Trade Costs

This paper surveys the measurement of trade costs --- what we know, and what we don't know but may usefully attempt to find out. Partial and incomplete data on direct measures of costs go together with inference on implicit costs from trade flows and prices. Total trade costs in rich countries are large. The ad valorem tax equivalent is about 170% when pushing the data very hard. Poor countries face even higher trade costs. There is a lot of variation across countries and across goods within countries, much of which makes economic sense. Theory looms large in our survey, providing interpretation and perspective on the one hand and suggesting improvements for the future on the other hand. Some new results are presented to apply and interpret gravity theory properly and to handle aggregation appropriately.

Subtidal algal community structure in kelp beds around the Cape Peninsula (Western Cape, South Africa)

The subtidal understorey seaweed communities were studied along a coastal distance of 104 km around the Cape Peninsula, which is situated in an overlap region between two marine provinces and characterized by a considerable temperature gradient. Sampling was carried out at six sites (4 to 10 quadrats per site) around the Cape Peninsula. For each of the quadrats, biomass of each species, grazing, and environmental variables such as temperature, wave exposure and sand cover were determined. The data were analysed using canonical correspondence analysis (CCA) and two way indicator species analysis (TWINSPAN). A total of 142 seaweed taxa were found at the six sites (21 Chlorophyta, 14 Phaeophyta and 107 Rhodophyta). The two sides of the Peninsula have a very different biomass-composition of Chlorophyta, Phaeophyta and Rhodophyta. The biomass of Rhodophyta in the Atlantic sites is much higher than in the Bay, and the biomass of Chlorophyta is higher in False Bay than on the west coast. A change in floristic composition of subtidal algal communities around the Cape Peninsula can be observed and is principally related to seawater temperature and wave exposure. Next to these physical factors, grazing is demonstrated to be important in determining species composition. A lower degree of wave exposure might result in a higher number of grazers in False Bay. The occurrence of a higher cover of encrusting corallines in the Bay is probably a consequence of the higher grazing pressure. Distinct community types can be recognized from TWINSPAN and CCA

Relative Efficiency of Charges and Quantity Controls in Fisheries with Continuous Stock Growth and Periodically Fixed Instrument Levels

This article presents a simple combination discrete-time/continuous-time model that incorporates continuous population dynamics and fishing activity together with periodic, rather than continuous, instrument adjustment into the decision process for choosing the optimal type and level of regulatory instrument. A per-unit tax and an allocated instantaneous harvest rate quota each drive the system along different time paths, and each results in a different present value of the stream of net benefits generated by harvesting the resource. The choice of instruments is fishery specific; it depends on the parameter values of the fishery in question.Environmental Economics and Policy, Resource /Energy Economics and Policy,

FACTORS AFFECTING WELFARE GAINS FROM FISHING GEAR RESTRICTIONS

While the use of gear restrictions to regulate fishing activity seldom has the objective of improving economic efficiency, it is capable of achieving that result under some conditions. It can also reduce economic efficiency. This paper explores the way several factors affect the sign and magnitude of welfare gains from fishing gear restrictions. These factors include, among others: the fixity or variability of the price of fish and the presence or absence of diminishing short-run average product of effort. Some generalizations are offered regarding the characteristics of fisheries in which gear restrictions are most likely to produce welfare gains.Resource /Energy Economics and Policy,

Taxes vs. Quotas for Regulating Fisheries Under Uncertainty: A Hybrid Discrete-Time Continuous-Time Model

There is a wide variety of regulatory instruments available for achieving economic efficiency in markets where externalities exist. All of them, when correctly designed, are equally effective, provided that complete information is available and that adjustments to the level of the instruments can be made costlessly. However, with the presence of uncertainty, it is well known that one instrument or another may produce a higher expected present value of net social benefits than the others. How uncertainty affects the choice of instrument specifically in fishery management and in other dynamic optimization settings is less well known. A combination discrete-time and continuous-time stochastic model of a dynamic fishery is used to compare the relative performance of a per unit tax and a quota in this paper. The analysis confirms the conclusion reached in the general literature on optimal instrument choice under uncertainty: which instrument performs most efficiently depends on the specific fishery being regulated.Environmental Economics and Policy, Resource /Energy Economics and Policy, Risk and Uncertainty,

Identification of dividing, determined sensory neuron precursors in the mammalian neural crest

Sensory and autonomic neurons of the vertebrate peripheral nervous system are derived from the neural crest. Here we use the expression of lineage-specific transcription factors as a means to identify neuronal subtypes that develop in rat neural crest cultures grown in a defined medium. Sensory neurons, identified by expression of the POU-domain transcription factor Brn-3.0, develop from dividing precursors that differentiate within 2 days following emigration from the neural tube. Most of these precursors generate sensory neurons even when challenged with BMP2, a factor that induces autonomic neurogenesis in many other cells in the explants. Moreover, BMP2 fails to prevent expression of the sensory-specific basic helix-loop-helix (bHLH) transcription factors neurogenin1, neurogenin2 and neuroD, although it induces expression of the autonomic-specific bHLH factor MASH1 and the paired homeodomain factor Phox2a in other cells. These data suggest that there are mitotically active precursors in the mammalian neural crest that can generate sensory neurons even in the presence of a strong autonomic-inducing cue. Further characterization of the neurons generated from such precursors indicates that, under these culture conditions, they exhibit a proprioceptive and/or mechanosensory, but not nociceptive, phenotype. Such precursors may therefore correspond to a lineally (Frank, E. and Sanes, J. (1991) Development 111, 895-908) and genetically (Ma, Q., Fode, C., Guillemot, F. and Anderson, D. J. (1999) Genes Dev. 13, in press) distinct subset of early-differentiating precursors of large-diameter sensory neurons identified in vivo

Surface Water and Flood Extent Mapping, Monitoring, and Modeling Products and Services for the SERVIR Regions

SERVIR is a joint NASA - US Agency for International Development (USAID) project to improve environmental decision-making using Earth observations and geospatial technologies. A common need identified among SERVIR regions has been improved information for disaster risk reduction and in specific surface water and flood extent mapping, monitoring and forecasting. Of the 70 SERVIR products (active, complete, and in development), 4 are related to surface water and flood extent mapping, monitoring or forecasting. Visit http://www.servircatalog.net for more product details

Conspiratorial Thinking: How Worldview and Mortality Salience Affect Belief

Conspiratorial thinking is widespread throughout the world, though the major social sciences have thus far chosen not to study them for a variety of reasons. This study attempts to understand what, in fact, makes individuals believe in conspiracy theories. Using aspects of terror management theory, Kruglanski\u27s theory of lay epistemology, participants\u27 political worldviews, and conspiracy type, this paper will explore what triggers conspiracy-prone individuals to see the world the way they do. It is anticipated that individuals who have thoughts of their death primed in their consciousness will structure the world more rigidly, cling to their worldviews and respond to information in a manner which will leave them susceptible to believing conspiracies