1,749 research outputs found
Pathways and Supply of Dissolved Iron in the Amundsen Sea (Antarctica)
Numerous coastal polynyas fringe the Antarctic continent and strongly inïŹuence the productivity of Antarctic shelf systems. Of the 46 Antarctic coastal polynyas documented in a recent study, the Amundsen Sea Polynya (ASP) stands out as having the highest net primary production per unit area. Incubation experiments suggest that this productivity is partly controlled by the availability of dissolved iron (dFe).As a ïŹrst step toward understanding the iron supply of the ASP, we introduce four plausible sources of dFe and simulate their steady spatial distribution using conservative numerical tracers. The modeled distributions replicate important features from observations including dFe maxima at the bottom of deep troughsand enhanced concentrations near the ice shelf fronts. A perturbation experiment with an idealized draw-down mimicking summertime biological uptake and subsequent resupply suggests that glacial meltwaterand sediment-derived dFe are the main contributors to the prebloom dFe inventory in the top 100 m of the ASP. The sediment-derived dFe depends strongly on the buoyancy-driven overturning circulation associated with the melting ice shelves (the ââmeltwater pumpââ) to add dFe to the upper 300 m of the water column. The results support the view that ice shelf melting plays an important direct and indirect role in the dFe supply and delivery to polynyas such as the ASP
Delusional beliefs and reason giving
Delusions are often regarded as irrational beliefs, but their irrationality is not sufficient to explain what is pathological about them. In this paper we ask whether deluded subjects have the capacity to support the content of their delusions with reasons, that is, whether they can author their delusional states. The hypothesis that delusions are characterised by a failure of authorship, which is a dimension of self knowledge, deserves to be
empirically tested because (a) it has the potential to account for the distinction between endorsing a delusion and endorsing a framework belief; (b) it contributes to a
philosophical analysis of the relationship between rationality and self knowledge; and (c) it informs diagnosis and therapy in clinical psychiatry. However, authorship cannot provide a demarcation criterion between delusions and other irrational belief states
Preliminary test results of the joint FAA-USAF-NASA runway research program. Part 2: Traction measurements of several runways under wet, snow covered, and dry conditions with a Douglas DC-9, a diagonal-braked vehicle, and a mu-meter
For abstract, see N77-27132
In situ phytoplankton distributions in the Amundsen Sea Polynya measured by autonomous gliders
The Amundsen Sea Polynya is characterized by large phytoplankton blooms, which makes this region disproportionately important relative to its size for the biogeochemistry of the Southern Ocean. In situ data on phytoplankton are limited, which is problematic given recent reports of sustained change in the Amundsen Sea. During two field expeditions to the Amundsen Sea during austral summer 2010-2011 and 2014, we collected physical and bio-optical data from ships and autonomous underwater gliders. Gliders documented large phytoplankton blooms associated with Antarctic Surface Waters with low salinity surface water and shallow upper mixed layers (\u3c 50 m). High biomass was not always associated with a specific water mass, suggesting the importance of upper mixed depth and light in influencing phytoplankton biomass. Spectral optical backscatter and ship pigment data suggested that the composition of phytoplankton was spatially heterogeneous, with the large blooms dominated by Phaeocystis and non-bloom waters dominated by diatoms. Phytoplankton growth rates estimated from field data (\u3c = 0.10 day(-1)) were at the lower end of the range measured during ship-based incubations, reflecting both in situ nutrient and light limitations. In the bloom waters, phytoplankton biomass was high throughout the 50-m thick upper mixed layer. Those biomass levels, along with the presence of colored dissolved organic matter and detritus, resulted in a euphotic zone that was often \u3c 10 m deep. The net result was that the majority of phytoplankton were light-limited, suggesting that mixing rates within the upper mixed layer were critical to determining the overall productivity; however, regional productivity will ultimately be controlled by water column stability and the depth of the upper mixed layer, which may be enhanced with continued ice melt in the Amundsen Sea Polynya
Theory of Cylindrical Tubules and Helical Ribbons of Chiral Lipid Membranes
We present a general theory for the equilibrium structure of cylindrical
tubules and helical ribbons of chiral lipid membranes. This theory is based on
a continuum elastic free energy that permits variations in the direction of
molecular tilt and in the curvature of the membrane. The theory shows that the
formation of tubules and helical ribbons is driven by the chirality of the
membrane. Tubules have a first-order transition from a uniform state to a
helically modulated state, with periodic stripes in the tilt direction and
ripples in the curvature. Helical ribbons can be stable structures, or they can
be unstable intermediate states in the formation of tubules.Comment: 43 pages, including 12 postscript figures, uses REVTeX 3.0 and
epsf.st
Freshwater distributions and water mass structure in the Amundsen Sea Polynya region, Antarctica
We present the first densely-sampled hydrographic survey of the Amundsen Sea Polynya (ASP) region, including a detailed characterization of its freshwater distributions. Multiple components contribute to the freshwater budget, including precipitation, sea ice melt, basal ice shelf melt, and iceberg melt, from local and non-local sources. We used stable oxygen isotope ratios in seawater (ÎŽ18O) to distinguish quantitatively the contributions from sea ice and meteoric-derived sources. Meteoric fractions were high throughout the winter mixed layer (WML), with maximum values of 2â3% (±0.5%). Because the ASP region is characterized by deep WMLs, column inventories of total meteoric water were also high, ranging from 10â13 m (±2 m) adjacent to the Dotson Ice Shelf (DIS) and in the deep trough to 7â9 m (±2 m) in shallower areas. These inventories are at least twice those reported for continental shelf waters near the western Antarctic Peninsula. Sea ice melt fractions were mostly negative, indicating net (annual) sea ice formation, consistent with this area being an active polynya. Independently determined fractions of subsurface glacial meltwater (as one component of the total meteoric inventory) had maximum values of 1â2% (±0.5%), with highest and shallowest maximum values at the DIS outflow (80â90 m) and in iceberg-stirred waters (150â200 m). In addition to these upwelling sites, contributions of subsurface glacial meltwater could be traced at depth along the ~ 27.6 isopycnal, from which it mixes into the WML through various processes. Our results suggest a quasi-continuous supply of melt-laden iron-enriched seawater to the euphotic zone of the ASP and help to explain why the ASP is Antarcticaâs most biologically productive polynya per unit area
The Amundsen Sea Polynya International Research Expedition (ASPIRE)
In search of an explanation for some of the greenest waters ever seen in coastal Antarctica and their possible link to some of the fastest melting glaciers and declining summer sea ice, the Amundsen Sea Polynya International Research Expedition (ASPIRE) challenged the capabilities of the US Antarctic Program and RVIB Nathaniel B. Palmer during Austral summer 2010â2011. We were well rewarded by both an extraordinary research platform and a truly remarkable oceanic setting. Here we provide further insights into the key questions that motivated our sampling approach during ASPIRE and present some preliminary findings, while highlighting the value of the Palmer for accomplishing complex, multifaceted oceanographic research in such a challenging environment
A framework for experimental-data-driven assessment of Magnetized Liner Inertial Fusion stagnation image metrics
A variety of spherical crystal x-ray imager (SCXI) diagnostics have been
developed and fielded on Magnetized Liner Inertial Fusion (MagLIF) experiments
at the Sandia National Laboratories Z-facility. These different imaging
modalities provide detailed insight into different physical phenomena such as
mix of liner material into the hot fuel, cold liner emission, or reduce impact
of liner opacity. However, several practical considerations ranging from the
lack of a consistent spatial fiducial for registration to different
point-spread-functions and tuning crystals or using filters to highlight
specific spectral regions make it difficult to develop broadly applicable
metrics to compare experiments across our stagnation image database without
making significant unverified assumptions. We leverage experimental data for a
model-free assessment of sensitivities to instrumentation-based features for
any specified image metric. In particular, we utilize a database of historical
and recent MagLIF data including image plate scans
gathered across different experiments to assess the
impact of a variety of features in the experimental observations arising from
uncertainties in registration as well as discrepancies in signal-to-noise ratio
and instrument resolution. We choose a wavelet-based image metric known as the
Mallat Scattering Transform for the study and highlight how alternate metric
choices could also be studied. In particular, we demonstrate a capability to
understand and mitigate the impact of signal-to-noise, image registration, and
resolution difference between images. This is achieved by utilizing multiple
scans of the same image plate, sampling random translations and rotations, and
applying instrument specific point-spread-functions found by ray tracing to
high-resolution datasets, augmenting our data in an effectively model-free
fashion.Comment: 17 pages, 14 figure
Fuzzy integral for rule aggregation in fuzzy inference systems
The fuzzy inference system (FIS) has been tuned and re-vamped many times over and applied to numerous domains. New and improved techniques have been presented for fuzzification, implication, rule composition and defuzzification, leaving one key component relatively underrepresented, rule aggregation. Current FIS aggregation operators are relatively simple and have remained more-or-less unchanged over the years. For many problems, these simple aggregation operators produce intuitive, useful and meaningful results. However, there exists a wide class of problems for which quality aggregation requires non- additivity and exploitation of interactions between rules. Herein, we show how the fuzzy integral, a parametric non-linear aggregation operator, can be used to fill this gap. Specifically, recent advancements in extensions of the fuzzy integral to \unrestricted" fuzzy sets, i.e., subnormal and non- convex, makes this now possible. We explore the role of two extensions, the gFI and the NDFI, discuss when and where to apply these aggregations, and present efficient algorithms to approximate their solutions
Exploring the parameter space of MagLIF implosions using similarity scaling. II. Current scaling
Magnetized Liner Inertial Fusion (MagLIF) is a magneto-inertial-fusion (MIF)
concept, which is presently being studied on the Z Pulsed Power Facility. The
MagLIF platform has achieved interesting plasma conditions at stagnation and
produced significant fusion yields in the laboratory. Given the relative
success of MagLIF, there is a strong interest to scale the platform to higher
peak currents. However, scaling MagLIF is not entirely straightforward due to
the large dimensionality of the experimental input parameter space and the
large number of distinct physical processes involved in MIF implosions. In this
work, we propose a novel method to scale MagLIF loads to higher currents. Our
method is based on similarity (or similitude) scaling and attempts to preserve
much of the physics regimes already known or being studied on today's Z
pulsed-power driver. By avoiding significant deviations into unexplored and/or
less well-understood regimes, the risk of unexpected outcomes on future
scaled-up experiments is reduced. Using arguments based on similarity scaling,
we derive the scaling rules for the experimental input parameters
characterizing a MagLIF load (as functions of the characteristic current
driving the implosion). We then test the estimated scaling laws for various
metrics measuring performance against results of 2D
radiation--magneto-hydrodynamic HYDRA simulations. Agreement is found between
the scaling theory and the simulation results.Comment: 19 pages, submitted to Physics of Plasma
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