bluuebunny/crossref_metadata_2025_split huggingface dataset:
Big mice die young: early life body weight predicts longevity in genetically heterogeneous mice
Authors: Miller Richard A. , Harper James M. , Galecki Andrzej , Burke David T. 
Published: March 2003

SummarySmall body size has been associated with long life span in four stocks of mutant dwarf mice, and in two varieties of dietary restriction in rodents. In this study, small body size at ages 2–24 months was shown to be a significant predictor of life span in a genetically heterogeneous mouse population derived from four common inbred mouse strains. The association was strongest for weights measured early in adult life, and somewhat weaker, though still statistically significant, at later ages. The effect was seen both in males and females, and was replicated in an independent population of the same genetic background. Body size at ages 2–4 months was correlated with levels of serum leptin in both males and females, and with levels of IGF‐I and thyroid hormone in females only. A genome scan showed the presence of polymorphic alleles on chromosomes 2, 6, 7 and 15 with significant effects on body weight at 2–4 months, at 10–12 months, or at both age ranges, showing that weight gain trajectory in this stock is under complex genetic control. Because it provides the earliest known predictor of life span, body weight may be usefully included in screens for induced mutations that alter aging. The evidence that weight in 2‐month‐old mice is a significant predictor of life span suggests that at least some of the lethal diseases of old age can be timed by factors that influence growth rate in juvenile rodents.
Oxidative stress and aging: beyond correlation
Authors: Golden Tamara R. , Hinerfeld Douglas A. , Melov Simon 
Published: March 2003

SummaryThe oxidative stress theory of aging has become increasingly accepted as playing a role in the aging process, based primarily on a substantial accumulation of circumstantial evidence. In recent years, the hypothesis that mitochondrially generated reactive oxygen species play a role in organismal aging has been directly tested in both invertebrate and mammalian model systems. Initial results imply that oxidative damage, specifically the level of superoxide, does play a role in limiting the lifespans of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. In mammalian model systems, the effect of oxidative stress on lifespan is less clear, but there is evidence that antioxidant treatment protects against age‐related dysfunction, including cognitive decline.
Regenerative potential of human skeletal muscle during aging
Authors: Renault Valérie , Thorne Lars‐Eric , Eriksson Per‐Olof , Butler‐Browne Gillian , Mouly Vincent 
Published: March 2003

SummaryIn this study, we have investigated the consequences of aging on the regenerative capacity of human skeletal muscle by evaluating two parameters: (i) variation in telomere length which was used to evaluate the in vivo turn‐over and (ii) the proportion of satellite cells calculated as compared to the total number of nuclei in a muscle fibre. Two skeletal muscles which have different types of innervation were analysed: the biceps brachii, a limb muscle, and the masseter, a masticatory muscle. The biopsies were obtained from two groups: young adults (23 ± 1.15 years old) and aged adults (74 ± 4.25 years old). Our results showed that during adult life, minimum telomere lengths and mean telomere lengths remained stable in the two muscles. The mean number of myonuclei per fibre was lower in the biceps brachii than in the masseter but no significant change was observed in either muscle with increasing age. However, the number of satellite cells, expressed as a proportion of myonuclei, decreased with age in both muscles. Therefore, normal aging of skeletal muscle in vivo is reflected by the number of satellite cells available for regeneration, but not by the mean number of myonuclei per fibre or by telomere lengths. We conclude that a decrease in regenerative capacity with age may be partially explained by a reduced availability of satellite cells.
Life history, ecology and longevity in bats
Authors: Wilkinson Gerald S. , South Jason M. 
Published: March 2003

SummaryThe evolutionary theory of aging predicts that life span should decrease in response to the amount of mortality caused by extrinsic sources. Using this prediction, we selected six life history and ecological factors to use in a comparative analysis of longevity among 64 bat species. On average, the maximum recorded life span of a bat is 3.5 times greater than a non‐flying placental mammal of similar size. Records of individuals surviving more than 30 years in the wild now exist for five species. Univariate and multivariate analyses of species data, as well as of phylogenetically independent contrasts obtained using a supertree of Chiroptera, reveal that bat life span significantly increases with hibernation, body mass and occasional cave use, but decreases with reproductive rate and is not influenced by diet, colony size or the source of the record. These results are largely consistent with extrinsic mortality risk acting as a determinant of bat longevity. Nevertheless, the strong association between life span and both reproductive rate and hibernation also suggests that bat longevity is strongly influenced by seasonal allocation of non‐renewable resources to reproduction. We speculate that hibernation may provide a natural example of caloric restriction, which is known to increase longevity in other mammals.
Differential regulation of Shc adaptor proteins in skeletal muscle, spinal cord and forebrain of aged rats with sensorimotor impairment
Authors: Jiang Xiaogang , Edstrom Erik , Altun Mikael , Ulfhake Brun 
Published: March 2003

SummaryThe Shc family of proteins participates in mitogenic and survival signalling through binding to receptor tyrosine kinases. We report here on the expression of Shc in forebrain, spinal cord and hind limb muscles from 30‐month‐old rats with different degrees of sensorimotor impairment. ShcA (mRNA and protein) is up‐regulated in skeletal muscles and spinal cord of aged rats, and this change relates to biological age, i.e. degree of behavioural incapacitation, rather than to chronological age. Western blot and RT‐PCR revealed that the increase in ShcA selectively affected the p46 isoform in the spinal cord, whereas in muscle tissue a robust increase of p66ShcA was also evident. Furthermore, in parallel with the up‐regulation of ShcA, an increase of p75NTR mRNA in the aged animals was observed. ShcB mRNA showed a tendency for down‐regulation in both spinal cord and skeletal muscles, whereas the expression of ShcC was unaltered. Our data show that the regulation of Shc mRNAs in senescence is region as well as isoform specific. The regulatory changes may reflect changes in mitogenic/survival signalling induced by age‐related cell and tissue damage. The coup‐regulation of p66ShcA and p75NTR is interesting since both molecules have been associated with apoptosis.
Apoptosis, necrosis and cellular senescence: chaperone occupancy as a potential switch
Authors: Sõti Csaba , Sreedhar Amere Subbarao , Csermely Péter 
Published: March 2003

SummaryChaperone function plays a key role in repairing proteotoxic damage and in the maintenance of cell survival. Here we compare the regulatory role of molecular chaperones (heat shock proteins, stress proteins) in cellular senescence, apoptosis and necrosis. We also review the current data on chaperone level and function in aging cells, and list some possible therapeutic interventions. Finally, we postulate a hypothesis, that increasing chaperone occupancy might be an important event which forces cells out of the normal cell cycle towards senescence. In the case of severe stress, this may lead to apoptosis or, following lethal stress, to cell necrosis.
Stop‐and‐Go Agricultural Policies
Authors: Bourgeon Jean‐Marc , Chambers Robert G. 
Published: March 2003

AbstractThe optimal design of farm policy and public investment in agriculture in the presence of asymmetric information between the government and farmers is studied. It is shown that a mix of capped deficiency payments and voluntary paid land diversion can implement the optimal policy outcome. Optimal program design requires large farmers to farm all their land, and small farmers may or may not divert acreage. Decoupled policies are never optimal.
The Goals of U.S. Agricultural Policy: A Mechanism Design Approach
Authors: Hueth Brent 
Published: March 2003

AbstractThis article examines motivations underlying the government's choice of alternative policy mechanisms for subsidizing agriculture. Optimal policies are analyzed for three government objectives: one where the government wishes to ensure a minimum level of net income for all farmers, a second where the government's only concern is to transfer income from consumers and taxpayers to the farm sector, and a final “augmented” income‐transfer objective. The analysis offers an explanation for agricultural policy mechanisms that involve overproduction by high‐cost producers, relative to a free‐market equilibrium. Such a distortion might arise from the existence of nonmarket values for the production of relatively high‐cost farmers in the government's objective.
Information Value and Risk Premium in Agricultural Production: The Case of Split Nitrogen Application for Corn
Authors: Bontems Philippe , Thomas Alban 
Published: March 2003

AbstractThis article considers an agricultural production model of sequential nitrogen application under risk. Because of random shocks between subsequent production stages, optimal fertilization decisions depend on the magnitude of farmers' risk aversion (risk premium), and the possibility for farmers to process information (value of information). We propose a joint estimation procedure of technology and risk aversion parameters, using a structural, simulation‐based econometric procedure. Parameter estimates allow to compute both the value of information and the risk premium, which account for about 30% of fertilizer cost for Midwest corn producers.
Valuation of Credit Risk in Agricultural Mortgages
Authors: Sherrick Bruce J. , Barry Peter J. , Ellinger Paul N. 
Published: March 2003

AbstractA credit‐risk valuation model is developed and empirically implemented to estimate the cost of insuring against credit risks in pools of agricultural mortgage loans. Probabilistic information about loss distributions across a broad set of loan‐level and pool‐level characteristics is used to assess insurance valuation and solvency likelihood. The effects on the value of credit‐risk insurance of pool size, deductibles, timing alterations, premium loadings, adverse loan selection, and changing underwriting standards are also estimated. Results indicate that actuarial insurance costs are initially highly sensitive and then become relatively insensitive as pool size increases.
Estimating the Demand for a New Technology: Bt Cotton and Insecticide Policies
Authors: Hubbell Bryan J. , Marra Michele C. , Carlson Gerald A. 
Published: March 2003

AbstractThis article examines the potential demand for Bt cotton in the Southeast from information gathered in the first year of commercialization. We combine revealed preference (RP) data on adoption of Bt cotton varieties with stated preference (SP) data on willingness to adopt to estimate demand using a double‐bounded maximum likelihood procedure. Using estimated demand equations, we simulate the costs of reducing conventional insecticide applications through subsidization of Bt cotton. Results indicate that reducing cotton insecticide applications by 40% in the Southeast would require a $@@‐@@21/acre subsidy, with total annual program costs between $@@‐@@53 million and $@@‐@@60 million.
Timber Price Dynamics Following a Natural Catastrophe
Authors: Prestemon Jeffrey P. , Holmes Thomas P. 
Published: March 2003

AbstractCatastrophic shocks to existing stocks of a renewable resource can cause long‐run price shifts. With timber, these long‐run price shifts may be accompanied by a short‐run price drop due to salvage. Hurricane Hugo damaged 20% of southern pine timber in the South Carolina Coastal Plain in 1989. To estimate the short‐ and long‐run effects of the hurricane on the prices of timber stocks, we estimated an intervention model of the residuals of cointegration of South Carolina sawtimber and pulpwood stumpage prices with prices of similar products from other regions. Modeling revealed a 30% negative price spike due to salvage and a long‐run enhancement effect, leading to prices that are 10% to 30% higher than they would have been had Hugo not occurred.
The Monthly Food Stamp Cycle: Shopping Frequency and Food Intake Decisions in an Endogenous Switching Regression Framework
Authors: Wilde Parke E. , Ranney Christine K. 
Published: March 2003

AbstractMean food spending by food stamp households peaks sharply in the first three days after benefits are received. For those who conduct major grocery shopping trips only once per month (42% of all food stamp households), mean food energy intake drops significantly by the fourth week of the month. For the remaining households, intake remains steady over the course of the month. These patterns motivate an empirical model that simultaneously accounts for the shopping frequency and food intake decisions over time. Results have implications for policies that may affect the frequency of grocery shopping by food stamp households.
Transactions Costs and Agricultural Household Supply Response
Authors: Key Nigel , Sadoulet Elisabeth , Janvry Alain De 
Published: March 2003

AbstractWe develop and estimate a model of supply response when transactions costs create a situation where some producers buy, others sell, and others do not participate in markets. We present two rationales for why producing households may have different relationships to the market: proportional and fixed transactions costs. Using data on Mexican corn producers, we estimate an empirical model that allows for separate tests of the significance of both types of transactions costs, revealing that both fixed and proportional transactions costs matter for the estimation. The results provide consistent estimates of supply elasticity and measures of the relative importance of factors determining both proportional and fixed transactions costs.
The Returns from Schooling in a Diversified Rural Economy
Authors: Taylor J. Edward , Yunez‐Naude Antonio 
Published: March 2003

AbstractControlling for the endogeneity of activity choice and considering both household‐head and family schooling, we findevid ence of high returns from schooling in both crop andnoncrop activities. As schooling levels increase, the returns from schooling shift away from crop production. Failure to control for activity selection andfamily schooling is likely to result in biasedestimates of the returns from schooling in individual activities.
A Test of Nutritional Quality Signaling in Food Markets Prior to Implementation of Mandatory Labeling
Authors: Mojduszka Eliza M. , Caswell Julie A. 
Published: March 2003

AbstractIn May 1994, new nutrition labeling regulations went into effect in the United States requiring mandatory disclosure of information on the nutritional content of foods. This article uses Grossman's model of totally effective quality signaling to evaluate whether markets were effective in information provision prior to the new regulation. If markets were effective in providing information to consumers on the nutritional quality of foods the new regulation would be unnecessary. The results of the logistic model, where the probability of voluntary information disclosure is linked to the nutritional quality of food products and their prices, indicate that private quality signaling was not reliably at work in food markets prior to implementation of the mandatory nutrition labeling regulation.
Valuing Water Supply Reliability
Authors: Griffin Ronald C. , Mjelde James W. 
Published: March 2003

AbstractInstead of creating water supply systems that fully insulate mankind from climate‐imposed water deficiencies, it is possible that for municipal water systems a nonzero probability of water supply shortfall is efficient. Perfect water supply reliability, meaning no chance of future shortfall, is not optimal when water development costs are high. Designing an efficient strategy requires an assessment of consumer preferences pertaining to the reliability of water supply. Contingent valuations of both current and future shortfalls are reported. The consistency of these measures is gauged using an expected utility model.
Nonparametric and Semi‐Nonparametric Recreational Demand Analysis
Authors: Cooper Joseph C. 
Published: March 2003

AbstractThis paper addresses issues of specification testing for the travel cost method (TCM). Two nonparametric approaches to TCM analysis are presented. In addition, semi‐nonparametric count models for TCM are developed. A numerical illustration is provided in which the three methods are applied to an actual TCM data set on waterfowl hunting and the results are compared to those from a parametric analysis.
Nonparametric Estimation of Crop Insurance Rates Revisited
Authors: Ker Alan P. , Goodwin Barry K. 
Published: March 2003

AbstractWith the crop insurance program becoming the cornerstone of U.S. agricultural policy, recovering accurate rates is of paramount interest. Lack of yield data presents, by far, the most fundamental obstacle to recovery of accurate rates. This article employs new methodology to estimate conditional yield densities and derive the insurance rates. In our application, we find the nonparametric kernel density estimator requires an additional twenty‐six years of yield data to estimate the shape of the conditional yield densities as accurately as the recently developed empirical Bayes nonparametric kernel density estimator. Such methodological improvements can significantly aid in ameliorating the data problem.
Brand Choice and Purchase Frequency Revisited: An Application to Recreation Behavior
Authors: Shaw W. Douglas , Shonkwiler J. Scott 
Published: March 2003

AbstractThe role that total purchases play in determining the choice among brands has been considered in microeconomic theory for quite some time, but for traditional goods only. Consumption of outdoor recreation is an unusual good, most often measured using an individual's recreational trip. Adding the trips made on a number of choice occasions seems the obvious way to aggregate this good, but doing so leads to several problems in defining a meaningful price index. The Hicks‐Leontief conditions for aggregation suggest that trips to destinations may be thought of as brand choices on consumption occasions, andthe continuous analogue to total purchases may in fact be the individual's total travel. An empirical example of the model is used to estimate welfare impacts for a group of anglers.
The Economic Threshold with a Stochastic Pest Population: A Real Options Approach
Authors: Saphores Jean‐Daniel M. 
Published: March 2003

AbstractUsing real options,this paper formulates an optimal stopping model for applying pest control measures when the density of a pest population varies randomly. A delay between successive pesticide applications is introduced to analyze the farmer's expected marginal cost of reentry. This model is applied to the control of a foliar pest of apples via a pesticide, and is solved numerically. A sensitivity analysis shows that the pest density that should trigger pesticide use can vary significantly with the pest density volatility. Incorporating pest randomness into simple decision rules may thus help better manage the chemicals applied to soils and crops.
Efficiency and Market Power in Greek Food Industries
Authors: Oustapassidis K. , Vlachvei A. , Notta O. 
Published: March 2003

AbstractThis paper uses firm level data to examine the market power versus efficiency hypothesis by taking into consideration both the long‐run behavior of profitability and the possible endogeneity bias among profitability, market share, and advertising variables. In a sample of 266 Greek food manufacturing firms in the period 1987–95, two‐stage least‐squares results show both a direct effect of firm characteristics and an indirect effect of industry characteristics on profitability which do not provide support for the efficiency hypothesis alone but they do show that profitability is affected by both firm and industry variables.
Crop Insurance under Catastrophic Risk
Authors: Duncan John , Myers Robert J. 
Published: March 2003

AbstractWe develop a new insurance model that shows how catastrophic risk affects the nature and existence of a crop insurance market equilibrium. A reservation preference level is used to characterize long‐run equilibrium when catastrophic risk makes insurance companies risk responsive. Catastrophic risk is shown to increase premiums, reduce farmer coverage levels and, under some conditions, lead to a complete breakdown of the crop insurance market. Reinsurance can help facilitate an equilibrium and/or increase participation, particularly if the reinsurance is subsidized. The analysis has important implications for the design and management of crop insurance and reinsurance programs.
Using Consumption and Asset Return Data to Estimate Farmers' Time Preferences and Risk Attitudes
Authors: Lence Sergio H. 
Published: March 2003

AbstractThe generalized expected utility model is fitted to U.S. farm data to estimate farm operator's time preferences and risk attitudes. The estimated farmer's utility parameters are quite “reasonable” and exhibit high accuracy. The forward‐looking expected utility model is soundly rejected in favor of the generalized expected utility paradigm. Importantly, the generalized expected utility model is also found to fit the data better than the myopic model typically used to study agricultural production under risk. Finally, U.S. farmers' relative aversion to risk appears to have diminished significantly over time
Regional Shifts in Pork Production: Implications for Competition and Food Safety
Authors: Önal Hayri , Unnevehr Laurian , Bekric Aleksandar 
Published: March 2003

AbstractU.S. pork production and processing is consolidating in larger, more economically efficient units, and shifting from the Midwest into the Southeast. A regionalmodelof farm supply and processing demand shows that smaller Midwest operations can survive only if processing capacity remains concentrated in that region. Salmonella incidence is higher in the Southeast and on larger farms. Restricting salmonella incidence in hogs delivered for processing to the minimum feasible level would increase total industry costs by 3%, due to increased production and delivery costs. It would also increase the comparative advantage of farms and processing firms in the Midwest.
Slippage Effects of the Conservation Reserve Program
Authors: Wu JunJie 
Published: March 2003

AbstractEach year, billions of dollars of public funds are expended to purchase conservation easements on farmland. One unintended impact of these programs is that they may bring non‐cropland into crop production. Such a slippage effect can be caused by increased output prices and by substitution effects. This article shows that for each one hundred acres of cropland retired under the Conservation Reserve Program (CRP) in the central United States, twenty acres of non‐cropland were converted to cropland, offsetting 9% and 14% of CRP water and wind erosion reduction benefits, respectively. Implications of these results for the design of conservation programs are discussed.