Electrodeposited carbon nanotube thin films

A successful attempt to grow carbon nanotubes (CNTs) by electrodeposition technique for the first time is reported here. Carbon nanotubes were grown on Si (001) substrate using acetonitrile (1% v/v) and water as electrolyte at an applied d.c. potential ∼20 V. The films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman, optical absorbance, Fourier Transform Infra Red spectroscopy (FTIR) and Electron Spin Resonance (ESR) measurements. The effect of magnetic field on the growth of nanotubes was studied critically. It was found that the presence of magnetic field during electro-deposition played a crucial role on the growth of carbon nanotubes and hence the electronic properties. Photoluminescence (PL) studies indicated band edge luminescence ∼0.72-0.83 eV. Field emission studies indicated lower turn-on voltage and higher current density for films deposited with magnetic field.     

Computationally efficient algorithms for multiple fault diagnosis in large graph-based systems

Graph-based systems are models wherein the nodes represent the components and the edges represent the fault propagation between the components. For critical systems, some components are equipped with smart sensors for on-board system health management. When an abnormal situation occurs, alarms will be triggered from these sensors. This paper considers the problem of identifying the set of potential failure sources from the set of ringing alarms in graph-based systems. However, the computational complexity of solving the optimal multiple fault diagnosis (MFD) problem is exponential. Based on Lagrangian relaxation and subgradient optimization, we present a heuristic algorithm to find approximately the most likely candidate fault set. A computationally cheaper heuristic algorithm - primal heuristic - has also been applied to the problem so that real-time MFD in systems with several thousand failure sources becomes feasible in a fraction of a second. This paper also considers systems with asymmetric and multivalued alarms (tests).     

Note: Compact high voltage pulse transformer made using a capacitor bank assembled in the shape of primary

The experimental results of an air-core pulse transformer are presented, which is very compact (<10 Kg in weight) and is primed by a capacitor bank that is fabricated in such a way that the capacitor bank with its switch takes the shape of single-turn rectangular shaped primary of the transformer. A high voltage capacitor assembly (pulse-forming-line capacitor, PFL) of 5.1 nF is connected with the secondary of transformer. The transformer output voltage is 160 kV in its second peak appearing in less than 2 μS from the beginning of the capacitor discharge. The primary capacitor bank can be charged up to a maximum of 18 kV, with the voltage delivery of 360 kV in similar capacitive loads.     

Comparison of multiobjective evolutionary algorithms: empirical results

In this paper, we provide a systematic comparison of various evolutionary approaches to multiobjective optimization using six carefully chosen test functions. Each test function involves a particular feature that is known to cause difficulty in the evolutionary optimization process, mainly in converging to the Pareto-optimal front (e.g., multimodality and deception). By investigating these different problem features separately, it is possible to predict the kind of problems to which a certain technique is or is not well suited. However, in contrast to what was suspected beforehand, the experimental results indicate a hierarchy of the algorithms under consideration. Furthermore, the emerging effects are evidence that the suggested test functions provide sufficient complexity to compare multiobjective optimizers. Finally, elitism is shown to be an important factor for improving evolutionary multiobjective search.     

A fast and elitist multiobjective genetic algorithm: NSGA-II

Multi-objective evolutionary algorithms (MOEAs) that use non-dominated sorting and sharing have been criticized mainly for: (1) their O(MN³) computational complexity (where M is the number of objectives and N is the population size); (2) their non-elitism approach; and (3) the need to specify a sharing parameter. In this paper, we suggest a non-dominated sorting-based MOEA, called NSGA-II (Non-dominated Sorting Genetic Algorithm II), which alleviates all of the above three difficulties. Specifically, a fast non-dominated sorting approach with O(MN²) computational complexity is presented. Also, a selection operator is presented that creates a mating pool by combining the parent and offspring populations and selecting the best N solutions (with respect to fitness and spread). Simulation results on difficult test problems show that NSGA-II is able, for most problems, to find a much better spread of solutions and better convergence near the true Pareto-optimal front compared to the Pareto-archived evolution strategy and the strength-Pareto evolutionary algorithm - two other elitist MOEAs that pay special attention to creating a diverse Pareto-optimal front. Moreover, we modify the definition of dominance in order to solve constrained multi-objective problems efficiently. Simulation results of the constrained NSGA-II on a number of test problems, including a five-objective, seven-constraint nonlinear problem, are compared with another constrained multi-objective optimizer, and the much better performance of NSGA-II is observed     

Negative photoconductivity in silver nanocubes prepared by simple photochemical method

Silver nanocubes embedded in polyvinyl alcohol matrix have been synthesised by photoirradiation technique. The composite films are characterised by FESEM, XRD, UV-Visible absorption and photoluminescence. These show characteristics of silver nanoparticles with FESEM showing the cubic shape. The photoconductivity study of these films shows decrease in photocurrent with light irradiation. Such negative photoconductivity behaviour may be attributed to dominant scattering of electrons by excited surface plasmon polaritons in nanoscale.     

Structural changes and biological responsiveness of an injectable and mouldable monetite bone graft generated by a facile synthetic method

Brushite (dicalcium phosphate dihydrate) and monetite (dicalcium phosphate anhydrous) are of considerable interest in bone augmentation owing to their metastable nature in physiological fluids. The anhydrous form of brushite, namely monetite, has a finer microstructure with higher surface area, strength and bioresorbability, which does not transform to the poorly resorbable hydroxyapatite, thus making it a viable alternative for use as a scaffold for engineering of bone tissue. We recently reported the formation of monetite cements by a simple processing route without the need of hydrothermal treatment by using a high concentration of sodium chloride in the reaction mix of β-tricalcium phosphate and monocalcium phosphate monohydrate. In this paper, we report the biological responsiveness of monetite formed by this method. The in vitro behaviour of monetite after interaction and ageing both in an acellular and cellular environment showed that the crystalline phase of monetite was retained over three weeks as evidenced from X-ray diffraction measurements. The crystal size and morphology also remained unaltered after ageing in different media. Human osteoblast cells seeded on monetite showed the ability of the cells to proliferate and express genes associated with osteoblast maturation and mineralization. Furthermore, the results showed that monetite could stimulate osteoblasts to undergo osteogenesis and accelerate osteoblast maturation earlier than cells cultured on hydroxyapatite scaffolds of similar porosity. Osteoblasts cultured on monetite cement also showed higher expression of osteocalcin, which is an indicator of the maturation stages of osteoblastogenesis and is associated with matrix mineralization and bone forming activity of osteoblasts. Thus, this new method of fabricating porous monetite can be safely used for generating three-dimensional bone graft constructs.     

Using light to control the interactions between self-rotating assemblies of active gels

Polymer gels undergoing the oscillating Belousov-Zhabotinsky (BZ) reaction exhibit an autonomous, periodic swelling and deswelling, where the mechanical oscillations are driven by the chemical reaction within the polymer network. Using computer simulations, we show that these BZ gels can undergo a form of auto-chemotaxis, enabling the gels to spontaneously move in response to self-generated chemical gradients. Focusing on four millimeter-sized pieces of these BZ gels, we show that the pieces can organize into self-rotating clusters that resemble a moving pinwheel or gear. By analyzing the factors that promote the formation of a single self-rotating cluster, we attempt to design systems of multiple, interacting gears. We show that light, which suppresses the oscillations of the gels, can be harnessed to promote the formation of two self-rotating clusters. These studies point to a novel form of photo-chemo-mechanical transduction, where light is utilized to control the conversion of chemical and mechanical energy in the system. Moreover, the interaction between the BZ gel gears reveals a new form of entrainment between these moving units. Namely, their coordinated motion is achieved through chemical coupling or communication, rather than a mechanical coupling. These findings can lead to the formation of chemically “communicating” devices that can be programmed to perform autonomous work through the use of light.     

Variability in rheology of cemented paste backfill with hydration age,binder and superplasticizer dosages

The use of (CPB) material to ameliorate geotechnical stability of underground mine is in nascent stage in India. Rheological properties of CPB change with travelling time as it is transported to underground mine stope through pipeline reticulation. In this paper, rheological properties of CPB based on mill tailings of a carbonate rich mineral processing waste are evaluated for different dosages of polycarboxylate (PC) based (SP). Each CPB sample having 78?wt% solids is mixed separately with 4%, 6% or 8% of binder dosages (ratio of the weight of dry binder to the weight of dry tailings) and, 0%, 0.5%, or 1.0% of SP dosages as weight of dry binder. The paper presents a methodology for determining yield stress, plastic viscosity and thixotropic behaviour of CPB mixture as a function of hydration age, binder and SP dosages. Results from the experimental campaigns indicate that SP content has significant influence on rheological behaviour of CPB and can be suitably exploited to enhance the flow characteristics of the carbonate rich process tailings. The study also develops multivariate linear regression models of yield stress, plastic viscosity and thixotropy of CPB depending on the hydration age, binder and SP dosages.