Breakup Effects Research Articles

Effects of intermodal dispersion on short pulse propagation in multi-core fibers

The effects of intermodal dispersion on ultrashort optical pulse propagation through multi-core fibers are analyzed theoretically, which has been ignored in previous studies. A three-core fiber with collinear and triangular configuration and a four-core fiber are considered. We demonstrate with numerical examples that the intermodal dispersion can cause pulse breakup effect in multi-core fibers.

Dispersion of longitudinal momentum distributions induced in fragmentation reactions

On the basis of systematic measurements of fragmentation reactions, which provide a detailed overview on the velocity distributions of residual nuclei, an improved description of the kinematical properties of the fragmentation residues is established. This work is dedicated to the fluctuations of their momentum distributions. In contrast to previous investigations, limited to close-to-projectile fragments, we extended our study to the entire production range, down to the lightest observed fragments. In this context, beside the contribution of abrasion and evaporation processes, we considered the effect of the thermal break-up on the width of the momentum distributions. Using approximated theoretical descriptions of the different reaction stages, a new analytical formula for the variance of the momentum distribution is derived, which is well adapted to technical applications.

Ab InitioMany-Body Calculations of theH3(d,n)He4andHe3(d,p)He4Fusion Reactions

We apply the ab initio no-core shell model combined with the resonating-group method approach to calculate the cross sections of the $^{3}\mathrm{H}(d,n)^{4}\mathrm{He}$ and $^{3}\mathrm{He}(d,p)^{4}\mathrm{He}$ fusion reactions. These are important reactions for the big bang nucleosynthesis and the future of energy generation on Earth. Starting from a selected similarity-transformed chiral nucleon-nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that predict the $S$ factor of both reactions. Virtual three-body breakup effects are obtained by including excited pseudostates of the deuteron in the calculation. Our results are in satisfactory agreement with experimental data and pave the way for microscopic investigations of polarization and electron-screening effects, of the $^{3}\mathrm{H}(d,\ensuremath{\gamma}n)^{4}\mathrm{He}$ bremsstrahlung and other reactions relevant to fusion research.

Firm break-up and performance

We analyze the effects of firm break-up on corporate performance. Our analysis is based on a unique data set for a large number of Czech firms spanning the period 1996–2000. We employ a propensity score matching procedure to deal with endogeneity problems. Our results, which are generally in line with the positive effects of firm break-up found in the developed-market literature, show that the initial effects of firm break-up are positive but after a certain point they disappear within a short time. Factors like changes in ownership structure or management are found to be behind later improvements in the performance of firms.

Role of neutron transfer and deformation effect in capture process at sub-barrier energies

The roles of nuclear deformation and neutron transfer in sub-barrier capture process are studied within the quantum diffusion approach. The change of the deformations of colliding nuclei with neutron exchange can crucially influence the sub-barrier fusion. The sub-barrier capture reactions following the neutron pair transfer are used for the indirect study of neutron-neutron correlation in the surface region of nucleus. The strong surface enhancement of the neutron pairing in nuclei 48 Ca, 64 Ni, and 116,124,132 Sn is demonstrated. Comparing the capture cross sections calculated without the breakup effect and experimental complete fusion cross sections, the breakup was analyzed in reactions with weakly bound projectiles 6,7,9 Li and 9 Be. A trend of a systematic behavior for the complete fusion suppression as a function of the target charge and bombarding energy is not achieved.

Development of fibrillar morphology in immiscible PP/PS blends under shear flow

AbstractThe formation dynamics of fibrillar morphology in dilute immiscible polypropylene (PP)/polystyrene blends under simple shear flow is investigated using optical‐shear technique. Two strategies in generating fibrillar droplets under shear flow, namely temperature quench and shear jump, are studied. It is found that the shear‐induced deformation of PP droplets is closely related to the total shear strain and changes of rheological properties of components during the temperature quench or shear‐jump process. The shape evolution of fibrillar droplets under shear flow displays large deviation to the prediction of affine deformation theory based on Newtonian fluids and that of three deformation models, which consider the viscoelastic properties of components. The possible effect of droplet coalescence, breakup, and interfacial slip on the deviation between the experimental data and the prediction values for droplet deformation are discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Fusion of 6Li with 152Sm: Role of projectile breakup versus target deformation

Abstract Complete fusion cross sections for 6 Li + 152 Sm reaction have been measured at beam energies ( E lab = 20 – 40 MeV ) near the Coulomb barrier. The sub-barrier fusion cross sections were found to be systematically larger than those for 6 Li + 144 Sm, as expected from the deformed shape of the 152 Sm nucleus. The coupled-channels (CC) calculations including both projectile and target couplings overpredict the experimental fusion cross sections at above barrier energies. Reduced fusion cross sections for the present system at above barrier energies are found to be smaller compared to those with tightly-bound projectiles forming similar compound nuclei and also to those predicted using proximity potential. These observations along with the comparison of derived barrier distributions conclude that the complete fusion cross sections at energies above the Coulomb barrier are suppressed by 28 ± 4 % . A large cross section measured for incomplete fusion indicates that the above suppression is due to the loss of incident flux caused by projectile breakup. Thus the effect of both target deformation and projectile breakup are found to coexist.

Vliv rozdělení českých podniků na ziskovost a produktivitu

In this article we analyze medium- and long-term effects of firm break-up (and subsequent change in ownership) on its profitability and productivity. We use an extensive data-set of the Czech firms for the period 1996-2005. We employ the propensity score based matching methodology to account for potential endogeneity. Our results show that initial effects of the firm break-up are positive but they vanish in five to seven years after the break-up. Hence, the break-up of large and less efficient companies delivers a positive effect on corporate performance for a period of time. The effect is not permanent, though. Subsequent development in profitability and productivity is likely affected by ownership structure, corporate governance and other micro-level factors.

Dynamical effects in proton breakup from exotic nuclei

We study dynamical effects in proton breakup from a weakly bound state in an exotic nucleus on a heavy target. The Coulomb interactions between the proton and the core and between the proton and the target are treated to all orders, including also the full multipole expansion of the Coulomb potential. The dynamics of proton nuclear and Coulomb breakup is compared to that of an equivalent neutron of higher binding energy in order to elucidate the differences with the well-understood neutron breakup mechanism. A number of experimentally measurable observables such as parallel momentum distributions, proton angular distributions, and total breakup cross sections are calculated. With respect to nuclear breakup it is found that a proton behaves exactly as a neutron of higher binding energy. The extra ``effective energy'' is caused by the combined core-target Coulomb barrier. In Coulomb breakup we distinguish the effect of the core-target Coulomb potential (called the recoil effect), with respect to which the proton behaves, again, as a more bound neutron, from the direct proton-target Coulomb potential. The latter gives cross sections about an order of magnitude larger than the recoil term. The two effects give rise to complicated interferences in the parallel momentum distributions. They are instead easily separable in the proton angular distributions, which are therefore suggested as a very useful observable for future experimental studies.

Elastic scattering and total reaction cross sections for theB8,Be7, andLi6+12C systems

Angular distributions for the elastic scattering of $^{8}\mathrm{B}$, $^{7}\mathrm{Be}$, and $^{6}\mathrm{Li}$ on a $^{12}\mathrm{C}$ target have been measured at ${E}_{\mathrm{lab}}=25.8$, 18.8, and 12.3 MeV, respectively. The analyses of these angular distributions have been performed in terms of the optical model using Woods-Saxon and double-folding type potentials. The effect of breakup in the elastic scattering of ${}^{8}\mathrm{B}+{}^{12}\mathrm{C}$ is investigated by performing coupled-channels calculations with the continuum discretized coupled-channel method and cluster-model folding potentials. Total reaction cross sections were deduced from the elastic-scattering analysis and compared with published data on elastic scattering of other weakly and tightly bound projectiles on $^{12}\mathrm{C}$, as a function of energy. With the exception of $^{4}\mathrm{He}$ and $^{16}\mathrm{O}$, the data can be described using a universal function for the reduced cross sections.

Three-dimensional CFD simulation of bubble–melt two-phase flow with air injecting and melt stirring

This paper reports on progress in developing CFD simulations of gas bubble–metallic melt turbulent flows induced by a pitched-blade impeller with an inclined shaft. Foaming process of aluminum foams, in which air is injected into molten aluminum composites and the melt is mechanical stirred by the impeller, has been investigated. A two-fluid model, incorporated with the Multiple Reference Frames (MRF) method is used to predict the three-dimensional gas–liquid flow in the foaming tank, in which a stirring shaft is positioned inclined into the melt. Locally average bubble size is also predicted by additively solving a transport equation for the bubble number density function, which accounts for effects of bubble breakup and coalescence phenomena. The computed bubble sizes are compared with experimental data from our water model measurement and reasonable agreements are obtained. Further, simulated results show that the volume averaged total and local gas fractions are generally increased with rising impeller speed and gas flow rate. The local averaged bubble size increases with increasing gas flow rate and orifice diameter and decreasing liquid viscosity, and decreases also with rising rotation speed of the impeller.

Experimental study ofHe6+Be9elastic scattering at low energies

New data for the $^{6}\mathrm{He}+^{9}\mathrm{Be}$ reaction at ${E}_{\mathrm{lab}}=16.2$ and 21.3 MeV have been taken and analyzed. The effect of the collective couplings to the excited states of the target has been studied by means of coupled-channels calculations, using a double-folding potential for the bare interaction between the colliding nuclei, supplemented with a phenomenological imaginary part of Woods-Saxon type. In addition, three- and four-body continuum-discretized coupled-channels calculations have been performed to investigate the effect of the projectile breakup on the elastic scattering. Both effects, the coupling to target and projectile excited states, are found to affect significantly the elastic scattering. The trivial local polarization potential extracted from the continuum-discretized coupled-channels calculations indicates that continuum couplings produce a repulsive real part and a long-range imaginary part in the projectile-target interaction.

FUSION OF 6He+238U SYSTEM: HALO AND BREAKUP EFFECTS

We have studied the role of spatial extension (Halo structure) of 6 He and that of breakup reaction channel in the fusion of 6 He +238 U system. The breakup channel effects are taken into account within the framework of the dynamic polarisation potential approach. It has been found that the fusion cross section enhances due to the static effects of spatial extension of the projectile in the entire energy region. The breakup effects, however, results in the above barrier suppression and below barrier small enhancement in the fusion cross section. The matching between the data and the predictions improves significantly by the inclusion of both static and breakup effects.

Experimental and Numerical Analysis of a Gas-liquid Flow Operating in the Heterogeneous Regime

Experimental and CFD studies in a laboratory scale cylindrical bubble column under different operational conditions were performed. Axial liquid velocities were measured with the non-intrusive PIV technique. The effects of breakup and coalescence were applied with population balance method. For the interfacial forces, only drag was considering by the Zhang and Vanderheyden model. The effects of turbulence in the continuous phase were applied for the continuous phase with the k-e model. It was found that the approach used in this work provided physically consistent results, showing good agreement between the experimental and numerical data obtained for a heterogeneous flow regime.

Ab initiomany-body calculations of deuteron-He4scattering andLi6states

We extend the ab initio no-core shell model/resonating-group method (NCSM/RGM) to projectile-target binary-cluster states where the projectile is a deuteron. We discuss the formalism in detail and give algebraic expressions for the integration kernels. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we calculate deuteron-$^{4}\mathrm{He}$ scattering and investigate $^{6}\mathrm{Li}$ bound and unbound states. Virtual three-body breakup effects are obtained in an approximated way by including excited pseudostates of the deuteron in the calculation. We compare our results to experiment and to a standard NCSM calculation for $^{6}\mathrm{Li}$.

Computational Investigation of Liquid Spray Dispersion Modification by Conical Nozzle Attachments

Liquid spray characteristics such as the droplet size and dispersion angle are determined by the atomizer design and the physical properties of the liquid and surrounding gas. One of the options to change these characteristics is to attach an especially designed piece to the nozzle exit. While these attachments can have a variety of shapes, we chose a conical geometry to exploit its axial symmetry and, at the same time, obtain the results that can be generalized to other configurations. Thus, we investigate an addition of the conically shaped attachment to the premixed gas-assisted high-pressure atomizer with the previously developed numerical model. This is a two-fluid Eulerian-Eulerian model with a catastrophic phase inversion that was developed for compressible gas-liquid mixtures and can be applied to both the flow through the nozzle-atomizer and to the dispersion of the spray. The model also accounts for the break-up and coalescence effects of bubbles and droplets. Our investigation reveals that the conical nozzle attachments act as spray limiters by reducing the natural expansion angle of a spray. Also, the droplets produced by the nozzle with a conical addition tend to be larger than the ones obtained with a stand alone nozzle. The largest droplets are generated by the smallest attachment angle considered, 10 deg. With the increase of the angle, the spraying characteristics become closer to those of the stand alone nozzle. It can be concluded that the conical shape of the attachments with a relatively small angle may be used when higher jet penetration and lower dispersion are desirable. The attachments with larger angles do not offer a substantial difference from the stand alone nozzle. Another important conclusion is that the dispersion of the jet is determined by the radial momentum transferred to the liquid before or immediately after the phase inversion takes place. Thus, for improved dispersion, the area where the atomization is taking place should not be restricted.

Fusion and reactions of exotic nuclei

Close to the drip lines, the scattering cross sections of halo nuclei show a different behaviour as compared to the tightly bound projectiles of the stability line. Several experiments carried out in the last decade have been dedicated to investigate the competition between transfer, breakup and fusion channels at energies around and below the Coulomb barrier. The rather complex scenario gives rise to conflicting conclusions concerning the effect of breakup and transfer on reaction dynamics and the sub-barrier fusion process. In this work we discuss recent experimental findings in fusion and reactions of 6He halo nucleus at energies around the Coulomb barrier.

Coupled channel effect in elastic scattering and fusion for6,7Li+28Si

The fusion excitation and elastic angular distribution were measured for 6,7 Li+28 Si from below to above Coulomb barrier (≤ 3Vb ) energies. The barrier distribution derived from the fusion data was found to be broad and asymmetric at the sub-barrier region, compared to 1D BPM estimation. Effect of rotational coupling on fusion was found to be not so dominant. Phenomenological optical potential parameters, with surface and volume type imaginary potentials, were obtained from f tting of elastic scattering data and energy dependence of real and imaginary surface strengths were investigated around the barrier. CDCC calculations considering only breakup of projectile were performed for 6,7 Li+28 Si with the elastic scattering data, using the code FRESCO. The effects of breakup of projectile on elastic cross section do not agree with the energy dependence of real and imaginary strength with volume type imaginary potential around the barrier.

Nuclear reactions studied by quasi-elastic measurements with high precision at backward angles

The excitation functions of quasi-elastic scatterings at backward angles were measured with high precision to study the mechanisms of heavy-ion reactions at near- and sub-barrier energies. The surface diffuseness parameters for the 16 O+ 144,152,154 Sm, 170 Er, 174 Yb, 184,186 W, 194,196 Pt, and 208 Pb systems have been extracted by the single-channel and coupled-channels calculations, respectively. No anomaly was found in these quasi-elastic processes. The barrier heights and barrier distributions were systematically investigated for these systems. Moreover, the coupled-channels effects of neutron transfers with positive Q-value and the breakup effects of weakly-bound nuclei on the fusion processes were also studied for the 32 S+ 90,96 Zr systems and the 6,7 Li, 9 Be+ 208 Pb systems, respectively.

Influence of velocity gradient on aluminum and iron floc property for NOM removal from low organic matter surfacewater by coagulation

Prehydrolyzed coagulants (polyaluminum chloride, denoted as PAC, and polyferric chloride, denoted as PFC) were used to study the effect of different velocity gradient values ( G ranging from 4.4 s −1 to 28.3 s −1) on the flocculation performance and floc properties from the low organic matter (OM) surfacewater. For different coagulants there were three distinct zones observed in terms of the magnitude of G. At low G values ( G < 7.6 s −1), mean particle diameter increased with G, showing that aggregation dominated over breakup. The flocs were loosely compacted with poor settling ability and high strength and recovery factors. At intermediate G values (7.6 s −1 < G < 15.1 s −1 for PFC; 7.6 s −1 < G < 11.2 s −1 for PAC), flocculation rates were maximized, resulting in large flocs with low strength and recovery factors. The residual turbidity was lower and the flocs were more compact. At higher G values ( G > 15.1 s −1 for PFC; G > 11.2 s −1 for PAC), the dominant effect of breakup was shown through reduced maximum floc size with increasing G values. The strength and recovery factors increased and the residual turbidity also increased due to the small flocs. In addition, the PFC-NOM flocs properties were more influenced by the velocity gradients. In terms of NOM removal, the differences of the residual UV 254 and DOC in the range of G studied were slight. The lowest SUVA value was achieved at G 7.6 s −1 and 15.2 s −1 respectively for PFC and PAC.