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51.
J. Angerer B. Heinzow K. H. Schaller D. Weltle G. Lehnert 《Fresenius' Journal of Analytical Chemistry》1992,342(4-5):433-438
Summary A sensitive, specific and analytically reliable method for the determination of mono-, di-, tri- and tetrachlorophenols in human urine has been elaborated. After acid hydrolysis and a simultaneous steam distillation of the urine samples, spiked with an internal standard, the chromatographically concentrated chlorophenols have been derivatized with pentafluorobenzoylchloride and analyzed by capillary gas chromatography/mass spectrometry. The detection limits for the chlorophenols ranged from 0.2 to 2.5 g/l. Using this method we were able to detect 4-MCP, 2,4-+2,5-DCP, 2,4,6-TCP, 2,4,5-TCP and 2,3,4,6-+2,3,5,6-TeCP in urine samples of a group of 258 men and women which had no known occupational contact to hazardous chemical substances. The 95 percentiles for the concentrations of these substances in the urine samples under investigation were 7.5 (4-MCP); 33.6(2,4-+2,5-DCP); 4,7 (2,4,6-TCP); 4,5 (2,4,5-TCP) and 22.2 (2,3,4,6-+2,3,5,6-TeCP) g per liter. That means, that these chlorophenols are constituents of urine of the normal population in concentrations which in part are greater than that of pentachlorophenol (PCP). 相似文献
52.
53.
Schaller RD Pietryga JM Goupalov SV Petruska MA Ivanov SA Klimov VI 《Physical review letters》2005,95(19):196401
We observe ultrafast 1P-to-1S intraband relaxation in PbSe and CdSe nanocrystals (NCs) that have distinct energy spectra. While ultrafast dynamics in CdSe NCs has typically been interpreted in terms of electron-hole energy transfer, this mechanism is not active in PbSe NCs because of sparse densities of states in the conduction and valence bands. Our observations of temperature activation and confinement-enhanced relaxation in PbSe NCs can be explained by efficient multiphonon emission triggered by nonadiabatic electron-phonon interactions and are indicative of large, size-dependent, intraband Huang-Rhys parameters. 相似文献
54.
Novel 2,3-O-hydroxyethyl- and 2,3-O-hydroxypropyl cellulose products were synthesized by heterogeneous etherification of 6-O-(4-monomethoxytrityl) cellulose (MMTC). Due to the very hydrophobic character of MMTC, the reaction was successful in the presence of anionic and non-ionic detergent in the reaction mixture yielding the 2,3-O-cellulose ethers with a molar degree of substitution (MS) varying between 0.25 and 2.00 after detritylation. The products were characterized by means of (1)H and (13)C NMR spectroscopy including two-dimensional methods. The 2,3-O-hydroxypropyl cellulose samples are soluble in water at a MS as low as 0.8. The spectroscopic studies showed that the unusual solubility results from a preferred substitution of hydroxy groups of the anhydroglucose unit while the newly formed hydroxy moieties are included in the reaction to a minor extent only. In contrast, conventionally synthesized hydroxypropyl cellulose is soluble in water starting at a MS of about 4.0 because of the formation of oxyethylene side chains. (13)C DEPT 135 NMR spectrum of 2,3-O-hydroxypropyl cellulose. 相似文献
55.
The determination of mercury concentrations in blood and urine is currently the best way of monitoring individual uptake of organic and inorganic mercury. In Germany these determinations must be carried out under the conditions of an external quality assurance programme. The German performance evaluation, based on reference values established by reference laboratories yields success rates in percent for the participants in the intercomparison programme of about 60%. A Canadian evaluation system based on two evaluations scores, yields success rates of 25-50% for "good performance" and of 65-80% for "acceptable performance". The determination of mercury in blood and urine is at present not carried out with the necessary reliability. 相似文献
56.
U. Treiber S. Kemmler-Sack A. Ehmann H.-U. Schaller E. Dürrschmidt I. Thumm H. Bader 《无机化学与普通化学杂志》1981,481(10):143-152
On Mixed Valent Perovskites Ba3B3+Ru24,5+O9 – Catalytic Activity of Perovskite Oxides with Noble Metals The black compounds Ba3B3+Ru2O9 crystallize with B3+ = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y in a hexagonal BaTiO3 structure (6 L, sequence (hcc)2) with an ordered distribution (1:2 order) of B3+ and ruthenium (BO6 single octahedra; Ru2O9 double groups). The mean oxidation state of ruthenium is about +4.5. The properties are compared with that of other isotypic stacking polytypes Ba3B3+M24,5O9 (M2 = IrRu, Ir2, PtRu) and Ba3B2+M25+O9 (M = Ru, Ir). The results of activity tests concerning the efficiency of perovskite oxides with noble metals in respect of the oxidation of CO or CHx and the reduction of NOx are reported. 相似文献
57.
58.
High efficiency carrier multiplication in PbSe nanocrystals: implications for solar energy conversion 总被引:2,自引:0,他引:2
We demonstrate for the first time that impact ionization (II) (the inverse of Auger recombination) occurs with very high efficiency in semiconductor nanocrystals (NCs). Interband optical excitation of PbSe NCs at low pump intensities, for which less than one exciton is initially generated per NC on average, results in the formation of two or more excitons (carrier multiplication) when pump photon energies are more than 3 times the NC band gap energy. The generation of multiexcitons from a single photon absorption event is observed to take place on an ultrafast (picosecond) time scale and occurs with up to 100% efficiency depending upon the excess energy of the absorbed photon. Efficient II in NCs can be used to considerably increase the power conversion efficiency of NC-based solar cells. 相似文献
59.
F. Kottmann W. Amir F. Biraben C. A. N. Conde S. Dhawan T. W. Hänsch F. J. Hartmann V. W. Hughes O. Huot P. Indelicato L. Julien P. Knowles S. Kazamias Y.-W. Liu F. Mulhauser F. Nez R. Pohl P. Rabinowitz J. M. F. dos Santos L. A. Schaller H. Schneuwly W. Schott D. Taqqu J. F. C. A. Veloso 《Hyperfine Interactions》2001,138(1-4):55-60
A measurement of the 2S Lamb shift in muonic hydrogen (μ−p) is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the energy difference
ΔE(25
P
3/2−23
S
1/2) by laser spectroscopy (λ≈6μm) to a precision of 30 ppm and to deduce the root mean square (rms) proton charge radius with
10−3 relative accuracy, 20 times more precise than presently known.
An important prerequisite to this experiment is the availability of long-lived μp2S
-atoms. A 2S-lifetime of ∼1 μs – sufficiently long to perform the laser experiment – at H2 gas pressures of 1–2 hPa was deduced from recent measurements of the collisional 2S-quenching rate. A new low-energy negative muon beam yields an order of magnitude more muon stops in a small low-density gas
volume than a conventional cloud muon beam. A stack of ultra-thin carbon foils is the key element of a fast detector for keV-muons.
The development of a 2 keV X-ray detector and a 3-stage laser system providing 0.5 mJ laser pulses at 6 μm is on the way.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
Gagik Ghazaryan Raphael Schaller Theo A. Tervoort 《Journal of polymer science. Part A, Polymer chemistry》2020,58(2):352-362
A new laboratory-scale method for continuous solid-state biaxial deformation of polymer materials is introduced. The tabletop biaxial drawing tool utilizes a heated metal disc-like triangular mandrel, which allows for continuous solid-state biaxial deformation of a precursor polymer tube with a controlled drawing speed. The new biaxial drawing tool features two independent heating zones. The main mandrel sets the biaxial drawing temperature. In addition, directly after the mandrel, an annealing unit with a separate heating zone is added for better control of important process parameters, such as post-relaxation and strain-induced crystallization. As such, the new biaxial drawing tool is a tabletop analogue of the industrial triple-bubble process. Finally, a detailed theoretical model describing the deformation field and the forces needed to perform biaxial drawing as a function of the biaxial drawing ratio is presented and compared to experimental values, using isotactic polypropylene as model material. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 352-362 相似文献