54 research outputs found

    From model-driven to data-driven : a review of hysteresis modeling in structural and mechanical systems

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    Hysteresis is a natural phenomenon that widely exists in structural and mechanical systems. The characteristics of structural hysteretic behaviors are complicated. Therefore, numerous methods have been developed to describe hysteresis. In this paper, a review of the available hysteretic modeling methods is carried out. Such methods are divided into: a) model-driven and b) datadriven methods. The model-driven method uses parameter identification to determine parameters. Three types of parametric models are introduced including polynomial models, differential based models, and operator based models. Four algorithms as least mean square error algorithm, Kalman filter algorithm, metaheuristic algorithms, and Bayesian estimation are presented to realize parameter identification. The data-driven method utilizes universal mathematical models to describe hysteretic behavior. Regression model, artificial neural network, least square support vector machine, and deep learning are introduced in turn as the classical data-driven methods. Model-data driven hybrid methods are also discussed to make up for the shortcomings of the two methods. Based on a multi-dimensional evaluation, the existing problems and open challenges of different hysteresis modeling methods are discussed. Some possible research directions about hysteresis description are given in the final section

    Towards bottom-up reconstitution of a functional FtsZ-based cell division machinery

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    Synthetic biology aims at the understanding of living organisms through an engineering perspective, with the goal of improving or creating new biological systems. The prospect of building a synthetic cell focuses on producing life from basic elements by combining synthetic and/or organic cellular components in a bottom-up manner. To create a synthetic cell, the minimal functions of life are required and cell-free synthetic biology offers a suitable framework for understanding biological processes outside the inherently noisy environment of cells. A synthetic cell is expected to exhibit characteristics of a living cell, such as fundamental metabolism, proliferation, and communication. The bottom-up approach utilizes a wide range of in vitro tools/technologies such as biomimetic membranes, protein reconstitution, cell-free expression reactions, and microfluidics. As tools, they enable the thorough characterization of functional modules such as metabolism, replication, and cell division. The ultimate goal is to integrate these modules to construct a predictable, customizable, and controllable entity. Among the functional modules of living organisms, cell division stands out as a hallmark feature. The machinery of division has evolved into a highly organized set of proteins with the aim of accurately splitting a mother cell into two daughter cells, while preserving the genetic information and cellular integrity. In the case of bacteria, and more concretely Escherichia coli, cell division is mediated by the divisome, a contractile ring consisting of a multiprotein complex that precisely assembles at midcell. At the center of this machinery is the essential FtsZ protein, which is able to polymerize and form the FtsZ-ring. This ring is key to the process, serving as a scaffold for the divisome and driving the division process. However, the molecular details of how the ring is functionally assembled, stabilized, and positioned are still not well understood. Therefore, the aim of this thesis is to develop and expand the knowledge about the molecular mechanism of the FtsZ-ring assembly and its function as a potential primary component in the minimal division machinery of synthetic cells. To this end, and following a bottom-up approach, we conducted assays based on the in vitro reconstitution of FtsZ in cellular mimic environments using lipid vesicles. This allows the characterization of FtsZ’s behavior and functionalities in environments that are similar to a potential synthetic cell. Firstly, we designed a microfluidic device to deform lipid vesicles into bacterial rod-shaped compartments to analyze the effect of different geometries and membrane tension on FtsZ. We found that FtsZ filaments align with the shorter axis of the rod-shaped vesicles and reorganize into cone-like structures when the membrane tension is lowered, causing membrane deformations. This suggests that there is a geometry and tension-dependent mechanism in the assembly of FtsZ structures on membranes. Secondly, we designed an in vitro reconstitution assay based on soft lipid tubes pulled from FtsZ-decorated vesicles using optical tweezers. We observed the transformation of lipid tubes into 3D spring-like structures, where the GTPase activity of FtsZ drives spring compression likely through torsional stress. This allowed us to gain mechanistic insights into the molecular dynamics behind the force generated by FtsZ filaments. Thirdly, we studied the spatiotemporal localization of the division ring by co-reconstituting FtsZ inside lipid vesicles with the MinCDE system, which is involved in positioning the divisome in vivo, and FtsA, the natural tether of FtsZ to the membrane. We achieved the assembly, placement, and onset of constriction of a minimal division ring inside lipid vesicles using two different approaches: purified components or cell-free expression of the MinCDE, FtsA, and FtsZ proteins. This represents a significant advance towards the in vitro reconstitution of functional modules in a synthetic cell and expands our understanding of the molecular mechanism underlying the spatiotemporal organization of the FtsZ-ring. Lastly, we employed biochemical studies combined with cryo-ET visualization to characterize the stabilization of the division ring and the crosslinking of FtsZ filaments by ZapD, a protein known as one of the stabilizers of the divisome. We observed the formation of toroidal structures in solution that are assembled by short FtsZ filaments connected by ZapD and have bacterial size. Their characterization in 3D brings valuable structural information about the FtsZ-ring and its functional stabilization, which is important for its further reconstitution in minimal systems. In conclusion, this thesis provides important insights into the molecular dynamics of the central protein of division in E. coli and most bacteria, addressing its activity on the membrane, mechanism of force constriction, spatiotemporal localization and stabilization of the FtsZ-ring. Furthermore, we demonstrate significant advancements towards the implementation of FtsZ-based division systems in minimal synthetic cells using a bottom-up approach

    Study and Development of Mechatronic Devices and Machine Learning Schemes for Industrial Applications

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    Obiettivo del presente progetto di dottorato è lo studio e sviluppo di sistemi meccatronici e di modelli machine learning per macchine operatrici e celle robotizzate al fine di incrementarne le prestazioni operative e gestionali. Le pressanti esigenze del mercato hanno imposto lavorazioni con livelli di accuratezza sempre più elevati, tempi di risposta e di produzione ridotti e a costi contenuti. In questo contesto nasce il progetto di dottorato, focalizzato su applicazioni di lavorazioni meccaniche (e.g. fresatura), che includono sistemi complessi quali, ad esempio, macchine a 5 assi e, tipicamente, robot industriali, il cui utilizzo varia a seconda dell’impiego. Oltre alle specifiche problematiche delle lavorazioni, si deve anche considerare l’interazione macchina-robot per permettere un’efficiente capacità e gestione dell’intero impianto. La complessità di questo scenario può evidenziare sia specifiche problematiche inerenti alle lavorazioni (e.g. vibrazioni) sia inefficienze più generali che riguardano l’impianto produttivo (e.g. asservimento delle macchine con robot, consumo energetico). Vista la vastità della tematica, il progetto si è suddiviso in due parti, lo studio e sviluppo di due specifici dispositivi meccatronici, basati sull’impiego di attuatori piezoelettrici, che puntano principalmente alla compensazione di vibrazioni indotte dal processo di lavorazione, e l’integrazione di robot per l’asservimento di macchine utensili in celle robotizzate, impiegando modelli di machine learning per definire le traiettorie ed i punti di raggiungibilità del robot, al fine di migliorarne l’accuratezza del posizionamento del pezzo in diverse condizioni. In conclusione, la presente tesi vuole proporre soluzioni meccatroniche e di machine learning per incrementare le prestazioni di macchine e sistemi robotizzati convenzionali. I sistemi studiati possono essere integrati in celle robotizzate, focalizzandosi sia su problematiche specifiche delle lavorazioni in macchine operatrici sia su problematiche a livello di impianto robot-macchina. Le ricerche hanno riguardato un’approfondita valutazione dello stato dell’arte, la definizione dei modelli teorici, la progettazione funzionale e l’identificazione delle criticità del design dei prototipi, la realizzazione delle simulazioni e delle prove sperimentali e l’analisi dei risultati.The aim of this Ph.D. project is the study and development of mechatronic systems and machine learning models for machine tools and robotic applications to improve their performances. The industrial demands have imposed an ever-increasing accuracy and efficiency requirement whilst constraining the cost. In this context, this project focuses on machining processes (e.g. milling) that include complex systems such as 5-axes machine tool and industrial robots, employed for various applications. Beside the issues related to the machining process itself, the interaction between the machining centre and the robot must be considered for the complete industrial plant’s improvement. This scenario´s complexity depicts both specific machining problematics (e.g. vibrations) and more general issues related to the complete plant, such as machine tending with an industrial robot and energy consumption. Regarding the immensity of this area, this project is divided in two parts, the study and development of two mechatronic devices, based on piezoelectric stack actuators, for the active vibration control during the machining process, and the robot machine tending within the robotic cell, employing machine learning schemes for the trajectory definition and robot reachability to improve the corresponding positioning accuracy. In conclusion, this thesis aims to provide a set of solutions, based on mechatronic devices and machine learning schemes, to improve the conventional machining centre and the robotic systems performances. The studied systems can be integrated within a robotic cell, focusing on issues related to the specific machining process and to the interaction between robot-machining centre. This research required a thorough study of the state-of-the-art, the formulation of theoretical models, the functional design development, the identification of the critical aspects in the prototype designs, the simulation and experimental campaigns, and the analysis of the obtained results

    Development of decellularised porcine osteochondral scaffolds as matrices for cell implantation

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    Osteoarthritis currently affects 8.75 million people in the UK alone. This can cause major issues for those living with the disease, such as immobility and pain, which are often accompanied with psychological distress due to a loss in quality of life. One cause of osteoarthritis is damage to the articular cartilage which triggers inflammation and progressive degeneration. Early intervention strategies are employed to prevent disease progression such as microfracture, mosaicplasty and more recently autologous chondrocyte implantation. However, these all have their limitations in either, insufficient quality of repair material, donor site morbidity or limited biomechanical function prior to tissue regeneration. This study first aimed to investigate the applicability of decellularised porcine osteochondral scaffolds in the treatment of large shallow cartilage lesions. This project built upon previous work, with an aim of enhancing these scaffolds through application with chondrocytes and self-assembling peptide hydrogel with chondroitin sulphate (P11-8/CS) incorporated. The hypothesis was that the resultant scaffold would be an ideal tissue replacement due to the retained native extracellular matrix structure, the increased regenerative potential offered by the cells and the enhanced biomechanical function from the addition of SAP-CS. These benefits, would ideally allow faster restoration of the healthy biomechanical function of the joint. Potential for cost-effectiveness versus matrix assisted chondrocyte implantation was observed. The dimensions of the decellularised scaffolds were adapted to dimensions which are clinically appropriate for the treatment of large shallow lesions. The resultant decellularisation quality, cytocompatibility and mechanical properties were all conserved, despite larger dimensions. Following this, a recellularization process was established for these decellularised scaffolds based using lyophilisation to increase cell penetration. These scaffolds were evaluated in a natural knee joint simulation model, which indicated viability of recellularised chondrocytes at Day 7. Following this, the ability of the P11-8/CS hydrogel alone to support chondrocyte cell proliferation and survival over a 14-day timecourse was demonstrated, whilst chondrogenic gene expression of encapsulated primary porcine chondrocytes was shown. The lyophilisation method was then developed to deliver SAP-GAG to the osteochondral scaffolds, which showed a trend for improved biomechanical properties. Overall, this work has shown the potential for both recellularised decellularised scaffolds and self-assembling peptides, as devices to support chondrocyte implantation to aid the regeneration of large shallow cartilage lesions and early stage lesions respectively

    Development of a femtosecond field synthesizer for ultrafast science

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    In this thesis, I present several new technologies aimed at improving ultrafast spectroscopy at attosecond timescales. The focus of the work was on femtosecond field synthesis, but work on attosecond streaking spectroscopy is also presented. We used CEP few-cycle near-infrared laser pulses to generate XUV isolated attosecond pulses for attosecond streaking spectroscopy on solid surfaces. We characterised the few-cycle pulses using a SEA-F-SPIDER and constructed a combined Second Harmonic/Transient Grating FROG to permit the characterisation of pulses from the UV to the short wavelength infrared. The isolated attosecond pulses were applied, with the few-cycle pulses, to the measurement of the photoemission time delay from gold and silver surfaces. We studied the effect of the few-cycle pulse's Gouy phase on streaking measurements and found that, for our system, the effect was larger than previous reports suggested. We then developed and implemented a bi-material target for surface streaking. This system minimised the systematic error resulting from Gouy phase shifts. We then used the system to measure the photoemission delay between the two materials, finding that gold valence photoelectrons were delayed by 171 ± 49 as relative to silver valence photoelectrons. We constructed a three-colour field synthesizer. The purpose of this system was to generate sub-cycle shaped pulses that could optimise attosecond pulse generation. The output of a CEP stable NIR amplifier was split with one channel being the CEP-stable few-cycle NIR pulse. The other two channels were a 40 fs duration, short wavelength infrared pulse centred at 1300 nm, generated using a commercial OPA system, and a 46 fs duration UV pulse centred at 405 nm generated by second-harmonic generation. The relative stability of each channel and was measured to be 0.179 rad for the second harmonic relative to the few-cycle pulse. For the infrared pulse relative to the few-cycle pulse, the stability was 13.2 rad, which was larger due to the phase instability in commercial OPA. The spatial quality of the beams was measured and found to be suitable for the driving HHG. Two of the three pulses in the synthesizer were used to generate attosecond pulses at 90 eV photon energy with a two-fold increase in flux compared to the single colour case. Synthesized-field waveform-dependent shifts in the cutoff were observed in the HHG spectrum. The resulting attosecond pulses were characterised using gas-phase attosecond streaking, showing that their duration was minimally affected by the presence of the weaker field due to spectral filtering by a multilayer mirror. From the streaking trace, we were able to accurately retrieve the spectrum of the multi-cycle pulse.Open Acces

    Nonlinear ESO-based vibration control for an all-clamped piezoelectric plate with disturbances and time delay: design and hardware implementation

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    Considering the problems of model uncertainties, higher harmonics, uncertain boundary conditions, external excitations and system time delay in practical vibration control system, a novel active vibration control method is proposed to suppress the vibration of a thin plate structure with acceleration sensor and piezoelectric bimorph actuator in this paper. First, a nonlinear extended state observer (NESO)-based controller is designed to ensure the anti-disturbance performance of the structural vibration control system. Then, an enhanced differentiator-based time delay compensation method is introduced to improve the vibration suppression performance of the NESO-based controller. A real time hardware-in-the-loop benchmark for an all-clamped piezoelectric thin plate is designed to verify and compare the performance of the developed controller against conventional ESO-based methods (linear ESO with/without time delay compensation, NESO without time compensation). The best vibration suppression and disturbance rejection performance of the proposed NESO-based controller with an enhanced time delay compensator is verified in the comparative experimental results. This work is able to provide practitioners with vital guidance in designing active vibration control system in the presence of disturbances and time delay

    Hybrid Integrator-Gain Systems:Analysis, Design, and Applications

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    A pneumatic conveyor robot for color detection and sorting

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    Despite numerous research works on conveyor robots, few works can be found on electropneumatic conveyor belt robots with two separated lines. The unique feature of this study is a combination of various systems to develop an electropneumatic robot. In this work, an automated and intelligent mechatronic conveyor system is designed and developed for transporting and positioning circular objects that can be used in the manufacturing and packaging industries. In addition to moving and positioning, timing can also be controlled on this conveyor belt robot. All control operations are handled by an electrical and programmable relay called a mini programmable logic controller (PLC), color sensor, gripper arm, and electronic switches. An electropneumatic system is used to control the robot for placing objects. The main goal of this study is to develop a novel 3D structural design which make the procedure unique for better efficiency and accuracy. The novelty of this work lies within the 3D design of two belts and assembly of all electropneumatic components which are helpful for manufacturing assembly lines. Also, TCS230 sensor and AVR microcontroller are used to identify the colors within the operation. The results show the accuracy of the developed system is reliable in terms of color and positioning detection. The system is able to work non-stop for more than 1 hour without any issues

    A Review of Modeling and Control of Piezoelectric Stick-Slip Actuators

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    Piezoelectric stick-slip actuators with high precision, large actuating force, and high displacement resolution are currently widely used in the field of high-precision micro-nano processing and manufacturing. However, the non-negligible, non-linear factors and complexity of their characteristics make its modeling and control quite difficult and affect the positioning accuracy and stability of the system. To obtain higher positioning accuracy and efficiency, modeling and control of piezoelectric stick-slip actuators are meaningful and necessary. Firstly, according to the working principle of stick-slip drive, this paper introduces the sub-models with different characteristics, such as hysteresis, dynamics, and friction, and presents the comprehensive modeling representative piezoelectric stick-slip actuators. Next, the control approaches suggested by different scholars are also summarized. Appropriate control strategies are adopted to reduce its tracking error and position error in response to the influence of various factors. Lastly, future research and application prospects in modeling and control are pointed out

    The design and construction of a scanning probe nitrogen vacancy centre magnetometer

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    The isolated spin of the nitrogen-vacancy (NV) centre in diamond, which is formed from a vacancy and an adjacent nitrogen atom replacing carbon atoms in the diamond lattice, provides a highly promising system to realise non-invasive high-sensitivity magnetometry, even at room temperatures. The combination of the atomically sized detection volume, which for a single NV centre is defined by the spatial extent of the wavefunction, and high magnetic field sensitivity makes the NV centre a highly promising sensor to investigate magnetism on the nanoscale. In recent years NV centres have been used to produce 2D maps of magnetic fields with nanoscale resolution by affixing single or small numbers of NV centres to the very tip of a scanning probe. To date, scanning probe NV magnetometers have produced images with some of the smallest probe-sample distances seen in magnetic field sensing, with probe-sample distances of the order 50 nm routinely achieved. Scanning probe NV magnetometry utilises two established scientific techniques; atomic force microscopy, which provides the scanning probe element required for the formation of 2D images, and confocal microscopy for magnetic field readout out via measurement of the NV centre's magnetically sensitive photoluminescence. Therefore, an instrument designed for scanning probe NV magnetometry will feature both optical instrumentation optimised to collect luminescence from atomically sized sources, in particular NV centres fixed to functionalised AFM probes, and an atomic force microscope that can be operated while simultaneously making optical measurements. In addition to the established imaging techniques of confocal microscopy and AFM, an instrument focusing on NV centre magnetometry requires a method of applying a high-frequency magnetic field for spin state manipulation and a variable strength, variable orientation bias magnetic field. While a prerequisite for NV magnetometry, these final components extend an NV magnetometer's functionality, enabling the study of other species that exhibit magnetically sensitive photoluminescence. As such, an instrument based on a scanning probe NV magnetometer will not only be able to perform high-resolution magnetometry, but also operate in a wide range of imaging modalities, providing a versatile tool for sub-micron sample characterisation. This thesis presents the design, assembly and performance of a custom-built sub-micron characterisation tool based on a scanning probe NV magnetometer. This research project's main output is the instrument itself, with the key results the figures of merit for each imaging modality. A sample of nanodiamonds deposited onto a silicon/silicon dioxide wafer serves as the test target for most of the imaging modes. The optical imaging modes' performance is presented through diffraction-limited spatial maps, both where photoluminescence and backscattered laser light provide the dominant signal. To demonstrate this instrument's capability to measure the temporal and spectral characteristics from diffraction-limited luminescent sources, time-correlated single photon counting measurements and emission spectra from sources on the nanodiamond sample are presented. The performance of custom-built AFM is demonstrated through the measurement of a calibration sample and then the suitability for NV magnetometry demonstrated by presenting simultaneously recorded AFM confocal microscope measurements. This instrument's capability for NV centre magnetometry is presented by showing optically detected magnetic resonances from photoluminescent sources in nanodiamonds. Finally, the progress towards NV centre magnetometry in this instrument is reviewed. The recent discovery of photoluminescence originating from single-photon sources in 2D materials, in particular from emitters in hexagonal boron nitride (hBN) which have shown such behaviour at room temperatures, has led to an active area of research investigating the structure and potential applications of point defects in 2D materials. To demonstrate this instrument's versatility and its potential to perform cutting-edge research in this emerging field, preliminary results characterising the nature of photoluminescence in a thin hBN film on a silicon carbide substrate are presented
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