Control of a process with unmeasured disturbances that change its steady-state gain sign

Because the sign of the steady-state gain of an industrial NOx reduction unit changes according to the magnitude of the main external disturbance (hydrogen flow rate), designing an appropriate controller is particularly challenging. To address this issue, theoretical analysis suggested that a simple linear controller can provide adequate control for this process. Interestingly, tuning of this controller deviates from well known guidelines of linear control theory, which dictate that closed-loop stability is maintained by sluggish enough control of a stable linear process. It turns out, that for this nonlinear process, controller tuning must be neither too sluggish nor too aggressive, in an intermediate range suggested by a variant of the small-gain theorem proven here for corresponding nonlinear operators. The operator-based analysis was confirmed via computer simulation on a simple first-principles model, calibrated on real plant data. It is expected that control performance and robustness may improve if a number of ideas suggested in the text are explored further.     

Dispersal and sink pathways of suspended particulate matter from the orographically enhanced SWM regime of the SE Arabian Sea

The magnitude of precipitation plays an important role in the yield and supply of terrigenous matter into the sea through fluvial supply. The influence of climate on the influx of total suspended matter (TSM) into the continental margin of the SE Arabian Sea has been evaluated from subweekly synoptic variations in TSM and its advection rates, currents and winds during the southwest monsoon (SWM) and postmonsoon season. Our study endorses the high influx of TSM during the SWM (>82 mg l^?1; advection 26–110 mg m^?2 s^?1), albeit that most of it is sequestered into the shallow coastal region. Over the mid-outer shelf, there is uniformly low TSM (12–24 mg l^?1) and a weak TSM advection (9–4 mg m^?2 s^?1) throughout the year. This trend is persistent also in areas having upwelling-induced high marine productivity. We therefore surmise that higher fluvial influx and primary production during the SWM do not necessarily enhance the supply of particulate matter into the deeper offshore regions of the SE Arabian Sea. We ascribe a vital role to the prevailing morphodynamic processes.     

Better Water and Land Allocation for Long-term Agricultural Sustainability

Water and land resources are limited and dwindling in quantity and quality due to pollution and the effects of climate change. The "world needs to produce over sixty percent more food to feed" its 9.9 billion population in 2050 using these dwindling resources. Increased food production is also necessary to achieve most of the "UN's SDGs such as SDG1 (No Poverty), SDG2 (Zero Hunger), SDG3 (Good Health and Well-Being), and SDG15 (Life on Land)", etc. The aforesaid "goal can be accomplished by optimizing the distribution of available water and land resources, which can be done through an optimization model". In this study, a water balance model was first developed "to assess the long-term groundwater recharge, which will help to understand the dynamics of the system". Then, after analyzing the results, an optimization model was formulated to maximize the net annual farm income in an irrigated region of India. The water balance model showed excellent results as indicated by "high R-squared (0.9728) and model efficiency (0.91)", and low RMSE (0.2516 m) and ME (-0.0526 m) values. The water balance analysis revealed "that the aquifer level has been rising at a steady rate" over the past two decades. The results of the water balance model were used to formulate various constraints of the optimization model. Under the optimal cropping system, the area of paddy decreases against an increase in the area of sorghum, pearl millet, and cotton during the monsoon. Whereas "during the winter, the area of wheat increases", and the area of mustard and barley decreases. Groundwater "abstraction has increased, eventually lowering the aquifer level and thus alleviating salinization and waterlogging problems in the region". Net yearly income in the region enhanced by more than twenty-two percent to ?821.24 million from the present ?671.33 million. The sensitivity analysis revealed that the crops' market price is the most sensitive factor in the optimization model. "It is recommended that government agencies and real-world agricultural farmers practice increased use of groundwater in conjunction with canal water to maximize farm income. The approach used is the first of its kind in the region under study, is easy to apply, and can be replicated in other regions of the world" dealing with comparative issues.

     

Polarization-based compensation of astigmatism

One approach to aberration compensation of an imaging system is to introduce a suitable phase mask at the aperture plane of an imaging system. We utilize this principle for the compensation of astigmatism. A suitable polarization mask used on the aperture plane together with a polarizer-retarder combination at the input of the imaging system provides the compensating polarization-induced phase steps at different quadrants of the apertures masked by different polarizers. The aberrant phase can be considerably compensated by the proper choice of a polarization mask and suitable selection of the polarization parameters involved. The results presented here bear out our theoretical expectation.     

Automated TB classification using ensemble of deep architectures

Multimedia Tools and Applications - Tuberculosis (TB) is an infectious disease that mainly affects the lung region. Its initial screening is mostly performed using chest radiograph, which is also...     

Ractions of SiC with H2/H2O/Ar Mixtures at 1300°C

The reactions of a sintered α-SiC with 5% H₂/H₂O/Ar at 1300°C were studied. Thermomchemical modeling indicates that three reaction regions are expected, depending on the initial water vapor or equivalently oxygen content of the gas stream. A high oxygen content ( P (O₂) > 10⁻²² atm) leads to a SiO₂ formation. This generally forms as a protective film and limits consumption of the SiC (passive oxidation). An intermediate oxygen content (10⁻²² atm > P (O₂) > 10⁻²⁶ atm) leads to SiO and CO formation. These gaseous products can lead to rapid consumption of the SiC (active oxidation). Thermogravimetric studies in this intermediate region gave reaction rates which appear to be controlled by H₂O gas-phase transport to the sample and reacted microstructures showed extensive grain-boundary attack in this region. Finally, a very low oxygen content ( P (O₂) < 10⁻²⁶ atm) is thermochemically predicted to lead to selective removal of carbon and formation of free silicon. Experimentally low weight losses and iron silicides are observed in this region. The iron silicides are attributed to reaction of free silicon and iron impurities in the system.     

Is the ubiquitous presence of barium carbonate responsible for the poor aqueous processing ability of barium titanate?

The ubiquitous presence of barium carbonate (BaCO₃ – BC) as an impurity in barium titanate (BaTiO₃ – BT) has been pointed out as the main reason for the well-known difficulties found by many investigators when attempting to process BT powders in aqueous media. Different and controversial arguments have been put forward to justify the observed aqueous processing difficulties of BT, but a satisfactory explanation is still to be found. With this aim, a systematic study was here undertaken to shed further light on the solid/liquid interactions occurring at the surface of BC and BT particles and their impact on the dispersion ability of both powders, separately and mixed in certain proportions. Long term colloidal stability and high solid loadings (60 vol.%) were obtained for BC, while colloidal instability and a lower maximum content of solids (50 vol.%) could be achieved for BT. This responds to the question risen in the title.     

LAMINAR FLOW AND HEAT TRANSFER IN BLOCKED ANNULI

Laminar flow and heal transfer in annular passages with axially nonuniform inner tubes are obtained numerically. A characteristic feature of these passages is that the flow separates in the streamwise direction. An axisymmetric coordinate system with an algebraic transformation in the radial direction kas been used. Fully elliptic vorticity-slream function and energy equations in the transformed coordinates are solved using an iterative alternate direction implicit (ADI) method. In an annulus with a smooth blockage, the flow separates immediately downstream of the blockage at Reynolds numbers greater than 100. The main features of the flow are established at a Reynolds number of 1000. The pressure drop is drastic near the maximum constriction. The heat flux is also high in the constricted region. A sharp increase in the heat transfer occurs where the fluid reattaches itself to the wall. The increase in the total pressure drop is about an order of magnitude greater than that in the average Nusselt number.