| 44161. |
- Koohestani, M., et al.
(author)
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Frequency Selective Surfaces for Electromagnetic Shielding of Pocket-Sized Transceivers
- 2020
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In: IEEE Transactions on Electromagnetic Compatibility. - 0018-9375 .- 1558-187X. ; 62:6, s. 2785-2792
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Journal article (peer-reviewed)abstract
- This article presents a comprehensive study of the use of small-sized frequency selective surfaces (FSS) to selectively shield pocket-sized devices against EM disturbances. A typical use case is to protect a 2.4-GHz transceiver (e.g. WiFi/Bluetooth) against ISM/GSM disturbances (around 868/915 MHz), using an 8.2 – 4.1 cm FSS structure. A detailed comparison is drawn between results in real and emulated far-fields for different FSS-to-antenna distances (5 and 25 mm), which is further confirmed by emission measurements employing an open transverse electromagnetic cell. Results demonstrate, in line with full-wave simulations including calculated Poynting integrals, that such a FSS can effectively reduce power by about 5 dB in the stopband, while providing no attenuation in the passband and is small enough for an easy integration. Moreover, it is shown that the farther the FSS from the antenna, the closer the results to a no-FSS scenario. This provides an insight to reconsider FSSs for the shielding of mobile and/or smart devices.
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| 44162. |
- Koohnavard, Tina, 1990, et al.
(author)
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Driving Simulator Studies - Opportunities to Elicit Important Knowledge from Experienced Truck Drivers
- 2017
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In: NORDIC ERGONOMICS SOCIETY ANNUAL CONFERENCE. ; , s. 321-327
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Conference paper (peer-reviewed)abstract
- Twelve experienced truck drivers participated in a driving simulator study with the overall aim to develop further knowledge on how driving postures are influenced by cab design features (e.g. head-up display and camera monitoring system (CMS). Objective data was collected on drivers' posture and subjective data on their experience of driving as well as thoughts on the new designs. The subjective data and the experience of the truck drivers brought additional value to the simulator studies in terms the pros and cons of different designs but also of suggestions how to improve the realism of the simulator; and reflections on drivers' behaviour in situations that did not exist in the simulator.
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| 44163. |
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| 44164. |
- Kooi, J., et al.
(author)
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HIFI stability as measured during ILT phase
- 2008
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In: 19th International Symposium on Space Terahertz Technology, ISSTT 2008; Groningen; Netherlands; 28 April 2008 through 30 April 2008. ; , s. 92-102
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Conference paper (peer-reviewed)abstract
- We present here the stability results of the high frequency heterodyne instrument (HIFI), to be flown on the Herschel space observatory. The measurements were taken as part of the instrument level tests (ILT) in the spring of 2007. Herschel is ESA's fourth cornerstone mission in the Horizon 2000+ program, and aims at observations in the Far-InfraRed and sub-millimeter wavelength region. HIFI itself is one of three instruments onboard Herschel. The other two being PACS, the photodetector array camera and spectrometer, and SPIRE, the spectral and photometric imaging receiver.
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| 44165. |
- Koopmans, Lucien, 1968
(author)
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HCCI Combustion by Retaining Residuals. Development and Analyses of a Method to Reduce Fuel Consumption for Passenger Car Gasoline Engines
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- The demand for more powerful engines on one hand, and greater fuel-efficiency on the other, requires a revolution in engine combustion technology. Homogeneous charge compression ignition (HCCI) can be a fuel-saving, low emissions approach that seems to be very suitable for large displacement passenger car engines. HCCI is used as a generic name for auto-ignited combustion in an engine, initiated by a temperature rise due to the compression of a mixture of fuel, air and/or residuals. Fuel consumption and carbon dioxide (CO2) emissions are reduced, in a window within a relevant engine speed and load domain, but the emissions levels are not compromised compared to a spark-ignited (SI) engine with catalytic exhaust-gas after-treatment, mainly due to the ultra low nitrogen-oxides (NOx) emissions. Since HCCI combustion can only be valid for a specified speed/load window (due to a required dilution of the combustion mixture), the method should be applied as a mode that can be engaged or disengaged, instead of running in it all the time, thus avoiding compromising the power output of the engine in SI mode. A very high temperature is required to auto-ignite gasoline (about 1100K), but by trapping hot combustion products (residuals) of the previous combustion using a negative valve overlap (NVO) this can be accomplished. The overlap is created with valve timings, different than during conventional SI mode, where the exhaust valves are closed early and the intake valves late. Also direct fuel injection can have a positive influence: before piston top dead center of the negative valve overlap a small amount of fuel can be injected (the pilot fuel) which will auto-ignite in the NVO, thereby elevating the temperature of the captured mixture further. There are no direct means for controlling the start of combustion (as the spark timing is for SI combustion). The auto-ignition timing, however, can be controlled by varying the negative valve overlap; a large overlap advances the auto-ignition timing while a shorter NVO period delays it. It can also be controlled by the excess air ratio, effective compression ratio (varied by adjusting the timing of the intake valve closure), timing of exhaust valve opening, direct fuel injection timing and the amount of pilot fuel. The thesis describes the result of engine experiments in which it was possible to utilize advanced hardware and equipment in combination with engine simulations (chemical kinetics, gas exchange and CFD) focusing on discovering the mechanisms behind the method (HCCI NVO). In addition to the detailed investigations published in the papers, which are added in the back of the thesis, more information can be found on: HCCI in general, different methods of generating HCCI combustion, the history of the project, the methods of experimenting, and HCCI NVO including a comparison with SI combustion.
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| 44166. |
- Koopmans, Lucien, 1968, et al.
(author)
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Location of the First Auto-Ignition Sites for Two HCCI Systems in a Direct Injection Engine
- 2004
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In: SAE Technical Paper Series, SAE paper 2004-01-0564. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Journal article (peer-reviewed)abstract
- To elucidate the processes controlling the auto-ignition timing and overall combustion duration in homogeneous charge compression ignition (HCCI) engines, the distribution of the auto-ignition sites, in both space and time, was studied. The auto-ignition locations were investigated using optical diagnosis of HCCI combustion, based on laser induced fluorescence (LIF) measurements of formaldehyde in an optical engine with fully variable valve actuation. This engine was operated in two different modes of HCCI. In the first, auto-ignition temperatures were reached by heating the inlet air, while in the second, residual mass from the previous combustion cycle was trapped using a negative valve overlap. The fuel was introduced directly into the combustion chamber in both approaches. To complement these experiments, 3-D numerical modeling of the gas exchange and compression stroke events was done for both HCCI-generating approaches. The STAR CD code was applied to predict the distributions of the local mixture temperature, residual gas fraction (RGF) and equivalence ratio throughout the cylinder at the end of the compression stroke. Knowledge of these distributions is important as they are strongly affect the ignition timing and burn duration of the HCCI combustion. Selected points from the calculated distribution maps were used as initial conditions for 0-D detailed-chemistry calculations, using the SENKIN code to identify combinations of properties that lead to first auto-ignition. Tracing corresponding points back to the STAR CD mesh gave information about the location of the auto-ignition sites. Results obtained in this way corresponded well to the auto-ignition locations derived from optical measurements.
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| 44167. |
- Koopmans, Lucien, 1968, et al.
(author)
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The Influence of PRF and Commercial Fuels with High Octane Number on the Auto-ignition Timing of an Engine Operated in HCCI Combustion Mode with Negative Valve Overlap
- 2004
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Conference paper (peer-reviewed)abstract
- A single-cylinder engine was operated in HCCI combustion mode with different kinds of commercial fuels. The HCCI combustion was generated by creating a negative valve overlap (early exhaust valve closing combined with late intake valve opening) thus trapping a large amount of residuals (~ 55%). Fifteen different fuels with high octane numbers were tested six of which were primary reference fuels (PRF's) and nine were commercial fuels or reference fuels. The engine was operated at constant operational parameters (speed/load, valve timing and equivalence ratio, intake air temperature, compression ratio, etc.) changing only the fuel type while the engine was running. Changing the fuel affected the auto-ignition timing, represented by the 50% mass fraction burned location (CA50). However these changes were not consistent with the classical RON and MON numbers, which are measures of the knock resistance of the fuel. Indeed, no correlation was found between CA50 and the RON or MON numbers. However, when only the PRF's were considered, a correlation was found between the auto-ignition timing and the RON number. Although a substantial difference in auto-ignition timing between PRF 70 ON and PRF 98 ON was expected, the difference was only 1.5 CAD. Furthermore, the differences in auto-ignition timing between all fuels spanned only 4.5 degrees. It was found that the reason for the different behavior of the fuels during these measurements was the method of generating the HCCI combustion mode. Retaining residuals with a negative valve overlap makes the combustion mode less sensitive to different fuel qualities. This is because chemical reactions during the negative valve overlap affect the auto-ignition timing proportionally to the amount of unburned hydrocarbons remaining from the main combustio
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| 44168. |
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| 44169. |
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| 44170. |
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