| 1. |
- Fluck, D., et al.
(författare)
-
Cerebrovascular reactivity is increased with acclimatization to 3,454m altitude
- 2015
-
Ingår i: Journal of Cerebral Blood Flow and Metabolism. - : SAGE Publications. - 0271-678X .- 1559-7016. ; 35:8, s. 1323-1330
-
Tidskriftsartikel (refereegranskat)abstract
- Controversy exists regarding the effect of high-altitude exposure on cerebrovascular CO2 reactivity (CVR). Confounding factors in previous studies include the use of different experimental approaches, ascent profiles, duration and severity of exposure and plausibly environmental factors associated with altitude exposure. One aim of the present study was to determine CVR throughout acclimatization to high altitude when controlling for these. Middle cerebral artery mean velocity (MCAv(mean)) CVR was assessed during hyperventilation (hypocapnia) and CO2 administration (hypercapnia) with background normoxia (sea level (SL)) and hypoxia (3,454 m) in nine healthy volunteers (26 +/- 4 years (mean +/- s.d.)) at SL, and after 30 minutes (HA0), 3 (HA3) and 22 (HA22) days of high-altitude (3,454 m) exposure. At altitude, ventilation was increased whereas MCAv(mean) was not altered. Hypercapnic CVR was decreased at HA0 (1.16% +/- 0.16%/mm Hg, mean +/- s.e.m.), whereas both hyper- and hypocapnic CVR were increased at HA3 (3.13% +/- 0.18% and 2.96% +/- 0.10%/mm Hg) and HA22 (3.32% +/- 0.12% and 3.24% +/- 0.14%/mm Hg) compared with SL (1.98% +/- 0.22% and 2.38% +/- 0.10%/mmHg; P<0.01) regardless of background oxygenation. Cerebrovascular conductance (MCAv(mean)/mean arterial pressure) CVR was determined to account for blood pressure changes and revealed an attenuated response. Collectively our results show that hypocapnic and hypercapnic CVR are both elevated with acclimatization to high altitude.
|
|
| 2. |
- Fluck, M., et al.
(författare)
-
Comparison of potential flow-based and measured pressure distributions over upwind sails
- 2010
-
Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics Inc.. - 0021-8669 .- 1533-3868. ; 47:6, s. 2174-2176
-
Tidskriftsartikel (refereegranskat)abstract
- The results of the comparative analysis of potential flow-based and measured pressure distributions over upwind sails were investigated. The sail models were supported by wires inside a frame, rather than being set on a yacht model that allowed trimming the models to several predefined positions very precisely and with good repeatability. The freestream dynamic pressure was q = 32.5 Pa, with a variation of ±1 Pa in the vicinity of the sails. The headsail and its image were considered to be one sail with a continuous deck-symmetrical circulation distribution. The vortex-lattice method (VLM) code uses mirror images of the sails to model the influence of the sea surface. The results indicated that the mast and hull, which are ignored in the theoretical analysis, lead to only a 3% reduction in lift of the headsail, but to a 7% reduction for the mainsail.
|
|
| 3. |
|
|
| 4. |
- Wang, Baochang, et al.
(författare)
-
Band gap engineering in BiNbO4 for visible-light photocatalysis
- 2012
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:18, s. 182102-
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electronic structure of anionic mono- (S, N, and C) and co-doping (N-N, C-N, S-C, and S-N) on BiNbO4 for the visible-light photocatalysis. The maximum band gap reduction of pure BiNbO4 is possible with the (C-S) co-doping and minimum with N mono-doping. The calculated binding energies show that the co-doped systems are more stable than their mono-doped counterparts. Our optical absorption curves indicate that the mono- (C) and co-anionic doped (N-N and C-S) BiNbO4 systems are promising materials for visible light photocatalysis.
|
|
| 5. |
- Xu, Xiangdong, 1984, et al.
(författare)
-
Enhanced accuracy in dielectric response material characterization by air reference method
- 2013
-
Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-4135 .- 1070-9878. ; 20:3, s. 913-321
-
Tidskriftsartikel (refereegranskat)abstract
- Dielectric response measurements are an important technique to characterize dielectric materials. However, the electrode arrangements as well as the accuracy of the measurement setup limit the precision of this characterization, especially in case of solid dielectric materials. An air reference method and a contact-free electrode arrangement are described in this paper to enhance the dielectric characterization accuracy by avoiding problems introduced by electrode contacts. It is shown that by performing a calibration with electrode gap filled with air under the same conditions as the material is tested, the air reference method can improve the measurement accuracy substantially. This type of approach also eliminates the need of a detailed model of the analog measurement circuit. In conjunction with the contact-free measurements, the approach allows for avoiding complicated and time-consuming sample preparation procedures. The measurement methodology as well as the electrode arrangement and error increase estimates are presented and evaluated by using different dielectric response instruments and materials.
|
|
| 6. |
- Xu, Xiangdong, 1984
(författare)
-
Enhancements in Dielectric Response Characterization of Insulation Materials
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing demand of integrating various renewable energy recourses in power system requires extensive use of power electronic solutions, such as HVDC and FACTS, as these techniques allow energy conversion between different frequencies and serves to stabilize the network. Consequently, electric stresses other than traditional 50/60 Hz sinusoidal voltage stress are acting on high voltage insulation materials. Therefore, a need for fast and accurate characterization methods, which can be used to study the influence on insulation materials of different types of voltage waveforms, has arisen. Dielectric response measurement is one commonly used non-destructive insulation test technique and has more than 100 years of history. Limitations like precision of the testing voltage waveform, high demand on a stable testing environmental condition, intricate specimen-electrode preparation, severe electrode geometric influences, etc., are however restraining the use of such measurements. In this project, several methods that are based on the Arbitrary Waveform Impedance Spectroscopy (AWIS) technique have been developed to enable fast and more accurate solid dielectric characterization.A test setup that is based on the AWIS technique can be optimized by implementing several techniques such as voltage divider, voltage follower, shielding box, etc., to reduce the measurement noise and to avoid crosstalk between adjacent signals.By utilizing optimized harmonic limited waveforms in the AWIS test setup, dielectric responses over a wide frequency spectrum can be determined simultaneously without degradation by signal aliasing. This also enables monitoring of the dielectric properties under fast changing test conditions as a source of systematic error is eliminated when all frequencies are obtained at the same time and at the same conditions. An air reference method and a contact-free electrode arrangement are described in this work to enhance the dielectric characterization accuracy by avoiding contact problems at the electrodes. It is shown that by performing a calibration with electrode gap filled with air under the same conditions as the material is tested, the air reference method can improve the measurement accuracy substantially. This type of approach also eliminates the need of a detailed model of the analog measurement circuit. In conjunction with the contact-free measurements, the approach allows for avoiding complicated and time-consuming specimen preparation procedures. The measurement methodology as well as the electrode arrangement and error estimation are presented and evaluated using different dielectric response instruments and materials.To improve the accuracy of dielectric permittivity, two methods are suggested in this work by either compensating or shielding the electrode setup from undesired geometric influences. One approach is to estimate a correction factor from a finite element method (FEM) model to improve the accuracy. The other approach uses a shielding guard electrode to avoid the geometric influence on measurement. Measurements of several PET films are used as an example to illustrate the use of correction factors in the application of contact free measurement. The latter method is only verified in FEM calculation.
|
|
