Low power laser generated ultrasound : signal processing for time domain data acquisition

The use of low power modulated laser diode systems has previously been established as a suitable method for non-destructive laser generation of ultrasound. Using a quasi-continuous optical excitation amplified by an erbium-doped fibre amplifier (EDFA) allows flexible generation of ultrasonic waves, offering control of further parameters such as the frequency content or signal shape. In addition, pseudo-random binary sequences (PRBS) can be used to improve the detected impulse response. Here we compare two sequences, the m-sequence and the Golay code, and discuss the advantages and practical limits of their application with laser diode based optical excitation of ultrasound

Low power laser generated ultrasound : signal processing for time domain data acquisition

The use of low power modulated laser diode systems has previously been established as a suitable method for non-destructive laser generation of ultrasound. Using a quasi-continuous optical excitation amplified by an erbium-doped fibre amplifier (EDFA) allows flexible generation of ultrasonic waves, offering control of further parameters such as the frequency content or signal shape. In addition, pseudo-random binary sequences (PRBS) can be used to improve the detected impulse response. Here we compare two sequences, the m-sequence and the Golay code, and discuss the advantages and practical limits of their application with laser diode based optical excitation of ultrasound

External Inverse-Compton Emission from Low-Luminosity Gamma-Ray Bursts: Application to GRB 190829A

The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The \hess telescopes recently observed very-high-energy (VHE) emission from a nearby low-luminosity GRB, GRB 190829A. Follow-up observations with, e.g., Swift-XRT, revealed unusual flare activities at $\sim 10^3\rm~s$, which can be caused by a long-lasting central engine. We show that the VHE emission during the H.E.S.S. observation time is naturally produced in the external inverse-Compton (EIC) scenario, where seed photons supplied by the flares or other late-time dissipation are upscattered to VHE energies by the non-thermal electrons accelerated at the external forward shock. Our calculations show that the EIC flare nearly coincides with the late-prompt flare, but extends $\sim3-4$ times longer than the duration of the late-prompt flare. The preferred kinetic energy and initial Lorentz factor used in our model are $\sim 10^{52}\rm~erg$ and $\sim 20$, respectively. Understanding the mechanisms of the VHE emission from low-luminosity GRBs will help us constrain the properties of the outflow and the central engine activities, as well as the particle acceleration mechanism.Comment: 12 pages, 6 figures, accepted for publication in ApJ. HESS data are added, figures are updated, appendix is extended, main conclusions unchange

Mixed Phase Modeling in GlennICE with Application to Engine Icing

A capability for modeling ice crystals and mixed phase icing has been added to GlennICE. Modifications have been made to the particle trajectory algorithm and energy balance to model this behavior. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to four mixed phase ice accretions performed in the Cox icing tunnel in order to calibrate an ice erosion model. A sample ice ingestion case was performed using the Energy Efficient Engine (E3) model in order to illustrate current capabilities. Engine performance characteristics were supplied using the Numerical Propulsion System Simulation (NPSS) model for this test case

Radiation distributions in TCV

Total radiative powers measured by foil bolometer and AXUV camera systems are compared to SOLPS5 simulations in low and high density deuterium and helium diverted discharges on the TCV tokamak. For low density the match between simulation and measurements is satisfactory, but at high density strongly radiating regions outside the SOLPS5 simulation grid are seen in measurements and this may indicate the presence of enhanced convective particle transport in the low field side midplane region. The chord coverage of the foil bolometer system does not, however, allow detailed resolution in this region. The comparison of foil and AXUV data also demonstrates that ageing of the AXUV diodes under plasma irradiation combined with the unevenness of the diode spectral response, strongly limits their application for total radiative power measurements. (c) 2007 Elsevier B.V. All rights reserved

Clinical features, anaesthetic management and perioperative complications seen in three horses with pheochromocytoma

Three horses presenting with colic signs to the Equine Referral Hospital at The Royal Veterinary College underwent general anaesthesia between September 2013 and November 2017 for emergency exploratory laparotomy. No obvious cause for the colic signs was identified in two horses, while a haemoperitoneum was identified in the third. All horses were euthanased within 12 hours of surgery due to deteriorating haemodynamic instability and/or intractable pain. Postmortem examination revealed an adrenal mass in each case, confirmed to be a pheochromocytoma on histopathology. In retrospect, each horse had some hallmark characteristics consistent with a functional pheochromocytoma, including hyperglycaemia and hyperlactataemia. Extremely high packed cell volume (PCV) (>65 per cent) was also identified in two horses, with a high-normal PCV found in the haemoperitoneum case. Perioperative haemodynamic instability was predominantly characterised by episodes of intermittent hypertension and tachycardia

Point source in a phononic grating: stop bands give rise to phonon-focusing caustics

We use locally-excited gigahertz surface phonon wavepackets in microscopic line structures of different pitches to reveal profound anisotropy in the radiation pattern of a point source in a grating. Time-domain data obtained by an ultrafast optical imaging technique and by numerical simulations are Fourier transformed to obtain frequency-filtered real-space acoustic field patterns and k-space phononic band structure. The numerically-obtained k-space images are processed to reveal an intriguing double-horn structure in the lowest-order group-velocity surface, which explains the observed non-propagation sectors bounded by caustics, noted at frequencies above the bottom of the first stop band. We account for these phonon-focusing effects, analogous to collimation effects previously observed in two- and three-dimensional lattices, with a simple analytical model of the band structure based on a plane wave expansion. As the frequency is increased, a transition to dominant waveguiding effects along the lines is also documented