An Analysis of the Shapes of Interstellar Extinction Curves. VI. The Near-IR Extinction Law

We combine new HST/ACS observations and existing data to investigate the wavelength dependence of NIR extinction. Previous studies suggest a power-law form, with a "universal" value of the exponent, although some recent observations indicate that significant sight line-to-sight line variability may exist. We show that a power-law model provides an excellent fit to most NIR extinction curves, but that the value of the power, beta, varies significantly from sight line-to-sight line. Therefore, it seems that a "universal NIR extinction law" is not possible. Instead, we find that as beta decreases, R(V) [=A(V)/E(B-V)] tends to increase, suggesting that NIR extinction curves which have been considered "peculiar" may, in fact, be typical for different R(V) values. We show that the power law parameters can depend on the wavelength interval used to derive them, with the beta increasing as longer wavelengths are included. This result implies that extrapolating power law fits to determine R(V) is unreliable. To avoid this problem, we adopt a different functional form for NIR extinction. This new form mimics a power law whose exponent increases with wavelength, has only 2 free parameters, can fit all of our curves over a longer wavelength baseline and to higher precision, and produces R(V) values which are consistent with independent estimates and commonly used methods for estimating R(V). Furthermore, unlike the power law model, it gives R(V)'s that are independent of the wavelength interval used to derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/E(B-V) - 0.79 can estimate R(V) to +/-0.12. Finally, we use model extinction curves to show that our extinction curves are in accord with theoretical expectations.Comment: To appear in the Astrophysical Journa

A recalibration of IUE NEWSIPS low dispersion data

While the low dispersion IUE NEWSIPS data products represent a significant improvement over original IUE SIPS data, they still contain serious systematic effects which compromise their utility for certain applications. We show that NEWSIPS low resolution data are internally consistent to only 10-15% at best, with the majority of the problem due to time dependent systematic effects. In addition, the NEWSIPS flux calibration is shown to be inconsistent by nearly 10%. We examine the origin of these problems and proceed to formulate and apply algorithms to correct them to ~ 3% level -- a factor of 5 improvement in accuracy. Because of the temporal systematics, transforming the corrected data to the IUE flux calibration becomes ambiguous. Therefore, we elect to transform the corrected data onto the HST FOS system. This system is far more self-consistent, and transforming the IUE data to it places data from both telescopes on a single system. Finally, we argue that much of the remaining 3% systematic effects in the corrected data is traceable to problems with the NEWSIPS intensity transformation function (ITF). The accuracy could probably be doubled by rederiving the ITF.Comment: Submitted to ApJ Supplement, 35 pages, 13 figures, LaTeX - AASTEX aas2pp4.st

Two-fluid magnetic island dynamics in slab geometry: I - Isolated islands

A set of reduced, 2-D, two-fluid, drift-MHD equations is derived. Using these equations, a complete and fully self-consistent solution is obtained for an isolated magnetic island propagating through a slab plasma with uniform but different ion and electron fluid velocities. The ion and electron fluid flow profiles around the island are uniquely determined, and are everywhere continuous. Moreover, the island phase-velocity is uniquely specified by the condition that there be zero net electromagnetic force acting on the island. Finally, the ion polarization current correction to the Rutherford island width evolution equation is evaluated, and found to be stabilizing provided that the anomalous perpendicular ion viscosity significantly exceeds the anomalous perpendicular electron viscosity

The Effect of Roadside Elements on Driver Behavior and Run-Off-the-Road Crash Severity

Roadside vegetation provides numerous environmental and psychological benefits to drivers. Previous studies have shown that natural landscapes can effectively lower crash rates and cause less stress and frustration to the driver. However, run-off-the-road crashes resulting in a collision with a tree are twice as likely to result in a fatality, thus reinforcing the need to examine the placement of vegetation within the clear zone. This study explores the relationship between the size of the clear zone and the presence of roadside vegetation on selected driver attributes, including both driver speed and lateral positioning. To evaluate the effect on the driver speed selection process, a static evaluation was employed. Completed by more than 100 drivers, the static evaluation was utilized to gather speed selections on both real and virtual roads containing four combinations of clear zone size and roadside vegetation density. Additionally, field data was collected to validate the findings of the static evaluation and to determine the extent to which roadside vegetation impacts driving attributes. When presented with a large clear zone, drivers positioned the vehicle further from the edge of the road as the vegetation density increased. Furthermore, the speeds observed in the field correlated with the speeds that participants selected when watching a video of the same road. Finally, the UMassSafe Traffic Safety Data Warehouse was utilized to link crash and roadway data, allowing for an in-depth analysis of run-off-the-road (ROR) crash severity. The results of this study further demonstrate the nature of the relationship between clear zone design and driver behavior

The Fundamental Theorem of Algebra

Algebra is indeed an interesting and intriguing field of knowledge. Many people fear and dread it, and­ yet what do they fear? Is not algebra a logical se­quence of simple facts based perhaps on a few self-evident truths? If people saw the value of algebra, they would strive more enthusiastically to understand its principles. John Locke has a fitting commentary on those who are unfamiliar with algebra

Evaluating the Impacts of Driver Behavior in the Speed Selection Process and the Related Outcomes

In the United States, traffic crashes claim the lives of 30,000 people every year and is the leading cause of death for 5-24 year olds. Driver error is the leading factor in over 90 percent of motor vehicle crashes, with the roadway and the vehicle each only accounting for about 2 percent of crashes. In the United States, nearly a third of fatal crashes are due to speeding and therefore, a critical step in improving traffic safety is research aimed to reduce speeding, such as crash data analysis, outreach campaigns, targeted enforcement, and understanding speed selection. In this dissertation, a multi-faceted approach was taken to improve roadway safety by examining the speeding-related crash designation, improving speed limit setting practices, and understanding the causes of speeding. Multiple experiments were conducted under this overarching goal. These experiments included an analysis of speeding-related crashes in Massachusetts, a naturalistic driving study, and a driving simulator study which investigated the causes of speeding. Collectively, the findings from these experiments can expand upon existing speed prediction models, improve crash data influence speed limit setting practices, guide speed management programs such as speed enforcement, and be used in public safety outreach campaigns

Intergovernmental (Dis)incentives, Free-Riding, Teacher Salaries and Teacher Pensions

In this paper, I document evidence that intergovernmental incentives inherent in public sector defined benefit pension systems distort the amount and timing of income for public school teachers. This intergovernmental incentive stems from the fact that, in many states, local school districts are responsible for setting the compensation that determines the size of pensions, but are not required to make contributions to cover the resulting pension fund liabilities. I use the introduction of a policy that required experience-rating on compensation increases above a certain limit in a differences-in-differences framework to identify whether districts are willing to pay the full costs of their compensation promises. In response to the policy, the size and distribution of compensation changed significantly. On average, public school employees received lower wages largely through the removal of retirement bonuses. However, the design of the policy led some districts to increase compensation, rendering the policy less effective that it might have otherwise been

Creating Mutual Fund Transparency: The Elimination Of Deceptive Communication

While the SEC debates the overall merits of forming mutual fund company boards with an independent chairman to go along with 75% make-up of independent board members, I question how this is going to create more transparency for the individual investor.  The real culprit is the flexibility given to mutual fund companies in allowing them to set fees as permitting trading within funds has confused the true cost to the consumer and has added insult to injury.  Dr. Edward O’Neal at Wake Forest states that “the average fund managers cannot recoup these expenses in the form of better performance.”  Gaspar, Massa and Matos (2006) brilliantly show that mutual fund families tend to charge various levels of fees on its member funds, forcing different funds to contribute unequally to the total profit.  They found that during the January 1991 to July 2001 time period, high value funds (i.e., high fees or high past performance) are favored inside fund families by 6-28 basis points of extra net-of-style performance per month (.7% - 3.3% per year) relative to the low value funds (i.e., low fees or low past performance), based on the criteria they used (i.e., fees or past performance).  How can all these deceptive practices be eradicated?  The author proposes a five-step “absolute” process in order to create mutual fund transparency:  the elimination of all soft dollar arrangements; creation of a mutual fund separateness statue to eliminate what Gaspar, Massa and Matos (2006) call the strategic Cross-Fund Subsidization; terminate all 12-B1 fees; eliminate all “rolling performance periods” by forcing one-year calendar performance periods with mandatory fee return to investors if the manager underperforms; and outlaw all front-end and back-end loads, thus forcing marketers to charge a direct commission.  The goal of any transparent system is to protect the consumer, and the individual investor can only be protected by implementing “absolute standards” that will allow no “wiggle room” for mutual fund companies

Does Working Longer Enhance Old Age?

Understanding the link between retirement and health is crucial for both improving people\u27s wellbeing and for designing optimal public policy around retirement. Yet, to date, the economics literature has been inconclusive about whether retirement causes improvements or deterioration in health. The lack of consensus is likely driven by differences in study design, population, and the age of workers and set of health outcomes studied. In this paper, I explain and distill the literature, highlight patterns in the highest-quality studies, and discuss the implications of the findings for longevity risk management and worker and retiree health going forward