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Heat loss analysis from a trapezoidal cavity receiver in LFR system using conduction-radiation model
No full textLinear Fresnel Reflector systems are medium temperature (100-400 degrees C) application systems where heat flux from the sun is concentrated on absorber tubes housed in a trapezoidal cavity by an array of mirrors. The absorber tubes carry working fluid inside them. Several earlier works have considered convective and radiative heat transfer from these trapezoidal cavities in LFR systems. It has also been shown that the convective heat transfer constitutes up to 15% of the total heat losses which is significant. On the other hand, it is seen that the flow velocities are negligible due to stratification of isotherms with hot air trapped on top of the cavity which suggests that convection should be negligible. In the present work, it is shown that the heat transfer which is considered as convective is actually, only conduction through (almost) static air inside the cavity. Due to the above mentioned reason, in the present work, only conduction-radiation problem is considered in the cavity which is far easier to solve due to the absence of complex Navier-Stokes equations. The comparison of heat transfer results obtained using conduction-radiation model and those obtained using convection-radiation model show that the difference between the two results is negligible. Moreover, new correlations are developed with fewer parameters to capture the underlying physics of the heat loss mechanism in such cavities
Analysis and Control of a Novel Transformer-Less Microinverter for PV-Grid Interface
No full textIn this paper, a novel single-phase, transformer-less microinverter configuration derived from the basic Cuk topology is proposed for photovoltaic (PV)-grid interface applications. The topology has a direct connection between the grid neutral and the negative terminal of the PV array, which completely eliminates the ground leakage current. Further, the proposed topology has several appealing features such as high reliability due to the absence of shoot-through problems, symmetrical operation, low grid current distortion, capability of processing reactive power, low voltage ride through capability, and simple control for tracking the output current reference. Small-signal analysis has been employed to derive the topology's dynamic model using which a proportional resonant (PR) controller is designed and implemented. A step by step design procedure for obtaining the optimized proportional and integral gains of the PR controller, considering the effects of pulsewidth modulation transport and digital sampling delays, is presented. Theoretical claims and simulation results are corroborated by experimental studies carried out on a 200 W laboratory prototype controlled by using DSP TMS320F28335 controller
A Flow-Network-Based Polynomial-Time Approximation Algorithm for the Minimum Constrained Input Structural Controllability Problem
No full textThis paper deals with minimum cost constrained input selection (minCCIS) for state-space structured systems. Our goal is to optimally select an input set from the given inputs such that the system is structurally controllable when the set of states that each input can influence is prespecified and each input has a cost associated with it. This problem is known to be NP-hard. First, we give a flow-network-based novel necessary and sufficient graph theoretic condition for checking structural controllability. Using this condition, we propose a polynomial time reduction of the problem to a known NP-hard problem: the minimum-cost fixed-flow problem (MCFF). Subsequently, we show that approximation schemes of MCFF directly apply to the minCCIS problem. Using the special structure of the flow-network constructed for the structured system, we formulate a polynomial time approximation algorithm based on minimum weight bipartite matching problem and a greedy scheme for solving the MCFF problem on the system flow-network. The proposed algorithm gives a so-called Delta-approximate solution to MCFF, where Delta denotes the maximumin-degree of input vertices in the flow-network of the structured system
Hot corrosion behavior of plasma sprayed powder-solution precursor hybrid thermal barrier coatings
No full textIn recent times, plasma sprayed powder-solution precursor hybrid composite thermal barrier coatings have been developed to harness the dual benefits of both conventional atmospheric plasma spraying (APS) and solution precursor plasma spraying (SPPS) processes. In this study, hot corrosion behavior of plasma sprayed powder solution precursor composite (PSP-SPC) YSZ TBCs in molten salt mixtures of 90 wt.% Na2SO4 + 5 wt.% V2O5 + 5 wt.% NaCl and 50 wt.% Na2SO4 + 50 wt.% V2O5 at 900 degrees C was investigated. The employed coating showed a bimodal microstructure comprising coarse splats derived from the powder feedstock as in the APS process and fine splats resulting from the solution precursor as typical of SPPS process. The PSP-SPC coatings showed a significantly higher resistance to spallation than APS, SPPS and EB-PVD coatings in both the salt environments. These coatings showed shorter life in vanadate environment compared to that of the chloride environments as the former promotes the formation of monoclinic ZrO2 and YVO4 phases more than the latter
IL-17 promotes human primary keratinocyte invasion potential by controlling cell mechanics: A novel MMP-independent mechanobiology pathway
No full textInequality in water supply in India: an assessment using the Gini and Theil indices
No full textProvision of drinking water is considered to be an essential public service. Ensuring adequate water supply remains a challenge in Indian cities that are experiencing rapid growth and often exhibit a mismatch between increasing demands and inadequate supply infrastructure. This study quantifies the existing inequality in water supply within Indian cities through Lorenz curve, Gini coefficient as well as Theil indices. Two types of Theil indices are estimated to gain different perspectives: water supply and population-weighted. Both the Theil indices are disaggregated, according to economic and regional categorisation of the cities, to explore the within- and between-group inequality. The water supply and population-weighted Theil indices provide different outlook of the inequality amongst the cities. But the population-weighted index is often better and pragmatic. Further, the inequality in access to tap water in India is studied by estimating modified Lorenz curves and Theil indices. Again, the Theil indices are decomposed into within and between components according to economic and regional grouping of states. The results suggest that there is disparity in supply of water in India, and infrastructure has to be boosted to meet the growing demand. This study is a step towards quantification of water supply inequality. The approach used in the study can contribute to monitoring of water supply equity as well as in formulating sustainable and equitable water policies
PCMO RRAM for Integrate-and-Fire Neuron in Spiking Neural Networks
No full textResistance random access memories (RRAM) or memristors with an analog change of conductance are widely explored as an artificial synapse, e.g., Pr0.7Ca0.3MnO3 (PCMO) RRAM-based synapses. In addition to synapses, scaled neurons are essential to enable a neuromorphic hardware. In this letter, we propose a PCMO RRAM for integrate and fire (IF) neuron. The analog conductance increase during SET process enables integration function. Upon exceeding a conductance threshold (i.e., fire) during a READ operation, a hard RESET is performed to reduce the conductance. The SET, READ, and RESET are performed in different phases of a clock to enable a PCMO for IF neuron. The availability of a non-volatile PCMO-based synapse makes PCMO for IF neuron attractive. Finally, PCMO-based neuron in spiking neural network yields software-equivalent classification accuracy as demonstrated on standard Fischer's Iris flower data set
Numerical simulations of porous medium with different permeabilities and positions in a laterally-heated cylindrical enclosure for crystal growth
No full textThis paper presents an investigation of flow and heat transfer in a large diameter (6.25 in) cylindrical enclosure heated laterally and containing a porous block that simulates the basket of nutrients used in a crystal growth reactor. The numerical model entails the use of a commercially available computational engine provided by ANSYS FLUENT, and based on a two-dimensional (2D) axisymmetric Reynolds-averaged Navier Stokes (RANS) equations. The porous medium is simulated using the Brinkman-extended model accounting for the Darcy and Forchheimer induced pressure drops. The porous 'plug' effects are analyzed as both its permeability/inertial resistance and locations in the reactor are changed on a parametric basis, while the Rayleigh number (Ra = g beta Delta TL3/v alpha) is kept constant at 1.98 x 10(9). Additionally, the effect of different ratios of the hot to the cold zone lengths are investigated as a part of the current effort. For all cases, the velocity and temperature distributions in the reactor are analyzed together with the flow patterns in, and around the porous block. A comprehensive discussion is provided with regard to the effects of the position of the porous block and its permeability on both the immediately adjacent, and far flows. The consequences on the temperature distribution in the enclosure, when the ratio of the length of the hot-to-cold zones is changed, are also analyzed. (C) 2017 Elsevier B.V. All rights reserved
Discrepancy estimates for generalized polynomials
No full textWe obtain an upper bound for the discrepancy of the sequence ([p(n) a] ss) n= 0 generated by the generalized polynomial [p(x) a] ss, where p(x) is a monic polynomial with real coefficients, a and ss are irrational numbers satisfying certain conditions
Role of (1,3) {Cu-Cu} Interaction on the Magneto-Caloric Effect of Trinuclear {Cu-II-Gd-III-Cu-II} Complexes: Combined DFT and Experimental Studies
No full textMolecular refrigeration is found to be of great interest in the field of coordination chemistry, and Gel ion based complexes are particularly attractive, as they exhibit a large magneto-caloric effect (MCE). As the magnetic coupling in Gd-III clusters is difficult to control, other avenues to enhance the MCE values have been explored and incorporation of 3d metal ions in the cluster aggregation with Gd-III yielding {3d-Gd} clusters are targeted. Among the transition-metal ions, the Cull ion is particularly attractive, as it does not possess any anisotropy, and in this regard, several di- and polynuclear {Cu-Gd} clusters are reported to yield attractive MCE values. While the role of near-neighbor {Cu-Gd} interactions in the MCE has been explored in detail, how the next nearest-neighbor interaction influences the MCE has not been explored. To explore the importance of next-nearest-neighbor (1,3) {Cu-Cu) interaction, we have undertaken detailed density functional studies on five trinuclear {Cu-II-Ud(III)-Cu-II} complexes that are reported in the literature. In addition, we also report the synthesis and magnetic and EPR studies of a novel complex [(CuSALen)(2)Gd(NO3)(3)} (6; where SALen is N,N'-ethylenebis(salicylaldiminato)). Both magnetic and EPR studies reveal an S = 9/2 ground state for 6 with a very small zero-field splitting parameter (+0.01 cm(-1)), which aid in the achievement of a large MCE value for this molecule. Magnetization data collected for 6 yield a magnetic entropy change (-Delta S-m) of 17 J Kg(-1) K-1 at 3.5 K by employing a 7 T magnetic field. Our calculations on all six complexes reveal that {Cu-Gd} exchange is ferromagnetic in nature, while the next-nearest-neighbor {Cu-Cu} exchange is found to vary from a weak ferromagnetic to a moderate antiferromagnetic interaction. In all of the cases studied, simulated susceptibility data are in excellent agreement with the experimental data, offering confidence in the computed] values. In addition, we have developed a mechanism of magnetic coupling for {Cu-II-Gd-III-Cu-II} trinuclear complexes, where the role of formally empty 5d, 6s, and 6p orbitals of Gel ion is established. In particular, our studies reveal that the next-nearest-neighbor {Cu-Cu} interaction is strongly correlated to Cu-Gd-Cu angle, with both smaller and larger angles yielding stronger antiferromagnetic exchange. The antiferromagnetic {Cu-Cu} interaction diminishes the gap between the ground S = 9/2 state and first excited S = 7/2 state, leading to enhancement of MCE values. In contrast to the general belief that weak interactions are desired for large MCE, our study advocates targeting a stronger antiferromagnetic {Cu-Cu} interaction to obtain larger MCE values in this class of clusters