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Root biomass accounts for about 25% of the carbon storage in mid-latitude forests. Estimation of root biomass for carbon cycling studies requires either direct measurement by excavation of root systems, or remote measurement using ground penetrating radar (GPR) or other geophysical methods. This study evaluated the ability of a 2-GHz multi-channel GPR system (IDS Hi-BrigHT) to detect and map white pine roots in managed forest near Turkey Point, southern Ontario. The GPR system employed eight dual-polarized antenna pairs separated at 10 cm intervals. GPR data were acquired as overlapping swaths (2 cm line spacing, 0.4 cm inline) across a 25-m2 test site (TP74-R) containing a juvenile white pine tree. Radargrams were processed to full 3-D radar volumes for time slicing and interpretation of root architecture and comparison with the excavated root network. Radargram signal processing was successful in suppressing airwave and other background noise and improved the detection of root diffractions on radargrams. The majority of roots were found in the rooting zone at a depth of 5-40 cm. Roots as small as 0.5 cm were detected with the 2-GHz frequency, but many roots <1.5 cm diameter could not be detected as continuous root structures. Root detection was strongly dependent on root orientation; large, coarse roots (>3-5 cm) were imaged as continuous root segments when oriented perpendicular to GPR profiles. Roots intersecting GPR profiles at angles <30-45 degrees were either imaged incompletely or not detected on radargrams. The highest rate of root detection was achieved with horizontally polarized (HH) antennas (dipole axis parallel with the root structures). Isosurface root models constructed from the Hilbert-transformed radargrams allowed mapping of the 3-D dimensional root architecture for large (> 3-5 cm diameter) roots. Isosurface models provide a means for estimating the coarse root volume for large roots and could be employed in future work to monitor temporal changes in root biomass by repeat survey at the same measurement site. Radargram signal processing was successful in suppressing airwave and other background noise and improved the detection of root diffractions on radargrams. The majority of roots were found in the rooting zone at a depth of 5-40 cm. Roots as small as 0.5 cm were detected with the 2-GHz frequency, but many roots <1.5 cm diameter could not be detected as continuous root structures. Many roots were not detected due to dependence of root reflection amplitude on root orientation. Roots oriented at >30-45 degrees to the survey swaths were imaged incompletely or not detected. Most large coarse roots (>5 cm diameter) were mapped as continuous structures when the root orientation was either parallel to, or perpendicular to the GPR transects. The highest rate of root detection was achieved with the horizontally polarized (HH) antennas, with the dipole axis perpendicular to the root structures. Isosurface root models constructed from the Hilbert-transformed radargrams allowed mapping of the 3-D dimensional root architecture for large (> 3-5 cm diameter) roots. The isosurface models provide a means for estimating the coarse volume and belowground biomass but further work is required to improve 3-D image resolution to allow detection of the entire root network. The method could be employed to measure the temporal changes in root biomass by conducting repeat surveys at the same measurement site. Radargram signal processing was successful in suppressing airwave and other background noise and improved the detection of root diffractions on radargrams. The majority of roots were found above a depth of 40 cm with the root zone being detected at a depth of10-15 cm. Roots as small as 0.5 cm were detected with the 2-GHz frequency, but many roots <1.5 cm diameter could not be detected as continuous root structures. Many roots were not detected due to dependence of root reflection amplitude on root orientation. Roots oriented at >30-45 degrees to the survey swaths were imaged incompletely or not detected. Most large coarse roots (>5 cm diameter) were mapped as continuous structures when the root orientation was either parallel to, or perpendicular to the GPR transects. The highest rate of root detection was achieved with the horizontally polarized (HH) antennas, with the dipole axis perpendicular to the root structures. Isosurface root models constructed from the Hilbert-transformed radargrams allowed mapping of the 3-D dimensional root architecture for large (> 3-5 cm diameter) roots. The isosurface models provide a means for estimating the coarse volume and belowground biomass but further work is required to improve 3-D image resolution to allow detection of the entire root network. / Thesis / Master of Science (MSc) / Forests play an important role in the global carbon cycle by removing carbon from the Earth’s atmosphere and storing it in tree tissues as biomass. Estimation of the amount of biomass and carbon stored in forests is critical to predictive climate change models, and increasingly employs remote sensing methods to detect both the above ground biomass (e.g. leaves, tree branches) and the belowground carbon in the tree root system. Measurement of the belowground biomass is most difficult, as it cannot be directly observed without destructive excavation of the tree root system. This study investigated the application of new technology, multi-channel ground penetrating radar (GPR), for mapping tree root systems. The GPR system (IDS Hi-BrigHT) employs ‘swath mapping’ using high frequency pulsed radio waves and multiple transmitting and receiving antennas to produce detailed maps of roots structure. The GPR capabilities were evaluated at a test site at the Turkey Point Flux Station (TPFS) in southern Ontario. The root system of a juvenile white pine tree (20-30 cm diameter) was swath mapped over a 25-m2 area with a line spacing of 2 cm. The GPR data were processed to produce a 3-dimensional radar volume, which can be ‘sliced’ in various orientations to reveal the root structure. The time slice maps show that roots as small as 1-cm can be detected and roots larger than 3 cm in diameter can be mapped as continuous root segments.

This thesis investigates distributed medium access control (MAC) protocols custom tailored to both impulse-based ultra wideband (I-UWB) radios and to large ad hoc and sensor networks. I-UWB is an attractive radio technology for large ad hoc and sensor networks due to its robustness to multipath fading effects, sub-centimeter ranging ability, and low-cost, low-power hardware. Current medium access control (MAC) protocols for I-UWB target small wireless personal area networks (WPANs) and cellular networks, but they are not suitable for large, multihop ad hoc and sensor networks. Therefore, this paper proposes a new type of MAC protocol that enables ad hoc and sensor networks to realize the benefits of I-UWB radios. First, we propose a method to overcome the challenges of quickly, reliably, and efficiently sensing medium activity in an ultra wideband network. This provides a base MAC protocol similar to carrier sense multiple access (CSMA) in narrowband systems. Next, we propose to exploit the unique signaling of I-UWB to improve performance over the base MAC protocol without the associated overhead of similar improvements in narrowband systems. I-UWB enables a distributed multichannel MAC protocol, which improves throughput. I-UWB also facilitates a busy signal MAC protocol, which reduces wasted energy from corrupt packets. Finally, because the I-UWB Physical Layer and MAC Layer affect the network and application layers, we propose a cross-layer adaptive system that optimizes performance. Physical Layer simulations show that both the base protocol and the improvements are practical for an I-UWB radio. Networks level simulations characterize the performance of the proposed MAC protocols and compare them to existing MAC protocols. / Ph. D.

This dissertation addresses the problem of channel assignment in multi-hop, multi-transceiver wireless networks. We investigate (1) how channels can be assigned throughout the network to ensure that the network is connected and (2) how the channel assignment can be adapted to suit the current traffic demands. We analyze a traffic-aware method for channel assignment that addresses both maintaining network connectivity and adapting the topology based on dynamic traffic demands. The traffic-aware approach has one component that assigns channels independently of traffic conditions and a second component that assigns channels in response to traffic conditions. The traffic-independent (TI) component is designed to allocate as few transceivers or radios as possible in order to maintain network connectivity, while limiting the aggregate interference induced by the topology. The traffic-driven (TD) component is then designed to maximize end-to-end flow rate using the resources remaining after the TI assignment is complete. By minimizing resources in the TI component, the TD component has more resources to adapt the topology to suit the traffic demands and support higher end-to-end flow rate. We investigate the fundamental tradeoff between how many resources are allocated to maintaining network connectivity versus how many resources are allocated to maximize flow rate. We show that the traffic-aware approach achieves an appropriately balanced resource allocation, maintaining a baseline network connectivity and adapting to achieve near the maximum theoretical flow rate in the scenarios evaluated. We develop a set of greedy, heuristic algorithms that address the problem of resource- minimized TI assignment, the first component of the traffic-aware assignment. We develop centralized and distributed schemes for nodes to assign channels to their transceivers. These schemes perform well as compared to the optimal approach in the evaluation. We show that both of these schemes perform within 2% of the optimum in terms of the maximum achievable flow rate. We develop a set of techniques for adapting the network's channel assignment based on traffic demands, the second component of the traffic-aware assignment. In our approach, nodes sense traffic conditions and adapt their own channel assignment independently to support a high flow rate and adapt when network demand changes. We demonstrate how our distributed TI and TD approaches complement each other in an event-driven simulation. / Ph. D.

With the rapid evolving IT technologies, today, the power factor correction (PFC) design is facing many challenges, such as power scalability, high entire-load-range efficiency, and high power density. Power scalability is a very desirable and cost-effective approach in the PFC design in order to keep up with servers' growing power requirements. Higher power density can eventually reduce the converter cost and allows for accommodating more equipment in the existing infrastructures. Driven strongly by economic and environmental concerns, high entire-load-range efficiency is more and more required by various organizations and programs, such as the U.S. Energy Star, Climate Savers, and German Blue Angel. Today, the existing boost PFC is reaching its limitations to meet these challenges simultaneously. Using the cutting-edge semiconductor devices, further efficiency improvement at light load is still needed. There are limited approaches available for increasing the power density due to the large EMI filter and inductor size. Interleaved multi-channel boost PFC is a promising candidate to meet those challenges, but the interleaved boost converter is a less explored area. On the other hand, the multi-channel interleaved buck converter for the VR application has been intensively studied and thoroughly explored. One basic approach of this study is trying to extend the existing knowledge and techniques obtained from multiphase buck converters to the multi-channel interleaved boost converters since there are similarities existed between the multi-phase buck and the multi-channel boost converters. The existing studies about the interleaving impact on the EMI filter design are based on the time domain ripple cancellation effect. This approach is good enough for most of the filter designs. However, unlike the conventional filter designs, the EMI filter design is a specification related process. Both the EMI standard and the EMI measurement are based on the frequency domain spectrum. Limited by the existing analysis approaches, it is difficult to provide a clear picture about how exactly the multi-channel interleaving will impact the EMI filter design. The interleaving impact on the Common Mode (CM) noise also has not been studied in any existing literatures for the same reason. In this study, the frequency domain analysis method was adopted. With the double Fourier integral transformation, a closed-form expression of all the harmonics of the noise sources can be obtained. With all the detailed phase relationship of the switching frequency harmonics and all the side band harmonics, the multi-channel interleaving impact on both the differential mode (DM) and CM filter design can be clearly understood and summarized. According to the design curves provided, the EMI filter size can be effectively reduced by properly choosing the interleaving channel number and the switching frequency. The multi-channel interleaving impact on the output capacitor current ripple is also studied and summarized in this dissertation. It should be pointed out that interleaving only reduces the total input and output current ripples; the inductor current in each channel still has large ripple if small inductance is used. Similar to the multi-phase buck converter, coupling inductors result in different equivalent inductances for input current ripple and inductor current ripple for boost converters. Keeping the inductor current ripple magnitude the same, inverse coupling inductors between the interleaved channels can reduce the inductor size. However, the DM filter size is increased due to larger input current. Based on the investigation on the total magnetic component weight, inverse coupling inductor can reduce the total magnetic component weight. The reduction is more pronounced for lower switching frequency design when the inductor size is dominating among the total magnetic components. Based on the harmonic cancellation, and with all the detailed phase relationship of the switching frequency harmonics and all the side band harmonics, a novel phase angle control method is proposed to maximize the reduction of the EMI filter. For example, in a 2-channel interleaved PFC, just by changing the interleaving scheme to 90 degree phase shift, 39% total volume reduction of the EMI filter can be achieved. The proposed phase angle controlled multi-channel PFC is experimentally demonstrated and verified on a digital controlled 4-channel PFC. The phase angle control method proposed in the multi-channel boost converter can be applied back to the multi-phase buck converter as well. The harmonic cancellation principle will be the same as the multi-channel boost converter. The same benefits can be obtained when the requirement is defined in the frequency domain, e.g. the EMI Standard. The interleaved multi-channel configuration makes it possible to implement the phase-shedding to improve the PFC light load efficiency. By decreasing the number of active channels according to the load, the PFC light load efficiency can be optimized. However, shedding phases can reduce the ripple cancellation effect as well, which will result in the EMI noise increase and losing the benefit on the EMI filter. By applying the proposed phase-shedding with phase angle control strategy, the phase shedding impact on the EMI filter design can be minimized. The light load efficiency can be improved without compromising the EMI filter size. Then, adaptive frequency controlled PFC is proposed to further improve the PFC light load efficiency. The proposed light load efficiency improvement strategies are combined and implemented on the platform of the digital controlled 4-channel PFC. The benefit of improving the light load efficiency is experimentally verified. The EMI performance is also evaluated with the EMI measurement results obtained from the PFC prototype. Following the same approach explored, the benefits of interleaved boost converter can be further extended other applications, such as the boost converter in the Hybrid Electric Vehicles (HEV) and photovoltaic (PV) system. / Ph. D.

The mammalian cochlea has been the inspiration to develope contemporary cochlear implants and active dynamic sensors that operate in the sensor's resonance region and possess favorable nonlinear characteristics. In the present work, multi-channel and self-sensing active artificial hair cells (AHCs) made of piezoelectric cantilevers and controlled by a cubic damping feedback controller are developed numerically and experimentally. These novel AHCs function near a Hopf bifurcation and amplify or compress the output by a one-third power-law relationship with the input, analogous to the mammalian cochlear amplifier. The multi-channel AHCs have extended frequency bandwidth to sense over multiple resonant frequencies, unlike conventional single-channel AHCs. Therefore, the adoption of these AHCs reduces the number of required sensors to cover the desired bandwidth of interest in an array format. Furthermore, a novel self-sensing active AHC is created in this study using quadmorph beams for future cochlear implants or sensor design applications. The self-sensing scheme allows miniaturization of the system, embedding AHCs in a limited space, and fabrication of AHC arrays by omitting external sensors from the system for practical implementation. Preliminary research on the extension of this research to MEMS AHCs and arrays of AHCs is also presented. The active AHCs can lead to transformative improvements in the dynamic range, sharpness of the response, and threshold of sound detection in cochlear implants to aid individuals with sensorineural hearing loss. Additionally, they can enhance the dynamic properties of sensors such as fluid flow sensors, microphones, and vibration sensors for various applications. / Doctor of Philosophy / In the mammalian auditory system, the acoustic wave that enters the ear canal is transmitted to the cochlea of the inner ear where it is decomposed into its frequency components. The cochlea then amplifies faint sounds and compresses high-level signals and as these processes stop due to damage, severe hearing loss occurs. Therefore, the present work is focused on developing artificial hair cells (AHCs) that can accurately replicate cochlea's behavior and aid the creation of prostheses for hearing restoration. In this work, the AHC is a beam with piezoelectric layers that is integrated with a control system designed to apply the cochlea-like amplification/compression on the beam. Experimental and simulation results show that the AHC is able to amplify or compress the output based on its input level similar to the mammalian cochlea. In contrast to previous designs of AHCs where each AHC could sense a single frequency, the system developed in this work possesses multiple sensing channels to increase the frequency range of the AHC. Furthermore, the development of a novel self-sensing scheme allows the omission of the external sensor that was required for the AHC operation in previous devices. This advancement in the self-sensing AHC design paves the way for creating fully implantable AHCs to replace the damaged parts of the cochlea. These multi-channel self-sensing AHCs have the potential to be used in the creation of cochlear implants, or sensors such as accelerometers, microphones, and hydrophones with improved dynamic properties. AHCs with different lengths, i.e. different sensing frequencies, can be mounted in an array format to cover the speech frequency range for speech recognition in individuals with hearing loss.

LED is widely used in many applications, such as indoor lighting, backlighting and street lighting, etc. For these application, multiple LED strings structure is adopted for reasons of cost-effectiveness, reliability and safety concerns. Several methods and topologies have been proposed to drive multiple LED strings. However, the output current balance and efficiency are always the two major concerns for LED driver. A simple two-stage multi-channel LED driver is proposed. It is composed of a buck converter as the first stage and a multi-channel constant current (MC3) CLL resonant converter as the second stage. For the CLL resonant converter, the magnetizing inductance of the transformer can be as large as possible. Therefore, the magnetizing current of the transformer has little influence on the output currents. In addition, the currents of two LED strings driven by the same transformer is balanced by a DC blocking capacitor. As a result, the current balance among LED strings is very good, even if the load is severely unbalanced. Meanwhile, the current flowing through the external inductance Lr1, instead of the magnetizing current is used to help the primary-side switches to achieve ZVS. Therefore, large magnetizing inductance is good for current balance and properly designed Lr1 is helpful for ZVS achievement. These properties of MC3 CLL are preferred to drive multi-channel LED strings. In the design procedure of MC3 CLL resonant converter, the parasitic junction capacitor of the secondary-side rectifier is taken into account. It influences the operation during dead time significantly when the voltage step-up transformer is applied. The junction capacitors of the secondary-side rectifiers, and the output capacitors of the primary-side switches will resonate with the inductor Le2 during the dead time. Finally, this resonance impact the ZVS achievement of the primary-side switches. Therefore, the inductors Lr1 and Le2 should be designed according the charge needed to achieve ZVS with considering the resonance. Additionally, the control strategy for this two-stage structure is simple. Only the current of one specific LED string is sensed for feedback control to regulate the bus voltage, and the currents of other LED strings are cross-regulated. Furthermore, the MC3 CLL is unregulated and always working around the resonant frequency point to achieve best efficiency. The compensator is designed based on the derived small signal model of this two-stage LED driver. Due to the special electrical characteristics of LED, the soft start-up process with a delayed dimming signal is adopted and investigated. With the soft start-up, there is no overshoot for the output current. Finally, a prototype of the two-stage LED driver is built. The current balance capability of the LED driver is verified with the experiment. Good current balance is achieved under balanced and severely unbalanced load condition. In addition, the efficiency of the LED driver is also presented. High efficiency is guaranteed within a wide load range. Therefore, this two-stage structure is a very promising candidate for multi-channel LED driving applications. / Master of Science

Recent research has shown that several spectrum bands are mostly underutilised. To resolve the issue of underutilisation of spectrum bands across the networks, the concept of Cognitive Radio (CR) technology was envisaged. The CR technology allows Secondary Users (SUs) to acquire opportunistic access to large parts of the underutilised spectrum bands on wireless networks. In CR networks, SUs may scan and identify the vacant channels in the wireless spectrum bands and then dynamically tune their receivers to identify vacant channels and transmitters, and commence communication among themselves without causing interference to Primary/Licensed Users (PUs). Despite the developments in the eld of CR technology, recent research shows that still there are many challenges unaddressed in the eld. Thus, there is a need to reduce additional handshaking over control and data channels, to minimise large sized control frames and to introduce reliable channel selection process and maintenance of SUs' communication when PUs return to a licensed channel. A fundamental challenge a ecting this technology is the identi cation of reliable Data Channels (DCHs) for SUs communication among available channels and the continuation of communication when the PU returns. This doctoral research investigates in detail how to resolve issues related to the protocol design for Cognitive Radio Networks (CRNs) on Medium Access Layers (MAC) for Ad-Hoc networks. As a result, a novel Reliable and Energy e cient Cognitive Radio multi-channel MAC protocol (RECR-MAC) for Ad-Hoc networks is proposed to overcome the shortcomings mentioned. After discussing the background, operation and architecture of CR technology, this research proposes numerous platforms and testbeds for the deployment of personal and commercial applications of the CRNs. Side by side, optimised control frames and a reduced number of handshakes over the CCH are suggested to extend the transmitting time for data communication. In addition, the reliable channel selection process is introduced instead of random selection of DCHs for successful data communication among the SUs. In RECR-MAC, the objective of every SU is to select reliable DCHs, thereby ensuring high connectivity and exchanging the successful data frames across the cognitive network. Moreover, the selection criteria of the DCHs are based on multiple factors, such as an initial selection based on the maximum free time recorded by the SUs over the DCH channel ranking, which is proportional to the number of positive/negative acknowledgements, and the past history of DCHs. If more than two DCHs have an equal value during the second, third and following iterations, then the DCHs are selected based upon the maximum free time. The priorities of the DCHs are then assigned based on Reliable Data Channels, that is, RDCH 1, RDCH 2, RDCH 3, and RDCH 4 respectively (where RDCH 1 and RDCH 2 have the highest priority, DRCH 3 and RDCH 4 have the next priority, and so on). The impacts of channel selection process and Backup Data Channel (BDC) over the proposed RECR-MAC protocol are analysed in combination with comparative benchmark CR-MAC protocols based on the timing diagrams proposed. Finally, the RECR-MAC protocol is validated by using a MATLAB simulator with PU impact over the DCHs, both with and without BDC, and by comparing results, such as communication time, transmitting energy and throughput, with benchmark CR-MAC protocols.

Bakgrund: Det har skett stora förändringar i tidningsbranschen vad gäller flerkanalspublicering och omstruktureringar. Tidningarnas huvudsakliga intäktskällor är från prenumerationer och annonsförsäljning. På grund av flerkanalspubliceringen råder en trend av vikande läsning i den tryckta tidningen. Forskningsfråga: Hur har intäktskällorna hos lokala tidningar i Västra Götaland påverkats av de förändringar som skett i branschen angående flerkanalspubliceringen samt nya ägarförhållanden? Syfte: Syftet är att genom en kvalitativ metod redogöra för hur lokala tidningar i Västra Götaland har påverkats av flerkanalspublicering och omstruktureringar i organisationerna vad gäller intäkter från annonser och prenumerationer. Metod: Vår studie är gjord genom en kvalitativ metod bestående av semistrukturerade intervjuer som har genomförts med åtta representanter från fyra olika tidningsorganisationer i Västra Götaland. Teoretisk referensram: Vår teoretiska referensram består av förändringar av arbetsprocesser inom organisationer, kopplat samman med en modell av mediekonvergens. Empiri: Här presenteras den empiri våra åtta intervjuer har gett oss under rubrikerna intäkter, flerkanalspublicering, mediekonvergens samt framgångsfaktorer. Analys: Analysen består av vår tolkning av det empiriska materialet från våra intervjuer med hjälp av vår teoretiska referensram, och är uppbyggt med samma rubriker som empirikapitlet. Slutsats: Här för vi en diskussion kring hur den lokala tidningsbranschens intäktskällor påverkats av digitaliseringen av nyheter. En viktig slutsats är; för att generera intäkter krävs att de satsar på de lokala nyheterna, som andra större konkurrerande kanaler inte fokuserar på. / Background: There have been major changes in the newspaper industry in terms of multi-channel publishing and restructuring. Their main sources of income are from subscriptions and advertising sales. Because of the multi-channel publishing there is a trend of declining reading the printed newspaper. Research question: How has the income sources of local newspapers in Västra Götaland been affected by the changes in the branch regarding multi-channel publishing and new ownership? Purpose: The purpose is, through a qualitative approach to explain how local newspapers in Västra Götaland have been affected by the multi-channel publishing and restructuring of organizations in terms of revenues from ads and subscriptions. Method: Our study is made through a qualitative approach consisting of semi-structured interviews that have been conducted with eight representatives from four different newspaper organizations in Västra Götaland. Theory: Our theoretical framework consists of changes in the newspaper branch, linked together with a model of media convergence. Empiricism: Here we present the empirical results our eight interviews have given us under the titles income, multi-channel publishing, media convergence and factors for success. Analysis: The analysis involves our interpretation of the empirical material from our interviews with the help of our theoretical framework, and is built with the same titles as the empirical chapter. Conclusion: Here we discuss how the revenue sources of the local newspaper industry are affected by the digitalization of the news. An important conclusion is that in order to generate revenue it’s needed to invest in the local news that other major competing channels are not focusing on.

<p>Purpose/Aim: The aim of the paper is to find out if there is a correlation between playing MMORPGs and having better skills in using multi-channel communication.</p><p>Material/Method: A media-skill test was conducted in the internet testing the participants’ ability to respond to targets in three different channels and media at the same time. The results of the study where used for statistical comparisons of the different groups of participants sorted according to their media use.</p><p>Main results: People who use the internet more and who play computer games, especially MMORPGs, have a better Multi-Media Multi-Channel Communication Literacy. There is fast learning visible for people with a use of the respective medium of up to five hours a week. Playing makes you better, not playing a lot.</p>