| 1. |
- Molisch, Andreas, et al.
(författare)
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A low-cost time-hopping impulse radio system for high data rate transmission
- 2005
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Ingår i: Eurasip Journal on Applied Signal Processing. - 1110-8657. ; :3, s. 397-412
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient, low-cost implementation of time-hopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for high-data-rate, short-range communications. Key features are (i) all-baseband implementation that obviates the need for passband components, (ii) symbol-rate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast acquisition due to novel search algorithms, and (iv) spectral shaping that can be adapted to accommodate different spectrum regulations and interference environments. Computer simulations show that this system can provide 110 Mbps at 7–10 m distance, as well as higher data rates at shorter distances under FCC emissions limits. Due to the spreading concept of time-hopping impulse radio, the system can sustain multiple simultaneous users, and can suppress narrowband interference effectively.
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| 2. |
- Schaap, M., et al.
(författare)
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Standardized evaluation methodology and reference database for evaluating coronary artery centerline extraction algorithms
- 2009
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Ingår i: Medical Image Analysis. - : Elsevier. - 1361-8415 .- 1361-8423. ; 13:5, s. 701-714
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Tidskriftsartikel (refereegranskat)abstract
- Efficiently obtaining a reliable coronary artery centerline from computed tomography angiography data is relevant in clinical practice. Whereas numerous methods have been presented for this purpose, up to now no standardized evaluation methodology has been published to reliably evaluate and compare the performance of the existing or newly developed coronary artery centerline extraction algorithms. This paper describes a standardized evaluation methodology and reference database for the quantitative evaluation of coronary artery centerline extraction algorithms. The contribution of this work is fourfold: (1) a method is described to create a consensus centerline with multiple observers, (2) well-defined measures are presented for the evaluation of coronary artery centerline extraction algorithms, (3) a database containing 32 cardiac CTA datasets with corresponding reference standard is described and made available, and (4) 13 coronary artery centerline extraction algorithms, implemented by different research groups, are quantitatively evaluated and compared. The presented evaluation framework is made available to the medical imaging community for benchmarking existing or newly developed coronary centerline extraction algorithms.
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| 3. |
- Chen, X. Y., et al.
(författare)
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Application of weak ferromagnetic BiFeO3 films as the photoelectrode material under visible-light irradiation
- 2007
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 91:2, s. 022114-
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Tidskriftsartikel (refereegranskat)abstract
- BiFeO3 films prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates were studied as photoelectrode for water splitting. Under visible-light irradiation, the photocurrent intensity of the polycrystalline BiFeO3 film was found to double that of the amorphous one in a three-electrode cell. The incident photon to current conversion efficiency for the polycrystalline BiFeO3 electrode was approximately 16% at 350 nm and 7% at 530 nm at 1.5 V (versus saturated calomel electrode). The ferromagnetism of the amorphous BiFeO3 film was an order of magnitude weaker than that of the polycrystalline one, supporting the "size effect" explanation for magnetic origin. (C) 2007 American Institute of Physics.
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| 4. |
- Yang, J. H., et al.
(författare)
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Effects of AlN layer and impurities on optical properties of GaN
- 2005
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Ingår i: Chemical Research in Chinese Universities. - 1005-9040. ; 21:1, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- The effects of the incorporated oxygen and the different buffer layers on the optical properties and surface morphology of GaN were studied. The results show that the decrease of the concentration of the incorporated oxygen has no effect on the surface morphology, but improves the optical properties. While the introduction of the AlN buffer layer makes not only the surface morphology but also the optical properties improve. Both the oxygen contamination from the nitrogen source and the resulted morphology are directly related to the line width of the low-temperature photoluminescence (PL) spectra.
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| 5. |
- Steck, T., et al.
(författare)
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Bias determination and precision validation of ozone profiles from MIPAS-Envisat retrieved with the IMK-IAA processor
- 2007
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 7:13, s. 3639-3662
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Tidskriftsartikel (refereegranskat)abstract
- This paper characterizes vertical ozone profiles retrieved with the IMK-IAA (Institute for Meteorology and Climate Research, Karlsruhe – Instituto de Astrofisica de Andalucia) science-oriented processor from high spectral resolution data (until March 2004) measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the environmental satellite Envisat. Bias determination and precision validation is performed on the basis of correlative measurements by ground-based lidars, Fourier transform infrared spectrometers, and microwave radiometers as well as balloon-borne ozonesondes, the balloon-borne version of MIPAS, and two satellite instruments (Halogen Occultation Experiment and Polar Ozone and Aerosol Measurement III). Percentage mean differences between MIPAS and the comparison instruments for stratospheric ozone are generally within ±10%. The precision in this altitude region is estimated at values between 5 and 10% which gives an accuracy of 15 to 20%. Below 18 km, the spread of the percentage mean differences is larger and the precision degrades to values of more than 20% depending on altitude and latitude. The main reason for the degraded precision at low altitudes is attributed to undetected thin clouds which affect MIPAS retrievals, and to the influence of uncertainties in the water vapor concentration.
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| 6. |
- Tang, C A, et al.
(författare)
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Fracture spacing in layered materials and pattern transition from parallel to polygonal fractures
- 2006
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 73:5, s. 056120-28
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Tidskriftsartikel (refereegranskat)abstract
- We perform three-dimensional simulations of fracture growth in a three-layered plate model with an embedded heterogeneous layer under horizontal biaxial stretch (representing stretch from directional to isotropic) by the finite element approach. The fractures develop under a quasistatical, slowly increasing biaxial strain. The material inhomogeneities are accounted for by assigning each element a failure threshold that is defined by a given statistical distribution. A universal scale law of fracture spacing to biaxial strain in terms of principal stress ratio is well demonstrated in a three-dimensional fashion. The numerically obtained fracture patterns show a continuous pattern transition from parallel fractures, laddering fracture to polygonal fractures, which depends strongly on the far-field loading conditions in terms of principal stress ratio ......
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| 7. |
- Zhang, Renyi Y, et al.
(författare)
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Remarkable variability in morphology, hygroscopicity and optical properties of soot aerosols during internal mixing in the atmosphere.
- 2008
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 105, s. 10291-10296
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric effects of soot aerosols include interference with radiative transfer, visibility impairment, and alteration of cloud formation and are highly sensitive to the manner by which soot is internally mixed with other aerosol constituents. We present experimental studies to show that soot particles acquire a large mass fraction of sulfuric acid during atmospheric aging, considerably altering their properties. Soot particles exposed to subsaturated sulfuric acid vapor exhibit a marked change in morphology, characterized by a decreased mobility-based diameter but an increased fractal dimension and effective density. These particles experience large hygroscopic size and mass growth at subsaturated conditions (<90% relative humidity) and act efficiently as cloud-condensation nuclei. Coating with sulfuric acid and subsequent hygroscopic growth enhance the optical properties of soot aerosols, increasing scattering by ≈10-fold and absorption by nearly 2-fold at 80% relative humidity relative to fresh particles. In addition, condensation of sulfuric acid is shown to occur at a similar rate on ambient aerosols of various types of a given mobility size, regardless of their chemical compositions and microphysical structures. Representing an important mechanism of atmospheric aging, internal mixing of soot with sulfuric acid has profound implications on visibility, human health, and direct and indirect climate forcing.
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| 8. |
- Zha, Chaolin, et al.
(författare)
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Dependence of Ordering Kinetics of FePt Thin Films on Different Substrates
- 2008
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 44:11, s. 3539-3542
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Tidskriftsartikel (refereegranskat)abstract
- FePt thin films are deposited on SMO3, MgO, and a 2 nm-FeOx underlayer on an Si substrate at room temperature and then annealed at elevated temperatures. Studies of the L1(0) ordering process in each case show that the ordering temperature for the FePt film on the nonepitaxial Si/FeOx substrate is similar to 150 degrees C lower than the epitaxial FePt films deposited on MgO and SrTiO3 substrates. We argue that internal stresses arising from lattice defects and a recrystallizing process as well as thermal strain from differences in thermal expansion between substrate and film are responsible for the differences in ordering kinetics from the A1 to L1(0) phase of FePt on the various substrates.
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| 9. |
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