Modeling the gravitational potential of a cosmological dark matter halo with stellar streams

Stellar streams result from the tidal disruption of satellites and star clusters as they orbit a host galaxy, and can be very sensitive probes of the gravitational potential of the host system. We select and study narrow stellar streams formed in a Milky-Way-like dark matter halo of the Aquarius suite of cosmological simulations, to determine if these streams can be used to constrain the present day characteristic parameters of the halo's gravitational potential. We find that orbits integrated in static spherical and triaxial NFW potentials both reproduce the locations and kinematics of the various streams reasonably well. To quantify this further, we determine the best-fit potential parameters by maximizing the amount of clustering of the stream stars in the space of their actions. We show that using our set of Aquarius streams, we recover a mass profile that is consistent with the spherically-averaged dark matter profile of the host halo, although we ignored both triaxiality and time evolution in the fit. This gives us confidence that such methods can be applied to the many streams that will be discovered by the Gaia mission to determine the gravitational potential of our Galaxy.Comment: ApJ sub

Action-space clustering of tidal streams to infer the Galactic potential

We present a new method for constraining the Milky Way halo gravitational potential by simultaneously fitting multiple tidal streams. This method requires full three-dimensional positions and velocities for all stars to be fit, but does not require identification of any specific stream or determination of stream membership for any star. We exploit the principle that the action distribution of stream stars is most clustered when the potential used to calculate the actions is closest to the true potential. Clustering is quantified with the Kullback-Leibler Divergence (KLD), which also provides conditional uncertainties for our parameter estimates. We show, for toy Gaia-like data in a spherical isochrone potential, that maximizing the KLD of the action distribution relative to a smoother distribution recovers the true values of the potential parameters. The precision depends on the observational errors and the number of streams in the sample; using KIII giants as tracers, we measure the enclosed mass at the average radius of the sample stars accurate to 3% and precise to 20-40%. Recovery of the scale radius is precise to 25%, and is biased 50% high by the small galactocentric distance range of stars in our mock sample (1-25 kpc, or about three scale radii, with mean 6.5 kpc). About 15 streams, with at least 100 stars per stream, are needed to obtain upper and lower bounds on the enclosed mass and scale radius when observational errors are taken into account; 20-25 streams are required to stabilize the size of the confidence interval. If radial velocities are provided for stars out to 100 kpc (10 scale radii), all parameters can be determined with 10% accuracy and 20% precision (1.3% accuracy in the case of the enclosed mass), underlining the need for ground-based spectroscopic follow-up to complete the radial velocity catalog for faint halo stars observed by Gaia.Comment: Accepted versio

Age-dependent transient shear banding in soft glasses

We study numerically the formation of long-lived transient shear bands during shear startup within two models of soft glasses (a simple fluidity model and an adapted `soft glassy rheology' model). The degree and duration of banding depends strongly on the applied shear rate, and on sample age before shearing. In both models the ultimate steady flow state is homogeneous at all shear rates, consistent with the underlying constitutive curve being monotonic. However, particularly in the SGR case, the transient bands can be extremely long lived. The banding instability is neither `purely viscous' nor `purely elastic' in origin, but is closely associated with stress overshoot in startup flow.Comment: 4 pages, 3 figure

Alaska Coastal Community Youth and the Future

The Alaska Sea Grant College Program. Project No. R/72-02.Executive Summary / Introduction / Background to the Research / Methods / Findings / Discussion and Policy Recommendations / Products from the Research / References Cited / Appendix A. Focus Group Protocol (High School) / Appendix B. Focus Group Protocol (12-20 year olds) / Appendix C. Focus Group Questionnaire / Appendix D. Occupational Rating Worksheet / Appendix E. Consent/Assent For

Escaping the Kmara Box: Reframing the Role of Civil Society in Georgia's Rose Revolution

"This article examines the role of civic groups in Georgia’s Rose Revolution using Larry Diamond’s framework of the democratic functions of civil society. The author argues that the contribution of civil society to the peaceful transfer of power in 2003 is best understood by expanding the analytical focus out from the Kmara youth movement to include a larger set of organisations. Rather than focusing on the Kmara youth movement as the primary civil society actor in 2003, the author contends that Kmara was, in fact, a product of the coordinated involvement of a cohort of NGOs. The article stresses the highly interconnected nature of Georgian civic leaders and organisations, particularly regarding networks with other NGOs, opposition politicians, and journalists from the Rustavi 2 television station." (author's abstract

A Convenient Synthetic Route to Partial-Cone p-Carboxylatocalix[4]arenes.

p-Carboxylatocalix[n]arenes have emerged as useful building blocks for the construction of a diverse range of supramolecular assemblies. A convenient route to a p-carboxylatocalix[4]arene that is locked in a partial-cone conformation is presented. The conformation gives the molecule markedly different topological directionality relative to those previously used in self- and metal-directed assembly studies

Innovations in Occupational Therapy Education: The Centralized Service Learning Model

Partnerships between community organizations and engaged university members creates realistic learning experiences for occupational therapy students while encouraging civic responsibility. The authors propose service learning as the core of an innovative course design framework using the Centralized Service Learning Model (CSLM). Three phases are described. Phase One provides a description of the CSLM using a generalizable model, with specific application within existing occupational therapy program coursework. Phase Two provides leadership opportunities for a subsequent cohort of students within the curriculum. Finally, Phase Three integrates faculty scholarship. To understand students’ knowledge-level awareness, a survey based on course objectives can be administered, and ongoing journaling using reflections that promote critical thought, such as guided reflection, may be utilized. Faculty members can utilize this innovative course design framework to provide meaning and engagement to students during service learning projects while simultaneously meeting service, scholarship, and teaching obligations