Effect of Layered MoS2 Nanoparticles on the Frictional Behavior and Microstructure of Lubricating Greases

Lithium stearate soap and layered MoS2 nanoparticles encapsulated in lithium stearate soap are prepared in the laboratory, and their lubricating properties are compared with respect to the particle and particle concentration. The tribotracks after friction test was investigated with Raman Spectroscopy, scanning electron microscopy (SEM) and 3D optical profilometry to understand the action mechanism. The status of the soap particles on a tribotrack changes with time, contact pressure and sliding speed. At low pressure and speed, individual solid undeformed soap particle stand proud of the surface and the topography shows marginal difference with sliding time. In these conditions, no frictional difference between the performance of grease with and without the nanoparticles is observed. Increasing the contact pressure and temperature (low speed and high speed) has a dramatic effect as the soap particles melt and the liquid soap flows over the track releasing the hitherto encapsulated nanoparticles. Consequently, the soap smears the track like a liquid, and the nanoparticles now come directly into the interface and are sheared to generate a low-friction tribofilm. At high particle concentration, the sliding time required for melting of the soap and release of MoS2 is reduced, and the tribofilm is more substantial and uniform consisting of smeared MoS2 and carboxylate soap as observed by SEM and 3D optical profilometry. A change in the Raman Spectra is observed with particle concentration, and this is related to morphology and microstructure of the tribofilm generated.

Viscoelastic Behavior of Human Lamin A Proteins in the Context of Dilated Cardiomyopathy

Lamins are intermediate filament proteins of type V constituting a nuclear lamina or filamentous meshwork which lines the nucleoplasmic side of the inner nuclear membrane. This protein mesh provides a supporting scaffold for the nuclear envelope and tethers interphase chromosome to the nuclear periphery. Mutations of mainly A-type lamins are found to be causative for at least 11 human diseases collectively termed as laminopathies majority of which are characterised by aberrant nuclei with altered structural rigidity, deformability and poor mechanotransduction behaviour. But the investigation of viscoelastic behavior of lamin A continues to elude the field. In order to address this problem, we hereby present the very first report on viscoelastic properties of wild type human lamin A and some of its mutants linked with Dilated cardiomyopathy (DCM) using quantitative rheological measurements. We observed a dramatic strain-softening effect on lamin A network as an outcome of the strain amplitude sweep measurements which could arise from the large compliance of the quasi-cross-links in the network or that of the lamin A rods. In addition, the drastic stiffening of the differential elastic moduli on superposition of rotational and oscillatory shear stress reflect the increase in the stiffness of the laterally associated lamin A rods. These findings present a preliminary insight into distinct biomechanical properties of wild type lamin A protein and its mutants which in turn revealed interesting differences.

Experimental study of fracture behavior of magnesium single crystals

In this work, the fracture behavior of magnesium single crystals is studied by conducting experiments with notched three point bend specimens of three crystallographic orientations. In the first and second orientations, the c-axis is along the normal to the flat surface of the notch, while in the third it is aligned with the notch front. For all the orientations, in situ electron back scattered diffraction observations made around the notch root show profuse tensile twinning of {10 (1) over bar2} type. Further, in the first two orientations basal and prismatic slip traces are identified from optical metallography. The width of the most prominent twin saturates at around 120-150 mu m, while twins continue to nucleate farther away to accommodate plastic deformation. In all the orientations, crack initiation occurs before the attainment of peak load and the crack grows stably along twin-matrix interface before deflecting at twin-twin intersections. Results show that profuse tensile twinning is an important energy dissipating mechanism that enhances the fracture toughness. (C) 2013 Elsevier B.V. All rights reserved.

Electrical switching behavior of amorphous Ge15Te85 Si--x(x) thin films with phase change memory applications

Amorphous Ge15Te85-xSix thin film switching devices (1 <= x <= 6) have been deposited in sandwich geometry, on glass substrates with aluminum electrodes, by flash evaporation technique. These devices exhibit memory type electrical switching, like bulk Ge15Te85-xSix glasses. However, unlike the bulk glasses, a-Ge15Te85-xSix films exhibit a smooth electrical switching behavior. The electrical switching fields of a-Ge15Te85-xSix thin film samples are also comparable with other chalcogenide samples used in memory applications. The switching fields of a-Ge15Te85-xSix films have been found to increase with increasing Si concentration. Also, the optical band gap of a-Ge15Te85-xSix films is found to increase with Si content. The observed results have been understood on the basis of increase in network connectivity and rigidity with Si addition. (C) 2013 Elsevier Ltd. All rights reserved.

Temperature dependent magnetic ordering and electrical transport behavior of nano zinc ferrite from 20 to 800 K

The nano ZnFe2O4 compound was prepared by eco-friendly hydrothermal method. The characterization of the sample for its structure, morphology and composition were done by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), dynamic light scattering, Fourier transform infrared spectroscopy, zeta surface profiler and UV-Visible spectroscopy studies. The PXRD measurement reveals that the compound shows spinel cubic phase belong Fd (3) over barm (227) space group. Morphology of the compound from SEM and surface profile shows nearly spherical agglomerated particles with well defined grains and grain boundaries. The material shows the semiconducting behavior with E-g of 2.3 eV at room temperature (RT). The variation in the magnetic ordering was observed for wide range of temperature. The compound behaves like a soft magnetic material with ferrimagnetic at various temperatures except at RT. Both magnetic and EPR studies supports the superparamagnetic behavior of the the sample. The DC conductivity, dielectric and AC conductivity behavior of the 1000 degrees C pellets sintered for 2 h shows good frequency dependent transport properties. The present study facilitate in selecting the suitable materials for the nanoelectronics and spintronic applications. (C) 2013 Elsevier B.V. All rights reserved.

Speed control of brushed DC motor for low cost electric cars

As petrol prices are going up in developing countries in upcoming decades low cost electric cars will become more and more popular in developing world. One of the main deciding factors for success of electric cars specially in developing world in upcoming decades will be its cost. This paper shows a cost effective method to control the speed of low cost brushed D.C. motor by combining a IC 555 Timer with a High Boost Converter. The main purpose of using High Boost Converter since electric cars needs high voltage and current which a High Boost Converter can provide even with low battery supply.

A Seventeen-level Inverter With a Single DC-link For Motor Drives

In the present paper, a novel topology for generating a 17-level inverter using three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors. The proposed circuit is analyzed and various aspects of it are presented in the paper. This circuit is experimentally verified and the results are shown. The stability of the capacitor balancing algorithm has been verified during sudden acceleration. This circuit has many pole voltage redundancies. This circuit has an advantage of balancing all the capacitor voltages instantaneously by switching through the redundancies. Another advantage of this topology is its ability to generate all the 17 pole voltages from a single DC link which enables back to back converter operation. Also, the proposed inverter can be operated at all load power factors and modulation indices. Another advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels.

Failure modes and fatigue behavior of conventional and refilled friction stir spot welds in AA 6061-T6 sheets

The fatigue behavior of conventional friction stir spot welding (FSSW) and friction stir spot welding refilled by the friction forming process (FSSW-FFP) in aluminum 6061-T6 lap shear specimens, are investigated based on the experimental observations. Optical micrographs of the welds after fatigue failure in both the cases are examined to study the fatigue crack propagation and failure modes. Experimental results indicate that the fatigue strength of the FSSW-FFP weld samples is higher than that of the conventional FSSW samples at all loads. Fracture surfaces are analyzed in detail using the scanning electron microscope. (C) 2013 Elsevier Ltd. All rights reserved.

Nearly Constant Switching Frequency Hysteresis Current Controller with Fast Online Computation of Boundary for a 2-Level Induction Motor Drive

A nearly constant switching frequency current hysteresis controller for a 2-level inverter fed induction motor drive is proposed in this paper: The salient features of this controller are fast dynamics for the current, inherent protection against overloads and less switching frequency variation. The large variation of switching frequency as in the conventional hysteresis controller is avoided by defining a current-error boundary which is obtained from the current-error trajectory of the standard space vector PWM. The current-error boundary is computed at every sampling interval based on the induction machine parameters and from the estimated fundamental stator voltage. The stator currents are always monitored and when the current-error exceeds the boundary, voltage space vector is switched to reduce the current-error. The proposed boundary computation algorithm is applicable in linear and over-modulation region and it is simple to implement in any standard digital signal processor: Detailed experimental verification is done using a 7.5 kW induction motor and the results are given to show the performance of the drive at various operating conditions and validate the proposed advantages.

Doping a Correlated Band Insulator: A New Route to Half-Metallic Behavior

We demonstrate in a simple model the surprising result that turning on an on-site Coulomb interaction U in a doped band insulator leads to the formation of a half-metallic state. In the undoped system, we show that increasing U leads to a first order transition at a finite value U-AF between a paramagnetic band insulator and an antiferomagnetic Mott insulator. Upon doping, the system exhibits half-metallic ferrimagnetism over a wide range of doping and interaction strengths on either side of U-AF. Our results, based on dynamical mean field theory, suggest a new route to half metallicity, and will hopefully motivate searches for new materials for spintronics.

Tuning of the electro-mechanical behavior of the cellular carbon nanotube structures with nanoparticle dispersions

The mechanical and electrical characteristics of cellular network of the carbon nanotubes (CNT) impregnated with metallic and nonmetallic nanoparticles were examined simultaneously by employing the nanoindentation technique. Experimental results show that the nanoparticle dispersion not only enhances the mechanical strength of the cellular CNT by two orders of magnitude but also imparts variable nonlinear electrical characteristics; the latter depends on the contact resistance between nanoparticles and CNT, which is shown to depend on the applied load while indentation. Impregnation with silver nanoparticles enhances the electrical conductance, the dispersion with copper oxide and zinc oxide nanoparticles reduces the conductance of CNT network. In all cases, a power law behavior with suppression in the differential conductivity at zero bias was noted, indicating electron tunneling through the channels formed at the CNT-nanoparticle interfaces. These results open avenues for designing cellular CNT foams with desired electro-mechanical properties and coupling. (C) 2014 AIP Publishing LLC.