Capacitance spectroscopy of a system of gapless Dirac fermions in a HgTe quantum well

Information on the density of states of two-dimensional Dirac fermions in a 6.6-nm-thick HgTe quantum well that corresponds to a transition from the direct to inverted spectrum is obtained for the first time by means of capacitance measurements. It is found that the density of states of Dirac electrons is a linear function of the Fermi energy at E _F > 30 meV with the corresponding velocity vDF = 8.2 × 10⁵ m/s. At lower energies, this dependence deviates from the linear law, indicating a strong effect of disorder, which is associated with fluctuations of a built-in charge, on the density of states of the studied system near the Dirac point. At negative energies, a sharp increase in the density of states is observed, which is associated with the tail of the density of states of valleys of heavy holes. The described behavior is in agreement with the proposed model, which includes both the features of the real spectrum of Dirac fermions and the effect of the fluctuation potential.     

Zur Chemie der Ketencarbonsäure-Derivate

Zusammenfassung Es werden an drei partiell deuterierten Systemen (Phenylmalonsäure-dianilid, 2-Amino-pyridin und Benzylmalonsäurebis-2,4,6-trichlorphenolester) weitere experimentelle Befunde erbracht, die beweisen, daß bei verschiedenen Cyclisierungsreaktionen mit reaktiven Malonsäure-derivaten intermediär Ketencarbonsäure-abkömmlinge gebildet werden.

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The chemistry of the derivatives of ketene carboxylic acid

With three partially deuterated systems (phenylmalonic dianilide, 2-aminopyridine, and 2.4.6-trichlorophenyl benzylmalonate) further experimental proof is given for the intermediate appearance of ketene carboxylic acid derivatives in cyclisation reactions with malonic acid derivatives. *** DIRECT SUPPORT *** A3615139 00011

     

Synthesen von Heterocyclen, 147. Mitt.: Chinolizine und Indolizine VII: Zur Synthese eines Benzindolizino-indigofarbstoffes

Zusammenfassung Durch saure Hydrolyse des Tetrahydrochinolin-8-glyoxalacetals7, welches in dreistufiger Reaktion aus dem Benzchinolizinon1 zugänglich ist, erhält man neben dem Benzindolizino-indigo8 den Indirubinfarbstoff9 sowie das Isatin-10 und das Dioxindolderivat11.

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Syntheses of heterocycles, CXLVII: Quinolizines and indolizines VII: The synthesis of a benzindolizino-indigo

Acid catalized hydrolysis of tetrahydroquinoline-8=glyoxalacetal7, obtained by a three step synthesis starting with the benzoquinolizinone1, yields not only the benzindolizino-indigo8, but also the indirubin dye9, the isatin derivative10, and the dioxindole derivative11.

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Mit 1 Abbildung

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Herrn Prof. Dr.R. Tschesche, Bonn, zum 65. Geburtstag gewidmet.     

Synthesen von Heterocyclen, 144. Mitt.: Über Synthesen mit Kohlensuboxid

Zusammenfassung N,N-Dimethyl- bzw. N,N-Diphenylhydrazone alicyclischer Ketone reagieren mit Kohlensuboxid sowohl zu den Pyridonen1–5 als auch zu den Pyrono-pyridonen6–10.

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Syntheses of heterocycles, CXLIV: Syntheses with carbon suboxide

N,N-Dimethyl- or N,N-diphenylhydrazones of alicyclic ketones react with carbon suboxide (C₃O₂) yielding the pyridones1–5 as well as the pyrono-pyridones6–10. *** DIRECT SUPPORT *** A3615139 00005

     

Substituent effect to prevent autoxidation and improve spectral stability in blue light-emitting polyfluorenes

A group of fluorene-based polymers, PF-1SOR and PF-2SOR, were synthesized and characterized as blue light-emitting materials. PF-1SOR and PF-2SOR displayed nematic liquid crystalline mesophase in films cast from solution. Compared with conventional polyfluorene, PF-1SOR and PF-2SOR display blue-shifted UV absorption and structureless blue fluorescence. The photoluminescence spectra of PF-1SOR and PF-2SOR were found insensitive against thermal treatment in air up to 200 degrees C and the blue electroluminescence in their light-emitting devices was independent of the driving voltage. Compared to the conventional polyfluorenes, the improved spectral stability of these polymers is attributed to the anti-oxidization effect of (3,5-di(tert-butyl)phenoxy)sulfonyl side groups attached to the backbone.     

Serum amyloid A protein in very low density--and high density lipoproteins during the course of acute myocardial infarction

In a preceding paper we reported on the detection and characterization of human serum amyloid A protein (SAA) in very low density lipoproteins (VLDL) and high density lipoproteins (HDL) of patients after acute myocardial infarction. Here we describe the time course of the occurrence of SAA in VLDL and HDL in the postinfarction period. SAA reached its maximum in VLDL and HDL approximately 53 h after the acute event. At the peak of the acute-phase response, SAA comprised as much as 38% of the total apoproteins of VLDL and HDL. SAA appeared at the same points in time and with nearly the same concentrations in VLDL and HDL. We conclude that SAA is not exchanged in plasma between lipoproteins of different densities and that this protein is secreted on its own by hepatocytes and not as a part of an already constituted lipoprotein particle.     

Time-dependent density functional theory based on a noncollinear formulation of the exchange-correlation potential

In this study we have introduced a formulation of time-dependent density functional theory (TDDFT) based on a noncollinear exchange-correlation potential. This formulation is a generalization of conventional TDDFT. The form of this formulation is exactly the same as that of the conventional TDDFT for the excitation energies of transitions that do not involve spin flips. In addition, this noncollinear TDDFT formulation allows for spin-flip transitions. This feature makes it possible to resolve more fully excited state spin multiplets, while for closed-shell systems, the spin-flip transitions will result in singlet-triplet excitations and this excitation energy calculated from this formulation of TDDFT is exactly the same as that from ordinary TDDFT. This formulation is applied to the dissociation of H(2) in its (1)Sigma(g) (+) ground state and (1)Sigma(u) (+) and (3)Sigma(u) (-) excited states with (3)Sigma(u) (-) (M(s)=+1) as the reference state and the multiplets splitting of some atoms.     

Copolymerization of ethylene with polar monomers: chain propagation and side reactions. A DFT theoretical study using zwitterionic Ni(II) and Pd(II) catalysts

Calculations utilizing anionic substituted derivates of the cationic N(wedge)N--Ni(II) and Pd(II) diimine Brookhart complex have been carried out on the barriers of ethylene and acrylonitrile insertion into a M- methyl, propyl and CH(CN)Et bond for M = Ni, Pd. The possibility of side reactions such as chelate formation with the polar functionality and oligomerization of the active species after acrylonitrile insertion are explored. The diimine ring system N--N = -NR' 'CR(1)CR(2)NR' ' with R' ' = 2,6-C(6)H(3)(i-Pr)(2) and R(1),R(2) = Me was functionalized by adding one or two anionic groups (BF(3)(-), etc.) in place of i-Pr on the aryl rings or by replacing one Me diimine backbone group (R(1)) with BH(3)(-). The objective of this investigation is computationally to design catalysts for ethylene/acrylonitrile copolymerization that have activities that are comparable to that of the cationic Ni(II) diimine or at least the Pd(II) diimine Brookhart system for ethylene homopolymerization. Complexes that might meet this objective are discussed.     

Synthesen von Heterocyclen, 106. Mitt.: 4-Hydroxy-pyridone-(2) durch Reaktion von Thioamiden mit Diketen

Zusammenfassung Thioamide reagieren mit Diketen in Eisessig oder Xylol in Gegenwart von p-Toluolsulfonsäure zu 4-Hydroxy-pyridonen-(2).

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The reaction of thioamides with diketene in acetic acid or xylene in the presence of p-toluene sulfonic acid yields 4-hydroxy-2-pyridones.