Conceptual development of a ground-based radio-beacon navigation system for use on the surface of the moon

A spread-spectrum radio-beacon navigation system for use on the lunar surface is described. The subjects discussed are principle of operation and specifications to include power requirements, operating frequencies, weight, size, and range

Accurate Noise Projection for Reduced Stochastic Epidemic Models

We consider a stochastic Susceptible-Exposed-Infected-Recovered (SEIR) epidemiological model. Through the use of a normal form coordinate transform, we are able to analytically derive the stochastic center manifold along with the associated, reduced set of stochastic evolution equations. The transformation correctly projects both the dynamics and the noise onto the center manifold. Therefore, the solution of this reduced stochastic dynamical system yields excellent agreement, both in amplitude and phase, with the solution of the original stochastic system for a temporal scale that is orders of magnitude longer than the typical relaxation time. This new method allows for improved time series prediction of the number of infectious cases when modeling the spread of disease in a population. Numerical solutions of the fluctuations of the SEIR model are considered in the infinite population limit using a Langevin equation approach, as well as in a finite population simulated as a Markov process.Comment: 38 pages, 10 figures, new title, Final revision to appear in Chao

Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos

We establish new dynamical constraints on the mass and abundance of compact objects in the halo of dwarf spheroidal galaxies. In order to preserve kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi dSph) against gravitational scattering, we place upper limits on the density of compact objects as a function of their assumed mass. The mass of the dark matter constituents cannot be larger than 1000 solar masses at a halo density in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario in which dark halo cores are formed by two-body relaxation processes. Our bounds on the fraction of dark matter in compact objects with masses >3000 solar masses improve those based on dynamical arguments in the Galactic halo. In particular, objects with masses $\sim 10^{5}$ solar masses can comprise no more than a halo mass fraction $\sim 0.01$. Better determinations of the velocity dispersion of old overdense regions in dSphs may result in more stringent constraints on the mass of halo objects. For illustration, if the preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed, compact objects with masses above $\sim 100$ solar masses could be excluded from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter

Switching barrier scaling near bifurcation points for non-Gaussian noise

We study noise-induced switching of a system close to bifurcation parameter values where the number of stable states changes. For non-Gaussian noise, the switching exponent, which gives the logarithm of the switching rate, displays a non-power-law dependence on the distance to the bifurcation point. This dependence is found for Poisson noise. Even weak additional Gaussian noise dominates switching sufficiently close to the bifurcation point, leading to a crossover in the behavior of the switching exponent

Synchrotron emitting Komissarov torus around naked singularities

From a theoretical perspective, matter accretion processes around compact objects are highly relevant as they serve as a natural laboratory to test general relativity in the strong field regime. This enables us to validate fundamental concepts such as the no-hair theorem, the cosmic censorship hypothesis, and the existence of alternative solutions to Einstein's equations that mimic the effects of black holes. In this study, we analyze the emission spectra of geometrically thick accretion disks, referred to as Polish doughnuts, around naked singularities described by the $q$-metric. To begin, we revisit the construction of equilibrium configurations of magnetized tori in this spacetime and evaluate the role of the deformation parameter over these configurations. Once we have systematically studied the disks in this spacetime, we use the \texttt{OSIRIS} code to perform a backward ray-tracing method, resulting in the first simulations of the intensity map and emission profiles of magnetized tori within this metric. Furthermore, we validate the effect of both the quadrupole moment and the angular momentum on observable quantities such as flux and intensity for optically thin and thick disks, since for values of $q < 0$, which correspond to objects with prolate deformation, and which in turn, are constructed with higher values of angular momentum, the emission spectrum exhibits higher intensity than that obtained for Schwarzschild's spacetime. Hence, we find a first differential feature that distinguishes tori formed around naked singularities from those around static black holes.Comment: 27 pages, 9 figures. Accepted for publication in Classical and Quantum Gravit

Bacterial and archaeal specific-predation in the North Atlantic Basin

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Seyler, L. M., Tuorto, S., McGuinness, L. R., Gong, D., & Kerkhof, L. J. Bacterial and archaeal specific-predation in the North Atlantic Basin. Frontiers in Marine Science, 6, (2019): 555, doi:10.3389/fmars.2019.00555.Stable isotope probing (SIP) was used to track prokaryotic and eukaryotic carbon uptake along a meridional transect (Long. 52°W) in the North Atlantic to assess if 13C-resource partitioning between bacteria and archaea and 13C-labeled eukaryotic predators could be detected. One-liter SIP microcosms were amended with 13C-acetate or 13C-urea and incubated for 48 h. Our data indicated archaea often outcompeted bacteria for 13C-urea while both archaea and bacteria could incorporate 13C-acetate. This 13C label could also be tracked into eukaryotic microbes. The largest number of 13C-labeled eukaryotic OTUs, and the greatest percentage of eukaryotic 13C signal, were observed in conjunction with both archaeal and bacterial 13C incorporation, suggesting that most eukaryotic predators do not distinguish between archaeal and bacterial prey. However, other 13C-eukaryotic OTUs were exclusively associated with either 13C-archaeal or 13C-bacterial OTUs. These archaeal-specific and bacterial-specific 13C-eukaryotic OTUs were related to known bactivorous predators including Ancyromonas, Amastigomonas, Cafeteria, and Caecitellus. Our SIP findings suggest both resource partitioning between bacteria and TACK (Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota) archaea and selective predation by eukaryotic predators. Determining the equalizing mechanisms for co-existence in the marine environment can help map predator/prey interactions to better estimate carbon flow in the deep ocean.This research was made possible through the support of the U.S Global Ocean Carbon and Repeat Hydrography Program and NSF Ocean Technology and Interdisciplinary Program grant (#1131022) to LK