Ashfaq Khan

Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope

The imaging resolution of a conventional optical microscope is limited by diffraction to ~200 nm in the visible spectrum. Efforts to overcome such limits have stimulated the development of optical nanoscopes using metamaterial superlenses, nanoscale solid immersion lenses and molecular fluorescence microscopy. These techniques either require an illuminating laser beam to resolve to 70 nm in the visible spectrum or have limited imaging resolution above 100 nm for a white-light source. Here we report a new 50-nm-resolution nanoscope that uses optically transparent microspheres (for example, SiO₂, with 2 μm<diameter<9 μm) as far-field superlenses (FSL) to overcome the white-light diffraction limit. The microsphere nanoscope operates in both transmission and reflection modes, and generates magnified virtual images with a magnification up to ×8. It may provide new opportunities to image viruses and biomolecules in real time.1 Laser Processing Research Centre, School of Mechanical, Aerospace, and Civil Engineering, University of Manchester, Manchester M60 1QD, UK 2 Corrosion and Protection Centre, School of Materials, University of Manchester, The Mill, University of Manchester, Manchester M60 1QD, UK 3 Data Storage Institute, DSI Building, 5 Engineering Drive 1, Singapore, 117608 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 *E-mail: zengbo.wang@manchester.ac.uk

Modulated Nd:YAG laser welding of Ti-6Al-4V

Abstract Modulating the output of Nd : YAG laser sources has been evaluated as a technique for producing high quality welds in titanium alloys. Welds with high internal quality were produced when a square wave form was used with a modulation frequency ≥125 Hz and a duty cycle of 50%. Undercut present in the weld profile can be reduced if the correct combination of modulation amplitude and laser beam focal plane position are used. High speed observation and subsequent Fourier analysis of the vapour plume and keyhole behaviour have shown that they both exhibit the same periodic tendencies. With the correct parameters, an oscillating wave can be set up in the weld pool, which appears to manipulate the vapour plume behaviour and hence reduce porosity formation.

Parallel near-field optical micro/nanopatterning on curved surfaces by transported micro-particle lens arrays

Although laser surface nanopatterning by particle lens arrays (PLA), utilizing near-field enhancement, has been extensively utilized previously, a suitable technique for the deposition of PLA on the curved surface of a cylinder was not available. In this paper, a novel technique for nanopatterning on curved surfaces using PLA is demonstrated. In the proposed technique, a hexagonal closed pack monolayer of SiO2 spheres is first formed by self-assembly on a flat glass surface. The formed monolayer of particles is then picked up by a flexible optically transparent sticky surface and placed on the substrate to be patterned. A 532 nm wavelength Nd : YVO4 laser was used to irradiate the substrate with the laser passing through the flexible, transparent surface and the particles. Experimental investigations are made to ascertain the properties of the patterns. In addition, the optical near-field distribution around the particles is numerically simulated. The proposed technique is validated for nanopatterning of the curved surface of a cylinder.

Turbine Blade Manufacturing Through Rapid Tooling (RT) Process and Its Quality Inspection

Rapid prototyping (RP) technologies have played vital role in product development and validation. Another aspect of RP is rapid tooling (RT). The development and manufacturing of conventional tools (die and molds) take considerable amount of time. RP technologies could be used to shorten the development time of these tools for shorten the time to production. This investigation focuses on the development of turbine blade through RT technique with quality inspection at three different stages, i.e., after manufacturing of master patterns, wax patterns, and casting in metal. Three different materials were considered for RT techniques, i.e., Room temperature vulcanization (RTV) silicon, polyurethane, and plaster of Paris. Master patterns were developed using stereolithography(SLA) and fused deposition modeling (FDM) process. Both master patterns were analyzed for surface roughness and dimensional accuracy. SLA pattern showed better results for surface finish and dimensional accuracy, and it was used for mold manufacturing. Wax patterns were produced from RTV silicon, polyurethane (PU), and plaster of Paris molds,and used for metal casting. Dimensional quality inspection was performed for both wax and metallic parts using noncontact three-dimensional (3D)digitizer. RTV silicon and SLA process were selected as the suitable mold material and process respectively for RT of turbine blade.

Lossless colour image compression using RCT for bi-level BWCA

A novel lossless colour image compression scheme based on a reversible colour transform (RCT) and Burrows–Wheeler compression algorithm (BWCA) is presented. The lossless transformation from RGB to YUV colour space provides highly correlated pixel intensities in the transformed image, thus aiding in higher compression. The proposed scheme uses a two-pass Burrows–Wheeler transform (BWT) for the individual source image colour planes to enhance grey-level homogeneity in the 2-D space. Compression efficiency is compared against various schemes including the JPEG 2000 lossless compression scheme and the previously developed kernel move-to-front transform-based BWCA (kernel BWCA). Validation is carried out via small- and large-size images. The proposed method using RCT with bi-level BWT results in better compression by taking advantage of the redundancy in the grey levels brought by the YUV colour space. For small-size images, it achieves 45 and 126 per cent more compression than the JPEG2000 lossless and kernel BWCA scheme, respectively. Among the different schemes compared, the proposed scheme achieves overall best performance and is well suited to small- and large-size image data compression.

Analysis of weld characteristics of micro-plasma arc welding and tungsten inert gas welding of thin stainless steel (304L) sheet

This research work focuses on comparison of the weld geometry, distortion, microstructure and mechanical properties of thin SS 304 L sheets (0.8 mm thickness) welded using micro-plasma arc welding and tungsten inert gas welding process. Initial experiments were performed to identify suitable processing parameters for micro-plasma arc welding and tungsten inert gas welding processes. Microstructures of welds were analysed using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate that the joint produced by micro-plasma arc welding exhibited higher tensile strength, higher ductility, smaller dendrite size and a narrow heat affected zone. Samples welded by micro-plasma arc welding process had lower distortion as compared to that welded by tungsten inert gas process. Micro-plasma arc welding was shown to be the suitable process for welding of thin 304 L sheets owing to its higher welding speed and better weld properties as compared to the tungsten inert gas welding process.

Environment Friendly Finishing for the Development of Oil and Water Repellent Cotton Fabric

ABSTRACT Two environment-friendly short chain fluorocarbons, oleophobol and phobol, were evaluated on cotton fabric. The effect of combination of two fluorocarbons and the combination of oleophobol with zero formaldehyde cross-linker (DHEU) to enhance the performance and durability was also scrutinized. Repellency performance of the treated fabric was appraised by measuring water repellency, oil repellency and contact angle. Washing durability of the finished fabric was also enhanced by the incorporation of the cross-linker (DHEU) into the recipe of oleophobol. The physical and comfort properties of the fabric were also examined by measuring the tensile strength, tear strength and water vapor permeability of the fabric.

Influence of Cu addition on transformation temperatures and thermal stability of TiNiPd high temperature shape memory alloys

In this research, four high temperature shape memory alloys, Ti50Ni25-xPd25Cux (x = 0, 5, 10 and 15) were developed and designated 0Cu, 5 Cu, 10 Cu, and 15Cu, respectively. The effect of 5%, 10%, and 15% (all in atomic percent) Cu addition was investigated through their microstructure analysis, transformation temperatures and thermal stability. After the alloying of Cu content in their desired percentage, the alloys were named as 0Cu, 5Cu, 10Cu and 15Cu alloys. The martensite onset temperature Ms of ternary 0Cu alloy increased by 12.5 ℃, 27.5 ℃ and 60.5 ℃, respectively, by replacement of Ni with 5%, 10% and 15% Cu. Similarly, the austenite finish temperature Af increased by 11 ℃, 25 ℃, and 52 ℃, respectively. At the same time, thermal hysteresis of the 5Cu, 10Cu, and 15Cu alloys decreased by 1.5 ℃, 2.5 ℃, and 8.5 ℃, respectively, as compared to 0Cu alloy. The thermal stability of ternary 0Cu alloy was improved by replacing Ni with Cu. During thermal cycling, the net drop in Ms and Af of 0Cu alloy was 7.5 ℃ and 14 ℃, respectively. By replacing Ni with 5%, 10%, and 15% Cu, the net drop in Ms decreased to 5 ℃, 3.7 ℃, and 3 ℃, respectively, whereas the net drop in Af decreased to 10 ℃, 8.7 ℃, and 5 ℃. The overall results suggested that by the addition of 5%, 10%, and 15% Cu in place of Ni in TiNiPd alloys, the transformation temperatures and thermal stability improved. At the same time, thermal hysteresis decreased to a reasonable level which has a positive effect on the actuation behavior.

A dialectical analysis of non-reference image quality measures (IQMs) and restoration filters for single image blind deblurring

Blind image deblurring relies on a good estimation of Point Spread Function (PSF) and the utilization of an effective restoration filter. Even if the PSF is estimated well, the deblurring result depends heavily on the abilities of the restoration filter to produce a good approximation of the pristine image. Blind Image Quality Measures (IQMs) that guide the deblurring algorithm are also dependent on the restored image data. This research work evaluated the performance of the restoration filters and the blind IQMs when the true PSF has been estimate dand presents the effectiveness of both for blind deblurring. Wiener, Richardson-Lucy and Total Variation deblurring filters and BRISQUE, NIQE, SSEQ, Curvelet QA (CQA) IQMs have been analysed. Simulations have been performed over a wide range of images various blurring types (Gaussian, out-of-focus and motion). The results show that TV deblurring filter in conjunction with CQA deliver a near estimate of the pristine image for the artifically blurred images. In the case of real blurred images, Wiener filter presents high quality deblurred images and both SSEQ and CQA depict high quality images.

Laser Micro Processing of Carbide Tool Insert

For a number of applications there is evidence that the tribological conditions for mating surfaces can be improved by surface texturing. Literature shows that texturing the tool rake face can have a positive influence on tribological properties. This research focuses of the texturing of tool rake surface by laser machining. Compared to other texturing techniques, laser provides the flexibility of machining customized textures on tool surface. This paper deals with the assessment and optimization of the process parameters for generation of textures on cemented carbide inserts under ambient conditions by using a femtosecond laser. The paper is a significant contribution to the efficient and rapid generation of customized surface texture on hard tool inserts.Copyright