388 research outputs found
Instabilities and disorder of the domain patterns in the systems with competing interactions
The dynamics of the domains is studied in a two-dimensional model of the
microphase separation of diblock copolymers in the vicinity of the transition.
A criterion for the validity of the mean field theory is derived. It is shown
that at certain temperatures the ordered hexagonal pattern becomes unstable
with respect to the two types of instabilities: the radially-nonsymmetric
distortions of the domains and the repumping of the order parameter between the
neighbors. Both these instabilities may lead to the transformation of the
regular hexagonal pattern into a disordered pattern.Comment: ReVTeX, 4 pages, 3 figures (postscript); submitted to Phys. Rev. Let
Non-meanfield deterministic limits in chemical reaction kinetics far from equilibrium
A general mechanism is proposed by which small intrinsic fluctuations in a
system far from equilibrium can result in nearly deterministic dynamical
behaviors which are markedly distinct from those realized in the meanfield
limit. The mechanism is demonstrated for the kinetic Monte-Carlo version of the
Schnakenberg reaction where we identified a scaling limit in which the global
deterministic bifurcation picture is fundamentally altered by fluctuations.
Numerical simulations of the model are found to be in quantitative agreement
with theoretical predictions.Comment: 4 pages, 4 figures (submitted to Phys. Rev. Lett.
Practical formula for the shear viscosity of Yukawa fluids
A simple practical formula for the shear viscosity coefficient of Yukawa
fluids is presented. This formula allows estimation of the shear viscosity in a
very extended range of temperatures, from the melting point to
times the melting temperature. It demonstrates reasonable agreement with the
available results from molecular dynamics simulations. Some aspects of the
temperature dependence of the shear viscosity and diffusion coefficients on
approaching the fluid-solid phase transition are discussed.Comment: 7 pages with 3 figure and 1 tabl
Self-replication and splitting of domain patterns in reaction-diffusion systems with fast inhibitor
An asymptotic equation of motion for the pattern interface in the
domain-forming reaction-diffusion systems is derived. The free boundary problem
is reduced to the universal equation of non-local contour dynamics in two
dimensions in the parameter region where a pattern is not far from the points
of the transverse instabilities of its walls. The contour dynamics is studied
numerically for the reaction-diffusion system of the FitzHugh-Nagumo type. It
is shown that in the asymptotic limit the transverse instability of the
localized domains leads to their splitting and formation of the multidomain
pattern rather than fingering and formation of the labyrinthine pattern.Comment: 9 pages (ReVTeX), 5 figures (postscript). To be published in Phys.
Rev.
Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies
We use cosmological simulations from the Feedback In Realistic Environments
(FIRE) project, which implement a comprehensive set of stellar feedback
processes, to study ultra-violet (UV) metal line emission from the
circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover
the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of
Lyman break galaxies. Of the transitions we analyze, the low-ionization C III
(977 A) and Si III (1207 A) emission lines are the most luminous, with C IV
(1548 A) and Si IV (1394 A) also showing interesting spatially-extended
structures. The more massive halos are on average more UV-luminous. The UV
metal line emission from galactic halos in our simulations arises primarily
from collisionally ionized gas and is strongly time variable, with
peak-to-trough variations of up to ~2 dex. The peaks of UV metal line
luminosity correspond closely to massive and energetic mass outflow events,
which follow bursts of star formation and inject sufficient energy into
galactic halos to power the metal line emission. The strong time variability
implies that even some relatively low-mass halos may be detectable. Conversely,
flux-limited samples will be biased toward halos whose central galaxy has
recently experienced a strong burst of star formation. Spatially-extended UV
metal line emission around high-redshift galaxies should be detectable by
current and upcoming integral field spectrographs such as the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web
Imager (KCWI).Comment: 16 pages, 8 figures, accepted for publication in MNRA
Steady operation of the electric drive of pipeline armature in the emergency situation at low ambient temperatures
This scientific work is devoted to the study of the electric drive operation of pipeline armature at low ambient temperatures. Hit of moisture into reducer and rare inclusions in operation of locking regulator are led to curdling lubricant that causes the increased wear of mechanical knots. There is a probability of freezing mechanical components; it leads to emergency situations. The problem of improving working efficiency of the electric drive of shut-off regulating armature at low ambient temperatures of the environment is solved in this work. A simulation model of the GUSAR electric drive was developed to solve this problem. Studies of the simulation model show the need to limit the torque increase rate on a drive motor shaft. The algorithm of setting of PI speed controller to obtain acceptable transient processes is suggested. Recommendations for the use of the algorithm in the microprocessor control system of electric drive are proposed. It is shown that the electric drive operation algorithm with torque increasing limitation on the motor shaft will be smoothly working off the perturbing actions that occur in pipeline armature
Synthesis and characterisation of nanocrystalline ZrN PVD coatings on AISI 430 stainless steel
The nanocrystalline films of zirconium nitride have been synthesized using ion-plasma vacuum-arc deposition technique in combination with high-frequency discharge (RF) on AISI 430 stainless steel at 150oC. Structure examinations X-ray fluorescent analysis (XRF), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) with microanalysis (EDS), and transmission electron microscopy (TEM), nanoidentation method β were performed to study phase and chemical composition, surface morphology, microstructure and nanohardness of coatings. The developed technology provided low-temperature coatings synthesis, minimized discharge breakdown decreasing formation of macroparticles (MPs) and allowed to deposit ZrN coatings with hardness variation 26.6β¦31.5 GPa. It was revealed that ZrN single-phase coatings of cubic modification with finecrystalline grains of 20 nm in size were formed
Domain structure of bulk ferromagnetic crystals in applied fields near saturation
We investigate the ground state of a uniaxial ferromagnetic plate with
perpendicular easy axis and subject to an applied magnetic field normal to the
plate. Our interest is the asymptotic behavior of the energy in macroscopically
large samples near the saturation field. We establish the scaling of the
critical value of the applied field strength below saturation at which the
ground state changes from the uniform to a branched domain magnetization
pattern and the leading order scaling behavior of the minimal energy.
Furthermore, we derive a reduced sharp-interface energy giving the precise
asymptotic behavior of the minimal energy in macroscopically large plates under
a physically reasonable assumption of small deviations of the magnetization
from the easy axis away from domain walls. On the basis of the reduced energy,
and by a formal asymptotic analysis near the transition, we derive the precise
asymptotic values of the critical field strength at which non-trivial
minimizers (either local or global) emerge. The non-trivial minimal energy
scaling is achieved by magnetization patterns consisting of long slender
needle-like domains of magnetization opposing the applied fieldComment: 38 pages, 7 figures, submitted to J. Nonlin. Sci
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