Mouth-Clicks used by Blind Expert Human Echolocators – Signal Description and Model Based Signal Synthesis

Echolocation is the ability to use sound-echoes to infer spatial information about the environment. Some blind people have developed extraordinary proficiency in echolocation using mouth-clicks. The first step of human biosonar is the transmission (mouth click) and subsequent reception of the resultant sound through the ear. Existing head-related transfer function (HRTF) data bases provide descriptions of reception of the resultant sound. For the current report, we collected a large database of click emissions with three blind people expertly trained in echolocation, which allowed us to perform unprecedented analyses. Specifically, the current report provides the first ever description of the spatial distribution (i.e. beam pattern) of human expert echolocation transmissions, as well as spectro-temporal descriptions at a level of detail not available before. Our data show that transmission levels are fairly constant within a 60° cone emanating from the mouth, but levels drop gradually at further angles, more than for speech. In terms of spectro-temporal features, our data show that emissions are consistently very brief (~3ms duration) with peak frequencies 2-4kHz, but with energy also at 10kHz. This differs from previous reports of durations 3-15ms and peak frequencies 2-8kHz, which were based on less detailed measurements. Based on our measurements we propose to model transmissions as sum of monotones modulated by a decaying exponential, with angular attenuation by a modified cardioid. We provide model parameters for each echolocator. These results are a step towards developing computational models of human biosonar. For example, in bats, spatial and spectro-temporal features of emissions have been used to derive and test model based hypotheses about behaviour. The data we present here suggest similar research opportunities within the context of human echolocation. Relatedly, the data are a basis to develop synthetic models of human echolocation that could be virtual (i.e. simulated) or real (i.e. loudspeaker, microphones), and which will help understanding the link between physical principles and human behaviour

Optimization of warpage defect in injection moulding process using ABS material

Plastic injection moulding process produces various defects such as warpage, sink marks, weld lines and shrinkage. The purpose of present paper is to analyze the warpage defect on Acrylonitrile Butadiene Styrene (ABS) for selected part using FEA simulation. The approach was based on Taguchipsilas Method and Analysis of Variance (ANOVA) to optimize the processing parameters namely packing pressure, mould temperature, melt temperature and packing time for effective process. It was found that the optimum parameters for ABS material are packing pressure at 375 MPa, mould temperature at 40degC, melt temperature at 200degC and packing time at 1 s. Melt temperature was found to be the most significant factor followed by packing time and mould temperature. Meanwhile, packing pressure was insignificant factor contributing to the warpage in present study

Contact Pressure Distribution During the Polishing Process of Ceramic Tiles: A Laboratory Investigation

During the polishing process of porcelain tiles the difference in scratching speed between innermost and peripheral abrasives leads to pressure gradients linearly distributed along the radial direction of the abrasive tool. The aim of this paper is to investigate such pressure gradient in laboratory scale. For this purpose polishing tests were performed on ceramic tiles according to the industrial practices using a custom-made CNC tribometer. Gradual wear on both abrasives and machined surface of the floor tile were measured. The experimental results suggested that the pressure gradient tends to cause an inclination of the abraded surfaces, which becomes stable after a given polishing period. In addition to the wear depth of the machined surface, the highest value of gloss and finest surface finish were observed at the lowest point of the worn out surface of the ceramic floor tile corresponding to the point of highest pressure and lowest scratching speed

Investigation on the effect of abrasive waterjet parameter on machining stainless steel

Abrasive waterjet machining (AWJM) can perform various machining operations on almost any material including hard to machine materials. However, performance of a process depends on the chosen set of parameters. AWJM has major parameters such as traverse rate, water pressure, standoff distance and abrasive flowrate that will affect its performance. The present study investigates the effects of AWJM parameters (i.e. traverse rate, water pressure and standoff distance) on the width, depth and roughness of a channel produced at the surface of stainless steel. The results showed that by reducing the standoff distance and water pressure, the width of the channel was also reduced. For channel depth, increasing traverse rate produced a shallower channel depth. In contrast, increasing the water pressure produced a deeper channel depth. The surface roughness of the channel showed significant improvement by reducing the water pressure at a lower traverse speed and standoff distance. A proper selection of parameters is required in order to produce a suitable channel during AWJM surface texturing process