89 research outputs found

    On the motion planning & control of nonlinear robotic systems

    Get PDF
    In the last decades, we saw a soaring interest in autonomous robots boosted not only by academia and industry, but also by the ever in- creasing demand from civil users. As a matter of fact, autonomous robots are fast spreading in all aspects of human life, we can see them clean houses, navigate through city traffic, or harvest fruits and vegetables. Almost all commercial drones already exhibit unprecedented and sophisticated skills which makes them suitable for these applications, such as obstacle avoidance, simultaneous localisation and mapping, path planning, visual-inertial odometry, and object tracking. The major limitations of such robotic platforms lie in the limited payload that can carry, in their costs, and in the limited autonomy due to finite battery capability. For this reason researchers start to develop new algorithms able to run even on resource constrained platforms both in terms of computation capabilities and limited types of endowed sensors, focusing especially on very cheap sensors and hardware. The possibility to use a limited number of sensors allowed to scale a lot the UAVs size, while the implementation of new efficient algorithms, performing the same task in lower time, allows for lower autonomy. However, the developed robots are not mature enough to completely operate autonomously without human supervision due to still too big dimensions (especially for aerial vehicles), which make these platforms unsafe for humans, and the high probability of numerical, and decision, errors that robots may make. In this perspective, this thesis aims to review and improve the current state-of-the-art solutions for autonomous navigation from a purely practical point of view. In particular, we deeply focused on the problems of robot control, trajectory planning, environments exploration, and obstacle avoidance

    Differential operators on sketches via alpha contours

    Full text link
    A vector sketch is a popular and natural geometry representation depicting a 2D shape. When viewed from afar, the disconnected vector strokes of a sketch and the empty space around them visually merge into positive space and negative space, respectively. Positive and negative spaces are the key elements in the composition of a sketch and define what we perceive as the shape. Nevertheless, the notion of positive or negative space is mathematically ambiguous: While the strokes unambiguously indicate the interior or boundary of a 2D shape, the empty space may or may not belong to the shape’s exterior. For standard discrete geometry representations, such as meshes or point clouds, some of the most robust pipelines rely on discretizations of differential operators, such as Laplace-Beltrami. Such discretizations are not available for vector sketches; defining them may enable numerous applications of classical methods on vector sketches. However, to do so, one needs to define the positive space of a vector sketch, or the sketch shape. Even though extracting this 2D sketch shape is mathematically ambiguous, we propose a robust algorithm, Alpha Contours, constructing its conservative estimate: a 2D shape containing all the input strokes, which lie in its interior or on its boundary, and aligning tightly to a sketch. This allows us to define popular differential operators on vector sketches, such as Laplacian and Steklov operators. We demonstrate that our construction enables robust tools for vector sketches, such as As-Rigid-As-Possible sketch deformation and functional maps between sketches, as well as solving partial differential equations on a vector sketch

    LIPIcs, Volume 258, SoCG 2023, Complete Volume

    Get PDF
    LIPIcs, Volume 258, SoCG 2023, Complete Volum

    Detection and Resolution of Interpenetrations of Woven Tows

    Get PDF
    Woven composite tows can be approximated by creating surfaces using the Virtual Textile Morphology Suite (VTMS) developed at the Air Force Research Lab (AFRL). These surfaces have interpenetrations between tow surface meshes which must be resolved in order to have strict, compatible mesh between all domains. A compatible mesh is desirable to reduce the complexity of the model and allow for a wider range of FEA tools to be used for analysis. To detect these interpenetrations, the surfaces were approximated using Non-Uniform Rational B-Spline (NURBS) surfaces with the SISL library from SINTEF. The interpenetration regions were then identified by B-Spline curves which, when included during the mesh generation process, allowed the surface interpenetrations to be removed and replaced with a compatible mesh between tows. The meshes are strictly tied together to investigate the effects of removing the thin slices of matrix from between tows in close proximity. These resulting meshes were subjected to a simple in-plane loading and compared to another method for removing interpenetrations that shrinks the tow cross-sections until they no longer penetrate. The predicted stresses show that the new method can create small regions of high magnitude stress in the tow local to the edge of the connected region between tows, and that high mesh refinement around these regions can increase the magnitude of these stress concentrations. In regions away from the boundary of the connected regions, both models predict similar stress responses. Also, the analysis predicts less matrix volume at high von Mises stress due to the lack of matrix between tows in the NURBS method meshes. While the analysis shows evidence of singularities, the size of the concentrations and the similar overall response as the previous method show that the new method has some merit, particularly when considering the potential use cases for compatible, connected regions between tow meshes

    Towards a circular economy: fabrication and characterization of biodegradable plates from sugarcane waste

    Get PDF
    Bagasse pulp is a promising material to produce biodegradable plates. Bagasse is the fibrous residue that remains after sugarcane stalks are crushed to extract their juice. It is a renewable resource and is widely available in many countries, making it an attractive alternative to traditional plastic plates. Recent research has shown that biodegradable plates made from Bagasse pulp have several advantages over traditional plastic plates. For example, they are more environmentally friendly because they are made from renewable resources and can be composted after use. Additionally, they are safer for human health because they do not contain harmful chemicals that can leach into food. The production process for Bagasse pulp plates is also relatively simple and cost-effective. Bagasse is first collected and then processed to remove impurities and extract the pulp. The pulp is then molded into the desired shape and dried to form a sturdy plate. Overall, biodegradable plates made from Bagasse pulp are a promising alternative to traditional plastic plates. They are environmentally friendly, safe for human health, and cost-effective to produce. As such, they have the potential to play an important role in reducing plastic waste and promoting sustainable practices. Over the years, the world was not paying strict attention to the impact of rapid growth in plastic use. As a result, uncontrollable volumes of plastic garbage have been released into the environment. Half of all plastic garbage generated worldwide is made up of packaging materials. The purpose of this article is to offer an alternative by creating bioplastic goods that can be produced in various shapes and sizes across various sectors, including food packaging, single-use tableware, and crafts. Products made from bagasse help address the issue of plastic pollution. To find the optimum option for creating bagasse-based biodegradable dinnerware in Egypt and throughout the world, researchers tested various scenarios. The findings show that bagasse pulp may replace plastics in biodegradable packaging. As a result of this value-added utilization of natural fibers, less waste and less of it ends up in landfills. The practical significance of this study is to help advance low-carbon economic solutions and to produce secure bioplastic materials that can replace Styrofoam in tableware and food packaging production

    Ligand-Promoted Dissolution of Uranyl Phosphate Across Scales

    Get PDF
    The formation of uranyl phosphate precipitate is a remediation strategy because the low solubility of uranyl phosphate minerals, like chernikovite, limits the mobility of uranium in contaminated soils. However, organic ligands can complex with aqueous metal cations to form more soluble species. For example, citrate is a commonly occurring organic ligand produced by plants and microbes that increases the solubility of uranium and therefore the dissolution of uranyl phosphate minerals in the uranyl phosphate-citrate system. This effect is an important control on the mobility of uranium in organic-rich, and near-surface vegetated environments. Nevertheless, key aspects of the citrate-uranyl phosphate system remain poorly understood, and this limits the ability to assess risks of exposure and strategies for remediating uranium contaminated soils. The goals of this research are to determine the mechanism, extent, and rate of citrate-promoted dissolution of uranyl phosphate and evaluate how ligand-promoted dissolution and solid-phase transformations of uranyl phosphate affect macro-scale uranium transport. Batch dissolution, continuously stirred tank reactor (CSTR), soil column, and field lysimeter experiments were conducted to span across spatial scales ranging from Ã…ngstrom to the meter scale. The results from all experiments indicate that the concentration of uranium dissolved from a chernikovite source increases with the concentration of citrate. However, this study determined that the rate of increase in uranium concentration diminishes at higher citrate concentrations and longer residence times and provided evidence of a uranyl-citrate alteration layer on the surfaces of uranyl phosphate grains after citrate exposure. These findings suggest that a combination of secondary-phase precipitation and ligand surface saturation hinder the release of uranium into solution. In the presence of soil, cations from the soil compete with uranium from the chernikovite to form citrate-complexes, slowing the dissolution of chernikovite. Soil cations, like potassium and calcium, can also integrate into the uranyl phosphate structure, altering the original chernikovite to a less soluble uranyl phosphate phase that is more resistant to citrate-promoted dissolution at lower citrate concentrations. The findings presented in this work show that although citrate promotes the dissolution of uranyl phosphate, other mechanisms hinder the release of uranium in the environment from a uranyl phosphate source

    Cornerstones in Contemporary Inorganic Chemistry

    Get PDF
    A collection of essential research articles and scientific reviews covering some of the most pertinent and topical areas of study that currently constitute Inorganic Chemistry in the early 21st century

    The Mechanical Behavior of Salt X

    Get PDF
    Rock salt formations have long been recognized as a valuable resource - not only for salt mining but for construction of oil and gas storage caverns and for isolation of radioactive and other hazardous wastes. Current interest is fast expanding towards construction and re-use of solution-mined caverns for storage of renewable energy in the form of hydrogen, compressed air and other gases. Evaluating the long term performance and safety of such systems demands an understanding of the coupled mechanical behavior and transport properties of salt. This volume presents a collection of 60 research papers defining the state-of-the-art in the field. Topics range from fundamental work on deformation mechanisms and damage of rock salt to compaction of engineered salt backfill. The latest constitutive models are applied in computational studies addressing the evolution and integrity of storage caverns, repositories, salt mines and entire salt formations, while field studies document ground truth at multiple scales. The volume is structured into seven themes: Microphysical processes and creep models Laboratory testing Geological isolation systems and geotechnical barriers Analytical and numerical modelling Monitoring and site-specific studies Cavern and borehole abandonment and integrity Energy storage in salt caverns The Mechanical Behavior of Salt X will appeal to graduate students, academics, engineers and professionals working in the fields of salt mechanics, salt mining and geological storage of energy and wastes, but also to researchers in rock physics in general
    • …
    corecore