| 1. |
- Cijvat, Pieternella, et al.
(författare)
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A fully integrated 2.45 GHz 0.25 mu m CMOS power amplifier
- 2003
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Ingår i: Proceedings of the 10th IEEE International Conference on Electronics, Circuits and Systems, ICECS 2003.. - : IEEE Press. - 0780381637 ; , s. 1094-1097
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Konferensbidrag (refereegranskat)abstract
- A fully integrated differential class-AB power amplifier has been designed in a 0.25 um CMOS technology. It is intended for medium output power ranges such as Bluetooth class 1, and has an operating frequency of 2.45 GHz. By using two parallel output stages that can be switched on or off, a high efficiency can be achieved for both high and low output power levels. The simulated maximum output power is 22.7 dBm, while the maximum power-added efficiency is 22%.
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| 2. |
- Johannesson, Björn
(författare)
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A theoretical model describing diffusion of a mixture of different types of ions in pore solution of concrete coupled to moisture transport
- 2003
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846 .- 1873-3948. ; 33:4, s. 481-488
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model is established for diffusion of different types of ions in pore solution of concrete and the coupling to moisture flow and moisture content. Mass exchanges between ions in pore solution and solid hydration products in the concrete are also considered. The basic concepts behind the so-called mixture theory are used. The development of a mass balance principle for ions in pore solution is established. This principle accounts for (i) diffusion caused by concentration gradients of ions and gradients of the so-called internal electrical potential, (ii) convection, i.e. the effect on the motion of ions due to a motion of the pore solution in concrete, (iii) the effect on the concentration due to changes in the moisture content, and finally, (iv) the effect of mass exchange of ions between solid hydration products and the bore solution phase. The model is general in the sense that all different types of ions appearing in pore solution phase can-be included and computed for during quite arbitrary boundary conditions.
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| 3. |
- Johannesson, Björn, et al.
(författare)
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Microstructural changes caused by carbonation of cement mortar
- 2001
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Ingår i: Cement and Concrete Research. - 0008-8846 .- 1873-3948. ; 31:6, s. 925-931
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Tidskriftsartikel (refereegranskat)abstract
- The change of specific surface area and pore size distribution due to carbonation of an ordinary Portland cement mortar is investigated. The adsorption of water vapor on noncarbonated and well-carbonated cement mortar is measured in order to evaluate the difference in specific surface area for the two samples using the BET theory. From the measured desorption the pore size distribution is calculated using the Kelvin formula. A sorption balance is used to measure the sorption characteristics for the two studied sample qualities. In this method dry and saturated air are mixed in desired proportion in a closed system. One of the benefits of the method is that the samples not are exposed to carbon dioxide during testing, i.e., undesired effects caused by carbonation on the sorption can be eliminated. The specific surface area for a noncarbonated sample was calculated, using the measured adsorption data, to be 8% higher than for the well-carbonated sample. The difference in pore size distributions was more marked than the difference in specific surface area for the two samples. The well-carbonated mortar had about twice as much volume attributed to small pores as the noncarbonated cement mortar.
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| 4. |
- Johannesson, Björn
(författare)
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Restrictions on the rate of absorption when evaluating sorption isotherms obtained using a micro-calorimetric technique
- 2001
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Ingår i: Journal of Building Physics. - 1744-2583. ; 25:2, s. 85-100
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Tidskriftsartikel (refereegranskat)abstract
- One interestingway of measuring sorption isotherms and heats of sorption is the newly developed micro-calorimetric method. It turns out, however, that the adsorption kinetics must be proven to be rapid enough to fulfill the assumptions behind the theory for the determination of the isotherm to be valid. Here, the lower limit of the accepted rate of adsorption will be analyzed by making calculations of the diffusion behavior in the calorimetric vessel. The evaluation of the adsorption isotherms is based on assumptions of a quasi-static nature. If the adsorption kinetics are slow the behavior in the calorimeter will turn to a more or less transient process. When the heat of adsorption is of interest and the sorption isotherm and kinetics of sorption can be determined by other methods, compensation for the transient effects can be made.
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| 5. |
- Johannesson, Björn, et al.
(författare)
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Test of four different experimental methods to determine sorption isotherms
- 2002
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Ingår i: Journal of Materials in Civil Engineering. - 0899-1561 .- 1943-5533. ; 14:6, s. 471-477
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Tidskriftsartikel (refereegranskat)abstract
- One important property of materials is their moisture fixation capacity, i.e., their ability to hold moisture at different relative humidities. The sorption isotherm is one of the main input data in moisture diffusion models, and it can also be used to evaluate properties of the microstructure. We have used four different methods to measure the sorption isotherm of sandstone and porous glass. The first method was to equilibrate samples over saturated salt solutions. The second was a sorption balance in which small material samples were weighed as they were exposed to different relative humidities. The third method was the pressure plate extractor, in which a totally wet sample was equilibrated at various overpressures, corresponding to certain relative humidities. The fourth method was a newly developed microcalorimetric technique to measure sorption isotherms. Despite the different natures of the methods, a satisfying agreement was found. (10 refs.)
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| 6. |
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| 7. |
- Johannesson, Björn
(författare)
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Transport and Sorption Phenomena in Concrete and Other Porous Media
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis is mainly focused on transport processes involved in service life predictions of concrete. Two papers and three reports deal with ion transport in pore solution of concrete. One paper and one report deals with moisture transport in concrete and the remaining papers and reports deal with absorption and physical properties related to adsorption for different materials. The fourteen contributions have the following contents:RI:1, Diffusion of a mixture of positively and negatively charged ions in pore solution of concrete is studied. Binding of dissolved ions in pore solution and leaching of ions from solid components into pore solution are included in the model. The material constants in the developed model are chosen to give the best match of simulation to experimental data. A finite element scheme is developed solving the governing coupled constituent equations.RI:2, The models established in RI:1 and P:1 are used to study the effect of different cements and pozzolans on chloride ingress into concrete.RI:3, The models established in RI:1 and P:1 are used to study the effect of curing conditions on chloride ingress in concrete. A drying period before exposure to chlorides is shown to decrease the penetration.RII:1, Capillary suction is studied using a Newtonian fluid assumption together with a momentum source term reflecting the influence of the pore walls on the capillary sucked fluid.RIII:1, The heat of adsorption of different molecule layers on dry surfaces is investigated using a calorimetric technique. Different types of BET-equations were used to predict the distribution of adsorbate among different discrete adsorbed layers. The classical way of calculating the adsorption heat and the measured values differed with about a factor of 2.5.RIII:2, The effect of different constant temperatures on the absorption isotherms and the heat of adsorption of first and second layer molecules on porous glass are investigated.P:1, Diffusion of a mixture of positively and negatively charged ions in water is studied. An electrical potential is included in the model, which makes it possible to study diffusion caused by internal electrical forces in a mixture of different types of ions.P:2, The paper presents a model for combined chloride ion diffusion and chloride ion convection caused by capillary suction.P:3, A numerical approach capable of solving diffusion-convection equations is discussed. The so-called Petrov-Galerkin weighting is shown to be a reliable method for the diffusion problem studied.P:4, Four different methods of measuring sorption isotherms are studied.P:5, The limit of the use of a quasi-static calorimetric technique measuring absorption is investigated theoretically by simulating the diffusion behavior in the instrument. Results shows that the material constant related to the sorption kinetics must exceed a certain value.P:6, Measurements of moisture storage capacity with sorption balance and pressure extractor are described in this paper.P:7, In this paper micro-structural changes caused by carbonation of cement mortar are discussed.P:8, Water vapor diffusion and transient condensation in cement mortar are treated in this paper.
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| 8. |
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| 9. |
- Moradi, Farokhbag, et al.
(författare)
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Deactivation of oxidation and SCR catalysts used in flue gas cleaning by exposure to aerosols of high- and low melting point salts, potassium salts and zinc chloride
- 2003
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier. - 0926-3373 .- 1873-3883. ; 46:1, s. 65-76
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Tidskriftsartikel (refereegranskat)abstract
- For the purpose of this deactivation study, Pt- and vanadia supported catalysts were used. The catalysts have been exposed to aerosol particles of inorganic salts, with high- or low melting points. The average diameter of the generated salt particle was kept constant at around 70 nm. The aerosol particle penetration depth for the samples exposed to potassium salt, was 1 μm as measured by scanning electron microscopy (SEM). The corresponding depth for zinc chloride salt (ZnCl2) was 5 μm. In order to validate the dependency of the catalytic decay rate to exposure temperature, Pt/wire-mesh catalyst was treated with potassium chloride at two temperatures, namely 300 and 500 °C. Pt/supported catalyst was also treated with ZnCl2 salt at 190 and 300 °C. The extent of decay was tested in the oxidation of CO for particle treated Pt/wire-mesh samples. The degree of the deactivation for the aerosol particle deactivated vanadia supported catalysts were also examined in the reduction of NOx. When the Pt/wire-mesh catalyst have been exposed to the poisons aerosol particles at higher temperature lead to the strongest deactivation in the CO oxidation. The Pt-supported catalysts that were treated with aerosol particles from potassium carbonate and potassium sulphate revealed a minor deactivation in the CO oxidation reaction. No significant deactivation was observed for the salt treated vanadia supported monolith samples used in selective catalytic reduction (SCR). A slight pronunced deactivation effect appeared when the vanadia supported wire-mesh catalysts were salt treated. Generally, the obtained results in this study do not indicate any correlation between the salt melting point and the degree of catalytic decay. The obtained results indicate that the exposure temperature during the deactivation procedure is the most critical parameter. Also, the higher the exposing temperature the stronger deactivated sample is produced.
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| 10. |
- Wahlberg, Patrik, et al.
(författare)
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Approximate time-variable coherence analysis of multichannel signals
- 2002
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Ingår i: Multidimensional Systems and Signal Processing. - Norwell : Kluwer Academic Publishers. - 0923-6082 .- 1573-0824. ; 13:3, s. 237-264
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Tidskriftsartikel (refereegranskat)abstract
- We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG signals. These signals are non-stationary which makes time-invariant filtering unsuitable. The new method assumes a signal model and performs denoising by filtering the signal of each channel using a time-variable filter which is an estimate of the Wiener filter. The approximate Wiener filters are obtained using the time-frequency coherence functions between all channel pairs, and a fix-point algorithm. We estimate the coherence functions using the multiple window method, after which the fix-point algorithm is applied. Simulations indicate that this method improves upon its restriction to assumed stationary signals for realistically non-stationary data, in terms of mean square error, and we show that it can also be used for time-frequency representation of noisy multichannel signals. The method was applied to two epileptic seizure onset signals, and it turned out that the most informative output of the method are the filters themselves studied in the time-frequency domain. They seem to reveal hidden features of the epileptic signal which are otherwise invisible. This algorithm can be used as preprocessing for seizure onset EEG signals prior to time-frequency representation and manual or algorithmic pattern classification.
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