Transport Phenomena and Structuring in Shear Flow of Suspensions near Solid Walls

In this paper we apply the lattice-Boltzmann method and an extension to particle suspensions as introduced by Ladd et al. to study transport phenomena and structuring effects of particles suspended in a fluid near sheared solid walls. We find that a particle free region arises near walls, which has a width depending on the shear rate and the particle concentration. The wall causes the formation of parallel particle layers at low concentrations, where the number of particles per layer decreases with increasing distance to the wall.Comment: 14 pages, 14 figure

Identification of high-spin proton configurations in Ba 136 and Ba 137

19 pags., 11 figs., 3 tabs.The high-spin structures of Ba136 and Ba137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Ba136 is populated in a Xe136+U238 MNT reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and in two Be9+Te130 fusion-evaporation reactions using the High-efficiency Observatory for γ-Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the B11+Te130 fusion-evaporation reaction utilizing the HORUS γ-ray array. The level scheme above the Jπ=10+ isomer in Ba136 is revised and extended up to an excitation energy of approximately 5.5 MeV. From the results of angular-correlation measurements, the Ex=3707- and Ex=4920-keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both Te132 and Xe134 are characterized by high-energy 12+→10+ transitions, the Ba136E2 ground-state band is interrupted by negative-parity states only a few hundred keV above the Jπ=10+ isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in Ba137. The new results close a gap along the high-spin structure of N<82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130, and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character.Furthermore, we express our thanks to Dr. E. Teruya and Dr. N. Yoshinaga from Saitama University, Japan, for providing the results of their shellmodel calculation with the PQM130 interaction. The research leading to these results has received funding from the German BMBF under Contracts No. 05P15PKFN9 TP1 and No. 05P18PKFN9 TP1, from the European Union Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 262010 - ENSAR, from the Spanish Ministerio de Ciencia e Innovación under Contract No. FPA2011-29854- C04, from the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5, and from the UK Science and Technology Facilities Council (STFC). L.K. and A.V. thank the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS) for financial support. One of the authors (A. Gadea) has been supported by the Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019, and EU under the FEDER program

High-spin structures in Xe 132 and Xe 133 and evidence for isomers along the N=79 isotones

The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features

Fusion of C12+Mg24 far below the barrier: Evidence for the hindrance effect

Background: The phenomenon of fusion hindrance may have important consequences on the nuclear processes occurring in astrophysical scenarios, if it is a general behavior of heavy-ion fusion at extreme subbarrier energies, including reactions involving lighter systems, e.g., reactions in the carbon and oxygen burning stages of heavy stars. The hindrance is generally identified by the observation of a maximum of the S-factor vs energy. Whether there is an S-factor maximum at very low energies for systems with a positive fusion Q value is an experimentally challenging question.Purpose: Our aim has been to search for evidence of fusion hindrance in C-12 + (24)g which is a medium-light m system with positive Q value for fusion, besides the heavier cases where hindrance is recognized to be a general phenomenon. C-12 + (24)mg is very close to the O-16 + O-16 and C-12 + C-12 systems that are important for the late evolution of heavy stars.Methods: The experiment has been performed in inverse kinematics using the Mg-24 beam from the XTU Tandem accelerator of LNL in the energy range 26-52 MeV with an intensity of 4-8 pnA. The targets were C-12 evaporations 50 mu g/cm(2) thick, isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E-Delta E-ToF detector telescope following an electrostatic beam deflector.Results: Previous measurements of fusion cross section for C-1(2) + (24)g were limited to above-barrier energies. m In the present experiment the excitation function has been extended down to similar or equal to 15 mu b and it appears that the S factor develops a clear maximum vs energy, indicating the presence of hindrance. This is the first convincing evidence of an S factor maximum in a medium-light system with a positive fusion Q value. These results have been fitted following a recently suggested method and a detailed analysis within the coupled-channels model that has been performed using a Woods-Saxon potential and including the ground state rotational band of 24 Mg. The coupled-channels calculations give a good account of the data near and above the barrier but overpredict the cross sections at very low energies.Conclusions: The hindrance phenomenon is clearly observed in C-12 + Mg-24, and its energy threshold is in reasonable agreement with the systematics observed for several medium-light systems. The fusion cross sections at the hindrance threshold show that the highest value (sigma(s) = 1.6 mb) is indeed found for this system. Therefore it may even be possible to extend the measurements further down in energy to better establish the position of the S-factor maximum

Fusion of ^{40}Ca+^{40}Ca and other Ca+Ca systems near and below the barrier

The fusion excitation function of Ca-40 + Ca-40 has been measured from well above the Coulomb barrier, down to low energies where the cross section is as small as similar or equal to 20 mu b, and the astrophysical S factor possibly reaches a maximum vs energy. The results of coupled-channels calculations using the M3Y + repulsion potential are presented. A detailed comparison is made with recently published data on the fusion of Ca-40 + Ca-48 and of Ca-48 + Ca-48, including the excitation functions, their low-energy slopes and the barrier distributions. The presence of the fusion hindrance phenomenon in all cases is pointed out, as well as the influence of the strong octupole excitation in Ca-40 and of nucleon transfer channels with positive Q values in Ca-40 + Ca-48

Sub-barrier fusion of 32S+48Ca

The fusion excitation function of 32S+48Ca has been measured in a wide energy range, from above the Coulomb barrier down to cross sections in the sub-\u3bcb region. The excitation function has a smooth behavior below the barrier with a rather flat slope, and no maximum of astrophysical factor S vs. energy has been observed. However, other interesting features of the dynamics of this system can be noted. In particular, the fusion barrier distribution has an unusual shape with two peaks of similar height, lower and higher than the Akyu\ua8z-Winther barrier. Preliminary coupledchannels calculations and a comparison with nearby systems yield information on the possible influence of nucleon transfer channels with positive Q-value

Intruder dominance in the 0(2)(+) state of Mg-32 studied with a novel technique for in-flight decays

The development of advanced gamma-ray tracking arrays allows for a sensitive new technique to investigate elusive states of exotic nuclei with fast rare-isotope beams. By taking advantage of the excellent energy and position resolution of the Gamma-Ray Energy Tracking In-beam Nuclear Array, we developed a novel technique to identify in-flight isomeric decays of the 0(2)(+) state in Mg-32 populated in a two-proton removal reaction. We confirm the 0(2)(+) -> 2(1)(+) gamma-ray transition of Mg-32 and constrain the 0(2)(+) decay lifetime, suggesting a large collectivity. The small partial cross section populating the 0(2)(+) state in this reaction provides experimental evidence for the reduced occupancy of the normal configuration of the 0(2)(+) state, indicating the intruder dominance of this state