Partners with God: A Celebration of Human Sexuality

Reviewed Book: Thomas, David. Partners with God: A Celebration of Human Sexuality. Winfield, BC: Wood Lake Books, 1988

Earth Trojan asteroids: A study in support of observational searches

Observational searches for asteroids orbiting near Earth's triangular Lagrange points face unique obstacles. A population of such asteroids would occupy a large projected area on the sky (possibly hundreds of square degrees) and is not favorably placed with respect to the Sun. Here we examine the properties of synthetic populations of Earth ``Trojans'' in order to aid in the optimization of observational searches for them. We find that the highest on-sky projected number densities are not located at the positions of the L4 and L5 points themselves, but rather a few degrees closer to the Sun. Also, asteroids on orbits about the L4 and L5 points typically brighten as the difference between their ecliptic longitude and that of the Sun increases owing to phase effects, but their number density on the sky concurrently falls rapidly.Comment: 20 pages, 5 figures and 3 tables. Submitted to Icaru

A long-lived horseshoe companion to the Earth

We present a dynamical investigation of a newly found asteroid, 2010 SO16, and the discovery that it is a horseshoe companion of the Earth. The object's absolute magnitude (H=20.7) makes this the largest object of its type known to-date. By carrying out numerical integrations of dynamical clones, we find that (a) its status as a horseshoe is secure given the current accuracy of its ephemeris, and (b) the time spent in horseshoe libration with the Earth is several times 10^5 yr, two orders of magnitude longer than determined for other horseshoe asteroids of the Earth. Further, using a model based on Hill's approximation to the three-body problem, we show that, apart from the low eccentricity which prevents close encounters with other planets or the Earth itself, its stability can be attributed to the value of its Jacobi constant far from the regime that allows transitions into other coorbital modes or escape from the resonance altogether. We provide evidence that the eventual escape of the asteroid from horseshoe libration is caused by the action of planetary secular perturbations and the stochastic evolution of the eccentricity. The questions of its origin and the existence of as-yet-undiscovered co-orbital companions of the Earth are discussed.Comment: Accepted in MNRAS; 6 pages, 3 figures, 2 table

Deep residual learning in CT physics: scatter correction for spectral CT

Recently, spectral CT has been drawing a lot of attention in a variety of clinical applications primarily due to its capability of providing quantitative information about material properties. The quantitative integrity of the reconstructed data depends on the accuracy of the data corrections applied to the measurements. Scatter correction is a particularly sensitive correction in spectral CT as it depends on system effects as well as the object being imaged and any residual scatter is amplified during the non-linear material decomposition. An accurate way of removing scatter is subtracting the scatter estimated by Monte Carlo simulation. However, to get sufficiently good scatter estimates, extremely large numbers of photons is required, which may lead to unexpectedly high computational costs. Other approaches model scatter as a convolution operation using kernels derived using empirical methods. These techniques have been found to be insufficient in spectral CT due to their inability to sufficiently capture object dependence. In this work, we develop a deep residual learning framework to address both issues of computation simplicity and object dependency. A deep convolution neural network is trained to determine the scatter distribution from the projection content in training sets. In test cases of a digital anthropomorphic phantom and real water phantom, we demonstrate that with much lower computing costs, the proposed network provides sufficiently accurate scatter estimation