Les propriétés hydrauliques d'un till du Nord du Québec en condition saturée et non saturée ont été étudiées en laboratoire à l'aide de l'essai de conductivité hydraulique et l'essai de succion qui permet d'obtenir la courbe de rétention d'eau. Les essais ont été réalisés avec des échantillons compactés sous différentes conditions de teneur en eau et de masse volumique sèche, de manière à évaluer l'influence de ces conditions sur les propriétés hydrauliques. Les études précédentes ont montré qu'une structure agrégée se développe dans le till lorsqu'il est compacté de côté sec de l'optimum Proctor, c'est-à-dire à un degré de saturation de compactage inférieur au degré de saturation optimum (Sr0 < Sr-opt). Le till étudié dans le cadre de cette étude diffère de ceux utilisés dans les études précédentes par son très faible pourcentage de particules argileuses (< 2 μm) de 0,7%. L'objectif principal de cette étude est d'évaluer l'influence des conditions de compactage sur la conductivité hydraulique et la courbe de rétention d'eau et de déterminer si une structure agrégée se développe lorsque le till est compacté du côté sec de l'optimum. Les résultats expérimentaux typiques de la conductivité hydraulique saturée obtenus pour les échantillons compactés du côté humide de l'optimum (Sr0 > Sr-opt) avec un indice des vides de 0,328 varient de 2,6 x 10-7 à 8,6 x 10-7 m/s. Les conductivités hydrauliques typiques obtenues pour les échantillons compactés du côté sec de l'optimum (Sr0 < Sr-opt) avec le même indice des vides étaient très similaires, variant entre 2,4 x 10-7 et 9,1 x 10-7 m/s. Les courbes de rétention d'eau mesurées en laboratoire sont très semblables entre elles, présentant toutes une structure de sol homogène, peu importe si l'échantillon a été compacté du côté sec ou du côté humide. Il apparait que la conductivité hydraulique et la courbe de rétention d'eau de ce till sont très peu influencées par le degré de saturation de compactage. Ceci peut être expliqué par le très faible pourcentage de particules argileuses, qui prévient la formation d'agrégations de particules dans la structure du till lorsqu'il est compacté du côté sec de l'optimum Proctor. Plusieurs modèles d'estimation de la conductivité hydraulique sont utilisés. Cette étude propose trois nouveaux modèles d'estimation de la conductivité hydraulique saturée pour les tills du Nord du Québec. Le premier modèle met en relation la conductivité hydraulique saturée avec le diamètre des grains de la fraction fine (d50 FF) et le deuxième modèle est une équation modifiée de Kozeny-Carman et Hazen basée sur la porosité et une taille de particule effective (d10). Finalement, un modèle permettant d'évaluer l'effet de l'agrégation avec l'équation de Kozeny-Carman modifiée dans les tills compactés est proposé.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Reinforced concrete structures, designed according to proper capacity design guidelines, can deform inelastically without loss of strength. Therefore, such structures need not be designed for full elastic seismic demand, but could be designed for a reduced demand. In codified design procedures this reduced demand is obtained by dividing the full elastic seismic demand by a code-defined behaviour factor. There is however not any consensus in the international community regarding the appropriate value to be assigned to the behaviour factor. This is evident in the wide range of behaviour factor values specified by international design codes. The purpose of this study is to assess the seismic drift of reinforced concrete structural walls in order to evaluate the current value of the behaviour factor prescribed by SANS 10160-4 (2009). This is done by comparing displacement demand to displacement capacity for a series of structural walls. Displacement demand is calculated according to equivalency principles (equal displacement principle and equal energy principle) and verified by means of a series of inelastic time history analyses (ITHA). In the application of the equivalency rules the fundamental periods of the structural walls were based on cracked sectional stiffness from moment-curvature analyses. Displacement capacity is defined by seismic design codes in terms of inter storey drift limits, with the purpose of preventing non-structural damage in building structures. In this study both the displacement demand and displacement capacity were converted to ductility to enable comparison. The first step in seismic force-based design is the estimation of the fundamental period of the structure. The influence of this first crucial step is investigated in this study by considering two period estimation methods. Firstly, the fundamental period may be calculated from an equation provided by the design code which depends on the height of the building. This equation is known to overestimate acceleration demand, and underestimate displacement demand. The second period estimation method involves an iterative procedure where the stiffness of the structure is based on the cracked sectional stiffness obtained from moment-curvature analysis. This method provides a more realistic estimate of the fundamental period of structures, but due to its iterative nature it is not often applied in design practice. It was found that, regardless of the design method, the current behaviour factor value prescribed in SANS 10160-4 (2010) is adequate to ensure that inter storey drift of structural walls would not exceed code-defined drift limits. Negligible difference between the equivalency principles and ITHA was observed. / AFRIKAANSE OPSOMMING: Gewapende beton strukture wat ontwerp is volgens goeie kapasiteitsontwerp-riglyne kan plasties vervorm sonder verlies aan sterkte. Gevolglik hoef hierdie strukture nie vir die volle elastiese seismiese aanvraag ontwerp te word nie, maar kan vir 'n verminderde aanvraag ontwerp word. In gekodifiseerde ontwerpriglyne word so 'n verminderde aanvraag verkry deur die volle elastiese aanvraag te deel deur 'n kode-gedefinieerde gedragsfaktor. Wat egter duidelik blyk uit die wye reeks van gedragsfaktor waardes in internasionale ontwerp kodes, is dat daar geen konsensus bestaan in die internasionale gemeenskap met betrekking tot die geskikte waarde van die gedragsfaktor nie. Die doel van hierdie studie is om seismiese verplasing van gewapende beton skuifmure te evalueer ten einde die waarde van die gedragsfaktor wat tans deur SANS 10160-4 (2009) voorgeskryf word te assesseer. Dit word gedoen deur verplasingsaanvraag te vergelyk met verplasingskapasiteit. In hierdie studie word verplasingsaanvraag bereken deur middel van gelykheidsbeginsels (gelyke verplasingsbeginsel en gelyke energiebeginsel) en bevestig deur middel van nie-elastiese tydsgeskiedenis analises (NTGA). Die effek van versagting as gevolg van nie-elastiese gedrag word in aanmerking geneem in die toepassing van die gelykheidsbeginsels. Verplasingskapasiteit word deur seismiese ontwerpkodes gedefinieer deur perke te stel op die relatiewe laterale beweging tussen verdiepings, met die doel om nie-strukturele skade te verhoed. Om verplasingsaanvraag en -kapasiteit te vergelyk in hierdie studie, word beide omgeskakel na verplasingsduktiliteit. Die eerste stap in kraggebaseerde seismiese ontwerp is om die fundamentele periode te beraam. Die invloed van hierdie eerste kritiese stap word in hierdie studie aangespreek deur twee periodeberamingsmetodes te ondersoek. Eerstens kan die fundamentele periode bereken word deur 'n vergelyking wat 'n funksie is van die hoogte van die gebou. Dit is egter algemeen bekend dat hierdie vergelyking versnellingsaanvraag oorskat en verplasingsaanvraag onderskat. Die tweede metode behels 'n iteratiewe prosedure waar die styfheid van die struktuur gebaseer word op die gekraakte snit eienskappe, verkry vanaf 'n moment-krommingsanalise. 'n Beter beraming van die fundamentele periode word verkry deur hierdie metode, maar as gevolg van die iteratiewe aard van die metode word dit selde toegepas in ontwerppraktyk. Die resultate van hierdie studie toon dat die huidige waarde van die gedragfaktor soos voorgeskryf in SANS 10160-4 (2010) geskik is om te verseker dat die relatiewe laterale beweging tussen verdiepings binne kode-gedefinieerde perke sal bly. Onbeduidende verskil is waargeneem tussen die resultate van gelykheidsbeginsels en NTGA.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The various consequences of climate change pose a significant threat to developments near the coast. These threats include saltwater intrusion, coastal erosion and flooding. In the coastal context, the climate change effect often raising the most concern is that of sea-level rise. Much work has therefore been done on the linear setback caused by a rise in sea-level. In order to get the full picture of possible changes caused by sea-level rise, the secondary effects of a rising sea-level also need to be considered. Sea-level rise could cause changes to the nearshore wave climate and could have impacts such as coastal erosion and changes to the coastline shape. The primary objective of this study was therefore to investigate the effects of sea-level rise on the nearshore wave climate and, consequently, the coastline stability. Other consequences of climate change considered in this study include increasing average wave heights and a rotation of offshore wave directions. The many headland-bay beaches on the South African coastline are generally in a state of dynamic equilibrium and find their planforms based on the local wave climate. Changes to the wave climate may therefore disrupt the equilibrium shapes of these bays. This study was therefore also aimed at investigating the effects of the changes to the wave climate on the stability of headland-bay beaches. The three consequences of climate change expected to affect the nearshore wave climate were identified as (1) sea-level rise; (2) an increased wave height; and (3) changing offshore wave angles. Although changes to storm frequency and intensity are also possible, the impacts of these changes were not studied. In order to assess the impacts of the three considered changes on a typical headland-bay beach, two numerical models were set up for Mossel Bay – a headland-bay beach on the southern coast of South Africa. The modelling approach included a wave transformation model to calculate nearshore wave climates from offshore data and a coastline model to assess the stability of the bay under the changed nearshore wave climates. The model results indicated that the rising sea-level alone would cause changes in the nearshore wave direction. These changes were shown to alter the longshore sediment transport regime such that rotations are expected in the south-western corner and eastern end of Mossel Bay. These rotations do not include the cross-shore effects of inundation and erosion, as suggested by models such as the Bruun Model. The results for an increased offshore wave height were inconclusive. The southerly rotation in offshore wave angles was shown to affect the nearshore wave angles. These changes affected the longshore transport regime such that the outward sediment transports were reduced. A minor accretion resulted in the centre of the bay for a 1° southerly rotation in offshore wave angles. For a 2° rotation, the extent of accretion increased and shifted towards the eastern end of the bay, primarily due to the dominance of south-westerly waves in the local wave climate. A valuable observation was made regarding the current stability of Mossel Bay. Inter-tidal reefs are present along three sections of the bay. These reefs protect the coastline such that the current bay shape contains sharp bends between the reefs. Under a rising sea-level, however, the effect of the reefs will become less pronounced. If a water level should be reached where these reefs become less significant, the planform of the bay is expected to smooth out through a significant redistribution of sediment. This smoothing effect was shown to cause erosion of the coastline in the order of 80m near the town of Klein Brak River. / AFRIKAANSE OPSOMMING: Die verskeie gevolge van klimaatsverandering bied ‘n merkwaardige bedreiging vir ontwikkelings naby die kus. Hierdie bedreigings sluit die versouting van varswaterbronne, kuserosie en oorstromings in. Vir kusgebiede is seevlakstyging gereeld die effek van klimaatsverandering wat die meeste kommer wek. Dus is heelwat navorsing rakende die direkte erosie as gevolg van seevlakstyging reeds gedoen. Om die volle beeld van die gevolge van ‘n stygende seevlak te verkry, is dit egter nodig om ook die sekondêre effekte hiervan in ag te neem. Seevlakstyging kan veranderinge in die golfklimaat naby die kus veroorsaak, en kan impakte soos kuserosie en veranderende baaivorms tot gevolg hê. Die primêre doel van hierdie studie is dus om die effek van seevlakstyging op die golfklimaat by die kus en gevolglik die stabiliteit van die kuslyn, te ondersoek. Benewens die styging van die seevlak word die effekte van groter gemiddelde golfhoogtes en die rotasie van diepsee golfrigtings ook in hierdie studie ondersoek. Die vele landpunt-baaie (headlandbay beaches) op die Suid-Afrikaanse kus is meestal in ‘n dinamiese ekwilibriumtoestand, waarvan die vorm deur die lokale golfklimaat bepaal word. Veranderinge aan dié golfklimaat mag dus die ekwilibrium vorms van sulke baaie versteur. Hierdie studie het dus ook die stabilititeit van landpuntbaaie onder ‘n veranderende golfklimaat ondersoek. Die drie gevolge van klimaatsverandering wat verwag word om die golfklimaat naby die kus te beïnvloed is geïdentifiseer as (1) seevlakstyging; (2) vergrote golfhoogtes; en (3) veranderende diepsee golfhoeke. Veranderinge aan die frekwensie en intensiteit van storms is ook moontlike gevolge van klimaatsverandering, maar die impakte hiervan is nie in die studie ondersoek nie. Twee numeriese modelle is toegepas om die impak van die drie bogenoemde gevolge op Mosselbaai – ‘n tipiese landpunt-baai aan die suidkus van Suid-Afrika – te ondersoek. ‘n Golfmodel is ingespan om die golfklimaat naby die kus te bepaal waarna ‘n kuslynmodel gebruik is om die stabiliteit van die baai onder die veranderde golfklimaat te ondersoek. Die resultate van die studie dui daarop dat die golfhoeke naby die kus beïnvloed word deur seevlakstyging. Daar is aangetoon dat dié veranderinge die langsstroomvervoer sodanig sal verander dat kuslynrotasies in die suid-westelike hoek asook die oostelike rand van Mosselbaai verwag word. Hierdie rotasies sluit nie die lineêre landwaartse verplasing van die kuslyn as gevolg van erosie en oorstroming in nie. Die effek van vergrote golfhoogtes kon nie met akkuraatheid ondersoek word nie. Daar is wel gevind dat die suidwaartse rotasie van diepsee golfhoeke rotasies in die golfklimaat naby die kus veroorsaak. Hierdie rotasies verander die langsstroom sedimentvervoer sodanig dat die uitwaartse sedimentvervoer verminder word en ‘n klein opbou van sediment in die middel van die baai vir ‘n 1° diepsee rotasie verwag word. Vir ‘n 2° suidwaartse rotasie is daar ‘n groter opbou van sediment wat verder ooswaarts veplaas is. Die ooswaartse veplasing is primêr ‘n gevolg van die oorheersing van suid-westelike golftoestande in die golfklimaat. ‘n Waardevolle gevolgtrekking rakende die huidige stabiliteit van Mosselbaai is ook gemaak. Langs drie gedeeltes van die Mosselbaaise kus word riwwe in die gebied tussen hoog- en laagwater aangetref. Hierdie riwwe beskerm die kus sodanig dat skerp kinkels in die vorm van die baai tussen die riwwe gesien kan word. Wanneer die seevlak styg, word die beskermende effek van die riwwe egter minder doeltreffend. Indien ‘n watervlak bereik word waar dié effek genoegsaam verminder is, word daar verwag dat die baai deur ‘n merkwaardige verplasing van sediment die kinkels sal uitstryk. Deur hierdie proses word erosie in die orde van 80m naby die dorp van Klein Brakrivier verwag.

Wood can be added to streams to create microhabitats that provide macroinvertebrates with an opportunity for re-colonization by making the stream more heterogeneous. I examined colonization on wood substrate by macroinvertebrates in semi-natural streams in northern Finland during a three month period. Each of the streams was divided in three sections A, B and C, half of which were provided with wood. The focus has been on whether the density of macroinvertebrates changes with time, along an upstream-downstream direction in the streams, or in streams with two wood sections if macroinvertebrates will colonize the first section with wood that they come in contact with (upstream section) or if they continue downstream to the second section with wood. Wood from Salix sp. was placed in nine of the 18 enclosures during mid-June. Samples of wood were removed from the streams on three different occasions from August to October 2014. A total of 32 taxa were identified from the wood and assigned to functional feeding groups: shredders, scrapers, active filter feeders, passive filter feeders, collectors, miners, piercers and predators. The results showed that collectors, miners and piercers increased in density during the month of October and the abundance of scrapers was higher in the upstream location than in the downstream location. Total number of macroinvertebrates, collectors, passive filter feeders and predators had a higher colonization on the first substrate they came into contact with. / Ved i homogena vattendrag skapar mikrohabitat och ger evertebrater en möjlighet att återkolonisera vattendraget genom att göra vattendraget mer heterogent. Jag har undersökt makroevertebraters kolonisation på ved i semi-naturliga bäckar under en tre månaders-period i norra Finland. Bäckarna var uppdelade i tre sektioner upp-, mellan- och nedströms respektive A, B och C. Av 18 sektioner var nio ved försedda. Jag har fokuserat på om tätheten av evertebrater och diversiteten förändras med tiden, längs bäckarna dvs. uppströms – nedströms, och om makroevertebrater kommer kolonisera den första vedförsedda sektionen de kommer i kontakt med eller fortsätta till den efterföljande vedförsedda sektionen. Ved från Salix sp. placerades i nio inhägnader i mitten på juni. Prov på ved togs vid tre olika tidpunkter under studieperioden från Augusti till Oktober 2014. En totala av 32 taxa identifierades från veden och grupperades i funktionella födogrupper: Sönderdelare, skrapare, aktiva filtrerare, passiva filtrerare, samlare, växtgrävare, växtsugare och predatorer. Resultatet visade att samlare, växtgrävare och växtsugare ökade i täthet under oktober månad samt att skapare föredrog ett uppströmsläge framför de andra två möjligheterna. Totala antalet evertebrater, samlare, passiva filtrerare och predatorer koloniserade det första substratet de kom i kontakt med i större utsträckning än de andra födogrupperna.

La capture de CO2 par adsorption sur des solides poreux (adsorbants) est une alternative prometteuse en raison de sa sélectivité et de sa faible consommation d’énergie. Nous avons étudié l'adsorption in-situ de CO2 sur des adsorbants solides en combinant la spectroscopie infrarouge par réflexion diffuse (DRIFT) avec la thermographie infrarouge afin de mieux comprendre les mécanismes d'interaction CO2-adsorbant et ainsi optimiser sa captation dans des procédés de capture en post-combustion. La thermographie IR est utilisée pour détecter la source de chaleur transitoire provenant de la surface de l’adsorbant au cours de l'adsorption de CO2. Un modèle de transfert de chaleur a été développé afin d’estimer les chaleurs d’adsorption. Un mini réacteur conçu pour la DRIFT nous a permis d’identifier les espèces adsorbées et d'étudier leur évolution sur la surface de l’adsorbant selon la température et l'atmosphère environnante. Enfin, le couplage d’informations provenant des deux approches nous a permis l’investigation haut-débit des paramètres clefs pour le choix des adsorbants les plus performants. / CO2 capture via adsorption process on porous materials (adsorbents) is a promising alternative due to its high selectivity and low energy penalties. We have investigated in-situ CO2 adsorption on solid adsorbents by combining Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT) with infrared thermography to better understand the mechanisms controlling CO2-adsorbent interactions and thus optimize its capture in post-combustion capture processes. Infrared thermography is used to detect the transient heat source coming from the adsorbent surface during CO2 adsorption. A heat transfer model has been developed in order to estimate the adsorption heats. A model chemical reactor designed for DRIFT allowed us to clearly evidence the adsorbed species and to study the surface species evolution according to the temperature and the surrounding atmosphere. Finally, the coupling of information coming from the two approaches allowed us a high-throughput investigation of key parameters for the selection of the most efficient adsorbents.

近年來社群平台(Social Media)的興起，提供了人與人之間簡便且快速互相交換各式各樣內容的機會。社群多媒體(Social Multimedia)指的就是使用者在社群平台上所互相交換的多媒體內容，相較於單純的多媒體內容而言，社群多媒體多了寶貴的大量社群平台使用者之間分享互動的記錄，以及社群平台使用者在社群網絡(Social Network)中的各項資訊。如此一來為多媒體內容提供了更多面向的資料，讓社群多媒體比起單純的多媒體內容有更多的應用的可能。 微網誌(Microblog)是個可以讓使用者自由的即時分享文字訊息的平台，有著許多使用者的當下的心情、眼前所看到聽到的事或與朋友對話等。而微網誌平台相較於其它單純用來分享多媒體內容的社群平台(例如YouTube或Flickr)而言，在微網誌平台上的多媒體內容有明顯的分享傳遞現象。而本研究的目標，就是要利用些多媒體內容在微網誌平台上的分享傳遞的特性與資料，針對群多媒體內容進行熱門預測。 隨著時間的前進，若以單一同樣的規則來進行熱門預測，將可能造成預測準確率的下降；再者，即使是在同樣的時間點，不同的多媒體內容會有各自隨著時間在熱門上的變化趨勢，還是會有需要不同的規則來進行熱門預測的可能性，也就是所謂的局部概念飄移現象。在此我們將熱門預測問題轉為資料探勘(Data Mining)中的分類(Classification)問題，並同時將局部概念飄移現象納入考慮，提出一個針對微網誌平台上多媒體內容的熱門預測方法。實驗結果顯示，有考慮局部概念飄移的熱門預測方法，在準確率的表現上明顯的優於GCD方法(平均有4%的提升)與Baseline方法(平均有10%的提升)，代表我們的熱門預測方法更適合微網誌平台上的多媒體內容，也代表的確有概念飄移與局部概念飄移的現象存在。 / In recent years, the rise of social media offers an easy and fast way for information exchange. Social multimedia refers to the multimedia content that users share on the social media. Different from traditional multimedia, social multimedia contains both the multimedia and user behavior information on social media. Microblog is one type of social media. Compared to other social media such as YouTube and Flickr, microblogs provide a more friendly environment for users to propagate social multimedia. The goal of this thesis is to make use of the characteristics and information of propagation on microblogs for popularity prediction of social multimedia. The popularity prediction method based on concept drift mining is proposed. In particular, the local concept drift mechanism is employed to capture the local characteristics of social multimedia. By taking the local concept drift into consideration, the task of popularity prediction is transformed into the ensemble classification problem. Experiments on social multimedia collected from plurk show that the proposed approach performs well.

Understanding sandbar dynamics and variability is integral to developing a predictive capacity for nearshore flows, sediment transport, morphological change, and ultimately for determining coastline exposure to damaging storm waves. Along the high-energy U.S. Pacific Northwest (PNW) coast, sandbars typically dominate the bathymetry of the active zone. Here we report on a nearshore bathymetric data set that covers an exceptionally long stretch of coast and crosses several littoral cell boundaries. Our study area stretches from Point Grenville, Washington to Cascade Head, Oregon, including 8 littoral cells and approximately 250 km in the alongshore. We describe and quantify the morphological variability of sandbars in the PNW over large spatial scales as well as attempt to explain the inter-littoral cell variability via trends and variability in environmental parameters. From 560 bathymetric profiles (~1000 km of measurements) we have extracted over 500 distinct subtidal sandbars. The bar zone extends to over 1km from the shoreline in the northern part of the study area, but only to about 600m in the southern part. Maximum bar crest depths are typically 7m below MLLW. Bar heights range from a step in the cross-shore profile to over 3m from crest to trough. The northernmost littoral cells typically have two or more bars per cross-shore profile whereas the littoral cells in the southern part of our study area have only one bar. The mean depths of the bars, however, are much more consistent across littoral cells. The mean depths remain consistent even while the upper shoreface slope significantly increases from north to south, requiring that the maximum bar distance from the shoreline decreases from north to south. This regional gradient in upper shoreface slope is likely a response, at least in part, to a general coarsening trend in the sediment from north to south and hence linked to variations in regional geology. / Graduation date: 2013

The state of Georgia has two large ports that are accessed by way of navigable entrance channels. One of these ports is located in Brunswick, Georgia, and is maintained by the United States Army Corps of Engineers via periodic dredging. Sediments removed from the channel are typically pumped several miles offshore of Brunswick and placed in dredged material mounds, thus removing the sediment from the littoral cycle. This offshore placement, while being the most economically viable method, often negatively impacts the sediment budget of the coastal region and causes erosion downdrift of the channel, specifically along Jekyll Island. Onshore placement of the dredged material is not feasible due to increased associated costs and the high fraction of fines present in the material; thus, nearshore placement is a potentially viable alternative. Nearshore placement could possibly reduce erosion rates and provide protection to property from waves and storms. The USACE initiated a thorough field data collection campaign in 2002 to study the possibility of beneficial placement of dredged material. The author analyzed the existing data to predict the rate and direction of sediment movement away from an existing dredge mound. These predictions are then compared to bathymetric survey data in an effort to validate the results and methodologies used for sediment transport predictions. The ultimate goal is to use the results of this study along with numerical models currently being developed by the Corps to assess the possibility of sediments being transported toward the shore thus re-entering the littoral cycle and providing a benefit to the coast of Georgia.

In the past decades, numerous single-molecule techniques have been developed to investigate individual bio-molecules and cellular machines. While a lot is known about the structure, localization, and interaction partners of such molecules, much less is known about their mechanical properties. To investigate the weak, non-covalent interactions that give rise to the mechanics of and between proteins, an instrument capable of resolving sub-nanometer displacements and piconewton forces is necessary. One of the most prominent biophysical tool with such capabilities is an optical tweezers. Optical tweezers is a non-invasive all-optical technique in which typically a dielectric microsphere is held by a tightly focused laser beam. This microsphere acts like a microscopic, three-dimensional spring and is used as a handle to study the biological molecule of interest. By interferometric detection methods, the resolution of optical tweezers can be in the picometer range on millisecond time scales. However, on a time scale of seconds—at which many biological reactions take place—instrumental noise such as thermal drift often limits the resolution to a few nanometers. Such a resolution is insufficient to resolve, for example, the ångstrom-level, stepwise translocation of DNA-binding enzymes corresponding to distances between single basepairs of their substrate. To reduce drift and noise, differential measurements, feedback-based drift stabilization techniques, and ‘levitated’ experiments have been developed. Such methods have the drawback of complicated and expensive experimental equipment often coupled to a reduced throughput of experiments due to a complex and serial assembly of the molecular components of the experiments. We developed a high-resolution optical tweezers apparatus capable of resolving distances on the ångstrom-level over a time range of milliseconds to 10s of seconds in surface-coupled assays. Surface-coupled assays allow for a higher throughput because the molecular components are assembled in a parallel fashion on many probes. The high resolution was a collective result of a number of simple, easy-to-implement, and cost-efficient noise reduction solutions. In particular, we reduced thermal drift by implementing a temperature feedback system with millikelvin precision—a convenient solution for biological experiments since it minimizes drift in addition to enabling the control and stabilization of the experiment’s temperature. Furthermore, we found that expanding the laser beam to a size smaller than the objective’s exit pupil optimized the amount of laser power utilized in generating the trapping forces. With lower powers, biological samples are less susceptible to photo-damage or, vice versa, with the same laser power, higher trapping forces can be achieved. With motorized and automated procedures, our instrument is optimized for high-resolution, high-throughput surface-coupled experiments probing the mechanics of individual biomolecules. In the future, the combination of this setup with single-molecule fluorescence, super-resolution microscopy or torque detection will open up new possibilities for investigating the nanomechanics of biomolecules.

Une analyse de données de sondeur multifaisceaux, de sondeur de sédiments (Chirp) et de sismique multitraces, présente la morphologie et la dynamique sédimentaire actuelle ainsi que l’évolution architecturale et stratigraphique du Néogène-Quaternaire opérant le long d’une marge leeward, au nord-ouest du Great Bahama Bank. L’analyse morpho-bathymétrique révèle un talus dominé par de la boue aragonitique, et une grande variété de structures sédimentaires, liées à des processus hydrodynamiques diversifiés. Les courants de density cascading associés aux courants de marée et aux vents d’est représentent les mécanismes de transports édimentaire dominant le long de la marge. La zone de Bimini présente localement un talus court et abrupt,stabilisé en bordure de plate-forme par une barrière récifale, ce qui limite l’export off-bank de sédiments.L’architecture stratigraphique montre une évolution complexe du talus au cours du Néogène. La fin du Paléogène est marquée par un talus continu aggradant détaché de la plate-forme par un escarpement sur faille. Ilpasse à un système très peu incliné de type slope-apron, attaché à la plate-forme au Miocène et se termine par un système en accrétion fortement incliné au Pléistocène. Bien que les dépôts de talus soient dominés par de la boue, ils présentent des variations latérales rapides du Sud au Nord tout au long du Néogène (< 30 km) avec la mise en place de tabliers turbiditiques, de nappes de débrites, et de larges Mass Transport Complexes. Ces faciès interagissent depuis le Langhien avec le Santaren Drift qui s’étend et migre progressivement le long du talus jusqu’à aujourd’hui. Le maximum d’empiétement des contourites se produit au Pliocène supérieur et coïncide avec une réorganisation océanographique globale ainsi que des changements climatiques majeurs dans l’hémisphère nord liés à la fermeture de la Central American Seaway. / An analysis of multi-beam echo sounder, sub-bottom profiler (Chirp) and multichannel seismic,highligths the present-day sedimentary dynamics and the Neogene-Quaternary architectural and stratigraphicevolution along the northwestern leeward margin of the Great Bahama Bank.The morpho-bathymetric analysis reveals an aragonite mud-dominated slope, and a broad spectrum ofsedimentary structures, related to various hydrodynamic processes. The density cascading currents associatedwith tidal currents and prevailing easterly winds correspond to the dominant transport mechanisms operatingalong the margin. The Bimini area displays a short and steep slope, stabilized at shelf edge by rimmed reefalbarrier, which constrains the off-bank export of materials.The stratigraphic architecture shows a complex evolution of the slope during the Neogene. The end ofthe Paleogene is marked by a continuous aggrading slope detached from the shelf by a fault escarpment. It passesinto a low angle slope-apron attached to the platform in the Miocene, and ends with an accretionary system witha steepened slope in the Pleistocene. Although the slope deposits are mud-dominated, they show rapid lateralvariations (< 30 km) from South to North throughout the Neogene with the establishment of turbidite aprons,debrite layers and large Mass Transport Complexes. These facies interact since the Langhian with the SantarenDrift which gradually extends and migrates along the slope until today. The maximum extent of the drift occursduring the upper Pliocene and coincides with a global oceanographic reorganization and major climate changesin the northern hemisphere, related to the closure of the Central American Seaway.