Investigation of the fusion of heavy nearly symmetric systems

Excitation functions in the vicinity of the Coulomb barrier have been measured for the formation of evaporation residues in¹⁰⁰Mo-induced fusion reactions with^{90, 92, 96}Zr,^{92, 96, 98, 100}Mo,¹⁰⁴Ru and¹¹⁰Pd as well as for the system⁹⁶Zr+⁹⁶Zr. From these data the fusion probability in central collisions was extracted covering a range of 4 orders of magnitude. At the fusion barriers expected from systematics we find that the fusion probability is suppressed by one to three orders of magnitude. It is rising very gradually at higher energies and reaches for the heaviest systems saturation only at energies as high as 30 MeV above the barrier. The observed hindrance of the fusion process increases roughly with the growing Coulomb repulsion between the collision partners, but there is also a distinct influence of their individual nuclear structure. The data are compared to the extra-push model, the surface-friction model and the diabatic fusion model. A parameterisation of the extra-push energy and its fluctuation in terms of a macroscopic quantity like the Coulomb repulsion combined with a microscopic quantity characterizing the nuclear structure is proposed. As a byproduct of this work a new alpha emitter,¹⁹¹Po, could be identified. Its half-life is (15.5 _–2.5 ⁺⁶ ) ms, the alpha energy is (7314±20) keV.     

Aggregation of cyclodextrins: An explanation of the abnormal solubility ofβ-cyclodextrin

-,- and -Cyclodextrins have been shown to exist as aggregates in solution bound together by a network of hydrogen bonds. Removal of this network by ionisation of the hydroxyl groups leads to a greatly increased solubility and removal of aggregation. The presence of aggregates in solution of structure breaking solutes in which the solubility of-cyclodextrin is greatly enhanced, leads to a proposal that the abnormally low solubility of-CD may be explained by the presence of aggregates and the unfavourable interaction of these aggregates with the hydrogen bonded structure of water.     

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Mass and charge distributions for binary reaction channels have been measured for the reactions⁸⁶Kr with⁷⁶Ge,¹⁰⁴Ru and¹³⁰Te at the Coulomb barrier using chemical separations and-ray spectroscopy. These systems span the region where dynamical hindrance to complete fusion sets in. The binary reactions can be subdivided into two components associated withi) reflection from the outer potential barrier (quasielastic), andii) reseparation after passing the barrier (complex reactions). The sum of complex-reaction channels and evaporation residues from complete fusion can be reproduced by a barrier passing calculation. The fraction of the barrier passing flux leading to reseparation increases from 26±10% for the lightest system to more than 90% for the heaviest system. The data indicate that fusion hindrance is primarily caused by reseparation shortly after passage of the barrier before Swiatecki's conditional saddlepoint is overcome, resulting in partitions close to the entrance channel configuration. In addition, for the heaviest system, a quasifission component representing somewhat less than 20% of the barrier-passing flux was observed. From the missing masses of fragment pairs we can deduce that the reseparating complex-reaction products have kinetic energies well below the fusion barrier and share the excitation energy in a way similar to the sawtooth-like curve known from low-energy fission. The quasielastic, predominantly one- and two-nucleon transfer channels, have strongly varying cross sections for the three systems despite similar effectiveQ-values. A systematics of one-neutron transfer cross sections at the Coulomb barrier is established and shown to differ considerably from the smooth behaviour observed at energies 20–30% above the barrier. The connection to nuclear polarization phenomena and orbit matching is pointed out.Nuclear reactions:⁷⁶Ge,¹⁰⁴Ru,¹³⁰Te(⁸⁶Kr, X).E=3.22 MeV/u, (3.64) 3.84 MeV/u, 3.96 MeV/u; enriched targets; catcher foil technique, chemical separations,-ray spectroscopy; deduced mass and charge distributions for binary reactions; competition with complete fusion     

Lifting measures to Markov extensions

Generalizing a theorem ofHofbauer (1979), we give conditions under which invariant measures for piecewise invertible dynamical systems can be lifted to Markov extensions. Using these results we prove:

1. IfT is anS-unimodal map with an attracting invariant Cantor set, then ∫log|T′|dμ=0 for the unique invariant measure μ on the Cantor set.
2. IfT is piecewise invertible, iff is the Radon-Nikodym derivative ofT with respect to a σ-finite measurem, if logf has bounded distortion underT, and if μ is an ergodicT-invariant measure satisfying a certain lower estimate for its entropy, then μ?m iffh _μ (T)=Σlogf dμ.

     

Preference intensity measurement

The concept of preference intensity has been criticized over the past sixty years for having no substantive meaning. Much of the controversy stems from the inadequacy of measurement procedures. In reviewing the shortcomings of existing procedures, we identify three objectives for developing a satisfactory procedure: (1) the capability of validating expressed preference differences by actual choices among naturally occurring options, (2) compatibility with the existing problem structure, and (3) no confounding of extraneous factors in the measurement of preference intensity. Several recently developed measurement procedures are criticized for failing one or more of these objectives. We then examine three different approaches for measuring preference intensity based on multiple perspectives. Thereplication approach emerges as a promising way of satisfying the three objectives above. This methodology applies to problems where an attribute can be replicated by parallel components that are independent, identical copies of the attribute. We illustrate the approach with two applications reported in the decision analysis literature. We also offer guidance on how to construct parallel components satisfying the requisite properties.     

Force- and loss-free transitions between flow states

Summary Force- and loss-free transitions between flow states in channels and vortex tubes are investigated. It is shown that in general a force-free transition appears either as a single transition which produces an entropy increase and connects an upstream supercritical flow state to a downstream subcritical flow state, or it appears as a two-stage transition, in which an isentropic transition leading to a second supercritical flow state is followed by a transition which produces an entropy increase and leads to a subcritical flow state. Depending on the downstream boundary condition either the single or the two-stage transition appears. For a certain regime of downstream boundary conditions both types of transitions are possible. Which of the two appears depends upon the startup of the flow. The result is a hysteresis. It is suggested that a particular kind of vortex breakdown can be understood in terms of the two transition types considered. Moreover, an apparent paradox is resolved which is associated with the fact that a vortex flow in a diffuser approaches the critical state. The analysis is based on an extension of a variational principle proposed by Benjamin [1]. Complete numerical results are presented which show loss-free transitions (including their internal structure) in a Rankine vortex.

---

Zusammenfassung Es werden kräfte- und verlustfreie Übergänge zwischen Strömungszuständen betrachtet. Es wird gezeigt, daß ein allgemeiner kräftefreier Übergang entweder als einfacher anisentroper Übergang auftritt, der von einem überkritischen zu einem unterkritischen Strömungszustand führt, oder als zweistufiger Übergang, wobei einem isentropen Übergang, der zu einem zweiten überkritischen Strömungszustand führt, ein anisentroper nachfolgt, der schließlich zu einem unterkritischen Zustand führt. Ob der einfache oder der zweistufige Übergang auftritt, hängt von der stromabwärts aufgeprägten Randbedingung ab. Innerhalb eines bestimmten Bereiches solcher Randbedingungen sind beide Arten von Übergängen möglich. Es hängt in diesem Fall von der Vorgeschichte ab, welche der Übergangsarten auftritt. Die Lösung besitzt also einen Hysteresecharakter. Es wird postuliert, daß eine Art von ortex-Breakdown mit Hilfe dieser beiden Übergangsarten erklärt werden kann. Außerdem wird ein scheinbares Paradoxon geklärt, welches mit der Tatsache zusammenhängt, daß eine Wirbelströmung in einem Diffusor dem kritischen Zustand entgegenstrebt. Die Theorie basiert auf einer Verallgemeinerung eines von Benjamin [1] vorgeschlagenen Variationsprinzips. Es werden vollständige numerische Resultate angegeben, die verlustfreie Übergänge (einschließlich ihrer inneren Struktur) in einem Rankine'schen Wirbel zeigen.

     

On the Applicability of Plasma Assisted Chemical Micropatterning to Different Polymeric Biomaterials

A plasma process sequence has been developed to prepare chemical micropatterns on polymeric biomaterial surfaces. These patterns induce a guided localized cell layover at microscopic dimension. Two subsequent plasma steps are applied. In the first functionalization step a microwave ammonia plasma introduces amino groups to obtain areas for very good cell adhesion; the second passivation step combines pattern generation and creation of cell repelling areas. This downstream microwave hydrogen plasma process removes functional groups and changes the linkages of polymer chains at the outermost surfaces. Similar results have been obtained on different polymers including polystyrene (PS), polyhydroxyethylmethacrylate (PHEMA), polyetheretherketone (PEEK), polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN). Such a rather universal chemical structuring process could widen the availability of biomaterials with specific surface preparations.     

Dynamical structure factor of the Frenkel-Kontorova model

We investigate the coherent dynamical structure factorS(q, ) of the Frenkel-Kontorova model with a continued fraction expansion. The model consists of harmonically interacting particles moving in a periodic potential. It applies to quasi-one-dimensional systems where two different periods and competing interactions are important. We study commensurability effects in the collective dynamical behaviour of the particles and their manifestation inS(q, ). Our theory gives detailed results for the inelastic scattering at high temperatures. For the quasielastic peak it predicts, among other things strong oscillations of the half-width as a function of the wave vectorq. Such a behaviour can be observed in neutron scattering experiments on superionic conductors.     

Präparation und Charakterisierung von PbBr2·C4H10O3 (Diethylenglykol)

Structural Chemistry of PbBr₂·C₄H₁₀O₃ (Diethyleneglycol) Crystals of PbBr₂·C₄H₁₀O₃ have been synthesized and structurally characterized by single‐crystal X‐ray diffraction. PbBr₂·C₄H₁₀O₃ crystallizes monoclinic in space group P2₁/n (No. 14) with a = 9.370(1)Å, b = 10.045(1)Å, c = 21.090(1)Å, β = 98.98(1)° and Z = 8. The compound contains compact Pb—Br groups, which build colums parallel to [0 1 0] direction by Hydrogen Bonding.