2,440 research outputs found
Flame resistant elastomeric polymer development
Elastomeric products were developed for use in the space shuttle program, and investigations were conducted to improve the properties of elastomers developed in previous programs, and to evaluate the possibility of using lower-cost general purpose polymers. Products were fabricated and processed on conventional processing equipment; these products include: foams based on fluorinated rubber flame-retarded compounds with a density of 20-30 pounds/cubic foot for use as padding and in helmets; foams based on urethane for use in instrument packaging in the space shuttle; flexible and semi-rigid films of fluorinated rubber and neoprene compounds that would not burn in a 70% nitrogen, 30% oxygen atmosphere, and in a 30% nitrogen, 70% oxygen atmosphere, respectively for use in packaging or in laminates; coated fabrics which used both nylon and Kelvar fabric substrates, coated with either fluorinated or neoprene polymer compositions to meet specific levels of flame retardancy; and other flame-resistant materials
The Mass Function of Dark Halos in Superclusters and Voids
A modification of the Press-Schechter theory allowing for presence of a
background large-scale structure (LSS) - a supercluster or a void, is proposed.
The LSS is accounted as the statistical constraints in form of linear
functionals of the random overdensity field. The deviation of the background
density within the LSS is interpreted in a pseudo-cosmological sense. Using the
constraints formalism may help us to probe non-trivial spatial statistics of
haloes, e.g. edge and shape effects on boundaries of the superclusters and
voids. Parameters of the constraints are connected to features of the LSS: its
mean overdensity, a spatial scale and a shape, and spatial momenta of higher
orders. It is shown that presence of a non-virialized LSS can lead to an
observable deviation of the mass function. This effect is exploited to build a
procedure to recover parameters of the background perturbation from the
observationally estimated mass function.Comment: 23 pages, 6 figures; to be appeared in Astronomy Reports, 2014, Vol.
58, No. 6, pp. 386-39
Non-flammable elastomeric fiber from a fluorinated elastomer and containing an halogenated flame retardant
Flame retardant elastomeric compositions are described comprised of either spandex type polyurethane having incorporated into the polymer chain halogen containing polyols, conventional spandex type polyurethanes in physical admixture with flame retardant additives, or fluoroelastomeric resins in physical admixture with flame retardant additives. Methods are described for preparing fibers of the flame retardant elastomeric materials and articles of manufacture comprised of the flame retardant clastomeric materials and non elastic materials such as polybenzimidazoles, fiberglass, nylons, etc
On the Distribution of Haloes, Galaxies and Mass
The stochasticity in the distribution of dark haloes in the cosmic density
field is reflected in the distribution function which gives
the probability of finding haloes in a volume with mass density
contrast . We study the properties of this function using
high-resolution -body simulations, and find that is
significantly non-Poisson. The ratio between the variance and the mean goes
from (Poisson) at to (sub-Poisson) at
to (super-Poisson) at . The mean bias
relation is found to be well described by halo bias models based on the
Press-Schechter formalism. The sub-Poisson variance can be explained as a
result of halo-exclusion while the super-Poisson variance at high
may be explained as a result of halo clustering. A simple phenomenological
model is proposed to describe the behavior of the variance as a function of
. Galaxy distribution in the cosmic density field predicted by
semi-analytic models of galaxy formation shows similar stochastic behavior. We
discuss the implications of the stochasticity in halo bias to the modelling of
higher-order moments of dark haloes and of galaxies.Comment: 10 pages, 6 figures, Latex using MN2e style. Minor changes. Accepted
for publication in MNRA
The Pairwise Peculiar Velocity Dispersion of Galaxies: Effects of the Infall
We study the reliability of the reconstruction method which uses a modelling
of the redshift distortions of the two-point correlation function to estimate
the pairwise peculiar velocity dispersion of galaxies. In particular, the
dependence of this quantity on different models for the infall velocity is
examined for the Las Campanas Redshift Survey. We make extensive use of
numerical simulations and of mock catalogs derived from them to discuss the
effect of a self-similar infall model, of zero infall, and of the real infall
taken from the simulation. The implications for two recent discrepant
determinations of the pairwise velocity dispersion for this survey are
discussed.Comment: minor changes in the discussion; accepted for publication in ApJ; 8
pages with 2 figures include
Evolution of the Pairwise Peculiar Velocity Distribution Function in Lagrangian Perturbation Theory
The statistical distribution of the radial pairwise peculiar velocity of
galaxies is known to have an exponential form as implied by observations and
explicitly shown in N-body simulations. Here we calculate its statistical
distribution function using the Zel'dovich approximation assuming that the
primordial density fluctuations are Gaussian distributed. We show that the
exponential distribution is realized as a transient phenomena on megaparsec
scales in the standard cold-dark-matter model.Comment: 19 pages, 8 Postscript figures, AAS LaTe
Using Bars As Signposts of Galaxy Evolution at High and Low Redshifts
An analysis of the NICMOS Deep Field shows that there is no evidence of a
decline in the bar fraction beyond z~0.7, as previously claimed; both
bandshifting and spatial resolution must be taken into account when evaluating
the evolution of the bar fraction. Two main caveats of this study were a lack
of a proper comparison sample at low redshifts and a larger number of galaxies
at high redshifts. We address these caveats using two new studies. For a proper
local sample, we have analyzed 134 spirals in the near-infrared using 2MASS
(main results presented by Menendez-Delmestre in this volume) which serves as
an ideal anchor for the low-redshift Universe. In addition to measuring the
mean bar properties, we find that bar size is correlated with galaxy size and
brightness, but the bar ellipticity is not correlated with these galaxy
properties. The bar length is not correlated with the bar ellipticity. For
larger high redshift samples we analyze the bar fraction from the 2-square
degree COSMOS ACS survey. We find that the bar fraction at z~0.7 is ~50%,
consistent with our earlier finding of no decline in bar fraction at high
redshifts.Comment: In the proceedings of "Penetrating Bars through Masks of Cosmic Dust:
The Hubble Tuning Fork strikes a New Note
Corrosion of Aircraft Aluminium Alloys in Acid Solutions & its Prevention by Inhibitors
THE corrosion of metals is a serious problem confronting
the industrially advanced countries of the world. Modern developments and war-time experiences have made it possible to manufacture metals at lower costs than before. Secondly, new sources of minerals have been discovered, thereby enabling each nation to increase its capacity for the production of metals. Iron and steel, aluminium,
copper and zinc are amongst the metals in common
use. In practice all of them are liable to corrode in various environments : atmosphere, soil and liquid
medium. The loss of metal due to corrosion necessitating
repair or removal of metal parts is one of fundamental importance affecting the economy of a country. The cost
of corrosion control is rather high, the estimated
figures per annum for some of the countries being U.S.A.' close to 10 billion dollars, U.K.2 600 million pounds, Canada3 500 million dollars, Australia4 100 million pounds. and India5 154 crore rupees. It becomes incre-asingly important to preserve available metals in use since a time may come when some of them approach exhaus-tion. From the available figures it has been indicated
that immediate attention should be given to the non-
ferrous metals, and greater attention to ferrous res-ources. In the case of iron the losses due to corrosion
are estimated to be about 7.6 per cent a year. Corrosion
control methods, therefore, assume great importance6
Constraints on the small-scale power spectrum of density fluctuations from high-redshift gamma-ray bursts
Cosmological models that include suppression of the power spectrum of density
fluctuations on small scales exhibit an exponential reduction of high-redshift,
non-linear structures, including a reduction in the rate of gamma ray bursts
(GRBs). Here we quantify the constraints that the detection of distant GRBs
would place on structure formation models with reduced small-scale power. We
compute the number of GRBs that could be detectable by the Swift satellite at
high redshifts (z > 6), assuming that the GRBs trace the cosmic star formation
history, which itself traces the formation of non-linear structures. We
calibrate simple models of the intrinsic luminosity function of the bursts to
the number and flux distribution of GRBs observed by the Burst And Transient
Source Experiment (BATSE). We find that a discovery of high-z GRBs would imply
strong constraints on models with reduced small-scale power. For example, a
single GRB at z > 10, or 10 GRBs at z > 5, discovered by Swift during its
scheduled two-year mission, would rule out an exponential suppression of the
power spectrum on scales below R_c=0.09 Mpc (exemplified by warm dark matter
models with a particle mass of m_x=2 keV). Models with a less sharp suppression
of small-scale power, such as those with a red tilt or a running scalar index,
n_s, are more difficult to constrain, because they are more degenerate with an
increase in the power spectrum normalization, sigma_8, and with models in which
star-formation is allowed in low-mass minihalos. We find that a tilt of \delta
n_s ~ 0.1 is difficult to detect; however, an observed rate of 1 GRB/yr at z >
12 would yield an upper limit on the running of the spectral index, alpha =
d(n_s)/d(ln k) > -0.05.Comment: 10 pages, 6 figures; Minor changes to match version published in Ap
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