We study connections between classical asymptotic density, computability and computable enumerability. In an earlier paper, the second two authors proved that there is a computably enumerable set A of density 1 with no computable subset of density 1. In the current paper, we extend this result in three different ways: The degrees of such sets A are precisely the nonlow c.e. degrees. There is a c.e. set A of density 1 with no computable subset of nonzero density. There is a (...) c.e. set A of density 1 such that every subset of A of density 1 is of high degree. We also study the extent to which c.e. sets A can be approximated by their computable subsets B in the sense that A\B has small density. There is a very close connection between the computational complexity of a set and the arithmetical complexity of its density and we characterize the lower densities, upper densities and densities of both computable and computably enumerable sets. We also study the notion of "computable at density r" where r is a real in the unit interval. Finally, we study connections between density and classical smallness notions such as immunity, hyperimmunity, and cohesiveness. (shrink)

The study of alternatives to conventional industrial agricultural production has intensified in recent years. While many types of alternative production systems, and the motivations of individuals to participate in them, have been studied, there are significant gaps in the literature. One such dearth is research on those participating in self-provisioning activities. This study begins to fill the gap by looking at the self-provisioning activity of home gardening using data from the 2008 Ohio Survey of Food, Agriculture, and Environmental Issues. Discerning (...) who household gardeners are is important given the recent economic, cultural, and political climate of the United States. The results show that home gardening occurs throughout the state of Ohio at surprisingly high levels. Bivariate and multivariate analyses reveal several noteworthy associations between gardening and household characteristics, including spatial location, pro-environmental and economic hardship behaviors, and level of participation in localized food systems. (shrink)

We classify the asymptotic densities of the sets according to their level in the Ershov hierarchy. In particular, it is shown that for, a real is the density of an n‐c.e. set if and only if it is a difference of left‐ reals. Further, we show that the densities of the ω‐c.e. sets coincide with the densities of the sets, and there are ω‐c.e. sets whose density is not the density of an n‐c.e. set for any.

Objective: While behavioral recommendations regarding physical activity commonly focus on reaching demanding goals by proposing ‘thresholds’, little attention has been paid to the question of how much of a behavioral change is needed to make people feel that they have changed. The present research investigated this relation between actual and felt behavior change. Design: Using data from two longitudinal community samples, Study 1 and 2 comprised 614 (63 % women) and 398 participants (61 % women) with a mean age of (...) 40.9 years (SD = 13.6) and 42.5 years (SD = 13.4), respectively. Using a stage-approach, participants were classified into four groups by asking them at the respective second measurement to indicate whether they had become more physically active since their last participation six months ago (“Changers”), had tried but did not succeed in becoming more physically active (“Attempters”), were already physically active on a regular basis (“Regular Actives”), or had not tried to become more physically active (“Non-Attempters”). Physical activity was measured using the International Physical Activity Questionnaire (IPAQ), and fitness level was assessed as physical working capacity (PWC) via bicycle ergometry. Mixed ANOVAs including Time and Perceived Change as within and between factors were conducted, followed up by simple effect analyses. Results: Participants stating to have become more active in the past six months (Changers) showed a significant increase in vigorous physical activity but not in moderate physical activity, with an average of 6.8 (Study 1) and 10.6 (Study 2) MET-h per week in vigorous activity. Corroborating these findings, objective fitness also significantly increased in the group of Changers. No systematic change in moderate or vigorous physical activity was observed for the three other ‘non-changer’ groups (regular actives, attempters, non-attempters). Conclusion: The intensity of physical activity is the crucial variable for people’s perception of change in physical activity. Moderate physical activity seems not to be perceived as an effective means for behavior change. It thus might fail to unfold sufficient motivational impact, despite its known positive effects on health. (shrink)

Participation in the local food movement has grown dramatically in the United States, with the farmers’ market being one of its most widespread and heavily promoted forums. Proponents argue that the interactions and transactions that occur at farmers’ markets benefit market participants, but, more importantly, have broader benefits for the neighborhoods they are located in and for society itself. The promise of these benefits raises several important questions, notably: where are farmers’ markets located and who has access to them? While (...) many works have examined the characteristics of individuals who frequent markets, few have examined the areas and inhabitants hosting these markets. Using data from the USDA and US Census, I explore the location of farmers’ markets areas across several geographic measurements, including at the national, census division, and census tract levels. Results reveal the following: Perhaps not being as white of a movement as critics have suggested, farmers’ markets are almost exclusively a middle to middle-upper class phenomenon; and Farmers’ markets are very unlikely to be found in neighborhoods with lower than average socio-economic statuses indicators, in specific divisions of the US, and in rural areas. Results from this research further illuminate our understanding of where farmers’ markets are located throughout United States while presenting some interesting questions for the local food movement as it continues to moves forward. (shrink)

Die Generales Inquisitiones von 1686 stellen die wichtigste geschlossene Arbeit Leibniz' zu Fragen der Logik dar. Wie in dem ebenfalls 1686 verfaßten Discours de Métaphysique (PhB 260) wird hier Leibniz' Auffassung deutlich, in seinem Denken eine gewisse systematische Geschlossenheit gefunden zu haben.