Collective Excitations in Spin-2 Bose-Einstein Condensates

The Green＇s functions and the correlation functions in spin-2 Bose-Einstein condensates at finite temperature are defined and the generalized Dyson-Beliaev equations are introduced. We discuss the spin conservation in z direction and decouple the Green＇s functions and the generalized Dyson-Beliaev equations according to different spin conservations in z direction. The anomalous vertex functions are introduced and the self-energies are separated into the proper self-energies and the improper self-energies. The generalized Dyson-Beliaev equations are decoupled according to separation of the self-energies. We calculate the Green＇s functions step by step in the Bogoliubov approximation and discuss the collective excitations in spin-2 Bose-Einstein condensates in the polar, ferromagnetic, and cyclic cases, respectively.     

Non-Abelian Topological Excitations in Spinor Condensates

We investigate the topological defects in atomic spln-1 and spin-2 Bose-Einstein condensates by applying the homotopy group theory. With this rigorous approach we clarify the previously controversial identification of symmetry groups and order parameter spaces for the spin-1 case, and show that the spin-2 case provides a rare example of a physical system with non-Abelian line defects, and the possibility to have winding numbers of 1/3 and its multiples.     

The Possibility of Wax Formation in Gas Fields： a Case Study

Natural gas production from a gas reservoir(Reservoir A)located in the south of Iran,presents solids deposition during processing because the condensate contains suspended and dissolved solids.Solids deposition occurs not only in the transportation lines from the wells to the separators but also in the various operating units of gas streams and condensate stream.In this study,the multisolid-phase model has been used to predict the wax precipitation from gas and gas condensate fluids.The properties of gas and liquid phases are described using the Soave-Redlich-Kwong(SRK)equation of state.The model is then used to predict the possibility of the wax formation in Reservoir A gas facilities,located at the south of Iran.Solid deposition which occurred in the various streams of that facility confirmed the calculated results.Finally,the wax appearance temperature(WAT),the weight percent of wax formation and the effects of pressure and temperature on the wax formation were also predicted.     

Phase Diagram and Phase Separation of a Trapped Interacting Bose-Fermi Gas Mixture

In six different regimes for a spatial phase diagram of a trapped interacting Bose-Fermi gas mixture at low temperatures, we present the conditions for the spatial demixing and separation of bosons and fermions. Starting from a semiclassically thermodynamic model for the local density functional of thermal bosons and fermions,the explicit analytical expressions for the fugacities of bosons and fermions are derived in different regimes by means of a first-order perturbation method in a local-density approximation. The critical values of the fermionboson interaction strength as a function of the fractional composition of fermions have a general feature: increase,extreme and decrease with increasing the fermionic composition slightly above Bose-Einstein critical temperature.     

Head-on collision of ring dark solitons in Bose--Einstein condensates

The ring dark solitons and their head-on collisions in a Bose--Einstein condensates with thin disc-shaped potential are studied. It is shown that the system admits a solution with two concentric ring solitons, one moving inwards and the other moving outwards, which in small-amplitude limit, are described by the two cylindrical KdV equations in the respective reference frames. By using the extended Poincar\'e--Lighthill--Kuo perturbation method, the analytical phase shifts following the head-on collisions between two ring dark solitary waves are derived. It is shown that the phase shifts decrease with the radial coordinate $r$ according to the $r^{-1/3}$ law and depend on the initial soliton amplitude and radius.     

Dissipative dynamics of dark solitons in elongated Bose--Einstein condensates

The dissipative dynamic stability is investigated of dark solitons in elongated Bose--Einstein condensates that can be described by the Gross--Pitaevskii equation including an additional term. Based on the direct perturbation theory for the nonlinear Schr?dinger equation, the dependence of the soliton velocity on time is explicitly given, and the shape of dark solitons remaining unchanged under the dissipative condition is confirmed theoretically for the first time. It is found that the dynamically stable dark solitons turn out to be thermodynamically unstable.     

Exact periodic wave and soliton solutions in two-component Bose--Einstein condensates

We present several families of exact solutions to a system of coupled nonlinear Schr\"{o}dinger equations. The model describes a binary mixture of two Bose--Einstein condensates in a magnetic trap potential. Using a mapping deformation method, we find exact periodic wave and soliton solutions, including bright and dark soliton pairs.     

科学家在对撞机碰撞试验中意外发现新物质

大型强子对撞机内部的粒子碰撞已经创造出一种看起来像是新形式的物质,这种新物质被称作玻色冷凝物。科学家并未预料到大型强子对撞机中的微粒碰撞会产生这种物质。然而,它或许可以解释在机器内部观察到的一些古怪现象。当科学家们加速质子和铅离子并且使它们相     

Direct Observation of Histone-Induced DNA Shortening

We construct a system of magnetic tweezers and apply it to study the interaction between histones and DNA. The condensation of DNA by purified histones at low ionic strengths is directly monitored by recording the length of the DNA as a function of elapsed time. It is found that DNA condensates in a dynamic manner. The binding of hist, ones to DNA is energetically favoured, but the ten,sion applied on DNA tends to unravel the DNA-histone complex, The competition between the two processes determiners the rate of the DNA condensation.