8,132 research outputs found
Space radiation resistant transparent polymeric materials
A literature search in the field of ultraviolet and charged particle irradiation of polymers was utilized in an experimental program aimed at the development of radiation stable materials for space applications. The rationale utilized for material selection and the synthesis, characterization and testing performed on several selected materials is described. Among the materials tested for ultraviolet stability in vacuum were: polyethyleneoxide, polyvinylnaphthalene, and the amino resin synthesized by the condensation of o-hydroxybenzoguanamine with formaldehyde. Particularly interesting was the radiation behavior of poly(ethyleneoxide), irradiation did not cause degradation of optical properties but rather an improvement in transparency as indicated by a decrease in solar absorptance with increasing exposure time
Investigation of space radiation effects in polymeric film-forming materials
The literature search in the field of ultraviolet radiation effects that was conducted during the previous program, Contract No. NAS1-12549, has been expanded to include the effects of charged particle radiation and high energy electromagnetic radiation. The literature from 1958 to 1969 was searched manually, while the literature from 1969 to present was searched by using a computerized keyword system. The information generated from this search was utilized for the design of an experimental program aimed at the development of materials with improved resistance to the vacuum-radiation environment of space. Preliminary irradiation experiments were performed which indicate that the approaches and criteria employed are very promising and may provide a solution to the challenging problem of polymer stability to combined ultraviolet/high energy radiation
Cosmic star formation history revealed by the AKARI, & Spatially-resolved spectroscopy of an E+A (Post-starburst) system
We reveal cosmic star-formation history obscured by dust using deep infrared
observation with the AKARI. A continuous filter coverage in the mid-IR
wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24um) by the AKARI satellite
allows us to estimate restframe 8um and 12um luminosities without using a large
extrapolation based on a SED fit, which was the largest uncertainty in previous
work. We found that restframe 8um (0.38<z<2.2), 12um (0.15<z<1.16), and total
infrared (TIR) luminosity functions (LFs) (0.2<z<1.6) constructed from the
AKARI NEP deep data, show a continuous and strong evolution toward higher
redshift. In terms of cosmic infrared luminosity density (Omega_IR), which was
obtained by integrating analytic fits to the LFs, we found a good agreement
with previous work at z<1.2, with Omega_IR propto (1+z)^4.4+-1.0. When we
separate contributions to Omega_IR by LIRGs and ULIRGs, we found more IR
luminous sources are increasingly more important at higher redshift. We found
that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from
z=0.35 to z=1.4.Comment: To appear in "Hunting for the Dark: The Hidden Side of Galaxy
Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista & C.C. Popescu, AIP
Conf. Se
Fundamental investigation of ultraviolet radiation effects in polymeric film-forming materials
A literature search from 1958 to present was conducted on the effect of ultraviolet radiation on polymeric materials, with particular emphasis on vacuum photolysis, mechanisms of degradation, and energy transfer phenomena. The literature from 1958 to 1968 was searched manually, while the literature from 1968 to present was searched by using a computerized keyword system. The primary objective was to provide the necessary background information for the design of new or modified materials with improved stability to the vacuum-radiation environment of space
Local spin and charge properties of beta-Ag0.33V2O5 studied by 51V NMR
Local spin and charge properties were studied on beta-Ag0.33V2O5, a
pressure-induced superconductor, at ambient pressure using 51V-NMR and
zero-field-resonance (ZFR) techniques. Three inequivalent Vi sites (i=1, 2, and
3) were identified from 51V-NMR spectra and the principal axes of the
electric-field-gradient (EFG) tensor were determined in a metallic phase and
the following charge-ordering phase. We found from the EFG analysis that the V1
sites are in a similar local environment to the V3 sites. This was also
observed in ZFR spectra as pairs of signals closely located with each other.
These results are well explained by a charge-sharing model where a 3d1 electron
is shared within a rung in both V1-V3 and V2-V2 two-leg ladders.Comment: 12pages, 16figure
Overdoped Cuprates With High Temperature Superconducting Transitions
Evidence for High Tc cuprate superconductivity is found in a region of the
phase diagram where non-superconducting Fermi liquid metals are expected. Cu
valences estimated independently from both x-ray absorption near-edge structure
(XANES) and bond valence sum (BVS) measurements are > 2.3 for structures in the
homologous series (Cu0.75Mo0.25)Sr2(Y,Ce)sCu2O5+2s+{\delta} with s = 1, 2, 3,
and 4. The s = 1 member, (Cu0.75Mo0.25)Sr2YCu2O7+{\delta}, 0 \leq {\delta} \leq
0.5, is structurally related to YBa2Cu3O7 in which 25% of the basal Cu cations
[i.e. those in the chain layer] are replaced by Mo, and the Ba cations are
replaced by Sr. After oxidation under high pressure the s = 1 member becomes
superconducting with Tc = 88K. The Cu valence is estimated to be ~2.5, well
beyond the ~2.3 value for which other High-Tc cuprates are considered to be
overdoped Fermi liquids. The increase in valence is attributed to the
additional 0.5 oxygen ions added per chain upon oxidation. The record short
apical oxygen distance, at odds with current theory, suggests the possibility
of a new pairing mechanism but further experiments are urgently needed to
obtain more direct evidence. From the structural point of view the members with
s \geq 2 are considered to be equivalent to single-layer cuprates. All have Tc
~ 56 K which is significantly higher than expected because they also have
higher than expected Cu valences. The XANES-determined valences normalized to
give values in the CuO2 layers are 2.24, 2.25, and 2.26 for s = 2, 3, and 4,
while the BVS values determined for the valence in the CuO2 layer alone are
2.31-2.34 for the s = 2 and 3 members. No evidence for periodic ordering has
been detected by electron diffraction and high resolution imaging studies. The
possibility that the charge reservoir layers are able to screen long range
coulomb interactions and thus enhance Tc is discussed
Differential Emission Measure Determination of Collisionally Ionized Plasma: II. Application to Hot Stars
In a previous paper we have described a technique to derive constraints on
the differential emission measure (DEM) distribution, a measure of the
temperature distribution, of collisionally ionized hot plasmas from their X-ray
emission line spectra. We apply this technique to the Chandra/HETG spectra of
all of the nine hot stars available to us at the time this project was
initiated. We find that DEM distributions of six of the seven O stars in our
sample are very similar but that theta Ori has an X-ray spectrum characterized
by higher temperatures. The DEM distributions of both of B stars in our sample
have lower magnitudes than those of the O stars and one, tau Sco, is
characterized by higher temperatures than the other, beta Cru. These results
confirm previous work in which high temperatures have been found for theta Ori
and tau Sco and taken as evidence for channeling of the wind in magnetic
fields, the existence of which are related to the stars' youth. Our results
demonstrate the utility of our method for deriving temperature information for
large samples of X-ray emission line spectra.Comment: The contents of this paper were formerly part of astro-ph/0403603
which was split into two paper
Non-Gaussianity in Cosmic Microwave Background Temperature Fluctuations from Cosmic (Super-)Strings
We compute analytically the small-scale temperature fluctuations of the
cosmic microwave background from cosmic (super-)strings and study the
dependence on the string intercommuting probability . We develop an
analytical model which describes the evolution of a string network and
calculate the numbers of string segments and kinks in a horizon volume. Then we
derive the probability distribution function (pdf) which takes account of
finite angular resolution of observation. The resultant pdf consists of a
Gaussian part due to frequent scatterings by long string segments and a
non-Gaussian tail due to close encounters with kinks. The dispersion of the
Gaussian part is reasonably consistent with that obtained by numerical
simulations by Fraisse et al.. On the other hand, the non-Gaussian tail
contains two phenomenological parameters which are determined by comparison
with the numerical results for P=1. Extrapolating the pdf to the cases with
, we predict that the non-Gaussian feature is suppressed for small .Comment: 6 pages, 2 figure, version accepted by JCA
Pressure-induced changes in the optical properties of quasi-one-dimensional -NaVO
The pressure-induced changes in the optical properties of
-NaVO single crystals at room temperature were studied
by polarization-dependent Raman and far-infrared reflectivity measurements
under high pressure. From the changes in the Raman- and infrared-active phonon
modes in the pressure range 9 - 12 GPa a transfer of charge between the
different V sites can be inferred. The importance of electron-phonon coupling
in the low-pressure regime is discussed.Comment: 7 pages, 5 figure
Time-averaged aerodynamic loads on the vane sets of the 40- by 80-foot and 80- by 120-foot wind tunnel complex
Time-averaged aerodynamic loads are estimated for each of the vane sets in the National Full-Scale Aerodynamic Complex (NFAC). The methods used to compute global and local loads are presented. Experimental inputs used to calculate these loads are based primarily on data obtained from tests conducted in the NFAC 1/10-Scale Vane-Set Test Facility and from tests conducted in the NFAC 1/50-Scale Facility. For those vane sets located directly downstream of either the 40- by 80-ft test section or the 80- by 120-ft test section, aerodynamic loads caused by the impingement of model-generated wake vortices and model-generated jet and propeller wakes are also estimated
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