Local and global optimal control for non-linear systems using two-level methods

The recent co-state coordination algorithm for the two-level optimization of nonlinear discrete dynamical systems with separable quadratic cost functions is specialized to ensure the satisfaction of both necessary and local sufficiency conditions. For an important subclass of the problems, global sufficiency can be guaranteed. This is demonstrated on a simple example where previous methods have yielded worse local optima.     

PARAMETER ESTIMATION FOR 2-PARAMETER LOG-LOGISTIC DISTRIBUTION (LLD2) BY MAXIMUM ENTROPY

The principle of maximum entropy (POME) was employed to derive a new method of parameter estimation for the 2-parameter log-logistic distribution (LLD2). Monte Carlo simulated data were used to evaluate this method and compare it with the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). Simulation results showed that POME's performance was superior in predicting quantiles of large recurrence intervals when population coefficient of variation was greater than or equal to 1.0. In all other cases, POME's performance was comparable to other methods. In terms of parameter bias and root mean square error, POME was comparable to MLE and superior to both MOM and PWM.     

Detection and localization of multiple cracks in a stepped shaft

The presence of a crack in a shaft causes a slope discontinuity in the elastic line of the shaft. There are crack detection techniques, available in the literature, exploiting the slope discontinuity arising because of the crack in the shaft. Steps present in a shaft are expected to interfere with the results obtained through these identification techniques based upon slope discontinuity. It would be even more difficult to identify a crack if it is near a step as both the step and the crack will cause slope discontinuities. A multi‐crack identification technique has been developed (Singh S. K. and Tiwari R. (2010). Mech. Machine Theory 45, 1813–1827; Singh S. K., Tiwari R. and Talukdar S. (2009). IUTAM Proc. in Recent Trends in Rotor Dynamics, March 23–26, IIT Delhi, India) which uses shaft‐forced responses at several frequencies to identify the number of cracks and their locations over the shaft. The algorithm uses normalization of quadratic coefficients obtained from measured responses of a cracked shaft and from simulated responses of the intact shaft for detecting the slope discontinuity. In the present work, the effect of steps in the shaft on crack identification has been analysed. Cracks are assumed to be both near the step and far from the step. The identification algorithm works well for both the simulation cases.     

Fractional M-band dual tree complex wavelet transform for digital watermarking

In this paper, a novel digital watermarking scheme using fractional M-band dual tree complex wavelet transform (Fr-M-band-DT-CWT) is proposed. High frequency channels have wide bandwidth and low frequency channels have narrow bandwidth. These characteristics are suitable for analysing low frequency signal, but not for relatively high frequency signal. The images often contain many edges, which may cause rich middle and high frequency components in the 2-band wavelet domain. Therefore, the ordinary 2-band dual tree complex wavelet transform (DT-CWT) is not well-suited for analysing the image. So, the M-band DT-CWT with the FrFT called Fr-M-band-DT-CWT is proposed in this paper to address this problem. Further, we integrate the Fr-M-Band-DT-CWT with singular value decomposition (SVD) in order to enhance the performance. Experimental results of the proposed watermarking scheme are compared with the previously available watermarking algorithms, fractional Fourier transform (FrFT), fractional wavelet transform (FrWT). Further, the proposed watermark extraction scheme is also tested on different attacks. The results of the present investigations show that the proposed watermarking scheme is superior as compared to other existing watermarking schemes.     

Numerical investigation of convective cooling in minimizing skin burns during radiofrequency ablation of breast tumor

Skin burns is one of the most common complications reported during treatment of early-stage breast cancer with radiofrequency ablation (RFA) technique. In this regard, the present study aims to analyze the efficacy of forced convection surface cooling in minimizing the skin burns during RFA of breast tumor. The study considers a heterogeneous three-dimensional numerical model of breast that has been constructed based on the anatomical details available in the literature. A spherical tumor of 1.5 cm has been embedded in the numerical model of breast to represent in-situ tumor in its early stage. A programmable temperature-controlled RFA has been performed by incorporating the closed-loop feedback PID controller into the numerical model. The thermo-electric analysis has been performed using a finite element based commercial solver COMSOL Multiphysics^® to obtain the temperature distribution by incorporating the coupled electric field distribution, Pennes bioheat equation and Arrhenius rate equation. The temperature dependent electrical and thermal conductivities of both the tissue and tumor along with damage dependent perfusion rate have been incorporated to achieve better correlation with the clinical RFA. The numerical simulation results revealed that, there is a significant reduction in the temperature at outer periphery of breast with increase in convective heat transfer coefficient. Further, the effects of variation in surface cooling on temperature distribution, input voltage requirement and treatment time required for complete tumor necrosis have been studied. The simultaneous application of forced convective surface cooling along with RFA could play a vital role in addressing the most common complication of skin burns during treatment of breast cancer.     

Investigating the role of ICT intervention in grassroots innovation using structural equation modelling approach

Research on information communication technologies (ICT) for entrepreneurship development is burgeoning, yet our understanding of the use of ICT in support of grassroots innovation remains unclear. This paper examines the moderating role of the use of ICT on the relationship between grassroots innovation (GRI) and entrepreneurial success (ES). The study involved 400 grassroots entrepreneurs selected from three states in India, and the moderating effect of the use of ICT was analysed using moderated structural equation modelling. The results revealed that the use of ICT partially moderates the relationship between the new learning practices and economic benefits. It also partially moderates the relationship between local solution and economic benefits, but it fully moderates the relationship between networking capabilities and economic benefits, where the relationship is stronger when the use of ICT is high. Furthermore, the study found that the use of ICT does not moderate the relationship between new learning practice and non-economic benefits, relationship between local solution and non-economic benefits and relationship between networking capabilities and non-economic benefits.     

Enhanced thermal conductivity of nano-SiC dispersed water based nanofluid

Silicon carbide (SiC) nanoparticle dispersed water based nanofluids were prepared using up to 0·1?vol% of nanoparticles. Use of suitable stirring routine ensured uniformity and stability of dispersion. Thermal conductivity ratio of nanofluid measured using transient hot wire device shows a significant increase of up to 12% with only 0·1?vol% nanoparticles and inverse dependence of conductivity on particle size. Use of ceramic nanoparticles appears more appropriate to ensure stability of dispersion in nanofluid in closed loop single-phase heat transfer applications.     

Effect of anodization on corrosion behaviour and biocompatibility of Cp-titanium in simulated body fluid

The objective of this investigation is to study the effectiveness of anodized surface of commercial purity titanium (Cp-Ti) on its corrosion behaviour in simulated body fluid (SBF) and proliferation of osteoblast cells on it, to assess its potentiality as a process of surface modification in enhancing corrosion resistance and osseointegration of dental implants. Highly ordered nano-porous oxide layer, with nano-sized pores, is developed on the surface of Cp-Ti through electrochemical anodization in the electrolyte of aqueous solution of 0·5% HF at 15 V for 30 min at 24 °C. The nano-porous feature of the anodized surface is characterized by field-emission scanning electron microscope (FESEM). Pores of some anodized samples are sealed by exposing the anodized surface in boiling water. Corrosion behaviour of the anodized specimen is studied in Ringer’s solution at 30 ± 2 °C, using electrochemical impedance and cyclic polarization technique. Biocompatibility of the anodized surface is accessed using MG63 osteoblast cells. Both corrosion as well as pitting resistance of Cp-Ti in simulated body fluid are found to be highest in the anodized and sealed condition and followed in decreasing order by those of anodized and unanodized ones. Significantly higher MG63 osteoblast cell proliferations are found on the anodized surface than that on the unanodized one. Anodized Cp-Ti develops nano-size surface pores, like that of natural bone. It enhances corrosion and pitting resistance and also the process of osteoblast cell proliferation on Cp-Ti.     

Effect of dynamic strain ageing on the tensile properties of a modified 9Cr–1Mo steel

Tensile testing of a modified 9Cr–1Mo steel in two microstructural conditions (710T– normalized at 1100°C, tempered at 710°C, and 550T – normalized at 1100°C tempered at 550°C) in the temperature range 25–450°C, under strain rates of 2.3×10-5–2.3×10-3s-1, exhibited serrated flow curves, with serrations appearing almost at the onset of deformation and disappearing before ultimate strengths were attained. The serrated flow curves (characteristics of dynamic strain ageing) were accompanied by increased ultimate strengths, loss of ductility and negative strain-rate sensitivity, relative to the ambient temperature properties. However, the increase in ultimate strength and the reduction in ductility were much larger for 710T specimens, as compared to 550T ones. In the dynamic strain ageing regime, the work-hardenability of 710T specimens increased rapidly while that of 550T specimens remained practically unaffected. Based on the microstructural consideration and the observed activation energy of 45 kJ mol-1, it is proposed that serrations are initiated by a nitrogen atmosphere formation on the waiting dislocations by a pipe diffusion mechanism, and they disappear by diffusion to the precipitate sinks during deformation. Because the fine alloy carbide precipitates in 550T specimens are more effective sinks than those of 710T ones, they can cause much faster depletion of the atmosphere, resulting in a much smaller effect of dynamic strain ageing on the tensile properties of 550T specimens.     

Magnetron Sputtered TiN Coatings Modified by Chromium,Nickel and Electroless Nickel (EN) Interlayers on Mild Steel

TiN films were deposited by reactive d.c. magnetron sputtering on mild steel substrate. Because of presence of inherent porosity and internal stresses, TiN coatings cannot be relied to give corrosion protection; also TiN coatings need a good load support. Electroplated chromium and nickel and electroless nickel (EN) were deposited by plating as interlayers below the TiN coatings to study comparatively the effect of these interlayers. Chromium was electrodeposited from conventional sulfate catalysed chromic acid bath and nickel using Watt's bath while EN by electroless deposition process using acidic hypophosphite bath. Three different thicknesses viz. 2, 4 and 10 μm of interlayers were employed to study their influence on TiN coatings. The corrosion behaviour of TiN coated mild steel samples with and without the interlayers was studied using potentiodynamic measurement technique in deaerated IN H₂SO₄ electrolyte. It was observed that TiN coatings on mild steel without any interlayer almost mimic the behaviour of the substrate, while the presence of any of the three interlayers showed a considerable improvement in the corrosion resistance.