Mini-jet thermalization and diffusion of transverse momentum correlation in high-energy heavy-ion collisions

Transverse momentum correlation in azimuthal angle of produced hadrons due to mini-jets are studied first within the HIJING Monte Carlo model in high-energy heavy-ion collisions. Jet quenching in the early stage of thermalization is shown to lead to significant diffusion (broadening) of the correlation. Evolution of the transverse momentum density fluctuation that gives rise to such correlation in azimuthal angle in the later stage of heavy-ion collisions is further investigated within a linearized diffusion-like equation and is shown to be determined by the shear viscosity of the evolving dense matter. Such a diffusion equation for the transverse momentum fluctuation is solved with initial values given by HIJING and together with the hydrodynamic equation for the bulk medium. The final transverse momentum correlation in azimuthal angle is calculated along the freeze-out hyper-surface and is found further diffused for larger values of shear viscosity to entropy density ratio $\eta/s \sim 0.2-0.4$. Therefore the final transverse momentum correlation in azimuthal angle can be used to study the thermalization of mini-jets in the early stage of heavy-ion collisions and the viscous effect in the hydrodynamic evolution of the strongly coupled quark gluon plasma.Comment: RevTex 4, 4 pages and 2 figures, the method to determine the fluctuation in transverse fluid velocity in the initial time of the hydro evolution has been improved. The relevant parts have been rewritten with some discussions and references adde

Aeroacoustic testing of the landing gear components

The sound field generated by full scale landing gear components was studied in an acoustic wind tunnel. Noise characteristics were evaluated. The noise contribution of each part was investigated by removing the gear part individually. Three design parameters were also obtained to assess the noise reduction potential. Test results indicate that the noise spectrum of the component is essentially broadband and mainly dominated by some peaks corresponding to the constant St. Sound pressure level scales with the sixth power velocity law. Noise radiation from the components has obvious directivities. The main strut is the least contributor while the bogie is the largest contributor to the total noise. It is also found that the noise level increases with the gear installation angle from 0° to 16.5° while it decreases via changing the torque link layout from the front of the main strut to its back or modifying the bogie shape by filling its holes

Fitness-driven deactivation in network evolution

Individual nodes in evolving real-world networks typically experience growth and decay --- that is, the popularity and influence of individuals peaks and then fades. In this paper, we study this phenomenon via an intrinsic nodal fitness function and an intuitive aging mechanism. Each node of the network is endowed with a fitness which represents its activity. All the nodes have two discrete stages: active and inactive. The evolution of the network combines the addition of new active nodes randomly connected to existing active ones and the deactivation of old active nodes with possibility inversely proportional to their fitnesses. We obtain a structured exponential network when the fitness distribution of the individuals is homogeneous and a structured scale-free network with heterogeneous fitness distributions. Furthermore, we recover two universal scaling laws of the clustering coefficient for both cases, $C(k) \sim k^{-1}$ and $C \sim n^{-1}$, where $k$ and $n$ refer to the node degree and the number of active individuals, respectively. These results offer a new simple description of the growth and aging of networks where intrinsic features of individual nodes drive their popularity, and hence degree.Comment: IoP Styl

Metamaterial absorber integrated microfluidic terahertz sensors

Spatial overlap between the electromagnetic fields and the analytes is a key factor for strong light-matter interaction leading to high sensitivity for label-free refractive index sensing. Usually, the overlap and therefore the sensitivity are limited by either the localized near field of plasmonic antennas or the decayed resonant mode outside the cavity applied to monitor the refractive index variation. In this paper, by constructing a metal microstructure array-dielectric-metal (MDM) structure, a novel metamaterial absorber integrated microfluidic (MAIM) sensor is proposed and demonstrated in terahertz (THz) range, where the dielectric layer of the MDM structure is hollow and acts as the microfluidic channel. Tuning the electromagnetic parameters of metamaterial absorber, greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave. A high sensitivity of 3.5 THz/RIU is predicted. The experimental results of devices working around 1 THz agree with the simulation ones well. The proposed idea to integrate metamaterial and microfluid with a large light-matter interaction can be extended to other frequency regions and has promising applications in matter detection and biosensing

Effect of fitness on mutual selection in network evolution

AbstractWe propose a new mechanism leading to scale-free networks which is based on the presence of an intrinsic character of a vertex called fitness. In our model, at each vertex i a fitness xi, drawn from a given probability distribution function f(x), is assigned. During network evolution, with rate p we add a vertex j and connect to an existing vertex i of selected preferentially to a linking probability function g(xi,xj) which depends on the fitnesses of the two vertices involved and, with rate 1−p we create an edge between two already existed vertices i and j, with a probability also preferential to the connection function g(xi,xj). For the proper choice of g, the resulting networks have power-law distributions of connectivity and small-world properties, irrespective of the fitness distribution of vertices