Long-Term Dynamics and the Orbital Inclinations of the Classical Kuiper Belt Objects

We numerically integrated the orbits of 1458 particles in the region of the classical Kuiper Belt (41 AU < a < 47 AU) to explore the role of dynamical instabilities in sculpting the inclination distribution of the classical Kuiper Belt Objects (KBOs). We find that the selective removal of low-inclination objects by overlapping secular resonances (nu_17 and nu_18) acts to raise the mean inclination of the surviving population of particles over 4 billion years of interactions with Jupiter, Saturn, Uranus and Neptune, though these long-term dynamical effects do not themselves appear to explain the discovery of KBOs with inclinations near 30 degrees. Our integrations also imply that after 3 billion years of interaction with the massive planets, high inclination KBOs more efficiently supply Neptune-encountering objects, the likely progenitors of short-period comets, Centaurs, and scattered KBOs. The secular resonances at low inclinations may indirectly cause this effect by weeding out objects unprotected by mean motion resonances during the first 3 billion years.Comment: 23 pages, including 10 figures. Accepted for publication in A

DEVELOPMENT OF A MOLDABLE COMPOSITE BONE GRAFT SUBSTITUTE RELEASING ANTIBACTERIAL AND OSTEOGENIC DRUGS

Large infected bone defects (IBD) are very complicated to treat due to their high variability; they often require multiple procedures. Bone autografts are the gold standard for treatment but have several drawbacks, such as a need for a second surgery site, limited grafting material, and donor site morbidity. The objective of this research was to develop a moldable synthetic bone grafting material capable of releasing both antimicrobial and osteogenic drugs over a clinically relevant time course for the treatment of IBDs. Current treatment methods for large IBDs require two separate procedures to treat the bone defect and the infection. This research sought to combine these two procedures into one implantable composite bone graft substitute for the treatment IBDs. To begin, the degradation and mechanical properties of the calcium sulfate (CS) based composite material were evaluated for different compositions. Next, the controlled drug release profiles from the composite was achieved by using a shell and core system incorporating poly(lactic-co-glycolic acid) microspheres (PLGAms). The release of vancomycin from the shell began immediately and continued over the course of 6 weeks, while the release of simvastatin from the core was delayed before being released over 4 weeks. Next, an infected, critically-sized rat femoral defect model was used to test different treatment methods with and without the composite bone graft substitute. Animals treated with locally released antibiotics had survivorship rates 24% higher than those treated with systemic antibiotics, and animals that received both antibiotics and an osteogenic drug had an increased amount of bone formation at 12 weeks compared to controls. Finally, several different anti-biofilm agents were evaluated for their ability to inhibit and/or disrupt the growth of Staphylococcus aureus (S. aureus) biofilms in vitro. Lysostaphin was the only drug investigated that was able to both inhibit and disrupt S. aureus biofilms. Furthermore, lysostaphin encapsulated into PLGAms maintained its bioactivity and may be useful for future incorporation into biofilm-combating materials. The bone grafting material developed here can be used to locally deliver drugs in a temporally controlled manner to reduce the number of procedures necessary for the treatment of complex IBDs

A Pan-STARRS1 Search for Planet Nine

We present a search for Planet Nine using the second data release of the Pan-STARRS1survey. We rule out the existence of a Planet Nine with the characteristics of that predicted in Brown & Batygin (2021) to a 50% completion depth of $V=21.5$. This survey, along with previous analyses of the Zwicky Transient Facility (ZTF) and Dark EnergySurvey (DES) data, rules out 78% of the Brown \& Batygin parameter space. Much of the remaining parameter space is at $V>21$ in regions near and in the area where the northern galactic plane crosses the ecliptic.Comment: AJ, in pres

Starvation Resistance is Associated with Developmentally Specified Changes in Sleep, Feeding and Metabolic Rate

Food shortage represents a primary challenge to survival, and animals have adapted diverse developmental, physiological and behavioral strategies to survive when food becomes unavailable. Starvation resistance is strongly influenced by ecological and evolutionary history, yet the genetic basis for the evolution of starvation resistance remains poorly understood. The fruit fly Drosophila melanogaster provides a powerful model for leveraging experimental evolution to investigate traits associated with starvation resistance. While control populations only live a few days without food, selection for starvation resistance results in populations that can survive weeks. We have previously shown that selection for starvation resistance results in increased sleep and reduced feeding in adult flies. Here, we investigate the ontogeny of starvation resistance-associated behavioral and metabolic phenotypes in these experimentally selected flies. We found that selection for starvation resistance resulted in delayed development and a reduction in metabolic rate in larvae that persisted into adulthood, suggesting that these traits may allow for the accumulation of energy stores and an increase in body size within these selected populations. In addition, we found that larval sleep was largely unaffected by starvation selection and that feeding increased during the late larval stages, suggesting that experimental evolution for starvation resistance produces developmentally specified changes in behavioral regulation. Together, these findings reveal a critical role for development in the evolution of starvation resistance and indicate that selection can selectively influence behavior during defined developmental time points

The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite

Hi'iaka is the larger outer satellite of the dwarf planet Haumea. Using relative photometry from the Hubble Space Telescope and Magellan and a phase dispersion minimization analysis, we have identified the rotation period of Hi'iaka to be ~9.8 hrs (double-peaked). This is ~120 times faster than its orbital period, creating new questions about the formation of this system and possible tidal evolution. The rapid rotation suggests that Hi'iaka could have a significant obliquity and spin precession that could be visible in light curves within a few years. We then turn to an investigation of what we learn about the (presently unclear) formation of the Haumea system and family based on this unexpectedly rapid rotation rate. We explore the importance of the initial semi-major axis and rotation period in tidal evolution theory and find they strongly influence the time required to despin to synchronous rotation, relevant to understanding a wide variety of satellite and binary systems. We find that despinning tides do not necessarily lead to synchronous spin periods for Hi'iaka, even if it formed near the Roche limit. Therefore the short rotation period of Hi'iaka does not rule out significant tidal evolution. Hi'iaka's spin period is also consistent with formation near its current location and spin up due to Haumea-centric impactors.Comment: 21 pages with 6 figures, to be published in The Astronomical Journa

Effective equations governing an active poroelastic medium

In this work we consider the spatial homogenization of a coupled transport and fluid-structure interaction model, to the end of deriving a system of effective equations describing the flow, elastic deformation, and transport in an active poroelastic medium. The `active' nature of the material results from a morphoelastic response to a chemical stimulant, in which the growth timescale is strongly separated from other elastic timescales. The resulting effective model is broadly relevant to the study of biological tissue growth, geophysical flows (e.g. swelling in coals and clays) and a wide range of industrial applications (e.g. absorbant hygiene products). The key contribution of this work is the derivation of a system of homogenized partial differential equations describing macroscale growth, coupled to transport of solute, that explicitly incorporates details of the structure and dynamics of the microscopic system, and, moreover, admits finite growth and deformation at the pore-scale. The resulting macroscale model comprises a Biot-type system, augmented with additional terms pertaining to growth, coupled to an advection-reaction-diffusion equation. The resultant system of effective equations is then compared to other recent models under a selection of appropriate simplifying asymptotic limits

The chameleon groups of Richard J. Thompson: automorphisms and dynamics

The automorphism groups of several of Thompson's countable groups of piecewise linear homeomorphisms of the line and circle are computed and it is shown that the outer automorphism groups of these groups are relatively small. These results can be interpreted as stability results for certain structures of PL functions on the circle. Machinery is developed to relate the structures on the circle to corresponding structures on the line

The Short Rotation Period of Nereid

We determine the period, p = 11.52 \pm 0.14 h, and a light curve peak-to-peak amplitude, a = 0.029 \pm 0.003 magnitudes, of the Neptunian irregular satellite Nereid. If the light curve variation is due to albedo variations across the surface, rather than solely to the shape of Nereid variations, the rotation period would be a factor of two shorter. In either case, such a rotation period and light curve amplitude, together with Nereid's orbital period, p=360.14 days, imply that Nereid is almost certainly in a regular rotation state, rather than the chaotic rotation state suggested by Schaefer and Schaefer (1988,2000) and Dobrovolskis (1995). Assuming that Nereid is perfectly spherical, the albedo variation is 3% across the observed surface. Assuming a uniform geometric albedo, the observed cross sectional area varies by 3%. We caution that the lightcurve found in this paper only sets limits on the combination of albedo and physical irregularity and that we cannot determine the orientation of Nereid's spin axis from our data.Comment: Accepted by ApJ Letters, 11 pages (incl. 1 figure