Entanglement between Demand and Supply in Markets with Bandwagon Goods

Whenever customers' choices (e.g. to buy or not a given good) depend on others choices (cases coined 'positive externalities' or 'bandwagon effect' in the economic literature), the demand may be multiply valued: for a same posted price, there is either a small number of buyers, or a large one -- in which case one says that the customers coordinate. This leads to a dilemma for the seller: should he sell at a high price, targeting a small number of buyers, or at low price targeting a large number of buyers? In this paper we show that the interaction between demand and supply is even more complex than expected, leading to what we call the curse of coordination: the pricing strategy for the seller which aimed at maximizing his profit corresponds to posting a price which, not only assumes that the customers will coordinate, but also lies very near the critical price value at which such high demand no more exists. This is obtained by the detailed mathematical analysis of a particular model formally related to the Random Field Ising Model and to a model introduced in social sciences by T C Schelling in the 70's.Comment: Updated version, accepted for publication, Journal of Statistical Physics, online Dec 201

Resonant inelastic x-ray incarnation of Young’s double-slit experiment

Young’s archetypal double-slit experiment forms the basis for modern diffraction techniques: The elastic scattering of waves yields an interference pattern that captures the real-space structure. Here, we report on an inelastic incarnation of Young’s experiment and demonstrate that resonant inelastic x-ray scattering (RIXS) measures interference patterns, which reveal the symmetry and character of electronic excited states in the same way as elastic scattering does for the ground state. A prototypical example is provided by the quasi-molecular electronic structure of insulating Ba 3 CeIr 2 O 9 with structural Ir dimers and strong spin-orbit coupling. The double “slits” in this resonant experiment are the highly localized core levels of the two Ir atoms within a dimer. The clear double-slit-type sinusoidal interference patterns that we observe allow us to characterize the electronic excitations, demonstrating the power of RIXS interferometry to unravel the electronic structure of solids containing, e.g., dimers, trimers, ladders, or other superstructures

Mechanism of insulin gene regulation by the pancreatic transcription factor Pdx-1: Application of pre-mRNA analysis and chromatin immunoprecipitation to assess formation of functional transcriptional complexes

The homeodomain factor Pdx-1 regulates an array of genes in the developing and mature pancreas, but whether regulation of each specific gene occurs by a direct mechanism (binding to promoter elements and activating basal transcriptional machinery) or an indirect mechanism (via regulation of other genes) is unknown. To determine the mechanism underlying regulation of the insulin gene by Pdx-1, we performed a kinetic analysis of insulin transcription following adenovirus-mediated delivery of a small interfering RNA specific for pdx-1 into insulinoma cells and pancreatic islets to diminish endogenous Pdx-1 protein, insulin transcription was assessed by measuring both a long half-life insulin mRNA (mature mRNA) and a short half-life insulin pre-mRNA species by real-time reverse transcriptase-PCR. Following progressive knock-down of Pdx-1 levels, we observed coordinate decreases in pre-mRNA levels (to about 40% of normal levels at 72 h). In contrast, mature mRNA levels showed strikingly smaller and delayed declines, suggesting that the longer half-life of this species underestimates the contribution of Pdx-1 to insulin transcription. Chromatin immunoprecipitation assays revealed that the decrease in insulin transcription was associated with decreases in the occupancies of Pdx-1 and p300 at the proximal insulin promoter. Although there was no corresponding change in the recruitment of RNA polymerase II to the proximal promoter, its recruitment to the insulin coding region was significantly reduced. Our results suggest that Pdx-1 directly regulates insulin transcription through formation of a complex with transcriptional coactivators on the proximal insulin promoter. This complex leads to enhancement of elongation by the basal transcriptional machinery. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc

The Nkx6.1 homeodomain transcription factor suppresses glucagon expression and regulates glucose-stimulated insulin secretion in islet beta cells

We have previously described rat insulinoma INS-1 derived cell lines with robust or poor glucose-stimulated insulin secretion (GSIS). In the current study, we have further resolved these lines into three classes: class 1, glucose-unresponsive glucagon-expressing; class 2, glucose-unresponsive glucagon-negative; and class 3, glucose-responsive glucagon-negative. The transcription factor Nkx2.2 was expressed with relative abundance of 3.3, 1.0, and 1.0 in class 1, class 2, and class 3 cells, respectively, whereas Nkx6.1 expression had the opposite trend: 1.0, 2.6, and 6.4 in class 1, class 2, and class 3 cells, respectively. In class 1 cells, overexpressed Nkx6.1 suppressed glucagon expression but did not affect the levels of several other prominent beta cell transcription factors. RNA interference (RNAi)-mediated suppression of Nkx6.1 in class 3 cells resulted in a doubling of glucagon mRNA, with no effect on Pdx1 levels, whereas suppression of Pdx1 in class 3 cells caused a 12-fold increase in glucagon transcript levels, demonstrating independent effects of Nkx6.1 and Pdx1 on glucagon expression in beta cell lines. RNAi-mediated suppression of Nkx6.1 expression in class 3 cells also caused a decrease in GSIS from 13.9- to 3.7-fold, whereas suppression of Pdx1 reduced absolute amounts of insulin secretion without affecting fold response. Finally, RNAi-mediated suppression of Nkx6.1 mRNA in primary rat islets was accompanied by a significant decrease in GSIS relative to control cells. In sum, our studies have revealed roles for Nkx6.1 in suppression of glucagon expression and control of GSIS in islet beta cells

Cell shape analysis of random tessellations based on Minkowski tensors

To which degree are shape indices of individual cells of a tessellation characteristic for the stochastic process that generates them? Within the context of stochastic geometry and the physics of disordered materials, this corresponds to the question of relationships between different stochastic models. In the context of image analysis of synthetic and biological materials, this question is central to the problem of inferring information about formation processes from spatial measurements of resulting random structures. We address this question by a theory-based simulation study of shape indices derived from Minkowski tensors for a variety of tessellation models. We focus on the relationship between two indices: an isoperimetric ratio of the empirical averages of cell volume and area and the cell elongation quantified by eigenvalue ratios of interfacial Minkowski tensors. Simulation data for these quantities, as well as for distributions thereof and for correlations of cell shape and volume, are presented for Voronoi mosaics of the Poisson point process, determinantal and permanental point processes, and Gibbs hard-core and random sequential absorption processes as well as for Laguerre tessellations of polydisperse spheres and STIT- and Poisson hyperplane tessellations. These data are complemented by mechanically stable crystalline sphere and disordered ellipsoid packings and area-minimising foam models. We find that shape indices of individual cells are not sufficient to unambiguously identify the generating process even amongst this limited set of processes. However, we identify significant differences of the shape indices between many of these tessellation models. Given a realization of a tessellation, these shape indices can narrow the choice of possible generating processes, providing a powerful tool which can be further strengthened by density-resolved volume-shape correlations.Comment: Chapter of the forthcoming book "Tensor Valuations and their Applications in Stochastic Geometry and Imaging" in Lecture Notes in Mathematics edited by Markus Kiderlen and Eva B. Vedel Jense

Au+Au Reactions at the AGS: Experiments E866 and E917

Particle production and correlation functions from Au+Au reactions have been measured as a function of both beam energy (2-10.7AGeV) and impact parameter. These results are used to probe the dynamics of heavy-ion reactions, confront hadronic models over a wide range of conditions and to search for the onset of new phenomena.Comment: 12 pages, 14 figures, Talk presented at Quark Matter '9

Choosing how to choose : Institutional pressures affecting the adoption of personnel selection procedures

The gap between science and practice in personnel selection is an ongoing concern of human resource management. This paper takes Oliver´s framework of organizations´ strategic responses to institutional pressures as a basis for outlining the diverse economic and social demands that facilitate or inhibit the application of scientifically recommended selection procedures. Faced with a complex network of multiple requirements, practitioners make more diverse choices in response to any of these pressures than has previously been acknowledged in the scientific literature. Implications for the science-practitioner gap are discussed

Thermodynamics of pyrope-majorite, Mg3Al2Si3O12-Mg4Si4O12, solid solution from atomistic model calculations

Static lattice energy calculations, based on empirical pair potentials have been performed for a large set of different structures with compositions between pyrope and majorite, and with different states of order of octahedral cations. The energies have been cluster expanded using pair and quaternary terms. The derived ordering constants have been used to constrain Monte Carlo simulations of temperature-dependent properties in the ranges of 1073 3673K and 0 20 GPa. The free energies of mixing have been calculated using the method of thermodynamic integration. At zero pressure the cubic/tetragonal transition is predicted for pure majorite at 3300 K. The transition temperature decreases with the increase of the pyrope mole fraction. A miscibility gap associated with the transition starts to develop at about 2000K and xmaj 0.8, and widens with the decrease in temperature and the increase in pressure. Activity composition relations in the range of 0 20 GPa and 1073 2673K are described with the help of a high-order Redlich Kister polynomial

Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure