Millimeter and Submillimeter Observations from the South Pole

During the past decade, a year-round observatory has been established at the geographic South Pole by the Center for Astrophysical Research in Antarctica (CARA). CARA has fielded several millimeter- and submillimeter-wave instruments: AST/RO (the Antarctic Submillimeter Telescope and Remote Observatory, a 1.7-m telescope outfitted with a variety of receivers at frequencies from 230 GHz to 810 GHz, including PoleSTAR, a heterodyne spectrometer array), Python (a degree-scale CMB telescope), Viper (a 2-m telescope which has been outfitted with SPARO, a submillimeter-wave bolometric array polarimeter, ACBAR, a multi-channel CMB instrument, and Dos Equis, a HEMT polarimeter), and DASI (the Degree-Angular Scale Interferometer). These instruments have obtained significant results in studies of the interstellar medium and observational cosmology, including detections of the 1 degree acoustic peak in the CMB and the Sunyaev-Zel'dovich effect. The South Pole environment is unique among observatory sites for unusually low wind speeds, low absolute humidity, and the consistent clarity of the submillimeter sky. The atmosphere is dessicated by cold: at the South Pole's average annual temperature of -49 C, the partial pressure of saturated water vapor is only 1.2% of what it is at 0 C. The low water vapor levels result in exceptionally low values of sky noise. This is crucial for large-scale observations of faint cosmological sources---for such observations the South Pole is unsurpassed.Comment: 9 pages, contribution to 2K1BC symposium "Experimental Cosmology at Millimeter Wavelengths", ed. M. De Petris and M. Gervas

Design Considerations for Large Detector Arrays on Submillimeter-wave Telescopes

The emerging technology of large (~ 10,000 pixel) submillimeter-wave bolometer arrays presents a novel optical design problem---how can such arrays be fed by diffraction-limited telescope optics where the primary mirror is less than 100,000 wavelengths in diameter? Standard Cassegrain designs for radiotelescope optics exhibit focal surface curvature so large that detectors cannot be placed more than 25 beam diameters from the central ray. The problem is worse for Ritchey-Cretien designs, because these minimize coma while increasing field curvature. Classical aberrations, including coma, are usually dominated by diffraction in submillimeter-wave single dish telescopes. The telescope designer must consider (1) diffraction, (2) aberration, (3) curvature of field, (4) cross-polarization, (5) internal reflections, (6) the effect of blockages, (7) means of beam chopping on- and off-source, (8) gravitational and thermal deformations of the primary mirror, (9) the physical mounting of large detector packages, and (10) the effect of gravity and (11) vibration on those detectors. Simultaneous optimization of these considerations in the case of large detector arrays leads to telescopes that differ considerably from standard radiotelescope designs. Offset optics provide flexibility for mounting detectors, while eliminating blockage and internal reflections. Aberrations and cross-polarization can be the same as on-axis designs having the same diameter and focal length. Trade-offs include the complication of primary mirror homology and an increase in overall cost. A dramatic increase in usable field of view can be achieved using shaped optics. Solutions having one to six mirrors will be discussed, including a possible six-mirror design for the proposed South Pole 10m telescope.Comment: in proceedings "Radio Telescopes" SPIE Astronomical Telescopes and Instrumentation, 30 March 2000, Munich. SPIE code 4015-46. 12 pages 4 figures Revised to fix typos, figur

Asymmetric Beams and CMB Statistical Anisotropy

Beam asymmetries result in statistically-anisotropic cosmic microwave background (CMB) maps. Typically, they are studied for their effects on the CMB power spectrum, however they more closely mimic anisotropic effects such as gravitational lensing and primordial power asymmetry. We discuss tools for studying the effects of beam asymmetry on general quadratic estimators of anisotropy, analytically for full-sky observations as well as in the analysis of realistic data. We demonstrate this methodology in application to a recently-detected 9 sigma quadrupolar modulation effect in the WMAP data, showing that beams provide a complete and sufficient explanation for the anomaly.Comment: updated to match PRD version + typo correction in Eq. B

A note on Dolby and Gull on radar time and the twin "paradox"

Recently a suggestion has been made that standard textbook representations of hypersurfaces of simultaneity for the travelling twin in the twin "paradox" are incorrect. This suggestion is false: the standard textbooks are in agreement with a proper understanding of the relativity of simultaneity.Comment: LaTeX, 3 pages, 2 figures. Update: added new section V and updated reference

\u3cem\u3ePlasmodium falciparum\u3c/em\u3e SSB Tetramer Wraps Single-Stranded DNA with Similar Topology but Opposite Polarity to \u3cem\u3eE. coli\u3c/em\u3e SSB

Single-stranded DNA binding (SSB) proteins play central roles in genome maintenance in all organisms. Plasmodium falciparum, the causative agent of malaria, encodes an SSB protein that localizes to the apicoplast and likely functions in the replication and maintenance of its genome. P. falciparum SSB (Pf-SSB) shares a high degree of sequence homology with bacterial SSB proteins but differs in the composition of its C-terminus, which interacts with more than a dozen other proteins in Escherichia coli SSB (Ec-SSB). Using sedimentation methods, we show that Pf-SSB forms a stable homo-tetramer alone and when bound to single-stranded DNA (ssDNA). We also present a crystal structure at 2.1 Å resolution of the Pf-SSB tetramer bound to two (dT)35 molecules. The Pf-SSB tetramer is structurally similar to the Ec-SSB tetramer, and ssDNA wraps completely around the tetramer with a “baseball seam” topology that is similar to Ec-SSB in its “65 binding mode”. However, the polarity of the ssDNA wrapping around Pf-SSB is opposite to that observed for Ec-SSB. The interactions between the bases in the DNA and the amino acid side chains also differ from those observed in the Ec-SSB–DNA structure, suggesting that other differences may exist in the DNA binding properties of these structurally similar proteins