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991.
M.K. Sharma Matthias Voelskow Ratnamala Chatterjee 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(10):1631-1636
We report thermal annealing and 100 MeV Si8+ swift heavy ion irradiation effects on the structural and magnetic properties of Ni-implanted HfO2 thin films. At low Ni doping concentration (∼1%), HfO2 thin films show ferromagnetic behavior. We clearly demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization vs. temperature data. Rutherford backscattering spectrometry is used to estimate the film thickness and to establish that Ni-ions are placed in the HfO2 matrix. By comparing the results for the annealed and swift heavy ion irradiated samples, it is concluded that the enhancement in magnetic signal is closely related to the dispersion/diffusion of implanted Ni and defect creation such as oxygen vacancies. The results of magnetic force microscopy supported the observation of room temperature ferromagnetism in Ni-implanted HfO2 films. 相似文献
992.
C. Sada N. Argiolas M.V. Ciampolillo P. Mazzoldi D.K. Avastshi 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(19):2937-2941
Iron ions were implanted with a total fluence of 6 × 1017 ions/m2 into lithium niobate crystals by way of a sequential implantation at different energies of 95, 100 and 105 MeV respectively through an energy retarder Fe foil to get a uniform Fe doping of about few microns from the surface. The implanted crystals were then annealed in air in the range 200-400 °C for different durations to promote the crystalline quality that was damaged by implantation. In order to understand the basic phenomena underlying the implantation process, compositional in-depth profiles obtained by the secondary ion mass spectrometry were correlated to the structural properties of the implanted region measured by the high resolution X-ray diffraction depending on the process parameters. The optimised preparation conditions are outlined in order to recover the crystalline quality, essential for integrated photorefractive applications. 相似文献
993.
Improvement of a mathematical model for low-pressure superheated steam drying of a biomaterial 总被引:2,自引:0,他引:2
Sommart Kittiworrawatt 《Chemical engineering science》2009,64(11):2644-2650
Although there currently are a number of works reporting experimental study of low-pressure superheated steam drying (LPSSD), which has proved to be an attractive alternative to drying heat-sensitive biomaterials, there are a very few works reporting the development of a mathematical model to predict the evolutions of product moisture content and temperature during LPSSD. Moreover, the predictions of those few developed models are still not satisfactory because, most of the time, the models do not include the effect of initial steam condensation; the use of mass transfer boundary condition is, in some cases, also not quite realistic. The aim of the present study was thus to develop a more realistic liquid diffusion based model to simulate the transport of heat and mass within a product undergoing LPSSD. The effect of initial steam condensation, in terms of film condensation, was included and a more realistic mass transfer boundary condition, in terms of the vapor pressure gradient and the physical condition at the drying surface, was applied in the newly developed model. The effect of the product shrinkage was also included directly in the model. The predictability of the model was tested against the available experimental data. The model with initial steam condensation was found to be able to predict the center temperature and average moisture content of the product undergoing LPSSD very well. However, at higher temperatures and lower pressures the product core temperature was still under predicted. 相似文献
994.
A qualitative computational study of mass transfer in upward bubble train flow through square and rectangular mini-channels 总被引:1,自引:0,他引:1
In this paper we present a new method for numerical simulation of conjugate mass transfer of a dilute species with resistance in both phases and an arbitrary equilibrium distribution coefficient. The method is based on the volume-of-fluid technique and accounts for the concentration jump at the interface by transforming the discontinuous physical concentration field into a continuous numerical one. The method is validated by several test problems and is used to investigate the mass transfer in upward bubble train flow within square and rectangular channels. Computations are performed for a single flow unit cell and a channel hydraulic diameter of 2 mm. The simulations consider the transfer of a dilute species from the dispersed gas into the continuous liquid phase. Optionally, the mass transfer is accompanied by a first-order homogeneous chemical reaction in the liquid phase or a first-order heterogeneous reaction at the channel walls. The results of this numerical study are qualitative in nature. First, because periodic boundary conditions in axial direction are not only used for the velocity field but also for the concentration field and second, because the species diffusivity in the liquid phase is arbitrarily increased so that the liquid phase Schmidt number is 0.8 and the thickness of the concentration and momentum boundary layer is similar. Two different equilibrium distribution coefficients are considered, one where the mass transfer is from high to low concentration, and one where it is vice versa. The numerical study focuses on the influence of the unit cell length, liquid slug length and channel aspect ratio on mass transfer. It is found that for the exposure times investigated the liquid film between the bubble and the wall is saturated and the mass transfer occurs by the major part through the bubble front and rear so that short unit cells are more efficient for mass transfer. Similar observations are made for the homogeneous reaction and for the heterogeneous reaction when the reaction is slow. In case of a fast heterogeneous reaction and when the main resistance to mass transfer is in the gas phase, it appears that for square channels long unit cells are more efficient, while large aspect ratio rectangular channels are more efficient than square channels, suggesting that for these conditions they might be more appropriate for use in monolithic catalysts. 相似文献
995.
A finite‐volume based mathematical model has been developed for modeling hydrogen production by a tubular cell of solid oxide steam electrolyzer (SOSE), taking into account the electrochemical reactions and heat/mass transfer effects. The model is composed of three systems of nonlinear equations that govern the electric current density, energy balance in the solid SOSE cell, and energy balance in the flow of steam and hydrogen. The simulated hydrogen production rate proportional to the applied potential agreed well with the experimental measurements published in the literature. The intermediate modeling results indicated that the activation effect dominate the overall cell overpotential due to low exchange current density through the SOSE cell electrodes. Thus, higher electrode activity was identified as an important factor for enhancing cell performance. Parametric modeling analyses were conducted to gain better understanding of the SOSE characteristics. It was found that low‐temperature gas intake would cause a high temperature gradient in the tubular cell material at the inlet, possibly leading to a thermal expansion problem. The risk could be reduced by increasing the gas inlet temperature. It was also found that energy‐efficient SOSE hydrogen production can be achieved by reducing the hydrogen content in the steam intake and regulating the steam intake flow rate to an optimum that minimizes the overall electrical and thermal requirements. More parametric modeling results are discussed in this paper. The tubular SOSE cell model developed in this study can easily be expanded to accomplish tubular SOSE stack analysis for comprehensive system design optimization. 相似文献
996.
997.
Nare Alpheus Mautjana Donq Wen Looi John R. Eyler Anna Brajter-Toth 《Electrochimica acta》2009,55(1):52-58
A cone-shaped MS inlet and on-line electrochemistry (EC) were used to enhance the ionization efficiency in electrospray ionization mass spectrometry (ESI MS) of purine bases. A pathway of positive ion mode ESI may involve oxidation of purine bases, guanine, adenine, xanthine and hypoxanthine, by 1e−, 1H+ processes. The electrospray process generates dimers of purine bases that are detected in ESI MS as protonated ions, except for xanthine, for which a protonated radical dimer is detected. Thus electrochemical oxidation of purine bases during ESI may generate reactive radicals that can subsequently dimerize. Dimer formation is facilitated in ESI MS when the carrier solution pH is high. The positive ion mode ESI MS ionization is consistent with the reactivity of the bases toward oxidation. Furthermore, the formation of the protonated ions, and Na+ and K+ adducts of the bases, expected in positive ion ESI MS, are observed. In addition, unusual H-bonding of purine bases guanine and xanthine is confirmed by ESI MS. Application of low EC voltage to the on-line EC cell in EC/ESI MS improves the sensitivity and correlates with the decrease of the intensity of the dimers, possibly as a result of their further oxidation. 相似文献
998.
S. Martemianov Yu. K. Evdokimov X. Adolphe 《Journal of Applied Electrochemistry》2007,37(11):1321-1328
Electrodiffusion diagnostics are widely used for measurement of local wall shear stresses in liquid flows. At present, this
method requires special electrolytes, so the applications are limited to laboratory conditions. Another problem concerns the
dependence of the limiting diffusion current on the electrode surface state and on the bulk concentration of the electroactive
species. In this paper, it is shown that the delay time between generation of the electroactive species and their detection
on the downstream electrode, is directly related to the local wall shear stress value. Thus, the measurements of the delay-time
open a new way for the study of near-wall hydrodynamics. This new method has been confirmed experimentally using an electrolyte
containing the conventional hexacyanoferrate(III/II) redox couple, as well as with the chlorine (chloric(I))/chloride couple
in an electrolyte similar to seawater. 相似文献
999.
Yoshihito Okubo 《Chemical engineering science》2008,63(16):4070-4077
Enhancement of mass transfer between two phases and improvement of extraction efficiency are expected if features of micro spaces are adopted for a liquid-liquid two-phase process. In this work, three extraction operations, contact flow in a Y-shaped microchannel, segmented flow and emulsification, have been investigated. Extraction using segmented flow is dependent on mass transfer by molecular diffusion and its rate is enhanced by the internal circulation flow generated inside slugs. The extraction rate can be controlled precisely by adjusting operational parameters such as the flow rate and the flow rate ratio. Liquid-liquid two-phase separation can be achieved instantly. Thus, continuous operation of a process involving liquid-liquid extraction and then two-phase separation is expected to be possible. For extraction based on emulsification, rapid extraction is made possible owing to significant increase in the interfacial area. Though extraction itself is rapid, liquid-liquid separation may take a long time because coalescence of stable emulsions requires time. It is suitable for systems strongly requiring only rapid extraction. Advanced reaction-separation systems can be developed by combining the extraction operations, making full use of the characteristics of segmented flow or emulsification and the reaction. 相似文献
1000.
The utility of mass spectrometry as a technique for the characterisation of polymeric formulations is discussed in general terms. The use of thermal techniques in which sufficient energy is given to the system to liberate volatile components of the formulation and, in some cases, to induce small amounts of polymer degradation, is described. Results obtained using this technique for a variety of polymer systems are discussed and the advantages of using this approach outlined. Recent developments in field desorption-mass spectrometry for the direct characterisation of modern polymer systems are discussed and some early results presented. 相似文献