackermann J Mattusch J Neue HU Tanneberg H Jahn R 《Journal of environmental quality》2007,36(6):1811-1820
Arsenate (As V) is the predominant form of arsenic in soils under aerobic conditions and competes with the major plant nutrient phosphorus (P) in the form of phosphate (PV) not only for sorption sites on mineral surfaces in soil but also for root membrane transporters. Plants have evolved several mechanisms for the mobilization of PV in soils in response to P deficiency, such as the release of organic anions and protons. The aim of the present study was to test whether these mechanisms result in a simultaneous mobilization of arsenate and what would be the consequences for As transfer from soil to plant. The compartment system approach with Zea mays as model crop was chosen as an experimental setup. The system is equipped with micro suction cups and allowed us to investigate processes occurring in the vicinity of roots. As a case study, an artificial quartz substrate with well defined soil physical properties was fertilized, spiked with As V, and amended with increasing amounts of goethite (0, 1, and 4 g kg(-1) in treatments G-0, G-1, and G-4, respectively). The addition of goethite alleviated the As V-induced growth reduction and reduced As V transfer from the substrate to the plant but induced P deficiency at the same time. When low amounts of goethite (1 g kg(-1)) were added, plants mobilized PV but not As V, which might be related to differences in surface complexation reported for PV and As V. No mobilization of PV or As V was observed with the addition of higher amounts of goethite, probably because of decreasing competition between organic anions, PV, and As V for binding sites. 相似文献
30.
Many technologies in precision agriculture (PA) require image analysis and image- processing with weed and background differentiations.
The detection of weeds on mulched cropland is one important image-processing task for sensor based precision herbicide applications.
The article introduces a special vegetation index, the Difference Index with Red Threshold (DIRT), for the weed detection
on mulched croplands. Experimental investigations in weed detection on mulched areas point out that the DIRT performs better
than the Normalized Difference Vegetation Index (NDVI). The result of the evaluation with four different decision criteria
indicate, that the new DIRT gives the highest reliability in weed/background differentiation on mulched areas. While using
the same spectral bands (infrared and red) as the NDVI, the new DIRT is more suitable for weed detection than the other vegetation
indices and requires only a small amount of additional calculation power. The new vegetation index DIRT was tested on mulched
areas during automatic ratings with a special weed camera system. The test results compare the new DIRT and three other decision
criteria: the difference between infrared and red intensity (Diff), the soil-adjusted quotient between infrared and red intensity
(Quotient) and the NDVI. The decision criteria were compared with the definition of a worse case decision quality parameter
Q, suitable for mulched croplands. Although this new index DIRT needs further testing, the index seems to be a good decision
criterion for the weed detection on mulched areas and should also be useful for other image processing applications in precision
agriculture.
The weed detection hardware and the PC program for the weed image processing were developed with funds from the German Federal
Ministry of Education and Research (BMBF). 相似文献