Kármán vortex street in a spin–orbit-coupled Bose–Einstein condensate with PT symmetry

The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.

Asymmetric scattering behaviors of spin wave dependent on magnetic vortex chirality

We investigate asymmetric spin wave scattering behaviors caused by vortex chirality in a cross-shaped ferromagnetic system by using the micromagnetic simulations.In the system,four scattering behaviors are found:(i)asymmetric skew scattering,depending on the polarity of vortex core,(ii)back scattering(reflection),depending on the vortex core stiffness,(iii)side deflection scattering,depending on structural symmetry of the vortex circulation,and(iv)geometrical scattering,depending on waveguide structure.The first and second scattering behaviors are attributed to nonlinear topological magnon spin Hall effect related to magnon spin-transfer torque effect,which has value for magnonic exploration and application.

Spin splitting of vortex beams on the surface of natural biaxial hyperbolic materials

We investigated the spin splitting of vortex beam on the surface of biaxial natural hyperbolic materials(NHMs)rotated by an angle with respect to the incident plane. An obvious asymmetry of spatial shifts produced by the left-handed circularly(LCP) component and right-handed circularly polarized(RCP) component is exhibited. We derived the analytical expression for in-and out-of-plane spatial shifts for each spin component of the vortex beam. The orientation angle of the optical axis plays a key role in the spin splitting between the two spin components, which can be reflected in the simple expressions for spatial shifts without the rotation angle. Based on an α-MoO_(3) biaxial NHM, the spatial shifts of the two spin components with the topological charge were investigated. As the topological charge increases, the spatial shifts also increase;in addition, a tiny spatial shift close to zero can be obtained if we control the incident frequency or the polarization of the reflected beams. It can also be concluded that the maximum of the spin splitting results from the LCP component at p-incidence and the RCP component at s-incidence in the RB-Ⅱ hyperbolic frequency band. The effect of the incident angle and the thickness of the α-MoO_(3) film on spin splitting is also considered. These results can be used for manipulating infrared radiation and optical detection.

Characterizing and Analyzing the Airflow Field inside the Nozzle Block of Murata Vortex Spinning

A three-dimensional computational fluid dynamics model is developed by software Fluent 6.2, to simulate the flow field inside the nozzle block of the Murata vortex spinning. The flowing state and the distribution law of static pressure and velocity are characterized and analyzed. The relationship between the flowing state and the structure of the vortex spun yarn is also discussed. The research results can enhance the understanding of the yarn formation principle from viewpoint of the airflow field law inside the nozzle block of Murata vortex spinning.

Design and Numerical Simulation of Low-Fiber Hollow Spindle in Air-Jet Vortex Spinning

Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is simulated numerically. The negative pressure effect is much bigger at the top of low-fiber hollow spindle than that in Murata No.861,which is more conducive for single fiber to get into the channel of hollow spindle. The tangential velocity in 0-3 mm at the top of hollow spindle increases and the fluctuation of radial velocity is much stronger,which enhance the wrapping effect. In the addition,the distribution of axial velocity remains the same.

Nonadiabatic spin-torque and damping effects on vortex core switching triggered by a single current pulse

Switching the orientation of a vortex core by spin-polarised pulse current introduces a promising concept for the reliable addressing of a single nanodisc element inside dense arrays. In this paper, micromagnetic simulations are employed to study the vortex core switching behaviour excited by a short in-plane Gaussian current pulse. We find that both the switching mechanism and the switching time are not sensitive to changes in the phenomenological parameters of spin-torque nonadiabaticity and Gilbert damping. The switching time, however, strongly depends on the current strength. In addition, we have theoretically predicted the parameter range of current pulses to achieve a single switching event.

Asymmetrical spiral spectra and orbital angular momentum density of non-uniformly polarized vortex beams in uniaxial crystals

To explore the effect of non-uniform polarization on orbital angular momentum(OAM) in anisotropic medium, in this work investigated are the evolution of the spiral spectra and OAM densities of non-uniformly polarized vortex(NUPV)beams in uniaxial crystals propagating orthogonal to the optical axis, and also the case of uniformly polarized vortex(UPV)beams with left-handed elliptical polarization. In the input plane, the NUPV beams present their spiral spectra of m-mode concentrated at m = l ± 1 modes rather than m = l mode, and reveal the relation among topological charge l, mode of spiral spectra m and the power weight value Rmexpressed by l=∑^(∞)_(m)=-∞Rm. is still satisfied for UPV beams in uniaxially anisotropic crystals, whereas for NUPV beams their relations are no longer valid owing to non-uniform polarization. Furthermore, the analysis indicates that the asymmetrical distribution of power weight of spiral spectra and the non-zero value in the sum of longitudinal OAM densities originate from the initial non-uniform polarization and anisotropy in uniaxial crystals rather than topological charges. In addition, the relation between spiral spectrum and longitudinal OAM density is numerically discussed. This work may provide an avenue for OAM-based communications,optical metrology, and imaging by varying the initial non-uniform polarization.

Vortex lines in a ferromagnetic spin-triplet superconductor

Based on Duan＇s topological current theory,we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines.Such defects are different from the Abrikosov vortices in one-component condensate systems.We investigate the inner topological structure of the vortex lines.The topological charge density,velocity,and topological current of the vortex lines can all be expressed in terms of 未 function,which indicates that the vortices can only arise from the zero points of an order parameter field.The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of-mapping.The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a 未-like function.Finally,based on the implicit function theorem and the Taylor expansion,we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.

Faster vortex core switching with lower current density using three-nanocontact spin-polarized currents in a confined structure

We perform micromagnetic simulations on the switching of magnetic vortex core by using spin-polarized currents through a three-nanocontact geometry. Our simulation results show that the current combination with an appropriate current flow direction destroys the symmetry of the total effective energy of the system so that the vortex core can be easier to excite,resulting in less critical current density and a faster switching process. Besides its fundamental significance, our findings provide an additional route to incorporating magnetic vortex phenomena into data storage devices.

Multi-segmented nanowires for vortex magnetic domain wall racetrack memory

A vortex domain wall's(VW) magnetic racetrack memory's high performance depends on VW structural stability,high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. Thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. This junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction(l) and vertically(d) in the y-direction. The VW structure became stable by manipulating magnetic properties, such as magnetic saturation(M_(4)) and magnetic anisotropy energy(K_(u)). In this case, increasing the values of M_(4) ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires,which contributes to maintenance of the storage memory's lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. Moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions(l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW(J_(d)) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the M_(4) and K_(u),can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires(multisegmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density(J_(d)) for moving the VW from one state to another was highly influenced by the offset area geometry(l and d) and the material's magnetic properties, such as the M_(4) and K_(u).

喷气涡流纺纱机及其关键技术的应用与研究进展

针对国内外纺纱企业在喷气涡流纺纱机的应用与相关技术的研发情况及其所存在的问题,综述了喷气涡流纺纱机及其关键技术的研究进展,介绍了喷气涡流纺纱机的历史发展及其纺纱系统关键技术,详细分析了喷气涡流纺纱机的导棉喂入、牵伸和输送机构,成纱器,纱线卷绕(横动)、卷装机构等零部件的特征与发展趋势。分析认为:喷气涡流纺纱技术的研究多集中在对现有规模化生产机器的喷气涡流成纱器的结构改进、工作机制探讨上,成果较多且较为成熟,但创新技术不突出;在构建新型成纱器的内部型腔结构和产生更理想的涡流形态上有望进一步突破,以提高喷气涡流纺纱的性能,满足多功能纱线的生产和扩大纺纱应用范围;同时科技进步也使更多智能控制系统的电子清纱器、异纤控制、短线诊断、可视化等技术在纺纱工序中有了应用和发展。

Vortex lines in a ferromagnetic spin-triplet superconductor

Based on Duan’s topological current theory,we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines.Such defects are different from the Abrikosov vortices in one-component condensate systems.We investigate the inner topological structure of the vortex lines.The topological charge density,velocity,and topological current of the vortex lines can all be expressed in terms of δ function,which indicates that the vortices can only arise from the zero points of an order parameter field.The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of-mapping.The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a δ-like function.Finally,based on the implicit function theorem and the Taylor expansion,we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.

层彩涡流色纺纱的开发与实践

针对牛仔纱的流行趋势及目前染色存在的不足,模拟牛仔色纱特征,开发一种层彩涡流色纺纱。融合了传统环锭纺和喷气涡流包芯纺技术,芯纱采用短纤维纱线代替长丝,以达到芯纱色彩可调、粗细可调、捻向可调;纺纱过程中通过芯纱与外包层纤维捻向相反组合技术,选择相应的捻系数,抵消纤维的加捻应力;利用喷气涡流纺包缠不均匀的特点,可呈现独特的露芯效果,内外层可采用不同颜色及配比。纺制的层彩涡流色纺纱可作为针织、机织用纱,丰富的色彩变化使层彩涡流色纺纱可用于生产无染牛仔织物。

喷气涡流纺纱机的发展现状及趋势

为了进一步推进喷气涡流纺纱机的发展,分析了喷气涡流纺纱机在全球的存量分布情况、近8年国内累计进口量及主要省份等市场情况,回顾了喷气涡流纺纱机的国内外技术发展历程,阐述了喷气涡流纺纱技术的创新应用,介绍了相关政策支持,并提出了喷气涡流纺纱机的发展思路。认为:我国喷气涡流纺纱机存量具有全球优势地位,正处于产业快速发展期,市场空间广阔,未来随着各种新工艺新技术层出不穷,在开发喷气涡流纺花式纱、包芯纱、细号纱以及差异化原料应用的优势将不断凸显,但国内急需开发拥有自主知识产权的喷气涡流纺纱机,突破关键技术装备和工艺,促使喷气涡流纺纱机在我国稳步健康发展。

喷气涡流纺长片段竹节段彩纱的设计与生产

探讨有色超短纤维在喷气涡流纺花式纱开发中的应用及生产要点。采用有色粘胶超短纤维与本色竹浆纤维、椰炭改性涤纶纤维,在并条机上加装竹节装置,利用喷气涡流纺纱技术纺制成长片段竹节段彩纱。针对粘胶纤维长度相对较短的特点,工艺上尝试采用短流程、减小隔距、降低打击件速度等技术措施。结果表明:开发的喷气涡流纺段彩纱具有段彩片段长、生产效率高的特点,其在布面上色点朦胧,时而形成连续分布,时而散点分布,形成不同于传统段彩纱的独特风格。

抽吸孔排列对喷气涡流纺喷嘴流场影响的数值模拟

为探究抽吸孔排列参数对负压抽吸式喷气涡流纺包芯纱成纱过程与质量的影响规律,建立喷嘴气流场的计算流体动力学模型,对抽吸孔周向列数与抽吸孔轴向间距对气流流动特性的影响进行数值模拟研究,并与纺纱试验结果进行对比分析。结果表明:成纱过程中落纤量的大小受锭子中引纱通道入口端面处气流轴向速度和径向速度的方向和大小影响显著,落纤量随该处气流轴向和径向速度值的增大而降低;成纱断裂强度受锭子入口附近抽吸孔中气流径向速度大小的影响较大,成纱断裂强度随径向速度的增大而提高。抽吸孔周向列数为3列和4列时落纤量均低于2列时,但抽吸孔周向列数为2列时成纱断裂强度最高;当抽吸孔轴向间距从1 mm增加至2 mm时,落纤量与成纱断裂强度均明显增加。抽吸孔排列参数对包芯纱成纱过程落纤量与成纱断裂强度影响的数值模拟结果与前期纺纱试验结果较为一致,为揭示参数对喷气涡流纺成纱过程与质量的影响机制提供了可行的方法。

不同芯丝对喷气涡流包芯纱及其织物性能的影响

为探究不同芯丝对喷气涡流包芯纱及其织物性能的影响规律,以莫代尔纤维和智能调温纤维为外包纤维,分别以T400长丝、涤纶DTY长丝和锦纶6长丝为芯丝纺制3种包芯纱,并织成针织物。探讨相同成纱条件下不同芯丝喷气涡流包芯纱的强伸性能、毛羽以及条干均匀度,同时分析相应针织物的悬垂性、耐折皱性和抗起毛起球性。结果显示:芯丝为T400长丝的包芯纱强伸性能最好,且其织物的抗起毛起球性最好;芯丝为涤纶DTY长丝的包芯纱织物挺括抗皱,保形性较好;芯丝为锦纶6长丝的包芯纱毛羽最少、条干最均匀,并且织物悬垂性、透气性最好。

喷气涡流纺新型纱线开发探析

为提升开发喷气涡流纺纱线的技术水平,介绍喷气涡流纺纱在我国的发展历程及存在问题,对比环锭纺、转杯纺、喷气涡流纺的优势、局限及技术特性;详细分析喷气涡流纺开发多种纤维混纺纱、包芯包覆纱、有色纱等特色纱线开发途径;总结发展喷气涡流纺需注意的问题。指出:喷气涡流纺纱尚无法替代环锭纺与转杯纺;开发喷气涡流纺纱线产品时,应避免同质化竞争,合理配置纺纱速度,不断优化纺纱工艺配置,努力拓宽喷气涡流纺纱线的应用领域。

新型抗菌喷气涡流纺纱线的研究

利用当前纺织领域先进的喷气涡流纺技术,将抗菌性能良好的海藻纤维与黏胶纤维进行混纺,获得了力学性能良好且兼具抗菌性能的纱线。对该具有抗菌功能的喷气涡流纺纱线进行分析,研究其纱线结构、性能和应用前景。测试与分析结果表明:相比普通环锭纺纱线,该纱线强度稍低;毛羽非常少,且基本都为短毛羽;纱线具有抗菌等优良性能。

喷气涡流纺纱技术发展现状与理论研究进展

为提高喷气涡流纺纱成纱质量,阐述喷气涡流纺纱设备的革新历程,及导引体、涡流管、纺锭等喷嘴关键元器件设计优化进展;以麻纤维纱线、包芯纱、功能性纱线为例,介绍喷气涡流纺纱线产品开发要点及成果;详细分析喷气涡流纺喷嘴内气流流动特性,模拟纤维在气流场中的运动。指出:喷气涡流纺纱技术向速度更快、自动化程度更高、纱线品种更加多样的方向发展,但不同纤维原料成纱质量差距较大,应借助仿真模拟技术研究喷嘴内流场分布和纤维运动规律,掌握纤维加捻成纱的根本原理,同时加强喷嘴结构设计和工艺参数优选方面的研究。