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Impacts of Mixed-Wettability on Brine Drainage and Supercritical CO2 Storage Efficiency in a 2.5-D Heterogeneous Micromodel
Geological carbon storage (GCS) involves unstable drainage processes, the formation of patterns in a morphologically unstable interface between two fluids in a porous medium during drainage. The unstable drainage processes affect CO2 storage efficiency and plume distribution and can be greatly complicated by the mixed-wet nature of rock surfaces common in hydrocarbon reservoirs where supercritical CO2 (scCO2) is used in enhanced oil recovery. We performed scCO2 injection (brine drainage) experiments at 8.5 MPa and 45°C in heterogeneous micromodels, two mixed-wet with varying water- and intermediate-wet patches, and one water-wet. The flow regime changes from capillary fingering through crossover to viscous fingering in the micromodels of the same pore geometry but different wetting surfaces at displacement rates with logCa (capillary number) increasing from −8.1 to −4.4. While the mixed-wet micromodel with uniformly distributed intermediate-wet patches yields ~0.15 scCO2 saturation increase at both capillary fingering and crossover flow regimes (−8.1 ≤ logCa ≤ − 6.1), the one heterogeneous wetting to scCO2 results in ~0.09 saturation increase only at the crossover flow regime (−7.1 ≤ logCa ≤ − 6.1). The interconnected flow paths in the former are quantified and compared to the channelized scCO2 flow through intermediate-wet patches in the latter by topological analysis. At logCa > − 6.1 (near well), the effects of wettability and pore geometry are suppressed by strong viscous force. Both scCO2 saturation and distribution suggest the importance of wettability on CO2 storage efficiency and plume shape in reservoirs and capillary leakage through caprock at GCS conditions
Spectral components at visual and infrared wavelengths in active galactic nuclei
Aperture-dependent infrared photometry of active galactic nuclei are presented which illustrate the importance of eliminating starlight of the galaxy in order to obtain the intrinsic spectral distribution of the active nuclei. Separate components of emission are required to explain the infrared emission with a spectral index of alpha approx = 2 and the typical visual-ultraviolet continuum with alpha approx = 0.3 (where F(nu) varies as nu(sup-alpha). Present evidence does not allow unique determination of the appropriate mechanisms, but the characteristics of each are discussed
MgII Absorption Lines in z=2.974 Damped Lyman-alpha System toward Gravitationally Lensed QSO APM 08279+5255: Detection of Small-scale Structure in MgII Absorbing Clouds
1.02-1.16 micron spectra (R ~ 7,000) of the gravitationally lensed QSO APM
08279+5255 at z_em=3.911 were obtained during the commissioning run of IRCS,
the 1-5 micron near-infrared camera and spectrograph for the Subaru 8.2 m
Telescope. Strong MgII doublet at 2976,2800 angstrom and FeII (2600 angstrom),
FeII (2587 angstrom) absorption lines at z_abs=2.974 were clearly detected in
the rest-frame UV spectra, confirming the presence of a damped Lyman-alpha
system at the redshift as suggested by Petitjean et al. Also MgI (2853
angstrom) absorption line is probably detected. An analysis of the absorption
lines including velocity decomposition was performed. This is a first detailed
study of MgII absorption system at high redshift (z > 2.5) where the MgII
doublet shifts into the near-infrared in the observer's frame.
The spectra of the lensed QSO pair A and B with 0.38 arcsec separation were
resolved in some exposure frames under excellent seeing condition. We extracted
the MgII doublet spectra of A and B separately. Although three velocity
components (v ~ -28, +5, +45 km/s) are known to exist in this MgII system
(Petitjean et al.), the v ~ +45 km/s absorption line was not detected toward
source B, showing that the +45 km/s MgII cloud lies only in the line of sight
to the source A. Our results suggests that the size of the MgII absorbing
clouds is as small as 200 pc, which corresponds to the separation of A and B at
the redshift of the absorber. This is the first direct detection of the
small-scale structure of MgII clouds at high-redshift, confirming the estimated
cloud sizes from photoionization model by Churchill and Charlton.Comment: ApJ in press (Vol.569, 20 April 2002 issue
Nodal degenerations of plane curves and Galois covers
Globally irreducible nodes (i.e. nodes whose branches belong to the same
irreducible component) have mild effects on the most common topological
invariants of an algebraic curve. In other words, adding a globally irreducible
node (simple nodal degeneration) to a curve should not change them a lot. In
this paper we study the effect of nodal degeneration of curves on fundamental
groups and show examples where simple nodal degenerations produce
non-isomorphic fundamental groups and this can be detected in an algebraic way
by means of Galois coverings.Comment: 16 pages, 3 figure
A strong 3.4 micron emission feature in comet Austin 1989c1
High resolution 2.8-4.0 micron spectra of the 'new' comet Austin 1989c1, taken on 15-16 May 1990 confirm the presence of the broad emission features around 3.4 and 3.52 micron seen in a number of bright comets and ascribed to organic material. Both the 3.4 micron band strength and the 3.52/3.36 micron flux ratios are among the largest so far observed. The data are consistent with the relationship between band strength and water production rate that was recently derived. Excess emission at 3.28 and 3.6 micron cannot be unambiguously identified as features due to the poor signal-to-noise ratio
Nonadiabatic transitions in a Stark decelerator
In a Stark decelerator, polar molecules are slowed down and focussed by an
inhomogeneous electric field which switches between two configurations. For the
decelerator to work, it is essential that the molecules follow the changing
electric field adiabatically. When the decelerator switches from one
configuration to the other, the electric field changes in magnitude and
direction, and this can cause molecules to change state. In places where the
field is weak, the rotation of the electric field vector during the switch may
be too rapid for the molecules to maintain their orientation relative to the
field. Molecules that are at these places when the field switches may be lost
from the decelerator as they are transferred into states that are not focussed.
We calculate the probability of nonadiabatic transitions as a function of
position in the periodic decelerator structure and find that for the
decelerated group of molecules the loss is typically small, while for the
un-decelerated group of molecules the loss can be very high. This loss can be
eliminated using a bias field to ensure that the electric field magnitude is
always large enough. We demonstrate our findings by comparing the results of
experiments and simulations for the Stark deceleration of LiH and CaF
molecules. We present a simple method for calculating the transition
probabilities which can easily be applied to other molecules of interest.Comment: 12 pages, 9 figures, minor revisions following referee suggestion
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