6,724 research outputs found
Use of clicks resembling those of the Atlantic bottlenose dolphin (Tursiops truncatus) with biased pulse summation sonar (BiaPSS) to improve target discrimination in bubbly water
No full textIn-situ detection of single particle impact, erosion/corrosion and surface roughening
No full textParticle impact is technologically important and can cause significant damage to a surface. Detecting the approach and impact of a particle would give key information on the process. High-speed imaging of this process gives information on a particle's velocity and movement but does not answer key questions relating to changes in electrochemical properties of a surface caused by the resultant damage on impact. Furthermore, it is difficult to apply in non-transparent media. To gain this key information, we have deployed a high-speed electrochemical impedance technique with the ability to determine the uncompensated resistance, Faradaic current and effective capacitance of an electrode. This technique has a time resolution of 1.25 μs. Individual impacts of sand particles in a fluid jet (jet velocity ~4–5 m s−1) are used to cause erosion/corrosion of an aluminium interface. Surface properties are shown to change after individual particle impacts, which is preceded by the electrochemical detection of the particle as it approached the solid/liquid interface. For the first time, the in-situ roughening of the electrode surface is reported for a single particle impact. A link between the effective mass loss of the electrode and the overall surface erosion is shown, with an equivalent roughening rate of 8.5 F g−1 as determined from the data. This study shows how individual sand particles, and the damage they cause to an interface, can be detected with high precision and new insight. This will improve our understanding of erosive environments
Pulsed laser evaporated boron atom reactions with acetylene: infrared spectra and quantum chemical structure and frequency calculations for several novel BC{O:2}H{O:2} and HBC{O:2} molecules
No full textBoron atom reactions with acetylene: ab initio calculated and observed isotopic infrared spectra of the borirene radical BC{O:2}H{O:2}: a fingerprint match
No full textBoron atom reactions with acetylene: ab initio calculated and observed isotopic infrared spectra of the borirene radical BC{O:2}H{O:2}: a fingerprint match
No full textDolphin-inspired target detection for sonar and radar
No full textGas bubbles in the ocean are produced by breaking waves, rainfall, methane seeps, exsolution, and a range of biological processes including decomposition, photosynthesis, respiration and digestion. However one biological process that produces particularly dense clouds of large bubbles, is bubble netting. This is practiced by several species of cetacean. Given their propensity to use acoustics, and the powerful acoustical attenuation and scattering that bubbles can cause, the relationship between sound and bubble nets is intriguing. It has been postulated that humpback whales produce ‘walls of sound’ at audio frequencies in their bubble nets, trapping prey. Dolphins, on the other hand, use high frequency acoustics for echolocation. This begs the question of whether, in producing bubble nets, they are generating echolocation clutter that potentially helps prey avoid detection (as their bubble nets would do with man-made sonar), or whether they have developed sonar techniques to detect prey within such bubble nets and distinguish it from clutter. Possible sonar schemes that could detect targets in bubble clouds are proposed, and shown to work both in the laboratory and at sea. Following this, similar radar schemes are proposed for the detection of buried explosives and catastrophe victims, and successful laboratory tests are undertaken
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Pulsed laser evaporated boron atom reactions with acetylene: infrared spectra and quantum chemical structure and frequency calculations for several novel BC{O:2}H{O:2} and HBC{O:2} molecules
No full textA cyclostationary analysis applied to detection and diagnosis of faults in helicopter gearboxes
No full textIn several cases the vibration signals generated by rotating machines can be modeled as cyclostationary processes. A cyclostationary process is defined as a non-stationary process which has a periodic time variation in some of its statistics, and which can be characterized in terms of its order of periodicity. This study is focused on the use of cyclic spectral analysis, as a tool to analyze second-order periodicity signals (SOP), such as, those who are generated by either localized or distributed defects in bearings. Cyclic spectral analysis mainly consists of the estimation of the random aspects as well as the periodic behavior of a vibration signal, based on estimation of the spectral correlation density. The usefulness of cyclic spectral analysis for the condition monitoring of bearings, is demonstrated in this paper, through the analysis of several sections of vibration data collected during an endurance test of one of the two main gearbox transmissions of a helicopter.Most of this work was carried out at the ISVR of University of Southampton, funded with a grant from the Marie Curie Host Fellowships for Early Stage Research Training. The authors gratefully acknowledge the help of William Hardman who supplied the test bed data from H-60 tests conducted at the U. S. Navy’s Helicopter Transmission Test Facility located at Patuxent River, Maryland and of Sally McInnery, University of Alabama
Scaling and intermittency in ocean turbulence: analysis of coastal water optical properties and sea surface temperature (SST)
No full textWe consider here some scaling and intermittency properties of oceanic turbulence, with a general aim of considering the impact of turbulence on the bio-optical dynamics. For that purpose, we tried two different approaches, using in situ and satellite data. For the in situ study we adopted one dimensional and for the satellite two dimensional approaches. Different techniques such as Fourier power spectrum, Empirical mode of decomposition (EMD), Hilbert spectral analysis (HSA) have been used for analyzing the intermittency characteristics of the in situ data. For analyzing the multi-scale properties of the satellite images, we have considered Structure functions (SF) and Fourier power spectrum (1D and 2D). The general objective is to understand the multi-scale oceanic variability using scaling tools developed in the field of intermittent turbulence studies
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