Reverse resistance anomaly and negative magnetoresistance of diluteY: Gd andSc: Gd

A logarithmical decrease in the resistivity below 10 K has been observed for 200 to 5,000 ppm Gd in Y and Sc. The decrease scales with the Gd concentration. The results are in line with previously published data forLu: Gd and LaAl₂: Gd, they are discussed in terms of a ferromagnetic (J>0) Kondoeffect. The scaling parameterT _K , and the extracted effective change interactionJ _eff are compared with other experimental results. In addition the negative magnetoresistance (the freezing out of spin-disorder scattering) has been measured up to 50 kG. Possible interference of potential and exchange scattering may have been observed in the magnetoresistance.Supported by special research fund Sfb 161 of the Deutsche Forschungsgemeinschaft     

Thermal stability of intermediate sized acetylenic compounds and the heats of formation of propargyl radicals

4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are In combination with previous results, rate expressions for propargyl C? C bond cleavage are related to that for the alkanes by the expression These results yield a propargyl resonance energy of D(nC₃H₇-H) – D(C₃H₃-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH₃C≡CCH₂-H) – D(C₃H₃-H) = 0.6 ± 3 kJ, D(sC₄H₉-H) – D(iC₃H₇-H) = 0 ± 3 kJ, D(iC₄H₉-H) – D(nC₃H₇-H) = 2 ± 3 kJ, and D(nC₃H₇-H) – D(iC₃H₇-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.     

A convolution approximation for Van Hove correlation function in liquids

The relative motions of particles in a simple liquid may be described as one-dimensional radial diffusion in an effective potential of the mean force. This effective potential may be obtained by an iteration procedure with the Vineyard approximation as the initial step. Using a harmonic approximation for the potential, the “distinct” part of the Van Hove time-dependent correlation function is then the convolution of a modified radial distribution function with a modified self-correlation function. The former describes the average positions of particles whereas the latter describes the density profile around the average position. For liquid argon, this modified convolution procedure appears to give results in satisfactory agreement with molecular dynamics.     

Anomalous surface enhanced molecular Raman scattering from inelastic tunneling spectroscopy junctions

Anomalously strong Raman spectra have been obtained from molecular monolayers adsorbed on the insulator in metal-insulator-metal tunnel junctions. We show unambiguously that Raman spectroscopy can readily detect molecular monolayers and consider the effects of surface roughness, the molecule-metal interface and the metal on our results.     

The dependence of inelastic electron tunneling on junction roughness

We have made a series of Al-Al₂O₃-benzoic acid-Pb inelastic electron tunneling spectroscopy (IETS) junctions on substrates roughened by varying thicknesses of CaF₂. The vibrational peaks due to the molecular monolayer of benzoic acid disappear as the substrates are made rougher. We speculate on the cause of this disappearance.     

XPS studies of ion-bombardment damage of transition metal sulfides

Radiation damage to the surface of transition metal sulfides under ～1-keV ion bombardment has been investigated by photoelectron spectroscopy. Under     

Dinuclear Zn(II) catalysts as biomimics of RNA and DNA phosphoryl transfer enzymes: changing the medium from water to alcohol provides enzyme‐like rate enhancements

Phosphodiesters are notoriously hydrolytically inert compounds that are demonstrated to have large accelerations of P‐OR cleavage promoted by transition and lanthanide metal ions in methanol and ethanol media. This review commentary describes recent findings of how a simple mononuclear and a dinuclear Zn(II) complex promote the cleavage of a series of RNA models and DNA models in alcohol media. The discussion centers on the analysis of the mechanisms of cleavage, energetics of the catalytic process, on recent findings of electrophilic assistance of leaving group departure, and the observation of a rapid hydrolytic reaction of a DNA model promoted by the dinuclear Zn(II) complex in ethanol containing less than 2% water. Copyright © 2009 John Wiley & Sons, Ltd.     

Efficient calculation of electron diffraction for the structural determination of nanomaterials

A critical advance in the technique of low-energy electron diffraction is presented and shown to enable determining detailed structures of nanomaterials, based on experimental methods that already exist or have been proposed. Our new cluster approach speeds up the computation to scale as n logn, rather than the current n3 or n2, with n the number of atoms, for example. Applications are illustrated for C60 molecules adsorbed on a Cu(111) surface, with and without coadsorbed metal atoms, exhibiting sensitivity to important structural features such as buckyball size and deformation.     

Neutron and proton transverse emission ratio measurements and the density dependence of the asymmetry term of the nuclear equation of state

Recent measurements of preequilibrium neutron and proton transverse emission from (112,124)Sn+(112,124)Sn reactions at 50 MeV/A have been completed at the National Superconducting Cyclotron Laboratory. Free nucleon transverse emission ratios are compared to those of A=3 mirror nuclei. Comparisons are made to Boltzmann-Uehling-Uhlenbeck (BUU) transport calculations and conclusions concerning the density dependence of the asymmetry term of the nuclear equation of state at subnuclear densities are made. Comparison to BUU model predictions indicate a density dependence of the asymmetry energy that is closer to a form in which the asymmetry energy increases as the square root of the density for the density region studied. A coalescent-invariant analysis is introduced as a means of reducing suggested difficulties with cluster emission in total nucleon emission.