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831.
Marcos Latorre‐Sánchez Ana Primo Pedro Atienzar Amparo Forneli Hermenegildo García 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(8):970-975
Nitrogen‐doped graphene [(N)G] obtained by pyrolysis at 900 °C of nanometric chitosan films exhibits a Hall effect characteristic of n‐type semiconductors. In contrast, boron‐doped graphene [(B)G] obtained by pyrolysis of borate ester of alginate behaves as a p‐type semiconductor based also on the Hall effect. A p–n heterojunction of (B)G‐(N)G films is built by stepwise coating of a quartz plate using a mask. The heterojunction is created by the partial overlapping of the (B)G‐(N)G films. Upon irradiation with a xenon lamp of aqueous solutions of H2PtCl6 and MnCl2 in contact with the heterojunction, preferential electron migration from (B)G to (N)G with preferential location of positive holes on (B)G is established by observation in scanning electron microscopy of the formation of Pt nanoparticles (NP) on (N)G and MnO2 NP on (B)G. The benefits of the heterojunction with respect to the devices having one individual component as a consequence of the electron migration through the p‐n heterojunction are illustrated by measuring the photocurrent in the (B)G‐(N)G heterojunction (180% current enhancement with respect to the dark current) and compared it to the photocurrent of the individual (B)G (15% enhancement) and (N)G (55% enhancement) components. 相似文献
832.
The lead-based relaxor ceramic Pb(Ca1/3Nb2/3)O3 was prepared by two-step solid-state reaction. The material stabilizes in the orthorhombic phase with refined lattice parameters a = 3.4814 Å, b = 12.9480 Å, and c = 14.2483 Å. The scanning electron micrograph is indicative of heterogeneous grain distribution with average grain size ~0.8–2.0 μm. The temperature-dependent dielectric response has a broad peak at 233.5°C (at 1 kHz, ε′ = 14523). A frequency-dependent shift toward higher temperature with increasing frequency is attributed to relaxor behaviour. Deviation from the Curie–Weiss law is observed at temperatures higher than the temperature, T m, at which the dielectric constant is maximum. The modified Curie–Weiss law was used to fit the dielectric data; the results were indicative of almost complete diffuse phase transition characteristics. The dielectric relaxation obeys the Vogel–Fulcher relationship with freezing temperature T f = 214.1°C, activation energy E a = 0.16 eV, and relaxation frequency ν 0 = 3.4 × 107 Hz. Electrical conduction is mainly attributed to the hopping mechanism. 相似文献
833.
Assessment of ball milling methodology to develop polylactide‐bacterial cellulose nanocrystals nanocomposites 下载免费PDF全文
Jesús Ambrosio‐Martín Amparo Lopez‐Rubio María José Fabra Giuliana Gorrasi Roberto Pantani Jose María Lagaron 《应用聚合物科学杂志》2015,132(10)
In this work, ball milling is evaluated as a methodology to develop polylactide (PLA)‐bacterial cellulose nanocrystals (BCNC) nanocomposites. This technique, widely used for clay‐based nanocomposites, is effective in breaking up to a very large extent the freeze‐dried nanocellulose aggregates, giving raise to transparent films similar to the neat PLA films. Incorporation of the nanofiller through this methodology enhances the polymer crystallinity index. An increase in the onset degradation temperature and a significant reinforcing effect in terms of an increase in the storage modulus and in the tan delta peak are also observed. Improved barrier to oxygen at high relative humidity (80%) is also noticed, reaching the best performance at the lowest BCNC loading (0.5 wt %). These improvements are related to the relatively good nanocellulose dispersion and distribution attained for low loadings of the nanofiller. Thus, the ball milling methodology appears as a feasible processing methodology for developing PLA‐BCNC nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41605. 相似文献
834.
Hydrothermal Degradation Behavior of Y‐TZP Ceramics Sintered by Nonconventional Microwave Technology 下载免费PDF全文
Álvaro Presenda Maria Dolores Salvador Rodrigo Moreno Amparo Borrell 《Journal of the American Ceramic Society》2015,98(12):3680-3689
Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low‐temperature degradation (LTD) resistance of 3Y‐TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro‐Raman spectroscopy, and electron microscopy. 3Y‐TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200°C) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y‐TZP commercial material. In the former, the presence of m‐phase was almost nonexistent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast‐technology by microwave heating is presented with a nonconventional sintering method to fabricate 3Y‐TZP ceramics for dental application with very high resistance against LTD and optimized mechanical properties. 相似文献
835.
836.
Géraldine Pastor María Jiménez-González Sandra Plaza-García Marta Beraza Torsten Reese 《Magma (New York, N.Y.)》2017,30(3):299-307
Objective
A newly adapted zoomed ultrafast low-angle RARE (U-FLARE) sequence is described for abdominal imaging applications at 11.7 Tesla and compared with the standard echo-plannar imaging (EPI) and snapshot fast low angle shot (FLASH) methods.Materials and methods
Ultrafast EPI and snapshot-FLASH protocols were evaluated to determine relaxation times in phantoms and in the mouse kidney in vivo. Owing to their apparent shortcomings, imaging artefacts, signal-to-noise ratio (SNR), and variability in the determination of relaxation times, these methods are compared with the newly implemented zoomed U-FLARE sequence.Results
Snapshot-FLASH has a lower SNR when compared with the zoomed U-FLARE sequence and EPI. The variability in the measurement of relaxation times is higher in the Look–Locker sequences than in inversion recovery experiments. Respectively, the average T1 and T2 values at 11.7 Tesla are as follows: kidney cortex, 1810 and 29 ms; kidney medulla, 2100 and 25 ms; subcutaneous tumour, 2365 and 28 ms.Conclusion
This study demonstrates that the zoomed U-FLARE sequence yields single-shot single-slice images with good anatomical resolution and high SNR at 11.7 Tesla. Thus, it offers a viable alternative to standard protocols for mapping very fast parameters, such as T1 and T2, or dynamic processes in vivo at high field.837.
Amparo Quiles Isabel Prez‐Munuera Isabel Hernando Ma ngeles Lluch 《Journal of the science of food and agriculture》2003,83(5):425-429
The chemical components of foods are organized in microscopic structures that can modify mass transfer. The study of material penetration in foods can be made using X‐ray microanalysis. In order to study the microstructural behaviour when fruit was osmotically dehydrated, a glucose molecule modified with chloral (1,2‐O‐2′,2′,2′‐trichloroethylidene‐α‐D ‐glucofuranose) was used as an osmotic standard with chlorine detectable by energy‐dispersive X‐ray analysis. Parenchyma of Granny Smith apple is a simple tissue, so it was chosen as reference. The results show that both the apoplastic and symplastic routes played an active role in mass transfer. The osmotic agent penetrated both the symplast and apoplast well into the depths of the fruit, although greater deterioration of cells was observed near the surface. Copyright © 2003 Society of Chemical Industry 相似文献
838.
María José García-Nebot Antonio Cilla Amparo Alegría Reyes Barberá María Jesús Lagarda Gonzalo Clemente 《Food chemistry》2010
Ferritin synthesis was evaluated in iron sulphate solutions and in fruit beverages supplemented with iron, with/without zinc in the presence of caseinophosphopeptides (CPPs), based on a system combining simulated gastrointestinal digestion and the Caco-2 cell model. In iron sulphate solutions with/without zinc, the addition of CPPs had no effect upon ferritin synthesis. When CPPs were added to the bioaccessible fraction of fruit beverages supplemented with iron, ferritin synthesis increased in the same proportion as with the addition of milk. The addition of zinc to fruit beverages supplemented with iron and to iron sulphate solutions decreased ferritin synthesis. Nevertheless, in fruit beverages with milk, this decrease in ferritin synthesis was not observed when zinc was present. 相似文献
839.
In the last years there is an increasing demand to produce wines with higher glycerol levels and lower ethanol contents. The production of these compounds by yeasts is influenced by many environmental variables, and could be controlled by the choice of optimized cultivation conditions. The present work studies, in a wine model system, the effects of temperature, pH and sugar concentration on the glycerol and ethanol syntheses by yeasts Saccharomyces cerevisiae T73, the type strain of Saccharomyces kudriavzevii IFO 1802T, and an interspecific hybrid between both species (W27), which was accomplished by the application of response surface methodology based in a central composite circumscribed design. Results show that carbon flux could be especially directed towards glycerol synthesis instead of ethanol at low pH, high sugar concentrations and low temperatures. In general, the non-wine yeast S. kudriavzevii produced higher glycerol levels and lower ethanol content than wine strains S. cerevisiae T73 and the hybrid W27, with specific and different glycerol production profiles as a function of temperature and pH. These results were congruent with the higher glycerol-3-phosphate dehydrogenase activities estimated for this species, chiefly at low temperatures (14 °C), which could explain why S. kudriavzevii is a cryotolerant yeast compared to S. cerevisiae. 相似文献
840.