Influence of aspect ratio, plasma viscosity, and radial position of the resonant surfaces on the plasmoid formation in the low resistivity plasma in Tokamak

In the present paper, we systematically investigate the nonlinear evolution of the resistive kink mode in the low resistivity plasma in Tokamak geometry. We find that the aspect ratio of the initial equilibrium can significantly influence the critical resistivity for plasmoid formation. With the aspect ratio of 3/1, the critical resistivity can be one magnitude larger than that in cylindrical geometry due to the strong mode-mode coupling. We also find that the critical resistivity for plasmoid formation decreases with increasing plasma viscosity in the moderately low resistivity regime. Due to the geometry of Tokamaks, the critical resistivity for plasmoid formation increases with the increasing radial location of the resonant surface.

A technique for determining three-dimensional storm cloud top locations using stereo optical lightning pulses observed from orbit

We have developed a technique to estimate the three-dimensional (3D) location of lightning optical pulses based on the stereo view of common lightning pulses from two different orbital instruments. The technique only requires the satellite position and the look vector to the lightning optical source. An example dataset of the Geostationary Lightning Mappers (GLMs) on GOES-16 and GOES-17 from 10 June 2019 is used to illustrate the technique. For this dataset, we find that the values for the stereo determination of cloud top altitudes are on average lower by 740 m than the ones calculated from the lightning ellipsoid that is currently applied during geolocation. When we compare the locations to the Advanced Baseline Imager (ABI) Cloud Height Algorithm (ACHA), we find that our technique also produces slightly lower altitude values by 240 m. There is greater spread in our technique than either the lightning ellipsoid or the ABI cloud-top height that is likely due to the incorrect pairing of Groups between the two GLMs and the 8 to 14 km resolution in the Group locations. Based on GLM location errors derived from comparisons to ground truth sources, the uncertainty in the radial location determined by the stereo location technique is 5.2 km, while the altitude uncertainty is 4.0 km. The technique can be used to 3D map lightning or other optical sources such as bolides and other upper atmospheric optical phenomena from any two orbital sensors with overlapping fields of view.

Sustained Annulus Pressure Diagnostics in Offshore Wells by Multisensory Spectral Acoustics

The monitoring of sustainable annulus pressure (SAP) in offshore wells plays an important role in the development of an oil reservoir with a massive gas cap. The method of spectral noise logging and high-precision temperature logging used to identify SAP source presented in work (Shtun 2020) proved to be good in determining the intervals of gas movement, however, the method is limited in answers. The most significant limitation of the spectral noise logging method is associated with the impossibility based on power spectrum to distinguish the zones of gas flow in the annular space and gas inflow zones from reservoir contributing SAP. This information is critical for proper workover planning to eliminate SAP. This limitation relates to the fact that the amplitude and frequency of the resulting signal depend on not only the aperture of space fluid flow through and depend on the turbulence of the fluid flow. The paper describes a novel technology of multisensory passive acoustics of radial location that is designed to differentiate far and near acoustic sources in wells to accurately define the sources of SAP. The results of laboratory and field cases in offshore oil wells were presented in this paper as well as the comparison between single sensor spectral noise logging and multisensory passive acoustics of radial location answers was given at the end of the paper based on real case studies. As shown in the paper the described technology provides a more accurate determination of the source of SAP and the geometry of fluid movement in the near-wellbore zone.

Research on Tree Pith Location in Radial Direction Based on Terrestrial Laser Scanning

Obtaining the direction of a diameter line through the tree pith is the basis of effective sampling by a micro-drill resistance instrument. In order to implement non-destructive tree pith location in the radial direction, the geometric property of tree pith, the longest chord through the tree pith on the cross-section will bisect outer contour circumference, as first proposed and proven in this paper. Based on this property, a non-destructive tree pith radial location method based on terrestrial laser scanning was developed. The experiments of pith radial location were made on the tree discs and the error of location is less than 1.5% for cross-section shape closed to ellipse on four tree species. The geometric property and location method of the tree pith in this research would play an important role in studying the growth process of standing trees, obtaining processed wood properties, and estimating tree age.

$$ T\overline{T} $$ , black holes and negative strings

String theory on AdS3 has a solvable single-trace irrelevant deformation that is closely related to $$ T\overline{T} $$ T T ¯ . For one sign of the coupling, it leads to an asymptotically linear dilaton spacetime, and a corresponding Hagedorn spectrum. For the other, the resulting spacetime has a curvature singularity at a finite radial location, and an upper bound on the energies of states. Beyond the singularity, the signature of spacetime is flipped and there is an asymptotically linear dilaton boundary at infinity. We study the properties of black holes and fundamental strings in this spacetime, and find a sensible picture. The singularity does not give rise to a hard ultraviolet wall for excitations -one must include the region beyond it to understand the theory. The size of black holes diverges as their energy approaches the upper bound, as does the location of the singularity. Fundamental strings pass smoothly through the singularity, but if their energy is above the upper bound, their trajectories are singular. From the point of view of the boundary at infinity, this background can be thought of as a vacuum of Little String Theory which contains a large number of negative strings.

Testing Propeller Tip Modifications to Reduce Acoustic Noise Generation on a Quadcopter Propeller

If vertical lift vehicles are to operate near population centers, they must be both quiet and efficient. The goal of this research is to develop a propeller that is more efficient and generates less noise than a stock DJI Phantom 2 quadcopter propeller. Reducing the generated tip vortex was the main objective. After studying the literature, seven promising tip treatments were selected and applied to a stock DJI Phantom 2 propeller to reduce the tip vortex. Several different configurations were tested for each tip treatment to determine the rpm and required power to hold 0.7 lbf thrust, the static hover condition. For each test, operating at the hover condition, a radial traverse 1 in. behind the propeller permitted the measurement of the near field sound pressure level (SPL) to find the maximum SPL and its radial location. Several configurations tested resulted in 8–10 dBA reductions in SPL when compared to the stock propeller; however, these configurations also resulted in an unacceptable increase in the power required to achieve the desired thrust. The most promising tip treatment tested was the trailing edge (TE) notch at a radial location of 0.95 r/R with a double slot width and a double depth (DSDD). The DSDD configuration as tested reduced the SPL 7.2 dBA with an increase in power required of only 3.96% over the stock propeller. This tradeoff, while not the largest reduction in noise generation measured, had an acceptable power increase for the decrease in SPL achieved.