On Fokker–Planck Equations for Turbulent Reacting Flows. Part 1. Probability Density Function for Reynolds-Averaged Navier–Stokes Equations

The accurate treatment of finite-rate chemistry is possible by the application of stochastic turbulence models which generalize Reynolds-averaged Navier–Stokes equations. Usually, one considers linear stochastic equations. In this way, fluctuations are generated by uncorrelated forces and relax with a frequency that is independent of the actual fluctuation. It has been proved that such linear equations are well appropriate to simulate near-equilibrium flows. However, the inapplicability or unfeasibility of other methods also results in a need for stochastic methods for more complex flow simulations. Their construction requires an extension of the simple mechanism of linear stochastic equations. Two ways to perform this are investigated here. The first way is the construction of a stochastic model for velocities where the relaxation frequency depends on the actual fluctuation. This is a requirement to involve relevant mixing variations due to large-scale flow structures. The stochastic model developed is applied to the simulation of convective boundary layer turbulence. Comparisons with the results of measurements provide evidence for its good performance and the advantages compared to existing methods. The second way presented here is the construction of scalar equations which involve memory effects regarding to both the stochastic forcing and relaxation of fluctuations. This allows to overcome shortcomings of existing stochastic methods. The model predictions are shown to be in excellent agreement with the results of the direct numerical simulation of scalar mixing in stationary, homogeneous and isotropic turbulence. The consideration of memory effects is found to be essential to simulate correctly the evolution of scalar fields within the first stage of mixing.     

Measurement of the branching ratio of the double Dalitz decayK L →e+e−e+e− and the CP parity of theK L -meson

Data from the NA31 experiment at CERN have been used to measure the branching ratio of the double Dalitz decay of the long-lived neutral kaon. Eight events have been found with negligible background. The measured distribution of the angle between the planes of the two e⁺e^?-pairs favours aCP=?1 state for the long-lived neutral kaon.     

Stoffwechselprodukte von Mikroorganismen. 233. Mitteilung. Danoxamin,der eisenbindende Teil des Sideromycin-Antibioticums Danomycin

Danoxamine, the Iron-Binding Moiety of the Sideromycin Antibiotic Danomycin The antibiotic danomycin was separated into its components, danomycin A and B ( 1 and 2 , resp.), by various methods. Danomycin A is a carbamate of danomycin B and can be transformed to the latter by boiling with H₂O. Both danomycins can be hydrolyzed by alkali to the Fe-containing moiety, danoxamine ( 3 ). The structure of the latter was determined by spectroscopy and chemical degradation as the Fe(III) complex of 5,16,27,32-tetrahydroxy-4,12,15,23,26-pentaoxo-5,11,16,22,27-pentaaza-dotriacontanoic acid. It belongs thus to the ferrioxamine family of siderophores. In the danomycins, this moiety is linked by an ester bond to a disaccharide moiety of unknown structure. One of the sugars is believed to be an aminohexane methyl ether. Chromatographically homogenous danomycins A and B are still mixtures of isomers, a neutral sugar being glucose or mannose.     

An improved typology of cutting and packing problems

The number of publications in the area of Cutting and Packing (C&P) has increased considerably over the last two decades. The typology of C&P problems introduced by Dyckhoff [Dyckhoff, H., 1990. A typology of cutting and packing problems. European Journal of Operational Research 44, 145–159] initially provided an excellent instrument for the organisation and categorisation of existing and new literature. However, over the years also some deficiencies of this typology became evident, which created problems in dealing with recent developments and prevented it from being accepted more generally. In this paper, the authors present an improved typology, which is partially based on Dyckhoff’s original ideas, but introduces new categorisation criteria, which define problem categories different from those of Dyckhoff. Furthermore, a new, consistent system of names is suggested for these problem categories. Finally, the practicability of the new scheme is demonstrated by using it as a basis for a categorisation of the C&P literature from the years between 1995 and 2004.     

Synthese eines cyclischen Depsipeptides mittels Amidcyclisierung

Synthesis of a Cyclic Depsipeptide via an Amide Cyclization The synthesis of (S)-Pms-(R)-Pro-(S)-Ala-Aib-N(CH₃)₂ ( 12 ) has been achieved according to Scheme 3. For the formation of fragment 11 , the reaction of Z-alanine (Z = benzyloxycarbonyl) and 3-dimethylamino-2,2-dimethyl-2-azirine ( 1 ) has been used, whereby 1 serves as an aminoisobutyric-acid dimethylamide (aib-N(CH₃)₂) equivalent. Treatment of a suspension of 12 in toluene with HCl gas at 100° led to the cyclic depsipeptide 13 in 72% yield (Scheme 4). In presence of water, the acid 14 was isolated as the sole product. A mechanism for the formation of 13 and 14 via an oxazolinone intermediate, is postulated in Scheme 4.     

Measurement of evaporation residue cross-sections of the reaction 30Si + 238U at subbarrier energies

The reaction ³⁰Si + ²³⁸U → ²⁶⁸Sg^* was studied at beam energies close to the Coulomb barrier. At a center-of-mass energy of E _c.m. = 144.0MeV for reactions at half thickness of the target we measured three decay chains of ²⁶³Sg produced by evaporation of five neutrons. The cross-section was ( 67⁺⁶⁷ _-37) pb. At E _c.m. = 133.0MeV we measured three spontaneously fissioning nuclei which we assigned to the isotope ²⁶⁴Sg. The production cross-section was ( 10⁺¹⁰ _-6) pb and a half-life of ( 120⁺¹²⁶ _-44) ms was determined. This half-life is a factor of twenty shorter than theoretical predictions. At E _c.m. = 128.0MeV an upper cross-section limit of 15pb was measured. The cross-section data reveal a strong influence of the orientation of the deformed target nucleus on the production yield. Compared to excitation functions measured for the lighter system ¹⁶O + ²³⁸U → ²⁵⁴Fm^*, a reduction of the fusion probability was observed at low beam energies indicating increasing competition from quasifission processes.