| 1. |
- Akca, Ozan, et al.
(author)
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WHO Needs High FIO2?
- 2017
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In: TURKISH JOURNAL OF ANAESTHESIOLOGY AND REANIMATION. - : AVES. - 2149-0937. ; 45:4, s. 181-192
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Journal article (peer-reviewed)abstract
- World Health Organization and the United States Center for Disease Control have recently recommended the use of 0.8 FIO2 in all adult surgical patients undergoing general anaesthesia, to prevent surgical site infections. This recommendation has arisen several discussions: As a matter of fact, there are numerous studies with different results about the effect of FIO2 on surgical site infection. Moreover, the clinical effects of FIO2 are not limited to infection control. We asked some prominent authors about their comments regarding the recent recommendations
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| 2. |
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| 3. |
- Andersson, Anders, 1957-, et al.
(author)
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Fourier Methods for harmonic scalar waves in general waveguides
- 2016
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In: Journal of Engineering Mathematics. - : Springer. - 0022-0833 .- 1573-2703. ; 98:1, s. 21-38
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Journal article (peer-reviewed)abstract
- A set of semi-analytic techniques based on Fourier analysis is used to solve wave-scattering problems in variously shaped waveguides with varying normal admittance boundary conditions. Key components are the newly developed conformal mapping methods, wave splitting, Fourier series expansions in eigenfunctions to non-normal operators, the building block method or the cascade technique, Dirichlet-to-Neumann operators, and reformulation in terms of stable differential equations for reflection and transmission matrices. For an example, the results show good correspondence with a finite element method solution to the same problem in the low- and medium-frequency domains. The Fourier method complements finite element analysis as a waveguide simulation tool. For inverse engineering involving tuning of straight waveguide parts joining complicated waveguide elements, the Fourier method is an attractive alternative including time aspects. The prime motivation for the Fourier method is its added physical understanding primarily at low frequencies.
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| 4. |
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| 5. |
- Biro, Thomas, et al.
(author)
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Substrate Integrated Waveguide
- 2008
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In: Proceedings of RVK08/MMWP08, Växjö June 9-13, 2008. - : Växjö universitet. ; , s. 284-286
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Conference paper (other academic/artistic)abstract
- A substrate integrated waveguide, SIW, is a waveguide that is integrated directly on a subtrate. These structeres has recently been developed for different applications. The simplest SIW design is a rectangular waveguide in a subtrate formed by metallization of the upper and lower surfaces of the substrate and by placing vertical metal vias periodically along two parallel lines. Different types of SIW are analyzed and simulated in this contribution. In particular wave propagation along an SIW is analyzed.
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| 6. |
- Guilford, Tim, et al.
(author)
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GPS tracking of the foraging movements of Manx Shearwaters Puffinus puffinus breeding on Skomer Island, Wales
- 2008
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In: Ibis. - 1474-919X. ; 150, s. 462-473
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Journal article (peer-reviewed)abstract
- We report the first successful use of miniature Global Positioning System loggers to track the ocean-going behaviour of a c. 400g seabird, the Manx Shearwater Puffinus puffinus. During three field seasons, breeding birds were tracked during the incubation and chick rearing periods on their foraging excursions from the large colony on Skomer Island, Pembrokeshire, UK. Foraging effort was concentrated in the Irish Sea. Likely foraging areas were identified to the north off the Mull of Galloway (some 330km from Skomer), in Dundalk Bay, Cardigan Bay, and more diffusely to the west of the colony both locally and off southern Ireland. No foraging excursions were recorded significantly to the south of the colony, conflicting with the conclusions of earlier studies based on ringing recoveries and off-shore observations. We discuss several explanations including the hypothesis that foraging may have shifted substantially northwards in recent decades (although the possibility that breeding birds forage further south in the very early part of the season remains open). We found no obvious relationship between birds’ positions and water depth, although night-time observations were more likely to be in shallower water than day-time observations. We also found that despite the fact that shearwaters can be observed rafting off-shore from their colonies in the hours prior to making landfall at night, breeding birds are usually located much further from the colony in the last eight hours before arrival, a finding that has significance for the likely effectiveness of marine protection areas if they are only local to the colony. Short sequences of precise second-by-second fixes gathered every two hours enabled us to measure movement speed and direction. Movement speeds were bimodal, corresponding to sitting on the water and flying, with flight behaviour separable into erratic (perhaps indicative of searching for food) and directional (perhaps indicative of travelling). Movement behaviour had a diurnal pattern, with flight predominating in the morning and evening, with more sitting at night and around midday. We also provide a first direct measurement of mean flight speed during directional flight (approximately 40 kmh-1), slower than a shearwater’s predicted Vmr (maximum range velocity) and suggesting that birds are exploiting wave or dynamic soaring during long-distance travel.
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| 7. |
- Gustafsson, Stefan, et al.
(author)
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Electromagnetic dispersion modeling and measurements for HVDC power cables
- 2014
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In: IEEE Transactions on Power Delivery. - : IEEE Press. - 0885-8977 .- 1937-4208. ; 29:6, s. 2439-2447
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Journal article (peer-reviewed)abstract
- This paper provides a general framework for electromagnetic (EM) modeling, sensitivity analysis, computation, and measurements regarding the wave propagation characteristics of high-voltage direct-current (HVDC) power cables. The modeling is motivated by the potential use with transient analysis, partial-discharge measurements, fault localization and monitoring, and is focused on very long (10 km or more) HVDC power cables with transients propagating in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant. Experimental time-domain measurement data from an 80-km-long HVDC power cable are used to validate the electromagnetic model, and a mismatch calibration procedure is devised to account for the connection between the measurement equipment and the cable. Quantitative sensitivity analysis is devised to study the impact of parameter uncertainty on wave propagation characteristics. The sensitivity analysis can be used to study how material choices affect the propagation characteristics, and to indicate which material parameters need to be identified accurately in order to achieve accurate fault localization. The analysis shows that the sensitivity of the propagation constant due to a change in the conductivity in the three metallic layers (the inner conductor, the intermediate lead shield, and the outer steel armor) is comparable to the sensitivity with respect to the permittivity of the insulating layer. Hence, proper modeling of the EM fields inside the metallic layers is crucial in the low-frequency regime of 0-100 kHz.
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| 8. |
- Lundbäck, Jonas, et al.
(author)
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A Digital Directional Coupler with Applications to Partial Discharge Measurements
- 2008
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In: IEEE Transactions on Instrumentation and Measurements. - 0018-9456. ; 57:11, s. 2561-2567
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Journal article (peer-reviewed)abstract
- This paper presents a digital directional coupler (DDC) that separates forward- and backward-traveling waves on a transmission line. Based on two independent wideband measurements of voltage and current and on frequency-domain digital wave splitting using a fast Fourier transform (FFT), the DDC is a versatile device for direction separation. A practical procedure is described for the calibration of the digital processor with respect to the particular transmission line and the voltage and current sensors that are being used. As an experiment, a DDC was designed and implemented using low-cost wideband sensors and was installed with medium-voltage equipment in a power distribution station. Partial discharge (PD) measurements were conducted on cross-linked polyethylene (XLPE)-insulated power cables to illustrate the directional separation capabilities of the DDC.
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| 9. |
- Nordebo, Sven, et al.
(author)
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Electromagnetic dispersion modeling and measurements for HVDC power cables
- 2011
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Reports (other academic/artistic)abstract
- This paper provides a general framework for electromagnetic modeling, computation and measurements regarding the wave propagation characteristics of High-Voltage Direct Current (HVDC) power cables. The modeling is focused on very long (10 km or more) HVDC power cables and the relevant frequency range is therefore in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant and the related characteristic impedance. Experimental time-domain measurement data from an 80 km long HVDC power cable is used to validate the model. It is concluded that a single-mode transmission line model is not adequate to account for the mismatch between the power cable and the instrumentation. A mismatch calibration procedure is therefore devised to account for the connection between the measurement equipment and the cable. A dispersion model is thus obtained that is accurate for early times of pulse arrival. To highlight the potential of accurate electromagnetic modeling, an example of high-resolution length-estimation is discussed and analyzed using statistical methods based on the Cramer-Rao lower bound. The analysis reveals that the estimation accuracy based on the present model (and its related model error) is in the order of 100 m for an 80 km long power cable, and that the potential accuracy using a perfect model based on the given measurement data is in the order of centimeters.
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| 10. |
- Nordebo, Sven, et al.
(author)
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Low-frequency dispersion characteristics of a multilayered coaxial cable
- 2013
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In: Journal of Engineering Mathematics. - : Springer Netherlands. - 0022-0833 .- 1573-2703. ; 83:1, s. 169-184
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Journal article (peer-reviewed)abstract
- This paper provides an exact asymptotic analysis regarding the low-frequency dispersion characteristics of a multilayered coaxial cable. A layer-recursive description of the dispersion function is derived that is well suited for asymptotic analysis. The recursion is based on two well-behaved (meromorphic) subdeterminants defined by a perfectly electrically conducting (PEC) and a perfectly magnetically conducting termination, respectively. For an open waveguide structure, the dispersion function is a combination of two such functions, and there is only one branch point that is related to the exterior domain. It is shown that if there is one isolating layer and a PEC outer shield, then the classical Weierstrass preparation theorem can be used to prove that the low-frequency behavior of the propagation constant is governed by the square root of the complex frequency, and an exact analytical expression for the dominating term of the asymptotic expansion is derived. It is furthermore shown that the same asymptotic expansion is valid to its lowest order even if the outer shield has finite conductivity and there is an infinite exterior region with finite nonzero conductivity. As a practical application of the theory, a high-voltage direct current (HVDC) power cable is analyzed and a numerical solution to the dispersion relation is validated by comparisons with the asymptotic analysis. The comparison reveals that the low-frequency dispersion characteristics of the power cable is very complicated and a first-order asymptotic approximation is valid only at extremely low frequencies (below 1 Hz). It is noted that the only way to come to this conclusion is to actually perform the asymptotic analysis. Hence, for practical modeling purposes, such as with fault localization, an accurate numerical solution to the dispersion relation is necessary and the asymptotic analysis is useful as a validation tool.
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