Predicting Turbulent Spectra in Drag-reduced Flows

In the present work we describe how turbulent skin-friction drag reduction obtained through near-wall turbulence manipulation modifies the spectral content of turbulent fluctuations and Reynolds shear stress with focus on the largest scales. Direct Numerical Simulations (DNS) of turbulent channels up to Re _τ = 1000 are performed in which drag reduction is achieved either via artificially removing wall-normal turbulent fluctuations in the vicinity of the wall or via streamwise-travelling waves of spanwise wall velocity. This near-wall turbulence manipulation is shown to modify turbulent spectra in a broad range of scales throughout the whole channel. Above the buffer layer, the observed changes can be predicted, exploiting the vertical shift of the logarithmic portion of the mean streamwise velocity profile, which is a classic performance measure for wall roughness or drag-reducing riblets. A simple model is developed for predicting the large-scale contribution to turbulent fluctuation and Reynolds shear stress spectra in drag-reduced turbulent channels in which a flow control acts at the wall. Any drag-reducing control that successfully interacts with large scales should deviate from the predictions of the present model, making it a useful benchmark for assessing the capability of a control to affect large scales directly.     

Reaktionen mit phosphororganischen Verbindungen, 24. Mitt.: Zur Umsetzung von α-Acyl-α-alkyl-methylentriphenylphosphoranen mit Acetylazid

Zusammenfassung -Acyl--alkyl-methylentriphenylphosphorane, (C₆H₅)₃P=CC(OR₁)(R₂), setzen sich mit Acetylazid zu 4-R₁-5-R₂-N-Acetyl-1,2,3-triazolen um. R₁ kann auch Doppelbindungen enthalten oder Äthoxyl sein. Dieselben Triazolverbindungen erhält man auch, wenn man die genannten -Oxophosphorylene zuerst mit Acetylchlorid, und anschließend mit NaN₃ umsetzt. Nur im Falle des Phosphorylens1g liefert die zuletzt genannte Führung der Reaktion ein anderes Produkt, die -Azidovinylcarbonylverbindung2g. Aus dem Phosphorylen1h entsteht auf beiden Reaktionswegen der -Azidoacrylester2d.

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Reactions with phosphoroorganic compounds, XXIV: Reaction of -acyl--alkyl-methylene-triphenyl-phosphoranes with acetyl azide

-Acyl--alkylmethylenetriphenylphosphoranes (C₆H₅)₃P=C(COR₁)(R₂) react with acetyl azide to give 4-R₁-5-R₂-N-acetyl-1,2,3-triazoles, where R₁ is an unsaturated lower alkyl or an ethoxy group. The same reaction products are formed by acylation and subsequent treatment with sodium azide. Only in the case of the phosphoroylene1g the two-step modification of the reaction leads to the -azidovinylcarbonyl compound2g. The -azidoacrylester2d, however, is formed from the phosphoroylene1h in either way.

     

Intramolecular exchange interaction in twofold spin-labelled platinum complexes

The synthesis and the crystal structures of two platinum bis-ethynyl-phenyl-nitronyl-nitroxide complexes are reported and solution EPR investigations evidenced the intramolecular exchange interaction through a diamagnetic transition metal based spacer.     

A copper(II) complex of a pentadentate ligand featuring large ferro- and antiferromagnetic interactions

A novel pentadentate ligand based on a 2,2'-bipyridine template and functionalized with two methylene bridged nitroxide arms provides mononuclear Cu(II) and Zn(II) complexes displaying a facial and meridional conformation, respectively; for Cu large intramolecular ferromagnetic (J/kB = +173 K) and antiferromagnetic (J'/kB = -170 K) exchange interactions are evidenced from magnetic measurements.     

Synthesis,Crystal Structure,and Optical Properties of (CH3NH3)2CoX4 (X = Cl,Br, I,Cl0.5Br0.5, Cl0.5I0.5, Br0.5I0.5)

The reaction of methylammonium halides and cobalt halides yielded the organic‐inorganic hybrid compounds of general formula (CH₃NH₃)₂CoX₄. By varying the different halides, we were able to synthesize the whole row from Cl to I as well as some mixed halides compounds and to determinate the crystal structures. (CH₃NH₃)₂CoX₄ (X = Cl, Br, Cl_0.5Br_0.5, Br_0.5I_0.5) crystallize isotypic to (CH₃NH₃)₂HgCl₄ in space group P2₁/c with Z = 4 [X = Cl: a = 7.6483(9), b = 12.6885(18), c = 10.8752(12) Å, β = 96.639(9)°; X = Cl_0.5Br_0.5: a = 7.8271(9), b = 12.9543(9), c = 11.1007(11) Å, β = 96.320(8)°; X = Br: a = 7.9782(2), b = 13.1673(2), c = 11.2602(2) Å, β = 96.3260(10)° and X = Br_0.5I_0.5: a = 8.2435(12), b = 13.645(2), c = 11.5856(18) Å, β = 95.54(2)°]. The mixed halides show a statistic distribution in both cases. In (CH₃NH₃)₂CoCl₂I₂ an ordered variant is realized representing a new structure type [C2/m, Z = 4, a = 18.808(4), b = 7.3604(7), c = 10.4109(17) Å, β = 120.364(13)°]. (CH₃NH₃)₂CoI₄ crystallizes again isotypic to the respective mercury compound [(CH₃NH₃)₂HgCl₄] [Pbca, Z = 8, a = 10.9265(5), b = 12.1552(5), c = 20.9588(9) Å]. All structures are build up by inorganic tetrahedral [CoX₄]^2– anions and organic (CH₃NH₄)⁺ cations. Additionally the Raman spectra as well as the optical reflectance spectra are discussed.     

结构非线性分析中求解预定荷载水平的改进弧长法

本文对目前广泛应用于结构非线性分析之中的弧长法进行改进。改进后的弧长法除保持原有优点外，能够在自动跟踪结构非线性平衡路径的同时，进一步求得位于结构平衡睡径任一区段的任意预先指定的荷载水平及相应的变形。本文的方法可以推广应用于求解预先指定的应力或位移。数值算例表明了本文方法的计算精度、效率及可靠性。     

The Molecular Basis of the Interaction of Cyclophilin A with α-Synuclein

Peptidylprolyl isomerases (PPIases) catalyze cis/trans isomerization of prolines. The PPIase CypA colocalizes with the Parkinson's disease (PD)-associated protein α-synuclein in cells and interacts with α-synuclein oligomers. Herein, we describe atomic insights into the molecular details of the α-synuclein/CypA interaction. NMR spectroscopy shows that CypA catalyzes isomerization of proline 128 in the C-terminal domain of α-synuclein. Strikingly, we reveal a second CypA-binding site formed by the hydrophobic sequence ⁴⁷GVVHGVATVA⁵⁶, termed PreNAC. The 1.38 Å crystal structure of the CypA/PreNAC complex displays a contact between alanine 53 of α-synuclein and glutamine 111 in the catalytic pocket of CypA. Mutation of alanine 53 to glutamate, as found in patients with early-onset PD, weakens the interaction of α-synuclein with CypA. Our study provides high-resolution insights into the structure of the PD-associated protein α-synuclein in complex with the most abundant cellular cyclophilin.     

Ueber das vollständige Combinantensystem zweier binärer Formen

Ohne Zusammenfassung