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791.
If we consider riparian areas as landscapes it means that we consider them as entities whose survival depends on ecological as well as on cultural sustainability. Ecological sustainability requires people’s understanding of the role of both diversity and connectivity of riparian areas. Cultural sustainability requires people’s attention and care towards diversity and connectivity. It is argued that interaction between ecological and cultural sustainabilities governs riparian management, and that we still have to promote such an interaction. 相似文献
792.
Abstract We propose a new shift-, scale-, rotation- and pose-invariant method for three-dimensional object recognition. The method is based on angular scanning about the centroid of two-dimensional images of the objects yielding features invariant under changes in position, orientation and scale and a modified feature space trajectory classifier for pose invariance. Experimental results are shown and optical implementation is discussed. 相似文献
793.
A thermoluminescence dosemeter (TLD)—entrance surfacedose (ESD) phantom combination was calibrated in terms of air-kermain IEC RQR X-ray radiation qualities between 50 and 150 kV.The ESD phantom was designed and constructed as a part of thework. With the combination, air-kermas were measured for fourradiological examinations (two chest and two lumbar spine examinationsin two hospitals), and converted to ESDa using Monte–Carlocalculated BSF data tabulated for different tube voltages, filtrationsand beam diameters at 1 m distance. The results agreed withthe ionisation-chamber measurements within the reported overalluncertainty of the TLD method. In the calibration, the ESD phantomcan be replaced by the ISO water slab phantom unaffecting thereported overall uncertainty. Backscatter-related parametersfor the ISO water slab phantom and the newly designed ESD phantomwere determined for the IEC RQR qualities used in the secondarystandard dosimetry laboratory of STUK at 1 m distance, includingan approximate Hp(10)/Hp(0.07) ratio. 相似文献
794.
We report on the fabrication of periodic arrays of deep nanopores with high aspect ratios in crystalline silicon. The radii and pitches of the pores were defined in a chromium mask by means of deep UV scan and step technology. The pores were etched with a reactive ion etching process with SF(6), optimized for the formation of deep nanopores. We have realized structures with pitches between 440 and 750?nm, pore diameters between 310 and 515?nm, and depth to diameter aspect ratios up to 16. To the best of our knowledge, this is the highest aspect ratio ever reported for arrays of nanopores in silicon made with a reactive ion etching process. Our experimental results show that the etching rate of the nanopores is aspect-ratio-dependent, and is mostly influenced by the angular distribution of the etching ions. Furthermore we show both experimentally and theoretically that, for sub-micrometer structures, reducing the sidewall erosion is the best way to maximize the aspect ratio of the pores. Our structures have potential applications in chemical sensors, in the control of liquid wetting of surfaces, and as capacitors in high-frequency electronics. We demonstrate by means of optical reflectivity that our high-quality structures are very well suited as photonic crystals. Since the process studied is compatible with existing CMOS semiconductor fabrication, it allows for the incorporation of the etched arrays in silicon chips. 相似文献
795.
Bruinink CM Burresi M de Boer MJ Segerink FB Jansen HV Berenschot E Reinhoudt DN Huskens J Kuipers L 《Nano letters》2008,8(9):2872-2877
A novel inverse imprinting procedure for nanolithography is presented which offers a transfer accuracy and feature definition that is comparable to state-of-the-art nanofabrication techniques. We illustrate the fabrication quality of a demanding nanophotonic structure: a photonic crystal waveguide. Local examination using photon scanning tunneling microscopy (PSTM) shows that the resulting nanophotonic structures have excellent guiding properties at wavelengths in the telecommunications range, which indicates a high quality of the local structure and the overall periodicity. 相似文献
796.
Jolanta Lewandowska Tien Dung Tran Ngoc Michel Vauclin Henri Bertin 《Canadian Metallurgical Quarterly》2008,134(2):231-243
This paper presents the experimental validation of a macroscopic model of unsaturated flow in double-porosity soils, which was developed using the asymptotic homogenization method. The model was implemented into a code which enables micro–macro coupled calculations of macroscopically one-dimensional and microscopically three-dimensional problems. A series of drainage experiments were carried out in a column filled with a double porosity medium. The porous medium is composed of Hostun sand and porous spheres made of sintered clay, periodically distributed in the sand. The characteristic pores sizes of the two media differ by two orders of magnitude. During the experiments the water content evolution inside the column, the capillary pressure, and the flux at the bottom of the column were measured. The numerical simulations results showed a good agreement with the experimental data, confirming the predictive ability of the model. The experimental and numerical evidence of the influence of the microporous inclusions on the flow dynamics (flux retardation, water retention in the microporosity), is clearly shown. 相似文献
797.
Ruiz AI Darder M Aranda P Jiménez R Van Damme H Ruiz-Hitzky E 《Journal of nanoscience and nanotechnology》2006,6(6):1602-1610
A new class of bio-nanocomposites based on hybrid gelatin-perovskite hydrogels was prepared by mixing exfoliated perovskite-tetraalkylammonium species in aqueous suspensions with gelatin solutions. Colloidal nanosheets derived from the CsCa2Nb3O10 layered perovskite re-stacked in the gelatin solutions give bio-nanocomposite materials with different content in the inorganic moiety. These films can be easily processed as homogeneous self-supported films. The partial exfoliation of the pristine mixed oxide is produced from alkylammonium exchanged phases, being the tetraalkylammonium ions (tetraethylammonium, TEA+) an efficient intermediate to give the colloid phase constituted by well exfoliated materials useful to generate homogeneous films. The nanosheets are highly oriented in the bio-nanocomposite films in agreement with the XRD patterns and the FTIR dichroism. This orientation could be considered as a characteristic of this type of hybrid materials leading to new potential applications. In this way, we have observed that the assembling of perovskite to gelatin produces a greater increase of the dielectric permittivity than the dielectric loss in the studied samples. 相似文献
798.
Petri Mäki-Ontto Jorma Luomi Henri Kinnunen 《Electrical Engineering (Archiv fur Elektrotechnik)》2006,88(6):465-472
The dual-bridge inverter approach, developed to eliminate the common-mode voltage and the resulting bearing current generated
by frequency converters, is investigated by means of experiments and simulations. The approach reduces the capacitive and
induced shaft voltages by more than 80% in the examined 1.4MW induction motor drive. The remaining shaft voltage is found
to be caused by the rectifiergenerated common-mode voltage and a time delay between the PWM pulses of the parallel inverter
units. 相似文献
799.
Aimeline Colbeaux Françoise Fenouillot Laurent David Jean‐François Gerard Mohamed Taha Henri Wautier 《应用聚合物科学杂志》2007,105(5):2605-2610
Amine and alcohol functional dendritic polymers were used as covalent coupling agents for maleic anhydride grafted polyethylene and their efficiency compared with metallic salt and zinc acetate, acting as an ionic coupling agent. The crosslinking reactions in the molten state were carried out at 150°C in an internal mixer and the resulting modified polyethylenes were characterized by dynamic mechanical analysis and Small angle X‐ray Scattering. These agents led to efficient coupling and crosslinking. The covalent coupling reactions were conducted in a heterogeneous multiphase system: The kinetics of crosslinking depends on the nature of the coupling agent: at 150°C, the reactions were completed within 5 min. with the amine hyperbranched polymer and 20 min. with the alcohol functionalized dendritic polymer. The zinc acetate forms ionic interactions with the grafted polyethylene in less than 1 min. Ionic interactions are thermo mechanically reversible; they correspond to electronic density fluctuations evidenced by SAXS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献