scholarly journals Onset of nanoscale dissipation in superfluid He4 at zero temperature: Role of vortex shedding and cavitation

2017 ◽  
Vol 96 (6) ◽  
Author(s):  
Francesco Ancilotto ◽  
Manuel Barranco ◽  
Jussi Eloranta ◽  
Martí Pi
Keyword(s):  
Vortex Shedding ◽  
Zero Temperature

scholarly journals Thrust Force Generated by Heaving Motion of a Plate: The Role of Vortex-Induced Force

2021 ◽  
Author(s):  
Kazuo Matsuuchi
Keyword(s):  
Vortex Shedding ◽  
Thrust Force ◽  
Unsteady Motion ◽  
Force Generation ◽  
Thrust Coefficient ◽  
Momentum Change ◽  
Vortex Element ◽  
Motion Characteristics ◽  
Vortex Systems

To understand the force acting on birds, insects, and fish, we take heaving motion as a simple example. This motion might deviate from the real one. However, since the mechanism of force generation is the vortex shedding due to the motion of an object, the heaving motion is important for understanding the force generated by unsteady motion. The vortices released from the object are closely related to the motion characteristics. To understand the force acting on an object, information about momentum change is necessary. However, in vortex systems, it is impossible to estimate the usual momentum. Instead of the momentum, the “virtual momentum,” or the impulse, is needed to generate the force. For calculating the virtual momentum, we traced all vortices over a whole period, which was carried out by using the vortex-element method. The force was then calculated based on the information on the vortices. We derived the thrust coefficient as a function of the ratio of the heaving to travelling velocity.

scholarly journals Fundamental dissipation due to bound fermions in the zero-temperature limit

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Autti ◽  
S. L. Ahlstrom ◽  
R. P. Haley ◽  
A. Jennings ◽  
G. R. Pickett ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Ground State ◽  
Bound States ◽  
Bound State ◽  
Temperature Limit ◽  
Pair Breaking ◽  
Zero Temperature ◽  
Andreev Bound States ◽  
Macroscopic Object

Abstract The ground state of a fermionic condensate is well protected against perturbations in the presence of an isotropic gap. Regions of gap suppression, surfaces and vortex cores which host Andreev-bound states, seemingly lift that strict protection. Here we show that in superfluid 3He the role of bound states is more subtle: when a macroscopic object moves in the superfluid at velocities exceeding the Landau critical velocity, little to no bulk pair breaking takes place, while the damping observed originates from the bound states covering the moving object. We identify two separate timescales that govern the bound state dynamics, one of them much longer than theoretically anticipated, and show that the bound states do not interact with bulk excitations.

PAIRWISE ENTANGLEMENT IN THE N-QUBIT XX MODEL WITH DZYALOSHINSKI–MORIYA INTERACTION AND MAGNETIC FIELD

2011 ◽  
Vol 25 (16) ◽  
pp. 2135-2148
Author(s):  
BIN ZHOU
Keyword(s):  
Magnetic Field ◽  
Critical Temperature ◽  
Magnetic Fields ◽  
Nearest Neighbor ◽  
Zero Temperature ◽  
Thermal Entanglement ◽  
Dm Interaction ◽  
Xx Model ◽  
Moriya Interaction

In this paper, we investigate the role of Dzyaloshinski–Moriya (DM) interaction in the pairwise entanglement in the three- and four-qubit XX models with magnetic field. In the four-qubit model, the pairwise entanglements of two nearest-neighbor qubits and two next-neighbor qubits are investigated, respectively. The dependences of the critical temperature at which the pairwise thermal entanglement disappears on DM interaction and magnetic fields are studied in details. At zero temperature, the entanglement can undergo sudden changes with adjustment of the parameters, and the general results of the concurrence are obtained in all cases.

What is the Role of the Stagnation Region in Karman Vortex Shedding?

2011 ◽  
Vol 18 (3) ◽  
pp. 361-370 ◽  
Author(s):  
Grzegorz Pankanin
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Flow Visualisation ◽  
Information Channel ◽  
Hot Wire ◽  
Stagnation Region ◽  
Karman Vortex ◽  
Experimental Findings ◽  
The Relationship

What is the Role of the Stagnation Region in Karman Vortex Shedding?This paper is devoted to the problem of the appearance of a stagnation region during Karman vortex shedding. This particular phenomenon has been addressed by G. Birkhoff in his model of vortices generation. Experimental results obtained by various research methods confirm the existence of a stagnation region. The properties of this stagnation region have been described based on experimental findings involving flow visualisation and hot-wire anemometry. Special attention has been paid to the relationship between the existence of a slit in the bluff body and the size of the stagnation region. The slit takes over the role of the stagnation region as an information channel for generating vortices.

DEPENDENCE OF THE PEAK EFFECT ON THE DENSITY OF PINNING SITES

2008 ◽  
Vol 22 (31) ◽  
pp. 3125-3134 ◽  
Author(s):  
I. M. OBAIDAT ◽  
U. AL KHAWAJA ◽  
M. BENKRAOUDA
Keyword(s):  
Critical Current Density ◽  
Driving Force ◽  
Peak Effect ◽  
Molecular Dynamic Simulations ◽  
Zero Temperature ◽  
Relative Height ◽  
Dynamic Simulations ◽  
One Dimensional ◽  
Matching Field

We have investigated the role of pinning density on the properties of the peak effect in the critical current density in superconducting systems. This study was conducted using a series of molecular dynamic simulations on two systems of nanostructures of periodic square arrays of pinning sites with different pining densities. We have found that the peak occurred in both systems only at zero temperature and for specific values of pinning strength. The most interesting result was that in both systems, the peak was found to occur only at nearly 0.5 fraction of the first matching field for all values of pinning strength. The properties of the peak were found to depend mainly on the initial positions of the vortices with respect to the positions of the pinning sites. The critical dipping force at the peak was found to increase linearly with the pinning strength and to have larger values for the system with the smaller density of pinning sites. The dependence of the relative height of the peak on the pinning strength was found be nearly the same in both systems. One-dimensional linear channels of moving vortices along the direction of the driving force were observed at the dip just before the peak.

scholarly journals ENTROPY IN QUANTUM CHROMODYNAMICS

2012 ◽  
Vol 27 (09) ◽  
pp. 1230011 ◽  
Author(s):  
JOHN M. CORNWALL
Keyword(s):  
Chiral Symmetry ◽  
Chiral Symmetry Breaking ◽  
Entanglement Entropy ◽  
Configurational Entropy ◽  
Zero Temperature ◽  
Massive Quark ◽  
Flux Tubes ◽  
Qcd Vacuum ◽  
Symmetry Breakdown

We review the role of zero-temperature entropy in several closely-related contexts in QCD. The first is entropy associated with disordered condensates, including [Formula: see text]. The second is effective vacuum entropy arising from QCD solitons such as center vortices, yielding confinement and chiral symmetry breaking. The third is entanglement entropy, which is entropy associated with a pure state, such as the QCD vacuum, when the state is partially unobserved and unknown. Typically, entanglement entropy of an unobserved three-volume scales not with the volume but with the area of its bounding surface. The fourth manifestation of entropy in QCD is the configurational entropy of light-particle world-lines and flux tubes; we argue that this entropy is critical for understanding how confinement produces chiral symmetry breakdown, as manifested by a dynamically-massive quark, a massless pion, and a [Formula: see text] condensate.

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