1,284 research outputs found
Land Quality and International Agricultural Productivity: A Distance Function Approach
Agricultural productivity measurement has been of great interest in recent years. Although analysts have long recognized that land quality plays an important role in agricultural productivity, land quality has been difficult to quantify and include in productivity models due to d ata limitations. Poor land quality, in the form of desertification, erosion, and poor soil quality, as well as climate and precipitation may limit growth in productivity over time. A Malmquist productivity index is proposed that decomposes productivity into efficiency change, technical change and land quality components and accounts for inter-country differences in land quality. The index is then applied to a 109-country data set covering 1980 to 2003. Many countries with lower productivity growth are limited by their resource endowment, and thus require policies and technology that reflect the needs of those environments.Land Economics/Use, Productivity Analysis,
USING RIGHTS OF FIRST REFUSAL FOR FARMLAND RETENTION
How can rights of first refusal protect prime agricultural land? This paper develops a theory for valuing rights of first refusal based on compensation for foreclosing future demand, information asymmetry, and advance purchase of market share. A procedure is developed for governments to use these rights to prevent conversion.Land Economics/Use,
Biological reserves Rare Species and the Opportunity Cost of Diversity
The preservation of species diversity generally suggests protection of either the greatest number of species possible or all species. Requiring representation of each species in at least one parcel in the system and seeking the minimum number of parcels in the reserve system to achieve this requirement is termed the Species Set Covering Problem (SSCP). Nonetheless, it is important, as well, to consider the rarest of species, as their populations are the most in need of protection to assure their survival. This paper uses zero-one programming models and an existing data set to study species protection, rarity and the opportunity costs of diversity. We employ for this purpose an integer programming model that uses the SSCP format to require at least one representation of each and every species, but that seeks in addition protection of the rarest species. This is achieved by maximizing redundant coverage of those species designated as rare. Results are then compared to those of the SSCP. Recognizing that resources available for conservation purchases could well be insufficient to represent all species at least once, we structure a model aimed at trading-off first coverage of the greatest number of species against redundant coverage of rare species. We develop a tradeoff curve for this multi-objective problem in order to evaluate the opportunity cost of covering more species as redundant coverage of rare species decreases Âand vice versa. Finally, various possible rarity sets and various budget proxies are considered along with their impacts on conservation policies, Pareto optimality and on the opportunity cost of diversity
THE SIGNIFICANCE OF INTERCEPTIONS OF FRESH PRODUCE FROM LATIN AMERICA AND THE CARIBBEAN INTO THE UNITED STATES
This paper develops a method to examine data on fresh produce imports from Latin America and the Caribbean into the United States from 1993-1999 to determine: 1) if there are significant differences in frequency of interceptions for a specific product for the region or a specific country within the region, and 2) whether significant changes in trade flows for specific products have occurred between points of origin and ports of entry. The results show that there are indeed differences between countries with respect to interception frequency, however current data on the fumigation frequency for a commodity/country or commodity/port of entry is not sufficient to determine the causes that underlie differences in frequencies between countries.International Relations/Trade,
The Zero Age Main Sequence of WIMP burners
We modify a stellar structure code to estimate the effect upon the main
sequence of the accretion of weakly interacting dark matter onto stars and its
subsequent annihilation. The effect upon the stars depends upon whether the
energy generation rate from dark matter annihilation is large enough to shut
off the nuclear burning in the star. Main sequence WIMP burners look much like
protostars moving on the Hayashi track, although they are in principle
completely stable. We make some brief comments about where such stars could be
found, how they might be observed and more detailed simulations which are
currently in progress. Finally we comment on whether or not it is possible to
link the paradoxically young OB stars found at the galactic centre with WIMP
burners.Comment: 4 pages, 3 figs. Matches published versio
Symmetry reduction and shape effects in concave chiral plasmonic structures
Chiral metamaterials have shown a number of interesting properties which result from the interaction of the chiral near-field they produce with light and matter. We investigate the influence of structural imperfections on the plasmonic properties of a chiral gold âgammadionâ, using electron energy loss spectroscopy to directly inform simulations of realistic, imperfect structures. Unlike structures of simple convex geometry, the lowest energy modes of the ideal concave gammadion have a quadrupole and dipole character, with the mode energies determined by the nature of electrostatic coupling between the gammadion arms. These modes are strongly affected by structural imperfections that are inherent to the material properties and lithographic patterning. Even subwavelength-scale imperfections reduce the symmetry, lift mode degeneracies convert dark modes into bright ones and significantly alter the mode energy, its near-field strength, and chirality. Such effects will be common to a number of multitipped concave structures currently being investigated for the chiral fields they support
AlGaInN laser diode technology for GHz high-speed visible light communication through plastic optical fiber and water
AlGaInN ridge waveguide laser diodes are fabricated to achieve single-mode operation with optical powers up to 100 mW at âŒ420âânmâŒ420âânm for visible free-space, underwater, and plastic optical fiber communication. We report high-frequency operation of AlGaInN laser diodes with data transmission up to 2.5 GHz for free-space and underwater communication and up to 1.38 GHz through 10 m of plastic optical fiber
969-100 Changing Profile of the Cardiac Donor
AbstractAs the demand for organs for cardiac transplantation has increased, donor criteria have evolved. We reviewed the characteristics of 190 cardiac donors from 1983 to 1993 to identify trends in donor profile and to determine if recipient outcome were affected. Donors were divided into early(1983â1987; n=86) and late (1988-1993; n=104) groups according to operative era, While mean donor age has not changed significantly (24 ± 0.9 to 26 ± 1.3 years), the proportion of donors older than 40 years has increased from 1% (1/86) to 15% (16/104) (p<0.001). Trauma was the cause of death in 93% (80/86) of the early group and 65% of the late group (68/104) (p<0.001); in the total series, donors older than 40 years were less likely to have died from trauma 131%; 5/16) than younger donors (83%; 143/173) (p=0.001). The proportion of out-of-state donors has fallen from 71% (61/86) to 27% (28/104) (p<0.001), while the proportion of ethnic minorities increased from 10% (9/86) to 25% (26/1041 (p<0.001). There have been no significant changes in gender profile; males constituted 78% (67/86) of the early group and 72% (75/104) of the late group. Five year survival after transplant was not predicted by donor age, mode of donor death, recipient age, or recipient UNOS status. In summary, donors in the current era are more likely (1) to be older, (2) to be within the state, (3) to come from an ethnic minority, and (4) to have died from causes other than trauma when compared to donors from the earlier era
Dolichopodidae catalog
114 p. : 2 ill. ; 26 cm.Includes bibliographical references (p. 81-97) and index.A catalog of the American species of Dolichopodidae north of Mexico is provided. Fifty-five valid genera and 1288 valid species and 3 subspecies in 14 subfamilies are listed. Compared to the North American catalog by Foote et al. (1965), 224 species are added, and there are 15 replacement names, 84 synonyms, 5 species removed from synonymy, and 76 transfers, as well as 10 species included in the previous catalog that are removed from the new list. Furthermore, 13 additional genera and 3 generic synonymies are included. Nomenclatural changes proposed in this catalog consist of 1 new generic synonymy, 4 new synonyms, 2 new names, 40 new combinations, and 1 species newly removed from synonymy. Additional nomenclatural changes and problems are discussed. All validly named taxa described before February 2004 are included. For each genus, the species list is preceded by notes on its distribution, biology, and ecology as well as a list of pertinent keys and revisions, when such information is available. For each valid species name, the list includes the author, year of publication, page number of original description, type depository and locality, and distribution in North America by state or province and occurrence in other realms, as well as taxonomic notes wherever applicable. Additional distribution records from the literature have been added. All known synonyms of genera and species as well as errors, emendations, and misidentifications are included. A bibliography of 492 publications is provided as well as an index to over 1838 included names. Statistics and comments on the history of North American dolichopodid research are presented. The diversity and distribution of Nearctic Dolichopodidae and their relationships with the fauna of other realms is tabulated and discussed
Searching for stochastic gravitational-wave background with the co-located LIGO interferometers
This paper presents techniques developed by the LIGO Scientific Collaboration
to search for the stochastic gravitational-wave background using the co-located
pair of LIGO interferometers at Hanford, WA. We use correlations between
interferometers and environment monitoring instruments, as well as time-shifts
between two interferometers (described here for the first time) to identify
correlated noise from non-gravitational sources. We veto particularly noisy
frequency bands and assess the level of residual non-gravitational coupling
that exists in the surviving data.Comment: Proceedings paper from the 7th Edoardo Amaldi Conference on
Gravitational Waves, held in Sydney, Australia from 8-14 July 2007. Accepted
to J. Phys.: Conf. Se
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