Synthesis and characterization of stable aqueous dispersions of graphene

A stable aqueous dispersion (5 mg ml^?1) of graphene was synthesized by a simple protocol based on three-step reduction of graphene oxide (GO) dispersion synthesized using the modified version of Hummers and Offeman method. Reduction of GO was carried out using sodium borohydride, hydrazine hydrate and dimethyl hydrazine as reducing agents. The chemically synthesized graphene was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopy, thermogravimetric analysis (TGA), optical microscopy. The stability of aqueous dispersions of graphene was confirmed through zeta potential measurements and the negative zeta potentials of 55–60 mV were obtained indicating the high stability of aqueous graphene dispersions.     

Bearing and uplift capacities of under-reamed piles in soft clay underlaid by stiff clay using lower-bound finite element limit analysis

Ensuring a safe foundation design in soft clay is always a challenging task to engineers. In the present study, the effectiveness of under-reamed piles in soft clay underlaid by stiff clay is numerically studied using the lower-bound finite element limit analysis (LB FELA). The bearing and uplift capacities of under-reamed piles are estimated through non-dimensional factors N_cul and F_cul, respectively. These factors increased remarkably and marginally compared to N_cul and F_cul of the piles without bulbs when the bulb is placed in stiff and soft clay, respectively. For a given ratio of undrained cohesion of stiff to soft clay (c₂/c₁), the factors N_cul and F_cul moderately increased with the increase in the length-to-shaft-diameter ratio (L_u/D) and adhesion factors in soft clay (α_s1) and stiff clay (α_s2). The variation of radial stress along the pile–soil interface, distribution of axial force in the under-reamed piles, and state of plastic shear failure in the soil are also studied under axial compression and tension. The results of this study are expected to be useful for the estimation of the bearing and uplift capacities of under-reamed piles in uniform clay and soft clay underlaid by stiff clay.     

Monte Carlo calculation of velocity-field characteristics in II-VI compound semiconductors

The velocity field characteristics of II–VI compound semiconductors at 77K have been obtained by the Monte Carlo simulation technique. The results agree with the available experimental data and with those obtained by solving the Boltzmann Transport Equation analytically. The simulation technique is described in detail and various aspects regarding the convergence of the simulation are discussed. The carrier distribution function has also been obtained from the simulation. The effects of the various simulation parameters, as well as those of the ionized impurity concentration, on the mobility values for the different semiconductors are discussed and results are presented.     

Assessment of Strength by Young's Modulus and Porosity: A Critical Evaluation

Literature data on strength, porosity, and Young's modulus at room temperature of reaction-bonded silicon nitride, sintered silicon nitride, and hot-pressed silicon nitride have been fitted into available and proposed strength-porosity relationships. In general, the Lewis method of iterative least-squares fitting in these relationships has been found to be better than conventional linearized least-squares fitting. Further a semiempirically proposed strength–Young's modulus relationship has been found to predict strength more precisely than the conventional strength-porosity relationship.     

Letter to the editor: Design of FIR notch filters by using Bernstein polynomials

In this paper, Bernstein polynomials have been used to derive an explicit formula for the coefficients of linear phase FIR notch filters which are maximally flat at ω=0 and π. The approach is relatively simple and enables us to design the filter for a specific notch frequency and bandwidth. © 1997 by John Wiley & Sons, Ltd.     

Comments on “A note on multigoal heuristic for facilities design problems: MUGHAL”

As manufacturers continue to automate their factories, they discover that existing cost measures should be updated. Much of the existing literature has discussed the ‘why's’ but there is little about the ‘how's’. This paper expands the cost concept to include quality and flexibility because they are critical factors for performance evaluation and project justification of advanced manufacturing systems. Then, a quantitative method of estimating the cost elements is illustrated. Finally, various approaches to collecting parametric values of the cost model and applications of the cost model are presented.     

VHF propagation characterization during atmospheric disturbances

Abstract

The propagation of a television (TV) signal is usually perturbed during periods of atmospheric disturbance such as in thunderstorms. The region under investigation here is situated in the coastal area of the Bay of Bengal and has experienced frequent thunderstorm activities. An investigation to study their effects on VHF signal propagation transmitted from Satkhira in Bangladesh and received at the Indian Statistical Institute, Calcutta, has been undertaken. The depths of the atmospheric disturbances within a 1?km range have been recorded and measured by acoustic sounder (sodar) operated continuously at the receiving station. The inset of the storm is marked by the enhanced signal level with deep fluctuations characteristic during the periods of thunderstorms.     

Elemental micro-segregation characteristic of fiber laser welded Hastelloy C-276 sheet

The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276 sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of elements, determined through EDS data, indicate the reduction in micro-segregation of elements compared with the previous reported literatures for laser welded Hastelloy C-276. High melting efficiency of ytterbium fiber laser, reduction in the amount of linear heat input, and high cooling rate of the mushy zone lead to the reduction in micro-segregation. The melting efficiency of ytterbium fiber laser for welding of Hastelloy C-276 of 64% is higher than that (48%) of conventional welding methods. High melting efficiency leads to the reduction in the linear heat input required for welding. Hence, in the present investigation, the same was found to substantially reduce as compared to the previous reported literature. The cooling rate from liquidus temperature to solidus temperature at the weld centerline was found to be in the order of 10³ °C/s. Cellular dendritic substructure that constituted for lower micro-segregation was formed at the weld centerline.