L'île de Taiwan résulte de la collision active entre les plaques Eurasienne et Philippine. Ce travail de thèse porte sur la détection et la mesure des déformations tectoniques inter-sismiques engendrées par cette collision. Pour réaliser ce travail, l'interférométrie radar différentielle, et plus précisément la méthode des réflecteurs permanents, a été choisie pour l'étude de Taiwan. Cette méthode repose sur l'analyse d'une série d'images radar acquises à différentes dates sur une même zone. Au final, une carte des déplacements moyens du sol est obtenue, ainsi qu'une série temporelle des déplacements du sol consistant en une mesure par date (la référence étant la date la plus ancienne). Les résultats obtenus présentent une densité de point et une qualité de mesure très riche pour le suivi et l'analyse des déformations tectoniques. Après un état de l'art sur l'interférométrie radar et la mesure des déplacements, abordant tour à tour le principe, les méthodes et les limites de cette mesure, le potentiel de son application à Taiwan est détaillé. Cette méthode est ensuite appliquée, avec des données ALOS PALSAR, à trois zones clés de l'orogène taiwanais : (1) la Vallée Longitudinale, à l'Est de l'île ; située entre la Chaîne Centrale et la Chaîne Côtière, le raccourcissement horizontal à travers la vallée est d'environ 3 cm/an. Grâce à la carte des déplacements moyens entre 2007 et 2010, la faille inverse de la Vallée Longitudinale a pu être localisée avec une grande précision (entre 50 et 100 mètres), améliorant grandement les précédentes cartes. Le taux de glissement inter-sismique a ainsi été estimé (entre 1 et 3,2 cm/an) et sa variation spatiale analysée. Les résultats obtenus ont été comparés avec les données GPS avec succès. (2) la péninsule de Hengchun, au Sud de l'île ; il s'agit des déformations les plus récentes observables à Taiwan. La péninsule, située au sommet du prisme d'accrétion actuel, la structure tectonique majeure est la faille inverse de Hengchun. A partir de la carte des déplacements du sol obtenue, la trace de la faille de Hengchun a été mise en évidence, de même que son glissement inter-sismique (environ 1 cm/an). (3) le front de déformation, à l'Ouest de l'île ; il s'agit d'une étude préliminaire des déformations affectant la Plaine Côtière. Plusieurs types de déformations ont pu être observés entre 1995 et 2010 : le soulèvement de l'anticlinal de Tainan, la subsidence de la plaine de Pingtung, l'activité de la faille de Fengshan et la subsidence près de la rivière Choshui / Pas de résumé en anglais

Human brain and related topics like neuron spikes and their active potentials have become more and more attractive to people these days, as these issues are extremely helpful for curing many neural injuries and cognitive diseases. One method to discover this field is by designing a chip embedded in brains with probes to actual neurons. It is obvious that batteries are not practical for these applications and thereby RF radiation is used as power sources, revealing that chips should operate under a very low power supply. Since neural signals are analog waveforms, analog-to-digital converter (A/D converter, ADC) is the key component in a neural recorder chip. This thesis proposes the complete design of a low power 8-bit successive approximation register (SAR) A/D converter for use in a wireless neural recorder chip, realizing the function of digitizing a sampled neural signal with a frequency distribution of 10Hz to 10kHz. A modified energy-saving capacitor array in the SAR structure is provided to help save power dissipation. Therefore, the ADC shall operate within a power budget of 20­μW maximum from a 1­V power source, at a clock frequency of 500kHz corresponding to a conversion rate of 55.5-kS/s. All the circuits are designed and implemented based on the IBM/Global Foundries 8HP 130nm BiCMOS technology. Simulations of schematic and layout versions are done respectively to verify the functionality, linearity and power consumption of the ADC. Key words: Successive approximation register analog-to-digital converter (SAR-ADC), low power design, energy-saving capacitor array, neural recorder applications

Avalanche forecasters need precise knowledge about avalanche activity in large remote areas. Manual methods for gathering this data have scalability issues. Synthetic aperture radar satellites may provide much needed complementary data. This report describes Avanor, a system presenting change detection images of such satellite data in a web map client. Field validation suggests that the data in Avanor show at least 75 percent of the largest avalanches in Scandinavia with some small avalanches visible as well. / Lavinprognosmakare är i stort behov av detaljerad data gällande lavinaktivitet i stora och avlägsna områden. Manuella metoder för observation är svåra att skala upp, och rymdbaserad syntetisk aperturradar kan tillhandahålla ett välbehövt komplement till existerande datainsamling. Den här rapporten beskriver Avanor, en mjukvaruplattform som visualiserar förändringsbilder av sådan radardata i en webbkarta. Fältvalidering visar att datan som presenteras i Avanor kan synliggöra minst 75 procent av de största lavinerna i Skandinavien och även vissa mindre laviner.

Os Veículos Aéreos Não Tripulados (VANTs) são ideais para operações de risco e estressante para o ser humano são as chamadas dull, dirty and dangerous missions. Portanto, uma importante aplicação desse tipo de robô aéreo diz respeito a operações de busca envolvendo múltiplos VANTs cooperativos, em que há risco de colisões entre aeronaves e o tempo de um voo é limitado, entre outros fatores, pela capacidade de um piloto trabalhar sem descanso. Entretanto, apesar de atualmente verificar-se um crescente número de pesquisas envolvendo VANTs e do grande potencial existente na utilização de VANTs, operações de busca cooperativas ainda não estão ocorrendo. Esse assunto é uma área de estudo multidisciplinar e nascente, que possui diversas linhas de pesquisa. Diferentes algoritmos de navegação e padrões de busca foram estudados visando selecionar o(s) mais adequado(s). Além disso, apresenta-se, neste trabalho, uma visão geral sobre os mecanismos de coordenação multiagente e avalia a adequação de cada uma delas à coordenação distribuída de agentes (VANTs), visando cooperação. Assim, com o objetivo de melhorar o desempenho de uma operação de busca, esta pesquisa de mestrado propõe um modelo de VANTs cooperativos que combina mecanismos de coordenação multiagente, algoritmos de navegação e padrões de busca estabelecidos pelos principais órgãos responsáveis pelas operações de busca e salvamento. Visando avaliar a sensibilidade do percentual médio de detecção de objetos, bem como o tempo médio de busca, foi desenvolvido um simulador e milhares de simulações foram realizadas. Observou-se que, utilizando o modelo, VANTs cooperativos podem reduzir, em média, 57% do tempo de busca (comparando com uma busca de dois VANTs não cooperativos no mesmo cenário), mantendo a probabilidade média de detecção dos objetos próxima de 100% e sobrevoando apenas 30% do espaço de busca. / There are an increasing number of researches into UAV (Unmanned Aerial Vehicle) in the literature. These robots are quite suitable to dull, dirty and dangerous missions. Thus, an important application of these vehicles is the search operations involving multiple UAVs in which there is risk of collisions among aircrafts and the flight time is limited by the maximum time of pilot working hours. However, despite the huge potential use of the UAVs, cooperative search operations with this kind of flying robots are not yet occurring. This research topic is a new and multidisciplinary area of study in its beginning and there are several issues that can be studied, such as centralized versus decentralized control, path planning for cooperative flights, agent reasoning for UAV tactical planning, safety assessments, reliability in automatic target reconnaissance by cameras, agent coordination mechanisms applied to UAV cooperation and the application itself. Different path planning algorithms were studied aiming to attain the most suitable to these kinds of operations, and the conclusions are presented. In addition, official documents of Search and Rescue operations are also studied in order to know the best practices already established for this kind of operations, and, finally, an overview of the coordination multi-agent theory is presented and evaluated to achieve the UAV coordination. This work proposes a model that combines path planning algorithms, search patterns and multi-agent coordination techniques to obtain a cooperative UAV model. The great goal for cooperative UAV is to achieve such performance that the performance of the group overcomes the sum of the individual performances isolatedly. Then, aiming to analyze the average percentage of objects detection, and the average search time, a simulator was developed and thousands of simulations were run. It was observed that, using the proposed model, two cooperative UAVs can perform a search operation 57% faster than two non cooperative UAVs, keeping the average probability of objects detection approaching at 100% and flying only 30% of the search space.

L’imagerie satellite radar propose un point de vue intéressant pour l’étude et la compréhension des océans. Là où l’altimétrie, reconnue et utilisée mondialement, a su s’imposer comme une source de données majeure, les observations de houle issues du SAR (de l’anglais « Synthetic Aperture Radar ») restent encore largement sous exploitées. L’objet de cette thèse est de promouvoir l’utilisation de ces données en proposant un modèle pour l’analyse et la prévision de la houle à l’échelle du globe qui soit indépendant des modèles numériques classiques comme Wavewatch-III. Ce travail s’inscrit dans une logique de pérennisation de la mesure de houle depuis l’espace avec le lancement dans les trois années à venir des trois missions satellites Sentinel-1 A et B et CFOSAT. Un des principaux résultats de ce travail est la capacité de la méthode développée à fournir une information plus précise que celle des modèles existants. Cette méthode permet également une meilleure caractérisation des mesures utilisées en entrée et des pistes d’amélioration de ces dernières sont dégagées pour les futures activités de calibration/validation. Ces travaux ouvrent également des perspectives sur les possibilités d’assimilation des sorties de ce nouveau modèle dans les modèles numériques classiques. / The capability to observe ocean swell using spaceborne Synthetic Aperture Radar (SAR) has been demonstrated starting with ERS-1 mission in 1992. This dissertation shows how ocean swell properties can be used to combine swell observations of heterogeneous quality and acquired at various times and locations for the observation and forecast of ocean swell fieldsusing ASAR instrument on-board ENVISAT. The first section is a review of how ocean swell spectra can be derived from the SAR complex images of the ocean surface using a quasi-linear transformation. Then, significant swell heights, peak periods and peak directions from in situ measurements are used to assess the accuracy of the SAR observed swell spectra. Using linear propagation in deep ocean, a new swell field reconstruction methodologyis developed in order to gather SAR swell observations related to the same swell field. Propagated from their generation region, these observations render the spatio-temporal properties of the emanating ocean swell fields. Afterwards, a methodology is developed for the exclusion of outliers taking advantage of the swell field consistency. Also, using the irregularly sampled SAR observations, quality controlled estimations of swell field integral parameters are produced on a regular space-time grid. Validation against in situ measurements reveals the dramatic impact of the density of propagated observations on the integral parameters estimated accuracy. Specifically, this parameter is shown to be very dependent on the satellite orbit. Finally, comparisons with the numerical wave model WAVEWATCH-III prove it could potentially benefit from the SAR swell field estimates for assimilation purposes.

A grande maioria da população mundial está crescentemente exposta à radiação eletromagnética proveniente de fontes que muitas vezes estão localizadas nas proximidades do corpo. A radiação eletromagnética é considerada um agente possivelmente cancerígeno para as pessoas, classificação 2B indicada pela Organização Mundial da Saúde-OMS (WHO/IARC, 2011). Devido às preocupações em relação aos riscos associados a esta exposição existem normas que recomendam os valores máximos de exposição permitidos (ICNIRP, 1998; FCC, 2001). A correta avaliação das doses de radiação é, portanto, relevante. Este trabalho tem a finalidade de avaliar o impacto dos resultados do cálculo da dose da Taxa de Absorção Específica (SAR) em usuários expostos a radiação por tablets operando na faixa de radiocomunicações Wi-fi. Os três modelos existentes de cabeça humana utilizados serão um manequim homogêneo SAM phantom e dois modelos de cabeça realistas heterogêneos: um adulto masculino e uma criança masculina. Será também utilizado nas simulações um modelo masculino de criança que foi desenvolvido através de imagens de tomografia computadorizada (TC) pelo processo de segmentação feito no software AMIRA. Será utilizado um modelo genérico de tablet. Os parâmetros dosimétricos usados para simulação da SAR serão computados pelo software SEMCAD X que é baseado no Método das Diferenças Finitas no Domínio do Tempo (FDTD). Será criado também um código do Método FDTD através do software MATLAB que servirá para a escolha dos parâmetros do SEMCAD X. A distância entre o tablet e os modelos de cabeças varia de 50 mm a 300 mm. Os resultados da SAR serão comparados com os limites de exposição recomendados pelas normas internacionais. Também serão simuladas diferentes posições da antena no tablet. Da análise dos resultados foi constatado que os valores de SAR são muito baixos e todos os resultados ficaram dentro dos limites do psSAR recomendados pela FCC de 1,6 W/kg em cada 1 g de tecido e de 2 W/kg em cada 10 g de tecido estabelecidos pela ICNIRP. Comparando os valores de SAR do modelo SAM com o modelo DUKE, o modelo SAM se mostra conservador, porém quando a comparação é feita com as crianças o SAM deixa de ser conservador. / The vast majority of the world population is increasingly exposed to electromagnetic radiation from sources which are often located near to the body. Electromagnetic radiation is considered a possible carcinogen for people, classification 2B indicated by the World Health Organization-WHO (WHO/IARC, 2011). Due to concerns regarding the risks associated with this exposition there are regulations suggesting maximum allowed exposure values (ICNIRP, 1998; FCC, 2001). The correct evaluation of radiation doses is therefore relevant. This work aims to assess the impact of the results of the calculation of Specific Absorption Rate dose (SAR) in users exposed to radiation from tablets operating in the Wi-fi band. The three existing models of human head used are a homogeneous dummy SAM phantom and two heterogeneous realistic head models: a male adult and a male child. It will also be used in the simulations a male child model which was developed from computed tomography (CT) imaging using the AMIRA software for the segmentation process. A generic model of tablet is used. Dosimetric parameters used for simulation of the SAR are computed using the SEMCAD X software which is based on the Finite Difference Method in Time Domain (FDTD). A FDTD code was developed using the MATLAB software in order to help to choose the input SEMCAD X parameters. The distances between the tablet and the head of the models varies from 50 mm to 300 mm. SAR results are compared with the exposure limits recommended by international standards. Different antenna positions on the tablet are simulated too. Examining the results it was found that the SAR values are very low and all results are within the psSAR limits recommended by FCC (1,6 W/kg averaged over 1 g of tissue) and by ICNIRP (2 W/kg in 10 g of tissue). Comparing the SAR in the SAM model with the SAR in the DUKE model, the SAM model shows to be conservative. However, when compared with the children, the SAM is not conservative.

Les toxines Shiga (Stx) sont produites par Shigella dysenteriae et certaines espèces d’E. coli transmisent aux humains par la consommation d'aliments contaminés et causant des maladies graves. La toxine Stx est libérée par les bactéries dans l'intestin et par la suite, traverse les vaisseaux sanguins en aval pour atteindre leurs principaux organes cibles, notamment les reins. Les dommages causés aux reins peuvent entraîner des complications graves notamment Le syndrome hémolytique urémique (SHU). A ce jour, il n’existe aucun traitement disponible contre le SHU. Les toxines Stx usent du transport rétrograde intracellulaire pour infester les cellules endothéliales rénales et atteindre leur cible cytosolique, l'ARN ribosomal 28S. Via un screening à haut débit, il a été démontré que le composé Rétro-2 bloque le trafic rétrograde de Stx à l'interface Endosome-TGN, sans affecter la morphologie des organites cellulaires et le trafic des protéines endogènes. Au cours de cette thèse, une analyse des relations structure fonction du composé Retro-2 nous a permis d’identifier les régions de l'inhibiteur qui sont critiques pour l'activité de protection. Nous avons identifié un dérivé dihydroquinazolinone nommé Rétro-2.1 qui est à ce jour l'inhibiteur le plus puissant contre les toxines Stx. Afin d’identifier la cible moléculaire de Retro-2.1, nous avons développé des sondes photo-activables bio-actives. En outre, les données de diffraction des rayons X ont révélé que de l'activité antitoxine réside principalement dans l’énantiomère S. (S) -Retro-2.1 est 500 fois plus puissant contre Stx (50 nM) que la molécule initiale. Cette étude peut donner lieu à un nouveau concept thérapeutique ciblant la voie de transport rétrograde de la toxine à l'intérieur de la cellule hôte. Une telle stratégie thérapeutique pourrait donc être étendue à d'autres agents pathogènes qui usent également du trafic rétrograde pour une intoxication des cellules hôtes. Ce nouveau concept thérapeutique qui permet de cibler les cellules hôtes et non l'agent pathogène représente une véritable percée dans la découverte de médicaments à large spectre et réduit le risque de développement d’une résistance chez l’agent pathogène. / Shiga toxins (Stx) are produced by Shigella dysenteriae and certain species of E. coli that can be transmitted to humans primarily through consumption of contaminated foods and may cause severe disease. Stx is released by the bacteria in the intestine and subsequently, could cross the downstream blood vessels to reach their main target organs such as kidney. Damage to the kidney can result in serious life-threatening complication hemolytic uremic syndrome, for which there is no proven safe treatment available other than supportive care. Stx invades renal endothelial cells in a retrograde manner from cell surface to the endoplasmic reticulum in order to gain access to its cytosolic target, 28S rRNA. By using HTS, it was previously demonstrated that the compound Retro-2 blocks retrograde trafficking of Stx at the early endosome-TGN interface, without affecting the morphology of cellular organelles and trafficking of other endogenous proteins. In this work, different regions of the lead inhibitor Retro-2 that are critical for the protective activity have been determined by systematic structure-activity relationship studies. It allowed us to identify a dihydroquinazolinone derivative, named Retro-2.1 that is the most potent inhibitor of Stx to date and also to develop bio-active photo-activatable probes with the aim of identifying the molecular target of Retro-2 derivatives. Further, crystal X-ray diffraction data revealed that the antitoxin activity resides mainly in the S-enantiomer. (S)-Retro-2.1 has displayed 500 fold more potency (50 nM) than parent molecule against Stx cytotoxicity. This study may result in a new therapeutic concept - targeting the retrograde transport route of toxin inside host cell - for the treatment of Stx-producing E. coli infections and could therefore be extended to other pathogens that also traffic via the retrograde transport. Such a new therapeutic concept that target the host cells and not the pathogen itself would represent a real breakthrough in drug discovery leading to broad spectrum drugs.

Os Veículos Aéreos Não Tripulados (VANTs) são ideais para operações de risco e estressante para o ser humano são as chamadas dull, dirty and dangerous missions. Portanto, uma importante aplicação desse tipo de robô aéreo diz respeito a operações de busca envolvendo múltiplos VANTs cooperativos, em que há risco de colisões entre aeronaves e o tempo de um voo é limitado, entre outros fatores, pela capacidade de um piloto trabalhar sem descanso. Entretanto, apesar de atualmente verificar-se um crescente número de pesquisas envolvendo VANTs e do grande potencial existente na utilização de VANTs, operações de busca cooperativas ainda não estão ocorrendo. Esse assunto é uma área de estudo multidisciplinar e nascente, que possui diversas linhas de pesquisa. Diferentes algoritmos de navegação e padrões de busca foram estudados visando selecionar o(s) mais adequado(s). Além disso, apresenta-se, neste trabalho, uma visão geral sobre os mecanismos de coordenação multiagente e avalia a adequação de cada uma delas à coordenação distribuída de agentes (VANTs), visando cooperação. Assim, com o objetivo de melhorar o desempenho de uma operação de busca, esta pesquisa de mestrado propõe um modelo de VANTs cooperativos que combina mecanismos de coordenação multiagente, algoritmos de navegação e padrões de busca estabelecidos pelos principais órgãos responsáveis pelas operações de busca e salvamento. Visando avaliar a sensibilidade do percentual médio de detecção de objetos, bem como o tempo médio de busca, foi desenvolvido um simulador e milhares de simulações foram realizadas. Observou-se que, utilizando o modelo, VANTs cooperativos podem reduzir, em média, 57% do tempo de busca (comparando com uma busca de dois VANTs não cooperativos no mesmo cenário), mantendo a probabilidade média de detecção dos objetos próxima de 100% e sobrevoando apenas 30% do espaço de busca. / There are an increasing number of researches into UAV (Unmanned Aerial Vehicle) in the literature. These robots are quite suitable to dull, dirty and dangerous missions. Thus, an important application of these vehicles is the search operations involving multiple UAVs in which there is risk of collisions among aircrafts and the flight time is limited by the maximum time of pilot working hours. However, despite the huge potential use of the UAVs, cooperative search operations with this kind of flying robots are not yet occurring. This research topic is a new and multidisciplinary area of study in its beginning and there are several issues that can be studied, such as centralized versus decentralized control, path planning for cooperative flights, agent reasoning for UAV tactical planning, safety assessments, reliability in automatic target reconnaissance by cameras, agent coordination mechanisms applied to UAV cooperation and the application itself. Different path planning algorithms were studied aiming to attain the most suitable to these kinds of operations, and the conclusions are presented. In addition, official documents of Search and Rescue operations are also studied in order to know the best practices already established for this kind of operations, and, finally, an overview of the coordination multi-agent theory is presented and evaluated to achieve the UAV coordination. This work proposes a model that combines path planning algorithms, search patterns and multi-agent coordination techniques to obtain a cooperative UAV model. The great goal for cooperative UAV is to achieve such performance that the performance of the group overcomes the sum of the individual performances isolatedly. Then, aiming to analyze the average percentage of objects detection, and the average search time, a simulator was developed and thousands of simulations were run. It was observed that, using the proposed model, two cooperative UAVs can perform a search operation 57% faster than two non cooperative UAVs, keeping the average probability of objects detection approaching at 100% and flying only 30% of the search space.

<div>Magnetic resonance imaging (MRI) has become an invaluable tool in health care. Despite its popularity, there is still an ever-increasing need for faster scans and better image quality. Multi-coil MRI, which uses multiple transmit and/or receive coils, holds the potential to address many of these MRI challenges. Multi-coil MRI systems can utilize parallel transmission (pTx) technology using multi-dimensional radio-frequency (RF) pulses for parallel excitation. The pTx platform is shown to be superior in high-field MRI. Therefore, this dissertation is focused on the RF pulse design and optimization on an MRI system with multiple transceiver coils.</div><div> </div><div>This dissertation addresses three major research topics. First, we investigate the optimization of pTx RF pulses when considering both transmitters and receivers of the MRI system. We term this framework multiple-input multiple-output (MIMO) MRI. The RF pulse design method is modeled by minimizing the excitation error while simultaneously maximizing the signal-to-noise ratio (SNR) of the reconstructed MR image. It further allows a key trade-off between the SNR and the excitation accuracy. Additionally, multiple acceleration factors, different numbers of used receive coils, maximum excitation error tolerance, and different excitation patterns are simulated and analyzed within this model. For a given excitation pattern, our method is shown to improve the SNR by 18-130% under certain acceleration schemes, as compared to conventional parallel transmission methods, while simultaneously controlling the excitation error in a desired scope.</div><div> </div><div>Second, we propose a pTx RF pulse design method that controls the peak local specific absorption rates (SARs) using a compressed set of SAR matrices. RF power, peak local SARs, excitation accuracy, and SNR are simultaneously controlled in the designed pTx RF pulses. An alternative compression method using k-means clustering algorithm is proposed for an upper-bounded estimation of peak local SARs. The performance of the pTx design method is simulated using a human head model and an eight-channel transceiver coil array. The proposed method reduces the 10-g peak local SAR by 44.6-54.2%, as compared to the unconstrained pTx approach, when it has a pre-defined lower bound of SNR and an upper bound of excitation error tolerance. The k-means clustering-based SAR compression model shows its efficiency as it generates a narrower and more accurate overestimation bound than the conventional SAR compression model.</div><div> </div><div>Finally, we propose two machine learning based pTx RF pulse design methods and test them for the ultra-fast pTx RF pulse prediction. The two methods proposed are the kernelized ridge regression (KRR) based pTx RF pulse design and the feedforward neural network (FNN) based pTx RF pulse design. These two methods learn the training pTx RF pulses from the extracted key features of their corresponding B1+ fields. These methods are compared with other supervised learning methods (nearest-neighbor methods, etc.). All learned pTx RF pulses should be reasonably SAR-efficient because training pTx RF pulses are SAR-efficient. Longer computation time and pre-scan time are the drawbacks of the current pTx approach, and we address this issue by instantaneously predicting pTx RF pulses using well-trained machine learning models.</div>

This thesis examines the role of remote sensing technology in providing information to northern residents of Kugluktuk and Cambridge Bay, Kitikmeot region of Nunavut, Western Canadian Arctic, for the purpose of improving sea ice trafficability and safety. The main objectives of this thesis include 1) the identification of northern community sea ice information needs that can be addressed using remote sensing, and 2) the creation of remote sensing-based products showing sea ice surface roughness information useful to community sea ice trafficability and safety. Thesis outcomes include the refinement and dissemination of information and products with these communities. Research methods involved interviews with northern community members that were analysed using thematic analysis, as well as quantitative assessments of sea ice roughness using satellite datasets. Maps of sea ice surface roughness were created using Sentinel-1 synthetic aperture radar and the Multi-angle Imaging Spectroradiometer, and were evaluated against fine-scale airborne LiDAR data. / Graduate / 2020-07-31