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| 4. |
- Zhu, H. Y., et al.
(författare)
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Localization of current dipoles in a realistic head shape model by a magnetoencephalogram-multiple signal classification algorithm
- 2003
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Ingår i: Wuli xuebao. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 52:7, s. 1812-1817
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Tidskriftsartikel (refereegranskat)abstract
- It has been proved that the magnetoencephalogram-multiple signal classification algorithm has many advantages over the general global optimization methods in localizing current dipoles in a spherically symmetrical conductor head model. Making use of this method, we can tell the total number of current dipoles conveniently and localize those dipoles one by one in a shorter time, simply by calculating generalized eigenvalues of a two- or three-dimensional matrix. In this paper, this method is used to localize the current dipoles in a realistic head shap e model. Numerical simulation demonstrates that this algorithm is effective and has great advantages in the localization of multiple dipoles.
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| 6. |
- Dubrovinsky, LS, et al.
(författare)
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Pressure-induced transformations of cristobalite
- 2001
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 333:3-4, s. 264-270
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Tidskriftsartikel (refereegranskat)abstract
- X-ray in situ studies in electrically and laser-heated diamond anvil cells (DACs) at pressures over 80 cpa and temperatures above 2500 K were used to determine stable silica phase at extreme conditions. We demonstrate that so far unidentified phases obtai
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- Guo, X. W., et al.
(författare)
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Effects of SiO2/Al2O3, MgO modification and hydrothermal treatment on the catalytic activity of HZSM-5 zeolites in the methylation of 4-methylbiphenyl with methanol
- 2004
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 261:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to study the effects Of SiO2/Al2O3 of HZSM-5, MgO modification and hydrothermal treatment on methylation of 4-methylbiphenyl (4-MBP) with methanol under fixed-bed down-flow conditions. The results show that, with an increase in the SiO2/Al2O3 of HZSM-5 (from 50 to 150, molar ratio), the selectivity to 4,4'-dimethylbiphenyl (4,4'-DMBP) increases from 25 to 79%. MgO modification also increases the selectivity to 4,4'-DMBP, but leads as well to low catalyst activity and rapid deactivation. Hydrothermal treatment not only increases the selectivity, but also improves the stability. When CBV1502 (SiO2/Al2O3 = 150) catalyst was hydrothermally treated at 500degreesC, the selectivity to 4,4'-DMBP increased to 85%. The selectivity to 4,4'-DMBP was further improved to about 90% by the increasing in the amount of mesitylene in the feed as solvent.
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| 8. |
- Guo, X. W., et al.
(författare)
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Methylation of 4-methylbiphenyl with methanol over metal oxide-modified HZSM-5 zeolite catalysts
- 2003
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Ingår i: Cuihuà xuébào. - 0253-9837 .- 1872-2067. ; 24:5, s. 333-337
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Tidskriftsartikel (refereegranskat)abstract
- A series of HZSM-5 zeolite catalysts modifed with metal oxides (MgO, CaO, SrO, BaO, ZnO, La2O3 and CeO2) were prepared by impregnation method and characterized by XRD, TPD and N-2-adsorption. Methylation of 4-methylbiphenyl (4-MBP) with methanol to 4,4'-dimethylbiphenyl (4,4'-DMBP) was carried out over the prepared catalysts under fixed-bed down-flow conditions. The results showed that the MgO-modified HZSM-5 can significantly improve the selectivity for target product 4,4'-DMBP (up to 80 % vs only 13 % over the parent HZSM-5). The effects of metal oxides on 4,4'-DMBP selectivity are arranged in the following order: MgO>SrOapproximate toZnOapproximate toCaOapproximate toLa(2)O(3)>BaO>CeO2. The effects of MgO contents, precursor-salt types, and loading methods were further investigated, and the results revealed that during 4-MBP conversion, proper MgO loading (5.6 %) can be more effective, and the ion-exchange methed is much better than the impregnation method. However, it is difficult to get higher metal oxide loading by using the ion-exchange method. The high selectivity over HZSM-5 modified with MgO largely results from the depression of 4,4-DMBP second reactions such as isomerization, dealkylation and alkylation, as demonstrated by the reaction of 4,4'-DMBP as reactant over MgO/ZSM-5 catalyst and HZSM-5 zeolite.
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| 9. |
- Guo, X. W., et al.
(författare)
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Shape-selective methylation of 4-methylbiphenyl to 4,4 '-dimethylbiphenyl over zeolite HZSM-5 modified with metal oxides of MgO, CaO, SrO, BaO, and ZnO
- 2003
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Ingår i: Catalysis Letters. - 1011-372X .- 1572-879X. ; 87:02-jan, s. 25-29
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Tidskriftsartikel (refereegranskat)abstract
- A series of ZSM-5 samples modified with metal oxides MO(M = Mg, Ca, Sr, Ba and Zn) were employed for the alkylation of 4-methylbiphenyl (4-MBP) with methanol to 4,4'-dimethylbiphenyl (4,4'-DMBP) under fixed-bed down-flow conditions. The methylation results showed that the use of basic metal oxides can effectively enhance the selectivity to the target product 4,4'-DMBP. MgO is the most effective modifier among the metal oxides used and it can improve selectivity to 4,4'-DMBP up to 80% as compared to only 13% over the parent zeolite HZSM-5. The modi. cation effectiveness of metal oxides on 4,4'-DMBP selectivity can be arranged in the order MgO> SrO similar to ZnO similar to CaO> BaO. The optimization of MgO modi. cation through the content, salt types and loading methods revealed that proper MgO loading (5.6 wt%) can be more effective, and the impregnation method is much better than ion exchange. The correlation of physicochemical properties (TPD, TGA, chemical analysis and chemical adsorption, etc.) of the modified HZSM-5 with the catalytic data showed that the high selectivity over ZSM-5 modified with MgO largely results from the effective suppression of 4,4'-DMBP secondary reactions such as isomerization, dealkylation and alkylation.
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| 15. |
- Peng, Hong, 1970-
(författare)
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Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process.The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.
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| 16. |
- Shen, H, et al.
(författare)
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Selective flotation separation of plastics by chemical conditioning with methyl cellulose
- 2002
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Ingår i: Resources, Conservation and Recycling. - 0921-3449 .- 1879-0658. ; 35, s. 229-241
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Tidskriftsartikel (refereegranskat)abstract
- The floatability of seven plastics (POM, PVC, PET, PMMA, PC, PS and ABS) in the presence of methyl cellulose (MC) and separation of plastics mixtures were investigated in this paper. It was found that the seven plastics can be separated into three groups by using the wetting agent MC. Group one includes POM and PVC. They are depressed at very low MC concentrations. Group two, including PET, PMMA and PC, has an intermediate floatability. Group three (ABS and PS) has a high floatability. They are almost not depressed within the given MC concentration range. In order to understand the mechanism of selective flotation of plastics and the chemical conditioning process, surface chemical factors, such as wettability of plastics and surface tension of flotation medium, and gravity factors, such as particle density and shape, were studied. It was found that the depressing effect of MC on plastics is ascribed mainly to its adsorption on the plastics surfaces. The MC molecules absorbed on plastics expose some of their polar groups oriented towards the aqueous phase, hence making the plastics surfaces hydrophilic. In addition, flotation selectivity for the plastics is dominated not only by wettability of plastics, but also by particle size, density and shape
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| 17. |
- Shen, Huiting, et al.
(författare)
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Selective flotation separation of plastics by particle control
- 2001
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Ingår i: Resources, Conservation and Recycling. - 0921-3449 .- 1879-0658. ; 33:1, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- A study on the control of particle size distribution (PSD) of the ground carbonate product in stirred media mills (wet Drais stirred bead mill and dry Sala Agitated Mill) is presented in this paper. The results indicated that the slope of product size distribution can be controlled by altering some operating parameters, such as size of grinding media and tip or peripheral speed. The profile of product size distribution from the stirred media mills was found to follow most closely the Rosin-Rammler-Bennett (RRB) model.
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| 19. |
- Shen, J. -Q, et al.
(författare)
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How to realize a negative refractive index material at the atomic level in an optical frequency range
- 2004
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Ingår i: JZUS-A - Journal of Zhejiang University. Science. - : Zhejiang University Press. - 1009-3095 .- 1673-565X .- 1862-1775. ; 5:11, s. 1322-1326
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Tidskriftsartikel (refereegranskat)abstract
- The theoretical mechanism for realizing a negative refractive index material in an optical frequency range with an atomic gas system of electromagnetically induced transparency (BIT) is studied. It is shown that under certain conditions such a dense gas can exhibit simultaneously negative permittivity and negative permeability, and negligibly small loss.
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| 23. |
- Zheng, Li-Rong, et al.
(författare)
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Design and implementation of system-on-package for radio and mixed-signal applications
- 2004
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Ingår i: PROCEEDINGS OF THE SIXTH IEEE CPMT CONFERENCE ON HIGH DENSITY MICROSYSTEM DESIGN AND PACKAGING AND COMPONENT FAILURE ANALYSIS (HDP'04). - NEW YORK : IEEE. - 0780386205 ; , s. 97-104
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Konferensbidrag (refereegranskat)abstract
- Emerging wireless applications for logistics, intelligent home networks, smart dusts, wireless body area networks (WBAN) will need integration and fusion of a diversity of technologies, which may include digital CMOS circuits, analog/RF circuits, sensors/MEMS, embedded software and memories, antenna, displays, polymer, packaging and interconnections, new materials and new integration process. System-on-package (SoP) is considered as a promising solution for the fundamental integration platform for such applications. In this paper, we show how SoP technology can address the integration platform for these applications and how this can be done in a better way than system-on-chip integration. We first demonstrate the integration process of, SoP in liquid-crystal polymer materials. We see that liquid-crystal-polymer is a promising material for low cost RF SoP. We then demonstrate some design examples. The first one is an integrated 5GHz RF receiver front-end in liquid crystal polymer. Due to high quality of passive components in SoP, superior RF performance is found in this module. In the second example, we address several critical design issues for on-chip versus off-chip passives in a multi-band multi-standard radio for beyond 3G applications. We find that not only RF performance can be improved. Cost benefits are also obvious for such a complex radio. Chip-package co-design for smart parasitic absorption is demonstrated through an RF module for an ultrawide band radio in gigabit wireless. Concept of a SoP pacemaker in a WBAN is shown. Finally, we discuss some system level integration issues and we show how a system can be smartly partitioned for SoP so that we can obtain an optimal total solution for low-cost and good-performance wireless integration.
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