Degenerate four-wave mixing in the copolymer of phenylacetylene and norbornene

The results of optical phase conjugation experiments in a degenerate four-wave mixing geometry are reported at 532 nm in a new block copolymer of phenylacetylene and norbornene. The copolymer sample with an equal number of repeating units for the two homopolymers prepared by sequential addition of the monomers gives a third-order susceptibility value which is twice that of the homopolymer of phenylacetylene.     

Flow of power law liquids through particle assemblages at intermediate reynolds numbers

The complete equations of motion and continuity have been solved numerically using the finite element method for the flow of power law liquids through assemblages of rigid spherical particles. The inter-particle interactions have been simulated using the free surface cell model. Extensive results on drag coefficients have been obtained under a wide range of physical and operating conditions (0.9999 ≥ 0.3), 1 ≥ n ≥ 0.4 and 20 ≥ Re ≥ 1. The observed dependence of drag coefficient on voidage and non-Newtonian flow behaviour index have been explained qualitatively with the aid of order of magnitude considerations. Finally, the theoretical predictions have been validated using suitable experimental data available in the literature.     

In Situ Study of Nanostructure and Electrical Resistance of Nanocluster Films Irradiated with Ion Beams

An in situ study is reported on the structural evolution in nanocluster films under He⁺ ion irradiation using an advanced helium ion microscope. The films consist of loosely interconnected nanoclusters of magnetite or iron‐magnetite (Fe‐Fe₃O₄) core‐shells. The nanostructure is observed to undergo dramatic changes under ion‐beam irradiation, featuring grain growth, phase transition, particle aggregation, and formation of nanowire‐like network and nanopores. Studies based on ion irradiation, thermal annealing and electron irradiation have indicated that the major structural evolution is activated by elastic nuclear collisions, while both electronic and thermal processes can play a significant role once the evolution starts. The electrical resistance of the Fe‐Fe₃O₄ films measured in situ exhibits a super‐exponential decay with dose. The behavior suggests that the nanocluster films possess an intrinsic merit for development of an advanced online monitor for fast neutron radiation with both high detection sensitivity and long‐term applicability, which can enhance safety measures in many nuclear operations.     

Role of Microstructure and Temperature on the Tensile Fracture Behavior of Oxide Dispersion Strengthened 18Cr Ferritic Steel

The tensile fracture behavior of oxide dispersion strengthened 18Cr (ODS-18Cr) ferritic steels milled for varying times was studied along with the oxide-free 18Cr steel (NODS) at 25, 200, 400, 600, and 800 °C. At all the test temperatures, the strengths of ODS–18Cr steels increased and total elongation decreased with the duration of milling time. Oxide dispersed 18Cr steel with optimum milling exhibited enhanced yield strength of 156 pct at room temperature and 300 pct at 800 °C when compared to oxide-free 18Cr steel. The ductility values of ODS-18Cr steels are in the range 20 to 35 pct for a temperature range 25 to 800 °C, whereas NODS alloy exhibited higher ductility of 37 to 82 pct. The enhanced strength of ODS steels when compared to oxide-free steel is due to the development of ultrafine grained structure along with nanosized dispersion of complex oxide particles. While the pre-necking elongation decreased with increasing temperature and milling time, post-necking elongation showed no change with the test temperature. Fractographic examination of both ODS and NODS 18Cr steel fractured tensile samples, revealed that the failure was in ductile fracture mode with distinct neck and shear lip formation for all milling times and at all test temperatures. The fracture mechanism is in general followed the sequence; microvoid nucleation at second phase particles, void growth and coalescence. The quantified dimple sizes and numbers per unit area were found to be in linear relation with the size and number density of dispersoids. It is clearly evident that even nanosized dispersoids acted as sites for microvoid nucleation at larger strains and assisted in dimple rupture.

     

Effect of Process Parameters and Heat Treatments on Properties of Cold Sprayed Copper Coatings

Cold gas dynamic spraying or cold spray is specifically suitable to obtain high-conductivity copper coatings for a variety of applications. Copper coatings at different coating parameters were deposited and subjected to various post treatments. The effect of process parameters and the treatment conditions on coating properties such as electrical conductivity, porosity, microhardness etc., was studied. The as-coated specimens exhibited low conductivities and conductivity was found to improve with heat treatment. Treatments were carried out in vacuum at different temperatures and for different durations and conductivities close to bulk annealed copper were achieved. Good correlation was observed between the conductivity, porosity and hardness of the as-coated and heat-treated specimens. Similar correlations were observed between conductivity-porosity and hardness-porosity of the coatings and the relative influence of cold work and porosity on coating properties was determined.     

Long‐Range,Entangled Carbon Nanotube Networks in Polycarbonate

A method is presented for dispersing ropes or bundles of single‐walled carbon nanotubes (RCNTs) in a polycarbonate (PC) matrix. Films of PC/RCNT composites are produced, with thicknesses ranging from 10 to 60 μm, and containing small concentrations (0.06–0.25 wt.‐%) of RCNT. Our process is based on a unique method of hot casting, annealing, and drying from dichlorobenzene solution. A wet annealing prior to complete drying yields a uniform and transparent film. Despite the low RCNT loading, scanning electron microscopy (SEM) analysis of the films after fracture reveals that the RCNTs form an entangled network throughout the film, which is a key requirement for enhanced properties. An increase of up to 30 % in the Young's modulus, as compared to PC, results with this method of composite fabrication.     

Adhesion and friction studies of silicon surfaces processed using a microparticle-based method

A surface processing method that combines electrostatic deposition of microparticles and dry etching is utilized to modify the surface topography of silicon surfaces to reduce adhesion and friction force. Microscale adhesion and friction tests were conducted on flat (smooth) and processed silicon surfaces with a low elastic modulus thermoplastic rubber (Santoprene) probe that allowed a large enough contact area to observe the feature size effect. Both adhesion and friction force of the processed surfaces were reduced comparing to that of the flat surfaces.     

Radiological and environmental aspects of Th-U fuel cycle facilities

The comparatively higher level of thorium reserves and the absence of long lived actinides of environmental concern offer real advantages for utilization of thorium in nuclear reactors. While use of uranium is likely to continue for some more time in view of investments already made, a shift to thorium eventually is an imperative necessity. It is in fact inevitable for a country like India. The paper presents a detailed comparative analysis of occupational radiation exposures as well as environmental releases. Different stages such as mining, fuel fabrication, reactor operation, spent fuel storage and reprocessing are considered. The factors that need to be taken into account include among others, the relatively lower occupational exposures and environmental releases in sodium cooled fast reactors compared to LWRs, the occurrence of thorium as surface deposits obviating the need for deep mining as in the case of uranium and the special dose reduction measures that need to be devised to minimize occupational exposures due to daughter products of ²³²U present in ²³³U during fuel fabrication operations. If once through mode of fuel cycle is to be adopted, thorium oxide materials are likely to be more enduring than would be the case with uranium.     

A finite element analysis of temperature in accelerated cutting

Temperature attained during machining has significant effects on the properties of tool, chip and workpiece. It governs the parameters like shear angle, cutting force, tool wear, surface finish etc. Review of literature reveals that hardly any information is available about the analytical determination of the tool-chip interface temperature and the temperature distribution during the accelerated cutting.

This paper presents the temperature analysis of accelerated cutting (i.e. taper turning and facing) as well as longitudinal turning, using the finite element technique. It has been concluded that the temperature distribution within the tool-chip-work system and the average tool-chip interface temperature for the two classes of machining (viz longitudinal turning and accelerated cutting) are not the same, even though the conditions of machining are identical. Further, the average tool-chip interface temperature is lowest in case of facing and highest in case of longitudinal turning.