11,623 research outputs found
Sculplexity: Sculptures of Complexity using 3D printing
We show how to convert models of complex systems such as 2D cellular automata
into a 3D printed object. Our method takes into account the limitations
inherent to 3D printing processes and materials. Our approach automates the
greater part of this task, bypassing the use of CAD software and the need for
manual design. As a proof of concept, a physical object representing a modified
forest fire model was successfully printed. Automated conversion methods
similar to the ones developed here can be used to create objects for research,
for demonstration and teaching, for outreach, or simply for aesthetic pleasure.
As our outputs can be touched, they may be particularly useful for those with
visual disabilities.Comment: Free access to article on European Physics Letter
Experimental investigations on sodium-filled heat pipes
The possibilities of producing heat pipes and, especially, the necessary capillary structures are discussed. Several types of heat pipes were made from stainless steel and tested at temperatures between 400 and 1055 deg C. The thermal power was determined by a calorimeter. Results indicate: bubble-free evaporation of sodium from rectangular open chennels is possible with a heat flux of more than 1,940 W/sq cm at 1055 C. The temperature drop along the tube could be measured only at low temperatures. A subdivided heat pipe worked against the gravitational field. A heat pipe with a capillary structure made of a rolled screen was supported by rings and bars operated at 250 W/sq cm heat flux in the evaporating region
Influence of Physics on the Distribution of Ichthyoplankton Across the Chesapeake Bay Plume
Most marine fish have retained pelagic larval stages that are spawned away from juvenile habitats. Physical and biological processes on a number of scales may affect larval survival. Mesoscale features like estuarine or riverine plumes and fronts are thought to affect larval survival by transporting larvae to juvenile habitats or by retaining larvae in favorable developmental habitats. It is likely that these features are major contributors in the regulation of shelf-spawned estuarine-dependent taxa.
This study examined how physical oceanographic features affected the spatial distribution of ichthyoplankton across the Chesapeake Bay Plume. Larval surveys were conducted across the shelf and within the baymouth during August 1988, July and August 1992, and from July through September, 1994. Samples were collected at varying horizontal and vertical scales to understand the variability in larval distribution across the plume.
The Chesapeake Bay outflow plume and its front affected the spatial distribution of larvae and ichthyoplankton assemblages at all spatial and temporal scales sampled. The plume front delineated the seaward extent of bay-spawned taxa as exemplified by Anchoa spp. Multi-specific larval peaks occurred inshore and offshore of the plume front, but aggregation within the plume front itself was nor observed. These multi-specific peaks consisted of pre-flexion and flexion larvae. and result from tidal oscillations of the front as it moves across the inner-shelf. This mechanism may retain larvae near shore, where the estuarine circulation can transport larvae into the bay.
Coastal upwelling associated with southerly winds transported plume and bay-spawned larvae to the shelf rapidly (days). Sub-surface water was transported to the coast during these upwelling events. Shelf-spawned larvae within this subsurface water were transported to the coast.
Larvae of the plume and shelf ichthyoplankton assemblages exhibited different vertical and ontogenetic distributions, across the inner-shelf. Etropus microstomus, a shelf-spawned and shelf-dependent taxa, exhibited differences in diel vertical distributions, and this may retain these larvae in shelf waters. Symphurus spp., a bay-spawned taxa exhibited an ontogenetic migration from the Chesapeake Bay plume to shelf waters, where its settles as a juvenile.
The results show that the Chesapeake Bay Plume outflow affects the spatial distribution of larval fish. The effect varies within members of an assemblage and between ontogenetic stages of some taxa. These findings support the hypothesis that estuarine plumes and mesoscale physical features may control larval survival by affecting spatial distribution
A fundamental measure theory for the sticky hard sphere fluid
We construct a density functional theory (DFT) for the sticky hard sphere
(SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the
hard sphere fluid [Phys. Rev. Lett. {\bf 63}, 980 (1989)], is based on a set of
weighted densities and an exact result from scaled particle theory (SPT). It is
demonstrated that the excess free energy density of the inhomogeneous SHS fluid
is uniquely defined when (a) it is solely a function of the
weighted densities from Kierlik and Rosinberg's version of FMT [Phys. Rev. A
{\bf 42}, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c)
it yields any given direct correlation function (DCF) from the class of
generalized Percus-Yevick closures introduced by Gazzillo and Giacometti [J.
Chem. Phys. {\bf 120}, 4742 (2004)]. The resulting DFT is shown to be in very
good agreement with simulation data. In particular, this FMT yields the correct
contact value of the density profiles with no adjustable parameters. Rather
than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT
produces them. Interestingly, although equivalent to Kierlik and Rosinberg's
FMT in the case of hard spheres, the set of weighted densities used for
Rosenfeld's original FMT is insufficient for constructing a DFT which yields
the SHS DCF.Comment: 11 pages, 3 figure
Strong Magnetization Measured in the Cool Cores of Galaxy Clusters
Tangential discontinuities, seen as X-ray edges known as cold fronts (CFs),
are ubiquitous in cool-core galaxy clusters. We analyze all 17 deprojected CF
thermal profiles found in the literature, including three new CFs we
tentatively identify (in clusters A2204 and 2A0335). We discover small but
significant thermal pressure drops below all nonmerger CFs, and argue that they
arise from strong magnetic fields below and parallel to the discontinuity,
carrying 10%-20% of the pressure. Such magnetization can stabilize the CFs, and
explain the CF-radio minihalo connection.Comment: PRL accepted, additional control tests adde
Liquidity measures and cost of trading in an illiquid market
We provide the first in-depth study of trading on the Ukrainian stock exchange, using trade-by-trade data. Although Ukraine has some large listed companies, the market is quite illiquid. We study the efficiency of five liquidity measures in the market. The proportion of no-trading days is the most reliable of the five, while turnover, which is widely used in the literature, is a poor measure. On trading cost, trades in all size categories are executed within the quoted spread, as in other dealership markets, with medium-sized trades being the cheapest. The cost of sales is higher than the cost of purchases under all market conditions
Slice Energy in Higher Order Gravity Theories and Conformal Transformations
We study the generic transport of slice energy between the scalar field
generated by the conformal transformation of higher-order gravity theories and
the matter component. We give precise relations for this exchange in the cases
of dust and perfect fluids. We show that, unless we are in a stationary
spacetime where slice energy is always conserved, in non-stationary situations
contributions to the total slice energy depend on whether or not test matter
follows geodesics in both frame representations of the dynamics, that is on
whether or not the two conformally related frames are physically
indistinguishable.Comment: 18 pages, references added, remark added in last Section related to
the choice of physical frame, various other improvements, final version to
appear in Gravitation and Cosmolog
Characteristics of Low-Latitude Coronal Holes near the Maximum of Solar cycle 24
We investigate the statistics of 288 low-latitude coronal holes extracted
from SDO/AIA-193 filtergrams over the time range 2011/01/01 to 2013/12/31. We
analyse the distribution of characteristic coronal hole properties, such as the
areas, mean AIA-193 intensities, and mean magnetic field densities, the local
distribution of the SDO/AIA-193 intensity and the magnetic field within the
coronal holes, and the distribution of magnetic flux tubes in coronal holes. We
find that the mean magnetic field density of all coronal holes under study is
3.0 +- 1.6 G, and the percentage of unbalanced magnetic flux is 49 +- 16 %. The
mean magnetic field density, the mean unsigned magnetic field density, and the
percentage of unbalanced magnetic flux of coronal holes depend strongly
pairwise on each other, with correlation coefficients cc > 0.92. Furthermore,
we find that the unbalanced magnetic flux of the coronal holes is predominantly
concentrated in magnetic flux tubes: 38 % (81 %) of the unbalanced magnetic
flux of coronal holes arises from only 1 % (10 %) of the coronal hole area,
clustered in magnetic flux tubes with field strengths > 50 G (10 G). The
average magnetic field density and the unbalanced magnetic flux derived from
the magnetic flux tubes correlate with the mean magnetic field density and the
unbalanced magnetic flux of the overall coronal hole (cc > 0.93). These
findings give evidence that the overall magnetic characteristics of coronal
holes are governed by the characteristics of the magnetic flux tubes.Comment: 15 figure
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