1,721,027 research outputs found
Collisionless sound of bosonic superfluids in lower dimensions
No full textThe superfluidity of low-temperature bosons is well established in the collisional regime. In the collisionless regime, however, the presence of superfluidity is not yet fully clarified, in particular in lower spatial dimensions. Here, we compare the Vlasov-Landau equation, which does not take into account the superfluid nature of the bosonic system, with the Andreev-Khalatnikov equations, which instead explicitly contain a superfluid velocity. We show that recent experimental data of the sound mode in a two-dimensional collisionless Bose gas of Rb87 atoms are in good agreement with both theories, but the sound damping is better reproduced by the Andreev-Khalatnikov equations below the Berezinskii-Kosterlitz-Thouless critical temperature Tc, while above Tc the Vlasov-Landau results are closer to the experimental ones. For one-dimensional bosonic fluids, where experimental data are not yet available, we find larger differences between the sound velocities predicted by the two transport theories and, also in this case, the existence of a superfluid velocity reduces the sound damping
On the convergence of the WKB series for the angular momentum operator
Full text linkIn this paper we prove a recent conjecture about the convergence of the WKB series for the angular momentum operator. We demonstrate that the WKB algorithm for the angular momentum gives the exact quantization formula if all orders are summed. Finally, we discuss the supersymmetric semiclassical quantum mechanics (SWKB), which gives the correct quantization of the angular momentum at the leading order
Chaos in coplanar classical collisions with particles interacting through r(-2) forces
Full text linkSWKB for the angular momentum
No full textIt has been recently shown [M. Robnik and L. Salasnich, J. Phys. A: Math. Gen. 30, 1719 (1997)] that the WKB series for the quantization of angular momentum L converges to the exact value L-2 = (h) over bar(2)l(l + 1), if summed over all orders, and gives the Langer formula L-2 = (h) over bar 2(l + 1/2)(2) at the leading order. In this work we solve the eigenvalue problem of the angular momentum operator by using the supersymmetric semiclassical quantum mechanics (SWKB), and show that it gives the correct quantization already at the leading order
Multiparameter generalization of nonextensive statistical mechanics
Full text linkWe show that the stochastic interpretation of Tsallis's thermostatistics given recently by Beck [Phys. Rev. Lett 87, 180601 (2001)] leads naturally to a multiparameter generalization. The resulting class of distributions is able to fit experimental results, which cannot be reproduced within Boltzmann's or Tsallis's formalism
Ion collisions in very strong electric fields
No full textA classical trajectory Monte Carlo (CTMC) simulation has been made of charge exchange and ionization processes between a hydrogen atom and fully stripped ions embedded in very strong static electric fields (of order of 10(10) V m(-1)), which are thought to exist in cosmic and laser-produced plasmas. Calculations show that the presence of the field affects absolute values of the cross sections, enhancing ionization and reducing charge exchange. Moreover, the overall effect depends upon the relative orientation between the field and the nuclear motion. Other features of a null-field situation, such as scaling laws, are revisited
A CTMC study of collisions between protons and H-2(+) molecular ions
No full textWe study numerically collisions between protons and H-2(+) molecular ions at intermediate impact energies by using the Classical Trajectory Monte Carlo method (CTMC). Total and differential cross sections are computed. The results are compared with: a) the standard one electron-two nucleon scattering, and b) the quantum mechanical treatment of the H+-H-2(+) scattering
A power-balance model of the density limit in fusion plasmas: application to the L-mode tokamak
Full text linkA power-balance model, with radiation losses from impurities and neutrals, gives a unified description of the density limit (DL) of the stellarator, the L-mode tokamak, and the reversed field pinch (RFP). The model predicts a Sudo-like scaling for the stellarator, a Greenwald- like scaling, alpha I-p(8/9), for the RFP and the ohmic tokamak, a mixed scaling, alpha (PIp4/9)-I-4/9, for the additionally heated L-mode tokamak. In a previous paper (Zanca et al 2017 Nucl. Fusion 57 056010) the model was compared with ohmic tokamak, RFP and stellarator experiments. Here, we address the issue of the DL dependence on heating power in the L-mode tokamak. Experimental data from high-density disrupted L-mode discharges performed at JET, as well as in other machines, arc taken as a term of comparison. The model fits the observed maximum densities better than the pure Greenwald limit
- …
