Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases

We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the 2D mean-field theory indicates that the quantum fluctuations are much more pronounced than those in 3D. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of 2D Bose gases and determine the ratio of the composite boson scattering length $a_{\rm B}$ to the fermion scattering length $a_{\rm 2D}$. We find $a_{\rm B}\simeq 0.56 a_{\rm 2D}$, in good agreement with the exact four-body calculation. We compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.Comment: Published versio

HYDRODYNAMIC PERFORMANCE OF NEIL PRYDE RS: X AND MISTRAL SAILBOARD

After Olympic Games in 2004, the once used board, MISTRAL (M), in Olympic Game has been substituted with NEIL PRYDE RS：X (NP). To meet the need of the national sailing team, the research group carried out the experiments on the hydrodynamic performance of the NP and M early or later. The resistances, transverse forces and wrest moments were measured by using the balance of the trisection force, the angle of the heel and pitch was measured by using the angle sensor. The sailboard could rise and sink freely, the pitch was free, the static angle could be adjusted by utilizing the weight and the balance was at the mast. The results showed that the resistance of NP sailboard was bigger as soon as the pitch angle was bigger and this was the same as that of M sailboard, the heel did not have any influence on the resistance of NP sailboard, the resistance became small continuously when the angle of the centerboard decreased and the resistance increased as the sailboard was heavier

Impact of Controlling Shareholder Equity Pledge on Corporate Value

As an innovative financing behavior, equity pledge breaks the limit of traditional financing, and broadens the financing channels of companies and major shareholders. This paper comprehensively considers the impact of controlling shareholder equity pledge on corporate value from three research perspectives. The main conclusions are as follows: (1) When the equity pledge is not considered, the cash flow rights and voting rights of the company owned by the controlling shareholder are positively correlated with corporate value. That is, this presents incentive effect, but the existence of the separation of the two powers brings the second type of agency problem and reduces corporate value. (2) When considering the equity pledge, the controlling shareholder’s equity pledge may weaken the incentive effect and strengthen the encroachment effect which causing a reduction of corporate value. (3) Based on the accounting point of view, the controlling shareholder’s equity pledge is negatively correlated with the corporate performance, while the concentration of ownership dilutes this negative effect. (4) The balance of equity weakens the negative effect of the controlling shareholder’s equity pledge on corporate value, thereby reduces the negative impact of the equity pledge

HYDRODYNAMIC ANALYSIS OF ROWING HULL BASED ON THE FLOAT POSE

The rowing is one of the important events in the Olympic Games. In order to study the hydrodynamic performance of rowing, we finished the linetype mapping and the calculated the parameters of the double rowing model. Based on the resistance data of rowing at different states, we obtained the rule of resistance of rowing at different speeds. The study indicated that the enhancement of the physical force of the athletes seemed to be in proportion to the weight of the athletes and the results based on research shallow affected and optimized the design

HYDRODYNAMIC PERFORMANCE OF THE ROWING HULL

The viscous resistance of the rowing hull was calculated by means of 8th ITTC formula; the wave-making resistance of the rowing hull at different velocity was calculated based on the Michell integral formula. The characteristic of the total resistance of the rowing hull was discussed. The results can guide coaches and athletes to train and compete