Detect-and-Avoid: Flight Test 6 Scripted Encounters Data Analysis

The Unmanned Aircraft System (UAS) in the National Airspace System (NAS) project conducted Flight Test 6 (FT6) in 2019. The ultimate goal of this flight test was to produce data to inform RTCA SC-228's Phase II Minimum Operational Performance Standards (MOPS) for Detect and Avoid (DAA) and Low Size, Weight, and Power Sensors. This report documents the analysis of scripted encounters' data. Scripted encounters own were analyzed and categorized based on the outcome of alert, maneuver guidance, and effectiveness of pilots' maneuver in resolving conflicts. Results indicate that UAS pilots' decisions as well as intruder maneuvers are leading factors that contribute to ineffective DAA maneuvers. Results also show that adding buffers to the DAA's suggested minimum turn angle improves effectiveness of the DAA maneuvers

Statistically Preserved Structures and Anomalous Scaling in Turbulent Active Scalar Advection

The anomalous scaling of correlation functions in the turbulent statistics of active scalars (like temperature in turbulent convection) is understood in terms of an auxiliary passive scalar which is advected by the same turbulent velocity field. While the odd-order correlation functions of the active and passive fields differ, we propose that the even-order correlation functions are the same to leading order (up to a trivial multiplicative factor). The leading correlation functions are statistically preserved structures of the passive scalar decaying problem, and therefore universality of the scaling exponents of the even-order correlations of the active scalar is demonstrated.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Interstellar solid hydrogen

We consider the possibility that solid molecular hydrogen is present in interstellar space. If so cosmic-rays and energetic photons cause ionization in the solid leading to the formation of H+6. This ion is not produced by gas-phase reactions and its radiative transitions therefore provide a signature of solid H2 in the astrophysical context. The vibrational transitions of H+6 are yet to be observed in the laboratory, but we have characterized them in a quantum-theoretical treatment of the molecule; our calculations include anharmonic corrections, which are large. Here we report on those calculations and compare our results with astronomical data. In addition to the H+6 isotopomer, we focus on the deuterated species (HD)+3 which is expected to dominate at low ionization rates as a result of isotopic condensation reactions. We can reliably predict the frequencies of the fundamental bands for five modes of vibration. For (HD)+3 all of these are found to lie close to some of the strongest of the pervasive mid-infrared astronomical emission bands, making it difficult to exclude hydrogen precipitates on observational grounds. By the same token these results suggest that (HD)+3 could be the carrier of the observed bands. We consider this possibility within the broader picture of interstellar medium photo-processes and we conclude that solid hydrogen may indeed be abundant in astrophysical environments

Active and Passive Fields in Turbulent Transport: the Role of Statistically Preserved Structures

We have recently proposed that the statistics of active fields (which affect the velocity field itself) in well-developed turbulence are also dominated by the Statistically Preserved Structures of auxiliary passive fields which are advected by the same velocity field. The Statistically Preserved Structures are eigenmodes of eigenvalue 1 of an appropriate propagator of the decaying (unforced) passive field, or equivalently, the zero modes of a related operator. In this paper we investigate further this surprising finding via two examples, one akin to turbulent convection in which the temperature is the active scalar, and the other akin to magneto-hydrodynamics in which the magnetic field is the active vector. In the first example, all the even correlation functions of the active and passive fields exhibit identical scaling behavior. The second example appears at first sight to be a counter-example: the statistical objects of the active and passive fields have entirely different scaling exponents. We demonstrate nevertheless that the Statistically Preserved Structures of the passive vector dominate again the statistics of the active field, except that due to a dynamical conservation law the amplitude of the leading zero mode cancels exactly. The active vector is then dominated by the sub-leading zero mode of the passive vector. Our work thus suggests that the statistical properties of active fields in turbulence can be understood with the same generality as those of passive fields.Comment: 13 pages, 13 figures, submitted to Phys. Rev.

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on spark plasma sintering of transparent alumina

A slurry of a-Al2O3 was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150-500 wt ppm and then freeze-dried to produce nanosized doped powder (~150 nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering emperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al2O3 was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization

Vortex Lines in Topological Insulator-Superconductor Heterostructures

3D topological insulator/s-wave superconductor heterostructures have been predicted as candidate systems for the observation of Majorana fermions in the presence of superconducting vortices. In these systems, Majorana fermions are expected to form at the interface between the topological insulator and the superconductor while the bulk plays no role. Yet the bulk of a 3D topological insulator penetrated by a magnetic flux is not inert and can gap the surface vortex modes destroying their Majorana nature. In this work, we demonstrate the circumstances under which only the surface physics is important and when the bulk physics plays an important role in the location and energy of the Majorana modes.Comment: 10 pages, 4 figure

Cosmological Spectral Deconvolution

One of the main goals of modern observational cosmology is to map the large scale structure of the Universe. A potentially powerful approach for doing this would be to exploit three-dimensional spectral maps, i.e. the specific intensity of extragalactic light as a function of wavelength and direction on the sky, to measure spatial variations in the total extragalactic light emission and use these as a tracer of the clustering of matter. A main challenge is that the observed intensity as a function of wavelength is a convolution of the source luminosity density with the rest-frame spectral energy distribution. In this paper, we introduce the method of spectral deconvolution as a way to invert this convolution and extract the clustering information. We show how one can use observations of the mean and angular fluctuations of extragalactic light as a function of wavelength, assuming statistical isotropy, to reconstruct jointly the rest-frame spectral energy distribution of the sources and the source spatial density fluctuations. This method is more general than the well known line mapping technique as it does not rely on spectral lines in the emitted spectra. After introducing the general formalism, we discuss its implementation and limitations. This formal paper sets the stage for future more practical studies

Effect of amount of doping agent on sintering, microstructure and optical properties of Zr- and La-doped alumina sintered by SPS

SPS-produced α-alumina samples are prepared from powders doped with different amounts of Zr4+ and La3+ cations. Zr4+ cations segregate at grain boundaries. m-ZrO2 particles are formed at 570 but not at 280 cat ppm. A β-alumina LaAl11O18 structure is found at 310 cat ppm when the lanthanum grain boundary solubility limit is exceeded (∼200 cat ppm). 100 cat ppm La is sufficient to block the diffusion path across grain boundaries and inhibit grain growth. Both doping cations disturb the grain boundary diffusion whatever their amount. They delay the densification at higher temperatures while limiting grain growth. The real in-line transmittance (RIT) of α-alumina is improved due to the reduced grain size. Nevertheless, increasing the cation amount leads to an increase in porosity or even the formation of secondary phase particles, both detrimental for optical properties. Finally, optimised amounts of cation of 200 and 150 cat ppm are found for La- and Zr-doped alumina, respectively