New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization

We present new measurements of the intensity of the ionizing ultraviolet background and the global emissivity of ionizing photons over 2 < z < 5. Our results are based on a suite of updated measurements of physical properties of the high-redshift intergalactic medium (IGM), including gas temperatures and the opacity of the IGM to Ly-alpha and ionizing photons. Consistent with previous works, we find a relatively flat hydrogen photoionization rate over 2 < z < 5, although our measurements are roughly a factor of two higher than the 2008 values of Faucher-Giguere et al., due primarily to our lower gas temperatures. The ionizing emissivity we derive is also generally higher than other recent estimates due to a combination of lower gas temperatures, higher ionizing opacity, and an accounting of cosmological radiative transfer effects. We find evidence that the emissivity increases from z~3 to 5, reaching ~5 ionizing photons per atom per gigayear at z=4.75 for realistic galaxy spectra. We further find that galaxies must dominate the emissivity near 1 Ryd at z > 4, and possibly at all redshifts z > 2.4. Our results suggest that the globally-averaged ionizing "efficiency" of star-forming galaxies increases substantially with redshift over 3.2 < z < 4.75. This trend is consistent with the conclusion often drawn from reionization models that the ionizing efficiency of galaxies must be higher during reionization in order for galaxies to reionize the IGM by z=6. Our emissivity values at z~5 suggest that ionizing photons may have been a factor of two more abundant during the final stages of reionization than previously indicated. The evolution of the ionizing emissivity over 2 < z < 5 suggests, moreover, that the steep decline in the photoionization rate from z~5 to 6 may indicate a rapid evolution in the mean free path at z > 5.Comment: 19 pages, 14 figures, MNRAS, in pres

Crowdsourcing Swarm Manipulation Experiments: A Massive Online User Study with Large Swarms of Simple Robots

Micro- and nanorobotics have the potential to revolutionize many applications including targeted material delivery, assembly, and surgery. The same properties that promise breakthrough solutions---small size and large populations---present unique challenges to generating controlled motion. We want to use large swarms of robots to perform manipulation tasks; unfortunately, human-swarm interaction studies as conducted today are limited in sample size, are difficult to reproduce, and are prone to hardware failures. We present an alternative. This paper examines the perils, pitfalls, and possibilities we discovered by launching SwarmControl.net, an online game where players steer swarms of up to 500 robots to complete manipulation challenges. We record statistics from thousands of players, and use the game to explore aspects of large-population robot control. We present the game framework as a new, open-source tool for large-scale user experiments. Our results have potential applications in human control of micro- and nanorobots, supply insight for automatic controllers, and provide a template for large online robotic research experiments.Comment: 8 pages, 13 figures, to appear at 2014 IEEE International Conference on Robotics and Automation (ICRA 2014

Does implied volatility reflect a wider information set than econometric forecasts?

Much research has addressed the relative performance of option implied volatilities and econometric model based forecasts in terms of forecasting asset return volatility. The general theme to come from this body of work is that implied volatility is a superior forecast. Some authors attribute this to the fact that option markets use a wider information set when forming their forecasts of volatility. This article considers this issue and determines whether S&P 500 implied volatility reflects a set of economic information beyond its impact on the prevailing level of volatility. It is found, that while the implied volatility subsumes this information, as do model based forecasts, this is only due to its impact on the current or prevailing level of volatility. Therefore, it appears as though implied volatility does not reflect a wider information set than model based forecasts, implying that implied volatility forecasts simply reflect volatility persistence in much the same way of as do econometric models.Implied volatility, VIX, volatility forecasts, informational efficiency

The New Forgotten Half and Research Directions to Support Them

This is one of a series of five papers outlining the particular domains and dimensions of inequality where new research may yield a better understanding of responses to this growing issue.Using data from the nationally representative Educational Longitudinal Survey (ELS), the authors examine the circumstances of youth who drop out of community college before attaining a credential, discuss institutional challenges in the era of increased college access, and outline a research agenda to help youth move beyond "some college" and achieve their potential

Loading and testing a light scattering cell with a binary fluid mixture near its critical composition

Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided

New Hypotheses and Unanswered Questions in Running Injury Research – comment on Nigg et al.

After critical evaluation of the evidence, Nigg et al.’s target article reject currently discussed hypotheses regarding relationships between impact forces, pronation, and running injuries.  In doing so, they highlight methodological questions underlying research in this field.  This commentary focuses on three such questions including: how are impact forces and the relationship between impact and injury being quantified, what are the methods currently used to measure foot pronation and what are metrics being extracted, and the importance of focusing on individual response patterns.   Each of these areas represents important venues for continued development in the field of running biomechanics and running injuries