1,305 research outputs found
Air/Sea Transfer of Highly Soluble Gases Over Coastal Waters
The deposition of soluble trace gases to the sea surface is not well studied due to a lack of flux measurements over the ocean. Here we report simultaneous air/sea eddy covariance flux measurements of water vapor, sulfur dioxide (SO2), and momentum from a coastal North Atlantic pier. Gas transfer velocities were on average about 20% lower for SO2 than for H2O. This difference is attributed to the difference in molecular diffusivity between the two molecules (DSO2/DH2O = 0.5), in reasonable agreement with bulk parameterizations in air/sea gas models. This study demonstrates that it is possible to observe the effect of molecular diffusivity on air-side resistance to gas transfer. The slope of observed relationship between gas transfer velocity and friction velocity is slightly smaller than predicted by gas transfer models, possibly due to wind/wave interactions that are unaccounted for in current models
Nonlinear rheology of colloidal dispersions
Colloidal dispersions are commonly encountered in everyday life and represent
an important class of complex fluid. Of particular significance for many
commercial products and industrial processes is the ability to control and
manipulate the macroscopic flow response of a dispersion by tuning the
microscopic interactions between the constituents. An important step towards
attaining this goal is the development of robust theoretical methods for
predicting from first-principles the rheology and nonequilibrium microstructure
of well defined model systems subject to external flow. In this review we give
an overview of some promising theoretical approaches and the phenomena they
seek to describe, focusing, for simplicity, on systems for which the colloidal
particles interact via strongly repulsive, spherically symmetric interactions.
In presenting the various theories, we will consider first low volume fraction
systems, for which a number of exact results may be derived, before moving on
to consider the intermediate and high volume fraction states which present both
the most interesting physics and the most demanding technical challenges. In
the high volume fraction regime particular emphasis will be given to the
rheology of dynamically arrested states.Comment: Review articl
Yours ever (well, maybe): Studies and signposts in letter writing
Electronic mail and other digital communications technologies seemingly threaten to end the era of handwritten and typed letters, now affectionately seen as part of snail mail. In this essay, I analyze a group of popular and scholarly studies about letter writing-including examples of pundits critiquing the use of e-mail, etiquette manuals advising why the handwritten letter still possesses value, historians and literary scholars studying the role of letters in the past and what it tells us about our present attitudes about digital communications technologies, and futurists predicting how we will function as personal archivists maintaining every document including e-mail. These are useful guideposts for archivists, providing both a sense of the present and the past in the role, value and nature of letters and their successors. They also provide insights into how such documents should be studied, expanding our gaze beyond the particular letters, to the tools used to create them and the traditions dictating their form and function. We also can discern a role for archivists, both for contributing to the literature about documents and in using these studies and commentaries, suggesting not a new disciplinary realm but opportunities for new interdisciplinary work. Examining a documentary form makes us more sensitive to both the innovations and traditions as it shifts from the analog to the digital; we can learn not to be caught up in hysteria or nostalgia about one form over another and archivists can learn about what they might expect in their labors to document society and its institutions. At one time, paper was part of an innovative technology, with roles very similar to the Internet and e-mail today. It may be that the shifts are far less revolutionary than is often assumed. Reading such works also suggests, finally, that archivists ought to rethink how they view their own knowledge and how it is constructed and used. © 2010 Springer Science+Business Media B.V
Icebergs in the North Atlantic: Modelling circulation changes and glacio-marine deposition
In order to investigate meltwater events in the North Atlantic, a simple iceberg generation, drift, and melting routine was implemented in a high-resolution OGCM. Starting from the modelled last glacial state, every 25th day cylindrical model icebergs 300 meters high were released at 32 specific points along the coasts. Icebergs launched at the Barents Shelf margin spread a light meltwater lid over the Norwegian and Greenland Seas, shutting down the deep convection and the anti-clockwise circulation in this area. Due to the constraining ocean circulation, the icebergs produce a tongue of relatively cold and fresh water extending eastward from Hudson Strait that must develop at this location, regardless of iceberg origin. From the total amount of freshwater inferred by the icebergs, the thickness of the deposited IRD could be calculated in dependance of iceberg sediment concentration. In this way, typical extent and thickness of Heinrich layers could be reproduced, running the model for 250 years of steady state with constant iceberg meltwater inflow
Lorenz-like systems and classical dynamical equations with memory forcing: a new point of view for singling out the origin of chaos
A novel view for the emergence of chaos in Lorenz-like systems is presented.
For such purpose, the Lorenz problem is reformulated in a classical mechanical
form and it turns out to be equivalent to the problem of a damped and forced
one dimensional motion of a particle in a two-well potential, with a forcing
term depending on the ``memory'' of the particle past motion. The dynamics of
the original Lorenz system in the new particle phase space can then be
rewritten in terms of an one-dimensional first-exit-time problem. The emergence
of chaos turns out to be due to the discontinuous solutions of the
transcendental equation ruling the time for the particle to cross the
intermediate potential wall. The whole problem is tackled analytically deriving
a piecewise linearized Lorenz-like system which preserves all the essential
properties of the original model.Comment: 48 pages, 25 figure
Post-Coring Entrapment Of Modern Air In Some Shallow Ice Cores Collected Near the Firn-Ice Transition: Evidence From Cfc-12 Measurements In Antarctic Firn Air and Ice Cores
In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition
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Argonne National Laboratory Reports
DISPL is a software package for solving some second-order nonlinear systems of partial differential equations including parabolic, elliptic, hyperbolic, and some mixed types such as parabolic-elliptic equations. Fairly general nonlinear boundary conditions are allowed as well as interface conditions for problems in an inhomogeneous media. The spatial domain is one- or two-dimensional with Cartesian, cylindrical, or spherical (in one dimension only) geometry. The numerical method is based on the use of Galerkin's procedure combined with the use of B-splines in order to reduce the system of PDE's to a system of ODE's. The latter system is then solved with a sophisticated ODE software package. Software features include extensive dump/restart facilities, free format input, moderate printed output capability, dynamic storage allocation, and three graphics packages
Biodegradable PEG-poly(ω-pentadecalactone- co - p -dioxanone) nanoparticles for enhanced and sustained drug delivery to treat brain tumors
Intracranial delivery of therapeutic agents is limited by penetration beyond the blood-brain barrier (BBB)
and rapid metabolism of the drugs that are delivered. Convection-enhanced delivery (CED) of drugloaded
nanoparticles (NPs) provides for local administration, control of distribution, and sustained
drug release. While some investigators have shown that repeated CED procedures are possible, longer
periods of sustained release could eliminate the need for repeated infusions, which would enhance
safety and translatability of the approach. Here, we demonstrate that nanoparticles formed from
poly(ethylene glycol)-poly(u-pentadecalactone-co-p-dioxanone) block copolymers [PEG-poly(PDL-co-
DO)] are highly efficient nanocarriers that provide long-term release: small nanoparticles (less than
100 nm in diameter) continuously released a radiosensitizer (VE822) over a period of several weeks
in vitro, provided widespread intracranial drug distribution during CED, and yielded significant drug
retention within the brain for over 1 week. One advantage of PEG-poly(PDL-co-DO) nanoparticles is that
hydrophobicity can be tuned by adjusting the ratio of hydrophobic PDL to hydrophilic DO monomers,
thus making it possible to achieve a wide range of drug release rates and drug distribution profiles. When
administered by CED to rats with intracranial RG2 tumors, and combined with a 5-day course of fractionated
radiation therapy, VE822-loaded PEG-poly(PDL-co-DO) NPs significantly prolonged survival
when compared to free VE822. Thus, PEG-poly(PDL-co-DO) NPs represent a new type of versatile
nanocarrier system with potential for sustained intracranial delivery of therapeutic agents to treat brain
tumors
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