An analysis of new techniqes for radiometric correction of LANDSAT-4 Thematic Mapper images

The utility of methods for generating TM RLUTS which can improve the quality of the resultant images was investigated. The TM-CCT-ADDS tape was changed to account for a different collection window for the calibration data. Several scenes of Terrebonne Bay, Louisiana and the Grand Bahamas were analyzed to evaluate the radiometric corrections operationally applied to the image data and to investigate several techniques for reducing striping in the images. Printer plots for the TM shutter data were produced and detector statistics were compiled and plotted. These statistics included various combinations of the average shutter counts for each scan before and after DC restore for forward and reverse scans. Results show that striping is caused by the detectors becoming saturated when they view a bright cloud and depress the DC restore level

Outcomes of tuberculosis patients who start antiretroviral therapy under routine programme conditions in Malawi

SETTING: Public sector facilities in Malawi providing antiretroviral therapy (ART) to human immunodeficiency virus (HIV) positive patients, including those with tuberculosis (TB). OBJECTIVES: To compare 6-month and 12-month cohort treatment outcomes of HIV-positive TB patients and HIV-positive non-TB patients treated with ART. DESIGN: Retrospective data collection using ART patient master cards and ART patient registers. RESULTS: Between July and September 2005, 7905 patients started ART, 6967 with a non-TB diagnosis and 938 with a diagnosis of active TB. 6-month cohort outcomes of non-TB and TB patients censored on 31 March 2006 showed significantly more TB patients alive and on ART (77%) compared with non-TB patients (71%) (P < 0.001). Between January and March 2005, 4580 patients started ART, 4179 with a non-TB diagnosis and 401 with a diagnosis of active TB. 12-month cohort outcomes of non-TB and TB patients censored on 31 March 2006 showed significantly more TB patients alive and on ART (74%) compared with non-TB patients (66%) (P < 0.001). Other outcomes of default and transfer out were also significantly less frequent in TB compared with non-TB patients. CONCLUSION: HIV-positive TB patients on ART in Malawi have generally good treatment outcomes, and more patients need to access this HIV treatment

A study of 2 GHz electromagnetic wave propagation over optical paths in three geographical regions of the United States

Statistical correlation between optical microwave propagation reliability, fade margin, path length, and geographic locatio

Discovery of an extended debris disk around the F2V star HD 15745

Using the Advanced Camera for Surveys aboard the Hubble Space Telescope, we have discovered dust-scattered light from the debris disk surrounding the F2V star HD 15745. The circumstellar disk is detected between 2.0" and 7.5" radius, corresponding to 128 - 480 AU radius. The circumstellar disk morphology is asymmetric about the star, resembling a fan, and consistent with forward scattering grains in an optically thin disk with an inclination of ~67 degrees to our line of sight. The spectral energy distribution and scattered light morphology can be approximated with a model disk composed of silicate grains between 60 and 450 AU radius, with a total dust mass of 10E-7 M_sun (0.03 M_earth) representing a narrow grain size distribution (1 - 10 micron). Galactic space motions are similar to the Castor Moving Group with an age of ~10E+8 yr, although future work is required to determine the age of HD 15745 using other indicators.Comment: 7 pages, 4 figures, ApJ Letters, in pres

A Ring of Warm Dust in the HD 32297 Debris Disk

We report the detection of a ring of warm dust in the edge-on disk surrounding HD 32297 with the Gemini-N/MICHELLE mid-infrared imager. Our N'-band image shows elongated structure consistent with the orientation of the scattered-light disk. The Fnu(11.2 um) = 49.9+/-2.1 mJy flux is significantly above the 28.2+/-0.6 mJy photosphere. Subtraction of the stellar point spread function reveals a bilobed structure with peaks 0.5"-0.6" from the star. An analysis of the stellar component of the SED suggests a spectral type later than A0, in contrast to commonly cited literature values. We fit three-dimensional, single-size grain models of an optically thin dust ring to our image and the SED using a Markov chain Monte Carlo algorithm in a Bayesian framework. The best-fit effective grain sizes are submicron, suggesting the same dust population is responsible for the bulk of the scattered light. The inner boundary of the warm dust is located 0.5"-0.7" (~65 AU) from the star, which is approximately cospatial with the outer boundary of the scattered-light asymmetry inward of 0.5". The addition of a separate component of larger, cooler grains that provide a portion of the 60 um flux improves both the fidelity of the model fit and consistency with the slopes of the scattered-light brightness profiles. Previous indirect estimates of the stellar age (~30 Myr) indicate the dust is composed of debris. The peak vertical optical depths in our models (~0.3-1 x 1e-2) imply that grain-grain collisions likely play a significant role in dust dynamics and evolution. Submicron grains can survive radiation pressure blow-out if they are icy and porous. Similarly, the inferred warm temperatures (130-200 K) suggest that ice sublimation may play a role in truncating the inner disk.Comment: ApJ accepted, 8 pages, 4 figure

Photon Shot Noise Limits on Optical Detection of Neuronal Spikes and Estimation of Spike Timing

AbstractOptical approaches for tracking neural dynamics are of widespread interest, but a theoretical framework quantifying the physical limits of these techniques has been lacking. We formulate such a framework by using signal detection and estimation theory to obtain physical bounds on the detection of neural spikes and the estimation of their occurrence times as set by photon counting statistics (shot noise). These bounds are succinctly expressed via a discriminability index that depends on the kinetics of the optical indicator and the relative fluxes of signal and background photons. This approach facilitates quantitative evaluations of different indicators, detector technologies, and data analyses. Our treatment also provides optimal filtering techniques for optical detection of spikes. We compare various types of Ca2+ indicators and show that background photons are a chief impediment to voltage sensing. Thus, voltage indicators that change color in response to membrane depolarization may offer a key advantage over those that change intensity. We also examine fluorescence resonance energy transfer indicators and identify the regimes in which the widely used ratiometric analysis of signals is substantially suboptimal. Overall, by showing how different optical factors interact to affect signal quality, our treatment offers a valuable guide to experimental design and provides measures of confidence to assess optically extracted traces of neural activity

First scattered light images of debris disks around HD 53143 and HD 139664

We present the first scattered light images of debris disks around a K star (HD 53143) and an F star (HD 139664) using the coronagraphic mode of the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). With ages 0.3 - 1 Gyr, these are among the oldest optically detected debris disks. HD 53143, viewed ~45 degrees from edge-on, does not show radial variation in disk structure and has width >55 AU. HD 139664 is seen close to edge-on and has belt-like morphology with a dust peak 83 AU from the star and a distinct outer boundary at 109 AU. We discuss evidence for significant diversity in the radial architecture of debris disks that appears unconnected to stellar spectral type or age. HD 139664 and possibly the solar system belong in a category of narrow belts 20-30 AU wide. HD 53143 represents a class of wide disk architecture with characteristic width >50 AU.Comment: 7 pages, 3 figure