Parallel Algorithm for Solving Kepler's Equation on Graphics Processing Units: Application to Analysis of Doppler Exoplanet Searches

[Abridged] We present the results of a highly parallel Kepler equation solver using the Graphics Processing Unit (GPU) on a commercial nVidia GeForce 280GTX and the "Compute Unified Device Architecture" programming environment. We apply this to evaluate a goodness-of-fit statistic (e.g., chi^2) for Doppler observations of stars potentially harboring multiple planetary companions (assuming negligible planet-planet interactions). We tested multiple implementations using single precision, double precision, pairs of single precision, and mixed precision arithmetic. We find that the vast majority of computations can be performed using single precision arithmetic, with selective use of compensated summation for increased precision. However, standard single precision is not adequate for calculating the mean anomaly from the time of observation and orbital period when evaluating the goodness-of-fit for real planetary systems and observational data sets. Using all double precision, our GPU code outperforms a similar code using a modern CPU by a factor of over 60. Using mixed-precision, our GPU code provides a speed-up factor of over 600, when evaluating N_sys > 1024 models planetary systems each containing N_pl = 4 planets and assuming N_obs = 256 observations of each system. We conclude that modern GPUs also offer a powerful tool for repeatedly evaluating Kepler's equation and a goodness-of-fit statistic for orbital models when presented with a large parameter space.Comment: 19 pages, to appear in New Astronom

Hedge Funds in Corporate Governance and Corporate Control.

Hedge funds have become critical players in both corporate governance and corporate control. In this article, we document and examine the nature of hedge fund activism, how and why it differs from activism by traditional institutional investors, and its implications for corporate governance and regulatory reform. We argue that hedge fund activism differs from activism by traditional institutions in several ways: it is directed at significant changes in individual companies (rather than small, systemic changes), it entails higher costs, and it is strategic and ex ante (rather than intermittent and ex post). The reasons for these differences may lie in the incentive structures of hedge fund managers as well as in the fact that traditional institutions face regulatory barriers, political constraints, or conflicts of interest that make activism less profitable than it is for hedge funds. But the differences may also be due to the fact that traditional institutions pursue a diversification strategy that is difficult to combine with strategic activism. Although hedge funds hold great promise as active shareholders, their intense involvement in corporate governance and control also potentially raises two kinds of problems: The interests of hedge funds sometimes diverge from those of their fellow shareholders; and the intensity of hedge fund activism imposes substantial stress that the regulatory system may not be able to withstand. The resulting problems, however, are relatively isolated and narrow, do not broadly undermine the value of hedge fund activism as a whole, and do not warrant major additional regulatory interventions. The sharpest accusation leveled against activist funds is that activism is designed to achieve a short-term payoff at the expense of long-term profitability. Although we consider this a potentially serious problem that arguably pervades hedge fund activism, we conclude that a sufficient case for legal intervention has not been made. This conclusion results from the uncertainties about whether short-termism is in fact a real problem and how much hedge fund activism is driven by excessive short-termism. But, most importantly, it stems from our view that market forces and adaptive devices taken by companies individually are better designed than regulation to deal with the potential negative effects of hedge fund short-termism while preserving the positive effects of hedge-fund activism

A re-randomisation design for clinical trials

Background: Recruitment to clinical trials is often problematic, with many trials failing to recruit to their target sample size. As a result, patient care may be based on suboptimal evidence from underpowered trials or non-randomised studies. Methods: For many conditions patients will require treatment on several occasions, for example, to treat symptoms of an underlying chronic condition (such as migraines, where treatment is required each time a new episode occurs), or until they achieve treatment success (such as fertility, where patients undergo treatment on multiple occasions until they become pregnant). We describe a re-randomisation design for these scenarios, which allows each patient to be independently randomised on multiple occasions. We discuss the circumstances in which this design can be used. Results: The re-randomisation design will give asymptotically unbiased estimates of treatment effect and correct type I error rates under the following conditions: (a) patients are only re-randomised after the follow-up period from their previous randomisation is complete; (b) randomisations for the same patient are performed independently; and (c) the treatment effect is constant across all randomisations. Provided the analysis accounts for correlation between observations from the same patient, this design will typically have higher power than a parallel group trial with an equivalent number of observations. Conclusions: If used appropriately, the re-randomisation design can increase the recruitment rate for clinical trials while still providing an unbiased estimate of treatment effect and correct type I error rates. In many situations, it can increase the power compared to a parallel group design with an equivalent number of observations

Economic evaluation of ASCOT-BPLA: Antihypertensive treatment with an amlodipine-based regimen is cost-effective compared to an atenolol-based regimen

Copyright © 2010 BMJ Publishing Group Ltd & British Cardiovascular Society. Internal or personal use of this material is permitted. However, permission to reprint/republish this material must be obtained from the Publisher.Objective: To compare the cost effectiveness of an amlodipine-based strategy and an atenolol-based strategy in the treatment of hypertension in the UK and Sweden. Design: A prospective, randomised trial complemented with a Markov model to assess long-term costs and health effects. Setting: Primary care. Patients: Patients with moderate hypertension and three or more additional risk factors. Interventions: Amlodipine 5–10 mg with perindopril 4–8 mg added as needed or atenolol 50–100 mg with bendroflumethiazide 1.25–2.5 mg and potassium added as needed Main outcome measures: Cost per cardiovascular event and procedure avoided, and cost per quality-adjusted life-year gained. Results: In the UK, the cost to avoid one cardiovascular event or procedure would be €18 965, and the cost to gain one quality-adjusted life-year would be €21 875. The corresponding figures for Sweden were €13 210 and €16 856. Conclusions: Compared with the thresholds applied by NICE and in the Swedish National Board of Health and Welfare’s Guidelines for Cardiac Care, an amlodipine-based regimen is cost effective for the treatment of hypertension compared with an atenolol-based regimen in the population studied.The study was supported by the principal funding source, Pfizer, New York, USA

On integrability of Hirota-Kimura type discretizations

We give an overview of the integrability of the Hirota-Kimura discretization method applied to algebraically completely integrable (a.c.i.) systems with quadratic vector fields. Along with the description of the basic mechanism of integrability (Hirota-Kimura bases), we provide the reader with a fairly complete list of the currently available results for concrete a.c.i. systems.Comment: 47 pages, some minor change

Simple model for the vibrations of embedded elastically cubic nanocrystals

The purpose of this work is to calculate the vibrational modes of an elastically anisotropic sphere embedded in an isotropic matrix. This has important application to understanding the spectra of low-frequency Raman scattering from nanoparticles embedded in a glass matrix. First some low frequency vibrational modes of a free cubically elastic sphere are found to be nearly independent of one combination of elastic constants. This is then exploited to obtain an isotropic approximation for these modes which enables to take into account the surrounding isotropic matrix. This method is then used to quantatively explain recent spectra of gold and copper nanocrystals in glasses.Comment: 6 pages, 5 figure

Allograft and Xenograft Acceptance under FK‐506 and Other Immunosuppressant Treatment

We will focus on two issues, both involving, but not confined to FK-506: first, the meaning of the graft acceptance, which is, after all, the objective of immunosuppression for the transplant surgeon; and second, how to take the next great step of xenotransplantation

Core pinning by intragranular nanoprecipitates in polycrystalline MgCNi_3

The nanostructure and magnetic properties of polycrystalline MgCNi_3 were studied by x-ray diffraction, electron microscopy, and vibrating sample magnetometry. While the bulk flux-pinning force curve F_p(H) indicates the expected grain-boundary pinning mechanism just below T_c = 7.2 K, a systematic change to pinning by a nanometer-scale distribution of core pinning sites is indicated by a shift of F_p(H) with decreasing temperature. The lack of scaling of F_p(H) suggests the presence of 10 to 20% of nonsuperconducting regions inside the grains, which are smaller than the diameter of fluxon cores 2xi at high temperature and become effective with decreasing temperature when xi(T) approaches the nanostructural scale. Transmission electron microscopy revealed cubic and graphite nanoprecipitates with 2 to 5 nm size, consistent with the above hypothesis since xi(0) = 6 nm. High critical current densities, more than 10^6 A/cm^2 at 1 T and 4.2 K, were obtained for grain colonies separated by carbon. Dirty-limit behavior seen in previous studies may be tied to electron scattering by the precipitates, indicating the possibility that strong core pinning might be combined with a technologically useful upper critical field if versions of MgCNi_3 with higher T_c can be found.Comment: 5 pages, 6 figures, submitted to PR

Brief of Corporate Law Professors as Amici Curie in Support of Respondents

The Supreme Court has looked to the rights of corporate shareholders in determining the rights of union members and non-members to control political spending, and vice versa. The Court sometimes assumes that if shareholders disapprove of corporate political expression, they can easily sell their shares or exercise control over corporate spending. This assumption is mistaken. Because of how capital is saved and invested, most individual shareholders cannot obtain full information about corporate political activities, even after the fact, nor can they prevent their savings from being used to speak in ways with which they disagree. Individual shareholders have no “opt out” rights or practical ability to avoid subsidizing corporate political expression with which they disagree. Nor do individuals have the practical option to refrain from putting their savings into equity investments, as doing so would impose damaging economic penalties and ignore conventional financial guidance for individual investors