Effects of Quasi-Static Aberrations in Faint Companion Searches

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. The camera's main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. The main limitation is non-common path aberrations between the three optical paths that slightly decorrelate the PSFs. Two types of PSF calibrations are combined with the differential simultaneous imaging technique to further attenuate the PSF: reference star subtraction and instrument rotation to smooth aberrations. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast Imaging, EAS Publications Serie

Mutual Wealth in Rural America

This essay contends that mutual wealth in rural America, particularly related to the use of land and other natural resources, has undergone three major paradigm shifts in the last 500 years, and may be at the threshold of a fourth. First, from the early 1500s to about 1800, European diseases and conquest destroyed the elaborate management systems for agriculture, forests, game, and other natural resources developed by North American Indians. Second, from the early 1500s to the early 1900s, European and white American settlers, induced by offers of land, repopulated the continent primarily with small and medium-sized farms and ranches. Third, beginning in the late 1800s, farmers revolted against low prices and high costs of production. a consequence of this revolt was the emergence of the rural cooperative movement in the United States, but a continuation of fragmented rural landownership. Fourth, largely as a result of increased productivity, the size of the farm population in the United States dropped dramatically in the 20th century. Especially in the past quarter century, there has been an emerging trend to manage land and other natural resources for the long-term. The essay concludes by noting the similarities and differences between the pre-colonial land ethic and the emerging one; and by identifying several public and private trends that are contributing to the current paradigm shift

Exploring Clinical Risk Factors for Breast Cancer among American Indian Women

Objective: Very little is known about the breast cancer risk profile among American Indian women. Previous research shows that the proportion of American Indian/Alaska Native women with baseline characteristics (commonly known breast cancer risk factors) differs from other ethnicities. This retrospective case control study was designed to the explore the association of these factors among American Indian women with and without breast cancer. Methods: Cases and controls were retrospectively selected from the medical records of American Indian women who obtained their health care from Quentin N. Burdick Memorial Health Care Facility (IHS) in Belcourt, ND. For each woman with breast cancer (n=141), two controls were selected when possible (n=278). Risk factors examined included woman’s age, age at first live birth, age of menarche, the number of previous benign breast biopsies, the total number of first-degree relatives with breast cancer, body mass index and parity. Odds ratios and 95% confidence intervals were calculated using logistic regression. Results: Many of the associations found among American Indian women who obtained their health care from Quentin N. Burdick Memorial Health Care Facility (IHS) in Belcourt, ND, between risk factors commonly identified in other populations and breast cancer were weakly positive. Nulliparity was the only risk factor to consistently show a positive significant association (OR = 2.87, 95% CI 1.16-.7.12). Conclusion: Disparities in breast cancer incidence, mortality and screening among Northern Plains American Indian emphasize the need to better understand the risk factors associated with breast cancer in this population. Based on the results of this study, the value of current risk prediction models in American Indian communities is uncertain and clinicians should be cautious in using these models to inform American Indian patients of their risk for breast cancer

Single Leptoquark Production at e+e−e^+e^- and γγ\gamma\gamma Colliders

We consider single production of leptoquarks (LQ's) at $e^+e^-$ and $\gamma\gamma$ colliders, for two values of the centre-of-mass energy, $\sqrt{s}=500$ GeV and 1 TeV. We find that LQ's which couple within the first generation are observable for LQ masses almost up to the kinematic limit, both at $e^+e^-$ and $\gamma\gamma$ colliders, for the LQ coupling strength equal to $\alpha_{em}$. The cross sections for single production of $2^{nd}$- and $3^{rd}$-generation LQ's at $e^+e^-$ colliders are too small to be observable. In $\gamma\gamma$ collisions, on the other hand, $2^{nd}$-generation LQ's with masses much larger than $\sqrt{s}/2$ can be detected. However, $3^{rd}$-generation LQ's can be seen at $\gamma\gamma$ colliders only for masses at most $\sim\sqrt{s}/2$, making their observation more probable via the pair production mechanism.Comment: plain TeX, 14 pages, 6 figures (not included but available on request), some minor changes to the text, one reference added, figures and conclusions unchanged, UdeM-LPN-TH-93-152, McGill-93/2

Test of Quantum Action for Inverse Square Potential

We present a numerical study of the quantum action previously introduced as a parametrisation of Q.M. transition amplitudes. We address the questions: Is the quantum action possibly an exact parametrisation in the whole range of transition times ($0 < T < \infty$)? Is the presence of potential terms beyond those occuring in the classical potential required? What is the error of the parametrisation estimated from the numerical fit? How about convergence and stability of the fitting method (dependence on grid points, resolution, initial conditions, internal precision etc.)? Further we compare two methods of numerical determination of the quantum action: (i) global fit of the Q.M. transition amplitudes and (ii) flow equation. As model we consider the inverse square potential, for which the Q.M. transition amplitudes are analytically known. We find that the relative error of the parametrisation starts from zero at T=0 increases to about $10^{-3}$ at $T=1/E_{gr}$ and then decreases to zero when $T \to \infty$. Second, we observe stability of the quantum action under variation of the control parameters. Finally, the flow equation method works well in the regime of large $T$ giving stable results under variation of initial data and consistent with the global fit method.Comment: Text (LaTeX), Figures(ps