Multiphase Jet Flow in Abrasive Water Jet Cutting

A numerical model for ultra-high velocity abrasive water jets (AWJ) is developed and jet dynamic characteristics are calculated under steady-state, turbulent, compressible, multi-phase flow conditions. The model is tested by comparison with analytical solutions for related theoretical problems, generally with very good agreement. Simulations of more realistic flows produce the expected values and behavior. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Desynchronization by phase slip patterns in networks of pulse-coupled oscillators with delays

Coupling delays may cause drastic changes in the dynamics of oscillatory networks. In the present paper we investigate how coupling delays alter synchronization processes in networks of all-to-all coupled pulse oscillators. We derive an analytic criterion for the stability of synchrony and study the synchronization areas in the space of the delay and coupling strength. Specific attention is paid to the scenario of destabilization on the borders of the synchronization area. We show that in bifurcation points the system possesses homoclinic loops, which give rise to complex long- or quasi-periodic solutions. These newly born solutions are characterized by a synchronous group, from which an oscillator periodically escapes, laps one period, and rejoins. We call such a dynamical regime “phase slip patterns”.     

Analytic extension of differentiable functions defined in closed sets by means of continuous linear operators

In this paper we solve the following problem posed by Schmets and Valdivia: Under which conditions does there exist an extension operator from the space of the Whitney jets on a closed set to so that the extended functions are real analytic outside ?

     

Pressure and time treatment for Chebyshev spectral solution of a Stokes problem

To investigate the influences of time scheme, pressure treatment and initial conditions in incompressible fluid dynamics, a Stokes problem is solved numerically on a slab geometry within the framework of spectral approximation in space. Four algorithms are examined: splitting schemes, influence matrix method, penalty formulation and pseudo-spectral space-time technique. It is shown that splitting schemes are less accurate than the other processes. Furthermore, the initial field should respect a compatibility condition to avoid singularities at the initial time. If it is not possible to build such a compatible field, the numerical procedure has to present good damping properties at the first steps of the time integration.     

Basische Metalle. XIV. Synthese und Kristallstruktur von C5H5(PMe3)CoS5: Ein neuer Metallapentathia-Heterocyclus

Basic Metals. XIV. Synthesis and Crystal Structure of C₅H₅(PMe₃)CoS₅: A New Metallapentathia Heterocycle The dinuclear complex C₅H₅(PMe₃)Co(μ-CO)₂Mn(CO)C₅H₄Me ( 3 ) reacts with stoi-chiometric amounts of S₈ to form C₅H₅(PMe₃)CoS₅ ( 4 ) in practically quantitative yields. The cobalt-apentathia heterocycle 4 is also obtained by the reaction of C₅H₅(PMe₃)Co(h²-CS₂) ( 5 ) with S₈. Crystals of 4 are monoclinio with a = 8.467(3) Å, b = 12.128(4) Å, c = 14.210(4) Å and Å = 102.20(2)°. The chair form of the six-membered CoS₅ ring corresponds to that of the compounds (C₅H₅)₂TiS₅ and (C₅H₅)₂VS₅. In 4 , the cyclopentadienyl ligand occupies the axial and the trimethylphosphine group the equatorial position.     

Electroosmotic flow variations caused by the volatility of buffer components: diagnosis and therapy

In order to separate a polar amine pharmaceutical and its potential impurities, a micellar electrokinetic chromatography method was developed. The main compound and 11 other substances were completely separated using a 20 mM Tris buffer, pH 8.0, containing 50 mM sodium dodecylsulfate (SDS) and 24% (v/v) acetonitrile. However, a strong, continuous reduction in the EOF occurred and quantification was not possible. The EOF reproducibility could not be improved by suitable rinsing procedures. Surface effects or interactions did not cause the EOF changes, but the evaporation of acetonitrile was identified as the major source for EOF instability. However, a high concentration of acetonitrile was decisive for selectivity. Thus a reliable protection against the evaporation of this buffer constituent had to be found. Paraffin and various silicon oils were tested as covering film. In order to quickly test buffer systems if the evaporation of electrophoresis solutions is acceptable, an alternative experimental design without doing CE experiments had to be found. Electrical conductivity was chosen as parameter, because it can be determined simply and fast. The buffers under investigation were placed in a 50-ml beaker with a magnetic stirring rod, placed on a magnetic stirrer. The buffer solution was kept in motion at 120 rev./min. The beaker was covered around the measuring head with laboratory film and in addition to this with paraffin or silicon oil. An acetonitrile content up to 10% (v/v) was acceptable if a coverage was used. The various cover liquids had a similar effect. A content of 15% (v/v) already increased the evaporation effect significantly. Higher acetonitrile contents are not acceptable. A buffer similar to the originally transferred method, 20 mM Tris (pH 8.0), 50 mM SDS containing 10% (v/v) acetonitrile as well as 10% (v/v) isopropanol showed an acceptably low evaporation in the conductivity experiments. With this buffer, a stable EOF was also obtained. Conductivity measurements are generally applicable to quickly test buffers that contain organic solvents.     

He capture by negatively charged Buckminsterfullerene

The first observation of capture of He atoms by negatively charged Buckminsterfullerence (C₆₀) is reported. The collision energy dependence of the production of the endohedral complex is presented in the region of the energetic threshold and compared directly with results obtained using positively charged C₆₀. The threshold for capture by negative ions is shifted by ≈ 1.5 eV to higher energies. This shift can be accounted for by considering the different internal energies of the positive and negative ions.