7,411 research outputs found
A Phase Space Approach to Gravitational Enropy
We examine the definition S = ln Omega as a candidate "gravitational entropy"
function. We calculate its behavior for gravitationl and density perturbations
in closed, open and flat cosmologies and find that in all cases it increases
monotonically. Using the formalism to calculate the gravitational entropy
produced during inflation gives the canonical answer. We compare the behavior
of S with the behavior of the square of the Weyl tensor. Applying the formalism
to black holes has proven more problematical.Comment: Talk delivered at South African Relativistic Cosmology Symposium, Feb
1999. Some new results over Rothman and Anninos 97. To appear in GRG, 17
page
Two-dimensional hydrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic fluid flow through porous media
The behaviour of two dimensional binary and ternary amphiphilic fluids under
flow conditions is investigated using a hydrodynamic lattice gas model. After
the validation of the model in simple cases (Poiseuille flow, Darcy's law for
single component fluids), attention is focussed on the properties of binary
immiscible fluids in porous media. An extension of Darcy's law which explicitly
admits a viscous coupling between the fluids is verified, and evidence of
capillary effects are described. The influence of a third component, namely
surfactant, is studied in the same context. Invasion simulations have also been
performed. The effect of the applied force on the invasion process is reported.
As the forcing level increases, the invasion process becomes faster and the
residual oil saturation decreases. The introduction of surfactant in the
invading phase during imbibition produces new phenomena, including
emulsification and micellisation. At very low fluid forcing levels, this leads
to the production of a low-resistance gel, which then slows down the progress
of the invading fluid. At long times (beyond the water percolation threshold),
the concentration of remaining oil within the porous medium is lowered by the
action of surfactant, thus enhancing oil recovery. On the other hand, the
introduction of surfactant in the invading phase during drainage simulations
slows down the invasion process -- the invading fluid takes a more tortuous
path to invade the porous medium -- and reduces the oil recovery (the residual
oil saturation increases).Comment: 48 pages, 26 figures. Phys. Rev. E (in press
Feminism, Abortion and Disability: irreconcilable differences?
There has been considerable discussion of the political allegiance between the feminist and disability movements, but the question of abortion remains a thorny one. Disability rights advocates have been keen to demonstrate that it is possible to believe in a woman's right to sovereignty over the body and, yet, be opposed to the selective abortion of an impaired foetus – describing the latter as a form of 'weak' eugenics.
The aim of this paper is to show that whilst there may be some points of agreement between the feminist and disability movements on the question of abortion, there exist fundamental and irreconcilable differences
Three dimensional hysdrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media
We report the results of a study of multiphase flow in porous media. A
Darcy's law for steady multiphase flow was investigated for both binary and
ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager
reciprocity were shown to be a good approximation of the simulation data. The
dependence of the relative permeability coefficients on water saturation was
investigated and showed good qualitative agreement with experimental data.
Non-steady state invasion flows were investigated, with particular interest in
the asymptotic residual oil saturation. The addition of surfactant to the
invasive fluid was shown to significantly reduce the residual oil saturation.Comment: To appear in Phys. Rev.
Interface Roughening in a Hydrodynamic Lattice-Gas Model with Surfactant
Using a hydrodynamic lattice-gas model, we study interface growth in a binary
fluid with various concentrations of surfactant. We find that the interface is
smoothed by small concentrations of surfactant, while microemulsion droplets
form for large surfactant concentrations. To assist in determining the
stability limits of the interface, we calculate the change in the roughness and
growth exponents and as a function of surfactant concentration
along the interface.Comment: 4 pages with 4 embedded ps figures. Requires psfig.tex. Will appear
in PRL 14 Oct 199
Effects of interdot dipole coupling in mesoscopic epitaxial Fe(100) dot arrays
The domain structure and the coercivity of epitaxial Fe(100) circular dot arrays of different diameters and separations have been studied using magnetic force microscopy (MFM) and focused magneto-optical Kerr effect (MOKE). The MFM images of the 1 µm diameter single domain dot arrays show direct evidence of strong interdot dipole coupling when the separation is reduced down to 0.1 µm. The coercivity of the dots is also found to be dependent on the separation, indicating the effect of the interdot dipole coupling on the magnetization reversal process
Far Infrared and Submillimeter Emission from Galactic and Extragalactic Photo-Dissociation Regions
Photodissociation Region (PDR) models are computed over a wide range of
physical conditions, from those appropriate to giant molecular clouds
illuminated by the interstellar radiation field to the conditions experienced
by circumstellar disks very close to hot massive stars. These models use the
most up-to-date values of atomic and molecular data, the most current chemical
rate coefficients, and the newest grain photoelectric heating rates which
include treatments of small grains and large molecules. In addition, we examine
the effects of metallicity and cloud extinction on the predicted line
intensities. Results are presented for PDR models with densities over the range
n=10^1-10^7 cm^-3 and for incident far-ultraviolet radiation fields over the
range G_0=10^-0.5-10^6.5, for metallicities Z=1 and 0.1 times the local
Galactic value, and for a range of PDR cloud sizes. We present line strength
and/or line ratio plots for a variety of useful PDR diagnostics: [C II] 158
micron, [O I] 63 and 145 micron, [C I] 370 and 609 micron, CO J=1-0, J=2-1,
J=3-2, J=6-5 and J=15-14, as well as the strength of the far-infrared
continuum. These plots will be useful for the interpretation of Galactic and
extragalactic far infrared and submillimeter spectra observable with ISO,
SOFIA, SWAS, FIRST and other orbital and suborbital platforms. As examples, we
apply our results to ISO and ground based observations of M82, NGC 278, and the
Large Magellenic Cloud.Comment: 54 pages, 20 figures, accepted for publication in The Astrophysical
Journa
The Relationship Between Promise and Performance in State Intervention in Family Life
JUDGE MIDONICK: We have a fantastic representation of our alumni here and we\u27ve overdone our 10:00 starting time and we\u27re supposed to stop at 12:00 promptly in order for us to go to the Low Memorial Library for lunch, for those who are having lunch with us. In order to be on time for this afternoon\u27s extravaganza we really ought to begin now. You must understand this program is entirely unrehearsed and therefore will be more interesting. We have with us today a panel of four whom I will introduce as they are to speak. The first speaker will speak for about forty-five minutes and he has a paper to present; and then we will have the others. At the end of that time, there will be a forty minute fun and games period when everyone here is entitled to make remarks. We are fortunate to have with us Dean Monrad Paulsen of the University of Virginia School of Law whom we hadn\u27t expected and who will be able not only to ask questions but give answers during the last forty minute period. I myself am eagerly awaiting an answer or two. Now, to begin, the paper which is to be given on the subject of the relationship between promise and performances in state intervention in family life will be given by Peter L. Strauss, Associate Professor of Law, Columbia Law School. His background is Harvard \u2761 in physics and chemistry, strangely, and so we have a person who is very well rounded and his law degree comes from Yale in 1964. He was editor-in-chief of the Yale Law Journal – he clerked as a law assistant for not only the Chief Judge of the Court of Appeals in the District of Columbia, David Bazelon, who is a great expert on child problems in the court himself, but Professor Strauss clerked after that for United States Supreme Court Justice William Brennan. He taught criminal law for two years at the Haile Sellassie I University in Addis Ababa, Ethiopia, and for three years was assistant to the Solicitor General of the United States. He joined Columbia\u27s faculty this fall, so be very gentle with him
Hidden cycle of dissolved organic carbon in the deep ocean
Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via δ[superscript 13]C and age via Δ[superscript 14]C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle.National Science Foundation (U.S.) (Grant OCE-0930866)National Science Foundation (U.S.) (Grant OCE-0930551
Granular Avalanches in Fluids
Three regimes of granular avalanches in fluids are put in light depending on
the Stokes number St which prescribes the relative importance of grain inertia
and fluid viscous effects, and on the grain/fluid density ratio r. In gas (r >>
1 and St > 1, e.g., the dry case), the amplitude and time duration of
avalanches do not depend on any fluid effect. In liquids (r ~ 1), for
decreasing St, the amplitude decreases and the time duration increases,
exploring an inertial regime and a viscous regime. These regimes are described
by the analysis of the elementary motion of one grain
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