36,506 research outputs found
A note on static dyonic diholes
In this brief note we argue that a dyonic generalization of the Emparan-Teo
dihole solution is described by a static diagonal metric and therefore,
contrary to the claim made in a recent paper by Cabrera-Munguia et al., does
not involve any "non-vanishing global angular momentum" and rotating charges.Comment: 4 pages, 1 figure; typos corrected, matches the published versio
Comparative energetic assessment of methanol production from COâ: chemical versus electrochemical process
Emerging emission-to-liquid (eTL) technologies that produce liquid fuels from COâ are a possible solution for both the global issues of greenhouse gas emissions and fossil fuel depletion. Among those technologies, COâ hydrogenation and high-temperature COâ electrolysis are two promising options suitable for large-scale applications. In this study, two COâ -to-methanol conversion processes, i.e., production of methanol by COâ hydrogenation and production of methanol based on high-temperature COâ electrolysis, are simulated using Aspen HYSYS. With Aspen Energy Analyzer, heat exchanger networks are optimized and minimal energy requirements are determined for the two different processes. The two processes are compared in terms of energy requirement and climate impact. It is found that the methanol production based on COâ electrolysis has an energy efficiency of 41%, almost double that of the COâ hydrogenation process provided that the required hydrogen is sourced from water electrolysis. The hydrogenation process produces more COâ when fossil fuel energy sources are used, but can result in more negative COâ emissions with renewable energies. The study reveals that both of the eTL processes can outperform the conventional fossil-fuel-based methanol production process in climate impacts as long as the renewable energy sources are implemented
Microscopic origin of granular ratcheting
Numerical simulations of assemblies of grains under cyclic loading exhibit
``granular ratcheting'': a small net deformation occurs with each cycle,
leading to a linear accumulation of deformation with cycle number. We show that
this is due to a curious property of the most frequently used models of the
particle-particle interaction: namely, that the potential energy stored in
contacts is path-dependent. There exist closed paths that change the stored
energy, even if the particles remain in contact and do not slide. An
alternative method for calculating the tangential force removes granular
ratcheting.Comment: 13 pages, 18 figure
Catalogue of the morphological features in the Spitzer Survey of Stellar Structure in Galaxies (SG)
A catalogue of the morphological features for the complete Spitzer Survey of
Stellar Structure in Galaxies (SG), including 2352 nearby galaxies, is
presented. The measurements are made using 3.6 m images, largely tracing
the old stellar population; at this wavelength the effects of dust are also
minimal. The measured features are the sizes, ellipticities, and orientations
of bars, rings, ringlenses, and lenses. Measured in a similar manner are also
barlenses (lens-like structures embedded in the bars), which are not lenses in
the usual sense, being rather the more face-on counterparts of the boxy/peanut
structures in the edge-on view. In addition, pitch angles of spiral arm
segments are measured for those galaxies where they can be reliably traced.
More than one pitch angle may appear for a single galaxy. All measurements are
made in a human-supervised manner so that attention is paid to each galaxy. We
used isophotal analysis, unsharp masking, and fitting ellipses to measured
structures. We find that the sizes of the inner rings and lenses normalized to
barlength correlate with the galaxy mass: the normalized sizes increase toward
the less massive galaxies; it has been suggested that this is related to the
larger dark matter content in the bar region in these systems. Bars in the low
mass galaxies are also less concentrated, likely to be connected to the mass
cut-off in the appearance of the nuclear rings and lenses. We also show
observational evidence that barlenses indeed form part of the bar, and that a
large fraction of the inner lenses in the non-barred galaxies could be former
barlenses in which the thin outer bar component has dissolved.Comment: 17 pages, 12 figures, accepted for publication in A&
Ballistic transport at room temperature in micrometer size multigraphene
The intrinsic values of the carriers mobility and density of the graphene
layers inside graphite, the well known structure built on these layers in the
Bernal stacking configuration, are not well known mainly because most of the
research was done in rather bulk samples where lattice defects hide their
intrinsic values. By measuring the electrical resistance through
microfabricated constrictions in micrometer small graphite flakes of a few tens
of nanometers thickness we studied the ballistic behavior of the carriers. We
found that the carriers' mean free path is micrometer large with a mobility
cm/Vs and a carrier density cm per graphene layer at room temperature. These distinctive
transport and ballistic properties have important implications for
understanding the values obtained in single graphene and in graphite as well as
for implementing this last in nanoelectronic devices.Comment: 6 pages, 6 figure
System Size Stochastic Resonance: General Nonequilibrium Potential Framework
We study the phenomenon of system size stochastic resonance within the
nonequilibrium potential's framework. We analyze three different cases of
spatially extended systems, exploiting the knowledge of their nonequilibrium
potential, showing that through the analysis of that potential we can obtain a
clear physical interpretation of this phenomenon in wide classes of extended
systems. Depending on the characteristics of the system, the phenomenon results
to be associated to a breaking of the symmetry of the nonequilibrium potential
or to a deepening of the potential minima yielding an effective scaling of the
noise intensity with the system size.Comment: LaTex, 24 pages and 9 figures, submitted to Phys. Rev.
Desalination effluents and the establishment of the non-indigenous skeleton shrimp Paracaprella pusilla Mayer, 1890 in the south-eastern Mediterranean
A decade long monitoring programme has revealed a flourishing population of the non-indigenous skeleton shrimp Paracaprella pusilla in the vicinity of outfalls of desalination plants off the Mediterranean coast of Israel. The first specimens were collected in 2010, thus predating all previously published records of this species in the Mediterranean Sea. A decade-long disturbance regime related to the construction and operation of the plants may have had a critical role in driving the population growth
Desalination effluents and the establishment of the non-indigenous skeleton shrimp Paracaprella pusilla Mayer, 1890 in the south-eastern Mediterranean
A decade long monitoring programme has revealed a flourishing population of the non-indigenous skeleton shrimp Paracaprella pusilla in the vicinity of outfalls of desalination plants off the Mediterranean coast of Israel. The first specimens were collected in 2010, thus predating all previously published records of this species in the Mediterranean Sea. A decade-long disturbance regime related to the construction and operation of the plants may have had a critical role in driving the population growth
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