17,201 research outputs found
Study of Permanent Magnet Focusing for Astronomical Camera Tubes
A design is developed of a permanent magnet assembly (PMA) useful as the magnetic focusing unit for the 35 and 70 mm (diagonal) format SEC tubes. Detailed PMA designs for both tubes are given, and all data on their magnetic configuration, size, weight, and structure of magnetic shields adequate to screen the camera tube from the earth's magnetic field are presented. A digital computer is used for the PMA design simulations, and the expected operational performance of the PMA is ascertained through the calculation of a series of photoelectron trajectories. A large volume where the magnetic field uniformity is greater than 0.5% appears obtainable, and the point spread function (PSF) and modulation transfer function(MTF) indicate nearly ideal performance. The MTF at 20 cycles per mm exceeds 90%. The weight and volume appear tractable for the large space telescope and ground based application
Recent Developments in Nonregular Fractional Factorial Designs
Nonregular fractional factorial designs such as Plackett-Burman designs and
other orthogonal arrays are widely used in various screening experiments for
their run size economy and flexibility. The traditional analysis focuses on
main effects only. Hamada and Wu (1992) went beyond the traditional approach
and proposed an analysis strategy to demonstrate that some interactions could
be entertained and estimated beyond a few significant main effects. Their
groundbreaking work stimulated much of the recent developments in design
criterion creation, construction and analysis of nonregular designs. This paper
reviews important developments in optimality criteria and comparison, including
projection properties, generalized resolution, various generalized minimum
aberration criteria, optimality results, construction methods and analysis
strategies for nonregular designs.Comment: Submitted to the Statistics Surveys (http://www.i-journals.org/ss/)
by the Institute of Mathematical Statistics (http://www.imstat.org
The advanced low-emissions catalytic-combuster program. Phase 1: Description and status
An overview of the ongoing program is presented. Objectives, plan, schedule, pollution and performance goals, catalyst advantages, present problems, and the present status of identified combustor concepts are discussed. The possible increase in upper atmosphere oxides of nitrogen (NOx) levels due to aircraft number density increases was predicted to adversely decrease ozone concentration levels. A technique for achieving low NOx emission levels was experimentally demonstrated with a lean, premixing prevaporizing flame-tube combustor
Factorial designs under baseline parameterization and space-filling designs with applications to big data
This dissertation reports my research work on three topics in the areas of two-level factorial designs under the baseline parameterization, space-filling designs, and sub-data selection for big data. When studying two-level factorial designs, factorial effects are usually given by the orthogonal parameterization. But if each factor has an intrinsic baseline level, the baseline parameterization is a more appropriate alternative. We obtain a relationship between these two types of parameterization, and show that certain design properties are invariant. The relationship also allows us to construct an attractive class of robust baseline designs. We then consider two classes of space-filling designs driven by very different considerations: uniform projection designs and strong orthogonal arrays (SOAs), where the former are obtained by minimizing the uniform projection criterion while the latter are a special kind of orthogonal arrays. We express the uniform projection criterion in terms of the stratification characteristics related to an SOA. This new expression is then used to show that certain SOAs are optimal or nearly optimal under the uniform projection criterion. Finally, we consider the problem of selecting a representative sub-dataset from a big dataset for the purpose of statistical analyses without massive computation. Under the nonparametric regression situation, we present a two-phase selection method, which embodies two important ideas. First, the sub-dataset should be a space-filling subset within the full dataset. Second, in the area where the response surface is more rugged, more data points should be selected. Simulations are conducted to demonstrate the usefulness of our method
A Micromegas-based low-background x-ray detector coupled to a slumped-glass telescope for axion research
We report on the design, construction and operation of a low background x-ray
detection line composed of a shielded Micromegas (micromesh gaseous structure)
detector of the microbulk technique. The detector is made from radiopure
materials and is placed at the focal point of a ~5 cm diameter, 1.3 m
focal-length, cone-approximation Wolter I x-ray telescope (XRT) comprised of
thermally-formed (or "slumped") glass substrates deposited with multilayer
coatings. The system has been conceived as a technological pathfinder for the
future International Axion Observatory (IAXO), as it combines two of the
techniques (optic and detector) proposed in the conceptual design of the
project. It is innovative for two reasons: it is the first time an x-ray optic
has been designed and fabricated specifically for axion research, and the first
time a Micromegas detector has been operated with an x-ray optic. The line has
been installed at one end of the CERN Axion Solar Telescope (CAST) magnet and
is currently looking for solar axions. The combination of the XRT and
Micromegas detector provides the best signal-to-noise ratio obtained so far by
any detection system of the CAST experiment with a background rate of
5.410counts per hour in the energy region-of-interest and
signal spot area.Comment: 21 pages, 16 figure
On the evolution of advanced propulsion systems for spacecraft
Use of earth-storable propellants in unmanned spacecraft propulsion systems for flights to near planets and moo
Status and New Ideas Regarding Liquid Argon Detectors
Large (up to kt) liquid argon time-projection chamber detectors
are presently being considered for proton decay searches and neutrino
astrophysics, as well as for far detectors for the next generation of
long-baseline neutrino oscillation experiments that aim to determine neutrino
mass hierarchy and search for CP violation in the leptonic sector. These
detectors rely on the capabilities to assemble large volumes of LAr in
ultrahigh-purity conditions, possibly in an underground environment, and to
achieve relatively long drifts for the ionization charge. Several proposals
have been developed, each of which takes a different approach to the design of
the cryogenic vessels and has different scales of modularity to reach the final
mass dictated by physics. New detector concepts, with innovative designs of
readout electronics and novel methods for the readout of the ionization charge
and scintillation light, have been proposed.Comment: accepted for publication by Ann. Rev. Nucl. Part. Sc
Spaceborne sensors (1983-2000 AD): A forecast of technology
A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given
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