Impact crater scaling laws

Impact craters are numerous on planetary bodies and furnish important information about the composition and past histories of those bodies. The interpretation of that information requires knowledge about the fundamental aspects of impact cratering mechanics. Since the typical conditions of impacts are at a size scale and velocity far in excess of experimental capabilities, direct simulations are precluded. Therefore, one must rely on extrapolation from experiments of relatively slow impacts of very small bodies, using physically based scaling laws, or must study the actual cases of interest using numerical code solutions of the fundamental physical laws that govern these processes. A progress report is presented on research on impact cratering scaling laws, on numerical studies that were designed to investigate those laws, and on various applications of the scaling laws developed by the author and his colleagues. These applications are briefly reviewed

Modeling asteroid collisions and impact processes

As a complement to experimental and theoretical approaches, numerical modeling has become an important component to study asteroid collisions and impact processes. In the last decade, there have been significant advances in both computational resources and numerical methods. We discuss the present state-of-the-art numerical methods and material models used in "shock physics codes" to simulate impacts and collisions and give some examples of those codes. Finally, recent modeling studies are presented, focussing on the effects of various material properties and target structures on the outcome of a collision.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV. Includes minor correction

P/2010 A2 LINEAR II: dynamical dust modelling

P/2010 A2 is an object on an asteroidal orbit that was observed to have an extended tail or debris trail in January 2010. In this work, we fit the outburst of P/2010 A2 with a conical burst model, and verify previous suspicions that this was a one--time collisional event rather than an sustained cometary outburst, implying that P/2010 A2 is not a new Main Belt Comet driven by ice sublimation. We find that the best--fit cone opening angle is about 40 to 50 degrees, in agreement with numerical and laboratory simulations of cratering events. Mapping debris orbits to sky positions suggests that the distinctive arc features in the debris correspond to the same debris cone inferred from the extended dust. From the velocity of the debris, and from the presence of a velocity maximum at around 15 cm/s, we infer that the surface of A2 probably has a very low strength (<1 kPa), comparable to lunar regolith.Comment: 14 pages, 25 figures; accepted by Astronomy and Astrophysic

Energy coupling in catastrophic collisions

The prediction of events leading to the catastrophic collisions and disruption of solar system bodies is fraught with the same difficulties as are other theories of impact events; since one simply cannot perform experiments in the regime of interest. In the catastrophic collisions of asteroids that regime involves bodies of a few tons to hundred of kilometers in diameter, and velocities of several kilometers pre second. For hundred kilometer bodies, gravitational stresses dominate material fracture strengths, but those gravitational stresses are essentially absent for laboratory experiments. Only numerical simulations using hydrocodes can in principle analyze the true problems, but they have their own major uncertainties about the correctness of the physical models and properties. The question of the measure of the impactor and its energy coupling is investigated using numerical code calculations. The material model was that of a generic silicate rock, including high pressure melt and vapor phases, and includes material nonlinearity and dissipation via a Mie-Gruniesen model. A series of calculations with various size ratios and impact velocities are reported

The politics of belonging in Gagauzia: negotiating language usage, ethnic labels, and citizenship

This case study of Gagauzia reveals the complex nature of belonging and its interplay with a wide variety of factors by bringing to light personal attitudes in Gagauzia towards ethnic labels and languages. Analysis of empirical data collected during three months of fieldwork explores in what situations ethnic categorizations are activated, identifies patterns of ethnic labeling, and draws conclusions on how ethnicity interlinks with negotiation of the politics of belonging. In doing so, this work reflects on how Soviet legacies, namely language policies and assigned ethnicity, continue to have a huge impact on the everyday realities of belonging in Gagauzia. Moreover, it illustrates the role that economic instability can play in negotiation of belonging by examining the effect that enormous out-migration has had not only on demographics, but on the standing of Gagauzian language and feelings of personal identification among Gagauzians. In multiethnic Gagauzia, ethnic identification, language usage, and citizenship very often do not align, and this thesis addresses how Gagauzians attach meaning to these elements, frame them in forming identity, and utilize them in the construction of boundaries. This work employs in-depth qualitative analysis that draws out relationships among various phenomena related to ever-changing conceptualizations of belonging in Gagauzia. It not only fills a void in ethnographic research on an understudied region, but it also contributes to the existing broader body of literature on topics of identity and belonging in the post-Soviet space.https://www.ester.ee/record=b5171861*es

Patient Navigation through the Justice System: A Response to the High Infant Mortality Rate in One Community

The purpose of this evaluative study was two-fold; one was to evaluate a grant supported program that used the justice system to offer patient navigation services and the second goal was to provide a qualitative evaluation of the women’s health care experiences as they went through a court mandated drug program. Primary data was obtained from interviews with forty-seven program participants (n=47) from March, 2008 until January, 2010, and participant observation was used to explore treatment modalities and options available to these women. Secondary data was obtained from program staff as well as a review of the survey evaluation process by the staff where data was collected through participant surveys. The findings suggest that poor outcomes for the women and their children are related to socioeconomic and/or behavioral barriers that produce difficulties forging successful relationships with traditional health care providers. When interventions that promote advocacy and empowerment are in place, there seems to be an improvement in outcomes for the mothers and their children

Patient Navigation through the Justice System: A Response to the High Infant Mortality Rate in One Community

The purpose of this evaluative study was two-fold; one was to evaluate a grant supported program that used the justice system to offer patient navigation services and the second goal was to provide a qualitative evaluation of the women’s health care experiences as they went through a court mandated drug program. Primary data was obtained from interviews with forty-seven program participants (n=47) from March, 2008 until January, 2010, and participant observation was used to explore treatment modalities and options available to these women. Secondary data was obtained from program staff as well as a review of the survey evaluation process by the staff where data was collected through participant surveys. The findings suggest that poor outcomes for the women and their children are related to socioeconomic and/or behavioral barriers that produce difficulties forging successful relationships with traditional health care providers. When interventions that promote advocacy and empowerment are in place, there seems to be an improvement in outcomes for the mothers and their children

DSM64: A Distributed Shared Memory System in User-Space

This paper presents DSM64: a lazy release consistent software distributed shared memory (SDSM) system built entirely in user-space. The DSM64 system is capable of executing threaded applications implemented with pthreads on a cluster of networked machines without any modifications to the target application. The DSM64 system features a centralized memory manager [1] built atop Hoard [2, 3]: a fast, scalable, and memory-efficient allocator for shared-memory multiprocessors. In my presentation, I present a SDSM system written in C++ for Linux operating systems. I discuss a straight-forward approach to implement SDSM systems in a Linux environment using system-provided tools and concepts avail- able entirely in user-space. I show that the SDSM system presented in this paper is capable of resolving page faults over a local area network in as little as 2 milliseconds. In my analysis, I present the following. I compare the performance characteristics of a matrix multiplication benchmark using various memory coherency models. I demonstrate that matrix multiplication benchmark using a LRC model performs orders of magnitude quicker than the same application using a stricter coherency model. I show the effect of coherency model on memory access patterns and memory contention. I compare the effects of different locking strategies on execution speed and memory access patterns. Lastly, I provide a comparison of the DSM64 system to a non-networked version using a system-provided allocator