700 research outputs found
An Optimal Size for Rural Tourism Villages with Agglomeration and Club-Good Effects
No full textHelping to sustain a viable rural sector, rural tourism enjoys public support in many countries. We claim that due to club-good and agglomeration externalities in the rural accommodation market, public support should be integrated in a broader local development policy that regulates the number of accommodation units in a locality. To demonstrate this we extended an equilibrium model that accounts for product differentiation and oligopolistic competition to address club-good and agglomeration effects and applied it to data collected in north Israel. We show that under the prevailing regulation, the number of units is by far higher than the social optimum.Community/Rural/Urban Development, International Development, Political Economy,
Modulation of mitochondrial functions by xenobiotic-induced microRNA: From environmental sentinel organisms to mammals
No full textMitochondria play a crucial role in energetic metabolism, signaling pathways, and overall cell viability. They are in the first line in facing cellular energy requirements in stress conditions, such as in response to xenobiotic exposure. Recently, a novel regulatory key role of microRNAs (miRNAs) in important signaling pathways in mitochondria has been proposed. Consequently, alteration in miRNAs expression by xenobiotics could outcome into mitochondrial dysfunction, reactive oxygen species overexpression, and liberation of apoptosis or necrosis activating proteins. The aim of this review is to show the highlights about mitochondria-associated miRNAs in cellular processes exposed to xenobiotic stress in different cell types involved in detoxification processes or sensitive to environmental hazards in marine sentinel organisms and mammals
On the Theory and Practice of Water Regulation
No full textWe study water regulation for a schematic water economy representing a wide range of real world situations. A water policy has inter- and intra-temporal components. The first determines the limits on extractions from the naturally replenished sources, given the stochastic nature of recharge processes associated with uncertain precipitation. The intra-temporal regulation is concerned mainly with the allocating of the extracted and produced water among the end-users. The prices that implement the optimal intra-temporal allocation are derived. Regulation issues associated with cost recovery and asymmetric information are discussed.scarcity, pricing, optimal allocation, water economy, Resource /Energy Economics and Policy, C61, D82, Q11, Q25,
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)
Combinatorial Auctions
No full textA comprehensive book on combinatorial auctions?auctions in which bidders can bid on packages of items. The book consists of original material intended for researchers, students, and practitioners of auction design. It includes a foreword by Vernon Smith, an introduction to combinatorial auctions, and twenty-three cross-referenced chapters in five parts. Part I covers mechanisms, such as the Vickrey auction and the ascending proxy auction. Part II is on bidding and efficiency issues. Part III examines computational issues and algorithmic considerations, especially the winner determination problem?how to identify the (tentative) winning set of bids that maximizes revenue. Part IV discusses implementation and methods of testing the performance of combinatorial auctions, including simulation and experiment. Part V considers four important applications: airport runway access, trucking, bus routes, and industrial procurement. The chapters develop and apply a unified language, integrating ideas from economics, operations research, and computer science. A glossary defines the central terms. The contributors are Lawrence Ausubel, Michael Ball, Martin Bichler, Sushil Bikhchandani, Craig Boutilier, Estelle Cantillon, Chris Caplice, Peter Cramton, Andrew Davenport, George Donohue, Karla Hoffman, Gail Hohner, Jayant Kalagnanam, Ailsa Land, Daniel Lehmann, Kevin Leyton-Brown, Dinesh Menon, Paul Milgrom, Rudolf Müller, Noam Nisan, Eugene Nudelman, Joseph Ostroy, David Parkes, Aleksandar Pekec, Martin Pesendorfer, Susan Powell, Amir Ronen, Michael Rothkopf, Tuomas Sandholm, Ilya Segal, Yossi Sheffi, Yoav Shoham, Richard Steinberg, Susara van den Heever, Thomas Wilson, and Makoto Yokoo.Auctions, Combinatorial Auctions, Market Design
Maternal and offspring fasting glucose and type 2 diabetes-associated genetic variants and cognitive function at age 8: a Mendelian randomization study in the Avon Longitudinal Study of Parents and Children
No full textBackground: In observational epidemiological studies type 2 diabetes (T2D) and both low and high plasma concentrations of fasting glucose have been found to be associated with lower cognitive performance. These associations could be explained by confounding. Methods: In this study we looked at the association between genetic variants, known to be robustly associated with fasting glucose and T2D risk, in the mother and her offspring to determine whether there is likely to be a causal link between early life exposure to glucose and child’s intelligence quotient (IQ) scores in the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. We generated a fasting glucose (FGGRS) and a T2D (T2DGRS) genetic risk score and used them in a Mendelian randomization approach. Results: We found a strong correlation between the FGGRS and fasting glucose plasma measurements that were available for a subset of children, but no association of either the maternal or the offspring FGGRS with child’s IQ was observed. In contrast, the maternal T2DGRS was positively associated with offspring IQ. Conclusions: Maternal and offspring genetic variants which are associated with glucose levels are not associated with offspring IQ, suggesting that there is unlikely to be a causal link between glucose exposure in utero and IQ in childhood. Further exploration in even larger cohorts is required to exclude the possibility that our null findings were due to a lack of statistical power.Carolina Bonilla, Debbie A Lawlor, Yoav Ben, Shlomo, Andrew R Ness, David Gunnell, Susan M Ring, George Davey Smith and Sarah J Lewi
Fluidic packaging of microengine and microrocket devices for high pressure and high temperature operation
No full textThe fluidic packaging of Power MEMS devices such as the MIT microengine and microrocket requires the fabrication of hermetic seals capable of withstanding temperature in the range 20-600/spl deg/C and pressures in the range 100-300 atm. We describe an approach to such packaging by attaching Kovar metal tubes to a silicon device using glass seal technology. Failure due to fracture of the seals is a significant reliability concern in the baseline process: microscopy revealed a large number of voids in the glass, pre-cracks in the glass and silicon, and poor wetting of the glass to silicon. The effects of various processing and materials parameters on these phenomena were examined. A robust procedure, based on the use of metal-coated silicon substrates, was developed to ensure good wetting. The bending strength of single-tube specimens was determined at several temperatures. The dominant failure mode changed from fracture at room temperature to yielding of the glass and Kovar at 600/spl deg/C. The strength in tension at room temperature was analyzed using Weibull statistics; these results indicate a probability of survival of 0.99 at an operational pressure of 125 atm at room temperature for single tubes and a corresponding probability of 0.9 for a packaged device with 11 joints. The residual stresses were analyzed using the method of finite elements and recommendations for the improvement of packaging reliability are suggested
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