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991.
Spectral fluence of photoneutrons generated in the head of the radiotherapeutic linac Varian 2100 C/D was measured by means of the Bonner spheres spectrometer whose active detector of thermal neutrons was replaced by a track detector, i.e. a sandwich of four CR-39s with the boron radiator inserted between them. Measurements with different collimator settings showed that the fluence of photoneutrons was higher for the more open collimator. 相似文献
992.
Immobilization of heavy metals (Pb, Cu, Cr, Zn, Cd, Mn) in the mineral additions containing concrete composites 总被引:2,自引:0,他引:2
The presented work determines the level of heavy metals (Pb+2, Cu+2, Zn+2, Cr+6, Cd+2, Mn+2) immobilization in the composites produced using Ordinary Portland Cement (OPC) as well as of binders containing large amount of mineral additives in its composition-siliceous fly ash (FA), fluidized bed combustion ash (FFA) and ground granulated blast furnace slag (GGBFS). Heavy metals were introduced to cementitious materials in the form of soluble salts as well as components of hazardous wastes (medical ash, metallurgical dust). It has been stated, that the level of heavy metals immobilization is combined with composites composition. Majority of analyzed heavy metals, added to binders' composition in the form of heavy metal salts achieves high level of immobilization, in mortar based on binder with 85% GGBFS and 15% OPC. The lowest immobilization level was reached for chromium Cr+6 added to hardening mortars as Na2Cr2O72H2O. The level ranges from 85.97% in mortars made on blended binder (20% OPC, 30% FFA and 50% GGBFS) to 93.33% in mortar produced on OPC. The increase of the so-called immobilization degree with time of hardened material maturing was found. This should be attributed to the pozzolanic or pozzolanic/hydraulic properties of components used; their effect on microstructure of hardened material is also important. Mineral additions enter the hydration reactions in the mixtures and favor the formation of specific microstructure promoting the immobilization of hazardous elements. 相似文献
993.
Double synchronized switch harvesting (DSSH): a new energy harvesting scheme for efficient energy extraction 总被引:2,自引:0,他引:2
Lallart M Garbuio L Petit L Richard C Guyomar D 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(10):2119-2130
This paper presents a new technique for optimized energy harvesting using piezoelectric microgenerators called double synchronized switch harvesting (DSSH). This technique consists of a nonlinear treatment of the output voltage of the piezoelectric element. It also integrates an intermediate switching stage that ensures an optimal harvested power whatever the load connected to the microgenerator. Theoretical developments are presented considering either constant vibration magnitude, constant driving force, or independent extraction. Then experimental measurements are carried out to validate the theoretical predictions. This technique exhibits a constant output power for a wide range of load connected to the microgenerator. In addition, the extracted power obtained using such a technique allows a gain up to 500% in terms of maximal power output compared with the standard energy harvesting method. It is also shown that such a technique allows a fine-tuning of the trade-off between vibration damping and energy harvesting. 相似文献
994.
Tamer Sınmazçelik Onur Çoban Mustafa Özgür Bora Volkan Günay İsmail Cürgül 《Applied Composite Materials》2008,15(2):99-113
The effects of thermal cycles on the impact fatigue properties of unidirectional carbon fibre reinforced polyetherimide (PEI)
matrix composites were investigated. During the thermal cycles, samples were immersed into boiling water (100 °C) and subsequently
to ice water (0 °C), 50, 200 and 500 times. The changes in viscoelastic properties of the composites were investigated by
means of dynamic mechanical thermal analyzer (DMTA). At the second step, thermal cycled composites were subjected to repeated
impact loadings, with different impact energies. Instrumented impact test results were presented as a function of force, energy,
deformation during the experiments. The scanning electron microscope (SEM) studies were done in order to understand the morphology
of fractured samples after impact fatigue loading. The number of thermal cycles and applied impact energy of the hammer are
found to have a great importance on the fracture morphology of repeatedly impacted material, as expected. 相似文献
995.
Leoni T Zoubkoff R Homri S Candoni N Vidakovic P Ranguis A Klein H Saúl A Dumas P 《Nanotechnology》2008,19(35):355401
Conductance-elongation curves of gold atomic wires are measured using a scanning tunneling microscope break junction technique at room temperature. Landauer's conductance plateaus are individually identified and statistically analyzed. Both the probabilities to observe and the lengths of the two last plateaus (at conductance values close to 2e(2)/h and 4e(2)/h) are studied. All results converge to show that the occurrences of these two conductance plateaus on a conductance-elongation curve are statistically independent events. 相似文献
996.
Mäkelä E Mäkelä EA Partio EK Juutilainen T Lähteenkorva K Törmälä P Rokkanen P 《Journal of materials science. Materials in medicine》2008,19(3):1061-1067
Self-reinforced polylactide–polyglycolide (80/20) composite rods, 2 mm in diameter and 36 mm in length, were implanted into
the dorsal subcutaneous tissue of 20 rabbits. Osteotomies of the distal femur were fixed with these rods (2 × 15 mm) in the
rabbits. The follow-up times varied from 3 to 104 weeks. After sacrifice, three-point bending and shear tests and molecular
weight measurements were performed for subcutaneously placed rods. Radiological, histological, microradiographic, oxytetracycline-fluorescence,
and histomorphometrical studies of the osteotomized and intact control femora were performed. After 6 weeks the mechanical
properties had decreased significantly, but osteotomies had healed uneventfully. The present investigation showed that the
mechanical strength and fixation properties of SR-Polylactide–glycolide (80/20) rods are suitable for fixation of cancellous
bone osteotomies in rabbits provided that the operative technique is correct. The present article is the first report on the
application of these rods for fixation of cancellous bone osteotomies. 相似文献
997.
998.
Basletic M Maurice JL Carrétéro C Herranz G Copie O Bibes M Jacquet E Bouzehouane K Fusil S Barthélémy A 《Nature materials》2008,7(8):621-625
At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO(3)/SrTiO(3) system . Although this state has been predicted and reported to be confined at the interface, some studies indicate a much broader spatial extension, thereby questioning its origin. Here, we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO(3)/SrTiO(3) samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending on specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of micrometres into SrTiO(3) to a few nanometres next to the LaAlO(3)/SrTiO(3) interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system. 相似文献
999.
The temperature dependence of the electrical conductivity of assemblies of ZnO nanocrystals, studied with an electrochemically gated transistor is very accurately described by the relation ln sigma=ln sigma0-(T0/T)(x) with x=2/3 over the entire temperature range from 7 to 200 K, independent of charge concentration and dielectric environment. These results cannot be explained by existing models but are supported by results on Au nanocrystals where an identical temperature dependence was observed (Zabet-Khosousi et al., Phys. Rev. Lett. 2006, 96 (15), 156403). We propose an adaptation of the Efros-Shklovskii variable-range hopping model by introducing an expression for nonresonant tunneling based on local energy fluctuations, which yields exactly the temperature dependence that is observed experimentally. 相似文献
1000.
Proust-Lima Cécile; Amieva Hélène; Letenneur Luc; Orgogozo Jean-Marc; Jacqmin-Gadda Hélène; Dartigues Jean-Fran?ois 《Canadian Metallurgical Quarterly》2008,23(3):608
In cognitive aging research, the study of a general cognitive factor has been shown to have a substantial explanatory power over the study of isolated tests. The authors aimed at differentiating the impact of gender and education on global cognitive change with age from their differential impact on 4 psychometric tests using a new latent process approach, which intermediates between a single-factor longitudinal model for sum scores and an item-response theory approach for longitudinal data. The analysis was conducted on a sample of 2,228 subjects from PAQUID, a population-based cohort of older adults followed for 13 years with repeated measures of cognition. Adjusted for vascular factors, the analysis confirmed that women performed better in tests involving verbal components, while men performed better in tests involving visuospatial skills. In addition, the model suggested that women had a slightly steeper global cognitive decline with oldest age than men, even after excluding incident dementia or death. Subjects with higher education exhibited a better mean score for the 4 tests, but this difference tended to attenuate with age for tests involving a speed component. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献