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1.
Hydroxyl free radicals produced in Fricke solution exposed to 80 kV X-rays or 23 kHz ultrasound (intensity 3 W cm−2) or 20 kHz ultrasound (intensity 18.9 W cm−2) or 3.5 MHz clinical ultrasound (intensity 1.47 W cm−2), as estimated from the Fricke dosimetric data, exhibited a linear dose-response relationship. The dosimeter was found to be effective in the concentration range 1.0–8.0 mM of FeSO4 solution. The hydroxyl radicals produced in Fricke solution were inhibited by the OH radical scavengers dimethyl sulfoxide (200 mM), -histidine (10 mM) and sodium benzoate (10 mM) in a manner proportional to the rate constants of their reaction with the OH radicals. The power threshold for OH radical formation, which is presumably the threshold for cavity formation, was estimated for 23 kHz ultrasound by this dosimeter as 1.28 W cm−2 for a 4 cm3 sample volume.  相似文献   

2.
The effects of dopants on the electrical conductivity of the perovskite-type oxide LaInO3 have been investigated. Replacement of La by Sr is the most effective way to enhance the conductivity of LaInO3, whereas Ca substitution for In is rather difficult due to the large difference in the ion radii. The optimum composition is La0.9Sr0.1InO3−δ whose maximum conductivity is 7.6×10−3 S cm−1 at 900°C. The electrical conductivity of La0.9Sr0.1InO3−δ has been measured over a wide range of oxygen partial pressure from pO2=1 to 10−25 atm. P-type and n-type behavior at high and low oxygen partial pressure have been observed, respectively, while at intermediate oxygen partial pressures, the electrical conductivity changes only slightly with the oxygen partial pressure. The concept of a single layer solid oxide fuel cell based on a La0.9Sr0.1InO3−δ ceramic pellet has been tested. A maximum power density of 3 mW cm−2 at 800°C was achieved when dilute H2 and air were used as fuel and oxidizing agent, respectively.  相似文献   

3.
Silicon nanocrystals have been synthesized in SiO2 matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO2 films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×1015, 3×1016, and 1×1017 cm−2. Implanted samples were subsequently annealed in an N2 ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×1017 cm−2 at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO2 sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×1015 cm−2. It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO2.  相似文献   

4.
The interaction of 180 fs, 775 nm laser pulses with aluminium under a flowing stream of helium at ambient pressure have been used to study the material re-deposition, ablation rate and residual surface roughness. Threshold fluence Fth0.4 J cm−2 and the volume ablation rate was measured to be 30<V<450 μm3 per pulse in the fluence range 1.4<F<21 J cm−2. The presence of helium avoids gas breakdown above the substrate and leads to improved surface micro-structure by minimising surface oxidation and debris re-deposition. At 1 kHz rep. rate, with fluence F>7 J cm−2 and >85 W cm−2 average power density, residual thermal effects result in melt and debris formation producing poor surface micro-structure. On the contrary, surface micro-machining at low fluence F1.4 J cm−2 with low power density, 3 W cm−2 produces much superior surface micro-structuring with minimum melt and measured surface roughness Ra1.1±0.1 μm at a depth D50 μm. By varying the combination of fluence/scan speed during ultra-fast ablation of aluminium at 1 kHz rep. rate, results suggest that maintaining average scanned power density to <5 W cm−2 combined with single pulse fluence <4 J cm−2 produces near optimum micro-structuring. The debris under these conditions contains pure aluminium nanoparticles carried with the helium stream.  相似文献   

5.
The FTIR spectroscopy of carbon monoxide adsorbed on polycrystalline MgO smoke has been investigated as a function of the CO equilibrium pressure at constant temperature (60 K) (optical isotherm) and of the temperature (in the 300–60 K range) at constant CO pressure (optical isobar). In both cases the spectra fully reproduce those of CO adsorbed on the (0 0 1) surface of UHV cleaved single crystals [Heidberg et al., Surf. Sci. 331–333 (1995) 1467]. This result, never attained in previous investigations on dispersed MgO, contribute to bridging the gap which is commonly supposed to exist between surface science and the study of “real” (defective) systems. Depending on the surface coverage θ the main spectral features due to the CO/MgO smoke interaction are a single band shifting from 2157.5 (at θ→0) to 2150.2 cm−1 (at θ=1/4) or a triplet, at 2151.5, 2137.2 and 2132.4 cm−1 (at θ>1/4). These manifestations are due to the ν(CO) modes of Mg5C2+· · · CO adducts formed on the (0 0 1) terminations of the cubic MgO smoke microcrystals. The formation of the CO monolayer is occurring in two different phases: (i) a first phase with CO oscillators perpendicularly oriented to the surface (2157–2150 cm−1) and (ii) a second phase constituted by an array of coexisting perpendicular and tilted species (triplet at 2151.5, 2137.2 and 2132.4 cm−1). A much weaker feature at 2167.5–2164 cm−1 is assigned to Mg4C2+· · · CO adducts at the edges of the microcrystals. The heat of adsorption of the perpendicular Mg5C2+· · · CO complex in the first phase has been estimated from the optical isobar and results to be 11 kJ mol−1.  相似文献   

6.
An industrial TEA-CO2 laser, operating at a wavelength of 10.6 μm, has been used to produced broadband ultrasonic pulses in polymers. The generation mechanism falls into three categories. At low power densities ≤ 107 W cm−2 a thermoelastic regime predominates. As the power density is increased in the range (1–5) × 107 W cm−2 ablation of the material surface plays an increasingly important role in the acoustic generation. Thirdly, at greater power densities, plasma breakdown just above the material surface serves as the means of generation. This paper describes the acoustic sources for these types of generation mechanism and presents theoretically calculated acoustic waveforms to match those recorded experimentally.  相似文献   

7.
We report surface vibrations in c(2 × 2) oxygen adlayers on Ni and Co thin films on a Cu(001) substrate measured at gG by high resolution EELS. For the Ni thin film surface, one phonon peak is measured for varying film thicknesses from 1.3 ML (monolayer) to 6 ML with a constant energy of 221 cm−1. For the Co thin film surface, three loss peaks are found, whose relative intensities change as the film thicknesses are varied. One loss peak at ˜520 cm−1 is tentatively assigned to the Fuchs-Kliewer mode of cobalt oxide (CoO). The other two peaks at 317 and 376 cm−1 are likely related to different bonding sites. Surface phonons on the p(2 × 2) Co thin film (389 cm−1) and a bulk resonance mode (115 cm−1) are also reported.  相似文献   

8.
Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu2O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10−4 Ω−1 cm−1 for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m−2 tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10−3 Ω−1 cm−1. These films are also photoconductive.  相似文献   

9.
Three kinds of peroxo-polytungstic acid (PPTA, C-PPTA and N-PPTA) were obtained by reacting hydrogen peroxide with metallic tungsten, tungsten carbide or tungsten nitride, respectively. Polytungstates, C-PPTA and N-PPTA, were found to contain oxalate and nitrate ligands. Their proton conductivities were compared using thin film specimens spin-coated from their water solution. Conductivity of each as-coated film was in the range from 10−3 to 10−4 S cm−1 under the relative humidity of 40% (25 °C). A sharp decrease in conductivity (to less than 10−7 S cm−1 at 25 °C) was observed for PPTA without acidic ligands after thermal treatment at 80 °C. However, the effect of thermal treatment on C-PPTA or N-PPTA was much milder. A 80 °C-treated C-PPTA film showed the conductivity of 1.0 × 10−5 S cm−1 (25 °C) with a very weak dependency on ambient humidity.  相似文献   

10.
D. B. Tata  G. Hahn  F. Dunn 《Ultrasonics》1993,31(6):447-450
Low intensity ultrasound (approximately 10−6 W cm−2) in the frequency range 0.5–6.0 MHz was employed to investigate the ultrasound absorption properties of doxorubicin (DOX) at several temperatures. At physiological temperatures, we found enhanced ultrasound absorption from DOX, and its closely related analogue daunorubicin (DNR), in the upper kilohertz frequency range. The findings do not conform to classical theory of ultrasound absorption, thus suggesting an ultrasound coupling with the drug molecules via structural and/or chemical relaxation processes. The absorption spectra are analysed from the point of view of the non-classical theory of sound absorption due to physical and/or chemical relaxations. Only one spectral difference between the two anti-cancer agents is observed, around 2 MHz, and may be attributed to the sole difference in the chemical make-up of the side chain of the two antibiotics.  相似文献   

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