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991.
Anca Bejenariu Marcel Popa Virginie Dulong Luc Picton Didier Le Cerf 《Polymer Bulletin》2009,62(4):525-538
Xanthan (Xan) is a biocompatible and biodegradable polysaccharide with a promising potential as substrate for controlled drug
delivery applications. Xan based hydrogels were synthesized in alkaline medium using trisodium trimetaphosphate (STMP) as
crosslinking agent. Hydrogels with various crosslinking agent/polymer ratios were synthesized and subsequently characterized
by the means of elemental analysis and dynamic swelling degree, model compound loading and releasing behaviour. Two physical
parameters (crosslinking density and phosphate charge) are manifesting antagonistic actions by stiffening or disrupting the
three-dimensional macromolecular ensemble. The highest swelling degree was obtained using an intermediate STMP:Xan ratio in
which case the opposing effects of the two forces are well balanced. The synthesized networks are pH sensitive. In acid and
alkaline media the swelling degrees are lower by comparison to neutral pH. The entrapping and releasing behaviour of the newly
synthesized xanthan networks were studied using methylene blue as a cationic model molecule. The releasing kinetics present
a first-order model. 相似文献
992.
Mihaela Silion Doina Hritcu Irina M. Jaba Bogdan Tamba Dunarea Ionescu Ostin C. Mungiu Ionel Marcel Popa 《Journal of materials science. Materials in medicine》2010,21(11):3009-3018
Ketoprofen (Ket) was intercalated into layered double hydroxides (ZnAlLDH and MgAlLDH) using the ionic exchange method. The
drug intercalation was confirmed by X-ray diffraction (XRD) and FTIR spectroscopy. Ket release from the inorganic matrix was
studied at pH 7.4 in continuous regime with a flow rate of 0.5 and respectively 1.0 ml/min. The kinetical data were interpreted
using the Ritger and Peppas model. The data prove that the release kinetics and mechanism depend on the eluent flow rate.
Quantification of gastric tolerance shows that the ulcerogenic effect of the intercalated drug is lower than the one of the
raw Ket. The antinociceptive effect of both formulations was studied by the hot-plate method performed on mice. The MgAlLDH_Ket
formulation shows a tendency towards a stronger antinociceptive effect than its ZnAlLDH_Ket counterpart during the 210 min
recorded period. 相似文献
993.
Hong Du Ph.D. Student Research Engineer Marcel A. J. Somers John Agren 《Metallurgical and Materials Transactions A》2000,31(1):195-211
Compound layers developed at 848 K during gaseous nitrocarburizing of iron and iron-carbon specimens were investigated for
several combinations of N and C activities imposed at the specimen surface by gas mixtures of NH3, N2, CO2, and CO. The microstructural evolution of the compound layer was studied by light microscopy and by X-ray diffraction analysis.
Composition-depth profiles were determined by electron probe (X-ray) microanalysis. Layer growth kinetics was investigated
by layer thickness measurements. The influence of the N and C activities on the microstructural and compositional evolution
and the growth kinetics of the compound layers formed is discussed for the iron substrate. The results indicate that the microstructure
is governed by a fast C and a slow N absorption at the surface in an early stage of gaseous nitrocarburizing. The influence
of carbon in the substrate on the microstructural and compositional evolutions and on the growth kinetics was evaluated from
comparing the results obtained for a normalized Fe-0.8C alloy with those for iron under identical nitrocarburizing conditions.
An erratum to this article is available at . 相似文献
994.
While in classical scheduling theory the locations of machines are assumed to be fixed we will show how to tackle location
and scheduling problems simultaneously. Obviously, this integrated approach enhances the modeling power of scheduling for
various real-life problems. In this paper, we introduce in an exemplary way theory and three polynomial solution algorithms
for the planar ScheLoc makespan problem, which includes a specific type of a scheduling and a rather general, planar location
problem, respectively. Finally, a report on numerical tests as well as a generalization of this specific ScheLoc problem is
presented. 相似文献
995.
Marcel Šimor Aleš Fiala Pavel Hlídek Robert Kuipers 《Surface & coatings technology》2007,201(18):7802-7812
Organosilicon plasma polymer layers were deposited by surface dielectric barrier discharge (DBD) at atmospheric pressure, in an attempt to enhance the corrosion protection of a reflective aluminium (Al) layer applied on a polyester (PET) fabric. A number of tests were carried out to characterize the improvement of corrosion resistance - namely sodium carbonate (Na2CO3), water vapor and Kesternich tests - as a function of plasma treatment time, type of carrier gas, admixture of oxygen, amount of hexamethyldisiloxane (HMDSO) precursor supplied to plasma and post-plasma-treatment heating. Moreover, plasma-deposited protective films were characterized by the scanning electron microscopy (SEM), infrared spectroscopy (DRIFT FTIR), and X-ray photoelectron spectroscopy (XPS). While aluminium was consumed in the Na2CO3 corrosive solution within a few minutes for the untreated surface, the optimally performing plasma polymerized layers revealed an extraordinary corrosion resistance. Furthermore, the best protective organosilicon coatings showed only a 1-2% absolute reduction of reflection compared to the untreated fabric, over the complete solar spectrum (250-2500 nm). 相似文献
996.
A series of uniaxial tension experiments has been conducted to investigate the size effect on strength and fracture energy
of quasi brittle materials like concrete and sandstone. This paper focuses on the results of the concrete tests, and specifically
deals with the variation of the nominal strength for specimens of six different sizes in a scale range of 1:32. It was found
that under given experimental conditions, the nominal strength strongly depended on the specimen size. More important however,
is the fact that most of this size effect could be attributed to strain gradients which were present in the cross section
of the specimens. These strain gradients were caused by the specimen shape, load eccentricity and material inhomogeneity.
Through a combination of experimental data and a simple linear elastic analysis, the importance of strain gradients with respect
to the ultimate load level could be visualized. This leads to the conclusion that studying a material size effect is not possible
without taking into account structural stress/strain gradients.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
Novel process for low temperature crystallization of a-SiC:H for optoelectronic applications 总被引:1,自引:0,他引:1
Maruf Hossain Jose Roberto Sanchez Perez Jose Marcel Rodriguez Rivera Keshab Gangopadhyay Shubhra Gangopadhyay 《Journal of Materials Science: Materials in Electronics》2009,20(Z1):412-415
Metal-induced crystallization (MIC) process was employed to crystallize hydrogenated amorphous silicon carbide (a-SiC:H) films
deposited by PECVD on n-type Si substrate. To optimize the crystallization process, Aluminum thin films of different thicknesses
were deposited on a-SiC:H films which were then annealed at 600 °C in N2 environment for 1 h. UV–visible spectrophotometer, atomic force microscopy (AFM) and hall measurement system were used to
characterize the films. It was observed from the UV–visible spectrum that the films crystallized using higher Al thickness
show absorption in the visible range whereas the samples crystallized with lower Al thickness did not show absorption in the
visible range but shows large absorption above the bandgap of the material. Considering UV–visible and Hall measurement data
it can be concluded that the sample crystallized with 50 nm of Al can be a good candidate for SiC–Si hetero-junction solar
cells. 相似文献
998.
DI Andrea Kreisler DI Johann Aigner DI Marcel Georg Liedermann Univ.-Prof. DI Helmut Habersack 《?sterreichische Wasser- und Abfallwirtschaft》2014,66(9-10):297-305
Bedload transport is an important aspect in the fields of river engineering, flood protection, torrent and avalanche control and ecology, as well as in the context of hydropower and waterway management. In addition to providing us with a better understanding of the process itself, bedload monitoring allows us to determine the initiation of motion of bedload particles, bedload transport rates and bedload yields – important variables for planning enhanced management strategies and implementing sustainable measures. Further, this monitoring data serves as the basis for selecting, applying, calibrating and validating bedload transport formulae and numerical models. As the bedload transport process is characterized by significant spatial and temporal variability and the specific conditions vary between monitoring stations, determining the most suitable measuring system is of great importance, as are standardization and quality assurance. This article provides an overview of bedload monitoring in Austria, introduces the methodology used to assess the bedload transport process, and presents selected results. 相似文献
999.
Thomas A. Huld Marcel úri Ewan D. Dunlop Fabio Micale 《Environmental Modelling & Software》2006,21(12):1650-1661
We present a methodology for estimating the average profiles of daytime and daily ambient temperature from a spatially-continuous database for any location within Europe. The primary database with 1-km grid resolution was developed by interpolation of monthly averages of 7 daily values of temperature: minimum and maximum and 5 measurements at 3-h intervals from 6:00 to 18:00 hours Greenwich Mean Time. With a little over 800 meteorological stations available, we obtained a cross-validation root mean square error of 1.0–1.2 °C, while the interpolation error is lower, at 0.5–0.7 °C.A polynomial fit was applied to estimate the daytime temperature profile (assuming only time from sunrise to sunset) from the interpolated 3-h measurements for each month. The curve fit coefficients make it possible to calculate a number of derived data, such as average daytime temperature, maximum daytime temperature and time of its occurrence within the region. An example demonstrates the coupling of the simulated daytime temperature profile with a model for assessing the relative efficiency of electricity generation by crystalline silicon photovoltaic modules.As an alternative to the polynomial fitting, a double-cosine method was applied to enable calculation of daily (24-h) temperature profiles for each month using interpolated minimum and maximum temperatures. Compared to the polynomial curve-fitting, this method does not offer lower errors, but it provides data which are more suitable for estimation of solar thermal heating or calculation of degree days for building heating/cooling. 相似文献
1000.
Marcel A. J. Somers Thomas Christiansen 《Journal of Phase Equilibria and Diffusion》2005,26(5):520-528
The incorporation of nitrogen or carbon in steel is widely applied to provide major improvements in materials performance with respect to fatigue, wear, tribology, and atmospheric corrosion. These improvements rely on a modification of the surface-adjacent region of the material by the (internal) precipitation of alloying element nitrides/carbides or by the development of a continuous layer of iron-based (carbo-) nitrides. The evolution of the microstructure during thermochemical treatments is not only determined by solid-state diffusion, but in many cases also by the kinetics of the surface reactions and the interplay with mechanical stress. In the present article a few examples, covering research on the interaction of carbon and/or nitrogen with iron-based metals, are included to illustrate the various aspects of gas-metal interactions. 相似文献