Nuclear shapes of the transitional nuclei 186, 188, 190, 192Os

Excitation functions at θ_lab = 130° have been measured for inelastic scattering of 13–24 MeV alpha particles from ^{186,188,190,192}Os. Data have been obtained for 0⁺, 2⁺, 4⁺, 2⁺' states in ^186,188,192Os and for 0⁺, 2⁺ states in ¹⁹⁰Os. Charge and mass quadrupole deformations, β₂^c and β₂^N, were deduced from coupled-channels analysis of the 2⁺ data. No simple model could provide good fits to the 4⁺ data over the entire energy range but the very deep interference minima observed establish the charge and mass hexadecapole moments, β₄^c and β₄^N, to be negative. The energies of the interference minima for the 4⁺ states could be reproduced by coupled-channels calculations only if large differences in β₄^c and β₄^N were allowed. Data for the (J, K)^π = (2, 2)⁺ states are inconsistent with an asymmetric rotational model.     

The C(Li, t)O reaction at 20 MeV

States in ¹⁶O op to an excitation energy of 16.9 MeV were observed from the ¹³C(⁶Li, t)¹⁶O reaction at 20 MeV. Differential cross sections were obtained from θ_lab = 15° to 105° for the triton groups corresponding to the states in ¹⁶O at 6.13, 6.92, 7.12, 8.87, 9.85, 10.35 and 11.09 MeV.     

Study of magnetic moments of nuclear excited states at Tristan

Facilities at the TRISTAN mass separator for measurement of magnetic moments of nuclear excited states are described and recent results for the N=82 isotones are presented.     

Design,synthesis and biological activity of rigid cannabinoid CB1 receptor antagonists

The design, synthesis and biological activities of potent pyrazole-based tricyclic CB1 receptor antagonists (2) are described. The key synthetic step involves the ring closure of the lithiated alpha, gamma-keto ester adduct (4). The optimal nitroderivative (28) in this series exhibits a high CB1 receptor affinity (pKi=7.2) as well as very potent antagonistic activity (pA2=8.8) in vitro. The regioselectivity of the pyrazole ring closure is shown to depend strongly on the aromatic substitution pattern of the applied arylhydrazine.     

Dispersion interactions enable the self-directed growth of linear alkane nanostructures covalently bound to silicon

Current interest in methods for controllably adding organic molecules to silicon surfaces relates to proposed hybrid silicon-organic devices. It was recently shown that a "self-directed" growth process, requiring only limited scanned probe intervention, has the potential to permit rapid, parallel production of ordered molecular nanostructures on silicon with predefined absolute position, structure, composition, and extent of growth. The hybrid organic-silicon structures formed are bound by strong covalent interactions. In this work, we use scanning tunneling microscopy and density functional theory techniques to show that molecule-surface dispersion interactions enable the growth process and play a crucial role in the final configurations of the nanostructures.     

Unusual temperature dependence of the positron lifetime in a polymer of intrinsic microporosity

The performance of polymeric membranes for gas separation is mainly determined by the free volume. Polymers of intrinsic microporosity are interesting due to the high abundance of accessible free volume. We performed measurements of the temperature dependence of the positron lifetime, generally accepted for investigation of free volume, in two polymers of intrinsic microporosity (PIM‐1 and PIM‐7) in the range from 143 to 523 K. The mean value of the free volume calculated from the ortho‐positronium lifetime is in the range of typical values for high free volume polymers. However, the temperature dependence of the local free volume is non‐monotonous in contrast to the macroscopic thermal expansion. The explanation is linked to the spirocenters in the polymer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-synchronization and dissipation-induced threshold in collective atomic recoil lasing

Networks of globally coupled oscillators exhibit phase transitions from incoherent to coherent states. Atoms interacting with the counterpropagating modes of a unidirectionally pumped high-finesse ring cavity form such a globally coupled network. The coupling mechanism is provided by collective atomic recoil lasing, i.e., cooperative Bragg scattering of laser light at an atomic density grating, which is self-induced by the laser light. Under the rule of an additional friction force, the atomic ensemble is expected to undergo a phase transition to a state of synchronized atomic motion. We present the experimental investigation of this phase transition by studying the threshold behavior of this lasing process.