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

How Literacy Coursework May Change the Perspectives of Preservice Speech-Language Pathologists: A Pilot Study

This pilot study investigated how perspectives of preservice speech-language pathologists (SLPs) may change after completion of a graduate course in literacy in a Communication Sciences and Disorders (CSD) program. Further, the study sought to reflect upon course design and instructional delivery practices related to the class. Data was collected via online survey completed by 21 volunteer CSD graduate students. The results suggested that students\u27 perspectives may evolve over the course of a semester-long CSD literacy class in some areas related to the components of reading, misconceptions about literacy, and the social justice implications of access to quality reading programs. Using active learning strategies and embedding content about viewing reading as a social justice issue appeared to add value to the classroom experience. This study aims to add to the body of literature to suggest that deliberately planned and consciously designed literacy coursework that focuses on preservice SLPs may be an effective way to promote change in their perspectives with the ultimate goal of increasing inservice school-based SLPs’ engagement with literacy in the children they serve

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