Processing and Photostability of Pyrromethene 567 Polycerams

Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with aQ-switched, frequency doubled Nd: YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm². UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.     

A kinetic treatment of glass formation VII: Transient nucleation in non-isothermal crystallization during cooling

The analysis of crystallization statistics has been modified to allow for time-dependent (transient) nucleation. To establish its accuracy, the numerical analysis has been applied to isothermal crystallization kinetics and shown to yield crystallization versus time curves which compare very closely with curves calculated analytically with or without the inclusion of transient nucleation.The numerical analysis including transient has been used to calculate the critical cooling rates for glass formation in anorthite and o-terphenyl considering (1) only homogeneous nucleation and (2) homogeneous nucleation + heterogeneous nucleation for 10⁷ heterogeneities cm^?3 with contact angles between 40° and 100°. It has been shown that inclusion of time-dependent nucleation in the calculations does not change the critical cooling rates for glass formation calculated assuming steady-state homogeneous nucleation in both materials. The critical cooling rate in anorthite calculated including steady-state heterogeneous nucleation was found to be decreased only slightly by the inclusion of time-dependent nucleation; while the critical cooling rates calculated for o-terphenyl were not change at all by the inclusion of time-dependent nncleation.The lack of an effect of time-dependent nucleation on the critical cooling rates calculated assuming only homogeneous nucleation is explained by the relatively small transient times on the high temperature side of the nucleation peak (a temperature range which has an overwhelming effect on the overall crystallization process because of the relatively high crystal growth rates in this range).Although the critical cooling rates associated with heterogeneous nucleation are large, the nucleation here takes place at relatively small undercooling where the transient times are relatively small. Thus, transient nucleation causes only a temporary delay in the over all crystallization, and its effect on the critical cooling rate is small.     

Local uniqueness for the fixed energy fixed angle inverse problem in obstacle scattering

We prove local uniqueness for the inverse problem in obstacle scattering at a fixed energy and fixed incident angle.

     

Influence of the Type of Junction in DNA-3′-Peptide Nucleic Acid (PNA) Chimeras on Their Binding Affinity to DNA and RNA

The automated on-line synthesis of DNA-3′-PNA (PNA=Polyamide Nucleic Acids) chimeras 1 – 3 is described, in which the 3′-terminal part of the oligonucleotide is linked to the aminoterminal part of the PNA either via a N-(2-mercaptoethyl)- (X=S), a N-(2-hydroxyethyl)- (X=O), or a N-(2-aminoethyl)- (X=NH) N-[(thymin-1-yl)acetyl]glycine unit. Furthermore, the DNA-3′-PNA chimera 4 without a nucleobase at the linking unit was prepared. The binding affinities of all chimeras were directly compared by determining their T_m values in the duplex with complementary DNA, RNA, or DNA containing a mismatch or abasic site opposite to the linker unit. We found that all investigated chimeras with a nucleobase at the junction form more stable duplexes with complementary DNA and RNA than the corresponding unmodified DNA. The influence of X on duplex stabilization was determined to be in the order O>S≈NH, rendering the phosphodiester bridge the most favored linkage at the DNA/PNA junction. The observed strong duplex-destabilizing effects, when base mismatches or non-basic sites were introduced opposite to the nucleobase at the DNA/PNA junction, suggest that the base at the linking unit contributes significantly to duplex stabilization.     

Some remarks on reflection positivity

The requirement of reflection positivity is investigated and its general applicability to different physical theories is pointed out. Its role is illustrated on an example from electrostatics and on several simple examples of field theories. Then, after presenting an abstract construction of the concept, the role of reflection positivity in classical lattice systems is discussed.Invited talk at the Symposium on Mathematical Methods in the Theory of Elementary Particles, Liblice castle, Czechoslovakia, June 18–23, 1978.For valuable discussions I should like to thank J.Löffenholz.     

Relative entropy and the Wigner-Yanase-Dyson-Lieb concavity in an interpolation theory

We show that the Wigner-Yanase-Dyson-Lieb concavity is a general property of an interpolation theory which works between pairs of (hilbertian) seminorms. As an application, the theory extends the relevant work of Lieb and Araki to positive linear forms of arbitrary *-algebras. In this context a relative entropy is defined for every pair of positive linear forms of a *-algebra with identity. For this generalized relative entropy its joint convexity and its decreasing under identity-preserving completely positive maps is proved.     

Glycosylidene Carbenes. Part 20. Synthesis of deprotected,spiro-linked C-glycosides of C60

Mannosylidenation of buckminsterfullerene (C₆₀; 1 ) with the 2,3-di-O-benzyl-4,6-O-benzylidene-protected diazirine 7 and the 2,3:4,6-di-O-isopropylidene-protected diazirine 8 leads to the spiro-linked C -glycosides 6 and 10 in 44 and 31% yield, respectively (Scheme). The diazirine 8 was prepared in five steps from 2,3:4,6-di-O-iso-propylidene-α-D -mannopyranose ( 11 ) via the oximes 12 , the (Z)-hydroximolactone 13 , the mesylate 14 , and the diaziridines 15 . Deprotection of the mannosylidenated fullerenes 6 and 10 under acidic conditions gave the partially deprotected diol 9 (97%) and the unprotected mannosylidenated fullerene 16 (73%), respectively. The mannosylidene-fullerenes 6, 9, 10 , and 16 possess a 6–6 ring-bridged σ-homoaromatic structure.     

Viscosity of liquid albite,a network material

The viscosity of liquid albite (NaAlSi₃O₈) has been determined over the temperature range 800–1000°C. The results are combined with data obtained at higher temperatures to obtain the overall log η versus $\text{1}\text{T}$ relation. The relation indicates Arrhenian behavior, with an apparent activation energy of ～95 kcal mol^?1. By comparing the viscous flow behavior of albite with that of the other materials, including SiO₂, GeO₂ and B₂O₃, it is suggested that liquid albite is a random network of SiO₄ and AlO₄ tetrahedra.