Theoretical Prediction of the Reaction Probabilities of H, O, and OH Radicals on the Polypropylene Surface.

To determine the H-abstraction reaction probabilities of H/O/OH radicals with a polypropylene (PP) surface, a first-principles calculation was performed based on the DLPNO-CCSD(T)/CBS//M06-2X-D3/def-TZVP theory level. The PP chain model used in this study was 2,4,6-trimethylheptane. The rate constants of the H/O/OH radicals with the isolated PP chain model were calculated based on the conventional transition-state theory. By comparing the experimental values and considering the error factors and their compensation, it was concluded that the orders of magnitude of the predicted rate constants were accurate. The resulting rate constants were converted to reaction probabilities between the H/O/OH radicals and the PP surface. The method used in this study is applicable for obtaining theoretical values of surface reaction probabilities based on first-principles calculations. The calculation at the DLPNO-CCSD(T)/CBS theory level has high accuracy but consumes a large amount of computational resources. The study also demonstrated that the double-hybrid functionals, wB97x-2-D3(BJ) and rev-DSD-PBEP86-D3(BJ), with a 3-ζ or 4-ζ basis set, could reproduce the electronic energy values obtained from DLPNO-CCSD(T)/CBS while using only approximately 1/100 of the computational resources required by the latter under our computer configuration.

A Novel Method to Suppress the Effect of Subdiaphragmatic Activity in 99mTc Myocardial Perfusion SPECT and Evaluation of Its Usefulness Using a Myocardial Phantom.

Background: Smoothing in 99mTc myocardial perfusion single-photon emission computed tomography (SPECT) often increases myocardial artifacts due to subdiaphragmatic activity near the heart. To reduce these artifacts, we developed a new process flow, masking on unsmoothed images (MUS), that includes the extraction of the myocardium by masking before smoothing. Methods: This study evaluated the relationships between matrix sizes and distances to the subdiaphragmatic activity using the MUS method compared to conventional methods using a combination of image reconstruction methods (filtered back-projection [FBP] and ordered subset expectation maximization [OSEM]) with or without corrections (attenuation [AC], scatter [SC], and resolution recovery [RR]) using a myocardial phantom. The results were compared for two matrix sizes (pixel sizes) (128×128 [3.3 mm] and 64×64 [6.6 mm]); four subdiaphragmatic activity distances (5, 10, 15, and 20 mm); and three reconstruction methods (FBP without correction; OSEM with RR; and OSEM with AC, SC, and RR). Results: In the conventional method, increasing distance resulted in interference with myocardial perfusion SPECT evaluation however, the artifacts were less apparent when the MUS method was applied. The images converted to 64×64 did not show the same effect as the 128×128 images, even when RR was used. The MUS method was useful for acquisition at 128×128, along with the use of RR in the reconstruction process. Conclusion: MUS mitigated the effects of subdiaphragmatic activity on myocardial perfusion SPECT, particularly combined with 128×128 acquisitions and iterative reconstruction with RR.

Development of small high-voltage AC power supply for a dielectric barrier discharge plasma actuator.

A dielectric-barrier discharge plasma actuator (DBDPA) is a promising flow control device that can prevent flow separation around an airfoil using electrical discharges. Miniaturizing the DBDPA power supply remains a crucial technological challenge because its size and weight determine the performance of fluid devices equipped with this type of actuator. In this study, we propose a compact high-voltage AC power supply for a DBDPA intended for installation on small airplanes, including unmanned aerial vehicles. The power supply, which consists of a power supply board, a main control board, and a DC/AC converter board, is ∼110 g in weight. It can drive a 300-mm long DBDPA without any substantial voltage drop. The power consumption in standby remains below 1 W, and the maximum consumption during discharge in burst mode at a burst ratio of 5% is 24 W. The power supply uses a lithium-ion battery with a capacity of 1800 mA h, which allows continuous DBDPA operation for ∼1.5 h. An experiment was conducted in a wind tunnel using an airfoil model whose cross-section corresponds to that of an airfoil from a commercial glider airplane. Experimental results reveal that the surface pressure around the airfoil is modified by DBDPA operation, clearly demonstrating the effectiveness of the developed power supply for operating a DBDPA as a flow control device. The size and weight of the proposed power supply can be established as a benchmark to further miniaturize and optimize DBDPA power supplies.

Successively accelerated ionic wind with integrated dielectric-barrier-discharge plasma actuator for low-voltage operation.

Electrohydrodynamic (EHD) force is used for active control of fluid motion and for the generation of propulsive thrust by inducing ionic wind with no moving parts. We propose a method of successively generating and accelerating ionic wind induced by surface dielectric-barrier-discharge (DBD), referred to as a DBD plasma actuator with multiple electrodes. A conventional method fails to generate unidirectional ionic wind, due to the generation of a counter ionic-wind with the multiple electrodes DBD plasma actuator. However, unidirectional ionic wind can be obtained by designing an applied voltage waveform and electrode arrangement suitable for the unidirectional EHD force generation. Our results demonstrate that mutually enhanced EHD force is generated by using the multiple electrodes without generating counter ionic-wind and highlights the importance of controlling the dielectric surface charge to generate the strong ionic wind. The proposed method can induce strong ionic wind without a high-voltage power supply, which is typically expensive and heavy, and is suitable for equipping small unmanned aerial vehicles with a DBD plasma actuator for a drastic improvement in the aerodynamic performance.

Standing Helicon Wave Induced by a Rapidly Bent Magnetic Field in Plasmas.

An electron energy probability function and a rf magnetic field are measured in a rf hydrogen helicon source, where axial and transverse static magnetic fields are applied to the source by solenoids and to the diffusion chamber by filter magnets, respectively. It is demonstrated that the helicon wave is reflected by the rapidly bent magnetic field and the resultant standing wave heats the electrons between the source and the magnetic filter, while the electron cooling effect by the magnetic filter is maintained. It is interpreted that the standing wave is generated by the presence of a spatially localized change of a refractive index.

Axial momentum lost to a lateral wall of a helicon plasma source.

Momentum exerted to a lateral wall of a helicon plasma source is individually measured for argon, krypton, and xenon gases. A significant loss of the axial plasma momentum to the lateral wall, which has been assumed to be negligible, is experimentally identified when an axially asymmetric density profile is formed in the source. This indicates that the radially lost ions deliver not only the radial momentum but also the axial momentum to the lateral wall. The formation of the axial asymmetry causing the momentum loss is interpreted with competition between the magnetic field and neutral depletion effects.

Measurement of plasma momentum exerted on target by a small helicon plasma thruster and comparison with direct thrust measurement.

Momentum, i.e., force, exerted from a small helicon plasma thruster to a target plate is measured simultaneously with a direct thrust measurement using a thrust balance. The calibration coefficient relating a target displacement to a steady-state force is obtained by supplying a dc to a calibration coil mounted on the target, where a force acting to a small permanent magnet located near the coil is directly measured by using a load cell. As the force exerted by the plasma flow to the target plate is in good agreement with the directly measured thrust, the validity of the target technique is demonstrated under the present operating conditions, where the thruster is operated in steady-state. Furthermore, a calibration coefficient relating a swing amplitude of the target to an impulse bit is also obtained by pulsing the calibration coil current. The force exerted by the pulsed plasma, which is estimated from the measured impulse bit and the pulse width, is also in good agreement with that obtained for the steady-state operation; hence, the thrust assessment of the helicon plasma thruster by the target is validated for both the steady-state and pulsed operations.