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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.
371

Giant Plasmonic Energy and Momentum Transfer on the Nanoscale

Durach, Maxim 16 October 2009 (has links)
We have developed a general theory of the plasmonic enhancement of many-body phenomena resulting in a closed expression for the surface plasmon-dressed Coulomb interaction. It is shown that this interaction has a resonant nature. We have also demonstrated that renormalized interaction is a long-ranged interaction whose intensity is considerably increased compared to bare Coulomb interaction over the entire region near the plasmonic nanostructure. We illustrate this theory by re-deriving the mirror charge potential near a metal sphere as well as the quasistatic potential behind the so-called perfect lens at the surface plasmon (SP) frequency. The dressed interaction for an important example of a metal–dielectric nanoshell is also explicitly calculated and analyzed. The renormalization and plasmonic enhancement of the Coulomb interaction is a universal effect, which affects a wide range of many-body phenomena in the vicinity of metal nanostructures: chemical reactions, scattering between charge carriers, exciton formation, Auger recombination, carrier multiplication, etc. We have described the nanoplasmonic-enhanced Förster resonant energy transfer (FRET) between quantum dots near a metal nanoshell. It is shown that this process is very efficient near high-aspect-ratio nanoshells. We have also obtained a general expression for the force exerted by an electromagnetic field on an extended polarizable object. This expression is applicable to a wide range of situations important for nanotechnology. Most importantly, this result is of fundamental importance for processes involving interaction of nanoplasmonic fields with metal electrons. Using the obtained expression for the force, we have described a giant surface-plasmoninduced drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. Under realistic conditions in nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to 10^5-10^6 V/cm. It can serve as a powerful nanoscale source of THz radiation. The giant SPIDER opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine. Additionally, the SPIDER is an ultrafast effect whose bandwidth for nanometric wires is 20 THz, which allows for detection of femtosecond pulses on the nanoscale.
372

Indirect measures of associations and psychopathology: applications to Spider Phobia

Ellwart, Thomas 28 March 2004 (has links) (PDF)
To study of cognitive fear networks and associations, indirect experimental paradigms like the Implicit Association Test (IAT, Greenwald et al., 1998) or the Extrinsic Affective Simon Task (EAST, De Houwer, 2003) may be helpful, as they promise to assess the structure of specific associations using a performance based approach without having to ask the participant for a verbal report. Three studies investigated the usefulness and characteristics of IAT and EAST. The aim of the first study was to measure fear associations towards spiders among spider phobic and non-phobic participants as well as in a group of spider enthusiasts. Results indicate that the IAT paradigm is sensitive to the strength of fear relevant associations and able to predict anxious behavior beyond the predictions of direct measures such as questionnaires. The second study focused on some of the mechanisms that underlie IAT effects. With a newly developed masked IAT, these experiments investigated the influences of individual stimuli and superordinate categories on IAT performance. Besides theoretical implications, the results also provide practical, relevant applications for the use of IAT experiments. A third study applied the EAST to investigate how different context conditions lead to differential activation of cognitive schemata in fear of spiders. One can conclude that the impact of automatic threat associations depends on the activated context, and that the EAST is suitable for the assessment of fear associations and their current activation level. This dissertation leads to the conclusion that the performance based methodology of the IAT and EAST is a useful and practical approach to reflect fear associations in phobia indirectly. At this point, the use of indirect measures is still at its beginning, and requires intensive methodological and theoretical efforts. These paradigms, however, may become useful for possible implications in psychopathology and other fields of psychology.
373

Biodiversity assessment of tetranychid mites in Kenya and the conservation hotspots of Tanzania / Faith Jebet Toroitich.

Toroitich, Faith Jebet January 2011 (has links)
The aims of this study were to develop a detailed record of the tetranychid mites of Kenya and Tanzania, to assess the diversity of tetranychid mites in the east African biodiversity hotspots and to determine female characters that can be used to identify the species of the economically important Tetranychus species found in these countries. The genetic diversity of the most abundant Tetranychus species (Tetranychus evansi Baker & Pritchard) was also assessed. The Tetranychidae (Acari) contain some of the most important pest species of phytophagous mites worldwide. Out of the almost 1,300 species in this family, 256 species are known to occur in Africa. Before this study, ten species had been reported from Kenya and only three in Tanzania. The genus Tetranychus to which most of the pest species belongs to, can only be identified to species level by the use of the male aedeagus that is often difficult to visualize. The natural habitat, the Eastern Arc Mountains and East African Coastal Forests in Kenya and Tanzania is recognized as biodiversity hotspots but prior to his study, information on Tetranychidae in these hotspots was lacking. Thus, no information on the natural mite fauna composition was available. In Kenya, 18 tetranychid mite species from various plant hosts have been recorded. Four of these species belong to the subfamily Bryobiinae and the other 14 to the subfamily Tetranychinae. Eight of the mite species identified belong to the genera Bryobia, Petrobia, Peltanobia, Paraplonobia, Duplanychus, Eutetranychus and Mixonychus and are being reported for the first time in Kenya while the other ten had already been reported before. For Tanzania, six species belonging to the genera Tetranychus, Eutetranychus and Mixonychus are being reported for the first time from Tanzania and other three had been reported before. A list of these species, their brief descriptions as well as a key for identification is provided. A redescription of Peltanobia erasmusi including previously undescribed male characters is given. Schizotetranychus kwalensis sp. nov. from Kenya and Brevinychus meshacki from Tanzania were collected on Omorcarpum kirkii (Fabaceae) from Matuga, Kwale district, Kenya and Philonoptera eriocalyx (Fabaceae) from Sangasanga, Mvomero district, Tanzania respectively and described. Revised keys of Brevinychus and of the African species of Schizotetranychus are also provided. Tetranychus evansi Baker & Pritchard ranked highest in abundance amongst all the tetranychid mites collected. It was found in four out of five fragments of the hotspot, and it survives in a wide range of altitudes from as low as 123 m to 1655 m. Molecular examination of T. evansi collected from Kenya and Tanzania and on different host plants revealed an identical DNA sequence of the mitochondrial COI fragment and 19 identical microsatellite alleles suggesting a single introduction of this species to this part of East Africa. Female characters of four Tetranychus species found in Kenya were explored using the scanning electron microscope. Differences in the distances between the duplex setae of species belonging to the desertorum group (Tetranychus evansi Baker & Pritchard and Tetranychus ludeni Zacher) and those grouped by Flechtmann and Knihinicki (2002) under group 9 (Tetranychus neocaledonicus Andre and Tetranychus urticae Koch) were observed. The dorsal striae of T. evansi, T. neocaledonicus and T. urticae have semicircular lobes whereas those on the dorsal striae of T. ludeni are triangular. / Thesis (PhD (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.
374

Biodiversity assessment of tetranychid mites in Kenya and the conservation hotspots of Tanzania / Faith Jebet Toroitich.

Toroitich, Faith Jebet January 2011 (has links)
The aims of this study were to develop a detailed record of the tetranychid mites of Kenya and Tanzania, to assess the diversity of tetranychid mites in the east African biodiversity hotspots and to determine female characters that can be used to identify the species of the economically important Tetranychus species found in these countries. The genetic diversity of the most abundant Tetranychus species (Tetranychus evansi Baker & Pritchard) was also assessed. The Tetranychidae (Acari) contain some of the most important pest species of phytophagous mites worldwide. Out of the almost 1,300 species in this family, 256 species are known to occur in Africa. Before this study, ten species had been reported from Kenya and only three in Tanzania. The genus Tetranychus to which most of the pest species belongs to, can only be identified to species level by the use of the male aedeagus that is often difficult to visualize. The natural habitat, the Eastern Arc Mountains and East African Coastal Forests in Kenya and Tanzania is recognized as biodiversity hotspots but prior to his study, information on Tetranychidae in these hotspots was lacking. Thus, no information on the natural mite fauna composition was available. In Kenya, 18 tetranychid mite species from various plant hosts have been recorded. Four of these species belong to the subfamily Bryobiinae and the other 14 to the subfamily Tetranychinae. Eight of the mite species identified belong to the genera Bryobia, Petrobia, Peltanobia, Paraplonobia, Duplanychus, Eutetranychus and Mixonychus and are being reported for the first time in Kenya while the other ten had already been reported before. For Tanzania, six species belonging to the genera Tetranychus, Eutetranychus and Mixonychus are being reported for the first time from Tanzania and other three had been reported before. A list of these species, their brief descriptions as well as a key for identification is provided. A redescription of Peltanobia erasmusi including previously undescribed male characters is given. Schizotetranychus kwalensis sp. nov. from Kenya and Brevinychus meshacki from Tanzania were collected on Omorcarpum kirkii (Fabaceae) from Matuga, Kwale district, Kenya and Philonoptera eriocalyx (Fabaceae) from Sangasanga, Mvomero district, Tanzania respectively and described. Revised keys of Brevinychus and of the African species of Schizotetranychus are also provided. Tetranychus evansi Baker & Pritchard ranked highest in abundance amongst all the tetranychid mites collected. It was found in four out of five fragments of the hotspot, and it survives in a wide range of altitudes from as low as 123 m to 1655 m. Molecular examination of T. evansi collected from Kenya and Tanzania and on different host plants revealed an identical DNA sequence of the mitochondrial COI fragment and 19 identical microsatellite alleles suggesting a single introduction of this species to this part of East Africa. Female characters of four Tetranychus species found in Kenya were explored using the scanning electron microscope. Differences in the distances between the duplex setae of species belonging to the desertorum group (Tetranychus evansi Baker & Pritchard and Tetranychus ludeni Zacher) and those grouped by Flechtmann and Knihinicki (2002) under group 9 (Tetranychus neocaledonicus Andre and Tetranychus urticae Koch) were observed. The dorsal striae of T. evansi, T. neocaledonicus and T. urticae have semicircular lobes whereas those on the dorsal striae of T. ludeni are triangular. / Thesis (PhD (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.
375

Towards a comparative evaluation of text-based specification formalisms and diagrammatic notations

Moremedi, Kobamelo 19 January 2017 (has links)
Specification plays a vital role in software engineering to facilitate the development of highly dependable software. The importance of specification in software development is to serve, amongst others, as a communication tool for stakeholders in the software project. The specification also adds to the understanding of operations, and describes the properties of a system. Various techniques may be used for specification work. Z is a formal specification language that is based on a strongly-typed fragment of Zermelo-Fraenkel set theory and first-order logic to provide for precise and unambiguous specifications. Z uses mathematical notation to build abstract data, which is necessary for a specification. The role of abstraction is to describe what the system does without prescribing how it should be done. Diagrams, on the other hand, have also been used in various areas, and in software engineering they could be used to add a visual component to software specifications. It is plausible that diagrams may also be used to reason in a semi-formal way about the properties of a specification. Many diagrammatic languages are based on contours and set theory. Examples of these languages are Euler-, Spider-, Venn- and Pierce diagrams. Euler diagrams form the foundation of most diagrams that are based on closed curves. Diagrams, on the other hand, have also been used in various areas, and in software engineering they could be used to add a visual component to software specifications. It is plausible that diagrams may also be used to reason in a semi-formal way about the properties of a specification. Many diagrammatic languages are based on contours and set theory. Examples of these languages are Euler-, Spider-, Venn- and Pierce diagrams. Euler diagrams form the foundation of most diagrams that are based on closed curves. The purpose of this research is to demonstrate the extent to which diagrams can be used to represent a Z specification. A case study is used to transform the specification modelled with Z language into a diagrammatic specification. Euler, spider, Venn and Pierce diagrams are combined for this purpose, to form one diagrammatic notation that is used to transform a Z specification / School of Computing / M. Sc. (Information Systems)
376

Analýza karyotypu u mesothelidních pavouků / Karyotype analysis of mesothelid spiders

Prokopcová, Lenka January 2018 (has links)
Cytogenetics of mesothelid spiders is largely unkown. The presented diploma thesis is focused on the karyotype evolution of these spiders. As it is the most basal group of spiders, the analysis of its cytogenetics can bring important data about ancestral spider karyotype. In the framework of my thesis, I analysed diploid chromosome numbers, chromosome morphology, meiotic division, sex chromosomes and the pattern of selected molecular markers that were detected by fluorescence in situ hybridization. According to my results, mesothelid spiders have a high number of chromosomes and the prevalence of monoarmed chromosomes. Unlike other spiders, mesothelids have little differentiated sex chromosomes. Key words: evolution, spider, chromosome, karyotype, fluorescence in situ hybridization, nucleolar organiser region, sex chromosomes
377

Biologia e potencial de controle de Tetranychus urticae Koch (Acari: Tetranychidae) com fungos entomopatogênicos em mamoeiro / Biology and potential control of Tetranychus urticae Koch (Acari: Tetranychidae) with entomopathogenic fungi on papaya

Moro, Larissa Benardino 10 December 2009 (has links)
Made available in DSpace on 2016-12-23T14:37:39Z (GMT). No. of bitstreams: 1 Larrissa Bernardino Moro.pdf: 381207 bytes, checksum: 5b08b4099b28c73e3fab34be979d1512 (MD5) Previous issue date: 2009-12-10 / O Brasil é o primeiro produtor mundial e terceiro exportador de mamão Carica papaya L., com destaque para o Estado do Espírito Santo que responde a 70% da exportação. As condições climáticas necessárias ao desenvolvimento do mamoeiro são altamente favoráveis para a ocorrência de problemas fitossanitários, sendo a espécie Tetranychus urticae (KOCH, 1836) (Acari: Tetranychidae) uma das pragas-chave, infestando o mamoeiro durante todo o ano. Este ácaro tem sido controlado por agrotóxicos, mas o uso em larga escala destes produtos pode levar ao rápido desenvolvimento de resistência, além de serem danosos ao ambiente. A utilização de cultivares resistentes e de fungos entomopatogênicos são alternativas de controle para esta praga, reduzindo os riscos de resistência do ácaro a acaricidas e a toxicidade ao ambiente. Este trabalho avalia o desenvolvimento e reprodução de T. urticae em cultivares de mamão e verifica se essas cultivares interferem na patogenicidade de Beauveria bassiana, Metarhizium anisopliae e Lecanicillium longisporum. Foram utilizados quatro cultivares de mamão, dois do grupo Formosa (Tainung 01 e Calimosa) e dois do grupo Solo (Golden e Sunrise). Para iniciar o bioensaio foi transferida uma fêmea fertilizada de T. urticae ao disco de folhas e a mesma foi retirada após um período de 12 horas, deixando um ovo por disco, que foi avaliado a cada 12h, registrando-se o período de incubação, duração do estágio de imaturo, longevidade e fecundidade dos adultos e viabilidade desses estágios. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey, a 5% de probabilidade. Para o bioensaio com fungos entomopatogênicos foram utilizadas fêmeas adultas de T. urticae provenientes da criação sobre feijão-de-porco Canavalia ensiformis (L.) e ácaros que permaneceram sobre folhas das cultivares de mamão por pelo menos uma geração. Foram transferidas dez fêmeas para as placas de Petri com disco de folha de C. ensiformis ou de C. papaya com a face abaxial voltada para cima sobre uma camada de algodão hidrófilo umedecida. Em seguida, os ácaros foram pulverizados com suspensões de conídios em Torre de Potter, utilizando-se volume de 5 mL de suspensão 5x107 conídios.mL-1. As suspensões de conídios foram preparadas a partir das formulações comerciais (Boveril® B. bassiana; Metarril® M. anisopliae; Vertirril® L. longisporum). Foi avaliada a mortalidade corrigida e confirmada. A duração do período de ovo na variedade Tainung 01 foi menor (4,0 dias) em relação às outras variedades. O mesmo ocorreu para a duração dos estágios de larva, protoninfa e período ovo-adulto entre as variedades analisadas, sendo maior para as variedades Calimosa, Sunrise e Golden. Esses resultados indicam que as variedades de mamão, Tainung 01, Calimosa, Sunrise e Golden são bons hospedeiros para T. urticae com destaque para Tainung 01, pois esta apresentou menor duração aos estágios de ovo, larva, protoninfa e período ovo-adulto. Os resultados indicaram que os fungos entomopatogênicos comerciais são promissores para o controle de T. urticae em mamoeiro. Testes de estimativa da CL50 e bioensaios em semi-campo e campo são necessários para a adoção desta tática de controle microbiano / Brazil is the worlds largest producer and third exporter of Papaya Carica papaya L., especially the state of Espírito Santo, which accounts for about 70% of exports. Climatic conditions necessary to the development of papaya are also highly favorable for the occurrence of phytosanitary problems, and the species Tetranychus urticae (Koch, 1836) (Acari: Tetranychidae) one of the key pest, infesting papaya plant throughout the year. This mite has been controlled by pesticides, but the widespread use of these products can lead to rapid development of resistance, besides being harmful to the environment. The use of resistant cultivars and entomopathogenic fungi are alternatives to control this pest, reducing the risk of mite resistance to acaricides and also the toxicity to the environment. The study was conducted to evaluate the development and reproduction of T. urticae in papaya cultivars and to verify if these cultivars interfere with the pathogenicity of Beauveria bassiana, Metarhizium anisopliae and Lecanicillium longisporum. Were assayed four varieties of papaya, two of the group "Formosa" (Tainung 01 and Calimosa) and two from the "Solo" (Golden and Sunrise). To initiate the bioassay, it was transferred a fertilized female T. urticae to a leaf dish and the female was removed after a period of 12 hours, leaving one egg per disc, that was evaluated every 12 hours recording the incubation period, length of immature stage, longevity and fecundity of adults and viability of these stages. Data were subjected to analysis of variance and means compared by Tukey test at 5% probability. For the bioassay with entomopathogenic fungi were used adult females of T. urticae from the rearing of jack bean Canavalia ensiformis (L.) and mites that remained on leaves of cultivars of papaya for at least a generation. Ten females were transferred to Petri dishes with leaf disk of C. ensiformis or C. papaya with the abaxial side up on a layer of cotton wool moistened. After that mites were sprayed with conidial suspension in a Potter Tower, using a volume of 5 mL of inoculum suspension 5x107 conidia.mL-1. Conidial suspensions were prepared from the commercial formulations (Boveril ® B. bassiana, Metarril ® M. anisopliae; Vertirril ® L. longisporum). We evaluated the mortality corrected and confirmed. The duration of the egg in the variety Tainung 01 was smaller (4.0 days) than to the other varieties. The same occurred for the duration of the larval stages, protonymph and egg-adult period between the varieties analyzed, being higher for varieties Calimosa, Sunrise and Golden. These results indicate that the varieties of papaya, Tainung 01, Calimosa, Sunrise and Golden are good hosts for T. urticae, especially Tainung 01, which showed a shorter duration of the egg, larva, protonymph and egg-adult period. The results also indicate that the fungi are promising for commercial control of T. urticae in papaya. Tests of estimation of the CL50 bioassays and in semi-field and field are required to use this tactic of microbial control
378

An interrogation of morality, power and plurality as evidenced in superhero comic books: a postmodernist perspective

Herman, Janique Luschan Vogl January 2013 (has links)
The desire for heroes is a global and cultural phenomenon that gives a view into society’s very heart. There is no better example of this truism than that of the superhero. Typically, Superheroes, with their affiliation to values and morality, and the notion of the grand narratives, should not fit well into postmodernist theory. However, at the very core of the superhero narrative is the ideal of an individual creating his/her own form of morality, and thus dispensing justice as the individual sees fit in resistance to metanarrative’s authoritarian and restrictive paradigms. This research will explore Superhero comic books, films, videogames and the characters Superman, Spider-Man and Batman through the postmodernist conceptions of power, plurality, and morality.
379

Appendage development and early distal-less regulation in arthropods : a study of the chelicerate Tetranychus urticae (Acarida)

Cyrus-Kent, Chlo January 2007 (has links)
A major goal of evolutionary developmental biology is to explore mechanisms and events underlying evolution of the myriad body plan morphologies expressed both genetically and phenotypically within the animal kingdom. Arthropods exhibit an astounding array of morphological diversity both within and between representative sub-phyla, thus providing an ideal phylum through which to address questions of body plan innovation and diversification. Major arthropod groups are recognised and defined by the distinct form and number of articulated appendages present along the antero-posterior axis of their segmented bodies. A great deal is known about the developmental genetics of limb development in the model insect Drosophila melanogaster, added to which, much comparative gene expression data and a growing body of functional genetic data is emerging for other arthropod species. Arthropod limb primordia are consistently marked by expression of the homeobox gene Distal-less (Dll), and the focus of this thesis is to compare signalling mediated by early Dll regulatory genes activity along antero-posterior and dorso-ventral embryonic axes during limb specification in Drosophila, with the activity of their orthologs in the widely disparate chelicerate, the spider mite Tetranychus urticae - interpreting new data with that available for other arthropods. Having made a detailed study of spider mite embryonic (and post-embryonic) development, to provide a basis for understanding mRNA transcription and protein activity patterns, I confirmed typical expression of Tetranychus Dll in prosomal limb primordia. I obtained limited results for the candidate antero-posterior positioning genes wingless and engrailed, although one of the two engrailed paralogs I identified is reportedly expressed in posterior segmental compartments, consistent with possible conservation of Engrailed-Wingless interactions in metameric patterning and positive regulation of Dll in arthropod limb specification. In Drosophila, wingless-dependent Dll transcription is restricted along the dorso-ventral axis by dorsal Dpp-mediated and ventral EGFR-mediated signalling gradients. Based on data from Tetranychus and other arthropods, neither dorsal nor ventral signalling regimes appear conserved outside the Drosophila system. Dll suppression in fly abdominal segments occurs due to powerful Hox (Ubx/AbdA) repression of the early Dll cis-regulatory element; this is discussed in relation to the independently evolved limbless chelicerate opisthosoma, informed by hypothetical scenarios of cis (regulatory DNA) and trans (coding sequence) evolution. Given practical difficulties and limitations encountered while working with spider mites, I offer a final assessment of the place of Tetranychus urticae as a non-model, and yet still valuable chelicerate species to consider carrying into the exciting future of evolutionary developmental biology.
380

Identification, caractérisations physico-chimiques et pharmacologiques de nouveaux inhibiteurs de la mélanogenèse isolés à partir de venins d'animaux : exemple de l'Argiotoxine-636 / Identification, physico-chemical and pharmacological characterizations of a new melanogenesis inhibitor, isolated from animal venoms : argiotoxin-636 example

Verdoni, Marion 01 June 2015 (has links)
La mélanogenèse engage 3 enzymes. La tyrosinase catalyse l’oxydation des 2 premiers substrats pour former la DOPAquinone. Celle-ci, en présence de cystéine peut s’y conjuguer pour produire des pheomélanines (pigments clairs). En son absence, la DOPAquinone est convertie en DOPAchrome, précurseur de la voie de synthèse des eumélanines (pigments foncés). Leur formation implique deux autres enzymes : TRP-1 et TRP-2. Un dérèglement de ce processus entraîne des dermatoses de type hyperpigmentations chez les phototypes IV à VI. Traiter ces problématiques efficacement sans effets secondaires nécessite d'identifier de nouvelles molécules actives capables de réguler la synthèse des eumélanines.Pour atteindre l'objectif, nous avons évalué l’effet inhibiteur de 100 venins d’animaux sur l’activité DOPA oxydase de la tyrosinase de champignon. Des analyses HPLC et spectrophotométriques alternées, ont permis de localiser la sous-fraction active conte-nant la molécule d'intérêt. La détermination du poids moléculaire par spectrométrie de masse conjuguée à l’analyse d'AA après hydrolyse acide a permis d'identifier l’Argiotoxine-636 (ARGTX-636). Elle est un inhibiteur mixte de la diphénolase. Des études préliminaires de SAR ont également été réalisées. En parallèle, une méthode analytique par HPLC/MS a été mise au point pour confirmer l'activité inhibitrice de la DHICA oxydase de l'enzyme par l'ARGTX-636.Pour la première fois est reportée l’isolation et la caractérisation d’un nouveau composé extrait d’un venin d’araignée capable de réguler la mélanogenèse. Cette approche peut avoir un impact majeur dans la recherche de nouvelles molécules actives dans le domaine de la dermo-cosmétique. / Melanogenesis involves three enzymes. Tyrosinase catalyses the oxidation of the two first substrates and leads to the formation of DOPAquinone, which may be conjugated with cysteine to produce pheomelanins (red-yellow pigments). In absence of cys-teine, DOPAquinone is spontaneously converted in DOPAchrome, the precursor of eumelanin products (brown-black pig-ments). The formation of eumelanin molecules partially relies on the activity of two other enzymes called Tyrosinase related protein 2 and Tyrosinase related protein 1. A dysregulation of this process engenders hyperpigmentation tasks into skin IV to VI phototypes. To treat these issues effectively without side effects requires the identification of new active molecules able to regulate the eumelanin synthesis.To achieve the objective, we evaluated the inhibitory effect of 100 animals venoms, on the DOPA oxidase activity of mushroom tyrosinase. HPLC and spectrophotometric analysis alternating, we allowed us to localize the active sub-fraction containing the interest molecule. The molecular weight determination by mass spectrometry combined with the AA analysis after acid hy-drolysis identified argiotoxin-636 (ARGTX-636). It is a mixed-type inhibitor on diphenolase activity. SAR preliminary stu-dies have also been conducted. In parallel, an analytical method by HPLC / MS was developed to confirm the DHICA oxy-dase activity inhibitory effect by ARGTX-636.For the first time is reported the isolation and characterization of a novel compound extracted from a spider venom able to regulate melanogenesis process. This approach can have a major impact in the search for new active compounds in the dermo-cosmetics field.

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