Reversible Mode Switching in Y coupled Terahertz Lasers

Electrically independent terahertz (THz) quantum cascade lasers (QCLs) are optically coupled in a Y configuration. Dual frequency, electronically switchable emission is achieved in one QCL using an aperiodic grating, designed using computer-generated hologram techniques, incorporated directly into the QCL waveguide by focussed ion beam milling. Multi-moded emission around 2.9 THz is inhibited, lasing instead occurring at switchable grating-selected frequencies of 2.88 and 2.92 THz. This photonic control and switching behaviour is selectively and reversibly transferred to the second, unmodified QCL via evanescent mode coupling, without the transfer of the inherent grating losses

Y coupled terahertz quantum cascade lasers

Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL) system. The two THz QCLs working around 2.85 THz are driven by independent electrical pulsers. Total peak THz output power of the Y system, with both arms being driven synchronously, is found to be more than the linear sum of the peak powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9 mW). Furthermore, we demonstrate that the emission spectra of this coupled system are significantly different to that of either arm alone, or to the linear combination of their individual spectra.Comment: 9 pages, 3 figure

LAAO Device Mass: A Classic Condition Involving a Not - So - Classic Device

Current evidence suggests Class 2a recommendation for a left atrial appendage occlusion with a closure device in patients with atrial fibrillation who have moderate to high risk of stroke (CHA2DS2-VASc score ≥2) and a contraindication to long-term oral anticoagulation due to a nonreversible cause.1 Watchman device (WD) related infection is infrequent due to complete endothelialization of the device in a few weeks.2 We report a highly challenging case of possible WD-related infection that involved complex decision-making

The Development and Use of A Piloted Flight Simulation Environment for Rotary-Wing Operation to the Queen Elizabeth Class Aircraft Carriers

Flight simulation is being used to inform the First of Class Flight Trials for the UK’s new Queen Elizabeth Class (QEC) aircraft carriers. The carriers will operate with the Lockheed Martin F-35B Lightning II fighter aircraft, i.e. the Advanced Short Take-Off and Vertical Landing variant of the F-35. The rotary wing assets that are expected to operate with QEC include Merlin, Wildcat, Chinook and Apache helicopters. An F-35B flight simulator has been developed and is operated by BAE Systems at Warton Aerodrome. The University of Liverpool is supporting this project by using Computational Fluid Dynamics (CFD) to provide the unsteady air flow field that is required in a realistic flight simulation environment. This paper is concerned with a research project that is being conducted using the University’s research simulator, HELIFLIGHT-R, to create a simulation environment for helicopter operations to the QEC. The paper briefly describes how CFD has been used to model the unsteady airflow over the 280m long aircraft carrier and how this is used to create a realistic flight simulation environment. Results are presented from an initial simulation trial in which test pilots have used the HELIFLIGHT-R simulator to conduct simulated helicopter landings to two landing spots on the carrier, one in a disturbed air flow and the other in clean air. As expected, the landing to the spot in disturbed air flow requires a greater pilot workload, shows greater deviation in its positional accuracy and requires more control activity. This initial trial is the first of a planned series of simulated helicopter deck landings for different wind angles and magnitudes

A Virtual Engineering Approach to the Ship-Helicopter Dynamic Interface; a decade of modelling and simulation research at The University of Liverpool

This paper reviews some of the research that has been carried out at the University of Liverpool where the Flight Science and Technology Research Group has developed its Heliflight-R full-motion research simulator to create a simulation environment for the launch and recovery of maritime helicopters to ships. HELIFLIGHT-R has been used to conduct flight trials to produce simulated Ship-Helicopter Operating Limits (SHOLs). This virtual engineering approach has led to a much greater understanding of how the dynamic interface between the ship and the helicopter contributes to the pilot's workload and the aircraft's handling qualities and will inform the conduct of future real-world SHOL trials. The paper also describes how modelling and simulation has been applied to the design of a ship's superstructure to improve the aerodynamic flow field in which the helicopter has to operate. The superstructure aerodynamics also affects the placement of the ship's anemometers and the dispersion of the ship's hot exhaust gases, both of which affect the operational envelope of the helicopter, and both of which can be investigated through simulation

Using piloted simulation to measure pilot workload of landing a helicopter on a small ship

When conducting landings to a ship's deck in strong winds, helicopter pilot workload is often dominated by the turbulence within the ship's airwake. Previous studies have shown that larger ships create more aggressive airwakes and simulated flight trials had shown that it can be easier to land to a smaller ship than a large one. However, there are helicopter-enabled ships that are less than 100m in length and these will have significantly greater ship motion in rough seas than a large ship. The study reported in this paper has used a motion-base flight simulator to evaluate the pilot workload when landing to three geometrically similar ships of lengths 100m, 150m and 200m. Ship motion software has been used to create realistic deck displacements for sea states 4, 5 and 6, which are consistent with the increasing wind speed over the deck. It has been shown that the 100m ship was the most difficult to land to, with deck motion being the limiting factor. The next most difficult ship to land to was the 200m ship, with airwake turbulence being the limiting factor. The 150m ship generated the lowest pilot workload. The study has demonstrated that when ship motion is excessive, as it will be with small ships in rough seas, pilot workload will be dominated by deck motion during a landing task, but as the ship gets larger and more stable, airwake disturbances will dominate. It is clear from this study that realistic ship motion is essential when using piloted flight simulation to conduct simulated ship-helicopter operations

The Queen Elizabeth Class Aircraft Carriers: Airwake Modelling and Validation for ASTOVL Flight Simulation

This paper outlines progress towards the development of a high-fidelity piloted flight simulation environment for the UK’s Queen Elizabeth Class (QEC) aircraft carriers which are currently under construction. It is intended that flight simulation will be used to de-risk the clearance of the F-35B Lightning-II to the ship, helping to identify potential wind-speeds/directions requiring high pilot workload or control margin limitations prior to First of Class Flight Trials. Simulated helicopter launch & recovery trials are also planned for the future. The paper details the work that has been undertaken at the University of Liverpool to support this activity, and which draws upon Liverpool’s considerable research experience into simulated launch and recovery of maritime helicopters to single-spot combat ships. Predicting the unsteady air flow over and around the QEC is essential for the simulation environment; the very large and complex flow field has been modelled using Computational Fluid Dynamics (CFD) and will be incorporated into the flight simulators at the University of Liverpool and BAE Systems Warton for use in future piloted simulation trials. The challenges faced when developing airwake models for such a large ship are presented together with details of the experimental setup being prepared to validate the CFD predictions. Finally, the paper describes experimental results produced to date for CFD validation purposes and looks ahead to the piloted simulation trials of aircraft launch and recovery operations to the carrier

Importance of the Assessment of Left Ventricular Function Following a Diagnosis of Left Bundle Branch Block

Background Left bundle branch block (LBBB) is a diagnosis often encountered in clinical practice. It can be seen as a harbinger of decreased left ventricular function in the future. LBBB has been associated with new onset congestive heart failure (CHF) and death from cardiovascular diseases.1 Problem Statement LBBB in and of itself is given inadequate follow-up and attention by clinicians. Project AIM: bring to light the delay in follow-up after diagnosis of LBBB