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排序方式: 共有825条查询结果,搜索用时 154 毫秒
51.
Marin Cernea Adrian Manea Daniele Piazza Carmen Galassi Eugeniu Vasile 《Journal of the American Ceramic Society》2007,90(6):1728-1732
Fine-grain BaTi0.87 Sn0.13 O3 (BTS13 ) powder was synthesized from an oxalate precursor and used to prepare sintered ferroelectric BTS13 ceramics. The evolution of the morphology and structure of a BTS13 precipitate precursor as a function of temperature was analyzed. We compare the sintering behavior as well as the dielectric properties of the BTS13 ceramics obtained using uniaxial and cold isostatic pressing. 相似文献
52.
The effect of the platinum particle diameter and the catalyst support was investigated for the aqueous phase selective oxidation
of methyl α-D-glucopyranoside, octyl α-D-glucopyranoside and α-cyclodextrin with molecular oxygen. No platinum particle size
effect was observed in the platinum particle diameter range of 1.4 to 3.0 nm. The structure-insensitivity is attributed to
the high degree of surface coverage by oxygen. The rate of deactivation due to over-oxidation of the catalyst increases to
a small extent with decreasing platinum particle diameter. The effect of the catalyst support is much larger than the platinum
particle size effect. The turnover frequency for platinum on activated carbon and carbon fibrils supported catalyst is 3-7
times higher than for graphite as the catalyst support. The support effect is attributed to the hydrophilic character of the
support.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
53.
V. A. Grigor’ev V. A. Kaplin T. L. Karavicheva O. V. Karavichev N. V. Kondrat’eva A. B. Kurepin A. N. Kurepin V. A. Loginov V. N. Marin A. I. Maevskaya A. I. Reshetin W. H. Trzaska 《Instruments and Experimental Techniques》2009,52(3):352-356
Measurements of the pulse heights in the T0 start trigger detector of the ALICE experiment are necessary both for time-amplitude offline correction of start signal T0 used in the time-of-flight TOF detector and for monitoring the state of the Cherenkov counters in the detector. A high amplitude resolution is not required for these tasks; what is needed is fast encoding and interfacing with the data readout system in which only time channels are available. Therefore, amplitudes are measured in the detector by pulse-height-to-time conversion using two independent methods, one of which involves quasi-logarithmic charge-to-time converter (QTC) and the other employs two—leading-edge (LED) and constant-fraction (CFD)—timing discriminators. The main characteristics of both methods and results of calibrations of the appropriate devices using a pulsed laser are presented. 相似文献
54.
55.
Marin?VincentEmail author Frédéric?Thiebaud Saifeddine?Bel Haj Khalifa Marc?Engels-Deutsch Tarak?Ben Zineb 《Journal of Materials Engineering and Performance》2015,24(10):4128-4139
The aim of the present paper is the development of endodontic Cu-based single crystal Shape Memory Alloy (SMA) instruments in order to eliminate the antimicrobial and mechanical deficiencies observed with the conventional Nickel-Titane (NiTi) SMA files. A thermomechanical constitutive law, already developed and implemented in a finite element code by our research group, is adopted for the simulation of the single crystal SMA behavior. The corresponding material parameters were identified starting from experimental results for a tensile test at room temperature. A computer-aided design geometry has been achieved and considered for a finite element structural analysis of the endodontic Cu-based single crystal SMA files. They are meshed with tetrahedral continuum elements to improve the computation time and the accuracy of results. The geometric parameters tested in this study are the length of the active blade, the rod length, the pitch, the taper, the tip diameter, and the rod diameter. For each set of adopted parameters, a finite element model is built and tested in a combined bending-torsion loading in accordance with ISO 3630-1 norm. The numerical analysis based on finite element procedure allowed purposing an optimal geometry suitable for Cu-based single crystal SMA endodontic files. The same analysis was carried out for the classical NiTi SMA files and a comparison was made between the two kinds of files. It showed that Cu-based single crystal SMA files are less stiff than the NiTi files. The Cu-based endodontic files could be used to improve the root canal treatments. However, the finite element analysis brought out the need for further investigation based on experiments. 相似文献
56.
57.
G. A. Kachurin S. G. Cherkova V. A. Skuratov D. V. Marin A. G. Cherkov 《Semiconductors》2010,44(4):525-530
SiO2 layers containing implanted excess Si are irradiated with Xe ions with an energy of 130 MeV and doses of 3 × 1012–1014 cm−2. In the samples irradiated with a dose of 3 × 1012 cm−2, ∼1012 cm−2 segregated clusters 3–4 nm in dimension are detected by transmission electron microscopy. With increasing dose, the dimensions
and number of these clusters increase. In the photoluminescence spectrum, a 660- to 680-nm band is observed, with the intensity
dependent on the dose. After passivation of the sample with hydrogen at 500°C, the band disappears, but a new ∼780-nm band
typical of Si nanocrystals becomes evident. On the basis of the entire set of data, it is concluded that the 660- to 680-nm
band is associated with imperfect Si nanocrystals grown in the tracks of Xe ions due to high ionization losses. The nonmonotonic
dependence of the photoluminescence intensity on the dose is attributed to the difference between the diameters of tracks
and the diameters of the displacements’ cascades responsible for defect formation. 相似文献
58.
Abhishek Dutta Rahul P. Ekatpure Geraldine J. Heynderickx Axel de Broqueville Guy B. Marin 《Chemical engineering science》2010,65(5):1678-1693
Computational fluid dynamics (CFD) simulations of the hydrodynamic behavior of rotating fluidized beds in static geometry (RFB-SG) are carried out for gas–solid flows. The rotating motion of the reactor bed is induced by the tangential injection of the gas along the circumference of the fluidization chamber. Steep gradients in the gas velocity fields both in radial and tangential direction generate turbulence. The radial and tangential drag forces fluidize the particle bed in both radial and tangential direction.An Eulerian two-fluid model is used. Gas phase turbulence is accounted for by a k–ε model adapted for rotational flows. The RFB-SG simulations provide guidelines for a design and operation with a high efficiency in gas–solid momentum transfer, excellent gas–solid separation and limited solids losses. Hydrodynamic variables like the centrifugal force, the injection pressure, the radial and tangential slip velocities, solids hold-up are calculated for both polymer particles (300 μm, 950 kg/m3, Geldart Group B) and glass beads (70 μm, 2500 kg/m3, Geldart Group A) to allow for a comparison among different fluidization chamber designs. Unstable bed behavior, like slugging and channeling, is also numerically predicted. 相似文献
59.
C. Vidal-Valverde Marin Prodanov Isabel Sierra 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1997,205(6):464-469
Lentils (Lens culinaris, var. vulgaris cultivar Magda-20) were naturally fermented for 96 h at different lentil flour concentrations (79, 150 and 221 g/l) and temperatures
(28, 35 and 42°C). During fermentation, samples were taken at 24-h intervals and the changes in thiamin (vitamin B1), riboflavin (vitamin B2) and total and available niacin (vitamin B3) were investigated. Preparation of the lentil flour suspension to be fermented (i.e. the process of mixing the flour and
sterilized tap water) caused an increase of the available niacin content in all batches, while changes in thiamin and riboflavin
content were related to the conditions in which the preparation of the suspensions was carried out. The whole natural fermentation
process (from the raw state to after 96 h of fermentation), either did not affect or produced a slight decrease in the thiamin
content of lentils. In contrast, riboflavin, available niacin and total niacin contents increased throughout the 96 h period,
which ended with a 35 – 82% increase of riboflavin, a 24 – 91% increase of available niacin and a 20 – 58% increase of total
niacin. The temperature during the fermentation procedure had significant effect on the levels of thiamin and riboflavin in
fermented lentils. To obtain lentil flours with an improved amount of riboflavin and available niacin with a minimum loss
of thiamin, the natural fermentation of lentils should be carried out for 96 h at 42°C and with a lentil flour concentration
of 221 g/l.
Received: 21 February 1997 相似文献
60.
Marko R. Djokic Kevin M. Van Geem Carlo Cavallotti Alessio Frassoldati Eliseo Ranzi Guy B. Marin 《Combustion and Flame》2014
The importance of 1,3-cyclopentadiene (CPD) and cyclopentadienyl (CPDyl) moieties in the growth of polycyclic aromatic hydrocarbons (PAHs) was studied using new experimental data and ab initio calculations. The experimental investigation was performed in a tubular continuous flow pyrolysis reactor under both high (24molN2/molCPD) and low (5molN2/molCPD) nitrogen dilutions, covering a temperature range of 873–1123 K, at a fixed pressure of 1.7 bara. At the most severe conditions up to 84% of CPD is converted, and the amount of PAHs is more than 65 wt%. Major products observed during CPD pyrolysis were benzene, indene, methyl-indenes and naphthalene, in line with previous studies. On-line GC × GC-FID/(TOF-MS) also allowed to quantify minor species (methane, toluene, styrene, phenanthrene, anthracene, etc.), never reported before at this level of accuracy. The new experimental data have been used to further analyze the role of the successive interactions of CPD, indene, and naphthalene as well as the recombination and addition reactions of their resonantly stabilized radicals and refine their kinetics. The results of the modeling study are in good agreement with existing and new experimental observations. 相似文献