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991.
Dick William D. McMurry Peter H. Weber Rodney J. Quant Frederick R. 《Journal of nanoparticle research》2000,2(1):85-90
Several of the most common methods for measuring nanoparticle size distributions employ the ultrafine condensation particle counter (UCPC) for detection purposes. Among these methods, the pulse height analysis (PHA) technique, in which the optical response of the UCPC detector is related to initial particle diameter in the 3–10nm range, prevails in applications where fast sampling is required or for which concentrations of nanoparticles are frequently very low. With the PHA technique, white light is required for particle illumination in order to obtain a monotonic relationship between initial particle diameter and optical response (pulse height). However, the popular, commercially available TSI Model 3025A UCPC employs a laser for particle detection. Here, we report on a novel white-light detection system developed for the 3025A UCPC that involves minimal alteration to the instrument and preserves normal counting operation. Performance is illustrated with pulse height spectra produced by differential mobility analyzer (DMA) – generated calibration aerosols in the 3–50nm range. 相似文献
992.
Resonances of the time evolution (Frobenius-Perron) operator P for phase space densities have recently been shown to play a key role for the interrelations of classical, semiclassical, and quantum dynamics. Efficient methods to determine resonances are thus in demand, in particular, for Hamiltonian systems displaying a mix of chaotic and regular behavior. We present a powerful method based on truncating P to a finite matrix which not only allows us to identify resonances but also the associated phase space structures. It is demonstrated to work well for a prototypical dynamical system. 相似文献
993.
Flink C Feick H McHugo SA Seifert W Hieslmair H Heiser T Istratov AA Weber ER 《Physical review letters》2000,85(23):4900-4903
Concentrations of mobile interstitial copper and precipitated copper in silicon were studied after a high temperature intentional contamination and quench to room temperature. It was found that below a critical contamination the copper predominantly diffuses out to the surface, while for higher initial copper concentrations it mainly precipitates in the bulk. The critical copper contamination equals the acceptor concentration plus 10(16) cm (-3). This behavior can be explained by the electrostatic interaction between the positively charged interstitial copper and the forming copper precipitates. 相似文献
994.
995.
996.
The lifetime of electrons deposited on the liquid surface of 4He was measured. It is smaller than 8 μs at 0.5 K and, as is concluded from its temperature dependence, governed by the electronic mobility parallel to the superfluid surface. 相似文献
997.
998.
W. Bartel D. Cords P. Dittmann R. Eichler R. Felst D. Haidt S. Kawabata H. Krehbiel B. Naroska L.H. ONeill J. Olsson P. Steffen E. Elsen M. Helm A. Petersen P. Warming G. Weber C. Yanagisawa 《Physics letters. [Part B]》1980,91(1):152-154
A search for narrow resonances in e+e? annihilation at c.m. energies between 29.90 and 31.46 GeV provides no evidence for the existence of such states. The 90% confidence upper limit on the integrated resonance cross section is 38 nb MeV, significantly below the value expected for the lowest (t,t?) bound state. 相似文献
999.
We report on Raman scattering from the magnons in CsCoCl3 with particular emphasis on two magnetic phase transitions occurring at TN = 20.82 K and at 8 K. The T → 0 magnon spectrum is fitted by a anisotropic Heisenberg model. With a simple cluster model we can explain the temperature behaviour of the magnon frequencies and intensities. The physics of the 8 K phase transition is also discussed. 相似文献
1000.
Trace analysis of chloramphenicol residues in egg powders by capillary gas chromatography-electron capture detection 总被引:4,自引:0,他引:4
L Weber 《Journal of chromatographic science》1990,28(10):501-504
Chloramphenicol (CAP) in egg powder samples was extracted with acetonitrile by sonication. After centrifugation, the supernatant was diluted with water and defatted with n-hexane, and cleanup was performed on a microcolumn of graphitized carbon black (GCB). Different silylation methods were compared for the derivatization of the analytes. Trimethylsilyl N,N-dimethylcarbamate produced stable di-TMS derivatives which were analyzed by capillary gas chromatography-electron capture detection (CGC-ECD) after splitless injection. The meta isomer of the chloramphenicol served as the internal standard for quantitation, and 80% + mean recovery was obtained in the 0.1-10 micrograms/kg (ppb) concentration range. 相似文献