Eccentricity fluctuations are not the only source of elliptic flow fluctuations in a multiphase transport model

Sources of event-by-event elliptic flow fluctuations in relativistic heavy-ion collisions are investigated in a multiphase parton transport model(AMPT).Besides the well-known initial eccentricity fluctuations,several other sources of elliptic flow dynamical fluctuations are identified.One is fluctuations in initial parton configurations at a given eccentricity.Configuration fluctuations are found to be as important as eccentricity fluctuations in elliptic flow development.A second is quantum fluctuations in parton-parton interactions during system evolution.A third is fluctuations caused by hadronization and final-state hadronic scatterings.The magnitudes of these fluctuations are investigated relative to the eccentricity fluctuations and the average elliptic flow magnitude.The fluctuations from the latter two sources are found to be negative.The results may have important implications for the interpretation of elliptic flow data.     

Pion polarizability in a chiral quark model

The pion polarizability is calculated in a chiral meson-quark model at the one-loop level. The results are in complete agreement with earlier ones obtained within a chiral meson-baryon theory. A critical discussion of a recent paper by Llanta and Tarrach is given.     

Variational model of granular flow in a three-dimensional rotating container

We considered a flow of a cohesionless granular material in a partially filled three-dimensional rotating container. A variational continuum mechanics model is suggested to describe the profile of the free surface of the granular material. A combination of a level set method and a variational form of energy conservation equation allows us to describe flow of granular material in arbitrary-shaped containers.     

Dense granular flow around a penetrating object: experiment and hydrodynamic model

We present in this Letter experimental results on the bidimensional flow field around a cylinder penetrating into dense granular matter, together with drag force measurements. A hydrodynamic model based on extended kinetic theory for dense granular flow reproduces well the flow localization close to the cylinder and the corresponding scalings of the drag force, which is found to not depend on velocity, but linearly on the pressure and on the cylinder diameter and weakly on the grain size. Such a regime is found to be valid at a low enough "granular" Reynolds number.     

Acoustic scattering by a rigid elliptic cylinder in a slightly viscous medium

A complete solution is obtained for the two-dimensional diffraction of a time-harmonic acoustic plane wave by an impenetrable elliptic cylinder in a viscous fluid. Arbitrary size, ellipticity, and angle of incidence are considered. The linearized equations of viscous flow are used to write down expressions for the dilatation and vorticity in terms of products of radially and angular dependent Mathieu functions. The no-slip condition on the rigid boundary then determines the coefficients. The resulting computations are facilitated by recently developed library routines for complex input parameters. The solution for the circular cylinder serves as a guide and a differently constructed solution for the strip is also given. Typical results in the "resonant" range of dimensionless wave number, displaying the surface vorticity and the far-field scattering pattern are included, with the latter allowing comparison with the inviscid case.     

Solid-fluid transition in a granular shear flow

The rheology of a granular shear flow is studied in a quasi-2D rotating cylinder. Measurements are carried out near the midpoint along the length of the surface flowing layer where the flow is steady and nonaccelerating. Streakline photography and image analysis are used to obtain particle velocities and positions. Different particle sizes and rotational speeds are considered. We find a sharp transition in the apparent viscosity (eta) variation with rms velocity (u). Below the transition depth we find that the rms velocity decreases with depth and eta proportional to u(-1.5) for all the different cases studied. The material approaches an amorphous solidlike state deep in the layer. The velocity distribution is Maxwellian above the transition point and a Poisson velocity distribution is obtained deep in the layer. The results indicate a sharp transition from a fluid to a fluid + solid state with decreasing rms velocity.     

Pion and photon bremsstrahlung in a heavy ion reaction model with friction

Based on a classical dynamical model of nuclear motion with a velocity dependent friction force we calculate pionic and electromagnetic bremsstrahlung emitted in heavy ion collisions with bombarding energies between 20 and 84 MeV/n. For arbitrary projectile-target combinations and with a fixed value of the only parameter of the model, the friction coefficientκ, our calculations reproduce the observed beam energy and target mass dependence for pions. The gamma yields, calculated with the same value ofκ, reproduce the measured dependence of the cross-section on energy and target mass, but underestimate the published data by a factor two. This is a good agreement in view of the discrepancies between different experimental groups.     

Pion and K meson production in the multiperipheral model

A simple multiperipheral model, that utilizes only three parameters, two coupling constants and exponential damping for each momentum transfer is developed and applied to the calculation of inclusive distributions. The pion rapidity and p_⊥² distributions are successfully predicted; as are the energy dependences of strange particle production cross sections. The development of inclusive distributions with increasing energy and possible improvements to the model are discussed.     

Towards a common origin of the elliptic flow,ridge, and alignment

It is claimed that elliptic flow, ridge and alignment are effects of azimuthal asymmetry, which have a common origin evolving with primary energy and stemming from the general structure of field-theoretical matrix elements. It interrelates a new ridge-phenomenon, recently found at the LHC and RHIC, with known coplanarity feature observed in collider jet physics as well as in cosmic ray studies.     

非对称黏性空气动力学声带模型及其病理喉声源分类

二质量块模型(SH模型)在模拟病理发声时未考虑弹性力对发声系统的影响,也未考虑黏性气流在声门闭合阶段的作用,本文提出一种非对称黏性空气动力学声带模型(ISAC模型)。对非对称振动时的附加弹性系数和弹性形变进行分析,修正质量块所受的碰撞力,随位移量变化调节原始模型中的劲度系数,模拟环甲肌和甲杓肌的张力作用;通过声门倾角变化得到声门处的气流分布,以实现声带壁上的非对称气流压力作用。该模型应用于发声病理诊断,模型仿真和病理喉声源分类识别的实验结果显示,各声门特征参数相对误差不超过1.5%,ISAC模型的加权平均误差低于SH模型,二分类识别率和细分准确率均高于SH模型。     

Physical hydrodynamic propulsion model study on creeping viscous flow through a ciliated porous tube

The present investigation focusses on a mathematical study of creeping viscous flow induced by metachronal wave propagation in a horizontal ciliated tube containing porous media. Creeping flow limitations are imposed, i.e. inertial forces are small compared to viscous forces and therefore a very low Reynolds number (Re ? 1) is taken into account. The wavelength of metachronal wave is also considered to be very large for cilia movement. The physical problem is linearized and exact solutions are developed for the differential equation problem. Mathematica software is used to compute and illustrate numerical results. The influence of slip parameter and Darcy number on velocity profile, pressure gradient and trapping of bolus are discussed with the aid of graphs. It is found that with increasing magnitude of the slip parameter, the trapped bolus inside the streamlines increases in size. The study is relevant to biological propulsion of medical micromachines in drug delivery.     

Free surface and flow problem for a viscous liquid

An exact closed system of equations is proposed for describing the shape of the free surface of a viscous steady-state liquid in the 2D case in terms of the surface itself. A method that lowers the dimensionality in the Navier-Stokes equation is demonstrated, and its application in problems of steady-state flow past solids is considered.     

Pion and nucleon thermal widths in the linear sigma model

We calculate the hadronic width (damping rate) of pions and nucleons at finite temperature in the framework of the linear sigma model, and to lowest order in the virial expansion. Results indicate a substantial growth of both widths even at moderately low temperatures.     

Radial, sideward and elliptic flow at AGS energies

We study the baryon transverse in-plane (sideward) and elliptic flow from SIS to AGS energies for AuAu collisions in a relativistic dynamical simulation model that includes all baryon resonances up to a mass of 2 GeV as well as string degrees of freedom for the higher mass continuum. There are two factors which dominantly determine the baryon flow at these energies: the momentum dependence of the scalar and vector potentials and the resonance-string degrees of freedom. We fix the explicit momentum dependence of the nucleon-meson couplings of NL3(hard) equation of state (EoS) by the nucleon optical potential up to 1 GeV of kinetic energy. We simultaneously reproduce the sideward flow, the elliptic flow and the radial transverse mass distribution of protons data at AGS energies. In order to study the sensitivity of different mean-field EoS, we use NL2(soft) and NL23(medium) along with NL3(hard) momenta-dependent mean-field EoS. We find that to describe data on both sideward and elliptic flow, NL3 model is better at 2 A·GeV, while NL23 model is at 4–8 A·GeV.