140 research outputs found
Bifurcations of equilibria in DNA elasticity
No full textDNA molecules in the familiar double helical B form are treated here as though they have rod-like structures obtained by stacking the
nearly planar base pairs comprising them one on top of another with each rotated by approximately one-tenth of a full turn with respect
to its immediate predecessor in the stack. As each base in a base pair is attached to the sugar-phosphate backbone chain of one of the
two DNA strands that have come together to form the Watson-Crick structure, and each phosphate group in a backbone chain bears one electronic charge, two such charges are associated with each base pair. Thus, each base pair is subject to not only the elastic forces and moments exerted on it by its neighboring base pairs but also to remote electrostatic forces that, because they are only partially screened out by positively charged counter ions, can render the molecule's equilibrium configurations sensitive to changes in the concentration c of salt in the medium.
The observation that the step from one base pair to the next can be one of several distinct types, each having its own mechanical properties that depend on the nucleotide composition of the step, and the assumption that a base pair is rigid, led to the development of a theory of sequence dependent DNA elasticity [Coleman, Olson, and Swigon, J. Chem. Phys. 118 ,7127-7140, (2003)]. The theory of DNA molecules in aqueous solution developed here is based on but goes beyond that theory. It takes into account the intramolecular electrostatic interactions of the negatively charged phosphate groups in the molecule and the impenetrability of the DNA molecule for cases in which the
electrostatic repulsive forces do not suffice to avoid self penetration. The theory permits one to calculate equilibrium configurations, to determine their stability, and to study the dependence of them on salt concentration and on all kinds of end conditions.
When the intramolecular electrostatic forces are taken into account, the equations of mechanical equilibrium for a DNA molecule with N+1 base pairs are a system of mu*N non-linear equations, where mu, the number of kinematical variables describing the relative displacement and orientation of adjacent base pairs is in general 6; it reduces to 3 when base-pair steps are assumed to be inextensible and non-shearable. An efficient numerically stable computational scheme is here presented for
solving those equations and determining the mechanical stability of the calculated equilibrium configurations. That scheme is employed to compute and analyze bifurcation diagrams in which c is the bifurcation parameter and to show that, for an intrinsically curved molecule, small changes in c can have a strong effect on stable
equilibrium configurations. Cases are presented in which self-contact must be taken into account even though the intramolecular electrostatic forces of repulsion are strong.Ph.D.Includes bibliographical references (p. 106-110)
RURAL LIVELIHOODS IN ARMENIA
No full textIn this paper the structure of the rural economy in Armenia is explored from a household perspective. The paper draws on the livelihoods framework, recognizing the different capitals and activities that support rural households' livelihood strategies. Ownership of capitals and access to activities are examined in relation to the incidence of poverty on the basis of data from a recent large-scale survey of rural households in Armenia. Different measures for the outcome of livelihood strategies in terms of well-being are observed, which are consistently linked to income levels across poor and other households. Income-poor households are found to be less well-endowed especially with financial and social capital. They derive smaller income shares from economic activities, and more from dissaving and social payments. The findings are relevant to policies aimed at alleviating rural poverty.Community/Rural/Urban Development, Labor and Human Capital,
LAND REFORM AND DEVELOPMENT OF AGRICULTURAL LAND MARKETS IN RUSSIA
No full textRussia has experienced dramatic changes in land ownership and land tenure since the dissolution of the Soviet Union at the end of 1991: agricultural land has been largely privatized, individual landowners now have legal rights to most agricultural land in the country, and previous prohibitions on buying and selling of land have been removed by recent laws. The necessary preconditions for the development of agricultural land markets have been met and we are beginning to witness transactions that involve individual landowners, and not only the state. However, further development of the embryonic land market is severely circumscribed by the inadequacy of the administrative and technical infrastructure. In this paper we discuss the dynamically evolving legal framework for land reform, consider the impacts of land reform on privatization and ownership structure of agricultural land, and analyze the development of land market transactions. The analysis is based on official statistical sources and the results of a questionnaire-based survey conducted by the authors in 2003 in three regions. The paper concludes with a review of the existing constraints on land transactions and some policy recommendations.International Development, Land Economics/Use,
RESOURCE EXPLOITATION, BIODIVERSITY LOSS AND ECOLOGICAL EVENTS
No full textWe study the management of a natural resource that supports ecosystems as well as human needs. The reduction in the resource base introduces a threat of occurrence of catastrophic ecological events, such as the sudden collapse of the national habitat that lead to severe loss of biodiversity. The event occurrence conditions involve uncertainty of various types, and the distinction among these types affects the optimal exploitation policies. When uncertainty is due to our ignorance of some aspects of the underlying ecology, the isolated equilibrium states characterizing optimal exploitation for many renewable resource problems become equilibrium intervals. Events triggered by genuinely stochastic environmental conditions maintain the structure of isolated equilibria, but the presence of event uncertainty shifts these equilibrium states relative to their position when occurrence conditions are known with certainty.ecosystem, resource management, event uncertainty, biodiversity, extinction, Resource /Energy Economics and Policy,
WELFARE MEASUREMENT UNDER THREATS OF ENVIRONMENTAL CATASTROPHES
No full textWelfare measures under threats of environmental catastrophes are studied using the "parable" apparatus of Weitzman and Lofgren [22]. The occurrence probability of the catastrophic event is driven (at least partly) by anthropogenic activities such as natural resource exploitation. Without external effects, the green NNP is a genuine welfare measure vis-à-vis a particular parable economy. Often, however, the occurrence hazard constitutes a public bad, treated as an externality by agents who ignore their own contribution to its accumulation. In such cases the green NNP, although accounting for the event hazard rate per se, fails to properly internalize future effects on the hazard rate of current economic activities and as a result overestimates welfare. The bias term associated with the green NNP is derived and expressed in a simply and interpretable form.green NNP, environmental catastrophes, hazard rate, uncertainty, Environmental Economics and Policy,
TURKMENISTAN'S NEW PRIVATE FARMERS: THE EFFECT OF HUMAN CAPITAL ON PERFORMANCE
No full textAlmost all former socialist countries are introducing private farming as part of land reform. In countries where such farming existed one or two generations ago, land might be restituted to former owners. In Turkmenistan, where there had been little private agriculture and no small landowners, land was distributed to new beneficiaries. This paper shows that the previous position of the new farm “owners” strongly affected what resources they had (land, capital, water) and how effectively they used them. The study is based on a survey conducted in 2000 on a sample of 143 farmers from Turkmenistan’s all five administrative regions. The farmers were divided for analysis into five categories, according to previous positions (managers, middle-level specialists, skilled and unskilled workers, and administrative staff). On the average, all categories of farmers turned a profit. However, the most successful were the middle-level specialists (agronomists, engineers). They had the largest plots, the best land, and the best-equipped farms. Like the managers and the administrative staff, they had savings, some of which they used as startup capital. They diversified their production more than others, and were better able to obtain credit. Former unskilled workers were the least successful, lacking capital, and unable to afford risks, thus growing only wheat and cotton at the expense of other crops and of livestock. Earlier studies have shown that former position affected the share of resources received by individuals in the ex Soviet Union. In addition to confirming the finding, we have shown that former position also affected the use of those resources, and the economic performance of the users. Unfortunately, the sample size was small, and our conclusions remain thus tentative.Farm Management,
TECHNICAL EFFICIENCY IN RUSSIAN AGRICULTURE
No full textFor decades, Russian agriculture had had little technological progress and virtually no foreign investment, which resulted in a stable production possibilities frontier and made the sector ideally suited to production function analysis. The production function estimations reported in Chapters 10-13 add to a series of previous studies of the input/output relationship in Russian agriculture (e.g., Clayton, 1980, 1984; Gray, 1981; Johnson and Brooks, 1983), which generally followed the same methodology. In the late 1970s and the 1980s, however, the average response production functions gave way in the economics literature to more sophisticated production analysis techniques that measured not only productivity but technical efficiency as well (Aigner, et al., 1977; Bauer, 1990). Some of the major methodological advances in applying technical efficiency analysis to individual firms were made by a joint Russian-American team in Moscow in the early 1980s (Jondrow, et al., 1982; Danlin et al., 1985), but lack of data for many sectors of the Russian economy precluded the application of this technique until the end of the decade. When the Soviet Union collapsed, the initial optimistic expectation was that many sectors of the new Russian economy could rapidly achieve both higher productivity and higher technical efficiency once market forces prevailed. Our research attempts to understand why this has not happened in Russian agriculture in terms of technical efficiency.Research and Development/Tech Change/Emerging Technologies,
LAND CONSOLIDATION AS A FACTOR FOR SUCCESSFUL DEVELOPMENT OF AGRICULTURE IN MOLDOVA
No full textSince 1991, Moldova has carried out a wide range of radical reforms affecting its social and economic system. The land reform, which was practically completed in 2000, created over 1 million landowners among the rural population. Many of them entrusted their land to managers of newly created corporate farms. Others used their privately owned land to establish independent family farms. The creation of independent family farms (so-called "peasant farms") was one of the primary goals of the land reform. More than 280,000 peasant farms have been created, averaging 1,86 hectares in size. The small size of the peasant farms, whose holdings are furthermore split into 3-4 parcels, raises considerable concerns about their long-term viability and has led to an intense public debate regarding the impacts of fragmentation. In this paper, we use the data from several recent surveys in Moldova to support the case for land consolidation. We show that, in the individual sector, larger farms produce higher family incomes and thus farm augmentation makes a positive contribution to the well-being of the rural population. We also show that, for farms of a given size, productivity increases as the number of parcels decreases. After demonstrating the economic advantages of consolidation, we proceed to discuss the actual use of various market mechanisms for land consolidation, including leasing as well as buying and selling of land. We then show that, in our surveys, farms with leased land are in fact larger than farms that rely on owned land only. This completes the logical circle of our argument: land consolidation leads to better economic performance, while land leasing is actually used as a market mechanism for consolidation, which benefits both lessees (through increased farm incomes) and lessors (through income from lease payments for their land).land consolidation, land lease, land market, Moldova, Land Economics/Use,
IRRIGATION PRODUCTION FUNCTIONS WITH WATER-CAPITAL SUBSTITUTION
No full textThe dynamics of biomass growth implies that the yield of irrigated crops depends, in addition to the total amount of water applied, on irrigation scheduling during the growing period. Advanced irrigation technologies relax constraints on irrigation rates and timing, allowing to better adjust irrigation scheduling to the varying needs of the plants along the growing period. Irrigation production functions, then, should include capital (or expenditures on irrigation equipment) in addition to aggregate water. We derive such functions and study their water-capital substitution properties. Implications for water demand and adoption of irrigation technologies are investigated. An empirical application confirms these properties.Resource /Energy Economics and Policy,
DUALITY OF FARM STRUCTURE IN TRANSITION AGRICULTURE: THE CASE OF MOLDOVA
No full textThe duality of farm structure in Moldova is manifested by the existence of a relatively small number of large corporate farms at one extreme and a very large number of small and very small family farms at the other. “Medium-sized” family farms, the backbone of any market agriculture, virtually do not exist in Moldova. Moldovan agriculture is characterized by a much greater concentration of land in large farms than agriculture in market economies. The small individual farms on the whole are more productive and more efficient than the large corporate farms. They produce higher incomes for rural families than corporate farms. The main conclusion of the paper is that land should be allowed to flow from large corporate farms to small family farms through the medium of land markets until an equilibrium is established between the two farm sectors at a new level closer to that observed in market economies.farm structure, efficiency, productivity, land fragmentation, land concentration, farm size, Moldova, Farm Management, Productivity Analysis,
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