The precise solar shape and its variability.

The precise shape of the Sun has not been convincingly determined, despite half a century of modern photoelectric observations. The expected deviation of the solar-limb shape from a perfect circle is very small, but such asphericity is sensitive to the Sun's otherwise invisible interior conditions, as well as the solar atmosphere. We use evidence from a long-running experiment based in space to show that, when analyzed with sufficiently high spatial resolution, the Sun's oblate shape is distinctly constant and almost completely unaffected by the solar-cycle variability seen on its surface. The solar oblateness is significantly lower than theoretical expectations by an amount that could be explained by a slower differential rotation in the outer few percent of the Sun.

Comment on "A large excess in apparent solar oblateness due to surface magnetism".

Fivian et al. (Reports, 24 October 2008, p. 560) analyzed data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager satellite and reported that the Sun is more oblate than previous measurements have suggested. We argue that their threshold-based analysis yields a biased measure of the solar limb shape geometry.

Modulated polarization microscopy: a promising new approach to visualizing cytoskeletal dynamics in living cells.

In an effort to visualize cytoskeletal filaments in living cells, we have developed modulated polarization microscopy. Modulated polarization microscopy visualizes cytoskeletal filaments based on their birefringence but differs from the standard polarization microscopy by exploiting the angle dependence of birefringence. A prototype instrument has been developed using two Faraday rotators under computer control to change the angle of plane polarized light at a known rate. By placing one Faraday rotator before and one after the specimen, rotation produced by the first Faraday rotator is cancelled by the second. This allows the use of fixed polarizer and analyzer in a crossed configuration and continuous imaging of the specimen between crossed polarizers. The variation in polarization angle of light illuminating the specimen causes birefringent elements to oscillate in brightness. Images acquired as polarization angle is varied are then processed by a Fourier filter image-processing algorithm. The Fourier filtering algorithm isolates those signals that vary at the proper rate, whereas static or random signals are removed. Here we show that the modulated polarization microscope can reveal cytoskeletal elements including stress fibers and microtubules in living cells.

Optical performance of the 6.5-m off-axis new planetary telescope.

We describe an off-axis design for a 6.5-m astronomical telescope optimized for low scattered light and low emissivity. This is part of a new concept for an instrument that we call the New Planetary Telescope. We show how the geometric optical performance can equal that of an on-axis conventional telescope while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The decentered concept also allows wide-field and versatile instrumentation configurations that are not possible with more-conventional designs.

Off-axis systems for 4-m class telescopes.

We describe here an off-axis design for a 4.0-m astronomical telescope. We show that the geometric optical performance of this configuration can equal that of an on-axis conventional configuration while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The specific optical design described here uses a single off-axis primary mirror to obtain three distinct final focus ports: an f/10 port (with corrector) for wide-field imaging and spectroscopy with a field of view (FOV) of 15 arc min; a small-field, 2-reflection f/10 port suitable for polarimetry and coronagraphy; and a slower, f/16(3-reflection) port with a 7 arc min FOV. For general astronomical observations requiring high optical throughput and low scattered light, this design is superior to conventional Ritchey-Chretien optical configurations.

No evidence of a circumsolar dust ring from infrared observations of the 1991 solar eclipse.

During the past 25 years there have been many attempts to detect a possible dust ring around the sun, with contradictory results. Before the 1991 eclipse, infrared eclipse experiments used single-element detectors to scan the corona along the ecliptic for excess surface brightness peaks. The availability of relatively large-format infrared array detectors now provides a considerable observational advantage: two-dimensional mapping of the brightness and polarization of the corona with high photometric precision. The 1991 eclipse path included the high-altitude Mauna Kea Observatory, a further advantage to measure the corona out to large angular distances from the sun. Results are reported from an experiment conducted on Mauna Kea with a HgCdTe-array detector sensitive to wavelengths between 1 and 2.5 micrometers, using broad-band J, H, and K filters. Although the sky conditions were not ideal, the H- and K-band surface brightnesses clearly show the inhomogeneous structure in the K-corona and the elliptical flattening of the F-corona, but no evidence of a circumsolar, local dust component out to 15 solar radii.

The central galaxy in abell 2029: an old supergiant.

A mosaic of images shows the extended structure of the cD galaxy that resides at the center of the rich cluster of galaxies Abell 2029. After correcting for the scattered light of nearby stars and galaxies, the faint halo of this giant can be traced out to a distance of more than 1 megaparsec, making it one of the largest and most luminous galaxies known. The smoothness of this halo suggests that it was formed early in the history of the cluster.

Diagnosis and treatment of iatrogenic cerebrospinal fluid leak and brain herniation during or following mastoidectomy.

Iatrogenic brain herniation, with meninges (meningoencephalocele) or without meninges (encephalocele), following mastoidectomy is rare. However, the seriousness of the complication and the potential for its prevention necessitate periodic review and emphasis. In this study, 6 patients with small iatrogenic dural injury during mastoidectomy, 1 patient with postoperative large encephalocele, and 2 patients with three spontaneous meningoencephaloceles are reviewed. These cases, and the literature, support the following: 1. A dural injury is necessary for herniation. 2. If the arachnoid remains intact, a meningoencephalocele results with the potential for cerebrospinal fluid leak into the middle ear and recurrent meningitis. 3. If the arachnoid is not intact, an encephalocele results which presents predominantly as a mass without a cerebrospinal fluid leak. 4. The dura and arachnoid may be torn during mastoidectomy, resulting in an immediate cerebrospinal fluid leak that can go easily unrecognized. Taking time to carefully inspect any area of dural exposure obviates this oversight. 5. A satisfactory technique of tegmen and dural-arachnoid repair in these ten cases is described.

The role of initial cineesophagography in caustic esophageal injury.

The accurate assessment of caustic ingestion requires a vigorous attempt to obtain as much information concerning the type, concentration, and amount of corrosive agent ingested as possible. Although early endoscopy is crucial for assessing the existence of esophageal burns, an accurate prediction of outcome, (for example, stricture) may not be possible from endoscopic study alone. The role of contrast cineesophagography has not been properly emphasized in the surgical literature. Our analysis of the relative accuracy of endoscopy and cineesophagography in esophageal burn evaluation has emphasized that cineesophagography helps in early identification of those patients who will develop strictures. In our experience, cineesophagographically visualized abnormalities, specifically disordered motility, when interpreted within the context of historical facts and physical findings, most accurately prognosticates the outcome of caustic esophageal injuries.