2,507 research outputs found
Meteorological assessment of SRM exhaust products' environmental impact
The environmental impact of solid rocket motor (SRM) exhaust products discharged into the free air stream upon the launching of space vehicles that depend upon SRM boosters to obtain large thrust was assessed. The emission of Al2O3 to the troposphere from the SRMs in each Shuttle launch is considered. The Al2O3 appears as particles suitable for heterogeneous nucleation of hydrochloric acid which under frequently occurring atmospheric conditions may form a highly acidic rain capable of damaging property and crops and of impacting upon the health of human and animal populations. The cloud processes leading to the formation of acid rain and the concentration of the acid that then reaches the ground, and the atmospheric situations that lead to the production of cloud and rain at and near a launch site, and the prediction of weather conditions that may permit or prohibit a launch operation are studied
A set-valued framework for birth-and-growth process
We propose a set-valued framework for the well-posedness of birth-and-growth
process. Our birth-and-growth model is rigorously defined as a suitable
combination, involving Minkowski sum and Aumann integral, of two very general
set-valued processes representing nucleation and growth respectively. The
simplicity of the used geometrical approach leads us to avoid problems arising
by an analytical definition of the front growth such as boundary regularities.
In this framework, growth is generally anisotropic and, according to a
mesoscale point of view, it is not local, i.e. for a fixed time instant, growth
is the same at each space point
Kinetics and Mechanism of Metal Nanoparticle Growth via Optical Extinction Spectroscopy and Computational Modeling: The Curious Case of Colloidal Gold
An overarching computational framework unifying several optical theories to
describe the temporal evolution of gold nanoparticles (GNPs) during a seeded
growth process is presented. To achieve this, we used the inexpensive and
widely available optical extinction spectroscopy, to obtain quantitative
kinetic data. In situ spectra collected over a wide set of experimental
conditions were regressed using the physical model, calculating light
extinction by ensembles of GNPs during the growth process. This model provides
temporal information on the size, shape, and concentration of the particles and
any electromagnetic interactions between them. Consequently, we were able to
describe the mechanism of GNP growth and divide the process into distinct
genesis periods. We provide explanations for several longstanding mysteries,
for example, the phenomena responsible for the purple-greyish hue during the
early stages of GNP growth, the complex interactions between nucleation,
growth, and aggregation events, and a clear distinction between agglomeration
and electromagnetic interactions. The presented theoretical formalism has been
developed in a generic fashion so that it can readily be adapted to other
nanoparticulate formation scenarios such as the genesis of various metal
nanoparticles.Comment: Main text and supplementary information (accompanying MATLAB codes
available on the journal webpage
On the Universality of Mesoscience: Science of 'the in-between'
The universality of mesoscales, ranging between elemental particles and the
universe, is discussed here by reviewing widely disparate fields and presenting
four cases, at differing hierarchical levels, from chemistry, chemical
engineering, meteorology, through to astronomy. An underpinning concept,
"Compromise in competition", is highlighted between various dominant, but
competing mechanisms, and is identified here to be the universal origin of
complexity and diversity in such examples. We therefore advance this as a key
underlying principle of an emerging science -- Mesoscience.Comment: 8 pages, 1 figur
Modelling Polycrystalline Materials: An Overview of Three-Dimensional Grain-Scale Mechanical Models
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