排序方式: 共有27条查询结果,搜索用时 10 毫秒
11.
J. K. Richard Weber Johan G. Abadie Thomas S. Key Kirsten Hiera Paul C. Nordine Ronald W. Waynant Ilko K. Ilev 《Journal of the American Ceramic Society》2002,85(5):1309-1311
Single-phase glasses containing 37.5 mol% Y2 O3 , 7 mol% La2 O3 , and 1 mol% Pr, Ho, Nd, Er, Sm, Tm, Eu, or Yb oxide substituted for part of the Y2 O3 were synthesized by containerless melting. The spectral transmission and absorption cross sections of the glasses were determined at wavelengths from 360 to 3300 nm. The electronic transitions were broadened compared with results obtained in a crystalline yttrium aluminum garnet (YAG) host. The infrared transmission of the host glass extended to 6000 nm. The optical and physicochemical properties of these glasses are well suited for optical device applications. 相似文献
12.
Lamiae Vernieres-Hassimi Rachida El Assoudi-Baikari Moulay-Ahmed Abdelghani-Idrissi Nordine Mouhab 《Chemical Engineering Communications》2016,203(2):174-181
This paper deals with an analytical method to assess the maximum temperature value along a tubular chemical reactor at steady state. This reactor is provided with a jacket in which a counter current cooling liquid flows. The thermal behavior of the chemical reactor is calculated with the McCormack numerical method. Comparison of the exothermic reaction generated flux with the removed flux from the separating wall leads to a two-part reactor subdivision. In the first part, the reactor behaves as an adiabatic reactor followed by a zone in which the flux removed from the wall is not negligible and remains constant. In the second part, the reactor behaves like a simple heat exchanger without internal energy source. Analytical integration of mass and energy balance equations in each subsystem was used to determine the analytical expression of maximum temperature. 相似文献
13.
Y. Chetouani N. Mouhab J. M. Cosmao L. Estel 《Chemical Engineering Communications》2013,200(9):1222-1241
In this paper, we present a method for detecting faults that can appear in some parts of a chemical plant. This method is based on statistical information generated by the Extended Kalman Filter (EKF) and is designed to reveal any drift from the normal behavior of the process. Although this method was originally developed for linear systems, our contribution consists in extending it to unsteady state nonlinear systems such as stirred reactors in the presence of exothermic chemical reactions. We examined the abnormal behavior of a chemical reactor due to three different faults in its control parameters. Each fault is caused by an abrupt variation in the value of one of the following parameters: the cooling temperature, the stirring rate of the reaction mass, and the feeding flow rate of the reactant. The objective of this experimental study is to detect the presence of such faults on-line and to pinpoint the moment each occurs, as well as to determine the delay in detection with respect to the decision threshold. 相似文献
14.
Nordine Leklou Jean-Emmanuel Aubert Gilles Escadeillas 《Materials and Structures》2009,42(10):1369-1378
This article, which deals with the study of the microscopic modifications of DEF-affected materials, has two main objectives.
The first one is to study the influence of sample preparation on the microcracks of specimens observed in Scanning Electron
Microscopy (SEM). From the results of this study, it can be concluded that direct observations of the samples are inappropriate
because they produce cracks that are not ascribable to the pathology. It is therefore preferable to use an indirect technique
of observation such as the replica technique. This technique was developed in the 1980s and used to study the evolution of
microcracking due to mechanical damage to the concrete. The results presented in this article show that it is possible to
use this technique to study the microcracking associated with delayed ettringite formation. The second objective is to study
ettringite formation during the swelling of DEF-affected specimens. The main results show that secondary ettringite is initially
formed in the paste–aggregate interface even at low levels of expansion. For these levels of expansion, there is no trace
of secondary ettringite or microcracks observable in the paste. However, for higher expansions, cracks filled with ettringite
appear in the paste. 相似文献
15.
J. K. Richard Weber Johan G. Abadie April D. Hixson Paul C. Nordine Gregory A. Jerman 《Journal of the American Ceramic Society》2000,83(8):1868-1872
We report formation of single- and two-phase glasses from rare-earth oxide–alumina materials. Liquids with the Y3 Al5 O12 and Er3 Al5 O12 compositions underwent a liquid–liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error. Clear, brilliant, single-phase glasses were obtained from La3 Al5 O12 , ErLaYAl5 O12 , and compositions containing ≥5 mol% La2 O3 substituted for the other rare-earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid–liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid–liquid phase transition is not observed. The results are discussed in the context of first-order liquid–liquid phase transitions (polyamorphism) and formation of single-phase glass from liquids that contain a high proportion of 4-coordinate aluminum ions. 相似文献
16.
J. K. Richard Weber Paul C. Nordine Shankar Krishnan 《Journal of the American Ceramic Society》1995,78(11):3067-3071
Values of the spectral absorption coefficient (α) of liquid aluminum oxide were determined by transmission of a pulsed dye laser beam incident on continuous-wave (CW) CO2 -laser-melted pendant drops attached to sapphire filaments. Measurements were made on molten drops of Verneuil sapphire at wavelengths of 0.450 and 0.633 μm, at ambient oxygen partial pressures from 10-10 to 1 bar in eight pure gases (Ar, CO, CO2 , H2 , H2 O, HCI, N2 and O2 ), in CO/CO2 mixtures, and in H2 /H2 O mixtures, and at a temperature of ca. 2400 K. Specimens contaminated with iron, magnesium, silicon, and tungsten were also investigated in an oxygen atmosphere. At a wavelength of 0.633 μm, the value of α was greater than 50 cm-1 under reducing or inert gas conditions. It decreased to a minimum at intermediate oxygen partial pressures of 5 × 10-5 bar in CO/CO2 mixtures and 5 × 10-3 bar in H2 /H2 O mixtures, and increased at larger oxygen partial pressures. The specimens were opaque (α > 55 cm-1 ) in hydrogen, in HCI at pressures above 0.04 bar. Specimens contaminated with 5000-10000 ppm of Fe, Mg, Si, or W were also opaque. At a wavelength of 0.45 μm the liquid aluminum oxide specimens were opaque in Ar and oxygen, and gave α= 46 cm-1 in CO2 . The dynamic response when the ambient gas was changed from CO2 to argon showed that the transmission maximum for = 0.45 μm was at p (O2 ) < 0.1 bar. 相似文献
17.
18.
J. K. Richard Weber Shankar Krishnan Collin D. Anderson Paul C. Nordine 《Journal of the American Ceramic Society》1995,78(3):583-587
The spectral extinction coefficient, k λ , and the absorption coefficient, αλ , of liquid aluminum oxide were determined from emission measurements on partially molten single-crystal sapphire filaments. Measurements were made at wavelengths from 0.385 to 0.780 μm in both argon and oxygen atmospheres and at 0.650 μm in a 10% H2 -90% N2 mixture. The values of αλ were found to vary with the time for which the specimen had been molten and achieved different steady-state values in the three processing atmospheres. A decrease in αλ with wavelength (Urbach tail) was observed from 0.385 μm to about 0.420 μm in argon and 0.490 μm in oxygen, and approximately constant values were obtained at longer wavelengths. Steady-state values of αλ at the optical pyrometer wavelength of 0.650 μm were 9 ± 2 cm−1 in argon, 41 ± 8 cm−1 in oxygen, and 14 ± 2 cm−1 in the 10% hydrogen-90% nitrogen gas mixture. 相似文献
19.
L. Vernieres-Hassimi D. Seguin M. A. Abdelghani-Idrissi N. Mouhab 《Chemical Engineering Communications》2013,200(1):70-77
This study deals with an observer built for distributed parameter systems described by nonlinear representations. This observer was applied to a tubular chemical reactor in order to estimate the maximum temperature of the reactant mixture and its position in stationary and transient regimes. This estimation uses a Luenberger observer, while MacCormack's numerical method was used for resolution of the partial differential equations. Furthermore, to take into account the nonlinearity of the system, the gain of this estimator was proposed as a function of the position along the chemical reactor. This observer requires the values of both concentration and temperature at the inlet but only of temperature at the outlet. The convergence and robustness of this estimator were experimentally tested with initialization and modeling errors. 相似文献
20.
Data Mining: A Key Contribution to E-business 总被引:5,自引:0,他引:5
Nordine Melab 《Information & Communications Technology Law》2001,10(3):309-318
Data mining consists of extracting knowledge from huge volumes of data, allowing better business decisions to be taken. In this paper, we show how data mining is integrated in the knowledge discovery process. We highlight its potential applications and the techniques that are often used to perform it. Association rule mining is presented as a case study. Furthermore, we show through an integrated architecture how data mining can contribute to e-business via the new technologies. Finally, we present some commercially-available architectures. 相似文献