2,274 research outputs found
A study to determine the optimum design of a photographic film for the lunar surface hand-held camera Final report
Design, and processing of photographic film for lunar surface hand operated camer
Multi-Satellite Attitude Prediction program/Orbiting Solar Observatory-8 (MSAP/OSO-8) operating guide
The sun's lower corona and chromosphere and their interaction in the X-ray and ultraviolet (UV) spectral regions were investigated to better understand the transport of energy from the photosphere to the corona. The interaction between the solar electromagnetic and particle radiation and the earth's environment was studied and the background component of cosmic X-rays was discussed
Software Engineering Laboratory (SEL). Data base organization and user's guide, revision 1
The structure of the Software Engineering Laboratory (SEL) data base is described. It defines each data base file in detail and provides information about how to access and use the data for programmers and other users. Several data base reporting programs are described also
Tunability of the optical absorption in small silver cluster-polymer hybrid systems
We have calculated the absorption characteristics of different hybrid systems
consisting of Ag, Ag2 or Ag3 atomic clusters and poly(methacrylic acid) (PMAA)
using the time-dependent density-functional theory. The polymer is found to
have an extensive structural-dependency on the spectral patterns of the hybrid
systems relative to the bare clusters. The absorption spectrum can be `tuned'
to the visible range for hybrid systems with an odd number of electrons per
silver cluster, whereas for hybrid systems comprising an even number of
electrons, the leading absorption edge can be shifted up to about 4.5 eV. The
results give theoretical support to the experimental observations on the
absorption in the visible range in metal cluster-polymer hybrid structures.Comment: Updated layout and minor changes in versions 2 and
From C/Mrkos to P/Halley: 30 years of cometary spectroscopy
An Atlas of Cometary Spectra was compiled, as a sequel to the well-known Atlas published by Swings and Haser in 1956. The new atlas comprises some 400 reproductions of cometary spectra secured in the world's largest observatories during the three decades or so from the passage of comet Mrkos 1957 V, for which the very first high-dispersion spectrum was obtained, to the return of Halley's comet. The illustrations refer to 40 different comet apparitions; they are grouped into a set of 186 loose 11 x 14 in. plates, while the texts, comments, and relevant data are given in a separate booklet. The main purpose of this atlas is to show in detail the tremendous progress which was achieved in cometary spectroscopy during the period covered, essentially thanks to the use of high-resolution coude spectrographs and large telescopes, the considerable extension of the observed wavelength range, and the advent of electronic detectors. It is divided into two parts. Part 1, which contains about two-thirds of the selected material, presents photographic spectra, while electronically recorded spectra covering the vacuum ultraviolet, through the optical, infrared, and radio regions appear in Part 2
Optical properties of SiC nanotubes: A systematic study
The band structure and optical dielectric function of
single-walled zigzag
[(3,0),(4,0),(5,0),(6,0),(8,0),(9,0),(12,0),(16,0),(20,0),(24,0)], armchair
[(3,3),(4,4),(5,5),(8,8),(12,12),(15,15)], and chiral
[(4,2),(6,2),(8,4),(10,4)] SiC-NTs as well as the single honeycomb SiC sheet
have been calculated within DFT with the LDA. It is found that all the SiC
nanotubes are semiconductors, except the ultrasmall (3,0) and (4,0) zigzag
tubes which are metallic. Furthermore, the band gap of the zigzag SiC-NTs which
is direct, may be reduced from that of the SiC sheet to zero by reducing the
diameter (), though the band gap for all the SiC nanotubes with a diameter
larger than ~20 \AA is almost independent of diameter. For the electric
field parallel to the tube axis (), the for
all the SiC-NTs with a moderate diameter (say, 8 \AA) in the
low-energy region (0~6 eV) consists of a single distinct peak at ~3 eV.
However, for the small diameter SiC nanotubes such as the (4,2),(4,4) SiC-NTs,
the spectrum does deviate markedly from this general behavior. In
the high-energy region (from 6 eV upwards), the for all the
SiC-NTs exhibit a broad peak centered at ~7 eV. For the electric field
perpendicular to the tube axis (), the spectrum of
all the SiC-NTs except the (4,4), (3,0) and (4,0) nanotubes, in the low energy
region also consists of a pronounced peak at around 3 eV whilst in the
high-energy region is roughly made up of a broad hump starting from 6 eV. The
magnitude of the peaks is in general about half of the magnitude of the
corresponding ones for
Spectra of comet P/Halley at R = 4 - 8 AU
Spectra of Comet Halley (lambda lambda = 3400-6500 A) were acquired at pre- and post-perihelion distances of 4.8 AU on 1985 Feb. 17 (Coma V equals 18.9 mag) and 1987 Feb. 1 (coma V = 15.9 mag) using the 4.5-m Multiple-Mirror Telescope (MMT) and the CTIO 4.0-m telescope, respectively. The CN(0,0) violet system band flux at 4.8 AU was approx. 15 times greater at the post-perhelion phase compared to pre-perihelion. Additional post-perihelion spectra, obtained on 1986 Nov. 28 to 30 with the MTT, showed CN(0,0) and very weak C3 4040 A emission. The MMT data are one-dimensional spectra (aperture: 5 arc sec diameter) obtained with an intensified Reticon while the CTIO data are two-dimensional spectra (slit length = 280 arc sec) obtained with a 2D-Frutti photon counting system. Extended CN(0,0) emission was detected in the 1987 Feb. 1 (at 4.8 AU) spectra to a distance of at least 70 arc sec in the solar and anti-solar directions. Additional CCD spectra obtained with the KPNO 2.2-meter telescope on 1988 Feb. 20 (at 7.9 AU) show scattered solar continuum approx. 32 arc sec diameter. However, no emission features were detected at 7.9 AU
Activated O2 dissociation and formation of oxide islands on the Be(0001) surface: Another atomistic model for metal oxidation
By simulating the dissociation of O2 molecules on the Be(0001) surface using
the first-principles molecular dynamics approach, we propose a new atomistic
model for the surface oxidation of sp metals. In our model, only the
dissociation of the first oxygen molecule needs to overcome an energy barrier,
while the subsequent oxygen molecules dissociate barrierlessly around the
adsorption area. Consequently, oxide islands form on the metal surface, and
grow up in a lateral way. We also discover that the firstly dissociated oxygen
atoms are not so mobile on the Be(0001) surface, as on the Al(111) surface. Our
atomistic model enlarges the knowledge on metal surface oxidations by perfectly
explaining the initial stage during the surface oxidation of Be, and might be
applicable to some other sp metal surfaces.Comment: 5 pages, 4 figure
Electronic Correlations in Oligo-acene and -thiophene Organic Molecular Crystals
From first principles calculations we determine the Coulomb interaction
between two holes on oligo-acene and -thiophene molecules in a crystal, as a
function of the oligomer length. The relaxation of the molecular geometry in
the presence of holes is found to be small. In contrast, the electronic
polarization of the molecules that surround the charged oligomer, reduces the
bare Coulomb repulsion between the holes by approximately a factor of two. In
all cases the effective hole-hole repulsion is much larger than the calculated
valence bandwidth, which implies that at high doping levels the properties of
these organic semiconductors are determined by electron-electron correlations.Comment: 5 pages, 3 figure
Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2
The temperature evolution of the crystal and magnetic structures of
ferroelectric sulfide AgCrS2 have been investigated by means of neutron
scattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition,
from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinic
structure with a polar Cm space group. In addition to being ferroelectric below
TN, the low temperature phase of AgCrS2 exhibits an unconventional collinear
magnetic structure that can be described as double ferromagnetic stripes
coupled antiferromagnetically, with the magnetic moment of Cr+3 oriented along
b within the anisotropic triangular plane. The magnetic couplings stabilizing
this structure are discussed using inelastic neutron scattering results.
Ferroelectricity below TN in AgCrS2 can possibly be explained in terms of
atomic displacements at the magneto-elastic induced structural distortion.
These results contrast with the behavior of the parent frustrated
antiferromagnet and spin-driven ferroelectric AgCrO2
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