Optical Monitoring of Quasars: I. Variability

We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratorio Nacional de Astrofisica, Brazil, between March 1993 and July 1996. A distinctive feature of this survey is its photometric accuracy, ~ 0.02 V mag, achieved through differential photometry with CCD detectors, what allows the detection of faint levels of variability. We find that the relative variability, delta = sigma / L, observed in the V band is anti-correlated with both luminosity and redshift, although we have no means of discovering the dominant relation, given the strong coupling between luminosity and redshift for the objects in our sample.We introduce a model for the dependence of quasar variability on frequency that is consistent with multi-wavelength observations of the nuclear variability of the Seyfert galaxy NGC 4151. We show that correcting the observed variability for this effect slightly increases the significance of the trends of variability with luminosity and redshift. Assuming that variability depends only on the luminosity, we show that the corrected variability is anti-correlated with luminosity and is in good agreement with predictions of a simple Poissonian model. The energy derived for the hypothetical pulses, ~ 10^50 erg, agrees well with those obtained in other studies. We also find that the radio-loud objects in our sample tend to be more variable than the radio-quiet ones, for all luminosities and redshifts.Comment: 17 pages, 12 figures, accepted for publication in MNRAS (uses MNRAS style

One place doesn't fit all: improving the effectiveness of sustainability standards by accounting for place

Includes bibliographical references (pages 8-10).The growing interest in incentivizing sustainable agricultural practices is supported by a large network of voluntary production standards, which aim to offer farmers and ranchers increased value for their product in support of reduced environmental impact. To be effective with producers and consumers alike, these standards must be both credible and broadly recognizable, and thus are typically highly generalizable. However, the environmental impact of agriculture is strongly place-based and varies considerably due to complex biophysical, socio-cultural, and management-based factors, even within a given sector in a particular region. We suggest that this contradiction between the placeless generality of standards and the placed-ness of agriculture renders many sustainability standards ineffective. In this policy and practice review, we examine this contradiction through the lens of beef production, with a focus on an ongoing regional food purchasing effort in Denver, Colorado, USA. We review the idea of place in the context of agricultural sustainability, drawing on life cycle analysis and diverse literature to find that recognition of place-specific circumstances is essential to understanding environmental impact and improving outcomes. We then examine the case of the Good Food Purchasing Program (GFPP), a broad set of food-purchasing standards currently being implemented for institutional purchasing in Denver. The GFPP was created through a lengthy stakeholder-inclusive process for use in Los Angeles, California, USA, and has since been applied to many cities across the country. The difference between Los Angeles' process and that of applying the result of Los Angeles' process to Denver is instructive, and emblematic of the flaws of generalizable sustainability standards themselves. We then describe the essential elements of a place-based approach to agricultural sustainability standards, pointing toward a democratic, process-based, and outcome-oriented strategy that results in standards that enable rather than hinder the creativity of both producers and consumers. Though prescription is anathema to our approach, we close by offering a starting point for the development of standards for beef production in Colorado that respect the work of people in place

Assessing the economic impacts of food hubs on regional economies: a framework that includes opportunity cost

Includes bibliographical references (pages 168-171).The number of food hubs—businesses that aggregate and distribute local food—in the United States is growing, fueled in part by increasing public support. However, there have been few data-driven assessments of the economic impacts of these ventures. Using an input-output-based methodology and a unique data set from a successful food hub, we measure net and gross impacts of a policy supporting their development. We estimate a gross output multiplier of 1.75 and an employment multiplier of 2.14. Using customer surveys, we estimate that every $1 increase in final demand for food hub products generates a$0.11 reduction in purchases in other sectors

Financial performance implications of differential marketing strategies: exploring farms that pursue local markets as a core competitive advantage, The

Includes bibliographical references (pages 502-504).This study explores how participation in direct and intermediated marketing channels and key operational factors influence agricultural producers’ financial performance. Accordingly, we divide the sample of local and regional food marketers into quartiles segmented by profitability performance as an initial exploration of how strong and weak performance may vary across scale, location, and choice of direct and intermediated channels. Moreover, other financial metrics that vary across types of producers and performance-based quartiles are analyzed. This paper provides initial evidence that participation in direct and intermediated markets may allow farms of any scale of sales volume to be financially viable

Community-supported agriculture marketing performance: results from pilot market channel assessments in Colorado

Includes bibliographical references (pages 13-14).Due in large part to rising consumer interest, the number of farmers and ranchers selling through local food markets is growing. Community-supported agriculture (CSA) is a unique local food channel adopted by producers that was initially established as a strategy for producers to directly benefit from the season-long investments of buyers who align with their community-focused mission. Although the U.S. Department of Agriculture has long collected data to improve farm performance, information on specific marketing channels is missing, and in response, this research provides some of the first evidence of the heterogeneity of performance among CSAs. In a pilot approach to understanding the economics of CSAs relative to other direct marketing channels, we conducted an assessment process, incorporating 42 farms in Colorado between June 2016 and October 2017. Results showed that farms that incorporated CSA sales in their direct market portfolios tended to be smaller in scale and utilize more diverse markets. Although these CSA farms have lower average weekly sales, they have the highest average marketing profit margins compared to other direct market channels

Community-supported agriculture marketing performance: results from pilot market channel assessments in Colorado

Includes bibliographical references (pages 13-14).Due in large part to rising consumer interest, the number of farmers and ranchers selling through local food markets is growing. Community-supported agriculture (CSA) is a unique local food channel adopted by producers that was initially established as a strategy for producers to directly benefit from the season-long investments of buyers who align with their community-focused mission. Although the U.S. Department of Agriculture has long collected data to improve farm performance, information on specific marketing channels is missing, and in response, this research provides some of the first evidence of the heterogeneity of performance among CSAs. In a pilot approach to understanding the economics of CSAs relative to other direct marketing channels, we conducted an assessment process, incorporating 42 farms in Colorado between June 2016 and October 2017. Results showed that farms that incorporated CSA sales in their direct market portfolios tended to be smaller in scale and utilize more diverse markets. Although these CSA farms have lower average weekly sales, they have the highest average marketing profit margins compared to other direct market channels