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"Mellinger, Axel"
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A Color All-Sky Panorama Image of the Milky Way
This article describes the assembly of an optical (RGB) all-sky mosaic image with an image scale of36″pixel-1
36
″
pixe
l
-
1
, a limiting magnitude of approximately 14 mag, and an 18 bit dynamic range. Using a portable low-cost CCD camera system, 70 fields (each covering40° × 27°
40
°
×
27
°
) were imaged over a time span of 22 months from dark-sky locations in South Africa, Texas, and Michigan. The fields were photometrically calibrated against standard catalog stars. Using sky background data from the Pioneer 10 and 11 space probes, gradients resulting from artificial light pollution, airglow, and zodiacal light were eliminated, while the large-scale galactic and extragalactic background resulting from unresolved sources was preserved. The 648 megapixel image is a valuable educational tool, being able to fully utilize the resolution and dynamic range of modern full-dome planetarium projection systems.
Journal Article
The Cambridge Photographic Star Atlas
Using the latest methods in digital photography and image processing, The Cambridge Photographic Star Atlas presents the whole sky through large-scale photographic images with corresponding charts. Each double-page spread shows a section of the night sky and is accompanied by an inverted chart highlighting and naming double stars, variable stars, open clusters, galactic and planetary nebulae, globular clusters and galaxies. The 82 large-scale charts, with a scale of 1° per cm, identify over 1500 deep-sky objects and 2500 stars. Providing a giant mosaic of the entire sky, this unique atlas is unparalleled in detail and completeness, making it indispensable for visual observers and astrophotographers.
eBook
Pressure dependence of space charge deposition in piezoelectric polymer foams: simulations and experimental verification
The piezoelectric activity of PQ-50 cellular polypropylene (PP) foam (an example of a so-called ferroelectret) is measured after repeated charging in a nitrogen atmosphere at a range of pressures between 61 and 381 kPa. The results are compared against simulations using a multilayer electromechanical model based on Townsend’s model of Paschen breakdown and a realistic distribution of void heights determined from scanning electron micrographs. The modeled piezoelectric coefficients versus pressure are in good agreement with experimental data when adjusted Paschen coefficients are used, indicating that the Paschen curve for electric breakdown in gases needs to be modified for dielectric barrier discharges in microcavities. The highest
d
33
coefficients were achieved for pressures above 251 kPa. For previously uncharged PP foam, the model predicts an optimal charging pressure of 186 kPa.
Journal Article
Thermal-Pulse Tomography of Space-charge and Polarization Distributions in Electret Polymers
A new, non-destructive technique for the analysis of electret materials is presented. Thermal-pulse tomography produces three-dimensional images of space-charge and polarization distributions with a lateral resolution of better than 50 μm and a depth resolution of less than 0.5 μm. A focused-pulsed laser heats a circular spot on the opaque upper electrode. While diffusing through the sample, the thermal pulse causes local changes in the sample geometry or dielectric properties, resulting in a short-circuit current in the presence of space charge or electric dipoles. From the transient current, the distribution of the internal electric field can be reconstructed by means of scale transformation or regularization methods.
Journal Article
Low-cost ultrasonic distance measurement in a mechanical resonance experiment
We present a low-cost, dual-probe position sensor in a mechanical resonance experiment suitable for deployment in large lab courses with multiple stations. The motion of the two ends of a driven, damped spring oscillator is recorded with US-100 ultrasonic distance sensors and ESP8266 microcontrollers. Sensor lag is compensated via a modified Savitzky-Golay filter. Data is downloaded to a computer via Wi-Fi in a format suitable for analysis in Logger Pro. Due to the simple and fast data acquisition process, students can gather sufficient data to plot curves of the amplitude and phase lag as a function of driving frequency.
Paper
A Color All-Sky Panorama Image of the Milky Way
This article describes the assembly of an optical (RGB) all-sky mosaic image with an image scale of 36 arcsec/pixel, a limiting magnitude of approx. 14 mag and an 18 bit dynamic range. Using a portable low-cost system, 70 fields (each covering 40 deg x 27 deg) were imaged over a time span of 21 months from dark-sky locations in South Africa, Texas and Michigan. The fields were photometrically calibrated against standard catalog stars. Using sky background data from the Pioneer 10 and 11 space probes, gradients resulting from artificial light pollution, airglow and zodiacal light were eliminated, while the large-scale galactic and extragalactic background resulting from unresolved sources was preserved. The 648 Megapixel image is a valuable educational tool, being able to fully utilize the resolution and dynamic range of modern full-dome planetarium projection systems.
Paper
Introduction
This photographic star atlas shows the entire sky on 82 charts. The chart arrangement is shown on the endpapers, and a schematic depiction is given on page 9. The scale at the center of each field is 1° per cm (2.54° per inch) for all charts. Stars are shown down to approximately 14th magnitude.Each two-page spread shows the original color image, as well as an inverted and labeled black and white copy. Brightness and contrast were individually optimized for each chart. Hence, charts of regions far from the Milky Way may show slightly fainter stars than those showing rich star fields inside the Milky Way. For printing, the original RGB files had to be converted to the CMYK color space, a process that in some cases may yield slight color shifts compared to the original image.In order to emphasize extended faint emission nebulae, the inverted maps were created from the red channel images only. For this reason, the brightness of individual stars may differ from their appearance on the color images (red stars appear brighter on the black and white charts, green and blue stars fainter).The star atlas lists 1593 deep sky objects, all of which can be identified on the photographs. Object designators are based on the catalog of the Eye & Telescope v3.0 software [Pfl2011], which features one of the best error-corrected object databases. In a few cases, these designators may differ from those found in non-corrected catalogs or planetarium software.
Book Chapter
Preface
A sky atlas is the counterpart to a topographic map – without it, we would find it very difficult to navigate an unknown terrain or sky. Since the beginnings of astronomy several thousand years ago, many attempts have been made to depict the night sky as accurately as possible. With the rapid progress of astrophotography in the twentieth century, photographic atlases have become available that provide a more natural view of large-scale star clouds and gas nebulae than hand-drawn (or even computer-generated) maps. Well-known examples are the Palomar Observatory Sky Survey and Hans Vehrenberg's Falkau Atlas and Atlas Stellarum.In the past two decades, astrophotography has been revolutionized by the availability of large-format CCD cameras, which have a vastly higher quantum efficiency than photographic plates and film. As a result, images taken with a CCD camera and a standard 50 mm lens reach almost the same limiting magnitude (14m) as the venerable Atlas Stellarum. The present atlas is the result of state-of-the-art digital image acquisition and processing techniques, combining more than 3000 individual photographs into a uniquely detailed view of the night sky. Axel Mellinger did all the imaging and computer processing, while Ronald Stoyan identified and labeled the stars and deep sky objects.We would like to thank all those who contributed to the success of this project.
Book Chapter