Geometric fermions

We study the Kähler-Dirac equation which linearizes the laplacian on the space of antisymmetric tensor fields. In flat space-time it is equivalent to the Dirac equation with internal symmetry and on the lattice it reproduces Susskind fermions. The KD equation in curved space-time differs from the Dirac equation by coupling the gravitational field to the internal symmetry generators. This new way of treating fermionic degrees of freedom may lead to a solution of the generation puzzle but is in conflict with the equivalence principle and with Lorentz invariance on the Planck-mass scale.     

Tris(perfluoroalkyl)silyl Entities as Unexpectedly Potent Tags for the Noncovalent Immobilization of Catalysts by Fluorous–Fluorous Interactions: Application to the Synthesis of Several Perfluoro‐Tagged Ligands

Unexpectedly high retention times were obtained in HPLC investigations for compounds equipped with (C₈F₁₇CH₂CH₂)₃Si tags on C₈F₁₇‐modified silica gel (Fig. 4). Hence, these tags have a high potential for the noncovalent immobilization of catalysts to be applied in organic solvents, allowing for an easy separation and re‐use of the catalyst by filtration and reapplication. The tris(perfluoroalkyl)silyl tag could be incorporated in a straightforward manner into ligands as demonstrated by the synthesis of several prominent classes of ligands (Schemes 4–6).     

Quantum control by ultrafast polarization shaping

We demonstrate that the use of time-dependent light polarization opens a new level of control over quantum systems. With potassium dimer molecules from a supersonic molecular beam, we show that a polarization-shaped laser pulse increases the ionization yield beyond that obtained with an optimally shaped linearly polarized laser pulse. This is due to the different multiphoton ionization pathways in K2 involving dipole transitions which favor different polarization directions of the exciting laser field. This experiment is a qualitative extension of quantum control mechanisms which opens up new directions giving access to the three-dimensional temporal response of molecular systems.     

Does metal ion complexation make radical clocks run fast?

Ab initio molecular orbital and density functional calculations at the CBS-RAD(QCISD,B3-LYP) level for Li+ and at B3LYP for Na+, K+, Cu+,and Ag+ reveal that the barrier to ring-closure of the 1-hexen-6-yl ("Delta(5)-hexenyl") radical to the cyclopentylmethyl radical, a so-called radical clock reaction, is decreased very significantly by complexation of the double bond to metal cations. This barrier lowering should occur on complexation with many metal ions, as shown by calculations on all of the monovalent ions listed above. Additional density functional calculations including explicit solvation of the model system complexed to the lithium ion with tetrahydrofuran suggest that the effect found is not limited to the gas phase but may also be significant in experimental radical clock reactions in solution, even for lithium.     

Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction

Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium.     

Layer-dependent shifts in ionization potential and auger energies for Kr/Cu (110)

Photoelectron spectra of the krypton 3d core-levels and MNN Auger spectra of krypton mono- and multilayers on Cu(110) have been recorded with synchrotron radiation. The Kr-3d line is found to shift to higher binding energies by 0.73 eV for first- and second-layer adsorption, respectively. This value is much larger than the work function decrease for Kr mono-layer adsorption, Δø = ?0.29eV. The shift in Auger line energies is found to be about three times larger than the 3d line shift. These observations can be readily explained in terms of image-charge screening of the hole states.     

Evolution of the modulated antiferromagnetic structure of CeAl2 in the presence of nonmagnetic impurities

Neutron diffraction studies show that the alloy system Ce_1-xLa_xAl₂ with x = 0.1 and 0.2 orders in the same incommensurate modulated antiferromagnetic structure as the pure compound CeAl₂. The existence and concentration dependence of a commensurate extra reflection ($\text{5}\text{2}$$\text{3}\text{2}$$\text{1}\text{2}$) is interpreted as being due to a modulation quenching of the CeAl₂ structure. This is in contrast to the suggestion that the magnetic order of CeAl₂ can be described by a triple-q structure.     

Bulk viscosity of a reactive (νenpe−) system

The bulk viscosity arising from neutrino absorption by neutrons, and electron capture by protons, is calculated for arbitrary degeneracy of the leptons. These reactions are the primary processes determining the bulk viscosity of collapsing stellar cores. In this context the value found is of the order of 10²⁴ g cm^?1s^?1.     

Polymere mit P-N-Bindungen. 4. Mitt.81P-NMR-Spektren von Poly-(dihalogenphosphazen)en und Poly(dipseudohalo-genphosphazen)en

Ohne Zusammenfassung