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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
821

Isolamento e caracterização de bactérias degradadoras de acefato. / Isolation and characterization of acephate degrading bacteria.

Karina Paschoal Góes 29 May 2009 (has links)
Quatro linhagens capazes de crescer com acefato foram isoladas a partir de solos com históricos de aplicação de deste composto. Stenotrophomonas maltophilia, Rhodococcus sp., Staphylococcus sp. e Pandoreae sp. foram identificadas através do rDNA 16S e perfil de ácidos graxos de membrana. Rhodococcus sp. foi o isolado mais eficiente na degradação de acefato, removendo 99.24% deste composto em meio de cultura com acefato como única fonte de carbono. Quando avaliado com acefato como fonte combinada de carbono e nitrogênio, este organismo degradou 19% de acefato com formação de metamidofós (17%). Staphylococcus sp. apresentou 21% de degradação de acefato utilizando-o como fonte de carbono e nitrogênio, mas não manteve o crescimento com este composto como fonte de carbono. Stenotrophomonas maltophilia e Pandoreae sp. não mantiveram crescimento com acefato como única fonte de carbono isoladamente. Estas linhagens apresentaram crescimento em acefato como fonte de nitrogênio e enxofre, porém, as análises de GC/MS demonstraram que não houve degradação nestas condições. / Four strains of microorganisms capable of growth on acephate were isolated from soil samples with a history of acephate application. Stenotrophomonas maltophilia, Rhodococcus sp., Staphylococcus sp. and Pandoreae sp. were identified based on 16S rRNA gene sequencing and fatty acid profiling. Rhodococcus sp. was the most efficient acephate degrader of the isolates, it removed 99.24% of acephate from defined growth media when the compound was provided as sole carbon source. When provided as a combined carbon and nitrogen source, the organisms degraded 19% of acephate with formation of methamidophos (17%). Staphylococcus sp. degraded 21% of acephate when provided as sole nitrogen and carbon source but did not grow on the compound as a sole source of carbon. Pandoreae sp. and Stenotrophomonas maltophilia failed to grow on acephate as sole source of carbon in defined medium. These strains grew in media where the pesticide was provided as a combined nitrogen and carbon source, but no acephate biodegradation could be demonstrated in these instances.
822

Sociolinguistic variation among Slovak immigrants in Edinburgh, Scotland

Elliott Slosarova, Zuzana January 2018 (has links)
This thesis investigates sociolinguistic variation among highly fluent Slovak-English bilingual women and also long-term immigrants residing in Edinburgh, Scotland. The present study adds to existing literature on urban migratory experiences (Block, 2008; Forsberg, Lundell and Bartning, 2015; Howley, 2015), comparing cross-cultural variation of immigrants' speech with their local peers (Drummond, 2010, 2012; Meyerhoff et al., 2009), by exploring linguistic and social constraints on language attitudes and accent acquisition among bilingual Slovak immigrants. Sociolinguistic interview data were obtained from 32 women, ages 22-46: 20 Slovak immigrants, 8 Edinburgh Scottish participants, and 6 bilingual Slovak teachers of English in Slovakia. By considering linguistic and social factors that influence Slovak immigrants' variation, in this thesis I ask not just whether and to what extent do local language communities shape immigrants' identity, but also how their identity affects their language attitudes and pronunciation. The thesis pays particular attention to how implicit and explicit language attitudes combine to establish what Block (2008) called a "multidimensional" identity in immigrants. Further investigation establishes a link between identity and production (Redinger and Llamas, 2014; Podesva et al., 2015) by drawing on the variationist sociolinguistic methodologies set out by Labov (1966, 2001, 2006). Implicit language attitudes were collected via a Verbal Guise Task (VGT), during which participants evaluated speakers of foreign and native English accents (Campbell- Kibler, 2006; McKenzie, 2015; McKenzie and Carrie, 2018). Explicit attitudes were collected via a questionnaire designed to elicit attitudes in a casual setting (Dörnyei and Csizér, 2012). The combination of methodologies revealed that immigrant participants in the study held complex attitudes and motivations in relation to their host country. The results for language attitudes suggested that long-term Slovak immigrants experienced shifts to their identity while residing in Scotland, with most adopting a transnational identity that made them amenable to local language communities while maintaining connections with their home country. Their identity represented a degree of integration with Scottish communities, but transnational immigrants often felt separate from both home and host countries as a result. The present study also explores connection between identity and production which is now well recognised (Kobiałka, 2016; Regan, 2016; Regan and Ni Chasaide, 2010; Bucholtz, 2011). Immigrant participants' pronunciations of FACE and GOAT vowel lexical sets (Wells, 1982) were evaluated in comparison to two language groups that represented different standards of pronunciation: native Scottish participants in Edinburgh, with more monophthongal pronunciations (Schützler, 2015); and English-Slovak bilinguals residing in Trnava, Slovakia, whose vowel productions were highly diphthongal and similar to Received Pronunciation (RP) constructions. Comparative study of pronunciations revealed that the immigrants' FACE and GOAT realisations were relatively more monophthongal than the non-immigrant Slovak group, yet more diphthongal than the native Scottish group - effectively making immigrant Slovaks' mean pronunciations separate and distinct from both native standard varieties. However, the immigrant's pronunciations varied widely, and data modelling revealed associations between key social factors and pronunciation. Settings of high formality, strong European and Slovak identities, and intentions to return to Slovakia were associated with relatively more diphthongal pronunciations. Decreased formality, strong Scottish identities, and lack of formal education before immigration were associated with relatively more monophthongal pronunciations. Key findings in the study reinforce observations of multi-cultural identities in longterm Slovak immigrants. Drawing on work that explores variation in language attitudes (Clark and Schleef, 2010) and production in migratory settings (Meyerhoff and Schleef, 2014), I argue that there is a tendency for immigrants to shape their multi-cultural identities in response to linguistic and social contexts. However, internal contexts such as self-definition were equally important in shaping identities, which in turn affected language attitudes and pronunciation.
823

Etude de la confusion des descripteurs locaux de points d'intérêt : application à la mise en correspondance d'images de documents / Study of keypoints and local features confusion : document images matching scenario

Royer, Emilien 24 October 2017 (has links)
Ce travail s’inscrit dans une tentative de liaison entre la communauté classique de la Vision par ordinateur et la communauté du traitement d’images de documents, analyse être connaissance (DAR). Plus particulièrement, nous abordons la question des détecteurs de points d’intérêts et des descripteurs locaux dans une image. Ceux-ci ayant été conçus pour des images issues du monde réel, ils ne sont pas adaptés aux problématiques issues du document dont les images présentent des caractéristiques visuelles différentes.Notre approche se base sur la résolution du problème de la confusion entre les descripteurs,ceux-ci perdant leur pouvoir discriminant. Notre principale contribution est un algorithme de réduction de la confusion potentiellement présente dans un ensemble de vecteurs caractéristiques d’une même image, ceci par une approche probabiliste en filtrant les vecteurs fortement confusifs. Une telle conception nous permet d’appliquer des algorithmes d’extractions de descripteurs sans avoir à les modifier ce qui constitue une passerelle entre ces deux mondes. / This work tries to establish a bridge between the field of classical computer vision and document analysis and recognition. Specificaly, we tackle the issue of keypoints detection and associated local features computation in the image. These are not suitable for document images since they were designed for real-world images which have different visual characteristic. Our approach is based on resolving the issue of reducing the confusion between feature vectors since they usually lose their discriminant power with document images. Our main contribution is an algorithm reducing the confusion between local features by filtering the ones which present a high confusing risk. We are tackling this by using tools from probability theory. Such a method allows us to apply features extraction algorithms without having to modify them, thus establishing a bridge between these two worlds.
824

Vocalização de suínos em grupo sob diferentes condições térmicas / Pig vocalization in group under different thermal conditions

Moura, Giselle Borges de 15 February 2013 (has links)
Quantificar e qualificar o bem-estar de animais de produção, ainda é um desafio. Em qualquer avaliação de bem-estar, deve-se analisar, principalmente, a ausência de sentimentos negativos fortes, como o sofrimento, e a presença de sentimentos positivos, como o prazer. O objetivo principal dessa pesquisa foi quantificar a vocalização de suínos em grupos sob diferentes condições térmicas. Em termos de objetivos específicos foram avaliar a existência de padrões vocálicos de comunicação entre animais alojados em grupo e extrair as características acústicas dos espectros sonoros das vocalizações relacionando com as diferentes condições do micro-clima da instalação. O experimento foi realizado em uma unidade de experimentação com suínos, junto à University of Illinois (EUA), com ambiente controlado. Quatro grupos de seis leitões foram utilizados para a coleta dos dados. Foram instalados dataloggers para registrar as variáveis ambientais (T, °C e UR, %) e posterior cálculo dos índices de conforto (ITU e Entalpia do ar). Foram instalados microfones do tipo cardióide no centro geométrico de cada baia que abrigava os leitões, para registro das vocalizações. Os microfones foram conectados a um amplificador de sinais, e este a uma placa de captura dos sinais de áudio e vídeo, instalados em um computador. Para as edições dos arquivos de áudio contendo as vocalizações dos leitões, o programa Goldwave® foi utilizado na separação, e aplicação de filtros para a retirada de ruídos. Na sequência, os áudios foram analisados com auxílio do programa Sounds Analysis Pro 2011, onde foram extraídos as características acústicas. A amplitude (dB), frequência fundamental (Hz), frequência média (Hz), frequência de pico (Hz) e entropia foram utilizados para caracterização do espectro sonoro das vocalizações do grupo de leitões nas diferentes condições térmicas. O delineamento do experimento foi em blocos casualizados, com dois tratamentos, e três repetições na semana, sendo executado em duas semanas. Os dados foram amostrados para uma análise do comportamento do banco de dados de vocalização em relação aos tratamentos que foram aplicados. Os dados foram submetidos a uma análise de variância utilizando o proc GLM do SAS. Dentre os parâmetros acústicos analisados, a amplitude (dB), frequência fundamental e entropia. Os tratamentos, condição de conforto e condição de calor, apresentaram diferenças significativas, pelo teste de Tukey (p<0,05). A análise de variância mostrou diferenças no formato da onda para cada condição térmica nos diferentes períodos do dia. É possível quantificar a vocalização em grupos de suínos em diferentes condições térmicas, por intermédio da extração das características acústicas das amostras sonoras. O espectro sonoro foi extraído, indicando possíveis variações do comportamento dos leitões nas diferentes condições térmicas dentro dos períodos do dia. No entanto, a etapa de reconhecimento de padrão, ainda necessita de um banco de dados maior e mais consistente para o reconhecimento do espectro em cada condição térmica, seja por análise das imagens ou pela extração das características acústicas. Dentre as características acústicas analisadas, a amplitude (dB), frequência fundamental (Hz) e entropia das vocalizações em grupo de suínos foram significativas para expressar a condição dos animais quando em diferentes condições térmicas. / To quantify and to qualify animal well-being in livestock farms is still a challenge. To assess animal well-being, it must be analyzed, mainly, the absence of strong negative feelings, like pain, and the presence of positive feelings, like pleasure. The main objective was to quantify vocalization in a group of pigs under different thermal conditions. The specific objectives were to assess the existence of vocal pattern of communication between housing groups of pigs, and get the acoustic characteristics of the sound spectrum from the vocalizations related to the different microclimate conditions. The trial was carried out in a controlled environment experimental unit for pigs, at the University of Illinois (USA). Four groups of six pigs were used in the data collection. Dataloggers were installed to record environmental variables (T, °C and RH, %). These environmental variable were used to calculate two thermal comfort index: Enthalpy and THI. Cardioid microphones were installed to record continuous vocalizations in the geometric center of each pen where the pigs were housing. Microphones were connected to an amplifier, and this was connected to a dvr card installed in a computer to record audio and video information. For doing the sound edition in a pig vocalization database, the Goldwave® software was used to separate, and filter the files excluding background noise. In the sequence, the sounds were analyzed using the software Sounds Analysis Pro 2011, and the acoustic characteristics were extracted. Amplitude (dB), pitch (Hz), mean frequency (Hz), peak frequency (Hz) and entropy were used to characterize the sound spectrum of vocalizations of the groups of piglets in the different thermal conditions. A randomized block design was used, composed by two treatments and three repetitions in a week and executed in two weeks. Data were sampled to analyze the behavior of the databank of vocalization as a relation to the applied treatments. Data were submitted to an analysis of variance using the proc GLM of SAS. Among the studied acoustic parameters, the amplitude (dB), pitch and entropy. The treatments (comfort and heat stress conditions) presented significative differences, through Tukey\'s test (p<0,05). The analysis of variance showed differences to the wave format to each thermal condition in the different periods of the day. The quantification of vocalization of swine in groups under different thermal conditions is possible, using the extraction of acoustic characteristics from the sound samples. The sound spectrum was extracted, which indicated possible alterations in the piglets behavior in the different thermal conditions during the periods of the day. However, the stage of pattern\'s recognition still needs a larger and more consistent database to the recognition of the spectrum in each thermal condition, through image analysis or by the extraction of the acoustic characteristics. Among he analyzed acoustic characteristics, the amplitude (dB), pitch (Hz) and entropy of the vocalizations of groups of swine were significative to express the condition of the animals in different thermal conditions.
825

Estudo da associação entre o gene KRAS e células tronco tumorais com características clínico-patológicas e sobrevida no câncer de cólon metastático / Association between KRAS gene and cancer stem cells with clinicopathologic features and survival in metastatic colon cancer

Ribeiro, Karen Bento 12 December 2013 (has links)
INTRODUÇÃO: Os múltiplos passos da carcinogênese do câncer de cólon envolvem a existência de subpopulações de células tronco tumorais (CSC), responsáveis pela transformação, crescimento e proliferação das células tumorais. As proteínas CD44 e CD166 são marcadores de CSC associados a sinalização celular, adesão, migração, metástase e resposta linfocitária. Alguns fatores podem modular a expressão CSC como a mutação KRAS. OBJETIVO: correlacionar a expressão dos marcadores CD44 e CD166 em carcinoma de cólon metastático e status do oncogene KRAS (selvagem/mutado) com as características clínico-patológicas e desfecho do paciente ao final do seguimento. MATERIAL E MÉTODOS: Foram coletadas 58 amostras de tecido tumoral de pacientes com neoplasia de cólon metastático, tratados com CapeOx no Serviço de Oncologia Clínica do HCFMRPUSP de 2003 a 2012. Foram coletadas informações do prontuário sobre status do gene KRAS, características clínico-patológicas e desfecho clínico, sendo também realizada imunohistoquímica para marcação CD44 e CD166 através da técnica de TMA. Utilizado software SPSS 17 para análise estatística e considerado valor de p<0,050 para significância dos dados. RESULTADOS: A expressão de CD44 e CD166 foi positiva em 41,4% e 43%, respectivamente, e o status KRAS mutado em 48,3%. No subgrupo kAs selvagem e nos idosos (>65 anos), houve associação entre CD44 e CD166, p=0,042 e p=0,001, respectivamente. Pacientes CD166 negativo tiveram 3 vezes mais chances de progressão de doença (p=0,02) do que CD166 positivo. Pacientes Kras mutado e CD166 negativo tiveram 8 vezes risco de progressão (p<0,01). Pacientes CD44 positivo tiveram 4 e 5 vezes mais chances de evoluir com metástases hepática e pulmonar (p<0,01) em relação aos CD44 negativo. Pacientes com a combinação KRAS mutado e CD44 positivo tiveram 7 vezes mais chance de evoluir com metástase pulmonar (p=0,02) em relação a pacientes KRAS selvagem e CD44 negativo. DISCUSSÃO: Na amostra estudada observamos a influência das expressões dos marcadores de CSC e suas combinações com o status de mutação do gene KRAS, de modo que pacientes com CD166 negativo no tumor primário apresentam um desfecho de maior recorrência e o CD44 positivo favorece a evolução para metástases pulmonar e hepática. A mutação do gene KRAS atua modulando a via do EGF influenciando o comportamento biologico do tumor e os desfechos (recidiva e metastases) diretamente relacionados com a expressão dos marcadores de CSC no cancer de colon metastatico. CONCLUSÃO: Este estudo demonstrou interação entre a expressão imuno-histoquímica dos marcadores CSC de cólon (CD166 e CD44) e o status KRAS, podendo carcterizar subgrupos de pacientes com maiores chances de evolução desfavorável e assim propor um modelo de tratamento e seguimento mais individualizado. / BACKGROUND: Colon cancer carcinogenesis has been recently correlated with specific cancer stem cell (CSC) subpopulations which are associated with transformation, growth and spread process of tumor cells. CD44 and CD166 are CSC markers correlated with cell signalization, adhesion, migration, metastasis, and lymphocyte response. Some factors as KRAS mutation could modulate CSC. OBJECTIVE: Analyze CD44 and CD166 expressions in metastatic colon carcinoma and its correlation with KRAS status, clinicopathological features, disease recurrence and patient survival. MATERIAL AND METHODS: Tissues were obtained from 58 patients with confirmed metastatic colon cancer, treated with CapeOx at FMRP-USP from 2003 to 2012. Clinical and outcomes informations and KRAS gene status were obtained from medical records. KRAS status was analyzed with RT-PCR. CD44 and CD166 were analyzed with TMA immunohistochemistry. Statistical analyses were performed using SPSS 17.0. A p-value <0,050 was considered to be statistically significant. RESULTS: CD44 and CD166 expressions were positive in 41,4% and 43%, respectively, and KRAS status was mutate in 48,3%. Wild-type KRAS in elderly patients had statistical association between CD44 and CD166, p=0,042 and p=0,001, respectively. Patients with CD166 negative had 3 fold increase in progression disease (p<0,01). Patients with CD44 positive had 4 and 5 fold increase in liver and lung metastasis (p<0,01), respectively. Patients with combined mutated KRAS and CD44 positive had 7 fold increase in lung metastasis (p=0,02) compared with wildtype KRAS and CD44 negative. DISCUSSION: In this study, the influence of markers expression of colon CSC (CD44 and CD166) and its combinations with status KRAS were proven. Patients with CD166 negative in primary colon tumor are more likely to present higher recurrence and, CD44 positive have a higher chance to develop lung and liver metastasis. KRAS mutation contributed, associated with studied CSC expressions, to cancer biological behavior and agressivness. CONCLUSIONS: This study demonstrated interaction between imunohistochemical expression of colonic CSC markers (CD166 and CD44) and KRAS gene status. Subgroups of patients with worse outcomes could be identified and this biological information contributed to personalized treatments and follow ups that should be proposed for these patients.
826

Dispensing Rates of Four Common Hearing Aid Product Features: Associations With Variations in Practice Among Audiologists

Johnson, Earl E., Ricketts, Todd A. 01 March 2010 (has links)
The purpose of the study was to develop and examine a list of potential variables that may account for variability in the dispensing rates of four common hearing aid features. A total of 29 potential variables were identified and placed into the following categories: (1) characteristics of the audiologist, (2) characteristics of the hearing aids dispensed by the audiologist, (3) characteristics of the audiologist?s patient population, and (4) evidence-based practice grades of recommendation for each feature. The potentially associative variables then were examined using regression analyses from the responses of 257 audiologists to a dispensing practice survey. There was a direct relation between price and level of hearing aid technology with the frequency of dispensing product features. There was also a direct relation between the belief by the audiologist that a feature might benefit patients and the frequency of dispensing that feature. In general, the results suggested that personal differences among audiologists and the hearing aids audiologists choose to dispense are related more strongly to dispensing rates of product features than to differences in characteristics of the patient population served by audiologists. An additional finding indicated that evidence-based practice recommendations were inversely related to dispensing rates of product features. This finding, however, may not be the result of dispensing trends as much as hearing aid manufacturing trends.
827

Associative CAD References in the Neutral Parametric Canonical Form

Staves, Daniel Robert 01 March 2016 (has links)
Due to the multiplicity of computer-aided engineering applications present in industry today, interoperability between programs has become increasingly important. A survey conducted among top engineering companies found that 82% of respondents reported using 3 or more CAD formats during the design process. A 1999 study by the National Institute for Standards and Technology (NIST) estimated that inadequate interoperability between the OEM and its suppliers cost the US automotive industry over $1 billion per year, with the majority spent fixing data after translations. The Neutral Parametric Canonical Form (NPCF) prototype standard developed by the NSF Center for e-Design, BYU Site offers a solution to the translation problem by storing feature data in a CAD-neutral format to offer higher-fidelity parametric transfer between CAD systems. This research has focused on expanding the definitions of the NPCF to enforce data integrity and to support associativity between features to preserved design intent through the neutralization process. The NPCF data structure schema was defined to support associativity while maintaining data integrity. Neutral definitions of new features was added including multiple types of coordinate systems, planes and axes. Previously defined neutral features were expanded to support new functionality and the software architecture was redefined to support new CAD systems. Complex models have successfully been created and exchanged by multiple people in real-time to validated the approach of preserving associativity and support for a new CAD system, PTC Creo, was added.
828

Normalizace dat časových řad Landsat metodou IR-MAD / Normalization of Time Series Data of Landsat

Svoboda, Jan January 2019 (has links)
Spectral reflectance of the Earth surface, obtained from the satellite images, should be independent from the external influences and should reflect the surface properties, specifically the proportion of the radiance reflected from the object. It was proved in this paper that the time series of the 63 images from the Landsat 5 satellite were visibly influenced by the external factors even in the case of the images already atmospherically corrected. These external factors were age of the image and WRS-2 position from which the image was obtained. Age of the image was documented with the steady decrease of the spectral reflectance values of the invariant features, especially in the visible part of the electromagnetic spectrum, caused by the sensor degradation. The influence of the WRS-2 position was documented especially in the infrared bands. The western parts of the images are lighter (have higher values of the surface reflectance) than the eastern parts. That may cause the difference between values when monitoring one spot in two overlapping WRS-2 positions. The method originally used for the relative radiometric normalization IR-MAD was here applied to normalize the surface reflectance data, and resulted in the fact that these influences did not show up any more. In order to extend the time...
829

Significance, the vessel and the domestic

Brown, Sandra Lois, School of Design, UNSW January 2004 (has links)
Throughout history, people have made or acquired vessels from which to sip their favourite beverage. In the contemporary domestic setting, households frequently accumulate multiples of the same type of object in numbers that are considerably greater than is necessary and practical for use alone. Of these many objects there are often individual pieces that have special significance for the owner or user. Some are so valued that they may even be removed and set aside because of their perceived importance. The research was initiated by a previous study of tea drinking vessels coupled with a desire, as an object maker and collector, to find out why people have special items that they designate as personally important. The aim was to identify how significance could be recognised in specific objects and whether the notion that a group of features used to gauge such objects could be conveyed into studio based work. The research outcomes are evidenced in a text-based document (which articulates the theoretical and empirical elements of the enquiry) and a body of creative studio work developed in response to aspects of the investigation. The document encompasses two components of the study. The first references material from the fields of museum and cultural studies, pivotal in focusing the enquiry. This contributed to the compilation of a general and speculative inventory of qualities that might pertain to objects deemed ???significant???. During these early investigations it became evident that a more in depth and contemporary analysis of significant drinking vessels, their owners and/or users was required. A Survey Questionnaire regarding personal use and special drinking vessels preceded a series of Interviews with a selected group of Australia curators, artists, academics and collectors who discussed and analysed their association with a personally significant drinking vessel. Subsequently, the content of these interviews became central to the focus of the research and outcomes. The research isolates a number of attributes that are commonly identified in objects that, whatever their condition, are deemed ???significant???. These describe the maker, usage, ownership, association and historical context. The perceived value or worth of the object for its owner, is recognised as a consequence of significance and declares the object as distinctive. This outcome is clearly validated by the interviews. The studio work develops from the fusion of personal narrative that has been enhanced by findings of the research. In particular, it references the cherished object, most especially those pieces that have been retained despite the ravages of time and use. The resulting work was exhibited as Trace Elements ??? Marking Time: Significance, the Vessel and the Domestic at Kudos Gallery, Paddington in April 2004.
830

Perceptual features for speech recognition

Haque, Serajul January 2008 (has links)
Automatic speech recognition (ASR) is one of the most important research areas in the field of speech technology and research. It is also known as the recognition of speech by a machine or, by some artificial intelligence. However, in spite of focused research in this field for the past several decades, robust speech recognition with high reliability has not been achieved as it degrades in presence of speaker variabilities, channel mismatch condi- tions, and in noisy environments. The superb ability of the human auditory system has motivated researchers to include features of human perception in the speech recognition process. This dissertation investigates the roles of perceptual features of human hearing in automatic speech recognition in clean and noisy environments. Methods of simplified synaptic adaptation and two-tone suppression by companding are introduced by temporal processing of speech using a zero-crossing algorithm. It is observed that a high frequency enhancement technique such as synaptic adaptation performs better in stationary Gaussian white noise, whereas a low frequency enhancement technique such as the two-tone sup- pression performs better in non-Gaussian non-stationary noise types. The effects of static compression on ASR parametrization are investigated as observed in the psychoacoustic input/output (I/O) perception curves. A method of frequency dependent asymmetric compression technique, that is, higher compression in the higher frequency regions than the lower frequency regions, is proposed. By asymmetric compression, degradation of the spectral contrast of the low frequency formants due to the added compression is avoided. A novel feature extraction method for ASR based on the auditory processing in the cochlear nucleus is presented. The processings for synchrony detection, average discharge (mean rate) processing and the two tone suppression are segregated and processed separately at the feature extraction level according to the differential processing scheme as observed in the AVCN, PVCN and the DCN, respectively, of the cochlear nucleus. It is further observed that improved ASR performances can be achieved by separating the synchrony detection from the synaptic processing. A time-frequency perceptual spectral subtraction method based on several psychoacoustic properties of human audition is developed and evaluated by an ASR front-end. An auditory masking threshold is determined based on these psychoacoustic e?ects. It is observed that in speech recognition applications, spec- tral subtraction utilizing psychoacoustics may be used for improved performance in noisy conditions. The performance may be further improved if masking of noise by the tonal components is augmented by spectral subtraction in the masked region.

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