55,613 research outputs found
Contact-eutectic-lens fabrication technique
Method enables use of crystal or semiconductor materials with selective spectral-response characteristics (ultraviolet, visible, or infrared wavelengths) in fabrication of contact lenses, reading glasses, and photographic processing equipment
Remote Detection of Saline Intrusion in a Coastal Aquifer Using Borehole Measurements of Self-Potential
Funded by NERC CASE studentship . Grant Number: NE/I018417/1Peer reviewedPublisher PD
Investigation of potential of differential absorption Lidar techniques for remote sensing of atmospheric pollutants
The NASA multipurpose differential absorption lidar (DIAL) system uses two high conversion efficiency dye lasers which are optically pumped by two frequency-doubled Nd:YAG lasers mounted rigidly on a supporting structure that also contains the transmitter, receiver, and data system. The DIAL system hardware design and data acquisition system are described. Timing diagrams, logic diagrams, and schematics, and the theory of operation of the control electronics are presented. Success in obtaining remote measurements of ozone profiles with an airborne systems is reported and results are analyzed
AUTOPLAN: A PC-based automated mission planning tool
A PC-based automated mission and resource planning tool, AUTOPLAN, is described, with application to small-scale planning and scheduling systems in the Space Station program. The input is a proposed mission profile, including mission duration, number of allowable slip periods, and requirement profiles for one or more resources as a function of time. A corresponding availability profile is also entered for each resource over the whole time interval under study. AUTOPLAN determines all integrated schedules which do not require more than the available resources
An experimental/analytical program to assess the utility of lidar for pollution monitoring
The development and demonstration of lidar techniques for the remote measurement of atmospheric constituents and transport processes in the lower troposphere was carried out. Particular emphasis was given to techniques for monitoring SO2 and particulates, the principal pollutants in power plant and industrial plumes. Data from a plume dispersion study conducted in Maryland during September and October 1976 were reduced, and a data base was assembled which is available to the scientific community for plume model verification. A UV Differential Absorption Lidar (DIAL) was built, and preliminary testing was done
Zero-gravity growth of NaF-NaCl eutectics in the NASA Skylab program
Continuous and discontinuous NaF fibers, embedded in a NaCl matrix, were produced in space and on earth. The production of continuous fibers in a eutectic mixture is attributed to the absence of convection current in the liquid during solidification in space. Image transmission and optical transmittance measurements of transverse sections of the space-grown and earth-grown ingots were made with a light microscope and a spectrometer. It is shown that better optical properties were obtained from samples grown in space. This was attributed to a better alignment of NaF fibers along the ingot axis. A new concept is advanced to explain the phenomenon of transmittance versus far infrared wavelength of the directionally solidified NaCl-NaF eutectic in terms of the two-dimensional Bragg Scattering and the polarization effect of Rayleigh scattering. This concept can be applied to other eutectic systems as long as the index of refraction of the matrix over a range of wavelengths is known. Experimental data are in agreement with the theoretical prediction
Multidimensional image selection and classification system based on visual feature extraction and scaling
Sorting and searching operations used for the selection of test images strongly affect the results of image quality investigations and require a high level of versatility. This paper describes the way that inherent image properties, which are known to have a visual impact on the observer, can be used to provide support and an innovative answer to image selection and classification. The selected image properties are intended to be comprehensive and to correlate with our perception. Results from this work aim to lead to the definition of a set of universal scales of perceived image properties that are relevant to image quality assessments.
The initial prototype built towards these objectives relies on global analysis of low-level image features. A multidimensional system is built, based upon the global image features of: lightness, contrast, colorfulness, color contrast, dominant hue(s) and busyness. The resulting feature metric values are compared against outcomes from relevant psychophysical investigations to evaluate the success of the employed algorithms in deriving image features that affect the perceived impression of the images
Chemical Segregation in Hot Cores With Disk Candidates: An investigation with ALMA
In the study of high-mass star formation, hot cores are empirically defined
stages where chemically rich emission is detected toward a massive YSO. It is
unknown whether the physical origin of this emission is a disk, inner envelope,
or outflow cavity wall and whether the hot core stage is common to all massive
stars. We investigate the chemical make up of several hot molecular cores to
determine physical and chemical structure. We use high spectral and spatial
resolution Cycle 0 ALMA observations to determine how this stage fits into the
formation sequence of a high mass star. We observed the G35.20-0.74N and
G35.03+0.35 hot cores at 350 GHz. We analyzed spectra and maps from four
continuum peaks (A, B1, B2 and B3) in G35.20, separated by 1000-2000 AU, and
one continuum peak in G35.03. We made all possible line identifications across
8 GHz of spectral windows of molecular emission lines and determined column
densities and temperatures for as many as 35 species assuming local
thermodynamic equilibrium. In comparing the spectra of the four peaks, we find
each has a distinct chemical composition expressed in over 400 different
transitions. In G35.20, B1 and B2 contain oxygen- and sulfur-bearing organic
and inorganic species but few nitrogen-bearing species whereas A and B3 are
strong sources of O, S, and N-bearing species (especially those with the
CN-bond). CHDCN is clearly detected in A and B3 with D/H ratios of 8 and
13, respectively, but is much weaker at B1 and undetected at B2. No
deuterated species are detected in G35.03, but similar molecular abundances to
G35.20 were found in other species. We also find co-spatial emission of HNCO
and NHCHO in both sources indicating a strong chemical link between the two
species. The chemical segregation between N-bearing organic species and others
in G35.20 suggests the presence of multiple protostars, surrounded by a disk or
torus.Comment: 14 pages with 13 figures main text, 54 pages appendi
Massless scalar field in two-dimensional de Sitter universe
We study the massless minimally coupled scalar field on a two--dimensional de
Sitter space-time in the setting of axiomatic quantum field theory. We
construct the invariant Wightman distribution obtained as the renormalized
zero--mass limit of the massive one. Insisting on gauge invariance of the model
we construct a vacuum state and a Hilbert space of physical states which are
invariant under the action of the whole de Sitter group. We also present the
integral expression of the conserved charge which generates the gauge
invariance and propose a definition of dual field.Comment: 13 page
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