Venusian extended ejecta deposits as time-stratigraphic markers

Use of impact crater ejects at time-stratigraphic markers was established during lunar geologic mapping efforts. The basic premise is that the deposition of impact ejecta, either by itself or mixed with impact-excavated material, is superimposed on a surface. The deposit becomes an observable, mappable unit produced in a single instant in geologic time. Up to two-thirds of Venus craters exhibit extended ejecta deposits. A reconnaissance survey of 336 craters (about 40 percent of the total population) was conducted. About half the craters examined were located in and around the Beta-Atla-Themis region, and half were spread over the western hemisphere of the planet. The survey was conducted using primarily C1-MIDR images. The preliminary survey shows: (1) of the 336 craters, 223 were found to have extended ejecta deposits. This proportion is higher than that found in other Venus crater databases by up to a factor of 2. (2) 53 percent of all extended ejecta craters were unambiguously superimposed on all volcanic and tectonic units. Crater Annia Faustina's associated parabolic ejecta deposit is clearly superimposed on volcanic flows coming from Gula Mons to the west. Parabola material from Faustina has covered the lava flows, smoothing the surface and reducing its specific backscatter cross section. The stratigraphy implies that the parabola material is the youngest observable unit in the region. (3) 12 percent of extended ejecta deposits are superimposed by volcanic materials. Crater Hwangcini has extended ejecta that has been covered by volcanic flows from a dome field to the northwest, implying that the volcanic units were emplaced subsequent to the ejecta deposit and are the youngest units in the locality. (4) It is difficult to determine the stratigraphic relationships of the remaining extended ejecta deposits in SAR at C1-MIDR resolution. Examination of higher resolution images and application of the other Magellan datasets in systematic manner should resolve most of the ambiguous cases. Results from the preliminary survey indicate that extended ejecta deposits are effective time-statigraphic markers for the localities. If stratigraphic relationships between the deposits and surrounding units are studied on a case-by-case basis over the whole planet, they should provide useful constraints on Venus history and development of the surface through time. The continuation of the research will expand the study to include the entire crater population and the Magellan emissivity, altimetry, reflectivity, and rms slope datasets

Gentrification and Displacement in the San Francisco Bay Area: A Comparison of Measurement Approaches.

Gentrification may play an important role in influencing health outcomes, but few studies have examined these associations. One major barrier to producing empirical evidence to establish this link is that there is little consensus on how to measure gentrification. To address this barrier, we compared three gentrification classification methodologies in relation to their ability to identify neighborhood gentrification in nine San Francisco Bay Area counties: the Freeman method, the Landis method, and the Urban Displacement Project (UDP) Regional Early Warning System. In the 1580 census tracts, 43% of the population had a bachelor's degree or higher. The average median household income was $79,671 in 2013. A comparison of gentrification methodologies revealed that the Landis and Freeman methodologies characterized the vast majority of census tracts as stable, and only 5.2% and 6.1% of tracts as gentrifying. UDP characterized 46.7% of tracts at risk, undergoing, or experiencing advanced stages of gentrification and displacement. There was substantial variation in the geographic location of tracts identified as gentrifying across methods. Given the variation in characterizations of gentrification across measures, studies evaluating associations between gentrification and health should consider using multiple measures of gentrification to examine the robustness of the study findings across measures

Comment on 'The Global Resurfacing of Venus' by R. G. Strom, G.G. Schaber, and D.D. Dawson

The distribution of impact craters on Venus has been the subject of a great deal of analysis since the return of Magellan data. Phillips el al. (1992) performed Monte Carlo two-dimensional (2-D) modeling of the areal distribution of craters, and the results of that exercise allowed a restricted, but still quite large, range of possible planetary resurfacing histories, including the possibility that the crater, were emplaced on a geologically inactive planet. However, the nonrandom distribution of embayed and deformed craters (Phillips el al., 1992), the hypsometric distribution of craters (Herrick and Phillips, 1994), the varied degradation states of craters (Izenberg et al., 1994), their nonrandom distribution with different geologic terrain types (Namiki and Solomon, 1994; Price et al, 1994), and three-dimensional resurfacing modeling (Bullock el al., 1993) all seem to argue against that particular possibility. In contrast, Strom el al. (1994) have collected a refined and more comprehensive data set of impact features, and they input these data into more sophisticated 2-D Monte Carlo modeling and statistical analyses of the areal distribution of craters, the hypsometric distribution of craters, and the number of embayed craters. They concluded that 'Venus experienced a global resurfacing event about 300 m.y. ago followed by a dramatic reduction of volcanism and tectonism. This global resurfacing event ended abruptly (less than 10 m.y.). The present crater population has accumulated since then and remains largely intact . . . only about 4%-6% of the planet has been volcanically resurfaced since the global event . . .' If these conclusions are well-founded, this work certainly represents a significant advancement in restricting tile number of plausible resurfacing histories for the planet. If Strom et al. (1994) are correct, it would also mean that all of the other aforementioned works are in error to various degrees, or at least represent overzealous interpretation of the data. However, we have identified apparent flaws in the observations, modeling, and interpretations presented by Strom el al. (1994) that lead us to question whether their conclusions are warranted. We limit our comments to three areas of their analysis: (1) observations pertaining to the number and area of disrupted and pristine craters and crater-related features, (2) modeling of the areal and elevation distribution of craters, and (3) interpretations of resurfacing models

A first-order model for impact crater degradation on Venus

A first-order impact crater aging model is presented based on observations of the global crater population of Venus. The total population consists of 879 craters found over the approximately 98 percent of the planet that has been mapped by the Magellan spacecraft during the first three cycles of its mission. The model is based upon three primary aspects of venusian impact craters: (1) extended ejecta deposits (EED's); (2) crater rims and continuous ejecta deposits; and (3) crater interiors and floors

Fair Influence Maximization: A Welfare Optimization Approach

Several behavioral, social, and public health interventions, such as suicide/HIV prevention or community preparedness against natural disasters, leverage social network information to maximize outreach. Algorithmic influence maximization techniques have been proposed to aid with the choice of "peer leaders" or "influencers" in such interventions. Yet, traditional algorithms for influence maximization have not been designed with these interventions in mind. As a result, they may disproportionately exclude minority communities from the benefits of the intervention. This has motivated research on fair influence maximization. Existing techniques come with two major drawbacks. First, they require committing to a single fairness measure. Second, these measures are typically imposed as strict constraints leading to undesirable properties such as wastage of resources. To address these shortcomings, we provide a principled characterization of the properties that a fair influence maximization algorithm should satisfy. In particular, we propose a framework based on social welfare theory, wherein the cardinal utilities derived by each community are aggregated using the isoelastic social welfare functions. Under this framework, the trade-off between fairness and efficiency can be controlled by a single inequality aversion design parameter. We then show under what circumstances our proposed principles can be satisfied by a welfare function. The resulting optimization problem is monotone and submodular and can be solved efficiently with optimality guarantees. Our framework encompasses as special cases leximin and proportional fairness. Extensive experiments on synthetic and real world datasets including a case study on landslide risk management demonstrate the efficacy of the proposed framework.Comment: The short version of this paper appears in the proceedings of AAAI-2

Pre-incarceration police harassment, drug addiction and HIV risk behaviours among prisoners in Kyrgyzstan and Azerbaijan: results from a nationally representative cross-sectional study.

INTRODUCTION: The expanding HIV epidemic in Azerbaijan and Kyrgyzstan is concentrated among people who inject drugs (PWID), who comprise a third of prisoners there. Detention of PWID is common but its impact on health has not been previously studied in the region. We aimed to understand the relationship between official and unofficial (police harassment) detention of PWID and HIV risk behaviours. METHODS: In a nationally representative cross-sectional study, soon-to-be released prisoners in Kyrgyzstan (N=368) and Azerbaijan (N=510) completed standardized health assessment surveys. After identifying correlated variables through bivariate testing, we built multi-group path models with pre-incarceration official and unofficial detention as exogenous variables and pre-incarceration composite HIV risk as an endogenous variable, controlling for potential confounders and estimating indirect effects. RESULTS: Overall, 463 (51%) prisoners reported at least one detention in the year before incarceration with an average of 1.3 detentions in that period. Unofficial detentions (13%) were less common than official detentions (41%). Optimal model fit was achieved (X (2)=5.83, p=0.44; Goodness of Fit Index (GFI) GFI=0.99; Comparative Fit Index (CFI) CFI=1.00; Root Mean Square Error of Approximation (RMSEA) RMSEA=0.00; PCLOSE=0.98) when unofficial detention had an indirect effect on HIV risk, mediated by drug addiction severity, with more detentions associated with higher addiction severity, which in turn correlated with increased HIV risk. The final model explained 35% of the variance in the outcome. The effect was maintained for both countries, but stronger for Kyrgyzstan. The model also holds for Kyrgyzstan using unique data on within-prison drug injection as the outcome, which was frequent in prisoners there. CONCLUSIONS: Detention by police is a strong correlate of addiction severity, which mediates its effect on HIV risk behaviour. This pattern suggests that police may target drug users and that such harassment may result in an increase in HIV risk-taking behaviours, primarily because of the continued drug use within prisons. These findings highlight the important negative role that police play in the HIV epidemic response and point to the urgent need for interventions to reduce police harassment, in parallel with interventions to reduce HIV transmission within and outside of prison

Sedimentary Processes on Venus

The sedimentary cycle, including the processes of erosion, transport, and lithification, is a key part of how planets evolve over time. Early images of Venus’s vast volcanic plains, numerous volcanoes, and rugged tectonic regions led to the interpretation that Venus is a volcanic planet with little sediment cover and perhaps few processes for generating sedimentary rocks. However, in the years since the Magellan mission in the 1990s we have developed a better understanding of sedimentary process on Venus. Impact craters are the largest present-day source of sediments, with estimates from the current crater population suggesting an average sediment layer 8–63 cm in thickness if distributed globally. There is clear evidence of fine-grained material in volcanic summit regions that is likely produced through volcanism, and dune fields and yardangs indicate transport of sediments and erosion of rocks through wind. Landslides and fine-grained materials in highland tessera regions demonstrate erosive processes that move sediment downhill. It is clear that sediments are an important part of Venus’s geology, and it is especially important to realize that they mantle features that may be of interest to future landed or low-altitude imaging missions. The sinks of sediments are less well known, as it has been difficult to identify sedimentary rocks with current data. Layering observed in Venera images and in Magellan images of some tessera regions, as well as calculated rock densities, suggest that sedimentary rocks are present on Venus. New data is needed to fully understand and quantify the present-day sedimentary cycle and establish with certainty whether sedimentary rock packages do, in fact, exist on Venus. These data sets will need to include higher-resolution optical and radar imaging, experimental and geochemical measurements to determine how chemical weathering and lithification can occur, and topography to better model mesospheric winds. Sediments and sedimentary rocks are critical to understanding how Venus works today, but are also extremely important for determining how Venus’s climate has changed through time and whether it was once a habitable planet