Communication over today’s IP-based networks are to some extent subject to packet loss. Most real-time applications, such as video streaming, need methods to hide this effect, since resending lost packets may introduce unacceptable delays. For IP-based video streaming applications such a method is referred to as a packet loss concealment scheme. In this thesis a recently proposed mixture model and least squares-based packet loss concealment scheme is implemented and evaluated together with three more well known concealment methods. The JM reference software is used as basis for the implementation, which is a public available software codec for the H.264 video coding standard. The evaluation is carried out by comparing the schemes in terms of objective measurements, subjective observations and a study with human observers. The recently proposed packet loss concealment scheme shows good performance with respect to the objective measures, and careful observations indicate better concealment of scenes with fast motion and rapidly changing video content. The study with human observers verifies the results for the case when a more sophisticated packetization technique is used. A new packet loss concealment scheme, based on joint modeling of motion vectors and pixels, is also investigated in the last chapter as an additional contribution of the thesis.

Given potential risk factors in the lives of adolescents, parents are usually motivated to monitor and protect their adolescents. There is a need to better understand what combinations of parental dimensions and practice best influence an adolescent's propensity to disclose or conceal personal information with their parents. This paper examines how parenting dimensions (warmth, psychological control, and harsh punishment) and the parenting practice of solicitation influence an adolescent's propensity to disclose or conceal information. Adolescents in 106 families (53 females; predominantly Caucasian) reported on their mothers' and fathers' parenting dimensions as well as their parents' effort to solicit information. Factor analysis was conducted on the measure typically used for disclosure to test whether the items measured only disclosure or if two distinct adolescent outcomes of disclosure and concealment were more appropriate. Results supported our contention that disclosure and concealment might be considered separately. Other results indicated a positive association between adolescents' disclosure and the positive parenting dimension warmth and parental solicitation. There was a negative association between disclosure and harsh punishment in the father-son dyad. Psychological control was positively associated with concealment for both adolescent boys and girls. With a few exceptions, same gendered dyads (father-son, mother-daughter) showed the most associations between parenting dimensions and practices and disclosure or concealment.

<p>Allocation concealment is the process of implementing the randomization sequence in a manner that prevents foreknowledge of upcoming group assignments. It protects against preferential enrolment of study participants, which could disrupt the prognostic balance that randomization aims to create in the first place. Envelopes are one method perceived by clinical trial authorities to adequately conceal allocation, despite evidence suggesting otherwise. We do not believe that envelopes are adequate, and we wanted to know the extent to which our sentiment resonated within the clinical trials community. We administered an internet-based survey to a random sample (n=1,926) of corresponding authors of recently published randomized clinical trials (RCTs). We sent non-responders up to two e-mail reminders starting from two weeks after the original invitation. We received 490 complete surveys (25.4% response rate) after collecting data for seven weeks. Most participants (61%) preferred central randomization to conceal allocation, yet a majority (64%) also accepted that envelopes are adequate. After they were shown examples that suggested envelopes’ vulnerability, 11% of participants shifted their preference away from envelopes and 38% of participants became less accepting of envelopes. Compared to their initial ratings and after they were shown the examples, significantly more participants (69%) preferred central randomization (p</p> / Master of Science (MSc)

La mise en œuvre de la prescription de l’action publique n’est pas, en principe, subordonnée à la connaissance de l’infraction par les personnes pouvant déclencher les poursuites pénales. Le législateur retient en effet comme point de départ du délai de prescription le jour de la commission des faits et non celui de leur découverte. Cette règle connaît toutefois une exception lorsque l’infraction est dite clandestine. Parce que le ministère public et la victime n’ont pas pu avoir connaissance de l’existence de cette infraction, la prescription ne court pas tant que les faits ne sont pas apparus et n’ont pu être constatés dans des conditions permettant l’exercice de l’action publique. L’exception de clandestinité empêche donc le temps de produire son effet destructeur sur l’action publique. Sa mise en œuvre évite ainsi que certaines infractions restent impunies par le seul jeu de l’écoulement du délai. S’il ne fait aucun doute que la clandestinité d’une infraction constitue un obstacle à la prescription de l’action publique, la notion même de clandestinité reste à circonscrire. Elle recouvre en effet, en droit positif, de multiples réalités qui rendent impossible sa systématisation. Aux termes de la recherche, il apparaît que le critère déterminant de la clandestinité consiste dans l’ignorance légitime de l’existence de l’infraction par les personnes habilitées à mettre en mouvement l’action publique. En application de l’adage contra non valentem agere non currit praescriptio, cette ignorance caractérisée devrait autoriser le report du point de départ de la prescription de l’action publique de toute infraction au jour où les faits peuvent être constatés par le ministère public ou par la personne lésée. / In criminal matters, the setting of the time limit for prosecution is theoretically not subject to the knowledge of the offense by the people who can trigger criminal proceedings. Indeed, according to the law, the starting point of the said time limit period is the day the offense was committed, and not the day it was discovered. However, an exception to this rule exists when the offense is said to be clandestine. When both the prosecutor and the victim could not have know of the existence of this offense, the time-limit period does not run until the facts appear and can be noticed in the same conditions. An exception of clandestinity prevents time to produce its destructive effect on the prosecution. It avoids certain offenses to remain unpunished by the single flow of time. Undoubtedly, clandestinity is an obstacle to the prosecution of an offense. Yet, the notion itself remains to be circumscribed. In substantive law, clandestinity refers to a wide variety of realities ; its systematization is thus impossible. In a prospective approach, a criterion is to be found in the justifiable ignorance of the offense by those who can initiate a criminal action. Under the adage “contra non valentem agere non currit praescriptio”, this specific ignorance allows postponement of the starting point of the time limit for prosecution of any offence on the day on which the facts have been noticed by the prosecutor or the victim.

African Americans have a higher proclivity to depression than other ethnic groups in the United States and also have a greater propensity to avoid seeking professional mental health treatment. The available research has shown that racial and cultural barriers such as perceived discrimination and self-concealment are the primary factors that negatively affect African Americans' attitudes toward mental health itself and mental health treatment. Perceived discrimination and self-concealment may also negatively affect whether African Americans seek help for depression and from whom, but further investigation was needed. The quantitative survey study provided answers to which factors influence whether and where African Americans seek help for major depression. A total of 147 participants were recruited through word of mouth, local churches, community organizations, and virtual venues such as electronic mail and social media. Multivariate analysis of variance revealed the mean scores of African Americans' use of natural supports and their use of outpatient treatment (dependent variables) were not equal across all levels of their self-concealment, perceived discrimination, and depressive symptoms (independent variables). Multivariate analysis of covariance revealed that the mean scores remained the same when controlling for gender, income, education, and relationship status (covariates). The results suggest that the latter factors influence African Americans' decisions on where to seek help for depression regardless of their gender and socioeconomic status. Increasing the propensity of African Americans to seek professional help for depression should improve the mental health of the population as a whole and reduce the incidents of serious mental illness of those who are treated.

A prey animal can use different strategies to avoid becoming eaten by predators. One such widely recognised strategy is the use of body colouration to decrease the risk of becoming detected, i.e. cryptic colouration. The principles of crypsis that I have studied are background matching, disruptive colouration and distractive markings. Further, I also studied the concealing effect of the visual background habitats. I used artificial prey items and backgrounds, and blue tits (Cyanistes caeruleus) as predators, to investigate prey concealment. In Paper I, I tested if high-contrast markings in prey coloration or in the background would result in a distracting effect. I found that such markings did increase prey search time, even when the prey markings were lighter or darker than the background. In Paper II, I studied the use of chromatic cues by predators when searching for prey. The birds easily detected prey that chromatically deviated from its background. Interestingly, background-matching prey was more difficult to detect when the colour scheme had low ultraviolet and high shortwave reflectance compared to when the reflectance bands were even. In Paper III, I studied optimisation of achromatic contrast within prey colour pattern and also the effect of shape diversity of background pattern elements on prey detection. I found that all prey types were more difficult to detect on the diverse background, but the level of contrast within prey pattern did not influence search times. In Paper IV, I further investigated how a prey should optimise its patterning with respect to background matching. I found that prey with repeated pattern elements was equally hard to detect as prey with more variable pattern. However, prey with a spatially regular pattern (aligned pattern elements) was easier to detect than prey with a spatially irregular pattern. In this paper I also found that high complexity of element shapes in the background, made the search task more difficult. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Accepted

Error Correction and Concealment of Block Based, Motion-Compensated Temporal Prediction, Transform Coded Video David L. Robie 133 Pages Directed by Dr. Russell M. Mersereau The use of the Internet and wireless networks to bring multimedia to the consumer continues to expand. The transmission of these products is always subject to corruption due to errors such as bit errors or lost and ill-timed packets; however, in many cases, such as real time video transmission, retransmission request (ARQ) is not practical. Therefore receivers must be capable of recovering from corrupted data. Errors can be mitigated using forward error correction in the encoder or error concealment techniques in the decoder. This thesis investigates the use of forward error correction (FEC) techniques in the encoder and error concealment in the decoder in block-based, motion-compensated, temporal prediction, transform codecs. It will show improvement over standard FEC applications and improvements in error concealment relative to the Motion Picture Experts Group (MPEG) standard. To this end, this dissertation will describe the following contributions and proofs-of-concept in the area of error concealment and correction in block-based video transmission. A temporal error concealment algorithm which uses motion-compensated macroblocks from previous frames. A spatial error concealment algorithm which uses the Hough transform to detect edges in both foreground and background colors and using directional interpolation or directional filtering to provide improved edge reproduction. A codec which uses data hiding to transmit error correction information. An enhanced codec which builds upon the last by improving the performance of the codec in the error-free environment while maintaining excellent error recovery capabilities. A method to allocate Reed-Solomon (R-S) packet-based forward error correction that will decrease distortion (using a PSNR metric) at the receiver compared to standard FEC techniques. Finally, under the constraints of a constant bit rate, the tradeoff between traditional R-S FEC and alternate forward concealment information (FCI) is evaluated. Each of these developments is compared and contrasted to state of the art techniques and are able to show improvements using widely accepted metrics. The dissertation concludes with a discussion of future work.

Multiview video is one of the emerging research areas especially among the video coding community. Transmission of multiview video over an error prone network is possible with efficient compression of these videos. But along with the studies for efficiently compressing the multiview video, new error concealment and error protection methods are also necessary to overcome the problems due to erroneous channel conditions in practical applications. In packet switching networks, packet losses may lead to block losses in a frame or the loss of an entire frame in an encoded video sequence. In recent years several algorithms are proposed to handle the loss of an entire frame efficiently. However methods for full frame losses in stereoscopic or multiview videos are limited in the literature. In this thesis a stereoscopic approach for full frame loss concealment of multiview video is proposed. In the proposed methods, the redundancy and disparity between the views and motion information between the previously decoded frames are used to estimate the lost frame. Even though multiview video can be composed of more than two views, at most three view are utilized for concealment. The performance of the proposed algorithms are tested against monoscopic methods and the conditions under which the proposed methods are superior are investigated. The proposed algorithms are applied to both stereoscopic and multiview video.

The advances in multimedia technologies increased the interest in utilizing three dimensional (3D) video applications in mobile devices. However, wireless transmission is significantly prone to errors. Typically, packets may be corrupted or lost due to transmission errors, causing blocking artifacts. Furthermore, because of compression and coding, the error propagates through the sequence and salient features of the video cannot be recovered until a key-frame or synchronization-frame is correctly received. Without the use of concealment and enhancement techniques, visible artifacts would inevitably and regularly appear in the decoded stream. In this thesis, error concealment techniques for full frame losses in depth plus video and stereo video structures are implemented and compared. Temporal and interview correlations are utilized to predict the lost frames while considering the memory usage and computational complexity.The concealment methods are implemented on jm17.2 decoder which is based on H.264/AVC specifications [1]. The simulation results are compared with the simple frame copy (FC) method for different sequences having different characteristics.

abstract: With tremendous increase in the popularity of networked multimedia applications, video data is expected to account for a large portion of the traffic on the Internet and more importantly next-generation wireless systems. To be able to satisfy a broad range of customers requirements, two major problems need to be solved. The first problem is the need for a scalable representation of the input video. The recently developed scalable extension of the state-of-the art H.264/MPEG-4 AVC video coding standard, also known as H.264/SVC (Scalable Video Coding) provides a solution to this problem. The second problem is that wireless transmission medium typically introduce errors in the bit stream due to noise, congestion and fading on the channel. Protection against these channel impairments can be realized by the use of forward error correcting (FEC) codes. In this research study, the performance of scalable video coding in the presence of bit errors is studied. The encoded video is channel coded using Reed Solomon codes to provide acceptable performance in the presence of channel impairments. In the scalable bit stream, some parts of the bit stream are more important than other parts. Parity bytes are assigned to the video packets based on their importance in unequal error protection scheme. In equal error protection scheme, parity bytes are assigned based on the length of the message. A quantitative comparison of the two schemes, along with the case where no channel coding is employed is performed. H.264 SVC single layer video streams for long video sequences of different genres is considered in this study which serves as a means of effective video characterization. JSVM reference software, in its current version, does not support decoding of erroneous bit streams. A framework to obtain H.264 SVC compatible bit stream is modeled in this study. It is concluded that assigning of parity bytes based on the distribution of data for different types of frames provides optimum performance. Application of error protection to the bit stream enhances the quality of the decoded video with minimal overhead added to the bit stream. / Dissertation/Thesis / M.S. Electrical Engineering 2011