Microleakage of Bulk-Fill Composites at Two Different Time Points

Objectives: Microleakage is the main concern in composite restorations. This study aimed to compare the microleakage of two bulk-fill and one conventional composite at two different time points.Methods: Class II cavities were prepared in 60 premolar teeth and divided into six groups of 20. Groups 1 and 4 were incrementally filled with Grandio composite. Groups 2 and 5 were filled with X-tra fil bulk-fill composite. Groups 3 and 6 were filled with Tetric-N-Ceram bulk-fill composite in one layer. The samples were thermocycled for 5000 cycles between 25-55°C. In groups 1-3, the samples were incubated for 24 hours and then immersed in 1% methylene blue dye. Groups 4-6 were incubated for three months and then immersed in dye. All samples were mesiodistally sectioned and degree of microleakage was scored under a light microscope. The data were analyzed using Mann Whitney and Kruskal-Wallis tests.Results: The results showed no significant difference among groups 1-5 and 6 in terms of microleakage (P>0.05) but a significant difference was noted between groups 1 and 4 in this regard (P=0.01). The microleakage in groups 4-6 was higher than that in groups 1-3 (P=0.02). Also, microleakage in gingival margins was greater than that in occlusal margins (P=0.02).Conclusion: The microleakage of bulk-fill composites is comparable to that of conventional composites both at 24 hours and three months after restoration

Multi-polarized sensing for cognitive radio

In this thesis the multi-polarized Cognitive Radios are studied. Cognitive Radios are proposed as an interesting way to more efficiently use the frequency resources. A Cognitive Radio secondary user finds the frequency bands which are not utilized by primary users and communicates on them without interfering with the primary users. In order to achieve this goal the secondary user must be able to detect reliably and quickly the presence of a primary user in a frequency band. In this thesis, the impact of polarization on the spectrum sensing performances of cognitive radio systems is studied.First the depolarization occurring in the wireless channel is studied for two cognitive radio scenarios. This is done through an extensive measurement campaign in two outdoor-to-indoor and indoor-to-indoor scenarios where the parameters characterizing the radiowaves polarization are characterized at three different spatial scales: small-scale variation, large-scale variation and distance variation. Second, a new approach is proposed in modeling of multi-polarized channels. The polarization of received fields is characterized from an electromagnetic point of view by modeling the polarization ellipse. Theoretical formulations are proposed in order to obtain the parameters characterizing the polarization ellipse based on the signals received on three cross-polarized antennas. A system-based statistical model of the time-dynamics of polarization is proposed based on an indoor-to-indoor measurement campaign. The analytical formulations needed in order to project the polarization ellipse onto a polarized multi-antenna system are given and it is shown how the model can be generated. Third, the impact of polarization on the spectrum sensing performances of energy detection method is presented and its importance is highlighted. The performance of spectrum sensing with multi-polarized antennas is compared with unipolar single and multi-antenna systems. This analysis is based on an analytical formulation applied to the results obtained from the multi-polarized measurement campaign. The detection probability as a function of distance between the primary transmitter and the secondary terminal and the inter-antenna correlation effect on the spectrum sensing performance are studied. An important limitation of energy detector is its dependence on the knowledge of the noise variance. An uncertainty on the estimation of the noise variance considerably affects the performance of energy detector. This limitation is resolved by proposing new multi-polarized spectrum sensing methods which do not require any knowledge neither on the primary signal nor on the noise variance. These methods, referred to as “Blind spectrum sensing methods”, are based on the use of three cross-polarized antennas at the secondary terminal. Based on an analytical formulation and the results obtained from the measurement campaign, the performances of the proposed methods are compared with each-other and with the energy detection method. The effect of antenna orientation on the spectrum sensing performance of the proposed methods and the energy detection method is studied using the proposed elliptical polarization model. Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Multi-polarized sensing for cognitive radio

In this thesis the multi-polarized Cognitive Radios are studied. Cognitive Radios are proposed as an interesting way to more efficiently use the frequency resources. A Cognitive Radio secondary user finds the frequency bands which are not utilized by primary users and communicates on them without interfering with the primary users. In order to achieve this goal the secondary user must be able to detect reliably and quickly the presence of a primary user in a frequency band. In this thesis, the impact of polarization on the spectrum sensing performances of cognitive radio systems is studied. First the depolarization occurring in the wireless channel is studied for two cognitive radio scenarios. This is done through an extensive measurement campaign in two outdoor-to-indoor and indoor-to-indoor scenarios where the parameters characterizing the radiowaves polarization are characterized at three different spatial scales: small-scale variation, large-scale variation and distance variation. Second, a new approach is proposed in modeling of multi-polarized channels. The polarization of received fields is characterized from an electromagnetic point of view by modeling the polarization ellipse. Theoretical formulations are proposed in order to obtain the parameters characterizing the polarization ellipse based on the signals received on three cross-polarized antennas. A system-based statistical model of the time-dynamics of polarization is proposed based on an indoor-to-indoor measurement campaign. The analytical formulations needed in order to project the polarization ellipse onto a polarized multi-antenna system are given and it is shown how the model can be generated. Third, the impact of polarization on the spectrum sensing performances of energy detection method is presented and its importance is highlighted. The performance of spectrum sensing with multi-polarized antennas is compared with unipolar single and multi-antenna systems. This analysis is based on an analytical formulation applied to the results obtained from the multi-polarized measurement campaign. The detection probability as a function of distance between the primary transmitter and the secondary terminal and the inter-antenna correlation effect on the spectrum sensing performance are studied. An important limitation of energy detector is its dependence on the knowledge of the noise variance. An uncertainty on the estimation of the noise variance considerably affects the performance of energy detector. This limitation is resolved by proposing new multi-polarized spectrum sensing methods which do not require any knowledge neither on the primary signal nor on the noise variance. These methods, referred to as “Blind spectrum sensing methods”, are based on the use of three cross-polarized antennas at the secondary terminal. Based on an analytical formulation and the results obtained from the measurement campaign, the performances of the proposed methods are compared with each-other and with the energy detection method. The effect of antenna orientation on the spectrum sensing performance of the proposed methods and the energy detection method is studied using the proposed elliptical polarization model.(FSA 3) -- UCL, 201

Polarization Statistics for Outdoor-to-Indoor and Indoor-to-Indoor Scenarios

info:eu-repo/semantics/nonPublishe

Tri-polarized spectrum sensing based on an experimental outdoor-to-indoor cognitive-radio scenario

Compared to classical spatially separated multiple antenna system, cross-polarized co-located antenna systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. In this paper the spectrum sensing of a Cognitive Radio (CR) system taking advantage of polarization diversity under Rayleigh fading is investigated and compared to an equivalent system using spatial diversity. This analysis is based on a theoretical formulation applied to a real-world scenario. For this purpose, an outdoor-to-indoor measurement campaign at a frequency of 3.5 GHz is realized, where an indoor secondary user senses the signals received from an outdoor primary base station. The signals received at each antenna are first combined and then applied to an energy detector. The theoretical expressions are simulated in the measurement context. The detection probability behavior as a function of distance between the Primary Transmitter (PTx) and the Secondary Terminal (STE) and the inter-antenna correlation effect on the sensing performance are studied

Performance of Polarized Sensing in Real-World Cognitive Radio Scenarios

The sensing performance of a cognitive radio system using a tri-polarized antenna at the secondary terminal is investigated in a real-world scenario. The analysis is based on an outdoor-to-indoor measurement campaign, where the secondary network is deployed indoor and senses the signals received from an outdoor primary base-station. By considering a minimum acceptable detection probability of 0.95, the use of diversity increases the range of acceptable sensing up to 18 meters. The minimum acceptable signal-to-noise ratio (SNR) is reduced up to 14 dB. As expected, the best performance is reached with maximum ratio combining. However, the detection performance is only slightly decreased with square law combining (SLC). As an example, for the multi-polarized reception scenario, SLC increases the minimum acceptable SNR by less than 2 dB and decreases the range of acceptable sensing by less than 3 meters. Finally, we show that polarized sensing is a good performance trade-off in realistic scenario where the polarization of the primary transmitter is unknown

Study of the temporal dynamics of the polarization of received electromagnetic waves based on an indoor-to-indoor measurement campaign

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while still maintaining low inter-antenna correlation. In this paper, the time-variation of the polarization of the received waves is investigated. In this scenario, a theoretical formulation is proposed in order to obtain the parameters of the elliptical polarization, based on the signals received on three perpendicularly polarized antennas. A measurement campaign has been performed in an indoor-to-indoor scenario and at a frequency of 3.6 GHz. Different measurement positions are considered in a Line-Of-Sight (LOS) and a Non-Line-of-Sight (NLOS) scenario. Based on these measurements and the proposed theoretical formulation, the time-variation of the parameters describing the polarization ellipse is analyzed and a time-variant statistical model is proposed.info:eu-repo/semantics/publishe

Tri-polarized spectrum sensing based on an experimental outdoor-to-indoor cognitive-radio scenario

Compared to classical spatially separated multiple antenna system, cross-polarized co-located antenna systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. In this paper the spectrum sensing of a Cognitive Radio (CR) system taking advantage of polarization diversity under Rayleigh fading is investigated and compared to an equivalent system using spatial diversity. This analysis is based on a theoretical formulation applied to a real-world scenario. For this purpose, an outdoor-to-indoor measurement campaign at a frequency of 3.5 GHz is realized, where an indoor secondary user senses the signals received from an outdoor primary base station. The signals received at each antenna are first combined and then applied to an energy detector. The theoretical expressions are simulated in the measurement context. The detection probability behavior as a function of distance between the Primary Transmitter (PTx) and the Secondary Terminal (STE) and the inter-antenna correlation effect on the sensing performance are studied. © 2012 Elsevier B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Cross-polar iscrimination statistics for outdoor-to-indoor and indoor-to-indoor channels

info:eu-repo/semantics/nonPublishe

Probabilistic co-existence and throughput of cognitive dual-polarized networks

Diversity techniques for cognitive radio networks are important since they enable the primary and secondary terminals to efficiently share the spectral resources in the same location simultaneously. In this paper, we investigate a simple, yet powerful, diversity scheme by exploiting the polarimetric dimension. More precisely, we evaluate a scenario where the cognitive terminals use cross-polarized communications with respect to the primary users. Our approach is network-centric, i.e. performance of the proposed dual-polarized system is investigated in terms of link throughput in the primary and the secondary networks. In order to carry out this analysis, we impose a probabilistic co-existence constraint derived from an information-theoretic approach, i.e. we enforce a guaranteed capacity for a primary terminal for a high fraction of time. Improvements brought about by the use of our scheme are demonstrated analytically and through simulations. In particular, the main simulation parameters are extracted from a measurement campaign dedicated to characterization of indoor-to-indoor and outdoor-to-indoor polarization behaviors. Our results suggest that the polarimetric dimension represents a remarkable opportunity, yet easily implementable, in the context of cognitive radio networks.SCOPUS: ar.jinfo:eu-repo/semantics/publishe