Quality Assessment of Mobile Cone-beam Computerized Tomography Scanner Made in Thailand: A Phantom Study

Background: In 2011, the National Science and Technology Development Agency had successfully developed the first local-made mobile conebeam computed tomography (CBCT) scanner, called MobiiScan. Before a computed tomography (CT) scanner can be used in clinical practice, it must pass a quality assurance process. Objective: To assess the performance of MobiiScan before it can be further evaluated in human subjects. Materials and Methods: Images from scanning of an imaging phantom by MobiiScan were compared to a commercial 64-slice (GE Discovery CT750 HD) and a mobile (Neurologica CereTom) CT scanner, which were used as controls. Spatial resolution, uniformity, noise, accuracy of CT number, and geometric accuracy were examined by three investigators. Results: According to the bone scanning protocol, spatial resolution of the images produced by MobiiScan was comparable to the mobile scanner, but it was less than the 64-slice scanner. In addition, the signal uniformity of MobiiScan was poorer compared to the controls. MobiiScan produced more noise than the mobile and the 64-slice scanners at the 120-kVp mode, but less noise than the 64-slice scanner at the 80-kVp mode. Using the brain protocol, the spatial resolution from the MobiiScan was higher than the mobile scanner, but comparable to the 64-slice scanner. Although the signal uniformity of the MobiiScan was superior compared to the controls, the noise production was more than the controls. At all settings, the MobiiScan gave underrated distances and inaccurate CT numbers. However, it delivered very low radiation doses. Conclusion: MobiiScan had a good spatial resolution and delivered low radiation dose, which suggested that it could be used for bone examination as intended by the creator. However, its noise production and inaccurate CT numbers suggest that MobiiScan should not be used to diagnose soft tissue problems. It is recommended that the hardware and software should be adjusted to provide a better signal uniformity, lower noise level, accurate CT number, and geometric accuracy. Keywords: X-ray computed tomography; Cone-beam computed tomography; Craniofacial abnormalities; Radiologic phantom; MobiiScan

Impact of Swirling Entropy Waves on a High Pressure Turbine

The harsh environment exiting modern gas turbine combustion chamber is characterized by vorticity and temperature perturbations, the latter commonly referred as entropy waves. The interaction of these unsteadiness with the first turbine stage causes non-negligible effects on the aerodynamic performance, blade cooling and noise production. The first of these drawbacks is addressed in this paper by means of an experimental campaign: entropy waves and swirl profile are injected upstream of an axial turbine stage through a novel combustor simulator. Two injection positions and different inlet conditions are considered. Steady and unsteady experimental measurements are carried out through the stage to address the combustor-turbine interaction characterizing the injected disturbance, the nozzle and rotor outlet aerothermal field. The experimental outcomes show a severe reduction of the temperature perturbation already at stator outlet. The generated swirl profile influences significantly the aerodynamic, as it interacts with the stator and rotor secondary flows and wakes. Furthermore, the clocking position changes the region most affected by the disturbance, showing a potential modifying the injection position to minimize the entropy wave and swirl profile impact on the stage. Finally, this work shows that in order to proficiently study entropy waves, the unsteady aerodynamic flow field stator downstream has to be addressed.

Trailing-edge noise reduction of a wing by a surface modification

There is an increased emphasis on reducing airframe noise in the last decades. Airframe noise is sound generated by the interaction of a turbulent flow with the aircraft geometry, and significantly contributes to the overall noise production during the landing phase. One examples of airframe noise is the noise generated at a wing's trailing edge, i.e., trailing-edge noise. In this contribution, we numerically explore the local application of riblets for the purpose of trailing-edge noise reduction. Two configurations are studied: i) a clean NACA0012 wing section as a reference, and ii) the same configuration with riblets installed at the wing's aft part. The numerical investigation follows a hybrid computational aeroacoustics approach, where the time-average flow is studied by means of RANS. Noise sources are generated by means of a stochastic approach called Fast Random Particle Mesh method. The results show a deceleration of the flow behind the riblets. Furthermore, the turbulent kinetic energy indicates increased unsteadiness behind the riblets which is shifted away from the wall due to the presence of the riblets. Lastly, the sound sources are investigated by means of the 3D Lamb-vector, which indicates a slight reduction in magnitude near the trailing edge.

Impact of Swirling Entropy Waves on a High Pressure Turbine

The harsh environment exiting modern gas turbine combustion chamber is characterized by vorticity and temperature perturbations, the latter commonly referred as entropy waves. The interaction of these unsteadiness with the first turbine stage causes non-negligible effects on the aerodynamic performance, blade cooling and noise production. The first of these drawbacks is addressed in this paper by means of an experimental campaign: entropy waves and swirl profile are injected upstream of an axial turbine stage through a novel combustor simulator. Two injection positions and different inlet conditions are considered. Steady and unsteady experimental measurements are carried out through the stage to address the combustor-turbine interaction characterizing the injected disturbance, the nozzle and rotor outlet aerothermal field. The experimental outcomes show a severe reduction of the temperature perturbation already at stator outlet. The generated swirl profile influences significantly the aerodynamic, as it interacts with the stator and rotor secondary flows and wakes. Furthermore, the clocking position changes the region most affected by the disturbance, showing a potential modifying the injection position to minimize the entropy wave and swirl profile impact on the stage. Finally, this work shows that in order to proficiently study entropy waves, the unsteady aerodynamic flow field stator downstream has to be addressed.

Robotic-Assisted Surgery for Cadaveric Skull Opening: A New Method of Autopsy Procedure

Background: Sawing of bone is an essential part of an autopsy procedure. An oscillating saw always generates noise, fine infectious dust particles, and the possibility of traumatic injuries, all of which can induce occupational hazard risks to autopsy workers, especially during the COVID-19 pandemic.Objectives: The first goal of this study was to explore the production of noise and bone dust emission, comparing an oscillating saw and a robotic autopsy saw during an autopsy. The second goal was to evaluate the performance of a new robotic autopsy method, used during skull opening. The third goal was to encourage mortuary workers to use robotic technology during the autopsy procedure to protect us away from occupational injuries as well as airborne infections.Materials and Methods: The experiments involved a comparison of noise levels and aerosol production during skull cutting between the oscillating saw and the robotic autopsy saw.Results: The results confirmed that noise production from the robotic autopsy saw was lower than the oscillating saw. However, the bone dust levels, produced by the robotic autopsy saw, were greater than the oscillating saw, but were not greater than the dust concentrations which were present before opening the skull.Conclusions: The use of a new robotic system might be an alternative choice for protecting against occupational damage among the healthcare workers. Further research might attempt to consider other healthcare problems which occur in the autopsy workplace and apply the robotic-assisted technology in autopsy surgery.

Novel Propulsion System for VTOL Aircraft Based on Cycloidal Rotors Coupled With Wings

Aircraft being capable of Vertical Take-off and Landing (VTOL) and hover are increasingly emerging in various critical and routine applications. Rescue missions in roads and environmental disasters, observance and monitoring-based carriers, surveillance and payload carriage in environments that require high maneuverability and controllability are just a few examples in which this type of aircraft is essential. Helicopters are the most typical aircraft in this kind, but concerning the thrusting mechanism, several alternatives are yet in hand. The tendency to equip aircraft with cycloidal rotors (shortly say, cyclorotors) as means of Vertical Take-Off and Landing thrusters has increased in recent years. These devices present several advantages such as considerably lower noise production and more stable hover and vertical displacements in comparison with conventional screw propellers as used in helicopters. In the present work a novel concept of propulsion system combining two cycloidal rotors with a pair-wing system is presented. A double wing assembly is designed to place in between the two cyclorotors on each side of the aircraft. The bottom wing is intended to divide the flow in two separate portions through the downwash region of the front cycloidal rotor. To improve the efficiency of this propulsion system, the implementation of plasma actuators in the pair-wing system will be experimentally studied. The concept behind this novel propulsion system is explained and numerical and experimental results, that support its operation concept, are presented.

Acoustic Emissions from Wind Turbine Blades

Research on broadband aerodynamic noise from wind turbine blades is becoming important in several countries. In this work, computer simulation of acoustic emissions from wind turbine blades are predicted using quasi empirical model for a three-bladed horizontal axis 3 MW turbine with blade length ~47 m. Sound power levels are investigated for source and receiver height of 80 m and 2 m above ground and located at a distance equal to total turbine height. The results are validated using existing experimental data for Siemens SWT-2.3 MW turbine having blade length of 47 m, as well as with 2.5 MW turbine. Aerofoil self-noise mechanisms are discussed in present work and results are demonstrated for wind speed of 8 m/s. Overall sound power levels for 3 MW turbine showed good agreements with the existing experiment data obtained for SWT-2.3 MW turbine. Noise map of single source sound power level, dBA of an isolated blade segment located at 75 %R for single blade is illustrated for wind speed of 8 m/s. The results demonstrated that most of the noise production occurred from outboard section of blade and for blade azimuth positions between 80° and 170°.