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Marjo Kettunen Riitta J. Silvennoinen Nikolay Houbenov Antti Nykänen Janne Ruokolainen Jani Sainio Viljami Pore Marianna Kemell Mikael Ankerfors Tom Lindström Mikko Ritala Robin H. A. Ras Olli Ikkala 《Advanced functional materials》2011,21(3):510-517
Chemical vapor deposition of a thin titanium dioxide (TiO2) film on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between water‐superabsorbent and water‐repellent states. Cellulose nanofibrils (diameters in the range of 5–20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here first formed by freeze‐drying from the corresponding aqueous gels. Well‐defined, nearly conformal TiO2 coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO2‐coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofibrils spontaneously aggregate into porous sheets of different length scales during freeze‐drying is relevant: in the water‐repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water‐spreading into the aerogel cavities by capillary effects. The TiO2‐coated nanocellulose aerogels also show photo‐oxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purification. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications. 相似文献
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The effect of inhomogeneous compression of GDL on the mass and charge transfer in PEMFC is studied. The model utilizes experimentally evaluated GDL parameters as a function of thickness. The modeling results are compared with a conventional model that excludes the effects. As a result, it is shown that the inhomogeneous compression has a significant effect on the current density distribution because of the varying contact resistance between GDL and electrode. This also implies that there are possible hot spots occurring inside the electrode, and thus inhomogeneous compression can have significant effects on the lifetime and local performance of the cell. According to the achieved results, the inhomogeneous compression of GDL cannot be neglected. 相似文献
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Ferrihydrite in water wells and bacterial enrichment cultures 总被引:1,自引:0,他引:1
The chemical and mineralogical composition of Fe(III)-precipitates formed in water wells and laboratory cultures was examined. Ferrihydrite, a poorly ordered Fe(III)-oxide of bulk formula 5Fe2O3 · 9H2O, was detected by X-ray diffraction analysis in all samples. The crystallinity varied from one sample to another. Fe was the only major element detected by energy-dispersive X-ray spectrometry; several other elements were present at minor levels reflecting the chemical composition of the medium. The results suggest that the biologically-catalyzed iron encrustation of water wells begins with the initial formation of ferrihydrite. 相似文献
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This paper presents a review of existing analog implementations of the median and other ranked-order filter operations. The basic properties of median signal processing are first reviewed. Different analog median filter architectural approaches and implementations, introduced by several authors, are then discussed. These include filters based on analog delay lines and either nonlinear selection networks or ramp voltage generators. The Linear-Median Hybrid filter concept is presented and two examples of analog circuit implementations are given. Finally, a neural network approach is discussed. 相似文献
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The effects of mechanical ventilation on the sick building syndrome (SBS) were studied in an office building with 2150 employees, where the mechanical ventilation and indoor air quality were commonly blamed for causing symptoms typical of the SBS (nasal, eye, and mucous membrane symptoms, lethargy, skin symptoms and headache). The mechanical ventilation rates in the building were high (mean 26 l/s/person). To test the hypothesis that mechanical ventilation causes the SBS, a controlled experimental study was carried out by shutting off the ventilation in one part of the building and reducing the ventilation rate by 75% and 60% in two areas while leaving one part unaltered as a control. The experimental reduction of the ventilation rate did not alleviate the symptoms. On the contrary, the reduction of the ventilation rate caused a slight but statistically significant relative increase in symptoms (p < 0.05). In the cross-sectional analysis of the baseline data the SBS symptoms did not associate significantly with the ventilation rate (range 7–70 l/s/person). In the linear regression model, a positive correlation was found between temperatures above 22°C and the occurrence of symptoms (p < 0.05). Subjects exposed to environmental tobacco smoke had more symptoms than those not exposed (p < 0.01). Women reported more symptoms than men (p < 0.001). In addition, any prior history of allergic diseases (p < 0.001) and a negative attitude towards the social atmosphere at work (p < 0.001) were significant determinants of the SBS. 相似文献
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Twenty-two monkeys (Macaca fascicularis) were utilized in this study. Ten animals were rendered parkinsonian with serial injections of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Five of these parkinsonian monkeys received L-dopa/carbidopa treatment, and five animals did not. The remaining twelve animals did not receive MPTP. Eight of these animals received no L-dopa treatment, two animals were treated chronically with L-dopa/carbidopa and two animals received L-dopa/carbidopa only on the day of sacrifice. All animals were given weekly scored neurologic examinations throughout the study. Their movement was quantitated in an activity box. All animals were sacrificed by an overdose of sodium pentobarbital. The parkinsonian animals were sacrificed 107-355 days after their last MPTP injection. The brains were removed and frozen. Punch samples were taken from the caudate and putamen for tissue dopamine determination. Selected areas of the basal ganglia were cut into 20 microns sections for quantitative receptor autoradiography. The density of D1 and D2 receptors was evaluated in the basal ganglia of these animals at the level of the anterior commissure. For the D2 assay, total binding was determined using various concentrations of [3H]spiperone in buffer containing 300 nm mianserin. For the D1 assay, total binding was determined using various concentrations of [3H]SCH-23390. Tissue isotope concentration was determined from the autoradiographs. The MPTP parkinsonian monkeys showed a mean striatal dopamine depletion of 93.5% and a mean clinical score of 9.0. The untreated parkinsonian monkeys demonstrated an increase in the number of D2 sites as compared to controls. This increase was greatest in the lateral putamen.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献