19,191 research outputs found
The optical properties of automatically darkening welding filters based on liquid crystal technology
No full textThis thesis addresses the problem of the poor optical angular properties displayed by the majority of automatically darkening welding filters currently on the market that are based on liquid crystal technology. It is shown that by reducing the twist-angle present in the liquid crystal cell to below that of 90 together with employment of a novel polariser arrangement, an optical shutter design based on a double-cell construction is obtained that boasts a reduced angular transmittance variation when in the activated phase. This gives an optical filter possessing a wide central viewing cone whilst maintaining the remaining optical parameters at a high level. The only point of compromise comes from the voltage increase requirement upon reduction of the twist- angle in order to maintain cell contrast. Although this inflates the power consumption of the system, beneficial effects upon the total light scattering provoked by the device are also observed. The final sections deal with a new mode of operation for a twisted-nematic liquid crystal cell when placed between crossed polarisers together with an interference filter possessing a high optical transmittance over the central part of the visible spectrum. This mode of operation means that the cell is in a dark state when inactivated. Application of a small stimulating voltage transmutes the unit into the light state, where upon further increment of the driving electronics beyond this point reverts the system back into a low transmittance phase. Such a mode of operation for a twisted-nematic cell offers several advantages over that of the normally white mode when considering the optical lens of an automatically darkening welding filter. In particular, a dark, fail-safe state is provided should the controlling electronics malfunction preventing the unit from holding in a potentially hazardous light phase, a property usually associated with the normally black mode of operation, whilst the fast switching speed from the light to the dark state associated with the normally white mode of operation is maintained. It is shown that there are only two cell types that display this phenomenon and the optical properties of these two systems are analysed in some detail with the view of developing an automatically darkening welding filter based on this technology. This thesis is submitted to the University of Durham for the degree of Master of Science. All work contained within this thesis was carried out by the author at Hornell Innovation AB in Sweden. No material contained within has been submitted for a previous degree and the copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged
Service-oriented models for audiovisual content storage
No full textWhat are the important topics to understand if involved with storage services to hold digital audiovisual content? This report takes a look at how content is created and moves into and out of storage; the storage service value networks and architectures found now and expected in the future; what sort of data transfer is expected to and from an audiovisual archive; what transfer protocols to use; and a summary of security and interface issues
AC-6-U.S. Naval Planes Flying in Formation, Langley Field, VA/Thank-You Card from Stephen Tury to the Hungarian Defense Council.
No full textThis postcard, which depicts U.S. Naval planes flying in formation, was sent to the Hungarian Defense Council by Private Stephen Tury. The Council was organized in New Brunswick by leaders of local Hungarian churches and societies. During the Second World War it sent supplies, such as the carton of cigarettes Tury is thanking it for, to members of the military of Hungarian descent from the New Brunswick area
Two-photon long-period grating inscription in pure-fused-silica photonic crystal fiber
No full textPhotochemical inscription of a long-period grating in a pure fused silica photonic crystal fiber (PCF) is reported. The inscription in PCF is found to be ten times more efficient than in a standard telecom fiber
Author Stephen Flynn Discusses Resiliency
No full textCenter for Homeland Defense and Security, PRESS RELEASESOn September 25, Author Stephen E. Flynn stopped by the Center’s National Capital Region campus to speak with CHDS Master’s degree students about his latest book, answer questions and discuss..
Letter from Carl Hayden to Stephen Mather, National Park Service
No full textLetter from Carl Hayden to Stephen Mather regarding the sale of Bass properties
Crystal Form, Zones, Crystal Habit
No full textThis site is a lecture by Dr. Stephen Nelson from Tulane University that explores the use of the Miller Index notation to designate crystal forms. Topics include crystal forms, general and special forms, and open and closed forms. Also discussed is the relationship between form and crystal faces, along with zones and zone symbols, the vectorial properties of crystals, and crystal habit. Tables and illustrations accompany the text. Educational levels: Graduate or professional, Undergraduate upper division
Letter from Carl Hayden to Stephen Mather, National Park Service
No full textLetter from Carl Hayden to Stephen Mather requesting that congress pay W. W. Bass the sum of twenty-five thousand dollars for his properties
Stephen Graham Jones - Sowell Conference 2017
No full textStephen Graham Jones, University of Colorado-Boulder, author of "Mongrels" and "Growing Up Dead in Texas
Letter from Stephen Mather, National Park Service to Carl Hayden
No full textLetter from Stephen Mather to Carl Hayden regarding the sale of Bass properties to the Santa Fe Railroad Company
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