| 1. |
- Abbasi, Saeed
(författare)
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Characterisation of airborne particles from rail traffic
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the investigation of wear particles in rail transport started in late-1910s, the high mass concentration of these particles has raised worries among researchers concerned with air quality. However, effective action has yet to be taken because of lack of relevant knowledge. This thesis provides applicable information for the airborne wear particles in rail transport. Some aspects of their characteristics such as diameter size, mass concentration, number concentration, and morphology of particles were investigated in field tests and laboratory tests.The effects on particle characterisations from different operational conditions in the field tests, and applying different braking materials, conducting tests in different applied loads or sliding velocities in the laboratory tests were studied. The main advantage of conducting laboratory tests was to focus on studying particles from one source. The possibility of repetition, using high sensitive instruments and conducting tests at low costs are the other advantages of laboratory studies. Paper A describes how a pin-on-disc machine was used to reproduce similar real operational conditions during mechanical braking in a train. The results were validated by comparing the field tests results with the laboratory studies. The particles morphology and size distribution were also studied.Paper B presents a summary of field tests results. The effects of curve negotiating and applying braking in different real conditions were investigated with an on-board measurement.The element composition of the particles and their potential sources were also investigated outside of the particles morphologies.Paper C presents comprehensive results from laboratory studies on airborne particles from different braking materials. The differences in the particle characteristics in similar test conditions were attributable to different material compositions and dominant wear mechanisms. A new index was introduced in this paper and is suggested to be used as a qualitative factor with regard to the airborne wear particle emission rate.Paper D is a review of the recent studies of exhaust emission and non-exhaust emission from rail vehicles. A summary of results, measurements, adverse health effects, and proposed or applied solutions are reviewed in this paper.
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| 2. |
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| 3. |
- Alayon Glazunov, Andres, et al.
(författare)
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On the mean effective gain expressed in terms of the spherical vector wave expansion of the electromagnetic field
- 2008
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Konferensbidrag (refereegranskat)abstract
- The mode expansion o®ers a general framework for the analysis of the interaction between antennas andpropagation channels. In this paper, the Mean E®ective Gain (MEG) of an antenna is expressed in termsof the spherical vector wave expansion of the electromagnetic ¯eld. An explicit expression of the MEG isprovided as a function of the normalized average power of modes excited in the propagation channel andthe correlation between the channel modes due to the polarization and spatial selectivity of plane wavesimpinging at the antenna.
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| 4. |
- Alayon Glazunov, Andres, et al.
(författare)
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On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field
- 2011
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Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128
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Tidskriftsartikel (refereegranskat)abstract
- This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain G(i) and the mean effective gain G(e) if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, spectively. The obtained limitations are on the maximum of G(i)/Q and G(e)/Q, which establish a trade-off between link gain and Q.
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| 5. |
- Alayon Glazunov, Andres, et al.
(författare)
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Physical modelling of multiple-input multiple-output antennas and channels by means of the spherical vector wave expansion
- 2010
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Ingår i: IET Microwaves, Antennas & Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725. ; 4:6, s. 778-791
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Tidskriftsartikel (refereegranskat)abstract
- The authors propose a new physically motivated model that allows the study of the interaction between the antennas and the propagation channel for multiple-input multiple-output (MIMO) systems. The key tools employed in the model are the expansion coefficients of the electromagnetic field in spherical vector waves and the scattering matrix representation of the properties of the antenna. The authors derive the expansion of the MIMO channel matrix, H, in spherical vector wave modes of the electromagnetic field of the antennas as well as the propagation channel. The authors also introduce the channel scattering dyadic, C, with a corresponding correlation model for co-polarised and cross-polarised elements and introduce the concept of mode-to-mode channel mapping, the M-matrix, between the receive and transmit antenna modes. The M-matrix maps the modes excited by the transmitting antenna to the modes exciting the receive antennas and vice versa. The covariance statistics of this M-matrix are expressed as a function of the double-directional power-angular spectrum (PAS) of co-polarised and cross-polarised components of the electromagnetic field. Their approach aims at gaining insights into the physics governing the interaction between antennas and channels and it is useful for studying the performance of different antenna designs in a specified propagation channel as well as for modelling the propagation channel. It can furthermore be used to quantify the optimal properties of antennas in a given propagation channel. The authors illustrate the developed methodology by analysing the interaction of a 2 x 2 system of slant polarised half-wavelength dipole antennas with some basic propagation channel models.
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| 6. |
- Alayon Glazunov, Andres, et al.
(författare)
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Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis
- 2009
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:7, s. 2055-2067
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in thosefields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.
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| 7. |
- Albinsson, Anton, 1989, et al.
(författare)
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Identification of tyre characteristics using active force excitation
- 2016
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Ingår i: The Dynamics of Vehicles on Roads and Tracks - Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics, IAVSD 2015. - : CRC Press. - 9781138028852 ; , s. 501-510
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the maximum tyre-road friction coefficient can improve active safety systems by defining actuator boundaries and adaptable intervention thresholds. Estimation of the coefficient of friction based on tyre response measurements requires large level of force excitation. Under normal driving conditions, manoeuvres with large tyre utilizations are rare. This study investigates a method where wheel torques with opposite signs are applied to the front and rear axle simultaneously. This procedure allows for an intervention with large tyre excitations without disturbing the motion of the vehicle. The intervention is evaluated in simulations and experiments. Further, a method is proposed which does not require measurement of the vehicle longitudinal velocity. The results show that it is possible to estimate the current friction coefficient with the proposed method, although the assumption made in the proposed method makes the friction estimate sensitive to measurement noise on the wheel speed signal.
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| 8. |
- Berger, Tobias, et al.
(författare)
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The impact of fluoride on Al abundance and speciation in boreal streams
- 2015
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 409, s. 118-124
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Tidskriftsartikel (refereegranskat)abstract
- The impact of fluoride on the abundance and speciation of aluminium (Al) was investigated in three boreal streams characterised by overall high concentrations of fluoride and dissolved organic matter. Stream-water sampling was carried out several times a year for at least 4 years, and a chemical equilibrium model (Visual MINTEQ) was applied in order to model the proportion of colloidal and organically/inorganically complexed Al in the waters. The Al concentrations in filtered (0.45 μm) water samples were inversely correlated with pH, and reached values up to approximately 1. mg/L during low pH conditions (pH < 6.0). In a stream with high fluoride concentrations, as compared to a similar stream with only moderately elevated fluoride concentrations, the Al concentrations were consistently elevated. For the stream with high concentrations of fluoride and Al, the model predicted both high concentrations and proportions of Al-fluoride complexation. This prediction indicates that high fluoride levels contribute to raise both the Al abundance and the ratio of inorganic to organic Al complexation in stream water. In contrast, for another stream with high fluoride concentrations and consistently high (near neutral) pH, there was no evidence of fluoride affecting Al concentration or complexation. These results show that it is important to focus future studies on the role of high levels of dissolved fluoride on both the speciation and the toxicity of Al in stream water.
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| 9. |
- Capek, Miloslav, et al.
(författare)
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Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.
- 2019
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Ingår i: IEEE Antennas & Propagation Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 1045-9243 .- 1558-4143. ; 61:4, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here, we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on the radiation quality factor (Q-factor) (maximizing single-resonance fractional bandwidth) but are far from reaching the associated physical bounds for efficiency. The relative performance of other canonical antenna designs is comparable in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.
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| 10. |
- Cha, Yingying, 1989-, et al.
(författare)
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On particulate emissions from individual trains in tunnel environments
- 2016
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Ingår i: Civil-Comp Proceedings. - : Civil-Comp Press. - 1759-3433. ; 110
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Tidskriftsartikel (refereegranskat)abstract
- In order to detect the concentrations and size distributions of airborne particles that were generated by individual moving trains on an underground railway platform, a series of real-time measurements were undertaken. The measurement range covered the ultrafine (less than 100 nm) and partly the fine (100 nm to 2.5 μm), but not the coarse fraction (2.5 to 10 μm). The results show that the individual trains with stop and start at the platform elevate substantially the particulate number concentrations with a diameter size greater than 100 nm. Two size modes of the particulate number concentrations are obtained. One mode peaks around 170 nm when a train stopped/started, while the other is around 30 nm when no train operated in the station. By using principal component analysis, four components are extracted from the thirty two-analyzed particulate sizes, indicating four different contributors in those detected particles. It is revealed from this study that the particulate matter released by individual moving trains (mainly through mechanical wear and turbulent resuspension) is a key contributing source of the fine particles on underground railway platforms, which can be separated from the background by their different size distributions.
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