Reversible end-to-end assembly of gold nanorods using a disulfide-modified polypeptide

Directing the self-assembly of colloidal particles into nanostructures is of great interest in nanotechnology. Here, reversible end-to-end assembly of gold nanorods (GNR) is induced by pH-dependent changes in the secondary conformation of a disulfide-modified poly(L-glutamic acid) (SSPLGA). The disulfide anchoring group drives chemisorption of the polyacid onto the end of the gold nanorods in an ethanolic solution. A layer of poly(vinyl pyrrolidone) is adsorbed on the positively charged, surfactant-stabilized GNR to screen the surfactant bilayer charge and provide stability for dispersion of the GNR in ethanol. For comparison, irreversible end-to-end assembly using a bidentate ligand, namely 1,6-hexanedithiol, is also performed. Characterization of the modified GNR and its end-to-end linking behavior using SSPLGA and hexanedithiol is performed using dynamic light scattering (DLS), UV-vis absorption spectroscopy and transmission electron microscopy (TEM). Experimental results show that, in a colloidal solution of GNR-SSPLGA at a pH～3.5, where the PLGA is in an α-helical conformation, the modified GNR self-assemble into one-dimensional nanostructures. The linking behavior can be reversed by increasing the pH (>8.5) to drive the conformation of the polypeptide to a random coil and this reversal with pH occurs rapidly within minutes. Cycling the pH multiple times between low and high pH values can be used to drive the formation of the nanostructures of the GNR and disperse them in solution.     

3D MHD cross flow over an exponential stretching porous surface

The present study aims to investigate the effects of thermal‐diffusion and diffusion‐thermo onan magnetohydrodynamic convective flow of viscous fluids over an exponentially stretching sheet. Thermal radiation effects are also considered in the study. This analysis is carried out in three dimensions and a similarity transformation is adopted to get a set of ordinary differential equations from a set of partial differential equations. And the Fourth‐order Runge‐Kutta method and shooting technique along with the secant method are employed to find out an iterative solution. We also analyze here the influence of the variable magnetic field, nonuniform permeability and variable chemical reaction on the fluid flow. The impact of various pertinent parameters of interest has extensively been explored through graphs and tables. The major findings of the present study are that resistive Lorentz force diminishes the fluid velocity and uplifts the thermal as well as concentration fields. Inclusion of porous matrix improves the viscous drag force which in turn augments wall shear stresses and peters out the heat and mass transfer rates from the sheet. In addition, the thermal expansion coefficient has an inverse relation with temperature.     

Particulate emissions from laser ignited and spark ignited hydrogen fueled engines

Exponentially increasing energy demand and stricter emission legislations have motivated researchers to explore alternative fuels and advanced engine technologies, which are more efficient and environment friendly. In last two decades, hydrogen has emerged as promising alternative fuel for internal combustion (IC) engines and vehicles. For gaseous fuels, laser ignition (LI) has emerged as a novel ignition technique due to its superior characteristics, leading to improved combustion, engine performance and emission characteristics. Numerous advantages of LI system such as flexibility of plasma location, lower NO_x emissions and capability of igniting ultra-lean fuel–air mixture makes LI system superior compared to conventional spark ignition (SI) system. This study experimentally compares particulate emissions from hydrogen fueled engine ignited by LI and SI systems. Experiments were performed in a constant speed engine prototype, which was suitably modified to operate on gaseous fuels using both LI as well as SI systems. Particulate were characterized using engine exhaust particle sizer (EEPS) spectrometer. Results showed that LI engine resulted in relatively higher particulate number concentration as well as particulate mass compared to SI engine. In both ignition systems, particulate emissions increased with increasing engine load however rate of increase was relatively higher in LI system. Relatively larger count mean diameter (CMD) of particulate emitted from SI engine compared to LI engine was another important observation. This showed emission of relatively smaller particles in larger numbers from LI engine, compared to baseline SI engine.     

Impulsively fractional-order time-delayed gene regulatory networks: Existence and asymptotic stability

This paper presents asymptotic stability criteria for fractional-order gene regulatory networks (FOGRNs) with impulses, time delays, and two numerical cases to illustrate the applicability of the results. The established system's boundedness, existence, and uniqueness are discussed using the Mittag–Leffler function, homeomorphism theory, and Cauchy–Schwartz inequality. The delay-independent asymptotic stability criteria for FOGRNs are derived using algebraic and LMI methods, famous inequality techniques, and Lyapunov stability theory.     

Analysis of hard turning process:thermal aspects

In manufacturing sector,hard turning has emerged as a vital machining process for cutting hardened steels.Besides many advantages of hard turning operations,one has to implement to achieve close tolerances in terms of surface finish,high product quality,reduced machining time,low operating cost and environmental friendly characteristics.In the study,three dimensional(3D) computer aided engineering(CAE) based simulation of hard turning by using commercial software DEFORM 3D has been compared to the experimental results of stresses,temperatures and tool forces in machining of AISI D3 and AISI H13 steel using mixed ceramic inserts(CC6050).In the following analysis,orthogonal cutting models are proposed,considering several processing parameters such as cutting speed,feed and depth of cut.An exhaustive friction modelling at the tool-work interface is carried out.Work material flow around the cutting edge is carefully modelled with adaptive re-meshing simulation capability of DEFORM 3D.The process simulations are performed at constant feed rate(0.075 mm/r) and cutting speed(155 m/min),and analysis is focused on stresses,forces and temperatures generated during the process of machining.Close agreement is observed between the CAE simulation and experimental values.     

Wear of Plasma Sprayed Conventional and Nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>, Based Coatings

An ever increasing demand for high-performance ceramic coatings has made it inevitable for developing techniques with precise control over the process parameters to enable the fabrication of coatings with the desired microstructure and improved structural properties. The literature on plasma sprayed nanostructured ceramic coatings such as of Al₂O₃, Cr₂O₃, and their composites obtained using reconstituted nano sized ceramic powders has been reviewed in this study. Ceramic coatings due to their enhanced properties are on the verge of replacing conventional ceramic coatings used for various applications like automotive systems, boiler components, power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, land-based and marine engine components, turbine blades etc. In such cases, the advantage is greater longevity and reliability for realizing the improved performance of ceramic coatings. It has been observed that the plasma sprayed nanostructured ceramic coatings show improvement in resistance to wear, erosion, corrosion, and mechanical properties as compared to their conventional counterparts. This article reviews various aspects concerning the plasma sprayed ceramic coatings such as (i) the present understanding of formation of plasma-spray coatings and factors affecting them, (ii) wear performance of nanostructured Al₂O₃, Cr₂O₃ and their composite ceramic coatings in comparison to their conventional counterparts, and (iii) mechanisms of wear observed for these coatings under various conditions of testing.     

Synthesis,charge transport studies,and microwave shielding behavior of nanocomposites of polyaniline with Ti-doped γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

This article reports the synthesis, charge transport studies, and microwave shielding properties of polyaniline–Ti-doped γ-Fe₂O₃ nanocomposite. The composite has been prepared by the in situ chemical oxidative polymerization using dodecylbenzenzesulfonic acid as a dopant. These resulting polymer composites have been found thermally stability up to 260 °C with magnetization value of ~10 emu/g. The temperature dependence of electrical conductivity reveals the applicability of Mott’s 3D-VRH model. The composites has shown the shielding effectiveness of 35.64–45.20 dB (>99.99% attenuation) in 12.4–18 GHz (Ku-Band) frequency range. The enhancement of SE has been due to combination of dielectric and magnetic losses leading to decrease in skin depth increase in total (σ_T) conductivity and better matching of input impedance.     

Environmental radioactivity studies in the proposed Lambapur and Peddagattu uranium mining areas of Andhra Pradesh, India

The present work was aimed at the establishment of baseline radioactive data in the proposed Lambapur and Peddagattu uranium mining areas in the Andhra Pradesh state, India. The background concentrations of naturally occurring radioactivity in the near-surface soils of the study areas were estimated and the results were analysed. The (238)U concentration in the near-surface soil of the study area was found to vary from 100 to 176 Bq kg(-1), with a mean of 138±24 Bq kg(-1). (232)Th in the study area soils was found to vary between 64 and 116 Bq kg(-1), with a mean of 83±15 Bq kg(-1). The (40)K concentration was found to vary between 309 and 373 Bq kg(-1), with a mean of 343±20 Bq kg(-1). The mean natural background radiation levels were also measured with thermoluminescence (TL) dosimetry technique and with a μR-survey meter, in the villages of the study area. Dose rates measured by TL are found to vary from 1287 to 3363 μGy y(-1), with a mean of 2509 ± 424 μGy y(-1). The dose rates measured in the same villages with a μR-survey meter were found to be in the range of 1211-3255 μGy y(-1), with a mean of 2524 ± 395 μGy y(-1). The mean radiation levels in the study area are found to be relatively high when compared with (Indian) national and international averages. Correlations among radon, thoron and gamma dose rates were found to be poor. The pre-operational data produced in this work will be useful for comparison with future radiation levels during the proposed uranium mining operations.     

Estimation of gestational age from fundal height: a solution for resource-poor settings

Many women in resource-poor settings lack access to reliable gestational age assessment because they do not know their last menstrual period; there is no ultrasound (US) and methods of newborn gestational age dating are not practised by birth attendants. A bespoke multiple-measures model was developed to predict the expected date of delivery determined by US. The results are compared with both a linear and a nonlinear model. Prospectively collected early US and serial symphysis-pubis fundal height (SFH) data were used in the models. The data were collected from Karen and Burmese women attending antenatal care on the Thai–Burmese border. The multiple-measures model performed best, resulting in a range of accuracy depending on the number of SFH measures recorded per mother (for example six SFH measurements resulted in a prediction accuracy of ±2 weeks). SFH remains the proxy for gestational age in much of the resource-poor world. While more accurate measures should be encouraged, we demonstrate that a formula that incorporates at least three SFH measures from an individual mother and the slopes between them provide a significant increase in the accuracy of prediction compared with the linear and nonlinear formulae also using multiple SFH measures.