660,546 research outputs found
Development and Validation of a Computational Model for Predicting the Behavior of Plumes from Large Solid Rocket Motors
Exhaust plumes from large solid rocket motors fired at ATK's Promontory test site carry particulates to high altitudes and typically produce deposits that fall on regions downwind of the test area. As populations and communities near the test facility grow, ATK has become increasingly concerned about the impact of motor testing on those surrounding communities. To assess the potential impact of motor testing on the community and to identify feasible mitigation strategies, it is essential to have a tool capable of predicting plume behavior downrange of the test stand. A software package, called PlumeTracker, has been developed and validated at ATK for this purpose. The code is a point model that offers a time-dependent, physics-based description of plume transport and precipitation. The code can utilize either measured or forecasted weather data to generate plume predictions. Next-Generation Radar (NEXRAD) data and field observations from twenty-three historical motor test fires at Promontory were collected to test the predictive capability of PlumeTracker. Model predictions for plume trajectories and deposition fields were found to correlate well with the collected dataset
Future Projections of Urban Waste Flows aand their Impacts in African Metropolises Cities
This paper presents future trends of urban wastes and their impacts on the environment of African cities using plausible mitigation scenarios. To accomplish this, an integrated dynamic model for urban waste flows was developed, tested, calibrated and validated. Its parameter sensitivity was analyzed. Using population projection up to 2052 with different levels of technological implementation, policy enforcement and awareness raising, four runs were executed. The “business as usual” run showed that with no additional mitigation measures, the environmental quality in Kampala and Dar es salaam Cities deteriorates. The “more enforcement” and “more collection” scenarios showed good reduction in environmental loads but they perform less well in resource recovery. The “proper management” scenario that combines enhanced technological implementation, awareness raising and policy enforcement, produced the smallest environmental loads, and recovered the largest amount of resources. Thus, the city authorities, general public, community based organisations and Non-governmental organizations would have to increase their efforts in finances and commitment to improve the urban environmental quality and increase resource recovery
Extreme TeV blazars and the intergalactic magnetic field
We study the four BL Lac objects (RGB J0152+017, 1ES 0229+200, 1ES 0347-121
and PKS 0548-322) detected in the TeV band but not present in the 1FGL
catalogue of the Fermi/Large Area Telescope. We analize the 24 months of LAT
data deriving gamma-ray fluxes or upper limits that we use to assemble their
spectral energy distributions (SED). We model the SEDs with a standard one-zone
leptonic model, also including the contribution of the reprocessed radiation in
the multi GeV band, emitted by the pairs produced through the conversion of the
primary TeV emission by interaction with the cosmic optical-IR background. For
simplicity, in the calculation of this component we adopt an analytical
approach including some simplifying assumptions, in particular i) the blazar
high energy emission is considered on average stable over times of the order of
10^7 years and ii) the observer is exactly on-axis. We compare the physical
parameters derived by the emission model with those of other high-energy
emitting BL Lacs, confirming that TeV BL Lacs with a rather small GeV flux are
characterized by extremely low values of the magnetic field and large values of
the electron energies. The comparison between the flux in the GeV band and that
expected from the reprocessed TeV emission allows us to confirm and strengthen
the lower limit of B >10^{-15} G for the intergalactic magnetic field using a
theoretically motivated spectrum for the primary high-energy photons.Comment: 11 pages, 7 figures, accepted for publication in M.N.R.A.
Magnetized Fast Isochoric Laser Heating for Efficient Creation of Ultra-High-Energy-Density States
The quest for the inertial confinement fusion (ICF) ignition is a grand
challenge, as exemplified by extraordinary large laser facilities. Fast
isochoric heating of a pre-compressed plasma core with a high-intensity
short-pulse laser is an attractive and alternative approach to create
ultra-high-energy-density states like those found in ICF ignition sparks. This
avoids the ignition quench caused by the hot spark mixing with the surrounding
cold fuel, which is the crucial problem of the currently pursued ignition
scheme. High-intensity lasers efficiently produce relativistic electron beams
(REB). A part of the REB kinetic energy is deposited in the core, and then the
heated region becomes the hot spark to trigger the ignition. However, only a
small portion of the REB collides with the core because of its large
divergence. Here we have demonstrated enhanced laser-to-core energy coupling
with the magnetized fast isochoric heating. The method employs a
kilo-tesla-level magnetic field that is applied to the transport region from
the REB generation point to the core which results in guiding the REB along the
magnetic field lines to the core. 7.7 1.3 % of the maximum coupling was
achieved even with a relatively small radial area density core (
0.1 g/cm). The guided REB transport was clearly visualized in a
pre-compressed core by using Cu- imaging technique. A simplified
model coupled with the comprehensive diagnostics yields 6.2\% of the coupling
that agrees fairly with the measured coupling. This model also reveals that an
ignition-scale areal density core ( 0.4 g/cm) leads to much
higher laser-to-core coupling ( 15%), this is much higher than that achieved
by the current scheme
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