排序方式: 共有53条查询结果,搜索用时 15 毫秒
31.
WILLIAM M. MOORE DENNIS J. FIFE MARY JO GRABNER GRACE I. WHYTE 《Photochemistry and photobiology》1991,53(4):439-444
The anaerobic photoreduction of riboflavin, flavin mononucleotide, N(3)-carboxymethylriboflavin, N(3)-methyl-lumiflavin, and lumiflavin by EDTA was studied in aqueous solution over the pH range 2.5–10. The electrostatic effects of the electron donor-acceptor pair produce a secondary effect on the reactivity, and this effect can be predicted from the product of the charges (ZD x ZA). The trianonic and tetraanonic species of EDTA have nitrogens which are free from intramolecular hydrogen bonding, and these species are potentially the most reactive. However, in some pH regions the electrostatic effect can become the dominant factor when both the electron donor and acceptor become negatively charged. The excited states of flavins are susceptible to charge effects whether the charge is localized on the side chain or involves the isoalloxazine ring system. 相似文献
32.
O. FRAZÃO L. A. FERREIRA F. M. ARAÚJO J. L. SANTOS 《Fiber and Integrated Optics》2013,32(3-4):227-244
Abstract In this article, approaches reported in the literature for multi-parameter measurement relying on fiber grating technology are reviewed. Due to its importance, the particular case of temperature/strain simultaneous measurement is addressed in further detail, as well as the techniques and sensing heads for temperature-independent strain measurement. Specific criteria are also proposed for sensing head classification in the context of multi-parameter measurement. 相似文献
33.
Pozo OJ Van Eenoo P Deventer K Elbardissy H Grimalt S Sancho JV Hernandez F Ventura R Delbeke FT 《Analytica chimica acta》2011,684(1-2):98-111
Triple quadrupole (QqQ), time of flight (TOF) and quadrupole-time of flight (QTOF) analysers have been compared for the detection of anabolic steroids in human urine. Ten anabolic steroids were selected as model compounds based on their ionization and the presence of endogenous interferences. Both qualitative and quantitative analyses were evaluated. QqQ allowed for the detection of all analytes at the minimum required performance limit (MRPL) established by the World Anti-Doping Agency (between 2 and 10 ng mL(-1) in urine). TOF and QTOF approaches were not sensitive enough to detect some of the analytes (3'-hydroxy-stanozolol or the metabolites of boldenone and formebolone) at the established MRPL. Although a suitable accuracy was obtained, the precision was unsatisfactory (RSD typically higher than 20%) for quantitative purposes irrespective of the analyser used. The methods were applied to 30 real samples declared positives either for the misuse of boldenone, stanozolol and/or methandienone. Most of the compounds were detected by every technique, however QqQ was necessary for the detection of some metabolites in a few samples. Finally, the possibility to detect non-target steroids has been explored by the use of TOF and QTOF. The use of this approach revealed that the presence of boldenone and its metabolite in one sample was due to the intake of androsta-1,4,6-triene-3,17-dione. Additionally, the intake of methandienone was confirmed by the post-target detection of a long-term metabolite. 相似文献
34.
Jorge Pey Barend L. van Drooge Anna Ripoll Teresa Moreno Joan O. Grimalt Xavier Querol Andrés Alastuey 《Particuology》2013,11(5):527-532
This study assessed air quality indicators before and after enactment of the Spanish anti-smoking law. Mass and number concentrations and the chemical composition of particles were evaluated. Microscopy analyses were also conducted. Real time concentrations of PM10, PM2.5, PM1 and ultrafine particles were measured under ventilated and non-ventilated conditions and PM10 samples were collected for detailed inorganic and organic chemical characterization. Before enactment of the law in 2010, tobacco smoke produced significant indoor ambient particulate matter pollution, with elevated particulate matter mass concentrations (PM10 and PM1 concentrations of 122–220 and 48–85 μg/m3, respectively) and ultrafine particle numbers (75,000 and 48,000 cm–3 under ventilated and non-ventilated conditions, respectively). Typical tobacco smoke tracers including iso- and anteiso-alkanes and elements including La and Ce from the ignition of lighters were abundant. Additionally, several toxic substances derived from tobacco smoke, including Cd (3.1 ng/m3) and benzo[a]pyrene (1.0 ng/m3) were present at concentrations approximately 10 times greater than those measured after enactment of the anti-smoking law. The anti-smoking law significantly reduced exposure to potentially toxic compounds by approximately 90%. This law is expected to have a positive health impact, particularly for people who spend considerable time in affected environments, such as employees. 相似文献
35.
Joan O. Grimalt Mike Howsam Daniel Carrizo Raquel Otero Mary Rosa Rodrigues de Marchi Esther Vizcaino 《Analytical and bioanalytical chemistry》2010,396(6):2265-2272
A rapid, robust and economical method for the analysis of persistent halogenated organic compounds in small volumes of human
serum and umbilical cord blood is described. The pollutants studied cover a broad range of molecules of contemporary epidemiological
and legislative concern, including polychlorobiphenyls (PCBs), polychlorobenzenes (CBs), hexachlorocyclohexanes (HCHs), DDTs,
polychlorostyrenes (PCSs) and polybromodiphenyl ethers (PBDEs). Extraction and clean-up with n-hexane and concentrated sulphuric acid was followed with analysis by gas chromatography coupled to electron capture (GC-ECD)
and GC coupled to negative ion chemical ionisation mass spectrometry (GC-NICI-MS). The advantages of this method rest in the
broad range of analytes and its simplicity and robustness, while the use of concentrated sulphuric acid extraction/clean-up
destroys viruses that may be present in the samples. Small volumes of reference serum between 50 and 1000 μL were extracted
and the limits of detection/quantification and repeatability were determined. Recoveries of spiked compounds for the extraction
of small volumes (≥300 μL) of the spiked reference serum were between 90% and 120%. The coefficients of variation of repeatability
ranged from 0.1–14%, depending on the compound. Samples of 4-year-old serum and umbilical cord blood (n = 73 and 40, respectively) from a population inhabiting a village near a chloro-alkali plant were screened for the above-mentioned
halogenated pollutants using this method and the results are briefly described. 相似文献
36.
37.
JO?O FIRMINO DA COSTA 《Pramana》2012,79(5):1215-1218
Results of searches for supersymmetry in events with significant missing transverse energy and two isolated leptons with the ATLAS experiment at the LHC are presented. Three analyses are presented here, the first two are analyses with leptons of opposite charge and same charge, respectively. The third one is an analysis that searches for an excess of same-flavour opposite-charge lepton pairs over those of different-flavour. Data corresponding to an integrated luminosity of 1 fb?1 are analysed. 相似文献
38.
The influence of the concatenation of arbitrary optical multiplexers/demultiplexers (MUX/DEMUXs) on the probability density function (PDF) of the output current of a transparent optical network is assessed. All PDF results obtained analytically are compared with estimates from Monte Carlo simulation and an excellent agreement is achieved. The non-Gaussian behavior of the PDFs, previously reported by other authors for square-law detectors, is significantly enhanced with the number of nodes increase due to the noise accumulation along the cascade of MUX/DEMUXs. The increase of the MUX/DEMUXs bandwidth and detuning also enhances the PDFs non-Gaussian behavior. The PDF shape variation with the detuning depends strongly on the number of nodes. Explanations for the Gaussian approximation (GA) accuracy on the assessment of the performance of a concatenation of optical MUX/DEMUXs are also provided. For infinite extinction ratio and tuned MUX/DEMUXs, the GA error probabilities are, in general, pessimistic, due to the inaccurate estimation of the error probability for both bits. For low extinction ratio, the GA is very accurate due to a balance between the error probabilities estimated for the bits “1” and “0.” With the detuning increase, the GA estimates can become optimistic. 相似文献
39.
Let (X , x 0) be a pointed smooth proper variety defined over an algebraically closed field. The Albanese morphism for (X , x 0) produces a homomorphism from the abelianization of the F-divided fundamental group scheme of X to the F-divided fundamental group of the Albanese variety of X. We prove that this homomorphism is surjective with finite kernel. The kernel is also described. 相似文献
40.
This study focuses on the extraction of climate signals and processes using a combined approach which includes the analysis of a high number of lipid molecules in marine sediments, and the chemometric analysis of the acquired data. Neutral and acidic fractions of marine sediments from site IODP-U1318 (south-west of the UK, Porcupine Seabight) were quantified by GC–MS. The alkenone unsaturation index, Uk′37, was estimated from the composition of C37 alkenones and it was then used for the estimation of sea surface temperatures (SST) for reference. Principal component analysis (PCA), explained 77.45% of the total data variance, and differentiated neutral fraction GC–MS total ion current (TIC) profiles according to SST values of the different sediment sections. GC–MS TIC chromatograms were correlated to sea surface temperatures (SST) by partial least squares regression (PLSR). The compounds more robustly in line with SST values at each sediment section explained 93% of the SST variance and they were identified using the variable importance in projection (VIP) scores method. The proposed approach enables an objective identification of organic compounds sensitive to SST variability throughout complete chromatographic profiles. As a result of this multivariate unbiased approach, lipid composition of sediments was differentiated between compounds of marine (long chain n-alkanes, long chain n-alkan-1-ols) and terrestrial (short chain n-alkan1-ols, alkenols, cholesterol, squalene) origin, whose concentrations were directly and inversely correlated to SST, respectively. 相似文献