Directed transverse flow and its disappearance for asymmetric reactions

We study the directed transverse flow for mass asymmetry reactions. This is done by keeping the target fixed and varying the projectile mass from ⁴He to ¹³¹Xe. We find that directed transverse flow is sensitive to the mass of the projectile. We also study the disappearance of flow at a particular impact parameter called Geometry of Vanishing Flow (GVF) for such mass asymmetry reactions. Our results indicate that GVF is sensitive to the beam energy as well as to the mass of the projectile.     

Impact parameter and beam energy dependence for azimuthal asymmetry of direct photons and free protons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have calculated the impact parameter and beam energy dependence for azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coeffcient v2, of direct photons and the corresponding free protons in intermediate energy heavy-ion collisions. It is further shown the anti-correlated azimuthal asymmetry between direct photons and free protons.     

Impact parameter and beam energy dependence for azimuthal asymmetry of direct photons and free protons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have calculated the impact parameter and beam energy dependence for azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coefficient v₂, of direct photons and the corresponding free protons in intermediate energy heavy-ion collisions. It is further shown the anti-correlated azimuthal asymmetry between direct photons and free protons.     

反馈控制棘轮的定向输运效率研究

研究了反馈耦合布朗棘轮中粒子处于负载力、时变外力及噪声作用下的定向输运问题.详细讨论了外力作用时间的不对称性、外势空间的不对称性及外力周期等对反馈耦合棘轮中粒子输运效率的影响.研究发现,外力的时间不对称度能促进反馈棘轮中粒子的定向输运,随时间不对称度的增大,反馈棘轮中粒子能获得较大的效率.然而,外势空间的不对称度能有效抑制耦合棘轮中粒子的扩散,达到增强耦合粒子定向输运的效果.同时还发现,存在最优的噪声强度能使耦合粒子的输运效率达到最大.     

Nature optimizes the swirling flow in the human left ventricle

The asymmetry of the blood flow in the human left ventricle is commonly assumed to facilitate the following ejection of blood in the primary circulation. The intraventricular flow is here studied by the numerical solution of the governing equations written in a prolate spheroid geometry with moving walls. The physiological parameters are taken from pediatric clinical data; then, the entering jet is artificially displaced to modify the asymmetry of the flow. The analysis of flow patterns confirms that the physiological case looks to best comply with the transition from the filling to the ejection phase. The flow energy dissipation is found to be minimized about the physiological conditions. An unnatural asymmetry, as given by cardiac diseases or valvular replacement, could reduce the efficiency of the heart pump by over 10%, thus augmenting the work required by the cardiac muscle.     

Effect of charge mobility on dielectric liquid flow driven by EHD conduction phenomenon

Electrohydrodynamic (EHD) conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field and dissociated charges from electrolytes. EHD conduction generated flow relies primarily upon the asymmetry of the electrodes where the flow is always directed toward the broken symmetry regardless of the electrodes polarity. This paper studies the effects of unequal positive and negative charge mobilities on the heterocharge layer structure and generated flow with symmetric and asymmetric electrode designs. The numerical simulations are conducted for a 2-D rectangular channel with the electrodes embedded against the channel wall.     

过阻尼布朗棘轮的斯托克斯效率研究

根据随机能量理论解析得到阻尼环境中布朗粒子的概率流和斯托克斯效率,并进一步研究布朗粒子的输运性能.详细讨论了空间的不对称性、外偏置力及外势结构等对棘轮定向输运的影响.研究发现,合适的外偏置力能使棘轮的定向输运达到最强.通过调节外势的不对称性可使棘轮中粒子的运动反向,当选择合适的空间不对称性时布朗粒子的反向输运可获得最强.此外,一定条件下合适的外势高度也能增强棘轮输运,且能使粒子克服黏滞阻力的斯托克斯效率达到最大.所得结论能够启发实验上设计合适的外势及外偏置来优化布朗棘轮的定向输运性能,并为生物纳米器件的研制提供一定的理论参考.     

系统非对称性及记忆性对布朗马达输运行为的影响

在对分数阶布朗马达输运现象研究的基础上,引入了描述系统势场对称性的参数(简称对称性参数),并详细分析了该参数及记忆性参数(分数阶阶数)对粒子输运状态的影响.仿真结果表明,分数阶阶数和对称性参数的共同作用会使得布朗粒子形成定向输运反向流,反向后达到最大平均流速所对应的阶数与外加驱动力频率无关联,但会随对称性参数的增加而单调递增.     

Collective flow of K~+ mesons in heavy-ion collisions predicted by the covariant Kaon dynamics

The directed and elliptic flow of positively charged kaons produced in5828Ni+5828Ni reactions at incident kinetic energy 1.91 AGe V are studied within the covariant kaon dynamics and compared to new data. We observe that the influence of the Lorentz force on the directed and differential directed flow of K+mesons is obvious. Our calculated results indicate that it is necessary for the Lorentz force to be included in the kaon dynamics in order to reasonably describe experimental data.     

Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter F   and elliptic asymmetry coefficient v₂$v_2$, for proton–neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive F   and negative v₂$v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow.     

Directed motion of vortices in a current-driven Josephson junction network

Dynamics of directed motion of vortices in a Josephson junction network (JJN) with a ladder structure is studied using a numerical simulation. By applying spatial and temporal modulation of external bias currents, directed motion of vortices occurs in the absence of a ratchet-type asymmetric potential. In the present system, the asymmetry of the directed motion emerges as a dynamical effect due to the modulated bias current. Some dynamical effects such as mode-locking and vortex–antivortex excitation are relevant to the directed dynamics. We clarify the details of the directed motion of vortices in the JJN.     

Synchronization transition of identical phase oscillators in a directed small-world network

We numerically study a directed small-world network consisting of attractively coupled, identical phase oscillators. While complete synchronization is always stable, it is not always reachable from random initial conditions. Depending on the shortcut density and on the asymmetry of the phase coupling function, there exists a regime of persistent chaotic dynamics. By increasing the density of shortcuts or decreasing the asymmetry of the phase coupling function, we observe a discontinuous transition in the ability of the system to synchronize. Using a control technique, we identify the bifurcation scenario of the order parameter. We also discuss the relation between dynamics and topology and remark on the similarity of the synchronization transition to directed percolation.     

Directing ultrasound at the cemento-enamel junction (CEJ) of human teeth: I. Asymmetry of ultrasonic path lengths

The diagnosis of degenerative changes in human teeth is of general interest because early detections can avoid greater health problems and further weakening effects. Since the wear of teeth determines their stability and lifetime in relation to the physiological load, an ultrasonic survey of any dimensional changes of the enamel layer and especially of the dentin wall thickness may be very helpful. However, an ultrasonographic diagnosis requires first to determine the anisotropic human tooth properties at clinically relevant locations and to simulate wave propagation phenomena in inhomogeneous tooth models with proper dimensions. The first article of a series that provides modular data of mineralized tissues in human teeth at the cemento-enamel junction (CEJ) deals with an ultrasonic method for measuring the asymmetry of dimensional characteristics of extracted human teeth and their ultrasonic path lengths (UPL). Heavily attenuating tooth halves were investigated with respect to the symmetry of normal and inclined oppositely directed radial ultrasonic paths. The measured UPLs ranged from 1.2 mm to 4.4 mm. The relative difference in inclined UPLs between the left and the right tooth halves reaches almost 30%. This reveals a large asymmetry. The mean difference of angles that represent fastest path lengths was 2.2+/-8.1 degrees, which indicates large asymmetry and anisotropy. Several aspects, which are required for a proper integration of asymmetric data into models designed for medical element engineering and simulation (MEES), are discussed.     

Supersymmetric ratchets

The overdamped Brownian motion in a periodic potential under far from equilibrium conditions is considered. A large class of systems with an intrinsic asymmetry, called supersymmetric ratchets, is identified for which the occurrence of directed transport can be ruled out without any fine-tuning of parameters.     

Role of the mass asymmetry of reaction on the geometry of vanishing flow

We study the transverse flow throughout the mass asymmetry range as a function of the impact parameter, keeping the total mass of the system fixed. We find that the geometry of vanishing flow (GVF) i.e. the impact parameter at which flow vanishes and its mass dependence is quite sensitive to the mass asymmetry of the reaction. With increase in the mass asymmetry, the value of GVF decreases, while its mass dependence increases. Our results indicate the sizable role of mass asymmetry on GVF as on balance energy.     

Directed segregation in compartmentalized bi-disperse granular gas

A bi-disperse granular gas in an asymmetrical two-compartment system is studied experimentally. The presence of asymmetry within the range of our experimental parameters results in a directed segregated state and a directed clustering state. This deterministic system does not depend on the initial conditions. A modified flux model based on Lohse's flux model for bi-disperse granular gases is derived. The modified flux model explains qualitatively the experimental results.     

Investigation of a turbulent wall jet in forced convection issuing into a directed coflow stream

In the present paper, we have studied numerically the directed coflow stream effects on mean and turbulent flow properties of a turbulent plane wall jet in forced convection emerging into a directed coflow stream. The system of equations governing the studied configuration is solved with a finite difference scheme using a staggered grid for numerical stability, not uniform in the two directions of the flow. The modified version of the first-order low Reynolds number k–? turbulence model is used and compared to existing experimental findings. It is found that predicted results are in satisfactory agreement with the experimental data and that the wall jet fluid decays faster in presence of a directed coflow stream. Results show also that the increase of coflow deviation angles causes an increase of the growth rates of the dynamic and thermal half-width of the jet and enhances the turbulent mixing. It is found that the longitudinal development of normalised forms of the jet characteristics parameters at different directed coflow velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale.     

动量相关势对直接流和椭圆流的影响

利用极端相对论量子分子动力学(UrQMD)模型,研究了两种不同强度的动量相关势对中子、质子、氢同位素和带电荷粒子等四种粒子直接流和椭圆流的影响.计算结果表明,在不可压缩系数K0一定的情况下,直接流几乎不敏感于动量相关势的变化,而高动量粒子的椭圆流v2则敏感于高动量处动量相关势强度的大小及其动量依赖.考虑高动能区强度较强...     

Large eddy simulation of a turbulent spray jet generated by high-pressure injection: impact of the in-nozzle flow

The turbulence properties of a gas spray jet generated through the injection of a high-pressure atomising spray were studied in the context of the Euler–Lagrange formulation using a large eddy simulation (LES) approach. The study's main aim was to investigate nozzle flow effects on flow and turbulence statistics for a two-phase jet flow in the near and far fields of the spray. The study investigated the injection of an existing in-nozzle flow at the spray inlet. Simulation results were compared with measurements obtained for non-evaporating sprays under quasi-steady conditions, which, in practice, correspond to a long-duration injection. Both simulated high-injection pressure cases showed a good agreement with experimental data. A two-stage evolution of the spray was observed. The flow of the gas jet first developed along the spray cone, followed by the appearance of highly vortical structures around and within the spray. Cavitation in the nozzle flow resulted in an observed asymmetry of the generated gas spray jet: on the gas spray jet side of the nozzle (relative to the cavitation side), stronger jet spreading occurred, and droplets were smaller and slower. The spray jet typically exhibited an ellipsoidal cross-sectional shape. The paper provides a characterisation of the asymmetry that persisted for the duration of the spray evolution (at least for the distances considered here).     

二维势场中弹性耦合粒子的定向输运研究

建立了二维势场中弹性耦合粒子的输运模型, 其中一维上加交流驱动及噪声, 另一维上不加驱动及噪声, 分析讨论了过阻尼情形下系统和外部参量对定向流的影响. 结果表明, 粒子可以通过相互耦合使一个方向上输入的驱动能量转化到垂直方向上, 从而使无能量输入的方向产生定向流. 适当的弹簧自由长度及耦合强度可以使定向流达到极值, 特别是当耦合强度及噪声强度固定时, 定向流会随弹簧自由长度的变化而振荡, 出现多峰现象. 研究还发现, 定向流随噪声强度的变化出现随机共振现象. 当产生定向流方向上的势的不对称度达到一定程度时会出现流反转现象. 关键词： 弹性耦合 定向输运 随机共振 流反转