Phase-Doppler Particle Sizing with Off-Axis Angles in Alexander's Darkband

A promising optical layout for standard phase-Doppler particle sizing instruments for use in two-phase flows with extremely limited optical access is presented. When applied to turbine oil of variable temperature and therefore refractive index (1.40< n < 1.46), the layout procedure leads to several suitable off-axis configurations. From these, a backscatter angle of ? = 125° is chosen owing to several geometrical restrictions. Although this angle lies in Alexander's darkband and therefore the intensities are low, the theoretical analysis indicates that this configuration is extremely insensitive to Gaussian-beam defects, which usually aggravate backscatter applications. Monosized droplet experiments confirmed the application of the configuration and showed an acceptable accuracy of the measurements. Experiments in a bearing chamber test rig gave reliable results and for the first time allowed an insight into the flow phenomena of this highly complex technical two-phase flow.     

Two interacting particles in a random potential: mapping onto one parameter localization theories without interaction

We consider two models for a pair of interacting particles in a random potential: (i) two particles with a Hubbard interaction in arbitrary dimensions and (ii) a strongly bound pair in one dimension. Establishing suitable correspondences we demonstrate that both cases can be described in terms familiar from theories of non-interacting particles. In particular, these two cases are shown to be controlled by a single scaling variable, namely the pair conductance g ₂. For an attractive or repulsive Hubbard interaction and starting from a certain effective Hamiltonian we derive a supersymmetric nonlinear σ model. Its action turns out to be closely related to the one found by Efetov for noninteracting electrons in disordered metals. This enables us to describe the diffusive motion of the particle pair on scales exceeding the oneparticle localization length L ₁ and to discuss the corresponding level statistics. For tightly bound pairs in one dimension, on the other hand, we follow early work by Dorokhov and exploit the analogy with the transfer matrix approach to quasi-1d conductors. Extending our study to M particles we obtain a M-particle localization length scaling like the Mth power of the one-particle localization length.     

Desorption induced GaN quantum dots on (0001) AlN by MOVPE

GaN quantum dots (QDs) are realized on (0001) AlN templates by growing a thin GaN layer on an AlN buffer layer and applying a subsequent desorption step without ammonia present. A growth interruption (GRI), which is commonly applied after the GaN growth allowing for QD formation, is systematically investigated regarding the temperature, duration and initial GaN coverage. Without GRI the initial GaN layer exhibits a two‐dimensional nonuniform growth at the step edges. In this study, the surface morphology only changes significantly if the GRI is performed without ammonia exposure. Thus, an initial two‐dimensional GaN layer can be shaped into three‐dimensional nanostructures. Presented coverage studies by atomic force microscopy (AFM) show desorption as the main driving force for island evolution. By tailoring the growth parameters, GaN QDs can be achieved. Uncapped GaN samples exhibit QDs with 1.2 nm in height and 30 nm in diameter. Additionally, capped GaN QDs exhibit excitonic luminescence lines at about 4.3 eV with FWHM down to 2 meV and an excitonic fine structure splitting of 7 meV. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spin Interactions and Magnetic Anisotropy in a Triangular Nickel(II) Complex with Triaminoguanidine Ligand Framework

The trinuclear nickel(II) complex [Ni₃(saltag^tBu)(bpy)₃(H₂O)₃]Cl (H₅saltag^tBu = 1,2,3-tris[(5-tert-butylsalicylidene)amino]guanidine) was synthesized and characterized by experimental as well as theoretical methods. The complex salt crystallizes with three molecules of dimethylformamide (dmf) and water as [Ni₃(saltag^tBu)(bpy)₃(H₂O)₃]Cl · 3dmf · 3H₂O ( 1 ) in the trigonal space group P3 , with the complex located on a threefold rotation axis, which is consistent with the molecular C₃ symmetry of the complex cation. Magnetic measurements reveal an antiferromagnetic coupling (J = –35.9 cm^–1) between the nickel(II) ions leading to a diamagnetic ground state for the trinuclear complex cation. Theoretical investigations based on broken-symmetry DFT confirm the antiferromagnetic exchange within the complex cation of 1 . Additional single-ion CASSCF ab initio studies reveal that magnetic anisotropy is present in the system. The experimental and theoretical results for 1 are compared with those of a structurally similar nickel(II) complex that is based on the bromo-substituted derivative of the triaminoguanidine ligand. The differences in their magnetic properties can be attributed to the stronger elongation of the pseudo-octahedral coordination sphere at the nickel(II) centers in case of 1 . The analysis of the magnetic properties of 1 clearly shows that for such exchange coupled systems reliable parameters for the magnetic anisotropy cannot be extracted from experimental data alone.     

Activation of Small Molecules by Phosphorus Biradicaloids

The reactivity of biradicaloid [P(μ‐NTer)]₂ was employed to activate small molecules bearing single, double, and triple bonds. Addition of chalcogens (O₂, S₈, Se_x and Te_x) led to the formation of dichalcogen‐bridged P₂N₂ heterocycles, except from the reaction with molecular oxygen, which gave a P₂N₂ ring featuring a dicoordinated P^III and a four‐coordinated P^V center. In formal [2πe+2πe] addition reactions, small unsaturated compounds such as ethylene, acetylene, acetone, acetonitrile, tolane, diphenylcarbodiimide, and bis(trimethylsilyl)sulfurdiimide are readily added to the P₂N₂ heterocycle of the biradicaloid [P(μ‐NTer)]₂, yielding novel heteroatom cage compounds. The synthesis, reactivity, and bonding of the biradicaloid [P(μ‐NTer)]₂ were studied in detail as well as the synthesis, properties, and structural features of all addition products.     

Discrimination of conventional and organic white cabbage from a long-term field trial study using untargeted LC-MS-based metabolomics

The influence of organic and conventional farming practices on the content of single nutrients in plants is disputed in the scientific literature. Here, large-scale untargeted LC-MS-based metabolomics was used to compare the composition of white cabbage from organic and conventional agriculture, measuring 1,600 compounds. Cabbage was sampled in 2 years from one conventional and two organic farming systems in a rigidly controlled long-term field trial in Denmark. Using Orthogonal Projection to Latent Structures–Discriminant Analysis (OPLS-DA), we found that the production system leaves a significant (p?=?0.013) imprint in the white cabbage metabolome that is retained between production years. We externally validated this finding by predicting the production system of samples from one year using a classification model built on samples from the other year, with a correct classification in 83 % of cases. Thus, it was concluded that the investigated conventional and organic management practices have a systematic impact on the metabolome of white cabbage. This emphasizes the potential of untargeted metabolomics for authenticity testing of organic plant products.     

Luminescence recognition of different organophosphorus pesticides by the luminescent Eu(III)–pyridine-2,6-dicarboxylic acid probe

Luminescence quenching of a novel long lived Eu(III)–pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol–water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)–(PDCA)₂ probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)–pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0–35.0 μM. The detection limits were 0.24–0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)–(PDCA)₂ were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)–(PDCA)₂–P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation.     

Complexes of Co(II) and Zn(II) with N-(Thio)phosphorylthioureas AdNHC(S)NHP(O)(OiPr)2 and MeNHC(S)NHP(S)(OiPr)2

The reaction of the potassium salt of the N-(thio)phosphorylated thioureas AdNHC(S)NHP(O)(OiPr)₂ (HL^I , Ad = Adamantyl) and MeNHC(S)NHP(S)(OiPr)₂ (HL^II ) with Co(II) and Zn(II) in aqueous EtOH leads to [ML^I,II ₂] chelate complexes. They were investigated by UV-vis, ¹H and ³¹P NMR spectroscopy, and microanalysis. The molecular structures of [ML^I ₂] were elucidated by single crystal X-ray diffraction analysis. The metal centers in both complexes are found to be in a distorted-tetrahedral O₂S₂ environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated L^I ligands. The photoluminescence properties of [ZnL^II ₂] are also reported.     

Desymmetrization of C2-Symmetric Bis(Boronic Esters) by Zweifel Olefinations

anti-Configured 1,3-dimethyl deoxypropionate motifs are important sub structures in natural products. Herein, we describe a bidirectional approach for the rapid construction of natural products featuring such motifs by using C₂-symmetrical 1,3-bis(boronic esters). As for its application in convergent syntheses it was important to establish a selective mono-Zweifel olefination we describe the scope and limitations by using different 1,3-bis(boronic esters) and nucleophiles. This protocol takes advantage of the combination of the Hoppe–Matteson–Zweifel chemistry, which was elegantly put into practice by Aggarwal et al. In order to show its applicability the total syntheses of two natural products, serricornin and (+)-invictolide, were performed.