Multiscale analysis of the mechanical behavior of needle-punched nonwoven fabrics

Los fieltros son una familia de materiales textiles constituidos por una red desordenada de fibras conectadas por medio de enlaces térmicos, químicos o mecánicos. Presentan menor rigidez y resistencia (al igual que un menor coste de procesado) que sus homólogos tejidos, pero mayor deformabilidad y capacidad de absorción de energía. Los fieltros se emplean en diversas aplicaciones en ingeniería tales como aislamiento térmico, geotextiles, láminas ignífugas, filtración y absorción de agua, impacto balístico, etc. En particular, los fieltros punzonados fabricados con fibras de alta resistencia presentan una excelente resistencia frente a impacto balístico, ofreciendo las mismas prestaciones que los materiales tejidos con un tercio de la densidad areal. Sin embargo, se sabe muy poco acerca de los mecanismos de deformación y fallo a nivel microscópico, ni sobre como influyen en las propiedades mecánicas del material. Esta carencia de conocimiento dificulta la optimización del comportamiento mecánico de estos materiales y también limita el desarrollo de modelos constitutivos basados en mecanismos físicos, que puedan ser útiles en el diseño de componentes estructurales. En esta tesis doctoral se ha llevado a cabo un estudio minucioso con el fin de determinar los mecanismos de deformación y las propiedades mecánicas de fieltros punzonados fabricados con fibras de polietileno de ultra alto peso molecular. Los procesos de deformación y disipación de energía se han caracterizado en detalle por medio de una combinación de técnicas experimentales (ensayos mecánicos macroscópicos a velocidades de deformación cuasi-estáticas y dinámicas, impacto balístico, ensayos de extracción de una o múltiples fibras, microscopía óptica, tomografía computarizada de rayos X y difracción de rayos X de gran ángulo) que proporcionan información de los mecanismos dominantes a distintas escalas. Los ensayos mecánicos macroscópicos muestran que el fieltro presenta una resistencia y ductilidad excepcionales. El estado inicial de las fibras es curvado, y la carga se transmite por el fieltro a través de una red aleatoria e isótropa de nudos creada por el proceso de punzonamiento, resultando en la formación de una red activa de fibra. La rotación y el estirado de las fibras activas es seguido por el deslizamiento y extracción de la fibra de los puntos de anclaje mecánico. La mayor parte de la resistencia y la energía disipada es proporcionada por la extracción de las fibras activas de los nudos, y la fractura final tiene lugar como consecuencia del desenredo total de la red en una sección dada donde la deformación macroscópica se localiza. No obstante, aunque la distribución inicial de la orientación de las fibras es isótropa, las propiedades mecánicas resultantes (en términos de rigidez, resistencia y energía absorbida) son muy anisótropas. Los ensayos de extracción de múltiples fibras en diferentes orientaciones muestran que la estructura de los nudos conecta más fibras en la dirección transversal en comparación con la dirección de la máquina. La mejor interconectividad de las fibras a lo largo de la dirección transversal da lugar a una esqueleto activo de fibras más denso, mejorando las propiedades mecánicas. En términos de afinidad, los fieltros deformados a lo largo de la dirección transversal exhiben deformación afín (la deformación macroscópica transfiere directamente a las fibras por el material circundante), mientras que el fieltro deformado a lo largo de la dirección de la máquina presenta deformación no afín, y la mayor parte de la deformación macroscópica no es transmitida a las fibras. A partir de estas observaciones experimentales, se ha desarrollado un modelo constitutivo para fieltros punzonados confinados por enlaces mecánicos. El modelo considera los efectos de la deformación no afín, la conectividad anisótropa inducida durante el punzonamiento, la curvatura y re-orientación de la fibra, así como el desenredo y extracción de la fibra de los nudos. El modelo proporciona la respuesta de un mesodominio del material correspondiente al volumen asociado a un elemento finito, y se divide en dos bloques. El primer bloque representa el comportamiento de la red y establece la relación entre el gradiente de deformación macroscópico y la respuesta microscópica, obtenido a partir de la integración de la respuesta de las fibras en el mesodominio. El segundo bloque describe el comportamiento de la fibra, teniendo en cuenta las características de la deformación de cada familia de fibras en el mesodominio, incluyendo deformación no afín, estiramiento, deslizamiento y extracción. En la medida de lo posible, se ha asignado un significado físico claro a los parámetros del modelo, por lo que se pueden identificar por medio de ensayos independientes. Las simulaciones numéricas basadas en el modelo se adecúan a los resultados experimentales de ensayos cuasi-estáticos y balísticos desde el punto de vista de la respuesta mecánica macroscópica y de los micromecanismos de deformación. Además, suministran información adicional sobre la influencia de las características microstructurales (orientación de la fibra, conectividad de la fibra anisótropa, afinidad, etc) en el comportamiento mecánico de los fieltros punzonados. Nonwoven fabrics are a class of textile material made up of a disordered fiber network linked by either thermal, chemical or mechanical bonds. They present lower stiffness and strength (as well as processing cost) than the woven counterparts but much higher deformability and energy absorption capability and are used in many different engineering applications (including thermal insulation, geotextiles, fireproof layers, filtration and water absorption, ballistic impact, etc). In particular, needle-punched nonwoven fabrics manufactured with high strength fibers present an excellent performance for ballistic protection, providing the same ballistic protection with one third of the areal weight as compared to dry woven fabrics. Nevertheless, very little is known about their deformation and fracture micromechanisms at the microscopic level and how they contribute to the macroscopic mechanical properties. This lack of knowledge hinders the optimization of their mechanical performance and also limits the development of physically-based models of the mechanical behavior that can be used in the design of structural components with these materials. In this thesis, a thorough study was carried out to ascertain the micromechanisms of deformation and the mechanical properties of a needle-punched nonwoven fabric made up by ultra high molecular weight polyethylene fibers. The deformation and energy dissipation processes were characterized in detail by a combination of experimental techniques (macroscopic mechanical tests at quasi-static and high strain rates, ballistic impact, single fiber and multi fiber pull-out tests, optical microscopy, X-ray computed tomography and wide angle X-ray diffraction) that provided information of the dominant mechanisms at different length scales. The macroscopic mechanical tests showed that the nonwoven fabric presented an outstanding strength and energy absorption capacity. It was found that fibers were initially curved and the load was transferred within the fabric through the random and isotropic network of knots created by needlepunching, leading to the formation of an active fiber network. Uncurling and stretching of the active fibers was followed by fiber sliding and pull-out from the entanglement points. Most of the strength and energy dissipation was provided by the extraction of the active fibers from the knots and final fracture occurred by the total disentanglement of the fiber network in a given section at which the macroscopic deformation was localized. However, although the initial fiber orientation distribution was isotropic, the mechanical properties (in terms of stiffness, strength and energy absorption) were highly anisotropic. Pull-out tests of multiple fibers at different orientations showed that structure of the knots connected more fibers in the transverse direction as compared with the machine direction. The better fiber interconnection along the transverse direction led to a denser active fiber skeleton, enhancing the mechanical response. In terms of affinity, fabrics deformed along the transverse direction essentially displayed affine deformation {i.e. the macroscopic strain was directly transferred to the fibers by the surrounding fabric, while fabrics deformed along the machine direction underwent non-affine deformation, and most of the macroscopic strain was not transferred to the fibers. Based on these experimental observations, a constitutive model for the mechanical behavior of the mechanically-entangled nonwoven fiber network was developed. The model accounted for the effects of non-affine deformation, anisotropic connectivity induced by the entanglement points, fiber uncurling and re-orientation as well as fiber disentanglement and pull-out from the knots. The model provided the constitutive response for a mesodomain of the fabric corresponding to the volume associated to a finite element and is divided in two blocks. The first one was the network model which established the relationship between the macroscopic deformation gradient and the microscopic response obtained by integrating the response of the fibers in the mesodomain. The second one was the fiber model, which took into account the deformation features of each set of fibers in the mesodomain, including non-affinity, uncurling, pull-out and disentanglement. As far as possible, a clear physical meaning is given to the model parameters, so they can be identified by means of independent tests. The numerical simulations based on the model were in very good agreement with the experimental results of in-plane and ballistic mechanical response of the fabrics in terms of the macroscopic mechanical response and of the micromechanisms of deformation. In addition, it provided additional information about the influence of the microstructural features (fiber orientation, anisotropic fiber connectivity, affinity) on the mechanical performance of mechanically-entangled nonwoven fabrics.

Alternating surgeries

This thesis is concerned with the question of when the double branched cover of an alternating knot can arise by Dehn surgery on a knot in S^3. We approach this problem using a surgery obstruction, first developed by Greene, which combines Donaldson's Diagonalization Theorem with the $d$-invariants of Ozsvath and Szabo's Heegaard Floer homology. This obstruction shows that if the double branched cover of an alternating knot or link L arises by surgery on S^3, then for any alternating diagram the lattice associated to the Goeritz matrix takes the form of a changemaker lattice. By analyzing the structure of changemaker lattices, we show that the double branched cover of L arises by non-integer surgery on S^3 if and only if L has an alternating diagram which can be obtained by rational tangle replacement on an almost-alternating diagram of the unknot. When one considers half-integer surgery the resulting tangle replacement is simply a crossing change. This allows us to show that an alternating knot has unknotting number one if and only if it has an unknotting crossing in every alternating diagram. These techniques also produce several other interesting results: they have applications to characterizing slopes of torus knots; they produce a new proof for a theorem of Tsukamoto on the structure of almost-alternating diagrams of the unknot; and they provide several bounds on surgeries producing the double branched covers of alternating knots which are direct generalizations of results previously known for lens space surgeries. Here, a rational number p/q is said to be characterizing slope for K in S^3 if the oriented homeomorphism type of the manifold obtained by p/q-surgery on K determines K uniquely. The thesis begins with an exposition of the changemaker surgery obstruction, giving an amalgamation of results due to Gibbons, Greene and the author. It then gives background material on alternating knots and changemaker lattices. The latter part of the thesis is then taken up with the applications of this theory.

Redundancy resolution using a tractrix and its application to real-time simulations of hyper-redundant manipulators, snakes and tying of knots

To realistically simulate the motion of flexible objects such as ropes, strings, snakes, or human hair,one strategy is to discretise the object into a large number of small rigid links connected by rotary or spherical joints. The discretised system is highly redundant and the rotations at the joints (or the motion of the other links) for a desired Cartesian motion of the end of a link cannot be solved uniquely. In this paper, we propose a novel strategy to resolve the redundancy in such hyper-redundant systems.We make use of the classical tractrix curve and its attractive features. For a desired Cartesian motion of the `head'of a link, the `tail' of the link is moved according to a tractrix,and recursively all links of the discretised objects are moved along different tractrix curves. We show that the use of a tractrix curve leads to a more `natural' motion of the entire object since the motion is distributed uniformly along the entire object with the displacements tending to diminish from the `head' to the `tail'. We also show that the computation of the motion of the links can be done in real time since it involves evaluation of simple algebraic, trigonometric and hyperbolic functions. The strategy is illustrated by simulations of a snake, tying of knots with a rope and a solution of the inverse kinematics of a planar hyper-redundant manipulator.

Extracellular BMP-antagonist regulation in development and disease: tied up in knots

Developmental processes are regulated by the bone morphogenetic protein (BMP) family of secreted molecules. BMPs bind to serine/threonine kinase receptors and signal through the canonical Smad pathway and other intracellular effectors. Integral to the control of BMPs is a diverse group of secreted BMP antagonists that bind to BMPs and prevent engagement with their cognate receptors. Tight temporospatial regulation of both BMP and BMP-antagonist expression provides an exquisite control system for developing tissues. Additional facets of BMP-antagonist biology, such as crosstalk with Wnt and Sonic hedgehog signaling during development, have been revealed in recent years. In addition, previously unappreciated roles for the BMP antagonists in kidney fibrosis and cancer have been elucidated. This review provides a description of BMP-antagonist biology, together with highlights of recent novel insights into the role of these antagonists in development, signal transduction and human disease.

Small home ranges and high site fidelity in red knots (Calidris c. canutus) wintering on the Banc d’Arguin, Mauritania

Using automated and manual radio-telemetry and resightings of individual colour-ringed birds, we assessed the daily use of space of red knots Calidris canutus canutus at a tropical wintering area along the Sahara coast, the Banc d Arguin in Mauritania. Confirming earlier suggestions, we found that birds were very faithful to their roosts and that the daily foraging range was small; in the course of several winter months birds used an area of only 2 16 km2 of intertidal area. We found no differences between their movements in daylight and at night. Additionally, individuals seem to return to exactly the same locations in subsequent winters. This pattern is very different from red knots wintering in the temperate Wadden Sea. Here, they readily change roost sites and easily cover areas of about 800 km2 in the course of weeks but, just as in Mauritania, no differences between day and night are apparent. In northern Patagonia and north-western Australia, red knots have range sizes closer to those on the Banc d Arguin, but here they do show differences in space use between day and night. Ecological explanations for these contrasting patterns require further comparative data based on in-depth studies on the predictability of the food base and the presence of diurnal and nocturnal predators.

Specifications for triple-expansion twin-screw propelling engines, with boilers and auxiliary machinery, for an armored cruiser about 9100 tons cruising displacement, to make a speed of twenty knots per hour at a displacement of 8150 tons.

Mode of access: Internet.

Knots in second-growth pine and the desirability of pruning /

"June 1938."

Social knots untied; a series of practical and popular sermons ... handsomely illustrated.

Mode of access: Internet.

Middle Eocene Fe and Ca counts, Ca/Fe ratios, revised splices and astronomical age models form different Sites of IODP Exp342

Accurate age models are a tool of utmost important in paleoclimatology. Constraining the rate and pace of past climate change are at the core of paleoclimate research, as such knowledge is crucial to our understanding of the climate system. Indeed, it allows for the disentanglement of the various drivers of climate change. The scarcity of highly resolved sedimentary records from the middle Eocene (Bartonian - Lutetian Stages; 47.8 - 37.8 Ma) has led to the existence of the "Eocene astronomical time scale gap" and hindered the establishment of a comprehensive astronomical time scale (ATS) for the entire Cenozoic. Sediments from the Newfoundland Ridge drilled during Integrated Ocean Drilling Program (IODP) Expedition 342 span the Eocene gap at an unprecedented stratigraphic resolution with carbonate bearing sediments. Moreover, these sediments exhibit cyclic lithological changes that allow for an astronomical calibration of geologic time. In this study, we use the dominant obliquity imprint in XRF-derived calcium-iron ratio series (Ca/Fe) from three sites drilled during IODP Expedition 342 (U1408, U1409, U1410) to construct a floating astrochronology. We then anchor this chronology to numerical geological time by tuning 173-kyr cycles in the amplitude modulation pattern of obliquity to an astronomical solution. This study is one of the first to use the 173-kyr obliquity amplitude cycle for astrochronologic purposes, as previous studies primarily use the 405-kyr long eccentricity cycle as a tuning target to calibrate the Paleogene geologic time scale. We demonstrate that the 173-kyr cycles in obliquity's amplitude are stable between 40 and 50 Ma, which means that one can use the 173-kyr cycle for astrochronologic calibration in the Eocene. Our tuning provides new age estimates for magnetochron reversals C18n.1n - C21r and a stratigraphic framework for key sites from Expedition 342 for the Eocene. Some disagreements emerge when we compare our tuning for the interval between C19r and C20r with previous tuning attempts from the South Atlantic. We therefore present a revision of the original astronomical interpretations for the latter records, so that the various astrochronologic age models for the middle Eocene in the North- and South-Atlantic are consistent.

The emotional knots of academicity: a collective biography of academic subjectivities and spaces

The highly imagined and contested space of higher education is invested with an affectively loaded ‘knowledge economy optimism’. Drawing on recent work in affect and critical geography, this paper considers the e/affects of the promises of the knowledge economy on its knowledge workers. We extend previous analyses of the discursive constitution of academic subjectivity through the figuration of ‘emotional knots’ as we explore three stories of the constitution of academic subjectivities in institutional spaces. These stories were composed in a collective biography workshop, where participants constructed accounts of the physical, social, material and imaginative dimensions of subjectivities in the ‘academic-city’ of higher education spaces. Identifying moments of ‘perturbation’ in these stories, this paper considers the micro-contexts of ‘becoming academic’: how bodies, affects and relations become knotted in precise times and places. The figuration of ‘knots’ provides an analytical strategy for unravelling how subjects affectively invest in the promises of spaces saturated with knowledge economy discourses, and moments of impasse where these promises ring hollow. We examine the affective bargains made in order to flourish in the corporate university and identify spaces of possibility where optimistic projections of alternative futures might be formed. These stories and their analysis complicate the metanarrative of ‘knowledge economy optimism’ that is currently driving higher education reform in Australia.

Collective equipments of power: The road and the city

A year ago, I became aware of the historical existence of the group CERFI— Le centre d’etudes, de recherches, et de formation institutionelles, or The Study Center for Institutional Research and Formation. CERFI emerged in 1967 under the hand of Lacanian psychiatrist and Trotskyite activist Félix Guattari, whose antonymous journal Recherches chronicled the group’s subversive experiences, experiments, and government-sponsored urban projects. It was a singularly bizarre meeting of the French bureaucracy with militant activist groups, the French intelligentsia, and architectural and planning practitioners at the close of the ‘60s. Nevertheless, CERFI’s analysis of the problems of society was undertaken precisely from the perspective of the state, and the Institute acknowledged a “deep complicity between the intellectual and statesman ... because the first critics of the State, are officials themselves!”1 CERFI developed out of FGERI (The Federation of Groups for Institutional Study and Research), started by Guattari two years earlier. While FGERI was created for the analysis of mental institutions stemming from Guattari’s work at La Borde, an experimental psychiatric clinic, CERFI marks the group’s shift toward urbanism—to the interrogation of the city itself. Not only a platform for radical debate on architecture and the city, CERFI was a direct agent in the development of urban planning schemata for new towns in France. 2 CERFI’s founding members were Guattari, the economist and urban theorist François Fourquet, feminist philosopher Liane Mozère, and urban planner and editor of Multitides Anne Querrien—Guattari’s close friend and collaborator. The architects Antoine Grumback, Alain Fabre, Macary, and Janine Joutel were also members, as well as urbanists Bruno Fortier, Rainier Hoddé, and Christian de Portzamparc. 3 CERFI was the quintessential social project of post-‘68 French urbanism. Located on the Far Left and openly opposed to the Communist Party, this Trotskyist cooperative was able to achieve what other institutions, according to Fourquet, with their “customary devices—the politburo, central committee, and the basic cells—had failed to do.”4 The decentralized institute recognized that any formal integration of the group was to “sign its own death warrant; so it embraced a skein of directors, entangled, forming knots, liquidating all at once, and spinning in an unknown direction, stopping short and returning back to another node.” Allergic to the very idea of “party,” CERFI was a creative project of free, hybrid-aesthetic blocs talking and acting together, whose goal was none other than the “transformation of the libidinal economy of the militant revolutionary.” The group believed that by recognizing and affirming a “group unconscious,” as well as their individual unconscious desires, they would be able to avoid the political stalemates and splinter groups of the traditional Left. CERFI thus situated itself “on the side of psychosis”—its confessed goal was to serve rather than repress the utter madness of the urban malaise, because it was only from this mad perspective on the ground that a properly social discourse on the city could be forged.

Watson-Crick pairing, the Heisenberg group and Milnor invariants

We study the secondary structure of RNA determined by Watson-Crick pairing without pseudo-knots using Milnor invariants of links. We focus on the first non-trivial invariant, which we call the Heisenber invariant. The Heisenberg invariant, which is an integer, can be interpreted in terms of the Heisenberg group as well as in terms of lattice paths. We show that the Heisenberg invariant gives a lower bound on the number of unpaired bases in an RNA secondary structure. We also show that the Heisenberg invariant can predict allosteric structures for RNA. Namely, if the Heisenberg invariant is large, then there are widely separated local maxima (i.e., allosteric structures) for the number of Watson-Crick pairs found.