Peritektische Zersetzung von YBa2Cu3O7−x

During the heating of YBCO a peritectic reaction takes place at 1020C, which can be described by: 2YBa₂Cu₃O_7–xY₂BaCuO₅+L+(1-2x)/2O₂ (1) whereL = 3BaCuO₂ +2CuO is a fluid with limited amount of yttrium.It has been reported, that many parameters can influence the reaction. From one side not only the starting size of grains but also the heating rate have an influence on the resulting Y₂BaCuO₅-phase. From the other side, there is a change of the peritectical temperature caused by changing of the partial pressure of O₂ and the presence of parasitic phase.From general kinetic consideration one can draw the conclusion, that different mechanisms (nucleation, phase-boundary reaction and diffusion) can control the reaction.Using DTA/TG measurements, the peritectic reaction has been examined. Classical kinetic methods (Kissinger and Friedman) has been used. The Friedman method has given the dependence of the activation energy from reaction degree. This suggests many steps reactions. The dependence of the DTA-peaks from the heat rate suggest a parallel steps of reaction. This assumption can be motivated by evaluation of free O₂, one solid and liquid phase formation. Amount of this phases depends on the heating rate. Additionally X-ray and microscopic methods has been used. In this way was shown, that the perovskit structure is stable up to peritectical temperature and than is dramatically destroyed. From microscopic observations has been got information about shape and size of solid phase and it's creation as a function of temperature, time and starting grain size.

Die Arbeit wurde BMBF gefördert und durch Land NRW unterschtützt.     

Measuring a colloidal particle's interaction with a flat surface under nonequilibrium conditions

A new and general approach is proposed to analyze the dynamics of a colloidal particle interacting with a nearby wall. This analysis can be used to determine the acting forces even when the system is non-stationary. As an illustration, we use total internal reflection microscopy to investigate the forces acting on a polystyrene sulfate latex particle as it is receding from a charged glass surface. Received 10 October 2002 Published online: 16 April 2003 RID="a" ID="a"Present address: Department of Polymer Physics, BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany RID="b" ID="b"Present address: Arryx. Inc., Chicago, IL 60601, USA     

The Braginskii model of the Rayleigh–Taylor instability. I. Effects of self-generated magnetic fields and thermal conduction in two dimensions

There exists a substantial disagreement between computer simulation results and high-energy density laboratory experiments of the Rayleigh–Taylor instability [1]. Motivated by the observed discrepancies in morphology and growth rates, we attempt to bring simulations and experiments into better agreement by extending the classic purely hydrodynamic model to include self-generation of magnetic fields and anisotropic thermal conduction.We adopt the Braginskii formulation for transport in hot, dense plasma, implement and verify the additional physics modules, and conduct a computational study of a single-mode RTI in two dimensions with various combinations of the newly implemented modules. We analyze physics effects on the RTI mixing and flow morphology, the effects of mutual physics interactions, and the evolution of magnetic fields.We find that magnetic fields reach levels on the order of 11 MG (plasma β ≈ 9.1 × 10^?2) in the absence of thermal conduction. These fields do not affect the growth of the mixed layer but substantially modify its internal structure on smaller scales. In particular, we observe denting of the RT spike tip and generation of additional higher order modes as a result of these fields. Contrary to interpretation presented in earlier work [2], the additional mode is not generated due to modified anisotropic heat transport effects but due to dynamical effect of self-generated magnetic fields. The overall flow morphology in self-magnetized, non-conducting models is qualitatively different from models with a pre-existing uniform field oriented perpendicular to the interface. This puts the usefulness of simple MHD models for interpreting the evolution of self-magnetizing HED systems with zero-field initial conditions into doubt.The main effects of thermal conduction are a reduction of the RT instability growth rate (by about 20% for conditions considered here) and inhibited mixing on small scales. In this case, the maximum self-generated magnetic fields are weaker (approximately 1.7 MG; plasma β ≈ 49). This is due to reduction of temperature and density gradients due to conduction. These self-generated magnetic fields are of very similar strength compared to magnetic fields observed recently in HED laboratory experiments [3].We find that thermal conduction plays the dominant role in the evolution of the model RTI system considered. It smears out small-scale structure and reduces the RTI growth rate. This may account for the relatively featureless RT spikes seen in experiments, but does not explain mass extensions observed in experiments.Resistivity, related heat source terms and the thermo-electric contribution to the heat flow were not included in the present work. We estimate their impact on RTI as modest and not affecting our main conclusions. These effects will be discussed in detail in the next paper in the series.     

Investigation of the differentiation of kinetic models

The differentiation of known kinetic models in appropriately chosen coordinate systems has been investigated. A new method of defining the control of chemical reaction rate has been presented, the suggested method being based on the use of known kinetic model equations. It consists in comparing the respective model courses with the experimental. For isothermal conditions, the model curves, f(α) vs. α, are compared with the experimental DTG vs. TG. For conditions of linear temperature increase, however, model courses of the type (1/f(α) (df(α)/dα) vs. α and corresponding experimental curves {[(DDTG/DTG²)—(Eγ/RT²)](1/DTG)} vs. TG are used for comparison: such visual comparison allows a rapid estimation of the closeness of experimental results and predicted models. This method was verified with positive results with experimental material under isothermal conditions (for the thermal decomposition of PbSO₄ and for the oxidation of copper in air) and for conditions of linear temperature increase (for the oxidation of copper in air).     

I[NI4] · NH3, ein neues Derivat des Iodstickstoffs

I[NI₄] · NH₃, a New Derivate of Nitrogen Triiodide The former unknown compound I[NI₄] · NH₃ can be prepared in a closed vessel in the presence of a trace of water from nitrogen triiodide NI₃ · NH₃. It crystallizes hexagonal in the space group P6₃mc with a = 842.5 pm, c = 876.5 pm and Z = 2 formula units. Three corners of a nearly regular tetrahedron (d(N–I) = 219.0, 223.6 pm) are connected by trigonal-pyramidal coordinated iodine atoms with d(I–I) = 308.8 pm to puckered layers stacked in the direction of the c-axis. The molecule NH₃ fills the space between the iodine layers. It is coordinated to that iodine atom of the NI₄-tetrahedron which is not involved in the iodine net. Some chemical properties of the compound are reported.     

Hardy’s Inequality for Laguerre Expansions of Hermite Type

Journal of Fourier Analysis and Applications - Hardy’s inequality for Laguerre expansions of Hermite type with the index $$\alpha \in (\{-1/2\}\cup [1/2,\infty ))^d$$ is proved in the...     

Kinetics of reduction of magnesium sulfate by carbon oxide

The thermodynamic analysis and the results of thermogravimetric investigation of the reduction of magnesium sulfate by carbon oxide are reported.The isothermal experiments were carried out in the temperature range 640 to 675°. A shrinking-core model was found to fit the reaction rate. An activation energy of 209.7±8.6 kJ/mol was obtained.

---

Zusammenfassung Es wird über thermodynamische Analyse und Resultate einer thermogravimetrischen Untersuchung der Reduktion von Magnesiumsulfat mit Kohlendioxid berichtet. Die isothermen Experimente wurden im Temperaturbereich 640 bis 675° durchgeführt. Zur Erklärung der Reaktionsgeschwindigkeit wurde eine Shrinking-Modell gefunden. Es wurde eine Aktivierungsenergie von 209.7±8.6 kJ/mol erhlten.

---

. 640–675°. , . 209,7±8,6 /.

     

Pulsar recoil by large-scale anisotropies in supernova explosions

Assuming that the neutrino luminosity from the neutron star core is sufficiently high to drive supernova explosions by the neutrino-heating mechanism, we show that low-mode (l=1,2) convection can develop from random seed perturbations behind the shock. A slow onset of the explosion is crucial, requiring the core luminosity to vary slowly with time, in contrast to the burstlike exponential decay assumed in previous work. Gravitational and hydrodynamic forces by the globally asymmetric supernova ejecta were found to accelerate the remnant neutron star on a time scale of more than a second to velocities above 500 km s(-1), in agreement with observed pulsar proper motions.     

Mode interaction through amplitudes and phases in a two-modegyrotron oscillator

An analysis is made of temporal evolution of electromagnetic modes in a two-mode gyrotron oscillator characterized by phase and amplitude interaction through the terms linear in the oscillator power. The problem is solved in the context of amplitudes and phases which vary slowly compared with the period of oscillation. Specific reference is made to competition between TE_11q modes in a closed cavity gyrotron. Qualitative features which are found include phase locking, beat frequencies, periodic pulling, and mode excitation. This work has applicability when the frequency separation between the modes is on the order of the frequency bandwidth of each mode, or the modes are equally spaced in frequency. Gyrotrons of this type include those with low-quality-factor modes or degenerate modes. Phase interaction in the case of equally spaced cavity modes is of importance in analyzing mode-locking phenomena     

Evaluation of Multiplexed CE with UV Detection for Rapid pK a Estimation of Active Pharmaceutical Ingredients

The acid dissociation constant (pK _a) is a key physicochemical parameter for characterizing active pharmaceutical ingredients (APIs). Early determination of pK _a values is highly desirable in drug discovery, pharmaceutical process research and formulation design. To overcome the challenges of limited sample availability and potential low purity of API samples at early stages of drug development, as well as to increase sample analysis throughput, a multiplexed 96-channel capillary electrophoresis with UV detection was evaluated as a practical approach for high throughput pK _a estimation of proprietary APIs in support of pharmaceutical research. Proprietary APIs with diverse structures were examined using the approach. The pK _a values were successfully determined with good accuracy and precision. System robustness was demonstrated and analysis of at least eight samples can be completed within 1 h. A rapid pK _a estimation procedure for marginally soluble APIs was proposed by performing single-point multiplexed CE–UV measurement without extrapolation using 10 or 20% methanol as co-solvent. Direct pK _a estimation of APIs using DMSO solution samples and crude reaction samples containing a large amount of solvents and reagents and high level of impurities was also demonstrated using the multiplexed CE–UV approach.