An integrated control/structure design method using multi-objective optimization

The benefits are demonstrated of a multiobjective optimization based control structure integrated design methodology. An application of the proposed CSI methodology to the integrated design of the Spacecraft COntrol Lab Experiment (SCOLE) configuration is presented. Integrated design resulted in reducing both the control performance measure and the mass. Thus, better overall performance is achieved through integrated design optimization. The mutliobjective optimization approach used provides Pareto optimal solutions by unconstrained minimization of a differentiable KS function. Furthermore, adjusting the parameters gives insight into the trade-offs involved between different objectives

Modeling and control of flexible space platforms with articulated payloads

The first steps in developing a methodology for spacecraft control-structure interaction (CSI) optimization are identification and classification of anticipated missions, and the development of tractable mathematical models in each mission class. A mathematical model of a generic large flexible space platform (LFSP) with multiple independently pointed rigid payloads is considered. The objective is not to develop a general purpose numerical simulation, but rather to develop an analytically tractable mathematical model of such composite systems. The equations of motion for a single payload case are derived, and are linearized about zero steady-state. The resulting model is then extended to include multiple rigid payloads, yielding the desired analytical form. The mathematical models developed clearly show the internal inertial/elastic couplings, and are therefore suitable for analytical and numerical studies. A simple decentralized control law is proposed for fine pointing the payloads and LFSP attitude control, and simulation results are presented for an example problem. The decentralized controller is shown to be adequate for the example problem chosen, but does not, in general, guarantee stability. A centralized dissipative controller is then proposed, requiring a symmetric form of the composite system equations. Such a controller guarantees robust closed loop stability despite unmodeled elastic dynamics and parameter uncertainties

Robust multivariable controller design for flexible spacecraft

Large, flexible spacecraft are typically characterized by a large number of significant elastic modes with very small inherent damping, low, closely spaced natural frequencies, and the lack of accurate knowledge of the structural parameters. Summarized here is some recent research on the design of robust controllers for such spacecraft, which will maintain stability, and possible performance, despite these problems. Two types of controllers are considered, the first being the linear-quadratic-Gaussian-(LQG)-type. The second type utilizes output feedback using collocated sensors and actuators. The problem of designing robust LQG-type controllers using the frequency domain loop transfer recovery (LTR) method is considered, and the method is applied to a large antenna model. Analytical results regarding the regions of stability for LQG-type controllers in the presence of actuator nonlinearities are also presented. The results obtained for the large antenna indicate that the LQG/LTR method is a promising approach for control system design for flexible spacecraft. For the second type of controllers (collocated controllers), it is proved that the stability is maintained in the presence of certain commonly encountered nonlinearities and first-order actuator dynamics. These results indicate that collocated controllers are good candidates for robust control in situations where model errors are large

Computer-aided design and distributed system technology development for large space structures

Proposed large space structures have many characteristics that make them difficult to analyze and control. They are highly flexible, with components mathematically modeled by partial differential equations or very large systems of ordinary differential equations. They have many resonant frequencies, typically low and closely spaced. Natural damping may be low and/or improperly modeled. Coupled with stringent operational requirements of orientation, shape control, and vibration suppression, and the inability to perform adequate ground testing, these characteristics present an unconventional identification and control design problem to the systems theorist. Some of the research underway within Langley's Spacecraft Control Branch, Guidance and Control Division aimed at developing theory and algorithms to treat large space structures systems identification and control problems is described. The research areas to be considered are computer-aided design algorithms, and systems identification and control of distributed systems

A Novel Role For Repetitive Sequences In Recognition Of The Drosophila Melanogaster X Chromosome

In humans and fruit flies, males have one X chromosome while females have two. This imbalance in gene dosage is potentially lethal, and the process of dosage compensation corrects it. The MSL (Male Specific Lethal) complex, which is composed of five proteins and one of two functionally redundant long non-coding roX (RNA on the X) RNAs, brings about dosage compensation in Drosophila melanogaster. In fruit fly dosage compensation, all the genes on the single male X chromosome are upregulated approximately twofold, via chromatin modifications, to equalize gene dosage with the two X chromosomes of females. This process calls for highly selective identification of the X chromosome in the nucleus. The current model for X-recognition does not explain how specific binding to the X-chromatin is achieved. It is known however, that the X chromosome assumes a distinct three-dimensional conformation in the male nucleus, and that the siRNA pathway aids in X-recognition. We hypothesized that repetitive sequences found exclusively on the X chromosome, called the 1.688X repeats, could be a possible source of siRNAs that play a role in specifying X identity, and thus promoting recognition by the MSL complex. To test this hypothesis, I designed a functional test that detects compensation of autosomal chromatin. This required generation of lethal autosomal deficiencies. These were made by recombining parts of the 2nd and Y chromosomes. These translocations can be separated meiotically to generate a duplication and a deficiency. I then generated a transgene carrying roX1 and 1.6883F (one of the repeat clusters), and integrated it on an autosome. The transgene was designed such that the role of each element could be tested individually. I discovered that all transgenes, including 1.6883F only, recruited the MSL complex to the autosome and increased the expression of nearby genes. When placed opposite the lethal deficiency, the transgenes partially rescued male flies to the pharate stage. Additionally, all transgenes led to a dramatic increase in recovery of male third instar larvae, which was further enhanced by expression of siRNA from 1.6883F. My findings strongly suggest that the 1.688X repeats act in cis to facilitate X-identification and dosage compensation. They also suggest that 1.688X repeats on the X are the targets of the siRNA pathway that contributes to X-recognition. The close proximity and sequence similarity of the repeat clusters 1.6883F and 1.6884A prompted us to ask if they share a redundant function in generation of the siRNA that promotes X chromosome recognition. We discovered that flies deleted for both repeat clusters did not show an apparent defect in male survival. Thus the specialized role of 1.6883F, and whether it is unique from other 1.688X repeats, remains ambiguous

INSTITUTIONAL CHANGE IN INDIAN AGRICULTURE

Globalization, privatization and scientific advancements pose new challenges and opportunities for the development of Indian agriculture. The emerging paradigm shifts focus to creation and application of new knowledge for agricultural development and global competitiveness. To facilitate this shift and realize greater economic efficiency, a new set of responsive institutions should emerge. This volume discusses the direction of institutional change in Indian agriculture. The roles of the state, markets and collective actions are examined for evolving the knowledge-intensive agriculture. The contributed papers from a number of leading researchers cover the institutions for R&D, land and water resources, credit, marketing, trade and agro-processing.Industrial Organization, International Development,

Adaptive Control in the Presence of Simultaneous Sensor Bias and Actuator Failures

The problem of simultaneously accommodating unknown sensor biases and unknown actuator failures in uncertain systems is considered in a direct model reference adaptive control (MRAC) setting for state tracking using state feedback. Sensor biases and actuator faults may be present at the outset or may occur at unknown instants of time during operation. A modified MRAC law is proposed, which combines sensor bias estimation with control gain adaptation for accommodation of sensor biases and actuator failures. This control law is shown to provide signal boundedness in the resulting system. For the case when an external asymptotically stable sensor bias estimator is available, an MRAC law is developed to accomplish asymptotic state tracking and signal boundedness. For a special case wherein biases are only present in the rate measurements and bias-free position measurements are available, an MRAC law is developed using a model-independent bias estimator, and is shown to provide asymptotic state tracking with signal boundedness

On Identifiability of Bias-Type Actuator-Sensor Faults in Multiple-Model-Based Fault Detection and Identification

This paper explores a class of multiple-model-based fault detection and identification (FDI) methods for bias-type faults in actuators and sensors. These methods employ banks of Kalman-Bucy filters to detect the faults, determine the fault pattern, and estimate the fault values, wherein each Kalman-Bucy filter is tuned to a different failure pattern. Necessary and sufficient conditions are presented for identifiability of actuator faults, sensor faults, and simultaneous actuator and sensor faults. It is shown that FDI of simultaneous actuator and sensor faults is not possible using these methods when all sensors have biases

MITIGATING EFFECTS OF ZINGIBER OFFICINALE AGAINST REPRODUCTIVE TOXICITY INDUCED BY DICHLOROVOS IN MALE RATS

Objective: Aim of this study was to evaluate the effect of Z. officinalein mitigating oxidative damage and reproductive toxicity in the testis, induced by chronic dichlorovos administration in male Wistar rats.Methods: Twenty four adult male Wistar rats were divided into 4 groups of 6 rats in each group. Group I received olive oil (1 ml/ kg bwt/day) and served as control group, while Group II was administered dichlorovos (20 mg/kg bwt/day) and Group III & IV received a combination of dichlorovos (20 mg/kg bwt) andZingiber officinale (ginger) extract (100 & 200 mg/kg bwt) for 45 days. At the end of the treatment period, the rats were sacrificed.Results: The weight of the reproductive organs and serum FSH, LH and testosterone levels were assayed. Lipid peroxidation (LPO) (indexed by MDA) and antioxidants enzymes GSH, SOD, CAT were also analysed. Dichlorovos treatment decreased the weight of testis, epididymis, prostate and seminal vesicle as well as the serumlevels of FSH, LH and testosterone. There was a decrease in the activities of GSH, SOD and CAT as well as an increase in MDA concentration.Conclusion: Co-administration of aqueous extract ofZingiber officinalewith dichlorovos showed protective effect and increases the reproductive organs weight and enhancesserum hormones level along with increased antioxidants activities and reduced lipid peroxidation. This indicates that Zingiber officinale mitigates reproductive toxicity and oxidative damage induced by dichlorovos exposure due to its antioxidant activity in the testes