| 11. |
- Aavikko, R, et al.
(författare)
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Observation of vacancy clusters in HTCVD grown SiC
- 2005
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Ingår i: Materials Science Forum, Vols. 483-485. ; , s. 469-472
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Konferensbidrag (refereegranskat)abstract
- Positron lifetime spectroscopy was used to study defects in semi-insulating (SI) silicon carbide (SiC) substrates grown by high-temperature chemical vapor deposition (HTCVD). The measured positron lifetime spectra can be decomposed into two components, of which the longer corresponds to vacancy clusters. We have carried out atomic superposition calculations to estimate the size of these clusters.
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| 12. |
- Aazh, H, et al.
(författare)
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Influence of ear canal occlusion and static pressure difference on bone conduction thresholds: Implications for mechanisms of bone conduction
- 2005
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Ingår i: International Journal of Audiology. - : Informa Healthcare. - 1499-2027 .- 1708-8186. ; 44:5, s. 302-306
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Tidskriftsartikel (refereegranskat)abstract
- The effect of air pressure change on bone conduction (BC) hearing thresholds in the occluded ear was investigated. The pump manometer system of an impedance bridge was used to change the air pressure in the ear canal of twenty-two normally hearing subjects. BC thresholds were measured with: (1) open ear; (2) the ear canal occluded with a probe tube and application of 0 daPa air pressure; and (3) the ear canal occluded with a probe tube and application of -350 daPa air pressure. Thresholds were lower in condition 2 than in condition 1, the difference decreasing from 27 dB at 2500 Hz to 4.5 dB at 2000 Hz. Thresholds were higher in condition 3 than in condition 2. The results are interpreted in terms of changes in the relative contribution of the three routes of transmission for BC sound produced by occlusion and by a static pressure difference.
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| 13. |
- Abad, Manuel David, et al.
(författare)
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Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films : Influence on the Electrical and Optical Properties
- 2011
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Ingår i: Plasma Processes and Polymers. - : Wiley. - 1612-8850 .- 1612-8869. ; 8:7, s. 579-588
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Tidskriftsartikel (refereegranskat)abstract
- The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB(2) (60: 40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiB(x)C(y)) or mixed binary (TiB(2) and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K-and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiB(x)C(y) compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiB(x)C(y) phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.
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| 14. |
- Abadei, S., et al.
(författare)
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Microwave properties of tunable capacitors basee on magnetron sputtered ferroelectric Na0.5K0.5NbO3 film on low and high resistivity silicon substrates
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 39:1-4, s. 359-366
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, small signal DC voltage dependent dielectric permittivity, loss tangent, and tuneability of magnetron sputtered epitaxial Na0.5K0.5NO3 films are studied experimentally. (100)-oriented Na0.5K0.5NbO3 films are deposited onto SiO2-buffered CMOS grade low resistivity (p = 10-20 cm) and high resistivity (p = 15-45 kcm) silicon substrates. Planar capacitors with 2 or 4 m gaps between electrodes have been fabricated on top of ferroelectric films. These devices have been characterized in the frequency range 1.0 MHz to 50 GHz at temperatures 30 - 300K. Na0.5K0.5NbO3/SiO2/Si structures on high resistivity silicon substrate exhibit C-V performances typical for Metal-Insulator- Semiconductor (MIS) capacitors. At low frequencies, f 1.0 GHz, the large tuneability and large losses are associated with the MIS structure, while at higher microwave frequencies the tuneability is mainly associated with the ferroelectric, film. At 1.0 MHz and room temperature, the tuneability of Na0.5K0.5NbO3/SiO2/Si structures more than 90%, reducing to 10-15 % at 50 GHz. The losses decrease with increasing the DC bias and frequency. A Q-factor more than 15 at 50 GHz is observed. The dielectric permittivity of the Na0.5K0.5NbO3 film is in the range 50-150 at frequencies 0.045-50 GHz. On low resistivity substrate the performance of Na0.5K0.5NbO3 films is completely screened by the high losses in silicon, and the tuneability is negligible. © 2001 Taylor and Francis.
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| 15. |
- Abbas, Ghazanfar, et al.
(författare)
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Preparation and Characterization of Nanocomposite Calcium Doped Ceria Electrolyte With Alkali Carbonates (NK-CDC) for SOFC
- 2011
-
Ingår i: Journal of Fuel Cell Science and Technology. - : ASME International. - 1550-624X .- 1551-6989. ; 8:4, s. 041013-
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Tidskriftsartikel (refereegranskat)abstract
- The entire world's challenge is to find out the renewable energy sources due to rapid depletion of fossil fuels because of their high consumption. Solid oxide fuel cells (SOFCs) are believed to be the best alternative source, which converts chemical energy into electricity without combustion. Nanostructure study is required to develop highly ionic conductive electrolytes for SOFCs. In this work, the calcium doped ceria (Ce0.8Ca0.2O1.9) coated with 20% molar ratio of two alkali carbonates (CDC-M: MCO3, where M = Na and K) electrolyte was prepared by coprecipitation method. Ni based electrode was used to fabricate the cell by dry pressing technique. The crystal structure and surface morphology were characterized by an X-ray diffractometer, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (TEM). The particle size was calculated in the range 10-20 nm by Scherer's formula and compared with SEM and TEM results. The ionic conductivity was measured by using ac electrochemical impedance spectroscopy method. The activation energy was also evaluated. The performance of the cell was measured 0.567 W/cm(2) at temperature 550 degrees C with hydrogen as a fuel.
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| 16. |
- Abbas, Muhammad, et al.
(författare)
-
Comparison of Multiplierless Implementation of Nonlinear-Phase Versus Linear-Phase FIR filters
- 2008
-
Konferensbidrag (refereegranskat)abstract
- FIR filters are often used because of their linear-phase response. However, there are certain applications where the linear-phase property is not required, such as signal energy estimation, but IIR filters can not be used due to the limitation of sample rate imposed by the recursive algorithm. In this work, we discuss multiplierless implementation of minimum order, and therefore nonlinear-phase, FIR filters and compare it to the linear-phase counterpart.
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| 17. |
- Abbas, Muhammad, et al.
(författare)
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Low-Complexity Parallel Evaluation of Powers Exploiting Bit-Level Redundancy
- 2010
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Ingår i: Conference Record of the Forty Fourth Asilomar Conference on Signals, Systems and Computers (ASILOMAR), 2010, 7-10 Nov. 2010. - Washington, DC, USA : IEEE Computer Society. - 9781424497225 ; , s. 1168-1172
-
Konferensbidrag (refereegranskat)abstract
- In this work, we investigate the problem of computing any requested set of power terms in parallel using summations trees. This problem occurs in applications like polynomial approximation, Farrow filters (polynomial evaluation part) etc. In the proposed technique, the partial product of each power term is initially computed independently. A redundancy check is then made in each and among all partial products matrices at bit level. The redundancy here relates to the fact that same three partial products may be present in more than one columns, and, hence, can be mapped to the same full adder. The proposed algorithm is tested for different sets of powers and wordlengths to exploit the sharing potential.
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| 18. |
- Abbas, Muhammad, et al.
(författare)
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On the Fixed-Point Implementation of Fractional-Delay Filters Based on the Farrow Structure
- 2013
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Ingår i: IEEE Transactions on Circuits and Systems Part 1. - : Institute of Electrical and Electronics Engineers (IEEE). - 1549-8328 .- 1558-0806. ; 60:4, s. 926-937
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the fixed-point implementation of adjustable fractional-delay filters using the Farrow structure is considered. Based on the observation that the sub-filters approximate differentiators, closed-form expressions for the L-2-norm scaling values at the outputs of each sub-filter as well as at the inputs of each delay multiplier are derived. The scaling values can then be used to derive suitable word lengths by also considering the round-off noise analysis and optimization. Different approaches are proposed to derive suitable word lengths including one based on integer linear programming, which always gives an optimal allocation. Finally, a new approach for multiplierless implementation of the sub-filters in the Farrow structure is suggested. This is shown to reduce register complexity and, for most word lengths, require less number of adders and subtracters when compared to existing approaches.
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| 19. |
- Abbas, Muhammad, et al.
(författare)
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Power Estimation of Recursive and Non-Recursive CIC Filters Implemented in Deep-Submicron Technology
- 2010
-
Ingår i: Proceedings of International Conference on Green Circuits and Systems (ICGCS), 2010, Date: 21-23 June, 2010. - : IEEE. - 9781424468775 - 9781424468768 ; , s. 221-225
-
Konferensbidrag (refereegranskat)abstract
- The power modeling of different realizations of cascaded integrator-comb (CIC) decimation filters has been a subject of several recent works. In this work we have extended these with modeling of leakage power, which is an important factor since the input sample rate may differ several orders of magnitude. Furthermore, we have pointed out the importance of the input wordlength on the comparison of recursive and nonrecursive implementations.
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| 20. |
- Abbas, Muhammad, et al.
(författare)
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Switching Activity Estimation of CIC Filter Integrators
- 2010
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Ingår i: Proceedings of Asia Pacific Conference on Postgraduate Research in Microelectronics and Electronics (PrimeAsia), 2010, Date:22-24 Sept. 2010. - : IEEE. - 9781424467365 - 9781424467358 ; , s. 21-24
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Konferensbidrag (refereegranskat)abstract
- In this work, a method for estimation of the switching activity in integrators is presented. To achieve low power, it is always necessary to develop accurate and efficient methods to estimate the switching activity. The switching activities are then used to estimate the power consumption. In our work, the switching activity is first estimated for the general purpose integrators and then it is extended for the estimation of switching activity in cascaded integrators in CIC filters.
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