First measurement of the Λ→nγ branching ratio

In an experiment performed at the CERN-SPS charged hyperon beam, we have observed the radiative decay Λ→nγ, using well identified Λ from the decays of Ο^? of 116 GeV/c momentum. Neutrons and photons from the Λ decays were observed in liquid argon and lead glass detectors. From a sample of 31 candidates, containing an estimated background of 7.3 events, the decay branching ratio was measured to be Γ(Λ→nγ)/Γ(Λ→all)=(1.02±0.33)×10^?3.     

Projectile coulomb excitation of Ne and Ne

The static quadrupole moments of the first excited J^π = 2⁺ states in ²⁰Ne and ²²Ne and the reduced electric quadrupole transition probabilities of these states to the ground states were measured via projectile Coulomb excitation. The quadrupole moments were deduced from the shapes of γ-ray angular distributions. The results are: Q(²⁰Ne, 2⁺) = −0.20±0.05 b and Q(²²Ne, 2⁺) = −0.11±0.05 b. The transition strengths were deduced from yield measurements and by comparison with the yields of target γ-rays. The results are: B(E2; 0⁺ → 2⁺, ²⁰Ne) = 0.037±0.003 e² · b² and B(E2; 0⁺ → 2⁺, ²²Ne) = 0.025±0.002 e²· b². The results for the transition strengths are consistent with the results of accurate timing methods and resolve discrepancies between previous experiments. The results for the quadrupole moments are consistent with earlier measurements, although the mean values we obtain are slightly lower. The experimental measurements are compared with theoretical predictions and a detailed discussion is given of corrections to this type of reorientation experiment.     

Synthesis of some substituted pyrido[1,2-a]pyrimidin-4-ones and 1,8-naphthyridines

The substituted 4H-pyrido[1, 2-a]pyrimidin-4-ones (I) were obtained by the condensation of substituted 2-aminopyridines with δ-ketocarboxylic esters in PPA. Some of the derivatives I were transformed into the corresponding 1, 8-naphthyridines II and III.     

Abnormal behaviour of some parameters revealed in the Georgian SSR before the Armenia earthquake of December 7, 1988: a preliminary report

Summary For more than ten years several measurements sites able to detect geophysical and geochemical precursory phenomena of earthquakes have been working in Soviet Georgia. On the occasion of the destructive Armenia earthquake of December 7, 1988 (M=6.9) premonitory signals relative to geophysical and geochemical parameters seem to be observed. In this paper anomalous variations of the water level in a well, of the helium content in thermal waters and of the electromagnetic signals in air, obtained in three measurements sites located at about 80 km from the epicentre, are reported. These variations appear beginning from about a month up to some hours before the occurrence of the earthquake and it seems reasonable to consider them as short-time or very short-time precursory phenomena of the earthquake.     

Surface supramolecular organization of a terbium(III) double-decker complex on graphite and its single molecule magnet behavior

The two-dimensional self-assembly of a terbium(III) double-decker phthalocyanine on highly oriented pyrolitic graphite (HOPG) was studied by atomic force microscopy (AFM), and it was shown that it forms highly regular rectangular two-dimensional nanocrystals on the surface, that are aligned with the graphite symmetry axes, in which the molecules are organized in a rectangular lattice as shown by scanning tunneling microscopy. Molecular dynamics simulations were run in order to model the behavior of a collection of the double-decker complexes on HOPG. The results were in excellent agreement with the experiment, showing that-after diffusion on the graphite surface-the molecules self-assemble into nanoscopic islands which align preferentially along the three main graphite axes. These low dimension assemblies of independent magnetic centers are only one molecule thick (as shown by AFM) and are therefore very interesting nanoscopic magnetic objects, in which all of the molecules are in interaction with the graphite substrate and might therefore be affected by it. The magnetic properties of these self-assembled bar-shaped islands on HOPG were studied by X-ray magnetic circular dichroism, confirming that the compounds maintain their properties as single-molecule magnets when they are in close interaction with the graphite surface.     

Scaling in structural complexity

Structural complexity has been shown to be a measure of the variety of load paths in structures with high degree of static indeterminacy, for example, frames. The variations of the value of complexity parameters across different structures have been investigated in previous researches. Herein, the effects of scaling on load distribution and on geometry of the structural scheme are outlined. A scale invariance is shown for load magnitude. Complexity variation is outlined for geometric similar structures, depending essentially on the consistency of the load set. A transition in the behavior of the structural scheme under loads is recorded in case of similar structures from small to large scales. The results are discussed. © 2014 Wiley Periodicals, Inc. Complexity 20: 57–63, 2014     

Interfacial electrostatics of self-assembled monolayers of alkane thiolates on Au(111): work function modification and molecular level alignments

We have isolated at T < 150 K a weakly adsorbed dimethyl disulfide (DMDS) layer on Au(111) and studied how the vibrational states, S core hole level shifts, valence band photoemission, and work function measurements evolve upon transforming this system into chemisorbed methylthiolate (MT) self-assembled monolayers (SAM) by heating above 200 K. By combining these observations with detailed theoretical electronic structure simulations, at the density functional level, we have been able to obtain a detailed picture of the electronic interactions at the interface between Au and adsorbed thiolates and disulfides. All of our measurements may be interpreted with a simple model where MT is bound to the Au surface with negligible charge transfer. Interfacial dipoles arising from Pauli repulsion between molecule and metal surface electrons are present for the weakly adsorbed DMDS layer but not for the chemisorbed species. Instead, for the chemisorbed species, interfacial dipoles are exclusively controlled by the molecular dipole, its interaction with the dipoles on neighboring molecules, and its orientation to the surface. The ramifications of these results for alignment of molecular levels and interfacial properties of this class of materials are discussed.