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41.
The humic acids, HA, extracted from a Spanish lignite and the nitrohumic acids, NHA, and nitrofulvic acids, NFA, extracted from the same lignite after its nitration, are hydrolysed with 6N HCI under reflux. The α-amino acids present in the hydrolysates are determined and thirteen α-amino acids are identified. The amounts of nitrogen in the amino-acids released by the hydrolysis increase according to the sequence: NFA > NHA > HA. 相似文献
42.
This paper proposes a formal model that analyzes the degree of openness chosen by start-ups when entering the software industry. In line with the literature, we label as degree of openness the extent to which software start-ups mix open source (OS) and proprietary solutions in the portfolio of software products they offer. We relate the choice of the degree of openness to two key characteristics of the market segments in which software start-ups operate: the strength of the network externalities and the competitive advantage of the incumbent. Specifically, by modelling (price) competition between an incumbent and an entrant in two ways, i.e., the entrant is price-setter or price-taker, we derive the necessary condition(s) in terms of the strength of network externalities for observing the adoption of a business model that comprises the offering of both proprietary and OS solutions by the entrant (i.e., hybrid business model). Then, we highlight that, if a hybrid business model is the choice, the degree of openness chosen in equilibrium increases along with both the strength of the network externalities and the competitive advantage of the incumbent. This result holds indifferently whether the software start-up is modelled as a price-setter or a price-taker. An empirical test run on a sample of European start-ups in the software industry supports these theoretical predictions. 相似文献
43.
Gina‐Gabriela Bumbu Cornelia Vasile Maria Cristina Popescu Hristea Darie Gabrielle Charlotte Chianu Gheorghe Singurel Adrian Carpov 《应用聚合物科学杂志》2003,88(11):2585-2597
The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003 相似文献
44.
Processing of a Silicon-Carbide-Whisker-Reinforced Glass-Ceramic Composite by Microwave Heating 总被引:1,自引:0,他引:1
Lifu Chen Cristina Leonelli Tiziano Manfredini Cristina Siligardi 《Journal of the American Ceramic Society》1997,80(12):3245-3249
A calcium magnesium aluminosilicate-based glass that contained 10 wt% of silicon carbide whiskers (SiC w ) as reinforcement was prepared by tape casting, followed by sintering either in a conventional furnace or in a microwave oven. The results were consistent with retardation of glass sintering through whisker bridging. The glass, by itself, was sintered to almost-full density at 750°C for 4 h by conventional furnace sintering; the best sintered composite, with an estimated density of ∼90%, was obtained at 800°C with a dwell time of 4 h. Sintering at a temperature of >800°C did not improve the densification but rather resulted in severe whisker oxidation. A reduced densification rate was observed for the samples that were sintered in nitrogen. By contrast, in the microwave oven, almost-full density for the glass and ∼95% of the theoretical density for the composite were obtainable at 850°C for 15 min, which represented a reduction of ∼10 h of the total processing time and a reduced SiC w oxidation. 相似文献
45.
The enzymatic degradation of poly(N‐isopropyl acrylamide) (PNIPAM) grafted to carboxymethylcellulose (CMC) copolymers with a cellulasic preparation (Trichoderma viride) was studied. The enzymatic activity of the cellulasic preparation against CMC and the grafted copolymers was determined by the Petterson–Porath method, while their reduced viscosity variation in the presence of the same preparation was also followed. It has been shown that the enzymatic degradation behavior depends on the copolymer composition and the reaction temperature. Reducing sugars analysis showed that the experimental values for the grafted copolymers were higher than the calculated ones. At 50°C, the enzymatic reaction is completed in about 20 min for the copolymers, whereas for CMC it takes more than 40 min. It can be concluded that their enzymatic degradation is facilitated by the presence of the PNIPAM grafts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1383–1386, 2003 相似文献
46.
Unai Diaz-Orueta Aitziber Etxaniz Mari Feli Gonzalez Cristina Buiza Elena Urdaneta Javier Yanguas 《Universal Access in the Information Society》2014,13(1):89-97
The complexity of new information technologies (IT) may limit the access of elderly people to the information society, exacerbating what is known as “the digital divide,” as they appear to be too challenging for elderly citizens regardless of the integrity of their cognitive status. This study is an attempt to clarify how some cognitive functions (such as attention or verbal memory) may determine the interaction of cognitively impaired elderly people with technology. Twenty participants ranging from mild cognitive impairment to moderate Alzheimer’s disease were assessed by means of a neuropsychological and functional battery and were asked to follow simple commands from an avatar appearing on a TV by means of a remote control, such as asking the participant to confirm their presence or to respond Yes/No to a proposal to see a TV program. The number of correct answers and command repetitions required for the user to respond were registered. The results show that participants with a better cognitive and functional state in specific tests show a significantly better performance in the TV task. The derived conclusion is that neuropsychological assessment may be used as a useful complementary tool for assistive technology developers in the adaptation of IT to the elderly with different cognitive and functional profiles. Further studies with larger samples are required to determine to what extent cognitive functions can actually predict older users’ interaction with technology. 相似文献
47.
Cristina Manresa-Yee Javier Varona Francisco J. Perales Iosune Salinas 《Universal Access in the Information Society》2014,13(4):471-482
This work focuses on camera-based systems that are designed for mouse replacement. Usually, these interfaces are based on computer vision techniques that capture the user’s face or head movements and are specifically designed for users with disabilities. The work identifies and reviews the key factors of these interfaces based on the lessons learnt by the authors’ experience and by a comprehensive analysis of the literature to describe the specific points to consider in their design. These factors are as follows: user features to track, initial user detection (calibration), position mapping, feedback, error recovery, event execution, profiles and ergonomics of the system. The work compiles the solutions offered by different systems to help new designers avoid problems already discussed by the others. 相似文献
48.
E. García-Bordej J.L. Pinilla M.J. Lzaro R. Moliner 《Applied catalysis. B, Environmental》2006,66(3-4):281-287
The objective of this research is to asses the impact of the addition of H2O, SO2, and both in the SCR of NO at low temperatures over sulphated vanadia on carbon-coated monoliths. The sulphated catalyst keeps a 100% conversion and total selectivity to N2 in the low temperature range, i.e. 473–500 K, when either H2O or SO2 is added to the gas feed. However, a decline of steady state conversion and selectivity occurs when both H2O and SO2 are added simultaneously because H2O speeds up the deposition of ammonium sulphate salts. This decrease of catalyst performance is reversed when the reaction is carried out under dry conditions at temperatures higher than 473 K but not at lower temperature (453 K). Thus, the catalyst has demonstrated to be a good candidate for the SCR of NO at low temperatures even in stack gases containing traces of undesired components. 相似文献
49.
The present study was designed to examine the effects of EFA deficiency (EFAD) on biochemical, functional, and structural
aspects of the kidney in growing and adult rats fed a normal or EFAD diet for 9 wk after weaning. Food and fluid intake (FI),
urine volume, and Na+ and K+ excretions were measured weekly from weeks 4 to 8 by placing the rats in individual metabolic cages for 24 h. At week 9,
Li+ and a 5% water load, respectively, were administered at 14 and 1.5 h prior to glomerular and proximal tubular function studies,
as assessed by 3-h creatinine (CCr) and Li+ (CLi+) clearances. Hematocrit and urine volume; serum and urine [Cr], [Li+], [Na+], and [K+]; and renal FA distribution were also measured. Data [corrected to 100 g/body weight (bw) and presented as means ±SEM] were
significant, at P<-0.05. Despite a similar ingestion of solids from weeks 4 to 7 (weeks 7 to 10 of life), the rats on the EFAD diet showed
a decreased body weight from week 5. From weeks 4 to 8, Fl and urine volume were similar for both groups, but the Fl increased
at week 6 in the EFAD group; 24-h Na+ and K+ excretions were similar at all weeks, except for an increase in the EFAD group for both ions at week 7. In the EFAD group,
CCr and CLi+ decreased by 27 and 56.3%, respectively (385.7±33.4 vs. 280±21.1, and 21.0±2.1 vs. 9.2±1.1 μL/min/100 g; n=9 vs. 10), the latter result suggesting increased proximal reabsorption. The 3-h Na+ and K+ excretions were similar, but the Li+ decreased (0.78±0.06×10−2 vs. 0.32±0.03×10−2 μeq/min/100 g) in the EFAD group, giving additional support to the suggestion. Renal structure was normal and similar for
both groups, but the EFAD group showed a more prominent proximal tubule brush border, together with heavier periodic acid-Schiff
staining in all specimens from weeks 5 to 9. In the EFAD group, FA of the n−9 and n−7 series were higher, but most of the
n−6 series were lower as a percentage of total lipids in the medulla and cortex. Medullary levels of 20∶4n−6 were maintained,
22∶4n−6 declined twice, arachidonic acid was maintained, and 20∶5n−3 was lower. The EFAD diet affected glomerular function,
proximal tubular structure and function, and FA distribution in the rat kidney. 相似文献
50.
Auguste Fernandes Maria Filipa Ribeiro Cristina Borges Joo Paulo Loureno Joo Rocha Zelimir Gabelica 《Microporous and mesoporous materials》2006,90(1-3):112-128
This study is aimed at exploring the ability of very small sized N-bearing molecules to generate and stabilize microporous aluminophosphates. Two new AlPO4-n materials, called IST-1 and IST-2, have been obtained in aqueous media using, as main template, methylamine (MA), directly added, or generated in situ from methylformamide (MF) degradation. While IST-1 topology proved to be novel, IST-2 appears structurally related to AlPO4-53(A). The obtained materials were characterized by powder XRD, TG/DSC, SEM and solid-state NMR. Tetraalkylammonium (TEA) cations were used as potential co-templates but only MA and water were found incorporated in the pore volumes of both structures, which argues for their true templating role. In IST-1, 13C solid-state NMR studies showed that half of MA species, presumably protonated, is H-bonded to framework oxygens while the other half surprisingly bonds directly to framework Al atoms. 13C NMR showed that only protonated MA occurs in IST-2 channels. TEA+ cations definitely do not play any specific template role. They indirectly favor the crystallization of IST-1 or IST-2 devoid from other crystalline or amorphous side phases, by interacting with part of the Al and P in solution and forming soluble [AlPO4(OH)]–[TEA,HMA] complexes, substantially modifying the compositions of gels precursors to each phase during nucleation and/or growth steps. While both IST-1 and IST-2 crystallize from gels of similar initial compositions, it was demonstrated that the new MA/T ratio (T = Al or P) obtained after in situ complexation was the key parameter that specifically governs the crystallization of each phase. 相似文献