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This paper addresses the effect of the post-process heat treatments on the microstructure and fatigue crack growth behaviour of the functionally graded (FG) laser powder bed fusion (L-PBF) Inconel 718 (IN718) superalloy. Sets of samples were additively manufactured (AM) altering the process parameters, namely the laser power, the laser scanning speed, layer thickness, hatch distance, and beam distribution function, resulting in distinctly different microstructures. Two categories of samples underwent heat treatment (HT) and hot isostatic pressing followed by HT (HIP+HT), while one category was kept in the as-processed (AP) condition to reveal the effects of the post-treatments. Additionally, to study the effect of microstructural anisotropy, samples were printed in horizontal (H) and vertical (V) building directions. To better understand the behaviour of the FG materials, non-graded (NG) L-PBF samples and wrought material were investigated as references. Significant variations in terms of porosity, grain size and elongation, crystallographic texture, and content of the strengthening precipitates or detrimental phases were found in different AM groups. The fatigue behaviour of the NG and FG materials was also studied by conducting three-point bending tests. Findings in terms of the role of different microstructures on the fatigue-crack initiation and fatigue crack growth rate are presented and discussed for all samples. The study demonstrated that heat treatments can enhance the damage tolerance of L-PBF IN718 to the level of wrought material. Interestingly, the effect of the roughness induced crack closure was found to be a function of build orientation, especially in the low stress ratio regime.

In this paper, the effect of microstructural anisotropy on the fatigue crack growth behaviour of the functionally graded Inconel 718 fabricated through laser powder bed fusion (L-PBF) is investigated. Different manufacturing parameters, including low and high laser powers, were used to produce a variety of non-graded (NG) and functionally graded (G) specimens in two build directions, vertical and horizontal. In addition, a group of heat treated wrought samples was tested as a reference. It was observed that the different manufacturing parameters result in various grain size, crystallographic textures, precipitates and Laves phases, porosity, and un-melted particles. Three-point bending fatigue tests were conducted to measure the threshold stress intensity factor (ΔKth) and fatigue crack growth rate (FCGR),da/dN. Only the lower laser power L-BPF Inconel material was found to have comparable to the wrought heat treated material fatigue crack growth behaviour. Furthermore, a new approach of automatically controlling ΔK as a function of the crack length was employed for graded specimens to investigate the crack growth rate as a function of local microstructure. The FCGR value of the vertical L-PBF samples, in which the crack direction was perpendicular to the build direction, remained constant. In contrast, the da/dN value of the horizontal samples with the crack direction parallel to the build direction increased constantly with the increase of the crack length. This behaviour is in good agreement with the hardness profile of the graded materials. Melt pool boundaries, graded interface boundaries, and grain orientations close to 〈001〉 were found to deflect the crack path. Additionally, it was found that L-PBF material is more affected (at a low stress ratio of R = 0.1) by the roughness-induced crack closure than the wrought counterparts. This study has successfully demonstrated the feasibility of using an additive manufacturing process to fabricate functionally graded materials featuring tailorable fatigue response of the local microstructures.

Chitin is one of the most widespread biopolymer found in nature. Shells of crustaceans such as prawns, crabs and lobsters are the main commercial sources of chitin. Chitin can be processed into chitosan, another, having varied industrial and biomedical significance. Lignin is another biomaterial, usually generated from agricultural waste and paper industry. The present work aims at synthesising chitosan from prawn shell and extracting lignin from wheat straw. It is further extended to form biocomposite films using these biomaterials by solution-casting technique. Appropriate analytical tests have been conducted like FTIR, SEM and tensile strength to study functional groups present, surface morphology and mechanical strength of the biomaterials synthesised and biocomposite films formed. The present work has successfully synthesised chitosan from crustacean shells and lignin from wheat straw. The results of analysis are encouraging & indicative of potential of lignin-chitosan biocomposite films specially in packaging of food material and in wound dressings. Use of lignin will reduce chitosan quantity and there by cost. It also utilises waste materials like crustaceans shell & wheat straw successfully in developing value added products chitosan and lignin

Block codes are viewed from a formal language theoretic perspective. It is shown that properties of trellises for subclasses of block codes called rectangular codes follow naturally from the Myhill Nerode theorem. A technique termed subtrellis overlaying is introduced with the object of reducing decoder complexity. Necessary and sufficient conditions for trellis overlaying are derived from the representation of the block code as a group, partitioned into a subgroup and its cosets. The conditions turn out to be simple constraints on coset leaders. It is seen that overlayed trellises are tail-biting trellises for which decoding is generally more efficient than that for conventional trellises. Finally, a decoding algorithm for tail-biting trellises is described, and the results of some simulations are presented.

AIM: This study aims to study normative choroidal thickness (CT) and Haller's and Sattler's layers thickness in normal Indian eyes. MATERIALS AND METHODS: The choroidal imaging of 73 eyes of 43 healthy Indian individuals was done using enhanced depth imaging feature of spectralis optical coherence tomography. Rraster scan protocol centered at fovea was used for imaging separately by two observers. CT was defined as the length of the perpendicular line drown from the outer border of hypereflective RPE-Bruch's complex to inner margin of choroidoscleral junction. Choroidal vessel layer thickness was measured after defining a largest choroidal vessel lumen within 750 μ on either side of the subfoveal CT vector. A perpendicular line was drawn to the innermost border of this lumen, and the distance between the perpendicular line and innermost border of choroidoscleral junction gave large choroidal vessel layer thickness (LCVLT, Haller's layer). Medium choroidal vessel layer thickness (MCVLT, Sattler's layer) was measured as the distance between same perpendicular line and outer border of hypereflective RPE-Bruch's complex. RESULTS: The mean age of individuals was 28.23 ± 15.29 years (range 14–59 years). Overall, the mean subfoveal CT was 331.6 ± 63.9 μ. Mean LCVLT was 227.08 ± 51.24 μ and the mean MCVLT was 95.65 ± 23.62 μ. CT was maximum subfoveally with gradual reduction in the thickness as the distance from the fovea increased. CONCLUSION: This is the first study describing the choroidal sublayer thickness, i.e., Haller's and Sattler's layer thickness along with CT in healthy Indian population.

This paper provides an overview of the robot control system of the UW Huskies, our entry in the RoboCup-2001 Sony AIBO legged robot league. Our development team consisted of one faculty member (D. Fox, team leader), one technical support staff (R. Pitkanen), one undergraduate student (J.K. Burns), and six graduate students. Since this was our first participation in RoboCup, we relied on the implementation of well-established techniques for robot control. These techniques include a layered control system, particle filters for robot localization, and efficient computer vision techniques for object recognition.

Block codes are first viewed as finite state automata represented as trellises. A technique termed subtrellis overlaying is introduced with the object of reducing decoder complexity. Necessary and sufficient conditions for subtrellis overlaying are next derived from the representation of the block code as a group, partitioned into a subgroup and its cosets. Finally a view of the code as a graph permits a combination of two shortest path algorithms to facilitate efficient decoding on an overlayed trellis.