Showing 4461 - 4470 of 5713 Items
New insights on obtaining phytoplankton concentration and composition from in situ multispectral Chlorophyll fluorescence
Date: 2010-01-01
Creator: Christopher W. Proctor, Collin S. Roesler
Access: Open access
- A three-channel excitation (435 nm, 470 nm, and 532 nm) Chlorophyll fluorometer (695 nm emission) was calibrated and characterized to improve uncertainty in estimated in situ Chlorophyll concentrations. Protocols for reducing sensor-related uncertainties as well as environmental-related uncertainties were developed. Sensor calibrations were performed with thirteen monospecific cultures in the laboratory, grown under limiting and saturating irradiance, and sampled at different growth phases. Resulting uncertainties in the calibration slope induced by natural variations in the in vivo fluorescence per extracted Chlorophyll yield were quantified. Signal variations associated with the sensors (i.e., dark current configurations, drift, and stability) and the environment (i.e., temperature dependent dark currents and contamination by colored dissolved organic matter [CDOM] fluorescence) yielded errors in estimating in situ Chlorophyll concentration exceeding 100%. Calibration protocols and concurrent observations of in situ temperature and CDOM fluorescence eliminate these uncertainties. Depending upon excitation channel, biomass calibration slopes varied between 6-and 10-fold between species and as a function of growth irradiance or growth phase. The largest source of slope variability was due to variations in accessory pigmentation, and thus the variance could be reduced among pigment-based taxonomic lines. Fluorescence ratios were statistically distinct among the pigment-based taxonomic groups, providing not only a means for approximating bulk taxonomic composition, but also for selecting the appropriate calibration slope to statistically improve the accuracy of in situ Chlorophyll concentration estimates. Application to 5 months of deployment in China Lake, Maine, USA reduced the error in estimating extracted Chlorophyll concentration from > 30% to < 6%. © 2010, by the American Society of Limnology and Oceanography, Inc.
Accounting for creativity: Lessons from the economic history of intellectual property and innovation
Date: 2020-01-01
Creator: B. Zorina Khan
Access: Open access
- Social progress depends on the realization of inventive ideas, and economic history provides valuable lessons about creativity in technology and culture. The empirical study of over one hundred thousand innovative individuals who obtained patents, copyrights, and prizes, sheds light on the relationship between institutions, incentives, and transformative ideas and expression, over the past two centuries. The European growth model assumed useful knowledge was scarce, and top-down administered innovation systems offered rights and rewards to “exclusive” groups. By contrast, American policies regarded creativity as widely distributed in the general population, and further promoted “inclusive” market-oriented mechanisms that fostered diversity in ideas and outcomes. The evidence suggests that property rights in patents facilitated markets in ideas, and ensured that returns were aligned with productivity and market demand. Whereas, such administered systems as innovation prizes and publisher’s copyrights in the “creative industries” benefited the few rather than overall social welfare.
Role of iron and organic carbon in mass-specific light absorption by particulate matter from louisiana coastal waters
Date: 2012-01-01
Creator: Margaret L. Estapa, Emmanuel Boss, Lawrence M. Mayer, Collin S. Roesler
Access: Open access
- We investigated the influences of organic content and mineralogical composition on light absorption by mostly mineral suspended particles in aquatic and coastal marine systems. Mass-specific absorption spectra of suspended particles and surface sediments from coastal Louisiana and the lower Mississippi and Atchafalaya rivers were measured with a centered sample-mount integrating sphere and analyzed in conjunction with organic carbon (OC), hydrochloric acid- (HCl-) extractable iron, and dithionite-extractable iron contents. Compositions and absorption properties were comparable to published values for similar particles. Dithionite-extractable iron was strongly correlated with absorption at ultraviolet (UV) and blue wavelengths, while OC and HCl-extractable iron were weakly but positively correlated. Oxidative removal of OC from sediments caused small and variable changes in absorption, while dithionite extraction of iron oxides strongly reduced absorption. Shoulders in the absorption spectra corresponded to absorption bands of iron oxide minerals, and their intensities were well correlated to dithionite-extractable iron contents of the samples. These findings support a primary role for iron oxide and hydroxide minerals in the mass-specific absorption of mostly inorganic particles from the terrestrially influenced coast of Louisiana. Riverine particles had higher dithionite-extractable iron contents and iron oxide- specific absorption features than did marine particles, consistent with current knowledge regarding differential transport of particulate iron oxides and hydroxides through estuarine salinity gradients and reductive alteration of these oxide phases on the Louisiana shelf. The quantifiable dependence of UV absorption features on iron oxide content suggests that, under certain conditions, in situ hyperspectral absorption measurements could be designed to monitor water-column iron mineral transport and transformation. © 2012, by the Association for the Sciences of Limnology and Oceanography, Inc.
US Household Demand for Organic Fruit
Date: 2017-08-31
Creator: Erik Nelson, John M Fitzgerald, Nathan Tefft, John L. Anderson
Access: Open access
- We estimate US household monthly elasticities of demand for some of the more popular organic fruits. To our knowledge, this is the first US-wide, multi-year analysis of price and income elasticities for various organic fruits. We calculate elasticities of demand for low-income, middle class, and rich income bracket households using three estimation techniques: two econometric methods and one machine learning method (least absolute shrinkage and selection operator (LASSO)). Demand estimates are based on Nielsen scanner data from approximately 60,000 households collected from 2011 to 2013. Generally, we find that own-price conditional and unconditional elasticities of demand for organic fruits are negative. Unconditional elasticity magnitudes tend to be largest in the representative middle-class household. Income elasticities of demand measurements are inconsistent and often statistically insignificant. This finding is consistent with the survey literature finding that many consumers buy organic food for mostly moral or ethical reasons. We run two policy experiments: a 10% subsidy of organic fruits, and a 10% tax on conventional fruits. Our hypothetical policies engender a stronger reaction among the general public than habitual buyers of organic fruit; unconditional purchase and expenditure elasticities are generally larger than conditional purchase and expenditure elasticities. Finally, we find that elasticities measured with the LASSO technique are not radically different than those measured with econometric methods. The most noticeable difference between the two analytical techniques is that LASSO is more likely to find price and income elasticities of demand that indistinguishable from zero, both substantively and statistically.
African Extensions: A Photographic Search for African Survivals in the Americas
Date: 1981-01-01
Creator: Reginald L. Jackson
Access: Open access
- Catalog for an exhibition co-sponsored by the Afro-American Studies Program, held at the Bowdoin College Museum of Art, John A. and Helen P. Becker Gallery, 7-22 March, 1991.
Erratum: Stochastic boolean satisfiability (Journal of Automated Reasoning (2001) 27 (251-296))
Date: 2002-01-01
Creator: Michael L. Littman, Stephen M. Majercik, Toniann Pitassi
Access: Open access
James Bowdoin III: Pursuing Style in the Age of Independence
Date: 2008-01-01
Creator: Vernon Scott
Access: Open access
- Catalog of an exhibition held at the Bowdoin College Museum of Art from Sept. 9, 2008, through June 7, 2009. Essay by V. Scott Dimond
On Kindleberger and Hegemony: From Berlin to M.I.T. and Back
Date: 2013-09-29
Creator: Stephen Meardon
Access: Open access
- The most notable idea of Charles P. Kindleberger’s later career is the value of a single country acting as stabilizer of an international economy prone to instability. It runs through his widely read books, The World in Depression, 1929-1939 (1973), Manias, Crises, and Panics (1978), A Financial History of Western Europe (1984), and kindred works. “Hegemonic stability,” the idea is called in the literature it inspired. This essay traces Kindleberger’s attachment to the idea back to his tenure as chief of the State Department’s Division of German and Austrian Economic Affairs from 1945 to 1947 and adviser to the European Recovery Program from 1947 to 1948. In both capacities Kindleberger observed and participated indirectly in the 1948 monetary reform in Western Germany. In the 1990s, during his octogenary decade, he revisited the German monetary reform with a fellow participant, economist, and longtime friend, F. Taylor Ostrander. Their collaborative essay marked Kindleberger’s effort to reclaim hegemonic stability theory from the scholars who developed it following his works of the 1970s and 1980s.