Design of tensegrity structures using parametric analysis and stochastic search

Tensegrity structures are lightweight structures composed of cables in tension and struts in compression. Since tensegrity systems exhibit geometrically nonlinear behavior, finding optimal structural designs is difficult. This paper focuses on the use of stochastic search for the design of tensegrity systems. A pedestrian bridge made of square hollow-rope tensegrity ring modules is studied. Two design methods are compared in this paper. Both methods aim to find the minimal cost solution. The first method approximates current practice in design offices. More specifically, parametric analysis that is similar to a gradient-based optimization is used to identify good designs. Parametric studies are executed for each system parameter in order to identify its influence on response. The second method uses a stochastic search strategy called probabilistic global search Lausanne. Both methods provide feasible configurations that meet civil engineering criteria of safety and serviceability. Parametric studies also help in defining search parameters such as appropriate penalty costs to enforce constraints while optimizing using stochastic search. Traditional design methods are useful to gain an understanding of structural behavior. However, due to the many local minima in the solution space, stochastic search strategies find better solutions than parametric studies.     

A comparison of simultaneous state and parameter estimation schemes for a continuous fermentor reactor

This article proposes a maximum likelihood algorithm for simultaneous estimation of state and parameter values in nonlinear stochastic state-space models. The proposed algorithm uses a combination of expectation maximization, nonlinear filtering and smoothing algorithms. The algorithm is tested with three popular techniques for filtering namely particle filter (PF), unscented Kalman filter (UKF) and extended Kalman filter (EKF). It is shown that the proposed algorithm when used in conjunction with UKF is computationally more efficient and provides better estimates. An online recursive algorithm based on nonlinear filtering theory is also derived and is shown to perform equally well with UKF and ensemble Kalman filter (EnKF) algorithms. A continuous fermentation reactor is used to illustrate the efficacy of batch and online versions of the proposed algorithms.     

Integration of soil moisture as an auxiliary parameter for the anchor pixel selection process in SEBAL using Landsat 8 and Sentinel - 1A images

ABSTRACT

The sensible heat flux component calculation in the Surface Energy Balance Algorithm for Land (SEBAL) completely relies upon the anchor pixel locations. The fragmented agriculture regions with diverse crops make the selection process more challenging with less probability to correlate with ground realities. The conventional methods for anchor pixel selection have limitations in capturing the soil moisture variations beneath the canopy as they utilize only the thermal remote sensing images and ancillary datasets like land cover and crop type maps. The current research attempts to reduce the existing gap between the ground realities and simulated results by adding soil moisture as a supplementary parameter. The prospects of semi-empirical Water Cloud Model (WCM) to estimate the soil moisture content was tested in a fragmented agricultural region for different time periods. The concurrent satellite data obtained from Sentinel - 1A and Landsat 8 were utilized to supply the inputs for inversion modelling based on the Levenberg-Marquardt approach. The current research introduced ‘virtual Normalized Difference Vegetation Index’ concept to refine the WCM and yielded reliable soil moisture output for supplementing the anchor pixel selection process. The robustness of the approach was justified by considering the available energy at anchor pixel locations. The research outcomes revealed that the anchor pixel selection with and without soil moisture criterion has a significant impact on actual evapotranspiration estimation. The research also explores the scope of the synergetic use of optical and Synthetic Aperture Radar (SAR) inputs in SEBAL.     

An evaluation of high-resolution multisatellite rainfall products over the Indian monsoon region

To date, more than half a dozen merged rainfall data sets are available to the research community. These data sets use different approaches for rainfall retrieval and combine different satellites or/and ground-based rainfall observations. However, these data sets appear to differ among themselves and deviate from in situ observations at regional and seasonal scales. Hence, it is becoming difficult to choose a suitable data set from these products for regional rainfall analyses. In the present study, four independently developed multisatellite high-resolution precipitation products (HRPPs), namely Climate Prediction Center Morphing (CMORPH) version 1.0, Naval Research Laboratory (NRL)–blended, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA)–3B42 version 7 are compared with quality-controlled gridded rain gauge data over India developed by the India Meteorological Department (IMD). A preliminary analysis is carried out for a 6 year period from 2004 to 2009 at daily scale for the summer monsoon season of June to September. Comparison of all-India seasonal (June to September) mean rainfall with rain gauge data shows a considerable underestimation by all HRPPs, although the underestimation is comparatively less for TMPA. Moreover, all the HRPPs are able to capture the important characteristic features of the summer monsoon rainfall such as intra-seasonal (active/break spells) and inter-annual (excess/deficient) variabilities reasonably well. Regional differences between observed rainfall and the HRPPs are also analysed. Results suggest that TMPA is comparatively closer to the ground-truth, possibly due to the incorporation of rain gauge observations. Furthermore, all the HRPPs show high probability of detection, low false alarm ratio, and high threat score in detection of rainfall events over most parts of India. It is also observed that all these HRPPs have certain issues in rainfall detection over the rain-shadow region of southeast peninsular India, semi-arid northwest parts of India, and hilly northern parts. Hence, results of the 6 year analysis over a region with a dense network of surface observations of rainfall suggest that the TMPA merged rainfall product is better than the other HRPPs due to (1) lower underestimation of rainfall, (2) higher correlation and lower root-mean-square error (RMSE), and (3) better performance over the west coast. Therefore, TMPA can be used with confidence as compared to other HRPPs for monsoon studies, particularly over the Indian land region with a considerable rain gauge network. This study also clarifies the fact that the merged satellite rainfall products with sufficient ground-truths can be the ideal product for monsoon and hydrological studies.     

Photoelectrocatalytic regeneration of NADH at poly(4,4′-diaminodiphenyl sulfone)/nano TiO2 composite film modified indium tin oxide electrode

Herein we report the photoelectrocatalytic regeneration of NADH at poly(4,4′-diaminodiphenyl sulfone)/nano TiO₂ (PDDS/TiO₂) composite modified indium tin oxide (ITO) electrode. The PDDS film growth was confirmed through in situ electrochemical quartz crystal microbalance (EQCM) studies. The prepared PDDS/TiO₂ composite was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) studies. SEM and AFM results confirmed that TiO₂ nanoparticles size is between 130 and 180 nm. XRD results showed that TiO₂ nanoparticles are crystalline and belong to anatase phase. Electrochemical impedance spectroscopy (EIS) and light induced EIS results substantiate a rapid electron transfer process at PDDS/TiO₂ composite surface. Cyclic voltammetry (CV) results demonstrated that composite film showed excellent response to the photoelectrocatalytic regeneration of NADH. The photoelectrocatalytic oxidation of NADH at composite film surface irradiated for 5 min (optimized irradiation time) produced a notable enhancement in anodic peak current and it was 18-fold higher than that of PDDS film and several folds higher than that of TiO₂ and bare ITO electrodes. Further, composite film showed higher sensitivity of 124.1 μA μM⁻¹ for NADH. From Square wave voltammetry (SWV) results, sensitivity of the irradiated composite film was obtained as 0.252 μA nM⁻¹ of NADH. The linear concentration range was between 23 and 39 nM NADH respectively. Further, the composite film exhibits good selectivity towards NADH and no significant interference effect was observed even when 200-fold excess of ascorbic acid (AA), dopamine (DA) and uric acid (UA) coexist in the same supporting electrolyte solution.     

Efficient staircase scheme with seamless channel transition mechanism

Video applications require large amount of bandwidth and also storage space. The Fast Broadcasting (FB) scheme is one of the simplest schemes to provide video services, but it requires considerably large buffer storage. This scheme assumes constant video popularity and thus has fixed amount of bandwidth requirement. The popularity of videos generally does not remain the same. It varies over a period of time and accordingly the bandwidth allocation should be adjusted. The variability in bandwidth requirement for videos based on popularity is overcome by incorporating seamless channel transition mechanism in a broadcasting scheme. After incorporating seamless channel transition mechanism, the scheme still delivers continuous video data to old and new users without jerks and hiccups. The FB scheme with seamless channel transition mechanism requires less buffer storage than the FB scheme. The staircase scheme also allocates a fixed amount of bandwidth to a video. The FB and staircase schemes divide a video into same number of segments; thus have same user’s waiting time. The basic difference between the FB and staircase schemes is that in the staircase scheme the segments are further divided into subsegments in order to reduce the buffer requirement. To consider variability of video popularity in the staircase scheme, seamless channel transition for staircase (SCTS) scheme has been discussed. The SCTS scheme performs better than the seamless Fast Broadcasting scheme as regard the buffer storage, while maintaining the same user’s waiting time. In this paper, we propose an efficient staircase scheme with seamless channel transition mechanism that performs better than the SCTS scheme. In the proposed scheme, the video (ESS scheme) data is downloaded at slower rate than that in the SCTS scheme without disrupting the user services and requiring less buffer storage.     

Combinatorial Delivery of miRNA‐Nanoparticle Conjugates in Human Adipose Stem Cells for Amplified Osteogenesis

It is becoming more apparent in tissue engineering applications that fine temporal control of multiple therapeutics is desirable to modulate progenitor cell fate and function. Herein, the independent temporal control of the co‐delivery of miR‐148b and miR‐21 mimic plasmonic nanoparticle conjugates to induce osteogenic differentiation of human adipose stem cells (hASCs), in a de novo fashion, is described. By applying a thermally labile retro‐Diels–Alder caging and linkage chemistry, these miRNAs can be triggered to de‐cage serially with discrete control of activation times. The method relies on illumination of the nanoparticles at their resonant wavelengths to generate sufficient local heating and trigger the untethering of the Diels–Alder cycloadduct. Characterization of the photothermal release using fluorophore‐tagged miRNA mimics in vitro is carried out with fluorescence measurements, second harmonic generation, and confocal imaging. Osteogenesis of hASCs from the sequential co‐delivery of miR‐21 and miR‐148b mimics is assessed using xylenol orange and alizarin red staining of deposited minerals, and quantitative polymerase chain reaction for gene expression of osteogenic markers. The results demonstrate that sequential miRNA mimic activation results in upregulation of osteogenic markers and mineralization relative to miR‐148b alone, and co‐activation of miR‐148b and miR‐21 at the same time.     

Examinations concerning the electric discharge machining of AZ91/5B4CP composites utilizing distinctive electrode materials

In this study, investigation has been conducted in the focus of obtaining better surface finish in the electro discharge machining (EDM) of AZ91/5B₄C_p magnesium composites using distinctive sort of anode viz. copper, tungsten–copper, brass, aluminum and 20Gr/AA6061 (GRAL-20) composites. The process parameters, pulse on time and current were performed to research the machining qualities through material removal rate (MRR) and tool wear rate (TWR). The machined composites were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The formation of black spots was observed on machining with copper–tungsten and these black spots were not found when GRAL-20 was used as electrode. Machined with GRAL-20 electrode leads to the increase in spark gap, hence adequate flushing occurs; it eliminates re-melted layers on machined surface results in better surface roughness value. The results revealed that GRAL-20 electrodes posses better MRR followed by copper electrode whereas tungsten–copper exhibits better TWR followed by GRAL-20 electrode.     

Analysis of powder metallurgy process parameters for mechanical properties of sintered Fe–Cr–Mo alloy steel

The present work involves an investigation to find out the best combination of process parameters for a Fe–Cr–Mo alloy with the help of Design of Experiments (DOE) tool. The Fe–Cr–Mo alloy containing 0, 0.4 and 0.8?wt.% carbon is compacted at 650?MPa pressure and sintered at 1120°C and 1200°C temperature, respectively, with 3.5 or 6°C/minute cooling rate. Quality characteristics like hardness and tensile strength are analyzed for various combinations of graphite weight %, sintering temperature, and cooling rate. The conducted experimental trials are based on the design matrix obtained from general factorial design. Significant regression models are developed from the above mentioned process parameters to predict the quality characteristics using DOE tool. The developed mathematical model during the course of research helped in investigating best combination of process parameters for powder processing. The desirability test showed its usefulness in finding out the number of optimization strategies to achieve the optimum values of hardness and tensile strength. The observed results are correlated with the microstructure. Diffusion of carbon during sintering decides the optimum amount of carbon. Higher carbon addition results in residual graphite which weakens the sintered alloy.