This paper investigates decentralised adaptive control of discrete‐time systems consisting of linear time‐invariant systems and a class of nonlinear systems. The parameters of the subsystems and the ...interconnection strengths between the subsystems are assumed unknown. Multiple adaptive prediction models with switching are used in this paper to address the relatively poor transient performance that typically results from a single prediction model. However, the application of this methodology requires indirect model reference discrete‐time adaptive control, and there appears to be very little focus in the literature on this. The principal contribution of this paper is to fill this void by arriving at proof of global stability of such decentralised adaptive systems using the theory of Lyapunov and properties of square‐summable sequences. The chosen representation of the system enables the same results to be directly applicable to both linear time‐invariant and linear‐in‐the‐parameters nonlinear subsystems. We consider two parametric update algorithms, one of which has a normalisation factor. Simulation studies included in this paper demonstrate the improvement in transient performance.
Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims. We wish to understand the reason for ...star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods. We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results. We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions. The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.
The principal drawback of traditional adaptive systems is the possibility of rather poor transient response. In this regard, the multiple-model methodology has been beneficial over the past couple of ...decades. However, the application of this methodology requires proven indirect model reference adaptive control. Such a gap exists in the case of discrete-time linear time-invariant systems with unknown parameters. The principal contribution of this paper is to fill this void by arriving at proof of global stability of discrete-time adaptive systems that use the prediction error rather than the control error to update the parameters of the prediction model. This proof is based on the theory of Lyapunov and the properties of square-summable sequences. An analysis of the available literature reveals that such a result is not available even for linear time-invariant systems. Therefore, the proof is first provided for adaptive systems with a single prediction model wherein the transfer function of the plant has an arbitrary relative degree. Subsequently, this proof is extended to the case of multiple prediction models in the context of multiple-model methodology with second-level adaptation. Two parameter update algorithms are considered. Simulation studies are included to demonstrate the improvement in transient performance.
In this paper, approximate optimal distributed control schemes for a class of nonlinear interconnected systems with strong interconnections are presented using continuous and event-sampled feedback ...information. The optimal control design is formulated as an <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>-player nonzero-sum game where the control policies of the subsystems act as players. An approximate Nash equilibrium solution to the game, which is the solution to the coupled Hamilton-Jacobi equation, is obtained using the approximate dynamic programming-based approach. A critic neural network (NN) at each subsystem is utilized to approximate the Nash solution and novel event-sampling conditions, that are decentralized, are designed to asynchronously orchestrate the sampling and transmission of state vector at each subsystem. To ensure the local ultimate boundedness of the closed-loop system state and NN parameter estimation errors, a hybrid-learning scheme is introduced and the stability is guaranteed using Lyapunov-based stability analysis. Finally, implementation of the proposed event-based distributed control scheme for linear interconnected systems is discussed. For completeness, Zeno-free behavior of the event-sampled system is shown analytically and a numerical example is included to support the analytical results.
We present a study of star-forming regions and their demographics in the nearby dwarf irregular galaxy WLM using Ultraviolet Imaging Telescope (UVIT) multiband observations in three filters, F148W, ...N245M, and N263M. We find that the UV emission is extended at least up to 1.7 kpc, with the NUV emission more extended than the FUV. We create UV color maps ((F148W − N245M) and (F148W − N263M)) to study the temperature morphology of young stellar complexes with the help of theoretical models. We identify several complexes with temperature T > 17,500 K, which are likely to be OB associations present in the galaxy. These complexes show good spatial correlation with the H -emitting regions, H i distribution, and HST-detected hot stars. The hot star-forming regions are found to be clumpy in nature and show a hierarchical structure, with sizes in the range of 4-50 pc, with a large number with sizes <10 pc. The southwestern part of the galaxy shows many hot star-forming regions, high levels of H emission, and low column density of H i, which altogether denote vigorous recent star formation. WLM is likely to have a large fraction of low-mass compact star-forming regions with mass M < 103 M , in agreement with the size and mass of the CO clouds. We estimate the star formation rate of WLM to be ∼0.008 M yr−1, which is similar to the average value measured for nearby dwarf irregular galaxies.
With MUSE, Chandra, VLA, ALMA, and UVIT data from the GASP program, we study the multiphase baryonic components in a jellyfish galaxy (JW100) with a stellar mass 3.2 × 1011 M hosting an active ...galactic nucleus (AGN). We present its spectacular extraplanar tails of ionized and molecular gas, UV stellar light, and X-ray and radio continuum emission. This galaxy represents an excellent laboratory to study the interplay between different gas phases and star formation and the influence of gas stripping, gas heating, and AGNs. We analyze the physical origin of the emission at different wavelengths in the tail, in particular in situ star formation (related to H , CO, and UV emission), synchrotron emission from relativistic electrons (producing the radio continuum), and heating of the stripped interstellar medium (ISM; responsible for the X-ray emission). We show the similarities and differences of the spatial distributions of ionized gas, molecular gas, and UV light and argue that the mismatch on small scales (1 kpc) is due to different stages of the star formation process. We present the relation H -X-ray surface brightness, which is steeper for star-forming regions than for diffuse ionized gas regions with a high O i/H ratio. We propose that ISM heating due to interaction with the intracluster medium (either for mixing, thermal conduction, or shocks) is responsible for the X-ray tail, observed O i excess, and lack of star formation in the northern part of the tail. We also report the tentative discovery in the tail of the most distant (and among the brightest) currently known ULX, a pointlike ultraluminous X-ray source commonly originating in a binary stellar system powered by either an intermediate-mass black hole or a magnetized neutron star.
This article focuses on making discrete-time Adaptive Iterative Learning Control more effective using multiple estimation models. Existing strategies use the tracking error to adjust the parametric ...estimates. Our strategy uses the last component of the identification error to tune these estimates of the model parameters. We prove that this strategy results in bounded estimates of the parameters, and bounded and convergent identification and tracking errors. We emphasise that the proof does not use the Key Technical Lemma. Rather, it uses the properties of square-summable sequences. We extend this strategy to include multiple estimation models and show that all the signals are bounded, and the errors converge. It is also shown that this works whether we switch between the models at every instant and every iteration or at the end of every iteration. Simulation results demonstrate the efficacy of the proposed method with a faster convergence using multiple estimation models.
Star-forming dwarf galaxies in the local volume are diverse and ideal test beds to understand the details of star formation in a variety of environments. Here we present a deep far-UV (FUV) imaging ...study of the nearby dwarf irregular galaxy IC 2574 using the Ultraviolet Imaging Telescope. We identified 419 FUV-bright regions with radii between 15 and 285 pc in the galaxy and found that 28.6% of them are located in H i shells, 12.6% inside holes, and 60.1% away from the holes. The H i column density is found to be more than 1021 cm−2 for 82.3% of the identified regions. Thirty of the 48 H i holes show triggered star formation in their shells, while 16 holes do not show any related FUV emission. Cross-matching with H emission, we found that 23 holes have both FUV and H emission in their shells, signifying a very recent trigger. Therefore, star formation in the galaxy has been partly triggered due to the expanding H i holes, whereas in the majority of the sites, it is driven by other mechanisms. Irrespective of the location, larger star-forming complexes were found to have multiple substructures. We report two resolved components for the remnant cluster of the supergiant shell and estimate their masses. The star formation rate of IC 2574 is found to be 0.57 M yr−1, which is slightly higher compared to the average value of other nearby dwarf irregular galaxies.
Neurosarcoidosis is a manifestation of sarcoidosis that affects the nervous system. It presents with a heterogeneous clinical picture. The diagnosis is established through clinical evaluation, ...imaging, and tissue biopsy in most cases. We discuss two cases that presented with symptoms suggestive of multiple sclerosis (MS) and stroke like features, but in fact yielded a diagnosis of neurosarcoidosis.The first is a 54-year-old male with a background of diplopia and paraesthesia of his limbs, who subsequently had acute ataxia with gait imbalance, and new onset of vertical diplopia. Neuroimaging revealed multiple pontine, cerebellar, and temporal lobe acute infarcts, and leptomeningeal spinal enhancement. Cerebrospinal fluid analysis was consistent with diagnosis of neurosarcoidosis. The second is a 45-year-old female presenting with lower limb paraesthesia and shock like symptoms when she flexed her neck. She had no objective clinical deficit. Neuroimaging was performed and demonstrated thickening and FLAIR signal hyperintensity of the Corpus Callosum. Spinal imaging showed a large longitudinal intradural extramedullary lesion posteriorly at C2 and a smaller lesion anteriorly around the C1 region. Lymph node biopsy revealed numerous non-caseating epithelioid cell granulomas, with no evidence of mycobacterium suggestive of neurosarcoidosis.Neurosarcoidosis should be considered in patients who present with symptoms suggestive of demyelinating or a stroke like episode(s). Early treatment is crucial for preventing disease-related morbidity and highlights the importance of clinician awareness of neurosarcoidosis and its diversity in presentation.
Time-series prediction is important in diverse fields. Traditionally, methods for time-series prediction were based on fixed linear models because of mathematical tractability. Researchers turned ...their attention to artificial neural networks due to their better approximation capability. In this paper, we use feedforward neural networks with a single hidden layer, and present a rather simple online sequential learning algorithm (OSLA) together with its proof. The convergence properties of this algorithm are those of the well-known recursive least squares algorithm. We demonstrate that the prediction performance is better than other OSLAs, and show that it is statistically different from them. In addition, we also present the multiple models, switching, and tuning methodology that enhances the prediction performance of the learning algorithm.
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