The term cognitive control refers to a variety of mental processes that support goal-directed behavior. In the current dissertation, I focus on the role of cognitive control in situations where a weaker (but task-relevant) source of information must be selected over a stronger (but task-irrelevant) source of information. The efficiency with which individuals select information in the face of distraction has classically been viewed as a function of static control settings tied to task instructions. Recent evidence suggests, however, that variations in the efficiency of cognitive control can be induced by variations in stimulus experience and that multiple control settings may be maintained for a single task. To date, little is known about the mechanisms that support this more flexible form of control. Across six experiments, I find evidence for the formation of multiple control settings that are relatively long lasting but fragile. Multiple control settings can be maintained within a single experiment and can last over relatively long periods of time, however, without the proper contextual support these control settings fall apart. These results emphasize the important role of stimulus experience in studies of cognitive control.

Sharing communication resources in wireless communication networks, due to the ever increasing growth in the number of users and the growing demand for higher data rates, appears to be inevitable. Consequently, present wireless communication networks should provide service for a large number of users through a frequency selective and interference limited medium rather than a single band, noise limited channel. In this thesis, we study a Gaussian interference network with orthogonal frequency sub-bands with slow faded and frequency-selective channel coefficients. The network is decentralized in the sense that there is no central node to assign the frequency sub-bands to the users. Moreover, due to lack of a feedback link between the two ends of any transmitter-receiver pair, all transmitters are unaware of the channel coefficients. Since the channel is assumed to be static during the communication period of interest, the concept of outage probability is employed in order to assess the performance of the network. In a scenario where all transmitters distribute their available power uniformly across the sub-bands, we investigate the problem of how establishing a nonzero correlation ρ among the Gaussian signals transmitted by each user along different frequency sub-bands can improve the outage probability at each of the receivers. Specifically, we show in a general k-user interference channel over N orthogonal frequency sub-bands that , when receivers treat interference as noise, ρ=0 is a point of local extremum for the achievable rate at each receiver, for any realization of channel coefficients. Moreover, in the case of K=2 with arbitrary number of sub-bands, it is verified that there exists a finite level of Signal-to-Noise Ratio (SNR) such that the achievable rate has a local minimum at ρ=0, which is not necessarily the case when K>2. We then concentrate on a 2-user interference channel over 2 orthogonal frequency sub-bands and characterize the behavior of the outage probability in the high SNR regime. We consider two simple decoding strategies at the receiver. In the first scenario, receivers simply treat interference as noise. In the second scenario, the receivers have the choice either to decode the desired signal treating interference as noise or to decode interference treating the desired signal as noise before decoding the interference free signal. Indeed, in both cases, we first show that the achievable rate is an increasing function of ρ in the high SNR regime, which suggests to repeat the same signal over the sub-bands. This observation, in a sense, reflects to the behavior of the outage probability, the scaling behavior of which in the high SNR regime is characterized for the Rayleigh fading scenario.

Substances of natural and synthetic origin were studied using analytical, bioassay guided isolation, metabolomics and medicinal chemistry techniques. In a section focused on the plant family Marcgraviaceae, a validated method for the quantification of six pentacyclic triterpenes (α and β Amyrin lupeol, ursolic acid, betulin and betulinic acid) in the Souroubea spp was developed. Quantification of the triterpenes in the crude extracts was achieved using HPLC-APCI mass selective detection. The calibration curves for the five triterpenes evaluated were highly linear (r2 >0.993) and percentage recovery from spiked samples were greater than 94% for all compounds. The LOD for betulinic acid was 0.01 µg for betulinic acid on column and LOQ was 0.03 µg. The method was successfully applied to 41 crude extracts from leaf and stem of Souroubea spp, from two locations in Costa Rica. The method is suitable for quality control of raw materials used in the manufacture of natural health products. The use of modern metabolomic techniques, UHPLC-QTOF allowed the identification of five putative makers that can potentially be used in distinguishing between the two Souroubea species. The validated method was used in the quantification of the above triterpenes in a total of thirteen Marcgraviaceae species collected in Costa Rica. It was established that betulinic acid and β- Amyrin could be used as makers for this family of tropical vines. These same thirteen plants extracts were evaluated in antifungal and quorum sensing inhibition bioassays. Marcgravia nervosa was the only species that showed significant activity in both bioassays. Bioassay guided fractionation of the crude ethanolic extract of M. nervosa led to the identification of 2-methoxynaphthoquinone as the bioactive compound responsible for the bioactivity. The crude leaf ethanolic extract from M. nervosa showed a significant inhibition of QS comparable or somewhat better than D. pulchra extracts with the M. nervosa extract showing stronger inhibiting QS with a halo of 21.8mm, more than D. pulcra extracts which generated a halo of 15.9mm. The active quinone has a MIC of 85 µM against Saccharomyces cerevisiaBY4741 (haploid) and 100 µM against Saccharomyces cerevisiae BY4743 (diploid) compared to berberine (positive control) with a MIC 600 µM for both strains. This quinone is not present in any of the other twelve species of Marcgraviaceae available to us. In work focusing on organic synthesis, a total of 57 semi-synthetic derivatives of dillapiol, safrol and piperonal were prepared and evaluated for their inhibitory activity in a CYP 3A4 bioassay to assess their potential use as pesticide synergists. The synergistic activity of dillapiol has been improved 45 fold; analog 31 has an IC50 = 0.2 µM compared with dillapiol IC50= 9.18 µM. A number of other compounds structurally related to 31 showed similar levels of activity. A screening of a compound library identified the amino sulfoxide 3 as a potential lead for the design of a selective connexin blocker with potential application in the treatment of spinal cord injuries. The use of X-ray crystallography permitted the correction of the original structure assigned to 3. Once the structure was corrected a total of 6 analogs were prepared. Compound 3 has the highest inhibition of GJIC whereas compound 8 and compound 2, reduced anionic hemi-channel activity. Compound 2 also reduced the cationic activity of the hemi-channels.

No description available.

Cognition is dynamic and complex, requiring specific sets of brain areas to cooperate for specific tasks. Neural synchronization is a proposed mechanism for transient functional integration of specific neural populations, enabling feature flexible binding and dynamic assignment of functional connectivity in the brain according to task demands. This thesis addresses the role of neural synchronization in selective attention and perceptual consciousness. The goals of this thesis are to test the hypothesis that synchronization between brain regions is relevant to network dynamics in selective attention and for perceptual organization, and to elucidate the function of synchronization in different frequency ranges. Using a selective visuospatial cuing paradigm it is shown that deploying attention to one visual hemifield yields transient long-distance gamma-band synchronization between contralateral visual cortex and other, widespread, brain regions. This is interpreted as a mechanism for establishing anticipatory biasing of communication in the cortex. Long-distance gamma synchrony, moreover, is periodically 'refreshed' at a theta rate, possibly serving to maintain this gamma network. While local alpha-band activity was found to be greater ipsilateral to the attended visual hemifield, alpha-band synchronization between primary visual cortex and higher visual areas was greater contralateral to attended locations. This suggests that local alpha synchrony is relevant for inhibition, while long-range alpha synchronization enacts functional coupling. The onset of a new conscious percept during binocular rivalry coincides with large-scale gamma-band synchronization which recurs at a theta rate. This suggests that gamma synchronization integrates features into a unified conscious percept while the theta cycle maintains that network. Using an audiovisual speech integration paradigm it is shown that large-scale gamma synchronization is greater when incongruence is detected between auditory and visual streams. This highlights an important distinction: neural synchronization reflects neural integration, not perceptual integration. Perceptual integration typically requires neural integration (feature binding), however, in this case detection of audiovisual mismatches requires cooperation within a distributed network, whereas audiovisual speech integration is largely accomplished in superior temporal cortex. These studies indicate that long-distance gamma synchronization establishes neural integration, the theta cycle maintains gamma synchronous networks, and local and long-range alpha synchrony reflect sustained inhibition and functional coupling mechanisms, respectively.

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: solution 13C-NMR study; olid phase peptide synthesis; bicyclic peptides; ammonium ionophores; valinomycin; ion selective electrode. Includes bibliographical references (p. 63-65).

Orientador: Luzenira Alves Brasileiro / Banca: Dib Gebara / Banca: Marisa Teresa Françoso / Resumo: Este trabalho apresenta um procedimento para analisar a sustentabilidade econômica do sistema de coleta seletiva de resíduos recicláveis urbanos. Com o intuito de caracterizar o cenário econômico, o objetivo da pesquisa é realizar uma análise de sustentabilidade econômica da coleta seletiva de resíduos sólidos urbanos recicláveis. Um estudo de caso foi realizado para a cidade de Votuporanga - SP. Os resultados mostram que o sistema de coleta seletiva analisado apresenta sustentabilidade econômica. O estudo demonstrou também que se a população urbana segregar todos os resíduos recicláveis que são gerados, o custo da coleta seletiva reduz significativamente. Um sistema de coleta seletiva eficiente e eficaz proporciona, além da sustentabilidade econômica, outros benefícios para a sociedade em geral, tais como: ambiental, educacional e social. / Abstract: This work presents a procedure for analyzing the economic sustainability of the system of selective collection of recyclable waste city. A case study was conducted for Votuporanga city. The results show that the selective collection system has analyzed economic sustainability. The study also showed that the urban population segregate all recyclable waste that are generated, the cost of selective reduced significantly. A selective collection system provides efficient and effective, and economic sustainability, other benefits to society in general, such as environmental, educational and social. / Mestre

The preferential grazing of an organism on certain particles from the environment (selective feeding) impacts particle compositions and distributions in aquatic systems. Historically, selective feeding has been examined almost exclusively through the lens of particle size. In this dissertation, I investigated size-based selection alongside particle shape, adhesive interactions, and the mechanical operation of the filter to characterize the selective-feeding capabilities of marine mucous-mesh filter-feeders (the planktonic appendicularian Oikopleura dioica and the benthic ascidians Herdmania momus and Styela plicata). I used high-speed videography to describe the feeding-filter mechanics of O. dioica and tested its capacity for size-based particle selection. I show for the first time how pulsatile flow coupled with elasticity of the filter facilitates prey detachment. Using synthetic beads, I showthat the food-concentrating filter selectively retains smaller particles because of their increased adhesion. Appendicularian houses may therefore retain particles size-selectively, which counters the historically-held assumption that appendicularians are non-selective grazers. I synthesized ellipsoidal microbeads to test the effect of particle length-to-width ratios on the capture efficiency of O. dioica and S. plicata. Both grazers retained ellipsoidal particles according to their minimum diameter. I identified the kinematic mechanism for retention patterns of ellipsoidal particles using high-speed videography and endoscopy of particle interactions with the mucous filters of O. dioica and H. momus, respectively. In the filters of both animals, ellipsoids oriented parallel to fluid streamlines and the minimum dimension of the particle intercepted the filters. I provide the first mesh-scale observations of particle capture by H. momus, show how particle shape influences hydrosol filtration by S. plicata, and suggest that ascidian filtration may not be adequately described by simple sieving.

Made available in DSpace on 2014-06-11T19:27:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-07-26Bitstream added on 2014-06-13T19:36:07Z : No. of bitstreams: 1 mota_rc_me_rcla.pdf: 864792 bytes, checksum: b5dc444d25c637c8318c55c35af6ecd9 (MD5) / A produção de lixo vem aumentando de forma preocupante em todo o mundo, estando este fato intrinsecamente ligado aos hábitos de consumo e ao estilo de vida das pessoas. Este é um dos graves problemas da atualidade e qualquer ação que vise sua solução, ou pelo menos sua minimização, é bem vinda. Assim, é dever de toda instituição pública, dentre elas as Universidades, desenvolver relacionados à questão da produção e destinação final dos resíduos sólidos. O presente trabalho tem o intuito de diagnosticar a atual situação de Programas de Coleta Seletiva desenvolvidos por algumas das principais instituições públicas de ensino superior do Estado de São Paulo, dando destaque ao Programa de Coleta Seletiva já em andamento na UNESP - Campus Rio Claro. Também é objetivo do trabalho entender a dinâmica deste Programa e de suas relações com a comunidade local, procurando formular ações que propiciem sua manutenção e continuidade, assim como a criação de novos Programas de minimização de resíduos. / The production of garbage is increasing in a dangerous way all over the world, and this fact is inherent to the consumption habits and the people's lifestyle. Nowadays, this is one of the greatest problems and any kind of action to solve or lessen it, is welcome. Thus, it is a duty for all the public institutions, including universities, to develop programs related to garbage production and destination. This research intends to diagnose the current situation of the Recycling Programs developed by some of the main public universities in the State of São Paulo, mainly the program that is happening in UNESP - Campus Rio Claro. It is also the objective of this research to know this program's dynamic and its relations with the local community, in order to formulate actions that assure its maintenance and continuation, as well as the creation of new recycling programs.