Development of New Adaptive Control Strategies for a Two-Link Flexible Manipulator

Manipulators with thin and light weight arms or links are called as Flexible-Link Manipulators (FLMs). FLMs offer several advantages over rigid-link manipulators such as achieving highspeed operation, lower energy consumption, and increase in payload carrying capacity and find applications where manipulators are to be operated in large workspace like assembly of freeflying space structures, hazardous material management from safer distance, detection of flaws in large structure like airplane and submarines. However, designing a feedback control system for a flexible-link manipulator is challenging due the system being non-minimum phase, underactuated and non-collocated. Further difficulties are encountered when such manipulators handle unknown payloads. Overall deflection of the flexible manipulator are governed by the different vibrating modes (excited at different frequencies) present along the length of the link. Due to change in payload, the flexible modes (at higher frequencies) are excited giving rise to uncertainties in the dynamics of the FLM. To achieve effective tip trajectory tracking whilst quickly suppressing tip deflections when the FLM carries varying payloads adaptive control is necessary instead of fixed gain controller to cope up with the changing dynamics of the manipulator. Considerable research has been directed in the past to design adaptive controllers based on either linear identified model of a FLM or error signal driven intelligent supervised learning e.g. neural network, fuzzy logic and hybrid neuro-fuzzy. However, the dynamics of the FLM being nonlinear there is a scope of exploiting nonlinear modeling approach to design adaptive controllers. The objective of the thesis is to design advanced adaptive control strategies for a two-link flexible manipulator (TLFM) to control the tip trajectory tracking and its deflections while handling unknown payloads. To achieve tip trajectory control and simultaneously suppressing the tip deflection quickly when subjected to unknown payloads, first a direct adaptive control (DAC) is proposed. The proposed DAC uses a Lyapunov based nonlinear adaptive control scheme ensuring overall system stability for the control of TLFM. For the developed control laws, the stability proof of the closed-loop system is also presented. The design of this DAC involves choosing a control law with tunable TLFM parameters, and then an adaptation law is developed using the closed loop error dynamics. The performance of the developed controller is then compared with that of a fuzzy learning based adaptive controller (FLAC). The FLAC consists of three major components namely a fuzzy logic controller, a reference model and a learning mechanism. It utilizes a learning mechanism, which automatically adjusts the rule base of the fuzzy controller so that the closed loop performs according to the user defined reference model containing information of the desired behavior of the controlled system. Although the proposed DAC shows better performance compared to FLAC but it suffers from the complexity of formulating a multivariable regressor vector for the TLFM. Also, the adaptive mechanism for parameter updates of both the DAC and FLAC depend upon feedback error based supervised learning. Hence, a reinforcement learning (RL) technique is employed to derive an adaptive controller for the TLFM. The new reinforcement learning based adaptive control (RLAC) has an advantage that it attains optimal control adaptively in on-line. Also, the performance of the RLAC is compared with that of the DAC and FLAC. In the past, most of the indirect adaptive controls for a FLM are based on linear identified model. However, the considered TLFM dynamics is highly nonlinear. Hence, a nonlinear autoregressive moving average with exogenous input (NARMAX) model based new Self-Tuning Control (NMSTC) is proposed. The proposed adaptive controller uses a multivariable Proportional Integral Derivative (PID) self-tuning control strategy. The parameters of the PID are adapted online using a nonlinear autoregressive moving average with exogenous-input (NARMAX) model of the TLFM. Performance of the proposed NMSTC is compared with that of RLAC. The proposed NMSTC law suffers from over-parameterization of the controller. To overcome this a new nonlinear adaptive model predictive control using the NARMAX model of the TLFM (NMPC) developed next. For the proposed NMPC, the current control action is obtained by solving a finite horizon open loop optimal control problem on-line, at each sampling instant, using the future predicted model of the TLFM. NMPC is based on minimization of a set of predicted system errors based on available input-output data, with some constraints placed on the projected control signals resulting in an optimal control sequence. The performance of the proposed NMPC is also compared with that of the NMSTC. Performances of all the developed algorithms are assessed by numerical simulation in MATLAB/SIMULINK environment and also validated through experimental studies using a physical TLFM set-up available in Advanced Control and Robotics Research Laboratory, National Institute of Technology Rourkela. It is observed from the comparative assessment of the performances of the developed adaptive controllers that proposed NMPC exhibits superior 7performance in terms of accurate tip position tracking (steady state error ≈ 0.01°) while suppressing the tip deflections (maximum amplitude of the tip deflection ≈ 0.1 mm) when the manipulator handles variation in payload (increased payload of 0.3 kg). The adaptive control strategies proposed in this thesis can be applied to control of complex flexible space shuttle systems, long reach manipulators for hazardous waste management from safer distance and for damping of oscillations for similar vibration systems

Photoswitching and thermoresponsive properties of conjugated multi-chromophore nanostructured materials

Conjugated multi-chromophore organic nanostructured materials have recently emerged as a new class of functional materials for developing efficient light-harvesting, photosensitization, photocatalysis, and sensor devices because of their unique photophysical and photochemical properties. Here, we demonstrate the formation of various nanostructures (fibers and flakes) related to the molecular arrangement (H-aggregation) of quaterthiophene (QTH) molecules and their influence on the photophysical properties. XRD studies confirm that the fiber structure consists of >95% crystalline material, whereas the flake structure is almost completely amorphous and the microstrain in flake-shaped QTH is significantly higher than that of QTH in solution. The influence of the aggregation of the QTH molecules on their photoswitching and thermoresponsive photoluminescence properties is revealed. Time-resolved anisotropic studies further unveil the relaxation dynamics and restricted chromophore properties of the self-assembled nano/microstructured morphologies. Further investigations should pave the way for the future development of organic electronics, photovoltaics, and light-harvesting systems based on π-conjugated multi-chromophore organic nanostructured materials

Liquid-Crystalline Star-Shaped Supergelator Exhibiting Aggregation-Induced Blue Light Emission

A family of closely related star-shaped stilbene-based molecules containing an amide linkage are synthesized, and their self-assembly in liquid-crystalline and gel states was investigated. The number and position of the peripheral alkyl tails were systematically varied to understand the structure–property relation. Interestingly, one of the molecules with seven peripheral chains was bimesomorphic, exhibiting columnar hexagonal and columnar rectangular phases, whereas the rest of them stabilized the room-temperature columnar hexagonal phase. The self-assembly of these molecules in liquid-crystalline and organogel states is extremely sensitive to the position and number of alkoxy tails in the periphery. Two of the compounds with six and seven peripheral tails exhibited supergelation behavior in long-chain hydrocarbon solvents. One of these compounds with seven alkyl chains was investigated further, and it has shown higher stability and moldability in the gel state. The xerogel of the same compound was characterized with the help of extensive microscopic and X-ray diffraction studies. The nanofibers in the xerogel are found to consist of molecules arranged in a lamellar fashion. Furthermore, this compound shows very weak emission in solution but an aggregation-induced emission property in the gel state. Considering the dearth of solid-state blue-light-emitting organic materials, this molecular design is promising where the self-assembly and emission in the aggregated state can be preserved. The nonsymmetric design lowers the phase-transition temperatures.The presence of an amide bond helps to stabilize columnar packing over a long range because of its polarity and intermolecular hydrogen bonding in addition to promoting organogelation

Perylo[1,12‑<i>b</i>,<i>c</i>,<i>d</i>] Thiophene Tetraesters: A New Class of Luminescent Columnar Liquid Crystals

Perylo­[1,12-<i>b</i>,<i>c</i>,<i>d</i>] thiophene tetraesters exhibiting wide-range hexagonal columnar phase have been synthesized. These compounds also exhibit good homeotropic alignment in the liquid-crystalline phase which is very important for the device fabrication. These compounds showed sky-blue luminescence in solution under the long-wavelength UV light. With high solubility and high quantum yield these compounds can serve as standards to measure quantum yields of unknown samples. This new class of materials is promising, considering the emissive nature and stabilization of hexagonal columnar mesophase over a wide thermal range and ease of synthesis

Weed Management and Crop Establishment Methods in Rice (<i>Oryza sativa</i> L.) Influence the Soil Microbial and Enzymatic Activity in Sub-Tropical Environment

Weed management has become the most important and inevitable aspect of crop management for achieving a higher rice yield. Nowadays, chemical herbicide application has become a popular practice for managing weeds in different rice cultures. However, herbicide application can have qualitative and quantitative impacts on soil microorganisms and soil enzymes, particularly in the case of new herbicide molecules and their indiscriminate use for a longer period. Further, different rice establishment methods also play a significant role in soil microbial population dynamics as well as soil biological properties. Keeping these in view, a field experiment was conducted at the Agronomy Main Research Farm, Orissa University of Agriculture and Technology (OUAT), India, during the kharif season of 2016 and 2017, on the impact of crop establishment methods and weed management practices on soil microbial and enzymatic status. The field experiment was laid out in a split-plot design with three replications with four crop establishment methods in the main plot, viz., M1, Direct Seeded Rice (DSR); M2, Wet Seeded Rice (WSR); M3,Unpuddled Transplanted Rice (NPTR); M4, Puddled Transplanted Rice (PTR), and six weed management practices in the sub-plot, viz., W1, Weedy check; W2, Bensulfuron methyl 0.6% + Pretilachlor 6% (pre-emergence (PE)) 0.660 kg ha−1 + Hand weeding (HW) at 30 days after sowing/transplanting (days after sowing/transplanting (DAS/T)); W3, Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) 0.495 kg ha−1 + HW at 30 DAS/T; W4, Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) 0.495 kg ha−1 + Bispyribac-Sodium (post-emergence(POE)) 0.025 kg ha−1 at 15 DAS/T; W5, Cono weeding (CW) at 15 DAS/T + hand weeding 30 DAS/T, and W6, Brown manuring/Green manuring. The initial decline in the microbial population was observed due to herbicide application in NPTR and PTR up to 7 DAS/T and then it increased up to 28 DAS/T. There was a reduction in soil microbial and enzymatic status after the application of herbicides Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) and Bispyribac-Sodium (POE) that again followed an upward graph with crop age. Significant variation in enzymatic activity and the microbial count was also observed among treatments involving crop establishment methods. The study revealed that improved microbial population and enzyme activity were noted in unpuddled transplanted rice under organic weed management due to favorable conditions, and chemical weed control initially affected microbial population and activities

Conversion of a Non-Cancer-Selective Promoter into a Cancer-Selective Promoter

Progression-elevated gene-3 (PEG-3) and rat growth arrest and DNA damage-inducible gene-34 (GADD34) display significant sequence homology with regulation predominantly transcriptional. The rat full-length (FL) and minimal (min) PEG-3 promoter display cancer-selective expression in rodent and human tumors, allowing for cancer-directed regulation of transgenes, viral replication and in vivo imaging of tumors and metastases in animals, whereas the FL- and min-GADD34-Prom lack cancer specificity. Min-PEG-Prom and min-GADD34-Prom have identical sequences except for two single-point mutation differences (at −260 bp and +159 bp). Engineering double mutations in the min-GADD34-Prom produce the GAPE-Prom. Changing one base pair (+159) or both point mutations in the min-GADD34-Prom, but not the FL-GADD34-Prom, results in cancer-selective transgene expression in diverse cancer cells (including prostate, breast, pancreatic and neuroblastoma) vs. normal counterparts. Additionally, we identified a GATA2 transcription factor binding site, promoting cancer specificity when both min-PEG-Prom mutations are present in the GAPE-Prom. Taken together, introducing specific point mutations in a rat min-GADD34-Prom converts this non-cancer-specific promoter into a cancer-selective promoter, and the addition of GATA2 with existing AP1 and PEA3 transcription factors enhances further cancer-selective activity of the GAPE-Prom. The GAPE-Prom provides a genetic tool to specifically regulate transgene expression in cancer cells

Cytoplasmic-delivery of polyinosine-polycytidylic acid inhibits pancreatic cancer progression increasing survival by activating Stat1-CCL2-mediated immunity

Background Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer without effective therapies and with poor prognosis, causing 7% of all cancer-related fatalities in the USA. Considering the lack of effective therapies for this aggressive cancer, there is an urgent need to define newer and more effective therapeutic strategies. Polyinosine–polycytidylic acid (pIC) is a synthetic double-stranded RNA (dsRNA) which directly activates dendritic cells and natural killer cells inhibiting tumor growth. When pIC is delivered into the cytoplasm using polyethyleneimine (PEI), pIC-PEI, programmed-cell death is induced in PDAC. Transfection of [pIC]PEI into PDAC cells inhibits growth, promotes toxic autophagy and also induces apoptosis in vitro and in vivo in animal models.Methods The KPC transgenic mouse model that recapitulates PDAC development in patients was used to interrogate the role of an intact immune system in vivo in PDAC in response to [pIC]PEI. Antitumor efficacy and survival were monitored endpoints. Comprehensive analysis of the tumor microenvironment (TME) and immune cells, cytokines and chemokines in the spleen, and macrophage polarization were analyzed.Results Cytosolic delivery of [pIC]PEI induces apoptosis and provokes strong antitumor immunity in vivo in immune competent mice with PDAC. The mechanism underlying the immune stimulatory properties of [pIC]PEI involves Stat1 activation resulting in CCL2 and MMP13 stimulation thereby provoking macrophage polarization. [pIC]PEI induces apoptosis via the AKT-XIAP pathway, as well as macrophage differentiation and T-cell activation via the IFNγ-Stat1-CCL2 signaling pathways in PDAC. In transgenic tumor mouse models, [pIC]PEI promotes robust and profound antitumor activity implying that stimulating the immune system contributes to biological activity. The [pIC]PEI anti-PDAC effects are enhanced when used in combination with a standard of care (SOC) treatment, that is, gemcitabine.Conclusions In summary, [pIC]PEI treatment is non-toxic toward normal pancreatic cells while displaying strong cytotoxic and potent immune activating activities in PDAC, making it an attractive therapeutic when used alone or in conjunction with SOC therapeutic agents, potentially providing a safe and effective treatment protocol with translational potential for the effective therapy of PDAC