1,458 research outputs found
Evidence for contact delocalization in atomic scale friction
We analyze an advanced two-spring model with an ultra-low effective tip mass
to predict nontrivial and physically rich 'fine structure' in the atomic
stick-slip motion in Friction Force Microscopy (FFM) experiments. We
demonstrate that this fine structure is present in recent, puzzling
experiments. This shows that the tip apex can be completely or partially
delocalized, thus shedding new light on what is measured in FFM and, possibly,
what can happen with the asperities that establish the contact between
macroscopic sliding bodies.Comment: 4 pages text and 3 figure
The 2nd order renormalization group flow for non-linear sigma models in 2 dimensions
We show that for two dimensional manifolds M with negative Euler
characteristic there exists subsets of the space of smooth Riemannian metrics
which are invariant and either parabolic or backwards-parabolic for the 2nd
order RG flow. We also show that solutions exists globally on these sets.
Finally, we establish the existence of an eternal solution that has both a UV
and IR limit, and passes through regions where the flow is parabolic and
backwards-parabolic
On the L_p-solvability of higher order parabolic and elliptic systems with BMO coefficients
We prove the solvability in Sobolev spaces for both divergence and
non-divergence form higher order parabolic and elliptic systems in the whole
space, on a half space, and on a bounded domain. The leading coefficients are
assumed to be merely measurable in the time variable and have small mean
oscillations with respect to the spatial variables in small balls or cylinders.
For the proof, we develop a set of new techniques to produce mean oscillation
estimates for systems on a half space.Comment: 44 pages, introduction revised, references expanded. To appear in
Arch. Rational Mech. Ana
Determination of the input filter parameters of the active rectifier with a fixed modulation frequency
Goal. Development of a methodology for calculating the parameters of the active rectifier-voltage source input filter operating with a fixed modulation frequency to ensure electromagnetic compatibility with the supply network acceptable by standards at minimum values of the input inductance and checking its main characteristics on a mathematical model. Methodology. The authors have developed a methodology for calculating the parameters of the input filter of an active rectifier-voltage source. The calculation results are verified on the constructed mathematical model of a frequency converter, the scheme of which is an active rectifier and an autonomous voltage inverter. A series of experiments was carried out on a mathematical model to study the dependence of the total harmonic distortion of current and mains voltage on the value of the input inductance for various parameters of the input filter. Results. The structure and calculation procedure the input filter of an active rectifier operating with a fixed modulation frequency are proposed. The simulation results showed that the inclusion of a filter at the input of the active rectifier significantly improves its electromagnetic compatibility with the supply network in the entire range of variation of the input inductance of the circuit and makes it possible to achieve the values of the total harmonic distortion permissible by the norms. Originality. A structure and a calculation procedure the input filter of an active rectifier-voltage source operating with a fixed modulation frequency are proposed. Practical significance. The dependencies obtained in the article allow us to evaluate the relationship between the parameters of the filter elements and its characteristics among themselves and come to a compromise between them when designing a scheme for specific technical conditions.Π ΡΡΠ°ΡΡΡ Π·Π°ΠΏΡΠΎΠΏΠΎΠ½ΠΎΠ²Π°Π½ΠΎ ΡΡΡΡΠΊΡΡΡΡ ΡΠ° ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΡ ΡΠΎΠ·ΡΠ°Ρ
ΡΠ½ΠΊΡ Π²Ρ
ΡΠ΄Π½ΠΎΠ³ΠΎ ΡΡΠ»ΡΡΡΡ Π°ΠΊΡΠΈΠ²Π½ΠΎΠ³ΠΎ Π²ΠΈΠΏΡΡΠΌΠ»ΡΡΠ°-Π΄ΠΆΠ΅ΡΠ΅Π»Π° Π½Π°ΠΏΡΡΠ³ΠΈ, ΡΠΊΠΈΠΉ ΠΏΡΠ°ΡΡΡ Π· ΡΡΠΊΡΠΎΠ²Π°Π½ΠΎΡ ΡΠ°ΡΡΠΎΡΠΎΡ ΠΌΠΎΠ΄ΡΠ»ΡΡΡΡ. ΠΡΡΠΈΠΌΠ°Π½Ρ Π·Π°Π»Π΅ΠΆΠ½ΠΎΡΡΡ Π΄ΠΎΠ·Π²ΠΎΠ»ΡΡΡΡ ΠΎΡΡΠ½ΠΈΡΠΈ Π²Π·Π°ΡΠΌΠΎΠ·Π²'ΡΠ·ΠΎΠΊ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΡΠ² Π΅Π»Π΅ΠΌΠ΅Π½ΡΡΠ² ΡΡΠ»ΡΡΡΠ° ΡΠ° ΠΉΠΎΠ³ΠΎ Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ ΠΌΡΠΆ ΡΠΎΠ±ΠΎΡ ΡΠ° Π΄ΡΠΉΡΠΈ ΠΊΠΎΠΌΠΏΡΠΎΠΌΡΡΡ ΠΌΡΠΆ Π½ΠΈΠΌΠΈ ΠΏΡΠ΄ ΡΠ°Ρ ΠΏΡΠΎΠ΅ΠΊΡΡΠ²Π°Π½Π½Ρ ΡΡ
Π΅ΠΌΠΈ Π΄Π»Ρ ΠΊΠΎΠ½ΠΊΡΠ΅ΡΠ½ΠΈΡ
ΡΠ΅Ρ
Π½ΡΡΠ½ΠΈΡ
ΡΠΌΠΎΠ². Π Π΅Π·ΡΠ»ΡΡΠ°ΡΠΈ ΠΌΠΎΠ΄Π΅Π»ΡΠ²Π°Π½Π½Ρ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ, ΡΠΎ Π²ΠΊΠ»ΡΡΠ΅Π½Π½Ρ Π΄ΠΎΠ΄Π°ΡΠΊΠΎΠ²ΠΎΠ³ΠΎ Π»Π°Π½ΡΡΠ³Π° RC ΡΡΠ»ΡΡΡΠ° Π½Π° Π²Ρ
ΠΎΠ΄Ρ Π°ΠΊΡΠΈΠ²Π½ΠΎΠ³ΠΎ Π²ΠΈΠΏΡΡΠΌΠ»ΡΡΠ° ΡΡΡΠΎΡΠ½ΠΎ ΠΏΠΎΠΊΡΠ°ΡΡΡ ΠΉΠΎΠ³ΠΎ Π΅Π»Π΅ΠΊΡΡΠΎΠΌΠ°Π³Π½ΡΡΠ½Ρ ΡΡΠΌΡΡΠ½ΡΡΡΡ Π· ΠΌΠ΅ΡΠ΅ΠΆΠ΅Ρ ΠΆΠΈΠ²Π»Π΅Π½Π½Ρ Ρ Π²ΡΡΠΎΠΌΡ Π΄ΡΠ°ΠΏΠ°Π·ΠΎΠ½Ρ Π·ΠΌΡΠ½ΠΈ Π²Ρ
ΡΠ΄Π½ΠΎΡ ΡΠ½Π΄ΡΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΡΡ
Π΅ΠΌΠΈ ΡΠ° Π΄ΠΎΠ·Π²ΠΎΠ»ΡΡ Π΄ΠΎΡΡΠ³Π°ΡΠΈ Π΄ΠΎΠΏΡΡΡΠΈΠΌΠΈΡ
Π½ΠΎΡΠΌΠ°ΠΌΠΈ Π·Π½Π°ΡΠ΅Π½Ρ ΡΡΠΌΠ°ΡΠ½ΠΎΠ³ΠΎ ΠΊΠΎΠ΅ΡΡΡΡΡΠ½ΡΡ Π³Π°ΡΠΌΠΎΠ½ΡΡΠ½ΠΈΡ
ΡΠΏΠΎΡΠ²ΠΎΡΠ΅Π½Ρ
Non-affine geometrization can lead to nonphysical instabilities
Geometrization of dynamics consists of representing trajectories by geodesics
on a configuration space with a suitably defined metric. Previously, efforts
were made to show that the analysis of dynamical stability can also be carried
out within geometrical frameworks, by measuring the broadening rate of a bundle
of geodesics. Two known formalisms are via Jacobi and Eisenhart metrics. We
find that this geometrical analysis measures the actual stability when the
length of any geodesic is proportional to the corresponding time interval. We
prove that the Jacobi metric is not always an appropriate parametrization by
showing that it predicts chaotic behavior for a system of harmonic oscillators.
Furthermore, we show, by explicit calculation, that the correspondence between
dynamical- and geometrical-spread is ill-defined for the Jacobi metric. We find
that the Eisenhart dynamics corresponds to the actual tangent dynamics and is
therefore an appropriate geometrization scheme.Comment: Featured on the Cover of the Journal. 9 pages, 6 figures:
http://iopscience.iop.org/1751-8121/48/7/07510
Largest Lyapunov Exponent for Many Particle Systems at Low Densities
The largest Lyapunov exponent for a dilute gas with short range
interactions in equilibrium is studied by a mapping to a clock model, in which
every particle carries a watch, with a discrete time that is advanced at
collisions. This model has a propagating front solution with a speed that
determines , for which we find a density dependence as predicted by
Krylov, but with a larger prefactor. Simulations for the clock model and for
hard sphere and hard disk systems confirm these results and are in excellent
mutual agreement. They show a slow convergence of with increasing
particle number, in good agreement with a prediction by Brunet and Derrida.Comment: 4 pages, RevTeX, 2 Figures (encapsulated postscript). Submitted to
Phys. Rev. Let
ΠΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΡΠ°Π±ΠΎΡΡ Π°ΠΊΡΠΈΠ²Π½ΠΎΠ³ΠΎ ΡΠΏΡΠ°Π²Π»ΡΠ΅ΠΌΠΎΠ³ΠΎ Π²ΡΠΏΡΡΠΌΠΈΡΠ΅Π»Ρ Π² ΡΠ΅ΠΆΠΈΠΌΠ΅ ΠΈΡΠΊΠ°ΠΆΠ΅Π½ΠΈΡ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ ΠΏΠΈΡΠ°ΡΡΠ΅ΠΉ ΡΠ΅ΡΠΈ
Goal. Checking the efficiency of the active rectifier with differences types of control systems in conditions of deep voltage distortions of a three-phase three-wire supply network. Methodology. The authors have used the Matlab/Simulink software environment to create a model of an active rectifier with various types of control systems as part of a frequency electric drive. We performed a series of simulations of the operating modes of an active rectifier with various control systems when the supply voltage is distorted. Results. When the active rectifier is operating in an unregulated mode, the distortions of the current and mains voltage exceed the maximum permissible values. The quality indicators of the mains current and mains voltage are significantly higher than the normally permissible values. In the absence of voltage distortions in the supply network, the operation of the active rectifier can effectively eliminate the distortions of the mains current, regardless of the type of control system of the active rectifier. In conditions of deep distortions of the supply network voltage, the operation of an active rectifier with a vector control system is more efficient than with a parametric control system. Originality. Criteria for determining the quality of consumed electricity at the connection point of the circuit are proposed. Practical significance. Recommendations have been developed for the use of active rectifier control systems when working with a distorted power supply voltage.Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½Π° ΡΠ°Π±ΠΎΡΠ° Π°ΠΊΡΠΈΠ²Π½ΠΎΠ³ΠΎ ΡΠΏΡΠ°Π²Π»ΡΠ΅ΠΌΠΎΠ³ΠΎ Π²ΡΠΏΡΡΠΌΠΈΡΠ΅Π»Ρ-ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ° Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ (ΠΠΠΠ) Ρ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΈ Π²Π΅ΠΊΡΠΎΡΠ½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΠ°ΠΌΠΈ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ, ΡΠ°Π±ΠΎΡΠ°ΡΡΠΈΡ
Ρ ΡΠΈΠΊΡΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΡΠ°ΡΡΠΎΡΠΎΠΉ ΠΌΠΎΠ΄ΡΠ»ΡΡΠΈΠΈ Π² ΡΠΎΡΡΠ°Π²Π΅ ΡΠ»Π΅ΠΊΡΡΠΎΠΏΡΠΈΠ²ΠΎΠ΄Π° ΠΌΠΎΡΠ½ΠΎΡΡΡΡ 315 ΠΊΠΡ ΠΏΠ°ΡΠ°Π»Π»Π΅Π»ΡΠ½ΠΎ Ρ Π΄ΡΡΠ³ΠΈΠΌΠΈ Π½Π°Π³ΡΡΠ·ΠΊΠ°ΠΌΠΈ Π² ΡΡΠ»ΠΎΠ²ΠΈΡΡ
ΠΈΡΠΊΠ°ΠΆΡΠ½Π½ΠΎΠ³ΠΎ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ° ΠΏΠΈΡΠ°Π½ΠΈΡ. ΠΡΠΏΠΎΠ»Π½Π΅Π½ΠΎ ΠΌΠ°ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΠΠΠ Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΡΠΌΠΈ ΡΠΈΡΡΠ΅ΠΌΠ°ΠΌΠΈ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ. ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Ρ ΠΊΡΠΈΡΠ΅ΡΠΈΠΈ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ ΠΊΠ°ΡΠ΅ΡΡΠ²Π° ΠΏΠΎΡΡΠ΅Π±Π»ΡΠ΅ΠΌΠΎΠΉ ΡΠ»Π΅ΠΊΡΡΠΎΡΠ½Π΅ΡΠ³ΠΈΠΈ Π² ΡΠΎΡΠΊΠ΅ ΠΏΠΎΠ΄ΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΡΡ
Π΅ΠΌΡ. Π Π°Π·ΡΠ°Π±ΠΎΡΠ°Π½Ρ ΡΠ΅ΠΊΠΎΠΌΠ΅Π½Π΄Π°ΡΠΈΠΈ ΠΏΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ ΡΠΈΡΡΠ΅ΠΌ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΠΠΠΠ ΠΏΡΠΈ ΡΠ°Π±ΠΎΡΠ΅ Ρ ΠΈΡΠΊΠ°ΠΆΡΠ½Π½ΡΠΌ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΠ΅ΠΌ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ° ΠΏΠΈΡΠ°Π½ΠΈΡ
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