Coulomb analogy for non-Hermitian degeneracies near quantum phase transitions

Degeneracies near the real axis in a complex-extended parameter space of a Hermitian Hamiltonian are studied. We present a method to measure distributions of such degeneracies on the Riemann sheet of a selected level and apply it in classification of quantum phase transitions. The degeneracies are shown to behave similarly as complex zeros of a partition function.     

Carbon nanotubes as schottky barrier transistors

We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.     

Experimental confirmation of the Alhassid-Whelan arc of regularity

Evidence is presented to show that a group of nuclei, spanning a range of structures, corresponds to a previously proposed isolated region of regular behavior between vibrational and rotational structures that was never before observed empirically. Nuclei predicted to show such regular spectra correspond to Hamiltonian parameters that lie amidst those giving more chaotic spectra. We identify a key observable that has a one-to-one correspondence to this arc of regularity and which therefore provides both an empirical signature for it and a clue to its underlying nature.     

Carboxymethyl Ethers of Cellulose and Starch – A Review

This review article deals with the technically important carboxymethyl ethers of cellulose and starch. Recent developments of synthesis, characterization, and application are presented considering adequately own research work in this field. In particular, the structure characterization by means of chromatographic (HPLC) and NMR-spectroscopic techniques as well as commercially important synthesis paths and alternative methods are described.     

Solid‐Phase Synthesis of Peptide Libraries Combining α‐Amino Acids with Inorganic and Organic Chromophores

The synthesis of two series of peptidic chains composed of bis(terpyridine)ruthenium(II) acceptor units and organic chromophores (coumarin, naphthalene, anthracene, fluorene) by stepwise solid‐phase peptide synthesis (SPPS) techniques is described. The first series of dyads comprises directly amide linked chromophores, while the second one possesses a glycine spacer between the two chromophores. All dyads were studied by UV/Vis and NMR spectroscopy, steady‐state luminescence, luminescence decay and electrochemistry, as well as by DFT calculations. The results of these studies indicate weak electronic coupling of the chromophores in the ground state. Absorpion spectra of all dyads are dominated by metal‐to‐ligand charge‐transfer (MLCT) bands around 500 nm. The bichromophoric systems, especially with coumarin as organic chromophore, display additional strong absorptions in the visible spectral region. All complexes are luminescent at room temperature (³MLCT). Efficient quenching of the fluorescence of the organic chromophore by the attached ruthenium complex is observed in all dyads. Excitation spectra indicate energy transfer from the organic dye to the ruthenium chromophore.     

Ammonium‐Based Cellulose Solvents Suitable for Homogeneous Etherification

New ammonium‐based cellulose solvents with triethylmethylammonium‐ and tributylmethylammonium cations and carboxylate anions were synthesized and investigated as potential solvents for cellulose. Triethylmethylammonium formate was found to dissolve cellulose. Small amounts of formic acid may be used to adjust the melting point of the organic salt and can increase the dissolution velocity of cellulose. Carboxymethylation as a common etherification reaction was investigated in the new ammonium‐based system. The watersoluble carboxymethyl cellulose obtained, had a degree of substitution as high as 1.55. An unconventional pattern of substitution was accessible.