Optimality and Natural Selection in Markets

Evolutionary arguments are often used to justify the fundamental behavioral postulates of competive equilibrium. Economists such as Milton Friedman have argued that natural selection favors profit maximizing firms over firms engaging in other behaviors. Consequently, producer efficiency, and therefore Pareto efficiency, are justified on evolutionary grounds. We examine these claims in an evolutionary general equilibrium model. If the economic environment were held constant, profitable firms would grow and unprofitable firms would shrink. In the general equilibrium model, prices change as factor demands and output supply evolves. Without capital markets, when firms can grow only through retained earnings, our model verifies Friedman's claim that natural selection favors profit maximization. But we show through examples that this does not imply that equilibrium allocations converge over time to efficient allocations. Consequently, Koopmans critique of Friedman is correct. When capital markets are added, and firms grow by attracting investment, Friedman's claim may fail. In either model the long-run outcomes of evolutionary market models are not well described by conventional General Equilibrium analysis with profit maximizing firms.evolution, natural selection, equilibrium, incomplete markets

Transport systems research vehicle color display system operations manual

A recent upgrade of the Transport Systems Research Vehicle operated by the Advanced Transport Operating Systems Program Office at the NASA Langley Research Center has resulted in an all-glass panel in the research flight deck. Eight ARINC-D size CRT color displays make up the panel. A major goal of the display upgrade effort was ease of operation and maintenance of the hardware while maintaining versatility needed for flight research. Software is the key to this required versatility and will be the area demanding the most detailed technical design expertise. This document is is intended to serve as a single source of quick reference information needed for routine operation and system level maintenance. Detailed maintenance and modification of the display system will require specific design documentation and must be accomplished by individuals with specialized knowledge and experience

Report and Recommendations on Two Chilean Labor Force Surveys

For many years, Chile has benefited from two surveys of labor force developments for the “Greater Santiago Area.” One of these surveys dates back to the 1950s and is conducted by the University of Chile. The other is a national survey, conducted by the National Institute of Statistics (NIS), from which data are also available for the Santiago Metropolitan Area. Results, especially the rate of unemployment, do not always coincide, and this has been particularly the case for all years since 1998. This report studies this problem of non concurrence, identifies a number of areas for possible explanation, and makes recommendations for improvement of survey operations. Both surveys were found to follow quite well recommendations of the International Labor Organization regarding the measurement of employment and unemployment. Two significant areas in the report concern the questionnaires used for the surveys and data estimation techniques. Fourteen recommendations for improvements in the surveys are offered, with major attention focused on plans by the NIS to introduce an entirely new questionnaire in the near future. With respect to the University’s survey, the authors recommend changes in the basic questionnaire and survey weighting procedures. They also recommend improving data analysis (NIS), maintaining error profiles for data collection (both surveys), and using seasonal adjustment for statistical analysis (both).

Implementation of Walrasian Expectations Equilibria

In an exchange economy with differentially informed traders, Non-exclusivity of information (NEI) is the condition that each trader's private information be perfectly predictable by an outside observer who has observed the private information of all other traders. NEI is one of a set of conditions which, taken together, are sufficient for the implementability of fully revealing expectations equilibria. Here we show that this condition is in fact necessary for the weak implementation of a much broader class of Walrasian equilibria, herein called expectations equilibria.Center for Research on Economic and Social Theory, Department of Economics, University of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/100640/1/ECON116.pd

Minority Becomes Majority in Social Networks

It is often observed that agents tend to imitate the behavior of their neighbors in a social network. This imitating behavior might lead to the strategic decision of adopting a public behavior that differs from what the agent believes is the right one and this can subvert the behavior of the population as a whole. In this paper, we consider the case in which agents express preferences over two alternatives and model social pressure with the majority dynamics: at each step an agent is selected and its preference is replaced by the majority of the preferences of her neighbors. In case of a tie, the agent does not change her current preference. A profile of the agents' preferences is stable if the preference of each agent coincides with the preference of at least half of the neighbors (thus, the system is in equilibrium). We ask whether there are network topologies that are robust to social pressure. That is, we ask if there are graphs in which the majority of preferences in an initial profile always coincides with the majority of the preference in all stable profiles reachable from that profile. We completely characterize the graphs with this robustness property by showing that this is possible only if the graph has no edge or is a clique or very close to a clique. In other words, except for this handful of graphs, every graph admits at least one initial profile of preferences in which the majority dynamics can subvert the initial majority. We also show that deciding whether a graph admits a minority that becomes majority is NP-hard when the minority size is at most 1/4-th of the social network size.Comment: To appear in WINE 201

Voter model with non-Poissonian interevent intervals

Recent analysis of social communications among humans has revealed that the interval between interactions for a pair of individuals and for an individual often follows a long-tail distribution. We investigate the effect of such a non-Poissonian nature of human behavior on dynamics of opinion formation. We use a variant of the voter model and numerically compare the time to consensus of all the voters with different distributions of interevent intervals and different networks. Compared with the exponential distribution of interevent intervals (i.e., the standard voter model), the power-law distribution of interevent intervals slows down consensus on the ring. This is because of the memory effect; in the power-law case, the expected time until the next update event on a link is large if the link has not had an update event for a long time. On the complete graph, the consensus time in the power-law case is close to that in the exponential case. Regular graphs bridge these two results such that the slowing down of the consensus in the power-law case as compared to the exponential case is less pronounced as the degree increases.Comment: 18 pages, 8 figure

Bony ingrowth potential of 3D-printed porous titanium alloy: a direct comparison of interbody cage materials in an in vivo ovine lumbar fusion model.

Background contextThere is significant variability in the materials commonly used for interbody cages in spine surgery. It is theorized that three-dimensional (3D)-printed interbody cages using porous titanium material can provide more consistent bone ingrowth and biological fixation.PurposeThe purpose of this study was to provide an evidence-based approach to decision-making regarding interbody materials for spinal fusion.Study designA comparative animal study was performed.MethodsA skeletally mature ovine lumbar fusion model was used for this study. Interbody fusions were performed at L2-L3 and L4-L5 in 27 mature sheep using three different interbody cages (ie, polyetheretherketone [PEEK], plasma sprayed porous titanium-coated PEEK [PSP], and 3D-printed porous titanium alloy cage [PTA]). Non-destructive kinematic testing was performed in the three primary directions of motion. The specimens were then analyzed using micro-computed tomography (µ-CT); quantitative measures of the bony fusion were performed. Histomorphometric analyses were also performed in the sagittal plane through the interbody device. Outcome parameters were compared between cage designs and time points.ResultsFlexion-extension range of motion (ROM) was statistically reduced for the PTA group compared with the PEEK cages at 16 weeks (p-value=.02). Only the PTA cages demonstrated a statistically significant decrease in ROM and increase in stiffness across all three loading directions between the 8-week and 16-week sacrifice time points (p-value≤.01). Micro-CT data demonstrated significantly greater total bone volume within the graft window for the PTA cages at both 8 weeks and 16 weeks compared with the PEEK cages (p-value<.01).ConclusionsA direct comparison of interbody implants demonstrates significant and measurable differences in biomechanical, µ-CT, and histologic performance in an ovine model. The 3D-printed porous titanium interbody cage resulted in statistically significant reductions in ROM, increases in the bone ingrowth profile, as well as average construct stiffness compared with PEEK and PSP

Biomechanical and Radiographic Evaluation of an Ovine Model for the Human Lumbar Spine

While various species of animal models have been used in preclinical investigations of spinal implant devices to assess their biological adaptation and biomechanical performance, few studies have made comprehensive comparisons to validate their suitability of modelling the human spine. The purpose of this study was to assess essential biomechanical behaviours and disc morphology of the ovine lumbar model. Flexibility testing was conducted on the spines (L3—L4 and L4—L5) of nine skeletally matured sheep. Segmental rotation and intradiscal pressure were measured and load sharing between the intervertebral disc and posterior elements were calculated on the basis of a simplified parallel spring model. Following the tests, the spinal segments were sectioned into a series of sagittal slabs, and transverse radiographs of these slabs were taken to evaluate the variation in the disc height and end-plate curvature. Comparing the biomechanical and radiographic results with published data on the human lumbar spine, good comparability between the ovine and cadaveric lumbar spines was found in terms of the general disc shape and in most of the biomechanical parameters including the range of motion, neutral zone, and load sharing between the intervertebral disc and posterior elements. A few distinctive differences were also found between the two, including flatter sagittal alignment, smaller disc dimensions, and greater lateral bending motion in the ovine model

Fabric Parameters and Pesticide Characteristics That Impact on Dermal Exposure of Applicators

Fabric functional finish and formulation of pesticides are factors that contribute to pesticide wicking, wetting, and penetration. Fluorocarbon soil-repellent finishes inhibit contamination of the fabric and of sentinel pads. An undergarment layer offers better protection than does a single layer. Spun-bonded olefin offers protection of the same magnitude as soil-repellent finishes. Methyl parathion residues after laundering were similar for the unfinished fabric, the durable-press finished fabric, and the soil-repellent finished fabric, but the initial contamination of the soil-repellent finished fabric was only 20~ of that of the other two fabrics