QUANTUM CELL MODEL FOR He II AT NONZERO TEMPERATURE

1966 ◽  
Vol 44 (11) ◽  
pp. 2775-2787
Author(s):  
G. C. Knollman
Keyword(s):  
Phase Transition ◽  
Specific Volume ◽  
Cell Model ◽  
Model Development ◽  
Absolute Zero ◽  
Superfluid Transition ◽  
Superfluid Phase ◽  
Nonzero Temperature ◽  
Repulsive Energy ◽  
Zero Momentum

A previous quantum cell-model development is expanded to treat the solid-superfluid phase transition and the zero-momentum occupation at temperatures other than absolute zero. Application is made to liquid He II, which is studied at various pressures out to temperatures of about a degree absolute. The effective repulsive energy, along the solid–superfluid transition, is determined for pairs of 4He atoms localized in cells of volume equal to the specific volume.

scholarly journals Renormalization group study of superfluid phase transition: Effect of compressibility

2020 ◽  
Vol 102 (2) ◽  
Author(s):  
Michal Dančo ◽  
Michal Hnatič ◽  
Tomáš Lučivjanský ◽  
Lukáš Mižišin
Keyword(s):  
Phase Transition ◽  
Renormalization Group ◽  
Superfluid Phase ◽  
Transition Effect

scholarly journals Manipulating the critical temperature for the superfluid phase transition in trapped atomic Fermi gases

2002 ◽  
Vol 65 (6) ◽  
Author(s):  
C. P. Search ◽  
H. Pu ◽  
W. Zhang ◽  
B. P. Anderson ◽  
P. Meystre
Keyword(s):  
Phase Transition ◽  
Critical Temperature ◽  
Fermi Gases ◽  
Superfluid Phase

Control Strategy Optimization of a Fuel-Cell Electric Vehicle

2008 ◽  
Vol 5 (2) ◽  
Author(s):  
Vanessa Paladini ◽  
Teresa Donateo ◽  
Arturo de Risi ◽  
Domenico Laforgia
Keyword(s):  
Fuel Cell ◽  
Control Strategy ◽  
Cell Model ◽  
Control Strategies ◽  
Storage System ◽  
Model Development ◽  
Cell System ◽  
Polymer Electrolyte Fuel Cell ◽  
Solid Polymer ◽  
Maximum Efficiency

In the last decades, due to emission reduction policies, research focused on alternative powertrains among which electric vehicles powered by fuel cells are becoming an attractive solution. The main issues of these vehicles are the energy management system and the overall fuel economy. An overview of the existing solutions with respect to their overall efficiency is reported in the paper. On the bases of the literature results, the more efficient powertrain scheme has been selected. The present investigation aims at identifying the best control strategy to power a vehicle with both fuel cell and battery to reduce fuel consumption. The optimization of the control strategy is achieved by using a genetic algorithm. To model the powertrain behavior, an on purpose made simulation program has been developed and implemented in MATLAB/SIMULINK. In particular, the fuel cell model is based on the theory of Amphlett et al. (1995, “Performance Modeling of the Ballard Mark IV Solid Polymer Electrolyte Fuel Cell. II. Empirical Model Development,” J. Electrochem. Soc., 142(1)) whereas the battery model also accounts for the charge/discharge efficiency. The analyzed powertrain is equipped with an energy recovery system. During acceleration, power is demanded to the storage system, while during deceleration the battery is recharged. All the tested control strategies assume charge sustaining operation for the battery and that the fuel cell system has to work around its maximum efficiency. All the tested strategies have been validated on four driving cycles.

Solid-Superfluid Transition inHe4at Absolute Zero

1965 ◽  
Vol 139 (6A) ◽  
pp. A1769-A1782 ◽  
Author(s):  
H. A. Gersch ◽  
J. M. Tanner
Keyword(s):  
Absolute Zero ◽  
Superfluid Transition

KNOTTED VORTICES AND SUPERFLUID PHASE TRANSITION

1993 ◽  
Vol 07 (23) ◽  
pp. 1523-1526 ◽  
Author(s):  
ROBERT OWCZAREK
Keyword(s):  
Phase Transition ◽  
Ising Model ◽  
Specific Heat ◽  
Superfluid Helium ◽  
Vortex Structures ◽  
Two Dimensional ◽  
Superfluid Phase ◽  
Λ Point

In this letter, studies of knotted vortex structures in superfluid helium are continued. A model of superfluid phase transition (λ-transition) is built in this framework. Similarities of this model to the two-dimensional Ising model are shown. Dependence of specific heat of superfluid helium on temperature near the λ point is explained.

scholarly journals Spin wave theory of spin-1/2 XY model with ring exchange on a triangular lattice

2013 ◽  
Vol 91 (7) ◽  
pp. 542-547 ◽  
Author(s):  
Solomon A. Owerre
Keyword(s):  
Phase Transition ◽  
Spin Wave ◽  
Triangular Lattice ◽  
Finite Temperature ◽  
Wave Theory ◽  
Square Lattice ◽  
Xy Model ◽  
Superfluid Phase ◽  
Zero Temperature ◽  
Ring Exchange

We present the linear spin wave theory calculation of the superfluid phase of a hard-core boson J-K model with nearest neighbour exchange J and four-particle ring-exchange K at half filling on the triangular lattice, as well as the phase diagrams of the system at zero and finite temperatures. A similar analysis has been done on a square lattice (Schaffer et al. Phys. Rev. B, 80, 014503 (2009)). We find similar behaviour to that of a square lattice but with different spin wave values of the thermodynamic quantities. We also find that the pure J model (XY model), which has a well-known uniform superfluid phase with an ordered parameter [Formula: see text] at zero temperature is quickly destroyed by the inclusion of negative-K ring-exchange interactions, favouring a state with a (4π/3, 0) ordering wavevector. We further study the behaviour of the finite-temperature Kosterlitz–Thouless phase transition (TKT) in the uniform superfluid phase, by forcing the universal quantum jump condition on the finite-temperature spin wave superfluid density. We find that for K < 0, the phase boundary monotonically decreases to T = 0 at K/J = −4/3, where a phase transition is expected and TKT decreases rapidly, while for positive K, TKT reaches a maximum at some K ≠ 0. It has been shown on a square lattice using quantum Monte Carlo (QMC) simulations that for small K > 0 away from the XY point, the zero-temperature spin stiffness value of the XY model is decreased (Melko and Sandvik. Ann. Phys. 321, 1651 (2006)). Our result seems to agree with this trend found in QMC simulations for two-dimensional systems.

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