Ontogeny and Adaptation: A Cross-Sectional Study of Primate Limb Elements

How primates achieve their adult skeletal form can be ascribed to two broad biological mechanisms: genetic inheritance, where morphological characters are regulated by an individual's phenotype over development; and plastic adaptation, where morphology responds to extrinsic factors engendered by the physical environment. While skeletal morphology should reflect an individual’s ecological demands throughout its life, only a limited amount of published research has considered how ontogeny and locomotor behaviour influence limb element form together. This thesis presents an investigation of long bone cross-sectional shape, size and strength, to inform how five catarrhine taxa adapt their limbs over development, and further, evaluate which limb regions more readily emit signals of plasticity or constraint along them. The sample includes Pan, Gorilla, Pongo, Hylobatidae and Macaca, subdivided into three developmental stages: infancy, juvenility and adulthood. Three-dimensional models of four upper (humerus and ulna) and lower (femur and tibia) limb elements were generated using a laser scanner and sectioned at proximal, midshaft and distal locations along each diaphysis. Three methods were used to compare geometry across the sample: 1) principal and anatomical axis ratios served as indices of section circularity, 2) polar section moduli evaluated relative strength between limb sections and 3) a geometric morphometric approach was developed to define section form. The results demonstrated that irrespective of taxonomic affinity, forelimb elements serve as strong indicators of posture and locomotor ontogenetic transitions, while hindlimb form is more reflective of body size and developmental shifts in body mass. Moreover, geometric variation at specific regions like the midhumerus was indistinguishable across all infant taxa in the sample, only exhibiting posture-specific signals among mature groups, while sections like the distal ulna exhibited little or no intraspecific variation over development. Identifying patterns of plasticity and constraint across taxonomic and developmental groups informs how limb cross-sections either allometrically or isometrically scale their form as they grow. These findings have direct implications to extant and extinct primate research pertaining to body mass estimation, functional morphology and behavioural ecology

Yentl: From Yeshiva Boy to Syndrome

How did the name Yentl become so iconic of the feminist struggle against gender bias? Dr. Pamela S. Nadell, Patrick Clendenen Professor of Women\u27s and Gender History; Director of the Jewish Studies Program, American University.https://digitalcommons.fairfield.edu/bennettcenter-posters/1319/thumbnail.jp

Minimum Weight Design of a Generic Axisymmetric Inlet

A new minimum weight design method for high-speed axisymmetric inlets was demonstrated on a generic inlet. The method uses Classical Beam Theory and shell buckling to determine the minimum required equivalent isotropic thickness for a stiffened shell based on prescribed structural design requirements and load conditions. The optimum spacing and equivalent isotropic thickness of ring frame supports are computed to prevent buckling. The method thus develops a preliminary structural design for the inlet and computes the structural weight. Finite element analyses were performed on the resulting inlet design to evaluate the analytical results. Comparisons between the analytical and finite element stresses and deflections identified areas needing improvement in the analytical method. The addition of the deflection due to shear and a torsional buckling failure mode to the new method brought its results in line with those from the finite element analyses. Final validation of the new method will be made using data from actual inlets

Axisymmetric inlet minimum weight design method

An analytical method for determining the minimum weight design of an axisymmetric supersonic inlet has been developed. The goal of this method development project was to improve the ability to predict the weight of high-speed inlets in conceptual and preliminary design. The initial model was developed using information that was available from inlet conceptual design tools (e.g., the inlet internal and external geometries and pressure distributions). Stiffened shell construction was assumed. Mass properties were computed by analyzing a parametric cubic curve representation of the inlet geometry. Design loads and stresses were developed at analysis stations along the length of the inlet. The equivalent minimum structural thicknesses for both shell and frame structures required to support the maximum loads produced by various load conditions were then determined. Preliminary results indicated that inlet hammershock pressures produced the critical design load condition for a significant portion of the inlet. By improving the accuracy of inlet weight predictions, the method will improve the fidelity of propulsion and vehicle design studies and increase the accuracy of weight versus cost studies

MEMS 411 Design Report Group O: Naked Mole Rat Trap

Naked mole-rats are mouse size rodents that live in underground colonies in East Africa. They are best known for having a queen and workers like bees. Prof Stan Braude has been studying them in Kenya and Ethiopia for over 25 years and has trapped over 10,000 of these animals, marked and released them. He is the world’s expert at trapping naked mole-rats and yet, he still needs a better trap. Prof. Stan Braude is looking forward to working with a team of real engineers and designers who can help him complete this project

Extracellular Polymeric Substance Production and Aggregated Bacteria Colonization Influence the Competition of Microbes in Biofilms

The production of extracellular polymeric substance (EPS) is important for the survival of biofilms. However, EPS production is costly for bacteria and the bacterial strains that produce EPS (EPS+) grow in the same environment as non-producers (EPS−) leading to competition between these strains for nutrients and space. The outcome of this competition is likely to be dependent on factors such as initial attachment, EPS production rate, ambient nutrient levels and quorum sensing. We use an Individual-based Model (IbM) to study the competition between EPS+ and EPS− strains by varying the nature of initial colonizers which can either be in the form of single cells or multicellular aggregates. The microbes with EPS+ characteristics obtain a competitive advantage if they initially colonize the surface as smaller aggregates and are widely spread-out between the cells of EPS−, when both are deposited on the substratum. Furthermore, the results show that quorum sensing-regulated EPS production may significantly reduce the fitness of EPS producers when they initially deposit as aggregates. The results provide insights into how the distribution of bacterial aggregates during initial colonization could be a deciding factor in the competition among different strains in biofilms

Universality in Bacterial Colonies

The emergent spatial patterns generated by growing bacterial colonies have been the focus of intense study in physics during the last twenty years. Both experimental and theoretical investigations have made possible a clear qualitative picture of the different structures that such colonies can exhibit, depending on the medium on which they are growing. However, there are relatively few quantitative descriptions of these patterns. In this paper, we use a mechanistically detailed simulation framework to measure the scaling exponents associated with the advancing fronts of bacterial colonies on hard agar substrata, aiming to discern the universality class to which the system belongs. We show that the universal behavior exhibited by the colonies can be much richer than previously reported, and we propose the possibility of up to four different sub-phases within the medium-to-high nutrient concentration regime. We hypothesize that the quenched disorder that characterizes one of these sub-phases is an emergent property of the growth and division of bacteria competing for limited space and nutrients.Comment: 12 pages, 5 figure

Bacterial defences: mechanisms, evolution and antimicrobial resistance

Throughout their evolutionary history, bacteria have faced diverse threats from other microorganisms, including competing bacteria, bacteriophages and predators. In response to these threats, they have evolved sophisticated defence mechanisms that today also protect bacteria against antibiotics and other therapies. In this Review, we explore the protective strategies of bacteria, including the mechanisms, evolution and clinical implications of these ancient defences. We also review the countermeasures that attackers have evolved to overcome bacterial defences. We argue that understanding how bacteria defend themselves in nature is important for the development of new therapies and for minimizing resistance evolution

Matrix-trapped viruses can prevent invasion of bacterial biofilms by colonizing cells

Bacteriophages can be trapped in the matrix of bacterial biofilms, such that the cells inside them are protected. It is not known whether these phages are still infectious and whether they pose a threat to newly arriving bacteria. Here, we address these questions using textitEscherichia coli and its lytic phage T7. Prior work has demonstrated that T7 phages are bound in the outermost curli polymer layers of the textitE. coli biofilm matrix. We show that these phages do remain viable and can kill colonizing cells that are T7-susceptible. If cells colonize a resident biofilm before phages do, we find that they can still be killed by phage exposure if it occurs soon thereafter. However, if colonizing cells are present on the biofilm long enough before phage exposure, they gain phage protection via envelopment within curli-producing clusters of the resident biofilm cells