Mars Encounters cause fresh surfaces on some near-Earth asteroids

All airless bodies are subject to the space environment, and spectral differences between asteroids and meteorites suggest many asteroids become weathered on very short (<1My) timescales. The spectra of some asteroids, particularly Q-types, indicate surfaces that appear young and fresh, implying they have been recently been exposed. Previous work found that Earth encounters were the dominant freshening mechanism and could be responsible for all near-Earth object (NEO) Q-types. In this work we increase the known NEO Q-type sample of by a factor of three. We present the orbital distributions of 64 Q-type near-Earth asteroids, and seek to determine the dominant mechanisms for refreshing their surfaces. Our sample reveals two important results: i) the relatively steady fraction of Q-types with increasing semi-major axis and ii) the existence of Q-type near-Earth asteroids with Minimum Orbit Intersection Distances (MOID) that do not have orbit solutions that cross Earth. Both of these are evidence that Earth-crossing is not the only scenario by which NEO Q-types are freshened. The high Earth-MOID asteroids represent 10% of the Q-type population and all are in Amor orbits. While surface refreshing could also be caused by Main Belt collisions or mass shedding from YORP spinup, all high Earth-MOID Q-types have the possibility of encounters with Mars indicating Mars could be responsible for a significant fraction of NEOs with fresh surfaces.Comment: Accepted for publication in Icarus -- 14 pages, 8 figures, 1 table, 2 appendice

Software and methods for oligonucleotide and cDNA array data analysis.

Two HTML-based programs were developed to analyze and filter gene-expression data: 'Bullfrog' for Affymetrix oligonucleotide arrays and 'Spot' for custom cDNA arrays. The programs provide intuitive data-filtering tools through an easy-to-use interface. A background subtraction and normalization program for cDNA arrays was also built that provides an informative summary report with data-quality assessments. These programs are freeware to aid in the analysis of gene-expression results and facilitate the search for genes responsible for interesting biological processes and phenotypes

From Rice Fields to Duck Marshes: Sport Hunters and Environmental Change on the South Carolina Coast, 1890–1950

In part because some historians are ethically opposed to their avocation, sport hunters of the Gilded Age and Progressive Era are an understudied group. As environmental actors, they have been virtually ignored. Based on the biological traits of their quarry, one particular subset of sportsmen, waterfowl hunters, were especially disposed to manipulating the environment in which they hunted. Their efforts to attract migratory waterfowl to privately owned wetlands through habitat management, which started nearly a half-century before federal engineers and biologists undertook similar work on the national wildlife refuges in the 1930s, were pioneering. By the midpoint of the twentieth century, sportsmen were managing several million acres of wetlands in the United States as waterfowl habitat. In areas with high concentrations of duck-shooting preserves, sportsmen’s management activities could alter the regional ecology. Strong evidence of duck hunters effecting widespread environmental change comes from South Carolina, where they purchased unprofitable rice plantations around the turn of the twentieth century and converted them to shooting preserves by employing a mixture of old and new approaches to wetland use. Initially, they carried on traditional agricultural practices and retained much of the ecological integrity of the rice plantations. Later, though, after adopting modern waterfowl-management techniques that sportsmen were using with good results in other parts of the country, they altered the ecology of the plantations by introducing new species of plants and reclaiming tidal impoundments. Managed duck marshes, artificial ecosystems created by the sportsmen, became a dominant feature of South Carolina’s coastal wetlandscape by the mid-twentieth century. At this point, hunters in South Carolina and elsewhere began passing on responsibility for managing waterfowl habitat to wildlife biologists

Shareholder Returns from Supplying Trade Credit

We examine shareholder wealth implications of supplying financing to customers. Robust results demonstrate that excess returns and trade receivables are directly and significantly related. Further evidence indicates the value of receivables is higher for suppliers with stronger motives relating to operating and contracting costs. The results also suggest a discounted value of receivables for financially unconstrained firms. Overall, we conclude that investors recognize trade credit as an effective instrument in mitigating frictions hindering sales growth. Thus, certain suppliers are positioned to derive increased strategic benefits from credit policy

Ground Reaction Forces Generated by Twenty-eight Hatha Yoga Postures

Int J Exerc Sci 5(2) : 114-126, 2012. Adherents claim many benefits from the practice of yoga, including promotion of bone health and prevention of osteoporosis. However, no known studies have investigated whether yoga enhances bone mineral density. Furthermore, none have estimated reaction forces applied by yoga practitioners. The purpose of this study was to collect ground reaction force (GRF) data on a variety of hatha yoga postures that would commonly be practiced in fitness centers or private studios. Twelve female and eight male volunteers performed a sequence of 28 hatha yoga postures while GRF data were collected with an AMTI strain-gauge force platform. The sequence was repeated six times by each study subject. Four dependent variables were studied: peak vertical GRF, mean vertical GRF, peak resultant GRF, and mean resultant GRF. Univariate analysis was used to identify mean values and standard deviations for the dependent variables. Peak vertical and resultant values of each posture were similar for all subjects, and standard deviations were small. Similarly, mean vertical and resultant values were similar for all subjects. This 28 posture yoga sequence produced low impact GRF applied to upper and lower extremities. Further research is warranted to determine whether these forces are sufficient to promote osteogenesis or maintain current bone health in yoga practitioners

A transit-timing variation study of the extrasolar planet TrES-3

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009.Includes bibliographical references (p. 105-106).Portable Occultation Eclipse and Transit System (POETS) detectors [7] mounted on the Wallace Astrophysical Observatory (WAO) 0.8m and NASA Infrared Telescope Facility (IRTF) 3m telescopes are used to observe five stellar transit events of the extrasolar planet TrES-3 [5]. Model light curves are fit to the five data sets and transit midtimes are determined. Midtimes obtained in this study, along with midtimes reported by Sozzetti et al. (2008) [8], are compared to the ephemeris of the planet. The transit timing variation (TTV) of each midtime is calculated. Based on these data the presence of a third body in the TrES-3 system cannot be determined. Mass and period of a hypothetical perturbing body are calculated for several illustrative cases.by Matthew Lockhart.S.M

Spheromak Merging And Field Reversed Configuration Formation At The Swarthmore Spheromak Experiment

The initial results of coaxial co- and counter-helicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are reported. In its new configuration, SSX is optimized to study field reversed configuration (FRC) formation and stability by counter-helicity spheromak merging. A pair of midplane coils magnetically restricts the merging process to determine how the stability of the resulting magnetic configuration depends upon the quantity of toroidal flux remaining from the initial spheromaks. The diagnostic set at SSX, featuring the capability of measuring up to 600 magnetic field components at 800 ns time resolution, permits detailed studies of the dynamic three-dimensional magnetic structures produced during these experiments. A compact array of magnetic probes examines the local reconnection process, while a distributed array of probes examines global magnetic structure. Counter-helicity merging produces a FRC that persists for several Alfvén times, although the oppositely directed toroidal field of the initial spheromaks does not completely annihilate. The m=1 (toroidal) mode dominates late in the evolution, and is consistent with the tilt instability. Co-helicity merging produces a single elongated spheromak that rapidly tilts