Hard Thermal Loops in the n-Dimensional ? 3 Theory

We derive a closed-form result for the leading thermal contributions which appear in the n-dimensional ? ³ theory at high temperature. These contributions become local only in the long wavelength and in the static limits, being given by different expressions in these two limits.     

The synthetic preparation of naturally-occurring aromatase inhibitors,morachalcone A,isogemichalcone B,and isogemichalcone C

A convergent synthesis applicable to the preparation of oxidized prenylchalcones is reported that relies on key Claisen–Schmidt, Mitsunobu, and vinyl/benzyl Stille coupling operations. The synthetic strategy was applied towards the preparation of the natural products morachalcone A and isogemichalcones B & C, allowing their preparation in less than 10 steps and 6–8% overall yield.     

Superfluid-helium converter for accumulation and extraction of ultracold neutrons

We report the first successful extraction of accumulated ultracold neutrons (UCN) from a converter of superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. Windowless UCN extraction is performed in vertical direction through a mechanical cold valve. This prototype of a versatile UCN source is comprised of a novel cryostat designed to keep the source portable and to allow for rapid cooldown. We measured time constants for UCN storage and extraction into a detector at room temperature, with the converter held at various temperatures between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of extracted UCN is close to the theoretical expectation.     

Structure and properties of Na-magadiite dependent on temperature

The mechanism of the thermal behaviour of Na-magadiite at a temperature range from 293–573 K was developed based on X-ray diffraction, DTA, DTL, Q-TG, and gravimetric measurements. A structure model (BRANDT et al.) previously proposed was additionally used. It is possible to show that there probably is a connection between the typical modifications of basal spacing and significant shiftings of silicate sheets. Different steps of dehydration, decrystallization and structure variations can be ascribed to the several thermal transitions. The results depend on sample treatment such as the existent or not existent solid-water vapour interaction and the establishment of equilibrium. It seems that there is a predominance of the first mentioned influence.     

Structural Elucidation of an Atropisomeric Entcassiflavan-(4β→8)-Epicatechin Isolated from Dalbergia monetaria L.f. Based on NMR and ECD Calculations in Comparison to Experimental Data

A rare dihydoxyflavan-epicatechin proanthocyanidin, entcassiflavan-(4β→8)-epicatechin, was isolated from Dalbergia monetaria, a plant widely used by traditional people from the Amazon to treat urinary tract infections. The constitution and relative configuration of the compound were elucidated by HR-MS and detailed 1D- and 2D-NMR measurements. By comparing the experimental electronic circular dichroism (ECD) spectrum with the calculated ECD spectra of all 16 possible isomers, the absolute configuration, the interflavan linkage, and the atropisomers could be determined.     

Electron and positron pair emission by low energy positron impact on surfaces

The emission of electron pairs from surfaces has the power to reveal details about the electron–electron interaction in condensed matter. This process, stimulated by a primary electron or photon beam, has been studied both in experiment and theory over the last two decades. An additional pathway, namely positron–electron pair emission, holds the promise to provide additional information. It is based on the notion that the Pauli exclusion principle does not need to be considered for this process.We have commissioned a laboratory based positron source and performed a systematic study on a variety of solid surfaces. In a symmetric emission geometry we can explore the fact that positron and electron are distinguishable particles. Following fundamental symmetry arguments we have to expect that the available energy is shared unequally among positron and electron. Experimentally we observe such a behavior for all materials studied. We find an universal feature for all materials in the sense that on average the positron carries a larger fraction of the available energy. This is qualitatively accounted for by a simplified scattering model. Numerical results, which we obtained by a microscopic theory of positron–electron emission from surfaces, reveal however that there are also cases in which the electron carries more energy. Whether the positron or the electron is more energetic depends on details of the bound electron state and of the emission geometry. The coincidence intensity is strongly material dependent and there exists an almost monotonic relation between the singles and coincidence intensity. These results resemble the findings obtained in electron and photon stimulated electron pair emission. An additional reaction channel is the emission of an electron pair upon positron impact. We will discuss the energy distributions and the material dependence of the coincidence signal which shows similar features as those for positron–electron pairs.     

Inverse Monte Carlo renormalization group transformations for critical phenomena

We introduce a computationally stable inverse Monte Carlo renormalization group transformation method that provides a number of advantages for the calculation of critical properties. We are able to simulate the fixed point of a renormalization group for arbitrarily large lattices without critical slowing down. The log-log scaling plots obtained with this method show remarkable linearity, leading to accurate estimates for critical exponents. We illustrate this method with calculations in two- and three-dimensional Ising models for a variety of renormalization group transformations.     

Thermal-field propagation in an exocontact zone of a magmatic body and its impact on radiogenic isotope concentrations in minerals

In application of radioactive isotope systems (K-Ar, Rb-Sr etc.) during the last decades, experience was gained not only on their geochronometrical uses, but also on estimations of some important parameters of geological processes, especially temperatures and durations of superimposed thermal events. In this paper, the formation of an exocontact thermal field of a magmatic intrusion is considered as a spreading of a thermal source delta-function. Appropriate solutions of the heat-transfer equation are deduced and correlated with diffusion parameters of the radiogenic argon, coupling radioactive, thermal and kinetic parameters in an exocontant zone of a magmatic body. These solutions were used for quantitative reinterpretations of data taken from Hart's classical paper [The petrology and isotopic mineral age relations of a contact zone in the Front Range, Colorado. J. Geol., 1964, v. 72, pp. 493-525]. Theoretic and measured radiogenic argon and strontium concentrations within exocontact aureoles are found to be in good concordance.     

New Molecular Receptors with Cyclophosphazene Subunits: Synthesis, Reactivity, and Structure-Property Relationships

A series of hydrophopic ( 2 and 3) and new hydrophilic ( 4– 7) molecular receptors of the PNP-lariat ether with tetra-substituted cyclotriphosphazene subunits have been prepared by the complete nucleophilic substitution of chlorine atoms in the reactive PNP-crown precursor 1 with the respective sodium cation-paired oxyanions (phenoxy 2, -naphthoxy 3, and methoxytrioxyethylenoxy 4) and aliphatic amines (n-propylamine 5 aziridine 6, and pyrrolidine 7). Their structures were established by MS and ³¹P NMR spectroscopy and their metal ion complexing properties tested by a TLC method. Comparison of the complexation behaviour for ligands 1– 7 shows that the affinity for particular cations is strongly substituent-dependent and, in general, is significantly enhanced by cooperation of the side arm donor atoms (O or N) with the parent PNP-crown structure in the binding process. The remarkable affinity of some ligands for selected cations, in particular lithium, cesium, and silver ions, is interpreted in terms of structure-property relationships.