Predicting the Equity Premium Out of Sample: Can Anything Beat the Historical Average?

A number of variables are correlated with subsequent returns on the aggregate US stock market in the 20th Century. Some of these variables are stock market valuation ratios, others reflect patterns in corporate finance or the levels of shortand long-term interest rates. Amit Goyal and Ivo Welch (2004) have argued that in-sample correlations conceal a systematic failure of these variables out of sample: None are able to beat a simple forecast based on the historical average stock return. In this note we show that forecasting variables with significant forecasting power insample generally have a better out-of-sample performance than a forecast based on the historical average return, once sensible restrictions are imposed on the signs of coefficients and return forecasts. The out-of-sample predictive power is small, but we find that it is economically meaningful. We also show that a variable is quite likely to have poor out-of-sample performance for an extended period of time even when the variable genuinely predicts returns with a stable coefficient.

Autonomous prealignment of a docking mechanism

Proposed future space exploration, such as lunar and Martian expeditions, will require autonomous docking of space vehicles. One proposed candidate method of autonomous docking utilizes a actively controlled parallel manipulator. Operation of the proposed docking manipulator can be segmented into four successive events: prealignment, capture/latching, attenuation, and structural rigidization. This paper discusses the development and testing of a digitally controlled, six-degree-of-freedom (6-DOF), parallel manipulator for the prealignment segment of a docking spacecraft

Student understanding of the Boltzmann factor

We present results of our investigation into student understanding of the physical significance and utility of the Boltzmann factor in several simple models. We identify various justifications, both correct and incorrect, that students use when answering written questions that require application of the Boltzmann factor. Results from written data as well as teaching interviews suggest that many students can neither recognize situations in which the Boltzmann factor is applicable, nor articulate the physical significance of the Boltzmann factor as an expression for multiplicity, a fundamental quantity of statistical mechanics. The specific student difficulties seen in the written data led us to develop a guided-inquiry tutorial activity, centered around the derivation of the Boltzmann factor, for use in undergraduate statistical mechanics courses. We report on the development process of our tutorial, including data from teaching interviews and classroom observations on student discussions about the Boltzmann factor and its derivation during the tutorial development process. This additional information informed modifications that improved students' abilities to complete the tutorial during the allowed class time without sacrificing the effectiveness as we have measured it. These data also show an increase in students' appreciation of the origin and significance of the Boltzmann factor during the student discussions. Our findings provide evidence that working in groups to better understand the physical origins of the canonical probability distribution helps students gain a better understanding of when the Boltzmann factor is applicable and how to use it appropriately in answering relevant questions

La nueva visibilidad

Este articulo examina las características de una nueva forma de visibilidad que se ha convertido en un aspecto dominante del mundo moderno vinculado al desarrollo de los medios de comunicación de masas. Con el desarrollo de los medios, la visibilidad de los individuos, sus acciones y acontecimientos, se ha separado del espacio común compartido. Ya no es necesario estar presente en el mismo escenario espacio-temporal con el fin de ver a los demás o ser testigo de un acto o suceso. La aparición de esta nueva forma de visibilidad mediada ha transformado las relaciones entre visibilidad y poder. Gracias a la visibilidad mediada, los dirigentes políticos pueden aparecer ante sus ciudadanos en formas y dimensiones que nunca han existido antes. Los políticos hábiles explotan esto en su favor. Con la ayuda de sus consejeros en relaciones públicas y sirviéndose de los medios de comunicación, tratan de crear y sostener una estructura de apoyo gestionando su visibilidad en el ámbito mediado de la política moderna. Pero la visibilidad mediada es una espada de doble filo: también crea nuevos riesgos a los líderes políticos, que se exponen a nuevos peligros. De ahí que la visibilidad creada por los medios de comunicación se convierte en la fuente de una nueva y distinta clase de fragilidad. Sin embargo, a pesar de que muchos líderes políticos tratan de gestionar su visibilidad, no pueden controlarla completamente: la visibilidad mediada puede resbalarles de las manos y, en algunos casos, volverse contra ellos.This article examines the characteristics of a new form of visibility which has become a pervasive feature of the modern world and which is linked to the development of communication media. With the development of the media, the visibility of individuals, actions and events is severed from the sharing of a common locale. One no longer has to be present in the same spatial-temporal setting in order to see the other or to witness an action or event. The rise of this new form of mediated visibility has transformed the relations between visibility and power. Thanks to mediated visibility, polítical rulers are able to appear before their subjects in ways and on a scale that never existed previously. Skilful politicians exploit this ti their advantage; with the help of their PR consultants and com- munications advisors, they seek to create and sustain a basis of support by managing their visibility in the mediated arena of modern politics. But mediated visibility is a double.edged sword: it also creates new risks for polítical leaders, who find themselves exposed to new kinds of dangers. Hence the visibility created by the media becomes the source of a new and distinctive kind of fragility. However much polítical leaders try to manage their visibility, they cannot completely control it: mediated visibility can slip out of their grasp and can, on occasion, work against them

Discerning Culture with Herman Bavinck

Bavinck does not intend that we simply adopt and casually integrate secular ideas into our Christian worldview. Instead, every idea must be brought into conformity with Christ. Posting about ­­­­­­­­Christianity\u27s influence in a hostile world from In All Things - an online journal for critical reflection on faith, culture, art, and every ordinary-yet-graced square inch of God’s creation. https://inallthings.org/discerning-culture-with-herman-bavinck

Identifying Student Difficulties with Entropy, Heat Engines, and the Carnot Cycle

We report on several specific student difficulties regarding the Second Law of Thermodynamics in the context of heat engines within upper-division undergraduates thermal physics courses. Data come from ungraded written surveys, graded homework assignments, and videotaped classroom observations of tutorial activities. Written data show that students in these courses do not clearly articulate the connection between the Carnot cycle and the Second Law after lecture instruction. This result is consistent both within and across student populations. Observation data provide evidence for myriad difficulties related to entropy and heat engines, including students' struggles in reasoning about situations that are physically impossible and failures to differentiate between differential and net changes of state properties of a system. Results herein may be seen as the application of previously documented difficulties in the context of heat engines, but others are novel and emphasize the subtle and complex nature of cyclic processes and heat engines, which are central to the teaching and learning of thermodynamics and its applications. Moreover, the sophistication of these difficulties is indicative of the more advanced thinking required of students at the upper division, whose developing knowledge and understanding give rise to questions and struggles that are inaccessible to novices

SPEAR-1: An experiment to measure current collection in the ionosphere by high voltage biased conductors

An experiment is described in which a high electrical potential difference, up to 45 kV, was applied between deployed conducting spheres and a sounding rocket in the ionosphere. Measurements were made of the applied voltage and the resulting currents for each of 24 applications of different high potentials. In addition, diagnostic measurements of optical emissions in the vicinity of the spheres, energetic particle flow to the sounding rocket, dc electric field and wave data were made. The ambient plasma and neutral environments were measured by a Langmuir probe and a cold cathode neutral ionization gauge, respectively. The payload is described and examples of the measured current and voltage characteristics are presented. The characteristics of the measured currents are discussed in terms of the diagnostic measurements and the in-situ measurements of the vehicle environment. In general, it was found that the currents observed were at a level typical of magnetically limited currents from the ionospheric plasma for potentials less than 12 kV, and slightly higher for larger potentials. However, due to the failure to expose the plasma contactor, the vehicle sheath modified the sphere sheaths and made comparisons with the analytic models of Langmuir-Blodgett and Parker-Murphy less meaningful. Examples of localized enhancements of ambient gas density resulting from the operation of the attitude control system thrusters (cold nitrogen) were obtained. Current measurements and optical data indicated localized discharges due to enhanced gas density that reduced the vehicle-ionosphere impedance