Large Spreading Rate Research Articles

Effective Methods of Restraining Diffusion in Terms of Epidemic Dynamics

Removing influential nodes or shortcuts in a network restrains epidemic or information diffusion, but this method destroys the connectivity of the network and changes the topological structure. As an alternative, an additional field can be imposed in the network to affect node behaviors and slow down diffusion dynamics. However, little research has been performed systematically to analyze and compare these methods. This paper investigates epidemic dynamics and proposes the following four methods to restrain the diffusion process: blocking nodes, blocking edges, distracting node attention, and propagating opposite information. We compare differences in the actions of these methods, and investigate their joint effects. Through numerical experiments in a scale-free network and a real network, we observe that these methods change the spreading threshold and final extent with different conditions. The method of blocking nodes is more efficient and economical than blocking edges. Propagating opposite information can effectively prevent diffusion of target information that has a large spreading rate, whereas distracting node attention only takes effect for the information with a small rate. Meanwhile, the effects of these two methods mainly depend on their action time. From the joint effects, we can select the optimal method for different situations.

Identifying node spreading influence for tunable clustering coefficient networks

Identifying the node spreading influence is of significant for information and innovation diffusion. In this paper, we argue that the spreading process should be taken into account for identifying the node spreading influence and investigate the effect of the network structure, measured by the clustering coefficient, on the performance of spreading dynamics. Firstly, we generate a series of networks with tunable clustering coefficients. Then, taking into account the spreading process, we explore the performances among the Dynamics-sensitive (DS) index and the degree, between, closeness, eigenvector indices. Comparing with the Susceptible–Infective–Removed (SIR) model, the extensive results show that, for different spreading time steps and clustering coefficients, the DS centrality outperforms the performance, τ>0.97, of degree, betweenness, closeness and eigenvector measures. Moreover, the accuracy of closeness and eigenvector centrality is similar and conducts better in networks with larger spreading rate β=0.20,τ>0.93. As the clustering coefficient increases, all the performances decrease but DS centrality with least percent of 1.16 at most under β=0.10, and Closeness with the largest percent of 9.75 under β=0.05. This work suggests that the spreading influence not only depends on the network structure, more importantly, the spreading dynamic process also affect the performance greatly, which should be taken into account simultaneously.

The prediction of Counterproductive Work Behaviours: Beyond the Five Factor Model

Identifying the node spreading influence is of significant for information and innovation diffusion. In this paper, we argue that the spreading process should be taken into account for identifying the node spreading influence and investigate the effect of the network structure, measured by the clustering coefficient, on the performance of spreading dynamics. Firstly, we generate a series of networks with tunable clustering coefficients. Then, taking into account the spreading process, we explore the performances among the Dynamics-sensitive (DS) index and the degree, between, closeness, eigenvector indices. Comparing with the Susceptible–Infective–Removed (SIR) model, the extensive results show that, for different spreading time steps and clustering coefficients, the DS centrality outperforms the performance, τ>0.97, of degree, betweenness, closeness and eigenvector measures. Moreover, the accuracy of closeness and eigenvector centrality is similar and conducts better in networks with larger spreading rate β=0.20,τ>0.93. As the clustering coefficient increases, all the performances decrease but DS centrality with least percent of 1.16 at most under β=0.10, and Closeness with the largest percent of 9.75 under β=0.05. This work suggests that the spreading influence not only depends on the network structure, more importantly, the spreading dynamic process also affect the performance greatly, which should be taken into account simultaneously.

Control of the coherent structure dynamics downstream of a backward facing step by DBD plasma actuator

A non-thermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step (U0=15m/s, Reh=30,000, Reθ=1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step and also to measure the global wall pressure fluctuation coefficients. A parametric study is performed where the voltage amplitude, the burst frequency and the duty-cycle of the input high voltage are investigated separately regarding their performance. Mean and phase-averaged velocity fields are obtained by time-resolved PIV and they are used to analyze the impact on the dynamic of the flow. The minimum reattaching position is achieved by forcing the flow at the shear layer mode through 2D periodic perturbations in the initial region at Sth=0.25 (Stθ=0.013), where a large spreading rate is obtained by increasing the organization and periodicity of the vortex street. A mean recirculation reduction by 22% is observed. Pressure fluctuations are maximized for an actuation at half the shear layer mode (Sth=0.125 or Stθ=0.006). For this subharmonic forcing mode by single-frequency perturbation, the vortex pairing is enhanced. The present study shows that the subharmonic mode corresponds to the well-known shedding mode that promotes flow structures remaining coherent over a long distance and dominating all the flow dynamics, this including the dynamics of the reattaching point.

Turbulent separated shear flow control by surface plasma actuator: experimental optimization by genetic algorithm approach

The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated flows. Here, a nonthermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step (U 0 = 15 m/s, Re h = 30,000, Re θ = 1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step (objective function #1) and also to measure the wall pressure fluctuation coefficients (objective function #2). An autonomous multi-variable optimization by genetic algorithm is implemented in an experiment for optimizing simultaneously the voltage amplitude, the burst frequency and the duty cycle of the high-voltage signal producing the surface plasma discharge. The single-objective optimization problems concern alternatively the minimization of the objective function #1 and the maximization of the objective function #2. The present paper demonstrates that when coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm can find the optimum forcing conditions in only a few generations. At the end of the iterative search process, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing process. The objective function #2 is maximized for an actuation at half the shear layer mode. In this specific forcing mode, time-resolved PIV shows that the vortex pairing is reduced and that the strong fluctuations of the wall pressure coefficients result from the periodic passages of flow structures whose size corresponds to the height of the step model.

Wetting kinetics of the AgCuTi filler metal on pure molybdenum substrate

Spreading of the AgCuTi filler metal over a pure molybdenum substrate under a high‐purity argon atmosphere was studied at elevated temperatures, within the range of 1283 ~ 1373 K. Real‐time in situ observations and quantitative measurements assisted by hot‐stage microscopy were used to analyze the kinetics of the triple‐line movement. The state of the interface between the substrate and the resolidified alloy and in the neighborhood of the triple line was considered. The empirical data indicate that wetting of AgCuTi alloy on the pure molybdenum substrate features a similar trend of the triple‐line kinetics. The triple‐line equivalent radius of the front during spreading increases initially, with a large spreading rate, and subsequently changes gradually the rate approaching to an asymptotic value. Kinetics of the triple‐line movement throughout the spreading process shows that the wetting follows the power law, Rn ~ t, n ~ 8. During spreading, Ag‐based solid solution, AgCu eutectic phase, and CuTi binary phase were formed along the interface within the joint zone, hence the spreading evolves under weak reactive conditions. Copyright © 2015 John Wiley & Sons, Ltd.

Impact of buoyancy on vortex ring development in the near field

The development of a buoyant vortex ring in the near field was examined experimentally, and the findings were compared with those of a non-buoyant ring with a similar Reynolds number. The experiments were performed in a water tank, and the vortices were produced by a cylindrical tube of aspect ratio 2. Laser sheet flow visualization and PIV measurements were carried out. In the near field, the initial column of the buoyant fluid breaks down due to the presence of Rayleigh–Taylor instability at the buoyant fluid interface. Subsequently, a large diameter vortex ring with a large spreading rate, compared with the non-buoyant ring, emerges. The celerity of buoyant vortex continued to decrease throughout the range examined, in contrast to the constant celerity of the non-buoyant ring. The vorticity in the core of buoyant and non-buoyant vortex rings is symmetric and has a Gaussian distribution. However, the buoyant vortex ring evolves into a thin core ring, whereas the non-buoyant ring becomes a thick core ring shortly after the ring formation. This difference is brought on by the rapid entrainment and the significant growth of the buoyant ring following the breakup of the initial formation.

Direct numerical simulation of passive scalars mixing in an axisymmetric swirl induced vortex breakdown flow

A swirling jet is comprised of axial momentum superimposed on angular momentum. It is a complicated flow whose characteristics and dynamics are not fully understood, although it is widely used in a variety of combusting situations. It is known, for example, that swirling jets have a larger spreading rate and higher mass entrainment than non-swirling jets (Panda & McLaughlin, 1994), however the mechanisms responsible for these characteristics are not known. In combusting flows, swirl is often a desirable commodity as it enhances mixing, stabilises the high intensity combustion process and promotes efficient and clean combustion in a variety of applications, including petrol and diesel engines, gas turbines and industrial furnaces. In determining the rate of combustion, a first approximation is to assume equal diffusivity of all reactants, and then the rate of mixing is the controlling factor determining the rate of combustion. In reality the turbulence will preferentially move a scalar with high molecular diffusivity relative to one with a lower molecular diffusivity. This process, called differential diffusion, is a potential complication of the mixing process and will influence the speed and efficiency of combustion.

Near-field pressure radiation and flow characteristics in low supersonic circular and elliptic jets

The near-field pressure fluctuations of circular and elliptic underexpanded supersonic jets were studied experimentally. Unlike the case of low subsonic jets, the pressure fluctuation characteristics at the minor axis plane of the elliptic jet were very different from those of the major axis plane. The amplitude of the pressure fluctuations at the minor axis was more than an order of magnitude higher than at the other plane. This section of the jet was also characterized by a larger spreading rate and higher amplification rate of the velocity fluctuations. The circular jet was similar to the major axis plane of the elliptic jet. The spectra of the near-field pressure fluctuations of both jets exhibited the highest peak at a frequency corresponding to the jets’ preferred mode frequency. The spectral peak related to the screech tone was much stronger at the minor axis plane and had the same frequency as at the other plane. The amplitude of the dominant pressure fluctuation frequencies was mapped in the entire near field, and each one was found to be dominant in a different region.

Flow characteristics of orifice and tapered jets

Two types of small-aspect-ratio slot jets were investigated. An orifice slot jet with a 3:1 aspect ratio was shown to have features similar to an elliptic jet with a well-designed contraction. A larger spreading rate and enhanced turbulent mixing, relative to a circular jet, can be obtained using this orifice nozzle, which is advantageous for many practical applications. By adding a conical contraction to the slot jet (tapered slot jet) the characteristics were totally altered. The axes switching, typical to an elliptic jet, did not occur and the spreading rate at the major axis plane was larger than at the minor axis plane. The turbulence amplification in the initial core region was higher than both in the circular and elliptic jets. The transition from the conical contraction of the nozzle to the slot shape of the outlet section produced three-dimensional vortical structures. These structures interacted with the asymmetric vortices shed from this noncircular configuration to enhance the small scale turbulence in the core region as well as in the jet circumference. The large spreading rate of the two configurations of slot jets is beneficial to increase the bulk mixing with the surrounding fluid through entrainment. The augmented turbulence level of the tapered slot jet is important for reacting flows where small scale mixing is required.