Active production of large aspheric optics for astronomy

This thesis is devoted mainly to tackling the unsolved problem of producing secondary mirrors for 8 m telescopes, which will be up to 2-2.5 m in diameter and in excess of 1000 waves aspheric. This cannot be done by traditional methods. The project directly addresses the problem and forms part of the UK's R and D contributions to the Gemini USA/UK/Canada/Brazil/Chile/Argentina project to produce two 8 m telescopes. Its aim was to develop a new active method. The thesis starts with a review of astronomical implications of 8 m telescope projects currently being undertaken or planned worldwide and continues with discussions on technological challenges specifically in main optics production. The first stage of producing the mirror is generation of the aspheric surface profile by diamond milling. This has been directly addressed by developing a new computer-controlled profiler based on the existing manual hardware of the Grubb-Parsons 2.5 m machine. An essential part of the development also includes a computer controlled contact profilometer. The system performance is presented, including calibration, error profile and convergence of error compensation. The main part of the project was to develop polishing using a full size active lap, by which the pressure distribution and hence ablation rate are modulated in real time. The progress of the project is described, starting with a review of other approaches being developed world wide. The overall philosophy and design of active components are presented. Following this, experiments with a sub-diameter polisher and a prototype active lap of 85 cm in diameter, as built, are also described, including methods of testing, ablation algorithm and control theory. The final part of this section discusses the performance of the active polishing lap in terms of functionality at component and system levels. The conclusion briefly summarises the evaluation of the active method and its impact on large optics production. It also gives ideas for future improvements of performance, research work still needed and viable applications for the technique

Studi Performa Migrasi Ipv4 ke Ipv6 pada Metode Dual Stack

Dengan ketersedian (space) dari pengalamatan IPv4 yang telah sedikit, itu telah menjadi alasan utama bagi penyedia layanan, Perusahaan, pengembang aplikasi, dan pemerintah untuk memulai beralih dengan IPv6. Sebuah migrasi dari IPv4 ke IPv6 sulit dicapai. Karena beberapa mekanisme yang diperlukan untuk menjamin kelancaran, komunikasi dan peralihan secara utuh ke IPv6. Tidak hanya transisi, integrasi IPv6 juga diperlukan ke dalam jaringan yang ada. Solusi (mekanisme) dapat dibagi menjadi tiga kategori: dual stack, tunneling dan translation. Dalam proyek ini mekanisme tr ansisi Dual-Stack diimplementasikan di GNS3 (Graphical Network Simulator), menggunakan CISCO router. Jaringan ini dilihat dengan bantuan Wireshark (Packet analyzer). kedua topologi dibandingkan, Dual-Stack dan Tunneling, yang dapat diamati dengan menangkap paket pada interface router

The Look-back Time Evolution of Far-UV Flux from Elliptical Galaxies: The Fornax Cluster and Abell 2670

In order to investigate the origin of the far-UV (FUV) flux from the early-type galaxies, Galaxy Evolution Explorer (GALEX) is collecting the UV data for the elliptical-rich clusters at moderate redshifts (z < 0.2) where the dominant FUV source is predicted to be hot horizontal-branch (HB) stars and their post-HB progeny. Here we present our first result for the early-type galaxies in Abell 2670 at z = 0.076. Compared to NGC 1399, a nearby giant elliptical galaxy in the Fornax cluster, it appears that the rest-frame FUV - V color of the giant ellipticals gets redder by ~ 0.7 mag at the distance of Abell 2670 (z = 0.076; look-back time ~ 1.0 Gyr). Although a detailed comparison with the models is postponed until more cluster data are accumulated, it is interesting to note that this value is consistent with the variation predicted by the population synthesis models where the mean temperature of HB stars declines rapidly with increasing look-back time.Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS

Cosmic ray oriented performance studies for the JEM-EUSO first level trigger

JEM-EUSO is a space mission designed to investigate Ultra-High Energy Cosmic Rays and Neutrinos (E > 5 ⋅ 1019 eV) from the International Space Station (ISS). Looking down from above its wide angle telescope is able to observe their air showers and collect such data from a very wide area. Highly specific trigger algorithms are needed to drastically reduce the data load in the presence of both atmospheric and human activity related background light, yet retain the rare cosmic ray events recorded in the telescope. We report the performance in offline testing of the first level trigger algorithm on data from JEM-EUSO prototypes and laboratory measurements observing different light sources: data taken during a high altitude balloon flight over Canada, laser pulses observed from the ground traversing the real atmosphere, and model landscapes reproducing realistic aspect ratios and light conditions as would be seen from the ISS itself. The first level trigger logic successfully kept the trigger rate within the permissible bounds when challenged with artificially produced as well as naturally encountered night sky background fluctuations and while retaining events with general air-shower characteristics

Physical Parameters of Late Type Spiral Galaxies I-Mass and Luminosity of NGC 6946

Using Brandt model the mass distribution of the late type spiral galaxy NGC 6946 was derived, and the total mass was reestimated to understand the M/L ratio of this galaxy. Two kinds of the rotation curve with shape parameter n = 1 and 3.3 were examined. The followings are the main results; (1) The total masses of NGC 6946 are 3.1 x 10^11*M (n=1) and 2.8 x 10^11*M (n=3.3) respectively, and the corresponding M/L are about 17 and 16 for both cases. (2) The optical image in the blue light, whose radius is 9.6 kpc, has 8 x 10^10*Msolar and 1.4 x 10^11*Msolar. These give the value of M/L about 5 and 8 respectively. (3) The masses and M/L of the nuclear region within 1.2 kpc are 4.0 x 10^9*Msolar, 4.7 x 10^9*Msolar and 3, 4 for both cases. Those of the disk from 1.2 kpc to 9.6 kpc are 7.6 x 10^10*Msolar, 1.4 x 10^11*Msolar, and 5, 8. (4) The masses of the outer halo extended to few hundreds kiloparsecs are 2.3 x 10^11*Msolar and 1.4 x 10^11*Msolar. The corresponding M/L are about 62 and 37

On the Nature of the Gamma-ray Bursts

Review of the γ-ray burst phenomena are presented. History of the γ-ray bursts, characteristics, and three radiation mechanisms of thermal bremsstrahlung, thermal synchrotron, and inverse Compton scattering processes are considered

Experimental Sensitivity Table Method for Precision Alignment of Amon-Ra Instrument

The Amon-Ra instrument is the main optical payload of the proposed EARTHSHINE satellite. It consists of a visible wavelength instrument and an IR energy channel instrument to measure a global Earth albedo. We report a new sensitivity technique for efficient alignment of the visible channel instrument. Whilst the sensitivity table method has been widely used in the alignment process, the straightforward application of the method tends to produce slow process convergence because of shop floor alignment practice uncertainties. We investigated the error sources commonly associated with alignment practices and used them when estimating the Zernike polynomial coefficients. Aided with single center field wavefront error (WFE) measurements and their corresponding Zernike polynomial coefficients, the method involves the construction and use of an experimental, instead of simulated, sensitivity table to be used for alignment state estimations. A trial alignment experiment for the Amon Ra optical system was performed and the results show that 71.28 nm in rms WFE was achieved only after two alignment iterations. This tends to demonstrate its superior performance to the conventional method

Grinding Optimization Model for Nanometric Surface Roughness for Aspheric Astronomical Optical Surfaces

Bound abrasive grinding is used for the initial fabrication phase of the precision aspheric mirrors for both space and ground based astronomical telescopes. We developed a new grinding optimization process that determines the input grinding variables for the target surface roughness, checks the grinding error magnitude in resulting surface roughnesses, and minimizes the required machining time. Using the machining data collected from the previous grinding runs and subsequently fed into the multi-variable regression engine, the process has the evolving controllability that suggests the optimum set of grinding variables for each target surface roughness. The process model was then used for ten grinding experiments that resulted in the grinding accuracy of =-0.906 ± 3.38(σ) nm (Ra) for the target surface roughnesses of Zerodur substrate ranging from 96.1 nm (Ra) to 65.0 nm (Ra). The results imply that the quantitative process optimization technique developed in this study minimizes the machining time and offers the nanometric surface roughness controllability superior to the traditional, qualitative, craftsman based grinding process for the astronomical optical surfaces

Initial On-Orbit Modulation Transfer Function Performance Analysis for Geostationary Ocean Color Imager

The world’s first geostationary ocean color imager (GOCI) is a three-mirror anastigmat optical system 140 mm in diameter. Designed for 500 m ground sampling distance, this paper deals with on-orbit modulation transfer function (MTF)measurement and analysis for GOCI. First, the knife-edge and point source methods were applied to the 8th band (865 nm) image measured April 5th, 2011. The target details used are the coastlines of the Korean peninsula and of Japan, and an island 400 meters in diameter. The resulting MTFs are 0.35 and 0.34 for the Korean East Coastline and Japanese West Coastline edge targets, respectively, and 0.38 for the island target. The daily and seasonal MTF variations at the Nyquist frequency were also checked, and the result is 0.32 ± 0.04 on average. From these results, we confirm that the GOCI on-orbit MTF performance satisfies the design requirements of 0.32 for 865 nm wavelength

Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position.

Background: To evaluate the toric intraocular lens (IOL) calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position (ELP). Methods Two thousand samples of corneal parameters with keratometric astigmatism >= 1.0 D were obtained using boot-strap methods. The probability distributions for incision-induced keratometric and posterior corneal astigmatisms, as well as ELP were estimated from the literature review. The predicted residual astigmatism error using method D with an IOL add power calculator (IAPC) was compared with those derived using methods A, B, and C through Monte-Carlo simulation. Method A considered the keratometric astigmatism and incision-induced keratometric astigmatism, method B considered posterior corneal astigmatism in addition to the A method, method C considered incision-induced posterior corneal astigmatism in addition to the B method, and method D considered ELP in addition to the C method. To verify the IAPC used in this study, the predicted toric IOL cylinder power and its axis using the IAPC were compared with ray-tracing simulation results. Results The median magnitude of the predicted residual astigmatism error using method D (0.25 diopters [D]) was smaller than that derived using methods A (0.42 D), B (0.38 D), and C (0.28 D) respectively. Linear regression analysis indicated that the predicted toric IOL cylinder power and its axis had excellent goodness-of-fit between the IAPC and ray-tracing simulation. Conclusions The IAPC is a simple but accurate method for predicting the toric IOL cylinder power and its axis considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and ELP.SRC program of the Center for Galaxy Evolution Research (CGER) [2010-0027910]; Korea Astronomy and Space Science Institute under the RD program [2014-9-710-03]; Busan Sungmo Eye Hospital Sodam Scholarship Committee, Busan, South KoreaFirst Online: 19 August 2016; 12 month embargo.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]