Combinations of covariance selections for graphical modelling.

We explore the possibility of composing the results of a fixed number of Gaussian graphical model selections on some partially overlapping variables. This appears to be an useful approach in all the research areas where a large amount of data from different sources and types of experiments is available. Therefore the focus is in binding together information coming from heterogeneous studies to improve the understanding of a particular phenomenon of interest. The proposed approach relies on numerical results on artificial and real data

La formació històrica per a l’ensenyament de les matemàtiques

L’ensenyament i aprenentatge de la història de les matemàtiques pot millorar la formació integral de l’alumnat. Els contextos històrics en les matemàtiques transmeten als alumnes una percepció de la matemàtica com a ciència útil, dinàmica, humana, interdisciplinària i heurística. En aquesta comunicació mostrarem a través de la programació d’un curs d’història de la ciència els objectius que cal assolir. La formació del professorat ha de contemplar que aquest conegui les fonts en què es basa el coneixement del passat, reconegui els canvis més significatius de la disciplina de Matemàtiques i reflexionin sobre el desenvolupament del pensament matemàtic i les transformacions de la filosofia natural. Finalment, cal assenyalar en aquesta formació la importància de les relacions socioculturals de les matemàtiques

CIR Modulation of the X-ray Flux from the O7.5 III(n)((f)) Star xi Persei?

We analyze a 162 ks HETG Chandra observation of the O7.5 III(n)((f)) star xi Per, together with contemporaneous H alpha observations. The X-ray spectrum of this star is similar to other single O stars, and not pathological in any way. Its UV wind lines are known to display cyclical time variability, with a period of 2.086 days, which is thought to be associated with co-rotating interaction regions (CIRs). We examine the Chandra and H alpha data for variability on this time scale. We find that the X-rays vary by about 15% over the course of the observations and that this variability is out of phase with variable absorption on the blue wing of the H alpha profiles (assumed to be a surrogate for the UV absorption associated with CIRs). While not conclusive, both sets of data are consistent with models where the CIRs are either a source of X-rays or modulate them.Comment: Accepted by MNRAS. 9 pages, 9 figure

NCERA-101 Station Report from Kennedy Space Center, FL, USA

This is our annual report to the North Central Extension Research Activity, which is affiliated with the USDA and Land Grant University Agricultural Experiment Stations. I have been a member of this committee for 25 years. The presentation will be given by Dr. Gioia Massa, Kennedy Space Cente

Vegetable Production Systems Component Tests

As long-term spaceflight missions become ever more imminent, astronaut nutrition and diet require further investigation and development. Dehydrated or stabilized food sources are currently used for spaceflight, but growing fresh produce aboard spacecraft can potentially supplement the astronauts diets. Further, having astronauts work with plants while in space can provide psychological benefits by serving as a tangible passage of time and representing a living component aboard an otherwise mechanical environment. As spaceflight duration will lengthen as missions head back to the Moon and to Mars, having the ability and knowledge to grow fresh produce will become even more vital. The following experiments were conducted in the late summer and fall of 2018. The purpose of these studies were to examine potential off-gas from a system component that could potentially inhibit plant germination, optimizing lighting methods and protocol for mizuna production, determining a fertilizer method that best promotes healthy mizuna yields, and troubleshooting tomato production for the next generation of the Vegetable Production System

Spatial linear stability of a hypersonic shear layer with nonequilibrium thermochemistry

We examine the spatial linear stability of a shear layer in a hypervelocity flow where high temperature effects such as chemical dissociation and vibrational excitation are present. A shock triple point is used to generate a free shear layer in a model problem which also occurs in several aerodynamic applications such as shock-boundary layer interaction. Calculations were performed using a state-resolved, three-dimensional forced harmonic oscillator thermochemical model. An extension of an existing molecular-molecular energy transfer rate model to higher collisional energies is presented and verified. Nonequilibrium model results are compared with calculations assuming equilibrium and frozen flows over a range of (frozen) convective Mach numbers from 0.341 to 1.707. A substantial difference in two- and three-dimensional perturbation growth rates is observed among the three models.Thermochemical nonequilibrium has a destabilizing effect on shear-layer perturbations for all convective Mach numbers considered. The analysis considers the evolution of the molecular vibrational quantum distribution during the instability growth by examining the perturbation eigenfunctions. Oxygen and nitrogen preserve a Boltzmann distribution of vibrational energy, while nitric oxide shows a significant deviation from equilibrium. The difference between translational and vibrational temperature eigenfunctions increases with the convective Mach number.Dissociation and vibration transfer effects on the perturbation evolution remain closely correlated at all convective Mach numbers

PN fast winds: Temporal structure and stellar rotation

To diagnose the time-variable structure in the fast winds of central stars of planetary nebulae (CSPN), we present an analysis of P Cygni line profiles in FUSE satellite far-UV spectroscopic data. Archival spectra are retrieved to form time-series datasets for the H-rich CSPN NGC 6826, IC 418, IC 2149, IC 4593 and NGC 6543. Despite limitations due to the fragmented sampling of the time-series, we demonstrate that in all 5 CSPN the UV resonance lines are variable primarily due to the occurrence of blueward migrating discrete absorption components (DACs). Empirical (SEI) line-synthesis modelling is used to determine the range of fluctuations in radial optical depth, which are assigned to the temporal changes in large-scale wind structures. We argue that DACs are common in CSPN winds, and their empirical properties are akin to those of similar structures seen in the absorption troughs of massive OB stars. Constraints on PN central star rotation velocities are derived from Fast-Fourier Transform analysis of photospheric lines for our target stars. Favouring the causal role of co-rotating interaction regions, we explore connections between normalised DAC accelerations and rotation rates of PN central stars and O stars. The comparative properties suggest that the same physical mechanism is acting to generate large-scale structure in the line-driven winds in the two different settings.Comment: Accepted for publication in MNRAS; 10 pages, 5 figure

Triple-point shear layers in gaseous detonation waves

Recent experiments have shown intriguing regions of intense luminescence or ‘hotspots’ in the vicinity of triple-point shear layers in propagating gaseous detonation waves. Localized explosions have also been observed to develop in these fronts. These features were observed in higher effective activation energy mixtures, but not in lower effective activation energy mixtures. The increased lead shock oscillation through a cell cycle in higher activation energy mixtures may result in a significantly increased disparity in the induction time on either side of the triple-point shear layer, and thus an enhanced mixing between reacted and non-reacted streams supported by Kelvin–Helmholtz instability. The relation between the shear-layer instability and the mixture effective activation energy is analysed by carrying out a spatial linear stability study for three mixtures with different activation energies and injection conditions that correspond to the experimental conditions. The role of vortical structures associated with Kelvin–Helmholtz instability in the formation of localized ignition is investigated by performing two-dimensional Navier–Stokes simulations with detailed chemical kinetics and transport. In the low activation energy mixture, large-scale vortical structures are observed to occur downstream of the induction distance; these structures do not have a noticeable effect on the reaction. In higher effective activation energy mixtures, a thin transverse ignition front develops near the interface between the two gas streams and results in a combustion structure decoupled from the entrainment region. The decoupling leads to attenuation of the instability growth rate when compared to frozen calculations, and a reduced heat release in the high vorticity region. The analysis indicates the instability plays a modest role in ignition events for high activation energy mixtures. The formation of localized explosions observed in high activation energy systems is instead linked to the impossibility of a one-dimensional reactive combustion wave supported by the injection conditions. In the absence of curvature effects and stream-tube divergence, a system of shock waves is formed which spreads the ignition to the cold gas stream