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AbstractThe City of Los Angeles Mayor’s Office of Gang Reduction and Youth Development (GRYD) program was conceived as a comprehensive response to gang violence. Unlike most comprehensive approaches, suppression was excluded from the primary model. Program services including community engagement, gang prevention and intervention services, and street-based violence interruption, were formally launched in late 2011. Strict geographic eligibility criteria mean that GRYD services were available in some Los Angeles communities and not others. Using the geographic structure of GRYD, we use a place-based difference-in-differences model to estimate the effect of GRYD services on both violent and property crime. The analyses suggest a reduction in violent crime of around 18% in areas exposed to GRYD Comprehensive Strategy services, including aggravated assault and robbery. Similar declines are not observed in property crimes including burglary and car theft. Comparison with evaluations of placed-based gang injunctions demonstrate that GRYD is able to achieve nearly one-half of the reductions in crime without a suppression focus.

Gaining a complete picture of the activity in a city using vast data sources is challenging yet potentially very valuable. One such source of data is Twitter which generates millions of short spatio-temporally localized messages that, as a collection, have information on city regions and many forms of city activity. The quantity of data, however, necessitates summarization in a way that makes consumption by an observer efficient, accurate, and comprehensive. We present a two-step process for analyzing geotagged twitter data within a localized urban environment. The first step involves an efficient form of latent Dirichlet allocation, using an expectation maximization, for topic content summarization of the text information in the tweets. The second step involves spatial and temporal analysis of information within each topic using two complimentary metrics. These proposed metrics characterize the distributional properties of tweets in time and space for all topics. We integrate the second step into a graphical user interface that enables the user to adeptly navigate through the space of hundreds of topics. We present results of a case study of the city of Madrid, Spain, for the year 2011 in which both large-scale protests and elections occurred. Our data analysis methods identify these important events, as well as other classes of more mundane routine activity and their associated locations in Madrid.

We identified and dated 18 occupational events at eight sites dating to ~14.7–10.8kiloannum before present (ka BP) during a decade of archaeological survey and excavation on the northeastern high Tibetan Plateau (TP) >3200m. The ephemeral nature of the earliest sites suggests they were created by small foraging groups during very short stays. By ~12ka BP, larger foraging groups began to occupy sites >4000m leading to a more intensive occupation of the high TP after ~9.5ka BP. This archaeologically-based chronology closely matches genetically-based Tibetan population histories showing an early growth in population size and initial split with Han populations ~15–9ka BP, and a second spike in population growth during the early-mid Holocene. We found no evidence for occupation of the high TP prior to or during the Last Glacial Maximum (LGM), suggesting the initial separation of Tibetan and Han populations may have occurred at lower elevations in the TP margins or after the LGM in the high TP.

The Tibetan Plateau is the highest contiguous terrain on the planet. It is cold, dry, poor in oxygen, and one of the last habitats to have been colonized by our species. Here we present the first quantitative chemical characterization of obsidian artifacts from the Tibetan Plateau. The artifacts in our sample come from 20 archeological sites spanning a large portion of the northeast and the southwest regions of the Plateau. We find that five varieties of obsidian were used at these sites. We also identify the geological source of one of the obsidian varieties as near Balung Tso in south-central Tibet. The five varieties of volcanic glass are distributed into two discrete zones in the northeast and the southwest of Tibet, suggesting that the two regions may have been occupied independently, and that interactions between them were limited. Finally, we also find that some of the transportation distances of obsidian are several hundred kilometers long.

Microblade technology was important in hunter‐gatherer adaptations throughout northern Asia from the late Pleistocene through the Pleistocene/Holocene transition and beyond. To date, most studies from the region are concerned with origins, technological lineages, and culture history. In contrast, we direct attention to issues involving the role of microlithic technology in adaptive strategies and problem solution among north Asian hunter‐gatherers by looking at artifact design and risk analysis. First we discuss the function of Asian microblades and outline the general costs and benefits of organic points with microblade insets over simple organic points and flaked stone points, as well as the relative advantages of wedge‐shaped and split‐pebble microcores in terms of the Z‐score model. We conclude with a review of the role of microlithic technology as a risk‐minimizing strategy of Arctic and sub‐Arctic large‐game hunters in northern Asia and suggest further lines of inquiry.

Coevolution is defined as reciprocal selective pressures that operate to make the evolution of one taxon partially dependent on the evolution another. This process often involves multiple species exploiting shared limiting resources. In classic coevolutionary models, populations of sympatric species are seen to diverge in one or more morphological, ecological, or behavioral traits to effect more even partitioning of resources and reduce levels of interspecific competition. Character displacement and resource partitioning are thought to be central not only to how species coexist on limited resources, but also to how species invade new resource niches. Hominid invasion of the predatory guild at least 2 my ago would have brought them into contact with a range of new selective pressures including competition with a number of large-bodied predators. This study explores resource partitioning between hominids and other Plio-Pleistocene large-bodied predators through analyses of predator food transport strategies. The anatomical content (head/limb MNE) of hominid transported faunal assemblages at Bed I Olduvai and FxJj 50 (Koobi Fora), when compared to modern predator control cases, suggests that Plio-Pleistocene hominids practiced food transport strategies intermediate between those of top predators such as wolves and those of confrontational scavengers such as spotted hyaenas. Plio-Pleistocene hominid food transport strategies do not resemble those of nonconfrontational scavengers such as brown and striped hyenas. The highly regular patterns differentiating bone assemblages accumulated by top predators, hominids, and confrontational and nonconfrontational scavengers suggest that hominid invasion of the predatory guild involved resource partitioning potentially based on some form of character displacement.Copyright 1998 Academic Press.