Using hybrid GPU/CPU kernel splitting to accelerate spherical convolutions

We present a general method for accelerating by more than an order of magnitude the convolution of pixelated functions on the sphere with a radially-symmetric kernel. Our method splits the kernel into a compact real-space component and a compact spherical harmonic space component. These components can then be convolved in parallel using an inexpensive commodity GPU and a CPU. We provide models for the computational cost of both real-space and Fourier space convolutions and an estimate for the approximation error. Using these models we can determine the optimum split that minimizes the wall clock time for the convolution while satisfying the desired error bounds. We apply this technique to the problem of simulating a cosmic microwave background (CMB) anisotropy sky map at the resolution typical of the high resolution maps produced by the Planck mission. For the main Planck CMB science channels we achieve a speedup of over a factor of ten, assuming an acceptable fractional rms error of order 1.e-5 in the power spectrum of the output map.Comment: 9 pages, 11 figures, 1 table, accepted by Astronomy & Computing w/ minor revisions. arXiv admin note: substantial text overlap with arXiv:1211.355

Frederick A. Milan (1924-1995)

Frederick A. Milan died on 28 January 1995 after a series of strokes and related illness of several years. ... His activities around the polar regions of the world are well known and fondly remembered. Fred was Professor Emeritus of Human Ecology and Anthropology at the University of Alaska, Fairbanks. ... His work as an assistant on the Harvard Peabody Museum Anthropological Expedition to the Aleutian Islands in 1949 heightened his interest in the Arctic. It also impressed upon him the utility of studying Russian for understanding the history of the region. Fred worked in the summers of 1950 and 1952 as an archaeological assistant at Deering and Kodiak, Alaska. He was a weather observer on the Juneau Icefield Research Project in the summer of 1951. His major scholastic interests were in anthropology and linguistics, and he graduated in 1952. In 1953 Fred began several years of association with the former United States Air Force Arctic Aeromedical Laboratory near Fairbanks. ... [In 1954] he and other Arctic Aeromedical Laboratory personnel participated in the Mount Wrangell Research Project, a high-latitude cosmic ray study. His role was as a collaborator in a study of high altitude acclimatization of the team members. ... Fred undertook graduate study at several institutions: the Universities of Oregon, Wisconsin and Copenhagen, and the London School of Economics. His linguistic skills became well developed, and he was especially interested in the Inuit language and culture. He spent one winter in northern Sweden traveling and living with a nomadic Sami family. Back in Alaska in 1956, he began his close association with the Inupiat Eskimo village of Wainwright, Alaska. His ability to speak the language enabled him to gain the villagers' confidence and elicit genealogical information, and endeared him to the people. These activities led eventually to successful completion of his M.S. and Ph.D. degrees at the University of Wisconsin. ... In the 1960s Fred played an important role in establishing a worldwide study of northern people as part of the Human Adaptability section of the International Biological Program. ... He was a longtime advocate for multidisciplinary study of the needs for health care delivery and for the international exchange of information about circumpolar health problems and research efforts. In 1967 Fred, Dr. C. Earl Albrecht and colleagues in Alaska and other parts of the United States, Canada, Sweden, Norway, Denmark, Iceland, Greenland and the Union of Soviet Socialist Republics organized, with the support of the Arctic Institute of North America, the First International Symposium on Circumpolar Health. The symposium was held at Fairbanks in July 1967, and these meetings have continued at three-year intervals at various circumpolar locations. Fred was the president of the Sixth International Congress on Circumpolar Health held at Anchorage in 1984. ... During the 1970s and 1980s Fred was a faculty member at the University of Alaska, Fairbanks. He was a much-respected teacher, and he was noted for conveying his enthusiasm for scholarly work and his respect for the people of anthropological study to students and colleagues. The Fred Milan we knew was a genuine free spirit--he looked at the world through eyes wide with perceptive curiosity and interpreted it with kindness and good humor. We have been made richer and wiser by sharing in some of his generous and stimulating life

Study of HST counterparts to Chandra X-ray sources in the Globular Cluster M71

We report on archival Hubble Space Telescope (HST) observations of the globular cluster M71 (NGC 6838). These observations, covering the core of the globular cluster, were performed by the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2). Inside the half-mass radius (r_h = 1.65') of M71, we find 33 candidate optical counterparts to 25 out of 29 Chandra X-ray sources while outside the half-mass radius, 6 possible optical counterparts to 4 X-ray sources are found. Based on the X-ray and optical properties of the identifications, we find 1 certain and 7 candidate cataclysmic variables (CVs). We also classify 2 and 12 X-ray sources as certain and potential chromospherically active binaries (ABs), respectively. The only star in the error circle of the known millisecond pulsar (MSP) is inconsistent with being the optical counterpart. The number of X-ray faint sources with L_x>4x10^{30} ergs/s (0.5-6.0 keV) found in M71 is higher than extrapolations from other clusters on the basis of either collision frequency or mass. Since the core density of M71 is relatively low, we suggest that those CVs and ABs are primordial in origin.Comment: 12 pages, 6 figures. Accepted for publication in Astronomy and Astrophysic

Latest results on Jovian disk X-rays from XMM-Newton

We present the results of a spectral study of the soft X-ray emission (0.2-2.5 keV) from low-latitude (`disk') regions of Jupiter. The data were obtained during two observing campaigns with XMM-Newton in April and November 2003. While the level of the emission remained approximately the same between April and the first half of the November observation, the second part of the latter shows an enhancement by about 40% in the 0.2-2.5 keV flux. A very similar, and apparently correlated increase, in time and scale, was observed in the solar X-ray and EUV flux. The months of October and November 2003 saw a period of particularly intense solar activity, which appears reflected in the behaviour of the soft X-rays from Jupiter's disk. The X-ray spectra, from the XMM-Newton EPIC CCD cameras, are all well fitted by a coronal model with temperatures in the range 0.4-0.5 keV, with additional line emission from Mg XI (1.35 keV) and Si XIII (1.86 keV): these are characteristic lines of solar X-ray spectra at maximum activity and during flares. The XMM-Newton observations lend further support to the theory that Jupiter's disk X-ray emission is controlled by the Sun, and may be produced in large part by scattering, elastic and fluorescent, of solar X-rays in the upper atmosphere of the planet.Comment: 17 pages, 7 figures, accepted for publication in a special issue of Planetary and Space Scienc

CMB lensing and primordial squeezed non-Gaussianity

Squeezed primordial non-Gaussianity can strongly constrain early-universe physics, but it can only be observed on the CMB after it has been gravitationally lensed. We give a new simple non-perturbative prescription for accurately calculating the effect of lensing on any squeezed primordial bispectrum shape, and test it with simulations. We give the generalization to polarization bispectra, and discuss the effect of lensing on the trispectrum. We explain why neglecting the lensing smoothing effect does not significantly bias estimators of local primordial non-Gaussianity, even though the change in shape can be >~10%. We also show how tau_NL trispectrum estimators can be well approximated by much simpler CMB temperature modulation estimators, and hence that there is potentially a ~10-30% bias due to very large-scale lensing modes, depending on the range of modulation scales included. Including dipole sky modulations can halve the tau_NL error bar if kinematic effects can be subtracted using known properties of the CMB temperature dipole. Lensing effects on the g_NL trispectrum are small compared to the error bar. In appendices we give the general result for lensing of any primordial bispectrum, and show how any full-sky squeezed bispectrum can be decomposed into orthogonal modes of distinct angular dependence.Comment: 22 pages, 6 figures; minor edits to match published versio