The function of photomechanical movements in the retina of the rainbow trout (Salmo gairdneri)

1. The function of photomechanical movements in the retina of rainbow trout (Salmo gairdneri) was investigated by determining both the effect of light on the level of extractable visual pigment, and the electroretinographic b-wave sensitivity, during various stages of photomechanical light and dark adaptation. 2. Dark-adapted fish, light-adapted fish, and dark-adapted fish exposed to ten minutes direct sunlight had on average visual pigment concentrations of 100, 82 and 36% respectively. 3. The intensity of illumination required to bleach a specified amount of visual pigment in the light-adapted retina was found to be 1.29 log units higher than that needed to bleach the same amount of visual pigment in a dark-adapted eye. 4. The level of extractable visual pigment was observed to be relatively constant over natural twilight periods. 5. A close temporal correlation was observed between the time course of electroretinographic adaptation, measured by the b-wave sensitivity, and photomechanical changes. 6. All these observations tend to support the hypothesis that photomechanical movements serve, at least in part, to protect the rod visual pigment from overstimulation in the light-adapted retina

An endogenous crepuscular rhythm of rainbow trout (Salmo gairdneri) photomechanical movements

1. The position of the epithelial pigment and cones in the retina of Salmo gairdneri was determined during extended periods of darkness in fish entrained to both artificial and natural light/dark cycles. 2. An endogenous rhythm of such photomechanical movements, unique among species so far examined, was observed in both groups of fish, with two peaks of light adaptation coincident with dawn and dusk. 3. It is suggested that such an apparently non-adaptive physiological rhythm is related to the behavioural pattern of trout and reveals a basic crepuscular organisation. 4. No endogenous rhythm was observed in continual light. 5. These results suggest that control of photomechanical changes in rainbow trout has two components: an endogenous component, that causes the bimodal pattern in maintained darkness, and a direct effect of light, that maintains light adaptation throughout a normal day

The last common bilaterian ancestor

Many regulatory genes appear to be utilized in at least superficially similar ways in the development of particular body parts in Drosophila and in chordates. These similarities have been widely interpreted as functional homologies, producing the conventional view of the last common protostome-deuterostome ancestor (PDA) as a complex organism that possessed some of the same body parts as modern bilaterians. Here we discuss an alternative view, in which the last common PDA had a less complex body plan than is frequently conceived. This reconstruction alters expectations for Neoproterozoic fossil remains that could illustrate the pathways of bilaterian evolution

Trends and Opportunities in Agriculture An Executive Interview with Lowell Catlett

Agriculture will change more in the next decade than it did in the last century. Lowell Catlett is a futurist sharing his knowledge and insight on the new trends and technologies shaping the future of agriculture and how those working in this sector can take advantage of new opportunities.innovation, communication, opportunity, technology, Research and Development/Tech Change/Emerging Technologies, Teaching/Communication/Extension/Profession, Q10, Q16,

Improving performance through concept formation and conceptual clustering

Research from June 1989 through October 1992 focussed on concept formation, clustering, and supervised learning for purposes of improving the efficiency of problem-solving, planning, and diagnosis. These projects resulted in two dissertations on clustering, explanation-based learning, and means-ends planning, and publications in conferences and workshops, several book chapters, and journals; a complete Bibliography of NASA Ames supported publications is included. The following topics are studied: clustering of explanations and problem-solving experiences; clustering and means-end planning; and diagnosis of space shuttle and space station operating modes

A Race to Develop: A Competing Risk Examination of the Pattern and Timing of Land Development in an Exurban County

Rural-urban fringe counties (i.e. counties adjacent to other counties with large and growing urban centers) often experience intense development pressure as a result of urban growth and expansion. While growth-initiated development can take many forms, the majority of the development that occurs in these exurban counties is in the form of single-family residential dwellings. Moreover, it is in the form of subdivision developments that range in size from very small two and three lot minor subdivisions to massive multi-phase major subdivisions with hundreds of lots and numerous amenities. In this paper, we focus on the land development patterns in Carroll County, MD, an urban-fringe county in the Baltimore-Washington D.C. metro region. The purpose of this paper is to explore whether a basic set of factors, both constant and time-dependent and acting at different spatial scales, can explain the timing and location of major versus minor subdivision developments in Carroll County. Using a micro-level panel of land parcel conversion, historical land records for subdivision development and ArcGIS software a new dataset was created that traces the entire history of the subdivision process in the county. Datasets were also created that trace the history of land preservation so that we could control for official open space and its interaction with the decision to subdivide through time. Using these data and a number of land use variables created from them from 1993-2007, we apply a competing risks duration model to analyze which factors affect major versus minor subdivision development. Visual inspection as well as a descriptive analysis of a series of landscape metrics based on distance from the metropolitan center reveals a different pattern outcome for small versus large subdivisions with larger developments following more closely to the predictions of the urban economic model. Empirically, we find further evidence that the factors affecting the timing of minor versus major subdivision developments are indeed different. Distance and access to road networks have less of an effect on minor over major developments, while surrounding preservation and the option to preserve have less of an effect on major subdivisions. To make the risk comparison relevant and to focus on areas that have experienced the most fragmentation as a result of residential land conversion as well as the most policy attention, we restrict our analysis to parcels located in minimum density zoning districts.Land Economics/Use,

Global Supply Chain: An Executive Interview with Mary Shelman

Mary Shelman discusses forces driving higher food prices and some of the changes which are impacting the global food supply chain. Shelman coordinates Harvard Business School’s premier Agribusiness Seminar attended annually by more than 200 CEOs and top managers from global firms. She also organizes and teaches similar programs in Europe, Latin America and Asia. Her research focuses on the forces shaping global agribusiness. Her experience bridges academia, as an author and teacher of dozens of case studies on strategic change and challenges in global agribusiness firms, with industry experience.global food supply chain, food prices, markets, Agribusiness, Demand and Price Analysis, Marketing, Q10, Q11, Q13,

Pareto-Improving Social Security Reform

social security reform