8,453 research outputs found

    Simulation of metal powder packing behaviour in laser-based powder bed fusion

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    Laser-based powder bed fusion (L-PBF) is a method of additive manufacturing, in which metal powder is fused into solid parts, layer by layer. L-PBF shows high promise for manufacture of functional Tungsten parts, but the development of Tungsten powder feedstock for L-PBF processing is demanding and expensive. Therefore, computer simulation is explored as a possible tool for Tungsten powder feedstock development at EOS Finland Oy, with whom this thesis was made. The aim of this thesis was to develop a simulation model of the recoating process of an EOS M 290 L-PBF system, as well as a validation method for the simulation. The validated simulation model can be used to evaluate the applicability of the used simulation software (FLOW-3D DEM) in powder material development, and possibly use the model as a platform for future application with Tungsten powder. In order to reduce complexity and uncertainties, the irregular Tungsten powder is not yet simulated, and a well-known, spherical EOS IN718 powder feedstock was used instead. The validation experiment is based on building a low, enclosed wall using the M 290 L-PBF system. Recoated powder is trapped inside as the enclosure is being built, making it possible to remove the sampled powder from a known volume. This enables measuring the powder packing density (PD) of the powder bed. The experiment was repeated five times and some sources of error were also quantified. Average PD was found to be 52 % with a standard deviation of 0.2 %. The simulation was modelled after the IN718 powder and corresponding process used in the M 290 system. Material-related input values were found by dynamic image analysis, pycnometry, rheometry, and from literature. PD was measured with six different methods, and the method considered as most analogous to the practical validation experiment yielded a PD of 52 %. Various particle behavior phenomena were also observed and analyzed. Many of the powder bed characterization methods found in literature were not applicable to L-PBF processing or were not representative of the simulated conditions. Many simulation studies were also found to use no validation, or used a validation method which is not based on the investigated phenomena. The validation model developed in this thesis accurately represents the simulated conditions and is found to produce reliable and repeatable results. The simulation model was parametrized with values acquired from practical experiments or literature and closely matched the validation experiment, and could therefore be considered a truthful representation of the powder recoating process of an EOS M 290. The model can be used as a platform for future development of Tungsten powder simulation

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Southern Adventist University Undergraduate Catalog 2022-2023

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    Southern Adventist University\u27s undergraduate catalog for the academic year 2022-2023.https://knowledge.e.southern.edu/undergrad_catalog/1121/thumbnail.jp

    Sputter deposition on composites : interplay between film and substrate properties

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    Development of Smart Polymeric Nanocontainers for the Therapy of Head and Brain Malignancies

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    Head and brain tumours account for 2% to 4% of all cancers globally. Despite progress made in diagnosis and adjuvant therapies, they remain a global burden with unsatisfactory survival rates, reduced treatment outcome, poor prognosis and high risks of recurrence. First line chemotherapy drugs used in current regimens lack specificity, which ensues long term and unpleasant side effects for the patient. Encapsulating the chemotherapy drugs within nanocontainers (NCs) is one approach to improving their efficacy and therapeutic outcome as well as reducing side effects. Due to their nano-size and suitable modified surface, polymeric NCs can reach critical areas in the head and brain without causing any damage to the healthy tissue. The aim was to synthesize polymeric NCs capable of carrying and delivering chemotherapy drugs in tumour cells to increase their efficacy and reduce their side effects. Hollow P(MAA-co-MBA-co-NIPAM-co-EGDMA) NCs with dual sensitivity were synthesised and characterized structurally and morphologically throughout the synthesis steps. Daunorubicin, cisplatin, and temozolomide loaded NCs, and free NCs were assessed by haemolysis assay, MTT assay, fluorescence microscopy, western blot, and flow cytometry in rhabdomyosarcoma TE671 cell line and glioblastoma U87 MG cell line. The free NCs showed high biocompatibility and non-toxicity trait with good cellular uptake. Also, the loading capacities were between 27% and 63%, and the release studies showed a sustained release profile for up to 72h. Treatment of rhabdomyosarcoma and glioblastoma cells with different drugs loaded in NCs showed high cancer cell cytotoxicity, variation in induced DNA damage levels, induced apoptosis and cell cycles arrest for 24h and 72h. Overall, smart polymeric NCs showed reliability in carrying and delivering chemotherapy drugs in rhabdomyosarcoma and glioblastoma cells with efficiency in tackling the tumour cells. Our polymeric NCs exhibited excellent potential as a novel therapeutic approach for targeted drug delivery in head and brain tumours. This could be verified in the preclinical models to assess their improved efficacy and reducing side effects of first line cancer therapies. It could further pave the way for clinical trials of head and brain cancers in human patients

    Emerging Power Electronics Technologies for Sustainable Energy Conversion

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    This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

    Pediatric and Adolescent Nephrology Facing the Future: Diagnostic Advances and Prognostic Biomarkers in Everyday Practice

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    The Special Issue entitled “Pediatric and adolescent nephrology facing the future: diagnostic advances and prognostic biomarkers in everyday practice” contains articles written in the era when COVID-19 had not yet been a major clinical problem in children. Now that we know its multifaceted clinical course, complications concerning the kidneys, and childhood-specific post-COVID pediatric inflammatory multisystem syndrome (PIMS), the value of diagnostic and prognostic biomarkers in the pediatric area should be appreciated, and their importance ought to increase

    Pathophysiology of Spinal Cord Injury (SCI)

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    Spinal cord injury (SCI) leads to paralysis, sensory, and autonomic nervous system dysfunctions. However, the pathophysiology of SCI is complex, and not limited to the nervous system. Indeed, several other organs and tissue are also affected by the injury, directly or not, acutely or chronically, which induces numerous health complications. Although a lot of research has been performed to repair motor and sensory functions, SCI-induced health issues are less studied, although they represent a major concern among patients. There is a gap of knowledge in pre-clinical models studying these SCI-induced health complications that limits translational applications in humans. This reprint describes several aspects of the pathophysiology of spinal cord injuries. This includes, but is not limited to, the impact of SCI on cardiovascular and respiratory functions, bladder and bowel function, autonomic dysreflexia, liver pathology, metabolic syndrome, bones and muscles loss, and cognitive functions

    Oxysterols as drivers of inflammatory diseases

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    Acoustic Metamaterials for Enhanced Wave Control

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    Acoustic metamaterials have redefined the limits of acoustic wave control with composite structures that realize effective material properties that go beyond those of natural materials. These extraordinary material properties enable imaging beyond the diffraction limit, negative effective sound speeds, and acoustic cloaking. Metamaterials continue to be a hot topic in the scientific community, as these resonant structures push the boundaries of acoustic wave control with unprecedented functionality. The primary goal of this work is to advance the prevalence, practicality, and scope of acoustic metamaterial research with novel materials that uniquely tailor wave fields for a variety of acoustic-based applications. Each chapter uses foundational metamaterial physics to advance our understanding of acoustic wave control with composite structures. The first section develops the theory and performs simulations for a non-Hermitian complementary metamaterial (NHCMM) with tunable active feedback loop circuits that improve the acoustic transmission through an intact human skull. This lays the foundation for ultrasonic brain imaging and neural therapies that require high frequency acoustic waves to penetrate deep within the brain. With a similarly designed metamaterial, we compare the accessible range of the effective density and bulk modulus for unit cells with symmetric and asymmetric feedback loop circuits. The asymmetric circuits result in a Willis coupled response that dramatically broadens the metamaterial’s attainable parameter range. We also demonstrate asymmetric wave transmission at high efficiency with passive Willis coupled metagratings for acoustic beam steering at extreme angles. Lastly, we use transformation acoustics to correct focused and self-bending acoustic beams that become distorted in anisotropic media. These developments advance acoustic-based technologies for biomedical imaging, noise control, underwater communication, and structural acoustic applications.Ph.D
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