Search results for "fluid"

Switching dynamics of dark-pulse Kerr frequency comb states in optical microresonators

2021

Dissipative Kerr solitons are localized structures that exist in nonlinear optical cavities. They lead to the formation of microcombs - chip-scale frequency combs that could facilitate precision frequency synthesis and metrology by capitalizing on advances in silicon photonics. Previous demonstrations have mainly focused on anomalous dispersion cavities. Notwithstanding, localized structures also exist in the normal dispersion regime in the form of circulating dark pulses, but their physical dynamics is far from being understood. Here, we explore dark-pulse Kerr combs generated in normal dispersion optical microresonators and report the discovery of reversible switching between coherent dar…

Numerical study of the primitive equations in the small viscosity regime

2018

In this paper we study the flow dynamics governed by the primitive equations in the small viscosity regime. We consider an initial setup consisting on two dipolar structures interacting with a no slip boundary at the bottom of the domain. The generated boundary layer is analyzed in terms of the complex singularities of the horizontal pressure gradient and of the vorticity generated at the boundary. The presence of complex singularities is correlated with the appearance of secondary recirculation regions. Two viscosity regimes, with different qualitative properties, can be distinguished in the flow dynamics.

Singular behavior of a vortex layer in the zero thickness limit

2017

The aim of this paper is to study the Euler dynamics of a 2D periodic layer of non uniform vorticity. We consider the zero thickness limit and we compare the Euler solution with the vortex sheet evolution predicted by the Birkhoff-Rott equation. The well known process of singularity formation in shape of the vortex sheet correlates with the appearance of several complex singularities in the Euler solution with the vortex layer datum. These singularities approach the real axis and are responsible for the roll-up process in the layer motion.

Mathematical background of the Riga dynamo experiment

2013

The Riga dynamo experiment is a laboratory model of the natural process that is responsible for all environmental magnetic-fields which are generated without human interference. This applies to the field of the Earth, the Sun, stars, and even galaxies which are produced by intense motions of large volumes of good electro-conducting fluids. For our experiment, we use molten sodium – the best liquid electro-conductor available in the laboratory. Approximately 2 m3 of molten sodium are filled into a prolonged cylinder, at the top of which rotates a propeller powered by 200 kW from two motors. The cylinder is divided by thin coaxial inner walls into three parts: in the inner tube the propeller …

A Coupled Solid-Fluid Method for Modeling Subduction

2007

International audience; We present a novel dynamic approach for solid/fluid coupling by joining two different numerical methods: Boundary Element Method (BEM) and Finite Element Method (FEM). FEM results describe the thermo-mechanical evolution of the solid while the fluid is solved with the BEM. The bidirectional feedback between the two domains evolves along a Lagrangian interface where the FEM domain is embedded inside the BEM domain. The feedback between the two codes is based on the calculation of a specific drag tensor for each boundary/finite element. The approach is presented here to solve the complex problem of the descent of a cold subducting oceanic plate into a hot fluid like ma…

Expressions of “fast” and “slow” chameleon dressed states in Autler–Townes spectra of alkali‐metal atoms

2021

Imaging of SN 1993J

2005

SN 1993J has been imaged with VLBI, and its angular expansion monitored, for almost ten years. The images show shell-like radio structures with almost circular symmetry. SN 1993J expands according to models of shock excited emission. The angular expansion has a changing deceleration rate and is best modeled with two different slopes. The swept-up mass estimate at an age of 3159 days (∼0.4 M⨀), comparable to the low-mass envelope, favors a binary scenario. The observed spectral index of SN 1993J has slowly flattened since age 1000 days onward (α has changed from −1 to −0.67 at an age of 2820 days).

Spectral analysis of two-dimensional Bose-Hubbard models

2016

One-dimensional Bose-Hubbard models are well known to obey a transition from regular to quantum-chaotic spectral statistics. We are extending this concept to relatively simple two-dimensional many-body models. Also in two dimensions a transition from regular to chaotic spectral statistics is found and discussed. In particular, we analyze the dependence of the spectral properties on the bond number of the two-dimensional lattices and the applied boundary conditions. For maximal connectivity, the systems behave most regularly in agreement with the applicability of mean-field approaches in the limit of many nearest-neighbor couplings at each site.

Time-optimal control of the purification of a qubit in contact with a structured environment

2019

We investigate the time-optimal control of the purification of a qubit interacting with a structured environment, consisting of a strongly coupled two-level defect in interaction with a thermal bath. On the basis of a geometric analysis, we show for weak and strong interaction strengths that the optimal control strategy corresponds to a qubit in resonance with the reservoir mode. We investigate under which conditions qubit coherence and correlation between the qubit and the environment can speed up the control process.

Kinetics of Domain Growth and Aging in a Two-Dimensional Off-lattice System

2020

We have used molecular dynamics simulations for a comprehensive study of phase separation in a two-dimensional single component off-lattice model where particles interact through the Lennard-Jones potential. Via state-of-the-art methods we have analyzed simulation data on structure, growth and aging for nonequilibrium evolutions in the model. These data were obtained following quenches of well-equilibrated homogeneous configurations, with density close to the critical value, to various temperatures inside the miscibility gap, having vapor-"liquid" as well as vapor-"solid" coexistence. For the vapor-liquid phase separation we observe that $\ell$, the average domain length, grows with time ($…