Bounce-off Effect Research Articles

New correlations for the initial collection efficiency of Brownian aerosol particles with the bounce-off effect considered in granular filtration

The effect of Brownian aerosol particles bouncing off the collector on the initial collection efficiency in the granular filtration process is investigated by using Brownian dynamics simulation method in this work. Based on the simulation results, a correlation for predicting the initial collection efficiency of submicron aerosols is derived. The correlation derived by Yoshida and Tien (1985) is combined with that derived in this work to yield a new correlation. When available aerosol experimental data of granular filtration are analyzed, it is found that this new correlation provides excellent predictions of collection efficiency for both micron and submicron aerosol particles.

Azimuthal correlation and collective behavior in nucleus-nucleus collisions

Various flow effects of nuclear and hadronic origin are investigated in nucleus-nucleus collisions. Nuclear emulsion data collected from 84Kr + Ag/Br interaction at an incident energy of 1.52 GeV per nucleon and from 28Si + Ag/Br interaction at an incident energy of 14.5 GeV per nucleon are used in the investigation. The transverse momentum distribution and the flow angle analysis show that collective behavior, like a bounce-off effect of the projectile spectators and a sidesplash effect of the target spectators, are present in our event samples. From an azimuthal angle analysis of the data we also see a direct flow of the projectile fragments and of the produced charged particles. On the other hand, for both data samples the target fragments exhibit a reverse flow, while the projectile fragments exhibit an elliptic flow. Relevant flow parameters are measured.

Collection of SiO 2, Al 2O 3 and Fe 2O 3 particles using a gas-solid fluidized bed filter

The filtration of SiO 2, Al 2O 3 and Fe 2O 3 particles with average sizes of 4 and 40 μm using a fluidized bed filter at 40 and 300 °C was studied. The collection mechanisms, interparticle forces and bounce-off effect between filtered particles and collectors were analyzed to determine their effect on particle filtration. Experimental results showed that the collection efficiency of 4 μm SiO 2 and Al 2O 3 particles exceeded that of 40 μm particles. Contrarily, the 40 μm Fe 2O 3 particles were collected more efficiently than the 4 μm particles, because of the differences between the microstructures of SiO 2, Al 2O 3, and Fe 2O 3 particles. The interaction between the particles affected the removal of mixed SiO 2, Al 2O 3 and Fe 2O 3. The particle size distribution (PSD) of the particles in the exit was governed by the operating temperature, the original size of the filtered particles, the interparticle force and the hardness of the particles and the collectors. The smallest particles were not those most easily elutriated from the fluidized bed filter because they agglomerated with each other or with large particles. The van der Waal's force dominated the forces between 4 and 40 μm particles. The main collection mechanism for 4 and 40 μm particles was direct interception. The effect of impaction increased with particle size above 40 μm. The strong impaction and bounce-off effect reduced the collection efficiency of 40 μm SiO 2 and Al 2O 3 particles. However, the strong interparticle force between Fe 2O 3 particles and collectors contributed to the high collection efficiency of the Fe 2O 3 particles.

Scaling violation of transverse flow in heavy ion collisions at AGS energies

The collective bounce-off effect is studied in the Quark Gluon String Model for S+S and Au+Au reactions at 11.6 A GeV/ c. The dependence of scale-invariant flow on the impact parameter shows a strong change from light to heavy colliding systems, as was predicted by viscous fluid dynamics, and was confirmed by the experiments at Bevalac energies.

Collective bounce-off phenomenon in139La+Ag(Br) reaction at 1.1 A GeV energy

Out of a total statistics of 896139La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and84Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionT(Φ ij ) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.

Circumstantial evidence for a stiff nuclear equation of state

We discuss the recent attempts to extract the nuclear equation of state from event-by-event data on high energy heavy ion collisions via the Vlasov-Uehling-Uhlenbeck theory. In this approach, the time evolution of the Wigner function is followed in configuration and momentum space. Rapid stopping of the projectile occurs at small impact parameters. For intermediate impact parameters, the theory predicts simultaneously the bounce-off effect of the projectile fragments and the sidewards flow of the participant matter. The latter can be displayed via a peak in the distribution of the flow angle Op at large values of Op, while the bounce-off is most easily observed via a pronounced maximum of the transverse momentum transfer p x(y) at the projectile rapidity. A drastic dependence of p x and Op on the mass of the colliding system, impact parameter, and bombarding energy is predicted. Recent data are used to extract an equation of state. The resulting EOS is consistently the same and in quantitative agreement with results obtained from pion multiplicities via various methods.

Stopping power, equilibration, and collective flow in the reactions Ar + Pb and Nb + Nb — A theoretical analysis

The approach to local kinetic equilibrium in relativistic heavy ion collisions is studied by following the time evolution of the Wigner function for Ar (770 MeV/N)+Pb in configuration and momentum space using the Vlasov-Uehling-Uhlenbeck theory. Rapid equilibrium of the participant region is observed within 10 fm/ c. Total stopping of the projectile occurs at small impact parameters. For intermediate impact parameters, the theory predicts simultaneously the bounce-off effect of the projectile fragments and the sidewards flow of the participant matter. The latter can be displayed via a large angle peak in the flow angle, θ f, distributions, while the bounce-off is most easily observed via a pronounced peak in the rapidity dependence of the transverse momentum transfer p x ( y). A drastic dependence of p x and θ f on impact parameter and bombarding energy is predicted for Ar + Pb and Nb + Nb. Recent data support our analysis.

Fokker-Planck and linear transport solutions to collective flow in heavy ion collisions.

Collective flow effects associated with bounceoff and side splash recently seen in Nb+Nb collisions are investigated. The nuclear bounceoff effect is studied using a folded optical potential. The velocity dependence of the two-body interaction is found to be important for bounceoff. The side-splash effect is studied using linear transport theory. Based on a relaxation time approximation to the Boltzmann equation, we are able to explicitly isolate two separate contributions to the kinetic flow tensor. Specifically, the kinetic flow tensor is related to the collective velocity field and the pressure tensor. In turn, the pressure tensor is related to the nuclear viscosity. The two contributions to kinetic flow interfere destructively. Assuming laminar flow, the viscous term is found to be important in the nuclear side-splash effect.

Cascade-Model Analysis of the Sideward "Splash" in Nb+Nb Collisions with High-Multiplicity Events

A cascade model has been applied to a global analysis of high-multiplicity events in 400-MeV/nucleon Ca+Ca and Nb+Nb collisions. The global analysis gives a sideward peak in the angular distribution of the high-multiplicity Nb+Nb events. The appearance of the peak is closely related to the development of cascade collisions from the participant region into the remaining (cold) region of the nuclei, which induces the recoil motion of these nuclei, i.e., the bounceoff effect.

Global variables and the dynamics of relativistic nucleus-nucleus collisions

Various global variables providing a simple description of high multiplicity events are reviewed. Many of them are calculated in the framework of an intra-nuclear cascade model, which describes the collision process as a series of binary on-shell relativistic baryon-baryon collisions and which includes inelasticity through the production of Δ-resonances. The calculations are first made for the Ar + KCl system at 0.8 GeV/A, with global variables including either all the nucleons or only the participant nucleons. The shape and the orientation of the ellipsoid of sphericity are particularly investigated. For both cases, on the average, the large axis of the ellipsoid is found to point in the beam direction. This result is discussed in comparison with hydrodynamics predictions and in relation with the mean free path. A kind of small “bounce-off effect” is detected for intermediate impact parameters. The possibility of extracting the value of the impact parameter b from the value of a global variable is shown to depend upon the variation of this variable with b and upon the fluctuation of the global variable for a given impact parameter. A quality factor is denned to quantify this possibility. No current global variable seems to be more appropriate than the number of participant nucleons for the impact parameter selection. The physical origin of the fluctuations inside the intranuclear cascade model is discussed and the possibility of extracting useful information on the dynamics of the system from the fluctuations is pointed out. The energy dependence of our results is discussed. Some results of the calculations at 250 and 400 MeV/A are also presented for the same system Ar + KC1.

Importance of nuclear viscosity and thermal conductivity and the analysis of the bounce-off effect in high energy heavy ion collisions

We present an analysis of high energy heavy ion collisions at intermediate impact parameters, using a two-dimensional fluid-dynamical model including shear and bulk viscosity, heat conduction, a realistic treatment of the nuclear binding, and an analysis of the final thermal emission of free nucleons. We find large collective momentum transfer to projectile and target residues (the highly inelastic bounce-off effect) and explosion of the hot compressed shock zones formed during the impact. As the calculated azimuthal dependence of energy spectra and angular distributions of emitted nucleons depends strongly on the coefficients of viscosity and thermal conductivity, future exclusive measurements may allow for an experimental determination of these transport coefficients. The importance of $4\ensuremath{\pi}$ measurements with full azimuthal information is pointed out.[NUCLEAR REACTIONS $^{20}\mathrm{Ne}$ + $^{238}\mathrm{U}$, ${E}_{1\mathrm{ab}}=400$ MeV/nucleon fluid dynamics, viscosity, heat conduction, cross sections.]