In this thesis, we propose a cost-based CLEAN algorithm to accurately find dense multi-path parameters and improve the performance of selective RAKE receiver in indoor UWB systems. RAKE receiver can resolve the dense multi-path interference problems with the multi-path parameters. Because the weak paths are of lower valuable for system performance improvement, selective RAKE receiver combines only the strongest multi-path components and reduce the number of fingers to lower the complexity of RAKE receiver. However, selective RAKE receiver needs accurate multi-path detection to decide the suitable number and parameters of fingers. In order to improve the performance of selective RAKE receiver, the main issue in this thesis is to detect the best paths of channel with the CLEAN algorithm. CLEAN algorithm uses the correlation of the received signal and the template signal as the basis for searching paths. If there are closely adjacent paths, or if one of signal paths is relatively stronger, the detection error of paths may occur and thus affects the performance of the receiver. EP-based CLEAN algorithm uses the cost function and the evolutionary programming (EP) to search the multi-path delay times and gain coefficients for minimizing the cost function. Accurate multi-path detection and high resolution of adjacent paths can be obtained. However, EP-based CLEAN algorithm makes a time-consuming blind search. In the thesis, a CLEAN algorithm based on the cost function is proposed. The proposed cost-based CLEAN algorithm searches the delay times near the peaks of the cross-correlation for local minimum of the cost function, and then uses CLEAN algorithm to extract autocorrelation components and obtain the accurate multi-path detection. By testing the IEEE802.15.3a UWB channel models, and comparing with CLEAN algorithm, the cost-based CLEAN algorithm in the thesis can achieve better detection accuracy in multi-path searching, and improve the performance of selective RAKE receiver.

One of the major drawbacks of multi-carrier systems is the high peak-to-average power ratio (PAPR) of the transmitted signals. In this paper, the proposed novel low-complexity selective mapping (SLM) schemes are applicable to interleaved-4 orthogonal frequency division multiple access (OFDMA) uplink systems for PAPR reduction. The novel scheme just needs one inverse fast Fourier transform (IFFT) block because that the phases of the transmitted signals in frequency domain are rotated by circular convolution with conversion vectors in time domain. Moreover, a special set of conversion vectors are proposed in novel scheme, which are not only computed with low complexity but also reduce the PAPR effectively. In proposed scheme, different conversion vectors and appropriate subcarriers mapping are picked up for different users. The scheme supplies a practicable low-complexity method for PAPR reduction in interleaved-4 OFDMA uplink systems. Besides, the bit error rate (BER) performance is as good as the SLM scheme.

<p>On 1 June 2010, a new Block Exemption Regulation (BER) and new Guidelines that affect the practical use of selective distribution systems enter into force. The BER exempts vertical agreements, such as selective distribution agreements, from the prohibition of Article 101 (1) TFEU. It is significant for individual market players to obtain knowledge of what impact the new BER and the new Guidelines have for the practical use of selective distribution systems.</p><p>The Commission has amended the new BER and the new Guidelines in the light of the development the last decade. Two main changes are noticed that affect the content of the new legislative documents. Firstly, it is established that many distributors have obtained larger market shares. Secondly, it is stated that Internet sales have increased largely. The basic principles of the new versions of the BER and the Guidelines are identical with the former versions but the present changes are although noticeable for companies and their selective distribution systems.</p><p>The new BER contains a new market share rule that is more restrictive than the corresponding rule in the former BER. However, the new market share rule is not an expression of a less tolerant approach towards selective distribution systems; rather an amendment necessary due to the development of distributors’ market shares.</p><p>The growth of distribution in the Internet the last ten years is reflected in the new Guidelines. The Commission’s approach towards the Internet as a distribution method seems in general to be positive. It is noticeable that the Commission wants that parties of selective distribution agreements shall be able to benefit from all the positive effects of online sales at the same time as the Commission tries to preserve the positive effects of selective distribution.</p><p>This thesis describes and examines the practical use of selective distribution systems. Different reasons for companies to use selective distribution systems and effects of the new BER and Guidelines are in particular examined.</p>

This dissertation shows a detailed investigation on reconfigurable low profile antennas using tunable high impedance surfaces (HIS). The specific class of HIS used in this dissertation is called a frequency selective surface (FSS). This type of periodic structure is fabricated to create artificial magnetic conductors (AMCs) that exhibit properties similar to perfect magnetic conductors (PMCs). The antennas are intended for radiometric sensing applications in the biomedical field. For the particular sensing application of interest in this dissertation, the performance of the antenna sub-system is the most critical aspect of the radiometer design where characteristics such as small size, light weight, conformability, simple integration, adjustment in response to adverse environmental loading, and the ability to block external radio frequency interference to maximize the detection sensitivity are desirable. The antenna designs in this dissertation are based on broadband dipole antennas over a tunable FSS to extend the usable frequency range. The main features of these antennas are the use of an FSS that does not include via connections to ground, their low profile and potentially conformal nature, high front-to-back radiation pattern ratio, and the ability to dynamically adjust the center frequency. The reduction of interlayer wiring on the tunable FSS minimizes the fabrication complexity and facilitates the use of flexible substrates. This dissertation aims to advance the state of the art in low profile tunable planar antennas. It shows a qualitative comparison between antennas backed with different unit cell geometries. It demonstrates the feasibility to use either semiconductor or ferroelectric thin film varactor-based tunable FSS to allow adjustment in the antenna frequency in response to environment loading in the near-field. Additionally, it illustrates how the coupling between antenna and HIS, and the impact of the varactor losses affect the antenna performance and it shows solutions to compensate these adverse effects. Novel hybrid manufacturing approaches to achieve flexibility on electrically thick antennas that could be transitioned to thin-film microelectronics are also presented. The semiconductor and ferroelectric varactor-based tunable low profile antennas demonstrated tunability from 2.2 GHz to 2.65 GHz with instantaneous bandwidths greater than 50 MHz within the tuning range. The antennas had maximum thicknesses of λ/45 at the central frequency and front to back-lobe radiation ratios of approximately 15dB. They also showed impedance match improvement in the presence of a Human Core Model (HCM) phantom at close proximity distances of the order of 10-20 mm. In addition, the use of thin film ferroelectric Barium Strontium Titanate (BST) varactors in the FSS layer enabled an antenna that had smaller size, lower cost and less weight compared to the commercially available options. The challenging problems of fabricating robust flexible antennas are also addressed and novel solutions are proposed. Two different types of flexible antennas were designed and built. A series of flexible microstrip antennas with slotted grounds which demonstrated to be robust and have 42% less mass than typically used technologies (e.g., microstrip antennas fabricated on Rogers® RT6010, RT/duroid® 5880, etc.); and flexible ferroelectric based tunable low profile antennas that showed tunability from 2.42 GHz to 2.66 GHz using overlapping metallic plates instead of a continuous ground plane. The bending test results demonstrated that, by placing cuts on the ground plane or using overlapping metallic layers that resemble fish scales, it was possible to create highly conductive surfaces that were extremely flexible even when attached to other solid materials. These new approaches were used to overcome limitations commonly encountered in the design of antennas that are intended for use on non-flat surfaces. The material presented in this dissertation represents the first investigation of reconfigurable low profile antennas using tunable high impedance surfaces where the desired electromagnetic performance as well as additional relevant features such as robustness, low weight, low cost and low complexity were demonstrated.

The purpose of this study is: 1) to explore the ways in which the Internet may affect individuals’ political diversity in different strengths of social relationships; 2) to identify which of strong-tie diversity and weak-tie diversity contributes more to political tolerance; and 3) to investigate the extent to which tolerant people are different from the less tolerant in their participation decisions when exposed to political diversity. In order to examine the contribution of Internet news use to political heterogeneity, the current study examines the moderation of the negative influence of politically selective exposure on the Internet on political diversity in social networks by Internet news use. To identify the better contributor to tolerance, the two diversities are compared. To assess the consequence of exposure to political difference for political participation for tolerant and less tolerant people, the present study examines any moderating effect of tolerance between political network heterogeneity and participation. It also observes the moderating effect in different tie strengths. This study utilizes data obtained from the U.S. Citizenship, Involvement, Democracy (CID) survey conducted by a collaboration of Center for Democracy and Civil Society at Georgetown University and the European Social Survey. The sample is 1,001 adults aged 18 and over and representative of the contiguous United States. The dataset contains items concerning Internet use, informal social networks, the composition and diversity of ties and associations, democratic values and tolerance under the primary themes of democracy, social capital and civic engagement. The data are analyzed by hierarchical and OLS regression. According to the findings, Internet news use contributes to individuals’ overall political diversity by reducing the negative influence of the selective exposure occurring from online interaction with homogeneous people. When examined in different strengths of interpersonal relationships, selective exposure discourages strong-tie diversity while encouraging weak-tie diversity. Internet news use positively affects strong-tie diversity but had no influence on weak-tie diversity. Weak-tie diversity is found to be a better contributor to political tolerance. Politically tolerant individuals tend to be discouraged for political participation when exposed to difference in their social relationships. Therefore, while political tolerance may increase overall political diversity, it may as well threaten the balance between deliberation and participation. Closer interpersonal associations are not found to reduce the demobilizing effect of exposure to difference for tolerant individuals. / text

While amputee gait has been studied in great detail, the influence of prosthetic foot sagittal and coronal plane stiffness on amputee walking biomechanics is not well understood. In order to investigate the effects of sagittal and coronal plane foot stiffness on amputee walking, a framework for manipulating the stiffness of a prosthetic foot needs to be developed. The sagittal and coronal plane stiffness of a low profile carbon fiber prosthetic foot was manipulated through coupling with selective-laser-sintered prosthetic ankles. The carbon fiber foot provided an underlying non-linear stiffness profile while the ankle modified the overall stiffness of the ankle-foot combination. A design of experiments was performed to determine the effect of four prosthetic ankle dimensions (keel thickness, keel width, space between the ankle top and bottom faces, and the location of the pyramid connection) on ankle-foot sagittal and coronal plane stiffness. Ankles were manufactured using selective laser sintering and statically tested to determine stiffness. Two of the dimensions, space between the ankle top and bottom faces and the location of the pyramid connection, were found to have the largest influence on both sagittal and coronal plane stiffness. A third dimension, keel thickness, influenced only coronal plane stiffness. A number of prosthetic ankle-foot combinations were created that encompassed a range of sagittal and coronal plane stiffness levels that were lower than that of the low profile carbon fiber foot alone. To further test the effectiveness of the framework to manipulate sagittal and coronal plane stiffness, two ankle-foot combinations, one stiffer than the other in the sagittal and coronal planes, were used in a case study analyzing amputee walking biomechanics. Differences in stiffness were large enough to cause noticeable changes in amputee kinematics and kinetics during turning and straight-line walking. Future work will expand the range of ankle-foot stiffness levels that can be created using this framework. The framework will then be used to create ankle-foot combinations to investigate the effect of sagittal and coronal plane stiffness on gait mechanics in a large sample of unilateral transtibial amputees. / text

Online public fora based on social media facilitate social interaction and synchronous online discussion. Social-media-based public fora resemble real-life political talks, and induce a larger number of and a wider variety of participants than blogs or Usenet newsgroups. By investigating two online groups centered on political discussions on Twitter, this study explores how information and influence flow, how diverse the actual discourse is, and to what extent the online groups communicate with the government. Using network analysis and content analysis/co-word analysis, this study has the findings as follows: In terms of the structural qualities, online public fora are relatively inclusive, but are centralized on a few participants and do not have a statistically significant indication of being equitable in discussion. The two-step flow of communication operates along with the presence of opinion leaders who turn out to be influentials but not content creators. Interestingly, the flow of influence is likely to be less centralized than the flow of information, which implies the importance of the reliability of a given message rather than that of the author. In terms of the actual discourse, participants turn to like-minded fellow citizens’ remarks. Discourses are more emotional than cognitive and exhibits more anger than anxiety. Influential discourses are those with negative emotion more so than with positive emotion and those that are cognitive rather than emotional. Among cognitive components, assertive and strong discourses have greater social influence than analytical discourses. In terms of the interaction with the e-government outlet, the distance between public authorities and private citizens is continuously present despite the decline of temporal and physical distance via the Internet. Based on the results, this study suggests a reconsideration of the Habermasian public sphere in online public fora. It contributes to the literature by empirically confirming the presence of the two-step flow of communication in online public fora and testing the difference between the flow of information and the flow of influence. In addition, it broadens the realm of research on political communication by exploring not only sources/ideological perspectives but also emotional/cognitive aspects in discussions. Methodologically, structure/context, multi-level, and quantitative/qualitative analyses allow this study to have a comprehensive account of online public fora. Practically, this study proposes to improve the interactivity with citizens as the next stage of e-government development. / text

Individuals with various lower-limb neuromuscular and musculoskeletal impairments are often prescribed passive-dynamic ankle-foot orthoses (PD-AFOs) to compensate for impaired ankle muscle weakness. Several studies have demonstrated the beneficial effects of PD-AFOs on pathological gait, but few studies have examined the influence of the AFO stiffness characteristics on gait performance. One challenge to performing such studies is the difficulty of manufacturing custom AFOs with a wide range of controlled stiffness levels. However, selective laser sintering (SLS) is a well-suited additive manufacturing technique for generating subject-specific PD-AFOs of varied stiffness. Therefore, the overall goal of this study was to use SLS manufactured PD-AFOs to identify the relationships between AFO stiffness and gait performance in patients with various lower-limb neuromuscular and musculoskeletal impairments. Six subjects with unilateral impairments were enrolled in this study. For each subject, one subject-specific PD-AFO equivalent to the subject’s clinically prescribed carbon fiber PD-AFO (nominal), one 20% more compliant and one 20% more stiff were manufactured using SLS. Three-dimensional kinematic and kinetic data were collected from each subject while ambulating with each PD-AFO at two different speeds to allow a comprehensive biomechanical analysis to assess the influence of PD-AFO stiffness on gait performance. The results showed that in the compliant AFO condition, the AFO limb vertical ground reaction force (GRF) impulse during loading and the non-AFO limb medial GRF impulse during push-off decreased. In addition, the AFO limb braking GRF impulse during loading and the non-AFO limb braking GRF impulse in early single-limb stance decreased. Furthermore, in the compliant AFO condition, negative knee work during early single-limb stance increased while positive hip work in early swing decreased in the AFO limb. Overall, as AFO stiffness decreased, the AFO limb contributed less to body support and braking. In addition, a decreased medial GRF impulse coupled with an increased vertical GRF impulse during non-AFO single-limb stance suggests that walking stability may be compromised as AFO stiffness decreases. Thus, a tradeoff may exist between preserving stability and increasing net propulsion, which should be considered when assessing the mobility needs of individuals prescribed PD-AFOs as a result of various neuromuscular and musculoskeletal impairments. / text

This dissertation seeks to improve our understanding of the process by which citizens' selective exposure contributes to attitudinal polarization and engagement in political activities. In this dissertation, I test two models that explicate the relationship between selective exposure and political polarization and participation. The knowledge model suggests that the effects of selective exposure on individuals' attitudinal polarization and political engagement are mediated by knowledge of candidate issue stances. The stereotype model proposes that selective exposure indirectly influences polarized attitudes and political participation via stereotypical perceptions of candidates (i.e., McCain's age and the prospect of a Black presidency). By posing issue knowledge and stereotypical perceptions as potential mediators, this study extends current literature to analyze why and how selective exposure leads to polarization and political participation. The results provide evidence that selective exposure influences individuals' stereotypical perceptions of the candidates' age and race, and these stereotypic perceptions influence attitudinal polarization and participation in campaign activities. There was no support for the knowledge model; selective exposure did not have a significant relationship with citizens' issue knowledge nor did it play a mediating role in the relationship between selective exposure and political polarization and participation. This dissertation thus challenges the argument that selective exposure is normatively desirable due to its contribution to citizens' greater levels of political participation. The findings of this study call into question such a contention because the results show that individuals who engage in selective exposure are motivated to participate in political activities by forming stereotypic perceptions of candidates rather than by gaining factual issue knowledge, which is in contrast to democratic theories' assumptions of informed citizenship. Turning to the role of exposure to dissonant media outlets, two contrasting roles were found. On one hand, results offer some evidence that dissonant media use contributes to gaining issue knowledge and inspiring citizen participation. On the other hand, some findings suggest that it reinforces, rather than attenuates, citizens' attitudinal polarization and stereotypical perceptions of candidates. Thus the findings from this study offer mixed support for encouraging citizen exposure to dissimilar viewpoints. / text

This thesis provides investigation into the interaction between quartz lamp emitters and polyether ether ketone (PEEK) powder. Calculations and experiments concerning the conductivity and emissivity of the powder at various temperatures are performed. The thermal profile of the emitter on a flat powder bed is captured using thermal imaging. The effect of exposing a pile of powder to the emitter and the subsequent thermal gradient through the pile is measured and analyzed. Based on these results, ramifications for the application of these emitters to selective laser sintering (SLS) machines for processing high temperature polymers such as PEEK are discussed. / text