bluuebunny/crossref_metadata_2025 huggingface dataset:
The Economics of Crop Hail Insurance
Authors: Vercammen James , Pannell David J.
Published: July 2005

The demand for crop hail insurance is examined in both static and dynamic models and both with and without all‐risk crop insurance. Contrary to general results on optimal insurance with background risk, crop revenue uncertainty induces the farmer to decrease rather than increase coverage. The underinsurance results are strengthened when farmers are able to dynamically update their insurance portfolio as information about the value of the crop is revealed over time. When hail insurance is purchased along with all‐risk crop insurance, two alternative approaches are examined and their efficiency properties compared.

Nous examinons la demande d'assurance‐grêle au moyen, à lafois, de modèles statiques et de modèles dynamiques, chacun intégré ou non à une assurance tout‐risque. Contrairement à ce qu'on observe généralement pour le niveau d'assurance optimal établi enprésence d'un risque sous‐jacent, l'incertitude quant au rendement des cultures attendu incite l'exploitant agricole à réduire, plutôt qu'à augmenter, sa couverture. Les résultats de cette sous‐assurance sont améliorés lorsque l'exploitant est capable d'actualiser régulièrement son portefeuille d'assurance à mesure que la valeur finale de la récolte se précise. Dans le cas de l'assurance‐grêle achetée dans le cadre d'une assurance‐récolte tout‐risque, nous comparons deux options quant à leur possibilité de rendement économique.
Success Factors for Marketing Clubs in Alberta
Authors: Witwicki Nicole , Krogman Naomi , Brooks Harvey , Krahn Harvey
Published: July 2005

This paper examines the factors most strongly associated with the perceived success of agricultural marketing clubs in Alberta. The literature suggests that members'perceptions of club success are a function of structural (group development, group diversity, meeting structure and outside support), process (goal formation, network formation and member commitment) and outcome factors (economic benefits). Data from a survey of 129 club leaders and members of agricultural marketing clubs in Alberta are used to examine the relationship between these factors and members'perception of success. The results suggest the most important factors are process factors, specifically goal and network factors. This research suggests that while marketing clubs provide a variety of benefits, members who view their clubs as successful belong to clubs that are able to articulate their main goals, steer the group toward reaching those goals, monitor the achievement of those goals over time and facilitate the formation of networks.

Le présent article étudie les facteurs qui sont le plus fortement associés è la perception comme succés des clubs de commercialisation agricole en Alberta. La documentation suggère que la perception qu'ont les membres du succes d'un club est liée è des facteurs de structure (mise en place du groupe, diversité du groupe, structure des réunions et soutien extérieur), de processus (établissement de buts, établissement de réseau et implication des membres) et de résultats (bénéfices économiques). Les données fournies par un sondage auprès de 129 responsables et membres de clubs de commercialisation agricole en Alberta permettent d'étudier les rapports entre ces facteurs et la perception de succès qu'ont les membres. II s'avère que les facteurs les plus importants sont ceux de processus et, spécifiquement, ceux ayant trait aux huts et au réseau. La présente recherche indique que, malgré la diversité des bénéfices apportés par les clubs de commercialisation, les membres qui estiment que leur club est un succés appartiennent è des clubs qui savent définir leurs objectifs principaux, diriger le groupe vers l'atteinte de ces objectifs, mesurer l'atteinte de ces objectifs au fil du temps et faciliter la création de réseaux.
A Welfare Analysis of Biological Technical Change under Different Supply Shift Assumptions: The Case of Cocoa in Malaysia
Authors: Gotsch Nikolaus , Wohlgenant Michael K.
Published: July 2005

Emerging modem biotechnological improvements will make possible the cultivation of crops with higher yields, while enhanced resistance to pests and diseases will facilitate a reduction in the use of pesticides. In this article, the welfare effects of a regional technical change in relation to a perennial crop are measured. Dynamic aspects of supply responses to prices as well as to changes in technology are addressed when the effects of biological lag and the variation of asset productivity are taken into consideration. The effects of the adoption of improved cultivars are assessed for both a parallel and a conservative, pivotal shift in the supply curve. The theoretical model is implemented for cocoa in Malaysia as a large producer country on the one hand and all other countries as an aggregate on the other. Relatively small price and quantity effects result from the adoption of new cultivars. Although the magnitude of the effects on producer benefits and total benefits in Malaysia depend crucially on the type of supply shift assumed, significant benefits occur for Malaysian producers. Consumersapos; gains in the ROW are approximately offset by producers' losses in the ROW, suggesting that a considerable share of the gains would benefit consumers in economically well‐developed northern hemisphere countries at the expense of producers who do not immediately adopt improved cultivars.

Les améliorations biotechnologies émergentes rendent possible la culture de variétés à plus haut rendement, munies d'une résistance élevée contre les maladies et ravageurs permettant la réduction des applications de produits phytosanitaires. Dans cette article, les effets sociaux bénéfiques d'un progrés technologique régional pour les cultures pérennes sont mesurés. Les aspects dynamiques de la réaction de l'offre à des changements de prix et de technologie sont étudiés en considération des effets du retardement biologique et d'une variation du capital fixe. Les effets de l'adoption de cultures améliorées sont étudiés lorsqu'un déplacement paralléle et pivoté de la fonction de l'offre est admis. Le modéle théorique est réalisé pour le cacao en Malaisie, avec d'un côté la Malaisie en tant que grand pays producteur et le reste du monde de l'autre côté. Les résultats montrent que les effets de l'adoption de cultures améliorées sur les prix et quantités sont relativement modestes. Bien que les effets sociaux bénéfiques totaux et notamment ceux pour les producteurs en Malaisie dépendent essentiellement du type de déplacement de la fonction de l'offre, des gains importants sont réalisés par les producteurs en Malaisie. Les gains des consommateurs du reste du monde sont à peu prés compensés par les pertes des producteurs dans le reste du monde ce qui suggére qu'une partie considérable des gains va en faveur des consommateurs dans les pays très développés de l'hémisphére nord au dépens des producteurs n'adoptant pas immédiatement les cultures améliorées.
Voting for Registration of New Varieties of Grains in Western Canada: A Collegial Process in a Competitive Time
Authors: Klein K. K. , Walburger A. M.
Published: July 2005

The key decision‐making body for licensing new varieties of grains in western Canada is the Prairie Registration and Recommending Committee for Grains (PRRCG). The current committee structure, set up to operate on principles of collegiality, has been instrumental in maintaining the internationally recognized high‐quality of Canadian wheat. But the system may be out of step with the new reality of incentives as a result of Plant Breeders' Rights legislation passed by the Canadian Parliament in 1990.

An econometric analysis was conducted on 19 years of data collected on the various characteristics of candidate cultivars and subsequent votes by members of the PRRCG. The analyses showed that in spite of the immense measures taken to assure objectivity in decisions to recommend for licensing, other influences have a greater impact on the eventual decisions than do the characteristics of the test wheat cultivars. This raises serious questions about the procedures for recommending acceptance of new varieties.

Le principal organe responsable de l'homologation des nouvelles variétés de céréales dans l'Ouest canadien est le Comité de recommandation des inscriptions au catalogue du grain des Prairies (CRICGP). Le Comité fonctionne selon les principes de la collégialité et cette structure a concouru à la production d'un blé mondialement reconnu pour sa grande qualité. Pareil système pourrait cependant s'avérer désuet face à la réalité actuelle, née de l'adoption de la Loi sur la protection des obtentions végétales par le gouvemement canadien, en 1991.

Les auteurs ont effectué une analyse économétrique de 19 ans de données sur les caractéristiques des cultivars candidats à l'homologation et sur le résultat du scrutin des membres du CRICPG. Cette analyse révèle qu'en dépit des dispositions considérables visant à garantir l'objectivité des décisions, d'autres facteurs que les propriétés des cultivars interviennent davantage dans le jugement des membres du Comité. Ces résultats laissent planer un sérieux doute sur la validité des méthodes conduisant à la recommandation des nouvelles variétés.
The Effect of the Elimination of Federal Milk Marketing Orders on Farm‐level Markets: A Laboratory Experiment
Authors: Doyon Maurice A.
Published: July 2005

Experimental markets are used to simulate U.S. dairy market conditions and the effect of the elimination of Federal Milk Marketing Orders. The experimental task is a simple 2x2 matrix laboratory game that is computer assisted. The treatments are oligopsony and regulation. Perishability is represented by advance production decision with no carryover and is kept constant across the experiments. Sellers make production decisions and receive a pool price, while buyers make a price (bid) and quantity decision. Experimental results indicate that, in the absence of regulation, buyers are successful in reducing market price and in capturing a larger share of market surplus than a perfectly competitive solution predicts. Regulation reduced the market power of buyers and the price fluctuation of raw milk, in an oligopsonistic market, and does not reduce the overall price efficiency of the market.

L'auteur s'est servi de marchés expérimentaux pour simuler la situation sur le marché américain des produits laitiers et les répercussions de l'abolition des Federal Milk Marketing Orders (décrets fédéraux de commercialisation du lait). L'expérience consistait en un simple jeu de laboratoire à matrice 2x2 assisté par ordinateur. Les deux situations examinées étaient l'oligopsone et la régiementation. L'aspect périssable des denrées est representé par une décision de production avant prix sans possibilité d'entre pasage, et est constante dans toutes les expériences. Les vendeurs prenaient des décisions à l'égard de la production et recevaient un prix commun, tandis que les décisions des acheteurs se rapportaient au prix (offre) et à la quantité. Les résultats de l'expérience indiquent qu'en l'absence de réglementation, les acheteurs réussissent a diminuer le prix de marché et à capturer une part du surplus économique plus importante que celle prévue dans une situation de concurrence idéale. La réglementation affaiblit le pouvoir de marché des acheteurs et atténue la fluctuation des prix du lait cru sur un marché oligopsone sans pour autant réduire l'efficacité du marché, dans l'ensemble.
Rules, Policy and Rent Seeking: A Cross‐border Comparison
Authors: Baylis Kathy , Rausser Gordon
Published: July 2005

The United States and Canada are similar in many ways, yet they have taken different approaches to agricultural policy. This paper discusses what affect the different constitutional arrangements have had on the development of agricultural policy. Constitutions can affect the policy bargaining process in several ways: they determine who has access to the bargaining process, what is the legal set of policy options and what is the admissible coalition. The two countries' Constitutions differ in where regions have access to the bargaining process, the use of the courts and the size of the admissible coalition. These differences have led to divergent policies, which are evidenced by the response to the recent drop in commodity prices.
What Future for Agricultural Safety Net Programs?
Authors: Mussell Allan , Martin Larry
Published: July 2005

The early 1990s held the promise of decoupled farm programs in Canada and the U.S.; however, the potential benefits of decoupling have been eroded by ad hoc disaster programs. This paper assesses the benefits and difficulties of disaster programs relative to traditional farm programs, and proposes gross margin insurance as an approach to safety nets that captures the benefits of both. Gross margin insurance is applied to hogs in Ontario and Minnesota as case studies, with the cost and level of income protection compared. We show that based on simple estimates of actuarially fair premium costs, gross margin insurance compares favorably with programs that have been used to support hog farm incomes in both regions.
Identification of Economies of Scope in a Stochastic Production Environment
Authors: Curtis Rita E. , Sarmiento Camilo
Published: July 2005

This paper extends the definition of economies of scope to multioutput firms that face an uncertain production environment. Identification of economies of scope in this environment, however, requires separability assumptions on the technology. These identification restrictions are demonstrated in the paper. For each identification restriction, the definition of economies of scope is generalized to the case of uncertain production and risk aversion.

L'article que voici élargit la définition des économies de gamme aux entreprises à produits multiples aux prises avec une situation incertaine au niveau de la production. Pour cerner les économies de gamme dans une telle situation, il faut poser l'hypothèse de la séparation des technologies. Les auteurs illustrent ces restrictions et généralisent la définition des économies de diversification pour chacune d'elles dans le cas d'une production incertaine et de l'aversion du risque.
Agro‐Climatic Conditions and Regional Technical Inefficiencies in Agriculture
Authors: Demir Nazmi , Mahmud Syed F.
Published: July 2005

A survey of applications of the Technical Inefficiency Effects (TIE) model suggests that agro‐climatic and other environment variables are customarily omitted in the model specifications. The justification for such an omission is the assumption that these variables are beyond the control of the farmers and therefore should be treated as random variables. In this paper, we argue that in applications dealing with regional agricultural data, agro‐climatic variables should not be treated as pure random terms. Historical differences in agro‐climatic conditions are known with a reasonable degree of certainty across a larger region. Therefore, omission of such variables from the analysis may lead to inaccurate interregional technical inefficiency comparisons. In order to demonstrate the importance of agro‐climatic variables in such analyses, we estimate the TIE model for Turkey. A translog stochastic frontier production function with agro‐climatic variables such as rainfall and land quality is estimated, and it is shown not only that the agro‐climatic variables are statistically significant but also that their omission substantially affects mean output elasticities and relative technical efficiencies.

Une étude sur les applications du modèle de l'effet d'inefficacité technique (EIT) laisse à supposer que les variables agro‐climatiques et les autres variables environnementales sont comme d'habitude omises dans les spécifications du modèle. Une telle omission est justifiée par l'hypothèse selon laquelle ces variables sont en dehors du contrôle des fermiers et devraient être considérées comme des variables aléatoires. Dans ce communiqué, nous affirmons que dans les applications concernant les données agricoles régionales, ces variables agro‐climatiques ne doivent pas être traitées comme de simples termes aléatoires. Les différences historiques dans les conditions agro‐climatiques sont connues avec un degré raisonnable de certitudes pour une grande région. Aussi l'omission de telles variables dans l'analyse peut‐elle donner lieu à de fausses comparaisons interrégionales d'inefficacité technique. Afin de démontrer l'importance des variables agro‐climatiques dans de telles analyses, nous considérons le modèle de l'effet d'inefficacité techniques de la Turquie. II s'agit d'une fonction de production frontalière translogue et stochastique avec des variables agro‐climatiques telles que la pluviosité, la qualité de sol et d'autres variables. Nous démontrons que les variables agro‐climatiques sont non seulement importantes statistiquement, mais que leur omission influence essentiellement les élasticités moyennes de production ainsi que les efficacités techniques relatives.
Policy Development for Novel Foods: Issues and Challenges for Functional Food
Authors: Veeman Michele
Published: July 2005

Challenges in policy development for novel foods arise from information asymmetry associated with these credence goods. Policy development reflects pressures by firms and investors to apply health claims in marketing functional food, nutraceuticals and natural health products, which are growing market segments, relative to mature food markets. However, the wordings on health claims are often misinterpreted by consumers. Despite tendencies for some convergence in approaches to health claim policies, policy differs internationally. Related issues considered include factors influencing consumer preferences for these products and uncertainties in the markets for them.
Functional Eating and Strategic Groups in Canada
Authors: Cloutier L. Martin , Salves Anne‐Laure
Published: July 2005

The emergence of the nutraceuticals and functional foods (NFFs) products is a challenge to economists and management scientists interested in studying the evolution of the sector. There are profound issues in product and in market classification. This paper reports the results of an exploratory study that illustrates the use of strategic groups as a means to research this emerging industry, using a sample of 280 companies in Canada. The analysis identifies six main strategic groups within the NFFs sector that compete on the market, product and capability strategic fields. The results indicate that the sector is widely heterogeneous in firm composition, markets served, and intragroup and intergroup product strategies.

L'émergence de produits nutraceutiques et aliments fonctionnels (NAF) pose un défi aux économistes et aux spécialistes en sciences administratives intéressés par l'étude de I'évolution de ce secteur où perdurent de nomhreux prohlémes de classification de produits et de marchés. Cet article présente les résultats d'une étude exploratoire qui démontre la pertinence de la notion de groupe stratégique dans l'analyse d'un échantillon de 280 compagnies de ce secteur au Canada. Cette etude identifie six groupes strategiques dans le secteur des NAF en concurrence au plan des champs stratégiques de marchés, de produits et de compétences. Les résultats de la recherche montrent que le secteur est largement hétérogène au niveau de la composition des firmes, des marchés desservis et des stratégies de produits intergroupes et intragroupes.
The Effect of Producers' Risk Attitudes on Sizing the Harvest and On‐farm Drying System
Authors: Davis Todd D. , Patrick George F.
Published: July 2005

A simulation model of an on‐farm grain harvest and drying system was used to determine net returns associated with alternative sized systems. The physical processes of corn and soybean planting, growth, harvest and drying were simulated under historical weather conditions for 33 years. Weather data determined the number of field days, physiological maturity date, harvest grain moisture, yield losses and dryer energy costs. Guidelines developed by agricultural engineers and agricultural economists were used to initially size the combine and dryer for three sizes of farms. Capacities of the combine and dryer were increased and decreased by 10, 20, 30, 40 and 50%, independently. Net returns to labor and management, reflecting yield and price correlations, were determined for each of the equipment combinations. Stochastic dominance was used to evaluate the distributions of net revenue and determine the risk efficient combine and dryer sets. It was found that there were small differences in net returns for systems that completed harvest and drying in the 27B32 day range for all three farm sizes. For a given size of farm, risk averse producers were found to prefer smaller capacity combines and dryers.

Les auteurs se sont servis d'un modèle simulant la récolte et le séchage du grain à la ferme pour calculer le revenu net de systèmes de production de taille variable. Les aspects physiques de la plantation, de la croissance, de la récolte et du séchage du maïs et du soja ont été reproduits en fonction des données météorologiques relevées pendant 33 ans. Ces données ont permis d'établir le nombre de jours de croissance, la date de la maturité physiologique, la teneur en eau du grain, les pertes de rendement et le coût de l'énergie nécessaire au séchage. Ensuite, les auteurs ont suivi les recommandations des agronomes et des économistes agricoles pour déterminer les dimensions initiales de la moissonneuse et du séchoir pour trois exploitations de taille différente. La capacité de la moissonneuse et celle du séchoir ont été augmentées ou réduites indépendamment de 10, de 20, de 30, de 40 et de 50 pour cent, puis on a calculé le revenu net venant du travail et de la gestion du producteur en tenant compte de la corrélation entre le rendement et les prix pour chaque combinaison. La dominance stochastique a permis d'estimer la distribution du revenu net et d'identifier les ensembles moissonneuse/séchoir rentables en fonction du risque. Les systèmes où la récolte et le séchage sont terminés au bout de 27 à 32 jours entraînent de légères variations du revenu net, pour les trois types d'exploitation. Peu importe la taille de la ferme, l'aversion pour le risque incite le producteur à choisir une moissonneuse et un séchoir de dimensions plus modestes.
Producer Willingness to Pay for Precision Application Technology: Implications for Government and the Technology Industry
Authors: Hudson Darren , Hite Diane
Published: July 2005

This paper focuses on the willingness to pay (WTP) for precision application/site‐specific management technologies on the part of agricultural producers. We use a contingent valuation survey to elicit WTP for a package of technologies and examine the impact of government subsidies on potential demand. Results suggest that producer WTP is significantly lower than current technology prices, necessitating a 60% government subsidy to induce adoption, on average. Agronomic factors such as soil characteristic variability and soil quality are important determinants of WTP. In addition, how well the technology integrates into current farming practices and equipment also appears important.
Economic‐Environmental Tradeoffs in Swine Finishing Operations
Authors: de Vos Greg W. , Weersink Alfons , Stonehouse D. Peter
Published: July 2005

This study examines the cost effectiveness of 81 alternative manure management systems for a swine finishing operation in reducing three pollutants associated with livestock waste: ammonia, nitrogen and phosphorus. The results are presented in terms of the tradeoff between the levels of these pollutants (environmental indicator) and the economic returns to the producer. The levels of the three manure residuals cannot be reduced by more than half from the present levels under the profit‐maximizing system for each farm size. Further reduction would require changes in hog numbers to reduce the volume of manure and consequently residual levels. However, the feasible reductions in residuals can be achieved at relatively low cost. Larger farms tend to have lower abatement costs as the percentage reduction in residuals increase. The attempt to reduce more than one of the residuals simultaneously is complicated by the conflicting effects of alternative manure management systems on ammonia and nitrogen levels.

L'étude évalue la rentabilité de 81 systèmes de gestion du fumier pour les élevages de porcs quant à la réduction de la concentration de trois polluants associés aux déchets animaux: l'ammoniaque, l'azote et le phosphore. Les auteurs présentent les résultats sous forme de compromis entre la concentration de polluants (indice environnemental) et le rendement de l'élevage pour le producteur. Quelle que soit la taille de l'exploitation, il est impossible de réduire la concentration des trois résidus du fumier à plus de la moitié de leur concentration actuelle dans un régime de maximisation des bénéfices. Pour réduire leur concentration davantage, il faudrait diminuer la taille du troupeau et le volume de fumier. Atteindre les réductions de concentration réalisables ne coûte cependant pas très cher. Dans les gros élevages, le coût des mesures de lutte contre la pollution a tendance à baisser avec la hausse de la réduction des résidus en pour cent. L'action contraire des différents systèmes de gestion du fumier sur la concentration d'ammoniaque et d'azote complique les efforts déployés pour réduire simultanément la concentration de plusieurs résidus.
Optimal Collective Investment in Generic Advertising, Export Market Promotion and Cost‐of‐Production‐Reducing Research
Authors: Cranfield J. A. L.
Published: July 2005

Optimal investment rules are developed for a producer agency investing in domestic‐market generic advertising, export market promotion, and cost‐of‐production‐reducing research. These rules are derived assuming either maximization of producers' surplus or social surplus. The form of the optimality rules differs according to which objective is pursued. Fixed producer agency budgets are also allowed by incorporating a constraint limiting total expenditure on the three activities. Addition of such a constraint substantially alters the structure of the optimal investment rules. Differences in these rules highlight the importance of accounting for the financing mechanism when modeling optimal checkoff fund investment decisions. Optimality rules are simulated using data for the Canadian beef sector. Results suggest historic underinvestment in domestic‐market generic advertising but overinvestment in export market promotion. Sensitivity of simulation results underscores the difficulty in assessing optimality of historic producer investment in cost‐of‐production‐reducing research.
Public Research Policy for Today's Agricultural Biotech Research Industry
Authors: Malla Stavroula , Gray Richard
Published: July 2005

While the public sector has historically played a very significant role in the direct provision of agricultural research, the appropriate role of government in the future is no longer apparent in a world with intellectual property rights (IPRs) and a concentrated privatized biotech research industry. This study develops a search/imperfect competition framework to examine the public role. The analysis shows that private firms have inadequate incentives to invest in research for varietal improvement relative to the social optimum even with completely enforceable IPRs. A government subsidy on research output can efficiently increase the amount of applied research to the socially optimal point. Government subsidy of the research cost can have the same effect on research and development expenditure. Expanding direct applied public research increases social welfare but cannot achieve a social optimum, as it reduces the already limited incentives for private firms to invest. Finally, in situations where basic research is underprovided, government should address these market failures as part of an optimal research policy. Overall, the analysis suggests that there is a role for public support of applied research, but this role is no longer direct public involvement in applied research where IPRs are well established.
Canadian Exports of Livestock and Meat to the United States
Authors: Wachenheim Cheryl J. , Mattson Jeremy W. , Koo Won W.
Published: July 2005

Canadian exports of beef and live cattle to the United States have increased significantly since the late 1980s. Hog and pork exports have increased since the mid‐1990s. Major factors affecting exports of beef, pork, cattle and hogs from Canada to the United States include the exchange rate, increased Canadian production, Canada‐U.S. price differentials and trade liberalization under the Canada‐United States Free Trade Agreement of 1989. Increased Canadian exports have resulted in small but significant reductions in U.S. domestic prices of beef, pork and hogs.
Implications of Seasonal Climate Forecasts on World Wheat Trade: A Stochastic, Dynamic Analysis
Authors: Hill Harvey S. J. , Mjelde James W. , Love H. Alan , Rubas Debra J. , Fuller Stephen W. , Rosenthal Wesley , Hammer Graeme
Published: July 2005

Improvements in seasonal climate forecasts have potential economic implications for international agriculture. A stochastic, dynamic simulation model of the international wheat economy is developed to estimate the potential effects of seasonal climate forecasts for various countries' wheat production, exports and world trade. Previous studies have generally ignored the stochastic and dynamic aspects of the effects associated with the use of climate forecasts. This study shows the importance of these aspects. In particular with free trade, the use of seasonal forecasts results in increased producer surplus across all exporting countries. In fact, producers appear to capture a large share of the economic surplus created by using the forecasts. Further, the stochastic dimensions suggest that while the expected long‐run benefits of seasonal forecasts are positive, considerable year‐to‐year variation in the distribution of benefits between producers and consumers should be expected. The possibility exists for an economic measure to increase or decrease over a 20‐year horizon, depending on the particular sequence of years.

Le progrès des prévisions saisonnières du climat a une portée économique pour l'agriculture internationale. Un modèle stochastique et dynamique de l'économie internationale du blé est développé afin d'estimer les effets potentiels des prévisions saisonnières du climat sur la production de blé de divers pays, leurs exportations et le commerce mondial. Les études précédentes ont généralement ignoré les aspects stochastiques et dynamiques des effets liés à l'utilisation des prévisions climatiques. Cette étude montre l'importance de ces aspects. En particulier avec le libre échange l'utilisation de ces prévisions aboutit à l'augmentation des excédents dans tous les pays exportateurs. En fait, il apparaît que les producteurs accaparent une grande part de l'excédent économique créé par l'utilisation de ces prévisions. De plus, les dimensions stochastiques suggèrent que bien que les bénéfices à long terme des prévisions climatiques puissent être substantiels, on s'attend à des variations considérables d'une année à l'autre dans la distribution des bénéfices entre les producteurs et les consommateurs. Il est possible qu'un indicateur économique varie à la baisse sur 20 ans eus fonction de la séquence de variation climatique.
Increasing the Homogeneity of CAT's Item‐Exposure Rates by Minimizing or Maximizing Varied Target Functions While Assembling Shadow Tests
Authors: Li Yuan H. , Schafer William D.
Published: July 2005

A computerized adaptive testing (CAT) algorithm that has the potential to increase the homogeneity of CAT's item‐exposure rates without significantly sacrificing the precision of ability estimates was proposed and assessed in the shadow‐test (van der Linden & Reese, 1998) CAT context. This CAT algorithm was formed by a combination of maximizing or minimizing varied target functions while assembling shadow tests. There were four target functions to be separately used in the first, second, third, and fourth quarter test of CAT. The elements to be used in the four functions were associated with (a) a random number assigned to each item, (b) the absolute difference between an examinee's current ability estimate and an item difficulty, (c) the absolute difference between an examinee's current ability estimate and an optimum item difficulty, and (d) item information. The results indicated that this combined CAT fully utilized all the items in the pool, reduced the maximum exposure rates, and achieved more homogeneous exposure rates. Moreover, its precision in recovering ability estimates was similar to that of the maximum item‐information method. The combined CAT method resulted in the best overall results compared with the other individual CAT item‐selection methods. The findings from the combined CAT are encouraging. Future uses are discussed.
A Comparison of Item‐Selection Methods for Adaptive Tests with Content Constraints
Authors: Van Der Linden Wim J.
Published: July 2005

In test assembly, a fundamental difference exists between algorithms that select a test sequentially or simultaneously. Sequential assembly allows us to optimize an objective function at the examinee's ability estimate, such as the test information function in computerized adaptive testing. But it leads to the non‐trivial problem of how to realize a set of content constraints on the test—a problem more naturally solved by a simultaneous item‐selection method. Three main item‐selection methods in adaptive testing offer solutions to this dilemma. The spiraling method moves item selection across categories of items in the pool proportionally to the numbers needed from them. Item selection by the weighted‐deviations method (WDM) and the shadow test approach (STA) is based on projections of the future consequences of selecting an item. These two methods differ in that the former calculates a projection of a weighted sum of the attributes of the eventual test and the latter a projection of the test itself. The pros and cons of these methods are analyzed. An empirical comparison between the WDM and STA was conducted for an adaptive version of the Law School Admission Test (LSAT), which showed equally good item‐exposure rates but violations of some of the constraints and larger bias and inaccuracy of the ability estimator for the WDM.
Separation of P/C‐ and U‐type inactivation pathways in Kv1.5 potassium channels
Authors: Kurata Harley T. , Doerksen Kyle W. , Eldstrom Jodene R. , Rezazadeh Saman , Fedida David
Published: July 2005

P/C‐type inactivation of Kv channels is thought to involve conformational changes in the outer pore of the channel, culminating in a partial constriction of the selectivity filter. Recent studies have identified a number of phenotypic differences in the inactivation properties of different Kv channels, including different sensitivities to elevation of extracellular K+ concentration, and different state dependencies of inactivation. We have demonstrated that an alternatively spliced short form of Kv1.5, resulting in disruption of the T1 domain, exhibits a shift in the state dependence of inactivation in this channel, and in the current study we have examined this further to contrast the properties of inactivation from open versus closed states. In a TEA+‐sensitive mutant of Kv1.5 (Kv1.5 R487T), 10 mm extracellular TEA+ inhibits inactivation in both full‐length and T1‐deleted channels, but does not inhibit closed‐state inactivation in T1‐deleted channel forms. Similarly, substitution of K+ and Na+ with Cs+ ions in the recording medium inhibits inactivation of both full‐length and T1‐deleted channel forms, but fails to inhibit closed‐state inactivation of T1‐deleted channels. Collectively, these data distinguish between open‐state and closed‐state inactivation, and suggest the presence of multiple possible mechanisms of inactivation coexisting in Kv1 channels.
A maternal cafeteria diet during gestation and lactation promotes adiposity and impairs skeletal muscle development and metabolism in rat offspring at weaning
Authors: Bayol Stéphanie A. , Simbi Bigboy H. , Stickland Neil C.
Published: July 2005

We examined the effects of a maternal cafeteria diet on skeletal muscle and adipose tissue development in the offspring at weaning. Rats born to mothers fed the cafeteria diet either during gestation alone or during both gestation and lactation exhibited a 25% reduction in muscle cross‐sectional area with approximately 20% fewer fibres compared with pups fed a balanced chow diet. Maintaining the cafeteria diet during lactation increased intramuscular lipid content and fat pad weights characterized by adipocyte hypertrophy but not hyperplasia. These pups also had elevated muscle IGF‐1, IGF‐1 receptor, and PPARγ mRNA levels, which may indicate an attempt to maintain normal insulin sensitivity. The increased adiposity and elevated IGF‐1, IGF‐1 receptor and PPARγ mRNAs were not seen in the pups rehabilitated to the balanced diet during lactation. However, these pups exhibited reduced muscle cell proliferation (PCNA) with reduced insulin receptor and a trend towards reduced glucose transporter (GLUT)‐4 mRNAs when compared with pups fed a balanced chow diet, indicating possible alterations in glucose uptake by muscle tissue. Therefore, rats born to mothers fed a cafeteria diet during gestation alone or during both gestation and lactation exhibited impaired skeletal muscle development and metabolic disorders normally associated with insulin resistance as early as the weaning stage.
Postprandial triacylglycerol uptake in the legs is increased during exercise and post‐exercise recovery
Authors: Enevoldsen L. H. , Simonsen L. , Bülow J.
Published: July 2005

Six young, healthy male subjects were each studied in two experiments: (1) during resting conditions before and for 360 min after a meal (54% of energy as carbohydrate, 30% of energy as lipid, and 16% of energy as protein) comprising 25% of their total daily energy intake (M→R); and (2) while exercising on a cycle ergometer for 60 min at 50% of the peak oxygen consumption commencing 60 min after the meal (M→E) and then for another 240 min. Regional metabolism was measured by Fick's Principle in a leg and in the splanchnic tissue. The combination of food intake and exercise led to increased plasma triacylglycerol (TAG) uptake and clearance in the exercising legs immediately and for at least 4 h post‐exercise, while food intake per se did not change leg plasma TAG uptake or clearance for up to 6 h. It is hypothesized that the effect of exercise on leg plasma TAG metabolism is a result of capillary recruitment leading to exposure of the plasma lipoprotein particles to a larger amount of active LPL. In spite of the increased TAG uptake in the exercising legs the arterial plasma TAG concentration had a tendency to increase faster during exercise after a meal than during rest, but it also decreased faster implying that the total lipaemic response was the same whether exercise was performed or not. The amount of lipid taken up in the legs was higher than could be accounted for by whole body lipid oxidation during post‐exercise recovery, indicating accumulation of lipid in skeletal muscle in this period. Neither food intake alone nor the combination of food and exercise affected the splanchnic net balance of TAG. Finally, there is an additive effect of exercise and food intake on splanchnic net glucose balance.
Water permeability of Na+–K+–2Cl− cotransporters in mammalian epithelial cells
Authors: Hamann Steffen , Herrera‐Perez José Jaime , Bundgaard Magnus , Alvarez‐Leefmans Francisco Javier , Zeuthen Thomas
Published: July 2005

Water transport properties of the Na+–K+–2Cl− cotransporter (NKCC) were studied in cultures of pigmented epithelial cells (PE) from the ciliary body of the eye. Here, the membrane that faces upwards contains NKCCs and can be subjected to rapid changes in bathing solution composition and osmolarity. The anatomy of the cultured cell layer was investigated by light and electron microscopy. The transport rate of the cotransporter was determined from the bumetanide‐sensitive component of 86Rb+ uptake, and volume changes were derived from quenching of the fluorescent dye calcein. The water permeability (Lp) of the membrane was halved by the specific inhibitor bumetanide. The bumetanide‐sensitive component of the water transport exhibited apparent saturation at osmotic gradients higher than 200 mosmol l−1. Cell shrinkages produced by NaCl or KCl were smaller than those elicited by equi‐osmolar applications of mannitol, indicating reflection coefficients for these salts close to zero. The activation energy of the bumetanide‐sensitive component of the Lp was 21 kcal mol−1, which is four times higher than that of an aqueous pore. The data suggest that osmotic transport via the cotransporter involves conformational changes of the cotransporter and interaction with Na+, K+ and Cl−. Similar measurements were performed on immortalized cell cultures from the thick ascending limb of the loop of Henle (TALH). Given similar overall transport rates of bumetanide‐sensitive 86Rb+, the NKCCs of this tissue did not contribute any bumetanide‐sensitive Lp. This suggests that the cotransporters of the two tissues are either different isoforms or the same cotransporter but in two different transport modes.
Evidence for Ectopic Neurotransmission at a Neuronal Synapse
Authors: Coggan Jay S. , Bartol Thomas M. , Esquenazi Eduardo , Stiles Joel R. , Lamont Stephan , Martone Maryann E. , Berg Darwin K. , Ellisman Mark H. , Sejnowski Terrence J.
Published: July 2005

Neurotransmitter release is well known to occur at specialized synaptic regions that include presynaptic active zones and postsynaptic densities. At cholinergic synapses in the chick ciliary ganglion, however, membrane formations and physiological measurements suggest that release distant from postsynaptic densities can activate the predominantly extrasynaptic α7 nicotinic receptor subtype. We explored such ectopic neurotransmission with a novel model synapse that combines Monte Carlo simulations with high-resolution serial electron microscopic tomography. Simulated synaptic activity is consistent with experimental recordings of miniature excitatory postsynaptic currents only when ectopic transmission is included in the model, broadening the possibilities for mechanisms of neuronal communication.
The
Trypanosoma cruzi
Proteome
Authors: Atwood J. A. , Weatherly D. B. , Minning T. A. , Bundy B. , Cavola C. , Opperdoes F. R. , Orlando R. , Tarleton R. L.
Published: July 2005

To complement the sequencing of the three kinetoplastid genomes reported in this issue, we have undertaken a whole-organism, proteomic analysis of the four life-cycle stages of
Trypanosoma cruzi
. Peptides mapping to 2784 proteins in 1168 protein groups from the annotated
T. cruzi
genome were identified across the four life-cycle stages. Protein products were identified from >1000 genes annotated as “hypothetical” in the sequenced genome, including members of a newly defined gene family annotated as mucin-associated surface proteins. The four parasite stages appear to use distinct energy sources, including histidine for stages present in the insect vectors and fatty acids by intracellular amastigotes.
Earthquake Source Fault Beneath Tokyo
Authors: Sato Hiroshi , Hirata Naoshi , Koketsu Kazuki , Okaya David , Abe Susumu , Kobayashi Reiji , Matsubara Makoto , Iwasaki Takaya , Ito Tanio , Ikawa Takeshi , Kawanaka Taku , Kasahara Keiji , Harder Steven
Published: July 2005

Devastating earthquakes occur on a megathrust fault that underlies the Tokyo metropolitan region. We identify this fault with use of deep seismic reflection profiling to be the upper surface of the Philippine Sea plate. The depth to the top of this plate, 4 to 26 kilometers, is much shallower than previous estimates based on the distribution of seismicity. This shallower plate geometry changes the location of maximum finite slip of the 1923 Kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the Tokyo region.
Chromatic Adaptation of Photosynthetic Membranes
Authors: Scheuring Simon , Sturgis James N.
Published: July 2005

Many biological membranes adapt in response to environmental conditions. We investigated how the composition and architecture of photosynthetic membranes of a bacterium change in response to light, using atomic force microscopy. Despite large modifications in the membrane composition, the local environment of core complexes remained unaltered, whereas specialized paracrystalline light-harvesting antenna domains grew under low-light conditions. Thus, the protein mixture in the membrane shows eutectic behavior and can be mimicked by a simple model. Such structural adaptation ensures efficient photon capture under low-light conditions and prevents photodamage under high-light conditions.
Simulations of a QuasiTaylor State Geomagnetic Field Including Polarity Reversals on the Earth Simulator
Authors: Takahashi Futoshi , Matsushima Masaki , Honkura Yoshimori
Published: July 2005

High-resolution, low-viscosity geodynamo simulations have been carried out on the Earth Simulator, one of the fastest supercomputers, in a dynamic regime similar to that of Earth's core, that is, in a quasi–Taylor state. Our dynamo models exhibit features of the geodynamo not only in spatial and temporal characteristics but also in dynamics. Polarity reversals occurred when magnetic flux patches at high latitudes moved poleward and disappeared; patches with reversed field at low and mid-latitudes then moved poleward.
Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between
Authors: Priestley Rodney D. , Ellison Christopher J. , Broadbelt Linda J. , Torkelson John M.
Published: July 2005

We analyzed the glassy-state structural relaxation of polymers near surfaces and interfaces by monitoring fluorescence in multilayer films. Relative to that of bulk, the rate of structural relaxation of poly(methyl methacrylate) is reduced by a factor of 2 at a free surface and by a factor of 15 at a silica substrate interface; the latter exhibits a nearly complete arresting of relaxation. The distribution in relaxation rates extends more than 100 nanometers into the film interior, a distance greater than that over which surfaces and interfaces affect the glass transition temperature.
Distinct Kinetic Changes in Neurotransmitter Release After SNARE Protein Cleavage
Authors: Sakaba Takeshi , Stein Alexander , Jahn Reinhard , Neher Erwin
Published: July 2005

Neurotransmitter release is triggered by calcium ions and depends critically on the correct function of three types of SNARE [soluble
N
-ethylmaleimide–sensitive factor attachment protein (SNAP) receptor] proteins. With use of the large calyx of Held presynaptic terminal from rats, we found that cleavage of different SNARE proteins by clostridial neurotoxins caused distinct kinetic changes in neurotransmitter release. When elevating calcium ion concentration directly at the presynaptic terminal with the use of caged calcium, cleavage of SNAP-25 by botulinum toxin A (BoNT/A) produced a strong reduction in the calcium sensitivity for release, whereas cleavage of syntaxin using BoNT/C1 and synaptobrevin using tetanus toxin (TeNT) produced an all-or-nothing block without changing the kinetics of remaining vesicles. When stimulating release by calcium influx through channels, a difference between BoNT/C1 and TeNT emerged, which suggests that cleavage of synaptobrevin modifies the coupling between channels and release-competent vesicles.