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Schulz M Fritze H Tuller HL Seh H 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2004,51(11):1381-1387
Oxygen and gallium diffusivities in langasite were experimentally determined by analysis of diffusion profiles of 18O and 71Ga tracers by SIMS analysis as functions of temperature and doping. Strontium-enhanced diffusivities and activation energies of approximately 1.2+/-0.2 eV confirm the predominant role of oxygen vacancies in controlling the electrical conductivity of langasite at elevated temperature and oxygen partial pressure. The potential impact of high levels of porosity and the use of an oxygen primary ion beam on the accuracy of some of the data is discussed. The gallium diffusivity, with activation energy of 3.13 eV, was found to be more than two orders of magnitude lower than that of oxygen. Surface exchange measurements enabled estimation of gallium loss at elevated temperatures and oxygen partial pressure; the level is not believed to be of major concern for resonator performance. 相似文献
24.
Shen HL Xin JH 《Journal of the Optical Society of America. A, Optics, image science, and vision》2004,21(7):1125-1130
A new method of spectral characterization for color scanners by the use of adaptive estimation is proposed. It deals with estimation of high-dimensional reflectance vectors from low-dimensional scanner response vectors when the scanner departs from linearity. We first investigate the spectral linearity of the scanner, and then estimate the spectral reflectance adaptively based on the local statistics of a set of neighboring training samples. As the proposed characterization method does not utilize the mathematically recovered spectral responsivity, its inherent inaccuracy is not critical to the spectral characterization. Experimental results showed significant advantage of adaptive estimation when compared with other methods. 相似文献
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Samarium and manganese-doped lead titanate ceramic fiber/epoxy 1-3 composite for high-frequency transducer application 总被引:1,自引:0,他引:1
Li K Chan HL Choy CL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(10):1371-1376
Samarium- (Sm) and manganese- (Mn) doped lead titanate ceramic fibers with a diameter of 35 /spl mu/m were prepared using a sol-gel method. The X-ray diffraction pattern shows that the fibers have a pure perovskite structure. The 1-3 composite disks with a thickness of 31-41 /spl mu/m and with ceramic volume fraction of /spl sim/0.68 have been prepared using the samarium and manganese doped lead titanate (PSmT) fibers. The resonance characteristics of the poled composite disks were measured. A focused transducer was fabricated using a concave 1-3 composite disk with nonuniform thickness in order to enhance its bandwidth. The insertion loss (IL), pulse-echo response and frequency spectrum of the composite transducer were measured. The center frequency of the transducer was /spl sim/31 MHz with a -3 dB bandwidth of /spl sim/123% and a low IL of 29.3 dB. 相似文献
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In this paper, an on-line trained neural network controller is applied to control the flow rate of a process control rig. The neural controller replaces a conventional controller in the forward path. The overall performance of this controller is compared with that of a PID controller in the presence of noise and non-linearity. It is shown that as the non-linearity is added to the system, the PID controller cannot track the set-point changes, however, the neural controller copes well under various conditions. 相似文献
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Concentrations of ultrafine particles at a highway toll collection booth and exposure implications for toll collectors 总被引:1,自引:0,他引:1
Research regarding the magnitude of ultrafine particle levels at highway toll stations is limited. This study measured ambient concentrations of ultrafine particles at a highway toll station from October 30 to November 1 and November 5 to November 6, 2008. A scanning mobility particle sizer was used to measure ultrafine particle concentrations at a ticket/cash tollbooth. Levels of hourly average ultrafine particles at the tollbooth were about 3-6 times higher than those in urban backgrounds, indicating that a considerable amount of ultrafine particles are exhausted from passing vehicles. A bi-modal size distribution pattern with a dominant mode at about < 6 nm and a minor mode at about 40 nm was observed at the tollbooth. The high amounts of nanoparticles in this study can be attributed to gas-to-particle reactions in fresh fumes emitted directly from vehicles. The influences of traffic volume, wind speed, and relative humidity on ultrafine particle concentrations were also determined. High ambient concentrations of ultrafine particles existed under low wind speed, low relative humidity, and high traffic volume. Although different factors account for high ambient concentrations of ultrafine particles at the tollbooth, measurements indicate that toll collectors who work close to traffic emission sources have a high exposure risk. 相似文献
29.
Anthropogenic tracers, endocrine disrupting chemicals, and endocrine disruption in Minnesota lakes 总被引:1,自引:0,他引:1
Writer JH Barber LB Brown GK Taylor HE Kiesling RL Ferrey ML Jahns ND Bartell SE Schoenfuss HL 《The Science of the total environment》2010,409(1):100-111
Concentrations of endocrine disrupting chemicals and endocrine disruption in fish were determined in 11 lakes across Minnesota that represent a range of trophic conditions and land uses (urban, agricultural, residential, and forested) and in which wastewater treatment plant discharges were absent. Water, sediment, and passive polar organic integrative samplers (POCIS) were analyzed for steroidal hormones, alkylphenols, bisphenol A, and other organic and inorganic molecular tracers to evaluate potential non-point source inputs into the lakes. Resident fish from the lakes were collected, and caged male fathead minnows were deployed to evaluate endocrine disruption, as indicated by the biological endpoints of plasma vitellogenin and gonadal histology. Endocrine disrupting chemicals, including bisphenol A, 17β-estradiol, estrone, and 4-nonylphenol were detected in 90% of the lakes at part per trillion concentrations. Endocrine disruption was observed in caged fathead minnows and resident fish in 90% of the lakes. The widespread but variable occurrence of anthropogenic chemicals in the lakes and endocrine disruption in fish indicates that potential sources are diverse, not limited to wastewater treatment plant discharges, and not entirely predictable based on trophic status and land use. 相似文献
30.
Yuan HL Wang YQ Zhou SM Liu LS Chen XL Lou SY Yuan RJ Hao YM Li N 《Nanoscale research letters》2010,5(11):1817-1821
Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics
of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron
microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic
behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed
CoFe2O4 MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role. 相似文献