| 41. |
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| 42. |
- Abbas, Taimoor, et al.
(författare)
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Directional Analysis of Vehicle-to-Vehicle Propagation in Different Traffic Environments
- 2010
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Ingår i: [Host publication title missing].
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a double directional analysis of vehicle-to-vehicle channel measurements conducted in two different traffic environments. Using a high-resolution algorithm, we derive channel parameters like angle-of- arrival, angle-of-departure, propagation delay and Doppler’s spread and identify underlying propagation mechanisms by combining these estimates with maps of the measurement sites. The results show that single-bounce interaction with static objects is the dominating effect in the absence of line-of-sight, and that the contribution from other vehicles is small. We also find that in the absence of line-of-sight the direction spread at both sides of link is large which indicates possible diversity gain using multi-antenna arrangements.
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| 43. |
- Abbas, Taimoor, et al.
(författare)
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Initial Investigation to study the Effect of Antenna Placement in Vehicle-to-Vehicle Communications
- 2011
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Ingår i: [Host publication title missing].
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present an analysis of the effects of antenna placement on the radio channel properties for Vehicle-to-Vehicle communications based on measurements performed in three different propagation scenarios; highway, urban and rural. Four omni-directional antennas were mounted at four different positions: roof, bumper, left-side mirror and inside windscreen of two standard station wagons (Volvo V70). The channel transfer functions were measured for all antenna combinations with a wideband MIMO channel sounder. The results from this initial analysis show that the antenna mounted on the left-side mirror outperforms other antennas when vehicles are moving in convoy and are aligned well to each other. Whereas, if the TX and RX are moving in opposite direction, i.e., towards each other, bumper antenna shows good performance as long as LOS is available in between the antenna elements. In total some kind of diversity arrangement with complementary antennas seems to be the preferred solution, to decrease the effect of shadowing.
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| 44. |
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| 45. |
- Abbas, Taimoor
(författare)
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Measurement Based Channel Characterization and Modeling for Vehicle-to-Vehicle Communications
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vehicle-to-Vehicle (V2V) communication is a challenging but fast growing technology that has potential to enhance traffic safety and efficiency. It can also provide environmental benefits in terms of reduced fuel consumption. The effectiveness and reliability of these applications highly depends on the quality of the V2V communication link, which rely upon the properties of the propagation channel. Therefore, understanding the properties of the propagation channel becomes extremely important. This thesis aims to fill some gaps of knowledge in V2V channel research by addressing four different topics. The first topic is channel characterization of some important safety critical scenarios (papers I and II). Second, is the accuracy or validation study of existing channel models for these safety critical scenarios (papers III and IV). Third, is about channel modeling (paper V) and, the fourth topic is the impact of antenna placement on vehicles and the possible diversity gains. This thesis consists of an introduction and six papers: Paper I presents a double directional analysis of vehicular channels based on channel measurement data. Using SAGE, a high-resolution algorithm for parameter estimation, we estimate channel parameters to identify underlying propagation mechanisms. It is found that, single-bounce reflections from static objects are dominating propagation mechanisms in the absence of line-of-sight (LOS). Directional spread is observed to be high, which encourages the use of diversity-based methods. Paper II presents results for V2V channel characterization based on channel measurements conducted for merging lanes on highway, and four-way street intersection scenarios. It is found that the merging lane scenario has the worst propagation condition due to lack of scatterers. Signal reception is possible only with the present LOS component given that the antenna has a good gain in the direction of LOS. Thus designing an antenna that has an omni-directional gain, or using multiple antennas that radiate towards different directions become more important for such safety critical scenarios. Paper III presents the results of an accuracy study of a deterministic ray tracing channel model for vehicle-to-vehicle (V2V) communication, that is compared against channel measurement data. It is found that the results from measurement and simulation show a good agreement especially in LOS situations where as in NLOS situations the simulations are accurate as far as existing physical phenomena of wave propagation are captured by the implemented algorithm. Paper IV presents the results of a validation study of a stochastic NLOS pathloss and fading model named VirtualSource11p for V2V communication in urban street intersections. The reference model is validated with the help of independent channel measurement data. It is found that the model is flexible and fits well to most of the measurements with a few exceptions, and we propose minor modifications to the model for increased accuracy. Paper V presents a shadow fading model targeting system simulations based on channel measurements. The model parameters are extracted from measurement data, which is separated into three categories; line-of-sight (LOS), LOS obstructed by vehicles (OLOS), and LOS blocked by buildings (NLOS), with the help of video information recorded during the measurements. It is found that vehicles obstructing the LOS induce an additional attenuation in the received signal power. The results from system level vehicular ad hoc network (VANET) simulations are also presented, showing that the LOS obstruction affects the packet reception probability and this can not be ignored. Paper VI investigates the impact of antenna placement based on channel measurements performed with four omni-directional antennas mounted on the roof, bumper, windscreen and left-side mirror of the transmitter and receiver cars. We use diversity combining methods to evaluate the performance differences for all possible single-input single-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) link combinations. This investigation suggests that a pair of antennas with complementary properties, e.g., a roof mounted antenna together with a bumper antenna is a good solution for obtaining the best reception performance, in most of the propagation environments. In summary, this thesis describes the channel behavior for safety-critical scenarios by statistical means and models it so that the system performance can be assessed in a realistic manner. In addition to that the influence of different antenna arrangements has also been studied to exploit the spatial diversity and to mitigate the shadowing effects. The presented work can thus enable more efficient design of future V2V communication systems.
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| 46. |
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| 47. |
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| 48. |
- Abbasi, Maisam
(författare)
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Exploring Themes and Challenges in Developing Sustainable Supply Chains - A Complexity Theory Perspective
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To develop sustainable supply chains in a way that their negative environmental and social effects are minimized, shortand long-term targets should be set. The transformation of supply chains towards these targets calls for the development of innovative strategies and the need to continuously identify, classify, and tackle the challenges that can hinder the execution of such strategies. To develop innovative strategies, the patterns of current trends and themes need to be learned and the missing ones need to be identified. The purpose of this research was to explore themes and challenges in developing sustainable supply chain activities from theoretical and empirical perspectives. Six research studies (RS) were designed and carried out. Two explored the patterns of the themes and challenges in making supply chains environmentally and socially sustainable in general (RS1, RS2). One explored freight transport (RS3), one, urban freight distribution (RS4), and one, logistical services (RS5) in particular. RS6 explored a complexity theory perspective (CTP) on managing, governing, and developing sustainable supply chains activities. A CTP was chosen because of its applicability and ability to provide an understanding of the complex phenomena that sustainable development and supply chains represent. During and after the design of each research study, data were collected from a variety of sources and then analyzed by different researchers on some occasions and by different methods. Thus, the research design, data collection, and data analysis were mixed and overlapping, because they were not completely sequentially carried out. The aim of the analysis was to generate knowledge by (re)organizing and categorizing the data collected, by exploring the meaning of the data (i.e., generating information), and identifying their patterns of associations. After assessing the quality of the synthesized knowledge, the results were communicated to several target groups through several communication channels. In RS1, five major themes and challenges were identified in making supply chains environmentally sustainable. RS5 led to a deeper understanding of the insights of logistics service providers (LSPs) about the challenges identified in RS1. RS2 led to the identification of five major themes and eight major challenges in making supply chains socially sustainable. In the context of freight transport in RS3, fifteen major themes and five major challenges emerged. In the context of urban freight distribution in RS4, these numbers were eight major themes and seven major challenges. However, the results (i.e., the generated knowledge) about the themes and challenges were subjective: They were influenced by my interpretation of what had been said, observed, or scientifically written. The results were also relative (related to what had been said, observed, or scientifically written), and influenced by the different methods for collection and analysis of data. By combining the thirty-three identified themes in the research studies and classifying them based on their similarities and overlap, four central themes in making supply chains sustainable emerged out: sustainability in goods and services, sustainability in resources, sustainability in corporation, and sustainability in management and/or governance. Similarly, by combining the twenty-four identified challenges in the research studies and classifying them based on their similarities and overlap, five central challenges in making supply chains sustainable emerged out: shifting the values, difficulties of operationalization, dealing with complexity, difficulties of corporate governance, and SMEs difficulties. Taking a CTP was beneficial in understanding the complexity involved in the central themes of making supply chains sustainable. It also led to further propositions for tackling the challenges.
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| 49. |
- Abbasi, Maisam
(författare)
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Themes and challenges in developing sustainable supply chains
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sustainable development is one of the greatest global challenges facing human beings in the 21st century. In order to tackle sustainability related problems, several global, European, and national targets for 2050 have been set. The transition of supply chains activities towards sustainability targets calls for designing new strategies and continuously identifying and tackling the challenges that can hinder the operationalization of such strategies. The purpose of this research was to explore and classify themes and challenges in developing sustainable supply chains activities in general, and freight transport and urban distribution in particular. Three research questions were defined followed by defining the scientific assumptions and research strategies. Three research studies were then designed and carried out to find trustworthy and authentic answers to the corresponding research questions. However, research design, data collection, and data analysis were mixed and overlapping as they were not completely sequentially carried out. Data were collected by triangulation of different research methods, namely, literature review, content analysis, and semi-structured interviews. Analysis of the data was guided by principles of content analysis, discourse analysis, analytic induction, and grounded theory. Synthesis of the analyzed data resulted in the emergence of categories of themes and challenges, the development of hypotheses, and further discussion. In total, five categories of themes were identified for making supply chains environmentally sustainable, fifteen for making freight transport sustainable, and eight for making urban freight distribution sustainable. Five categories of challenges were identified for making supply chains environmentally sustainable, five for making freight transport sustainable, and seven for making urban freight distribution sustainable. All the themes and challenges were then synthesized to determine the patterns of their association. Five major themes in developing sustainable supply chains emerged, namely, increasing sustainability awareness, closing the loop of supply chains, making supply chains energy-efficient, making supply chains environmentally responsible, and managerial issues. Five major challenges in developing sustainable supply chains emerged, namely, change of behavior, costs, implementation, corporate governance, and antagonistic effects and paradoxical conflicts. As the nature of supply chains and the challenges identified in developing them sustainably is complex, a complexity theory perspective was considered beneficial for dealing with them. Such a perspective can enable us to: take a more holistic view of available sustainability-oriented strategies and activities; analyze the antagonistic effects of strategies and activities on each other; recognize conflicts of a paradoxical character that exist in supply chains; analyze the changes influencing and influenced by the strategies and activities; appreciate enough diversity and freedom among the sub-systems rather than too much simplification of them; design and redesign the transition paths for different types of supply chains. A complexity theory perspective can also be beneficial when governing a transformative transition of supply chains towards sustainability targets. Lessons are suggested in the discussion chapter that may help policy and decision makers in designing the future strategies and in tackling the challenges. The themes identified can be beneficial for increasing the absorptive capacity of industries, practitioners, and policy makers while they design innovative strategies for transitions towards sustainability targets. The identified challenges can also be beneficial for reducing the inertia and uncertainties against operationalization of sustainable development in practice.
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| 50. |
- Abbondanza, Giuseppe
(författare)
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Ordered arrays of low-dimensional Au and Pd : synthesis and in situ observations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrodeposition of metals in templates of nano-porous anodic aluminum oxide (NP-AAO) is a versatile way of fabricating ordered arrays of metal nanowires. Thanks to the self-arranged long-range hexagonal order of the pores, electrodeposition in NP-AAO is an easily scalable bottom-up synthesis route and an attractive alternative to traditional top-down fabrication methods such as electron beam lithography.Since NP-AAO is a non-conductive medium and since it is potentially soluble in non-neutral pH solutions, the electrodeposition of metals in NP-AAO represents a challenge. These aspects are discussed in this thesis, aiming to establish a reproducible and reliable protocol for the electrodeposition of Au and Pd.By using ex situ x-ray diffraction, it has been found that the growth of Au and Pd in the confined environment of nano-pores leads (i) to a deformation of the crystalline structure, as the lattice constant is smaller along the nanowire radius and larger along the nanowire axis, compared to the bulk lattice constant, and (ii) to a crystallite size anisotropy: it is limited by the pore radius in the horizontal direction and it is larger in the direction of growth.The electrochemical growth of Au and Pd nanowires was followed in situ by x-ray scattering methods. In the case of Au nanowires, the time-resolved measurements revealed that the anisotropy of the lattice parameter progresses as a function of time, which suggests that the strain state of the nanomaterials can be artificially selected. This findings might be beneficial in the strain-engineering of Au nanoelectrode arrays for electrocatalysis. In the case of Pd nanowires, the measurements revealed strain variations, as well as phase transitions attributed to the existence of alpha- and beta-phase Pd hydride in the NP-AAO template, due to the exposure of Pd to hydrogen evolved at the working electrode. These findings suggest that Pd in NP-AAO has potential applications in the design of hydrogen storage devices.
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