63,996 research outputs found
Thermodynamic consistency of liquid-gas lattice Boltzmann simulations
Lattice Boltzmann simulations have been very successful in simulating
liquid-gas and other multi-phase fluid systems. However, the underlying second
order analysis of the equation of motion has long been known to be insufficient
to consistently derive the fourth order terms that are necessary to represent
an extended interface. These same terms are also responsible for thermodynamic
consistency, i.e. to obtain a true equilibrium solution with both a constant
chemical potential and a constant pressure. In this article we present an
equilibrium analysis of non-ideal lattice Boltzmann methods of sufficient order
to identify those higher order terms that lead to a lack of thermodynamic
consistency. We then introduce a thermodynamically consistent forcing method.Comment: 12 pages, 8 figure
Three-dimensional pantograph for use in hazardous environments
Material measurement device is used with radioactive probes which can be approached only to distance of 3 feet. Tracer-following unit is capable of precisely controlled movement in X-Y-Z planes. Pantograph is usable in industrial processes involving chemical corrosives, poisons, and bacteriological hazards, as well as nuclear applications
Evolution of Feedback Loops in Oscillatory Systems
Feedback loops are major components of biochemical systems. Many systems show
multiple such (positive or negative) feedback loops. Nevertheless, very few
quantitative analyses address the question how such multiple feedback loops
evolved. Based on published models from the mitotic cycle in embryogenesis, we
build a few case studies. Using a simple core architecture (transcription,
phosphorylation and degradation), we define oscillatory models having either
one positive feedback or one negative feedback, or both loops. With these
models, we address the following questions about evolvability: could a system
evolve from a simple model to a more complex one with a continuous transition
in the parameter space? How do new feedback loops emerge without disrupting the
proper function of the system? Our results show that progressive formation of a
second feedback loop is possible without disturbing existing oscillatory
behavior. For this process, the parameters of the system have to change during
evolution to maintain predefined properties of oscillations like period and
amplitude.Comment: Proceedings of the 2009 FOSBE conference in Denver, CO, USA. 4 page
Propagating plane harmonic waves through finite length plates of variable thickness using finite element techniques
An analysis is given using finite element techniques which addresses the propagaton of a uniform incident pressure wave through a finite diameter axisymmetric tapered plate immersed in a fluid. The approach utilized in developing a finite element solution to this problem is based upon a technique for axisymmetric fluid structure interaction problems. The problem addressed is that of a 10 inch diameter axisymmetric fixed plate totally immersed in a fluid. The plate increases in thickness from approximately 0.01 inches thick at the center to 0.421 inches thick at a radius of 5 inches. Against each face of the tapered plate a cylindrical fluid volume was represented extending five wavelengths off the plate in the axial direction. The outer boundary of the fluid and plate regions were represented as a rigid encasement cylinder as was nearly the case in the physical problem. The primary objective of the analysis is to determine the form of the transmitted pressure distribution on the downstream side of the plate
The Superconducting Toroid for the New International AXion Observatory (IAXO)
IAXO, the new International AXion Observatory, will feature the most
ambitious detector for solar axions to date. Axions are hypothetical particles
which were postulated to solve one of the puzzles arising in the standard model
of particle physics, namely the strong CP (Charge conjugation and Parity)
problem. This detector aims at achieving a sensitivity to the coupling between
axions and photons of one order of magnitude beyond the limits of the current
detector, the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a
high-magnetic field distributed over a very large volume to convert solar
axions to detectable X-ray photons. Inspired by the ATLAS barrel and end-cap
toroids, a large superconducting toroid is being designed. The toroid comprises
eight, one meter wide and twenty one meters long racetrack coils. The assembled
toroid is sized 5.2 m in diameter and 25 m in length and its mass is about 250
tons. The useful field in the bores is 2.5 T while the peak magnetic field in
the windings is 5.4 T. At the operational current of 12 kA the stored energy is
500 MJ. The racetrack type of coils are wound with a reinforced Aluminum
stabilized NbTi/Cu cable and are conduction cooled. The coils optimization is
shortly described as well as new concepts for cryostat, cold mass, supporting
structure and the sun tracking system. Materials selection and sizing,
conductor, thermal loads, the cryogenics system and the electrical system are
described. Lastly, quench simulations are reported to demonstrate the system's
safe quench protection scheme.Comment: To appear in IEEE Trans. Appl. Supercond. MT 23 issue. arXiv admin
note: substantial text overlap with arXiv:1308.2526, arXiv:1212.463
New Superconducting Toroidal Magnet System for IAXO, the International AXion Observatory
Axions are hypothetical particles that were postulated to solve one of the
puzzles arising in the standard model of particle physics, namely the strong CP
(Charge conjugation and Parity) problem. The new International AXion
Observatory (IAXO) will incorporate the most promising solar axions detector to
date, which is designed to enhance the sensitivity to the axion-photon coupling
by one order of magnitude beyond the limits of the current state-of-the-art
detector, the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a
high-magnetic field distributed over a very large volume to convert solar
axions into X-ray photons. Inspired by the successful realization of the ATLAS
barrel and end-cap toroids, a very large superconducting toroid is currently
designed at CERN to provide the required magnetic field. This toroid will
comprise eight, one meter wide and twenty one meter long, racetrack coils. The
system is sized 5.2 m in diameter and 25 m in length. Its peak magnetic field
is 5.4 T with a stored energy of 500 MJ. The magnetic field optimization
process to arrive at maximum detector yield is described. In addition,
materials selection and their structure and sizing has been determined by force
and stress calculations. Thermal loads are estimated to size the necessary
cryogenic power and the concept of a forced flow supercritical helium based
cryogenic system is given. A quench simulation confirmed the quench protection
scheme.Comment: Accepted for publication in Adv. Cryo. Eng. (CEC/ICMC 2013 special
issue
Comment on "Regularizing capacity of metabolic networks"
In a recent paper, Marr, Muller-Linow and Hutt [Phys. Rev. E 75, 041917
(2007)] investigate an artificial dynamic system on metabolic networks. They
find a less complex time evolution of this dynamic system in real networks,
compared to networks of reference models. The authors argue that this suggests
that metabolic network structure is a major factor behind the stability of
biochemical steady states. We reanalyze the same kind of data using a dynamic
system modeling actual reaction kinetics. The conclusions about stability, from
our analysis, are inconsistent with those of Marr et al. We argue that this
issue calls for a more detailed type of modeling
Gas gain and signal length measurements with a triple-GEM at different pressures of Ar-, Kr- and Xe-based gas mixtures
We investigate the gas gain behaviour of a triple-GEM configuration in gas
mixtures of argon, krypton and xenon with ten and thirty percent of carbon
dioxide at pressures between 1 and 3 bar. Since the signal widths affect the
dead time behaviour of the detector we present signal length measurements to
evaluate the use of the triple-GEM in time-resolved X-ray imaging.Comment: 19 pages, 21 figures, revised version, accepted for publication in
Nucl. Instr. and Meth.
Phase relaxation of Faraday surface waves
Surface waves on a liquid air interface excited by a vertical vibration of a
fluid layer (Faraday waves) are employed to investigate the phase relaxation of
ideally ordered patterns. By means of a combined frequency-amplitude modulation
of the excitation signal a periodic expansion and dilatation of a square wave
pattern is generated, the dynamics of which is well described by a Debye
relaxator. By comparison with the results of a linear theory it is shown that
this practice allows a precise measurement of the phase diffusion constant.Comment: 5 figure
The last glacial-interglacial cycle in Lake Ohrid (Macedonia/Albania): testing diatom response to climate
Lake Ohrid is a site of global importance for palaeoclimate research. This study presents results of diatom analysis of a ca. 136 ka sequence, Co1202, from the northeast of the lake basin. It offers the opportunity to test diatom response across two glacial-interglacial transitions and within the Last Glacial, while setting up taxonomic protocols for future research. The results are outstanding in demonstrating the sensitivity of diatoms to climate change, providing proxy evidence for temperature change marked by glacial-interglacial shifts between the dominant planktonic taxa, Cyclotella fottii and C. ocellata, and exact correlation with geochemical proxies to mark the start of the Last Interglacial at ca. 130 ka. Importantly, diatoms show much stronger evidence in this site for warming during MIS3 than recorded in other productivity-related proxies, peaking at ca. 39 ka, prior to the extreme conditions of the Last Glacial maximum. In the light of the observed patterns, and from the results of analysis of early Holocene sediments from a second core, Lz1120, the lack of a response to Late Glacial and early Holocene warming from ca. 15-7.4 ka suggests the Co1202 sequence may be compromised during this phase. After ca. 7.4 ka, there is evidence for enhanced nutrient enrichment compared to the Last Interglacial, following by a post-Medieval cooling trend. Taxonomically, morphological variability in C. fottii shows no clear trends linked to climate, but an intriguing change in central area morphology occurs after ca. 48.7 ka, coincident with a tephra layer. In contrast, C. ocellata shows morphological variation in the number of ocelli between interglacials, suggesting climatically-forced variation or evolutionary selection pressure. The application of a simple dissolution index does not track preservation quality very effectively, underlining the importance of diatom concentration data in future studies
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