Application of atom-photon coincidence techniques to the determination of the differential cross section for excitation ofK(42 P) in low-energy K-N2, CO collisions

The differential cross section for the processK(4² S)+N₂, CO→K(4² P)+ N₂, CO is presented for reduced scattering angles τ<2·10⁴ eV deg. The inelastic process is identified by determining the time-correlation between the inelastically scattered potassium atom and the emittedK(4² P→4² S)photon. The performance of different coincidence techniques is compared. From the differential cross sections values for the position of the curve crossing responsible for the excitation process are derived (R _c=2.77, 2.48 Å andV(R _c )=0.55, 1.00 eV for K-N₂, CO respectively). The values indicate that the lowest ionic intermediate state of the form K⁺-N ₂ ^? , CO^? is responsible for the excitation process.     

Coexistence of Two Different Distorted Octahedral [MnF6]3− Sites in K3[MnF6]: Manifestation in Spectroscopy and Magnetism

As a consequence of the static Jahn-Teller effect of the ⁵E ground state of Mn^III in cubic structures with octahedral parent geometries, their octahedral coordination spheres become distorted. In the case of six fluorido ligands, [MnF₆]³⁻ anions with two longer and four shorter Mn−F bonds making elongated octahedra are usually observed. Herein, we report the synthesis of the compound K₃[MnF₆] through a high-temperature approach and its crystallization by a high-pressure/high-temperature route. The main structural motifs are two quasi-isolated, octahedron-like [MnF₆]³⁻ anions of quite different nature compared to that met in ideal octahedral Mn^III Jahn-Teller systems. Owing to the internal electric field of C_i symmetry dominated by the next-neighbour K⁺ ions acting on the Mn^III sites, both sites, the pseudo-rhombic (site 1) and the pseudo-tetragonally elongated (site 2) [MnF₆]³⁻ anions are present in K₃[MnF₆]. The compound was characterized by single-crystal and powder X-ray diffraction, and magnetometry as well as by FTIR, Raman, and ligand field spectroscopy. A theoretical interpretation of the electronic structure and molecular geometry of the two Mn sites in the lattice is given by using a vibronic coupling model with parameters adjusted from multireference ab-initio cluster calculations.     

The Intrusion of the Meissen Pluton (Elbe Valley-Zone): Evidence from Geochemical and Isotopic Data

Abstract

Geochemical and mineralogical investigations of plutonic rocks from the Meiβen massif indicate different magmatic evolution trends of the Freital sequence as well as for the central part of the complex Constant ε-Nd_T-345 values of ?1.5 of the Freital sequence and major/trace element data point to a fractional crystallization process. Based on ε-Nd values, ¹⁴⁷Sm/¹⁴⁴Nd ratios as well as on geochemical data affinities to alkali basalts cannot be excluded.

Analogous conclusions have been drawn regarding mineral chemical data [10] and cathodoluminescence spectra of apatite [13]. Assimilation of old continental crust, reflected by relics of apatite and zircon, may be the reason that the ε-Nd values plot at the lower end of the “mantle array”. The pyroxene-monzodiorite from Gröba belongs to the same source environment as the Freital sequence (Nd-characteristics).

The geological evolution of the central part of the studied plutonic complex is completely different to the Freital sequence: most of the intrusions show signatures of open system fractionation processes. The ε-Nd_T-345 value of ?1.46 of the Leuben monzonite indicates a narrow relation to the Freital sequence, whereas the ε-Nd_T-345 value of +2.27 of the Spitzgrund monzonite either reflects the derivation of another basic material then the Freital-type or the participation of other mixing component(s) from geologically young crust.

Fabric and mineral chemical investigations of the porphyry-like granite GII point to a mixing process of basic xenocrysts, resembling the corresponding minerals of the Freital sequence, and granite melts [10]. Large amounts of old zircon cores [11] indicate the inheritance of continental crust components by the Hauptgranit. Isotopic investigations on various granitic samples (GII, Hauptgranit and Riesensteingranit) reflect an increasing trend towards the crustal source(s) of their parental melts. The ε-Nd_T-345 values are ?3.75, ?4.16 and ?6.13, respectively.

Chemical parameters and the ε-Nd_T value of the Riesensteingranit agree with data of granites from the Saxonian Granulite Massif (see e.g. Wand et al. [8]; von Quadt, 1992). Thus, it may be possible that both granite types derived from similar sources.     

Lewis acid-base adducts of zwitterionic alkali metal methanides and silanides with BH3

The synthesis, structures and spectroscopic properties of M(MeOCH₂CH₂OMe₂Si)₃CBH₃ (M-1-BH₃) and M(MeOCH₂CH₂OMe₂Si)₃SiBH₃ (M-2-BH₃) (M?=?Li, Na, K) derived from reactions of BH₃ with the alkali metal zwitterions [M(MeOCH₂CH₂OMe₂Si)₃C] (M-1) and [M(MeOCH₂CH₂OMe₂Si)₃Si] (M-2) (M?=?Li, Na, K), resp., are reported. X-ray analysis and DFT calculations reveal discrete zwitterionic structures with the octahedral alkali metal cations rigidly locked and charge separated from the BH₃ units via pendant donors groups. Solution experiments with the hydride acceptors B(C₆F₅)₃ and [Ph₃C]₂[B₁₂C₁₂] indicate that Na-1-BH₃ can donate hydrides to form cations of formula [Na(MeOCH₂CH₂OMe₂Si)₃CBH₂]⁺.     

Cellulose Iβ investigated by IR-spectroscopy at low temperatures

Highly crystalline oriented Halocynthia roretzi cellulose Iβ films were investigated by IR-spectroscopy between ?180 and +10 °C. Changes in the IR-spectra induced by temperature were compared to published changes induced by mechanical stretching. This made it possible to conclude that frequency shifts in the O–H stretching region of the IR-spectra due to temperature were not predominantly an indirect effect of thermal expansion leading to greater O–O distances, but were due directly to the effect of temperature on the O–H···O hydrogen bonds. Temperature induced frequency shifts of C–H stretching bands were consistent with the presence of weak inter-sheet C–H···O bonds. Furthermore, no phase transition in cellulose Iβ was found between ?180 and +10 °C.     

Geochemical investigation of alluvial sediments: validation of ICP-OES determination of heavy metals. A case study from the Utrata River Valley (central Poland)

The development and validation of a reliable analytical procedure for the determination of selected metals (Cd, Cr, Cu, Pb, Zn and Mn) in sediments accumulated in the Utrata River (Poland) is described. The aqua regia extraction followed by inductively coupled plasma optical emission spectrometry (ICP-OES) was used for this purpose. The optimized analytical procedure was validated, and adequate quality control actions were implemented in order to provide reliable data. The precision under’ within-laboratory’ reproducibility conditions was estimated from duplicate analysis. Certified reference material (CRM) was used in order to evaluate the accuracy of the results regarding the sewage sludge amended soil CRM 143R. The detection limits for all elements of interest were well-below their content in the investigated sediment samples. The obtained reliable data could be used for assessment of the relationship between human economic activity in the past and the geochemical features of the sediments.     

Microswimmers – From Single Particle Motion to Collective Behavior

Locomotion of autonomous microswimmers is a fascinating field at the cutting edge of science. It combines the biophysics of self-propulsion via motor proteins, artificial propulsion mechanisms, swimming strategies at low Reynolds numbers, the hydrodynamic interaction of swimmers, and the collective motion and synchronisation of large numbers of agents. The articles of this Special Issue are based on the lecture notes of an international summer school, which was organized by the DFG Priority Programme 1726 “Microswimmers – From Single Particle Motion to Collective Behaviour” in the fall of 2015. The minireviews provide a broad overview of the field, covering both elementary and advanced material, as well as selected areas from current research.     

Oxidation stability of various Ti-alloys

Since titanium metal first became a commercial reality in 1950, corrosion resistance has been an important consideration in its selection as an engineering structural material. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material. Titanium, like any other metal, is subject to corrosion in environments of air, oxygen, moisture, and so on. In this work, high-temperature stability of Ti and various Ti-alloys (by ASTM standard) was investigated. The best results showed that for Ti-Gr.5 alloy, the oxidation at 800 °C was 3.39% and at 900 °C 8.35%. For the comparison, commercial pure Ti-alloys Ti-Gr.2 and Ti-Gr.37 containing Al were used, whereas the oxidation resistance was much worse.