ClimbAR - An Arkansas Rock Climbing Documentary

The goal of this thesis project, ‘ClimbAR’ - a rock climbing documentary - is to tell the story of a fringe sport/outdoor activity in the state of Arkansas. The history of the sport has been passed down primarily by word of mouth and contained within a small, tight knit group of Arkansas rock climbers since its humble beginnings in the 1980s. Though many of the original climbers in the state have since moved on, a new generation of adventurers have taken the reins. This film focuses on the newest generation of Arkansas rock climbers. Like many climbers in the state, this story uses Cole Fennel’s guidebooks, “Rock Climbing Arkansas” Vol. I & II, to more accurately portray the wide variety of rock climbing locations in the Ozarks

A multidimensional perspective on microbial interactions

Beyond being simply positive or negative, beneficial or inhibitory, microbial interactions can involve a diverse set of mechanisms, dependencies and dynamical properties. These more nuanced features have been described in great detail for some specific types of interactions, (e.g. pairwise metabolic cross-feeding, quorum sensing or antibiotic killing), often with the use of quantitative measurements and insight derived from modeling. With a growing understanding of the composition and dynamics of complex microbial communities for human health and other applications, we face the challenge of integrating information about these different interactions into comprehensive quantitative frameworks. Here, we review the literature on a wide set of microbial interactions, and explore the potential value of a formal categorization based on multidimensional vectors of attributes. We propose that such an encoding can facilitate systematic, direct comparisons of interaction mechanisms and dependencies, and we discuss the relevance of an atlas of interactions for future modeling and rational design efforts.R01 GM121950 - NIGMS NIH HHSPublished versio

Collision rates in the present-day Kuiper Belt and Centaur Regions: Applications to surface activation and modification on Comets, Kuiper Belt Objects, Centaurs, and Pluto-Charon

We extend previous results showing that the surfaces of Edgeworth-Kuiper Belt objects are not primordial and have been moderately to heavily reworked by collisions. Objects smaller than about $r = 2.5$ km have collisional disruption lifetimes less than 3.5 Gyr in the present-day collisional environment and have been heavily damaged in their interiors by large collisions. In the 30--50 AU region, impacts of 1 km radius comets onto individual 100 km radius objects occur on $7\times10^7$--$4\times10^8$ yr timescales, cratering the surfaces of the larger objects with $\sim$8--54 craters 6 km in diameter over 3.5 Gyr. Collision time scales for impacts of 4 meter radius projectiles onto 1 km radius comets range from 3--5 $\times 10^7$ yr. The cumulative fraction of the surface area of 1 and 100 km radius objects cratered by projectiles with radii larger than 4 m ranges from a few to a few tens percent over 3.5 Gyr. The flux of EKO projectiles onto Pluto and Charon is also calculated and is found to be $\sim$3--5 times that of previous estimates. Our impact model is also applied to Centaur objects in the 5--30 AU region. We find the collisional/cratering histories of Centaurs are dominated by the time spent in the Edgeworth-Kuiper Belt rather than the time spent on planet-crossing orbits. Hence, the predominant surface activity of Centaur objects like Chiron is almost certainly not impact-induced.Comment: 17 pages, 8 figures. Icarus, 2000, in pres

Collisional evolution in the Vulcanoid region: Implications for present-day population constraints

We explore the effects of collisional evolution on putative Vulcanoid ensembles in the region between 0.06 and 0.21 AU from the Sun, in order to constrain the probable population density and population structure of this region today. Dynamical studies have shown that the Vulcanoid Zone (VZ) could be populated. However, we find that the frequency and energetics of collisional evolution this close to the Sun, coupled with the efficient radiation transport of small debris out of this region, together conspire to create an active and highly intensive collisional environment which depletes any very significant population of rocky bodies placed in it, unless the bodies exhibit orbits that are circular to ~10^-3 or less, or highly lossy mechanical properties that correspond to a fraction of impact energy significantly less than 10% being imparted to ejecta. The most favorable locale for residual bodies to survive in this region is in highly circular orbits near the outer edge of the dynamically stable Vulcanoid Zone (i.e., near 0.2 AU), where collisional evolution and radiation transport of small bodies and debris proceed most slowly. If the mean random orbital eccentricity in this region exceeds ~10^-3, then our work suggests it is unlikely that more than a few hundred objects with radii larger than 1 km will be found in the entire VZ; assuming the largest objects have a radius of 30 km, then the total mass of bodies in the VZ down to 0.1 km radii is likely to be no more than ~10^-6Mearth, <10^-3 the mass of the asteroid belt. Despite the dynamical stability of large objects in this region (Evans & Tabachnik 1999), it is plausible that the entire region is virtually empty of km-scale and larger objects.Comment: text plus 7 .ps figures, gzipped. Icarus, 2000, in pres

Status of MICE

Muon ionization cooling is the only practical method for preparing high-brilliance beams needed for a neutrino factory or muon collider. The muon ionization cooling experiment (MICE) under development at the Rutherford Appleton Laboratory comprises a dedicated beamline to generate a range of input emittance and momentum, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. A first measurement of emittance is performed in the upstream magnetic spectrometer with a scintillating-fiber tracker. A cooling cell will then follow, alternating energy loss in liquid hydrogen with RF acceleration. A second spectrometer identical to the first and a particle identification system will measure the outgoing emittance. Plans for measurements of emittance and cooling are described.Comment: Poster presented at ICHEP08 Conference, Philadelphia, USA, July 2008. 3 pages, 3 figure

The Significance of Federal Taxes as Automatic Stabilizers

Using the TAXSIM model for the period 1962-95, we consider the federal tax system's impact as an automatic stabilizer. Despite the many changes in the tax system, there has been relatively little change in its role as an automatic stabilizer. We estimate that individual federal taxes offset perhaps as much as 8 percent of initial shocks to GDP. We also suggest that the progressive income tax may help to stabilize output via its effect on the supply of labor, an additional effect that may even be of similar magnitude to the more traditional path of stabilization through aggregate demand.

Using the regression discontinuity design with implicit partitions: The impacts of comunidades solidarias rurales on schooling in El Salvador

Regression discontinuity design (RDD) is a useful tool for evaluating programs when a single variable is used to determine program eligibility. RDD has also been used to evaluate programs when eligibility is based on multiple variables that have been aggregated into a single index using explicit, often arbitrary, weights. In this paper, we show that under specific conditions, regression discontinuity can be used in instances when more than one variable is used to determine eligibility, without assigning explicit weights to map those variables into a single measure.Regression discontinuity design, partitioned cluster analysis, Schooling, Impact evaluation,

Costless metabolic secretions as drivers of interspecies interactions in microbial ecosystems

Metabolic exchange mediates interactions among microbes, helping explain diversity in microbial communities. As these interactions often involve a fitness cost, it is unclear how stable cooperation can emerge. Here we use genome-scale metabolic models to investigate whether the release of “costless” metabolites (i.e. those that cause no fitness cost to the producer), can be a prominent driver of intermicrobial interactions. By performing over 2 million pairwise growth simulations of 24 species in a combinatorial assortment of environments, we identify a large space of metabolites that can be secreted without cost, thus generating ample cross-feeding opportunities. In addition to providing an atlas of putative interactions, we show that anoxic conditions can promote mutualisms by providing more opportunities for exchange of costless metabolites, resulting in an overrepresentation of stable ecological network motifs. These results may help identify interaction patterns in natural communities and inform the design of synthetic microbial consortia.We thank Dr. Niels Klitgord for pioneering ideas that inspired launch of this work. We are also grateful to David Bernstein, Joshua E. Goldford, Meghan Thommes, Demetrius DiMucci, and all members of the Segre Lab for helpful discussions. A.R.P. is supported by a National Academies of Sciences, Engineering, and Medicine Ford Foundation Predoctoral Fellowship and a Howard Hughes Medical Institute Gilliam Fellowship. This work was supported by funding from the Defense Advanced Research Projects Agency (purchase request no. HR0011515303, contract no. HR0011-15-C-0091), the U.S. Department of Energy (grants DE-SC0004962 and DE-SC0012627), the NIH (grants 5R01DE024468, R01GM121950, and Sub_P30DK036836_P&F), the National Science Foundation (grants 1457695 and NSFOCE-BSF 1635070), MURI Grant W911NF-12-1-0390, the Human Frontiers Science Program (grant RGP0020/2016), and the Boston University Inter-disciplinary Biomedical Research Office. (National Academies of Sciences, Engineering, and Medicine Ford Foundation Predoctoral Fellowship; Howard Hughes Medical Institute Gilliam Fellowship; HR0011515303 - Defense Advanced Research Projects Agency; HR0011-15-C-0091 - Defense Advanced Research Projects Agency; DE-SC0004962 - U.S. Department of Energy; DE-SC0012627 - U.S. Department of Energy; 5R01DE024468 - NIH; R01GM121950 - NIH; Sub_P30DK036836_PF - NIH; 1457695 - National Science Foundation; NSFOCE-BSF 1635070 - National Science Foundation; W911NF-12-1-0390 - MURI Grant; RGP0020/2016 - Human Frontiers Science Program; Boston University Inter-disciplinary Biomedical Research Office)Published versio