17,050 research outputs found
CO2 pipelines material and safety considerations
This paper presents an overview of some of the most important factors and areas of uncertainty
affecting integrity and accurate hazard assessment of CO2 pipelines employed as part of the
Carbon Capture and Sequestration (CCS) chain. These include corrosion, hydrate formation, hydrogen
embrittlement and propensity to fast running ductile and brittle factures. Special consideration
is given to the impact of impurities within the CO2 feed from the various capture technologies on
these possible hazards. Knowledge gaps in the modelling of outflow and subsequent dispersion of
CO2 following the accidental rupture of pressurised CO2 pipelines, central to their safety assessment,
are also presented
Macro- and microscale gaseous diffusion in a Stagnic Luvisol as affected by compaction and reduced tillage
Intensification of mechanical agriculture has increased the risk for soil compaction and deformation. Simultaneously, reduced tillage practices have become popular due to energy saving and environmental concerns, as they may strengthen and improve the functioning of structured soil pore system. Soil aeration is affected by both compaction and reduced tillage through changes in soil structure and in the distribution of easily decomposable organic matter. We investigated whether a single wheeling by a 35 000 kg sugar-beet harvester in a Stagnic Luvisol derived from loess near Göttingen, Germany, influenced the gas transport properties (air permeability, gaseous macro- and microdiffusivities, oxygen diffusion rate) in the topsoil and subsoil samples, and whether the effects were different between long-term reduced tillage and mouldboard ploughing. Poor structure in the topsoil resulted in slow macro- and microscale gas transport at moisture contents near field capacity. The macrodiffusivities in the topsoil under conventional tillage were slower compared with those under conservation treatment, and soil compaction reduced the diffusivities by about half at the soil depths studied. This shows that even one pass with heavy machinery near field capacity impairs soil structure deep into the profile, and supports the view that reduced tillage improves soil structure and aeration compared with ploughing, especially in the topsoil
Inverse problems in the design, modeling and testing of engineering systems
Formulations, classification, areas of application, and approaches to solving different inverse problems are considered for the design of structures, modeling, and experimental data processing. Problems in the practical implementation of theoretical-experimental methods based on solving inverse problems are analyzed in order to identify mathematical models of physical processes, aid in input data preparation for design parameter optimization, help in design parameter optimization itself, and to model experiments, large-scale tests, and real tests of engineering systems
Experimental pulse technique for the study of microbial kinetics in continuous culture
A novel technique was developed for studying the growth kinetics of microorganisms in continuous culture. The method is based on following small perturbations of a chemostat culture by on-line measurement of the dynamic response in oxygen consumption rates. A mathematical model, incorporating microbial kinetics and mass transfer between gas and liquid phases, was applied to interpret the data. Facilitating the use of very small disturbances, the technique is non-disruptive as well as fast and accurate. The technique was used to study the growth kinetics of two cultures, Methylosinus trichosporium OB3b growing on methane, both in the presence and in the absence of copper, and Burkholderia (Pseudomonas) cepacia G4 growing on phenol. Using headspace flushes, gas blocks and liquid substrate pulse experiments, estimates for limiting substrate concentrations, maximum conversion rates Vmax and half saturation constants Ks could rapidly be obtained. For M. trichosporium OB3b it was found that it had a far higher affinity for methane when particulate methane monooxygenase (pMMO) was expressed than when the soluble form (sMMO) was expressed under copper limitation. While for B. cepacia G4 the oxygen consumption pattern during a phenol pulse in the chemostat indicated that phenol was transiently converted to an intermediate (4-hydroxy-2-oxovalerate), so that initially less oxygen was used per mole of phenol.
The length of stellar bars in SB galaxies and N-body simulations
We have investigated the accuracy and reliability of six methods used to
determine the length of stellar bars in galaxies or N-body simulations. All
these methods use ellipse fitting and Fourier decomposition of the surface
brightness. We have applied them to N-body simulations that include stars, gas,
star formation, and feedback. Stellar particles were photometrically calibrated
to make B and K-band mock images. Dust absorption is also included. We discuss
the advantages and drawbacks of each method, the effects of projection and
resolution, as well as the uncertainties introduced by the presence of dust.
The use of N-body simulations allows us to compare the location of Ultra
Harmonic Resonance (UHR or 4/1) and corotation (CR) with measured bar lengths.
We show that the minimum of ellipticity located just outside the bulk of the
bar is correlated with the corotation, whereas the location of the UHR can be
approximated using the phase of the fitted ellipses or the phase of the m=2
Fourier development of the surface brightness. We give evidence that the
classification of slow/fast bars, based on the ratio R = Rcr/Rbar could
increase from 1 (fast bar) to 1.4 (slow bar) just by a change of method. We
thus conclude that one has to select the right bar-length estimator depending
on the application, since these various estimators do not define the same
physical area.Comment: Major revision, A&A in pres
The HPx software for multicomponent reactive transport during variably-saturated flow: Recent developments and applications
Abstract
HPx is a multicomponent reactive transport model which uses HYDRUS as the flow and transport solver and PHREEQC-3 as the biogeochemical solver. Some recent adaptations have significantly increased the flexibility of the software for different environmental and engineering applications. This paper gives an overview of the most significant changes of HPx, such as coupling transport properties to geochemical state variables, gas diffusion, and transport in two and three dimensions. OpenMP allows for parallel computing using shared memory. Enhancements for scripting may eventually simplify input definitions and create possibilities for defining templates for generic (sub)problems. We included a discussion of root solute uptake and colloid-affected solute transport to show that most or all of the comprehensive features of HYDRUS can be extended with geochemical information. Finally, an example is used to demonstrate how HPx, and similar reactive transport models, can be helpful in implementing different factors relevant for soil organic matter dynamics in soils. HPx offers a unique framework to couple spatial-temporal variations in water contents, temperatures, and water fluxes, with dissolved organic matter and CO2 transport, as well as bioturbation processes
Synthesis of a control model for a liquid nitrogen cooled, closed circuit, cryogenic nitrogen wind tunnel and its validation
The details of the efforts to synthesize a control-compatible multivariable model of a liquid nitrogen cooled, gaseous nitrogen operated, closed circuit, cryogenic pressure tunnel are presented. The synthesized model was transformed into a real-time cryogenic tunnel simulator, and this model is validated by comparing the model responses to the actual tunnel responses of the 0.3 m transonic cryogenic tunnel, using the quasi-steady-state and the transient responses of the model and the tunnel. The global nature of the simple, explicit, lumped multivariable model of a closed circuit cryogenic tunnel is demonstrated
Numerical Structure Analysis of Regular Hydrogen-Oxygen Detonations
Large-scale numerical simulations have been carried out to analyze the internal
wave structure of a regular oscillating low-pressure H2 : O2 : Ar-Chapman-Jouguet
detonation in two and three space-dimensions. The chemical reaction is modeled
with a non-equilibrium mechanism that consists of 34 elementary reactions and uses
nine thermally perfect gaseous species. A high local resolution is achieved dynamically
at run-time by employing a block-oriented adaptive finite volume method that
has been parallelized efficiently for massively parallel machines. Based on a highly
resolved two-dimensional simulation we analyze the temporal development of the
ow field around a triple point during a detonation cell in great detail. In particular,
the influence of the reinitiation phase at the beginning of a detonation cell
is discussed. Further on, a successful simulation of the cellular structure in three
space-dimensions for the same configuration is presented. The calculation reproduces
the experimentally observed three-dimensional mode of propagation called
"rectangular-mode-in-phase" with zero phase shift between the transverse waves in
both space-directions perpendicular to the detonation front and shows the same
oscillation period as the two-dimensional case
The Shape of Dark Matter Halos
Techniques for inferring the radial and geometric form of dark matter halos
and the results they have produced to date are reviewed. Dark halos appear to
extend to at least ~50 kpc with total enclosed masses that rise linearly with
radius R. Whether this behavior can be extrapolated to distances as large as
200 kpc and beyond is controversial; results at this radius are
model-dependent. Observationally, the geometrical form of the dark halo can be
characterized by the equatorial axis ratio b/a (ovalness) and
vertical-to-equatorial axis ratio c/a (flattening) of the total density.
Different techniques consistently yield b/a > 0.7 (and thus b/a > 0.9 for the
potential) at R~20 kpc, with more axisymmetric values, b/a >~ 0.8, being more
likely. Results are less consistent for the vertical flattening, perhaps due to
the difference in the spatial regions probed by different techniques or
inappropriate assumptions. Techniques that probe furthest from the stellar
plane z~15 kpc consistently implicate substantially flattened c/a = 0.5 +/- 0.2
dark halos. These axis ratios are in acceptable agreement with expectations
from N-body simulations of cold dark matter mixed with ~10% dissipational gas.Comment: Invited Review to appear in Galaxy Dynamics, 1999, eds. D. Merritt,
J.A. Sellwood and M. Valluri, ASP, LaTex using paspconf.sty, 3 figures in 5
postscript file
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