Adding Vision to a Quadrotor: A Design-Build-Test Adventure

Quadrotors are small and exceptionally agile vehicles with maneuverability that permits both indoor and outdoor flight. The vast majority of quadrotors are flown autonomously as drones or remotely by a human-operator. Applications of quadrotors range from commercial deliveries, to military and law reconnaissance as well as research tools for various fields. Our lab at Western Kentucky University built a quadrotor in 2013, and we have been exploring various modifications to refine its performance and various applications in which it could be productively employed. Recently, research has focused on the addition of a camera to add capabilities for first person view (FPV) piloting, photogrammetry, and real-time visual inspection. The new camera system was to be designed, built, and tested as part of a Faculty-Undergraduate Student Engagement (FUSE) grant. The system consists of a gimbal with pan/tilt capabilities has been designed and built via a Stratasys rapid prototyping machine The camera mount has met not only sizing and weight requirements, but also video transmission, recording, and live-viewing requirements. The design process has been successful in developing a pan/tilt camera mount for our lab’s quadrotor, and in creating countless learning outcomes as it produced multiple areas of research involving a variety of students with differing interests

Where do "red and dead" early-type void galaxies come from?

Void regions of the Universe offer a special environment for studying cosmology and galaxy formation, which may expose weaknesses in our understanding of these phenomena. Although galaxies in voids are observed to be predominately gas rich, star forming and blue, a sub-population of bright red void galaxies can also be found, whose star formation was shut down long ago. Are the same processes that quench star formation in denser regions of the Universe also at work in voids? We compare the luminosity function of void galaxies in the 2dF Galaxy Redshift Survey, to those from a galaxy formation model built on the Millennium Simulation. We show that a global star formation suppression mechanism in the form of low luminosity "radio mode" AGN heating is sufficient to reproduce the observed population of void early-types. Radio mode heating is environment independent other than its dependence on dark matter halo mass, where, above a critical mass threshold of approximately M_vir~10^12.5 M_sun, gas cooling onto the galaxy is suppressed and star formation subsequently fades. In the Millennium Simulation, the void halo mass function is shifted with respect to denser environments, but still maintains a high mass tail above this critical threshold. In such void halos, radio mode heating remains efficient and red galaxies are found; collectively these galaxies match the observed space density without any modification to the model. Consequently, galaxies living in vastly different large-scale environments but hosted by halos of similar mass are predicted to have similar properties, consistent with observations.Comment: 6 pages, 3 figures, accepted MNRA

Examination of Annular-Electrode Spark Discharges in Flowing Oxygen - An Overview

A parametric study of annular spark gaps, pressures, and spark discharges in flowing oxygen gas was performed with a Champion spark exciter. The range of the pressure-distance product for the experiment is from approximately 50 torr-cm to 2500 torr-cm. Measurements of breakdown voltage qualitatively trend with Paschen's curve. Spark duration remained constant until the pressure-distance product exceeded 200 torr-cm, and then steadily increased. The mean spark energy increases linearly with the pressure-distance on a log-log plot indicating that a definite power relationship exists. The distribution of sparks at low energies and low pressures is not Gaussian and has no dominant peaks. Moderate and high spark energies are bimodal, with the dominant mode near 80 mJ. As pressure increases, dominant and secondary modes approach the same probability

Examination of Annular-Electrode Spark Discharges in Flowing Oxygen Experimental Nuances

Microsecond sparks and the resulting plume of hot gas/plasma were examined against a parametric pressure-distance matrix. Schlieren imaging is used to capture the spatial and temporal location of spark discharge exhaust for two milliseconds. Low pressure and larger gap widths created the largest size and intensity signal for the spark-affected plumes. Experimental exit-plume velocities trend well with analytic predictions using a mean pressure between the chamber and atmospheric conditions. Due to the quadratic relation of the annulus area and gap width, larger gap width velocities are more accurately represented by analytic predictions using atmospheric pressure as the larger exit area restricts the flow less. The same pressure adjustment, when applied to breakdown voltages, improves data alignment with Paschens Curve

The Structure of Halos: Implications for Group and Cluster Cosmology

The dark matter halo mass function is a key repository of cosmological information over a wide range of mass scales, from individual galaxies to galaxy clusters. N-body simulations have established that the friends-of-friends (FOF) mass function has a universal form to a surprising level of accuracy (< 10%). The high-mass tail of the mass function is exponentially sensitive to the amplitude of the initial density perturbations, the mean matter density parameter, Omega_m, and to the dark energy controlled late-time evolution of the density field. Observed group and cluster masses, however, are usually stated in terms of a spherical overdensity (SO) mass which does not map simply to the FOF mass. Additionally, the widely used halo models of structure formation -- and halo occupancy distribution descriptions of galaxies within halos -- are often constructed exploiting the universal form of the FOF mass function. This again raises the question of whether FOF halos can be simply related to the notion of a spherical overdensity mass. By employing results from Monte Carlo realizations of ideal Navarro-Frenk-White (NFW) halos and N-body simulations, we study the relationship between the two definitions of halo mass. We find that the vast majority of halos (80-85%) in the mass-range 10^{12.5}-10^{15.5} M_sun/h indeed allow for an accurate mapping between the two definitions (~ 5%), but only if the halo concentrations are known. Nonisolated halos fall into two broad classes: those with complex substructure that are poor fits to NFW profiles and those ``bridged'' by the (isodensity-based)FOF algorithm. A closer investigation of the bridged halos reveals that the fraction of these halos and their satellite mass distribution is cosmology dependent. (abridged)Comment: Submitted to Ap

Mergers in Lambda-CDM: Uncertainties in Theoretical Predictions and Interpretations of the Merger Rate

Different methodologies lead to order-of-magnitude variations in predicted galaxy merger rates. We examine and quantify the dominant uncertainties. Different halo merger rates and subhalo 'destruction' rates agree to within a factor ~2 given proper care in definitions. If however (sub)halo masses are not appropriately defined or are under-resolved, the major merger rate can be dramatically suppressed. The dominant differences in galaxy merger rates owe to baryonic physics. Hydrodynamic simulations without feedback and older models that do not agree with the observed galaxy mass function propagate factor ~5 bias in the resulting merger rates. However, if the model matches the galaxy mass function, properties of central galaxies are sufficiently converged to give small differences in merger rates. But variations in baryonic physics of satellites also have dramatic effects. The known problem of satellite 'over-quenching' in most semi-analytic models (SAMs), whereby SAM satellites are too efficiently stripped of gas, could lead to order-of-magnitude under-estimates of merger rates for low-mass, gas-rich galaxies. Fixing the satellite properties to observations tends to predict higher merger rates, but with factor ~2 empirical uncertainties. Choice of mass ratio definition matters: at low masses, most true major mergers (in baryonic/dynamical galaxy mass) will appear to be minor mergers in their stellar or luminosity mass ratio. Observations and models using these criteria may underestimate major merger rates by factors ~5. Orbital parameters and gas fractions also introduce factor ~3 differences in amount of bulge formed by mergers, even for fixed mass ratio encounters.Comment: 32 Pages, 15 figures, accepted to ApJ (revised to match accepted version and correct Fig. 12

The clustering of the first galaxy halos

We explore the clustering properties of high redshift dark matter halos, focusing on halos massive enough to host early generations of stars or galaxies at redshift 10 and greater. Halos are extracted from an array of dark matter simulations able to resolve down to the "mini-halo" mass scale at redshifts as high as 30, thus encompassing the expected full mass range of halos capable of hosting luminous objects and sources of reionization. Halo clustering on large-scales agrees with the Sheth, Mo & Tormen halo bias relation within all our simulations, greatly extending the regime where large-scale clustering is confirmed to be "universal" at the 10-20% level (which means, for example, that 3sigma halos of cluster mass at z=0 have the same large-scale bias with respect to the mass distribution as 3sigma halos of galaxy mass at z=10). However, on small-scales, the clustering of our massive halos (> ~10^9 Msun/h) at these high redshifts is stronger than expected from comparisons with small-scale halo clustering extrapolated from lower redshifts. This implies "non-universality" in the scale-dependence of halo clustering, at least for the commonly used parameterizations of the scale-dependence of bias that we consider. We provide a fit for the scale-dependence of bias in our results. This study provides a basis for using extraordinarily high redshift galaxies (redshift ~10) as a probe of cosmology and galaxy formation at its earliest stages. We show also that mass and halo kinematics are strongly affected by finite simulation volumes. This suggests the potential for adverse affects on gas dynamics in hydrodynamic simulations of limited volumes, such as is typical in simulations of the formation of the "first stars", though further study is warranted.Comment: MNRAS accepte

Measures of Galaxy Environment - I. What is "Environment"?

The influence of a galaxy's environment on its evolution has been studied and compared extensively in the literature, although differing techniques are often used to define environment. Most methods fall into two broad groups: those that use nearest neighbours to probe the underlying density field and those that use fixed apertures. The differences between the two inhibit a clean comparison between analyses and leave open the possibility that, even with the same data, different properties are actually being measured. In this work we apply twenty published environment definitions to a common mock galaxy catalogue constrained to look like the local Universe. We find that nearest neighbour-based measures best probe the internal densities of high-mass haloes, while at low masses the inter-halo separation dominates and acts to smooth out local density variations. The resulting correlation also shows that nearest neighbour galaxy environment is largely independent of dark matter halo mass. Conversely, aperture-based methods that probe super-halo scales accurately identify high-density regions corresponding to high mass haloes. Both methods show how galaxies in dense environments tend to be redder, with the exception of the largest apertures, but these are the strongest at recovering the background dark matter environment. We also warn against using photometric redshifts to define environment in all but the densest regions. When considering environment there are two regimes: the 'local environment' internal to a halo best measured with nearest neighbour and 'large-scale environment' external to a halo best measured with apertures. This leads to the conclusion that there is no universal environment measure and the most suitable method depends on the scale being probed.Comment: 14 pages, 9 figures, 1 table, published in MNRA

Shaping 3D root system architecture

Plants are sessile organisms rooted in one place. The soil resources that plants require are often distributed in a highly heterogeneous pattern. To aid foraging, plants have evolved roots whose growth and development are highly responsive to soil signals. As a result, 3D root architecture is shaped by myriad environmental signals to ensure resource capture is optimised and unfavourable environments are avoided. The first signals sensed by newly germinating seeds — gravity and light — direct root growth into the soil to aid seedling establishment. Heterogeneous soil resources, such as water, nitrogen and phosphate, also act as signals that shape 3D root growth to optimise uptake. Root architecture is also modified through biotic interactions that include soil fungi and neighbouring plants. This developmental plasticity results in a ‘custom-made’ 3D root system that is best adapted to forage for resources in each soil environment that a plant colonises