Shear instability in skin tissue

We propose two toy-models to describe, predict, and interpret the wrinkles appearing on the surface of skin when it is sheared. With the first model, we account for the lines of greatest tension present in human skin by subjecting a layer of soft tissue to a pre-stretch, and for the epidermis by endowing one of the layer's faces with a surface tension. For the second model, we consider an anisotropic model for the skin, to reflect the presence of stiff collagen fibres in a softer elastic matrix. In both cases, we find an explicit bifurcation criterion, linking geometrical and material parameters to a critical shear deformation accompanied by small static wrinkles, with decaying amplitudes normal to the free surface of skin

Matched asymptotic solution for crease nucleation in soft solids

A soft solid subjected to a large compression develops sharp self-contacting folds at its free surface, known as creases. Creasing is physically different from structural elastic instabilities, like buckling or wrinkling. Indeed, it is a fully nonlinear material instability, similar to a phase-transformation. This work provides theoretical insights of the physics behind crease nucleation. Creasing is proved to occur after a global bifurcation allowing the co-existence of an outer deformation and an inner solution with localised self-contact at the free surface. The most fundamental result here is the analytic prediction of the nucleation threshold, in excellent agreement with experiments and numerical simulations. A matched asymptotic solution is given within the intermediate region between the two co-existing states. The self-contact acts like the point-wise disturbance in the Oseen's correction for the Stokes flow past a circle. Analytic expressions of the matching solution and its range of validity are also derived

Buckling instability in growing tumor spheroids

International audienceA growing tumor is subjected to intrinsic physical forces, arising from the cellular turnover in a spatially constrained environment. This work demonstrates that such residual solid stresses can provoke a buckling instability in heterogeneous tumor spheroids. The growth rate ratio between the outer shell of proliferative cells and the inner necrotic core is the control parameter of this instability. The buckled morphology is found to depend both on the elastic and the geometric properties of the tumor components, suggesting a key role of residual stresses for promoting tumor invasiveness. DOI: 10.1103/PhysRevLett.110.15810

Modeling the Morphology of Modern Barrier Islands to Reconstruct Past Coastal Change

Barrier islands are dynamic landforms that protect 10% of all coasts, not accounting for barriers in bays and lakes. Yet, the ability to predict their future response to changes in sediment availability, rate of sea-level rise, and storm frequency is impeded by the lack of historical records detailing their past behavior. Using models and targeted field investigations, Dr. Ciarletta will explain novel approaches to use the morphology of modern U.S. east coast barriers to reverse-engineer their past evolutions and sediment budgets

Characterization of Eocene-Oligocene Depocenters in Prydz Bay, East Antarctica : A Lithostratigraphic Correlation of ODP Sites 739, 742, and 1166

The Eocene-Oligocene transition (EOT) marked a profound shift in the Earth’s climate, as the global greenhouse o f the early Cenozoic gave way to ‘icehouse’ conditions, or a climatic regime influenced by the waxing and waning o f glacial ice. Antarctica was dramatically altered during this time; its formerly cool temperate ecosystems nearly obliterated by the first major episode o f continental glaciation. A record o f this transition appears to be partly preserved in approximately half a kilometer o f sediments recovered from three holes (at ODP Sites 739, 742, and 1166) bored in the continental margin at Prydz Bay, an embayment o f the East Antarctic coast. Until recently, these holes were never completely described with common nomenclature and analysis. This study re-evaluated these cores under a unified regime, using a laser particle sizer to generate matrix grain size distribution profiles for 253 samples collected from the combined sediment column. Additional analysis o f select samples was performed with a scanning electron microscope to classify grain textures, as well as ICP-OES to provide geochemical information. The results o f this study support stratigraphic relationships between the ODP sites that were previously only inferred through seismic acquisition. This provides a much more complete picture o f the sedimentation processes occurring through the EOT. Chemical and microtextural weathering signals also provide a new window into the environment o f Prydz Bay during the EOT. These signals seem to confirm hypotheses from previous researches that the site featured a cool/temperate environment with tidewater glacial systems in the late Eocene that transitioned into near polar glacier conditions dominated by ice sheet growth by the early Oligocene. Crucially, the results o f this investigation suggest that enhanced glaciation o f the Prydz Bay region was already occurring before the start o f the Oligocene, which suggests that an initial step down in global temperature during the late Eocene (proxied from the foraminiferal oxygen isotope record) may be directly related to the initiation o f continental ice expansion

Reconstructing Barrier Island Behavior from Overstepped Deposits and Relict Onshore Morphology : Modeling and Field Approaches

Barrier Islands comprise 10% of the Earth’s shorelines, fringing every continent except Antarctica. Despite their ubiquity, much about the medium to long-term evolution of these coastal systems remain poorly understood, mostly due to the destruction of the geologic record as barriers migrate landward under the influence of rising sea level. Even where modern barriers and related strandplain systems have prograded and regressed, leaving evidence of their former geometries in the form of relict shorelines, field investigations often require intensive labor and time commitments to interpret past evolution. In this work, several investigations are undertaken to use novel numerical modeling techniques coupled with field interpretation and comparison to gain insights into the evolution of barrier islands from relict geomorphic features preserved on the continental shelf seabed and the surfaces of modern barriers. Much of these efforts focus on ‘drowned’ barrier features, or the remnants of barrier islands left stranded on the shelf during landward migration that occurred in the late Pleistocene and early Holocene, as well as patterns of abandoned foredune ridges generated during late Holocene shoreline progradation. Among the most intriguing results herein is the possibility that the internal dynamics of barrier islands can lead to periodic backstepping and partial deposition of the barrier structure without the need to invoke changing environmental forcing. Moreover, it can be shown that combinations of internal dynamic state and environmental forcing from relatively sudden changes in rate of sea-level rise could lead to a rich suite of barrier retreat behaviors. This might explain the morphologies of drowned barrier features produced during glacial meltwater and outburst flood ‘pulses’ prior to 8 kya. More importantly, these insights may prove practical in modern systems, where anthropogenic climate change threatens barrier islands with historically unprecedented rates of sea-level rise

Identifying risk factors for early pregnancy loss in Holstein cows

Includes bibliographical references.2022 Fall.Adequate reproductive performance is a key factor in the success of dairy production. However, events such as early pregnancy loss occur in 15 to 17% of dairy pregnancies and result in diminished fertility and increased culling within herds. Identifying risk factors for pregnancy loss will help farmers use evidence to formulate effective breeding and management protocols to maximize efficiency and welfare. This thesis is focused on identifying risk factors in early pregnancy and explaining the impacts that factors such as body condition and health status pose on the maintenance of pregnancy.Chapter 1 presented relevant literature involving the transition period, reproductive advancements, and reproductive challenges within the dairy industry. The objective of chapter 2 was to characterize the associations between body condition score (BCS) and BCS change, utilizing an automated camera system during early lactation and close to artificial insemination, and pregnancy loss. A secondary objective was to identify the impact of disease on pregnancy loss over multiple periods throughout lactation. Overall, the dynamics of BCS differed between animals that lost pregnancy and those that maintained pregnancy. During the period close to artificial insemination, low BCS, and a significant loss in BCS, as well as disease resulted in higher rates of pregnancy loss