2,349 research outputs found
Method of evaporation
Liquids, such as juices, milk, molten metal and the like are concentrated by forming uniformly-sized, small droplets in a precision droplet forming assembly and deploying the droplets in free fall downwardly as a central column within an evacuated column with cool walls. A portion of the solvent evaporates. The vapor flows to the wall, condenses, and usually flows down the wall as a film to condensate collector and drain. The vertical column of freely falling droplets enters the splash guard. The condensate can be collected, sent to other towers or recycled
Modelling ion populations in astrophysical plasmas: carbon in the solar transition region
The aim of this work is to improve the modelling of ion populations in higher
density, lower temperature astrophysical plasmas, of the type commonly found in
lower solar and stellar atmospheres. Ion population models for these regions
frequently employ the coronal approximation, which assumes conditions more
suitable to the upper solar atmosphere, where high temperatures and lower
densities prevail. Using the coronal approximation for modelling the solar
transition region gives theoretical lines intensities for the Li-like and
Na-like isoelectronic sequences which can be factors of 2-5 times lower than
observed. The works of Burgess & Summers (1969) and Nussbaumer & Storey (1975)
showed the important part ions in excited levels play when included in the
modelling. Their models, however, used approximations for the atomic rates to
determine the ion balance. Presented here is the first stage in updating these
earlier models of carbon by using rates from up-to-date atomic calculations and
more recent photo-ionising radiances for the quiet Sun. Where such atomic rates
are not readily available, in the case of electron-impact direct ionisation and
excitation--auto-ionisation, new calculations have been made and compared to
theoretical and experimental studies. The effects each atomic process has on
the ion populations as density changes is demonstrated, and final results from
the modelling are compared to the earlier works. Lastly, the new results for
ion populations are used to predict line intensities for the solar transition
region in the quiet Sun, and these are compared with predictions from
coronal-approximation modelling and with observations. Significant improvements
in the predicted line intensities are seen in comparison to those obtained from
zero-density modelling of carbon.Comment: Draft accepted by A&A, 13 pages, 15 figure
Fluid-driven deformation of a soft granular material
Compressing a porous, fluid-filled material will drive the interstitial fluid
out of the pore space, as when squeezing water out of a kitchen sponge.
Inversely, injecting fluid into a porous material can deform the solid
structure, as when fracturing a shale for natural gas recovery. These
poromechanical interactions play an important role in geological and biological
systems across a wide range of scales, from the propagation of magma through
the Earth's mantle to the transport of fluid through living cells and tissues.
The theory of poroelasticity has been largely successful in modeling
poromechanical behavior in relatively simple systems, but this continuum theory
is fundamentally limited by our understanding of the pore-scale interactions
between the fluid and the solid, and these problems are notoriously difficult
to study in a laboratory setting. Here, we present a high-resolution
measurement of injection-driven poromechanical deformation in a system with
granular microsctructure: We inject fluid into a dense, confined monolayer of
soft particles and use particle tracking to reveal the dynamics of the
multi-scale deformation field. We find that a continuum model based on
poroelasticity theory captures certain macroscopic features of the deformation,
but the particle-scale deformation field exhibits dramatic departures from
smooth, continuum behavior. We observe particle-scale rearrangement and
hysteresis, as well as petal-like mesoscale structures that are connected to
material failure through spiral shear banding
Brownian Dynamics of a Sphere Between Parallel Walls
We describe direct imaging measurements of a colloidal sphere's diffusion
between two parallel surfaces. The dynamics of this deceptively simple
hydrodynamically coupled system have proved difficult to analyze. Comparison
with approximate formulations of a confined sphere's hydrodynamic mobility
reveals good agreement with both a leading-order superposition approximation as
well as a more general all-images stokeslet analysis.Comment: 4 pages, 3 figures, REVTeX with PostScript figure
Equilibrium Commodity Prices with Irreversible Investment and Non-Linear Technology
We model equilibrium spot and futures oil prices in a general equilibrium production economy. In our model production of the consumption good requires two inputs: the consumption good and a commodity, e.g., Oil. Oil is produced by wells whose flow rate is costly to adjust. Investment in new Oil wells is costly and irreversible. As a result in equilibrium, investment in Oil wells is infrequent and lumpy. Even though the state of the economy is fully described by a one-factor Markov process, the spot oil price is not Markov (in itself). Rather it is best described as a regime-switching process, the regime being an investment `proximity' indicator. The resulting equilibrium oil price exhibits mean-reversion and heteroscedasticity. Further, the risk premium for exposure to commodity risk is time-varying, positive in the far-from-investment regime but negative in the near-investment regime. Further, our model captures many of the stylized facts of oil futures prices, such as backwardation and the `Samuelson effect.' The futures curve exhibits backwardation as a result of a convenience yield, which arises endogenously. We estimate our model using the Simulated Method of Moments with economic aggregate data and crude oil futures prices. The model successfully captures the first two moments of the futures curves, the average non-durable consumption-output ratio, the average oil consumption-output and the average real interest rate. The estimation results suggest the presence of convex adjustment costs for the investment in new oil wells. We also propose and test a linear approximation of the equilibrium regime-shifting dynamics implied by our model, and test its empirical implication for time-varying risk-premia.
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