Overconfidence vs. Market Efficiency in the National Football League

A question of increasing interest to researchers in a variety of fields is whether the incentives and experience present in many "real world" settings mitigate judgment and decision-making biases. To investigate this question, we analyze the decision making of National Football League teams during their annual player draft. This is a domain in which incentives are exceedingly high and the opportunities for learning rich. It is also a domain in which multiple psychological factors suggest teams may overvalue the "right to choose" in the draft -- non-regressive predictions, overconfidence, the winner's curse and false consensus all suggest a bias in this direction. Using archival data on draft-day trades, player performance and compensation, we compare the market value of draft picks with the historical value of drafted players. We find that top draft picks are overvalued in a manner that is inconsistent with rational expectations and efficient markets and consistent with psychological research.

Pixelation effects in weak lensing

Weak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space-based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, & Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade-off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09 '' for a 0.14 '' FWHM point-spread function (PSF). The pixel scale could be increased to similar to 0.16 '' if images dithered by exactly half-pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape measurement method

A Comparison of Weak Lensing Measurements From Ground- and Space-Based Facilities

We assess the relative merits of weak lensing surveys, using overlapping imaging data from the ground-based Subaru telescope and the Hubble Space Telescope (HST). Our tests complement similar studies undertaken with simulated data. From observations of 230,000 matched objects in the 2 square degree COSMOS field, we identify the limit at which faint galaxy shapes can be reliably measured from the ground. Our ground-based shear catalog achieves sub-percent calibration bias compared to high resolution space-based data, for galaxies brighter than i'~24.5 and with half-light radii larger than 1.8". This selection corresponds to a surface density of ~15 galaxies per sq arcmin compared to ~71 per sq arcmin from space. On the other hand the survey speed of current ground-based facilities is much faster than that of HST, although this gain is mitigated by the increased depth of space-based imaging desirable for tomographic (3D) analyses. As an independent experiment, we also reconstruct the projected mass distribution in the COSMOS field using both data sets, and compare the derived cluster catalogs with those from X-ray observations. The ground-based catalog achieves a reasonable degree of completeness, with minimal contamination and no detected bias, for massive clusters at redshifts 0.2<z<0.5. The space-based data provide improved precision and a greater sensitivity to clusters of lower mass or at higher redshift.Comment: 12 pages, 8 figures, submitted to ApJ, Higher resolution figures available at http://www.astro.caltech.edu/~mansi/GroundvsSpace.pd

Charge transfer inefficiency in the Hubble Space Telescope since Servicing Mission 4

We update a physically motivated model of radiation damage in the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, using data up to mid-2010. We find that charge transfer inefficiency increased dramatically before shuttle Servicing Mission 4, with ∼1.3 charge traps now present per pixel. During detector readout, charge traps spuriously drag electrons behind all astronomical sources, degrading image quality in a way that affects object photometry, astrometry and morphology. Our detector readout model is robust to changes in operating temperature and background level, and can be used to iteratively remove the trailing by pushing electrons back to where they belong. The result is data taken in mid-2010 that recovers the quality of imaging obtained within the first six months of orbital operations

Mechanistic studies of azolium ions and their role in organocatalysis

Azolium ion precursors to N-heterocyclic carbenes (NHCs) have risen to prominence as versatile organocatalysts for a broad range of synthetic transformations. In recent years, methodologies have been developed for the generation and exploitation of azolium homoenolates, azolium enolates, and acyl azolium intermediates, leading to a diverse range of asymmetric products. It is common in many synthetic procedures to generate the active NHC in situ by deprotonation of the parent azolium ion. Knowledge of the kinetic and thermodynamic acidities of these species is therefore an essential first step in understanding their catalytic behaviour. We have used a kinetic method to determine kinetic acidities and aqueous pKa values for a set of triazolium, thiazolium and imidazolium ions at the C(3)-H or C(2)-H positions. Using 1H NMR spectroscopy to follow deuterium exchange, pseudo-first-order rate constants for exchange, kex (s-1), were determined at a range of pDs in D2O at 25 °C and I = 1.0 (KCl), from which second-order rate constants for deprotonation by deuteroxide ion, kDO (M-1 s-1) could be obtained. By application of a secondary solvent isotope effect (kDO/kHO = 2.4), corresponding values of kHO were calculated. General base catalysis experiments support the conclusion that the rate constant for carbene protonation by solvent water is limited by solvent reorganisation, and occurs with a rate constant of kHOH = kreorg = 1011 s-1. These values of kHO and kHOH permitted the calculation of carbon acid pKa values for ionisation of the azolium ion in water. For a homologous series of catalytically-relevant triazolium salts, the effect of the N-aryl substituent on values of kDO and pKa was probed, and comparisons between azolium ion families will be made. The pD-rate profile of an N-C6F5 substituted triazolium ion indicates that in acidic media, protonation at the N(1) position may occur to give a dicationic triazolium ion. Using this methodology, the kinetic acidities of the conjugate acids of ‘mesoionic’ or ‘abnormal’ carbenes were also investigated. For a series of 1,2,3-triazolium ions and C(2)-alkylated 1,3-imidazolium ions, rate constants for exchange at the C(4)-H and C(5)-H positions were determined. Our results suggest that these sites are 105-fold less acidic than the C(3)-H and C(2)-H positions of ‘classical’ triazolium and imidazolium ions. To explain the deviation from a first-order dependence on deuteroxide ion for the imidazolium ions in strong KOD solution, we have proposed a number of exchange pathways that proceed via a hydrate. The effects of N-aryl substituent and counterion on kDO and pKa are also discussed. We have also conducted mechanistic studies of the triazol-3-ylidene-catalysed benzoin condensation. In situ 1H NMR spectroscopic studies of the reaction in triethylamine-buffered methanol-d4 at 25 °C show that the 3-(hydroxyaryl)triazolium adduct, generated from addition of the NHC to the aldehyde, is the only intermediate observed over the course of the reaction. Evidence is presented to show that the formation of these intermediates under these conditions is reversible, and reliable equilibrium and rate constants for the formation of these species have been determined using independent approaches. Our results suggest that N-mesityl substituents on the catalyst, and ortho-alkoxyl groups on the aromatic aldehyde result in significantly enhanced equilibrium concentrations of this intermediate. Slow deprotonation of these intermediates results in the benzoin product. Rate constants for the deprotonation step suggest that electron-deficient adducts result in the fastest rates of deprotonation. Finally, an initial rates study of the benzoin condensation at catalytic concentrations of azolium ion precatalyst has also been undertaken. An HPLC analysis method was used to determine the concentrations of benzoin and benzaldehyde over the course of the reaction in triethylamine-buffered methanol at 50 °C. Our results suggest that the thiazolium-catalysed reaction is first-order with respect to aldehyde over the full range of benzaldehyde concentrations studied (0.32 – 1.60 M). In contrast, the triazolium-catalysed reaction displays a first-order dependence at low aldehyde concentrations, before changing to a zero-order dependence at higher benzaldehyde concentrations. From the maximum rate of catalysis in this zero-order region, the effect of N-aryl substituent on rate of turnover was investigated for a homologous series of triazolium precatalysts

Why Campaigns for Local Transportation Initiatives Succeed or Fail: An Analysis of Four Communities and National Data, MTI Report 00-01

As funding from state and national sources has dwindled and demands for relief from traffic and congestion have grown, local governments and transportation agencies are increasingly left to develop their own sources of enhanced revenues. Frequently the bid to increase available revenues comprises a local ballot measure, enabling the citizens served by these governments and agencies to express their preferences for or against increased taxation in support of an improved transportation system. What determines the success of campaigns in support of such ballot measures? To answer this question, this report includes the use of two different approaches and data sources. 1) A statistical analysis of community-level characteristics. Data from localities across the nation, as well those within the state of California, that have conducted elections for transportation tax increase are analyzed to determine what factors seem to affect the outcome of such elections. 2) Case studies of four communities that recently conducted elections for transportation tax increases (Santa Clara and Sonoma Counties in California, and the Denver and Seattle metropolitan areas). The case studies allow for in-depth, qualitative understanding of what election strategies and other campaign elements comprise successful or unsuccessful efforts to raise local revenues. Among the most significant findings from the statistical analysis of local elections were the following: Efforts to fund transportation with taxes where the proportion of elderly is greater than 9 percent are more likely to succeed In communities where the percentage of elderly is greater than 9 percent, the analysis indicates that voters may be more willing to accept local transportation taxes. However, in communities where the percentage of elderly is less than 9 percent, transportation measures may require significantly more determined marketing to enhance the probability of passage. Efforts to increase sales taxes for transportation programs will be less successful in communities with higher sales taxes. A relatively strong and negative relationship between sales tax and support for transportation tax initiatives was identified in the national election data. This suggests that communities with relatively higher sales taxes will be hard pressed to convince citizens to support additional increases

Development of a direct evaporation bismuth Hall thruster

Hall thrusters have been under active development around the world since the 1960’s. Thrusters using traditional propellants such as xenon have been flown on a variety of satellite orbit raising and maintenance missions with an excellent record. To expand the mission envelope, it is necessary to lower the specific impulse of the thrusters but xenon and krypton are poor performers at specific impulses below 1,200 seconds. To enhance low specific impulse performance, this dissertation examines the development of a Hall-effect thruster which uses bismuth as a propellant. Bismuth, the heaviest non-radioactive element, holds many advantages over noble gas propellants from an energetics as well as a practical economic standpoint. Low ionization energy, large electron-impact crosssection and high atomic mass make bismuth ideal for low-specific impulse applications. The primary disadvantage lies in the high temperatures which are required to generate the bismuth vapors. Previous efforts carried out in the Soviet Union relied upon the complete bismuth vaporization and gas phase delivery to the anode. While this proved successful, the power required to vaporize and maintain gas phase throughout the mass flow system quickly removed many of the efficiency gains expected from using bismuth. To solve these problems, a unique method of delivering liquid bismuth to the anode has been developed. Bismuth is contained within a hollow anode reservoir that is capped by a porous metallic disc. By utilizing the inherent waste heat generated in a Hall thruster, liquid bismuth is evaporated and the vapors pass through the porous disc into the discharge chamber. Due to the high temperatures and material compatibility requirements, the anode was fabricated out of pure molybdenum. The porous vaporizer was not available commercially so a method of creating a refractory porous plate with 40-50% open porosity was developed. Molybdenum also does not respond well to most forms of welding so a diffusion bonding process was also developed to join the molybdenum porous disc to the molybdenum anode. Operation of the direct evaporation bismuth Hall thruster revealed interesting phenomenon. By utilizing constant current mode on a discharge power supply, the discharge voltage settles out to a stable operating point which is a function of discharge current, anode face area and average pore size on the vaporizer. Oscillations with a 40 second period were also observed. Preliminary performance data suggests that the direct evaporation bismuth Hall thruster performs similar to xenon and krypton Hall thrusters. Plume interrogation with a Retarding Potential Analyzer confirmed that bismuth ions were being efficiently accelerated while Faraday probe data gave a view of the ion density in the exhausted plume