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

Journal Self-Citation II: The Quest for High Impact – Truth and Consequences?

For the information systems discipline, it is important to have means for assessing the performance exhibited by individual faculty members, groups of researchers, and the journals that publish their work. Such assessments affect the outcomes of university decisions about these individuals, groups, and journals. Various kinds of data can be used in the processes that lead to the decisions about performance. In this paper we consider one type of data that seems to be increasingly adopted, either explicitly or implicitly, as an indicator of performance: the journal impact factor (JIF), which is periodically reported in the Journal Citation Reports (JCR). The allure of JIFs for rating performance is that they come from a third party source (Thomson Reuters), are systematically determined in a largely transparent fashion, and yield a single number for each journal that is covered in the JCR. However, behind this allure several issues give us pause when it comes to interpreting or applying JIFs in the context of deciding on performance ratings. It appears that these issues are rarely understood or pondered by those in the information systems world who adopt JIFs for such decisions – at least not in an overt way. We examine these issues to understand the advisability of employing JIFs to produce performance ratings, the underlying assumptions, and the consequences. We conclude that use of JIFs in university decision making should be undertaken only with great caution, alternative decision inputs should be considered, and that judging the impact of a specific article by the journal in which it appears is questionable