Search results for "scale [mass]"
showing 10 items of 997 documents
Quantum rings for beginners II: Bosons versus fermions
2012
The purpose of this overview article, which can be viewed as a supplement to our previous review on quantum rings, [S. Viefers {\it et al}, Physica E {\bf 21} (2004), 1-35], is to highlight the differences of boson and fermion systems in one-dimensional (1D) and quasi-one-dimensional (Q1D) quantum rings. In particular this involves comparing their many-body spectra and other properties, in various regimes and models, including spinless and spinful particles, finite versus infinite interaction, and continuum versus lattice models. Our aim is to present the topic in a comprehensive way, focusing on small systems where the many-body problem can be solved exactly. Mapping out the similarities a…
Rotating quantum liquids crystallize
2006
Small crystallites form when finite quantal systems are set highly rotating. This crystallization is independent of the statistics of the particles, and occurs for both trapped bosons and fermions. The spin degree of freedom does not change the tendency for localization. In a highly rotating state, the strongly correlated bosonic and fermionic systems approach to that of classical particles.
Spin-transfer torque driven motion, deformation, and instabilities of magnetic skyrmions at high currents
2020
In chiral magnets, localized topological magnetic whirls, magnetic skyrmions, can be moved by spin polarized electric currents. Upon increasing the current strength, with prospects for high-speed skyrmion motion for spintronics applications in mind, isolated skyrmions deform away from their typical circular shape. We analyze the influence of spin-transfer torques on the shape of a single skyrmion, including its stability upon adiabatically increasing the strength of the applied electric current. For rather compact skyrmions at uniaxial anisotropies well above the critical anisotropy for domain wall formation, we find for high current densities that the skyrmion assumes a non-circular shape …
Phase sticking in one-dimensional Josephson junction chains
2013
Published version of an article in the journal: Physical Review B - Condensed Matter and Materials Physics. Also available from the publisher at: http://dx.doi.org/10.1103/PhysRevB.88.104501 We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, EJ EC. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, Ichain at high bias. Our experiments showed that Ichain is not only voltage-independent but it is also practically temperature-independent up to T=0.7TC. We have successfully model the tr…
Laser-induced collective excitations in a two-component Fermi gas
2002
We consider the linear density response of a two-component (superfluid) Fermi gas of atoms when the perturbation is caused by laser light. We show that various types of laser excitation schemes can be transformed into linear density perturbations, however, a Bragg spectroscopy scheme is needed for transferring energy and momentum into a collective mode. This makes other types of laser probing schemes insensitive for collective excitations and therefore well suited for the detection of the superfluid order parameter. We show that for the special case when laser light is coupled between the two components of the Fermi gas, density response is always absent in a homogeneous system.
Universal vortex formation in rotating traps with bosons and fermions.
2004
When a system consisting of many interacting particles is set rotating, it may form vortices. This is familiar to us from every-day life: you can observe vortices while stirring your coffee or watching a hurricane. In the world of quantum mechanics, famous examples of vortices are superconducting films and rotating bosonic $^4$He or fermionic $^3$He liquids. Vortices are also observed in rotating Bose-Einstein condensates in atomic traps and are predicted to exist for paired fermionic atoms. Here we show that the rotation of trapped particles with a repulsive interaction leads to a similar vortex formation, regardless of whether the particles are bosons or (unpaired) fermions. The exact, qu…
Flat-band superconductivity in periodically strained graphene: mean-field and Berezinskii–Kosterlitz–Thouless transition
2019
In the search of high-temperature superconductivity one option is to focus on increasing the density of electronic states. Here we study both the normal and $s$-wave superconducting state properties of periodically strained graphene, which exhibits approximate flat bands with a high density of states, with the flatness tunable by the strain profile. We generalize earlier results regarding a one-dimensional harmonic strain to arbitrary periodic strain fields, and further extend the results by calculating the superfluid weight and the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_\text{BKT}$ to determine the true transition point. By numerically solving the self-consistency …
Towards human cell simulation
2019
The faithful reproduction and accurate prediction of the phe-notypes and emergent behaviors of complex cellular systems are among the most challenging goals in Systems Biology. Although mathematical models that describe the interactions among all biochemical processes in a cell are theoretically feasible, their simulation is generally hard because of a variety of reasons. For instance, many quantitative data (e.g., kinetic rates) are usually not available, a problem that hinders the execution of simulation algorithms as long as some parameter estimation methods are used. Though, even with a candidate parameterization, the simulation of mechanistic models could be challenging due to the extr…
Controllable Solid Rocket Motor Nozzle Operations in Conditions of Limited-Amplitude Fluctuations
2009
A nonlinear multi scale analysis of a controllable solid rocket motor operating in conditions ranging from high-amplitude fluctuations in combustion chamber to conditions lying in limit cycle is presented and the motor behavior subsequent to some relevant nozzle operations is investigated. Effects of acoustic-vorticity-entropy wave coupling, wave steepening, rotational/viscous flow losses, steep-fronted wave losses are taken into account and oscillatory energy losses in pintle-nozzle, unsteady combustion and chamber geometry changes resulting from grain regression are included. The analysis provides evidence that the unsteady energy balance and the motor wave amplitude evolution are influen…
Initiation of deep convection at marginal instability in an ensemble of mesoscale models: a case-study from COPS
2011
The present study investigates the initiation of precipitating deep convection in an ensemble of convection-resolving mesoscale models. Results of eight different model runs from five non-hydrostatic models are compared for a case of the Convective and Orographically-induced Precipitation Study (COPS). An isolated convective cell initiated east of the Black Forest crest in southwest Germany, although convective available potential energy was only moderate and convective inhibition was high. Measurements revealed that, due to the absence of synoptic forcing, convection was initiated by local processes related to the orography. In particular, the lifting by low-level convergence in the planet…