Browsing by Author "Costa, Rita Alexandra Santos da"
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- Automatic determination of pauses in speech for classification of stuttering disorderPublication . Teixeira, João Paulo; Fernandes, Maria Goreti Antunes; Costa, Rita Alexandra Santos daAn algorithm to automatically identify segments of silence or speech is presented. The algorithm was developed to measure the silence periods in spontaneous and read speech. These silence periods are one of the parameters used to know the degree of severity of stuttered speech. For this purpose the three longer disfluent events (pauses or other disfluent events) and also the percentage of silence are useful. The algorithm is based on the evaluation of the energy and the zero crossing rate of the signal compared to the threshold values previously determined in silence. One experiment with eight subjects is described using the Stuttering Severity Instrument for Children and Adults – SSI and the percentage of silence in speech. It was concluded that the percentage of silence is good enough to separate stuttered from the normal speech but alone is not capable of measuring the degree of severity of the stuttered speech.
- Measure and comparison of speech pause duration in subjects with disfluency speechPublication . Teixeira, João Paulo; Fernandes, Maria Goreti Antunes; Costa, Rita Alexandra Santos daThis work has lhe goal of comparing the pause duration in lhe disfluency speech and nonnal speech. Disfluency and normal sponlaneous spccch was rccordcd in a contcxl were the subjcels had to deseribe a scenc fram each othcr. 1l1C pause determin;Jtion algorithm was dcvelopcd. The automatic pause determinations allowed lhe measure of percenlage of silence along the record of several minutcs of spcech. As expecled lhese paramelers is ralher diffcrent in subjecIs with and wi thout disfluency spcech. but it do nol scems that it is proponional la lhe sevcrity of lhe disfluency.
- Measure and comparison of speech pause duration in subjects with disfluency speechPublication . Teixeira, João Paulo; Fernandes, Maria Goreti Antunes; Costa, Rita Alexandra Santos daThis work has the goal of comparing the pause duration in the disfluency speech and normal speech. Disfluency and normal spontaneous speech was recorded in a context were the subjects had to describe a scene from each other. The pause determination algorithm was developed. The automatic pause determinations allowed the measure of percentage of silence along the record of several minutes of speech. As expected these parameters is rather different in subjects with and without disfluency speech, but it do not seems that it is proportional to the severity of the disfluency.
- Pause duration of disfluent speechPublication . Teixeira, João Paulo; Fernandes, Maria Goreti Antunes; Costa, Rita Alexandra Santos daThis work has the goal of comparing the pause duration in the disfluent speech and normal speech. Disfluency and normal spontaneous speech was recorded in a context were the subjects had to describe a scene from each other. The pause determination algorithm is presented. The automatic pause determinations allowed the measure of percentage of silence along the record of several minutes of speech. The stuttering scale is used to compare the severity of the subject. As expected, the percentage of speech pauses parameters is rather different in subjects with and without disfluent speech, but it does not seem that it is proportional to the severity of the disfluency.
- Síntese e teste de hidrogéis inteligentes para a libertação controlada de fármacosPublication . Costa, Rita Alexandra Santos da; Dias, RolandoNeste trabalho foram sintetizados hidrogéis inteligentes, sensíveis ao pH e à temperatura, tendo sido também realizados testes de libertação de quatro fármacos diferentes a partir dos materiais preparados. Com o objetivo de estudar o efeito das condições de síntese sobre as propriedades e desempenho dos hidrogéis, foi feita a sua produção em suspensão inversa (a morfologia das partículas obtidas foi analisada por microscopia eletrónica de varrimento – SEM) e em solução. Foram considerados dois mecanismos diferentes de reação: polimerização radicalar clássica (FRP) e a polimerização por transferência de cadeia reversível por adição-fragmentação (RAFT). Usando diferentes combinações dos monómeros de partida, foram sintetizados hidrogéis polielectrólitos de diferentes tipos, nomeadamente aniónicos, catiónicos e anfotéricos e também hidrogéis não iónicos. Foi observada a efetiva sensibilidade dos materiais obtidos à variação das condições envolventes, nomeadamente variações no pH de soluções aquosas, temperatura, força iónica ou presença de solvente desidratante. Demonstrou-se assim a possibilidade de fazer transitar os hidrogéis entre estados de inchamento/colapso em consequência da alteração de parâmetros pré-definidos. As propriedades únicas destes materiais foram exploradas na libertação estimulada de fármacos, nomeadamente de 5-fluoruracilo (usado no tratamento do cancro), ibuprofeno (anti-inflamatório/analgésico), isoniazida (usada no tratamento da tuberculose) e cafeína (atuador do sistema nervoso central). As dinâmicas de libertação dos fármacos foram medidas experimentalmente através de espectroscopia de ultravioleta. Neste contexto, foram consideradas diferentes combinações hidrogel/estímulo/fármaco tendo em vista a procura de condições que possam potenciar os processos de libertação. Fez-se também uma descrição mecanicista simples da dinâmica de libertação dos fármacos, considerando para esse efeito modelos matemáticos alternativos (modelo exponencial e lei de potência). Esta investigação procura contribuir para o desenvolvimento de ferramentas que possam ser usadas no projeto de condições de síntese, visando a produção de materiais avançados com propriedades por medida e com aplicações em biomedicina.
- Stimuli-responsive hydrogels synthesis using free radical and RAFT polymerizationPublication . Gonçalves, Miguel A.D.; Pinto, Virgínia; Costa, Rita Alexandra Santos da; Dias, Rolando; Hernándes-Ortiz, Júlio; Costa, Mário RuiTemperature and pH stimuli-responsive hydrogel particles were synthesized using inverse-suspension polymerization in batch stirred reactor. Different water soluble co-monomers were present in the initial mixture (e.g. N-isopropylacrylamide and acrylic acid) as well as crosslinkers with different functionalities. Different operating conditions such as polymerization temperature, monomers dilution, neutralization and the initial ratios of co-monomers and monomers/crosslinker were also tried. Hydrogel particles were produced considering classical free-radical polymerization (FRP) and also RAFT polymerization. Commercially available RAFT agents 4-cyano-4-phenylcarbonothioylthio-pentanoic acid (CPA), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) and cyanomethyl dodecyl trithiocarbonate (CDT) were alternatively used. Sampling at different polymerization times allowed the study of the kinetics of polymerization through the analysis by SEC of the soluble phase. A tetra-detector array with simultaneous detection of refractive index, light scattering, intrinsic viscosity and ultra-violet signals was used in these studies. Usefulness of in-line FTIR-ATR monitoring to study the building process of such networks was also assessed. The performance of hydrogel beads was studied through drug delivery tests triggered by changes in the environmental temperature and pH. This research aims to contribute for the elucidation of the connection between the synthesis conditions, molecular architecture and properties/performance of such advanced materials.