Search results for "cyclic"

Die stufenweise Synthese von 4,11,18,25-Tetra-tert-butyl-[1.1.1.1]metacyclophan-7,14,21,28-tetraol und 4,11-Dimethyl-[1.1.1.1]-metacyclophan-7,14,21,…

1978

Two phenolic alcohols with four phenolic units in their molecules are obtained by stepwise synthesis starting from simple phenolic derivatives. The phenolic alcohols are cyclized by boiling of a diluted solution in acetic acid. A third cyclic compound is obtained by debutylation of that cyclic compound which contains two neighbouringtert-butyl groups and two methyl groupspara to the phenolic hydroxyl groups.

Die spektroskopische untersuchung einer cyclischen, tetrameren verbindung aus p-kresol und formaldehyd

1972

In Anlehnung an den Syntheseweg von HAYES und HUNTER wurde eine cyclische, tetramere Verbindung (VII) uber eine linear 4-Kernverbindung (VI) (aus p-Kresol und Formaldehyd) hergestellt. Ihre Struktur wurde spektroskopisch untersucht. Mittels UV- und IR-Spektren last sich VII von der Ausgangsstufe VI und einem Konkurrenzprodukt VIII unterscheiden. Die H-NMR-Spektren der Ringverbindung und ihrer Ausgangsverbindung (VI) stimmen vollstandig mit den angegebenen Strukturformeln uberein; sie geben, bei 20 und 60°C aufgenommen, Hinweise auf bestimmte Konformere der Ringverbindung. Das massenspektrometrisch bestimmte Molekulargewicht (480) stimmt mit dem berechneten (480,6) uberein. Following the syn…

Multiple catenanes based on tetraloop derivatives of calix[4]arenes

2009

Abstract Four novel tetraarylurea calix[4]arenes ( 4a – d ) have been synthesized, substituted by ω-alkenyloxy residues in 3,5-positions of the arylurea residues. The eight alkenyl groups were pairwise connected by olefin metathesis and subsequent hydrogenation. The ring-closure reaction was carried out with heterodimers exclusively formed by 4 with a tetratosylurea calix[4]arene 1 , which serves as a template in this reaction step. The potential trans-cavity bridging is entirely suppressed in this way. Bis- and tetraloop calix[4]arenes cannot form dimers due to overlapping loops. However, they readily form heterodimers with open-chain tetraureas, as long as their urea residues can pass thr…

Differential geometric LARS via cyclic coordinate descent method

2012

We address the problem of how to compute the coefficient path implicitly defined by the differential geometric LARS (dgLARS) method in a high-dimensional setting. Although the geometrical theory developed to define the dgLARS method does not need of the definition of a penalty function, we show that it is possible to develop a cyclic coordinate descent algorithm to compute the solution curve in a high-dimensional setting. Simulation studies show that the proposed algorithm is significantly faster than the prediction-corrector algorithm originally developed to compute the dgLARS solution curve.

Organotitanium reagents in organic synthesis a simple means to adjust reactivity and selectivity of carbanions

1982

Fatigue resistance of fiber post and cement/build-up materials.

2004

Objectives:The purpose of this study was to evaluate the fatigue resistance to cycling loading of teeth restored with fiber post and different build-up systems. Methods: Forty human, sound single-rooted teeth were selected and stored in 0.02% thymol solution. The crowns were removed by cutting the teeth at the cement-enamel junction, thereafter endodontic treatment was performed using the vertical condensation technique. The roots were partially embedded in epoxy resin and randomly assigned to four groups. The specimens were restored with the same type of quartz fiber posts (DT Light Post, RTD, Grenoble, France), but different cements and build-up systems were used: 1)All-Bond2+C&B Cement+B…

Effect of endodontic treatment on fatigue resistance of fiber posts bonding

2003

Objectives: The aim of this study is to evaluate the effect of the endodontic treatment on the fatigue resistance of endodontic post adhesive interfaces. Materials and methods: 50 single-rooted human teeth have been severed at the cement-enamel junction and randomly assigned to 5 groups receiving different endodontic treatments as follows: 1) distilled water + gutta-percha (control); 2) NaOCl 5% + gutta-percha and Pulp Canal Sealer EWT (Kerr); 3) NaOCl 5% + gutta-percha and Top Seal (Dentsply-Maillefer); 4) NaOCl 5% and EDTA 10% (alternatively) + gutta-percha and Pulp Canal Sealer EWT; 5) NaOCl 5% and EDTA 10% (alternatively) + gutta-percha and Top Seal. Subsequently, Light-Post DT #2 quart…

Incremental Delamination Processes under Cyclic Loading

2012

Hematopoietins: New Tools in the Treatment of Hematopoietic Insufficiency

1993

The number of circulating blood cells and their function are regulated by a variety of peptide hormones, the so-called hematopoietic growth factors (HGFs) or hematopoietins. In a complex regulatory network of stimulating and inhibiting peptide hormones [1], the number of circulating blood cells is kept at a physiological level. Because many of these blood cells have a relatively short half-life, the bone marrow is in a state of constant active proliferation in order to produce the necessary blood cells. For instance, granulocytes are made at a rate of 5 × 107–10 × 107 cells/s. It is unclear whether additional, hematopoietin-independent regulatory mechanisms exist, which might be responsible…

Variational methods for the steady state response of elastic–plastic solids subjected to cyclic loads

2003

Abstract Solids (or structures) of elastic–plastic internal variable material models and subjected to cyclic loads are considered. A minimum net resistant power theorem, direct consequence of the classical maximum intrinsic dissipation theorem of plasticity theory, is envisioned which describes the material behavior by determining the plastic flow mechanism (if any) corresponding to a given stress/hardening state. A maximum principle is provided which characterizes the optimal initial stress/hardening state of a cyclically loaded structure as the one such that the plastic strain and kinematic internal variable increments produced over a cycle are kinematically admissible. A steady cycle min…