3,670 research outputs found
Tunable diode laser heterodyne radiometer measurement of atmospheric absorption of solar radiation
A tunable infrared heterodyne radiometer (TIHR) which uses a diode laser as the local oscillator is described as well as methods for the evaluation of the excess noise characteristics of the tunable diode laser. Preliminary atmospheric absorption data taken with the TIHR are presented and show the capability of the TIHR for making the highest resolution atmospheric measurements to date
Use of LARS system for the quantitative determination of smoke plume lateral diffusion coefficients from ERTS images of Virginia
A technique for measuring smoke plume of large industrial sources observed by satellite using LARSYS is proposed. A Gaussian plume model is described, integrated in the vertical, and inverted to yield a form for the lateral diffusion coefficient, Ky. Given u, wind speed; y sub l, the horizontal distance of a line of constant brightness from the plume symmetry axis a distance x sub l, downstream from reference point at x=x sub 2, y=0, then K sub y = u ((y sub 1) to the 2nd power)/2 x sub 1 1n (x sub 2/x sub 1). The technique is applied to a plume from a power plant at Chester, Virginia, imaged August 31, 1973 by LANDSAT I. The plume bends slightly to the left 4.3 km from the source and estimates yield Ky of 28 sq m/sec near the source, and 19 sq m/sec beyond the bend. Maximum ground concentrations are estimated between 32 and 64 ug/cu m. Existing meteorological data would not explain such concentrations
Ambient ammonia measurements using laser photo-acoustic spectroscopy
Ammonia concentrations reached minimal levels (approximately 0.1 ppb) in early winter, followed by a sudden later winter increase. A direct relationship between ambient ammonia levels and air temperature was inferred from the data (linear correlation coefficient r=0.53). Ammonia concentrations were determined to be directly related to the absolute humidity of the air (r=0.72); a weaker relationship between ammonia concentrations and relative humidity was discovered (r=0.37). The data also indicated that ammonia levels were generally higher within continental air masses than those of maritime origin. Soil parameters such as pH and moisture content were found to have a major bearing on the release of gaseous ammonia from soils in the region
Remote detection of aerosol pollution by ERTS
Photogrammetric and densitometric examination of ERTS-1 MSS imagery of Eastern Virginia coupled with extensive ground truth air quality and meteorological data has shown that the identification and surveying of fixed particulate emitters (smoke plumes) is feasible. A description of the ground truth network is included. The quantitative monitoring of smoke stacks from orbital altitudes over state size regions appears possible when tied to realistic plume models and minimal ground truth. Contrast reductions over urban areas can possibly be utilized to produce isopleths of particulates when supplemented by local measurements
Initial Conditions for Supersymmetric Inflation
We perform a numerical investigation of the fields evolution in the
supersymmetric inflationary model based on radiative corrections. Supergravity
corrections are also included. We find that, out of all the examined initial
data, only about 10% give an adequate amount of inflation and can be considered
as ''natural''. Moreover, these successful initial conditions appear scattered
and more or less isolated.Comment: 15 pages RevTeX 4 eps figure
Scaling in a SU(2)/Z_3 model of cosmic superstring networks
Motivated by recent developments in superstring theory in the cosmological
context, we examine a field theory which contains string networks with 3-way
junctions. We perform numerical simulations of this model, identify the length
scales of the network that forms, and provide evidence that the length scales
tend towards a scaling regime, growing in proportion to time. We infer that the
presence of junctions does not in itself cause a superstring network to
dominate the energy density of the early Universe.Comment: 12pp, 3 fig
Cosmological perturbation spectra from SL(4,R)-invariant effective actions
We investigate four-dimensional cosmological vacuum solutions derived from an
effective action invariant under global SL(n,R) transformations. We find the
general solutions for linear axion field perturbations about homogeneous
dilaton-moduli-vacuum solutions for an SL(4,R)-invariant action and find the
spectrum of super-horizon perturbations resulting from vacuum fluctuations in a
pre big bang scenario. We show that for SL(n,R)-invariant actions with n>3
there exists a regime of parameter space of non-zero measure where all the
axion field spectra have positive spectral tilt, as required if light axion
fields are to provide a seed for anisotropies in the microwave background and
large-scale structure in the universe.Comment: 8 pages, 3 figures, revtex plus epsf, minor typos corrected, version
to appear in Physical Review
Anisotropic String Cosmology at Large Curvatures
We study the effect of the antisymmetric tensor field on the
large curvature phase of string cosmology. It is well-known that a
non-vanishing value of leads to an anisotropic expansion of the spatial
dimensions. Correspondingly, in the string phase of the model, including
corrections, we find anisotropic fixed points of the evolution,
which act as regularizing attractors of the lowest order solutions. The
attraction basin can also include isotropic initial conditions for the scale
factors. We present explicit examples at order for different values
of the number of spatial dimensions and for different ans\"{a}tze for .Comment: 16 pages, Latex, 2 figure
Reconnection of Colliding Cosmic Strings
For vortex strings in the Abelian Higgs model and D-strings in superstring
theory, both of which can be regarded as cosmic strings, we give analytical
study of reconnection (recombination, inter-commutation) when they collide, by
using effective field theories on the strings. First, for the vortex strings,
via a string sigma model, we verify analytically that the reconnection is
classically inevitable for small collision velocity and small relative angle.
Evolution of the shape of the reconnected strings provides an upper bound on
the collision velocity in order for the reconnection to occur. These analytical
results are in agreement with previous numerical results. On the other hand,
reconnection of the D-strings is not classical but probabilistic. We show that
a quantum calculation of the reconnection probability using a D-string action
reproduces the nonperturbative nature of the worldsheet results by Jackson,
Jones and Polchinski. The difference on the reconnection -- classically
inevitable for the vortex strings while quantum mechanical for the D-strings --
is suggested to originate from the difference between the effective field
theories on the strings.Comment: 29 pages, 14 eps figures, JHEP style; references added, typos
correcte
On the evolution of cosmic-superstring networks
We model the behaviour of a network of interacting (p,q) strings from IIB
string theory by considering a field theory containing multiple species of
string, allowing us to study the effect of non-intercommuting events due to two
different species crossing each other. This then has the potential for a string
dominated Universe with the network becoming so tangled that it freezes. We
give numerical evidence, explained by a one-scale model, that such freezing
does not take place, with the network reaching a scaling limit where its
density relative to the background increases with N, the number of string
types.Comment: Extra references added showing constraints on cosmic superstrings, 7
pages, 7 figure
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