High-spin alkali trimers on helium nanodroplets: spectral separation and analysis

Electronic excitation spectra of homo- (K(3),Rb(3)) and heteronuclear (K(2)Rb,KRb(2)) alkali trimers in the high-spin quartet state have been investigated in a broad spectral range (10,600-17,400 cm(-1)). Ten new bands showing laser induced fluorescence (LIF) were measured. Due to the pickup statistics, overlapping spectra of all possible oligomers are present at once, complicating the unraveling and assignment of individual spectra. To circumvent the problem, two variations of beam depletion spectroscopy were employed in addition to the conventional analysis of the relation between signal and pickup pressure: A two-laser V-type double resonance scheme combining beam depletion with LIF, and a mass selective beam depletion scheme. In principle, these allow accurate separation of an arbitrary number of overlapping spectra. The benefits and drawbacks of each method are discussed. Assignment to electronic states is achieved by comparison with ab initio complete active space self-consistent field calculations of the excited electronic level structure of the molecules.     

A kinetic expression for the pyrolytic decomposition of polytetrafluoroethylene

Despite the fact that the thermal decomposition of polytetrafluoroethylene has been extensively studied over the past six decades, some inconsistencies regarding the kinetic parameters, e.g. the order of the reaction, remain. Representative kinetic data are essential for practical purposes such as reactor design and scaling. In general the literature data refer to homogeneous bulk heating, whereas the case of the non-homogeneous heating of a single particle has not received attention. Data (reaction rate and pre-exponential factor) applicable to this latter case were experimentally determined from isothermal thermogravimetric analyses of the depolymerisation reaction of PTFE. The kinetic data obtained on coarse granules (800-1000 μm) are reported here. The rate law is consistent with a shrinking particle kinetic model, with chemical kinetics controlling phase-boundary movement. The mass loss rate is directly proportional to surface area. A rate law applicable to this case, and useable for geometries of arbitrary shape, is derived.     

Photoacoustic measurement of electron injection efficiencies and energies from excited sensitizer dyes into nanocrystalline TiO2 films

Time-resolved photoacoustic calorimetry is used to measure the energy released upon injection of an electron from an electronically excited dye adsorbed to nanocrystalline TiO2 into the conduction band of this material. More energy is released when the environment of the dye is made less polar, because the energy of the dye-oxidized state has a more pronounced solvent dependence than the edge of the conduction band of the TiO2 semiconductor. Such energy dependences should be considered in the design of more efficient dye-sensitized solar cells.     

On Green's functions for the reduced wave equation in a circular annular domain with dirichlet, Neumann and radiation type boundary conditions

Summary In this paper Green's functions for the reduced wave equation (Helmholtz equation) in a circular annular domain with the Dirichlet, the radiation, and Neumann boundary conditions are derived. The convergence of the series representing Green's functions is then established. Finally it is shown that these functions reduce to Green's function for the exterior of a circle as given by Franz and Etiènne when the outer radius is moved towards infinity.     

Rational Structure‐Based Design of Bright GFP‐Based Complexes with Tunable Dimerization

Fluorescent proteins are transformative tools; thus, any brightness increase is a welcome improvement. We invented the “vGFP strategy” based on structural analysis of GFP bound to a single‐domain antibody, predicting tunable dimerization, enhanced brightness (ca. 50 %), and improved pH resistance. We verified all of these predictions using biochemistry, crystallography, and single‐molecule studies. We applied the vsfGFP proteins in three diverse scenarios: single‐step immunofluorescence in vitro (3× brighter due to dimerization); expression in bacteria and human cells in vivo (1.5× brighter); and protein fusions showing better pH resistance in human cells in vivo. The vGFP strategy thus allows upgrading of existing applications, is applicable to other fluorescent proteins, and suggests a method for tuning dimerization of arbitrary proteins and optimizing protein properties in general.     

Reactivity and Passivation of Fe Nanoclusters on h-BN/Rh(111)

The reactivity of iron nanocluster arrays on h-BN/Rh(111) was studied using in situ high-resolution X-ray photoelectron spectroscopy. The morphology and reactivity of the iron nanoclusters (Fe-NCs) were investigated by CO adsorption. On-top and hollow/edge sites were determined to be the available adsorption sites on the as-prepared Fe-NCs and CO dissociation was observed at 300 K. C- and O-precovered Fe-NCs showed no catalytic activity towards CO dissociation because the hollow/edge sites were blocked by the C and O atoms. Therefore, these adsorption sites were identified to be the most active sites of the Fe-NCs.     

Asymmetric Flow Field-Flow Fractionation: Current Status,Possibilities, Analytical Limitations and Future Trends

Chromatographia - The development and applications of asymmetric flow field-flow fractionation (AF4) are outlined in comparison with the older and better-known size exclusion chromatography. Recent...     

Baryon-rich quark-gluon plasma in nuclear collisions

The maximum achievable temperature (energy density) and minimum kinetic energy required for the formation of a baryon-rich quark-gluon plasma formed at central rapidity in small impact parameter nuclear collisions is estimated. A possible mechanism leading to the pile-up of matter is introduced. Plasma formation is expected to appear at about 15 GeV/Nucleon uranium beam energy on a stationary target or 2.7 GeV/Nucleon in colliding beams.     

Epothilone B and its Derivatives as Novel Antitumor Drugs: Total and Partial Synthesis and Biological Evaluation

 Microtubule stabilizing natural products, as exemplified by paclitaxel (taxol^?), are being considered as novel drugs against malignant therapy resistent solid tumors. Among these compounds, epothilone B and some of its derivatives have emerged as particularly promising candidates for industrial development. The total and partial syntheses of these compounds are described in detail, and some of the most important recent results on their biological activity are discussed.