Radioactivity in Cervidae antlers

The experience gained in this study indicated that Cervidae antlers afford a convenient means for measuring levels of ambient radioactivity over large areas. By the use of antlers, it was possible to compare Sr⁹⁰ levels resulting from bomb testing “fallout” year by year from 1943 through 1958 in a number of areas in the United States, Canada, and Alaska. The most surprising finding was the very high levels for Alaska in 1958. From calculations based on total beta counts in antlers, it was possible to show that the radiation dose delivered to bone from short-lived fission products is insignificant as compared to the dose delivered by Sr⁹⁰/Y⁹⁰.     

Influence of Sequential Modifications and Carbohydrate Variations in Synthetic AFGP Analogues on Conformation and Antifreeze Activity

Certain Arctic and Antarctic ectotherm species have developed strategies for survival under low temperature conditions that, among others, consist of antifreeze glycopeptides (AFGP). AFGP form a class of biological antifreeze agents that exhibit the ability to inhibit ice growth in vitro and in vivo and, hence, enable life at temperatures below the freezing point. AFGP usually consist of a varying number of (Ala‐Ala‐Thr)_n units (n=4–55) with the disaccharide β‐D ‐galactosyl‐(1→3)‐α‐N‐acetyl‐D ‐galactosamine glycosidically attached to every threonine side chain hydroxyl group. AFGP have been shown to adopt polyproline II helical conformation. Although this pattern is highly conserved among different species, microheterogeneity concerning the amino acid composition usually occurs; for example, alanine is occasionally replaced by proline in smaller AFGP. The influence of minor and major sequence mutations on conformation and antifreeze activity of AFGP analogues was investigated by replacement of alanine by proline and glycosylated threonine by glycosylated hydroxyproline. The target compounds were prepared by using microwave‐enhanced solid phase peptide synthesis. Furthermore, artificial analogues were obtained by copper‐catalyzed azide–alkyne cycloaddition (CuAAC): propargyl glycosides were treated with polyproline helix II‐forming peptides comprising (Pro‐Azp‐Pro)_n units (n=2–4) that contained 4‐azidoproline (Azp). The conformations of all analogues were examined by circular dichroism (CD). In addition, microphysical analysis was performed to provide information on their inhibitory effect on ice recrystallization.     

Complete Classifications of Generalized Kac–Moody Algebras Possessing Special Imaginary Roots and Strictly Imaginary Property

In this article, we consider all generalized Kac–Moody algebras (GKM algebras) for the purpose of finding out special imaginary roots and strictly imaginary roots. We give a complete classification of GKM algebras possessing special imaginary roots and also give a complete classification of GKM algebras possessing strictly imaginary property (GKM algebras whose imaginary roots are strictly imaginary). We also conclude that the Monster Lie algebra has no special imaginary root and does not satisfy strictly imaginary property.     

Resistivity of dilute 2D electrons in an undoped GaAs heterostructure

We report resistivity measurements from 0.03 to 10 K in a dilute high mobility 2D electron system. Using an undoped GaAs/AlGaAs heterojunction in a gated field-effect transistor geometry, a wide range of densities, 0.16 x 10(10) to 7.5 x 10(10) cm(-2), are explored. For high densities, the results are quantitatively shown to be due to scattering by acoustic phonons and impurities. In an intermediate range of densities, a peak in the resistivity is observed for temperatures below 1 K. This nonmonotonic resistivity can be understood by considering the known scattering mechanisms of phonons, bulk, and interface ionized impurities. Still lower densities appear insulating to the lowest temperature measured.     

Reaktionen mit Allylidenphosphoranen,IV. Einfache Synthese von Cyclopentadienonen (Cyclonen)

Reactions with Allylidenephosphoranes, IV. An Easy Synthesis of Cyclopentadienones (Cyclones) The allylidenephosphoranes 2 react with α-ketocarbonyl chlorides 3 readily to afford the cyclopentadienones 4 and their Diels-Alder dimers 5 . With an excess of 2a, 4a undergoes competitive Michael additions yielding a mixture of 4-allylidene-2-cyclopentenone 6 and 4-(1-propenyl)-2-cyclopentenone 7 .     

Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high-mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this 2D electron system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of approximately 1.4 approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.     

neue Heterocyclisierungen mit Malonestern 1,3-Dithiole; 1,3-Oxathiole; Δ2-Oxazoline und das Vinylendipyridiniumdikation

The reaction of diethyl bromomalonate (1) or diethyl diazomalonate (6) with benzoyl isothiocyanate (2) proceeds via the carbene intermediates4, 7 or12 to afford the 1,3-dithiole5, the 2-oxazoline8 or the 1,3-oxathioles9 depending upon the catalyst employed. In contrast, the bis(ethoxycarbonyl)methylpyridinium bromides14 upon treatment with benzoyl isocyanates15 in pyridine give rise to vinylene dipyridinium dibromides18.